title: Signal transmission through the CXC chemokine receptor 4 (CXCR4) transmembrane helices.
abstract: The atomic-level mechanisms by which G protein-coupled receptors (GPCRs) transmit extracellular ligand binding events through their transmembrane helices to activate intracellular G proteins remain unclear. Using a comprehensive library of mutations covering all 352 residues of the GPCR CXC chemokine receptor 4 (CXCR4), we identified 41 amino acids that are required for signaling induced by the chemokine ligand CXCL12 (stromal cell-derived factor 1). CXCR4 variants with each of these mutations do not signal properly but remain folded, based on receptor surface trafficking, reactivity to conformationally sensitive monoclonal antibodies, and ligand binding. When visualized on the structure of CXCR4, the majority of these residues form a continuous intramolecular signaling chain through the transmembrane helices; this chain connects chemokine binding residues on the extracellular side of CXCR4 to G protein-coupling residues on its intracellular side. Integrated into a cohesive model of signal transmission, these CXCR4 residues cluster into five functional groups that mediate (i) chemokine engagement, (ii) signal initiation, (iii) signal propagation, (iv) microswitch activation, and (v) G protein coupling. Propagation of the signal passes through a "hydrophobic bridge" on helix VI that coordinates with nearly every known GPCR signaling motif. Our results agree with known conserved mechanisms of GPCR activation and significantly expand on understanding the structural principles of CXCR4 signaling.
authors.affiliation: Integral Molecular, Philadelphia, PA 19104;
authors.forename: Melanie P
authors.initials: MP
authors.lastname: Wescott
authors.affiliation: Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California, San Diego, La Jolla, CA 92093.
authors.forename: Irina
authors.initials: I
authors.lastname: Kufareva
authors.affiliation: Integral Molecular, Philadelphia, PA 19104;
authors.forename: Cheryl
authors.initials: C
authors.lastname: Paes
authors.affiliation: Integral Molecular, Philadelphia, PA 19104;
authors.forename: Jason R
authors.initials: JR
authors.lastname: Goodman
authors.affiliation: Integral Molecular, Philadelphia, PA 19104;
authors.forename: Yana
authors.initials: Y
authors.lastname: Thaker
authors.affiliation: Integral Molecular, Philadelphia, PA 19104;
authors.forename: Bridget A
authors.initials: BA
authors.lastname: Puffer
authors.affiliation: Integral Molecular, Philadelphia, PA 19104;
authors.forename: Eli
authors.initials: E
authors.lastname: Berdougo
authors.affiliation: Integral Molecular, Philadelphia, PA 19104;
authors.forename: Joseph B
authors.initials: JB
authors.lastname: Rucker
authors.affiliation: Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California, San Diego, La Jolla, CA 92093.
authors.forename: Tracy M
authors.initials: TM
authors.lastname: Handel
authors.affiliation: Integral Molecular, Philadelphia, PA 19104; bdoranz@integralmolecular.com.
authors.forename: Benjamin J
authors.initials: BJ
authors.lastname: Doranz
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites / Q000235:genetics; D054377:Chemokine CXCL12 / Q000737:chemistry / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D008024:Ligands; D008958:Models, Molecular; D009154:Mutation; D011485:Protein Binding; D011487:Protein Conformation; D055503:Protein Multimerization; D019718:Receptors, CXCR4 / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction
chemical_list: C515255:CXCL12 protein, human; D054377:Chemokine CXCL12; D008024:Ligands; D019718:Receptors, CXCR4
keywords: G protein; GPCR activation; chemokine receptor; hydrophobic bridge; shotgun mutagenesis