Rotational motions of solvent site–dipole field around a protein

Directional correlation of solvent site–dipole field, resulted from orientational ordering of individual water molecules around human lysozyme, was studied with three molecular dynamic simulations done at different ion concentrations. The rotational diffusion of the site–dipole field was strongly restrained by the protein in the first-layer solvent region, and was suppressed in a range where protein–solvent distance ⩽10 Å. Motions of the whole solvent dipoles highly correlated with ionic motions. Current work proposes a biological role of the fluctuations of the site–dipole field as an interaction arm moving to capture other molecules, when molecular binding takes place.