Identification and characterization of large galactosyltransferase gene families: galactosyltransferases for all functions

Enzymatic glycosylation of proteins and lipids is an abundant and important biological process. A great diversity of oligosaccharide structures and ty pes of glycoconjugates is found in nature, and these are synthesized by a l arge number of glycosyltransferases. Glycosyltransferases have high donor a nd acceptor substrate specificities and are in general limited to catalysis of one unique glycosidic linkage. Emerging evidence indicates that formati on of many glycosidic linkages is covered by large homologous glycosyltrans ferase gene families, and that the existence of multiple enzyme isoforms pr ovides a degree of redundancy as well as a higher level of regulation of th e glycoforms synthesized. Here, we discuss recent cloning strategies enabli ng the identification of these large glycosyltransferase gene families and exemplify the implication this has for our understanding of regulation of g lycosylation by discussing two galactosyltransferase gene families. (C) 199 9 Elsevier Science B.V. All rights reserved.