Molecular determinants of neuronal protein homeostasis through plasma membrane-localized proteasome complexes.

项目摘要/摘要 细胞不断地对生理信号和潜在的病理性扰动做出反应。在……里面 反应、蛋白质合成和蛋白质降解，后者主要由泛素- 蛋白酶体系统，相互重塑细胞内蛋白质组。蛋白质周转的动态决定了 对各种信号或干扰的生理反应，对人类有重大影响 生理学。事实上，四十多年来对泛素结合级联和26S蛋白酶体的研究 阐明了泛素-蛋白酶体系统在几乎每一个细胞过程中的重要作用。这个 蛋白质周转的主要原则是泛素化是底物标记所必需的，而且 26S蛋白酶体是唯一能降解泛素-蛋白质结合物的蛋白酶体。虽然是20多岁 蛋白酶体构成了26S复合体的核心，由于之前缺乏明确的研究，它们在很大程度上仍然没有得到充分的研究 有证据表明细胞中存在功能正常的20S颗粒，但没有深入了解20S特定的底物靶向。我最近 发现了一种通过高度专业化的20多岁的泛素不依赖的蛋白质周转的新机制 与神经细胞质膜密切相关的蛋白酶体。这些神经细胞膜 蛋白酶体(NMP)直接与核糖体结合，降解~250-500个新生链底物 不依赖泛素化。NMP通过膜降解底物，释放产生的多肽 碎片进入细胞外空间，在其他神经元中诱导信号传递，因此代表着一种新的 神经调节机制。在这里，我提出的研究将为理解这一点奠定必要的基础 蛋白质周转的新范式。在我的第一个目标中，我将确定NMP如何与质膜相关联 并揭示了这种膜复合体的分子组成。在第二个目标中，我将确定如何 实现了NMP介导的初生链降解的特异性。在最终目标中，我将深入了解 NMP介导的降解调节的生物过程。这项拟议的研究具有重要意义 因为它开启了研究神经元中非标准蛋白质周转的新领域。这项工作将产生 了解NMP介导的降解是如何在和 与脊椎动物神经系统相关。这不仅将揭示新的机制 通过NMP进行神经调节，但也提供了与蛋白质周转异常相关的框架， 是多种人类神经病变的基础。

PROJECT SUMMARY / ABSTRACT Cells continuously respond to physiological signals and potentially pathological perturbations. In response, protein synthesis and protein degradation, the latter of which is predominantly driven by the ubiquitin- proteasome system, reciprocally remodel the intracellular proteome. The dynamics of protein turnover determine the physiological response to a large diversity of signals or perturbations and have major ramifications on human physiology. Indeed, over four decades of work on the ubiquitin conjugating cascade and the 26S proteasome has elucidated essential roles for the ubiquitin-proteasome system in nearly every cellular process. The prevailing principles in protein turnover have been that ubiquitylation is necessary for substrate tagging and that the 26S proteasome is the only proteasome species that degrades ubiquitin-protein conjugates. Though 20S proteasomes form the core of the 26S complex, they remain largely understudied because of a prior lack of clear evidence for functional 20S particles in cells and no insight into 20S-specific substrate targeting. I recently discovered a new mechanism of ubiquitin-independent protein turnover through a highly specialized 20S proteasome that is tightly associated with neuronal plasma membranes. These neuronal membrane proteasomes (NMPs) directly associate with ribosomes to degrade ~250-500 nascent chain substrates independent of ubiquitylation. The NMP degrades substrates across the membrane, releasing resulting peptide fragments into the extracellular space that induce signaling in other neurons, and therefore represents a new mechanism of neuromodulation. Here, I propose studies that will lay the foundation necessary to understand this new paradigm in protein turnover. In my first aim, I will identify how NMPs associate with the plasma membrane and reveal the molecular components of this membrane complex. In the second aim, I will determine how the specificity of NMP-mediated degradation of nascent chains is achieved. In the final aim, I will gain insights into the biological processes that NMP-mediated degradation regulates. The proposed research is significant because it opens a new field of research into non-canonical protein turnover in neurons. This work will generate the tools and mechanistic insight necessary to understanding how NMP-mediated degradation is codified in and relevant to the vertebrate nervous system. This will not only shed light onto the new mechanism of neuromodulation through NMPs, but also provide a framework relevant to abnormalities in protein turnover that underlie multiple human neuropathologies.