<p>Ferritin is one of the major non-haem iron storage proteins in animals, plants, and microorganisms. Ferritin is a multisubunit protein with a hollow interior, which contains a mineral core of hydrated ferric oxide, thereby ensuring its solubility in an aqueous environment [<cite idref="PUB00013235"/>]. Each subunit consists of a closed, four-helical bundle with a left-handed twist and one crossover connection.</p><p>This family contains ferritin and other ferritin-like proteins such as bacterioferritin (cytochrome b1) that binds haem between two subunits, non-haem ferritin, dodecameric ferritin homologue (DPS) that binds to and protects DNA, and the N-terminal domain of rubrerythrin that is found in many air-sensitive bacteria and archaea [<cite idref="PUB00013236"/>]. In addition, ribonucleotide reductase-like proteins show a similar structure to the ferritin-like fold; these di-iron carboxylate proteins constitute a diverse class of non-haem iron enzymes performing a multitude of redox reactions [<cite idref="PUB00013315"/>]. This family includes the alpha and beta subunits of methane monooxygenase hydrolase, delta 9-stearoyl-acyl carrier protein desaturase and manganese catalase (T-catalase).</p>