title: Dynamic conformational switching in the chemokine ligand is essential for G-protein-coupled receptor activation.
abstract: Chemokines mediate diverse functions from organogenesis to mobilizing leucocytes, and are unusual agonists for class-A GPCRs (G-protein-coupled receptors) because of their large size and multi-domain structure. The current model for receptor activation, which involves interactions between chemokine N-loop and receptor N-terminal residues (Site-I) and between chemokine N-terminal and receptor extracellular loop/transmembrane residues (Site-II), fails to describe differences in ligand/receptor selectivity and the activation of multiple signalling pathways. In the present study, we show in neutrophil-activating chemokine CXCL8 that the highly conserved GP (glycine-proline) motif located distal to both N-terminal and N-loop residues couples Site-I and Site-II interactions. GP mutants showed large differences from native-like to complete loss of function that could not be correlated with the specific mutation, receptor affinity or subtype, or a specific signalling pathway. NMR studies indicated that the GP motif does not influence Site-I interactions, but molecular dynamics simulations suggested that this motif dictates substates of the CXCL8 conformational ensemble. We conclude that the GP motif enables diverse receptor functions by controlling cross-talk between Site-I and Site-II, and further propose that the repertoire of chemokine functions is best described by a conformational ensemble model in which a network of long-range coupled indirect interactions mediate receptor activity.
authors.affiliation: *Department of Biochemistry and Molecular Biology, The University of Texas Medical Branch, 301 University Boulevard, Galveston, TX 77555-1055, U.S.A.
authors.forename: Prem Raj B
authors.initials: PR
authors.lastname: Joseph
authors.forename: Kirti V
authors.initials: KV
authors.lastname: Sawant
authors.forename: Angela
authors.initials: A
authors.lastname: Isley
authors.forename: Mesias
authors.initials: M
authors.lastname: Pedroza
authors.forename: Roberto P
authors.initials: RP
authors.lastname: Garofalo
authors.forename: Ricardo M
authors.initials: RM
authors.lastname: Richardson
authors.forename: Krishna
authors.initials: K
authors.lastname: Rajarathnam
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D001665:Binding Sites; D020013:Calcium Signaling; D002460:Cell Line; D017124:Conserved Sequence; D005260:Female; D016209:Interleukin-8 / Q000737:chemistry* / Q000378:metabolism; D008024:Ligands; D051379:Mice; D008807:Mice, Inbred BALB C; D056004:Molecular Dynamics Simulation; D008969:Molecular Sequence Data; D009504:Neutrophils / Q000276:immunology; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D051381:Rats; D023062:Receptors, Interleukin-8A / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D023063:Receptors, Interleukin-8B / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D016209:Interleukin-8; D008024:Ligands; D023062:Receptors, Interleukin-8A; D023063:Receptors, Interleukin-8B
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