Cargo protein of a type 1 encapsulin nanocompartment. A ferritin-like ferroxidase that mineralizes iron inside the encapsulin nanocompartment. Converts Fe(2+) to Fe(3+) that is released to the exterior of the decameric complex for deposition in the encapsulin nanocompartment. In solution the decamer binds 10-15 iron cations; in the encapsulin nanocompartment the decamer can bind up to 48 ions, perhaps via its internal channel and on its exterior. The empty encapsulin nanocompartment sequesters about 2200 Fe ions while the cargo-loaded nanocompartment can maximally sequester about 4150 Fe ions. EncFtn retains ferroxidase activity when encapsulated (PubMed:27529188). Flux in the active site di-iron metal center is thought to be controlled by the 'entry site' of the protein, which both attracts metal and controls the rate of iron oxidation (Probable). Encapsulation in the nanocompartment does not alter either function of this protein (PubMed:32878987). 4 Fe(2+) + 4 H(+) + O2 = 4 Fe(3+) + 2 H2O Binds a di-iron center symmetrically between each dimer. Fe(2+), Zn(2+) and Co(2+) but not Fe(3+), Ca(2+), Mg(2+) or Mn(2+) induce protein oligomerization. Binds 1 Ca cation symmetrically between each dimer in what is called the entry site; in vivo this may be an Fe cation. Ferroxidase activity inhibited by Zn(2+); mutants at Glu-31, Glu-34 and Trp-38 are also inhibited by Zn(2+). Monomers form antiparallel dimers which assemble in a decameric ring 7 nm in diameter and 4.5 nm thick with a central channel (construct without targeting peptide) (PubMed:27529188, Ref.3, PubMed:32878987). Growth in Fe(2+)-rich medium induces oligomerization, the monomer does not bind metals (PubMed:27529188, PubMed:32878987). The target peptide probably extends away from the ring, to allow binding to the interior of the encapsulin nanocompartment shell (Probable). Belongs to the ferritin-like superfamily. EncFtn family.