Protein-linked oligosaccharide implicated in cell-cell adhesion in two Dictyostelium species

Monoclonal antibody d-41, previously shown to block in vitro cell-cell adhesion in aggregating Dictyostelium discoideum, also blocks adhesion in aggregating D. purpureum. In both species the antibody reacts with proteins with Mr approximately 80,000, 37,000, and 27,000, presumed to be glycoproteins since the d-41 epitope is destroyed by periodate oxidation but unaffected by extensive Pronase digestion. Polyclonal antibodies raised against the mixture of d-41 reactive glycoproteins that had been purified by immunoaffinity chromatography are potent inhibitors of D. discoideum adhesion, and adhesion-blocking activity is neutralized extensively and equivalently by each of the purified glycoproteins from D. discoideum with which d-41 reacts. In contrast, polyclonal antibodies raised against the same purified glycoproteins after they had been oxidized with periodate do not block cell-cell adhesion although they react with the glycoproteins with Mr approximately 80,000, 37,000, and 27,000 and bind as extensively to the surface of aggregating D. discoideum cells as do the adhesion-blocking polyclonal antibodies. When taken together, these results raise the possibility that some component of the d-41 binding oligosaccharide participates in cell-cell adhesion.