Figure 4.

(a) Amide proton temperature coefficients (determined using chemical shifts referenced to DSS) for pWT apoSOD1^2SH, (b) temperature coefficient differences (relative to pWT) resulting from the H46R mutation, and (c) the metal‐binding region of apoSOD1^2SH showing overlaid H46 (pink) and R46 (purple, semitransparent) side chains. Light gray indicates that data are not available. The monomeric, rather than dimeric form of apoSOD1^2SH predominates, but in (a) and (b), we project the data onto a dimeric SOD1 structure (PDB ID: 2AF2)26 with a semitransparent second subunit in order to illustrate the residues that form the dimer interface and present two views (one rotated ∼ 180° relative to the other). In holoSOD1 (PDB ID: 1HL5),27 the H46 residue coordinates the Cu²⁺ ion (orange, semitransparent), while in H46R (PDB ID: 1OZT) the positively charged guanidinium group of the R46 side chain sits between the vacant Cu²⁺ and Zn²⁺ (light gray, semitransparent) binding sites. Figure prepared using PyMOL28