MAGI介导的蛋白复合物在肾病综合症发病机制中的结构与功能研究

Nephrotic syndrome (NS) is a heterogeneous group of disorders characterized by heavy proteinuria with hypoalbuminemia,edema and dyslipidemia.Urinary losses of macromolecules reflect a dysfunction of the normally highly permselective glomerular filtration barrier.As one of the most important barrier, the Podocyte is a highly specialized epithelial cell covering the outside of the glomerular capillary. The slit diaphragm (SD) is a highly specialized cell–cell junction of podocytes that interconnects adjacent foot processes.In the last decade, studies of familial cases of steroid-resistant NS have led to the identification of highly conserved cell polarity protein complexes which are involved in the assembly and dynamic regulation of SD. MAGI, one of the most important members of MAGUK family scaffold protein, mediates signalling pathway in SD via protein complexes including MAGI/Nephrin and MAGI/α-actinin4, which is essential for the normal function of SD. However, little is known about how MAGI-mediated complexes assembles. Here, we plan to systematically study the molecular details of MAGI/Nephrin and MAGI/α-actinin4 interactions using biochemical and structural tools. In addition, we will study the function of MAGI-mediated protein complex in regulating the formation and dynamic changes in SD in vivo using the MDCK cell system. We hope that our biochemical and structural discoveries will largely improve our understanding the molecular basis of SD assembly and dynamics and provide valuable information for the drug design for Nephrotic syndrome.

肾病综合症是一组以大量蛋白尿为主要症状的临床综合性肾脏功能失调疾病，其主要致病原因与肾小球滤过屏障结构和功能的异常密切相关。肾小球裂孔隔膜是肾脏阻止血液蛋白渗漏进入尿液的最主要的屏障。研究表明，大量保守的与细胞连接及细胞极性相关的蛋白复合物参与裂孔隔膜的构成并调节其动态平衡。MAGUK家族蛋白，特别是MAGI介导的蛋白复合物（MAGI/Nephrin, MAGI/α-actinin4）能够有效的将裂孔隔膜的细胞粘连分子与细胞骨架系统有机联系起来，稳定并调控细胞连接。但MAGI介导的蛋白复合物的分子组装机制尚不明确。本项目计划详细研究蛋白复合物的相互作用机制、解析蛋白复合物的三维结构，并利用MDCK细胞株研究其在细胞连接稳定及动态变化过程中的作用机理。研究成果将为全面了解肾小球滤过系统的分子机制提供结构信息并为治疗肾病综合症相关的药物的设计与开发提供理论基础。

肾病综合症与肾小球滤过屏障结构和功能的异常密切相关。裂孔隔膜是肾小球滤过屏障中最重要的结构。大量细胞极性蛋白复合物（包括MAGUK家族蛋白）参与裂孔隔膜的组装。本项目拟通过对MAGUK家族成员MAGI介导的蛋白复合物的生化与结构研究，为全面了解肾小球滤过系统的分子机制提供结构信息，并为治疗肾病综合征相关药物的设计与开发提供理论基础。. 通过本项目的实施，结果表明MAGI1的PDZ3结构域特异识别Nephrin羧基端的PDZ结构域结合序列（PBM），MAGI1-PDZ3/Nephrin-PBM蛋白复合物晶体结构阐释了MAGI1作为关键支架蛋白在组装裂孔隔膜中的分子机制。