The dynamics of water-protein interactions.

The magnetic field and temperature dependence of the water proton nuclear spin-lattice relaxation rate requires that the motion timescale for water molecules in contact with proteins is close to that for pure water at room temperature. Nevertheless, there are a few water molecules, which may be detected by high-resolution, cross-relaxation spectroscopy, that must have relatively long protein-bound lifetimes and that carry the bulk of the relaxation coupling between the protein and the water. The water-protein magnetic coupling affects the interpretation of water relaxation rates in heterogeneous protein systems, such as tissues, and provides new ways to extract useful information about the immobilized components through the effects on the water NMR spectrum. The discussion shows that the conclusions concerning the rapid water molecule motions at the interface are not in conflict with the observations of many water oxygen atom positions in protein crystal structures.