Cellular protein maturation and degradation

描述（由申请人提供）：本项目的总体目标是确定哺乳动物内质网（ER）中蛋白质质量控制的机制。拟议的研究将利用定义良好的哺乳动物细胞系统来确定异常的分泌货物是如何被选择和靶向破坏的，以及内质网内质量控制机制的组织如何协调蛋白质的转运和成熟。质量控制过程由一系列相互关联的步骤组成，包括对是否运输底物或将其转移以保留或降解内质网做出关键选择。绝大多数

DESCRIPTION (provided by applicant): The overarching goals of this project are to define mechanisms of protein quality control in the mammalian endoplasmic reticulum (ER). The proposed research will utilize well-defined mammalian cell systems to determine how aberrant secretory cargo is selected and targeted for destruction and how organization of the quality control machinery within the ER coordinates protein transit and maturation. The quality control process is comprised of a series of interlocking steps that involve making critical choices on whether to transport a substrate or divert it for ER retention or degradation. The vast majority of proteins that traverse the mammalian secretory pathway receive N-linked glycans that are added shortly after a consensus N- glycosylation site emerges into the ER lumen. The composition of N-glycans is dynamic because they act as signals to recruit factors that assist the protein maturation and quality control processes. N-glycans support recruitment of the carbohydrate binding chaperones calnexin and calreticulin, which bind to monoglucosylated side chains. Persistent lectin chaperone binding is directed by UDP-glucose: glycoprotein glucosyltransferase (UGT1). Although UGT1 has been studied in reconstituted systems, the cellular role of this critical ER factor is poorly defined. Mannose trimming is proposed to be involved in sorting aberrant proteins to the ER-associated degradation (ERAD) pathway as inhibition of mannosidase activity stabilizes ERAD substrates. However, many questions still remain about the role of mannose trimming in quality control. While the over expression of the ER mannosidase-like protein EDEM1 accelerates the turnover of glycosylated ERAD substrates, its role in the quality control and sorting processes is unclear. Our results indicate that EDEM1 serves as a central link to deliver defective cargo to an ERAD dislocation complex by possessing bipartite binding properties. Finally, the exquisite spatial organization of the ER contributes to the efficiencies by which the ER temporally coordinates processes including protein maturation, quality control and ERAD. Tetratricopeptide repeat (TPR) domains are universal adaptor motifs that support protein-protein interactions involved in post-translational translocation and the formation of chaperone complexes within the cell. We have recently discovered a family of ER resident TPR-rich proteins that we propose to play a role in ER organization. This research proposal has three aims: (1) to define how UGT1 participates in ER quality control in a cellular context; (2) to elucidate the role and mechanism of action for EDEM1 in the ERAD process; and (3) to determine how novel TPR-containing proteins function in ER organization and homeostasis. A deeper knowledge of the processes in the early secretory pathway has widespread implications for understanding basic cell biology and the etiology of a range of human maladies as a growing number of diseases states are caused by defects in protein maturation and ER homeostasis.