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Moura ACM, Asare IK, Cruz MF, Aguado AJF, Tuck KD, Campbell CC, Scheyer MW, Obaseki I, Alston S, Kravats AN, Sanders CR, Lorigan GA, Sahu ID. Studying Conformational Properties of Transmembrane Domain of KCNE3 in a Lipid Bilayer Membrane Using Molecular Dynamics Simulations. MEMBRANES 2024; 14:45. [PMID: 38392672 PMCID: PMC10890134 DOI: 10.3390/membranes14020045] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/31/2023] [Revised: 01/22/2024] [Accepted: 01/29/2024] [Indexed: 02/24/2024]
Abstract
KCNE3 is a single-pass integral membrane protein that regulates numerous voltage-gated potassium channel functions such as KCNQ1. Previous solution NMR studies suggested a moderate degree of curved α-helical structure in the transmembrane domain (TMD) of KCNE3 in lyso-myristoylphosphatidylcholine (LMPC) micelles and isotropic bicelles with the residues T71, S74 and G78 situated along the concave face of the curved helix. During the interaction of KCNE3 and KCNQ1, KCNE3 pushes its transmembrane domain against KCNQ1 to lock the voltage sensor in its depolarized conformation. A cryo-EM study of KCNE3 complexed with KCNQ1 in nanodiscs suggested a deviation of the KCNE3 structure from its independent structure in isotropic bicelles. Despite the biological significance of KCNE3 TMD, the conformational properties of KCNE3 are poorly understood. Here, all atom molecular dynamics (MD) simulations were utilized to investigate the conformational dynamics of the transmembrane domain of KCNE3 in a lipid bilayer containing a mixture of POPC and POPG lipids (3:1). Further, the effect of the interaction impairing mutations (V72A, I76A and F68A) on the conformational properties of the KCNE3 TMD in lipid bilayers was investigated. Our MD simulation results suggest that the KCNE3 TMD adopts a nearly linear α helical structural conformation in POPC-POPG lipid bilayers. Additionally, the results showed no significant change in the nearly linear α-helical conformation of KCNE3 TMD in the presence of interaction impairing mutations within the sampled time frame. The KCNE3 TMD is more stable with lower flexibility in comparison to the N-terminal and C-terminal of KCNE3 in lipid bilayers. The overall conformational flexibility of KCNE3 also varies in the presence of the interaction-impairing mutations. The MD simulation data further suggest that the membrane bilayer width is similar for wild-type KCNE3 and KCNE3 containing mutations. The Z-distance measurement data revealed that the TMD residue site A69 is close to the lipid bilayer center, and residue sites S57 and S82 are close to the surfaces of the lipid bilayer membrane for wild-type KCNE3 and KCNE3 containing interaction-impairing mutations. These results agree with earlier KCNE3 biophysical studies. The results of these MD simulations will provide complementary data to the experimental outcomes of KCNE3 to help understand its conformational dynamic properties in a more native lipid bilayer environment.
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Affiliation(s)
| | - Isaac K Asare
- Natural Science Division, Campbellsville University, Campbellsville, KY 42718, USA
| | - Mateo Fernandez Cruz
- Natural Science Division, Campbellsville University, Campbellsville, KY 42718, USA
| | | | - Kaeleigh Dyan Tuck
- Natural Science Division, Campbellsville University, Campbellsville, KY 42718, USA
| | - Conner C Campbell
- Natural Science Division, Campbellsville University, Campbellsville, KY 42718, USA
| | - Matthew W Scheyer
- Natural Science Division, Campbellsville University, Campbellsville, KY 42718, USA
| | - Ikponwmosa Obaseki
- Department of Chemistry and Biochemistry, Miami University, Oxford, OH 45056, USA
| | - Steve Alston
- Natural Science Division, Campbellsville University, Campbellsville, KY 42718, USA
| | - Andrea N Kravats
- Department of Chemistry and Biochemistry, Miami University, Oxford, OH 45056, USA
| | - Charles R Sanders
- Department of Biochemistry and Center for Structural Biology, Vanderbilt University, Nashville, TN 37232, USA
| | - Gary A Lorigan
- Department of Chemistry and Biochemistry, Miami University, Oxford, OH 45056, USA
| | - Indra D Sahu
- Natural Science Division, Campbellsville University, Campbellsville, KY 42718, USA
- Department of Chemistry and Biochemistry, Miami University, Oxford, OH 45056, USA
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Scheyer MW, Campbell C, William PL, Hussain M, Begum A, Fonseca SE, Asare IK, Dabney P, Dabney-Smith C, Lorigan GA, Sahu ID. Electron paramagnetic resonance spectroscopic characterization of the human KCNE3 protein in lipodisq nanoparticles for structural dynamics of membrane proteins. Biophys Chem 2023; 301:107080. [PMID: 37531799 DOI: 10.1016/j.bpc.2023.107080] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2023] [Revised: 07/07/2023] [Accepted: 07/24/2023] [Indexed: 08/04/2023]
Abstract
One of the major challenges in solubilization of membrane proteins is to find the optimal physiological environment for their biophysical studies. EPR spectroscopy is a powerful biophysical technique for studying the structural and dynamic properties of macromolecules. However, the challenges in the membrane protein sample preparation and flexible motion of the spin label limit the utilization of EPR spectroscopy to a majority of membrane protein systems in a physiological membrane-bound state. Recently, lipodisq nanoparticles or styrene-maleic acid copolymer-lipid nanoparticles (SMALPs) have emerged as a membrane mimetic system for investigating the structural studies of membrane proteins. However, its detail characterization for membrane protein studies is still poorly understood. Recently, we characterized the potassium channel membrane protein KCNQ1 voltage sensing domain (KCNQ1-VSD) and KCNE1 reconstituted into lipodisq nanoparticles using EPR spectroscopy. In this study, the potassium channel accessory protein KCNE3 containing flexible N- and C-termini was encapsulated into proteoliposomes and lipodisq nanoparticles and characterized for studying its structural and dynamic properties using nitroxide based site-directed spin labeling EPR spectroscopy. CW-EPR lineshape analysis data indicated an increase in spectral line broadenings with the addition of the styrene-maleic acid (SMA) polymer which approaches close to the rigid limit providing a homogeneous stabilization of the protein-lipid complex. Similarly, EPR DEER measurements indicated an enhanced quality of distance measurements with an increase in the phase memory time (Tm) values upon incorporation of the sample into lipodisq nanoparticles, when compared to proteoliposomes. These results agree with the solution NMR structural structure of the KCNE3 and EPR studies of other membrane proteins in lipodisq nanoparticles. This study along with our earlier studies will provide the reference characterization data that will provide benefit to the membrane protein researchers for studying structural dynamics of challenging membrane proteins.
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Affiliation(s)
- Matthew W Scheyer
- Natural Science Division, Campbellsville University, Campbellsville, KY 42718, USA
| | - Conner Campbell
- Natural Science Division, Campbellsville University, Campbellsville, KY 42718, USA
| | - Patrick L William
- Natural Science Division, Campbellsville University, Campbellsville, KY 42718, USA
| | - Mustakim Hussain
- Natural Science Division, Campbellsville University, Campbellsville, KY 42718, USA
| | - Afsana Begum
- Natural Science Division, Campbellsville University, Campbellsville, KY 42718, USA
| | | | - Isaac K Asare
- Natural Science Division, Campbellsville University, Campbellsville, KY 42718, USA
| | - Peyton Dabney
- Natural Science Division, Campbellsville University, Campbellsville, KY 42718, USA
| | - Carole Dabney-Smith
- Department of Chemistry and Biochemistry, Miami University, Oxford, OH 45056, USA
| | - Gary A Lorigan
- Department of Chemistry and Biochemistry, Miami University, Oxford, OH 45056, USA
| | - Indra D Sahu
- Natural Science Division, Campbellsville University, Campbellsville, KY 42718, USA; Department of Chemistry and Biochemistry, Miami University, Oxford, OH 45056, USA.
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3
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Kodirov SA. Adam, amigo, brain, and K channel. Biophys Rev 2023; 15:1393-1424. [PMID: 37975011 PMCID: PMC10643815 DOI: 10.1007/s12551-023-01163-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2023] [Accepted: 09/28/2023] [Indexed: 11/19/2023] Open
Abstract
Voltage-dependent K+ (Kv) channels are diverse, comprising the classical Shab - Kv2, Shaker - Kv1, Shal - Kv4, and Shaw - Kv3 families. The Shaker family alone consists of Kv1.1, Kv1.2, Kv1.3, Kv1.4, Kv1.5, Kv1.6, and Kv1.7. Moreover, the Shab family comprises two functional (Kv2.1 and Kv2.2) and several "silent" alpha subunits (Kv2.3, Kv5, Kv6, Kv8, and Kv9), which do not generate K current. However, e.g., Kv8.1, via heteromerization, inhibits outward currents of the same family or even that of Shaw. This property of Kv8.1 is similar to those of designated beta subunits or non-selective auxiliary elements, including ADAM or AMIGO proteins. Kv channels and, in turn, ADAM may modulate the synaptic long-term potentiation (LTP). Prevailingly, Kv1.1 and Kv1.5 are attributed to respective brain and heart pathologies, some of which may occur simultaneously. The aforementioned channel proteins are apparently involved in several brain pathologies, including schizophrenia and seizures.
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Affiliation(s)
- Sodikdjon A. Kodirov
- Department of Biological Sciences, University of Texas at Brownsville, Brownsville, TX 78520 USA
- Pavlov Institute of Physiology, Russian Academy of Sciences, Saint Petersburg, Russia
- Instituto de Medicina Molecular, Universidade de Lisboa, 1649-028 Lisbon, Portugal
- Almazov Federal Heart, Blood and Endocrinology Centre, Saint Petersburg, 197341 Russia
- Institute for Physiology and Pathophysiology, Johannes Kepler University, Linz, Austria
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Lancaster MC, Chen HH, Shoemaker MB, Fleming MR, Baker JT, Polikowsky HG, Samuels DC, Huff CD, Roden DM, Below JE. Detection of distant familial relatedness in biobanks for identification of undiagnosed carriers of a Mendelian disease variant: application to Long QT syndrome. MEDRXIV : THE PREPRINT SERVER FOR HEALTH SCIENCES 2023:2023.04.19.23288831. [PMID: 37163006 PMCID: PMC10168417 DOI: 10.1101/2023.04.19.23288831] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
Importance The diagnosis and study of rare genetic disease is often limited to referral populations, leading to underdiagnosis and a biased assessment of penetrance and phenotype. Objective To develop a generalizable method of genotype inference based on distant relatedness and to deploy this to identify undiagnosed Type 5 Long QT Syndrome (LQT5) rare variant carriers in a non-referral population. Participants We identified 9 LQT5 probands and 3 first-degree relatives referred to a single Genetic Arrhythmia clinic, each carrying D76N (p.Asp76Asn), the most common variant implicated in LQT5. The non-referral population consisted of 69,879 ancestry-matched subjects in BioVU, a large biobank that links electronic health records to dense array data. Participants were enrolled from 2007-2022. Data analysis was performed in 2022. Exposures We developed and applied a novel approach to genotype inference (Distant Relatedness for Identification and Variant Evaluation, or DRIVE) to identify shared, identical-by-descent (IBD) large chromosomal segments in array data. Main Outcomes and Measures We sought to establish genetic relatedness among the probands and to use genomic segments underlying D76N to identify other potential carriers in BioVU. We then further studied the role of D76N in LQT5 pathogenesis. Results Genetic reconstruction of pedigrees and distant relatedness detection among clinic probands using DRIVE revealed shared recent common ancestry and identified a single long shared haplotype. Interrogation of the non-referral population in BioVU identified a further 23 subjects sharing this haplotype, and sequencing confirmed D76N carrier status in 22, all previously undiagnosed with LQT5. The QTc was prolonged in D76N carriers compared to BioVU controls, with 40% penetrance of QTc ≥ 480 msec. Among D76N carriers, a QTc polygenic score was additively associated with QTc prolongation. Conclusions and Relevance Detection of IBD shared chromosomal segments around D76N enabled identification of distantly related and previously undiagnosed rare-variant carriers, demonstrated the contribution of polygenic risk to monogenic disease penetrance, and further established LQT5 as a primary arrhythmia disorder. Analysis of shared chromosomal regions spanning disease-causing mutations can identify undiagnosed cases of genetic diseases.
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Affiliation(s)
| | - Hung-Hsin Chen
- Vanderbilt University Medical Center, Nashville, Tennessee
| | | | | | - James T Baker
- Vanderbilt University Medical Center, Nashville, Tennessee
| | | | | | - Chad D Huff
- University of Texas MD Anderson Cancer Center, Houston, Texas
| | - Dan M Roden
- Vanderbilt University Medical Center, Nashville, Tennessee
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5
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Campbell C, Faleel FDM, Scheyer MW, Haralu S, Williams PL, Carbo WD, Wilson-Taylor AS, Patel NH, Sanders CR, Lorigan GA, Sahu ID. Comparing the structural dynamics of the human KCNE3 in reconstituted micelle and lipid bilayered vesicle environments. BIOCHIMICA ET BIOPHYSICA ACTA. BIOMEMBRANES 2022; 1864:183974. [PMID: 35716725 DOI: 10.1016/j.bbamem.2022.183974] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/20/2021] [Revised: 05/12/2022] [Accepted: 05/25/2022] [Indexed: 06/15/2023]
Abstract
KCNE3 is a single transmembrane protein of the KCNE family that modulates the function and trafficking of several voltage-gated potassium channels, including KCNQ1. Structural studies of KCNE3 have been previously conducted in a wide range of model membrane mimics. However, it is important to assess the impact of the membrane mimics used on the observed conformation and dynamics. In this study, we have optimized a method for the reconstitution of the KCNE3 into POPC/POPG lipid bilayer vesicles for electron paramagnetic resonance (EPR) spectroscopy. Our CD spectroscopic data suggested that the degree of regular secondary structure for KCNE3 protein reconstituted into lipid bilayered vesicle is significantly higher than in DPC detergent micelles. Electron paramagnetic resonance (EPR) spectroscopy in combination with site-directed spin labeling (SDSL) was used to probe the structural dynamics of S49C, M59C, L67C, V85C, and S101C mutations of KCNE3 in both DPC micelles and in POPC/POPG lipid bilayered vesicles. Our CW-EPR power saturation data suggested that the site S74C is buried inside the lipid bilayered membrane while the site V85C is located outside the membrane, in contrast to DPC micelle results. These results suggest that the KCNE3 micelle structures need to be refined using data obtained in the lipid bilayered vesicles in order to ascertain the native structure of KCNE3. This work will provide guidelines for detailed structural studies of KCNE3 in a more native membrane environment and comparing the lipid bilayer results to the isotropic bicelle structure and to the KCNQ1-bound cryo-EM structure.
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Affiliation(s)
- Conner Campbell
- Natural Science Division, Campbellsville University, Campbellsville, KY, United States of America
| | | | - Matthew W Scheyer
- Natural Science Division, Campbellsville University, Campbellsville, KY, United States of America
| | - Samuel Haralu
- Natural Science Division, Campbellsville University, Campbellsville, KY, United States of America
| | - Patrick L Williams
- Natural Science Division, Campbellsville University, Campbellsville, KY, United States of America
| | - William David Carbo
- Natural Science Division, Campbellsville University, Campbellsville, KY, United States of America
| | | | - Nima H Patel
- Natural Science Division, Campbellsville University, Campbellsville, KY, United States of America
| | - Charles R Sanders
- Department of Biochemistry and Center for Structural Biology, Vanderbilt University, Nashville, TN, United States of America
| | - Gary A Lorigan
- Department of Chemistry and Biochemistry, Miami University, Oxford, OH, United States of America
| | - Indra D Sahu
- Natural Science Division, Campbellsville University, Campbellsville, KY, United States of America; Department of Chemistry and Biochemistry, Miami University, Oxford, OH, United States of America.
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6
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Abbott GW. Kv Channel Ancillary Subunits: Where Do We Go from Here? Physiology (Bethesda) 2022; 37:0. [PMID: 35797055 PMCID: PMC9394777 DOI: 10.1152/physiol.00005.2022] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2022] [Revised: 04/29/2022] [Accepted: 04/29/2022] [Indexed: 01/10/2023] Open
Abstract
Voltage-gated potassium (Kv) channels each comprise four pore-forming α-subunits that orchestrate essential duties such as voltage sensing and K+ selectivity and conductance. In vivo, however, Kv channels also incorporate regulatory subunits-some Kv channel specific, others more general modifiers of protein folding, trafficking, and function. Understanding all the above is essential for a complete picture of the role of Kv channels in physiology and disease.
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Affiliation(s)
- Geoffrey W Abbott
- Bioelectricity Laboratory, Department of Physiology and Biophysics, School of Medicine, University of California, Irvine, California
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7
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Botte M, Huber S, Bucher D, Klint JK, Rodríguez D, Tagmose L, Chami M, Cheng R, Hennig M, Abdul Rahman W. Apo and ligand-bound high resolution Cryo-EM structures of the human Kv3.1 channel reveal a novel binding site for positive modulators. PNAS NEXUS 2022; 1:pgac083. [PMID: 36741467 PMCID: PMC9896932 DOI: 10.1093/pnasnexus/pgac083] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/22/2022] [Accepted: 06/08/2022] [Indexed: 02/07/2023]
Abstract
Kv3 ion-channels constitute a class of functionally distinct voltage-gated ion channels characterized by their ability to fire at a high frequency. Several disease relevant mutants, together with biological data, suggest the importance of this class of ion channels as drug targets for CNS disorders, and several drug discovery efforts have been reported. Despite the increasing interest for this class of ion channels, no structure of a Kv3 channel has been reported yet. We have determined the cryo-EM structure of Kv3.1 at 2.6 Å resolution using full-length wild type protein. When compared to known structures for potassium channels from other classes, a novel domain organization is observed with the cytoplasmic T1 domain, containing a well-resolved Zinc site and displaying a rotation by 35°. This suggests a distinct cytoplasmic regulation mechanism for the Kv3.1 channel. A high resolution structure was obtained for Kv3.1 in complex with a novel positive modulator Lu AG00563. The structure reveals a novel ligand binding site for the Kv class of ion channels located between the voltage sensory domain and the channel pore, a region which constitutes a hotspot for disease causing mutations. The discovery of a novel binding site for a positive modulator of a voltage-gated potassium channel could shed light on the mechanism of action for these small molecule potentiators. This finding could enable structure-based drug design on these targets with high therapeutic potential for the treatment of multiple CNS disorders.
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Affiliation(s)
- Mathieu Botte
- leadXpro AG, PARK InnovAARE, 5234 Villigen, Switzerland
| | - Sophie Huber
- leadXpro AG, PARK InnovAARE, 5234 Villigen, Switzerland
| | - Denis Bucher
- leadXpro AG, PARK InnovAARE, 5234 Villigen, Switzerland
| | | | | | - Lena Tagmose
- H. Lundbeck A/S, Ottiliavej 9, 2500 Valby, Denmark
| | - Mohamed Chami
- BioEM laboratory, Biozentrum, University of Basel, Spitalstrasse 41, 4056, Basel, Switzerland
| | - Robert Cheng
- leadXpro AG, PARK InnovAARE, 5234 Villigen, Switzerland
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Asare IK, Galende AP, Garcia AB, Cruz MF, Moura ACM, Campbell CC, Scheyer M, Alao JP, Alston S, Kravats AN, Sanders CR, Lorigan GA, Sahu ID. Investigating Structural Dynamics of KCNE3 in Different Membrane Environments Using Molecular Dynamics Simulations. MEMBRANES 2022; 12:membranes12050469. [PMID: 35629795 PMCID: PMC9147993 DOI: 10.3390/membranes12050469] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/11/2022] [Revised: 03/21/2022] [Accepted: 04/21/2022] [Indexed: 11/27/2022]
Abstract
KCNE3 is a potassium channel accessory transmembrane protein that regulates the function of various voltage-gated potassium channels such as KCNQ1. KCNE3 plays an important role in the recycling of potassium ion by binding with KCNQ1. KCNE3 can be found in the small intestine, colon, and in the human heart. Despite its biological significance, there is little information on the structural dynamics of KCNE3 in native-like membrane environments. Molecular dynamics (MD) simulations are a widely used as a tool to study the conformational dynamics and interactions of proteins with lipid membranes. In this study, we have utilized all-atom molecular dynamics simulations to characterize the molecular motions and the interactions of KCNE3 in a bilayer composed of: a mixture of POPC and POPG lipids (3:1), POPC alone, and DMPC alone. Our MD simulation results suggested that the transmembrane domain (TMD) of KCNE3 is less flexible and more stable when compared to the N- and C-termini of KCNE3 in all three membrane environments. The conformational flexibility of N- and C-termini varies across these three lipid environments. The MD simulation results further suggested that the TMD of KCNE3 spans the membrane width, having residue A69 close to the center of the lipid bilayers and residues S57 and S82 close to the lipid bilayer membrane surfaces. These results are consistent with previous biophysical studies of KCNE3. The outcomes of these MD simulations will help design biophysical experiments and complement the experimental data obtained on KCNE3 to obtain a more detailed understanding of its structural dynamics in the native membrane environment.
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Affiliation(s)
- Isaac K. Asare
- Natural Science Division, Campbellsville University, Campbellsville, KY 42718, USA; (I.K.A.); (A.P.G.); (A.B.G.); (M.F.C.); (A.C.M.M.); (C.C.C.); (M.S.); (S.A.)
| | - Alberto Perez Galende
- Natural Science Division, Campbellsville University, Campbellsville, KY 42718, USA; (I.K.A.); (A.P.G.); (A.B.G.); (M.F.C.); (A.C.M.M.); (C.C.C.); (M.S.); (S.A.)
| | - Andres Bastidas Garcia
- Natural Science Division, Campbellsville University, Campbellsville, KY 42718, USA; (I.K.A.); (A.P.G.); (A.B.G.); (M.F.C.); (A.C.M.M.); (C.C.C.); (M.S.); (S.A.)
| | - Mateo Fernandez Cruz
- Natural Science Division, Campbellsville University, Campbellsville, KY 42718, USA; (I.K.A.); (A.P.G.); (A.B.G.); (M.F.C.); (A.C.M.M.); (C.C.C.); (M.S.); (S.A.)
| | - Anna Clara Miranda Moura
- Natural Science Division, Campbellsville University, Campbellsville, KY 42718, USA; (I.K.A.); (A.P.G.); (A.B.G.); (M.F.C.); (A.C.M.M.); (C.C.C.); (M.S.); (S.A.)
| | - Conner C. Campbell
- Natural Science Division, Campbellsville University, Campbellsville, KY 42718, USA; (I.K.A.); (A.P.G.); (A.B.G.); (M.F.C.); (A.C.M.M.); (C.C.C.); (M.S.); (S.A.)
| | - Matthew Scheyer
- Natural Science Division, Campbellsville University, Campbellsville, KY 42718, USA; (I.K.A.); (A.P.G.); (A.B.G.); (M.F.C.); (A.C.M.M.); (C.C.C.); (M.S.); (S.A.)
| | - John Paul Alao
- Department of Chemistry and Biochemistry, Miami University, Oxford, OH 45056, USA; (J.P.A.); (A.N.K.)
| | - Steve Alston
- Natural Science Division, Campbellsville University, Campbellsville, KY 42718, USA; (I.K.A.); (A.P.G.); (A.B.G.); (M.F.C.); (A.C.M.M.); (C.C.C.); (M.S.); (S.A.)
| | - Andrea N. Kravats
- Department of Chemistry and Biochemistry, Miami University, Oxford, OH 45056, USA; (J.P.A.); (A.N.K.)
| | - Charles R. Sanders
- Center for Structural Biology, Department of Biochemistry, Vanderbilt University, Nashville, TN 37232, USA;
| | - Gary A. Lorigan
- Department of Chemistry and Biochemistry, Miami University, Oxford, OH 45056, USA; (J.P.A.); (A.N.K.)
- Correspondence: (G.A.L.); (I.D.S.); Tel.: +1-(513)-529-2813 (G.A.L.); +1-(270)-789-5597 (I.D.S.)
| | - Indra D. Sahu
- Natural Science Division, Campbellsville University, Campbellsville, KY 42718, USA; (I.K.A.); (A.P.G.); (A.B.G.); (M.F.C.); (A.C.M.M.); (C.C.C.); (M.S.); (S.A.)
- Department of Chemistry and Biochemistry, Miami University, Oxford, OH 45056, USA; (J.P.A.); (A.N.K.)
- Correspondence: (G.A.L.); (I.D.S.); Tel.: +1-(513)-529-2813 (G.A.L.); +1-(270)-789-5597 (I.D.S.)
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9
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Kodirov SA, Brachmann J, Safonova TA, Zhuravlev VL. Inactivation of Native K Channels. J Membr Biol 2021; 255:13-31. [PMID: 34383081 DOI: 10.1007/s00232-021-00195-w] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2021] [Accepted: 06/30/2021] [Indexed: 01/12/2023]
Abstract
We have experimented with isolated cardiomyocytes of mollusks Helix. During the whole-cell patch-clamp recordings of K+ currents a considerable decrease in amplitude was observed upon repeated voltage steps at 0.96 Hz. For these experiments, ventricular cells were depolarized to identical + 20 mV from a holding potential of - 50 mV. The observed spontaneous inhibition of outward currents persisted in the presence of 4-aminopyridine, tetraethylammonium chloride or E-4031, the selective class III antiarrhythmic agent that blocks HERG channels. Similar tendency was retained when components of currents sensitive to either 4-AP or TEA were mathematically subtracted. Waveforms of currents sensitive to 1 and 10 micromolar concentration of E-4031 were distinct comprising prevailingly those activated during up to 200 ms pulses. The outward current activated by a voltage ramp at 60 mV x s-1 rate revealed an inward rectification around + 20 mV. This feature closely resembles those of the mammalian cardiac delayed rectifier IKr.
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Affiliation(s)
- Sodikdjon A Kodirov
- Department of Cardiology, Medical University Hospital Heidelberg, 69120, Heidelberg, Germany. .,Department of General Physiology, Saint Petersburg University, 199034, Saint Petersburg, Russia. .,Cardiovascular Division, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, 02115, USA. .,Department of Biophysics, Saint Petersburg University, 199034, Saint Petersburg, Russia. .,Instituto de Medicina Molecular João Lobo Antunes, Faculdade de Medicina da Universidade de Lisboa, Avenida Professor Egas Moniz, 1649-028, Lisboa, Portugal.
| | - Johannes Brachmann
- Department of Cardiology, Medical University Hospital Heidelberg, 69120, Heidelberg, Germany
| | - Tatiana A Safonova
- Department of General Physiology, Saint Petersburg University, 199034, Saint Petersburg, Russia
| | - Vladimir L Zhuravlev
- Department of Cardiology, Medical University Hospital Heidelberg, 69120, Heidelberg, Germany.,Department of General Physiology, Saint Petersburg University, 199034, Saint Petersburg, Russia
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Fenyves BG, Arnold A, Gharat VG, Haab C, Tishinov K, Peter F, de Quervain D, Papassotiropoulos A, Stetak A. Dual Role of an mps-2/KCNE-Dependent Pathway in Long-Term Memory and Age-Dependent Memory Decline. Curr Biol 2020; 31:527-539.e7. [PMID: 33259792 DOI: 10.1016/j.cub.2020.10.069] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2020] [Revised: 09/14/2020] [Accepted: 10/21/2020] [Indexed: 01/24/2023]
Abstract
Activity-dependent persistent changes in neuronal intrinsic excitability and synaptic strength are underlying learning and memory. Voltage-gated potassium (Kv) channels are potential regulators of memory and may be linked to age-dependent neuronal disfunction. MinK-related peptides (MiRPs) are conserved transmembrane proteins modulating Kv channels; however, their possible role in the regulation of memory and age-dependent memory decline are unknown. Here, we show that, in C. elegans, mps-2 is the sole member of the MiRP family that controls exclusively long-term associative memory (LTAM) in AVA neuron. In addition, we demonstrate that mps-2 also plays a critical role in age-dependent memory decline. In young adult worms, mps-2 is transcriptionally upregulated by CRH-1/cyclic AMP (cAMP)-response-binding protein (CREB) during LTAM, although the mps-2 baseline expression is CREB independent and instead, during aging, relies on nhr-66, which acts as an age-dependent repressor. Deletion of nhr-66 or its binding element in the mps-2 promoter prevents age-dependent transcriptional repression of mps-2 and memory decline. Finally, MPS-2 acts through the modulation of the Kv2.1/KVS-3 and Kv2.2/KVS-4 heteromeric potassium channels. Altogether, we describe a conserved MPS-2/KVS-3/KVS-4 pathway essential for LTAM and also for a programmed control of physiological age-dependent memory decline.
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Affiliation(s)
- Bank G Fenyves
- Transfaculty Research Platform Molecular and Cognitive Neurosciences, University of Basel, Birmannsgasse 8, 4055 Basel, Switzerland; Division of Molecular Neuroscience, Department of Psychology, University of Basel, Birmannsgasse 8, 4055 Basel, Switzerland; Department of Molecular Biology, Semmelweis University, Tűzoltó u. 37-47, 1094 Budapest, Hungary
| | - Andreas Arnold
- Transfaculty Research Platform Molecular and Cognitive Neurosciences, University of Basel, Birmannsgasse 8, 4055 Basel, Switzerland; Division of Molecular Neuroscience, Department of Psychology, University of Basel, Birmannsgasse 8, 4055 Basel, Switzerland
| | - Vaibhav G Gharat
- Transfaculty Research Platform Molecular and Cognitive Neurosciences, University of Basel, Birmannsgasse 8, 4055 Basel, Switzerland; Division of Molecular Neuroscience, Department of Psychology, University of Basel, Birmannsgasse 8, 4055 Basel, Switzerland
| | - Carmen Haab
- Division of Molecular Neuroscience, Department of Psychology, University of Basel, Birmannsgasse 8, 4055 Basel, Switzerland
| | - Kiril Tishinov
- Biozentrum, University of Basel, Klingelbergstrasse 50/70, 4056 Basel, Switzerland
| | - Fabian Peter
- Transfaculty Research Platform Molecular and Cognitive Neurosciences, University of Basel, Birmannsgasse 8, 4055 Basel, Switzerland; Division of Molecular Neuroscience, Department of Psychology, University of Basel, Birmannsgasse 8, 4055 Basel, Switzerland
| | - Dominique de Quervain
- Transfaculty Research Platform Molecular and Cognitive Neurosciences, University of Basel, Birmannsgasse 8, 4055 Basel, Switzerland; Division of Cognitive Neuroscience, Department of Psychology, University of Basel, Birmannsgasse 8, 4055 Basel, Switzerland; University Psychiatric Clinics, University of Basel, Wilhelm Klein-Strasse 27, 4055 Basel, Switzerland
| | - Andreas Papassotiropoulos
- Transfaculty Research Platform Molecular and Cognitive Neurosciences, University of Basel, Birmannsgasse 8, 4055 Basel, Switzerland; Division of Molecular Neuroscience, Department of Psychology, University of Basel, Birmannsgasse 8, 4055 Basel, Switzerland; Biozentrum, Life Sciences Training Facility, University of Basel, Klingelbergstrasse 50/70, 4056 Basel, Switzerland; University Psychiatric Clinics, University of Basel, Wilhelm Klein-Strasse 27, 4055 Basel, Switzerland
| | - Attila Stetak
- Transfaculty Research Platform Molecular and Cognitive Neurosciences, University of Basel, Birmannsgasse 8, 4055 Basel, Switzerland; Division of Molecular Neuroscience, Department of Psychology, University of Basel, Birmannsgasse 8, 4055 Basel, Switzerland; University Psychiatric Clinics, University of Basel, Wilhelm Klein-Strasse 27, 4055 Basel, Switzerland.
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11
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Lisewski U, Köhncke C, Schleussner L, Purfürst B, Lee SM, De Silva A, Manville RW, Abbott GW, Roepke TK. Hypochlorhydria reduces mortality in heart failure caused by Kcne2 gene deletion. FASEB J 2020; 34:10699-10719. [PMID: 32584506 DOI: 10.1096/fj.202000013rr] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2020] [Revised: 05/20/2020] [Accepted: 06/02/2020] [Indexed: 12/23/2022]
Abstract
Heart failure (HF) is an increasing global health crisis, affecting 40 million people and causing 50% mortality within 5 years of diagnosis. A fuller understanding of the genetic and environmental factors underlying HF, and novel therapeutic approaches to address it, are urgently warranted. Here, we discovered that cardiac-specific germline deletion in mice of potassium channel β subunit-encoding Kcne2 (Kcne2CS-/- ) causes dilated cardiomyopathy and terminal HF (median longevity, 28 weeks). Mice with global Kcne2 deletion (Kcne2Glo-/- ) exhibit multiple HF risk factors, yet, paradoxically survived over twice as long as Kcne2CS-/- mice. Global Kcne2 deletion, which inhibits gastric acid secretion, reduced the relative abundance of species within Bacteroidales, a bacterial order that positively correlates with increased lifetime risk of human cardiovascular disease. Strikingly, the proton-pump inhibitor omeprazole similarly altered the microbiome and delayed terminal HF in Kcne2CS-/- mice, increasing survival 10-fold at 44 weeks. Thus, genetic or pharmacologic induction of hypochlorhydria and decreased gut Bacteroidales species are associated with lifespan extension in a novel HF model.
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Affiliation(s)
| | - Clemens Köhncke
- Experimental and Clinical Research Center, Berlin, Germany.,Department of Cardiology, Campus Virchow - Universitätsmedizin Berlin, Berlin, Germany
| | | | - Bettina Purfürst
- Electron Microscopy Core Facility, Max-Delbrück-Center for Molecular Medicine, Berlin, Germany
| | - Soo Min Lee
- Bioelectricity Laboratory, Department of Physiology and Biophysics, School of Medicine, University of California, Irvine, CA, USA
| | - Angele De Silva
- Bioelectricity Laboratory, Department of Physiology and Biophysics, School of Medicine, University of California, Irvine, CA, USA
| | - Rían W Manville
- Bioelectricity Laboratory, Department of Physiology and Biophysics, School of Medicine, University of California, Irvine, CA, USA
| | - Geoffrey W Abbott
- Bioelectricity Laboratory, Department of Physiology and Biophysics, School of Medicine, University of California, Irvine, CA, USA
| | - Torsten K Roepke
- Experimental and Clinical Research Center, Berlin, Germany.,Department of Cardiology and Angiology, Campus Mitte, Charité - Universitätsmedizin Berlin, Berlin, Germany
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12
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Hu Z, Liu J, Zhou L, Tian X, Abbott GW. AKT and ERK1/2 activation via remote ischemic preconditioning prevents Kcne2-dependent sudden cardiac death. Physiol Rep 2020; 7:e13957. [PMID: 30737904 PMCID: PMC6368489 DOI: 10.14814/phy2.13957] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2018] [Accepted: 11/26/2018] [Indexed: 02/05/2023] Open
Abstract
Sudden cardiac death (SCD) is the leading global cause of mortality. SCD often arises from cardiac ischemia reperfusion (IR) injury, pathologic sequence variants within ion channel genes, or a combination of the two. Alternative approaches are needed to prevent or ameliorate ventricular arrhythmias linked to SCD. Here, we investigated the efficacy of remote ischemic preconditioning (RIPC) of the limb versus the liver in reducing ventricular arrhythmias in a mouse model of SCD. Mice lacking the Kcne2 gene, which encodes a potassium channel β subunit associated with acquired Long QT syndrome were exposed to IR injury via coronary ligation. This resulted in ventricular arrhythmias in all mice (15/15) and SCD in 5/15 mice during reperfusion. Strikingly, prior RIPC (limb or liver) greatly reduced the incidence and severity of all ventricular arrhythmias and completely prevented SCD. Biochemical and pharmacological analysis demonstrated that RIPC cardioprotection required ERK1/2 and/or AKT phosphorylation. A lack of alteration in GSK‐3β phosphorylation suggested against conventional reperfusion injury salvage kinase (RISK) signaling pathway protection. If replicated in human studies, limb RIPC could represent a noninvasive, nonpharmacological approach to limit dangerous ventricular arrhythmias associated with ischemia and/or channelopathy‐linked SCD.
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Affiliation(s)
- Zhaoyang Hu
- Laboratory of Anesthesiology & Critical Care Medicine, Translational Neuroscience Center, West China Hospital, Sichuan University, Chengdu, Sichuan, China
| | - Jin Liu
- Department of Anesthesiology, West China Hospital, Sichuan University, Chengdu, Sichuan, China
| | - Leng Zhou
- Department of Anesthesiology, West China Hospital, Sichuan University, Chengdu, Sichuan, China
| | - Xin Tian
- Laboratory of Anesthesiology & Critical Care Medicine, Translational Neuroscience Center, West China Hospital, Sichuan University, Chengdu, Sichuan, China
| | - Geoffrey W Abbott
- Bioelectricity Laboratory, Department of Physiology and Biophysics, School of Medicine, University of California, Irvine, California
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13
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Kodirov SA. Tale of tail current. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2019; 150:78-97. [PMID: 31238048 DOI: 10.1016/j.pbiomolbio.2019.06.002] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/15/2019] [Revised: 05/22/2019] [Accepted: 06/20/2019] [Indexed: 02/07/2023]
Abstract
The largest biomass of channel proteins is located in unicellular organisms and bacteria that have no organs. However, orchestrated bidirectional ionic currents across the cell membrane via the channels are important for the functioning of organs of organisms, and equally concern both fauna or flora. Several ion channels are activated in the course of action potentials. One of the hallmarks of voltage-dependent channels is a 'tail current' - deactivation as observed after prior and sufficient activation predominantly at more depolarized potentials e.g. for Kv while upon hyperpolarization for HCN α subunits. Tail current also reflects the timing of channel closure that is initiated upon termination of stimuli. Finally, deactivation of currents during repolarization could be a selective estimate for given channel as in case of HERG, if dedicated long and more depolarized 'tail pulse' is used. Since from a holding potential of e.g. -70 mV are often a family of outward K+ currents comprising IA and IK are simultaneously activated in native cells.
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Affiliation(s)
- Sodikdjon A Kodirov
- Pavlov Institute of Physiology, Russian Academy of Sciences, Saint Petersburg, Russia; Cardiovascular Division, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, 02115, USA; Almazov Federal Heart, Blood and Endocrinology Centre, Saint Petersburg, 197341, Russia; Institute of Experimental Medicine, I. P. Pavlov Department of Physiology, Russian Academy of Medical Sciences, Saint Petersburg, Russia; Laboratory of Emotions' Neurobiology, Nencki Institute of Experimental Biology, Polish Academy of Sciences, Warsaw, 02-093, Poland.
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14
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Haworth AS, Brackenbury WJ. Emerging roles for multifunctional ion channel auxiliary subunits in cancer. Cell Calcium 2019; 80:125-140. [PMID: 31071485 PMCID: PMC6553682 DOI: 10.1016/j.ceca.2019.04.005] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2019] [Revised: 04/16/2019] [Accepted: 04/16/2019] [Indexed: 02/07/2023]
Abstract
Several superfamilies of plasma membrane channels which regulate transmembrane ion flux have also been shown to regulate a multitude of cellular processes, including proliferation and migration. Ion channels are typically multimeric complexes consisting of conducting subunits and auxiliary, non-conducting subunits. Auxiliary subunits modulate the function of conducting subunits and have putative non-conducting roles, further expanding the repertoire of cellular processes governed by ion channel complexes to processes such as transcellular adhesion and gene transcription. Given this expansive influence of ion channels on cellular behaviour it is perhaps no surprise that aberrant ion channel expression is a common occurrence in cancer. This review will focus on the conducting and non-conducting roles of the auxiliary subunits of various Ca2+, K+, Na+ and Cl- channels and the burgeoning evidence linking such auxiliary subunits to cancer. Several subunits are upregulated (e.g. Cavβ, Cavγ) and downregulated (e.g. Kvβ) in cancer, while other subunits have been functionally implicated as oncogenes (e.g. Navβ1, Cavα2δ1) and tumour suppressor genes (e.g. CLCA2, KCNE2, BKγ1) based on in vivo studies. The strengthening link between ion channel auxiliary subunits and cancer has exposed these subunits as potential biomarkers and therapeutic targets. However further mechanistic understanding is required into how these subunits contribute to tumour progression before their therapeutic potential can be fully realised.
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Affiliation(s)
- Alexander S Haworth
- Department of Biology, University of York, Heslington, York, YO10 5DD, UK; York Biomedical Research Institute, University of York, Heslington, York, YO10 5DD, UK
| | - William J Brackenbury
- Department of Biology, University of York, Heslington, York, YO10 5DD, UK; York Biomedical Research Institute, University of York, Heslington, York, YO10 5DD, UK.
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15
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Kaczmarek LK, Zhang Y. Kv3 Channels: Enablers of Rapid Firing, Neurotransmitter Release, and Neuronal Endurance. Physiol Rev 2017; 97:1431-1468. [PMID: 28904001 PMCID: PMC6151494 DOI: 10.1152/physrev.00002.2017] [Citation(s) in RCA: 107] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2017] [Revised: 04/24/2017] [Accepted: 05/05/2017] [Indexed: 12/11/2022] Open
Abstract
The intrinsic electrical characteristics of different types of neurons are shaped by the K+ channels they express. From among the more than 70 different K+ channel genes expressed in neurons, Kv3 family voltage-dependent K+ channels are uniquely associated with the ability of certain neurons to fire action potentials and to release neurotransmitter at high rates of up to 1,000 Hz. In general, the four Kv3 channels Kv3.1-Kv3.4 share the property of activating and deactivating rapidly at potentials more positive than other channels. Each Kv3 channel gene can generate multiple protein isoforms, which contribute to the high-frequency firing of neurons such as auditory brain stem neurons, fast-spiking GABAergic interneurons, and Purkinje cells of the cerebellum, and to regulation of neurotransmitter release at the terminals of many neurons. The different Kv3 channels have unique expression patterns and biophysical properties and are regulated in different ways by protein kinases. In this review, we cover the function, localization, and modulation of Kv3 channels and describe how levels and properties of the channels are altered by changes in ongoing neuronal activity. We also cover how the protein-protein interaction of these channels with other proteins affects neuronal functions, and how mutations or abnormal regulation of Kv3 channels are associated with neurological disorders such as ataxias, epilepsies, schizophrenia, and Alzheimer's disease.
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Affiliation(s)
- Leonard K Kaczmarek
- Departments of Pharmacology and of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut
| | - Yalan Zhang
- Departments of Pharmacology and of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut
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16
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King EC, Patel V, Anand M, Zhao X, Crump SM, Hu Z, Weisleder N, Abbott GW. Targeted deletion of Kcne3 impairs skeletal muscle function in mice. FASEB J 2017; 31:2937-2947. [PMID: 28356343 DOI: 10.1096/fj.201600965rr] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2016] [Accepted: 03/13/2017] [Indexed: 11/11/2022]
Abstract
KCNE3 (MiRP2) forms heteromeric voltage-gated K+ channels with the skeletal muscle-expressed KCNC4 (Kv3.4) α subunit. KCNE3 was the first reported skeletal muscle K+ channel disease gene, but the requirement for KCNE3 in skeletal muscle has been questioned. Here, we confirmed KCNE3 transcript and protein expression in mouse skeletal muscle using Kcne3-/- tissue as a negative control. Whole-transcript microarray analysis (770,317 probes, interrogating 28,853 transcripts) findings were consistent with Kcne3 deletion increasing gastrocnemius oxidative metabolic gene expression and the proportion of type IIa fast-twitch oxidative muscle fibers, which was verified using immunofluorescence. The down-regulated transcript set overlapped with muscle unloading gene expression profiles (≥1.5-fold change; P < 0.05). Gastrocnemius K+ channel α subunit remodeling arising from Kcne3 deletion was highly specific, involving just 3 of 69 α subunit genes probed: known KCNE3 partners KCNC4 and KCNH2 (mERG) were down-regulated, and KCNK4 (TRAAK) was up-regulated (P < 0.05). Functionally, Kcne3-/- mice exhibited abnormal hind-limb clasping upon tail suspension (63% of Kcne3-/- mice ≥10-mo-old vs. 0% age-matched Kcne3+/+ littermates). Whereas 5 of 5 Kcne3+/+ mice exhibited the typical biphasic decline in contractile force with repetitive stimuli of hind-limb muscle, both in vivo and in vitro, this was absent in 6 of 6 Kcne3-/- mice tested. Finally, myoblasts isolated from Kcne3-/- mice exhibit faster-inactivating and smaller sustained outward currents than those from Kcne3+/+ mice. Thus, Kcne3 deletion impairs skeletal muscle function in mice.-King, E. C., Patel, V., Anand, M., Zhao, X., Crump, S. M., Hu, Z., Weisleder, N., Abbott, G. W. Targeted deletion of Kcne3 impairs skeletal muscle function in mice.
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Affiliation(s)
- Elizabeth C King
- Department of Pharmacology, Weill Medical College of Cornell University, New York, New York, USA
| | - Vishal Patel
- Department of Physiology and Biophysics, University of Medicine and Dentistry of New Jersey-Robert Wood Johnson Medical School, Piscataway, New Jersey, USA
| | - Marie Anand
- Department of Pharmacology, School of Medicine, University of California, Irvine, California, USA.,Department of Physiology and Biophysics, School of Medicine, University of California, Irvine, Irvine, California, USA
| | - Xiaoli Zhao
- Department of Physiology and Biophysics, University of Medicine and Dentistry of New Jersey-Robert Wood Johnson Medical School, Piscataway, New Jersey, USA
| | - Shawn M Crump
- Department of Pharmacology, School of Medicine, University of California, Irvine, California, USA.,Department of Physiology and Biophysics, School of Medicine, University of California, Irvine, Irvine, California, USA
| | - Zhaoyang Hu
- Department of Pharmacology, School of Medicine, University of California, Irvine, California, USA.,Department of Physiology and Biophysics, School of Medicine, University of California, Irvine, Irvine, California, USA
| | - Noah Weisleder
- Department of Physiology and Biophysics, University of Medicine and Dentistry of New Jersey-Robert Wood Johnson Medical School, Piscataway, New Jersey, USA;
| | - Geoffrey W Abbott
- Department of Pharmacology, School of Medicine, University of California, Irvine, California, USA; .,Department of Physiology and Biophysics, School of Medicine, University of California, Irvine, Irvine, California, USA
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17
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Lee SM, Baik J, Nguyen D, Nguyen V, Liu S, Hu Z, Abbott GW. Kcne2 deletion impairs insulin secretion and causes type 2 diabetes mellitus. FASEB J 2017; 31:2674-2685. [PMID: 28280005 DOI: 10.1096/fj.201601347] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2016] [Accepted: 02/21/2017] [Indexed: 02/05/2023]
Abstract
Type 2 diabetes mellitus (T2DM) represents a rapidly increasing threat to global public health. T2DM arises largely from obesity, poor diet, and lack of exercise, but it also involves genetic predisposition. Here we report that the KCNE2 potassium channel transmembrane regulatory subunit is expressed in human and mouse pancreatic β cells. Kcne2 deletion in mice impaired glucose tolerance as early as 5 wk of age in pups fed a Western diet, ultimately causing diabetes. In adult mice fed normal chow, skeletal muscle expression of insulin receptor β and insulin receptor substrate 1 were down-regulated 2-fold by Kcne2 deletion, characteristic of T2DM. Kcne2 deletion also caused extensive pancreatic transcriptome changes consistent with facets of T2DM, including endoplasmic reticulum stress, inflammation, and hyperproliferation. Kcne2 deletion impaired β-cell insulin secretion in vitro up to 8-fold and diminished β-cell peak outward K+ current at positive membrane potentials, but also left-shifted its voltage dependence and slowed inactivation. Interestingly, we also observed an aging-dependent reduction in β-cell outward currents in both Kcne2+/+ and Kcne2-/- mice. Our results demonstrate that KCNE2 is required for normal β-cell electrical activity and insulin secretion, and that Kcne2 deletion causes T2DM. KCNE2 may regulate multiple K+ channels in β cells, including the T2DM-linked KCNQ1 potassium channel α subunit.-Lee, S. M., Baik, J., Nguyen, D., Nguyen, V., Liu, S., Hu, Z., Abbott, G. W. Kcne2 deletion impairs insulin secretion and causes type 2 diabetes mellitus.
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Affiliation(s)
- Soo Min Lee
- Bioelectricity Laboratory, Department of Pharmacology and Department of Physiology and Biophysics, School of Medicine, University of California, Irvine, California, USA
| | - Jasmine Baik
- Bioelectricity Laboratory, Department of Pharmacology and Department of Physiology and Biophysics, School of Medicine, University of California, Irvine, California, USA
| | - Dara Nguyen
- Bioelectricity Laboratory, Department of Pharmacology and Department of Physiology and Biophysics, School of Medicine, University of California, Irvine, California, USA
| | - Victoria Nguyen
- Bioelectricity Laboratory, Department of Pharmacology and Department of Physiology and Biophysics, School of Medicine, University of California, Irvine, California, USA
| | - Shiwei Liu
- Bioelectricity Laboratory, Department of Pharmacology and Department of Physiology and Biophysics, School of Medicine, University of California, Irvine, California, USA
| | - Zhaoyang Hu
- Laboratory of Anesthesiology and Critical Care Medicine, Translational Neuroscience Center, West China Hospital, Sichuan University, Chengdu, Sichuan, China
| | - Geoffrey W Abbott
- Bioelectricity Laboratory, Department of Pharmacology and Department of Physiology and Biophysics, School of Medicine, University of California, Irvine, California, USA;
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18
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Kroncke BM, Van Horn WD, Smith J, Kang C, Welch RC, Song Y, Nannemann DP, Taylor KC, Sisco NJ, George AL, Meiler J, Vanoye CG, Sanders CR. Structural basis for KCNE3 modulation of potassium recycling in epithelia. SCIENCE ADVANCES 2016; 2:e1501228. [PMID: 27626070 PMCID: PMC5017827 DOI: 10.1126/sciadv.1501228] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/03/2015] [Accepted: 08/10/2016] [Indexed: 05/25/2023]
Abstract
The single-span membrane protein KCNE3 modulates a variety of voltage-gated ion channels in diverse biological contexts. In epithelial cells, KCNE3 regulates the function of the KCNQ1 potassium ion (K(+)) channel to enable K(+) recycling coupled to transepithelial chloride ion (Cl(-)) secretion, a physiologically critical cellular transport process in various organs and whose malfunction causes diseases, such as cystic fibrosis (CF), cholera, and pulmonary edema. Structural, computational, biochemical, and electrophysiological studies lead to an atomically explicit integrative structural model of the KCNE3-KCNQ1 complex that explains how KCNE3 induces the constitutive activation of KCNQ1 channel activity, a crucial component in K(+) recycling. Central to this mechanism are direct interactions of KCNE3 residues at both ends of its transmembrane domain with residues on the intra- and extracellular ends of the KCNQ1 voltage-sensing domain S4 helix. These interactions appear to stabilize the activated "up" state configuration of S4, a prerequisite for full opening of the KCNQ1 channel gate. In addition, the integrative structural model was used to guide electrophysiological studies that illuminate the molecular basis for how estrogen exacerbates CF lung disease in female patients, a phenomenon known as the "CF gender gap."
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Affiliation(s)
- Brett M. Kroncke
- Department of Biochemistry, Vanderbilt University, Nashville, TN 37240, USA
- Center for Structural Biology, Vanderbilt University, Nashville, TN 37240, USA
| | - Wade D. Van Horn
- Department of Biochemistry, Vanderbilt University, Nashville, TN 37240, USA
- Center for Structural Biology, Vanderbilt University, Nashville, TN 37240, USA
- School of Molecular Sciences, Arizona State University, Tempe, AZ 85287, USA
- Biodesign Institute, Arizona State University, Tempe, AZ 85287, USA
- Center for Personalized Diagnostics, Arizona State University, Tempe, AZ 85287, USA
| | - Jarrod Smith
- Department of Biochemistry, Vanderbilt University, Nashville, TN 37240, USA
- Center for Structural Biology, Vanderbilt University, Nashville, TN 37240, USA
| | - CongBao Kang
- Department of Biochemistry, Vanderbilt University, Nashville, TN 37240, USA
- Center for Structural Biology, Vanderbilt University, Nashville, TN 37240, USA
- Experimental Therapeutics Centre, Agency for Science Technology and Research, Singapore, Singapore
| | - Richard C. Welch
- Department of Medicine, Vanderbilt University Medical Center, Nashville, TN 37240, USA
| | - Yuanli Song
- Department of Biochemistry, Vanderbilt University, Nashville, TN 37240, USA
- Center for Structural Biology, Vanderbilt University, Nashville, TN 37240, USA
| | - David P. Nannemann
- Center for Structural Biology, Vanderbilt University, Nashville, TN 37240, USA
- Department of Chemistry, Vanderbilt University, Nashville, TN 37235, USA
| | - Keenan C. Taylor
- Department of Biochemistry, Vanderbilt University, Nashville, TN 37240, USA
- Center for Structural Biology, Vanderbilt University, Nashville, TN 37240, USA
| | - Nicholas J. Sisco
- School of Molecular Sciences, Arizona State University, Tempe, AZ 85287, USA
- Biodesign Institute, Arizona State University, Tempe, AZ 85287, USA
- Center for Personalized Diagnostics, Arizona State University, Tempe, AZ 85287, USA
| | - Alfred L. George
- Department of Pharmacology, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA
| | - Jens Meiler
- Center for Structural Biology, Vanderbilt University, Nashville, TN 37240, USA
- Department of Chemistry, Vanderbilt University, Nashville, TN 37235, USA
| | - Carlos G. Vanoye
- Department of Pharmacology, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA
| | - Charles R. Sanders
- Department of Biochemistry, Vanderbilt University, Nashville, TN 37240, USA
- Center for Structural Biology, Vanderbilt University, Nashville, TN 37240, USA
- Department of Medicine, Vanderbilt University Medical Center, Nashville, TN 37240, USA
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19
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Kv3.1 uses a timely resurgent K(+) current to secure action potential repolarization. Nat Commun 2015; 6:10173. [PMID: 26673941 PMCID: PMC4703866 DOI: 10.1038/ncomms10173] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2015] [Accepted: 11/10/2015] [Indexed: 01/07/2023] Open
Abstract
High-frequency action potential (AP) transmission is essential for rapid information processing in the central nervous system. Voltage-dependent Kv3 channels play an important role in this process thanks to their high activation threshold and fast closure kinetics, which reduce the neuron's refractory period. However, premature Kv3 channel closure leads to incomplete membrane repolarization, preventing sustainable AP propagation. Here, we demonstrate that Kv3.1b channels solve this problem by producing resurgent K+ currents during repolarization, thus ensuring enough repolarizing power to terminate each AP. Unlike previously described resurgent Na+ and K+ currents, Kv3.1b's resurgent current does not originate from recovery of channel block or inactivation but results from a unique combination of steep voltage-dependent gating kinetics and ultra-fast voltage-sensor relaxation. These distinct properties are readily transferrable onto an orthologue Kv channel by transplanting the voltage-sensor's S3–S4 loop, providing molecular insights into the mechanism by which Kv3 channels contribute to high-frequency AP transmission. Kv3 potassium channels have an important role in the repolarization of action potentials in fast-spiking neurons. Here, the authors use electrophysiology and modelling to report on an interesting mechanism that might explain their gating behaviour.
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20
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Abbott GW. KCNE1 and KCNE3: The yin and yang of voltage-gated K(+) channel regulation. Gene 2015; 576:1-13. [PMID: 26410412 DOI: 10.1016/j.gene.2015.09.059] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2015] [Revised: 09/03/2015] [Accepted: 09/22/2015] [Indexed: 12/20/2022]
Abstract
The human KCNE gene family comprises five genes encoding single transmembrane-spanning ion channel regulatory subunits. The primary function of KCNE subunits appears to be regulation of voltage-gated potassium (Kv) channels, and the best-understood KCNE complexes are with the KCNQ1 Kv α subunit. Here, we review the often opposite effects of KCNE1 and KCNE3 on Kv channel biology, with an emphasis on regulation of KCNQ1. Slow-activating IKs channel complexes formed by KCNQ1 and KCNE1 are essential for human ventricular myocyte repolarization, while constitutively active KCNQ1-KCNE3 channels are important in the intestine. Inherited sequence variants in human KCNE1 and KCNE3 cause cardiac arrhythmias but by different mechanisms, and each is important for hearing in unique ways. Because of their contrasting effects on KCNQ1 function, KCNE1 and KCNE3 have proved invaluable tools in the mechanistic understanding of how channel gating can be manipulated, and each may also provide a window into novel insights and new therapeutic opportunities in K(+) channel pharmacology. Finally, findings from studies of Kcne1(-/-) and Kcne3(-/-) mouse lines serve to illustrate the complexity of KCNE biology and KCNE-linked disease states.
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Affiliation(s)
- Geoffrey W Abbott
- Bioelectricity Laboratory, Dept. of Pharmacology and Dept. of Physiology and Biophysics, School of Medicine, University of California, Irvine, CA, USA; 360 Medical Surge II, Dept. of Pharmacology, School of Medicine, University of California, Irvine, CA 92697, USA.
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A distinct three-helix centipede toxin SSD609 inhibits I(ks) channels by interacting with the KCNE1 auxiliary subunit. Sci Rep 2015; 5:13399. [PMID: 26307551 PMCID: PMC4549624 DOI: 10.1038/srep13399] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2015] [Accepted: 07/24/2015] [Indexed: 01/03/2023] Open
Abstract
KCNE1 is a single-span transmembrane auxiliary protein that modulates the voltage-gated potassium channel KCNQ1. The KCNQ1/KCNE1 complex in cardiomyocytes exhibited slow activated potassium (I(ks)) currents. Recently, a novel 47-residue polypeptide toxin SSD609 was purified from Scolopendra subspinipes dehaani venom and showed I(ks) current inhibition. Here, chemically synthesized SSD609 was shown to exert I(ks) inhibition in extracted guinea pig cardiomyocytes and KCNQ1/KCNE1 current attenuation in CHO cells. The K(+) current attenuation of SSD609 showed decent selectivity among different auxiliary subunits. Solution nuclear magnetic resonance analysis of SSD609 revealed a distinctive three-helix conformation that was stabilized by a new disulfide bonding pattern as well as segregated surface charge distribution. Structure-activity studies demonstrated that negatively charged Glu19 in the amphipathic extracellular helix of KCNE1 was the key residue that interacted with SSD609. The distinctive three-helix centipede toxin SSD609 is known to be the first polypeptide toxin acting on channel auxiliary subunit KCNE1, which suggests a new type of pharmacological regulation for ion channels in cardiomyocytes.
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Graeff M, Wenkel S. Regulation of protein function by interfering protein species. Biomol Concepts 2014; 3:71-8. [PMID: 25436525 DOI: 10.1515/bmc.2011.053] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2011] [Accepted: 11/02/2011] [Indexed: 11/15/2022] Open
Abstract
Abstract Most proteins do not function alone but act in protein complexes. For several transcriptional regulators, it is known that they have to homo- or heterodimerize prior to DNA binding. These protein interactions occur through defined protein-protein-interaction (PPI) domains. More than two decades ago, inhibitor of DNA binding (ID), a small protein containing a single helix-loop-helix (HLH) motif was identified. ID is able to interact with the larger DNA-binding basic helix-loop-helix (bHLH) transcription factors, but due to the lack of the basic domain required for DNA binding, ID traps bHLH proteins in non-functional complexes. Work in plants has, in the recent years, identified more small proteins acting in analogy to ID. A hallmark of these small negative acting proteins is the presence of a protein-interaction domain and the absence of other functional domains required for transcriptional activation or DNA binding. Because these proteins are often very small and function in analogy to microRNAs (meaning in a dominant-negative manner), we propose to refer to these protein species as 'microProteins' (miPs). miPs can be encoded in the genome as individual transcription units but can also be produced by alternative splicing. Other negatively acting proteins, consisting of more than one domain, have also been identified, and we propose to call these proteins 'interfering proteins' (iPs). The aim of this review is to state more precisely how to discriminate miPs from iPs. Therefore, we will highlight recent findings on both protein species and describe their mode of action. Furthermore, miPs have the ability to regulate proteins of diverse functions, emphasizing their value as biotechnological tools.
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Mutational Consequences of Aberrant Ion Channels in Neurological Disorders. J Membr Biol 2014; 247:1083-127. [DOI: 10.1007/s00232-014-9716-2] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2014] [Accepted: 07/25/2014] [Indexed: 12/25/2022]
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Wang W, Kim HJ, Lee JH, Wong V, Sihn CR, Lv P, Perez Flores MC, Mousavi-Nik A, Doyle KJ, Xu Y, Yamoah EN. Functional significance of K+ channel β-subunit KCNE3 in auditory neurons. J Biol Chem 2014; 289:16802-13. [PMID: 24727472 DOI: 10.1074/jbc.m113.545236] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
The KCNE3 β-subunit interacts with and regulates the voltage-dependent gating, kinetics, and pharmacology of a variety of Kv channels in neurons. Because a single neuron may express multiple KCNE3 partners, it is impossible to predict the overall functional relevance of the single transmembrane domain peptide on the pore-forming K(+) channel subunits with which it associates. In the inner ear, the role of KCNE3 is undefined, despite its association with Meniere disease and tinnitus. To gain insights on the functional significance of KCNE3 in auditory neurons, we examined the properties of spiral ganglion neurons (SGNs) in Kcne3 null mutant neurons relative to their age-matched controls. We demonstrate that null deletion of Kcne3 abolishes characteristic wide variations in the resting membrane potentials of SGNs and yields age-dependent alterations in action potential and firing properties of neurons along the contour of the cochlear axis, in comparison with age-matched wild-type neurons. The properties of basal SGNs were markedly altered in Kcne3(-/-) mice compared with the wild-type controls; these include reduced action potential latency, amplitude, and increased firing frequency. Analyses of the underlying conductance demonstrate that null mutation of Kcne3 results in enhanced outward K(+) currents, which is sufficient to explain the ensuing membrane potential changes. Additionally, we have demonstrated that KCNE3 may regulate the activity of Kv4.2 channels in SGNs. Finally, there were developmentally mediated compensatory changes that occurred such that, by 8 weeks after birth, the electrical properties of the null mutant neurons were virtually indistinguishable from the wild-type neurons, suggesting that ion channel remodeling in auditory neurons progresses beyond hearing onset.
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Affiliation(s)
- Wenying Wang
- From the Key Laboratory of Neural and Vascular Biology, Ministry of Education, Hebei Medical University, Shijiazhuang 050017, China, the Department of Anesthesiology and Pain Medicine, Program in Communication and Sensory Sciences, University of California at Davis School of Medicine, Davis, California 95618, and
| | - Hyo Jeong Kim
- the Department of Anesthesiology and Pain Medicine, Program in Communication and Sensory Sciences, University of California at Davis School of Medicine, Davis, California 95618, and
| | - Jeong-Han Lee
- the Department of Anesthesiology and Pain Medicine, Program in Communication and Sensory Sciences, University of California at Davis School of Medicine, Davis, California 95618, and
| | - Victor Wong
- the Department of Anesthesiology and Pain Medicine, Program in Communication and Sensory Sciences, University of California at Davis School of Medicine, Davis, California 95618, and
| | - Choong-Ryoul Sihn
- the Department of Anesthesiology and Pain Medicine, Program in Communication and Sensory Sciences, University of California at Davis School of Medicine, Davis, California 95618, and
| | - Ping Lv
- the Department of Anesthesiology and Pain Medicine, Program in Communication and Sensory Sciences, University of California at Davis School of Medicine, Davis, California 95618, and the Department of Pharmacology, Hebei Medical University, Shijiazhuang 050017, China
| | - Maria Cristina Perez Flores
- the Department of Anesthesiology and Pain Medicine, Program in Communication and Sensory Sciences, University of California at Davis School of Medicine, Davis, California 95618, and
| | - Atefeh Mousavi-Nik
- the Department of Anesthesiology and Pain Medicine, Program in Communication and Sensory Sciences, University of California at Davis School of Medicine, Davis, California 95618, and
| | - Karen Jo Doyle
- the Department of Anesthesiology and Pain Medicine, Program in Communication and Sensory Sciences, University of California at Davis School of Medicine, Davis, California 95618, and
| | - Yanfang Xu
- From the Key Laboratory of Neural and Vascular Biology, Ministry of Education, Hebei Medical University, Shijiazhuang 050017, China,
| | - Ebenezer N Yamoah
- the Department of Anesthesiology and Pain Medicine, Program in Communication and Sensory Sciences, University of California at Davis School of Medicine, Davis, California 95618, and
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Cotella D, Hernandez-Enriquez B, Duan Z, Wu X, Gazula VR, Brown MR, Kaczmarek LK, Sesti F. An evolutionarily conserved mode of modulation of Shaw-like K⁺ channels. FASEB J 2012; 27:1381-93. [PMID: 23233530 DOI: 10.1096/fj.12-222778] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Voltage-gated K(+) channels of the Shaw family (also known as the KCNC or Kv3 family) play pivotal roles in mammalian brains, and genetic or pharmacological disruption of their activities in mice results in a spectrum of behavioral defects. We have used the model system of Caenorhabditis elegans to elucidate conserved molecular mechanisms that regulate these channels. We have now found that the C. elegans Shaw channel KHT-1, and its mammalian homologue, murine Kv3.1b, are both modulated by acid phosphatases. Thus, the C. elegans phosphatase ACP-2 is stably associated with KHT-1, while its mammalian homolog, prostatic acid phosphatase (PAP; also known as ACPP-201) stably associates with murine Kv3.1b K(+) channels in vitro and in vivo. In biochemical experiments both phosphatases were able to reverse phosphorylation of their associated channel. The effect of phosphorylation on both channels is to produce a decrease in current amplitude and electrophysiological analyses demonstrated that dephosphorylation reversed the effects of phosphorylation on the magnitude of the macroscopic currents. ACP-2 and KHT-1 were colocalized in the nervous system of C. elegans and, in the mouse nervous system, PAP and Kv3.1b were colocalized in subsets of neurons, including in the brain stem and the ventricular zone. Taken together, this body of evidence suggests that acid phosphatases are general regulatory partners of Shaw-like K(+) channels.
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Affiliation(s)
- Diego Cotella
- Department of Neuroscience and Cell Biology, Robert Wood Johnson Medical School, University of Medicine and Dentistry of New Jersey, Piscataway, New Jersey 08854, USA
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Abstract
PURPOSE OF REVIEW The Brugada syndrome has been investigated in depth since its description in 1992 both on a clinical and on a basic research level. Since the discovery of the first genetic defect in 1998, several genes have been subsequently identified. However, to date all these genes together explain only 30% of the cases, indicating that there is still an important amount of work to be done to totally unravel the genetic basis of this lethal disease. In the present study, we will focus on recent achievements in the genetic basis of this disease. RECENT FINDINGS In 2009, several additional genetic mutations have been associated with the disease. Additionally, a common variant has been described as a genetic modulator of Brugada syndrome among carriers of a SCN5A mutation. SUMMARY The number of scientific publications dealing with the syndrome has continued to increase substantially in recent years. New polymorphisms, mutations and genes associated with the disease have been described. However, despite the advances, knowledge of the genetic determinants of the Brugada syndrome remains limited.
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Abstract
KCNE2, originally designated MinK-related peptide 1 (MiRP1), belongs to a five-strong family of potassium channel ancillary (β) subunits that, despite the diminutive size of the family and its members, has loomed large in the field of ion channel physiology. KCNE2 dictates K (+) channel gating, conductance, α subunit composition, trafficking and pharmacology, and also modifies functional properties of monovalent cation-nonselective HCN channels. The Kcne2 (-/-) mouse exhibits cardiac arrhythmia and hypertrophy, achlorhydria, gastric neoplasia, hypothyroidism, alopecia, stunted growth and choroid plexus epithelial dysfunction, illustrating the breadth and depth of the influence of KCNE2, mutations which are also associated with human cardiac arrhythmias. Here, the modus operandi and physiological roles of this potent regulator of membrane excitability and ion secretion are reviewed with particular emphasis on the ability of KCNE2 to shape the electrophysiological landscape of both excitable and non-excitable cells.
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Affiliation(s)
- Geoffrey W Abbott
- Departments of Pharmacology and Physiology and Biophysics, University of California, Irvine, Irvine, CA, USA.
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The voltage-gated channel accessory protein KCNE2: multiple ion channel partners, multiple ways to long QT syndrome. Expert Rev Mol Med 2011; 13:e38. [DOI: 10.1017/s1462399411002092] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
The single-pass transmembrane protein KCNE2 or MIRP1 was once thought to be the missing accessory protein that combined with hERG to fully recapitulate the cardiac repolarising current IKr. As a result of this role, it was an easy next step to associate mutations in KCNE2 to long QT syndrome, in which there is delayed repolarisation of the heart. Since that time however, KCNE2 has been shown to modify the behaviour of several other channels and currents, and its role in the heart and in the aetiology of long QT syndrome has become less clear. In this article, we review the known interactions of the KCNE2 protein and the resulting functional effects, and the effects of mutations in KCNE2 and their clinical role.
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Kanda VA, Lewis A, Xu X, Abbott GW. KCNE1 and KCNE2 provide a checkpoint governing voltage-gated potassium channel α-subunit composition. Biophys J 2011; 101:1364-75. [PMID: 21943417 DOI: 10.1016/j.bpj.2011.08.014] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2011] [Revised: 07/25/2011] [Accepted: 08/05/2011] [Indexed: 11/28/2022] Open
Abstract
Voltage-gated potassium (Kv) currents generated by N-type α-subunit homotetramers inactivate rapidly because an N-terminal ball domain blocks the channel pore after activation. Hence, the inactivation rate of heterotetrameric channels comprising both N-type and non-N-type (delayed rectifier) α-subunits depends upon the number of N-type α-subunits in the complex. As Kv channel inactivation and inactivation recovery rates regulate cellular excitability, the composition and expression of these heterotetrameric complexes are expected to be tightly regulated. In a companion article, we showed that the single transmembrane segment ancillary (β) subunits KCNE1 and KCNE2 suppress currents generated by homomeric Kv1.4, Kv3.3, and Kv3.4 channels, by trapping them early in the secretory pathway. Here, we show that this trapping is prevented by coassembly of the N-type α-subunits with intra-subfamily delayed rectifier α-subunits. Extra-subfamily delayed rectifier α-subunits, regardless of their capacity to interact with KCNE1 and KCNE2, cannot rescue Kv1.4 or Kv3.4 surface expression unless engineered to interact with them using N-terminal A and B domain swapping. The KCNE1/2-enforced checkpoint ensures N-type α-subunits only reach the cell surface as part of intra-subfamily mixed-α complexes, thereby governing channel composition, inactivation rate, and-by extension-cellular excitability.
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Affiliation(s)
- Vikram A Kanda
- Department of Pharmacology, Weill Medical College of Cornell University, New York, New York, USA
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Kanda VA, Lewis A, Xu X, Abbott GW. KCNE1 and KCNE2 inhibit forward trafficking of homomeric N-type voltage-gated potassium channels. Biophys J 2011; 101:1354-63. [PMID: 21943416 DOI: 10.1016/j.bpj.2011.08.015] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2011] [Revised: 07/25/2011] [Accepted: 08/04/2011] [Indexed: 11/18/2022] Open
Abstract
Potassium currents generated by voltage-gated potassium (Kv) channels comprising α-subunits from the Kv1, 2, and 3 subfamilies facilitate high-frequency firing of mammalian neurons. Within these subfamilies, only three α-subunits (Kv1.4, Kv3.3, and Kv3.4) generate currents that decay rapidly in the open state because an N-terminal ball domain blocks the channel pore after activation-a process termed N-type inactivation. Despite its importance to shaping cellular excitability, little is known of the processes regulating surface expression of N-type α-subunits, versus their slowly inactivating (delayed rectifier) counterparts. Here we found that currents generated by homomeric Kv1.4, Kv3.3, and Kv3.4 channels are all strongly suppressed by the single transmembrane domain ancillary (β) subunits KCNE1 and KCNE2. A combination of electrophysiological, biochemical, and immunofluorescence analyses revealed this suppression is due to KCNE1 and KCNE2 retaining Kv1.4 and Kv3.4 intracellularly, early in the secretory pathway. The retention is specific, requires α-β coassembly, and does not involve the dynamin-dependent endocytosis pathway. However, the small fraction of Kv3.4 that escapes KCNE-dependent retention is regulated by dynamin-dependent endocytosis. The findings illustrate two contrasting mechanisms controlling surface expression of N-type Kv α-subunits and therefore, potentially, cellular excitability and refractory periods.
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Affiliation(s)
- Vikram A Kanda
- Department of Pharmacology, Weill Medical College of Cornell University, New York, New York, USA
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Roepke TK, Kanda VA, Purtell K, King EC, Lerner DJ, Abbott GW. KCNE2 forms potassium channels with KCNA3 and KCNQ1 in the choroid plexus epithelium. FASEB J 2011; 25:4264-73. [PMID: 21859894 DOI: 10.1096/fj.11-187609] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Cerebrospinal fluid (CSF) is crucial for normal function and mechanical protection of the CNS. The choroid plexus epithelium (CPe) is primarily responsible for secreting CSF and regulating its composition by mechanisms currently not fully understood. Previously, the heteromeric KCNQ1-KCNE2 K(+) channel was functionally linked to epithelial processes including gastric acid secretion and thyroid hormone biosynthesis. Here, using Kcne2(-/-) tissue as a negative control, we found cerebral expression of KCNE2 to be markedly enriched in the CPe apical membrane, where we also discovered expression of KCNQ1. Targeted Kcne2 gene deletion in C57B6 mice increased CPe outward K(+) current 2-fold. The Kcne2 deletion-enhanced portion of the current was inhibited by XE991 (10 μM) and margatoxin (10 μM) but not by dendrotoxin (100 nM), indicating that it arose from augmentation of KCNQ subfamily and KCNA3 but not KCNA1 K(+) channel activity. Kcne2 deletion in C57B6 mice also altered the polarity of CPe KCNQ1 and KCNA3 trafficking, hyperpolarized the CPe membrane by 9 ± 2 mV, and increased CSF [Cl(-)] by 14% compared with wild-type mice. These findings constitute the first report of CPe dysfunction caused by cation channel gene disruption and suggest that KCNE2 influences blood-CSF anion flux by regulating KCNQ1 and KCNA3 in the CPe.
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Affiliation(s)
- Torsten K Roepke
- Department of Pharmacology, Weill Cornell Medical College, 1300 York Ave., New York, NY 10021, USA
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McCallum LA, Pierce SL, England SK, Greenwood IA, Tribe RM. The contribution of Kv7 channels to pregnant mouse and human myometrial contractility. J Cell Mol Med 2011; 15:577-86. [PMID: 20132415 PMCID: PMC3922379 DOI: 10.1111/j.1582-4934.2010.01021.x] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Premature birth accounts for approximately 75% of neonatal mortality and morbidity in the developed world. Despite this, methods for identifying and treating women at risk of preterm labour are limited and many women still present in preterm labour requiring tocolytic therapy to suppress uterine contractility. The aim of this study was to assess the utility of Kv7 channel activators as potential uterine smooth muscle (myometrium) relaxants in tissues from pregnant mice and women. Myometrium was obtained from early and late pregnant mice and from lipopolysaccharide (LPS)-injected mice (day 15 of gestation; model of infection in pregnancy). Human myometrium was obtained at the time of Caesarean section from women at term (38–41 weeks). RT-PCR/qRT-PCR detected KCNQ and KCNE expression in mouse and human myometrium. In mice, there was a global suppression of all KCNQ isoforms, except KCNQ3, in early pregnancy (n= 6, P < 0.001 versus late pregnant); expression subsequently increased in late pregnancy (n= 6). KCNE isoforms were also gestationally regulated (P < 0.05). KCNQ and KCNE isoform expression was slightly down-regulated in myometrium from LPS-treated-mice versus controls (P < 0.05, n= 3–4). XE991 (10 μM, Kv7 inhibitor) significantly increased spontaneous myometrial contractions in vitro in both human and mouse myometrial tissues (P < 0.05) and retigabine/flupirtine (20 μM, Kv7 channel activators) caused profound myometrial relaxation (P < 0.05). In summary, Kv7 activators suppressed myometrial contraction and KCNQ gene expression was sustained throughout gestation, particularly at term. Consequently, activation of the encoded channels represents a novel mechanism for treatment of preterm labour.
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Affiliation(s)
- Laura A McCallum
- Maternal and Fetal Research Unit, Division of Reproduction and Endocrinology, King's College London, St Thomas' Hospital Campus, London, UK
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Protein kinase C downregulates I(Ks) by stimulating KCNQ1-KCNE1 potassium channel endocytosis. Heart Rhythm 2011; 8:1641-7. [PMID: 21699843 DOI: 10.1016/j.hrthm.2011.04.034] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/23/2011] [Accepted: 04/29/2011] [Indexed: 11/21/2022]
Abstract
BACKGROUND The slow-activating cardiac repolarization K(+) current (I(Ks)), generated by the KCNQ1-KCNE1 potassium channel complex, is controlled via sympathetic and parasympathetic regulation in vivo. Inherited KCNQ1 and KCNE1 mutations predispose to ventricular fibrillation and sudden death, often triggered by exercise or emotional stress. Protein kinase C (PKC), which is activated by α1 adrenergic receptor stimulation, is known to downregulate I(Ks) via phosphorylation of KCNE1 serine 102, but the underlying mechanism has remained enigmatic. We previously showed that KCNE1 mediates dynamin-dependent endocytosis of KCNQ1-KCNE1 complexes. OBJECTIVE This study sought to determine the potential role of endocytosis in I(Ks) downregulation by PKC. METHODS We utilized patch clamping and fluorescence microscopy to study Chinese hamster ovary (CHO) cells coexpressing KCNQ1, KCNE1, and wild-type or dominant-negative mutant (K44A) dynamin 2, and neonatal mouse ventricular myocytes. RESULTS The PKC activator phorbol 12-myristate 13-acetate (PMA) decreased I(Ks) density by >60% (P < .05) when coexpressed with wild-type dynamin 2 in CHO cells, but had no effect when coexpressed with K44A-dynamin 2. Thus, functional dynamin was required for downregulation of I(Ks) by PKC activation. PMA increased KCNQ1-KCNE1 endocytosis in CHO cells expressing wild-type dynamin 2, but had no effect on KCNQ1-KCNE1 endocytosis in CHO cells expressing K44A-dynamin 2, determined using the Pearson correlation coefficient to quantify endosomal colocalization of KCNQ1 and KCNE1 with internalized fluorescent transferrin. KCNE1-S102A abolished the effect of PMA on I(Ks) currents and endocytosis. Importantly, PMA similarly stimulated endocytosis of endogenous KCNQ1 and KCNE1 in neonatal mouse myocytes. CONCLUSION PKC activation downregulates I(Ks) by stimulating KCNQ1-KCNE1 channel endocytosis.
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Ma LJ, Ohmert I, Vardanyan V. Allosteric features of KCNQ1 gating revealed by alanine scanning mutagenesis. Biophys J 2011; 100:885-94. [PMID: 21320432 DOI: 10.1016/j.bpj.2010.12.3726] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2010] [Revised: 11/29/2010] [Accepted: 12/15/2010] [Indexed: 01/10/2023] Open
Abstract
Controlled opening and closing of an ion-selective pathway in response to changes of membrane potential is a fundamental feature of voltage-gated ion channels. In recent decades, various details of this process have been revealed with unprecedented precision based on studies of prototypic potassium channels. Though current scientific efforts are focused more on a thorough description of voltage-sensor movement, much less is known about the similarities and differences of the gating mechanisms among potassium channels. Here, we describe the peculiarities of the KCNQ1 gating process in parallel comparison to Shaker. We applied alanine scanning mutagenesis to the S4-S5 linker and pore region and followed the regularities of gating perturbations in KCNQ1. We found a fractional constitutive conductance for wild-type KCNQ1. This component increased significantly in mutants with considerably leftward-shifted steady-state activation curves. In contrast to Shaker, no correlation between V(1/2) and Z parameters was observed for the voltage-dependent fraction of KCNQ1. Our experimental findings are explained by a simple allosteric gating scheme with voltage-driven and voltage-independent transitions. Allosteric features are discussed in the context of extreme gating adaptability of KCNQ1 upon interaction with KCNE β-subunits.
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Affiliation(s)
- Li-Juan Ma
- Institut für Neurale Signalverarbeitung, Zentrum für Molekulare Neurobiologie, Universität Hamburg, Hamburg, Germany
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Abstract
Since the first discovery of Kvbeta-subunits more than 15 years ago, many more ancillary Kv channel subunits were characterized, for example, KChIPs, KCNEs, and BKbeta-subunits. The ancillary subunits are often integral parts of native Kv channels, which, therefore, are mostly multiprotein complexes composed of voltage-sensing and pore-forming Kvalpha-subunits and of ancillary or beta-subunits. Apparently, Kv channels need the ancillary subunits to fulfill their many different cell physiological roles. This is reflected by the large structural diversity observed with ancillary subunit structures. They range from proteins with transmembrane segments and extracellular domains to purely cytoplasmic proteins. Ancillary subunits modulate Kv channel gating but can also have a great impact on channel assembly, on channel trafficking to and from the cellular surface, and on targeting Kv channels to different cellular compartments. The importance of the role of accessory subunits is further emphasized by the number of mutations that are associated in both humans and animals with diseases like hypertension, epilepsy, arrhythmogenesis, periodic paralysis, and hypothyroidism. Interestingly, several ancillary subunits have in vitro enzymatic activity; for example, Kvbeta-subunits are oxidoreductases, or modulate enzymatic activity, i.e., KChIP3 modulates presenilin activity. Thus different modes of beta-subunit association and of functional impact on Kv channels can be delineated, making it difficult to extract common principles underlying Kvalpha- and beta-subunit interactions. We critically review present knowledge on the physiological role of ancillary Kv channel subunits and their effects on Kv channel properties.
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Affiliation(s)
- Olaf Pongs
- Institut für Neurale Signalverarbeitung, Zentrum für Molekulare Neurobiologie Hamburg, Universitätsklinikum Hamburg-Eppendorf, Universität Hamburg, Hamburg, Germany.
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Preston P, Wartosch L, Günzel D, Fromm M, Kongsuphol P, Ousingsawat J, Kunzelmann K, Barhanin J, Warth R, Jentsch TJ. Disruption of the K+ channel beta-subunit KCNE3 reveals an important role in intestinal and tracheal Cl- transport. J Biol Chem 2010; 285:7165-75. [PMID: 20051516 DOI: 10.1074/jbc.m109.047829] [Citation(s) in RCA: 83] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
The KCNE3 beta-subunit constitutively opens outwardly rectifying KCNQ1 (Kv7.1) K(+) channels by abolishing their voltage-dependent gating. The resulting KCNQ1/KCNE3 heteromers display enhanced sensitivity to K(+) channel inhibitors like chromanol 293B. KCNE3 was also suggested to modify biophysical properties of several other K(+) channels, and a mutation in KCNE3 was proposed to underlie forms of human periodic paralysis. To investigate physiological roles of KCNE3, we now disrupted its gene in mice. kcne3(-/-) mice were viable and fertile and displayed neither periodic paralysis nor other obvious skeletal muscle abnormalities. KCNQ1/KCNE3 heteromers are present in basolateral membranes of intestinal and tracheal epithelial cells where they might facilitate transepithelial Cl(-) secretion through basolateral recycling of K(+) ions and by increasing the electrochemical driving force for apical Cl(-) exit. Indeed, cAMP-stimulated electrogenic Cl(-) secretion across tracheal and intestinal epithelia was drastically reduced in kcne3(-/-) mice. Because the abundance and subcellular localization of KCNQ1 was unchanged in kcne3(-/-) mice, the modification of biophysical properties of KCNQ1 by KCNE3 is essential for its role in intestinal and tracheal transport. Further, these results suggest KCNE3 as a potential modifier gene in cystic fibrosis.
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Affiliation(s)
- Patricia Preston
- Leibniz-Institut für Molekulare Pharmakologie and Max-Delbrück-Centrum für Molekulare Medizin, 13125 Berlin, Germany
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Hedley PL, Jørgensen P, Schlamowitz S, Moolman-Smook J, Kanters JK, Corfield VA, Christiansen M. The genetic basis of Brugada syndrome: a mutation update. Hum Mutat 2009; 30:1256-66. [PMID: 19606473 DOI: 10.1002/humu.21066] [Citation(s) in RCA: 125] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Brugada syndrome (BrS) is a condition characterized by a distinct ST-segment elevation in the right precordial leads of the electrocardiogram and, clinically, by an increased risk of cardiac arrhythmia and sudden death. The condition predominantly exhibits an autosomal dominant pattern of inheritance with an average prevalence of 5:10,000 worldwide. Currently, more than 100 mutations in seven genes have been associated with BrS. Loss-of-function mutations in SCN5A, which encodes the alpha-subunit of the Na(v)1.5 sodium ion channel conducting the depolarizing I(Na) current, causes 15-20% of BrS cases. A few mutations have been described in GPD1L, which encodes glycerol-3-phosphate dehydrogenase-1 like protein; CACNA1C, which encodes the alpha-subunit of the Ca(v)1.2 ion channel conducting the depolarizing I(L,Ca) current; CACNB2, which encodes the stimulating beta2-subunit of the Ca(v)1.2 ion channel; SCN1B and SCN3B, which, in the heart, encodes beta-subunits of the Na(v)1.5 sodium ion channel, and KCNE3, which encodes the ancillary inhibitory beta-subunit of several potassium channels including the Kv4.3 ion channel conducting the repolarizing potassium I(to) current. BrS exhibits variable expressivity, reduced penetrance, and "mixed phenotypes," where families contain members with BrS as well as long QT syndrome, atrial fibrillation, short QT syndrome, conduction disease, or structural heart disease, have also been described.
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Affiliation(s)
- Paula L Hedley
- Department of Clinical Biochemistry and Immunology, Statens Serum Institut, Copenhagen, Denmark
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Cai SQ, Wang Y, Park KH, Tong X, Pan Z, Sesti F. Auto-phosphorylation of a voltage-gated K+ channel controls non-associative learning. EMBO J 2009; 28:1601-11. [PMID: 19387491 DOI: 10.1038/emboj.2009.112] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2008] [Accepted: 03/30/2009] [Indexed: 11/09/2022] Open
Abstract
Here, we characterize a new K(+) channel-kinase complex that operates in the metazoan Caenorhabditis elegans to control learning behaviour. This channel is composed of a pore-forming subunit, dubbed KHT-1 (73% homology to human Kv3.1), and the accessory subunit MPS-1, which shows kinase activity. Genetic, biochemical and electrophysiological evidence show that KHT-1 and MPS-1 form a complex in vitro and in native mechanosensory PLM neurons, and that KHT-1 is a substrate for the kinase activity of MPS-1. Behavioural analysis further shows that the kinase activity of MPS-1 is specifically required for habituation to repetitive mechanical stimulation. Thus, worms bearing an inactive MPS-1 variant (D178N) respond normally to touch on the body but do not habituate to repetitive mechanical stimulation such as tapping on the side of the Petri dish. Hence, the phosphorylation status of KHT-1-MPS-1 seems to be linked to distinct behavioural responses. In the non-phosphorylated state the channel is necessary for the normal function of the touch neurons. In the auto-phosphorylated state the channel acts to induce neuronal adaptation to mechanical stimulation. Taken together, these data establish a new mechanism of dynamic regulation of electrical signalling in the nervous system.
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Affiliation(s)
- Shi-Qing Cai
- Department of Physiology and Biophysics, Robert Wood Johnson Medical School, University of Medicine and Dentistry of New Jersey, Piscataway, NJ, USA
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Regulation of the Kv2.1 potassium channel by MinK and MiRP1. J Membr Biol 2009; 228:1-14. [PMID: 19219384 DOI: 10.1007/s00232-009-9154-8] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2008] [Accepted: 01/13/2009] [Indexed: 12/17/2022]
Abstract
Kv2.1 is a voltage-gated potassium (Kv) channel alpha-subunit expressed in mammalian heart and brain. MinK-related peptides (MiRPs), encoded by KCNE genes, are single-transmembrane domain ancillary subunits that form complexes with Kv channel alpha-subunits to modify their function. Mutations in human MinK (KCNE1) and MiRP1 (KCNE2) are associated with inherited and acquired forms of long QT syndrome (LQTS). Here, coimmunoprecipitations from rat heart tissue suggested that both MinK and MiRP1 form native cardiac complexes with Kv2.1. In whole-cell voltage-clamp studies of subunits expressed in CHO cells, rat MinK and MiRP1 reduced Kv2.1 current density three- and twofold, respectively; slowed Kv2.1 activation (at +60 mV) two- and threefold, respectively; and slowed Kv2.1 deactivation less than twofold. Human MinK slowed Kv2.1 activation 25%, while human MiRP1 slowed Kv2.1 activation and deactivation twofold. Inherited mutations in human MinK and MiRP1, previously associated with LQTS, were also evaluated. D76N-MinK and S74L-MinK reduced Kv2.1 current density (threefold and 40%, respectively) and slowed deactivation (60% and 80%, respectively). Compared to wild-type human MiRP1-Kv2.1 complexes, channels formed with M54T- or I57T-MiRP1 showed greatly slowed activation (tenfold and fivefold, respectively). The data broaden the potential roles of MinK and MiRP1 in cardiac physiology and support the possibility that inherited mutations in either subunit could contribute to cardiac arrhythmia by multiple mechanisms.
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Xu X, Kanda VA, Choi E, Panaghie G, Roepke TK, Gaeta SA, Christini DJ, Lerner DJ, Abbott GW. MinK-dependent internalization of the IKs potassium channel. Cardiovasc Res 2009; 82:430-8. [PMID: 19202166 DOI: 10.1093/cvr/cvp047] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
AIMS KCNQ1-MinK potassium channel complexes (4alpha:2beta stoichiometry) generate IKs, the slowly activating human cardiac ventricular repolarization current. The MinK ancillary subunit slows KCNQ1 activation, eliminates its inactivation, and increases its unitary conductance. However, KCNQ1 transcripts outnumber MinK transcripts five to one in human ventricles, suggesting KCNQ1 also forms other heteromeric or even homomeric channels there. Mechanisms governing which channel types prevail have not previously been reported, despite their significance: normal cardiac rhythm requires tight control of IKs density and kinetics, and inherited mutations in KCNQ1 and MinK can cause ventricular fibrillation and sudden death. Here, we describe a novel mechanism for this control. METHODS AND RESULTS Whole-cell patch-clamping, confocal immunofluorescence microscopy, antibody feeding, biotin feeding, fluorescent transferrin feeding, and protein biochemistry techniques were applied to COS-7 cells heterologously expressing KCNQ1 with wild-type or mutant MinK and dynamin 2 and to native IKs channels in guinea-pig myocytes. KCNQ1-MinK complexes, but not homomeric KCNQ1 channels, were found to undergo clathrin- and dynamin 2-dependent internalization (DDI). Three sites on the MinK intracellular C-terminus were, in concert, necessary and sufficient for DDI. Gating kinetics and sensitivity to XE991 indicated that DDI decreased cell-surface KCNQ1-MinK channels relative to homomeric KCNQ1, decreasing whole-cell current but increasing net activation rate; inhibiting DDI did the reverse. CONCLUSION The data redefine MinK as an endocytic chaperone for KCNQ1 and present a dynamic mechanism for controlling net surface Kv channel subunit composition-and thus current density and gating kinetics-that may also apply to other alpha-beta type Kv channel complexes.
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Affiliation(s)
- Xianghua Xu
- Greenberg Division of Cardiology, Department of Medicine, Weill Medical College of Cornell University, Starr 463, 520 East 70th Street, New York, NY 10065, USA
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Roepke TK, Kontogeorgis A, Ovanez C, Xu X, Young JB, Purtell K, Goldstein PA, Christini DJ, Peters NS, Akar FG, Gutstein DE, Lerner DJ, Abbott GW. Targeted deletion of kcne2 impairs ventricular repolarization via disruption of I(K,slow1) and I(to,f). FASEB J 2008; 22:3648-60. [PMID: 18603586 DOI: 10.1096/fj.08-110171] [Citation(s) in RCA: 89] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Mutations in human KCNE2, which encodes the MiRP1 potassium channel ancillary subunit, associate with long QT syndrome (LQTS), a defect in ventricular repolarization. The precise cardiac role of MiRP1 remains controversial, in part, because it has marked functional promiscuity in vitro. Here, we disrupted the murine kcne2 gene to define the role of MiRP1 in murine ventricles. kcne2 disruption prolonged ventricular action potential duration (APD), suggestive of reduced repolarization capacity. Accordingly, kcne2 (-/-) ventricles exhibited a 50% reduction in I(K,slow1), generated by Kv1.5--a previously unknown partner for MiRP1. I(to,f), generated by Kv4 alpha subunits, was also diminished, by approximately 25%. Ventricular MiRP1 protein coimmunoprecipitated with native Kv1.5 and Kv4.2 but not Kv1.4 or Kv4.3. Unexpectedly, kcne2 (-/-) ventricular membrane fractions exhibited 50% less mature Kv1.5 protein than wild type, and disruption of Kv1.5 trafficking to the intercalated discs. Consistent with the reduction in ventricular K(+) currents and prolonged ventricular APD, kcne2 deletion lengthened the QT(c) under sevoflurane anesthesia. Thus, targeted disruption of kcne2 has revealed a novel cardiac partner for MiRP1, a novel role for MiRPs in alpha subunit targeting in vivo, and a role for MiRP1 in murine ventricular repolarization with parallels to that proposed for the human heart.
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Affiliation(s)
- Torsten K Roepke
- Greenberg Division of Cardiology, Department of Medicine, Weill Medical College of Cornell University, 1300 York Ave., New York, NY 10065, USA
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Gain of function in IKs secondary to a mutation in KCNE5 associated with atrial fibrillation. Heart Rhythm 2008; 5:427-35. [PMID: 18313602 DOI: 10.1016/j.hrthm.2007.12.019] [Citation(s) in RCA: 93] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/22/2007] [Accepted: 12/14/2007] [Indexed: 12/12/2022]
Abstract
BACKGROUND Atrial fibrillation (AF) is the most common clinical arrhythmia and a major cause of cardiovascular morbidity and mortality. Among the gene defects previously associated with AF is a gain of function of the slowly activating delayed rectifier potassium current IKs, secondary to mutations in KCNQ1. Coexpression of KCNE5, the gene encoding the MiRP4 beta-subunit, has been shown to reduce IKs. OBJECTIVE The purpose of this study was to test the hypothesis that mutations in KCNE5 are associated with AF in a large cohort of patients with AF. METHODS One-hundred fifty-eight patients with AF were screened for mutations in the coding region of KCNE5. RESULTS A missense mutation involving substitution of a phenylalanine for leucine at position 65 (L65F) was identified in one patient. This patient did not have a history of familial AF, and neither KCNQ1 nor KCNE2 mutations were found. Transient transfection of Chinese hamster ovary (CHO) cells expressing IKs(KCNQ1+KCNE1) with KCNE5 suppressed the developing and tail currents of IKs in a concentration-dependent manner. Transient transfection with KCNE5-L65F failed to suppress IKs, yielding a current indistinguishable from that recorded in the absence of KCNE5. Developing currents recorded during a test pulse to +60 mV and tail currents recorded upon repolarization to -40 mV both showed a significant concentration-dependent gain of function in IKs with expression of KCNE5-L65F vs KCNE5-WT. CONCLUSION The results of this study suggest that a missense mutation in KCNE5 may be associated with nonfamilial or acquired forms of AF. The arrhythmogenic mechanism most likely is a gain of function of IKs.
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Bett GCL, Rasmusson RL. Modification of K+ channel-drug interactions by ancillary subunits. J Physiol 2007; 586:929-50. [PMID: 18096604 DOI: 10.1113/jphysiol.2007.139279] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Reconciling ion channel alpha-subunit expression with native ionic currents and their pharmacological sensitivity in target organs has proved difficult. In native tissue, many K(+) channel alpha-subunits co-assemble with ancillary subunits, which can profoundly affect physiological parameters including gating kinetics and pharmacological interactions. In this review, we examine the link between voltage-gated potassium ion channel pharmacology and the biophysics of ancillary subunits. We propose that ancillary subunits can modify the interaction between pore blockers and ion channels by three distinct mechanisms: changes in (1) binding site accessibility; (2) orientation of pore-lining residues; (3) the ability of the channel to undergo post-binding conformational changes. Each of these subunit-induced changes has implications for gating, drug affinity and use dependence of their respective channel complexes. A single subunit may modulate its associated alpha-subunit by more than one of these mechanisms. Voltage-gated potassium channels are the site of action of many therapeutic drugs. In addition, potassium channels interact with drugs whose primary target is another channel, e.g. the calcium channel blocker nifedipine, the sodium channel blocker quinidine, etc. Even when K(+) channel block is the intended mode of action, block of related channels in non-target organs, e.g. the heart, can result in major and potentially lethal side-effects. Understanding factors that determine specificity, use dependence and other properties of K(+) channel drug binding are therefore of vital clinical importance. Ancillary subunits play a key role in determining these properties in native tissue, and so understanding channel-subunit interactions is vital to understanding clinical pharmacology.
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Affiliation(s)
- Glenna C L Bett
- Center for Cellular and Systems Electrophysiology, Department of Physiology and Biophysics, School of Medicine and Biomedical Sciences, 124 Sherman Hall, State University of New York at Buffalo, Buffalo, NY 14214-3005, USA
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Um SY, McDonald TV. Differential association between HERG and KCNE1 or KCNE2. PLoS One 2007; 2:e933. [PMID: 17895974 PMCID: PMC1978535 DOI: 10.1371/journal.pone.0000933] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2007] [Accepted: 09/04/2007] [Indexed: 12/16/2022] Open
Abstract
The small proteins encoded by KCNE1 and KCNE2 have both been proposed as accessory subunits for the HERG channel. Here we report our investigation into the cell biology of the KCNE-HERG interaction. In a co-expression system, KCNE1 was more readily co-precipitated with co-expressed HERG than was KCNE2. When forward protein trafficking was prevented (either by Brefeldin A or engineering an ER-retention/retrieval signal onto KCNE cDNA) the intracellular abundance of KCNE2 and its association with HERG markedly increased relative to KCNE1. HERG co-localized more completely with KCNE1 than with KCNE2 in all the membrane-processing compartments of the cell (ER, Golgi and plasma membrane). By surface labeling and confocal immunofluorescence, KCNE2 appeared more abundant at the cell surface compared to KCNE1, which exhibited greater co-localization with the ER-marker calnexin. Examination of the extracellular culture media showed that a significant amount of KCNE2 was extracellular (both soluble and membrane-vesicle-associated). Taken together, these results suggest that during biogenesis of channels HERG is more likely to assemble with KCNE1 than KCNE2 due to distinctly different trafficking rates and retention in the cell rather than differences in relative affinity. The final channel subunit constitution, in vivo, is likely to be determined by a combination of relative cell-to-cell expression rates and differential protein processing and trafficking.
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Affiliation(s)
- Sung Yon Um
- Department of Medicine, Albert Einstein College of Medicine, Bronx, New York, USA
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Gittis AH, du Lac S. Firing properties of GABAergic versus non-GABAergic vestibular nucleus neurons conferred by a differential balance of potassium currents. J Neurophysiol 2007; 97:3986-96. [PMID: 17392422 DOI: 10.1152/jn.00141.2007] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Neural circuits are composed of diverse cell types, the firing properties of which reflect their intrinsic ionic currents. GABAergic and non-GABAergic neurons in the medial vestibular nuclei, identified in GIN and YFP-16 lines of transgenic mice, respectively, exhibit different firing properties in brain slices. The intrinsic ionic currents of these cell types were investigated in acutely dissociated neurons from 3- to 4-wk-old mice, where differences in spontaneous firing and action potential parameters observed in slice preparations are preserved. Both GIN and YFP-16 neurons express a combination of four major outward currents: Ca(2+)-dependent K(+) currents (I(KCa)), 1 mM TEA-sensitive delayed rectifier K(+) currents (I(1TEA)), 10 mM TEA-sensitive delayed rectifier K(+) currents (I(10TEA)), and A-type K(+) currents (I(A)). The balance of these currents varied across cells, with GIN neurons tending to express proportionately more I(KCa) and I(A), and YFP-16 neurons tending to express proportionately more I(1TEA) and I(10TEA). Correlations in charge densities suggested that several currents were coregulated. Variations in the kinetics and density of I(1TEA) could account for differences in repolarization rates observed both within and between cell types. These data indicate that diversity in the firing properties of GABAergic and non-GABAergic vestibular nucleus neurons arises from graded differences in the balance and kinetics of ionic currents.
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Affiliation(s)
- Aryn H Gittis
- University of California, San Diego Graduate Program in Neuroscience, The Salk Institute for Biological Studies, Howard Hughes Medical Institute, La Jolla, California 92037, USA
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46
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Panaghie G, Abbott GW. The role of S4 charges in voltage-dependent and voltage-independent KCNQ1 potassium channel complexes. ACTA ACUST UNITED AC 2007; 129:121-33. [PMID: 17227916 PMCID: PMC2154355 DOI: 10.1085/jgp.200609612] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Voltage-gated potassium (Kv) channels extend their functional repertoire by coassembling with MinK-related peptides (MiRPs). MinK slows the activation of channels formed with KCNQ1 α subunits to generate the voltage-dependent IKs channel in human heart; MiRP1 and MiRP2 remove the voltage dependence of KCNQ1 to generate potassium “leak” currents in gastrointestinal epithelia. Other Kv α subunits interact with MiRP1 and MiRP2 but without loss of voltage dependence; the mechanism for this disparity is unknown. Here, sequence alignments revealed that the voltage-sensing S4 domain of KCNQ1 bears lower net charge (+3) than that of any other eukaryotic voltage-gated ion channel. We therefore examined the role of KCNQ1 S4 charges in channel activation using alanine-scanning mutagenesis and two-electrode voltage clamp. Alanine replacement of R231, at the N-terminal side of S4, produced constitutive activation in homomeric KCNQ1 channels, a phenomenon not observed with previous single amino acid substitutions in S4 of other channels. Homomeric KCNQ4 channels were also made constitutively active by mutagenesis to mimic the S4 charge balance of R231A-KCNQ1. Loss of single S4 charges at positions R231 or R237 produced constitutively active MinK-KCNQ1 channels and increased the constitutively active component of MiRP2-KCNQ1 currents. Charge addition to the CO2H-terminal half of S4 eliminated constitutive activation in MiRP2-KCNQ1 channels, whereas removal of homologous charges from KCNQ4 S4 produced constitutively active MiRP2-KCNQ4 channels. The results demonstrate that the unique S4 charge paucity of KCNQ1 facilitates its unique conversion to a leak channel by ancillary subunits such as MiRP2.
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Affiliation(s)
- Gianina Panaghie
- Greenberg Division of Cardiology, Department of Medicine, Cornell University, Weill Medical College, New York, NY 10021, USA
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Chandrasekhar KD, Bas T, Kobertz WR. KCNE1 subunits require co-assembly with K+ channels for efficient trafficking and cell surface expression. J Biol Chem 2006; 281:40015-23. [PMID: 17065152 DOI: 10.1074/jbc.m604398200] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
KCNE peptides are a class of type I transmembrane beta subunits that assemble with and modulate the gating and ion conducting properties of a variety of voltage-gated K(+) channels. Accordingly, mutations that disrupt the assembly and trafficking of KCNE-K(+) channel complexes give rise to disease. The cellular mechanisms responsible for ensuring that KCNE peptides assemble with voltage-gated K(+) channels have yet to be elucidated. Using enzymatic deglycosylation, immunofluorescence, and quantitative cell surface labeling experiments, we show that KCNE1 peptides are retained in the early stages of the secretory pathway until they co-assemble with specific K(+) channel subunits; co-assembly mediates KCNE1 progression through the secretory pathway and results in cell surface expression. We also address an apparent discrepancy between our results and a previous study in human embryonic kidney cells, which showed wild type KCNE1 peptides can reach the plasma membrane without exogenously expressed K(+) channel subunits. By comparing KCNE1 trafficking in three cell lines, our data suggest that the errant KCNE1 trafficking observed in human embryonic kidney cells may be due, in part, to the presence of endogenous voltage-gated K(+) channels in these cells.
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Affiliation(s)
- Kshama D Chandrasekhar
- Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, Massachusetts 01605, USA
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Abstract
Voltage-gated potassium channels regulate cell membrane potential and excitability in neurons and other cell types. A precise control of neuronal action potential patterns underlies the basic functioning of the central and peripheral nervous system. This control relies on the adaptability of potassium channel activities. The functional diversity of potassium currents, however, far exceeds the considerable molecular diversity of this class of genes. Potassium current diversity contributes to the specificity of neuronal firing patterns and may be achieved by regulated transcription, RNA splicing, and posttranslational modifications. Another mechanism for regulation of potassium channel activity is through association with interacting proteins and accessory subunits. Here the authors highlight recent work that addresses this growing area of exploration and discuss areas of future investigation.
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Affiliation(s)
- Yan Li
- Department of Medicine, Albert Einstein College of Medicine, Bronx, NY 10461, USA
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Roepke TK, Anantharam A, Kirchhoff P, Busque SM, Young JB, Geibel JP, Lerner DJ, Abbott GW. The KCNE2 potassium channel ancillary subunit is essential for gastric acid secretion. J Biol Chem 2006; 281:23740-7. [PMID: 16754665 DOI: 10.1074/jbc.m604155200] [Citation(s) in RCA: 125] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Genes in the KCNE family encode single transmembrane domain ancillary subunits that co-assemble with voltage-gated potassium (Kv) channel alpha subunits to alter their function. KCNE2 (also known as MiRP1) is expressed in the heart, is associated with human cardiac arrhythmia, and modulates cardiac Kv alpha subunits hERG and KCNQ1 in vitro. KCNE2 and KCNQ1 are also expressed in parietal cells, leading to speculation they form a native channel complex there. Here, we disrupted the murine kcne2 gene and found that kcne2 (-/-) mice have a severe gastric phenotype with profoundly reduced parietal cell proton secretion, abnormal parietal cell morphology, achlorhydria, hypergastrinemia, and striking gastric glandular hyperplasia arising from an increase in the number of non-acid secretory cells. KCNQ1 exhibited abnormal distribution in gastric glands from kcne2 (-/-) mice, with increased expression in non-acid secretory cells. Parietal cells from kcne2 (+/-) mice exhibited normal architecture but reduced proton secretion, and kcne2 (+/-) mice were hypochlorhydric, indicating a gene-dose effect and a primary defect in gastric acid secretion. These data demonstrate that KCNE2 is essential for gastric acid secretion, the first genetic evidence that a member of the KCNE gene family is required for normal gastrointestinal function.
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Affiliation(s)
- Torsten K Roepke
- Greenberg Division of Cardiology, Department of Medicine, Cornell University, Weill Medical College, New York, New York 10021, USA
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Deng Q, Rashid AJ, Fernandez FR, Turner RW, Maler L, Dunn RJ. A C-terminal domain directs Kv3.3 channels to dendrites. J Neurosci 2006; 25:11531-41. [PMID: 16354911 PMCID: PMC6726014 DOI: 10.1523/jneurosci.3672-05.2005] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Pyramidal neurons of the electrosensory lateral line lobe (ELL) of Apteronotus leptorhynchus express Kv3-type voltage-gated potassium channels that give rise to high-threshold currents at the somatic and dendritic levels. Two members of the Kv3 channel family, AptKv3.1 and AptKv3.3, are coexpressed in these neurons. AptKv3.3 channels are expressed at uniformly high levels in each of four ELL segments, whereas AptKv3.1 channels appear to be expressed in a graded manner with higher levels of expression in segments that process high-frequency electrosensory signals. Immunohistochemical and recombinant channel expression studies show a differential distribution of these two channels in the dendrites of ELL pyramidal neurons. AptKv3.1 is concentrated in somas and proximal dendrites, whereas AptKv3.3 is distributed throughout the full extent of the large dendritic tree. Recombinant channel expression of AptKv3 channels through in vivo viral injections allowed directed retargeting of AptKv3 subtypes over the somadendritic axis, revealing that the sequence responsible for targeting channels to distal dendrites lies within the C-terminal domain of the AptKv3.3 protein. The targeting domain includes a consensus sequence predicted to bind to a PDZ (postsynaptic density-95/Discs large/zona occludens-1)-type protein-protein interaction motif. These findings reveal that different functional roles for Kv3 potassium channels at the somatic and dendritic level of a sensory neuron are attained through specific targeting that selectively distributes Kv3.3 channels to the dendritic compartment.
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Affiliation(s)
- Qingwei Deng
- Department of Neurology and Neurosurgery, Centre for Research in Neuroscience, McGill University Health Research Institute, Montreal, Quebec, H3G 1A4, Canada
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