Towards a systems-level understanding of the novel redox-regulated mitochondrial protein import and disulphide bond formation pathway

线粒体是至关重要的细胞器-通常被描述为真核细胞内的动力室。它们为维持人类生命的生物活动产生主要能量，并调节细胞生长和细胞死亡（凋亡）。线粒体与超过40种人类疾病有关，包括糖尿病、耳聋、衰老和癌症。例如，线粒体内的肌张力障碍蛋白1（DDP 1）中的单个Cys突变会导致Mohr-Tranebjaerg/肌张力障碍综合征，这是一种X连锁神经退行性疾病。蛋白质输入对于线粒体的生物发生是必不可少的，因为99%的线粒体蛋白质是在细胞质中合成的，并且必须输入到线粒体中以实现其生物学功能。每个细胞器都被一层双层膜包围，将细胞器分为四个亚区：外膜、膜间空间（IMS）、内膜和基质。线粒体IMS含有许多含Cys的蛋白质，这些蛋白质对于线粒体的生物发生和细胞的活力是必需的。我们和其他人最近的一项重要生物学发现是IMS中存在新型氧化还原调节的线粒体输入和组装（MIA）机制。MIA机制包括两种基本组分蛋白质，Mia 40和Erv 1，它们形成二硫键中继系统，负责新输入的IMS蛋白质中的输入和正确的二硫键形成。然而，这种机制的功能的分子基础尚不清楚。许多重要的问题，如电子和/或二硫键如何在Mia 40-Erv 1系统内转移;是什么调节系统与其底物蛋白之间的二硫键转移;蛋白质-蛋白质相互作用和识别如何调节;有害的过氧化氢（H2 O2）是氧化反应的真实的产物，仍然有待回答。因此，本提案将使用广泛的生物物理、生物化学和生物学方法来回答这些问题。这一当前热门的研究课题一直是许多生物学家关注的焦点。对细胞系统的生物学研究通常采取自上而下的方法来识别新的候选者和系统中的潜在相关性。然后，他们制定的经验关系，但很少导致制定的分子机制。因此，一个自下而上的机制为基础的研究是及时和必要的，它依赖于热力学，动力学和蛋白质相互作用的可测量参数的知识。在这个提议中，我们将确定那些功能上重要的热力学，动力学和结构的蛋白质，以确定Mia 40-Erv 1系统的分子机制。本研究不仅对蛋白质二硫键形成和线粒体生物合成本身，而且对氧化还原调节和氧化应激的原因提供了新的见解。所有这些过程都与线粒体生理学、衰老、功能障碍和治疗干预密不可分。

Mitochondria are vitally important organelles - often described as the powerhouses within eukaryotic cells. They generate the primary energy for biological activities that sustain human life, and regulate cell growth and cell death (apoptosis). Mitochondria are implicated in >40 human diseases, including diabetes, deafness, ageing and cancer. For example, a single Cys mutation in the mitochondrial deafness-dystonia protein 1 (DDP1) causes Mohr-Tranebjaerg/deafness-dystonia syndrome, an X-linked neurodegenerative disorder. Protein import is essential for the biogenesis of mitochondria, since 99% of mitochondrial proteins are synthesized in the cytosol and have to be imported into mitochondria for their biological function. Each mitochondrion is enclosed by a double membrane that divides the organelle into four sub-compartments: outer membrane, intermembrane space (IMS), inner membrane, and matrix. The mitochondrial IMS harbors many Cys-containing proteins that are essential for the biogenesis of mitochondria and viability of the cells. A recent important biological finding by us and others is the presence of novel redox regulated mitochondrial import and assembly (MIA) machinery in the IMS. The MIA machinery includes two essential component proteins, Mia40 and Erv1, which form a disulphide bond relay system responsible for the import and correct disulphide bond formation in the newly imported IMS proteins. However, the molecular basis for the function of this machinery is not clear. Many important questions, such as how are electrons and/or disulphide bonds transferred within the Mia40-Erv1 system; what regulates the disulphide bond transfer between the system and its substrate proteins; how are the protein-protein interactions and recognition regulated; is the harmful hydrogen peroxide (H2O2) the real product of the oxidation reaction, remain to be answered. Thus, this proposal will use a wide range of biophysical, biochemical, and biological methods to provide answers to these questions. This currently heated research topic has been a focus of many biologists. Biological studies on cellular systems often take the form of top-down approaches to identify new candidates and potential correlations in the systems. They are then formulated in terms of empirical relations, but rarely lead to the formulation of molecular mechanisms. Thus, a bottom-up mechanism-based study is timely and essential, which relies on knowledge of thermodynamics, kinetics, and measurable parameters of protein interactions. In this proposal, we will determine those functionally important thermodynamic, kinetic and structural properties of the proteins in order to define the molecular mechanism of the Mia40-Erv1 system. This study will provide insights in not only protein disulphide bond formation and mitochondrial biogenesis per se, but also redox regulation and cause of oxidative stress. All these processes are inextricably linked to mitochondrial physiology, ageing, dysfunction and therapeutic intervention.