Interaction of iturin A, a lipopeptide antibiotic, with Saccharomyces cerevisiae cells: influence of the sterol membrane composition.

The binding of the membrane-active lipopeptide antibiotic iturin A to yeast cells was studied using radioactive iturin A. Saccharomyces cerevisiae had a maximum binding capacity of 5.6 x 10(9) molecules per single cell. The Scatchard plot of binding showed a biphasic profile, with a lower dissociation constant for small concentrations of iturin A. The break of slope at 30 microM iturin A corresponds to the micellization of antibiotic in solution. The binding is also dependent on the nature of the sterol present in the membrane. A mutant yeast strain with a membrane containing cholesterol instead of ergosterol showed the highest affinity for iturin A and the highest sensitivity to this antibiotic, as measured by K+ ion release. In contrast the presence of stigmasterol increased the resistance of the cells to iturin A.