Structural analysis of haemin demetallation by L-chain apoferritins
de Val, N. and Declercq, J.P. and Lim, Chang-Kee and Crichton, R.R. (2012) Structural analysis of haemin demetallation by L-chain apoferritins. Journal of Inorganic Biochemistry 112 , pp. 77-84. ISSN 0162-0134.
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, 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 (1.16 Å) 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 1.5 Å). 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.
|Keyword(s) / Subject(s):||Ferritin, bacterioferritin, crystal structure, haemin, demetallation|
|School:||Birkbeck Schools and Departments > School of Science > Biological Sciences|
|Date Deposited:||09 Mar 2012 16:36|
|Last Modified:||17 Apr 2013 12:22|
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