Hydration and temperature dependence of protein dynamics studied by incoherent inelastic neutron scattering

Nakagawa, Hiroshi   ; Shibata, Kaoru  ; Jochi, Yasumasa*; Tokuhisa, Atsushi*; Kataoka, Mikio*; Go, Nobuhiro

Protein dynamics is essential for the protein function. In order to understand the dynamical properties of protein, the effects of hydration and temperature on the dynamics of staphylococcal nuclease were intensively examined by incoherent inelastic neutron scattering with LAM-40 instrument in KENS, Japan. Inelastic neutron scattering of dry, DO-hydrated and HO-hydrated protein were measured at various temperatures between 100 and 300K. The spectra of dry protein at low temperatures shows the peak at around 3 meV, which was shifted to around 4meV with DO-hydrated protein. This indicates that the vibrational frequency distribution was changed by the hydration. The anomalous decrease in the Debye-Waller factor at high temperatures is corresponding to an increase of the mean-square displacement, which is called the dynamical transition. This is accompanied by the appearance of a quasielastic scattering. The natures of the motions above the dynamical transition temperature were characterized by the analysis of the quasielastic scattering. The dynamical transition was striking with the hydrated protein. This suggests that the hydration water has strongly effects on the protein dynamics. The scattering profile of the hydration water was calculated by the subtraction of the scattering profiles of a D2O-hydrated protein from that of a HO-hydrated protein. We will discuss the relation between hydration water dynamics and the protein dynamics.