Impact of Water-Protein Interactions on Protein Dynamics(Nguyen Q. Vinh, Department of Physics and Center for Soft Matter and Biological Physics, Virginia Tech, Blacksburg, VA 24061)*

Proteins function only in aqueous environments and their dynamics is strongly influenced by physiological conditions. The dynamics of hydration water as well as hydrated proteins lead to rotating and oscillating dipoles that, in turn, give rise to a strong megahertz to terahertz absorption. Investigating the impact of hydration on protein dynamics and the spectral features of water molecules influenced by protein, however, is extremely challenging because of the strong absorption of water in the megahertz to terahertz frequency region. In response, we have employed a broad-band megahertz to terahertz spectroscopy with ultrahigh precision, assisted by molecular dynamics simulations, to investigate the dynamics of water molecules within hydration shells of proteins as well as the collective vibrational motions of hydrated proteins, which are vital to protein conformation and functionality. Our results reveal that the dynamics of water molecules in a protein solution is heterogeneous, exhibiting a hierarchy of several distinct relaxation times ranging from ∼8 ps to 1 ns, and the hydration structure of a protein extend beyond the first hydration layer. The low-frequency collective vibrational modes of hydrated proteins have been identified and found to be sensitive to environmental conditions including temperature and hydration level. The results reveal critical information on hydrated protein dynamics and protein-water interfaces, which impact the biochemical functions and reactivity of proteins.