Schizosaccharomyces pombe mutants that are defective in glycoprotein galactosylation

Several mutants of Schizosaccharomyces pombe were obtained that are defective in protein glycosylation. One of the mutants, strain Sp550, makes galactomannoproteins with about half of the wild-type amount of galactose, whereas another strain, Sp137, makes glycoproteins that are almost devoid of galactose. Nondenaturing gel electrophoresis of cell extracts of both mutants revealed that they make invertases with a greatly increased mobility relative to the wild type. Additional study showed that Sp137 invertase has a subunit molecular mass that is about half that reported for the wild-type enzyme, owing to a reduction in carbohydrate content, whereas the native multimeric state appears unaltered. Structural studies on bulk cell-wall glycoprotein from Sp137 showed that the N-linked carbohydrate chains consist of a typical branched core oligosaccharide to which is attached an unsubstituted alpha 1-->6-polymannose outer chain. Consequently, the cells are agglutinated by antibodies against alpha 1-->6-linked mannose and have N-linked carbohydrate chains that are structurally analogous to the mnn2 mutant of Saccharomyces cerevisiae.