Complex carbohydrate–lectin interaction at the interface: a model for cellular adhesion. II. Reactivity of both the oligosaccharide chain and sugar‐binding domain of a glycoprotein lectin

We describe studies of a new model cell adhesion system involving liposomes bearing lectins and the glycosphingolipid, asialomonosialoganglioside (asialoGM 1 ). The model provides a simple analysis of experimental data to elucidate the mechanism of heterophilic cell–cell adhesion mediated by multiple protein–carbohydrate interactions. Phospholipid vesicles bearing the fatty acid conjugate of a glycoprotein lectin from Ricinus communis (RCAI vesicle) are shown to react with vesicles bearing the fatty acid conjugate of Concanavalin A (Con A) and asialoGM 1 (Con A vesicle). The kinetics of aggregation and monosaccharide‐induced disaggregation of the two types of vesicles were followed by monitoring the time‐dependent change in turbidity. Depending on the surface density of the asialoGM 1 , 40–60% of the resulting precipitin complex was dissociable only in the presence of both RCAI‐specific galactose and Con A‐specific α‐methyl‐ D ‐mannoside. Results indicate simultaneous participation of both the saccharide‐binding domain and carbohydrage sequence of RCAI, a model cell adhesion molecule, to stabilize the encounter complex by two types of interactions. These findings support the possibility of stable cell–cell adhesion in vivo occurring via interactions between cell adhesion molecules on apposing cell‐surface membranes.