高尔基体结构蛋白GRASP55参与膜融合的功能鉴定和调控机制研究

高尔基体是细胞蛋白质运输及修饰中心，它不仅在生理条件下高度动态，在接受外界刺激或病理条件下，其结构与功能都能做出应激反应，因此高尔基体还被视为信号中转站。GRASP55是维持高尔基体扁平囊膜堆叠结构以及保证蛋白质糖基化精确修饰的重要结构蛋白。我们的前期研究意外发现GRASP55能够通过其O-GlcNAc糖基化修饰水平感受外界刺激，改变与其他蛋白如自噬体蛋白LC3的结合能力来调控细胞自噬进程，显示GRASP55是高尔基体上接受外界信号的关键分子。因此，本项目将深入研究GRASP55在细胞自噬中与自噬成熟分子机器的相互作用及调控机制，并进一步系统性的研究GRASP55在接受外界刺激后参与其他细胞器膜融合的新的分子机制，积极探索高尔基体参与细胞内外环境变化引起的细胞器互作的动态调控机制。

The Golgi apparatus is a central intracellular membrane organelle with key functions in trafficking and processing of newly synthesized membrane and secretory proteins. The Golgi structure is dynamic but tightly regulated in physiological conditions, and its structure and function is often disrupted under certain stresses and pathological conditions. Therefore, the Golgi has been more recently recognized as a hub of signaling pathways. The Golgi ReAssembly Stacking Protein GRASP55 is best characterized for its roles in Golgi structure formation, including stacking and ribbon linking. Knockdown or knockout of GRASP55 impairs proper glycosylation of membrane and secretory proteins. More recently, our study discovered that GRASP55 regulate autophagy upon energy deprivation. Under growth condition, GRASP55 is O-GlcNAcylated and localizes on Golgi membranes for stacking. However, upon glucose starvation, GRASP55 is de-O-GlcNAcylated, which allows it to translocate to the interface between autophagosomes and lysosomes, where it interacts with LC3 and LAMP2 to facilitate autophagosome-lysosome fusion. Therefore, GRASP55 acts as an energy sensor on the Golgi and regulates autophagy. In this proposal, we plan to study the interaction and regulation between GRASP55 and molecular machineries involved in autophagosome maturation, aiming to investigate the novel mechanism of GRASP55 in membrane fusion. Furthermore, we will determine the role of GRASP55 in other membrane fusion process by unbiased and systematic analysis of GRASP55 interactome under stress conditions. We believe that our study will provide new information on how GRASP55 and the Golgi apparatus sense the energy level and regulate the dynamics of other membrane organelles in stress response.