Control of protein interfacial affinity by nonionic cosolvents

In a biological cell, proteins perform their functions in a highly complex environment comprising crowding and confinement effects as well as interactions with interfaces, cosolvents, and other biomolecules. Cosolvents can stabilize or destabilize the native folded structure of proteins in solution. In this study, we show that nonionic cosolvents also affect the interfacial affinity of proteins. We use bovine ribonuclease A and a planar silica-water interface as model system and apply neutron and optical reflectometry to analyze this system. The degree of protein adsorption and-the density profile of adsorbed protein molecules were determined in the absence and the presence of cosolvents. It has been found that both the protein stabilizing glycerol and the protein destabilizing urea cause a distinct reduction in protein interfacial affinity, which may represent a rather unexpected result. However, it is suggested that different mechanisms are underlying the similar effects of glycerol and urea.