Cellular protein maturation and degradation

 描述(申请人提供)：内质网(ER)中蛋白质成熟步骤的保真度通过质控过程进行监测，质控过程质疑蛋白质副产物的结构完整性，并允许正确折叠的蛋白质进一步通过 通过分泌途径。相反，非天然蛋白质的目标是内质网保留，以便可以修复这种异常，或者如果无法修复，则选择用于降解和成分循环。一个组织良好的大分子复合体网络控制着内质网的过程。碳水化合物结合(或凝集素)伴侣蛋白，钙粘蛋白和钙网蛋白，通过以区域特异性的方式选择性地与成熟蛋白质上的单糖化侧链结合，指导分泌途径货物的折叠和运输。这些伴侣可以控制折叠反应的轨迹和蛋白质通过分泌途径的流动。因此，通过内质网的各种蛋白质的适当成熟和流量在很大程度上是由它们的糖基化状态控制的。这些问题有多重要 在自然环境中添加标签是ER的一个突出问题，目前还很差 明白了。内质网转运蛋白的糖基化状态由尿苷二磷酸-葡萄糖(UDP-GLC)：糖蛋白葡萄糖转移酶1(UGGT1)控制，它选择性地修饰未糖化的未成熟和非天然客户，以支持持久的伴侣结合和内质网滞留。我们的主要假设是UGGT1作为中央质量控制门卫，控制哺乳动物分泌途径中数千种底物的折叠和通过。虽然UGGT1已被广泛研究，使用纯化和工程组件分离，但对它及其同系物(UGGT2)在活细胞中的活性知之甚少。这项建议的重点是了解行动机制和 UGGT蛋白在其自然环境--内质网管腔中的作用。该项目的长期目标是了解质量控制系统帮助复杂蛋白质折叠的机制，并评估成熟过程的保真度，以调节通过分泌途径的运输。在三个目标(AIMS)中提出的研究将使人们更深入地了解UGGT如何选择要修改的货物，以及它们如何通过分泌途径控制它们的通量(目标1)。这些研究将包括如何从凝集素伴侣结合循环中提取客户并选择进行销毁(目标2)，以及如何在ER内组织质量控制机制以维持细胞动态平衡(目标3)。该项目的成功完成将有助于更好地了解蛋白质质量控制的基本机制，并对针对越来越多的构象疾病制定治疗策略具有潜在的影响。

 DESCRIPTION (provided by applicant): The fidelity of the protein maturation steps in the endoplasmic reticulum (ER) is monitored by a quality control process that interrogates the structural integrity of the protein byproducts, and allows properly folded proteins to pass further through the secretory pathway. In contrast, non-native proteins are targeted for ER retention so that the aberration can be repaired, or if irreparable, selected for degradation and the recycling of components. A well-organized network of macromolecular complexes controls the processes of the ER. The carbohydrate binding (or lectin) chaperones, calnexin and calreticulin, direct the folding and trafficking of secretory pathway cargo by selectively binding to monoglucosylated side chains on maturing proteins in a region-specific manner. These chaperones can control the trajectory of the folding reaction and the flow of proteins through the secretory pathway. Therefore, the proper maturation and flux of the enormously diverse range of proteins that passage through the ER is in large part controlled by their glucosylation state. How these critical tags are added in the natural setting of the ER is an outstanding question that is currently poorly understood. The glucosylation status of ER-trafficked proteins is controlled by uridine diphosphate-glucose (UDP-Glc): glycoprotein glucosyltransferase 1 (UGGT1), which selectively modifies unglucosylated immature and non-native clients to support persistent chaperone binding and ER retention. Our main hypothesis is that UGGT1 serves as the central quality control gatekeeper that controls folding and the passage of thousands of substrates in the mammalian secretory pathway. Although UGGT1 has been studied extensively in isolation using purified and engineered components, little is known about it, and its homologue (UGGT2), activity in live cells. The focus of this proposal is to understand the mechanism of action and the roles of the UGGT proteins in their natural environment, the ER lumen. The long-term goal of this project is to understand the mechanism by which the quality control system aids the folding of complex proteins and evaluates the fidelity of the maturation process to regulate trafficking through the secretory pathway. The studies proposed in three aims will provide a deeper understanding of how the UGGTs select cargo for modification and how they control their flux through the secretory pathway (aim 1). These studies will include how clients are extracted from the lectin chaperone binding cycle and selected for destruction (aim 2), and how the quality control machinery is organized within the ER to maintain cellular homeostasis (aim 3). RELEVANCE Successful completion of this project will lead to a better understanding of the fundamental mechanism of protein quality control, and have a potential impact on the development of therapeutic strategies directed towards the growing number of conformational diseases.