The tuberculosis necrotizing toxin kills macrophages by hydrolyzing NAD

Nat Struct Mol Biol. 2015 Sep;22(9):672-8. doi: 10.1038/nsmb.3064. Epub 2015 Aug 3.


Mycobacterium tuberculosis (Mtb) induces necrosis of infected cells to evade immune responses. Recently, we found that Mtb uses the protein CpnT to kill human macrophages by secreting its C-terminal domain, named tuberculosis necrotizing toxin (TNT), which induces necrosis by an unknown mechanism. Here we show that TNT gains access to the cytosol of Mtb-infected macrophages, where it hydrolyzes the essential coenzyme NAD(+). Expression or injection of a noncatalytic TNT mutant showed no cytotoxicity in macrophages or in zebrafish zygotes, respectively, thus demonstrating that the NAD(+) glycohydrolase activity is required for TNT-induced cell death. To prevent self-poisoning, Mtb produces an immunity factor for TNT (IFT) that binds TNT and inhibits its activity. The crystal structure of the TNT-IFT complex revealed a new NAD(+) glycohydrolase fold of TNT, the founding member of a toxin family widespread in pathogenic microorganisms.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Bacterial Outer Membrane Proteins / chemistry
  • Bacterial Outer Membrane Proteins / metabolism*
  • Bacterial Toxins / chemistry
  • Bacterial Toxins / metabolism*
  • Crystallography, X-Ray
  • Host-Pathogen Interactions*
  • Humans
  • Hydrolysis
  • Macrophages / microbiology*
  • Models, Molecular
  • Mycobacterium tuberculosis / enzymology*
  • Mycobacterium tuberculosis / physiology
  • NAD / metabolism*
  • Protein Conformation
  • Zebrafish
  • Zygote / microbiology


  • Bacterial Outer Membrane Proteins
  • Bacterial Toxins
  • Rv3903 protein, Mycobacterium tuberculosis
  • NAD

Associated data

  • PDB/4QLP