NOVEL BIOCHEMICAL ROLES FOR IRON REGULATORY PROTEIN 2

描述(由申请人提供)： 由于其独特的化学性质，铁在生物学中具有巨大的多功能性。尽管这种金属被用于无数的关键过程，但在有氧环境中，这会以对蛋白质、DNA/RNA和脂质的氧化损伤的形式对细胞造成潜在的高成本。因此，哺乳动物进化出了致力于铁稳态的复杂调节机制，其中铁调节蛋白2(IRP2)起着关键作用。IRP2是一种RNA结合蛋白，调节编码铁储存(铁蛋白)和铁吸收(转铁蛋白受体)重要蛋白的mRNAs。细胞铁与这些和其他mRNAs的适当调节是通过铁和氧刺激IRP2泛素化/降解实现的。确定IRP2感知铁和氧的生理变化的分子机制以及这种信号对其降解的影响对于全面了解哺乳动物的铁稳态是至关重要的。为此，我们最近在IRP2中发现了一个可能的铁结合基序。我们假设这个位点赋予IRP2一种新的依赖于铁和氧的酶活性，这种活性参与了IRP2的降解，这种活性是通过自我修饰机制或催化其他底物的修饰来实现的。本R21应用中涉及的具体目标是：(1)表征与IRP2上假定的铁结合部位的铁结合，并研究其在介导IRP2降解或直接调节IRP2靶mRNAs方面的潜在作用；以及(2)检测新的铁依赖的IRP2酶活性。这项工作的目标是定义迄今尚未确定的IRP2生化活性，并确定其参与的途径。这项工作被作为R21的应用程序提出，因为它通过代表一个具有潜在高影响的探索性高风险研究来满足R21机制的目标。

DESCRIPTION (provided by applicant): Due to its unique chemical properties iron has immense versatility in biology. Although this metal is used for myriad of critical processes, in an aerobic environment this comes at a potentially high cost to cells in the form of oxidative damage to proteins, DNA/RNA, and lipids. Mammals have therefore evolved complex regulatory mechanisms devoted to iron homeostasis, where iron regulatory protein 2 (IRP2) serves a critical function. IRP2 is an RNA-binding protein that regulates mRNAs encoding proteins important in iron storage (ferritin) and iron uptake (transferrin receptor). The coupling of cellular iron with the appropriate regulation of these, and other mRNAs, is achieved through iron and oxygen stimulation of IRP2 ubiquitination/degradation. Defining the molecular mechanisms by which IRP2 senses physiologic changes in iron and oxygen and how this signals for its degradation is essential for a comprehensive understanding of mammalian iron homeostasis. Towards this end, we have recently identified a putative iron-binding motif in IRP2. We hypothesize that this site confers a novel iron- and oxygen-dependent enzymatic activity to IRP2, and that this activity is involved in its degradation through a self-modifying mechanism or in catalyzing modifications on other substrates. The specific aims addressed in this R21 application are: (1) Characterize iron-binding to the putative iron-binding site on IRP2 and examine its potential role in mediating IRP2 degradation or in direct regulation of IRP2 target mRNAs and (2) Examine novel iron-dependent IRP2 enzymatic activity. The goal of this work is to define hitherto unidentified IRP2 biochemical activity and identify pathways in which it participates. This work is presented as an R21 application since it satisfies the aims of the R21 mechanism by representing an exploratory high risk study with potentially high impact.