Cholesterol shows preference for the interior of polyunsaturated lipid membranes

Recent neutron scattering experiments showed a striking manifestation of the aversion between polyunsaturated fatty acid (PUFA)-containing lipids and cholesterol. Selectively deuterated cholesterol/ 1,2-diarachidonylphosphatidylcholine (DAPC) samples revealed that the hydroxyl of the sterol resides at the center of the bilayer. Here we use a recently parametrized coarse grain simulation model to shed light on these puzzling experimental observations. Using a simulation setup in close correspondence to the experimental conditions, we reproduce the experimental neutron scattering profiles to a large extent. The simulations allow us to analyze the behavior of cholesterol in detail; we show that the interaction of cholesterol with the PUFA chains of DAPC leads to a fast flip-flop rate for the sterol and an increased preference of the sterol for the unusual location embedded between the monolayer leaflets.