Monoclonal Antibody against Cytoplasmic Lectins ofDictyostelium discoideum:Cross-Reactivity with a Membrane Glycoprotein, Contact Site A, and with E.coliβ-Galactosidase andlacRepressor

Monoclonal antibodies were raised against two soluble, galactose-binding lectins from cells of Dictyostelium discoideum, discoidin I and II. These antibodies reacted not only with both discoidins, but also with a plasma membrane glycoprotein of aggregation competent cells, called contact site A, and with two carbohydrate-binding proteins of E. coli, beta-galactosidase and lac repressor. The possibility that the antibody recognizes a structure common to different carbohydrate-binding proteins is discussed. The two carbohydrate-binding proteins of E. coli share with discoidin I the sequence -Ser-X-X-Ile-His(Pro)-Pro(His)-Leu-Thr- which might be responsible for the cross-reactivity.