How well does charge reparametrisation account for solvent screening in molecular mechanics calculations? The example of myosin

The rate constant of an enzyme-catalysed reaction is one of the major target properties to understand protein function. Atomic-detail computer simulations can in principle be used to estimate rate constants from the energy profile along the reaction coordinate. For such simulations, molecular mechanics is combined with a quantum description of the reaction process. In molecular mechanics calculations, the electrostatic field is represented by the Coulomb potential of partial atomic charges which have been parametrised for small building blocks in vacuum and transferred to the macromolecule. In aqueous solution, however, the electrostatic interactions are affected by the solvent polarization. While this can be described by numerically solving the Poisson-Boltzmann equation, it is computationally expensive. A simple approximation to this is to optimally reproduce the electrostatic potential in solution by reparametrising the partial atomic charges in such a way that a simple Coulomb potential can still be used. Such a procedure would allow to perform fast calculations of reaction processes in proteins while accounting for the solvent screening effect. Here, this method is tested on myosin, a motor protein that is both an enzyme and exists in very different conformations.