MOLECULAR BIOLOGY OF GLUTAMATE RECEPTORS IN TASTE BUDS

味精是一种独特的味觉刺激物质，存在于富含蛋白质的食物和其他食物中。谷氨酸代谢受体mGluR4在大鼠味蕾中表达，似乎是味精的味觉受体。作用于mGluR4的配体模仿味精的味道。最近，我们克隆了一种新的味觉特异性mGluR4，它具有严重截断的谷氨酸结合位点。这种名为taste- mglur4的受体只有在高浓度谷氨酸的情况下才会被激活，正如人们对味觉受体的预期一样。我们假设改变的结合位点解释了味精味道的一些独特特征。在味觉细胞中也存在嗜离子性谷氨酸受体（iGluRs）的功能和分子证据。项目#1的目标是使用分子技术来确定单独的taste- mglur4是否是味精的味觉受体，以及iGluRs的激活是否也有助于转导。我们将通过比较来自味觉细胞的克隆受体与味觉细胞本身的功能特性来解决这个问题，以确定味精味觉转导的关键参与者。具体来说，我们将：1。验证taste- mglur4是味精的味觉受体的假设。我们将在CHO细胞中表达taste- mglur4，并测量其对谷氨酸、谷氨酸激动剂和增强味精味道的核苷酸的反应。我们还将使用Western blots和启动子分析来测试味蕾是否能够表达这种新的GluR。2. 确定cAMP和/或cGMP是否如味觉中预测的那样是谷氨酸味觉转导的第二信使。3. 对我们从味觉组织中克隆的一个新的iGluR样序列进行详细的分子和功能分析。我们将研究这种受体是否在味觉细胞中发现了一种不寻常的谷氨酸门控离子电导，以及这种受体是否在味精味觉中起作用。我们还将在味觉组织中寻找更多的味精，以实现味精味觉转导的全面描述。这些分子和细胞方法的数据将与项目#2和#3中对相同问题进行的电生理和行为分析的结果密切协调。

The monosodium salt of L-glutamate (MSG) is a distinctive taste stimulus found naturally in protein-rich and other foods. A metabotropic receptor for glutamate, mGluR4, is expressed in rat taste buds and appears to function as a taste receptor for MSG. Ligands acting at mGluR4 mimic the taste of MSG. Recently, we have cloned a novel taste-specific form of mGluR4, that has a severely truncated glutamate-binding site. The receptor, taste-mGluR4, is activated only by high concentrations of glutamate, as expected for a taste receptor. We postulate that the altered binding site accounts for some of the unique features of MSG taste. Functional and molecular evidence also exists for ionotropic glutamate receptors (iGluRs) in taste cells. The goal of Project #1 is to use molecular techniques to address whether taste-mGluR4 alone is the taste receptor for MSG for whether activation of iGluRs also contributes to transduction. We will address this question by comparing the functional properties of cloned receptors from taste cells against the functions of taste cells themselves, to identify the key players in MSG taste transduction. Specifically, we will: 1. Test the hypothesis that taste-mGluR4 is a taste receptor for MSG. We will express taste-mGluR4 in CHO cells and measure its response to glutamate, GluR agonists and nucleotides that enhance MSG taste. We will also use Western blots and promoter analyses to test whether taste buds are able to express this novel GluR. 2. Determine if cAMP and/or cGMP are 2nd messengers in glutamate taste transduction as predicted in taste mGluR4 is a taste receptor for MSG. 3. Conduct detailed molecular and functional analyses of a novel iGluR- like sequence we have cloned from taste tissue. We will examine whether this receptor underlies an unusual glutamate-gated ionic conductance found in taste cells, and whether this receptor plays a role in MSG taste. We will also search for additional GluRs in taste tissue in order to achieve a comprehensive description of the taste transduction of MSG. The data from these molecular and cellular approaches will be closely coordinated with results from electrophysiological and behavioral analyses of the same questions, conducted from Projects #2 and #3.