Hydrogen bonding dynamics during protein folding of reduced cytochrome c: temperature and denaturant concentration dependence.

Folding dynamics of reduced cytochrome c triggered by the laser-induced reduction method is investigated from a viewpoint of the intermolecular interaction change. Change of the diffusion coefficient of cytochrome c during the refolding process is traced in the time domain from the unfolded value to the native value continuously at various denaturant (guanidine hydrochloride (GdnHCl)) concentrations and temperatures. In the temperature range of 288 K-308 K and GdnHCl concentration range of 2.5 M-4.25 M, the diffusion change can be analyzed well by the two-state model consistently. It was found that the m(double dagger)-value and the activation energy of the transition state from the unfolded state for the hydrogen bonding network change are surprisingly similar to that for the local structural change around the heme group monitored by the fluorescence quenching experiment. This agreement suggests the existence of common or similar fundamental dynamics including water molecular movement to control the refolding dynamics. The nature of the transition state is discussed.