CHARACTERIZATION OF THE N-LINKED OLIGOSACCHARIDES IN GLYCOPROTEINS SYNTHESIZED BY MICROFILARIAE OF DIROFILARIA-IMMITIS

In this report, we describe studies on the structures of the N-linked oligosaccharides contained in glycoproteins synthesized by microfilari ae of the canine heartworm, Dirofilaria immitis. Microfilariae were in cubated in media containing either 2-[H-3]mannose, 6-[H-3]glucosamine, or 6-[H-3]galactose. Sodium dodecyl sulfate-polyacrylamide gel electr ophoresis and fluorographic analyses indicated that many glycoproteins were radiolabeled by both the mannose and glucosamine, whereas glycop roteins were not radiolabeled by the galactose. Glycopeptides from the se total glycoproteins were fractionated and purified by serial lectin affinity chromatography, and the structures of the oligosaccharides i n the isolated glycopeptides were analyzed by a variety of techniques. The N-linked oligosaccharides were shown to contain mannose (Man), fu cose, N-acetylglucosamine (GlcNAc),and N-acetylgalactosamine (GalNAc). However, they lacked sialic acid and galactose, which are commonly fo und in mammalian glycoproteins. GalNAc was shown to be in an unusual t erminal position and beta-linked in the sequence GalNAc beta GlcNAc be ta Man-R, where R is the typical branch of complex-type N-linked oligo saccharides. Similar structures were recently found by us to be synthe sized by the helminthic parasite Schistosoma mansoni. These results de monstrate that glycoproteins synthesized by microfilariae of D. immiti s have unusual carbohydrate moieties and may lead to a better understa nding of the specific roles of glycoprotein oligosaccharides in host-p arasite interactions.