Specificities of limulin and wheat-germ agglutinin towards some derivatives of GM3 gangliosides.

Lipid vesicles containing derivatives of GM3 ganglioside (II3-N-acetylneuraminosyllactosyl ceramide) were used to study the specificities of two lectins (limulin and wheat germ agglutinin) towards N-acetyl neuraminic acid and N-glycoloylneuraminic acid and some of their natural and chemically modified derivatives. The extent of the lectin binding to the gangliosides was related to the aggregation process of the lipid vesicles which was monitored as an absorbance increase. Limulin binds specifically to lipid vesicles containing N-glycoloyl derivatives of GM3. The hydroxyl group at C-4 and the carboxyl group of neuraminic acid have to be free for the binding to limulin. The side chain of neuraminic acid is not involved in the binding site of limulin. Wheat germ agglutinin binds to GM3 ganglioside only when the hydrophilic tail of the neuraminic group is cut off (C7 analogues). The acetamido group but not the carboxyl group is involved in the binding to wheat germ agglutinin. The wheat-germ-agglutinin-induced aggregation of vesicles containing derivatives of GM3-ganglioside is dependent on the pH, on the ionic strength and on the presence of Ca2+ ions. The dependence on ionic strength and Ca2+ is a consequence of the electrostatic repulsion of the vesicles. The wheat-germ-agglutinin-induced aggregation process of vesicles containing any suitable GM3-ganglioside derivative was reversed by the addition of N-acetylglucosamine showing that the N-acetylneuraminic acid derivatives bind to the N-acetylglucosamine binding site.