Nucleotidyltransferase toxin MenT extends aminoacyl acceptor ends of serine tRNAs to control Mycobacterium tuberculosis growth

Toxins of toxin-antitoxin systems use diverse mechanisms to inhibit bacterial growth. In this study, we characterize the translation inhibitor toxin MenT3 of Mycobacterium tuberculosis , the bacterium responsible for tuberculosis in humans. We show that MenT3 is a robust cytidine specific tRNA nucleotidyltransferase in vitro, capable of modifying the aminoacyl acceptor ends of most tRNA but with a marked preference for tRNA Ser , to which long stretches of cytidines are added. Furthermore, transcriptomic-wide analysis of MenT3 targets in M. tuberculosis identifies tRNA Ser as the sole target of MenT3 and reveals significant detoxification attempts by the essential CCA-adding enzyme PcnA in response to MenT3. Finally, under physiological conditions, only in the presence the native menAT3 operon, an active pool of endogenous MenT3 targeting tRNA Ser in M. tuberculosis is detected, likely reflecting the importance of MenT3 during infection. In this work, author demonstrate that the Mycobacterium tuberculosis MenT toxin is capable of specifically depleting its pool of serine tRNA available for protein synthesis.