Structure and Function of Iron Regulatory Proteins

描述（由申请人提供）：几乎所有的生命形式都需要铁。环境中的大多数铁都被氧化了，几乎不溶。更复杂的是，铁的水化学反应会产生剧毒的氧化物质。因此，生物体必须严格调节细胞内铁的数量和状态。在人类中，不能从饮食中获得足够的铁会导致缺铁性贫血，这是一个世界性的主要营养问题。此外，铁代谢失衡，如遗传性高铁蛋白血症和血色素沉着症，可导致人类许多疾病，包括失明、肝硬化、心脏病、神经系统疾病和癌症。铁在动物细胞中的运输、利用和储存是由两个铁调节蛋白IRP1和IRP2转录后调控的。IRPs可逆地结合编码铁转运和储存蛋白的mrna中高度保守的茎环结构，即铁响应元件（IREs），从而提供协调的、相互的铁调控。IRPs本身受细胞铁状态的调节，其中高细胞内铁浓度抑制其IRE结合活性。高铁水平将IRP1转化为胞质乌头酸酶，并形成Fe-S簇。因此，IRP1具有双重功能，其两种形式之间的相互转换是其调控基因表达的基础。IRP: IRE系统是最容易理解的转录后调控机制之一，但直到现在，还没有结构信息可用。我们最近确定了三个IRP1: IRE复合物的结构。利用这些结果，我们开发了一个模型来解释IRPI在多重ire识别中的选择性，我们还提出了一个调节IRP1相互转换的开关机制的模型。为了验证这些假设，并完成解释这一关键代谢调节因子控制的分子细节的长期目标，我们将：1)确定IRP1识别IRE和差异调节的结构基础；2)确定IRP1中开关机制的性质。这些实验将使用分子生物学和x射线晶体学的方法进行。该结果将潜在地为铁代谢疾病的治疗方法提供新的靶点。

DESCRIPTION (provided by applicant): Practically all life forms require iron. Most iron in the environment is oxidized and virtually insoluble. A further complication is that iron's aqueous chemistry can generate highly toxic oxidizing species. Hence organisms must tightly regulate both the quantity and the state of iron in the cell. In humans, the failure to acquire adequate iron from the diet results in iron deficiency anemia, a major nutritional problem worldwide. In addition, imbalances in iron metabolism such as hereditary hyperferritinemia and hemochromatosis can lead to a number of diseases in humans, including blindness, cirrhosis, cardiac disease, neurological disorders, and cancer. Iron transport, utilization, and storage in animal cells is regulated post-transcriptionally by two iron regulatory proteins, IRP1 and IRP2. The IRPs reversibly bind to highly conserved stem-loop structures known as iron responsive elements (IREs) in the mRNAs encoding the iron transport and storage proteins, thereby providing coordinated, reciprocal iron regulation. The IRPs are themselves regulated by the cellular iron status, where high intracellular iron concentrations suppress their IRE binding activities. High iron levels convert IRP1 into a cytosolic aconitase enzyme, complete with an Fe-S cluster. Thus IRP1 is bifunctional, and the interconversion between its two forms underlies its regulation of gene expression. The IRP: IRE system is one of the best-understood post-transcriptional mechanisms of regulation, but until now, no structural information was available. We have recently determined the structure of three IRP1: IRE complexes. Using those results, we have developed a model to explain IRPI's selectivity in multiple-IRE recognition, and we have also proposed a model for the switch mechanism that regulates IRP1 interconversion. To test these hypotheses, and to complete the long-term objective of explaining the molecular details of control by this key metabolic regulator, we will 1) Determine the structural basis for IRE recognition and differential regulation by IRP1; and 2) Determine the nature of the switch mechanism in IRP1. These experiments will be performed using the methods of molecular biology and x-ray crystallography. The results will potentially generate novel targets for therapeutic approaches to diseases of iron metabolism.