2V2I: Wild Type Recombinant Horse Spleen Apoferritin Cocrystallized With Haemin In Acidic Conditions

There are extensive structural similarities between eukaryotic and prokaryotic ferritins. However, there is one essential difference between these two types of ferritins: bacterioferritins contain haem whereas eukaryotic ferritins are considered to be non-haem proteins. In vitro experiments had shown that horse spleen apoferritin or recombinant horse L chain apoferritins, when co-crystallised with haemin, undergoes demetallation of the porphyrin. In the present study a cofactor has been isolated directly from horse spleen apoferritin and from crystals of the mutant horse L chain apoferritin (E53Q, E56Q, E57Q, E60Q and R59M) which had been co-crystallised with haemin. In both cases the HPLC/ESI-MS results confirm that the cofactor is a N-ethylprotoporphyrin IX. Crystal structures of wild type L chain horse apoferritin and its three mutants co-crystallised with haemin have been determined to high resolution and in all cases a metal-free molecule derived from haemin was found in the hydrophobic pocket, close to the two-fold axis. The X-ray structure of the E53Q, E56Q, E57Q, E60Q+R59M recombinant horse L-chain apoferritin has been obtained at a higher resolution (1.16A) than previously reported for any mammalian apoferritins. Similar evidence for a metal-free molecule derived from haemin was found in the electron density map of horse spleen apoferritin (at a resolution of 1.5A). The out-of-plane distortion of the observed porphyrin is clearly compatible with an N-alkyl porphyrin. We conclude that L-chain ferritins are capable of binding and demetallating haemin, generating in the process N-ethylprotoporphyrin IX both in vivo and in vitro.
PDB ID: 2V2IDownload
MMDB ID: 65052
PDB Deposition Date: 2007/6/6
Updated in MMDB: 2008/06
Experimental Method:
x-ray diffraction
Resolution: 2  Å
Source Organism:
Similar Structures:
Biological Unit for 2V2I: 24-meric; determined by author and by software (PISA)
Molecular Components in 2V2I
Label Count Molecule
Proteins (24 molecules)
Ferritin Light Chain(Gene symbol: FTL)
Molecule annotation
Chemicals (238 molecules)
* Click molecule labels to explore molecular sequence information.

Citing MMDB