Immunochemical analysis of the carbohydrate moiety of yeast killer toxin K28

Killer toxin K28, a 16 kd protein secreted by the wine yeast Saccharomyces cerevisiae strain 28, was reversibly bound by a column of Concanavalin A-Sepharose, confirming its glycoprotein nature. HPLC analysis of acid hydrolyzates of K28 toxin as well as Western-blots of beta-eliminated and/or endo H-treated killer toxin preparations probed with polyclonal alpha-toxin antibodies revealed that the carbohydrate moiety of K28 consists of D-mannose only, which is O-glycosidically linked via Ser/Thr residues to the protein part. The change in gel mobility of K28 after beta-elimination was caused by a decrease in molecular mass of about 1,800, corresponding to a carbohydrate moiety of 10 mannose residues per killer toxin molecule.