Fig. 3.

Misligation of Zn²⁺ to the Cu site of the SOD1 monomer. (A) Structural superposition of the misligated SOD1 monomer (orange) and the monomeric holo SOD1 (gray). The misligated Zn ion and water molecules in the Cu-binding site are shown in blue and red, respectively. Interpretable electron densities for loops IV and VII are missing in the misligated protein. (B) Close-up of the Cu site showing that Zn binding to the Cu site of the SOD1 mutant causes H48 to change rotamer. This altered orientation of H48 is sterically incompatible with the native arrangement of loop IV. Electron densities are shown as green mesh.