Gregory A. Voth

The multiscale coarse-graining (MS-CG) method obtains CG interactions from atomistic configurations, as demonstrated previously for a variety of soft matter and biological systems. In this article, recent advances in MS-CG algorithms are described, and a recently developed computer program MSCGFM for MS-CG calculations is introduced. The algorithms enhance the efficiency and stability of MS-CG computations, and these algorithms are incorporated into the MSCGFM program. As a result of these efforts, MS-CG calculations on large scale systems such as peptide and proteins can become tractable, and the numerical stability of solutions for ill-posed MS-CG problems can be regularized efficiently. Various parallelization strategies are also discussed.

This work develops a method for the construction of multiscale coarse-grained (MS-CG) force fields at different temperatures based on available atomistic data at a given reference temperature. The validity of this theory is demonstrated numerically by applying it to construct MS-CG models of the Lennard-Jones liquid and simple point charge water model systems.

Human carbonic anhydrase II (HCA II) is one of the fastest known enzymes, which utilizes a rate-limiting proton transport (PT) step in its enzymatic reaction. To evaluate the PT event at an atomistic level, the multistate empirical valence bond (MS-EVB) method has been utilized in this work. It is observed that the PT event in HCA II exploits a transient active site water cluster to transport the excess proton between the catalytic zinc-bound water/hydroxide and the proton shuttling residue, His64. This PT event is found to be dependent on the enzyme’s ability to form and stabilize the active site water cluster in addition to its ability to orient His64 in a favorable conformation. Evaluation of the PT free energy barrier for different orientations of His64 reveals this residue’s vital role as a proton transporter and elucidates its direct effect on the barrier to PT through the active site water. It is suggested that the rate-limiting step oscillates between the active site water PT event to His64 and the de/protonation of His64 depending on the exogenous buffer concentration and the orientation of His64. In the absence of a PT acceptor/donor at position 64, it is found that the excess proton will utilize one of three distinct paths to enter/leave the active site. This latter result not only allows for an increased understanding of how enzymes capitalize on the protein/solvent interface to guide excess protons to/from areas of interest, it also provides valuable insight into the chemical rescue experiments on HCA II mutants.

An effective force coarse-graining (EF-CG) method is presented in this paper that complements the more general multiscale coarse-graining (MS-CG) methodology. The EF-CG method determines effective pairwise forces between coarse-grained sites by averaging over the atomistic forces between the corresponding atomic groups in configurations sampled from equilibrium all-atom molecular dynamics simulations. The EF-CG method extracts the transferable part of the MS-CG force field at the cost of reduced accuracy in reproducing certain structural properties. Therefore, the EF-CG method provides an alternative to the MS-CG approach for determining CG force fields that give improved transferability but reduced structural accuracy. The EF-CG method is especially suitable for coarse-graining large molecules with high symmetry, such as bulky organic molecules, and for studying complex phenomena across a range of thermodynamic conditions. The connection between the EF-CG and MS-CG approaches as well as the limitations of the EF-CG method are also discussed. Numerical results for neopentane, methanol and ionic liquid systems illustrate the utility of the method.

A solvent-free coarse-grained model for a 1:1 mixed dioleoylphosphatidylcholine (DOPC) and a dioleoylphospatidylethanolamine (DOPE) bilayer is developed using the multiscale coarse-graining (MS-CG) approach. B-spline basis functions are implemented instead of the original cubic spline basis functions in the MS-CG method. The new B-spline basis functions are able to dramatically reduce memory requirements and increase computational efficiency of the MS-CG calculation. Various structural properties from the CG simulations are compared with their corresponding all-atom counterpart in order to validate the CG model. The resulting CG structural properties agree well with atomistic results, which shows that the MS-CG force field can reasonably approximate the many-body potential of mean force in the coarse-grained coordinates. Fast lipid lateral diffusion in the CG simulations, as a result of smoother free energy landscape, makes the study of phase behavior of the binary mixture possible. Small clusters of distinct lipid composition are identified by analyzing the DOPC/DOPE lipid lateral distribution, indicating a nonuniform distribution for the mixed bilayer. The results of lipid phase behavior are compared to experimental results, and connections between the experimental and simulation conclusions are discussed.