Structural Basis of Chemokine Receptor Function—A Model for Binding Affinity and Ligand Selectivity

Chemokine receptors play fundamental roles in human physiology from embryogenesis to inflammatory response. The receptors belong to the G-protein coupled receptor class, and are activated by chemokine ligands with a range of specificities and affinities that result in a complicated network of interactions. The molecular basis for function is largely a black box, and can be directly attributed to the lack of structural information on the receptors. Studies to date indicate that function can be best described by a two-site model, that involves interactions between the receptor N-domain and ligand N-terminal loop residues (site-I), and between receptor extracellular loop and the ligand N-terminal residues (site-II). In this review, we describe how the two-site model could modulate binding affinity and ligand selectivity, and also highlight some of the unique chemokine receptor features, and their role in function.