Glassy Dynamics in the Folding Landscape of Cytochrome c Detected by Laser Photolysis

Ferrocytochrome c liganded with CO refolds to a nativelike compact state, called the M state, where the non-native Fe2+−CO contact persists. The M state resembles the generic molten globule-like states and can be driven to the native state by pulsed laser photolysis of the CO ligand. The microsecond kinetics measured all across the guanidine hydrochloride unfolding transition of the protein produce a chevron plot with accentuated rollover in the folding limb, suggesting a glass transition of M en route to N. The rate of exit of the folding structure from the kinetic trap(s) limits the overall rate of folding of M to N. Sulfate-induced deceleration of the observed folding rate suggests that the folding structure indeed is transiently frozen in glassy traps. The results connect the post-transition features of the funnel paradigm.