FIGURE 13.

(Top) Rough nearly downhill free-energy surface in blue; the same surface with an added linear free-energy bias for a 10°C temperature jump is shown in red. The root mean-square roughness (δ²G ≈ 0.64 k²T²) is comparable to the barrier height and to a recent experimental estimate for trpzip2 (Yang and Gruebele, 2004). The length scale of the roughness will be larger for real folding surfaces, and more than one coordinate is required for a full description (Yang and Gruebele, unpublished). (Middle) Langevin dynamics on the model surface quantitatively reproduces the fast and slow timescales, as well as the amplitudes for the λD14A mutant at 63°C (black); the populations at x < 0.83 and x > 0.83 were assigned different spectroscopic signals to compute a signal change from the population change. (Bottom) Residuals of the single and double-exponential fits to the simulation.