Amino acid residues crucial for specificity of toxin–antitoxin interactions in the homologous A xe– T xe and Y ef M – Y oe B complexes

Toxin–antitoxin complexes are ubiquitous in bacteria. The specificity of interactions between toxins and antitoxins from homologous but non‐interacting systems was investigated. Based on molecular modeling, selected amino acid residues were changed to assess which positions were crucial in the specificity of toxin–antitoxin interaction in the related A xe– T xe and Yef M – Y oe B complexes. No cross‐interactions between wild‐type proteins were detected. However, a single amino acid substitution that converts a T xe‐specific residue to a Y oe B ‐specific residue reduced, but did not abolish, Txe interaction with the Axe antitoxin. Interestingly, this alteration ( T xe‐Asp83 T yr) promoted functional interactions between T xe and the Y ef M antitoxin. The interactions between T xe‐ A sp83Tyr and Y ef M were sufficiently strong to abolish Txe toxicity and to allow effective corepression by YefM‐Txe‐Asp83Tyr of the promoter from which yefM – yoeB is expressed. We conclude that Asp83 in Txe is crucial for the specificity of toxin–antitoxin interactions in the A xe– T xe complex and that swapping this residue for the equivalent residue in Y oe B relaxes the specificity of the toxin–antitoxin interaction. Structured digital abstractAxe and Txe physically interact by two hybrid ( View interaction ) YoeB and YefM physically interact by two hybrid ( View interaction )