Journal of the American Chemical Society, Vol.130, No.24, 7540-7540, 2008
Probing the bottom of a folding funnel using conformationally gated electron transfer reactions
The effect of global stability on the kinetics of interconversion between the native (N) and a compact, partially unfolded form (I) of iso-1-cytochrome c stabilized by His73-heme ligation is investigated using a novel conformationally gated ET method. For the K73H variant and the 2-fold less stable AcH73 variant, the N and I conformers are of nearly equal stability at pH 7.5. The pH jump kinetic data yield k(obs) = k(NI) + k(IN) of 35-40 s(-1) at final pH values from 6 to 8 for the AcH73 variant, about 3-fold faster than for the more stable K73H variant. Gated ET measurements give k(NI) = 28 s(-1) and k(IN) = 13 s(-1) for the AcH73 variant, 10- and 2- fold greater than that for the more stable K73H variant. Thus, funneled landscape have evolved such that loss of global stability lowers barriers at the bottom of a folding funnel, still allowing for efficient folding.