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Vallée C, Howlin B, Lewis R. Ion Selectivity in the ENaC/DEG Family: A Systematic Review with Supporting Analysis. Int J Mol Sci 2021; 22:ijms222010998. [PMID: 34681656 PMCID: PMC8536179 DOI: 10.3390/ijms222010998] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2021] [Revised: 10/01/2021] [Accepted: 10/05/2021] [Indexed: 12/16/2022] Open
Abstract
The Epithelial Sodium Channel/Degenerin (ENaC/DEG) family is a superfamily of sodium-selective channels that play diverse and important physiological roles in a wide variety of animal species. Despite their differences, they share a high homology in the pore region in which the ion discrimination takes place. Although ion selectivity has been studied for decades, the mechanisms underlying this selectivity for trimeric channels, and particularly for the ENaC/DEG family, are still poorly understood. This systematic review follows PRISMA guidelines and aims to determine the main components that govern ion selectivity in the ENaC/DEG family. In total, 27 papers from three online databases were included according to specific exclusion and inclusion criteria. It was found that the G/SxS selectivity filter (glycine/serine, non-conserved residue, serine) and other well conserved residues play a crucial role in ion selectivity. Depending on the ion type, residues with different properties are involved in ion permeability. For lithium against sodium, aromatic residues upstream of the selectivity filter seem to be important, whereas for sodium against potassium, negatively charged residues downstream of the selectivity filter seem to be important. This review provides new perspectives for further studies to unravel the mechanisms of ion selectivity.
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Affiliation(s)
- Cédric Vallée
- Leverhulme Quantum Biology Doctoral Training Centre, University of Surrey, Guildford GU2 5XH, UK; (C.V.); (B.H.)
- Department of Chemistry, Faculty of Engineering and Physical Sciences, University of Surrey, Guildford GU2 7XH, UK
- School of Veterinary Medicine, Faculty of Health and Medical Sciences, University of Surrey, Guildford GU2 7AL, UK
| | - Brendan Howlin
- Leverhulme Quantum Biology Doctoral Training Centre, University of Surrey, Guildford GU2 5XH, UK; (C.V.); (B.H.)
- Department of Chemistry, Faculty of Engineering and Physical Sciences, University of Surrey, Guildford GU2 7XH, UK
| | - Rebecca Lewis
- Leverhulme Quantum Biology Doctoral Training Centre, University of Surrey, Guildford GU2 5XH, UK; (C.V.); (B.H.)
- School of Veterinary Medicine, Faculty of Health and Medical Sciences, University of Surrey, Guildford GU2 7AL, UK
- Correspondence:
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2
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Catacuzzeno L, Sforna L, Franciolini F. Voltage-dependent gating in K channels: experimental results and quantitative models. Pflugers Arch 2019; 472:27-47. [PMID: 31863286 DOI: 10.1007/s00424-019-02336-6] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2019] [Revised: 11/27/2019] [Accepted: 11/28/2019] [Indexed: 12/18/2022]
Abstract
Voltage-dependent K channels open and close in response to voltage changes across the cell membrane. This voltage dependence was postulated to depend on the presence of charged particles moving through the membrane in response to voltage changes. Recording of gating currents originating from the movement of these particles fully confirmed this hypothesis, and gave substantial experimental clues useful for the detailed understanding of the process. In the absence of structural information, the voltage-dependent gating was initially investigated using discrete Markov models, an approach only capable of providing a kinetic and thermodynamic comprehension of the process. The elucidation of the crystal structure of the first voltage-dependent channel brought in a dramatic change of pace in the understanding of channel gating, and in modeling the underlying processes. It was now possible to construct quantitative models using molecular dynamics, where all the interactions of each individual atom with the surroundings were taken into account, and its motion predicted by Newton's laws. Unfortunately, this modeling is computationally very demanding, and in spite of the advances in simulation procedures and computer technology, it is still limited in its predictive ability. To overcome these limitations, several groups have developed more macroscopic voltage gating models. Their approaches understandably require a number of approximations, which must however be physically well justified. One of these models, based on the description of the voltage sensor as a Brownian particle, that we have recently developed, is able to simultaneously describe the behavior of a single voltage sensor and to predict the macroscopic gating current originating from a population of sensors. The basics of this model are here described, and a typical application using the Kv1.2/2.1 chimera channel structure is also presented.
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Affiliation(s)
- Luigi Catacuzzeno
- Department of Chemistry, Biology and Biotechnology, University of Perugia, Via Elce di Sotto 8, 06123, Perugia, Italy.
| | - Luigi Sforna
- Department of Chemistry, Biology and Biotechnology, University of Perugia, Via Elce di Sotto 8, 06123, Perugia, Italy
| | - Fabio Franciolini
- Department of Chemistry, Biology and Biotechnology, University of Perugia, Via Elce di Sotto 8, 06123, Perugia, Italy.
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3
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Piggott BJ, Peters CJ, He Y, Huang X, Younger S, Jan LY, Jan YN. Paralytic, the Drosophila voltage-gated sodium channel, regulates proliferation of neural progenitors. Genes Dev 2019; 33:1739-1750. [PMID: 31753914 PMCID: PMC6942049 DOI: 10.1101/gad.330597.119] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2019] [Accepted: 10/28/2019] [Indexed: 12/23/2022]
Abstract
In this study, Piggott et al. set out to examine the role of paralytic, the sole voltage-gated sodium channel in Drosophila, in neural progenitors. Using cell biology assays and electrophysiological analysis, the authors report for the first time a developmental role of voltage-gated sodium channels in regulating neural progenitor proliferation in Drosophila larvae. Proliferating cells, typically considered “nonexcitable,” nevertheless, exhibit regulation by bioelectric signals. Notably, voltage-gated sodium channels (VGSC) that are crucial for neuronal excitability are also found in progenitors and up-regulated in cancer. Here, we identify a role for VGSC in proliferation of Drosophila neuroblast (NB) lineages within the central nervous system. Loss of paralytic (para), the sole gene that encodes Drosophila VGSC, reduces neuroblast progeny cell number. The type II neuroblast lineages, featuring a population of transit-amplifying intermediate neural progenitors (INP) similar to that found in the developing human cortex, are particularly sensitive to para manipulation. Following a series of asymmetric divisions, INPs normally exit the cell cycle through a final symmetric division. Our data suggests that loss of Para induces apoptosis in this population, whereas overexpression leads to an increase in INPs and overall neuroblast progeny cell numbers. These effects are cell autonomous and depend on Para channel activity. Reduction of Para expression not only affects normal NB development, but also strongly suppresses brain tumor mass, implicating a role for Para in cancer progression. To our knowledge, our studies are the first to identify a role for VGSC in neural progenitor proliferation. Elucidating the contribution of VGSC in proliferation will advance our understanding of bioelectric signaling within development and disease states.
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Affiliation(s)
- Beverly J Piggott
- Department of Physiology, Department of Biochemistry and Biophysics, University of California at San Francisco, San Francisco, California 94158, USA.,Howard Hughes Medical Institute
| | - Christian J Peters
- Department of Physiology, Department of Biochemistry and Biophysics, University of California at San Francisco, San Francisco, California 94158, USA
| | - Ye He
- Neuroscience Initiative, Advanced Science Research Center, the Graduate Center, City University of New York, New York 10031, New York
| | - Xi Huang
- Program in Developmental and Stem Cell Biology, The Hospital for Sick Children, Toronto, Ontario, M5G 1X8, Canada.,Arthur and Sonia Labatt Brain Tumour Research Centre, The Hospital for Sick Children, Toronto, Ontario, M5G 1X8, Canada.,Department of Molecular Genetics, University of Toronto, Toronto, Ontario, M5S 3E1, Canada
| | - Susan Younger
- Department of Physiology, Department of Biochemistry and Biophysics, University of California at San Francisco, San Francisco, California 94158, USA.,Howard Hughes Medical Institute
| | - Lily Yeh Jan
- Department of Physiology, Department of Biochemistry and Biophysics, University of California at San Francisco, San Francisco, California 94158, USA.,Howard Hughes Medical Institute
| | - Yuh Nung Jan
- Department of Physiology, Department of Biochemistry and Biophysics, University of California at San Francisco, San Francisco, California 94158, USA.,Howard Hughes Medical Institute
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4
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Xu L, Ding X, Wang T, Mou S, Sun H, Hou T. Voltage-gated sodium channels: structures, functions, and molecular modeling. Drug Discov Today 2019; 24:1389-1397. [PMID: 31129313 DOI: 10.1016/j.drudis.2019.05.014] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2019] [Revised: 04/02/2019] [Accepted: 05/17/2019] [Indexed: 10/26/2022]
Abstract
Voltage-gated sodium channels (VGSCs), formed by 24 transmembrane segments arranged into four domains, have a key role in the initiation and propagation of electrical signaling in excitable cells. VGSCs are involved in a variety of diseases, including epilepsy, cardiac arrhythmias, and neuropathic pain, and therefore have been regarded as appealing therapeutic targets for the development of anticonvulsant, antiarrhythmic, and local anesthetic drugs. In this review, we discuss recent advances in understanding the structures and biological functions of VGSCs. In addition, we systematically summarize eight pharmacologically distinct ligand-binding sites in VGSCs and representative isoform-selective VGSC modulators in clinical trials. Finally, we review studies on molecular modeling and computer-aided drug design (CADD) for VGSCs to help understanding of biological processes involving VGSCs.
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Affiliation(s)
- Lei Xu
- Institute of Bioinformatics and Medical Engineering, School of Electrical and Information Engineering, Jiangsu University of Technology, Changzhou 213001, China
| | - Xiaoqin Ding
- Beijing Institute of Pharmaceutical Chemistry, Beijing 102205, China
| | - Tianhu Wang
- Institute of Bioinformatics and Medical Engineering, School of Electrical and Information Engineering, Jiangsu University of Technology, Changzhou 213001, China
| | - Shanzhi Mou
- School of Mathematics and Physics, Jiangsu University of Technology, Changzhou 213001, China
| | - Huiyong Sun
- Department of Medicinal Chemistry, School of Pharmacy, State Key Laboratory of Natural Medicines, China Pharmaceutical University, Nanjing 210009, China.
| | - Tingjun Hou
- College of Pharmaceutical Sciences, Zhejiang University, Hangzhou 310058, China.
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5
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Xu L, Li D, Ding J, Pan L, Ding X. Insight into tetrodotoxin blockade and resistance mechanisms of Na v 1.2 sodium channel by theoretical approaches. Chem Biol Drug Des 2018; 92:1445-1457. [PMID: 29673065 DOI: 10.1111/cbdd.13310] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2018] [Revised: 03/08/2018] [Accepted: 03/17/2018] [Indexed: 11/30/2022]
Abstract
Nav 1.2, a member of voltage-gated sodium channels (Nav s) that are responsible for the generation and propagation of action potentials along the cell membrane, and play a vital role in the process of information transmission within the nervous system and muscle contraction, is preferentially expressed in the central nervous system. As a potent and selective blocker of Nav s, tetrodotoxin (TTX) has been extensively studied in biological and chemical sciences, whereas the detailed mechanism by which it blocks nine Nav 1 channel subtypes remain elusive. Despite the high structural similarity, the TTX metabolite 4,9-anhydro-TTX is 161 times less effective toward the mammalian Nav 1.2, which puzzled us to ask a question why such a subtle structural variation results in the largely binding affinity difference. In the current work, an integrated computational strategy, including homology modeling, induced fit docking, explicit-solvent MD simulations, and free energy calculations, was employed to investigate the binding mechanism and conformational determinants of TTX analogs. Based on the computational results, the H-bond interactions between C4-OH and C9-OH of TTX and the outer ring carboxylates of the selectivity-filter residues, and the cation-π interaction between the primary amine of guanidinium of TTX and Phe385 determine the difference of their binding affinities. Moreover, the computationally simulations were carried out for the D384N and E945K mutants of hNav 1.2-TTX, and the rank of the predicted binding free energies is in accordance with the experimental data. These observations provide a valuable model to design potent and selective neurotoxins of Nav 1.2 and shed light on the blocking mechanism of TTX to sodium channels.
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Affiliation(s)
- Lei Xu
- Institute of Bioinformatics and Medical Engineering, School of Electrical and Information Engineering, Jiangsu University of Technology, Changzhou, China
| | - Dayu Li
- Beijing Institute of Pharmaceutical Chemistry, Beijing, China
| | - Junjie Ding
- Beijing Institute of Pharmaceutical Chemistry, Beijing, China
| | - Li Pan
- Beijing Institute of Pharmaceutical Chemistry, Beijing, China
| | - Xiaoqin Ding
- Beijing Institute of Pharmaceutical Chemistry, Beijing, China
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6
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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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8
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Dudev T, Lim C. Evolution of Eukaryotic Ion Channels: Principles Underlying the Conversion of Ca2+-Selective to Na+-Selective Channels. J Am Chem Soc 2014; 136:3553-9. [DOI: 10.1021/ja4121132] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Todor Dudev
- Institute
of Biomedical Sciences, Academia Sinica, Taipei 11529, Taiwan
| | - Carmay Lim
- Institute
of Biomedical Sciences, Academia Sinica, Taipei 11529, Taiwan
- Department
of Chemistry, National Tsing Hua University, Hsinchu 300, Taiwan
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9
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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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10
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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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11
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Cervenka R, Zarrabi T, Lukacs P, Todt H. The outer vestibule of the Na+ channel-toxin receptor and modulator of permeation as well as gating. Mar Drugs 2010; 8:1373-93. [PMID: 20479982 PMCID: PMC2866490 DOI: 10.3390/md8041373] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2010] [Revised: 03/31/2010] [Accepted: 04/19/2010] [Indexed: 12/19/2022] Open
Abstract
The outer vestibule of voltage-gated Na(+) channels is formed by extracellular loops connecting the S5 and S6 segments of all four domains ("P-loops"), which fold back into the membrane. Classically, this structure has been implicated in the control of ion permeation and in toxin blockage. However, conformational changes of the outer vestibule may also result in alterations in gating, as suggested by several P-loop mutations that gave rise to gating changes. Moreover, partial pore block by mutated toxins may reverse gating changes induced by mutations. Therefore, toxins that bind to the outer vestibule can be used to modulate channel gating.
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Affiliation(s)
| | | | - Peter Lukacs
- Institute of Pharmacology, Centre of Physiology and Pharmacology, Medical University of Vienna, 1090 Vienna, Austria; E-Mails:
(R.C.);
(T.Z.);
(P.L.)
| | - Hannes Todt
- Institute of Pharmacology, Centre of Physiology and Pharmacology, Medical University of Vienna, 1090 Vienna, Austria; E-Mails:
(R.C.);
(T.Z.);
(P.L.)
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12
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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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13
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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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Groome JR, Alexander HM, Fujimoto E, Sherry M, Petty D. Central Charged Residues in DIIIS4 Regulate Deactivation Gating in Skeletal Muscle Sodium Channels. Cell Mol Neurobiol 2006; 27:87-106. [PMID: 17151947 DOI: 10.1007/s10571-006-9120-2] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2006] [Accepted: 09/11/2006] [Indexed: 10/23/2022]
Abstract
1. Mutations in the S4 segment of domain III in the voltage gated skeletal muscle sodium channel hNa(V)1.4 were constructed to test the roles of each charged residue in deactivation gating. Mutations comprised charge reversals at K1-R6, charge neutralization, and substitution at R4 and R5. 2. Charge-reversing mutations at R4 and R5 produced the greatest alteration of activation parameters compared to hNa(V)1.4. Effects included depolarization of the conductance/voltage (g/V) curve, decreased valence and slowing of kinetics. 3. Reversal of charge at R2 to R4 hyperpolarized, and reversal at R5 or R6 depolarized the h (infinity) curve. Most DIIIS4 mutations slowed inactivation from the open state. R4E slowed closed state fast inactivation and R5E inhibited its completion .4. Deactivation from the open and/or inactivated state was prolonged in mutations reversing charge at R2 to R4 but accelerated by reversal of charge at R5 or R6. Effects were most pronounced at central charges R4 and R5. 5. Charge and structure each contribute to effects of mutations at R4 and R5 on channel gating. Effects of mutations on activation and deactivation at R4 and, to a lesser extent R5, were primarily owing to charge alteration, whereas effects on fast inactivation were charge independent.
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Affiliation(s)
- James R Groome
- Department of Biological Sciences, Idaho State University, Pocatello, ID 83204, USA.
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15
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Moran O, Picollo A, Conti F. Tonic and phasic guanidinium toxin-block of skeletal muscle Na channels expressed in Mammalian cells. Biophys J 2003; 84:2999-3006. [PMID: 12719231 PMCID: PMC1302862 DOI: 10.1016/s0006-3495(03)70026-5] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
Abstract
The blockage of skeletal muscle sodium channels by tetrodotoxin (TTX) and saxitoxin (STX) have been studied in CHO cells permanently expressing rat Nav1.4 channels. Tonic and use-dependent blockage were analyzed in the framework of the ion-trapped model. The tonic affinity (26.6 nM) and the maximum affinity (7.7 nM) of TTX, as well as the "on" and "off" rate constants measured in this preparation, are in remarkably good agreement with those measured for Nav1.2 expressed in frog oocytes, indicating that the structure of the toxin receptor of Nav1.4 and Nav1.2 channels are very similar and that the expression method does not have any influence on the pore properties of the sodium channel. The higher affinity of STX for the sodium channels (tonic and maximum affinity of 1.8 nM and 0.74 nM respectively) is explained as an increase on the "on" rate constant (approximately 0.03 s(-1) nM(-1)), compared to that of TTX (approximately 0.003 s(-1) nM(-1)), while the "off" rate constant is the same for both toxins (approximately 0.02 s(-1)). Estimations of the free-energy differences of the toxin-channel interaction indicate that STX is bound in a more external position than TTX. Similarly, the comparison of the toxins free energy of binding to a ion-free, Na(+)- and Ca(2+)-occupied channel, is consistent with a binding site in the selectivity filter for Ca(2+) more external than for Na(+). This data may be useful in further attempts at sodium-channel pore modeling.
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Affiliation(s)
- Oscar Moran
- Istituto di Biofisica, Sezione di Genova, CNR, Italy.
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Khan A, Romantseva L, Lam A, Lipkind G, Fozzard HA. Role of outer ring carboxylates of the rat skeletal muscle sodium channel pore in proton block. J Physiol 2002; 543:71-84. [PMID: 12181282 PMCID: PMC2290475 DOI: 10.1113/jphysiol.2002.021014] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Voltage-gated Na+ current is reduced by acid solution. Protons reduce peak Na+ conductance by lowering single channel conductance and shift the voltage range of gating by neutralizing surface charges. Structure-function studies identify six carboxyls and a lysine in the channel's outer vestibule. We examined the roles of the superficial ring of carboxyls in acid block of Na(v)1.4 (the rat skeletal muscle Na+ channel isoform) by measuring the effects of their neutralization or their substitution by lysine on sensitivity to acid solutions, using the two-micropipette voltage clamp in Xenopus oocytes. Alteration of the outer ring of carboxylates had little effect on the voltage for half-activation of Na+ current, as if they are distant from the channels' voltage sensors. The mutations did not abolish proton block; rather, they all shifted the pK(a) (-log of the dissociation constant) in the acid direction. Effects of neutralization on pK(a) were not identical for different mutations, with E758Q > D1241A > D1532N > E403Q. E758K showed double the effect of E758Q, and the other lysine mutations all produced larger effects than the neutralizing mutations. Calculation of the electrostatic potential produced by these carboxylates using a pore model showed that the pK(a) values of carboxylates of Glu-403, Glu-758, and Asp-1532 are shifted to values similar to the experimentally measured pK(a). Calculations also predict the experimentally observed changes in pK(a) that result from mutational neutralization or introduction of a positive charge. We propose that proton block results from partial protonation of these outer ring carboxylates and that all of the carboxylates contribute to a composite Na+ site.
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Affiliation(s)
- A Khan
- The Cardiac Electrophysiology Laboratories, Department of Medicine, The University of Chicago, Chicago, IL 60637, USA
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17
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Affiliation(s)
- R J French
- Department of Physiology and Biophysics, University of Calgary, Alberta, Canada
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Greeff NG, Kühn FJ. Variable ratio of permeability to gating charge of rBIIA sodium channels and sodium influx in Xenopus oocytes. Biophys J 2000; 79:2434-53. [PMID: 11053121 PMCID: PMC1301129 DOI: 10.1016/s0006-3495(00)76487-3] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
Whole-cell gating current recording from rat brain IIA sodium channels in Xenopus oocytes was achieved using a high-expression system and a newly developed high-speed two-electrode voltage-clamp. The resulting ionic currents were increased by an order of magnitude. Surprisingly, the measured corresponding gating currents were approximately 5-10 times larger than expected from ionic permeability. This prompted us to minimize uncertainties about clamp asymmetries and to quantify the ratio of sodium permeability to gating charge, which initially would be expected to be constant for a homogeneous channel population. The systematic study, however, showed a 10- to 20-fold variation of this ratio in different experiments, and even in the same cell during an experiment. The ratio of P(Na)/Q was found to correlate with substantial changes observed for the sodium reversal potential. The data suggest that a cytoplasmic sodium load in Xenopus oocytes or the energy consumption required to regulate the increase in cytoplasmic sodium represents a condition where most of the expressed sodium channels keep their pore closed due to yet unknown mechanisms. In contrast, the movements of the voltage sensors remain undisturbed, producing gating current with normal properties.
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Affiliation(s)
- N G Greeff
- Physiologisches Institut, Universität Zürich-Irchel, CH-8057 Zürich, Switzerland.
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19
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Li RA, Vélez P, Chiamvimonvat N, Tomaselli GF, Marbán E. Charged residues between the selectivity filter and S6 segments contribute to the permeation phenotype of the sodium channel. J Gen Physiol 2000; 115:81-92. [PMID: 10613920 PMCID: PMC1887778 DOI: 10.1085/jgp.115.1.81] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/1999] [Accepted: 12/06/1999] [Indexed: 12/03/2022] Open
Abstract
The deep regions of the Na(+) channel pore around the selectivity filter have been studied extensively; however, little is known about the adjacent linkers between the P loops and S6. The presence of conserved charged residues, including five in a row in domain III (D-III), hints that these linkers may play a role in permeation. To characterize the structural topology and function of these linkers, we neutralized the charged residues (from position 411 in D-I and its homologues in D-II, -III, and -IV to the putative start sites of S6) individually by cysteine substitution. Several cysteine mutants displayed enhanced sensitivities to Cd(2+) block relative to wild-type and/or were modifiable by external sulfhydryl-specific methanethiosulfonate reagents when expressed in TSA-201 cells, indicating that these amino acids reside in the permeation pathway. While neutralization of positive charges did not alter single-channel conductance, negative charge neutralizations generally reduced conductance, suggesting that such charges facilitate ion permeation. The electrical distances for Cd(2+) binding to these residues reveal a secondary "dip" into the membrane field of the linkers in domains II and IV. Our findings demonstrate significant functional roles and surprising structural features of these previously unexplored external charged residues.
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Affiliation(s)
- Ronald A. Li
- From the Institute of Molecular Cardiobiology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - Patricio Vélez
- From the Institute of Molecular Cardiobiology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - Nipavan Chiamvimonvat
- From the Institute of Molecular Cardiobiology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - Gordon F. Tomaselli
- From the Institute of Molecular Cardiobiology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - Eduardo Marbán
- From the Institute of Molecular Cardiobiology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
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20
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Boccaccio A, Moran O, Imoto K, Conti F. Tonic and phasic tetrodotoxin block of sodium channels with point mutations in the outer pore region. Biophys J 1999; 77:229-40. [PMID: 10388752 PMCID: PMC1300324 DOI: 10.1016/s0006-3495(99)76884-0] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
Abstract
Tonic and use-dependent block by tetrodotoxin (TTX) has been studied in cRNA-injected Xenopus oocytes expressing mutants W386Y, E945Q, D1426K, and D1717Q, of the outer-pore region of the rat brain IIA alpha-subunit of sodium channels. The various phenotypes are tonically half-blocked at TTX concentrations, IC50(t), that span a range of more than three orders of magnitude, from 4 nM in mutant D1426K to 11 microM in mutant D1717Q. When stimulated with repetitive depolarizing pulses at saturating frequencies, all channels showed a monoexponential increase in their TTX-binding affinity with time constants that span an equally wide range of values ([TTX] approximately IC50(t), from approximately 60 s for D1426K to approximately 30 ms for D1717Q) and are in most phenotypes roughly inversely proportional to IC50(t). In contrast, all phenotypes show the same approximately threefold increase in their TTX affinity under stimulation. The invariance of the free-energy difference between tonic and phasic configurations of the toxin-receptor complex, together with the extreme variability of phasic block kinetics, is fully consistent with the trapped-ion mechanism of use dependence suggested by and developed by. Using this model, we estimated for each phenotype both the second-order association rate constant, kon, and the first-order dissociation rate constant, koff, for TTX binding. Except for mutant E945Q, all phenotypes have roughly the same value of kon approximately 2 microM-1 s-1 and owe their large differences in IC50(t) to different koff values. However, a 60-fold reduction in kon is the main determinant of the low TTX sensitivity of mutant E945Q. This suggests that the carboxyl group of E945 occupies a much more external position in the pore vestibule than that of the homologous residue D1717.
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Affiliation(s)
- A Boccaccio
- Istituto di Cibernetica e Biofisica, CNR, I-16149 Genova, Italy
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21
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Sato C, Sato M, Iwasaki A, Doi T, Engel A. The sodium channel has four domains surrounding a central pore. J Struct Biol 1998; 121:314-25. [PMID: 9704503 DOI: 10.1006/jsbi.1998.3990] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The voltage-gated sodium channel generates the action potential. This 300-kDa protein has four homologous regions, which are also homologous to the voltage-sensitive tetrameric potassium channel. We isolated sodium channels from Electrophorus electricus electroplax by detergent solubilization and immunoaffinity chromatography and studied their structure by electron microscopy of negatively stained specimens. Different projections were aligned, classified, and averaged. In side view, the channel protein exhibits the shape of a truncated cone, 14 nm in height. One end has a diameter of 12 nm and is asymmetric, while the other is more symmetric and has a diameter of 7-10 nm. In top views, the sodium channel appears to consist of four domains of different size and to have a stain-filled pore in the center.
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Affiliation(s)
- C Sato
- Electrotechnical Laboratory, Supermolecular Science Division, Tsukuba, Japan
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22
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Dyer JR, Johnston WL, Castellucci VF, Dunn RJ. Cloning and tissue distribution of the Aplysia Na+ channel alpha-subunit cDNA. DNA Cell Biol 1997; 16:347-56. [PMID: 9115644 DOI: 10.1089/dna.1997.16.347] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Voltage-gated Na+ channels generate the depolarizing inward current that is critical for the initiation and conduction of action potentials. To study the roles of Na+ channels in neuronal signaling, we have begun the molecular analysis of Na+ channels in Aplysia californica. We have isolated cDNAs that encode a neuronal Na+ channel alpha-subunit, which we have named SCAP1. DNA sequence analysis of the SCAP1 cDNA revealed an open reading frame that predicts a protein of 1,993 amino acids, which is highly similar to other members of the Na+ channel alpha-subunit gene family. RNase protection assays carried out on various Aplysia tissues indicated that SCAP1 is expressed predominantly in the nervous system. All of the nonneuronal tissues tested were negative with the exceptions that low levels of expression were observed in ovotestis and parapodium, probably due to the presence of small numbers of neurons within these tissue preparations. Southern blot hybridization at reduced stringency indicated that the genome of Aplysia contains more than one Na+ channel alpha-subunit gene.
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Affiliation(s)
- J R Dyer
- Center for Research in Neuroscience, McGill University, Montreal, Canada
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23
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Abstract
Recombinant brain, skeletal muscle, and heart voltage-gated Na+ channel alpha subunits differ in their functional responses to an accessory beta 1 subunit when coexpressed in Xenopus oocytes. We exploited the distinct beta 1 subunit responses observed for the human heart (hH1) and human skeletal muscle (hSkM1) isoforms to identify determinants of this response. Chimeric alpha subunits were constructed by exchanging the S5-S6 interhelical loops of each domain between hH1 and hSkM1 and then examined for effects on inactivation induced by coexpressed beta 1 subunit in oocytes. Substitution of single S5-S6 loops in either domain 1 (D1/S5-S6) or domain 4 (D4/S5-S6) of hSkM1 by the corresponding segments of hH1 produced channels that exhibited an attenuated response to coexpressed beta 1 subunit. Substitutions of both D1/S5-S6 and D4/S5-S6 in hSkM1 by the corresponding loops from hH1 completely abolished the effects of the beta 1 subunit on inactivation. The reciprocal chimera in which both D1/S5-S6 and D4/S5-S6 from hSkM1 were transplanted into hH1 exhibited significant beta 1 responsiveness (accelerated inactivation). The region within D4/S5-S6 that conferred beta 1 responsiveness was determined to reside primarily within an extracellular loop between the putative pore-forming segment SS2 and D4/S6. Gating modulation was also demonstrated using a chimeric beta subunit consisting of the extracellular domains of beta 1 and the transmembrane and C-terminal domains of the rat brain beta 2 subunit. These results suggest that the D1/S5-S6 and D4/S5-S6 loops in the alpha subunit and the extracellular domain of the beta 1 subunit are important determinants of the beta 1 subunit-induced gating modulation in Na+ channels.
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24
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Conti F, Gheri A, Pusch M, Moran O. Use dependence of tetrodotoxin block of sodium channels: a revival of the trapped-ion mechanism. Biophys J 1996; 71:1295-312. [PMID: 8874004 PMCID: PMC1233597 DOI: 10.1016/s0006-3495(96)79330-x] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
The use-dependent block of sodium channels by tetrodotoxin (TTX) has been studied in cRNA-injected Xenopus oocytes expressing the alpha-subunit of rat brain IIA channels. The kinetics of stimulus-induced extra block are consistent with an underlying relaxation process involving only three states. Cumulative extra block induced by repetitive stimulations increases with hyperpolarization, with TTX concentration, and with extracellular Ca2+ concentration. We have developed a theoretical model based on the suggestion by Salgado et al. that TTX blocks the extracellular mouth of the ion pore less tightly when the latter has its external side occupied by a cation, and that channel opening favors a tighter binding by allowing the escape of the trapped ion. The model provides an excellent fit of the data, which are consistent with Ca2+ being more efficient than Na+ in weakening TTX binding and with bound Ca2+ stabilizing the closed state of the channel, as suggested by Armstrong and Cota. Reports arguing against the trapped-ion mechanism are critically discussed.
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Affiliation(s)
- F Conti
- Istituto di Cibernetica e Biofisica, CNR, Genoa, Italy.
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25
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Chiamvimonvat N, Pérez-García MT, Ranjan R, Marban E, Tomaselli GF. Depth asymmetries of the pore-lining segments of the Na+ channel revealed by cysteine mutagenesis. Neuron 1996; 16:1037-47. [PMID: 8630242 DOI: 10.1016/s0896-6273(00)80127-0] [Citation(s) in RCA: 93] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
We used serial cysteine mutagenesis to study the structure of the outer vestibule and selectivity region of the voltage-gated Na channel. The voltage dependence of Cd(2+) block enabled us to determine the locations within the electrical field of cysteine-substituted mutants in the P segments of all four domains. The fractional electrical distances of the substituted cysteines were compared with the differential sensitivity to modification by sulfhydryl-specific modifying reagents. These experiments indicate that the P segment of domain II is external, while the domain IV P segment is displaced internally, compared with the first and third domain P segments. Sulfhydryls with a steep voltage dependence for Cd(2+) block produced changes in monovalent cation selectivity; these included substitutions at the presumed selectivity filter, as well as residues in the domain IV P segment not previously recognized as determinants of selectivity. A new structural model is presented in which each of the P segments contribute unique loops that penetrate the membrane to varying depths to form the channel pore.
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Affiliation(s)
- N Chiamvimonvat
- Departments of Medicine and Biochemical Engineering, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
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26
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Baumgarten CM, Dudley SC, Rogart RB, Fozzard HA. Unitary conductance of Na+ channel isoforms in cardiac and NB2a neuroblastoma cells. THE AMERICAN JOURNAL OF PHYSIOLOGY 1995; 269:C1356-63. [PMID: 8572163 DOI: 10.1152/ajpcell.1995.269.6.c1356] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Unitary conductances of native Na+ channel isoforms (gamma Na) have been determined under a variety of conditions, making comparisons of gamma Na difficult. To allow direct comparison, we measured gamma Na in cell-attached patches on NB2a neuroblastoma cells and rabbit ventricular myocytes under identical conditions [pipette solution (in mM): 280 Na+ and 2 Ca2+, pH 7.4; 10 degrees C]. gamma Na of NB2a channels, 22.9 +/- 0.9 pS, was 21% greater than that of cardiac channels, 18.9 +/- 0.9 pS. In contrast, respective extrapolated reversal potentials, +62.4 +/- 4.6 and +57.9 +/- 5.1 mV, were not significantly different. Several kinetic differences between the channel types were also noted. Negative to -20 mV, mean open time (MOT) of the NB2a isoform was significantly less than that of cardiac channels, and, near threshold, latency to channel opening decayed more rapidly in NB2a. On the basis of analysis of MOT between -60 and 0 mV, the rate constants at 0 mV for the open-to-closed (O-->C) and open-to-inactivated (O-->I) transitions were 0.42 +/- 0.11 and 0.47 +/- 0.11 ms-1 in NB2a and 0.10 +/- 0.06 and 1.19 +/- 0.07 ms-1 in myocytes. The slope factors were -38.9 +/- 8.7 and +10.7 +/- 6.1 mV in NB2a and -27.3 +/- 7.1 and +23.7 +/- 4.9 mV in myocytes. Transition rate constants were significantly different in NB2a and cardiac cells, but voltage dependence was not.
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Affiliation(s)
- C M Baumgarten
- Department of Physiology, Medical College of Virginia, Virginia Commonwealth University, Richmond 23298, USA
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27
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Taglialatela M, Brown AM. Structural motifs underlying voltage-dependent K+ channel function. Kidney Int 1995; 48:918-22. [PMID: 8569100 DOI: 10.1038/ki.1995.372] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Affiliation(s)
- M Taglialatela
- Department of Neurosciences, 2nd School of Medicine, University of Naples Federico II, Italy
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28
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Tomaselli GF, Chiamvimonvat N, Nuss HB, Balser JR, Pérez-García MT, Xu RH, Orias DW, Backx PH, Marban E. A mutation in the pore of the sodium channel alters gating. Biophys J 1995; 68:1814-27. [PMID: 7612823 PMCID: PMC1282084 DOI: 10.1016/s0006-3495(95)80358-9] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Ion permeation and channel gating are classically considered independent processes, but site-specific mutagenesis studies in K channels suggest that residues in or near the ion-selective pore of the channel can influence activation and inactivation. We describe a mutation in the pore of the skeletal muscle Na channel that alters gating. This mutation, I-W53C (residue 402 in the mu 1 sequence), decreases the sensitivity to block by tetrodotoxin and increases the sensitivity to block by externally applied Cd2+ relative to the wild-type channel, placing this residue within the pore near the external mouth. Based on contemporary models of the structure of the channel, this residue is remote from the regions of the channel known to be involved in gating, yet this mutation abbreviates the time to peak and accelerates the decay of the macroscopic Na current. At the single-channel level we observe a shortening of the latency to first opening and a reduction in the mean open time compared with the wild-type channel. The acceleration of macroscopic current kinetics in the mutant channels can be simulated by changing only the activation and deactivation rate constants while constraining the microscopic inactivation rate constants to the values used to fit the wild-type currents. We conclude that the tryptophan at position 53 in the domain IP-loop may act as a linchpin in the pore that limits the opening transition rate. This effect could reflect an interaction of I-W53 with the activation voltage sensors or a more global gating-induced change in pore structure.
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Affiliation(s)
- G F Tomaselli
- Department of Medicine, Johns Hopkins School of Medicine, Baltimore, Maryland 21205, USA
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29
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Affiliation(s)
- R MacKinnon
- Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115, USA
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30
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Cherbavaz DB. Trimethyloxonium modification of batrachotoxin-activated Na channels alters functionally important protein residues. Biophys J 1995; 68:1337-46. [PMID: 7787022 PMCID: PMC1282028 DOI: 10.1016/s0006-3495(95)80306-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
The extracellular side of single batrachotoxin-activated voltage-dependent Na channels isolated from rat skeletal muscle membranes incorporated into neutral planar lipid bilayers were treated in situ with the carboxyl methylating reagent, trimethyloxonium (TMO). These experiments were designed to determine whether TMO alters Na channel function by a general through-space electrostatic mechanism or by methylating specific carboxyl groups essential to channel function. TMO modification reduced single-channel conductance by decreasing the maximal turnover rate. Modification increased channel selectivity for sodium ions relative to potassium ions as measured under biionic conditions. TMO modification increased the mu-conotoxin (muCTX) off-rate by three orders of magnitude. Modification did not alter the muCTX on-rate at low ionic strength or Na channel voltage-dependent gating characteristics. These data demonstrate that TMO does not act via a general electrostatic mechanism. Instead, TMO targets protein residues specifically involved in ion conduction, ion selectivity, and muCTX binding. These data support the hypothesis that muCTX blocks open-channel current by physically obstructing the ion channel pore.
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Affiliation(s)
- D B Cherbavaz
- Graduate Program in Biophysics, Brandeis University, Waltham, Massachusetts 02254, USA
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31
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Kirsch GE, Alam M, Hartmann HA. Differential effects of sulfhydryl reagents on saxitoxin and tetrodotoxin block of voltage-dependent Na channels. Biophys J 1994; 67:2305-15. [PMID: 7696471 PMCID: PMC1225615 DOI: 10.1016/s0006-3495(94)80716-7] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
We have probed a cysteine residue that confers resistance to tetrodotoxin (TTX) block in heart Na channels, with membrane-impermeant, cysteine-specific, methanethiosulfonate (MTS) analogs. Covalent addition of a positively charged group to the cysteinyl sulfhydryl reduced pore conductance by 87%. The effect was selectively prevented by treatment with TTX, but not saxitoxin (STX). Addition of a negatively charged group selectively inhibited STX block without affecting TTX block. These results agree with models that place an exposed cysteinyl sulfhydryl in the TTX site adjacent to the mouth of the pore, but do not support the contention that STX and TTX are interchangeable. The surprising differences between the two toxins are consistent with the hypothesis that the toxin-receptor complex can assume different conformations when STX or TTX bound.
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Affiliation(s)
- G E Kirsch
- Department of Anesthesiology, Baylor College of Medicine, Houston, Texas 77030
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32
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33
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Hebert TE, Monette R, Stone JC, Drapeau P, Dunn RJ. Insertion mutations of the RIIA Na+ channel reveal novel features of voltage gating and protein kinase A modulation. Pflugers Arch 1994; 427:500-9. [PMID: 7971148 DOI: 10.1007/bf00374267] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
A linker insertion mutagenesis strategy was developed to probe functional subdomains of the RIIA Na+ channel alpha-subunit. We describe mutations within the first two repeat domains that provide new functional information for three segments of the channel structure. 1. The insertion of two alanine residues within the short peptide segment joining helices S4 and S5 in domain II had two effects: a depolarizing shift of steady-state activation and reduced single-channel currents. These results suggest that the peptide segment following the S4 voltage sensor is involved in the activation process and is facing the ion pore. 2. An insertion immediately N-terminal to the proposed transmembrane helix S1 in domain II shifted the steady-state activation in the depolarizing direction, suggesting a functional role in channel gating. 3. Insertions in the large, cytoplasmic loop between domains I and II affect two channel functions: inactivation and protein kinase A modulation. These results demonstrate that the linker insertion approach can provide novel insights into the structure-function relationships of large, multi-domain ion channel proteins.
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Affiliation(s)
- T E Hebert
- Centre for Research in Neuroscience, McGill University, Montreal General Hospital, Québec, Canada
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34
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Elliott JR, Elliott AA. The effects of alcohols and other surface-active compounds on neuronal sodium channels. Prog Neurobiol 1994; 42:611-83. [PMID: 7938543 DOI: 10.1016/0301-0082(94)90045-0] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Affiliation(s)
- J R Elliott
- Department of Anatomy and Physiology, University, Dundee, U.K
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35
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McCormack K, Joiner WJ, Heinemann SH. A characterization of the activating structural rearrangements in voltage-dependent Shaker K+ channels. Neuron 1994; 12:301-15. [PMID: 8110460 DOI: 10.1016/0896-6273(94)90273-9] [Citation(s) in RCA: 94] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
In response to changes in membrane potential, voltage-dependent ion channel proteins undergo conformational rearrangements that lead to channel opening. These rearrangements move a net charge, measured as "gating current", across the membrane. Here we characterize the effects of the pharmacological blocker 4-aminopyridine on both the K+ and gating currents of wild-type and mutant Shaker K+ channels. Our results indicate that the activation of these channels involves two distinct types of structural rearrangement. In addition to independent Hodgkin and Huxley type rearrangements for each of the four subunits, which are responsible for most of the gating charge movement, Shaker channels interconvert between two quaternary conformations during activation. The transition between the two quaternary states moves about 10% of the total gating charge, and it is selectively blocked by 4-aminopyridine.
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Affiliation(s)
- K McCormack
- Max-Planck-Institut für Experimentelle Medizin, Göttingen, Federal Republic of Germany
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36
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Stephan MM, Potts JF, Agnew WS. The microI skeletal muscle sodium channel: mutation E403Q eliminates sensitivity to tetrodotoxin but not to mu-conotoxins GIIIA and GIIIB. J Membr Biol 1994; 137:1-8. [PMID: 7911843 DOI: 10.1007/bf00234993] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Voltage-sensitive Na channels from nerve and muscle are blocked by the guanidinium toxins tetrodotoxin (TTX) and saxitoxin (STX). Mutagenesis studies of brain RII channels have shown that glutamate 387 (E387) is essential for current block by these toxins. We demonstrate here that mutation of glutamate 403 (E403) of the adult skeletal muscle microI channel (corresponding to E387 of RII) also prevents current blockade by TTX and STX, and by neo-saxitoxin. However, the mutation fails to prevent blockade by the peptide neurotoxins, mu-conotoxin GIIIA and GIIIB; these toxins are thought to bind to the same or overlapping sites with TTX and STX. The E403Q mutation may have utility as a marker for exogenous Na channels in transgenic expression studies, since there are no known native channels with the same pharmacological profile.
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Affiliation(s)
- M M Stephan
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06510
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37
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Affiliation(s)
- M Noda
- Division of Molecular Neurobiology, National Institute for Basic Biology, Okazaki, Japan
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38
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Affiliation(s)
- K Imoto
- Department of Medical Chemistry, Kyoto University Faculty of Medicine, Japan
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39
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Grove A, Tomich JM, Iwamoto T, Montal M. Design of a functional calcium channel protein: inferences about an ion channel-forming motif derived from the primary structure of voltage-gated calcium channels. Protein Sci 1993; 2:1918-30. [PMID: 7505682 PMCID: PMC2142287 DOI: 10.1002/pro.5560021113] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
To identify sequence-specific motifs associated with the formation of an ionic pore, we systematically evaluated the channel-forming activity of synthetic peptides with sequence of predicted transmembrane segments of the voltage-gated calcium channel. The amino acid sequence of voltage-gated, dihydropyridine (DHP)-sensitive calcium channels suggests the presence in each of four homologous repeats (I-IV) of six segments (S1-S6) predicted to form membrane-spanning, alpha-helical structures. Only peptides representing amphipathic segments S2 or S3 form channels in lipid bilayers. To generate a functional calcium channel based on a four-helix bundle motif, four-helix bundle proteins representing IVS2 (T4CaIVS2) or IVS3 (T4CaIVS3) were synthesized. Both proteins form cation-selective channels, but with distinct characteristics: the single-channel conductance in 50 mM BaCl2 is 3 pS and 10 pS. For T4CaIVS3, the conductance saturates with increasing concentration of divalent cation. The dissociation constants for Ba2+, Ca2+, and Sr2+ are 13.6 mM, 17.7 mM, and 15.0 mM, respectively. The conductance of T4CaIVS2 does not saturate up to 150 mM salt. Whereas T4CaIVS3 is blocked by microM Ca2+ and Cd2+, T4CaIVS2 is not blocked by divalent cations. Only T4CaIVS3 is modulated by enantiomers of the DHP derivative BayK 8644, demonstrating sequence requirement for specific drug action. Thus, only T4CaIVS3 exhibits pore properties characteristic also of authentic calcium channels. The designed functional calcium channel may provide insights into fundamental mechanisms of ionic permeation and drug action, information that may in turn further our understanding of molecular determinants underlying authentic pore structures.
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MESH Headings
- 3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester/analogs & derivatives
- 3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester/pharmacology
- Amino Acid Sequence
- Calcium Channel Agonists/pharmacology
- Calcium Channels/chemistry
- Calcium Channels/drug effects
- Calcium Channels/metabolism
- Electric Conductivity
- Ion Channel Gating
- Lipid Bilayers
- Models, Molecular
- Molecular Sequence Data
- Peptide Fragments/chemistry
- Peptide Fragments/drug effects
- Peptide Fragments/metabolism
- Protein Structure, Secondary
- Protein Structure, Tertiary
- Stereoisomerism
- Structure-Activity Relationship
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Affiliation(s)
- A Grove
- Department of Biology, University of California at San Diego, La Jolla 92093-0357
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40
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Kim MS, Morii T, Sun LX, Imoto K, Mori Y. Structural determinants of ion selectivity in brain calcium channel. FEBS Lett 1993; 318:145-8. [PMID: 8382625 DOI: 10.1016/0014-5793(93)80009-j] [Citation(s) in RCA: 129] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Glutamic acid residues in the SS2 segment of the internal repeats III and IV of the brain calcium channel BI were subjected to single point mutations. The mutant channels were tested for macroscopic current properties and sensitivities to inorganic blockers. The mutation that replaces glutamic acid 1,469 with glutamine altered ion-selection properties and strongly reduced the sensitivity to Cd2+, whereas the analogous mutation of glutamic acid 1,765 exerted smaller effects on ion-selection properties. Our results indicate that these glutamic acid residues, equivalently positioned in the aligned sequences, play different roles in the selective permeability of the calcium channel.
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Affiliation(s)
- M S Kim
- Third Department of Internal Medicine, Kyoto University Faculty of Medicine, Japan
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41
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Doyle DD, Guo Y, Lustig SL, Satin J, Rogart RB, Fozzard HA. Divalent cation competition with [3H]saxitoxin binding to tetrodotoxin-resistant and -sensitive sodium channels. A two-site structural model of ion/toxin interaction. J Gen Physiol 1993; 101:153-82. [PMID: 8384241 PMCID: PMC2216764 DOI: 10.1085/jgp.101.2.153] [Citation(s) in RCA: 51] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Monovalent and divalent cations competitively displace tetrodotoxin and saxitoxin (STX) from their binding sites on nerve and skeletal muscle Na channels. Recent studies of cloned cardiac (toxin-resistant) and brain (toxin-sensitive) Na channels suggest important structural differences in their toxin and divalent cation binding sites. We used a partially purified preparation of sheep cardiac Na channels to compare monovalent and divalent cation competition and pH dependence of binding of [3H]STX between these toxin-resistant channels and toxin-sensitive channels in membranes prepared from rat brain. The effects of several chemical modifiers of amino acid groups were also compared. Toxin competition curves for Na+ in heart and Cd2+ in brain yielded similar KD values to measurements of equilibrium binding curves. The monovalent cation sequence for effectiveness of [3H]STX competition is the same for cardiac and brain Na channels, with similar KI values for each ion and slopes of -1. The effectiveness sequence corresponds to unhydrated ion radii. For seven divalent cations tested (Ca2+, Mg2+, Mn2+, Co2+, Ni2+, Cd2+, and Zn2+) the sequence for [3H]STX competition was also similar. However, whereas all ions displaced [3H]STX from cardiac Na channels at lower concentrations, Cd2+ and Zn2+ did so at much lower concentrations. In addition, and by way of explication, the divalent ion competition curves for both brain and cardiac channels (except for Cd2+ and Zn2+ in heart and Zn2+ in brain) had slopes of less than -1, consistent with more than one interaction site. Two-site curves had statistically better fits than one-site curves. The derived values of KI for the higher affinity sites were similar between the channel types, but the lower affinity KI's were larger for heart. On the other hand, the slopes of competition curves for Cd2+ and Zn2+ were close to -1, as if the cardiac Na channel had one dominant site of interaction or more than one site with similar values for KI. pH titration of [3H]STX binding to cardiac channels showed a pKa of 5.5 and a slope of 0.6-0.9, compared with a pKa of 5.1 and slope of 1 for brain channels. Tetramethyloxonium (TMO) treatment abolished [3H]STX binding to cardiac and brain channels and STX protected channels, but the TMO effect was less dramatic for cardiac channels. Trinitrobenzene sulfonate preferentially abolished [3H]STX binding to brain channels by action at an STX protected site.(ABSTRACT TRUNCATED AT 400 WORDS)
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Affiliation(s)
- D D Doyle
- University of Chicago, Department of Medicine, Illinois 60637
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42
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Abstract
On the basis of our recent results of the complete amino acid sequence of the squid Loligo bleekeri sodium channel deduced by cloning and sequence analysis of the complementary DNA (Sato, C. and Matsumoto, G. Biochem. Biophys. Res. Comm. 186, 1), we have proposed a tertiary structure model of the sodium channel where the transmembrane segments are octagonally aligned and the four linkers of S5-6 between segments S5 and S6 play a crucial role in the activation gate, voltage sensor and ion selective pore, which can slide, depending on membrane potentials, along inner walls consisting of segments S2 and S4 alternately. The proposed model is contrasted with that of Noda et al. (Nature 320; 188-192, 1986).
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Affiliation(s)
- C Sato
- Electrotechnical Laboratory, Supermolecular Science Division, Ibaraki, Japan
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43
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Backx PH, Yue DT, Lawrence JH, Marban E, Tomaselli GF. Molecular localization of an ion-binding site within the pore of mammalian sodium channels. Science 1992; 257:248-51. [PMID: 1321496 DOI: 10.1126/science.1321496] [Citation(s) in RCA: 221] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Sodium channels are the major proteins that underlie excitability in nerve, heart, and skeletal muscle. Chemical reaction rate theory was used to analyze the blockage of single wild-type and mutant sodium channels by cadmium ions. The affinity of cadmium for the native tetrodotoxin (TTX)-resistant cardiac channel was much higher than its affinity for the TTX-sensitive skeletal muscle isoform of the channel (microliters). Mutation of Tyr401 to Cys, the corresponding residue in the cardiac sequence, rendered microliters highly susceptible to cadmium blockage but resistant to TTX. The binding site was localized approximately 20% of the distance down the electrical field, thus defining the position of a critical residue within the sodium channel pore.
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Affiliation(s)
- P H Backx
- Department of Medicine, Johns Hopkins University, Baltimore, MD 21205
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44
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Abstract
The past year has seen major advances in our understanding of voltage-gated ion channels through a powerful combination of patch-clamp and molecular biological techniques. These approaches have identified regions (in some cases single amino acid residues) that are essential for voltage-dependent activation and inactivation, lining of the pore, and regulation of channel function.
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Affiliation(s)
- W Stühmer
- Abteilung Membranebiophysik, Max Planck Institute für Biophysikalische Chemie, Göttingen, Germany
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45
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Heinemann SH, Terlau H, Stühmer W, Imoto K, Numa S. Calcium channel characteristics conferred on the sodium channel by single mutations. Nature 1992; 356:441-3. [PMID: 1313551 DOI: 10.1038/356441a0] [Citation(s) in RCA: 616] [Impact Index Per Article: 19.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The sodium channel, one of the family of structurally homologous voltage-gated ion channels, differs from other members, such as the calcium and the potassium channels, in its high selectivity for Na+. This selectivity presumably reflects a distinct structure of its ion-conducting pore. We have recently identified two clusters of predominantly negatively charged amino-acid residues, located at equivalent positions in the four internal repeats of the sodium channel as the main determinants of sensitivity to the blockers tetrodotoxin and saxitoxin. All site-directed mutations reducing net negative charge at these positions also caused a marked decrease in single-channel conductance. Thus these two amino-acid clusters probably form part of the extracellular mouth and/or the pore wall of the sodium channel. We report here the effects on ion selectivity of replacing lysine at position 1,422 in repeat III and/or alanine at position 1,714 in repeat IV of rat sodium channel II (ref. 3), each located in one of the two clusters, by glutamic acid, which occurs at the equivalent positions in calcium channels. These amino-acid substitutions, unlike other substitutions in the adjacent regions, alter ion-selection properties of the sodium channel to resemble those of calcium channels. This result indicates that lysine 1,422 and alanine 1,714 are critical in determining the ion selectivity of the sodium channel, suggesting that these residues constitute part of the selectivity filter of the channel.
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Affiliation(s)
- S H Heinemann
- Max-Planck-Institut für biophysikalische Chemie, Abteilung Membranbiophysik, Göttingen, Germany
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46
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Durell SR, Guy HR. Atomic scale structure and functional models of voltage-gated potassium channels. Biophys J 1992; 62:238-47; discussion 247-50. [PMID: 1600096 PMCID: PMC1260525 DOI: 10.1016/s0006-3495(92)81809-x] [Citation(s) in RCA: 277] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Recent mutagenesis experiments have confirmed our hypothesis that a segment between S5 and S6 forms the ion selective portion of voltage-gated ion channels. Based on these and other new data, we have revised previous models of the general folding pattern of voltage-gated channel proteins and have developed atomic scale models of the entire transmembrane region of the Shaker A K+ channel. In these models, the ion selective region is a beta-barrel that spans the outer half of the membrane. The inner half of the pore is larger. The voltage-dependent conformational changes of activation gating are modeled to occur by the "helical screw" mechanism, in which the four S4 segments move along and rotate about their axes. These changes are followed by a voltage-independent conformational change, in which the segments linking S4 to S5 move from blocking the intracellular entrance of the pore to forming part of the lining of the large inner portion of the pore. The NH2-terminal of the protein was modeled as an alpha-helix that plugs the intracellular half of the pore to inactivate the channel.
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Affiliation(s)
- S R Durell
- Laboratory of Mathematical Biology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892
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47
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Lee CY. A possible biological role of the electron transfer between tyrosine and tryptophan. Gating of ion channels. FEBS Lett 1992; 299:119-23. [PMID: 1312037 DOI: 10.1016/0014-5793(92)80228-9] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Experiments have demonstrated that four tryptophan residues are located near the tetrodotoxin binding site in Na+ channels, and that conserved tyrosine and tryptophan residues are located in the pore-forming region of voltage-sensitive K+ channels. This paper proposes an activation mechanism involving electron transfer between these residues. The K+ channel may be closed by four tyrosine residues forming hydrogen bonds with each other. After electron transfer, these hydrogen bonds will be broken, thereby opening the channel. The Na+ channel could be activated by a similar mechanism. This idea can be tested directly by observing tyrosine or tryptophan radicals when the channels are in the open state.
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Affiliation(s)
- C Y Lee
- Chemical Dynamics Corporation, Guilderland, NY 12084
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48
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Terlau H, Heinemann SH, Stühmer W, Pusch M, Conti F, Imoto K, Numa S. Mapping the site of block by tetrodotoxin and saxitoxin of sodium channel II. FEBS Lett 1991; 293:93-6. [PMID: 1660007 DOI: 10.1016/0014-5793(91)81159-6] [Citation(s) in RCA: 341] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The SS2 and adjacent regions of the 4 internal repeats of sodium channel II were subjected to single mutations involving, mainly, charged amino acid residues. These sodium channel mutants, expressed in Xenopus oocytes by microinjection of cDNA-derived mRNAs, were tested for sensitivity to tetrodotoxin and saxitoxin and for single-channel conductance. The results obtained show that mutations involving 2 clusters of predominantly negatively charged residues, located at equivalent positions in the SS2 segment of the 4 repeats, strongly reduce toxin sensitivity, whereas mutations of adjacent residues exert much smaller or no effects. This suggests that the 2 clusters of residues, probably forming ring structures, take part in the extracellular mouth and/or the pore wall of the sodium channel. This view is further supported by our finding that all mutations reducing net negative charge in these amino acid clusters cause a marked decrease in single-channel conductance.
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Affiliation(s)
- H Terlau
- Max-Planck-Institut für biophysikalische Chemie, Göttingen, Germany
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