Thermodynamics and kinetics of protein folding: A mean field theory

The kinetic Ising model in the mean field approximation is applied to study the equilibrium and kinetic behaviors of protein folding-unfolding. In our model, we regard a protein as a topological collection of interacting peptide bonds (or other protein units). According to this model, thermodynamics and kinetics of protein folding-unfolding are related to the elementary process of folding ↔ unfolding of such interacting units. We shall show that even for the so-called two-state case of protein folding-unfolding, the kinetic behaviors are predicted to be in general non-exponential and that universal curves exist separately for the thermodynamic behaviors and kinetics behaviors of protein folding-unfolding. Our model can treat the effect of temperature and denaturant concentration on the thermodynamics and kinetics of protein folding-unfolding and provide the chevron plot. Satisfactory demonstrations are presented for treating experimental observations on the thermodynamical and kinetic responses of protein folding-unfolding to the changes in temperature and denaturant concentration and for exhibiting universal plots of proteins.