The interplay between endoplasmic reticulum and mitochondria in protein targeting and mistargeting

真核细胞被分成不同的隔间，每个隔间都有自己的一套定义蛋白质。分子细胞生物学中的一个基本问题是了解在胞质核糖体上合成的蛋白质是如何到达各自的细胞内地址的。我们和其他人最近的研究表明，这种靶向过程是在严格的质量控制措施的监督下进行的，并且可以在蛋白质被错误定位到不适当的位置的情况下进行修改和纠正。在线粒体和内质网(ER)的情况下，维持精确的细胞器蛋白质组尤其需要。这两个隔间交织在一系列精心设计的物理接触中，代谢物、脂类和共同驻留蛋白的多重交换反应，以及相互关联的应激反应途径。新合成的线粒体和内质网蛋白的生物发生依赖于靶向、整合以及从两个细胞器的膜中提取的精细平衡，这是一种复杂的相互作用，尽管它很重要，但在很大程度上尚不清楚。在这个合作项目中，我们将结合三个小组的互补专业知识来阐明内质网在线粒体蛋白质生物发生中的作用。在这个项目中，我们将在三个不同的工作包中研究ER表面在概念上的三个不同的功能，以靶向线粒体蛋白质，每个工作包都由一个小组带头，但依赖于所有三个小组的密切合作：在Herrmann小组的领导下，我们将研究ER表面如何通过我们最近发现的ER-SURF过程来支持将前体蛋白靶向线粒体的生产。我们将定义底物库和ER-SURF途径的分子机制。在Rapaport团队的带领下，我们将研究哪些线粒体前体被错误定位，以及这些蛋白质如何恢复或降解，这是一个特别针对外膜蛋白的问题。在Schuldiner小组的领导下，我们将鉴定形成内质网和线粒体永久驻留的双重定位蛋白，并阐明这些蛋白调控靶向这两个目的地的分子特征。为了实现这三个目标，我们将使用面包师酵母作为模式生物，并结合每个实验室的专业知识-高通量基因筛查、荧光显微镜、生物化学和生理分析。拟议项目的成功显然有赖于所有三个参与小组的紧密合作--过去十年的事实证明，这三个小组是一个强大的组合。总体而言，这一合作、及时和创新的项目将使我们能够揭开线粒体蛋白靶向方面令人兴奋的、迄今大部分尚未确定的早期反应。

Eukaryotic cells are divided into distinct compartments each with their own defining set of proteins. A fundamental problem in molecular cell biology is to understand how proteins that are synthesized on cytosolic ribosomes reach their respective intracellular address. Recent studies by us and others demonstrated that such targeting processes occur under surveillance of stringent quality control measures and can be revised and corrected in cases where a protein was mislocalized to an inappropriate location. Maintaining the precise organellar proteome is especially demanding in the case of mitochondria and the endoplasmic reticulum (ER). These two compartments are intertwined in an elaborate array of physical contacts, multifold exchange reactions for metabolites, lipids and common resident proteins, and interconnected stress response pathways. The biogenesis of newly synthesized mitochondrial and ER proteins relies on a fine balance of targeting to, integration into, as well as extraction from membranes of both organelles, a complex interplay that, despite its importance, is largely uncharacterized. In this collaborative project, we will combine the complementing expertise of three groups to elucidate the role of the ER for the biogenesis of mitochondrial proteins. For this project, we will study the three conceptually distinct functions of the ER surface for the targeting of mitochondrial proteins in three distinct work packages, each spearheaded by one group but dependent on the close collaboration of all three: Led by the Herrmann group we will study how the ER surface can support the productive targeting of precursor proteins to mitochondria through the process of ER-SURF that we have recently discovered. We will define the substrate repertoire and the molecular mechanisms of the ER-SURF pathway. Led by the Rapaport group, we will study which mitochondrial precursors get mistargeted and how these proteins can be recovered or degraded, a problem which particularly arises for outer membrane proteins. Led by the Schuldiner group we will identify the dual localized proteins which form permanent residents of both the ER and mitochondria and elucidate the molecular features underlying the regulated targeting of these proteins to both destinations. For these three aims, we will use bakers’ yeast as a model organism and combine the powerful approaches that are the expertise of each lab - high throughput genetic screens, fluorescence microscopy, biochemistry and physiological assays. The success of the proposed project is clearly dependent on the tight collaboration of all three participating groups – proven over the last decade to be a powerful combination. Collectively, this collaborative, timely, and innovative project will allow us to unravel the exciting, and so far largely uncharacterized, early reactions in mitochondrial protein targeting.