1
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Hasan SM, Aswad N, Al-Sabah S. A positively charged residue at the Kv1.1 T1 interface is critical for voltage-dependent activation and gating kinetics. Am J Physiol Cell Physiol 2024; 327:C790-C797. [PMID: 39099423 DOI: 10.1152/ajpcell.00422.2024] [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: 06/21/2024] [Revised: 07/17/2024] [Accepted: 07/18/2024] [Indexed: 08/06/2024]
Abstract
Within the tetramerization domain (T1) of most voltage-gated potassium channels (Kv) are highly conserved charged residues that line the T1-T1 interface. We investigated the Kv1.1 residue R86 located at the narrowest region of the T1 interface. A Kv1.1 R86Q mutation was reported in a child diagnosed with lower limb dyskinesia (Set KK, Ghosh D, Huq AHM, Luat AF. Mov Disord Clin Pract 4: 784-786, 2017). The child did not present with episodic ataxia 1 (EA1) symptoms typically associated with Kv1.1 loss-of-function mutations. We characterized the electrophysiological outcome of the R86Q substitution by expressing Kv1.1 in Xenopus laevis oocytes. Mutated α-subunits were able to form functional channels that pass delayed rectifier currents. Oocytes that expressed only mutated α-subunits produced a significant reduction in Kv1.1 current and showed a positive shift in voltage dependence of activation. In addition, there was substantially slower activation and faster deactivation implying a reduction in the time the channel is in its open state. Oocytes co-injected with both mutated and wild-type cRNA in equal amounts, to mimic the heterozygous condition of the disease, showed a decrease in current amplitude at -10 mV, a positive shift in activation voltage-dependence and faster deactivation kinetics when compared with the wild-type channel. These findings indicate that T1 plays a role in Kv1.1's voltage-dependent activation and in its kinetics of activation and deactivation.NEW & NOTEWORTHY This is the first Kv1.1 study to characterize the electrophysiological and structural phenotype of a tetramerization (T1) domain mutation. Surprisingly, the mutated α-subunits were able to tetramerize, albeit with different gating kinetics and voltage dependence. This novel finding points to a clear role of T1 in the channel's voltage dependence and gating. Mimicking the heterozygous condition resulted in milder alterations in channel function when compared with previously reported mutations. This is in agreement with the child's milder symptoms.
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Affiliation(s)
- Sonia Majed Hasan
- Department of Physiology, Faculty of Medicine, Kuwait University, Safat, Kuwait
| | - Nawal Aswad
- Department of Physiology, Faculty of Medicine, Kuwait University, Safat, Kuwait
| | - Suleiman Al-Sabah
- Department of Pharmacology & Toxicology, Faculty of Medicine, Kuwait University, Safat, Kuwait
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2
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Kariev AM, Green ME. Water, Protons, and the Gating of Voltage-Gated Potassium Channels. MEMBRANES 2024; 14:37. [PMID: 38392664 PMCID: PMC10890431 DOI: 10.3390/membranes14020037] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/21/2023] [Revised: 01/17/2024] [Accepted: 01/23/2024] [Indexed: 02/24/2024]
Abstract
Ion channels are ubiquitous throughout all forms of life. Potassium channels are even found in viruses. Every cell must communicate with its surroundings, so all cells have them, and excitable cells, in particular, especially nerve cells, depend on the behavior of these channels. Every channel must be open at the appropriate time, and only then, so that each channel opens in response to the stimulus that tells that channel to open. One set of channels, including those in nerve cells, responds to voltage. There is a standard model for the gating of these channels that has a section of the protein moving in response to the voltage. However, there is evidence that protons are moving, rather than protein. Water is critical as part of the gating process, although it is hard to see how this works in the standard model. Here, we review the extensive evidence of the importance of the role of water and protons in gating these channels. Our principal example, but by no means the only example, will be the Kv1.2 channel. Evidence comes from the effects of D2O, from mutations in the voltage sensing domain, as well as in the linker between that domain and the gate, and at the gate itself. There is additional evidence from computations, especially quantum calculations. Structural evidence comes from X-ray studies. The hydration of ions is critical in the transfer of ions in constricted spaces, such as the gate region and the pore of a channel; we will see how the structure of the hydrated ion fits with the structure of the channel. In addition, there is macroscopic evidence from osmotic experiments and streaming current measurements. The combined evidence is discussed in the context of a model that emphasizes the role of protons and water in gating these channels.
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Affiliation(s)
- Alisher M Kariev
- Department of Chemistry and Biochemistry, The City College of New York, New York, NY 10031, USA
| | - Michael E Green
- Department of Chemistry and Biochemistry, The City College of New York, New York, NY 10031, USA
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3
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Fernández-Mariño AI, Tan XF, Bae C, Huffer K, Jiang J, Swartz KJ. Inactivation of the Kv2.1 channel through electromechanical coupling. Nature 2023; 622:410-417. [PMID: 37758949 PMCID: PMC10567553 DOI: 10.1038/s41586-023-06582-8] [Citation(s) in RCA: 20] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2023] [Accepted: 08/30/2023] [Indexed: 09/29/2023]
Abstract
The Kv2.1 voltage-activated potassium (Kv) channel is a prominent delayed-rectifier Kv channel in the mammalian central nervous system, where its mechanisms of activation and inactivation are critical for regulating intrinsic neuronal excitability1,2. Here we present structures of the Kv2.1 channel in a lipid environment using cryo-electron microscopy to provide a framework for exploring its functional mechanisms and how mutations causing epileptic encephalopathies3-7 alter channel activity. By studying a series of disease-causing mutations, we identified one that illuminates a hydrophobic coupling nexus near the internal end of the pore that is critical for inactivation. Both functional and structural studies reveal that inactivation in Kv2.1 results from dynamic alterations in electromechanical coupling to reposition pore-lining S6 helices and close the internal pore. Consideration of these findings along with available structures for other Kv channels, as well as voltage-activated sodium and calcium channels, suggests that related mechanisms of inactivation are conserved in voltage-activated cation channels and likely to be engaged by widely used therapeutics to achieve state-dependent regulation of channel activity.
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Affiliation(s)
- Ana I Fernández-Mariño
- Molecular Physiology and Biophysics Section, Porter Neuroscience Research Center, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, USA
| | - Xiao-Feng Tan
- Molecular Physiology and Biophysics Section, Porter Neuroscience Research Center, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, USA
| | - Chanhyung Bae
- Molecular Physiology and Biophysics Section, Porter Neuroscience Research Center, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, USA
| | - Kate Huffer
- Molecular Physiology and Biophysics Section, Porter Neuroscience Research Center, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, USA
- Department of Biology, Johns Hopkins University, Baltimore, MD, USA
| | - Jiansen Jiang
- Laboratory of Membrane Proteins and Structural Biology, Biochemistry and Biophysics Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD, USA
| | - Kenton J Swartz
- Molecular Physiology and Biophysics Section, Porter Neuroscience Research Center, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, USA.
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4
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Catacuzzeno L, Conti F, Franciolini F. Fifty years of gating currents and channel gating. J Gen Physiol 2023; 155:e202313380. [PMID: 37410612 PMCID: PMC10324510 DOI: 10.1085/jgp.202313380] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2023] [Revised: 05/12/2023] [Accepted: 06/02/2023] [Indexed: 07/08/2023] Open
Abstract
We celebrate this year the 50th anniversary of the first electrophysiological recordings of the gating currents from voltage-dependent ion channels done in 1973. This retrospective tries to illustrate the context knowledge on channel gating and the impact gating-current recording had then, and how it continued to clarify concepts, elaborate new ideas, and steer the scientific debate in these 50 years. The notion of gating particles and gating currents was first put forward by Hodgkin and Huxley in 1952 as a necessary assumption for interpreting the voltage dependence of the Na and K conductances of the action potential. 20 years later, gating currents were actually recorded, and over the following decades have represented the most direct means of tracing the movement of the gating charges and gaining insights into the mechanisms of channel gating. Most work in the early years was focused on the gating currents from the Na and K channels as found in the squid giant axon. With channel cloning and expression on heterologous systems, other channels as well as voltage-dependent enzymes were investigated. Other approaches were also introduced (cysteine mutagenesis and labeling, site-directed fluorometry, cryo-EM crystallography, and molecular dynamics [MD] modeling) to provide an integrated and coherent view of voltage-dependent gating in biological macromolecules. The layout of this retrospective reflects the past 50 years of investigations on gating currents, first addressing studies done on Na and K channels and then on other voltage-gated channels and non-channel structures. The review closes with a brief overview of how the gating-charge/voltage-sensor movements are translated into pore opening and the pathologies associated with mutations targeting the structures involved with the gating currents.
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Affiliation(s)
- Luigi Catacuzzeno
- Department of Chemistry Biology and Biotechnology, University of Perugia, Perugia, Italy
| | - Franco Conti
- Department of Physics, University of Genova, Genova, Italy
| | - Fabio Franciolini
- Department of Chemistry Biology and Biotechnology, University of Perugia, Perugia, Italy
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5
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Szanto TG, Papp F, Zakany F, Varga Z, Deutsch C, Panyi G. Molecular rearrangements in S6 during slow inactivation in Shaker-IR potassium channels. J Gen Physiol 2023; 155:e202313352. [PMID: 37212728 PMCID: PMC10202832 DOI: 10.1085/jgp.202313352] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2023] [Revised: 04/14/2023] [Accepted: 05/04/2023] [Indexed: 05/23/2023] Open
Abstract
Voltage-gated K+ channels have distinct gates that regulate ion flux: the activation gate (A-gate) formed by the bundle crossing of the S6 transmembrane helices and the slow inactivation gate in the selectivity filter. These two gates are bidirectionally coupled. If coupling involves the rearrangement of the S6 transmembrane segment, then we predict state-dependent changes in the accessibility of S6 residues from the water-filled cavity of the channel with gating. To test this, we engineered cysteines, one at a time, at S6 positions A471, L472, and P473 in a T449A Shaker-IR background and determined the accessibility of these cysteines to cysteine-modifying reagents MTSET and MTSEA applied to the cytosolic surface of inside-out patches. We found that neither reagent modified either of the cysteines in the closed or the open state of the channels. On the contrary, A471C and P473C, but not L472C, were modified by MTSEA, but not by MTSET, if applied to inactivated channels with open A-gate (OI state). Our results, combined with earlier studies reporting reduced accessibility of residues I470C and V474C in the inactivated state, strongly suggest that the coupling between the A-gate and the slow inactivation gate is mediated by rearrangements in the S6 segment. The S6 rearrangements are consistent with a rigid rod-like rotation of S6 around its longitudinal axis upon inactivation. S6 rotation and changes in its environment are concomitant events in slow inactivation of Shaker KV channels.
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Affiliation(s)
- Tibor G. Szanto
- Department of Biophysics and Cell Biology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - Ferenc Papp
- Department of Biophysics and Cell Biology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - Florina Zakany
- Department of Biophysics and Cell Biology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - Zoltan Varga
- Department of Biophysics and Cell Biology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - Carol Deutsch
- Department of Physiology, University of Pennsylvania, Philadelphia, PA, USA
| | - Gyorgy Panyi
- Department of Biophysics and Cell Biology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
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6
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Coonen L, Martinez-Morales E, Van De Sande DV, Snyders DJ, Cortes DM, Cuello LG, Labro AJ. The nonconducting W434F mutant adopts upon membrane depolarization an inactivated-like state that differs from wild-type Shaker-IR potassium channels. SCIENCE ADVANCES 2022; 8:eabn1731. [PMID: 36112676 PMCID: PMC9481120 DOI: 10.1126/sciadv.abn1731] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/08/2021] [Accepted: 08/01/2022] [Indexed: 06/15/2023]
Abstract
Voltage-gated K+ (Kv) channels mediate the flow of K+ across the cell membrane by regulating the conductive state of their activation gate (AG). Several Kv channels display slow C-type inactivation, a process whereby their selectivity filter (SF) becomes less or nonconductive. It has been proposed that, in the fast inactivation-removed Shaker-IR channel, the W434F mutation epitomizes the C-type inactivated state because it functionally accelerates this process. By introducing another pore mutation that prevents AG closure, P475D, we found a way to record ionic currents of the Shaker-IR-W434F-P475D mutant at hyperpolarized membrane potentials as the W434F-mutant SF recovers from its inactivated state. This W434F conductive state lost its high K+ over Na+ selectivity, and even NMDG+ can permeate, features not observed in a wild-type SF. This indicates that, at least during recovery from inactivation, the W434F-mutant SF transitions to a widened and noncationic specific conformation.
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Affiliation(s)
- Laura Coonen
- Department of Biomedical Sciences, Faculty of Pharmaceutical, Biomedical and Veterinary Sciences, University of Antwerp, 2610 Antwerp, Belgium
| | - Evelyn Martinez-Morales
- Department of Biomedical Sciences, Faculty of Pharmaceutical, Biomedical and Veterinary Sciences, University of Antwerp, 2610 Antwerp, Belgium
| | - Dieter V. Van De Sande
- Department of Biomedical Sciences, Faculty of Pharmaceutical, Biomedical and Veterinary Sciences, University of Antwerp, 2610 Antwerp, Belgium
| | - Dirk J. Snyders
- Department of Biomedical Sciences, Faculty of Pharmaceutical, Biomedical and Veterinary Sciences, University of Antwerp, 2610 Antwerp, Belgium
| | - D. Marien Cortes
- Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, TX 79430, USA
| | - Luis G. Cuello
- Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, TX 79430, USA
| | - Alain J. Labro
- Department of Biomedical Sciences, Faculty of Pharmaceutical, Biomedical and Veterinary Sciences, University of Antwerp, 2610 Antwerp, Belgium
- Department of Basic and Applied Medical Sciences, Faculty of Medicine, Ghent University, 9000 Ghent, Belgium
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7
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Malik C, Ghosh S. A mutation in the S6 segment of the KvAP channel changes the secondary structure and alters ion channel activity in a lipid bilayer membrane. Amino Acids 2022; 54:1461-1475. [PMID: 35896819 DOI: 10.1007/s00726-022-03188-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2021] [Accepted: 07/04/2022] [Indexed: 11/01/2022]
Abstract
The peptide segment S6 is known to form the inner lining of the voltage-gated K+ channel KvAP (potassium channel of archaea-bacterium, Aeropyrum pernix). In our previous work, it has been demonstrated that S6 itself can form an ion channel on a bilayer lipid membrane (BLM). In the present work, the role of a specific amino acid sequence 'LIG' in determining the secondary structure of S6 has been investigated. For this purpose, 22-residue synthetic peptides named S6-Wild (S6W) and S6-Mutant (S6M) were used. Sequences of these peptides are similar except that the two amino acids isoleucine and glycine of the wild peptide interchanged in the mutant peptide. Channel forming capabilities of both the peptides were checked electro-physiologically on BLM composed of DPhPC and cholesterol. Bilayer electrophysiological experiments showed that the conductance of S6M is higher than that of S6W. Significant differences in the current versus voltage (I-V) plot, open probability, and gating characteristics were observed. Interestingly, two sub-types of channels, S6M Type 1 and Type 2, were identified in S6M differing in conductances and open probability patterns. Circular dichroism (CD) spectroscopy indicated that the secondary structures of the two peptides are different in phosphatidyl choline/asolectin liposomes and 1% SDS detergent. Reduced helicity of S6M was also noticed in membrane mimetic liposomes and 1% SDS detergent micelles. These results are interpreted in view of the difference in hydrophobicity of the two amino acids, isoleucine and glycine. It is concluded that the 'LIG' stretch regulates the structure and pore-forming ability of the S6 peptide.
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Affiliation(s)
- Chetan Malik
- Department of Biophysics, University of Delhi South Campus, Benito Juarez Road, New Delhi, 110021, India
| | - Subhendu Ghosh
- Department of Biophysics, University of Delhi South Campus, Benito Juarez Road, New Delhi, 110021, India.
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8
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Dinoi G, Morin M, Conte E, Mor Shaked H, Coppola MA, D’Adamo MC, Elpeleg O, Liantonio A, Hartmann I, De Luca A, Blunck R, Russo A, Imbrici P. Clinical and Functional Study of a De Novo Variant in the PVP Motif of Kv1.1 Channel Associated with Epilepsy, Developmental Delay and Ataxia. Int J Mol Sci 2022; 23:ijms23158079. [PMID: 35897654 PMCID: PMC9331732 DOI: 10.3390/ijms23158079] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2022] [Revised: 07/15/2022] [Accepted: 07/18/2022] [Indexed: 02/05/2023] Open
Abstract
Mutations in the KCNA1 gene, encoding the voltage-gated potassium channel Kv1.1, have been associated with a spectrum of neurological phenotypes, including episodic ataxia type 1 and developmental and epileptic encephalopathy. We have recently identified a de novo variant in KCNA1 in the highly conserved Pro-Val-Pro motif within the pore of the Kv1.1 channel in a girl affected by early onset epilepsy, ataxia and developmental delay. Other mutations causing severe epilepsy are located in Kv1.1 pore domain. The patient was initially treated with a combination of antiepileptic drugs with limited benefit. Finally, seizures and ataxia control were achieved with lacosamide and acetazolamide. The aim of this study was to functionally characterize Kv1.1 mutant channel to provide a genotype–phenotype correlation and discuss therapeutic options for KCNA1-related epilepsy. To this aim, we transfected HEK 293 cells with Kv1.1 or P403A cDNAs and recorded potassium currents through whole-cell patch-clamp. P403A channels showed smaller potassium currents, voltage-dependent activation shifted by +30 mV towards positive potentials and slower kinetics of activation compared with Kv1.1 wild-type. Heteromeric Kv1.1+P403A channels, resembling the condition of the heterozygous patient, confirmed a loss-of-function biophysical phenotype. Overall, the functional characterization of P403A channels correlates with the clinical symptoms of the patient and supports the observation that mutations associated with severe epileptic phenotype cluster in a highly conserved stretch of residues in Kv1.1 pore domain. This study also strengthens the beneficial effect of acetazolamide and sodium channel blockers in KCNA1 channelopathies.
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Affiliation(s)
- Giorgia Dinoi
- Department of Pharmacy-Drug Sciences, University of Bari “Aldo Moro”, 70125 Bari, Italy; (G.D.); (E.C.); (M.A.C.); (A.L.); (A.D.L.)
| | - Michael Morin
- Department of Physics, Université de Montréal, Montreal, QC H3C 3J7, Canada; (M.M.); (R.B.)
- CIRCA, Center for Interdisciplinary Research on Brain and Learning, Université de Montréal, Montreal, QC H3C 3J7, Canada
| | - Elena Conte
- Department of Pharmacy-Drug Sciences, University of Bari “Aldo Moro”, 70125 Bari, Italy; (G.D.); (E.C.); (M.A.C.); (A.L.); (A.D.L.)
| | - Hagar Mor Shaked
- Department of Genetics, Hadassah Medical Center, Jerusalem 91120, Israel; (H.M.S.); (O.E.)
| | - Maria Antonietta Coppola
- Department of Pharmacy-Drug Sciences, University of Bari “Aldo Moro”, 70125 Bari, Italy; (G.D.); (E.C.); (M.A.C.); (A.L.); (A.D.L.)
| | | | - Orly Elpeleg
- Department of Genetics, Hadassah Medical Center, Jerusalem 91120, Israel; (H.M.S.); (O.E.)
| | - Antonella Liantonio
- Department of Pharmacy-Drug Sciences, University of Bari “Aldo Moro”, 70125 Bari, Italy; (G.D.); (E.C.); (M.A.C.); (A.L.); (A.D.L.)
| | - Inbar Hartmann
- Pediatric Neurology Clinic, Shamir Medical Center (Assaf Harofeh), Zerifin 7033001, Israel;
| | - Annamaria De Luca
- Department of Pharmacy-Drug Sciences, University of Bari “Aldo Moro”, 70125 Bari, Italy; (G.D.); (E.C.); (M.A.C.); (A.L.); (A.D.L.)
| | - Rikard Blunck
- Department of Physics, Université de Montréal, Montreal, QC H3C 3J7, Canada; (M.M.); (R.B.)
- CIRCA, Center for Interdisciplinary Research on Brain and Learning, Université de Montréal, Montreal, QC H3C 3J7, Canada
- Department of Pharmacology and Physiology, Université de Montréal, Montreal, QC H3C 3J7, Canada
| | - Angelo Russo
- Child Neurology Unit, IRCCS, Institute of Neurological Sciences of Bologna, 40139 Bologna, Italy;
| | - Paola Imbrici
- Department of Pharmacy-Drug Sciences, University of Bari “Aldo Moro”, 70125 Bari, Italy; (G.D.); (E.C.); (M.A.C.); (A.L.); (A.D.L.)
- Correspondence:
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Szanto TG, Gaal S, Karbat I, Varga Z, Reuveny E, Panyi G. Shaker-IR K+ channel gating in heavy water: Role of structural water molecules in inactivation. J Gen Physiol 2021; 153:212166. [PMID: 34014250 PMCID: PMC8148028 DOI: 10.1085/jgp.202012742] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2020] [Accepted: 04/30/2021] [Indexed: 01/01/2023] Open
Abstract
It has been reported earlier that the slow (C-type) inactivated conformation in Kv channels is stabilized by a multipoint hydrogen-bond network behind the selectivity filter. Furthermore, MD simulations revealed that structural water molecules are also involved in the formation of this network locking the selectivity filter in its inactive conformation. We found that the application of an extracellular, but not intracellular, solution based on heavy water (D2O) dramatically slowed entry into the slow inactivated state in Shaker-IR mutants (T449A, T449A/I470A, and T449K/I470C, displaying a wide range of inactivation kinetics), consistent with the proposed effect of the dynamics of structural water molecules on the conformational stability of the selectivity filter. Alternative hypotheses capable of explaining the observed effects of D2O were examined. Increased viscosity of the external solution mimicked by the addition of glycerol had a negligible effect on the rate of inactivation. In addition, the inactivation time constants of K+ currents in the outward and the inward directions in asymmetric solutions were not affected by a H2O/D2O exchange, negating an indirect effect of D2O on the rate of K+ rehydration. The elimination of the nonspecific effects of D2O on our macroscopic current measurements supports the hypothesis that the rate of structural water exchange at the region behind the selectivity filter determines the rate of slow inactivation, as proposed by molecular modeling.
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Affiliation(s)
- Tibor G Szanto
- Department of Biophysics and Cell Biology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - Szabolcs Gaal
- Department of Biophysics and Cell Biology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - Izhar Karbat
- Department of Biomolecular Sciences, Weizmann Institute of Science, Rehovot, Israel
| | - Zoltan Varga
- Department of Biophysics and Cell Biology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - Eitan Reuveny
- Department of Biomolecular Sciences, Weizmann Institute of Science, Rehovot, Israel
| | - Gyorgy Panyi
- Department of Biophysics and Cell Biology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
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10
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Refining Genotypes and Phenotypes in KCNA2-Related Neurological Disorders. Int J Mol Sci 2021; 22:ijms22062824. [PMID: 33802230 PMCID: PMC7999221 DOI: 10.3390/ijms22062824] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2021] [Revised: 03/03/2021] [Accepted: 03/04/2021] [Indexed: 02/06/2023] Open
Abstract
Pathogenic variants in KCNA2, encoding for the voltage-gated potassium channel Kv1.2, have been identified as the cause for an evolving spectrum of neurological disorders. Affected individuals show early-onset developmental and epileptic encephalopathy, intellectual disability, and movement disorders resulting from cerebellar dysfunction. In addition, individuals with a milder course of epilepsy, complicated hereditary spastic paraplegia, and episodic ataxia have been reported. By analyzing phenotypic, functional, and genetic data from published reports and novel cases, we refine and further delineate phenotypic as well as functional subgroups of KCNA2-associated disorders. Carriers of variants, leading to complex and mixed channel dysfunction that are associated with a gain- and loss-of-potassium conductance, more often show early developmental abnormalities and an earlier onset of epilepsy compared to individuals with variants resulting in loss- or gain-of-function. We describe seven additional individuals harboring three known and the novel KCNA2 variants p.(Pro407Ala) and p.(Tyr417Cys). The location of variants reported here highlights the importance of the proline(405)–valine(406)–proline(407) (PVP) motif in transmembrane domain S6 as a mutational hotspot. A novel case of self-limited infantile seizures suggests a continuous clinical spectrum of KCNA2-related disorders. Our study provides further insights into the clinical spectrum, genotype–phenotype correlation, variability, and predicted functional impact of KCNA2 variants.
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Wu X, Larsson HP. Insights into Cardiac IKs (KCNQ1/KCNE1) Channels Regulation. Int J Mol Sci 2020; 21:ijms21249440. [PMID: 33322401 PMCID: PMC7763278 DOI: 10.3390/ijms21249440] [Citation(s) in RCA: 30] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2020] [Revised: 12/05/2020] [Accepted: 12/09/2020] [Indexed: 12/19/2022] Open
Abstract
The delayed rectifier potassium IKs channel is an important regulator of the duration of the ventricular action potential. Hundreds of mutations in the genes (KCNQ1 and KCNE1) encoding the IKs channel cause long QT syndrome (LQTS). LQTS is a heart disorder that can lead to severe cardiac arrhythmias and sudden cardiac death. A better understanding of the IKs channel (here called the KCNQ1/KCNE1 channel) properties and activities is of great importance to find the causes of LQTS and thus potentially treat LQTS. The KCNQ1/KCNE1 channel belongs to the superfamily of voltage-gated potassium channels. The KCNQ1/KCNE1 channel consists of both the pore-forming subunit KCNQ1 and the modulatory subunit KCNE1. KCNE1 regulates the function of the KCNQ1 channel in several ways. This review aims to describe the current structural and functional knowledge about the cardiac KCNQ1/KCNE1 channel. In addition, we focus on the modulation of the KCNQ1/KCNE1 channel and its potential as a target therapeutic of LQTS.
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12
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Iwahashi Y, Toyama Y, Imai S, Itoh H, Osawa M, Inoue M, Shimada I. Conformational equilibrium shift underlies altered K + channel gating as revealed by NMR. Nat Commun 2020; 11:5168. [PMID: 33057011 PMCID: PMC7560842 DOI: 10.1038/s41467-020-19005-3] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2020] [Accepted: 09/23/2020] [Indexed: 01/30/2023] Open
Abstract
The potassium ion (K+) channel plays a fundamental role in controlling K+ permeation across the cell membrane and regulating cellular excitabilities. Mutations in the transmembrane pore reportedly affect the gating transitions of K+ channels, and are associated with the onset of neural disorders. However, due to the lack of structural and dynamic insights into the functions of K+ channels, the structural mechanism by which these mutations cause K+ channel dysfunctions remains elusive. Here, we used nuclear magnetic resonance spectroscopy to investigate the structural mechanism underlying the decreased K+-permeation caused by disease-related mutations, using the prokaryotic K+ channel KcsA. We demonstrated that the conformational equilibrium in the transmembrane region is shifted toward the non-conductive state with the closed intracellular K+-gate in the disease-related mutant. We also demonstrated that this equilibrium shift is attributable to the additional steric contacts in the open-conductive structure, which are evoked by the increased side-chain bulkiness of the residues lining the transmembrane helix. Our results suggest that the alteration in the conformational equilibrium of the intracellular K+-gate is one of the fundamental mechanisms underlying the dysfunctions of K+ channels caused by disease-related mutations. Potassium ion channels control K+ permeation across cell membranes and mutations that cause cardiovascular and neural diseases are known. Here, the authors perform NMR measurements with the prototypical K+ channel from Streptomyces lividans, KcsA and characterise the effects of disease causing mutations on the conformational dynamics of K+ channels in a physiological solution environment.
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Affiliation(s)
- Yuta Iwahashi
- Graduate School of Pharmaceutical Sciences, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan
| | - Yuki Toyama
- Graduate School of Pharmaceutical Sciences, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan
| | - Shunsuke Imai
- Graduate School of Pharmaceutical Sciences, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan
| | - Hiroaki Itoh
- Graduate School of Pharmaceutical Sciences, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan
| | - Masanori Osawa
- Graduate School of Pharmaceutical Sciences, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan.,Keio University Faculty of Pharmacy, Shibakoen, Minato-ku, Tokyo, 105-8512, Japan
| | - Masayuki Inoue
- Graduate School of Pharmaceutical Sciences, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan
| | - Ichio Shimada
- Graduate School of Pharmaceutical Sciences, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan. .,RIKEN Center for Biosystems Dynamics Research, Kanagawa, 230-0045, Japan.
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13
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Gupta K, Toombes GE, Swartz KJ. Exploring structural dynamics of a membrane protein by combining bioorthogonal chemistry and cysteine mutagenesis. eLife 2019; 8:50776. [PMID: 31714877 PMCID: PMC6850778 DOI: 10.7554/elife.50776] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2019] [Accepted: 10/11/2019] [Indexed: 12/12/2022] Open
Abstract
The functional mechanisms of membrane proteins are extensively investigated with cysteine mutagenesis. To complement cysteine-based approaches, we engineered a membrane protein with thiol-independent crosslinkable groups using azidohomoalanine (AHA), a non-canonical methionine analogue containing an azide group that can selectively react with cycloalkynes through a strain-promoted azide-alkyne cycloaddition (SPAAC) reaction. We demonstrate that AHA can be readily incorporated into the Shaker Kv channel in place of methionine residues and modified with azide-reactive alkyne probes in Xenopus oocytes. Using voltage-clamp fluorometry, we show that AHA incorporation permits site-specific fluorescent labeling to track voltage-dependent conformational changes similar to cysteine-based methods. By combining AHA incorporation and cysteine mutagenesis in an orthogonal manner, we were able to site-specifically label the Shaker Kv channel with two different fluorophores simultaneously. Our results identify a facile and straightforward approach for chemical modification of membrane proteins with bioorthogonal chemistry to explore their structure-function relationships in live cells. Living cells can sense cues from their environment via molecules located at the interface between the inside and the outside of the cell. These molecules are mostly proteins and are made up of building blocks known as amino acids. To understand how these proteins work, fluorescent probes can be attached to amino acids within them – which can then tell when different parts of proteins move in response to a signal. Scientists often target fluorescent probes at the amino acid cysteine, because it has a chemically reactive side group and is rare enough so that unique positions can be labeled in the protein of interest. However, being able to target other amino acids would allow scientists to ask, and potentially solve, more precise questions about these proteins. Methionine is another amino acid that has a low abundance in most proteins. Previous research has shown that the cell’s normal protein-building machinery can incorporate synthetic versions of methionine into proteins. This suggested that the introduction of chemically reactive alternatives to methionine could offer a way to label membrane proteins with fluorescent probes and free up the cysteines to be targeted with other approaches. Gupta et al. set out to develop a straightforward method to achieve this and started with a well-studied membrane protein, called Shaker, and cells from female African clawed frogs, which are widely used to study membrane proteins. Gupta et al. found that the cells could readily take up a chemically reactive methionine alternative called azidohomoalanine (AHA) from their surrounding solution and incorporate it within the Shaker protein. The AHA took the place of the methionines that are normally found in Shaker, and just like in cysteine-based methods, fluorescent probes could be easily attached to the AHAs in this membrane protein. Shaker is a protein that allows potassium ions to flow across the cell membrane by changing shape in response to the membrane voltage. The fluorescence from those probes also changed with the membrane voltage in a way that was comparable to cysteine-mediated approaches. This indicated that the AHA modification could also be used to track structural changes in the Shaker protein. Finally, Gupta et al. showed that AHA- and cysteine-mediated labeling approaches could be combined to attach two different fluorescent probes onto the Shaker protein. This method will expand the toolbox for researchers studying the relationship between the structure and function of membrane proteins in live cells. In future, it could be applied more widely once the properties of the fluorescent probes for AHA-mediated labeling can be optimized.
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Affiliation(s)
- Kanchan Gupta
- Molecular Physiology and Biophysics Section, Porter Neuroscience Research Center, National Institute of Neurological Diseases and Stroke, National Institutes of Health, Bethesda, United States
| | - Gilman Es Toombes
- Molecular Physiology and Biophysics Section, Porter Neuroscience Research Center, National Institute of Neurological Diseases and Stroke, National Institutes of Health, Bethesda, United States
| | - Kenton J Swartz
- Molecular Physiology and Biophysics Section, Porter Neuroscience Research Center, National Institute of Neurological Diseases and Stroke, National Institutes of Health, Bethesda, United States
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14
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Black KA, Jin R, He S, Gulbis JM. Changing perspectives on how the permeation pathway through potassium channels is regulated. J Physiol 2019; 599:1961-1976. [PMID: 31612997 DOI: 10.1113/jp278682] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2019] [Accepted: 09/25/2019] [Indexed: 11/08/2022] Open
Abstract
The primary means by which ion permeation through potassium channels is controlled, and the key to selective intervention in a range of pathophysiological conditions, is the process by which channels switch between non-conducting and conducting states. Conventionally, this has been explained by a steric mechanism in which the pore alternates between two conformations: a 'closed' state in which the conduction pathway is occluded and an 'open' state in which the pathway is sufficiently wide to accommodate fully hydrated ions. Recently, however, 'non-canonical' mechanisms have been proposed for some classes of K+ channels. The purpose of this review is to illuminate structural and dynamic relationships underpinning permeation control in K+ channels, indicating where additional data might resolve some of the remaining issues.
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Affiliation(s)
- Katrina A Black
- Structural Biology Division, Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, 3052, Australia.,Department of Medical Biology, University of Melbourne, Parkville, Victoria, 3052, Australia
| | - Ruitao Jin
- La Trobe Institute for Molecular Science, La Trobe University, Melbourne, Victoria, 3086, Australia
| | - Sitong He
- La Trobe Institute for Molecular Science, La Trobe University, Melbourne, Victoria, 3086, Australia
| | - Jacqueline M Gulbis
- Structural Biology Division, Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, 3052, Australia.,Department of Medical Biology, University of Melbourne, Parkville, Victoria, 3052, Australia
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15
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Ben-Abu Y. The dynamics of K + channel gates as a biological transistor. Biophys Chem 2019; 252:106196. [PMID: 31203196 DOI: 10.1016/j.bpc.2019.106196] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2019] [Revised: 06/02/2019] [Accepted: 06/02/2019] [Indexed: 11/17/2022]
Abstract
Potassium channels are pore-forming membrane proteins that open and close in response to changes in a chemical or electrical potential, thereby regulating the flow of potassium ions across biological membranes. Two regions of the same channels are acting in tandem and enable ion flow through the channel pore. I refer to this coupled action as a "gate linker". To closely examine the role of the gate linker in the channel function, I mutated the amino acids in the cDNA of this region, and used from knowen mutaion, either alone or together with the amino acids of adjacent regions. I have emphasized the importance of the linker between these two gates - mutations in this region may cause conformational changes that play a fundamental role in mediating the coupling between the voltage sensor, activation gate and selectivity filter elements of Kv channels. I observe that free energy considerations show the significance of the coupling between the activation and inactivation gates. Moreover, a symmetry between the coupling and sensor spring strength leads to the destruction of ion conductivity. I present a thermodynamic framework for the possible study of multiple channel blocks. The arising physical perspective of the gating process gives rise to new research avenues of the coupling mode of potassium channels and may assist in explaining the centrality of the "gate linker" to the channel function.
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Affiliation(s)
- Yuval Ben-Abu
- Department of Physics and Project Unit, Sapir Academic College, Sderot, Hof Ashkelon, 79165, Israel.
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16
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Idikuda V, Gao W, Su Z, Liu Q, Zhou L. cAMP binds to closed, inactivated, and open sea urchin HCN channels in a state-dependent manner. J Gen Physiol 2018; 151:200-213. [PMID: 30541772 PMCID: PMC6363418 DOI: 10.1085/jgp.201812019] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2018] [Revised: 07/08/2018] [Accepted: 11/13/2018] [Indexed: 01/11/2023] Open
Abstract
Mammalian hyperpolarization-activated cyclic-nucleotide–modulated (HCN) channels bind cAMP preferably in the open state. Using sea urchin HCN channels, Idikuda et al. reveal less cAMP binding to the closed state and further reduced binding to the inactivated state and thus demonstrate intricate communication between the gate and ligand-binding domain. Hyperpolarization-activated cyclic-nucleotide–modulated (HCN) channels are nonselective cation channels that regulate electrical activity in the heart and brain. Previous studies of mouse HCN2 (mHCN2) channels have shown that cAMP binds preferentially to and stabilizes these channels in the open state—a simple but elegant implementation of ligand-dependent gating. Distinct from mammalian isoforms, the sea urchin (spHCN) channel exhibits strong voltage-dependent inactivation in the absence of cAMP. Here, using fluorescently labeled cAMP molecules as a marker for cAMP binding, we report that the inactivated spHCN channel displays reduced cAMP binding compared with the closed channel. The reduction in cAMP binding is a voltage-dependent process but proceeds at a much slower rate than the movement of the voltage sensor. A single point mutation in the last transmembrane domain near the channel’s gate, F459L, abolishes inactivation and concurrently reverses the response to hyperpolarizing voltage steps from a decrease to an increase in cAMP binding. ZD7288, an open channel blocker that interacts with a region close to the activation/inactivation gate, dampens the reduction of cAMP binding to inactivated spHCN channels. In addition, compared with closed and “locked” closed channels, increased cAMP binding is observed in channels purposely locked in the open state upon hyperpolarization. Thus, the order of cAMP-binding affinity, measured by the fluorescence signal from labeled cAMP, ranges from high in the open state to intermediate in the closed state to low in the inactivated state. Our work on spHCN channels demonstrates intricate state-dependent communications between the gate and ligand-binding domain and provides new mechanistic insight into channel inactivation/desensitization.
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Affiliation(s)
- Vinay Idikuda
- Department of Physiology and Biophysics, School of Medicine, Virginia Commonwealth University, Richmond, VA
| | - Weihua Gao
- Department of Physiology and Biophysics, School of Medicine, Virginia Commonwealth University, Richmond, VA
| | - Zhuocheng Su
- Department of Physiology and Biophysics, School of Medicine, Virginia Commonwealth University, Richmond, VA
| | - Qinglian Liu
- Department of Physiology and Biophysics, School of Medicine, Virginia Commonwealth University, Richmond, VA
| | - Lei Zhou
- Department of Physiology and Biophysics, School of Medicine, Virginia Commonwealth University, Richmond, VA
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17
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Infield DT, Matulef K, Galpin JD, Lam K, Tajkhorshid E, Ahern CA, Valiyaveetil FI. Main-chain mutagenesis reveals intrahelical coupling in an ion channel voltage-sensor. Nat Commun 2018; 9:5055. [PMID: 30498243 PMCID: PMC6265297 DOI: 10.1038/s41467-018-07477-3] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2018] [Accepted: 11/01/2018] [Indexed: 11/20/2022] Open
Abstract
Membrane proteins are universal signal decoders. The helical transmembrane segments of these proteins play central roles in sensory transduction, yet the mechanistic contributions of secondary structure remain unresolved. To investigate the role of main-chain hydrogen bonding on transmembrane function, we encoded amide-to-ester substitutions at sites throughout the S4 voltage-sensing segment of Shaker potassium channels, a region that undergoes rapid, voltage-driven movement during channel gating. Functional measurements of ester-harboring channels highlight a transitional region between α-helical and 310 segments where hydrogen bond removal is particularly disruptive to voltage-gating. Simulations of an active voltage sensor reveal that this region features a dynamic hydrogen bonding pattern and that its helical structure is reliant upon amide support. Overall, the data highlight the specialized role of main-chain chemistry in the mechanism of voltage-sensing; other catalytic transmembrane segments may enlist similar strategies in signal transduction mechanisms. The helical transmembrane segments of membrane proteins play central roles in sensory transduction but the mechanistic basis for their function remains unresolved. Here the authors identify regions in the S4 voltage-sensing segment of Shaker potassium channels where local helical structure is reliant upon backbone amide support.
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Affiliation(s)
- Daniel T Infield
- Department of Molecular Physiology and Biophysics, Iowa Neuroscience Institute, University of Iowa, Iowa City, IA, 52242, USA
| | - Kimberly Matulef
- Program in Chemical Biology, Department of Physiology and Pharmacology, Oregon Health Sciences University, Portland, 97239, OR, USA
| | - Jason D Galpin
- Department of Molecular Physiology and Biophysics, Iowa Neuroscience Institute, University of Iowa, Iowa City, IA, 52242, USA
| | - Kin Lam
- Department of Physics, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA.,NIH Center for Macromolecular Modeling and Bioinformatics, Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA
| | - Emad Tajkhorshid
- Department of Physics, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA.,NIH Center for Macromolecular Modeling and Bioinformatics, Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA.,Department of Biochemistry, Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA
| | - Christopher A Ahern
- Department of Molecular Physiology and Biophysics, Iowa Neuroscience Institute, University of Iowa, Iowa City, IA, 52242, USA.
| | - Francis I Valiyaveetil
- Program in Chemical Biology, Department of Physiology and Pharmacology, Oregon Health Sciences University, Portland, 97239, OR, USA.
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18
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Abstract
Kobertz comments on the family of “silent” Kv2-related regulatory subunits and a new study investigating their assembly idiosyncrasies.
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Affiliation(s)
- William R Kobertz
- Department of Biochemistry and Molecular Pharmacology, Programs in Neuroscience and Chemical Biology, University of Massachusetts Medical School, Worcester, MA
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19
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Pisupati A, Mickolajczyk KJ, Horton W, van Rossum DB, Anishkin A, Chintapalli SV, Li X, Chu-Luo J, Busey G, Hancock WO, Jegla T. The S6 gate in regulatory Kv6 subunits restricts heteromeric K + channel stoichiometry. J Gen Physiol 2018; 150:1702-1721. [PMID: 30322883 PMCID: PMC6279357 DOI: 10.1085/jgp.201812121] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2018] [Revised: 07/03/2018] [Accepted: 09/26/2018] [Indexed: 11/24/2022] Open
Abstract
Atypical substitutions in the S6 activation gate sequence distinguish “regulatory” Kv subunits, which cannot homotetramerize due to T1 self-incompatibility. Pisupati et al. show that such substitutions in Kv6 work together with self-incompatibility to restrict Kv2:Kv6 heteromeric stoichiometry to 3:1. The Shaker-like family of voltage-gated K+ channels comprises four functionally independent gene subfamilies, Shaker (Kv1), Shab (Kv2), Shaw (Kv3), and Shal (Kv4), each of which regulates distinct aspects of neuronal excitability. Subfamily-specific assembly of tetrameric channels is mediated by the N-terminal T1 domain and segregates Kv1–4, allowing multiple channel types to function independently in the same cell. Typical Shaker-like Kv subunits can form functional channels as homotetramers, but a group of mammalian Kv2-related genes (Kv5.1, Kv6s, Kv8s, and Kv9s) encodes subunits that have a “silent” or “regulatory” phenotype characterized by T1 self-incompatibility. These channels are unable to form homotetramers, but instead heteromerize with Kv2.1 or Kv2.2 to diversify the functional properties of these delayed rectifiers. While T1 self-incompatibility predicts that these heterotetramers could contain up to two regulatory (R) subunits, experiments show a predominance of 3:1R stoichiometry in which heteromeric channels contain a single regulatory subunit. Substitution of the self-compatible Kv2.1 T1 domain into the regulatory subunit Kv6.4 does not alter the stoichiometry of Kv2.1:Kv6.4 heteromers. Here, to identify other channel structures that might be responsible for favoring the 3:1R stoichiometry, we compare the sequences of mammalian regulatory subunits to independently evolved regulatory subunits from cnidarians. The most widespread feature of regulatory subunits is the presence of atypical substitutions in the highly conserved consensus sequence of the intracellular S6 activation gate of the pore. We show that two amino acid substitutions in the S6 gate of the regulatory subunit Kv6.4 restrict the functional stoichiometry of Kv2.1:Kv6.4 to 3:1R by limiting the formation and function of 2:2R heteromers. We propose a two-step model for the evolution of the asymmetric 3:1R stoichiometry, which begins with evolution of self-incompatibility to establish the regulatory phenotype, followed by drift of the activation gate consensus sequence under relaxed selection to limit stoichiometry to 3:1R.
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Affiliation(s)
- Aditya Pisupati
- Department of Biology, Pennsylvania State University, University Park, PA.,Medical Scientist Training Program, College of Medicine, Pennsylvania State University, Hershey, PA
| | - Keith J Mickolajczyk
- Department of Biomedical Engineering, Pennsylvania State University, University Park, PA
| | - William Horton
- Department of Animal Science, Pennsylvania State University, University Park, PA
| | - Damian B van Rossum
- The Jake Gittlen Laboratories for Cancer Research, College of Medicine, Pennsylvania State University, Hershey, PA.,Division of Experimental Pathology, Department of Pathology, College of Medicine, Pennsylvania State University, Hershey, PA
| | - Andriy Anishkin
- Department of Biology, University of Maryland, College Park, MD
| | - Sree V Chintapalli
- Arkansas Children's Nutrition Center and Department of Pediatrics, University of Arkansas for Medical Sciences, Little Rock, AR
| | - Xiaofan Li
- Department of Biology, Pennsylvania State University, University Park, PA
| | - Jose Chu-Luo
- Department of Biology, Pennsylvania State University, University Park, PA
| | - Gregory Busey
- Department of Biology, Pennsylvania State University, University Park, PA
| | - William O Hancock
- Department of Biomedical Engineering, Pennsylvania State University, University Park, PA
| | - Timothy Jegla
- Department of Biology, Pennsylvania State University, University Park, PA .,Huck Institutes of the Life Sciences, Pennsylvania State University, University Park, PA
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20
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Zubcevic L, Le S, Yang H, Lee SY. Conformational plasticity in the selectivity filter of the TRPV2 ion channel. Nat Struct Mol Biol 2018; 25:405-415. [PMID: 29728656 PMCID: PMC6025827 DOI: 10.1038/s41594-018-0059-z] [Citation(s) in RCA: 62] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2018] [Accepted: 03/22/2018] [Indexed: 12/13/2022]
Abstract
Transient receptor potential vanilloid (TRPV) channels are activated by ligands and heat and are involved in various physiological processes. In contrast to the architecturally related voltage-gated cation channels, TRPV1 and TRPV2 subtypes possess another activation gate at the selectivity filter that can open widely enough to permeate large organic cations. Despite recent structural advances, the mechanism of selectivity filter gating and permeation for both metal ions and large molecules by TRPV1 or TRPV2 is not well known. Here, we determined two crystal structures of rabbit TRPV2 in its Ca2+-bound and resiniferatoxin (RTx)- and Ca2+-bound forms, to 3.9 Å and 3.1 Å, respectively. Notably, our structures show that RTx binding leads to two-fold symmetric opening of the selectivity filter of TRPV2 that is wide enough for large organic cation permeation. Combined with functional characterizations, our studies reveal a structural basis for permeation of Ca2+ and large organic cations in TRPV2.
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Affiliation(s)
- Lejla Zubcevic
- Department of Biochemistry, Duke University School of Medicine, Durham, NC, USA
| | - Son Le
- Department of Biochemistry, Duke University School of Medicine, Durham, NC, USA
| | - Huanghe Yang
- Department of Biochemistry, Duke University School of Medicine, Durham, NC, USA.,Department of Neurobiology, Duke University School of Medicine, Durham, NC, USA
| | - Seok-Yong Lee
- Department of Biochemistry, Duke University School of Medicine, Durham, NC, USA.
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21
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Gating interaction maps reveal a noncanonical electromechanical coupling mode in the Shaker K + channel. Nat Struct Mol Biol 2018; 25:320-326. [PMID: 29581567 PMCID: PMC6170002 DOI: 10.1038/s41594-018-0047-3] [Citation(s) in RCA: 50] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2017] [Accepted: 02/05/2018] [Indexed: 11/08/2022]
Abstract
Membrane potential regulates the activity of voltage-dependent ion channels via specialized voltage-sensing modules but the mechanisms involved in coupling voltage-sensor movement to pore opening remain unclear due to lack of resting state structures and robust methods to identify allosteric pathways. Here, using a newly developed interaction energy analysis, we probe the interfaces of the voltage-sensing and pore modules in the drosophila Shaker K+ channel. Our measurements reveal unexpectedly strong equilibrium gating interactions between contacts at the S4 and S5 helices in addition to those between S6 and S4–S5 linker. Network analysis of MD trajectories shows that the voltage-sensor and pore motions are linked by two distinct pathways- canonical one through the S4–S5 linker and a hitherto unknown pathway akin to rack and pinion coupling involving S4 and S5 helices. Our findings highlight the central role of the S5 helix in electromechanical transduction in the VGIC superfamily.
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22
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Abstract
Armstrong and Hollingworth discuss inactivation in the light of modern structural data from K and Na channels. We are wired with conducting cables called axons that rapidly transmit electrical signals (e.g., “Ouch!”) from, for example, the toe to the spinal cord. Because of the high internal resistance of axons (salt water rather than copper), a signal must be reinforced after traveling a short distance. Reinforcement is accomplished by ion channels, Na channels for detecting the signal and reinforcing it by driving it further positive (to near 50 mV) and K channels for then restoring it to the resting level (near −70 mV). The signal is called an action potential and has a duration of roughly a millisecond. The return of membrane voltage (Vm) to the resting level after an action potential is facilitated by “inactivation” of the Na channels: i.e., an internal particle diffuses into the mouth of any open Na channel and temporarily blocks it. Some types of K channels also show inactivation after being open for a time. N-type inactivation of K channels has a relatively fast time course and involves diffusion of the N-terminal of one of the channel’s four identical subunits into the channel’s inner mouth, if it is open. This mechanism is similar to Na channel inactivation. Both Na and K channels also display slower inactivation processes. C inactivation in K channels involves changes in the channel’s outer mouth, the “selectivity filter,” whose normal function is to prevent Na+ ions from entering the K channel. C inactivation deforms the filter so that neither K+ nor Na+ can pass.
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Affiliation(s)
- Clay M Armstrong
- Department of Physiology, University of Pennsylvania, Philadelphia, PA
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23
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Crystal structure of an inactivated mutant mammalian voltage-gated K + channel. Nat Struct Mol Biol 2017; 24:857-865. [PMID: 28846092 DOI: 10.1038/nsmb.3457] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2017] [Accepted: 08/02/2017] [Indexed: 11/08/2022]
Abstract
C-type inactivation underlies important roles played by voltage-gated K+ (Kv) channels. Functional studies have provided strong evidence that a common underlying cause of this type of inactivation is an alteration near the extracellular end of the channel's ion-selectivity filter. Unlike N-type inactivation, which is known to reflect occlusion of the channel's intracellular end, the structural mechanism of C-type inactivation remains controversial and may have many detailed variations. Here we report that in voltage-gated Shaker K+ channels lacking N-type inactivation, a mutation enhancing inactivation disrupts the outermost K+ site in the selectivity filter. Furthermore, in a crystal structure of the Kv1.2-2.1 chimeric channel bearing the same mutation, the outermost K+ site, which is formed by eight carbonyl-oxygen atoms, appears to be slightly too small to readily accommodate a K+ ion and in fact exhibits little ion density; this structural finding is consistent with the functional hallmark of C-type inactivation.
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24
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25
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Sun J, MacKinnon R. Cryo-EM Structure of a KCNQ1/CaM Complex Reveals Insights into Congenital Long QT Syndrome. Cell 2017; 169:1042-1050.e9. [PMID: 28575668 PMCID: PMC5562354 DOI: 10.1016/j.cell.2017.05.019] [Citation(s) in RCA: 226] [Impact Index Per Article: 28.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2017] [Revised: 04/19/2017] [Accepted: 05/10/2017] [Indexed: 01/08/2023]
Abstract
KCNQ1 is the pore-forming subunit of cardiac slow-delayed rectifier potassium (IKs) channels. Mutations in the kcnq1 gene are the leading cause of congenital long QT syndrome (LQTS). Here, we present the cryoelectron microscopy (cryo-EM) structure of a KCNQ1/calmodulin (CaM) complex. The conformation corresponds to an "uncoupled," PIP2-free state of KCNQ1, with activated voltage sensors and a closed pore. Unique structural features within the S4-S5 linker permit uncoupling of the voltage sensor from the pore in the absence of PIP2. CaM contacts the KCNQ1 voltage sensor through a specific interface involving a residue on CaM that is mutated in a form of inherited LQTS. Using an electrophysiological assay, we find that this mutation on CaM shifts the KCNQ1 voltage-activation curve. This study describes one physiological form of KCNQ1, depolarized voltage sensors with a closed pore in the absence of PIP2, and reveals a regulatory interaction between CaM and KCNQ1 that may explain CaM-mediated LQTS.
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Affiliation(s)
- Ji Sun
- Laboratory of Molecular Neurobiology and Biophysics and Howard Hughes Medical Institute, The Rockefeller University, 1230 York Avenue, New York, NY 10065, USA
| | - Roderick MacKinnon
- Laboratory of Molecular Neurobiology and Biophysics and Howard Hughes Medical Institute, The Rockefeller University, 1230 York Avenue, New York, NY 10065, USA.
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26
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Starek G, Freites JA, Bernèche S, Tobias DJ. Gating energetics of a voltage-dependent K + channel pore domain. J Comput Chem 2017; 38:1472-1478. [PMID: 28211063 DOI: 10.1002/jcc.24742] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2016] [Revised: 01/03/2017] [Accepted: 01/05/2017] [Indexed: 01/14/2023]
Abstract
We used targeted molecular dynamics, informed by experimentally determined inter-atomic distances defining the pore region of open and closed states of the KvAP voltage-gated potassium channel, to generate a gating pathway of the pore domain in the absence of the voltage-sensing domains. We then performed umbrella sampling simulations along this pathway to calculate a potential of mean force that describes the free energy landscape connecting the closed and open conformations of the pore domain. The resulting energetic landscape displays three minima, corresponding to stable open, closed, and intermediate conformations with roughly similar stabilities. We found that the extent of hydration of the interior of the pore domain could influence the free energy landscape for pore opening/closing. © 2017 Wiley Periodicals, Inc.
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Affiliation(s)
- Greg Starek
- Swiss Institute of Bioinformatics and Biozentrum, University of Basel, Klingelbergstrasse 50/70, Basel, CH-4056, Switzerland.,Department of Chemistry, University of California, Irvine, California, 92697-2025
| | - J Alfredo Freites
- Department of Chemistry, University of California, Irvine, California, 92697-2025
| | - Simon Bernèche
- Swiss Institute of Bioinformatics and Biozentrum, University of Basel, Klingelbergstrasse 50/70, Basel, CH-4056, Switzerland
| | - Douglas J Tobias
- Department of Chemistry, University of California, Irvine, California, 92697-2025
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Bohnen MS, Peng G, Robey SH, Terrenoire C, Iyer V, Sampson KJ, Kass RS. Molecular Pathophysiology of Congenital Long QT Syndrome. Physiol Rev 2017; 97:89-134. [PMID: 27807201 PMCID: PMC5539372 DOI: 10.1152/physrev.00008.2016] [Citation(s) in RCA: 114] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Ion channels represent the molecular entities that give rise to the cardiac action potential, the fundamental cellular electrical event in the heart. The concerted function of these channels leads to normal cyclical excitation and resultant contraction of cardiac muscle. Research into cardiac ion channel regulation and mutations that underlie disease pathogenesis has greatly enhanced our knowledge of the causes and clinical management of cardiac arrhythmia. Here we review the molecular determinants, pathogenesis, and pharmacology of congenital Long QT Syndrome. We examine mechanisms of dysfunction associated with three critical cardiac currents that comprise the majority of congenital Long QT Syndrome cases: 1) IKs, the slow delayed rectifier current; 2) IKr, the rapid delayed rectifier current; and 3) INa, the voltage-dependent sodium current. Less common subtypes of congenital Long QT Syndrome affect other cardiac ionic currents that contribute to the dynamic nature of cardiac electrophysiology. Through the study of mutations that cause congenital Long QT Syndrome, the scientific community has advanced understanding of ion channel structure-function relationships, physiology, and pharmacological response to clinically employed and experimental pharmacological agents. Our understanding of congenital Long QT Syndrome continues to evolve rapidly and with great benefits: genotype-driven clinical management of the disease has improved patient care as precision medicine becomes even more a reality.
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Affiliation(s)
- M S Bohnen
- Department of Pharmacology, Columbia University Medical Center, New York, New York; and The New York Stem Cell Foundation Research Institute, New York, New York
| | - G Peng
- Department of Pharmacology, Columbia University Medical Center, New York, New York; and The New York Stem Cell Foundation Research Institute, New York, New York
| | - S H Robey
- Department of Pharmacology, Columbia University Medical Center, New York, New York; and The New York Stem Cell Foundation Research Institute, New York, New York
| | - C Terrenoire
- Department of Pharmacology, Columbia University Medical Center, New York, New York; and The New York Stem Cell Foundation Research Institute, New York, New York
| | - V Iyer
- Department of Pharmacology, Columbia University Medical Center, New York, New York; and The New York Stem Cell Foundation Research Institute, New York, New York
| | - K J Sampson
- Department of Pharmacology, Columbia University Medical Center, New York, New York; and The New York Stem Cell Foundation Research Institute, New York, New York
| | - R S Kass
- Department of Pharmacology, Columbia University Medical Center, New York, New York; and The New York Stem Cell Foundation Research Institute, New York, New York
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Giese MH, Gardner A, Hansen A, Sanguinetti MC. Molecular mechanisms of Slo2 K + channel closure. J Physiol 2016; 595:2321-2336. [PMID: 27682982 DOI: 10.1113/jp273225] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2016] [Accepted: 09/20/2016] [Indexed: 01/02/2023] Open
Abstract
KEY POINTS Intracellular Na+ -activated Slo2 potassium channels are in a closed state under normal physiological conditions, although their mechanisms of ion permeation gating are not well understood. A cryo-electron microscopy structure of Slo2.2 suggests that the ion permeation pathway of these channels is closed by a single constriction of the inner pore formed by the criss-crossing of the cytoplasmic ends of the S6 segments (the S6 bundle crossing) at a conserved Met residue. Functional characterization of mutant Slo2 channels suggests that hydrophobic interactions between Leu residues in the upper region of the S6 segments contribute to stabilizing the inner pore in a non-conducting state. Mutation of the conserved Met residues in the S6 segments to the negatively-charged Glu did not induce constitutive opening of Slo2.1 or Slo2.2, suggesting that ion permeation of Slo2 channels is not predominantly gated by the S6 bundle crossing. ABSTRACT Large conductance K+ -selective Slo2 channels are in a closed state unless activated by elevated [Na+ ]i . Our previous studies suggested that the pore helix/selectivity filter serves as the activation gate in Slo2 channels. In the present study, we evaluated two other potential mechanisms for stabilization of Slo2 channels in a closed state: (1) dewetting and collapse of the inner pore (hydrophobic gating) and (2) constriction of the inner pore by tight criss-crossing of the cytoplasmic ends of the S6 α-helical segments. Slo2 channels contain two conserved Leu residues in each of the four S6 segments that line the inner pore region nearest the bottom of the selectivity filter. To evaluate the potential role of these residues in hydrophobic gating, Leu267 and Leu270 in human Slo2.1 were each replaced by 15 different residues. The relative conductance of mutant channels was highly dependent on hydrophilicity and volume of the amino acid substituted for Leu267 and was maximal with L267H. Consistent with their combined role in hydrophobic gating, replacement of both Leu residues with the isosteric but polar residue Asn (L267N/L270N) stabilized channels in a fully open state. In a recent cryo-electron microscopy structure of chicken Slo2.2, the ion permeation pathway of the channel is closed by a constriction of the inner pore formed by criss-crossing of the S6 segments at a conserved Met. Inconsistent with the S6 segment crossing forming the activation gate, replacement of the homologous Met residues in human Slo2.1 or Slo2.2 with the negatively-charged Glu did not induce constitutive channel opening.
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Affiliation(s)
- M Hunter Giese
- Nora Eccles Harrison Cardiovascular Research & Training Institute
| | - Alison Gardner
- Nora Eccles Harrison Cardiovascular Research & Training Institute
| | - Angela Hansen
- Nora Eccles Harrison Cardiovascular Research & Training Institute
| | - Michael C Sanguinetti
- Nora Eccles Harrison Cardiovascular Research & Training Institute.,Department of Internal Medicine, Division of Cardiovascular Medicine, University of Utah, Salt Lake City, UT, USA
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Naranjo D, Moldenhauer H, Pincuntureo M, Díaz-Franulic I. Pore size matters for potassium channel conductance. J Gen Physiol 2016; 148:277-91. [PMID: 27619418 PMCID: PMC5037345 DOI: 10.1085/jgp.201611625] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2016] [Accepted: 08/10/2016] [Indexed: 01/31/2023] Open
Abstract
Ion channels are membrane proteins that mediate efficient ion transport across the hydrophobic core of cell membranes, an unlikely process in their absence. K+ channels discriminate K+ over cations with similar radii with extraordinary selectivity and display a wide diversity of ion transport rates, covering differences of two orders of magnitude in unitary conductance. The pore domains of large- and small-conductance K+ channels share a general architectural design comprising a conserved narrow selectivity filter, which forms intimate interactions with permeant ions, flanked by two wider vestibules toward the internal and external openings. In large-conductance K+ channels, the inner vestibule is wide, whereas in small-conductance channels it is narrow. Here we raise the idea that the physical dimensions of the hydrophobic internal vestibule limit ion transport in K+ channels, accounting for their diversity in unitary conductance.
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Affiliation(s)
- David Naranjo
- Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de Valparaíso, Playa Ancha, Valparaíso 2360103, Chile
| | - Hans Moldenhauer
- Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de Valparaíso, Playa Ancha, Valparaíso 2360103, Chile
| | - Matías Pincuntureo
- Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de Valparaíso, Playa Ancha, Valparaíso 2360103, Chile Programa de Doctorado en Ciencias, mención Biofísica y Biología Computacional, Universidad de Valparaíso, Valparaíso 2360103, Chile
| | - Ignacio Díaz-Franulic
- Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de Valparaíso, Playa Ancha, Valparaíso 2360103, Chile Center for Bioinformatics and Integrative Biology, Universidad Andrés Bello, Santiago 8370146, Chile Fraunhofer Chile Research, Las Condes 7550296, Chile
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31
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Balajthy A, Somodi S, Pethő Z, Péter M, Varga Z, Szabó GP, Paragh G, Vígh L, Panyi G, Hajdu P. 7DHC-induced changes of Kv1.3 operation contributes to modified T cell function in Smith-Lemli-Opitz syndrome. Pflugers Arch 2016; 468:1403-18. [DOI: 10.1007/s00424-016-1851-4] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2016] [Revised: 06/08/2016] [Accepted: 06/10/2016] [Indexed: 02/06/2023]
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Affiliation(s)
- Jon T Sack
- Department of Physiology and Membrane Biology and Department of Anesthesiology and Pain Medicine, University of California, Davis, Davis, CA 95616 Department of Physiology and Membrane Biology and Department of Anesthesiology and Pain Medicine, University of California, Davis, Davis, CA 95616
| | - Drew C Tilley
- Department of Physiology and Membrane Biology and Department of Anesthesiology and Pain Medicine, University of California, Davis, Davis, CA 95616
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Díaz-Franulic I, Sepúlveda RV, Navarro-Quezada N, González-Nilo F, Naranjo D. Pore dimensions and the role of occupancy in unitary conductance of Shaker K channels. ACTA ACUST UNITED AC 2016. [PMID: 26216859 PMCID: PMC4516780 DOI: 10.1085/jgp.201411353] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The resistance of the inner vestibule limits Shaker’s conductance. K channels mediate the selective passage of K+ across the plasma membrane by means of intimate interactions with ions at the pore selectivity filter located near the external face. Despite high conservation of the selectivity filter, the K+ transport properties of different K channels vary widely, with the unitary conductance spanning a range of over two orders of magnitude. Mutation of Pro475, a residue located at the cytoplasmic entrance of the pore of the small-intermediate conductance K channel Shaker (Pro475Asp (P475D) or Pro475Gln (P475Q)), increases Shaker’s reported ∼20-pS conductance by approximately six- and approximately threefold, respectively, without any detectable effect on its selectivity. These findings suggest that the structural determinants underlying the diversity of K channel conductance are distinct from the selectivity filter, making P475D and P475Q excellent probes to identify key determinants of the K channel unitary conductance. By measuring diffusion-limited unitary outward currents after unilateral addition of 2 M sucrose to the internal solution to increase its viscosity, we estimated a pore internal radius of capture of ∼0.82 Å for all three Shaker variants (wild type, P475D, and P475Q). This estimate is consistent with the internal entrance of the Kv1.2/2.1 structure if the effective radius of hydrated K+ is set to ∼4 Å. Unilateral exposure to sucrose allowed us to estimate the internal and external access resistances together with that of the inner pore. We determined that Shaker resistance resides mainly in the inner cavity, whereas only ∼8% resides in the selectivity filter. To reduce the inner resistance, we introduced additional aspartate residues into the internal vestibule to favor ion occupancy. No aspartate addition raised the maximum unitary conductance, measured at saturating [K+], beyond that of P475D, suggesting an ∼200-pS conductance ceiling for Shaker. This value is approximately one third of the maximum conductance of the large conductance K (BK) channel (the K channel of highest conductance), reducing the energy gap between their K+ transport rates to ∼1 kT. Thus, although Shaker’s pore sustains ion translocation as the BK channel’s does, higher energetic costs of ion stabilization or higher friction with the ion’s rigid hydration cage in its narrower aqueous cavity may entail higher resistance.
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Affiliation(s)
- Ignacio Díaz-Franulic
- Centro Interdisciplinario de Neurociencia de Valparaíso and Programa de Doctorado en Ciencias mención Neurociencia, Universidad de Valparaíso, Valparaíso 2360103, Chile Centro Interdisciplinario de Neurociencia de Valparaíso and Programa de Doctorado en Ciencias mención Neurociencia, Universidad de Valparaíso, Valparaíso 2360103, Chile
| | - Romina V Sepúlveda
- Center for Bioinformatics and Integrative Biology, Universidad Andrés Bello, Santiago 8370146, Chile
| | - Nieves Navarro-Quezada
- Centro Interdisciplinario de Neurociencia de Valparaíso and Programa de Doctorado en Ciencias mención Neurociencia, Universidad de Valparaíso, Valparaíso 2360103, Chile
| | - Fernando González-Nilo
- Centro Interdisciplinario de Neurociencia de Valparaíso and Programa de Doctorado en Ciencias mención Neurociencia, Universidad de Valparaíso, Valparaíso 2360103, Chile Center for Bioinformatics and Integrative Biology, Universidad Andrés Bello, Santiago 8370146, Chile
| | - David Naranjo
- Centro Interdisciplinario de Neurociencia de Valparaíso and Programa de Doctorado en Ciencias mención Neurociencia, Universidad de Valparaíso, Valparaíso 2360103, Chile
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Okuda H, Yonezawa Y, Takano Y, Okamura Y, Fujiwara Y. Direct Interaction between the Voltage Sensors Produces Cooperative Sustained Deactivation in Voltage-gated H+ Channel Dimers. J Biol Chem 2016; 291:5935-5947. [PMID: 26755722 PMCID: PMC4786727 DOI: 10.1074/jbc.m115.666834] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2015] [Revised: 12/23/2015] [Indexed: 01/31/2023] Open
Abstract
The voltage-gated H(+) channel (Hv) is a voltage sensor domain-like protein consisting of four transmembrane segments (S1-S4). The native Hv structure is a homodimer, with the two channel subunits functioning cooperatively. Here we show that the two voltage sensor S4 helices within the dimer directly cooperate via a π-stacking interaction between Trp residues at the middle of each segment. Scanning mutagenesis showed that Trp situated around the original position provides the slow gating kinetics characteristic of the dimer's cooperativity. Analyses of the Trp mutation on the dimeric and monomeric channel backgrounds and analyses with tandem channel constructs suggested that the two Trp residues within the dimer are functionally coupled during Hv deactivation but are less so during activation. Molecular dynamics simulation also showed direct π-stacking of the two Trp residues. These results provide new insight into the cooperative function of voltage-gated channels, where adjacent voltage sensor helices make direct physical contact and work as a single unit according to the gating process.
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Affiliation(s)
- Hiroko Okuda
- From Division of Integrative Physiology, Graduate School of Medicine
| | - Yasushige Yonezawa
- the High Pressure Protein Research Center, Institute of Advanced Technology, Kinki University, Kinokawa 649-6493, Wakayama, Japan, and
| | - Yu Takano
- the Institute for Protein Research, and; the Graduate School of Information Sciences, Hiroshima City University, Hiroshima 731-3194, Hiroshima, Japan
| | - Yasushi Okamura
- From Division of Integrative Physiology, Graduate School of Medicine,; the Graduate School of Frontier Biosciences, Osaka University, Suita 565-0871, Osaka, Japan
| | - Yuichiro Fujiwara
- From Division of Integrative Physiology, Graduate School of Medicine,.
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Yonkunas M, Kurnikova M. The Hydrophobic Effect Contributes to the Closed State of a Simplified Ion Channel through a Conserved Hydrophobic Patch at the Pore-Helix Crossing. Front Pharmacol 2015; 6:284. [PMID: 26640439 PMCID: PMC4661268 DOI: 10.3389/fphar.2015.00284] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2015] [Accepted: 11/10/2015] [Indexed: 11/13/2022] Open
Abstract
Ion selectivity-filter structures are strikingly similar throughout the large family of K++ channels and other p-loop-like receptors (i.e., glutamate receptors). At the same time, the triggers for opening these channels, or gating, are diverse. Two questions that remain unanswered regarding these channels are: (1) what force(s) stabilize the closed non-conducting channel-pore conformation? And (2) what is the free energy associated with transitioning from a closed (non-conducting) to an open (conducting) channel-pore conformation? The effects of charge and hydrophobicity on the conformational states of a model tetrameric biological ion channel are shown utilizing the amino acid sequence from the K+ channel KcsA as the model “channel”. Its widely conserved hydrophobic bundle crossing located adjacent to the lipid head-groups at the intracellular side of the membrane was calculated to have a 5 kcal/mol free energy difference between modeled open and closed conformations. Simulated mutants of amino acids within the hydrophobic region significantly contribute to the size of this difference. Specifically for KcsA, these residues are part of the pH sensor important for channel gating and our results are in agreement with published electrophysiology data. Our simulations support the idea that the hydrophobic effect contributes significantly to the stability of the closed conformation in tetrameric ion channels with a hydrophobic bundle crossing positioned in proximity to the lipid head groups of the biological membrane.
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Affiliation(s)
- Michael Yonkunas
- Department of Chemistry, Carnegie Mellon University, Pittsburgh PA, USA
| | - Maria Kurnikova
- Department of Chemistry, Carnegie Mellon University, Pittsburgh PA, USA
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36
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Stas JI, Bocksteins E, Labro AJ, Snyders DJ. Modulation of Closed-State Inactivation in Kv2.1/Kv6.4 Heterotetramers as Mechanism for 4-AP Induced Potentiation. PLoS One 2015; 10:e0141349. [PMID: 26505474 PMCID: PMC4623978 DOI: 10.1371/journal.pone.0141349] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2015] [Accepted: 10/06/2015] [Indexed: 12/26/2022] Open
Abstract
The voltage-gated K+ (Kv) channel subunits Kv2.1 and Kv2.2 are expressed in almost every tissue. The diversity of Kv2 current is increased by interacting with the electrically silent Kv (KvS) subunits Kv5-Kv6 and Kv8-Kv9, into functional heterotetrameric Kv2/KvS channels. These Kv2/KvS channels possess unique biophysical properties and display a more tissue-specific expression pattern, making them more desirable pharmacological and therapeutic targets. However, little is known about the pharmacological properties of these heterotetrameric complexes. We demonstrate that Kv5.1, Kv8.1 and Kv9.3 currents were inhibited differently by the channel blocker 4-aminopyridine (4-AP) compared to Kv2.1 homotetramers. In contrast, Kv6.4 currents were potentiated by 4-AP while displaying moderately increased affinities for the channel pore blockers quinidine and flecainide. We found that the 4-AP induced potentiation of Kv6.4 currents was caused by modulation of the Kv6.4-mediated closed-state inactivation: suppression by 4-AP of the Kv2.1/Kv6.4 closed-state inactivation recovered a population of Kv2.1/Kv6.4 channels that was inactivated at resting conditions, i.e. at a holding potential of -80 mV. This modulation also resulted in a slower initiation and faster recovery from closed-state inactivation. Using chimeric substitutions between Kv6.4 and Kv9.3 subunits, we demonstrated that the lower half of the S6 domain (S6c) plays a crucial role in the 4-AP induced potentiation. These results demonstrate that KvS subunits modify the pharmacological response of Kv2 subunits when assembled in heterotetramers and illustrate the potential of KvS subunits to provide unique pharmacological properties to the heterotetramers, as is the case for 4-AP on Kv2.1/Kv6.4 channels.
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Affiliation(s)
- Jeroen I. Stas
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp, CDE, Universiteitsplein 1, Antwerp, Belgium
| | - Elke Bocksteins
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp, CDE, Universiteitsplein 1, Antwerp, Belgium
| | - Alain J. Labro
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp, CDE, Universiteitsplein 1, Antwerp, Belgium
| | - Dirk J. Snyders
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp, CDE, Universiteitsplein 1, Antwerp, Belgium
- * E-mail:
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37
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Critical role for Orai1 C-terminal domain and TM4 in CRAC channel gating. Cell Res 2015; 25:963-80. [PMID: 26138675 DOI: 10.1038/cr.2015.80] [Citation(s) in RCA: 70] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2015] [Revised: 03/30/2015] [Accepted: 05/22/2015] [Indexed: 01/12/2023] Open
Abstract
Calcium flux through store-operated calcium entry is a major regulator of intracellular calcium homeostasis and various calcium signaling pathways. Two key components of the store-operated calcium release-activated calcium channel are the Ca(2+)-sensing protein stromal interaction molecule 1 (STIM1) and the channel pore-forming protein Orai1. Following calcium depletion from the endoplasmic reticulum, STIM1 undergoes conformational changes that unmask an Orai1-activating domain called CAD. CAD binds to two sites in Orai1, one in the N terminal and one in the C terminal. Most previous studies suggested that gating is initiated by STIM1 binding at the Orai1 N-terminal site, just proximal to the TM1 pore-lining segment, and that binding at the C terminal simply anchors STIM1 within reach of the N terminal. However, a recent study had challenged this view and suggested that the Orai1 C-terminal region is more than a simple STIM1-anchoring site. In this study, we establish that the Orai1 C-terminal domain plays a direct role in gating. We identify a linker region between TM4 and the C-terminal STIM1-binding segment of Orai1 as a key determinant that couples STIM1 binding to gating. We further find that Proline 245 in TM4 of Orai1 is essential for stabilizing the closed state of the channel. Taken together with previous studies, our results suggest a dual-trigger mechanism of Orai1 activation in which binding of STIM1 at the N- and C-terminal domains of Orai1 induces rearrangements in proximal membrane segments to open the channel.
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38
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Liin SI, Barro-Soria R, Larsson HP. The KCNQ1 channel - remarkable flexibility in gating allows for functional versatility. J Physiol 2015; 593:2605-15. [PMID: 25653179 DOI: 10.1113/jphysiol.2014.287607] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2014] [Accepted: 01/30/2015] [Indexed: 12/12/2022] Open
Abstract
The KCNQ1 channel (also called Kv7.1 or KvLQT1) belongs to the superfamily of voltage-gated K(+) (Kv) channels. KCNQ1 shares several general features with other Kv channels but also displays a fascinating flexibility in terms of the mechanism of channel gating, which allows KCNQ1 to play different physiological roles in different tissues. This flexibility allows KCNQ1 channels to function as voltage-independent channels in epithelial tissues, whereas KCNQ1 function as voltage-activated channels with very slow kinetics in cardiac tissues. This flexibility is in part provided by the association of KCNQ1 with different accessory KCNE β-subunits and different modulators, but also seems like an integral part of KCNQ1 itself. The aim of this review is to describe the main mechanisms underlying KCNQ1 flexibility.
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Affiliation(s)
- Sara I Liin
- Department of Physiology and Biophysics, University of Miami, Miami, FL 33136, USA
| | - Rene Barro-Soria
- Department of Physiology and Biophysics, University of Miami, Miami, FL 33136, USA
| | - H Peter Larsson
- Department of Physiology and Biophysics, University of Miami, Miami, FL 33136, USA
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39
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Kasimova MA, Zaydman MA, Cui J, Tarek M. PIP₂-dependent coupling is prominent in Kv7.1 due to weakened interactions between S4-S5 and S6. Sci Rep 2015; 5:7474. [PMID: 25559286 PMCID: PMC4284513 DOI: 10.1038/srep07474] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2014] [Accepted: 11/21/2014] [Indexed: 02/06/2023] Open
Abstract
Among critical aspects of voltage-gated potassium (Kv) channels' functioning is the effective communication between their two composing domains, the voltage sensor (VSD) and the pore. This communication, called coupling, might be transmitted directly through interactions between these domains and, as recently proposed, indirectly through interactions with phosphatidylinositol-4,5-bisphosphate (PIP₂), a minor lipid of the inner plasma membrane leaflet. Here, we show how the two components of coupling, mediated by protein-protein or protein-lipid interactions, both contribute in the Kv7.1 functioning. On the one hand, using molecular dynamics simulations, we identified a Kv7.1 PIP₂ binding site that involves residues playing a key role in PIP₂-dependent coupling. On the other hand, combined theoretical and experimental approaches have shown that the direct interaction between the segments of the VSD (S4-S5) and the pore (S6) is weakened by electrostatic repulsion. Finally, we conclude that due to weakened protein-protein interactions, the PIP2-dependent coupling is especially prominent in Kv7.1.
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Affiliation(s)
- Marina A Kasimova
- 1] Université de Lorraine, Theory, Modeling and Simulations, UMR 7565, Vandoeuvre-lés-Nancy, F-54506 France [2] Lomonosov Moscow State University, Moscow, 119991, Russian Federation
| | - Mark A Zaydman
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Diseases, Cardiac Bioelectricity and Arrhythmia Center, Washington University in St. Louis, St. Louis, MO 63130-4862
| | - Jianmin Cui
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Diseases, Cardiac Bioelectricity and Arrhythmia Center, Washington University in St. Louis, St. Louis, MO 63130-4862
| | - Mounir Tarek
- 1] Université de Lorraine, Theory, Modeling and Simulations, UMR 7565, Vandoeuvre-lés-Nancy, F-54506 France [2] Centre National de la Recherche Scientifique, UMR 7565, Vandoeuvre-lés-Nancy, F-54506 France
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40
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Proline scan of the HERG channel S6 helix reveals the location of the intracellular pore gate. Biophys J 2014; 106:1057-69. [PMID: 24606930 DOI: 10.1016/j.bpj.2014.01.035] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2013] [Revised: 01/14/2014] [Accepted: 01/23/2014] [Indexed: 11/23/2022] Open
Abstract
In Shaker-like channels, the activation gate is formed at the bundle crossing by the convergence of the inner S6 helices near a conserved proline-valine-proline motif, which introduces a kink that allows for electromechanical coupling with voltage sensor motions via the S4-S5 linker. Human ether-a-go-go-related gene (hERG) channels lack the proline-valine-proline motif and the location of the intracellular pore gate and how it is coupled to S4 movement is less clear. Here, we show that proline substitutions within the S6 of hERG perturbed pore gate closure, trapping channels in the open state. Performing a proline scan of the inner S6 helix, from Ile(655) to Tyr(667) revealed that gate perturbation occurred with proximal (I655P-Q664P), but not distal (R665P-Y667P) substitutions, suggesting that Gln(664) marks the position of the intracellular gate in hERG channels. Using voltage-clamp fluorimetry and gating current analysis, we demonstrate that proline substitutions trap the activation gate open by disrupting the coupling between the voltage-sensing unit and the pore of the channel. We characterize voltage sensor movement in one such trapped-open mutant channel and demonstrate the kinetics of what we interpret to be intrinsic hERG voltage sensor movement.
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41
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Tu YC, Kuo CC. The differential contribution of GluN1 and GluN2 to the gating operation of the NMDA receptor channel. Pflugers Arch 2014; 467:1899-917. [PMID: 25339225 DOI: 10.1007/s00424-014-1630-z] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2014] [Revised: 09/27/2014] [Accepted: 10/12/2014] [Indexed: 11/25/2022]
Abstract
The Ν-methyl-D-aspartate (NMDA) receptor channel is an obligatory heterotetramer formed by two GluN1 and two GluN2 subunits. However, the differential contribution of the two different subunits to channel operation is not clear. We found that the apparent affinity of glycine to GluN1 (K gly ∼ 0.6 μM) is much higher than NMDA or glutamate to GluN2 (K NMDA ∼ 36 μM, K glu ∼ 4.8 μM). The binding rate constant (derived from the linear regression of the apparent macroscopic binding rates) of glycine to GluN1 (∼9.8 × 10(6) M(-1) s(-1)), however, is only slightly faster than NMDA to GluN2 (∼4.1 × 10(6) M(-1) s(-1)). Accordingly, the apparent unbinding rates of glycine from activated GluN1 (time constant ∼2 s) are much slower than NMDA from activated GluN2 (time constant ∼70 ms). Moreover, the decay of NMDA currents upon wash-off of both glycine and NMDA seems to follow the course of NMDA rather than glycine unbinding. But if only glycine is washed off, the current decay is much slower, apparently following the course of glycine unbinding. The apparent binding rate of glycine to the fully deactivated channel, in the absence of NMDA, is roughly the same as that measured with co-application of both ligands, whereas the apparent binding rate of NMDA to the fully deactivated channel in the absence of glycine is markedly slower. In this regard, it is interesting that the seventh residue in the highly conserved SYTANLAAF motif (A7) in GluN1 and GluN2 are so close that they may interact with each other to control the dimension of the external pore mouth. Moreover, specific mutations involving A7 in GluN1 but not in GluN2 result in channels showing markedly enhanced affinity to both glycine and NMDA and readily activated by only NMDA, as if the channel is already partially activated. We conclude that GluN2 is most likely directly responsible for the activation gate of the NMDA channel, whereas GluN1 assumes a role of more global control, especially on the gating conformational changes in GluN2. Structurally, this intersubunit regulatory interaction seems to involve the SYTANLAAF motif, especially the A7 residue.
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Affiliation(s)
- Ya-Chi Tu
- Department of Physiology, National Taiwan University College of Medicine, 1, Jen-Ai Road, 1st Section, Taipei, 100, Taiwan
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42
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Chowdhury S, Haehnel BM, Chanda B. Interfacial gating triad is crucial for electromechanical transduction in voltage-activated potassium channels. ACTA ACUST UNITED AC 2014; 144:457-67. [PMID: 25311635 PMCID: PMC4210428 DOI: 10.1085/jgp.201411185] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Gating interaction analysis reveals a cluster of three conserved amino acids that couple structural transitions in the potassium channel voltage sensor to those in the pore. Voltage-dependent potassium channels play a crucial role in electrical excitability and cellular signaling by regulating potassium ion flux across membranes. Movement of charged residues in the voltage-sensing domain leads to a series of conformational changes that culminate in channel opening in response to changes in membrane potential. However, the molecular machinery that relays these conformational changes from voltage sensor to the pore is not well understood. Here we use generalized interaction-energy analysis (GIA) to estimate the strength of site-specific interactions between amino acid residues putatively involved in the electromechanical coupling of the voltage sensor and pore in the outwardly rectifying KV channel. We identified candidate interactors at the interface between the S4–S5 linker and the pore domain using a structure-guided graph theoretical approach that revealed clusters of conserved and closely packed residues. One such cluster, located at the intracellular intersubunit interface, comprises three residues (arginine 394, glutamate 395, and tyrosine 485) that interact with each other. The calculated interaction energies were 3–5 kcal, which is especially notable given that the net free-energy change during activation of the Shaker KV channel is ∼14 kcal. We find that this triad is delicately maintained by balance of interactions that are responsible for structural integrity of the intersubunit interface while maintaining sufficient flexibility at a critical gating hinge for optimal transmission of force to the pore gate.
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Affiliation(s)
- Sandipan Chowdhury
- Graduate Program in Biophysics and Department of Neuroscience, University of Wisconsin, Madison, WI 53705 Graduate Program in Biophysics and Department of Neuroscience, University of Wisconsin, Madison, WI 53705
| | - Benjamin M Haehnel
- Graduate Program in Biophysics and Department of Neuroscience, University of Wisconsin, Madison, WI 53705 Graduate Program in Biophysics and Department of Neuroscience, University of Wisconsin, Madison, WI 53705
| | - Baron Chanda
- Graduate Program in Biophysics and Department of Neuroscience, University of Wisconsin, Madison, WI 53705 Graduate Program in Biophysics and Department of Neuroscience, University of Wisconsin, Madison, WI 53705
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43
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Martinez-Morales E, Snyders DJ, Labro AJ. Mutations in the S6 gate isolate a late step in the activation pathway and reduce 4-AP sensitivity in shaker K(v) channel. Biophys J 2014; 106:134-44. [PMID: 24411245 DOI: 10.1016/j.bpj.2013.11.025] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2013] [Revised: 10/28/2013] [Accepted: 11/12/2013] [Indexed: 01/12/2023] Open
Abstract
Kv channels detect changes in the membrane potential via their voltage-sensing domains (VSDs) that control the status of the S6 bundle crossing (BC) gate. The movement of the VSDs results in a transfer of the S4 gating charges across the cell membrane but only the last 10-20% of the total gating charge movement is associated with BC gate opening, which involves cooperative transition(s) in the subunits. Substituting the proline residue P475 in the S6 of the Shaker channel by a glycine or alanine causes a considerable shift in the voltage-dependence of the cooperative transition(s) of BC gate opening, effectively isolating the late gating charge component from the other gating charge that originates from earlier VSD movements. Interestingly, both mutations also abolished Shaker's sensitivity to 4-aminopyridine, which is a pharmacological tool to isolate the late gating charge component. The alanine substitution (that would promote a α-helical configuration compared to proline) resulted in the largest separation of both gating charge components; therefore, BC gate flexibility appears to be important for enabling the late cooperative step of channel opening.
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Affiliation(s)
- Evelyn Martinez-Morales
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, University of Antwerp, Antwerp, Belgium
| | - Dirk J Snyders
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, University of Antwerp, Antwerp, Belgium
| | - Alain J Labro
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, University of Antwerp, Antwerp, Belgium.
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Chowdhury S, Jarecki BW, Chanda B. A molecular framework for temperature-dependent gating of ion channels. Cell 2014; 158:1148-1158. [PMID: 25156949 DOI: 10.1016/j.cell.2014.07.026] [Citation(s) in RCA: 81] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2014] [Revised: 07/02/2014] [Accepted: 07/18/2014] [Indexed: 12/13/2022]
Abstract
Perception of heat or cold in higher organisms is mediated by specialized ion channels whose gating is exquisitely sensitive to temperature. The physicochemical underpinnings of this temperature-sensitive gating have proven difficult to parse. Here, we took a bottom-up protein design approach and rationally engineered ion channels to activate in response to thermal stimuli. By varying amino acid polarities at sites undergoing state-dependent changes in solvation, we were able to systematically confer temperature sensitivity to a canonical voltage-gated ion channel. Our results imply that the specific heat capacity change during channel gating is a major determinant of thermosensitive gating. We also show that reduction of gating charges amplifies temperature sensitivity of designer channels, which accounts for low-voltage sensitivity in all known temperature-gated ion channels. These emerging principles suggest a plausible molecular mechanism for temperature-dependent gating that reconcile how ion channels with an overall conserved transmembrane architecture may exhibit a wide range of temperature-sensing phenotypes. :
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Affiliation(s)
- Sandipan Chowdhury
- Graduate Program in Biophysics, 1111 Highland Ave, School of Medicine and Public Health, University of Wisconsin, Madison, Madison, WI 53705, USA; Department of Neuroscience, 1111 Highland Ave, School of Medicine and Public Health, University of Wisconsin, Madison, Madison, WI 53705, USA
| | - Brian W Jarecki
- Department of Neuroscience, 1111 Highland Ave, School of Medicine and Public Health, University of Wisconsin, Madison, Madison, WI 53705, USA
| | - Baron Chanda
- Graduate Program in Biophysics, 1111 Highland Ave, School of Medicine and Public Health, University of Wisconsin, Madison, Madison, WI 53705, USA; Department of Neuroscience, 1111 Highland Ave, School of Medicine and Public Health, University of Wisconsin, Madison, Madison, WI 53705, USA.
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45
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Garg P, Gardner A, Garg V, Sanguinetti MC. Structural basis of ion permeation gating in Slo2.1 K+ channels. ACTA ACUST UNITED AC 2014; 142:523-42. [PMID: 24166878 PMCID: PMC3813382 DOI: 10.1085/jgp.201311064] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
The activation gate of ion channels controls the transmembrane flux of permeant ions. In voltage-gated K+ channels, the aperture formed by the S6 bundle crossing can widen to open or narrow to close the ion permeation pathway, whereas the selectivity filter gates ion flux in cyclic-nucleotide gated (CNG) and Slo1 channels. Here we explore the structural basis of the activation gate for Slo2.1, a weakly voltage-dependent K+ channel that is activated by intracellular Na+ and Cl−. Slo2.1 channels were heterologously expressed in Xenopus laevis oocytes and activated by elevated [NaCl]i or extracellular application of niflumic acid. In contrast to other voltage-gated channels, Slo2.1 was blocked by verapamil in an activation-independent manner, implying that the S6 bundle crossing does not gate the access of verapamil to its central cavity binding site. The structural basis of Slo2.1 activation was probed by Ala scanning mutagenesis of the S6 segment and by mutation of selected residues in the pore helix and S5 segment. Mutation to Ala of three S6 residues caused reduced trafficking of channels to the cell surface and partial (K256A, I263A, Q273A) or complete loss (E275A) of channel function. P271A Slo2.1 channels trafficked normally, but were nonfunctional. Further mutagenesis and intragenic rescue by second site mutations suggest that Pro271 and Glu275 maintain the inner pore in an open configuration by preventing formation of a tight S6 bundle crossing. Mutation of several residues in S6 and S5 predicted by homology modeling to contact residues in the pore helix induced a gain of channel function. Substitution of the pore helix residue Phe240 with polar residues induced constitutive channel activation. Together these findings suggest that (1) the selectivity filter and not the bundle crossing gates ion permeation and (2) dynamic coupling between the pore helix and the S5 and S6 segments mediates Slo2.1 channel activation.
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Affiliation(s)
- Priyanka Garg
- Nora Eccles Harrison Cardiovascular Research and Training Institute, 2 Department of Pharmaceutics and Pharmaceutical Chemistry, and 3 Department of Internal Medicine, University of Utah, Salt Lake City, UT 84112
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Moving gating charges through the gating pore in a Kv channel voltage sensor. Proc Natl Acad Sci U S A 2014; 111:E1950-9. [PMID: 24782544 DOI: 10.1073/pnas.1406161111] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Voltage sensor domains (VSDs) regulate ion channels and enzymes by transporting electrically charged residues across a hydrophobic VSD constriction called the gating pore or hydrophobic plug. How the gating pore controls the gating charge movement presently remains debated. Here, using saturation mutagenesis and detailed analysis of gating currents from gating pore mutations in the Shaker Kv channel, we identified statistically highly significant correlations between VSD function and physicochemical properties of gating pore residues. A necessary small residue at position S240 in S1 creates a "steric gap" that enables an intracellular access pathway for the transport of the S4 Arg residues. In addition, the stabilization of the depolarized VSD conformation, a hallmark for most Kv channels, requires large side chains at positions F290 in S2 and F244 in S1 acting as "molecular clamps," and a hydrophobic side chain at position I237 in S1 acting as a local intracellular hydrophobic barrier. Finally, both size and hydrophobicity of I287 are important to control the main VSD energy barrier underlying transitions between resting and active states. Taken together, our study emphasizes the contribution of several gating pore residues to catalyze the gating charge transfer. This work paves the way toward understanding physicochemical principles underlying conformational dynamics in voltage sensors.
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Randich AM, Cuello LG, Wanderling SS, Perozo E. Biochemical and structural analysis of the hyperpolarization-activated K(+) channel MVP. Biochemistry 2014; 53:1627-36. [PMID: 24490868 PMCID: PMC3985891 DOI: 10.1021/bi4014243] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
![]()
In
contrast to the majority of voltage-gated ion channels, hyperpolarization-activated
channels remain closed at depolarizing potentials and are activated
at hyperpolarizing potentials. The basis for this reverse polarity
is thought to be a result of differences in the way the voltage-sensing
domain (VSD) couples to the pore domain. In the absence of structural
data, the molecular mechanism of this reverse polarity coupling remains
poorly characterized. Here we report the characterization of the structure
and local dynamics of the closed activation gate (lower S6 region)
of MVP, a hyperpolarization-activated potassium channel from Methanococcus jannaschii, by electron paramagnetic resonance
(EPR) spectroscopy. We show that a codon-optimized version of MVP
has high expression levels in Escherichia coli, is
purified as a stable tetramer, and exhibits expected voltage-dependent
activity when reconstituted in liposomes. EPR analysis of the mid
to lower S6 region revealed positions exhibiting strong spin–spin
coupling, indicating that the activation gate of MVP is closed at
0 mV. A comparison of local environmental parameters along the activation
gate for MVP and KcsA indicates that MVP adopts a different closed
conformation. These structural details set the stage for future evaluations
of reverse electromechanical coupling in MVP.
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Affiliation(s)
- Amelia M Randich
- Department of Biochemistry and Molecular Biology, The University of Chicago , Chicago, Illinois 60637, United States
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Fowler PW, Sansom MSP. The pore of voltage-gated potassium ion channels is strained when closed. Nat Commun 2013; 4:1872. [PMID: 23695666 PMCID: PMC3674235 DOI: 10.1038/ncomms2858] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2012] [Accepted: 04/10/2013] [Indexed: 12/22/2022] Open
Abstract
Voltage-gated potassium channels form potassium-selective pores in cell membranes. They open or close in response to changes in the transmembrane potential and are essential for generating action potentials, and thus for the functioning of heart and brain. While a mechanism for how these channels close has been proposed, it is not clear what drives their opening. Here we use free energy molecular dynamics simulations to show that work must be done on the pore to reduce the kink in the pore-lining (S6) α-helices, thereby forming the helix bundle crossing and closing the channel. Strain is built up as the pore closes, which subsequently drives opening. We also determine the effect of mutating the PVPV motif that causes the kink in the S6 helix. Finally, an approximate upper limit on how far the S4 helix is displaced as the pore closes is estimated. Voltage-gated potassium channels open and close in response to changes in transmembrane potential, but their opening mechanism is poorly understood. Here, free energy molecular dynamics simulations show that strain accumulates as the pore closes, which subsequently drives opening.
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Affiliation(s)
- Philip W Fowler
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, UK.
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49
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BK channel opening involves side-chain reorientation of multiple deep-pore residues. Proc Natl Acad Sci U S A 2013; 111:E79-88. [PMID: 24367115 DOI: 10.1073/pnas.1321697111] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Three deep-pore locations, L312, A313, and A316, were identified in a scanning mutagenesis study of the BK (Ca(2+)-activated, large-conductance K(+)) channel S6 pore, where single aspartate substitutions led to constitutively open mutant channels (L312D, A313D, and A316D). To understand the mechanisms of the constitutive openness of these mutant channels, we individually mutated these three sites into the other 18 amino acids. We found that charged or polar side-chain substitutions at each of the sites resulted in constitutively open mutant BK channels, with high open probability at negative voltages, as well as a loss of voltage and Ca(2+) dependence. Given the fact that multiple pore residues in BK displayed side-chain hydrophilicity-dependent constitutive openness, we propose that BK channel opening involves structural rearrangement of the deep-pore region, where multiple residues undergo conformational changes that may increase the exposure of their side chains to the polar environment of the pore.
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50
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González C, Baez-Nieto D, Valencia I, Oyarzún I, Rojas P, Naranjo D, Latorre R. K(+) channels: function-structural overview. Compr Physiol 2013; 2:2087-149. [PMID: 23723034 DOI: 10.1002/cphy.c110047] [Citation(s) in RCA: 152] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Potassium channels are particularly important in determining the shape and duration of the action potential, controlling the membrane potential, modulating hormone secretion, epithelial function and, in the case of those K(+) channels activated by Ca(2+), damping excitatory signals. The multiplicity of roles played by K(+) channels is only possible to their mammoth diversity that includes at present 70 K(+) channels encoding genes in mammals. Today, thanks to the use of cloning, mutagenesis, and the more recent structural studies using x-ray crystallography, we are in a unique position to understand the origins of the enormous diversity of this superfamily of ion channels, the roles they play in different cell types, and the relations that exist between structure and function. With the exception of two-pore K(+) channels that are dimers, voltage-dependent K(+) channels are tetrameric assemblies and share an extremely well conserved pore region, in which the ion-selectivity filter resides. In the present overview, we discuss in the function, localization, and the relations between function and structure of the five different subfamilies of K(+) channels: (a) inward rectifiers, Kir; (b) four transmembrane segments-2 pores, K2P; (c) voltage-gated, Kv; (d) the Slo family; and (e) Ca(2+)-activated SK family, SKCa.
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Affiliation(s)
- Carlos González
- Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile
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