Protein degradation and cholesterol regulation

描述(申请人提供)：HMG-CoA还原酶(HMGR)是甾醇合成的限速酶。HMGR是一种完整的膜蛋白，它通过内质网相关降解或ERAD来调节降解，以响应细胞对甾醇不断变化的需求。我们最初证明，酵母HMGR同工酶Hmg2p的调节方式与哺乳动物的酶相似，使我们能够利用酵母中独特的研究机会。Hmg2p通过Hrdlp E3泛素连接酶的作用通过HRD途径进行降解，而固醇途径分子FPP调节HRD依赖的Hmg2p的降解。HRD途径也在内质网质量控制中发挥作用，编程破坏许多错误折叠的内质网蛋白。因此，我们提出了调控的结构转变假说：FPP来源的信号导致Hmg2p经历转变为具有HRD质量控制底物特征的结构。我们一直在测试这个模型，同时增加我们对HRD途径的理解，开发几种新的生化分析方法来直接解决这些问题。在目前的工作中，我们将1)继续我们对HRD泛素连接酶复合体的分析，2)分析Hmg2p蛋白的特征，使其能够通过类固醇途径信号进行调节，3)描述控制Hmg2p进入HRD途径的脂信号的身份和作用。4)研究Hmg2p ERAD所需HRD途径底物的逆转位机制。Hmg2p的降解位于固醇调节和蛋白质质量控制的交界处。因此，我们的工作与理解细胞控制类固醇合成和破坏错误折叠的蛋白质都是相关的，这两个领域是广泛的和当前的医学意义。

DESCRIPTION (provided by applicant): HMG-CoA reductase (HMGR) is the rate-limiting enzyme of sterol synthesis. HMGR is an integral membrane protein that undergoes regulated degradation by ER-associated degradation, or ERAD, in response to changing cellular demand for sterols. We originally showed that the yeast HMGR isozyme Hmg2p is regulated in a manner similar to the mammalian enzyme, allowing us to exploit unique study opportunities available in yeast. Hmg2p undergoes degradation by the HRD pathway, through the action of the Hrdlp E3 ubiquitin ligase, and the sterol pathway molecule FPP regulates HRD-dependent Hmg2p degradation. The HRD pathway also functions in ER quality control, programming the destruction of many misfolded ER proteins. Accordingly, we have proposed the structural transition hypothesis for regulation: that an FPP-derived signal causes Hmg2p to undergo transition to a structure with features of a HRD quality control substrate. We have been testing this model and at the same time increasing our understanding of the HRD pathway, developing several new biochemical assays to directly address these issues. In the current work we will 1) Continue our analysis of the HRD ubiquitin ligase complex, 2) Analyze the features of the Hmg2p protein that allow its regulation by sterol pathway signals, 3) Delineate the identity and action of the lipid signals that control Hmg2p entry into the HRD pathway. 4) Study the mechanism of retrotranslocation of HRD pathway substrates required for ERAD of Hmg2p. Hmg2p degradation lies at the interface of sterol regulation and protein quality control. Thus, our work is relevant both to understanding the cellular control of sterol synthesis, and the destruction of misfolded proteins; two areas of broad and current medical import.