Ferritins for chemistry and for life

► Ferritins synthesize caged hydrated ferric oxide nanominerals as metabolic iron concentrates and antioxidants, trapping Fe from damaged proteins. ► Multiple (24 or 12 polypeptides), folded in 4-α-helix bundles, self-assemble to form ferritin cages. ► Fe2+ enters and exits water soluble ferritin through ion channels, similar to membrane ion channels, Fe2+ and O2 react at diiron oxidoreductase sites to initiate mineral synthesis with diferric oxo complexes and in some ferritins larger, protein-based, ferric multimers. ► Ferritin proteins cages are being developed for nanomaterials, nanocatalysts, nanodevices and tissue imaging.