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

项目总结/摘要 细胞不断响应生理信号和潜在的病理扰动。在 反应，蛋白质合成和蛋白质降解，后者主要由泛素驱动， 蛋白酶体系统，从而重塑细胞内蛋白质组。蛋白质周转的动力学决定了 对各种各样的信号或扰动的生理反应，并对人类产生重大影响 physiology.事实上，在泛素结合级联和26 S蛋白酶体的40多年的研究中， 已经阐明了泛素-蛋白酶体系统在几乎每一个细胞过程中的重要作用。的 蛋白质周转的主要原则是泛素化是底物标记所必需的， 26 S蛋白酶体是唯一降解泛素-蛋白质缀合物的蛋白酶体种类。虽然20 S 蛋白酶体形成26 S复合物的核心，但由于先前缺乏明确的 细胞中功能性20 S颗粒的证据，并且没有对20 S特异性底物靶向的洞察。我最近 发现了一种新的机制，通过一个高度专业化的20 S泛素独立的蛋白质周转 与神经元质膜紧密结合的蛋白酶体。这些神经细胞膜 蛋白酶体（NMP）直接与核糖体结合，降解约250-500个新生链底物 独立于泛素化。NMP降解跨膜底物，释放所得肽 碎片进入细胞外空间，诱导其他神经元的信号传导，因此代表了一种新的 神经调节机制。在这里，我建议进行研究，为理解这一点奠定必要的基础。 蛋白质周转的新范例。在我的第一个目标中，我将确定NMPs如何与质膜结合 并揭示这种膜复合物的分子组成。在第二个目标中，我将确定 获得了NMP介导的新生链降解的特异性。在最后的目标中，我将深入了解 NMP介导的降解调节的生物过程。所提出的研究是有意义的 因为它开辟了一个新的研究领域，研究神经元中的非规范蛋白质周转。这项工作将产生 了解NMP介导的降解是如何编码的工具和必要的机制见解， 与脊椎动物的神经系统有关。这不仅将揭示新的机制， 通过NMPs的神经调节，而且还提供了与蛋白质周转异常相关的框架， 是多种人类神经病理学的基础

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.