Figure 1. Arrestin binding to ACKR3 depends on GRK2/5 phosphorylation.

(A) Sequence of the ACKR3 C-tail with the observed GRK2 phosphorylation sites highlighted in orange and the unique sites observed for GRK5 in blue. (B) A flag pulldown assay shows that comparable amounts of Arr2_3A, but not WT Arr2, binds to ACKR3 phosphorylated by GRK2 or GRK5. The interaction is abolished when ACKR3 is not phosphorylated. (C) Flag pulldown assays show that Fab7 coelutes with pACKR3(GRK2)–Arr2_3A and pACKR3(GRK5)–Arr2_3A. This interaction is dependent on GRK activity because non-phosphorylated ACKR3 does not pulldown Arr2_3A or Fab7.