Cell Wall Receptor for Yeast Killer Toxin: Involvement of (1 → 6)-β- d -Glucan

Abstract

The linear (1 → 6)-β- d -glucans pustulan and luteose were effective competitive inhibitors of killer toxin action. Affinity chromatography of killer toxin on a pustulan-Sepharose column showed that toxin bound directly to a (1 → 6)-β-linked polysaccharide. Other polysaccharides found in yeast cell walls, including (1 → 3)-β- d -glucan, mannan, chitin, and glycogen, were not effective as inhibitors of toxin. Fractionation of yeast cell walls was attempted to identify the toxin receptor in sensitive Saccharomyces cerevisiae . The receptor activity was retained among the insoluble glucans in alkali-washed cells; yeast mannan and alkali-soluble glucan had little receptor activity. A minor fraction of receptor activity was removed from alkali-washed cells by hot acetic acid extraction, a procedure which solubilized some (1 → 6)-β- d -glucan and glycogen. The major fraction (>70%) of receptor activity remained with the acid-insoluble (1 → 6)-β-and (1 → 3)-β-glucans. Zymolyase, an endo-(1 → 3)-β- d -glucanase, solubilized a substantial fraction of the receptor activity in the acid-insoluble glucans. The receptor activity in yeast cell walls was periodate and (1 → 6)-β- d -glucanase sensitive, but was resistant to (1 → 3)-β- d -glucanase and α-amylase. The acid-soluble glucan fractions of a sensitive strain and a krel-l receptor-defective toxin-resistant mutant were examined. The krel-l strain had a reduced amount (ca. 50%) of (1 → 6)-β- d -glucan compared with the sensitive parent strain. A sensitive revertant of the krel-l strain regained the parental level of glucan. These results implicate (1 → 6)-β- d -glucan as a component of the yeast cell wall receptor for killer toxin.