The MarR/DUF24-Family QsrR Repressor Senses Quinones and Oxidants by Thiol Switch Mechanisms in .

The MarR/DUF24-family QsrR and YodB repressors control quinone detoxification pathways in and . In , the QsrR regulon also confers resistance to antimicrobial compounds with quinone-like elements, such as rifampicin, ciprofloxacin, and pyocyanin. Although QsrR was shown to be inhibited by thiol--alkylation of its conserved Cys4 residue by 1,4-benzoquinone, YodB senses quinones and diamide by the formation of reversible intermolecular disulfides. In this study, we aimed at further investigating the redox-regulation of QsrR and the role of its Cys4, Cys29, and Cys32 residues under quinone and oxidative stress in . The QsrR regulon was strongly induced by quinones and oxidants, such as diamide, allicin, hypochlorous acid (HOCl), and AGXX in . Transcriptional induction of by quinones and oxidants required Cys4 and either Cys29' or Cys32' of QsrR for redox sensing . DNA-binding assays revealed that QsrR is reversibly inactivated by quinones and oxidants, depending on Cys4. Using mass spectrometry, QsrR was shown to sense diamide by an intermolecular thiol-disulfide switch, involving Cys4 and Cys29' of opposing subunits . In contrast, allicin caused -thioallylation of all three Cys residues in QsrR, leading to its dissociation from the operator sequence. Further, the QsrR regulon confers resistance against quinones and oxidants, depending on Cys4 and either Cys29' or Cys32'. QsrR was characterized as a two-Cys-type redox-sensing regulator, which senses the oxidative mode of quinones and strong oxidants, such as diamide, HOCl, and the antimicrobial compound allicin different thiol switch mechanisms.