2V2J

Structural Analysis of Haemin Demetallation by L-Chain Apoferritins

(2012) J Inorg Biochem 112: 77

• PubMed: 22561545 Search on PubMed
• DOI: https://doi.org/10.1016/j.jinorgbio.2012.02.031
• Primary Citation of Related Structures:  
  2V2I, 2V2J, 2V2L, 2V2M, 2V2N, 2V2O, 2V2P, 2V2R, 2V2S, 2W0O


• PubMed Abstract: 
  

  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 (1.16Å) 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 1.5Å). 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.

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Organizational Affiliation: 

Institute of Life Sciences, University of Louvain, Place Croix du Sud, 1348 Louvain-la-Neuve, Belgium. [email protected]