Adaptation and Constraint in the Atypical Chemokine Receptor Family in Mammals

Figure 4

The ACKR1 receptors do not signal in response to ligand binding but rather internalize the ligand and target it for intracellular degradation. The key to the lack of signaling is the absence of DRY motif in the second intracellular loop of ACKR1. The positively selective site was located in the second extracellular loop, which is responsible for ligand recognition and binding.