An NAD+ Phosphorylase Toxin Triggers Mycobacterium tuberculosis Cell Death

Abstract

Summary 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.

Depletion of the DarG antitoxin in Mycobacterium tuberculosis triggers the DNA‐damage response and leads to cell death

“…Activation of DarT Mtb has a bactericidal effect (Figure 3b), similar to induction of MbcT, the toxin of the only other characterized TA system in Mtb harboring an essential antitoxin (Freire et al, 2019).…”

The Variety in the Common Theme of Translation Inhibition by Type II Toxin–Antitoxin Systems

“…It is worth noting that the translation machinery and topoisomerases are also among the most common targets of antibiotics. Lastly, novel enzymatic activities and targets of TA toxins have been increasingly reported, for example ADP-rybosyltransferase-fold toxins were shown to act by NAD + phosphorolysis and its depletion, or by DNA ribosylation (Jankevicius et al, 2016;Freire et al, 2019). These are the first examples of ADPribosyltransferase toxins (ART) involved in TA systems, however, many examples of secreted ART toxins are known and predicted, those also involve translation inhibitors, such as the diphtheria toxin (Zhang et al, 2012).…”

The extracellular contractile injection system is enriched in environmental microbes and associates with numerous toxins

“…We iden fied several cases of toxin-immunity gene pairs next to eCIS operons suppor ng the an bacterial role of these eCIS loci as they require immunity genes (an toxins) to protect from self-intoxica on ( Figure 5A). In one case, The toxin, EAT5, resembles RES (Figure 4b), an NADase that is accompanied by an an toxin called Xre 50,51 . We iden fied a gene, EX18DRAFT_03239, encoding an unknown protein located upstream of the toxin.…”