The role of protein-solvent hydrogen bond dynamics in the structural relaxation of a protein in glycerol versus water.

We used MD simulations to investigate the dependence of the dynamics of a soluble protein, RNase A, on temperature and solvent environment. Consistent with neutron scattering data, the simulations predict that the protein undergoes a dynamical transition in both glycerol and aqueous solutions that is absent in the dry protein. The temperature of the transition is higher, while the rate of increase with temperature of the amplitudes of motion on the 100 ps timescale is lower, in glycerol versus water. Analysis of the dynamics of hydrogen bonds revealed that the protein dynamical transition is connected to the relaxation of the protein-solvent hydrogen bond network, which, in turn, is associated with solvent translational diffusion. Thus, it appears that the role of solvent dynamics in affecting the protein dynamical transition is qualitatively similar in water and glycerol.