Two distinct determinants of ligand specificity in T1R1/T1R3 (the umami taste receptor).
Two distinct determinants of ligand specificity in T1R1/T1R3 (the umami taste receptor).
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T1R1/T1R3（鲜味的味觉受体）中配体特异性的两个不同决定因素。
DOI：
10.1074/jbc.m113.494443
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发表时间：
2013-12-27
期刊：
影响因子：
--
通讯作者：
Misaka T
中科院分区：
文献类型：
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作者：
Toda Y;Nakagita T;Hayakawa T;Okada S;Narukawa M;Imai H;Ishimaru Y;Misaka T
背景：T1R1/T1R3在配体特异性上表现出物种依赖性差异。结果：配体的特异性取决于正构位点的氨基酸选择性和非正构位点的受体活性调节的组合。结论：已经阐明了T1R1/T1R3氨基酸识别的分子机制。意义：本研究为人类T1R1/T1R3中l- glu特异性应答的分子机制提供了新的认识。哺乳动物的鲜味感知是由两个g蛋白偶联受体T1R1和T1R3的异质复合物介导的。T1R1/T1R3在配体特异性上表现出物种依赖性差异；人类T1R1/T1R3对l-Glu有特异性反应，而小鼠T1R1/T1R3对其他l-氨基酸的反应比l-Glu更强烈。这种物种差异背后的机制尚不清楚。在这项研究中，我们分析了嵌合的人-小鼠受体和T1R1/T1R3点突变体，并在T1R1的细胞外捕蝇草结构域中鉴定了12个关键残基，这些残基在人-鼠型反应中调节氨基酸识别。分子模型显示，对人类型酸性氨基酸识别至关重要的残基位于正位配体结合位点。相比之下，小鼠型广泛反应的所有关键残基都位于肌苷-5 ' -单磷酸腺苷（IMP）的正构配体结合位点和变构结合位点之外的区域，IMP是一种已知的天然鲜味增强剂。位点定向突变表明，新发现的小鼠型应答的关键残基以不同于通过IMP进行变构调节的方式调节受体活性。多点突变的分析表明，两个不同的决定因素——正构位点的氨基酸选择性和非正构位点的受体活性调节，可能介导了T1R1/T1R3的配体特异性。这一假设得到了非人灵长类动物T1R1受体研究结果的支持。哺乳动物T1R1/T1R3配体特异性的确定是一个复杂的分子机制，涉及到T1R1正位和非正位位点的性质变化。
Background: T1R1/T1R3 exhibits species-dependent differences in ligand specificity. Results: The ligand specificity is dependent on a combination of amino acid selectivity at the orthosteric site and receptor activity modulation at the non-orthosteric site. Conclusion: The molecular mechanism underlying the amino acid recognition of T1R1/T1R3 has been elucidated. Significance: This study provides new insights into the molecular mechanisms of the l-Glu-specific response in human T1R1/T1R3. Umami taste perception in mammals is mediated by a heteromeric complex of two G-protein-coupled receptors, T1R1 and T1R3. T1R1/T1R3 exhibits species-dependent differences in ligand specificity; human T1R1/T1R3 specifically responds to l-Glu, whereas mouse T1R1/T1R3 responds more strongly to other l-amino acids than to l-Glu. The mechanism underlying this species difference remains unknown. In this study we analyzed chimeric human-mouse receptors and point mutants of T1R1/T1R3 and identified 12 key residues that modulate amino acid recognition in the human- and mouse-type responses in the extracellular Venus flytrap domain of T1R1. Molecular modeling revealed that the residues critical for human-type acidic amino acid recognition were located at the orthosteric ligand binding site. In contrast, all of the key residues for the mouse-type broad response were located at regions outside of both the orthosteric ligand binding site and the allosteric binding site for inosine-5′-monophosphate (IMP), a known natural umami taste enhancer. Site-directed mutagenesis demonstrated that the newly identified key residues for the mouse-type responses modulated receptor activity in a manner distinct from that of the allosteric modulation via IMP. Analyses of multiple point mutants suggested that the combination of two distinct determinants, amino acid selectivity at the orthosteric site and receptor activity modulation at the non-orthosteric sites, may mediate the ligand specificity of T1R1/T1R3. This hypothesis was supported by the results of studies using nonhuman primate T1R1 receptors. A complex molecular mechanism involving changes in the properties of both the orthosteric and non-orthosteric sites of T1R1 underlies the determination of ligand specificity in mammalian T1R1/T1R3.