Abstract
Protein dynamics is characterized by fluctuations among different conformational substates, i.e. the different minima of their energy landscape. At temperatures above ~200 K, these fluctuations lead to a steep increase in the thermal dependence of all dynamical properties, phenomenon known as Protein Dynamical Transition. In spite of the intense studies, little is known about the effects of pressure on these processes, investigated mostly near room temperature. We studied by neutron scattering the dynamics of myoglobin in a wide temperature and pressure range. Our results show that high pressure reduces protein motions, but does not affect the onset temperature for the Protein Dynamical Transition, indicating that the energy differences and barriers among conformational substates do not change with pressure. Instead, high pressure values strongly reduce the average structural differences between the accessible conformational substates, thus increasing the roughness of the free energy landscape of the system.
Highlights
Protein dynamics is characterized by fluctuations among different conformational substates, i.e. the different minima of their energy landscape
The peculiar dynamical properties of proteins arise from their complex nature, which can be well described in terms of a multi-minima energy landscape
At high temperature, typically above ~200 K, proteins start to fluctuate among different conformational substates (CS) and this brings about a steep increase in all their dynamical properties, in particular in the Mean Square Displacements (MSD) of their atoms[3,4]
Summary
Protein dynamics is characterized by fluctuations among different conformational substates, i.e. the different minima of their energy landscape. The amount of water present in the sample was sufficient to allow the flexibility necessary for protein function[32] and its high viscosity assures that overall protein diffusion and rotation have no influence on the dynamical properties measured in the time window of our experiment (~100 ps, see Materials and Methods) In this respect, it is worth of noting that the results that we obtained at low pressure are in excellent agreement with those relative to standard hydrated protein samples and in particular to myoglobin, as investigated by Doster et al.[4] (see below). For hydrated proteins, as it is in our sample, when the dynamical properties of non-exchangeable hydrogen atoms are compared to those of backbone atoms[36] or of all atoms of the molecules[35,37], analogous results are generally obtained This holds, concerning our specific study, in investigations about the effects of pressure on protein dynamics[27]
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