Solvent-exposed backbone loosens the hydration shell of soluble folded proteins.

The hydration shell of a soluble folded protein is not uniform: its tightness, marked by the mobility of interfacial water, is site dependent and modulates the propensity for protein associations. We found that the most pronounced interfacial dehydration propensity for representative folds is promoted by solvent-exposed intramolecular hydrogen bonds that are incompletely shielded from water attack. These bonds are poorly wrapped by surrounding nonpolar groups from the side chains and their dehydration is energetically favored.