The G protein-coupled receptor (GPCR) chemokine-like receptor 1 (CMKLR1) is expressed mostly on the surface of cells of the adaptive immune system like macrophages and den¬dritic cells. As activation of CMKLR1 by the endogenous ligand chemerin results in chemotaxis of these cells, it has been proposed to be part of a group of chemoattractant receptors. Two active isoforms, consisting of 156 or 157 amino acids and produced by enzymatic cleavage of prochemerin have been described.
The endogenous ligand of CMKLR1 is the adipokine chemerin, which plays an important role in obesity and in inflammatory conditions. Therefore, investigating the mechanism of binding and activation of this GPCR is crucial for the development of ligands that can be used in the investigation and treatment of diseases related to inflammation such as psoriasis, inflammatory bowel diseases or the metabolic syndrome.
Here, we report on the identification of the binding mode of CMKLR1 and chemerin. Synthesis and testing of multiple active cyclic peptides suggested a hairpin-like binding conformation of the C-terminus of the ligand. Based on homology modeling and signal transduction assays, several conserved residues were identified to impede activation by a C terminally derived peptide after mutation to alanine. Additional investigations uncovered the N-terminus of the receptor as a secondary site of interaction, which binds positively charged patches found on the surface of the ligand. We present a novel model on this experimental basis. Our results will facilitate the development of more CMKLR1-targeting compounds.