Partial characterization of oligosaccharides expressed on midgut microvillar glycoproteins of the mosquito, Anopheles stephensi Liston

Midguts of the malaria-transmitting mosquito, Anopheles stephensi, were hom ogenized and microvillar membranes prepared by calcium precipitation and di fferential centrifugation. Oligosaccharides present on the microvillar glyc oproteins were identified by lectin blotting before and after in vitro and in situ treatments with endo- and exo-glycosidases. Twenty-eight glycoprote ins expressed a structurally restricted range of terminal sugars and oligos accharide linkages. Twenty-three glycoproteins expressed oligomannose and/o r hybrid N-linked oligosaccharides, some with alpha1-6 linked fucose as a c ore residue. Complex-type N-linked oligosaccharides on eight glycoproteins all possessed terminal N-acetylglucosamine, and alpha- and beta -linked N-a cetylgalactosamine. Eight glycoproteins expressed O-linked oligosaccharides all containing N-acetylgalactosamine with or without further substitutions of fucose and/or galactose. Galactose beta1-3/4/6N-acetylglucosamine-, sia lic acid alpha2-3/6galactose-, fucosea1-2galactose- and galactoseal-3galact ose-were not detected. Terminal a-linked N-acetylgalactosamine residues on N-linked oligosaccharides are described for the first time in insects. The nature and function of these midgut glycoproteins have yet to be identified . but the oligosaccharide side chains are candidate receptors for ookinete binding and candidate targets for transmission blocking strategies (C) 2001 Elsevier Science Ltd. All rights reserved.