atypical chemokine receptor 4, member of the class A family of seven-transmembrane G protein-coupled receptors
ACKR4 was first reported to bind several CC chemokines including CCL19, CCL21, and CCL25 and was originally designated CCR11. AKCR4 is unable to couple to G-protein and, instead, it preferentially mediates beta-arrestin dependent processes, such as receptor internalization, after ligand binding. Thus, ACKR4 may act as a scavenger receptor to suppress the effects of proinflammatory chemokines. Unlike the classical chemokine receptors that contain a conserved DRYLAIV motif in the second intracellular loop, which is required for G-protein coupling, the ACKRs lack this conserved motif and fail to couple to G-proteins and induce classical GPCR signaling. Five receptors have been identified for the ACKR family, including CC-chemokine receptors like 1 and 2 (CCRL1 and CCRL2), CXCR7, Duffy antigen receptor for chemokine (DARC), and D6. Both ACKR1 (DARC) and ACKR3 (CXCR7) show low sequence homology to the classic chemokine receptors.
Comment:Small-molecule chemical ligands tend to bind deeper within the receptor core, compared to a peptide ligand neurotensin, which binds towards the extracellular surface of its receptor.
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