Chemokine receptors constitute an important subfamily of G protein-coupled receptors (GPCRs), and they are critically involved in a broad range of immune response mechanisms. Ligand promiscuity among these receptors makes them an interesting target to explore multiple aspects of biased agonism. Here, we comprehensively characterize two chemokine receptors namely, CXCR4 and CXCR7, in terms of their transducer-coupling and downstream signaling upon their stimulation by a common chemokine agonist, CXCL12, and a small molecule agonist, VUF11207. We observe that CXCR7 lacks G-protein-coupling while maintaining robust βarr recruitment with a major contribution of GRK5/6. On the other hand, CXCR4 displays robust G-protein activation as expected but exhibits significantly reduced βarr-coupling compared to CXCR7. These two receptors induce distinct βarr conformations even when activated by the same agonist, and CXCR7, unlike CXCR4, fails to activate ERK1/2 MAP kinase. We also identify a key contribution of a single phosphorylation site in CXCR7 for βarr recruitment and endosomal localization. Our study provides molecular insights into intrinsic-bias encoded in the CXCR4-CXCR7 system with broad implications for drug discovery.

趋化因子受体是 G 蛋白偶联受体 (GPCR) 的一个重要亚家族，它们在广泛的免疫反应机制中发挥着重要作用。这些受体之间的配体混杂使它们成为探索偏向激动的多个方面的有趣目标。在这里，我们全面描述了两种趋化因子受体，即 CXCR4 和 CXCR7，在它们被常见趋化因子激动剂 CXCL12 和小分子激动剂 VUF11207 刺激后的传感器耦合和下游信号传导方面。我们观察到 CXCR7 缺乏 G 蛋白偶联，但在 GRK5/6 的主要贡献下保持了强大的 βarr 募集。另一方面，CXCR4 正如预期的那样表现出强大的 G 蛋白激活，但与 CXCR7 相比，βarr 偶联显着减少。即使被相同的激动剂激活，这两种受体也会诱导不同的 βarr 构象，并且 CXCR7 与 CXCR4 不同，无法激活 ERK1/2 MAP 激酶。我们还确定了 CXCR7 中单个磷酸化位点对 βarr 募集和内体定位的关键贡献。我们的研究提供了对 CXCR4-CXCR7 系统中编码的内在偏差的分子见解，对药物发现具有广泛的影响。