Insights into CC Chemokine Ligand 2/Chemokine Receptor 2 Molecular Recognition: A Step Forward toward Antichemotactic Agents

Chemokine ligand 2 (CCL2), also known as monocyte chemoattractant protein 1 (MCP-1), is a chemokine that recruits immune cells to inflammatory sites by interacting with G protein-coupled receptor CCR2. The CCL2/CCR2 axis is also involved in pathological processes such as tumor growth and metastasis and hence is currently considered as an important drug target. CCL2 exists in a dynamic monomer–dimer equilibrium that is modulated by CCR2 binding. We used solution nuclear magnetic resonance (NMR) spectroscopy and molecular dynamics simulations to study the interactions between CCL2 and a sulfopeptide corresponding to the N-terminal sequence of CCR2 (CCR218–31). Peptide binding induced the dissociation of CCL2 into monomers, forming stable CCL2/CCR218–31 complexes. NMR relaxation measurements indicated that residues around the CCR218–31 binding site, which are located at the dimer interface, undergo a complex regime of motions. NMR data were used to construct a three-dimensional structural model of the CCL2/CCR218–31 complex, revealing that CCR218–31 occupies a binding site juxtaposed to the dimer interface, partially replacing monomer–monomer contacts, explaining why CCR218–31 binding weakens the dimer interface and induces dissociation. We found that the main interactions governing receptor binding are highly stable salt bridges with conserved chemokine residues as well as hydrophobic interactions. These data provide new insights into the structure–function relationship of the CCL2–CCR2 interaction and may be helpful for the design of novel antichemotactic agents.