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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.

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Official URL: http://dx.doi.org/10.1016/j.jinorgbio.2012.02.031

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, 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.

Item Type: Article
Keyword(s) / Subject(s): Ferritin, bacterioferritin, crystal structure, haemin, demetallation
School or Research Centre: Birkbeck Schools and Research Centres > School of Science > Biological Sciences
Depositing User: Administrator
Date Deposited: 09 Mar 2012 16:36
Last Modified: 17 Apr 2013 12:22
URI: http://eprints.bbk.ac.uk/id/eprint/4630

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