The highly individual plasma membrane expression and cAMP signaling of odorant receptors have hampered their ligand assignment and functional characterization in test cell systems. Chaperones have been identified to support the cell surface expression of only a portion of odorant receptors, with mechanisms remaining unclear. The presence of amino acid motifs that might be responsible for odorant receptors' individual intracellular retention or cell surface expression, and thus, for cAMP signaling, is under debate: so far, no such protein motifs have been suggested. Here, we demonstrate the existence of highly conserved C-terminal amino acid motifs, which discriminate at least between class-I and class-II odorant receptors, with their numbers of motifs increasing during evolution, by comparing C-terminal protein sequences from 4808 receptors across eight species. Truncation experiments and mutation analysis of C-terminal motifs, largely overlapping with helix 8, revealed single amino acids and their combinations to have differential impact on the cell surface expression and on stimulus-dependent cAMP signaling of odorant receptors in NxG 108CC15 cells. Our results demonstrate class-specific and individual C-terminal motif equipment of odorant receptors, which instruct their functional expression in a test cell system, and in situ may regulate their individual cell surface expression and intracellular cAMP signaling.

中文翻译：

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气味受体中保守的 C 端基序指示它们的细胞表面表达和 cAMP 信号传导

气味受体的高度个体质膜表达和 cAMP 信号阻碍了它们在测试细胞系统中的配体分配和功能表征。已经鉴定出分子伴侣仅支持一部分气味受体的细胞表面表达，其机制尚不清楚。氨基酸基序的存在可能对气味受体的个体细胞内滞留或细胞表面表达负责，因此对于 cAMP 信号传导，存在争议：到目前为止，还没有提出此类蛋白质基序。在这里，我们证明了高度保守的 C 端氨基酸基序的存在，它们至少可以区分 I 类和 II 类气味受体，并且它们的基序数量在进化过程中会增加，通过比较来自 8 个物种的 4808 个受体的 C 端蛋白质序列。C 末端基序的截断实验和突变分析，主要与螺旋 8 重叠，揭示了单个氨基酸及其组合对 NxG 108CC15 细胞中气味受体的细胞表面表达和刺激依赖性 cAMP 信号传导具有不同的影响。我们的结果证明了气味受体的类别特异性和个体 C 末端基序设备，它们指示它们在测试细胞系统中的功能表达，并且原位可以调节它们的个体细胞表面表达和细胞内 cAMP 信号传导。揭示单个氨基酸及其组合对 NxG 108CC15 细胞中的细胞表面表达和气味受体的刺激依赖性 cAMP 信号传导具有不同的影响。我们的结果证明了气味受体的类别特异性和个体 C 末端基序设备，它们指示它们在测试细胞系统中的功能表达，并且原位可以调节它们的个体细胞表面表达和细胞内 cAMP 信号传导。揭示单个氨基酸及其组合对 NxG 108CC15 细胞中的细胞表面表达和气味受体的刺激依赖性 cAMP 信号传导具有不同的影响。我们的结果证明了气味受体的类别特异性和个体 C 末端基序设备，它们指示它们在测试细胞系统中的功能表达，并且原位可以调节它们的个体细胞表面表达和细胞内 cAMP 信号传导。