Figure 14. Model of iron oxidation in encapsulin nanocompartments.
(A) Model of EncFtnsH docking to the encapsulin shell. A single pentamer of the icosahedral T. maritima encapsulin structure (PDBID: 3DKT) (Sutter et al., 2008) is shown as a blue surface with the encapsulin localization sequence of EncFtn shown as a purple surface. The C-terminal regions of the EncFtn subunits correspond to the position of the localization sequences seen in 3DKT. Alignment of EncFtnsH with 3DKT positions the central channel directly above the pore in the 3DKT pentamer axis (shown as a grey pentagon). (B) Surface view of EncFtn within the encapsulin nanocompartment (grey and blue respectively). The lumen of the encapsulin nanocompartment is considerably larger than the interior of ferritin (shown in orange behind the encapsulin for reference) and thus allows the storage of significantly more iron. The proposed pathway for iron movement through the encapsulin shell and EncFtn FOC is shown with arrows. (C) Model ofiron oxidation within an encapsulin nanocompartment. As EncFtn is unable to mineralize iron on its surface directly, Fe2+ must pass through the encapsulin shell to access the first metal binding site within the central channel of EncFtnsH (entry site) prior to oxidation within the FOC and release as Fe3+ to the outer surface of the protein where it can be mineralized within the lumen of the encapsulin cage.