Structural insights into the mechanism of oxidative activation of heme-free H-NOX from Vibrio cholerae

Biochem J. 2020 Mar 27;477(6):1123-1136. doi: 10.1042/BCJ20200124.


Bacterial heme nitric oxide/oxygen (H-NOX) domains are nitric oxide (NO) or oxygen sensors. This activity is mediated through binding of the ligand to a heme cofactor. However, H-NOX from Vibrio cholerae (Vc H-NOX) can be easily purified in a heme-free state that is capable of reversibly responding to oxidation, suggesting a heme-independent function as a redox sensor. This occurs by oxidation of Cys residues at a zinc-binding site conserved in a subset of H-NOX homologs. Remarkably, zinc is not lost from the protein upon oxidation, although its ligation environment is significantly altered. Using a combination of computational and experimental approaches, we have characterized localized structural changes that accompany the formation of specific disulfide bonds between Cys residues upon oxidation. Furthermore, the larger-scale structural changes accompanying oxidation appear to mimic those changes observed upon NO binding to the heme-bound form. Thus, Vc H-NOX and its homologs may act as both redox and NO sensors by completely separate mechanisms.

Keywords: disulphide bonds; redox signalling; zinc.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Bacterial Proteins / chemistry
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • Binding Sites / physiology
  • Computational Biology / methods
  • Crystallography, X-Ray
  • Heme / chemistry
  • Heme / genetics
  • Heme / metabolism*
  • Nitric Oxide / chemistry
  • Nitric Oxide / genetics
  • Nitric Oxide / metabolism*
  • Oxidative Stress / physiology*
  • Protein Structure, Secondary
  • Vibrio cholerae / chemistry
  • Vibrio cholerae / genetics
  • Vibrio cholerae / metabolism*


  • Bacterial Proteins
  • Nitric Oxide
  • Heme