Understanding folding and design: Replica-exchange simulations of ``Trp-cage'' miniproteins

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Abstract
Replica-exchange molecular dynamics simulations in implicit solvent have been carried out to study the folding thermodynamics of a designed 20-residue peptide, or ``miniprotein.'' The simulations in this study used the amber (parm94) force field along with the generalized Born/solvent-accessible surface area implicit solvent model, and they spanned a range of temperatures from 273 to 630 K. Starting from a completely extended initial conformation, simulations of one peptide sequence sample conformations that are α rms positional deviation from structures in the corresponding NMR ensemble. These folded states are thermodynamically stable with a simulated melting temperature of ≈400 K, and they satisfy the majority of experimentally observed NMR restraints. Simulations of a related mutant peptide show a degenerate ensemble of states at low temperature, in agreement with experimental results.