Seminars Archive

Dynamical properties of DNA and protein hydration water

Abstract
Water molecules within a few Å of the protein surface are able to effectively perturb both the diffusive and vibrational dynamics of biomolecules, as shown by experimental and theoretical investigations. This kind of water, referred to as protein hydration water, has been shown to play a role in efficient enzymatic catalysis, in folding processes, as well as in molecular recognition and in mediating protein-protein interactions. Indeed, fluctuations in the hydration shell have been suggested to control fast fluctuations of proteins, thus having profound implications for their biological activity by driving key internal processes such as the migration of ligands within biomolecules. Apart from its crucial biological role, protein hydration water is also a unique system to study the physical properties of the water molecular network in conditions where it is sensibly altered with respect to the bulk, due to local topography and specific interactions with the protein surface. This results in a sensitive alteration of the dynamical properties of water molecules at the protein interface compared to the bulk. While most of the studies are devoted to investigate the diffusive motions of protein hydration water, little is known about the behaviour of vibrational excitations in the meV energy range – or the THz frequency range – when the temperature increases from the harmonic regime and crosses the protein dynamical transition. These excitations are usually described in terms of hydrogen-bond bending (HBB), hydrogen-bond stretching (HBS) and librational (LIB) modes, located at about 6, 22 and 80 meV respectively. In this seminar I report the results of inelastic incoherent and coherent neutron scattering experiments performed on protein and DNA hydration water to investigate the temperature behaviour of the solvent low-frequency vibrational features, including the so-called Boson peak. The coupling with the biomolecule's dynamics and the possible relationship with its functional activity are also addressed.