Cell-cell recognition in yeast: isolation of intact alpha-agglutinin from Saccharomyces kluyveri.

The heat-labile sexual agglutinin from Saccharomyces kluyveri strain 17 (alpha-agglutinin) has been isolated in an apparently intact form from wild-type and mnn1 (glycosylation-defective) cells. The wild-type agglutinin is polydisperse, due to variable degrees of glycosylation, and migrates on native gels with an apparent mass of greater than 400 kDa, whereas under denaturing conditions it appears somewhat smaller. The mnn1 agglutinin is also heterogeneous but has a lower molecular mass due to the presence of shorter N- and O-linked polymannose chains. Both agglutinins are converted sequentially by proteolysis to active fragments of approximately equal to 150 and 60 kDa, but the rate of proteolysis of the more highly glycosylated wild-type agglutinin is much slower than that of the mnn1 agglutinin. The 60-kDa fragment was isolated by HPLC and found to contain 46% carbohydrate as mannose, all of which was linked to serine and threonine. Thus, the N-linked oligosaccharides are restricted to that part of the agglutinin molecule that presumably anchors the agglutinin in the cell wall.