  First shells of 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
between water molecules pertaining to the first shell of the protein
conformation may be either mainly formed or broken. At thermal equilibrium,
hydrogen bonds are formed at low temperature and are broken at high
temperature. To explore the solvent effect, we follow the folding of a large
sampling of protein chains, using a master-equation evolution. The dynamics
shows a clear mechanism. Above the glass-transition temperature, a large ratio
of chains fold very rapidly into the native structure irrespective of the
temperature, following pathways of high transition rates through structures
surrounded by the solvent with broken hydrogen bonds. Although these states
have an infinitesimal probability, they act as strong dynamical attractors and
fast folding proceeds along these routes rather than pathways with small
transition rates between configurations of much higher equilibrium
probabilities. At a given low temperature, a broad jump in the folding times is
observed. Below this glass temperature, the pathways where hydrogen bonds are
mainly formed become those of highest rates although with conformational
changes of huge relaxation times. The present results reveal that folding obeys
a double-funnel mechanism.
