1
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Artigas P, Meyer DJ, Young VC, Spontarelli K, Eastman J, Strandquist E, Rui H, Roux B, Birk MA, Nakanishi H, Abe K, Gatto C. A Na pump with reduced stoichiometry is up-regulated by brine shrimp in extreme salinities. Proc Natl Acad Sci U S A 2023; 120:e2313999120. [PMID: 38079564 PMCID: PMC10756188 DOI: 10.1073/pnas.2313999120] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2023] [Accepted: 10/27/2023] [Indexed: 12/18/2023] Open
Abstract
Brine shrimp (Artemia) are the only animals to thrive at sodium concentrations above 4 M. Salt excretion is powered by the Na+,K+-ATPase (NKA), a heterodimeric (αβ) pump that usually exports 3Na+ in exchange for 2 K+ per hydrolyzed ATP. Artemia express several NKA catalytic α-subunit subtypes. High-salinity adaptation increases abundance of α2KK, an isoform that contains two lysines (Lys308 and Lys758 in transmembrane segments TM4 and TM5, respectively) at positions where canonical NKAs have asparagines (Xenopus α1's Asn333 and Asn785). Using de novo transcriptome assembly and qPCR, we found that Artemia express two salinity-independent canonical α subunits (α1NN and α3NN), as well as two β variants, in addition to the salinity-controlled α2KK. These β subunits permitted heterologous expression of the α2KK pump and determination of its CryoEM structure in a closed, ion-free conformation, showing Lys758 residing within the ion-binding cavity. We used electrophysiology to characterize the function of α2KK pumps and compared it to that of Xenopus α1 (and its α2KK-mimicking single- and double-lysine substitutions). The double substitution N333K/N785K confers α2KK-like characteristics to Xenopus α1, and mutant cycle analysis reveals energetic coupling between these two residues, illustrating how α2KK's Lys308 helps to maintain high affinity for external K+ when Lys758 occupies an ion-binding site. By measuring uptake under voltage clamp of the K+-congener 86Rb+, we prove that double-lysine-substituted pumps transport 2Na+ and 1 K+ per catalytic cycle. Our results show how the two lysines contribute to generate a pump with reduced stoichiometry allowing Artemia to maintain steeper Na+ gradients in hypersaline environments.
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Affiliation(s)
- Pablo Artigas
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, TX79430
| | - Dylan J. Meyer
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, TX79430
| | - Victoria C. Young
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, TX79430
| | - Kerri Spontarelli
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, TX79430
| | - Jessica Eastman
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, TX79430
| | - Evan Strandquist
- School of Biological Sciences, Illinois State University, Normal, IL61790
| | - Huan Rui
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL60637
| | - Benoît Roux
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL60637
| | - Matthew A. Birk
- Department of Biology, Saint Francis University, Loretto, PA15940
| | - Hanayo Nakanishi
- Department of Basic Medical Sciences, Cellular and Structural Physiology Institute, Graduate School of Pharmaceutical Sciences, Nagoya University, Nagoya464-8601, Japan
| | - Kazuhiro Abe
- Department of Basic Medical Sciences, Cellular and Structural Physiology Institute, Graduate School of Pharmaceutical Sciences, Nagoya University, Nagoya464-8601, Japan
| | - Craig Gatto
- School of Biological Sciences, Illinois State University, Normal, IL61790
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2
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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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3
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Kanai R, Cornelius F, Vilsen B, Toyoshima C. Cryo-electron microscopy of Na + ,K + -ATPase reveals how the extracellular gate locks in the E2·2K + state. FEBS Lett 2022; 596:2513-2524. [PMID: 35747985 DOI: 10.1002/1873-3468.14437] [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: 05/16/2022] [Revised: 06/15/2022] [Accepted: 06/15/2022] [Indexed: 11/08/2022]
Abstract
Na+ ,K+ -ATPase (NKA) is one of the most important members of the P-type ion-translocating ATPases and plays a pivotal role in establishing electrochemical gradients for Na+ and K+ across the cell membrane. Presented here is a 3.3 Å resolution structure of NKA in the E2·2K+ state solved by cryo-electron microscopy. It is a stable state with two occluded K+ after transferring three Na+ into the extracellular medium and releasing inorganic phosphate bound to the cytoplasmic P domain. We describe how the extracellular ion pathway wide open in the E2P state becomes closed and locked in E2·2K+ , linked to events at the phosphorylation site more than 50 Å away. We also show, though at low resolution, how ATP binding to NKA in E2·2K+ relaxes the gating machinery and thereby accelerates the transition into the next step, that is, the release of K+ into the cytoplasm, more than 100 times.
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Affiliation(s)
- Ryuta Kanai
- Institute for Quantitative Biosciences, The University of Tokyo, Bunkyo-ku, Tokyo, 113-0032, Japan
| | | | - Bente Vilsen
- Department of Biomedicine, Aarhus University, 8000, Aarhus C, Denmark
| | - Chikashi Toyoshima
- Institute for Quantitative Biosciences, The University of Tokyo, Bunkyo-ku, Tokyo, 113-0032, Japan
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4
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Cryoelectron microscopy of Na +,K +-ATPase in the two E2P states with and without cardiotonic steroids. Proc Natl Acad Sci U S A 2022; 119:e2123226119. [PMID: 35380894 PMCID: PMC9169807 DOI: 10.1073/pnas.2123226119] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
The E2P state of Na+,K+-ATPase, in which the ATPase is phosphorylated and of low affinity to Na+ with the extracellular gate opened, shows different biochemical properties depending on whether the phosphate is transferred from ATP in the forward reaction or from inorganic phosphate (Pi) in the backward reaction. We present here cryoelectron microscopy structures of Na+,K+-ATPase in the two E2P states, explaining their different biochemical properties established a half century ago. The new electron microscopy maps show previously unseen structural features, including unexpected binding modes of cardiotonic steroids, specific and medically important inhibitors of the ATPase, and stabilization by ATP of the E2P state. Cryoelectron microscopy (cryo-EM) was applied to Na+,K+-ATPase (NKA) to determine the structures of two E2P states, one (E2PATP) formed by ATP and Mg2+ in the forward reaction, and the other (E2PPi) formed by inorganic phosphate (Pi) and Mg2+ in the backward reaction, with and without ouabain or istaroxime, representatives of classical and new-generation cardiotonic steroids (CTSs). These two E2P states exhibit different biochemical properties. In particular, K+-sensitive acceleration of the dephosphorylation reaction is not observed with E2PPi, attributed to the presence of a Mg2+ ion in the transmembrane cation binding sites. The cryo-EM structures of NKA demonstrate that the two E2P structures are nearly identical but Mg2+ in the transmembrane binding cavity is identified only in E2PPi, corroborating the idea that it should be denoted as E2PPi·Mg2+. We can now explain why the absence of transmembrane Mg2+ in E2PATP confers the K+ sensitivity in dephosphorylation. In addition, we show that ATP bridges the actuator (A) and nucleotide binding (N) domains, stabilizing the E2PATP state; CTS binding causes hardly any changes in the structure of NKA, both in E2PATP and E2PPi·Mg2+, indicating that the binding mechanism is conformational selection; and istaroxime binds to NKA, extending its aminoalkyloxime group deep into the cation binding site. This orientation is upside down compared to that of classical CTSs with respect to the steroid ring. Notably, mobile parts of NKA are resolved substantially better in the electron microscopy (EM) maps than in previous X-ray structures, including sugars sticking out from the β-subunit and many phospholipid molecules.
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5
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Tejral G, Sopko B, Necas A, Schoner W, Amler E. Computer modelling reveals new conformers of the ATP binding loop of Na +/K +-ATPase involved in the transphosphorylation process of the sodium pump. PeerJ 2017; 5:e3087. [PMID: 28316890 PMCID: PMC5354106 DOI: 10.7717/peerj.3087] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2016] [Accepted: 02/14/2017] [Indexed: 01/02/2023] Open
Abstract
Hydrolysis of ATP by Na+/K+-ATPase, a P-Type ATPase, catalyzing active Na+ and K+ transport through cellular membranes leads transiently to a phosphorylation of its catalytical α-subunit. Surprisingly, three-dimensional molecular structure analysis of P-type ATPases reveals that binding of ATP to the N-domain connected by a hinge to the P-domain is much too far away from the Asp369 to allow the transfer of ATP’s terminal phosphate to its aspartyl-phosphorylation site. In order to get information for how the transfer of the γ-phosphate group of ATP to the Asp369 is achieved, analogous molecular modeling of the M4–M5 loop of ATPase was performed using the crystal data of Na+/K+-ATPase of different species. Analogous molecular modeling of the cytoplasmic loop between Thr338 and Ile760 of the α2-subunit of Na+/K+-ATPase and the analysis of distances between the ATP binding site and phosphorylation site revealed the existence of two ATP binding sites in the open conformation; the first one close to Phe475 in the N-domain, the other one close to Asp369 in the P-domain. However, binding of Mg2+•ATP to any of these sites in the “open conformation” may not lead to phosphorylation of Asp369. Additional conformations of the cytoplasmic loop were found wobbling between “open conformation” <==> “semi-open conformation <==> “closed conformation” in the absence of 2Mg2+•ATP. The cytoplasmic loop’s conformational change to the “semi-open conformation”—characterized by a hydrogen bond between Arg543 and Asp611—triggers by binding of 2Mg2+•ATP to a single ATP site and conversion to the “closed conformation” the phosphorylation of Asp369 in the P-domain, and hence the start of Na+/K+-activated ATP hydrolysis.
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Affiliation(s)
- Gracian Tejral
- Department of Biophysics, 2nd Faculty of Medicine, Charles University Prague, Prague, Czech Republic; Laboratory of Tissue Engineering, Institute of Experimental Medicine, Academy of Sciences of the Czech Republic, Prague, Czech Republic
| | - Bruno Sopko
- Department of Medical Chemistry and Clinical Biochemistry, 2nd Faculty of Medicine, Charles University Prague , Prague , Czech Republic
| | - Alois Necas
- Small Animal Clinic, Faculty of Veterinary Medicine, University of Veterinary and Pharmaceutical Science , Brno , Czech Republic
| | - Wilhelm Schoner
- Institute of Biochemistry and Endocrinology, University of Giessen , Giessen , Germany
| | - Evzen Amler
- Department of Biophysics, 2nd Faculty of Medicine, Charles University Prague, Prague, Czech Republic; Laboratory of Tissue Engineering, Institute of Experimental Medicine, Academy of Sciences of the Czech Republic, Prague, Czech Republic
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6
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Clausen JD, McIntosh DB, Woolley DG, Andersen JP. Determination of the ATP Affinity of the Sarcoplasmic Reticulum Ca(2+)-ATPase by Competitive Inhibition of [γ-(32)P]TNP-8N3-ATP Photolabeling. Methods Mol Biol 2016; 1377:233-59. [PMID: 26695037 DOI: 10.1007/978-1-4939-3179-8_22] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The photoactivation of aryl azides is commonly employed as a means to covalently attach cross-linking and labeling reagents to proteins, facilitated by the high reactivity of the resultant aryl nitrenes with amino groups present in the protein side chains. We have developed a simple and reliable assay for the determination of the ATP binding affinity of native or recombinant sarcoplasmic reticulum Ca(2+)-ATPase, taking advantage of the specific photolabeling of Lys(492) in the Ca(2+)-ATPase by [γ-(32)P]2',3'-O-(2,4,6-trinitrophenyl)-8-azido-adenosine 5'-triphosphate ([γ-(32)P]TNP-8N3-ATP) and the competitive inhibition by ATP of the photolabeling reaction. The method allows determination of the ATP affinity of Ca(2+)-ATPase mutants expressed in mammalian cell culture in amounts too minute for conventional equilibrium binding studies. Here, we describe the synthesis and purification of the [γ-(32)P]TNP-8N3-ATP photolabel, as well as its application in ATP affinity measurements.
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Affiliation(s)
- Johannes D Clausen
- Department of Biomedicine, Aarhus University, Ole Worms Allé 4, Building 1160, 8000, Aarhus C, Denmark.
| | - David B McIntosh
- Institute of Infectious Diseases and Molecular Medicine, Division of Chemical Pathology, Faculty of Health Sciences, University of Cape Town, Observatory, Cape Town, South Africa
| | - David G Woolley
- Institute of Infectious Diseases and Molecular Medicine, Division of Chemical Pathology, Faculty of Health Sciences, University of Cape Town, Observatory, Cape Town, South Africa
| | - Jens Peter Andersen
- Department of Biomedicine, Aarhus University, Ole Worms Allé 4, Building 1160, 8000, Aarhus C, Denmark
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7
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Middleton DA, Fedosova NU, Esmann M. Long-Range Effects of Na(+) Binding in Na,K-ATPase Reported by ATP. Biochemistry 2015; 54:7041-7. [PMID: 26538123 DOI: 10.1021/acs.biochem.5b00893] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
This paper addresses the question of long-range interactions between the intramembranous cation binding sites and the cytoplasmic nucleotide binding site of the ubiquitous ion-transporting Na,K-ATPase using (13)C cross-polarization magic-angle spinning (CP-MAS) solid-state nuclear magnetic resonance. High-affinity ATP binding is induced by the presence of Na(+) as well as of Na-like substances such as Tris(+), and these ions are equally efficient promoters of nucleotide binding. CP-MAS analysis of bound ATP with Na,K-ATPase purified from pig kidney membranes reveals subtle differences in the nucleotide interactions within the nucleotide site depending on whether Na(+) or Tris(+) is used to induce binding. Differences in chemical shifts for ATP atoms C1' and C5' observed in the presence of Na(+) or Tris(+) suggest alterations in the residues surrounding the bound nucleotide, hydrogen bonding, and/or conformation of the ribose ring. This is taken as evidence of a long-distance communication between the Na(+)-filled ion sites in the membrane interior and the nucleotide binding site in the cytoplasmic domain and reflects the first conformational change ultimately leading to phosphorylation of the enzyme. Stopped-flow fluorescence measurements with the nucleotide analogue eosin show that the dissociation rate constant for eosin is larger in Tris(+) than in Na(+), giving kinetic evidence of the difference in structural effects of Na(+) and Tris(+). According to the recent crystal structure of the E1·AlF4(-)·ADP·3Na(+) form, the coupling between the ion binding sites and the nucleotide side is mediated by, among others, the M5 helix.
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Affiliation(s)
- David A Middleton
- Department of Chemistry, B8 Faraday Building, Lancaster University , Lancaster LA1 4YB, U.K
| | - Natalya U Fedosova
- Department of Biomedicine, University of Aarhus , Ole Worms Allé 6, DK-8000 Aarhus C, Denmark
| | - Mikael Esmann
- Department of Biomedicine, University of Aarhus , Ole Worms Allé 6, DK-8000 Aarhus C, Denmark
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8
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Feng M, Wang X, Wang C, Qin L, Wei Z, Wang Z. Antioxidant status and Na(+), K (+)-ATPase activity in freshwater fish Carassius auratus exposed to different combustion products of Nafion 117 membrane: an integrated biomarker approach. ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH INTERNATIONAL 2015; 22:3408-3418. [PMID: 25398218 DOI: 10.1007/s11356-014-3826-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/21/2013] [Accepted: 11/06/2014] [Indexed: 06/04/2023]
Abstract
Nafion 117 membrane (N117), an important polymer electrolyte membrane (PEM), has been widely applied in numerous chemical technologies. Its increasing production and utilization will inevitably lead to the problem of waste disposal, with incineration as an important method. However, toxicity data of its combustion products on aquatic organisms have been seldom reported. The present study was therefore conducted to investigate the antioxidant response and Na(+), K(+)-ATPase activity in liver of Carassius auratus exposed to different combustion products of N117 for 5, 15, and 30 days. The concentrations of fluorine ion (F(-)) in the aquaria among the exposure durations were analyzed using the ion chromatography system. The results showed that these treatments have the capability to induce oxidative stress and suppress Na(+), K(+)-ATPase activity, as indicated by some significant alterations on these measured toxicity end-points in fish liver. According to the integrated biomarker response (IBR) index, the toxicity intensity of these experimental treatments was tentatively ranked. Taken together, these observations provided some preliminary data on the potential toxicity of the combustion products of N117 on aquatic organisms and could fill the information gaps in the toxicity database of the current-use PEM.
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Affiliation(s)
- Mingbao Feng
- State Key Laboratory of Pollution Control and Resources Reuse, School of the Environment, Nanjing University, Jiangsu, Nanjing, 210046, People's Republic of China
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9
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Abstract
1. This is a concise review of the field of ion pumping from the perspective of the authors. 2. The period covered spans the discovery of Na(+) and K(+) concentration gradients across animal cell membranes by Carl Schmidt in the 1850s, through the isolation of the Na(+) /K(+) -ATPase by Skou in 1957 (for which he was awarded the 1997 Nobel Prize in Chemistry), to the publication of the first crystal structure of the enzyme in 2007 and beyond. 3. Contributions of the authors' research group to the resolution of the questions of the mechanism of the allosteric role of ATP within the Na(+) /K(+) -ATPase reaction cycle and how protomeric versus diprotomeric states of the enzyme influence its kinetics are discussed within the context of the research field. 4. The results obtained indicate that the Na(+) /K(+) -ATPase has a single ATP binding site, which can be catalytic or allosteric in different parts of the enzyme's reaction cycle. 5. The long-running controversy over whether P-type ATPases function as protomers or diprotomers can be resolved in the case of the Na(+) /K(+) -ATPase by an ATP-induced dissociation of (αβ)(2) diprotomers into separate αβ protomers. 6. Kinetic data suggest that protein-protein interactions between the two αβ protomers within an (αβ)(2) diprotomer result in a much lower enzymatic turnover (i.e. a lower gear) when only one of the α-subunits of the diprotomer has bound ATP. The inactive αβ protomer within the diprotomer can be thought of as causing a drag on the active protomer.
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Affiliation(s)
- Ronald J Clarke
- School of Chemistry, University of Sydney, New South Wales, Australia.
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10
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Abstract
Chemical kinetics underwent a revolution in the 1950–60s with the development by Manfred Eigen of relaxation kinetic techniques and theory for the analysis of the results obtained. The techniques he introduced extended the time scale of measurable reactions into the microsecond range and beyond. Since then, computing power has increased astronomically. Some of the approximations traditionally used in the analysis of relaxation kinetic data to reduce mathematical complexity are, therefore, now no longer a necessity. Numerical integration of coupled series of differential rate equations can be performed in seconds or less on desk-top computers. In research on the mechanism of the Na+,K+-ATPase, it has been found that traditional approaches to relaxation kinetic data can sometimes lead to erroneous conclusions or to an incomplete description of the mechanism. Therefore, one needs to be flexible in one’s approach to kinetic data analysis and carefully consider the validity of any approximations used.
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11
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Middleton DA, Hughes E, Fedosova NU, Esmann M. Solid-state NMR studies of adenosine 5'-triphosphate freeze-trapped in the nucleotide site of Na,K-ATPase. Chembiochem 2009; 10:1789-92. [PMID: 19565594 DOI: 10.1002/cbic.200900167] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- David A Middleton
- School of Biological Sciences, University of Liverpool, Crown Street, Liverpool L69 7ZB, UK.
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12
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Pilotelle-Bunner A, Matthews JM, Cornelius F, Apell HJ, Sebban P, Clarke RJ. ATP binding equilibria of the Na(+),K(+)-ATPase. Biochemistry 2009; 47:13103-14. [PMID: 19006328 DOI: 10.1021/bi801593g] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Reported values of the dissociation constant, K(d), of ATP with the E1 conformation of the Na(+),K(+)-ATPase fall in two distinct ranges depending on how it is measured. Equilibrium binding studies yield values of 0.1-0.6 microM, whereas presteady-state kinetic studies yield values of 3-14 microM. It is unacceptable that K(d) varies with the experimental method of its determination. Using simulations of the expected equilibrium behavior for different binding models based on thermodynamic data obtained from isothermal titration calorimetry we show that this apparent discrepancy can be explained in part by the presence in presteady-state kinetic studies of excess Mg(2+) ions, which compete with the enzyme for the available ATP. Another important contributing factor is an inaccurate assumption in the majority of presteady-state kinetic studies of a rapid relaxation of the ATP binding reaction on the time scale of the subsequent phosphorylation. However, these two factors alone are insufficient to explain the previously observed presteady-state kinetic behavior. In addition one must assume that there are two E1-ATP binding equilibria. Because crystal structures of P-type ATPases indicate only a single bound ATP per alpha-subunit, the only explanation consistent with both crystal structural and kinetic data is that the enzyme exists as an (alphabeta)(2) diprotomer, with protein-protein interactions between adjacent alpha-subunits producing two ATP affinities. We propose that in equilibrium measurements the measured K(d) is due to binding of ATP to one alpha-subunit, whereas in presteady-state kinetic studies, the measured apparent K(d) is due to the binding of ATP to both alpha-subunits within the diprotomer.
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13
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Mechanism of allosteric effects of ATP on the kinetics of P-type ATPases. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2009; 39:3-17. [PMID: 19225774 DOI: 10.1007/s00249-009-0407-3] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/25/2008] [Revised: 12/14/2008] [Accepted: 12/14/2008] [Indexed: 10/21/2022]
Abstract
The roles of allosteric effects of ATP and protein oligomerisation in the mechanisms of P-type ATPases belong to the most controversial and least well understood topics in the field. Recent crystal structural and kinetic data, however, now allow certain hypotheses to be definitely excluded and consistent hypotheses to be developed. The aim of this review is to critically discuss recent results and, in the light of them, to present a set of conclusions which could form the basis of future research. The major conclusions are: (1) at saturating ATP concentrations P-type ATPases function as monomeric enzymes, (2) the catalytic units of P-type ATPases only possess a single ATP binding site, (3) at non-saturating ATP concentrations P-type ATPases exist as diprotomeric (or higher oligomeric) complexes, (4) protein-protein interactions within a diprotomeric complex enhances the enzymes' ATP binding affinity, (5) ATP binding to both protomers within a diprotomeric complex causes it to dissociate into two separate monomers. The physiological role of protein-protein interactions within a diprotomer may be to enhance ATP binding affinity so as to scavenge ATP and maximize the ion pumping rate under hypoxic or anoxic conditions. For the first time a structural basis for the well-known ATP allosteric acceleration of the E2 --> E1 transition is presented. This is considered to be due to a minimization of steric hindrance between neighbouring protomers because of the ability of ATP to induce a compact conformation of the enzymes' cytoplasmic domains.
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14
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Glynn IM, Karlish SJ. Different approaches to the mechanism of the sodium pump. CIBA FOUNDATION SYMPOSIUM 2008:205-23. [PMID: 125188 DOI: 10.1002/9780470720134.ch12] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The way in which the sodium pump uses energy from the hydrolysis of ATP to perform osmotic and electrical work is not yet understood. We attempt to bring together the results of a number of different approaches to this problem. One approach has been to correlate biochemical changes and ionic fluxes, both when the pump operates normally and when it operates in various abnormal 'modes' in particular unphysiological conditions. A second approach has been to expose fragments of cell membrane to (gamma-32P)ATP and to study the properties of components of the membrane that become labelled. It is now clear that 32P can be transferred to the beta-carboxy group of an aspartyl residue in a pump polypeptide, but there is controversy about the interrelations of different forms of this polypeptide and its role, if any, in the normal functioning of the pump. A third approach has been to attempt to purify the pump and to determine the properties of the pure enzyme. It seems that the pump contains a polypeptide (molecular weight about 100,000), which bears the phosphorylation site, and a smaller glycopeptide, but there is disagreement about the molecular ratios. The results of these and other approaches cannot yet be fitted into a satisfactory model for the sodium pump, but we shall consider some of the problems involved in this task.
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15
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Conformational analysis of Na,K-ATPase in drug-protein complexes. JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY 2008; 91:167-74. [PMID: 18374596 DOI: 10.1016/j.jphotobiol.2008.01.013] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/14/2007] [Revised: 01/22/2008] [Accepted: 01/23/2008] [Indexed: 11/22/2022]
Abstract
This review reports the effects of several drugs such as AZT (anti-AIDS), cis-Pt (antitumor), aspirin (anti-inflammatory) and vitamin C (antioxidant) on the stability and conformation of Na,K-ATPase in vitro. Drug-enzyme binding was found to be via H-bonding to the polypeptide CO and C-N groups with two binding constants K(1(AZT))=5.30 (+/-2.1)x10(5)M(-1) and K(2(AZT))=9.80 (+/-2.9)x10(3)M(-1) for AZT and one binding constant K(cis)(-Pt)=1.93 (+/-1.2)x10(4)M(-1) for cis-Pt, K(aspirin)=6.45 (+/-2.5)x10(3)M(-1) and K(ascorbate)=1.04 (+/-0.5)x10(4)M(-1) for aspirin and ascorbic acid. The enzyme secondary structure was altered with major increase of alpha-helix from 19.9% (free protein) to 22-26% and reduction of beta-sheet from 25.6% (free protein) to 17-23% upon drug complexation indicating a partial stabilization of protein conformation. The order of induced stability is AZT>cis-Pt>ascorbate>aspirin.
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Abstract
The kinetics of the phosphorylation and subsequent conformational change of Na(+),K(+)-ATPase was investigated via the stopped-flow technique using the fluorescent label RH421 (pH 7.4, 24 degrees C). The enzyme was preequilibrated in buffer containing 130 mM NaCl to stabilize the E1(Na(+))(3) state. On mixing with ATP in the presence of Mg(2+), a fluorescence increase occurred, due to enzyme conversion into the E2P state. The fluorescence change accelerated with increasing ATP concentration until a saturating limit in the hundreds of micromolar range. The amplitude of the fluorescence change (DeltaF/F(0)) increased to 0.98 at 50 microM ATP. DeltaF/F(0) then decreased to 0.82 at 500 microM. The decrease was attributed to an ATP-induced allosteric acceleration of the dephosphorylation reaction. The ATP concentration dependence of the time course and the amplitude of the fluorescence change could not be explained by either a one-site monomeric enzyme model or by a two-pool model. All of the data could be explained by an (alphabeta)(2) dimeric model, in which the enzyme cycles at a low rate with ATP hydrolysis by one alpha-subunit or at a high rate with ATP hydrolysis by both alpha-subunits. Thus, we propose a two-gear bicyclic model to replace the classical monomeric Albers-Post model for kidney Na(+),K(+)-ATPase.
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Affiliation(s)
- Ronald J Clarke
- School of Chemistry, University of Sydney, Sydney, Australia.
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17
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Clarke RJ, Apell HJ, Kong BY. Allosteric effect of ATP on Na(+),K(+)-ATPase conformational kinetics. Biochemistry 2007; 46:7034-44. [PMID: 17511477 DOI: 10.1021/bi700619s] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The kinetics of the E2 --> E1 conformational change of unphosphorylated Na+,K+-ATPase was investigated via the stopped-flow technique using the fluorescent label RH421 (pH 7.4, 24 degrees C). The enzyme was pre-equilibrated in a solution containing 25 mM histidine and 0.1 mM EDTA to stabilize the E2 conformation. When rabbit enzyme was mixed with 130 mM NaCl alone or with 130 mM NaCl and varying concentrations of Na2ATP simultaneously, a fluorescence decrease was observed. In the absence of ATP, the fluorescence decrease followed a biexponential time course, but at ATP concentrations after mixing of >or=50 microM, the fluorescence transient could be adequately fitted by a single exponential. On the basis of the agreement between theoretical simulations and experimental traces, we propose that in the absence of bound ATP the conformational transition occurs as a two step reversible process within a protein dimer, E2:E2 --> E2:E1 --> E1:E1. In the presence of 130 mM NaCl, the sum of the forward and backward rate constants for the E2:E2 --> E2:E1 and E2:E1 --> E1:E1 transitions were found to be 10.4 (+/-1.0) and 0.49 (+/-0.02) s-1, respectively. At saturating concentrations of ATP, however, the transition occurs in a single reversible step with the sum of its forward and backward rate constants equal to 35.2 (+/-0.3) s-1. It was found that ATP acting at a high affinity site (Kd approximately 0.25 microM), stimulated the reverse reaction, E1ATP --> E2ATP, in addition to its known allosteric low affinity (Kd approximately 71 microM) stimulation of the forward reaction, E2ATP --> E1ATP.
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Affiliation(s)
- Ronald J Clarke
- School of Chemistry, University of Sydney, Sydney, NSW 2006, Australia, and Faculty of Biology, University of Konstanz, D-78435 Konstanz, Germany.
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18
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Middleton DA, Jakobsen LO, Esmann M. Detection of nucleotide binding to Na,K-ATPase in an aqueous membrane suspension by 13C cross-polarization magic-angle spinning NMR spectroscopy. FEBS Lett 2006; 580:6685-9. [PMID: 17126327 DOI: 10.1016/j.febslet.2006.11.026] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2006] [Revised: 11/07/2006] [Accepted: 11/08/2006] [Indexed: 11/18/2022]
Abstract
Binding of uniformly (13)C labelled ATP to Na,K-ATPase was studied by (13)C cross-polarization magic-angle spinning (CP-MAS) NMR. In the presence of 30 mM Na(+) , and with sample- and time-averaging, NMR spectra obtained at 4 degrees C exhibited several resonances for the bound nucleotide. Chemical shifts suggested that site-specific changes in the micro-environment or conformation of the nucleotide occurred in the high affinity binding site. These experiments permit further studies of nucleotide dynamics, structure and binding under physiologically relevant conditions.
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Affiliation(s)
- David A Middleton
- School of Biological Sciences, University of Liverpool, Crown Street, Liverpool L79 7ZB, United Kingdom
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19
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Ward DG, Taylor M, Lilley KS, Cavieres JD. TNP-8N3-ADP photoaffinity labeling of two Na,K-ATPase sequences under separate Na+ plus K+ control. Biochemistry 2006; 45:3460-71. [PMID: 16519541 DOI: 10.1021/bi051927k] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
ATP has high- and low-affinity effects on the sodium pump and other P-type ATPases. We have approached this question by using 2',3'-O-(trinitrophenyl)-8-azidoadenosine 5'-diphosphate (TNP-8N(3)-ADP) to photoinactivate and label Na,K-ATPase, both in its native state and after covalent FITC block of its high-affinity ATP site. With the native enzyme, the photoinactivation rate constant increases hyperbolically with a K(D(TNP-8N)3(-)(ADP)) of 0.11 microM; TNP-ATP and ATP protect the site with high affinities. The inactivation does not require Na(+), but K(+) inhibits with a K(K)' of 12 microM; Na(+) reverses this effect, with a K(Na) of 0.17 mM. This pattern suggests that Na(+) and K(+) are binding at sites in their "intracellular" conformation. It was known that FITC did not abolish the reverse phosphorylation by P(i), or the K(+)-phosphatase activity, and that TNP-8N(3)-ADP could subsequently photoinactivate the latter with >100-fold lower affinity; in that case, the cation sites acted as if facing outward [Ward, D. G., and Cavieres, J. D. (1998) J. Biol. Chem. 273, 14277-14284, 33759-33765]. Native and FITC-modified enzymes have now been photolabeled with TNP-8N(3)-[alpha-(32)P]ADP and alpha-chain soluble tryptic peptides separated by reverse-phase HPLC. With native Na,K-ATPase, three labeled peaks lead to the unique sequence alpha-(470)Ile-Val-Glu-Ile-Pro-Phe-Asn-Ser-Thr-Asn-X-Tyr-Gln-Leu-Ser-Ile-His-Lys(487), the dropped residue being alphaLys480. With the FITC enzyme, instead, two independent labeling and purification cycles return the sequence alpha-(721)Ala-Asp-Ile-Gly-Val-Ala-Met-Gly-Ile-Ala-Gly-Ser-Asp-Val-Ser-Lys(736). These results suggest that Na,K-ATPase also has a low-affinity nucleotide binding region, one that is under distinctive allosteric control by Na(+) and K(+). Moreover, the cation effects seem compatible with a slow, passive Na(+)/K(+) carrier behavior of the FITC-modified sodium pump.
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Affiliation(s)
- Douglas G Ward
- Transport ATPase Laboratory, Department of Cell Physiology and Pharmacology, Faculty of Medicine and Biological Sciences, University of Leicester, Leicester LE1 9HN, United Kingdom
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20
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Abstract
The identification of the sodium potassium pump as a Na+, K+-ATPase is described.
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Affiliation(s)
- Jens Chr Skou
- Department of Biophysics, University of Aarhus, Ole Worms Allé 185, 8000 Aarhus C, DK, Denmark
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21
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Patzelt-Wenczler R, Schoner W. Evidence for two different reactive sulfhydryl groups in the ATP-binding sites of (Na+ + K+)-ATPase. EUROPEAN JOURNAL OF BIOCHEMISTRY 2005; 114:79-87. [PMID: 6260491 DOI: 10.1111/j.1432-1033.1981.tb06175.x] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
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22
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Becker S, Schneider H, Scheiner-Bobis G. The highly conserved extracellular peptide, DSYG(893-896), is a critical structure for sodium pump function. ACTA ACUST UNITED AC 2004; 271:3821-31. [PMID: 15373828 DOI: 10.1111/j.1432-1033.2004.04305.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
The peptide sequence DSYG(893-896) of the sheep sodium pump alpha 1 subunit is highly conserved among all K(+)-transporting P-type ATPases. To obtain information about its function, single mutations were introduced and the mutants were expressed in yeast and analysed for enzymatic activity, ion recognition, and alpha/beta subunit interactions. Mutants of Ser894 or Tyr895 were all active. Conservative phenylalanine and tryptophan mutants of Tyr895 displayed properties that were similar to the properties of the wild-type enzyme. Replacement of the same amino acid by cysteine, however, produced heat-sensitive enzymes, indicating that the aromatic group contributes to the stability of the enzyme. Mutants of the neighbouring Ser894 recognized K(+) with altered apparent affinities. Thus, the Ser894-->Asp mutant displayed a threefold higher apparent affinity for K(+) (EC(50) = 1.4 +/- 0.06 mm) than the wild-type enzyme (EC(50) = 3.8 +/- 0.33 mm). In contrast, the mutant Ser894-->Ile had an almost sixfold lower apparent affinity for K(+) (EC(50) = 21.95 +/- 1.41 mm). Mutation of Asp893 or Gly896 produced inactive proteins. When an anti-beta 1 subunit immunoglobulin was used to co-immunoprecipitate the alpha 1 subunit, neither the Gly896-->Arg nor the Gly896-->Ile mutant could be visualized by subsequent probing with an anti-alpha 1 subunit immunoglobulin. On the other hand, co-immunoprecipitation was obtained with the inactive Asp893-->Arg and Asp893-->Glu mutants. Thus, it might be that Asp893 is involved in enzyme conformational transitions required for ATP hydrolysis and/or ion translocation. The results obtained here demonstrate the importance of the highly conserved peptide DSYG(893-896) for the function of alpha/beta heterodimeric P-type ATPases.
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Affiliation(s)
- Susanne Becker
- Institut für Biochemie und Endokrinologie, Fachbereich Veterinärmedizin, Justus-Liebig-Universität Giessen, D-35392 Giessen, Germany
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23
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Abstract
Correlation between the Na,K-ATPase affinity to ADP and the cation (its nature and concentration) present in the medium was investigated. In buffer with low ionic strength (I approximately 1 mM) high-affinity ADP binding was not observed, while a stepwise increase in the concentrations of added cation (Na(+), Tris(+), imidazole(+), N-methylglucamine(+), choline(+)) induced an increase in the ADP affinity. The effect was fully saturated at 30-50 mM for all of the cations tested. The maximal affinity for ADP was slightly higher in the presence of Na(+), Tris(+), or imidazole(+) than in the presence of N-methylglucamine(+) or choline(+) (equilibrium dissociation constant K(d) 0.2-0.3 vs 0.7 microM). The ADP dissociation rates from its complex with enzyme in the presence of Na(+) or Tris(+) were similar, implying identity of the nucleotide-binding enzyme conformations, which therefore are assigned to E(1). The ability to compete with K(+) clearly distinguished Na(+) from other cations, which speaks against the sole involvement of the transport sites in the induction of the ADP-binding E(1) conformation. Since the cations are similar in their mode of induction of the high ADP affinity but they demonstrate a pronounced difference in ability to compete with K(+), their effects cannot be combined within any scheme with only one type of cation-binding sites. We suggest that the high affinity toward nucleotide is induced by cation interactions within the protein or lipid and that these nucleotide-domain-related sites coexist with the transport sites, which bind only Na(+) or K(+).
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Affiliation(s)
- Natalya U Fedosova
- Department of Biophysics, University of Aarhus, Ole Worms Allé 185, DK-8000 Aarhus C, Denmark.
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24
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Peluffo RD. Effect of ADP on Na(+)-Na(+) exchange reaction kinetics of Na,K-ATPase. Biophys J 2004; 87:883-98. [PMID: 15298896 PMCID: PMC1304497 DOI: 10.1529/biophysj.103.030643] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2003] [Accepted: 05/05/2004] [Indexed: 11/18/2022] Open
Abstract
The whole-cell voltage-clamp technique was used in rat cardiac myocytes to investigate the kinetics of ADP binding to phosphorylated states of Na,K-ATPase and its effects on presteady-state Na(+)-dependent charge movements by this enzyme. Ouabain-sensitive transient currents generated by Na,K-ATPase functioning in electroneutral Na(+)-Na(+) exchange mode were measured at 23 degrees C with pipette ADP concentrations ([ADP]) of up to 4.3 mM and extracellular Na(+) concentrations ([Na](o)) between 36 and 145 mM at membrane potentials (V(M)) from -160 to +80 mV. Analysis of charge-V(M) curves showed that the midpoint potential of charge distribution was shifted toward more positive V(M) both by increasing [ADP] at constant Na(+)(o) and by increasing [Na](o) at constant ADP. The total quantity of mobile charge, on the other hand, was found to be independent of changes in [ADP] or [Na](o). The presence of ADP increased the apparent rate constant for current relaxation at hyperpolarizing V(M) but decreased it at depolarizing V(M) as compared to control (no added ADP), an indication that ADP binding facilitates backward reaction steps during Na(+)-Na(+) exchange while slowing forward reactions. Data analysis using a pseudo three-state model yielded an apparent K(d) of approximately 6 mM for ADP binding to and release from the Na,K-ATPase phosphoenzyme; a value of 130 s(-1) for k(2), a rate constant that groups Na(+) deocclusion/release and the enzyme conformational transition E(1) approximately P --> E(2)-P; a value of 162 s(-1)M(-1) for k(-2), a lumped second-order V(M)-independent rate constant describing the reverse reactions; and a Hill coefficient of approximately 1 for Na(+)(o) binding to E(2)-P. The results are consistent with electroneutral release of ADP before Na(+) is deoccluded and released through an ion well. The same approach can be used to study additional charge-moving reactions and associated electrically silent steps of the Na,K-pump and other transporters.
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Affiliation(s)
- R Daniel Peluffo
- Department of Pharmacology and Physiology, University of Medicine and Dentistry of New Jersey, New Jersey Medical School, Newark, New Jersey 07101, USA.
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25
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Esmann M, Fedosova NU. Anion interactions with Na,K-ATPase: simultaneous binding of nitrate and eosin. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2004; 33:683-90. [PMID: 15565441 DOI: 10.1007/s00249-004-0411-6] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/12/2003] [Revised: 04/02/2004] [Accepted: 04/05/2004] [Indexed: 11/27/2022]
Abstract
Nucleotide binding affinity to Na,K-ATPase is reduced by a number of anions such as nitrate and perchlorate in comparison with affinity in the presence of chloride (all with sodium as the cation). The reduction correlates with the position of these anions in the Hofmeister series. Transient kinetic experiments using the fluorescent dye eosin-which binds to the nucleotide site of the Na,K-ATPase-show that simultaneous anion binding, exemplified with nitrate, and eosin binding is possible. The effect of nitrate on eosin binding is reflected in a decreased binding-rate constant and an increased dissociation rate constant, leading to a decreased equilibrium binding constant for eosin. Since eosin binding is analogous with nucleotide binding to Na,K-ATPase, the results suggest the simultaneous presence of nucleotide and anion binding sites.
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Affiliation(s)
- Mikael Esmann
- Department of Biophysics, University of Aarhus, Ole Worms Allé 185, 8000, Aarhus, Denmark.
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26
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Apell HJ. Structure-function relationship in P-type ATPases--a biophysical approach. Rev Physiol Biochem Pharmacol 2004; 150:1-35. [PMID: 12811587 DOI: 10.1007/s10254-003-0018-9] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
P-type ATPases are a large family of membrane proteins that perform active ion transport across biological membranes. In these proteins the energy-providing ATP hydrolysis is coupled to ion-transport that builds up or maintains the electrochemical potential gradients of one or two ion species across the membrane. P-type ATPases are found in virtually all eukaryotic cells and also in bacteria, and they are transporters of a broad variety of ions. So far, a crystal structure with atomic resolution is available only for one species, the SR Ca-ATPase. However, biochemical and biophysical studies provide an abundance of details on the function of this class of ion pumps. The aim of this review is to summarize the results of preferentially biophysical investigations of the three best-studied ion pumps, the Na,K-ATPase, the gastric H,K-ATPase, and the SR Ca-ATPase, and to compare functional properties to recent structural insights with the aim of contributing to the understanding of their structure-function relationship.
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Affiliation(s)
- H-J Apell
- Department of Biology, University of Konstanz, Fach M635, 78457 Konstanz, Germany.
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27
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de Lima Santos H, Ciancaglini P. Kinetic characterization of Na,K-ATPase from rabbit outer renal medulla: properties of the (alpha beta)(2) dimer. Comp Biochem Physiol B Biochem Mol Biol 2003; 135:539-49. [PMID: 12831774 DOI: 10.1016/s1096-4959(03)00139-8] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
We describe and compare the main kinetic characteristics of the (alpha beta)(2) form of rabbit kidney Na,K-ATPase. The dependence of ATPase activity on ATP concentration revealed high (K(0.5)=4 microM) and low (K(0.5)=1.4 mM) affinity sites for ATP, exhibiting negative cooperativity and a specific activity of approximately 700 U/mg. For p-nitrophenylphosphate (PNPP) as substrate, a single saturation curve was found, with a smaller apparent affinity of the enzyme for this substrate (K(0.5)=0.5 mM) and a lower hydrolysis rate (V(M)=42 U/mg). Stimulation of ATPase activity by K(+) (K(0.5)=0.63 mM), Na(+) (K(0.5)=11 mM) and Mg(2+) (K(0.5)=0.60 mM) all showed V(M)'s of approximately 600 U/mg and negative cooperativity. K(+) (K(0.5)=0.69 mM) and Mg(2+) (K(0.5)=0.57 mM) also stimulated PNPPase activity of the (alpha beta)(2) form. Ouabain (K(0.5)=0.01 microM and K(0.5)=0.1 mM) and orthovanadate (K(0.5)=0.06 microM) completely inhibited the ATPase activity of the (alpha beta)(2) form. The kinetic characteristics obtained constitute reference values for diprotomeric (alpha beta)(2)-units of Na,K-ATPase, thus contributing to a better understanding of the biochemical mechanisms of the enzyme.
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Affiliation(s)
- Hérica de Lima Santos
- Departamento de Química, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto-FFCLRP, Universidade de São Paulo-USP, Av. Bandeirantes 3900, SP, 14040-901, Ribeirão Preto, Brazil
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28
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Ward DG, Cavieres JD. Inactivation of Na,K-ATPase following Co(NH3)4ATP binding at a low affinity site in the protomeric enzyme unit. J Biol Chem 2003; 278:14688-97. [PMID: 12591931 DOI: 10.1074/jbc.m211128200] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The Na(+)-dependent or E1 stages of the Na,K-ATPase reaction require a few micromolar ATP, but submillimolar concentrations are needed to accelerate the K(+)-dependent or E2 half of the cycle. Here we use Co(NH(3))(4)ATP as a tool to study ATP sites in Na,K-ATPase. The analogue inactivates the K(+) phosphatase activity (an E2 partial reaction) and the Na,K-ATPase activity in parallel, whereas ATP-[(3)H]ADP exchange (an E1 reaction) is affected less or not at all. Although the inactivation occurs as a consequence of low affinity Co(NH(3))(4)ATP binding (K(D) approximately 0.4-0.6 mm), we can also measure high affinity equilibrium binding of Co(NH(3))(4)[(3)H]ATP (K(D) = 0.1 micro m) to the native enzyme. Crucially, we find that covalent enzyme modification with fluorescein isothiocyanate (which blocks E1 reactions) causes little or no effect on the affinity of the binding step preceding Co(NH(3))(4)ATP inactivation and only a 20% decrease in maximal inactivation rate. This suggests that fluorescein isothiocyanate and Co(NH(3))(4)ATP bind within different enzyme pockets. The Co(NH(3))(4)ATP enzyme was solubilized with C(12)E(8) to a homogeneous population of alphabeta protomers, as verified by analytical ultracentrifugation; the solubilization did not increase the Na,K-ATPase activity of the Co(NH(3))(4)ATP enzyme with respect to parallel controls. This was contrary to the expectation for a hypothetical (alphabeta)(2) membrane dimer with a single ATP site per protomer, with or without fast dimer/protomer equilibrium in detergent solution. Besides, the solubilized alphabeta protomer could be directly inactivated by Co(NH(3))(4)ATP, to less than 10% of the control Na,K-ATPase activity. This suggests that the inactivation must follow Co(NH(3))(4)ATP binding at a low affinity site in every protomeric unit, thus still allowing ATP and ADP access to phosphorylation and high affinity ATP sites.
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Affiliation(s)
- Douglas G Ward
- Transport ATPase Laboratory, Department of Cell Physiology and Pharmacology, Faculty of Medicine and Biological Sciences, University of Leicester, Leicester LE1 9HN, United Kingdom
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29
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Fedosova NU, Champeil P, Esmann M. Rapid filtration analysis of nucleotide binding to Na,K-ATPase. Biochemistry 2003; 42:3536-43. [PMID: 12653558 DOI: 10.1021/bi0268302] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Transient kinetic analysis of nucleotide binding to pig kidney Na,K-ATPase using a rapid filtration technique shows that the interaction between nucleotide and enzyme apparently follows simple first-order kinetics both for ATP in the absence of Mg(2+) and for ADP in the presence or absence of Mg(2+). Rapid filtration experiments with Na,K-ATPase membrane sheets may nevertheless suffer from a problem of accessibility for a fraction of the ATPase binding sites. Accordingly, we estimate from these data that for ATP binding in the absence of Mg(2+) and the presence of 35 mM Na(+) at pH 7.0 at 20 degrees C, the bimolecular binding rate constant k(on) is about 30 microM(-1) x s(-1) and the dissociation rate constant k(off) is about 8 s(-1). In the presence of 10 mM Mg(2+), the binding rate constant is the same as that in the absence of Mg(2+). For ADP or MgADP the binding rate constant is about 20 microM(-1) x s(-1) and the dissociation rate constant is about 12 s(-1). Results of rapid-mixing stopped-flow experiments with the fluorescent dye eosin are also consistent with a one-step mechanism of binding of eosin to the ATPase nucleotide site. The implication of these results is that nucleotide binding to Na,K-ATPase both in the absence and presence of Mg(2+) appears to be a single-step event, at least on the time scale accessible in these experiments.
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Affiliation(s)
- Natalya U Fedosova
- Department of Biophysics, University of Aarhus, Ole Worms Allé 185, DK-8000 Aarhus C, Denmark
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30
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Neault JF, Malonga H, Diamantoglou S, Carpentier R, Stepp RL, Tajmir-Riahi HA. Secondary structural analysis of the Na(+),K(+)-ATPase and its Na(+) (E(1)) and K(+) (E(2)) complexes by FTIR spectroscopy. J Biomol Struct Dyn 2002; 20:173-8. [PMID: 12354069 DOI: 10.1080/07391102.2002.10506833] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
Abstract
The Na(+),K(+)-ATPase is an integral membrane protein which transports sodium and potassium cations against an electrochemical gradient. The transport of Na(+) and K(+) ions is presumably connected to an oscillation of the enzyme between the two conformational states, the E(1) (Na(+)) and the E(2) (K(+)) conformations. The E(1) and E(2) states have different affinities for ligand interaction. However, the determination of the secondary structure of this enzyme in its sodium and potassium forms has been the subject of much controversy. This study was designed to provide a quantitative analysis of the secondary structure of the Na(+),K(+)-ATPase in its sodium (E(1)) and potassium (E(2)) states in both H(2)O and D(2)O solutions at physiological pH, using Fourier transform infrared (FTIR) with its self-deconvolution and second derivative resolution enhancement methods, as well as curve-fitting procedures. Spectroscopic analysis showed that the secondary structure of the sodium salt of the Na(+),K(+)-ATPase in H(2)O solution contains alpha-helix 19.8+/-1%, beta-sheet 25.6+/-1%, turn 9.1+/-1%, and beta-anti 7.5+/-1%, whereas in D(2)O solution, the enzyme shows alpha-helix 16.8+/-1%, beta-sheet 24.5+/-1.5%, turn 10.9+/-1%, beta-anti 9.8+/-1%, and random coil 38.0+/-2%. Similarly, the potassium salt in H(2)O solution contains alpha-helix 16.6+/-1%, beta-sheet 26.4+/-1.5%, turn 8.9+/-1%, and beta-anti 8.1+/-1%, while in D(2)O solution it shows alpha-helix 16.2+/-1%, beta-sheet 24.5+/-1.5%, turn 10.3+/-1%, beta-anti 9.0+/-1%, and random coil 40+/-2%. Thus the main differences for the sodium and potassium forms of the Na(+),K(+)-ATPase are alpha-helix 3.2% in H(2)O and 0.6% in D(2)O, beta-sheet (pleated and anti) 1.5% in H(2)O and random structure 2% (D(2)O), while for other minor components (turn structure), the differences are less than 1%.
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Affiliation(s)
- J F Neault
- Groupe de Recherche en Energie et Information Biomoléculaires, Université du Québec Trois-Rivières, Canada
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31
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Abstract
This article gives a history of the evidence (a) that animal cell membranes contain pumps that expel sodium ions in exchange for potassium ions; (b) that the pump derives energy from the hydrolysis of ATP; (c) that it is thermodynamically reversible-artificially steep transmembrane ion gradients make it run backward synthesizing ATP from ADP and orthophosphate; (d) that its mechanism is a ping-pong one, in which phosphorylation of the pump by ATP is associated with an efflux of three sodium ions, and hydrolysis of the phosphoenzyme is associated with an influx of two potassium ions; (e) that each half of the working cycle involves both the transfer of a phosphate group and a conformational change-the phosphate transfer being associated with the occlusion of ions bound at one surface and the conformational change releasing the occluded ions at the opposite surface.
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Affiliation(s)
- Ian M Glynn
- Trinity College, Cambridge CB2 1TQ, England.
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32
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Gonzalez-Lebrero RM, Kaufman SB, Garrahan PJ, Rossi RC. The Occlusion of Rb(+) in the Na(+)/K(+)-ATPase. II. The effects of Rb(+), Na(+), Mg2(+), or ATP on the equilibrium between free and occluded Rb(+). J Biol Chem 2002; 277:5922-8. [PMID: 11739378 DOI: 10.1074/jbc.m105887200] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We used the direct route of occlusion to study the equilibrium between free and occluded Rb(+) in the Na(+)/K(+)-ATPase, in media with different concentrations of ATP, Mg(2+), or Na(+). An empirical equation, with the restrictions imposed by the stoichiometry of ligand binding was fitted to the data. This allowed us to identify which states of the enzyme were present in each condition and to work out the schemes and equations that describe the equilibria between the ATPase, Rb(+), and ATP, Mg(2+), or Na(+). These equations were fitted to the corresponding experimental data to find out the values of the equilibrium constants of the reactions connecting the different enzyme states. The three ligands decreased the apparent affinity for Rb(+) occlusion without affecting the occlusion capacity. With [ATP] tending to infinity, enzyme species with one or two occluded Rb(+) seem to be present and full occlusion seems to occur in enzymes saturated with the nucleotide. In contrast, when either [Mg(2+)] or [Na(+)] tended to infinity no occlusion was detectable. Both Mg(2+) and Na(+) are displaced by Rb(+) through a process that seems to need the binding and occlusion of two Rb(+), which suggests that in these conditions Rb(+) occlusion regains the stoichiometry of the physiological operation of the Na(+) pump.
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Affiliation(s)
- Rodolfo M Gonzalez-Lebrero
- Instituto de Quimica y Fisicoquimica Biológicas and the Departamento de Quimica Biológica, Facultad de Farmacia y Bioquimica, Universidad de Buenos Aires, Junin 956, C1113AAD Buenos Aires, Argentina
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33
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Fedosova NU, Champeil P, Esmann M. Nucleotide Binding to Na,K-ATPase: The Role of Electrostatic Interactions. Biochemistry 2002; 41:1267-73. [PMID: 11802726 DOI: 10.1021/bi011887u] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The contribution of electrostatic forces to the interaction of Na,K-ATPase with adenine nucleotides was investigated by studying the effect of ionic strength on nucleotide binding. At pH 7.0 and 20 degrees C, there was a qualitative correlation between the equilibrium dissociation constant (K(d)) values for ATP, ADP, and MgADP and their total charges. All K(d) values increased with increasing ionic strength. According to the Debye-Hückel theory, this suggests that the nucleotide binding site and its ligands have "effective" charges of opposite signs. However, quantitative analysis of the dependence on ionic strength shows that the product of the effective electrostatic charges on the ligand and the binding site is the same for all nucleotides, and is therefore independent of the total charge of the nucleotide. The data suggest that association of nucleotides with Na,K-ATPase is governed by a partial charge rather than the total charge of the nucleotide. This charge, interacting with positive charges on the protein, is probably the one corresponding to the alpha-phosphate of the nucleotide. Dissociation rate constants measured in complementary transient kinetic experiments were 13 s(-1) for ATP and 27 s(-1) for ADP, independent of the ionic strength in the range 0.1-0.5 M. This implies similar association rate constants for the two nucleotides (about 40 x 10(6) M(-1) s(-1) at I = 0.1 M). The results suggest that long-range Coulombic forces, affecting association rates, are not the main contributors to the observed differences in affinities, and that local interactions, affecting dissociation rates, may play an even greater role.
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Affiliation(s)
- Natalya U Fedosova
- Department of Biophysics, University of Aarhus, Ole Worms Allé185, DK-8000 Aarhus C, Denmark.
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34
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Neault JF, Benkiran A, Malonga H, Tajmir-Riahi HA. The effects of anions on the solution structure of Na,K-ATPase. J Biomol Struct Dyn 2001; 19:95-102. [PMID: 11565855 DOI: 10.1080/07391102.2001.10506723] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
Abstract
Anions interact with protein to induce structural changes at ligand binding sites. The effects of anion complexation include structural stabilization and promote cation-protein interaction. This study was designed to examine the interaction of aspirin and ascorbate anions with the Na+, K+-dependent adenosine triphosphatase (Na,K-ATPase) in H2O and D2O solutions at physiological pH, using anion concentrations of 0.1 microM to 1 mM with final protein concentration of 0.5 to 1 mg/ml. Absorption spectra and Fourier transform infrared (FTIR) difference spectroscopy with its self-deconvolution, second derivative resolution enhancement and curve-fitting procedures were applied to characterize the anion binding mode, binding constant, and the protein secondary structure in the anion-ATPase complexes. Spectroscopic evidence showed that the anion interaction is mainly through the polypeptide C=O and C-N groups with minor perturbation of the lipid moiety. Evidence for this came from major spectral changes (intensity variations) of the protein amide I and amide II vibrations at 1651 and 1550 cm(-1). respectively. The anion-ATPase binding constants were K=6.45 x 10(3) M(-1) for aspirin and K=1.04 x 10(4) M(-1) for ascorbate complexes. The anion interaction resulted in major protein secondary structural changes from that of the alpha-helix 19.8%; beta-pleated sheet 25.6%; turn 9.1%; beta-antiparallel 7.5% and random 38% in the free Na,K-ATPase to that of the alpha-helix 24-26%; beta-pleated 17-18%; turn 8%; beta-antiparallel 5-3% and random 45.0% in the anion-ATPase complexes.
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Affiliation(s)
- J F Neault
- Department of Chemistry-Biology, University of Québec at Trois-Rivières, Canada
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35
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Cornelius F. Modulation of Na,K-ATPase and Na-ATPase activity by phospholipids and cholesterol. I. Steady-state kinetics. Biochemistry 2001; 40:8842-51. [PMID: 11467945 DOI: 10.1021/bi010541g] [Citation(s) in RCA: 142] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The effects of phospholipid acyl chain length (n(c)), degree of acyl chain saturation, and cholesterol on Na,K-ATPase reconstituted into liposomes of defined lipid composition are described. The optimal acyl chain length of monounsaturated phosphatidylcholine in the absence of cholesterol was found to be 22 but decreased to 18 in the presence of 40 mol % cholesterol. This indicates that the hydrophobic matching of the lipid bilayer and the transmembrane hydrophobic core of the membrane protein is a crucial parameter in supporting optimal Na,K-ATPase activity. In addition, the increased bilayer order induced by both cholesterol and saturated phospholipids could be important for the conformational mobility of the Na,K-ATPase changing the distribution of conformations. Lipid fluidity was important for several parameters of reconstitution, e.g., the amount of protein inserted and the orientation in the liposomes. The temperature dependence of the Na,K-ATPase as well of the Na-ATPase reactions depends both on phospholipid acyl chain length and on cholesterol. Cholesterol increased significantly both the enthalpy of activation and entropy of activation for Na,K-ATPase activity and Na-ATPase activity of Na,K-ATPase reconstituted with monounsaturated phospholipids. In the presence of cholesterol the free energy of activation was minimum at a lipid acyl chain length of 18, the same that supported maximum turnover. In the case of ATPase reconstituted without cholesterol, the minimum free energy of activation and the maximum turnover both shifted to longer acyl chain lengths of about 22.
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Affiliation(s)
- F Cornelius
- Department of Biophysics, University of Aarhus, DK-8000 Denmark.
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36
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Scheiner-Bobis G, Schreiber S. Glutamic acid 472 and lysine 480 of the sodium pump alpha 1 subunit are essential for activity. Their conservation in pyrophosphatases suggests their involvement in recognition of ATP phosphates. Biochemistry 1999; 38:9198-208. [PMID: 10413494 DOI: 10.1021/bi983010+] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
P-type ATPases such as the Na+,K+-ATPase (sodium pump) hydrolyze ATP to pump ions through biological membranes against their electrochemical gradients. The mechanisms that couple ATP hydrolysis to the vectorial ion transport are not yet understood, but unveiling structures that participate in ATP binding and in the formation of the ionophore might help to gain insight into this process. Looking at the alpha- and beta-phosphates of ATP as a pyrophosphate molecule, we found that peptides highly conserved among all soluble inorganic pyrophosphatases are also present in ion-transporting ATPases. Included therein are Glu48 and Lys56 of the Saccharomyces cerevisiae pyrophosphatase (SCE1-PPase) that are essential for the activity of this enzyme and have been shown in crystallographic analysis to interact with phosphate molecules. To test the hypothesis that equivalent amino acids are also essential for the activity of ion-transporting ATPases, Glu472 and Lys480 of the sodium pump alpha 1 subunit corresponding to Glu48 and Lys56 of SCE1-PPase were mutated to various amino acids. Mutants of the sodium pump alpha1 subunit were expressed in yeast and analyzed for their ATPase activity and their ability to bind ouabain in the presence of either ATP, Mg2+, and Na+ or phosphate and Mg2+. All four mutants investigated, Glu472Ala, Glu472Asp, Lys480Ala, and Lys480Arg, display only a fraction of the ATPase activity obtained with the wild-type enzyme. The same applies with respect to their ability to bind ouabain, where maximum ouabain binding to the mutants accounts for only about 10% of the binding obtained with the wild-type enzyme. On the basis of our results, we conclude that Glu472 and Lys480 are essential for the activity of the sodium pump. Their function is probably to arrest the alpha- and beta-phosphate groups of ATP in a proper position prior to hydrolysis of the gamma-phosphate group. The identification of these amino acids as essential components of the ATP-recognizing mechanism of the pump has resulted in a testable hypothesis for the initial interactions of the sodium pump, and possibly of other P-type ATPases, with ATP.
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Affiliation(s)
- G Scheiner-Bobis
- Institut für Biochemie und Endokrinologie, Fachbereich Veterinärmedizin, Justus-Liebig-Universität Giessen, Germany.
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37
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Tran CM, Farley RA. Catalytic activity of an isolated domain of Na,K-ATPase expressed in Escherichia coli. Biophys J 1999; 77:258-66. [PMID: 10388755 PMCID: PMC1300327 DOI: 10.1016/s0006-3495(99)76887-6] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Fusion proteins of glutathione-S-transferase and fragments from the large cytoplasmic domain of the sheep Na,K-ATPase alpha1-subunit were expressed in Escherichia coli. The Na,K-ATPase sequences begin at Ala345 and terminate at either Arg600 (DP600f), Thr610 (DP610f), Gly731 (DP731f), or Glu779 (DP779f). After affinity purification on glutathione-Sepharose, the fusion proteins were labeled with [alpha-32P]-2-N3-ATP, and incorporation of the radiolabel into the fusion proteins was measured by scintillation counting after sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Kd values of 220-290 microM for 2-N3-ATP binding to the fusion proteins were obtained from the photolabeling experiments. Approximately 1 mol of 2-N3-ATP was calculated to be incorporated per mole of fusion protein after correction for photochemical incorporation efficiency. Labeling of all of the fusion proteins by 25 microM 2-N3-ATP was reduced in the presence of MgATP, Na2ATP, MgCl2, 2',3'-O-(2,4, 6-trinitrophenyl)-ATP, and p-nitrophenylphosphate, and Ki values of 2-11 mM for Na2ATP, 0.2-5 mM for MgCl2, 0.1-5 mM for MgATP, and 20-300 microM for p-nitrophenylphosphate were calculated for these ligands. All of the fusion proteins catalyze the hydrolysis of p-nitrophenylphosphate. The reaction requires MgCl2 and is inhibited by inorganic phosphate, which is similar to the hydrolysis of p-nitrophenylphosphate by native Na,K-ATPase. Based on these observations, it appears that the soluble fragments from the large cytoplasmic domain of Na,K-ATPase expressed in bacterial cells are folded in an E2-like conformation and are likely to retain much of the native structure.
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Affiliation(s)
- C M Tran
- Department of Physiology and Biophysics, University of Southern California School of Medicine, Los Angeles, California 90033 USA
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38
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Ward DG, Cavieres JD. Affinity labeling of two nucleotide sites on Na,K-ATPase using 2'(3')-O-(2,4,6-trinitrophenyl)8-azidoadenosine 5'-[alpha-32P]diphosphate (TNP-8N3-[alpha-32P]ADP) as a photoactivatable probe. Label incorporation before and after blocking the high affinity ATP site with fluorescein isothiocyanate. J Biol Chem 1998; 273:33759-65. [PMID: 9837964 DOI: 10.1074/jbc.273.50.33759] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
ATP and its analogues act on the minimal functional unit of Na, K-ATPase, the alpha beta protomer, with high and low affinity effects. Fluorescein isothiocyanate (FITC) irreversibly blocks the high affinity, or catalytic, ATP site, and yet the surviving K+-phosphatase activity of soluble FITC-modified alphabeta protomers can be photoinactivated by 2'(3')-O-trinitrophenyl (TNP)-8N3-ADP (Ward, D. G., and Cavieres, J. D. (1998) J. Biol. Chem. 273, 14277-14284). We have now used TNP-8N3-[alpha-32P]ADP as a photoaffinity label for Na,K-ATPase. The native enzyme can be photolabeled at 5 microM TNP-8N3-[alpha-32P]ADP, and ATP or FITC treatment prevents labeling of the alpha chain. At 25 microM, however, TNP-8N3-[alpha-32P]ADP can be incorporated in the FITC-modified alpha chain, concurrently with the inactivation of the K+-phosphatase activity, to an extrapolated level of 0.5-1.2 mol of 32P-probe per mol of alpha chain. Photoinactivation and labeling are prevented by TNP-ADP, vanadate, or strophanthidin and are promoted by Na+ or Mg2+, but not K+. The cation effects suggest that the fluorescein-modified enzyme incorporates the TNP-8N3-[alpha-32P]ADP. Mg complex preferentially, and the free probe when in the E1 enzyme form and after occupation of a low-affinity Na+ site. Partial trypsinolysis reveals that the point of TNP-8N3-[alpha-32P]ADP attachment is on the C-terminal 58-kDa fragment of the FITC-modified alpha chain. The affinity labeling of the fluorescein enzyme by TNP-8N3-[alpha-32P]ADP endorses the view that two nucleotide sites can be occupied simultaneously in each alpha subunit of Na,K-ATPase.
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Affiliation(s)
- D G Ward
- Transport ATPase Laboratory, Department of Cell Physiology and Pharmacology, University of Leicester, Leicester LE1 9HN, United Kingdom
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39
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40
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Gatto C, Wang AX, Kaplan JH. The M4M5 cytoplasmic loop of the Na,K-ATPase, overexpressed in Escherichia coli, binds nucleoside triphosphates with the same selectivity as the intact native protein. J Biol Chem 1998; 273:10578-85. [PMID: 9553118 DOI: 10.1074/jbc.273.17.10578] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Escherichia coli was used to overexpress the large cytoplasmic loop of the rat Na,K-ATPase. A 1260-base DNA segment encoding Lys354-Lys774 of the rat alpha1-subunit was constructed via polymerase chain reaction. The polymerase chain reaction product was successfully subcloned into the expression vector pET-28 (Novagen), which produces an N-terminal 6-histidine-tagged fusion protein. The pET-28 vector containing rat alpha-loop, i.e. pAN, was used to transform calcium-competent E. coli BL21(DE3) cells, and positive clones were selected by kanamycin resistance. Bacterial cultures were grown, and protein synthesis was induced with isopropyl beta-D-thiogalactoside. Cells were harvested and lysed, revealing production of the His-tagged fusion protein ( approximately 46 kDa). The fusion protein was affinity-purified from other soluble cellular proteins via a Ni-NTA column, which routinely yielded approximately 20 mg of soluble His6-alpha-loop/L cell culture. The His6-alpha-loop retained significant native structure, as evidenced by the ability of ATP and ADP (but not AMP, CTP, GTP, or UTP) to protect against chemical modification by either fluorescein isothiocyanate or maleimidylanilinonapthalene sulfonic acid. More specifically, circular dichroism spectroscopy was used to estimate the secondary structure of the His6 loop, revealing an ordered folding composed of 23% alpha-helix, 23% antiparallel beta-sheet, 4% parallel beta-sheet, 19% beta-turn, and 32% random coil. The 6-histidine loop bound the fluorescent ATP analog trinitrophenyl-ATP with high affinity, as determined by measuring the fluorescence changes associated with binding. Affinities for ATP ( approximately 350 microM) and ADP ( approximately 550 microM) were determined by their ability to compete with and displace 2',3'-O-[2,4,6,-trinitrophenyl]-ATP. These nucleotide affinities are similar to those observed for the E2 conformation of the intact Na,K-ATPase.
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Affiliation(s)
- C Gatto
- Department of Biochemistry and Molecular Biology, Oregon Health Sciences University, Portland, Oregon 97201-3098, USA
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41
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Esmann M, Fedosova NU. Eosin as a probe for conformational transitions and nucleotide binding in Na,K-ATPase. Ann N Y Acad Sci 1997; 834:310-21. [PMID: 9405817 DOI: 10.1111/j.1749-6632.1997.tb52261.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Affiliation(s)
- M Esmann
- Department of Biophysics, University of Aarhus, Denmark.
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42
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Kane DJ, Fendler K, Grell E, Bamberg E, Taniguchi K, Froehlich JP, Clarke RJ. Stopped-flow kinetic investigations of conformational changes of pig kidney Na+,K+-ATPase. Biochemistry 1997; 36:13406-20. [PMID: 9341234 DOI: 10.1021/bi970598w] [Citation(s) in RCA: 50] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The kinetics of Na+-dependent partial reactions of the Na+,K+-ATPase were investigated via the stopped-flow technique using the fluorescent labels RH421 and BIPM. After the enzyme is mixed with MgATP, both labels give almost identical kinetic responses. Under the chosen experimental conditions two exponential time functions are necessary to fit the data. The dominant fast phase, 1/tau1 approximately 180 s-1 (saturating [ATP] and [Na+], pH 7.4 and 24 degrees C), is attributed to phosphorylation of the enzyme and a subsequent conformational change (E1ATP(Na+)3 --> E2P(Na+)3 + ADP). The rate of the phosphorylation reaction measured by the acid quenched-flow technique was 190 s-1 at 100 microM ATP, suggesting that phosphorylation controls the kinetics of the RH421 signal and that the conformational change is very fast (>/=600 s-1). The rate of the RH421 signal was optimal at pH 7.5. The Na+ concentration dependence of 1/tau1 showed half-saturation at a Na+ concentration of 8-10 mM with positive cooperativity involved in the occupation of the Na+ binding sites. The apparent dissociation constant of the high affinity ATP binding site determined from the ATP concentration dependence of 1/tau1 was 7.0 (+/-0.6) microM, while the apparent Kd for the low affinity site and the rate constant for the E2 to E1 conformational change evaluated in the absence of Mg2+ were 143 (+/-17) microM and </= 28 s-1. At RH421 concentrations in the micromolar range, a decrease in the value of 1/tau1 is observed. On the basis of rapid quenched-flow measurements, this inhibition can be attributed to a reaction step subsequent to phosphorylation. This accounts for previously observed kinetic discrepancies between RH421 and BIPM.
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Affiliation(s)
- D J Kane
- Department of Biophysical Chemistry, Max-Planck-Institut für Biophysik, Kennedyallee 70, D-60596 Frankfurt am Main, Germany,
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43
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Schneider H, Scheiner-Bobis G. Involvement of the M7/M8 extracellular loop of the sodium pump alpha subunit in ion transport. Structural and functional homology to P-loops of ion channels. J Biol Chem 1997; 272:16158-65. [PMID: 9195913 DOI: 10.1074/jbc.272.26.16158] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Mutations were introduced in the motif 884DDRW887 from an extracellular peptide of the sodium pump alpha subunit localized between M7 and M8 membrane spans to investigate a possible role of this structure in ion recognition. A homologous sequence 399QDCW402 that occurs in the P-loops of Na+ channels was shown earlier to be important for ion gating. Mutant sodium pumps were expressed in yeast and subsequently investigated for their behavior toward ouabain, Na+, K+, and ATP. Native enzyme and D884A, D884R, D885A, D885E, or D885R mutants all bind ouabain in the presence of phosphate and Mg2+. The KD values determined from Scatchard analysis are in the range 5-8 nM for the native enzyme and the D884A, D885E, or D885A mutants, and 15.7 +/- 2.04 and 30.1 +/- 4.32 nM for mutants D884R and D885R, respectively. This ouabain binding is reduced in the presence of K+ in a similar way for both native or mutant sodium pumps with relative affinities (K0.5) for K+ ranging from 1.4 to 3.7 mM. Ouabain binding in the presence of 100 microM ATP is promoted by Na+ with K0.5 = 1.64 +/- 0.01 mM for the native enzyme and K0.5 = 8. 6 +/- 1.35 mM for the D884R mutant. The K0.5 values of the two enzymes for ATP are 0.66 +/- 0.16 microM and 1.1 +/- 0.12 microM, respectively. Ouabain binding as a function of Na+ concentration, on the other hand, is very low for the D885R mutant, even at an ATP concentration of 2 mM. Phosphate or eosin, however, are recognized by this mutant enzyme, so that a major conformational change within the ATP-binding site appears unlikely. The inability of the D885R mutant to bind ouabain in the presence of Na+ and ATP could be explained by assuming that the M7/M8 connecting extracellular loop, which also contains the mutated amino acids, is invaginated within the plane of the plasma membrane and possibly involved in acceptance and/or release of Na+ ions coming from cytosolic areas of the protein. In this case, the placement of an additional positive charge might repel Na+ ions and interrupt their flow, thus not allowing the enzyme to assume the proper conformational state for ouabain binding. Such invaginated hydrophilic protein structures, such as the P-loops of Na+ and K+ channels, are already known and have been shown to participate in ion conduction.
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Affiliation(s)
- H Schneider
- Institut für Biochemie und Endokrinologie, Fachbereich Veterinärmedizin, Justus-Liebig-Universität Giessen, D-35392 Giessen, Germany
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44
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Nørby JG, Esmann M. The effect of ionic strength and specific anions on substrate binding and hydrolytic activities of Na,K-ATPase. J Gen Physiol 1997; 109:555-70. [PMID: 9154904 PMCID: PMC2217059 DOI: 10.1085/jgp.109.5.555] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/1996] [Accepted: 02/10/1997] [Indexed: 02/04/2023] Open
Abstract
The physiological ligands for Na,K-ATPase (the Na,K-pump) are ions, and electrostatic forces, that could be revealed by their ionic strength dependence, are therefore expected to be important for their reaction with the enzyme. We found that the affinities for ADP3-, eosine2-, p-nitrophenylphosphate, and V(max) for Na,K-ATPase and K+-activated p-nitrophenylphosphatase activity, were all decreased by increasing salt concentration and by specific anions. Equilibrium binding of ADP was measured at 0-0.5 M of NaCl, Na2SO4, and NaNO3 and in 0.1 M Na-acetate, NaSCN, and NaClO4. The apparent affinity for ADP decreased up to 30 times. At equal ionic strength, I, the ranking of the salt effect was NaCl approximately Na2SO4 approximately Na-acetate < NaNO3 < NaSCN < NaCl04. We treated the influence of NaCl and Na2SO4 on K(diss) for E x ADP as a "pure" ionic strength effect. It is quantitatively simulated by a model where the binding site and ADP are point charges, and where their activity coefficients are related to I by the limiting law of Debye and Hückel. The estimated net charge at the binding site of the enzyme was about +1. Eosin binding followed the same model. The NO3- effect was compatible with competitive binding of NO3- and ADP in addition to the general I-effect. K(diss) for E x NO3 was approximately 32 mM. Analysis of V(max)/K(m) for Na,K-ATPase and K+-p-nitrophenylphosphatase activity shows that electrostatic forces are important for the binding of p-nitrophenylphosphate but not for the catalytic effect of ATP on the low affinity site. The net charge at the p-nitrophenylphosphate-binding site was also about +1. The results reported here indicate that the reversible interactions between ions and Na,K-ATPase can be grouped according to either simple Debye-Hückel behavior or to specific anion or cation interactions with the enzyme.
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Affiliation(s)
- J G Nørby
- Department of Biophysics, University of Aarhus, Denmark.
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45
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Farley RA, Heart E, Kabalin M, Putnam D, Wang K, Kasho VN, Faller LD. Site-directed mutagenesis of the sodium pump: analysis of mutations to amino acids in the proposed nucleotide binding site by stable oxygen isotope exchange. Biochemistry 1997; 36:941-51. [PMID: 9020794 DOI: 10.1021/bi962153y] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
A model for the active site of P type ATPases has been tested by site-directed mutagenesis of amino acids in two conserved sequences of Mg(2+)-dependent and Na(+)- and K(+)-stimulated ATPase. The mutants K501R, K501E, D586E, D586N, P587A, and P588A were expressed in yeast cells and compared with wild type. In addition to previously published assays of adenosine 5'-triphosphate binding and hydrolysis, measurements of 18O exchange between Pi and water have been used to identify steps in the E2 half of the reaction cycle affected by the mutations. The study supports the prediction that K501 in the KGAP sequence interacts with adenosine 5'-triphosphate. However, quantitative comparisons of the effect of mutation K501E on the activity with the effects of mutations to an enzyme of known structure that also catalyzes phosphoryl group transfer make a direct role for the positive charge on the side chain of K501 in catalysis by stabilizing the transition state unlikely. No evidence for the predicted interaction between D586 and the hydroxyl groups of ribose was found. However, the data do indicate that the spatial organization of the loop containing the DPPR sequence is critical for phosphorylation of the enzyme. A role for D586 in coordinating the Mg2+ that is required for activity is proposed.
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Affiliation(s)
- R A Farley
- Department of Physiology and Biophysics, University of Southern California School of Medicine, Los Angeles 90033, USA
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46
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The ATP Binding Sites of P-Type ION Transport ATPases: Properties, Structure, Conformations, and Mechanism of Energy Coupling. ACTA ACUST UNITED AC 1997. [DOI: 10.1016/s1569-2558(08)60152-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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47
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Kimura K, Suzuki H, Daiho T, Yamasaki K, Kanazawa T. Identification of arginyl residues located at the ATP binding site of sarcoplasmic reticulum Ca2+-ATPase. Modification with 1,2-cyclohexanedione. J Biol Chem 1996; 271:28933-41. [PMID: 8910542 DOI: 10.1074/jbc.271.46.28933] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Sarcoplasmic reticulum vesicles were treated with 1, 2-cyclohexanedione (CHD) in sodium borate (pH 8.0). The Ca2+-ATPase activity was completely inhibited. Inhibition of Mg.ATP and Mg.ADP binding to the high affinity ATP binding site as well as inhibition of phosphorylation with ATP occurred simultaneously with the inhibition of the Ca2+-ATPase activity. Phosphorylation with acetyl phosphate was not inhibited. The Ca2+-ATPase was strongly protected by Mg.ATP, Mg.ADP, and Mg.AMP against this inhibition. Binding of acetyl phosphate or Pi to the enzyme gave no protection. Phosphorylation with acetyl phosphate also had no protective effect. Peptide mapping of the tryptic digests, detection of peptides containing CHD-modified arginyl residues with Girard's reagent T, and sequencing revealed that Arg-489, Arg-505, and Arg-678 were modified with CHD. Arg-489 and Arg-678 were almost completely protected by Mg.ATP against this modification, but partially protected by prelabeling with fluorescein 5-isothiocyanate, which occupies the adenosine binding region in the ATP binding site. In contrast, Arg-505 was slightly protected by Mg.ATP and almost completely protected by prelabeling with fluorescein 5-isothiocyanate. Taken together, these findings suggest that Arg-489 and Arg-678 are located in or near the region occupied by the triphosphate moiety of ATP, either or both of these residues being in or close to the region occupied by the alpha-phosphoryl group in the high affinity ATP binding site and involved in the CHD-induced inhibition of this enzyme and that Arg-505 is very close to (but slightly out of) the adenosine binding region in the ATP binding site. The acetyl phosphatase activity and phosphorylation with Pi were also inhibited by the CHD treatment, but the inhibitions were considerably slower than those described above. This suggests that the arginyl residues involved in these inhibitions are distinct from that involved in the inhibition of the Ca2+-ATPase activity.
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Affiliation(s)
- K Kimura
- Department of Biochemistry, Asahikawa Medical College, Asahikawa 078, Japan.
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48
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Daly SE, Lane LK, Blostein R. Structure/function analysis of the amino-terminal region of the 1 and 2 subunits of Na,K-ATPase. J Biol Chem 1996; 271:23683-9. [PMID: 8798590 DOI: 10.1074/jbc.271.39.23683] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
The alpha2 isoform of the Na,K-ATPase exhibits kinetic behavior distinct from that of the alpha1 isoform. The distinctive behavior is apparent when the reaction is carried out under conditions (micromolar ATP concentration) in which the K+ deocclusion pathway of the reaction cycle is rate-limiting; the alpha1 activity is inhibited by K+, whereas alpha2 is stimulated. When 32 NH2-terminal amino acid residues are removed from alpha1, the kinetic behavior of the mutant enzyme (alpha1M32) is similar to that of alpha2 (Daly, S. E., Lane, L. K., and Blostein, R. (1994) J. Biol. Chem. 269, 23944-23948). In the current study, the region of the alpha1 NH2 terminus involved in modulating this kinetic behavior has been localized to the highly charged sequence comprising residues 24-32. Within this nonapeptide, differences between alpha1 and alpha2 are conservative and are confined to residues 25-27. The behavior of two chimeric enzymes: (i) alpha1 with the first 32 residues identical to the alpha2 sequence, alpha1 (1-32alpha2), and (ii) alpha2 with the first 32 residues identical to the alpha1 sequence, alpha2(1-32alpha1), indicates that the distinctive kinetic behavior of alpha1 and alpha2 is not due to the 24-32 NH2-terminal domain, per se, but rather to its interaction with other, isoform-specific region(s) of the alpha1 protein. We also demonstrate that the distinct K+ activation profiles of either alpha2 or alpha1M32, compared to alpha1 is due to a faster release of K+ from the K+-occluded enzyme, and to a higher affinity for ATP. This was determined in studies using two approaches: (i) kinetic analysis of the reaction modeled according to a branched pathway of K+ deocclusion through low and high affinity ATP pathways and, (ii) measurements of the (rapid) phosphorylation of the enzyme (E1 conformation) by [gamma-32P]ATP following the rate-limiting formation of the K+-free enzyme from the K+-occluded state (E2(K) --> E1 + K+). The observed kinetic differences between alpha2 and alpha1 suggest that these Na,K-ATPase isoforms differ in the steady-state distribution of E1 and E2 conformational states.
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Affiliation(s)
- S E Daly
- Department of Medicine, McGill University, Montreal, Canada
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49
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Keillor JW, Jencks WP. Phosphorylation of the sodium--potassium adenosinetriphosphatase proceeds through a rate-limiting conformational change followed by rapid phosphoryl transfer. Biochemistry 1996; 35:2750-3. [PMID: 8611581 DOI: 10.1021/bi951370g] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The sodium-potassium adenosinetriphosphatase of sheep kidney, preincubated with sodium and magnesium (E.Nae), reacts with 0.01-2.00 mM ATP to form covalent phosphoenzyme (E-P). The first order rate constant for phosphorylation increases hyperbolically with ATP concentration with a maximum value of (4.6 +/- 0.9) x 10(2) s-1 and K0.5 = 75 +/- 25 microM (ph 7.4, 25 degrees C, 120 mM NaCl, and 3 mM MgCl2). If the phosphoryl-transfer step were rate-limiting, the approach to equilibrium to give 50% E-P in the presence of ADP would follow kobsd=Kf+Kr+9.2 x 10(2) s-1. However, the formation of phosphoenzyme from E.Na3 with 1.0 mM ATP plus 2.0 mM ADP proceeds to 50% completion with kobsd=(4.2 +/- 0.8) x 10(2) s-1. This result show that phosphoryl transfer from bound ATP to the enzyme is not the rate limiting step for phosphoenzyme formation from E.Na3. The result is consistent with a rate-limiting conformational change of the E.Na3.ATP intermediate that is followed by rapid phosphoryl transfer, with kcat > or = 3000 s-1.
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Affiliation(s)
- J W Keillor
- Graduate Department of Biochemistry, Brandeis University, Waltham Massachusetts 02254-9110, USA
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50
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Scheiner-Bobis G, Antonipillai J, Farley RA. Simultaneous binding of phosphate and TNP-ADP to FITC-modified NA+,K(+)-ATPase. Biochemistry 1993; 32:9592-9. [PMID: 8396968 DOI: 10.1021/bi00088a011] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Double-reciprocal plots of the rate of ATP hydrolysis by Na+,K(+)-ATPase versus ATP concentration are not linear, and may reflect either two distinct binding sites for ATP or a single ATP binding site whose affinity for the nucleotide alternates between high-affinity and low-affinity states. In order to determine whether multiple nucleotides or nucleotide analogs can bind simultaneously to Na,+,K(+)-ATPase, the effects of nucleotides on the hydrolysis of p-nitrophenyl phosphate and on the dephosphorylation rate of Na+,K(+)-ATPase modified by fluorescein 5'-isothiocyanate (FITC) were measured. FITC blocks the high-affinity binding site for ATP on the Na+K(+)-ATPase and inhibits ATP hydrolysis at ATP concentrations as high as 8.3 mM. The hydrolysis of p-nitrophenyl phosphate and phosphoenzyme formation from inorganic phosphate and Mg2+ were not affected by FITC modification. The p-nitrophenylphosphatase activity of unmodified Na+,K(+)-ATPase was stimulated by low concentrations of ATP (10-100 microM) and other nucleotides, and was inhibited at higher nucleotide concentrations. In contrast, there was no effect on p-nitrophenyl phosphate hydrolysis by FITC-modified Na,K(+)-ATPase at ATP concentrations less than 100 microM. The hydrolysis of p-nitrophenyl phosphate by FITC-modified Na+,K(+)-ATPase was inhibited at ATP concentrations greater than 100 microM. These observations demonstrate that the effects of ATP acting at high-affinity sites are absent in FITC-modified Na+,K(+)-ATPase but the effects of ATP acting at low-affinity sites are still observed. In unmodified Na+,K(+)-ATPase, the rate of dephosphorylation of the phosphoenzyme formed from inorganic phosphate and Mg2+ was inhibited by ATP.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- G Scheiner-Bobis
- Department of Physiology and Biophysics, University of Southern California, School of Medicine, Los Angeles 90033
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