title: The tuberculosis necrotizing toxin kills macrophages by hydrolyzing NAD.
abstract: 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.
authors.affiliation: Department of Microbiology, University of Alabama at Birmingham, Birmingham, Alabama, USA.
authors.forename: Jim
authors.identifier: http://orcid.org/0000-0002-6873-6052
authors.initials: J
authors.lastname: Sun
authors.affiliation: Department of Microbiology, University of Alabama at Birmingham, Birmingham, Alabama, USA.
authors.forename: Axel
authors.initials: A
authors.lastname: Siroy
authors.affiliation: Department of Biochemistry and Molecular Biology, Thomas Jefferson University, Philadelphia, Pennsylvania, USA.
authors.forename: Ravi K
authors.initials: RK
authors.lastname: Lokareddy
authors.affiliation: Department of Microbiology, University of Alabama at Birmingham, Birmingham, Alabama, USA.
authors.forename: Alexander
authors.initials: A
authors.lastname: Speer
authors.affiliation: Department of Microbiology, University of Alabama at Birmingham, Birmingham, Alabama, USA.
authors.forename: Kathryn S
authors.initials: KS
authors.lastname: Doornbos
authors.affiliation: Department of Biochemistry and Molecular Biology, Thomas Jefferson University, Philadelphia, Pennsylvania, USA.
authors.forename: Gino
authors.initials: G
authors.lastname: Cingolani
authors.affiliation: Department of Microbiology, University of Alabama at Birmingham, Birmingham, Alabama, USA.
authors.forename: Michael
authors.initials: M
authors.lastname: Niederweis
mesh_terms: D000818:Animals; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry / Q000378:metabolism*; D001427:Bacterial Toxins / Q000737:chemistry / Q000378:metabolism*; D018360:Crystallography, X-Ray; D054884:Host-Pathogen Interactions; D006801:Humans; D006868:Hydrolysis; D008264:Macrophages / Q000382:microbiology*; D008958:Models, Molecular; D009169:Mycobacterium tuberculosis / Q000201:enzymology* / Q000502:physiology; D009243:NAD / Q000378:metabolism*; D011487:Protein Conformation; D015027:Zebrafish; D015053:Zygote / Q000382:microbiology
chemical_list: D001425:Bacterial Outer Membrane Proteins; D001427:Bacterial Toxins; C000589201:Rv3903 protein, Mycobacterium tuberculosis; D009243:NAD