An adaptor protein network that controls general and regulated proteolysis in Bacillus subtilis

蛋白质质量控制系统是确保细胞蛋白质稳态和监测所有细胞中蛋白质的折叠和活性状态所必需的。这些高度保守的系统包括伴侣系统，也包括细菌中的AAA+蛋白酶复合物，如Hsp100/Clp蛋白。通过伴侣蛋白挽救和修复功能蛋白和/或通过降解去除潜在毒性错误折叠蛋白的能力可以被认为是同一细胞蛋白质质量控制系统的两个分支。有趣的是，相同的AAA+蛋白酶系统同时参与信号转导和通过转录因子等调节蛋白水解来控制细胞和发育过程。蛋白质水解是由专门的分子机器介导的，这些分子机器是由环形成的六聚体AAA+运动蛋白形成的，与区隔化的桶状肽酶相关。这种蛋白水解复合物的例子是真核细胞中的蛋白酶体或与ClpP相互作用的原核Hsp100/Clp蛋白。通常，相同的蛋白水解机器还用于调节目的，例如，调节关键转录因子的蛋白水解，以控制例如发育过程。我们感兴趣的是了解在原核细胞中，由于不同的调节或蛋白质质量控制原因，降解蛋白质的重要和终端细胞决定是如何进行的。土壤细菌枯草芽孢杆菌的ClpCP参与一般蛋白质质量控制和调控过程。我们可以证明ClpCP的衔接蛋白如MecA、YpbH或McsB是激活ClpCP蛋白酶所必需的，对底物识别和选择也很重要。根据我们最近的研究结果，我们建议更详细地讨论该系统的两个有趣的新方面。(1)我们希望在体内和体外研究并可能了解Hsp100/Clp蛋白的展开或重塑与蛋白水解模式之间的相互作用。(2)我们想研究接头蛋白介导的ClpC激活的作用和功能，特别强调蛋白精氨酸激酶McsB。我们将通过各种体内和体外实验来验证我们关于McsB在蛋白质分解中的潜在作用的假设。

Protein quality control systems are essential to ensure cellular protein homeostasis and monitor the folding and active state of proteins in all cells. These highly conserved systems include chaperone systems but also AAA+ protease complexes such as Hsp100/Clp proteins in bacteria. The ability to rescue and repair functional proteins by chaperones and/or to remove potentially toxic misfolded protein species by degradation could be considered as two branches of the same cellular protein quality control system. Interestingly, the same AAA+ protease systems are concurrently involved in the signal transduction and control of cellular and developmental processes by regulatory proteolysis of e.g. transcription factors. Proteolysis is mediated by dedicated molecular machines, which are formed by ringforming hexameric AAA+ motor proteins, associated with compartmentalized barrel-like peptidases. Examples for such proteolytic complexes are the proteasome in eukaryotic cells or the prokaryotic Hsp100/Clp proteins interacting with ClpP. Often the same proteolytic machines are used in addition for regulatory purposes, e.g. like regulated proteolysis of key transcription factors to control for example developmental processes. We are interested to understand how in prokaryotic cells the important and terminal cellular decision to degrade a protein for distinct and different regulatory or protein quality control reasons is taken. ClpCP of the soil bacterium Bacillus subtilis is involved in general protein quality control and regulatory processes. We could demonstrate for ClpCP that adaptor proteins like MecA, YpbH or McsB are necessary to activate the ClpCP protease and important for substrate recognition and selection. Based on our recent results we propose to address two interesting and new aspects of this system in more detail. (1) We want to investigate and possibly understand the interplay between the unfolding or remodeling and proteolytic mode of the Hsp100/Clp proteins both in vivo and in vitro. (2) We want to investigate the role and function of the adaptor protein mediated ClpC activation with a special emphasis on the protein arginine kinase McsB. We will test our hypothesis concerning the potential role of McsB in protein disaggregation using various in vivo and in vitro experiments.