Fig. 5.

E–G5² can fold by an alternative folding pathway. Mutations in the G5 domain that destabilize the folding nucleus cause a switch in pathway in E–G5² manifested by a change in the dependence of lnk_f on [urea]. (A) Structure of E–G5² showing the location of residues mutated or used to engineer the FRET pair. (B and C) Equilibrium denaturation curves for G5² and E–G5², respectively. (D) Chevron plots for WT E–G5² and mutants. Note the change in slope of the folding limb of the chevron plot for all of these mutants. (E) Mutations using Y625W as a pseudo-WT. Chevron plots for WT E–G5² (black), E–G5²–Y625W (green), and Pro-to-Ala mutants of E–G5² in the background of Y625W. Note that the interface mutant (P599A) causes the slope to revert to the WT. The other mutants have Φ-values that differ from those in the WT background.