1
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Manori B, Da'adoosh B, Haitin Y, Giladi M. Identification of a magnesium-binding site at the primary allosteric calcium sensor of the sodium-calcium exchanger: Implications for physiological regulation. Protein Sci 2024; 33:e5114. [PMID: 38989557 PMCID: PMC11237548 DOI: 10.1002/pro.5114] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2024] [Revised: 06/14/2024] [Accepted: 06/29/2024] [Indexed: 07/12/2024]
Abstract
Sodium-calcium exchanger (NCX) proteins are ubiquitously expressed and play a pivotal role in cellular calcium homeostasis by mediating uphill calcium efflux across the cell membrane. Intracellular calcium allosterically regulates the exchange activity by binding to two cytoplasmic calcium-binding domains, CBD1 and CBD2. However, the calcium-binding affinities of these domains are seemingly inadequate to sense physiological calcium oscillations. Previously, magnesium binding to either domain was shown to tune their affinity for calcium, bringing it into the physiological range. However, while the magnesium-binding site of CBD2 was identified, the identity of the CBD1 magnesium site remains elusive. Here, using molecular dynamics in combination with differential scanning fluorimetry and mutational analysis, we pinpoint the magnesium-binding site in CBD1. Specifically, among four calcium-binding sites (Ca1-Ca4) in this domain, only Ca1 can accommodate magnesium with an affinity similar to its free intracellular concentration. Moreover, our results provide mechanistic insights into the modulation of the regulatory calcium affinity by magnesium, which allows an adequate NCX activity level throughout varying physiological needs.
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Affiliation(s)
- Bar Manori
- Department of Physiology and Pharmacology, Faculty of Medical and Health SciencesTel Aviv UniversityTel AvivIsrael
| | - Benny Da'adoosh
- Blavatnic Center for Drug DiscoveryTel Aviv UniversityTel AvivIsrael
| | - Yoni Haitin
- Department of Physiology and Pharmacology, Faculty of Medical and Health SciencesTel Aviv UniversityTel AvivIsrael
- Sagol School of Neuroscience, Tel Aviv UniversityTel AvivIsrael
| | - Moshe Giladi
- Department of Physiology and Pharmacology, Faculty of Medical and Health SciencesTel Aviv UniversityTel AvivIsrael
- Tel Aviv Sourasky Medical CenterTel AvivIsrael
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2
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Gök C, Fuller W. Rise of palmitoylation: A new trick to tune NCX1 activity. BIOCHIMICA ET BIOPHYSICA ACTA. MOLECULAR CELL RESEARCH 2024; 1871:119719. [PMID: 38574822 DOI: 10.1016/j.bbamcr.2024.119719] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/22/2023] [Revised: 03/11/2024] [Accepted: 03/27/2024] [Indexed: 04/06/2024]
Abstract
The cardiac Na+/Ca2+ Exchanger (NCX1) controls transmembrane calcium flux in numerous tissues. The only reversible post-translational modification established to regulate NCX1 is palmitoylation, which alters the ability of the exchanger to inactivate. Palmitoylation creates a binding site for the endogenous XIP domain, a region of the NCX1 intracellular loop established to inactivate NCX1. The binding site created by NCX1 palmitoylation sensitizes the transporter to XIP. Herein we summarize our recent knowledge on NCX1 palmitoylation and its association with cardiac pathologies, and discuss these findings in the light of the recent cryo-EM structures of human NCX1.
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Affiliation(s)
- Caglar Gök
- School of Cardiovascular and Metabolic Health (SCMH), Sir James Black Building, University of Glasgow, Glasgow G12 8QQ, United Kingdom.
| | - William Fuller
- School of Cardiovascular and Metabolic Health (SCMH), Sir James Black Building, University of Glasgow, Glasgow G12 8QQ, United Kingdom
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3
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Khananshvili D. Newly uncovered Cryo-EM structures of mammalian NCXs set a new stage for resolving the underlying molecular mechanisms and drug discovery. Cell Calcium 2024; 119:102867. [PMID: 38422779 DOI: 10.1016/j.ceca.2024.102867] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2024] [Accepted: 02/24/2024] [Indexed: 03/02/2024]
Abstract
The membrane-abundant NCX proteins mediate an electrogenic ion exchange (3Na+:1Ca2+) in the Ca2+-exit or Ca2+-entry mode. The structurally related isoform/splice variants of NCX are expressed in a tissue-specific manner to shape Ca2+ signalling/homeostasis in diverse cell types. The lack of mammalian NCX structure hampered the functional and regulatory resolution of tissue-specific NCX variants and their pharmacological targeting. Recently unveiled Cryo-EM structures of human cardiac NCX1.1[1] and kidney NCX1.3[2] provide new opportunities for resolving structure/functional divergences among NCX variants and their pharmacological targeting.
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Affiliation(s)
- Daniel Khananshvili
- Department of Physiology and Pharmacology, Faculty of Medicine, Tel-Aviv University, Tel Aviv 69978, Israel.
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4
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Giladi M, Fojtík L, Strauss T, Da'adoosh B, Hiller R, Man P, Khananshvili D. Structural dynamics of Na + and Ca 2+ interactions with full-size mammalian NCX. Commun Biol 2024; 7:463. [PMID: 38627576 PMCID: PMC11021524 DOI: 10.1038/s42003-024-06159-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2023] [Accepted: 04/05/2024] [Indexed: 04/19/2024] Open
Abstract
Cytosolic Ca2+ and Na+ allosterically regulate Na+/Ca2+ exchanger (NCX) proteins to vary the NCX-mediated Ca2+ entry/exit rates in diverse cell types. To resolve the structure-based dynamic mechanisms underlying the ion-dependent allosteric regulation in mammalian NCXs, we analyze the apo, Ca2+, and Na+-bound species of the brain NCX1.4 variant using hydrogen-deuterium exchange mass spectrometry (HDX-MS) and molecular dynamics (MD) simulations. Ca2+ binding to the cytosolic regulatory domains (CBD1 and CBD2) rigidifies the intracellular regulatory loop (5L6) and promotes its interaction with the membrane domains. Either Na+ or Ca2+ stabilizes the intracellular portions of transmembrane helices TM3, TM4, TM9, TM10, and their connecting loops (3L4 and 9L10), thereby exposing previously unappreciated regulatory sites. Ca2+ or Na+ also rigidifies the palmitoylation domain (TMH2), and neighboring TM1/TM6 bundle, thereby uncovering a structural entity for modulating the ion transport rates. The present analysis provides new structure-dynamic clues underlying the regulatory diversity among tissue-specific NCX variants.
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Affiliation(s)
- Moshe Giladi
- Department of Physiology and Pharmacology, Faculty of Medicine, Tel-Aviv University, Tel Aviv, 69978, Israel.
- Tel-Aviv Sourasky Medical Center, Tel Aviv, 6423906, Israel.
| | - Lukáš Fojtík
- Division BioCeV, Institute of Microbiology of the Czech Academy of Sciences, Prumyslova, 595, 252 50 Vestec, Prague, Czech Republic
- Department of Biochemistry, Faculty of Science, Charles University, 128 00, Prague, Czech Republic
| | - Tali Strauss
- Department of Physiology and Pharmacology, Faculty of Medicine, Tel-Aviv University, Tel Aviv, 69978, Israel
| | - Benny Da'adoosh
- Blavatnik Center for Drug Discovery, Tel Aviv University, Tel Aviv, 69978, Israel
| | - Reuben Hiller
- Department of Physiology and Pharmacology, Faculty of Medicine, Tel-Aviv University, Tel Aviv, 69978, Israel
| | - Petr Man
- Division BioCeV, Institute of Microbiology of the Czech Academy of Sciences, Prumyslova, 595, 252 50 Vestec, Prague, Czech Republic.
- Department of Biochemistry, Faculty of Science, Charles University, 128 00, Prague, Czech Republic.
| | - Daniel Khananshvili
- Department of Physiology and Pharmacology, Faculty of Medicine, Tel-Aviv University, Tel Aviv, 69978, Israel.
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5
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Dong Y, Yu Z, Li Y, Huang B, Bai Q, Gao Y, Chen Q, Li N, He L, Zhao Y. Structural insight into the allosteric inhibition of human sodium-calcium exchanger NCX1 by XIP and SEA0400. EMBO J 2024; 43:14-31. [PMID: 38177313 PMCID: PMC10897212 DOI: 10.1038/s44318-023-00013-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2023] [Revised: 11/10/2023] [Accepted: 11/15/2023] [Indexed: 01/06/2024] Open
Abstract
Sodium-calcium exchanger proteins influence calcium homeostasis in many cell types and participate in a wide range of physiological and pathological processes. Here, we elucidate the cryo-EM structure of the human Na+/Ca2+ exchanger NCX1.3 in the presence of a specific inhibitor, SEA0400. Conserved ion-coordinating residues are exposed on the cytoplasmic face of NCX1.3, indicating that the observed structure is stabilized in an inward-facing conformation. We show how regulatory calcium-binding domains (CBDs) assemble with the ion-translocation transmembrane domain (TMD). The exchanger-inhibitory peptide (XIP) is trapped within a groove between the TMD and CBD2 and predicted to clash with gating helices TMs1/6 at the outward-facing state, thus hindering conformational transition and promoting inactivation of the transporter. A bound SEA0400 molecule stiffens helix TM2ab and affects conformational rearrangements of TM2ab that are associated with the ion-exchange reaction, thus allosterically attenuating Ca2+-uptake activity of NCX1.3.
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Affiliation(s)
- Yanli Dong
- Key Laboratory of Biomacromolecules (CAS), National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101, China
| | - Zhuoya Yu
- Key Laboratory of Biomacromolecules (CAS), National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101, China
- State Key Laboratory of Brain and Cognitive Science, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Beijing, 100101, China
- College of Life Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Yue Li
- Key Laboratory of Biomacromolecules (CAS), National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101, China
- State Key Laboratory of Brain and Cognitive Science, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Beijing, 100101, China
- College of Life Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Bo Huang
- Beijing StoneWise Technology Co Ltd., 15 Haidian street, Haidian district, Beijing, China
| | - Qinru Bai
- Key Laboratory of Biomacromolecules (CAS), National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101, China
- State Key Laboratory of Brain and Cognitive Science, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Beijing, 100101, China
- College of Life Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Yiwei Gao
- Key Laboratory of Biomacromolecules (CAS), National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101, China
- State Key Laboratory of Brain and Cognitive Science, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Beijing, 100101, China
- College of Life Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Qihao Chen
- Key Laboratory of Biomacromolecules (CAS), National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101, China
- State Key Laboratory of Brain and Cognitive Science, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Beijing, 100101, China
- College of Life Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Na Li
- Heart Center and Beijing Key Laboratory of Hypertension, Beijing Chaoyang Hospital, Capital Medical University, Beijing, 100020, China
| | - Lingli He
- Key Laboratory of Biomacromolecules (CAS), National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101, China
| | - Yan Zhao
- Key Laboratory of Biomacromolecules (CAS), National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101, China.
- State Key Laboratory of Brain and Cognitive Science, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Beijing, 100101, China.
- College of Life Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China.
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6
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Khananshvili D. Neuronal and astrocyte NCX isoform/splice variants: How do they participate in Na + and Ca 2+ signalling? Cell Calcium 2023; 116:102818. [PMID: 37918135 DOI: 10.1016/j.ceca.2023.102818] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2023] [Revised: 10/20/2023] [Accepted: 10/22/2023] [Indexed: 11/04/2023]
Abstract
NCX1, NCX2, and NCX3 gene isoforms and their splice variants are characteristically expressed in different regions of the brain. The tissue-specific splice variants of NCX1-3 isoforms show specific expression profiles in neurons and astrocytes, whereas the relevant NCX isoform/splice variants exhibit diverse allosteric modes of Na+- and Ca2+-dependent regulation. In general, overexpression of NCX1-3 genes leads to neuroprotective effects, whereas their ablation gains the opposite results. At this end, the partial contributions of NCX isoform/splice variants to neuroprotective effects remain unresolved. The glutamate-dependent Na+ entry generates Na+ transients (in response to neuronal cell activities), whereas the Na+-driven Ca2+ entry (through the reverse NCX mode) raises Ca2+ transients. This special mode of signal coupling translates Na+ transients into the Ca2+ signals while being a part of synaptic neurotransmission. This mechanism is of general interest since disease-related conditions (ischemia, metabolic stress, and stroke among many others) trigger Na+ and Ca2+ overload with deadly outcomes of downstream apoptosis and excitotoxicity. The recently discovered mechanisms of NCX allosteric regulation indicate that some NCX variants might play a critical role in the dynamic coupling of Na+-driven Ca2+ entry. In contrast, the others are less important or even could be dangerous under altered conditions (e.g., metabolic stress). This working hypothesis can be tested by applying advanced experimental approaches and highly focused computational simulations. This may allow the development of structure-based blockers/activators that can selectively modulate predefined NCX variants to lessen the life-threatening outcomes of excitotoxicity, ischemia, apoptosis, metabolic deprivation, brain injury, and stroke.
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Affiliation(s)
- Daniel Khananshvili
- Department of Physiology and Pharmacology, Faculty of Medicine, Tel-Aviv University, Tel Aviv 69978, Israel.
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7
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Xue J, Zeng W, Han Y, John S, Ottolia M, Jiang Y. Structural mechanisms of the human cardiac sodium-calcium exchanger NCX1. Nat Commun 2023; 14:6181. [PMID: 37794011 PMCID: PMC10550945 DOI: 10.1038/s41467-023-41885-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2023] [Accepted: 09/22/2023] [Indexed: 10/06/2023] Open
Abstract
Na+/Ca2+ exchangers (NCX) transport Ca2+ in or out of cells in exchange for Na+. They are ubiquitously expressed and play an essential role in maintaining cytosolic Ca2+ homeostasis. Although extensively studied, little is known about the global structural arrangement of eukaryotic NCXs and the structural mechanisms underlying their regulation by various cellular cues including cytosolic Na+ and Ca2+. Here we present the cryo-EM structures of human cardiac NCX1 in both inactivated and activated states, elucidating key structural elements important for NCX ion exchange function and its modulation by cytosolic Ca2+ and Na+. We demonstrate that the interactions between the ion-transporting transmembrane (TM) domain and the cytosolic regulatory domain define the activity of NCX. In the inward-facing state with low cytosolic [Ca2+], a TM-associated four-stranded β-hub mediates a tight packing between the TM and cytosolic domains, resulting in the formation of a stable inactivation assembly that blocks the TM movement required for ion exchange function. Ca2+ binding to the cytosolic second Ca2+-binding domain (CBD2) disrupts this inactivation assembly which releases its constraint on the TM domain, yielding an active exchanger. Thus, the current NCX1 structures provide an essential framework for the mechanistic understanding of the ion transport and cellular regulation of NCX family proteins.
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Affiliation(s)
- Jing Xue
- Howard Hughes Medical Institute and Department of Physiology, The University of Texas Southwestern Medical Center, Dallas, TX, USA
- Department of Biophysics, The University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Weizhong Zeng
- Howard Hughes Medical Institute and Department of Physiology, The University of Texas Southwestern Medical Center, Dallas, TX, USA
- Department of Biophysics, The University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Yan Han
- Howard Hughes Medical Institute and Department of Physiology, The University of Texas Southwestern Medical Center, Dallas, TX, USA
- Department of Biophysics, The University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Scott John
- Department of Medicine (Cardiology), David Geffen School of Medicine, University of California Los Angeles, Los Angeles, CA, USA
| | - Michela Ottolia
- Department of Anesthesiology and Perioperative Medicine, Division of Molecular Medicine, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, CA, USA
| | - Youxing Jiang
- Howard Hughes Medical Institute and Department of Physiology, The University of Texas Southwestern Medical Center, Dallas, TX, USA.
- Department of Biophysics, The University of Texas Southwestern Medical Center, Dallas, TX, USA.
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8
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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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9
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Ottolia M, John S, Hazan A, Goldhaber JI. The Cardiac Na + -Ca 2+ Exchanger: From Structure to Function. Compr Physiol 2021; 12:2681-2717. [PMID: 34964124 DOI: 10.1002/cphy.c200031] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Ca2+ homeostasis is essential for cell function and survival. As such, the cytosolic Ca2+ concentration is tightly controlled by a wide number of specialized Ca2+ handling proteins. One among them is the Na+ -Ca2+ exchanger (NCX), a ubiquitous plasma membrane transporter that exploits the electrochemical gradient of Na+ to drive Ca2+ out of the cell, against its concentration gradient. In this critical role, this secondary transporter guides vital physiological processes such as Ca2+ homeostasis, muscle contraction, bone formation, and memory to name a few. Herein, we review the progress made in recent years about the structure of the mammalian NCX and how it relates to function. Particular emphasis will be given to the mammalian cardiac isoform, NCX1.1, due to the extensive studies conducted on this protein. Given the degree of conservation among the eukaryotic exchangers, the information highlighted herein will provide a foundation for our understanding of this transporter family. We will discuss gene structure, alternative splicing, topology, regulatory mechanisms, and NCX's functional role on cardiac physiology. Throughout this article, we will attempt to highlight important milestones in the field and controversial topics where future studies are required. © 2021 American Physiological Society. Compr Physiol 12:1-37, 2021.
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Affiliation(s)
- Michela Ottolia
- Department of Anesthesiology and Perioperative Medicine, Division of Molecular Medicine, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California, USA
| | - Scott John
- Department of Medicine (Cardiology), UCLA, Los Angeles, California, USA
| | - Adina Hazan
- Smidt Heart Institute, Cedars Sinai Medical Center, Los Angeles, California, USA
| | - Joshua I Goldhaber
- Smidt Heart Institute, Cedars Sinai Medical Center, Los Angeles, California, USA
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10
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Pan-phylum genome-wide identification of sodium calcium exchangers reveal heterogeneous expansions and possible roles in nematode parasitism. Gene 2021; 810:146052. [PMID: 34756961 DOI: 10.1016/j.gene.2021.146052] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2021] [Revised: 10/19/2021] [Accepted: 10/26/2021] [Indexed: 12/13/2022]
Abstract
Calcium signaling is ubiquitous in nematode development from fertilization to cell specification to apoptosis. Calcium also regulates dauer entry in Caenorhabditis elegans, which corresponds to the infective stage of parasitic nematodes. In diverse parasites such as Trypanosoma cruzi and Toxoplasma gondii calcium has been shown to regulate host cell entry and egress, and perturbing calcium signaling represents a possible route to inhibit infection and parasitism in these species. Sodium calcium exchangers are considered the most important mechanism of calcium efflux, and our lab has previously characterized the sodium calcium exchanger gene family in C. elegans and studied the diversity of this family across a subset of specific nematode species. Here we build upon these data and explore sodium calcium exchangers across 108 species of nematodes. Our data reveal substantial differences in sodium calcium exchanger counts across the Phylum and detail expansions and contractions of specific exchanger subtypes within certain nematode clades. Finally, we also provide evidence for a role of sodium calcium exchangers in parasite activation by examining differentially expressed genes in non-activated versus activated infective stage larvae. Taken together our findings paint a heterogeneous picture of sodium calcium exchanger evolution across the Phylum Nematoda that may reflect unique adaptations to free-living and parasitic lifestyles.
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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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Scranton K, John S, Escobar A, Goldhaber JI, Ottolia M. Modulation of the cardiac Na +-Ca 2+ exchanger by cytoplasmic protons: Molecular mechanisms and physiological implications. Cell Calcium 2019; 87:102140. [PMID: 32070924 DOI: 10.1016/j.ceca.2019.102140] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2019] [Revised: 12/06/2019] [Accepted: 12/07/2019] [Indexed: 01/31/2023]
Abstract
A precise temporal and spatial control of intracellular Ca2+ concentration is essential for a coordinated contraction of the heart. Following contraction, cardiac cells need to rapidly remove intracellular Ca2+ to allow for relaxation. This task is performed by two transporters: the plasma membrane Na+-Ca2+ exchanger (NCX) and the sarcoplasmic reticulum (SR) Ca2+-ATPase (SERCA). NCX extrudes Ca2+ from the cell, balancing the Ca2+entering the cytoplasm during systole through L-type Ca2+ channels. In parallel, following SR Ca2+ release, SERCA activity replenishes the SR, reuptaking Ca2+ from the cytoplasm. The activity of the mammalian exchanger is fine-tuned by numerous ionic allosteric regulatory mechanisms. Micromolar concentrations of cytoplasmic Ca2+ potentiate NCX activity, while an increase in intracellular Na+ levels inhibits NCX via a mechanism known as Na+-dependent inactivation. Protons are also powerful inhibitors of NCX activity. By regulating NCX activity, Ca2+, Na+ and H+ couple cell metabolism to Ca2+ homeostasis and therefore cardiac contractility. This review summarizes the recent progress towards the understanding of the molecular mechanisms underlying the ionic regulation of the cardiac NCX with special emphasis on pH modulation and its physiological impact on the heart.
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Affiliation(s)
- Kyle Scranton
- Department of Anesthesiology and Perioperative Medicine, Division of Molecular Medicine, UCLA, Los Angeles, CA 90095, USA
| | - Scott John
- Department of Medicine (Cardiology), UCLA, Los Angeles, CA 90095, USA; Cardiovascular Research Laboratory, UCLA, Los Angeles, CA 90095, USA
| | - Ariel Escobar
- Department of Bioengineering, School of Engineering, UC Merced, Merced, CA 95343, USA
| | - Joshua I Goldhaber
- Smidt Heart Institute, Cedars Sinai Medical Center, Los Angeles, CA 90048, USA
| | - Michela Ottolia
- Department of Anesthesiology and Perioperative Medicine, Division of Molecular Medicine, UCLA, Los Angeles, CA 90095, USA; Cardiovascular Research Laboratory, UCLA, Los Angeles, CA 90095, USA.
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14
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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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15
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Yuan J, Yuan C, Xie M, Yu L, Bruschweiler-Li L, Brüschweiler R. The Intracellular Loop of the Na +/Ca 2+ Exchanger Contains an "Awareness Ribbon"-Shaped Two-Helix Bundle Domain. Biochemistry 2018; 57:5096-5104. [PMID: 29898361 DOI: 10.1021/acs.biochem.8b00300] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
The Na+/Ca2+ exchanger (NCX) is a ubiquitous single-chain membrane protein that plays a major role in regulating the intracellular Ca2+ homeostasis by the counter transport of Na+ and Ca2+ across the cell membrane. Other than its prokaryotic counterpart, which contains only the transmembrane domain and is self-sufficient as an active ion transporter, the eukaryotic NCX protein possesses in addition a large intracellular loop that senses intracellular calcium signals and controls the activation of ion transport across the membrane. This provides a necessary layer of regulation for the more complex function of eukaryotic cells. The Ca2+ sensor in the intracellular loop is known as the Ca2+-binding domain (CBD12). However, how the signaling of the allosteric intracellular Ca2+ binding propagates and results in transmembrane ion transportation still lacks a detailed explanation. Further structural and dynamics characterization of the intracellular loop flanking both sides of CBD12 is therefore imperative. Here, we report the identification and characterization of another structured domain that is N-terminal to CBD12 in the intracellular loop using solution nuclear magnetic resonance (NMR) spectroscopy. The atomistic structure of this domain reveals that two tandem long α-helices, connected by a short linker, form a stable crossover two-helix bundle (THB), resembling an "awareness ribbon". Considering the highly conserved amino acid sequence of the THB domain, the detailed structural and dynamics properties of the THB domain will be common among NCXs from different species and will contribute toward the understanding of the regulatory mechanism of eukaryotic Na+/Ca2+ exchangers.
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Affiliation(s)
- Jiaqi Yuan
- Department of Chemistry and Biochemistry , The Ohio State University , Columbus , Ohio 43210 , United States
| | - Chunhua Yuan
- Campus Chemical Instrument Center , The Ohio State University , Columbus , Ohio 43210 , United States
| | - Mouzhe Xie
- Department of Chemistry and Biochemistry , The Ohio State University , Columbus , Ohio 43210 , United States
| | - Lei Yu
- Department of Chemistry and Biochemistry , The Ohio State University , Columbus , Ohio 43210 , United States
| | - Lei Bruschweiler-Li
- Campus Chemical Instrument Center , The Ohio State University , Columbus , Ohio 43210 , United States
| | - Rafael Brüschweiler
- Department of Chemistry and Biochemistry , The Ohio State University , Columbus , Ohio 43210 , United States.,Campus Chemical Instrument Center , The Ohio State University , Columbus , Ohio 43210 , United States.,Department of Biological Chemistry and Pharmacology , The Ohio State University , Columbus , Ohio 43210 , United States
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16
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de Godoy CMG, Vasques ÊR, Caricati-Neto A, Tavares JGP, Alves BJ, Duarte J, Miranda-Ferreira R, Lima MA, Nader HB, Tersariol ILDS. Heparin Oligosaccharides Have Antiarrhythmic Effect by Accelerating the Sodium-Calcium Exchanger. Front Cardiovasc Med 2018; 5:67. [PMID: 29930947 PMCID: PMC5999778 DOI: 10.3389/fcvm.2018.00067] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2017] [Accepted: 05/17/2018] [Indexed: 01/15/2023] Open
Abstract
Background: Blockage of the Na+/Ca2+ exchanger (NCX) is used to determine the role of NCX in arrhythmogenesis. Trisulfated heparin disaccharide (TD) and Low Molecular Weight Heparins (LMWHs) can directly interact with the NCX and accelerate its activity. Objective: In this work, we investigated the antiarrhythmic effect of heparin oligosaccharides related to the NCX activity. Methods: The effects of heparin oligosaccharides were tested on the NCX current (patch clamping) and intracellular calcium transient in rat cardiomyocytes. The effects of heparin oligosaccharides were further investigated in arrhythmia induced in isolated rat atria and rats in vivo. Results: The intracellular Ca2+ concentration decreases upon treatment with either enoxaparin or ardeparin. These drugs abolished arrhythmia induction in isolated atria. The NCX antagonist KB-R7943 abolished the enoxaparin or ardeparin antiarrhythmic effects in isolated atria. In the in vivo measurements, injection of TD 15 min both before coronary occlusion or immediately after reperfusion, significantly prevented the occurrence of reperfusion-induced arrhythmias (ventricular arrhythmia and total AV block) and reduced the lethality rate. The patch clamping experiments showed that, mechanistically, TD increases the forward mode NCX current. Conclusion: Together, the data shows that heparin oligosaccharides may constitute a new class of antiarrhythmic drug that acts by accelerating the forward mode NCX under calcium overload.
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Affiliation(s)
- Carlos M G de Godoy
- Institute of Science and Technology, Universidade Federal de São Paulo, São Paulo, Brazil
| | - Ênio R Vasques
- Department of Gastroenterology (LIM 37), Medical School, University of São Paulo, São Paulo, Brazil.,Núcleo de Pesquisas Tecnológicas, Universidade de Mogi das Cruzes, Mogi das Cruzes, Brazil
| | - Afonso Caricati-Neto
- Department of Pharmacology, Universidade Federal de São Paulo, São Paulo, Brazil
| | - José G P Tavares
- Department of Pharmacology, Universidade Federal de São Paulo, São Paulo, Brazil
| | - Beatriz J Alves
- Department of Pharmacology, Universidade Federal de São Paulo, São Paulo, Brazil
| | - Juliana Duarte
- Núcleo de Pesquisas Tecnológicas, Universidade de Mogi das Cruzes, Mogi das Cruzes, Brazil
| | | | - Marcelo A Lima
- Department of Biochemistry, Universidade Federal de São Paulo, São Paulo, Brazil
| | - Helena B Nader
- Department of Biochemistry, Universidade Federal de São Paulo, São Paulo, Brazil
| | - Ivarne L Dos Santos Tersariol
- Department of Biochemistry, Universidade Federal de São Paulo, São Paulo, Brazil.,Centro Interdisciplinar de Investigação Bioquímica, Universidade de Mogi das Cruzes, Mogi das Cruzes, Brazil
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17
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John S, Kim B, Olcese R, Goldhaber JI, Ottolia M. Molecular determinants of pH regulation in the cardiac Na +-Ca 2+ exchanger. J Gen Physiol 2018; 150:245-257. [PMID: 29301861 PMCID: PMC5806679 DOI: 10.1085/jgp.201611693] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2016] [Revised: 05/25/2017] [Accepted: 11/29/2017] [Indexed: 11/20/2022] Open
Abstract
The cardiac Na+-Ca2+ exchanger (NCX) plays a critical role in the heart by extruding Ca2+ after each contraction and thus regulates cardiac contractility. The activity of NCX is strongly inhibited by cytosolic protons, which suggests that intracellular acidification will have important effects on heart contractility. However, the mechanisms underlying this inhibition remain elusive. It has been suggested that pH regulation originates from the competitive binding of protons to two Ca2+-binding domains within the large cytoplasmic loop of NCX and requires inactivation by intracellular Na+ to fully develop. By combining mutagenesis and electrophysiology, we demonstrate that NCX pH modulation is an allosteric mechanism distinct from Na+ and Ca2+ regulation, and we show that cytoplasmic Na+ can affect the sensitivity of NCX to protons. We further identify two histidines (His 124 and His 165) that are important for NCX proton sensitivity and show that His 165 plays the dominant role. Our results reveal a complex interplay between the different allosteric mechanisms that regulate the activity of NCX. Because of the central role of NCX in cardiac function, these findings are important for our understanding of heart pathophysiology.
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Affiliation(s)
- Scott John
- Department of Medicine and Cardiology, David Geffen School of Medicine at UCLA, Los Angeles, CA
| | - Brian Kim
- Cedars-Sinai Heart Institute, Los Angeles, CA
| | - Riccardo Olcese
- Department of Anesthesiology and Perioperative Medicine, Division of Molecular Medicine, David Geffen School of Medicine at UCLA, Los Angeles, CA.,Department of Physiology, David Geffen School of Medicine at UCLA, Los Angeles, CA
| | - Joshua I Goldhaber
- Cedars-Sinai Heart Institute, Los Angeles, CA.,Division of Applied Cell Biology and Physiology, Cedars-Sinai Medical Center, Los Angeles, CA
| | - Michela Ottolia
- Department of Anesthesiology and Perioperative Medicine, Division of Molecular Medicine, David Geffen School of Medicine at UCLA, Los Angeles, CA
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18
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Khananshvili D. How a helix imposes palmitoylation of a membrane protein: What one can learn from NCX. J Biol Chem 2017. [PMID: 28646126 DOI: 10.1074/jbc.h116.773945] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Palmitoylation is a critical post-translational modification that anchors proteins to, and regulates transport across, the lipid bilayer. Palmitoylation enzymes have been assumed to select their substrates based on a protein's primary sequence, but a consensus sequence has been slow to emerge. A study of the sodium/calcium exchanger now suggests that secondary structure may hold the key to understanding the determinants of this modification.
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Affiliation(s)
- Daniel Khananshvili
- From the Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Ramat-Aviv 69978, Israel
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19
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Plain F, Congreve SD, Yee RSZ, Kennedy J, Howie J, Kuo CW, Fraser NJ, Fuller W. An amphipathic α-helix directs palmitoylation of the large intracellular loop of the sodium/calcium exchanger. J Biol Chem 2017; 292:10745-10752. [PMID: 28432123 PMCID: PMC5481580 DOI: 10.1074/jbc.m116.773945] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2016] [Revised: 04/19/2017] [Indexed: 11/06/2022] Open
Abstract
The electrogenic sodium/calcium exchanger (NCX) mediates bidirectional calcium transport controlled by the transmembrane sodium gradient. NCX inactivation occurs in the absence of phosphatidylinositol 4,5-bisphosphate and is facilitated by palmitoylation of a single cysteine at position 739 within the large intracellular loop of NCX. The aim of this investigation was to identify the structural determinants of NCX1 palmitoylation. Full-length NCX1 (FL-NCX1) and a YFP fusion protein of the NCX1 large intracellular loop (YFP-NCX1) were expressed in HEK cells. Single amino acid changes around Cys-739 in FL-NCX1 and deletions on the N-terminal side of Cys-739 in YFP-NCX1 did not affect NCX1 palmitoylation, with the exception of the rare human polymorphism S738F, which enhanced FL-NCX1 palmitoylation, and D741A, which modestly reduced it. In contrast, deletion of a 21-amino acid segment enriched in aromatic amino acids on the C-terminal side of Cys-739 abolished YFP-NCX1 palmitoylation. We hypothesized that this segment forms an amphipathic α-helix whose properties facilitate Cys-739 palmitoylation. Introduction of negatively charged amino acids to the hydrophobic face or of helix-breaking prolines impaired palmitoylation of both YFP-NCX1 and FL-NCX1. Alanine mutations on the hydrophilic face of the helix significantly reduced FL-NCX1 palmitoylation. Of note, when the helix-containing segment was introduced adjacent to cysteines that are not normally palmitoylated, they became palmitoylation sites. In conclusion, we have identified an amphipathic α-helix in the NCX1 large intracellular loop that controls NCX1 palmitoylation. NCX1 palmitoylation is governed by a distal secondary structure element rather than by local primary sequence.
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Affiliation(s)
- Fiona Plain
- From the Division of Molecular and Clinical Medicine, School of Medicine, Ninewells Hospital, University of Dundee, Dundee DD1 9SY, Scotland, United Kingdom
| | - Samitha Dilini Congreve
- From the Division of Molecular and Clinical Medicine, School of Medicine, Ninewells Hospital, University of Dundee, Dundee DD1 9SY, Scotland, United Kingdom
| | - Rachel Sue Zhen Yee
- From the Division of Molecular and Clinical Medicine, School of Medicine, Ninewells Hospital, University of Dundee, Dundee DD1 9SY, Scotland, United Kingdom
| | - Jennifer Kennedy
- From the Division of Molecular and Clinical Medicine, School of Medicine, Ninewells Hospital, University of Dundee, Dundee DD1 9SY, Scotland, United Kingdom
| | - Jacqueline Howie
- From the Division of Molecular and Clinical Medicine, School of Medicine, Ninewells Hospital, University of Dundee, Dundee DD1 9SY, Scotland, United Kingdom
| | - Chien-Wen Kuo
- From the Division of Molecular and Clinical Medicine, School of Medicine, Ninewells Hospital, University of Dundee, Dundee DD1 9SY, Scotland, United Kingdom
| | - Niall J Fraser
- From the Division of Molecular and Clinical Medicine, School of Medicine, Ninewells Hospital, University of Dundee, Dundee DD1 9SY, Scotland, United Kingdom
| | - William Fuller
- From the Division of Molecular and Clinical Medicine, School of Medicine, Ninewells Hospital, University of Dundee, Dundee DD1 9SY, Scotland, United Kingdom
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20
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Structure-based dynamic arrays in regulatory domains of sodium-calcium exchanger (NCX) isoforms. Sci Rep 2017; 7:993. [PMID: 28428550 PMCID: PMC5430519 DOI: 10.1038/s41598-017-01102-x] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2017] [Accepted: 03/24/2017] [Indexed: 02/06/2023] Open
Abstract
Mammalian Na+/Ca2+ exchangers, NCX1 and NCX3, generate splice variants, whereas NCX2 does not. The CBD1 and CBD2 domains form a regulatory tandem (CBD12), where Ca2+ binding to CBD1 activates and Ca2+ binding to CBD2 (bearing the splicing segment) alleviates the Na+-induced inactivation. Here, the NCX2-CBD12, NCX3-CBD12-B, and NCX3-CBD12-AC proteins were analyzed by small-angle X-ray scattering (SAXS) and hydrogen-deuterium exchange mass-spectrometry (HDX-MS) to resolve regulatory variances in the NCX2 and NCX3 variants. SAXS revealed the unified model, according to which the Ca2+ binding to CBD12 shifts a dynamic equilibrium without generating new conformational states, and where more rigid conformational states become more populated without any global conformational changes. HDX-MS revealed the differential effects of the B and AC exons on the folding stability of apo CBD1 in NCX3-CBD12, where the dynamic differences become less noticeable in the Ca2+-bound state. Therefore, the apo forms predefine incremental changes in backbone dynamics upon Ca2+ binding. These observations may account for slower inactivation (caused by slower dissociation of occluded Ca2+ from CBD12) in the skeletal vs the brain-expressed NCX2 and NCX3 variants. This may have physiological relevance, since NCX must extrude much higher amounts of Ca2+ from the skeletal cell than from the neuron.
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21
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Structure-Dynamic Coupling Through Ca2+-Binding Regulatory Domains of Mammalian NCX Isoform/Splice Variants. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2017; 981:41-58. [DOI: 10.1007/978-3-319-55858-5_3] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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22
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Kinetic and equilibrium properties of regulatory Ca2+-binding domains in sodium–calcium exchangers 2 and 3. Cell Calcium 2016; 59:181-8. [DOI: 10.1016/j.ceca.2016.01.008] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2015] [Revised: 01/14/2016] [Accepted: 01/23/2016] [Indexed: 12/21/2022]
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23
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Abiko LA, Vitale PM, Favaro DC, Hauk P, Li DW, Yuan J, Bruschweiler-Li L, Salinas RK, Brüschweiler R. Model for the allosteric regulation of the Na+/Ca2+exchanger NCX. Proteins 2016; 84:580-90. [DOI: 10.1002/prot.25003] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2015] [Revised: 01/21/2016] [Accepted: 01/25/2016] [Indexed: 11/06/2022]
Affiliation(s)
- Layara Akemi Abiko
- Institute of Chemistry; University of São Paulo; São Paulo SP 05508-000 Brazil
| | - Phelipe M. Vitale
- Institute of Chemistry; University of São Paulo; São Paulo SP 05508-000 Brazil
| | - Denize C. Favaro
- Institute of Chemistry; University of São Paulo; São Paulo SP 05508-000 Brazil
| | - Pricila Hauk
- Institute of Chemistry; University of São Paulo; São Paulo SP 05508-000 Brazil
| | - Da-Wei Li
- Campus Chemical Instrument Center; The Ohio State University; Columbus Ohio 43210
| | - Jiaqi Yuan
- Department of Chemistry & Biochemistry; The Ohio State University; Columbus Ohio 43210
| | - Lei Bruschweiler-Li
- Campus Chemical Instrument Center; The Ohio State University; Columbus Ohio 43210
| | - Roberto K. Salinas
- Institute of Chemistry; University of São Paulo; São Paulo SP 05508-000 Brazil
| | - Rafael Brüschweiler
- 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
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24
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Giladi M, Tal I, Khananshvili D. Structural Features of Ion Transport and Allosteric Regulation in Sodium-Calcium Exchanger (NCX) Proteins. Front Physiol 2016; 7:30. [PMID: 26903880 PMCID: PMC4746289 DOI: 10.3389/fphys.2016.00030] [Citation(s) in RCA: 44] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2015] [Accepted: 01/19/2016] [Indexed: 01/14/2023] Open
Abstract
Na(+)/Ca(2+) exchanger (NCX) proteins extrude Ca(2+) from the cell to maintain cellular homeostasis. Since NCX proteins contribute to numerous physiological and pathophysiological events, their pharmacological targeting has been desired for a long time. This intervention remains challenging owing to our poor understanding of the underlying structure-dynamic mechanisms. Recent structural studies have shed light on the structure-function relationships underlying the ion-transport and allosteric regulation of NCX. The crystal structure of an archaeal NCX (NCX_Mj) along with molecular dynamics simulations and ion flux analyses, have assigned the ion binding sites for 3Na(+) and 1Ca(2+), which are being transported in separate steps. In contrast with NCX_Mj, eukaryotic NCXs contain the regulatory Ca(2+)-binding domains, CBD1 and CBD2, which affect the membrane embedded ion-transport domains over a distance of ~80 Å. The Ca(2+)-dependent regulation is ortholog, isoform, and splice-variant dependent to meet physiological requirements, exhibiting either a positive, negative, or no response to regulatory Ca(2+). The crystal structures of the two-domain (CBD12) tandem have revealed a common mechanism involving a Ca(2+)-driven tethering of CBDs in diverse NCX variants. However, dissociation kinetics of occluded Ca(2+) (entrapped at the two-domain interface) depends on the alternative-splicing segment (at CBD2), thereby representing splicing-dependent dynamic coupling of CBDs. The HDX-MS, SAXS, NMR, FRET, equilibrium (45)Ca(2+) binding and stopped-flow techniques provided insights into the dynamic mechanisms of CBDs. Ca(2+) binding to CBD1 results in a population shift, where more constraint conformational states become highly populated without global conformational changes in the alignment of CBDs. This mechanism is common among NCXs. Recent HDX-MS studies have demonstrated that the apo CBD1 and CBD2 are stabilized by interacting with each other, while Ca(2+) binding to CBD1 rigidifies local backbone segments of CBD2, but not of CBD1. The extent and strength of Ca(2+)-dependent rigidification at CBD2 is splice-variant dependent, showing clear correlations with phenotypes of matching NCX variants. Therefore, diverse NCX variants share a common mechanism for the initial decoding of the regulatory signal upon Ca(2+) binding at the interface of CBDs, whereas the allosteric message is shaped by CBD2, the dynamic features of which are dictated by the splicing segment.
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Affiliation(s)
- Moshe Giladi
- Department of Physiology and Pharmacology, Sackler Faculty of Medicine, Tel Aviv University Tel Aviv, Israel
| | - Inbal Tal
- Department of Physiology and Pharmacology, Sackler Faculty of Medicine, 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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25
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Lee SY, Giladi M, Bohbot H, Hiller R, Chung KY, Khananshvili D. Structure‐dynamic basis of splicing‐dependent regulation in tissue‐specific variants of the sodium‐calcium exchanger. FASEB J 2015; 30:1356-66. [DOI: 10.1096/fj.15-282251] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2015] [Accepted: 11/23/2015] [Indexed: 12/21/2022]
Affiliation(s)
- Su Youn Lee
- School of PharmacySungkyunkwan UniversityJangan‐guSuwonSouth Korea
| | - Moshe Giladi
- Department of Physiology and PharmacologyTel‐Aviv UniversityTel‐AvivIsrael
| | - Hilla Bohbot
- Department of Physiology and PharmacologyTel‐Aviv UniversityTel‐AvivIsrael
| | - Reuben Hiller
- Department of Physiology and PharmacologyTel‐Aviv UniversityTel‐AvivIsrael
| | - Ka Young Chung
- School of PharmacySungkyunkwan UniversityJangan‐guSuwonSouth Korea
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26
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Reilly L, Howie J, Wypijewski K, Ashford MLJ, Hilgemann DW, Fuller W. Palmitoylation of the Na/Ca exchanger cytoplasmic loop controls its inactivation and internalization during stress signaling. FASEB J 2015; 29:4532-43. [PMID: 26174834 PMCID: PMC4608915 DOI: 10.1096/fj.15-276493] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2015] [Accepted: 06/30/2015] [Indexed: 01/02/2023]
Abstract
The electrogenic Na/Ca exchanger (NCX) mediates bidirectional Ca movements that are highly sensitive to changes of Na gradients in many cells. NCX1 is implicated in the pathogenesis of heart failure and a number of cardiac arrhythmias. We measured NCX1 palmitoylation using resin-assisted capture, the subcellular location of yellow fluorescent protein–NCX1 fusion proteins, and NCX1 currents using whole-cell voltage clamping. Rat NCX1 is substantially palmitoylated in all tissues examined. Cysteine 739 in the NCX1 large intracellular loop is necessary and sufficient for NCX1 palmitoylation. Palmitoylation of NCX1 occurs in the Golgi and anchors the NCX1 large regulatory intracellular loop to membranes. Surprisingly, palmitoylation does not influence trafficking or localization of NCX1 to surface membranes, nor does it strongly affect the normal forward or reverse transport modes of NCX1. However, exchangers that cannot be palmitoylated do not inactivate normally (leading to substantial activity in conditions when wild-type exchangers are inactive) and do not promote cargo-dependent endocytosis that internalizes 50% of the cell surface following strong G-protein activation or large Ca transients. The palmitoylated cysteine in NCX1 is found in all vertebrate and some invertebrate NCX homologs. Thus, NCX palmitoylation ubiquitously modulates Ca homeostasis and membrane domain function in cells that express NCX proteins.—Reilly, L., Howie, J., Wypijewski, K., Ashford, M. L. J., Hilgemann, D. W., Fuller, W. Palmitoylation of the Na/Ca exchanger cytoplasmic loop controls its inactivation and internalization during stress signaling.
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Affiliation(s)
- Louise Reilly
- *Division of Cardiovascular and Diabetes Medicine, Medical Research Institute, College of Medicine, Dentistry, and Nursing, University of Dundee, Dundee, United Kingdom; and Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas, USA
| | - Jacqueline Howie
- *Division of Cardiovascular and Diabetes Medicine, Medical Research Institute, College of Medicine, Dentistry, and Nursing, University of Dundee, Dundee, United Kingdom; and Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas, USA
| | - Krzysztof Wypijewski
- *Division of Cardiovascular and Diabetes Medicine, Medical Research Institute, College of Medicine, Dentistry, and Nursing, University of Dundee, Dundee, United Kingdom; and Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas, USA
| | - Michael L J Ashford
- *Division of Cardiovascular and Diabetes Medicine, Medical Research Institute, College of Medicine, Dentistry, and Nursing, University of Dundee, Dundee, United Kingdom; and Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas, USA
| | - Donald W Hilgemann
- *Division of Cardiovascular and Diabetes Medicine, Medical Research Institute, College of Medicine, Dentistry, and Nursing, University of Dundee, Dundee, United Kingdom; and Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas, USA
| | - William Fuller
- *Division of Cardiovascular and Diabetes Medicine, Medical Research Institute, College of Medicine, Dentistry, and Nursing, University of Dundee, Dundee, United Kingdom; and Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas, USA
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27
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Structure-dynamic determinants governing a mode of regulatory response and propagation of allosteric signal in splice variants of Na+/Ca2+ exchange (NCX) proteins. Biochem J 2015; 465:489-501. [DOI: 10.1042/bj20141036] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Ca2+ binding to CBD1 (calcium-binding domain 1) and CBD2 regulates Na+/Ca2+ exchangers (NCX). In the present study, we demonstrate that Ca2+ binding rigidifies the main chain of CBD2, but not of CBD1, in a splice variant-dependent manner. The dynamic differences account for variant-dependent responses to Ca2+.
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28
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Almagor L, Giladi M, van Dijk L, Buki T, Hiller R, Khananshvili D. Functional asymmetry of bidirectional Ca2+-movements in an archaeal sodium-calcium exchanger (NCX_Mj). Cell Calcium 2014; 56:276-84. [PMID: 25218934 DOI: 10.1016/j.ceca.2014.08.010] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2014] [Revised: 08/11/2014] [Accepted: 08/20/2014] [Indexed: 11/25/2022]
Abstract
Dynamic features of Ca(2+) interactions with transport and regulatory sites control the Ca(2+)-fluxes in mammalian Na(+)/Ca(2+)(NCX) exchangers bearing the Ca(2+)-binding regulatory domains on the cytosolic 5L6 loop. The crystal structure of Methanococcus jannaschii NCX (NCX_Mj) may serve as a template for studying ion-transport mechanisms since NCX_Mj does not contain the regulatory domains. The turnover rate of Na(+)/Ca(2+) exchange (kcat=0.5±0.2 s(-1)) in WT-NCX_Mj is 10(3)-10(4) times slower than in mammalian NCX. In NCX_Mj, the intrinsic equilibrium (Kint) for bidirectional Ca(2+) movements (defined as the ratio between the cytosolic and extracellular Km of Ca(2+)/Ca(2+) exchange) is asymmetric, Kint=0.15±0.5. Therefore, the Ca(2+) movement from the cytosol to the extracellular side is ∼7-times faster than in the opposite direction, thereby representing a stabilization of outward-facing (extracellular) access. This intrinsic asymmetry accounts for observed differences in the cytosolic and extracellulr Km values having a physiological relevance. Bidirectional Ca(2+) movements are also asymmetric in mammalian NCX. Thus, the stabilization of the outward-facing access along the transport cycle is a common feature among NCX orthologs despite huge differences in the ion-transport kinetics. Elongation of the cytosolic 5L6 loop in NCX_Mj by 8 or 14 residues accelerates the ion transport rates (kcat) ∼10 fold, while increasing the Kint values 100-250-fold (Kint=15-35). Therefore, 5L6 controls both the intrinsic equilibrium and rates of bidirectional Ca(2+) movements in NCX proteins. Some additional structural elements may shape the kinetic variances among phylogenetically distant NCX variants, although the intrinsic asymmetry (Kint) of bidirectional Ca(2+) movements seems to be comparable among evolutionary diverged NCX variants.
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Affiliation(s)
- Lior Almagor
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Ramat-Aviv 69978, Israel
| | - Moshe Giladi
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Ramat-Aviv 69978, Israel
| | - Liat van Dijk
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Ramat-Aviv 69978, Israel
| | - Tal Buki
- 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
| | - Daniel Khananshvili
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Ramat-Aviv 69978, Israel.
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Khananshvili D. Sodium-calcium exchangers (NCX): molecular hallmarks underlying the tissue-specific and systemic functions. Pflugers Arch 2013; 466:43-60. [PMID: 24281864 DOI: 10.1007/s00424-013-1405-y] [Citation(s) in RCA: 88] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2013] [Revised: 11/06/2013] [Accepted: 11/09/2013] [Indexed: 12/19/2022]
Abstract
NCX proteins explore the electrochemical gradient of Na(+) to mediate Ca(2+)-fluxes in exchange with Na(+) either in the Ca(2+)-efflux (forward) or Ca(2+)-influx (reverse) mode, whereas the directionality depends on ionic concentrations and membrane potential. Mammalian NCX variants (NCX1-3) and their splice variants are expressed in a tissue-specific manner to modulate the heartbeat rate and contractile force, the brain's long-term potentiation and learning, blood pressure, renal Ca(2+) reabsorption, the immune response, neurotransmitter and insulin secretion, apoptosis and proliferation, mitochondrial bioenergetics, etc. Although the forward mode of NCX represents a major physiological module, a transient reversal of NCX may contribute to EC-coupling, vascular constriction, and synaptic transmission. Notably, the reverse mode of NCX becomes predominant in pathological settings. Since the expression levels of NCX variants are disease-related, the selective pharmacological targeting of tissue-specific NCX variants could be beneficial, thereby representing a challenge. Recent structural and biophysical studies revealed a common module for decoding the Ca(2+)-induced allosteric signal in eukaryotic NCX variants, although the phenotype variances in response to regulatory Ca(2+) remain unclear. The breakthrough discovery of the archaebacterial NCX structure may serve as a template for eukaryotic NCX, although the turnover rates of the transport cycle may differ ~10(3)-fold among NCX variants to fulfill the physiological demands for the Ca(2+) flux rates. Further elucidation of ion-transport and regulatory mechanisms may lead to selective pharmacological targeting of NCX variants under disease conditions.
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Affiliation(s)
- Daniel Khananshvili
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Ramat-Aviv, Tel-Aviv, 69978, Israel,
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Khananshvili D. The SLC8 gene family of sodium-calcium exchangers (NCX) - structure, function, and regulation in health and disease. Mol Aspects Med 2013; 34:220-35. [PMID: 23506867 DOI: 10.1016/j.mam.2012.07.003] [Citation(s) in RCA: 153] [Impact Index Per Article: 13.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2011] [Accepted: 03/08/2012] [Indexed: 01/12/2023]
Abstract
The SLC8 gene family encoding Na(+)/Ca(2+) exchangers (NCX) belongs to the CaCA (Ca(2+)/Cation Antiporter) superfamily. Three mammalian genes (SLC8A1, SLC8A2, and SLC8A3) and their splice variants are expressed in a tissue-specific manner to mediate Ca(2+)-fluxes across the cell-membrane and thus, significantly contribute to regulation of Ca(2+)-dependent events in many cell types. A long-wanted mitochondrial Na(+)/Ca(2+) exchanger has been recently identified as NCLX protein, representing a gene product of SLC8B1. Distinct NCX isoform/splice variants contribute to excitation-contraction coupling, long-term potentiation of the brain and learning, blood pressure regulation, immune response, neurotransmitter and insulin secretion, mitochondrial bioenergetics, etc. Altered expression and regulation of NCX proteins contribute to distorted Ca(2+)-homeostasis in heart failure, arrhythmia, cerebral ischemia, hypertension, diabetes, renal Ca(2+) reabsorption, muscle dystrophy, etc. Recently, high-resolution X-ray structures of Ca(2+)-binding regulatory domains of eukaryotic NCX and of full-size prokaryotic NCX have become available and the dynamic properties have been analyzed by advanced biophysical approaches. Molecular silencing/overexpression of NCX in cellular systems and organ-specific KO mouse models provided useful information on the contribution of distinct NCX variants to cellular and systemic functions under various pathophysiological conditions. Selective inhibition or activation of predefined NCX variants in specific diseases might have clinical relevance, although this breakthrough has not yet been realized. A better understanding of the underlying molecular mechanisms as well as the development of in vitro procedures for high-throughput screening of "drug-like" compounds may lead to selective pharmacological targeting of NCX variants.
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Affiliation(s)
- Daniel Khananshvili
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Ramat-Aviv, Tel-Aviv 69978, Israel.
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31
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Giladi M, Michaeli L, Almagor L, Bar-On D, Buki T, Ashery U, Khananshvili D, Hirsch JA. The C2B domain is the primary Ca2+ sensor in DOC2B: a structural and functional analysis. J Mol Biol 2013; 425:4629-41. [PMID: 23994332 DOI: 10.1016/j.jmb.2013.08.017] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2013] [Revised: 08/12/2013] [Accepted: 08/21/2013] [Indexed: 12/21/2022]
Abstract
DOC2B (double-C2 domain) protein is thought to be a high-affinity Ca(2+) sensor for spontaneous and asynchronous neurotransmitter release. To elucidate the molecular features underlying its physiological role, we determined the crystal structures of its isolated C2A and C2B domains and examined their Ca(2+)-binding properties. We further characterized the solution structure of the tandem domains (C2AB) using small-angle X-ray scattering. In parallel, we tested structure-function correlates with live cell imaging tools. We found that, despite striking structural similarity, C2B binds Ca(2+) with considerably higher affinity than C2A. The C2AB solution structure is best modeled as two domains with a highly flexible orientation and no difference in the presence or absence of Ca(2+). In addition, kinetic studies of C2AB demonstrate that, in the presence of unilamellar vesicles, Ca(2+) binding is stabilized, as reflected by the ~10-fold slower rate of Ca(2+) dissociation than in the absence of vesicles. In cells, isolated C2B translocates to the plasma membrane (PM) with an EC50 of 400 nM while the C2A does not translocate at submicromolar Ca(2+) concentrations, supporting the biochemical observations. Nevertheless, C2AB translocates to the PM with an ~2-fold lower EC50 and to a greater extent than C2B. Our results, together with previous studies, reveal that the C2B is the primary Ca(2+) sensing unit in DOC2B, whereas C2A enhances the interaction of C2AB with the PM.
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Affiliation(s)
- Moshe Giladi
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Ramat-Aviv 69978, Israel
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Giladi M, Hiller R, Hirsch JA, Khananshvili D. Population shift underlies Ca2+-induced regulatory transitions in the sodium-calcium exchanger (NCX). J Biol Chem 2013; 288:23141-9. [PMID: 23798674 DOI: 10.1074/jbc.m113.471698] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
In eukaryotic Na(+)/Ca(2+) exchangers (NCX) the Ca(2+) binding CBD1 and CBD2 domains form a two-domain regulatory tandem (CBD12). An allosteric Ca(2+) sensor (Ca3-Ca4 sites) is located on CBD1, whereas CBD2 contains a splice-variant segment. Recently, a Ca(2+)-driven interdomain switch has been described, albeit how it couples Ca(2+) binding with signal propagation remains unclear. To resolve the dynamic features of Ca(2+)-induced conformational transitions we analyze here distinct splice variants and mutants of isolated CBD12 at varying temperatures by using small angle x-ray scattering (SAXS) and equilibrium (45)Ca(2+) binding assays. The ensemble optimization method SAXS analysis demonstrates that the apo and Mg(2+)-bound forms of CBD12 are highly flexible, whereas Ca(2+) binding to the Ca3-Ca4 sites results in a population shift of conformational landscape to more rigidified states. Population shift occurs even under conditions in which no effect of Ca(2+) is observed on the globally derived Dmax (maximal interatomic distance), although under comparable conditions a normal [Ca(2+)]-dependent allosteric regulation occurs. Low affinity sites (Ca1-Ca2) of CBD1 do not contribute to Ca(2+)-induced population shift, but the occupancy of these sites by 1 mM Mg(2+) shifts the Ca(2+) affinity (Kd) at the neighboring Ca3-Ca4 sites from ∼ 50 nM to ∼ 200 nM and thus, keeps the primary Ca(2+) sensor (Ca3-Ca4 sites) within a physiological range. Thus, Ca(2+) binding to the Ca3-Ca4 sites results in a population shift, where more constraint conformational states become highly populated at dynamic equilibrium in the absence of global conformational transitions in CBD alignment.
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Affiliation(s)
- Moshe Giladi
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Ramat-Aviv 69978, Israel
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Giladi M, Friedberg I, Fang X, Hiller R, Wang YX, Khananshvili D. G503 is obligatory for coupling of regulatory domains in NCX proteins. Biochemistry 2012; 51:7313-20. [PMID: 22924554 DOI: 10.1021/bi300739z] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
In multidomain proteins, interdomain linkers allow an efficient transfer of regulatory information, although it is unclear how the information encoded in the linker structure coins dynamic coupling. Allosteric regulation of NCX proteins involves Ca(2+)-driven tethering of regulatory CBD1 and CBD2 (through a salt bridge network) accompanied by alignment of CBDs and Ca(2+) occlusion at the interface of the two CBDs. Here we investigated "alanine-walk" substitutions in the CBD1-CBD2 linker (501-HAGIFT-506) and found that among all linker residues, only G503 is obligatory for Ca(2+)-induced reorientations of CBDs and slow dissociation of occluded Ca(2+). Moreover, swapping between positions A502 and G503 in the CBD1-CBD2 linker results in a complete loss of slow dissociation of occluded Ca(2+), meaning that dynamic coupling of CBDs requires an exact pose of glycine at position 503. Therefore, accumulating data revealed that position 503 occupied by glycine is absolutely required for Ca(2+)-driven tethering of CBDs, which in turn limits the linker's flexibility and, thus, restricts CBD movements. Because G503 is extremely well conserved in eukaryotic NCX proteins, the information encoded in G503 is essential for dynamic coupling of the two-domain CBD tandem and, thus, for propagation of the allosteric signal.
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Affiliation(s)
- Moshe Giladi
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Ramat-Aviv 69978, Israel
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Breukels V, Touw WG, Vuister GW. NMR structure note: solution structure of Ca²⁺ binding domain 2B of the third isoform of the Na⁺/Ca²⁺ exchanger. JOURNAL OF BIOMOLECULAR NMR 2012; 54:115-121. [PMID: 22806131 DOI: 10.1007/s10858-012-9654-1] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/16/2012] [Accepted: 06/30/2012] [Indexed: 06/01/2023]
Affiliation(s)
- Vincent Breukels
- Institute for Molecules and Materials, Radboud University Nijmegen, Geert Grooteplein 26-28, 6525 GA, Nijmegen, The Netherlands
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