Ferritin is a major non-haem iron storage protein in animal, plants and microorganisms. Iron is required by most organisms, but is potentially toxic due to its reactivity, which is counteracted by sequestering it into ferritin. It consists of a mineral core of hydrated ferric oxide, and a multi-subunit protein shell which encloses the former and assures its solubility in an aqueous environment. In animals, the protein is mainly cytoplasmic and there are generally two or more genes that encode closely related subunits (in mammals there are two subunits which are known as H(eavy) and L(ight)). In plants, ferritin is found in the chloroplast.

This superfamily consists of a four-helix bundle domain found in ferritin and homologous proteins. This ferritin domain consists of a 4-helical bundle core, and contains a bimetal-ion centre (Fe or Mn dimer). The four helices are arranged in an antiparallel manner, with a left-handed twist. This helical bundle has a distinctively long connection between the second and third helices. Other proteins with this structure include: haem-containing bacteriferritins PMID:18946693, rubrerythrin found in anaerobic sulphate-reducing bacteria and archaea, which has a role in anaerobic detoxification pathway for reactive oxygen species INTERPRO:IPR003251,PMID:15547260,PMID:7830612, Dps (DNA-binding proteins from starved cells) used to protect DNA against oxidative stress during nutrient starvation INTERPRO:IPR002177, INTERPRO:IPR023067,PMID:1340475 ; and CRD1 (AcsF), which is required for the maintenance of photosystem I PMID:10811605.

INTERPRO:IPR012347, INTERPRO:IPR001519, PFAM:PF00210, Pfam clan [PfamClan:CL0044],PMID:3304136