Reconstitution of discoidin hemagglutination activity by lipid extracts of Dictyostelium discoideum cells.

The developmentally regulated carbohydrate binding protein discoidin (from Dictyostelium discoideum) has been purified in a nonagglutinating form. While substantial agglutination activity is present in cell lysates, this activity is consistently lost upon affinity purification of discoidin. The lack of agglutination activity is not due to a mutational event or a nutritional deficiency. The carbohydrate binding site of the protein is functional, and dissociation of the oligomeric protein into subunits has not occurred. The addition of aqueous dispersions of a CHCl3/CH3OH extract of a slime-mold particulate fraction to the purified discoidin reconstitutes agglutination activity in a concentration-dependent manner. The reconstituted agglutination activity has the specificity of discoidin's carbohydrate binding sites. The reconstitutive ability of the CHCl3/CH3OH extract is due to a lipid component. Treatments of the lipid extract and fractionation of the active species suggest that it may be unsaturated fatty acid. Of many purified lipids tested, only high concentrations of cisvaccenic acid (C18:1 delta11) or oleic acid (C18:1 delta9) significantly reconstituted agglutination activity.