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Fabri LM, Moraes CM, Garçon DP, McNamara JC, Faria SC, Leone FA. Primary amino acid sequences of decapod (Na +, K +)-ATPase provide evolutionary insights into osmoregulatory mechanisms. Comp Biochem Physiol A Mol Integr Physiol 2024; 296:111696. [PMID: 39004301 DOI: 10.1016/j.cbpa.2024.111696] [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: 04/29/2024] [Revised: 07/08/2024] [Accepted: 07/08/2024] [Indexed: 07/16/2024]
Abstract
Decapod Crustacea exhibit a marine origin, but many taxa have occupied environments ranging from brackish to fresh water and terrestrial habitats, overcoming their inherent osmotic challenges. Osmotic and ionic regulation is achieved by the gill epithelia, driven by two active ATP-hydrolyzing ion transporters, the basal (Na+, K+)-ATPase and the apical V(H+)-ATPase. The kinetic characteristic of gill (Na+, K+)-ATPase and the mRNA expression of its α subunit have been widely studied in various decapod species under different salinity challenges. However, the evolution of the primary structure has not been explored, especially considering the functional modifications associated with decapod phylogeny. Here, we proposed a model for the topology of the decapod α subunit, identifying the sites and motifs involved in its function and regulation, as well as the patterns of its evolution assuming a decapod phylogeny. We also examined both the amino acid substitutions and their functional implications within the context of biochemical and physiological adaptation. The α-subunit of decapod crustaceans shows greater conservation (∼94% identity) compared to the β-subunit (∼40%). While the binding sites for ATP and modulators are conserved in the decapod enzyme, the residues involved in the α-β interaction are only partially conserved. In the phylogenetic context of the complete sequence of (Na+, K+)-ATPase α-subunit, most substitutions appear to be characteristic of the entire group, with specific changes for different subgroups, especially among brachyuran crabs. Interestingly, there was no consistent separation of α-subunit partial sequences related to habitat, suggesting that the convergent evolution for freshwater or terrestrial modes of life is not correlated with similar changes in the enzyme's primary amino acid sequence.
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Affiliation(s)
- Leonardo M Fabri
- Departamento de Bioquímica e Imunologia, Faculdade de Medicina de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, São Paulo, Brazil
| | - Cintya M Moraes
- Departamento de Bioquímica e Imunologia, Faculdade de Medicina de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, São Paulo, Brazil
| | | | - John C McNamara
- Departamento de Biologia Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, São Paulo, Brazil; Centro de Biologia Marinha, Universidade de São Paulo, São Sebastião, São Paulo, Brazil
| | - Samuel C Faria
- Centro de Biologia Marinha, Universidade de São Paulo, São Sebastião, São Paulo, Brazil
| | - Francisco A Leone
- Departamento de Química, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, São Paulo, Brazil.
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Zádor E. The Meeting of Micropeptides with Major Ca 2+ Pumps in Inner Membranes-Consideration of a New Player, SERCA1b. MEMBRANES 2023; 13:274. [PMID: 36984661 PMCID: PMC10058886 DOI: 10.3390/membranes13030274] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/21/2022] [Revised: 02/20/2023] [Accepted: 02/23/2023] [Indexed: 06/18/2023]
Abstract
Calcium is a major signalling bivalent cation within the cell. Compartmentalization is essential for regulation of calcium mediated processes. A number of players contribute to intracellular handling of calcium, among them are the sarco/endoplasmic reticulum calcium ATP-ases (SERCAs). These molecules function in the membrane of ER/SR pumping Ca2+ from cytoplasm into the lumen of the internal store. Removal of calcium from the cytoplasm is essential for signalling and for relaxation of skeletal muscle and heart. There are three genes and over a dozen isoforms of SERCA in mammals. These can be potentially influenced by small membrane peptides, also called regulins. The discovery of micropeptides has increased in recent years, mostly because of the small ORFs found in long RNAs, annotated formerly as noncoding (lncRNAs). Several excellent works have analysed the mechanism of interaction of micropeptides with each other and with the best known SERCA1a (fast muscle) and SERCA2a (heart, slow muscle) isoforms. However, the array of tissue and developmental expressions of these potential regulators raises the question of interaction with other SERCAs. For example, the most abundant calcium pump in neonatal and regenerating skeletal muscle, SERCA1b has never been looked at with scrutiny to determine whether it is influenced by micropeptides. Further details might be interesting on the interaction of these peptides with the less studied SERCA1b isoform.
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Affiliation(s)
- Ernő Zádor
- Institute of Biochemistry, Albert Szent-Györgyi Faculty of Medicine, University of Szeged, Dóm tér 9, H-6720 Szeged, Hungary
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3
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Fedosova NU, Habeck M, Nissen P. Structure and Function of Na,K-ATPase-The Sodium-Potassium Pump. Compr Physiol 2021; 12:2659-2679. [PMID: 34964112 DOI: 10.1002/cphy.c200018] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Na,K-ATPase is an ubiquitous enzyme actively transporting Na-ions out of the cell in exchange for K-ions, thereby maintaining their concentration gradients across the cell membrane. Since its discovery more than six decades ago the Na-pump has been studied extensively and its vital physiological role in essentially every cell has been established. This article aims at providing an overview of well-established biochemical properties with a focus on Na,K-ATPase isoforms, its transport mechanism and principle conformations, inhibitors, and insights gained from crystal structures. © 2021 American Physiological Society. Compr Physiol 11:1-21, 2021.
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Affiliation(s)
| | - Michael Habeck
- Department of Molecular Biology and Genetics, Danish Research Institute of Translational Neuroscience - DANDRITE, Nordic EMBL Partnership for Molecular Medicine, Aarhus University, Aarhus, Denmark
| | - Poul Nissen
- Department of Molecular Biology and Genetics, Danish Research Institute of Translational Neuroscience - DANDRITE, Nordic EMBL Partnership for Molecular Medicine, Aarhus University, Aarhus, Denmark
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4
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Ygberg S, Akkuratov EE, Howard RJ, Taylan F, Jans DC, Mahato DR, Katz A, Kinoshita PF, Portal B, Nennesmo I, Lindskog M, Karlish SJD, Andersson M, Lindstrand A, Brismar H, Aperia A. A missense mutation converts the Na +,K +-ATPase into an ion channel and causes therapy-resistant epilepsy. J Biol Chem 2021; 297:101355. [PMID: 34717959 PMCID: PMC8637647 DOI: 10.1016/j.jbc.2021.101355] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2021] [Revised: 10/14/2021] [Accepted: 10/25/2021] [Indexed: 11/16/2022] Open
Abstract
The ion pump Na+,K+-ATPase is a critical determinant of neuronal excitability; however, its role in the etiology of diseases of the central nervous system (CNS) is largely unknown. We describe here the molecular phenotype of a Trp931Arg mutation of the Na+,K+-ATPase catalytic α1 subunit in an infant diagnosed with therapy-resistant lethal epilepsy. In addition to the pathological CNS phenotype, we also detected renal wasting of Mg2+. We found that membrane expression of the mutant α1 protein was low, and ion pumping activity was lost. Arginine insertion into membrane proteins can generate water-filled pores in the plasma membrane, and our molecular dynamic (MD) simulations of the principle states of Na+,K+-ATPase transport demonstrated massive water inflow into mutant α1 and destabilization of the ion-binding sites. MD simulations also indicated that a water pathway was created between the mutant arginine residue and the cytoplasm, and analysis of oocytes expressing mutant α1 detected a nonspecific cation current. Finally, neurons expressing mutant α1 were observed to be depolarized compared with neurons expressing wild-type protein, compatible with a lowered threshold for epileptic seizures. The results imply that Na+,K+-ATPase should be considered a neuronal locus minoris resistentia in diseases associated with epilepsy and with loss of plasma membrane integrity.
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Affiliation(s)
- Sofia Ygberg
- Neuropediatric Unit, Department of Women's and Children's Health, Karolinska Institutet, Stockholm, Sweden; Centre for Inherited Metabolic Diseases (CMMS), Karolinska University Hospital, Stockholm, Sweden
| | - Evgeny E Akkuratov
- Science for Life Laboratory, Department of Applied Physics, Royal Institute of Technology, Stockholm, Sweden
| | - Rebecca J Howard
- Science for Life Laboratory, Department of Biochemistry and Biophysics, Stockholm University, Stockholm, Sweden
| | - Fulya Taylan
- Department of Molecular Medicine and Surgery, Center for Molecular Medicine, Karolinska Institutet, Stockholm, Sweden; Department of Neurobiology, Care Sciences and Society, Karolinska Institutet, Stockholm, Sweden
| | - Daniel C Jans
- Science for Life Laboratory, Department of Applied Physics, Royal Institute of Technology, Stockholm, Sweden
| | | | - Adriana Katz
- Department of Biomolecular Sciences, Weizmann Institute of Science, Rehovoth, Israel
| | - Paula F Kinoshita
- Department of Pharmacology, Institute of Biomedical Science, University of São Paulo, São Paulo, Brazil
| | - Benjamin Portal
- Department of Neurobiology, Care Sciences and Society, Karolinska Institutet, Stockholm, Sweden
| | - Inger Nennesmo
- Department of Pathology, Karolinska University Hospital, Stockholm, Sweden
| | - Maria Lindskog
- Department of Neurobiology, Care Sciences and Society, Karolinska Institutet, Stockholm, Sweden
| | - Steven J D Karlish
- Department of Biomolecular Sciences, Weizmann Institute of Science, Rehovoth, Israel
| | | | - Anna Lindstrand
- Department of Molecular Medicine and Surgery, Center for Molecular Medicine, Karolinska Institutet, Stockholm, Sweden; Department of Clinical Genetics, Karolinska University Hospital, Stockholm, Sweden
| | - Hjalmar Brismar
- Science for Life Laboratory, Department of Applied Physics, Royal Institute of Technology, Stockholm, Sweden; Science for Life Laboratory, Department of Women's and Children's Health, Karolinska Institutet, Stockholm, Sweden.
| | - Anita Aperia
- Science for Life Laboratory, Department of Women's and Children's Health, Karolinska Institutet, Stockholm, Sweden
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5
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Distinct effects of Q925 mutation on intracellular and extracellular Na + and K + binding to the Na +, K +-ATPase. Sci Rep 2019; 9:13344. [PMID: 31527711 PMCID: PMC6746705 DOI: 10.1038/s41598-019-50009-2] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2019] [Accepted: 09/03/2019] [Indexed: 11/09/2022] Open
Abstract
Three Na+ sites are defined in the Na+-bound crystal structure of Na+, K+-ATPase. Sites I and II overlap with two K+ sites in the K+-bound structure, whereas site III is unique and Na+ specific. A glutamine in transmembrane helix M8 (Q925) appears from the crystal structures to coordinate Na+ at site III, but does not contribute to K+ coordination at sites I and II. Here we address the functional role of Q925 in the various conformational states of Na+, K+-ATPase by examining the mutants Q925A/G/E/N/L/I/Y. We characterized these mutants both enzymatically and electrophysiologically, thereby revealing their Na+ and K+ binding properties. Remarkably, Q925 substitutions had minor effects on Na+ binding from the intracellular side of the membrane - in fact, mutations Q925A and Q925G increased the apparent Na+ affinity - but caused dramatic reductions of the binding of K+ as well as Na+ from the extracellular side of the membrane. These results provide insight into the changes taking place in the Na+-binding sites, when they are transformed from intracellular- to extracellular-facing orientation in relation to the ion translocation process, and demonstrate the interaction between sites III and I and a possible gating function of Q925 in the release of Na+ at the extracellular side.
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Roenn CP, Li M, Schack VR, Forster IC, Holm R, Toustrup-Jensen MS, Andersen JP, Petrou S, Vilsen B. Functional consequences of the CAPOS mutation E818K of Na +,K +-ATPase. J Biol Chem 2018; 294:269-280. [PMID: 30409907 DOI: 10.1074/jbc.ra118.004591] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2018] [Revised: 11/04/2018] [Indexed: 11/06/2022] Open
Abstract
The cerebellar ataxia, areflexia, pes cavus, optic atrophy, and sensorineural hearing loss (CAPOS) syndrome is caused by the single mutation E818K of the α3-isoform of Na+,K+-ATPase. Here, using biochemical and electrophysiological approaches, we examined the functional characteristics of E818K, as well as of E818Q and E818A mutants. We found that these amino acid substitutions reduce the apparent Na+ affinity at the cytoplasmic-facing sites of the pump protein and that this effect is more pronounced for the lysine and glutamine substitutions (3-4-fold) than for the alanine substitution. The electrophysiological measurements indicated a more conspicuous, ∼30-fold reduction of apparent Na+ affinity for the extracellular-facing sites in the CAPOS mutant, which was related to an accelerated transition between the phosphoenzyme intermediates E1P and E2P. The apparent affinity for K+ activation of the ATPase activity was unaffected by these substitutions, suggesting that primarily the Na+-specific site III is affected. Furthermore, the apparent affinities for ATP and vanadate were WT-like in E818K, indicating a normal E1-E2 equilibrium of the dephosphoenzyme. Proton-leak currents were not increased in E818K. However, the CAPOS mutation caused a weaker voltage dependence of the pumping rate and a stronger inhibition by cytoplasmic K+ than the WT enzyme, which together with the reduced Na+ affinity of the cytoplasmic-facing sites precluded proper pump activation under physiological conditions. The functional deficiencies could be traced to the participation of Glu-818 in an intricate hydrogen-bonding/salt-bridge network, connecting it to key residues involved in Na+ interaction at site III.
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Affiliation(s)
- Christian P Roenn
- Department of Biomedicine, Aarhus University, DK-8000 Aarhus C, Denmark
| | - Melody Li
- Florey Institute of Neuroscience and Mental Health, Parkville, 3052 Victoria, Australia
| | - Vivien R Schack
- Department of Biomedicine, Aarhus University, DK-8000 Aarhus C, Denmark
| | - Ian C Forster
- Florey Institute of Neuroscience and Mental Health, Parkville, 3052 Victoria, Australia
| | - Rikke Holm
- Department of Biomedicine, Aarhus University, DK-8000 Aarhus C, Denmark
| | | | - Jens P Andersen
- Department of Biomedicine, Aarhus University, DK-8000 Aarhus C, Denmark
| | - Steven Petrou
- Florey Institute of Neuroscience and Mental Health, Parkville, 3052 Victoria, Australia
| | - Bente Vilsen
- Department of Biomedicine, Aarhus University, DK-8000 Aarhus C, Denmark.
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Abstract
The calcium pump (a.k.a. Ca2+-ATPase or SERCA) is a membrane transport protein ubiquitously found in the endoplasmic reticulum (ER) of all eukaryotic cells. As a calcium transporter, SERCA maintains the low cytosolic calcium level that enables a vast array of signaling pathways and physiological processes (e.g. synaptic transmission, muscle contraction, fertilization). In muscle cells, SERCA promotes relaxation by pumping calcium ions from the cytosol into the lumen of the sarcoplasmic reticulum (SR), the main storage compartment for intracellular calcium. X-ray crystallographic studies have provided an extensive understanding of the intermediate states that SERCA populates as it progresses through the calcium transport cycle. Historically, SERCA is also known to be regulated by small transmembrane peptides, phospholamban (PLN) and sarcolipin (SLN). PLN is expressed in cardiac muscle, whereas SLN predominates in skeletal and atrial muscle. These two regulatory subunits play critical roles in cardiac contractility. While our understanding of these regulatory mechanisms are still developing, SERCA and PLN are one of the best understood examples of peptide-transporter regulatory interactions. Nonetheless, SERCA appeared to have only two regulatory subunits, while the related sodium pump (a.k.a. Na+, K+-ATPase) has at least nine small transmembrane peptides that provide tissue specific regulation. The last few years have seen a renaissance in our understanding of SERCA regulatory subunits. First, structures of the SERCA-SLN and SERCA-PLN complexes revealed molecular details of their interactions. Second, an array of micropeptides concealed within long non-coding RNAs have been identified as new SERCA regulators. This chapter will describe our current understanding of SERCA structure, function, and regulation.
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8
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Razavi AM, Delemotte L, Berlin JR, Carnevale V, Voelz VA. Molecular simulations and free-energy calculations suggest conformation-dependent anion binding to a cytoplasmic site as a mechanism for Na +/K +-ATPase ion selectivity. J Biol Chem 2017; 292:12412-12423. [PMID: 28588025 DOI: 10.1074/jbc.m117.779090] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2017] [Revised: 06/05/2017] [Indexed: 12/14/2022] Open
Abstract
Na+/K+-ATPase transports Na+ and K+ ions across the cell membrane via an ion-binding site becoming alternatively accessible to the intra- and extracellular milieu by conformational transitions that confer marked changes in ion-binding stoichiometry and selectivity. To probe the mechanism of these changes, we used molecular simulation and free-energy perturbation approaches to identify probable protonation states of Na+- and K+-coordinating residues in E1P and E2P conformations of Na+/K+-ATPase. Analysis of these simulations revealed a molecular mechanism responsible for the change in protonation state: the conformation-dependent binding of an anion (a chloride ion in our simulations) to a previously unrecognized cytoplasmic site in the loop between transmembrane helices 8 and 9, which influences the electrostatic potential of the crucial Na+-coordinating residue Asp926 This mechanistic model is consistent with experimental observations and provides a molecular-level picture of how E1P to E2P enzyme conformational transitions are coupled to changes in ion-binding stoichiometry and selectivity.
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Affiliation(s)
- Asghar M Razavi
- Department of Chemistry, Temple University, Philadelphia, Pennsylvania 19122
| | - Lucie Delemotte
- Institute for Computational Molecular Science, Temple University, Philadelphia, Pennsylvania 19122; Science for Life Laboratory, Department of Theoretical Physics, KTH Royal Institute of Technology, Stockholm 11428, Sweden
| | - Joshua R Berlin
- Department of Pharmacology, Physiology and Neuroscience, New Jersey Medical School, Rutgers University, Newark, New Jersey 07103
| | - Vincenzo Carnevale
- Department of Chemistry, Temple University, Philadelphia, Pennsylvania 19122; Institute for Computational Molecular Science, Temple University, Philadelphia, Pennsylvania 19122.
| | - Vincent A Voelz
- Department of Chemistry, Temple University, Philadelphia, Pennsylvania 19122; Institute for Computational Molecular Science, Temple University, Philadelphia, Pennsylvania 19122.
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9
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Holm R, Toustrup-Jensen MS, Einholm AP, Schack VR, Andersen JP, Vilsen B. Neurological disease mutations of α3 Na +,K +-ATPase: Structural and functional perspectives and rescue of compromised function. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2016; 1857:1807-1828. [PMID: 27577505 DOI: 10.1016/j.bbabio.2016.08.009] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/05/2016] [Revised: 08/19/2016] [Accepted: 08/25/2016] [Indexed: 11/26/2022]
Abstract
Na+,K+-ATPase creates transmembrane ion gradients crucial to the function of the central nervous system. The α-subunit of Na+,K+-ATPase exists as four isoforms (α1-α4). Several neurological phenotypes derive from α3 mutations. The effects of some of these mutations on Na+,K+-ATPase function have been studied in vitro. Here we discuss the α3 disease mutations as well as information derived from studies of corresponding mutations of α1 in the light of the high-resolution crystal structures of the Na+,K+-ATPase. A high proportion of the α3 disease mutations occur in the transmembrane sector and nearby regions essential to Na+ and K+ binding. In several cases the compromised function can be traced to disturbance of the Na+ specific binding site III. Recently, a secondary mutation was found to rescue the defective Na+ binding caused by a disease mutation. A perspective is that it may be possible to develop an efficient pharmaceutical mimicking the rescuing effect.
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Affiliation(s)
- Rikke Holm
- Department of Biomedicine, Aarhus University, 8000 Aarhus C, Denmark.
| | | | - Anja P Einholm
- Department of Biomedicine, Aarhus University, 8000 Aarhus C, Denmark.
| | - Vivien R Schack
- Department of Biomedicine, Aarhus University, 8000 Aarhus C, Denmark.
| | - Jens P Andersen
- Department of Biomedicine, Aarhus University, 8000 Aarhus C, Denmark.
| | - Bente Vilsen
- Department of Biomedicine, Aarhus University, 8000 Aarhus C, Denmark.
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10
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Directed evolution of a sphingomyelin flippase reveals mechanism of substrate backbone discrimination by a P4-ATPase. Proc Natl Acad Sci U S A 2016; 113:E4460-6. [PMID: 27432949 DOI: 10.1073/pnas.1525730113] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Phospholipid flippases in the type IV P-type ATPase (P4-ATPases) family establish membrane asymmetry and play critical roles in vesicular transport, cell polarity, signal transduction, and neurologic development. All characterized P4-ATPases flip glycerophospholipids across the bilayer to the cytosolic leaflet of the membrane, but how these enzymes distinguish glycerophospholipids from sphingolipids is not known. We used a directed evolution approach to examine the molecular mechanisms through which P4-ATPases discriminate substrate backbone. A mutagenesis screen in the yeast Saccharomyces cerevisiae has identified several gain-of-function mutations in the P4-ATPase Dnf1 that facilitate the transport of a novel lipid substrate, sphingomyelin. We found that a highly conserved asparagine (N220) in the first transmembrane segment is a key enforcer of glycerophospholipid selection, and specific substitutions at this site allow transport of sphingomyelin.
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11
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Friedrich T, Tavraz NN, Junghans C. ATP1A2 Mutations in Migraine: Seeing through the Facets of an Ion Pump onto the Neurobiology of Disease. Front Physiol 2016; 7:239. [PMID: 27445835 PMCID: PMC4914835 DOI: 10.3389/fphys.2016.00239] [Citation(s) in RCA: 57] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2016] [Accepted: 06/03/2016] [Indexed: 12/31/2022] Open
Abstract
Mutations in four genes have been identified in familial hemiplegic migraine (FHM), from which CACNA1A (FHM type 1) and SCN1A (FHM type 3) code for neuronal voltage-gated calcium or sodium channels, respectively, while ATP1A2 (FHM type 2) encodes the α2 isoform of the Na(+),K(+)-ATPase's catalytic subunit, thus classifying FHM primarily as an ion channel/ion transporter pathology. FHM type 4 is attributed to mutations in the PRRT2 gene, which encodes a proline-rich transmembrane protein of as yet unknown function. The Na(+),K(+)-ATPase maintains the physiological gradients for Na(+) and K(+) ions and is, therefore, critical for the activity of ion channels and transporters involved neuronal excitability, neurotransmitter uptake or Ca(2+) signaling. Strikingly diverse functional abnormalities have been identified for disease-linked ATP1A2 mutations which frequently lead to changes in the enzyme's voltage-dependent properties, kinetics, or apparent cation affinities, but some mutations are truly deleterious for enzyme function and thus cause full haploinsufficiency. Here, we summarize structural and functional data about the Na(+),K(+)-ATPase available to date and an overview is provided about the particular properties of the α2 isoform that explain its physiological relevance in electrically excitable tissues. In addition, current concepts about the neurobiology of migraine, the correlations between primary brain dysfunction and mechanisms of headache pain generation are described, together with insights gained recently from modeling approaches in computational neuroscience. Then, a survey is given about ATP1A2 mutations implicated in migraine cases as documented in the literature with focus on mutations that were described to completely destroy enzyme function, or lead to misfolded or mistargeted protein in particular model cell lines. We also discuss whether or not there are correlations between these most severe mutational effects and clinical phenotypes. Finally, perspectives for future research on the implications of Na(+),K(+)-ATPase mutations in human pathologies are presented.
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Affiliation(s)
- Thomas Friedrich
- Department of Physical Chemistry/Bioenergetics, Institute of Chemistry, Technical University of BerlinBerlin, Germany
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12
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Kubala M, Čechová P, Geletičová J, Biler M, Štenclová T, Trouillas P, Biedermann D. Flavonolignans As a Novel Class of Sodium Pump Inhibitors. Front Physiol 2016; 7:115. [PMID: 27065883 PMCID: PMC4812144 DOI: 10.3389/fphys.2016.00115] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2016] [Accepted: 03/14/2016] [Indexed: 11/13/2022] Open
Abstract
We examined the inhibitory effects of three flavonolignans and their dehydro- derivatives, taxifolin and quercetin on the activity of the Na+/K+-ATPase (NKA). The flavonolignans silychristin, dehydrosilychristin and dehydrosilydianin inhibited NKA with IC50 of 110 ± 40 μM, 38 ± 8 μM, and 36 ± 14 μM, respectively. Using the methods of molecular modeling, we identified several possible binding sites for these species on NKA and proposed the possible mechanisms of inhibition. The binding to the extracellular- or cytoplasmic C-terminal sites can block the transport of cations through the plasma membrane, while the binding on the interface of cytoplasmic domains can inhibit the enzyme allosterically. Fluorescence spectroscopy experiments confirmed the interaction of these three species with the large cytoplasmic segment connecting transmembrane helices 4 and 5 (C45). The flavonolignans are distinct from the cardiac glycosides that are currently used in NKA treatment. Because their binding sites are different, the mechanism of inhibition is different as well as the range of active concentrations, one can expect that these new NKA inhibitors would exhibit also a different biomedical actions than cardiac glycosides.
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Affiliation(s)
- Martin Kubala
- Department of Biophysics, Faculty of Science, Centre of Region Haná for Biotechnological and Agricultural Research, Palacký University Olomouc, Czech Republic
| | - Petra Čechová
- Department of Biophysics, Faculty of Science, Centre of Region Haná for Biotechnological and Agricultural Research, Palacký University Olomouc, Czech Republic
| | - Jaroslava Geletičová
- Department of Biophysics, Faculty of Science, Centre of Region Haná for Biotechnological and Agricultural Research, Palacký University Olomouc, Czech Republic
| | - Michal Biler
- Department of Biophysics, Faculty of Science, Centre of Region Haná for Biotechnological and Agricultural Research, Palacký UniversityOlomouc, Czech Republic; INSERM UMR 850, School of Pharmacy, University LimogesLimoges, France
| | - Tereza Štenclová
- Department of Biophysics, Faculty of Science, Centre of Region Haná for Biotechnological and Agricultural Research, Palacký University Olomouc, Czech Republic
| | - Patrick Trouillas
- INSERM UMR 850, School of Pharmacy, University LimogesLimoges, France; Department of Physical Chemistry, Faculty of Science, Regional Centre of Advanced Technologies and Materials, Palacký UniversityOlomouc, Czech Republic
| | - David Biedermann
- Laboratory of Biotransformation, Institute of Microbiology, Czech Academy of Sciences Prague, Czech Republic
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13
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Einholm AP, Nielsen HN, Holm R, Toustrup-Jensen MS, Vilsen B. Importance of a Potential Protein Kinase A Phosphorylation Site of Na+,K+-ATPase and Its Interaction Network for Na+ Binding. J Biol Chem 2016; 291:10934-47. [PMID: 27013656 DOI: 10.1074/jbc.m115.701201] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2015] [Indexed: 12/29/2022] Open
Abstract
The molecular mechanism underlying PKA-mediated regulation of Na(+),K(+)-ATPase was explored in mutagenesis studies of the potential PKA site at Ser-938 and surrounding charged residues. The phosphomimetic mutations S938D/E interfered with Na(+) binding from the intracellular side of the membrane, whereas Na(+) binding from the extracellular side was unaffected. The reduction of Na(+) affinity is within the range expected for physiological regulation of the intracellular Na(+) concentration, thus supporting the hypothesis that PKA-mediated phosphorylation of Ser-938 regulates Na(+),K(+)-ATPase activity in vivo Ser-938 is located in the intracellular loop between transmembrane segments M8 and M9. An extended bonding network connects this loop with M10, the C terminus, and the Na(+) binding region. Charged residues Asp-997, Glu-998, Arg-1000, and Lys-1001 in M10, participating in this bonding network, are crucial to Na(+) interaction. Replacement of Arg-1005, also located in the vicinity of Ser-938, with alanine, lysine, methionine, or serine resulted in wild type-like Na(+) and K(+) affinities and catalytic turnover rate. However, when combined with the phosphomimetic mutation S938E only lysine substitution of Arg-1005 was compatible with Na(+),K(+)-ATPase function, and the Na(+) affinity of this double mutant was reduced even more than in single mutant S938E. This result indicates that the positive side chain of Arg-1005 or the lysine substituent plays a mechanistic role as interaction partner of phosphorylated Ser-938, transducing the phosphorylation signal into a reduced affinity of Na(+) site III. Electrostatic interaction of Glu-998 is of minor importance for the reduction of Na(+) affinity by phosphomimetic S938E as revealed by combining S938E with E998A.
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Affiliation(s)
- Anja P Einholm
- From the Department of Biomedicine, Aarhus University, DK-8000 Aarhus C, Denmark
| | - Hang N Nielsen
- From the Department of Biomedicine, Aarhus University, DK-8000 Aarhus C, Denmark
| | - Rikke Holm
- From the Department of Biomedicine, Aarhus University, DK-8000 Aarhus C, Denmark
| | | | - Bente Vilsen
- From the Department of Biomedicine, Aarhus University, DK-8000 Aarhus C, Denmark
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14
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Abstract
The vital gradients of Na+ and K+ across the plasma membrane of animal cells are maintained by the Na,K-ATPase, an αβ enzyme complex, whose α subunit carries out the ion transport and ATP hydrolysis. The specific roles of the β subunit isoforms are less clear, though β2 is essential for motor physiology in mammals. Here, we show that compared to β1 and β3, β2 stabilizes the Na+-occluded E1P state relative to the outward-open E2P state, and that the effect is mediated by its transmembrane domain. Molecular dynamics simulations further demonstrate that the tilt angle of the β transmembrane helix correlates with its functional effect, suggesting that the relative orientation of β modulates ion binding at the α subunit. β2 is primarily expressed in granule neurons and glomeruli in the cerebellum, and we propose that its unique functional characteristics are important to respond appropriately to the cerebellar Na+ and K+ gradients.
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15
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Viollet L, Glusman G, Murphy KJ, Newcomb TM, Reyna SP, Sweney M, Nelson B, Andermann F, Andermann E, Acsadi G, Barbano RL, Brown C, Brunkow ME, Chugani HT, Cheyette SR, Collins A, DeBrosse SD, Galas D, Friedman J, Hood L, Huff C, Jorde LB, King MD, LaSalle B, Leventer RJ, Lewelt AJ, Massart MB, Mérida MR, Ptáček LJ, Roach JC, Rust RS, Renault F, Sanger TD, Sotero de Menezes MA, Tennyson R, Uldall P, Zhang Y, Zupanc M, Xin W, Silver K, Swoboda KJ. Alternating Hemiplegia of Childhood: Retrospective Genetic Study and Genotype-Phenotype Correlations in 187 Subjects from the US AHCF Registry. PLoS One 2015; 10:e0127045. [PMID: 25996915 PMCID: PMC4440742 DOI: 10.1371/journal.pone.0127045] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2014] [Accepted: 04/11/2015] [Indexed: 11/21/2022] Open
Abstract
Mutations in ATP1A3 cause Alternating Hemiplegia of Childhood (AHC) by disrupting function of the neuronal Na+/K+ ATPase. Published studies to date indicate 2 recurrent mutations, D801N and E815K, and a more severe phenotype in the E815K cohort. We performed mutation analysis and retrospective genotype-phenotype correlations in all eligible patients with AHC enrolled in the US AHC Foundation registry from 1997-2012. Clinical data were abstracted from standardized caregivers’ questionnaires and medical records and confirmed by expert clinicians. We identified ATP1A3 mutations by Sanger and whole genome sequencing, and compared phenotypes within and between 4 groups of subjects, those with D801N, E815K, other ATP1A3 or no ATP1A3 mutations. We identified heterozygous ATP1A3 mutations in 154 of 187 (82%) AHC patients. Of 34 unique mutations, 31 (91%) are missense, and 16 (47%) had not been previously reported. Concordant with prior studies, more than 2/3 of all mutations are clustered in exons 17 and 18. Of 143 simplex occurrences, 58 had D801N (40%), 38 had E815K (26%) and 11 had G937R (8%) mutations. Patients with an E815K mutation demonstrate an earlier age of onset, more severe motor impairment and a higher prevalence of status epilepticus. This study further expands the number and spectrum of ATP1A3 mutations associated with AHC and confirms a more deleterious effect of the E815K mutation on selected neurologic outcomes. However, the complexity of the disorder and the extensive phenotypic variability among subgroups merits caution and emphasizes the need for further studies.
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Affiliation(s)
- Louis Viollet
- Pediatric Motor Disorders Research Program, Departments of Neurology and Pediatrics, University of Utah, Salt Lake City, Utah, United States of America
| | - Gustavo Glusman
- Institute for Systems Biology, Seattle, Washington, United States of America
| | - Kelley J. Murphy
- Pediatric Motor Disorders Research Program, Departments of Neurology and Pediatrics, University of Utah, Salt Lake City, Utah, United States of America
| | - Tara M. Newcomb
- Pediatric Motor Disorders Research Program, Departments of Neurology and Pediatrics, University of Utah, Salt Lake City, Utah, United States of America
| | - Sandra P. Reyna
- Pediatric Motor Disorders Research Program, Departments of Neurology and Pediatrics, University of Utah, Salt Lake City, Utah, United States of America
| | - Matthew Sweney
- Pediatric Motor Disorders Research Program, Departments of Neurology and Pediatrics, University of Utah, Salt Lake City, Utah, United States of America
| | - Benjamin Nelson
- Pediatric Motor Disorders Research Program, Departments of Neurology and Pediatrics, University of Utah, Salt Lake City, Utah, United States of America
| | - Frederick Andermann
- Neurogenetics Unit, Montreal Neurologic Institute and Hospital, McGill University, Montreal Quebec, Canada
| | - Eva Andermann
- Neurogenetics Unit, Montreal Neurologic Institute and Hospital, McGill University, Montreal Quebec, Canada
| | - Gyula Acsadi
- Departments of Pediatrics and Neurology, Connecticut Children's Medical Center and University of Connecticut School of Medicine, Hartford, CT, United States of America
| | - Richard L. Barbano
- Department of Neurology, University of Rochester School of Medicine, Rochester, New York, United States of America
| | - Candida Brown
- Diablo Valley Child Neurology, an affiliate of Stanford Health Alliance, Pleasant Hill, California, United States of America
| | - Mary E. Brunkow
- Institute for Systems Biology, Seattle, Washington, United States of America
| | - Harry T. Chugani
- Division of Pediatric Neurology, Children's Hospital of Michigan, Wayne State University, Detroit, Michigan, United States of America
| | - Sarah R. Cheyette
- Department of Child Neurology, Palo Alto Medical Foundation Redwood City Clinic, Redwood City, California, United States of America
| | - Abigail Collins
- Department of Pediatric Neurology, Children’s Hospital Colorado, University of Colorado Hospital, Aurora, Colorado, United States of America
| | - Suzanne D. DeBrosse
- Departments of Genetics and Genome Sciences, Pediatrics, and Neurology, Case Western Reserve University and University Hospitals Case Medical Center, Cleveland, Ohio, United States of America
| | - David Galas
- Pacific Northwest Diabetes Research Institute, Seattle, Washington, United States of America
| | - Jennifer Friedman
- Departments of Neuroscience and Pediatrics, University of California San Diego, San Diego, California, United States of America
| | - Lee Hood
- Institute for Systems Biology, Seattle, Washington, United States of America
| | - Chad Huff
- Department of Epidemiology, The University of Texas M.D. Anderson Cancer Center, Houston, Texas, United States of America
| | - Lynn B. Jorde
- Department of Human Genetics, University of Utah, Salt Lake City, Utah, United States of America
| | - Mary D. King
- Departments of Pediatrics and Neurology, University College Dublin School of Medicine and Medical Science, Dublin, Ireland
| | - Bernie LaSalle
- Department of Biomedical Informatics, University of Utah School of Medicine, Salt Lake City, Utah, United States of America
| | - Richard J. Leventer
- Children’s Neuroscience Centre, Murdoch Childrens Research Institute, University of Melbourne Department of Paediatrics, The Royal Children’s Hospital Melbourne, Parkville Victoria, Australia
| | - Aga J. Lewelt
- Department of Pediatrics, College of Medicine Jacksonville, University of Florida, Jacksonville, Florida, United States of America
| | - Mylynda B. Massart
- Department of Family Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States of America
| | - Mario R. Mérida
- Stevens Henager College, Salt Lake City, Utah, United States of America
| | - Louis J. Ptáček
- Department of Neurology, University of California San Francisco, San Francisco, California, United States of America
| | - Jared C. Roach
- Institute for Systems Biology, Seattle, Washington, United States of America
| | - Robert S. Rust
- Center for Medical Ethics and Humanities in Medicine, University Of Virginia UVA health system, Charlottesville, Virginia, United States of America
| | - Francis Renault
- Departement de Neurophysiologie. Hopital Armand Trousseau APHP, Paris, France
| | - Terry D. Sanger
- Department of Biomedical Engineering, University of Southern California, Los Angeles, California, United States of America
| | | | - Rachel Tennyson
- Pediatric Motor Disorders Research Program, Departments of Neurology and Pediatrics, University of Utah, Salt Lake City, Utah, United States of America
| | - Peter Uldall
- Department of Paediatrics and Adolescent Medicine, Juliane Marie Centre, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark
| | - Yue Zhang
- Study Design and Biostatistics Center, University of Utah, Salt Lake City, Utah, United States of America
| | - Mary Zupanc
- Department of Neurology, Children’s Hospital Orange County, and Department of Pediatrics, University of California, Orange, California, United States of America
| | - Winnie Xin
- Center for Human Genetic Research, Department of Neurology, Massachusetts General Hospital, Boston, Massachusetts, United States of America
| | - Kenneth Silver
- Departments of Pediatrics and Neurology, University of Chicago and Comer Children's Hospital, Chicago, Illinois, United States of America
| | - Kathryn J. Swoboda
- Pediatric Motor Disorders Research Program, Departments of Neurology and Pediatrics, University of Utah, Salt Lake City, Utah, United States of America
- * E-mail:
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16
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Holm R, Einholm AP, Andersen JP, Vilsen B. Rescue of Na+ affinity in aspartate 928 mutants of Na+,K+-ATPase by secondary mutation of glutamate 314. J Biol Chem 2015; 290:9801-11. [PMID: 25713066 DOI: 10.1074/jbc.m114.625509] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2014] [Indexed: 11/06/2022] Open
Abstract
The Na(+),K(+)-ATPase binds Na(+) at three transport sites denoted I, II, and III, of which site III is Na(+)-specific and suggested to be the first occupied in the cooperative binding process activating phosphorylation from ATP. Here we demonstrate that the asparagine substitution of the aspartate associated with site III found in patients with rapid-onset dystonia parkinsonism or alternating hemiplegia of childhood causes a dramatic reduction of Na(+) affinity in the α1-, α2-, and α3-isoforms of Na(+),K(+)-ATPase, whereas other substitutions of this aspartate are much less disruptive. This is likely due to interference by the amide function of the asparagine side chain with Na(+)-coordinating residues in site III. Remarkably, the Na(+) affinity of site III aspartate to asparagine and alanine mutants is rescued by second-site mutation of a glutamate in the extracellular part of the fourth transmembrane helix, distant to site III. This gain-of-function mutation works without recovery of the lost cooperativity and selectivity of Na(+) binding and does not affect the E1-E2 conformational equilibrium or the maximum phosphorylation rate. Hence, the rescue of Na(+) affinity is likely intrinsic to the Na(+) binding pocket, and the underlying mechanism could be a tightening of Na(+) binding at Na(+) site II, possibly via movement of transmembrane helix four. The second-site mutation also improves Na(+),K(+) pump function in intact cells. Rescue of Na(+) affinity and Na(+) and K(+) transport by second-site mutation is unique in the history of Na(+),K(+)-ATPase and points to new possibilities for treatment of neurological patients carrying Na(+),K(+)-ATPase mutations.
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Affiliation(s)
- Rikke Holm
- From the Department of Biomedicine, Aarhus University, Ole Worms Allé 4, Building 1160, DK-8000 Aarhus C, Denmark
| | - Anja P Einholm
- From the Department of Biomedicine, Aarhus University, Ole Worms Allé 4, Building 1160, DK-8000 Aarhus C, Denmark
| | - Jens P Andersen
- From the Department of Biomedicine, Aarhus University, Ole Worms Allé 4, Building 1160, DK-8000 Aarhus C, Denmark
| | - Bente Vilsen
- From the Department of Biomedicine, Aarhus University, Ole Worms Allé 4, Building 1160, DK-8000 Aarhus C, Denmark
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17
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P2C-Type ATPases and Their Regulation. Mol Neurobiol 2015; 53:1343-1354. [DOI: 10.1007/s12035-014-9076-z] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2014] [Accepted: 12/29/2014] [Indexed: 12/12/2022]
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18
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Khundmiri SJ. Advances in understanding the role of cardiac glycosides in control of sodium transport in renal tubules. J Endocrinol 2014; 222:R11-24. [PMID: 24781255 DOI: 10.1530/joe-13-0613] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Cardiotonic steroids have been used for the past 200 years in the treatment of congestive heart failure. As specific inhibitors of membrane-bound Na(+)/K(+) ATPase, they enhance cardiac contractility through increasing myocardial cell calcium concentration in response to the resulting increase in intracellular Na concentration. The half-minimal concentrations of cardiotonic steroids required to inhibit Na(+)/K(+) ATPase range from nanomolar to micromolar concentrations. In contrast, the circulating levels of cardiotonic steroids under physiological conditions are in the low picomolar concentration range in healthy subjects, increasing to high picomolar levels under pathophysiological conditions including chronic kidney disease and heart failure. Little is known about the physiological function of low picomolar concentrations of cardiotonic steroids. Recent studies have indicated that physiological concentrations of cardiotonic steroids acutely stimulate the activity of Na(+)/K(+) ATPase and activate an intracellular signaling pathway that regulates a variety of intracellular functions including cell growth and hypertrophy. The effects of circulating cardiotonic steroids on renal salt handling and total body sodium homeostasis are unknown. This review will focus on the role of low picomolar concentrations of cardiotonic steroids in renal Na(+)/K(+) ATPase activity, cell signaling, and blood pressure regulation.
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Affiliation(s)
- Syed Jalal Khundmiri
- Division of Nephrology and HypertensionDepartment of MedicineDepartment of Physiology and BiophysicsUniversity of Louisville, 570 S. Preston Street, Louisville, Kentucky 40202, USADivision of Nephrology and HypertensionDepartment of MedicineDepartment of Physiology and BiophysicsUniversity of Louisville, 570 S. Preston Street, Louisville, Kentucky 40202, USA
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19
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Molecular characterization and transcriptional regulation of the Na +/K+ ATPase α subunit isoforms during development and salinity challenge in a teleost fish, the Senegalese sole (Solea senegalensis). Comp Biochem Physiol B Biochem Mol Biol 2014; 175:23-38. [PMID: 24947209 DOI: 10.1016/j.cbpb.2014.06.004] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2014] [Revised: 04/28/2014] [Accepted: 06/06/2014] [Indexed: 01/12/2023]
Abstract
In the present work, five genes encoding different Na(+),K(+) ATPase (NKA) α-isoforms in the teleost Solea senegalensis are described for the first time. Sequence analysis of predicted polypeptides revealed a high degree of conservation across teleosts and mammals. Phylogenetic analysis clustered the five genes into three main clades: α1 (designated atp1a1a and atp1a1b), α2 (designated atp1a2) and α3 (designated atp1a3a and atp1a3b) isoforms. Transcriptional analysis in larvae showed distinct expression profiles during development. In juvenile tissues, the atp1a1a gene was highly expressed in osmoregulatory organs, atp1a2 in skeletal muscle, atp1a1b in brain and heart and atp1a3a and atp1a3b mainly in brain. Quantification of mRNA abundance after a salinity challenge showed that atp1a1a transcript levels increased significantly in the gill of soles transferred to high salinity water (60 ppt). In contrast, atp1a3a transcripts increased at low salinity (5 ppt). In situ hybridization (ISH) analysis revealed that the number of ionocytes expressing atp1a1a transcripts in the primary gill filaments was higher at 35 and 60 ppt than at 5 ppt and remained undetectable or at very low levels in the lamellae at 5 and 35 ppt but increased at 60 ppt. Immunohistochemistry showed a higher number of positive cells in the lamellae. Whole-mount analysis of atp1a1a mRNA in young sole larvae revealed that it was localized in gut, pronephric tubule, gill, otic vesicle, yolk sac ionocytes and chordacentrum. Moreover, atp1a1a mRNAs increased at mouth opening (3 DPH) in larvae incubated at 36 ppt with a greater signal in gills.
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20
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Mahmmoud YA, Shattock M, Cornelius F, Pavlovic D. Inhibition of K+ transport through Na+, K+-ATPase by capsazepine: role of membrane span 10 of the α-subunit in the modulation of ion gating. PLoS One 2014; 9:e96909. [PMID: 24816799 PMCID: PMC4016139 DOI: 10.1371/journal.pone.0096909] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2013] [Accepted: 04/14/2014] [Indexed: 11/25/2022] Open
Abstract
Capsazepine (CPZ) inhibits Na+,K+-ATPase-mediated K+-dependent ATP hydrolysis with no effect on Na+-ATPase activity. In this study we have investigated the functional effects of CPZ on Na+,K+-ATPase in intact cells. We have also used well established biochemical and biophysical techniques to understand how CPZ modifies the catalytic subunit of Na+,K+-ATPase. In isolated rat cardiomyocytes, CPZ abolished Na+,K+-ATPase current in the presence of extracellular K+. In contrast, CPZ stimulated pump current in the absence of extracellular K+. Similar conclusions were attained using HEK293 cells loaded with the Na+ sensitive dye Asante NaTRIUM green. Proteolytic cleavage of pig kidney Na+,K+-ATPase indicated that CPZ stabilizes ion interaction with the K+ sites. The distal part of membrane span 10 (M10) of the α-subunit was exposed to trypsin cleavage in the presence of guanidinum ions, which function as Na+ congener at the Na+ specific site. This effect of guanidinium was amplified by treatment with CPZ. Fluorescence of the membrane potential sensitive dye, oxonol VI, was measured following addition of substrates to reconstituted inside-out Na+,K+-ATPase. CPZ increased oxonol VI fluorescence in the absence of K+, reflecting increased Na+ efflux through the pump. Surprisingly, CPZ induced an ATP-independent increase in fluorescence in the presence of high extravesicular K+, likely indicating opening of an intracellular pathway selective for K+. As revealed by the recent crystal structure of the E1.AlF4-.ADP.3Na+ form of the pig kidney Na+,K+-ATPase, movements of M5 of the α-subunit, which regulate ion selectivity, are controlled by the C-terminal tail that extends from M10. We propose that movements of M10 and its cytoplasmic extension is affected by CPZ, thereby regulating ion selectivity and transport through the K+ sites in Na+,K+-ATPase.
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Affiliation(s)
- Yasser A. Mahmmoud
- Department of Biomedicine, University of Aarhus, DK-8000 Aarhus C, Denmark
- * E-mail:
| | - Michael Shattock
- Cardiovascular Division, King's College London, The Rayne Institute, St. Thomas' Hospital, London, United Kingdom
| | - Flemming Cornelius
- Department of Biomedicine, University of Aarhus, DK-8000 Aarhus C, Denmark
| | - Davor Pavlovic
- Cardiovascular Division, King's College London, The Rayne Institute, St. Thomas' Hospital, London, United Kingdom
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Critical roles of isoleucine-364 and adjacent residues in a hydrophobic gate control of phospholipid transport by the mammalian P4-ATPase ATP8A2. Proc Natl Acad Sci U S A 2014; 111:E1334-43. [PMID: 24706822 DOI: 10.1073/pnas.1321165111] [Citation(s) in RCA: 82] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
P4-ATPases (flippases) translocate specific phospholipids such as phosphatidylserine from the exoplasmic leaflet of the cell membrane to the cytosolic leaflet, upholding an essential membrane asymmetry. The mechanism of flipping this giant substrate has remained an enigma. We have investigated the importance of amino acid residues in transmembrane segment M4 of mammalian P4-ATPase ATP8A2 by mutagenesis. In the related ion pumps Na(+),K(+)-ATPase and Ca(2+)-ATPase, M4 moves during the enzyme cycle, carrying along the ion bound to a glutamate. In ATP8A2, the corresponding residue is an isoleucine, which recently was found mutated in patients with cerebellar ataxia, mental retardation, and dysequilibrium syndrome. Our analyses of the lipid substrate concentration dependence of the overall and partial reactions of the enzyme cycle in mutants indicate that, during the transport across the membrane, the phosphatidylserine head group passes near isoleucine-364 (I364) and that I364 is critical to the release of the transported lipid into the cytosolic leaflet. Another M4 residue, N359, is involved in recognition of the lipid substrate on the exoplasmic side. Our functional studies are supported by structural homology modeling and molecular dynamics simulations, suggesting that I364 and adjacent hydrophobic residues function as a hydrophobic gate that separates the entry and exit sites of the lipid and directs sequential formation and annihilation of water-filled cavities, thereby enabling transport of the hydrophilic phospholipid head group in a groove outlined by the transmembrane segments M1, M2, M4, and M6, with the hydrocarbon chains following passively, still in the membrane lipid phase.
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22
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Toustrup-Jensen MS, Einholm AP, Schack VR, Nielsen HN, Holm R, Sobrido MJ, Andersen JP, Clausen T, Vilsen B. Relationship between intracellular Na+ concentration and reduced Na+ affinity in Na+,K+-ATPase mutants causing neurological disease. J Biol Chem 2013; 289:3186-97. [PMID: 24356962 DOI: 10.1074/jbc.m113.543272] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The neurological disorders familial hemiplegic migraine type 2 (FHM2), alternating hemiplegia of childhood (AHC), and rapid-onset dystonia parkinsonism (RDP) are caused by mutations of Na(+),K(+)-ATPase α2 and α3 isoforms, expressed in glial and neuronal cells, respectively. Although these disorders are distinct, they overlap in phenotypical presentation. Two Na(+),K(+)-ATPase mutations, extending the C terminus by either 28 residues ("+28" mutation) or an extra tyrosine ("+Y"), are associated with FHM2 and RDP, respectively. We describe here functional consequences of these and other neurological disease mutations as well as an extension of the C terminus only by a single alanine. The dependence of the mutational effects on the specific α isoform in which the mutation is introduced was furthermore studied. At the cellular level we have characterized the C-terminal extension mutants and other mutants, addressing the question to what extent they cause a change of the intracellular Na(+) and K(+) concentrations ([Na(+)]i and [K(+)]i) in COS cells. C-terminal extension mutants generally showed dramatically reduced Na(+) affinity without disturbance of K(+) binding, as did other RDP mutants. No phosphorylation from ATP was observed for the +28 mutation of α2 despite a high expression level. A significant rise of [Na(+)]i and reduction of [K(+)]i was detected in cells expressing mutants with reduced Na(+) affinity and did not require a concomitant reduction of the maximal catalytic turnover rate or expression level. Moreover, two mutations that increase Na(+) affinity were found to reduce [Na(+)]i. It is concluded that the Na(+) affinity of the Na(+),K(+)-ATPase is an important determinant of [Na(+)]i.
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23
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Henriksen C, Kjaer-Sorensen K, Einholm AP, Madsen LB, Momeni J, Bendixen C, Oxvig C, Vilsen B, Larsen K. Molecular cloning and characterization of porcine Na⁺/K⁺-ATPase isoforms α1, α2, α3 and the ATP1A3 promoter. PLoS One 2013; 8:e79127. [PMID: 24236096 PMCID: PMC3827302 DOI: 10.1371/journal.pone.0079127] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2013] [Accepted: 09/17/2013] [Indexed: 11/18/2022] Open
Abstract
Na⁺/K⁺-ATPase maintains electrochemical gradients of Na⁺ and K⁺ essential for a variety of cellular functions including neuronal activity. The α-subunit of the Na⁺/K⁺-ATPase exists in four different isoforms (α1-α4) encoded by different genes. With a view to future use of pig as an animal model in studies of human diseases caused by Na⁺/K⁺-ATPase mutations, we have determined the porcine coding sequences of the α1-α3 genes, ATP1A1, ATP1A2, and ATP1A3, their chromosomal localization, and expression patterns. Our ATP1A1 sequence accords with the sequences from several species at five positions where the amino acid residue of the previously published porcine ATP1A1 sequence differs. These corrections include replacement of glutamine 841 with arginine. Analysis of the functional consequences of substitution of the arginine revealed its importance for Na⁺ binding, which can be explained by interaction of the arginine with the C-terminus, stabilizing one of the Na⁺ sites. Quantitative real-time PCR expression analyses of porcine ATP1A1, ATP1A2, and ATP1A3 mRNA showed that all three transcripts are expressed in the embryonic brain as early as 60 days of gestation. Expression of α3 is confined to neuronal tissue. Generally, the expression patterns of ATP1A1, ATP1A2, and ATP1A3 transcripts were found similar to their human counterparts, except for lack of α3 expression in porcine heart. These expression patterns were confirmed at the protein level. We also report the sequence of the porcine ATP1A3 promoter, which was found to be closely homologous to its human counterpart. The function and specificity of the porcine ATP1A3 promoter was analyzed in transgenic zebrafish, demonstrating that it is active and drives expression in embryonic brain and spinal cord. The results of the present study provide a sound basis for employing the ATP1A3 promoter in attempts to generate transgenic porcine models of neurological diseases caused by ATP1A3 mutations.
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Affiliation(s)
- Carina Henriksen
- Department of Molecular Biology and Genetics, Aarhus University, Tjele, Denmark
- Department of Biomedicine, Aarhus University, Aarhus C, Denmark
| | | | | | - Lone Bruhn Madsen
- Department of Molecular Biology and Genetics, Aarhus University, Tjele, Denmark
| | - Jamal Momeni
- Department of Molecular Biology and Genetics, Aarhus University, Tjele, Denmark
| | - Christian Bendixen
- Department of Molecular Biology and Genetics, Aarhus University, Tjele, Denmark
| | - Claus Oxvig
- Department of Molecular Biology and Genetics, Aarhus University, Aarhus C, Denmark
| | - Bente Vilsen
- Department of Biomedicine, Aarhus University, Aarhus C, Denmark
| | - Knud Larsen
- Department of Molecular Biology and Genetics, Aarhus University, Tjele, Denmark
- * E-mail:
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24
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C-terminal truncations of the Saccharomyces cerevisiae PMA1 H+-ATPase have major impacts on protein conformation, trafficking, quality control, and function. EUKARYOTIC CELL 2013; 13:43-52. [PMID: 24186948 DOI: 10.1128/ec.00201-13] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The C-terminal tail of yeast plasma membrane (PM) H(+)-ATPase extends approximately 38 amino acids beyond the final membrane-spanning segment (TM10) of the protein and is known to be required for successful trafficking, stability, and regulation of enzyme activity. To carry out a detailed functional survey of the entire length of the tail, we generated 15 stepwise truncation mutants. Eleven of them, lacking up to 30 amino acids from the extreme terminus, were able to support cell growth, even though there were detectable changes in plasma membrane expression, protein stability, and ATPase activity. Three functionally distinct regions of the C terminus could be defined. (i) Truncations upstream of Lys(889), removing more than 30 amino acid residues, yielded no viable mutants, and conditional expression of such constructs supported the conclusion that the stretch from Ala(881) (at the end of TM10) to Gly(888) is required for stable folding and PM targeting. (ii) The stretch between Lys(889) and Lys(916), a region known to be subject to kinase-mediated posttranslational modification, was shown here to be ubiquitinated in carbon-starved cells as part of cellular quality control and to be essential for normal ATPase folding and stability, as well as for autoinhibition of ATPase activity during glucose starvation. (iii) Finally, removal of even one or two residues (Glu(917) and Thr(918)) from the extreme C terminus led to visibly reduced expression of the ATPase at the plasma membrane. Thus, the C terminus is much more than a simple appendage and profoundly influences the structure, biogenesis, and function of the yeast H(+)-ATPase.
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Crystal structure of a Na+-bound Na+,K+-ATPase preceding the E1P state. Nature 2013; 502:201-6. [PMID: 24089211 DOI: 10.1038/nature12578] [Citation(s) in RCA: 225] [Impact Index Per Article: 20.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2013] [Accepted: 08/16/2013] [Indexed: 11/08/2022]
Abstract
Na(+),K(+)-ATPase pumps three Na(+) ions out of cells in exchange for two K(+) taken up from the extracellular medium per ATP molecule hydrolysed, thereby establishing Na(+) and K(+) gradients across the membrane in all animal cells. These ion gradients are used in many fundamental processes, notably excitation of nerve cells. Here we describe 2.8 Å-resolution crystal structures of this ATPase from pig kidney with bound Na(+), ADP and aluminium fluoride, a stable phosphate analogue, with and without oligomycin that promotes Na(+) occlusion. These crystal structures represent a transition state preceding the phosphorylated intermediate (E1P) in which three Na(+) ions are occluded. Details of the Na(+)-binding sites show how this ATPase functions as a Na(+)-specific pump, rejecting K(+) and Ca(2+), even though its affinity for Na(+) is low (millimolar dissociation constant). A mechanism for sequential, cooperative Na(+) binding can now be formulated in atomic detail.
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Nyblom M, Poulsen H, Gourdon P, Reinhard L, Andersson M, Lindahl E, Fedosova N, Nissen P. Crystal structure of Na+, K(+)-ATPase in the Na(+)-bound state. Science 2013; 342:123-7. [PMID: 24051246 DOI: 10.1126/science.1243352] [Citation(s) in RCA: 140] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
The Na(+), K(+)-adenosine triphosphatase (ATPase) maintains the electrochemical gradients of Na(+) and K(+) across the plasma membrane--a prerequisite for electrical excitability and secondary transport. Hitherto, structural information has been limited to K(+)-bound or ouabain-blocked forms. We present the crystal structure of a Na(+)-bound Na(+), K(+)-ATPase as determined at 4.3 Å resolution. Compared with the K(+)-bound form, large conformational changes are observed in the α subunit whereas the β and γ subunit structures are maintained. The locations of the three Na(+) sites are indicated with the unique site III at the recently suggested IIIb, as further supported by electrophysiological studies on leak currents. Extracellular release of the third Na(+) from IIIb through IIIa, followed by exchange of Na(+) for K(+) at sites I and II, is suggested.
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Affiliation(s)
- Maria Nyblom
- Centre for Membrane Pumps in Cells and Disease-PUMPkin, Danish National Research Foundation, DK-8000 Aarhus, Denmark
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Dürr KL, Tavraz NN, Spiller S, Friedrich T. Measuring cation transport by Na,K- and H,K-ATPase in Xenopus oocytes by atomic absorption spectrophotometry: an alternative to radioisotope assays. J Vis Exp 2013:e50201. [PMID: 23462593 DOI: 10.3791/50201] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022] Open
Abstract
Whereas cation transport by the electrogenic membrane transporter Na(+),K(+)-ATPase can be measured by electrophysiology, the electroneutrally operating gastric H(+),K(+)-ATPase is more difficult to investigate. Many transport assays utilize radioisotopes to achieve a sufficient signal-to-noise ratio, however, the necessary security measures impose severe restrictions regarding human exposure or assay design. Furthermore, ion transport across cell membranes is critically influenced by the membrane potential, which is not straightforwardly controlled in cell culture or in proteoliposome preparations. Here, we make use of the outstanding sensitivity of atomic absorption spectrophotometry (AAS) towards trace amounts of chemical elements to measure Rb(+) or Li(+) transport by Na(+),K(+)- or gastric H(+),K(+)-ATPase in single cells. Using Xenopus oocytes as expression system, we determine the amount of Rb(+) (Li(+)) transported into the cells by measuring samples of single-oocyte homogenates in an AAS device equipped with a transversely heated graphite atomizer (THGA) furnace, which is loaded from an autosampler. Since the background of unspecific Rb(+) uptake into control oocytes or during application of ATPase-specific inhibitors is very small, it is possible to implement complex kinetic assay schemes involving a large number of experimental conditions simultaneously, or to compare the transport capacity and kinetics of site-specifically mutated transporters with high precision. Furthermore, since cation uptake is determined on single cells, the flux experiments can be carried out in combination with two-electrode voltage-clamping (TEVC) to achieve accurate control of the membrane potential and current. This allowed e.g. to quantitatively determine the 3Na(+)/2K(+) transport stoichiometry of the Na(+),K(+)-ATPase and enabled for the first time to investigate the voltage dependence of cation transport by the electroneutrally operating gastric H(+),K(+)-ATPase. In principle, the assay is not limited to K(+)-transporting membrane proteins, but it may work equally well to address the activity of heavy or transition metal transporters, or uptake of chemical elements by endocytotic processes.
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Bublitz M, Musgaard M, Poulsen H, Thøgersen L, Olesen C, Schiøtt B, Morth JP, Møller JV, Nissen P. Ion pathways in the sarcoplasmic reticulum Ca2+-ATPase. J Biol Chem 2013; 288:10759-65. [PMID: 23400778 DOI: 10.1074/jbc.r112.436550] [Citation(s) in RCA: 104] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The sarco/endoplasmic reticulum Ca(2+)-ATPase (SERCA) is a transmembrane ion transporter belonging to the P(II)-type ATPase family. It performs the vital task of re-sequestering cytoplasmic Ca(2+) to the sarco/endoplasmic reticulum store, thereby also terminating Ca(2+)-induced signaling such as in muscle contraction. This minireview focuses on the transport pathways of Ca(2+) and H(+) ions across the lipid bilayer through SERCA. The ion-binding sites of SERCA are accessible from either the cytoplasm or the sarco/endoplasmic reticulum lumen, and the Ca(2+) entry and exit channels are both formed mainly by rearrangements of four N-terminal transmembrane α-helices. Recent improvements in the resolution of the crystal structures of rabbit SERCA1a have revealed a hydrated pathway in the C-terminal transmembrane region leading from the ion-binding sites to the cytosol. A comparison of different SERCA conformations reveals that this C-terminal pathway is exclusive to Ca(2+)-free E2 states, suggesting that it may play a functional role in proton release from the ion-binding sites. This is in agreement with molecular dynamics simulations and mutational studies and is in striking analogy to a similar pathway recently described for the related sodium pump. We therefore suggest a model for the ion exchange mechanism in P(II)-ATPases including not one, but two cytoplasmic pathways working in concert.
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Affiliation(s)
- Maike Bublitz
- Centre for Membrane Pumps in Cells and Disease (PUMPkin), Aarhus University, DK-8000 Aarhus C, Denmark
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Azarias G, Kruusmägi M, Connor S, Akkuratov EE, Liu XL, Lyons D, Brismar H, Broberger C, Aperia A. A specific and essential role for Na,K-ATPase α3 in neurons co-expressing α1 and α3. J Biol Chem 2012. [PMID: 23195960 DOI: 10.1074/jbc.m112.425785] [Citation(s) in RCA: 92] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Most neurons co-express two catalytic isoforms of Na,K-ATPase, the ubiquitous α1, and the more selectively expressed α3. Although neurological syndromes are associated with α3 mutations, the specific role of this isoform is not completely understood. Here, we used electrophysiological and Na(+) imaging techniques to study the role of α3 in central nervous system neurons expressing both isoforms. Under basal conditions, selective inhibition of α3 using a low concentration of the cardiac glycoside, ouabain, resulted in a modest increase in intracellular Na(+) concentration ([Na(+)](i)) accompanied by membrane potential depolarization. When neurons were challenged with a large rapid increase in [Na(+)](i), similar to what could be expected following suprathreshold neuronal activity, selective inhibition of α3 almost completely abolished the capacity to restore [Na(+)](i) in soma and dendrite. Recordings of Na,K-ATPase specific current supported the notion that when [Na(+)](i) is elevated in the neuron, α3 is the predominant isoform responsible for rapid extrusion of Na(+). Low concentrations of ouabain were also found to disrupt cortical network oscillations, providing further support for the importance of α3 function in the central nervous system. The α isoforms express a well conserved protein kinase A consensus site, which is structurally associated with an Na(+) binding site. Following activation of protein kinase A, both the α3-dependent current and restoration of dendritic [Na(+)](i) were significantly attenuated, indicating that α3 is a target for phosphorylation and may participate in short term regulation of neuronal function.
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Affiliation(s)
- Guillaume Azarias
- Department of Women's and Children's Health, Karolinska Institutet, 171 76 Stockholm, Sweden
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Na⁺/K⁺-ATPase E960 and phospholemman F28 are critical for their functional interaction. Proc Natl Acad Sci U S A 2012. [PMID: 23185013 DOI: 10.1073/pnas.1207866109] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Na(+)-K(+)-ATPase (NKA) establishes the transmembrane [Na(+)] gradient in cells. In heart, phospholemman (PLM) inhibits NKA activity by reducing its apparent Na(+) affinity, an effect that is relieved by PLM phosphorylation. The NKA crystal structure suggests regions of PLM-NKA interaction, but the sites important for functional effects in live cells are not known. We tested wild type (WT) and CFP-NKA-α1 point mutants (alanine substitution at F956, E960, L964, and F967) for fluorescence resonance energy transfer (FRET) with WT-PLM-YFP in HEK293 cells. NKA-PLM FRET was unaltered with F956A or F967A, reduced with L964A, and nearly abolished with E960A. Mutating the PLM site (F28A) identified by structural analysis to interact with E960-NKA also nearly abolished NKA-PLM FRET. In contrast, NKA-PLM coimmunoprecipitation was only slightly reduced by E960A-NKA or F28A-PLM mutants, consistent with an additional interaction site. FRET titrations indicate that the additional site has higher affinity than that between E960-NKA and F28-PLM. To test whether the FRET-preventing mutations also prevent PLM functional effects, we measured NKA-mediated Na(+)-transport in intact cells. For WT-NKA, PLM reduced apparent Na(+)-affinity of NKA and PLM phosphorylation reversed the effect. In contrast, for E960A-NKA the apparent Na(+)-affinity was unaltered by either PLM or forskolin-induced PLM phosphorylation. We conclude that E960 on NKA and F28 on PLM are critical for PLM effects on both NKA function and NKA-PLM FRET, but also there is at least one additional site that is critical for tethering PLM to NKA.
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Paulsen PA, Jurkowski W, Apostolov R, Lindahl E, Nissen P, Poulsen H. The C-terminal cavity of the Na,K-ATPase analyzed by docking and electrophysiology. Mol Membr Biol 2012; 30:195-205. [DOI: 10.3109/09687688.2012.713520] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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32
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Poulsen H, Nissen P, Mouritsen OG, Khandelia H. Protein kinase A (PKA) phosphorylation of Na+/K+-ATPase opens intracellular C-terminal water pathway leading to third Na+-binding site in molecular dynamics simulations. J Biol Chem 2012; 287:15959-65. [PMID: 22433860 DOI: 10.1074/jbc.m112.340406] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Phosphorylation is one of the major mechanisms for posttranscriptional modification of proteins. The addition of a compact, negatively charged moiety to a protein can significantly change its function and localization by affecting its structure and interaction network. We have used all-atom Molecular Dynamics simulations to investigate the structural consequences of phosphorylating the Na(+)/K(+)-ATPase (NKA) residue Ser(936), which is the best characterized phosphorylation site in NKA, targeted in vivo by protein kinase A (PKA). The Molecular Dynamics simulations suggest that Ser(936) phosphorylation opens a C-terminal hydrated pathway leading to Asp(926), a transmembrane residue proposed to form part of the third sodium ion-binding site. Simulations of a S936E mutant form, for which only subtle effects are observed when expressed in Xenopus oocytes and studied with electrophysiology, does not mimic the effects of Ser(936) phosphorylation. The results establish a structural association of Ser(936) with the C terminus of NKA and indicate that phosphorylation of Ser(936) can modulate pumping activity by changing the accessibility to the ion-binding site.
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Affiliation(s)
- Hanne Poulsen
- PUMPKIN-Centre for Membrane Pumps in Cells and Disease, Aarhus University, Aarhus 8000 C, Denmark
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Affiliation(s)
- Michael G. Palmgren
- Center for Membrane Pumps in Cells and Disease – PUMPKIN, Danish National Research Foundation, University of Copenhagen, DK-1871 Frederiksberg C, Denmark;
| | - Poul Nissen
- Center for Membrane Pumps in Cells and Disease – PUMPKIN, Danish National Research Foundation, Aarhus University, DK-8000 Århus C, Denmark;
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Morth JP, Pedersen BP, Buch-Pedersen MJ, Andersen JP, Vilsen B, Palmgren MG, Nissen P. A structural overview of the plasma membrane Na+,K+-ATPase and H+-ATPase ion pumps. Nat Rev Mol Cell Biol 2011; 12:60-70. [PMID: 21179061 DOI: 10.1038/nrm3031] [Citation(s) in RCA: 244] [Impact Index Per Article: 18.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Plasma membrane ATPases are primary active transporters of cations that maintain steep concentration gradients. The ion gradients and membrane potentials derived from them form the basis for a range of essential cellular processes, in particular Na(+)-dependent and proton-dependent secondary transport systems that are responsible for uptake and extrusion of metabolites and other ions. The ion gradients are also both directly and indirectly used to control pH homeostasis and to regulate cell volume. The plasma membrane H(+)-ATPase maintains a proton gradient in plants and fungi and the Na(+),K(+)-ATPase maintains a Na(+) and K(+) gradient in animal cells. Structural information provides insight into the function of these two distinct but related P-type pumps.
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Affiliation(s)
- J Preben Morth
- Danish National Research Foundation, Centre for Membrane Pumps in Cells and Disease - PUMPKIN, Denmark
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35
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Einholm AP, Toustrup-Jensen MS, Holm R, Andersen JP, Vilsen B. The rapid-onset dystonia parkinsonism mutation D923N of the Na+, K+-ATPase alpha3 isoform disrupts Na+ interaction at the third Na+ site. J Biol Chem 2010; 285:26245-54. [PMID: 20576601 PMCID: PMC2924038 DOI: 10.1074/jbc.m110.123976] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2010] [Revised: 05/31/2010] [Indexed: 11/06/2022] Open
Abstract
Rapid-onset dystonia parkinsonism (RDP), a rare neurological disorder, is caused by mutation of the neuron-specific alpha3-isoform of Na(+), K(+)-ATPase. Here, we present the functional consequences of RDP mutation D923N. Relative to the wild type, the mutant exhibits a remarkable approximately 200-fold reduction of Na(+) affinity for activation of phosphorylation from ATP, reflecting a defective interaction of the E(1) form with intracellular Na(+). This is the largest effect on Na(+) affinity reported so far for any Na(+), K(+)-ATPase mutant. D923N also affects the interaction with extracellular Na(+) normally driving the E(1)P to E(2)P conformational transition backward. However, no impairment of K(+) binding was observed for D923N, leading to the conclusion that Asp(923) is specifically associated with the third Na(+) site that is selective toward Na(+). The crystal structure of the Na(+), K(+)-ATPase in E(2) form shows that Asp(923) is located in the cytoplasmic half of transmembrane helix M8 inside a putative transport channel, which is lined by residues from the transmembrane helices M5, M7, M8, and M10 and capped by the C terminus, recently found involved in recognition of the third Na(+) ion. Structural modeling of the E(1) form of Na(+), K(+)-ATPase based on the Ca(2+)-ATPase crystal structure is consistent with the hypothesis that Asp(923) contributes to a site binding the third Na(+) ion. These results in conjunction with our previous findings with other RDP mutants suggest that a selective defect in the handling of Na(+) may be a general feature of the RDP disorder.
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Affiliation(s)
- Anja Pernille Einholm
- From the Centre for Membrane Pumps in Cells and Disease-PUMPKIN, Danish National Research Foundation, Department of Physiology and Biophysics, Aarhus University, DK-8000 Aarhus C, Denmark
| | - Mads S. Toustrup-Jensen
- From the Centre for Membrane Pumps in Cells and Disease-PUMPKIN, Danish National Research Foundation, Department of Physiology and Biophysics, Aarhus University, DK-8000 Aarhus C, Denmark
| | - Rikke Holm
- From the Centre for Membrane Pumps in Cells and Disease-PUMPKIN, Danish National Research Foundation, Department of Physiology and Biophysics, Aarhus University, DK-8000 Aarhus C, Denmark
| | - Jens Peter Andersen
- From the Centre for Membrane Pumps in Cells and Disease-PUMPKIN, Danish National Research Foundation, Department of Physiology and Biophysics, Aarhus University, DK-8000 Aarhus C, Denmark
| | - Bente Vilsen
- From the Centre for Membrane Pumps in Cells and Disease-PUMPKIN, Danish National Research Foundation, Department of Physiology and Biophysics, Aarhus University, DK-8000 Aarhus C, Denmark
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36
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Poulsen H, Khandelia H, Morth JP, Bublitz M, Mouritsen OG, Egebjerg J, Nissen P. Neurological disease mutations compromise a C-terminal ion pathway in the Na(+)/K(+)-ATPase. Nature 2010; 467:99-102. [PMID: 20720542 DOI: 10.1038/nature09309] [Citation(s) in RCA: 97] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2010] [Accepted: 06/24/2010] [Indexed: 12/14/2022]
Abstract
The Na(+)/K(+)-ATPase pumps three sodium ions out of and two potassium ions into the cell for each ATP molecule that is split, thereby generating the chemical and electrical gradients across the plasma membrane that are essential in, for example, signalling, secondary transport and volume regulation in animal cells. Crystal structures of the potassium-bound form of the pump revealed an intimate docking of the alpha-subunit carboxy terminus at the transmembrane domain. Here we show that this element is a key regulator of a previously unrecognized ion pathway. Current models of P-type ATPases operate with a single ion conduit through the pump, but our data suggest an additional pathway in the Na(+)/K(+)-ATPase between the ion-binding sites and the cytoplasm. The C-terminal pathway allows a cytoplasmic proton to enter and stabilize site III when empty in the potassium-bound state, and when potassium is released the proton will also return to the cytoplasm, thus allowing an overall asymmetric stoichiometry of the transported ions. The C terminus controls the gate to the pathway. Its structure is crucial for pump function, as demonstrated by at least eight mutations in the region that cause severe neurological diseases. This novel model for ion transport by the Na(+)/K(+)-ATPase is established by electrophysiological studies of C-terminal mutations in familial hemiplegic migraine 2 (FHM2) and is further substantiated by molecular dynamics simulations. A similar ion regulation is likely to apply to the H(+)/K(+)-ATPase and the Ca(2+)-ATPase.
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Affiliation(s)
- Hanne Poulsen
- PUMPKIN - Centre for Membrane Pumps in Cells and Disease, Danish National Research Foundation, Department of Molecular Biology, Aarhus University, DK-8000 Aarhus C, Denmark.
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Vedovato N, Gadsby DC. The two C-terminal tyrosines stabilize occluded Na/K pump conformations containing Na or K ions. ACTA ACUST UNITED AC 2010; 136:63-82. [PMID: 20548052 PMCID: PMC2894553 DOI: 10.1085/jgp.201010407] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Interactions of the three transported Na ions with the Na/K pump remain incompletely understood. Na/K pump crystal structures show that the extended C terminus of the Na,K-adenosine triphosphatase (ATPase) alpha subunit directly contacts transmembrane helices. Deletion of the last five residues (KETYY in almost all Na/K pumps) markedly lowered the apparent affinity for Na activation of pump phosphorylation from ATP, a reflection of cytoplasmic Na affinity for forming the occluded E1P(Na3) conformation. ATPase assays further suggested that C-terminal truncations also interfere with low affinity Na interactions, which are attributable to extracellular effects. Because extracellular Na ions traverse part of the membrane's electric field to reach their binding sites in the Na/K pump, their movements generate currents that can be monitored with high resolution. We report here electrical measurements to examine how Na/K pump interactions with extracellular Na ions are influenced by C-terminal truncations. We deleted the last two (YY) or five (KESYY) residues in Xenopus laevis alpha1 Na/K pumps made ouabain resistant by either of two kinds of point mutations and measured their currents as 10-mM ouabain-sensitive currents in Xenopus oocytes after silencing endogenous Xenopus Na/K pumps with 1 microM ouabain. We found the low affinity inhibitory influence of extracellular Na on outward Na/K pump current at negative voltages to be impaired in all of the C-terminally truncated pumps. Correspondingly, voltage jump-induced transient charge movements that reflect pump interactions with extracellular Na ions were strongly shifted to more negative potentials; this signals a several-fold reduction of the apparent affinity for extracellular Na in the truncated pumps. Parallel lowering of Na affinity on both sides of the membrane argues that the C-terminal contacts provide important stabilization of the occluded E1P(Na3) conformation, regardless of the route of Na ion entry into the binding pocket. Gating measurements of palytoxin-opened Na/K pump channels additionally imply that the C-terminal contacts also help stabilize pump conformations with occluded K ions.
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Affiliation(s)
- Natascia Vedovato
- Laboratory of Cardiac/Membrane Physiology, The Rockefeller University, New York, NY 10065, USA
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38
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Poulsen H, Morth P, Egebjerg J, Nissen P. Phosphorylation of the Na+,K+-ATPase and the H+,K+-ATPase. FEBS Lett 2010; 584:2589-95. [PMID: 20412804 DOI: 10.1016/j.febslet.2010.04.035] [Citation(s) in RCA: 75] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2010] [Accepted: 04/13/2010] [Indexed: 01/11/2023]
Abstract
Phosphorylation is a widely used, reversible means of regulating enzymatic activity. Among the important phosphorylation targets are the Na(+),K(+)- and H(+),K(+)-ATPases that pump ions against their chemical gradients to uphold ionic concentration differences over the plasma membrane. The two pumps are very homologous, and at least one of the phosphorylation sites is conserved, namely a cAMP activated protein kinase (PKA) site, which is important for regulating pumping activity, either by changing the cellular distribution of the ATPases or by directly altering the kinetic properties as supported by electrophysiological results presented here. We further review the other proposed pump phosphorylations.
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Affiliation(s)
- Hanne Poulsen
- Danish National Research Foundation, Centre for Membrane Pumps in Cells and Disease-PUMPKIN, Aarhus University, Department of Molecular Biology, Denmark.
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Meier S, Tavraz NN, Dürr KL, Friedrich T. Hyperpolarization-activated inward leakage currents caused by deletion or mutation of carboxy-terminal tyrosines of the Na+/K+-ATPase {alpha} subunit. ACTA ACUST UNITED AC 2010; 135:115-34. [PMID: 20100892 PMCID: PMC2812498 DOI: 10.1085/jgp.200910301] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The Na(+)/K(+)-ATPase mediates electrogenic transport by exporting three Na(+) ions in exchange for two K(+) ions across the cell membrane per adenosine triphosphate molecule. The location of two Rb(+) ions in the crystal structures of the Na(+)/K(+)-ATPase has defined two "common" cation binding sites, I and II, which accommodate Na(+) or K(+) ions during transport. The configuration of site III is still unknown, but the crystal structure has suggested a critical role of the carboxy-terminal KETYY motif for the formation of this "unique" Na(+) binding site. Our two-electrode voltage clamp experiments on Xenopus oocytes show that deletion of two tyrosines at the carboxy terminus of the human Na(+)/K(+)-ATPase alpha(2) subunit decreases the affinity for extracellular and intracellular Na(+), in agreement with previous biochemical studies. Apparently, the DeltaYY deletion changes Na(+) affinity at site III but leaves the common sites unaffected, whereas the more extensive DeltaKETYY deletion affects the unique site and the common sites as well. In the absence of extracellular K(+), the DeltaYY construct mediated ouabain-sensitive, hyperpolarization-activated inward currents, which were Na(+) dependent and increased with acidification. Furthermore, the voltage dependence of rate constants from transient currents under Na(+)/Na(+) exchange conditions was reversed, and the amounts of charge transported upon voltage pulses from a certain holding potential to hyperpolarizing potentials and back were unequal. These findings are incompatible with a reversible and exclusively extracellular Na(+) release/binding mechanism. In analogy to the mechanism proposed for the H(+) leak currents of the wild-type Na(+)/K(+)-ATPase, we suggest that the DeltaYY deletion lowers the energy barrier for the intracellular Na(+) occlusion reaction, thus destabilizing the Na(+)-occluded state and enabling inward leak currents. The leakage currents are prevented by aromatic amino acids at the carboxy terminus. Thus, the carboxy terminus of the Na(+)/K(+)-ATPase alpha subunit represents a structural and functional relay between Na(+) binding site III and the intracellular cation occlusion gate.
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Affiliation(s)
- Susan Meier
- Technical University of Berlin, Institute of Chemistry, D-10623 Berlin, Germany
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40
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Altered Na+ transport after an intracellular alpha-subunit deletion reveals strict external sequential release of Na+ from the Na/K pump. Proc Natl Acad Sci U S A 2009; 106:15507-12. [PMID: 19706387 DOI: 10.1073/pnas.0903752106] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
The Na/K pump actively exports 3 Na(+) in exchange for 2 K(+) across the plasmalemma of animal cells. As in other P-type ATPases, pump function is more effective when the relative affinity for transported ions is altered as the ion binding sites alternate between opposite sides of the membrane. Deletion of the five C-terminal residues from the alpha-subunit diminishes internal Na(+) (Na(i)(+)) affinity approximately 25-fold [Morth et al. (2007) Nature 450:1043-1049]. Because external Na(+) (Na(o)(+)) binding is voltage-dependent, we studied the reactions involving this process by using two-electrode and inside-out patch voltage clamp in normal and truncated (DeltaKESYY) Xenopus-alpha1 pumps expressed in oocytes. We observed that DeltaKESYY (i) decreased both Na(o)(+) and Na(i)(+) apparent affinities in the absence of K(o)(+), and (ii) did not affect apparent Na(o)(+) affinity at high K(o)(+). These results support a model of strict sequential external release of Na(+) ions, where the Na(+)-exclusive site releases Na(+) before the sites shared with K(+) and the DeltaKESYY deletion only reduces Na(o)(+) affinity at the shared sites. Moreover, at nonsaturating K(o)(+), DeltaKESYY induced an inward flow of Na(+) through Na/K pumps at negative potentials. Guanidinium(+) can also permeate truncated pumps, whereas N-methyl-D-glucamine cannot. Because guanidinium(o)(+) can also traverse normal Na/K pumps in the absence of both Na(o)(+) and K(o)(+) and can also inhibit Na/K pump currents in a Na(+)-like voltage-dependent manner, we conclude that the normal pathway transited by the first externally released Na(+) is large enough to accommodate guanidinium(+).
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