Description of Hydration Water in Protein (GFP) Solution

The term, hydration water, describes the structurally and dynamically perturbed water surrounding proteins and biomolecules. This population of water has a defining influence on the structure and function of biomolecules, especially proteins; implying a fundamental connection between the dynamical properties of hydration water and many vital biochemical processes including protein folding, protein–ligand recognition, membrane, enzyme function, and DNA stability. This makes the extent of the perturbation (the hydration number, NH) and degree of perturbation (the retardation factor, ξ) of great practical interest. We present an experimental description of the dynamical perturbation of hydration water around green fluorescent protein in solution using neutron scattering methods. We find that less than two shells (∼5.5 A) were perturbed, with dynamics a factor of 2‒10 times slower than bulk water, depending on their distance from the protein surface and the probe length of the measurement, which neutron scattering allows us to vary. This dependence on probe length demonstrates that hydration water undergoes sub-diffusive motions (for the first hydration shell, for perturbed waters in the second shell), an important difference with neat water which demonstrates diffusive behavior ().