1
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Pietrobon D, Conti F. Astrocytic Na +, K + ATPases in physiology and pathophysiology. Cell Calcium 2024; 118:102851. [PMID: 38308916 DOI: 10.1016/j.ceca.2024.102851] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2023] [Revised: 01/26/2024] [Accepted: 01/26/2024] [Indexed: 02/05/2024]
Abstract
The Na+, K+ ATPases play a fundamental role in the homeostatic functions of astrocytes. After a brief historic prologue and discussion of the subunit composition and localization of the astrocytic Na+, K+ ATPases, the review focuses on the role of the astrocytic Na+, K+ pumps in extracellular K+ and glutamate homeostasis, intracellular Na+ and Ca2+ homeostasis and signaling, regulation of synaptic transmission and neurometabolic coupling between astrocytes and neurons. Loss-of-function mutations in the gene encoding the astrocytic α2 Na+, K+ ATPase cause a rare monogenic form of migraine with aura (familial hemiplegic migraine type 2). On the other hand, the α2 Na+, K+ ATPase is upregulated in spinal cord and brain samples from amyotrophic lateral sclerosis and Alzheimer disease patients, respectively. In the last part, the review focuses on i) the migraine relevant phenotypes shown by familial hemiplegic migraine type 2 knock-in mice with 50 % reduced expression of the astrocytic α2 Na+, K+ ATPase and the insights into the pathophysiology of migraine obtained from these genetic mouse models, and ii) the evidence that upregulation of the astrocytic α2 Na+, K+ ATPase in mouse models of amyotrophic lateral sclerosis and Alzheimer disease promotes neuroinflammation and contributes to progressive neurodegeneration.
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Affiliation(s)
- Daniela Pietrobon
- Department of Biomedical Sciences and Padova Neuroscience Center (PNC), University of Padova, Padova 35131, Italy.
| | - Fiorenzo Conti
- Section of Neuroscience and Cell Biology, Department of Experimental and Clinical Medicine, Università Politecnica delle Marche, Ancona, Italy; Center for Neurobiology of Aging, IRCCS INRCA, Ancona, Italy.
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2
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Clarke RJ. Electrostatic switch mechanisms of membrane protein trafficking and regulation. Biophys Rev 2023; 15:1967-1985. [PMID: 38192346 PMCID: PMC10771482 DOI: 10.1007/s12551-023-01166-2] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2023] [Accepted: 11/17/2023] [Indexed: 01/10/2024] Open
Abstract
Lipid-protein interactions are normally classified as either specific or general. Specific interactions refer to lipid binding to specific binding sites within a membrane protein, thereby modulating the protein's thermal stability or kinetics. General interactions refer to indirect effects whereby lipids affect membrane proteins by modulating the membrane's physical properties, e.g., its fluidity, thickness, or dipole potential. It is not widely recognized that there is a third distinct type of lipid-protein interaction. Intrinsically disordered N- or C-termini of membrane proteins can interact directly but nonspecifically with the surrounding membrane. Many peripheral membrane proteins are held to the cytoplasmic surface of the plasma membrane via a cooperative combination of two forces: hydrophobic anchoring and electrostatic attraction. An acyl chain, e.g., myristoyl, added post-translationally to one of the protein's termini inserts itself into the lipid matrix and helps hold peripheral membrane proteins onto the membrane. Electrostatic attraction occurs between positively charged basic amino acid residues (lysine and arginine) on one of the protein's terminal tails and negatively charged phospholipid head groups, such as phosphatidylserine. Phosphorylation of either serine or tyrosine residues on the terminal tails via regulatory protein kinases allows for an electrostatic switch mechanism to control trafficking of the protein. Kinase action reduces the positive charge on the protein's tail, weakening the electrostatic attraction and releasing the protein from the membrane. A similar mechanism regulates many integral membrane proteins, but here only electrostatic interactions are involved, and the electrostatic switch modulates protein activity by altering the stabilities of different protein conformational states.
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Affiliation(s)
- Ronald J. Clarke
- School of Chemistry, University of Sydney, Sydney, NSW 2006 Australia
- The University of Sydney Nano Institute, Sydney, NSW 2006 Australia
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3
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Peluffo RD, Hernández JA. The Na +,K +-ATPase and its stoichiometric ratio: some thermodynamic speculations. Biophys Rev 2023; 15:539-552. [PMID: 37681108 PMCID: PMC10480117 DOI: 10.1007/s12551-023-01082-5] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2023] [Accepted: 06/18/2023] [Indexed: 09/09/2023] Open
Abstract
Almost seventy years after its discovery, the sodium-potassium adenosine triphosphatase (the sodium pump) located in the cell plasma membrane remains a source of novel mechanistic and physiologic findings. A noteworthy feature of this enzyme/transporter is its robust stoichiometric ratio under physiological conditions: it sequentially counter-transports three sodium ions and two potassium ions against their electrochemical potential gradients per each hydrolyzed ATP molecule. Here we summarize some present knowledge about the sodium pump and its physiological roles, and speculate whether energetic constraints may have played a role in the evolutionary selection of its characteristic stoichiometric ratio.
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Affiliation(s)
- R. Daniel Peluffo
- Group of Biophysical Chemistry, Department of Biological Sciences, CENUR Litoral Norte, Universidad de La República, Rivera 1350, CP: 50000 Salto, Uruguay
| | - Julio A. Hernández
- Biophysics and Systems Biology Section, Department of Cell and Molecular Biology, Facultad de Ciencias, Universidad de La República, Iguá 4225, CP: 11400 Montevideo, Uruguay
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4
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Bernal AF, Mota N, Pamplona R, Area-Gomez E, Portero-Otin M. Hakuna MAM-Tata: Investigating the role of mitochondrial-associated membranes in ALS. Biochim Biophys Acta Mol Basis Dis 2023; 1869:166716. [PMID: 37044239 DOI: 10.1016/j.bbadis.2023.166716] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2023] [Accepted: 04/03/2023] [Indexed: 04/14/2023]
Abstract
Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease leading to selective and progressive motor neuron (MN) death. Despite significant heterogeneity in pathogenic and clinical terms, MN demise ultimately unifies patients. Across the many disturbances in neuronal biology present in the disease and its models, two common trends are loss of calcium homeostasis and dysregulations in lipid metabolism. Since both mitochondria and endoplasmic reticulum (ER) are essential in these functions, their intertwin through the so-called mitochondrial-associated membranes (MAMs) should be relevant in this disease. In this review, we present a short overview of MAMs functional aspects and how its dysfunction could explain a substantial part of the cellular disarrangements in ALS's natural history. MAMs are hubs for lipid synthesis, integrating glycerophospholipids, sphingolipids, and cholesteryl ester metabolism. These lipids are essential for membrane biology, so there should be a close coupling to cellular energy demands, a role that MAMs may partially fulfill. Not surprisingly, MAMs are also host part of calcium signaling to mitochondria, so their impairment could lead to mitochondrial dysfunction, affecting oxidative phosphorylation and enhancing the vulnerability of MNs. We present data supporting that MAMs' maladaptation could be essential to MNs' vulnerability in ALS.
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Affiliation(s)
- Anna Fernàndez Bernal
- Metabolic Pathophysiology Research Group, Department of Experimental Medicine, University of Lleida-IRBLleida, Edifici Biomedicina I, Avda Rovira Roure 80, E25196 Lleida, Spain.
| | - Natàlia Mota
- Metabolic Pathophysiology Research Group, Department of Experimental Medicine, University of Lleida-IRBLleida, Edifici Biomedicina I, Avda Rovira Roure 80, E25196 Lleida, Spain.
| | - Reinald Pamplona
- Metabolic Pathophysiology Research Group, Department of Experimental Medicine, University of Lleida-IRBLleida, Edifici Biomedicina I, Avda Rovira Roure 80, E25196 Lleida, Spain.
| | - Estela Area-Gomez
- Centro de Investigaciones Biológicas Margarita Salas CSIC, C. Ramiro de Maeztu, 9, 28040 Madrid, Spain.
| | - Manuel Portero-Otin
- Metabolic Pathophysiology Research Group, Department of Experimental Medicine, University of Lleida-IRBLleida, Edifici Biomedicina I, Avda Rovira Roure 80, E25196 Lleida, Spain.
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5
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Zhang H, Zhang Y, Xu P, Bai C. Exploring the Phospholipid Transport Mechanism of ATP8A1-CDC50. Biomedicines 2023; 11:biomedicines11020546. [PMID: 36831082 PMCID: PMC9953615 DOI: 10.3390/biomedicines11020546] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2022] [Revised: 02/09/2023] [Accepted: 02/10/2023] [Indexed: 02/16/2023] Open
Abstract
P4-ATPase translocates lipids from the exoplasmic to the cytosolic plasma membrane leaflet to maintain lipid asymmetry distribution in eukaryotic cells. P4-ATPase is associated with severe neurodegenerative and metabolic diseases such as neurological and motor disorders. Thus, it is important to understand its transport mechanism. However, even with progress in X-ray diffraction and cryo-electron microscopy techniques, it is difficult to obtain the dynamic information of the phospholipid transport process in detail. There are still some problems required to be resolved: (1) when does the lipid transport happen? (2) How do the key residues on the transmembrane helices contribute to the free energy of important states? In this work, we explore the phospholipid transport mechanism using a coarse-grained model and binding free energy calculations. We obtained the free energy landscape by coupling the protein conformational changes and the phospholipid transport event, taking ATP8A1-CDC50 (the typical subtype of P4-ATPase) as the research object. According to the results, we found that the phospholipid would bind to the ATP8A1-CDC50 at the early stage when ATP8A1-CDC50 changes from E2P to E2Pi-PL state. We also found that the electrostatic effects play crucial roles in the phospholipid transport process. The information obtained from this work could help us in designing novel drugs for P-type flippase disorders.
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Affiliation(s)
- Honghui Zhang
- Warshel Institute for Computational Biology, School of Life and Health Sciences, School of Medicine, The Chinese University of Hong Kong, Shenzhen 518172, China
| | - Yue Zhang
- Warshel Institute for Computational Biology, School of Life and Health Sciences, School of Medicine, The Chinese University of Hong Kong, Shenzhen 518172, China
- School of Chemistry and Materials Science, University of Science and Technology of China, Hefei 230026, China
| | - Peiyi Xu
- Warshel Institute for Computational Biology, School of Life and Health Sciences, School of Medicine, The Chinese University of Hong Kong, Shenzhen 518172, China
| | - Chen Bai
- Warshel Institute for Computational Biology, School of Life and Health Sciences, School of Medicine, The Chinese University of Hong Kong, Shenzhen 518172, China
- Chenzhu (MoMeD) Biotechnology Co., Ltd., Hangzhou 310005, China
- Correspondence:
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Chen Q, Xu K, Xu Y, Ji D, Chen C, Xie C, Wang W. Na + /K + -ATPase regulates the K + /Na + homeostasis in the intertidal macroalgae, Neoporphyra haitanensis, in response to salt stress. FRONTIERS IN PLANT SCIENCE 2023; 13:1040142. [PMID: 36684749 PMCID: PMC9846634 DOI: 10.3389/fpls.2022.1040142] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/03/2022] [Accepted: 12/14/2022] [Indexed: 06/17/2023]
Abstract
In plants under hypersaline stress, the main transporter that extrudes sodium ions (Na + ) is the Na + /H + antiporter SOS1. Different from land plants, the intertidal macroalgae, Neopyropia/Neoporphyra contains an animal-type Na + /K + -ATPase as well as the SOS1 system. However, the contribution of Na + /K + -ATPase to the K + /Na + homeostasis of intertidal macroalgae remains unclear. In this study, we analyzed the function of Na + /K + -ATPase in the response of Neoporphyra haitanensis to salt stress from the perspective of ion transport dynamics. Both the transcript level of NhNKA2 and enzyme activity of Na + /K + -ATPase increased in the early response of N. haitanensis thalli to hypersaline stress. Addition of ouabain, an inhibitor of Na + /K + -ATPase, resulted in Na + accumulation in the cells, severe K + leakage from the thalli, and then remarkably disturbed the K + /Na + homeostasis in N. haitanensis thalli. This disruption might induce a significant decrease in photosynthesis and a severe oxidative damage in thalli. Accordingly, these results suggested that the important role of Na + /K + -ATPase in the resistance of intertidal macroalgae to hypersaline stress, and shed light on the diversity of K + /Na + homeostasis maintenance mechanisms in plants.
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Affiliation(s)
- Qi Chen
- Fisheries College, Jimei University, Xiamen, China
- Fujian Engineering Research Center of Aquatic Breeding and Healthy Aquaculture, Fujian Development and Reform Commission, Xiamen, China
- Key Laboratory of Healthy Mariculture for the East China Sea, Ministry of Agriculture, Xiamen, China
| | - Kai Xu
- Fisheries College, Jimei University, Xiamen, China
- Fujian Engineering Research Center of Aquatic Breeding and Healthy Aquaculture, Fujian Development and Reform Commission, Xiamen, China
- Key Laboratory of Healthy Mariculture for the East China Sea, Ministry of Agriculture, Xiamen, China
| | - Yan Xu
- Fisheries College, Jimei University, Xiamen, China
- Fujian Engineering Research Center of Aquatic Breeding and Healthy Aquaculture, Fujian Development and Reform Commission, Xiamen, China
- Key Laboratory of Healthy Mariculture for the East China Sea, Ministry of Agriculture, Xiamen, China
| | - Dehua Ji
- Fisheries College, Jimei University, Xiamen, China
- Fujian Engineering Research Center of Aquatic Breeding and Healthy Aquaculture, Fujian Development and Reform Commission, Xiamen, China
- Key Laboratory of Healthy Mariculture for the East China Sea, Ministry of Agriculture, Xiamen, China
| | - Changsheng Chen
- Fisheries College, Jimei University, Xiamen, China
- Fujian Engineering Research Center of Aquatic Breeding and Healthy Aquaculture, Fujian Development and Reform Commission, Xiamen, China
- Key Laboratory of Healthy Mariculture for the East China Sea, Ministry of Agriculture, Xiamen, China
| | - Chaotian Xie
- Fisheries College, Jimei University, Xiamen, China
- Fujian Engineering Research Center of Aquatic Breeding and Healthy Aquaculture, Fujian Development and Reform Commission, Xiamen, China
- Key Laboratory of Healthy Mariculture for the East China Sea, Ministry of Agriculture, Xiamen, China
| | - Wenlei Wang
- Fisheries College, Jimei University, Xiamen, China
- Fujian Engineering Research Center of Aquatic Breeding and Healthy Aquaculture, Fujian Development and Reform Commission, Xiamen, China
- Key Laboratory of Healthy Mariculture for the East China Sea, Ministry of Agriculture, Xiamen, China
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7
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Faraj SE, Valsecchi WM, Ferreira-Gomes M, Centeno M, Saint Martin EM, Fedosova NU, Rossi JPFC, Montes MR, Rossi RC. Measurements of Na +-occluded intermediates during the catalytic cycle of the Na +/K +-ATPase provide novel insights into the mechanism of Na + transport. J Biol Chem 2022; 299:102811. [PMID: 36539036 PMCID: PMC9860123 DOI: 10.1016/j.jbc.2022.102811] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2022] [Revised: 12/11/2022] [Accepted: 12/12/2022] [Indexed: 12/23/2022] Open
Abstract
The Na+/K+-ATPase is an integral plasma membrane glycoprotein of all animal cells that couples the exchange of intracellular Na+ for extracellular K+ to the hydrolysis of ATP. The asymmetric distribution of Na+ and K+ is essential for cellular life and constitutes the physical basis of a series of fundamental biological phenomena. The pumping mechanism is explained by the Albers-Post model. It involves the presence of gates alternatively exposing Na+/K+-ATPase transport sites to the intracellular and extracellular sides and includes occluded states in which both gates are simultaneously closed. Unlike for K+, information is lacking about Na+-occluded intermediates, as occluded Na+ was only detected in states incapable of performing a catalytic cycle, including two Na+-containing crystallographic structures. The current knowledge is that intracellular Na+ must bind to the transport sites and become occluded upon phosphorylation by ATP to be transported to the extracellular medium. Here, taking advantage of epigallocatechin-3-gallate to instantaneously stabilize native Na+-occluded intermediates, we isolated species with tightly bound Na+ in an enzyme able to perform a catalytic cycle, consistent with a genuine occluded state. We found that Na+ becomes spontaneously occluded in the E1 dephosphorylated form of the Na+/K+-ATPase, exhibiting positive interactions between binding sites. In fact, the addition of ATP does not produce an increase in Na+ occlusion as it would have been expected; on the contrary, occluded Na+ transiently decreases, whereas ATP lasts. These results reveal new properties of E1 intermediates of the Albers-Post model for explaining the Na+ transport pathway.
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Affiliation(s)
- Santiago E. Faraj
- Universidad de Buenos Aires, Facultad de Farmacia y Bioquímica, Departamento de Química Biológica, Buenos Aires, Argentina,Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) – Universidad de Buenos Aires, Instituto de Química y Fisicoquímica Biológicas "Prof. Alejandro C. Paladini" (IQUIFIB), Buenos Aires, Argentina
| | - Wanda M. Valsecchi
- Universidad de Buenos Aires, Facultad de Farmacia y Bioquímica, Departamento de Química Biológica, Buenos Aires, Argentina,Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) – Universidad de Buenos Aires, Instituto de Química y Fisicoquímica Biológicas "Prof. Alejandro C. Paladini" (IQUIFIB), Buenos Aires, Argentina
| | - Mariela Ferreira-Gomes
- Universidad de Buenos Aires, Facultad de Farmacia y Bioquímica, Departamento de Química Biológica, Buenos Aires, Argentina,Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) – Universidad de Buenos Aires, Instituto de Química y Fisicoquímica Biológicas "Prof. Alejandro C. Paladini" (IQUIFIB), Buenos Aires, Argentina
| | - Mercedes Centeno
- Universidad de Buenos Aires, Facultad de Farmacia y Bioquímica, Departamento de Química Biológica, Buenos Aires, Argentina,Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) – Universidad de Buenos Aires, Instituto de Química y Fisicoquímica Biológicas "Prof. Alejandro C. Paladini" (IQUIFIB), Buenos Aires, Argentina
| | - Elina Malén Saint Martin
- Universidad de Buenos Aires, Facultad de Farmacia y Bioquímica, Departamento de Química Biológica, Buenos Aires, Argentina
| | | | - Juan Pablo FC. Rossi
- Universidad de Buenos Aires, Facultad de Farmacia y Bioquímica, Departamento de Química Biológica, Buenos Aires, Argentina,Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) – Universidad de Buenos Aires, Instituto de Química y Fisicoquímica Biológicas "Prof. Alejandro C. Paladini" (IQUIFIB), Buenos Aires, Argentina
| | - Mónica R. Montes
- Universidad de Buenos Aires, Facultad de Farmacia y Bioquímica, Departamento de Química Biológica, Buenos Aires, Argentina,Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) – Universidad de Buenos Aires, Instituto de Química y Fisicoquímica Biológicas "Prof. Alejandro C. Paladini" (IQUIFIB), Buenos Aires, Argentina
| | - Rolando C. Rossi
- Universidad de Buenos Aires, Facultad de Farmacia y Bioquímica, Departamento de Química Biológica, Buenos Aires, Argentina,Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) – Universidad de Buenos Aires, Instituto de Química y Fisicoquímica Biológicas "Prof. Alejandro C. Paladini" (IQUIFIB), Buenos Aires, Argentina,For correspondence: Rolando C. Rossi
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8
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Moreno C, Jiao S, Yano S, Holmgren M. Disease mutations of human α3 Na +/K +-ATPase define extracellular Na + binding/occlusion kinetics at ion binding site III. PNAS NEXUS 2022; 1:pgac205. [PMID: 36304555 PMCID: PMC9585393 DOI: 10.1093/pnasnexus/pgac205] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/03/2022] [Accepted: 09/23/2022] [Indexed: 11/06/2022]
Abstract
Na+/K+-ATPase, which creates transmembrane electrochemical gradients by exchanging 3 Na+ for 2 K+, is central to the pathogenesis of neurological diseases such as alternating hemiplegia of childhood. Although Na+/K+-ATPase has 3 distinct ion binding sites I-III, the difficulty of distinguishing ion binding events at each site from the others hinders kinetic study of these transitions. Here, we show that binding of Na+ at each site in the human α3 Na+/K+-ATPase can be resolved using extracellular Na+-mediated transient currents. When Na+/K+-ATPase is constrained to bind and release only Na+, three kinetic components: fast, medium, and slow, can be isolated, presumably corresponding to the protein dynamics associated with the binding (or release depending on the voltage step direction) and the occlusion (or deocclusion) of each of the 3 Na+. Patient-derived mutations of residues which coordinate Na+ at site III exclusively impact the slow component, demonstrating that site III is crucial for deocclusion and release of the first Na+ into the extracellular milieu. These results advance understanding of Na+/K+-ATPase mutation pathogenesis and provide a foundation for study of individual ions' binding kinetics.
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Affiliation(s)
- Cristina Moreno
- Molecular Neurophysiology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA
| | - Song Jiao
- Molecular Neurophysiology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA
| | - Sho Yano
- Molecular Neurophysiology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA,Medical Genetics and Genomic Medicine Training Program, National Human Genome Research Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - Miguel Holmgren
- Correspondence should be addressed: Miguel Holmgren, Ph.D. Molecular Neurophysiology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA. Tel: +1-(301) 451-6259; E-mail:
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9
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Alcicek FC, Mohaissen T, Bulat K, Dybas J, Szczesny-Malysiak E, Kaczmarska M, Franczyk-Zarow M, Kostogrys R, Marzec KM. Sex-Specific Differences of Adenosine Triphosphate Levels in Red Blood Cells Isolated From ApoE/LDLR Double-Deficient Mice. Front Physiol 2022; 13:839323. [PMID: 35250640 PMCID: PMC8895041 DOI: 10.3389/fphys.2022.839323] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2021] [Accepted: 01/27/2022] [Indexed: 12/16/2022] Open
Abstract
In this study for the first time, we investigated the correlation between sex-specific differences in adenosine triphosphate (ATP) levels in red blood cells (RBCs) and their mechanical, biochemical, and morphological alterations during the progression of atherosclerosis in ApoE/LDLR double-deficient (ApoE/LDLR−/−) mice. Our results indicate that both sex and age affect alterations in RBCs of both ApoE/LDLR−/− and C57BL/6J mice. When compared with male RBCs, female RBCs were characterized by lower basal ATP and mean corpuscular hemoglobin concentration (MCHC), higher hemoglobin concentration (HGB), mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), deformability, and phosphatidylserine (PS) exposure levels, regardless of age in both, ApoE/LDLR−/− and C57BL/6J mice. ApoE/LDLR−/− mice compared with age-matched controls showed lower basal ATP levels regardless of age and sex. Intracellular ATP level of RBCs was decreased solely in senescent female C57BL/6J mice, while it was elevated in males. Basal extracellular ATP levels were 400 times lower than corresponding intracellular level. In conclusion, basal ATP levels, RBC morphology, deformability, PS exposure levels alterations are sex-dependent in mice. Changes in basal ATP levels were correlated with PS exposure and trends of changes in MCV. Trends of changes of the most RBC parameters were similar in both sexes of ApoE/LDLR−/− mice compared with age-matched controls; however, their kinetics and levels vary greatly between different stages of disease progression.
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Affiliation(s)
- Fatih Celal Alcicek
- Jagiellonian Centre for Experimental Therapeutics, Jagiellonian University, Krakow, Poland
| | - Tasnim Mohaissen
- Jagiellonian Centre for Experimental Therapeutics, Jagiellonian University, Krakow, Poland
- Chair and Faculty of Pharmacy, Jagiellonian University Medical College, Krakow, Poland
| | - Katarzyna Bulat
- Jagiellonian Centre for Experimental Therapeutics, Jagiellonian University, Krakow, Poland
- Łukasiewicz Research Network - Krakow Institute of Technology, Krakow, Poland
| | - Jakub Dybas
- Jagiellonian Centre for Experimental Therapeutics, Jagiellonian University, Krakow, Poland
| | - Ewa Szczesny-Malysiak
- Jagiellonian Centre for Experimental Therapeutics, Jagiellonian University, Krakow, Poland
| | - Magdalena Kaczmarska
- Jagiellonian Centre for Experimental Therapeutics, Jagiellonian University, Krakow, Poland
| | - Magdalena Franczyk-Zarow
- Department of Human Nutrition and Dietetics, Faculty of Food Technology, University of Agriculture, Krakow, Poland
| | - Renata Kostogrys
- Department of Human Nutrition and Dietetics, Faculty of Food Technology, University of Agriculture, Krakow, Poland
| | - Katarzyna M. Marzec
- Jagiellonian Centre for Experimental Therapeutics, Jagiellonian University, Krakow, Poland
- Łukasiewicz Research Network - Krakow Institute of Technology, Krakow, Poland
- *Correspondence: Katarzyna M. Marzec,
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10
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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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11
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Hossain KR, Clayton D, Goodchild SC, Rodger A, Payne RJ, Cornelius F, Clarke RJ. Order-disorder transitions of cytoplasmic N-termini in the mechanisms of P-type ATPases. Faraday Discuss 2021; 232:172-187. [PMID: 34549220 DOI: 10.1039/d0fd00040j] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Membrane protein structure and function are modulated via interactions with their lipid environment. This is particularly true for integral membrane pumps, the P-type ATPases. These ATPases play vital roles in cell physiology, where they are associated with the transport of cations and lipids, thereby generating and maintaining crucial (electro-)chemical potential gradients across the membrane. Several pumps (Na+, K+-ATPase, H+, K+-ATPase and the plasma membrane Ca2+-ATPase) which are located in the asymmetric animal plasma membrane have been found to possess polybasic (lysine-rich) domains on their cytoplasmic surfaces, which are thought to act as phosphatidylserine (PS) binding domains. In contrast, the sarcoplasmic reticulum Ca2+-ATPase, located within an intracellular organelle membrane, does not possess such a domain. Here we focus on the lysine-rich N-termini of the plasma-membrane-bound Na+, K+- and H+, K+-ATPases. Synthetic peptides corresponding to the N-termini of these proteins were found, via quartz crystal microbalance and circular dichroism measurements, to interact via an electrostatic interaction with PS-containing membranes, thereby undergoing an increase in helical or other secondary structure content. As well as influencing ion pumping activity, it is proposed that this interaction could provide a mechanism for sensing the lipid asymmetry of the plasma membrane, which changes drastically when a cell undergoes apoptosis, i.e. programmed cell death. Thus, polybasic regions of plasma membrane-bound ion pumps could potentially perform the function of a "death sensor", signalling to a cell to reduce pumping activity and save energy.
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Affiliation(s)
| | - Daniel Clayton
- School of Chemistry, University of Sydney, Sydney, NSW 2006, Australia.
| | - Sophia C Goodchild
- Department of Molecular Sciences, Macquarie University, Sydney, NSW 2109, Australia
| | - Alison Rodger
- Department of Molecular Sciences, Macquarie University, Sydney, NSW 2109, Australia
| | - Richard J Payne
- School of Chemistry, University of Sydney, Sydney, NSW 2006, Australia.
| | - Flemming Cornelius
- Department of Biomedicine, University of Aarhus, DK-8000 Aarhus C, Denmark
| | - Ronald J Clarke
- School of Chemistry, University of Sydney, Sydney, NSW 2006, Australia. .,The University of Sydney Nano Institute, Sydney, NSW 2006, Australia
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12
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Meyer DJ, Bijlani S, de Sautu M, Spontarelli K, Young VC, Gatto C, Artigas P. FXYD protein isoforms differentially modulate human Na/K pump function. J Gen Physiol 2021; 152:211559. [PMID: 33231612 PMCID: PMC7690937 DOI: 10.1085/jgp.202012660] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2020] [Accepted: 10/29/2020] [Indexed: 12/28/2022] Open
Abstract
Tight regulation of the Na/K pump is essential for cellular function because this heteromeric protein builds and maintains the electrochemical gradients for Na+ and K+ that energize electrical signaling and secondary active transport. We studied the regulation of the ubiquitous human α1β1 pump isoform by five human FXYD proteins normally located in muscle, kidney, and neurons. The function of Na/K pump α1β1 expressed in Xenopus oocytes with or without FXYD isoforms was evaluated using two-electrode voltage clamp and patch clamp. Through evaluation of the partial reactions in the absence of K+ but presence of Na+ in the external milieu, we demonstrate that each FXYD subunit alters the equilibrium between E1P(3Na) and E2P, the phosphorylated conformations with Na+ occluded and free from Na+, respectively, thereby altering the apparent affinity for Na+. This modification of Na+ interaction shapes the small effects of FXYD proteins on the apparent affinity for external K+ at physiological Na+. FXYD6 distinctively accelerated both the Na+-deocclusion and the pump-turnover rates. All FXYD isoforms altered the apparent affinity for intracellular Na+ in patches, an effect that was observed only in the presence of intracellular K+. Therefore, FXYD proteins alter the selectivity of the pump for intracellular ions, an effect that could be due to the altered equilibrium between E1 and E2, the two major pump conformations, and/or to small changes in ion affinities that are exacerbated when both ions are present. Lastly, we observed a drastic reduction of Na/K pump surface expression when it was coexpressed with FXYD1 or FXYD6, with the former being relieved by injection of PKA's catalytic subunit into the oocyte. Our results indicate that a prominent effect of FXYD1 and FXYD6, and plausibly other FXYDs, is the regulation of Na/K pump trafficking.
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Affiliation(s)
- Dylan J Meyer
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock TX
| | - Sharan Bijlani
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock TX
| | - Marilina de Sautu
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock TX
| | - Kerri Spontarelli
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock TX
| | - Victoria C Young
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock TX
| | - Craig Gatto
- School of Biological Sciences, Illinois State University. Normal, IL
| | - Pablo Artigas
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock TX
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13
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Giamogante F, Poggio E, Barazzuol L, Covallero A, Calì T. Apoptotic signals at the endoplasmic reticulum-mitochondria interface. ADVANCES IN PROTEIN CHEMISTRY AND STRUCTURAL BIOLOGY 2021; 126:307-343. [PMID: 34090618 DOI: 10.1016/bs.apcsb.2021.02.007] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The maintenance of cellular homeostasis involves the participation of multiple organelles, such as the endoplasmic reticulum (ER) and mitochondria. Specifically, ER plays a key role in calcium (Ca2+) storage, lipid synthesis, protein folding, and assembly, while mitochondria are the "energy factories" and provide energy to drive intracellular processes. Hence, alteration in ER or mitochondrial homeostasis has detrimental effects on cell survival, being linked to the triggering of apoptosis, a programmed form of cell death. Besides, ER stress conditions affect mitochondria functionality and vice-versa, as ER and mitochondria communicate via mitochondria-associated ER membranes (MAMs) to carry out a number of fundamental cellular functions. It is not surprising, thus, that also MAMs perturbations are involved in the regulation of apoptosis. This chapter intends to accurately discuss the involvement of MAMs in apoptosis, highlighting their crucial role in controlling this delicate cellular process.
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Affiliation(s)
- Flavia Giamogante
- Department of Biomedical Sciences, University of Padova, Padova, Italy
| | - Elena Poggio
- Department of Biomedical Sciences, University of Padova, Padova, Italy
| | - Lucia Barazzuol
- Department of Biomedical Sciences, University of Padova, Padova, Italy
| | - Alberto Covallero
- Department of Biomedical Sciences, University of Padova, Padova, Italy
| | - Tito Calì
- Department of Biomedical Sciences, University of Padova, Padova, Italy.
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14
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Zimna A, Kaczmarska M, Szczesny-Malysiak E, Wajda A, Bulat K, Alcicek FC, Zygmunt M, Sacha T, Marzec KM. An Insight into the Stages of Ion Leakage during Red Blood Cell Storage. Int J Mol Sci 2021; 22:ijms22062885. [PMID: 33809183 PMCID: PMC7998123 DOI: 10.3390/ijms22062885] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2021] [Revised: 03/08/2021] [Accepted: 03/08/2021] [Indexed: 12/20/2022] Open
Abstract
Packed red blood cells (pRBCs), the most commonly transfused blood product, are exposed to environmental disruptions during storage in blood banks. In this study, temporal sequence of changes in the ion exchange in pRBCs was analyzed. Standard techniques commonly used in electrolyte measurements were implemented. The relationship between ion exchange and red blood cells (RBCs) morphology was assessed with use of atomic force microscopy with reference to morphological parameters. Variations observed in the Na+, K+, Cl−, H+, HCO3−, and lactate ions concentration show a complete picture of singly-charged ion changes in pRBCs during storage. Correlation between the rate of ion changes and blood group type, regarding the limitations of our research, suggested, that group 0 is the most sensitive to the time-dependent ionic changes. Additionally, the impact of irreversible changes in ion exchange on the RBCs membrane was observed in nanoscale. Results demonstrate that the level of ion leakage that leads to destructive alterations in biochemical and morphological properties of pRBCs depend on the storage timepoint.
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Affiliation(s)
- Anna Zimna
- Jagiellonian Centre for Experimental Therapeutics, Jagiellonian University, 14 Bobrzynskiego St., 30-348 Krakow, Poland; (A.Z.); (E.S.-M.); (A.W.); (K.B.); (F.C.A.)
- Faculty of Pharmacy, Jagiellonian University Medical College, 9 Medyczna St., 30-688 Krakow, Poland;
| | - Magdalena Kaczmarska
- Jagiellonian Centre for Experimental Therapeutics, Jagiellonian University, 14 Bobrzynskiego St., 30-348 Krakow, Poland; (A.Z.); (E.S.-M.); (A.W.); (K.B.); (F.C.A.)
- Correspondence: (M.K.); (K.M.M.); Tel.: +48-12-297-5472 (M.K.); +48-12-664-5476 (K.M.M.)
| | - Ewa Szczesny-Malysiak
- Jagiellonian Centre for Experimental Therapeutics, Jagiellonian University, 14 Bobrzynskiego St., 30-348 Krakow, Poland; (A.Z.); (E.S.-M.); (A.W.); (K.B.); (F.C.A.)
| | - Aleksandra Wajda
- Jagiellonian Centre for Experimental Therapeutics, Jagiellonian University, 14 Bobrzynskiego St., 30-348 Krakow, Poland; (A.Z.); (E.S.-M.); (A.W.); (K.B.); (F.C.A.)
- Faculty of Materials Science and Ceramics, AGH University of Science and Technology, 30 Mickiewicza St., 30-059 Krakow, Poland
| | - Katarzyna Bulat
- Jagiellonian Centre for Experimental Therapeutics, Jagiellonian University, 14 Bobrzynskiego St., 30-348 Krakow, Poland; (A.Z.); (E.S.-M.); (A.W.); (K.B.); (F.C.A.)
| | - Fatih Celal Alcicek
- Jagiellonian Centre for Experimental Therapeutics, Jagiellonian University, 14 Bobrzynskiego St., 30-348 Krakow, Poland; (A.Z.); (E.S.-M.); (A.W.); (K.B.); (F.C.A.)
| | - Malgorzata Zygmunt
- Faculty of Pharmacy, Jagiellonian University Medical College, 9 Medyczna St., 30-688 Krakow, Poland;
| | - Tomasz Sacha
- Chair of Haematology, Faculty of Medicine, Jagiellonian University Medical College, 12 sw. Anny St., 30-008 Krakow, Poland;
- Department of Haematology, Jagiellonian University Hospital, 17 Kopernika St., 31-501 Krakow, Poland
| | - Katarzyna Maria Marzec
- Jagiellonian Centre for Experimental Therapeutics, Jagiellonian University, 14 Bobrzynskiego St., 30-348 Krakow, Poland; (A.Z.); (E.S.-M.); (A.W.); (K.B.); (F.C.A.)
- Correspondence: (M.K.); (K.M.M.); Tel.: +48-12-297-5472 (M.K.); +48-12-664-5476 (K.M.M.)
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15
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Xu Y, Jiang X, Xu J, Qu W, Xie Z, Jiang RW, Feng F. A previously undescribed phenylethanoid glycoside from Callicarpa kwangtungensis Chun acts as an agonist of the Na/K-ATPase signal transduction pathway. PHYTOCHEMISTRY 2021; 181:112577. [PMID: 33190100 DOI: 10.1016/j.phytochem.2020.112577] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/18/2020] [Revised: 10/23/2020] [Accepted: 10/24/2020] [Indexed: 06/11/2023]
Abstract
The new concept that Na/K-ATPase acts as a receptor prompted us to look for new ligands from Callicarpa kwangtungensis Chun. Using column chromatography, an undescribed phenethyl alcohol glycoside, callicarpanoside A, and an undescribed benzyl alcohol glycoside, callicarpanoside B, along with twelve known polyphenols were isolated from Callicarpa kwangtungensis Chun. All the isolated compounds were evaluated for their Na/K-ATPase (NKA) inhibitory activities. Using our NKA technology platform-based screening assay protocols, callicarpanoside B was identified as an undescribed Na/K-ATPase agonist. In particular, the newly identified benzyl alcohol glycoside was found to bind NKA and activate the receptor NKA/Src complex, resulting in the activation of protein kinase cascades. These cascades included extracellular signal-regulated kinases and protein kinase C epsilon, as well as NKA α1 endocytosis at nanomolar concentrations. Unlike the class of cardiotonic steroids, callicarpanoside B showed less inhibition of NKA activity and caused less cellular toxicity. Moreover, callicarpanoside B was found to bind NKA at a different site other than the cardiotonic steroids binding site. Thus, we have identified an undescribed NKA α1 agonist that may be used to enhance the physiological processes of NKA α1 signaling.
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Affiliation(s)
- Yunhui Xu
- Marshall Institute for Interdisciplinary Research, Marshall University, Huntington, WV, 25701, United States
| | - Xueyang Jiang
- Department of Natural Medicinal Chemistry, China Pharmaceutical University, Nanjing, 210009, PR China; Jiangsu Food and Pharmaceutical Science College, Huai'an, 223003, PR China
| | - Jian Xu
- Department of Natural Medicinal Chemistry, China Pharmaceutical University, Nanjing, 210009, PR China; Jiangsu Food and Pharmaceutical Science College, Huai'an, 223003, PR China
| | - Wei Qu
- Department of Natural Medicinal Chemistry, China Pharmaceutical University, Nanjing, 210009, PR China; Jiangsu Food and Pharmaceutical Science College, Huai'an, 223003, PR China
| | - Zijian Xie
- Marshall Institute for Interdisciplinary Research, Marshall University, Huntington, WV, 25701, United States
| | - Ren-Wang Jiang
- Guangdong Province Key Laboratory of Pharmacodynamic Constituents of TCM and New Drugs Research, College of Pharmacy, Jinan University, Guangzhou, 510632, PR China; International Cooperative Laboratory of Traditional Chinese Medicine Modernization and Innovative Drug Development of Chinese Ministry of Education, College of Pharmacy, Jinan University, Guangzhou, 510632, PR China.
| | - Feng Feng
- Department of Natural Medicinal Chemistry, China Pharmaceutical University, Nanjing, 210009, PR China; Jiangsu Food and Pharmaceutical Science College, Huai'an, 223003, PR China.
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16
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Moreno C, Yano S, Bezanilla F, Latorre R, Holmgren M. Transient Electrical Currents Mediated by the Na +/K +-ATPase: A Tour from Basic Biophysics to Human Diseases. Biophys J 2020; 119:236-242. [PMID: 32579966 PMCID: PMC7376075 DOI: 10.1016/j.bpj.2020.06.006] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2020] [Revised: 04/06/2020] [Accepted: 06/03/2020] [Indexed: 01/14/2023] Open
Abstract
The Na+/K+-ATPase is a chemical molecular machine responsible for the movement of Na+ and K+ ions across the cell membrane. These ions are moved against their electrochemical gradients, so the protein uses the free energy of ATP hydrolysis to transport them. In fact, the Na+/K+-ATPase is the single largest consumer of energy in most cells. In each pump cycle, the protein sequentially exports 3Na+ out of the cell, then imports 2K+ into the cell at an approximate rate of 200 cycles/s. In each half cycle of the transport process, there is a state in which ions are stably trapped within the permeation pathway of the protein by internal and external gates in their closed states. These gates are required to open alternately; otherwise, passive ion diffusion would be a wasteful end of the cell's energy. Once one of these gates open, ions diffuse from their binding sites to the accessible milieu, which involves moving through part of the electrical field across the membrane. Consequently, ions generate transient electrical currents first discovered more than 30 years ago. They have been studied in a variety of preparations, including native and heterologous expression systems. Here, we review three decades' worth of work using these transient electrical signals to understand the kinetic transitions of the movement of Na+ and K+ ions through the Na+/K+-ATPase and propose the significance that this work might have to the understanding of the dysfunction of human pump orthologs responsible for some newly discovered neurological pathologies.
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Affiliation(s)
- Cristina Moreno
- Molecular Neurophysiology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland
| | - Sho Yano
- Medical Genetics and Genomic Medicine Training Program, National Human Genome Research Institute, National Institutes of Health, Bethesda, Maryland
| | - Francisco Bezanilla
- Department of Biochemistry and Molecular Biology, University of Chicago, Gordon Center for Integrative Sciences, Chicago, Illinois
| | - Ramon Latorre
- Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de Valparaíso, Valparaíso, Chile
| | - Miguel Holmgren
- Molecular Neurophysiology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland.
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17
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The role of mitochondria-associated membranes in cellular homeostasis and diseases. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2019; 350:119-196. [PMID: 32138899 DOI: 10.1016/bs.ircmb.2019.11.002] [Citation(s) in RCA: 71] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Mitochondria and endoplasmic reticulum (ER) are fundamental in the control of cell physiology regulating several signal transduction pathways. They continuously communicate exchanging messages in their contact sites called MAMs (mitochondria-associated membranes). MAMs are specific microdomains acting as a platform for the sorting of vital and dangerous signals. In recent years increasing evidence reported that multiple scaffold proteins and regulatory factors localize to this subcellular fraction suggesting MAMs as hotspot signaling domains. In this review we describe the current knowledge about MAMs' dynamics and processes, which provided new correlations between MAMs' dysfunctions and human diseases. In fact, MAMs machinery is strictly connected with several pathologies, like neurodegeneration, diabetes and mainly cancer. These pathological events are characterized by alterations in the normal communication between ER and mitochondria, leading to deep metabolic defects that contribute to the progression of the diseases.
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18
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Andersen OS, Nairn AC, Palmer LG, Shapley RM. In Memoriam: David C. Gadsby, PhD. J Gen Physiol 2019. [PMCID: PMC6683670 DOI: 10.1085/jgp.201912400] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Andersen et al. commemorate the life of the eminent physiologist, David Gadsby.
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Affiliation(s)
- Olaf S. Andersen
- Department of Physiology and Biophysics, Weill Cornell Medical College, New York, NY,Correspondence to Olaf S. Andersen:
| | - Angus C. Nairn
- Department of Psychiatry, Yale University, New Haven, CT
| | - Lawrence G. Palmer
- Department of Physiology and Biophysics, Weill Cornell Medical College, New York, NY
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19
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Zhao X, Sun W, Geng D, Fu W, Dan J, Xie Y, Kent PRC, Zhou W, Pennycook SJ, Loh KP. Edge Segregated Polymorphism in 2D Molybdenum Carbide. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2019; 31:e1808343. [PMID: 30785651 DOI: 10.1002/adma.201808343] [Citation(s) in RCA: 30] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/27/2018] [Revised: 02/03/2019] [Indexed: 05/26/2023]
Abstract
Molybdenum carbide (Mo2 C), a class of unterminated MXene, is endowed with rich polymorph chemistry, but the growth conditions of the various polymorphs are not understood. Other than the most commonly observed T-phase Mo2 C, little is known about other phases. Here, Mo2 C crystals are successfully grown consisting of mixed polymorphs and polytypes via a diffusion-mediated mechanism, using liquid copper as the diffusion barrier between the elemental precursors of Mo and C. By controlling the thickness of the copper diffusion barrier layer, the crystal growth can be controlled between a highly uniform AA-stacked T-phase Mo2 C and a "wedding cake" like Mo2 C crystal with spatially delineated zone in which the Bernal-stacked Mo2 C predominate. The atomic structures, as well as the transformations between distinct stackings, are simulated and analyzed using density functional theory (DFT)-based calculations. Bernal-stacked Mo2 C has a d band closer to the Fermi energy, leading to a promising performance in catalysis as verified in hydrogen evolution reaction (HER).
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Affiliation(s)
- Xiaoxu Zhao
- Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore, 17543, Singapore
- NUS Graduate School for Integrative Sciences and Engineering, National University of Singapore, 13 Centre for Life Sciences, #05-01, 28 Medical Drive, Singapore, 117456, Singapore
| | - Weiwei Sun
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA
| | - Dechao Geng
- Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore, 17543, Singapore
| | - Wei Fu
- Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore, 17543, Singapore
| | - Jiadong Dan
- NUS Graduate School for Integrative Sciences and Engineering, National University of Singapore, 13 Centre for Life Sciences, #05-01, 28 Medical Drive, Singapore, 117456, Singapore
- Department of Materials Science and Engineering, National University of Singapore, 9 Engineering Drive 1, Singapore, 117575, Singapore
| | - Yu Xie
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA
| | - Paul R C Kent
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA
- Computational Sciences and Engineering Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA
| | - Wu Zhou
- School of Physical Sciences and CAS Centre for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Stephen J Pennycook
- NUS Graduate School for Integrative Sciences and Engineering, National University of Singapore, 13 Centre for Life Sciences, #05-01, 28 Medical Drive, Singapore, 117456, Singapore
- Department of Materials Science and Engineering, National University of Singapore, 9 Engineering Drive 1, Singapore, 117575, Singapore
| | - Kian Ping Loh
- Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore, 17543, Singapore
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20
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Effect of Cholesterol on the Dipole Potential of Lipid Membranes. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2019; 1115:135-154. [DOI: 10.1007/978-3-030-04278-3_6] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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21
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Rui H, Das A, Nakamoto R, Roux B. Proton Countertransport and Coupled Gating in the Sarcoplasmic Reticulum Calcium Pump. J Mol Biol 2018; 430:5050-5065. [PMID: 30539761 DOI: 10.1016/j.jmb.2018.10.014] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2018] [Revised: 09/25/2018] [Accepted: 10/20/2018] [Indexed: 10/28/2022]
Abstract
The calcium pump of the sarcoplasmic reticulum (SERCA) is an ATP-driven active transporter of Ca2+ ions that functions via an "alternating-access" cycle mechanism. In each cycle, SERCA transports two Ca2+ ions toward the lumen of the sarcoplasmic reticulum and two to three protons to the cytoplasm. How the latter conformational transition is coupled to cytoplasmic release of protons remains poorly understood. The present computational study shows how the mechanism of proton countertransport is coupled to the alternating access gating process in SERCA. Molecular dynamics simulation trajectories are generated starting from a series of configurations taken along the E2 to E1 transition pathway determined by the string method with swarms-of-trajectories. Simulations of different protonation configurations at the binding sites reveal how deprotonation events affect the opening of the cytoplasmic gate. The results show that there is a strong coupling between the chronological order of deprotonation, the entry of water molecules into the TM region, and the opening of the cytoplasmic gate. Deprotonation of E309 and E771 is sequential with E309 being the first to lose the proton. The deprotonation promotes the opening of the cytoplasmic gate but leads to a productive gating transition only if it occurs after the transmembrane domain has reached an intermediate conformation. Deprotonation of E309 and E771 is unproductive when it occurs too early because it causes the re-opening of the luminal gate.
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Affiliation(s)
- Huan Rui
- Department of Biochemistry and Molecular Biology, The University of Chicago, 929 East 57th Street, Chicago, IL 60637, USA
| | - Avisek Das
- Department of Biochemistry and Molecular Biology, The University of Chicago, 929 East 57th Street, Chicago, IL 60637, USA
| | - Robert Nakamoto
- Department of Molecular Physiology and Biological Physics, University of Virginia School of Medicine, PO Box 800886, 480 Ray C. Hunt Drive, Charlottesville, VA 22908, USA
| | - Benoît Roux
- Department of Biochemistry and Molecular Biology, The University of Chicago, 929 East 57th Street, Chicago, IL 60637, USA.
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22
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Dubey V, Han M, Kopec W, Solov'yov IA, Abe K, Khandelia H. K + binding and proton redistribution in the E 2P state of the H +, K +-ATPase. Sci Rep 2018; 8:12732. [PMID: 30143663 PMCID: PMC6109069 DOI: 10.1038/s41598-018-30885-w] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2018] [Accepted: 08/07/2018] [Indexed: 12/13/2022] Open
Abstract
The H+, K+-ATPase (HKA) uses ATP to pump protons into the gastric lumen against a million-fold proton concentration gradient while counter-transporting K+ from the lumen. The mechanism of release of a proton into a highly acidic stomach environment, and the subsequent binding of a K+ ion necessitates a network of protonable residues and dynamically changing protonation states in the cation binding pocket dominated by five acidic amino acid residues E343, E795, E820, D824, and D942. We perform molecular dynamics simulations of spontaneous K+ binding to all possible protonation combinations of the acidic amino acids and carry out free energy calculations to determine the optimal protonation state of the luminal-open E2P state of the pump which is ready to bind luminal K+. A dynamic pKa correlation analysis reveals the likelihood of proton transfer events within the cation binding pocket. In agreement with in-vitro measurements, we find that E795 is likely to be protonated, and that E820 is at the center of the proton transfer network in the luminal-open E2P state. The acidic residues D942 and D824 are likely to remain protonated, and the proton redistribution occurs predominantly amongst the glutamate residues exposed to the lumen. The analysis also shows that a lower number of K+ ions bind at lower pH, modeled by a higher number of protons in the cation binding pocket, in agreement with the 'transport stoichiometry variation' hypothesis.
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Affiliation(s)
- Vikas Dubey
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Odense, 5230 M, Denmark
- MEMPHYS-Center for Biomembrane Physics, Odense, Denmark
| | - Minwoo Han
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Odense, 5230 M, Denmark
- MEMPHYS-Center for Biomembrane Physics, Odense, Denmark
| | - Wojciech Kopec
- Computational Biomolecular Dynamics Group, Max Planck Institute for Biophysical Chemistry, 37077, Göttingen, Germany
| | - Ilia A Solov'yov
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Odense, 5230 M, Denmark
| | - Kazuhiro Abe
- Cellular and Structural Physiology Institute and Department of Medicinal Science, Graduate School of Pharmaceutical Sciences, Nagoya University, Nagoya, 464-8601, Japan
| | - Himanshu Khandelia
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Odense, 5230 M, Denmark.
- MEMPHYS-Center for Biomembrane Physics, Odense, Denmark.
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23
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Raguimova ON, Smolin N, Bovo E, Bhayani S, Autry JM, Zima AV, Robia SL. Redistribution of SERCA calcium pump conformers during intracellular calcium signaling. J Biol Chem 2018; 293:10843-10856. [PMID: 29764938 PMCID: PMC6052202 DOI: 10.1074/jbc.ra118.002472] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2018] [Revised: 05/01/2018] [Indexed: 11/06/2022] Open
Abstract
The conformational changes of a calcium transport ATPase were investigated with molecular dynamics (MD) simulations as well as fluorescence resonance energy transfer (FRET) measurements to determine the significance of a discrete structural element for regulation of the conformational dynamics of the transport cycle. Previous MD simulations indicated that a loop in the cytosolic domain of the SERCA calcium transporter facilitates an open-to-closed structural transition. To investigate the significance of this structural element, we performed additional MD simulations and new biophysical measurements of SERCA structure and function. Rationally designed in silico mutations of three acidic residues of the loop decreased SERCA domain-domain contacts and increased domain-domain separation distances. Principal component analysis of MD simulations suggested decreased sampling of compact conformations upon N-loop mutagenesis. Deficits in headpiece structural dynamics were also detected by measuring intramolecular FRET of a Cer-YFP-SERCA construct (2-color SERCA). Compared with WT, the mutated 2-color SERCA shows a partial FRET response to calcium, whereas retaining full responsiveness to the inhibitor thapsigargin. Functional measurements showed that the mutated transporter still hydrolyzes ATP and transports calcium, but that maximal enzyme activity is reduced while maintaining similar calcium affinity. In live cells, calcium elevations resulted in concomitant FRET changes as the population of WT 2-color SERCA molecules redistributed among intermediates of the transport cycle. Our results provide novel insights on how the population of SERCA pumps responds to dynamic changes in intracellular calcium.
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Affiliation(s)
- Olga N Raguimova
- From the Department of Cell and Molecular Physiology, Loyola University Chicago, Maywood, Illinois 60153 and
| | - Nikolai Smolin
- From the Department of Cell and Molecular Physiology, Loyola University Chicago, Maywood, Illinois 60153 and
| | - Elisa Bovo
- From the Department of Cell and Molecular Physiology, Loyola University Chicago, Maywood, Illinois 60153 and
| | - Siddharth Bhayani
- From the Department of Cell and Molecular Physiology, Loyola University Chicago, Maywood, Illinois 60153 and
| | - Joseph M Autry
- the Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455
| | - Aleksey V Zima
- From the Department of Cell and Molecular Physiology, Loyola University Chicago, Maywood, Illinois 60153 and
| | - Seth L Robia
- From the Department of Cell and Molecular Physiology, Loyola University Chicago, Maywood, Illinois 60153 and
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24
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Abstract
A voltage change across a membrane protein moves charges or dipoles producing a gating current that is an electrical expression of a conformational change. Many membrane proteins sense the voltage across the membrane where they are inserted, and their function is affected by voltage changes. The voltage sensor consists of charges or dipoles that move in response to changes in the electric field, and their movement produces an electric current that has been called gating current. In the case of voltage-gated ion channels, the kinetic and steady-state properties of the gating charges provide information of conformational changes between closed states that are not visible when observing ionic currents only. In this Journal of General Physiology Milestone, the basic principles of voltage sensing and gating currents are presented, followed by a historical description of the recording of gating currents. The results of gating current recordings are then discussed in the context of structural changes in voltage-dependent membrane proteins and how these studies have provided new insights on gating mechanisms.
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Affiliation(s)
- Francisco Bezanilla
- Department of Biochemistry and Molecular Biology, Institute for Biophysical Dynamics, University of Chicago, Chicago, IL
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25
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Lu FM, Hilgemann DW. Na/K pump inactivation, subsarcolemmal Na measurements, and cytoplasmic ion turnover kinetics contradict restricted Na spaces in murine cardiac myocytes. J Gen Physiol 2017; 149:727-749. [PMID: 28606910 PMCID: PMC5496509 DOI: 10.1085/jgp.201711780] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2017] [Accepted: 05/23/2017] [Indexed: 11/20/2022] Open
Abstract
The Na/K pump exports cytoplasmic Na ions while importing K ions, and its activity is thought to be affected by restricted intracellular Na diffusion in cardiac myocytes. Lu and Hilgemann find instead that the pump can enter an inactivated state and that inactivation can be relieved by cytoplasmic Na. Decades ago, it was proposed that Na transport in cardiac myocytes is modulated by large changes in cytoplasmic Na concentration within restricted subsarcolemmal spaces. Here, we probe this hypothesis for Na/K pumps by generating constitutive transsarcolemmal Na flux with the Na channel opener veratridine in whole-cell patch-clamp recordings. Using 25 mM Na in the patch pipette, pump currents decay strongly during continuous activation by extracellular K (τ, ∼2 s). In contradiction to depletion hypotheses, the decay becomes stronger when pump currents are decreased by hyperpolarization. Na channel currents are nearly unchanged by pump activity in these conditions, and conversely, continuous Na currents up to 0.5 nA in magnitude have negligible effects on pump currents. These outcomes are even more pronounced using 50 mM Li as a cytoplasmic Na congener. Thus, the Na/K pump current decay reflects mostly an inactivation mechanism that immobilizes Na/K pump charge movements, not cytoplasmic Na depletion. When channel currents are increased beyond 1 nA, models with unrestricted subsarcolemmal diffusion accurately predict current decay (τ ∼15 s) and reversal potential shifts observed for Na, Li, and K currents through Na channels opened by veratridine, as well as for Na, K, Cs, Li, and Cl currents recorded in nystatin-permeabilized myocytes. Ion concentrations in the pipette tip (i.e., access conductance) track without appreciable delay the current changes caused by sarcolemmal ion flux. Importantly, cytoplasmic mixing volumes, calculated from current decay kinetics, increase and decrease as expected with osmolarity changes (τ >30 s). Na/K pump current run-down over 20 min reflects a failure of pumps to recover from inactivation. Simulations reveal that pump inactivation coupled with Na-activated recovery enhances the rapidity and effectivity of Na homeostasis in cardiac myocytes. In conclusion, an autoregulatory mechanism enhances cardiac Na/K pump activity when cytoplasmic Na rises and suppresses pump activity when cytoplasmic Na declines.
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Affiliation(s)
- Fang-Min Lu
- Department of Physiology, University of Texas Southwestern Medical Center at Dallas, Dallas, TX
| | - Donald W Hilgemann
- Department of Physiology, University of Texas Southwestern Medical Center at Dallas, Dallas, TX
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26
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Garcia A, Pratap PR, Lüpfert C, Cornelius F, Jacquemin D, Lev B, Allen TW, Clarke RJ. The voltage-sensitive dye RH421 detects a Na + ,K + -ATPase conformational change at the membrane surface. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2017; 1859:813-823. [DOI: 10.1016/j.bbamem.2017.01.022] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/19/2016] [Revised: 01/09/2017] [Accepted: 01/19/2017] [Indexed: 10/20/2022]
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27
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28
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Han M, Kopec W, Solov’yov IA, Khandelia H. Glutamate Water Gates in the Ion Binding Pocket of Na + Bound Na +, K +-ATPase. Sci Rep 2017; 7:39829. [PMID: 28084301 PMCID: PMC5233988 DOI: 10.1038/srep39829] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2016] [Accepted: 11/25/2016] [Indexed: 11/15/2022] Open
Abstract
The dynamically changing protonation states of the six acidic amino acid residues in the ion binding pocket of the Na+, K+ -ATPase (NKA) during the ion transport cycle are proposed to drive ion binding, release and possibly determine Na+ or K+ selectivity. We use molecular dynamics (MD) and density functional theory (DFT) simulations to determine the protonation scheme of the Na+ bound conformation of NKA. MD simulations of all possible protonation schemes show that the bound Na+ ions are most stably bound when three or four protons reside in the binding sites, and that Glu954 in site III is always protonated. Glutamic acid residues in the three binding sites act as water gates, and their deprotonation triggers water entry to the binding sites. From DFT calculations of Na+ binding energies, we conclude that three protons in the binding site are needed to effectively bind Na+ from water and four are needed to release them in the next step. Protonation of Asp926 in site III will induce Na+ release, and Glu327, Glu954 and Glu779 are all likely to be protonated in the Na+ bound occluded conformation. Our data provides key insights into the role of protons in the Na+ binding and release mechanism of NKA.
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Affiliation(s)
- Minwoo Han
- MEMPHYS−Center for Biomembrane Physics, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
| | - Wojciech Kopec
- MEMPHYS−Center for Biomembrane Physics, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
| | - Ilia A. Solov’yov
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark
| | - Himanshu Khandelia
- MEMPHYS−Center for Biomembrane Physics, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
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29
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Dimitrov AG. An approach to expand description of the pump and co-transporter steady-state current. J Theor Biol 2017; 412:94-99. [PMID: 27765532 DOI: 10.1016/j.jtbi.2016.10.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2016] [Revised: 10/06/2016] [Accepted: 10/15/2016] [Indexed: 11/16/2022]
Abstract
The membrane transporters (pumps and co-transporters) are the main players in maintaining the cell homeostasis. Models of various types, each with their own drawbacks, describe transporter behavior. The aim of this study is to find the link between the biophysically based and empirical models to face and solve their specific problems. Instead of decreasing the number of states and using few complex rate constants as is usually done, we use the number of states as great as possible. Then, each transition in the cycle can represent an elementary process and we can apply the mass action law, according to which if rate constants depend on concentrations the dependence is linear. Thus, the expression for the steady state transporter current can be transformed from a function of rate constants into a function of concentrations. When transporter states form a single cycle, it can be characterized by two modes of action - forward and backward ones. Specific mode is realized depending on the available free energy. Each mode of action is characterized by a set of transporter affinities together with a parameter that describes the maximal turning rate. Except standard affinities corresponding to the substances that are binding to the transporter, affinities for the substances that are released are also defined. Such scheme provides great possibilities to construct approximations as each individual affinity could be estimated from experiments as precisely as possible. The approximations may be used for not only description and study of the transporter current but also in cellular models that attempt to describe wide variety of processes in excitable cells.
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Affiliation(s)
- A G Dimitrov
- Institute of Biophysics and Biomedical Engineering, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 105, Sofia 1113, Bulgaria.
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30
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Janthon P, Viñes F, Sirijaraensre J, Limtrakul J, Illas F. Carbon dissolution and segregation in platinum. Catal Sci Technol 2017. [DOI: 10.1039/c6cy02253g] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Density functional studies at show the feasibility of C subsurface incorporation in Platinum occupying tetrahedral sites. A comparative with Ni and Pd highlights that surface relaxation is critical in C dissolution, specially at low-coordinated sites of Pt nanoparticles. Results explain phenomena such as C dissolution and segregation to form graphene from below, and may serve to tune the Pt surface chemical reactivity.
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Affiliation(s)
- Patanachai Janthon
- Departament de Ciència de Materials i Química Física &
- Institut de Química Teòrica i Computacional (IQTCUB)
- Universitat de Barcelona
- Barcelona 08028
- Spain
| | - Francesc Viñes
- Departament de Ciència de Materials i Química Física &
- Institut de Química Teòrica i Computacional (IQTCUB)
- Universitat de Barcelona
- Barcelona 08028
- Spain
| | | | - Jumras Limtrakul
- Department of Materials Science and Engineering
- School of Molecular Science and Engineering
- Vidyasirimedhi Institute of Science and Technology
- Rayong 21210
- Thailand
| | - Francesc Illas
- Departament de Ciència de Materials i Química Física &
- Institut de Química Teòrica i Computacional (IQTCUB)
- Universitat de Barcelona
- Barcelona 08028
- Spain
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31
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Sumikama T, Oiki S. Digitalized K+ Occupancy in the Nanocavity Holds and Releases Queues of K+ in a Channel. J Am Chem Soc 2016; 138:10284-92. [DOI: 10.1021/jacs.6b05270] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Affiliation(s)
- Takashi Sumikama
- Department of Molecular Physiology
and Biophysics, Faculty of Medical Sciences, University of Fukui, Fukui 910-1193, Japan
| | - Shigetoshi Oiki
- Department of Molecular Physiology
and Biophysics, Faculty of Medical Sciences, University of Fukui, Fukui 910-1193, Japan
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32
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Dipole-Potential-Mediated Effects on Ion Pump Kinetics. Biophys J 2016; 109:1513-20. [PMID: 26488640 DOI: 10.1016/j.bpj.2015.08.022] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2015] [Revised: 08/11/2015] [Accepted: 08/21/2015] [Indexed: 12/30/2022] Open
Abstract
The kinetics of conformational changes of P-type ATPases necessary for the occlusion or deocclusion of transported ions are known to be sensitive to the composition of the surrounding membrane, e.g., phospholipid content, mole percentage of cholesterol, and the presence of lipid-bound anions. Research has shown that many membrane components modify the dipole potential of the lipid head-group region. Based on the observation that occlusion/deocclusion reactions of ion pumps perturb the membrane surrounding the protein, a mechanism is suggested whereby dipole potential modifiers induce preferential stabilization or destabilization of occluded or nonoccluded states of the protein, leading to changes in the forward and backward rate constants for the transition. The mechanism relies on the assumption that conformational changes of the protein are associated with changes in its hydrophobic thickness that requires a change in local lipid packing density to allow hydrophobic matching with the membrane. The changes in lipid packing density cause changes in local lipid dipole potential that are responsible for the dependence of conformational kinetics on dipole potential modifiers. The proposed mechanism has the potential to explain effects of lipid composition on the kinetics of any membrane protein undergoing significant changes in its membrane cross-sectional area during its activity.
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33
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Gao L, Emond MJ, Louie T, Cheadle C, Berger AE, Rafaels N, Vergara C, Kim Y, Taub MA, Ruczinski I, Mathai SC, Rich SS, Nickerson DA, Hummers LK, Bamshad MJ, Hassoun PM, Mathias RA, Barnes KC. Identification of Rare Variants in ATP8B4 as a Risk Factor for Systemic Sclerosis by Whole-Exome Sequencing. Arthritis Rheumatol 2016; 68:191-200. [PMID: 26473621 DOI: 10.1002/art.39449] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2014] [Accepted: 09/24/2015] [Indexed: 01/02/2023]
Abstract
OBJECTIVE To determine the contribution of rare variants as genetic modifiers of the expressivity, penetrance, and severity of systemic sclerosis (SSc). METHODS We performed whole-exome sequencing of 78 European American patients with SSc, including 35 patients without pulmonary arterial hypertension (PAH) and 43 patients with PAH. Association testing of case-control probability for rare variants was performed using the unified sequence kernel association test with optimal kernel weighting and small sample adjustment by comparing all SSc patients with a reference population of 3,179 controls from the Exome Sequencing Project 5,500 exome data set. Replication genotyping was performed in an independent sample of 3,263 patients (415 patients with SSc and 2,848 controls). We conducted expression profiling of messenger RNA from 61 SSc patients (19 without PAH and 42 with PAH) and 41 corresponding controls. RESULTS The ATP8B4 gene was associated with a significant increase in the risk of SSc (P = 2.77 × 10(-7)). Among the 64 ATP8B4 variants tested, a single missense variant, c.1308C>G (F436L, rs55687265), provided the most compelling evidence of association (P = 9.35 × 10(-10), odds ratio [OR] 6.11), which was confirmed in the replication cohort (P = 0.012, OR 1.86) and meta-analysis (P = 1.92 × 10(-7), OR 2.5). Genes involved in E3 ubiquitin-protein ligase complex (ASB10) and cyclic nucleotide gated channelopathies (CNGB3) as well as HLA-DRB5 and HSPB2 (heat-shock protein 27) provided additional evidence of association (P < 10(-5)). Differential ATP8B4 expression was observed among the SSc patients compared to the controls (P = 0.0005). CONCLUSION ATP8B4 may represent a putative genetic risk factor for SSc and pulmonary vascular complications.
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Affiliation(s)
- Li Gao
- Johns Hopkins University, Baltimore, Maryland
| | | | | | | | | | | | | | - Yoonhee Kim
- National Human Genome Research Institute, NIH, Baltimore, Maryland
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34
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Clausen MV, Nissen P, Poulsen H. The α4 isoform of the Na⁺,K⁺-ATPase is tuned for changing extracellular environments. FEBS J 2015; 283:282-93. [PMID: 26476261 DOI: 10.1111/febs.13567] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2015] [Revised: 09/20/2015] [Accepted: 10/15/2015] [Indexed: 11/30/2022]
Abstract
In their journey from the male to the female reproductive tract, spermatozoa are confronted with a constantly changing environment. To cope with the associated challenges, spermatozoa express a distinct set of transporters, channels and pumps. One of the membrane proteins unique to spermatozoa is the α4 isoform of the Na(+) ,K(+) -ATPase. In addition to α4, spermatozoa express the ubiquous α1 variant. To get a detailed understanding of how α1 and α4 differ, and why spermatozoa need an additional Na(+) ,K(+) -ATPase, we have conducted an electrophysiological comparison of the rodent isoforms (rat α4 versus mouse α1-3) using the Xenopus oocyte expression system. We demonstrate isoform-specific differences in the voltage sensitivity of steady-state turnover, with α2 being the more sensitive, and α1 and α2 having faster Na(+) release kinetics than α3 and α4. Our data further show that the α1 and α2 turnover rates are fast compared with those of α3 and α4. Finally, α4 is less influenced by changes in extracellular Na(+) and temperature than α1. Based on these findings, we discuss the possibility that evolution has selected robust activity rather than rapid turnover for α4.
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Affiliation(s)
| | - Poul Nissen
- Department of Molecular Biology and Genetics, Aarhus University, Denmark
| | - Hanne Poulsen
- Department of Molecular Biology and Genetics, Aarhus University, Denmark
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35
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Sadeghian M, Mullali G, Pocock JM, Piers T, Roach A, Smith KJ. Neuroprotection by safinamide in the 6-hydroxydopamine model of Parkinson's disease. Neuropathol Appl Neurobiol 2015; 42:423-35. [PMID: 26300398 DOI: 10.1111/nan.12263] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2015] [Accepted: 08/11/2015] [Indexed: 02/02/2023]
Abstract
AIMS Current therapies in Parkinson's disease mainly treat symptoms rather than provide effective neuroprotection. We examined the effects of safinamide (monoamine oxidase B and sodium channel blocker) on microglial activation and the degeneration of dopaminergic neurons in a rat model of PD in vivo, and on microglia in vitro. METHODS Rats received unilateral stereotaxic injection of 6-hydroxydopamine into the medial forebrain bundle on day 0: The contralateral side served as control. Safinamide or vehicle was delivered from days 0 or 1, for 7 days, via sub-cutaneous mini-pumps. RESULTS In vehicle-treated rats 6-hydroxydopamine caused a significant increase in the number of activated MHC-II(+) microglia compared with the contralateral side, and only 50% of the dopaminergic neurons survived in the ipsilateral SNc. In contrast, rats treated daily with safinamide 50 and 150 mg/ml (on day 0 or 1) exhibited a significantly reduced number of activated microglia (55% reduction at 150 mg/ml) and a significant protection of dopaminergic neurons (80% of neurons survived) (P < 0.001) compared with vehicle-treated controls. Rasagiline, a monoamine oxidase B inhibitor, and lamotrigine, a sodium channel blocking drug, also protected dopaminergic neurons, indicating that safinamide may act by either or both mechanisms. Safinamide also reduced the activation of microglial cells in response to lipopolysaccharide exposure in vitro. CONCLUSION Safinamide therapy suppresses microglial activation and protects dopaminergic neurons from degeneration in the 6-hydroxydopamine model of PD, suggesting that the drug not only treats symptoms but also provides neuroprotection.
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Affiliation(s)
- Mona Sadeghian
- Department of Neuroinflammation, Queen Square Multiple Sclerosis Centre, UCL Institute of Neurology, London, UK
| | - Gizem Mullali
- Department of Neuroinflammation, Queen Square Multiple Sclerosis Centre, UCL Institute of Neurology, London, UK
| | - Jennifer M Pocock
- Department of Neuroinflammation, Queen Square Multiple Sclerosis Centre, UCL Institute of Neurology, London, UK
| | - Thomas Piers
- Department of Neuroinflammation, Queen Square Multiple Sclerosis Centre, UCL Institute of Neurology, London, UK
| | - Arthur Roach
- Parkinson's UK, London, UK.,Chord. Therapeutics, Geneva, Switzerland
| | - Kenneth J Smith
- Department of Neuroinflammation, Queen Square Multiple Sclerosis Centre, UCL Institute of Neurology, London, UK
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36
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Abstract
The Na+/K+-ATPase restores sodium
(Na+) and potassium (K+)
electrochemical gradients dissipated by action potentials and ion-coupled transport
processes. As ions are transported, they become transiently trapped between
intracellular and extracellular gates. Once the external gate opens, three
Na+ ions are released, followed by the binding and
occlusion of two K+ ions. While the mechanisms of
Na+ release have been well characterized by the study of
transient Na+ currents, smaller and faster transient
currents mediated by external K+ have been more difficult to
study. Here we show that external K+ ions travelling to
their binding sites sense only a small fraction of the electric field as they
rapidly and simultaneously become occluded. Consistent with these results, molecular
dynamics simulations of a pump model show a wide water-filled access channel
connecting the binding site to the external solution. These results suggest a
mechanism of K+ gating different from that of
Na+ occlusion. During transport by the
Na+/K+-ATPase,
Na+ and K+ ions become occluded
between intra- and extracellular gates. Here Castillo et al. measure transient
electrical signals arising from K+ occlusion and use molecular
simulations to describe a K+ gating mechanism fundamentally
different to that of Na+.
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37
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Abstract
When the Na,K-ATPase pumps at each turnover two K(+) ions into the cytoplasm, this translocation consists of several reaction steps. First, the ions diffuse consecutively from the extracellular phase through an access pathway to the binding sites where they are coordinated. In the next step, the enzyme is dephosphorylated and the ions are occluded inside the membrane domain. The subsequent transition to the E1 conformation produces a deocclusion of the binding sites to the cytoplasmic side of the membrane and allows in the last steps ion dissociation and diffusion to the aqueous phase. The interaction and competition of K(+) with various quaternary organic ammonium ions have been used to gain insight into the molecular mechanism of the ion binding process from the extracellular side in the P-E2 conformation of the enzyme. Using the electrochromic styryl dye RH421, evidence has been obtained that the access pathway consists of a wide and water-filled funnel-like part that is accessible also for bulky cations such as the benzyltriethylammonium ion, and a narrow part that permits passage only of small cations such as K(+) and NH4(+) in a distinct electrogenic way. Benzyltriethylammonium ions inhibit K(+) binding in a competitive manner that can be explained by a stopper-like function at the interface between the wide and narrow parts of the access pathway. In contrast to other quaternary organic ammonium ions, benzyltriethylammonium ions show a specific binding to the ion pump in a position inside the access pathway where it blocks effectively the access to the binding sites.
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Affiliation(s)
| | - Hans-Jürgen Apell
- Department of Biology, University of Konstanz, 78464 Konstanz, Germany
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38
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Vedovato N, Gadsby DC. Route, mechanism, and implications of proton import during Na+/K+ exchange by native Na+/K+-ATPase pumps. ACTA ACUST UNITED AC 2014; 143:449-64. [PMID: 24688018 PMCID: PMC3971657 DOI: 10.1085/jgp.201311148] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The Na+/K+ pump is a hybrid transporter that can also import protons at physiological K+ and Na+ concentrations. A single Na+/K+-ATPase pumps three Na+ outwards and two K+ inwards by alternately exposing ion-binding sites to opposite sides of the membrane in a conformational sequence coupled to pump autophosphorylation from ATP and auto-dephosphorylation. The larger flow of Na+ than K+ generates outward current across the cell membrane. Less well understood is the ability of Na+/K+ pumps to generate an inward current of protons. Originally noted in pumps deprived of external K+ and Na+ ions, as inward current at negative membrane potentials that becomes amplified when external pH is lowered, this proton current is generally viewed as an artifact of those unnatural conditions. We demonstrate here that this inward current also flows at physiological K+ and Na+ concentrations. We show that protons exploit ready reversibility of conformational changes associated with extracellular Na+ release from phosphorylated Na+/K+ pumps. Reversal of a subset of these transitions allows an extracellular proton to bind an acidic side chain and to be subsequently released to the cytoplasm. This back-step of phosphorylated Na+/K+ pumps that enables proton import is not required for completion of the 3 Na+/2 K+ transport cycle. However, the back-step occurs readily during Na+/K+ transport when external K+ ion binding and occlusion are delayed, and it occurs more frequently when lowered extracellular pH raises the probability of protonation of the externally accessible carboxylate side chain. The proton route passes through the Na+-selective binding site III and is distinct from the principal pathway traversed by the majority of transported Na+ and K+ ions that passes through binding site II. The inferred occurrence of Na+/K+ exchange and H+ import during the same conformational cycle of a single molecule identifies the Na+/K+ pump as a hybrid transporter. Whether Na+/K+ pump–mediated proton inflow may have any physiological or pathophysiological significance remains to be clarified.
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Affiliation(s)
- Natascia Vedovato
- The Laboratory of Cardiac/Membrane Physiology, The Rockefeller University, New York, NY 10065
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39
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Lewalle A, Niederer SA, Smith NP. Species-dependent adaptation of the cardiac Na+/K+ pump kinetics to the intracellular Na+ concentration. J Physiol 2014; 592:5355-71. [PMID: 25362154 DOI: 10.1113/jphysiol.2014.279810] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
The Na(+)/K(+) ATPase (NKA) plays a critical role in maintaining ionic homeostasis and dynamic function in cardiac myocytes, within both the in vivo cell and in silico models. Physiological conditions differ significantly between mammalian species. However, most existing formulations of NKA used to simulate cardiac function in computational models are derived from a broad range of experimental sources spanning many animal species. The resultant inability of these models to discern species-specific features is a significant obstacle to achieving a detailed quantitative and comparative understanding of physiological behaviour in different biological contexts. Here we present a framework for characterising the steady-state NKA current using a biophysical mechanistic model specifically designed to provide a mechanistic explanation of the NKA flux supported by self-consistent species-specific data. We thus compared NKA kinetics specific to guinea- pig and rat ventricular myocytes. We observe that the apparent binding affinity for sodium in the rat is significantly lower, whereas the overall pump cycle rate is doubled, in comparison to the guinea pig. This sensitivity of NKA to its regulatory substrates compensates for the differences in Na(+) concentrations between the cell types. NKA is thereby maintained within its dynamic range over a wide range of pacing frequencies in these two species, despite significant disparities in sodium concentration. Hence, by replacing a conventional generic NKA model with our rat-specific NKA formula into a whole-cell simulation, we have, for the first time, been able to accurately reproduce the action potential duration and the steady-state sodium concentration as functions of pacing frequency.
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Affiliation(s)
- Alexandre Lewalle
- Department of Biomedical Engineering, Division of Imaging Sciences and Biomedical Engineering, King's College London, King's Health Partners, St Thomas's Hospital, London, SE1 7EH, UK
| | - Steven A Niederer
- Department of Biomedical Engineering, Division of Imaging Sciences and Biomedical Engineering, King's College London, King's Health Partners, St Thomas's Hospital, London, SE1 7EH, UK
| | - Nicolas P Smith
- Department of Biomedical Engineering, Division of Imaging Sciences and Biomedical Engineering, King's College London, King's Health Partners, St Thomas's Hospital, London, SE1 7EH, UK
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Holmgren M, Rosenthal JJ. Regulation of Ion Channel and Transporter Function Through RNA Editing. Curr Issues Mol Biol 2014; 17:23-36. [PMID: 25347917 PMCID: PMC5248560] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023] Open
Abstract
A large proportion of the recoding events mediated by RNA editing are in mRNAs that encode ion channels and transporters. The effects of these events on protein function have been characterized in only a few cases. In even fewer instances are the mechanistic underpinnings of these effects understood. This review focuses on how RNA editing affects protein function and higher order physiology. In mammals, particular attention is given to the GluA2, an ionotropic glutamate receptor subunit, and K(v) 1.1, a voltage-dependent K+ channel, because they are particularly well understood. In K(v) addition, work on cephalopod K+ channels and Na+/K+-ATPases has also provided important clues on the rules used by RNA editing to regulate excitability. Finally, we discuss some of the emerging targets for editing and how this process may be used to regulate nervous function in response to a variable environment.
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Affiliation(s)
- Miguel Holmgren
- Molecular Neurophysiology Section, Porter Neuroscience Research Center, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, USA
| | - Joshua J.C. Rosenthal
- Institute of Neurobiology and Department of Biochemistry, University of Puerto Rico Medical Sciences Campus, San Juan, Puerto Rico
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41
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Hilgemann DW. Fishing for holes in transporters: how protons breach the Na/K pump security gates. ACTA ACUST UNITED AC 2014; 143:437-41. [PMID: 24688016 PMCID: PMC3971659 DOI: 10.1085/jgp.201411189] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Affiliation(s)
- Donald W Hilgemann
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas, TX 75390
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Braz FAF, Cruz JS, Faria-Campos AC, Campos SVA. Probabilistic model checking analysis of palytoxin effects on cell energy reactions of the Na+/K+-ATPase. IEEE/ACM TRANSACTIONS ON COMPUTATIONAL BIOLOGY AND BIOINFORMATICS 2013; 10:1530-1541. [PMID: 24407310 DOI: 10.1109/tcbb.2013.97] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Probabilistic model checking (PMC) is a technique used for the specification and analysis of complex systems. It can be applied directly to biological systems which present these characteristics, including cell transport systems. These systems are structures responsible for exchanging ions through the plasma membrane. Their correct behavior is essential for animal cells, since changes on those are responsible for diseases. In this work, PMC is used to model and analyze the effects of the palytoxin toxin (PTX) interactions with one of these systems. Our model suggests that ATP could inhibit PTX action. Therefore, individuals with ATP deficiencies, such as in brain disorders, may be more susceptible to the toxin. We have also used heat maps to enhance the kinetic model, which is used to describe the system reactions. The map reveals unexpected situations, such as a frequent reaction between unlikely pump states, and hot spots such as likely states and reactions. This type of analysis provides a better understanding on how transmembrane ionic transport systems behave and may lead to the discovery and development of new drugs to treat diseases associated to their incorrect behavior.
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Affiliation(s)
| | - Jader S Cruz
- Universidade Federal de Minas Gerais, Belo Horizonte
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Clarke RJ, Catauro M, Rasmussen HH, Apell HJ. Quantitative calculation of the role of the Na+,K+-ATPase in thermogenesis. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2013; 1827:1205-12. [DOI: 10.1016/j.bbabio.2013.06.010] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/11/2013] [Revised: 06/26/2013] [Accepted: 06/30/2013] [Indexed: 11/30/2022]
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Garcia A, Rasmussen HH, Apell HJ, Clarke RJ. Kinetic comparisons of heart and kidney Na+,K(+)-ATPases. Biophys J 2013; 103:677-88. [PMID: 22947929 DOI: 10.1016/j.bpj.2012.07.032] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2012] [Revised: 07/17/2012] [Accepted: 07/23/2012] [Indexed: 10/28/2022] Open
Abstract
Most kinetic measurements of the partial reactions of Na(+),K(+)-ATPase have been conducted on enzyme from mammalian kidney. Here we present a kinetic model that is based on the available equilibrium and kinetic parameters of purified kidney enzyme, and allows predictions of its steady-state turnover and pump current in intact cells as a function of ion and ATP concentrations and the membrane voltage. Using this model, we calculated the expected dependence of the pump current on voltage and extracellular Na(+) concentration. The simulations indicate a lower voltage dependence at negative potentials of the kidney enzyme in comparison with heart muscle Na(+),K(+)-ATPase, in agreement with experimental results. The voltage dependence is enhanced at high extracellular Na(+) concentrations. This effect can be explained by a voltage-dependent depopulation of extracellular K(+) ion binding sites on the E2P state and an increase in the proportion of enzyme in the E1P(Na(+))(3) state in the steady state. This causes a decrease in the effective rate constant for occlusion of K(+) by the E2P state and hence a drop in turnover. Around a membrane potential of zero, negligible voltage dependence is observed because the voltage-independent E2(K(+))(2) → E1 + 2K(+) transition is the major rate-determining step.
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Affiliation(s)
- Alvaro Garcia
- Department of Cardiology, Royal North Shore Hospital, and Kolling Institute, University of Sydney, Sydney, Australia
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