Thermodynamic Properties of Protein in Solution

Abstract

To reveal the relationships between structure, property, and function of protein, we have determined the various thermodynamic properties (partial specific volume, compressibility, expansibility coefficient, intrinsic viscosity, activation free energy for viscous flow, preferential solvation, and T_m, ΔH, ΔS, ΔG, and ΔC_p for conformational change) of proteins in solution with various conditions as temperature, pressure, solvents, additives, and protein modifications. The cyclodextrin (CD) destabilized the folded state of lysozyme by stabilizing the unfolded state by including hydrophobic part of unfolded state into interior of CD. The destabilization effect of CD was weaker than guanidine hydrochloride and was dependent on the interior diameter and the substituent. The strong water-dimethyl sulfoxide (DMSO) interaction caused lysozyme unfolding with increasing partial specific volume and intrinsic viscosity. DMSO was bound to lysozyme at low DMSO concentration and was preferentially excluded from lysozyme at high DMSO concentration. The sorbitol stabilizes protein through enhancing the hydrophobic interaction in protein. The molten globule state induced by sorbitol had thermodynamic properties somewhat like native state by preferential solvent interactions and osmotic pressure of the medium. Thus, thermodynamic properties can sensitively reflect the conformational changes and interactions with solvent, and hence will be an effective approach to give quantitative and valuable index to protein.