STRUCTURE OF THE LIPID-LINKED OLIGOSACCHARIDES THAT ACCUMULATE IN CLASS-E THY-1-NEGATIVE MUTANT LYMPHOMAS

Studies reported in the preceding paper (Trowbridge and Hyman, 1979) have demonstrated that Thy-1- mutant lymphoma cells of the class E complementation group lack the normal high molecular weight lipid-linked oligosaccharide, but instead accumulate two smaller species termed I and II. This paper reports studies which elucidate the structures of lipid-linked oligosaccharides I and II. By subjecting oligosaccharides radiolabeled with 3H-mannose, 3H-glucose or 3H-glucosamine to methylation, acetolysis, periodate oxidation and exoglycosidase digestion, the structures were shown to be: where R = GlcNac B1,4(3) GlcNAc. A comparison of I and II with lipid-linked oligosaccharides from normal Chinese hamster ovary cells indicates that both I and II are normal biosynthetic intermediates. On the basis of these data we suggest that the defect in the class E mutant cells is the lack of an α1,3 mannosyltransferase involved in the conversion of the Man5GlcNAc2 lipid-linked oligosaccharide to the Man6GlcNAc2 intermediate. It is also impossible that the same enzyme is involved in conversion of the Glc3Man5GlcNAc2 lipid-linked oligosaccharide to Glc3Man6GlcNAc2. The latter reaction, however, has not yet been demonstrated in normal cells. © 1979.