Identification of endogenous binding proteins for the lectin discoidin-I in Dictyostelium discoideum.

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Abstract
Recent biochemical and genetic evidence has shown that the endogenous lectin discoidin-I is involved in intercellular adhesion during development of the cellular slime mold D. discoideum. Dicoidin-I affinity columns were prepared to isolate the lectin receptors. By using the cell surface radioiodination method, 11 discoidin-I binding proteins were identified in wild-type NC4 cells by gel electrophoresis, with apparent MW of 95,000, 85,000, 78,000, 72,000, 60,000, 33,000, 31,000, 28,000, 25,000, 21,000 and 15,000. Only 3 (gp33, gp31 and pg28) were under developmental regulation. The amount of gp31 increased 8- to 10-fold during aggregation and it was the predominant discoidin-I binding protein synthesized at the aggregation stage. Discoidin-I binding proteins derived from aggregation stage cells were potent inhibitors of discoidin-I in a hemagglutination assay in vitro. The same preparation promoted aggregation of cells bearing discoidin-I on the surface, suggesting a multivalent interaction.