Effect of Hydration on a Lipid Membrane Composed of Ceramide[NP] 24,Lignoceric Acid,and Cholesterol:A Molecular Dynamics Simulation Study

摘要

Stratum comeum(SC)lipids serve as a barrier against exogenous chemicals and microbes.Interpretation of an experimental observation made on the SC lipids is a formidable task due to an extremely large variation in the chain length and headgroup of the lipids.Therefore much work has been done on model systems with a simple composition of well-defined components.Experiments on the model membranes support for the hydration of the headgroup region but its effect on the membrane properties needs to be studied systematically through a molecular modeling.In this study MD simulation has been performed on a membrane containing an equimolar mixture of ceramide[NP]24,lignoceric acid,and cholesterol for which a neutron diffraction study has been reported recently.Structure and the dynamic properties of the lipids demonstrated that the membrane was in a hexagonally packed gel phase.Hydration of the headgroup region promoted the lateral motion.Water formed multiple hydrogen bonds with the lipids and the majority of water molecules were clustered together to form pools.Water molecules outside of the pools were less mobile and sometimes stuck in an anhydrous region maldng it difficult to jump to the headgroup region of the opposing lipid layer.Such interactions slowed down the diffusion of water by one or two orders of magnitude compared with the bulk water.Repeat distance and neutron scattering length density calculated from the MD simulation were in good agreement with the experimentally determined values when the bilayer was hydrated by 2 H2O per lipid.