UDP-gal: BetaGlcNAc beta 1,3-galactosyltransferase, polypeptide 4 (B3GALT4)

Abstract

UDP-Gal: GM2 beta 1,3-galactosyltransferase IV (B3GALT4) catalyzes the transfer of galactose from UDP-galactose to ganglioside GM2 to form GM1 (Miyazaki et al. 1997) as shown in Fig. 8.1. However, this enzyme can catalyze the synthesis of not only GM1 but also of GD1b and GA1 (asialo-GM1) from GM2, GD2, and asialo-GM2, respectively. These structures except GA1 are molecules being considered as main acidic glycosphingolipids in brain tissues of mammals and birds (Yu et al. 1988). They are also important molecules as precursors for GD1a, GT1b, and GQ1b, major gangliosides in nervous tissues. The cDNA clones of B3GALT4 were isolated by a eukaryocyte expression cloning system in 1997 (Miyazaki et al. 1997). This enzyme utilizes only glycolipid acceptors, not glycoproteins, and no other glycosyltransferases (genes) catalyzing similar functions have been isolated to date. Following the isolation of rat cDNA of B3GALT4, a highly homologous gene as an orthologue to rat cDNA was identified in the mouse genome (Mus musculus major histocompatibility locus class II region) by Rowen et al.