The N-terminal Region of CXCL11 as Structural Template for CXCR3 Molecular Recognition: Synthesis, Conformational Analysis, and Binding Studies

The chemokines and their receptors play a key role in immune and inflammatory responses by promoting recruitment and activation of different subpopulations of leukocytes. The membrane receptor CXCR3 binds three chemokines, CXCL9, CXCL10, and CXCL11, and its involvement is recognized in many inflammatory diseases and cancers. Therefore, the inhibition of CXCR3 pathway through interactions with three ligands was indicated as putative therapeutic target for the treatment of these diseases, and some inhibitory compounds have already been described in the literature. Recently, we studied the interaction between CXCR3 and its three natural ligands and showed that three CXCR3 ligands bound the receptor mainly by their N-terminal regions using aromatic and electrostatic interactions, and, in particular, CXCL11 had the highest affinity for CXCR3. In light of these results, we focused our attention on what structural region(s) of CXCL11 interacted with CXCR3 and what were the structural features. Therefore, we have synthesized three peptides, corresponding to the N-terminal region of CXCL11, but with different aromatic amino acids, analyzed their conformations by circular dichroism, NMR, and molecular dynamics simulations, simulated their complexes with CXCR3 by docking methods, and validated these data by in vitro studies. The results showed that two peptides were able to bind CXCR3 and to mimic the molecular recognition of CXCL11 and demonstrated that N-terminal region of CXCL11 can be used as template and starting point to obtain new molecules by de novo design approaches.