Osmotic Second Virial Coefficients and Phase Diagrams for Aqueous Proteins from a Much-Improved Poisson−Boltzmann Equation

Abstract

A much-improved Poisson - Boltzmann equation for two globular proteins using bispherical coordinates is used to establish the potential of mean force (PMF) between two globular lysozyme particles. Calculations presented here include previously ignored ion-protein nonelectrostatic potentials. The lysozyme - lysozyme PMF is used to calculate osmotic second virial coeffiencients. The theoretical PMF curve as a function of sodium chloride concentration is successfully compared with that from experiment. Our theoretical PMF shows how the second virial coefficient and the phase diagram depends on salt concentration, pH and, most notably, on the choice of salt in the aquous solution. © 2007 American Chemical Society.