CHARACTERIZATION OF BIOMPHALARIA-ALEXANDRINA-DERIVED LECTINS RECOGNIZING A FUCOSYLLACTOSE-RELATED DETERMINANT ON SCHISTOSOMES

Two novel lectins that bind selectively to a schistosome-associated fu cosyllactose-related determinant have been characterized and purified from the hemolymph of Biomphalaria alexandrina, the snail vector of Sc histosoma mansoni. Both lectins were purified by affinity chromatograp hy on a column of equimolar mixture of D- and L-glucose coupled to epo xy-activated Sepharose 6B and sequential elution by D-glucose (designa ted BaSI) and L-fucose (designated BaSII). Assessment of the structura l characteristics, by one- and two-dimensional polyacrylamide gel elec trophoresis, indicated that BaSI and BaSII were structurally distinct, and exist in their native forms as multimers of non-covalently associ ated subunits, that were of different sizes in BaSI and of equal size in BaSII. Removal of N-linked glycans by Endo-beta-N-acetylglucosamini dase F resolved the heterodisperse pattern of BaSI subunits into two s pots of 13.2 kDa (pI 7.2) and 10.1 kDa (pI 5.8), and collapsed the aci dic charge microheterogeneity of the BaSII subunit into a single spot that corresponded in terms of molecular weight and pi to the basic 13. 2-kDa subunit of BaSI. In miracidial binding and inhibition assays wit h different sugars, both lectins exhibited selectivity towards a fucos yllactose sequence, but BaSII had a higher binding preference to fucos e moieties. BaSII-Sepharose 4B affinity chromatography and analysis on two-dimensional gels indicated that multiple copies of the fucosyllac tose-related determinant were expressed by heterogeneous, acidic glyco proteins in the miracidial stage of S. mansoni.