Toxin/antitoxin (TA) systems are present in nearly all bacterial and archaeal strains and consist of a toxin that reduces growth and an antitoxin that masks toxin activity. Currently there are six primary classes for TA systems based on the nature of the antitoxin and the way that the antitoxin inactivates the toxin. Here we show that there now are at least three additional and distinct TA systems in which the antitoxin is an enzyme and the cognate toxin is the direct target of the antitoxin: Hha/TomB (antitoxin oxidizes Cys18 of the toxin), TglT/TakA (antitoxin phosphorylates Ser78 of the toxin), and HepT/MntA (antitoxin adds three AMPs to Tyr104 of the toxin). Thus, we suggest the type VII TA system should be used to designate those TA systems in which the enzyme antitoxin chemically modifies the toxin post-translationally to neutralize it. Defining the type VII TA system using this specific criterion will aid researchers in classifying newly discovered TA systems as well as refine the framework for recognizing the diverse biochemical functions in TA systems.

毒素/抗毒素 (TA) 系统几乎存在于所有细菌和古细菌菌株中，由抑制生长的毒素和掩盖毒素活性的抗毒素组成。目前，根据抗毒素的性质和抗毒素灭活毒素的方式，TA 系统有六个主要类别。在这里，我们表明现在至少有三个不同的 TA 系统，其中抗毒素是一种酶，同源毒素是抗毒素的直接目标：Hha/TomB（抗毒素氧化毒素的 Cys18）、TglT/TakA（抗毒素磷酸化毒素的 Ser78）和 HepT/MntA（抗毒素将三个 AMP 添加到毒素的 Tyr104）。因此，我们建议使用 VII 型 TA 系统来指定那些 TA 系统，其中抗毒素酶在翻译后化学修饰毒素以中和它。