MOLECULAR BIOLOGY OF GLUTAMATE RECEPTORS IN TASTE BUDS

L-谷氨酸盐(味精)是一种独特的味觉刺激物，天然存在于蛋白质丰富的食物和其他食物中。谷氨酸的代谢性受体mGluR4在大鼠的味蕾中表达，似乎是味精的味觉受体。作用于mGluR4的配体模拟味精的味道。最近，我们克隆了一种新的味觉特异形式的mGluR4，它具有严重截断的谷氨酸结合位点。味觉受体，味觉-mGluR4，只被高浓度的谷氨酸激活，正如味觉受体所预期的那样。我们推测，改变的结合位点解释了味精味道的一些独特特征。味觉细胞中的离子型谷氨酸受体(IGluRs)也存在功能和分子证据。项目1的目标是使用分子技术来解决味觉-mGluR4是否单独是味精的味觉受体，以及iGluRs的激活是否也有助于转导。我们将通过比较味觉细胞克隆受体的功能特性和味觉细胞本身的功能来解决这个问题，以确定味觉转导中的关键角色。具体地说，我们将：1.检验味觉-mGluR4是味精味觉受体的假设。我们将在CHO细胞中表达味觉-mGluR4，并测量其对谷氨酸、GluR激动剂和提高味精味道的核苷酸的反应。我们还将使用Western blotts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是否是味觉转导中的第二信使mGluR4是味觉受体。3.对我们从味觉组织中克隆的一个新的类iGluR序列进行了详细的分子和功能分析。我们将研究这种受体是否是味觉细胞中发现的一种不寻常的谷氨酸门控离子电导的基础，以及这种受体是否在味精味道中发挥作用。我们还将在味觉组织中寻找额外的GluRs，以实现对味精味觉转导的全面描述。来自这些分子和细胞方法的数据将与项目#2和#3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.