1
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Zou X, Zhang Z, Lu H, Zhao W, Pan L, Chen Y. Functional effects of drugs and toxins interacting with Na V1.4. Front Pharmacol 2024; 15:1378315. [PMID: 38725668 PMCID: PMC11079311 DOI: 10.3389/fphar.2024.1378315] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2024] [Accepted: 04/08/2024] [Indexed: 05/12/2024] Open
Abstract
NaV1.4 is a voltage-gated sodium channel subtype that is predominantly expressed in skeletal muscle cells. It is essential for producing action potentials and stimulating muscle contraction, and mutations in NaV1.4 can cause various muscle disorders. The discovery of the cryo-EM structure of NaV1.4 in complex with β1 has opened new possibilities for designing drugs and toxins that target NaV1.4. In this review, we summarize the current understanding of channelopathies, the binding sites and functions of chemicals including medicine and toxins that interact with NaV1.4. These substances could be considered novel candidate compounds or tools to develop more potent and selective drugs targeting NaV1.4. Therefore, studying NaV1.4 pharmacology is both theoretically and practically meaningful.
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Affiliation(s)
- Xinyi Zou
- Zhejiang Provincial Key Laboratory of Resources Protection and Innovation of Traditional Chinese Medicine, College of Food and Health, Zhejiang Agriculture and Forestry University, Hangzhou, China
| | - Zixuan Zhang
- Zhejiang Provincial Key Laboratory of Resources Protection and Innovation of Traditional Chinese Medicine, College of Food and Health, Zhejiang Agriculture and Forestry University, Hangzhou, China
| | - Hui Lu
- Zhejiang Provincial Key Laboratory of Resources Protection and Innovation of Traditional Chinese Medicine, College of Food and Health, Zhejiang Agriculture and Forestry University, Hangzhou, China
| | - Wei Zhao
- Zhejiang Provincial Key Laboratory of Resources Protection and Innovation of Traditional Chinese Medicine, College of Food and Health, Zhejiang Agriculture and Forestry University, Hangzhou, China
| | - Lanying Pan
- Key Laboratory of Artificial Organs and Computational Medicine in Zhejiang Province, Shulan International Medical College, Zhejiang Shuren University, Hangzhou, China
| | - Yuan Chen
- Zhejiang Provincial Key Laboratory of Resources Protection and Innovation of Traditional Chinese Medicine, College of Food and Health, Zhejiang Agriculture and Forestry University, Hangzhou, China
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2
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Reimche JS, Del Carlo RE, Brodie ED, McGlothlin JW, Schlauch K, Pfrender ME, Brodie ED, Leblanc N, Feldman CR. The road not taken: Evolution of tetrodotoxin resistance in the Sierra garter snake (Thamnophis couchii) by a path less traveled. Mol Ecol 2022; 31:3827-3843. [PMID: 35596742 DOI: 10.1111/mec.16538] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2021] [Revised: 04/28/2022] [Accepted: 05/12/2022] [Indexed: 11/27/2022]
Abstract
The repeated evolution of tetrodotoxin (TTX) resistance provides a model for testing hypotheses about the mechanisms of convergent evolution. This poison is broadly employed as a potent antipredator defense, blocking voltage-gated sodium channels (Nav ) in muscles and nerves, paralyzing and sometimes killing predators. Resistance in taxa bearing this neurotoxin and a few predators appears to come from convergent replacements in specific Nav residues that interact with TTX. This stereotyped genetic response suggests molecular and phenotypic evolution may be constrained and predictable. Here, we investigate the extent of mechanistic convergence in garter snakes (Thamnophis) that prey on TTX-bearing newts (Taricha) by examining the physiological and genetic basis of TTX resistance in the Sierra garter snake (Th. couchii). We characterize variation in this predatory adaptation across populations at several biological scales: whole-animal TTX resistance; skeletal muscle resistance, functional genetic variation in three Nav encoding loci; and levels of gene expression for one of these loci. We found Th. couchii possess extensive geographic variation in resistance at the whole-animal and skeletal muscle levels. As in other Thamnophis, resistance at both levels is highly correlated, suggesting convergence across the biological levels linking organism to organ. However, Th. couchii shows no functional variation in Nav loci among populations or difference in candidate gene expression. Local variation in TTX resistance in Th. couchii cannot be explained by the same relationship between genotype and phenotype seen in other taxa. Thus, historical contingencies may lead different species of Thamnophis down alternative routes to local adaptation.
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Affiliation(s)
- Jessica S Reimche
- Department of Biology, Evolution, and Conservation Biology, University of Nevada, Reno, NV, USA.,Program in Ecology, Evolution, and Conservation Biology, University of Nevada, Reno, NV, USA
| | - Robert E Del Carlo
- Department of Pharmacology and 4Program in Cellular and Molecular Pharmacology and Physiology, University of Nevada, Reno, NV, USA
| | - Edmund D Brodie
- Department of Biology, Utah State University, Logan, UT, USA
| | - Joel W McGlothlin
- Department of Biological Sciences, Virginia Tech, Blacksburg, VA, USA
| | | | - Michael E Pfrender
- Department of Biological Sciences, University of Notre Dame, Notre Dame, IN, USA
| | - Edmund D Brodie
- Department of Biology, University of Virginia, Charlottesville, VA, USA
| | - Normand Leblanc
- Department of Pharmacology and 4Program in Cellular and Molecular Pharmacology and Physiology, University of Nevada, Reno, NV, USA
| | - Chris R Feldman
- Department of Biology, Evolution, and Conservation Biology, University of Nevada, Reno, NV, USA.,Program in Ecology, Evolution, and Conservation Biology, University of Nevada, Reno, NV, USA
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3
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Zhang J, Yuan H, Yao X, Chen S. Endogenous ion channels expressed in human embryonic kidney (HEK-293) cells. Pflugers Arch 2022; 474:665-680. [PMID: 35567642 DOI: 10.1007/s00424-022-02700-z] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2022] [Revised: 04/25/2022] [Accepted: 04/30/2022] [Indexed: 12/21/2022]
Abstract
Mammalian expression systems, particularly the human embryonic kidney (HEK-293) cells, combined with electrophysiological studies, have greatly benefited our understanding of the function, characteristic, and regulation of various ion channels. It was previously assumed that the existence of endogenous ion channels in native HEK-293 cells could be negligible. Still, more and more ion channels are gradually reported in native HEK-293 cells, which should draw our attention. In this regard, we summarize the different ion channels that are endogenously expressed in HEK-293 cells, including voltage-gated Na+ channels, Ca2+ channels, K+ channels, Cl- channels, nonselective cation channels, TRP channels, acid-sensitive ion channels, and Piezo channels, which may complicate the recording of the heterogeneously expressed ion channels to a certain degree. We noted that the expression patterns and channel profiles varied with different studies, which may be due to the distinct originality of the cells, cell culture conditions, passage numbers, and different recording protocols. Therefore, a better knowledge of endogenous ion channels may help minimize potential problems in characterizing heterologously expressed ion channels. Based on this, it is recommended that HEK-293 cells from unknown sources should be examined before transfection for the characterization of their functional profile, especially when the expression level of exogenous ion channels does not overwhelm the endogenous ion channels largely, or the current amplitude is not significantly higher than the native currents.
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Affiliation(s)
- Jun Zhang
- School of Biomedical Sciences and Li Ka Shing Institute of Health Science, The Chinese University of Hong Kong, Hong Kong, China
| | - Huikai Yuan
- Department of General Surgery, The First Affiliated Hospital of Harbin Medical University, Harbin, China
| | - Xiaoqiang Yao
- School of Biomedical Sciences and Li Ka Shing Institute of Health Science, The Chinese University of Hong Kong, Hong Kong, China
| | - Shuo Chen
- Department of Biopharmaceutical Sciences, School of Pharmacy, Harbin Medical University at Daqing, No. 39 Xinyang Rd, High-tech District, Daqing, 163319, Heilongjiang Province, China.
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4
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Haverinen J, Badr A, Vornanen M. Cardiac Toxicity of Cadmium Involves Complex Interactions Among Multiple Ion Currents in Rainbow Trout (Oncorhynchus mykiss) Ventricular Myocytes. ENVIRONMENTAL TOXICOLOGY AND CHEMISTRY 2021; 40:2874-2885. [PMID: 34255886 DOI: 10.1002/etc.5161] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/01/2021] [Revised: 05/11/2021] [Accepted: 07/08/2021] [Indexed: 06/13/2023]
Abstract
Cadmium (Cd2+ ) is cardiotoxic to fish, but its effect on the electrical excitability of cardiac myocytes is largely unknown. To this end, we used the whole-cell patch-clamp method to investigate the effects of Cd2+ on ventricular action potentials (APs) and major ion currents in rainbow trout (Oncorhynchus mykiss) ventricular myocytes. Trout were acclimated to +4 °C, and APs were measured at the acclimated temperature and elevated temperature (+18 °C). Cd2+ (10, 20, and 100 µM) altered the shape of the ventricular AP in a complex manner. The early plateau fell to less positive membrane voltages, and the total duration of AP prolonged. These effects were obvious at both +4 °C and +18 °C. The depression of the early plateau is due to the strong Cd2+ -induced inhibition of the L-type calcium (Ca2+ ) current (ICaL ), whereas the prolongation of the AP is an indirect consequence of the ICaL inhibition: at low voltages of the early plateau, the delayed rectifier potassium (K+ ) current (IKr ) remains small, delaying repolarization of AP. Cd2+ reduced the density and slowed the kinetics of the Na+ current (INa ) but left the inward rectifier K+ current (IK1 ) intact. These altered cellular and molecular functions can explain several Cd2+ -induced changes in impulse conduction of the fish heart, for example, slowed propagation of the AP in atrial and ventricular myocardia (inhibition of INa ), delayed relaxation of the ventricle (prolongation of ventricular AP duration), bradycardia, and atrioventricular block (inhibition of ICaL ). These findings indicate that the cardiotoxicity of Cd2+ in fish involves multiple ion currents that are directly and indirectly altered by Cd2+ . Through these mechanisms, Cd2+ may trigger cardiac arrhythmias and impair myocardial contraction. Elevated temperature (+18 °C) slightly increases Cd2+ toxicity in trout ventricular myocytes. Environ Toxicol Chem 2021;40:2874-2885. © 2021 SETAC.
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Affiliation(s)
- Jaakko Haverinen
- Department of Environmental and Biological Sciences, University of Eastern Finland, Joensuu, Finland
| | - Ahmed Badr
- Department of Environmental and Biological Sciences, University of Eastern Finland, Joensuu, Finland
- Zoology Department, Sohag University, Sohag, Egypt
| | - Matti Vornanen
- Department of Environmental and Biological Sciences, University of Eastern Finland, Joensuu, Finland
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5
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Onkal R, Fraser SP, Djamgoz MB. Cationic Modulation of Voltage-Gated Sodium Channel (Nav1.5): Neonatal Versus Adult Splice Variants-2. Divalent (Cd 2+) and Trivalent (Gd 3+) Ions. Bioelectricity 2019; 1:148-157. [PMID: 34471817 PMCID: PMC8370281 DOI: 10.1089/bioe.2019.0014] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Background: A "neonatal" splice-form of the voltage-gated sodium channel Nav1.5 is functionally expressed in human cancers and potentiates metastatic cell behaviors. Splicing causes the replacement of 7 amino acids, including a negatively charged aspartate211 in the "adult" Nav1.5 (aNav1.5) to a positively charged lysine in the "neonatal" (nNav1.5). These changes occur in the region surrounding the DI:S3-S4 extracellular linker. The splice variants respond differently to changes in extracellular H+ and this could be of pathophysiological significance. However, how the two differentially charged splice variants would react to cations of higher valency is not known. Materials and Methods: We used patch-clamp recording to compare the electrophysiological effects of Cd2+ and Gd3+ on "adult" and "neonatal" Nav1.5 expressed stably in EBNA-293 cells. Several parameters were determined for the two channels and statistically compared. Results: Both cations inhibited peak I Na through reducing G max and induced a positive shift in the voltage range of activation. However, unlike Gd3+, Cd2+ had only a weak effect on voltage dependence of activation, and no effect on voltage dependence of inactivation, recovery from inactivation, or the kinetics of activation/inactivation. Conclusions: The electrophysiological effects of Cd2+ and Gd3+ studied were essentially the same for "neonatal" and "adult" Nav1.5, although these splice variants possess differences in their external charges. In contrast, the effects of H+ were shown earlier to be significantly differential. Taken together, these results suggest that limited adjustment of the charged structure of pharmacological agents could enable selective targeting of neonatal Nav1.5 associated with several cancers.
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Affiliation(s)
- Rustem Onkal
- Department of Life Sciences, Neuroscience Solutions to Cancer Research Group, Imperial College London, London, United Kingdom
- Institute of Biotechnology Research (IBR), Cyprus International University, North Cyprus
| | - Scott P. Fraser
- Department of Life Sciences, Neuroscience Solutions to Cancer Research Group, Imperial College London, London, United Kingdom
| | - Mustafa B.A. Djamgoz
- Department of Life Sciences, Neuroscience Solutions to Cancer Research Group, Imperial College London, London, United Kingdom
- Institute of Biotechnology Research (IBR), Cyprus International University, North Cyprus
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6
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Márquez R, Ramírez‐Castañeda V, Amézquita A. Does batrachotoxin autoresistance coevolve with toxicity in
Phyllobates
poison‐dart frogs? Evolution 2019; 73:390-400. [DOI: 10.1111/evo.13672] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2018] [Accepted: 11/29/2018] [Indexed: 12/01/2022]
Affiliation(s)
- Roberto Márquez
- Department of Ecology and Evolution University of Chicago 1101 East 57th St. Chicago Illinois 60637
- Department of Biological Sciences Universidad de los Andes A.A. 4976 Bogotá Colombia
| | | | - Adolfo Amézquita
- Department of Biological Sciences Universidad de los Andes A.A. 4976 Bogotá Colombia
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7
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Moreau A, Chahine M. A New Cardiac Channelopathy: From Clinical Phenotypes to Molecular Mechanisms Associated With Na v1.5 Gating Pores. Front Cardiovasc Med 2018; 5:139. [PMID: 30356750 PMCID: PMC6189448 DOI: 10.3389/fcvm.2018.00139] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2018] [Accepted: 09/19/2018] [Indexed: 12/19/2022] Open
Abstract
Voltage gated sodium channels (NaV) are broadly expressed in the human body. They are responsible for the initiation of action potentials in excitable cells. They also underlie several physiological processes such as cognitive, sensitive, motor, and cardiac functions. The NaV1.5 channel is the main NaV expressed in the heart. A dysfunction of this channel is usually associated with the development of pure electrical disorders such as long QT syndrome, Brugada syndrome, sinus node dysfunction, atrial fibrillation, and cardiac conduction disorders. However, mutations of Nav1.5 have recently been linked to the development of an atypical clinical entity combining complex arrhythmias and dilated cardiomyopathy. Although several Nav1.5 mutations have been linked to dilated cardiomyopathy phenotypes, their pathogenic mechanisms remain to be elucidated. The gating pore may constitute a common biophysical defect for all NaV1.5 mutations located in the channel's VSDs. The creation of such a gating pore may disrupt the ionic homeostasis of cardiomyocytes, affecting electrical signals, cell morphology, and cardiac myocyte function. The main objective of this article is to review the concept of gating pores and their role in structural heart diseases and to discuss potential pharmacological treatments.
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Affiliation(s)
- Adrien Moreau
- PhyMedExp, Université de Montpellier, INSERM, CNRS, Montpellier, France
| | - Mohamed Chahine
- CERVO Research Centre, Institut Universitaire en Santé Mentale de Québec, Quebec City, QC, Canada.,Department of Medicine, Université Laval, Quebec City, QC, Canada
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8
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Perry BW, Card DC, McGlothlin JW, Pasquesi GIM, Adams RH, Schield DR, Hales NR, Corbin AB, Demuth JP, Hoffmann FG, Vandewege MW, Schott RK, Bhattacharyya N, Chang BSW, Casewell NR, Whiteley G, Reyes-Velasco J, Mackessy SP, Gamble T, Storey KB, Biggar KK, Passow CN, Kuo CH, McGaugh SE, Bronikowski AM, de Koning APJ, Edwards SV, Pfrender ME, Minx P, Brodie ED, Brodie ED, Warren WC, Castoe TA. Molecular Adaptations for Sensing and Securing Prey and Insight into Amniote Genome Diversity from the Garter Snake Genome. Genome Biol Evol 2018; 10:2110-2129. [PMID: 30060036 PMCID: PMC6110522 DOI: 10.1093/gbe/evy157] [Citation(s) in RCA: 62] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/26/2018] [Indexed: 12/26/2022] Open
Abstract
Colubridae represents the most phenotypically diverse and speciose family of snakes, yet no well-assembled and annotated genome exists for this lineage. Here, we report and analyze the genome of the garter snake, Thamnophis sirtalis, a colubrid snake that is an important model species for research in evolutionary biology, physiology, genomics, behavior, and the evolution of toxin resistance. Using the garter snake genome, we show how snakes have evolved numerous adaptations for sensing and securing prey, and identify features of snake genome structure that provide insight into the evolution of amniote genomes. Analyses of the garter snake and other squamate reptile genomes highlight shifts in repeat element abundance and expansion within snakes, uncover evidence of genes under positive selection, and provide revised neutral substitution rate estimates for squamates. Our identification of Z and W sex chromosome-specific scaffolds provides evidence for multiple origins of sex chromosome systems in snakes and demonstrates the value of this genome for studying sex chromosome evolution. Analysis of gene duplication and loss in visual and olfactory gene families supports a dim-light ancestral condition in snakes and indicates that olfactory receptor repertoires underwent an expansion early in snake evolution. Additionally, we provide some of the first links between secreted venom proteins, the genes that encode them, and their evolutionary origins in a rear-fanged colubrid snake, together with new genomic insight into the coevolutionary arms race between garter snakes and highly toxic newt prey that led to toxin resistance in garter snakes.
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Affiliation(s)
- Blair W Perry
- Department of Biology, University of Texas at Arlington, Arlington
| | - Daren C Card
- Department of Biology, University of Texas at Arlington, Arlington
| | - Joel W McGlothlin
- Department of Biological Sciences, Virginia Tech, Blacksburg, Virginia
| | | | - Richard H Adams
- Department of Biology, University of Texas at Arlington, Arlington
| | - Drew R Schield
- Department of Biology, University of Texas at Arlington, Arlington
| | - Nicole R Hales
- Department of Biology, University of Texas at Arlington, Arlington
| | - Andrew B Corbin
- Department of Biology, University of Texas at Arlington, Arlington
| | - Jeffery P Demuth
- Department of Biology, University of Texas at Arlington, Arlington
| | - Federico G Hoffmann
- Department of Biochemistry, Molecular Biology, Entomology and Plant Pathology, Mississippi State University, Mississippi State.,Institute for Genomics, Biocomputing and Biotechnology, Mississippi State University, Starkville
| | - Michael W Vandewege
- Department of Biology, Institute for Genomics and Evolutionary Medicine, Temple University
| | - Ryan K Schott
- Department of Ecology and Evolutionary Biology, Department of Cell and Systems Biology, Centre for the Analysis of Genome Evolution & Function, University of Toronto, Ontario, Canada.,Department of Vertebrate Zoology, National Museum of Natural History, Smithsonian Institution, Washington, District of Columbia
| | - Nihar Bhattacharyya
- Department of Cell and Systems Biology, University of Toronto, Ontario, Canada
| | - Belinda S W Chang
- Department of Ecology and Evolutionary Biology, Department of Cell and Systems Biology, Centre for the Analysis of Genome Evolution & Function, University of Toronto, Ontario, Canada
| | - Nicholas R Casewell
- Alistair Reid Venom Research Unit, Parasitology Department, Liverpool School of Tropical Medicine, Pembroke Place, Liverpool, United Kingdom
| | - Gareth Whiteley
- Alistair Reid Venom Research Unit, Parasitology Department, Liverpool School of Tropical Medicine, Pembroke Place, Liverpool, United Kingdom
| | - Jacobo Reyes-Velasco
- Department of Biology, University of Texas at Arlington, Arlington.,Department of Biology, New York University Abu Dhabi, Saadiyat Island, Abu Dhabi, United Arab Emirates
| | | | - Tony Gamble
- Department of Biological Sciences, Marquette University, Milwaukee, WI 53201, USA.,Bell Museum of Natural History, University of Minnesota, Saint Paul, MN, USA
| | - Kenneth B Storey
- Institute of Biochemistry, Carleton University, Ottawa, Ontario, Canada
| | - Kyle K Biggar
- Institute of Biochemistry, Carleton University, Ottawa, Ontario, Canada
| | | | - Chih-Horng Kuo
- Institute of Plant and Microbial Biology, Academia Sinica, Taipei, Taiwan
| | | | - Anne M Bronikowski
- Department of Ecology, Evolution, and Organismal Biology, Iowa State University
| | - A P Jason de Koning
- Department of Biochemistry and Molecular Biology, Department of Medical Genetics, Alberta Children's Hospital Research Institute, Cumming School of Medicine, University of Calgary, Alberta, Canada
| | - Scott V Edwards
- Department of Organismic and Evolutionary Biology and Museum of Comparative Zoology, Harvard University
| | - Michael E Pfrender
- Department of Biological Sciences and Environmental Change Initiative, University of Notre Dame
| | - Patrick Minx
- The McDonnell Genome Institute, Washington University School of Medicine, St. Louis
| | | | | | - Wesley C Warren
- The McDonnell Genome Institute, Washington University School of Medicine, St. Louis
| | - Todd A Castoe
- Department of Biology, University of Texas at Arlington, Arlington
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9
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Shen H, Li Z, Jiang Y, Pan X, Wu J, Cristofori-Armstrong B, Smith JJ, Chin YKY, Lei J, Zhou Q, King GF, Yan N. Structural basis for the modulation of voltage-gated sodium channels by animal toxins. Science 2018; 362:science.aau2596. [DOI: 10.1126/science.aau2596] [Citation(s) in RCA: 150] [Impact Index Per Article: 25.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2018] [Accepted: 07/17/2018] [Indexed: 12/31/2022]
Abstract
Animal toxins that modulate the activity of voltage-gated sodium (Nav) channels are broadly divided into two categories—pore blockers and gating modifiers. The pore blockers tetrodotoxin (TTX) and saxitoxin (STX) are responsible for puffer fish and shellfish poisoning in humans, respectively. Here, we present structures of the insect Navchannel NavPaS bound to a gating modifier toxin Dc1a at 2.8 angstrom-resolution and in the presence of TTX or STX at 2.6-Å and 3.2-Å resolution, respectively. Dc1a inserts into the cleft between VSDIIand the pore of NavPaS, making key contacts with both domains. The structures with bound TTX or STX reveal the molecular details for the specific blockade of Na+access to the selectivity filter from the extracellular side by these guanidinium toxins. The structures shed light on structure-based development of Navchannel drugs.
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10
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Abstract
Chemical aminoacylation of orthogonal tRNA allows for the genetic encoding of a wide range of synthetic amino acids without the need to evolve specific aminoacyl-tRNA synthetases. This method, when paired with protein expression in the Xenopus laevis oocyte expression system, can extract atomic scale functional data from a protein structure to advance the study of membrane proteins. The utility of the method depends on the orthogonality of the tRNA species used to deliver the amino acid. Here, we report that the pyrrolysyl tRNA (pylT) from Methanosarcina barkeri fusaro is orthogonal and highly competent for genetic code expansion experiments in the Xenopus oocyte. The data show that pylT is amendable to chemical acylation in vitro; it is then used to rescue a cytoplasmic site within a voltage-gated sodium channel. Further, the high fidelity of the pylT is demonstrated via encoding of lysine within the selectivity filter of the sodium channel, where sodium ion recognition by the distal amine of this side-chain is essential. Thus, pylT is an appropriate tRNA species for delivery of amino acids via nonsense suppression in the Xenopus oocyte. It may prove useful in experimental contexts wherein reacylation of suppressor tRNAs have been observed.
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11
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Abstract
Voltage-gated sodium (Na+) channels are expressed in virtually all electrically excitable tissues and are essential for muscle contraction and the conduction of impulses within the peripheral and central nervous systems. Genetic disorders that disrupt the function of these channels produce an array of Na+ channelopathies resulting in neuronal impairment, chronic pain, neuromuscular pathologies, and cardiac arrhythmias. Because of their importance to the conduction of electrical signals, Na+ channels are the target of a wide variety of local anesthetic, antiarrhythmic, anticonvulsant, and antidepressant drugs. The voltage-gated family of Na+ channels is composed of α-subunits that encode for the voltage sensor domains and the Na+-selective permeation pore. In vivo, Na+ channel α-subunits are associated with one or more accessory β-subunits (β1-β4) that regulate gating properties, trafficking, and cell-surface expression of the channels. The permeation pore of Na+ channels is divided in two parts: the outer mouth of the pore is the site of the ion selectivity filter, while the inner cytoplasmic pore serves as the channel activation gate. The cytoplasmic lining of the permeation pore is formed by the S6 segments that include highly conserved aromatic amino acids important for drug binding. These residues are believed to undergo voltage-dependent conformational changes that alter drug binding as the channels cycle through the closed, open, and inactivated states. The purpose of this chapter is to broadly review the mechanisms of Na+ channel gating and the models used to describe drug binding and Na+ channel inhibition.
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Affiliation(s)
- M E O'Leary
- Cooper Medical School of Rowan University, Camden, NJ, USA
| | - M Chahine
- CERVO Brain Research Center, Institut universitaire en santé mentale de Québec, Quebec City, QC, Canada.
- Department of Medicine, Université Laval, Quebec City, QC, Canada.
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12
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Roncalli V, Lenz PH, Cieslak MC, Hartline DK. Complementary mechanisms for neurotoxin resistance in a copepod. Sci Rep 2017; 7:14201. [PMID: 29079725 PMCID: PMC5660226 DOI: 10.1038/s41598-017-14545-z] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2017] [Accepted: 10/12/2017] [Indexed: 12/16/2022] Open
Abstract
Toxin resistance is a recurring evolutionary response by predators feeding on toxic prey. These adaptations impact physiological interaction and community ecology. Mechanisms for resistance vary depending on the predator and the nature of the toxin. Potent neurotoxins like tetrodotoxin (TTX) and saxitoxin (STX) that are highly toxic to humans and other vertebrates, target conserved voltage-gated sodium channels (NaV) of nerve and muscle, causing paralysis. The copepod Calanus finmarchicus consumes the STX-producing dinoflagellate, Alexandrium fundyense with no effect on survival. Using transcriptomic approaches to search for the mechanism that confers resistance in C. finmarchicus, we identified splice variants of NaVs that were predicted to be toxin resistant. These were co-expressed with putatively non-resistant form in all developmental stages. However its expression was unresponsive to toxin challenge nor was there any up-regulation of genes involved in multi-xenobiotic resistance (MXR) or detoxification (phases I or II). Instead, adults consistently regulated genes encoding digestive enzymes, possibly to complement channel resistance by limiting toxin assimilation via the digestive process. The nauplii, which were more susceptible to STX, did not regulate these enzymes. This study demonstrates how deep-sequencing technology can elucidate multiple mechanisms of toxin resistance concurrently, revealing the linkages between molecular/cellular adaptations and the ecology of an organism.
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Affiliation(s)
- Vittoria Roncalli
- Békésy Laboratory of Neurobiology, Pacific Biosciences Research Center, School of Ocean and Earth Science and Technology, University of Hawai'i at Manoa, 1993 East-West Road, Honolulu, HI 96822, USA.
| | - Petra H Lenz
- Békésy Laboratory of Neurobiology, Pacific Biosciences Research Center, School of Ocean and Earth Science and Technology, University of Hawai'i at Manoa, 1993 East-West Road, Honolulu, HI 96822, USA
| | - Matthew C Cieslak
- Békésy Laboratory of Neurobiology, Pacific Biosciences Research Center, School of Ocean and Earth Science and Technology, University of Hawai'i at Manoa, 1993 East-West Road, Honolulu, HI 96822, USA
| | - Daniel K Hartline
- Békésy Laboratory of Neurobiology, Pacific Biosciences Research Center, School of Ocean and Earth Science and Technology, University of Hawai'i at Manoa, 1993 East-West Road, Honolulu, HI 96822, USA
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13
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Exploring cation-π interaction in half sandwiches and sandwiches with X X triple bonds (X C, Si and Ge): A DFT study. COMPUT THEOR CHEM 2017. [DOI: 10.1016/j.comptc.2017.06.006] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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14
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Paiz-Candia B, Islas AA, Sánchez-Solano A, Mancilla-Simbro C, Scior T, Millan-PerezPeña L, Salinas-Stefanon EM. Mefloquine inhibits voltage dependent Nav1.4 channel by overlapping the local anaesthetic binding site. Eur J Pharmacol 2017; 796:215-223. [DOI: 10.1016/j.ejphar.2017.01.002] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2016] [Revised: 12/21/2016] [Accepted: 01/02/2017] [Indexed: 10/20/2022]
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15
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Satone H, Nonaka S, Lee JM, Shimasaki Y, Kusakabe T, Kawabata SI, Oshima Y. Tetrodotoxin- and tributyltin-binding abilities of recombinant pufferfish saxitoxin and tetrodotoxin binding proteins of Takifugu rubripes. Toxicon 2016; 125:50-52. [PMID: 27845057 DOI: 10.1016/j.toxicon.2016.11.245] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2016] [Revised: 11/04/2016] [Accepted: 11/10/2016] [Indexed: 11/25/2022]
Abstract
We investigated the ability of recombinant pufferfish saxitoxin and tetrodotoxin binding protein types 1 and 2 of Takifugu rubripes (rTrub.PSTBP1 and rTrub.PSTBP2) to bind to tetrodotoxin (TTX) and tributyltin. Both rTrub.PSTBPs bound to tributyltin in an ultrafiltration binding assay but lost this ability on heat denaturation. In contrast, only rTrub.PSTBP2 bound to TTX even heat denaturation. This result suggests that the amino acid sequence of PSTBP2 may be contributed for its affinity for TTX.
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Affiliation(s)
- Hina Satone
- Department of Applied Chemistry and Biotechnology, Graduate School of Natural Science and Technology, Okayama University, Tsushimanaka, Okayama 700-8530, Japan
| | - Shohei Nonaka
- Laboratory of Marine Environmental Science, Faculty of Agriculture, Kyushu University, Hakozaki, Fukuoka 812-8581, Japan
| | - Jae Man Lee
- Laboratory of Insect Genome Science, Graduate School of Bioresource and Bioenvironmental Sciences, Kyushu University, Hakozaki, Fukuoka 812-8581, Japan
| | - Yohei Shimasaki
- Laboratory of Marine Environmental Science, Faculty of Agriculture, Kyushu University, Hakozaki, Fukuoka 812-8581, Japan
| | - Takahiro Kusakabe
- Laboratory of Insect Genome Science, Graduate School of Bioresource and Bioenvironmental Sciences, Kyushu University, Hakozaki, Fukuoka 812-8581, Japan
| | - Shun-Ichiro Kawabata
- Department of Biology, Faculty of Science, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan
| | - Yuji Oshima
- Laboratory of Marine Environmental Science, Faculty of Agriculture, Kyushu University, Hakozaki, Fukuoka 812-8581, Japan.
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16
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Liu XP, Wooltorton JRA, Gaboyard-Niay S, Yang FC, Lysakowski A, Eatock RA. Sodium channel diversity in the vestibular ganglion: NaV1.5, NaV1.8, and tetrodotoxin-sensitive currents. J Neurophysiol 2016; 115:2536-55. [PMID: 26936982 DOI: 10.1152/jn.00902.2015] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2015] [Accepted: 02/02/2016] [Indexed: 01/02/2023] Open
Abstract
Firing patterns differ between subpopulations of vestibular primary afferent neurons. The role of sodium (NaV) channels in this diversity has not been investigated because NaV currents in rodent vestibular ganglion neurons (VGNs) were reported to be homogeneous, with the voltage dependence and tetrodotoxin (TTX) sensitivity of most neuronal NaV channels. RT-PCR experiments, however, indicated expression of diverse NaV channel subunits in the vestibular ganglion, motivating a closer look. Whole cell recordings from acutely dissociated postnatal VGNs confirmed that nearly all neurons expressed NaV currents that are TTX-sensitive and have activation midpoints between -30 and -40 mV. In addition, however, many VGNs expressed one of two other NaV currents. Some VGNs had a small current with properties consistent with NaV1.5 channels: low TTX sensitivity, sensitivity to divalent cation block, and a relatively negative voltage range, and some VGNs showed NaV1.5-like immunoreactivity. Other VGNs had a current with the properties of NaV1.8 channels: high TTX resistance, slow time course, and a relatively depolarized voltage range. In two NaV1.8 reporter lines, subsets of VGNs were labeled. VGNs with NaV1.8-like TTX-resistant current also differed from other VGNs in the voltage dependence of their TTX-sensitive currents and in the voltage threshold for spiking and action potential shape. Regulated expression of NaV channels in primary afferent neurons is likely to selectively affect firing properties that contribute to the encoding of vestibular stimuli.
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Affiliation(s)
- Xiao-Ping Liu
- Speech and Hearing Bioscience and Technology Program, Harvard-Massachusetts Institute of Technology Health Sciences and Technology Program, Cambridge, Massachusetts; Eaton-Peabody Laboratories, Massachusetts Eye and Ear, and Department of Otology and Laryngology, Harvard Medical School, Boston, Massachusetts
| | | | - Sophie Gaboyard-Niay
- Department of Anatomy and Cell Biology, University of Illinois at Chicago, Chicago, Illinois
| | - Fu-Chia Yang
- Dana-Farber Cancer Institute, Boston, Massachusetts; Department of Neurobiology, Harvard Medical School, Boston, Massachusetts; and
| | - Anna Lysakowski
- Department of Anatomy and Cell Biology, University of Illinois at Chicago, Chicago, Illinois; Department of Otolaryngology-Head and Neck Surgery, University of Illinois at Chicago, Chicago, Illinois
| | - Ruth Anne Eatock
- Eaton-Peabody Laboratories, Massachusetts Eye and Ear, and Department of Otology and Laryngology, Harvard Medical School, Boston, Massachusetts; Department of Neurobiology, Harvard Medical School, Boston, Massachusetts; and Department of Otolaryngology-Head and Neck Surgery, University of Illinois at Chicago, Chicago, Illinois
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17
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Feldman CR, Durso AM, Hanifin CT, Pfrender ME, Ducey PK, Stokes AN, Barnett KE, Brodie III ED, Brodie Jr ED. Is there more than one way to skin a newt? Convergent toxin resistance in snakes is not due to a common genetic mechanism. Heredity (Edinb) 2016; 116:84-91. [PMID: 26374236 PMCID: PMC4675877 DOI: 10.1038/hdy.2015.73] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2015] [Revised: 06/07/2015] [Accepted: 06/08/2015] [Indexed: 02/08/2023] Open
Abstract
Convergent evolution of tetrodotoxin (TTX) resistance, at both the phenotypic and genetic levels, characterizes coevolutionary arms races between amphibians and their snake predators around the world, and reveals remarkable predictability in the process of adaptation. Here we examine the repeatability of the evolution of TTX resistance in an undescribed predator-prey relationship between TTX-bearing Eastern Newts (Notophthalmus viridescens) and Eastern Hog-nosed Snakes (Heterodon platirhinos). We found that that local newts contain levels of TTX dangerous enough to dissuade most predators, and that Eastern Hog-nosed Snakes within newt range are highly resistant to TTX. In fact, these populations of Eastern Hog-nosed Snakes are so resistant to TTX that the potential for current reciprocal selection might be limited. Unlike all other cases of TTX resistance in vertebrates, H. platirhinos lacks the adaptive amino acid substitutions in the skeletal muscle sodium channel that reduce TTX binding, suggesting that physiological resistance in Eastern Hog-nosed Snakes is conferred by an alternate genetic mechanism. Thus, phenotypic convergence in this case is not due to parallel molecular evolution, indicating that there may be more than one way for this adaptation to arise, even among closely related species.
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Affiliation(s)
- C R Feldman
- Department of Biology, University of Nevada Reno, Reno, NV, USA
| | - A M Durso
- Department of Biology, Utah State University, Logan, UT, USA
| | - C T Hanifin
- Department of Biology, Utah State University, Logan, UT, USA
- Department of Biology, Utah State University, Uintah Basin, Vernal, UT, USA
| | - M E Pfrender
- Department of Biological Sciences, University of Notre Dame, Notre Dame, IN, USA
| | - P K Ducey
- Department of Biological Sciences, State University of New York–Cortland, Cortland, NY, USA
| | - A N Stokes
- Department of Biology, California State University Bakersfield, Bakersfield, CA, USA
| | - K E Barnett
- New York State Department of Environmental Conservation, Albany, NY, USA
| | - E D Brodie III
- Mountain Lake Biological Station and Department of Biology, University of Virginia, Charlottesville, VA, USA
| | - E D Brodie Jr
- Department of Biology, Utah State University, Logan, UT, USA
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18
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Convergent Evolution of Tetrodotoxin-Resistant Sodium Channels in Predators and Prey. CURRENT TOPICS IN MEMBRANES 2016; 78:87-113. [DOI: 10.1016/bs.ctm.2016.07.006] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
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19
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Mahdavi S, Kuyucak S. Mechanism of Ion Permeation in Mammalian Voltage-Gated Sodium Channels. PLoS One 2015; 10:e0133000. [PMID: 26274802 PMCID: PMC4537306 DOI: 10.1371/journal.pone.0133000] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2015] [Accepted: 06/22/2015] [Indexed: 12/30/2022] Open
Abstract
Recent determination of the crystal structures of bacterial voltage-gated sodium (NaV) channels have raised hopes that modeling of the mammalian counterparts could soon be achieved. However, there are substantial differences between the pore domains of the bacterial and mammalian NaV channels, which necessitates careful validation of mammalian homology models constructed from the bacterial NaV structures. Such a validated homology model for the NaV1.4 channel was constructed recently using the extensive mutagenesis data available for binding of μ-conotoxins. Here we use this NaV1.4 model to study the ion permeation mechanism in mammalian NaV channels. Linking of the DEKA residues in the selectivity filter with residues in the neighboring domains is found to be important for keeping the permeation pathway open. Molecular dynamics simulations and potential of mean force calculations reveal that there is a binding site for a Na+ ion just inside the DEKA locus, and 1-2 Na+ ions can occupy the vestibule near the EEDD ring. These sites are separated by a low free energy barrier, suggesting that inward conduction occurs when a Na+ ion in the vestibule goes over the free energy barrier and pushes the Na+ ion in the filter to the intracellular cavity, consistent with the classical knock-on mechanism. The NaV1.4 model also provides a good description of the observed Na+/K+ selectivity.
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Affiliation(s)
- Somayeh Mahdavi
- School of Physics, University of Sydney, Sydney, New South Wales 2006, Australia
| | - Serdar Kuyucak
- School of Physics, University of Sydney, Sydney, New South Wales 2006, Australia
- * E-mail:
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20
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Dick IE, Limpitikul WB, Niu J, Banerjee R, Issa JB, Ben-Johny M, Adams PJ, Kang PW, Lee SR, Sang L, Yang W, Babich J, Zhang M, Bazazzi H, Yue NC, Tomaselli GF. A rendezvous with the queen of ion channels: Three decades of ion channel research by David T Yue and his Calcium Signals Laboratory. Channels (Austin) 2015; 10:20-32. [PMID: 26176690 DOI: 10.1080/19336950.2015.1051272] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
David T. Yue was a renowned biophysicist who dedicated his life to the study of Ca(2+) signaling in cells. In the wake of his passing, we are left not only with a feeling of great loss, but with a tremendous and impactful body of work contributed by a remarkable man. David's research spanned the spectrum from atomic structure to organ systems, with a quantitative rigor aimed at understanding the fundamental mechanisms underlying biological function. Along the way he developed new tools and approaches, enabling not only his own research but that of his contemporaries and those who will come after him. While we cannot hope to replicate the eloquence and style we are accustomed to in David's writing, we nonetheless undertake a review of David's chosen field of study with a focus on many of his contributions to the calcium channel field.
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Affiliation(s)
- Ivy E Dick
- a Calcium Signals Laboratory; Department of Biomedical Engineering ; Johns Hopkins University School of Medicine ; Baltimore , MD USA
| | - Worawan B Limpitikul
- a Calcium Signals Laboratory; Department of Biomedical Engineering ; Johns Hopkins University School of Medicine ; Baltimore , MD USA
| | - Jacqueline Niu
- a Calcium Signals Laboratory; Department of Biomedical Engineering ; Johns Hopkins University School of Medicine ; Baltimore , MD USA
| | - Rahul Banerjee
- a Calcium Signals Laboratory; Department of Biomedical Engineering ; Johns Hopkins University School of Medicine ; Baltimore , MD USA
| | - John B Issa
- a Calcium Signals Laboratory; Department of Biomedical Engineering ; Johns Hopkins University School of Medicine ; Baltimore , MD USA
| | - Manu Ben-Johny
- a Calcium Signals Laboratory; Department of Biomedical Engineering ; Johns Hopkins University School of Medicine ; Baltimore , MD USA
| | - Paul J Adams
- a Calcium Signals Laboratory; Department of Biomedical Engineering ; Johns Hopkins University School of Medicine ; Baltimore , MD USA.,b Kwantlen Polytechnic University ; Surrey , BC Canada
| | - Po Wei Kang
- a Calcium Signals Laboratory; Department of Biomedical Engineering ; Johns Hopkins University School of Medicine ; Baltimore , MD USA
| | - Shin Rong Lee
- a Calcium Signals Laboratory; Department of Biomedical Engineering ; Johns Hopkins University School of Medicine ; Baltimore , MD USA
| | - Lingjie Sang
- a Calcium Signals Laboratory; Department of Biomedical Engineering ; Johns Hopkins University School of Medicine ; Baltimore , MD USA
| | - Wanjun Yang
- a Calcium Signals Laboratory; Department of Biomedical Engineering ; Johns Hopkins University School of Medicine ; Baltimore , MD USA
| | - Jennifer Babich
- a Calcium Signals Laboratory; Department of Biomedical Engineering ; Johns Hopkins University School of Medicine ; Baltimore , MD USA
| | - Manning Zhang
- a Calcium Signals Laboratory; Department of Biomedical Engineering ; Johns Hopkins University School of Medicine ; Baltimore , MD USA
| | - Hojjat Bazazzi
- a Calcium Signals Laboratory; Department of Biomedical Engineering ; Johns Hopkins University School of Medicine ; Baltimore , MD USA
| | - Nancy C Yue
- a Calcium Signals Laboratory; Department of Biomedical Engineering ; Johns Hopkins University School of Medicine ; Baltimore , MD USA
| | - Gordon F Tomaselli
- a Calcium Signals Laboratory; Department of Biomedical Engineering ; Johns Hopkins University School of Medicine ; Baltimore , MD USA.,c Division of Cardiology; Department of Medicine ; Johns Hopkins University School of Medicine ; Baltimore , MD USA
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21
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Dudev T, Lim C. Ion selectivity strategies of sodium channel selectivity filters. Acc Chem Res 2014; 47:3580-7. [PMID: 25343535 DOI: 10.1021/ar5002878] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
CONSPECTUS: Sodium ion channels selectively transport Na(+) cations across the cell membrane. These integral parts of the cell machinery are implicated in regulating the cardiac, skeletal and smooth muscle contraction, nerve impulses, salt and water homeostasis, as well as pain and taste perception. Their malfunction often results in various channelopathies of the heart, brain, skeletal muscles, and lung; thus, sodium channels are key drug targets for various disorders including cardiac arrhythmias, heart attack, stroke, migraine, epilepsy, pain, cancer, and autoimmune disorders. The ability of sodium channels to discriminate the native Na(+) among other competing ions in the surrounding fluids is crucial for proper cellular functions. The selectivity filter (SF), the narrowest part of the channel's open pore, lined with amino acid residues that specifically interact with the permeating ion, plays a major role in determining Na(+) selectivity. Different sodium channels have different SFs, which vary in the symmetry, number, charge, arrangement, and chemical type of the metal-ligating groups and pore size: epithelial/degenerin/acid-sensing ion channels have generally trimeric SFs lined with three conserved neutral serines and/or backbone carbonyls; eukaryotic sodium channels have EKEE, EEKE, DKEA, and DEKA SFs with an invariant positively charged lysine from the second or third domain; and bacterial voltage-gated sodium (Nav) channels exhibit symmetrical EEEE SFs, reminiscent of eukaryotic voltage-gated calcium channels. How do these different sodium channel SFs achieve high selectivity for Na(+) over its key rivals, K(+) and Ca(2+)? What factors govern the metal competition in these SFs and which of these factors are exploited to achieve Na(+) selectivity in the different sodium channel SFs? The free energies for replacing K(+) or Ca(2+) bound inside different model SFs with Na(+), evaluated by a combination of density functional theory and continuum dielectric calculations, have shed light on these questions. The SFs of epithelial and eukaryotic Nav channels select Na(+) by providing an optimal number and ligating strength of metal ligands as well as a rigid pore whose size fits the cognate Na(+) ideally. On the other hand, the SFs of bacterial Nav channels select Na(+), as the protein matrix attenuates ion-protein interactions relative to ion-solvent interactions by enlarging the pore and allowing water to enter, so the ion interacts indirectly with the conserved glutamates via bridging water molecules. This shows how these various SFs have adapted to the specific physicochemical properties of the native ion, using different strategies to select Na(+) among its contenders.
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Affiliation(s)
- Todor Dudev
- Faculty of Chemistry and Pharmacy, Sofia University, Sofia 1164, Bulgaria
| | - Carmay Lim
- Institute of Biomedical Sciences, Academia Sinica, Taipei 115, Taiwan
- Department of Chemistry, National Tsing Hua University, Hsinchu 300, Taiwan
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22
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Abstract
Although cardiac sodium channel blocking drugs can exert antiarrhythmic actions, they can also provoke life-threatening arrhythmias through a variety of mechanisms. This review addresses the way in which drugs interact with the channel, and how these effects translate to clinical beneficial or detrimental effects. A further understanding of the details of channel function and of drug-channel interactions may lead to the development of safer and more effective antiarrhythmic therapies.
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Affiliation(s)
- Dan M Roden
- Departments of Medicine and Pharmacology, Vanderbilt University School of Medicine, Nashville, TN 37232
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23
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Mahdavi S, Kuyucak S. Molecular dynamics study of binding of µ-conotoxin GIIIA to the voltage-gated sodium channel Na(v)1.4. PLoS One 2014; 9:e105300. [PMID: 25133704 PMCID: PMC4136838 DOI: 10.1371/journal.pone.0105300] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2014] [Accepted: 07/22/2014] [Indexed: 12/27/2022] Open
Abstract
Homology models of mammalian voltage-gated sodium (NaV) channels based on the crystal structures of the bacterial counterparts are needed to interpret the functional data on sodium channels and understand how they operate. Such models would also be invaluable in structure-based design of therapeutics for diseases involving sodium channels such as chronic pain and heart diseases. Here we construct a homology model for the pore domain of the NaV1.4 channel and use the functional data for the binding of µ-conotoxin GIIIA to NaV1.4 to validate the model. The initial poses for the NaV1.4-GIIIA complex are obtained using the HADDOCK protein docking program, which are then refined in molecular dynamics simulations. The binding mode for the final complex is shown to be in broad agreement with the available mutagenesis data. The standard binding free energy, determined from the potential of mean force calculations, is also in good agreement with the experimental value. Because the pore domains of NaV1 channels are highly homologous, the model constructed for NaV1.4 will provide an excellent template for other NaV1 channels.
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Affiliation(s)
- Somayeh Mahdavi
- School of Physics, University of Sydney, Sydney, New South Wales, Australia
| | - Serdar Kuyucak
- School of Physics, University of Sydney, Sydney, New South Wales, Australia
- * E-mail:
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24
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Abstract
The paralytic agent (+)-saxitoxin (STX), most commonly associated with oceanic red tides and shellfish poisoning, is a potent inhibitor of electrical conduction in cells. Its nefarious effects result from inhibition of voltage-gated sodium channels (Na(V)s), the obligatory proteins responsible for the initiation and propagation of action potentials. In the annals of ion channel research, the identification and characterization of Na(V)s trace to the availability of STX and an allied guanidinium derivative, tetrodotoxin. The mystique of STX is expressed in both its function and form, as this uniquely compact dication boasts more heteroatoms than carbon centers. This Review highlights both the chemistry and chemical biology of this fascinating natural product, and offers a perspective as to how molecular design and synthesis may be used to explore Na(V) structure and function.
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Affiliation(s)
- Arun P Thottumkara
- Department of Chemistry, Stanford University, Stanford, CA 94305-5080 (USA)
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25
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26
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Visualizing individual sodium channels on the move. ACTA ACUST UNITED AC 2014; 19:790-1. [PMID: 22840766 DOI: 10.1016/j.chembiol.2012.07.002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Visualization of voltage-gated sodium channels at work is an important requirement for the understanding of rapid electrical signaling in nerve cells. In this issue of Chemistry & Biology, Ondrus and colleagues have mastered this challenge by chemical synthesis of a fluorescent antagonist and by monitoring single sodium channels in living cells with unprecedented optical resolution.
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27
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Finol-Urdaneta RK, Wang Y, Al-Sabi A, Zhao C, Noskov SY, French RJ. Sodium channel selectivity and conduction: prokaryotes have devised their own molecular strategy. ACTA ACUST UNITED AC 2014; 143:157-71. [PMID: 24420772 PMCID: PMC4001777 DOI: 10.1085/jgp.201311037] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The molecular strategy for alkali cation selectivity by a bacterial sodium channel resembles those of eukaryotic calcium and potassium channels, rather than those of eukaryotic sodium channels. Striking structural differences between voltage-gated sodium (Nav) channels from prokaryotes (homotetramers) and eukaryotes (asymmetric, four-domain proteins) suggest the likelihood of different molecular mechanisms for common functions. For these two channel families, our data show similar selectivity sequences among alkali cations (relative permeability, Pion/PNa) and asymmetric, bi-ionic reversal potentials when the Na/K gradient is reversed. We performed coordinated experimental and computational studies, respectively, on the prokaryotic Nav channels NaChBac and NavAb. NaChBac shows an “anomalous,” nonmonotonic mole-fraction dependence in the presence of certain sodium–potassium mixtures; to our knowledge, no comparable observation has been reported for eukaryotic Nav channels. NaChBac’s preferential selectivity for sodium is reduced either by partial titration of its highly charged selectivity filter, when extracellular pH is lowered from 7.4 to 5.8, or by perturbation—likely steric—associated with a nominally electro-neutral substitution in the selectivity filter (E191D). Although no single molecular feature or energetic parameter appears to dominate, our atomistic simulations, based on the published NavAb crystal structure, revealed factors that may contribute to the normally observed selectivity for Na over K. These include: (a) a thermodynamic penalty to exchange one K+ for one Na+ in the wild-type (WT) channel, increasing the relative likelihood of Na+ occupying the binding site; (b) a small tendency toward weaker ion binding to the selectivity filter in Na–K mixtures, consistent with the higher conductance observed with both sodium and potassium present; and (c) integrated 1-D potentials of mean force for sodium or potassium movement that show less separation for the less selective E/D mutant than for WT. Overall, tight binding of a single favored ion to the selectivity filter, together with crucial inter-ion interactions within the pore, suggests that prokaryotic Nav channels use a selective strategy more akin to those of eukaryotic calcium and potassium channels than that of eukaryotic Nav channels.
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Affiliation(s)
- Rocio K Finol-Urdaneta
- Department of Physiology and Pharmacology, 2 Hotchkiss Brain Institute, and 3 Department of Biological Sciences, Institute for Biocomplexity and Informatics, University of Calgary, Calgary, Alberta T2N 4N1, Canada
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28
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Goldschen-Ohm MP, Chanda B. Probing gating mechanisms of sodium channels using pore blockers. Handb Exp Pharmacol 2014; 221:183-201. [PMID: 24737237 DOI: 10.1007/978-3-642-41588-3_9] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Several classes of small molecules and peptides bind at the central pore of voltage-gated sodium channels either from the extracellular or intracellular side of the membrane and block ion conduction through the pore. Biophysical studies that shed light on the chemical nature, accessibility, and kinetics of binding of these naturally occurring and synthetic compounds reveal a wealth of information about how these channels gate. Here, we discuss insights into the structural underpinnings of gating of the channel pore and its coupling to the voltage sensors obtained from pore blockers including site 1 neurotoxins and local anesthetics.
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29
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Isacoff EY, Jan LY, Minor DL. Conduits of life's spark: a perspective on ion channel research since the birth of neuron. Neuron 2013; 80:658-74. [PMID: 24183018 DOI: 10.1016/j.neuron.2013.10.040] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Heartbeats, muscle twitches, and lightning-fast thoughts are all manifestations of bioelectricity and rely on the activity of a class of membrane proteins known as ion channels. The basic function of an ion channel can be distilled into, "The hole opens. Ions go through. The hole closes." Studies of the fundamental mechanisms by which this process happens and the consequences of such activity in the setting of excitable cells remains the central focus of much of the field. One might wonder after so many years of detailed poking at such a seemingly simple process, is there anything left to learn?
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Affiliation(s)
- Ehud Y Isacoff
- Helen Wills Neuroscience Institute, University of California, Berkeley, CA 94720, USA; Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720, USA; Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
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30
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Dudev T, Lim C. Competition among metal ions for protein binding sites: determinants of metal ion selectivity in proteins. Chem Rev 2013; 114:538-56. [PMID: 24040963 DOI: 10.1021/cr4004665] [Citation(s) in RCA: 274] [Impact Index Per Article: 24.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Affiliation(s)
- Todor Dudev
- Institute of Biomedical Sciences, Academia Sinica , Taipei 11529, Taiwan
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31
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Markgraf R, Leipold E, Schirmeyer J, Paolini-Bertrand M, Hartley O, Heinemann SH. Mechanism and molecular basis for the sodium channel subtype specificity of µ-conopeptide CnIIIC. Br J Pharmacol 2013; 167:576-86. [PMID: 22537004 DOI: 10.1111/j.1476-5381.2012.02004.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
BACKGROUND AND PURPOSE Voltage-gated sodium channels (Na(V) channels) are key players in the generation and propagation of action potentials, and selective blockade of these channels is a promising strategy for clinically useful suppression of electrical activity. The conotoxin µ-CnIIIC from the cone snail Conus consors exhibits myorelaxing activity in rodents through specific blockade of skeletal muscle (Na(V) 1.4) Na(V) channels. EXPERIMENTAL APPROACH We investigated the activity of µ-CnIIIC on human Na(V) channels and characterized its inhibitory mechanism, as well as the molecular basis, for its channel specificity. KEY RESULTS Similar to rat paralogs, human Na(V) 1.4 and Na(V) 1.2 were potently blocked by µ-CnIIIC, the sensitivity of Na(V) 1.7 was intermediate, and Na(V) 1.5 and Na(V) 1.8 were insensitive. Half-channel chimeras revealed that determinants for the insensitivity of Na(V) 1.8 must reside in both the first and second halves of the channel, while those for Na(V) 1.5 are restricted to domains I and II. Furthermore, domain I pore loop affected the total block and therefore harbours the major determinants for the subtype specificity. Domain II pore loop only affected the kinetics of toxin binding and dissociation. Blockade by µ-CnIIIC of Na(V) 1.4 was virtually irreversible but left a residual current of about 5%, reflecting a 'leaky' block; therefore, Na(+) ions still passed through µ-CnIIIC-occupied Na(V) 1.4 to some extent. TTX was excluded from this binding site but was trapped inside the pore by µ-CnIIIC. CONCLUSION AND IMPLICATIONS Of clinical significance, µ-CnIIIC is a potent and persistent blocker of human skeletal muscle Na(V) 1.4 that does not affect activity of cardiac Na(V) 1.5.
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Affiliation(s)
- René Markgraf
- Center for Molecular Biomedicine, Department of Biophysics, Friedrich Schiller University of Jena & Jena University Hospital, Germany
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32
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Huang CJ, Schild L, Moczydlowski EG. Use-dependent block of the voltage-gated Na(+) channel by tetrodotoxin and saxitoxin: effect of pore mutations that change ionic selectivity. ACTA ACUST UNITED AC 2013; 140:435-54. [PMID: 23008436 PMCID: PMC3457692 DOI: 10.1085/jgp.201210853] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Voltage-gated Na(+) channels (NaV channels) are specifically blocked by guanidinium toxins such as tetrodotoxin (TTX) and saxitoxin (STX) with nanomolar to micromolar affinity depending on key amino acid substitutions in the outer vestibule of the channel that vary with NaV gene isoforms. All NaV channels that have been studied exhibit a use-dependent enhancement of TTX/STX affinity when the channel is stimulated with brief repetitive voltage depolarizations from a hyperpolarized starting voltage. Two models have been proposed to explain the mechanism of TTX/STX use dependence: a conformational mechanism and a trapped ion mechanism. In this study, we used selectivity filter mutations (K1237R, K1237A, and K1237H) of the rat muscle NaV1.4 channel that are known to alter ionic selectivity and Ca(2+) permeability to test the trapped ion mechanism, which attributes use-dependent enhancement of toxin affinity to electrostatic repulsion between the bound toxin and Ca(2+) or Na(+) ions trapped inside the channel vestibule in the closed state. Our results indicate that TTX/STX use dependence is not relieved by mutations that enhance Ca(2+) permeability, suggesting that ion-toxin repulsion is not the primary factor that determines use dependence. Evidence now favors the idea that TTX/STX use dependence arises from conformational coupling of the voltage sensor domain or domains with residues in the toxin-binding site that are also involved in slow inactivation.
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Knapp O, Nevin ST, Yasuda T, Lawrence N, Lewis RJ, Adams DJ. Biophysical properties of Na(v) 1.8/Na(v) 1.2 chimeras and inhibition by µO-conotoxin MrVIB. Br J Pharmacol 2012; 166:2148-60. [PMID: 22452751 DOI: 10.1111/j.1476-5381.2012.01955.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
BACKGROUND AND PURPOSE Voltage-gated sodium channels are expressed primarily in excitable cells and play a pivotal role in the initiation and propagation of action potentials. Nine subtypes of the pore-forming α-subunit have been identified, each with a distinct tissue distribution, biophysical properties and sensitivity to tetrodotoxin (TTX). Na(v) 1.8, a TTX-resistant (TTX-R) subtype, is selectively expressed in sensory neurons and plays a pathophysiological role in neuropathic pain. In comparison with TTX-sensitive (TTX-S) Na(v) α-subtypes in neurons, Na(v) 1.8 is most strongly inhibited by the µO-conotoxin MrVIB from Conus marmoreus. To determine which domain confers Na(v) 1.8 α-subunit its biophysical properties and MrVIB binding, we constructed various chimeric channels incorporating sequence from Na(v) 1.8 and the TTX-S Na(v) 1.2 using a domain exchange strategy. EXPERIMENTAL APPROACH Wild-type and chimeric Na(v) channels were expressed in Xenopus oocytes, and depolarization-activated Na⁺ currents were recorded using the two-electrode voltage clamp technique. KEY RESULTS MrVIB (1 µM) reduced Na(v) 1.2 current amplitude to 69 ± 12%, whereas Na(v) 1.8 current was reduced to 31 ± 3%, confirming that MrVIB has a binding preference for Na(v) 1.8. A similar reduction in Na⁺ current amplitude was observed when MrVIB was applied to chimeras containing the region extending from S6 segment of domain I through the S5-S6 linker of domain II of Na(v) 1.8. In contrast, MrVIB had only a small effect on Na⁺ current for chimeras containing the corresponding region of Na(v) 1.2. CONCLUSIONS AND IMPLICATIONS Taken together, these results suggest that domain II of Na(v) 1.8 is an important determinant of MrVIB affinity, highlighting a region of the α-subunit that may allow further nociceptor-specific ligand targeting.
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Affiliation(s)
- O Knapp
- Health Innovations Research Institute, RMIT University, Melbourne, Vic, Australia
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Dudev T, Lim C. Competition among Ca2+, Mg2+, and Na+ for model ion channel selectivity filters: determinants of ion selectivity. J Phys Chem B 2012; 116:10703-14. [PMID: 22889116 DOI: 10.1021/jp304925a] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Because voltage-gated ion channels play critical biological roles, understanding how they can discriminate the native metal ion from rival cations in the milieu is of great interest. Although Ca(2+), Mg(2+), and Na(+) are present in comparable concentrations outside the cell, the factors governing the competition among these cations for the selectivity filter of voltage-gated Ca(2+) ion channel remain unclear. Using density functional theory combined with continuum dielectric methods, we evaluate the effect of (1) the number, chemical type, and charge of the ligands lining the pore, (2) the pore's rigidity, size, symmetry, and solvent accessibility, and (3) the Ca(2+) hydration number outside the selectivity filter on the competition among Ca(2+), Mg(2+), and Na(+) in model selectivity filters. The calculations show how the outcome of this competition depends on the interplay between electronic and solvation effects. Selectivity for monovalent Na(+) over divalent Ca(2+)/Mg(2+) is achieved when solvation effects outweigh electrostatic effects; thus filters comprising a few weak charge-donating groups such as Ser/Thr side chains, where electrostatic effects are relatively weak and are easily overcome by solvation effects, are Na(+)-selective. In contrast, selectivity for divalent Ca(2+)/Mg(2+) over monovalent Na(+) is achieved when metal-ligand electrostatic effects outweigh solvation effects. The key differences in selectivity between Mg(2+) and Ca(2+) lie in the pore size, oligomericity, and solvent accessibility. The results, which are consistent with available experimental data, reveal how the structure and composition of the ion channel selectivity pore had adapted to the specific physicochemical properties of the native metal ion to enhance the competitiveness of the native metal toward rival cations.
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Affiliation(s)
- Todor Dudev
- Institute of Biomedical Sciences, Academia Sinica, Taipei 115, Taiwan
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Constraint shapes convergence in tetrodotoxin-resistant sodium channels of snakes. Proc Natl Acad Sci U S A 2012; 109:4556-61. [PMID: 22392995 DOI: 10.1073/pnas.1113468109] [Citation(s) in RCA: 105] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Natural selection often produces convergent changes in unrelated lineages, but the degree to which such adaptations occur via predictable genetic paths is unknown. If only a limited subset of possible mutations is fixed in independent lineages, then it is clear that constraint in the production or function of molecular variants is an important determinant of adaptation. We demonstrate remarkably constrained convergence during the evolution of resistance to the lethal poison, tetrodotoxin, in six snake species representing three distinct lineages from around the globe. Resistance-conferring amino acid substitutions in a voltage-gated sodium channel, Na(v)1.4, are clustered in only two regions of the protein, and a majority of the replacements are confined to the same three positions. The observed changes represent only a small fraction of the experimentally validated mutations known to increase Na(v)1.4 resistance to tetrodotoxin. These results suggest that constraints resulting from functional tradeoffs between ion channel function and toxin resistance led to predictable patterns of evolutionary convergence at the molecular level. Our data are consistent with theoretical predictions and recent microcosm work that suggest a predictable path is followed during an adaptive walk along a mutational landscape, and that natural selection may be frequently constrained to produce similar genetic outcomes even when operating on independent lineages.
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Investigations into matrix components affecting the performance of the official bioassay reference method for quantitation of paralytic shellfish poisoning toxins in oysters. Toxicon 2012; 59:215-30. [DOI: 10.1016/j.toxicon.2011.11.013] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2011] [Revised: 11/16/2011] [Accepted: 11/17/2011] [Indexed: 11/20/2022]
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Gating transitions in the selectivity filter region of a sodium channel are coupled to the domain IV voltage sensor. Proc Natl Acad Sci U S A 2012. [PMID: 22308389 DOI: 10.1073/pnas.1115575109] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Voltage-dependent ion channels are crucial for generation and propagation of electrical activity in biological systems. The primary mechanism for voltage transduction in these proteins involves the movement of a voltage-sensing domain (D), which opens a gate located on the cytoplasmic side. A distinct conformational change in the selectivity filter near the extracellular side has been implicated in slow inactivation gating, which is important for spike frequency adaptation in neural circuits. However, it remains an open question whether gating transitions in the selectivity filter region are also actuated by voltage sensors. Here, we examine conformational coupling between each of the four voltage sensors and the outer pore of a eukaryotic voltage-dependent sodium channel. The voltage sensors of these sodium channels are not structurally symmetric and exhibit functional specialization. To track the conformational rearrangements of individual voltage-sensing domains, we recorded domain-specific gating pore currents. Our data show that, of the four voltage sensors, only the domain IV voltage sensor is coupled to the conformation of the selectivity filter region of the sodium channel. Trapping the outer pore in a particular conformation with a high-affinity toxin or disulphide crossbridge impedes the return of this voltage sensor to its resting conformation. Our findings directly establish that, in addition to the canonical electromechanical coupling between voltage sensor and inner pore gates of a sodium channel, gating transitions in the selectivity filter region are also coupled to the movement of a voltage sensor. Furthermore, our results also imply that the voltage sensor of domain IV is unique in this linkage and in the ability to initiate slow inactivation in sodium channels.
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Dudev T, Lim C. Why voltage-gated Ca2+ and bacterial Na+ channels with the same EEEE motif in their selectivity filters confer opposite metal selectivity. Phys Chem Chem Phys 2012; 14:12451. [DOI: 10.1039/c2cp00036a] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/30/2023]
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39
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Lin N, Badie N, Yu L, Abraham D, Cheng H, Bursac N, Rockman HA, Wolf MJ. A method to measure myocardial calcium handling in adult Drosophila. Circ Res 2011; 108:1306-15. [PMID: 21493892 DOI: 10.1161/circresaha.110.238105] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
RATIONALE Normal cardiac physiology requires highly regulated cytosolic Ca(2+) concentrations and abnormalities in Ca(2+) handling are associated with heart failure. The majority of approaches to identifying the components that regulate intracellular Ca(2+) dynamics rely on cells in culture, mouse models, and human samples. However, a genetically robust system for unbiased screens of mutations that affect Ca(2+) handling remains a challenge. OBJECTIVE We sought to develop a new method to measure myocardial Ca(2+) cycling in adult Drosophila and determine whether cardiomyopathic fly hearts recapitulate aspects of diseased mammalian myocardium. METHODS AND RESULTS Using engineered transgenic Drosophila that have cardiac-specific expression of Ca(2+)-sensing fluorescent protein, GCaMP2, we developed methods to measure parameters associated with myocardial Ca(2+) handling. The following key observations were identified: (1) Control w(1118) Drosophila hearts have readily measureable Ca(2+)-dependent fluorescent signals that are dependent on L-type Ca(2+) channels and SR Ca(2+) stores and originate from rostral and caudal pacemakers. (2) A fly mutant, held-up(2) (hdp(2)), that has a point mutation in troponin I and has a dilated cardiomyopathic phenotype demonstrates abnormalities in myocardial Ca(2+) handling that include increases in the duration of the 50% rise in intensity to peak intensity, the half-time of fluorescence decline from peak, the full duration at half-maximal intensity, and decreases in the linear slope of decay from 80% to 20% intensity decay. (3) Hearts from hdp(2) mutants had reductions in caffeine-induced Ca(2+) increases and reductions in ryanodine receptor (RyR) without changes in L-type Ca(2+) channel transcripts in comparison with w(1118). CONCLUSIONS Our results show that the cardiac-specific expression of GCaMP2 provides a means of characterizing propagating Ca(2+) transients in adult fly hearts. Moreover, the adult fruit fly heart recapitulates several aspects of Ca(2+) regulation observed in mammalian myocardium. A mutation in Drosophila that causes an enlarged cardiac chamber and impaired contractile function is associated with abnormalities in the cytosolic Ca(2+) transient as well as changes in transcript levels of proteins associated with Ca(2+) handling. This new methodology has the potential to permit an examination of evolutionarily conserved myocardial Ca(2+)-handing mechanisms by applying the vast resources available in the fly genomics community to conduct genetic screens to identify new genes involved in generated Ca(2+) transients and arrhythmias.
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Affiliation(s)
- Na Lin
- Institute of Molecular Medicine, Peking University, Beijing, China
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Leipold E, Markgraf R, Miloslavina A, Kijas M, Schirmeyer J, Imhof D, Heinemann SH. Molecular determinants for the subtype specificity of μ-conotoxin SIIIA targeting neuronal voltage-gated sodium channels. Neuropharmacology 2011; 61:105-11. [PMID: 21419143 DOI: 10.1016/j.neuropharm.2011.03.008] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2011] [Accepted: 03/09/2011] [Indexed: 11/29/2022]
Abstract
Voltage-gated sodium channels (Na(V) channels) play a pivotal role in neuronal excitability; they are specifically targeted by μ-conotoxins from the venom of marine cone snails. These peptide toxins bind to the outer vestibule of the channel pore thereby blocking ion conduction through Na(V) channels. μ-Conotoxin SIIIA from Conus striatus was shown to be a potent inhibitor of neuronal sodium channels and to display analgesic effects in mice, albeit the molecular targets are not unambiguously known. We therefore studied recombinant Na(V) channels expressed in mammalian cells using the whole-cell patch-clamp method. Synthetic μSIIIA slowly and partially blocked rat Na(V)1.4 channels with an apparent IC(50) of 0.56 ± 0.29 μM; the block was not complete, leaving at high concentration a residual current component of about 10% with a correspondingly reduced single-channel conductance. At 10 μM, μSIIIA potently blocked rat Na(V)1.2, rat and human Na(V)1.4, and mouse Na(V)1.6 channels; human Na(V)1.7 channels were only inhibited by 58.1 ± 4.9%, whereas human Na(V)1.5 as well as rat and human Na(V)1.8 were insensitive. Employing domain chimeras between rNa(V)1.4 and hNa(V)1.5, we located the determinants for μSIIIA specificity in the first half of the channel protein with a major contribution of domain-2 and a minor contribution of domain-1. The latter was largely accounted for by the alteration in the TTX-binding site (Tyr401 in rNa(V)1.4, Cys for Na(V)1.5, and Ser for Na(V)1.8). Introduction of domain-2 pore loops of all tested channel isoforms into rNa(V)1.4 conferred the μSIIIA phenotype of the respective donor channels highlighting the importance of the domain-2 pore loop as the major determinant for μSIIIA's subtype specificity. Single-site substitutions identified residue Ala728 in rNa(V)1.4 as crucial for its high sensitivity toward μSIIIA. Likewise, Asn889 at the homologous position in hNa(V)1.7 is responsible for the channel's reduced μSIIIA sensitivity. These results will pave the way for the rational design of selective Na(V)-channel antagonists for research and medical applications.
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Affiliation(s)
- Enrico Leipold
- Center for Molecular Biomedicine, Department of Biophysics, Friedrich Schiller University of Jena & University Hospital Jena, Hans-Knoell-Str. 2, D-07745 Jena, Germany
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Tikhonov DB, Zhorov BS. Possible roles of exceptionally conserved residues around the selectivity filters of sodium and calcium channels. J Biol Chem 2010; 286:2998-3006. [PMID: 21081490 DOI: 10.1074/jbc.m110.175406] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022] Open
Abstract
In the absence of x-ray structures of sodium and calcium channels their homology models are used to rationalize experimental data and design new experiments. A challenge is to model the outer-pore region that folds differently from potassium channels. Here we report a new model of the outer-pore region of the NaV1.4 channel, which suggests roles of highly conserved residues around the selectivity filter. The model takes from our previous study (Tikhonov, D. B., and Zhorov, B. S. (2005) Biophys. J. 88, 184-197) the general disposition of the P-helices, selectivity filter residues, and the outer carboxylates, but proposes new intra- and inter-domain contacts that support structural stability of the outer pore. Glycine residues downstream from the selectivity filter are proposed to participate in knob-into-hole contacts with the P-helices and S6s. These contacts explain the adapted tetrodotoxin resistance of snakes that feed on toxic prey through valine substitution of isoleucine in the P-helix of repeat IV. Polar residues five positions upstream from the selectivity filter residues form H-bonds with the ascending-limb backbones. Exceptionally conserved tryptophans are engaged in inter-repeat H-bonds to form a ring whose π-electrons would facilitate passage of ions from the outer carboxylates to the selectivity filter. The outer-pore model of CaV1.2 derived from the NaV1.4 model is also stabilized by the ring of exceptionally conservative tryptophans and H-bonds between the P-helices and ascending limbs. In this model, the exceptionally conserved aspartate downstream from the selectivity-filter glutamate in repeat II facilitates passage of calcium ions to the selectivity-filter ring through the tryptophan ring. Available experimental data are discussed in view of the models.
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Affiliation(s)
- Denis B Tikhonov
- Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, Ontario L8N 325, Canada
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42
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The tetrodotoxin binding site is within the outer vestibule of the sodium channel. Mar Drugs 2010; 8:219-34. [PMID: 20390102 PMCID: PMC2852835 DOI: 10.3390/md8020219] [Citation(s) in RCA: 91] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2009] [Revised: 01/10/2010] [Accepted: 01/28/2010] [Indexed: 12/21/2022] Open
Abstract
Tetrodotoxin and saxitoxin are small, compact asymmetrical marine toxins that block voltage-gated Na channels with high affinity and specificity. They enter the channel pore’s outer vestibule and bind to multiple residues that control permeation. Radiolabeled toxins were key contributors to channel protein purification and subsequent cloning. They also helped identify critical structural elements called P loops. Spacial organization of their mutation-identified interaction sites in molecular models has generated a molecular image of the TTX binding site in the outer vestibule and the critical permeation and selectivity features of this region. One site in the channel’s domain I P loop determines affinity differences in mammalian isoforms.
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Dudev T, Lim C. Factors Governing the Na+ vs K+ Selectivity in Sodium Ion Channels. J Am Chem Soc 2010; 132:2321-32. [DOI: 10.1021/ja909280g] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Todor Dudev
- Institute of Biomedical Sciences, Academia Sinica, Taipei 115, Taiwan, and the Department of Chemistry, National Tsing Hua University, Hsinchu 300, Taiwan
| | - Carmay Lim
- Institute of Biomedical Sciences, Academia Sinica, Taipei 115, Taiwan, and the Department of Chemistry, National Tsing Hua University, Hsinchu 300, Taiwan
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Human embryonic kidney (HEK293) cells express endogenous voltage-gated sodium currents and Na v 1.7 sodium channels. Neurosci Lett 2009; 469:268-72. [PMID: 20006571 DOI: 10.1016/j.neulet.2009.12.012] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2009] [Revised: 12/04/2009] [Accepted: 12/07/2009] [Indexed: 01/03/2023]
Abstract
Human embryonic kidney (HEK293) cells are widely used for the heterologous expression of voltage- and ligand-gated ion channels. Patch clamp analysis of HEK293 cells in the whole-cell configuration identified voltage-gated, rapidly inactivating inward currents. Peak current amplitudes ranged from less than 100 pA to more than 800 pA, with the majority (84 of 130 cells) in the 100-400 pA range. Transient inward currents were separated into three components on the basis of sensitivity to cadmium and tetrodotoxin (TTX). Application of cadmium (300 microM) reduced current amplitude to 65% of control, consistent with the existence of current carried by a cadmium-sensitive nonspecific cation channel previously identified in HEK293 cells. Application of TTX (500 nM) reduced current amplitude by 47%, consistent with the existence of current carried by a TTX-sensitive voltage-gated sodium channel. Joint application of cadmium and TTX was additive, reducing current amplitude to 28% of control. The residual cadmium- and TTX-resistant currents represent a third pharmacologically distinct component of the rapidly inactivating inward current that was not characterized further. The pyrethroid insecticide tefluthrin (10 microM) prolonged the inactivation of transient currents and induced slowly decaying tail currents, effects that are characteristic of sodium channel modification by pyrethroids. The use of sodium channel isoform-specific primers in polymerase chain reaction amplifications on HEK293 cell first-strand cDNA detected the consistent expression of the human Na(v)1.7 sodium channel isoform in cells that expressed the TTX-sensitive component of current. These results provide evidence for an endogenous TTX-sensitive sodium current in HEK293 cells that is associated primarily with the expression of the Na(v)1.7 sodium channel isoform.
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Du Y, Nomura Y, Liu Z, Huang ZY, Dong K. Functional expression of an arachnid sodium channel reveals residues responsible for tetrodotoxin resistance in invertebrate sodium channels. J Biol Chem 2009; 284:33869-75. [PMID: 19828457 DOI: 10.1074/jbc.m109.045690] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Tetrodotoxin (TTX) is a potent blocker of voltage-gated sodium channels, but not all sodium channels are equally sensitive to inhibition by TTX. The molecular basis of differential TTX sensitivity of mammalian sodium channels has been largely elucidated. In contrast, our knowledge about the sensitivity of invertebrate sodium channels to TTX remains poor, in part because of limited success in functional expression of these channels. In this study, we report the functional characterization in Xenopus oocytes of the first non-insect, invertebrate voltage-gated sodium channel from the varroa mite (Varroa destructor), an ecto-parasite of the honeybee. This arachnid sodium channel activates and inactivates rapidly with half-maximal activation at -18 mV and half-maximal fast inactivation at -29 mV. Interestingly, this arachnid channel showed surprising TTX resistance. TTX blocked this channel with an IC(50) of 1 microM. Subsequent site-directed mutagenesis revealed two residues, Thr-1674 and Ser-1967, in the pore-forming region of domains III and IV, respectively, which were responsible for the observed resistance to inhibition by TTX. Furthermore, sequence comparison and additional amino acid substitutions suggested that sequence polymorphisms at these two positions could be a widespread mechanism for modulating TTX sensitivity of sodium channels in diverse invertebrates.
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Affiliation(s)
- Yuzhe Du
- Department of Entomology, Genetics and Neuroscience Programs, Michigan State University, East Lansing, Michigan 48824, USA
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Xi Y, Wu G, Yang L, Han K, Du Y, Wang T, Lei X, Bai X, Ma A. Increased late sodium currents are related to transcription of neuronal isoforms in a pressure-overload model. Eur J Heart Fail 2009; 11:749-57. [PMID: 19584134 DOI: 10.1093/eurjhf/hfp092] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Affiliation(s)
- Yutao Xi
- Department of Cardiovascular Medicine; the First Affiliated Hospital of Xi'an Jiaotong University; 277 West Yanta Road Xi'an Shaanxi 710061 China
- Key Laboratory of Environment and Genes Related to Diseases, Ministry of Education; Xi'an Jiaotong University; 277 West Yanta Road Xi'an Shaanxi 710061 China
| | - Geru Wu
- Department of Cardiovascular Medicine; the First Affiliated Hospital of Xi'an Jiaotong University; 277 West Yanta Road Xi'an Shaanxi 710061 China
- Key Laboratory of Environment and Genes Related to Diseases, Ministry of Education; Xi'an Jiaotong University; 277 West Yanta Road Xi'an Shaanxi 710061 China
| | - Lin Yang
- Department of Cardiovascular Medicine; the First Affiliated Hospital of Xi'an Jiaotong University; 277 West Yanta Road Xi'an Shaanxi 710061 China
- Key Laboratory of Environment and Genes Related to Diseases, Ministry of Education; Xi'an Jiaotong University; 277 West Yanta Road Xi'an Shaanxi 710061 China
| | - Ke Han
- Department of Cardiovascular Medicine; the First Affiliated Hospital of Xi'an Jiaotong University; 277 West Yanta Road Xi'an Shaanxi 710061 China
- Key Laboratory of Environment and Genes Related to Diseases, Ministry of Education; Xi'an Jiaotong University; 277 West Yanta Road Xi'an Shaanxi 710061 China
| | - Yuan Du
- Department of Cardiovascular Medicine; the First Affiliated Hospital of Xi'an Jiaotong University; 277 West Yanta Road Xi'an Shaanxi 710061 China
- Key Laboratory of Environment and Genes Related to Diseases, Ministry of Education; Xi'an Jiaotong University; 277 West Yanta Road Xi'an Shaanxi 710061 China
| | - Tingzhong Wang
- Department of Cardiovascular Medicine; the First Affiliated Hospital of Xi'an Jiaotong University; 277 West Yanta Road Xi'an Shaanxi 710061 China
- Key Laboratory of Environment and Genes Related to Diseases, Ministry of Education; Xi'an Jiaotong University; 277 West Yanta Road Xi'an Shaanxi 710061 China
| | - Xinjun Lei
- Department of Cardiovascular Medicine; the First Affiliated Hospital of Xi'an Jiaotong University; 277 West Yanta Road Xi'an Shaanxi 710061 China
- Key Laboratory of Environment and Genes Related to Diseases, Ministry of Education; Xi'an Jiaotong University; 277 West Yanta Road Xi'an Shaanxi 710061 China
| | - Xiaojun Bai
- Department of Cardiovascular Medicine; the First Affiliated Hospital of Xi'an Jiaotong University; 277 West Yanta Road Xi'an Shaanxi 710061 China
- Key Laboratory of Environment and Genes Related to Diseases, Ministry of Education; Xi'an Jiaotong University; 277 West Yanta Road Xi'an Shaanxi 710061 China
| | - Aiqun Ma
- Department of Cardiovascular Medicine; the First Affiliated Hospital of Xi'an Jiaotong University; 277 West Yanta Road Xi'an Shaanxi 710061 China
- Key Laboratory of Environment and Genes Related to Diseases, Ministry of Education; Xi'an Jiaotong University; 277 West Yanta Road Xi'an Shaanxi 710061 China
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Dib-Hajj SD, Binshtok AM, Cummins TR, Jarvis MF, Samad T, Zimmermann K. Voltage-gated sodium channels in pain states: Role in pathophysiology and targets for treatment. ACTA ACUST UNITED AC 2009; 60:65-83. [DOI: 10.1016/j.brainresrev.2008.12.005] [Citation(s) in RCA: 112] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/29/2008] [Indexed: 12/19/2022]
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Zhang MM, McArthur JR, Azam L, Bulaj G, Olivera BM, French RJ, Yoshikami D. Synergistic and antagonistic interactions between tetrodotoxin and mu-conotoxin in blocking voltage-gated sodium channels. Channels (Austin) 2009; 3:32-8. [PMID: 19221510 DOI: 10.4161/chan.3.1.7500] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Tetrodotoxin (TTX) is the quintessential ligand of voltage-gated sodium channels (NaVs). Like TTX, mu-conotoxin peptides are pore blockers, and both toxins have helped to define the properties of neurotoxin receptor Site 1 of NaVs. Here, we report unexpected results showing that the recently discovered mu-conotoxin KIIIA and TTX can simultaneously bind to Site 1 and act in concert. Results with saturating concentrations of peptide applied to voltage-clamped Xenopus oocytes expressing brain NaV1.2, and single-channel recordings from brain channels in lipid bilayers, show that KIIIA or its analog, KIIIA[K7A], block partially, with a residual current that can be completely blocked by TTX. In addition, the kinetics of block by TTX and peptide are each affected by the prior presence of the other toxin. For example, bound peptide slows subsequent binding of TTX (an antagonistic interaction) and slows TTX dissociation when both toxins are bound (a synergistic effect on block). The overall functional consequence resulting from the combined action of the toxins depends on the quantitative balance between these opposing actions. The results lead us to postulate that in the bi-liganded NaV complex, TTX is bound between the peptide and the selectivity filter. These observations refine our view of Site 1 and open new possibilities in NaV pharmacology.
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Affiliation(s)
- Min-Min Zhang
- Department of Biology, University of Utah, Salt Lake City, UT 84112, USA
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Sun H, Varela D, Chartier D, Ruben PC, Nattel S, Zamponi GW, Leblanc N. Differential interactions of Na+ channel toxins with T-type Ca2+ channels. ACTA ACUST UNITED AC 2008; 132:101-13. [PMID: 18591418 PMCID: PMC2442173 DOI: 10.1085/jgp.200709883] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Two types of voltage-dependent Ca2+ channels have been identified in heart: high (ICaL) and low (ICaT) voltage-activated Ca2+ channels. In guinea pig ventricular myocytes, low voltage–activated inward current consists of ICaT and a tetrodotoxin (TTX)-sensitive ICa component (ICa(TTX)). In this study, we reexamined the nature of low-threshold ICa in dog atrium, as well as whether it is affected by Na+ channel toxins. Ca2+ currents were recorded using the whole-cell patch clamp technique. In the absence of external Na+, a transient inward current activated near −50 mV, peaked at −30 mV, and reversed around +40 mV (HP = −90 mV). It was unaffected by 30 μM TTX or micromolar concentrations of external Na+, but was inhibited by 50 μM Ni2+ (by ∼90%) or 5 μM mibefradil (by ∼50%), consistent with the reported properties of ICaT. Addition of 30 μM TTX in the presence of Ni2+ increased the current approximately fourfold (41% of control), and shifted the dose–response curve of Ni2+ block to the right (IC50 from 7.6 to 30 μM). Saxitoxin (STX) at 1 μM abolished the current left in 50 μM Ni2+. In the absence of Ni2+, STX potently blocked ICaT (EC50 = 185 nM) and modestly reduced ICaL (EC50 = 1.6 μM). While TTX produced no direct effect on ICaT elicited by expression of hCaV3.1 and hCaV3.2 in HEK-293 cells, it significantly attenuated the block of this current by Ni2+ (IC50 increased to 550 μM Ni2+ for CaV3.1 and 15 μM Ni2+ for CaV3.2); in contrast, 30 μM TTX directly inhibited hCaV3.3-induced ICaT and the addition of 750 μM Ni2+ to the TTX-containing medium led to greater block of the current that was not significantly different than that produced by Ni2+ alone. 1 μM STX directly inhibited CaV3.1-, CaV3.2-, and CaV3.3-mediated ICaT but did not enhance the ability of Ni2+ to block these currents. These findings provide important new implications for our understanding of structure–function relationships of ICaT in heart, and further extend the hypothesis of a parallel evolution of Na+ and Ca2+ channels from an ancestor with common structural motifs.
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Affiliation(s)
- Hui Sun
- Excigen, Inc., Baltimore, MD 21224, USA
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Two critical residues in p-loop regions of puffer fish Na+ channels on TTX sensitivity. Toxicon 2008; 51:381-7. [DOI: 10.1016/j.toxicon.2007.10.014] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2007] [Revised: 10/20/2007] [Accepted: 10/23/2007] [Indexed: 11/18/2022]
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