Isolation and partial purification of mannose-specific agglutinin from brewer's yeast involved in flocculation.

Yeast cell-agglutinating activity, designated agglutinin (possible lectin), was isolated from cell walls of both non-flocculent and flocculent brewer's yeast cells. Agglutinin-mediated aggregation of yeast cells in a manner similar to flocculation with respect to specific mannose-sensitivity, pH-dependence and calcium-dependence. Agglutinating activity was found to be heat-stable and protease-insensitive. Furthermore, addition of agglutinin to flocculent cells strongly stimulated the flocculation ability of the cells, whereas addition to non-flocculent cells rendered these cells weakly flocculent. Agglutinin was found to be released from flocculent cells during the course of a flocculation assay, but not from non-flocculent cells. Presence of mannose during the assay inhibited release of agglutinin. Our results suggest that (i) mannose-specific agglutinin is continuously synthesized during growth of brewer's yeast cells, (ii) agglutinin is present in cell walls of non-flocculent cells but is unable to bind its ligand on other cells, and (iii) the ability of yeast cells to flocculate in a flocculation assay depends, among other factors, on release of agglutinin from the cells. A 10-kDa polypeptide might represent one form of agglutinin.