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

Pellicer Martinez, Maria Teresa, Crack, Jason, Stewart, Melissa, Bradley, Justin, Svistunenko, Dimitri A., Johnston, Andrew, Cheesman, Myles, Todd, Jonathan and Le Brun, Nick (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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Abstract

RirA is a global regulator of iron homeostasis in Rhizobium 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 O2. The data indicate that the key iron-sensing step is the O2-independent, reversible dissociation of Fe2+ from [4Fe-4S]2+ to form [3Fe-4S]0. The dissociation constant for this process was determined as Kd = ~3 µM, which is consistent with the sensing of ‘free’ iron in the cytoplasm. O2-sensing occurs through enhanced cluster degradation under aerobic conditions, via O2-mediated oxidation of the [3Fe-4S]0 intermediate to form [3Fe-4S]1+. This work provides a detailed mechanistic/functional view of an iron-responsive regulator.

Item Type: Article
Faculty \ School: Faculty of Science > School of Chemistry
Faculty of Science > School of Biological Sciences
Depositing User: LivePure Connector
Date Deposited: 12 Aug 2019 08:30
Last Modified: 21 Sep 2020 23:56
URI: https://ueaeprints.uea.ac.uk/id/eprint/71930
DOI: 10.7554/eLife.47804

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