Vicia graminea anti-N lectin: partial characterization of the purified lectin and its binding to erythrocytes.

Abstract

Vicia graminea lectin, purified by affinity chromatography, was homogeneous in sodium dodecylsulphate/polyacrylamide gel electrophoresis and migrated with a velocity corresponding to a molecular weight of 125 000. Heating of 0.1% sodium dodecylsulphate at 100 degrees C caused dissociation of the lectin into subunits with an apparent molecular weight of 31 000. The results of isoelectric focusing suggested non-identity of the lectin subunits and existence of several molecular forms of the lectin. The lectin was neither dissociated nor activated by succinylation, but was irreversibly inactivated by 8 M urea. The lectin was totally bound to concanavalin-A-Sepharose and could be eluted with alpha-D-mannopyranoside. Binding of the 125I-labeled Vicia graminea lectin to untreated and desialylated human erythrocytes of blood groups M and N, horse and bovine erythrocytes was characterized. The lectin was bound specifically to sites specific for blood group N on untreated human erythrocytes with an uniform affinity, and association constant Ka = 1.5 X 10(8) M-1. Desialylated human NN and MM erythrocytes bound more lectin, with a distinctly higher, but non-uniform affinity. Vicia graminea lectin bound weakly to horse erythrocytes, and the effect of their desialylation was similar to that obtained with human erythrocytes. The lectin was not bound either to untreated or to desialylated bovine erythrocytes. Binding of the labeled lectin to human NN erythrocytes was inhibited by desialylated glycoproteins of the M and N blood groups, by untreated N glycoprotein, and weakly by untreated M glycoprotein.