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A 60-heme reductase complex from an anammox bacterium shows an extended electron transfer pathway

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Dietl,  Andreas
Department of Biomolecular Mechanisms, Max Planck Institute for Medical Research, Max Planck Society;

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Barends,  Thomas R. M.
Department of Biomolecular Mechanisms, Max Planck Institute for Medical Research, Max Planck Society;

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Citation

Dietl, A., Maalcke, W. J., Ferousi, C., Jetten, M. S. M., Kartal, B., & Barends, T. R. M. (in press). A 60-heme reductase complex from an anammox bacterium shows an extended electron transfer pathway. Acta Crystallographica Section D: Structural Biology, 75, 1-9. doi:10.1107/S2059798318017473.


Cite as: http://hdl.handle.net/21.11116/0000-0003-1A93-A
Abstract
The hydroxylamine oxidoreductase/hydrazine dehydrogenase (HAO/HDH) protein family constitutes an important group of octaheme cytochromes c (OCCs). The majority of these proteins form homotrimers, with their subunits being covalently attached to each other via a rare cross-link between the catalytic heme moiety and a conserved tyrosine residue in an adjacent subunit. This covalent cross-link has been proposed to modulate the active-site heme towards oxidative catalysis by distorting the heme plane. In this study, the crystal structure of a stable complex of an HAO homologue (KsHAOr) with its diheme cytochrome c redox partner (KsDH) from the anammox bacterium Kuenenia stuttgartiensis was determined. KsHAOr lacks the tyrosine cross-link and is therefore tuned to reductive catalysis. The molecular model of the KsHAOr–KsDH complex at 2.6 Å resolution shows a heterododecameric (α6β6) assembly, which was also shown to be the oligomeric state in solution by analytical ultracentrifugation and multi-angle static light scattering. The 60-heme-containing protein complex reveals a unique extended electron transfer pathway and provides deeper insights into catalysis and electron transfer in reductive OCCs.