A nucleotidyltransferase toxin inhibits growth of Mycobacterium tuberculosis through inactivation of tRNA acceptor stems

Abstract

Toxin-antitoxin systems are widespread stress-responsive elements, many of whose functions remain largely unknown. Here, we characterize the four DUF1814-family nucleotidyltransferase-like toxins (MenT1-4) encoded by the human pathogen Mycobacterium tuberculosis. Toxin MenT3 inhibited growth of M. tuberculosis when not antagonized by its cognate antitoxin, Men A3. We solved the structures of toxins Men T3 and Men T4 to 1.6 and 1.2 A resolution, respectively, and identified the biochemical activity and target of Men T3. Men T3 blocked in vitro protein expression and prevented tRNA charging in vivo. Men T3 added pyrimidines (C or U) to the 3'-CCA acceptor stems of uncharged tRNAs and exhibited strong substrate specificity in vitro, preferentially targeting tRNASer from among the 45 M. tuberculosis tRNAs. Our study identifies a previously unknown mechanism that expands the range of enzymatic activities used by bacterial toxins, uncovering a new way to block protein synthesis and potentially treat tuberculosis and other infections.