title: Functional elements of the gastric inhibitory polypeptide receptor: Comparison between secretin- and rhodopsin-like G protein-coupled receptors.
abstract: Innovative crystallographic techniques have resulted in an exponential growth in the number of solved G-protein coupled receptor (GPCR) structures and a better understanding of the mechanisms of class A receptor activation and G protein binding. The recent release of the type 1 receptor for the corticotropin-releasing factor and the glucagon receptor structures, two members of the secretin-like family, gives the opportunity to understand these mechanisms of activation in this family of GPCRs. Here, we addressed the comparison of the functional elements of class A and secretin-like GPCRs, using the glucose-dependent insulinotropic polypeptide receptor (GIPR) as a model receptor. Inactive and active models of GIPR permitted to select, by structural homology with class A GPCRs, several residues that may form key interactions presumably involved in receptor activation and Gs coupling, for pharmacological evaluation. Mutants on these amino acids were expressed in HEKT 293 cells and characterized in terms of GIP-induced cAMP production. We identified various functional domains spanning from the peptide-binding to the G protein pockets: including: a network linking the extracellular part of transmembrane (TM) 6 with TMs 2 and 7; a polar lock that resembles the ionic-lock in class A GPCRs; an interaction between TMs 3 and 7 that favors activation; and two clusters of polar/charged and of hydrophobic residues that interact with the C-terminus of the Gα. The results show that despite the low degree of sequence similarity between rhodopsin- and secretin-like GPCRs, the two families share conserved elements in their mechanisms of activation and G protein binding.
authors.affiliation: Laboratori de Medicina Computacional, Unitat de Bioestadística, Facultat de Medicina, Universitat Autònoma de Barcelona, 08193 Barcelona, Spain.
authors.forename: Arnau
authors.initials: A
authors.lastname: Cordomí
authors.affiliation: Université de Toulouse 3, EA 4552, Toulouse, France.
authors.forename: Sadek
authors.initials: S
authors.lastname: Ismail
authors.affiliation: Laboratori de Medicina Computacional, Unitat de Bioestadística, Facultat de Medicina, Universitat Autònoma de Barcelona, 08193 Barcelona, Spain.
authors.forename: Minos-Timotheos
authors.initials: MT
authors.lastname: Matsoukas
authors.affiliation: Université de Toulouse 3, EA 4552, Toulouse, France.
authors.forename: Chantal
authors.initials: C
authors.lastname: Escrieut
authors.affiliation: Université de Toulouse 3, EA 4552, Toulouse, France.
authors.forename: Marie-Julie
authors.initials: MJ
authors.lastname: Gherardi
authors.affiliation: Laboratori de Medicina Computacional, Unitat de Bioestadística, Facultat de Medicina, Universitat Autònoma de Barcelona, 08193 Barcelona, Spain.
authors.forename: Leonardo
authors.initials: L
authors.lastname: Pardo
authors.affiliation: Université de Toulouse 3, EA 4552, Toulouse, France. Electronic address: daniel.fourmy@inserm.fr.
authors.forename: Daniel
authors.initials: D
authors.lastname: Fourmy
mesh_terms: D000595:Amino Acid Sequence; D000242:Cyclic AMP / Q000737:chemistry*; D005749:Gastric Inhibitory Polypeptide / Q000737:chemistry* / Q000235:genetics; D015870:Gene Expression; D057809:HEK293 Cells; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D007700:Kinetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010446:Peptide Fragments / Q000737:chemistry* / Q000235:genetics; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs; D017433:Protein Structure, Secondary; D011964:Receptors, Gastrointestinal Hormone / Q000737:chemistry* / Q000235:genetics; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics; D012243:Rhodopsin / Q000737:chemistry* / Q000235:genetics; D012633:Secretin / Q000737:chemistry* / Q000235:genetics; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D055672:Static Electricity; D040681:Structural Homology, Protein
chemical_list: D010446:Peptide Fragments; D011964:Receptors, Gastrointestinal Hormone; D011994:Recombinant Proteins; D012633:Secretin; D005749:Gastric Inhibitory Polypeptide; D012243:Rhodopsin; C041086:gastric inhibitory polypeptide receptor; D000242:Cyclic AMP
keywords: G protein; G protein-coupled receptor (GPCR); Gastric glucose-dependent insulinotropic polypeptide receptor (GIPR); Homology modeling; Molecular modeling; Secretin-like receptor; Site-directed mutagenesis