Metabotropic glutamate receptor 4 (mGlu₄) is one of eight mGlu receptors within the Class C G protein-coupled receptor superfamily. mGlu₄ is primarily localized to the presynaptic membrane of neurons where it functions as an auto and heteroreceptor controlling synaptic release of neurotransmitter. mGlu₄ is implicated in numerous disorders and is a promising drug target; however, more remains to be understood about its regulation and pharmacology. Using high-throughput sequencing, we have validated and quantified an adenosine-to-inosine (A-to-I) RNA editing event that converts glutamine 124 to arginine in mGlu₄; additionally, we have identified a rare but novel K129R site. Using an in vitro editing assay, we then validated the pre-mRNA duplex that allows for editing by ADAR enzymes and predicted its conservation across the mammalian species. Structural modeling of the mGlu₄ protein predicts the Q124R substitution to occur in the B helix of the receptor that is critical for receptor dimerization and activation. Interestingly, editing of a receptor homodimer does not disrupt G protein activation in response to the endogenous agonist, glutamate. Using an assay designed to specifically measure heterodimer populations at the surface, however, we found that Q124R substitution decreased the propensity of mGlu₄ to heterodimerize with mGlu₂ and mGlu₇. Our study is the first to extensively describe the extent and regulatory factors of RNA editing of mGlu₄ mRNA transcripts. In addition, we have proposed a novel functional consequence of this editing event that provides insights regarding its effects in vivo and expands the regulatory capacity for mGlu receptors.

中文翻译：

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mGlu4 RNA编辑的调控和功能后果

代谢型谷氨酸受体 4 (mGlu ₄ ) 是 CG 类蛋白偶联受体超家族中的八种 mGlu 受体之一。mGlu ₄主要定位于神经元的突触前膜，在那里它作为一种自体和异体受体控制神经递质的突触释放。mGlu ₄与许多疾病有关，是一种很有前途的药物靶点；然而，关于它的调节和药理学还有更多的需要了解。_{使用高通量测序，我们验证并量化了将 mGlu 4}中的谷氨酰胺 124 转化为精氨酸的腺苷到肌苷 (A-to-I) RNA 编辑事件; 此外，我们还发现了一个罕见但新颖的 K129R 位点。然后，我们使用体外编辑试验验证了允许 ADAR 酶进行编辑的前 mRNA 双链体，并预测了它在哺乳动物物种中的保守性。mGlu ₄蛋白的结构模型预测 Q124R 取代发生在受体的 B 螺旋中，这对受体二聚化和激活至关重要。有趣的是，受体同源二聚体的编辑不会破坏 G 蛋白对内源性激动剂谷氨酸的反应。然而，使用专门测量表面异二聚体群体的测定法，我们发现 Q124R 取代降低了 mGlu ₄与 mGlu ₂和 mGlu _{7异二聚化的倾向}. _{我们的研究首次广泛描述了 mGlu 4} mRNA 转录物的 RNA 编辑的程度和调节因素。此外，我们提出了这一编辑事件的新功能结果，提供了关于其在体内的影响的见解，并扩大了 mGlu 受体的调节能力。