Abstract
Hydration water is the natural matrix of biological macromolecules and is essential for their activity in cells. The coupling between water and protein dynamics has been intensively studied, yet it remains controversial. Here we combine protein perdeuteration, neutron scattering and molecular dynamics simulations to explore the nature of hydration water motions at temperatures between 200 and 300 K, across the so-called protein dynamical transition, in the intrinsically disordered human protein tau and the globular maltose binding protein. Quasi-elastic broadening is fitted with a model of translating, rotating and immobile water molecules. In both experiment and simulation, the translational component markedly increases at the protein dynamical transition (around 240 K), regardless of whether the protein is intrinsically disordered or folded. Thus, we generalize the notion that the translational diffusion of water molecules on a protein surface promotes the large-amplitude motions of proteins that are required for their biological activity.
Highlights
Elastic incoherent neutron-scattering experiments on D2O-hydrated, non-deuterated tau[5] and non-deuterated MBP15 samples have indicated that a protein dynamical transition (Fig. 1) takes place at a similar temperature in both proteins
We evaluated the temperature dependence of two types of protein– water hydrogen bond (HB) lifetimes computed from the simulations: the continuous hydrogen bonds (HBs) relaxation time, tHBC, and the intermittent HB relaxation time, tHBI. tHBC is the average time before a protein–water HB breaks, while tHBI represents the timescale for relaxation of the protein–water HB network[46]
We addressed the relation between hydration water motions and the dynamics of both an IDP and a folded protein (MBP) by combining protein perdeuteration, neutron scattering and Molecular dynamics (MD) simulations
Summary
The other dynamical parameters (that is, rotational correlation rate and translational diffusion coefficient) reveal a perturbation of protein hydration water with respect to bulk water as already reported in the literature (see Supplementary Fig. 6). We evaluated the temperature dependence of two types of protein– water hydrogen bond (HB) lifetimes computed from the simulations: the continuous HB relaxation time ( known as the fast HB relaxation time), tHBC, and the intermittent HB relaxation time ( referred as the slow HB network relaxation time), tHBI. We computed for both protein powders the MSD of the hydration water oxygen atoms, assessing thereby the translational dynamics of water molecules. The MSD, plotted at 100 ps as a function of temperature, show a sharp increase at around 240 K, signalling the onset of water translational diffusion The MSD, plotted at 100 ps as a function of temperature in Fig. 5c, show a sharp increase at around 240 K, signalling the onset of water translational diffusion
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