Characterization of the molecular interactions of interleukin-8 (CXCL8), growth related oncogen α (CXCL1) and a non-peptide antagonist (SB 225002) with the human CXCR2

Neutrophil recruitment to inflammatory sites is mediated by two related receptors: CXC chemokine receptors 1 (CXCR1) and 2 (CXCR2). Both receptors share two ligands, interleukin-8 (CXCL8) and GCP-2 (CXCL6), whereas several chemokines, including growth related oncogen alpha (CXCL1) and a non-peptide antagonist (SB 225002) are specific for CXCR2. The objective of this study was to map the different amino acids involved in the binding and activation/inhibition of human CXCR2. This was performed by exchanging non-conserved amino acids of CXCR2 with their counterparts in CXCR1. The mutants generated showed that: (a) for CXCL8 binding, the N-terminus of CXCR1 and the second extra-cellular loop of CXCR2 are determinant, the N-terminus of CXCR2 is not sufficient and the transmembrane domain seven is probably involved; (b) for CXCL1, the N-terminus of CXCR2 is necessary but not sufficient for binding. The activation study indicated that amino acids critical for activation are not necessarily involved in binding process. Finally, the mechanism of binding of a non-peptide antagonist on CXCR2 was investigated: it occurred through epitopes (a) which were disseminated within the receptor, (b) which differed according to the use of CXCL8 or CXCL1 as a competitor and (c) which did not necessarily overlap with agonist binding sites. We also showed that inhibition of binding and inhibition of activation involved different amino acids.