Molecular cloning of chick lysyl hydroxylase. Little homology in primary structure to the two types of subunit of prolyl 4-hydroxylase

Lysyl hydroxylase (EC 1.14.11.4), an alpha 2 dimer, catalyzes the formation of hydroxylysine in collagens by the hydroxylation of lysine residues in X-Lys-Gly sequences. We report here on the isolation of cDNA clones coding for the enzyme from a chick embryo lambda gt11 library. Several overlapping clones covering all the coding sequences of the 4-kilobase mRNA and virtually all the noncoding sequences were characterized. These clones encode a polypeptide of 710 amino acid residues and a signal peptide of 20 amino acids. The polypeptide has four potential attachment sites for asparagine-linked oligosaccharides and 9 cysteine residues, at least one of which is likely to be involved in the binding of the Fe2+ atom to a catalytic site. A surprising finding was that no significant homology was found between the primary structures of lysyl hydroxylase and prolyl 4-hydroxylase in spite of the marked similarities in kinetic properties between these two enzymes. A computer-assisted comparison indicated only an 18% identity between lysyl hydroxylase and the alpha-subunit of prolyl 4-hydroxylase and a 19% identity between lysyl hydroxylase and the beta-subunit of prolyl 4-hydroxylase. Visual inspection of the most homologous areas nevertheless indicated the presence of several regions of 20-40 amino acids in which the identity between lysyl hydroxylase and one of the prolyl 4-hydroxylase subunits exceeded 30% or similarity exceeded 40%. Southern blot analyses of chick genomic DNA indicated the presence of only one gene coding for lysyl hydroxylase