Cloning of the alpha subunit of prolyl 4-hydroxylase from Drosophila and expression and characterization of the corresponding enzyme tetramer with some unique properties.
Prolyl 4-hydroxylase catalyzes the formation of 4-hydroxyproline in collagens. The vertebrate enzymes are alpha2beta2 tetramers, whereas the Caenorhabditis elegans enzyme is an alphabeta dimer, the beta subunit being identical to protein-disulfide isomerase (PDI). We report here that the processed Drosophila melanogaster alpha subunit is 516 amino acid residues in length and shows 34 and 35% sequence identities to the two types of human alpha subunit and 31% identity to the C. elegans alpha subunit. Its coexpression in insect cells with the Drosophila PDI polypeptide produced an active enzyme tetramer, and small amounts of a hybrid tetramer were also obtained upon coexpression with human PDI. Four of the five recently identified critical residues at the catalytic site were conserved, but a histidine that probably helps the binding of 2-oxoglutarate to the Fe2+ and its decarboxylation was replaced by arginine 490. The enzyme had a higher Km for 2-oxoglutarate, a lower reaction velocity, and a higher percentage of uncoupled decarboxylation than the human enzymes. The mutation R490H reduced the percentage of uncoupled decarboxylation, whereas R490S increased the Km for 2-oxoglutarate, reduced the reaction velocity, and increased the percentage of uncoupled decarboxylation. The recently identified peptide-binding domain showed a relatively low identity to those from other species, and the Km of the Drosophila enzyme for (Pro-Pro-Gly)10 was higher than that of any other animal prolyl 4-hydroxylase studied. A 1. 9-kilobase mRNA coding for this alpha subunit was present in Drosophila larvae.
Annunen
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Collagen Research Unit, Biocenter and the Department of Medical Biochemistry, University of Oulu, FIN-90220 Oulu, Finland.
Koivunen
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Kivirikko
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D000595:Amino Acid Sequence; D000818:Animals; D003001:Cloning, Molecular; D004331:Drosophila melanogaster / Q000235:genetics*; D004789:Enzyme Activation; D017344:Genes, Insect; D006801:Humans; D008969:Molecular Sequence Data; D011393:Procollagen-Proline Dioxygenase / Q000096:biosynthesis / Q000235:genetics*; D016415:Sequence Alignment
D011393:Procollagen-Proline Dioxygenase