Model-potential-free analysis of small angle scattering of proteins in solution: insights into solvent effects on protein-protein interaction.

To extract protein-protein interaction from experimental small-angle scattering of proteins in solutions using liquid state theory, a model potential consisting of a hard-sphere repulsive potential and the excess interaction potential has been introduced. In the present study, we propose a model-potential-free integral equation method that extracts the excess interaction potential by using the experimental small-angle scattering data without specific model potential such as the Derjaguin-Landau-Verwey-Overbeek (DLVO)-type model. Our analysis of experimental small-angle X-ray scattering data for lysozyme solution shows both the stabilization of contact configurations of protein molecules and a large activation barrier against the formation of the contact configurations in addition to the screened Coulomb repulsion. These characteristic features, which are not well-described by the DLVO-type model, are interpreted as solvent effects.