Protein degradation and cholesterol regulation

描述（由申请人提供）：HMG-CoA还原酶（HMGR）是甾醇合成的限速酶。HMGR是一种整合的膜蛋白，其响应于细胞对固醇的需求变化而通过ER相关降解或ERAD进行调节性降解。我们最初表明，酵母HMGR同工酶Hmg 2 p以类似于哺乳动物酶的方式进行调节，使我们能够利用酵母中独特的研究机会。Hmg 2 p通过HRD途径通过Hrdlp E3泛素连接酶的作用经历降解，并且固醇途径分子FPP调节HRD依赖性Hmg 2 p降解。HRD途径还在ER质量控制中起作用，编程破坏许多错误折叠的ER蛋白。因此，我们提出了调节的结构转换假说：FPP衍生的信号导致Hmg 2 p经历过渡到具有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，开发几种新的生化检测方法来直接解决这些问题。在目前的工作中，我们将1）继续我们的分析的HRD泛素连接酶复合物，2）分析的Hmg 2 p蛋白的特点，使其调节甾醇途径的信号，3）描绘的身份和行动的脂质信号控制Hmg 2 p进入HRD途径。4)研究Hmg 2 p ERAD所需的HRD途径底物的逆转位机制。hmg 2 p降解位于甾醇调节和蛋白质质量控制的界面。因此，我们的工作是相关的理解细胞控制固醇合成，和破坏错误折叠的蛋白质;两个领域的广泛和当前的医疗进口。

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.