Structural Basis of Signal Instigation Through Metabotropic Glutamate Receptors

摘要 代谢性谷氨酸受体(MGluRs)属于G蛋白C家族 偶联受体(GPCRs)对神经元兴奋性、突触的重要调节作用 氨基酸和兴奋性的识别传递和可塑性 神经递质谷氨酸。许多中枢神经系统疾病都与 通过谷氨酸能系统的神经元兴奋性的改变。因此， MGluRs一直是一项巨大的药物发现努力的主题，因为它们 代表了治疗众多生理性疾病的主要治疗靶点 功能障碍以及神经退行性疾病和神经精神疾病。分开 从典型的七个跨膜螺旋(7TM)结构域来看，mGluRs还 包括一个较大的细胞外捕蝇器(VFT)结构域，该结构域构成 谷氨酸结合位点和半胱氨酸富含结构域(CRD)将VFT连接到 7Tm。谷氨酸与胞外VFT结构域的结合触发了大量的 VFT结构域从开放到封闭的构象变化 构象。胞外区的这种蛤壳状闭合导致了 神经节细胞内侧G蛋白的受体结合和激活 跨膜结构域。受体激活的G蛋白然后作用于 增强或抑制二级信使信号级联。尽管强度很大 努力，跨细胞膜的变构通讯机制，通过 由于缺乏完整的结构信息，mGluRs仍然是个谜。 长度蛋白质。在这里，我们建议应用单粒子低温电子 显微镜(冷冻-EM)可视化，以表征结构 激活和失活状态以及复合体中的mGluR5和mGluR2 以及它们的同源G蛋白。所获得的结构将用于分子 旨在揭示构象分子基础的动力学模拟 与信号煽动或沉默相耦合的转换。鉴于mGluR是 包括帕金森氏症在内的几种中枢神经系统疾病的重要药物靶点， 脆性X综合征/自闭症谱系障碍，精神分裂症，认知， 上瘾、抑郁、焦虑和痛苦，所获得的结果都将是深刻的 生物医学的兴趣，并将成为设计新的治疗方法的基础 对抗神经性疾病的策略。

Abstract Metabotropic Glutamate receptors (mGluRs) belong to the Family C of G-protein coupled receptors (GPCRs) and critically regulate neuronal excitability, synaptic transmission and plasticity through recognition of the amino acid and excitatory neurotransmitter glutamate. Many disorders of the CNS have been linked to alterations in neuronal excitability via the glutamatergic system. Accordingly, mGluRs have been the subject of an enormous drug discovery effort as they represent major therapeutic targets for treating numerous physiological dysfunctions and for neurodegenerative and neuropsychiatric conditions. Apart from the prototypical seven transmembrane helix (7TM) domain, mGluRs also include a large extracellular `venus fly trap' (VFT) domain that constitutes the glutamate binding site and a cysteine rich domain (CRD) that links the VFT to the 7TM. Binding of glutamate to the extracellular VFT domain triggers a large conformational change in the VFT domains from an open to a closed conformation. This clam-shell like closure of the extracellular domain results in receptor engagement and activation of G-proteins on the intracellular side of the transmembrane domain. Receptor activated G proteins then act to either enhance or repress secondary messenger signaling cascades. Despite intensive efforts, the mechanism of allosteric communication across the cell membrane by the mGluRs remains enigmatic due to the lack of structural information on full- length proteins. Here we propose to apply single-particle cryo-electron microscopy (cryo-EM) visualization in order to characterize the structure of mGluR5 and mGluR2 in activated and inactivated states and also in complex with their cognate G-proteins. The obtained structures will be used for molecular dynamics simulations aiming to unravel the molecular basis for conformational transitions coupled to signal instigation or silencing. Given that mGluRs are important drug targets for several CNS conditions including Parkinson's disease, Fragile X syndrome/autism spectrum disorders, schizophrenia, cognition, addiction, depression, anxiety and pain, the results obtained will have profound biomedical interest and will form the basis for the design of novel therapeutic strategies against neurological disorders.