Key residues controlling bidirectional ion movements in Na+/Ca2+ exchanger. (December 2018)

• Record Type: Journal Article
• Authors: van Dijk, Liat; Giladi, Moshe; Refaeli, Bosmat; Hiller, Reuben; Cheng, Mary Hongying; Bahar, Ivet; Khananshvili, Daniel
• Is Part Of: Cell calcium. Volume 76(2018)
• Page Start: 10
• Page End: 22
• Publication Date: 2018-12
• Subjects: NCX sodium–calcium exchanger -- CBD calcium binding domain -- Mops 3-(N-morpholino)propanesulfonic acid -- Tris tris(hydroxymethyl)-aminomethane -- HEPES 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid -- MES 2-(N-morpholino)ethanesulfonic acid -- Fluo-3 N-[2-[2[bis-(carboxymethyl)-amino]-5-(2, 7dichloro-6-hydroxy-3-oxy-3Hxanthen-9-yl) henoxy]ethoxy]-4methylphenyl]-N(carboxymethyl)glycine -- SDS-PAGE sodium dodecyl sulfatepolyacrylamide gel electrophoresis -- EGTA ethyleneglycoltetraacetic acid -- PMSF phenylmethanesulfonyl fluoride -- HDX-MS Hydrogen-deuterium exchange mass spectrometry -- DTT 1, 4-dithiothreitol; Calcium -- Metabolism -- Periodicals; Vertebrates -- Physiology -- Periodicals; Calcium -- Physiological effect -- Periodicals; Cell physiology -- Periodicals; Calcium in the body -- Periodicals; 572.516
• DOI: 10.1016/j.ceca.2018.09.004
• Languages: English
• ISSNs: 0143-4160

Abstract

Graphical abstract: Highlights: Distinct residues differentially control the functional asymmetry and turnover rates in NCX. The key residues are located at specific segments and contribute to functionally important conformational transitions. The key residues control conformational flexibility of ion-transporting helices and thus, limit the dynamic features of critical conformational transitions. The underlying mechanisms can shape dynamic response of NCX variants to cell-specific Ca 2+ and Na + signaling. Abstract: Prokaryotic and eukaryotic Na + /Ca 2+ exchangers (NCX) control Ca 2+ homeostasis. NCX orthologs exhibit up to 10 4 -fold differences in their turnover rates ( k cat ), whereas the ratios between the cytosolic (cyt) and extracellular (ext) Km values (Kint = Km Cyt /Km Ext ) are highly asymmetric and alike (Kint ≤ 0.1) among NCXs. The structural determinants controlling a huge divergence in k cat at comparable Kint remain unclear, although 11 (out of 12) ion-coordinating residues are highly conserved among NCXs. The crystal structure of the archaeal NCX (NCX_Mj) was explored for testing the mutational effects of pore-allied and loop residues on k cat and Kint . Among 55 tested residues, 26 mutations affect either k cat or Kint, where two major groups can be distinguished. The first group of mutations (14 residues) affect k cat rather than Kint . The majority of these residues (10 out of 14) are located within the extracellular vestibule near the pore center. The second group of mutations (12 residues) affect Kint rather than k cat, whereas the majority of residues (9 out 12) are randomly dispersed within the extracellular vestibule. In conjunction with computational modeling-simulations and hydrogen-deuterium exchange mass-spectrometry (HDX-MS), the present mutational analysis highlights structural elements that differentially govern the intrinsic asymmetry and transport rates. The key residues, located at specific segments, can affect the characteristic features of local backbone dynamics and thus, the conformational flexibility of ion-transporting helices contributing to critical conformational transitions. The underlying mechanisms might have a physiological relevance for matching the response modes of NCX variants to cell-specific Ca 2+ and Na + signaling.