Mammalian sensory systems detect sweet taste through the activation of a single heteromeric T1R2/T1R3 receptor belonging to class C G-protein-coupled receptors. Allosteric ligands are known to interact within the transmembrane domain, yet a complete view of receptor activation remains elusive. By combining site-directed mutagenesis with computational modeling, we investigate the structure and dynamics of the allosteric binding pocket of the T1R3 sweet-taste receptor in its apo form, and in the presence of an allosteric ligand, cyclamate. A novel positively charged residue at the extracellular loop 2 is shown to interact with the ligand. Molecular dynamics simulations capture significant differences in the behavior of a network of conserved residues with and without cyclamate, although they do not directly interact with the allosteric ligand. Structural models show that they adopt alternate conformations, associated with a conformational change in the transmembrane region. Site-directed mutagenesis confirms that these residues are unequivocally involved in the receptor function and the allosteric signaling mechanism of the sweet-taste receptor. Similar to a large portion of the transmembrane domain, they are highly conserved among mammals, suggesting an activation mechanism that is evolutionarily conserved. This work provides a structural basis for describing the dynamics of the receptor, and for the rational design of new sweet-taste modulators.

中文翻译：

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保守的残基控制着哺乳动物甜味受体的T1R3特异性变构信号通路。

哺乳动物的感觉系统通过激活属于C类G蛋白偶联受体的单个异源T1R2 / T1R3受体来检测甜味。已知变构配体在跨膜结构域内相互作用，但是对受体激活的完整了解仍然难以捉摸。通过将定点诱变与计算模型相结合，我们研究了A1形式的T1R3甜味受体的变构结合口袋的结构和动力学，并且存在变构配体甜蜜素。显示在细胞外环2处的新的带正电荷的残基与配体相互作用。分子动力学模拟捕获具有和没有甜蜜素的保守残基网络行为的显着差异，尽管它们不与变构配体直接相互作用。结构模型表明，它们采用了交替的构象，与跨膜区域的构象变化有关。定点诱变证实这些残基明确参与了甜味受体的受体功能和变构信号传导机制。与跨膜结构域的大部分相似，它们在哺乳动物中高度保守，提示其进化机制是保守的。这项工作为描述受体的动力学和合理设计新型甜味调节剂提供了结构基础。定点诱变证实这些残基明确参与了甜味受体的受体功能和变构信号传导机制。与跨膜结构域的大部分相似，它们在哺乳动物中高度保守，提示其进化机制是保守的。这项工作为描述受体的动力学和合理设计新型甜味调节剂提供了结构基础。定点诱变证实这些残基明确参与了甜味受体的受体功能和变构信号传导机制。与跨膜结构域的大部分相似，它们在哺乳动物中高度保守，提示其进化机制是保守的。这项工作为描述受体的动力学和合理设计新型甜味调节剂提供了结构基础。