Studies of Lipid Bilayer Structure and Dynamics

Abstract

<p>The biological membrane is one of the fundamental components in nature, however it is still not well understood. The variety of lipids and other macromolecules found in the membrane makes it very difficult to discern its properties in vivo. Lipid bilayers form the backbone of biological membranes and provide an ideal model system with which to study membrane function and properties. Here we present the results of studies of lipid bilayer structure and dynamics with neutron and x-ray scattering techniques. In particular, the diffusion of single solid supported bilayers and the collective dynamics of lipid-ethanol systems were studied. The first observations of single bilayer diffusion with quasi-elastic neutron scattering are presented. Single solid supported bilayers of 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine (DMPC) were prepared and examined with a backscattering spectrometer. Diffusion constants were found to be consistent with multilamellar systems. Single solid ! supported bilayer diffusion was also found to exhibit a continuous character with enhanced diffusion at the nearest neighbour distance.</p> <p>Investigations of the effects of ethanol on collective lipid tail dynamics are also presented. Highly oriented multilamellar solid supported DMPC bilayers were prepared and immersed in a 5% ethanol/water solution. Inelastic neutron scattering experiments and all atom molecular dynamics simulations reveal the presence of a new low-energy dynamic mode in the lipid tails of DMPC-ethanol systems. This mode exhibits little dispersion and appears in addition to the high energy acoustic mode associated with lipid tail fluctuations in pure lipid systems, which is also observed. Both modes demonstrate in-plane and perpendicular character which may be related to the transport of small molecules through the membrane core. Additional x-ray diffraction studies of DMPC-ethanol systems hydrated from the vapour phase demonstrate that lipid tail fluctuations in DMPC-ethanol systems exhibit lengthscales equal or less than the thickness of the bilayer.</p>