ftnA

ftnA is a gene encoding a ferritin-like protein in bacteria and some archaea. The protein belongs to the ferritin superfamily and functions primarily in iron storage and detoxification, helping to maintain cellular iron homeostasis and protect against oxidative stress by limiting the labile iron pool.

Structure and biochemistry: The FtnA protein typically forms a hollow, spherical nanocage composed of 24 subunits. Each subunit contributes to a central cavity that mineralizes iron as ferric oxide-hydroxide, allowing storage of substantial amounts of iron within the shell. The 24-subunit architecture is highly conserved among ferritin family members and provides a robust, reusable iron reservoir that can be mobilized when needed.

Genetic and regulatory context: In many species, ftnA expression is regulated by iron availability through metal-responsive regulators such as Fur in Gram-negative bacteria or DtxR/PerR in Gram-positive species. Expression tends to increase under conditions of iron excess or oxidative stress to sequester iron and limit reactive oxygen species formation. The gene is often located near other iron metabolism genes or operons, reflecting its role in coordinated iron homeostasis.

Physiological role and applications: FtnA contributes to iron storage, detoxification, and homeostasis, helping bacteria adapt to fluctuating environmental iron levels. It is studied as a model ferritin for understanding iron metabolism, and its nanoparticle cage architecture has inspired applications in nanotechnology, including biocompatible iron storage mimetics, enzyme encapsulation, and potential drug delivery systems.

Notable variants: Many bacteria possess ftnA homologs with similar function; sequences typically encode ~170–190 amino acids and are annotated as ferritin-like proteins in genome databases.