Investigating the Influence of the Lipid Structure on the Global Membrane Organization: Effect of the Fatty Acids

Lipid molecules are involved in a wide range of fundamental cell functions, explaining the enormous structural diversity of lipids, partly due to the large number of different fatty acids, which can vary in length and in the number and position of unsaturated bond(s). Interestingly, imbalances between (un)saturated species have been reported in various pathologies. Hence, it is of particular importance to study in detail the structural consequences associated with variations in the nature of the lipid hydrocarbon tails. To this end, 17 single-component lipid bilayers, varying only in the nature of the hydrocarbon core are studied by molecular dynamics (MD) simulations. The structural analysis reveals that the effect of the nature of the two fatty acids on the overall membrane structure is additive. In addition, TDDFT quantum mechanical (QM) calculations are performed to study the modulations of the nonlinear optical (NLO) properties of an embedded probe, serving as local structural microscopes. However, these calculations highlight the difficulty of rationalizing changes in the NLO responses, in relation with the nature of the hydrocarbon region of the host environment. Nevertheless, less dense and packed membranes, which allow the probe to adopt more planar conformations, are associated with larger NLO responses. Investigation of the influence of fatty acid structures in terms of length and degree of unsaturation on the global organization of the cell membrane, as revealed by the nonlinear optical responses of an embedded chromophore.image