Hydration, cavities and volume in protein folding, aggregation and amyloid assembly.

Differential hydration dictates various biological processes, including protein folding, ligand binding, macromolecular assembly, enzyme kinetics and signal transduction. If water is partially or totally removed (experimentally or in silico), the outcome of these processes can be significantly affected. The aggregation of proteins into amyloids or other aggregate forms also results in profound changes in hydration. High hydrostatic pressure is a unique tool to study hydration, as increases in water binding usually lead to decreases in volume. Pressure changes can favor the formation or disassembly of amyloids depending on the volume changes associated with protein folding and misfolding/aggregation. The packing and formation of cavities will also contribute to changes in volume, and therefore, to sensitivity to pressure. Therefore, the formation of water-excluding cavities is predicted to be an important event in folding and aggregation landscapes.