EGOC复合物调控TORC1信号通路的分子机制

真核生物TORC1通过响应环境中营养和能量水平，调节细胞合成代谢和分解代谢的动态平衡，对生长和增殖相关生命活动进行调控。在哺乳动物中氨基酸通过感应蛋白激活小G蛋白Rag，并与Ragulator复合物协同介导mTORC1在溶酶体上的定位和激活。但是氨基酸是如何调控Rag-Ragulator复合物的分子机制还不清晰。前期我们发现酵母中TORC1信号通路的调控机制与哺乳动物有相似性但又有差异：由Ego1、Ego2和Ego3组成的复合物与Rag同源蛋白Gtr1和Gtr2组装成EGOC复合物，通过在内吞体和囊泡膜上的不同定位，调控TORC1信号通路的功能。本项目拟以酵母TORC1信号通路为研究对象，运用生物化学和结构生物学等方法，寻找和鉴定EGOC的相互作用蛋白，研究这些蛋白复合物的结构与功能，揭示酵母中氨基酸对TORC1信号通路的调控机制，为哺乳动物中mTORC1信号通路的调控机制研究提供启示。

In response to environmental inputs, including nutrients and growth factors, the eukaryotic mammalian/mechanistic target of rapamycin complex 1 (mTORC1) balances the anabolic processes and the catabolic degradation pathways in cell, and regulates biosynthesis of proteins, lipids, and nucleotides. Amino acids are particularly potent signaling molecules for activating mTORC1 signaling. In higher eukaryote, amino acid sensing proteins mediate the activation of Rag GTPases, which further recruit mTORC1 to the lysosomal membrane with the scaffold complex of Ragulator. After that, the kinase activity of mTORC1 is stimulated by small GTPase Rheb. However, the mechanisms for the activation of the Rag-Ragulator complex and rendering the signals to downstream mTORC1 remain unclear. Previously, we and other groups found that most of the mTORC1/TORC1 pathway components are well conserved in mammalian and yeast. The yeast EGO-TC, consisting of Ego1, Ego2 and Ego3, interacts with Gtr1-Gtr2 to form a pentameric EGO complex (EGOC). The EGOC assembles at the surfaces of vacuoles and perivacuolar endosomes and regulates spatially distinct pools of TORC1 which phosphorylate functionally divergent effectors. The structural and functional data combined demonstrate that the EGOC and the Ragulator-Rag complex are structurally conserved, and that the EGO-TC is essential and sufficient to recruit Gtr1-Gtr2 to vacuolar and endosomal membranes to ensure appropriate mTORC1 signaling. In this project, we will use a combination of biochemistry, molecular biology, and cell biology to identify potent effector(s) and activator(s) of EGOC. The succedent structural and functional studies might elucidate the regulatory mechanism of how TORC1 responds to environmental amino acid level in yeast, and provide biological implications for the mechanism of mTORC1 regulation in mammalian.