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Probing the electronic structure of the heterobimetallic Mn/Fe cofactor of the R2lox proteins using advanced EPR techniques

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Shafaat,  Hannah S.
Research Department Lubitz, Max Planck Institute for Chemical Energy Conversion, Max Planck Society;

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Pantazis,  Dimitrios A.
Research Department Neese, Max Planck Institute for Chemical Energy Conversion, Max Planck Society;

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Neese,  Frank
Research Department Neese, Max Planck Institute for Chemical Energy Conversion, Max Planck Society;

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Lubitz,  Wolfgang
Research Department Lubitz, Max Planck Institute for Chemical Energy Conversion, Max Planck Society;

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Cox,  Nicholas
Research Department Lubitz, Max Planck Institute for Chemical Energy Conversion, Max Planck Society;

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Citation

Shafaat, H. S., Pantazis, D. A., Neese, F., Lubitz, W., Cox, N., Griese, J. J., et al. (2013). Probing the electronic structure of the heterobimetallic Mn/Fe cofactor of the R2lox proteins using advanced EPR techniques. Poster presented at XVIth International Conference on Biological Inorganic CHemistry, Grenoble, France.


Cite as: http://hdl.handle.net/21.11116/0000-0007-A280-0
Abstract
Metalloproteins containing heterobimetallic Mn/Fe cofactors are prevalent in pathogens and extremophiles and thus are highly relevant to understand. The recently discovered R2lox class of proteins is one such example, as they are upregulated in virulent strains of Mycobacterium tuberculosis (Andersson, C. S.; Hoegbom, M. Proc. Natl. Acad. Sci. U. S. A. 2009, 106, 5633). X-ray crystallography shows that the aerobically prepared Mn/Fe cofactor is bridged by an oxygen-derived μ-oxo or μ-hydroxo ligand and a carboxylate from an exogenous lipid, suggesting that the in vivo function of R2lox is that of a lipid oxidase or desaturase. Multiple spectroscopic techniques, including CW-EPR, pulse-EPR, and 57Mössbauer, provide a comprehensive picture of the electronic structure of the cofactor and the primary coordination sphere of the active site. Consistent with the crystallographic result, each site is found to have distinct metal-binding preferences; site 1 is selective for Mn, while site 2 is selective for Fe, a deviation from the expected Irving-Williams series of metal-binding affinities. Direct characterization of the ligands unambiguously shows that one bridge between the metals must be a μ-hydroxo species, establishing new spectral fingerprints for this motif. Furthermore, visible illumination of the R2lox protein at cryogenic temperatures gives rise to a new, thermally unstable form of the Mn/Fe cofactor. The spectra of the photoinduced state strongly resemble those of the homologous Mn/Fe cofactor seen in class lc ribonucleotide reducatase (R2c) (Jiang, W. et al. Science 2007, 316, 1188). This analysis provides structural insight into the yet-uncharacterized Mn/Fe R2c cofactor. Overall, these results have important implications for understanding the distinctions between the R2lox and R2c proteins and the divergent chemistry that these systems perform.