Centre for Life Sciences, Skolkovo Institute of Science and Technology, Skolkovo 143025, Russia.
Center for Precision Genome Editing and Genetic Technologies for Biomedicine, Institute of Gene Biology, Russian Academy of Sciences, 119334 Moscow, Russia.
Nucleic Acids Res. 2020 Sep 4;48(15):8617-8625. doi: 10.1093/nar/gkaa551.
Type II toxin-antitoxins systems are widespread in prokaryotic genomes. Typically, they comprise two proteins, a toxin, and an antitoxin, encoded by adjacent genes and forming a complex in which the enzymatic activity of the toxin is inhibited. Under stress conditions, the antitoxin is degraded liberating the active toxin. Though thousands of various toxin-antitoxins pairs have been predicted bioinformatically, only a handful has been thoroughly characterized. Here, we describe the AtaT2 toxin from a toxin-antitoxin system from Escherichia coli O157:H7. We show that AtaT2 is the first GNAT (Gcn5-related N-acetyltransferase) toxin that specifically targets charged glycyl tRNA. In vivo, the AtaT2 activity induces ribosome stalling at all four glycyl codons but does not evoke a stringent response. In vitro, AtaT2 acetylates the aminoacyl moiety of isoaccepting glycyl tRNAs, thus precluding their participation in translation. Our study broadens the known target specificity of GNAT toxins beyond the earlier described isoleucine and formyl methionine tRNAs, and suggest that various GNAT toxins may have evolved to specificaly target other if not all individual aminoacyl tRNAs.
II 型毒素-抗毒素系统广泛存在于原核生物基因组中。通常，它们由两个蛋白质组成，一个是毒素，一个是抗毒素，由相邻的基因编码，并形成一个复合物，其中毒素的酶活性被抑制。在应激条件下，抗毒素被降解，释放出活性毒素。尽管已经从生物信息学上预测了数千对不同的毒素-抗毒素对，但只有少数得到了彻底的表征。在这里，我们描述了来自大肠杆菌 O157:H7 的毒素-抗毒素系统中的 AtaT2 毒素。我们表明，AtaT2 是第一个专门针对带电荷甘氨酰 tRNA 的 GNAT（Gcn5 相关 N-乙酰转移酶）毒素。在体内，AtaT2 的活性会导致核糖体在所有四个甘氨酰密码子处停滞，但不会引发严格反应。在体外，AtaT2 乙酰化同种接受体甘氨酰 tRNAs 的氨酰部分，从而阻止它们参与翻译。我们的研究拓宽了 GNAT 毒素的已知靶标特异性，超出了之前描述的异亮氨酸和甲酰甲硫氨酸 tRNAs，并表明各种 GNAT 毒素可能已经进化为专门针对其他（如果不是所有）个别氨酰 tRNAs。
