Molecular dynamics simulations of dry and partially hydrated plastocyanin have been performed at 13 temperatures, in the 20-350 K range, for 600 ps to investigate the role of hydration water on the thermal activation of protein dynamics. The analysis of results points out that a sharp dynamical transition occurs in the hydrated protein at about 220 K; such a transition appearing to be smeared out in the dry protein. The dynamical transition, which is much more marked for the solvent-exposed side chains than for the Cα atoms, is strongly coupled to the hydrogen bond network restructuring dynamics involving the interfacial water.

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