(A) Dimeric structure of E. coli MnSOD (PDB code: 1D5N), with each subunit depicted by a different color (subunit A is colored cyan while subunit B is colored green). (B) Active sites of E. coli MnSOD depicting the inner sphere residues coordinating with the manganese cofactor and highlighting the hydrogen bonding formed between Glu170 and His171 between the two monomeric subunits. Manganese is depicted as a purple sphere. (C) The active sites of the E170A mutant using PyMol to reflect the disrupted hydrogen bonding and subsequent destabilization of the dimer structure. Metal specificity is altered in the E170A mutant; hence, iron is depicted as an orange sphere. The red spheres represent the water molecules coordinating with the metal cofactor. Hydrogen bonding is depicted by black dashes. All figures were generated using PyMol [31].