51
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Zhang F, Hanson SM, Jara-Oseguera A, Krepkiy D, Bae C, Pearce LV, Blumberg PM, Newstead S, Swartz KJ. Engineering vanilloid-sensitivity into the rat TRPV2 channel. eLife 2016; 5:e16409. [PMID: 27177419 PMCID: PMC4907692 DOI: 10.7554/elife.16409] [Citation(s) in RCA: 42] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2016] [Accepted: 05/12/2016] [Indexed: 01/08/2023] Open
Abstract
The TRPV1 channel is a detector of noxious stimuli, including heat, acidosis, vanilloid compounds and lipids. The gating mechanisms of the related TRPV2 channel are poorly understood because selective high affinity ligands are not available, and the threshold for heat activation is extremely high (>50°C). Cryo-EM structures of TRPV1 and TRPV2 reveal that they adopt similar structures, and identify a putative vanilloid binding pocket near the internal side of TRPV1. Here we use biochemical and electrophysiological approaches to investigate the resiniferatoxin(RTx) binding site in TRPV1 and to explore the functional relationships between TRPV1 and TRPV2. Collectively, our results support the interaction of vanilloids with the proposed RTx binding pocket, and demonstrate an allosteric influence of a tarantula toxin on vanilloid binding. Moreover, we show that sensitivity to RTx can be engineered into TRPV2, demonstrating that the gating and permeation properties of this channel are similar to TRPV1.
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Affiliation(s)
- Feng Zhang
- Molecular Physiology and Biophysics Section, Porter Neuroscience Research Center, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, United States
| | - Sonya M Hanson
- Molecular Physiology and Biophysics Section, Porter Neuroscience Research Center, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, United States
- Department of Biochemistry, University of Oxford, Oxford, United Kingdom
| | - Andres Jara-Oseguera
- Molecular Physiology and Biophysics Section, Porter Neuroscience Research Center, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, United States
| | - Dmitriy Krepkiy
- Molecular Physiology and Biophysics Section, Porter Neuroscience Research Center, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, United States
| | - Chanhyung Bae
- Molecular Physiology and Biophysics Section, Porter Neuroscience Research Center, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, United States
| | - Larry V Pearce
- Laboratory of Cancer Biology and Genetics, Center for Cancer Research, National Cancer Institute, Bethesda, United States
| | - Peter M Blumberg
- Laboratory of Cancer Biology and Genetics, Center for Cancer Research, National Cancer Institute, Bethesda, United States
| | - Simon Newstead
- Department of Biochemistry, University of Oxford, Oxford, United Kingdom
| | - Kenton J Swartz
- Molecular Physiology and Biophysics Section, Porter Neuroscience Research Center, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, United States
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52
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Kim DM, Nimigean CM. Voltage-Gated Potassium Channels: A Structural Examination of Selectivity and Gating. Cold Spring Harb Perspect Biol 2016; 8:a029231. [PMID: 27141052 PMCID: PMC4852806 DOI: 10.1101/cshperspect.a029231] [Citation(s) in RCA: 76] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Voltage-gated potassium channels play a fundamental role in the generation and propagation of the action potential. The discovery of these channels began with predictions made by early pioneers, and has culminated in their extensive functional and structural characterization by electrophysiological, spectroscopic, and crystallographic studies. With the aid of a variety of crystal structures of these channels, a highly detailed picture emerges of how the voltage-sensing domain reports changes in the membrane electric field and couples this to conformational changes in the activation gate. In addition, high-resolution structural and functional studies of K(+) channel pores, such as KcsA and MthK, offer a comprehensive picture on how selectivity is achieved in K(+) channels. Here, we illustrate the remarkable features of voltage-gated potassium channels and explain the mechanisms used by these machines with experimental data.
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Affiliation(s)
- Dorothy M Kim
- Department of Anesthesiology, Weill Cornell Medical College, New York, New York 10065
| | - Crina M Nimigean
- Department of Anesthesiology, Weill Cornell Medical College, New York, New York 10065
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53
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Abstract
Voltage-gated potassium channels or Kv's are membrane proteins with fundamental physiological roles. They are composed of 2 main functional protein domains, the pore domain, which regulates ion permeation, and the voltage-sensing domain, which is in charge of sensing voltage and undergoing a conformational change that is later transduced into pore opening. The voltage-sensing domain or VSD is a highly conserved structural motif found in all voltage-gated ion channels and can also exist as an independent feature, giving rise to voltage sensitive enzymes and also sustaining proton fluxes in proton-permeable channels. In spite of the structural conservation of VSDs in potassium channels, there are several differences in the details of VSD function found across variants of Kvs. These differences are mainly reflected in variations in the electrostatic energy needed to open different potassium channels. In turn, the differences in detailed VSD functioning among voltage-gated potassium channels might have physiological consequences that have not been explored and which might reflect evolutionary adaptations to the different roles played by Kv channels in cell physiology.
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Affiliation(s)
- León D Islas
- a Departamento de Fisiología, Facultad de Medicina ; National Autonomous University of Mexico (UNAM), Ciudad Universitaria , México City , México
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54
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Kuzmenkov AI, Grishin EV, Vassilevski AA. Diversity of Potassium Channel Ligands: Focus on Scorpion Toxins. BIOCHEMISTRY (MOSCOW) 2016; 80:1764-99. [DOI: 10.1134/s0006297915130118] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
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55
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Brunet T, Arendt D. From damage response to action potentials: early evolution of neural and contractile modules in stem eukaryotes. Philos Trans R Soc Lond B Biol Sci 2016; 371:20150043. [PMID: 26598726 PMCID: PMC4685582 DOI: 10.1098/rstb.2015.0043] [Citation(s) in RCA: 51] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/23/2015] [Indexed: 12/14/2022] Open
Abstract
Eukaryotic cells convert external stimuli into membrane depolarization, which in turn triggers effector responses such as secretion and contraction. Here, we put forward an evolutionary hypothesis for the origin of the depolarization-contraction-secretion (DCS) coupling, the functional core of animal neuromuscular circuits. We propose that DCS coupling evolved in unicellular stem eukaryotes as part of an 'emergency response' to calcium influx upon membrane rupture. We detail how this initial response was subsequently modified into an ancient mechanosensory-effector arc, present in the last eukaryotic common ancestor, which enabled contractile amoeboid movement that is widespread in extant eukaryotes. Elaborating on calcium-triggered membrane depolarization, we reason that the first action potentials evolved alongside the membrane of sensory-motile cilia, with the first voltage-sensitive sodium/calcium channels (Nav/Cav) enabling a fast and coordinated response of the entire cilium to mechanosensory stimuli. From the cilium, action potentials then spread across the entire cell, enabling global cellular responses such as concerted contraction in several independent eukaryote lineages. In animals, this process led to the invention of mechanosensory contractile cells. These gave rise to mechanosensory receptor cells, neurons and muscle cells by division of labour and can be regarded as the founder cell type of the nervous system.
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Affiliation(s)
- Thibaut Brunet
- European Molecular Biology Laboratory, Developmental Biology Unit, Heidelberg 69012, Germany
| | - Detlev Arendt
- European Molecular Biology Laboratory, Developmental Biology Unit, Heidelberg 69012, Germany
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56
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Ando M, Akiyama M, Okuno D, Hirano M, Ide T, Sawada S, Sasaki Y, Akiyoshi K. Liposome chaperon in cell-free membrane protein synthesis: one-step preparation of KcsA-integrated liposomes and electrophysiological analysis by the planar bilayer method. Biomater Sci 2016; 4:258-64. [DOI: 10.1039/c5bm00285k] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Chaperoning functions of liposomes were investigated using cell-free membrane protein synthesis.
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Affiliation(s)
- M. Ando
- Department of Polymer Chemistry
- Graduate School of Engineering
- Kyoto University
- Kyoto
- Japan
| | - M. Akiyama
- Department of Polymer Chemistry
- Graduate School of Engineering
- Kyoto University
- Kyoto
- Japan
| | - D. Okuno
- Laboratory for Cell Dynamics Observation
- Quantitative Biology Center
- RIKEN
- Osaka 565-0874
- Japan
| | - M. Hirano
- Laboratory for Cell Dynamics Observation
- Quantitative Biology Center
- RIKEN
- Osaka 565-0874
- Japan
| | - T. Ide
- Graduate School of Natural Science and Technology
- Okayama University
- Okayama 700-8530
- Japan
| | - S. Sawada
- Department of Polymer Chemistry
- Graduate School of Engineering
- Kyoto University
- Kyoto
- Japan
| | - Y. Sasaki
- Department of Polymer Chemistry
- Graduate School of Engineering
- Kyoto University
- Kyoto
- Japan
| | - K. Akiyoshi
- Department of Polymer Chemistry
- Graduate School of Engineering
- Kyoto University
- Kyoto
- Japan
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57
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Ahuja S, Mukund S, Deng L, Khakh K, Chang E, Ho H, Shriver S, Young C, Lin S, Johnson JP, Wu P, Li J, Coons M, Tam C, Brillantes B, Sampang H, Mortara K, Bowman KK, Clark KR, Estevez A, Xie Z, Verschoof H, Grimwood M, Dehnhardt C, Andrez JC, Focken T, Sutherlin DP, Safina BS, Starovasnik MA, Ortwine DF, Franke Y, Cohen CJ, Hackos DH, Koth CM, Payandeh J. Structural basis of Nav1.7 inhibition by an isoform-selective small-molecule antagonist. Science 2015; 350:aac5464. [DOI: 10.1126/science.aac5464] [Citation(s) in RCA: 218] [Impact Index Per Article: 24.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
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58
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Designer and natural peptide toxin blockers of the KcsA potassium channel identified by phage display. Proc Natl Acad Sci U S A 2015; 112:E7013-21. [PMID: 26627718 DOI: 10.1073/pnas.1514728112] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Peptide neurotoxins are powerful tools for research, diagnosis, and treatment of disease. Limiting broader use, most receptors lack an identified toxin that binds with high affinity and specificity. This paper describes isolation of toxins for one such orphan target, KcsA, a potassium channel that has been fundamental to delineating the structural basis for ion channel function. A phage-display strategy is presented whereby ∼1.5 million novel and natural peptides are fabricated on the scaffold present in ShK, a sea anemone type I (SAK1) toxin stabilized by three disulfide bonds. We describe two toxins selected by sorting on purified KcsA, one novel (Hui1, 34 residues) and one natural (HmK, 35 residues). Hui1 is potent, blocking single KcsA channels in planar lipid bilayers half-maximally (Ki) at 1 nM. Hui1 is also specific, inhibiting KcsA-Shaker channels in Xenopus oocytes with a Ki of 0.5 nM whereas Shaker, Kv1.2, and Kv1.3 channels are blocked over 200-fold less well. HmK is potent but promiscuous, blocking KcsA-Shaker, Shaker, Kv1.2, and Kv1.3 channels with Ki of 1-4 nM. As anticipated, one Hui1 blocks the KcsA pore and two conserved toxin residues, Lys21 and Tyr22, are essential for high-affinity binding. Unexpectedly, potassium ions traversing the channel from the inside confer voltage sensitivity to the Hui1 off-rate via Arg23, indicating that Lys21 is not in the pore. The 3D structure of Hui1 reveals a SAK1 fold, rationalizes KcsA inhibition, and validates the scaffold-based approach for isolation of high-affinity toxins for orphan receptors.
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59
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A Disease Mutation Causing Episodic Ataxia Type I in the S1 Links Directly to the Voltage Sensor and the Selectivity Filter in Kv Channels. J Neurosci 2015; 35:12198-206. [PMID: 26338330 DOI: 10.1523/jneurosci.1419-15.2015] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
UNLABELLED The mutation F184C in Kv1.1 leads to development of episodic ataxia type I (EA1). Although the mutation has been said to alter activation kinetics and to lower expression, we show here that the underlying molecular mechanisms may be more complex. Although F184 is positioned in the "peripheral" S1 helix, it occupies a central position in the 3D fold. We show in cut-open oocyte voltage-clamp recordings of gating and ionic currents of the Shaker Kv channel expressed in Xenopus oocytes that F184 not only interacts directly with the gating charges of the S4, but also creates a functional link to the selectivity filter of the neighboring subunit. This link leads to impaired fast and slow inactivation. The effect on fast inactivation is of an allosteric nature considering that fast inactivation is caused by a linked cytosolic ball peptide. The extensive effects of F184C provide a new mechanism underlying EA. SIGNIFICANCE STATEMENT Episodic ataxia (EA) is an inherited disease that leads to occasional loss of motor control in combination with variable other symptoms such as vertigo or migraine. EA type I (EA1), studied here, is caused by mutations in a voltage-gated potassium channel that contributes to the generation of electrical signals in the brain. The mechanism by which mutations in voltage-gated potassium channels lead to EA is still unknown and there is no consistent pharmacological treatment. By studying in detail one disease-causing mutation in Kv1.1, we describe a novel molecular mechanism distinct from mechanisms described previously. This mechanism contributes to the understanding of potassium channel function in general and might lead to a better understanding of how EA develops.
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60
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Zubcevic L, Wang S, Bavro VN, Lee SJ, Nichols CG, Tucker SJ. Modular Design of the Selectivity Filter Pore Loop in a Novel Family of Prokaryotic 'Inward Rectifier' (NirBac) channels. Sci Rep 2015; 5:15305. [PMID: 26470642 PMCID: PMC4607889 DOI: 10.1038/srep15305] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2015] [Accepted: 09/11/2015] [Indexed: 11/09/2022] Open
Abstract
Potassium channels exhibit a modular design with distinct structural and functional domains; in particular, a highly conserved pore-loop sequence that determines their ionic selectivity. We now report the functional characterisation of a novel group of functionally non-selective members of the prokaryotic 'inward rectifier' subfamily of K(+) channels. These channels share all the key structural domains of eukaryotic and prokaryotic Kir/KirBac channels, but instead possess unique pore-loop selectivity filter sequences unrelated to any other known ionic selectivity filter. The strikingly unusual architecture of these 'NirBac' channels defines a new family of functionally non-selective ion channels, and also provides important insights into the modular design of ion channels, as well as the evolution of ionic selectivity within this superfamily of tetrameric cation channels.
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Affiliation(s)
- Lejla Zubcevic
- Clarendon Laboratory, Department of Physics, University of Oxford, Oxford, United Kingdom
| | - Shizhen Wang
- Washington University St. Louis, School Of Medicine, Centre for the Investigation of Membrane Excitability Diseases (CIMED), St. Louis, MO, USA
| | - Vassiliy N. Bavro
- Clarendon Laboratory, Department of Physics, University of Oxford, Oxford, United Kingdom
| | - Sun-Joo Lee
- Washington University St. Louis, School Of Medicine, Centre for the Investigation of Membrane Excitability Diseases (CIMED), St. Louis, MO, USA
| | - Colin G. Nichols
- Washington University St. Louis, School Of Medicine, Centre for the Investigation of Membrane Excitability Diseases (CIMED), St. Louis, MO, USA
| | - Stephen J. Tucker
- Clarendon Laboratory, Department of Physics, University of Oxford, Oxford, United Kingdom
- OXION Initiative in Ion Channels and Disease, University of Oxford, Oxford, United Kingdom
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61
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Entropic clocks in the service of electrical signaling: ‘Ball and chain’ mechanisms for ion channel inactivation and clustering. FEBS Lett 2015; 589:2441-7. [DOI: 10.1016/j.febslet.2015.06.010] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2015] [Revised: 06/05/2015] [Accepted: 06/08/2015] [Indexed: 12/19/2022]
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62
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Kuang Q, Purhonen P, Hebert H. Structure of potassium channels. Cell Mol Life Sci 2015; 72:3677-93. [PMID: 26070303 PMCID: PMC4565861 DOI: 10.1007/s00018-015-1948-5] [Citation(s) in RCA: 167] [Impact Index Per Article: 18.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2015] [Revised: 05/09/2015] [Accepted: 06/03/2015] [Indexed: 12/25/2022]
Abstract
Potassium channels ubiquitously exist in nearly all kingdoms of life and perform diverse but important functions. Since the first atomic structure of a prokaryotic potassium channel (KcsA, a channel from Streptomyces lividans) was determined, tremendous progress has been made in understanding the mechanism of potassium channels and channels conducting other ions. In this review, we discuss the structure of various kinds of potassium channels, including the potassium channel with the pore-forming domain only (KcsA), voltage-gated, inwardly rectifying, tandem pore domain, and ligand-gated ones. The general properties shared by all potassium channels are introduced first, followed by specific features in each class. Our purpose is to help readers to grasp the basic concepts, to be familiar with the property of the different domains, and to understand the structure and function of the potassium channels better.
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Affiliation(s)
- Qie Kuang
- Department of Biosciences and Nutrition, Karolinska Institutet, Novum, 14183, Huddinge, Sweden.
- School of Technology and Health, KTH Royal Institute of Technology, Novum, 14183, Huddinge, Sweden.
| | - Pasi Purhonen
- Department of Biosciences and Nutrition, Karolinska Institutet, Novum, 14183, Huddinge, Sweden
| | - Hans Hebert
- Department of Biosciences and Nutrition, Karolinska Institutet, Novum, 14183, Huddinge, Sweden
- School of Technology and Health, KTH Royal Institute of Technology, Novum, 14183, Huddinge, Sweden
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63
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Voltage Sensing in Membranes: From Macroscopic Currents to Molecular Motions. J Membr Biol 2015; 248:419-30. [PMID: 25972106 DOI: 10.1007/s00232-015-9805-x] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2015] [Accepted: 04/24/2015] [Indexed: 01/06/2023]
Abstract
Voltage-sensing domains (VSDs) are integral membrane protein units that sense changes in membrane electric potential, and through the resulting conformational changes, regulate a specific function. VSDs confer voltage-sensitivity to a large superfamily of membrane proteins that includes voltage-gated Na[Formula: see text], K[Formula: see text], Ca[Formula: see text] ,and H[Formula: see text] selective channels, hyperpolarization-activated cyclic nucleotide-gated channels, and voltage-sensing phosphatases. VSDs consist of four transmembrane segments (termed S1 through S4). Their most salient structural feature is the highly conserved positions for charged residues in their sequences. S4 exhibits at least three conserved triplet repeats composed of one basic residue (mostly arginine) followed by two hydrophobic residues. These S4 basic side chains participate in a state-dependent internal salt-bridge network with at least four acidic residues in S1-S3. The signature of voltage-dependent activation in electrophysiology experiments is a transient current (termed gating or sensing current) upon a change in applied membrane potential as the basic side chains in S4 move across the membrane electric field. Thus, the unique structural features of the VSD architecture allow for competing requirements: maintaining a series of stable transmembrane conformations, while allowing charge motion, as briefly reviewed here.
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64
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Cadmium-cysteine coordination in the BK inner pore region and its structural and functional implications. Proc Natl Acad Sci U S A 2015; 112:5237-42. [PMID: 25848005 DOI: 10.1073/pnas.1500953112] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
To probe structure and gating-associated conformational changes in BK-type potassium (BK) channels, we examined consequences of Cd(2+) coordination with cysteines introduced at two positions in the BK inner pore. At V319C, the equivalent of valine in the conserved Kv proline-valine-proline (PVP) motif, Cd(2+) forms intrasubunit coordination with a native glutamate E321, which would place the side chains of V319C and E321 much closer together than observed in voltage-dependent K(+) (Kv) channel structures, requiring that the proline between V319C and E321 introduces a kink in the BK S6 inner helix sharper than that observed in Kv channel structures. At inner pore position A316C, Cd(2+) binds with modest state dependence, suggesting the absence of an ion permeation gate at the cytosolic side of BK channel. These results highlight fundamental structural differences between BK and Kv channels in their inner pore region, which likely underlie differences in voltage-dependent gating between these channels.
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65
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Lörinczi É, Gómez-Posada JC, de la Peña P, Tomczak AP, Fernández-Trillo J, Leipscher U, Stühmer W, Barros F, Pardo LA. Voltage-dependent gating of KCNH potassium channels lacking a covalent link between voltage-sensing and pore domains. Nat Commun 2015; 6:6672. [PMID: 25818916 PMCID: PMC4389246 DOI: 10.1038/ncomms7672] [Citation(s) in RCA: 69] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2014] [Accepted: 02/18/2015] [Indexed: 12/25/2022] Open
Abstract
Voltage-gated channels open paths for ion permeation upon changes in membrane potential, but how voltage changes are coupled to gating is not entirely understood. Two modules can be recognized in voltage-gated potassium channels, one responsible for voltage sensing (transmembrane segments S1 to S4), the other for permeation (S5 and S6). It is generally assumed that the conversion of a conformational change in the voltage sensor into channel gating occurs through the intracellular S4–S5 linker that provides physical continuity between the two regions. Using the pathophysiologically relevant KCNH family, we show that truncated proteins interrupted at, or lacking the S4–S5 linker produce voltage-gated channels in a heterologous model that recapitulate both the voltage-sensing and permeation properties of the complete protein. These observations indicate that voltage sensing by the S4 segment is transduced to the channel gate in the absence of physical continuity between the modules. The pore of voltage-gated ion channels opens in response to membrane depolarization sensed by a separate voltage-sensing domain. Here, Lörinczi et al. show that, contrary to assumptions, no physical linker is required to transmit changes from the voltage-sensing to the permeation domain of KCNH channels.
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Affiliation(s)
- Éva Lörinczi
- Department of Molecular Biology of Neuronal Signals, Max Planck Institute of Experimental Medicine, Hermann-Rein-Straße 3, 37075 Göttingen, Germany
| | - Juan Camilo Gómez-Posada
- Department of Molecular Biology of Neuronal Signals, Max Planck Institute of Experimental Medicine, Hermann-Rein-Straße 3, 37075 Göttingen, Germany
| | - Pilar de la Peña
- Departamento de Bioquímica y Biología Molecular, Universidad de Oviedo, Edificio Santiago Gascón, Campus de El Cristo, 33006 Oviedo, Spain
| | - Adam P Tomczak
- Oncophysiology Group, Max Planck Institute of Experimental Medicine, Hermann-Rein-Straße 3, 37075 Göttingen, Germany
| | - Jorge Fernández-Trillo
- Oncophysiology Group, Max Planck Institute of Experimental Medicine, Hermann-Rein-Straße 3, 37075 Göttingen, Germany
| | - Ulrike Leipscher
- Oncophysiology Group, Max Planck Institute of Experimental Medicine, Hermann-Rein-Straße 3, 37075 Göttingen, Germany
| | - Walter Stühmer
- Department of Molecular Biology of Neuronal Signals, Max Planck Institute of Experimental Medicine, Hermann-Rein-Straße 3, 37075 Göttingen, Germany.,Cluster of Excellence Nanoscale Microscopy and Molecular Physiology of the Brain, 37073 Göttingen, Germany
| | - Francisco Barros
- Departamento de Bioquímica y Biología Molecular, Universidad de Oviedo, Edificio Santiago Gascón, Campus de El Cristo, 33006 Oviedo, Spain
| | - Luis A Pardo
- Oncophysiology Group, Max Planck Institute of Experimental Medicine, Hermann-Rein-Straße 3, 37075 Göttingen, Germany
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66
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Alternative splicing modulates Kv channel clustering through a molecular ball and chain mechanism. Nat Commun 2015; 6:6488. [DOI: 10.1038/ncomms7488] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2014] [Accepted: 02/02/2015] [Indexed: 01/22/2023] Open
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67
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Moran Y, Barzilai MG, Liebeskind BJ, Zakon HH. Evolution of voltage-gated ion channels at the emergence of Metazoa. J Exp Biol 2015; 218:515-25. [DOI: 10.1242/jeb.110270] [Citation(s) in RCA: 85] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Voltage-gated ion channels are large transmembrane proteins that enable the passage of ions through their pore across the cell membrane. These channels belong to one superfamily and carry pivotal roles such as the propagation of neuronal and muscular action potentials and the promotion of neurotransmitter secretion in synapses. In this review, we describe in detail the current state of knowledge regarding the evolution of these channels with a special emphasis on the metazoan lineage. We highlight the contribution of the genomic revolution to the understanding of ion channel evolution and for revealing that these channels appeared long before the appearance of the first animal. We also explain how the elucidation of channel selectivity properties and function in non-bilaterian animals such as cnidarians (sea anemones, corals, jellyfish and hydroids) can contribute to the study of channel evolution. Finally, we point to open questions and future directions in this field of research.
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Affiliation(s)
- Yehu Moran
- Department of Ecology, Evolution and Behavior, Alexander Silberman Institute of Life Sciences, Faculty of Science, Hebrew University of Jerusalem, Jerusalem 91904, Israel
| | - Maya Gur Barzilai
- Department of Molecular Biology and Ecology of Plants, George S. Wise Faculty of Life Sciences, Tel-Aviv University, Tel-Aviv 69978, Israel
| | - Benjamin J. Liebeskind
- Department of Integrative Biology and Center for Computational Biology and Bioinformatics, University of Texas, Austin, TX 78712, USA
| | - Harold H. Zakon
- Department of Integrative Biology and Center for Computational Biology and Bioinformatics, University of Texas, Austin, TX 78712, USA
- Department of Neuroscience, University of Texas at Austin, TX 78712, USA
- Josephine Bay Paul Center for Molecular Biology and Evolution, Marine Biological Laboratory, Woods Hole, MA 02543, USA
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68
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Yang H, Zhang G, Cui J. BK channels: multiple sensors, one activation gate. Front Physiol 2015; 6:29. [PMID: 25705194 PMCID: PMC4319557 DOI: 10.3389/fphys.2015.00029] [Citation(s) in RCA: 77] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2015] [Accepted: 01/19/2015] [Indexed: 01/01/2023] Open
Abstract
Ion transport across cell membranes is essential to cell communication and signaling. Passive ion transport is mediated by ion channels, membrane proteins that create ion conducting pores across cell membrane to allow ion flux down electrochemical gradient. Under physiological conditions, majority of ion channel pores are not constitutively open. Instead, structural region(s) within these pores breaks the continuity of the aqueous ion pathway, thereby serves as activation gate(s) to control ions flow in and out. To achieve spatially and temporally regulated ion flux in cells, many ion channels have evolved sensors to detect various environmental stimuli or the metabolic states of the cell and trigger global conformational changes, thereby dynamically operate the opening and closing of their activation gate. The sensors of ion channels can be broadly categorized as chemical sensors and physical sensors to respond to chemical (such as neural transmitters, nucleotides and ions) and physical (such as voltage, mechanical force and temperature) signals, respectively. With the rapidly growing structural and functional information of different types of ion channels, it is now critical to understand how ion channel sensors dynamically control their gates at molecular and atomic level. The voltage and Ca2+ activated BK channels, a K+ channel with an electrical sensor and multiple chemical sensors, provide a unique model system for us to understand how physical and chemical energy synergistically operate its activation gate.
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Affiliation(s)
- Huanghe Yang
- Ion Channel Research Unit, Duke University Medical Center Durham, NC, USA ; Department of Biochemistry, Duke University Medical Center Durham, NC, USA
| | - Guohui Zhang
- Department of Biomedical Engineering, Washington University in Saint Louis St. Louis, MO, USA
| | - Jianmin Cui
- Department of Biomedical Engineering, Washington University in Saint Louis St. Louis, MO, USA ; Cardiac Bioelectricity and Arrhythmia Center, Washington University in Saint Louis St. Louis, MO, USA ; Center for The Investigation of Membrane Excitability Disorders, Washington University in Saint Louis St. Louis, MO, USA
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69
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A charged residue in S4 regulates coupling among the activation gate, voltage, and Ca2+ sensors in BK channels. J Neurosci 2015; 34:12280-8. [PMID: 25209270 DOI: 10.1523/jneurosci.1174-14.2014] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Coupling between the activation gate and sensors of physiological stimuli during ion channel activation is an important, but not well-understood, molecular process. One difficulty in studying sensor-gate coupling is to distinguish whether a structural perturbation alters the function of the sensor, the gate, or their coupling. BK channels are activated by membrane voltage and intracellular Ca(2+) via allosteric mechanisms with coupling among the activation gate and sensors quantitatively defined, providing an excellent model system for studying sensor-gate coupling. By studying BK channels expressed in Xenopus oocytes, here we show that mutation E219R in S4 alters channel function by two independent mechanisms: one is to change voltage sensor activation, shifting voltage dependence, and increase valence of gating charge movements; the other is to regulate coupling among the activation gate, voltage sensor, and Ca(2+) binding via electrostatic interactions with E321/E324 located in the cytosolic side of S6 in a neighboring subunit, resulting in a shift of the voltage dependence of channel opening and increased Ca(2+) sensitivity. These results suggest a structural arrangement of the inner pore of BK channels differing from that in other voltage gated channels.
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70
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Kasimova MA, Zaydman MA, Cui J, Tarek M. PIP₂-dependent coupling is prominent in Kv7.1 due to weakened interactions between S4-S5 and S6. Sci Rep 2015; 5:7474. [PMID: 25559286 PMCID: PMC4284513 DOI: 10.1038/srep07474] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2014] [Accepted: 11/21/2014] [Indexed: 02/06/2023] Open
Abstract
Among critical aspects of voltage-gated potassium (Kv) channels' functioning is the effective communication between their two composing domains, the voltage sensor (VSD) and the pore. This communication, called coupling, might be transmitted directly through interactions between these domains and, as recently proposed, indirectly through interactions with phosphatidylinositol-4,5-bisphosphate (PIP₂), a minor lipid of the inner plasma membrane leaflet. Here, we show how the two components of coupling, mediated by protein-protein or protein-lipid interactions, both contribute in the Kv7.1 functioning. On the one hand, using molecular dynamics simulations, we identified a Kv7.1 PIP₂ binding site that involves residues playing a key role in PIP₂-dependent coupling. On the other hand, combined theoretical and experimental approaches have shown that the direct interaction between the segments of the VSD (S4-S5) and the pore (S6) is weakened by electrostatic repulsion. Finally, we conclude that due to weakened protein-protein interactions, the PIP2-dependent coupling is especially prominent in Kv7.1.
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Affiliation(s)
- Marina A Kasimova
- 1] Université de Lorraine, Theory, Modeling and Simulations, UMR 7565, Vandoeuvre-lés-Nancy, F-54506 France [2] Lomonosov Moscow State University, Moscow, 119991, Russian Federation
| | - Mark A Zaydman
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Diseases, Cardiac Bioelectricity and Arrhythmia Center, Washington University in St. Louis, St. Louis, MO 63130-4862
| | - Jianmin Cui
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Diseases, Cardiac Bioelectricity and Arrhythmia Center, Washington University in St. Louis, St. Louis, MO 63130-4862
| | - Mounir Tarek
- 1] Université de Lorraine, Theory, Modeling and Simulations, UMR 7565, Vandoeuvre-lés-Nancy, F-54506 France [2] Centre National de la Recherche Scientifique, UMR 7565, Vandoeuvre-lés-Nancy, F-54506 France
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71
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Wang X, Umetsu Y, Gao B, Ohki S, Zhu S. Mesomartoxin, a new Kv1.2-selective scorpion toxin interacting with the channel selectivity filter. Biochem Pharmacol 2015; 93:232-9. [DOI: 10.1016/j.bcp.2014.12.002] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2014] [Revised: 12/03/2014] [Accepted: 12/05/2014] [Indexed: 12/21/2022]
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72
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Zaydman MA, Kasimova MA, McFarland K, Beller Z, Hou P, Kinser HE, Liang H, Zhang G, Shi J, Tarek M, Cui J. Domain-domain interactions determine the gating, permeation, pharmacology, and subunit modulation of the IKs ion channel. eLife 2014; 3:e03606. [PMID: 25535795 PMCID: PMC4381907 DOI: 10.7554/elife.03606] [Citation(s) in RCA: 65] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2014] [Accepted: 11/19/2014] [Indexed: 01/22/2023] Open
Abstract
Voltage-gated ion channels generate electrical currents that control muscle
contraction, encode neuronal information, and trigger hormonal release.
Tissue-specific expression of accessory (β) subunits causes these channels to
generate currents with distinct properties. In the heart, KCNQ1 voltage-gated
potassium channels coassemble with KCNE1 β-subunits to generate the
IKs current (Barhanin et al.,
1996; Sanguinetti et al., 1996),
an important current for maintenance of stable heart rhythms. KCNE1 significantly
modulates the gating, permeation, and pharmacology of KCNQ1 (Wrobel et al., 2012; Sun et
al., 2012; Abbott, 2014). These
changes are essential for the physiological role of IKs (Silva and Rudy, 2005); however, after 18 years
of study, no coherent mechanism explaining how KCNE1 affects KCNQ1 has emerged. Here
we provide evidence of such a mechanism, whereby, KCNE1 alters the state-dependent
interactions that functionally couple the voltage-sensing domains (VSDs) to the
pore. DOI:http://dx.doi.org/10.7554/eLife.03606.001 Cells are surrounded by a membrane that prevents charged molecules from flowing
directly into or out of the cell. Instead ions move through channel proteins within
the cell membrane. Most ion channel proteins are selective and only allow one or a
few types of ion to cross. Ion channels can also be ‘gated’, and have a
central pore that can open or close to allow or stop the flow of selected ions. This
gating can be affected by the channel sensing changes in conditions, such as changes
in the voltage across the cell membrane. Research conducted more than half a century ago—before the discovery of
channel proteins—led to a mathematical model of the flow of potassium ions
across a membrane in response to changes in voltage. This model made a number of
assumptions, many of which are still widely accepted. However, Zaydman et al. have
now called into question some of the assumptions of this model. Based on the original model, it has been long assumed that the voltage-sensing
domains that open or close the central pore in response to changes in voltage must be
fully activated to allow the channel to open. It had also been assumed that the
voltage-sensing domains do not affect the flow of ions once the channel is open.
Zaydman et al. have now shown that these assumptions are not valid for a specific
voltage-gated potassium channel called KCNQ1. Instead, this ion channel opens when
its voltage-sensing domains are either partially or fully activated. Zaydman found
that the intermediate-open and activated-open states had different preferences for
passing various types of ion; therefore, the gating of the channel and the flow of
ions through the open channel are both dependent on the state of the voltage-sensing
domains. This is in direct contrast to what had previously been assumed. The original model cannot reproduce the gating of KCNQ1, nor can any other
established model. Therefore, Zaydman et al. devised a new model to understand how
the interactions between different states of the voltage-sensing domains and the pore
lead to gating. Zaydman et al. then used their model to address how another protein
called KCNE1 is able to alter properties of the KCNQ1 channel. KCNE1 is a protein that is expressed in the heart muscle cell and mutations affecting
KCNQ1 or KCNE1 have been associated with potentially fatal heart conditions. Based on
the assumptions of the original model, it had been difficult to understand how KCNE1
was able to affect different properties of the KCNQ1 channel. Thus, for nearly 20
years it has been debated whether KCNE1 primarily affects the activation of the
voltage-sensing domains or the opening of the pore. Zaydman et al. found instead that
KCNE1 alters the interactions between the voltage-sensing domains and the pore, which
prevented the intermediate-open state and modified the properties of the
activated-open state. This mechanism provides one of the most complete explanations
for the action of the KCNE1 protein. DOI:http://dx.doi.org/10.7554/eLife.03606.002
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Affiliation(s)
- Mark A Zaydman
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Diseases, Washington University in St Louis, St Louis, United States
| | - Marina A Kasimova
- Theory, Modeling, and Simulations, UMR 7565, Université de Lorraine, Nancy, France
| | - Kelli McFarland
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Diseases, Washington University in St Louis, St Louis, United States
| | - Zachary Beller
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Diseases, Washington University in St Louis, St Louis, United States
| | - Panpan Hou
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Diseases, Washington University in St Louis, St Louis, United States
| | - Holly E Kinser
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Diseases, Washington University in St Louis, St Louis, United States
| | - Hongwu Liang
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Diseases, Washington University in St Louis, St Louis, United States
| | - Guohui Zhang
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Diseases, Washington University in St Louis, St Louis, United States
| | - Jingyi Shi
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Diseases, Washington University in St Louis, St Louis, United States
| | - Mounir Tarek
- Theory, Modeling, and Simulations, UMR 7565, Université de Lorraine, Nancy, France
| | - Jianmin Cui
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Diseases, Washington University in St Louis, St Louis, United States
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73
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Pless SA, Elstone FD, Niciforovic AP, Galpin JD, Yang R, Kurata HT, Ahern CA. Asymmetric functional contributions of acidic and aromatic side chains in sodium channel voltage-sensor domains. ACTA ACUST UNITED AC 2014; 143:645-56. [PMID: 24778431 PMCID: PMC4003186 DOI: 10.1085/jgp.201311036] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Conserved acidic and aromatic residues in the four sodium channel voltage-sensor domains make domain-specific functional contributions. Voltage-gated sodium (NaV) channels mediate electrical excitability in animals. Despite strong sequence conservation among the voltage-sensor domains (VSDs) of closely related voltage-gated potassium (KV) and NaV channels, the functional contributions of individual side chains in Nav VSDs remain largely enigmatic. To this end, natural and unnatural side chain substitutions were made in the S2 hydrophobic core (HC), the extracellular negative charge cluster (ENC), and the intracellular negative charge cluster (INC) of the four VSDs of the skeletal muscle sodium channel isoform (NaV1.4). The results show that the highly conserved aromatic side chain constituting the S2 HC makes distinct functional contributions in each of the four NaV domains. No obvious cation–pi interaction exists with nearby S4 charges in any domain, and natural and unnatural mutations at these aromatic sites produce functional phenotypes that are different from those observed previously in Kv VSDs. In contrast, and similar to results obtained with Kv channels, individually neutralizing acidic side chains with synthetic derivatives and with natural amino acid substitutions in the INC had little or no effect on the voltage dependence of activation in any of the four domains. Interestingly, countercharge was found to play an important functional role in the ENC of DI and DII, but not DIII and DIV. These results suggest that electrostatic interactions with S4 gating charges are unlikely in the INC and only relevant in the ENC of DI and DII. Collectively, our data highlight domain-specific functional contributions of highly conserved side chains in NaV VSDs.
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Affiliation(s)
- Stephan A Pless
- Department of Anesthesiology, Pharmacology and Therapeutics, and 2 Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada
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74
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Affiliation(s)
- Gilman E S Toombes
- Molecular Physiology and Biophysics Section, Porter Neuroscience Research Center, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892
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75
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Payandeh J, Minor DL. Bacterial voltage-gated sodium channels (BacNa(V)s) from the soil, sea, and salt lakes enlighten molecular mechanisms of electrical signaling and pharmacology in the brain and heart. J Mol Biol 2014; 427:3-30. [PMID: 25158094 DOI: 10.1016/j.jmb.2014.08.010] [Citation(s) in RCA: 62] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2014] [Revised: 08/11/2014] [Accepted: 08/18/2014] [Indexed: 12/19/2022]
Abstract
Voltage-gated sodium channels (Na(V)s) provide the initial electrical signal that drives action potential generation in many excitable cells of the brain, heart, and nervous system. For more than 60years, functional studies of Na(V)s have occupied a central place in physiological and biophysical investigation of the molecular basis of excitability. Recently, structural studies of members of a large family of bacterial voltage-gated sodium channels (BacNa(V)s) prevalent in soil, marine, and salt lake environments that bear many of the core features of eukaryotic Na(V)s have reframed ideas for voltage-gated channel function, ion selectivity, and pharmacology. Here, we analyze the recent advances, unanswered questions, and potential of BacNa(V)s as templates for drug development efforts.
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Affiliation(s)
- Jian Payandeh
- Department of Structural Biology, Genentech, Inc., South San Francisco, CA 94080, USA.
| | - Daniel L Minor
- Cardiovascular Research Institute, Departments of Biochemistry and Biophysics and Cellular and Molecular Pharmacology, California Institute for Quantitative Biomedical Research, University of California, San Francisco, CA 93858-2330, USA; Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
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76
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Lenaeus MJ, Burdette D, Wagner T, Focia PJ, Gross A. Structures of KcsA in complex with symmetrical quaternary ammonium compounds reveal a hydrophobic binding site. Biochemistry 2014; 53:5365-73. [PMID: 25093676 PMCID: PMC4139162 DOI: 10.1021/bi500525s] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
![]()
Potassium channels allow for the
passive movement of potassium
ions across the cell membrane and are instrumental in controlling
the membrane potential in all cell types. Quaternary ammonium (QA)
compounds block potassium channels and have long been used to study
the functional and structural properties of these channels. Here we
describe the interaction between three symmetrical hydrophobic QAs
and the prokaryotic potassium channel KcsA. The structures demonstrate
the presence of a hydrophobic pocket between the inner helices of
KcsA and provide insight into the binding site and blocking mechanism
of hydrophobic QAs. The structures also reveal a structurally hidden
pathway between the central cavity and the outside membrane environment
reminiscent of the lateral fenestration observed in sodium channels
that can be accessed through small conformational changes in the pore
wall. We propose that the hydrophobic binding pocket stabilizes the
alkyl chains of long-chain QA molecules and may play a key role in
hydrophobic drug binding in general.
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Affiliation(s)
- Michael J Lenaeus
- Department of Molecular Pharmacology and Biological Chemistry, Northwestern University Medical School , 303 East Chicago Avenue, Chicago, Illinois 60611, United States
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77
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Zaydman MA, Cui J. PIP2 regulation of KCNQ channels: biophysical and molecular mechanisms for lipid modulation of voltage-dependent gating. Front Physiol 2014; 5:195. [PMID: 24904429 PMCID: PMC4034418 DOI: 10.3389/fphys.2014.00195] [Citation(s) in RCA: 93] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2014] [Accepted: 05/08/2014] [Indexed: 12/28/2022] Open
Abstract
Voltage-gated potassium (Kv) channels contain voltage-sensing (VSD) and pore-gate (PGD) structural domains. During voltage-dependent gating, conformational changes in the two domains are coupled giving rise to voltage-dependent opening of the channel. In addition to membrane voltage, KCNQ (Kv7) channel opening requires the membrane lipid phosphatidylinositol 4,5-bisphosphate (PIP2). Recent studies suggest that PIP2 serves as a cofactor to mediate VSD-PGD coupling in KCNQ1 channels. In this review, we put these findings in the context of the current understanding of voltage-dependent gating, lipid modulation of Kv channel activation, and PIP2-regulation of KCNQ channels. We suggest that lipid-mediated coupling of functional domains is a common mechanism among KCNQ channels that may be applicable to other Kv channels and membrane proteins.
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Affiliation(s)
- Mark A Zaydman
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Diseases, Cardiac Bioelectricity and Arrhythmia Center, Washington University in St. Louis St. Louis, MO, USA
| | - Jianmin Cui
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Diseases, Cardiac Bioelectricity and Arrhythmia Center, Washington University in St. Louis St. Louis, MO, USA
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78
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Potassium channels in the central nervous system of the snail, Helix pomatia: Localization and functional characterization. Neuroscience 2014; 268:87-101. [DOI: 10.1016/j.neuroscience.2014.03.006] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2013] [Revised: 03/04/2014] [Accepted: 03/05/2014] [Indexed: 01/27/2023]
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79
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Tronin A, Nordgren CE, Strzalka JW, Kuzmenko I, Worcester DL, Lauter V, Freites JA, Tobias DJ, Blasie JK. Direct evidence of conformational changes associated with voltage gating in a voltage sensor protein by time-resolved X-ray/neutron interferometry. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2014; 30:4784-4796. [PMID: 24697545 PMCID: PMC4007984 DOI: 10.1021/la500560w] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/13/2014] [Indexed: 06/03/2023]
Abstract
The voltage sensor domain (VSD) of voltage-gated cation (e.g., Na(+), K(+)) channels central to neurological signal transmission can function as a distinct module. When linked to an otherwise voltage-insensitive, ion-selective membrane pore, the VSD imparts voltage sensitivity to the channel. Proteins homologous with the VSD have recently been found to function themselves as voltage-gated proton channels or to impart voltage sensitivity to enzymes. Determining the conformational changes associated with voltage gating in the VSD itself in the absence of a pore domain thereby gains importance. We report the direct measurement of changes in the scattering-length density (SLD) profile of the VSD protein, vectorially oriented within a reconstituted phospholipid bilayer membrane, as a function of the transmembrane electric potential by time-resolved X-ray and neutron interferometry. The changes in the experimental SLD profiles for both polarizing and depolarizing potentials with respect to zero potential were found to extend over the entire length of the isolated VSD's profile structure. The characteristics of the changes observed were in qualitative agreement with molecular dynamics simulations of a related membrane system, suggesting an initial interpretation of these changes in terms of the VSD's atomic-level 3-D structure.
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Affiliation(s)
- Andrey
Y. Tronin
- Department
of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
| | - C. Erik Nordgren
- Department
of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
| | - Joseph W. Strzalka
- X-ray
Science Division, Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, United States
| | - Ivan Kuzmenko
- X-ray
Science Division, Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, United States
| | - David L. Worcester
- Department
of Physiology & Biophysics, University
of California Irvine, Irvine, California 92697, United States
| | - Valeria Lauter
- Spallation
Neutron Source, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - J. Alfredo Freites
- Department
of Chemistry, University of California Irvine, Irvine, California 92697, United States
| | - Douglas J. Tobias
- Department
of Chemistry, University of California Irvine, Irvine, California 92697, United States
| | - J. Kent Blasie
- Department
of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
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80
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Randich AM, Cuello LG, Wanderling SS, Perozo E. Biochemical and structural analysis of the hyperpolarization-activated K(+) channel MVP. Biochemistry 2014; 53:1627-36. [PMID: 24490868 PMCID: PMC3985891 DOI: 10.1021/bi4014243] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
![]()
In
contrast to the majority of voltage-gated ion channels, hyperpolarization-activated
channels remain closed at depolarizing potentials and are activated
at hyperpolarizing potentials. The basis for this reverse polarity
is thought to be a result of differences in the way the voltage-sensing
domain (VSD) couples to the pore domain. In the absence of structural
data, the molecular mechanism of this reverse polarity coupling remains
poorly characterized. Here we report the characterization of the structure
and local dynamics of the closed activation gate (lower S6 region)
of MVP, a hyperpolarization-activated potassium channel from Methanococcus jannaschii, by electron paramagnetic resonance
(EPR) spectroscopy. We show that a codon-optimized version of MVP
has high expression levels in Escherichia coli, is
purified as a stable tetramer, and exhibits expected voltage-dependent
activity when reconstituted in liposomes. EPR analysis of the mid
to lower S6 region revealed positions exhibiting strong spin–spin
coupling, indicating that the activation gate of MVP is closed at
0 mV. A comparison of local environmental parameters along the activation
gate for MVP and KcsA indicates that MVP adopts a different closed
conformation. These structural details set the stage for future evaluations
of reverse electromechanical coupling in MVP.
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Affiliation(s)
- Amelia M Randich
- Department of Biochemistry and Molecular Biology, The University of Chicago , Chicago, Illinois 60637, United States
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81
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Tsutsui H, Jinno Y, Tomita A, Okamura Y. Optically detected structural change in the N-terminal region of the voltage-sensor domain. Biophys J 2014; 105:108-15. [PMID: 23823229 DOI: 10.1016/j.bpj.2013.05.051] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2013] [Revised: 05/30/2013] [Accepted: 05/31/2013] [Indexed: 11/16/2022] Open
Abstract
The voltage-sensor domain (VSD) is a functional module that undergoes structural transitions in response to membrane potential changes and regulates its effectors, thereby playing a crucial role in amplifying and decoding membrane electrical signals. Ion-conductive pore and phosphoinositide phosphatase are the downstream effectors of voltage-gated channels and the voltage-sensing phosphatase, respectively. It is known that upon transition, the VSD generally acts on the region C-terminal to S4. However, whether the VSD also induces any structural changes in the N-terminal region of S1 has not been addressed directly. Here, we report the existence of such an N-terminal effect. We used two distinct optical reporters-one based on the Förster resonance energy transfer between a pair of fluorescent proteins, and the other based on fluorophore-labeled HaloTag-and studied the behavior of these reporters placed at the N-terminal end of the monomeric VSD derived from voltage-sensing phosphatase. We found that both of these reporters were affected by the VSD transition, generating voltage-dependent fluorescence readouts. We also observed that whereas the voltage dependencies of the N- and C-terminal effects appear to be tightly coupled, the local structural rearrangements reflect the way in which the VSD is loaded, demonstrating the flexible nature of the VSD.
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Affiliation(s)
- Hidekazu Tsutsui
- Laboratory of Integrative Physiology, Graduate School of Medicine, Osaka University, Osaka, Japan.
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82
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Abstract
Temperature-sensitive transient receptor potential (TRP) channels are structurally similar to other tetrameric cation channels, but can be potently activated by heat. Recent studies suggest that the pore-forming region directly participates in activation gating. In this chapter, we summarize major findings from both structural and functional studies concerning the gating role of the pore region, focusing in particular on TRPV1. The emerging picture is that the peripheral S1-S4 region of TRPV1 is rigid and plays a supporting role for the pore to undergo conformational rearrangements. This places the pore region in the center of activation gating.
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83
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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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84
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Tian C, Zhu R, Zhu L, Qiu T, Cao Z, Kang T. Potassium Channels: Structures, Diseases, and Modulators. Chem Biol Drug Des 2013; 83:1-26. [DOI: 10.1111/cbdd.12237] [Citation(s) in RCA: 63] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Affiliation(s)
- Chuan Tian
- School of Life Sciences and Technology; Tongji University; Shanghai 200092 China
- School of Pharmacy; Liaoning University of Traditional Chinese Medicine; Dalian Liaoning 116600 China
| | - Ruixin Zhu
- School of Life Sciences and Technology; Tongji University; Shanghai 200092 China
| | - Lixin Zhu
- Department of Pediatrics; Digestive Diseases and Nutrition Center; The State University of New York at Buffalo; Buffalo NY 14226 USA
| | - Tianyi Qiu
- School of Life Sciences and Technology; Tongji University; Shanghai 200092 China
| | - Zhiwei Cao
- School of Life Sciences and Technology; Tongji University; Shanghai 200092 China
| | - Tingguo Kang
- School of Pharmacy; Liaoning University of Traditional Chinese Medicine; Dalian Liaoning 116600 China
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85
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González C, Baez-Nieto D, Valencia I, Oyarzún I, Rojas P, Naranjo D, Latorre R. K(+) channels: function-structural overview. Compr Physiol 2013; 2:2087-149. [PMID: 23723034 DOI: 10.1002/cphy.c110047] [Citation(s) in RCA: 143] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Potassium channels are particularly important in determining the shape and duration of the action potential, controlling the membrane potential, modulating hormone secretion, epithelial function and, in the case of those K(+) channels activated by Ca(2+), damping excitatory signals. The multiplicity of roles played by K(+) channels is only possible to their mammoth diversity that includes at present 70 K(+) channels encoding genes in mammals. Today, thanks to the use of cloning, mutagenesis, and the more recent structural studies using x-ray crystallography, we are in a unique position to understand the origins of the enormous diversity of this superfamily of ion channels, the roles they play in different cell types, and the relations that exist between structure and function. With the exception of two-pore K(+) channels that are dimers, voltage-dependent K(+) channels are tetrameric assemblies and share an extremely well conserved pore region, in which the ion-selectivity filter resides. In the present overview, we discuss in the function, localization, and the relations between function and structure of the five different subfamilies of K(+) channels: (a) inward rectifiers, Kir; (b) four transmembrane segments-2 pores, K2P; (c) voltage-gated, Kv; (d) the Slo family; and (e) Ca(2+)-activated SK family, SKCa.
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Affiliation(s)
- Carlos González
- Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile
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86
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Shem-Ad T, Irit O, Yifrach O. Inter-subunit interactions across the upper voltage sensing-pore domain interface contribute to the concerted pore opening transition of Kv channels. PLoS One 2013; 8:e82253. [PMID: 24340010 PMCID: PMC3858418 DOI: 10.1371/journal.pone.0082253] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2013] [Accepted: 10/22/2013] [Indexed: 12/31/2022] Open
Abstract
The tight electro-mechanical coupling between the voltage-sensing and pore domains of Kv channels lies at the heart of their fundamental roles in electrical signaling. Structural data have identified two voltage sensor pore inter-domain interaction surfaces, thus providing a framework to explain the molecular basis for the tight coupling of these domains. While the contribution of the intra-subunit lower domain interface to the electro-mechanical coupling that underlies channel opening is relatively well understood, the contribution of the inter-subunit upper interface to channel gating is not yet clear. Relying on energy perturbation and thermodynamic coupling analyses of tandem-dimeric Shaker Kv channels, we show that mutation of upper interface residues from both sides of the voltage sensor-pore domain interface stabilizes the closed channel state. These mutations, however, do not affect slow inactivation gating. We, moreover, find that upper interface residues form a network of state-dependent interactions that stabilize the open channel state. Finally, we note that the observed residue interaction network does not change during slow inactivation gating. The upper voltage sensing-pore interaction surface thus only undergoes conformational rearrangements during channel activation gating. We suggest that inter-subunit interactions across the upper domain interface mediate allosteric communication between channel subunits that contributes to the concerted nature of the late pore opening transition of Kv channels.
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Affiliation(s)
- Tzilhav Shem-Ad
- Department of Life Sciences and the Zlotowski Center for Neurosciences, Ben-Gurion University of the Negev, Beer Sheva, Israel
| | - Orr Irit
- Department of Life Sciences and the Zlotowski Center for Neurosciences, Ben-Gurion University of the Negev, Beer Sheva, Israel
| | - Ofer Yifrach
- Department of Life Sciences and the Zlotowski Center for Neurosciences, Ben-Gurion University of the Negev, Beer Sheva, Israel
- * E-mail:
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87
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Pless SA, Niciforovic AP, Galpin JD, Nunez JJ, Kurata HT, Ahern CA. A novel mechanism for fine-tuning open-state stability in a voltage-gated potassium channel. Nat Commun 2013; 4:1784. [PMID: 23653196 PMCID: PMC3644096 DOI: 10.1038/ncomms2761] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2012] [Accepted: 03/18/2013] [Indexed: 12/23/2022] Open
Abstract
Voltage-gated potassium channels elicit membrane hyperpolarization through voltage-sensor domains that regulate the conductive status of the pore domain. To better understand the inherent basis for the open-closed equilibrium in these channels, we undertook an atomistic scan using synthetic fluorinated derivatives of aromatic residues previously implicated in the gating of Shaker potassium channels. Here we show that stepwise dispersion of the negative electrostatic surface potential of only one site, Phe481, stabilizes the channel open state. Furthermore, these data suggest that this apparent stabilization is the consequence of the amelioration of an inherently repulsive open-state interaction between the partial negative charge on the face of Phe481 and a highly co-evolved acidic side chain, Glu395, and this interaction is potentially modulated through the Tyr485 hydroxyl. We propose that the intrinsic open-state destabilization via aromatic repulsion represents a new mechanism by which ion channels, and likely other proteins, fine-tune conformational equilibria. Voltage-gated potassium channels cycle between closed and open states through poorly-defined transitions. Pless and colleagues incorporate artificial amino acids into Shaker potassium channels and find that that the negative electrostatic surface potential of Phe481, destabilizes the channel open state.
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Affiliation(s)
- Stephan A Pless
- Department of Anesthesiology, Pharmacology and Therapeutics, University of British Columbia, 2350 Health Science Mall, Vancouver, British Columbia, Canada V6T 1Z3
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88
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Arrigoni C, Schroeder I, Romani G, Van Etten JL, Thiel G, Moroni A. The voltage-sensing domain of a phosphatase gates the pore of a potassium channel. ACTA ACUST UNITED AC 2013; 141:389-95. [PMID: 23440279 PMCID: PMC3581695 DOI: 10.1085/jgp.201210940] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The modular architecture of voltage-gated K(+) (Kv) channels suggests that they resulted from the fusion of a voltage-sensing domain (VSD) to a pore module. Here, we show that the VSD of Ciona intestinalis phosphatase (Ci-VSP) fused to the viral channel Kcv creates Kv(Synth1), a functional voltage-gated, outwardly rectifying K(+) channel. Kv(Synth1) displays the summed features of its individual components: pore properties of Kcv (selectivity and filter gating) and voltage dependence of Ci-VSP (V(1/2) = +56 mV; z of ~1), including the depolarization-induced mode shift. The degree of outward rectification of the channel is critically dependent on the length of the linker more than on its amino acid composition. This highlights a mechanistic role of the linker in transmitting the movement of the sensor to the pore and shows that electromechanical coupling can occur without coevolution of the two domains.
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Affiliation(s)
- Cristina Arrigoni
- Department of Biosciences, Consiglio Nazionale delle Ricerche, Università degli Studi di Milano, 20133 Milano, Italy
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89
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Two Alternative Conformations of a Voltage-Gated Sodium Channel. J Mol Biol 2013; 425:4074-88. [DOI: 10.1016/j.jmb.2013.06.036] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2013] [Revised: 06/11/2013] [Accepted: 06/12/2013] [Indexed: 11/21/2022]
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90
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Shaya D, Findeisen F, Abderemane-Ali F, Arrigoni C, Wong S, Nurva SR, Loussouarn G, Minor DL. Structure of a prokaryotic sodium channel pore reveals essential gating elements and an outer ion binding site common to eukaryotic channels. J Mol Biol 2013; 426:467-83. [PMID: 24120938 DOI: 10.1016/j.jmb.2013.10.010] [Citation(s) in RCA: 111] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2013] [Revised: 09/20/2013] [Accepted: 10/05/2013] [Indexed: 12/18/2022]
Abstract
Voltage-gated sodium channels (NaVs) are central elements of cellular excitation. Notwithstanding advances from recent bacterial NaV (BacNaV) structures, key questions about gating and ion selectivity remain. Here, we present a closed conformation of NaVAe1p, a pore-only BacNaV derived from NaVAe1, a BacNaV from the arsenite oxidizer Alkalilimnicola ehrlichei found in Mono Lake, California, that provides insight into both fundamental properties. The structure reveals a pore domain in which the pore-lining S6 helix connects to a helical cytoplasmic tail. Electrophysiological studies of full-length BacNaVs show that two elements defined by the NaVAe1p structure, an S6 activation gate position and the cytoplasmic tail "neck", are central to BacNaV gating. The structure also reveals the selectivity filter ion entry site, termed the "outer ion" site. Comparison with mammalian voltage-gated calcium channel (CaV) selectivity filters, together with functional studies, shows that this site forms a previously unknown determinant of CaV high-affinity calcium binding. Our findings underscore commonalities between BacNaVs and eukaryotic voltage-gated channels and provide a framework for understanding gating and ion permeation in this superfamily.
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Affiliation(s)
- David Shaya
- Cardiovascular Research Institute, University of California, San Francisco, CA 94158-9001, USA
| | - Felix Findeisen
- Cardiovascular Research Institute, University of California, San Francisco, CA 94158-9001, USA
| | - Fayal Abderemane-Ali
- Institut National de la Santé et de la Recherche Médicale, UMR 1087, F-44000 Nantes, France; Centre National de la Recherche Scientifique, UMR 6291, F-44000 Nantes, France; L'institut du thorax, L'UNAM, Université de Nantes, F-44000 Nantes, France
| | - Cristina Arrigoni
- Cardiovascular Research Institute, University of California, San Francisco, CA 94158-9001, USA
| | - Stephanie Wong
- Cardiovascular Research Institute, University of California, San Francisco, CA 94158-9001, USA
| | - Shailika Reddy Nurva
- Cardiovascular Research Institute, University of California, San Francisco, CA 94158-9001, USA
| | - Gildas Loussouarn
- Institut National de la Santé et de la Recherche Médicale, UMR 1087, F-44000 Nantes, France; Centre National de la Recherche Scientifique, UMR 6291, F-44000 Nantes, France; L'institut du thorax, L'UNAM, Université de Nantes, F-44000 Nantes, France
| | - Daniel L Minor
- Cardiovascular Research Institute, University of California, San Francisco, CA 94158-9001, USA; Departments of Biochemistry and Biophysics and Cellular and Molecular Pharmacology, University of California, San Francisco, CA 94158-9001, USA; California Institute for Quantitative Biomedical Research, University of California, San Francisco, CA 94158-9001, USA; Physical Biosciences Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
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91
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Fowler P, Beckstein O, Abad E, Sansom MSP. Detailed Examination of a Single Conduction Event in a Potassium Channel. J Phys Chem Lett 2013; 4:3104-3109. [PMID: 24143269 PMCID: PMC3797101 DOI: 10.1021/jz4014079] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2013] [Accepted: 08/29/2013] [Indexed: 06/02/2023]
Abstract
Although extensively studied, it has proved difficult to describe in detail how potassium ion channels conduct cations and water. We present a computational study that, by using stratified umbrella sampling, examines nearly an entire conduction event of the Kv1.2/2.1 paddle chimera and thereby identifies the expected stable configurations of ions and waters in the selectivity filter of the channel. We describe in detail the motions of the ions and waters during a conduction event, focusing on how waters and ions enter the filter, the rotation of water molecules inside the filter, and how potassium ions are coordinated as they move from a water to a protein environment. Finally, we analyze the small conformational changes undergone by the protein, showing that the stable configurations are most similar to the experimental crystal structure.
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Affiliation(s)
- Philip
W. Fowler
- Department of Biochemistry, University
of Oxford, South Parks Road, Oxford OX1 3QU, United Kingdom
| | | | | | - Mark S. P. Sansom
- Department of Biochemistry, University
of Oxford, South Parks Road, Oxford OX1 3QU, United Kingdom
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92
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Membrane channels as integrators of G-protein-mediated signaling. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2013; 1838:521-31. [PMID: 24028827 DOI: 10.1016/j.bbamem.2013.08.018] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/29/2013] [Revised: 08/14/2013] [Accepted: 08/21/2013] [Indexed: 01/03/2023]
Abstract
A variety of extracellular stimuli regulate cellular responses via membrane receptors. A well-known group of seven-transmembrane domain-containing proteins referred to as G protein-coupled receptors, directly couple with the intracellular GTP-binding proteins (G proteins) across cell membranes and trigger various cellular responses by regulating the activity of several enzymes as well as ion channels. Many specific populations of ion channels are directly controlled by G proteins; however, indirect modulation of some channels by G protein-dependent phosphorylation events and lipid metabolism is also observed. G protein-mediated diverse modifications affect the ion channel activities and spatio-temporally regulate membrane potentials as well as of intracellular Ca(2+) concentrations in both excitatory and non-excitatory cells. This article is part of a Special Issue entitled: Reciprocal influences between cell cytoskeleton and membrane channels, receptors and transporters. Guest Editor: Jean Claude Hervé.
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93
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Exploring structure-function relationships between TRP and Kv channels. Sci Rep 2013; 3:1523. [PMID: 23519328 PMCID: PMC3605605 DOI: 10.1038/srep01523] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2013] [Accepted: 03/07/2013] [Indexed: 12/18/2022] Open
Abstract
The molecular mechanisms underlying the activation of Transient Receptor Potential (TRP) ion channels are poorly understood when compared to those of the voltage-activated potassium (Kv) channels. The architectural and pharmacological similarities between the members of these two families of channels suggest that their structure-function relationships may have common features. We explored this hypothesis by replacing previously identified domains and critical structural motifs of the membrane-spanning portions of Kv2.1 with corresponding regions of two TRP channels, TRPM8 and TRPV1. Our results show that the S3b-S4 paddle motif of Kv2.1, but not other domains, can be replaced by the analogous regions of both TRP channels without abolishing voltage-activation. In contrast, replacement of portions of TRP channels with those of Kv2.1 consistently yielded non-functional channels. Taken together, these results suggest that most structural elements within TRP channels and Kv channels are not sufficiently related to allow for the creation of hybrid channels.
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94
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Schow EV, Freites JA, Nizkorodov A, White SH, Tobias DJ. Coupling between the voltage-sensing and pore domains in a voltage-gated potassium channel. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2013; 1818:1726-36. [PMID: 22425907 DOI: 10.1016/j.bbamem.2012.02.029] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/03/2011] [Revised: 02/24/2012] [Accepted: 02/28/2012] [Indexed: 10/28/2022]
Abstract
Voltage-dependent potassium (Kv), sodium (Nav), and calcium channels open and close in response to changes in transmembrane (TM) potential, thus regulating cell excitability by controlling ion flow across the membrane. An outstanding question concerning voltage gating is how voltage-induced conformational changes of the channel voltage-sensing domains (VSDs) are coupled through the S4-S5 interfacial linking helices to the opening and closing of the pore domain (PD). To investigate the coupling between the VSDs and the PD, we generated a closed Kv channel configuration from Aeropyrum pernix (KvAP) using atomistic simulations with experiment-based restraints on the VSDs. Full closure of the channel required, in addition to the experimentally determined TM displacement, that the VSDs be displaced both inwardly and laterally around the PD. This twisting motion generates a tight hydrophobic interface between the S4-S5 linkers and the C-terminal ends of the pore domain S6 helices in agreement with available experimental evidence.
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Affiliation(s)
- Eric V Schow
- Department of Chemistry, University of California, Irvine, CA 92697-2025, USA
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95
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Kv7.1 ion channels require a lipid to couple voltage sensing to pore opening. Proc Natl Acad Sci U S A 2013; 110:13180-5. [PMID: 23861489 DOI: 10.1073/pnas.1305167110] [Citation(s) in RCA: 145] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Voltage-gated ion channels generate dynamic ionic currents that are vital to the physiological functions of many tissues. These proteins contain separate voltage-sensing domains, which detect changes in transmembrane voltage, and pore domains, which conduct ions. Coupling of voltage sensing and pore opening is critical to the channel function and has been modeled as a protein-protein interaction between the two domains. Here, we show that coupling in Kv7.1 channels requires the lipid phosphatidylinositol 4,5-bisphosphate (PIP2). We found that voltage-sensing domain activation failed to open the pore in the absence of PIP2. This result is due to loss of coupling because PIP2 was also required for pore opening to affect voltage-sensing domain activation. We identified a critical site for PIP2-dependent coupling at the interface between the voltage-sensing domain and the pore domain. This site is actually a conserved lipid-binding site among different K(+) channels, suggesting that lipids play an important role in coupling in many ion channels.
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96
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Milescu M, Lee HC, Bae CH, Kim JI, Swartz KJ. Opening the shaker K+ channel with hanatoxin. ACTA ACUST UNITED AC 2013; 141:203-16. [PMID: 23359283 PMCID: PMC3557313 DOI: 10.1085/jgp.201210914] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Voltage-activated ion channels open and close in response to changes in membrane voltage, a property that is fundamental to the roles of these channels in electrical signaling. Protein toxins from venomous organisms commonly target the S1–S4 voltage-sensing domains in these channels and modify their gating properties. Studies on the interaction of hanatoxin with the Kv2.1 channel show that this tarantula toxin interacts with the S1–S4 domain and inhibits opening by stabilizing a closed state. Here we investigated the interaction of hanatoxin with the Shaker Kv channel, a voltage-activated channel that has been extensively studied with biophysical approaches. In contrast to what is observed in the Kv2.1 channel, we find that hanatoxin shifts the conductance–voltage relation to negative voltages, making it easier to open the channel with membrane depolarization. Although these actions of the toxin are subtle in the wild-type channel, strengthening the toxin–channel interaction with mutations in the S3b helix of the S1-S4 domain enhances toxin affinity and causes large shifts in the conductance–voltage relationship. Using a range of previously characterized mutants of the Shaker Kv channel, we find that hanatoxin stabilizes an activated conformation of the voltage sensors, in addition to promoting opening through an effect on the final opening transition. Chimeras in which S3b–S4 paddle motifs are transferred between Kv2.1 and Shaker Kv channels, as well as experiments with the related tarantula toxin GxTx-1E, lead us to conclude that the actions of tarantula toxins are not simply a product of where they bind to the channel, but that fine structural details of the toxin–channel interface determine whether a toxin is an inhibitor or opener.
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Affiliation(s)
- Mirela Milescu
- Molecular Physiology and Biophysics Section, Porter Neuroscience Research Center, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA
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97
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Kalstrup T, Blunck R. Dynamics of internal pore opening in K(V) channels probed by a fluorescent unnatural amino acid. Proc Natl Acad Sci U S A 2013; 110:8272-7. [PMID: 23630265 PMCID: PMC3657800 DOI: 10.1073/pnas.1220398110] [Citation(s) in RCA: 77] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Atomic-scale models on the gating mechanism of voltage-gated potassium channels (Kv) are based on linear interpolations between static structures of their initial and final state derived from crystallography and molecular dynamics simulations, and, thus, lack dynamic structural information. The lack of information on dynamics and intermediate states makes it difficult to associate the structural with the dynamic functional data obtained with electrophysiology. Although voltage-clamp fluorometry fills this gap, it is limited to sites extracellularly accessible, when the key region for gating is located at the cytosolic side of the channels. Here, we solved this problem by performing voltage-clamp fluorometry with a fluorescent unnatural amino acid. By using an orthogonal tRNA-synthetase pair, the fluorescent unnatural amino acid was incorporated in the Shaker voltage-gated potassium channel at key regions that were previously inaccessible. Thus, we defined which parts act independently and which parts act cooperatively and found pore opening to occur in two sequential transitions.
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Affiliation(s)
- Tanja Kalstrup
- Groupe d’étude des protéines membranaires (GÉPROM) and Departments of Physics and Physiology, Université de Montréal, Montreal, QC, Canada H3C 3J7
| | - Rikard Blunck
- Groupe d’étude des protéines membranaires (GÉPROM) and Departments of Physics and Physiology, Université de Montréal, Montreal, QC, Canada H3C 3J7
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98
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Gray NW, Zhorov BS, Moczydlowski EG. Interaction of local anesthetics with the K (+) channel pore domain: KcsA as a model for drug-dependent tetramer stability. Channels (Austin) 2013; 7:182-93. [PMID: 23545989 DOI: 10.4161/chan.24455] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Local anesthetics and related drugs block ionic currents of Na (+) , K (+) and Ca ( 2+) conducted across the cell membrane by voltage-dependent ion channels. Many of these drugs bind in the permeation pathway, occlude the pore and stop ion movement. However channel-blocking drugs have also been associated with decreased membrane stability of certain tetrameric K (+) channels, similar to the destabilization of channel function observed at low extracellular K (+) concentration. Such drug-dependent stability may result from electrostatic repulsion of K (+) from the selectivity filter by a cationic drug molecule bound in the central cavity of the channel. In this study we used the pore domain of the KcsA K (+) channel protein to test this hypothesis experimentally with a biochemical assay of tetramer stability and theoretically by computational simulation of local anesthetic docking to the central cavity. We find that two common local anesthetics, lidocaine and tetracaine, promote thermal dissociation of the KcsA tetramer in a K (+) -dependent fashion. Docking simulations of these drugs with open, open-inactivated and closed crystal structures of KcsA yield many energetically favorable drug-channel complexes characterized by nonbonded attraction to pore-lining residues and electrostatic repulsion of K (+) . The results suggest that binding of cationic drugs to the inner cavity can reduce tetramer stability of K (+) channels.
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Affiliation(s)
- Noel W Gray
- Neuroscience & Physiology, SUNY Upstate Medical University, Syracuse, NY, USA
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99
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Energetic role of the paddle motif in voltage gating of Shaker K(+) channels. Nat Struct Mol Biol 2013; 20:574-81. [PMID: 23542156 PMCID: PMC3777420 DOI: 10.1038/nsmb.2535] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2012] [Accepted: 02/08/2013] [Indexed: 11/23/2022]
Abstract
Voltage-gated ion channels underlie rapid electric signaling in excitable cells. Electrophysiological studies have established that the N-terminal half of the fourth transmembrane segment (NTS4) of these channels functions as the primary voltage sensor, whereas crystallographic studies have shown that NTS4 is not located within a proteinaceous pore. Rather, NTS4 and the C-terminal half of S3 (CTS3 or S3b) form a helix-turn-helix motif, termed the voltage-sensor paddle. This unexpected structural finding raises two fundamental questions: does the paddle motif also exist in voltage-gated channels in a biological membrane and, if so, what is its function in voltage gating. Here, we provide evidence that the paddle motif exists in the open state of Drosophila Shaker voltage-gated K+ channels expressed in Xenopus oocytes and that CTS3 acts as an extracellular hydrophobic "stabilizer" for NTS4, biasing the gating chemical equilibrium towards the open state.
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100
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Feng J, Hu Y, Yi H, Yin S, Han S, Hu J, Chen Z, Yang W, Cao Z, De Waard M, Sabatier JM, Li W, Wu Y. Two conserved arginine residues from the SK3 potassium channel outer vestibule control selectivity of recognition by scorpion toxins. J Biol Chem 2013; 288:12544-53. [PMID: 23511633 DOI: 10.1074/jbc.m112.433888] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Potassium channel functions are often deciphered by using selective and potent scorpion toxins. Among these toxins, only a limited subset is capable of selectively blocking small conductance Ca(2+)-activated K(+) (SK) channels. The structural bases of this selective SK channel recognition remain unclear. In this work, we demonstrate the key role of the electric charges of two conserved arginine residues (Arg-485 and Arg-489) from the SK3 channel outer vestibule in the selective recognition by the SK3-blocking BmP05 toxin. Indeed, individually substituting these residues with histidyl or lysyl (maintaining the positive electric charge partially or fully), although decreasing BmP05 affinity, still preserved the toxin sensitivity profile of the SK3 channel (as evidenced by the lack of recognition by many other types of potassium channel-sensitive charybdotoxin). In contrast, when Arg-485 or Arg-489 of the SK3 channel was mutated to an acidic (Glu) or alcoholic (Ser) amino acid residue, the channel lost its sensitivity to BmP05 and became susceptible to the "new" blocking activity by charybdotoxin. In addition to these SK3 channel basic residues important for sensitivity, two acidic residues, Asp-492 and Asp-518, also located in the SK3 channel outer vestibule, were identified as being critical for toxin affinity. Furthermore, molecular modeling data indicate the existence of a compact SK3 channel turret conformation (like a peptide screener), where the basic rings of Arg-485 and Arg-489 are stabilized by strong ionic interactions with Asp-492 and Asp-518. In conclusion, the unique properties of Arg-485 and Arg-489 (spatial orientations and molecular interactions) in the SK3 channel account for its toxin sensitivity profile.
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Affiliation(s)
- Jing Feng
- State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan 430072, China
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