STRUCTURE OF ASPARAGINE-LINKED OLIGOSACCHARIDES OF AN ASPARTIC PROTEINASE FROM THE ZYGOMYCETE FUNGUS RHIZOMUCOR PUSILLUS

The zygomycete fungus Rhizomucor pusillus (previously called Mucor pus illus) secretes an aspartic proteinase containing two asparagine-linke d, high-mannose type oligosaccharide chains at Asn(79) and Asn(188). F or structural elucidation of the carbohydrate moieties, the protein wa s divided into two portions, an N-terminal portion containing Asn(79) and a C-terminal portion containing Asn(188), by a specific autocataly tic cleavage under alkaline conditions. Each of the asparagine-linked oligosaccharides was then released by peptide-N-glycosidase F digestio n and pyridylaminated with a fluorescent reagent, 2-aminopyridine, at the reducing end. High-performance liquid chromatography analyses show ed that the structure of the asparagine-linked oligosaccharide chain a ttached to residue Asn(79) was Man(5)GlcNAc(2), and that bound to resi due Asn(188) was Man(5)GlcNAc(2) and Man(6)GlcNAc(2). These observatio ns suggest that the processing of mannose residues in asparagine-linke d oligosaccharides in the Golgi apparatus of Rhizomucor resembles that in mammalian cells.