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An NAD+ Phosphorylase Toxin Triggers Mycobacterium tuberculosis Cell Death.

ABSTRACT: Toxin-antitoxin (TA) systems regulate fundamental cellular processes in bacteria and represent potential therapeutic targets. We report a new RES-Xre TA system in multiple human pathogens, including Mycobacterium tuberculosis. The toxin, MbcT, is bactericidal unless neutralized by its antitoxin MbcA. To investigate the mechanism, we solved the 1.8 Å-resolution crystal structure of the MbcTA complex. We found that MbcT resembles secreted NAD+-dependent bacterial exotoxins, such as diphtheria toxin. Indeed, MbcT catalyzes NAD+ degradation in vitro and in vivo. Unexpectedly, the reaction is stimulated by inorganic phosphate, and our data reveal that MbcT is a NAD+ phosphorylase. In the absence of MbcA, MbcT triggers rapid M. tuberculosis cell death, which reduces mycobacterial survival in macrophages and prolongs the survival of infected mice. Our study expands the molecular activities employed by bacterial TA modules and uncovers a new class of enzymes that could be exploited to treat tuberculosis and other infectious diseases.

SUBMITTER: Freire DM

PROVIDER: S-EPMC6436930 | biostudies-literature | 2019 Mar

REPOSITORIES: biostudies-literature

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An NAD<sup>+</sup> Phosphorylase Toxin Triggers Mycobacterium tuberculosis Cell Death.

Freire Diana Mendes DM Gutierrez Claude C Garza-Garcia Acely A Grabowska Anna D AD Sala Ambre J AJ Ariyachaokun Kanchiyaphat K Panikova Terezie T Beckham Katherine S H KSH Colom André A Pogenberg Vivian V Cianci Michele M Tuukkanen Anne A Boudehen Yves-Marie YM Peixoto Antonio A Botella Laure L Svergun Dmitri I DI Schnappinger Dirk D Schneider Thomas R TR Genevaux Pierre P de Carvalho Luiz Pedro Sorio LPS Wilmanns Matthias M Parret Annabel H A AHA Neyrolles Olivier O

Molecular cell 20190218 6

Toxin-antitoxin (TA) systems regulate fundamental cellular processes in bacteria and represent potential therapeutic targets. We report a new RES-Xre TA system in multiple human pathogens, including Mycobacterium tuberculosis. The toxin, MbcT, is bactericidal unless neutralized by its antitoxin MbcA. To investigate the mechanism, we solved the 1.8 Å-resolution crystal structure of the MbcTA complex. We found that MbcT resembles secreted NAD<sup>+</sup>-dependent bacterial exotoxins, such as diph ...[more]

PMID: 30792174

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Project description:BackgroundDepletion of T cells following infection by Mycobacterium tuberculosis (Mtb) impairs disease resolution, and interferes with clinical test performance that relies on cell-mediated immunity. A number of mechanisms contribute to this T cell suppression, such as activation-induced death and trafficking of T cells out of the peripheral circulation and into the diseased lungs. The extent to which Mtb infection of human macrophages affects T cell viability however, is not well characterised.Methodology/principal findingsWe found that lymphopenia (<1.5 × 10(9) cells/l) was prevalent among culture-positive tuberculosis patients, and lymphocyte counts significantly improved post-therapy. We previously reported that Mtb-infected human macrophages resulted in death of infected and uninfected bystander macrophages. In the current study, we sought to examine the influence of infected human alveolar macrophages on T cells. We infected primary human alveolar macrophages (the primary host cell for Mtb) or PMA-differentiated THP-1 cells with Mtb H37Ra, then prepared cell-free supernatants. The supernatants of Mtb-infected macrophages caused dose-dependent, caspase-dependent, T cell apoptosis. This toxic effect of infected macrophage secreted factors did not require TNF-α or Fas. The supernatant cytotoxic signal(s) were heat-labile and greater than 50 kDa in molecular size. Although ESAT-6 was toxic to T cells, other Mtb-secreted factors tested did not influence T cell viability; nor did macrophage-free Mtb bacilli or broth from Mtb cultures. Furthermore, supernatants from Mycobacterium bovis Bacille de Calmette et Guerin (BCG)- infected macrophages also elicited T cell death suggesting that ESAT-6 itself, although cytotoxic, was not the principal mediator of T cell death in our system.ConclusionsMtb-Infected macrophages secrete heat-labile factors that are toxic to T cells, and may contribute to the immunosuppression seen in tuberculosis as well as interfere with microbial eradication in the granuloma.

Dataset Information

An NAD+ Phosphorylase Toxin Triggers Mycobacterium tuberculosis Cell Death.

Publications

An NAD<sup>+</sup> Phosphorylase Toxin Triggers Mycobacterium tuberculosis Cell Death.

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