Direct observation of the folding and unfolding of a beta-hairpin in explicit water through computer simulation.

The cooperative folding and unfolding of a beta-hairpin structure are observed in explicit water at native folding conditions through self-guided molecular dynamics simulation. The folded structure agrees excellently with the NMR NOE data. After going through a fully hydrated state, the peptide folds into a beta-hairpin structure in a highly cooperative process. During the folding process it is observed that side chain interaction occurs first, while intrapeptide hydrogen bonds only form at the final stage. On the contrary, the unfolding process starts with the breaking of interstrand hydrogen bonds. Energetic analysis indicates that the driving force of the folding is the intrapeptide interaction, while the solvent interaction opposes the folding.