Department of Chemistry and Biochemistry, University of Oklahoma, Norman, OK 73019, USA.
Toxins (Basel). 2020 Jun 26;12(6):422. doi: 10.3390/toxins12060422.
The diversity of Type-II toxin-antitoxin (TA) systems in bacterial genomes requires tightly controlled interaction specificity to ensure protection of the cell, and potentially to limit cross-talk between toxin-antitoxin pairs of the same family of TA systems. Further, there is a redundant use of toxin folds for different cellular targets and complexation with different classes of antitoxins, increasing the apparent requirement for the insulation of interactions. The presence of Type II TA systems has remained enigmatic with respect to potential benefits imparted to the host cells. In some cases, they play clear roles in survival associated with unfavorable growth conditions. More generally, they can also serve as a "cure" against acquisition of highly similar TA systems such as those found on plasmids or invading genetic elements that frequently carry virulence and resistance genes. The latter model is predicated on the ability of these highly specific cognate antitoxin-toxin interactions to form cross-reactions between chromosomal antitoxins and invading toxins. This review summarizes advances in the Type II TA system models with an emphasis on antitoxin cross-reactivity, including with invading genetic elements and cases where toxin proteins share a common fold yet interact with different families of antitoxins.
细菌基因组中 II 型毒素-抗毒素 (TA) 系统的多样性需要严格控制相互作用的特异性，以确保细胞得到保护，并有可能限制同一 TA 系统家族的毒素-抗毒素对之间的串扰。此外，不同的细胞靶标使用毒素折叠，与不同类别的抗毒素复合，增加了相互作用隔离的明显需求。II 型 TA 系统的存在对于赋予宿主细胞的潜在益处仍然是一个谜。在某些情况下，它们在与不利生长条件相关的生存中发挥着明显的作用。更普遍的是，它们还可以作为一种“治疗”手段，防止获得高度相似的 TA 系统，如质粒或入侵遗传元件上发现的那些系统，这些系统通常携带毒力和抗性基因。后一种模型基于这些高度特异性的同源抗毒素-毒素相互作用在染色体抗毒素和入侵毒素之间形成交叉反应的能力。这篇综述总结了 II 型 TA 系统模型的进展，重点介绍了抗毒素的交叉反应性，包括与入侵遗传元件以及毒素蛋白具有共同折叠但与不同家族的抗毒素相互作用的情况。
