title: Identification of an L-phenylalanine binding site enhancing the cooperative responses of the calcium-sensing receptor to calcium.
abstract: Functional positive cooperative activation of the extracellular calcium ([Ca(2+)]o)-sensing receptor (CaSR), a member of the family C G protein-coupled receptors, by [Ca(2+)]o or amino acids elicits intracellular Ca(2+) ([Ca(2+)]i) oscillations. Here, we report the central role of predicted Ca(2+)-binding site 1 within the hinge region of the extracellular domain (ECD) of CaSR and its interaction with other Ca(2+)-binding sites within the ECD in tuning functional positive homotropic cooperativity caused by changes in [Ca(2+)]o. Next, we identify an adjacent L-Phe-binding pocket that is responsible for positive heterotropic cooperativity between [Ca(2+)]o and L-Phe in eliciting CaSR-mediated [Ca(2+)]i oscillations. The heterocommunication between Ca(2+) and an amino acid globally enhances functional positive homotropic cooperative activation of CaSR in response to [Ca(2+)]o signaling by positively impacting multiple [Ca(2+)]o-binding sites within the ECD. Elucidation of the underlying mechanism provides important insights into the longstanding question of how the receptor transduces signals initiated by [Ca(2+)]o and amino acids into intracellular signaling events.
authors.affiliation: From the Department of Chemistry, Center for Diagnostics and Therapeutics, Georgia State University, Atlanta, Georgia 30303 and.
authors.forename: Chen
authors.initials: C
authors.lastname: Zhang
authors.forename: Yun
authors.initials: Y
authors.lastname: Huang
authors.forename: Yusheng
authors.initials: Y
authors.lastname: Jiang
authors.forename: Nagaraju
authors.initials: N
authors.lastname: Mulpuri
authors.forename: Ling
authors.initials: L
authors.lastname: Wei
authors.forename: Donald
authors.initials: D
authors.lastname: Hamelberg
authors.forename: Edward M
authors.initials: EM
authors.lastname: Brown
authors.forename: Jenny J
authors.initials: JJ
authors.lastname: Yang
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D002118:Calcium / Q000494:pharmacology*; D057809:HEK293 Cells; D006801:Humans; D042541:Intracellular Space / Q000187:drug effects / Q000378:metabolism; D056004:Molecular Dynamics Simulation; D008969:Molecular Sequence Data; D050505:Mutant Proteins / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D010649:Phenylalanine; D025341:Principal Component Analysis; D017434:Protein Structure, Tertiary; D044169:Receptors, Calcium-Sensing / Q000737:chemistry / Q000378:metabolism*; D016415:Sequence Alignment; D013816:Thermodynamics
chemical_list: D050505:Mutant Proteins; D044169:Receptors, Calcium-Sensing; D010649:Phenylalanine; D002118:Calcium
keywords: Amino Acid; Calcium Imaging; Calcium Oscillation; Calcium Signaling; Calcium-sensing Receptor; Cooperativity; G Protein-coupled Receptors (GPCR)