A Family of Human β3-Galactosyltransferases

Abstract

BLAST analysis of expressed sequence tags (ESTs) using the coding sequence of a human UDP-galactose:␤-N-acetylglucosamine ␤-1,3-galactosyltransferase, designated ␤3Gal-T1, revealed no ESTs with identical sequences but a large number with similarity. Three different sets of overlapping ESTs with sequence similarities to ␤3Gal-T1 were compiled, and complete coding regions of these genes were obtained. Expression of two of these genes in the Baculo virus system showed that one represented a UDP-galactose:␤-N-acetylglucosamine ␤-1,3-galactosyltransferase (␤3Gal-T2) with similar kinetic properties as ␤3Gal-T1. Another gene represented a UDP-galactose:␤-N-acetyl-galactosamine ␤-1,3-galactosyltransferase (␤3Gal-T4) involved in G M1 /G D1 ganglioside synthesis, and this gene was highly similar to a recently reported rat G D1 synthase (Miyazaki, H., Fukumoto, S., Okada, M., Hasegawa, T., and Furukawa, K. (1997) J. Biol. Chem. 272, 24794-24799). Northern analysis of mRNA from human organs with the four homologous cDNA revealed different expression patterns. ␤3Gal-T1 mRNA was expressed in brain, ␤3Gal-T2 was expressed in brain and heart, and ␤3Gal-T3 and -T4 were more widely expressed. The coding regions for each of the four genes were contained in single exons. ␤3Gal-T2, -T3, and -T4 were localized to 1q31, 3q25, and 6p21.3, respectively, by EST mapping. The results demonstrate the existence of a family of homologous ␤3-galactosyltransferase genes.

Biosynthesis of the Linkage Region of Glycosaminoglycans

“…22), revealing three different transcripts of ϳ1.6, 2.4, and 3.3 kilobases. This pattern differs from the expression profiles of the other ␤3GalTs, which tend to be restricted to specific tissues (13,15,16,18,19). The presence of multiple transcripts suggests that additional exons exist encoding 5Ј-and 3Ј-untranslated regions.…”

“…The transmembrane domain is followed by a segment rich in Ser, Pro, Ala, and Gly, which has been described as the "SPLAG" domain in other transferases (37), and presumably represents a stem region that determines the distance between the catalytic domain and the membrane. All of the other motifs identified previously in the ␤3GalTs presumably define essential folds in the catalytic domain (13,15,22). These were also found in similar locations in GAG GalTII, but the conserved cysteine residues are either absent or located differently.…”

“…A large family of ␤1,3-galactosyltransferases has been described based on expressed sequence tags exhibiting a high degree of homology and by use of PCR-based cloning strategies (13)(14)(15)(16)(17)(18)(19)(20). ␤3GalT1, -2, -3, and -5 utilize GlcNAc-terminated oligosaccharide as acceptor substrates, producing linkages characteristic of type 1 N-acetyllactosamine repeat units on N-and O-linked oligosaccharides and glycolipids, whereas ␤3GalT4 transfers galactose to the terminal GalNAc unit of the ganglioside series GM2, GD2, and GA2 acceptors (35).…”

“…Five members of this family have already been described (13)(14)(15)(16)(17)(18)(19)(20), with a possible homolog in Drosophila (Braniac) (21). None of the ␤3GalT enzymes characterized to date have activity with galactose-terminated oligosaccharide acceptors, suggesting that another member of the family must exist in order to catalyze the formation of the linkage region of glycosaminoglycans.…”

Molecular genetic analysis of the glycosyltransferase Fringe in Drosophila

“…These motifs overlap sequences identified as being shared within certain families of glycosyltransferases (9,(18)(19)(20)(21), but, with the exception of the DXD sequence within motif ii (19), have not been identified as common to all ␤3GTs. Only one known class of ␤3GTs in Drosophila consisting of three GlcATs (22), was not identified by PSI-BLAST or BLASTP as being related to our proposed ␤3GT superfamily.…”