Slowdown of Water Dynamics from the Top to the Bottom of the GroEL Cavity.

The GroE molecular chaperone system is a critical protein machine that assists the folding of substrate proteins in its cavity. Water in the cavity is suspected to play a role in substrate protein folding, but the mechanism is currently unknown. Herein, we report measurements of water dynamics in the equatorial and apical domains of the GroEL cavity in the apo and football states, using site-specific tryptophanyl mutagenesis as an intrinsic optical probe with femtosecond resolution combined with molecular dynamics simulations. We observed clearly different water dynamics in the two domains with a slowdown of the cavity water from the apical to equatorial region in the football state. The results suggest that the GroEL cavity provides a unique water environment that may facilitate substrate protein folding.

Ultrafast Dynamics of Water-Protein Coupled Motions around the Surface of Eye Crystallin.

Water dynamics on the protein surface mediate both protein structure and function. However, many questions remain about the role of the protein hydration layers in protein fluctuations and how the dynamics of these layers relate to specific protein properties. The fish eye lens protein γM7-crystallin (γM7) is found in vivo at extremely high concentrations nearing the packing limit, corresponding to only a few water layers between adjacent proteins. In this study, we conducted a site-specific probing of hydration water motions and side-chain dynamics at nine selected sites around the surface of γM7 using a tryptophan scan with femtosecond spectroscopy and NMR nuclear spin relaxation (NSR). We observed correlated fluctuations between hydration water and protein side chains on the time scales of a few picoseconds and hundreds of picoseconds, corresponding to local reorientations and network restructuring, respectively. These motions are heterogeneous over the protein surface and relate to the various steric and chemical properties of the local protein environment. Overall, we found that γM7 has relatively slower water dynamics within the hydration shell than a similar ß-sheet protein, which may contribute to the high packing limit of this unique protein.