[WS5] Non-equilibrium state molecular movies: a new frontier in structural and functional studies on proteins

[WS5-4(2P-61)] Role of freezable and unfreezable hydration water for the activation of protein dynamics revealed by neutron scattering

^○Naoki Yamamoto (Div. Biophys., Dept. of Physiol., School of Med., Jichi Med. Univ.)

Hydration water plays a crucial role for activating the protein dynamics required for functional expression. In our previous studies, we observed a temperature-hysteresis phenomenon of the rotational dynamics of hydration water only when hydration level was high. This temperature hysteresis, which is due to the supercooling of freezable hydration water, is a key phenomenon to understand which hydration water, unfreezable or freezable hydration water, is crucial for the activation of protein dynamics. For this purpose, we performed neutron scattering experiments on a lysozyme hydrated with D₂O. Using coherent scattering profile, we revealed that the temperature-hysteresis phenomenon is indeed due to the supercooling of freezable hydration water. However, incoherent neutron scattering of protein revealed that protein dynamics did not show any temperature hysteresis. These results show that the protein dynamics is not coupled with freezable hydration water. Rather, unfreezable hydration water is essential for the activation of protein dynamics required for its function. Decoupling of the dynamics between unfreezable and freezable hydration water could be the cause of the distinct contributions of hydration water to protein dynamics.