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Kariev AM, Green ME. Water, Protons, and the Gating of Voltage-Gated Potassium Channels. MEMBRANES 2024; 14:37. [PMID: 38392664 PMCID: PMC10890431 DOI: 10.3390/membranes14020037] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/21/2023] [Revised: 01/17/2024] [Accepted: 01/23/2024] [Indexed: 02/24/2024]
Abstract
Ion channels are ubiquitous throughout all forms of life. Potassium channels are even found in viruses. Every cell must communicate with its surroundings, so all cells have them, and excitable cells, in particular, especially nerve cells, depend on the behavior of these channels. Every channel must be open at the appropriate time, and only then, so that each channel opens in response to the stimulus that tells that channel to open. One set of channels, including those in nerve cells, responds to voltage. There is a standard model for the gating of these channels that has a section of the protein moving in response to the voltage. However, there is evidence that protons are moving, rather than protein. Water is critical as part of the gating process, although it is hard to see how this works in the standard model. Here, we review the extensive evidence of the importance of the role of water and protons in gating these channels. Our principal example, but by no means the only example, will be the Kv1.2 channel. Evidence comes from the effects of D2O, from mutations in the voltage sensing domain, as well as in the linker between that domain and the gate, and at the gate itself. There is additional evidence from computations, especially quantum calculations. Structural evidence comes from X-ray studies. The hydration of ions is critical in the transfer of ions in constricted spaces, such as the gate region and the pore of a channel; we will see how the structure of the hydrated ion fits with the structure of the channel. In addition, there is macroscopic evidence from osmotic experiments and streaming current measurements. The combined evidence is discussed in the context of a model that emphasizes the role of protons and water in gating these channels.
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Affiliation(s)
- Alisher M Kariev
- Department of Chemistry and Biochemistry, The City College of New York, New York, NY 10031, USA
| | - Michael E Green
- Department of Chemistry and Biochemistry, The City College of New York, New York, NY 10031, USA
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2
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Naranjo D, Diaz-Franulic I. Sweetening K-channels: what sugar taught us about permeation and gating. Front Mol Biosci 2023; 10:1063796. [PMID: 37122567 PMCID: PMC10140501 DOI: 10.3389/fmolb.2023.1063796] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2022] [Accepted: 04/03/2023] [Indexed: 05/02/2023] Open
Abstract
Because they enable for the modification of both viscosity and osmolarity, sugars have been used as a biophysical probe of voltage-gated K-channels for a while. Viscosity variations made it possible to measure the pore sizes in large and small conductance K-channels using techniques similar to those used in the 1980s to study the gramicidin A channel. These analyses led to the finding that the size of the internal mouth appears to be the primary cause of the conductance differences between Shaker-like channels and large conductance BK-channels. As an osmotic agent, adding sugar unilaterally causes streaming potentials that indicate H2O/K+ cotransport across the BK-channel pore. Osmotic experiments on Shaker K-channels suggest that the pore gate operation and the slow inactivation displace comparable amounts of water. Functionally isolated voltage sensors allow estimation of individual osmotic work for each voltage sensing charge during voltage-activation, reporting dramatic internal and external remodeling of the Voltage Sensing Domain´s solvent exposed surfaces. Remarkably, each charge of the VSD appears to take a unique trajectory. Thus, manipulation of viscosity and osmolarity, together with 3D structures, brings in solid grounds to harmonize function and structure in membrane proteins such as K-channels and, in a wider scope, other structurally dynamic proteins.
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Affiliation(s)
- David Naranjo
- Instituto de Neurociencia, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile
- *Correspondence: David Naranjo, ; Ignacio Diaz-Franulic,
| | - Ignacio Diaz-Franulic
- Center for Bioinformatics and Integrative Biology, Facultad de Ciencias de la Vida, Universidad Andrés Bello, Santiago, Chile
- Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile
- *Correspondence: David Naranjo, ; Ignacio Diaz-Franulic,
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3
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Fernandes CAH, Zuniga D, Fagnen C, Kugler V, Scala R, Péhau-Arnaudet G, Wagner R, Perahia D, Bendahhou S, Vénien-Bryan C. Cryo-electron microscopy unveils unique structural features of the human Kir2.1 channel. SCIENCE ADVANCES 2022; 8:eabq8489. [PMID: 36149965 PMCID: PMC9506730 DOI: 10.1126/sciadv.abq8489] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/10/2022] [Accepted: 08/04/2022] [Indexed: 06/16/2023]
Abstract
We present the first structure of the human Kir2.1 channel containing both transmembrane domain (TMD) and cytoplasmic domain (CTD). Kir2.1 channels are strongly inward-rectifying potassium channels that play a key role in maintaining resting membrane potential. Their gating is modulated by phosphatidylinositol 4,5-bisphosphate (PIP2). Genetically inherited defects in Kir2.1 channels are responsible for several rare human diseases, including Andersen's syndrome. The structural analysis (cryo-electron microscopy), surface plasmon resonance, and electrophysiological experiments revealed a well-connected network of interactions between the PIP2-binding site and the G-loop through residues R312 and H221. In addition, molecular dynamics simulations and normal mode analysis showed the intrinsic tendency of the CTD to tether to the TMD and a movement of the secondary anionic binding site to the membrane even without PIP2. Our results revealed structural features unique to human Kir2.1 and provided insights into the connection between G-loop and gating and the pathological mechanisms associated with this channel.
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Affiliation(s)
- Carlos A. H. Fernandes
- UMR 7590, CNRS, Muséum National d’Histoire Naturelle, IRD, Institut de Minéralogie, Physique des Matériaux et de Cosmochimie, IMPMC, Sorbonne Université, 75005 Paris, France
| | - Dania Zuniga
- UMR 7590, CNRS, Muséum National d’Histoire Naturelle, IRD, Institut de Minéralogie, Physique des Matériaux et de Cosmochimie, IMPMC, Sorbonne Université, 75005 Paris, France
| | - Charline Fagnen
- UMR 7590, CNRS, Muséum National d’Histoire Naturelle, IRD, Institut de Minéralogie, Physique des Matériaux et de Cosmochimie, IMPMC, Sorbonne Université, 75005 Paris, France
| | - Valérie Kugler
- IMPReSs Facility, Biotechnology and Cell Signaling UMR 7242, CNRS–University of Strasbourg, Illkirch, Cedex, France
| | - Rosa Scala
- CNRS UMR7370, LP2M, Labex ICST, Faculté de Médecine, Université Côte d’Azur, Nice, France
| | - Gérard Péhau-Arnaudet
- Ultrastructural BioImaging Core Facility/UMR 3528, Institut Pasteur, 75724 Paris Cedex 15, France
| | - Renaud Wagner
- IMPReSs Facility, Biotechnology and Cell Signaling UMR 7242, CNRS–University of Strasbourg, Illkirch, Cedex, France
| | - David Perahia
- Laboratoire de Biologie et Pharmacologie Appliquée, Ecole Normale Supérieure Paris-Saclay, 4 Ave. des Sciences, 91190 Gif-sur-Yvette, France
| | - Saïd Bendahhou
- CNRS UMR7370, LP2M, Labex ICST, Faculté de Médecine, Université Côte d’Azur, Nice, France
| | - Catherine Vénien-Bryan
- UMR 7590, CNRS, Muséum National d’Histoire Naturelle, IRD, Institut de Minéralogie, Physique des Matériaux et de Cosmochimie, IMPMC, Sorbonne Université, 75005 Paris, France
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4
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Ye W, Zhao H, Dai Y, Wang Y, Lo YH, Jan LY, Lee CH. Activation and closed-state inactivation mechanisms of the human voltage-gated K V4 channel complexes. Mol Cell 2022; 82:2427-2442.e4. [PMID: 35597238 DOI: 10.1016/j.molcel.2022.04.032] [Citation(s) in RCA: 16] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2021] [Revised: 03/03/2022] [Accepted: 04/24/2022] [Indexed: 12/30/2022]
Abstract
The voltage-gated ion channel activity depends on both activation (transition from the resting state to the open state) and inactivation. Inactivation is a self-restraint mechanism to limit ion conduction and is as crucial to membrane excitability as activation. Inactivation can occur when the channel is open or closed. Although open-state inactivation is well understood, the molecular basis of closed-state inactivation has remained elusive. We report cryo-EM structures of human KV4.2 channel complexes in inactivated, open, and closed states. Closed-state inactivation of KV4 involves an unprecedented symmetry breakdown for pore closure by only two of the four S4-S5 linkers, distinct from known mechanisms of open-state inactivation. We further capture KV4 in a putative resting state, revealing how voltage sensor movements control the pore. Moreover, our structures provide insights regarding channel modulation by KChIP2 and DPP6 auxiliary subunits. Our findings elucidate mechanisms of closed-state inactivation and voltage-dependent activation of the KV4 channel.
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Affiliation(s)
- Wenlei Ye
- Department of Physiology, University of California, San Francisco, CA 94158, USA
| | - Hongtu Zhao
- Department of Structural Biology, St. Jude Children's Research Hospital, Memphis, TN 38105, USA
| | - Yaxin Dai
- Department of Structural Biology, St. Jude Children's Research Hospital, Memphis, TN 38105, USA
| | - Yingdi Wang
- Department of Structural Biology, St. Jude Children's Research Hospital, Memphis, TN 38105, USA
| | - Yu-Hua Lo
- Department of Structural Biology, St. Jude Children's Research Hospital, Memphis, TN 38105, USA
| | - Lily Yeh Jan
- Department of Physiology, University of California, San Francisco, CA 94158, USA; Howard Hughes Medical Institute, University of California, San Francisco, CA 94158, USA.
| | - Chia-Hsueh Lee
- Department of Structural Biology, St. Jude Children's Research Hospital, Memphis, TN 38105, USA.
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5
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Insights into the crystallization and vitrification of cryopreserved cells. Cryobiology 2022; 106:13-23. [DOI: 10.1016/j.cryobiol.2022.04.008] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2021] [Revised: 02/05/2022] [Accepted: 04/30/2022] [Indexed: 12/11/2022]
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6
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Chen M, Blum D, Engelhard L, Raunser S, Wagner R, Gatsogiannis C. Molecular architecture of black widow spider neurotoxins. Nat Commun 2021; 12:6956. [PMID: 34845192 PMCID: PMC8630228 DOI: 10.1038/s41467-021-26562-8] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2021] [Accepted: 10/11/2021] [Indexed: 12/14/2022] Open
Abstract
Latrotoxins (LaTXs) are presynaptic pore-forming neurotoxins found in the venom of Latrodectus spiders. The venom contains a toxic cocktail of seven LaTXs, with one of them targeting vertebrates (α-latrotoxin (α-LTX)), five specialized on insects (α, β, γ, δ, ε- latroinsectotoxins (LITs), and one on crustaceans (α-latrocrustatoxin (α-LCT)). LaTXs bind to specific receptors on the surface of neuronal cells, inducing the release of neurotransmitters either by directly stimulating exocytosis or by forming Ca2+-conductive tetrameric pores in the membrane. Despite extensive studies in the past decades, a high-resolution structure of a LaTX is not yet available and the precise mechanism of LaTX action remains unclear. Here, we report cryoEM structures of the α-LCT monomer and the δ-LIT dimer. The structures reveal that LaTXs are organized in four domains. A C-terminal domain of ankyrin-like repeats shields a central membrane insertion domain of six parallel α-helices. Both domains are flexibly linked via an N-terminal α-helical domain and a small β-sheet domain. A comparison between the structures suggests that oligomerization involves major conformational changes in LaTXs with longer C-terminal domains. Based on our data we propose a cyclic mechanism of oligomerization, taking place prior membrane insertion. Both recombinant α-LCT and δ-LIT form channels in artificial membrane bilayers, that are stabilized by Ca2+ ions and allow calcium flux at negative membrane potentials. Our comparative analysis between α-LCT and δ-LIT provides first crucial insights towards understanding the molecular mechanism of the LaTX family. The venom of Latrodectus spiders contains seven Latrotoxins (LaTXs), among them α-latrocrustatoxin (LCT) and δ- latroinsectotoxins δ-LIT. LaTXs bind to specific receptors on the surface of neuronal cells and target the molecular exocytosis machinery. Here, the authors present the cryo-EM structure of the α-LCT monomer and the δ-LIT dimer, which reveal that LaTXs are organized in four domains and they discuss the potential oligomerisation mechanism that takes place before LaTXs membrane insertion. Both recombinant α-LCT and δ-LIT form channels in artificial membrane bilayers, that are stabilized by Ca2+ ions.
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Affiliation(s)
- Minghao Chen
- Institute for Medical Physics and Biophysics and Center for Soft Nanoscience, Westfälische Wilhelms Universität Münster, 48149, Münster, Germany.,Department of Structural Biochemistry, Max Planck Institute of Molecular Physiology, 44227, Dortmund, Germany
| | - Daniel Blum
- MOLIFE Research Center, Jacobs University Bremen, 28759, Bremen, Germany
| | - Lena Engelhard
- Department of Structural Biochemistry, Max Planck Institute of Molecular Physiology, 44227, Dortmund, Germany
| | - Stefan Raunser
- Department of Structural Biochemistry, Max Planck Institute of Molecular Physiology, 44227, Dortmund, Germany
| | - Richard Wagner
- MOLIFE Research Center, Jacobs University Bremen, 28759, Bremen, Germany
| | - Christos Gatsogiannis
- Institute for Medical Physics and Biophysics and Center for Soft Nanoscience, Westfälische Wilhelms Universität Münster, 48149, Münster, Germany. .,Department of Structural Biochemistry, Max Planck Institute of Molecular Physiology, 44227, Dortmund, Germany.
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7
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Lu C, Hu C, Ritt CL, Hua X, Sun J, Xia H, Liu Y, Li DW, Ma B, Elimelech M, Qu J. In Situ Characterization of Dehydration during Ion Transport in Polymeric Nanochannels. J Am Chem Soc 2021; 143:14242-14252. [PMID: 34431669 DOI: 10.1021/jacs.1c05765] [Citation(s) in RCA: 55] [Impact Index Per Article: 18.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The transport of hydrated ions across nanochannels is central to biological systems and membrane-based applications, yet little is known about their hydrated structure during transport due to the absence of in situ characterization techniques. Herein, we report experimentally resolved ion dehydration during transmembrane transport using modified in situ liquid ToF-SIMS in combination with MD simulations for a mechanistic reasoning. Notably, complete dehydration was not necessary for transport to occur across membranes with sub-nanometer pores. Partial shedding of water molecules from ion solvation shells, observed as a decrease in the average hydration number, allowed the alkali-metal ions studied here (lithium, sodium, and potassium) to permeate membranes with pores smaller than their solvated size. We find that ions generally cannot hold more than two water molecules during this sterically limited transport. In nanopores larger than the size of the solvation shell, we show that ionic mobility governs the ion hydration number distribution. Viscous effects, such as interactions with carboxyl groups inside the membrane, preferentially hinder the transport of the mono- and dihydrates. Our novel technique for studying ion solvation in situ represents a significant technological leap for the nanofluidics field and may enable important advances in ion separation, biosensing, and battery applications.
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Affiliation(s)
- Chenghai Lu
- State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, People's Republic of China.,University of Chinese Academy of Sciences, Beijing 100049, People's Republic of China
| | - Chengzhi Hu
- State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, People's Republic of China.,University of Chinese Academy of Sciences, Beijing 100049, People's Republic of China
| | - Cody L Ritt
- Department of Chemical and Environmental Engineering, Yale University, New Haven, Connecticut 06520, United States
| | - Xin Hua
- School of Chemistry and Molecular Engineering, East China University of Science and Technology, Shanghai 200237, People's Republic of China
| | - Jingqiu Sun
- State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, People's Republic of China.,University of Chinese Academy of Sciences, Beijing 100049, People's Republic of China
| | - Hailun Xia
- School of Chemistry and Molecular Engineering, East China University of Science and Technology, Shanghai 200237, People's Republic of China
| | - Yingya Liu
- School of Chemistry and Molecular Engineering, East China University of Science and Technology, Shanghai 200237, People's Republic of China
| | - Da-Wei Li
- School of Chemistry and Molecular Engineering, East China University of Science and Technology, Shanghai 200237, People's Republic of China
| | - Baiwen Ma
- State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, People's Republic of China.,University of Chinese Academy of Sciences, Beijing 100049, People's Republic of China
| | - Menachem Elimelech
- Department of Chemical and Environmental Engineering, Yale University, New Haven, Connecticut 06520, United States
| | - Jiuhui Qu
- State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, People's Republic of China.,University of Chinese Academy of Sciences, Beijing 100049, People's Republic of China
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8
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HCN2 activation modulation: An electrophysiological and molecular study of the well-preserved LCI sequence in the pore channel. Arch Biochem Biophys 2020; 689:108436. [DOI: 10.1016/j.abb.2020.108436] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2020] [Revised: 05/21/2020] [Accepted: 05/25/2020] [Indexed: 11/17/2022]
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9
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Ostolaza H, González-Bullón D, Uribe KB, Martín C, Amuategi J, Fernandez-Martínez X. Membrane Permeabilization by Pore-Forming RTX Toxins: What Kind of Lesions Do These Toxins Form? Toxins (Basel) 2019; 11:toxins11060354. [PMID: 31216745 PMCID: PMC6628442 DOI: 10.3390/toxins11060354] [Citation(s) in RCA: 29] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2019] [Revised: 06/12/2019] [Accepted: 06/16/2019] [Indexed: 12/22/2022] Open
Abstract
Pore-forming toxins (PFTs) form nanoscale pores across target membranes causing cell death. The pore-forming cytolysins of the RTX (repeats in toxin) family belong to a steadily increasing family of proteins characterized by having in their primary sequences a number of glycine- and aspartate-rich nonapeptide repeats. They are secreted by a variety of Gram-negative bacteria and form ion-permeable pores in several cell types, such as immune cells, epithelial cells, or erythrocytes. Pore-formation by RTX-toxins leads to the dissipation of ionic gradients and membrane potential across the cytoplasmic membrane of target cells, which results in cell death. The pores formed in lipid bilayers by the RTX-toxins share some common properties such as cation selectivity and voltage-dependence. Hemolytic and cytolytic RTX-toxins are important virulence factors in the pathogenesis of the producing bacteria. And hence, understanding the function of these proteins at the molecular level is critical to elucidating their role in disease processes. In this review we summarize the current state of knowledge on pore-formation by RTX toxins, and include recent results from our own laboratory regarding the pore-forming activity of adenylate cyclase toxin (ACT or CyaA), a large protein toxin secreted by Bordetella pertussis, the bacterium causative of whooping cough.
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Affiliation(s)
- Helena Ostolaza
- Departamento de Bioquímica y Biología Molecular (UPV/EHU) and Instituto Biofisika (UPV/EHU, CSIC), Aptdo. 644, 48080 Bilbao, Spain.
| | - David González-Bullón
- Departamento de Bioquímica y Biología Molecular (UPV/EHU) and Instituto Biofisika (UPV/EHU, CSIC), Aptdo. 644, 48080 Bilbao, Spain.
| | - Kepa B Uribe
- Departamento de Bioquímica y Biología Molecular (UPV/EHU) and Instituto Biofisika (UPV/EHU, CSIC), Aptdo. 644, 48080 Bilbao, Spain.
| | - Cesar Martín
- Departamento de Bioquímica y Biología Molecular (UPV/EHU) and Instituto Biofisika (UPV/EHU, CSIC), Aptdo. 644, 48080 Bilbao, Spain.
| | - Jone Amuategi
- Departamento de Bioquímica y Biología Molecular (UPV/EHU) and Instituto Biofisika (UPV/EHU, CSIC), Aptdo. 644, 48080 Bilbao, Spain.
| | - Xabier Fernandez-Martínez
- Departamento de Bioquímica y Biología Molecular (UPV/EHU) and Instituto Biofisika (UPV/EHU, CSIC), Aptdo. 644, 48080 Bilbao, Spain.
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10
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A Structural Model of the Inactivation Gate of Voltage-Activated Potassium Channels. Biophys J 2019; 117:377-387. [PMID: 31278002 DOI: 10.1016/j.bpj.2019.06.008] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2019] [Revised: 05/21/2019] [Accepted: 06/07/2019] [Indexed: 11/24/2022] Open
Abstract
After opening, the Shaker voltage-gated potassium (KV) channel rapidly inactivates when one of its four N-termini enters and occludes the channel pore. Although it is known that the tip of the N-terminus reaches deep into the central cavity, the conformation adopted by this domain during inactivation and the nature of its interactions with the rest of the channel remain unclear. Here, we use molecular dynamics simulations coupled with electrophysiology experiments to reveal the atomic-scale mechanisms of inactivation. We find that the first six amino acids of the N-terminus spontaneously enter the central cavity in an extended conformation, establishing hydrophobic contacts with residues lining the pore. A second portion of the N-terminus, consisting of a long 24 amino acid α-helix, forms numerous polar contacts with residues in the intracellular entryway of the T1 domain. Double mutant cycle analysis revealed a strong relationship between predicted interatomic distances and empirically observed thermodynamic coupling, establishing a plausible model of the transition of KV channels to the inactivated state.
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11
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Gating-induced large aqueous volumetric remodeling and aspartate tolerance in the voltage sensor domain of Shaker K + channels. Proc Natl Acad Sci U S A 2018; 115:8203-8208. [PMID: 30038023 DOI: 10.1073/pnas.1806578115] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Neurons encode electrical signals with critically tuned voltage-gated ion channels and enzymes. Dedicated voltage sensor domains (VSDs) in these membrane proteins activate coordinately with an unresolved structural change. Such change conveys the transmembrane translocation of four positively charged arginine side chains, the voltage-sensing residues (VSRs; R1-R4). Countercharges and lipid phosphohead groups likely stabilize these VSRs within the low-dielectric core of the protein. However, the role of hydration, a sign-independent charge stabilizer, remains unclear. We replaced all VSRs and their neighboring residues with negatively charged aspartates in a voltage-gated potassium channel. The ensuing mild functional effects indicate that hydration is also important in VSR stabilization. The voltage dependency of the VSR aspartate variants approached the expected arithmetic summation of charges at VSR positions, as if negative and positive side chains faced similar pathways. In contrast, aspartates introduced between R2 and R3 did not affect voltage dependence as if the side chains moved outside the electric field or together with it, undergoing a large displacement and volumetric remodeling. Accordingly, VSR performed osmotic work at both internal and external aqueous interfaces. Individual VSR contributions to volumetric works approached arithmetical additivity but were largely dissimilar. While R1 and R4 displaced small volumes, R2 and R3 volumetric works were massive and vectorially opposed, favoring large aqueous remodeling during VSD activation. These diverse volumetric works are, at least for R2 and R3, not compatible with VSR translocation across a unique stationary charge transfer center. Instead, VSRs may follow separated pathways across a fluctuating low-dielectric septum.
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12
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Revisiting structure and dynamics of preferential solvation of K(I) ion in aqueous ammonia using QMCF-MD simulation. Chem Phys Lett 2018. [DOI: 10.1016/j.cplett.2018.03.067] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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13
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Wawrzkiewicz-Jałowiecka A, Borys P, Grzywna ZJ. Impact of geometry changes in the channel pore by the gating movements on the channel's conductance. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2017; 1859:446-458. [PMID: 28064020 DOI: 10.1016/j.bbamem.2017.01.002] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/31/2016] [Revised: 11/28/2016] [Accepted: 01/02/2017] [Indexed: 11/28/2022]
Abstract
Kv 1.2 are voltage-dependent potassium channels of great biological importance. Despite the existence of many reports considering structure - function relations of the Kv 1.2 channel's quantitative domains, some details of the voltage gating remain ambiguous, or even unknown. One of the examples is the range of the S4-S6 domains motions involved in channel activation and gating. Another important question is to what extent the channel geometry influences the observable channel conductance at different voltages, and what mechanism stands behind. Does the narrowing of the pore reduce the conductance by ohmic resistance growth? The answer is surprisingly negative. But it can be explained in an alternative way by considering the fluctuations. To address these problems, we formulate geometric models that mimic the generic features of voltage sensor movement and trigger the movement of the other domains involved in gating. We carry out a complete simulation of S4-S6 domains translations and tilts. The obtained pore profiles allow to estimate the (ohmic) conductance dependency on the voltage. From a family of analysed models, we choose the one most concurring with the experimental data. The results allow to suggest the most probable scenario of S4-S6 domains movement during channel activation by membrane depolarization.
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Affiliation(s)
- Agata Wawrzkiewicz-Jałowiecka
- Department of Physical Chemistry and Technology of Polymers, Section of Physics and Applied Mathematics, Silesian University of Technology, 44-100 Gliwice, Ks. M. Strzody 9, Poland.
| | - Przemysław Borys
- Department of Physical Chemistry and Technology of Polymers, Section of Physics and Applied Mathematics, Silesian University of Technology, 44-100 Gliwice, Ks. M. Strzody 9, Poland
| | - Zbigniew J Grzywna
- Department of Physical Chemistry and Technology of Polymers, Section of Physics and Applied Mathematics, Silesian University of Technology, 44-100 Gliwice, Ks. M. Strzody 9, Poland
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14
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Naranjo D, Moldenhauer H, Pincuntureo M, Díaz-Franulic I. Pore size matters for potassium channel conductance. J Gen Physiol 2016; 148:277-91. [PMID: 27619418 PMCID: PMC5037345 DOI: 10.1085/jgp.201611625] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2016] [Accepted: 08/10/2016] [Indexed: 01/31/2023] Open
Abstract
Ion channels are membrane proteins that mediate efficient ion transport across the hydrophobic core of cell membranes, an unlikely process in their absence. K+ channels discriminate K+ over cations with similar radii with extraordinary selectivity and display a wide diversity of ion transport rates, covering differences of two orders of magnitude in unitary conductance. The pore domains of large- and small-conductance K+ channels share a general architectural design comprising a conserved narrow selectivity filter, which forms intimate interactions with permeant ions, flanked by two wider vestibules toward the internal and external openings. In large-conductance K+ channels, the inner vestibule is wide, whereas in small-conductance channels it is narrow. Here we raise the idea that the physical dimensions of the hydrophobic internal vestibule limit ion transport in K+ channels, accounting for their diversity in unitary conductance.
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Affiliation(s)
- David Naranjo
- Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de Valparaíso, Playa Ancha, Valparaíso 2360103, Chile
| | - Hans Moldenhauer
- Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de Valparaíso, Playa Ancha, Valparaíso 2360103, Chile
| | - Matías Pincuntureo
- Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de Valparaíso, Playa Ancha, Valparaíso 2360103, Chile Programa de Doctorado en Ciencias, mención Biofísica y Biología Computacional, Universidad de Valparaíso, Valparaíso 2360103, Chile
| | - Ignacio Díaz-Franulic
- Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de Valparaíso, Playa Ancha, Valparaíso 2360103, Chile Center for Bioinformatics and Integrative Biology, Universidad Andrés Bello, Santiago 8370146, Chile Fraunhofer Chile Research, Las Condes 7550296, Chile
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15
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Abstract
BK channels are universal regulators of cell excitability, given their exceptional unitary conductance selective for K(+), joint activation mechanism by membrane depolarization and intracellular [Ca(2+)] elevation, and broad expression pattern. In this chapter, we discuss the structural basis and operational principles of their activation, or gating, by membrane potential and calcium. We also discuss how the two activation mechanisms interact to culminate in channel opening. As members of the voltage-gated potassium channel superfamily, BK channels are discussed in the context of archetypal family members, in terms of similarities that help us understand their function, but also seminal structural and biophysical differences that confer unique functional properties.
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Affiliation(s)
- A Pantazis
- David Geffen School of Medicine, University of California at Los Angeles, Los Angeles, CA, United States
| | - R Olcese
- David Geffen School of Medicine, University of California at Los Angeles, Los Angeles, CA, United States.
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