Temperature-induced conformational changes of native lysozyme in aqueous solution studied by dielectric spectroscopy

We report dielectric measurements at radiofrequencies on lysozyme in aqueous solution at two values of pH (3.5 and 6) as a function of temperature in the interval 5–55°C. From the analysis of the dielectric relaxation of the protein solution, the effective hydrodynamic radius r and the electric dipole moment μ of the protein were calculated. The results show that temperature causes continuous gradual changes of r and μ with a maximum at 25–30°C where the Gibbs free energy for native lysozyme shows an analogous trend. We suggest that the gradual variations of r and μ are the manifestation of a redistribution of microscopic state populations of the protein within the same macroscopic native state.