THE BETA-1,6-GLUCAN CONTAINING SIDE-CHAIN OF CELL-WALL PROTEINS OF SACCHAROMYCES-CEREVISIAE IS BOUND TO THE GLYCAN CORE OF THE GPI MOIETY

Cell wall proteins of Saccharomyces cerevisiae are anchored by means o f a beta-1,6-glucan-containing side-chain. It is not known whether thi s chain is linked to the protein part (e.g. through carbohydrate side- chains) or to the glycosylphosphatidyliositol (GPI) moiety of cell wal l proteins. An IgA protease recognition site was introduced in Cwp2p, a beta-1,6-glucosylated cell wall protein, immediately N-terminal from the omega amino acid (the attachment site of the GPI moiety). Proteol ytic cleavage of this site revealed that the beta-1,6-glucan epitope w as not linked to the protein part. We conclude that neither N- or O-gl ycosylation is involved in beta-glucosylation of cell wall proteins. T his confirms that the glycan core of the GPI moiety is the probable be ta-1,6-glucan attachment site.