Mutant of Chinese hamster ovary cells with altered mannose 6-phosphate receptor activity is unable to synthesize mannosylphosphoryldolichol

Abstract

B4-2-1 is a Chinese hamster ovary cell mutant previously isolated and characterized as deficient in mannose 6-phosphate receptor activity. We show here that B4-2-1 is a pleiotropic mutant, defective in biosynthesis of asparagine-linked oligosaccharides, B4-2-1 is unable to synthesize mannosylphosphoryldolichol; the consequences of this defect on glycosylation are (i) biosynthesis of one major lipid-linked oligosaccharide, characterized by its resistance to endoglycosidase H and decreased size; this oligosaccharide is similar to a minor species of lipid-liked oligosaccharide found in parental cells; (ii) transfer of this oligosaccharide to newly synthesized proteins; and (iii) absence of normal "high-mannose" oligosaccharides on mature glycoproteins isolated from B4-2-1; glycoproteins from the mutant contain complex oligosaccharides as well as endoglycosidase H-resistant, alpha-mannosidase-sensitive species. While the glycosylation defect may alter adversely the function of several glycoproteins in the mutant, including that of the mannose 6-phosphate receptor, it appears to have no effect on the formation or function of the mannose 6-phosphate recognition marker on acid hydrolases of B4-2-1.