Figure 4. Loss of Cu^1+/2+ and Zn²⁺ ions leads to increased backbone dynamics of the active-site loops IV and VII.

The backbone dynamics of monomeric apo- and holoSOD1 evaluated by NMR relaxation experiments. (A) Structural representation of the SOD1 monomer showing the regions of increased dynamic motions in the apo state. (B) Amino-acid sequence of loops IV and VII. (C) Increased dynamics in the intermediate time scale is indicated by increased values of R₁/R₂ and increased fast dynamics as increased negative values of (NOE-1)R₁. In the apoSOD1 monomer, the regions of loops IV and VII show increased dynamics [31], whereas in the metallated monomer [71] the loops are as fixed as the rest of the protein. Figure outline adapted from Nordlund et al. [32].