MAGI2介导的蛋白复合物在神经突触发育与信号转导中的结构与功能研究

Synaptic development and signalling transduction are essential for various biological processes in human being.The postsynaptic density (PSD) is located at the postsynaptic side of excitatory synapse, which has pivotal roles in orchestrating synaptic structure and function. Membrane-associated guanylate kinases (MAGUKs) are a family of scaffold proteins that are highly enriched in synapses and are responsible for organizing the numerous protein complexes required for synaptic development and plasticity. Mutations in genes encoding MAGUKs and their interacting proteins can cause a broad spectrum of human psychiatric disorders. MAGI, one of the most important members of MAGUK family scaffold protein, mediates signalling pathway in PSD via protein complex MAGI2/SAPAP/Shank, which is essential for the plasticity of synapse. However, little is known about how MAGI2-mediated complex assembles. Here, we plan to systematically study the molecular details of MAGI2-mediated protein complex using biochemical and structural tools. In addition, we will study the function of MAGI2-mediated protein complex in regulating the formation and dynamic changes in PSD in vivo. We hope that our biochemical and structural discoveries will largely improve our understanding the molecular basis of PSD assembly and dynamics and provide valuable information for the drug design for psychiatric disorders.

神经系统的正常发育及信号传导是人类完成各项生理活动的基础。神经信号的精确传导受到神经突触后膜附近的突触后致密区（PSD）的精密调控。研究表明，MAGUK家族蛋白在建立与维持神经突触连接、调节PSD的动态组成过程中发挥着重要的作用，其功能失调会导致一系列精神疾病的发生。MAGUK家族成员MAGI2介导的蛋白复合物（MAGI2/SAPAP/Shank）能够将神经信号从受体传导到细胞骨架，调控神经信号转导可塑性。该蛋白复合物功能的缺失将导致精神分裂症、躁郁症、自闭症及强迫症的发生。目前MAGI2介导的蛋白复合物的分子组装机制尚不明确。本项目计划研究该蛋白复合物的相互作用机制、解析其三维结构，并利用小鼠海马神经元细胞研究其在树突棘形态变化及信号转导过程中的作用机理。研究成果将为全面了解MAGUK家族蛋白在调控神经信号传导过程中的作用提供结构信息并为治疗相关神经疾病的药物的设计与开发提供理论基础。

MAGI家族支架蛋白通过其多个结构域在细胞连接(如神经突触和肾小球滤过屏障裂孔隔膜)组织多种信号转导复合物发挥生物学功能，其功能缺失与神经疾病及肾病综合征的发生发展密切相关。了解其结构域识别下游信号蛋白的基本规律，对于我们全面阐释相关信号转导机制及制定精准的疾病防控策略提供坚实理论基础。. 通过本项目的实施，我们发现MAGI2的PDZ0-GK串联结构域能够特异的识别磷酸化多肽（如磷酸化SAPAP多肽,pSAPAP）。MAGI2/pSAPAP复合物结构阐释了这一磷酸化相互作用的分子机制，并总结出MAGI2 PDZ0-GK识别目标蛋白的保守特征序列。根据该序列，我们鉴定出全新的MAGI2的目标蛋白如Ephexin4和SGEF等。进一步，我们验证了MAGI2/SGEF复合物在足细胞迁移过程的重要功能。该工作极大拓展了人们对MAGI2家族蛋白介导的信号复合物的认知。此外，我们还研究了MAGI2/SAPAP复合物下游的GIT-PIX复合物自发形成相分离调控神经突触发育的分子机理；探索了Ephexin4 RhoGEF的自抑制和激活的结构生物学基础。