Type II toxin-antitoxin system in bacteria: activation, function, and mode of action

The toxin-antitoxin (TA) system is composed of a stable toxin and an unstable antitoxin that neutralizes the toxin. Being perhaps the most studied among the different TA types, type II TA systems are widely distributed and often exist in multiple copies within chromosomes of eubacteria and archaea. Exhibiting diverse molecular activities such as RNases, kinases, and acetyltransferases, type II TA systems have been confirmed to be involved in diverse biological processes including plasmid maintenance, phage inhibition, persistence, stress response, and biofilm formation. In this review, we summarize the current state of the research in the type II TA field, emphasizing the activation mechanism, structure-function relationship, and biological functions of type II TA systems.