基于磷脂纳米盘（Nanodiscs）体系的G蛋白偶联受体激活过程的构象变化研究

GPCR enzymology has been hampered by their special structures and has necessitated the use of model membranes. However, current model membranes suffer from problems of surfactants usage and instability. The long-time interactions between surfactants and GPCR often result in the instability, inactivity of GPCR and the independence of membrane protein structure and function as well. In addition, the transitional mechanisms of GPCR from a silent inactive state to an active state remain unclear，though GPCR have been widely applied as drug targets. In the present project, CCR3 will be chosen as the model GPCR, which is directly involved in human allergic diseases. After being recombinant expressed and purified using ultrafiltration, it will be assembled into phospholipid bilayer Nanodiscs by the optimization of multisystem of CCR3, membrane scaffold protein and phospholipid. The agonist-induced conformational transition and dynamics of CCR3 will studied using single molecular fluorescence resonance energy transfer, which will provide detailed insight into the dynamic process of biased agonist-induced CCR3 activation. The intermediate conformations of CCR3 will be also determined to provide basic information on the mechanism of CCR3 activation and to lay the theoretical foundation of a safe and effective drug design.

由于GPCR结构的特殊性，使得其结构生物学研究必需在模拟膜环境中进行，然而现有模拟生物膜体系中表面活性剂的使用，会造成GPCR结构的不稳定，甚至变性失活，导致解析的蛋白质结构与其功能状态无关。此外，尽管GPCR作为药物靶点已被广泛应用，但人们对于GPCR如何从非活性状态转变为活性状态的激活机制尚不清楚。 本项目拟选择与人类过敏性疾病密切相关的CCR3作为研究对象，在实现其重组表达及超滤分离的基础上，通过对CCR3、膜脚手架蛋白、磷脂等多元体系自组装过程的优化，实现CCR3在新型模拟生物膜Nanodiscs体系中的组装；利用单分子荧光共振能量转移（smFRET）技术，考察CCR3与不同配体作用下的构象变化及其动力学参数，为CCR3特异性激活的动态过程提供基础信息；同时通过对不同配体作用下CCR3中间态构象的表征，阐明 CCR3选择性激活的分子机制，为更安全高效的药物设计奠定理论基础。

本项目以G蛋白偶联受体CCR3作为研究对象，建立并系统研究了以磷脂纳米盘（Nanodiscs）为模拟生物膜的膜蛋白组装技术，及以荧光共振能量转移（FRET）技术为基础的膜蛋白构象检测方法。首先，利用构建的重组菌，通过发酵、分离提取，制备出G蛋白偶联受体CCR3和膜脚手架蛋白MSP1、MSP2，并对它们的纯度和结构进行了表征；其次，系统优化了磷脂纳米盘Nanodiscs的组装条件，先后制备出未含有CCR3和含有CCR3的磷脂纳米盘，并对其粒径分布进行了分析；再次，对组装到磷脂纳米盘中的CCR3的生物活性进行了检测，同时考察了CCR3跨膜多肽与折叠助剂GroEL之间的相互作用；最后，利用FRET技术对CCR3与配体结合过程中的构象变化进行了分析。本项目的研究成果解决了现有模拟生物膜无法满足膜蛋白稳定性要求和膜蛋白构象检测方面的关键技术问题，同时为其他种类G蛋白偶联受体的Nanodiscs组装及构象变化研究提供科学依据。