The crystal structure of recombinant ferritin from Helicobacter pylori has been determined in its apo, low-iron-bound, intermediate, and high-iron-bound states. Similar to other members of the ferritin family, the bacterial ferritin assembles as a spherical protein shell of 24 subunits, each of which folds into a four-α-helix bundle. Significant conformational changes were observed at the BC loop and the entrance of the 4-fold symmetry channel in the intermediate and high-iron-bound states, whereas no change was found in the apo and low-iron-bound states. The imidazole rings of His149 at the channel entrance undergo conformational changes that bear resemblance to heme configuration and are directly coupled to axial translocation of Fe ions through the 4-fold channel. Our results provide the first structural evidence of the translocation of Fe ions through the 4-fold channel in prokaryotes and the transition from a protein-dominated process to a mineral-surface-dominated process during biomineralization.
Bibliographical noteFunding Information:
This work was supported by the Biogreen 21 Program (20080401-034-008), the Basic Research Program of the Korea Science and Engineering Foundation, and the Korea Research Foundation, funded by the Korean Government (KRF-313-C00616). We thank the staff at Beamline 4A of Pohang Light Source for their help with data collection.
- 4-fold channel
- Helicobacter pylori
- iron uptake mechanism