Influence of sterol structure on yeast plasma membrane properties

Fluorescence anisotropy measurements indicated that physical changes occurred in the lipids of plasma membranes of yeast sterol mutants but not in the plasma membrane of an ergosterol wild-type. Parallel experiments with model membrane liposomes verified that the physical changes in lipids observed in the sterol mutants are dependent on the sterol present and not the phospholipid composition. In addition, the physical changes in lipids observed in liposomes derived from wild-type phospholipids were eliminated by addition of ergosterol but persisted in the presence of cholesterol, cholestanol, ergostanol, or sterols from the sterol mutants. No physical changes in lipids were observed, however, in plasma membranes from a sterol auxotroph, even when the auxotroph was grown on cholesterol or cholestanol. The lack of physical changes in lipids in the sterol auxotroph may reflect the ability of the auxotroph to modify its phospholipid composition with respect to its sterol composition. These results indicate that high specificity 'sparking' sterol is not required for the regulation of overall bulk lipid properties of the plasma membrane.