Fig. 2.

The effects of Zn-site mutation and metallation on folding and stability of the SOD1 monomer. SOD1_pWT^apo (black), SOD1_mut^apo (red) and SOD1_mut^Zn (blue). (A) Chevron plots of logk_obs = log(k_f+k_u) vs. [urea] (Eq. 2). (B) Equilibrium unfolding transitions at 0 and 500 μM [Zn] (Eq. 1). Measurements at 50 and 500 μM [Zn] yield indistinguishable results. (C) The corresponding folding free-energy profiles, showing the unfolded state (U), the transition state (‡) and the folded monomer (F). The folded state becomes more solvent accessible upon Zn binding to the Cu site, indicated by decreased value of m_u (Eqs. 1 and 2 and Table 1).