title: Helix 3 acts as a conformational hinge in Class A GPCR activation: An analysis of interhelical interaction energies in crystal structures.
abstract: A collection of crystal structures of rhodopsin, β2-adrenergic and adenosine A2A receptors in active, intermediate and inactive states were selected for structural and energetic analyses to identify the changes involved in the activation/deactivation of Class A GPCRs. A set of helix interactions exclusive to either inactive or active/intermediate states were identified. The analysis of these interactions distinguished some local conformational changes involved in receptor activation, in particular, a packing between the intracellular domains of transmembrane helices H3 and H7 and a separation between those of H2 and H6. Also, differential movements of the extracellular and intracellular domains of these helices are apparent. Moreover, a segment of residues in helix H3, including residues L/I3.40 to L3.43, is identified as a key component of the activation mechanism, acting as a conformational hinge between extracellular and intracellular regions. Remarkably, the influence on the activation process of some glutamic and aspartic acidic residues and, as a consequence, the influence of variations on local pH is highlighted. Structural hypotheses that arose from the analysis of rhodopsin, β2-adrenergic and adenosine A2A receptors were tested on the active and inactive M2 muscarinic acetylcholine receptor structures and further discussed in the context of the new mechanistic insights provided by the recently determined active and inactive crystal structures of the μ-opioid receptor. Overall, the structural and energetic analyses of the interhelical interactions present in this collection of Class A GPCRs suggests the existence of a common general activation mechanism featuring a chemical space useful for drug discovery exploration.
authors.affiliation: Laboratory of Molecular Neuropharmacology and Bioinformatics, Institut de Neurociències and Unitat de Bioestadística, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain.
authors.forename: Isaias
authors.initials: I
authors.lastname: Lans
authors.affiliation: Laboratory of Molecular Neuropharmacology and Bioinformatics, Institut de Neurociències and Unitat de Bioestadística, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain.
authors.forename: James A R
authors.initials: JAR
authors.lastname: Dalton
authors.affiliation: Laboratory of Molecular Neuropharmacology and Bioinformatics, Institut de Neurociències and Unitat de Bioestadística, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain. Electronic address: Jesus.Giraldo@uab.es.
authors.forename: Jesús
authors.initials: J
authors.lastname: Giraldo
mesh_terms: D001665:Binding Sites; D018360:Crystallography, X-Ray; D004789:Enzyme Activation / Q000502:physiology; D008958:Models, Molecular; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D043705:Receptor, Adenosine A2A / Q000378:metabolism / Q000648:ultrastructure*; D043585:Receptor, Muscarinic M2 / Q000378:metabolism / Q000648:ultrastructure*; D018343:Receptors, Adrenergic, beta-2 / Q000378:metabolism / Q000648:ultrastructure*; D017450:Receptors, Opioid, mu / Q000378:metabolism / Q000648:ultrastructure*; D012243:Rhodopsin / Q000378:metabolism / Q000648:ultrastructure*; D015398:Signal Transduction / Q000502:physiology
chemical_list: D043705:Receptor, Adenosine A2A; D043585:Receptor, Muscarinic M2; D018343:Receptors, Adrenergic, beta-2; D017450:Receptors, Opioid, mu; D012243:Rhodopsin
keywords: Activation mechanism; Conformational changes; GPCR; Interhelical interactions; Transmembrane helices