Link to bioRxiv paper: http://biorxiv.org/cgi/content/short/2020.07.28.225664v1?rss=1 Authors: Rajarathnam, K., Sepuru, K. M., Nair, V., Prakash, P., Gorfe, A. Abstract: Chemokines are unusual class-A GPCR agonists because of their large size (~10 kDa) and binding at two distinct receptor sites: N-terminal domain (Site-I, unique to chemokines) and a groove defined by extracellular loop/transmembrane helices (Site-II, shared with all small molecule class-A ligands). Whereas binding at Site-II triggers receptor activation, the role of Site-I is not known. Structures and sequence analysis reveal that the receptor N-terminal domains (N-domains) are flexible and contain intrinsic disorder. Using a hybrid NMR-MD approach, we characterized the role of Site-I interactions for the CXCL8-CXCR1 pair. NMR data indicate that the CXCR1 N-domain becomes structured on binding and that the binding interface is extensive with 30% of CXCL8 residues participating in this initial interaction. MD simulations indicate that CXCL8 bound at Site-I undergoes extensive reorganization on engaging Site-II with several residues initially engaged at Site-I also engaging Site-II. We conclude that structural plasticity of Site-I interactions plays an active role in driving ligand recognition by a chemokine receptor. Copy rights belong to original authors. Visit the link for more info