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Lookup NU author(s): Daniil Baranov, Dr Agnieszka Bronowska
This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).
© 2025 Nguyen et al. The MarR-family regulator MhqR of Staphylococcus aureus (SaMhqR) was previously characterized as a quinone-sensing repressor of the mhqRED operon. Here, we solved the crystal structures of apo-SaMhqR and the 2-methylbenzoquinone (MBQ)bound SaMhqR complex. AlphaFold3 modeling was used to predict the structure of SaMhqR in complex with its operator DNA. In the DNA-bound SaMhqR state, S65 and S66 of an allosteric α3–α4 loop adopted a helically wound conformation to elongate helix α4 for optimal DNA binding. Key residues for MBQ interaction were identified as F11, F39, E43, and H111, forming the MBQ-binding pocket. MBQ binding prevented the formation of the extended helix α4 in the allosteric loop, leading to steric clashes with the DNA. Molecular dynamics (MD) simulations revealed an increased intrinsic dynamics within the allosteric loop and the β1/β2-wing regions after MBQ binding to prevent DNA binding. Using mutational analyses, we validated that F11, F39, and H111 are required for quinone sensing in vivo, whereas S65 and S66 of the allosteric loop and D88, K89, V91, and Y92 of the β1/β2-wing are essential for DNA binding in vitro and in vivo. In conclusion, our structure-guided modeling and mutational analyses identified a quinone-binding pocket in SaMhqR and the mechanism of SaMhqR inactivation, which involves local structural rearrangements of an allosteric loop and high intrinsic dynamics to prevent DNA interactions. Our results provide novel insights into the redox mechanism of the conserved SaMhqR repressor, which functions as an important determinant of quinone and antimicrobial resistance in S. aureus.
Author(s): Nguyen TT-P, Weiland P, Van Loi V, Kiontke S, Burchert F, Zegarra V, Kern A, Fritsch VN, Baranov D, Bronowska AK, Bange G, Antelmann H
Publication type: Article
Publication status: Published
Journal: mBio
Year: 2026
Volume: 17
Issue: 2
Print publication date: 11/02/2026
Online publication date: 31/12/2025
Acceptance date: 15/12/2025
Date deposited: 25/02/2026
ISSN (print): 2161-2129
ISSN (electronic): 2150-7511
Publisher: American Society for Microbiology
URL: https://doi.org/10.1128/mbio.03292-25
DOI: 10.1128/mbio.03292-25
Data Access Statement: The authors confirm that the data supporting the findings of this study are available within the article and its supplementary materials. The crystal structure data of the S. aureus SaMhqR proteins are available in the PDB database under accession numbers 9QDR (apo SaMhqR) and 9SMZ (MBQ-bound SaMhqR).
PubMed id: 41474324
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