The chemokines CCL5 and CXCL12 exhibit high‐affinity binding to N‐terminal peptides of the non‐cognate receptors CXCR4 and CCR5, respectively

CC and CXC chemokines are distinct chemokine subfamilies. CC chemokines usually do not bind CXC‐chemokine receptors and vice versa. CCR5 and CXCR4 receptors are activated by CCL5 and CXCL12 chemokines, respectively, and are also used as HIV‐1 coreceptors. CCL5 contains one conserved binding site for a sulfated tyrosine residue, whereas CXCL12 is unique in having two additional sites for sulfated/nonsulfated tyrosine residues. In this study, N‐terminal (Nt) CXCR4 peptides were found to bind CCL5 with somewhat higher affinities in comparison to those of short Nt‐CCR5(8–20) peptides with the same number of sulfated tyrosine residues. Similarly, a long Nt‐CCR5(1–27)( s Y3, s Y10, s Y14) peptide cross reacts with CXCL12 and with lower K D in comparison to its binding to CCL5. Intermolecular nuclear overhauser effect (NOE) measurements were used to decipher the mechanism of the chemokine/Nt‐receptor peptide binding. The Nt‐CXCR4 peptides interact with the conserved CCL5 tyrosine sulfate‐binding site by an allovalency mechanism like that observed for CCL5 binding of Nt‐CCR5 peptides. Nt‐CCR5 peptides bind CXCL12 in multiple modes analogous to their binding to HIV‐1 gp120 and interact with all three tyrosine/sulfated tyrosine‐binding pockets of CXCL12. We suggest that the chemokine‐receptors Nt‐segments bind promiscuously to cognate and non‐cognate chemokines and in a mechanism that is dependent on the number of binding pockets for tyrosine residues found on the chemokine. In conclusion, common features shared among the chemokine‐receptors' Nt‐segments such as multiple tyrosine residues that are potentially sulfated, and a large number of negatively charged residues are the reason of the cross binding observed in this study.