Homology Modeling of the Transmembrane Domain of the Human Calcium Sensing Receptor and Localization of an Allosteric Binding Site

Susanne U. Miedlich, Lucio Gama, Klaus Seuwen, Romain M. Wolf, Gerda E. Breitwieser

Research output: Contribution to journalArticlepeer-review

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 VIII) to Ile (or Gln) reduced the inhibitory effects of NPS 2143 on [Ca 2+]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 Ca 2+ of 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.

Original languageEnglish (US)
Pages (from-to)7254-7263
Number of pages10
JournalJournal of Biological Chemistry
Volume279
Issue number8
DOIs
StatePublished - Feb 20 2004

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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