Protein hydration water: Structure and thermodynamics

Abstract

Characterization of the physical properties of protein surface hydration water is critical for understanding protein structure and folding. Recent X-ray and neutron solution scattering data indicate that the density of water on the surface of lysozyme is significantly higher than that of bulk water. Recent molecular dynamics simulation work shows also that variation in the first hydration shell density is determined by electrostatic properties of the protein surface and local surface topography. The thermodynamics of binding of well-ordered structural water to proteins is also examined. Using normal mode analysis, the vibrational entropy change on burial of a crystallographically well-ordered water molecule in Bovine Pancreatic Trypsin Inhibitor (BPTI) is calculated. The vibrational entropy content of the complex is 13.4 cal/mol/K higher than that of the unbound protein. An analysis is performed of how the translational and rotational degrees of freedom of the isolated water molecule are transformed into vibrational modes in the complex.