GPI-Modified Proteins Non-covalently Attached to Saccharomyces cerevisiae Yeast Cell Wall

Yeast cell wall GPI-anchored proteins lack the lipid part of the anchor and are covalently bound to the high-molecular-weight polysaccharides glucan and/or chitin through the mannose residues. They perform many functions, including participation in the cell wall molecular ensemble formation and providing cell resistance to stress. In this work, we identified a pool of GPI-modified proteins firmly bound to the cell wall by non-covalent interactions with the high-molecular-weight structural polysaccharides. We believe that the detected proteins are intermediate forms in the processing of the cell wall GPI-proteins, since they had already lost the lipid part of the GPI anchor and are absent in the lipoprotein fraction extracted according to Folch, but were not yet incorporated into the cell wall by the covalent binding to high-molecular-weight polysaccharides because they could be extracted into water by heating of delipidized cell walls. This group of previously unknown proteins might be present in the cell wall in a form of lipid-associated microcompartments represented by transport vesicles recently found in yeast. GPI-modified proteins non-covalently attached to the high-molecular-weight polysaccharides were found in the cell walls of both the parent strain and yeast devoid of glucanosyltransglycosylase Bg12, which indicates that the pathway of their incorporation into the cell wall is independent on this enzyme.