RECOGNITION OF THE ACCEPTOR BETA-D-GLCPNAC-(1-]2)-ALPHA-D-MAN P-(1-]6)-BETA-D-GLCP-OR BY N-ACETYLGLUCOSAMINYLTRANSFERASE-V - NONE OF THE HYDROXYL-GROUPS ON THE GLC-RESIDUE ARE IMPORTANT

The enzyme, N-acetylglucosaminyltransferase-V (GlcNAcT-V, E.C 2.4.1.15 5), transters a beta-D-GlcpNAc residue, from UDP-GlcNAc, to the OH-6 g roup of the Man residue in the synthetic acceptor beta-D-GlcpNAc-(1 -- > 2)-alpha-D-Manp-(l --> 6)-beta-D-Glcp-O(CH2)7CH3 (3). Trisaccharide 3 is an excellent substrate for the enzyme from hamster kidney with a K(m) value of 26 muM. In this paper we examine the contribution of the Glc residue in 3 to acceptor recognition by this enzyme. Beta-D-GlcpN Ac-(1 --> 2)-alpha-D-Manp-O(CH2)7CH3 (5), where the Glc residue in 3 h as been deleted, was synthesized and found to be a very poor substrate with a K(m) value elevated to almost 2 mM. Two other analogues of 3, where the Glc residue was 0-trimethylated (6) or 0-tribenzylated (7), respectively, possessed K(m) values very near to those of 3. The Glc r esidue in 3 is thereby shown to present an important recognition eleme nt for GlcNAcT-V, but none of the free hydroxyl groups are required. T his observation should facilitate the design of more hydrophobic and m embrane-permeable analogues of 3 that are expected to function as spec ific glycosylation inhibitors.