Monte Carlo Simulations on an Equilibrium Globular Protein Folding Model

Monte Carlo simulations were performed on a diamond lattice, globular protein model in which the trans conformational state is energetically favored over the gauche states (thereby perhaps favoring a β -sheet secondary structure) and in which nonspecific nonbonded nearest-neighbor attractive interactions are allowed. If the attractive interactions are sufficiently weak that the molecule possesses a relatively high fraction of trans states in the denatured state, then on collapse, a β -barrel tertiary structure, highly reminiscent of the ``native'' structure seen in β -proteins, spontaneously forms. If, however, the attractive interactions are dominant, a coil-to-random globule collapse transition is observed. The roles of short-, medium-, and long-range interactions and topological constraints in determining the observed tertiary structure are addressed, and the implications and limitations of the simulations for the equilibrium folding process in real globular proteins are explored.