Dynamic Membrane association of the bacterial SRP receptor in E. coli

在共翻译过程中，SRP受体(SR)将可溶性SRP-核糖体新生链状复合体(RNC)与膜结合的SecY转位连接起来。在真核生物中，SR由两个亚基组成：SRα负责将SRP-RNC招募到膜上，而SRβ负责感知缺失的转运子并协调RNC从SRP到转位子的转移。虽然细菌SR只由SRα同源的FtsY组成，但我们的数据表明FtsY能够执行真核SR的两个功能。这就提出了几个关键问题：(1)FtsY如何协调RNC与转位蛋白的结合？(2)FtsY的转位蛋白结合部位是什么，以及FtsY如何从转位蛋白中被驱离以暴露RNC的结合部位？(3)观察到FtsY与细菌细胞骨架的相互作用表明，通过SRP途径进行的共翻译蛋白靶向和整合在空间上是协调的吗？这些问题将通过结合体内技术，如体内定点交联、FRET和荧光显微镜，与体外技术，如我们建立的体外转录/翻译系统和重组蛋白脂质体系统来解决。

During co-translational protein targeting the SRP-receptor (SR) connects the soluble SRP-ribosome nascent chain complex (RNC) to the membrane-bound SecY translocon. In eukaryotes, the SR consists of two subunits: SRα recruits the SRP-RNC to the membrane whereas SRβ is responsible for sensing vacant translocons and for coordinating RNC-transfer from SRP to the translocon. Although the bacterial SR consists of only the SRα-homolog FtsY, our data indicate that FtsY is able to execute both functions of the eukaryotic SR. This raises several crucial questions: (1) How does FtsY coordinate RNC binding to the translocon? (2) What is the translocon binding site of FtsY and how is FtsY dispelled from the translocon to expose the binding sites for the RNC? (3) Are co-translational protein targeting and integration by the SRP pathway spatially coordinated as indicated by the observation that FtsY interacts with components of the bacterial cytoskeleton? These questions will be addressed by combining in vivo techniques, such as in vivo site-directed cross-linking, FRET and fluorescence microscopy, with in vitro techniques, such as our established in vitro transcription/translation systems and reconstituted proteoliposome systems.