Folding Pathways of a Helix−Turn−Helix Model Protein

A small model polypeptide represented in atomic detail is folded using Monte Carlo dynamics. The polypeptide is designed to have a native conformation similar to the central part of the helix-turn-helix protein ROP. Starting from a β-strand conformation or two different loop conformations of the protein glutamine synthetase, six trajectories are generated using the so-called window move in dihedral angle space. This move changes conformations locally and leads to realistic, quasi-continuously evolving trajectories. Four of the six trajectories end in stable native-like conformations. Their folding pathways show a fast initial development of a helix−bend−helix motif, followed by a dynamic behavior predicted by the diffusion−collision model of Karplus and Weaver. The phenomenology of the pathways is consistent with experimental results.