bacterioferritins

Bacterioferritins are iron-storage proteins found in many bacteria and some archaea. They resemble ferritin in overall architecture, forming a hollow 24-subunit nanocage that stores iron as a ferrihydrite-like mineral inside the interior. This arrangement helps detoxify excess iron and provides a buffered iron supply for cellular processes.

A distinctive feature of bacterioferritins is the presence of a heme B prosthetic group located at the interface between subunits. The heme participates in electron transfer during iron mobilization. Each subunit contributes to a ferroxidase center that catalyzes the oxidation of Fe2+ to Fe3+ as iron is deposited into the mineral core. Iron moves through channels at the threefold and fourfold symmetry axes that connect the interior with the outside of the cage, enabling controlled loading and release.

Iron storage and release in bacterioferritins are linked to cellular redox partners. Electrons can be conveyed via the heme to reduce stored ferric iron, allowing mobilization of iron when the cell requires it. This makes bacterioferritins important for iron homeostasis and for protection against oxidative stress that can arise from free iron.

Bacterioferritin genes, typically named bfr, are regulated by iron-responsive networks such as Fur in many bacteria. Expression often responds to iron availability and oxidative stress rather than being constitutive. In comparison with nongroup ferritins, bacterioferritins are distinguished by their heme cofactor and specific features of their ferroxidase centers, while retaining the shared ferritin-like shell and mineral core.