Interplay between the Signal Recognition Particle and Trigger Factor at the Ribos

描述(由申请人提供)：细胞竭尽全力确保蛋白质的适当生物发生。在翻译过程中，核糖体与修饰酶、伴侣和靶向复合体等多种因素结合，以确保最终产物具有活性、正确折叠并正确定位到适当的细胞位置。如果没有这些因素，细胞将充满不活跃、错误折叠、聚集和/或错误分配的蛋白质。这种情况可能会导致细胞发生故障和死亡，导致许多毁灭性的疾病。已经进行了许多研究来了解核糖体与这些分子机制的相互作用；然而，这些研究都没有着眼于核糖体如何处理和与多个复合体通信。在这个建议中，我们建议研究翻译核糖体与两个确保适当生物发生的核糖体相关因子的相互作用：信号识别粒子(SRP)和触发因子(TF)。SRP是一种普遍保守的靶向机制，负责将膜和分泌蛋白输送到质膜或内质网。另一方面，转铁蛋白是一种细菌伴侣蛋白，有助于胞浆和周质蛋白的折叠。SRP和Tf已被证明同时与核糖体结合，然而，新出现的蛋白质是如何被输送到SRP途径或Tf途径的分子基础仍不清楚。我建议(1)测试SRP和TF是否以及如何竞争与核糖体新生复合体(RNC)的结合；(2)确定SRP受体的招募是否有助于排除TF；以及(3)测试新生链的进一步延长是否有利于TF的相互作用并将SRP从核糖体中移除。总体而言，这些拟议的实验结果将提供一个全面和定量的分子机制，说明核糖体是如何实现“决策”的，并将作为一个重要的框架来理解其他核糖体相关分子机制的相互作用。

DESCRIPTION (provided by applicant): A cell goes to great lengths to ensure the proper biogenesis of proteins. During translation, the ribosome associates with multiple factors such as modification enzymes, chaperones and targeting complexes to guarantee that the final product is active, properly folded and correctly localized to the appropriate cellular location. Without these factors, the cell will be filled inactive, misfolded, aggregated and/or incorrectly allocated proteins. Such a scenario can result in the cell's malfunction and death, leading to many devastating diseases. Many studies have been carried out to understand the interaction of the ribosome with these molecular machineries; however, none of these studies look at how the ribosome handles and communicates with multiple complexes. In this proposal, we propose to study the interaction of a translating ribosome with two ribosome-associated factors that ensure proper biogenesis: the signal recognition particle (SRP) and the trigger factor (TF). SRP is a universally conserved targeting machinery and is responsible for delivering membrane and secretory proteins to the plasma membrane or to the endoplasmic reticulum. On the other hand, TF is a bacterial chaperone that aids in the folding of cytosolic and periplasmic proteins. SRP and TF have been shown to simultaneously bind to the ribosome, however, the molecular basis of how newly emerging proteins is funneled to either the SRP pathway or the TF pathway remains unclear. I propose to (1) test whether and how SRP and TF compete for binding to ribosome nascent chain complexes (RNCs); (2) determine if the recruitment of the SRP receptor helps exclude TF; and (3) test whether further elongation of the nascent chain favors TF interaction and removes SRP from the ribosome. Overall, the results of these proposed experiments will provide a comprehensive and quantitative molecular mechanism of how 'decision-making' is achieved by the ribosome and will serve as an important framework to understand the interplay of other ribosome- associated molecular machineries.