Not Throwing Baby Out with the Bathwater.
Not Throwing Baby Out with the Bathwater.
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不要把婴儿和洗澡水一起倒掉。
DOI：
10.1105/tpc.15.00801
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发表时间：
2015
期刊：
影响因子：
--
通讯作者：
Chien,Peter
中科院分区：
文献类型：
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作者：
Chien,Peter
蛋白质的降解在所有生命王国中都至关重要。在细菌和真核细胞器中，特定的能量依赖性蛋白酶负责破坏不再需要或不需要的蛋白质。这个过程在应激反应期间尤其重要，因为受损蛋白质的积累可能导致有毒蛋白质聚集。这些系统面临的普遍挑战是需要快速强力降解特定靶标而不牺牲剩余的稳定蛋白质库。叶绿体 Clp 蛋白酶家族特别复杂，异源寡聚 ClpP 肽酶通过与三个 ATP 依赖性 ClpC/ClpD 分子伴侣、蛋白酶组装所需的其他植物特异性因子 (ClpT1/2) 以及已知细菌底物接头的直向同源物 (ClpS1/2) 配合形成活性蛋白酶。这些蛋白酶对植物生长至关重要，但人们对底物如何传递到叶绿体中的这些蛋白酶知之甚少，也不清楚需要哪些额外因素来确保蛋白酶的特异性。在他们的突破性报告中，van Wijk 及其同事（Nishimura 等人，2015）发现了一种新的调节器，它可以作为 Clp 蛋白酶机制和叶绿体中特定目标底物之间的这种寻求的连接。细菌中的 Clp 家族蛋白酶经常使用接头来调节特异性，并且已知 ClpS 接头可将 N 端规则底物传递给 ClpA 伴侣（ClpC 的同源物）。先前对细菌 ClpS 的详细分析揭示了这些 N 端规则底物的特异性结合口袋（Wang 等人，2008）。在之前的工作中，van Wijk 及其同事确定 ClpF 是叶绿体 ClpS1 的相互作用伙伴，不依赖于底物结合袋（Nishimura 等人，2013）。在目前的工作中，他们表明 ClpF 不仅与 ClpS1 结合，而且还直接与 ClpC 相互作用。有趣的是，这些成分之间存在协同相互作用，其中 ClpF-ClpS1-ClpC 复合物比任何单独的二元相互作用都更稳定。此外，ClpF 还促进体内 ClpS1-ClpC 复合物的形成，这使得作者提出 ClpF 在调节 ClpC 依赖性蛋白质降解中的生理作用。在生物信息学的指导下，他们使用纯化的蛋白质来分离 ClpF 中每种相互作用所需的特定结构域，从而定义所需的最小组件。使用基于质谱的蛋白质组学，他们表明缺乏 clpF 和 clpS 的细胞在蛋白质组变化方面表现出相似的趋势，并进一步发现 ClpF 结合 Clp 蛋白酶系统的假定底物 GluTR。这些数据共同支持了一个模型，通过该模型，Clp 蛋白酶底物（例如 GluTR）通过 ClpF 和 ClpS1 传递至 ClpC 蛋白酶复合物（见图）。二级接头与一级接头一起控制蛋白酶特异性的概念是一个令人兴奋的概念，它强调了许多可以通过组合使用模块化接头蛋白来调节不可逆过程（蛋白质降解）的细胞策略。有趣的是，类似类型的调控架构存在于其他蛋白酶系统中，最值得注意的是
The degradation of proteins is critical in all kingdoms of life. In bacteria and eukaryotic organelles, specific energy-dependent proteases are responsible for destroying proteins that are no longer needed or desired. This process is particularly important during stress responses, as accumulation of damaged proteins can lead to toxic protein aggregation. The universal challenge that these systems face is the demand to robustly degrade particular targets rapidly without sacrificing the remaining pool of stable proteins. The chloroplast Clp protease family is particularly complex, with a hetero-oligomeric ClpP peptidase forming active proteases by partnering with three ATP-dependent ClpC/ClpD chaperones, additional plant-specific factors needed for protease assembly (ClpT1/2), and orthologs of known bacterial substrate adaptors (ClpS1/2). These proteases are critical for plant growth, but how substrates are delivered to these proteases in the chloroplast is poorly understood, and it is unclear what additional factors are needed to ensure protease specificity. In their Breakthrough Report, van Wijk and colleagues (Nishimura et al., 2015) identify a new regulator that may serve as this sought after connection between the Clp protease machinery and specific target substrates in the chloroplast. The Clp family proteases in bacteria often use adaptors to regulate specificity, and the ClpS adaptor is known to deliver N-end rule substrates to the ClpA chaperone (a homolog of ClpC). Prior detailed analysis of the bacterial ClpS revealed a specific binding pocket for these N-end rule substrates (Wang et al., 2008). In a previous work, van Wijk and colleagues identified ClpF as an interacting partner with the chloroplast ClpS1 that does not depend on the substrate binding pocket (Nishimura et al., 2013). In the current work, they show that ClpF not only binds to ClpS1, but it also interacts with ClpC directly. Interestingly, there is a synergistic interaction between these components, where the ClpF-ClpS1-ClpC complex is more stable that any of the binary interactions alone.Furthermore, ClpF also promotes ClpS1-ClpC complex formation in vivo, leading the authors to suggest a physiological role for ClpF in regulating ClpC-dependent protein degradation. Guided by bioinformatics, they use purified proteins to isolate specific domains within ClpF needed for each of these interactions, defining the minimal components needed. Using mass spectrometrybased proteomics, they show that cells deficient in clpF and clpS show similar trends in proteome changes and further find that ClpF binds a putative substrate of the Clp protease system, GluTR. Together, these data support a model whereby Clp protease substrates such as GluTR are delivered via ClpF and ClpS1 to a ClpC protease complex (see figure). This concept of secondary adaptors working with primary adaptors to govern protease specificity is an exciting one, and it highlights the many cellular strategies that can regulate an irreversible process (protein degradation) through combinatorial use of modular adaptor proteins. Interestingly, similar types of regulatory architectures exist in other protease systems, most notably in