Cloning and Expression of a Proteoglycan UDP-Galactose: beta -Xylose beta 1,4-Galactosyltransferase I: A Seventh Member of the Human beta 4-Galactosyltransferase Gene Family

• Published in: The Journal of biological chemistry 1999-09, Vol.274 (37), p.26165-26171
• Main Authors: Almeida, R, Levery, S B, Mandel, U, Kresse, H, Schwientek, T, Bennett, E P, Clausen, H
• Format: Article
• Language: English
• ISSN: 0021-9258
• DOI: 10.1074/jbc.274.37.26165

A seventh member of the human beta 4-galactosyltransferase family, beta 4Gal-T7, was identified by BLAST analysis of expressed sequence tags. The coding region of beta 4Gal-T7 depicts a type II transmembrane protein with sequence similarity to beta 4-galactosyltransferases, but the sequence was distinct in known motifs and did not contain the cysteine residues conserved in the other six members of the beta 4Gal-T family. The genomic organization of beta 4Gal-T7 was different from previous beta 4Gal-Ts. Expression of beta 4Gal-T7 in insect cells showed that the gene product had beta 1,4-galactosyltransferase activity with beta -xylosides, and the linkage formed was Gal beta 1-4Xyl. Thus, beta 4Gal-T7 represents galactosyltransferase I enzyme (xylosylprotein beta 1,4-galactosyltransferase; EC 2.4.1.133), which attaches the first galactose in the proteoglycan linkage region GlcA beta 1-3Gal beta 1-3Gal beta 1-4Xyl beta 1-O-Ser. Sequence analysis of beta 4Gal-T7 from a fibroblast cell line of a patient with a progeroid syndrome and signs of the Ehlers-Danlos syndrome, previously shown to exhibit reduced galactosyltransferase I activity (Quentin, E., Gladen A., Roden, L., and Kresse, H. (1990) Proc. Natl. Acad. Sci. U. S. A. 87, 1342-1346), revealed two inherited allelic variants, beta 4Gal-T7 super(186D) and beta 4Gal-T7 super(206P) each with a single missense substitution in the putative catalytic domain of the enzyme. beta 4Gal-T7 super(186D) exhibited a 4-fold elevated Km for the donor substrate, whereas essentially no activity was demonstrated with beta 4Gal-T7 super(206P). Molecular cloning of beta 4Gal-T7 should facilitate general studies of its pathogenic role in progeroid syndromes and connective tissue disorders with affected proteoglycan biosynthesis.