THE PROMISCUOUS CHEMOKINE BINDING PROFILE OF THE DUFFY ANTIGEN RECEPTOR FOR CHEMOKINES IS PRIMARILY LOCALIZED TO SEQUENCES IN THE AMINO-TERMINAL DOMAIN

The Duffy antigen (DARC) is a promiscuous chemokine receptor that also binds Plasmodium vivax. DARC belongs to a family of heptahelical chem okine receptors that includes specific (IL-8RA) and shared (IL-8RB) IL -8 receptors, Ligand binding specificity of IL-8 receptors was localiz ed to the amino terminal extracellular (El) domain, To determine the b asis for promiscuous chemokine binding by DARC, a chimeric receptor co mposed of the E1 domain of DARC and hydrophobic helices and loops from IL-8RB (DARC(e1)/IL-8RB) was constructed, Scatchard analysis of stabl e transfectants demonstrated that the DARC(e1)/IL-8RB chimeric recepto r bound IL-8 and melanoma growth stimulating activity (MGSA) with K-D values almost identical to the native receptors, The hybrid receptor a lso bound RANTES, MCP-1, and MGSA E(6)A (which binds DARC, but not IL- 8RB), but not MIP-1 alpha, similarly to DARC, Ligand binding to DARC t ransfectants was unaltered by anti-Fy3, but inhibited by Fy6, which bi nds an epitope in the El domain, The epitope recognized by Fy3 was loc alized to the third extracellular loop by analysis of insect cells exp ressing chimeric receptors composed of complementary portions of DARC and IL-8RB. These findings implicate the El domain of DARC in multispe cific chemokine binding.