SELECTIVITY AND ANTAGONISM OF CHEMOKINE RECEPTORS

The chemokine superfamily can be subdivided into two groups based on t heir amino terminal cysteine spacing, The CXC chemokines are primarily involved in neutrophil-mediated inflammation and, so far, two human r eceptors have been cloned. The CC chemokines tend to be involved in ch ronic inflammation, and recently we have cloned a fourth leukocyte rec eptor for this group of ligands. Understanding what makes one receptor bind its range of agonists is important if we are to develop potent s elective antagonists, We have started to investigate the molecular bas is of this receptor selectivity by looking at why CC chemokines do not bind to the CXC receptors in several ways, First, we looked at the ro le of the three-dimensional structure of the ligand, and have solved t he three-dimensional structure of RANTES using nuclear magnetic: reson ance spectroscopy, The structure is similar to that already determined for the CC chemokine macrophage inflammatory protein-1 beta, and it h as a completely different dimer interface to that of the CXC chemokine interleukin-8 (IL-8), However, the monomer structures of all the chem okines are very similar, and at physiological concentrations the prote ins are likely to be monomeric, Second, by examining all the known CC and CXC chemokines, we have found a region that differs between the tw o subfamilies, Mutations of one of the residues in this region, Leu-25 in IL-8, to tyrosine (which is conserved at this position in CC chemo kines) enables the mutant IL-8 to bind CC-chemokine receptor-1 (CC-CKR -1) and introduces monocyte chemoattractant activity, Using other muta tions in this region, we can show a direct interaction with the N-term inus of CC-CKR-1, Third, we have found that modification of the amino termimus of RANTES by addition of one amino acid makes it into an anta gonist with nanomolar potency, Taken together, this data suggests a tw o-site model for receptor activation and for selectivity between CC an d CXC chemokines, with an initial receptor contact provided by the mai n body of the chemokine, and activation provided by the amino terminal region.