UDP-GlcNAc: BetaGal beta-1,3-NAcetylglucosaminyltransferase 7 (B3GNT7)

Abstract

UDP-GlcNAc:betaGal beta-1,3-N-acetylglucosaminyltransferase 7 (B3GNT7, β3GnT7, EC, 2.4.1.-) is one of the members of large β1,3-GlcNAc/Gal/GalNAc-transferase family (Narimatsu 2006). Like as many other glycosyltransferases, this enzyme is a type II membrane-bound protein, orienting its catalytic domain into the lumenal side of the Golgi apparatus. B3GNT7 preferentially acts on sulfated type 2 glycans as described below, indicating that B3GNT7 is responsible for the elongation of backbone structure of keratan sulfate: (1) 6-O-sulfation of nonreducing terminal GlcNAc residues by CHST6, (2) β-galactosylation at the 4-OH of SO3−→6GlcNAc by B4GALT4, (3) β-N-acetylglucosaminylation of the 3-OH of Gal residue by B3GNT7, (4) repeating (1)-(3), and (5) 6-O-sulfation of Gal residues by CHST1 (Fig. 31.1).