U.S. patent application number 09/104769 was filed with the patent office on 2002-08-01 for overexpression of phytase genes in yeast systems.
Invention is credited to LEI, XINGEN.
Application Number | 20020102692 09/104769 |
Document ID | / |
Family ID | 22302276 |
Filed Date | 2002-08-01 |
United States Patent
Application |
20020102692 |
Kind Code |
A1 |
LEI, XINGEN |
August 1, 2002 |
OVEREXPRESSION OF PHYTASE GENES IN YEAST SYSTEMS
Abstract
The present invention relates to a method of producing a
heterologous protein or polypeptide having phytase activity in a
yeast system. The invention also provides proteins having phytase
activity which have increased thermostability. Yeast strains which
produce a heterologous phytase and the vectors used to produce the
phytase are also provided.
Inventors: |
LEI, XINGEN; (ITHACA,
NY) |
Correspondence
Address: |
MICHAEL L GOLDMAN
NIXON PEABODY LLP
CLINTON SQUARE
PO BOX 31051
ROCHESTER
NY
14603
US
|
Family ID: |
22302276 |
Appl. No.: |
09/104769 |
Filed: |
June 25, 1998 |
Current U.S.
Class: |
435/196 ;
435/254.2; 435/254.21; 435/254.23; 435/254.3; 435/320.1; 435/69.1;
435/72; 536/23.1; 536/23.2; 536/23.4 |
Current CPC
Class: |
C12P 7/18 20130101; C12N
9/16 20130101; A23K 20/189 20160501; A23K 50/60 20160501; A23K
50/30 20160501 |
Class at
Publication: |
435/196 ; 435/72;
435/69.1; 435/320.1; 435/254.2; 435/254.21; 435/254.23; 435/254.3;
536/23.1; 536/23.2; 536/23.4 |
International
Class: |
C12P 007/02 |
Claims
What is claimed:
1. A method of producing phytase in yeast comprising: providing a
heterologous gene which encodes a protein or polypeptide with
phytase activity, and expressing said gene in a yeast strain.
2. The method according to claim 1, wherein the protein or
polypeptide, led by a signal peptide, is secreted by the cell into
growth media or just expressed intracellularly.
3. The method according to claim 2, wherein the protein or
polypeptide is secreted into the growth media and has a
concentration greater than 300 units/ml.
4. The method according to claim 1, wherein the heterologous gene
which encodes a protein or polypeptide with phytase activity is
spliced in frame with a transcriptional enhancer element
5. The method according to claim 1, wherein the heterologous gene
is carried on a stable vector.
6. The method according to claim 1, wherein the heterologous gene
is carried on an artificial chromosome.
7. The method according to claim 1, wherein the heterologous gene
is integrated into the chromosome of the yeast strain.
8. The method according to claim 1, wherein the heterologous gene
is isolated from plant cells.
9. The method according to claim 1, wherein the heterologous gene
is isolated from fungal cells.
10. The method according to claim 9, wherein the heterologous gene
is a phyA gene of Aspergillus niger.
11. The method according to claim 1, wherein the yeast strain is
selected from the group consisting of Saccharomyces, Kluyveromyces,
Torulaspora, and Schizosaccharomyces.
12. The method according to claim 11, wherein the yeast strain is
Saccromyces cerivesia.
13. The method according to claim 10, wherein the yeast strain is
in a methylotrophic yeast strain.
14. The method according to claim 9, wherein the methylotrophic
yeast strain is Pichia pastoris.
15. The method according to claim 1, wherein the heterologous gene
is isolated from bacterial cells.
16. The method according to claim 15, wherein the heterologous gene
is an appA gene of Escherichia coli.
17. The method according to claim 16, wherein the yeast strain is
selected from the group consisting of Saccharomyces, Kluyveromyces,
Torulaspora, and Schizosaccharomyces.
18. The method according to claim 17, wherein the yeast strain is
Saccromyces cerivesia.
19. The method according to claim 15, wherein the yeast strain is a
methylotrophic yeast strain.
20. The method according to claim 19, wherein the methylotrophic
yeast strain is Pichia pastoris.
21. A protein or polypeptide produced by the method according to
claim 1.
22. The protein or polypeptide according to claim 21, wherein the
protein or polypeptide comprises a signal peptide.
23. The protein or polypeptide according to claim 21, wherein the
heterologous gene is a phyA gene of Aspergillus niger.
24. The protein or polypeptide according to claim 21, wherein the
heterologous gene is an appA gene of Escherichia coli.
25. A protein or polypeptide according to claim 21 having phytase
activity with optimum activity in a temperature range of
57-65.degree. C. and at a pH of 2.5 to 3.5 or 5 to 5.5.
26. The protein or polypeptide according to claim 25, wherein the
temperature range for optimum activity is from 58 to 62.degree.
C.
27. The protein or polypeptide according to claim 21 having phytase
activity where the protein retains at least 40% of its activity
after heating the protein for 15 minutes at 90.degree. C.
28. The protein or polypeptide of claim 27, wherein the protein
retains between 40% and 60% of its activity after heating the
protein for 15 minutes at 90.degree. C.
29. A protein or polypeptide according to claim 21 having phytase
activity where the protein retains at least 60% of its activity
after heating the protein for 15 minutes at 60.degree. C.
30. A yeast strain comprising: a heterologous gene which encodes a
protein or polypeptide with phytase activity and which is
functionally linked to a promoter capable of expressing phytase in
yeast.
31. The yeast strain according to claim 30, wherein the
heterologous gene is a phyA gene of Aspergillus niger.
32. The yeast strain according to claim 31, wherein the yeast
strain is selected from the group consisting of Saccharomyces,
Kluyveromyces, Torulaspora, and Schizosaccharomyces.
33. The yeast strain according to claim 32, wherein the yeast
strain is Saccharomyces cerevisiae.
34. The yeast strain according to claim 31, wherein the yeast
strain is a methylotrophic yeast strain.
35. The yeast strain according to claim 34, wherein the
methylotrophic yeast strain is Pichia pastoris.
36. The yeast strain according to claim 30, wherein the
heterologous gene is an appaA gene of Escherichia coli.
37. The yeast strain according to claim 36, wherein the yeast
strain is selected from the group consisting of Saccharomyces,
Kluyveromyces, Torulaspora, and Schizosaccharomyces.
38. The yeast strain according to claim 37, wherein the yeast
strain is Saccromyces cerivesia.
39. The yeast strain according to claim 36, wherein the yeast
strain is methylotrophic yeast strain.
40. The yeast strain according to claim 39, wherein the
methylotrophic yeast strain is Pichia pastoris.
41. A vector comprising: a gene from a non-yeast organism which
encodes a protein or polypeptide with phytase activity; a promoter
functionally linked to the gene encoding a peptide with phytase
activity, said promoter capable of initiating transcription in
yeast; and an origin of replication capable of maintaining the
vector in yeast.
42. The vector according to claim 41 further comprising: a
selectable marker.
43. The vector according to claim 42, wherein the selectable marker
is selected from the group consisting of URA3, LEU2, TRP1, HIS3,
HIS4, ARG4, and an antibiotic resistance gene.
44. The vector according to claim 41, further comprising: an origin
of replication capable of replication in a bacterial cell.
45. The vector according to claim 44, wherein the origin of
replication is selected from the group consisting of ColE1, Ori,
and oriT.
46. The vector according to claim 41, wherein the heterologous gene
is isolated from a bacterial cell.
47. The vector according to claim 46, wherein the heterologous gene
is a phyA gene of Aspergillus niger.
48. The vector according to claim 46, wherein the heterologous gene
is an appaA gene of Escherichia coli.
49. A method of producing a protein or polypeptide having phytase
activity comprising: providing an isolated appA gene, which encodes
a protein or polypeptide with phytase activity and expressing said
gene in host cell.
50. The method according to claim 49, wherein the appA gene is
isolated from Escherichia coli.
51. The method according to claim 49, wherein the host cell is a
yeast strain or a filamentous fungi.
52. The method according to claim 51, wherein the filamentous fungi
is Aspergillus niger.
53. The method according to claim 51, wherein the yeast strain is
selected from the group consisting of Saccharomyces, Kluyveromyces,
Torulaspora, and Schizosaccharomyces.
54. The method according to claim 53, wherein the yeast strain is
Saccromyces cerivesia.
55. The method according to claim 49, wherein the protein or
polypeptide, led by a signal peptide, is secreted by the cell into
growth media or just expressed intracellularly.
56. A method of converting phytate to inositol and inorganic
phosphorus comprising: providing an appA gene; expressing a protein
or polypeptide with phytase activity from said gene in a host cell;
and contacting the protein or polypeptide with phytate to catalyze
the conversion of phytate to inositol and inorganic phosphorus.
57. The method according to claim 56, wherein the phytate is
contained in food or feed.
58. The method according to claim 56, wherein the appA gene is
isolated from Escherichia coli.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a method of producing
phytase in yeast, yeast strains which express heterologous phytase,
and the heterologous phytase produced by yeast.
BACKGROUND OF THE INVENTION
[0002] Phytases, a specific group of monoester phosphatases, are
required to initiate the release of phosphate ("P") from phytate
(myo-inositol hexophosphate), the major storage form of P in cereal
foods or feeds (Reddy, N. R. et al., "Phytates in Legumes and
Cereals," Advances in Food Research, 28:1 (1982)). Because
simple-stomached animals like swine and poultry as well as humans
have little phytase activity in their gastrointestinal tracts,
nearly all of the ingested phytate P is indigestible. This results
in the need for supplementation of inorganic P, an expensive and
non-renewable nutrient, in diets for these animals. More
undesirably, the unutilized phytate-P excreted through manure of
these animals becomes P pollution of the environment (Cromwell, G.
L. et al., "P- A Key Essential Nutrient, Yet a Possible Major
Pollutant--Its Central Role in Animal Nutrition," Biotechnology In
the Feed Industry; Proceedings Alltech 7th Annual Symposium, p. 133
(1991)). Furthermore, phytate chelates with essential trace
elements like zinc and produces nutrient deficiencies such as
growth and mental retardation in children ingesting mainly plant
origin foods without removal of phytate.
[0003] Two phytases, phyA and phyB, from Aspergillus niger NRRL3135
have been cloned and sequenced (Ehrlich, K. C. et al.,
"Identification and Cloning of a Second Phytase Gene (phys) from
Aspergillus niger (ficuum)," Biochem. Biophys. Res. Commun.,
195:53-57 (1993); Piddington, C. S. et al., "The Cloning and
Sequencing of the Genes Encoding Phytase (phy) and pH 2.5-optimum
Acid Phosphatase (aph) from Aspergillus niger var. awamori," Gene,
133:56-62 (1993)). Recently, new phytase genes have been isolated
from Aspergillus terreus and Myceliophthora thermophila (Mitchell
et al., "The Phytase Subfamily of Histidine Acid Phosphatases:
Isolation of Genes for Two Novel Phytases From the Fungi
Aspergillus terreus and Myceliophthora thermophila," Microbiology
143:245-252, (1997)), Aspergillus fumigatus (Pasamontes et al.,
"Gene Cloning, Purification, and Characterization of a Heat-Stable
Phytase from the Fungus Aspergillus fumigatus" Appl. Environ.
Microbiol., 63:1696-1700 (1997)), Emericella nidulans and
Talaromyces thermophilus (Pasamontes et al., "Cloning of the
Phytase from Emericella nidulans and the Thermophilic Fungus
Talaromyces thermophilus," Biochim. Biophys. Acta., 1353:217-223
(1997)), and maize (Maugenest et al., "Cloning and Characterization
of a cDNA Encoding a Maize Seedling Phytase," Biochem. J.
322:511-517, 1997)).
[0004] Various types of phytase enzymes have been isolated and/or
purified from Enterobacter sp. 4 (Yoon et al., "Isolation and
Identification of Phytase-Producing Bacterium, Enterobacter sp. 4,
and Enzymatic Properties of Phytase Enzyme.," Enzyme and Microbial
Technology 18:449-454 (1996)), Klebsiella lerrigena (Greiner et
al., "Purification and Characterization of a Phytase from
Klebsiella terrigena," Arch. Biochem. Biophys. 341:201-206 (1997)),
and Bacillus sp. DS11 (Kim et al., "Purification and Properties of
a Thermostable Phytase from Bacillus sp. DS11," Enzyme and
Microbial Technology 22:2-7 (1998)). Properties of these enzyme
have been studied. In addition, the crystal structure of phy A from
Aspergillus ficuum has been reported (Kostrewa et al., "Crystal
Structure of Phytase from Aspergillus ficuum at 2.5 A Resolution,"
Nature Structure Biology 4:185-190 (1997)).
[0005] Hartingsveldt et al. introduced phyA gene into A. niger and
obtained a ten-fold increase of phytase activity compared to the
wild type. ("Cloning, Characterization and Overexpression of the
Phytase-Encoding Gene (phya) of Aspergillus Niger," Gene 127:87-94
(1993)). Supplemental microbial phytase of this source in the diets
for pigs and poultry has been shown to be effective in improving
utilization of phytate-P and zinc (Simons et al., "Improvement of
Phosphorus Availability By Microbial Phytase in Broilers and Pigs,"
Br. J. Nutr., 64:525 (1990); Lei, X. G. et al., "Supplementing
Corn-Soybean Meal Diets With Microbial Phytase Linearly Improves
Phytate P Utilization by Weaning Pigs," J. Anim. Sci., 71:3359
(1993); Lei, X. G. et al., "Supplementing Corn-Soybean Meal Diets
With Microbial Phytase Maximizes Phytate P Utilization by Weaning
Pigs," J. Anim. Sci., 71:3368 (1993); Cromwell, G. L. et al., "P- A
Key Essential Nutrient, Yet a Possible Major Pollutant--Its Central
Role in Animal Nutrition," Biotechnology In the Feed Industry;
Proceedings Alltech 7th Annual Symposium, p. 133 (1991)). But,
expenses of the limited available commercial phytase supply and the
activity instability of the enzyme to heat of feed pelleting
preclude its practical use in animal industry (Jongbloed, A. W. et
al., "Effect of Pelleting Mixed Feeds on Phytase Activity and
Apparent Absorbability of Phosphorus and Calcium in Pigs," Animal
Feed Science and Technology, 28:233-242 (1990)). Moreover, phytase
produced from A. niger is presumably not the safest source for
human food manufacturing.
[0006] Yeast can be used to produce enzymes effectively while grown
on simple and inexpensive media. With a proper signal sequence, the
enzyme can be secreted into the media for convenient collection.
Some yeast expression systems have the added advantage of being
well accepted in the food industry and are safe and effective
producers of food products.
[0007] Pichia pastoris is a methylotrophic yeast, capable of
metabolizing methanol as its sole carbon source. This system is
well-known for its ability to express high levels of heterologous
proteins. Because it is an eukaryote, Pichia has many of the
advantages of higher eukaryotic expression systems such as protein
processing, folding, and post-transcriptional modification.
[0008] Thus, there is a need to develop an efficient and simple
system to produce phytase economically for the application of food
and feed industry.
SUMMARY OF THE INVENTION
[0009] The present invention relates to a method of producing
phytase in yeast by introducing a heterologous gene which encodes a
protein or polypeptide with phytase/acid phosphatase activity into
a yeast strain and expressing that gene.
[0010] The present invention also relates to a protein or
polypeptide having phytase activity with optimum activity in a
temperature range of 57-65.degree. C. at pH of 2.5 to 3.5 or of
5.5. Optimal pH at 2.5 to 3.5 is particularly important for
phytase, because that is the stomach pH of animals.
[0011] The invention further provides a yeast cell carrying a
heterologous gene which encodes a protein or polypeptide with
phytase activity and which is functionally linked to a promoter
capable of expressing phytase in yeast.
[0012] Yet another aspect of the invention is a vector having a
gene from a non-yeast organism which encodes a protein or
polypeptide with phytase activity, a promoter which is capable of
initiating transcription in yeast functionally linked to the gene
encoding a peptide with phytase activity, and with an origin of
replication capable of maintaining the vector in yeast or being
capable of integrating into the host genome.
[0013] The invention also provides a method for producing a protein
or polypeptide having phytase activity. An isolated appA gene,
which encodes a protein or polypeptide with phytase activity, is
expressed in a host cell.
[0014] The invention also includes a method of converting phytate
to inositol and inorganic phosphate. The appA gene expresses a
protein of polypeptide with phytase activity in a host cell. The
protein or polypeptide is then contacted with phytate to catalyze
the conversion of phytate to inositol and inorganic phosphate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 shows an SDS-PAGE analysis of soluble protein
prepared from the phytase gene transformed E. coli induced with
IPTG. The cells were grown 4 hours before harvesting. Lane 1:
Marker; Lanes 2 and 3: Transformants of pEP1 (the expressed protein
was approximately 55 kDa); Lane 4: Transformant with only the
expression vector pET25b(+).
[0016] FIG. 2 shows the Western blot analysis of the expressed
phytase protein in E. coli. The antibody was raised against
purified native phytase of A. niger. Each lane contained 50 .mu.g
total intracellular protein. Lanes 1 and 2: Recombinants after and
before induction. Lanes 3 and 4: control (only the expressing
vector) after and before induction.
[0017] FIG. 3 is a scan image of Northern blotting analysis of the
mRNA of PhyA in E. coli. A 1.4 kb PhyA probe was used. Each lane
contained 20 .mu.g of total RNA. Lanes 1 and 2: RNA isolated from
the control cells (only the expression vector) before and after
induction. Lanes 3 and 4: RNA isolated from the recombinants
containing PhyA before and after induction.
[0018] FIG. 4 is a time course of the induced expression of phytase
(pEP1) in E. coli BL21(DE3). The cells were induced when the
OD.sub.600 reached 0.5. The soluble protein, prepared at each time
point, was quantified by SDS-PAGE analysis.
[0019] FIG. 5 shows an SDS-PAGE analysis of the expressed
extracellular phytase protein by the phytase transformed S.
lividans after growing for 72 hours. Cells were spun for 15 minutes
at 8,000.times. g, and the supernatant was subjected to gel
electrophoresis. Lane 1: Marker; Lane 2: Control with the only
expression vector; Lane 3: Positive colony expressed phytase and
the size was approximately 57 kDa.
[0020] FIG. 6 shows the Western blot analysis of the phytase
expressed by S. lividans, using a phytase antibody raised against
purified native phytase of A. niger. Each lane was loaded with 20
.mu.g medium (supernatant) protein. Lane 1: Supernatant from the
vector transformed control cell culture; Lane 2: Supernatant from
the culture inoculated with the positive colony.
[0021] FIG. 7 depicts an SDS-PAGE analysis of the extracellular
phytase expressed by S. cerevisiae. Each lane was loaded with 50
.mu.g medium (supernatant) protein. Lanes 1 to 3: Supernatant from
the culture inoculated with the positive colony harvested at 5, 10,
and 25 hours after induction, respectively; Lanes 4 to 6:
Supernatant from the vector-transformed control cell culture
harvested at 5, 10, and 25 hours after induction, respectively;
Lane 7: Marker (kDa). The expressed phytase was approximately 110
kDa (confirmed by Western blot).
[0022] FIG. 8 is a time course of the extracellular phytase
activity expressed by the pYPP1 construct transformed S. cerevisiae
after induced by galactose. The activity was analyzed in the
supernatant of the collected medium.
[0023] FIG. 9 shows the Western blot analysis of the extracellular
phytase expressed by S. cerevisiae before and after deglycosylation
(Endo H), using a phytase antibody raised against purified native
phytase in A. niger. Lane 1: Prestained SDS-PAGE standards (kDa)
from Bio-Rad; Lanes 2 and 3: deglycosylated 10 and 20 .mu.g phytase
protein, respectively; Lane 4: glycosylated phytase (20 .mu.g
protein).
[0024] FIG. 10 is a scan image of Northern blot analysis for total
RNA isolated from transformed S. cerevisiae cells. Lane 1: Control
(with only the expression vector pYES2); Lanes 2 and 3:
Tranformants of pYPP1.
[0025] FIG. 11 is a time course of the extracellular phyA phytase
activity produced by Pichia pastoris transformants of Mut.sup.S
(KM71) and Mut+ (X33) after induction.
[0026] FIG. 12 depicts an SDS-PAGE analysis of the overexpressed
phytase in Pichia, with construct of pPICZ.alpha.A-PhyA in KM71
(MUT.sup.S). Lane 1: protein ladder. Lane 2: 40 .mu.l of the
supernatant of AK1 (a colony showed 21,700 mU/ml of extracellular
phytase), collected 108 hours after induction. Lane 3: 40 .mu.l of
the supernatant of a control strain overexpressing human serum
albumin (HAS, 6.7 kDa) at a level of 1 g/L. Lane 4: 40 .mu.l of the
supernatant of the KM71 control.
[0027] FIG. 13 depicts effects of deglycosylation by Endo H on the
thermostability of the expressed phytase in Pichia. Phytase
activity was measured after the enzymes were heated for 15 minutes
under 37 or 80.degree. C. in 0.2 M citrate buffer, pH 5.5.
[0028] FIG. 14 is a scan image of Northern analysis of the
expressed phyA mRNA by the transformed Pichia pastoris strains
(KM71 and X33). A 1.3 kb phyA probe was used for blotting. Lanes 1
and 2: the transformant of KM71 before and after induction; Lanes 3
and 4: the transformant of X33 after and before induction.
[0029] FIG. 15 shows the optimum pH of the expressed extracellular
phytase by Pichia (X33). Buffers of 0.2 M glycine-HCl for pH 1.5,
2.5, 3.5; 0.2 M sodium citrate for pH 4.5, 5.5, 6.5, and 0.2 M
Tris-HCl for pH 7.5 and 8.5 were used.
[0030] FIG. 16 shows the optimum temperature of the expressed
extracellular phytase by Pichia (X33). The assays were conducted in
0.2 M citrate buffer, pH 5.5.
[0031] FIG. 17 depicts the release of free phosphorus from soybean
by the expressed phytase in Pichia (X33). Five grams of soybean
were suspended in 25 ml of 0.2 M citrate, pH 5.5, with different
amounts of the enzyme. The incubation was conducted for 4 hours
under 37.degree. C. and the free phosphorus released in the
supernatant was determined.
[0032] FIG. 18 shows a time course of the expression of the
extracellular phytase activity from five transformants of Pichia
pastoris containing the E. coli appA gene.
[0033] FIG. 19 graphically shows the relationship between medium pH
and the expression of phytase activity by Pichia pastoris.
[0034] FIG. 20 is an SDS-PAGE analysis of the E. coli phytase
overexpressed in Pichia pastoris. Lane 1: Protein ladder; Lanes 2
to 4: Supernatants collected from the cultures of positive colonies
23, 22, and 11, respectively, at 118 hours after induction.
[0035] FIG. 21 graphically shows the optimum pH of the
overexpressed E. coli phytase by Pichia pastoris.
[0036] FIG. 22 graphically shows the optimum temperature of the
overexpressed E. coli phytase by Pichia pastoris.
[0037] FIG. 23 shows the amount of free phosphorus released from
soybean meal by the overexpressed E. coli phytase from Pichia
pastoris after four hours treatment.
DETAILED DESCRIPTION OF THE INVENTION
[0038] The present invention provides a method of producing phytase
in yeast. According to this method, a heterologous gene which
encodes a protein or polypeptide with phytase activity is expressed
in a yeast strain.
[0039] The enzymes which catalyze the conversion of phytate to
inositol and inorganic phosphorus are broadly known as phytases.
Phytase producing microorganisms comprise bacteria such as Bacillus
subtilis (Paver et al., J. Bacteriol. 151, 1102 (1982), which is
hereby incorporated by reference) and Pseudomonas (Cosgrove,
Austral. J. Biol. Sci. 23:1207 (1970), which is hereby incorporated
by reference); yeasts, such as Saccharomyces cerevisiae (Nayini et
al., Lebensmittel Wissenschaft und Technologie 17:24 (1984), which
is hereby incorporated by reference); and fungi, such as
Aspergillus terreus (Yamada et al., Agric. Biol. Chem. 32:1275
(1986), which is hereby incorporated by reference), and
Aspergillius ficuum (van Gorcom et al., European Patent Application
89/202,436, which is hereby incorporated by reference).
[0040] Phytases are also endogenously present in many plant
species. Loewus, In: Plant Biology vol. 9: "Inositol Metabolism in
Plants" (eds. D. J. Morre, W. F. Boss, F. A. Loewus) 13 (1990); and
Gellatly, et al., Plant Physiology (supplement) 93:562 (1990),
which are hereby incorporated by reference, mention the isolation
and characterization of a phytase cDNA clone obtained from potato
tubers. Gibson, et al., J. Cell Biochem., 12C:L407 (1988) and
Christen, et al., J. Cell Biochem., 12C:L402 (1988), which are
hereby incorporated by reference, mentions the synthesis of
endogenous phytase during the germination of soybean seeds.
[0041] Preferably, the protein or polypeptide with phytase activity
is secreted by the cell into growth media. This allows for higher
expression levels and easier isolation of the product. The protein
or polypeptide with phytase activity is coupled to a signal
sequence capable of directing the protein out of the cell.
Preferably, the signal sequence is cleaved from the protein.
[0042] In a preferred embodiment, the heterologous gene, which
encodes a protein or polypeptide with phytase activity, is spliced
in frame with a transcriptional enhancer element.
[0043] Preferred heterologous genes encoding proteins with phytase
activity are isolated from a bacterial cell. A more preferred gene
is the phyA gene of Aspergillus niger. A gene encoding phytase,
phyA, from Aspergillus niger NRRL3135 has been cloned and sequenced
(Piddington, C. S. et al., "The Cloning and Sequencing of the Genes
Encoding Phytase (phy) and pH 2.5-optimum Acid Phosphatase (aph)
from Aspergillus niger var. awamori," Gene, 133:56-62 (1993), which
are hereby incorporated by reference). Hartingsveldt et al.
introduced phyA gene into A. niger, and obtained a tenfold increase
of phytase activity compared to the wild type. (Hartingsveldt et
al., "Cloning, Characterization and Overexpression of the
Phytase-Encoding Gene (phyA) of Aspergillus Niger," Gene 127:87-94
(1993), which is hereby incorporated by reference.)
[0044] Another preferred heterologous gene is the appA gene of E.
coli. The gene, originally defined as E. coli periplasmic
phosphoanhydride phosphohydrolase (appA) gene, contains 1,298
nucleotides (GeneBank accession number: M58708). The gene was first
found to code for an acid phosphatase protein of optimal pH of 2.5
(EcAP) in E. coli. The acid phosphatase is a monomer with a
molecular mass of 44,644 daltons. Mature EcAP contains 410 amino
acids (Dassa, J. et al., "The Complete Nucleotide Sequence of the
Escherichia Coli Gene AppA Reveals Significant Homology Between Ph
2.5 Acid Phosphatase and Glucose-1-Phosphatase," J. Bacteriology,
172:5497-5500 (1990), which is hereby incorporated by reference).
Ostanin, et al. overexpressed appA in E. coli BL21 using a pT7
vector and increased its acid phosphatase activity by approximately
400-folds (440 mU/mg protein) (Ostanin, K. et al., "Overexpression,
Site-Directed Mutagenesis, and Mechanism of Escherichia Coli Acid
Phosphatase," J. Biol. Chem., 267:22830-36 (1992), which is hereby
incorporated by reference). The product of the appA gene was not
previously known to have phytase activity.
[0045] The appA or phyA gene can be expressed in any prokaryotic or
eukaryotic expression system. A variety of host-vector systems may
be utilized to express the protein-encoding sequence(s). Preferred
vectors include a viral vector, plasmid, cosmid or an
oligonucleotide. 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, etc.); insect cell systems
infected with virus (e.g., baculovirus); and plant cells infected
by bacteria. 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.
[0046] Preferred hosts for expressing appA or phyA include fungal
cells, including species of yeast or filamentous fungi, may be used
as host cells in accordance with the present invention. Preferred
yeast host cells include different strains of Saccharomyces
cerevisiae. Other yeasts like Kluyveromyces, Torulaspora, and
Schizosaccharomyces can also be used. In a preferred embodiment,
the yeast strain used to overexpress the protein is Saccharomyces
cerevisiae. Preferred filamentous fungi host cells include
Aspergillus and Neurospora. A more preferred strain of Aspergillus
is Aspergillus niger.
[0047] In another preferred embodiment of the present invention,
the yeast strain is a methylotrophic yeast strain. Methylotrophic
yeast are those yeast genera capable of utilizing methanol as a
carbon source for the production of the energy resources necessary
to maintain cellular function and containing a gene for the
expression of alcohol oxidase. Typical methylotrophic yeasts
include members of the genera Pichia, Hansenula, Torulopsis,
Candida, and Karwinskia. These yeast genera can use methanol as a
sole carbon source. In a more preferred embodiment, the
methylotrophic yeast strain is Pichia pastoris.
[0048] The present invention also provides a protein or polypeptide
with phytase activity. PhyA is expressed in Pichia and the
resulting protein produced has much higher extracellular activity
(.about.65 mU/ml). The phytase activity yield was approximately
30-fold greater than that in phyA transformed Saccharomyces
cerevisiae, 21-fold greater than that in wild type of Aspergillus
niger, and 65,000-fold greater than that in the untransformed
Pichia. The optimal pH of the expressed phytase was 2.5 and 5.5,
and the optimal temperature was 60.degree. C. Similarly, appA is
expressed in Pichia and Saccharomyces cerevisiae with the resulting
protein having much higher extracellular activity and a much
preferred optimal pH of 2.5 to 3.5.
[0049] A preferred embodiment of the invention is a protein or
polypeptide having phytase activity with optimum activity in a
temperature range of 57 to 65.degree. C. A more preferred
embodiment is a protein or polypeptide having phytase activity,
where its temperature range for optimum activity is from 58 to
62.degree. C.
[0050] Yet another preferred embodiment is a protein or polypeptide
having phytase activity where the protein retains at least 40% of
its activity after heating the protein for 15 minutes at 80.degree.
C. More preferred is a protein or polypeptide having phytase
activity where the protein retains at least 60% of its activity
after heating the protein for 15 minutes at 60.degree. C.
[0051] Purified protein may be obtained by several methods. The
protein or polypeptide of the present invention is preferably
produced in purified form (preferably at least about 80%, more
preferably 90%. pure) by conventional techniques. Typically, the
protein or polypeptide of the present invention is secreted into
the growth medium of recombinant host cells. Alternatively, the
protein or polypeptide of the present invention is produced but not
secreted into growth medium. In such cases, to isolate the protein,
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 sub
jected to sequential ammonium sulfate precipitation. The fraction
containing the polypeptide or protein of the present invention is
subjected to gel filtration in an appropriately sized dextran or
polyacrylamide column to separate the proteins. If necessary, the
protein fraction may be further purified by HPLC.
[0052] The present invention also provides a yeast strain having a
heterologous gene which encodes a protein or polypeptide with
phytase activity. The heterologous gene should be functionally
linked to a promoter capable of expressing phytase in yeast.
[0053] Yet another aspect of the invention is a vector for
expressing phytase in yeast. The vector carries a gene from a
non-yeast organism which encodes a protein or polypeptide with
phytase activity. The phytase gene can be cloned into any vector
which replicates autonomously or integrates into the genome of
yeast. The copy number of autonomously replicating plasmids, e.g.
YEp plasmids may be high, but their mitotic stability may be
insufficient (Bitter et al., "Expression and Secretion Vectors for
Yeast," Meth. Enzymol. 153:516-44 (1987), which is hereby
incorporated by reference). They may contain the 2 mu-plasmid
sequence responsible for autonomous replication, and an E. coli
sequence responsible for replication in E. coli. The vectors
preferably contain a genetic marker for selection of yeast
transformants, and an antibiotic resistance gene for selection in
E. coli. The episomal vectors containing the ARS and CEN sequences
occur as a single copy per cell, and they are more stable than the
YEp vectors. Integrative vectors are used when a DNA fragment is
integrated as one or multiple copies into the yeast genome. In this
case, the recombinant DNA is stable and no selection is needed
(Struhl et al., "High-Frequency Transformation of Yeast: Autonomous
Replication of Hybrid DNA Molecules," Proc. Nat'l Acad. Sci. USA
76:1035-39 (1979); Powels et al., Cloning Vectors, I-IV, et seq.
Elsevier, (1985); Sakai et al., "Enhanced Secretion of Human Nerve
Growth Factor from Saccharomyces Cerevisiae Using an Advanced
.delta.-Integration System," Biotechnology 9:1382-85 (1991), which
are hereby incorporated by reference). Some vectors have an origin
of replication, which functions in the selected host cell. Suitable
origins of replication include 2 .mu., ARS1, and 25 .mu.M. The
vectors have restriction endonuclease sites for insertion of the
fusion gene and promoter sequences, and selection markers. The
vectors may be modified by removal or addition of restriction
sites, or removal of other unwanted nucleotides.
[0054] The phytase gene can be placed under the control of any
promoter (Stetler et al. "Secretion of Active, Full- and
Half-Length Human Secretory Leukocyte Protease Inhibitor by
Saccharomyces cerevisiae," Biotechnology 7:55-60, (1989), which is
hereby incorporated by reference). One can choose a constitutive or
regulated yeast promoter. Suitable promoter sequences for yeast
vectors include, among others, promoters for metallothionein,
3-phosphoglycerate kinase (Hitzeman et al., J. Biol. Chem. 255:2073
(1980), which is hereby incorporated by reference) or other
glycolytic enzymes (Hess et al., J. Adv. Enzyme Reg. 7:149 (1968);
and Holland et al., Biochem. 17:4900, (1978), which are hereby
incorporated by reference), such as enolase,
glyceraldehyde-3-phosphate dehydrogenase, hexokinase, pyruvate
decarboxylase, phosphofructokinase, glucose-6-phosphate isomerase,
3-phosphoglycerate mutase, pyruvate kinase, triosephosphate
isomerase. phosphoglucose isomerase, and glucokinase. Other
suitable vectors and promoters for use in yeast expression are
further described in EP A-73,657 to Hitzeman, which is hereby
incorporated by reference. Another alternative is the
glucose-repressible ADH2 promoter described by Russell et al., J.
Biol. Chem. 258:2674 (1982) and Beier et al., Nature 300:724
(1982), which are hereby incorporated by reference.
[0055] One can choose a constitutive or regulated yeast promoter.
The strong promoters of e.g., phosphoglycerate kinase (PGK) gene,
other genes encoding glycolytic enzymes, and the alpha-factor gene,
are constitutive. When a constitutive promoter is used, the product
is synthesized during cell growth. The ADH2 promoter is regulated
with ethanol and glucose, the GAL-1-10 and GAL7 promoters with
galactose and glucose, the PHO5 promoter with phosphate, and the
metallothionine promoter with copper. The heat shock promoters, to
which the HSP150 promoter belongs, are regulated by temperature.
Hybrid promoters can also be used. A regulated promoter is used
when continuous expression of the desired product is harmful for
the host cells. Instead of yeast promoters, a strong prokaryotic
promoter such as the T7 promoter, can be used, but in this case the
yeast strain has to be transformed with a gene encoding the
respective polymerase. For transcription termination, the HSP150
terminator, or any other functional terminator is used. Here,
promoters and terminators are called control elements. The present
invention is not restricted to any specific vector, promoter, or
terminator.
[0056] The vector may also carry a selectable marker. Selectable
markers are often antibiotic resistance genes or genes capable of
complementing strains of yeast having well characterized metabolic
deficiencies, such as tryptophan or histidine deficient mutants.
Preferred selectable markers include URA3, LEU2, HIS3, TRP1, HIS4,
ARG4, or antibiotic resistance genes.
[0057] The vector may also have an origin of replication capable of
replication in a bacterial cell. Manipulation of vectors is more
efficient in bacterial strains. Preferred bacterial origin of
replications are ColE1, Ori, or oriT.
[0058] A leader sequence either from the yeast or from phytase
genes or other sources can be used to support the secretion of
expressed phytase enzyme into the medium. The present invention is
not restricted to any specific type of leader sequence or signal
peptide.
[0059] Suitable leader sequences include the yeast alpha factor
leader sequence, which may be employed to direct secretion of the
phytase. The alpha factor leader sequence is often inserted between
the promoter sequence and the structural gene sequence (Kurjan et
al., Cell 30:933, (1982); Bitter et al., Proc. Natl. Acad. Sci. USA
81:5330, (1984); U.S. Pat. No. 4,546,082; and European published
Patent application No. 324,274, which are hereby incorporated by
reference). Another suitable leader sequence is the S. cerevisiae
MF alpha 1 (alpha-factor) is synthesized as a prepro form of 165
amino acids comprising signal-or prepeptide of 19 amino acids
followed by a "leader" or propeptide of 64 amino acids,
encompassing three N-linked glycosylation sites followed by
(LysArg(Asp/Glu, Ala)2-3 alpha-factor)4 (Kurjan, et al., Cell
30:933-43 (1982), which is hereby incorporated by reference). The
signal-leader part of the preproMF alpha 1 has been widely employed
to obtain synthesis and secretion of heterologous proteins in S.
cerivisiae. Use of signal/leader peptides homologous to yeast is
Inown from. U.S. Pat. No. 4.546,082, European Patent Applications
Nos. 116,201; 123,294; 123,544; 163,529; and 123,289 and DK Patent
Application No. 3614/83, which are hereby incorporated by
reference. In European Patent Application No. 123,289, which is
hereby incorporated by reference, utilization of the S. cerevisiae
.alpha.-factor precursor is described whereas WO 84/01153, which is
hereby incorporated by reference, indicates utilization of the
Saccharomyces cerevisiae invertase signal peptide, and German
Patent Application DK 3614/83, which is hereby incorporated by
reference, indicates utilization of the Saccharomyces cerevisiae
PH05 signal peptide for secretion of foreign proteins.
[0060] The alpha-factor signal-leader from Saccharomyces cerevisiae
(MF alpha 1 or MF alpha 2) may also be utilized in the secretion
process of expressed heterologous proteins in yeast (U.S. Pat. No.
4,546,082, European Patent Applications Nos. 16,201; 123,294; 123
544; and 163,529, which are hereby incorporated by reference). By
fusing a DNA sequence encoding the S. cerevisiea MF alpha 1
signal/leader sequence at the 5' end of the gene for the desired
protein secretion and processing of the desired protein was
demonstrated. The use of the mouse salivary amylase signal peptide
(or a mutant thereof) to provide secretion of heterologous proteins
expressed in yeast has been described in Published PCT Applications
Nos. WO 89/02463 and WO 90/10075, which are hereby incorporated by
reference.
[0061] U.S. Pat. No. 5,726,038 describes the use of the signal
peptide of the yeast aspartic protease 3, which is capable of
providing improved secretion of proteins expressed in yeast. Other
leader sequences suitable for facilitating secretion of recombinant
polypeptides from yeast hosts are known to those of skill in the
art. A leader sequence may be modified near its 3' end to contain
one or more restriction sites. This will facilitate fusion of the
leader sequence to the structural gene.
[0062] Yeast transformation protocols are known to those of skill
in the art. One such protocol is described by Hinnen et al., Proc.
Natl. Acad. Sci. USA 75:1929 (1978), which is hereby incorporated
by reference. The Hinnen et al. protocol selects for Trp
transformants in a selective medium, wherein the selective medium
consists of 0.67% yeast nitrogen base, 0.5% casamino acids, 2%
glucose, 10 .mu.g/ml adenine and 20 .mu.g/ml uracil.
[0063] The gene may be maintained on stable expression vector, an
artificial chromosome, or by integration into the yeast host cell
chromosome. Integration into the chromosome may be accomplished by
cloning the phytase gene into a vector which will recombine into a
yeast chromosome. Suitable vectors may include nucleotide sequences
which are homologous to nucleotide sequences in the yeast
chromosome. Alternatively, the phytase gene may be located between
recombination sites, such as transposable elements, which can
mobilize the gene into the chromosome.
[0064] The present invention also provides a method of producing
phytase by providing an isolated appA gene, which encodes a protein
or polypeptide with phytase activity, and expressing the gene in
host cell. Preferably the appA gene is isolated from Escherichia
coli. Preferred host cells include yeast or filamentous fungi. The
preferred filamentous fungi is Aspergillus niger and the preferred
yeast are Saccharomyces, Kluyveromyces, Torulaspora, and
Schizosaccharomyces, in particular, the yeast strain, Saccromyces
cerivesia.
[0065] A method of converting phytate to inositol and inorganic
phosphorus is also provided. An appA gene is isolated from an
organism, using techniques well known in the art. A protein or
polypeptide with phytase activity is then expressed from the gene
in a host cell. The resulting protein or polypeptide is mixed or
contacted with phyate. This technique is especially useful for
treating phytate in food or animal feed.
[0066] The preferred appA gene is isolated from Escherichia
coli.
[0067] While the phytase enzyme produced in a yeast system released
phytate-P from corn and soy as effectively as the currently
commercial phytase, it appeared to be more thermostable. This
phytase overexpression system in yeast can be used to provide
thermostable phytase for use in the food and feed industries.
EXAMPLES
Example 1
Materials and Methods for Overexpressing PhyA in E. Coli, S.
Lividans, and a Saccharomyces System
[0068] Phytase Gene, Host Strains, and Expression Plasmids.
[0069] Phytase gene, phyA, was kindly provided by Dr. E. J.
Mullaney of the USDA. The gene (GenBank Accession number M94550)
was contained in plasmid pMD4.21 in E. coli strain HB101. A 2.7 kb
SphI fragment of A. niger DNA contained the coding region of the
deglycosylated phytase and its 5' and 3' flanking sequences. A
plasmid containing the signal peptide sequence, Spxy, of the active
xylanase gene of Aureobasidum pullulans (GenBank Accession number
U10298) was kindly provided by Dr. X. L. Li of the University of
Georgia. The E. coli strain DH5.alpha. was used as an initial host
for all the recombinant plasmids. In order to express phyA in E.
coli, the expression vector, pET25b(+) (Novagen, Madison, Wis.) and
the expression host, BL21 (DE3)pLysS, were used. In order to
express phyA in S. lividans TK 24, plasmid pSES1 (Jung, E. D. et
al., "DNA Sequences and Expression in Streptomyces
Lividansoglucanase Gene and an Endoglucanase Gene from
Thermomonospora Fusca," Appl. Environ. Microbiol., 59:3032-43
(1993), which is hereby incorporated by reference), was used to
construct the shuttle plasmid (from Dr. D. B. Wilson of Cornell
University and he obtained it from Dr. D. A. Hopwood, John Innes
Institute, Norwich, England). In order to express phyA in yeast,
the expression vector pYES2 and the host S. cerevisiae strain,
INVSc1 (Invitrogen, San Diego, Calif.) were used.
[0070] Plasmid Cassette Constructions and Transformations.
[0071] All the constructed plasmids and the correspondent hosts are
listed in Table 1. A 1.4 kb PCR fragment of phyA gene was amplified
from the pMD4.21 by using two primers: upstream 5'-CGG AAT TCG TCA
CCT CCG GAC T-3' (SEQ ID No. 1) and downstream 5'-CCC AAG CTT CTA
AGC AAA ACA CTC-3' (SEQ ID No. 2). The resulting fragment contained
the sequence coding for the deglycosylated phytase of A. niger,
PhyA, and EcoRI and HindIII restriction site upstream and
downstream, respectively. After purification with Geneclean II kit
(Bio101, Inc., La Jolla, Calif.), the fragment was inserted into
pET25b(+), and the resulting construct pEP1 (6893 bp) was
transformed into BL21(DE3)pLysS after initial confirmation in
DH5.alpha. cells. The expression was under the control of T7
promoter followed by the lead sequence (pel B) encoding 21 amino
acids, and phyA. The host transformed with the pET25(+) vector only
was used as the control.
1TABLE 1 Expression vectors, constructs, and their host strains
used in the study Plasmid Host Description.sup.1 Reference.sup.2
pET25b(+) E. coli DH5.alpha. and Expression vector Novagen BL21
(DE3)pLysS pEP1 E. coli BL21 pET25ba(+) + This paper (DE3)pLysS
phyA gene PSES2 E. coli DH5.alpha. and Expression vector Jung et
al..sup.2, S. lividans TK24 1993 PSPP1 E. coli DH5.alpha. and pSES2
+ Spe2 + This paper S. lividans TK24 phyA PYES2 E. coli DH5.alpha.
and Expression vector Invitrogen S. cerevisiae INVSc1 PYEP1 E. coli
DH5.alpha. and pYES2 + Spe2 + This paper S. cerevisiae INVSc1 phyA
PYXP1 E. coli DH5.alpha. and pYES2 + Spxy + This paper S.
cerevisiae INVSc1 phyA PYPP1 E. coli DH5.alpha. and pYES2 + Sphy +
This paper S. cerevisiae INVSc1 phyA .sup.1Spe2 is the signal
peptide for endoglucanase E2 of T. fusca (Wilson, D.B.,
"Biochemistry # and Genetics of Actinomycete Cellulases," Crit.
Rev. Biotechnol., 12:45-63 (1992), which is hereby # incorporated
by reference); Spxy is the signal peptide for xylanase of A.
pullulans (Li and Ljungdahl, # "Cloning, Sequencing, and Regulation
of a Xylanase Gene from the Fungus Aureobasidium pullulans #
Y-2331-1," Appl. Environ. Microbiol., 60:3160-66 (1994); Li and
Ljungdahl, "Expression of # Aureobasidium pullulans xynA in, and
Secretion of the Xylanase from, Saccharomyces cerevisiae," # Appl.
Environ, Microbiol., 62:209-13 (1996), which are hereby
incorporated by reference); and Sphy is the signal # peptide for
phyA of A. niger (Hartingsveldt et al., "Cloning, Characterization
and Overexpression of the # Phytase-Encoding Gene (phyA) of
Aspergillus Niger," Gene 127:87-94 (1993), which is hereby #
incorporated by reference). .sup.2Jung, E.D. et al., "DNA Sepuences
and Expression in Streptomyces Lividansoglucanase Gene and # an
Endoglucanase Gene from Themomonospora Fusca," Appl. Environ.
Microbiol., 59:3032-43 (1993), which # is hereby incorporated by
reference).
[0072] The construction of the plasmid for phyA expression in S.
lividans started with the synthesis of a fragment containing pLT1
promoter and Spe2 signal peptide (Lao, G. et al., "DNA Sequences of
Three Beta-1,4-endoglucanase Genes From Thermomonospora Fusca," J.
Bacteriol., 173:3397-407 (1991), which is hereby incorporated by
reference) by PCR. An upstream primer, 5'-CAG CTA TGA CCA TGA TTA
CGC C-3' (SEQ ID No. 3), and a downstream primer. 5'-CCT AGA ACG
GGA ATT CAT TGG CCG CC-3' (SEQ ID No. 4), contained Pstl and EcoRI
restriction sites, respectively. The fragment was amplified from
pBW2 (Jung, E. D. et al., "DNA Sequences and Expression in
Streptomyces Lividans of an Exoglucanase Gene and an Endoglucanase
Gene From Thermomonospora Fusca," Appl. Environ. Microbiol.,
59:3032-43 (1993), which is hereby incorporated by reference) and
then digested with PstI and EcoRI, while the construct pEP1 and
plasmid pBluescript SK.sup.+ (Strategene, La Jolla, Calif.) were
digested with EcoRI and HindIII, and PstI and HindII, respectively.
The three digested fragments were subsequently purified using
Geneclean II kit and ligated into a single recombinant construct
that contained the desired restriction sites of PstI and KpnI (from
pBluescript SK*), pLT1 promoter and Spe2 leading peptide of
endoglucanase E2 (551 bp, Lao, G. et al., "DNA Sequences of Three
Beta-1,4-endoglucanase Genes From Thermomonospora Fusca," J.
Bacteriol., 173:3397-407 (1991), which is hereby incorporated by
reference), and phyA gene (1365 bp). After the construct was
digested with PstI and KpnI, the resulting fragment was inserted
into the expression vector pSES1, and the formed shuttle plasmid
(pSPP1, 9131 bp) was transformed into the host S. lividans
protoplasts according to Hopwood et al. (Hopwood, D. A., et al.,
Genetic Manipulation of Streptomyces--A Laboratory Manual, The John
Innes Foundation, Norwich, England (1985), which is hereby
incorporated by reference). Likewise, a control was prepared by
transforming S. lividans with expression vector pSES2.
[0073] Three shuttle plasmids with three different signal peptide
sequences were constructed to express phyA in the yeast system (See
Table 2). The first plasmid was originated from a HindIII digested
fragment of pSPp1, including the promoter pLT1, lead sequence Spe2,
and the coding region sequence of phyA. The fragment was ligated
into the HindIII site of pYES2 treated with calf intestinal
alkaline phosphatase and the plasmid was named pYEP1 (7783 bp)
after its right orientation was confirmed. The second plasmid
contained Spxy, a signal peptide sequence of xylanase gene from A.
pullulans (Li, X. L. et al., "Cloning, Sequencing, and Regulation
of a Xylanase Gene From the Fungus Aureobasidium Pullulans)
Y-2311-1," Appl. Environ. Microbiol., 60:3160-166 (1994); Li, X. L.
et al., "Expression of Aureobasidium Pullulans XynA in, and
Secretion of the Xylanase From, Saccharomyces Cerevisiaea," Appl.
Environ. Microbiol., 62:209-13 (1996), which are hereby
incorporated by reference), and phyA gene. Spxy was spliced with
phyA by overlap extension (Horton, R. M., "In Vitro Recombination
and Mutagenesis of DNA: SOEing Together Tailor-Made Genes," PCR
Protocols: Current Methods and Applications, 251-61 (1993), which
is hereby incorporated by reference) with two successive steps of
PCR. One was to amplify Spxy sequence from pCE4 (Li, X. L. et al.,
"Expression of Aureobasidium Pullulans XynA in, and Secretion of
the Xylanase From, Saccharomyces Cerevisiaea," Appl. Environ.
Microbiol., 62:209-13 (1996), which is hereby incorporated by
reference) using upstream primer (5'-CCC AAG CTT GAT CAC ATC CAT
TCA-3') (SEQ ID No. 5) with a HindIII restriction site (primer 1)
and overlapping downstream primer (5'-CGG GGA CTG CTA GCG CAC GTT
CGA T-3', primer 2) (SEQ ID No. 6). The other PCR was to amplify
the coding region of phya from pEP1 using overlapping upstream
primer (5'-ATC GAA CGT GCG CTA GCA GCA GTC CCC G-3', primer 3) (SEQ
ID No. 7) and downstream primer (5'-GCT CTA GAC TAA GCA AAA CAC
TCC-3', primer 4) (SEQ ID No. 8) with a XbaI restriction site. The
second step of PCR was conducted to merge the two fragments
generated from the above two PCR by using the two purified
fragments as the templates and primers 1 and 4. The resulting
fragment contained HindIII and XbaI restriction sites and was
cloned into pSES2. This plasmid was named pYXP1 (7219 bp). The
third plasmid contained the signal peptide (Sphy) sequence of phya
and the coding region of phyA, excluding the intron between them
(Hartingsveldt, W. van., et al., "Cloning, Characterization and
Overexpression of the Phytase-Encoding Gene (phyA) of Aspergillus
Niger," Gene 127:87-94 (1993), which is hereby incorporated by
reference). Two primers, including a 70 bp of upstream primer
contained the signal peptide with an engineered KpnI restriction
site and a downstream primer that was the same one used for pYXP1
construction (primer 4) were used to amplify the desired fragment
from pEP1. The PCR product was digested with KpnI and XbaI and
cloned into pSES2, resulting in a plasmid named pYPP1(7176 bp). All
the above three constructs were transformed into S. cerevisiae by
the method of Ito et al., "Transformation of Intact Yeast Cells
Treated with Alkali Cations," J. Bacteriol., 153:163-68 (1983),
which is hereby incorporated by reference.
2TABLE 2 Signal peptides used for expression of phyA in S.
cerevisiae Phytase Construct Size activity.sup.1 (bp) Peptide Gene
Organism (mPU/ml) pYEP1 7783 Spe2 Cellulase T. fusca .80 (93 bp) E2
pYXP1 7219 Spxy Xylanase A A. pullulans Non-detectable (102 bp)
pYPP1 7176 Sphy PhyA A. niger 146 (57 bp) Phytase pSES1.sup.2 7224
S. cerevisiae Non-detectable .sup.1The phytase activity was
detected in the supernatant of cell culture of Sabouraud-raffinose
medium 15 hours after induced by adding galactose. See text for #
definition of phytase units. .sup.2Expression vector for S.
cerevisiae, used as a control.
[0074] Growth Medium and Induction of the Gene Expression.
[0075] In the E. coli system, the transformants were grown in 50 ml
of LB medium containing 50 .mu.g/ml of ampicillin at 30.degree. C.
After the OD.sub.600 value of the medium reached 0.5 to 0.6,
phytase gene expression was induced by adding IPTG (isopropyl
b-D-thiogalactopyranosid- e) into the medium to a final
concentration of 1 m. Three hours after the induction, cells were
collected by spinning down at 8000.times. g for 15 minutes, washed
with 1.times. PBS, and lysed by lysozyme. Soluble and insoluble
fractions of the cells were prepared, and a sample containing 500
.mu.g of total protein (Lowry, O. H. et al., "Protein Measurement
With the Folin Phenol Reagent," J. Biol. Chem., 193:265-75 (1951),
which is hereby incorporated by reference) was suspended in the
same volume of 2.times. SDS buffer and analyzed by SDS-PAGE
(Laemmli, U. K., "Cleavage of Structural Proteins During the
Assembly of the Head of Bacteriophage T4," Nature (London),
227:680-85 (1970), which is hereby incorporated by reference).
[0076] Recombinant S. lividans was grown in TSB broth with 5
.mu.g/ml of thiostrepton at 30.degree. C. (Jung, E. D. et al., "DNA
Sequences and Expression in Streptomyces Lividans of an
Exoglucanase Gene and an Endoglucanase Gene from Thermomonospora
Fusca," Appl. Environ. Microbiol., 59:3032-43 (1993), which is
hereby incorporated by reference). After 72 hours incubation, the
cells and medium were harvested and prepared for SDS-PAGE (Wilson,
D. B., "Biochemistry and Genetics of Actinomycete Cellulases,"
Crit. Rev. Biotechnol., 12:45-63 (1992), which is hereby
incorporated by reference).
[0077] Transformants of S. cerevisiae were initially grown in
Sabouraud-raffinose (4%) medium (100 ml) without uracil for 48
hours, sterile galactose was then added into the medium (2%) to
induce phytase expression. Samples of media and cells were
collected at various time points, and extracellular and
intracellular samples were prepared as described by Li and
Ljungdahl, "Expression of Aureobasidium pullulans xynA in, and
Secretion of the Xylanase from, Saccharomyces cerevisiae," Appl.
Environ. Microbiol., 62:209-13 (1996), which is hereby incorporated
by reference. When needed, the supernatant of the expressed cell
culture fractions was concentrated with Stirred Cells of Amicon
(Beverly, Mass.) by using YM10 membranes (MW cutoff of 10,000).
Other media were tested accordingly.
[0078] Enzyme Protein and Activity Assay.
[0079] Amounts of expressed phytase protein under various
conditions were quantified by the relative densitometry of specific
bands in SDS-PAGE, using IS-1000 Digital Imaging System (Alpha
Innotech Corporation, San Leandro, Calif.). Phytase activity in the
sarnples of media and cells was determined as previously described
(Piddington, C. S. et al., "The Cloning and Sequencing of the Genes
Encoding Phytase (phy) and pH 2.5-optimum Acid Phosphatase (aph)
from Aspergillus niger var. awamori," Gene. 133:56-62 (1993), which
is hereby incorporated by reference) and the inorganic phosphate
released was assayed by the method of Chen, P. S. et al.,
"Microdetermination of P," Anal. Chem., 28:1756-58 (1956), which is
hereby incorporated by reference. One phytase unit (PU) was defined
as the amount of enzyme that releases one .mu.mol of inorganic
phosphate from sodium phytate per minute at 37.degree. C.
[0080] Western Blotting (Immunoblot) Analysis.
[0081] The soluble fraction of the cell mass of the phytase
transformed E. coli and the medium supernatant of S. lividans and
S. cerevisiae transformants were collected as for SDS-PAGE. After
electrophoresis, the proteins were then transferred onto
Protran.RTM. nitrocellulose membrane (Schleicher & Schuell,
Keene, N.H., USA) in 20 mM Tris-HCl (pH 8.3), 20% methanol, and
0.1% SDS, by using a Mini Trans-Blot cell (Bio-Rad Laboratories).
Transfer was done overnight at a constant 50 V and the initial
buffer temperature was 4.degree. C. The membranes were then
subjected to Western blot analysis. A rabbit polyclonal IgG (Kindly
provided by Dr. A. H. J. Ullah of USDA. Dilution, 1: 5.000) against
purified native A. niger phytase was used as the first antibody.
The blotting was finalized using Immuno-Blot Assay Kit (Bio-Rad
Laboratories) containing a second antibody conjugated with
horseradish peroxidase.
[0082] Total RNA Isolation and Analysis.
[0083] Total RNA was isolated with TRIzol.TM. Reagent (GIBCO BRL,
Gaithersburg, Md.) from E. coli and S. cerevisiae transformants 3
and 15 hours after induction, respectively. RNA samples (10 .mu.g
per lane) were then separated by formaldehyde agarose (1.5%,
wt/vol) gel electrophoresis and transferred to Hyblot membranes
(National Labnet, Woodbridge, N.J.) (Davis et al., Basic Methods in
Molecular Biology, 2nd Ed., Appleton and Lange, Norwalle, Conn.
(1994), which is hereby incorporated by reference). A 1.4 kb
EcoRI-HindIII fragment in plasmid pEP1 was prepared and was
random-primed labeled with .sup.32P using a DNA labeling kit
followed by G-50 column purification (Pharmacia Biotech.,
Piscataway, N.J.) and then hybridized with the blotted RNA
membranes in a hybridization oven (Hybaid, Middlesex, UK). The
hybridized membranes were exposed to screens in Fuji Imaging Plate
and analyzed by Bio-Imaging Analyzer (Kohshin Graphic Systems,
Fuji, Japan).
Example 2
Expression of PhyA in E. coli
[0084] Four hours after the induction, a specific band (.about.55
kDa) was viewed in SDS-PAGE (12.5%) of the soluble cell fraction,
compared to the only expression vector transformed control (See
FIGS. 1 and 2). This band represented 3.8% of the total soluble
protein of this fraction. Correspondingly, northern analysis showed
overexpression of phyA mRNA in these phytase gene transformants and
no signal was viewed in the control cells (See FIG. 3).
[0085] In order to optimize phytase protein expression, the time
course and the effects of a series of factors on the expression
were studied. These factors included incubation temperature (30 and
37.degree. C.), medium pH (4.0, 5.0, 6.0, 7.0, 8.0, and 9.0),
anaerobiosis (adding sterile mineral oil on the top of the growing
cells), inorganic phosphate level in the medium (Dassa, E. et al.,
"The Acid Phosphatases with Optimum pH of 2.5 of Escherichia coli,"
J. Bio. Chem., 257:6669-76 (1982), which is hereby incorporated by
reference), and sodium phytate (0, 0. 1, 0.2, 0.3, 0.4, and 0.5
mM). Results indicated that expression of phytase protein was
accumulated linearly with time for the first six hours after
induction (See FIG. 4). Thereafter, the expression remained
relatively unchanged although bacterial cells continued to grow.
Only medium pH and sodium phytate concentration significantly
affected the phytase protein expression. Maximum protein was shown
at pH 6.0 and 0.3 mM of sodium phytate, in which phytase protein
was increased from 3.8 to 9.6% of the total soluble protein.
[0086] No phytase activity was detected extracellularly or
intracellularly. This may not be completely unexpected, because the
native phytase from A. niger is a glycoprotein with a size of 70-80
kDa (Hartingsveldt et al., "Cloning, Characterization and
Overexpression of the Phytase-Encoding Gene (phyA) of Aspergillus
Niger," Gene 127:87-94 (1993), which is hereby incorporated by
reference). The protein expressed in the E. coli system of this
study had a size of approximately 55 kDa. Presumably, the lack of
glycosylation of the protein and other necessary post-translational
modifications during secretion would preclude phytase activity.
Example 3
Expression of PhyA in S. lividans
[0087] Heterologous genes have been expressed in S. lividans, and
the resulting products secreted into the medium with enzymatic
activity (Ghangas, G. S. et al., "Cloning of the Thermomonospora
Fusca Endoglucanase E2 Gene in Streptomyces Lividans: Affinity
Purification and Functional Domains of the Cloned Gene Product,"
Appl. Environ. Microbiol., 54:2521-26 (1988); Wilson, D. B.,
"Biochemistry and Genetics of Actinomycete Cellulases," Crit. Rev.
Biotechnol., 12:45-63 (1992); Jung, E. D. et al., "DNA Sequences
and Expression in Streptomyces Lividans of an Exoglucanase Gene and
an Endoglucanase Gene from Thermomonospora Fusca," Environ.
Microbiol., 59:3032-43 (1993), which are hereby incorporated by
reference). Similarly, phyA gene was expressed in S. lividans and
the protein was introduced into the medium, as shown in a specific
band in the SDS-PAGE analyzed medium samples (See FIGS. 5 and 6).
This suggested that the signal peptide from endoglucanase E2 gene
of T. fusca was able to lead phytase protein out of the cell. This
protein was 57 kDa and represented 16.2% of the total protein in
the medium. Changing medium pH to 6.0 and adding 0.3 mM of sodium
phytate in the medium improved the protein yield to 20.3% of the
total protein. Because phytase protein was secreted into the medium
in such a high level, it should be easy to purify and used
effectively for a variety of purposes such as producing phytase
antibody. Once again, no increased phytase activity was found
either in the medium or in the lysed cells. Although the protein
size increased a little bit (2-3%) compared to the one expressed in
E. coli, presumably due to glycosylation of phytase protein in this
expression system, there was still no phytase activity.
Example 4
Expression of PhyA in S. cerevisiae
[0088] Three different signal peptides were used to compare the
efficiency in leading the expressed protein out of the cells (See
Table 2). The phytase activity was substantially increased in the
Sabouraud-raffinose medium growing the transformants of pYEP1 and
pYPP1, but not pYXP1. Visible phytase protein was shown by SDS-PAGE
20 hours after induction (FIG. 7).
[0089] The expression of transformants of pYEP1 and pYPP1 were
determined in three different types of medium: Sabouraud-raffinose
(Li, X. L. et al., "Expression of Aureobasidium Pullulans XynA in,
and Secretion of the Xylanase From, Saccharomyces Cerevisiaea,"
Appi. Environ. Microbiol., 62:209-13 (1996), which is hereby
incorporated by reference), Sabouraud-glycerol, and a modified
general-purposed YEPD medium. As to transformants of pYEP1, similar
phytase activity was expressed in the Sabouraud-raffinose and
Sabouraud-medium, but there was no activity detected in the YEPD
medium. In contrast, phytase activity in the medium cultured with
transformants of pYPP1 varied greatly with the different types of
medium. The activity was enhanced to 375 mU/ml when
Sabouraud-glycerol medium was used. The activity was further
increased to 1675 mU/ml, when the medium was changed to YEPD (See
Table 3). While the YEPD medium was much cheaper than the
Sabouraud-raffinose medium, the phytase yield was increased more
than ten-folds. Thus, the putative signal peptide from the fungal
phytase gene achieved the most efficient expression of the
extracellular phytase activity. Nearly all the protein produced was
secreted into the YEPD medium, because very little activity was
detected in the yeast cells. The time course of the phytase
expression in this system was shown in FIG. 8.
3TABLE 3 Phytase activity expressed from transformant with pYPP1 in
different media Hours after induction (mPU/ml).sup.1 Medium 0 10 15
Sabouraud-raffinose 22 136 146 Sabouraud-glycerol 6 174 375 YEPD 18
1238 1675 .sup.1The phytase activity was detected in the
supernatant of cell culture of the three media # 0, 10, and 15
hours after induced by adding galactose. See text for definition of
phytase units.
[0090] A variety of microorganisms including bacilli, yeasts, and
filamentous fungi have phytase activity, while A. niger NRRL3135
strain produces the highest activity (340 mU/ml, Shieh, T. R. et
al., "Survey of Microorganisms for the Production of Extracellular
Phytase," Appl. Environ. Microbiol., 16:1348-51 (1968), which is
hereby incorporated by reference). Schwanniomyces castellii CBS
2863 has the highest phytase activity among 21 yeast strains (140
mU/ml, Lambrechts. C. et al., "Utilization of Phytate by Some
Yeasts," Biotechnology Letters, 14:61-6 (1992), which is hereby
incorporated by reference). Clearly, the recombinant yeast strain
transformed with pYPP1 in the present study produced much higher
phytase activity (1675 mU/ml) than A. niger (4-fold) and S.
castellii CBS 2863 (11-fold). Maximum phytase production can be
obtained in the system by optimizing the incubation conditions and
modifying the plasmid cassettes (Demolder, J. W. et al., "Efficient
Synthesis of Secreted Murine Interleukin-2 by Saccharomyces
Cerevisiae: Influence of 3'-Untranslated Regions and Codon Usage,"
Gene, 111:207-13 (1992), which is hereby incorporated by
reference).
[0091] The high level of phytase activity expression in S.
cerevisiae was most likely due to the sufficient glycosylation of
phytase protein and other post-translational modifications by
yeast. After the medium supernatant was concentrated and subjected
to SDS-PAGE analysis, there was a band with approximately 110 kDa
(See FIGS. 7 and 9), which was larger than the size of the native
protein from A. niger (Hartingsveldt, W. van. et al., "Cloning,
Characterization and Overexpression of the Phytase-Encoding Gene
(phyA) of Aspergillus Niger," Gene 127:87-94 (1993), which is
hereby incorporated by reference). Northern analysis confirmed the
specific overexpression of phyA mRNA (See FIG. 10). These results
indicated that the yeast system was efficient to overexpress
actively extracellular phytase enzyme. Yeast system has several
advantages over bacteria or other systems such as A. niger
(Hartingsveldt, W. van. et al., "Cloning, Characterization and
Overexpression of the Phytase-Encoding Gene (phyA) of Aspergillus
Niger," Gene 127:87-94 (1993), which is hereby incorporated by
reference). It carries out post-translational modifications,
including proper folding, glycosylation, disulfide bond formation,
and proteolysis, during the translocation of proteins through the
endoplasmic reticulum and the cell membrane. The secretion of
proteins is facilitated by hydrophobic short signal peptides at the
N-terminal regions of the protein precursors (Li, X. L. et al.,
"Expression of Aureobasidium Pullulans XynA in, and Secretion of
the Xylanase From, Saccharomyces Cerevisiaea," Appl. Environ.
Microbiol., 62:209-13 (1996), which is hereby incorporated by
reference). Proteins secreted by yeast cells are protected from
aggregation and protease degradation. Most importantly, enzyme
proteins produced by S. cerevisiae are easily purified, because it
secretes only a few proteins. Considering the well-known safety of
yeast products to both human beings and animals, this system is of
great potential for human food and animal feed industry.
Example 5
Properties of the PhyA Phytase Overexpressed in Saccharomyces
cerevisiae
[0092] The overexpressed phytase from transformants of pYPP1
plasmid was concentrated and used to study its property (See Table
4). The enzyme showed two optimum pH ranges: 2 to 2.5 and 5.0 to
5.5. However, enzyme activity at pH 2 to 2.5 was only 60% of the
activity at pH 5 to 5.5. There was no activity detected at either
pH 1 or 8. The optimum pH was virtually the same as the phytase
from A. niger (Simons et al., "Improvement of Phosphorus
Availability by Microbial Phytase in Broilers and Pigs," Br. J.
Nutr., 64:525 (1990), which is hereby incorporated by reference),
thus active function in hydrolysis of phytate-P in the
gastrointestinal tracts would certainly be expected. The optimum
temperature of the enzyme was 60.degree. C., while the current one
on the market produced by Gist-Brocades is 55.degree. C. (BASF,
1996). More than 80% of the activity remained at 50 to 55.degree.
C., but little activity was detected at 75 or 80.degree. C. Heating
the enzyme for 15 min at 37 and 80.degree. C., the remaining
activity for the expressed yeast phytase of the present invention
was 100 and 63%, respectively, and for BASF Gist-Brocades phytase
was 100 and 52%, respectively. The differences between the two
enzyme sources at any given temperature were significant (See Table
5). Thus, the yeast phytase appeared to be more heat stable than
the current commercial phytase product.
4TABLE 4 Characteristics of the overexpressed phytase in
yeast.sup.1 Optimum pH.sup.2 pH 1.0.sup. 2.0 2.5 3.0 4.0 5.0 5.5
6.0 8.0 Relative .5.sup.c 59.7.sup.c 64.8.sup.c 48.1.sup.d
81.0.sup.b 100.0.sup.a 95.0.sup.a 66.3.sup.c .8.sup.e Activity (%)
.+-..2 .+-.3 .+-.6 .+-.4 .+-.5 .+-.1 .+-.6 .+-.1 .4 Optimum
Temperature.sup.3 .degree. C. 25 37 45 50 55 60 75 80 Relative
24.2.sup.c 44.6.sup.d 63.9.sup.c 83.6.sup.b 89.8.sup.b 100.0.sup.a
.6.sup.f .9.sup.f activity (%) .+-..8 .+-.3 .+-.8 .+-.2 .+-.4 .+-.4
.+-..1 .+-..2 .sup.1Data are means of relative activity .+-.
standard deviation (n = 4). Means in a row with different
superscript letters differ (P < 0.05). The general linear model
of the statistical analysis system (1988) was used to analyze the
main treatment effects as randomized complete designs and
Bonferroni t-test was used for multiple treatment mean comparison.
Significance level was set as P < 0.05. .sup.2The activity was
assayed at 37.degree. C. (see context for phytase unit definition).
Different buffers were used: 0.2 mM glycine-HCI buffer for pH 1.0
to 3.5; 0.2 mM sodium citrate buffer for pH 4.0 to 6.5; and 0.2 mM
Tris-HCI buffer for pH over 7. .sup.3Optimum temperature was
determined at pH 5.5 (0.2 mM sodium citrate buffer).
[0093]
5TABLE 5 Comparison of the thermostability of overexpressed phytase
in yeast and Gist-Brocades phytase produced by A. niger.sup.1,2
Relative activity, % 37.degree. C. 80.degree. C. Yeast phytase
100.sup.a .+-. 1 63.sup.b .+-. 1 A. niger phytase 100.sup.x .+-. 3
52.sup.y .+-. 2 p.sup.3 < .03 .sup.1Data are means of relative
activity .+-. standard deviation (n = 3). Means in a row with the #
different superscript letters differ (P < 0.05). The general
linear model of the statistical analysis # system (1988) was used
to analyze the main treatment effects as randomized complete
designs and Bonferroni # t-test was used for multiple treatment
mean comparison. Significance level was set as P < 0.05.
.sup.2The enzyme was heated for 15 minutes at different
temperatures before reacting at 37.degree. C. and pH 5.5.
.sup.3Significance (P values) of t-test between the activity of the
two phytases at each temperature setting.
[0094] Although it is unclear how such improvement in
thermostability is related to different post-translational
modifications (folding, cleavage, glycosylation, etc.), (Li, X. L.
et al., "Expression of Aureobasidiuni Pullulans XynA in, and
Secretion of the Xylanase From, Saccharomyces Cerevisiaea," Appl.
Environ. Microbiol., 62:209-13 (1996), which is hereby incorporated
by reference), it is certainly advantageous to have more
thermostable phytase enzyme that can hopefully be resistant to the
heat during feed pelleting, which is a problem with the current
Gist-Brocades phytase.
Example 6
In vitro Hydrolysis of Phytate-P from Corn, Soy, and Wheat
Middlings by the Expressed Yeast Phytase
[0095] The expressed yeast phytase released phytate-P from corn and
soybean meal as effectively as the Gist-Brocades phytase based on
per unit activity (See Table 6). As expected, the hydrolysis of
phytate-P was a function of time and activity dosage. The expressed
yeast phytase was also effective in releasing phytate-P from wheat
middling, indicating its great potential in bread fermentation.
Because the wheat middling used in this study contained much higher
intrinsic phytase activity than commonly used wheat flour, much
greater effect of the expressed yeast phytase on improving flour
phytate-P hydrolysis and in trace element releasing would be
expected, when it is used in a bakery (Hall, M. N. et al., "The
Early Days of Yeast Genetics," Cold Spring Harbor Laboratory Press
(1993), which is hereby incorporated by reference).
6TABLE 6 Free phosphorus released from corn, soybean meal (SBM),
and wheat middlings by overexpressed yeast phytase and fungus A.
niger phytase in vitro.sup.1 250 Yeast phytase (fungus (PU/kg) 0
100 250 500 1000 phytase) Free phosphorus (mg/g) Corn: 1 hour
.23.sup.d .+-. .03 .64.sup.c .+-. .08 1.14.sup.b .+-. .18
1.46.sup.a .+-. .04 1.54.sup.a .+-. .04 1.16.sup.b .+-. .15 4 hour
.36.sup.c .+-. .02.sup. .sup. 1.26.sup.b .+-. .04 1.60.sup.a .+-.
.03.sup. 1.66.sup.a .+-. .06 1.72.sup.a .+-. .04 1.68.sup.a .+-.
.04.sup. SBM: 1 hour .68.sup.d .+-. .0l.sup. 1.18.sup.cd .+-. .02
.sup. 1.62.sup.c .+-. .18.sup. .sup. 2.48.sup.b .+-. .32 3.13.sup.a
.+-. .19 1.68.sup.c .+-. .2.sup. 4 hour .73.sup.d .sup. 1.67.sup.c
.sup. 2.69.sup.b .sup. 3.41.sup.a .sup. 3.71.sup.a .sup. 2.78.sup.b
.sup. Wheat Middlings: 1 hour 3.56 .+-. .39.sup. 4.11 .+-. .64.sup.
4.67.sup.2 .+-. .05 4 hour 5.63 .+-. .5 .sup. 6.02 .+-. .48.sup.
6.38.sup.2 .+-. .07 .sup.1Each sample of 5 g was stirred in 20 ml
of 0.2 mM sodium citrate buffer at 37.degree. C. for 1 or 4 hours.
The supernatant was obtained by spinning for 15 minutes at 8000 g.
After going through Whatman 541 filter paper, the sample was
subjected to free P assay by the method of Chen, P. S. et al.,
"Microdetermination of P," Anal. Chem., 28: 1756-58 (1956), which
is hereby incorporated by reference. Data in the table are means of
relative activity .+-. standard deviation #(n = 4). The General
Linear Model of the Statistical Analysis System (1988) was used to
analyze the main treatment effects as randomized complete designs
and Bonferroni t-test was used for multiple treatment mean
comparison. Significance level was set as P < 0.05. A
significant difference existed between 1 and 4 hour for every feed
at each dose of enzyme as analyzed by t-test. Means in a row with
different superscript letters differ (P < 0.05). .sup.2n = 2
[0096] The overexpression of Aspergillus niger phytase (phyA) in
Escherichia coli, Streptomyces lividans, and Saccharomyces
cerevisiae were compared to develop an efficient and simple system
to produce phytase economically. A 55 kDa soluble intracellular
protein, representing 9.6% of the total soluble protein, was
expressed in E. coli by using pET25b(+) system. A 57 kDa
extracellular protein, representing 20.3% of the total protein in
the medium, was expressed in S. lividans by using a shuttle plasmid
containing the pLT1 promoter and SpelI leading peptide of
endoglucanase E2. No increase in phytase activity was shown in
either expression system, presumably due to the lack of
glycosylation and other necessary post-translational modification.
In contrast, high extracellular phytase activity was produced in S.
cerevisiae transformed with phyA gene. Three different signal
peptides and three different types of medium were compared to
identify the best expression vector and condition. Use of the
signal peptide Sphy from phyA gene and YEPD medium produced the
highest extracellular phytase activity. The overexpressed phytase
in yeast was approximately 110 kDa, had two pH optima: 2.0 to 2.5
and 5.5 to 6.0, and the optimum temperature was at 60.degree.
C.
Example 7
Methods and Materials for Expression of phyA in Pichia
[0097] Host and Vector
[0098] An EasySelect.TM. Pichia Expression Kit was purchased from
Invitrogen (San Diego, Calif.). The kit provides hosts and vectors
to express the gene either intracellularly or extracellularly, in
strains of either Mut.sup.+ or Mut.sup.S (Methanol utilization
normal or slow). X33 was used as a Mut.sup.+ strain and KM71 as a
Mut.sup.S strain. Two vectors were used, pPICZ B (3.3 kb) and
pPICZ.alpha.A (3.6 kb), both use AOX1 as the promoter.
[0099] Construction of the Expressing Vectors.
[0100] To compare the effect of different signal peptides on the
expression of PhyA in Pichia system, two constructs were prepared.
First, a 1.4 kb EcoRI-KpnI fragment, containing the PhyA sequence
encoding the mature phytase protein, was ligated into
pPICZ.alpha.A. In this plasmid (pPICZ.alpha.-phyA), PhyA was led by
an alpha-factor, a very general-used signal peptide from
Saccharomyces cerevisiae. Second, a 1.4 kb KpnI-XbaI fragment of
pYPP1 was ligated into the vector (the coding region of phyA was
led by its own signal peptide that was very effective in secreting
the expressed phytase in Saccharomyces cerevisiae.)
[0101] Transformation and Expression.
[0102] The confirmed constructs were linearized by PmeI and
transformed into GS115 and KM71, by EasyComp.TM. provided by the
kit. Neocin.TM. was used to select the positive colonies. After a
single colony was inoculated into 10 ml of MGY medium and grown to
OD.sub.600 of 2-6 at 30.degree. C., the cells were collected by
centrifugation and resuspended into 10 ml of MMY medium (containing
0.5% of methanol). The samples were collected every 12 or 24 h
after induction. The cells were separated from the supernatant and
lysed with glass beads in breaking buffer. Phytase activity in the
supernatant and cells was assayed as described previously. SDS-PAGE
and Western blot were conducted to determine the size and relative
amount of the expressed protein.
Example 8
PhyA Phytase Activity in Pichia
[0103] The expression construct using alpha-factor as the signal
peptide for phyA was transformed into two Pichia strains. KM71 is a
methanol utilization slow strain, while X33 is a Pichia wild-type
utilizing methanol efficiently. The screening and incubation were
conducted in 10 ml shake flasks under 29-30.degree. C. For the
transformants of KM71, 19 out of 20 picked colonies had
extracellular phytase activity greater than 6 units/ml of culture
supernatant after induction for 24 hours. Colony No. 13 showed the
highest activity of 26 units/ml after incubated for 108 hours. For
the transformants of X33, all colonies (20/20) had more than 10
units/ml after induced for 24 hours. One of the colonies (#101)
produced phytase activity of 65 units/ml of supernatant. A time
course study of the phytase expression in KM71 and X33 was
summarized in FIG. 11. Despite the difference of these two strains
in utilizing methanol and, therefore, the ability in expressing
phytase, it was found that alpha-factor was correctly processed by
yeast cells. Besides, almost all of the expressed protein was
secreted into the medium since not more than 5% of the total
activity expressed was found intracellularly.
[0104] Effects of inorganic phosphorus and pH of media on the
phytase expression were studied in the media (BMGY and BMMY) using
a phyA recombinant of X33 (#101). The medium containing 50 mM
phosphate produced the highest phytase activity, 66 units/ml at 168
hours after induction. By including 50 mM phosphate in the media,
the effect of different pH of this buffer (3, 4, 5, 6, 7, and 8) on
expression was also studied. When the pH was 6, this X33
transformant produced 75 units phytase/ml supernatant. Based on the
protein concentration and SDS-PAGE analysis, the expression phytase
protein yield was estimated to be between 3 to 4 mg/ml.
Example 9
Properties of the PhyA Phytase Expressed in Pichia
[0105] Molecular Size and Deglycosylation of the Expressed
Phytase.
[0106] After the supernatant of the medium inoculated with the phyA
transformant was subjected to SDS-PAGE, a strong band around 95 kDa
was seen (FIG. 12). This was almost the only viewed protein in the
supernatant. The expressed phytase reacted efficiently with the
rabbit polyclonal antibody raised against purified native A. niger
phytase. This indicated that the immunoreactivity of the expressed
phytase was essentially the same as that of the native phytase from
A. niger. The size was decreased to 50 kDa by deglycosylation using
Endo H. The phyA antibody also reacted with the deglycosylated
phytase. In addition, deglycosylation, conducted under native
conditions, reduced the phytase activity about 15%, indicating that
glycosylation was important for the activity of the phytases.
Moreover, glycosylation affected the thermostability of the enzymes
(FIG. 13).
[0107] Northern Analysis.
[0108] As showed in FIG. 14, a 1.3 kb phyA DNA probe hybridized
with the mRNA of the induced transformants from both KM71 (#13) and
X33 (#101). Response was also seen from the transformants prior to
induction. Probably, the expression of phyA in this system was not
controlled strictly at the level of transcription.
[0109] Optimal pH and Temperature and Phytate-phosphorus
Hydrolysis.
[0110] Similar to A. niger phytase, the expressed phytase had two
optimum pH, 2.5 and 5.5 (FIG. 15). The optimum temperature of the
expressed phytase was 60.degree. C. (FIG. 16). When the expressed
phytase was incubated with soy samples at 100, 200, 400, 800 mU/g
of sample at 37.degree. C., phosphorus was released in a linear
fashion with the phytase dose (FIG. 17).
Example 10
Methods and Materials for Overexpression of E. coli appA Gene in
Saccharomyces cerevisiae
[0111] Gene and Protein.
[0112] This gene, originally defined as E. coli periplasmic
phosphoanhydride phosphohydrolase (appA) gene, contains 1,298
nucleotides (GeneBank accession number: M58708). The gene was first
found to code for an acid phosphatase protein of optimal pH of 2.5
(ECAP) in E. coli. The acid phosphatase is a monomer with a
molecular mass of 44,644 daltons. Mature EcAP contains 410 amino
acids (Dassa, J. et al., "The Complete Nucleotide Sequence of the
Escherichia coli Gene appA Reveals Significant Homology Between pH
2.5 Acid Phosphatase and Glucose-1-Phosphatase," J. Bacteriology,
172:5497-5500 (1990), which is hereby incorporated by reference).
Ostanin, K. et al. ("Overexpression, Site-Directed Mutagenesis, and
Mechanism of Escherichia coli Acid Phosphatase," J. Biol. Chem.,
267:22830-36 (1992), which is hereby incorporated by reference),
overexpressed appA in E. coli BL21 using a pT7 vector and increased
its acid phosphatase activity by approximately 400-fold (440 mU/mg
protein).
[0113] The gene and a host E. coli strain CU 1869 (No. 47092) were
purchased from ATCC. The gene, an insert of 1.3 kb, was transformed
into E. coli strain BL21 (no. 87441) using an expression vector
pAPPA1 (Ostanin, K. et al., "Overexprcssion, Site-Directed
Mutagenesis, and Mechanism of Escherichia coli Acid Phosphatase,"
J. Biol. Chem., 267:22830-36 (1992), which is hereby incorporated
by reference).
[0114] Host and Vector. The vector for overexpressing appA gene in
Saccharomyces cerevisiae was pYES2 and the host was INVScI
(Invitrogen, San Diego, Calif.).
[0115] Construction of the Expression Vector.
[0116] Initially, a 1.3 kb Xbal fragment was isolated from pAPPA1.
This fragment contained the appA gene with its own signal peptide.
After being ligated into the XbaI site of pYES2, the construct
(PYES2-appA) was transformed into Saccharomyces cerevisiae. But, no
phytase activity was increased in either extra- or intra-cellular
parts compared to the controls. pAPPA1 and pYPP1 (PhyA and its
signal peptide in pYES2) were cotransformed into the yeast strain.
Again, no increase in phytase activity due to pAPPA1 was detected
in the media or the yeast cells.
[0117] Two primers were synthesized to construct the signal peptide
of PhyA gene with the coding region of appA gene. One was 80 bp
long containing the PhyA signal peptide and a KpnI site at 5'
end:
7 GGG GTA CCA TGG GCG TCT CTG CTG TTC TAC TTC CTT TGT ATC (SEQ ID
No. 9). TCC TGT CTG GAG TCA CCT CCG GAC AGA GTG AGC CGG AG
[0118] The other primer was 24 bp long, with an EcoRI site at its
3' end: GGG AAT TCA TTA CAA ACT GCA GGC (SEQ ID No. 10). The PCR
was run for 25 cycles, with 1 min denaturing at 95.degree. C., 1
min annealing at 58.degree. C., and 1 min chain extending at
72.degree. C. A 1.3 kb fragment was amplified, digested, and
ligated into pYES2. After the insert was confirmed by restriction
mapping, the construct (pYES2-SphyA-appA) was transformed into
INVScI by lithium acetate method.
[0119] Expression.
[0120] The selected transformants were inoculated into YEPD medium.
The expression was induced by adding galactose into the culture
after OD.sub.600 reached 2, as described previously. The cells were
harvested 15 or 20 h after induction.
[0121] Activity Assay.
[0122] Acid phosphatase activity was assayed at 37.degree. C. in 25
mM glycine-HCl buffer (pH 2.5), using p-nitrophenyl phosphate as
the substrate (stock 250 mM). Reaction buffer of 1.7 ml was added
into 0.1 ml samples. After they were incubated for 5 min in a
37.degree. C. waterbath, 0.2 ml of prewarmed substrate was added
and mixed. The reaction solution was transferred into a prewarmed
cuvette and incubated for 2 min in a 37.degree. C.
spectrophotometric compartment. The released p-nitrophenol was read
continuously for 5 min at 405 nm for enzyme activity
calculation.
[0123] In vitro Study.
[0124] Soybean meal (5.0 g) was suspended into 20 ml of 20 mM
citrate buffer, pH 5.5, mixed with 200 mU of phytase, incubated at
37.degree. C. for 4 h with continuous shaking. After chilling on
ice for 10 min, the slurry was transferred into a centrifuge tube
and spun for 15 min at 15,000.times. g. The supernatant was used to
determine free phosphorus.
Example 11
Quantitation of Phytase Activity from Overexpression of E. coli
appA Gene in Saccharomyces cerevisiae
[0125] The intracellular acid phosphatase activity in the appA
overexpressed E. coli (pAPPA1) was 440 mU/mg protein.
Unprecedently, an intracellular phytase activity greater than 4900
mU/mg protein was found in the transformed strain. But, there was
only minimal phytase activity in the control (BL21). Thus, this
acid phosphatase gene also codes for a phytase. The appA gene
sequence was aligned with that of PhyA and found that these two
genes shared 23% of identity.
[0126] Transforming INVScI with the construct of pYES2-Sphy-appA
(led by the signal peptide of PhyA) produced extracellular phytase
activity in the supernatant that was 2,000-fold greater than those
of the wild type or of the transformant containing appA gene plus
its own signal peptide (See Table 7).
8TABLE 7 Extracellular phytase activity in transformants of appA
gene with different signal peptides Activity (mU/mg Construct
Signal Activity (mU/ml) protein) PYES-appA appA Undetectable
Undetectable pYES2-SphyA- PhyA 1,158 445 appA
[0127] The effects of medium (YEPD) inorganic phosphorus, phytate,
pH, and temperature on the expression of phytase activity by
pYES2-Sphy-A-appA are presented in Table 8. The highest phytase
activity was 2,286 mU/ml (633 mU/mg protein) at the optimal
condition.
9TABLE 8 Effect of different conditions in the YEPD medium on
phytase activity expression of pYES2-SphyA-appA in yeast. Activity
Medium Conditions (mU/ml) Phosphorus, mg/100 ml 0 1402 1 714 5 722
10 456 Sodium phytate, g/100 ml 0 870 0.1 1019 1.0 1748 pH 5.0 892
7.0 996 8.0 2286 Temperature, .degree. C. 25 312 30 1036 37 996
[0128] The thermostability of the overexpressed extracellular
phytase activity produced by the yeast transformant was greater
than that of the intracellular phytase produced by E. coli
transformed with pAPPA1 (See Table 9). Heating the extracellular
phytase for 15 min at 80.degree. C. resulted in 30% of loss of its
phytase activity, while almost all the phytase activity from E.
coli was lost under the same condition.
10TABLE 9 Effect of heating different sources of phytases under
80.degree. C. for 15 min on their activities Phytase Relative
activity after heating, % appA in E. coli 0.1 appA in S. cerevisiae
69 PhyA in S. cerevisiae 66 BASF phytase 50
[0129] Comparisons of the effect on releasing phosphorus from
soybean meal by phytases (200 mU) of E. coli, overexpressed AppA in
yeast, and BASF are presented in Table 10. The results indicate
that all three sources of phytases released phytate-phosphorus
effectively from soybean meal.
11TABLE 10 Free phosphorus released from soybean meal by different
sources of phytases Phytase Phosphorus (mg/g) appA in E. coli 1.11
appA in S. cerevisiae 0.69 BASF 0.87
[0130] E. coli appA (acid phosphatase) gene when expressed in
Sacchacromyces cerevisiae produces extracellular phytase activity
in the media that was more than 2,000-fold greater than the
control. The overexpressed phytase effectively releases
phytate-phosphorus from soybean meal, and seems to be more
thermostable than the presently available commercial phytase or the
intracellular phytase produced in E. coli by the same gene
(appA).
Example 12
Methods and Materials for Overexpressing the E. coli appA Gene
Encoding an Acid Phosphatase/Phytase in Pichia pastoris
[0131] Gene and Protein.
[0132] The appA gene and the host E. coli strain CU 1867 (No.
47092) were obtained from ATCC. The gene, an insert of 1.3 kb, was
transformed into E. coli strain BL21 (No. 87441) using an
expression vector pAPPA1 (Ostanin, K. et al., "Overexpression,
Site-Directed Mutagenesis, and Mechanism of Escherichia coli Acid
Phosphatase," J. Biol. Chem., 267:22830-36 (1992), which is hereby
incorporated by reference).
[0133] Host and Vector.
[0134] An EasySelect.TM. Pichia Expression Kit was obtained from
Invitrogen (San Diego, Calif.). The kit provides hosts and vectors
to express the gene either intracellularly or extracellularly in a
wild-type strain (X-33). Two vectors were used, pPICZ B (3.3 kb)
and pPICZ.alpha.A (3.6 kb), both use AOX1 as the promoter.
[0135] Construction of the Expression Vector.
[0136] Two primers were used to amplify the appA gene from pAPPA1
and two restriction sites EcoRI and KpnI were produced at the 5'
and 3' ends, respectively.
12 Upstream primer: GGA ATT CCA GAG TGA GCC GGA (SEQ ID No. 11)
Downstream primer: GGG GTA CCT TAC AAA CTG CAC G (SEQ ID No.
12)
[0137] Template: pAPPA1 DNA isolated from ATCC 87441
[0138] PCR was run for 30 cycles, with 1 min denaturing at
94.degree. C., 1 min annealing at 55.degree. C., and 1 min chain
extending at 72.degree. C. A 1,245 base-pair fragment was
amplified, digested with EcoRI and KpnI, and ligated (16.degree. C.
overnight) into pPICZ B (3.3 kb) and pPICZ.alpha.A (3.6 kb). The
ligation was confirmed by restriction mapping after transforming
the constructs into DH5.alpha..
[0139] Transformation of the construct into Pichia (X33). For each
transformation, 100 .mu.g of plasmid DNA was prepared and
linearized by digesting with PmeI. After linearization, the DNA was
purified and resuspended into 10 , .mu.L of sterile, deionized
water. Half amount of the DNA was actually used for each
transformation. Electroporation and the EasyComp chemical kit
(Invitrogen) were both used to transform the DNA into X33. In the
case of electroporation, an Electro Cell Manipulator (ECM 600,
Gentromics, BTX Instrument Division, San Diego, Calif. 92121) and 2
mm cuvettes were used. The resistance was 186 Ohm, the charging
voltage was 1.5 kilovolts, and the actual charging length was
approximately 7 milliseconds. The electroporated cells were
incubated on YPD agar plates containing 100 mg Zeocin/mL at
30.degree. C. for 2-4 days for colony growth. In the case of
chemical transformation, cells were grown on YPDS agar plates
containing 100 mg Zeocin/mL. Compared with the electroporation, the
chemical method had lower transformation efficiency.
[0140] Expression.
[0141] Single colonies were inoculated into 10 ml of MGY medium (30
ml tube) and grown (16-18 h) to OD.sub.600 of 5-6 at 28-30.degree.
C. in a shaking incubator (200 rpm). The cells were collected by
centrifugation (2,000 rpm) and resuspended into 10 ml of BMMY
medium (containing 0.5% of methanol) to induce the expression. The
samples (200 .mu.L) were collected every 12 or 24 h after
induction. Methanol (100%) was added at 100 .mu.L every 24 to
maintain a concentration of 0.5-1% in the media.
[0142] Assays.
[0143] The cells were separated from the media (supernatant) and
lysed with glass beads in breaking buffer. Extracellular phytase
activity in the supernatant and intracellular phytase activity in
the lysed cells were assayed as described previously (0.2 M citrate
buffer, pH 5.5 under 37.degree. C. using 10 mM sodium phytate).
Acid phosphatase activity was assayed at 37.degree. C. in 25 mM
glycine-HCl buffer (pH 2.5), using p-nitrophenyl phosphate as the
substrate (stock 250 mM). Reaction buffer of 1.7 ml was added into
0.1 ml samples. The released p-nitrophenol was read continuously
for 5 min at 405 nm for enzyme activity calculation. SDS-PAGE (12%)
was conducted to determine the size and relative amount of the
expressed protein. The optimal pH and temperature of the expressed
phytase were determined as described in the results.
[0144] In vitro Study.
[0145] Soybean meal (5.0 g) was suspended into 20 ml of 20 mM
citrate buffer, pH 5.5, mixed with different levels of phytase, and
incubated at 37.degree. C. for 4 h with continuous shaking. After
being chilled on ice for 10 min, the slurry was transferred into a
centrifuge tube and spun for 15 min at 15,000.times. g. The
supernatant was used to determine free phosphorus.
Example 13
Colony Phytase Activity Screening for Phicia pastoris
Overexpressing the E. coli appA Gene
[0146] Wild-type Pichia X33 produces minimal phytase activity
intracellularly (<0.03 U/mg protein) or extracellularly
(<0.05 U/mL). The X33 cells transformed with the appA gene
inserted into pPICZB (without the .alpha.-factor and presumably
produces intracellular phytase) did not show any increase in
phytase activity (extracellular, 0.2 U/mL and intracellular, 0.05
U/mg protein).
[0147] Transforming X33 cells with the construct of pPIZccA-appA
(led by the signal peptide of .alpha.-factor) produced
extracellular phytase activity in the media. Initially, 72 colonies
were screened. Only two colonies had activity <1 U/mL 40 hours
after induction. Most of the colonies had activity ranging from 10
to 20 U/mL 40 hours after induction. All of the 70 colonies had
phytase activity >80 U/mL 118 hours after induction. The highest
phytase activity so far detected was 215 U/mL, 192 hours after the
induction (See Table 11).
13TABLE 11 Range of extracellular phytase activity in X33 colonies
transformed with pP1Z.alpha.A-appA 40 and 118 hours after
induction. 118 hours after Number of Colonies 40 hours after
induction induction 2 <1 U/mL 6 1 to 10 U/mL 36 11 to 20 U/mL 28
>20 U/mL 70 >80 U/mL
[0148] Phytase and acid phosphatase activities in the transformant
expressing 215U phytase activity/mL were compared with those of the
wild-type of X33 (192 hours after induction) (See Table 12). Almost
all of the expressed phytase protein was secreted from the cells,
indicating that .alpha.-factor was a very effective signal peptide
for phytase secretion.
14TABLE 12 Phytase and acid phosphatase activities in the
pP1Z.alpha.A-appA transformant and the wild-type of X33 192 hours
after induction. Wild- type X33 pP1Z.alpha.A-appA transformant
Extracellular Intracellular Extracellular Intracellular U/mL U/mg
protein U/mL U/mg protein Phytase 0.05 0.03 215 0.5 Acid 0.01 0.002
5.88 0.9 phosphatase
[0149] Transformants of E. coli with the same acid phosphatase appA
gene had intracellular phytase activity of 5 U/mg protein (Ostanin
et al., "Overexpression, Site-Directed Mutagenesis, and Mechanism
of Escherichia coli Acid Phosphatase," J. Biol. Chem., 267:22830-36
(1992), which is hereby incorporated by reference). Transforming
PhyA gene in A. niger produced an extracellular activity of 7.6
U/ml (Hartingsveldt et al., "Cloning, Characterization and
Overexpression of the Phytase-Encoding Gene (phyA) of Aspergillus
Niger," Gene 127:87-94 (1993), which is hereby incorporated by
reference). Compared with these results, the phytase expression
system in Pichia is a very efficient expression system.
Example 14
Time-course of Phytase Expression
[0150] There was a linear increase in extracellular phytase
activity in the media almost in all of the selected colonies up to
192 hours after induction. FIG. 18 summarized the activity changes
of five selected colonies from 24 to 163 hours after induction.
Example 15
Effects of Medium pH on the Expression of Phytase (Colony #23,
Activity 136 U/mL at 186 h)
[0151] Using 0.1 M phosphate buffered media, the effects of
different pH on the production of extracellular phytase in the
transformants were studied against a control medium without buffer
(pH 7.0). The medium buffered to pH 6 produced the highest phytase
activity (See FIG. 19).
Example 16
Size of the Expressed Extracellular Phytase
[0152] Using SDS-PAGE (12% gel) analysis, a clear band was noticed
in the medium supernatant of culture inoculated with three
different colonies (See FIG. 20). The size was around 55 kDa,
probably partially glycosylated. Because the expressed protein
represented almost the only visible band in the supernatant, it
would be convenient to collect the enzyme product without the need
for a tedious purification.
Example 17
Optimum pH and Temperature of the Expressed Extracellular Phytase
(Colony #23)
[0153] The optimum pH of the expressed phytase was 2.5 to 3.5 (See
FIG. 21). This is significantly different from that of phyA phytase
either from A. niger (BASF) or our other expression systems. It is
ideal for phytase function at the stomach pH.
[0154] The optimum temperature of the expressed enzyme was
60.degree. C. (See FIG. 22).
Example 18
Effect of the Expressed Phytase on Phytate-Phosphorus Hydrolysis
from Soybean Meal
[0155] This overexpressed E. coli phytase (Colony #23) effectively
hydrolyzed phytate-phosphorus from soybean meal (See FIG. 23). The
release of free phosphorus in the mixture was linear from 0 to 800
mU of phytase/g of feed.
Example 19
Effects of the Expressed E. coli AppA Phytase by Pichia pastoris on
Phytate Phosphorus Bioavailability to Weanling Pigs
[0156] To determine the nutritional values of the expressed E. coli
phytase by Pichia in swine diets, the efficacy of this new phytase
was compared with those of inorganic phosphorus or the commercially
available microbial phytase (Natuphos.TM., BASF Corp., Mt. Olive,
N.J.). Forty-eight weanling pigs were selected from multiparous
sows at Cornell Swine Research Farm. The pigs were weaned at 21
days of age and fed a commercial creep feed until day 28. They were
then placed two per pen with six pens assigned randomly per
treatment. The pigs were given two weeks to adjust to the
corn-soybean meal basal diet (Table 13).
15TABLE 13 Formulation of the Experiment Diets for Pigs. +C -C YP
MP Ingredient % diet % diet % diet % diet Corn 60.5 61.57 61.07
61.07 Whey Protein Concentrate 3 3 3 3 SBM 44% 30 30 30 30 Corn Oil
3 3 3 3 Lime 0.8 0.93 0.93 0.93 Di-calcium phosphate 1.2 0 0 0
Vitamin and Mineral 0.5 0.5 0.5 0.5 premix ECAP premix 0 0 0.5 0 MP
premix 0 0 0 0.5 Salt 0.5 0.5 0.5 0.5 CSP 250 0.5 0.5 0.5 0.5 Total
100 100 100 100 CP 20.6 20.6 20.6 20.6 Ca 0.73 0.47 0.47 0.47
P.sub.total 0.6 0.39 0.39 0.39 Note: All premixes use corn as the
carrier Vitamin and Mineral Premix supplies: 2,540 IU Vit. A, 660
IU Vit. D, 15 IU Vit. E, 2.2 mg Vit. K, 3.3 mg Riboflavin, 13.2 mg
Pantothenic acid, 17.6 mg Niacin, 110.1 mg Choline, 1.98 ug B-12,
37.4 mg Mn, 0.6 mg I, 10 mg Cu, 0.3 mg Se, 100 mg Zn, and 100 mg Fe
per Kg of diet
[0157] Then, each pen received one of the four treatment diets. The
positive control group (+C) received the basal diet supplemented
with dicalcium phosphate. The negative control group (-C) received
just the basal diet. The yeast phytase group (YP) received the
basal diet supplemented with the expressed E. coli phytase at 1,200
U/kg of feed. The microbial phytase group (MP) received the basal
diet supplemented with the BASF phytase at 1,200 U/kg of feed. Pigs
were given free access to feed and water. Body weight gain of
individual pigs was recorded weekly. Daily feed intake of
individual pens was recorded daily. Blood samples from each of the
individual pigs were taken weekly to assay plasma inorganic
phosphorus concentrations. The results of body weight (BW), average
daily gain (ADG), average feed intake (ADFI), and feed/gain ratio
(F:G), and plasma inorganic phosphorus (PP) are presented in Table
14.
16TABLE 14 Summary of PP, BW, ADG, ADFI, and F:G of Pigs as
Effected by Dietary Phytase..sup.1 +C -C YP MP Initial PP 12.99
13.02 13.07 13.54 BW 11.54 11.63 12 11.5 Week 1 PP 10.83.sup.A
6.48.sup.C 8.59.sup.B 8.35.sup.B BW 14 13.83 14.29 13.92 ADG .351
.316 .327 .345 ADFI .700 .684 .697 .697 F:G 2.04 2.20 2.18 2.13
Week 2 PP 9.76.sup.A 5.64.sup.D 8.72.sup.B 7.84.sup.C BW 18.04
17.42 17.83 17.71 ADG .578 .512 .506 .542 ADFI .833 .855 .784 .837
F:G 1.46.sup.B 1.67.sup.A 1.56.sup.AB 1.55.sup.AB Week 3 PP
11.sup.A 6.26.sup.C 8.64.sup.B 8.13.sup.B BW 22.58 21.17 22 22.21
ADG .649.sup.A .536.sup.B .595.sup.AB .643.sup.AB ADFI 1.166 1.02
1.001 1.003 F:G 1.8 1.92 1.71 1.36 Week 4 PP 10.94.sup.A 6.31.sup.C
9.65.sup.B 9.2.sup.B BW 27.54 25.29 27.79 27.38 ADG .708.sup.AB
.589.sup.B .827.sup.A .738.sup.AB ADFI 1.395.sup.A 1.049.sup.B
1.3O9.sup.A 1.273.sup.AB F:G 1.98 1.87 1.59 1.73 .sup.1Numbers in
the same row without sharing a common letter are significantly
different. Analysis of difference was conducted with the Bonferroni
(Dunn) T-tests with alpha = 0.05 and df = 20
[0158] In addition, there was severe phosphorus deficiency in the
negative control group in the end of the four-week experiment. But,
there was no sign of phosphorus deficiency in the other three
groups. Clearly, the expressed E. coli phytase by Pichia was at
least, if not more, effective as the commercial microbial phytase
in improving bioavailability of phytate-phosphorus from the
corn-soybean meal diets for weanling pigs. It can be used to
replace inorganic phosphorus supplementation to weanling pigs.
Example 20
Effects of the Expressed E. coli AppA Phytase by Pichia pastoris on
Iron (Fe) and Phytate Phosphorus Bioavailability to Weanling
Pigs
[0159] To determine the effect of the overexpressed E. coli phytase
by Pichia on dietary phytate--bound Fe bioavailability to weanling
pigs, 20 anemic pigs (21 days old and 7.3 g hemoglobin (Hb)/dL
blood) were selected. The pigs were fed an Fe-deficient creep feed
for 7 days and housed in metabolic cages at the age of 28 days old.
The pigs were then fed the experimental diets at the age of 35 days
old for 5 weeks. The treatment diets were as follows: Fe-deficient
basal diet (-C, with added inorganic phosphorus), Fe-supplemented
diet (+C), the Fe- and phosphorus-deficient diet supplemented with
the expressed E. coli phytase (YP), or the commercial microbial
phytase (BASF, MP) at 1,200 U/kg of feed. Body weight (BW). packed
cell volume (PCV), Hb, and plasma inorganic phosphorus (PP) were
determined weekly. The results are presented in Table 15.
17TABLE 15 Summary of PCV, Hb, BW, and PP of Pigs as Effected by
Dietary Phytase..sup.1 +C -C YP MP Initial PCV 25 25 26 24 Hb 7.73
7.22 7.85 7.08 BW 8.14 8.27 8.17 7.45 PP 7.92 7.76 7.21 7.36 Week 1
PCV 25 26 29 27 Hb 7.62 8.3 8.77 7.88 BW 9.44 8.84 9.63 8.57 PP
8.41 8.45 8.48 8.22 Week 2 PCV 29 26 30 28 Hb 8.6 7.34 8.93 8.27 BW
12.32 10.13 11.91 10.84 PP 10.28.sup.a 9.05.sup.ab 8.89.sup.ab
8.22.sup.a Week 3 PCV 36.sup.a 29.sup.b 34.sup.a 33.sup.a Hb
11.55.sup.a 8.2.sup.b 10.84.sup.a 9.96.sup.ab BW 16.77.sup.a
13.sup.b 15.62.sup.ab 14.62.sup.ab PP 12.14.sup.a 11.37.sup.ab
10.25.sup.bc 9.71.sup.c Week 4 PCV 39 34 38 36 Hb 12.99.sup.a
10.11.sup.b 12.27.sup.a 11.35.sup.ab BW 21.36.sup.a 17.37.sup.b
19.44.sup.ab 18.56.sup.ab PP 10.19.sup.a 9.34.sup.ab 9.49.sup.ab
8.8.sup.b Week 5 PCV 40 38 40 39 Hb 13.52.sup.a 12.24.sup.b
13.64.sup.a 13.13.sup.ab BW 26.53 22.59 24.27 23.43 PP 9.27.sup.a
8.95.sup.ab 8.79.sup.ab 8.02.sup.n .sup.1Values are means (n = 5).
Means within the same row without sharing a common superscript
ltter are significantly different (P < 0.10).
[0160] In conclusion, the overexpressed E. coli phytase by Pichia
was at least as effective as the BASF phytase in improving
phytate-phosphorus and Fe utilization in corn-soy diets for
weanling pigs.
[0161] 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 therefore are considered within
the scope of the invention as defined in the claims which follow.
Sequence CWU 1
1
* * * * *