Fig. 1. Arrestin recruitment of N-terminally truncated ACKR3 variants.

(A) Extracellular portion of the ACKR3:CXCL12 complex from experimentally-driven molecular model (8) and sequences of ACKR3 truncation mutants. Truncated regions are highlighted according to the color scheme in the model. (B) Representative examples of recruitment of GFP10-β-arrestin-2 to ACKR3-Rluc3 variants stimulated with different concentrations of CXCL12_WT, CXCL11 and CCX662 measured by BRET. Each point corresponds to the average and standard error of two measurements. (C and D) Potency (C) and efficacy (D) of ligand-induced β-arrestin-2 recruitment determined relative to ACKR3_WT from fitting of dose response curves. pEC₅₀ and E_max values for truncation mutants were determined as ΔpEC₅₀=pEC_50,mutant-pEC_50,WT and %E_max =E_max,mutant/E_max,WT × 100. Data are mean and standard error of three or more experiments. Significantly lowered potency or efficacy relative to ACKR3_WT with the same ligand is noted: *P<0.05, **P<0.01, ***P<0.001 from one-way ANOVA with Dunnett’s multiple comparison test. # in (C) indicates that CXCL11-induced arrestin recruitment by ACKR3_d29 could not be accurately fit and ΔpEC50 was estimated from the raw data to be >−2.2.