Entropy Changes in Water Networks Promote Protein Denaturation.

For over a century, an explanation for how concentrated ions denature proteins has proven elusive. Here, we report a novel mechanism of protein denaturation driven by entropy changes in water networks. Experiments and simulations show that ion pairs like LiBr and LiCl localize water molecules and disrupt the water network's structure, while others exert a more global effect without compromising network integrity. This disruption reduces the entropy penalty when proteins sequester water molecules during unfolding, resulting in a peculiar yet universal "inverse hydrophobic effect" that potentiates protein denaturation. Through successful isolation and systematic study of indirect solute effects, our findings offer a universal approach to salt induced protein denaturation and provide a unified framework for the decoding of the protein-water-solute nexus.