The metabotropic glutamate (mGlu) receptors are class C G protein-coupled receptors (GPCRs) that modulate synaptic activity and plasticity throughout the mammalian brain. Signal transduction is initiated by glutamate binding to the venus flytrap domains (VFT), which initiates a conformational change that is transmitted to the conserved heptahelical domains (7TM) and results ultimately in the activation of intracellular G proteins. While both mGlu₁ and mGlu₅ activate Gα_q G-proteins, they also increase intracellular cAMP concentration through an unknown mechanism. To study directly the G protein coupling properties of the human mGlu₅ receptor homodimer, we purified the full-length receptor, which required careful optimisation of the expression, N-glycosylation and purification. We successfully purified functional mGlu₅ that activated the heterotrimeric G protein Gq. The high-affinity agonist-PAM VU0424465 also activated the purified receptor in the absence of an orthosteric agonist. In addition, it was found that purified mGlu₅ was capable of activating the G protein Gs either upon stimulation with VU0424465 or glutamate, although the later induced a much weaker response. Our findings provide important mechanistic insights into mGlu₅ G protein-dependent activity and selectivity.

中文翻译：

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洗涤剂纯化的人mGlu5受体与异源三聚体G蛋白Gq和Gs的直接偶联。

代谢型谷氨酸（mGlu）受体是CG类蛋白偶联受体（GPCR），可调节整个哺乳动物大脑的突触活性和可塑性。谷氨酸与维纳斯捕蝇器结构域（VFT）结合可启动信号转导，这可引发构象变化，该构象变化可传递至保守的七螺旋结构域（7TM），并最终导致细胞内G蛋白的活化。虽然两者的mGlu ₁和组mGlu ₅激活Gα _q G蛋白，它们也通过未知的机制增加细胞内cAMP浓度。直接研究人类mGlu ₅的G蛋白偶联特性受体同源二聚体，我们纯化了全长受体，需要仔细优化表达，N-糖基化和纯化。我们成功地纯化了激活异三聚体G蛋白Gq的功能性mGlu ₅。在没有正构激动剂的情况下，高亲和力激动剂-PAM VU0424465也激活了纯化的受体。另外，发现纯化的mGlu ₅在用VU0424465或谷氨酸刺激后能够激活G蛋白Gs，尽管后者诱导的应答弱得多。我们的发现为了解mGlu ₅ G蛋白依赖的活性和选择性提供了重要的机理见解。