Mechanistic studies of mitochondrial ferritin, a key player in iron mediated oxidative stress response and cellular iron metabolism

铁对几乎所有形式的生命都是必不可少的，在生命所依赖的许多反应中起着核心作用。在包括人类在内的动物体内，许多必需的含铁辅助因子是在一种叫做线粒体的细胞器中合成的，因此线粒体对铁有很高的需求，可以被认为是铁代谢的主要细胞中枢。尽管它很重要，但我们目前对铁是如何在线粒体中调节的知之甚少。其中一个重要的参与者是线粒体铁蛋白，它是铁蛋白家族的一员。铁蛋白可以被认为是像足球一样的分子，中间有一个中空的中心，里面可以储存成千上万的铁原子，形成一种铁矿物——如果没有蛋白质外壳的溶解作用，这种铁矿物就会形成不可溶的沉淀物。铁的储存有两个重要功能。首先，它使细胞能够在铁含量低的时候提取储备；其次，它克服了铁的潜在毒性，这种毒性是由铁对生命有用的特性产生的：如果没有适当的控制，铁会导致活性氧的产生，从而导致严重的细胞损伤。线粒体铁蛋白的功能似乎主要是防止铁中毒。因此，它只在代谢高活性、高氧周转的组织中表达，因此特别容易受到氧化应激的影响。这些组织包括心脏、睾丸和脑神经细胞，研究表明，这种铁蛋白可以保护这些细胞中的线粒体免受氧化应激。据推测，这是通过隔离潜在有害的多余游离铁来实现的，但这一过程的细节尚不清楚。线粒体铁蛋白还参与调节不同细胞间的铁分布，该蛋白水平升高与胞质铁和胞质铁蛋白水平降低相关。其原因目前尚不清楚。最后，线粒体铁蛋白参与神经退行性疾病的发病机制；它的表达水平在一系列疾病中增加，包括帕金森病、阿尔茨海默病、不宁腿综合征和弗里德赖希共济失调，但它与这些疾病的关系尚不清楚。虽然对线粒体铁蛋白在体内作用的研究在范围和广度上都在增加，但对其机制特性的理解-它如何与铁相互作用并实现其细胞功能-却很落后。在这里，我们提出了一个研究计划，我们将应用最先进的方法，这将导致关于线粒体铁蛋白如何结合，氧化和储存铁的重要新信息，从而最大限度地减少其毒性。我们的初步研究表明，线粒体铁蛋白中的铁氧化涉及基于蛋白质的自由基形成。我们将确定自由基在线粒体铁蛋白中所起的作用，在此过程中，我们将发现它如何阻止导致氧化应激的活性氧的形成。我们还将研究从线粒体铁蛋白中释放的铁，确定隔离的铁是否可以回收利用。这将提供重要的新信息，解释为什么线粒体铁蛋白的表达会导致其他细胞区室缺铁。

Iron is essential for virtually all forms of life, playing central roles in many of the reactions on which life depends. In animals, including humans, many of the iron-containing cofactors that are essential are synthesized in a cellular organelle called the mitochondrion, which consequently has a high requirement for iron and can be regarded as the major cellular hub for iron metabolism. Despite its importance, we currently have a rather incomplete picture of how iron is regulated in mitochondria. An important player in this is mitochondrial ferritin, a member of the remarkable ferritin family of proteins. Ferritins can be thought of as being football-like molecules with a hollow centre in which thousands of iron atoms can be stored in the form of an iron mineral - one that would form insoluble precipitates were it not for the solubilising effect of the protein coat. The storage of iron serves two important functions. Firstly, it enables cells to draw on reserves when iron is low, and secondly, it overcomes the potential toxicity of iron that results from the very properties that make it useful to life: without proper control, iron can lead to the generation of reactive oxygen species that can cause severe cellular damage. The function of mitochondrial ferritin appears to be principally one of protecting against iron toxicity. Accordingly, it is only expressed in tissues that are metabolically highly active with a high turnover of oxygen, and consequently particularly susceptible to oxidative stress. These tissues include heart, testis and brain neurones, and it has been shown that this ferritin protects mitochondria in these cells from oxidative stress. It is presumed that it does this through the sequestration of potentially harmful excess free iron, but the details of this process are unclear. Mitochondrial ferritin also participates in the regulation of iron distribution between different cellular compartments, with increased levels of the protein associated with low cytosolic iron and cytosolic ferritin levels. The reason for this is currently not clear. Finally, mitochondrial ferritin is involved in pathogenesis of neurodegenerative diseases; its expression levels are increased in a range of disorders, including Parkinson's diseases, Alzheimer's disease, restless legs syndrome and Friedreich's ataxia, but its connection to these diseases is unclear.While studies of the in vivo roles of mitochondrial ferritin are increasing in scope and breadth, understanding of its mechanistic properties - how it interacts with iron and fulfils its cellular function - are lagging behind. Here, we propose a programme of research in which we will apply state of the art methodologies that will lead to important new information about how mitochondrial ferritin binds, oxidises and stores iron, and hence minimises its toxicity. Our preliminary studies have revealed that iron oxidation in mitochondrial ferritin involves protein-based radical formation. We will determine the role that the radical plays in mitochondrial ferritin and, in doing so, we will discover how it prevents the formation of reactive oxygen species that cause oxidative stress. We will also investigate iron release from mitochondrial ferritin, determining whether sequestered iron can be recycled. This will provide important new information about why the expression of mitochondrial ferritin causes iron deficiency in other cellular compartments.