Free energy barriers separating interfacial water molecules from hydration layer at the surface of a protein to the bulk reveal a strong sensitivity to the secondary structure of chicken villin head piece (HP-36). We find a region near the junction of first and second helix that contains a cluster of water molecules which are slow in motion, characterized by long residence times (of the order of 100 ps or more) and separated by large free energy barrier from the bulk. However, these 'slow' water molecules constitute only 5% of the total hydration layer water molecules. Nevertheless, they play important role in stabilizing protein conformations. Water molecules near 3rd helix are enthalpically least stable and exhibit fastest dynamics. For quasi-bound water molecules we use well-known Kramers' theory to estimate residence time from the free energy surface and compared with simulation. We discuss possible biological function of the slow, quasi-bound water molecules.

Free energy barriers for escape of water molecules from protein  hydration layer

243rd National Meeting (2012)

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