Fig 5.
Complex time evolution of intermediate populations. The wild-type and mutant fractional populations were fit with a kinetic model featuring multiple three-state pathways [unfolded → I1 (helix-hairpin 1) or I2 (helix-hairpin 2) or I3 (β1-β4 sheet) → N]. The model fitting was done in the following manner: (i) a single exponential was first fitted to the unfolded population data; (ii) the observed pathway branching ratios were then used to determine the three U → I1 or I2 or I3 rates; and (iii) the I1, I2, and I3 population curves were then each separately fitted to determine the I1, I2, and I3 → N rates. For the wild type, the fit is very good for the first billion MC steps, but systematic deviation is observed afterward. This result is best explained by the presence of low-energy sidechain packing traps (7), which results in slower, non-exponential relaxation of the unfolded state. The fit of the model for the mutant was worse overall. We did not find a straightforward explanation for this finding, and we thus attribute it to statistical error. For wild type, kU→I1 = 1.56 × 10−9, kU→I2 = 7.91 × 10−10, kU→I3 = 2.90 × 10−10, kI1→F =7.56 × 10−9, kI2→U =1.09 × 10−8, kI3→F =1.55 × 10−9; for the mutant: kU→I1 = 8.63 × 10−10, kU→I2 = 1.82 × 10−10, kI1→F =6.71 × 10−9, and kI2→F =1.33 × 10−8.