美国加州大学圣迭戈分校Kevin D. Corbett课题组发现细菌抗病毒防御中的一种真核样泛素化系统。相关论文于2024年7月17日在线发表在《自然》杂志上。

研究人员证明了一个与噬菌体防御岛相关的细菌操纵子编码了完整的泛素化途径。两种细菌E1-E2-Ubl复合物的结构揭示了与经典真核泛素化机制惊人的结构相似性。细菌E1具有一个氨基末端的非活性腺苷酸化域和一个羧基末端的活性腺苷酸化域，其中包含一个可移动的α螺旋插入物，带有催化半胱氨酸（CYS域）。一种结构揭示了细菌Ubl C末端定位用于腺苷酸化的反应前状态，另一种结构模拟了E1到E2的硫酯化状态，E1 CYS域与结合的E2相邻。

研究人员展示了同一路径中的去泛素化酶对细菌Ubl进行预处理，暴露其C末端的甘氨酸用于腺苷酸化。最后，研究人员展示了细菌E1和E2协作将Ubl连接到靶蛋白的赖氨酸残基上。综合这些数据，研究人员表明细菌拥有真正的泛素化系统，与经典真核泛素化途径在机制和结构上有强烈的相似性，暗示这些途径首先在细菌中出现。

据了解，泛素化途径在蛋白质稳态、信号传导和先天免疫中具有关键作用。在这些途径中，由E1、E2和E3蛋白组成的酶促级联反应将泛素或类似泛素的蛋白（Ubl）连接到靶蛋白的赖氨酸残基上。细菌编码与硫代谢相关的E1和Ubl蛋白的古老亲缘体，但这些蛋白不介导Ubl-靶蛋白的连接，因此细菌是否能够进行类似泛素化的蛋白连接仍然是一个开放的问题。

附：英文原文

Title: A eukaryotic-like ubiquitination system in bacterial antiviral defence

Author: Chambers, Lydia R., Ye, Qiaozhen, Cai, Jiaxi, Gong, Minheng, Ledvina, Hannah E., Zhou, Huilin, Whiteley, Aaron T., Suhandynata, Raymond T., Corbett, Kevin D.

Issue&Volume: 2024-07-17

Abstract: Ubiquitination pathways have crucial roles in protein homeostasis, signalling and innate immunity1,2,3. In these pathways, an enzymatic cascade of E1, E2 and E3 proteins conjugates ubiquitin or a ubiquitin-like protein (Ubl) to target-protein lysine residues4. Bacteria encode ancient relatives of E1 and Ubl proteins involved in sulfur metabolism5,6, but these proteins do not mediate Ubl–target conjugation, leaving open the question of whether bacteria can perform ubiquitination-like protein conjugation. Here we demonstrate that a bacterial operon associated with phage defence islands encodes a complete ubiquitination pathway. Two structures of a bacterial E1–E2–Ubl complex reveal striking architectural parallels with canonical eukaryotic ubiquitination machinery. The bacterial E1 possesses an amino-terminal inactive adenylation domain and a carboxy-terminal active adenylation domain with a mobile α-helical insertion containing the catalytic cysteine (CYS domain). One structure reveals a pre-reaction state with the bacterial Ubl Cterminus positioned for adenylation, and a second structure mimics an E1-to-E2 transthioesterification state with the E1 CYS domain adjacent to the bound E2. We show that a deubiquitinase in the same pathway preprocesses the bacterial Ubl, exposing its C-terminal glycine for adenylation. Finally, we show that the bacterial E1 and E2 collaborate to conjugate Ubl to target-protein lysine residues. Together, these data reveal that bacteria possess bona fide ubiquitination systems with strong mechanistic and architectural parallels to canonical eukaryotic ubiquitination pathways, suggesting that these pathways arose first in bacteria.

DOI: 10.1038/s41586-024-07730-4

Source: https://www.nature.com/articles/s41586-024-07730-4