Molecular dynamics simulations of the charge-induced unfolding and refolding of unsolvated cytochrome c

The charge-induced unfolding and refolding of unsolvated cytochrome c have been studied by molecular dynamics (MD) simulations. Simulations were perfo rmed for protonated charge states between +3 and +19. The charge-induced un folding of cytochrome c in the gas phase has previously been examined by io n mobility measurements. The main features of the experimental results are reproduced by the MD simulations reported here. The simulations provide ins ight into how the energy landscape changes with charge, and into the nature of the unfolded conformations of the higher charge states. Experiments hav e shown that unsolvated cytochrome c refolds when the charge is reduced. MD simulations of this refolding process were also performed. When the charge is reduced, the protein ions collapse, but they became trapped in random l oop conformations with little secondary structure.