Mechanism of aminoacyl-tRNA acetylation by an aminoacyl-tRNA acetyltransferase AtaT from enterohemorrhagic E. coli

Toxin-antitoxin systems in bacteria contribute to stress adaptation, dormancy, and persistence. AtaT, a type-II toxin in enterohemorrhagic E. coli, reportedly acetylates the α-amino group of the aminoacyl-moiety of initiator Met-tRNAf(Met), thus inhibiting translation initiation. Here, we show that AtaT has a broader specificity for aminoacyl-tRNAs than initially claimed. AtaT efficiently acetylates Gly-tRNA(Gly), Trp-tRNA(Trp), Tyr-tRNA(Tyr) and Phe-tRNA(Phe) isoacceptors, in addition to Met-tRNAf(Met), and inhibits global translation. AtaT interacts with the acceptor stem of tRNAf(Met), and the consecutive G-C pairs in the bottom-half of the acceptor stem are required for acetylation. Consistently, tRNA(Gly), tRNA(Trp), tRNA(Tyr) and tRNA(Phe) also possess consecutive G-C base-pairs in the bottom halves of their acceptor stems. Furthermore, misaminoacylated valyl-tRNAf(Met) and isoleucyl-tRNAf(Met) are not acetylated by AtaT. Therefore, the substrate selection by AtaT is governed by the specific acceptor stem sequence and the properties of the aminoacyl-moiety of aminoacyl-tRNAs.