Kinetics of hydrogen-bonding of protein hydration water and its dynamical coupling with protein dynamics

Nakagawa, Hiroshi   ; Kataoka, Mikio

Unique physical properties of water are originated from the hydrogen bond. The hydrogen bond determines the spatial network patterns and water dynamics. Hydration water around the molecules, such as ions, polymers and bio-molecules, has quite different physical properties from bulk water. The protein hydration affects the biological function of the protein. Here, by using the molecular dynamics simulation, we show that the hydrogen bond kinetics of the protein hydration water is strongly affected by the local bonding patterns near the tagged hydrogen bond and that percolation of hydration water on the protein surface essentially determines the cooperative hydrogen bond forming and breaking dynamics. These dynamical characters of hydration water are quite different from those of the bulk water. The hydrogen bond kinetics between hydration water is correlated with the kinetics between the protein and hydration water, suggesting the dynamical coupling between them. The percolation of hydrogen bond network would contribute to the physical properties of protein hydration water. This hydration water dynamics induces the protein dynamical transition observed by neutron inelastic scattering. The dynamical coupling between hydration water and protein should be essential for protein thermal fluctuation and functionality.