Abstract
We study the lipid and phase transferability of our recently developed systematically coarse-grained solvent-free membrane model. The force field was explicitly parameterized to describe a fluid 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC) bilayer at 310 K with correct structure and area per lipid, while gaining at least three orders of magnitude in computational efficiency (see Wang and Deserno 2010 J. Phys. Chem. B 114 11207–20). Here, we show that exchanging CG tails, without any subsequent re-parameterization, creates reliable models of 1,2-dioleoylphosphatidylcholine (DOPC) and 1,2-dipalmitoylphosphatidylcholine (DPPC) lipids in terms of structure and area per lipid. Furthermore, all CG lipids undergo a liquid–gel transition upon cooling, with characteristics like those observed in experiments and all-atom simulations during phase transformation. These studies suggest a promising transferability of our force field parameters to different lipid species and thermodynamic state points, properties that are a prerequisite for even more complex systems, such as mixtures.
Highlights
Single-component fluid lipid membranes are often used as the simplest model system for biological membranes [2,3] and have been extensively studied in experiments [4]–[12] and simulations [13,14]
Aiming to perform mesoscopic quantitative bilayer simulations, we previously presented a solvent-free CG lipid model with efforts to preserve both computational efficiency and local structural and chemical information
Since a reliable performance of any CG model away from its point of parameterization, or the usage of the same interaction potentials for different molecular topologies, is never guaranteed, we investigated the lipid and phase transferability of this solvent-free CG lipid model
Summary
Single-component fluid lipid membranes (i.e. in their Lα phase) are often used as the simplest model system for biological membranes [2,3] and have been extensively studied in experiments [4]–[12] and simulations [13,14]. The aim of this paper is to probe whether changes of lipid topology or temperature—without further reparameterization—result in lipid membranes with satisfactory physical properties, making headway towards the ultimate goal of studying complex membranes using efficient CG force fields. Each 1,2-dipalmitoylphosphatidylcholine (DPPC), POPC and 1,2dioleoylphosphatidylcholine (DOPC) lipid molecule is mapped onto a structure consisting of 15, 16 and 17 CG sites, respectively This requires eight different bead types for characteristic chemical moieties (see figure 1), which we denote as follows: CH for the choline entity of the head group; PH for the phosphate group; GL for the glycerol backbone; E1 and E2 for the ester groups of the sn-1 and sn-2 tails of the lipid, respectively; AS, AD and AE for the hydrocarbon groups —(CH2—CH2 CH2)—,—(CH2=CH2)—and—(CH2— CH3), respectively. We transfer the parameters of this CG force field to the topologically different lipids DOPC and DPPC without any additional modification
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