Zheng Kevin, Smith Jeffrey S, Eiger Dylan S, Warman Anmol, Choi Issac, Honeycutt Christopher C, Boldizsar Noelia, Gundry Jaimee N, Pack Thomas F, Inoue Asuka, Caron Marc G, Rajagopal Sudarshan
Department of Biochemistry, Duke University Medical Center, Durham, NC 27710, USA.
Harvard Medical School, Boston, MA 02115, USA.
Sci Signal. 2022 Mar 22;15(726):eabg5203. doi: 10.1126/scisignal.abg5203.
G protein-coupled receptors (GPCRs) are the largest family of cell surface receptors and signal through the proximal effectors, G proteins and β-arrestins, to influence nearly every biological process. The G protein and β-arrestin signaling pathways have largely been considered separable; however, direct interactions between Gα proteins and β-arrestins have been described that appear to be part of a distinct GPCR signaling pathway. Within these complexes, Gα, but not other Gα protein subtypes, directly interacts with β-arrestin, regardless of the canonical Gα protein that is coupled to the GPCR. Here, we report that the endogenous biased chemokine agonists of CXCR3 (CXCL9, CXCL10, and CXCL11), together with two small-molecule biased agonists, differentially formed Gα:β-arrestin complexes. Formation of the Gα:β-arrestin complexes did not correlate well with either G protein activation or β-arrestin recruitment. β-arrestin biosensors demonstrated that ligands that promoted Gα:β-arrestin complex formation generated similar β-arrestin conformations. We also found that Gα:β-arrestin complexes did not couple to the mitogen-activated protein kinase ERK, as is observed with other receptors such as the V2 vasopressin receptor, but did couple with the clathrin adaptor protein AP-2, which suggests context-dependent signaling by these complexes. These findings reinforce the notion that Gα:β-arrestin complex formation is a distinct GPCR signaling pathway and enhance our understanding of the spectrum of biased agonism.
G蛋白偶联受体（GPCRs）是细胞表面受体中最大的家族，通过近端效应器G蛋白和β-抑制蛋白进行信号传导，从而影响几乎所有的生物学过程。G蛋白和β-抑制蛋白信号通路在很大程度上被认为是可分离的；然而，已经描述了Gα蛋白与β-抑制蛋白之间的直接相互作用，这似乎是一个独特的GPCR信号通路的一部分。在这些复合物中，Gα而非其他Gα蛋白亚型直接与β-抑制蛋白相互作用，无论与GPCR偶联的是哪种典型Gα蛋白。在此，我们报告CXCR3的内源性偏向趋化因子激动剂（CXCL9、CXCL10和CXCL11），连同两种小分子偏向激动剂，差异地形成Gα:β-抑制蛋白复合物。Gα:β-抑制蛋白复合物的形成与G蛋白激活或β-抑制蛋白募集均无良好的相关性。β-抑制蛋白生物传感器表明，促进Gα:β-抑制蛋白复合物形成的配体产生相似的β-抑制蛋白构象。我们还发现，Gα:β-抑制蛋白复合物不像其他受体（如血管升压素V2受体）那样与丝裂原活化蛋白激酶ERK偶联，但确实与网格蛋白衔接蛋白AP-2偶联，这表明这些复合物存在依赖于背景的信号传导。这些发现强化了Gα:β-抑制蛋白复合物形成是一条独特的GPCR信号通路这一观点，并增进了我们对偏向激动作用谱的理解。
