Structural evolution of an ancient nucleotidyltransferase underlies divergence of AbiE antitoxins.

AbiE-like type VII toxin–antitoxin systems in IMG/M are paired with six antitoxin groups, and cognate antitoxins phosphorylate conserved serine or threonine residues to inactivate toxins.

• Why it matters: The distribution and regulatory diversity of AbiE-like type VII systems are unclear, limiting understanding of how PTM-based antitoxin control evolved and varies across lineages.
• What they did: A comprehensive IMG/M database search identified AbiE TA systems with a conserved toxin family and six distinct antitoxin groups, including four newly identified groups, and structural predictions plus experiments tested a shared phosphorylation mechanism.
• The result: Antitoxin CTDs are structurally homologous to nucleotidyltransferases, suggesting type VII antitoxins may have evolved from an ancestral NTase superfamily, while DNA-binding functions diverge among antitoxin groups.

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