title: Using ergosterol to mitigate the deleterious effects of ethanol on bilayer structure.
abstract: In wine fermentations, yeast is exposed to concentrated ethanol solutions. Ergosterol, a sterol that is found in lower eukaryotic membranes, helps preserve the structural integrity of yeast membranes in stressful environmental conditions. A premature arrest in ethanol production due to unknown metabolic changes in yeasts results in undesirably large concentrations of residual sugar and may be caused by the formation of an ethanol-induced interdigitated phase. We use atomistic molecular dynamics simulations to examine the induction of the interdigitated phase in model yeast membranes that contain either 0, 10, 20, 25 mol % ergosterol in ethanol concentrations of 0, 10, 15 vol %. The 25 mol % ergosterol system shows a similar level of interdigitation for the 0 and 10 vol % ethanol solutions, indicating that ergosterol molecules in this system are able to effectively counteract the disruptive behavior of ethanol molecules. However, at a 15 vol % ethanol solution, the amount of interdigitation triples and this ethanol concentration is similar to the concentrations found in stuck fermentations. The other three ergosterol concentrations studied (0, 10, 20 mol %) show larger quantities of interdigitation in the 10 vol % ethanol solution than the 0 vol % solution. Thus, the 25 mol % ergosterol bilayer, which is representative of the ergosterol concentrations seen in yeast membranes, is unique in the systems examined in its ability to delay the onset of ethanol-induced interdigitation. The concentration of ergosterol affects the permeability of a fluid-phase bilayer, where the 10 mol % ergosterol bilayer is more permeable to ethanol than either a bilayer containing no ergosterol molecules or a bilayer containing 20/25 mol % ergosterol. This lipid permeability appears to be correlated with the existence of a lipid region whose lipids neither have direct contact with ergosterol molecules nor exhibit bulk lipid/lipid interactions.
authors.affiliation: Department of Chemical Engineering and Materials Science University of California Davis, Davis, California 95616, USA.
authors.forename: Allison N
authors.initials: AN
authors.lastname: Dickey
authors.forename: Wen-Sau
authors.initials: WS
authors.lastname: Yim
authors.forename: Wen-Saul
authors.initials: WS
authors.lastname: Yim
authors.forename: Roland
authors.initials: R
authors.lastname: Faller
mesh_terms: D003198:Computer Simulation; D004875:Ergosterol / Q000737:chemistry*; D000431:Ethanol / Q000737:chemistry*; D008051:Lipid Bilayers / Q000737:chemistry*; D008055:Lipids / Q000737:chemistry; D010539:Permeability; D013696:Temperature
chemical_list: D008051:Lipid Bilayers; D008055:Lipids; D000431:Ethanol; D004875:Ergosterol