Protein Folding and the Minimum Rate of Entropy Production

Protein folding displays a very narrow range of stability energy as measured by the ΔG° value associated with the process of protein folding from the unfolded sequence of amino acids defining a particular protein. We have recently reported the Gaussian distribution of ΔG° values obtained from a Data Base, constituted by more than five hundred data points from protein folding processes. An average value of ΔG° = −30.9 kJ/mol was obtained. Considering that a protein solution may include thousands of hydrogen bonds in water solution, this is an extremely low value, approximately equivalent to two hydrogen bonds. The enthalpy–entropy compensation has been repeatedly used as the main empirical mechanism, based in classical thermodynamics, to explain the low energy involved in stabilizing proteins. I present here a different approach, based on the thermodynamics of steady states in open systems, in an attempt to complement the achievements obtained through the EEC. The main conclusions explain the narrow range of ΔG° values reported previously as a consequence of environmental conditions, such as the protein solubility, and the plausible concentration, “in vivo,” of both protein forms, folded and unfolded. Particularly relevant is the condition of increasing the entropy of irreversible processes inside adiabatic systems. It is also worth noting the observation that, according to the results obtained from the theoretical model used, any protein could be folded with slightly different stability values of ΔG°, following the theorem of minimum entropy production rate.