Temperature and timescale dependence of protein dynamics in methanol : water mixtures

Abstract

Experimental and computer simulation studies have suggested the presence of a transition in the dynamics of hydrated proteins at around 180-220 K. This transition is manifested by nonlinear behaviour in the temperature dependence of the average atomic mean-square displacement which increases at high temperature. Here, we present results of a dynamic neutron scattering analysis of the transition for a simple enzyme: xylanase in water : methanol solutions of varying methanol concentrations. In order to investigate motions on different timescales, two different instruments were used: one sensitive to B100 ps timescale motions and the other to Bns timescale motions. The results reveal distinctly different behaviour on the two timescales examined. On the shorter timescale the dynamics are dictated by the properties of the surrounding solvent: the temperature of the dynamical transition lowers with increasing methanol concentration closely following the melting behaviour of the corresponding water : methanol solution. This contrasts with the longer (ns) timescale results in which the dynamical transition appears at temperatures lower than the corresponding melting point of the cryosolvent. These results are suggested to arise from a collaborative effect between the protein surface and the solvent which lowers the effective melting temperature of the protein hydration layer. Taken together, the results suggest that the protein solvation shell may play a major role in the temperature dependence of protein solution dynamics.

Protein and solvent dynamics as studied by QENS and dielectric spectroscopy

“…For instance, anharmonic protein motions occur at a considerably lower temperature when methanol is used as solvent, compared to when the protein is hydrated with water. This finding is in accordance with a recent study [30] of a protein in methanol water mixtures, where it was shown that the onset temperature of anharmonic protein motions decreased with increasing methanol concentration. However, more interesting is the result that the fastest (i.e.…”

First-order transitions in glasses and melts induced by solid superclusters nucleated and melted by homogeneous nucleation instead of surface melting

“…The enthalpy difference between Liquid 1 and Liquid 2 depending on  2 creates an undercooled phase, that I call Phase 3, which is transformed in glass below Tg and in ordered liquid phase above Tg. Phase 3 has two homogeneous nucleation temperatures Tn+ for melting above Tm and formation below Tm [34]. Its presence has been recognized in supercooled water below Tm and in superheated water under pressure [21,35].…”

Biomolecular Structure and Dynamics with Neutrons: The View from Simulation

“…[29] The results revealed distinctly different behavior on the two timescales examined. In order to investigate motions on different timescales, two different instruments were used: one sensitive to approximately 100 ps timescale motions and the other to approximately 1 ns timescale motions.…”

“…In order to investigate motions on different timescales, two different instruments were used: one sensitive to approximately 100 ps timescale motions and the other to approximately 1 ns timescale motions. [29] The results revealed distinctly different behavior on the two timescales examined. On the shorter timescale, the dynamics are dictated by the properties of the surrounding solvent: the temperature of the dynamical transition lowers with increasing methanol concentration, closely following the melting behavior of the corresponding water-methanol solution.…”