Nanocomposite of Fullerenes and Natural Rubbers: MARTINI Force Field Molecular Dynamics Simulations

The mechanical properties of natural rubber (NR) composites depend on many factors, including the filler loading, filler size, filler dispersion, and filler-rubber interfacial interactions. Thus, NR composites with nano-sized fillers have attracted a great deal of attention for improving properties such as stiffness, chemical resistance, and high wear resistance. Here, a coarse-grained (CG) model based on the MARTINI force field version 2.1 has been developed and deployed for simulations of cis-1,4-polyisoprene (cis-PI). The model shows qualitative and quantitative agreement with the experiments and atomistic simulations. Interestingly, only a 0.5% difference with respect to the experimental result of the glass transition temperature (Tg) of the cis-PI in the melts was observed. In addition, the mechanical and thermodynamical properties of the cis-PI-fullerene(C60) composites were investigated. Coarse-grained molecular dynamics (MD) simulations of cis-PI-C60 composites with varying fullerene concentrations (0–32 parts per hundred of rubber; phr) were performed over 200 microseconds. The structural, mechanical, and thermal properties of the composites were determined. The density, bulk modulus, thermal expansion, heat capacity, and Tg of the NR composites were found to increase with increasing C60 concentration. The presence of C60 resulted in a slight increasing of the end-to-end distance and radius of the gyration of the cis-PI chains. The contribution of C60 and cis-PI interfacial interactions led to an enhancement of the bulk moduli of the composites. This model should be helpful in the investigations and design of effective fillers of NR-C60 composites for improving their properties.

Application of molecular dynamics simulation in self-assembly

During the past few years, numerous studies have been done in self-assembly. Among most of these studies, Molecular Dynamic Simulation is widely used to construct the experiment model. This work firstly introduced three practical applications of MD simulation in self-assembly. Then, two main kinds of simulation are discussed including all-atom simulation and coarse-grained simulation, together with the way of thoughts before the simulation start. It is found that researchers always start with the whole analysis of the substances that need to be studied. It helps to confirm the appropriate model that can apply in the simulation naturally. Besides, depended on the principles that need to be studied, the way of establishing the simulation system varies, ranging from separation experiment in both types of simulation to the change of essential parameters. Furthermore, the adoption of L-J potential in MD simulation proves to be a wise option on account of its convenient and simple model. It is remarkable that, considering some small details like the differences between implicit and explicit solution, classical Martini force field is replaced by Dry Martini force field.

Improved Parameterization of Phosphatidylinositide Lipid Headgroups for the Martini 3 Coarse Grain Force Field

Phosphoinositides are a family of membrane phospholipids that play crucial roles in membrane regulatory events. As such, these lipids are often a key part of molecular dynamics simulation studies of biological membranes, in particular of those employing coarse-grain models because of the potential long times and sizes of the involved membrane processes. Version 3 of the widely used Martini coarse grain force field has been recently published, greatly refining many aspects of biomolecular interactions. In order to properly use it for lipid membrane simulations with phosphoinositides, we put forth the Martini 3-specific parameterization of inositol, phosphatidylinositol, the seven physiologically relevant phosphorylated derivatives of phosphatidylinositol. Compared to parameterizations for earlier Martini versions, focus was put on a more accurate reproduction of the behavior seen in both atomistic simulations and experimental studies, including the signaling relevant phosphoinositide interaction with divalent cations. The models we develop improve upon the conformational dynamics of phosphoinositides in the Martini force field and provide stable topologies at typical Martini timesteps. They are able to reproduce experimentally known protein-binding poses as well as phosphoinositide aggregation tendencies. The latter were tested both in the presence and absence of calcium, and include correct behavior of PI(4,5)P2 calcium-induced clusters, which can be of relevance for regulation.

Improved Parameterization of Phosphatidylinositide Lipid Headgroups for the Martini 3 Coarse Grain Force Field

Phosphoinositides are a family of membrane phospholipids that play crucial roles in membrane regulatory events. As such, these lipids are often a key part of molecular dynamics simulation studies of biological membranes, in particular of those employing coarse-grain models because of the potential long times and sizes of the involved membrane processes. Version 3 of the widely used Martini coarse grain force field has been recently published, greatly refining many aspects of biomolecular interactions. In order to properly use it for lipid membrane simulations with phosphoinositides, we put forth the Martini 3-specific parameterization of inositol, phosphatidylinositol, the seven physiologically relevant phosphorylated derivatives of phosphatidylinositol. Compared to parameterizations for earlier Martini versions, focus was put on a more accurate reproduction of the behavior seen in both atomistic simulations and experimental studies, including the signaling relevant phosphoinositide interaction with divalent cations. The models we develop improve upon the conformational dynamics of phosphoinositides in the Martini force field and provide stable topologies at typical Martini timesteps. They are able to reproduce experimentally known protein-binding poses as well as phosphoinositide aggregation tendencies. The latter were tested both in the presence and absence of calcium, and include correct behavior of PI(4,5)P2 calcium-induced clusters, which can be of relevance for regulation.

Improved Parameterization of Phosphatidylinositide Lipid Headgroups for the Martini 3 Coarse Grain Force Field

Phosphoinositides are a family of membrane phospholipids that play crucial roles in membrane regulatory events. As such, these lipids are often a key part of molecular dynamics simulation studies of biological membranes, in particular of those employing coarse-grain models because of the potential long times and sizes of the involved membrane processes. Version 3 of the widely used Martini coarse grain force field has been recently published, greatly refining many aspects of biomolecular interactions. In order to properly use it for lipid membrane simulations with phosphoinositides, we put forth the Martini 3-specific parameterization of inositol, phosphatidylinositol, the seven physiologically relevant phosphorylated derivatives of phosphatidylinositol. Compared to parameterizations for earlier Martini versions, focus was put on a more accurate reproduction of the behavior seen in both atomistic simulations and experimental studies, including the signaling relevant phosphoinositide interaction with divalent cations. The models we develop improve upon the conformational dynamics of phosphoinositides in the Martini force field and provide stable topologies at typical Martini timesteps. They are able to reproduce experimentally known protein-binding poses as well as phosphoinositide aggregation tendencies. The latter were tested both in the presence and absence of calcium, and include correct behavior of PI(4,5)P2 calcium-induced clusters, which can be of relevance for regulation.

Coarse Grained Molecular Dynamic Simulations for the Study of TNF Receptor Family Members' Transmembrane Organization

The Tumor Necrosis Factor (TNF) and the TNF receptor (TNFR) superfamilies are composed of 19 ligands and 30 receptors, respectively. The oligomeric properties of ligands, both membrane bound and soluble, has been studied most. However, less is known about the oligomeric properties of TNFRs. Earlier reports identified the extracellular, membrane-distal, cysteine-rich domain as a pre-ligand assembly domain which stabilizes receptor dimers and/or trimers in the absence of ligand. Nevertheless, recent reports based on structural nuclear magnetic resonance (NMR) highlight the intrinsic role of the transmembrane domains to form dimers (p75NTR), trimers (Fas), or dimers of trimers (DR5). Thus, understanding the structural basis of transmembrane oligomerization may shed light on the mechanism for signal transduction and the impact of disease-associated mutations in this region. To this end, here we used an in silico coarse grained molecular dynamics approach with Martini force field to study TNFR transmembrane homotypic interactions. We have first validated this approach studying the three TNFR described by NMR (p75NTR, Fas, and DR5). We have simulated membrane patches composed of 36 helices of the same receptor equidistantly distributed in order to get unbiassed information on spontaneous proteins assemblies. Good agreement was found in the specific residues involved in homotypic interactions and we were able to observe dimers, trimers, and higher-order oligomers corresponding to those reported in NMR experiments. We have, applied this approach to study the assembly of disease-related mutations being able to assess their impact on oligomerization stability. In conclusion, our results showed the usefulness of coarse grained simulations with Martini force field to study in an unbiased manner higher order transmembrane oligomerization.

Lipid distributions and transleaflet cholesterol migration near heterogeneous surfaces in asymmetric bilayers

Specific and nonspecific protein-lipid interactions in cell membranes have important roles in an abundance of biological functions. We have used coarse-grained (CG) molecular dynamics (MD) simulations to assess lipid distributions and cholesterol flipping dynamics around surfaces in a model asymmetric plasma membrane containing one of six structurally distinct entities: aquaporin-1 (AQP1), the bacterial β-barrel outer membrane proteins OmpF and OmpX, KcsA potassium channel, WALP23 peptide, and a carbon nanotube (CNT). Our findings revealed varied lipid partitioning and cholesterol flipping times around the different solutes, and putative cholesterol binding sites in AQP1 and KcsA. The results suggest that protein-lipid interactions can be highly variable, and that surface-dependant lipid profiles are effectively manifested in CG simulations with the Martini force field.

Coarse-grained Simulation of Anionic Surfactant Sodium Dodecyl Sulfate

Through analyzing the deficiency of the current coarse-grained (CG) model, a new CG model for the ionic surfactant was proposed based on the Martini force field and iterative Boltzmann inversion method. In this model, the electrostatic interaction can be tackled by using a self-defined piecewise function to avoid the disadvantage of using coarse-grained solvents, and the VDW interaction parameters were derived by iterative methods. Using the improved model, the radial distribution function of NaCl and SDS solution in all-atom OPLS can be completely reproduced. The successful setup of the new coarse-grained model provides a good example of the construction of a high-precision coarse-grained force field.