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Gillman C, Patel K, Unge J, Gonen T. The structure of the neurotoxin palytoxin determined by MicroED. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.03.31.535166. [PMID: 37034718 PMCID: PMC10081313 DOI: 10.1101/2023.03.31.535166] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Palytoxin (PTX) is a potent neurotoxin found in marine animals that can cause serious symptoms such as muscle contractions, haemolysis of red blood cells and potassium leakage. Despite years of research, very little is known about the mechanism of PTX. However, recent advances in the field of cryoEM, specifically the use of microcrystal electron diffraction (MicroED), have allowed us to determine the structure of PTX. It was discovered that PTX folds into a hairpin motif and is able to bind to the extracellular gate of Na,K-ATPase, which is responsible for maintaining the electrochemical gradient across the plasma membrane. These findings, along with molecular docking simulations, have provided important insights into the mechanism of PTX and can potentially aid in the development of molecular agents for treating cases of PTX exposure.
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Affiliation(s)
- Cody Gillman
- Department of Biological Chemistry, University of California, Los Angeles CA, USA
- Molecular Biology Institute, University of California, Los Angeles CA, USA
| | - Khushboo Patel
- Department of Biological Chemistry, University of California, Los Angeles CA, USA
| | - Johan Unge
- Department of Biological Chemistry, University of California, Los Angeles CA, USA
| | - Tamir Gonen
- Department of Biological Chemistry, University of California, Los Angeles CA, USA
- Molecular Biology Institute, University of California, Los Angeles CA, USA
- Department of Physiology, University of California, Los Angeles CA, USA
- Howard Hughes Medical Institute, University of California, Los Angeles CA, USA
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Fedosova NU, Habeck M, Nissen P. Structure and Function of Na,K-ATPase-The Sodium-Potassium Pump. Compr Physiol 2021; 12:2659-2679. [PMID: 34964112 DOI: 10.1002/cphy.c200018] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Na,K-ATPase is an ubiquitous enzyme actively transporting Na-ions out of the cell in exchange for K-ions, thereby maintaining their concentration gradients across the cell membrane. Since its discovery more than six decades ago the Na-pump has been studied extensively and its vital physiological role in essentially every cell has been established. This article aims at providing an overview of well-established biochemical properties with a focus on Na,K-ATPase isoforms, its transport mechanism and principle conformations, inhibitors, and insights gained from crystal structures. © 2021 American Physiological Society. Compr Physiol 11:1-21, 2021.
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Affiliation(s)
| | - Michael Habeck
- Department of Molecular Biology and Genetics, Danish Research Institute of Translational Neuroscience - DANDRITE, Nordic EMBL Partnership for Molecular Medicine, Aarhus University, Aarhus, Denmark
| | - Poul Nissen
- Department of Molecular Biology and Genetics, Danish Research Institute of Translational Neuroscience - DANDRITE, Nordic EMBL Partnership for Molecular Medicine, Aarhus University, Aarhus, Denmark
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Guppy R, Ackbarali C, Ibrahim D. Toxicity of crude organic extracts from the zoanthid Palythoa caribaeorum: A biogeography approach. Toxicon 2019; 167:117-122. [PMID: 31211958 DOI: 10.1016/j.toxicon.2019.06.020] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2019] [Revised: 06/06/2019] [Accepted: 06/14/2019] [Indexed: 01/21/2023]
Abstract
Marine isolates such as palytoxin (PTX) are of concern within the Caribbean region due to their toxicity. PTX for example has been described as a one of the most known potent marine toxins, known to prevent predation from larger species (e.g. vertebrates) as well as the prevention of being overgrown from other coral species. PTX is a polyhydroxylated polyether toxin with a very large and complex chemical structure that possesses both hydrophilic and lipophilic properties. Previous acute toxicity tests using brine shrimp (Artemia salina) and PTX extract had shown it to be moderately toxic. In humans, PTX has been credited to be responsible for extreme symptoms such anaphylactic shock, rapid cardiac failure and eventual death occurring within minutes. Extrapolation for human dose ranges has therefore been suggested to be between 2.3 and 31.5 μg. This study isolates a potentially PTX-enriched extract from Palythoa caribaeorum and examines its organic extract toxicity from a biogeography perspective from a within-colony to a variety of reef sites around Trinidad and Tobago that are popular for marine visitors. This research represents an acute study with a high level of crude organic extract toxicity on A. salina whilst postulating potential factors which may contribute to its extreme toxicity and the risk posed to users of these environments.
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Affiliation(s)
- Reia Guppy
- Centre for Maritime and Ocean Studies, Marine Sciences, The University of Trinidad and Tobago, Chaguaramas, Trinidad and Tobago.
| | - Christopher Ackbarali
- Centre for Maritime and Ocean Studies, Marine Sciences, The University of Trinidad and Tobago, Chaguaramas, Trinidad and Tobago
| | - Damien Ibrahim
- Centre for Maritime and Ocean Studies, Marine Sciences, The University of Trinidad and Tobago, Chaguaramas, Trinidad and Tobago
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Vleeskens E, Clarke RJ. Kinetic contribution to extracellular Na +/K + selectivity in the Na +/K + pump. FEBS Open Bio 2018; 8:854-859. [PMID: 29744299 PMCID: PMC5929939 DOI: 10.1002/2211-5463.12418] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2017] [Revised: 03/16/2018] [Accepted: 03/22/2018] [Indexed: 11/25/2022] Open
Abstract
The sodium potassium pump (Na+,K+‐ATPase) shows a high selectivity for K+ over Na+ binding from the extracellular medium. To understand the K+ selectivity in the presence of a high concentration of competing Na+ ions requires consideration of more than just ion binding affinities. Here, equilibrium‐based calculations of the extracellular occupation of the Na+,K+‐ATPase transport sites by Na+ and K+ are compared to fluxes through Na+ and K+ transport pathways. The results show that, under physiological conditions, there is a 332‐fold selectivity for pumping of K+ from the extracellular medium into the cytoplasm relative to Na+, whereas equilibrium calculations alone predict only a 7.5‐fold selectivity for K+. Thus, kinetic effects make a major contribution to the determination of extracellular K+ selectivity.
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Affiliation(s)
| | - Ronald J Clarke
- School of Chemistry University of Sydney Australia.,The University of Sydney Nano Institute Australia
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Patocka J, Gupta RC, Wu QH, Kuca K. Toxic potential of palytoxin. ACTA ACUST UNITED AC 2015; 35:773-780. [DOI: 10.1007/s11596-015-1506-3] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2014] [Revised: 07/06/2015] [Indexed: 01/07/2023]
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8
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Guo B, Gurel PS, Shu R, Higgs HN, Pellegrini M, Mierke DF. Monitoring ATP hydrolysis and ATPase inhibitor screening using (1)H NMR. Chem Commun (Camb) 2014; 50:12037-9. [PMID: 25170530 PMCID: PMC4262093 DOI: 10.1039/c4cc04399e] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We present a versatile method to characterize ATPase and kinase activities and discover new inhibitors of these proteins. The proton NMR-based assay directly monitors ATP turnover and is easy to implement, requires no additional reagents and can potentially be applied to GTP. We validated the method's accuracy, applied it to the monitoring of ATP turnover by actin and to the screening of ATPase inhibitors, and showed that it is also applicable for the monitoring of GTP hydrolysis.
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Affiliation(s)
- Bingqian Guo
- Department of Chemistry, Dartmouth College, Hanover 03755, USA
| | - Pinar S. Gurel
- Department of Biochemistry, Geisel School of Medicine, Dartmouth College, Hanover 03755, USA
| | - Rui Shu
- Department of Biochemistry, Geisel School of Medicine, Dartmouth College, Hanover 03755, USA
| | - Henry N. Higgs
- Department of Biochemistry, Geisel School of Medicine, Dartmouth College, Hanover 03755, USA
| | | | - Dale F. Mierke
- Department of Chemistry, Dartmouth College, Hanover 03755, USA
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9
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Damnjanovic B, Apell HJ. Role of protons in the pump cycle of KdpFABC investigated by time-resolved kinetic experiments. Biochemistry 2014; 53:3218-28. [PMID: 24766073 DOI: 10.1021/bi500336w] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The time-resolved kinetics of the KdpFABC complex solubilized in Aminoxide WS-35 was investigated by ATP concentration jump experiments. ATP was photoreleased from its inactive precursor, caged ATP, and charge movements in the membrane domain of the KdpFABC were detected by the electrochromic dye RH421. At low ATP concentrations, the ATP binding step became rate-limiting with an apparent, pH-independent ATP binding affinity of ~70 μM. At saturating ATP concentrations, the rate-limiting step is the conformational transition (E1-P → P-E2) with a rate constant of ~1.7 s(-1) at 20 °C that was independent of K(+) concentration. This observation together with the detected fluorescence decrease indicates that K(+) (or another positive ion) is bound in the membrane domain after enzyme phosphorylation and the conformational transition to the P-E2 state. pH dependence experiments revealed different roles of H(+) in the transport mechanism. Two different functions of protons for the ion pump must be distinguished. On one hand, there are electrogenically bound "functional" protons, which are not transported but prerequisite for the performance of the ATP-driven half-cycle. On the other hand, protons bind to the transport sites, acting as weak congeners of K(+). There possibly are noncompetitively bound protons, affecting the enzyme activity and/or coupling between KdpA and KdpB subunits. Finally, the recently proposed Post-Albers model for the KdpFABC complex was supplemented with stoichiometry factors of 2 for K(+) and 3 for H(+), and additional inhibitory side reactions controlled by H(+) were introduced, which are relevant at pH <6.5 and/or in the absence of K(+).
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Pelin M, Boscolo S, Poli M, Sosa S, Tubaro A, Florio C. Characterization of palytoxin binding to HaCaT cells using a monoclonal anti-palytoxin antibody. Mar Drugs 2013; 11:584-98. [PMID: 23442788 PMCID: PMC3705359 DOI: 10.3390/md11030584] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2012] [Revised: 01/12/2013] [Accepted: 02/15/2013] [Indexed: 01/14/2023] Open
Abstract
Palytoxin (PLTX) is the reference compound for a group of potent marine biotoxins, for which the molecular target is Na+/K+-ATPase. Indeed, ouabain (OUA), a potent blocker of the pump, is used to inhibit some PLTX effects in vitro. However, in an effort to explain incomplete inhibition of PLTX cytotoxicity, some studies suggest the possibility of two different binding sites on Na+/K+-ATPase. Hence, this study was performed to characterize PLTX binding to intact HaCaT keratinocytes and to investigate the ability of OUA to compete for this binding. PLTX binding to HaCaT cells was demonstrated by immunocytochemical analysis after 10 min exposure. An anti-PLTX monoclonal antibody-based ELISA showed that the binding was saturable and reversible, with a K(d) of 3 × 10-10 M. However, kinetic experiments revealed that PLTX binding dissociation was incomplete, suggesting an additional, OUA-insensitive, PLTX binding site. Competitive experiments suggested that OUA acts as a negative allosteric modulator against high PLTX concentrations (0.3-1.0 × 10-7 M) and possibly as a non-competitive antagonist against low PLTX concentrations (0.1-3.0 × 10-9 M). Antagonism was supported by PLTX cytotoxicity inhibition at OUA concentrations that displaced PLTX binding (1 × 10-5 M). However, this inhibition was incomplete, supporting the existence of both OUA-sensitive and -insensitive PLTX binding sites.
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Affiliation(s)
- Marco Pelin
- Department of Life Sciences, University of Trieste, Via A. Valerio 6, 34127 Trieste, Italy; E-Mails: (M.P.); (S.B.); (S.S.); (C.F.)
| | - Sabrina Boscolo
- Department of Life Sciences, University of Trieste, Via A. Valerio 6, 34127 Trieste, Italy; E-Mails: (M.P.); (S.B.); (S.S.); (C.F.)
| | - Mark Poli
- U.S. Army Medical Research Institute of Infectious Diseases, Ft Detrick, MD 21701, USA; E-Mail:
| | - Silvio Sosa
- Department of Life Sciences, University of Trieste, Via A. Valerio 6, 34127 Trieste, Italy; E-Mails: (M.P.); (S.B.); (S.S.); (C.F.)
| | - Aurelia Tubaro
- Department of Life Sciences, University of Trieste, Via A. Valerio 6, 34127 Trieste, Italy; E-Mails: (M.P.); (S.B.); (S.S.); (C.F.)
- Author to whom correspondence should be addressed; E-Mail: ; Tel.: +39-040-5588835; Fax: +39-040-5583215
| | - Chiara Florio
- Department of Life Sciences, University of Trieste, Via A. Valerio 6, 34127 Trieste, Italy; E-Mails: (M.P.); (S.B.); (S.S.); (C.F.)
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11
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Gervásio OL, Phillips WD, Cole L, Allen DG. Caveolae respond to cell stretch and contribute to stretch-induced signaling. J Cell Sci 2011; 124:3581-90. [PMID: 22045729 DOI: 10.1242/jcs.084376] [Citation(s) in RCA: 70] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Caveolae are invaginations of the plasma membrane that are formed by caveolins. Caveolar membranes are also enriched in cholesterol, glycosphingolipids and signaling enzymes such as Src kinase. Here we investigate the effect of cell stretch upon caveolar dynamics and signaling. Transfection of C2 myoblasts with caveolin-3-YFP led to the formation of caveolae-like membrane pits 50-100 nm in diameter. Glycosphingolipids became immobilized and tightly packed together within caveolin-rich regions of the plasma membrane. Fluorescence resonance energy transfer (FRET) was used to assess the degree of glycosphingolipid packing. Myoblasts were subjected to a brief (1 minute) stretch on an elastic substratum. Stretch caused a reduction in glycosphingolipid FRET, consistent with a reversible unfolding of caveolar pits in response to membrane tension. Cells expressing caveolin-3-YFP also displayed an enhanced stretch-induced activation of Src kinase, as assessed by immunofluorescence. Repeated stretches resulted in the trafficking and remodeling of caveolin-3-rich membrane domains and accelerated turnover of membrane glycosphingolipids. The stretch-induced unfolding of caveolae, activation of Src and redistribution of caveolin and glycosphingolipids might reflect mechanisms of the cellular adaptation to mechanical stresses.
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Affiliation(s)
- Othon L Gervásio
- School of Medical Sciences, Discipline of Physiology (F13), Bosch Institute, University of Sydney, NSW 2006, Australia
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12
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Confining the sodium pump in a phosphoenzyme form: the effect of lead(II) ions. Biophys J 2011; 99:2087-96. [PMID: 20923642 DOI: 10.1016/j.bpj.2010.07.050] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2010] [Revised: 07/22/2010] [Accepted: 07/23/2010] [Indexed: 11/21/2022] Open
Abstract
The effect of Pb(2+) ions on the Na(+),K(+)-ATPase was investigated in detail by means of steady-state fluorescence spectroscopy. Experiments were performed by using the electrochromic styryl dye RH421. It is shown that Pb(2+) ions can bind reversibly to the protein and do not affect the Na(+) and K(+) binding affinities in the E(1) and P-E(2) conformations of the enzyme. The pH titrations indicate that lead(II) favors binding of one H(+) to the P-E(2) conformation in the absence of K(+). A model scheme is proposed that accounts for the experimental results obtained for backdoor phosphorylation of the enzyme in the presence of Pb(2+) ions. Taken together, our results clearly indicate that Pb(2+) bound to the enzyme stabilizes an E(2)-type conformation. In particular, under conditions that promote enzyme phosphorylation, Pb(2+) ions are able to confine the Na(+),K(+)-ATPase into a phosphorylated E(2) state.
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13
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Rossini GP, Bigiani A. Palytoxin action on the Na(+),K(+)-ATPase and the disruption of ion equilibria in biological systems. Toxicon 2010; 57:429-39. [PMID: 20932855 DOI: 10.1016/j.toxicon.2010.09.011] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2010] [Revised: 09/03/2010] [Accepted: 09/24/2010] [Indexed: 11/29/2022]
Abstract
Palytoxin-group toxins (PlTX) exert their potent biological activity by altering mechanisms of ion homeostasis in excitable and non-excitable tissues. This review will describe major aspects that led to the relatively early identification of the Na(+),K(+)-ATPase as the molecular target and receptor of the toxin in sensitive systems. The importance of this pump in the normal functioning of animal cells has driven extensive investigative efforts. The recognized molecular mechanism of action of PlTX involves its binding to the extracellular portion of alpha subunit of this plasma membrane protein, which converts an enzyme carrying ions against their concentration gradients at the expense of chemical energy (ATP) into a non-selective cation channel, allowing passive flow of ions following their concentration gradients. More recent findings have indicated that PlTX would interfere with the normal strict coupling between inner and outer gates of the pump controlling the ion access to the Na(+),K(+)-ATPase, allowing the gates to be simultaneously open. The ability of PlTX to make internal portions of the Na(+),K(+)-ATPase accessible to relatively large molecules has been exploited to characterize the structure-function relationship of the pump, leading to a better understanding of its ion translocation pathway. Thus, forty years from the isolation of this potent marine biotoxin, a considerable understanding of its mode of action and of its potential as a research tool have been achieved and are the basis for promising future advancement in the characterization of biological systems and their alteration by PlTX.
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Affiliation(s)
- Gian Paolo Rossini
- Dipartimento di Scienze Biomediche, Università di Modena e Reggio Emilia, Via G. Campi 287, I-41125 Modena, Italy.
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Takeuchi A, Reyes N, Artigas P, Gadsby DC. Visualizing the mapped ion pathway through the Na,K-ATPase pump. Channels (Austin) 2009; 3:383-6. [PMID: 19806033 DOI: 10.4161/chan.3.6.9775] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
The Na(+),K(+)-ATPase pump achieves thermodynamically uphill exchange of cytoplasmic Na(+) ions for extracellular K(+) ions by using ATP-mediated phosphorylation, followed by autodephosphorylation, to power conformational changes that allow ion access to the pump's binding sites from only one side of the membrane at a time. Formally, the pump behaves like an ion channel with two tightly coupled gates that are constrained to open and close alternately. The marine agent palytoxin disrupts this coupling, allowing both gates to sometimes be open, so temporarily transforming a pump into an ion channel. We made a cysteine scan of Na(+),K(+)-ATPase transmembrane (TM) segments TM1 to TM6, and used recordings of Na(+) current flow through palytoxin-bound pump-channels to monitor accessibility of introduced cysteine residues via their reaction with hydrophilic methanethiosulfonate (MTS) reagents. To visualize the open-channel pathway, the reactive positions were mapped onto a homology model of Na(+),K(+)-ATPase based on the structure of the related sarcoplasmicand endoplasmic-reticulum (SERCA) Ca(2+)-ATPase in a BeF(3)(-)-trapped state,(1,2) in which the extra-cytoplasmic gate is wide open (although the cytoplasmic access pathway is firmly shut). The results revealed a single unbroken chain of reactive positions that traverses the pump from the extracellular surface to the cytoplasm, comprises residues from TM1, TM2, TM4 and TM6, and passes through the equivalent of cation binding site II in SERCA, but not through site I. Cavity search analysis of the homology model validated its use for mapping the data by yielding a calculated extra-cytoplasmic pathway surrounded by MTS-reactive residues. As predicted by previous experimental results, that calculated extra-cytoplasmic pathway abruptly broadens above residue T806, at the outermost end of TM6 that forms the floor of the extracellular-facing vestibule. These findings provide a structural basis for further understanding cation translocation by the Na(+),K(+)-ATPase and by other P-type pumps like the Ca(2+)- and H(+),K(+)-ATPases.
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Affiliation(s)
- Ayako Takeuchi
- Laboratory of Cardiac/Membrane Physiology, The Rockefeller University, New York, NY, USA
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Sinkins WG, Estacion M, Prasad V, Goel M, Shull GE, Kunze DL, Schilling WP. Maitotoxin converts the plasmalemmal Ca(2+) pump into a Ca(2+)-permeable nonselective cation channel. Am J Physiol Cell Physiol 2009; 297:C1533-43. [PMID: 19794142 DOI: 10.1152/ajpcell.00252.2009] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Abstract
Maitotoxin (MTX) activates Ca(2+)-permeable nonselective cation channels and causes a dramatic increase in cytosolic free Ca(2+) concentration ([Ca(2+)](i)) in every cell examined to date, but the molecular identity of the channels involved remains unknown. A clue came from studies of a structurally related marine toxin called palytoxin (PTX). PTX binds to the plasmalemmal Na(+)-K(+)-ATPase (NKA) and converts the Na(+) pump into a nonselective cation channel. Given the high permeability of the MTX channel for Ca(2+), we considered the possibility that MTX may bind to the plasmalemmal Ca(2+)-ATPase (PMCA) pump, and like PTX, convert the pump into a channel. To test this hypothesis, the PMCA was overexpressed in Spodoptera frugiperda (Sf9) insect cells and in human embryonic kidneys (HEK) 293 cells. In both cell types, enhanced expression of the PMCA was associated with a significant increase in MTX-induced whole cell membrane currents. The effect of MTX on whole cell currents in both wild-type and PMCA overexpressing HEK cells was sensitive to pump ligands including Ca(2+) and ATP. MTX-induced currents were significantly reduced by knockdown of PMCA1 in HEK cells using small interfering RNA or in mouse embryonic fibroblasts from genetically modified mice with the PMCA1(+/-) PMCA4(-/-) genotype. Finally, PMCA catalytic activity (i.e., Ca(2+)-ATPase) in isolated membranes, or in purified PMCA preparations, was inhibited by MTX. Together, these results suggest that MTX binds to and converts the PMCA pump into a Ca(2+)-permeable nonselective cation channel.
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Affiliation(s)
- William G Sinkins
- Department of Physiology, Rammelkamp Center for Education and Research, Case Western Reserve University School of Medicine, Cleveland, Ohio, USA
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Rodrigues AM, Infantosi AFC, de Almeida ACG. Palytoxin and the sodium/potassium pump—phosphorylation and potassium interaction. Phys Biol 2009; 6:036010. [DOI: 10.1088/1478-3975/6/3/036010] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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17
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Ares IR, Cagide E, Louzao MC, Espiña B, Vieytes MR, Yasumoto T, Botana LM. Ostreocin-D impact on globular actin of intact cells. Chem Res Toxicol 2009; 22:374-81. [PMID: 19154108 DOI: 10.1021/tx800273f] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Ostreocin-D, discovered in the past decade, is a marine toxin produced by dinoflagellates. It shares structure with palytoxin, a toxic compound responsible for the seafood intoxication named clupeotoxism. At the cellular level, the action sites and pharmacological effects for ostreocin-D are still almost unknown. Previously, we demonstrated that these toxins change the filamentous actin cytoskeleton, which is essential for multiple cellular functions. However, nothing has yet been reported about what happens with the unpolymerized actin pool. Here (i) the effects induced by ostreocin-D on unpolymerized actin, (ii) the Ca2+ role in such a process, and (iii) the cytotoxic activity of ostreocin-D on the human neuroblastoma BE(2)-M17 cell line are shown for the first time. Fluorescently labeled DNase I was used for staining of monomeric actin prior to detection with both laser-scanning cytometry and confocal microscopy techniques. Cellular viability was tested through a microplate metabolic activity assay. Ostreocin-D elicited a rearrangement of monomeric actin toward the nuclear region. This event was not accompanied by changes in its content. In addition, the presence or absence of external Ca2+ did not change these results. This toxin was also found to cause a decrease in the viability of neuroblastoma cells, which was inhibited by the specific blocker of Na+/K+-ATPase, ouabain. All these responses were comparable to those obtained with palytoxin under identical conditions. The data suggest that ostreocin-D modulates the unassembled actin pool, activating signal transduction pathways not related to Ca2+ influx in the same way as palytoxin.
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Affiliation(s)
- Isabel R Ares
- Departamento de Farmacología, Facultad de Veterinaria, Universidad de Santiago de Compostela, Campus de Lugo, 27002 Lugo, Spain
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Gadsby DC, Takeuchi A, Artigas P, Reyes N. Review. Peering into an ATPase ion pump with single-channel recordings. Philos Trans R Soc Lond B Biol Sci 2009; 364:229-38. [PMID: 18986966 DOI: 10.1098/rstb.2008.0243] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
In principle, an ion channel needs no more than a single gate, but a pump requires at least two gates that open and close alternately to allow ion access from only one side of the membrane at a time. In the Na+,K+-ATPase pump, this alternating gating effects outward transport of three Na+ ions and inward transport of two K+ ions, for each ATP hydrolysed, up to a hundred times per second, generating a measurable current if assayed in millions of pumps. Under these assay conditions, voltage jumps elicit brief charge movements, consistent with displacement of ions along the ion pathway while one gate is open but the other closed. Binding of the marine toxin, palytoxin, to the Na+,K+-ATPase uncouples the two gates, so that although each gate still responds to its physiological ligand they are no longer constrained to open and close alternately, and the Na+,K+-ATPase is transformed into a gated cation channel. Millions of Na+ or K+ ions per second flow through such an open pump-channel, permitting assay of single molecules and allowing unprecedented access to the ion transport pathway through the Na+,K+-ATPase. Use of variously charged small hydrophilic thiol-specific reagents to probe cysteine targets introduced throughout the pump's transmembrane segments allows mapping and characterization of the route traversed by transported ions.
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Affiliation(s)
- David C Gadsby
- Laboratory of Cardiac/Membrane Physiology, The Rockefeller University, New York, NY 10065, USA.
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Investigating the potassium interactions with the palytoxin induced channels in Na+/K+ pump. Comput Biol Chem 2009; 33:14-21. [DOI: 10.1016/j.compbiolchem.2008.07.008] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2007] [Revised: 07/03/2008] [Accepted: 07/06/2008] [Indexed: 11/18/2022]
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Takeuchi A, Reyes N, Artigas P, Gadsby DC. The ion pathway through the opened Na(+),K(+)-ATPase pump. Nature 2008; 456:413-6. [PMID: 18849964 PMCID: PMC2585603 DOI: 10.1038/nature07350] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2008] [Accepted: 08/20/2008] [Indexed: 11/09/2022]
Abstract
P-type ATPases pump ions across membranes, generating steep electrochemical gradients that are essential for the function of all cells. Access to the ion-binding sites within the pumps alternates between the two sides of the membrane to avoid the dissipation of the gradients that would occur during simultaneous access. In Na(+),K(+)-ATPase pumps treated with the marine agent palytoxin, this strict alternation is disrupted and binding sites are sometimes simultaneously accessible from both sides of the membrane, transforming the pumps into ion channels (see, for example, refs 2, 3). Current recordings in these channels can monitor accessibility of introduced cysteine residues to water-soluble sulphydryl-specific reagents. We found previously that Na(+),K(+) pump-channels open to the extracellular surface through a deep and wide vestibule that emanates from a narrower pathway between transmembrane helices 4 and 6 (TM4 and TM6). Here we report that cysteine scans from TM1 to TM6 reveal a single unbroken cation pathway that traverses palytoxin-bound Na(+),K(+) pump-channels from one side of the membrane to the other. This pathway comprises residues from TM1, TM2, TM4 and TM6, passes through ion-binding site II, and is probably conserved in structurally and evolutionarily related P-type pumps, such as sarcoplasmic- and endoplasmic-reticulum Ca(2+)-ATPases and H(+),K(+)-ATPases.
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Affiliation(s)
- Ayako Takeuchi
- Laboratory of Cardiac/Membrane Physiology, The Rockefeller University, New York, New York 10065, USA
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Franchini A, Casarini L, Ottaviani E. Toxicological effects of marine palytoxin evaluated by FETAX assay. CHEMOSPHERE 2008; 73:267-271. [PMID: 18672264 DOI: 10.1016/j.chemosphere.2008.06.043] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/09/2008] [Revised: 05/22/2008] [Accepted: 06/15/2008] [Indexed: 05/26/2023]
Abstract
The FETAX (frog embryo teratogenesis assay Xenopus) is considered a useful bioassay to detect health hazard substances. In the study of the marine toxin palytoxin (PTX), FETAX has revealed evident impacts on embryo mortality, teratogenesis and growth at the two highest (370 and 37nM) concentrations used. Significant mortality rates, peaks in the number of malformed embryos and delays in growth were found, while the total sample number fell by about 80% at the end of the assay with the concentrated dose. The histological analysis to evaluate the morpho-functional induced modifications demonstrated damage to the nervous and muscle tissue, a general reduction in the size of the main inner visceral organs and severe injury to the heart structure in some specimens. No inflammatory response was observed.
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Affiliation(s)
- Antonella Franchini
- Department of Animal Biology, University of Modena and Reggio Emilia, via Campi 213/D, 41100 Modena, Italy
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Rodrigues AM, Almeida ACG, Infantosi AFC. Effect of palytoxin on the sodium–potassium pump: model and simulation. Phys Biol 2008; 5:036005. [DOI: 10.1088/1478-3975/5/3/036005] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Abstract
The effect of the antimycotic drug clotrimazole (CLT) on the Na,K-ATPase was investigated using fluorescence and electrical measurements. The results obtained by steady-state fluorescence experiments with the electrochromic styryl dye RH421 were combined with those achieved by a pre-steady-state method based on fast solution exchange on a solid supported membrane that adsorbs the protein. Both techniques are suitable for monitoring the electrogenic steps of the pump cycle and are in general complementary, yielding distinct kinetic information. The experiments show clearly that CLT affects specific partial reactions of the pump cycle of the Na,K-ATPase with an affinity in the low micromolar range and in a reversible manner. All results can be consistently explained by proposing the CLT-promoted formation of an ion-occluded-CLT-bound conformational E(2) state, E(2)(CLT)(X(2)) that acts as a "dead-end" side track of the pump cycle, where X stands for H+ or K+. Na+ binding, enzyme phosphorylation, and Na+ transport were not affected by CLT, and at high CLT concentrations approximately (1/3) of the enzyme remained active in the physiological transport mode. The presence of Na+ and K+ destabilized the inactivated form of the Na,K-ATPase.
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Rodrigues AM, Almeida ACG, Infantosi AFC, Teixeira HZ, Duarte MA. Model and simulation of Na+/K+ pump phosphorylation in the presence of palytoxin. Comput Biol Chem 2008; 32:5-16. [PMID: 17897885 DOI: 10.1016/j.compbiolchem.2007.08.001] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2006] [Accepted: 08/10/2007] [Indexed: 10/22/2022]
Abstract
The ATP hydrolysis reactions responsible for the Na(+)/K(+)-ATPase phosphorylation, according to recent experimental evidences, also occur for the PTX-Na(+)/K(+) pump complex. Moreover, it has been demonstrated that PTX interferes with the enzymes phosphorylation status. However, the reactions involved in the PTX-Na(+)/K(+) pump complex phosphorylation are not very well established yet. This work aims at proposing a reaction model for PTX-Na(+)/K(+) pump complex, with similar structure to the Albers-Post model, to contribute to elucidate the PTX effect over Na(+)/K(+)-ATPase phosphorylation and dephosphorylation. Computational simulations with the proposed model support several hypotheses and also suggest: (i) phosphorylation promotes an increase of the open probability of induced channels; (ii) PTX reduces the Na(+)/K(+) pump phosphorylation rate; (iii) PTX may cause conformational changes to substates where the Na(+)/K(+)-ATPase may not be phosphorylated; (iv) PTX can bind to substates of the two principal states E1 and E2, with highest affinity to phosphorylated enzymes and with ATP bound to its low-affinity sites. The proposed model also allows previewing the behavior of the PTX-pump complex substates for different levels of intracellular ATP concentrations.
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Affiliation(s)
- Antônio M Rodrigues
- Biomedical Engineering Program, COPPE, Federal University of Rio de Janeiro, Brazil
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Rakowski RF, Artigas P, Palma F, Holmgren M, De Weer P, Gadsby DC. Sodium flux ratio in Na/K pump-channels opened by palytoxin. ACTA ACUST UNITED AC 2007; 130:41-54. [PMID: 17562821 PMCID: PMC2085370 DOI: 10.1085/jgp.200709770] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Palytoxin binds to Na+/K+ pumps in the plasma membrane of animal cells and opens an electrodiffusive cation pathway through the pumps. We investigated properties of the palytoxin-opened channels by recording macroscopic and microscopic currents in cell bodies of neurons from the giant fiber lobe, and by simultaneously measuring net current and 22Na+ efflux in voltage-clamped, internally dialyzed giant axons of the squid Loligo pealei. The conductance of single palytoxin-bound “pump-channels” in outside-out patches was ∼7 pS in symmetrical 500 mM [Na+], comparable to findings in other cells. In these high-[Na+], K+-free solutions, with 5 mM cytoplasmic [ATP], the K0.5 for palytoxin action was ∼70 pM. The pump-channels were ∼40–50 times less permeable to N-methyl-d-glucamine (NMG+) than to Na+. The reversal potential of palytoxin-elicited current under biionic conditions, with the same concentration of a different permeant cation on each side of the membrane, was independent of the concentration of those ions over the range 55–550 mM. In giant axons, the Ussing flux ratio exponent (n') for Na+ movements through palytoxin-bound pump-channels, over a 100–400 mM range of external [Na+] and 0 to −40 mV range of membrane potentials, averaged 1.05 ± 0.02 (n = 28). These findings are consistent with occupancy of palytoxin-bound Na+/K+ pump-channels either by a single Na+ ion or by two Na+ ions as might be anticipated from other work; idiosyncratic constraints are needed if the two Na+ ions occupy a single-file pore, but not if they occupy side-by-side binding sites, as observed in related structures, and if only one of the sites is readily accessible from both sides of the membrane.
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Affiliation(s)
- R F Rakowski
- Marine Biological Laboratory, Woods Hole, MA 02543, USA.
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Vale-Gonzalez C, Pazos MJ, Alfonso A, Vieytes MR, Botana LM. Study of the neuronal effects of ouabain and palytoxin and their binding to Na,K-ATPases using an optical biosensor. Toxicon 2007; 50:541-52. [PMID: 17548099 DOI: 10.1016/j.toxicon.2007.04.024] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2007] [Revised: 04/27/2007] [Accepted: 04/30/2007] [Indexed: 10/23/2022]
Abstract
The phycotoxin palytoxin (PTX) binds to Na,K-ATPase, inhibiting its activity and converting the pump into a channel. These mechanisms are poorly understood. We examined the effect of PTX on membrane potential (E(m)), intracellular calcium concentration ([Ca2+]i) and intracellular pH (pH(i)) in primary cultures of cerebellar granule cells (CGC) and compared PTX and ouabain actions in the same cellular parameters. In this system, PTX caused depolarization, intracellular calcium increase and acidification. This is similar to the effect of ouabain. Preincubation of the cells with ouabain, before addition of PTX, altered E(m), [Ca2+]i, and pH(i) in a fashion similar to that of ouabain alone. This suggest a direct interaction of PTX with the Na,K-ATPase. Therefore, we used a resonant mirror biosensor to evaluate the binding of PTX and ouabain to immobilized Na,K-ATPase. Ouabain binding to immobilized Na,K-ATPase was concentration-dependent. No binding of PTX to Na,K-ATPase was observed with up to 10 microM, or with PTX addition in the presence of ATP. The fact that ouabain binds to the pump in an immobilized conformation whereas not binding of PTX was observed indicates that PTX and ouabain do not share the same binding site, and PTX binding may require the tridimensional pump structure.
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Affiliation(s)
- C Vale-Gonzalez
- Departamento de Farmacología, Universidad de Santiago de Compostela, Campus Universitario s/n 27002 Lugo, Spain
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