title: Homology modeling of the transmembrane domain of the human calcium sensing receptor and localization of an allosteric binding site.
abstract: A homology model for the human calcium sensing receptor (hCaR) transmembrane domain utilizing bovine rhodopsin (bRho) structural information was derived and tested by docking the allosteric antagonist, NPS 2143, followed by mutagenesis of predicted contact sites. Mutation of residues Phe-668 (helix II), Arg-680, or Phe-684 (helix III) to Ala (or Val or Leu) and Glu-837 (helix VII) to Ile (or Gln) reduced the inhibitory effects of NPS 2143 on [Ca2+]i responses. The calcimimetic NPS R-568 increases the potency of Ca2+ in functional assays of CaR. Mutations at Phe-668, Phe-684, or Glu-837 attenuated the effects of this compound, but mutations at Arg-680 had no effect. In all cases, mutant CaRs responded normally to Ca2+ or phenylalanine, which act at distinct site(s). Discrimination by the Arg-680 mutant is consistent with the structural differences between NPS 2143, which contains an alkyl bridge hydroxyl group, and NPS R-568, which does not. The homology model of the CaR transmembrane domain robustly accounts for binding of both an allosteric antagonist and agonist, which share a common site, and provides a basis for the development of more specific and/or potent allosteric modulators of CaR. These studies suggest that the bRho backbone can be used as a starting point for homology modeling of even distantly related G protein-coupled receptors and provide a rational framework for investigation of the contributions of the transmembrane domain to CaR function.
authors.affiliation: Department of Biology, Syracuse University, Syracuse, New York 13244, USA.
authors.forename: Susanne U
authors.initials: SU
authors.lastname: Miedlich
authors.forename: Lucio
authors.initials: L
authors.lastname: Gama
authors.forename: Klaus
authors.initials: K
authors.lastname: Seuwen
authors.forename: Romain M
authors.initials: RM
authors.lastname: Wolf
authors.forename: Gerda E
authors.initials: GE
authors.lastname: Breitwieser
mesh_terms: D000495:Allosteric Site; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000737:chemistry / Q000378:metabolism; D002417:Cattle; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D008024:Ligands; D008956:Models, Chemical; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D017354:Point Mutation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D044169:Receptors, Calcium-Sensing / Q000737:chemistry* / Q000378:metabolism; D012243:Rhodopsin / Q000737:chemistry; D017386:Sequence Homology, Amino Acid; D013997:Time Factors; D014162:Transfection
chemical_list: D008024:Ligands; D044169:Receptors, Calcium-Sensing; D012243:Rhodopsin; D002118:Calcium