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The molecular basis of protein toxin HicA– dependent binding of the protein antitoxin HicB to DNA

Research output: Contribution to journalArticle

Original languageEnglish
Pages (from-to)19429-19440
Number of pages12
JournalJournal of Biological Chemistry
Issue number50
Early online date18 Oct 2018
DateAccepted/In press - 16 Oct 2018
DateE-pub ahead of print - 18 Oct 2018
DatePublished (current) - 14 Dec 2018


Toxin–antitoxin (TA) systems are present in many bacteria and play important roles in bacterial growth, physiology, and pathogenicity. Those that are best studied are the type II TA systems, in which both toxins and antitoxins are proteins. The HicAB system is one of the prototypic TA systems, found in many bacterial species. Complex interactions between the protein toxin (HicA), the protein antitoxin (HicB), and the DNA upstream of the encoding genes regulate the activity of this system, but few structural details are available about how HicA destabilizes the HicB–DNA complex. Here, we determined the X-ray structures of HicB and the HicAB complex to 1.8 and 2.5 Å resolution, respectively, and characterized their DNA interactions. This revealed that HicB forms a tetramer and HicA and HicB form a heterooctameric complex that involves structural reorganization of the C-terminal (DNA-binding) region of HicB. Our observations indicated that HicA has a profound impact on binding of HicB to DNA sequences upstream of hicAB in a stoichiometric-dependent way. At low ratios of HicA:HicB, there was no effect on DNA binding, but at higher ratios, the affinity for DNA declined cooperatively, driving dissociation of the HicA:HicB:DNA complex. These results reveal the structural mechanisms by which HicA de-represses the HicB–DNA complex.

    Structured keywords

  • Bristol BioDesign Institute
  • BrisSynBio

    Research areas

  • structural biology, X-ray crystallography, DNA-binding protein, protein-protein interaction, bacterial toxin, antibiotic resistance, conditional cooperativity, HicAB, persistence, toxin-antitoxin system, type ii TA system, SYNTHETIC BIOLOGY

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    Rights statement: This is the author accepted manuscript (AAM). The final published version (version of record) is available online via American Society for Biochemistry and Molecular Biology at Please refer to any applicable terms of use of the publisher.

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  • Full-text PDF (final published version)

    Rights statement: This is the final published version of the article (version of record). It first appeared online via American Society for Biochemistry and Molecular Biology at Please refer to any applicable terms of use of the publisher.

    Final published version, 3 MB, PDF document


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