Water-mediated biomolecular dynamics and allostery.

Dynamic coupling with water contributes to regulating the functional dynamics of a biomolecule. We discuss protein-water dynamics, with emphasis on water that is partially confined, and the role of protein-confined water dynamics in allosteric regulation. These properties are illustrated with two systems, a homodimeric hemoglobin from Scapharca inaequivalvis (HbI) and an A adenosine receptor (AAR). For HbI, water-protein interactions, long known to contribute to the thermodynamics of cooperativity, are seen to influence the dynamics of the protein not only around the protein-water interface but also into the core of each globule, where dynamic and entropic changes upon ligand binding are coupled to protein-water contact dynamics. Similarly, hydration waters trapped deep inside the core region of AAR enable the formation of an allosteric network made of water-mediated inter-residue contacts. Extending from the ligand binding pocket to the G-protein binding site, this allosteric network plays key roles in regulating the activity of the receptor.