Hydration-coupled dynamics in proteins studied by neutron scattering and NMR: The case of the typical EF-hand calcium-binding parvalbumin

The influence of hydration on the internal dynamics of a typical EF-hand ca lciprotein, parvalbumin, was investigated by incoherent quasi-elastic neutr on scattering (IQNS) and solid-state C-13-NMR spectroscopy using the powder ed protein at different hydration levels. Both approaches establish an incr ease in protein dynamics upon progressive hydration above a threshold that only corresponds to partial coverage of the protein surface by the water mo lecules. Selective motions are apparent by NMR in the 10-ns time scale at t he level of the polar lysyl side chains (externally located), as well as of more internally located side chains (from Ala and Ire), whereas IQNS monit ors 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 resid ues mainly involve the ammonium extremity of the side chain, as shown by NM R. The combined results suggest that peripheral water-protein interactions influence the protein dynamics in a global manner. There is a progressive i nduction 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.