Abstract
The molecular mechanics force field Slipids developed in a series of works by Jämbeck and Lyubartsev (J. Phys. Chem. B2012, 116, 3164–3179; J. Chem. Theory Comput.2012, 8, 2938–2948) generally provides a good description of various lipid bilayer systems. However, it was also found that order parameters of C–H bonds in the glycerol moiety of the phosphatidylcholine headgroup deviate significantly from NMR results. In this work, the dihedral force field parameters have been reparameterized in order to improve the agreement with experiment. For this purpose, we have computed energies for a large amount of lipid headgroup conformations using density functional theory on the B3P86/cc-pvqz level and optimized dihedral angle parameters simultaneously to provide the best fit to the quantum chemical energies. The new parameter set was validated for three lipid bilayer systems against a number of experimental properties including order parameters, area per lipid, scattering form factors, bilayer thickness, area compressibility and lateral diffusion coefficients. In addition, the order parameter dependence on cholesterol content in the POPC bilayer was investigated. It is shown that the new force field significantly improves agreement with the experimental order parameters for the lipid headgroup while keeping good agreement with other experimentally measured properties.
Highlights
Lipids are key components of biological membranes which are crucial parts of all cells.[1]
The quality of fit was quantified by the Pearson coefficient, indicating the correlation between the force field energies and the reference energies, and by the sum of squared deviations (SSD) between same quantities
We investigated the effect of cholesterol content on order parameters
Summary
Lipids are key components of biological membranes which are crucial parts of all cells.[1]. In order to test the performance of the fitted parameters, MD simulations were carried out for fully hydrated bilayers consisting of three different lipids (DMPC, POPC, and DPPC); see Figure 1.
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