Identification of a ubiquitin-ligase which recognizes oxidized proteins.

我们已经证明，RNA结合蛋白，铁调节蛋白2 (IRP2)，已知是铁代谢的主要调节因子，在铁存在下被蛋白酶体降解。我们还表明，铁对蛋白质的氧化在IRP2降解之前为其泛素化创造了信号。在本研究中，我们试图确定铁与IRP2结合的模式，铁和识别氧化IRP2的泛素连接酶（E3）引起IRP2的氧化修饰。我们发现，铝通过竞争性地抑制铁诱导的蛋白质氧化来稳定IRP2，这表明IRP2中存在铁结合位点，铝可以竞争性地与IRP2的铁结合位点结合。考虑到生物在进化过程中没有遇到铝，它们获得了对铁具有高度选择性的金属结合位点。现在，我们正在分析铁结合位点的确切性质。虽然我们还没有发表，但我们发现IDD结构域蛋白可以铁依赖的方式结合到IRP2的E3上。IDD结构域是IRP2铁依赖降解所必需的。换句话说，IDD结构域作为铁结合位点，被铁氧化并被E3识别为IRP2。我们目前正在使用该检测系统鉴定IRP2的E3基因。此外，我们已经确定家族性帕金森病基因产物Parkin是一种泛素蛋白连接酶，来自Juntendo大学的Y.Mizuno教授和东京都市医学研究所的K.Tanaka博士共同参与了这项研究。

We have been shown that the RNA binding protein, iron regulatory protein 2 (IRP2), which is known to be a master regulator of iron metabolism, is degraded by proteasome in the presence of iron. We have also shown that oxidation of the protein by iron creates the signal for the ubiquitination of IRP2 prior to its degradation. In the present study, we tried to identify the mode of iron binding to IRP2, the oxidative modification of IRP2 provoked by iron and ubiquitin-ligase (E3) recognizing oxidized IRP2. We identified that aluminum stabilizes IRP2 by inhibiting iron-induced oxidation of the protein competitively, which suggest that iron binding site (s) are present in IRP2 and that aluminum can bind to the iron binding site of IRP2 competitively to iron. Considering that organisms have not been encountered to aluminum during the evolution, they acquired the metal binding site that is highly selective to iron. Now, we are analyzing the exact nature of the iron binding site. Although we have not published yet, we have found that the IDD domain protein, which domain is necessary for the iron-dependent degradation of IRP2, can bind to E3 for IRP2 in an iron-dependent manner. In other word, the IDD domain serves as the site of iron binding, oxidized by iron and recognized by E3 for IRP2. We are currently identifying E3 for IRP2 by using this assay system. Moreover, we have been identified that Familial Parkinson's disease gene product, Parkin, is a ubiquitin-protein ligase together with Professor Y.Mizuno at Juntendo University and Dr. K.Tanaka at Tokyo Metropolitan Institute of Medical Science.