DUF1814 family toxin AbiEii inhibits translation by branching tRNA anticodon loop
Nucleotidyltransferases (NTases) control diverse physiological processes, including DNA replication and repair, antibiotic resistance, and RNA modification. The Streptococcus agalactiae abortive infection toxin, AbiEii, belongs to the DUF1814 superfamily of NTases and blocks bacterial growth through an as yet unknown mechanism. Here, we demonstrate that antitoxin AbiEi binds to AbiEii to form a stable toxin-antitoxin complex in solution and prevent toxicity. Antitoxin binding ultimately leads to AbiEii auto-phosphorylation and an abolition of NTase activity. These data reclassify AbiE systems as Type VII toxin-antitoxin systems. Toxin phosphorylation appears to be a dynamic and reversible process, as the sole serine/threonine phosphatase SaSTP of S. agalactiae can efficiently dephosphorylate AbiEii in vitro. We show that the activated AbiEii toxin uses UTP and CTP to specifically modify tRNALeu-3 and block translation. Deleterious UMPylation and CMPylation modifications of tRNALeu-3 occur on the third position of the anticodon loop. The resulting branched tRNA structure is then further extended by AbiEii NTase polymerization activity. These previously unknown forms of RNA modification expand the catalytic activities of DUF1814 enzymes and reveal the mechanism of action for the widespread AbiE phage defense and toxin-antitoxin systems.
Nucleotidyltransferases (NTases) control diverse physiological processes, including DNA replication and repair, antibiotic resistance, and RNA modification. The Streptococcus agalactiae abortive infection toxin, AbiEii, belongs to the DUF1814 superfamily of NTases and blocks bacterial growth through an as yet unknown mechanism. Here, we demonstrate that antitoxin AbiEi binds to AbiEii to form a stable toxin-antitoxin complex in solution and prevent toxicity. Antitoxin binding ultimately leads to AbiEii auto-phosphorylation and an abolition of NTase activity. These data reclassify AbiE systems as Type VII toxin-antitoxin systems. Toxin phosphorylation appears to be a dynamic and reversible process, as the sole serine/threonine phosphatase SaSTP of S. agalactiae can efficiently dephosphorylate AbiEii in vitro. We show that the activated AbiEii toxin uses UTP and CTP to specifically modify tRNALeu-3 and block translation. Deleterious UMPylation and CMPylation modifications of tRNALeu-3 occur on the third position of the anticodon loop. The resulting branched tRNA structure is then further extended by AbiEii NTase polymerization activity. These previously unknown forms of RNA modification expand the catalytic activities of DUF1814 enzymes and reveal the mechanism of action for the widespread AbiE phage defense and toxin-antitoxin systems.
Centre national de la recherche scientifique