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

Ashley J. Winter, Christopher Williams, Michail N. Isupov, Hannah Crocker, Mariya Gromova, Philip Marsh, Oliver J. Wilkinson, Mark S. Dillingham, Nicholas J. Harmer, Richard W. Titball*, Matthew P. Crump

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

4 Citations (Scopus)
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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.

Original languageEnglish
Pages (from-to)19429-19440
Number of pages12
JournalJournal of Biological Chemistry
Issue number50
Early online date18 Oct 2018
Publication statusPublished - 14 Dec 2018

Structured keywords

  • Bristol BioDesign Institute
  • BrisSynBio


  • 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


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