Structural Studies of Mammalian Mitochondrial Ribosomes

描述(申请人提供)：哺乳动物线粒体翻译系统是一个非常独特的系统，也是所有系统中最不被理解的系统之一。哺乳动物线粒体核糖体除了在蛋白质生物合成中起主要作用外，还参与细胞凋亡和各种线粒体疾病状态。线粒体核糖体与细菌核糖体相似，然而，大约一半的线粒体核糖体蛋白在细菌和细胞质核糖体蛋白中没有任何同源物。拟议研究的主要焦点是确定新发现的蛋白质在线粒体蛋白质合成机制中的作用。一些与细菌同源的蛋白质负责与核糖体的mRNA、tRNA和因子结合。哺乳动物线粒体核糖体中缺少许多重要的细菌核糖体蛋白。新的核糖体蛋白将取代缺失的细菌同源物，将通过蛋白质组学方法在定位和配体结合实验中确定。此外，我们还利用蛋白质组学的方法在线粒体核糖体的小亚基中发现了三种不同的S18S(MRP-S18S)变体。这一发现清楚地表明，线粒体核糖体中存在三个不同构象的小亚基亚群。在这个方案中，我们建议研究新的一类核糖体蛋白和三种不同的MRP-S18s变体在哺乳动物线粒体蛋白质生物合成中的作用和功能。此外，对这些蛋白质的翻译后修饰的研究将使我们能够更好地了解线粒体翻译机制在疾病状态和细胞凋亡中的调控。

DESCRIPTION (provided by applicant): The mammalian mitochondrial translation system is a very unique system and is one of the least understood systems of all. Besides their primary roles in protein biosynthesis, mammalian mitochondrial ribosomes are involved in apoptosis and various mitochondrial disease states. Mitochondrial ribosomes resemble the bacterial ribosomes; however, approximately half of the mitochondrial ribosomal proteins do not have any homologs among the bacterial and cytoplasmic ribosomal proteins. The major focus of the proposed research is to determine the roles of newly identified proteins in protein synthesis machinery of the mitochondria. Some of the proteins with the bacterial homologs are responsible for mRNA, tRNA, and factor binding to ribosomes. A number of the crucial bacterial ribosomal proteins are missing in the mammalian mitochondrial ribosome. The new class ribosomal proteins replacing the missing bacterial homologs will be determined in the localization and ligand binding experiments using proteomics approaches. In addition, we have discovered the presence of three different variants of S18s (MRP-S18s) in the small subunit of mitochondrial ribosomes using a proteomics approach. This finding clearly implies the presence of three conformationally different sub-populations of small subunits in mitochondrial ribosomes. In this proposal, we are proposing to study roles and functions of the new class ribosomal proteins and the three different variants of MRP-S18s in the protein biosynthesis in mammalian mitochondria. Furthermore, studies on post-translational modifications of these proteins will enable us to better understand the regulation of the mitochondrial translational machinery in disease states and apoptosis.