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Ryan M, Gao L, Valiyaveetil FI, Zanni MT, Kananenka AA. Probing Ion Configurations in the KcsA Selectivity Filter with Single-Isotope Labels and 2D IR Spectroscopy. J Am Chem Soc 2023; 145:18529-18537. [PMID: 37578394 PMCID: PMC10450685 DOI: 10.1021/jacs.3c05339] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2023] [Indexed: 08/15/2023]
Abstract
The potassium ion (K+) configurations of the selectivity filter of the KcsA ion channel protein are investigated with two-dimensional infrared (2D IR) spectroscopy of amide I vibrations. Single 13C-18O isotope labels are used, for the first time, to selectively probe the S1/S2 or S2/S3 binding sites in the selectivity filter. These binding sites have the largest differences in ion occupancy in two competing K+ transport mechanisms: soft-knock and hard-knock. According to the former, water molecules alternate between K+ ions in the selectivity filter while the latter assumes that K+ ions occupy the adjacent sites. Molecular dynamics simulations and computational spectroscopy are employed to interpret experimental 2D IR spectra. We find that in the closed conductive state of the KcsA channel, K+ ions do not occupy adjacent binding sites. The experimental data is consistent with simulated 2D IR spectra of soft-knock ion configurations. In contrast, the simulated spectra for the hard-knock ion configurations do not reproduce the experimental results. 2D IR spectra of the hard-knock mechanism have lower frequencies, homogeneous 2D lineshapes, and multiple peaks. In contrast, ion configurations of the soft-knock model produce 2D IR spectra with a single peak at a higher frequency and inhomogeneous lineshape. We conclude that under equilibrium conditions, in the absence of transmembrane voltage, both water and K+ ions occupy the selectivity filter of the KcsA channel in the closed conductive state. The ion configuration is central to the mechanism of ion transport through potassium channels.
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Affiliation(s)
- Matthew
J. Ryan
- Department
of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, United States
| | - Lujia Gao
- Department
of Chemical Physiology and Biochemistry, Oregon Health & Science University, Portland, Oregon 97239, United States
| | - Francis I. Valiyaveetil
- Department
of Chemical Physiology and Biochemistry, Oregon Health & Science University, Portland, Oregon 97239, United States
| | - Martin T. Zanni
- Department
of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, United States
| | - Alexei A. Kananenka
- Department
of Physics and Astronomy, University of
Delaware, Newark, Delaware 19716, United States
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2
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Sosa RD, Geng X, Agarwal A, Palmer JC, Conrad JC, Reynolds MA, Rimer JD. Acidic Polysaccharides as Green Alternatives for Barite Scale Dissolution. ACS APPLIED MATERIALS & INTERFACES 2020; 12:55434-55443. [PMID: 33233879 DOI: 10.1021/acsami.0c16653] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Barium sulfate (barite) scale poses significant challenges for processes ranging from water treatment to fossil fuel production. Here, we identify alginate (a polysaccharide derived from brown algae) as a potent, "green" alternative to commercial barite demineralizing agents. Unlike conventional treatments of inorganic scales that require caustic conditions, alginate polymers dissolve barite at near-neutral conditions. In this study, we benchmark the demineralizing efficacy of alginate against a commercial dissolver, diethylenetriaminepentaacetic acid (DTPA), using a combination of bulk dissolution assays, scanning probe microscopy, and molecular dynamics simulations. Time-resolved rates of dissolution measured in a microfluidic device show that demineralization is enhanced more than an order of magnitude under flow. In situ atomic force microscopy reveals that alginate and DTPA exhibit distinct mechanisms of surface dissolution; and surprisingly, their binary combination in alkaline media results in a synergistic cooperativity that enhances the overall rate of barite dissolution. These studies collectively demonstrate a unique approach to demineralization using an inexpensive and abundant biopolymer that enables environmentally friendly treatment of inorganic scales.
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Affiliation(s)
- Ricardo D Sosa
- Department of Chemical and Biomolecular Engineering, University of Houston, Houston, Texas 77204-4004, United States
| | - Xi Geng
- Department of Chemical and Biomolecular Engineering, University of Houston, Houston, Texas 77204-4004, United States
| | - Ankur Agarwal
- Department of Chemical and Biomolecular Engineering, University of Houston, Houston, Texas 77204-4004, United States
| | - Jeremy C Palmer
- Department of Chemical and Biomolecular Engineering, University of Houston, Houston, Texas 77204-4004, United States
| | - Jacinta C Conrad
- Department of Chemical and Biomolecular Engineering, University of Houston, Houston, Texas 77204-4004, United States
| | - Michael A Reynolds
- Shell Exploration and Production Company, Houston, Texas 77079, United States
| | - Jeffrey D Rimer
- Department of Chemical and Biomolecular Engineering, University of Houston, Houston, Texas 77204-4004, United States
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3
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Rohaim A, Gong L, Li J, Rui H, Blachowicz L, Roux B. Open and Closed Structures of a Barium-Blocked Potassium Channel. J Mol Biol 2020; 432:4783-4798. [PMID: 32615129 DOI: 10.1016/j.jmb.2020.06.012] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2020] [Revised: 05/27/2020] [Accepted: 06/12/2020] [Indexed: 11/26/2022]
Abstract
Barium (Ba2+) is a classic permeant blocker of potassium (K+) channels. The "external lock-in effect" in barium block experiments, whereby the binding of external K+ impedes the forward translocation of the blocker, provides a powerful avenue to investigate the selectivity of the binding sites along the pore of potassium channels. Barium block experiments show that the external lock-in site is highly selective for K+ over Na+. Wild-type KcsA was crystallized in low K+ conditions, and the crystals were soaked in solutions containing various concentrations of barium. Structural analysis reveals open and closed gate conformations of the KcsA channel. Anomalous diffraction experiments show that Ba2+ primarily binds to the innermost site S4 of the selectivity filter of the open-gate conformation and also the site S2, but no binding is detected with the closed-gate conformation. Alchemical free-energy perturbation calculations indicate that the presence of a Ba2+ ion in the selectivity filter boosts the specificity of K+ binding relative to Na+ in the external sites S0-S2.
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Affiliation(s)
- Ahmed Rohaim
- Department of Biochemistry and Molecular Biology, University of Chicago, Gordon Center for Integrative Science, 929 E 57th St, Chicago, IL 60637, USA; Department of Biophysics, Faculty of Science, Cairo University, Giza 12613, Egypt
| | - LiDong Gong
- School of Chemistry and Chemical Engineering, Liaoning Normal University, Dalian 116029, China
| | - Jing Li
- Department of Biochemistry and Molecular Biology, University of Chicago, Gordon Center for Integrative Science, 929 E 57th St, Chicago, IL 60637, USA
| | - Huan Rui
- Department of Biochemistry and Molecular Biology, University of Chicago, Gordon Center for Integrative Science, 929 E 57th St, Chicago, IL 60637, USA
| | - Lydia Blachowicz
- Department of Biochemistry and Molecular Biology, University of Chicago, Gordon Center for Integrative Science, 929 E 57th St, Chicago, IL 60637, USA
| | - Benoît Roux
- Department of Biochemistry and Molecular Biology, University of Chicago, Gordon Center for Integrative Science, 929 E 57th St, Chicago, IL 60637, USA.
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4
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Migliorati V, Caruso A, D’Angelo P. Unraveling the Hydration Properties of the Ba2+ Aqua Ion: the Interplay of Quantum Mechanics, Molecular Dynamics, and EXAFS Spectroscopy. Inorg Chem 2019; 58:14551-14559. [DOI: 10.1021/acs.inorgchem.9b02204] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Affiliation(s)
- Valentina Migliorati
- Dipartimento di Chimica, Università di Roma “La Sapienza”, P.le A. Moro 5, 00185 Roma, Italy
| | - Alessandro Caruso
- Dipartimento di Chimica, Università di Roma “La Sapienza”, P.le A. Moro 5, 00185 Roma, Italy
| | - Paola D’Angelo
- Dipartimento di Chimica, Università di Roma “La Sapienza”, P.le A. Moro 5, 00185 Roma, Italy
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5
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Song Z, Cao X, Horng TL, Huang H. Selectivity of the KcsA potassium channel: Analysis and computation. Phys Rev E 2019; 100:022406. [PMID: 31574673 DOI: 10.1103/physreve.100.022406] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2019] [Indexed: 11/07/2022]
Abstract
Ion channels regulate the flux of ions through cell membranes and play significant roles in many physiological functions. Most of the existing literature focuses on computational approaches based on molecular dynamics simulation or numerical solution of the modified Poisson-Nernst-Planck (PNP) system. In this paper, we present an analytical and computational study of a mathematical model of the KcsA potassium channel, including the effects of ion size (Bikerman model) and solvation energy (Born model). Under equilibrium conditions, we obtain an analytical solution of our modified PNP system, which is used to explain selectivity of KcsA of various ions (K^{+}, Na^{+}, Cl^{-}, Ca^{2+}, and Ba^{2+}) due to negative permanent charges inside the filter region and the effect of ion sizes. Our results show that K^{+} is always selected over Na^{+}, as smaller Na^{+} ions have larger solvation energy. As the amount of negative charges in the filter exceeds a critical value, divalent ions (Ca^{2+} and Ba^{2+}) can enter the filter region and block the KcsA channel. For the nonequilibrium cases, due to difficulties associated with a pure analytical or numerical approach, we use a hybrid analytical-numerical method to solve the modified PNP system. Our predictions of selectivity of KcsA channels and saturation phenomenon of the current-voltage (I-V) curve agree with experimental observations.
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Affiliation(s)
- Zilong Song
- Department of Mathematics and Statistics, York University, Toronto, Ontario, Canada M3J 1P3
| | - Xiulei Cao
- Department of Mathematics and Statistics, York University, Toronto, Ontario, Canada M3J 1P3
| | - Tzyy-Leng Horng
- Department of Applied Mathematics, Feng Chia University, Taichung 40724, Taiwan and National Center for Theoretical Sciences, Taipei Office, Taipei, Taiwan 10617
| | - Huaxiong Huang
- Department of Mathematics and Statistics, York University, Toronto, Ontario, Canada M3J 1P3 and Fields Institute for Research in Mathematical Sciences, Toronto, Ontario, Canada M5T 3J1
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6
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Paz SA, Maragliano L, Abrams CF. Effect of Intercalated Water on Potassium Ion Transport through Kv1.2 Channels Studied via On-the-Fly Free-Energy Parametrization. J Chem Theory Comput 2018; 14:2743-2750. [DOI: 10.1021/acs.jctc.8b00024] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Affiliation(s)
- S. Alexis Paz
- Universidad Nacional de Córdoba, Facultad de Ciencias Químicas, Departamento de Química Teórica y Computacional, Córdoba, Argentina
- INFIQC, CONICET, X5000HUA, Córdoba, Argentina
| | - Luca Maragliano
- Center for Synaptic Neuroscience and Technology, Fondazione Istituto Italiano di Tecnologia, 16132 Genoa, Italy
| | - Cameron F. Abrams
- Department of Chemical and Biological Engineering, Drexel University, Philadelphia, Pennsylvania 19104, United States
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7
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Computational Studies of Molecular Permeation through Connexin26 Channels. Biophys J 2017; 110:584-599. [PMID: 26840724 DOI: 10.1016/j.bpj.2015.11.3528] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2015] [Revised: 10/21/2015] [Accepted: 11/23/2015] [Indexed: 11/22/2022] Open
Abstract
A signal property of connexin channels is the ability to mediate selective diffusive movement of molecules through plasma membrane(s), but the energetics and determinants of molecular movement through these channels have yet to be understood. Different connexin channels have distinct molecular selectivities that cannot be explained simply on the basis of size or charge of the permeants. To gain insight into the forces and interactions that underlie selective molecular permeation, we investigated the energetics of two uncharged derivatized sugars, one permeable and one impermeable, through a validated connexin26 (Cx26) channel structural model, using molecular dynamics and associated analytic tools. The system is a Cx26 channel equilibrated in explicit membrane/solvent, shown by Brownian dynamics to reproduce key conductance characteristics of the native channel. The results are consistent with the known difference in permeability to each molecule. The energetic barriers extend through most of the pore length, rather than being highly localized as in ion-specific channels. There is little evidence for binding within the pore. Force decomposition reveals how, for each tested molecule, interactions with water and the Cx26 protein vary over the length of the pore and reveals a significant contribution from hydrogen bonding and interaction with K(+). The flexibility of the pore width varies along its length, and the tested molecules have differential effects on pore width as they pass through. Potential sites of interaction within the pore are defined for each molecule. The results suggest that for the tested molecules, differences in hydrogen bonding and entropic factors arising from permeant flexibility substantially contribute to the energetics of permeation. This work highlights factors involved in selective molecular permeation that differ from those that define selectivity among atomic ions.
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Kratochvil HT, Carr JK, Matulef K, Annen AW, Li H, Maj M, Ostmeyer J, Serrano AL, Raghuraman H, Moran SD, Skinner JL, Perozo E, Roux B, Valiyaveetil FI, Zanni MT. Instantaneous ion configurations in the K+ ion channel selectivity filter revealed by 2D IR spectroscopy. Science 2016; 353:1040-1044. [PMID: 27701114 PMCID: PMC5544905 DOI: 10.1126/science.aag1447] [Citation(s) in RCA: 143] [Impact Index Per Article: 17.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2016] [Accepted: 08/03/2016] [Indexed: 11/02/2022]
Abstract
Potassium channels are responsible for the selective permeation of K+ ions across cell membranes. K+ ions permeate in single file through the selectivity filter, a narrow pore lined by backbone carbonyls that compose four K+ binding sites. Here, we report on the two-dimensional infrared (2D IR) spectra of a semisynthetic KcsA channel with site-specific heavy (13C18O) isotope labels in the selectivity filter. The ultrafast time resolution of 2D IR spectroscopy provides an instantaneous snapshot of the multi-ion configurations and structural distributions that occur spontaneously in the filter. Two elongated features are resolved, revealing the statistical weighting of two structural conformations. The spectra are reproduced by molecular dynamics simulations of structures with water separating two K+ ions in the binding sites, ruling out configurations with ions occupying adjacent sites.
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Affiliation(s)
- Huong T Kratochvil
- Department of Chemistry, University of Wisconsin-Madison, Madison, WI 53706, USA
| | - Joshua K Carr
- Department of Chemistry, University of Wisconsin-Madison, Madison, WI 53706, USA
| | - Kimberly Matulef
- Program in Chemical Biology, Department of Physiology and Pharmacology, Oregon Health and Science University, Portland, OR 97239, USA
| | - Alvin W Annen
- Program in Chemical Biology, Department of Physiology and Pharmacology, Oregon Health and Science University, Portland, OR 97239, USA
| | - Hui Li
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL 60637, USA
| | - Michał Maj
- Department of Chemistry, University of Wisconsin-Madison, Madison, WI 53706, USA
| | - Jared Ostmeyer
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL 60637, USA
| | - Arnaldo L Serrano
- Department of Chemistry, University of Wisconsin-Madison, Madison, WI 53706, USA
| | - H Raghuraman
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL 60637, USA
| | - Sean D Moran
- Department of Chemistry, University of Wisconsin-Madison, Madison, WI 53706, USA
| | - J L Skinner
- Department of Chemistry, University of Wisconsin-Madison, Madison, WI 53706, USA
| | - Eduardo Perozo
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL 60637, USA.
| | - Benoît Roux
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL 60637, USA.
| | - Francis I Valiyaveetil
- Program in Chemical Biology, Department of Physiology and Pharmacology, Oregon Health and Science University, Portland, OR 97239, USA.
| | - Martin T Zanni
- Department of Chemistry, University of Wisconsin-Madison, Madison, WI 53706, USA.
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9
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Medovoy D, Perozo E, Roux B. Multi-ion free energy landscapes underscore the microscopic mechanism of ion selectivity in the KcsA channel. BIOCHIMICA ET BIOPHYSICA ACTA 2016; 1858:1722-32. [PMID: 26896693 PMCID: PMC4939264 DOI: 10.1016/j.bbamem.2016.02.019] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/29/2015] [Revised: 01/20/2016] [Accepted: 02/13/2016] [Indexed: 11/28/2022]
Abstract
Potassium (K(+)) channels are transmembrane proteins that passively and selectively allow K(+) ions to flow through them, after opening in response to an external stimulus. One of the most critical functional aspects of their function is their ability to remain very selective for K(+) over Na(+) while allowing high-throughput ion conduction at a rate close to the diffusion limit. Classically, it is assumed that the free energy difference between K(+) and Na(+) in the pore relative to the bulk solution is the critical quantity at the origin of selectivity. This is the thermodynamic view of ion selectivity. An alternative view assumes that kinetic factors play the dominant role. Recent results from a number of studies have also highlighted the great importance of the multi-ion single file on the selectivity of K(+) channels. The data indicate that having multiple K(+) ions bound simultaneously is required for selective K(+) conduction, and that a reduction in the number of bound K(+) ions destroys the multi-ion selectivity mechanism utilized by K(+) channels. In the present study, multi-ion potential of mean force molecular dynamics computations are carried out to clarify the mechanism of ion selectivity in the KcsA channel. The computations show that the multi-ion character of the permeation process is a critical element for establishing the selective ion conductivity through K(+)-channels. This article is part of a Special Issue entitled: Membrane Proteins edited by J.C. Gumbart and Sergei Noskov.
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Affiliation(s)
- David Medovoy
- Biochemistry and Molecular Biology, Institute for Biophysical Dynamics, Gordon Center for Integrative Science, The University of Chicago, 929 E 57th Street, Chicago, IL 60637, USA
| | - Eduardo Perozo
- Biochemistry and Molecular Biology, Institute for Biophysical Dynamics, Gordon Center for Integrative Science, The University of Chicago, 929 E 57th Street, Chicago, IL 60637, USA
| | - Benoît Roux
- Biochemistry and Molecular Biology, Institute for Biophysical Dynamics, Gordon Center for Integrative Science, The University of Chicago, 929 E 57th Street, Chicago, IL 60637, USA.
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10
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Abstract
The hydration structure of Ba(2+) ion is important for understanding blocking mechanisms in potassium ion channels. Here, we combine statistical mechanical theory, ab initio molecular dynamics simulations, and electronic structure methods to calculate the hydration free energy and local hydration structure of Ba(2+)(aq). The predicted hydration free energy (-304 ± 1 kcal/mol) agrees with the experimental value (-303 kcal/mol) when a maximally occupied, unimodal inner solvation shell is treated. In the local environment defined by the first shell of hydrating waters, Ba(2+) is directly and stably coordinated by eight (8) waters. Octa-coordination resembles the crystal structure of Ba(2+) and K(+) bound in potassium ion channels, but differs from the local hydration structure of K(+)(aq) determined earlier.
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Affiliation(s)
- Mangesh I Chaudhari
- †Center for Biological and Engineering Sciences, Sandia National Laboratories, Albuquerque, New Mexico 87185, United States
| | - Marielle Soniat
- ‡Department of Chemistry, University of New Orleans, New Orleans, Louisiana 70148, United States
| | - Susan B Rempe
- †Center for Biological and Engineering Sciences, Sandia National Laboratories, Albuquerque, New Mexico 87185, United States
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11
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LIU BAOXIN, LI SHUANG, SU YANG, XIONG MENGTING, XU YAWEI. Comparative study of the protective effects of terfenadine and amiodarone on barium chloride/aconitine-induced ventricular arrhythmias in rats: A potential role of terfenadine. Mol Med Rep 2014; 10:3217-26. [DOI: 10.3892/mmr.2014.2640] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2013] [Accepted: 07/22/2014] [Indexed: 11/06/2022] Open
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12
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Guo R, Zeng W, Cui H, Chen L, Ye S. Ionic interactions of Ba2+ blockades in the MthK K+ channel. ACTA ACUST UNITED AC 2014; 144:193-200. [PMID: 25024268 PMCID: PMC4113901 DOI: 10.1085/jgp.201411192] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The movement and interaction of multiple ions passing through in single file underlie various fundamental K(+) channel properties, from the effective conduction of K(+) ions to channel blockade by Ba(2+) ions. In this study, we used single-channel electrophysiology and x-ray crystallography to probe the interactions of Ba(2+) with permeant ions within the ion conduction pathway of the MthK K(+) channel. We found that, as typical of K(+) channels, the MthK channel was blocked by Ba(2+) at the internal side, and the Ba(2+)-blocking effect was enhanced by external K(+). We also obtained crystal structures of the MthK K(+) channel pore in both Ba(2+)-Na(+) and Ba(2+)-K(+) environments. In the Ba(2+)-Na(+) environment, we found that a single Ba(2+) ion remained bound in the selectivity filter, preferably at site 2, whereas in the Ba(2+)-K(+) environment, Ba(2+) ions were predominantly distributed between sites 3 and 4. These ionic configurations are remarkably consistent with the functional studies and identify a molecular basis for Ba(2+) blockade of K(+) channels.
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Affiliation(s)
- Rui Guo
- Life Sciences Institute and Innovation Center for Cell Biology, Zhejiang University, Hangzhou 310058, China
| | - Weizhong Zeng
- Howard Hughes Medical Institute, Department of Physiology, University of Texas Southwestern Medical Center, Dallas, TX 75390
| | - Hengjun Cui
- Life Sciences Institute and Innovation Center for Cell Biology, Zhejiang University, Hangzhou 310058, China
| | - Liping Chen
- Howard Hughes Medical Institute, Department of Physiology, University of Texas Southwestern Medical Center, Dallas, TX 75390
| | - Sheng Ye
- Life Sciences Institute and Innovation Center for Cell Biology, Zhejiang University, Hangzhou 310058, China
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13
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Abstract
Ion channels are membrane-bound enzymes whose catalytic sites are ion-conducting pores that open and close (gate) in response to specific environmental stimuli. Ion channels are important contributors to cell signaling and homeostasis. Our current understanding of gating is the product of 60 plus years of voltage-clamp recording augmented by intervention in the form of environmental, chemical, and mutational perturbations. The need for good phenomenological models of gating has evolved in parallel with the sophistication of experimental technique. The goal of modeling is to develop realistic schemes that not only describe data, but also accurately reflect mechanisms of action. This review covers three areas that have contributed to the understanding of ion channels: traditional Eyring kinetic theory, molecular dynamics analysis, and statistical thermodynamics. Although the primary emphasis is on voltage-dependent channels, the methods discussed here are easily generalized to other stimuli and could be applied to any ion channel and indeed any macromolecule.
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14
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Eisenach C, Papanatsiou M, Hillert EK, Blatt MR. Clustering of the K+ channel GORK of Arabidopsis parallels its gating by extracellular K+. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2014; 78:203-14. [PMID: 24517091 PMCID: PMC4309415 DOI: 10.1111/tpj.12471] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/10/2013] [Revised: 01/18/2014] [Accepted: 01/22/2014] [Indexed: 05/04/2023]
Abstract
GORK is the only outward-rectifying Kv-like K(+) channel expressed in guard cells. Its activity is tightly regulated to facilitate K(+) efflux for stomatal closure and is elevated in ABA in parallel with suppression of the activity of the inward-rectifying K(+) channel KAT1. Whereas the population of KAT1 is subject to regulated traffic to and from the plasma membrane, nothing is known about GORK, its distribution and traffic in vivo. We have used transformations with fluorescently-tagged GORK to explore its characteristics in tobacco epidermis and Arabidopsis guard cells. These studies showed that GORK assembles in puncta that reversibly dissociated as a function of the external K(+) concentration. Puncta dissociation parallelled the gating dependence of GORK, the speed of response consistent with the rapidity of channel gating response to changes in the external ionic conditions. Dissociation was also suppressed by the K(+) channel blocker Ba(2+) . By contrast, confocal and protein biochemical analysis failed to uncover substantial exo- and endocytotic traffic of the channel. Gating of GORK is displaced to more positive voltages with external K(+) , a characteristic that ensures the channel facilitates only K(+) efflux regardless of the external cation concentration. GORK conductance is also enhanced by external K(+) above 1 mm. We suggest that GORK clustering in puncta is related to its gating and conductance, and reflects associated conformational changes and (de)stabilisation of the channel protein, possibly as a platform for transmission and coordination of channel gating in response to external K(+) .
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Affiliation(s)
| | - Maria Papanatsiou
- Laboratory of Plant Physiology and Biophysics, Institute of Molecular, Cell and Systems Biology, University of GlasgowBower Building, Glasgow, G12 8QQ, UK
| | - Ellin-Kristina Hillert
- Laboratory of Plant Physiology and Biophysics, Institute of Molecular, Cell and Systems Biology, University of GlasgowBower Building, Glasgow, G12 8QQ, UK
| | - Michael R Blatt
- Laboratory of Plant Physiology and Biophysics, Institute of Molecular, Cell and Systems Biology, University of GlasgowBower Building, Glasgow, G12 8QQ, UK
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