Phospholipid, glycolipid, and ion dependencies of concanavalin A- and Ricinus communis agglutinin I-induced agglutination of lipid vesicles.

The recent availability of a series of model glycolipids (N-alkylaldobionamides) allowed the systematic investigation of glycolipid-specific agglutination of lipid vesicles by the lectins concanavalin A (Con A) and Ricinus communis agglutinin I (RCA,). The carbohydrate-binding specificities of the lectins determined which glycolipid-containing vesicles were agglutinated and which sugars specifically inhibited vesicle agglutination. Con A agglutinated negatively charged a-D-glucosyl glycolipid-containing vesicles prepared from a mixture of phosphatidylcholine (PC) and the acid phospholipids, phosphatidylserine (PS), cardiolipin (CL), or phosphatidic acid (PA). The agglutination was abolished not only by methyl a-D-mannopyranoside but also by elevated ionic strength. Con A did not agglutinate a-Dglucosyl glycolipid-containing neutral vesicles composed of phosphatidylcholine (PC) or a mixture of PC and phosphatidylethanolamine (PE). Con A-induced agglutination of glycolipid-containing vesicles may involve both nonelectrostatic, lectin-carbohydrate interaction, and electrostatic interaction between Con A and vesicles. RCAr agglutinated both neutral and negatively charged vesicles containing a-D-galaCtOSyl glycolipids. Although the binding of sugars and of pure glycolipid micelles by RCAl is not Ca2’-dependent, agglutination of a-D-galactosyl glycolipid-containing PC-PS vesicles had an absolute requirements for Ca2+ or other divalent ions and could be reversed by adding either EDTA or methyl a-D-galactopyranoside.