title: Dynamic features of allosteric Ca2+ sensor in tissue-specific NCX variants.
abstract: The Na(+)-Ca(2+) exchanger (NCX) mediated Ca(2+) fluxes are essential for handling Ca(2+) homeostasis in many cell-types. Eukaryotic NCX variants contain regulatory CBD1 and CBD2 domains, whereas in distinct variants the Ca(2+) binding to Ca3-Ca4 sites of CBD1 results either in sustained activation, inhibition or no effect. CBD2 contains an alternatively spliced segment, which is expressed in a tissue-specific manner although its impact on allosteric regulation remains unclear. Recent studies revealed that the Ca(2+) binding to Ca3-Ca4 sites results in interdomain tethering of CBDs, which rigidifies CBDs movements with accompanied slow dissociation of "occluded" Ca(2+). Here we investigate the effects of CBD2 variants on Ca(2+) occlusion in the two-domain construct (CBD12). Mutational studies revealed that both sites (Ca3 and Ca4) contribute to Ca(2+) occlusion, whereas after dissociation of the first Ca(2+) ion the second Ca(2+) ion becomes occluded. This mechanism is common for the brain, kidney and cardiac splice variants of CBD12, although the occluded Ca(2+) exhibits 20-50-fold difference in off-rates among the tested variants. Therefore, the spliced exons on CBD2 affect the rate-limiting step of the occluded Ca(2+) dissociation at the primary regulatory sensor to shape dynamic features of allosteric regulation in NCX variants.
authors.affiliation: Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Ramat-Aviv, Israel.
authors.forename: Moshe
authors.initials: M
authors.lastname: Giladi
authors.forename: Hilla
authors.initials: H
authors.lastname: Bohbot
authors.forename: Tal
authors.initials: T
authors.lastname: Buki
authors.forename: Dan H
authors.initials: DH
authors.lastname: Schulze
authors.forename: Reuben
authors.initials: R
authors.lastname: Hiller
authors.forename: Daniel
authors.initials: D
authors.lastname: Khananshvili
mesh_terms: D000494:Allosteric Regulation; D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D001923:Brain Chemistry; D002118:Calcium / Q000737:chemistry*; D020013:Calcium Signaling; D003001:Cloning, Molecular; D004285:Dogs; D029721:Drosophila Proteins / Q000737:chemistry / Q000235:genetics; D004331:Drosophila melanogaster / Q000235:genetics; D004926:Escherichia coli / Q000737:chemistry / Q000235:genetics; D005091:Exons; D007668:Kidney / Q000737:chemistry; D008969:Molecular Sequence Data; D009154:Mutation; D017354:Point Mutation; D011485:Protein Binding; D011487:Protein Conformation; D020033:Protein Isoforms / Q000737:chemistry; D017434:Protein Structure, Tertiary; D019831:Sodium-Calcium Exchanger / Q000737:chemistry*
chemical_list: D029721:Drosophila Proteins; D020033:Protein Isoforms; D019831:Sodium-Calcium Exchanger; D002118:Calcium