Seifert R, Gether U, Wenzel-Seifert K, Kobilka B K
Howard Hughes Medical Institute, Stanford University Medical School, Stanford, California, USA.
Mol Pharmacol. 1999 Aug;56(2):348-58. doi: 10.1124/mol.56.2.348.
The aim of our study was to examine the effects of different purine nucleotides [GTP, ITP, and xanthosine 5'-triphosphate (XTP)] on receptor/G protein coupling. As a model system, we used a fusion protein of the beta(2)-adrenergic receptor and the alpha subunit of the G protein G(s). GTP was more potent and efficient than ITP and XTP at inhibiting ternary complex formation and supporting adenylyl cyclase (AC) activation. We also studied the effects of several beta(2)-adrenergic receptor ligands on nucleotide hydrolysis and on AC activity in the presence of GTP, ITP, and XTP. The efficacy of agonists at promoting GTP hydrolysis correlated well with the efficacy of agonists for stimulating AC in the presence of GTP. This was, however, not the case for ITP hydrolysis and AC activity in the presence of ITP. The efficacy of ligands at stimulating AC in the presence of XTP differed considerably from the efficacies of ligands in the presence of GTP and ITP, and there was no evidence for receptor-regulated XTP hydrolysis. Our findings support the concept of multiple ligand-specific receptor conformations and demonstrate the usefulness of purine nucleotides as tools to study conformational states of receptors.
我们研究的目的是检测不同嘌呤核苷酸[鸟苷三磷酸（GTP）、肌苷三磷酸（ITP）和黄苷5'-三磷酸（XTP）]对受体/G蛋白偶联的影响。作为一个模型系统，我们使用了β₂肾上腺素能受体与G蛋白Gₛ的α亚基的融合蛋白。在抑制三元复合物形成和支持腺苷酸环化酶（AC）激活方面，GTP比ITP和XTP更有效。我们还研究了几种β₂肾上腺素能受体配体在存在GTP、ITP和XTP时对核苷酸水解和AC活性的影响。激动剂促进GTP水解的效能与激动剂在存在GTP时刺激AC的效能密切相关。然而，在存在ITP时ITP水解和AC活性的情况并非如此。配体在存在XTP时刺激AC的效能与在存在GTP和ITP时配体的效能有很大差异，并且没有证据表明存在受体调节的XTP水解。我们的研究结果支持多种配体特异性受体构象的概念，并证明了嘌呤核苷酸作为研究受体构象状态工具的有用性。
