Subunit dissociation and metal binding by Escherichia coli apo-manganese superoxide dismutase

► The X-ray crystal structure of apo-MnSOD shows that the protein defines the metal coordination geometry. ► Apo-MnSOD undergoes rapid subunit exchange during metal uptake. ► Conformationally gated metal uptake by apo-MnSOD involves dissociation of the dimeric protein. ► Small-zone size exclusion chromatography indicates μM stability of the protein dimer. ► Metal uptake by apo-MnSOD is very similar in vitro and in vivo.