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Structure-Based Function and Regulation of NCX Variants: Updates and Challenges. Int J Mol Sci 2022; 24:ijms24010061. [PMID: 36613523 PMCID: PMC9820601 DOI: 10.3390/ijms24010061] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2022] [Revised: 12/14/2022] [Accepted: 12/15/2022] [Indexed: 12/24/2022] Open
Abstract
The plasma-membrane homeostasis Na+/Ca2+ exchangers (NCXs) mediate Ca2+ extrusion/entry to dynamically shape Ca2+ signaling/in biological systems ranging from bacteria to humans. The NCX gene orthologs, isoforms, and their splice variants are expressed in a tissue-specific manner and exhibit nearly 104-fold differences in the transport rates and regulatory specificities to match the cell-specific requirements. Selective pharmacological targeting of NCX variants could benefit many clinical applications, although this intervention remains challenging, mainly because a full-size structure of eukaryotic NCX is unavailable. The crystal structure of the archaeal NCX_Mj, in conjunction with biophysical, computational, and functional analyses, provided a breakthrough in resolving the ion transport mechanisms. However, NCX_Mj (whose size is nearly three times smaller than that of mammalian NCXs) cannot serve as a structure-dynamic model for imitating high transport rates and regulatory modules possessed by eukaryotic NCXs. The crystal structures of isolated regulatory domains (obtained from eukaryotic NCXs) and their biophysical analyses by SAXS, NMR, FRET, and HDX-MS approaches revealed structure-based variances of regulatory modules. Despite these achievements, it remains unclear how multi-domain interactions can decode and integrate diverse allosteric signals, thereby yielding distinct regulatory outcomes in a given ortholog/isoform/splice variant. This article summarizes the relevant issues from the perspective of future developments.
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2
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Giladi M, Mitra S, Simhaev L, Hiller R, Refaeli B, Strauss T, Baiz CR, Khananshvili D. Exploring the Li + transporting mutant of NCX_Mj for assigning ion binding sites of mitochondrial NCLX. Cell Calcium 2022; 107:102651. [PMID: 36116246 PMCID: PMC10124574 DOI: 10.1016/j.ceca.2022.102651] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2022] [Revised: 08/14/2022] [Accepted: 09/01/2022] [Indexed: 11/02/2022]
Abstract
The plasma membrane (NCX) and mitochondrial (NCLX) Na+/Ca2+ exchangers are structurally related proteins, although they operate under strictly different ionic conditions and membrane potentials. In contrast with NCX, NCLX can transport either Li+ or Na+ in exchange for Ca2+. Whereas the crystal structure of the archaeal NCX (NCX_Mj) describes the binding sites for alternative binding of 3Na+ or 1Ca2+, these features remain elusive for NCLX due to the lack of structural information. To elucidate the ion-binding features of mitochondrial NCLX, we analyzed here the Li+-transporting NCLX_Mj mutant, produced by replacing the ion-coordinating residues in the archaeal NCX (NCX_Mj) to match the ion-coordinating residues of human NCLX. The NCLX_Mj-mediated Na+/Ca2+ or Li+/Ca2+ exchange rates are insensitive to varying voltage, consistent with an electroneutral ion exchange. Molecular dynamics (MD) simulations revealed that NCLX_Mj contains two novel Li+ binding sites with four ion-coordinating residues, derived from the three Na+ binding sites of NCX_Mj. The ion-coordination modes, observed in the MD simulations, were further supported by two-dimensional infrared (2D IR) spectroscopy and by testing the mutational effects on the ion fluxes. Collectively, our results revealed a structural basis for Li+ binding and electroneutral transport (2Na+/Li+:1Ca2+) by NCLX_Mj, meaning that the NCLX-mediated electroneutral transport may predefine mitochondrial Ca2+ and Na+ signaling to modulate cellular functions.
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Affiliation(s)
- Moshe Giladi
- Department of Physiology and Pharmacology, Sackler Faculty of Medicine, Tel-Aviv University, Tel Aviv 69978, Israel; Tel-Aviv Sourasky Medical Center, Tel Aviv 6423906, Israel
| | - Sunayana Mitra
- Department of Chemistry, University of Texas at Austin, Austin, TX 78712-1224, USA
| | - Luba Simhaev
- Computer-Assisted Drug Design Unit, Blavatnik Center for Drug Discovery, Tel-Aviv University, Tel Aviv 69978, Israel
| | - Reuben Hiller
- Department of Physiology and Pharmacology, Sackler Faculty of Medicine, Tel-Aviv University, Tel Aviv 69978, Israel
| | - Bosmat Refaeli
- Department of Physiology and Pharmacology, Sackler Faculty of Medicine, Tel-Aviv University, Tel Aviv 69978, Israel
| | - Tali Strauss
- Department of Physiology and Pharmacology, Sackler Faculty of Medicine, Tel-Aviv University, Tel Aviv 69978, Israel
| | - Carlos R Baiz
- Department of Chemistry, University of Texas at Austin, Austin, TX 78712-1224, USA.
| | - Daniel Khananshvili
- Department of Physiology and Pharmacology, Sackler Faculty of Medicine, Tel-Aviv University, Tel Aviv 69978, Israel.
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3
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Garbincius JF, Elrod JW. Mitochondrial calcium exchange in physiology and disease. Physiol Rev 2022; 102:893-992. [PMID: 34698550 PMCID: PMC8816638 DOI: 10.1152/physrev.00041.2020] [Citation(s) in RCA: 136] [Impact Index Per Article: 68.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2021] [Revised: 08/16/2021] [Accepted: 10/19/2021] [Indexed: 12/13/2022] Open
Abstract
The uptake of calcium into and extrusion of calcium from the mitochondrial matrix is a fundamental biological process that has critical effects on cellular metabolism, signaling, and survival. Disruption of mitochondrial calcium (mCa2+) cycling is implicated in numerous acquired diseases such as heart failure, stroke, neurodegeneration, diabetes, and cancer and is genetically linked to several inherited neuromuscular disorders. Understanding the mechanisms responsible for mCa2+ exchange therefore holds great promise for the treatment of these diseases. The past decade has seen the genetic identification of many of the key proteins that mediate mitochondrial calcium uptake and efflux. Here, we present an overview of the phenomenon of mCa2+ transport and a comprehensive examination of the molecular machinery that mediates calcium flux across the inner mitochondrial membrane: the mitochondrial uniporter complex (consisting of MCU, EMRE, MICU1, MICU2, MICU3, MCUB, and MCUR1), NCLX, LETM1, the mitochondrial ryanodine receptor, and the mitochondrial permeability transition pore. We then consider the physiological implications of mCa2+ flux and evaluate how alterations in mCa2+ homeostasis contribute to human disease. This review concludes by highlighting opportunities and challenges for therapeutic intervention in pathologies characterized by aberrant mCa2+ handling and by summarizing critical unanswered questions regarding the biology of mCa2+ flux.
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Affiliation(s)
- Joanne F Garbincius
- Center for Translational Medicine, Lewis Katz School of Medicine at Temple University, Philadelphia, Pennsylvania
| | - John W Elrod
- Center for Translational Medicine, Lewis Katz School of Medicine at Temple University, Philadelphia, Pennsylvania
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Proton-modulated interactions of ions with transport sites of prokaryotic and eukaryotic NCX prototypes. Cell Calcium 2021; 99:102476. [PMID: 34564055 DOI: 10.1016/j.ceca.2021.102476] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2021] [Revised: 09/13/2021] [Accepted: 09/16/2021] [Indexed: 11/23/2022]
Abstract
The cytosolic pH decline from 7.2 to 6.9 results in 90% inactivation of mammalian Na+/Ca2+ exchangers (NCXs) due to protons interactions with regulatory and transport domains ("proton block"). Remarkably, the pH titration curves of mammalian and prokaryotic NCXs significantly differ, even after excluding the allosteric effects through regulatory domains. This is fascinating since "only" three (out of twelve) ion-coordinating residues (T50S, E213D, and D240N) differ between the archaeal NCX_Mj and mammalian NCXs although they contain either three or two carboxylates, respectively. To resolve the underlying mechanisms of pH-dependent regulation, the ion-coordinating residues of NCX_Mj were mutated to imitate the ion ligation arrays of mammalian NCXs; the mutational effects were tested on the ion binding/transport by using ion-flux assays and two-dimensional infrared (2D IR) spectroscopy. Our analyses revealed that two deprotonated carboxylates ligate 3Na+ or 1Ca2+ in NCX prototypes with three or two carboxylates. The Na+/Ca2+ exchange rates of NCX_Mj reach saturation at pH 5.0, whereas the Na+/Ca2+ exchange rates of the cardiac NCX1.1 gradually increase even at alkaline pHs. The T50S replacement in NCX_Mj "recapitulates" the pH titration curves of mammalian NCX by instigating an alkaline shift. Proteolytic shaving of regulatory CBD domains activates NCX1.1, although the normalized pH-titration curves are comparable in trypsin treated and untreated NCX1.1. Thus, the T50S-dependent alkaline shift sets a dynamic range for "proton block" function at physiological pH, whereas the CBDs (and other regulatory modes) modulate incremental changes in the transport rates rather than affect the shape of pH dependent curves.
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5
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Khananshvili D. The Archaeal Na +/Ca 2+ Exchanger (NCX_Mj) as a Model of Ion Transport for the Superfamily of Ca 2+/CA Antiporters. Front Chem 2021; 9:722336. [PMID: 34409017 PMCID: PMC8366772 DOI: 10.3389/fchem.2021.722336] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2021] [Accepted: 07/20/2021] [Indexed: 11/13/2022] Open
Abstract
The superfamily of Calcium/Cation (Ca2+/CA) antiporters extrude Ca2+ from the cytosol or subcellular compartments in exchange with Na+, K+, H+, Li+, or Mg2+ and thereby provide a key mechanism for Ca2+ signaling and ion homeostasis in biological systems ranging from bacteria to humans. The structure-dynamic determinants of ion selectivity and transport rates remain unclear, although this is of primary physiological significance. Despite wide variances in the ion selectivity and transport rates, the Ca2+/CA proteins share structural motifs, although it remains unclear how the ion recognition/binding is coupled to the ion translocation events. Here, the archaeal Na+/Ca2+ exchanger (NCX_Mj) is considered as a structure-based model that can help to resolve the ion transport mechanisms by using X-ray, HDX-MS, ATR-FTIR, and computational approaches in conjunction with functional analyses of mutants. Accumulating data reveal that the local backbone dynamics at ion-coordinating residues is characteristically constrained in apo NCX_Mj, which may predefine the affinity and stability of ion-bound species in the ground and transition states. The 3Na+ or 1Ca2+ binding to respective sites of NCX_Mj rigidify the backbone dynamics at specific segments, where the ion-dependent compression of the ion-permeating four-helix bundle (TM2, TM3, TM7, and TM8) induces the sliding of the two-helix cluster (TM1/TM6) on the protein surface to switch the OF (outward-facing) and IF (inward-facing) conformations. Taking into account the common structural elements shared by Ca2+/CAs, NCX_Mj may serve as a model for studying the structure-dynamic and functional determinants of ion-coupled alternating access, transport catalysis, and ion selectivity in Ca2+/CA proteins.
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Affiliation(s)
- Daniel Khananshvili
- Department of Physiology and Pharmacology, Sackler Faculty of Medicine, Tel-Aviv University, Tel-Aviv, Israel
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6
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Assali EA, Sekler I. Sprinkling salt on mitochondria: The metabolic and pathophysiological roles of mitochondrial Na + signaling mediated by NCLX. Cell Calcium 2021; 97:102416. [PMID: 34062329 DOI: 10.1016/j.ceca.2021.102416] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2021] [Revised: 04/25/2021] [Accepted: 04/26/2021] [Indexed: 11/25/2022]
Abstract
NCLX, the mitochondrial Na+/Ca2+ transporter is a key player in Ca2+ signaling. However, its role in Na+ signaling is poorly understood. In this review we focus on Na+ signaling by NCLX, and discuss recent physiological and pathophysiological roles attributed to the Na+ influx into mitochondria.
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Affiliation(s)
- Essam A Assali
- Department of Physiology and Cell Biology, Faculty of Health Sciences, Ben-Gurion University, Beer-Sheva, 84105, Israel
| | - Israel Sekler
- Department of Physiology and Cell Biology, Faculty of Health Sciences, Ben-Gurion University, Beer-Sheva, 84105, Israel.
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Katoshevski T, Ben-Kasus Nissim T, Sekler I. Recent studies on NCLX in health and diseases. Cell Calcium 2021; 94:102345. [PMID: 33508514 DOI: 10.1016/j.ceca.2020.102345] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2020] [Revised: 12/29/2020] [Accepted: 12/29/2020] [Indexed: 12/27/2022]
Abstract
The mitochondria is a major hub for cellular Ca 2+ signaling. The identification of MCU, the mitochondrial Ca 2+ influx mediator, and the mitochondrial Ca 2+ extruder NCLX, were major breakthroughs in this field. Their identification provided novel molecular tools and animal models to interrogate their physiological function and mode of regulation. Here we will focus on the mitochondrial Na + / Ca 2+ exchanger NCLX that plays a dual role in mitochondrial Na + and Ca 2+ signaling. We will discuss recent advances in NCLX mods of regulation by kinases and mitochondrial ΔΨ. We will also focus on the heterogeneity of its expression in distinct mitochondrial populations and the pathophysiological implication of its excessive degradation. We will describe the ongoing debate on the stoichiometry of Na + to Ca 2+ transport, mediated by NCLX, and its physiological implication. We will focus on the major effects of mitochondrial Na + signaling by NCLX on mitochondrial metabolism in health; and finally, we will discuss the role NCLX plays in a wide range of health disorders, from heart failure and cancer to Parkinson and Alzheimer disease, making it a prime candidate for therapeutic targeting.
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Affiliation(s)
- Tomer Katoshevski
- Department of Physiology and Cell Biology, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer-Sheva, 84105, Israel
| | - Tsipi Ben-Kasus Nissim
- Department of Physiology and Cell Biology, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer-Sheva, 84105, Israel
| | - Israel Sekler
- Department of Physiology and Cell Biology, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer-Sheva, 84105, Israel.
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8
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Gyimesi G, Hediger MA. Sequence Features of Mitochondrial Transporter Protein Families. Biomolecules 2020; 10:E1611. [PMID: 33260588 PMCID: PMC7761412 DOI: 10.3390/biom10121611] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2020] [Revised: 11/20/2020] [Accepted: 11/22/2020] [Indexed: 02/08/2023] Open
Abstract
Mitochondrial carriers facilitate the transfer of small molecules across the inner mitochondrial membrane (IMM) to support mitochondrial function and core cellular processes. In addition to the classical SLC25 (solute carrier family 25) mitochondrial carriers, the past decade has led to the discovery of additional protein families with numerous members that exhibit IMM localization and transporter-like properties. These include mitochondrial pyruvate carriers, sideroflexins, and mitochondrial cation/H+ exchangers. These transport proteins were linked to vital physiological functions and disease. Their structures and transport mechanisms are, however, still largely unknown and understudied. Protein sequence analysis per se can often pinpoint hotspots that are of functional or structural importance. In this review, we summarize current knowledge about the sequence features of mitochondrial transporters with a special focus on the newly included SLC54, SLC55 and SLC56 families of the SLC solute carrier superfamily. Taking a step further, we combine sequence conservation analysis with transmembrane segment and secondary structure prediction methods to extract residue positions and sequence motifs that likely play a role in substrate binding, binding site gating or structural stability. We hope that our review will help guide future experimental efforts by the scientific community to unravel the transport mechanisms and structures of these novel mitochondrial carriers.
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Affiliation(s)
- Gergely Gyimesi
- Membrane Transport Discovery Lab, Department of Nephrology and Hypertension, and Department of Biomedical Research, Inselspital, University of Bern, Kinderklinik, Freiburgstrasse 15, CH-3010 Bern, Switzerland;
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9
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Iwaki M, Refaeli B, van Dijk L, Hiller R, Giladi M, Kandori H, Khananshvili D. Structure-affinity insights into the Na + and Ca 2+ interactions with multiple sites of a sodium-calcium exchanger. FEBS J 2020; 287:4678-4695. [PMID: 32056381 DOI: 10.1111/febs.15250] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2019] [Revised: 12/22/2019] [Accepted: 02/12/2020] [Indexed: 01/30/2023]
Abstract
Selective recognition and transport of Na+ and Ca2+ ions by sodium-calcium exchanger (NCX) proteins is a primary prerequisite for Ca2+ signaling and homeostasis. Twelve ion-coordinating residues are highly conserved among NCXs, and distinct NCX orthologs contain two or three carboxylates, while sharing a common ion-exchange stoichiometry (3Na+ :1Ca2+ ). How these structural differences affect the ion-binding affinity, selectivity, and transport rates remains unclear. Here, the mutational effects of three carboxylates (E54, E213, and D240) were analyzed on the ion-exchange rates in the archaeal NCX from Methanococcus jannaschii and ion-induced structure-affinity changes were monitored by attenuated total reflection-Fourier-transform infrared spectroscopy (ATR-FTIR). The D240N mutation elevated the ion-transport rates by twofold to threefold, meaning that the deprotonation of D240 is not essential for transport catalysis. In contrast, mutating E54 or E213 to A, D, N, or Q dramatically decreased the ion-transport rates. ATR-FTIR revealed high- and low-affinity binding of Na+ or Ca2+ with E54 and E213, but not with D240. These findings reveal distinct structure-affinity states at specific ion-binding sites in the inward-facing (IF) and outward-facing orientation. Collectively, two multidentate carboxylate counterparts (E54 and E213) play a critical role in determining the ion coordination/transport in prokaryotic and eukaryotic NCXs, whereas the ortholog substitutions in prokaryotes (aspartate) and eukaryotes (asparagine) at the 240 position affect the ion-transport rates differently (kcat ), probably due to the structural differences in the transition state.
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Affiliation(s)
- Masayo Iwaki
- Department of Life Science and Applied Chemistry and OptoBioTechnology Research Center, Nagoya Institute of Technology, Japan
| | - Bosmat Refaeli
- Department of Physiology and Pharmacology, Tel-Aviv University, Israel
| | - Liat van Dijk
- Department of Physiology and Pharmacology, Tel-Aviv University, Israel
| | - Reuben Hiller
- Department of Physiology and Pharmacology, Tel-Aviv University, Israel
| | - Moshe Giladi
- Department of Physiology and Pharmacology, Tel-Aviv University, Israel
| | - Hideki Kandori
- Department of Life Science and Applied Chemistry and OptoBioTechnology Research Center, Nagoya Institute of Technology, Japan
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10
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Giladi M, Khananshvili D. Hydrogen-Deuterium Exchange Mass-Spectrometry of Secondary Active Transporters: From Structural Dynamics to Molecular Mechanisms. Front Pharmacol 2020; 11:70. [PMID: 32140107 PMCID: PMC7042309 DOI: 10.3389/fphar.2020.00070] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2019] [Accepted: 01/24/2020] [Indexed: 12/13/2022] Open
Abstract
Membrane transporters allow the selective transport of otherwise poorly permeable solutes across the cell membrane and thus, play a key role in maintaining cellular homeostasis in all kingdoms of life. Importantly, these proteins also serve as important drug targets. Over the last decades, major progress in structural biology methods has elucidated important structure-function relationships in membrane transporters. However, structures obtained using methods such as X-ray crystallography and high-resolution cryogenic electron microscopy merely provide static snapshots of an intrinsically dynamic, multi-step transport process. Therefore, there is a growing need for developing new experimental approaches capable of exploiting the data obtained from the high-resolution snapshots in order to investigate the dynamic features of membrane proteins. Here, we present the basic principles of hydrogen-deuterium exchange mass-spectrometry (HDX-MS) and recent advancements in its use to study membrane transporters. In HDX-MS experiments, minute amounts of a protein sample can be used to investigate its structural dynamics under native conditions, without the need for chemical labelling and with practically no limit on the protein size. Thus, HDX-MS is instrumental for resolving the structure-dynamic landscapes of membrane proteins in their apo (ligand-free) and ligand-bound forms, shedding light on the molecular mechanism underlying the transport process and drug binding.
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Affiliation(s)
- Moshe Giladi
- Department of Physiology and Pharmacology, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel.,Tel Aviv Sourasky Medical Center, Tel Aviv University, Tel Aviv, Israel
| | - Daniel Khananshvili
- Department of Physiology and Pharmacology, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel
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11
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Multipurpose Na + ions mediate excitation and cellular homeostasis: Evolution of the concept of Na + pumps and Na +/Ca 2+ exchangers. Cell Calcium 2020; 87:102166. [PMID: 32006802 DOI: 10.1016/j.ceca.2020.102166] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2020] [Accepted: 01/21/2020] [Indexed: 12/14/2022]
Abstract
Ionic signalling is the most ancient form of regulation of cellular functions in response to environmental challenges. Signals, mediated by Na+ fluxes and spatio-temporal fluctuations of Na+ concentration in cellular organelles and cellular compartments contribute to the most fundamental cellular processes such as membrane excitability and energy production. At the very core of ionic signalling lies the Na+-K+ ATP-driven pump (or NKA) which creates trans-plasmalemmal ion gradients that sustain ionic fluxes through ion channels and numerous Na+-dependent transporters that maintain cellular and tissue homeostasis. Here we present a brief account of the history of research into NKA, Na+ -dependent transporters and Na+ signalling.
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12
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Basic and editing mechanisms underlying ion transport and regulation in NCX variants. Cell Calcium 2020; 85:102131. [DOI: 10.1016/j.ceca.2019.102131] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2019] [Revised: 11/20/2019] [Accepted: 11/20/2019] [Indexed: 12/28/2022]
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13
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Giladi M, Lee SY, Refaeli B, Hiller R, Chung KY, Khananshvili D. Structure-dynamic and functional relationships in a Li+-transporting sodium‑calcium exchanger mutant. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2019; 1860:189-200. [DOI: 10.1016/j.bbabio.2018.11.015] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/16/2018] [Revised: 08/27/2018] [Accepted: 11/07/2018] [Indexed: 12/20/2022]
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14
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Functional properties and mode of regulation of the mitochondrial Na +/Ca 2+ exchanger, NCLX. Semin Cell Dev Biol 2019; 94:59-65. [PMID: 30658153 DOI: 10.1016/j.semcdb.2019.01.009] [Citation(s) in RCA: 35] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2018] [Revised: 01/14/2019] [Accepted: 01/14/2019] [Indexed: 12/23/2022]
Abstract
Mitochondrial Ca2+ transient is the earliest discovered organellar Ca2+ signaling pathway. It consist of a Ca2+ influx, mediated by mitochondrial Ca2+ uniporter (MCU), and mitochondrial Ca2+ efflux mediated by a Na+/Ca2+ exchanger (NCLX). Mitochondrial Ca2+ signaling machinery plays a fundamental role in linking metabolic activity to cellular Ca2+ signaling, and in controlling local Ca2+ concertation in distinct cellular compartments. Impaired balance between mitochondrial Ca2+ influx and efflux leads to mitochondrial Ca2+ overload, an early and key event in ischemic or neurodegenerative syndromes. Molecular identification of NCLX and MCU happened only recently. Surprisingly, MCU knockout yielded a relatively mild phenotype while conditional knockout of NCLX led to a rapid fatal heart failure. Here we will focus on recent functional and molecular studies on NCLX structure and its mode of regulation. We will describe the unique crosstalk of this exchanger with Na+ and Ca2+ signaling pathways in the cell membrane and the endoplasmic reticulum, and with protein kinases that posttranslationally modulate NCLX activity. We will critically compare selectivity of pharmacological blockers versus molecular control of NCLX expression and activity. Finally we will discuss why this exchanger is essential for survival and can serve as an attractive therapeutic target.
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15
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van Dijk L, Giladi M, Refaeli B, Hiller R, Cheng MH, Bahar I, Khananshvili D. Key residues controlling bidirectional ion movements in Na +/Ca 2+ exchanger. Cell Calcium 2018; 76:10-22. [PMID: 30248574 PMCID: PMC6688843 DOI: 10.1016/j.ceca.2018.09.004] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2018] [Revised: 09/13/2018] [Accepted: 09/13/2018] [Indexed: 01/06/2023]
Abstract
Prokaryotic and eukaryotic Na+/Ca2+ exchangers (NCX) control Ca2+ homeostasis. NCX orthologs exhibit up to 104-fold differences in their turnover rates (kcat), whereas the ratios between the cytosolic (cyt) and extracellular (ext) Km values (Kint = KmCyt/KmExt) are highly asymmetric and alike (Kint ≤ 0.1) among NCXs. The structural determinants controlling a huge divergence in kcat 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 kcat and Kint. Among 55 tested residues, 26 mutations affect either kcat or Kint, where two major groups can be distinguished. The first group of mutations (14 residues) affect kcat 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 kcat, 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 Ca2+ and Na+ signaling.
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Affiliation(s)
- Liat van Dijk
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Ramat-Aviv, Tel-Aviv, 69978, Israel
| | - Moshe Giladi
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Ramat-Aviv, Tel-Aviv, 69978, Israel
| | - Bosmat Refaeli
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Ramat-Aviv, Tel-Aviv, 69978, Israel
| | - Reuben Hiller
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Ramat-Aviv, Tel-Aviv, 69978, Israel
| | - Mary Hongying Cheng
- Department of Computational & Systems Biology, School of Medicine, University of Pittsburgh, Pittsburgh, PA, 15213, USA
| | - Ivet Bahar
- Department of Computational & Systems Biology, School of Medicine, University of Pittsburgh, Pittsburgh, PA, 15213, USA.
| | - Daniel Khananshvili
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Ramat-Aviv, Tel-Aviv, 69978, Israel.
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16
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Valle-Solis M, Bolaños J, Orozco E, Huerta M, García-Rivera G, Salas-Casas A, Chávez-Munguía B, Rodríguez MA. A Calcium/Cation Exchanger Participates in the Programmed Cell Death and in vitro Virulence of Entamoeba histolytica. Front Cell Infect Microbiol 2018; 8:342. [PMID: 30327757 PMCID: PMC6174217 DOI: 10.3389/fcimb.2018.00342] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2018] [Accepted: 09/10/2018] [Indexed: 01/17/2023] Open
Abstract
Entamoeba histolytica is the etiologic agent of human amoebiasis, disease that causes 40,000 to 100,000 deaths annually worldwide. The cytopathic activity as well as the growth and differentiation of this microorganism is dependent on both, extracellular and free cytoplasmic calcium. However, few is known about the proteins that regulate the calcium flux in this parasite. In many cells, the calcium extrusion from the cytosol is performed by plasma membrane Ca2+-ATPases and calcium/cation exchangers. The aim of this work was to identify a calcium/cation exchanger of E. histolytica and to analyze its possible role in some cellular processes triggered by calcium flux, such as the programmed cell death and in vitro virulence. By searching putative calcium/cation exchangers in the genome database of E. histolyica we identified a protein belonging to the CCX family (EhCCX). We generated a specific antibody against EhCCX, which showed that this protein was expressed in higher levels in E. histolytica than its orthologous in the non-pathogenic amoeba E. dispar. In addition, the expression of EhCCX was increased in trophozoites incubated with hydrogen peroxide. This E. histolytica exchanger was localized in the plasma membrane and in the membrane of some cytoplasmic vesicles. However, after 10 min of erythrophagocytosis, EhCCX was found predominantly in the plasma membrane of the trophozoites. On the other hand, the parasites that overexpress this exchanger contained higher cytosolic calcium levels than control, but the extrusion of calcium after the addition of hydrogen peroxide was more efficient in EhCCX-overexpressing trophozoites; consequently, the programmed cell death was retarded in these parasites. Interestingly, the overexpression of EhCCX increased the in vitro virulence of trophozoites. These results suggest that EhCCX plays important roles in the programmed cell death and in the in vitro virulence of E. histolytica.
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Affiliation(s)
- Martha Valle-Solis
- Departamento de Infectómica y Patogénesis Molecular, CINVESTAV-IPN, Mexico City, Mexico
| | - Jeni Bolaños
- Departamento de Infectómica y Patogénesis Molecular, CINVESTAV-IPN, Mexico City, Mexico
| | - Esther Orozco
- Departamento de Infectómica y Patogénesis Molecular, CINVESTAV-IPN, Mexico City, Mexico
| | - Miriam Huerta
- Departamento de Infectómica y Patogénesis Molecular, CINVESTAV-IPN, Mexico City, Mexico
| | | | - Andrés Salas-Casas
- Área Académica de Gerontología, Instituto de Ciencias de la Salud, Universidad Autónoma del Estado de Hidalgo, Pachuca, Mexico
| | | | - Mario A Rodríguez
- Departamento de Infectómica y Patogénesis Molecular, CINVESTAV-IPN, Mexico City, Mexico
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17
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Function, regulation and physiological role of the mitochondrial Na + /Ca 2+ exchanger, NCLX. CURRENT OPINION IN PHYSIOLOGY 2018. [DOI: 10.1016/j.cophys.2018.02.007] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
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18
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Shlosman I, Marinelli F, Faraldo-Gómez JD, Mindell JA. The prokaryotic Na +/Ca 2+ exchanger NCX_Mj transports Na + and Ca 2+ in a 3:1 stoichiometry. J Gen Physiol 2017; 150:51-65. [PMID: 29237756 PMCID: PMC5749117 DOI: 10.1085/jgp.201711897] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2017] [Accepted: 11/17/2017] [Indexed: 12/17/2022] Open
Abstract
Sodium–calcium exchangers contribute to the generation of intracellular Ca2+ signals in numerous physiological processes. Shlosman et al. determine the ion stoichiometry of the only sodium–calcium exchanger of known atomic structure, revealing its functional similarity to mammalian exchangers. Intracellular Ca2+ signals control a wide array of cellular processes. These signals require spatial and temporal regulation of the intracellular Ca2+ concentration, which is achieved in part by a class of ubiquitous membrane proteins known as sodium–calcium exchangers (NCXs). NCXs are secondary-active antiporters that power the translocation of Ca2+ across the cell membrane by coupling it to the flux of Na+ in the opposite direction, down an electrochemical gradient. Na+ and Ca2+ are translocated in separate steps of the antiport cycle, each of which is thought to entail a mechanism whereby ion-binding sites within the protein become alternately exposed to either side of the membrane. The prokaryotic exchanger NCX_Mj, the only member of this family with known structure, has been proposed to be a good functional and structural model of mammalian NCXs; yet our understanding of the functional properties of this protein remains incomplete. Here, we study purified NCX_Mj reconstituted into liposomes under well-controlled experimental conditions and demonstrate that this homologue indeed shares key functional features of the NCX family. Transport assays and reversal-potential measurements enable us to delineate the essential characteristics of this antiporter and establish that its ion-exchange stoichiometry is 3Na+:1Ca2+. Together with previous studies, this work confirms that NCX_Mj is a valid model system to investigate the mechanism of ion recognition and membrane transport in sodium–calcium exchangers.
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Affiliation(s)
- Irina Shlosman
- Theoretical Molecular Biophysics Laboratory, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD.,Membrane Transport Biophysics Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD
| | - Fabrizio Marinelli
- Theoretical Molecular Biophysics Laboratory, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD
| | - José D Faraldo-Gómez
- Theoretical Molecular Biophysics Laboratory, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD
| | - Joseph A Mindell
- Membrane Transport Biophysics Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD
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Jakobsson E, Argüello-Miranda O, Chiu SW, Fazal Z, Kruczek J, Nunez-Corrales S, Pandit S, Pritchet L. Towards a Unified Understanding of Lithium Action in Basic Biology and its Significance for Applied Biology. J Membr Biol 2017; 250:587-604. [PMID: 29127487 PMCID: PMC5696506 DOI: 10.1007/s00232-017-9998-2] [Citation(s) in RCA: 87] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2017] [Accepted: 10/21/2017] [Indexed: 01/14/2023]
Abstract
Lithium has literally been everywhere forever, since it is one of the three elements created in the Big Bang. Lithium concentration in rocks, soil, and fresh water is highly variable from place to place, and has varied widely in specific regions over evolutionary and geologic time. The biological effects of lithium are many and varied. Based on experiments in which animals are deprived of lithium, lithium is an essential nutrient. At the other extreme, at lithium ingestion sufficient to raise blood concentration significantly over 1 mM/, lithium is acutely toxic. There is no consensus regarding optimum levels of lithium intake for populations or individuals-with the single exception that lithium is a generally accepted first-line therapy for bipolar disorder, and specific dosage guidelines for sufferers of that condition are generally agreed on. Epidemiological evidence correlating various markers of social dysfunction and disease vs. lithium level in drinking water suggest benefits of moderately elevated lithium compared to average levels of lithium intake. In contrast to other biologically significant ions, lithium is unusual in not having its concentration in fluids of multicellular animals closely regulated. For hydrogen ions, sodium ions, potassium ions, calcium ions, chloride ions, and magnesium ions, blood and extracellular fluid concentrations are closely and necessarily regulated by systems of highly selective channels, and primary and secondary active transporters. Lithium, while having strong biological activity, is tolerated over body fluid concentrations ranging over many orders of magnitude. The lack of biological regulation of lithium appears due to lack of lithium-specific binding sites and selectivity filters. Rather lithium exerts its myriad physiological and biochemical effects by competing for macromolecular sites that are relatively specific for other cations, most especially for sodium and magnesium. This review will consider what is known about the nature of this competition and suggest using and extending this knowledge towards the goal of a unified understanding of lithium in biology and the application of that understanding in medicine and nutrition.
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Affiliation(s)
- Eric Jakobsson
- Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL, USA.
- Center for Biophysics and Computational Biology, University of Illinois at Urbana-Champaign, Urbana, IL, USA.
- Carl R. Woese Institute for Genomic Biology, University of Illinois at Urbana-Champaign, Urbana, IL, USA.
- Neuroscience Program, University of Illinois at Urbana-Champaign, Urbana, IL, USA.
- National Center for Supercomputing Applications, University of Illinois at Urbana-Champaign, Urbana, IL, USA.
- Department of Molecular and Integrative Physiology, University of Illinois at Urbana-Champaign, Urbana, IL, USA.
| | | | - See-Wing Chiu
- Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL, USA
- National Center for Supercomputing Applications, University of Illinois at Urbana-Champaign, Urbana, IL, USA
| | - Zeeshan Fazal
- Department of Biosciences, COMSATS Institute of Information Technology, Islamabad, Pakistan
- Department of Animal Sciences, University of Illinois at Urbana-Champaign, Urbana, IL, USA
| | - James Kruczek
- Department of Physics, University of South Florida, Tampa, FL, USA
| | - Santiago Nunez-Corrales
- National Center for Supercomputing Applications, University of Illinois at Urbana-Champaign, Urbana, IL, USA
- Illinois Informatics Institute, University of Illinois at Urbana-Champaign, Urbana, IL, USA
| | - Sagar Pandit
- Department of Physics, University of South Florida, Tampa, FL, USA
| | - Laura Pritchet
- Neuroscience Program, University of Illinois at Urbana-Champaign, Urbana, IL, USA
- Department of Psychological and Brain Sciences, University of California at Santa Barbara, Santa Barbara, CA, USA
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20
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Giladi M, van Dijk L, Refaeli B, Almagor L, Hiller R, Man P, Forest E, Khananshvili D. Dynamic distinctions in the Na +/Ca 2+ exchanger adopting the inward- and outward-facing conformational states. J Biol Chem 2017; 292:12311-12323. [PMID: 28572509 DOI: 10.1074/jbc.m117.787168] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2017] [Revised: 05/18/2017] [Indexed: 12/16/2022] Open
Abstract
Na+/Ca2+ exchanger (NCX) proteins operate through the alternating access mechanism, where the ion-binding pocket is exposed in succession either to the extracellular or the intracellular face of the membrane. The archaeal NCX_Mj (Methanococcus jannaschii NCX) system was used to resolve the backbone dynamics in the inward-facing (IF) and outward-facing (OF) states by analyzing purified preparations of apo- and ion-bound forms of NCX_Mj-WT and its mutant, NCX_Mj-5L6-8. First, the exposure of extracellular and cytosolic vestibules to the bulk phase was evaluated as the reactivity of single cysteine mutants to a fluorescent probe, verifying that NCX_Mj-WT and NCX_Mj-5L6-8 preferentially adopt the OF and IF states, respectively. Next, hydrogen-deuterium exchange-mass spectrometry (HDX-MS) was employed to analyze the backbone dynamics profiles in proteins, preferentially adopting the OF (WT) and IF (5L6-8) states either in the presence or absence of ions. Characteristic differences in the backbone dynamics were identified between apo NCX_Mj-WT and NCX_Mj-5L6-8, thereby underscoring specific conformational patterns owned by the OF and IF states. Saturating concentrations of Na+ or Ca2+ specifically modify HDX patterns, revealing that the ion-bound/occluded states are much more stable (rigid) in the OF than in the IF state. Conformational differences observed in the ion-occluded OF and IF states can account for diversifying the ion-release dynamics and apparent affinity (Km ) at opposite sides of the membrane, where specific structure-dynamic elements can effectively match the rates of bidirectional ion movements at physiological ion concentrations.
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Affiliation(s)
- Moshe Giladi
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Ramat-Aviv 69978, Israel; Tel-Aviv Sourasky Medical Center, Tel-Aviv 39040, Israel
| | - Liat van Dijk
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Ramat-Aviv 69978, Israel
| | - Bosmat Refaeli
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Ramat-Aviv 69978, Israel
| | - Lior Almagor
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Ramat-Aviv 69978, Israel
| | - Reuben Hiller
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Ramat-Aviv 69978, Israel
| | - Petr Man
- BioCeV-Institute of Microbiology, Academy of Sciences of the Czech Republic, CZ-14220 Prague, Czech Republic; Faculty of Science, Charles University, CZ-14220 Prague, Czech Republic
| | - Eric Forest
- University of Grenoble Alpes, Institut de Biologie Structurale (IBS), F-38044 Grenoble, France; CNRS, IBS, F-38044 Grenoble, France; Commissariat à l'Energie Atomique, IBS, F-38044 Grenoble, France
| | - Daniel Khananshvili
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Ramat-Aviv 69978, Israel.
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21
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Roy S, Dey K, Hershfinkel M, Ohana E, Sekler I. Identification of residues that control Li + versus Na + dependent Ca 2+ exchange at the transport site of the mitochondrial NCLX. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2017; 1864:997-1008. [PMID: 28130126 DOI: 10.1016/j.bbamcr.2017.01.011] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/07/2016] [Revised: 01/07/2017] [Accepted: 01/10/2017] [Indexed: 11/25/2022]
Abstract
BACKGROUND The Na+/Ca2+/Li+ exchanger (NCLX) is a member of the Na+/Ca2+ exchanger family. NCLX is unique in its capacity to transport both Na+ and Li+, unlike other members, which are Na+ selective. The major aim of this study was twofold, i.e., to identify NCLX residues that confer Li+ or Na+ selective Ca2+ transport and map their putative location on NCLX cation transport site. METHOD We combined molecular modeling to map transport site of NCLX with euryarchaeal H+/Ca2+ exchanger, CAX_Af, and fluorescence analysis to monitor Li+ versus Na+ dependent mitochondrial Ca2+ efflux of transport site mutants of NCLX in permeabilized cells. RESULT Mutation of Asn149, Pro152, Asp153, Gly176, Asn467, Ser468, Gly494 and Asn498 partially or strongly abolished mitochondrial Ca2+ exchange activity in intact cells. In permeabilized cells, N149A, P152A, D153A, N467Q, S468T and G494S demonstrated normal Li+/Ca2+ exchange activity but a reduced Na+/Ca2+ exchange activity. On the other hand, D471A showed dramatically reduced Li+/Ca2+ exchange, but Na+/Ca2+ exchange activity was unaffected. Finally, simultaneous mutation of four putative Ca2+ binding residues was required to completely abolish both Na+/Ca2+ and Li+/Ca2+ exchange activities. CONCLUSIONS We identified distinct Na+ and Li+ selective residues in the NCLX transport site. We propose that functional segregation in Li+ and Na+ sites reflects the functional properties of NCLX required for Ca2+ exchange under the unique membrane potential and ion gradient across the inner mitochondrial membrane. GENERAL SIGNIFICANCE The results of this study provide functional insights into the unique Li+ and Na+ selectivity of the mitochondrial exchanger. This article is part of a Special Issue entitled: ECS Meeting edited by Claus Heizmann, Joachim Krebs and Jacques Haiech.
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Affiliation(s)
- Soumitra Roy
- Department of Physiology and Cell Biology, Faculty of Health Sciences, Ben-Gurion University of the Negev, 84105 Beer Sheva, Israel
| | - Kuntal Dey
- Department of Physiology and Cell Biology, Faculty of Health Sciences, Ben-Gurion University of the Negev, 84105 Beer Sheva, Israel
| | - Michal Hershfinkel
- Department of Physiology and Cell Biology, Faculty of Health Sciences, Ben-Gurion University of the Negev, 84105 Beer Sheva, Israel
| | - Ehud Ohana
- Department of Clinical Biochemistry and Pharmacology, Faculty of Health Sciences, Ben Gurion University of the Negev, 84105 Beer Sheva, Israel.
| | - Israel Sekler
- Department of Physiology and Cell Biology, Faculty of Health Sciences, Ben-Gurion University of the Negev, 84105 Beer Sheva, Israel.
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22
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Giladi M, Shor R, Lisnyansky M, Khananshvili D. Structure-Functional Basis of Ion Transport in Sodium-Calcium Exchanger (NCX) Proteins. Int J Mol Sci 2016; 17:E1949. [PMID: 27879668 PMCID: PMC5133943 DOI: 10.3390/ijms17111949] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2016] [Revised: 11/13/2016] [Accepted: 11/14/2016] [Indexed: 01/19/2023] Open
Abstract
The membrane-bound sodium-calcium exchanger (NCX) proteins shape Ca2+ homeostasis in many cell types, thus participating in a wide range of physiological and pathological processes. Determination of the crystal structure of an archaeal NCX (NCX_Mj) paved the way for a thorough and systematic investigation of ion transport mechanisms in NCX proteins. Here, we review the data gathered from the X-ray crystallography, molecular dynamics simulations, hydrogen-deuterium exchange mass-spectrometry (HDX-MS), and ion-flux analyses of mutants. Strikingly, the apo NCX_Mj protein exhibits characteristic patterns in the local backbone dynamics at particular helix segments, thereby possessing characteristic HDX profiles, suggesting structure-dynamic preorganization (geometric arrangements of catalytic residues before the transition state) of conserved α₁ and α₂ repeats at ion-coordinating residues involved in transport activities. Moreover, dynamic preorganization of local structural entities in the apo protein predefines the status of ion-occlusion and transition states, even though Na⁺ or Ca2+ binding modifies the preceding backbone dynamics nearby functionally important residues. Future challenges include resolving the structural-dynamic determinants governing the ion selectivity, functional asymmetry and ion-induced alternating access. Taking into account the structural similarities of NCX_Mj with the other proteins belonging to the Ca2+/cation exchanger superfamily, the recent findings can significantly improve our understanding of ion transport mechanisms in NCX and similar proteins.
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Affiliation(s)
- Moshe Giladi
- Department of Physiology and Pharmacology, Sackler Faculty of Medicine, Tel-Aviv University, Tel-Aviv 699780, Israel.
- Tel-Aviv Sourasky Medical Center, Tel-Aviv 6423906, Israel.
| | - Reut Shor
- Department of Physiology and Pharmacology, Sackler Faculty of Medicine, Tel-Aviv University, Tel-Aviv 699780, Israel.
| | - Michal Lisnyansky
- Department of Physiology and Pharmacology, Sackler Faculty of Medicine, Tel-Aviv University, Tel-Aviv 699780, Israel.
| | - Daniel Khananshvili
- Department of Physiology and Pharmacology, Sackler Faculty of Medicine, Tel-Aviv University, Tel-Aviv 699780, Israel.
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