Fig. 4.

ψ, ϕ analysis. (A) The ψ₀, ϕ values are mapped onto the protein structure by coloring the biHis side chains and ribbon according to the associated ϕ^biHis and ψ₀ values, respectively. The D38 and A63 Cα atoms are denoted with colored spheres according to their ϕ^A→G values. (B) Measured ψ, ϕ values. (C) Proposed folding pathway. The 3₁₀ helix is not shown for simplicity and lack of information; HX measurements are consistent with it forming before α2. (D) Chevron plots. Shown are biHis mutant data without (black) and with 1 mM Zn²⁺ (red) and glycine (green) and alanine (blue) variants; orange vertical lines designate the [urea] at which ΔΔG_f and ΔΔG_u are used for the ψ calculation, obtained by simultaneously folding and unfolding data (SI Materials and Methods).