title: Model for the allosteric regulation of the Na+/Ca2+ exchanger NCX.
abstract: The Na(+) /Ca(2+) exchanger provides a major Ca(2+) extrusion pathway in excitable cells and plays a key role in the control of intracellular Ca(2+) concentrations. In Canis familiaris, Na(+) /Ca(2+) exchanger (NCX) activity is regulated by the binding of Ca(2+) to two cytosolic Ca(2+) -binding domains, CBD1 and CBD2, such that Ca(2+) -binding activates the exchanger. Despite its physiological importance, little is known about the exchanger's global structure, and the mechanism of allosteric Ca(2+) -regulation remains unclear. It was found previously that for NCX in the absence of Ca(2+) the two domains CBD1 and CBD2 of the cytosolic loop are flexibly linked, while after Ca(2+) -binding they adopt a rigid arrangement that is slightly tilted. A realistic model for the mechanism of the exchanger's allosteric regulation should not only address this property, but also it should explain the distinctive behavior of Drosophila melanogaster's sodium/calcium exchanger, CALX, for which Ca(2+) -binding to CBD1 inhibits Ca(2+) exchange. Here, NMR spin relaxation and residual dipolar couplings were used to show that Ca(2+) modulates CBD1 and CBD2 interdomain flexibility of CALX in an analogous way as for NCX. A mechanistic model for the allosteric Ca(2+) regulation of the Na(+) /Ca(2+) exchanger is proposed. In this model, the intracellular loop acts as an entropic spring whose strength is modulated by Ca(2+) -binding to CBD1 controlling ion transport across the plasma membrane.
authors: Institute of Chemistry, University of São Paulo, São Paulo, SP, 05508-000, Brazil.
authors: Layara Akemi
authors: LA
authors: Abiko
authors: Institute of Chemistry, University of São Paulo, São Paulo, SP, 05508-000, Brazil.
authors: Phelipe M
authors: PM
authors: Vitale
authors: Institute of Chemistry, University of São Paulo, São Paulo, SP, 05508-000, Brazil.
authors: Denize C
authors: DC
authors: Favaro
authors: Institute of Chemistry, University of São Paulo, São Paulo, SP, 05508-000, Brazil.
authors: Pricila
authors: P
authors: Hauk
authors: Campus Chemical Instrument Center, The Ohio State University, Columbus, Ohio, 43210.
authors: Da-Wei
authors: DW
authors: Li
authors: Department of Chemistry & Biochemistry, The Ohio State University, Columbus, Ohio, 43210.
authors: Jiaqi
authors: J
authors: Yuan
authors: Campus Chemical Instrument Center, The Ohio State University, Columbus, Ohio, 43210.
authors: Lei
authors: L
authors: Bruschweiler-Li
authors: Institute of Chemistry, University of São Paulo, São Paulo, SP, 05508-000, Brazil.
authors: Roberto K
authors: RK
authors: Salinas
authors: Campus Chemical Instrument Center, The Ohio State University, Columbus, Ohio, 43210.|Department of Chemistry & Biochemistry, The Ohio State University, Columbus, Ohio, 43210.|Department of Biological Chemistry and Pharmacology, The Ohio State University, Columbus, Ohio, 43210.
authors: Rafael
authors: R
authors: Brüschweiler
mesh_terms: D000494:Allosteric Regulation; D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D004285:Dogs; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular; D011487:Protein Conformation; D019831:Sodium-Calcium Exchanger / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D019831:Sodium-Calcium Exchanger; D002118:Calcium
keywords: Na+/Ca2+ exchanger; allosteric regulation; protein plasticity; solution NMR