Molecular Mechanism of Protein Targeting by the Signal Recognition Particle

描述(由申请人提供)：蛋白质的正确定位对所有细胞都至关重要。信号识别颗粒(SRP)及其受体(SR)构成了介导大约三分之一的细胞蛋白共翻译靶向的主要细胞机制 真核生物的内质网，或细菌质膜。虽然对SRP途径的了解已经取得了很大进展，但其分子机制的许多基本方面仍有待阐明。我们的总体目标是在生化和生物物理水平上破译这台普遍保守的靶向机器复杂的内部工作原理。我们的具体目标是破译SRP上装载的货物蛋白与其快速递送和高效卸载到易位机制相结合的分子机制，并开始了解在核糖体出口部位拥挤环境下SRP的机制。为此，我们设想了三个目标：(1)我们将破译SRP RNA在调节货物与SRP和SR GTP酶之间的通信中的作用；(2)我们将阐明货物蛋白从靶向转移到易位机制的确切机制；以及(3)我们将破译主要的共翻译伴侣，即触发因子，是否以及如何调节SRP途径的效率和保真度。最终，这些研究不仅将促进我们对细胞内蛋白质定位过程的理解，而且还将提供新的见解 分子识别和调控的基本原理。拟议的研究是最基本的性质，将有助于我们在分子水平上全面了解所有活细胞的生理学和病理学。

DESCRIPTION (provided by applicant): Proper localization of proteins is crucial for all cells. The signal recognition particle (SRP) and its receptor (SR) constitute the major cellular machinery that mediates the co-translational targeting of roughly one third of cellular proteins to the eukaryotic endoplasmic reticulum, or the bacterial plasma membrane. Although rapid progress has been made in understanding the SRP pathway, many fundamental aspects of its molecular mechanism remain to be elucidated. Our general goal is to decipher, at a biochemical and biophysical level, the intricate inner workings of this universally conserved targeting machine. Our specific goal is to decipher the molecular mechanisms by which the loading of the cargo proteins on the SRP is coupled to its rapid delivery and efficient unloading to the translocation machinery, and to begin understand the mechanism of SRP in the context of the crowded environment at the ribosome exit site. To this end, three aims are envisioned: (1) We will decipher the role of the SRP RNA in mediating the communication between the cargo and the SRP and SR GTPases; (2) We will elucidate the precise mechanisms by which the cargo protein is transferred from the targeting to the translocation machinery; and (3) We will decipher whether and how the major co-translational chaperone, trigger factor, modulates the efficiency and fidelity of the SRP pathway. Ultimately, these studies will not only advance our understanding of the process of protein localization within the cell, but also provide new insights into the general principles of molecular recognition and regulation at a fundamental level. The proposed research is of a most basic nature, and will contribute profoundly to our general understanding of physiology and pathology of all living cells at the molecular level.