Characterization of the high mannose asparagine-linked oligosaccharides synthesized by microfilariae of Dirofilaria immitis.

This report describes the structures of high-mannose-type N-linked oligosaccharides in glycoproteins synthesized by the microfilariae of Dirofilaria immitis. Microfilariae of D. immitis were incubated in vitro in media containing 2-[3H] mannose to allow metabolic radiolabeling of the oligosaccharide moieties of newly synthesized glycoproteins. Glycopeptides were prepared from the radiolabeled glycoproteins by digestion with pronase and fractionation by chromatography on concanavalin A-Sepharose. Thirty eight percent of 2-[3H] mannose incorporated into the microfilariae of D. immitis glycopeptides was recovered in high mannose-type asparagine-linked oligosaccharides which were bound to the immobilized lectin. Upon treatment of 2-[3H] mannose labeled glycopeptides with endo-beta-N-acetylglucosaminidase H, the high mannosetype chains were released and their structures were determined by high performance liquid chromatography and exoglycosidase digestion. The major species of high mannosetype chains synthesized by microfilariae of D. immitis have the composition Man5GlcNAc2, Man6ClcNAc2, Man7GlcNAc2, and Man8GlcNAc2. Structural analyses indicate that these oligosaccharides are similar to high mannose-type chains synthesized by vertebrates.