Hydration shell of the TS-Kappa protein: Higher density than bulk water

The density of the water molecules in the presence of hydrophobic and hydrophilic amino acids was studied. Molecular dynamic simulation were employed to analyze the behavior of hydrated IS Kappa protein in SPC/E and TIP4P-2005 water models. The simulations were performed in the NPT ensemble with the Nose-Hoover thermostat and the Parrinello-Rahman barostat. The density profile of these systems were obtained for different temperatures at constant pressure. Two complementary phenomena were observed. The protein-water system exhibits a temperature of maximum density lower than the temperature observed in the pure water system. The densities of the water in vicinity of the hydrophobic and hydrophilic sites are higher than the density of the water in the bulk. Our results suggest that interactions between protein and water and the water-water Hydrogen bonds are essential to the understanding of these phenomena. (C) 2015 Elsevier B.V. All rights reserved.