Metabotropic glutamate receptor 6, mGluR6, interacts with scaffold proteins and Gβγ subunits via its intracellular C-terminal domain (CTD). The mGluR6 pathway is critically involved in the retinal processing of visual signals. We herein investigated whether the CTD (residues 840–871) was necessary for mGluR6 cell surface localization and G-protein coupling using mGluR6-CTD mutants with immunocytochemistry, surface biotinylation assays, and electrophysiological approaches. We used 293T cells and primary hippocampal neurons as model systems. We examined C-terminally truncated mGluR6 and showed that the removal of up to residue 858 did not affect surface localization or glutamate-induced G-protein-mediated responses, whereas a 15-amino acid deletion (Δ857-871) impaired these functions. However, a 21-amino acid deletion (Δ851-871) restored surface localization and glutamate-dependent responses, which were again attenuated when the entire CTD was removed. The sequence alignment of group III mGluRs showed conserved amino acids resembling an ER retention motif in the CTD. These results suggest that the intracellular CTD is required for the cell surface transportation and receptor function of mGluR6, whereas it may contain regulatory elements for intracellular trafficking and signaling.

中文翻译：

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C末端结构域参与mGluR6的细胞表面定位和G蛋白偶联

代谢型谷氨酸受体 6，mGluR6，通过其细胞内 C 末端结构域 (CTD) 与支架蛋白和 Gβγ 亚基相互作用。mGluR6 通路与视觉信号的视网膜处理密切相关。我们在此研究了 CTD（残基 840-871）是否是 mGluR6 细胞表面定位和 G 蛋白偶联所必需的，使用 mGluR6-CTD 突变体与免疫细胞化学、表面生物素化测定和电生理学方法。我们使用 293T 细胞和原代海马神经元作为模型系统。我们检查了 C 末端截短的 mGluR6，并表明去除残基 858 不会影响表面定位或谷氨酸诱导的 G 蛋白介导的反应，而 15 个氨基酸的缺失（Δ857-871）会损害这些功能。然而，21 个氨基酸的缺失 (Δ851-871) 恢复了表面定位和谷氨酸依赖性反应，当整个 CTD 被移除时，这些反应再次减弱。III 组 mGluR 的序列比对显示了类似于 CTD 中 ER 保留基序的保守氨基酸。这些结果表明细胞内 CTD 是 mGluR6 的细胞表面运输和受体功能所必需的，而它可能包含细胞内运输和信号传导的调控元件。