SACCHAROMYCES-CEREVISIAE A-AGGLUTININ AND ALPHA-AGGLUTININ - CHARACTERIZATION OF THEIR MOLECULAR INTERACTION

An O-glycosylated protein of approximately 18 kDa responsible for mating type specific agglutination has been isolated from Saccharomyces cerevisiae a cells, purified to homogeneity and via peptide sequences the gene was cloned by PCR. An open reading frame codes for a protein of 69 amino acids. A minimum of five serine and five threonine residues of the mature protein are glycosylated. Alpha-agglutinin is a highly N-glycosylated protein of approximately 250 kDa. Both purified agglutinins form a specific 1:1 complex in vitro. Pretreatment of alpha-agglutinin, but not of a-agglutinin, with diethylpyrocarbonate (DEPC) prevents formation of the complex; treatment of alpha-agglutinin in the presence of a-agglutinin protects the former from DEPC inactivation. By carboxy terminal shortening of the alpha-agglutinin gene and by replacing three of its eight histidyl residues by arginine, the active region of alpha-agglutinin for interaction with a-agglutinin has been defined. Neither the N- nor the O-linked saccharides of the two agglutinins seem to be essential for their interaction.