Detection and quantitation of cell-surface sugar receptor(s) of Leishmania donovani by application of neoglycoenzymes

Abstract

Promastigote culture forms of the log growth phase of Leishmania donovani stock LRC L 51 were investigated for expression of cell-surface carbohydrate-binding sites using 15 types of a chemically glycosylated enzyme termed neoglycoenzyme. Carbohydrate conjugation and coupling yield were kept constant to ensure that the type of carbohydrate moiety was the only variable feature of the applied tools. Para-aminophenyl derivatives of the following carbohydrate residues were used for the glycosylation of beta-galactosidase from Escherichia coli: beta-D-lactose, beta-D-thiogalactose, alpha-D-mannose, alpha-L-rhamnose, alpha-D-N-acetylgalactosamine, beta-D-N-acetylgalactosamine, beta-D-N-acetylglucosamine, the alpha- and beta-glucosides maltose and cellobiose, beta-D-xylose, alpha-D-mannose-6-phosphate, the alpha-galactoside melibiose, alpha-L-fucose, and beta-D-glucuronic acid as well as sialic acid. Only melibiose, fucose, and glucuronic acid showed no binding affinity for the cultured flagellates; this served as an internal control reaction to exclude any binding to the linker group. This result demonstrates that many but not all sugar types can be recognized by appropriate receptor structure(s) on the surface of the promastigote Leishmania. Transformation of the binding data for neoglycoenzymes exposing lactose, mannose, rhamnose, and N-acetylated hexose residues, which was carried out to obtain the dissociation constants and to estimate the number of binding sites at saturation, revealed KD values of around 100 mM and around 10(4) binding sites for the polyvalent ligands.