Effect of Cholesterol on the Structure of Networked Water at the Surface of a Model Lipid Membrane.

Using all-atom molecular dynamics simulations and network analysis, we investigated the effect of membrane cholesterol level on the structure of organized water at the interface between bulk water and a model lipid membrane. Irrespective of membrane cholesterol content, interfacial water structure is largely perturbed by the presence of the membrane surface due to water-phospholipid interactions, which deplete the chance of hydrogen bonding among water molecules. In contrast, the addition of cholesterol suppresses the disturbing effect of the membrane on water-water hydrogen bonding as cholesterol provides a more bulklike environment for the interfacial water molecules, as evidenced by enhancement of local water density, a reduction in their orientational bias, and increases in both the number of hydrogen bonds and the topological complexity of the hydrogen bond network.