The Mammalian Signal Recognition Particle

描述（由申请人提供）：信号识别颗粒（SRP）结合从翻译核糖体出现的N-末端多肽信号序列，并将该核糖体复合物靶向内质网膜上的受体。多肽以GTP调节的方式易位到膜间隙中。哺乳动物SRP由两个结构域组成：Alu和大亚基。大亚基（LS）含有一半的RNA（~ 150 nt）和SRP 19、SRP 54和SRP 68/SRP 72异二聚体蛋白。大亚基执行SRP的大部分功能，包括信号序列识别、GTP结合和水解、受体对接，以及部分延长停滞。该项目的长期目标是以基本和定量的方式了解蛋白质和RNA组分的相互作用以及信号肽和核苷酸底物在哺乳动物SRP大亚基的合作组装和功能中的结合。具体目标是：（1）确定SRP 19和SRP 54在组装和功能中强协同性的分子基础。(2)了解天然未折叠的SRP 19蛋白与SRP RNA的组装机制。(3)以核苷酸分辨率绘制单个SRP 68和SRP 72蛋白以及SRP 68/72异二聚体的RNA结合位点，并定量与SRP 54和SRP 19的协同结合。这些实验的严格分析是可能的发展，在我们的实验室，强大的单核苷酸分辨率的方法来确定多组分RNA-蛋白质复合物的平衡结合常数。(4)分析完整的SRP大亚基与鸟苷酸和信号肽两类底物的相互作用。总体而言，这项工作将解决SRP蛋白和RNA组分之间的合作相互作用如何进行信号肽识别和核苷酸结合的关键特征。此外，这项工作旨在确定可推广到其他生物学和医学上突出的核糖核蛋白复合物的原则。

DESCRIPTION (provided by applicant): The signal recognition particle (SRP) binds the N-terminal polypeptide signal sequence emerging from a translating ribosome and targets this ribosomal complex to a receptor at the endoplasmic reticulum membrane. Polypeptides are translocated into the intermembrane space in a GTP-regulated manner. The mammalian SRP is comprised of two domains: the Alu and large subunits. The large subunit (LS) contains one-half of the RNA (-150 nts) and the SRP19, SRP54, and SRP68/SRP72 heterodimer proteins. The large subunit performs most of the functions of the SRP including signal sequence recognition, GTP binding and hydrolysis, receptor docking, and, in part, elongation arrest. The long term goals of this project are to understand, in a fundamental and quantitative way, the interplay of protein and RNA components and of binding by signal peptide and nucleotide substrates in the cooperative assembly and functioning of the large subunit of the mammalian SRP. Specific aims are: (1) To determine the molecular basis for the strong cooperativity in the assembly and function of SRP19 and SRP54. (2) To understand the mechanism of assembly of the natively unfolded SRP19 protein with the SRP RNA. (3) To map at nucleotide resolution the RNA binding sites for the individual SRP68 and SRP72 proteins and for the SRP68/72 heterodimer and to quantify cooperative binding with SRP54 and SRP19. Rigorous analysis of these experiments is made possible by the development, in our lab, of robust single-nucleotide resolution approaches for determining equilibrium binding constants in multi-component RNA-protein complexes. (4) To analyze interaction of the complete SRP large subunit with its two classes of substrates: guanosine nucleotides and signal peptides. Overall, this work will address key features of how cooperative interactions between SRP protein and RNA components function to carry out signal peptide recognition and nucleotide binding. Moreover, the work is designed to identify principles generalizable to other biologically and medically prominent ribonucleoprotein complexes.