Molecular basis of promiscuous chemokine binding and structural mimicry at the C-X-C chemokine receptor, CXCR2.

Selectivity of natural agonists for their cognate receptors is a hallmark of G-protein-coupled receptors (GPCRs); however, this selectivity often breaks down at the chemokine receptors. Chemokines often display promiscuous binding to chemokine receptors, but the underlying molecular determinants remain mostly elusive. Here, we perform a comprehensive transducer-coupling analysis, testing all known C-X-C chemokines on every C-X-C type chemokine receptor to generate a global fingerprint of the selectivity and promiscuity encoded within this system. Taking lead from this, we determine cryoelectron microscopy (cryo-EM) structures of the most promiscuous receptor, C-X-C chemokine receptor 2 (CXCR2), in complex with several chemokines. These structural snapshots elucidate the details of ligand-receptor interactions, including structural motifs, which are validated using mutagenesis and functional experiments. We also observe that most chemokines position themselves on CXCR2 as a dimer while CXCL6 exhibits a monomeric binding pose. Taken together, our findings provide the molecular basis of chemokine promiscuity at CXCR2 with potential implications for developing therapeutic molecules.