Preprotein Binding by the SecA ATPase

这项研究提案涉及细菌蛋白质分泌，即细菌将蛋白质分子从细胞内合成部位运输到外部环境的过程。所有细菌都有一个“总分泌系统”(GSS)，或“前蛋白转位酶”，能够识别要分泌的蛋白质(带有分泌信号序列的蛋白质，也称为“前蛋白”)。一旦它们被识别为分泌蛋白，前蛋白就会被阻止折叠，然后定位到细胞膜上的位置，在那里它们可以通过一个孔进入外部环境，这一过程被称为“易位”。靶向和转位过程是由SecA ATPase介导的，该酶利用ATP水解的能量来催化蛋白质的分泌。 这种GSS是细菌生长所必需的，在哺乳动物细胞中不存在。在此基础上，GSS，特别是SecA ATPase，是治疗抗生素的良好潜在靶点。此外，某些细菌，如结核分枝杆菌，含有两个SecA分子，SecA1和SecA2。SecA2完成特殊的功能，包括分泌毒力因子，使细菌能够在宿主细胞中生存。因此，增加我们对GSS工作原理的了解可以为抗菌治疗开辟新的途径。对GSS功能的深入了解还将使开发用于生物技术应用的细菌中蛋白质表达和分泌的新系统成为可能。 拟议的研究集中在了解SecA是如何与其前蛋白底物结合的。这种结合作用对于前蛋白的初始识别非常重要，当前蛋白合成时，这种结合作用发生在核糖体上，并确保前蛋白正确地靶向分泌途径。SecA-前蛋白的相互作用对易位也很重要，在易位中，前蛋白由SecA引导通过膜孔。

The research proposal addresses bacterial protein secretion, the process by which bacteria transport protein molecules from their site of synthesis inside the cell, to the exterior environment. All bacteria have a "General Secretory System" (GSS), or "Preprotein Translocase", that is able to recognize proteins that are destined for secretion (proteins with a secretory signal sequence, otherwise known as "preproteins"). Once they are recognized as secretory proteins, preproteins are prevented from folding, and then targeted to sites on the cell membrane where they can be passed through a pore to the outside environment, a process termed "translocation". The targeting and translocation processes are mediated by the SecA ATPase, which uses the energy of ATP hydrolysis to catalyze protein secretion. This GSS is absolutely required for bacterial growth, and is not present in mammalian cells. On this basis, the GSS, and in particular the SecA ATPase, are good potential targets for therapeutic antibiotics. In addition, certain bacteria, such as Mycobacterium tuberculosis, contain two SecA molecules, SecA1 and SecA2. SecA2 fulfills specialized functions including the secretion of virulence factors that allow the bacteria to survive in host cells. Therefore, increasing our understanding of how the GSS works could open new avenues for antimicrobial therapies. A deeper knowledge of GSS function will also enable the development of novel systems for protein expression and secretion in bacteria for biotechnological applications. The proposed research is focussed on understanding how SecA binds to its preprotein substrates. This binding interaction is important for the initial recognition of the preprotein, which takes place at the ribosome as the preprotein is synthesized, and ensures that the preprotein is correctly targeted to the secretion pathway. SecA-preprotein interactions are also important for translocation, where the preprotein is guided through a membrane pore by SecA.