Differentiated, promoter-specific response of [4Fe-4S] NsrR DNA-binding to reaction with nitric oxide

Jason Crack, Dimitri A. Svistunenko, John Munnoch, Andrew Thomson, Matthew Hutchings, Nicolas Le Brun

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NsrR is an iron-sulfur cluster protein that regulates the nitric oxide (NO) stress response of many bacteria. NsrR from Streptomyces coelicolor regulates its own expression and that of only two other genes, hmpA1 and hmpA2, which encode HmpA enzymes predicted to detoxify NO. NsrR binds promoter DNA with high affinity only when coordinating a [4Fe-4S] cluster. Here we show that reaction of [4Fe-4S] NsrR with NO affects DNA-binding differently depending on the gene promoter. Binding to the hmpA2 promoter was abolished at ~2 NO per cluster, while for the hmpA1 and nsrR promoters, ~4 and ~8 NO molecules, respectively, were required to abolish DNA binding. Spectroscopic and kinetic studies of the NO reaction revealed a rapid, multi-phase, non-concerted process involving up to 8 – 10 NO molecules per cluster, leading to the formation of several iron-nitrosyl species. A distinct intermediate was observed at ~2 NO per cluster, along with two further intermediates at ~4 and ~6 NO. The NsrR nitrosylation reaction was not significantly affected by DNA-binding. These results show that NsrR regulates different promoters in response to different concentrations of NO. Spectroscopic evidence indicates that this is achieved by different NO-FeS complexes.
Original languageEnglish
Pages (from-to)8663-8672
Number of pages10
JournalJournal of Biological Chemistry
Early online date17 Feb 2016
Publication statusPublished - 15 Apr 2016


  • iron
  • iron-sulfur
  • nitric oxide
  • regulator
  • DNA-binding protein
  • spectroscopy

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