Research in polymorphisms in human taste receptor genes and taste disorder

T2Rs是一个G蛋白偶联受体超家族，含有功能性苦味受体。我们在染色体7q31上发现了人类T2R基因(hT2R3、hT2R4和hT2R5)的编码单核苷酸多态(CSNPs)。我们在T2R受体基因中发现了6个cSNPs。HT2R4和hT2R5分别含有4个和on cSNPs，导致错义突变，而hT2R3含有1个沉默的核苷酸突变。然而，我们在开放阅读框架内没有发现任何导致移码或过早终止密码子的无义突变。T2R受体和G蛋白α亚单位(Gα)被认为是其感知的关键分子，但对其相互作用的分子基础知之甚少。我们使用异源表达系统来确定T2R偶联所需的Gustducin的特定结构域。两个在C端含有37和44个Gustducin特异序列的嵌合Gα16蛋白(G16/Gust37和G16/Gust44)与不同的T2R受体反应，但G16/Gust23、G16/Gust11和G16/Gust5不能与不同的T2R受体反应。前两个嵌合体包含一个预测的β6片断、一个α5螺旋和一个极端的Gustducin C末端，所有这些结构域都是表达T2R活性所必需的。我们还表达了与其他GαI蛋白、锥体转导蛋白(GαT2)、Gαi2和Gαz(G16/T2、G16/i2和G16/z)对应的结构域的G16蛋白嵌合体。因此，G16/T2和G16/i2产生了T2Rs的特异性反应，而G16/z没有。使用基于Gα16的嵌合体和hT2R16变异体，我们检测了对水杨素的敏感性。鉴定人类T2R受体的核苷酸多样性和氨基酸多态有助于阐明个体对苦味化合物的接受性和敏感度的差异。

T2Rs comprise a G-protein-coupled receptor superfamily that contains functionally defined bitter taste receptors. We found coding single-nucleotide polymorphisms (cSNPs) in human T2R genes (hT2R3, hT2R4, and hT2R5) on chromosome 7q31. We identified six cSNPs within the T2R receptor genes. The hT2R4 and hT2R5 contained four and on cSNPs that cause missense mutations, respectively, while hT2R3 included one silent nucleotide mutation. However, we could not find any nonsense mutations that resulted in a frameshift or a premature stop codon within the open reading frames. T2R receptors and a G-protein α subunit (Gα), gustducin, are believed to be key molecules for its perception, but little is known about the molecular basis for its interaction. We use a heterologous expression system to determine a specific domain of gustducin necessary for T2R coupling. Two chimeric Gα16 proteins harboring 37 and 44 gustducin-specific sequences at their C termini (G16/gust37 and G16/gust44) responded to different T2R receptors with known ligands, but G16/gust23, G16/gust11, and G16/gust5 did not. The former two chimeras contained a predicted β6 sheet, an α5 helix, and an extreme C terminus of gustducin, and all the domains were indispensable to the expression of T2R activity. We also expressed G16 protein chimeras with the corresponding domain from other Gαi proteins, cone-transducin (Gαt2), Gαi2, and Gαz (G16/t2, G16/i2, and G16/z). As a result, G16/t2 and G16/i2 produced specific responses of T2Rs, but G16/z did not. Using Gα16-based chimeras and hT2R16 variants, we examined sensitivity to salicin. Identification of nucleotide diversity and amino acid polymorphisms in human T2R receptors could help clarify individual differences in the acceptability and sensitivity to bitter compounds.