Physiology and pathology of the ubiquitin-mediated quality control system

1.HOIL-1泛素连接酶的功能分析HOIL-1的靶识别机制IRP2中的一个血红素调节基序(HRM)是IRP2的血红素结合部位。HOIL-1识别由血红素与HRM和氧结合而产生的IRP2的氧化修饰，从而导致IRP2泛素化。从这些分析中，我们展示了一种新的铁感应机制，其中细胞通过血红素感知铁浓度的变化(自然细胞生物学，2003；分子细胞，2005)。HOIL-1连接酶复合体的功能由HOIP和HOIL-1L组成的LUBAC泛素连接酶复合体产生一种新的多泛素链，其中泛素的C端甘氨酸残基与泛素N端蛋氨酸的氨基连接(EMBO J.2006)。HOIL-1连接酶的生理作用我们已经证明了LUBAC通过NEMO的线性泛素化选择性地激活了NF-kB通路(提交)。我们发现，SCF^&lt；Fbs1&gt；连接酶选择性地识别N-连接糖链的壳二糖部分，这种识别机制适合于选择性识别变性糖蛋白(自然，2002；NAT。昂首阔步。摩尔。Biol.，2004)。我们已经建立了在神经元中表达IRP2的转基因小鼠(IRP2TG)，并分析了铁代谢扰动产生的氧化应激在神经退行性疾病中的作用。虽然没有观察到大量的铁积累，但IRP2TG神经元中有反应性Fe2+积累，从而引起这些细胞的氧化损伤。此外，在老年IRP2TG小鼠中也观察到神经元丢失和共济失调(提交)。

1. Functional analyses of the HOIL-1 ubiquitin ligasea. Mechanism of target recognition by HOIL-1 A heme-regulatory motif (HRM) in IRP2 is the heme-binding site of IRP2. Oxidative modification of IRP2, generated by heme bound to the HRM and oxygen is recognized by HOIL-1, which leads to IRP2 ubiquitination. From these analyses, we show a novel iron-sensing mechanism, in which cells are sensing changes in iron concentration through heme (Nature Cell Biology, 2003; Molecular Cell, 2005).b. Function of the ligase complex containing HOIL-1 The LUBAC ubiquitin ligase complex, composed of HOIP and HOIL-1L, an isoform of HOIL-1, generates a novel polyubiquitin chain, in which C-terminal Gly residue of ubiquitin is conjugated to a-amino group of N-terminal Met of ubiquitin (EMBO J. 2006).c. Physiological roles of the HOIL-1 ligase We have shown that LUBAC selectively activates the NF-kB pathway through linear ubiquitination of NEMO (In submission).2. We showed that the SCF^<Fbs1> ligase selectively recognizes the chitobiose portion of the N-linked sugar chain, which recognition mechanism is suitable for selective recognition of denatured glycoproteins (Nature, 2002; Nat. Strut. Mol. Biol., 2004).3. We have generated transgenic mice expressing IRP2 in neuron (IRP2 Tg) and analyzed the roles of oxidative stress generated by perturbation of iron metabolism in neurodegenerative disorders. Although massive iron accumulation was not observed, reactive Fe 2+ was accumulated in IRP2 Tg neurons, which provokes oxidative damages in those cells. Also, neuronal loss and ataxia was observed in aged IRP2 Tg mice (In submission).