FOLDING THERMODYNAMICS OF A MODEL 3-HELIX-BUNDLE PROTEIN

The calculated folding thermodynamics of a simple off-lattice three-he lix-bundle protein model under equilibrium conditions shows the experi mentally observed protein transitions: a collapse transition, a disord ered-to-ordered globule transition, a globule to native-state transiti on, and the transition from the active native state to a frozen inacti ve state. The cooperativity and physical origin of the various transit ions are explored with a single ''optimization'' parameter and charact erized with the Lindemann criterion for liquid versus solid-state dyna mics. Below the folding temperature, the model has a simple free energ y surface with a single basin near the native state; the surface is si milar to that calculated from a simulation of the same three-helix-bun dle protein with an all-atom representation [Boczko, E. M. & Brooks II I, C. L. (1995) Science 269, 393-396].