Human homolog of Caenorhabditis elegans sqv-3 gene is galactosyltransferase I involved in the biosynthesis of the glycosaminoglycan-protein linkage region of proteoglycans

A cDNA encoding a novel galactosyltransferase was identified based on BLAST analysis of expressed sequence tags, and the cDNA clones were isolated fro m a human melanoma line library. The new cDNA sequence encoded a type II me mbrane protein with 327 amino acid sequence and showed 38% homology to the Cae norhabditis elegans sqv-3 gene involved in the vulval invagination and oocyte development. Extracts from L cells transfected with the galactosyltr ansferase cDNA in an expression vector and a fusion protein with protein A exhibited marked galactosyltransferase activity specific for p-nitrophenyl- beta-D-xylopyranoside. Moreover, transfection with the cloned cDNA restored glycosaminoglycan synthesis of galactosyltransferase I-deficient Chinese h amster ovary mutant pgsB-761 cells. Analysis of the enzyme product by beta- galactosidase digestion, mass spectroscopy, and NMR spectroscopy revealed t hat the reaction product was formed via beta-1,4 linkage, indicating that t he enzyme is galactosyltransferase I (UDP-galactose:O-beta-D-xylosylprotein 4-beta-D-galactosyltransferase, EC 2.4.1.133) involved in the synthesis of the glycosaminoglycan-protein linkage region of proteoglycans.