CLONING AND CHARACTERIZATION OF A 3RD HUMAN LYSYL HYDROXYLASE ISOFORM

Lysyl hydroxylase (EC 1.14.11.4), a ho modimer, catalyzes the formatio n of hydroxylysine in collagens. Recently, an isoenzyme termed lysyl h ydroxylase 2 has been cloned from human sources [M. Valtavaara, H. Pap ponen, A.-M. Pirttila, K. Hiltunen, H. Helander and R. Myllyla (1997) J. Biol. Chem. 272, 6831-6834]. We report here on the cloning of a thi rd human lysyl hydroxylase isoenzyme, termed lysyl hydroxylase 3. The cDNA clones encode a 738 amino acid polypeptide, including a signal pe ptide of 24 residues. The overall amino acid sequence identity between the processed human lysyl hydroxylase 3 and 1 polypeptides is 59%, an d that between the processed lysyl hydroxylase 3 and 2 polypeptides is 57%, whereas the identity to the processed Caenorhabditis elegans pol ypeptide is only 45%. All four recently identified critical residues a t the catalytic site, two histidines, one aspartate, and one arginine, are conserved in all these polypeptides. The mRNA for lysyl hydroxyla se 3 was found to be expressed in a variety of tissues, but distinct d ifferences appear to exist in the expression patterns of the three iso enzyme mRNAs. Recombinant lysyl hydroxylase 3 expressed in insect cell s by means of a baculovirus vector was found to be more soluble than l ysyl hydroxylase 1 expressed in the same cell type. No differences in catalytic properties were found between the recombinant lysyl hydroxyl ase 3 and 1 isoenzymes. Deficiency in lysyl hydroxylase 1 activity is known to cause the type M variant of the Ehlers-Danlos syndrome, and i t is therefore possible that deficiency in lysyl hydroxylase 3 activit y may lead to some other variant of this syndrome or to some other her itable connective tissue disorder.