CXCR7 constitutively interacts with, but does not activate, G_αi1 proteins. (A,B) BRET signal between G_αi1-Rluc and either CXCR4-YFP (A), CXCR4-N119K-YFP (A), or CXCR7-YFP (B) was measured 48 hours after transfection of HEK-293T cells, after preincubation or not with GTP-γS (200 μM) for 90 minutes at 25°C or PTX (100 ng/mL) overnight at 37°C and stimulation or not by 1 μM CXCL12. (C,D) BRET saturation assays were performed on cells transfected with a constant amount of the G_αi1-Rluc fusion protein and increasing amounts of CXCR4-YFP (C) or CXCR7-YFP (D). BRET signals were determined in the absence (control) or presence of 1 μM CXCL12. Data represent 3 independent experiments. (C) BRET_max signals were significantly increased by CXCL12 compared with basal conditions (P < .05). ***P < .001; **P < .01; *P < .05.