Free energy for cholesterol insertion into lipid bilayers studied by molecular dynamic simulations
(English)Article in journal (Other academic) Submitted
Lipid bilayers consisting of binary mixtures of phospholipids and cholesterol are studied above and below the main phase transition temperature using coarse grained (CG) and united atom (UA) models by molecular dynamics simulations. The purpose is to explore whether phase segregation into cholesterol-rich and cholesterol-poor domains is favorable from a free energy point of view and what the required size of these domains would be. We observe directly in simulations that phase separated fluid phase systems mix in less than 200 ns. Since, the dynamics is about 2 orders of magnitude slower in the gel phase mixing was not observed in such system. The chemical potential for cholesterol insertion was calculated from simulations. This resulted in a small bulk free energy of about 0.3kBT per lipid that favors phase separation while a small line tension (a couple of pN) between cholesterol-rich and -poor regions favors mixing. Although a simple continuum theory would indicate stabilization of domains as small as 1-2 nm in size, this was not observed in direct simulations.
Cholesterol, phospholipids, domain formation, line tension
IdentifiersURN: urn:nbn:se:kth:diva-102276OAI: oai:DiVA.org:kth-102276DiVA: diva2:552042
QS 20122012-09-122012-09-122012-09-13Bibliographically approved