SOLVENT STRUCTURE AT A HYDROPHOBIC PROTEIN SURFACE

The impact of an extensive, uniform and hydrophobic protein surface on the behavior of the surrounding solvent is investigated, In particula r, focus is placed on the possible enhancement of the structure of wat er at the interface, one model for the hydrophobic effect, Solvent res idence times and radial distribution functions are analyzed around thr ee types of atomic sites (methyl, polar, and positively charged sites) in 1 ns molecular dynamics simulations of the alpha-helical polypepti de SP-C in water, in methanol and in chloroform, For comparison, water residence times at positively and negatively charged sites are obtain ed from a simulation of a highly charged alpha-helical polypeptide fro m the protein titin in water, In the simulations the structure of wate r is not enhanced at the hydrophobic protein surface, but instead is d isrupted and devoid of positional correlation beyond the first solvati on sphere, Comparing solvents of different polarity, no clear trend to ward the most polar solvent being more ordered is found, In addition, comparison of the water residence times at nonpolar, polar, positively charged, or negatively charged sites on the surface of SP-C or titin does not reveal pronounced or definite differences, It is shown, howev er, that the local environment may considerably affect solvent residen ce times, The implications of this work for the interpretation of the hydrophobic effect are discussed. (C) 1997 Wiley-Liss, Inc.