PURIFICATION AND PARTIAL CHARACTERIZATION OF A CELL-ADHESION MOLECULE (GP150) INVOLVED IN POSTAGGREGATION STAGE CELL-CELL BINDING IN DICTYOSTELIUM-DISCOIDEUM

A cell surface glycoprotein of apparent M(r) 150,000 (gp150) has been implicated in mediating EDTA-resistant cell-cell adhesion in Dictyostelium discoideum. A simple purification scheme making use of high-performance liquid chromatography has been devised to purify gp150 to near homogeneity. Purified gp150 was capable of neutralizing the effect of a rabbit antiserum raised against gel-purified gp150, which was previously reported to be a potent inhibitor of cell-cell adhesion (Geltosky, J. E., Weseman, J., Bakke, A., and Lerner, R. A. (1979) Cell 18, 391-398). The binding of I-125-labeled gp150 to intact cells was both dose-dependent and saturable, demonstrating the presence of specific cell surface binding sites for gp150. When reassociation of postaggregation stage cells was carried out in the presence of soluble gp150, aggregate formation was strongly inhibited. In contrast, gp150 failed to exert any effect on cells at the aggregation stage. The inhibitory effect of gp150 was sensitive to protease treatment, suggesting that the protein moiety is crucial to gp150 function. These results, taken together, provide direct evidence that gp150 is a cell-cell adhesion molecule involved in cell-cell binding in the postaggregation stage of Dictyostelium development.