Figure 2.

(a) PyMOL illustrations of the tetraeicosameric assembly observed in Archaeoglobus fulgidus ferritin viewed along different molecular symmetry axes. Left: One of four pores of the nanocage structure shown along the threefold noncrystallographic symmetry axis. Right: Engineered closed ferritin shell viewed along the axis the fourfold molecular symmetry axis¹⁵ (reprinted from Johnson, E., Cascio, D., Sawaya, M.R., Gingery, M. & Schroder, I. Crystal structures of a tetrahedral open pore ferritin from the hyperthermophilic archaeon Archaeoglobus fulgidus. Structure 13/4, 637–648. Copyright (2005), with permission from Elsevier). (b) Transmission electron micrograph of engineered A. fulgidus ferritin, scale bar=50 nm¹⁶ (reprinted from Sana, B., Johnson, E., Sheah, K., Poh, C.L. & Lim, S. Iron-based ferritin nanocore as a contrast agent. Biointerphases 5/3, FA48–FA52. Copyright (2010), with permission from Springer).