Abstracts Category : Other

Insights on PUFA-containing lipid membranes probed by MD simulations

by Xiaoling Leng

Indiana University-Purdue University Indianapolis (IUPUI) The cell membrane serves as a barrier between the interior and exterior of a living cell. Its main structural component is the lipid bilayer, which is composed of various kinds of lipids that segregate into domains. These lipid domains, distinguished in composition and physical properties from the bulk lipids that surround them, are believed to modulate the function of resident proteins by providing an appropriate lipid environment. Polyunsaturated fatty acids (PUFA) are a type of fatty acid that contain multiple C=C double bonds. They have a lot of health benefits, which may originate in part due to their incorporation into lipids in the plasma membrane. Hypotheses that PUFA-containing lipids laterally separate into domains and/or modulate the structure of existing domains have been raised to explain the fundamental role played by PUFA. In our research, we use molecular dynamics (MD) simulations to simulate model membranes composed of PUFA-containing phospholipids and to investigate their interaction with cholesterol and vitamin E that are influential membrane constituents. The presumptive function for vitamin E in membranes is to protect PUFA against oxidation. Although the chemistry of the process is well established, the role played by the molecular structure that we address with atomistic molecular dynamics (MD) simulations remains controversial. We compared the behavior of vitamin E in lipid bilayers composed of 1-stearoyl-2-docosahexaenoylphosphatidylcholine (SDPC, 18:0-22-6PC) and 1-stearoyl-2-oleoylphosphatidylcholine (SOPC, 18:0-18:1PC) via all-atom MD simulations at 37 C. SDPC represents a PUFA-containing lipid, and SOPC serves as monounsaturated control. From the calculation of van der Waals energy of interaction between vitamin E and fatty acid (FA) chains, we found higher probability that the PUFA chains surround the chromanol head group on vitamin E. This is further demonstrated by probability density maps of acyl chains around vitamin E molecules. Also, an ability to more easily penetrate deep into the PUFA containing bilayer of vitamin E is detected by faster flip-flop rate of vitamin E observed in the SDPC bilayers. These results showed that the high disorder of polyunsaturated docosahexaenoic acid (DHA) chains allows vitamin E to easily tunnel down into the bilayer and often brings the PUFA chains up to the surface of the bilayer, improving the likelihood that the reactive (hydroxyl) group on vitamin E would encounter a lipid peroxyl radical and terminate the oxidation process. Thus, the simulations indicate that the molecular structure of vitamin E supports its role as an antioxidant in a PUFA-containing membrane.A subsequent study on the partitioning of vitamin E into PUFA-containing lipids was done by analyzing the binding energy of vitamin E in the corresponding lipid bilayer. The binding energy is obtained from the potential of mean force (PMF) profile of vitamin E alone the membrane normal direction (z), which is calculatedAdvisors/Committee Members: Wassall, Stephen.