Conventional and unconventional GPCR-G protein coupling

项目摘要/摘要 G蛋白偶联受体(GPCRs)是激素、神经递质和大约 FDA批准的三分之一的药物。这些受体通过与四个家族的转导蛋白偶联来传递信号。 异源三聚体G蛋白和四个阻滞剂家族。最近的结构和功能研究已经定义了 一种传统的变构机制，通过与受体的配体结合促进G蛋白的激活和 逮捕。然而，在数百个GPCR和16个G蛋白上存在广泛的功能多样性， 而许多生理学和药理学的例子并不符合传统的模式。例如, 我们发现GPCR选择合适的G蛋白的机制存在显著的变异性，并且 一些受体识别非常规G蛋白决定因素的选择性。我们还发现了一些 自相矛盾地抑制G蛋白信号而不是通常的激活的受体，这是一种GPCR-G 蛋白质偶联是无效的。最后，我们发现了与G蛋白相关的受体 配体结合并在激活后平均释放G蛋白，这是一种反向耦合，可以解释 这类受体的非常规药理作用。完全理解GPCR介导的信号转导将 需要更好地了解这些非常规的GPCR-G蛋白偶联机制。此外，它还 将有必要将对模型细胞中过度表达的分子进行的分子研究转化为 在天然环境中内源性表达GPCRs和G蛋白，其中表达水平、化学计量比 亚细胞区划与体内情况更接近。据此，我们将开展 绘制非常规选择性决定因素的研究，确定患病率和生理学 非生产性和反向GPCR-G蛋白偶联的意义，并更好地理解 GPCRs在细胞膜上的构象动力学，以及这种构象格局如何随着 受体与配体结合，并与转导分子相互作用。

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.