E3泛素连接酶FEM1C识别底物的分子机制研究

泛素-蛋白酶体系统通过降解细胞内异常的蛋白从而维持体内蛋白质的稳态，其不稳定调控和人类疾病密切相关。在这个系统中E3泛素连接酶负责识别底物的降解信号并介导底物的泛素化降解。研究发现蛋白质的N末端氨基酸和C末端氨基酸都是潜在的蛋白质降解信号，可以被相应的E3泛素连接酶所识别。申请人之前的研究，阐述了N末端识别因子GID4能特异性识别底物N末端的脯氨酸，并通过N末端通路介导蛋白质降解的机制。而最近鉴定的FEM1C作为底物C末端的识别因子，其底物识别的分子机制并不清楚。本项目拟利用结构生物学解析FEM1C与底物的复合物结构，鉴定FEM1C识别底物的关键位点，并结合生物化学和细胞学分析阐明FEM1C介导底物识别和降解的分子机制。本项目的研究对于深入理解C末端通路中E3连接酶识别底物的机制具有重要意义，不仅有利于更多生理底物的鉴定，也为后续基于FEM1C的PROTACs药物小分子设计提供结构基础。

The ubiquitin (Ub)-proteasome system (UPS) is a critical protein degradation pathway that maintains protein homeostasis by eliminating damaged, misfolded or unnecessary proteins. Aberrations of the UPS associated proteins contribute to many different human diseases, including neurodegeneration and cancers. In the UPS, the E3 Ub ligases are responsible for recognizing substrates’ degradation signals (degrons) and delivering into proteasome, leading to their ultimate destructions. The N-degrons and C-degrons have been identified as essential degradation signals that can be recognized by specific E3 ubiquitin ligases. We have delineated the molecular mechanism behind human GID4-mediated recognition of N-terminal proline degron in the Pro/N-degron pathway. FEM1C, as a new substrate receptor, is able to recognize the C-degron, but its molecular mechanism of substrate recognition remains largely elusive. Here, we intend to employ X-ray crystallography to determinate the crystal structure of FEM1C in complex with C-degrons and present the detailed substrate-binding sites of FEM1C. Together with our biochemical and cellular studies will further elucidate the molecular mechanism of C-degron substrate recognition by FEM1C. This study will be essential to extend our understanding of the molecular mechanism of substrate recognition by E3 ligases in the C-degron pathway, and facilitate to identify bona fide substrates as well as develop structure-based PROTAC (proteolysis targeting chimera) degraders based on FEM1C.