Topography and polypeptide distribution of terminal N-acetylglucosamine residues on the surfaces of intact cells. Evidence for O-linked GlcNAc

Bovine milk galactosyltransferase has been used, in conjunction with UDP-[3H] galactose, as an impermeant probe for accessible GlcNAc residues on the surfaces of lymphocytes, red blood cells and macrophages. Kinetics of labeling are biphasic, leveling off at approximately 30 minutes. The data strongly indicate vectorial surface labeling and covalent attachment of galactose. Thymocytes, T-lymphocytes, and B-lymphocytes have approximately 106, 3 x 106, and 5 x 106 galactosylatable sites on their cell surfaces, respectively. Numerous proteins are exo-galactosylated that differ quantitatively among the major functional subsets of lymphocytes. In thymocytes 49% of the exo-galactosylated oligosaccharides are alkali-labile, whereas 80% and 90% of that derived from T-lymphocytes and B-lymphocytes can be β-eliminated, respectively. Composition, size, and HPLC on two types of high-resolution columns establish that the bulk of the exo-galactosylated, β-eliminated oligosaccharides are Galβ1-4GlcNAcitol. These data suggest the presence of O-glycosidically linked GlcNAc monosaccharide on many lymphocyte cell-surface proteins. These studies not only describe dramatic differences in the amounts and distribution of terminal GlcNAc residues on phenotypically different lymphocyte populations, but they also describe the presence of a novel protein-saccharide linkage, which is present on numerous lymphocyte proteins