Dielectric spectroscopy as a probe for the investigation of conformational properties of proteins

In this brief paper, we review recent and significant results obtained in our laboratory by dielectric spectroscopy (DS). This is a multi purpose and very sensitive approach to investigate structural features of biological systems. DS at radiofrequencies is particularly powerful in the study of structural and conformational properties of proteins. We report on results obtained on three well-known proteins: lysozyme, cytochrome-c and metmyoglobin, which represent very useful models for folding/unfolding studies. The influence of pH and temperature as well as presence of trehalose as a co-solvent, was determined by estimation of the effective hydrodynamic radius and electric dipole moment of the protein in solution. In particular, trehalose was shown to affect the alkaline transition of cytochrome. Conformational effects on the three above-mentioned proteins were observed in a temperature range near the physiological ones. Dynamical properties of lysozyme in mixtures water-glycerol are also discussed. Parallel measurements of photon correlation spectroscopy (PCS) and DS indicated that both translational and rotational diffusive behavior are coherent with the Debye-Stokes-Einstein hydrodynamic model.