Abstract
The influence of hydration on the internal dynamics of a typical EF-hand calciprotein, parvalbumin, was investigated by incoherent quasi-elastic neutron scattering (IQNS) and solid-state 13C-NMR spectroscopy using the powdered protein at different hydration levels. Both approaches establish an increase in protein dynamics upon progressive hydration above a threshold that only corresponds to partial coverage of the protein surface by the water molecules. Selective motions are apparent by NMR in the 10-ns time scale at the level of the polar lysyl side chains (externally located), as well as of more internally located side chains (from Ala and Ile), whereas IQNS monitors diffusive motions of hydrogen atoms in the protein at time scales up to 20 ps. Hydration-induced dynamics at the level of the abundant lysyl residues mainly involve the ammonium extremity of the side chain, as shown by NMR. The combined results suggest that peripheral water-protein interactions influence the protein dynamics in a global manner. There is a progressive induction of mobility at increasing hydration from the periphery toward the protein interior. This study gives a microscopic view of the structural and dynamic events following the hydration of a globular protein.