Influence of pressure on the low-frequency vibrational modes of lysozyme and water: a complementary inelastic neutron scattering and molecular dynamics simulation study.

We performed complementary inelastic neutron scattering (INS) experiments and molecular dynamics (MD) simulations to study the influence of pressure on the low-frequency vibrational modes of lysozyme in aqueous solution in the 1 atm-6 kbar range. Increasing pressure induces a high-frequency shift of the low-frequency part (<10 meV = 80 cm(-1)) of the vibrational density of states (VDOS), g(ω), of both lysozyme and water that reveals a stiffening of the interactions ascribed to the reduction of the protein and water volumes. Accordingly, high pressures increase the curvature of the free energy profiles of the protein quasiharmonic vibrational modes. Furthermore, the nonlinear influence of pressure on the g(ω) of lysozyme indicates a change of protein dynamics that reflects the nonlinear pressure dependence of the protein compressibility. An analogous dynamical change is observed for water and stems from the distortion of its tetrahedral structure under pressure. Moreover, our study reveals that the structural, dynamical, and vibrational properties of the hydration water of lysozyme are less sensitive to pressure than those of bulk water, thereby evidencing the strong influence of the protein surface on hydration water.