PHASE PROPERTIES OF PROTEIN SOLUTIONS AND PROTEIN DENATURATION

Abstract

The formation of protein-containing condensed phases (crystals, oligomers, other solid aggregates, as well as dense liquids and gels), including membraneless micro and nanophases, plays an important role in the functional activity of proteins in the cytoplasm of a living cell, presents a significant aspect of protein studies and biotechnologies, and causes various pathologies in a living body. Numerous phenomena bound to the arising of the folding intermediates of protein molecules do not appear to have been thermodynamically defined so far. This reduces the predictive power of the phase diagrams of protein solution states used to describe the state of the protein molecule in various physiological and biotechnological conditions. This paper is aimed at examining the relationship of liquid-liquid (L–L) type phase transitions of globular protein solutions with the phenomena of thermal and cold denaturation. We have shown that the analysis of phase diagram isobars in pressure-temperature and temperature-entropy coordinates allows predicting the new phase states formed by folding intermediates in protein dispersion. They are in metastable equilibrium with the macroscopic phase formed by native and denatured forms of protein molecules. Thermodynamic equilibrium is established due to the formation of microscale phases containing folding intermediates. They are stabilized by the capillary effect. This ensures the equality of the chemical potentials of all protein molecules with the same external pressure acting on the dispersion, which is a necessary condition for the stability of the system. The intermediates take the basic configuration outside the denaturation temperature range, and the L–L phase transition occurs, since there are no longer reasons for phase separation. This allows us to conclude that the metastable native protein – intermediate and denatured protein – intermediate phase equilibria have properties of L–L type equilibrium in the range of both low and high temperatures, and to explain the presence of such equilibria in the region of first-order phase transitions.

Keywords

• phase diagrams of protein solution
• thermal and cold denaturation of protein
• binodal
• protein folding intermediates
• phase transitions
• capillary pressure.