Fig. 4.

Folding and unfolding pathways. (A) Collapse kinetics monitored by the time-dependent average 〈R_g(t)〉 as a function of t. Collapse (expansion) decreases (increases) in 〈R_g(t)〉 can be fit using a single exponential function. The Inset shows P(R_g; t) at t = 0, t ≈ τ_c ≈ (k_c([C] = 1.0 M))^-1 ≈ 4.2 ms, and t = 34 ms, the first passage time for the slowest trajectory, respectively. (B) Projection of kinetic folding trajectories in terms of fraction of secondary structure formation, f_ss, and 〈R_g〉. (C) First passage time for formation of various interactions, indicated in the figure, from the sixty folding trajectories at [C] = 1.0 M. The solid black symbols show the correlation between and , which are first passage times for formation of interactions β₁ - β₂ and β₂ - β₃, respectively. (D) Same as (C) except the results are for unfolding at [C] = 6.0 M. Similarity between (C) and (D) establishes the reversibility between folding and unfolding.