Aggregation of sponge cells. Function of a lectin in its homologous biological system.

For the first time, the biological role of a lectin in the process of reaggregation of single cells from the same species (marine sponge: Geodia cydonium Jam.) is described. The galactose-specific lectin does not promote aggregation, but prevents the antiaggregation receptor from disaggregating cell clumps. Competition experiments showed that the lectin inactivates the antiaggregation receptor by binding to it, most likely via its terminal galactose residues. The lectin converts reversibly aggregation-deficient cells (carrying functional cell membrane-bound antiaggregation receptor molecules) to aggregation-susceptible cells.