Enzymatic transfer of a beta1,6-linked N-acetylglucosamine to the alpha-galactose of globo-N-tetraose: in vitro synthesis of a novel hybrid pentasaccharide of lacto-globo type.

A novel saccharide was synthesized by incubating globo-N-tetraose, GalNAc beta1-3Gal alpha1-4Gal beta1-4Glc, and UDP[3H]GlcNAc with hog gastric mucosal microsomes, known to contain beta1,6-N-acetylglucosaminyltransferase activity of a broad acceptor specificity. Chromatography and MALDI-TOF mass spectrometry of the product, as well as the amount of incorporated radioactivity indicated that one [3H]GlcNAc residue was transferred to the acceptor saccharide. One- and two-dimensional 1H NMR-spectroscopic analysis of the product and ESI-CID mass spectrometry of the pentasaccharide in permethylated form established its structure as GalNAc beta1-3([3H]GlcNAc beta1-6)Gal alpha1-4Gal beta1-4Glc. The new enzyme activity possesses substrate specificity features common to a purified beta1,6-GlcNAc-transferase from bovine tracheal epithelium, which forms branches at the subterminal beta1,3-substituted galactose and accepts both GlcNAc- and Gal-configuration at the terminal residue of the acceptor (Ropp et al. (1991) J. Biol. Chem., 266, 23863-23871). The new beta1,6-GlcNAc-branch was readily galactosylated by bovine milk beta1,4-galactosyltransferase, revealing a pathway to novel hybrid type glycans with N-acetyllactosamine chains on globotype saccharides. This pathway may lead to the rare IP blood-group antigen and to globoside-like molecules mediating cell adhesion.