Statistical Physics Group

First shell hydration and bulk solvent plays a crucial role in the folding of proteins. Here, the role of water in the dynamics of proteins has been investigated using a theoretical protein-solvent model and a statistical physics approach. We formulate a hydration model where the hydrogen bonds of the water molecules of the first shell around each protein conformation may be either mainly formed or broken. At thermal equilibrium, the hydrogen bonds are formed at low temperature and they are broken at high temperature. To explore the solvent effect, we follow the folding of a large sampling of chains, using a master equation evolution. The dynamics shows a clear mechanism. Above a glass transition temperature, a large ratio of chains fold very fast into the native structure whatever the temperature by following pathways of high transition rates through structures surrounded by solvent with broken hydrogen bonds. Although these states have a infinitesimal probability, they act as strong dynamical attractors and the proteins fold very fast following these routes rather than pathways with small transition rates between configurations with much higher equilibrium probabilities. At a given low temperature, a broad jump of the folding times is observed. Below this glass temperature, the pathways where hydrogen bonds are mainly formed become those of highest rates but with moves of huge relaxation times. Finally, a double funnel picture of the folding is given.