Protein hydroxylation: prolyl 4‐hydroxylase, an enzyme with four cosubstrates and a multifunctional subunit

Abstract

Prolyl 4-hydroxylase (EC 1.14.11.2) catalyzes the formation of 4-hydroxyproline in collagens by the hydroxylation of proline residues in X-Pro-Gly sequences. The reaction requires Fe2+, 2-oxoglutarate, O2, and ascorbate and involves an oxidative decarboxylation of 2-oxoglutarate. Ascorbate is not consumed during most catalytic cycles, but the enzyme also catalyzes decarboxylation of 2-oxoglutarate without subsequent hydroxylation, and ascorbate is required as a specific alternative oxygen acceptor in such uncoupled reaction cycles. A number of compounds inhibit prolyl 4-hydroxylase competitively with respect to some of its cosubstrates or the peptide substrate, and recently many suicide inactivators have also been described. Such inhibitors and inactivators are of considerable interest, because the prolyl 4-hydroxylase reaction would seem a particularly suitable target for chemical regulation of the excessive collagen formation found in patients with various fibrotic diseases. The active prolyl 4-hydroxylase is an alpha 2 beta 2 tetramer, consisting of two different types of inactive monomer and probably containing two catalytic sites per tetramer. The large catalytic site may be cooperatively built up of both the alpha and beta subunits, but the alpha subunit appears to contribute the major part. The beta subunit has been found to be identical to the enzyme protein disulfide isomerase and a major cellular thyroid hormone-binding protein and shows partial homology with a phosphoinositide-specific phospholipase C, thioredoxins, and the estrogen-binding domain of the estrogen receptor. The COOH-terminus of this beta subunit has the amino acid sequence Lys-Asp-Glu-Leu, which was recently suggested to be necessary for the retention of a polypeptide within the lumen of the endoplasmic reticulum. The alpha subunit does not have this COOH-terminal sequence, and thus one function of the beta subunit in the prolyl 4-hydroxylase tetramer appears to be to retain the enzyme within this cell organelle.

Molecular characterization of flayanone 3β‐hydroxylases

“…They are involved in a broad spectrum of primary and secondary biosynthetic pathways including the post-translational hydroxylation of proline and lysine residues in procollagens (Kivirikko et al, 1989), the biosynthesis of carnitine ) and blood-coagulation-factor VII (Stenflo et al, 1989) in mammals, the conversion of thymidine into uracil (Holme et al, 1970(Holme et al, , 1971Bankel et al, 1977) and of penicillins into cephalosporins (Baldwin and Abraham, 1988) in bacteria and fungi, the biosynthesis of clavulanic acid (Elson et al, 1987) and the macrolide antibioticum tylosin (Omura et al, 1984) in fungi, the formation of hydroxyproline-rich glycoproteins in plants (Chrispeels, 1969;Tanaka et al, 1980) and the biosynthesis of plant secondary products such a5 flavonoids Britsch et al, 1981), the alkaloids scopolamine (Hashimot0 and Yamada, 1986) and vindoline (De Carolis et al, 1990) and gibberellins (Hedden and Graebe, 1982).…”

Activation of the Prolyl Hydroxylase Oxygen-sensor Results in Induction of GLUT1, Heme Oxygenase-1, and Nitric-oxide Synthase Proteins and Confers Protection from Metabolic Inhibition to Cardiomyocytes

“…Three mammalian prolyl hydroxylase-domain-containing proteins (PHD 1, 2, and 3) have been identified and characterized as oxygen-sensing enzymes (2). This family of PHD enzymes depends upon the cofactors Fe 2ϩ , ␣-ketoglutarate, and ascorbate for hydroxylating activity (22). EDHB and DMOG are known to inhibit prolyl hydroxylation in C. elegans (16).…”

The prolyl 3-hydroxylases P3H2 and P3H3 are novel targets for epigenetic silencing in breast cancer

“…The prolyl 4-hydroxylases (P4H) have been extensively studied and are known to reside in either the endoplasmic reticulum (ER) or cytoplasm, where their function is to hydroxylate proline residues in the X-Pro-Gly sequence in collagens (Kivirikko et al, 1989) or to hydroxylate the 564 proline residue in the a-subunit of the hypoxia-inducible factor (HIF; Bruick and McKnight, 2001;Epstein et al, 2001;Ivan et al, 2001). The c-P4H enzymes have a key function in the biosynthesis of collagen allowing appropriate folding of the procollagen chains to form a triple helical structure (Myllyharju, 2003).…”