Abstract

Lysyl hydroxylase (EC 1.14.11.4, procollagen-lysine 2-oxoglutarate 5-dioxygenase, PLOD) catalyzes the hydroxylation of lysine residues in collagens and other proteins. It occurs as a post-translational event. The hydroxylysine residues participate in the formation of covalent cross-links to stabilize the collagenous structure in tissues. The hydroxylysine residues can be glycosylated to galactosyl- or glucosylgalactosylhydroxylysine residues.

Novel human lysyl hydroxylases, 2a, 2b and 3 isoforms, were characterized in this study. Lysyl hydroxylases 2a and 2b are alternatively spliced forms of lysyl hydroxylase 2. Lysyl hydroxylase 2b contains an additional exon of 63 nucleotides. The polypeptide size of lysyl hydroxylase 2a is 737 amino acids, lysyl hydroxylase 2b is 758 amino acids and lysyl hydroxylase 3 is 738 amino acids. The putative signal peptide is 25 amino acids in lysyl hydroxylases 2a and 2band 24 amino acids in lysyl hydroxylase 3. Lysyl hydroxylases 2aand 2b contain 7 possible N-glycosylation sites and lysyl hydroxylase3 contains 2 sites.

Tissue distribution of novel isoforms were studied on Northern blots. The expression of lysyl hydroxylases 2a, 2b and 3 differ from the expression of previously characterized lysyl hydroxylase 1. Lysyl hydroxylase 1 is expressed constitutively in all tissues whereas the expression of novel isoforms is more strictly regulated. Lysyl hydroxylase 2 is highly expressed in heart, placenta, liver and pancreas. Lysyl hydroxylase 2b expression is highest in heart and skeletal muscle and lysyl hydroxylase 3 expression is highest in heart, placenta and pancreas. Brain, lung and kidney contain the lowest amounts of these isoforms.

Novel isoforms were expressed as recombinant proteins in baculovirus expression system in vitro. All these novel isoforms were able to hydroxylate lysine residues in short collagenous peptides. A more detailed kinetic analysis was performed on lysyl hydroxylase 2a and 2b in order to find out if they differed from each other. The binding affinity of ascorbate and peptide substrate is different in lysyl hydroxylase 2a from 2b.

Chromosomal assignments were carried out on human lysyl hydroxylases 2 and 3. Lysyl hydroxylase 2 was localized to chromosome 3q23–q24 and lysyl hydroxylase 3 to chromosome 7q36.