Prolyl 4-hydroxylase: molecular cloning and the primary structure of the alpha subunit from chicken embryo

Prolyl and lysyl hydroxylases in collagen synthesis

Collagens are the most abundant proteins in the extracellular matrix. They provide a framework to build organs and tissues and give structural support to make them resistant to mechanical load and forces. Several intra- and extracellular modifications are needed to make functional collagen molecules, intracellular post-translational modifications of proline and lysine residues having key roles in this. In this article, we provide a review on the enzymes responsible for the proline and lysine modifications, that is collagen prolyl 4-hydroxylases, 3-hydroxylases and lysyl hydroxylases, and discuss their biological functions and involvement in diseases.

Genes Differentially Expressed in Titanium Implant Healing

Bone generation occurs around titanium implants; however, its underlying mechanisms are unknown. We hypothesized that molecular determinants distinct from those undertaking normal bone healing regulate osseointegration. Using differential display-polymerase chain-reaction in the male rat model, we isolated 3 genes that are differentially expressed in bone healing with implants, but not in osteotomy healing. A homology search indicated that these 3 genes are apolipoprotein E, prolyl 4-hydroxylase α-subunit, and an unknown transcript. Differential expression of these genes was remarkable during early healing stages up to week 2, and accelerated with rough acid-etched surfaces compared with machined surfaces. The differential expression was confirmed in the female rats, with enhanced expression for the acid-etched surfaces. The osseointegration-unfavorable condition created by gonadal estrogen deficiency reduced the level of differential expression. This study provides evidence that selected gene transcripts are induced by titanium implants under regulatory control strongly associated with the nature of osseointegration.

Identifying specific proteins involved in eggshell membrane formation using gene expression analysis and bioinformatics

Background

The avian eggshell membranes surround the egg white and provide a structural foundation for calcification of the eggshell which is essential for avian reproduction; moreover, it is also a natural biomaterial with many potential industrial and biomedical applications. Due to the insoluble and stable nature of the eggshell membrane fibres, their formation and protein constituents remain poorly characterized. The purpose of this study was to identify genes encoding eggshell membrane proteins, particularly those responsible for its structural features, by analyzing the transcriptome of the white isthmus segment of the oviduct, which is the specialized region responsible for the fabrication of the membrane fibres.

Results

The Del-Mar 14 K chicken microarray was used to investigate up-regulated expression of transcripts in the white isthmus (WI) compared with the adjacent magnum (Ma) and uterine (Ut) segments of the hen oviduct. Analysis revealed 135 clones hybridizing to over-expressed transcripts (WI/Ma + WI/Ut), and corresponding to 107 NCBI annotated non-redundant Gallus gallus gene IDs. This combined analysis revealed that the structural proteins highly over-expressed in the white isthmus include collagen X (COL10A1), fibrillin-1 (FBN1) and cysteine rich eggshell membrane protein (CREMP). These results validate previous proteomics studies which have identified collagen X (α-1) and CREMP in soluble eggshell extracts. Genes encoding collagen-processing enzymes such as lysyl oxidase homologs 1, 2 and 3 (LOXL1, LOXL2 and LOXL3), prolyl 4 hydroxylase subunit α-2 and beta polypeptide (P4HA2 and P4HB) as well as peptidyl-prolyl cis-trans isomerase C (PPIC) were also over-expressed. Additionally, genes encoding proteins known to regulate disulfide cross-linking, including sulfhydryl oxidase (QSOX1) and thioredoxin (TXN), were identified which suggests that coordinated up-regulation of genes in the white isthmus is associated with eggshell membrane fibre formation.

Conclusions

The present study has identified genes associated with the processing of collagen, other structural proteins, and disulfide-mediated cross-linking during eggshell membrane formation in the white isthmus. Identification of these genes will provide new insight into eggshell membrane structure and mechanisms of formation that will assist in the development of selection strategies to improve eggshell quality and food safety of the table egg.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-2013-3) contains supplementary material, which is available to authorized users.

Proteomic analysis of the nuclear phosphorylated proteins in dairy cow mammary epithelial cells treated with estrogen

Estrogen regulates a variety of physiological processes, including mammary gland growth, morphogenesis of the mammary gland, proliferation and differentiation, and elevating the expression of milk proteins. Many nuclear phosphorylated proteins such as pStat5 and mTOR regulate milk protein synthesis. But the detail of milk protein synthesis controlled at the transcript level and posttranslational level is not well-known. To contribute to the understanding of the molecular mechanism underlying estrogen action on the dairy cow mammary epithelial cells (DCMECs), nuclear phosphorylated proteins regulated by estrogen in DCMECs were identified. Two-dimensional gel electrophoresis and matrix-assisted laser desorption/ionization/time of flight mass spectrometry were used to identify the changes of nuclear phosphorylated proteins in DCMECs treated with estrogen. Seven proteins were identified differentially up-expressed in DCMECs after 24-h estrogen exposure: including glycyl-tRNA synthetase, previously reported in milk protein synthesis of DCMECs, belonging to the class-II aminoacyl-tRNA synthetase family; proteins involved in other cellular functions, such as translation initiation factors, GTP-binding nuclear proteins, heat-shock proteins, and proteins belonging to ubiquitin-proteasome system. This screening reveals that estrogen influences the levels of nuclear phosphorylated proteins of DCMECs which opens new avenue for the study of the molecular mechanism linking to milk synthesis.

A novel platform for the production of nonhydroxylated gelatins based on the methylotrophic yeastHansenula polymorpha

The use of yeast as a host for heterologous expression of proteins that are normally derived from animal tissue is a promising way to ensure defined products that are devoid of potential harmful animal side products. Here we report on the production and secretion of a custom-designed gelatin, Hu3-His8, by the yeast Hansenula polymorpha. We observed that Hu3-His8 was poorly secreted by the heterologous Saccharomyces cerevisiae invertase secretion signal. In contrast, the S. cerevisiae mating factor alpha prepro sequence efficiently directed secretion into the culture medium. However, at higher copy numbers, intracellular accumulation of Hu3-His8 precursors occurred. Overproduction of Erv29p, a protein required for packaging of the glycosylated pro-alpha factor into COPII vesicles, did not improve gelatin secretion in the multicopy strain. Previously, H. polymorpha was reported to hydroxylate proline residues in gelatinous sequences. In contrast, we were unable to detect hydroxyprolines in the secreted Hu3-His8. Also, we failed to identify a gene encoding prolyl-4-hydroxylase in the H. polymorpha genome.

Production of human prolyl 4-hydroxylase in Escherichia coli

Prolyl 4-hydroxylase (P4H) catalyzes the post-translational hydroxylation of proline residues in collagen strands. The enzyme is an alpha2beta2 tetramer in which the alpha subunits contain the catalytic active sites and the beta subunits (protein disulfide isomerase) maintain the alpha subunits in a soluble and active conformation. Heterologous production of the native alpha2beta2 tetramer is challenging and had not been reported previously in a prokaryotic system. Here, we describe the production of active human P4H tetramer in Escherichia coli from a single bicistronic vector. P4H production requires the relatively oxidizing cytosol of Origami B(DE3) cells. Induction of the wild-type alpha(I) cDNA in these cells leads to the production of a truncated alpha subunit (residues 235-534), which assembles with the beta subunit. This truncated P4H is an active enzyme, but has a high Km value for long substrates. Replacing the Met235 codon with one for leucine removes an alternative start codon and enables production of full-length alpha subunit and assembly of the native alpha2beta2 tetramer in E. coli cells to yield 2 mg of purified P4H per liter of culture (0.2 mg/g of cell paste). We also report a direct, automated assay of proline hydroxylation using high-performance liquid chromatography. We anticipate that these advances will facilitate structure-function analyses of P4H.

Enhanced intrinsic biomechanical properties of osteoblastic mineralized tissue on roughened titanium surface

The biological mechanisms underlying bone-titanium integration and biomechanical properties of the integrated bone are poorly understood. This study assesses intrinsic biomechanical properties of mineralized tissue cultured on titanium having different surface topographies. The osteoblastic phenotypes associated with mineral deposition and collagen synthesis underlying the biomechanical modulation are also reported. Rat bone marrow-derived osteoblastic cells were cultured either on the machined titanium disc or acid-etched titanium disc. Nano-indentation study of day 28 culture revealed that the mineralized tissue on the acid-etched surface shows 3-3.5 times greater hardness than that on the machined surface (p < 0.01). Elastic modulus of the mineralized tissue was also 2.5-3 times greater on the acid-etched surface than on the machined surface (p < 0.01). After 28 days of culture, mineralized nodule area was significantly lower on the acid-etched surface than on the machined surface (p = 0.0105), while total calcium deposition did not differ between the two surfaces, indicating denser mineral deposition on the acid-etched surface. Osteopontin and osteocalcin gene expressions assayed by the reverse transcriptase-polymerase chain reaction were upregulated in the acid-etched titanium culture. Collagen synthesis measured by Sirius red stain-based colorimetry was 1.5-10 times higher on the acid-etched surface than on the machined surface in the initial culture period of day 1 to day 14 (p < 0.0001). The amount of collagen synthesis corresponded with the enhanced gene expression of prolyl 4-hydroxylase, a key enzyme for post-translational modification of collagen chains. Scanning electron microscopic images revealed that tissue cultured on the acid-etched titanium exhibited plate-like, compact surface morphology, while the tissue on the machined titanium appeared porous and was covered by fibrous and punctate structures. We conclude that culturing osteoblasts on rougher titanium surfaces enhances hardness and elastic modulus of the mineralized tissue, associated with condensed mineralization, accelerated collagen synthesis, and upregulated expression of selected bone-related genes.

The peptide-substrate-binding domain of human collagen prolyl 4-hydroxylases. Backbone assignments, secondary structure, and binding of proline-rich peptides

The collagen prolyl 4-hydroxylases (C-P4Hs) catalyze the formation of 4-hydroxyproline by the hydroxylation of proline residues in -Xaa-Pro-Gly-sequences. The vertebrate enzymes are alpha 2 beta 2 tetramers in which protein-disulfide isomerase serves as the beta subunit. Two isoforms of the catalytic alpha subunit have been identified and shown to form [alpha(I)]2 beta 2 and [alpha(II)]2 beta 2 tetramers, the type I and type II C-P4Hs, respectively. The peptide-substrate-binding domain of type I C-P4H has been shown to be located between residues 138 and 244 in the 517-residue alpha(I) subunit and to be distinct from the catalytic domain that is located in the C-terminal region. We report here that a recombinant human C-P4H alpha(I) polypeptide Phe144-Ser244 forms a folded domain consisting of five alpha helices and one short beta strand. This structure is quite different from those of other proline-rich peptide-binding modules, which consist mainly of beta strands. Binding of the peptide (Pro-Pro-Gly)2 to this domain caused major chemical shifts in many backbone amide resonances, the residues showing the largest shifts being mainly hydrophobic, including three tyrosines. The Kd values determined by surface plasmon resonance and isothermal titration calorimetry for the binding of several synthetic peptides to the alpha(I) and the corresponding alpha(II) domain were very similar to the Km and Ki values for these peptides as substrates and inhibitors of the type I and type II C-P4H tetramers. The Kd values of the alpha(I) and alpha(II) domains for (Gly-Pro-4Hyp)5 were much higher than those for (Pro-Pro-Gly)5, indicating a marked decrease in the affinity of hydroxylated peptides for the domain. Many characteristic features of the binding of peptides to the type I and type II C-P4H tetramers can thus be explained by the properties of binding to this domain rather than the catalytic domain.

Cell density regulates prolyl 4-hydroxylase activity independent of mRNA levels

In embryonic avian tendon, cell density regulates collagen production. This control is propagated through the alpha-subunit of prolyl 4-hydroxylase where protein levels were previously shown to rise fivefold with increasing cell density. In contrast, mRNA levels are now shown not to change by both Northern and RNAse protection assays. This lack of increase contrasts with previous reports as does the mRNA length: this is 50% larger as confirmed by sequencing the 3' end. Alternative sites for cell density regulation of the enzyme could rely on its sensitivity to sulfhydryl groups. Using a fluorescent sulfhydryl probe as well as a sulfhydryl inhibitor, one observes a strong cell density response, supporting the hypothesis that cellular redox potential could alter protein stability.

Production of recombinant human type I procollagen trimers using a four-gene expression system in the yeast Saccharomyces cerevisiae

The expression of stable recombinant human collagen requires an expression system capable of post-translational modifications and assembly of the procollagen polypeptides. Two genes were expressed in the yeast Saccharomyces cerevisiae to produce both propeptide chains that constitute human type I procollagen. Two additional genes were expressed coding for the subunits of prolyl hydroxylase, an enzyme that post-translationally modifies procollagen and that confers heat (thermal) stability to the triple helical conformation of the collagen molecule. Type I procollagen was produced as a stable heterotrimeric helix similar to type I procollagen produced in tissue culture. A key requirement for glutamate was identified as a medium supplement to obtain high expression levels of type I procollagen as heat-stable heterotrimers in Saccharomyces. Expression of these four genes was sufficient for correct assembly and processing of type I procollagen in a eucaryotic system that does not produce collagen.

Prolyl 4-hydroxylase is required for viability and morphogenesis in Caenorhabditis elegans

The genome of Caenorhabditis elegans possesses two genes, dpy-18 and phy-2, that encode alpha subunits of the enzyme prolyl 4-hydroxylase. We have generated deletions within each gene to eliminate prolyl 4-hydroxylase activity from the animal. The dpy-18 mutant has an aberrant body morphology, consistent with a role of prolyl 4-hydroxylase in formation of the body cuticle. The phy-2 mutant is phenotypically wild type. However, the dpy-18; phy-2 double mutant is not viable, suggesting an essential role for prolyl 4-hydroxylase that is normally accomplished by either dpy-18 or phy-2. The effects of the double mutation were mimicked by small-molecule inhibitors of prolyl 4-hydroxylase, validating the genetic results and suggesting that C. elegans can serve as a model system for the discovery of new inhibitors.

Collagen hydroxylases and the protein disulfide isomerase subunit of prolyl 4-hydroxylases

Prolyl 4-hydroxylases catalyze the formation of 4-hydroxyproline in collagens and other proteins with an appropriate collagen-like stretch of amino acid residues. The enzyme requires Fe(II), 2-oxoglutarate, molecular oxygen, and ascorbate. This review concentrates on recent progress toward understanding the detailed mechanism of 4-hydroxylase action, including: (a) occurrence and function of the enzyme in animals; (b) general molecular properties; (c) intracellular sites of hydroxylation; (d) peptide substrates and mechanistic roles of the cosubstrates; (e) insights into the development of antifibrotic drugs; (f) studies of the enzyme's subunits and their catalytic function; and (g) mutations that lead to Ehlers-Danlos Syndrome. An account of the regulation of collagen hydroxylase activities is also provided.

Baculovirus expression of two protein disulphide isomerase isoforms from Caenorhabditis elegans and characterization of prolyl 4-hydroxylases containing one of these polypeptides as their beta subunit

Protein disulphide isomerase (PDI; EC 5.3.4.1) is a multifunctional polypeptide that is identical to the beta subunit of prolyl 4-hydroxylases. We report here on the cloning and expression of the Caenorhabditis elegans PDI/beta polypeptide and its isoform. The overall amino acid sequence identity and similarity between the processed human and C. elegans PDI/beta polypeptides are 61% and 85% respectively, and those between the C. elegans PDI/beta polypeptide and the PDI isoform 46% and 73%. The isoform differs from the PDI/beta and ERp60 polypeptides in that its N-terminal thioredoxin-like domain has an unusual catalytic site sequence -CVHC-. Expression studies in insect cells demonstrated that the C. elegans PDI/beta polypeptide forms an active prolyl 4-hydroxylase alpha 2 beta 2 tetramer with the human alpha subunit and an alpha beta dimer with the C. elegans alpha subunit, whereas the C. elegans PDI isoform formed no prolyl 4-hydroxylase with either alpha subunit. Removal of the 32-residue C-terminal extension from the C. elegans alpha subunit totally eliminated alpha beta dimer formation. The C. elegans PDI/beta polypeptide formed less prolyl 4-hydroxylase with both the human and C. elegans alpha subunits than did the human PDI/beta polypeptide, being particularly ineffective with the C. elegans alpha subunit. Experiments with hybrid polypeptides in which the C-terminal regions had been exchanged between the human and C. elegans PDI/beta polypeptides indicated that differences in the C-terminal region are one reason, but not the only one, for the differences in prolyl 4-hydroxylase formation between the human and C. elegans PDI/beta polypeptides. The catalytic properties of the C. elegans prolyl 4-hydroxylase alpha beta dimer were very similar to those of the vertebrate type II prolyl 4-hydroxylase tetramer, including the K(m) for the hydroxylation of long polypeptide substrates.

Co-expression of the alpha subunit of human prolyl 4-hydroxylase with BiP polypeptide in insect cells leads to the formation of soluble and insoluble complexes. Soluble alpha-subunit-BiP complexes have no prolyl 4-hydroxylase activity

Prolyl 4-hydroxylase (EC 1.14.11.2) catalyses the post-translational formation of 4-hydroxyproline in collagens. The vertebrate enzymes are alpha2beta2 tetramers, their beta subunit being identical to protein disulphide isomerase (PDI). The function of the PDI-beta subunit in prolyl 4-hydroxylases is not fully understood, but it seems to be that of keeping the highly insoluble alpha subunits in solution. We report here that expression of the alpha subunit of human type I prolyl 4-hydroxylase in insect cells together with BiP polypeptide leads to the formation of both soluble and insoluble alpha-subunit-BiP complexes. Formation of the soluble complexes was evident from (1) a marked increase in the amount of the alpha subunit in the soluble fraction of the cell homogenates when expressed together with BiP, (2) immunoprecipitation experiments and (3) demonstration of the presence of some of the complexes by polyacrylamide gel electrophoresis under non-denaturing conditions. Formation of the insoluble complexes was suggested by an increase in the amount of BiP in the insoluble fraction when expressed together with the alpha subunit. Nevertheless the soluble alpha-subunit-BiP complexes had no prolyl 4-hydroxylase activity. This indicates that the function of the PDI-beta subunit in the prolyl 4-hydroxylase tetramer is not only that of keeping the alpha subunits in solution but appears to be more specific, probably that of keeping them in a catalytically active, non-aggregated conformation.

Cloning, baculovirus expression, and characterization of a second mouse prolyl 4-hydroxylase alpha-subunit isoform: formation of an alpha 2 beta 2 tetramer with the protein disulfide-isomerase/beta subunit

Prolyl 4-hydroxylase (EC 1.14.11.2) catalyzes the posttranslational formation of 4-hydroxyproline in collagens. The vertebrate enzyme is an alpha 2 beta 2 tetramer, the beta subunit of which is a highly unusual multifunctional polypeptide, being identical to protein disulfide-isomerase (EC 5.3.4.1). We report here the cloning of a second mouse alpha subunit isoform, termed the alpha (II) subunit. This polypeptide consists of 518 aa and a signal peptide of 19 aa. The processed polypeptide is one residue longer than the mouse alpha (I) subunit (the previously known type), the cloning of which is also reported here. The overall amino acid sequence identity between the mouse alpha (II) and alpha (I) subunits is 63%. The mRNA for the alpha (II) subunit was found to be expressed in a variety of mouse tissues. When the alpha (II) subunit was expressed together with the human protein disulfide-isomerase/beta subunit in insect cells by baculovirus vectors, an active prolyl 4-hydroxylase was formed, and this protein appeared to be an alpha (II) 2 beta 2 tetramer. The activity of this enzyme was very similar to that of the human alpha (I) 2 beta 2 tetramer, and most of its catalytic properties were also highly similar, but it differed distinctly from the latter in that it was inhibited by poly(L-proline) only at very high concentrations. This property may explain why the type II enzyme was not recognized earlier, as an early step in the standard purification procedure for prolyl 4-hydroxylase is affinity chromatography on a poly(L-proline) column.

Site-directed mutagenesis of the alpha subunit of human prolyl 4-hydroxylase. Identification of three histidine residues critical for catalytic activity

Prolyl 4-hydroxylase (EC 1.14.11.2) catalyzes the formation of 4-hydroxyproline in collagens. The vertebrate enzyme is an alpha 2 beta 2 tetramer in which the alpha subunits contribute to most parts of the two catalytic sites. To study the roles of histidine and cysteine residues in this catalytic activity we converted all 5 histidines that are conserved between species, 4 nonconserved histidines, and 3 conserved cysteines of the human alpha subunit individually to serine and expressed the mutant alpha subunits together with the wild-type beta subunit in insect cells by means of baculovirus vectors. Mutation of any of the 3 conserved histidines, residues 412, 483, and 501, inactivated the enzyme completely or essentially completely, with no effect on tetramer assembly or binding of the tetramer to poly(L-proline). These histidines are likely to provide the three ligands needed for the binding of Fe2+ to a catalytic site. Mutation of either of the other 2 conserved histidines reduced the amount of enzyme tetramer by 20-25% and the activity of the tetramer by 30-60%. Mutation of the nonconserved histidine 324 totally prevented tetramer assembly, whereas mutation of the 3 other nonconserved histidines had no effects. Two of the 3 cysteine to serine mutations, those involving residues 486 and 511, totally prevented tetramer assembly under the present conditions, whereas the third, involving residue 150, had only a minor effect in reducing tetramer assembly and activity. The data do not support previous suggestions that cysteine residues are involved in Fe2+ binding sites. Additional mutagenesis experiments demonstrated that the two glycosylated asparagines have no role in tetramer assembly or catalytic activity.

A fully active catalytic domain of bovine aspartyl (asparaginyl) beta-hydroxylase expressed in Escherichia coli: characterization and evidence for the identification of an active-site region in vertebrate alpha-ketoglutarate-dependent dioxygenases

The alpha-ketoglutarate-dependent dioxygenase aspartyl (asparaginyl) beta-hydroxylase (EC 1.14.11.16) specifically hydroxylates one aspartic or asparagine residue in certain epidermal growth factor-like domains of a number of proteins. The expression in Escherichia coli, purification, characterization of a fully active catalytic domain, and evidence for the identification of an active-site region of this enzyme are described. Sequence alignment analyses among the vertebrate alpha-ketoglutarate-dependent dioxygenases and chemical modification studies were undertaken aimed at locating specific regions of 52-kDa recombinant aspartyl (asparaginyl) beta-hydroxylase involved in substrate binding and/or catalysis. Based upon these studies, an alignment of the C-terminal regions of prolyl and lysyl hydroxylase and of aspartyl (asparaginyl) beta-hydroxylase is proposed. When histidine-675, an invariant residue located in a region of homology within this alignment, was mutated to an alanine residue in aspartyl (asparaginyl) beta-hydroxylase (H675A), no enzymatic activity was detected. Chemical modification studies show that the wild-type protein is protected from iodo[14C]acetamide labeling by Fe2+/alpha-ketoglutarate whereas the H675A mutant protein is not, suggesting that this mutant does not bind Fe2+/alpha-ketoglutarate.

The myrosinase (thioglucoside glucohydrolase) gene family in Brassicaceae

The glucosinolate hydrolyzing enzymes myrosinase (thioglucoside glucohydrolase, EC 3.2.3.1) are encoded by a multigene family consisting of two subgroups. The first two nuclear genes representing each of these two subgroups of the new gene family, Myr1.Bn1 and Myr2.Bn1, from Brassica napus have been cloned and sequenced. Based on conserved regions in cDNA of three species, PCR (polymerase chain reaction) primers were made, and used to amplify and characterize the structure of the myrosinase genes in seven species of Brassicaceae. Southern hybridization analysis of PCR products and genomic DNA indicates that myrosinase is encoded by at least 14 genes in B. napus, with similar numbers in the other species of Brassicaceae investigated. The Myr1 gene cloned from B. napus has a 19 amino acid signal peptide and consists of 11 exons of sizes ranging from 54 to 256 bp and 10 introns of sizes from 75 to 229 bp. The Myr2 gene has a 20 amino acid signal peptide and consists of 12 exons ranging in size from 35 to 262 bp and 11 introns of sizes from 81 to 131 bp. The exons from the two genes have 83% homology at the amino acid level. The intron-exon splice sites are of GT..AG consensus type. The signal peptides and presence of sites for N-linked glycosylation, suggest transport and glycosylation through the ER-Golgi complex. The differences between the two genes are discussed on the basis of their predicted expression at different developmental stages in the plant. Both genes show homology to a conserved motif representing the glycosyl hydrolase family of enzymes.

gamma-Butyrobetaine hydroxylase. Structural characterization of the Pseudomonas enzyme

gamma-Butyrobetaine hydroxylase is a 2-oxoglutarate-dependent dioxygenase that catalyzes the hydroxylation of gamma-butyrobetaine to carnitine, the last step in the biosynthesis of carnitine from lysine. The primary structure of the enzyme from Pseudomonas sp. AK1 has been determined. Sequence analysis of the intact protein and of peptides from essentially three different digests established the presence of a peptide chain containing 383 residues, and an N-terminal truncated form of 382 residues. The two chains have molecular masses of 43,321 Da and 43,207 Da, respectively, and are identical except for the presence or absence of an N-terminal asparagine residue; the shorter form starts with an alanine residue. In preparations of the dimeric protein, the two chains occur in an approximate ratio of 1:1. There are nine cysteine residues and 13 histidine residues, i.e. amino acids which have been postulated as ligands for iron binding. In spite of functional similarities, there appears to be no clear sequence similarities with any of the other mammalian 2-oxoglutarate-dependent dioxygenases so far characterized.

Human 4-hydroxyphenylpyruvate dioxygenase. Primary structure and chromosomal localization of the gene

We report the primary structure of 4-hydroxyphenylpyruvate dioxygenase [4-hydroxyphenyl-pyruvate:oxygen oxidoreductase (hydroxylating, decarboxylating)]. The work is based on the isolation of cDNA clones from human liver lambda gt11 libraries. Several overlapping clones covering the coding sequence were characterized. In parallel, peptides from four different digests of the purified protein were analysed for their amino-acid sequence. These peptide sequences covered 86% of the cDNA-derived amino-acid sequence. This gives the sequence for a polypeptide of 392 amino acids with a calculated molecular mass of 44.8 kDa. There is more than 80% identity between the human and the pig enzymes and also between these enzymes and the F antigen from rat and the two allelic forms of this antigen from mouse. The enzyme has 53% conserved amino acids and 27% identical amino acids in common with 4-hydroxyphenylpyruvate dioxygenase from Pseudomonas sp. P.J. 874 and 52% conserved and 28% identical residues, with a protein from Shewanella colwelliana. At the C-terminus there is 61% identity between the seven proteins. These results indicate that these proteins are all 4-hydroxyphenylpyruvate dioxygenases. The identity of the C-terminus makes this part of the molecule a candidate for a functional role in the catalytic process. At conserved positions in all seven enzymes, there are two tyrosine residues and three histidine residues, i.e. amino acids which have been implicated as ligands for iron in 2-oxoacid-dependent dioxygenases. The gene encoding the enzyme was localized to chromosome 12q14-->qter by Southern-blot analysis of human-rodent somatic-cell hybrids.

Characterization of a partial cDNA for lysyl hydroxylase from human skin fibroblasts; lysyl hydroxylase mRNAs are regulated differently by minoxidil derivatives and hydralazine

Lysyl hydroxylase (LH) is an essential enzyme in collagen biosynthesis that catalyzes the formation of hydroxylysine required for intermolecular crosslinking of collagen. We have isolated a partial (2.2-kb) cDNA for LH from human skin fibroblasts using PCR. DNA sequencing revealed 72% homology of the human coding sequence with the chick LH sequence at the nucleotide level and 76% homology predicted at the amino acid level. The LH cDNA hybridized strongly with two mRNA species of 2.4 and 3.4 kb on Northern blots of normal fibroblast RNA. Administration of minoxidil decreased both mRNA species without affecting levels of the mRNAs for the beta subunit of prolyl 4-hydroxylase (PH) or alpha 1(I) collagen. Two derivatives of minoxidil (3' hydroxyminoxidil and 4' hydroxyminoxidil) produced similar decreases in LH mRNAs. In contrast hydralazine increased the mRNAs for LH in parallel with its previously reported effect on the mRNA for the beta subunit of PH. This effect is accompanied by virtual elimination of the alpha 1(I) collagen mRNAs. These results on the action of minoxidil and hydralazine at the pretranslational level correlate well with their previously reported effect on enzyme activity and collagen biosynthesis and indicate that changes in steady-state mRNA levels can account directly for changes at the protein level. Moreover, the unique action of minoxidil in specifically decreasing LH mRNAs contrasts with the less specific stimulatory effects of hydralazine and suggests that these pharmaceuticals are regulating expression of LH at a pretranslational level by different mechanisms.

Site-directed mutagenesis of human protein disulphide isomerase: effect on the assembly, activity and endoplasmic reticulum retention of human prolyl 4-hydroxylase in Spodoptera frugiperda insect cells

Protein disulphide isomerase (PDI) is a highly unusual multifunctional polypeptide, identical to the beta-subunit of prolyl 4-hydroxylase. It has two -Cys-Gly-His-Cys- sequences which represent two independently acting catalytic sites of PDI activity. We report here on the expression in baculovirus vectors of various mutant PDI/beta-subunits together with a wild-type alpha-subunit of the human prolyl 4-hydroxylase alpha 2 beta 2 tetramer in Spodoptera frugiperda insect cells. When either one or both of the -Cys-Gly-His-Cys- sequences was converted to -Ser-Gly-His-Cys-, a tetramer was formed as with wild-type PDI/beta-subunit. This tetramer was fully active prolyl 4-hydroxylase. The data demonstrate that PDI activity of the PDI/beta-subunit is not required for tetramer assembly or for the prolyl 4-hydroxylase activity of the tetramer, and thus other sequences of the PDI/beta-subunit may be critical for keeping the alpha-subunits in a catalytically active, non-aggregated conformation. Measurements of the PDI activities of tetramers containing the various mutant PDI/beta-subunits demonstrated that the activity of the wild-type tetramer is almost exclusively due to the C-terminal PDI catalytic sites, which explains the finding that the PDI activity of the PDI/beta-subunit present in the tetramer is about half that in the free polypeptide.(ABSTRACT TRUNCATED AT 250 WORDS)

Modification of vertebrate and algal prolyl 4-hydroxylases and vertebrate lysyl hydroxylase by diethyl pyrocarbonate. Evidence for histidine residues in the catalytic site of 2-oxoglutarate-coupled dioxygenases

A search for conserved amino acid residues within the cDNA-derived amino acid sequences of 2-oxoglutarate-coupled dioxygenases revealed the presence of two distinct motifs, spaced 49-71 amino acids apart, toward the C-terminal regions of these proteins. Each of the two common motifs contains an invariant histidine residue at a conserved position. The 2-oxoglutarate-coupled dioxygenases function in diverse processes, including the post-translational hydroxylation of proline and lysine residues in vertebrate collagens and the biosynthesis of microbial cephalosporins, yet they have a common reaction mechanisms, which requires the binding of Fe2+, 2-oxoglutarate, O2 and ascorbate at the catalytic site. The two regions of homology, and specifically the identical histidines, potentially represent functionally important sites related to their catalytic activity. Modification of histidine residues by diethyl pyrocarbonate inactivated vertebrate and algal prolyl 4-hydroxylase and vertebrate lysyl hydroxylase, indicating that histidine residues function in the catalytic site of these 2-oxoglutarate-coupled dioxygenases. Inactivation was prevented by the presence of co-substrates, but not by the peptide substrate. It is proposed that the histidine residues in the conserved motifs may function as Fe(2+)-binding ligands.

Characterization of the human prolyl 4-hydroxylase tetramer and its multifunctional protein disulfide-isomerase subunit synthesized in a baculovirus expression system

Prolyl 4-hydroxylase (EC 1.14.11.2), an alpha 2 beta 2 tetramer, catalyzes the posttranslational formation of 4-hydroxyproline in collagens. The enzyme can easily be dissociated into its subunits, but all attempts to associate a tetramer from the dissociated subunits in vitro have been unsuccessful. Molecular cloning of the catalytically important alpha subunit has identified two types of cDNA clone due to mutually exclusive alternative splicing. The beta subunit is a highly unusual multifunctional polypeptide, being identical to the enzyme protein disulfide-isomerase (EC 5.3.4.1). We report here on expression of the alpha and beta subunits of prolyl 4-hydroxylase and a fully active enzyme tetramer in Spodoptera frugiperda insect cells by baculovirus vectors. When the beta subunit was expressed alone, the polypeptide produced was found in a 0.1% Triton X-100 extract of the cell homogenate and was a fully active protein disulfide-isomerase. When either form of the alpha subunit was expressed alone, only traces of the alpha subunit could be extracted from the cell homogenate with 0.1% Triton X-100, and 1% SDS was required to obtain efficient solubilization. These alpha subunits had no prolyl 4-hydroxylase activity. When the cells were coinfected with both alpha- and beta-subunit-producing viruses, an enzyme tetramer was formed, but significant amounts of alpha and beta subunits remained unassociated. The recombinant tetramer was indistinguishable from that isolated from vertebrate tissue in terms of its specific activity and kinetic constants for cosubstrates and the peptide substrate. The two alternatively spliced forms of the alpha subunit gave enzyme tetramers with identical catalytic properties. Baculovirus expression seems to be an excellent system for mass production of the enzyme tetramer and for detailed investigation of the mechanisms involved in the association of the monomers.

Minoxidil specifically decreases the expression of lysine hydroxylase in cultured human skin fibroblasts

The levels of lysine hydroxylase protein and the levels of the mRNAs for lysine hydroxylase and the alpha- and beta-subunits of proline 4-hydroxylase were measured in cultured human skin fibroblasts treated with 1 mM-minoxidil. The data demonstrate that minoxidil decreases the amount of lysine hydroxylase protein, this being due to a decrease in the level of lysine hydroxylase mRNA. The effect of minoxidil appears to be highly specific, as no changes were observed in the amounts of mRNAs for the alpha- and beta-subunits of proline 4-hydroxylase.

Comparison between avian and human prolyl 4-hydroxylases: studies on the holomeric enzymes and their constituent subunits

Prolyl 4-hydroxylase, a key enzyme in collagen biosynthesis, catalyzes the conversion of selected prolyl residues to trans-hydroxyproline in nascent or completed pro-alpha chains of procollagen. The enzyme is a tetramer composed of two nonidentical subunits, designated alpha and beta. To compare the enzyme and its subunits from different sources, the chick embryo and human placental prolyl 4-hydroxylases were purified to homogeneity and their physicochemical and immunological properties were determined. Both enzymes were glycoproteins with estimated apparent molecular weights ranging between 400 and 600 kDa. Amino acid and carbohydrate analyses showed slight differences between the two holomeric enzymes, consistent with their deduced amino acid sequences from their respective cDNAs. Human placental prolyl 4-hydroxylase contained more tightly bound iron than the chick embryo enzyme. Immunodiffusion of the human placental enzyme with antibodies raised against the purified chick embryo prolyl 4-hydroxylase demonstrated partial identity, indicating different antigenic determinants in their tertiary structures. The enzymes could be separated by high-resolution capillary electrophoresis, indicating differential charge densities for the native chick embryo and human placental proteins. Electrophoretic studies revealed that the human prolyl 4-hydroxylase is a tetrameric enzyme containing two nonidentical subunits of about 64 and 62 kDa, in a ratio of approximately 1 to 2, designated alpha and beta, respectively. In contrast, the chick embryo alpha and beta subunit ratio was 1 to 1. Notably, the human alpha subunit was partially degraded when subjected to electrophoresis under denaturing conditions. Analogously, when the chick embryo enzyme was subjected to limited proteolysis, selective degradation of the alpha subunit was observed. Finally, only the alpha subunit was bound to Concanavalin A demonstrating that the alpha subunits of prolyl 4-hydroxylase in both species were glycosylated. Using biochemical techniques, these results demonstrated that the 4-trans-hydroxy-L-proline residues in human placental collagens are synthesized by an enzyme whose primary structure and immunological properties differ from those of the previously well-characterized chick embryo enzyme, consistent with their recently deduced primary structures from cDNA sequences.

Protein disulphide isomerase from human peripheral blood neutrophils

Protein disulphide isomerase (PDI) is a 56 kDa resident polypeptide of the endoplasmic reticulum of many cell types. We evaluated the ability of human peripheral blood polymorphonuclear neutrophils (PMN) to synthesize both mRNA and proteins. Using in vitro [35S]-methionine labeling of purified PMN, followed by immunoprecipitation of cell lysates with immobilized polyclonal and monoclonal antibodies and analysis by gel electrophoresis, PMN were shown to synthesize many proteins, including actin. In contrast, incorporation of [35S]-methionine into PDI was not detected. Purification of total RNA from PMN and analysis by Northern blots demonstrated the presence in PMN of PDI-RNA. Western immunoblot evaluations of total PMN protein display an immunoreactive-PDI of 56 kDa. Indirect immunofluorescence studies suggest an abundance of immunoreactive-PDI throughout PMN. We therefore conclude that PDI is synthesized in precursor cells of the bone marrow. Phorbol 12-myristate 13-acetate, a reagent known to affect the degranulation of specific granules, causes the release of immunoreactive-PDI into a post-centrifugation supernatant. PDI, a ubiquitous endoplasmic reticulum resident protein, is shown here to be associated with specific granules in a cell type which has lost its intracellular membrane network during terminal differentiation.