Institute of Biochemical Sciences, College of Life Science, National Taiwan University, Taipei, Taiwan.
CSIR-Centre for Cellular and Molecular Biology, Hyderabad, India.
mBio. 2019 Aug 6;10(4):e01129-19. doi: 10.1128/mBio.01129-19.
Carboxyl (C)-terminal processing proteases (CTPs) participate in protective and regulatory proteolysis in bacteria. The PDZ domain is central to the activity of CTPs but plays inherently different regulatory roles. For example, the PDZ domain inhibits the activity of the signaling protease CtpB by blocking the active site but is required for the activation of Prc (or Tsp), a tail-specific protease that degrades SsrA-tagged proteins. Here, by structural and functional analyses, we show that in the unliganded resting state of Prc, the PDZ domain is docked inside the bowl-shaped scaffold without contacting the active site, which is kept in a default misaligned conformation. In Prc, a hydrophobic substrate sensor distinct from CtpB engages substrate binding to the PDZ domain and triggers a structural remodeling to align the active-site residues. Therefore, this work reveals the structural basis for understanding the contrasting roles of the PDZ domain in the regulation of CTPs. Prc, also known previously as Tsp, is the founding member of the carboxyl-terminal processing protease (CTP) family of PDZ domain-containing proteases that include CtpA and CtpB. The substrate-binding PDZ domain is responsible for regulating the protease activity of CTP proteases; however, the regulatory role of PDZ domain is stimulatory in Prc but inhibitory in CtpA/B. By determining a series of crystal structures of Prc in the unliganded resting state, this study presents the structural basis for PDZ-dependent activation of Prc, the results of which explain the contrasting roles of the PDZ domain in the regulation of the protease activity of CTPs.
羧基（C）-末端加工蛋白酶（CTPs）参与细菌中的保护和调节蛋白水解。PDZ 结构域是 CTPs 活性的核心，但发挥着固有不同的调节作用。例如，PDZ 结构域通过阻止活性位点来抑制信号蛋白酶 CtpB 的活性，但对于激活 Prc（或 Tsp）是必需的，Prc 是一种靶向特定尾部的蛋白酶，可降解带有 SsrA 标签的蛋白质。在这里，通过结构和功能分析，我们表明在 Prc 的未配体静息状态下，PDZ 结构域在没有接触活性位点的情况下停靠在碗状支架内，该活性位点保持默认的未对准构象。在 Prc 中，一种与 CtpB 不同的疏水性底物传感器与底物结合到 PDZ 结构域并触发结构重塑以对齐活性位点残基。因此，这项工作揭示了理解 PDZ 结构域在 CTP 蛋白酶调节中对比作用的结构基础。Prc 以前也称为 Tsp，是 PDZ 结构域包含蛋白酶家族中的羧基末端加工蛋白酶（CTP）家族的创始成员，该家族包括 CtpA 和 CtpB。底物结合的 PDZ 结构域负责调节 CTP 蛋白酶的蛋白酶活性；然而，PDZ 结构域在 Prc 中的调节作用是刺激的，而在 CtpA/B 中则是抑制的。通过确定一系列无配体静息状态下的 Prc 晶体结构，本研究提出了 PDZ 依赖性 Prc 激活的结构基础，其结果解释了 PDZ 结构域在调节 CTP 蛋白酶活性中的对比作用。
