Glycolipid modulation of membrane adhesion

A novel test of carbohydrate-mediated adhesion has been developed. At the tips of two syringes, large spherical model membranes have been made from phosphatidylcholine and varying amounts of mixed brain gangliosides dissolved inn-decane. The apposition of two such membranes resulted in adhesion, not fusion, as judged by the absence of fluorescence mixing in the junction with NBD-phosphatidylethanolamine in one membrane and perylene in the other. Adhesion was observed without gangliosides. The rate of formation of the adhesion area (rate of adhesion) was unchanged from 0 to 0.8 mol% gangliosides. A slightly lower but constant rate was observed within the physiological range from 2 to 10 mol%. Adhesion was frequently blocked at 11 to 15 mol% gangliosides. The rate of adhesion with pure gangliosides increased with the number of sialic acid residues: G_T1>G_D1a>G_M1. These results are interpreted in terms of a sialic acid-dependent segregation of gangliosides into the adhesion zone.