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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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2
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Bazzone A, Zerlotti R, Barthmes M, Fertig N. Functional characterization of SGLT1 using SSM-based electrophysiology: Kinetics of sugar binding and translocation. Front Physiol 2023; 14:1058583. [PMID: 36824475 PMCID: PMC9941201 DOI: 10.3389/fphys.2023.1058583] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2022] [Accepted: 01/17/2023] [Indexed: 02/10/2023] Open
Abstract
Beside the ongoing efforts to determine structural information, detailed functional studies on transporters are essential to entirely understand the underlying transport mechanisms. We recently found that solid supported membrane-based electrophysiology (SSME) enables the measurement of both sugar binding and transport in the Na+/sugar cotransporter SGLT1 (Bazzone et al, 2022a). Here, we continued with a detailed kinetic characterization of SGLT1 using SSME, determining KM and KD app for different sugars, kobs values for sugar-induced conformational transitions and the effects of Na+, Li+, H+ and Cl- on sugar binding and transport. We found that the sugar-induced pre-steady-state (PSS) charge translocation varies with the bound ion (Na+, Li+, H+ or Cl-), but not with the sugar species, indicating that the conformational state upon sugar binding depends on the ion. Rate constants for the sugar-induced conformational transitions upon binding to the Na+-bound carrier range from 208 s-1 for D-glucose to 95 s-1 for 3-OMG. In the absence of Na+, rate constants are decreased, but all sugars bind to the empty carrier. From the steady-state transport current, we found a sequence for sugar specificity (Vmax/KM): D-glucose > MDG > D-galactose > 3-OMG > D-xylose. While KM differs 160-fold across tested substrates and plays a major role in substrate specificity, Vmax only varies by a factor of 1.9. Interestingly, D-glucose has the lowest Vmax across all tested substrates, indicating a rate limiting step in the sugar translocation pathway following the fast sugar-induced electrogenic conformational transition. SGLT1 specificity for D-glucose is achieved by optimizing two ratios: the sugar affinity of the empty carrier for D-glucose is similarly low as for all tested sugars (KD,K app = 210 mM). Affinity for D-glucose increases 14-fold (KD,Na app = 15 mM) in the presence of sodium as a result of cooperativity. Apparent affinity for D-glucose during transport increases 8-fold (KM = 1.9 mM) compared to KD,Na app due to optimized kinetics. In contrast, KM and KD app values for 3-OMG and D-xylose are of similar magnitude. Based on our findings we propose an 11-state kinetic model, introducing a random binding order and intermediate states corresponding to the electrogenic transitions detected via SSME upon substrate binding.
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Affiliation(s)
- Andre Bazzone
- Nanion Technologies GmbH, Munich, Germany,*Correspondence: Andre Bazzone,
| | - Rocco Zerlotti
- Nanion Technologies GmbH, Munich, Germany,Department of Structural Biology, Faculty of Biology and Pre-Clinics, Institute of Biochemistry, Genetics and Microbiology, University of Regensburg, Regensburg, Germany
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3
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Maleckar MM, Martín-Vasallo P, Giles WR, Mobasheri A. Physiological Effects of the Electrogenic Current Generated by the Na +/K + Pump in Mammalian Articular Chondrocytes. Bioelectricity 2020; 2:258-268. [PMID: 34471850 PMCID: PMC8370340 DOI: 10.1089/bioe.2020.0036] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Background: Although the chondrocyte is a nonexcitable cell, there is strong interest in gaining detailed knowledge of its ion pumps, channels, exchangers, and transporters. In combination, these transport mechanisms set the resting potential, regulate cell volume, and strongly modulate responses of the chondrocyte to endocrine agents and physicochemical alterations in the surrounding extracellular microenvironment. Materials and Methods: Mathematical modeling was used to assess the functional roles of energy-requiring active transport, the Na+/K+ pump, in chondrocytes. Results: Our findings illustrate plausible physiological roles for the Na+/K+ pump in regulating the resting membrane potential and suggest ways in which specific molecular components of pump can respond to the unique electrochemical environment of the chondrocyte. Conclusion: This analysis provides a basis for linking chondrocyte electrophysiology to metabolism and yields insights into novel ways of manipulating or regulating responsiveness to external stimuli both under baseline conditions and in chronic diseases such as osteoarthritis.
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Affiliation(s)
| | - Pablo Martín-Vasallo
- UD of Biochemistry and Molecular Biology, Universidad de La Laguna, San Cristóbal de La Laguna, Spain.,Instituto de Tecnologías Biomédicas de Canarias, Universidad de La Laguna, San Cristóbal de La Laguna, Spain
| | - Wayne R Giles
- Department of Physiology and Pharmacology, University of Calgary, Calgary, Canada
| | - Ali Mobasheri
- Research Unit of Medical Imaging, Physics and Technology, Faculty of Medicine, University of Oulu, Oulu, Finland.,Department of Regenerative Medicine, State Research Institute Centre for Innovative Medicine, Vilnius, Lithuania.,Department of Orthopedics, Rheumatology and Clinical Immunology, University Medical Center Utrecht, Utrecht, The Netherlands
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4
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Tadini-Buoninsegni F. Protein Adsorption on Solid Supported Membranes: Monitoring the Transport Activity of P-Type ATPases. Molecules 2020; 25:molecules25184167. [PMID: 32933017 PMCID: PMC7570688 DOI: 10.3390/molecules25184167] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2020] [Revised: 09/01/2020] [Accepted: 09/02/2020] [Indexed: 02/07/2023] Open
Abstract
P-type ATPases are a large family of membrane transporters that are found in all forms of life. These enzymes couple ATP hydrolysis to the transport of various ions or phospholipids across cellular membranes, thereby generating and maintaining crucial electrochemical potential gradients. P-type ATPases have been studied by a variety of methods that have provided a wealth of information about the structure, function, and regulation of this class of enzymes. Among the many techniques used to investigate P-type ATPases, the electrical method based on solid supported membranes (SSM) was employed to investigate the transport mechanism of various ion pumps. In particular, the SSM method allows the direct measurement of charge movements generated by the ATPase following adsorption of the membrane-bound enzyme on the SSM surface and chemical activation by a substrate concentration jump. This kind of measurement was useful to identify electrogenic partial reactions and localize ion translocation in the reaction cycle of the membrane transporter. In the present review, we discuss how the SSM method has contributed to investigate some key features of the transport mechanism of P-type ATPases, with a special focus on sarcoplasmic reticulum Ca2+-ATPase, mammalian Cu+-ATPases (ATP7A and ATP7B), and phospholipid flippase ATP8A2.
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5
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Tadini-Buoninsegni F, Palchetti I. Label-Free Bioelectrochemical Methods for Evaluation of Anticancer Drug Effects at a Molecular Level. SENSORS 2020; 20:s20071812. [PMID: 32218227 PMCID: PMC7181070 DOI: 10.3390/s20071812] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/14/2020] [Revised: 03/19/2020] [Accepted: 03/21/2020] [Indexed: 02/06/2023]
Abstract
Cancer is a multifactorial family of diseases that is still a leading cause of death worldwide. More than 100 different types of cancer affecting over 60 human organs are known. Chemotherapy plays a central role for treating cancer. The development of new anticancer drugs or new uses for existing drugs is an exciting and increasing research area. This is particularly important since drug resistance and side effects can limit the efficacy of the chemotherapy. Thus, there is a need for multiplexed, cost-effective, rapid, and novel screening methods that can help to elucidate the mechanism of the action of anticancer drugs and the identification of novel drug candidates. This review focuses on different label-free bioelectrochemical approaches, in particular, impedance-based methods, the solid supported membranes technique, and the DNA-based electrochemical sensor, that can be used to evaluate the effects of anticancer drugs on nucleic acids, membrane transporters, and living cells. Some relevant examples of anticancer drug interactions are presented which demonstrate the usefulness of such methods for the characterization of the mechanism of action of anticancer drugs that are targeted against various biomolecules.
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Affiliation(s)
| | - Ilaria Palchetti
- Department of Chemistry "Ugo Schiff", University of Florence, 50019 Sesto Fiorentino, Italy
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6
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Abstract
Here, we present a protocol for the functional characterization of the H+-coupled human peptide transporter PepT1 and sufficient notes to transfer the protocol to the Na+-coupled sugar transporter SGLT1, the organic cation transporter OCT2, the Na+/Ca2+ exchanger NCX, and the neuronal glutamate transporter EAAT3.The assay was developed for the commercially available SURFE2R N1 instrument (Nanion Technologies GmbH) which applies solid supported membrane (SSM)-based electrophysiology. This technique is widely used for the functional characterization of membrane transporters with more than 100 different transporters characterized so far. The technique is cost-effective, easy to use, and capable of high-throughput measurements.SSM-based electrophysiology utilizes SSM-coated gold sensors to physically adsorb membrane vesicles containing the protein of interest. A fast solution exchange provides the substrate and activates transport. For the measurement of PepT1 activity, we applied a peptide concentration jump to activate H+/peptide symport. Proton influx charges the sensor. A capacitive current is measured reflecting the transport activity of PepT1 . Multiple measurements on the same sensor allow for comparison of transport activity under different conditions. Here, we determine EC50 for PepT1-mediated glycylglycine transport and perform an inhibition experiment using the specific peptide inhibitor Lys[Z(NO2)]-Val.
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Phosphatidylserine flipping by the P4-ATPase ATP8A2 is electrogenic. Proc Natl Acad Sci U S A 2019; 116:16332-16337. [PMID: 31371510 DOI: 10.1073/pnas.1910211116] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Phospholipid flippases (P4-ATPases) utilize ATP to translocate specific phospholipids from the exoplasmic leaflet to the cytoplasmic leaflet of biological membranes, thus generating and maintaining transmembrane lipid asymmetry essential for a variety of cellular processes. P4-ATPases belong to the P-type ATPase protein family, which also encompasses the ion transporting P2-ATPases: Ca2+-ATPase, Na+,K+-ATPase, and H+,K+-ATPase. In comparison with the P2-ATPases, understanding of P4-ATPases is still very limited. The electrogenicity of P4-ATPases has not been explored, and it is not known whether lipid transfer between membrane bilayer leaflets can lead to displacement of charge across the membrane. A related question is whether P4-ATPases countertransport ions or other substrates in the opposite direction, similar to the P2-ATPases. Using an electrophysiological method based on solid supported membranes, we observed the generation of a transient electrical current by the mammalian P4-ATPase ATP8A2 in the presence of ATP and the negatively charged lipid substrate phosphatidylserine, whereas only a diminutive current was generated with the lipid substrate phosphatidylethanolamine, which carries no or little charge under the conditions of the measurement. The current transient seen with phosphatidylserine was abolished by the mutation E198Q, which blocks dephosphorylation. Likewise, mutation I364M, which causes the neurological disorder cerebellar ataxia, mental retardation, and disequilibrium (CAMRQ) syndrome, strongly interfered with the electrogenic lipid translocation. It is concluded that the electrogenicity is associated with a step in the ATPase reaction cycle directly involved in translocation of the lipid. These measurements also showed that no charged substrate is being countertransported, thereby distinguishing the P4-ATPase from P2-ATPases.
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Tadini-Buoninsegni F, Smeazzetto S, Gualdani R, Moncelli MR. Drug Interactions With the Ca 2+-ATPase From Sarco(Endo)Plasmic Reticulum (SERCA). Front Mol Biosci 2018; 5:36. [PMID: 29696147 PMCID: PMC5904271 DOI: 10.3389/fmolb.2018.00036] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2018] [Accepted: 03/26/2018] [Indexed: 11/13/2022] Open
Abstract
The sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) is an intracellular membrane transporter that utilizes the free energy provided by ATP hydrolysis for active transport of Ca2+ ions from the cytoplasm to the lumen of sarco(endo)plasmic reticulum. SERCA plays a fundamental role for cell calcium homeostasis and signaling in muscle cells and also in cells of other tissues. Because of its prominent role in many physiological processes, SERCA dysfunction is associated to diseases displaying various degrees of severity. SERCA transport activity can be inhibited by a variety of compounds with different chemical structures. Specific SERCA inhibitors were identified which have been instrumental in studies of the SERCA catalytic and transport mechanism. It has been proposed that SERCA inhibition may represent a novel therapeutic strategy to cure certain diseases by targeting SERCA activity in pathogens, parasites and cancer cells. Recently, novel small molecules have been developed that are able to stimulate SERCA activity. Such SERCA activators may also offer an innovative and promising therapeutic approach to treat diseases, such as heart failure, diabetes and metabolic disorders. In the present review the effects of pharmacologically relevant compounds on SERCA transport activity are presented. In particular, we will discuss the interaction of SERCA with specific inhibitors and activators that are potential therapeutic agents for different diseases.
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Affiliation(s)
| | - Serena Smeazzetto
- Department of Chemistry "Ugo Schiff," University of Florence, Florence, Italy
| | - Roberta Gualdani
- Laboratory of Cell Physiology, Institute of Neuroscience, Université Catholique de Louvain, Louvain-la-Neuve, Belgium
| | - Maria Rosa Moncelli
- Department of Chemistry "Ugo Schiff," University of Florence, Florence, Italy
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9
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Abstract
Functional characterization of transport proteins using conventional electrophysiology can be challenging, especially for low turnover transporters or transporters from bacteria and intracellular compartments. Solid-supported membrane (SSM)-based electrophysiology is a sensitive and cell-free assay technique for the characterization of electrogenic membrane proteins. Purified proteins reconstituted into proteoliposomes or membrane vesicles from cell culture or native tissues are adsorbed to the sensor holding an SSM. A substrate or a ligand is applied via rapid solution exchange. The electrogenic transporter activity charges the sensor, which is recorded as a transient current. The high stability of the SSM allows cumulative measurements on the same sensor using different experimental conditions. This allows the determination of kinetic properties including EC50, IC50, Km, KD, and rate constants of electrogenic reactions. About 100 different transporters have been measured so far using this technique, among them symporters, exchangers, uniporters, ATP-, redox-, and light-driven ion pumps, as well as receptors and ion channels. Different instruments apply this technique: the laboratory setups use a closed flow-through arrangement, while the commercially available SURFE2R N1 resembles a pipetting robot. For drug screening purposes high-throughput systems, such as the SURFE2R 96SE enable the simultaneous measurement of up to 96 sensors.
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Affiliation(s)
- Andre Bazzone
- Max Planck Institute of Biophysics, Frankfurt/Main, Germany; Nanion Technologies GmbH, Munich, Germany
| | | | - Klaus Fendler
- Max Planck Institute of Biophysics, Frankfurt/Main, Germany.
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10
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Friedrich T, Tavraz NN, Junghans C. ATP1A2 Mutations in Migraine: Seeing through the Facets of an Ion Pump onto the Neurobiology of Disease. Front Physiol 2016; 7:239. [PMID: 27445835 PMCID: PMC4914835 DOI: 10.3389/fphys.2016.00239] [Citation(s) in RCA: 57] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2016] [Accepted: 06/03/2016] [Indexed: 12/31/2022] Open
Abstract
Mutations in four genes have been identified in familial hemiplegic migraine (FHM), from which CACNA1A (FHM type 1) and SCN1A (FHM type 3) code for neuronal voltage-gated calcium or sodium channels, respectively, while ATP1A2 (FHM type 2) encodes the α2 isoform of the Na(+),K(+)-ATPase's catalytic subunit, thus classifying FHM primarily as an ion channel/ion transporter pathology. FHM type 4 is attributed to mutations in the PRRT2 gene, which encodes a proline-rich transmembrane protein of as yet unknown function. The Na(+),K(+)-ATPase maintains the physiological gradients for Na(+) and K(+) ions and is, therefore, critical for the activity of ion channels and transporters involved neuronal excitability, neurotransmitter uptake or Ca(2+) signaling. Strikingly diverse functional abnormalities have been identified for disease-linked ATP1A2 mutations which frequently lead to changes in the enzyme's voltage-dependent properties, kinetics, or apparent cation affinities, but some mutations are truly deleterious for enzyme function and thus cause full haploinsufficiency. Here, we summarize structural and functional data about the Na(+),K(+)-ATPase available to date and an overview is provided about the particular properties of the α2 isoform that explain its physiological relevance in electrically excitable tissues. In addition, current concepts about the neurobiology of migraine, the correlations between primary brain dysfunction and mechanisms of headache pain generation are described, together with insights gained recently from modeling approaches in computational neuroscience. Then, a survey is given about ATP1A2 mutations implicated in migraine cases as documented in the literature with focus on mutations that were described to completely destroy enzyme function, or lead to misfolded or mistargeted protein in particular model cell lines. We also discuss whether or not there are correlations between these most severe mutational effects and clinical phenotypes. Finally, perspectives for future research on the implications of Na(+),K(+)-ATPase mutations in human pathologies are presented.
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Affiliation(s)
- Thomas Friedrich
- Department of Physical Chemistry/Bioenergetics, Institute of Chemistry, Technical University of BerlinBerlin, Germany
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11
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Tadini-Buoninsegni F, Bartolommei G. Electrophysiological Measurements on Solid Supported Membranes. Methods Mol Biol 2016; 1377:293-303. [PMID: 26695041 DOI: 10.1007/978-1-4939-3179-8_26] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
The solid supported membrane (SSM) represents a convenient model system for a biological membrane with the advantage of being mechanically so stable that solutions can be rapidly exchanged at the surface. The SSM consists of a hybrid alkanethiol-phospholipid bilayer supported by a gold electrode. Proteoliposomes, membrane vesicles, or membrane fragments containing the transport protein of interest are adsorbed on the SSM surface and are subjected to a rapid substrate concentration jump. The substrate concentration jump activates the protein and the charge displacement concomitant with its transport activity is recorded as a current transient. Since this technique is well suited for the functional characterization of electrogenic membrane transporters, it is expected to become a promising platform technology for drug screening and development.
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Affiliation(s)
| | - Gianluca Bartolommei
- Department of Chemistry "Ugo Schiff", University of Florence, 50019, Sesto Fiorentino, Italy
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12
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Tashkin VY, Gavrilchik AN, Ilovaisky AI, Apell HJ, Sokolov VS. Electrogenic binding of ions at the cytoplasmic side of the Na+,K+-ATPase. BIOCHEMISTRY MOSCOW SUPPLEMENT SERIES A-MEMBRANE AND CELL BIOLOGY 2015. [DOI: 10.1134/s1990747815020105] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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13
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Guha P, Roy B, Karmakar G, Nahak P, Koirala S, Sapkota M, Misono T, Torigoe K, Panda AK. Ion-pair amphiphile: a neoteric substitute that modulates the physicochemical properties of biomimetic membranes. J Phys Chem B 2015; 119:4251-62. [PMID: 25715819 DOI: 10.1021/jp512212u] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Ion-pair amphiphiles (IPAs) are neoteric pseudo-double-tailed compounds with potential as a novel substitute of phospholipid. IPA, synthesized by stoichiometric/equimolar mixing of aqueous solution of hexadecyltrimethylammonium bromide (HTMAB) and sodium dodecyl sulfate (SDS), was used as a potential substituent of naturally occurring phospholipid, soylecithin (SLC). Vesicles were prepared using SLC and IPA in different ratios along with cholesterol. The impact of IPA on SLC was examined by way of surface pressure (π)-area (A) measurements. Associated thermodynamic parameters were evaluated; interfacial miscibility between the components was found to depend on SLC/IPA ratio. Solution behavior of the bilayers, in the form of vesicles, was investigated by monitoring the hydrodynamic diameter, zeta potential, and polydispersity index over a period of 100 days. Size and morphology of the vesicles were also investigated by electron microscopic studies. Systems comprising 20 and 40 mol % IPA exhibited anomalous behavior. Thermal behavior of the vesicles, as scrutinized by differential scanning calorimetry, was correlated with the hydrocarbon chain as well as the headgroup packing. Entrapment efficiency (EE) of the vesicles toward the cationic dye methylene blue (MB) was also evaluated. Vesicles were smart enough to entrap the dye, and the efficiency was found to vary with IPA concentration. EE was found to be well above 80% for some stable dispersions. Such formulations thus could be considered to have potential as novel drug delivery systems.
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Affiliation(s)
- Pritam Guha
- †Department of Chemistry, University of North Bengal, Darjeeling 734 013, West Bengal, India
| | - Biplab Roy
- †Department of Chemistry, University of North Bengal, Darjeeling 734 013, West Bengal, India
| | - Gourab Karmakar
- †Department of Chemistry, University of North Bengal, Darjeeling 734 013, West Bengal, India
| | - Prasant Nahak
- †Department of Chemistry, University of North Bengal, Darjeeling 734 013, West Bengal, India
| | - Suraj Koirala
- ‡Department of Pharmaceutics, Himalayan Pharmacy Institute, Majhitar, Rangpo, East Sikkim 737136, India
| | - Manish Sapkota
- ‡Department of Pharmaceutics, Himalayan Pharmacy Institute, Majhitar, Rangpo, East Sikkim 737136, India
| | - Takeshi Misono
- §Department of Pure and Applied Chemistry, Tokyo University of Science, 2641 Yamazaki, Noda, Tokyo 278-8510, Japan
| | - Kanjiro Torigoe
- §Department of Pure and Applied Chemistry, Tokyo University of Science, 2641 Yamazaki, Noda, Tokyo 278-8510, Japan
| | - Amiya Kumar Panda
- †Department of Chemistry, University of North Bengal, Darjeeling 734 013, West Bengal, India
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14
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A Comparative Study of Phase States of the Peribacteroid Membrane from Yellow Lupin and Broad Bean Nodules. Res Lett Biochem 2014; 2014:527393. [PMID: 24804101 PMCID: PMC3996879 DOI: 10.1155/2014/527393] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2014] [Revised: 03/12/2014] [Accepted: 03/17/2014] [Indexed: 11/17/2022] Open
Abstract
A comparative study of the lipid bilayer phase status and structure of the outer membrane of free-living Bradyrhizobium strain 359a (Nod+Fix+) and 400 (Nod+FixL) or Rhizobium leguminosarum 97 (Nod+Fix+, effective) and 87 (Nod+FixL, ineffective) has been carried out. Also, the effect of the symbiotic pair combination on the lipid bilayer structure of the bacteroid outer membrane and peribacteroid membrane, isolated from the nodules of Lupinus luteus L. or Vicia faba L., has been studied. As a result, it is shown that the lipid bilayer status of the bacteroid outer membrane is mainly determined by microsymbiont, but not the host plant. In the contrast, the lipid bilayer status of the peribacteroid membrane and, as a consequence, its properties depend on interaction of both symbiotic partners.
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15
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Crystal structure of a Na+-bound Na+,K+-ATPase preceding the E1P state. Nature 2013; 502:201-6. [PMID: 24089211 DOI: 10.1038/nature12578] [Citation(s) in RCA: 225] [Impact Index Per Article: 20.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2013] [Accepted: 08/16/2013] [Indexed: 11/08/2022]
Abstract
Na(+),K(+)-ATPase pumps three Na(+) ions out of cells in exchange for two K(+) taken up from the extracellular medium per ATP molecule hydrolysed, thereby establishing Na(+) and K(+) gradients across the membrane in all animal cells. These ion gradients are used in many fundamental processes, notably excitation of nerve cells. Here we describe 2.8 Å-resolution crystal structures of this ATPase from pig kidney with bound Na(+), ADP and aluminium fluoride, a stable phosphate analogue, with and without oligomycin that promotes Na(+) occlusion. These crystal structures represent a transition state preceding the phosphorylated intermediate (E1P) in which three Na(+) ions are occluded. Details of the Na(+)-binding sites show how this ATPase functions as a Na(+)-specific pump, rejecting K(+) and Ca(2+), even though its affinity for Na(+) is low (millimolar dissociation constant). A mechanism for sequential, cooperative Na(+) binding can now be formulated in atomic detail.
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16
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Jiang Y, Gao S, Xia S, Wang J, Zhuo K, Hu M. Volumetric Properties and Volumetric Interaction Parameters of the CsCl-saccharides (D-glucose, D-fructose)-water Solutions at 298.15 K. J CHIN CHEM SOC-TAIP 2013. [DOI: 10.1002/jccs.200300133] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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17
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Toyoshima C, Cornelius F. New crystal structures of PII-type ATPases: excitement continues. Curr Opin Struct Biol 2013; 23:507-14. [PMID: 23871101 DOI: 10.1016/j.sbi.2013.06.005] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2013] [Revised: 06/11/2013] [Accepted: 06/12/2013] [Indexed: 11/29/2022]
Abstract
P-type ATPases are ATP-powered ion pumps, classified into five subfamilies (PI-PV). Of these, PII-type ATPases, including Ca2+-ATPase, Na+,K+-ATPase and gastric H+,K+-ATPase, among others, have been the most intensively studied. Best understood structurally and biochemically is Ca2+-ATPase from sarcoplasmic reticulum of fast twitch skeletal muscle (sarco(endo)plasmic reticulum Ca2+-ATPase 1a, SERCA1a). Since publication of the first crystal structure in 2000, it has continuously been a source of excitement, as crystal structures for new reaction intermediates always show large structural changes. Crystal structures now exist for most of the reaction intermediates, almost covering the entire reaction cycle. This year the crystal structure of a missing link, the E1·Mg2+ state, finally appeared, bringing another surprise: bound sarcolipin (SLN). The current status of two other important PII-type ATPases, Na+,K+-ATPase and H+,K+-ATPase, is also briefly described.
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Affiliation(s)
- Chikashi Toyoshima
- Institute of Molecular and Cellular Biosciences, The University of Tokyo, Tokyo 113-0032, Japan.
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18
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Garcia A, Rasmussen HH, Apell HJ, Clarke RJ. Kinetic comparisons of heart and kidney Na+,K(+)-ATPases. Biophys J 2013; 103:677-88. [PMID: 22947929 DOI: 10.1016/j.bpj.2012.07.032] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2012] [Revised: 07/17/2012] [Accepted: 07/23/2012] [Indexed: 10/28/2022] Open
Abstract
Most kinetic measurements of the partial reactions of Na(+),K(+)-ATPase have been conducted on enzyme from mammalian kidney. Here we present a kinetic model that is based on the available equilibrium and kinetic parameters of purified kidney enzyme, and allows predictions of its steady-state turnover and pump current in intact cells as a function of ion and ATP concentrations and the membrane voltage. Using this model, we calculated the expected dependence of the pump current on voltage and extracellular Na(+) concentration. The simulations indicate a lower voltage dependence at negative potentials of the kidney enzyme in comparison with heart muscle Na(+),K(+)-ATPase, in agreement with experimental results. The voltage dependence is enhanced at high extracellular Na(+) concentrations. This effect can be explained by a voltage-dependent depopulation of extracellular K(+) ion binding sites on the E2P state and an increase in the proportion of enzyme in the E1P(Na(+))(3) state in the steady state. This causes a decrease in the effective rate constant for occlusion of K(+) by the E2P state and hence a drop in turnover. Around a membrane potential of zero, negligible voltage dependence is observed because the voltage-independent E2(K(+))(2) → E1 + 2K(+) transition is the major rate-determining step.
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Affiliation(s)
- Alvaro Garcia
- Department of Cardiology, Royal North Shore Hospital, and Kolling Institute, University of Sydney, Sydney, Australia
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Kaneko S. [Automated electrophysiological system for the measurement of transporter/channel activities]. Nihon Yakurigaku Zasshi 2011; 138:239-43. [PMID: 22156260 DOI: 10.1254/fpj.138.239] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/14/2022]
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20
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Preissl S, Bick I, Obrdlik P, Diekert K, Gul S, Gribbon P. Development of an assay for Complex I/Complex III of the respiratory chain using solid supported membranes and its application in mitochondrial toxicity screening in drug discovery. Assay Drug Dev Technol 2010; 9:147-56. [PMID: 21133681 DOI: 10.1089/adt.2010.0320] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Membrane-bound transporter proteins are involved in cell signal transduction and metabolism as well as influencing key pharmacological properties such as drug bioavailability. The functional activity of transporters that belong to the group of electrically active membrane proteins can be directly monitored using the solid-supported membrane-based SURFE(2)R™ technology (SURFace Electrogenic Event Reader; Scientific Devices Heidelberg GmbH, Heidelberg, Germany). The method makes use of membrane fragments or vesicles containing transport proteins adsorbed onto solid-supported membrane-covered electrodes and allows the direct measurement of their activity. This technology has been used to develop a robust screening compatible assay for Complex I/Complex III, key components of the respiratory chain in 96-well microtiter plates. The assay was screened against 1,000 compounds from the ComGenex Lead-like small molecule library to ascertain whether mitochondrial liabilities might be an underlying, although undesirable feature of typical commercial screening libraries. Some 105 hits (compounds exhibiting >50% inhibition of Complex I/Complex III activity at 10 μM) were identified and their activities were subsequently confirmed in duplicate, yielding a confirmation rate of 68%. Analysis of the confirmed hits also provided evidence of structure-activity relationships and two compounds from one structural class were further evaluated in dose-response experiments. This study provides evidence that profiling of compounds for potential mitochondrial liabilities, even at an early stage of drug discovery, may be a necessary additional quality filter that should be considered during the compound screening and profiling cascade.
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Garcia-Celma JJ, Ploch J, Smirnova I, Kaback HR, Fendler K. Delineating electrogenic reactions during lactose/H+ symport. Biochemistry 2010; 49:6115-21. [PMID: 20568736 PMCID: PMC2907097 DOI: 10.1021/bi100492p] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2010] [Revised: 06/17/2010] [Indexed: 01/03/2023]
Abstract
Electrogenic reactions accompanying downhill lactose/H(+) symport catalyzed by the lactose permease of Escherichia coli (LacY) have been assessed using solid-supported membrane-based electrophysiology with improved time resolution. Rates of charge translocation generated by purified LacY reconstituted into proteoliposomes were analyzed over a pH range from 5.2 to 8.5, which allows characterization of two electrogenic steps in the transport mechanism: (i) a weak electrogenic reaction triggered by sugar binding and observed under conditions where H(+) translocation is abolished either by acidic pH or by a Glu325 --> Ala mutation in the H(+) binding site (this step with a rate constant of approximately 200 s(-1) for wild-type LacY leads to an intermediate proposed to represent an "occluded" state) and (ii) a major electrogenic reaction corresponding to 94% of the total charge translocated at pH 8, which is pH-dependent with a maximum rate of approximately 30 s(-1) and a pK of 7.5. This partial reaction is assigned to rate-limiting H(+) release on the cytoplasmic side of LacY during turnover. These findings together with previous electrophysiological results and biochemical-biophysical studies are included in an overall kinetic mechanism that allows delineation of the electrogenic steps in the reaction pathway.
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Affiliation(s)
- Juan J. Garcia-Celma
- Department of Biophysical Chemistry, Max-Planck-Institute of Biophysics, D-60438 Frankfurt/M, Germany
| | - Julian Ploch
- Department of Biophysical Chemistry, Max-Planck-Institute of Biophysics, D-60438 Frankfurt/M, Germany
| | | | - H. Ronald Kaback
- Department of Physiology
- Department of Microbiology and Immunology
- Department of Molecular Genetics
| | - Klaus Fendler
- Department of Biophysical Chemistry, Max-Planck-Institute of Biophysics, D-60438 Frankfurt/M, Germany
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Meier S, Tavraz NN, Dürr KL, Friedrich T. Hyperpolarization-activated inward leakage currents caused by deletion or mutation of carboxy-terminal tyrosines of the Na+/K+-ATPase {alpha} subunit. ACTA ACUST UNITED AC 2010; 135:115-34. [PMID: 20100892 PMCID: PMC2812498 DOI: 10.1085/jgp.200910301] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The Na(+)/K(+)-ATPase mediates electrogenic transport by exporting three Na(+) ions in exchange for two K(+) ions across the cell membrane per adenosine triphosphate molecule. The location of two Rb(+) ions in the crystal structures of the Na(+)/K(+)-ATPase has defined two "common" cation binding sites, I and II, which accommodate Na(+) or K(+) ions during transport. The configuration of site III is still unknown, but the crystal structure has suggested a critical role of the carboxy-terminal KETYY motif for the formation of this "unique" Na(+) binding site. Our two-electrode voltage clamp experiments on Xenopus oocytes show that deletion of two tyrosines at the carboxy terminus of the human Na(+)/K(+)-ATPase alpha(2) subunit decreases the affinity for extracellular and intracellular Na(+), in agreement with previous biochemical studies. Apparently, the DeltaYY deletion changes Na(+) affinity at site III but leaves the common sites unaffected, whereas the more extensive DeltaKETYY deletion affects the unique site and the common sites as well. In the absence of extracellular K(+), the DeltaYY construct mediated ouabain-sensitive, hyperpolarization-activated inward currents, which were Na(+) dependent and increased with acidification. Furthermore, the voltage dependence of rate constants from transient currents under Na(+)/Na(+) exchange conditions was reversed, and the amounts of charge transported upon voltage pulses from a certain holding potential to hyperpolarizing potentials and back were unequal. These findings are incompatible with a reversible and exclusively extracellular Na(+) release/binding mechanism. In analogy to the mechanism proposed for the H(+) leak currents of the wild-type Na(+)/K(+)-ATPase, we suggest that the DeltaYY deletion lowers the energy barrier for the intracellular Na(+) occlusion reaction, thus destabilizing the Na(+)-occluded state and enabling inward leak currents. The leakage currents are prevented by aromatic amino acids at the carboxy terminus. Thus, the carboxy terminus of the Na(+)/K(+)-ATPase alpha subunit represents a structural and functional relay between Na(+) binding site III and the intracellular cation occlusion gate.
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Affiliation(s)
- Susan Meier
- Technical University of Berlin, Institute of Chemistry, D-10623 Berlin, Germany
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Electrophysiological characterization of ATPases in native synaptic vesicles and synaptic plasma membranes. Biochem J 2010; 427:151-9. [PMID: 20100168 DOI: 10.1042/bj20091380] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Vesicular V-ATPase (V-type H+-ATPase) and the plasma membrane-bound Na+/K+-ATPase are essential for the cycling of neurotransmitters at the synapse, but direct functional studies on their action in native surroundings are limited due to the poor accessibility via standard electrophysiological equipment. We performed SSM (solid supported membrane)-based electrophysiological analyses of synaptic vesicles and plasma membranes prepared from rat brains by sucrose-gradient fractionation. Acidification experiments revealed V-ATPase activity in fractions containing the vesicles but not in the plasma membrane fractions. For the SSM-based electrical measurements, the ATPases were activated by ATP concentration jumps. In vesicles, ATP-induced currents were inhibited by the V-ATPase-specific inhibitor BafA1 (bafilomycin A1) and by DIDS (4,4'-di-isothiocyanostilbene-2,2'-disulfonate). In plasma membranes, the currents were inhibited by the Na+/K+-ATPase inhibitor digitoxigenin. The distribution of the V-ATPase- and Na+/K+-ATPase-specific currents correlated with the distribution of vesicles and plasma membranes in the sucrose gradient. V-ATPase-specific currents depended on ATP with a K0.5 of 51+/-7 microM and were inhibited by ADP in a negatively co-operative manner with an IC50 of 1.2+/-0.6 microM. Activation of V-ATPase had stimulating effects on the chloride conductance in the vesicles. Low micromolar concentrations of DIDS fully inhibited the V-ATPase activity, whereas the chloride conductance was only partially affected. In contrast, NPPB [5-nitro-2-(3-phenylpropylamino)-benzoic acid] inhibited the chloride conductance but not the V-ATPase. The results presented describe electrical characteristics of synaptic V-ATPase and Na+/K+-ATPase in their native surroundings, and demonstrate the feasibility of the method for electrophysiological studies of transport proteins in native intracellular compartments and plasma membranes.
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Gramigni E, Tadini-Buoninsegni F, Bartolommei G, Santini G, Chelazzi G, Moncelli MR. Inhibitory effect of Pb2+ on the transport cycle of the Na+,K+-ATPase. Chem Res Toxicol 2010; 22:1699-704. [PMID: 19678672 DOI: 10.1021/tx9001786] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The effect of Pb(2+) on the transport cycle of the Na(+),K(+)-ATPase was characterized in detail at a molecular level by combining electrical and biochemical measurements. Electrical measurements were performed by adsorbing purified membrane fragments containing Na(+),K(+)-ATPase on a solid-supported membrane. Upon adsorption, the Na(+),K(+)-ATPase was activated by carrying out concentration jumps of different activating substrates, for example, Na(+) and ATP. Charge movements following Na(+),K(+)-ATPase activation were measured in the presence of various Pb(2+) concentrations to investigate the effect of Pb(2+) on different ion translocating steps of the pump cycle. These charge measurements were then compared to biochemical measurements of ATPase activity in the presence of increasing Pb(2+) concentration. Our results indicate that Pb(2+) inhibits cycling of the enzyme, but it does not affect cytoplasmic Na(+) binding and release of Na(+) ions at the extracellular side at concentrations below 10 muM. To explain the inhibitory effect of Pb(2+) on the Na(+),K(+)-ATPase, we propose that Pb(2+) may interfere with the hydrolytic cleavage of the phosphorylated intermediate E(2)P, which occurs in the K(+)-related branch of the pump cycle.
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Affiliation(s)
- Elisa Gramigni
- Department of Evolutionary Biology Leo Pardi, University of Florence, 50125 Florence, Italy
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25
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Xu J, Sigworth FJ, LaVan DA. Synthetic protocells to mimic and test cell function. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2010; 22:120-7. [PMID: 20217710 PMCID: PMC2845179 DOI: 10.1002/adma.200901945] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/17/2023]
Abstract
Synthetic protocells provide a new means to probe, mimic and deconstruct cell behavior; they are a powerful tool to quantify cell behavior and a useful platform to explore nanomedicine. Protocells are not simple particles; they mimic cell design and typically consist of a stabilized lipid bilayer with membrane proteins. With a finite number of well characterized components, protocells can be designed to maximize useful outputs. Energy conversion in cells is an intriguing output; many natural cells convert transmembrane ion gradients into electricity by membrane-protein regulated ion transport. Here, a synthetic cell system comprising two droplets separated by a lipid bilayer is described that functions as a biological battery. The factors that affect its electrogenic performance are explained and predicted by coupling equations of the electrodes, transport proteins and membrane behavior. We show that the output of such biological batteries can reach an energy density of 6.9 x 10(6) J m(-3), which is approximately 5% of the volumetric energy density of a lead-acid battery. The configuration with maximum power density has an energy conversion efficiency of 10%.
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Affiliation(s)
- Jian Xu
- School of Engineering and Applied Science, Yale University, New Haven, CT 06511 (USA)
| | - Fred J. Sigworth
- Department of Cellular and Molecular Physiology, Yale University, New Haven, CT 06520 (USA)
| | - David A. LaVan
- Ceramics Division, Materials Science and Engineering Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899 (USA)
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Schulz P, Dueck B, Mourot A, Hatahet L, Fendler K. Measuring ion channels on solid supported membranes. Biophys J 2009; 97:388-96. [PMID: 19580777 DOI: 10.1016/j.bpj.2009.04.022] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2009] [Revised: 04/06/2009] [Accepted: 04/13/2009] [Indexed: 10/20/2022] Open
Abstract
Application of solid supported membranes (SSMs) for the functional investigation of ion channels is presented. SSM-based electrophysiology, which has been introduced previously for the investigation of active transport systems, is expanded for the analysis of ion channels. Membranes or liposomes containing ion channels are adsorbed to an SSM and a concentration gradient of a permeant ion is applied. Transient currents representing ion channel transport activity are recorded via capacitive coupling. We demonstrate the application of the technique to liposomes reconstituted with the peptide cation channel gramicidin, vesicles from native tissue containing the nicotinic acetylcholine receptor, and membranes from a recombinant cell line expressing the ionotropic P2X2 receptor. It is shown that stable ion gradients, both inside as well as outside directed, can be applied and currents are recorded with an excellent signal/noise ratio. For the nicotinic acetylcholine receptor and the P2X2 receptor excellent assay quality factors of Z' = 0.55 and Z' = 0.67, respectively, are obtained. This technique opens up new possibilities in cases where conventional electrophysiology fails like the functional characterization of ion channels from intracellular compartments. It also allows for robust fully automatic assays for drug screening.
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Affiliation(s)
- Patrick Schulz
- Max Planck Institut für Biophysik, D-60438 Frankfurt/Main, Germany
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Bartolommei G, Moncelli MR, Rispoli G, Kelety B, Tadini-Buoninsegni F. Electrogenic ion pumps investigated on a solid supported membrane: comparison of current and voltage measurements. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2009; 25:10925-10931. [PMID: 19518101 DOI: 10.1021/la901469n] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Current and voltage measurements were performed on Na,K-ATPase and sarcoplasmic reticulum (SR) Ca-ATPase. Measurements of current transients under short-circuit conditions and of voltage transients under open-circuit conditions were carried out by employing a solid supported membrane (SSM). Purified membrane fragments containing Na,K-ATPase or native SR vesicles were adsorbed on a SSM and were activated by performing substrate concentration jumps. Current and voltage transients were recorded in the external circuit. They are related to pump activity and can be attributed to electrogenic events in the reaction cycles of the two enzymes. While current transients of very small amplitude are difficult to detect, the corresponding voltage transients can be measured with higher accuracy because of a much more favorable signal-to-noise ratio. Therefore, voltage measurements are preferable for the investigation of slow processes generating low current signals, e.g., for the analysis of low turnover transporters.
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Affiliation(s)
- G Bartolommei
- Department of Chemistry, University of Florence, Via della Lastruccia 3, 50019 Sesto Fiorentino, Italy
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28
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Nielsen CH. Biomimetic membranes for sensor and separation applications. Anal Bioanal Chem 2009; 395:697-718. [DOI: 10.1007/s00216-009-2960-0] [Citation(s) in RCA: 137] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2009] [Revised: 07/02/2009] [Accepted: 07/07/2009] [Indexed: 01/04/2023]
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Garcia-Celma JJ, Dueck B, Stein M, Schlueter M, Meyer-Lipp K, Leblanc G, Fendler K. Rapid activation of the melibiose permease MelB immobilized on a solid-supported membrane. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2008; 24:8119-8126. [PMID: 18572928 DOI: 10.1021/la800428h] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Rapid solution exchange on a solid-supported membrane (SSM) is investigated using fluidic structures and a solid-supported membrane of 1 mm diameter in wall jet geometry. The flow is analyzed with a new technique based on specific ion interactions with the surface combined with an electrical measurement. The critical parameters affecting the time course of the solution exchange and the transfer function describing the time resolution of the SSM system are determined. The experimental data indicate that solution transport represents an intermediate situation between the plug flow and the Hagen-Poiseuille laminar flow regime. However, to a good approximation the rise of the surface concentration can be described by Hagen-Poiseuille flow with ideal mixing at the surface of the SSM. Using an improved cuvette design, solution exchange as fast as 2 ms was achieved at the surface of a solid-supported membrane. As an application of the technique, the rate constant of a fast electrogenic reaction in the melibiose permease MelB, a bacterial ( Escherichia coli) sugar transporter, is determined. For comparison, the kinetics of a conformational transition of the same transporter was measured using stopped-flow tryptophan fluorescence spectroscopy. The relaxation time constant obtained for the charge displacement agrees with that determined in the stopped-flow experiments. This demonstrates that upon sugar binding MelB undergoes an electrogenic conformational transition with a rate constant of k approximately 250 s (-1).
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Affiliation(s)
- Juan J Garcia-Celma
- Department of Biophysical Chemistry, Max Planck Institute of Biophysics, D-60438 Frankfurt, Germany
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30
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Tadini-Buoninsegni F, Bartolommei G, Moncelli MR, Fendler K. Charge transfer in P-type ATPases investigated on planar membranes. Arch Biochem Biophys 2008; 476:75-86. [PMID: 18328799 DOI: 10.1016/j.abb.2008.02.031] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2008] [Revised: 02/19/2008] [Accepted: 02/20/2008] [Indexed: 11/18/2022]
Abstract
Planar lipid bilayers, e.g., black lipid membranes (BLM) and solid supported membranes (SSM), have been employed to investigate charge movements during the reaction cycle of P-type ATPases. The BLM/SSM method allows a direct measurement of the electrical currents generated by the cation transporter following chemical activation by a substrate concentration jump. The electrical current transients provides information about the reaction mechanism of the enzyme. In particular, the BLM/SSM technique allows identification of electrogenic steps which in turn may be used to localize ion translocation during the reaction cycle of the pump. In addition, using the high time resolution of the technique, especially when rapid activation via caged ATP is employed, rate constants of electrogenic and electroneutral steps can be determined. In the present review, we will discuss the main results obtained by the BLM and SSM methods and how they have contributed to unravel the transport mechanism of P-type ATPases.
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31
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Bartolommei G, Tadini-Buoninsegni F, Moncelli MR, Guidelli R. Electrogenic steps of the SR Ca-ATPase enzymatic cycle and the effect of curcumin. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2007; 1778:405-13. [PMID: 18005661 DOI: 10.1016/j.bbamem.2007.10.016] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/30/2007] [Revised: 10/10/2007] [Accepted: 10/17/2007] [Indexed: 11/18/2022]
Abstract
Sarcoplasmic reticulum (SR) vesicles were adsorbed on an octadecanethiol/phosphatidylcholine mixed bilayer anchored to a gold electrode, and the Ca-ATPase contained in the vesicles was activated by ATP concentration jumps in the presence of calcium ions. The resulting capacitive current transients are compared with those calculated on the basis of the enzymatic cycle of the calcium pump. This comparison provides information on the kinetics of the E(2)-E(1) conformational change and on its pH dependence. The alteration in the current transients following ATP concentration jumps in the presence of curcumin is examined. In particular, curcumin decreases the rate of slippage of the Ca-ATPase, and at concentrations above 10 microM reduces calcium transport by this pump.
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Affiliation(s)
- Gianluca Bartolommei
- Department of Chemistry, University of Florence, via della Lastruccia 3, 50019 Sesto Fiorentino (FI), Italy
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Kelety B, Diekert K, Tobien J, Watzke N, Dörner W, Obrdlik P, Fendler K. Transporter assays using solid supported membranes: a novel screening platform for drug discovery. Assay Drug Dev Technol 2006; 4:575-82. [PMID: 17115928 DOI: 10.1089/adt.2006.4.575] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Transporters are important targets in drug discovery. However, high throughput-capable assays for this class of membrane proteins are still missing. Here we present a novel drug discovery platform technology based on solid supported membranes. The functional principles of the technology are described, and a sample selection of transporter assays is discussed: the H(+)-dependent peptide transporter PepT1, the gastric proton pump, and the Na(+)/Ca(2+) exchanger. This technology promises to have an important impact on the drug discovery process.
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Tadini-Buoninsegni F, Bartolommei G, Moncelli MR, Guidelli R, Inesi G. Pre-steady state electrogenic events of Ca2+/H+ exchange and transport by the Ca2+-ATPase. J Biol Chem 2006; 281:37720-7. [PMID: 17032645 DOI: 10.1074/jbc.m606040200] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Native or recombinant SERCA (sarco(endo)plasmic reticulum Ca(2+) ATPase) was adsorbed on a solid supported membrane and then activated with Ca(2+) and ATP concentration jumps through rapid solution exchange. The resulting electrogenic events were recorded as electrical currents flowing along the external circuit. Current transients were observed following Ca(2+) jumps in the absence of ATP and following ATP jumps in the presence of Ca(2+). The related charge movements are attributed to Ca(2+) reaching its binding sites in the ground state of the enzyme (E(1)) and to its vectorial release from the enzyme phosphorylated by ATP (E(2)P). The Ca(2+) concentration and pH dependence as well as the time frames of the observed current transients are consistent with equilibrium and pre-steady state biochemical measurements of sequential steps within a single enzymatic cycle. Numerical integration of the current transients recorded at various pH values reveal partial charge compensation by H(+) in exchange for Ca(2+) at acidic (but not at alkaline) pH. Most interestingly, charge movements induced by Ca(2+) and ATP vary over different pH ranges, as the protonation probability of residues involved in Ca(2+)/H(+) exchange is lower in the E(1) than in the E(2)P state. Our single cycle measurements demonstrate that this difference contributes directly to the reduction of Ca(2+) affinity produced by ATP utilization and results in the countertransport of two Ca(2+) and two H(+) within each ATPase cycle at pH 7.0. The effects of site-directed mutations indicate that Glu-771 and Asp-800, within the Ca(2+) binding domain, are involved in the observed Ca(2+)/H(+) exchange.
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Meyer-Lipp K, Séry N, Ganea C, Basquin C, Fendler K, Leblanc G. The Inner Interhelix Loop 4–5 of the Melibiose Permease from Escherichia coli Takes Part in Conformational Changes after Sugar Binding. J Biol Chem 2006; 281:25882-92. [PMID: 16822867 DOI: 10.1074/jbc.m601259200] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Cytoplasmic loop 4-5 of the melibiose permease from Escherichia coli is essential for the process of Na+-sugar translocation (Abdel-Dayem, M., Basquin, C., Pourcher, T., Cordat, E., and Leblanc, G. (2003) J. Biol. Chem. 278, 1518-1524). In the present report, we analyze functional consequences of mutating each of the three acidic amino acids in this loop into cysteines. Among the mutants, only the E142C substitution impairs selectively Na+-sugar translocation. Because R141C has a similar defect, we investigated these two mutants in more detail. Liposomes containing purified mutated melibiose permease were adsorbed onto a solid supported lipid membrane, and transient electrical currents resulting from different substrate concentration jumps were recorded. The currents evoked by a melibiose concentration jump in the presence of Na+, previously assigned to an electrogenic conformational transition (Meyer-Lipp, K., Ganea, C., Pourcher, T., Leblanc, G., and Fendler, K. (2004) Biochemistry 43, 12606-12613), were much smaller for the two mutants than the corresponding signals in cysteineless MelB. Furthermore, in R141C the stimulating effect of melibiose on Na+ affinity was lost. Finally, whereas tryptophan fluorescence spectroscopy revealed impaired conformational changes upon melibiose binding in the mutants, fluorescence resonance energy transfer measurements indicated that the mutants still show cooperative modification of their sugar binding sites by Na+. These data suggest that: 1) loop 4-5 contributes to the coordinated interactions between the ion and sugar binding sites; 2) it participates in an electrogenic conformational transition after melibiose binding that is essential for the subsequent obligatory coupled translocation of substrates. A two-step mechanism for substrate translocation in the melibiose permease is suggested.
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Affiliation(s)
- Kerstin Meyer-Lipp
- Max Planck Institute of Biophysics, Max-von-Laue-Strasse 3, 60438 Frankfurt/M, Germany
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35
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Bartolommei G, Tadini-Buoninsegni F, Hua S, Moncelli MR, Inesi G, Guidelli R. Clotrimazole Inhibits the Ca2+-ATPase (SERCA) by Interfering with Ca2+ Binding and Favoring the E2 Conformation. J Biol Chem 2006; 281:9547-51. [PMID: 16452481 DOI: 10.1074/jbc.m510550200] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Clotrimazole (CLT) is an antimycotic imidazole derivative that is known to inhibit cytochrome P-450, ergosterol biosynthesis and proliferation of cells in culture, and to interfere with cellular Ca(2+) homeostasis. We found that CLT inhibits the Ca(2+)-ATPase of rabbit fast-twitch skeletal muscle (SERCA1), and we characterized in detail the effect of CLT on this calcium transport ATPase. We used biochemical methods for characterization of the ATPase and its partial reactions, and we also performed measurements of charge movements following adsorption of sarcoplasmic reticulum vesicles containing the ATPase onto a gold-supported biomimetic membrane. CLT inhibits Ca(2+)-ATPase and Ca(2+) transport with a K(I) of 35 mum. Ca(2+) binding in the absence of ATP and phosphoenzyme formation by the utilization of ATP in the presence of Ca(2+) are also inhibited within the same CLT concentration range. On the other hand, phosphoenzyme formation by utilization of P(i) in the absence of Ca(2+) is only minimally inhibited. It is concluded that CLT inhibits primarily Ca(2+) binding and, consequently, the Ca(2+)-dependent reactions of the SERCA cycle. It is suggested that CLT resides within the membrane-bound region of the transport ATPase, thereby interfering with binding and the conformational effects of the activating cation.
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Affiliation(s)
- Gianluca Bartolommei
- Department of Chemistry, University of Florence, 50019 Sesto Fiorentino, Florence, Italy
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Jiang Y, Hu M, Fan P, Wang J, Zhuo K. Activity coefficients and thermodynamic parameters for RbCl/CsCl + amide (acetamide, propanamide, and n-butanamide) + water system at 298.15 K. Biophys Chem 2005; 118:25-30. [PMID: 16039039 DOI: 10.1016/j.bpc.2005.06.010] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2005] [Revised: 06/19/2005] [Accepted: 06/19/2005] [Indexed: 11/19/2022]
Abstract
Electromotive force (emf) of the chemical cell without liquid-junction K-ISE | RbCl/CsCl ( m(E)) | ISE-Cl and K-ISE | RbCl/CsCl (m(E)), amide (m(N)) | ISE-Cl, have been measured at 298.15 K, where m(E)=(0.005 to 0.5) mol kg(-1) and m(N)= (0.05 to 3.0) mol kg(-1). The activity coefficients of RbCl/CsCl in amide (acetamide, propanamide, and n-butanamide) + water mixture can be obtained from these electromotive force data and in the mean time the Gibbs free energy interaction parameters of RbCl/CsCl + amide pair in water, g(EN), as well as the salt constant, k(S), can be evaluated. The results show that both g(EN)>0, k(S)>0 at 298.15 K, and all the activity coefficients of electrolyte in amide + water mixture increase with increasing the m(N), but it is a little complicated for the dependence of activity coefficients on m(E). These thermodynamic parameters were discussed in terms of a model of the structural interaction and electrostatic interaction and the dependence of them on the number of carbon atoms in amide as well as the radius of metal ions were interpreted by the group additivity principle.
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Affiliation(s)
- Yucheng Jiang
- College of Chemistry and Materials Science, Shaanxi Normal University, Chang-an South Road, 199 Xi'an, Shaanxi 710062, PR China.
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Bartolommei G, Buoninsegni FT, Moncelli MR. Calcium transport by sarcoplasmic reticulum Ca-ATPase can be investigated on a solid-supported membrane. Bioelectrochemistry 2004; 63:157-60. [PMID: 15110266 DOI: 10.1016/j.bioelechem.2003.07.010] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2003] [Revised: 07/17/2003] [Accepted: 07/22/2003] [Indexed: 10/26/2022]
Abstract
Sarcoplasmic reticulum (SR) native vesicles incorporating Ca-ATPase are adsorbed on a solid-supported lipid membrane (SSM). Upon adsorption, the ion pumps are chemically activated by concentration jumps of ATP and the capacitive current transients generated by SR Ca-ATPase are measured under potentiostatic conditions. The Michaelis-Menten constant, K(M), for ATP is evaluated by varying the concentration of ATP in the activating solution. This preliminary result shows that ion transport by SR Ca-ATPase can be suitably investigated by a technique based on concentration jumps on an SSM.
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Affiliation(s)
- G Bartolommei
- Laboratory of Bioelectrochemistry, Chemistry Department, University of Florence, via della Lastruccia 3, 50019 Sesto Fiorentino, Florence, Italy
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Matsuno N, Murawsky M, Ridgeway J, Cuppoletti J. Solid support membranes for ion channel arrays and sensors: application to rapid screening of pharmacological compounds. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2004; 1665:184-90. [PMID: 15471584 DOI: 10.1016/j.bbamem.2004.07.010] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/19/2003] [Revised: 07/20/2004] [Accepted: 07/29/2004] [Indexed: 11/28/2022]
Abstract
The use of solid supported membranes (SSM) was investigated for reconstitution of ion channels and for potential application to screen pharmacological reagents affecting ion channel function. The voltage-gated Kv1.5 K+ channel was reconstituted on an SSM and a current was measured. This current was dependent on the presence of K+, but not Na+, indicating that the Kv1.5 K+ channel maintained cation specificity when reconstituted on SSM. Two pharmacological reagents applied to Kv1.5 K+ channels reconstituted on SSM had similar inhibitory effects as those measured using Kv1.5 in biological membranes. SSM-mounted ion channels were stable enough to be washed with buffer solution and reused many times, allowing solution exchange essential for pharmacological drug screening.
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Affiliation(s)
- Nobunaka Matsuno
- Department of Chemistry, University of Cincinnati, Cincinnati, OH 45221-0172, USA
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Tadini Buoninsegni F, Bartolommei G, Moncelli MR, Inesi G, Guidelli R. Time-resolved charge translocation by sarcoplasmic reticulum Ca-ATPase measured on a solid supported membrane. Biophys J 2004; 86:3671-86. [PMID: 15189864 PMCID: PMC1304269 DOI: 10.1529/biophysj.103.036608] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2003] [Accepted: 03/01/2004] [Indexed: 11/18/2022] Open
Abstract
Sarcoplasmic reticulum vesicles were adsorbed on an octadecanethiol/phosphatidylcholine mixed bilayer anchored to a gold electrode, and the Ca-ATPase contained in the vesicles was activated by ATP concentration jumps both in the absence and in the presence of K(+) ions and at different pH values. Ca(2+) concentration jumps in the absence of ATP were also carried out. The resulting capacitive current transients were analyzed together with the charge under the transients. The relaxation time constants of the current transients were interpreted on the basis of an equivalent circuit. The current transient after ATP concentration jumps and the charge after Ca(2+) concentration jumps in the absence of ATP exhibit almost the same dependence upon the Ca(2+) concentration, with a half-saturating value of approximately 1.5 microM. The pH dependence of the charge after Ca(2+) translocation demonstrates the occurrence of one H(+) per one Ca(2+) countertransport at pH 7 by direct charge-transfer measurements. The presence of K(+) decreases the magnitude of the current transients without altering their shape; this decrease is explained by K(+) binding to the cytoplasmic side of the pump in the E(1) conformation and being released to the same side during the E(1)-E(2) transition.
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40
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Tadini Buoninsegni F, Dolfi A, Guidelli R. Two Photobioelectrochemical Applications of Self-Assembled Films on Mercury. ACTA ACUST UNITED AC 2004. [DOI: 10.1135/cccc20040292] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
The homogeneous, defect-free surface of a hanging mercury drop electrode was used to self-assemble films apt for the investigation of two photobioelectrochemical systems. Monolayers of straight-chain C12-C18alkane-1-thiols were anchored to a hanging mercury drop electrode and a film of chlorophyll was self-assembled on the top of them. The dependence of the photocurrents generated by illumination of the chlorophyll film with red light, on the thickness of the alkane-1-thiol monolayer and the applied potential is discussed. The photocurrents of purple membrane fragments, adsorbed on a mixed hexadecane-1-thiol/ dioleoylphosphatidylcholine bilayer self-assembled on mercury, were investigated in the presence of sodium perchlorate, chloride and acetate. The effect of the anions on the kinetics of the light-driven proton transport by bacteriorhodopsin has been determined.
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41
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Transport Proteins on Solid-Supported Membranes: From Basic Research to Drug Discovery. ACTA ACUST UNITED AC 2004. [DOI: 10.1007/978-3-662-05204-4_13] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/11/2023]
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42
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Burzik C, Kaim G, Dimroth P, Bamberg E, Fendler K. Charge displacements during ATP-hydrolysis and synthesis of the Na+-transporting FoF1-ATPase of Ilyobacter tartaricus. Biophys J 2003; 85:2044-54. [PMID: 12944317 PMCID: PMC1303376 DOI: 10.1016/s0006-3495(03)74632-3] [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] [Received: 08/16/2002] [Accepted: 04/03/2003] [Indexed: 11/21/2022] Open
Abstract
Transient electrical currents generated by the Na(+)-transporting F(o)F(1)-ATPase of Ilyobacter tartaricus were observed in the hydrolytic and synthetic mode of the enzyme. Two techniques were applied: a photochemical ATP concentration jump on a planar lipid membrane and a rapid solution exchange on a solid supported membrane. We have identified an electrogenic reaction in the reaction cycle of the F(o)F(1)-ATPase that is related to the translocation of the cation through the membrane bound F(o) subcomplex of the ATPase. In addition, we have determined rate constants for the process: For ATP hydrolysis this reaction has a rate constant of 15-30 s(-1) if H(+) is transported and 30-60 s(-1) if Na(+) is transported. For ATP synthesis the rate constant is 50-70 s(-1).
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Abstract
In the Na,K-ATPase the charge-translocating reaction steps were found to be binding of the third Na(+) ion to the cytoplasmic side and the release of all three Na(+) ions to the extracellular side as well as binding of the two K(+) ions on the extracellular side. The conformation transition E(1) --> E(2) was only of minor electrogenicity; all other reaction steps produced no significant charge movements. In the SR Ca-ATPase and the gastric H,K-ATPase, all ion-binding and -release steps were identified to move charge through the membrane. The high-resolution structure of the SR Ca-ATPase in state E(1) revealed the position of the ion-binding sites in the transmembrane part of the protein. If the same arrangement is assumed for the Na pump, the missing expected charge movements in state E(1) may to be assumed to be apparent effects. With the proposal that binding of 2 Na(+) or 2 K(+) is compensated correspondingly by H(+) ions, agreement between structural and functional aspects is obtained. Investigations of the pH-dependence of ion-binding steps indicate competition between the ions and electrogenic H(+) binding in support of this concept.
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Tadini-Buoninsegni F, Nassi P, Nediani C, Dolfi A, Guidelli R. Investigation of Na(+),K(+)-ATPase on a solid supported membrane: the role of acylphosphatase on the ion transport mechanism. BIOCHIMICA ET BIOPHYSICA ACTA 2003; 1611:70-80. [PMID: 12659947 DOI: 10.1016/s0005-2736(02)00722-8] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Charge translocation by Na(+),K(+)-ATPase was investigated by adsorbing membrane fragments containing Na(+),K(+)-ATPase from pig kidney on a solid supported membrane (SSM). Upon adsorption, the ion pumps were activated by performing ATP concentration jumps at the surface of the SSM, and the capacitive current transients generated by Na(+),K(+)-ATPase were measured under potentiostatic conditions. To study the behavior of the ion pump under multiple turnover conditions, ATP concentration jump experiments were carried out in the presence of Na(+) and K(+) ions. Current transients induced by ATP concentration jumps were also recorded in the presence of the enzyme alpha-chymotrypsin. The effect of acylphosphatase (AcP), a cytosolic enzyme that may affect the functioning of Na(+),K(+)-ATPase by hydrolyzing its acylphosphorylated intermediate, was investigated by performing ATP concentration jumps both in the presence and in the absence of AcP. In the presence of Na(+) but not of K(+), the addition of AcP causes the charge translocated as a consequence of ATP concentration jumps to decrease by about 50% over the pH range from 6 to 7, and to increase by about 20% at pH 8. Conversely, no appreciable effect of pH upon the translocated charge is observed in the absence of AcP. The above behavior suggests that protons are involved in the AcP-catalyzed dephosphorylation of the acylphosphorylated intermediate of Na(+),K(+)-ATPase.
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45
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Apell HJ, Diller A. Do H+ ions obscure electrogenic Na+ and K+ binding in the E1 state of the Na,K-ATPase? FEBS Lett 2002; 532:198-202. [PMID: 12459489 DOI: 10.1016/s0014-5793(02)03675-x] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
In contrast to other P-type ATPases, the Na,K-ATPase binding and release of ions on the cytoplasmic side, to the state called E1, is not electrogenic with the exception of the third Na+. Since the high-resolution structure of the closely related SR Ca-ATPase in state E1 revealed the ion-binding sites deep inside the transmembrane part of the protein, the missing electrogenicity in state E1 can be explained by an obscuring counter-movement of H+ ions. Evidence for such a mechanism is presented by analysis of pH effects on Na+ and K+ binding and by electrogenic H+ movements in the E1 conformation of the Na,K-ATPase.
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Affiliation(s)
- Hans-Jürgen Apell
- University of Konstanz, Biology, Universitätsstrasse 10, Konstanz 78457, Germany.
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46
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Bamberg E, Clarke RJ, Fendler K. Electrogenic properties of the Na+,K+-ATPase probed by presteady state and relaxation studies. J Bioenerg Biomembr 2001; 33:401-5. [PMID: 11762915 DOI: 10.1023/a:1010667407003] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Electrical measurements on planar lipid bilayers, patch/voltage clamp experiments, and spectroscopic investigations involving a potential sensitive dye are reviewed. These experiments were performed to analyze the kinetics of charge translocation of the Na+,K+-ATPase. High time resolution was achieved by applying caged ATP, voltage-jump, and stopped-flow techniques, respectively. Kinetic parameters and the electrogenicity of the relevant transitions in the Na+,K+-ATPase reaction cycle are discussed.
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Affiliation(s)
- E Bamberg
- Max-Planck-Institut für Biophysik, Frankfurt am Main, Germany.
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48
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Salonikidis PS, Kirichenko SN, Tatjanenko LV, Schwarz W, Vasilets LA. Extracellular pH modulates kinetics of the Na(+),K(+)-ATPase. BIOCHIMICA ET BIOPHYSICA ACTA 2000; 1509:496-504. [PMID: 11118558 DOI: 10.1016/s0005-2736(00)00356-4] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
To investigate effects of pH on the Na(+),K(+)-ATPase, we used the Xenopus oocytes to measure transient charge movements in the absence of extracellular K(+), and steady-state currents mediated by the pump as well as ATPase activity. The activity of purified Na(+), K(+)-ATPase strongly depends on pH, which has been attributed to protonation of intracellular sites. The steady-state current reflects pump activity, the transient charge movement voltage-dependent interaction of external Na(+) ions with the pump molecule and/or conformational changes during Na(+)/Na(+) exchange. The steady-state current exhibits a characteristic voltage dependence with maximum at about 0 mV at low external K(+) (< or =2 mM) and with 50 Na(+). This dependency is not significantly affected by changes in external pH in the range from pH 9 to pH 6. Only below pH 6, the voltage dependence of pump current becomes less steep, and may be attributed to a pH-dependent inhibition of the forward pump cycle by external Na(+). External stimulation of the pump by K(+) in the absence of Na(+) can be described by a voltage-dependent K(m) value with an apparent valency z(K). At higher external pH the z(K) value is reduced. The transient current signal in the absence of external K(+) can be described by the sum of three exponentials with voltage-dependent time constants of about 50 ms, 700 micros and less than 100 micros during pulses to 0 mV. The charge distribution was calculated by integration of the transient current signals. The slowest component and the associated charge distributions do not significantly depend on external pH changes. The intermediate component of the transients is represented by a voltage-dependent rate constant which shows a minimum at about -120 mV and increases with decreasing pH. Nevertheless, the contribution to the charge movement is not altered by pH changes due to a simultaneous increase of the amplitude of this component. We conclude that reduction of external pH counteracts external K(+) and Na(+) binding.
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Krysinski P, Moncelli MR, Tadini-Buoninsegni F. A voltammetric study of monolayers and bilayers self-assembled on metal electrodes. Electrochim Acta 2000. [DOI: 10.1016/s0013-4686(99)00412-0] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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50
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Domaszewicz W, Apell H. Binding of the third Na+ ion to the cytoplasmic side of the Na,K-ATPase is electrogenic. FEBS Lett 1999; 458:241-6. [PMID: 10481073 DOI: 10.1016/s0014-5793(99)01162-x] [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: 11/15/2022]
Abstract
A new experimental setup was constructed to allow parallel measurements of total internal reflection fluorescence and of capacitance changes in Na,K-ATPase-containing membranes. Effects correlated with cytoplasmic sodium binding to Na,K-ATPase were investigated. Ion binding-induced fluorescence changes of the electrochromic dye RH421 in membrane fragments adsorbed on a transparent capacitative electrode corresponded perfectly to capacitance increases detected by a lock-in technique. From these electric measurements it was possible to estimate a dielectric coefficient of about 0.25 for the electrogenic binding of the third Na+ ion. Binding of K+ to cytoplasmic sites was electroneutral.
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Affiliation(s)
- W Domaszewicz
- Department of Biology, University of Konstanz, Germany
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