title: NMR structure of the thromboxane A2 receptor ligand recognition pocket.
abstract: To overcome the difficulty of characterizing the structures of the extracellular loops (eLPs) of G protein-coupled receptors (GPCRs) other than rhodopsin, we have explored a strategy to generate a three-dimensional structural model for a GPCR, the thromboxane A(2) receptor. This three-dimensional structure was completed by the assembly of the NMR structures of the computation-guided constrained peptides that mimicked the extracellular loops and connected to the conserved seven transmembrane domains. The NMR structure-based model reveals the structural features of the eLPs, in which the second extracellular loop (eLP(2)) and the disulfide bond between the first extracellular loop (eLP(1)) and eLP(2) play a major role in forming the ligand recognition pocket. The eLP(2) conformation is dynamic and regulated by the oxidation and reduction of the disulfide bond, which affects ligand docking in the initial recognition. The reduced form of the thromboxane A(2) receptor experienced a decrease in ligand binding activity due to the rearrangement of the eLP(2) conformation. The ligand-bound receptor was, however, resistant to the reduction inactivation because the ligand covered the disulfide bond and stabilized the eLP(2) conformation. This molecular mechanism of ligand recognition is the first that may be applied to other prostanoid receptors and other GPCRs.
authors.affiliation: Vascular Biology Research Center and Division of Hematology, Department of Internal Medicine, The University of Texas Health Science Center, Houston, TX 77030, USA. kruan@uth.tmc.edu
authors.forename: Ke-He
authors.initials: KH
authors.lastname: Ruan
authors.forename: Jiaxin
authors.initials: J
authors.lastname: Wu
authors.forename: Shui-Ping
authors.initials: SP
authors.lastname: So
authors.forename: Lori A
authors.initials: LA
authors.lastname: Jenkins
authors.forename: Cheng-Huai
authors.initials: CH
authors.lastname: Ruan
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D004220:Disulfides / Q000737:chemistry; D006801:Humans; D008024:Ligands; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D010084:Oxidation-Reduction; D010455:Peptides / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D044244:Receptors, Thromboxane A2, Prostaglandin H2 / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment
chemical_list: D004220:Disulfides; D008024:Ligands; D010455:Peptides; D044244:Receptors, Thromboxane A2, Prostaglandin H2