Atomic-scale lateral heterogeneity and dynamics of two-component lipid bilayers composed of saturated and unsaturated phosphatidylcholines

Studies of lateral heterogeneity in cell membranes are important since they help to understand the physical origin of lipid domains and rafts. The simplest membrane mimics are hydrated bilayers composed of saturated and unsaturated lipids. While their atomic structural details resist easy experimental characterization, important insight can be gained via computer modeling. We present the results of all-atom molecular dynamics simulations for a series of fluid dioleoylphosphatidylcholine (DOPC) and dipalmitoylphosphatidylcholine (DPPC) bilayers. Lateral arrangement of lipids in these systems is not random and reveals small geometrical and hydrophobic clusters on the surface. Being "sharp" inside the bilayer, lateral heterogeneity is very 'fuzzy" on the surface. This picture is highly dynamic - lifetimes of clusters are similar to 1 ns. In the binary system, DPPC acts as an "order-preferring" agent, which efficiently modulates behavior of DOPC. Bilayer properties are tuned in a wide range by the chemical nature and relative content of lipids. The impact that the micro-heterogeneity may have on formation of lateral domains in response to external signals is discussed. Understanding of such effects creates a basis for rational design of artificial membranes with predefined properties.