Modeling two-state cooperativity in protein folding

A protein model with the pairwise interaction energies varying as the local environment changes, i.e., including some kind of collective effect between the contacts, is proposed. Lattice Monte Carlo simulations on the thermodynamical characteristics and free energy profile show a well-defined two-state behavior and cooperativity of folding for such a model. As a comparison, related simulations for the usual G (o) over bar model, where the interaction energies are independent of the local conformation, are also made. Our results indicate that the evolution of interactions during the folding process plays an important role in the two-state cooperativity in protein folding.