Partitioning of Misfolded Membrane Proteins Between Different Degradatory Fates

描述（由申请人提供）：错误折叠蛋白质和蛋白质聚集体的积累可以扰乱蛋白质稳态并导致广泛的细胞损伤。细胞有各种质量控制（QC）系统来识别和处理错误折叠和聚集的蛋白质。这些质量控制系统的故障可能导致许多疾病，包括与年龄有关的疾病阿尔茨海默病、帕金森病和白内障。细胞因子，包括分子伴侣和E3泛素连接酶，识别错误折叠的蛋白质，并试图重新折叠蛋白质或通过蛋白酶体靶向降解它们。此外，已知存在一种通过自噬对蛋白质和聚集体进行选择性质量控制的不明确机制。确定蛋白质QC的机制是很重要的，这样我们就可以深入了解蛋白质错误折叠疾病的细胞基础。许多疾病是由膜蛋白的突变引起的，这些突变破坏了它们的跨膜结构域，导致它们错误折叠，并被质量控制机器降解。促性腺激素释放激素受体（GnRHR）是一种G蛋白偶联受体（GPCR），不含胞质或胞外结构域，仅由7个跨膜结构域组成。因此，GnRHR生物发生的研究为理解错误折叠TM蛋白QC的基本原理提供了机会。此外，有23种已知疾病（促性腺功能减退症）引起GnRHR突变，其中许多导致错误折叠。细胞培养模型的初步数据表明，各种GnRHR突变体的质量控制途径非常不同。S168R GnRHR通过RMA1 E3泛素连接酶复合物进行QC，并被蛋白酶体降解。与之形成鲜明对比的是，E90K GnRHR通过自噬降解。这是质膜蛋白在自噬和蛋白酶体质量控制之间选择性分离的第一个例子。在Aim 1中，我将确定错误折叠的S168R GnRHR是如何被识别并靶向蛋白酶体降解的。在Aim 2中，我将确定为什么以及如何选择E90K GnRHR进行自噬而不是蛋白酶体质量控制。这里获得的结果将极大地促进我们对细胞如何识别跨膜跨越中的缺陷以及这些蛋白质被降解的机制的了解。

DESCRIPTION (provided by applicant): The accumulation of misfolded proteins and protein aggregates can perturb protein homeostasis and cause extensive cellular damage. The cell has various quality control (QC) systems to recognize and dispose of misfolded and aggregated proteins. Failure of these QC systems can result in number of diseases, including the age-related diseases Alzheimer's disease, Parkinson's disease, and cataract. Cellular factors, including molecular chaperones and E3 ubiquitin ligases, recognize misfolded proteins and either attempt to refold the proteins or target them for degradation via the proteasome. Additionally, a poorly defined mechanism for selective quality control of proteins and aggregates via autophagy is known to exist. It is important to define the mechanisms for protein QC so that we may gain insight into the cellular basis of protein misfolding diseases. A number of diseases are caused by mutations to membrane proteins that disrupt their transmembrane domains, causing them to misfold, and be degraded by quality control machinery. Gonadotropin releasing hormone receptor (GnRHR), a G protein-coupled receptor (GPCR), contains no cytoplasmic or extracellular domains and is comprised of only a seven-transmembrane span domain. Therefore, study of GnRHR biogenesis provides an opportunity for understanding basic principles for QC of misfolded TM proteins. In addition, there are twenty-three known disease (hypogonadotropic hypogonadism) causing GnRHR mutations and many cause misfolding. Preliminary data in a cell culture model indicates that quality control pathways for various GnRHR mutants are very different. S168R GnRHR undergoes QC via the RMA1 E3 ubiquitin ligase complex and is degraded by the proteasome. In stark contrast, E90K GnRHR is degraded by autophagy. This represents the first example of a plasma membrane protein being selectively partitioned between autophagic and proteasomal quality control. In Aim 1, I will determine how misfolded S168R GnRHR is recognized and targeted for proteasomal degradation. In Aim 2, I will determine why and how E90K GnRHR is selected for autophagy instead of proteasomal quality control. The results obtained here will greatly further our knowledge of how the cell recognizes defects in transmembrane spans and the mechanisms by which those proteins are degraded.