UDP-gal: BetaGlcNAc beta 1,4- galactosyltransferase, polypeptide 2-6; xylosylprotein beta 1,4- galactosyltransferase, polypeptide 7 (galactosyltransferase I) (B4GALT2-7)

Abstract

The Galβ1 → 4GlcNAc structure is commonly found in the outer chain moieties of N- and O-glycans. The terminal galactose itself is involved in galectin-mediated biological events including apoptosis and growth regulation of cells (Perillo et al. 1995; Tadokoro et al. 2009), and many biologically active carbohydrate determinants involved in cell adhesion processes such as polysialic acid, HNK-1 carbohydrate, poly-N-acetyllactosamine, Lewis X, and sialyl Lewis X are expressed on the Galβ1 → 4GlcNAc group. In glycolipids, diverse structures classified into lacto-, neolacto-, ganglio-, and globo-series are all constructed on the Galβ1 → 4Glc group of lactosylceramide. Similarly, a variety of glycosaminoglycans including chondroitin sulfate and heparan sulfate chains are attached to core proteins through the Galβ1 → 4Xyl group. Therefore, β4-galactosyltransferases (β4GalTs), which transfer galactose from UDP-Gal to N-acetylglucosamine, glucose, or xylose, are key enzymes in glycobiology. Targeted inactivation of some of the mouse β4GalTs showed that the galactose-containing glycans are important for cell growth and differentiation and higher brain functions (Asano et al. 1997; Kido et al. 1998; Kumagai et al. 2009; Lu et al. 1997; Nishie et al. 2010; Yoshihara et al. 2009). To date, seven mammalian β4GalT genes have been isolated and shown to be in the family (reviewed in Amado et al. 1999; Furukawa and Sato 1999). There are also several genes homologous to those of mammalian β4GalTs in invertebrates such as the nematoda and snail (reviewed in Amado et al. 1999; Lo et al. 1998). This review mainly summarizes the properties of six mammalian β4GalTs although some of their acceptor specificities have not yet been established.