The terahertz dance of water with the proteins: the effect of protein flexibility on the dynamical hydration shell of ubiquitin

The role of water in the functioning of proteins has been a hot topic over the years. We use terahertz (THz) spectroscopy as an experimental tool to probe the protein-induced fast solvation dynamics of ubiquitin. In order to investigate the effect of protein flexibility on the changes in the solvation dynamics, we have measured the concenteration-dependent THz absorption of several site-specific ubiquitin mutants. The non-linear dependence of absorption oil concentration is it signature of a long-range hydration shell with properties distinct from hulk water. We determined it dynamical hydration shelf of it thickness of ill least 18 angstrom oil the protein surface. This exceeds the static hydration layer as it is typically observed by scattering methods (3 angstrom) by far. We also conclude that any increase in flexibility obtained by side-chain truncations that decrease the structural rigidity of the protein results in more bulk-like behaviour of the dynamical hydration shell. Furthermore, our THz measurements show that a single phenylalanine-tryptophan substitution to introduce a fluorescent marker leads to measurable changes in the solvation dynamics.