title: Conformational, receptor interaction and alanine scan studies of glucose-dependent insulinotropic polypeptide.
abstract: Glucose-dependent insulinotropic polypeptide (GIP) is an insulinotropic incretin hormone that stimulates insulin secretion during a meal. GIP has glucose lowering abilities and hence is considered as a potential target molecule for type 2 diabetes therapy. In this article, we present the solution structure of GIP in membrane-mimicking environments by proton NMR spectroscopy and molecular modelling. GIP adopts an α-helical conformation between residues Phe(6)-Gly(31) and Ala(13)-Gln(29) for micellar and bicellar media, respectively. Previously we examined the effect of N-terminal Ala substitution in GIP, but here eight GIP analogues were synthesised by replacing individual residues within the central 8-18 region with alanine. These studies showed relatively minor changes in biological activity as assessed by insulin releasing potency. However, at higher concentration, GIP(Ala(16)), and GIP(Ala(18)) showed insulin secreting activity higher than the native GIP (P<0.01 to P<0.001) in cultured pancreatic BRIN-BD11 cells. Receptor interaction studies of the native GIP with the extracellular domain of its receptor were performed by using two different docking algorithms. At the optimised docking conformation, the complex was stabilised by the presence of hydrophobic interactions and intermolecular hydrogen bonding. Further, we have identified some potentially important additional C-terminal interactions of GIP with its N-terminal extracellular receptor domain.
authors.affiliation: School of Biomolecular and Biomedical Science, Centre for Synthesis and Chemical Biology, SEC Strategic Research Cluster, UCD Conway Institute, University College Dublin, Dublin 4, Ireland.
authors.forename: Kalyana C
authors.initials: KC
authors.lastname: Venneti
authors.forename: J Paul G
authors.initials: JP
authors.lastname: Malthouse
authors.forename: Finbarr P M
authors.initials: FP
authors.lastname: O'Harte
authors.forename: Chandralal M
authors.initials: CM
authors.lastname: Hewage
mesh_terms: D000409:Alanine / Q000737:chemistry* / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D045744:Cell Line, Tumor; D004305:Dose-Response Relationship, Drug; D005749:Gastric Inhibitory Polypeptide / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology; D005947:Glucose / Q000494:pharmacology; D006801:Humans; D006860:Hydrogen Bonding; D057927:Hydrophobic and Hydrophilic Interactions; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology; D011485:Protein Binding; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011964:Receptors, Gastrointestinal Hormone / Q000737:chemistry* / Q000378:metabolism
chemical_list: D007328:Insulin; D010446:Peptide Fragments; D011964:Receptors, Gastrointestinal Hormone; C101760:gastric inhibitory polypeptide (1-42); D005749:Gastric Inhibitory Polypeptide; C041086:gastric inhibitory polypeptide receptor; D005947:Glucose; D000409:Alanine