Alpha-1,4-N-Acetylglucosaminyltransferase (a4GNT)

A4GNT catalyzes the transfer of N-acetylglucosamine (GlcNAc) to core 2 branched O-glycans. It forms a unique glycan, GlcNAcalpha1-->4Galbeta-->R and is largely associated with the Golgi apparatus membrane. Glycosyltransferases that transfer GlcNAc and Gal to βGal residues with α1,4-linkages on glycoprotein and glycolipid templates, respectively, are categorized as α1,4-linkage glycosyltransferases. At present, two enzymes, namely, α1,4-N-acetylglucosaminyltransferase (α4GnT) and α1,4-galactosyltransferase (α4GalT, Gb3/CD77 synthase) are assigned to this family. α4GnT is responsible for biosynthesis of GlcNAcα1 → 4Galβ → R attached to O-glycans, whereas α4GalT is a key enzyme in the formation of Gb3/CD77 (Fig. 1). Since cDNAs encoding both enzymes were cloned by expression cloning by the authors.