Cell wall glucomannoproteins of Saccharomyces cerevisiae mnn9

Abstract

Mannoproteins were isolated from Saccharomyces cerevisiae mnn9 mutant cell walls by laminarinase digestion and purified by affinity and anion‐exchange chromatography. The purified mannoprotein fraction contained three predominant proteins with molecular masses of 300 kDa, 220 kDa and 160 kDa. These compounds were absent in an SDS extrct of cell walls or in a hot‐citrate extract of mnn9 cells.The carbohydrate part of the purified mannoproteins consisted of (N‐acetyl)glucosamine, mannose and glucose in a molar ratio of 1:53:4. O‐Glycosidically linked chains, containing 70% of the mannose, were released by mild β‐elimination. N‐Glycosidically linked chains, representing 80% of the (N‐acetyl)glucosamine and 20% of the mannose, were released by peptide N‐glycosidase F (PNGase F) digestion. Complete degradation of protein by alkaline hydrolysis released besides the N‐ and O‐glycosidically linked chains, another type of carbohydrate chain containing the residual (N‐acetyl)glucosamine, mannose and most of the glucose in a molar ratio of 1:17:18. Glucose was β‐glycosidically linked.The results indicate that β‐glucose is linked to PNGase F‐resistant N‐linked chains present on cell wall mannoproteins. We propose that these chains are responsible for the linkage between mannoproteins and glucan in the cell wall.