Glucomannoproteins in the cell wall of Saccharomyces cerevisiae contain a novel type of carbohydrate side chain.

Mannoproteins in the walls of mnn9 cells of Saccharomyces cerevisiae were released by laminarinase, and purified by concanavalin A affinity chromatography and ion-exchange chromatography. Carbohydrate analysis revealed that they contained N-acetylglucosamine, mannose, and glucose. An antiserum raised against beta (1-6)-glucan reacted with four proteins with molecular masses of 66, 100, 155, and 220 kDa, respectively. Recognition by the antiserum was competitively inhibited by beta (1-6)-glucan, but not by beta (1-3)-glucan, mannan, or dextran (an alpha (1-6)-glucan). Mild periodate treatment of the wall proteins completely abolished recognition by the antiserum. Glucose-containing side chains were isolated and compared with N- and O-carbohydrate side chains. The glucose-containing side chains consisted of about equal amounts of glucose and mannose and some N-acetylglucosamine, and were larger than N-chains. They were, however, not extended N-chains, because after acetolysis, which preferentially cleaves (1-6)-linkages, their elution profiles differed strongly. A model is presented of how glucose-containing side chains might anchor mannoproteins into the glucan layer of the cell wall.