Influence of chemical chaperones on the properties of lysozyme and the reaction center protein from Rhodobacter sphaeroides

The influence of three chemical chaperones: glycerol, 4-hexylresorcinol, and 5-methylresorcinol on the structure, equilibrium fluctuations, and functional activity of the hydrophilic enzyme lysozyme and the transmembrane reaction center (RC) protein from Rb. sphaeroides in a broad range of concentrations has been studied. The chosen chemical chaperones differ strongly in their structure and action on hydrophilic and membrane proteins. The influence of the chemical chaperones (except methylresorcinol) on the structure, dynamics, and functional properties of lysozyme and RC protein are well described in the framework of extended models of preferential hydration and preferential interaction of protein with a chemical chaperone. A molecule of hexylresorcinol consists of a hydrophobic (alkyl radical) and a hydrophilic (aromatic core) moieties; this provides for additional regulation of the functional activity of lysozyme and RC by hexylresorcinol. The influence of methylresorcinol on proteins differs from that of glycerol and hexylresorcinol. Methylresorcinol interacts with the surface of lysozyme directly, not via water hydrogen bonds. This leads to a decrease in the denaturation temperature and an increase in the amplitude of equilibrium fluctuations, allowing it to be a powerful activator. Methylresorcinol interacts with the membrane RC protein only by the condensation of hydration water, which is negligible in this case. Therefore, methylresorcinol does not affect the functional properties of the RC protein. It is concluded that different chaperones at the same concentration as well as one and the same chaperone at different concentrations produce protein 3D structures differing in dynamic and functional characteristics.