PDF(Pubmed)
Abstract：
The metabotropic glutamate receptors (mGluRs) are neuromodulatory family C G protein coupled receptors which assemble as dimers and allosterically couple extracellular ligand binding domains (LBDs) to transmembrane domains (TMDs) to drive intracellular signaling. Pharmacologically, mGluRs can be targeted at the LBDs by glutamate and synthetic orthosteric compounds or at the TMDs by allosteric modulators. Despite the potential of allosteric compounds as therapeutics, an understanding of the functional and structural basis of their effects is limited. Here we use multiple approaches to dissect the functional and structural effects of orthosteric versus allosteric ligands. We find, using electrophysiological and live cell imaging assays, that both agonists and positive allosteric modulators (PAMs) can drive activation and internalization of group II and III mGluRs. The effects of PAMs are pleiotropic, boosting the maximal response to orthosteric agonists and serving independently as internalization-biased agonists across mGluR subtypes. Motivated by this and intersubunit FRET analyses, we determine cryo-electron microscopy structures of mGluR3 in the presence of either an agonist or antagonist alone or in combination with a PAM. These structures reveal PAM-driven re-shaping of intra- and inter-subunit conformations and provide evidence for a rolling TMD dimer interface activation pathway that controls G protein and beta-arrestin coupling.
摘要：
代谢型谷氨酸受体（mGluRs）是神经调节家族CG蛋白偶联受体，其组装为二聚体，并将细胞外配体结合域（LBD）变构偶联至跨膜结构域（TMD）以驱动细胞内信号传导。药理学上,mGluR可以通过谷氨酸和合成的正构化合物靶向LBD或通过变构调节剂靶向TMD。尽管变构化合物具有作为治疗药物的潜力,对其作用的功能和结构基础的理解是有限的。在这里，我们使用多种方法来剖析正构与变构配体的功能和结构效应。我们发现,使用电生理和活细胞成像测定，激动剂和正变构调节剂（PAMs）都可以驱动II和III组mGluR的激活和内化。PAMs的作用是多效性的，增强对正构激动剂的最大反应，并独立充当mGluR亚型的内化偏向激动剂。受此和亚基间FRET分析的启发，我们在激动剂或拮抗剂单独或与PAM联合存在的情况下测定mGluR3的低温电子显微镜结构。这些结构揭示了PAM驱动的亚基内和亚基间构象的重塑，并为控制G蛋白和β-抑制蛋白偶联的滚动TMD二聚体界面激活途径提供了证据。
