Ferritin-like superfamily of diiron-containing four-helix-bundle proteinsFerritin-like, diiron-carboxylate proteins participate in a range of functions including iron regulation, mono-oxygenation, and reactive radical production. These proteins are characterized by the fact that they catalyze dioxygen-dependent oxidation-hydroxylation reactions within diiron centers; one exception is manganese catalase, which catalyzes peroxide-dependent oxidation-reduction within a dimanganese center. Diiron-carboxylate proteins are further characterized by the presence of duplicate metal ligands, glutamates and histidines (ExxH) and two additional glutamates within a four-helix bundle. Outside of these conserved residues there is little obvious homology. Members include bacterioferritin, ferritin, rubrerythrin, aromatic and alkene monooxygenase hydroxylases (AAMH), ribonucleotide reductase R2 (RNRR2), acyl-ACP-desaturases (Acyl_ACP_Desat), manganese (Mn) catalases, demethoxyubiquinone hydroxylases (DMQH), DNA protecting proteins (DPS), and ubiquinol oxidases (AOX), and the aerobic cyclase system, Fe-containing subunit (ACSF).