Perturbation of hydration layer in solvated proteins by external electric and electromagnetic fields: Insights from...

Given the fundamental role of water in governing the biochemistry of enzymes, and in regulating their wider biological activity (e.g., by local water concentration surrounding biomolecules), the influence of extraneous electric and electromagnetic (e/m) fields thereon is of central relevance to biophysics and, more widely, biology. With the increase in levels of local and atmospheric microwave-frequency radiation present in modern life, as well as other electric-field exposure, the impact upon hydration-water layers surrounding proteins, and biomolecules generally, becomes a particularly pertinent issue. Here, we present a (non-equilibrium) molecular-dynamics-simulation study on a model protein (hen egg-white lysozyme) hydrated in water, in which we determine, inter alia, translational self-diffusivities for both hen egg-white lysozyme and its hydration layer together with relaxation dynamics of the hydrogen-bond network between the protein and its hydration-layer water molecules on a residue-per-residue basis. Crucially, we perform this analysis both above and below the dynamical-transition temperature (at ∼220 K), at 300 and 200 K, respectively, and we compare the effects of external static-electric and e/m fields with linear-response-régime (r.m.s.) intensities of 0.02 V/Å. It was found that the translational self-diffusivity of hen egg-white lysozyme and its hydration-water layer are increased substantially in static fields, primarily due to the induced electrophoretic motion, whilst the water-protein hydrogen-bond-network-rearrangement kinetics can also undergo rather striking accelerations, primarily due to the enhancement of a larger-amplitude local translational and rotational motion by charged and dipolar residues, which serves to promote hydrogen-bond breakage and re-formation kinetics. These external-field effects are particularly evident at 200 K, where they serve to induce the protein- and solvation-layer-response effects redolent of dynamical transition at a lower temperature (∼200 K) vis-à-vis the zero-field case (∼220 K).