Effect of Cholesterol vs. Ergosterol on DPPC Bilayer Properties: Insights from Atomistic Simulations

Abstract

Cholesterol and ergosterol are two dominant sterols in the membranes of eukaryotic and yeast cells, respectively. Although their chemical structure is very similar, their impact on the structure and dynamics of membranes differs. In this work, we have explored the effect of these two sterols on binary mixtures with 1,2-dipalnitoyl-sn-glycerol-3-phosphocholine (DPPC) lipid bilayer at various sterol concentration and temperatures, employing molecular dynamics simulations. The simulations revealed that cholesterol has a stronger impact on the ordering of the lipid chains and leads to more condensed membranes with respect to ergosterol. This difference likely arises from a more planar structure of the ring part as well as the better alignment of cholesterol among the DPPC chains with respect to ergosterol. The degree of the planarity of the ring system affects the orientation of the methyl groups on the rough side and distribute the lipid chains on the two sides of the sterols differently. Similar to the structural observations, cholesterol also has a stronger influence on the dynamics, and consistently, establishes stronger DPPC-sterol interactions when compared to ergosterol. Although our findings are consistent with some previous simulations as well as recent experiments, they are at odds with some other studies. Therefore, the presented results may shed new lights on the impact of sterols on the saturated lipids bilayers with implications for binary mixtures of lipids as well as lipid rafts.SignificanceCholesterol and ergosterol are crucial lipid molecules of eukaryotic and prokaryotic cells, respectively, with an important role for the characteristics of the membranes. Surprisingly, many experimental studies have reported opposing results concerning their relative impact. Our work aims to understand the molecular mechanism behind the influence of these sterols on the properties of saturated DPPC chains via a systematic computational approach at atomic resolution. The results show that cholesterol has a higher impact on the ordering, condensing and dynamics of the lipid chains and closely interact with them due to its more planar structure as compared to ergosterol. These effects can have implications in lipid rafts and the interaction of therapeutic drugs with membranes.