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 (MenT
) encoded by the human pathogen
. Toxin MenT
inhibited growth of
when not antagonized by its cognate antitoxin, MenA
. We solved the structures of toxins MenT
and MenT
to 1.6 and 1.2 Å resolution, respectively, and identified the biochemical activity and target of MenT
. MenT
blocked in vitro protein expression and prevented tRNA charging in vivo. MenT
added pyrimidines (C or U) to the 3'-CCA acceptor stems of uncharged tRNAs and exhibited strong substrate specificity in vitro, preferentially targeting tRNA
from among the 45
.
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.