Solvent frictional forces in the rotational diffusion of proteins in water

Abstract

Rotational diffusion of a protein is determined largely by its interaction with the surrounding solvent, water. This interaction derives contributions from both the size (short-range interaction) and the charge distribution (long-range interaction) of the protein. Here we show that if the size and shape of the proteins are properly included in the hydrodynamic calculation of Stoke's friction and the correctly estimated charges are used in the calculation of dielectric friction, then the combined friction provides an accurate description of the solvent-induced rotational friction on the proteins. We also discuss the effects of protein-protein interaction in determining the concentration dependence of the rotational diffusion of proteins.