Alpha2 subunit of prolyl 4-hydroxylase

Abstract

The present invention relates to novel isoforms of the &agr; subunit of prolyl 4-hydroxylase, polynucleotide sequences encoding these novel proteins, and methods for making such proteins.

Description

[0001] This application is a continuation of U.S. application Ser. No. 09/686,322, filed Oct. 10, 2000, which is a continuation of U.S. application Ser. No. 09/196,581, filed Nov. 20, 1998, which is a divisional of U.S. application Ser. No. 08/633,879, filed Apr. 10, 1996, now U.S. Pat. No. 5,928,922, issued Jul. 27, 1999.

1. INTRODUCTION

[0002] The present invention relates to the identity and characterization of novel &agr; subunits of prolyl 4-hydroxylase, variants thereof; polynucleotide sequences which encode the novel &agr;2 subunits of prolyl 4-hydroxylase, and methods for using and making such novel polynucleotides and polypeptides. The present invention also relates to the recombinant production of active: (1) prolyl 4-hydroxylase, or variants thereof, and (2) collagen, comprising the use of the novel human a subunit of prolyl 4-hydroxylase of the present invention.

[0003] The present invention more specifically relates to polynucleotides encoding a novel isoform of the a subunit of prolyl 4-hydroxylase, designated the “&agr;2 subunit,” and derivatives thereof, methods for producing such isoforms or related derivatives and the use of these proteins and polynucleotides in the production of recombinant collagen.

2. BACKGROUND

[0004] General Information Regarding Collagen.

[0005] Collagen fibrils, proteoglycan aggregates and glycoproteins are critical components of the cartilage extracellular matrix that, collectively, resist compression and the tensile and shear forces that are generated during articulation. Heineg.ang.rd and Oldberg (1989) FASEB J. 3:2042-2051; Mayne and Brewton (1993) Cartilage Degradation: Basic and Clinical Aspects (Woessner, J. F. and Howell, D. S., eds.) Marcel Dekker, Inc., New York, pp. 81-108. Mutations in cartilage matrix genes or the genes that encode the enzymes that affect the biosynthesis, assembly or interactions between these various matrix components may contribute to degradation of the cartilage matrix and the loss of normal cartilage function.

[0006] The Role of Prolyl 4-Hydroxylase in the Production of Collagen.

[0007] Prolyl 4-hydroxylase plays a crucial role in the synthesis of all collagens. Specifically, the enzyme catalyzes the formation of 4-hydroxyproline in collagens and related proteins by the hydroxylation of proline residues in -Xaa-Pro-Gly-sequences. These 4-hydroxyproline residues are essential for the folding of newly synthesized collagen polypeptide chains into triple-helical molecules.

[0008] The vertebrate prolyl 4-hydroxylase is an &agr;2&bgr;2 tetramer in which the a subunits contribute to most parts of the catalytic sites. See, Kivirikko et al. (1989) FASEB J. 3, 1609-1617; Kivirikko et al. (1990) Ann. N.Y. Acad. Sci. 580, 132-142; Kivirikko et al. (1992) Post Translational Modifications of Proteins (Harding, J. J. and Crabbe, M. J. C., eds.) CRC, Boca Raton, Fla., pp. 1-51. The &bgr; subunit has been cloned from many sources (id.; see also, Noiva and Lennatz (1992) J. Biol. Chem. 267:6447-49; Freedman et al. (1994) Trends Biochem. Sci. 19:331-336) and has been found to be a highly unusual multifunctional polypeptide that is identical to the enzyme protein disulfide-isomerase (Pihlajaniemi et al. (1987) EMBO J. 6:643-649; Kojvu et al. (1987) J. Biol. Chem. 262:6447-49), a cellular thyroid hormone-binding protein (Cheng et al. (1987) J. Biol. Chem. 262:11221-27), the smaller subunit of the microsomal triacylglycerol transfer protein (Wetterau et al. (1990) J. Biol. Chem. 265:9800-07), and an endoplasmic reticulum luminal polypeptide which uniquely binds to various peptides (Freedman, supra; Noiva et al. (1991) J. Biol. Chem. 266:19645-649; Noiva et al. (1993) J. Biol. Chem. 268:19210-217).

[0009] A catalytically important &agr; subunit, designated the &agr;1 subunit, has been cloned from human (Helaakoski et al. (1989) Proc. Natl. Acad. Sci. USA 86:4392-96), chicken (Bassuk et al. (1989) Proc. Natl. Acad. Sci. USA 86:7382-886) and Caenorhabditis elegans (Veijola et al. (1994) J. Biol. Chem. 269:26746-753), and its RNA transcripts have been shown to undergo alternative splicing involving sequences encoded by two consecutive, homologous 71-bp exons (Helaakoski, supra; Helaakoski et al. (1994) J. Biol. Chem. 269:27847-854). A second a subunit, designated the a2 subunit has been previously obtained from mouse. Helaakoski et al. (1995) Proc. Natl. Acad. Sci. USA 92:4427-4431.

3. SUMMARY OF THE INVENTION

[0010] The present invention is directed to the cloning and characterization of human &agr;-subunit isoforms of prolyl 4-hydroxylase. More specifically, the present invention relates to human subunit isoforms of the a subunit of prolyl 4-hydroxylase designated the &agr;2 subunit, and the polynucleotide sequences which encode them. Also described herein are methods for producing the &agr;2 subunit of prolyl 4-hydroxylase, prolyl 4-hydroxylase and collagen, wherein said prolyl 4-hydroxylase is comprised of the &agr;2 subunit of the present invention and said collagen is processed into its proper form by such prolyl 4-hydroxylase. In accordance with the invention, any nucleotide sequence that encodes the amino acid sequence of claimed &agr;2 subunit of prolyl 4-hydroxylase can be used to generate recombinant molecules that direct the expression of human prolyl 4-hydroxylase.

[0011] The present invention is further directed to the use of the coding sequence for the &agr;2 subunit of prolyl 4-hydroxylase to produce an expression vector which may be used to transform appropriate host cells. The host cells of the present invention are then induced to express the coding sequence and thereby produce the &agr;2 subunit of prolyl 4-hydroxylase, or more generally, in combination with the p subunit, prolyl 4-hydroxylase.

4. DETAILED DESCRIPTION

[0012] The present invention relates to human &agr;2 subunits of prolyl 4-hydroxylase and nucleic acid sequences encoding these &agr;2 subunits of the prolyl 4-hydroxylase and derivatives thereof. In accordance with the invention, any nucleotide sequence which encodes the amino acid sequence of claimed human &agr;2 subunit of prolyl 4-hydroxylase can be used to generate recombinant molecules which direct the expression of prolyl 4-hydroxylase. Also within the scope of the invention are methods of using and making these &agr;2 subunits of prolyl-4hydroxylase.

[0013] a. Definitions

[0014] The term “&agr;2 subunit of prolyl-4-hydroxylase” refers to isoforms of the a subunit of prolyl 4-hydroxylase, as encoded by a single gene as set forth at SEQ ID NO: 3, and genes which contain conservative substitutions thereto.

[0015] “Active human prolyl 4-hydroxylase” refers to a protein complex comprising a prolyl 4-hydroxylase &agr;2&bgr;2 tetramer, and may be recombinantly produced.

[0016] The phrase “stringent conditions” as used herein refers to those hybridizing conditions that (1) employ low ionic strength and high temperature for washing, for example, 0.015 M NaCl/0.0015 M sodium citrate/0.1% SDS at 50° C.; (2) employ during hybridization a denaturing agent such as formamide, for example, 50% (vol/vol) formamide with 0.1% bovine serum albumin/0.1% Ficoll/0.1% polyvinylpyrrolidone/50 mM sodium phosphate buffer at pH 6.5 with 750 mM NaCl, 75 mM sodium citrate at 42° C.; or (3) employ 50% formamide, 5× SSC (0.75 M NaCl, 0.075 M Sodium citrate), 5× Denhardt's solution, sonicated salmon sperm DNA (50 g/ml), 0.1% SDS, and 10% dextran sulfate at 42° C., with washes at 42° C. in 0.2× SSC and 0.1% SDS.

[0017] The term “purified” as used in reference to prolyl 4-hydroxylase denotes that the indicated molecules are present in the substantial absence of other biological macromolecules, e.g., polynucleotides, proteins, and the like. The term “purified” as used herein preferably means at least 95% by weight, more preferably at least 99.8% by weight, of the indicated biological macromolecules present (but water, buffers, and other small molecules, especially molecules having a molecular weight of less than 1000 daltons can be present).

[0018] The term “isolated” as used herein refers to a protein molecule separated not only from other proteins that are present in the source of the protein, but also from other proteins, and preferably refers to a protein found in the presence of (if anything) only a solvent, buffer, ion, or other component normally present in a solution of the same. The terms “isolated” and “purified” do not encompass proteins present in their natural source.

b. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIGS. 1A and 1B (FIG. 1A, FIG. 1B) set forth the nucleotide (SEQ ID NO:1) and deduced amino acid sequence (SEQ ID NO:2) for the &agr;(2) subunit of mouse prolyl 4-hydroxylase.

[0020] FIGS. 2A, 2B, and 2C (FIG. 2A, FIG. 2B, FIG. 2C) set forth the nucleotide (SEQ ID NO:3) and deduced amino acid sequence (SEQ ID NO:4) for the &agr;(2) subunit of human prolyl 4-hydroxylase, as derived from cDNA clones.

[0021] FIG. 3 (FIG. 3) sets forth the nucleotide (SEQ ID NO:5) and deduced amino acid sequence (SEQ ID NO:6) for EXON 2 (as identified in FIG. 2) and flanking intron sequences.

[0022] FIG. 4 (FIG. 4) sets forth the nucleotide (SEQ ID NO:7) and deduced amino acid sequence (SEQ ID NO:8) for EXON 3 (as identified in FIG. 2) and flanking intron sequences.

[0023] FIG. 5 (FIG. 5) sets forth the nucleotide (SEQ ID NO:9) and deduced amino acid sequence (SEQ ID NO:10) for EXON 4 (as identified in FIG. 2) and flanking intron sequences.

[0024] FIG. 6 (FIG. 6) sets forth the nucleotide (SEQ ID NO:11) and deduced amino acid sequence (SEQ ID NO:12) for EXON 5 (as identified in FIG. 2) and flanking intron sequences.

[0025] FIG. 7 (FIG. 7) sets forth the nucleotide (SEQ ID NO:13) and deduced amino acid sequence (SEQ ID NO: 14) for EXON 6 (as identified in FIG. 2) and flanking intron sequences.

[0026] FIG. 8 (FIG. 8) sets forth the nucleotide (SEQ ID NO: 15) and deduced amino acid sequence (SEQ ID NO: 16) for EXON 7 (as identified in FIG. 2) and flanking intron sequences.

[0027] FIGS. 9A, 9B and 9C (FIG. 9A, FIG. 9B, FIG. 9C) set forth the nucleotide (SEQ ID NO:17) and deduced amino acid sequence (SEQ ID NO:18) for EXON 8 (as identified in FIG. 2) and flanking intron sequences.

c. EXPRESSION Of The &agr;2 SUBUNIT OF PROLYL 4-HYDROXYLASE OF THE INVENTION

[0028] (1) Coding Sequences

[0029] In accordance with the invention, polynucleotide sequences which encode a human isoform of the a subunit of prolyl 4-hydroxylase, or functional equivalents thereof, may be used to generate recombinant DNA molecules that direct the expression of the human &agr;2 subunit of prolyl 4-hydroxylase or its derivatives, and prolyl 4-hydroxylase comprising the &agr;2 subunit of prolyl 4-hydroxylase, or a functional equivalent thereof, in appropriate host cells. Such sequences of an &agr;2 subunit of prolyl 4-hydroxylase, as well as other polynucleotides which selectively hybridize to at least a part of such polynucleotides or their complements, may also be used in nucleic acid hybridization assays, Southern and Northern blot analyses, etc.

[0030] Due to the inherent degeneracy of the genetic code, other nucleic acid sequences which encode substantially the same or a functionally equivalent amino acid sequence, may be used in the practice of the invention for the cloning and expression of &agr;2 subunit of prolyl 4-hydroxylase proteins. Such nucleic acid sequences include those which are capable of hybridizing to the appropriate &agr;2 subunit of prolyl 4-hydroxylase sequence under stringent conditions.

[0031] Altered nucleic acid sequences which may be used in accordance with the invention include deletions, additions or substitutions of different nucleotide residues resulting in a sequence that encodes the same or a functionally equivalent gene product. The nucleic acid product itself may contain deletions, additions or substitutions of amino acid residues within an &agr;2 subunit of the prolyl 4-hydroxylase sequence, which result in a silent change thus producing a functionally equivalent a subunit. Such amino acid substitutions may be made on the basis of similarity in polarity, charge, solubility, hydrophobicity, hydrophilicity, and/or the amphipathic nature of the residues involved. For example, negatively charged amino acids include aspartic acid and glutamic acid; positively charged amino acids include lysine and arginine; amino acids with uncharged polar head groups having similar hydrophilicity values include the following: leucine, isoleucine, valine; glycine, alanine; asparagine, glutamine; serine, threonine; phenylalanine, tyrosine.

[0032] The nucleic acid sequences of the invention may be engineered in order to alter the &agr;2 subunit of the prolyl 4-hydroxylase coding sequence for a variety of ends including but not limited to alterations which modify processing and expression of the gene product. For example, alternative secretory signals may be substituted for the native human secretory signal and/or mutations may be introduced using techniques which are well known in the art, e.g., site-directed mutagenesis, to insert new restriction sites, to alter glycosylation patterns, phosphorylation, etc.

[0033] Additionally, when expressing in non-human cells, the polynucleotides encoding the prolyl 4-hydroxylase of the invention may be modified so as to better conform to the codon preference of the particular host organism.

[0034] In an alternate embodiment of the invention, the coding sequence of the &agr;2 subunit of prolyl 4-hydroxylase of the invention could be synthesized in whole or in part, using chemical methods well known in the art. See, for example, Caruthers et al. (1980) Nucleic Acids Symp. Ser. 7:215-233; Crea and Horn (1980) Nucleic Acids Res. 9(10):2331; Matteucci and Caruthers (1980) Tetrahedron Letters 21:719; and Chow and Kempe (1981) Nucleic Acids Res. 9(12):2807-2817. Alternatively, the protein itself could be produced using chemical methods to synthesize the desired &agr;2 subunit amino acid sequence at least in part. For example, peptides can be synthesized by solid phase techniques, cleaved from the resin, and purified by preparative high performance liquid chromatography. See, e.g., Creighton (1983) Proteins Structures And Molecular Principles, W.H. Freeman and Co., New York, pp. 50-60. The composition of the synthetic peptides may be confirmed by amino acid analysis or sequencing (e.g., the Edman degradation procedure; see Creighton (1983) Proteins, Structures and Molecular Principles, W.H. Freeman and Co., New York, pp. 34-49.

[0035] In order to express the &agr;2 subunit of prolyl 4-hydroxylase of the invention, the nucleotide sequence encoding the &agr;2 subunit of prolyl 4-hydroxylase, or a functional equivalent, is inserted into an appropriate expression vector, i.e., a vector which contains the necessary elements for the transcription and translation of the inserted coding sequence.

[0036] (2) Expression Systems

[0037] Methods which are well known to those skilled in the art can be used to construct expression vectors containing an &agr;2 subunit of prolyl 4-hydroxylase coding sequence for prolyl 4-hydroxylase and appropriate transcriptional/translational control signals. These methods include in vitro recombinant DNA techniques, synthetic techniques and in vivo recombination. See, for example, the techniques described in Maniatis et al. (1989) Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Laboratory, New York and Ausubel et al. (1989) Current Protocols in Molecular Biology, Greene Publishing Associates and Wiley Interscience, New York.

[0038] A variety of host-expression vector systems may be utilized to express a coding sequence of an &agr;2 subunit of prolyl 4-hydroxylase. These include but are not limited to microorganisms such as bacteria transformed with recombinant bacteriophage DNA, plasmid DNA or cosmid DNA expression vectors containing a coding sequence of an &agr;2 subunit of prolyl 4-hydroxylase; yeast transformed with recombinant yeast expression vectors containing a coding sequence of an &agr;2 subunit of prolyl 4-hydroxylase; insect cell systems infected with recombinant virus expression vectors (e.g., baculovirus) containing sequence encoding the &agr;2 subunit of prolyl 4-hydroxylase; plant cell systems infected with recombinant virus expression vectors (e.g., cauliflower mosaic virus, CaMV; tobacco mosaic virus, TMV) or transformed with recombinant plasmid expression vectors (e.g., Ti plasmid) containing a coding sequence of an &agr;2 subunit of prolyl 4-hydroxylase; or animal cell systems infected with appropriate vectors, preferably semliki forest virus.

[0039] Additionally, the &agr;2 subunit of prolyl 4-hydroxylase of the invention may be expressed in transgenic non-human animals wherein the desired enzyme product may be recovered from the milk of the transgenic animal. The expression elements of these systems vary in their strength and specificities. Depending on the host/vector system utilized, any of a number of suitable transcription and translation elements, including constitutive and inducible promoters, may be used in the expression vector. For example, when cloning in bacterial systems, inducible promoters such as pL of bacteriophage &lgr;, plac, ptrp, ptac (ptrp-lac hybrid promoter) and the like may be used; when cloning in insect cell systems, promoters such as the baculovirus polyhedron promoter may be used; when cloning in plant cell systems, promoters derived from the genome of plant cells (e.g., heat shock promoters; the promoter for the small subunit of RUBISCO; the promoter for the chlorophyll a/b binding protein) or from plant viruses (e.g., the 35S RNA promoter of CaMV; the coat protein promoter of TMV) may be used; when cloning in mammalian cell systems, promoters derived from the genome of mammalian cells (e.g., metallothionein promoter) or from mammalian viruses (e.g., the adenovirus late promoter; the vaccinia virus 7.5 K promoter) may be used; when generating cell lines that contain multiple copies of an &agr;2 subunit of prolyl 4-hydroxylase DNA, SV40-, BPV- and EBV-based vectors may be used with an appropriate selectable marker.

[0040] In bacterial systems a number of expression vectors may be advantageously selected depending upon the use intended for the &agr;2 subunit of the prolyl 4-hydroxylase expressed. For example, when large quantities of the polypeptides of the invention are to be produced, vectors which direct the expression of high levels of protein products that are readily purified may be desirable. Such vectors include but are not limited to the E. coli expression vector pUR278 (Ruther et al. (1983) EMBO J. 2:1791), in which the polypeptide coding sequence may be ligated into the vector in frame with the lac Z coding region so that a hybrid AS-lac Z protein is produced; pIN vectors (Inouye and Inouye (1985) Nucleic Acids Res. 13:3101-3109; Van Heeke and Schuster (1989) J. Biol. Chem. 264:5503-5509); and the like. pGEX vectors may also be used to express foreign polypeptides as proteins with glutathione S-transferase (GST). In general, such proteins are soluble and can easily be purified from lysed cells by adsorption to glutathione-agarose beads followed by elution in the presence of free glutathione. The pGEX vectors are designed to include thrombin or factor Xa protease cleavage sites so that the cloned polypeptide of interest can be released from the GST moiety.

[0041] A preferred expression system is a yeast expression system. In yeast, a number of vectors containing constitutive or inducible promoters may be used. For a review see Ausubel et al. (1988) Current Protocols in Molecular Biology, Vol. 2, Greene Publish. Assoc. & Wiley Interscience, Ch. 13; Grant et al. (1987) Expression and Secretion Vectors for Yeast, in Methods in Enzymology, Ed. Wu & Grossman, Acad. Press, New York 153:516-544; Glover (1986) DNA Cloning, Vol. II, IRL Press, Washington, D.C., Ch. 3; Bitter (1987) Heterologous Gene Expression in Yeast, in Methods in Enzymology, (Berger and Kimmel, eds.) Acad. Press, New York 152:673-684; and Strathern et al. (1982) The Molecular Biology of the Yeast Saccharomyces, Cold Spring Harbor Press, Vols. I and II.

[0042] A particularly preferred system useful for cloning and expression of the proteins of the invention uses host cells from the yeast Pichia. Species of non-Saccharomyces yeast such as Pichia pastoris appear to have special advantages in producing high yields of recombinant protein in scaled up procedures. Additionally, a Pichia expression kit is available from Invitrogen Corporation (San Diego, Calif.).

[0043] There are a number of methanol responsive genes in methylotrophic yeasts such as Pichia pastoris, the expression of each being controlled by methanol responsive regulatory regions (also referred to as promoters). Any of such methanol responsive promoters are suitable for use in the practice of the present invention. Examples of specific regulatory regions include the promoter for the primary alcohol oxidase gene from Pichia pastoris AOX1, the promoter for the secondary alcohol oxidase gene from P. pastoris AX02, the promoter for the dihydroxyacetone synthase gene from P. pastoris (DAS), the promoter for the P40 gene from P. pastoris, the promoter for the catalase gene from P. pastoris, and the like.

[0044] Typical expression in Pichia pastoris is obtained by the promoter from the tightly regulated AOX1 gene. See Ellis et al. (1985) Mol. Cell. Biol. 5:1111, and U.S. Pat. No. 4,855,231. This promoter can be induced to produce high levels of recombinant protein after addition of methanol to the culture. By subsequent manipulations of the same cells, expression of genes for the &agr;2 subunit of prolyl 4-hydroxylase of the invention described herein is achieved under conditions where a recombinant collagen protein is adequately hydroxylated by the prolyl 4-hydroxylase of the present invention and, therefore, can fold into a stable helix that is required for the normal biological function of the collagen in forming fibrils.

[0045] Another particularly preferred yeast expression system makes use of the methylotrophic yeast Hansenula polymorpha. Growth on methanol results in the induction of key enzymes of the methanol metabolism, namely MOX (methanol oxidase), DAS (dihydroxyacetone synthase) and FMHD (formate dehydrogenase). These enzymes can constitute up to 30-40% of the total cell protein. The genes encoding MOX, DAS, and FMDH production are controlled by very strong promoters which are induced by growth on methanol and repressed by growth on glucose. Any or all three of these promoters may be used to obtain high level expression of heterologous nucleic acid sequences in H. polymorpha. The nucleic acid sequence encoding a &agr;2 subunit of prolyl 4-hydroxylase of the invention is cloned into an expression vector under the control of an inducible H. polymorpha promoter. If secretion of the product is desired, a polynucleotide encoding a signal sequence for secretion in yeast, such as the S. cerevisiae prepro-mating factor &agr;1, is fused in frame with the coding sequence for the &agr;2 subunit of the prolyl 4-hydroxylase of the invention. The expression vector preferably contains an auxotrophic marker gene, such as URA3 or LEU2, which may be used to complement the deficiency of an auxotrophic host.

[0046] The expression vector is then used to transform H. polymorpha host cells using techniques known to those of skill in the art. An interesting and useful feature of H. polymorpha transformation is the spontaneous integration of up to 100 copies of the expression vector into the genome. In most cases, the integrated DNA forms multimers exhibiting a head-to-tail arrangement. The integrated foreign DNA has been shown to be mitotically stable in several recombinant strains, even under non-selective conditions. This phenomena of high copy integration further adds to the high productivity potential of the system.

[0047] In cases where plant expression vectors are used, the expression of sequences encoding the &agr;2 subunits of the invention may be driven by any of a number of promoters. For example, viral promoters such as the 35S RNA and 19S RNA promoters of CaMV (Brisson et al. (1984) Nature 310:511-514), or the coat protein promoter of TMV (Takamatsu et al. (1987) EMBO J. 6:307-311) may be used; alternatively, plant promoters such as the small subunit of RUBISCO (Coruzzi et al. (1984) EMBO J. 3:1671-1680; Broglie et al. (1984) Science 224:838-843); or heat shock promoters, e.g., soybean hsp17.5-E or hsp17.3-B (Gurley et al. (1986) Mol. Cell. Biol. 6:559-565) may be used. These constructs can be introduced into plant cells using Ti plasmids, Ri plasmids, plant virus vectors, direct DNA transformation, microinjection, electroporation, etc. For reviews of such techniques see, for example, Weissbach and Weissbach (1988) Methods for Plant Molecular Biology, Academic Press, New York, Section VIII, pp. 421-463; and Grierson and Corey (1988) Plant Molecular Biology, 2d Ed., Blackie, London, Ch. 7-9.

[0048] An alternative expression system which could be used to express the &agr;2 subunit of prolyl 4-hydroxylase of the invention is an insect system. In one such system, Autographa californica nuclear polyhidrosis virus (AcNPV) is used as a vector to express foreign genes. The virus grows in Spodoptera frugiperda cells. Coding sequence for the &agr;2 subunit of prolyl 4-hydroxylase of the invention may be cloned into non-essential regions (for example the polyhedron gene) of the virus and placed under control of an AcNPV promoter (for example, the polyhedron promoter). Successful insertion of a &agr;2 subunit of prolyl 4-hydroxylase coding sequence will result in inactivation of the polyhedron gene and production of non-occluded recombinant virus (i.e., virus lacking the proteinaceous coat coded for by the polyhedron gene). These recombinant viruses are then used to infect Spodoptera frugiperda cells in which the inserted gene is expressed. (See, e.g., Smith et al. (1983) J. Virol. 46:584; Smith, U.S. Pat. No. 4,215,051.)

[0049] In mammalian host cells, a number of viral based expression systems may be utilized. In cases where an adenovirus is used as an expression vector, coding sequence for the &agr;2 subunit prolyl 4-hydroxylase of the invention may be ligated to an adenovirus transcription/translation control complex, e.g., the late promoter and tripartite leader sequence. This gene may then be inserted in the adenovirus genome by in vitro or in vivo recombination. Insertion in a non-essential region of the viral genome (e.g., region E1 or E3) will result in a recombinant virus that is viable and capable of expressing the polypeptide in infected hosts. (See, e.g., Logan and Shenk (1984) Proc. Natl. Acad. Sci. USA 81:3655-3659.) Alternatively, the vaccinia 7.5 K promoter may be used. (See, e.g., Mackett et al. (1982) Proc. Natl. Acad. Sci. USA 79:7415-7419; Mackett et al. (1984) J. Virol. 49:857-864; and Panicali et al. (1982) Proc. Natl. Acad. Sci. 79:4927-4931.)

[0050] Specific initiation signals may also be required for efficient translation of inserted prolyl 4-hydroxylase coding sequences. These signals include the ATG initiation codon and adjacent sequences. In cases where the entire polypeptide gene, including its own initiation codon and adjacent sequences, is inserted into the appropriate expression vector, no additional translational control signals may be needed. However, in cases where only a portion of a coding sequence is inserted, exogenous translational control signals, including the ATG initiation codon, must be provided. Furthermore, the initiation codon must be in phase with the reading frame of the &agr;2 subunit of prolyl 4-hydroxylase coding sequence to ensure translation of the entire insert. These exogenous translational control signals and initiation codons can be of a variety of origins, both natural and synthetic. The efficiency of expression may be enhanced by the inclusion of appropriate transcription enhancer elements, transcription terminators, etc. (see Bittner et al. (1987) Methods in Enzymol. 153:516-544).

[0051] One preferred expression system for the recombinant production of the &agr;2 subunit of prolyl 4-hydroxylase of the invention is in transgenic non-human animals, wherein the desired polypeptide may be recovered from the milk of the transgenic animal. Such a system is constructed by operably linking the DNA sequence encoding the &agr;2 subunit of the invention to a promoter and other required or optional regulatory sequences capable of effecting expression in mammary glands. Likewise, required or optional post-translational enzymes may be produced simultaneously in the target cells, employing suitable expression systems, as disclosed in, inter alia, U.S. application, Ser. No. 8/037,728, operable in the targeted milk protein producing mammary gland cells.

[0052] For expression in milk, the promoter of choice would preferably be from one of the abundant milk-specific proteins, such as alpha S1-casein, or &bgr;-lactoglobulin. For example, 5′ and 3′ regulatory sequences of alpha S1-casein have been successfully used for the expression of the human lactoferrin cDNA, and similarly, the &bgr;-lactoglobin promoter has effected the expression of human antitrypsin gene fragments in sheep milk producing cells. Wright et al. (1991) Biotechnology 9:830-833. In transgenic goats, the whey acid promoter has been used for the expression of human tissue plasminogen activator, resulting in the secretion of human tissue plasminogen activator in the milk of the transgenics. Ebert et al. (1991) Biotechnology 9:835-838. Using such expression systems, animals are obtained which secrete the polypeptides of the invention into milk. Using procedures well-known by those of the ordinary skill in the art, the gene encoding the desired prolyl 4-hydroxylase chain can simply be ligated to suitable control sequences which function in the mammary cells of the chosen animal species. Expression systems for the genes encoding the &agr;2 subunit of prolyl 4-hydroxylase are constructed analogously.

[0053] Preferably, the prolyl 4-hydroxylase of the invention is expressed as a secreted protein. When the engineered cells used for expression of the proteins are non-human host cells, it is often advantageous to replace the human secretory signal peptide of the prolyl 4-hydroxylase protein with an alternative secretory signal peptide which is more efficiently recognized by the host cell's secretory targeting machinery. The appropriate secretory signal sequence is particularly important in obtaining optimal fungal expression of mammalian genes. For example, in methylotrophic yeasts, a DNA sequence encoding the in-reading frame S. cerevisiae &agr;-mating factor pre-pro sequence may be inserted at the amino-terminal end of the coding sequence. The &agr;MF pre-pro sequence is a leader sequence contained in the &agr;MF precursor molecule, and includes the lys-arg encoding sequence which is necessary for proteolytic processing and secretion (see, e.g., Brake et al. (1984) Proc. Natl. Acad. Sci. USA, 81:4642).

[0054] Also preferably, the &agr;2 subunits of prolyl 4-hydroxylase of the present invention are co-expressed by the host cell with a &bgr; subunit of prolyl 4-hydroxylase and/or collagen, as described generally in PCT Application No. PCT/US92/09061 (WO 93/07889), such that an &agr;2&bgr;2 prolyl 4-hydroxylase tetramer is formed and this enzyme catalyzes the formation of 4-hydroxyproline in the expressed collagen.

[0055] Alternatively, a host cell strain may be chosen which modulates the expression of the inserted sequences, or modifies and processes the gene product in the specific fashion desired. Such modifications (e.g., glycosylation) and processing (e.g., cleavage) of protein products may be important for the function of the protein. Different host cells have characteristic and specific mechanisms for the post-translational processing and modification of proteins. Appropriate cells lines or host systems can be chosen to ensure the correct modification and processing of the foreign protein expressed. To this end, eukaryotic host cells which possess the cellular machinery for proper processing of the primary transcript, glycosylation, and phosphorylation of the gene product may be used. Such mammalian host cells include but are not limited to CHO, VERO, BHK, HeLa, COS, MDCK, 293, W138, etc. Additionally, host cells may be engineered to express various enzymes to ensure the proper processing of the collagen molecules. For example, the genes for prolyl 4-hydroxylase (i.e., the gene encoding the a subunit or prolyl 4-hydroxylase and the gene encoding the &agr; subunit of prolyl 4-hydroxylase), may be coexpressed with the collagen gene in the host cell.

[0056] For long-term, high-yield production of recombinant proteins, stable expression is preferred. For example, cell lines which stably express an &agr;2 subunit of prolyl 4-hydroxylase of the invention may be engineered. Rather than using expression vectors which contain viral origins of replication, host cells can be transformed with &agr;2 subunit encoding DNA controlled by appropriate expression control elements (e.g., promoter, enhancer, sequences, transcription terminators, polyadenylation sites, etc.), and a selectable marker. Following the introduction of foreign DNA, engineered cells may be allowed to grow for 1-2 days in an enriched media, and then are switched to a selective media. The selectable marker in the recombinant plasmid confers resistance to the selection and allows cells to stably integrate the plasmid into their chromosomes and grow to form foci which in turn can be cloned and expanded into cell lines. This method may advantageously be used to engineer cell lines which express a desired &agr;2 subunit of prolyl 4-hydroxylase.

[0057] A number of selection systems may be used, including but not limited to the herpes simplex virus thymidine kinase (Wigler et al. (1977) Cell 11:223), hypoxanthine-guanine phosphoribosyltransferase (Szybalska & Szybalski (1962) Proc. Natl. Acad. Sci. USA 48:2026), and adenine phosphoribosyltransferase (Lowy et al. (1980) Cell 22:817) genes can be employed in tk−, hgprt− or aprt− cells, respectively. Also, antimetabolite resistance can be used as the basis of selection for dhfr, which confers resistance to methotrexate (Wigler et al. (1980) Natl. Acad. Sci. USA 77:3567; O'Hare et al. (1981) Proc. Natl. Acad. Sci. USA 78:1527); gpt, which confers resistance to mycophenolic acid (Mulligan and Berg (1981) Proc. Natl. Acad. Sci. USA 78:2072); neo, which confers resistance to the aminoglycoside G-418 (Colberre-Garapin et al. (1981) J. Mol. Biol. 150:1); and hygro, which confers resistance to hygromycin (Santerre et al. (1984) Gene 30:147). Recently, additional selectable genes have been described, namely trpB, which allows cells to utilize indole in place of tryptophan; hisD, which allows cells to utilize histinol in place of histidine (Hartman and Mulligan (1988) Proc. Natl. Acad. Sci. USA 85:8047); and ODC (omithine decarboxylase) which confers resistance to the omithine decarboxylase inhibitor, 2-(difluoromethyl)-DL-ornithine, DFMO (McConlogue L. (1987) In: Current Communications in Molecular Biology, Cold Spring Harbor Laboratory).

d. IDENTIFICATION OF TRANSFECTANTS OR TRANSFORMANTS THAT EXPRESS THE &agr;2 SUBUNIT PROTEIN OF THE INVENTION AND PURIFICATION OF THE EXPRESSED PROTEINS

[0058] The host cells which contain the coding sequence and which express the biologically active gene product may be identified by at least four general approaches; (a) DNA-DNA or DNA-RNA hybridization; (b) the presence or absence of “marker” gene functions; (c) assessing the level of transcription as measured by the expression of &agr;2 subunit mRNA transcripts in the host cell; and (d) detection of the gene product as measured by immunoassay or by its biological activity.

[0059] In the first approach, the presence of the enzyme coding sequence inserted in the expression vector can be detected by DNA-DNA or DNA-RNA hybridization using probes comprising nucleotide sequences that are homologous to the &agr;2 subunit of prolyl 4-hydroxylase coding sequence, respectively, or portions or derivatives thereof.

[0060] In the second approach, the recombinant expression vector/host system can be identified and selected based upon the presence or absence of certain “marker” gene functions (e.g., thymidine kinase activity, resistance to antibiotics, resistance to methotrexate, transformation phenotype, occlusion body formation in baculovirus, etc.). For example, if the &agr;2 subunit coding sequence is inserted within a marker gene sequence of the vector, recombinant cells containing coding sequence of the &agr;2 subunit of prolyl 4-hydroxylase can be identified by the absence of the marker gene function. Alternatively, a marker gene can be placed in tandem with the &agr;2 subunit sequence under the control of the same or different promoter used to control the expression of the &agr;2 subunit coding sequence. Expression of the marker in response to induction or selection indicates expression of the &agr;2 subunit coding sequence.

[0061] In the third approach, transcriptional activity of the &agr;2 subunit coding region can be assessed by hybridization assays. For example, RNA can be isolated and analyzed by Northern blot using a probe homologous to the &agr;2 subunit coding sequence or particular portions thereof. Alternatively, total nucleic acids of the host cell may be extracted and assayed for hybridization to such probes.

[0062] In the fourth approach, the expression of the enzyme product can be assessed immunologically, for example by Western blots, immunoassays such as radioimmuno-precipitation, enzyme-linked immunoassays and the like.

[0063] The expressed enzyme of the invention, which is secreted into the culture medium, is purified to homogeneity, e.g., by chromatography. In one embodiment, the recombinant &agr;2 subunit of prolyl 4-hydroxylase protein is purified by size exclusion chromatography.

[0064] However, other purification techniques known in the art can also be used, including ion exchange chromatography, and reverse-phase chromatography.

5. EXAMPLES

[0065] The invention will be further understood by reference to the following examples, which are intended to be purely exemplary of the invention.

Example 1

Isolation of Mouse CDNA Clones

[0066] A cDNA clone for the mouse &agr;2 subunit, designated BT14.1, was obtained from a BALB/c mouse brain cDNA library in &lgr;gt10 (Clontech, Palo Alto Calif.) by using as a probe, a cDNA encoding the thymic shared antigen 1, as described in MacNeil, et al. (1993) J. Immunol. 151:6913-23. The BT14.1 clone had a high degree of homology to the human and chicken prolyl 4-hydroxylase a subunit. The cDNA clone BT14.1, however, did not contain sequences coding for the N-terminal region of the polypeptide. It was therefore used as a probe to screen mouse brain and skeletal muscle cDNA libraries.

[0067] Among 600,000 recombinants, 4 positive clones were obtained. Two of them, M1 and M4 were found to be identical, while M2 had a deletion and M3 contained two unrelated inserts. The clone M1, was used to screen 1.6×106 plaques of a mouse skeletal muscle cDNA library in &lgr;gt10 (Clontech). One positive clone, M6, was obtained. This clone was characterized further and was found to be included in BT14.1. The 5′ ends of M1 and BT14.1 were at the same internal EcoRI site (at nucleotide position 220 of the sequence shown in FIG. 1). The extreme 5′ clone was isolated by using Ml to screen a mouse skeletal muscle cDNA library, and one positive clone was obtained, M6. As set forth below, at Example 2, the cDNA clones, considered in combination, cover the whole coding region of the mouse &agr;2 subunit. cDNA clones for the mouse &agr;1 subunit were then isolated by screening a 3T3 fibroblast &lgr;gt11 cDNA library (Clontech) with the human cDNA clone PA-49 for the &agr;1 subunit, as described in Helaakoski et al. (1989) Proc. Natl. Acad. Sci. USA 86:4392-96, and eight positive clones were obtained out of 600,000 plaques.

[0068] Three of these clones, MA3, MA4, and MA7, were isolated and sequenced. The nucleotide and predicted amino acid sequences of the clones showed a significant similarity to those of the human and chick prolyl 4-hydroxylase a subunit. Two of the clones, MA3 and MA4, were found to represent the mouse counterparts of human mRNA containing the alternatively spliced exon 10 sequences, whereas MA7 contained exon 9 sequences. The cDNA clones did not contain the extreme 5′ end of the mRNA. Comparison of the cDNA derived amino acid sequences with those of the human and chick &agr;1 subunits suggests that the cDNA clones cover the whole processed polypeptide but do not cover the 5′ untranslated region or the sequences corresponding to the N-terminal half of the signal peptide. See, GenBank database, accession no. U16162.

Example 2

Nucleotide Sequencing, Sequence Analysis, and Northern Blot Analysis

[0069] The nucleotide sequences for the clones described in Example 1 were determined by the dideoxynucleotide chain-termination method, as described in Sanger et al. (1977) Proc. Natl. Acad. Sci. USA 74:5463-67, with T7 DNA polymerase (Pharmacia, Peapack N.J.). Vector-specific or sequence-specific primers synthesized in an Applied Biosystems DNA synthesizer (Department of Biochemistry, University of Oulu) were used. The DNASIS and PROSIS version 6.00 sequence analysis software (Pharmacia), ANTHEPROT (as disclosed in Deleage et al. (1988) Comput. Appl. Biosci. 4:351-356), the Wisconsin Genetics Computer Group package version 8 (September 1994), and BOXSHADE (Kay Hofmann, Bioinformatics Group, Institut Suisse de Recherches Experimentales sur le Cancer Lausanne, Switzerland) were used to compile the sequence data.

[0070] The cDNA clones cover 2168 not of the corresponding mRNA and encode a 537-aa polypeptide (FIG. 1). A putative signal peptide is present at the N terminus of the deduced polypeptide, the most likely first amino acid of the mature &agr;2 subunit being tryptophan, based on the computational parameters of von Hejne (1986) Nucleic Acid Res. 14:4683-90, which means that the size of the signal sequence would be 19 aa and that of the processed &agr;2 subunit 518 aa. The molecular weight of the processed polypeptide is 59,000. The cDNA clones also cover 150 bp and 407 bp of the 5′ and 3′ untranslated sequences, respectively (FIG. 1). The 3′ untranslated sequence contains a canonical polyadenylylation signal, which is accompanied 12 nucleotides downstream by a poly(A) tail of 15 nucleotide position.

[0071] The mouse &agr;2 and mouse &agr;1 polypeptides are of similar sizes, &agr;2 being 518 and &agr;1 517 amino acids, assuming that the &agr;2 polypeptide begins with a tryptophan residue and &agr;1 with a histidine residue, as does the human &agr;1 polypeptide. The processed human &agr;1 subunit contains 517 amino acids and the chick &agr;1 subunit 516 amino acids (as described in Bassuk, et al., supra), whereas the processed C. elegans a subunit is longer, 542 aa (Veijola, et al., supra), the difference being mainly due to a 32 aa extension present in the C terminus of the polypeptide (FIG. 2).

[0072] The mouse &agr;2 and &agr;1 subunits contain two potential attachment sites for asparagine-linked oligosaccharides; the positions of the -Asn-Leu-Ser-and -Asn-Glu-Thr- sequences of the &agr;2 subunit are indicated in FIG. 1. The positions of the five cysteine residues present in the human, mouse, and chicken &agr;1 subunits and the C. elegans a subunit are all conserved in the &agr;2 subunit, but the latter contains an additional cysteine between the fourth and fifth cysteines of the &agr;1 subunits. Interestingly, this is located at a site where the conserved stretch of amino acids is also interrupted in the mouse &agr;1 and C. elegans a subunits.

[0073] The overall amino acid sequence identity and similarity between the mouse &agr;2 and mouse al subunits are 63% and 83%, respectively, and those between the mouse &agr;2 and C. elegans a subunits are 41% and 67%, respectively, which are almost the same as between the mouse &agr;1 and C. elegans a subunits, 43% and 67%. The identity is not distributed equally, however, being highest within the C-terminal domain, which is believed to represent the catalytically important part of the &agr;1 subunit (id.; Myllyla et al. (1992) Biochem. J. 286:923-927). The two histidines, residues 412 and 483 in the mouse &agr;1 subunit (FIG. 2), that have been suggested to be involved in the Fe2+ binding sites of prolyl 4-hydroxylase are both conserved and are both located within the conserved C-terminal domain.

[0074] A mouse multitissue Northern blot (Clontech) containing 2 &mgr;g of poly(A)′ RNA per sample isolated from various mouse tissues was hybridized under the stringent conditions suggested in the manufacture's instructions. The probe used was 32P labeled cDNA clone BT14.1 or MA7.

[0075] The expression patterns of both types of a &agr;-subunit mRNA were found to be very similar, the intensities of the hybridization signals being highest in the heart, lung, and brain. The size of the &agr;2 subunit mRNA was 2.4 kb. The mouse &agr;1 subunit was found to have two mRNA transcripts, at least in the heart, brain, and lungs: the more intense the signal was at 3.4 kb and the weaker one at 4.3 kb.

Example 3

Cell Cultures and Generation of Recombinant Baculoviruses

[0076] Since it was not known initially whether the &agr;2 polypeptide represented an a subunit of prolyl 4-hydroxylase, a subunit of prolyl 3-hydroxylase, or some other 2-oxoglutarate dioxygenase, a recombinant polypeptide was expressed in insect cells to elucidate its function. Specifically, Spodopiera frugiperda Sf9 insect cells were cultured at 27° C. in TNM-FH medium (Sigma-Aldrich, St. Louis Mo.) supplemented with 10% fetal bovine serum (Invitrogen). To construct an &agr;(11)-subunit cDNA for expression, the clone BT14.1 was digested with the BamHI and EcoRI restriction enzymes, giving a fragment encompassing bp 592-2168. The 5′ fragment was amplified from the X DNA of M6. The primers used were cDNA specific, M3PH (5′-AAGTTGCGGCCGCGAGCATCAGCAAGGTACTGC-3′) (SEQ ID NO: 19), containing an artificial NotI site and M65′PCR (5′-TCTCCGGATCCAGTTTGTACGTGTC-3′) (SEQ ID NO:20), containing a natural BamHI site. PCR was performed under the conditions recommended by the supplier of the Taq polymerase (Promega, Madison Wis.), and the reactions were cycled 27 times as follows: denaturation at 94° C. for 1 min, annealing at 66° C. for 1 min, and extension at 72° C. for 3 min. The product was digested with Not I and BamHI restriction enzymes to give a fragment that extended from bp 120 to 591. The two Not I-BamHI and BamNI-EcoRI fragments were then cloned into the PBLUESCRIPT vector (Stratagene, La Jolla Calif.), the construct was digested with Not I and EcoRV, and the resulting fragment was ligated into a Not I-Sma I site of the baculovirus transfer vector pVL1392, wherein said vector was obtained according to the methods described in Luckow and Summers (1989) Virology 170:31-39. The pVI construct was cotransfected into Sf9 insect cells with a modified Autographa californica nuclear polyhedrosis virus DNA by using the BACULOGOLD transfection kit (PharMingen, San Diego Calif.). The resultant viral pool was collected 4 days later, amplified, and plague purified. The recombinant virus was checked by PCR-based methods, as described in Malitschek and Schartl (1991) BioTechniques 11:177-178.

Example 4

Expression and Analysis of Recombinant Proteins

[0077] A recombinant baculovirus coding for the mouse &agr;2 subunit was generated and used to infect S. frugiperda insect cells with or without the human PDI/&bgr; subunit, wherein the insect cells were infected at a multiplicity of 5. For production of an enzyme tetramer, the human &agr;59 1 (see, Vuori, et al., supra) or mouse &agr;2 viruses and the PDI/&bgr; viruses (id.) were used in a 1:1 or 2:1 ratio. The cells were harvested 72 hours after infection, homogenized in 0.01 M tris, pH 7.8/0.1 M NaCl/0.1 M glycine/10 &mgr;M dithiothreitol/0.1% Triton X-100, and centrifuged. The resulting supematants were analyzed by SDS/8% PAGE or nondenaturing 7.5% PAGE and assayed for enzyme activities. The cell pellets were further solubilized in 1% SDS, and the 0.1% Triton X-100-soluble and 1% SDS-soluble proteins were analyzed by SDS/PAGE under reducing for the &agr;1 subunit of prolyl 4-hydroxylase (Veijola et al., supra; Vuori et al., supra; John et al. (1993) EMBO J. 2:1587-95). The polypeptide formed insoluble aggregates, and efficient extraction of the recombinant mouse &agr;2 subunit from the cell homogenates required the use of 1% SDS.

Example 5

Enzyme Activity Assays

[0078] Prolyl 4-hydroxylase activity was assayed by a method based on the decarboxylation of 2-oxoH 14C-glutarate, as disclosed in Kivirriko and Myllyla (1982) Methods Enzymol. 82:245-304. The Km values were determined by varying the concentration of one substrate in the presence of fixed concentrations of the second while the concentrations of the other substrates were kept constant, as set forth in Myllyla et al. (1977) Eur. J. Biochem. 80:349-357.

[0079] The 0.1% Triton X-100 extracts from cell homogenates containing either the mouse-human type II or the human type I enzyme were analyzed for prolyl 4-hydroxylase activity with an assay based on the hydroxylation-coupled decarbosylation of 2-oxo[114C]glutarate (Kivirikko and Myllyla, supra). The activities were very similar for both.

[0080] To show that the activity of the mouse/human type 2 enzyme was prolyl 4-hydroxylase activity, the amount of 4-hydroxyproline in a (Pro-Pro-Gly)10 substrate was determined after the reaction. The values indicated that the type 2 and type 1 enzymes behaved very similarly and that the activity of the type 2 enzyme was indeed prolyl 4-hydroxylase activity. The Km values for Fe2+, 2-oxoglutarate, and ascorbate and the Ki value for pyridine-2,4,-dicarboxylate, which acts as a competitive inhibitor with respect to 2-oxoglutarate, were likewise highly similar for the two enzymes, as shown in Table I. 1 TABLE I Km values for cosubstrates and the peptide substrate and K1 values for certain inhibitors of the human type 1 and mouse/human type 2 prolyl 4-hydroxylase tetramers. Km or Ki, &mgr;M Cosubstrate, substrate, or inhibitor Constant &agr;12&bgr;2 &agr;22&bgr;2 Fe2+ Km 4  4 2-Oxoglutatrate Km 22 12 Ascorbate Km 330 340  (Pro--Pro--Gly) Km 18 45 Poly(t-proline), Mt 7000 Ki 0.5 300* Poly(t-proline), Mt 44,000 Ki 0.02  30* Pyridine-2,4-dicarboxylate Ki 2  1 *Values determined as IC50.

[0081] Notably, the values differed distinctly in that the type 2 enzyme was inhibited by poly (L-proline) only at very high concentrations. As poly (L-proline) is a well-recognized, effective competitive inhibitor of type 1 prolyl 4-hydroxylase from all vertebrate sources studied and as poly (L-proline) is an effective polypeptide substrate for all plant prolyl 4-hydroxylases studied. Such finding was unexpected. Distinct differences thus appear to exist in the structures of the peptide binding sites of various prolyl 4-hydroxylases, but no detailed data are currently available on this aspect.

Example 6

Expression of the Mouse &agr;2 Subunit and an Active Mouse &agr;2 PDI/&bgr;Enzyme Tetramer in Insect Cells

[0082] Insect cells were coinfected with two recombinant viruses coding for the two polypeptides in order to study whether an association between the mouse &agr;2 subunit and the human PDI/&bgr;-subunit could be achieved. A hybrid protein was formed and was soluble in a buffer containing 0.1% Triton X-100, as shown by PAGE performed under nondenaturing conditions. The mouse &agr;2 subunit expressed alone did not give any extractable recombinant protein under the same conditions, termed here the type 1 tetramer, indicating that the hybrid protein is likely to be an &agr;22&bgr;2 tetramer, termed the type 2 tetramer. No difference was found in the association of the &agr;2 and &agr;1 subunits with the PDI/&bgr; subunit into the tetramer. To show that the hybrid protein formed contains the human PDI/&bgr; subunit, Western blotting was performed. When the mouse &agr;2 subunit was expressed together with the human PDI/&bgr; subunit, the protein complex contained the PDI/&bgr; subunit.

Example 7

Isolation and Sequencing of Human &agr;2 Subunit Gene

[0083] A human lung fibroblast genomic library (cloned in the lamda FIX vector (Stratagene)) and a human chromosome 5 library (cloned in the lamda vector Charon 40 (American Type Culture Collection, Manassas Va.)) were screened with probes comprising 32P-labelled nick-translated PCR fragments corresponding to the previously characterized human prolyl 4-hydroxylase a subunit cDNA sequence.

[0084] Positive clones from both the human lung fibroblast library and the human chromosome 5 library were identified, isolated and analyzed by southern blotting. Suitable fragments were subcloned into pSP72 vector (Promega) for further analysis.

[0085] Five positive clones, designated GL-2, GL-5, GL-20, GL-141 and GL-142 were obtained from the human lung fibroblast genomic library. Two of these clones, GL-2 and GL-141 were identical. Clones corresponding to the 5′ and 3′-ends of the gene encoding the &agr;2 subunit of prolyl 4-hydroxylase were not obtained.

[0086] The human chromosome 5 library was screened twice with two separate probes. The first probe corresponded to the 5′-end of the previously characterized cDNA sequence for &agr;2 subunit of prolyl 4-hydroxylase. The second probe corresponded to the 3′-end of the same cDNA sequence. Several positive clones were obtained, including GL-3, GL-4, GL-9, GL-11, GL-11B, and GL-156GL-3, GL-4, GL-9 and GL-11B corresponded to the 5′-end of the protein. GL-11A and GL-156 corresponded to the 3′-end of the protein clones GL-11A and GL-156 were found to be identical.

[0087] The derived sequence corresponding to the gene is more than 30 kb in size and is comprised of 15 exons. The exons that encode solely protein sequences vary from 54 to 240 base pairs and the introns vary from 241 to at least 3200 base pairs (see, FIGS. 2-9).

[0088] As compared to the gene sequence for the &agr;1 subunit, only one exon of the &agr;2 subunit corresponds to the two mutually exclusive spliced exons of the a l subunit gene (EXON 9 of the &agr;1 subunit gene).

[0089] The deduced amino acid sequence is 63% homologous to the known &agr;(1) subunit.

Example 8

Expression of the Human &agr;2 Subunit of Prolyl 4-Hydroxylase in Insect Cells

[0090] Using the methods of Examples 3, 4 and 6, the &agr;2 subunit isoform of prolyl 4-hydroxylase was expressed and analyzed. Expression data in insect cells demonstrated that the &agr;2 subunit isoform forms an active type 2 prolyl-4-hydroxyl &agr;2&bgr;2 tetramer with the human &bgr; subunit.

[0091] Various modifications of the invention, in addition to those shown and described herein, will become apparent to those skilled in the art from the foregoing description. Such modifications are intended to fall within the scope of the appended claims. It is also to be understood that all base pair sizes given for nucleotides are approximate and are used for purposes of description.

[0092] All references cited herein are hereby incorporated by reference in their entirety.

Claims

1. A polypeptide comprising a human isoform of the a subunit of prolyl 4-hydroxylase.

2. The polypeptide of claim 1 wherein the a subunit of prolyl 4-hydroxylase is an &agr;2 subunit.

3. The polypeptide of claim 2 wherein the amino acid sequence of said polypeptide comprises:

(a) the amino acid sequence of SEQ ID NO:3;

(b) fragments of the amino acid sequence of SEQ ID NO:3; or

(c) amino acid derivatives of the amino acid sequence of SEQ ID NO:3.