Duffy antigen receptor for chemokines, member of the class A family of seven-transmembrane G protein-coupled receptors
Atypical chemokine receptor 1 (ACKR1), also known as DARC (Duffy antigen receptor for chemokines) or Fy glycoprotein (GpFy), was originally identified on erythrocytes. ACKR1 is also ubiquitously expressed by endothelial cells of venules and is highly promiscuous among all chemokine receptor. It binds many proinflammatory chemokines from both the CC and CXC subfamilies, including CCL2, CCL5, CCL7, CCL11, CXCL1, CXCL2, CXCL3, and CXCL5. Erythrocyte ACKR1 is thought to act as a chemokine sink, limiting the levels of circulating chemokines, thereby controlling leukocyte activation. ACKR1-deficient erythrocytes are shown to confer resistance to the malarial parasite, Plasmodium vivax. On the other hand, ACKR1-expressing endothelial cells can internalize chemokines. ACKR1-internalized chemokines can be moved intact across the endothelium and promotes neutrophil transmigration. 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, DARC, and D6. Both ACKR1 (DARC) and ACKR3 (CXCR7) show low sequence homology to the classic chemokine receptors.