Yeast flocculation-the role of cell wall proteins

Abstract

Yeast flocculation results from the interaction of different cell wall components, including carbohydrates and proteins. In addition to the interactions involving aminoacyl carboxyl groups, experimental data support the role of Ca2+ as a modulator of a surface lectin conformation, thus indicating the important role of the protein moiety. The identification of specific proteins responsible for the cell interactions leading to flocculation (floeculins) has revealed proteins with different molecular mass in Saccharomyces cerevisiae. In both Hansenula anomala and Kluyveromyces marxianus, proteins with molecular masses of 37 kDa were identified as putative floeculins. Recent results indicated that the protein (p37) in K. marxianus is a glyceraldehyde-3-phosphate dehydrogenase-like protein, and in this yeast as in other cell types, this protein is associated with cell adhesion. In contrast to K. marxianus, flocculent S. cerevisiae do not accumulate a p37 in the cell wall. However, in S. cerevisiae NCYC 1195 the accumulation of proteins with molecular masses of 54 and 67 kDa in the cell surface is well correlated with the development of flocculation. So far, two types of surface lectins have been suggested as being implicated in S. cerevisiae flocculation and it is likely that yeast cells can also possess specific receptors that are probably the side chains of the mannoproteins intrinsic to the yeast cell wall. An analysis of cell wall proteins from different flocculent yeast strains and the putative role of specific proteins as floeculins is discussed.