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Brown, BL, Grigoriu, S, Kim, Y, Arruda, JM, Davenport, A, Wood, TK, Peti, W and Page, R (2009) Three dimensional structure of the MqsR:MqsA complex: a novel TA pair comprised of a toxin homologous to RelE and an antitoxin with unique properties. PLoS Pathog. 5:e1000706


One mechanism by which bacteria survive environmental stress is through the formation of bacterial persisters, a sub-population of genetically identical quiescent cells that exhibit multidrug tolerance and are highly enriched in bacterial toxins. Recently, the Escherichia coli gene mqsR (b3022) was identified as the gene most highly upregulated in persisters. Here, we report multiple individual and complex three-dimensional structures of MqsR and its antitoxin MqsA (B3021), which reveal that MqsR:MqsA form a novel toxin:antitoxin (TA) pair. MqsR adopts an alpha/beta fold that is homologous with the RelE/YoeB family of bacterial ribonuclease toxins. MqsA is an elongated dimer that neutralizes MqsR toxicity. As expected for a TA pair, MqsA binds its own promoter. Unexpectedly, it also binds the promoters of genes important for E. coli physiology (e.g., mcbR, spy). Unlike canonical antitoxins, MqsA is also structured throughout its entire sequence, binds zinc and coordinates DNA via its C- and not N-terminal domain. These studies reveal that TA systems, especially the antitoxins, are significantly more diverse than previously recognized and provide new insights into the role of toxins in maintaining the persister state.


PubMed PMC2791442 Online version:10.1371/journal.ppat.1000706


Bacterial Toxins/chemistry; Electrophoresis, Polyacrylamide Gel; Electrophoretic Mobility Shift Assay; Escherichia coli/chemistry; Escherichia coli Proteins/chemistry; Genes, Bacterial; Models, Molecular; Protein Structure, Quaternary


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This work is significant because it shows for the first time the three-dimensional structures of toxin MqsR and antitoxin MqsA; this structural information shows that toxin MqsR is a ribonuclease, and that it is related to mRNA interferase RelE[1]. In addition, it shows for the first time that an antitoxin, MqsA, is able to bind more than its own promoter[1]; this implies that antitoxins may regulate more than the genes that encode them. MqsA binds DNA via its helix-turn-helix in its C-terminal domain[1]. Unlike most TA pairs including RelE/RelB, YoeB/YefM and MazF/MazE, the MqsR toxin gene precedes the antitoxin gene in the bicistronic operon. Furthermore, the MqsR/MqsA TA pair is unique in that (i) the antitoxin is larger than the toxin, (ii) both toxin and antitoxin are basic (typically the toxin is basic while the antitoxin is acidic), (iii) the mqsRA sequences are not homologous to any member of a recognized TA system, (iv) the antitoxin binds the toxin at its amino terminus and requires a metal, zinc, for structural stability, (v) the antitoxin is structured throughout its entire sequence, and (vi) the antitoxin binds more than its own promoter (e.g., mqsRA, mcbR, and spy) via its C-terminal domain. Also, MqsR cleaves mRNA at GCU sites [2].

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  1. 1.0 1.1 1.2 Brown, BL et al. (2009) Three dimensional structure of the MqsR:MqsA complex: a novel TA pair comprised of a toxin homologous to RelE and an antitoxin with unique properties. PLoS Pathog. 5 e1000706 PubMed EcoliWiki page
  2. Yamaguchi, Y et al. (2009) MqsR, a crucial regulator for quorum sensing and biofilm formation, is a GCU-specific mRNA interferase in Escherichia coli. J. Biol. Chem. 284 28746-53 PubMed EcoliWiki page