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Mechanisms of iron- and O₂-sensing by the [4Fe-4S] cluster of the global iron regulator RirA.

Pellicer Martinez, Ma Teresa and Crack, Jason C and Stewart, Melissa Yy and Bradley, Justin M and Svistunenko, Dimitri A and Johnston, Andrew Wb and Cheesman, Myles R and Todd, Jonathan D and Le Brun, Nick E (2019) 'Mechanisms of iron- and O₂-sensing by the [4Fe-4S] cluster of the global iron regulator RirA.' eLife, 8. ISSN 2050-084X

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RirA is a global regulator of iron homeostasis in <i>Rhizobium</i> and related α-proteobacteria. In its [4Fe-4S] cluster-bound form it represses iron uptake by binding to IRO Box sequences upstream of RirA-regulated genes. Under low iron and/or aerobic conditions, [4Fe-4S] RirA undergoes cluster conversion/degradation to apo-RirA, which can no longer bind IRO Box sequences. Here, we apply time-resolved mass spectrometry and electron paramagnetic resonance spectroscopy to determine how the RirA cluster senses iron and O<sub>2</sub>. The data indicate that the key iron-sensing step is the O<sub>2</sub>-independent, reversible dissociation of Fe<sup>2+</sup> from [4Fe-4S]<sup>2+</sup> to form [3Fe-4S]<sup>0</sup>. The dissociation constant for this process was determined as <i>K</i><sub>d</sub> = ~3 µM, which is consistent with the sensing of 'free' iron in the cytoplasm. O<sub>2</sub>-sensing occurs through enhanced cluster degradation under aerobic conditions, via O<sub>2</sub>-mediated oxidation of the [3Fe-4S]<sup>0</sup> intermediate to form [3Fe-4S]<sup>1+</sup>. This work provides a detailed mechanistic/functional view of an iron-responsive regulator.

Item Type: Article
Uncontrolled Keywords: Rhizobium, Oxygen, Iron, Bacterial Proteins, Iron-Sulfur Proteins, Electron Spin Resonance Spectroscopy, Oxidation-Reduction, Mass Spectrometry, Proteolysis
Divisions: Faculty of Science and Health > Life Sciences, School of
Depositing User: Elements
Date Deposited: 13 Aug 2021 12:10
Last Modified: 13 Aug 2021 12:10

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