Conventional and unconventional GPCR-G protein coupling

项目总结/摘要 G蛋白偶联受体（GPCRs）是激素、神经递质和神经递质的重要靶点， 三分之一的FDA批准的药物。这些受体通过与来自四个家族的转导蛋白偶联来发出信号 异三聚体G蛋白和四种抑制蛋白家族。最近的结构和功能研究已经定义了 一种常规的变构机制，其中配体与受体结合促进G蛋白的活化， 抑制素然而，在数百种GPCR和16种G蛋白中存在广泛的功能多样性， 并且许多生理学和药理学的实例不符合常规模型。比如说， 我们已经发现GPCR选择合适的G蛋白的机制存在显著的变异性， 一些识别非常规G蛋白决定簇的受体。我们还发现了一些 一种自相矛盾地抑制G蛋白信号而不是通常的激活的受体，一种GPCR-G 蛋白质偶联是无效的。最后，我们已经发现了与G蛋白相关的受体， 配体结合和平均释放G蛋白激活后，一种类型的反向耦合，可以解释 这种受体的特殊药理学。对GPCR介导的信号传导的完整理解将 需要更好地了解这些非常规的GPCR-G蛋白偶联机制。此外还 将有必要将在模型细胞中过表达分子的分子研究转化为 内源性表达的GPCR和G蛋白在其天然环境中，其中表达水平、化学计量 和亚细胞区室化更紧密地匹配体内情况。因此，我们将执行 研究绘制非传统的选择性决定因素，确定患病率和生理 非生产性和反向GPCR-G蛋白偶联的意义，并更好地了解 细胞膜中GPCR的构象动力学，以及这种构象景观如何随着 受体结合配体并与转换分子相互作用。

PROJECT SUMMARY/ABSTRACT G protein-coupled receptors (GPCRs) are important targets of hormones, neurotransmitters and approximately one-third of FDA-approved drugs. These receptors signal by coupling to transducer proteins from four families of heterotrimeric G proteins and a family of four arrestins. Recent structural and functional studies have defined a conventional allosteric mechanism whereby ligand binding to receptors promotes activation of G proteins and arrestins. However, there is extensive functional diversity across hundreds of GPCRs and sixteen G proteins, and many examples of physiology and pharmacology do not conform to the conventional model. For example, we have found significant variability in the mechanism whereby GPCRs select appropriate G proteins, and some receptors that recognize unconventional G protein determinants for selectivity. We have also found some receptors that paradoxically inhibit G protein signaling instead of the usual activation, a type of GPCR-G protein coupling that is unproductive. Finally, we have found receptors that associate with G proteins prior to ligand binding and on average release G proteins after activation, a type of inverse coupling that can explain the unusal pharmacology of such receptors. A complete understanding of GPCR-mediated signaling will require a better understanding of these unconventional GPCR-G protein coupling mechanisms. In addition, it will be necessary to translate molecular studies carried out with overexpressed molecules in model cells to endogenously-expressed GPCRs and G proteins in their native context, where expression levels, stoichiometry and subcellular compartmentalization more closely match the in vivo situation. Accordingly, we will carry out studies to map unconventional selectivity determinants, determine the prevalence and physiological significance of unproductive and inverse GPCR-G protein coupling, and to better understand the conformational dynamics of GPCRs in cell membranes, and how this conformational landscape changes as receptors bind ligands and interact with transducer molecules.