U.S. patent application number 14/517883 was filed with the patent office on 2015-02-05 for recombinant factor viii having enhanced stability following mutation at the a1-c2 domain interface.
This patent application is currently assigned to UNIVERSITY OF ROCHESTER. The applicant listed for this patent is Philip J. Fay, Hironao Wakabayashi. Invention is credited to Philip J. Fay, Hironao Wakabayashi.
Application Number | 20150037301 14/517883 |
Document ID | / |
Family ID | 45807292 |
Filed Date | 2015-02-05 |
United States Patent
Application |
20150037301 |
Kind Code |
A1 |
Fay; Philip J. ; et
al. |
February 5, 2015 |
RECOMBINANT FACTOR VIII HAVING ENHANCED STABILITY FOLLOWING
MUTATION AT THE A1-C2 DOMAIN INTERFACE
Abstract
The invention relates to a recombinant factor VIII that includes
one or more mutations at an interface of A1 and C2 domains of
recombinant factor VIII. The one or more mutations include
substitution of one or more amino acid residues with either a
cysteine or an amino acid residue having a higher hydrophobicity.
This results in enhanced stability of factor VIII. Methods for
making the recombinant factor VIII, pharmaceutical compositions
containing the recombinant factor VIII, and use of the recombinant
factor VIII for treating hemophilia A are also disclosed.
Inventors: |
Fay; Philip J.; (Pittsford,
NY) ; Wakabayashi; Hironao; (Rochester, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Fay; Philip J.
Wakabayashi; Hironao |
Pittsford
Rochester |
NY
NY |
US
US |
|
|
Assignee: |
UNIVERSITY OF ROCHESTER
Rochester
NY
|
Family ID: |
45807292 |
Appl. No.: |
14/517883 |
Filed: |
October 19, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14141983 |
Dec 27, 2013 |
8865154 |
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14517883 |
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13231948 |
Sep 13, 2011 |
8637448 |
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14141983 |
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61382919 |
Sep 14, 2010 |
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Current U.S.
Class: |
424/93.21 ;
435/252.33; 435/254.11; 435/254.2; 435/254.21; 435/257.2;
435/320.1; 435/348; 435/352; 435/414; 435/419; 514/14.1; 530/383;
536/23.5 |
Current CPC
Class: |
C07K 14/755 20130101;
A61P 7/04 20180101; A61K 38/00 20130101; A61K 38/37 20130101 |
Class at
Publication: |
424/93.21 ;
530/383; 514/14.1; 536/23.5; 435/320.1; 435/352; 435/252.33;
435/348; 435/254.11; 435/254.2; 435/254.21; 435/419; 435/414;
435/257.2 |
International
Class: |
C07K 14/755 20060101
C07K014/755; A61K 38/37 20060101 A61K038/37 |
Goverment Interests
[0002] This invention was made with government support under grant
number HL38199 and HL76213 awarded by the National Institutes of
Health. The government has certain rights in the invention.
Claims
1. A recombinant factor VIII comprising substitution of two or more
amino acid residues with a Cysteine residue at an interface of A1
and C2 domains of the recombinant factor VIII to afford a disulfide
bond between the A1 and C2 domains, and one or more of the
following: (i) a substitution of one or more amino acid residues
with an amino acid residue having a higher hydrophobicity at a C2
domain interface of the A1 domain; (ii) a substitution of one or
more amino acid residues with an amino acid residue having a higher
hydrophobicity at an A1 domain interface of the C2 domain; and
(iii) a substitution of one or more charged amino acid residues
with a hydrophobic amino acid residue at an interface of A1 and A2
domains or an interface of A2 and A3 domains of the recombinant
factor VIII.
2. The recombinant factor VIII according to claim 1, wherein the A1
domain having the Cysteine substitution comprises the sequence SXXX
(SEQ ID NO: 20) wherein X at the third position is Cysteine, and
the C2 domain having the Cysteine substitution comprises the
sequence PPXX (SEQ ID NO: 23) wherein X at the fourth position is
Cysteine.
3. The recombinant factor VIII according to claim 1, wherein the
two or more amino acid residues substituted with a Cysteine residue
comprise an Arg.fwdarw.Cys substitution at a position corresponding
to residue 121 of SEQ ID NO: 2 and an Leu.fwdarw.Cys substitution
at a position corresponding to residue 2302 of SEQ ID NO: 2.
4. The recombinant factor VIII according to claim 1, wherein the
substitution of one or more amino acid residues with an amino acid
residue having a higher hydrophobicity at a C2 domain interface of
the A1 domain is present.
5. The recombinant factor VIII according to claim 4, wherein the C2
domain interface of the A1 domain comprises the amino acid sequence
of: KXS (SEQ ID NO: 19), where the substitution is at the second
position and X is Valine, Isoleucine, or Leucine; or TYXW (SEQ ID
NO: 21), where the substitution is at the third position and X is
Leucine, Isoleucine, or Valine.
6. The recombinant factor VIII according to claim 4, wherein the
substitution of one or more amino acid residues with an amino acid
residue having a higher hydrophobicity at the C2 domain interface
of the A1 domain comprises an Ala.fwdarw.Ile substitution at a
position corresponding to residue 108 of SEQ ID NO: 2.
7. The recombinant factor VIII according to claim 1, wherein the
substitution of one or more amino acid residues with an amino acid
residue having a higher hydrophobicity at an A1 domain interface of
the C2 domain is present.
8. The recombinant factor VIII according to claim 1, wherein the
substitution of one or more charged amino acid residues with a
hydrophobic amino acid residue at an interface of A1 and A2 domains
or an interface of A2 and A3 domains of the recombinant factor VIII
is present.
9. The recombinant factor VIII according to claim 8, wherein the
charged amino acid residue is either Glu or Asp, and the
hydrophobic amino acid substitution is one of Ala, Val, Ile, Leu,
Met, Phe, or Trp.
10. The recombinant factor VIII according to claim 8 wherein the
substitution of one or more charged amino acid residues with a
hydrophobic amino acid residue at the interface of A1 and A2
domains or the interface of A2 and A3 domains of the recombinant
factor VIII comprises substitution of a Glu287 residue of wild type
factor VIII, substitution of an Asp302 residue of wild type factor
VIII, substitution of an Asp519 residue of wild type factor VIII,
substitution of a Glu665 residue of wild type factor VIII,
substitution of a Glu1984 residue of wildtype factor VIII, or a
combination thereof.
11. The recombinant factor VIII according to claim 8, wherein the
substitution of one or more charged amino acid residues with a
hydrophobic amino acid residue at an interface of A1 and A2 domains
or an interface of A2 and A3 domains of the recombinant factor VIII
comprises: (i) an Asp.fwdarw.Ala substitution at a position
corresponding to residue 302 of SEQ ID NO: 2; (ii) a Glu.fwdarw.Ala
substitution at a position corresponding to residue 287 of SEQ ID
NO: 2; (iii) a Glu.fwdarw.Ala or Glu.fwdarw.Val substitution at a
position corresponding to residue 665 of SEQ ID NO: 2; (iv) an
Asp.fwdarw.Ala or Asp.fwdarw.Val substitution at a position
corresponding to residue 519 of SEQ ID NO: 2; (v) a Glu.fwdarw.Ala
or Glu.fwdarw.Val substitution at a position corresponding to
residue 1984 of SEQ ID NO: 2; or (vi) combinations of any two or
more of the substitutions (i)-(v).
12. The recombinant factor VIII according to claim 1, wherein the
recombinant factor VIII further comprises one or more of (i) factor
IXa and/or factor X binding domains modified to enhance the
affinity of the recombinant factor VIII for one or both of factor
IXa and factor X; (ii) modified sites that enhance secretion in
culture; (iii) modified serum protein binding sites that enhance
the circulating half-life thereof; (iv) at least one glycosylation
recognition sequence that is effective in decreasing antigenicity
and/or immunogenicity thereof; (v) a modified A1 domain
calcium-binding site that improves specific activity of the
recombinant factor VIIIa; and (vi) a modified activated protein
C-cleavage site.
13. A pharmaceutical composition comprising the recombinant factor
VIII according to claim 1 and a pharmaceutically acceptable
carrier.
14. A method of treating an animal for hemophilia A, said method
comprising: administering to an animal exhibiting hemophilia A an
effective amount of the recombinant factor VIII of claim 1, whereby
the animal exhibits effective blood clotting following vascular
injury.
15. An isolated nucleic acid molecule encoding the recombinant
factor VIII according to claim 1.
16. The isolated nucleic acid molecule according to claim 15,
wherein the nucleic acid is DNA.
17. A recombinant expression system comprising a DNA molecule of
claim 16.
18. A recombinant host cell comprising the nucleic acid molecule
according to claim 15.
19. An implantable device comprising a plurality of the recombinant
host cells according to claim 18 contained within the device.
20. A method of treating an animal for hemophilia A, said method
comprising: administering to an animal exhibiting hemophilia A a
recombinant host cell of claim 18, whereby the recombinant host
cell expresses the recombinant factor VIII and the animal exhibits
effective blood clotting following vascular injury.
Description
[0001] This application is a continuation of U.S. patent
application Ser. No. 14/141,983, filed Dec. 27, 2013, now U.S. Pat.
No. 8,865,154, which is a division of U.S. patent application Ser.
No. 13/231,948, filed Sep. 13, 2011, now U.S. Pat. No. 8,637,448,
which claims the priority benefit of U.S. Provisional Patent
Application Ser. No. 61/382,919, filed Sep. 14, 2010, which are
hereby incorporated by reference in their entirety.
BACKGROUND OF THE INVENTION
[0003] Hemophilia A, the most common of the severe, inherited
bleeding disorders, results from a deficiency or defect in the
plasma protein factor VIII. There is no cure for Hemophilia A and
treatment consists of replacement therapy using preparations of
(purified) plasma or the recombinant protein.
[0004] Factor VIII circulates as a non-covalent, metal
ion-dependent heterodimer. This procofactor form of the protein
contains a heavy chain (HC) comprised of A1(a1)A2(a2)B domains and
a light chain (LC) comprised of (a3)A3C1C2 domains, with the lower
case a representing short (.about.30-40 residue) segments rich in
acidic residues (see Fay, "Activation of Factor VIII and Mechanisms
of Cofactor Action," Blood Rev. 18:1-15 (2004)). Factor VIII is
activated by proteolytic cleavages at the A1A2, A2B and A3A3
junctions catalyzed by thrombin or factor Xa. The product of this
reaction, factor VIIIa, is a heterotrimer comprised of subunits
designated A1, A2, and A3C1C2 that functions as a cofactor for the
serine protease factor IXa in the membrane-dependent conversion of
zymogen factor X to the serine protease, factor Xa (see Fay,
"Activation of Factor VIII and Mechanisms of Cofactor Action,"
Blood Rev. 18:1-15 (2004)).
[0005] Reconstitution studies have shown that the factor VIII
heterodimeric structure is supported by both electrostatic and
hydrophobic interactions (Fay, "Reconstitution of Human Factor VIII
from Isolated Subunits," Arch Biochem Biophys. 262:525-531 (1988);
Ansong et al., "Factor VIII A1 Domain Residues 97-105 Represent a
Light Chain-interactive Site," Biochemistry 45:13140-13149 (2006)),
and the inter-chain affinity is further strengthened by factor VIII
binding von Willebrand factor (Fay, "Reconstitution of Human Factor
VIII from Isolated Subunits," Arch Biochem Biophys. 262:525-531
(1988); Kaufman et al., "Regulation of Factor VIII Expression and
Activity by von Willebrand Factor," Thromb Haemost. 82:201-208
(1999)). Metal ions also contribute to the inter-chain affinity and
activity parameters (Wakabayashi et al., "Metal Ion-independent
Association of Factor VIII Subunits and the Roles of Calcium and
Copper Ions for Cofactor Activity and Inter-subunit Affinity,"
Biochemistry 40:10293-10300 (2001)). Calcium is required to yield
the active factor VIII conformation. Mutagenesis studies mapped a
calcium-binding site to a segment rich in acidic residues within
the A1 domain (residues 110-126) and identified specific residues
within this region prominent in the coordination of the ion
(Wakabayashi et al., "Residues 110-126 in the A1 Domain of Factor
VIII Contain a Ca.sup.2+ Binding Site Required for Cofactor
Activity," J Biol Chem. 279:12677-12684 (2004)). A recent
intermediate resolution X-ray structure (Shen et al., "The Tertiary
Structure and Domain Organization of Coagulation Factor VIII,"
Blood 111:1240-1247 (2008)) confirmed this calcium-binding site as
well as suggested a second potential site within the A2 domain.
This structure also showed occupancy of the two type 1 copper ion
sites within the A1 and A3 domains. Earlier functional studies have
shown that copper ions facilitate the association of the heavy and
light chains to form the heterodimer, increasing the inter-chain
affinity by several-fold at physiologic pH (Fay et al., "Human
Factor VIIIa Subunit Structure: Reconstruction of Factor VIIIa from
the Isolated A1/A3-C1-C2 Dimer and A2 Subunit," J Biol Chem.
266:8957-8962 (1991); Wakabayashi et al., "pH-dependent Association
of Factor VIII Chains: Enhancement of Affinity at Physiological pH
by Cu.sup.2+," Biochim Biophys Acta. 1764:1094-1101 (2006); Ansong
et al., "Factor VIII A3 Domain Residues 1954-1961 Represent an A1
Domain-Interactive Site," Biochemistry 44:8850-8857 (2005)).
[0006] The instability of factor VIIIa results from weak
electrostatic interactions between the A2 subunit and the A1/A3C1C2
dimer (Fay et al., "Human Factor VIIIa Subunit Structure:
Reconstruction of Factor VIIIa from the Isolated A1/A3-C1-C2 Dimer
and A2 Subunit," J Biol Chem. 266:8957-8962 (1991); Lollar et al.,
"pH-dependent Denaturation of Thrombin-activated Porcine Factor
VIII," J Biol Chem. 265:1688-1692 (1990)) and leads to dampening of
factor Xase activity (Lollar et al., "Coagulant Properties of
Hybrid Human/Porcine Factor VIII Molecules," J Biol Chem.
267:23652-23657 (1992); Fay et al., "Model for the Factor
VIIIa-dependent Decay of the Intrinsic Factor Xase: Role of Subunit
Dissociation and Factor IXa-catalyzed Proteolysis," J Biol Chem.
271:6027-6032 (1996)). Limited information is available regarding
the association of the A2 subunit in factor VIIIa, and residues in
both the A1 and A3 domains appear to make contributions to the
retention of this subunit. Several factor VIII point mutations have
been shown to facilitate the dissociation of A2 relative to WT and
these residues localize to either the A1-A2 domain interface (Pipe
et al., "Mild Hemophilia A Caused by Increased Rate of Factor VIII
A2 Subunit Dissociation: Evidence for Nonproteolytic Inactivation
of Factor VIIIa in vivo," Blood 93:176-183 (1999); Pipe et al.,
"Hemophilia A Mutations Associated with 1-stage/2-stage Activity
Discrepancy Disrupt Protein-protein Interactions within the
Triplicated A Domains of Thrombin-activated Factor VIIIa," Blood
97:685-691 (2001)) or the A2-A3 domain interface (Hakeos et al.,
"Hemophilia A Mutations within the Factor VIII A2-A3 Subunit
Interface Destabilize Factor VIIIa and Cause One-stage/Two-stage
Activity Discrepancy," Thromb Haemost. 88:781-787 (2002)). These
factor VIII variants demonstrate a characteristic
one-stage/two-stage assay discrepancy (Duncan et al., "Familial
Discrepancy Between the One-stage and Two-stage Factor VIII Methods
in a Subgroup of Patients with Haemophilia A," Br J Haematol.
87:846-848 (1994); Rudzki et al., "Mutations in a Subgroup of
Patients with Mild Haemophilia A and a Familial Discrepancy Between
the One-stage and Two-stage Factor VIII:C Methods," Br J Haematol.
94:400-406 (1996)), with significant reductions in activity values
determined by the latter assay as a result of increased rates of A2
subunit dissociation.
[0007] Significant interest exists in stabilizing factor VIIIa,
since a more stable form of the protein would represent a superior
therapeutic for hemophilia A, potentially requiring less material
to treat the patient (Fay et al., "Mutating Factor VIII: Lessons
from Structure to Function," Blood Reviews 19:15-27 (2005)). To
this end, preparations of factor VIII have been described where
mutations have been made in the recombinant protein to prevent the
dissociation of the A2 subunit by introducing novel covalent bonds
between A2 and other factor VIII domains (Pipe et al.,
"Characterization of a Genetically Engineered
Inactivation-resistant Coagulation Factor VIIIa," Proc Natl Acad
Sci USA 94:11851-11856 (1997); Gale et al., "An Engineered
Interdomain Disulfide Bond Stabilizes Human Blood Coagulation
Factor VIIIa," J. Thromb. Haemostasis 1:1966-1971 (2003)). However,
it has since been suggested that these types of mutation may not be
desirable in a therapeutic factor VIII, because they substantially
eliminate means for down-regulation. This situation could yield a
prothrombotic condition, which may cause harm. Thus, it would be
desirable to enhance the stability of both factor VIII and factor
VIIIa, but in a manner that minimizes the likelihood of promoting
prothrombotic conditions.
[0008] In U.S. Patent Application Publ. No. 20090118184, a number
of recombinant factor VIII proteins are identified that possess one
or more mutations that result in enhanced stability of both factor
VIII and factor VIIIa. These recombinant factor VIII proteins have
one or more substitutions of a charged amino acid residue with a
hydrophobic amino acid residue at either or both of the A1-A2 or
A2-A3 domain interfaces. Despite the improvements made in the
stability of recombinant factor VIII proteins (and their active
forms, factor VIIIa), the need for further improvements continue to
exist.
[0009] The intermediate resolution X-ray structures of factor VIII
(Shen et al., "The Tertiary Structure and Domain Organization of
Coagulation Factor VIII," Blood 111:1240-1247 (2008); Ngo et al.,
"Crystal Structure of Human Factor VIII: Implications for the
Formation of the Factor IXa:Factor VIIIa Complex," Structure
16:597-606 (2008)) show close contact between A1 (heavy chain) and
C2 (light chain) domains. It was recently reported that a factor
VIII variant lacking the C2 domain retained the capacity to bind
phospholipid membranes, albeit with a marked reduction in affinity
(Wakabayashi et al., "Factor VIII Lacking the C2 Domain Retains
Cofactor Activity in vitro," J. Biol. Chem 285:25176-25184 (2010)),
supporting a direct role for the C1 domain in this interaction.
Furthermore, deletion of the C2 domain did not grossly alter a
number of functional properties including the rate of procofactor
activation by thrombin, affinity of factor VIIIa for factor IXa,
K.sub.m of factor Xase for substrate factor X, or k.sub.cat for
factor Xa generation. However, this deletion did significantly
destabilize the cofactor, as judged by increased rates of activity
decay following exposure to elevated temperature or chemical
denaturants. While contacts between the A1 and C2 domains of factor
VIII appear to contribute to protein, and in particular heterodimer
stability, little information is available on specific interactions
and their functional significance. It would be desirable,
therefore, to identify amino acid residues that can be modified to
enhance stability between the A1 (heavy chain) and C2 (light chain)
domains.
[0010] The present invention is directed to overcoming these and
other deficiencies in the art.
SUMMARY OF THE INVENTION
[0011] A first aspect of the present invention relates to a
recombinant factor VIII that includes one or more mutations at an
interface of A1 and C2 domains of recombinant factor VIII. This
results in enhanced stability of factor VIII. The one or more
mutations include substitution of one or more amino acid residues
with either a cysteine or an amino acid residue having a higher
hydrophobicity.
[0012] According to one embodiment, the recombinant factor VIII
includes one or more mutations at an interface of A1 and C2 domains
of recombinant factor VIII that result in enhanced stability of
factor VIII, wherein the one or more mutations comprise
substitution of one or more amino acid residues with an amino acid
residue having a higher hydrophobicity.
[0013] According to another embodiment, the recombinant factor VIII
includes (i) two or more mutations at an interface of A1 and C2
domains of recombinant factor VIII, wherein the two or more
mutations comprise substitution of two or more amino acid residues
with a Cysteine residue to afford a disulfide bond between the A1
and C2 domains; and (ii) one or more mutations at an interface of
A1 and A2 domains or an interface of A2 and A3 domains of
recombinant factor VIII, said one or more mutations comprising
substitution of one or more charged amino acid residues with a
hydrophobic amino acid residue. The recombinant factor VIII
possessing these mutations exhibits enhanced stability of both
factor VIII and factor VIIIa.
[0014] A second aspect of the present invention relates to the
recombinant factor VIII according to the first aspect of the
present invention, wherein the recombinant factor VIII further
includes one or more of (i) factor IXa and/or factor X binding
domains modified to enhance the affinity of the recombinant factor
VIII for one or both of factor IXa and factor X; (ii) modified
sites that enhance secretion in culture; (iii) modified serum
protein binding sites that enhance the circulating half-life
thereof; (iv) at least one glycosylation recognition sequence that
is effective in decreasing antigenicity and/or immunogenicity
thereof; (v) a modified A1 domain calcium-binding site that
improves specific activity of the recombinant factor Villa; (vi)
modified activated protein C-cleavage site; (vii) a modified A1 and
A2 domain interface; and (viii) a modified A2 and A3 domain
interface.
[0015] A third aspect of the present invention relates to a
pharmaceutical composition that includes the recombinant factor
VIII according to the present invention.
[0016] A fourth aspect of the present invention relates to an
isolated nucleic acid molecule encoding a recombinant factor VIII
of the present invention. Also included within this aspect of the
present invention are recombinant DNA expression systems that
contain a DNA molecule encoding the recombinant factor VIII of the
present invention, and recombinant host cells that contain the DNA
molecule and/or recombinant expression system.
[0017] A fifth aspect of the present invention relates to a method
of making a recombinant factor VIII that includes: growing a host
cell according to the fourth aspect of the present invention under
conditions whereby the host cell expresses the recombinant factor
VIII; and isolating the recombinant factor VIII.
[0018] A sixth aspect of the present invention relates to a method
of treating an animal for hemophilia A. This method of treatment
includes: administering to an animal exhibiting hemophilia A an
effective amount of the recombinant factor VIII of the present
invention, whereby the animal exhibits effective blood clotting
following vascular injury.
[0019] The present invention demonstrates that a number of residues
at the interface of A1 and C2 domains do not participate in
non-covalent bonding, but instead may be destabilizing to factor
VIII structure. Replacement of these residues with more hydrophobic
residues--with the aim of increasing the buried hydrophobic area
and reducing the buried hydrophilic area--was shown in the
accompanying Examples to enhance inter-domain binding affinity.
Stability parameters were assessed by following the activity of the
factor VIII variants. Results from these studies demonstrated that
a number of mutations yielded increased stability parameters. These
stabilized variants of factor VIII and activated cofactor VIIIa
should afford an improved therapeutic for treatment of hemophilia
A.
[0020] To explore the role of this region in factor VIII and factor
VIIIa stability, a variant containing a disulfide bond between A1
and C2 domains was generated by mutating Arg121 and Leu2302 to Cys
(R121C-L2302C) and a second variant was generated by substituting a
bulkier hydrophobic group (Ala108Ile) to better occupy a cavity
between A1 and C2 domains. Disulfide bonding in the R121C-L2302C
variant was >90% efficient as judged by western blots. Binding
affinity between the Ala108Ile A1 and A3C1C2 subunits was increased
.about.3.7-fold in the variant compared with WT as judged by
changes in fluorescence of acrylodan labeled-A1 subunits. Factor
VIII thermal and chemical stability were monitored following rates
of loss of factor VIII activity at 57.degree. C. or in guanidinium
by factor Xa generation assays. The rate of decay of factor VIIIa
activity was monitored at 23.degree. C. following activation by
thrombin. Both R121C-L2302C and Ala108Ile variants showed up to
.about.4-fold increases in thermal stability but minimal
improvements in chemical stability. The purified A1 subunit of
Ala108Ile reconstituted with the A3C1C2 subunit showed a
.about.4.6-fold increase in thermal stability while reconstitution
of the variant A1 with a truncated A3C1 subunit showed similar
stability values as compared with WT A1. Together, these results
suggest that altering contacts at this A1-C2 junction by covalent
modification or increasing hydrophobicity increases inter-chain
affinity and functionally enhances factor VIII stability. Moreover,
by combining these mutations with one or more mutations at the
A1-A2 and/or A2-A3 domain interfaces, including Asp519Ala,
Asp519Val, Glu665Ala, Glu665Val, Glu1984Ala, and Glu1984Val, double
and triple mutants displayed .about.2-10 fold increases in the
stability of factor VIIIa.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 shows alignment of partial A1 domain sequences of
eight mammalian factor VIII molecules starting from amino acid
residue A100 of human factor VIII. The partial amino acid sequences
are from human factor VIII (residues 100-140 of SEQ ID NO: 2); pig
factor VIII (SEQ ID NO: 3); canine factor VIII (SEQ ID NO: 4);
mouse factor VIII (SEQ ID NO: 5); rabbit factor VIII (SEQ ID NO:
6); bat factor VIII (SEQ ID NO: 7); rat factor VIII (SEQ ID NO: 8);
and sheep factor VIII (SEQ ID NO: 9). The figure also shows the
consensus amino acid sequence (SEQ ID NO: 10) for the partial A1
domain. Underlined residues represent a C2 domain interface of the
A1 domain.
[0022] FIG. 2 shows alignment of partial C2 domain sequences from
eight mammalian factor VIII molecules starting from amino acid
residue Q2231 of human factor VIII. The partial amino acid
sequences are from human factor VIII (residues 2231-2334 of SEQ ID
NO: 2); pig factor VIII (SEQ ID NO: 11); canine factor VIII (SEQ ID
NO: 12); mouse factor VIII (SEQ ID NO: 13); rabbit factor VIII (SEQ
ID NO: 14); bat factor VIII (SEQ ID NO: 15); rat factor VIII (SEQ
ID NO: 16); and sheep factor VIII (SEQ ID NO: 17). The figure also
shows the consensus amino acid sequence (SEQ ID NO: 18) for the
partial C2 domain. Underlined residues represent an A1 domain
interface of the C2 domain.
[0023] FIGS. 3A-C illustrate a model of selected residues at the
A1-C2 domain interface. In FIG. 3A, the molecular surface of the
factor VIII X-ray crystal structure, drawn by Swiss PDB viewer,
shows the A1 domain (residues 1-336) in yellow, A2 domain (residues
373-711) in blue, A3 domain (residues 1690-2020) in red, C1 domain
(residues 2021-2169) in green, and C2 domain (residues 2170-2332)
in grey (FIG. 3A). Higher magnification of the A1-C2 contact region
(yellow circle) is presented in FIGS. 3B-C. Side chains of Arg121
and Leu2302 (drawn as stick models) mutated to Cys residues are
modeled by Swiss PDB viewer (FIG. 3B). In FIG. 3C, residues
surrounding Ala108 (Leu2302, Ala2328, and Gln2329) are highlighted
as stick models. C.beta. carbon of Ala108, C.delta. of Leu2302,
C.beta. of Ala2328, and C.gamma. of Gln2329 are indicated by arrows
(FIG. 3C, left panel). Ala108 mutated to Ile was modeled by Swiss
PDB viewer (FIG. 3C, right panel). In the stick models hydrogen,
carbon, oxygen, nitrogen, and sulfur are colored as cyan, white,
red, blue, and yellow, respectively. Ribbon structures represent
.alpha.-helix (red) and .beta.-strand (green).
[0024] FIG. 4 is a Western blot analysis of R121C-L2302C and WT
factor VIII. Purified WT and mutant factor VIII proteins were
electrophoresed under non-reducing (lanes 1, 2, 5, and 6) or
reducing (lanes 3, 4, 7, and 8) conditions, transferred, and probed
with 58.12 (anti-A1 domain antibody, lane 1-4) or 2D2 (anti-A3
domain antibody, lane 5-8). Protein bands were visualized by
chemifluorescence as described in the accompanying Examples. Shown
are WT (lane 1, 3, 5, and 7) and the R121C-L2302C factor VIII
variant (lane 2, 4, 6, and 8) proteins.
[0025] FIG. 5 is a graph showing the binding affinity of A1 subunit
from WT or Ala108Ile for the A3C1C2 subunit. Acrylodan-labeled A1
subunit from WT (circles) or Ala108Ile (triangles) was titrated
with A3C1C2 and binding was detected by the change of fluorescence
as described in the accompanying Examples. Data points averaged
from 3 separate determinations were fitted to a quadratic equation
curve by non-linear least squares regression.
[0026] FIGS. 6A-C are graphs that illustrate factor VIII
R121C-L2302C and Ala108Ile variant stability. FIG. 6A shows the
factor VIII activity decay at elevated temperature. Factor VIII (4
nM) was incubated at 57.degree. C. and at the indicated times
aliquots were removed and activity was measured by factor Xa
generation assays as described in the accompanying Examples. Data
were fitted to a single exponential decay curve by non-linear least
squares regression. FIG. 6B shows the inhibition of factor VIII by
guanidinium. FVIII (50 nM) in 0-1.2 M guanidinium chloride was
incubated for 2 hrs at 23.degree. C., diluted 1/50 and factor VIII
activity was measured by factor Xa generation. Data were fitted to
a linear equation by least squares regression. Bars represent
standard error values of 3 measurements. FIG. 6C shows factor VIIIa
decay. Thrombin-activated factor VIIIa (1.5 nM) was incubated at
23.degree. C., aliquots were taken at indicated time points and
activity was measured by factor Xa generation assay as described in
the accompanying Examples. Data were fitted to a single exponential
decay curve by non-linear least squares regression. Symbols denote
WT (circles), R121C-L2302C (triangles), and Ala108Ile (squares).
Each point represents the value averaged from three separate
determinations.
[0027] FIGS. 7A-B are graphs showing the thermal stability of A1
subunit reconstituted with A3C1C2 or A3C1 subunit. Thermal decay of
reconstituted heterodimer of A1 subunit from WT (circles) or
Ala108Ile (triangles) with WT A3C1C2 subunit at 55.degree. C. (FIG.
7A) or A3C1 subunit at 52.degree. C. (FIG. 7B) was detected by
residual factor VIIIa activity following addition of A2 subunit as
described in the accompanying Examples. Data were fitted to a
single exponential decay curve by non-linear least squares
regression. Data points averaged from 3 separate determinations
were fitted to a single exponential decay curve to obtain
rates.
[0028] FIGS. 8A-C are bar graphs comparing the thermal stability
(FIG. 8A), chemical stability in the presence of guanidinium (FIG.
8B), and factor VIIIa decay (FIG. 8C) of WT and combination
mutants. The combination mutants include one or more of the A1-C2
domain interface mutations (A108I or R121C-L2302C) in combination
with one or more A1-A2 or A2-A3 domain interface mutations. Factor
VIII activity decay, guanidinium inhibition, and factor VIIIa decay
were measured as described in the accompanying Examples.
[0029] FIG. 9 is a graph comparing the effects of Ala108Ile,
Asp519Val/Glu665Val, and the combined Ala108Ile/Asp519Val/Glu665Val
variants, relative to wildtype, as measured using a thrombin
generation assay.
DETAILED DESCRIPTION OF THE INVENTION
[0030] The present invention relates to a recombinant factor VIII
having one or more mutations that result in enhanced stability of
factor VIII, in particular improved thermal and/or chemical
stability of factor VIII.
[0031] The recombinant factor VIII of the present invention can be
prepared by modifying the amino acid sequence of a wild-type factor
VIII or a mutant factor VIII that has otherwise been modified to
affect other properties of the factor VIII, such as antigenicity,
factor VIIIa stability, circulating half-life, protein secretion,
affinity for factor IXa and/or factor X, altered factor
VIII-inactivation cleavage sites, immunogenicity, shelf-life,
etc.
[0032] Suitable wild-type factor VIII that can be modified in
accordance with the present invention can be from various animals
including, without limitation, mammals such as humans (see, e.g.,
GenBank Accession Nos. AAA52484 (amino acid) and K01740
(nucleotide); and GenBank Accession Nos. CAD97566 (amino acid) and
AX746360 (nucleotide), which are hereby incorporated by reference
in their entirety), rats (see, e.g., GenBank Accession Nos.
AAQ21580 (amino acid) and AY362193 (nucleotide), which are hereby
incorporated by reference in their entirety), mice (see, e.g.,
GenBank Accession Nos. AAA37385 (amino acid) and L05573
(nucleotide), which are hereby incorporated by reference in their
entirety), guinea pigs, dogs (see, e.g., GenBank Accession Nos.
AAB87412 (amino acid) and AF016234 (nucleotide); and GenBank
Accession Nos. AACO5384 (amino acid) and AF049489 (nucleotide),
which are hereby incorporated by reference in their entirety),
cats, monkeys, chimpanzees (see, e.g., GenBank Accession Nos.
XP.sub.--529212 (amino acid) and XM.sub.--529212 (nucleotide),
which are hereby incorporated by reference in their entirety),
orangutans, cows, horses, sheep, pigs (see, e.g., GenBank Accession
Nos. NP.sub.--999332 (amino acid) and NM.sub.--214167 (nucleotide),
which are hereby incorporated by reference in their entirety),
goats, rabbits, and chickens. These and other sequences are also
available electronically via the Haemophilia A Mutation, Structure,
Test and Resource Site (or HAMSTeRS), which further provides an
alignment of human, porcine, murine, and canine factor VIII
proteins. Thus, the conservation and homology among mammalian
factor VIII proteins is well known.
[0033] By way of example, the human factor VIII cDNA nucleotide and
predicted amino acid sequences are shown below in SEQ ID NOs: 1 and
2, respectively. Human factor VIII is synthesized as an
approximately 300 kDa single chain protein with internal sequence
homology that defines the "domain" sequence
NH.sub.2-A1-A2-B-A3-C1-C2-COOH. In a factor VIII molecule, a
"domain," as used herein, is a continuous sequence of amino acids
that is defined by internal amino acid sequence identity and sites
of proteolytic cleavage by thrombin. Unless otherwise specified,
factor VIII domains include the following amino acid residues, when
the sequences are aligned with the human amino acid sequence (SEQ
ID NO: 2):
[0034] A1, residues Ala.sub.1-Arg.sub.372;
[0035] A2, residues Ser.sub.373-Arg.sub.740;
[0036] B, residues Ser.sub.741-Arg.sub.1648;
[0037] A3, residues Ser.sub.1690-Ile.sub.2032;
[0038] C1, residues Arg.sub.2033-Asn.sub.2172; and
[0039] C2, residues Ser.sub.2173-TYr.sub.2332.
[0040] The A3-C1-C2 sequence includes residues
Ser.sub.1690-Tyr.sub.2332. The remaining sequence, residues
Glu.sub.1649-Arg.sub.1689, is usually referred to as the factor
VIII light chain activation peptide. Factor VIII is proteolytically
activated by thrombin or factor Xa, which dissociates it from von
Willebrand factor, forming factor VIIIa, which has procoagulant
function. The biological function of factor VIIIa is to increase
the catalytic efficiency of factor IXa toward factor X activation
by several orders of magnitude. Thrombin-activated factor VIIIa is
a 160 kDa A1/A2/A3-C1-C2 heterotrimer that forms a complex with
factor IXa and factor X on the surface of platelets or monocytes. A
"partial domain" as used herein is a continuous sequence of amino
acids forming part of a domain.
[0041] As used herein, a residue corresponding to a particular
position refers to the residue at that position in wild type human
factor VIII; however the same position will retain its numbering
even though the residue may be at a different location in a
recombinant factor VIII of the present invention. For example, a B
domainless factor VIII lacks the B domain yet it still retains the
conventional residue numbering for domains A3, C1, and C2.
[0042] The cDNA encoding wild-type human factor VIII has a
nucleotide sequence of SEQ ID NO: 1, as follows:
TABLE-US-00001 1 GCCACCAGAA GATACTACCT GGGTGCAGTG GAACTGTCAT
GGGACTATAT 51 GCAAAGTGAT CTCGGTGAGC TGCCTGTGGA CGCAAGATTT
CCTCCTAGAG 101 TGCCAAAATC TTTTCCATTC AACACCTCAG TCGTGTACAA
AAAGACTCTG 151 TTTGTAGAAT TCACGGATCA CCTTTTCAAC ATCGCTAAGC
CAAGGCCACC 201 CTGGATGGGT CTGCTAGGTC CTACCATCCA GGCTGAGGTT
TATGATACAG 251 TGGTCATTAC ACTTAAGAAC ATGGCTTCCC ATCCTGTCAG
TCTTCATGCT 301 GTTGGTGTAT CCTACTGGAA AGCTTCTGAG GGAGCTGAAT
ATGATGATCA 351 GACCAGTCAA AGGGAGAAAG AAGATGATAA AGTCTTCCCT
GGTGGAAGCC 401 ATACATATGT CTGGCAGGTC CTGAAAGAGA ATGGTCCAAT
GGCCTCTGAC 451 CCACTGTGCC TTACCTACTC ATATCTTTCT CATGTGGACC
TGGTAAAAGA 501 CTTGAATTCA GGCCTCATTG GAGCCCTACT AGTATGTAGA
GAAGGGAGTC 551 TGGCCAAGGA AAAGACACAG ACCTTGCACA AATTTATACT
ACTTTTTGCT 601 GTATTTGATG AAGGGAAAAG TTGGCACTCA GAAACAAAGA
ACTCCTTGAT 651 GCAGGATAGG GATGCTGCAT CTGCTCGGGC CTGGCCTAAA
ATGCACACAG 701 TCAATGGTTA TGTAAACAGG TCTCTGCCAG GTCTGATTGG
ATGCCACAGG 751 AAATCAGTCT ATTGGCATGT GATTGGAATG GGCACCACTC
CTGAAGTGCA 801 CTCAATATTC CTCGAAGGTC ACACATTTCT TGTGAGGAAC
CATCGCCAGG 851 CGTCCTTGGA AATCTCGCCA ATAACTTTCC TTACTGCTCA
AACACTCTTG 901 ATGGACCTTG GACAGTTTCT ACTGTTTTGT CATATCTCTT
CCCACCAACA 951 TGATGGCATG GAAGCTTATG TCAAAGTAGA CAGCTGTCCA
GAGGAACCCC 1001 AACTACGAAT GAAAAATAAT GAAGAAGCGG AAGACTATGA
TGATGATCTT 1051 ACTGATTCTG AAATGGATGT GGTCAGGTTT GATGATGACA
ACTCTCCTTC 1101 CTTTATCCAA ATTCGCTCAG TTGCCAAGAA GCATCCTAAA
ACTTGGGTAC 1151 ATTACATTGC TGCTGAAGAG GAGGACTGGG ACTATGCTCC
CTTAGTCCTC 1201 GCCCCCGATG ACAGAAGTTA TAAAAGTCAA TATTTGAACA
ATGGCCCTCA 1251 GCGGATTGGT AGGAAGTACA AAAAAGTCCG ATTTATGGCA
TACACAGATG 1301 AAACCTTTAA GACTCGTGAA GCTATTCAGC ATGAATCAGG
AATCTTGGGA 1351 CCTTTACTTT ATGGGGAAGT TGGAGACACA CTGTTGATTA
TATTTAAGAA 1401 TCAAGCAAGC AGACCATATA ACATCTACCC TCACGGAATC
ACTGATGTCC 1451 GTCCTTTGTA TTCAAGGAGA TTACCAAAAG GTGTAAAACA
TTTGAAGGAT 1501 TTTCCAATTC TGCCAGGAGA AATATTCAAA TATAAATGGA
CAGTGACTGT 1551 AGAAGATGGG CCAACTAAAT CAGATCCTCG GTGCCTGACC
CGCTATTACT 1601 CTAGTTTCGT TAATATGGAG AGAGATCTAG CTTCAGGACT
CATTGGCCCT 1651 CTCCTCATCT GCTACAAAGA ATCTGTAGAT CAAAGAGGAA
ACCAGATAAT 1701 GTCAGACAAG AGGAATGTCA TCCTGTTTTC TGTATTTGAT
GAGAACCGAA 1751 GCTGGTACCT CACAGAGAAT ATACAACGCT TTCTCCCCAA
TCCAGCTGGA 1801 GTGCAGCTTG AGGATCCAGA GTTCCAAGCC TCCAACATCA
TGCACAGCAT 1851 CAATGGCTAT GTTTTTGATA GTTTGCAGTT GTCAGTTTGT
TTGCATGAGG 1901 TGGCATACTG GTACATTCTA AGCATTGGAG CACAGACTGA
CTTCCTTTCT 1951 GTCTTCTTCT CTGGATATAC CTTCAAACAC AAAATGGTCT
ATGAAGACAC 2001 ACTCACCCTA TTCCCATTCT CAGGAGAAAC TGTCTTCATG
TCGATGGAAA 2051 ACCCAGGTCT ATGGATTCTG GGGTGCCACA ACTCAGACTT
TCGGAACAGA 2101 GGCATGACCG CCTTACTGAA GGTTTCTAGT TGTGACAAGA
ACACTGGTGA 2151 TTATTACGAG GACAGTTATG AAGATATTTC AGCATACTTG
CTGAGTAAAA 2201 ACAATGCCAT TGAACCAAGA AGCTTCTCCC AGAATTCAAG
ACACCCTAGC 2251 ACTAGGCAAA AGCAATTTAA TGCCACCACA ATTCCAGAAA
ATGACATAGA 2301 GAAGACTGAC CCTTGGTTTG CACACAGAAC ACCTATGCCT
AAAATACAAA 2351 ATGTCTCCTC TAGTGATTTG TTGATGCTCT TGCGACAGAG
TCCTACTCCA 2401 CATGGGCTAT CCTTATCTGA TCTCCAAGAA GCCAAATATG
AGACTTTTTC 2451 TGATGATCCA TCACCTGGAG CAATAGACAG TAATAACAGC
CTGTCTGAAA 2501 TGACACACTT CAGGCCACAG CTCCATCACA GTGGGGACAT
GGTATTTACC 2551 CCTGAGTCAG GCCTCCAATT AAGATTAAAT GAGAAACTGG
GGACAACTGC 2601 AGCAACAGAG TTGAAGAAAC TTGATTTCAA AGTTTCTAGT
ACATCAAATA 2651 ATCTGATTTC AACAATTCCA TCAGACAATT TGGCAGCAGG
TACTGATAAT 2701 ACAAGTTCCT TAGGACCCCC AAGTATGCCA GTTCATTATG
ATAGTCAATT 2751 AGATACCACT CTATTTGGCA AAAAGTCATC TCCCCTTACT
GAGTCTGGTG 2801 GACCTCTGAG CTTGAGTGAA GAAAATAATG ATTCAAAGTT
GTTAGAATCA 2851 GGTTTAATGA ATAGCCAAGA AAGTTCATGG GGAAAAAATG
TATCGTCAAC 2901 AGAGAGTGGT AGGTTATTTA AAGGGAAAAG AGCTCATGGA
CCTGCTTTGT 2951 TGACTAAAGA TAATGCCTTA TTCAAAGTTA GCATCTCTTT
GTTAAAGACA 3001 AACAAAACTT CCAATAATTC AGCAACTAAT AGAAAGACTC
ACATTGATGG 3051 CCCATCATTA TTAATTGAGA ATAGTCCATC AGTCTGGCAA
AATATATTAG 3101 AAAGTGACAC TGAGTTTAAA AAAGTGACAC CTTTGATTCA
TGACAGAATG 3151 CTTATGGACA AAAATGCTAC AGCTTTGAGG CTAAATCATA
TGTCAAATAA 3201 AACTACTTCA TCAAAAAACA TGGAAATGGT CCAACAGAAA
AAAGAGGGCC 3251 CCATTCCACC AGATGCACAA AATCCAGATA TGTCGTTCTT
TAAGATGCTA 3301 TTCTTGCCAG AATCAGCAAG GTGGATACAA AGGACTCATG
GAAAGAACTC 3351 TCTGAACTCT GGGCAAGGCC CCAGTCCAAA GCAATTAGTA
TCCTTAGGAC 3401 CAGAAAAATC TGTGGAAGGT CAGAATTTCT TGTCTGAGAA
AAACAAAGTG 3451 GTAGTAGGAA AGGGTGAATT TACAAAGGAC GTAGGACTCA
AAGAGATGGT 3501 TTTTCCAAGC AGCAGAAACC TATTTCTTAC TAACTTGGAT
AATTTACATG 3551 AAAATAATAC ACACAATCAA GAAAAAAAAA TTCAGGAAGA
AATAGAAAAG 3601 AAGGAAACAT TAATCCAAGA GAATGTAGTT TTGCCTCAGA
TACATACAGT 3651 GACTGGCACT AAGAATTTCA TGAAGAACCT TTTCTTACTG
AGCACTAGGC 3701 AAAATGTAGA AGGTTCATAT GACGGGGCAT ATGCTCCAGT
ACTTCAAGAT 3751 TTTAGGTCAT TAAATGATTC AACAAATAGA ACAAAGAAAC
ACACAGCTCA 3801 TTTCTCAAAA AAAGGGGAGG AAGAAAACTT GGAAGGCTTG
GGAAATCAAA 3851 CCAAGCAAAT TGTAGAGAAA TATGCATGCA CCACAAGGAT
ATCTCCTAAT 3901 ACAAGCCAGC AGAATTTTGT CACGCAACGT AGTAAGAGAG
CTTTGAAACA 3951 ATTCAGACTC CCACTAGAAG AAACAGAACT TGAAAAAAGG
ATAATTGTGG 4001 ATGACACCTC AACCCAGTGG TCCAAAAACA TGAAACATTT
GACCCCGAGC 4051 ACCCTCACAC AGATAGACTA CAATGAGAAG GAGAAAGGGG
CCATTACTCA 4101 GTCTCCCTTA TCAGATTGCC TTACGAGGAG TCATAGCATC
CCTCAAGCAA 4151 ATAGATCTCC ATTACCCATT GCAAAGGTAT CATCATTTCC
ATCTATTAGA 4201 CCTATATATC TGACCAGGGT CCTATTCCAA GACAACTCTT
CTCATCTTCC 4251 AGCAGCATCT TATAGAAAGA AAGATTCTGG GGTCCAAGAA
AGCAGTCATT 4301 TCTTACAAGG AGCCAAAAAA AATAACCTTT CTTTAGCCAT
TCTAACCTTG 4351 GAGATGACTG GTGATCAAAG AGAGGTTGGC TCCCTGGGGA
CAAGTGCCAC 4401 AAATTCAGTC ACATACAAGA AAGTTGAGAA CACTGTTCTC
CCGAAACCAG 4451 ACTTGCCCAA AACATCTGGC AAAGTTGAAT TGCTTCCAAA
AGTTCACATT 4501 TATCAGAAGG ACCTATTCCC TACGGAAACT AGCAATGGGT
CTCCTGGCCA 4551 TCTGGATCTC GTGGAAGGGA GCCTTCTTCA GGGAACAGAG
GGAGCGATTA 4601 AGTGGAATGA AGCAAACAGA CCTGGAAAAG TTCCCTTTCT
GAGAGTAGCA 4651 ACAGAAAGCT CTGCAAAGAC TCCCTCCAAG CTATTGGATC
CTCTTGCTTG 4701 GGATAACCAC TATGGTACTC AGATACCAAA AGAAGAGTGG
AAATCCCAAG 4751 AGAAGTCACC AGAAAAAACA GCTTTTAAGA AAAAGGATAC
CATTTTGTCC 4801 CTGAACGCTT GTGAAAGCAA TCATGCAATA GCAGCAATAA
ATGAGGGACA 4851 AAATAAGCCC GAAATAGAAG TCACCTGGGC AAAGCAAGGT
AGGACTGAAA 4901 GGCTGTGCTC TCAAAACCCA CCAGTCTTGA AACGCCATCA
ACGGGAAATA 4951 ACTCGTACTA CTCTTCAGTC AGATCAAGAG GAAATTGACT
ATGATGATAC 5001 CATATCAGTT GAAATGAAGA AGGAAGATTT TGACATTTAT
GATGAGGATG 5051 AAAATCAGAG CCCCCGCAGC TTTCAAAAGA AAACACGACA
CTATTTTATT 5101 GCTGCAGTGG AGAGGCTCTG GGATTATGGG ATGAGTAGCT
CCCCACATGT 5151 TCTAAGAAAC AGGGCTCAGA GTGGCAGTGT CCCTCAGTTC
AAGAAAGTTG 5201 TTTTCCAGGA ATTTACTGAT GGCTCCTTTA CTCAGCCCTT
ATACCGTGGA 5251 GAACTAAATG AACATTTGGG ACTCCTGGGG CCATATATAA
GAGCAGAAGT 5301 TGAAGATAAT ATCATGGTAA CTTTCAGAAA TCAGGCCTCT
CGTCCCTATT 5351 CCTTCTATTC TAGCCTTATT TCTTATGAGG AAGATCAGAG
GCAAGGAGCA 5401 GAACCTAGAA AAAACTTTGT CAAGCCTAAT GAAACCAAAA
CTTACTTTTG 5451 GAAAGTGCAA CATCATATGG CACCCACTAA AGATGAGTTT
GACTGCAAAG 5501 CCTGGGCTTA TTTCTCTGAT GTTGACCTGG AAAAAGATGT
GCACTCAGGC 5551 CTGATTGGAC CCCTTCTGGT CTGCCACACT AACACACTGA
ACCCTGCTCA 5601 TGGGAGACAA GTGACAGTAC AGGAATTTGC TCTGTTTTTC
ACCATCTTTG 5651 ATGAGACCAA AAGCTGGTAC TTCACTGAAA ATATGGAAAG
AAACTGCAGG 5701 GCTCCCTGCA ATATCCAGAT GGAAGATCCC ACTTTTAAAG
AGAATTATCG 5751 CTTCCATGCA ATCAATGGCT ACATAATGGA TACACTACCT
GGCTTAGTAA 5801 TGGCTCAGGA TCAAAGGATT CGATGGTATC TGCTCAGCAT
GGGCAGCAAT 5851 GAAAACATCC ATTCTATTCA TTTCAGTGGA CATGTGTTCA
CTGTACGAAA 5901 AAAAGAGGAG TATAAAATGG CACTGTACAA TCTCTATCCA
GGTGTTTTTG 5951 AGACAGTGGA AATGTTACCA TCCAAAGCTG GAATTTGGCG
GGTGGAATGC 6001 CTTATTGGCG AGCATCTACA TGCTGGGATG AGCACACTTT
TTCTGGTGTA 6051 CAGCAATAAG TGTCAGACTC CCCTGGGAAT GGCTTCTGGA
CACATTAGAG 6101 ATTTTCAGAT TACAGCTTCA GGACAATATG GACAGTGGGC
CCCAAAGCTG 6151 GCCAGACTTC ATTATTCCGG ATCAATCAAT GCCTGGAGCA
CCAAGGAGCC 6201 CTTTTCTTGG ATCAAGGTGG ATCTGTTGGC ACCAATGATT
ATTCACGGCA
6251 TCAAGACCCA GGGTGCCCGT CAGAAGTTCT CCAGCCTCTA CATCTCTCAG 6301
TTTATCATCA TGTATAGTCT TGATGGGAAG AAGTGGCAGA CTTATCGAGG 6351
AAATTCCACT GGAACCTTAA TGGTCTTCTT TGGCAATGTG GATTCATCTG 6401
GGATAAAACA CAATATTTTT AACCCTCCAA TTATTGCTCG ATACATCCGT 6451
TTGCACCCAA CTCATTATAG CATTCGCAGC ACTCTTCGCA TGGAGTTGAT 6501
GGGCTGTGAT TTAAATAGTT GCAGCATGCC ATTGGGAATG GAGAGTAAAG 6551
CAATATCAGA TGCACAGATT ACTGCTTCAT CCTACTTTAC CAATATGTTT 6601
GCCACCTGGT CTCCTTCAAA AGCTCGACTT CACCTCCAAG GGAGGAGTAA 6651
TGCCTGGAGA CCTCAGGTGA ATAATCCAAA AGAGTGGCTG CAAGTGGACT 6701
TCCAGAAGAC AATGAAAGTC ACAGGAGTAA CTACTCAGGG AGTAAAATCT 6751
CTGCTTACCA GCATGTATGT GAAGGAGTTC CTCATCTCCA GCAGTCAAGA 6801
TGGCCATCAG TGGACTCTCT TTTTTCAGAA TGGCAAAGTA AAGGTTTTTC 6851
AGGGAAATCA AGACTCCTTC ACACCTGTGG TGAACTCTCT AGACCCACCG 6901
TTACTGACTC GCTACCTTCG AATTCACCCC CAGAGTTGGG TGCACCAGAT 6951
TGCCCTGAGG ATGGAGGTTC TGGGCTGCGA GGCACAGGAC CTCTACTGA
[0043] The wild-type human factor VIII encoded by SEQ ID NO: 1 has
an amino acid sequence of SEQ ID NO: 2, as follows:
TABLE-US-00002 1 ATRRYYLGAV ELSWDYMQSD LGELPVDARF PPRVPKSFPF
NTSVVYKKTL 51 FVEFTVHLFN IAKPRPPWMG LLGPTIQAEV YDTVVITLKN
MASHPVSLHA 101 VGVSYWKASE GAEYDDQTSQ REKEDDKVFP GGSHTYVWQV
LKENGPMASD 151 PLCLTYSYLS HVDLVKDLNS GLIGALLVCR EGSLAKEKTQ
TLHKFILLFA 201 VFDEGKSWHS ETKNSLMQDR DAASARAWPK MHTVNGYVNR
SLPGLIGCHR 251 KSVYWHVIGM GTTPEVHSIF LEGHTFLVRN HRQASLEISP
ITFLTAQTLL 301 MDLGQFLLFC HISSHQHDGM EAYVKVDSCP EEPQLRMKNN
EEAEDYDDDL 351 TDSEMDVVRF DDDNSPSFIQ IRSVAKKHPK TWVHYIAAEE
EDWDYAPLVL 401 APDDRSYKSQ YLNNGPQRIG RKYKKVRFMA YTDETFKTRE
AIQHESGILG 451 PLLYGEVGDT LLIIFKNQAS RPYNIYPHGI TDVRPLYSRR
LPKGVKHLKD 501 FPILPGEIFK YKWTVTVEDG PTKSDPRCLT RYYSSFVNME
RDLASGLIGP 551 LLICYKESVD QRGNQIMSDK RNVILFSVFD ENRSWYLTEN
IQRFLPNPAG 601 VQLEDPEFQA SNIMHSINGY VFDSLQLSVC LHEVAYWYIL
SIGAQTDFLS 651 VFFSGYTFKH KMVYEDTLTL FPFSGETVFM SMENPGLWIL
GCHNSDFRNR 701 GMTALLKVSS CDKNTGDYYE DSYEDISAYL LSKNNAIEPR
SFSQNSRHPS 751 TRQKQFNATT IPENDIEKTD PWFAHRTPMP KIQNVSSSDL
LMLLRQSPTP 801 HGLSLSDLQE AKYETFSDDP SPGAIDSNNS LSEMTHFRPQ
LHHSGDMVFT 851 PESGLQLRLN EKLGTTAATE LKKLDFKVSS TSNNLISTIP
SDNLAAGTDN 901 TSSLGPPSMP VHYDSQLDTT LFGKKSSPLT ESGGPLSLSE
ENNDSKLLES 951 GLMNSQESSW GKNVSSTESG RLFKGKRAHG PALLTKDNAL
FKVSISLLKT 1001 NKTSNNSATN RKTHIDGPSL LIENSPSVWQ NILESDTEFK
KVTPLIHDRM 1051 LMDKNATALR LNHMSNKTTS SKNMEMVQQK KEGPIPPDAQ
NPDMSFFKML 1101 FLPESARWIQ RTHGKNSLNS GQGPSPKQLV SLGPEKSVEG
QNFLSEKNKV 1151 VVGKGEFTKD VGLKEMVFPS SRNLFLTNLD NLHENNTHNQ
EKKIQEEIEK 1201 KETLIQENVV LPQIHTVTGT KNFMKNLFLL STRQNVEGSY
EGAYAPVLQD 1251 FRSLNDSTNR TKKHTAHFSK KGEEENLEGL GNQTKQIVEK
YACTTRISPN 1301 TSQQNFVTQR SKRALKQFRL PLEETELEKR IIVDDTSTQW
SKNMKHLTPS 1351 TLTQIDYNEK EKGAITQSPL SDCLTRSHSI PQANRSPLPI
AKVSSFPSIR 1401 PIYLTRVLFQ DNSSHLPAAS YRKKDSGVQE SSHFLQGAKK
NNLSLAILTL 1451 EMTGDQREVG SLGTSATNSV TYKKVENTVL PKPDLPKTSG
KVELLPKVHI 1501 YQKDLFPTET SNGSPGHLDL VEGSLLQGTE GAIKWNEANR
PGKVPFLRVA 1551 TESSAKTPSK LLDPLAWDNH YGTQIPKEEW KSQEKSPEKT
AFKKKDTILS 1601 LNACESNHAI AAINEGQNKP EIEVTWAKQG RTERLCSQNP
PVLKRHQREI 1651 TRTTLQSDQE EIDYDDTISV EMKKEDFDIY DEDENQSPRS
FQKKTRHYFI 1701 AAVERLWDYG MSSSPHVLRN RAQSGSVPQF KKVVFQEFTD
GSFTQPLYRG 1751 ELNEHLGLLG PYIRAEVEDN IMVTFRNQAS RPYSFYSSLI
SYEEDQRQGA 1801 EPRKNFVKPN ETKTYFWKVQ HHMAPTKDEF DCKAWAYFSD
VDLEKDVHSG 1851 LIGPLLVCHT NTLNPAHGRQ VTVQEFALFF TIFDETKSWY
FTENMERNCR 1901 APCNIQMEDP TFKENYRFHA INGYIMDTLP GLVMAQDQRI
RWYLLSMGSN 1951 ENIHSIHFSG HVFTVRKKEE YKMALYNLYP GVFETVEMLP
SKAGIWRVEC 2001 LIGEHLHAGM STLFLVYSNK CQTPLGMASG HIRDFQITAS
GQYGQWAPKL 2051 ARLHYSGSIN AWSTKEPFSW IKVDLLAPMI IHGIKTQGAR
QKFSSLYISQ 2101 FIIMYSLDGK KWQTYRGNST GTLMVFFGNV DSSGIKHNIF
NPPIIARYIR 2151 LHPTHYSIRS TLRMELMGCD LNSCSMPLGM ESKAISDAQI
TASSYFTNMF 2201 ATWSPSKARL HLQGRSNAWR PQVNNPKEWL QVDFQKTMKV
TGVTTQGVKS 2251 LLTSMYVKEF LISSSQDGHQ WTLFFQNGKV KVFQGNQDSF
TPVVNSLDPP 2301 LLTRYLRIHP QSWVHQIALR MEVLGCEAQD LY
[0044] A first aspect of the present invention relates to a
recombinant factor VIII that includes one or more mutations at an
interface of A1 and C2 domains of the recombinant factor VIII. This
mutation results in enhanced stability, particularly enhanced
thermal and/or chemical stability, of factor VIII. The one or more
mutations include substitution of one or more amino acid residues
with an amino acid residue having a higher hydrophobicity, or
substitution of two or more amino acid residues with Cysteine to
afford a disulfide bond between the A1 and C2 domains.
[0045] As used herein, an amino acid having a higher hydrophobicity
refers to a residue having a higher measurement or ranking of
hydrophobicity relative to a particular wild type residue at the
location of interest. The hydrophobic effect represents the
tendency of water to exclude non-polar molecules. Hydropathy scale
is a ranking list for the relative hydrophobicity of amino acid
residues and proteins. The "hydropathy index" of a protein or amino
acid is a number representing its hydrophilic or hydrophobic
properties. Different methods have been used in the art to
calculate the relative hydrophobicity of amino acid residues and
proteins (Kyte et al., "A Simple Method for Displaying the
Hydropathic Character of a Protein," J. Mol. Biol. 157: 105-32
(1982); Eisenberg D, "Three-dimensional Structure of Membrane and
Surface Proteins," Ann. Rev. Biochem. 53: 595-623 (1984); Rose et
al., "Hydrogen Bonding, Hydrophobicity, Packing, and Protein
Folding," Annu. Rev. Biomol. Struct. 22: 381-415 (1993); Kauzmann,
"Some Factors in the Interpretation of Protein Denaturation," Adv.
Protein Chem. 14: 1-63 (1959), which are hereby incorporated by
reference in their entirety). Any one of these hydrophobicity
scales can be used for the purposes of the present invention;
however, the Kyte-Doolittle hydrophobicity scale is perhaps the
most often referenced scale. The hydropathy index is directly
proportional to the hydrophobicity of the amino acid or the
protein.
[0046] As used herein, the term "interface" is used to describe a
protein surface where the atoms of the protein come in contact with
the solvent (solvent-protein interface) or with another domain
(domain interface). Domain interfaces can be either inter-domain
(between domains) or intra-domain (within domains). Various methods
are known in the art to identify interfaces. For example, the
geometric distance between atoms that belong to same or different
domains can be used to identify intra-domain or inter-domain
interfaces (structural information, such as atomic coordinates, is
available at the Protein Databank; Berman et al., "The Protein Data
Bank," Nucleic Acid Res 28:235-242 (2000), which is hereby
incorporated by reference in its entirety). Another approach is the
Accessible Surface Area (ASA), which detects the buried region of a
protein that is detached from a solvent (Jones et al., "Analysis of
Protein-protein Interaction Sites Using Surface Patches," J Mol
Biol 272:121-132 (1997), which is hereby incorporated by reference
in its entirety). A further approach is the Voronoi diagram, a
computational geometry method that uses a mathematical definition
of interface regions (Ban et al., "Interface Surfaces for
Protein-protein Complexes," Proceedings of the Research in
Computational Molecular Biology, San Diego 27-31 (2004); Poupon A,
"Voronoi and Voronoi-Related Tessellations in Studies of Protein
Structure and Interaction," Curr Opin Struct Biol 14:233-241
(2004); Kim et al., "Euclidean Voronoi Diagrams of 3D Spheres and
Applications to Protein Structure Analysis," Japan Journal of
Industrial and Applied Mathematics 2005, 22:251-265 (2005), which
are hereby incorporated by reference in their entirety). As
described herein, the factor VIII crystal structure (Shen et al.,
"The Tertiary Structure and Domain Organization of Coagulation
Factor VIII," Blood 111:1240-1247 (2008); Ngo et al., "Crystal
Structure of Human Factor VIII: Implications for the Formation of
the Factor IXa:Factor VIIIa Complex," Structure 16:597-606 (2008),
which is hereby incorporated by reference in its entirety) can be
modeled using Swiss PDB Viewer to identify residues that upon
substitution with Cysteine will allow for disulfide bond formation
(see FIG. 3B) or residues that are suitable for substitution with
an amino acid having higher hydrophobicity (see FIG. 3C).
[0047] As used herein, a region of the A1 domain that interfaces
with the C2 domain is referred to as a "C2 domain interface" and a
region of the C2 domain that interfaces with the A1 domain is
referred to as an "A1 domain interface."
[0048] The wild type (WT) factor VIII can be such that the A1
domain of the WT factor VIII includes a C2 domain interface having
the amino acid sequence of (i) KXS (aa 8-10 of SEQ ID NO: 10) where
"X" is A or S; (ii) SXXE (aa 20-23 of SEQ ID NO: 10) where "X" at
the 2.sup.nd position can be Q, K, or P, and "X" at the 3.sup.rd
position can be R, K, M, T, or A; and/or (iii) TYXW (aa 36-39 of
SEQ ID NO: 10), where "X" at the 3.sup.rd position can be V or A.
These are illustrated in FIG. 1.
[0049] The WT factor VIII can be such that the C2 domain of the WT
factor VIII includes an A1 domain interface having the amino acid
sequence of (i) XVT (aa 9-11 of SEQ ID NO: 18), where "X" is K or
R; (ii) PPXX (aa 68-71 of SEQ ID NO: 18), where "X" at the 3.sup.rd
position is L or R, and "X" at the 4.sup.th position is L, F, or V;
and/or (iii) XXQX (aa 96-99 of SEQ ID NO: 18), where the "X" at the
1.sup.st position is E or D, "X" at the 2.sup.nd position is A or
T, and "X" at the 4.sup.th position is D or Q. These are
illustrated in FIG. 2.
[0050] According to one embodiment, one or both of the A1 domain
interface and C2 domain interface include a substitution to
introduce a Cysteine residue. In preferred embodiments, the
substitution of amino acid residues at the interface of A1 and C2
domains is carried out such that at least a pair of amino acids are
substituted with Cysteine. In this embodiment, the pair of Cysteine
residues form an inter-domain (A1 to C2 domain) disulfide bond such
that the stability of the recombinant factor VIII is enhanced.
[0051] In another embodiment of the recombinant factor VIII of the
present invention, the one or more mutations at the interface of A1
and C2 domains of the recombinant factor VIII is the replacement of
one or more amino acid residues with an amino acid incapable of
forming disulfide bonds but having a higher hydrophobicity
index.
[0052] In a further embodiment, multiple mutations are introduced
at several interfaces of the A1 and C2 domains of factor VIII,
including: (i) a pair of substitutions to introduce a pair of
Cysteine residues that are capable of forming an inter-domain (A1
to C2 domain) disulfide bond; and (ii) the replacement of one or
more amino acid residues with an amino acid incapable of forming
disulfide bonds but having a higher hydrophobicity index.
[0053] The recombinant factor VIII according to several embodiments
of the present invention are characterized by an A1 domain that
includes a C2 domain interface having the amino acid sequence of
(i) KXS (SEQ ID NO: 19), where "X" is T, G, A, M, C, F, L, V, or I;
(ii) SXXX (SEQ ID NO: 20), where "X" at the 2.sup.nd position is
wild type (Q, K, or P) or E, D, N, H, Y, W, S, T, G, A, M, C, F, L,
V, or I, "X" at the 3.sup.rd position can be any amino acid other
than R or preferably any amino acid other than R, K, M, T, or A;
and "X" at the 4.sup.th position is wild type (E) or Q, D, N, H, P,
Y, W, S, T, G, A, M, C, F, L, V, or I; and/or (iii) TYXW (SEQ ID
NO: 21), where "X" is M, C, F, L, V, or I. In at least one of the
C2 domain interfaces, one of the X residues represents a
substitution of a wild type residue.
[0054] The recombinant factor VIII according to several embodiments
of the present invention are characterized by a C2 domain that
includes an A1 domain interface having the amino acid sequence of
(i) XVT (SEQ ID NO: 22), where "X" can be any amino acid other than
K or R; (ii) PPXX (SEQ ID NO: 23), where "X" at the 3.sup.rd
position can be any amino acid besides L or R and "X" at the
4.sup.th position is L, V, or I; and/or (iii) XXQX (SEQ ID NO: 24),
where "X" at the 1.sup.st position is wild type (E or D) or Q, N,
H, P, Y, W, S, T, G, A, M, C, F, L, V, or I, "X" at the 2.sup.nd
position is wild type (A or T) or G, M, C, F, L, V, or I, and "X"
at the 4.sup.th position is wild type (D or Q) or N, H, P, Y, W, S,
T, G, A, M, C, F, L, V, or I. In at least one of the A1 domain
interfaces, one of the X residues represents a substitution of a
wild type residue.
[0055] In certain embodiments, where a disulfide linkage is formed
between A1 and C2 domains using a cysteine substitution, the
cysteine substitution occurs at residue 121 of human factor VIII
(i.e., the C2 domain interface is SEQ ID NO: 20, where X at the
third position is cysteine) and residue 2302 of human factor VIII
(i.e., the A1 domain interface is SEQ ID NO: 23, where X at the
fourth position is cysteine). In other embodiments, the cysteine
substitution occurs at a residue other than residues 121 and 2302
of human factor VIII.
[0056] One embodiment of the recombinant factor VIII of the present
invention includes an A1 domain having a C2 domain interface that
includes the amino acid sequence KXS (SEQ ID NO: 19), where the
second residue (corresponding to position 108 of SEQ ID NO: 2) is
Valine, Isoleucine, or Leucine.
[0057] A further embodiment of the recombinant factor VIII of the
present invention includes a C2 domain having an A1 domain
interface that includes the amino acid sequence of XVT (SEQ ID NO:
22), where X (corresponding to position 2328 of SEQ ID NO: 2) is
other than Lysine or Arginine.
[0058] Another embodiment of the recombinant factor VIII includes
an A1 domain having a C2 domain interface that includes the amino
acid sequence of SXXE (SEQ ID NO: 25), where the second residue can
be Q, K, P, E, D, N, H, Y, W, S, T, G, A, M, C, F, L, V, or I and
the third residue (corresponding to position 121 of SEQ ID NO: 2)
is cysteine; and a C2 domain having an A1 domain interface that
includes the amino acid sequence of PPXX (SEQ ID NO: 23), where X
at the 3.sup.rd position is any amino acid besides L or R, and X at
the 4.sup.th position (corresponding to position 2302 of SEQ ID NO:
2) is cysteine.
[0059] Yet another embodiment of the recombinant factor includes a
C2 domain having an A1 domain interface that includes the amino
acid sequence of XXQX (SEQ ID NO: 24), where the 1.sup.st residue
is E, D, Q, N, H, P, Y, W, S, T, G, A, M, C, F, L, V, or I; the
2.sup.nd residue (corresponding to position 2328 of SEQ ID NO: 2)
is Valine, Isoleucine, or Leucine; and the 4.sup.th residue is D,
Q, N, H, P, Y, W, S, T, G, A, M, C, F, L, V, or I.
[0060] The recombinant factor VIII according to the present
invention can also have more than one mutation as described supra.
In one preferred embodiment the recombinant factor VIII has two or
more amino acid substitutions.
[0061] According to one embodiment, the recombinant factor VIII
includes (i) an A1 domain having a C2 domain interface that
includes the amino acid sequence of KXS (SEQ ID NO: 19), where X
(corresponding to position 108 of SEQ ID NO: 2) is Isoleucine,
Leucine, or Valine; and (ii) a C2 domain having an A1 domain
interface that includes the amino acid sequence XXQX (SEQ ID NO:
24), where the 1.sup.st and 4.sup.th residues are as described
above and the 2.sup.nd residue (corresponding to position 2328 of
SEQ ID NO: 2) is Isoleucine, Leucine, or Valine.
[0062] Suitable mutant factor VIII sequences that can be modified
in accordance with the present invention can also include any
previously known or subsequently identified mutant factor VIII
sequences that have modified properties with regard to various
attributes, including, without limitation, antigenicity,
circulating half-life, factor VIIIa stability, protein secretion,
affinity for factor IXa and/or factor X, altered factor
VIII-inactivation cleavage sites, altered activated Protein C
cleavage sites, enhanced specific activity of factor VIIIa,
immunogenicity, and shelf-life.
[0063] In one embodiment the recombinant factor VIII of the present
invention further comprises one or more of (i) factor IXa and/or
factor X binding domains modified to enhance the affinity of the
recombinant factor VIII for one or both of factor IXa and factor X;
(ii) modified sites that enhance secretion in culture; (iii)
modified serum protein binding sites that enhance the circulating
half-life thereof; (iv) at least one glycosylation recognition
sequence that is effective in decreasing antigenicity and/or
immunogenicity thereof; (v) a modified A1 domain calcium-binding
site that improves specific activity of the recombinant factor
Villa; (vi) modified activated protein C-cleavage site; (vii) a
modified A1 and A2 domain interface to enhance factor VIIIa
stability; and (viii) a modified A2 and A3 domain interface to
enhance factor VIIIa stability.
[0064] The recombinant factor VIII of the present invention can be
one that has a combination of mutations, including one or more
mutations at an interface of A1 and C2 domains of recombinant
factor VIII as described supra and one or more mutations at the A1
and A2 domain interface and/or the A2 and A3 domain interface. Such
a recombinant factor VIII in addition to the one or more mutations
at the A1 and C2 domain interface also includes substitution of one
or more charged amino acid residues with a hydrophobic amino acid
residue at either or both of the A1 and A2 or A2 and A3 domain
interfaces.
[0065] Preferably, the charged residue to be replaced is either a
Glu or Asp residue that does not participate in hydrogen bonding
between the A1 and A2 or A2 and A3 domains. The hydrophobic amino
acid residue that replaces the charged residue can be any of Ala,
Val, Ile, Leu, Met, Phe, or Trp. Particularly preferred recombinant
factor VIII of the present invention includes a substitution of the
residue corresponding to Glu287 of wild type factor VIII, a
substitution of the residue corresponding to Asp302 of wild type
factor VIII, a substitution of the residue corresponding to Asp519
of wild type factor VIII, a substitution of the residue
corresponding to Glu665 of wild type factor VIII, a substitution of
the residue corresponding to Glu1984 of wild type factor VIII, or
combinations thereof. The D302A, E287A, E665A, E665V, D519A, D519V,
E1984A, and E1984V substitutions are preferred for achieving a
recombinant factor VIII that has enhanced stability of both factor
VIII and factor VIIIa. Preferred combinations of these
substitutions include, without limitation, those corresponding to
D519AE665V, D519VE665V, and D519VE1984A mutants, as well as
D519AE665VE1984A and D519VE665VE1984A mutants. The enhanced
stability of these mutants is believed to be achieved by
stabilizing the inter-domain interface in factor VIII as well as
reducing A2 subunit dissociation from A1/A3C1C2 as compared to wild
type factor VIIIa. Exemplary mutants of this type are described in
U.S. Patent Application Publ. No. US2009/0118184 to Fay et al.,
which is hereby incorporated by reference in its entirety.
[0066] Examples of mutant factor VIII possessing substitutions at
the A1-C2 domain interface as well as one or both of the A1-A2 and
A2-A3 domain interfaces include, without limitation,
A108ID519AE665V, A108ID519VE665V, A108ID519VE1984A,
A108ID519AE665VE1984A, A108ID519VE665VE1984A,
R121C-L2302C/D519AE665V, R121C-L2302C/D519VE665V,
R121C-L2302C/D519VE1984A, R121C-L2302C/D519AE665VE1984A, and
R121C-L2302C/D519VE665VE1984A. Each of these mutant factor VIII can
be expressed in a B-domainless form, as described below.
[0067] Another example of a suitable mutant factor VIII that can be
modified in accordance with the present invention is a factor VIII
having a modified calcium binding site, preferably at an amino acid
corresponding to residue 113 of SEQ ID NO: 2. This affords a factor
VIIIa having enhanced specific activity. Exemplary mutants of this
type are described in U.S. Patent Application Publ. No.
US2007/0265199 to Fay et al., which is hereby incorporated by
reference in its entirety. Preferably, the residue 113 mutant also
is modified in accordance with one or more of the mutations
described above (e.g., at positions 287, 302, 519, 665, and/or
1984) to afford a high stability/high specific activity factor VIII
protein. Exemplary high stability/high specific activity factor
VIII proteins include, without limitation: those possessing
combined substitutions E113AD519A, E113AD519V, E113AE665A,
E113AE665V, E113AE1984V, E113AD519AE665V, E113AD519VE665V,
E113AD519VE1984A, E113AD519AE665VE1984A, and
E113AD519VE665VE1984A.
[0068] Examples of mutant factor VIII possessing substitutions at
the A1-C2 domain interface as well as the residue 113 substitution,
and one or both of the A1-A2 and A2-A3 domain interface
substitutions include, without limitation, A108IE113AD519AE665V,
A108IE113AD519VE665V, A108IE113AD519VE1984A,
A108IE113AD519AE665VE1984A, A108IE113AD519VE665VE1984A,
R121C-L2302C/E113AD519AE665V, R121C-L2302C/E113AD519VE665V,
R121C-L2302C/E113AD519VE1984A, R121C-L2302C/E113AD519AE665VE1984A,
and R121C-L2302C/E113AD519VE665VE1984A. Each of these mutant factor
VIII can be expressed in a B-domainless form, as described
below.
[0069] A third example of a suitable mutant factor VIII that can be
modified in accordance with the present invention is a B-domainless
factor VIII that contains amino acid residues 1-740 and 1690-2332
of SEQ ID NO: 2 (see, e.g., U.S. Pat. No. 6,458,563 to Lollar,
which is hereby incorporated by reference in its entirety).
[0070] In one embodiment of the B-domainless recombinant factor
VIII of the present invention, the B-domain is replaced by a DNA
linker segment and at least one codon is replaced with a codon
encoding an amino acid residue that has the same charge as a
corresponding residue of porcine factor VIII (see, e.g., U.S.
Patent Application Publication No. 2004/0197875 to Hauser et al.,
which is hereby incorporated by reference in its entirety).
[0071] In another embodiment of the B-domainless recombinant factor
VIII of the present invention, the modified mutant factor VIII is
encoded by a nucleotide sequence having a truncated factor IX
intron 1 inserted in one or more locations (see, e.g., U.S. Pat.
No. 6,800,461 to Negrier and U.S. Pat. No. 6,780,614 to Negrier,
each of which is hereby incorporated by reference in its entirety).
This recombinant factor VIII can be used for yielding higher
production of the recombinant factor VIII in vitro as well as in a
transfer vector for gene therapy (see, e.g., U.S. Pat. No.
6,800,461 to Negrier, which is hereby incorporated by reference in
its entirety). In a particular example of this embodiment, the
recombinant factor VIII can be encoded by a nucleotide sequence
having a truncated factor IX intron 1 inserted in two locations,
and having a promoter that is suitable for driving expression in
hematopoietic cell lines, and specifically in platelets (see, e.g.,
U.S. Pat. No. 6,780,614 to Negrier, which is hereby incorporated by
reference in its entirety).
[0072] Regardless of the embodiment, the B-domainless factor VIII
preferably contains one or more of the mutations described above
(e.g., modified A1 domain interface and/or C2 domain interface, as
well as any other mutations to affect other properties of the
resulting factor VIII). Recombinant factor VIII proteins prepared
in accordance with the Examples herein are B-domainless.
[0073] A fourth example of a suitable mutant factor VIII that can
be modified in accordance with the present invention is a chimeric
human/animal factor VIII that contains one or more domains, or
portions thereof, from human factor VIII and one or more domains,
or portions thereof, from a non-human mammalian factor VIII. One or
more animal amino acid residues can be substituted for human amino
acid residues that are responsible for the antigenicity of human
factor VIII. In particular, animal (e.g., porcine) residue
substitutions can include, without limitation, one or more of the
following: R484A, R488G, P485A, L486S, Y487L, Y487A, S488A, S488L,
R489A, R4895, R490G, L491S, P492L, P492A, K493A, G494S, V495A,
K496M, H497L, L498S, K499M, D500A, F501A, P502L, 1503M, L504M,
P505A, G506A, E507G, 1508M, 1508A, M2199I, F2200L, L2252F, V2223A,
K2227E, and/or L2251 (U.S. Pat. No. 5,859,204 to Lollar, U.S. Pat.
No. 6,770,744 to Lollar, and U.S. Patent Application Publication
No. 2003/0166536 to Lollar, each of which is hereby incorporated by
reference in its entirety). Preferably, the recombinant chimeric
factor VIII contains one or more of the mutations described above
(e.g., modified A1 domain interface and/or C2 domain
interface).
[0074] A fifth example of a suitable mutant factor VIII that can be
modified in accordance with the present invention is a factor VIII
that has enhanced affinity for factor IXa (see, e.g., Fay et al.,
"Factor VIIIa A2 Subunit Residues 558-565 Represent a Factor IXa
Interactive Site," J. Biol. Chem. 269(32):20522-7 (1994); Bajaj et
al., "Factor IXa: Factor VIIIa Interaction. Helix 330-338 of Factor
IXa Interacts with Residues 558-565 and Spatially Adjacent Regions
of the A2 Subunit of Factor VIIIa," J. Biol. Chem. 276(19):16302-9
(2001); and Lenting et al., "The Sequence Glu1811-Lys1818 of Human
Blood Coagulation Factor VIII Comprises a Binding Site for
Activated Factor IX," J. Biol. Chem. 271(4):1935-40 (1996), each of
which is hereby incorporated by reference in its entirety) and/or
factor X (see, e.g., Lapan et al., "Localization of a Factor X
Interactive Site in the A1 Subunit of Factor VIIIa," J. Biol. Chem.
272:2082-88 (1997), which is hereby incorporated by reference in
its entirety). Preferably, the enhanced-affinity factor VIII
contains one or more of the mutations described above (e.g.,
modified A1 domain interface and/or C2 domain interface).
[0075] A sixth example of a suitable mutant factor VIII that can be
modified in accordance with the present invention is a factor VIII
that is modified to enhance secretion of the factor VIII (see,
e.g., Swaroop et al., "Mutagenesis of a Potential
Immunoglobulin-Binding Protein-Binding Site Enhances Secretion of
Coagulation Factor VIII," J. Biol. Chem. 272(39):24121-4 (1997),
which is hereby incorporated by reference in its entirety).
Preferably, the secretion enhanced mutant factor VIII contains one
or more of the mutations identified above (e.g., modified A1 domain
interface and/or C2 domain interface).
[0076] A seventh example of a suitable mutant factor VIII that can
be modified in accordance with the present invention is a factor
VIII with an increased circulating half-life. This modification can
be made using various approaches, including, without limitation, by
reducing interactions with heparan sulfate (Sarafanov et al., "Cell
Surface Heparan Sulfate Proteoglycans Participate in Factor VIII
Catabolism Mediated by Low Density Lipoprotein Receptor-Related
Protein," J. Biol. Chem. 276(15):11970-9 (2001), which is hereby
incorporated by reference in its entirety) and/or low-density
lipoprotein receptor-related protein ("LRP") (Saenko et al., "Role
of the Low Density Lipoprotein-Related Protein Receptor in
Mediation of Factor VIII Catabolism," J. Biol. Chem.
274(53):37685-92 (1999); and Lenting et al., "The Light Chain of
Factor VIII Comprises a Binding Site for Low Density Lipoprotein
Receptor-Related Protein," J. Biol. Chem. 274(34):23734-9 (1999),
each of which is hereby incorporated by reference in its entirety).
Preferably, the half-life enhanced mutant factor VIII contains one
or more of the mutations described above (e.g., modified A1 domain
interface and/or C2 domain interface).
[0077] An eighth example of a suitable mutant factor VIII that can
be modified in accordance with the present invention is a modified
factor VIII encoded by a nucleotide sequence modified to code for
amino acids within known, existing epitopes to produce a
recognition sequence for glycosylation at asparagines residues
(see, e.g., U.S. Pat. No. 6,759,216 to Lollar, which is hereby
incorporated by reference in its entirety). The mutant factor VIII
of this example can be useful in providing a modified factor VIII
that escapes detection by existing inhibitory antibodies (low
antigenicity factor VIII) and which decreases the likelihood of
developing inhibitory antibodies (low immunogenicity factor VIII).
In one particular embodiment of this example, the modified factor
VIII is mutated to have a consensus amino acid sequence for
N-linked glycosylation. An example of such a consensus sequence is
N--X-S/T, where N is asparagine, X is any amino acid, and S/T
stands for serine or threonine (see U.S. Pat. No. 6,759,216 to
Lollar, which is hereby incorporated by reference in its entirety).
Preferably, the glycosylation site-modified factor VIII contains
one or more of the mutations identified above (e.g., modified A1
domain interface and/or C2 domain interface).
[0078] A ninth example of a suitable mutant factor VIII that can be
modified in accordance with the present invention is a modified
factor VIII that is a procoagulant-active factor VIII having
various mutations (see, e.g., U.S. Patent Application Publication
No. 2004/0092442 to Kaufman et al., which is hereby incorporated by
reference in its entirety). One example of this embodiment relates
to a modified factor VIII that has been modified to (i) delete the
von Willebrand factor binding site, (ii) add a mutation at Arg 740,
and (iii) add an amino acid sequence spacer between the A2- and
A3-domains, where the amino acid spacer is of a sufficient length
so that upon activation, the procoagulant-active factor VIII
protein becomes a heterodimer (see U.S. Patent Application
Publication No. 2004/0092442 to Kaufman et al., which is hereby
incorporated by reference in its entirety). Preferably,
procoagulant active factor VIII is also modified to contain one or
more of the mutations described above (e.g., at positions modified
A1 domain interface and/or C2 domain interface).
[0079] A tenth example of a suitable mutant factor VIII that can be
modified in accordance with the present invention is a modified
factor VIII that includes a substitution of one or more amino acid
residues within a region surrounding an activated protein C
cleavage site, except that the cleavable Arg scissile bond (at
Arg336 and/or Arg562) is not substituted (see, e.g., U.S. Patent
Application Publication No. 2009/0118185 to Fay et al., which is
hereby incorporated by reference in its entirety). In the most
preferred embodiments, the one or more substitutions appears within
the P4-P3' activated protein C cleavage site, which can be the site
corresponding to wild type residues 333-339 of the A1 domain or the
site corresponding to residues 559-565 of the A2 domain. Exemplary
mutant P4-P3' regions, which include the substitution of one or
more amino acids include, without limitation, VDQRGNQ (SEQ ID NO:
26) neighboring Arg562, VDQRMKN (SEQ ID NO: 27) neighboring Arg562,
and PQLRGNQ (SEQ ID NO: 28) neighboring Arg336, PDLRMKN (SEQ ID NO:
29) neighboring Arg336, PQQRMKN (SEQ ID NO: 30) neighboring Arg336,
PQRRMKN (SEQ ID NO: 31) neighboring Arg336, PQLRGKN (SEQ ID NO: 32)
neighboring Arg336, PQLRMIN (SEQ ID NO: 33) neighboring Arg336, and
PQLRMNN (SEQ ID NO: 34) neighboring Arg336. These substitutions are
preferred for achieving a mutant factor VIIIa having a reduced rate
of inactivation by activated protein C, but unlike mutants having
single mutation replacements of the P1 Arg residue the resulting
factor VIIIa is capable of being inactivated by activated protein
C. Preferably, factor VIII having a modified activated protein C
cleavage site is also modified to contain one or more of the
mutations described above (e.g., at positions modified A1 domain
interface and/or C2 domain interface).
[0080] Further, the mutant factor VIII can be modified to take
advantage of various advancements regarding recombinant coagulation
factors generally (see, e.g., Saenko et al., "The Future of
Recombinant Coagulation Factors," J. Thrombosis and Haemostasis
1:922-930 (2003), which is hereby incorporated by reference in its
entirety).
[0081] The recombinant factor VIII of the present invention can be
modified at any residue to stabilize the A1/C2 domain interfaces
(includes positions corresponding to 108, 121, 2302, 2328 of the WT
factor VIII), as well as be modified at any charged residue that
destabilizes the A1A2 or A2A3 domain interfaces (including
positions 287, 302, 519, 665, or 1984), be modified to be
B-domainless, to be chimeric, to have modified calcium binding
sites that enhance factor VIIIa activity (e.g., at position 113),
to have altered inactivation cleavage sites, to have enhanced
factor IXa and/or factor X affinity, to have enhanced secretion, to
have an increased circulating half-life, or to have mutant
glycosylation sites; or to possess any one or more of such
modifications in addition to the one or more modifications to
charged residues, including a modified calcium-binding site that
improves activity of the recombinant factor VIII. A number of
exemplary B-domainless high stability recombinant factor VIII
proteins are described in the Examples.
[0082] The recombinant factor VIII is preferably produced in a
substantially pure form. In a particular embodiment, the
substantially pure recombinant factor VIII is at least about 80%
pure, more preferably at least 90% pure, most preferably at least
95% pure. A substantially pure recombinant factor VIII can be
obtained by conventional techniques well known in the art.
Typically, the substantially pure recombinant factor VIII is
secreted into the growth medium of recombinant host cells.
Alternatively, the substantially pure recombinant factor VIII is
produced but not secreted into growth medium. In such cases, to
isolate the substantially pure recombinant factor VIII, the host
cell carrying a recombinant plasmid is propagated, lysed by
sonication, heat, or chemical treatment, and the homogenate is
centrifuged to remove cell debris. The supernatant is then
subjected to sequential ammonium sulfate precipitation. The
fraction containing the substantially pure recombinant factor VIII
is subjected to gel filtration in an appropriately sized dextran or
polyacrylamide column to separate the recombinant factor VIII. If
necessary, a protein fraction (containing the substantially pure
recombinant factor VIII) may be further purified by high
performance liquid chromatography ("HPLC").
[0083] Another aspect of the present invention relates to an
isolated nucleic acid molecule that encodes the recombinant factor
VIII of the present invention. The isolated nucleic acid molecule
encoding the recombinant factor VIII can be either RNA or DNA.
[0084] In another embodiment the isolated nucleic acid molecule can
have a nucleotide sequence encoding a recombinant factor VIII
according to the present invention which further comprises one or
more of (i) factor IXa and/or factor X binding domains modified to
enhance the affinity of the recombinant factor VIII for one or both
of factor IXa and factor X; (ii) modified sites that enhance
secretion in culture; (iii) modified serum protein binding sites
that enhance the circulating half-life thereof; (iv) at least one
glycosylation recognition sequence that is effective in decreasing
antigenicity and/or immunogenicity thereof; (v) a modified
calcium-binding site that improves specific activity of the
recombinant factor Villa; (vi) modified activated protein
C-cleavage site; (vii) a modified A1 and A2 domain interface; and
(viii) a modified A2 and A3 domain interface.
[0085] In one embodiment, the isolated nucleic acid molecule can
have a nucleotide sequence encoding a modified A1/A2 domain
interface or A2/A3 domain interface (e.g., at positions
corresponding to positions 287, 302, 519, 665, 1984 and/or 332-340
of SEQ ID NO: 2), as modified with one or more of the substitutions
affecting the A1/C2 domain interfaces (e.g., SEQ ID NOS:
19-25).
[0086] In another embodiment, the isolated nucleic acid molecule
can have a nucleotide sequence encoding a mutation at position 113
that enhances factor VIII specific activity, as modified with one
or more of the substitutions affecting the A1/C2 domain interfaces
(e.g., SEQ ID NOS: 19-25).
[0087] In another embodiment, the isolated nucleic acid molecule
can have a nucleotide sequence encoding a B-domainless factor VIII
of the type described above, as modified with one or more of the
substitutions affecting the A1/C2 domain interfaces (e.g., SEQ ID
NOS: 19-25).
[0088] In another embodiment, the isolated nucleic acid molecule
can have a nucleotide sequence encoding a chimeric human/porcine of
the type described above, as modified with one or more of the
substitutions affecting the A1/C2 domain interfaces (e.g., SEQ ID
NOS: 19-25).
[0089] In another embodiment, the isolated nucleic acid molecule
can have a nucleotide sequence encoding a factor VIII whose
inactivation sites have been modified as described above, as
further modified with one or more of the substitutions affecting
the A1/C2 domain interfaces (e.g., SEQ ID NOS: 19-25).
[0090] In yet another embodiment, the isolated nucleic acid
molecule can have a nucleotide sequence encoding a factor VIII
whose affinity for factor IXa and/or factor X has been enhanced, as
further modified with one or more of the substitutions affecting
the A1/C2 domain interfaces (e.g., SEQ ID NOS: 19-25).
[0091] In a still further embodiment, the isolated nucleic acid
molecule can have a nucleotide sequence encoding a factor VIII
whose affinity for various serum-binding proteins has been altered
to increase its circulating half-life, as further modified with one
or more of the substitutions affecting the A1/C2 domain interfaces
(e.g., SEQ ID NOS: 19-25).
[0092] In a further embodiment, the isolated nucleic acid molecule
can have a nucleotide sequence encoding a factor VIII that has
increased secretion in culture, as further modified with one or
more of the substitutions affecting the A1/C2 domain interfaces
(e.g., SEQ ID NOS: 19-25).
[0093] In a further embodiment, the isolated nucleic acid molecule
can have a nucleotide sequence encoding a factor VIII that
possesses one or more non-naturally occurring glycosylation site,
as further modified with one or more of the substitutions affecting
the A1/C2 domain interfaces (e.g., SEQ ID NOS: 19-25).
[0094] In a still further embodiment, the isolated nucleic acid
molecule can have a nucleotide sequence encoding a factor VIII that
has a modified activated protein C cleavage site, as further
modified with one or more of the substitutions affecting the A1/C2
domain interfaces (e.g., SEQ ID NOS: 19-25).
[0095] In yet another embodiment, the isolated nucleic acid
molecule encodes a recombinant factor VIII that is modified at any
one or more charged residues as described above and is also
modified to possess any two or more of the following: modified to
be B-domainless, modified to be chimeric, modified to have altered
inactivation cleavage sites, modified to have enhanced factor IXa
and/or factor X affinity, modified to have enhanced secretion,
modified to have an increased circulating half-life, modified to
possess one or more non-naturally occurring glycosylation site,
modified within a calcium-binding site (e.g., at position 113) such
that the specific activity of the recombinant factor VIII is
improved, modified activated protein C-cleavage site, a modified A1
and A2 domain interface, and a modified A2 and A3 domain
interface.
[0096] Another aspect of the present invention relates to a
recombinant DNA expression system that includes an isolated DNA
molecule of the present invention, which expression system encodes
a recombinant factor VIII. In one embodiment, the DNA molecule is
in sense orientation relative to a promoter.
[0097] A further aspect of the present invention relates to a host
cell including an isolated nucleic acid molecule encoding the
recombinant factor VIII of the present invention. In a particular
embodiment, the host cell can contain the isolated nucleic acid
molecule in DNA molecule form, either as a stable plasmid or as a
stable insertion or integration into the host cell genome. In
another embodiment, the host cell can contain a DNA molecule in an
expression system. Suitable host cells can be, without limitation,
animal cells (e.g., baby hamster kidney ("BHK") cells), bacterial
cells (e.g., E. coli), insect cells (e.g., Sf9 cells), fungal
cells, yeast cells (e.g., Saccharomyces or Schizosaccharomyces),
plant cells (e.g., Arabidopsis or tobacco cells), or algal
cells.
[0098] The recombinant DNA expression system and host cells can be
produced using various recombinant techniques well-known in the
art, as further discussed below.
[0099] The DNA molecule encoding the recombinant factor VIII of the
present invention can be incorporated in cells using conventional
recombinant DNA technology. Generally, this involves inserting the
DNA molecule into an expression system to which the DNA molecule is
heterologous (i.e., not normally present). The heterologous DNA
molecule is inserted into the expression system or vector in sense
orientation and correct reading frame. The vector contains the
necessary elements for the transcription and translation of the
inserted protein-coding sequences. Thus, one embodiment of the
present invention provides a DNA construct containing the isolated
nucleic acid of the present invention, which is operably linked to
both a 5' promoter and a 3' regulatory region (i.e., transcription
terminator) capable of affording transcription and expression of
the encoded recombinant factor VIII of the present invention in
host cells or host organisms.
[0100] With respect to the recombinant expression system of the
present invention, an expression vector containing a DNA molecule
encoding the recombinant factor VIII of the present invention can
be made using common techniques in the art. The nucleic acid
molecules of the present invention can be inserted into any of the
many available expression vectors using reagents that are well
known in the art. In preparing a DNA vector for expression, the
various DNA sequences may normally be inserted or substituted into
a bacterial plasmid. Any convenient plasmid may be employed, which
will be characterized by having a bacterial replication system, a
marker which allows for selection in a bacterium, and generally one
or more unique, conveniently located restriction sites. The
selection of a vector will depend on the preferred transformation
technique and target host for transformation.
[0101] A variety of host-vector systems may be utilized to express
the recombinant factor VIII-encoding sequence(s). Primarily, the
vector system must be compatible with the host cell used.
Host-vector systems include but are not limited to the following:
bacteria transformed with bacteriophage DNA, plasmid DNA, or cosmid
DNA; microorganisms such as yeast containing yeast vectors;
mammalian cell systems infected with virus (e.g., vaccinia virus,
adenovirus, adeno-associated virus, etc.); insect cell systems
infected with virus (e.g., baculovirus); and plant cells infected
by bacteria (e.g., Agrobacterium). The expression elements of these
vectors vary in their strength and specificities. Depending upon
the host-vector system utilized, any one of a number of suitable
transcription and translation elements can be used.
[0102] When recombinantly produced, the factor VIII protein or
polypeptide (or fragment or variant thereof) is expressed in a
recombinant host cell, typically, although not exclusively, a
eukaryote.
[0103] Suitable vectors for practicing the present invention
include, but are not limited to, the following viral vectors such
as lambda vector system gt11, gtWES.tB, Charon 4, and plasmid
vectors such as pCMV, pBR322, pBR325, pACYC177, pACYC184, pUC8,
pUC9, pUC18, pUC19, pLG339, pR290, pKC37, pKC101, SV 40,
pBluescript II SK +/- or KS +/- (see "Stratagene Cloning Systems"
Catalog (1993)), pQE, pIH821, pGEX, pET series (Studier et al, "Use
of T7 RNA Polymerase to Direct Expression of Cloned Genes," Methods
in Enzymology 185:60-89 (1990), which is hereby incorporated by
reference in its entirety), and any derivatives thereof. Any
appropriate vectors now known or later described for genetic
transformation are suitable for use with the present invention.
[0104] Recombinant molecules can be introduced into cells via
transformation, particularly transduction, conjugation,
mobilization, or electroporation. The DNA sequences are cloned into
the vector using standard cloning procedures in the art, as
described by Maniatis et al., Molecular Cloning: A Laboratory
Manual, Cold Springs Harbor, N.Y.: Cold Springs Laboratory, (1982),
which is hereby incorporated by reference in its entirety.
[0105] U.S. Pat. No. 4,237,224 issued to Cohen and Boyer, which is
hereby incorporated by reference in its entirety, describes the
production of expression systems in the form of recombinant
plasmids using restriction enzyme cleavage and ligation with DNA
ligase. These recombinant plasmids are then introduced by means of
transformation and replicated in unicellular cultures including
prokaryotic organisms and eukaryotic cells grown in tissue
culture.
[0106] Different genetic signals and processing events control many
levels of gene expression (e.g., DNA transcription and messenger
RNA (mRNA) translation).
[0107] Transcription of DNA is dependent upon the presence of a
promoter which is a DNA sequence that directs the binding of RNA
polymerase and thereby promotes mRNA synthesis. The DNA sequences
of eukaryotic promoters differ from those of prokaryotic promoters.
Furthermore, eukaryotic promoters and accompanying genetic signals
may not be recognized in or may not function in a prokaryotic
system, and, further, prokaryotic promoters are not recognized and
do not function in eukaryotic cells.
[0108] Similarly, translation of mRNA in prokaryotes depends upon
the presence of the proper prokaryotic signals which differ from
those of eukaryotes. Efficient translation of mRNA in prokaryotes
requires a ribosome binding site called the Shine-Dalgarno ("SD")
sequence on the mRNA. This sequence is a short nucleotide sequence
of mRNA that is located before the start codon, usually AUG, which
encodes the amino-terminal methionine of the protein. The SD
sequences are complementary to the 3'-end of the 16S rRNA
(ribosomal RNA) and probably promote binding of mRNA to ribosomes
by duplexing with the rRNA to allow correct positioning of the
ribosome. For a review on maximizing gene expression, see Roberts
and Lauer, Methods in Enzymology 68:473 (1979), which is hereby
incorporated by reference in its entirety.
[0109] Promoters vary in their "strength" (i.e., their ability to
promote transcription). For the purposes of expressing a cloned
gene, it is generally desirable to use strong promoters in order to
obtain a high level of transcription and, hence, expression of the
gene. Depending upon the host cell system utilized, any one of a
number of suitable promoters may be used. For instance, when
cloning in Escherichia coli, its bacteriophages, or plasmids,
promoters such as the T7 phage promoter, lac promoter, trp
promoter, recA promoter, ribosomal RNA promoter, the P.sub.R and
P.sub.L promoters of coliphage lambda and others, including but not
limited, to lacUV5, ompF, bla, lpp, and the like, may be used to
direct high levels of transcription of adjacent DNA segments.
Additionally, a hybrid trp-lacUV5 (tac) promoter or other E. coli
promoters produced by recombinant DNA or other synthetic DNA
techniques may be used to provide for transcription of the inserted
gene.
[0110] Bacterial host cell strains and expression vectors may be
chosen which inhibit the action of the promoter unless specifically
induced. In certain operations, the addition of specific inducers
is necessary for efficient transcription of the inserted DNA. For
example, the lac operon is induced by the addition of lactose or
IPTG (isopropylthio-beta-D-galactoside). A variety of other
operons, such as trp, pro, etc., are under different controls.
[0111] Specific initiation signals are also required for efficient
gene transcription and translation in prokaryotic cells. These
transcription and translation initiation signals may vary in
"strength" as measured by the quantity of gene specific messenger
RNA and protein synthesized, respectively. The DNA expression
vector, which contains a promoter, may also contain any combination
of various "strong" transcription and/or translation initiation
signals. For instance, efficient translation in E. coli requires an
SD sequence about 7-9 bases 5' to the initiation codon ("ATG") to
provide a ribosome binding site. Thus, any SD-ATG combination that
can be utilized by host cell ribosomes may be employed. Such
combinations include but are not limited to the SD-ATG combination
from the cro gene or the N gene of coliphage lambda, or from the E.
coli tryptophan E, D, C, B or A genes. Additionally, any SD-ATG
combination produced by recombinant DNA or other techniques
involving incorporation of synthetic nucleotides may be used.
[0112] In one embodiment, the nucleic acid molecule of the present
invention is incorporated into an appropriate vector in the sense
direction, such that the open reading frame is properly oriented
for the expression of the encoded protein under control of a
promoter of choice. This involves the inclusion of the appropriate
regulatory elements into the DNA-vector construct. These include
non-translated regions of the vector, useful promoters, and 5' and
3' untranslated regions which interact with host cellular proteins
to carry out transcription and translation. Such elements may vary
in their strength and specificity. Depending on the vector system
and host utilized, any number of suitable transcription and
translation elements, including constitutive and inducible
promoters, may be used.
[0113] A constitutive promoter is a promoter that directs
expression of a gene throughout the development and life of an
organism.
[0114] An inducible promoter is a promoter that is capable of
directly or indirectly activating transcription of one or more DNA
sequences or genes in response to an inducer. In the absence of an
inducer, the DNA sequences or genes will not be transcribed.
[0115] The DNA construct of the present invention can also include
an operable 3' regulatory region, selected from among those which
are capable of providing correct transcription termination and
polyadenylation of mRNA for expression in the host cell of choice,
operably linked to a DNA molecule which encodes for a protein of
choice.
[0116] The vector of choice, promoter, and an appropriate 3'
regulatory region can be ligated together to produce the DNA
construct of the present invention using well known molecular
cloning techniques as described in Sambrook et al., Molecular
Cloning: A Laboratory Manual, Second Edition, Cold Spring Harbor
Press, NY (1989), and Ausubel, F. M. et al. Current Protocols in
Molecular Biology, New York, N.Y.: John Wiley & Sons (1989),
each of which is hereby incorporated by reference in its
entirety.
[0117] As noted, one alternative to the use of prokaryotic host
cells is the use of eukaryotic host cells, such as mammalian cells,
which can also be used to recombinantly produce the recombinant
factor VIII of the present invention. Mammalian cells suitable for
carrying out the present invention include, among others: COS
(e.g., ATCC No. CRL 1650 or 1651), BHK (e.g., ATCC No. CRL 6281),
CHO (e.g., ATCC No. CCL 61), HeLa (e.g., ATCC No. CCL 2), 293 (ATCC
No. 1573), CHOP, and NS-1 cells.
[0118] Suitable expression vectors for directing expression in
mammalian cells generally include a promoter, as well as other
transcription and translation control sequences known in the art.
Common promoters include SV40, MMTV, metallothionein-1, adenovirus
Ela, CMV, immediate early, immunoglobulin heavy chain promoter and
enhancer, and RSV-LTR.
[0119] Once the DNA construct of the present invention has been
prepared, it is ready to be incorporated into a host cell.
Accordingly, another aspect of the present invention relates to a
method of making a recombinant cell. Basically, this method is
carried out by transforming a host cell with a DNA construct of the
present invention under conditions effective to yield transcription
of the DNA molecule in the host cell. Recombinant molecules can be
introduced into cells via transformation, particularly
transduction, conjugation, mobilization, or electroporation.
[0120] In view of the recombinant technology discussed herein,
another aspect of the present invention relates to a method of
making a recombinant factor VIII of the present invention. This
method involves growing a host cell of the present invention under
conditions whereby the host cell expresses the recombinant factor
VIII of the present invention. The recombinant factor VIII is then
isolated. In one embodiment, the host cell is grown in vitro in a
growth medium. In a particular embodiment, suitable growth media
can include, without limitation, a growth medium containing a von
Willebrand Factor (referred to herein as "VWF"). In this
embodiment, the host cell can contain a transgene encoding a VWF or
the VWF can be introduced to the growth medium as a supplement. VWF
in the growth medium will allow for greater expression levels of
the recombinant factor VIII. Once the recombinant factor VIII is
secreted into the growth medium, it can then be isolated from the
growth medium using techniques well-known by those of ordinary
skill in the relevant recombinant DNA and protein arts (including
those described herein). In another embodiment, the method of
making the recombinant factor VIII of the present invention further
involves disrupting the host cell prior to isolation of the
recombinant factor VIII. In this embodiment, the recombinant factor
VIII is isolated from cellular debris.
[0121] The modifications at positions corresponding to 108,
121/2302, 2328 of the WT factor VIII are particularly preferred,
because they result in enhanced stability of factor VIII and, when
used in combination with modifications at residues 519, 665, and/or
1984, result in significantly enhanced stability of both factor
VIII and factor VIIIa. This increased stability is important with
regard to circulating half-life of factor VIII and the activity of
factor VIIIa during blood clotting. Furthermore, this property is
significant in terms of enhancing the recovery of usable factor
VIII during the purification and preparation of the protein for
therapeutic use, particularly given the improved thermal and
chemical stability of factor VIII.
[0122] When an expression vector is used for purposes of in vivo
transformation to induce factor VIII expression in a target cell,
promoters of varying strength can be employed depending on the
degree of enhancement desired. One of skill in the art can readily
select appropriate mammalian promoters based on their strength as a
promoter. Alternatively, an inducible promoter can be employed for
purposes of controlling when expression or suppression of factor
VIII is desired. One of skill in the art can readily select
appropriate inducible mammalian promoters from those known in the
art. Finally, tissue specific mammalian promoters can be selected
to restrict the efficacy of any gene transformation system to a
particular tissue. Tissue specific promoters are known in the art
and can be selected based upon the tissue or cell type to be
treated.
[0123] Another aspect of the present invention relates to a method
of treating an animal for a blood disorder such as hemophilia,
particularly hemophilia A. This method involves administering to an
animal exhibiting hemophilia A an effective amount of the
recombinant factor VIII of the present invention, whereby the
animal exhibits effective blood clotting following vascular injury.
A suitable effective amount of the recombinant factor VIII can
include, without limitation, between about 10 to about 50 units/kg
body weight of the animal. The animal can be any mammal, but
preferably a human, a rat, a mouse, a guinea pig, a dog, a cat, a
monkey, a chimpanzee, an orangutan, a cow, a horse, a sheep, a pig,
a goat, or a rabbit.
[0124] The recombinant factor VIII of the present invention can be
used to treat uncontrolled bleeding due to factor VIII deficiency
(e.g., intraarticular, intracranial, or gastrointestinal
hemorrhage) in hemophiliacs with and without inhibitory antibodies
and in patients with acquired factor VIII deficiency due to the
development of inhibitory antibodies. In a particular embodiment,
the recombinant factor VIII, alone, or in the form of a
pharmaceutical composition (i.e., in combination with stabilizers,
delivery vehicles, and/or carriers) is infused into patients
intravenously according to the same procedure that is used for
infusion of human or animal factor VIII.
[0125] Alternatively, or in addition thereto, the recombinant
factor VIII can be administered by administering a viral vector
such as an adeno-associated virus (Gnatenko et al., "Human Factor
VIII Can Be Packaged and Functionally Expressed in an
Adeno-associated Virus Background: Applicability to Hemophilia A
Gene Therapy," Br. J. Haematol. 104:27-36 (1999), which is hereby
incorporated by reference in its entirety), or by transplanting
cells genetically engineered to produce the recombinant factor
VIII, typically via implantation of a device containing such cells.
Such transplantation typically involves using recombinant dermal
fibroblasts, a non-viral approach (Roth et al., "Nonviral Transfer
of the Gene Encoding Coagulation Factor VIII in Patients with Sever
Hemophilia," New Engl. J. Med. 344:1735-1742 (2001), which is
hereby incorporated by reference in its entirety).
[0126] The treatment dosages of recombinant factor VIII that should
be administered to a patient in need of such treatment will vary
depending on the severity of the factor VIII deficiency. Generally,
dosage level is adjusted in frequency, duration, and units in
keeping with the severity and duration of each patient's bleeding
episode. Accordingly, the recombinant factor VIII is included in a
pharmaceutically acceptable carrier, delivery vehicle, or
stabilizer in an amount sufficient to deliver to a patient a
therapeutically effective amount of the protein to stop bleeding,
as measured by standard clotting assays.
[0127] Factor VIII is classically defined as that substance present
in normal blood plasma that corrects the clotting defect in plasma
derived from individuals with hemophilia A. The coagulant activity
in vitro of purified and partially-purified forms of factor VIII is
used to calculate the dose of recombinant factor VIII for infusions
in human patients and is a reliable indicator of activity recovered
from patient plasma and of correction of the in vivo bleeding
defect. There are no reported discrepancies between standard assay
of novel factor VIII molecules in vitro and their behavior in the
dog infusion model or in human patients, according to Lusher et
al., "Recombinant Factor VIII for the Treatment of Previously
Untreated Patients with Hemophilia A--Safety, Efficacy, and
Development of Inhibitors," New Engl. J. Med. 328:453-459 (1993);
Pittman et al., "A2 Domain of Human Recombinant-derived Factor VIII
is Required for Procoagulant Activity but not for Thrombin
Cleavage," Blood 79:389-397 (1992); and Brinkhous et al., "Purified
Human Factor VIII Procoagulant Protein: Comparative Hemostatic
Response After Infusions into Hemophilic and von Willebrand Disease
Dogs," Proc. Natl. Acad. Sci. 82:8752-8755 (1985), which are hereby
incorporated by reference in their entirety.
[0128] Usually, the desired plasma factor VIII activity level to be
achieved in the patient through administration of the recombinant
factor VIII is in the range of 30-100% of normal. In one
embodiment, administration of the therapeutic recombinant factor
VIII is given intravenously at a preferred dosage in the range from
about 5 to 50 units/kg body weight, and particularly in a range of
10-50 units/kg body weight, and further particularly at a dosage of
20-40 units/kg body weight; the interval frequency is in the range
from about 8 to 24 hours (in severely affected hemophiliacs); and
the duration of treatment in days is in the range from 1 to 10 days
or until the bleeding episode is resolved. See, e.g., Roberts and
Jones, "Hemophilia and Related Conditions--Congenital Deficiencies
of Prothrombin (Factor II, Factor V, and Factors VII to XII)," Ch.
153, 1453-1474, 1460, in Hematology, Williams, W. J., et al., ed.
(1990), which is hereby incorporated by reference in its entirety.
Patients with inhibitors may require a different amount of
recombinant factor VIII than their previous form of factor VIII.
For example, patients may require less recombinant factor VIII
because of its higher specific activity than the wild-type VIII and
its decreased antibody reactivity. As in treatment with human or
plasma-derived factor VIII, the amount of therapeutic recombinant
factor VIII infused is defined by the one-stage factor VIII
coagulation assay and, in selected instances, in vivo recovery is
determined by measuring the factor VIII in the patient's plasma
after infusion. It is to be understood that for any particular
subject, specific dosage regimens should be adjusted over time
according to the individual need and the professional judgment of
the person administering or supervising the administration of the
compositions, and that the concentration ranges set forth herein
are exemplary only and are not intended to limit the scope or
practice of the claimed recombinant factor VIII.
[0129] Treatment can take the form of a single intravenous
administration of the recombinant factor VIII or periodic or
continuous administration over an extended period of time, as
required. Alternatively, therapeutic recombinant factor VIII can be
administered subcutaneously or orally with liposomes in one or
several doses at varying intervals of time.
[0130] The recombinant factor VIII can also be used to treat
uncontrolled bleeding due to factor VIII deficiency in hemophiliacs
who have developed antibodies to human factor VIII.
[0131] It has been demonstrated herein that the recombinant factor
VIII of the present invention can differ in specific activity from
the wild-type factor VIII and retain a higher specific activity for
a longer duration following activation. Factor VIII proteins having
greater procoagulant activity from wild-type factor VIII are useful
in treatment of hemophilia because lower dosages will be required
to correct a patient's factor VIII deficiency. This will not only
reduce medical expense for both the patient and the insurer, but
also reduce the likelihood of developing an immune response to the
factor VIII (because less antigen is administered).
EXAMPLES
[0132] The following examples are provided to illustrate
embodiments of the present invention, but they are by no means
intended to limit its scope.
Materials & Methods
[0133] Reagents:
[0134] Recombinant factor VIII (KOGENATE.TM.) and the monoclonal
antibodies 58.12 and 2D2 were generous gifts from Dr. Lisa Regan of
Bayer Corporation (Berkeley, Calif.). Phospholipid vesicles
containing 20% phosphatidylcholine (PC), 40%
phosphatidylethanolamine (PE), and 40% phosphatidylserine (PS) were
prepared using octylglucoside as described previously (Mimms et
al., "Phospholipid Vesicle Formation and Transmembrane Protein
Incorporation Using Octyl Glucoside," Biochemistry 20:833-840
(1981), which is hereby incorporated by reference in its entirety).
The reagents .alpha.-thrombin, factor VIIa, factor IXa.beta.,
factor X, and factor Xa (Enzyme Research Laboratories, South Bend,
Ind.), hirudin (DiaPharma, West Chester, Ohio), phospholipids
(Avanti Polar Lipids, Alabaster, Ala.), the chromogenic Xa
substrate, Pefachrome Xa (Pefa-5523,
CH.sub.3OCO-D-Cha-Gly-Arg-pNAAcOH; Centerchem Inc. Norwalk Conn.),
recombinant human tissue factor (rTF), Innovin (Dade Behring,
Newark, Del.), fluorogenic substrate, Z-Gly-Gly-Arg-AMC
(Calbiochem, San Diego, Calif.), thrombin calibrator (Diagnostica
Stago, Parsippany, N.J.), and acrylodan (Molecular Probes, Eugene,
Oreg.) were purchased from the indicated vendors.
[0135] Expression and Purification of WT and Variant Factor
VIII:
[0136] Recombinant WT and variant factor VIII forms were stably
expressed in BHK cells and purified as described previously
(Wakabayashi et al., "Residues 110-126 in the A1 Domain of Factor
VIII Contain a Ca.sup.2+ Binding Site Required for Cofactor
Activity," J Biol Chem. 279:12677-12684 (2004), which is hereby
incorporated by reference in its entirety). After transfection
there were no significant differences in the amounts of factor VIII
secretion among the variants. Protein yields for the variants
ranged from >10 to .about.100 .mu.g from two 750 cm.sup.2
culture flasks, with purity from .about.85% to >95% as judged by
SDS-PAGE. The primary contaminant in the factor VIII preparations
was albumin and at the concentrations present in the factor VIII
showed no effect on stability or activity parameters. Factor VIII
concentration was measured by ELISA and factor VIII activity was
determined by one-stage clotting assay and two-stage chromogenic
factor Xa generation assay, both of which are described below.
[0137] Western Blotting:
[0138] Factor VIII proteins (0.34 .mu.g) were activated by thrombin
(20 nM) for 30 min at 23.degree. C. and subjected to
electrophoresis under either non-reducing or reducing (0.1 M
dithiothreitol) conditions using 10% polyacrylamide gels run at
constant voltage (150V). Gels were transferred to a polyvinylidene
fluoride membrane, probed with an anti-A1 domain (58.12) or anti-A3
domain (2D2) monoclonal antibody and protein bands were visualized
using chemifluorescence. The chemifluorescence substrate (ECF
substrate, GE Healthcare, Piscataway, N.J.) was reacted and the
fluorescence signal scanned using a phosphoimager (Storm 860, GE
Healthcare).
[0139] ELISA:
[0140] A sandwich ELISA was performed to measure the concentration
of factor VIII proteins as previously described (Wakabayashi et
al., "A Glu113Ala Mutation within a Factor VIII Ca.sup.2+-Binding
Site Enhances Cofactor Interactions in Factor Xase," Biochemistry
44:10298-10304 (2005), which is hereby incorporated by reference in
its entirety) using purified commercial recombinant factor VIII
(KOGENATE.TM., Bayer Corporation) as a standard. Factor VIII
capture used the anti-C2 monoclonal antibody (GMA8003, Green
Mountain Antibodies) and the anti-A2 monoclonal antibody, R8B12
(GMA8012, Green Mountain Antibodies) was employed for factor VIII
detection following biotinylation.
[0141] One-Stage Clotting Assay:
[0142] One-stage clotting assays were performed using substrate
plasma chemically depleted of factor VIII (Over, "Methodology of
the One-stage Assay of Factor VIII (VIII:C)," Scand J Haematol
Suppl. 41:13-24 (1984), which is hereby incorporated by reference
in its entirety) and assayed using a Diagnostica Stago clotting
instrument. Plasma was incubated with APTT reagent (General
Diagnostics) for 6 min at 37.degree. C. after which a dilution of
factor VIII was added to the cuvette. After 1 min the mixture was
recalcified, and clotting time was determined and compared to a
pooled normal plasma standard.
[0143] Two-Stage Chromogenic Factor Xa Generation Assay:
[0144] The rate of conversion of factor X to factor Xa was
monitored in a purified system (Lollar et al., "Factor VIII and
Factor VIIIa," Methods Enzymol. 222:128-143 (1993), which is hereby
incorporated by reference in its entirety) according to methods
previously described (Wakabayashi et al., "Metal Ion-independent
Association of Factor VIII Subunits and the Roles of Calcium and
Copper Ions for Cofactor Activity and Inter-subunit Affinity,"
Biochemistry 40:10293-10300 (2001); Wakabayashi et al., "Ca.sup.2+
Binding to Both the Heavy and Light Chains of Factor VIII Is
Required for Cofactor Activity," Biochemistry 41:8485-8492 (2002),
each of which is hereby incorporated by reference in its entirety).
Factor VIII (1 nM) in buffer containing 20 mM
N-[2-hydroxyethyl]piperazine-N'-[2-ethanesulfonic acid] (HEPES), pH
7.2, 0.1 M NaCl, 0.01% Tween 20, 0.01% BSA, 5 mM CaCl.sub.2 (Buffer
B), and 10 .mu.M PSPCPE vesicles was activated with 20 nM
.alpha.-thrombin for 1 min. The reaction was stopped by adding
hirudin (10 U/ml) and the resulting factor VIIIa was reacted with
factor IXa (40 nM) for 1 min. Factor X (300 nM) was added to
initiate reactions which were quenched after 1 min by the addition
of 50 mM EDTA. Factor Xa generated was determined following
reaction with the chromogenic substrate Pefachrome Xa (0.46 mM
final concentration). All reactions were run at 23.degree. C.
[0145] Factor VIII Activity at Elevated Temperature:
[0146] WT factor VIII or factor VIII variants (4 nM) in buffer B
were incubated at 57.degree. C. (pH at this temperature=6.94).
Aliquots were removed at the indicated times, cooled to room
temperature, and residual factor VIII activity was determined using
a two-stage factor Xa generation assay.
[0147] Factor Villa Activity Decay:
[0148] WT and mutant factor VIII (1.5 nM) in buffer B containing 20
.mu.M PSPCPE vesicles were activated using 20 nM thrombin for 1 mM
at 23.degree. C. Reactions were immediately quenched by hirudin (10
U/ml) to inactivate thrombin, aliquots removed at the indicated
times, and activity was determined using the factor Xa generation
assay following addition of factor IXa (40 nM) and factor X (300
nM).
[0149] Factor VIII Activity Inhibition by Guanidinium Chloride:
[0150] WT and factor VIII variants (50 nM) in buffer B plus 0-1.8 M
guanidinium chloride were incubated for 2 hrs at 23.degree. C.
Aliquots were diluted (1/50) in buffer A containing 20 .mu.M PSPCPE
vesicles and activated by 5 nM thrombin for 1 min. Reactions were
immediately quenched with hirudin (10 U/ml) and activity was
determined by factor Xa generation assay following addition of
factor IXa (40 nM) and FX (300 nM). Residual guanidinium chloride
(<36 mM) did not inhibit the proteolytic activation of factor
VIII or its cofactor activity.
[0151] Thermal Denaturation of Reconstituted A1 and A3C1C2 or A3C1
Subunit as Detected by FXa Generation Assay--
[0152] A1 subunit (50 nM) from WT or Ala108Ile factor VIII was
reconstituted with A3C1C2 (200 nM) or A3C1 (500 nM) at 37.degree.
C. for 2 hr in 10 mM MES, pH 6.5, 0.15 M NaCl, 0.01% Tween 20,
0.01% BSA, 5 mM CaCl.sub.2. Samples were incubated at 55.degree. C.
(A3C1C2) or 52.degree. C. (A3C1) (pH at this temperature=6.94),
aliquots were taken at indicated times, and further incubated with
200 nM A2 subunit at 23.degree. C. for 30 min Samples were then
diluted 1:20 with buffer B containing 20 .mu.M PSPCPE vesicles and
reconstituted factor VIIIa activity was measured directly by factor
Xa generation assay in the absence of the thrombin activation step.
Data were fitted to the single exponential decay equation by
non-linear least squares regression and parameter values were
obtained.
[0153] Thrombin Generation Assay--
[0154] The amount of thrombin generated in plasma was measured by
Calibrated Automated Thrombography using methods previously
described (Wakabayashi et al., "Combining Mutations of Charged
Residues at the A2 Domain Interface Enhances Factor VIII Stability
over Single Point Mutations," J. Thromb. Haemost. 7:438-444 (2009),
which is hereby incorporated by reference in its entirety).
Briefly, factor VIII deficient plasma (<1% residual activity,
platelet-poor) from severe hemophilia A patients lacking factor
VIII inhibitor (George King Bio-Medical, Overland Park, Kans.) was
mixed at 37.degree. C. with a final concentration of 0.3 nM factor
VIII, 0.5 pM rTF, 4 .mu.M PSPCPE vesicles, 433 .mu.M fluorogenic
substrate, 13.3 mM CaCl.sub.2, and 105 nM thrombin calibrator. The
development of a fluorescent signal was monitored at 8 second
intervals using a Microplate Spectrofluorometer (Spectramax Gemini,
Molecular Devices, Sunnyvale, Calif.) with a 355 nm
(excitation)/460 nm (emission) filter set. Fluorescent signals were
corrected by the reference signal from the thrombin calibrator
samples and actual thrombin generation in nM was calculated.
[0155] Data Analysis:
[0156] For activity decay analysis of factor VIII/VIIIa, activity
values as a function of time were fitted to a single exponential
decay curve by non-linear least squares regression using the
equation,
A=A.sub.0e.sup.-kt
where A is residual factor VIIIa activity (nM/min/nM factor VIII),
A.sub.0 is the initial activity, k is the apparent rate constant,
and t is the time (minutes) of reaction of factor VIII (for factor
VIII thermal decay experiments) or of factor VIIIa after thrombin
was quenched (for factor VIIIa decay measurements). Factor VIII
activity inhibition by guanidinium was fitted to a linear equation
by least squares regression using the equation,
A=50k(X-IC.sub.50)
where A is the normalized activity [=100(%)], IC.sub.50 is the
inhibitor (guanidinium chloride) concentration (M) at 50% activity,
X is the guanidinium chloride concentration (M), and k is the
slope. Determinations for A1-A3C1C2 binding affinity used the
quadratic equation:
F = F max B ( B + K d + X ) 2 - ( B + K d + X ) 2 - 4 B X 2
##EQU00001##
where F.sub.max is the maximum increase in fluorescence at
saturation, B is the A1 concentration (=15 nM), K.sub.d is the
dissociation constant, and X is the concentration of A3C1C2 in nM,
Nonlinear least-squares regression analysis was performed using
Kaleidagraph (Synergy, Reading, Pa.). A Student's t-test was
performed for statistical analysis.
Example 1
Recombinant Expression and Purification of Factor VIII Mutants
Possessing Modified A1 and C2 Domain Interactions
[0157] The A1 and C2 domains show close proximity to one another in
the factor VIII crystal structure (FIG. 3A). These regions were
investigated with the aim towards enhancing inter-domain
interactions to positively alter affinity and stability parameters.
Examination of the A1-C2 interface provided two possible approaches
for increasing the inter-domain affinity. Although the orientation
of side chains cannot be discerned due to the resolution (.about.4
.ANG.) of the structure (4), the putative spatial separation of
several paired residues indicated that mutagenesis of these
residues to Cys could result in formation of a nascent inter-domain
disulfide bridge. Paired A1/C2 domain residues were identified that
appeared to meet this distance requirement and included
Ser119/Pro2300, Gln120/Pro2299, Arg121/Leu2302, Ala108/Ala2328, and
Trp106/Ala2328.
[0158] Double mutations where each residue of the respective pair
was replaced with Cys were prepared as B-domainless factor
VIII--lacking residues Gln744-Ser1637 in the B-domain (Doering et
al., "Expression and Characterization of Recombinant Murine Factor
VIII," Thromb. Haemost 88:450-458 (2002), which is hereby
incorporated by reference in its entirety)--using previously
described methods (Wakabayashi et al., "Residues 110-126 in the A1
Domain of Factor VIII Contain a Ca.sup.2+-Binding Site Required for
Cofactor Activity," J. Biol. Chem 279:12677-12684 (2004), which is
hereby incorporated by reference in its entirety). Briefly,
B-domainless factor VIII cDNA was restricted from the factor VIII
expression construct HSQ-MSAB-NotI-RENeo using the endonucleases
XhoI and NotI, and then cloned into the Bluescript II K/S-vector.
Factor VIII molecules bearing one or more point mutations were
constructed by introducing mutations into shuttle constructs using
the Stratagene QuikChange site-directed mutagenesis kit. Upon
confirmation of the presence of only the desired mutations by
sequencing, the appropriate fragment was restricted and cloned back
into the factor VIII expression construct. Presence of only the
desired mutations was again confirmed by a second round of
sequencing. Of the five variants examined, only the
Arg121Cys/Leu2302Cys variant (FIG. 3B) retained a wild-type like
specific activity (.about.86% the WT value, Table 1) and was
further evaluated.
[0159] Recombinant WT and variant factor VIII forms were stably
expressed in BHK cells and purified as previously described (Lollar
and Parker, "pH-dependent Denaturation of Thrombin-activated
Porcine Factor VIII," J. Biol. Chem 265:1688-1692 (1990), which is
hereby incorporated by reference in its entirety). Protein yields
for the variants ranged from >10 to .about.100 .mu.g from two
750 cm.sup.2 culture flasks, with purity >90% as judged by
SDS-PAGE. The primary contaminant in the factor VIII preparations
was albumin. Factor VIII concentrations were measured using an
Enzyme-Linked Immunoadsorbant Assay (ELISA) and factor VIII
activity was determined by one-stage clotting and two-stage
chromogenic factor Xa generation assays described supra.
[0160] In addition, a small cavity in the A1-C2 interface that
potentially exists was noted, this putative cavity is mainly
surrounded by alkyl groups from Ala108, Ala2328, Leu2302, and
Gln2329 (FIG. 3C), with the side chain of Ala108 proposed to be
directed towards the C2 domain. In an effort to increase
hydrophobic interactions within this area, several variants were
prepared to introduce bulky hydrophobic groups in these domains.
This was carried out by mutating Ala residues to Ile, Leu, and Val
(Ala108Ile, Ala108Leu, Ala108Val, Ala232811e, Ala2328Leu, and
Ala2328Val) in a B-domainless factor VIII cDNA using the procedures
described in the preceding paragraph. Of the variants prepared, the
Ala108Ile factor VIII variant showed minimal effects on factor VIII
specific activity (.about.74% the WT value, Table 1); the Ala108Leu
and Ala108Val variants showed greater diminution of factor VIII
specific activity.
[0161] The A1 subunit was purified from WT or Ala108Ile factor
VIII. Factor VIII (1-3 .mu.M) was reacted with thrombin (50 nM) in
20 mM HEPES, pH 7.2, 0.1 M NaCl, 0.01% Tween 20 (buffer A) for 30
min and treated with 50 mM EDTA overnight at 4.degree. C. After a
1:4 dilution with buffer A, the samples were subjected to
chromatography using a heparin Sepharose column (1.5 cm.times.0.7
cm in diameter, GE Healthcare, Piscataway, N.J.). The flow through
fraction was collected and applied to a Q-Sepharose column (1.5
cm.times.0.7 cm in diameter, GE Healthcare). After the column was
washed with buffer A, bound A1 subunit was eluted with 20 mM HEPES,
pH 7.2, 0.8 M NaCl, 0.01% Tween20, and purified A1 subunit was kept
frozen at 80.degree. C. until use. A2 and A3C1C2 subunits were
completely absorbed by the heparin Sepharose column step and the
final A1 product was >95% pure as judged by SDS-PAGE. A2 and
A3C1C2 subunits were purified from recombinant factor VIII
(Kogenate.TM.) as described previously (Fay and Smudzin,
"Characterization of the Interaction Between the A2 Subunit and
A1/A3-C1-C2 Dimer in Human Factor VIIIa," J. Biol. Chem
267:13246-13250 (1992), which is hereby incorporated by reference
in its entirety). A3C1 subunit was purified from C2 domain-deleted
factor VIII (Wakabayashi et al., "Factor VIII Lacking the C2 Domain
Retains Cofactor Activity in vitro," J. Biol. Chem 285:25176-25184
(2010), which is hereby incorporated by reference in its entirety)
using the same method for A3C1C2 purification.
[0162] Purified A1 subunit from WT and Ala108Ile factor VIII was
labeled with acrylodan by sulfhydryl specific protein modification
as previously described (Wakabayashi et al., "Metal Ion-independent
Association of Factor VIII Subunits and the Roles of Calcium and
Copper Ions for Cofactor Activity and Inter-subunit Affinity,"
Biochemistry 40:10293-10300 (2001), which is hereby incorporated by
reference in its entirety). A1 (15 nM) from WT or Ala108Ile factor
VIII was reconstituted with A3C1C2 subunit (0-300 nM) at 37.degree.
C. for 2 h in buffer B at pH 7.4. Fluorescence measurements were
performed using an Aminco-Bowman Series 2 Luminescence Spectrometer
(Thermo Spectronic, Rochester, N.Y.) at 23.degree. C. at an
excitation wavelength of 395 nm (2 nm bandwidth). Fluorescence
emission was monitored at 480-490 nm (8 nm bandwidth) and all
spectra were corrected for background. Data were fitted to a
quadratic equation by non-linear least squares regression and
parameter values were obtained.
Example 2
Confirmation of Disulfide Bridge in Arg121Cys/Leu2302Cys Factor
VIII Variant
[0163] Evidence for high efficiency disulfide bridging between
factor VIII A1 and A3C1C2 domains in this double mutant, as judged
by Western Blotting is shown in FIG. 4. For this analysis, WT
factor VIII and the Arg121Cys/Leu2302Cys factor VIII variant were
cleaved with thrombin to generate the factor VIIIa heterotrimer
prior to SDS-PAGE, which was then run in the absence and presence
of disulfide bond reduction using DTT. Blots were probed with an
anti-A1 antibody (58.12, lanes 1-4) and an anti-A3 antibody (2D2,
lanes 5-8). Both A1 and A3C1C2 subunits derived from the factor
VIII Arg121Cys/Leu2302Cys variant were detected at the .about.120
kDa band, consistent with the sum of their mol masses under
non-reducing conditions (lanes 2 and 6), while reduction by 0.1 M
DTT yielded the separated subunits (lanes 4 and 8). Based upon the
band densities of bridged and free subunits in the non-reduced
lanes, it appeared that >90% of the variant molecules were
disulfide-linked.
Example 3
Affinity of the WT and Ala108Ile Factor VIII Variant A1 Subunits
for A3C1C2
[0164] To assess the affinity of the Ala108Ile A1 domain for C2
domain, the purified factor VIII variant and WT were treated with
thrombin and the A1 subunits were separately purified as described
supra. A1 subunits were then reacted with the environment-sensitive
fluorescent probe, acrylodan, and these reagents were used to probe
binding with the A3C1C2 subunit. The site for acrylodan attachment
is likely the lone free thiol in A1 at Cys310, which is in close
proximity (<15 .ANG.) to residues in the A3 domain of light
chain (Ngo et al., "Crystal Structure of Human Factor VIII:
Implications for the Formation of the Factor IXa:Factor VIIIa
Complex," Structure 16:597-606 (2008), which is hereby incorporated
by reference in its entirety). Indeed, increases in the emission
fluorescence from acrylodan-labeled A1 (AcA1) subunit have been
previously observed when A3C1C2 was bound to the molecule
(Wakabayashi et al, "Metal-ion Independent Factor VIII Subunit
Association and the Role of Calcium and Copper for Its Affinity and
Activity," Biochemistry 40:10293-10300 (2001); Ansong et al.,
"Factor VIII A3 Domain Residues 1954-1961 Represent an A1
Domain-Interactive Site," Biochemistry 44:8850-8857 (2005), each of
which is hereby incorporated by reference in its entirety).
Titration of AcA1 with A3C1C2 was performed as described supra and
the results are shown in FIG. 5. AcA1 (15 nM) fluorescence from
both the WT and Ala108Ile subunits saturably increased as the
A3C1C2 concentration increased. The estimated K.sub.d of this
interaction for WT and Ala108Ile A1 subunits were 88.7.+-.9.8 nM
and 24.1.+-.4.1 nM, respectively. The K.sub.d value for WT was
somewhat higher than a previously reported value (.about.50 nM)
(Ansong et al., "Factor VIII A3 Domain Residues 1954-1961 Represent
an A1 Domain-Interactive Site," Biochemistry 44:8850-8857 (2005),
which is hereby incorporated by reference in its entirety) likely
due to slightly higher pH (7.4) employed for the binding conditions
(Wakabayashi et al., "pH-dependent Association of Factor VIII
Chains: Enhancement of Affinity at Physiological pH by Cu.sup.2+,"
Biochim. Biophys. Acta 1764:1094-1101 (2006), which is hereby
incorporated by reference in its entirety). This result indicated a
.about.4-fold increase in affinity of Ala108Ile A1 for A3C1C2 as
compared with the WT A1 subunit for A3C1C2. The estimated maximal
values in fluorescence for WT and Ala108Ile were 0.221.+-.0.009 and
0.245.+-.0.011 respectively, and were not significantly different
(p>0.1).
Example 4
Stability of Factor VIII Arg121Cys/Leu2302Cys and Ala108Ile
Variants
[0165] The above results demonstrate that introduction of the
disulfide bridge or increasing the hydrophobic character at the
A1-C2 interface stabilizes this inter-domain interaction. To test
the functional consequences of these mutations, stability
parameters of factor VIII (factor VIIIa) were evaluated by several
methods. Thermal denaturation experiments were performed at
57.degree. C. as described supra. Data shown in FIG. 6A were fitted
to a single exponential decay curve using non-linear least squares
regression. WT factor VIII (circles) decayed to .about.40% the
initial activity level in 6-7 min at 57.degree. C. On the other
hand, the Arg121Cys/Leu2302Cys variant (triangles) retained >40%
activity up to 20 min, whereas the Ala108Ile variant (squares)
retained this level for >30 min. Overall, decay rates for the
Arg121Cys/Leu2302Cys and Ala108Ile variants obtained by curve-fit
were reduced by 3.1- and 4.2-fold, respectively, compared to the WT
factor VIII value (see Table 1 below).
TABLE-US-00003 TABLE 1 Properties of Wild type Factor VIII and
Variants Specific Factor VIII Factor VIIIa Activity Decay Rate
IC.sub.50 Decay Rate (%) (min.sup.-1) (M) (min.sup.-1) WT 100.0
.+-. 8.2 0.143 .+-. 0.003 (1.0) 0.814 .+-. 0.010 (1.00) 0.154 .+-.
0.006 (1.00) R121C/L2302C 86.4 .+-. 3.8 0.047 .+-. 0.001 (0.32)
0.826 .+-. 0.005 (1.01) 0.132 .+-. 0.004 (0.86) A108I 73.7 .+-. 3.9
0.034 .+-. 0.002 (0.24) 0.892 .+-. 0.008 (1.10) 0.119 .+-. 0.008
(0.77) Specific activity was determined by factor Xa generation
assay as described above and expressed as a relative activity
compared to WT value. Factor VIII decay data at 57.degree. C. as
shown in FIG. 6A, and factor Villa spontaneous decay data as shown
in FIG. 6C were fitted to a single exponential decay curve.
Guanidinium denaturation data as shown in FIG. 6B were fitted to a
linear response curve by non-linear least squares regression and
IC.sub.50 values with standard deviations were obtained. Values in
parentheses are relative to the WT value.
[0166] In a complementary series of experiments, factor VIII
stability was examined following a 2 h exposure to 0.6-1.2 M
guanidinium (FIG. 6B). As the concentration of guanidinium
increased, factor VIII activity was reduced to near zero as an
indication of denaturation. Using the range of linear response
(.about.0.6-1 M), data points were fitted by a linear equation and
the IC.sub.50 values were obtained (see Table 1). Factor VIII
activity of the Ala108Ile variant was significantly more stable
than WT showing a .about.10% higher IC.sub.50 values compared with
WT (p<0.001), while the IC.sub.50 determined for the
Arg121Cys/Leu2302Cys variant was only slightly increased (.about.2%
greater than WT, Table 1). Overall, the stability data for the
disulfide bridged variant suggested that the covalent bond between
A1 and C2 subunits significantly increased factor VIII thermal
stability while showing little stabilizing effect in the presence
of guanidinium. This result indicated that dissociation of factor
VIII heavy and light chains may be a prominent cause for activity
loss at elevated temperature, but that chain dissociation may not
represent a primary mode for activity loss due to chemical
denaturation. Alternatively, the Ala108Ile mutation demonstrated a
more global protective effect in increasing factor VIII stability
towards either thermal or chemical denaturation. Control
experiments were performed to determine whether there was any
time-dependent change in activity following the thermal or chemical
denaturation step and return of factor VIII to either ambient
temperature or dilution of denaturant, respectively. Factor VIII
was assayed from 30 seconds to 1 hour, and no significant change in
activity was observed.
[0167] Factor VIIIa activity is labile due to A2 subunit
dissociation following proteolytic activation (Fay et al., "Human
Factor VIIIa Subunit Structure: Reconstitution of Factor VIIIa from
the Isolated A1/A3-C1-C2 Dimer and A2 Subunit," J. Biol. Chem
266:8957-8962 (1991); Lollar et al., "pH-dependent Denaturation of
Thrombin-activated Porcine Factor VIII," J. Biol. Chem
265:1688-1692 (1990); Lollar et al., "Coagulant Properties of
Hybrid Human/Porcine Factor VIII Molecules," J. Biol. Chem
267:23652-23657 (1992), each of which is hereby incorporated by
reference in its entirety) To determine whether these mutations
affected factor VIIIa decay, experiments were performed to assess
rates of loss of factor VIIIa activity over time. As shown in FIG.
6C, reaction conditions employed resulted in the loss of .about.50%
of WT factor VIIIa activity at .about.6 min after thrombin
activation, while .about.10% activity remained after 16 min. The
observed factor VIIIa activity decay was slightly reduced for both
Arg121Cys/Leu2302Cys and Ala108Ile variants which showed .about.40%
activity in 7-8 min and demonstrated decay rates that were 1.2- and
1.3-fold greater than WT factor VIII, respectively (see Table 1).
These results demonstrated only minor effects on the inter-subunit
interactions involving A2 subunit following modification of the A1
and C2 domain interface.
Example 5
Stability of Reconstituted Ala108Ile or WT A1 Subunit with A3C1C2
or A3C1 Subunits
[0168] The thermal stability for the A1/A3C1C2 dimer was assessed
following its reconstitution from isolated subunits. Purified WT A1
or Ala108Ile A1 subunits was reconstituted with A3C1C2 subunit at
37.degree. C. for 2 hrs and the stability of the A1/A3C1C2 dimer at
elevated temperature (55.degree. C.) was measured by factor Xa
generation assay following addition of A2 subunit as described in
Methods. As shown in FIG. 7A, factor VIIIa activity reconstituted
from WT-A1 decayed to .about.25% its original value at 20 min
(circles) while .about.80% of the original activity level remained
for the A1 subunit containing the Ala108Ile mutation (triangles).
The estimated decay rates for WT and the mutant factor VIIIa forms
were 0.066.+-.0.005 and 0.014.+-.0.001 min.sup.-1, respectively,
showing a 4.6-fold rate reduction for the variant compared to WT
factor VIII.
[0169] Similar reconstitution experiments were performed using the
A3C1 subunit derived from the C2 domain-deleted factor VIII
variant. The rationale for this experiment was that if the enhanced
stability of the Ala108Ile A1 were due to interaction with the C2
domain following reassociation with A3C1C2, then use of the
truncated A3C1 for reconstitution would abrogate the enhanced
stability of the variant. Experiments performed with a C2-domain
deleted factor VIII, described in an earlier report (Wakabayashi et
al., "Factor VIII Lacking the C2 Domain Retains Cofactor Activity
in vitro," J. Biol. Chem 285:25176-25184 (2010), which is hereby
incorporated by reference in its entirety), showed that this
variant was marked less stable than WT factor VIII at elevated
temperatures and rates of decay needed to be monitored at a
relatively lower temperature (52.degree. C.). Under these
conditions, the C2-domain deleted factor VIII variant decayed
.about.40-fold faster than WT factor VIII. For this reason,
stability studies following factor VIII reconstitutions with the
A3C1 light chain were performed at 52.degree. C. Furthermore, in an
earlier study (Wakabayashi et al., "Generation of Enhanced
Stability Factor VIII Variants by Replacement of Charged Residues
at the A2 Domain Interface," Blood 112:2761-2769 (2008), which is
hereby incorporated by reference in its entirety), it was
demonstrated that factor VIII stability measured over a range of
temperatures from 52-60.degree. C. yielded similar relative rates
of decay when comparing a given factor VIII variant to WT.
Consistent with observations using the C2 domain-deleted factor
VIII, reconstitutions using either A1 form with A3C1 were observed
to yield an overall faster decay (FIG. 7B), with .about.50%
activity reduction at 4 min at 52.degree. C., than results observed
following reconstitutions with the intact A3C1C2. The estimated
decay rates for WT and the variant factor VIIIa forms were similar
(0.166.+-.0.001 and 0.154.+-.0.013 min.sup.-1, respectively). That
the observed increase in thermal stability of the Ala108Ile variant
was also observed following reconstitutions using purified
components supports the conclusion that the enhanced stability of
the variant as compared with WT derived from improved
interaction(s) between A1 and A3C1C2 subunits and required the
presence of C2 subunit.
Discussion of Examples 1-5
[0170] The preceding Examples illustrate interactions at the
interface between factor VIII A1 and C2 domains following
preparation of two factor VIII variants, Arg121Cys/Leu2302Cys
factor VIII, which possesses a nascent disulfide bond spanning
these domains, and Ala108Ile factor VIII, which has a larger
hydrophobic side chain to better fill the inter-domain space.
Several other mutations were prepared at this region in an attempt
to create a disulfide bond or to increase hydrophobicity. These
variants yielded low specific activity values, possibly resulting
from unfavorable changes in conformation, and their
characterization was not pursued further. However, both variants
studied exhibited enhanced inter-A1-C2 domain affinity resulting in
increases in the observed stability of the factor VIII variants,
especially related to thermal denaturation.
[0171] The intermediate resolution (.about.4 .ANG.) X-ray structure
of factor VIII (Ngo et al., "Crystal Structure of Human Factor
VIII: Implications for the Formation of the Factor IXa:Factor VIIIa
Complex," Structure 16:597-606 (2008), which is hereby incorporated
by reference in its entirety) predicts the close proximity of
Arg121 and Leu2302 with 7.7 .ANG. separating C.alpha. atoms
(PDB#3CDZ). This spatial separation suggested the potential to
bridge this distance by a disulfide bond (.about.4-6 .ANG.)
following replacement of these residues with Cys, and provided that
the side chains were in an acceptable orientation. Results
evaluating the Arg121Cys/Leu2302Cys factor VIII protein by western
blotting in the absence and presence of disulfide bond reduction
showed high efficiency bridging (>90%) constituting experimental
proof for the opposing orientation of side chains of these two
residues in factor VIII. In addition, the X-ray structure also
showed that the A1-C2 junction adjacent to Ala108 is rich in
hydrophobic groups represented by the C.beta. carbon of Ala108 from
the C.delta. of Leu2302, the C.beta. of Ala2328, or the C.gamma. of
Gln2329 (see FIG. 3C). Thus, it was believed that extended alkyl
groups of side chains larger than the methyl group of Ala might
contribute to enhanced binding energy. Of several variants prepared
to this region, replacement of Ala108 with Ile yielded a variant
possessing near WT-like specific activity.
[0172] Both Arg121Cys/Leu2302Cys and Ala108Ile variants exhibited
superior stability parameters as compared with the WT protein. For
example, the thermal decay rates for the Arg121Cys/Leu2302Cys and
Ala108Ile factor VIII variants were reduced by 3.1- and 4.2-fold,
respectively, as compared with WT. Further dissection of the
interaction with the Ala108Ile variant was obtained following
reconstitution of the A1/A3C1C2 dimer using WT and variant A1
subunits as well as the truncated A3C1 subunit derived from the C2
domain-deleted factor VIII. Enhanced stability of the variant
compared with WT was observed using native A3C1C2, but similar
stability parameter values for variant and WT were observed even in
the absence of the C2 domain. Taken together, these observations
support the belief that modulating the A1-C2 interface, either
through covalent bridging or increased hydrophobic interaction,
appeared to make an important contribution to overall protein
stability.
[0173] The primary cause for thermal decay of FVIII is attributed
to dissociation of the heavy and light chains (Ansong et al.,
"Factor VIII A3 Domain Residues 1954-1961 Represent an A1
Domain-Interactive Site," Biochemistry 44:8850-8857 (2005), which
is hereby incorporated by reference in its entirety). This result
is supported by the present study showing that bridging the factor
VIII heavy chain and light chain via a disulfide bond between A1
and C2 domains preferentially reduced thermal decay as compared
with chemical denaturation. Thus, chemical denaturation appears to
represent a more global effect on factor VIII structure and less
specific for chain dissociation. It was reported earlier that
several residues at the A2-A3 interface (Tyr1792, Tyr1786 and
Asp666) possibly contributed to the binding energy only in the
active factor VIIIa form (Wakabayashi et al., "Identification of
Residues Contributing to A2 Domain-dependent Structural Stability
in Factor VIII and Factor VIIIa," J. Biol. Chem 283:11645-11651
(2008), which is hereby incorporated by reference in its entirety).
Thus, interactions between the A2 domain of the heavy chain and
A3C1C2 domains of the light chain may be minimal in the
pro-cofactor. Based upon that earlier report and the present study,
it is believed that in the factor VIII heterodimer, the predominant
sources for binding energy likely derive from A1 interactions with
both the A3 and C2 domains.
[0174] On the other hand, the instability of factor VIIIa results
from weak electrostatic interactions between the A2 subunit and the
A1/A3C1C2 dimer (Fay et al., "Human Factor VIIIa Subunit Structure:
Reconstitution of Factor VIIIa from the Isolated A1/A3-C1-C2 Dimer
and A2 Subunit," J. Biol. Chem 266:8957-8962 (1991); Lollar et al.,
"pH-dependent Denaturation of Thrombin-activated Porcine Factor
VIII," J. Biol. Chem 265:1688-1692 (1990), each of which is hereby
incorporated by reference in its entirety) and its dissociation
leads to dampening of factor Xase activity (Lollar et al.,
"Coagulant Properties of Hybrid Human/Porcine Factor VIII
Molecules," J. Biol. Chem 267:23652-23657 (1992); Fay et al.,
"Model for the Factor VIIIa-dependent Decay of the Intrinsic Factor
Xase: Role of Subunit Dissociation and Factor IXa-catalyzed
Proteolysis," J. Biol. Chem 271:6027-6032 (1996), each of which is
hereby incorporated by reference in its entirety). Several factor
VIII point mutations have been shown to facilitate the rate of
dissociation of A2 relative to wild type (WT) and these residues
localize to either the A1-A2 domain interface (Pipe et al., "Mild
Hemophilia A Caused by Increased Rate of Factor VIII A2 Subunit
Dissociation: Evidence for Nonproteolytic Inactivation of Factor
VIIIa in vivo," Blood 93:176-183 (1999); Pipe et al., "Hemophilia A
Mutations Associated with 1-stage/2-stage Activity Discrepancy
Disrupt Protein-protein Interactions within the Triplicated A
Domains of Thrombin-activated Factor VIIIa," Blood 97:685-691
(2001), each of which is hereby incorporated by reference in its
entirety) or the A1 and C2 domains (Hakeos et al., "Hemophilia A
Mutations Within the Factor VIII A2-A3 Subunit Interface
Destabilize Factor VIIIa and Cause One-Stage/Two-Stage Activity
Discrepancy," Thromb. Haemost 88: 781-787 (2002), which is hereby
incorporated by reference in its entirety). In U.S. Patent
Application Publ. No. 20090118184 to Fay et al., which is hereby
incorporated by reference in its entirety, it was demonstrated that
replacing the charged residues Asp519, Glu665, and Glu1984 with Ala
or Val yielded increased factor VIII stability and in particular
enhanced retention of the A2 subunit in factor VIIIa.
Interestingly, neither the single mutants nor combinations of these
mutations yielded factor VIII variants that showed reductions in
the rate of thermal decay of greater than 2.3-fold, whereas the
variants examined in the present study showed thermal decay rate
reductions of 3- to 4-fold. Thus, the magnitude of stability
enhancement observed for the A1-C2 interface variants appears
somewhat larger than for the A2 domain-mediated interactions.
However, while these variants clearly showed superior factor VIII
stability, results from this study indicated essentially little if
any effect of the interactions involving the A1 and C2 domains in
stabilizing the factor VIIIa cofactor, suggesting no linkage of
these sites with sites involved in A2 subunit retention. For this
reason, it is the combinations of these A1-C2 domain stabilizing
mutations with A1-A2 or A3-A2 domain stabilizing mutations that
appear to be most desirable.
[0175] A1 domain residues 110-126 are in close contact to the C2
domain. These residues contain a Ca.sup.2+ binding site predicted
by Ala-scanning mutagenesis (Wakabayashi et al., "Residues 110-126
in the A1 Domain of Factor VIII Contain a Ca.sup.2+ Binding Site
Required for Cofactor Activity," J. Biol. Chem 279:12677-12684
(2004), which is hereby incorporated by reference in its entirety)
and subsequently identified in the X-ray crystal structure (Shen et
al., "The Tertiary Structure and Domain Organization of Coagulation
Factor VIII," Blood 111:1240-1247 (2008); Ngo et al., "Crystal
Structure of Human Factor VIII: Implications for the Formation of
the Factor IXa:Factor VIIIa Complex," Structure 16:597-606 (2008),
each of which is hereby incorporated by reference in its entirety).
Interestingly, preliminary experiments assessing chelation of
Ca.sup.2+ (and/or Cu.sup.2+) in factor VIII by EGTA yielded
dramatic losses in activity of WT factor VIII while showing more
minimal effects on the activity of Arg121Cys/Leu2302Cys and
Ala108Ile variants. Without being bound by belief, it is believed
the functional effects of Ca.sup.2+ occupancy at 110-126 in factor
VIII were replaced by enhanced stabilizing interactions between the
A1 and C2 domains in the variants.
[0176] In conclusion, results from Examples 1-5 demonstrate that
interactions between the A1 and C2 domains of factor VIII
contribute to the integrity of the protein, providing significant
energy for stabilizing the multi-domain structure of factor VIII.
Furthermore, observations for enhancing factor VIII stability, in
particular by increasing non-covalent, hydrophobic interactions at
the A1-C2 domain interface suggests that these variants could
potentially represent superior therapeutics in the treatment of
hemophilia.
Example 6
Combination of R121C/L2302C or Ala108Ile Substitution with One or
More Substitutions at the A1-A2 or A2-A3 Domain Interfaces
[0177] Based on the improved thermal and/or chemical stability
afforded by the A1-C2 variants, it was also determined whether the
mutations at the A1-C2 interface can be combined with the mutation
at one of the A1-A2 or A2-A3 interfaces to generate a factor VIII
with even greater stability. Previously tested stable factor VIII
mutants, as described in U.S. Patent Application Publ. No.
2009/0118184 to Fay et al., which is hereby incorporated by
reference in its entirety, showed up to 2-fold increases in thermal
stability compared with WT factor VIII in any combination of the
mutation with Asp519Ala, Asp519Val, Glu665Ala, Glu665Val,
Glu1984Ala, and Glu1984Val (A1-A2 or A2-A3 domain mutants).
[0178] These single point mutations or the double mutation
Asp519Val/Glu665Val were combined with either R121C/L2302C or
Ala108Ile in a B-domainless factor VIII cDNA using the procedures
described in Example 1. These factor VIII mutants were expressed
and purified using the procedures described in Example 1. Specific
activity values showed that most of the mutants (10 out of 13)
showed normal factor VIII activity values (>60% WT) as measured
by factor Xa generation assay (see Table 2 below). Thermal
stability values were determined as described above in Example 4.
Many of the resulting mutants exhibited >5 fold increase in
thermal stability (10/13 mutants, FIG. 8A), with
Ala108Ile/Glu665Val and Ala108Ile/Asp519Val/Glu665Val being the
most stable mutants (.about.10 fold increase relative to WT). Most
of the mutants also showed 15-30% increases in IC.sub.50 value
(guanidinium experiment) compared with WT (FIG. 8B). In addition,
the high factor VIIIa stability of the A domain mutants was mostly
preserved (mutants (11/13) showed 2-10 fold increase in factor
VIIIa stability relative to WT, FIG. 8C). Collectively,
modification at the A1-C2 contacting region by covalent attachment
or increasing hydrophobic interaction improved factor VIII
stability and these modifications can be combined with A2 domain
interface mutations to provide essentially additive effects
compared with either type of mutation alone.
TABLE-US-00004 TABLE 2 Specific Activity of Factor VIII Variants
FVIII variants Activity (%) FVIII variants Activity (%) WT 100
D519V/E665V 90.0 Ala108Ile 73.7 121CL 86.4 A108I/D519A 77.7
121CL/D519A 60.7 A108I/D519V 69.5 121CL/D519V 79.5 A108I/E665A 98.8
121CL/E665A 0 A108I/E665V 83.8 121CL/E665V 22.2 A108I/E1984A 43.4
121CL/E1984A 63.4 A108I/E1984V 94.1 121CL/E1984V 90.3
A108I/D519V/E665V 76.5 Activity was measured by FXa generation
assay and expressed as relative values compared to WT activity. The
single letter code is used to designate amino acid residues: I
(Ile), E (Glu), D (Asp), A (Ala) and V (Val). The variant 121CL
represents R121C/L2302C.
[0179] Thrombin generation assays were performed as previously
described (Wakabayashi et al., "Combining Mutations of Charged
Residues at the A2 Domain Interface Enhances Factor VIII Stability
over Single Point Mutations," J. Thromb. Haemost. 7:438-444 (2009),
which is hereby incorporated by reference in its entirety) to
determine the effects of combining the Ala108Ile mutation with an
A2 domain interface mutation. For this analysis, the
Asp519Val/Glu665Val double mutation was employed. Results in FIG. 9
compare WT factor VIII with Ala108Ile, Asp519Val/Glu665Val and the
combined Ala108Ile/Asp519Val/Glu665Val variants. Both the Ala108Ile
and the Asp519Val/Glu665Val variants showed improved thrombin
generation parameter values compared with WT (see Table 3 below).
In addition, the combined Ala108Ile/Asp519Val/Glu665Val mutation
yielded somewhat greater thrombin peak values and endogenous
thrombin potential ("ETP", which is the area under the curve and
represents total thrombin generated) than either individual
variant. This indicates a positive effect in combining these
mutations.
TABLE-US-00005 TABLE 3 Thrombin Generation Assay Parameter Values
Latent Time Peak Time Peak Value ETP FVIII variants (min) (min)
(nM) (nM min) WT 7.59 .+-. 0.09 (1.00) 16.1 .+-. 0.22 (1.00) 88.2
.+-. 6.60 (1.00) 1217 .+-. 34 (1.00) A108I 7.09 .+-. 0.41 (0.93)
12.7 .+-. 0.56 (0.79) 175.3 .+-. 17.0 (1.98) 1831 .+-. 183 (1.50)
D519V/E665V 8.19 .+-. 0.18 (1.07) 13.4 .+-. 0.16 (0.83) 203.4 .+-.
18.2 (2.30) 1939 .+-. 251 (1.59) A108I/D519V/E665V 7.05 .+-. 0.27
(0.92) 11.9 .+-. 0.31 (0.73) 222.8 .+-. 10.7 (2.52) 1990 .+-. 122
(1.64) Thrombin generation assays in the presence of 0.5 nM factor
VIII proteins, 0.5 pM rTF, and 4 .mu.M PSPCPE vesicles were
performed and parameter values were calculated. Data represents the
average values of triplicate samples. Values in parentheses are
relative to the WT value. The single letter code is used to
designate amino acid residues: I (Ile), E (Glu), D (Asp), A (Ala)
and V (Val).
[0180] Although preferred embodiments have been depicted and
described in detail herein, it will be apparent to those skilled in
the relevant art that various modifications, additions,
substitutions, and the like can be made without departing from the
spirit of the invention and these are therefore considered to be
within the scope of the invention as defined in the claims which
follow.
Sequence CWU 1
1
3416999DNAHuman 1gccaccagaa gatactacct gggtgcagtg gaactgtcat
gggactatat gcaaagtgat 60ctcggtgagc tgcctgtgga cgcaagattt cctcctagag
tgccaaaatc ttttccattc 120aacacctcag tcgtgtacaa aaagactctg
tttgtagaat tcacggatca ccttttcaac 180atcgctaagc caaggccacc
ctggatgggt ctgctaggtc ctaccatcca ggctgaggtt 240tatgatacag
tggtcattac acttaagaac atggcttccc atcctgtcag tcttcatgct
300gttggtgtat cctactggaa agcttctgag ggagctgaat atgatgatca
gaccagtcaa 360agggagaaag aagatgataa agtcttccct ggtggaagcc
atacatatgt ctggcaggtc 420ctgaaagaga atggtccaat ggcctctgac
ccactgtgcc ttacctactc atatctttct 480catgtggacc tggtaaaaga
cttgaattca ggcctcattg gagccctact agtatgtaga 540gaagggagtc
tggccaagga aaagacacag accttgcaca aatttatact actttttgct
600gtatttgatg aagggaaaag ttggcactca gaaacaaaga actccttgat
gcaggatagg 660gatgctgcat ctgctcgggc ctggcctaaa atgcacacag
tcaatggtta tgtaaacagg 720tctctgccag gtctgattgg atgccacagg
aaatcagtct attggcatgt gattggaatg 780ggcaccactc ctgaagtgca
ctcaatattc ctcgaaggtc acacatttct tgtgaggaac 840catcgccagg
cgtccttgga aatctcgcca ataactttcc ttactgctca aacactcttg
900atggaccttg gacagtttct actgttttgt catatctctt cccaccaaca
tgatggcatg 960gaagcttatg tcaaagtaga cagctgtcca gaggaacccc
aactacgaat gaaaaataat 1020gaagaagcgg aagactatga tgatgatctt
actgattctg aaatggatgt ggtcaggttt 1080gatgatgaca actctccttc
ctttatccaa attcgctcag ttgccaagaa gcatcctaaa 1140acttgggtac
attacattgc tgctgaagag gaggactggg actatgctcc cttagtcctc
1200gcccccgatg acagaagtta taaaagtcaa tatttgaaca atggccctca
gcggattggt 1260aggaagtaca aaaaagtccg atttatggca tacacagatg
aaacctttaa gactcgtgaa 1320gctattcagc atgaatcagg aatcttggga
cctttacttt atggggaagt tggagacaca 1380ctgttgatta tatttaagaa
tcaagcaagc agaccatata acatctaccc tcacggaatc 1440actgatgtcc
gtcctttgta ttcaaggaga ttaccaaaag gtgtaaaaca tttgaaggat
1500tttccaattc tgccaggaga aatattcaaa tataaatgga cagtgactgt
agaagatggg 1560ccaactaaat cagatcctcg gtgcctgacc cgctattact
ctagtttcgt taatatggag 1620agagatctag cttcaggact cattggccct
ctcctcatct gctacaaaga atctgtagat 1680caaagaggaa accagataat
gtcagacaag aggaatgtca tcctgttttc tgtatttgat 1740gagaaccgaa
gctggtacct cacagagaat atacaacgct ttctccccaa tccagctgga
1800gtgcagcttg aggatccaga gttccaagcc tccaacatca tgcacagcat
caatggctat 1860gtttttgata gtttgcagtt gtcagtttgt ttgcatgagg
tggcatactg gtacattcta 1920agcattggag cacagactga cttcctttct
gtcttcttct ctggatatac cttcaaacac 1980aaaatggtct atgaagacac
actcacccta ttcccattct caggagaaac tgtcttcatg 2040tcgatggaaa
acccaggtct atggattctg gggtgccaca actcagactt tcggaacaga
2100ggcatgaccg ccttactgaa ggtttctagt tgtgacaaga acactggtga
ttattacgag 2160gacagttatg aagatatttc agcatacttg ctgagtaaaa
acaatgccat tgaaccaaga 2220agcttctccc agaattcaag acaccctagc
actaggcaaa agcaatttaa tgccaccaca 2280attccagaaa atgacataga
gaagactgac ccttggtttg cacacagaac acctatgcct 2340aaaatacaaa
atgtctcctc tagtgatttg ttgatgctct tgcgacagag tcctactcca
2400catgggctat ccttatctga tctccaagaa gccaaatatg agactttttc
tgatgatcca 2460tcacctggag caatagacag taataacagc ctgtctgaaa
tgacacactt caggccacag 2520ctccatcaca gtggggacat ggtatttacc
cctgagtcag gcctccaatt aagattaaat 2580gagaaactgg ggacaactgc
agcaacagag ttgaagaaac ttgatttcaa agtttctagt 2640acatcaaata
atctgatttc aacaattcca tcagacaatt tggcagcagg tactgataat
2700acaagttcct taggaccccc aagtatgcca gttcattatg atagtcaatt
agataccact 2760ctatttggca aaaagtcatc tccccttact gagtctggtg
gacctctgag cttgagtgaa 2820gaaaataatg attcaaagtt gttagaatca
ggtttaatga atagccaaga aagttcatgg 2880ggaaaaaatg tatcgtcaac
agagagtggt aggttattta aagggaaaag agctcatgga 2940cctgctttgt
tgactaaaga taatgcctta ttcaaagtta gcatctcttt gttaaagaca
3000aacaaaactt ccaataattc agcaactaat agaaagactc acattgatgg
cccatcatta 3060ttaattgaga atagtccatc agtctggcaa aatatattag
aaagtgacac tgagtttaaa 3120aaagtgacac ctttgattca tgacagaatg
cttatggaca aaaatgctac agctttgagg 3180ctaaatcata tgtcaaataa
aactacttca tcaaaaaaca tggaaatggt ccaacagaaa 3240aaagagggcc
ccattccacc agatgcacaa aatccagata tgtcgttctt taagatgcta
3300ttcttgccag aatcagcaag gtggatacaa aggactcatg gaaagaactc
tctgaactct 3360gggcaaggcc ccagtccaaa gcaattagta tccttaggac
cagaaaaatc tgtggaaggt 3420cagaatttct tgtctgagaa aaacaaagtg
gtagtaggaa agggtgaatt tacaaaggac 3480gtaggactca aagagatggt
ttttccaagc agcagaaacc tatttcttac taacttggat 3540aatttacatg
aaaataatac acacaatcaa gaaaaaaaaa ttcaggaaga aatagaaaag
3600aaggaaacat taatccaaga gaatgtagtt ttgcctcaga tacatacagt
gactggcact 3660aagaatttca tgaagaacct tttcttactg agcactaggc
aaaatgtaga aggttcatat 3720gacggggcat atgctccagt acttcaagat
tttaggtcat taaatgattc aacaaataga 3780acaaagaaac acacagctca
tttctcaaaa aaaggggagg aagaaaactt ggaaggcttg 3840ggaaatcaaa
ccaagcaaat tgtagagaaa tatgcatgca ccacaaggat atctcctaat
3900acaagccagc agaattttgt cacgcaacgt agtaagagag ctttgaaaca
attcagactc 3960ccactagaag aaacagaact tgaaaaaagg ataattgtgg
atgacacctc aacccagtgg 4020tccaaaaaca tgaaacattt gaccccgagc
accctcacac agatagacta caatgagaag 4080gagaaagggg ccattactca
gtctccctta tcagattgcc ttacgaggag tcatagcatc 4140cctcaagcaa
atagatctcc attacccatt gcaaaggtat catcatttcc atctattaga
4200cctatatatc tgaccagggt cctattccaa gacaactctt ctcatcttcc
agcagcatct 4260tatagaaaga aagattctgg ggtccaagaa agcagtcatt
tcttacaagg agccaaaaaa 4320aataaccttt ctttagccat tctaaccttg
gagatgactg gtgatcaaag agaggttggc 4380tccctgggga caagtgccac
aaattcagtc acatacaaga aagttgagaa cactgttctc 4440ccgaaaccag
acttgcccaa aacatctggc aaagttgaat tgcttccaaa agttcacatt
4500tatcagaagg acctattccc tacggaaact agcaatgggt ctcctggcca
tctggatctc 4560gtggaaggga gccttcttca gggaacagag ggagcgatta
agtggaatga agcaaacaga 4620cctggaaaag ttccctttct gagagtagca
acagaaagct ctgcaaagac tccctccaag 4680ctattggatc ctcttgcttg
ggataaccac tatggtactc agataccaaa agaagagtgg 4740aaatcccaag
agaagtcacc agaaaaaaca gcttttaaga aaaaggatac cattttgtcc
4800ctgaacgctt gtgaaagcaa tcatgcaata gcagcaataa atgagggaca
aaataagccc 4860gaaatagaag tcacctgggc aaagcaaggt aggactgaaa
ggctgtgctc tcaaaaccca 4920ccagtcttga aacgccatca acgggaaata
actcgtacta ctcttcagtc agatcaagag 4980gaaattgact atgatgatac
catatcagtt gaaatgaaga aggaagattt tgacatttat 5040gatgaggatg
aaaatcagag cccccgcagc tttcaaaaga aaacacgaca ctattttatt
5100gctgcagtgg agaggctctg ggattatggg atgagtagct ccccacatgt
tctaagaaac 5160agggctcaga gtggcagtgt ccctcagttc aagaaagttg
ttttccagga atttactgat 5220ggctccttta ctcagccctt ataccgtgga
gaactaaatg aacatttggg actcctgggg 5280ccatatataa gagcagaagt
tgaagataat atcatggtaa ctttcagaaa tcaggcctct 5340cgtccctatt
ccttctattc tagccttatt tcttatgagg aagatcagag gcaaggagca
5400gaacctagaa aaaactttgt caagcctaat gaaaccaaaa cttacttttg
gaaagtgcaa 5460catcatatgg cacccactaa agatgagttt gactgcaaag
cctgggctta tttctctgat 5520gttgacctgg aaaaagatgt gcactcaggc
ctgattggac cccttctggt ctgccacact 5580aacacactga accctgctca
tgggagacaa gtgacagtac aggaatttgc tctgtttttc 5640accatctttg
atgagaccaa aagctggtac ttcactgaaa atatggaaag aaactgcagg
5700gctccctgca atatccagat ggaagatccc acttttaaag agaattatcg
cttccatgca 5760atcaatggct acataatgga tacactacct ggcttagtaa
tggctcagga tcaaaggatt 5820cgatggtatc tgctcagcat gggcagcaat
gaaaacatcc attctattca tttcagtgga 5880catgtgttca ctgtacgaaa
aaaagaggag tataaaatgg cactgtacaa tctctatcca 5940ggtgtttttg
agacagtgga aatgttacca tccaaagctg gaatttggcg ggtggaatgc
6000cttattggcg agcatctaca tgctgggatg agcacacttt ttctggtgta
cagcaataag 6060tgtcagactc ccctgggaat ggcttctgga cacattagag
attttcagat tacagcttca 6120ggacaatatg gacagtgggc cccaaagctg
gccagacttc attattccgg atcaatcaat 6180gcctggagca ccaaggagcc
cttttcttgg atcaaggtgg atctgttggc accaatgatt 6240attcacggca
tcaagaccca gggtgcccgt cagaagttct ccagcctcta catctctcag
6300tttatcatca tgtatagtct tgatgggaag aagtggcaga cttatcgagg
aaattccact 6360ggaaccttaa tggtcttctt tggcaatgtg gattcatctg
ggataaaaca caatattttt 6420aaccctccaa ttattgctcg atacatccgt
ttgcacccaa ctcattatag cattcgcagc 6480actcttcgca tggagttgat
gggctgtgat ttaaatagtt gcagcatgcc attgggaatg 6540gagagtaaag
caatatcaga tgcacagatt actgcttcat cctactttac caatatgttt
6600gccacctggt ctccttcaaa agctcgactt cacctccaag ggaggagtaa
tgcctggaga 6660cctcaggtga ataatccaaa agagtggctg caagtggact
tccagaagac aatgaaagtc 6720acaggagtaa ctactcaggg agtaaaatct
ctgcttacca gcatgtatgt gaaggagttc 6780ctcatctcca gcagtcaaga
tggccatcag tggactctct tttttcagaa tggcaaagta 6840aaggtttttc
agggaaatca agactccttc acacctgtgg tgaactctct agacccaccg
6900ttactgactc gctaccttcg aattcacccc cagagttggg tgcaccagat
tgccctgagg 6960atggaggttc tgggctgcga ggcacaggac ctctactga
699922332PRTHuman 2Ala Thr Arg Arg Tyr Tyr Leu Gly Ala Val Glu Leu
Ser Trp Asp Tyr 1 5 10 15 Met Gln Ser Asp Leu Gly Glu Leu Pro Val
Asp Ala Arg Phe Pro Pro 20 25 30 Arg Val Pro Lys Ser Phe Pro Phe
Asn Thr Ser Val Val Tyr Lys Lys 35 40 45 Thr Leu Phe Val Glu Phe
Thr Val His Leu Phe Asn Ile Ala Lys Pro 50 55 60 Arg Pro Pro Trp
Met Gly Leu Leu Gly Pro Thr Ile Gln Ala Glu Val 65 70 75 80 Tyr Asp
Thr Val Val Ile Thr Leu Lys Asn Met Ala Ser His Pro Val 85 90 95
Ser Leu His Ala Val Gly Val Ser Tyr Trp Lys Ala Ser Glu Gly Ala 100
105 110 Glu Tyr Asp Asp Gln Thr Ser Gln Arg Glu Lys Glu Asp Asp Lys
Val 115 120 125 Phe Pro Gly Gly Ser His Thr Tyr Val Trp Gln Val Leu
Lys Glu Asn 130 135 140 Gly Pro Met Ala Ser Asp Pro Leu Cys Leu Thr
Tyr Ser Tyr Leu Ser 145 150 155 160 His Val Asp Leu Val Lys Asp Leu
Asn Ser Gly Leu Ile Gly Ala Leu 165 170 175 Leu Val Cys Arg Glu Gly
Ser Leu Ala Lys Glu Lys Thr Gln Thr Leu 180 185 190 His Lys Phe Ile
Leu Leu Phe Ala Val Phe Asp Glu Gly Lys Ser Trp 195 200 205 His Ser
Glu Thr Lys Asn Ser Leu Met Gln Asp Arg Asp Ala Ala Ser 210 215 220
Ala Arg Ala Trp Pro Lys Met His Thr Val Asn Gly Tyr Val Asn Arg 225
230 235 240 Ser Leu Pro Gly Leu Ile Gly Cys His Arg Lys Ser Val Tyr
Trp His 245 250 255 Val Ile Gly Met Gly Thr Thr Pro Glu Val His Ser
Ile Phe Leu Glu 260 265 270 Gly His Thr Phe Leu Val Arg Asn His Arg
Gln Ala Ser Leu Glu Ile 275 280 285 Ser Pro Ile Thr Phe Leu Thr Ala
Gln Thr Leu Leu Met Asp Leu Gly 290 295 300 Gln Phe Leu Leu Phe Cys
His Ile Ser Ser His Gln His Asp Gly Met 305 310 315 320 Glu Ala Tyr
Val Lys Val Asp Ser Cys Pro Glu Glu Pro Gln Leu Arg 325 330 335 Met
Lys Asn Asn Glu Glu Ala Glu Asp Tyr Asp Asp Asp Leu Thr Asp 340 345
350 Ser Glu Met Asp Val Val Arg Phe Asp Asp Asp Asn Ser Pro Ser Phe
355 360 365 Ile Gln Ile Arg Ser Val Ala Lys Lys His Pro Lys Thr Trp
Val His 370 375 380 Tyr Ile Ala Ala Glu Glu Glu Asp Trp Asp Tyr Ala
Pro Leu Val Leu 385 390 395 400 Ala Pro Asp Asp Arg Ser Tyr Lys Ser
Gln Tyr Leu Asn Asn Gly Pro 405 410 415 Gln Arg Ile Gly Arg Lys Tyr
Lys Lys Val Arg Phe Met Ala Tyr Thr 420 425 430 Asp Glu Thr Phe Lys
Thr Arg Glu Ala Ile Gln His Glu Ser Gly Ile 435 440 445 Leu Gly Pro
Leu Leu Tyr Gly Glu Val Gly Asp Thr Leu Leu Ile Ile 450 455 460 Phe
Lys Asn Gln Ala Ser Arg Pro Tyr Asn Ile Tyr Pro His Gly Ile 465 470
475 480 Thr Asp Val Arg Pro Leu Tyr Ser Arg Arg Leu Pro Lys Gly Val
Lys 485 490 495 His Leu Lys Asp Phe Pro Ile Leu Pro Gly Glu Ile Phe
Lys Tyr Lys 500 505 510 Trp Thr Val Thr Val Glu Asp Gly Pro Thr Lys
Ser Asp Pro Arg Cys 515 520 525 Leu Thr Arg Tyr Tyr Ser Ser Phe Val
Asn Met Glu Arg Asp Leu Ala 530 535 540 Ser Gly Leu Ile Gly Pro Leu
Leu Ile Cys Tyr Lys Glu Ser Val Asp 545 550 555 560 Gln Arg Gly Asn
Gln Ile Met Ser Asp Lys Arg Asn Val Ile Leu Phe 565 570 575 Ser Val
Phe Asp Glu Asn Arg Ser Trp Tyr Leu Thr Glu Asn Ile Gln 580 585 590
Arg Phe Leu Pro Asn Pro Ala Gly Val Gln Leu Glu Asp Pro Glu Phe 595
600 605 Gln Ala Ser Asn Ile Met His Ser Ile Asn Gly Tyr Val Phe Asp
Ser 610 615 620 Leu Gln Leu Ser Val Cys Leu His Glu Val Ala Tyr Trp
Tyr Ile Leu 625 630 635 640 Ser Ile Gly Ala Gln Thr Asp Phe Leu Ser
Val Phe Phe Ser Gly Tyr 645 650 655 Thr Phe Lys His Lys Met Val Tyr
Glu Asp Thr Leu Thr Leu Phe Pro 660 665 670 Phe Ser Gly Glu Thr Val
Phe Met Ser Met Glu Asn Pro Gly Leu Trp 675 680 685 Ile Leu Gly Cys
His Asn Ser Asp Phe Arg Asn Arg Gly Met Thr Ala 690 695 700 Leu Leu
Lys Val Ser Ser Cys Asp Lys Asn Thr Gly Asp Tyr Tyr Glu 705 710 715
720 Asp Ser Tyr Glu Asp Ile Ser Ala Tyr Leu Leu Ser Lys Asn Asn Ala
725 730 735 Ile Glu Pro Arg Ser Phe Ser Gln Asn Ser Arg His Pro Ser
Thr Arg 740 745 750 Gln Lys Gln Phe Asn Ala Thr Thr Ile Pro Glu Asn
Asp Ile Glu Lys 755 760 765 Thr Asp Pro Trp Phe Ala His Arg Thr Pro
Met Pro Lys Ile Gln Asn 770 775 780 Val Ser Ser Ser Asp Leu Leu Met
Leu Leu Arg Gln Ser Pro Thr Pro 785 790 795 800 His Gly Leu Ser Leu
Ser Asp Leu Gln Glu Ala Lys Tyr Glu Thr Phe 805 810 815 Ser Asp Asp
Pro Ser Pro Gly Ala Ile Asp Ser Asn Asn Ser Leu Ser 820 825 830 Glu
Met Thr His Phe Arg Pro Gln Leu His His Ser Gly Asp Met Val 835 840
845 Phe Thr Pro Glu Ser Gly Leu Gln Leu Arg Leu Asn Glu Lys Leu Gly
850 855 860 Thr Thr Ala Ala Thr Glu Leu Lys Lys Leu Asp Phe Lys Val
Ser Ser 865 870 875 880 Thr Ser Asn Asn Leu Ile Ser Thr Ile Pro Ser
Asp Asn Leu Ala Ala 885 890 895 Gly Thr Asp Asn Thr Ser Ser Leu Gly
Pro Pro Ser Met Pro Val His 900 905 910 Tyr Asp Ser Gln Leu Asp Thr
Thr Leu Phe Gly Lys Lys Ser Ser Pro 915 920 925 Leu Thr Glu Ser Gly
Gly Pro Leu Ser Leu Ser Glu Glu Asn Asn Asp 930 935 940 Ser Lys Leu
Leu Glu Ser Gly Leu Met Asn Ser Gln Glu Ser Ser Trp 945 950 955 960
Gly Lys Asn Val Ser Ser Thr Glu Ser Gly Arg Leu Phe Lys Gly Lys 965
970 975 Arg Ala His Gly Pro Ala Leu Leu Thr Lys Asp Asn Ala Leu Phe
Lys 980 985 990 Val Ser Ile Ser Leu Leu Lys Thr Asn Lys Thr Ser Asn
Asn Ser Ala 995 1000 1005 Thr Asn Arg Lys Thr His Ile Asp Gly Pro
Ser Leu Leu Ile Glu 1010 1015 1020 Asn Ser Pro Ser Val Trp Gln Asn
Ile Leu Glu Ser Asp Thr Glu 1025 1030 1035 Phe Lys Lys Val Thr Pro
Leu Ile His Asp Arg Met Leu Met Asp 1040 1045 1050 Lys Asn Ala Thr
Ala Leu Arg Leu Asn His Met Ser Asn Lys Thr 1055 1060 1065 Thr Ser
Ser Lys Asn Met Glu Met Val Gln Gln Lys Lys Glu Gly 1070 1075 1080
Pro Ile Pro Pro Asp Ala Gln Asn Pro Asp Met Ser Phe Phe Lys 1085
1090 1095 Met Leu Phe Leu Pro Glu Ser Ala Arg Trp Ile Gln Arg Thr
His 1100 1105 1110 Gly Lys Asn Ser Leu Asn Ser Gly Gln Gly Pro Ser
Pro Lys Gln 1115 1120 1125 Leu Val Ser Leu Gly Pro Glu Lys Ser Val
Glu Gly Gln Asn Phe 1130 1135 1140 Leu Ser Glu Lys Asn Lys Val Val
Val Gly Lys Gly Glu Phe Thr 1145 1150 1155 Lys Asp Val Gly Leu Lys
Glu Met Val Phe Pro Ser Ser Arg Asn 1160 1165 1170 Leu Phe Leu Thr
Asn Leu Asp Asn Leu His Glu Asn Asn Thr His 1175 1180 1185 Asn Gln
Glu Lys Lys Ile Gln Glu Glu Ile Glu Lys Lys Glu Thr 1190 1195 1200
Leu Ile Gln Glu Asn Val Val Leu Pro Gln Ile His Thr Val Thr 1205
1210 1215
Gly Thr Lys Asn Phe Met Lys Asn Leu Phe Leu Leu Ser Thr Arg 1220
1225 1230 Gln Asn Val Glu Gly Ser Tyr Glu Gly Ala Tyr Ala Pro Val
Leu 1235 1240 1245 Gln Asp Phe Arg Ser Leu Asn Asp Ser Thr Asn Arg
Thr Lys Lys 1250 1255 1260 His Thr Ala His Phe Ser Lys Lys Gly Glu
Glu Glu Asn Leu Glu 1265 1270 1275 Gly Leu Gly Asn Gln Thr Lys Gln
Ile Val Glu Lys Tyr Ala Cys 1280 1285 1290 Thr Thr Arg Ile Ser Pro
Asn Thr Ser Gln Gln Asn Phe Val Thr 1295 1300 1305 Gln Arg Ser Lys
Arg Ala Leu Lys Gln Phe Arg Leu Pro Leu Glu 1310 1315 1320 Glu Thr
Glu Leu Glu Lys Arg Ile Ile Val Asp Asp Thr Ser Thr 1325 1330 1335
Gln Trp Ser Lys Asn Met Lys His Leu Thr Pro Ser Thr Leu Thr 1340
1345 1350 Gln Ile Asp Tyr Asn Glu Lys Glu Lys Gly Ala Ile Thr Gln
Ser 1355 1360 1365 Pro Leu Ser Asp Cys Leu Thr Arg Ser His Ser Ile
Pro Gln Ala 1370 1375 1380 Asn Arg Ser Pro Leu Pro Ile Ala Lys Val
Ser Ser Phe Pro Ser 1385 1390 1395 Ile Arg Pro Ile Tyr Leu Thr Arg
Val Leu Phe Gln Asp Asn Ser 1400 1405 1410 Ser His Leu Pro Ala Ala
Ser Tyr Arg Lys Lys Asp Ser Gly Val 1415 1420 1425 Gln Glu Ser Ser
His Phe Leu Gln Gly Ala Lys Lys Asn Asn Leu 1430 1435 1440 Ser Leu
Ala Ile Leu Thr Leu Glu Met Thr Gly Asp Gln Arg Glu 1445 1450 1455
Val Gly Ser Leu Gly Thr Ser Ala Thr Asn Ser Val Thr Tyr Lys 1460
1465 1470 Lys Val Glu Asn Thr Val Leu Pro Lys Pro Asp Leu Pro Lys
Thr 1475 1480 1485 Ser Gly Lys Val Glu Leu Leu Pro Lys Val His Ile
Tyr Gln Lys 1490 1495 1500 Asp Leu Phe Pro Thr Glu Thr Ser Asn Gly
Ser Pro Gly His Leu 1505 1510 1515 Asp Leu Val Glu Gly Ser Leu Leu
Gln Gly Thr Glu Gly Ala Ile 1520 1525 1530 Lys Trp Asn Glu Ala Asn
Arg Pro Gly Lys Val Pro Phe Leu Arg 1535 1540 1545 Val Ala Thr Glu
Ser Ser Ala Lys Thr Pro Ser Lys Leu Leu Asp 1550 1555 1560 Pro Leu
Ala Trp Asp Asn His Tyr Gly Thr Gln Ile Pro Lys Glu 1565 1570 1575
Glu Trp Lys Ser Gln Glu Lys Ser Pro Glu Lys Thr Ala Phe Lys 1580
1585 1590 Lys Lys Asp Thr Ile Leu Ser Leu Asn Ala Cys Glu Ser Asn
His 1595 1600 1605 Ala Ile Ala Ala Ile Asn Glu Gly Gln Asn Lys Pro
Glu Ile Glu 1610 1615 1620 Val Thr Trp Ala Lys Gln Gly Arg Thr Glu
Arg Leu Cys Ser Gln 1625 1630 1635 Asn Pro Pro Val Leu Lys Arg His
Gln Arg Glu Ile Thr Arg Thr 1640 1645 1650 Thr Leu Gln Ser Asp Gln
Glu Glu Ile Asp Tyr Asp Asp Thr Ile 1655 1660 1665 Ser Val Glu Met
Lys Lys Glu Asp Phe Asp Ile Tyr Asp Glu Asp 1670 1675 1680 Glu Asn
Gln Ser Pro Arg Ser Phe Gln Lys Lys Thr Arg His Tyr 1685 1690 1695
Phe Ile Ala Ala Val Glu Arg Leu Trp Asp Tyr Gly Met Ser Ser 1700
1705 1710 Ser Pro His Val Leu Arg Asn Arg Ala Gln Ser Gly Ser Val
Pro 1715 1720 1725 Gln Phe Lys Lys Val Val Phe Gln Glu Phe Thr Asp
Gly Ser Phe 1730 1735 1740 Thr Gln Pro Leu Tyr Arg Gly Glu Leu Asn
Glu His Leu Gly Leu 1745 1750 1755 Leu Gly Pro Tyr Ile Arg Ala Glu
Val Glu Asp Asn Ile Met Val 1760 1765 1770 Thr Phe Arg Asn Gln Ala
Ser Arg Pro Tyr Ser Phe Tyr Ser Ser 1775 1780 1785 Leu Ile Ser Tyr
Glu Glu Asp Gln Arg Gln Gly Ala Glu Pro Arg 1790 1795 1800 Lys Asn
Phe Val Lys Pro Asn Glu Thr Lys Thr Tyr Phe Trp Lys 1805 1810 1815
Val Gln His His Met Ala Pro Thr Lys Asp Glu Phe Asp Cys Lys 1820
1825 1830 Ala Trp Ala Tyr Phe Ser Asp Val Asp Leu Glu Lys Asp Val
His 1835 1840 1845 Ser Gly Leu Ile Gly Pro Leu Leu Val Cys His Thr
Asn Thr Leu 1850 1855 1860 Asn Pro Ala His Gly Arg Gln Val Thr Val
Gln Glu Phe Ala Leu 1865 1870 1875 Phe Phe Thr Ile Phe Asp Glu Thr
Lys Ser Trp Tyr Phe Thr Glu 1880 1885 1890 Asn Met Glu Arg Asn Cys
Arg Ala Pro Cys Asn Ile Gln Met Glu 1895 1900 1905 Asp Pro Thr Phe
Lys Glu Asn Tyr Arg Phe His Ala Ile Asn Gly 1910 1915 1920 Tyr Ile
Met Asp Thr Leu Pro Gly Leu Val Met Ala Gln Asp Gln 1925 1930 1935
Arg Ile Arg Trp Tyr Leu Leu Ser Met Gly Ser Asn Glu Asn Ile 1940
1945 1950 His Ser Ile His Phe Ser Gly His Val Phe Thr Val Arg Lys
Lys 1955 1960 1965 Glu Glu Tyr Lys Met Ala Leu Tyr Asn Leu Tyr Pro
Gly Val Phe 1970 1975 1980 Glu Thr Val Glu Met Leu Pro Ser Lys Ala
Gly Ile Trp Arg Val 1985 1990 1995 Glu Cys Leu Ile Gly Glu His Leu
His Ala Gly Met Ser Thr Leu 2000 2005 2010 Phe Leu Val Tyr Ser Asn
Lys Cys Gln Thr Pro Leu Gly Met Ala 2015 2020 2025 Ser Gly His Ile
Arg Asp Phe Gln Ile Thr Ala Ser Gly Gln Tyr 2030 2035 2040 Gly Gln
Trp Ala Pro Lys Leu Ala Arg Leu His Tyr Ser Gly Ser 2045 2050 2055
Ile Asn Ala Trp Ser Thr Lys Glu Pro Phe Ser Trp Ile Lys Val 2060
2065 2070 Asp Leu Leu Ala Pro Met Ile Ile His Gly Ile Lys Thr Gln
Gly 2075 2080 2085 Ala Arg Gln Lys Phe Ser Ser Leu Tyr Ile Ser Gln
Phe Ile Ile 2090 2095 2100 Met Tyr Ser Leu Asp Gly Lys Lys Trp Gln
Thr Tyr Arg Gly Asn 2105 2110 2115 Ser Thr Gly Thr Leu Met Val Phe
Phe Gly Asn Val Asp Ser Ser 2120 2125 2130 Gly Ile Lys His Asn Ile
Phe Asn Pro Pro Ile Ile Ala Arg Tyr 2135 2140 2145 Ile Arg Leu His
Pro Thr His Tyr Ser Ile Arg Ser Thr Leu Arg 2150 2155 2160 Met Glu
Leu Met Gly Cys Asp Leu Asn Ser Cys Ser Met Pro Leu 2165 2170 2175
Gly Met Glu Ser Lys Ala Ile Ser Asp Ala Gln Ile Thr Ala Ser 2180
2185 2190 Ser Tyr Phe Thr Asn Met Phe Ala Thr Trp Ser Pro Ser Lys
Ala 2195 2200 2205 Arg Leu His Leu Gln Gly Arg Ser Asn Ala Trp Arg
Pro Gln Val 2210 2215 2220 Asn Asn Pro Lys Glu Trp Leu Gln Val Asp
Phe Gln Lys Thr Met 2225 2230 2235 Lys Val Thr Gly Val Thr Thr Gln
Gly Val Lys Ser Leu Leu Thr 2240 2245 2250 Ser Met Tyr Val Lys Glu
Phe Leu Ile Ser Ser Ser Gln Asp Gly 2255 2260 2265 His Gln Trp Thr
Leu Phe Phe Gln Asn Gly Lys Val Lys Val Phe 2270 2275 2280 Gln Gly
Asn Gln Asp Ser Phe Thr Pro Val Val Asn Ser Leu Asp 2285 2290 2295
Pro Pro Leu Leu Thr Arg Tyr Leu Arg Ile His Pro Gln Ser Trp 2300
2305 2310 Val His Gln Ile Ala Leu Arg Met Glu Val Leu Gly Cys Glu
Ala 2315 2320 2325 Gln Asp Leu Tyr 2330 341PRTPorcine 3Ala Val Gly
Val Ser Phe Trp Lys Ser Ser Glu Gly Ala Glu Tyr Glu 1 5 10 15 Asp
His Thr Ser Gln Arg Glu Lys Glu Asp Asp Lys Val Leu Pro Gly 20 25
30 Lys Ser Gln Thr Tyr Val Trp Gln Val 35 40 441PRTCanine 4Ala Val
Gly Val Ser Tyr Trp Lys Ala Ser Glu Gly Ala Glu Tyr Glu 1 5 10 15
Asp Gln Thr Ser Gln Lys Glu Lys Glu Asp Asp Asn Val Ile Pro Gly 20
25 30 Glu Ser His Thr Tyr Val Trp Gln Val 35 40 541PRTMouse 5Ala
Val Gly Val Ser Tyr Trp Lys Ala Ser Glu Gly Asp Glu Tyr Glu 1 5 10
15 Asp Gln Thr Ser Gln Met Glu Lys Glu Asp Asp Lys Val Phe Pro Gly
20 25 30 Glu Ser His Thr Tyr Val Trp Gln Val 35 40 641PRTRabbit
6Ala Val Gly Val Ser Tyr Trp Lys Ala Ser Glu Gly Ala Glu Tyr Asp 1
5 10 15 Asp Gln Thr Ser Gln Arg Glu Lys Glu Asp Asp Lys Ile Phe Pro
Gly 20 25 30 Glu Ser His Thr Tyr Val Trp Gln Val 35 40 741PRTBat
7Ala Val Gly Val Ser Tyr Trp Lys Ala Ser Glu Gly Ala Glu Tyr Glu 1
5 10 15 Asp Glu Thr Ser Lys Thr Glu Lys Glu Asp Asp Lys Val Ile Pro
Gly 20 25 30 Glu Ser His Thr Tyr Val Trp His Val 35 40 841PRTRat
8Ala Val Gly Met Ser Phe Trp Lys Ala Ser Glu Gly Ala Ala Tyr Asp 1
5 10 15 Asp His Ser Ser Pro Ala Glu Lys Asp Asp Asp Lys Val Leu Pro
Gly 20 25 30 Glu Ser His Thr Tyr Ala Trp Gln Val 35 40 941PRTSheep
9Ala Ile Gly Val Ser Tyr Trp Lys Ser Ser Glu Gly Ala Ala Tyr Lys 1
5 10 15 Asp Glu Thr Ser Gln Arg Glu Lys Glu Asp Asp Lys Val Ile Pro
Gly 20 25 30 Lys Ser His Thr Tyr Val Trp His Ile 35 40
1041PRTArtificialConsensus 10Ala Xaa Gly Xaa Ser Xaa Trp Lys Xaa
Ser Glu Gly Xaa Xaa Tyr Xaa 1 5 10 15 Asp Xaa Xaa Ser Xaa Xaa Glu
Lys Xaa Asp Asp Xaa Xaa Xaa Pro Gly 20 25 30 Xaa Ser Xaa Thr Tyr
Xaa Trp Xaa Xaa 35 40 11102PRTPorcine 11Gln Val Asp Leu Gln Lys Thr
Val Lys Val Thr Gly Ile Thr Thr Gln 1 5 10 15 Gly Val Lys Ser Leu
Leu Ser Ser Met Tyr Val Lys Glu Phe Leu Val 20 25 30 Ser Ser Ser
Gln Asp Gly Arg Arg Trp Thr Leu Phe Leu Gln Asp Gly 35 40 45 His
Thr Lys Val Phe Gln Gly Asn Gln Asp Ser Ser Thr Pro Val Val 50 55
60 Asn Ala Leu Asp Pro Pro Leu Phe Thr Arg Tyr Leu Arg Ile His Pro
65 70 75 80 Thr Ser Trp Ala Gln His Ile Ala Leu Arg Leu Glu Val Leu
Gly Cys 85 90 95 Glu Ala Gln Asp Leu Tyr 100 12102PRTCanine 12Gln
Val Asp Phe Arg Lys Thr Met Lys Val Thr Gly Ile Thr Thr Gln 1 5 10
15 Gly Val Lys Ser Leu Leu Ile Ser Met Tyr Val Lys Glu Phe Leu Ile
20 25 30 Ser Ser Ser Gln Asp Gly His Asn Trp Thr Leu Phe Leu Gln
Asn Gly 35 40 45 Lys Val Lys Val Phe Gln Gly Asn Arg Asp Ser Ser
Thr Pro Val Arg 50 55 60 Asn Arg Leu Glu Pro Pro Leu Val Ala Arg
Tyr Val Arg Leu His Pro 65 70 75 80 Gln Ser Trp Ala His His Ile Ala
Leu Arg Leu Glu Val Leu Gly Cys 85 90 95 Asp Thr Gln Gln Pro Ala
100 13102PRTMouse 13Gln Val Asp Leu Gln Lys Thr Met Lys Val Thr Gly
Ile Ile Thr Gln 1 5 10 15 Gly Val Lys Ser Leu Phe Thr Ser Met Phe
Val Lys Glu Phe Leu Ile 20 25 30 Ser Ser Ser Gln Asp Gly His His
Trp Thr Gln Ile Leu Tyr Asn Gly 35 40 45 Lys Val Lys Val Phe Gln
Gly Asn Gln Asp Ser Ser Thr Pro Met Met 50 55 60 Asn Ser Leu Asp
Pro Pro Leu Leu Thr Arg Tyr Leu Arg Ile His Pro 65 70 75 80 Gln Ile
Trp Glu His Gln Ile Ala Leu Arg Leu Glu Ile Leu Gly Cys 85 90 95
Glu Ala Gln Gln Gln Tyr 100 14102PRTRabbit 14Gln Val Asp Leu Arg
Lys Thr Met Lys Val Thr Gly Ile Thr Thr Gln 1 5 10 15 Gly Val Lys
Ser Leu Leu Thr Ser Met Tyr Val Thr Glu Phe Leu Ile 20 25 30 Ser
Ser Ser Gln Asp Gly His His Trp Thr Leu Val Leu Gln Lys Gly 35 40
45 Lys Leu Lys Val Phe Lys Gly Asn Gln Asp Ser Phe Thr Pro Val Leu
50 55 60 Asn Ser Leu Asp Pro Pro Leu Leu Thr Arg Tyr Leu Arg Ile
His Pro 65 70 75 80 Lys Ser Trp Val His Gln Ile Ala Leu Arg Leu Glu
Val Leu Gly Cys 85 90 95 Glu Ala Gln Gln Leu Tyr 100 15102PRTBat
15Gln Val Asp Phe Gln Lys Thr Met Lys Val Thr Gly Ile Thr Thr Gln 1
5 10 15 Gly Val Lys Ser Leu Leu Thr Ser Met Tyr Val Lys Glu Phe Leu
Ile 20 25 30 Ser Ser Ser Gln Asp Gly His Asn Trp Thr Pro Phe Leu
Gln Asn Gly 35 40 45 Lys Val Lys Val Phe Gln Gly Asn Gln Asp Ser
Phe Thr Pro Val Leu 50 55 60 Asn Ser Leu Asp Pro Pro Leu Leu Thr
Arg Tyr Leu Arg Ile His Pro 65 70 75 80 Gln Ser Trp Val His Gln Ile
Ala Leu Arg Leu Glu Val Leu Gly Cys 85 90 95 Glu Ala Gln Gln Leu
Tyr 100 16102PRTRat 16Gln Val Asp Leu Gln Arg Thr Val Lys Val Thr
Gly Val Val Thr Gln 1 5 10 15 Gly Ala Arg Ser Leu Leu Thr Ala Met
Phe Val Lys Lys Phe Leu Val 20 25 30 Ser Thr Ser Gln Asp Gly Arg
His Trp Thr His Val Leu Gln Asp Gly 35 40 45 Lys Val Lys Val Phe
Gln Gly Asn Arg Asp Ala Ser Thr Pro Met Val 50 55 60 Asn Ser Leu
His Pro Pro Arg Phe Thr Arg Tyr Leu Arg Ile His Pro 65 70 75 80 Gln
Val Trp Glu Arg Gln Ile Ala Leu Arg Leu Glu Ile Leu Gly Cys 85 90
95 Glu Ala Gln Gln Leu Asp 100 17102PRTSheep 17Gln Val Asp Phe Gln
Lys Thr Met Arg Val Thr Gly Ile Thr Thr Gln 1 5 10 15 Gly Val Lys
Ser Leu Leu Thr Ser Met Tyr Val Lys Glu Phe Leu Ile 20 25 30 Ser
Ser Ser Gln Glu Gly His Asn Trp Thr Pro Phe Leu Gln Asn Gly 35 40
45 Lys Val Lys Val Phe Gln Gly Asn Gln Asp Ser Phe Thr Pro Val Val
50 55 60 Asn Thr Leu Asp Pro Pro Leu Phe Thr Arg Phe Leu Arg Ile
His Pro 65 70 75 80 Gln Ser Trp Val His His Ile Ala Leu Arg Leu Glu
Phe Trp Gly Cys 85 90 95 Glu Ala Gln Gln Gln Tyr 100
18102PRTArtificialConsensus 18Gln Val Asp Xaa Xaa Lys Thr Xaa Xaa
Val Thr Gly Xaa Xaa Thr Gln 1 5 10 15 Gly Xaa Xaa Ser Leu Xaa Xaa
Xaa Met Xaa Val Xaa Xaa Phe Leu Xaa 20 25 30 Ser Xaa Ser Gln Xaa
Gly Xaa Xaa Trp Thr Xaa Xaa Xaa Xaa Xaa Gly 35 40 45 Xaa Xaa Lys
Val Phe Xaa Gly Asn Xaa Asp Xaa Xaa Thr Pro Xaa Xaa 50
55 60 Asn Xaa Leu Xaa Pro Pro Xaa Xaa Xaa Arg Xaa Xaa Arg Xaa His
Pro 65 70 75 80 Xaa Xaa Trp Xaa Xaa Xaa Ile Ala Leu Arg Xaa Glu Xaa
Xaa Gly Cys 85 90 95 Xaa Xaa Gln Xaa Xaa Xaa 100
193PRTArtificialMutant 19Lys Xaa Ser 1 204PRTArtificialMutant 20Ser
Xaa Xaa Xaa 1 214PRTArtificialMutant 21Thr Tyr Xaa Trp 1
223PRTArtificialMutant 22Xaa Val Thr 1 234PRTArtificialMutant 23Pro
Pro Xaa Xaa 1 244PRTArtificialMutant 24Xaa Xaa Gln Xaa 1
254PRTArtificialMutant 25Ser Xaa Xaa Glu 1 267PRTArtificialMutant
26Val Asp Gln Arg Gly Asn Gln 1 5 277PRTArtificialMutant 27Val Asp
Gln Arg Met Lys Asn 1 5 287PRTArtificialMutant 28Pro Gln Leu Arg
Gly Asn Gln 1 5 297PRTArtificialMutant 29Pro Asp Leu Arg Met Lys
Asn 1 5 307PRTArtificialMutant 30Pro Gln Gln Arg Met Lys Asn 1 5
317PRTArtificialMutant 31Pro Gln Arg Arg Met Lys Asn 1 5
327PRTArtificialMutant 32Pro Gln Leu Arg Gly Lys Asn 1 5
337PRTArtificialMutant 33Pro Gln Leu Arg Met Ile Asn 1 5
347PRTArtificialMutant 34Pro Gln Leu Arg Met Asn Asn 1 5
* * * * *