Replica Exchange Molecular Dynamics Method for Protein Folding Simulation

Understanding protein folding is one of the most challenging problems remaining in molecular biology. In this chapter, a highly parallel replica exchange molecular dynamics (REMD) method and its application to protein folding are described. The REMD method couples molecular dynamics trajectories with a temperature exchange Monte Carlo process for efficient sampling of the conformational space. A series of replicas are run in parallel at temperatures ranging from the desired temperature to a high temperature at which the replica can easily surmount the energy barriers. From time to time the configurations of neighboring replicas are exchanged and this exchange is accepted or rejected based on a Metropolis acceptance criterion that guarantees the detailed balance. Two example protein systems, one α-helix and one β-hairpin, are used as case studies to demonstrate the power of the algorithm. Up to 64 replicas of solvated protein systems are simulated in parallel over a wide range of temperatures. The simulation results show that the combined trajectories in temperature and configurational space allow a replica to overcome free energy barriers present at low temperatures. These large-scale simulations also reveal detailed results on folding mechanisms, intermediate state structures, thermodynamic properties, and the temperature dependences for both protein systems.