ABSTRACT
Water covers more than 70% of the surface of the earth. Nearly all biological processes take place in water. It is now widely recognized that hydration water in the proximity of protein surfaces plays an essential role for the structure, stability, and dynamics of proteins. Hydrogen bond networks have been proposed to stabilize intermediates during protein folding or protein aggregation and have recently been visualized as forming extended water channels in photosystems. Yet, it is part of an ongoing scientic debate whether solvent dynamics inuences, or even enslaves, the dynamics of biomolecules or, more speculative, whether solvent uctuations actually contribute to biomolecular (mal) function, for example, in biological assembly, protein-substrate binding, or enzymatic turnover. Going beyond individual proteins, the active role of water in protein interactions, protein aggregation, and conformational diseases is currently a topic of intense and even controversial debate. Whereas in bulk water the hydrogen bonds break and reform every picosecond (ps) on average, in the vicinity of huge biological solutes like proteins and enzymes, water molecules show a change in the dynamics of the hydrogen bond network. Terahertz (THz) absorption spectroscopy is an experimental tool to detect subtle changes of nonlocal dipole uctuations due to intermolecular vibrations, giving direct access to collective water network dynamics. THz absorption spectroscopy allows to report on long-ranged, solute-induced changes of solvent dynamics (solute-induced changes of the THz absorption were found up to 5-6 Ǻ for disaccharides and beyond 15 Ǻ for proteins by THz spectroscopy), which was much more far reaching than had been anticipated before. e combination of THz spectroscopy and stopped-ow methods allows the
8.1 Introduction ......................................................................................135 8.2 Concepts for Understanding THz Hydration ..............................139 8.3 THz Absorbance of Aqueous Protein Solutions ..........................141 8.4 KITA of Protein Folding and Enzyme Catalysis .........................144 8.5 Discussion and Outlook ..................................................................147 Acknowledgment ..........................................................................................148 References ......................................................................................................148
