The och1 mutant of schizosaccharomyces pombe produces galactosylated core structures of n-linked oligosaccharides

Unlike the budding yeast Saccharomyces cerevisiae, the fission yeast Schizosaccharomyces pombe synthesizes large outer chains on the N-linked oligosaccharides that consist mainly of D-Gal and D-Man residues. The fission yeast och1₊ gene product has γ1,6-mannosyltransferase activity, and Och1p is the key enzyme in the initiation of outer chain elongation. Although the in vitro substrate specificity of S. pombe Och1p has been reported (Yoko-o et al., FEBS Lett., 489, 75-80 (2001)), the structure of the N-linked oligosaccharides of och1δ cells has not been investigated. In this study, we report a structural analysis of S. pombe N-linked oligosaccharides. Lectin blot analysis indicated that galactose residues were attached to the cell surface glycoproteins of the och1δ cells. We conducted a structural analysis of pyridylaminated N-linked oligosaccharides prepared from galactomannoproteins by HPLC and 1H NMR. These analyses revealed that the N-linked oligosaccharides of the och1δ cells displayed heterogeneity in the glycan consisting of Hex_11-15GlcNAc₂. The structural heterogeneity arose mainly from the addition of γ1,2- and γ1,3-Gal residues to the Man₉GlcNAc₂ core structure.