Luo Qingdai, Liu Qiuyang, Liu Ting, Wang Xingyu, Wu Xiaodong, Chen Qiang, Yu Yamei
Department of Biotherapy, Cancer Center and State Key Laboratory of Biotherapy, West China Hospital, Sichuan University, Chengdu, 610041, China.
Xizang Changdu People's Hospital, Changdu, 854000, Tibet, China.
Biochem Biophys Res Commun. 2025 Aug 30;776:152217. doi: 10.1016/j.bbrc.2025.152217. Epub 2025 Jun 17.
Toll/interleukin-1 receptor (TIR) domain serves as a canonical component in both animal and plant innate immunity pathways and is indicated, in some cases, to mediate nicotinamide adenine dinucleotide (NAD) cleavage via self-association. Recent studies have revealed the involvement of TIR domains in a bacterial anti-phage defense system called Thoeris. The Thoeris system consists of two core proteins, ThsA and ThsB. Phage infection triggers the TIR-containing ThsB to produce an isomer of cyclic ADP-ribose, which is then transferred to and activates ThsA, leading to NAD depletion and subsequent cell death. However, the mechanism of ThsB activation remains elusive. Here, we present high-resolution crystal structures of E. coli ThsA and ThsB. Notably, an intact NAD molecule is observed in the active site of ThsB, implying that monomeric ThsB does not possess NADase activity. We demonstrate that ThsB forms 7-fold oligomers through negative staining electron microscopy, suggesting that self-association activates ThsB NAD hydrolase. Our findings indicate a new TIR self-association assembly in bacterial anti-phage systems.
Toll/白细胞介素-1受体（TIR）结构域是动物和植物先天免疫途径中的一个典型组成部分，在某些情况下，它可通过自缔合介导烟酰胺腺嘌呤二核苷酸（NAD）的裂解。最近的研究揭示了TIR结构域参与一种名为Thoeris的细菌抗噬菌体防御系统。Thoeris系统由两种核心蛋白ThsA和ThsB组成。噬菌体感染会触发含TIR的ThsB产生环状ADP核糖的异构体，然后该异构体被转移至ThsA并激活ThsA，导致NAD耗竭及随后的细胞死亡。然而，ThsB的激活机制仍不清楚。在此，我们展示了大肠杆菌ThsA和ThsB的高分辨率晶体结构。值得注意的是，在ThsB的活性位点观察到一个完整的NAD分子，这意味着单体ThsB不具备NAD酶活性。我们通过负染色电子显微镜证明ThsB形成七聚体，表明自缔合激活了ThsB的NAD水解酶。我们的研究结果表明细菌抗噬菌体系统中存在一种新的TIR自缔合组装形式。
