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

Promastigote culture forms of the log growth phase ofLeishamania 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 -galactosidase fromEscherichia coli: -d-lactose, -d-thiogalactose, -d-mannose, -l-rhamnose, -d-N-acetylgalactosamine, -d-N-acetylgalactosamine, -d-N-acetylgalactosamine, -d-N-acetylgalactosamine, -d-N-acetylglucosamine, the - and -glucosides maltose and cellobiose, -d-xylose, -d-mannose-6-phosphate, the -galactoside melibiose, -l-fucose, and -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 promastigoteLeishmania. Transformation of the binding data for neoglycoenzymes exposing lactose, mannose, rhamnose, andN-acetylated hexose residues, which was carried out to obtain the dissociation constants and to estimate the number of binding sites at saturation, revealedK _D values of around 100mm and around 10⁴ binding sites for the polyvalent ligands.