Protein Protein Interactions - the Effects of Cosolvents, Crowding and Pressure

Abstract

The effects of various kosmotropic and chaotropic cosolvents and salts on the intermolecular interaction potential of proteins (e.g., lysozyme, SNase) was evaluated at low to high protein concentrations by using synchrotron small-angle X-ray scattering in combination with liquid state theoretical approaches. The experimentally derived static structure factors S(Q) obtained without and with added cosolvents and salts were analyzed with a statistical mechanical model based on the DLVO potential which accounts for repulsive and attractive interactions between the protein molecules. Different cosolvents and salts influence the interactions between protein molecules differently as a result of changes in the hydration level or solvation, in charge screening, specific adsorption of the additives at the protein surface, or increased hydrophobic interactions. Experimentally derived static structure factors were also obtained for the aggregation-prone protein insulin. The data reveal that the protein self-assembles into equilibrium clusters already at low concentrations. Striking differences regarding interaction forces between aggregation-prone proteins such as insulin in the pre-aggregated regime and natively stable globular proteins are found. Finally, the effects of crowding and pressure on the solvational properties and intermolecular interaction of the proteins were studied, and a tentative temperature-concentration-pressure phase diagram has been obtained.