Inhibition of intercellular adhesion in a cellular slime mould by univalent antibody against a cell-surface lectin.

Abstract

THE cellular slime moulds, Dictyostelium discoideum and Polysphondylium pallidum contain carbohydrate-binding proteins (lectins) that increase significantly in amount in soluble crude extracts as amoebae differentiate from the vegetative stage (when the cells do not associate) to the aggregation-competent stage (when the cells can form stable intercellular contacts)1–3. Lectins from the two species, assayed as agglutinins of erythrocytes, have been purified by affinity techniques and, on the basis of their carbohydrate-binding specificities, as well as several physicochemical properties, have been shown to be distinct proteins3–5. Distinct lectin activities have also been identified in four other species of slime moulds6. The lectins from D. discoideum and P. pallidum accumulate on the cell surface with development of aggregation competence as demonstrated by erythrocyte–rosette experiments1,2,7, immunofluorescent and immunoferritin techniques7,8, and lactoperoxidase-catalysed iodination of intact cells9. Both species also contain cell-surface receptors with a very high affinity for the homotypic lectin and a lesser affinity for the heterotypic lectin10, suggesting a possible basis for species-specific intercellular affinities. In the case of D. discoideum, we have shown that the high affinity receptor appears on the cell surface as amoebae differentiate into the cohesive state10.