Structure and dynamics of the protein hydration water at the protein dynamical transition

蛋白質の動力学転移における水和水の構造とダイナミクス

中川 洋   ; 城地 保昌*; 北尾 彰朗*; 片岡 幹雄

Nakagawa, Hiroshi; Jochi, Yasumasa*; Kitao, Akio*; Kataoka, Mikio

The dynamical transition of a protein has been observed at 200 - 240 K with the hydrated protein. We studied hydration level dependence of the hydration water structure and dynamics at the dynamical transition of a protein Staphylococcal nuclease by inelastic neutron scattering and molecular dynamics simulation. It was found that hydration dependent protein dynamical transition was observed around 240K, which was more significant above the threshold hydration level between 0.30 and 0.42 (g water/g protein). Above the threshold hydration level, the connectivities of the hydration water via hydrogen bond spread over the protein surface. Furthermore the hydrogen bond network among the hydration water encircles the whole protein, and the hydration water is percolated on the protein surface. Therefore, the protein dynamical transition is highly correlated with the percolation transition of the hydration water. At the percolation transition the translational dynamics of the hydration water markedly increase. The dynamical behavior of hydration water is coupled with the protein dynamics via hydrogen-bond network at protein-water interface. Such a dynamical coupling drives the hydration dependent protein dynamical transition.