Complete exon-intron organization of the gene for human lysyl hydroxylase 3 (LH3).

Lysyl hydroxylase (LH) catalyzes the formation of hydroxylysine in collagens and related proteins by the hydroxylation of lysine residues in peptide linkages. Three isoenzymes of LH have so far been characterized. We report here that the human LH3 gene is 11.6 kb in size and consists of 19 exons. Transcription is initiated at one major site and several minor sites, the first exon containing 249-335 bp of untranslated sequences and 109 bp of a translated sequence. Exons 2-18 are similar in size to those of the human LH1 gene, whereas the introns are markedly shorter. The LH3 gene contains a total of 15 full length Alu retroposons or partial Alu fragments of more than 100 bp, in introns 5, 6, 12, 15 and 17. These generate a potential for genomic rearrangements, as has been shown for the LH1 gene in Ehlers-Danlos syndrome type VI. The 5'-flanking region of the LH3 gene was found to be entirely different from that of the LH1 gene, suggesting different regulation of these two genes.

Cloning and characterization of a third human lysyl hydroxylase isoform.

Lysyl hydroxylase (EC 1.14.11.4), a homodimer, catalyzes the formation of hydroxylysine in collagens. Recently, an isoenzyme termed lysyl hydroxylase 2 has been cloned from human sources [M. Valtavaara, H. Papponen, A.-M. Pirttilä, K. Hiltunen, H. Helander and R. Myllylä (1997) J. Biol. Chem. 272, 6831-6834]. We report here on the cloning of a third human lysyl hydroxylase isoenzyme, termed lysyl hydroxylase 3. The cDNA clones encode a 738 amino acid polypeptide, including a signal peptide of 24 residues. The overall amino acid sequence identity between the processed human lysyl hydroxylase 3 and 1 polypeptides is 59%, and that between the processed lysyl hydroxylase 3 and 2 polypeptides is 57%, whereas the identity to the processed Caenorhabditis elegans polypeptide is only 45%. All four recently identified critical residues at the catalytic site, two histidines, one aspartate, and one arginine, are conserved in all these polypeptides. The mRNA for lysyl hydroxylase 3 was found to be expressed in a variety of tissues, but distinct differences appear to exist in the expression patterns of the three isoenzyme mRNAs. Recombinant lysyl hydroxylase 3 expressed in insect cells by means of a baculovirus vector was found to be more soluble than lysyl hydroxylase 1 expressed in the same cell type. No differences in catalytic properties were found between the recombinant lysyl hydroxylase 3 and 1 isoenzymes. Deficiency in lysyl hydroxylase 1 activity is known to cause the type VI variant of the Ehlers-Danlos syndrome, and it is therefore possible that deficiency in lysyl hydroxylase 3 activity may lead to some other variant of this syndrome or to some other heritable connective tissue disorder.