51
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Subramanyam P, Colecraft HM. Ion channel engineering: perspectives and strategies. J Mol Biol 2014; 427:190-204. [PMID: 25205552 DOI: 10.1016/j.jmb.2014.09.001] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2014] [Accepted: 09/01/2014] [Indexed: 01/19/2023]
Abstract
Ion channels facilitate the passive movement of ions down an electrochemical gradient and across lipid bilayers in cells. This phenomenon is essential for life and underlies many critical homeostatic processes in cells. Ion channels are diverse and differ with respect to how they open and close (gating) and to their ionic conductance/selectivity (permeation). Fundamental understanding of ion channel structure-function mechanisms, their physiological roles, how their dysfunction leads to disease, their utility as biosensors, and development of novel molecules to modulate their activity are important and active research frontiers. In this review, we focus on ion channel engineering approaches that have been applied to investigate these aspects of ion channel function, with a major emphasis on voltage-gated ion channels.
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Affiliation(s)
- Prakash Subramanyam
- Department of Physiology and Cellular Biophysics, Columbia University, NY, 10032, USA
| | - Henry M Colecraft
- Department of Physiology and Cellular Biophysics, Columbia University, NY, 10032, USA.
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52
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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: 8.1] [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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53
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Dudek J, Pfeffer S, Lee PH, Jung M, Cavalié A, Helms V, Förster F, Zimmermann R. Protein transport into the human endoplasmic reticulum. J Mol Biol 2014; 427:1159-75. [PMID: 24968227 DOI: 10.1016/j.jmb.2014.06.011] [Citation(s) in RCA: 54] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2014] [Accepted: 06/11/2014] [Indexed: 12/22/2022]
Abstract
Protein transport into the endoplasmic reticulum (ER) is essential for all eukaryotic cells and evolutionary related to protein transport into and across the cytoplasmic membrane of eubacteria and archaea. It is based on amino-terminal signal peptides in the precursor polypeptides plus various transport components in cytosol plus ER and can occur either cotranslationally or posttranslationally. The two mechanisms merge at the heterotrimeric Sec61 complex in the ER membrane, which forms an aqueous polypeptide-conducting channel. Since the mammalian ER is also the main intracellular calcium storage organelle, the Sec61 complex is tightly regulated in its dynamics between the open and closed conformations by various ligands, such as precursor polypeptides at the cytosolic face and the Hsp70-type molecular chaperone BiP at the ER lumenal face (Hsp, heat shock protein). Furthermore, BiP binding to the incoming precursor polypeptide contributes to unidirectionality and efficiency of transport. Recent insights into the structural dynamics of the Sec61 complex and related complexes in eubacteria and archaea have various mechanistic and functional implications.
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Affiliation(s)
- Johanna Dudek
- Medical Biochemistry and Molecular Biology, Saarland University, 66421 Homburg, Germany
| | - Stefan Pfeffer
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany
| | - Po-Hsien Lee
- Computational Biology, Saarland University, 66041 Saarbrücken, Germany
| | - Martin Jung
- Medical Biochemistry and Molecular Biology, Saarland University, 66421 Homburg, Germany
| | - Adolfo Cavalié
- Experimental and Clinical Pharmacology and Toxicology, Saarland University, 66421 Homburg, Germany
| | - Volkhard Helms
- Computational Biology, Saarland University, 66041 Saarbrücken, Germany
| | - Friedrich Förster
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany
| | - Richard Zimmermann
- Medical Biochemistry and Molecular Biology, Saarland University, 66421 Homburg, Germany.
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54
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Zaydman MA, Cui J. PIP2 regulation of KCNQ channels: biophysical and molecular mechanisms for lipid modulation of voltage-dependent gating. Front Physiol 2014; 5:195. [PMID: 24904429 PMCID: PMC4034418 DOI: 10.3389/fphys.2014.00195] [Citation(s) in RCA: 95] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2014] [Accepted: 05/08/2014] [Indexed: 12/28/2022] Open
Abstract
Voltage-gated potassium (Kv) channels contain voltage-sensing (VSD) and pore-gate (PGD) structural domains. During voltage-dependent gating, conformational changes in the two domains are coupled giving rise to voltage-dependent opening of the channel. In addition to membrane voltage, KCNQ (Kv7) channel opening requires the membrane lipid phosphatidylinositol 4,5-bisphosphate (PIP2). Recent studies suggest that PIP2 serves as a cofactor to mediate VSD-PGD coupling in KCNQ1 channels. In this review, we put these findings in the context of the current understanding of voltage-dependent gating, lipid modulation of Kv channel activation, and PIP2-regulation of KCNQ channels. We suggest that lipid-mediated coupling of functional domains is a common mechanism among KCNQ channels that may be applicable to other Kv channels and membrane proteins.
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Affiliation(s)
- Mark A Zaydman
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Diseases, Cardiac Bioelectricity and Arrhythmia Center, Washington University in St. Louis St. Louis, MO, USA
| | - Jianmin Cui
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Diseases, Cardiac Bioelectricity and Arrhythmia Center, Washington University in St. Louis St. Louis, MO, USA
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55
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Feeling the hidden mechanical forces in lipid bilayer is an original sense. Proc Natl Acad Sci U S A 2014; 111:7898-905. [PMID: 24850861 DOI: 10.1073/pnas.1313364111] [Citation(s) in RCA: 199] [Impact Index Per Article: 19.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Life's origin entails enclosing a compartment to hoard material, energy, and information. The envelope necessarily comprises amphipaths, such as prebiotic fatty acids, to partition the two aqueous domains. The self-assembled lipid bilayer comes with a set of properties including its strong anisotropic internal forces that are chemically or physically malleable. Added bilayer stretch can alter force vectors on embedded proteins to effect conformational change. The force-from-lipid principle was demonstrated 25 y ago when stretches opened purified Escherichia coli MscL channels reconstituted into artificial bilayers. This reductionistic exercise has rigorously been recapitulated recently with two vertebrate mechanosensitive K(+) channels (TREK1 and TRAAK). Membrane stretches have also been known to activate various voltage-, ligand-, or Ca(2+)-gated channels. Careful analyses showed that Kv, the canonical voltage-gated channel, is in fact exquisitely sensitive even to very small tension. In an unexpected context, the canonical transient-receptor-potential channels in the Drosophila eye, long presumed to open by ligand binding, is apparently opened by membrane force due to PIP2 hydrolysis-induced changes in bilayer strain. Being the intimate medium, lipids govern membrane proteins by physics as well as chemistry. This principle should not be a surprise because it parallels water's paramount role in the structure and function of soluble proteins. Today, overt or covert mechanical forces govern cell biological processes and produce sensations. At the genesis, a bilayer's response to osmotic force is likely among the first senses to deal with the capricious primordial sea.
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56
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Xie L, Ge X, Tan H, Xie L, Zhang Y, Hart T, Yang X, Bourne PE. Towards structural systems pharmacology to study complex diseases and personalized medicine. PLoS Comput Biol 2014; 10:e1003554. [PMID: 24830652 PMCID: PMC4022462 DOI: 10.1371/journal.pcbi.1003554] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Genome-Wide Association Studies (GWAS), whole genome sequencing, and high-throughput omics techniques have generated vast amounts of genotypic and molecular phenotypic data. However, these data have not yet been fully explored to improve the effectiveness and efficiency of drug discovery, which continues along a one-drug-one-target-one-disease paradigm. As a partial consequence, both the cost to launch a new drug and the attrition rate are increasing. Systems pharmacology and pharmacogenomics are emerging to exploit the available data and potentially reverse this trend, but, as we argue here, more is needed. To understand the impact of genetic, epigenetic, and environmental factors on drug action, we must study the structural energetics and dynamics of molecular interactions in the context of the whole human genome and interactome. Such an approach requires an integrative modeling framework for drug action that leverages advances in data-driven statistical modeling and mechanism-based multiscale modeling and transforms heterogeneous data from GWAS, high-throughput sequencing, structural genomics, functional genomics, and chemical genomics into unified knowledge. This is not a small task, but, as reviewed here, progress is being made towards the final goal of personalized medicines for the treatment of complex diseases.
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Affiliation(s)
- Lei Xie
- Department of Computer Science, Hunter College, The City University of New York, New York, New York, United States of America
- Ph.D. Program in Computer Science, Biology, and Biochemistry, The Graduate Center, The City University of New York, New York, New York, United States of America
- * E-mail:
| | - Xiaoxia Ge
- Department of Computer Science, Hunter College, The City University of New York, New York, New York, United States of America
| | - Hepan Tan
- Department of Computer Science, Hunter College, The City University of New York, New York, New York, United States of America
| | - Li Xie
- Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California San Diego, La Jolla, California, United States of America
| | - Yinliang Zhang
- Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California San Diego, La Jolla, California, United States of America
| | - Thomas Hart
- Department of Biological Sciences, Hunter College, The City University of New York, New York, New York, United States of America
| | - Xiaowei Yang
- School of Public Health, Hunter College, The City University of New York, New York, New York, United States of America
| | - Philip E. Bourne
- Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California San Diego, La Jolla, California, United States of America
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57
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Perry MD, Wong S, Ng CA, Vandenberg JI. Hydrophobic interactions between the voltage sensor and pore mediate inactivation in Kv11.1 channels. ACTA ACUST UNITED AC 2014; 142:275-88. [PMID: 23980196 PMCID: PMC3753607 DOI: 10.1085/jgp.201310975] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Kv11.1 channels are critical for the maintenance of a normal heart rhythm. The flow of potassium ions through these channels is controlled by two voltage-regulated gates, termed "activation" and "inactivation," located at opposite ends of the pore. Crucially in Kv11.1 channels, inactivation gating occurs much more rapidly, and over a distinct range of voltages, compared with activation gating. Although it is clear that the fourth transmembrane segments (S4), within each subunit of the tetrameric channel, are important for controlling the opening and closing of the activation gate, their role during inactivation gating is much less clear. Here, we use rate equilibrium free energy relationship (REFER) analysis to probe the contribution of the S4 "voltage-sensor" helix during inactivation of Kv11.1 channels. Contrary to the important role that charged residues play during activation gating, it is the hydrophobic residues (Leu529, Leu530, Leu532, and Val535) that are the key molecular determinants of inactivation gating. Within the context of an interconnected multi-domain model of Kv11.1 inactivation gating, our REFER analysis indicates that the S4 helix and the S4-S5 linker undergo a conformational rearrangement shortly after that of the S5 helix and S5P linker, but before the S6 helix. Combining REFER analysis with double mutant cycle analysis, we provide evidence for a hydrophobic interaction between residues on the S4 and S5 helices. Based on a Kv11.1 channel homology model, we propose that this hydrophobic interaction forms the basis of an intersubunit coupling between the voltage sensor and pore domain that is an important mediator of inactivation gating.
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Affiliation(s)
- Matthew D Perry
- Molecular Cardiology and Biophysics Division, Victor Chang Cardiac Research Institute, Darlinghurst, NSW 2010, Australia
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58
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Tsutsui H, Jinno Y, Tomita A, Okamura Y. Optically detected structural change in the N-terminal region of the voltage-sensor domain. Biophys J 2014; 105:108-15. [PMID: 23823229 DOI: 10.1016/j.bpj.2013.05.051] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2013] [Revised: 05/30/2013] [Accepted: 05/31/2013] [Indexed: 11/16/2022] Open
Abstract
The voltage-sensor domain (VSD) is a functional module that undergoes structural transitions in response to membrane potential changes and regulates its effectors, thereby playing a crucial role in amplifying and decoding membrane electrical signals. Ion-conductive pore and phosphoinositide phosphatase are the downstream effectors of voltage-gated channels and the voltage-sensing phosphatase, respectively. It is known that upon transition, the VSD generally acts on the region C-terminal to S4. However, whether the VSD also induces any structural changes in the N-terminal region of S1 has not been addressed directly. Here, we report the existence of such an N-terminal effect. We used two distinct optical reporters-one based on the Förster resonance energy transfer between a pair of fluorescent proteins, and the other based on fluorophore-labeled HaloTag-and studied the behavior of these reporters placed at the N-terminal end of the monomeric VSD derived from voltage-sensing phosphatase. We found that both of these reporters were affected by the VSD transition, generating voltage-dependent fluorescence readouts. We also observed that whereas the voltage dependencies of the N- and C-terminal effects appear to be tightly coupled, the local structural rearrangements reflect the way in which the VSD is loaded, demonstrating the flexible nature of the VSD.
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Affiliation(s)
- Hidekazu Tsutsui
- Laboratory of Integrative Physiology, Graduate School of Medicine, Osaka University, Osaka, Japan.
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59
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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: 4.5] [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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60
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Tian C, Zhu R, Zhu L, Qiu T, Cao Z, Kang T. Potassium Channels: Structures, Diseases, and Modulators. Chem Biol Drug Des 2013; 83:1-26. [DOI: 10.1111/cbdd.12237] [Citation(s) in RCA: 63] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Affiliation(s)
- Chuan Tian
- School of Life Sciences and Technology; Tongji University; Shanghai 200092 China
- School of Pharmacy; Liaoning University of Traditional Chinese Medicine; Dalian Liaoning 116600 China
| | - Ruixin Zhu
- School of Life Sciences and Technology; Tongji University; Shanghai 200092 China
| | - Lixin Zhu
- Department of Pediatrics; Digestive Diseases and Nutrition Center; The State University of New York at Buffalo; Buffalo NY 14226 USA
| | - Tianyi Qiu
- School of Life Sciences and Technology; Tongji University; Shanghai 200092 China
| | - Zhiwei Cao
- School of Life Sciences and Technology; Tongji University; Shanghai 200092 China
| | - Tingguo Kang
- School of Pharmacy; Liaoning University of Traditional Chinese Medicine; Dalian Liaoning 116600 China
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61
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Yang F, Ma L, Cao X, Wang K, Zheng J. Divalent cations activate TRPV1 through promoting conformational change of the extracellular region. ACTA ACUST UNITED AC 2013; 143:91-103. [PMID: 24344245 PMCID: PMC3874565 DOI: 10.1085/jgp.201311024] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Divalent cations Mg2+ and Ba2+ selectively and directly potentiate transient receptor potential vanilloid type 1 heat activation by lowering the activation threshold into the room temperature range. We found that Mg2+ potentiates channel activation only from the extracellular side; on the intracellular side, Mg2+ inhibits channel current. By dividing the extracellularly accessible region of the channel protein into small segments and perturbing the structure of each segment with sequence replacement mutations, we observed that the S1–S2 linker, the S3–S4 linker, and the pore turret are all required for Mg2+ potentiation. Sequence replacements at these regions substantially reduced or eliminated Mg2+-induced activation at room temperature while sparing capsaicin activation. Heat activation was affected by many, but not all, of these structural alternations. These observations indicate that extracellular linkers and the turret may interact with each other. Site-directed fluorescence resonance energy transfer measurements further revealed that, like heat, Mg2+ also induces structural changes in the pore turret. Interestingly, turret movement induced by Mg2+ precedes channel activation, suggesting that Mg2+-induced conformational change in the extracellular region most likely serves as the cause of channel activation instead of a coincidental or accommodating structural adjustment.
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Affiliation(s)
- Fan Yang
- Department of Physiology and Membrane Biology, University of California School of Medicine, Davis, Davis, CA 95616
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62
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Perez-Reyes E, Lee JH. Ins and outs of T-channel structure function. Pflugers Arch 2013; 466:627-33. [PMID: 24337909 DOI: 10.1007/s00424-013-1419-5] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2013] [Accepted: 12/03/2013] [Indexed: 02/07/2023]
Abstract
We review the ins and outs of T-channel structure, focusing on the extracellular high-affinity metal-binding site and intracellular loops. The high-affinity metal-binding site was localized to repeat I of Cav3.2. Interestingly, a similar binding site was found in the high voltage-activated Cav2.3 channel where it controls the channels' voltage dependence. Histidine at position 191 has a particularly interesting role in the high-affinity binding site, and its modification plays an important role in channel regulation by pharmacological agents that alter redox reactions. The intracellular loop connecting repeats I and II plays two important roles in Cav3.2 properties: one, its gating; and two, its surface expression. These studies have also identified a highly conserved intracellular gating brake that is predicted to form a helix-loop-helix structure. We conclude that the gating brake establishes important contacts with the gating machinery, thereby stabilizing a closed state of T-channels. This interaction is disrupted by depolarization, allowing the S6 segments to open and allowing Ca(2+) ions to flow through. Studies in cultured hippocampal neurons provided novel insights into how mutations found in idiopathic generalized epilepsy patients increase seizure susceptibility by both altering T-current pacemaker currents and by activating Ca-activated transcription factors that regulate dendritic arborization. These studies reveal novel roles for T-channels to control cellular physiology.
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Affiliation(s)
- Edward Perez-Reyes
- Department of Pharmacology, University of Virginia, Charlottesville, VA, USA,
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63
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González C, Baez-Nieto D, Valencia I, Oyarzún I, Rojas P, Naranjo D, Latorre R. K(+) channels: function-structural overview. Compr Physiol 2013; 2:2087-149. [PMID: 23723034 DOI: 10.1002/cphy.c110047] [Citation(s) in RCA: 143] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Potassium channels are particularly important in determining the shape and duration of the action potential, controlling the membrane potential, modulating hormone secretion, epithelial function and, in the case of those K(+) channels activated by Ca(2+), damping excitatory signals. The multiplicity of roles played by K(+) channels is only possible to their mammoth diversity that includes at present 70 K(+) channels encoding genes in mammals. Today, thanks to the use of cloning, mutagenesis, and the more recent structural studies using x-ray crystallography, we are in a unique position to understand the origins of the enormous diversity of this superfamily of ion channels, the roles they play in different cell types, and the relations that exist between structure and function. With the exception of two-pore K(+) channels that are dimers, voltage-dependent K(+) channels are tetrameric assemblies and share an extremely well conserved pore region, in which the ion-selectivity filter resides. In the present overview, we discuss in the function, localization, and the relations between function and structure of the five different subfamilies of K(+) channels: (a) inward rectifiers, Kir; (b) four transmembrane segments-2 pores, K2P; (c) voltage-gated, Kv; (d) the Slo family; and (e) Ca(2+)-activated SK family, SKCa.
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Affiliation(s)
- Carlos González
- Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile
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64
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Multistate structural modeling and voltage-clamp analysis of epilepsy/autism mutation Kv10.2-R327H demonstrate the role of this residue in stabilizing the channel closed state. J Neurosci 2013; 33:16586-93. [PMID: 24133262 DOI: 10.1523/jneurosci.2307-13.2013] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Voltage-gated potassium channel Kv10.2 (KCNH5) is expressed in the nervous system, but its functions and involvement in human disease are poorly understood. We studied a human Kv10.2 channel mutation (R327H) recently identified in a child with epileptic encephalopathy and autistic features. Using multistate structural modeling, we demonstrate that the Arg327 residue in the S4 helix of voltage-sensing domain has strong ionic interactions with negatively charged residues within the S1-S3 helices in the resting (closed) and early-activation state but not in the late-activation and fully-activated (open) state. The R327H mutation weakens ionic interactions between residue 327 and these negatively charged residues, thus favoring channel opening. Voltage-clamp analysis showed a strong hyperpolarizing (∼70 mV) shift of voltage dependence of activation and an acceleration of activation. Our results demonstrate the critical role of the Arg327 residue in stabilizing the channel closed state and explicate for the first time the structural and functional change of a Kv10.2 channel mutation associated with neurological disease.
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65
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Shem-Ad T, Irit O, Yifrach O. Inter-subunit interactions across the upper voltage sensing-pore domain interface contribute to the concerted pore opening transition of Kv channels. PLoS One 2013; 8:e82253. [PMID: 24340010 PMCID: PMC3858418 DOI: 10.1371/journal.pone.0082253] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2013] [Accepted: 10/22/2013] [Indexed: 12/31/2022] Open
Abstract
The tight electro-mechanical coupling between the voltage-sensing and pore domains of Kv channels lies at the heart of their fundamental roles in electrical signaling. Structural data have identified two voltage sensor pore inter-domain interaction surfaces, thus providing a framework to explain the molecular basis for the tight coupling of these domains. While the contribution of the intra-subunit lower domain interface to the electro-mechanical coupling that underlies channel opening is relatively well understood, the contribution of the inter-subunit upper interface to channel gating is not yet clear. Relying on energy perturbation and thermodynamic coupling analyses of tandem-dimeric Shaker Kv channels, we show that mutation of upper interface residues from both sides of the voltage sensor-pore domain interface stabilizes the closed channel state. These mutations, however, do not affect slow inactivation gating. We, moreover, find that upper interface residues form a network of state-dependent interactions that stabilize the open channel state. Finally, we note that the observed residue interaction network does not change during slow inactivation gating. The upper voltage sensing-pore interaction surface thus only undergoes conformational rearrangements during channel activation gating. We suggest that inter-subunit interactions across the upper domain interface mediate allosteric communication between channel subunits that contributes to the concerted nature of the late pore opening transition of Kv channels.
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Affiliation(s)
- Tzilhav Shem-Ad
- Department of Life Sciences and the Zlotowski Center for Neurosciences, Ben-Gurion University of the Negev, Beer Sheva, Israel
| | - Orr Irit
- Department of Life Sciences and the Zlotowski Center for Neurosciences, Ben-Gurion University of the Negev, Beer Sheva, Israel
| | - Ofer Yifrach
- Department of Life Sciences and the Zlotowski Center for Neurosciences, Ben-Gurion University of the Negev, Beer Sheva, Israel
- * E-mail:
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66
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Pless SA, Niciforovic AP, Galpin JD, Nunez JJ, Kurata HT, Ahern CA. A novel mechanism for fine-tuning open-state stability in a voltage-gated potassium channel. Nat Commun 2013; 4:1784. [PMID: 23653196 PMCID: PMC3644096 DOI: 10.1038/ncomms2761] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2012] [Accepted: 03/18/2013] [Indexed: 12/23/2022] Open
Abstract
Voltage-gated potassium channels elicit membrane hyperpolarization through voltage-sensor domains that regulate the conductive status of the pore domain. To better understand the inherent basis for the open-closed equilibrium in these channels, we undertook an atomistic scan using synthetic fluorinated derivatives of aromatic residues previously implicated in the gating of Shaker potassium channels. Here we show that stepwise dispersion of the negative electrostatic surface potential of only one site, Phe481, stabilizes the channel open state. Furthermore, these data suggest that this apparent stabilization is the consequence of the amelioration of an inherently repulsive open-state interaction between the partial negative charge on the face of Phe481 and a highly co-evolved acidic side chain, Glu395, and this interaction is potentially modulated through the Tyr485 hydroxyl. We propose that the intrinsic open-state destabilization via aromatic repulsion represents a new mechanism by which ion channels, and likely other proteins, fine-tune conformational equilibria. Voltage-gated potassium channels cycle between closed and open states through poorly-defined transitions. Pless and colleagues incorporate artificial amino acids into Shaker potassium channels and find that that the negative electrostatic surface potential of Phe481, destabilizes the channel open state.
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Affiliation(s)
- Stephan A Pless
- Department of Anesthesiology, Pharmacology and Therapeutics, University of British Columbia, 2350 Health Science Mall, Vancouver, British Columbia, Canada V6T 1Z3
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67
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Arrigoni C, Schroeder I, Romani G, Van Etten JL, Thiel G, Moroni A. The voltage-sensing domain of a phosphatase gates the pore of a potassium channel. ACTA ACUST UNITED AC 2013; 141:389-95. [PMID: 23440279 PMCID: PMC3581695 DOI: 10.1085/jgp.201210940] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The modular architecture of voltage-gated K(+) (Kv) channels suggests that they resulted from the fusion of a voltage-sensing domain (VSD) to a pore module. Here, we show that the VSD of Ciona intestinalis phosphatase (Ci-VSP) fused to the viral channel Kcv creates Kv(Synth1), a functional voltage-gated, outwardly rectifying K(+) channel. Kv(Synth1) displays the summed features of its individual components: pore properties of Kcv (selectivity and filter gating) and voltage dependence of Ci-VSP (V(1/2) = +56 mV; z of ~1), including the depolarization-induced mode shift. The degree of outward rectification of the channel is critically dependent on the length of the linker more than on its amino acid composition. This highlights a mechanistic role of the linker in transmitting the movement of the sensor to the pore and shows that electromechanical coupling can occur without coevolution of the two domains.
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Affiliation(s)
- Cristina Arrigoni
- Department of Biosciences, Consiglio Nazionale delle Ricerche, Università degli Studi di Milano, 20133 Milano, Italy
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68
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Fowler P, Abad E, Beckstein O, Sansom MSP. Energetics of Multi-Ion Conduction Pathways in Potassium Ion Channels. J Chem Theory Comput 2013; 9:5176-5189. [PMID: 24353479 PMCID: PMC3864263 DOI: 10.1021/ct4005933] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2013] [Indexed: 12/18/2022]
Abstract
Potassium ion channels form pores in cell membranes, allowing potassium ions through while preventing the passage of sodium ions. Despite numerous high-resolution structures, it is not yet possible to relate their structure to their single molecule function other than at a qualitative level. Over the past decade, there has been a concerted effort using molecular dynamics to capture the thermodynamics and kinetics of conduction by calculating potentials of mean force (PMF). These can be used, in conjunction with the electro-diffusion theory, to predict the conductance of a specific ion channel. Here, we calculate seven independent PMFs, thereby studying the differences between two potassium ion channels, the effect of the CHARMM CMAP forcefield correction, and the sensitivity and reproducibility of the method. Thermodynamically stable ion-water configurations of the selectivity filter can be identified from all the free energy landscapes, but the heights of the kinetic barriers for potassium ions to move through the selectivity filter are, in nearly all cases, too high to predict conductances in line with experiment. This implies it is not currently feasible to predict the conductance of potassium ion channels, but other simpler channels may be more tractable.
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Affiliation(s)
- Philip
W. Fowler
- Department
of Biochemistry, University of Oxford, Oxford OX1 3QU, United Kingdom
| | - Enrique Abad
- Department
of Biochemistry, University of Oxford, Oxford OX1 3QU, United Kingdom
| | - Oliver Beckstein
- Department
of Biochemistry, University of Oxford, Oxford OX1 3QU, United Kingdom
| | - Mark S. P. Sansom
- Department
of Biochemistry, University of Oxford, Oxford OX1 3QU, United Kingdom
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69
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Demers-Giroux PO, Bourdin B, Sauvé R, Parent L. Cooperative activation of the T-type CaV3.2 channel: interaction between Domains II and III. J Biol Chem 2013; 288:29281-93. [PMID: 23970551 PMCID: PMC3795230 DOI: 10.1074/jbc.m113.500975] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2013] [Revised: 08/02/2013] [Indexed: 12/28/2022] Open
Abstract
T-type CaV3 channels are important mediators of Ca(2+) entry near the resting membrane potential. Little is known about the molecular mechanisms responsible for channel activation. Homology models based upon the high-resolution structure of bacterial NaV channels predict interaction between the S4-S5 helix of Domain II (IIS4-S5) and the distal S6 pore region of Domain II (IIS6) and Domain III (IIIS6). Functional intra- and inter-domain interactions were investigated with a double mutant cycle analysis. Activation gating and channel kinetics were measured for 47 single mutants and 20 pairs of mutants. Significant coupling energies (ΔΔG(interact) ≥ 1.5 kcal mol(-1)) were measured for 4 specific pairs of mutants introduced between IIS4-S5 and IIS6 and between IIS4-S5 and IIIS6. In agreement with the computer based models, Thr-911 in IIS4-S5 was functionally coupled with Ile-1013 in IIS6 during channel activation. The interaction energy was, however, found to be stronger between Val-907 in IIS4-S5 and Ile-1013 in IIS6. In addition Val-907 was significantly coupled with Asn-1548 in IIIS6 but not with Asn-1853 in IVS6. Altogether, our results demonstrate that the S4-S5 and S6 helices from adjacent domains are energetically coupled during the activation of a low voltage-gated T-type CaV3 channel.
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Affiliation(s)
- Pierre-Olivier Demers-Giroux
- From the Département de Physiologie, Membrane Protein Research Group, Université de Montréal, Montréal, Quebec H3C 3J7, Canada
| | - Benoîte Bourdin
- From the Département de Physiologie, Membrane Protein Research Group, Université de Montréal, Montréal, Quebec H3C 3J7, Canada
| | - Rémy Sauvé
- From the Département de Physiologie, Membrane Protein Research Group, Université de Montréal, Montréal, Quebec H3C 3J7, Canada
| | - Lucie Parent
- From the Département de Physiologie, Membrane Protein Research Group, Université de Montréal, Montréal, Quebec H3C 3J7, Canada
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70
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Chowdhury S, Chanda B. Perspectives on: conformational coupling in ion channels: thermodynamics of electromechanical coupling in voltage-gated ion channels. ACTA ACUST UNITED AC 2013. [PMID: 23183697 PMCID: PMC3514737 DOI: 10.1085/jgp.201210840] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Affiliation(s)
- Sandipan Chowdhury
- Graduate Program in Biophysics, University of Wisconsin, Madison, WI 53706, USA
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71
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Exploring structure-function relationships between TRP and Kv channels. Sci Rep 2013; 3:1523. [PMID: 23519328 PMCID: PMC3605605 DOI: 10.1038/srep01523] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2013] [Accepted: 03/07/2013] [Indexed: 12/18/2022] Open
Abstract
The molecular mechanisms underlying the activation of Transient Receptor Potential (TRP) ion channels are poorly understood when compared to those of the voltage-activated potassium (Kv) channels. The architectural and pharmacological similarities between the members of these two families of channels suggest that their structure-function relationships may have common features. We explored this hypothesis by replacing previously identified domains and critical structural motifs of the membrane-spanning portions of Kv2.1 with corresponding regions of two TRP channels, TRPM8 and TRPV1. Our results show that the S3b-S4 paddle motif of Kv2.1, but not other domains, can be replaced by the analogous regions of both TRP channels without abolishing voltage-activation. In contrast, replacement of portions of TRP channels with those of Kv2.1 consistently yielded non-functional channels. Taken together, these results suggest that most structural elements within TRP channels and Kv channels are not sufficiently related to allow for the creation of hybrid channels.
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72
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Importance of lipid-pore loop interface for potassium channel structure and function. Proc Natl Acad Sci U S A 2013; 110:13008-13. [PMID: 23882077 DOI: 10.1073/pnas.1305563110] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Potassium (i.e., K(+)) channels allow for the controlled and selective passage of potassium ions across the plasma membrane via a conserved pore domain. In voltage-gated K(+) channels, gating is the result of the coordinated action of two coupled gates: an activation gate at the intracellular entrance of the pore and an inactivation gate at the selectivity filter. By using solid-state NMR structural studies, in combination with electrophysiological experiments and molecular dynamics simulations, we show that the turret region connecting the outer transmembrane helix (transmembrane helix 1) and the pore helix behind the selectivity filter contributes to K(+) channel inactivation and exhibits a remarkable structural plasticity that correlates to K(+) channel inactivation. The transmembrane helix 1 unwinds when the K(+) channel enters the inactivated state and rewinds during the transition to the closed state. In addition to well-characterized changes at the K(+) ion coordination sites, this process is accompanied by conformational changes within the turret region and the pore helix. Further spectroscopic and computational results show that the same channel domain is critically involved in establishing functional contacts between pore domain and the cellular membrane. Taken together, our results suggest that the interaction between the K(+) channel turret region and the lipid bilayer exerts an important influence on the selective passage of potassium ions via the K(+) channel pore.
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73
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Schow EV, Freites JA, Nizkorodov A, White SH, Tobias DJ. Coupling between the voltage-sensing and pore domains in a voltage-gated potassium channel. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2013; 1818:1726-36. [PMID: 22425907 DOI: 10.1016/j.bbamem.2012.02.029] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/03/2011] [Revised: 02/24/2012] [Accepted: 02/28/2012] [Indexed: 10/28/2022]
Abstract
Voltage-dependent potassium (Kv), sodium (Nav), and calcium channels open and close in response to changes in transmembrane (TM) potential, thus regulating cell excitability by controlling ion flow across the membrane. An outstanding question concerning voltage gating is how voltage-induced conformational changes of the channel voltage-sensing domains (VSDs) are coupled through the S4-S5 interfacial linking helices to the opening and closing of the pore domain (PD). To investigate the coupling between the VSDs and the PD, we generated a closed Kv channel configuration from Aeropyrum pernix (KvAP) using atomistic simulations with experiment-based restraints on the VSDs. Full closure of the channel required, in addition to the experimentally determined TM displacement, that the VSDs be displaced both inwardly and laterally around the PD. This twisting motion generates a tight hydrophobic interface between the S4-S5 linkers and the C-terminal ends of the pore domain S6 helices in agreement with available experimental evidence.
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Affiliation(s)
- Eric V Schow
- Department of Chemistry, University of California, Irvine, CA 92697-2025, USA
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74
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Li P, Chen Z, Xu H, Sun H, Li H, Liu H, Yang H, Gao Z, Jiang H, Li M. The gating charge pathway of an epilepsy-associated potassium channel accommodates chemical ligands. Cell Res 2013; 23:1106-18. [PMID: 23797855 PMCID: PMC3773576 DOI: 10.1038/cr.2013.82] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2013] [Revised: 04/16/2013] [Accepted: 05/09/2013] [Indexed: 01/05/2023] Open
Abstract
Voltage-gated potassium (Kv) channels derive their voltage sensitivity from movement of gating charges in voltage-sensor domains (VSDs). The gating charges translocate through a physical pathway in the VSD to open or close the channel. Previous studies showed that the gating charge pathways of Shaker and Kv1.2-2.1 chimeric channels are occluded, forming the structural basis for the focused electric field and gating charge transfer center. Here, we show that the gating charge pathway of the voltage-gated KCNQ2 potassium channel, activity reduction of which causes epilepsy, can accommodate various small molecule ligands. Combining mutagenesis, molecular simulation and electrophysiological recording, a binding model for the probe activator, ztz240, in the gating charge pathway was defined. This information was used to establish a docking-based virtual screening assay targeting the defined ligand-binding pocket. Nine activators with five new chemotypes were identified, and in vivo experiments showed that three ligands binding to the gating charge pathway exhibit significant anti-epilepsy activity. Identification of various novel activators by virtual screening targeting the pocket supports the presence of a ligand-binding site in the gating charge pathway. The capability of the gating charge pathway to accommodate small molecule ligands offers new insights into the gating charge pathway of the therapeutically relevant KCNQ2 channel.
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Affiliation(s)
- Ping Li
- CAS Key Laboratory of Receptor Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, 555 Zuchongzhi Road, Shanghai 201203, China
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75
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Dou Y, Goodchild SJ, Velde RV, Wu Y, Fedida D. The neutral, hydrophobic isoleucine at position I521 in the extracellular S4 domain of hERG contributes to channel gating equilibrium. Am J Physiol Cell Physiol 2013; 305:C468-78. [PMID: 23761630 DOI: 10.1152/ajpcell.00147.2013] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The human ether-a-go-go related (hERG) potassium channel has unusual functional characteristics in that the rates of channel activation and deactivation are much slower than inactivation, which is attributed to specific structural elements within the NH2 terminus and the S1-S4 voltage-sensing domains (VSD). Although the charged residues in the VSD have been extensively modified and mutated as a result, the role and importance of specific hydrophobic residues in the S4 has been much less explored in studies of hERG gating. We found that charged, but not neutral or hydrophobic, amino acid substitution of isoleucine 521 at the outer end of the S4 transmembrane domain resulted in channels activating at much more negative voltages associated with a marked hyperpolarization of the conductance-voltage (G-V) relationship. The contributions of different physicochemical properties to this effect were probed by chemical modification of channels substituted with cysteine at position I521. When positively charged reagents including tetramethyl-rhodamine-5-maleimide (TMRM), 1-(2-maleimidylethyl)-4-[5-(4-methoxyphenyl)oxazol-2-yl] pyridinium methane-sulfonate (PyMPO), [2-(trimethylammonium)ethyl] methanethiosulfonate chloride (MTSET), and 2-aminoethyl methanethiosulfonate hydrobromide (MTSEA) were bound to the cysteine, I521C channels activated at more negative membrane potentials. To examine the contributions to hERG gating of other residues at the outer end of S4 (520-528), we performed a cysteine scan combined with MTSET modification. Only L520C, along with I521C, shows a substantial hyperpolarizing shift of the G-V relationship upon MTSET modification. The data indicate that the neutral, hydrophobic residue I521 at the extracellular end of S4 is critical for stabilizing the closed conformation of the hERG channel relative to the open state and by comparison with Shaker supports the alignment of hERG I521 with Shaker L361.
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Affiliation(s)
- Ying Dou
- Department of Anesthesiology, Pharmacology and Therapeutics, University of British Columbia, Vancouver, British Columbia, Canada
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76
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Schneider T, Dibué M, Hescheler J. How "Pharmacoresistant" is Cav2.3, the Major Component of Voltage-Gated R-type Ca2+ Channels? Pharmaceuticals (Basel) 2013; 6:759-76. [PMID: 24276260 PMCID: PMC3816731 DOI: 10.3390/ph6060759] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2013] [Revised: 04/26/2013] [Accepted: 05/06/2013] [Indexed: 12/04/2022] Open
Abstract
Membrane-bound voltage-gated Ca2+ channels (VGCCs) are targets for specific signaling complexes, which regulate important processes like gene expression, neurotransmitter release and neuronal excitability. It is becoming increasingly evident that the so called “resistant” (R-type) VGCC Cav2.3 is critical in several physiologic and pathophysiologic processes in the central nervous system, vascular system and in endocrine systems. However its eponymous attribute of pharmacologic inertness initially made in depth investigation of the channel difficult. Although the identification of SNX-482 as a fairly specific inhibitor of Cav2.3 in the nanomolar range has enabled insights into the channels properties, availability of other pharmacologic modulators of Cav2.3 with different chemical, physical and biological properties are of great importance for future investigations. Therefore the literature was screened systematically for molecules that modulate Cav2.3 VGCCs.
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Affiliation(s)
- Toni Schneider
- Institute of Neurophysiology, University of Cologne, Robert-Koch-Str. 39, Cologne D-50931, Germany; E-Mail:
- Authors to whom correspondence should be addressed; E-Mails: (T.S.); (M.D.); Tel.: +49-221-478-69446 (T.S.); Fax: +49-221-478-6965 (T.S.)
| | - Maxine Dibué
- Institute of Neurophysiology, University of Cologne, Robert-Koch-Str. 39, Cologne D-50931, Germany; E-Mail:
- Department for Neurosurgery, Medical Faculty, Heinrich Heine University, Moorenstraße 5, Duesseldorf D-40225, Germany & Center of Molecular Medicine, Cologne D-50931, Germany
- Authors to whom correspondence should be addressed; E-Mails: (T.S.); (M.D.); Tel.: +49-221-478-69446 (T.S.); Fax: +49-221-478-6965 (T.S.)
| | - Jürgen Hescheler
- Institute of Neurophysiology, University of Cologne, Robert-Koch-Str. 39, Cologne D-50931, Germany; E-Mail:
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77
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Colenso CK, Sessions RB, Zhang YH, Hancox JC, Dempsey CE. Interactions between voltage sensor and pore domains in a hERG K+ channel model from molecular simulations and the effects of a voltage sensor mutation. J Chem Inf Model 2013; 53:1358-70. [PMID: 23672495 DOI: 10.1021/ci4000739] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
The hERG K(+) channel is important for establishing normal electrical activity in the human heart. The channel's unique gating response to membrane potential changes indicates specific interactions between voltage sensor and pore domains that are poorly understood. In the absence of a crystal structure we constructed a homology model of the full hERG membrane domain and performed 0.5 μs molecular dynamics (MD) simulations in a hydrated membrane. The simulations identify potential interactions involving residues at the extracellular surface of S1 in the voltage sensor and at the N-terminal end of the pore helix in the hERG model. In addition, a diffuse interface involving hydrophobic residues on S4 (voltage sensor) and pore domain S5 of an adjacent subunit was stable during 0.5 μs of simulation. To assess the ability of the model to give insight into the effects of channel mutation we simulated a hERG mutant that contains a Leu to Pro substitution in the voltage sensor S4 helical segment (hERG L532P). Consistent with the retention of gated K(+) conductance, the L532P mutation was accommodated in the S4 helix with little disruption of helical structure. The mutation reduced the extent of interaction across the S4-S5 interface, suggesting a structural basis for the greatly enhanced deactivation rate in hERG L532P. The study indicates that pairwise comparison of wild-type and mutated channel models is a useful approach to interpreting functional data where uncertainty in model structures exist.
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Affiliation(s)
- Charlotte K Colenso
- School of Biochemistry, Medical Sciences Building, University of Bristol, University Walk, Bristol BS8 1TD, UK
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78
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Probing the energy landscape of activation gating of the bacterial potassium channel KcsA. PLoS Comput Biol 2013; 9:e1003058. [PMID: 23658510 PMCID: PMC3642040 DOI: 10.1371/journal.pcbi.1003058] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2012] [Accepted: 03/27/2013] [Indexed: 11/19/2022] Open
Abstract
The bacterial potassium channel KcsA, which has been crystallized in several conformations, offers an ideal model to investigate activation gating of ion channels. In this study, essential dynamics simulations are applied to obtain insights into the transition pathways and the energy profile of KcsA pore gating. In agreement with previous hypotheses, our simulations reveal a two phasic activation gating process. In the first phase, local structural rearrangements in TM2 are observed leading to an intermediate channel conformation, followed by large structural rearrangements leading to full opening of KcsA. Conformational changes of a highly conserved phenylalanine, F114, at the bundle crossing region are crucial for the transition from a closed to an intermediate state. 3.9 µs umbrella sampling calculations reveal that there are two well-defined energy barriers dividing closed, intermediate, and open channel states. In agreement with mutational studies, the closed state was found to be energetically more favorable compared to the open state. Further, the simulations provide new insights into the dynamical coupling effects of F103 between the activation gate and the selectivity filter. Investigations on individual subunits support cooperativity of subunits during activation gating.
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79
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Santos JS, Syeda R, Montal M. Stabilization of the conductive conformation of a voltage-gated K+ (Kv) channel: the lid mechanism. J Biol Chem 2013; 288:16619-16628. [PMID: 23609443 DOI: 10.1074/jbc.m113.468728] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Voltage-gated K(+) (Kv) channels are molecular switches that sense membrane potential and in response open to allow K(+) ions to diffuse out of the cell. In these proteins, sensor and pore belong to two distinct structural modules. We previously showed that the pore module alone is a robust yet dynamic structural unit in lipid membranes and that it senses potential and gates open to conduct K(+) with unchanged fidelity. The implication is that the voltage sensitivity of K(+) channels is not solely encoded in the sensor. Given that the coupling between sensor and pore remains elusive, we asked whether it is then possible to convert a pore module characterized by brief openings into a conductor with a prolonged lifetime in the open state. The strategy involves selected probes targeted to the filter gate of the channel aiming to modulate the probability of the channel being open assayed by single channel recordings from the sensorless pore module reconstituted in lipid bilayers. Here we show that the premature closing of the pore is bypassed by association of the filter gate with two novel open conformation stabilizers: an antidepressant and a peptide toxin known to act selectively on Kv channels. Such stabilization of the conductive conformation of the channel is faithfully mimicked by the covalent attachment of fluorescein at a cysteine residue selectively introduced near the filter gate. This modulation prolongs the occupancy of permeant ions at the gate. It is this longer embrace between ion and gate that we conjecture underlies the observed stabilization of the conductive conformation. This study provides a new way of thinking about gating.
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Affiliation(s)
- Jose S Santos
- Section of Neurobiology, Division of Biological Sciences, University of California San Diego, La Jolla, California 92093
| | - Ruhma Syeda
- Section of Neurobiology, Division of Biological Sciences, University of California San Diego, La Jolla, California 92093
| | - Mauricio Montal
- Section of Neurobiology, Division of Biological Sciences, University of California San Diego, La Jolla, California 92093.
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80
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Wang Z, Dou Y, Goodchild SJ, Es-Salah-Lamoureux Z, Fedida D. Components of gating charge movement and S4 voltage-sensor exposure during activation of hERG channels. ACTA ACUST UNITED AC 2013; 141:431-43. [PMID: 23478995 PMCID: PMC3607828 DOI: 10.1085/jgp.201210942] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The human ether-á-go-go–related gene (hERG) K+ channel encodes the pore-forming α subunit of the rapid delayed rectifier current, IKr, and has unique activation gating kinetics, in that the α subunit of the channel activates and deactivates very slowly, which focuses the role of IKr current to a critical period during action potential repolarization in the heart. Despite its physiological importance, fundamental mechanistic properties of hERG channel activation gating remain unclear, including how voltage-sensor movement rate limits pore opening. Here, we study this directly by recording voltage-sensor domain currents in mammalian cells for the first time and measuring the rates of voltage-sensor modification by [2-(trimethylammonium)ethyl] methanethiosulfonate chloride (MTSET). Gating currents recorded from hERG channels expressed in mammalian tsA201 cells using low resistance pipettes show two charge systems, defined as Q1 and Q2, with V1/2’s of −55.7 (equivalent charge, z = 1.60) and −54.2 mV (z = 1.30), respectively, with the Q2 charge system carrying approximately two thirds of the overall gating charge. The time constants for charge movement at 0 mV were 2.5 and 36.2 ms for Q1 and Q2, decreasing to 4.3 ms for Q2 at +60 mV, an order of magnitude faster than the time constants of ionic current appearance at these potentials. The voltage and time dependence of Q2 movement closely correlated with the rate of MTSET modification of I521C in the outermost region of the S4 segment, which had a V1/2 of −64 mV and time constants of 36 ± 8.5 ms and 11.6 ± 6.3 ms at 0 and +60 mV, respectively. Modeling of Q1 and Q2 charge systems showed that a minimal scheme of three transitions is sufficient to account for the experimental findings. These data point to activation steps further downstream of voltage-sensor movement that provide the major delays to pore opening in hERG channels.
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Affiliation(s)
- Zhuren Wang
- Department of Anesthesiology, Pharmacology and Therapeutics, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada
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81
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Moscoso C, Vergara-Jaque A, Márquez-Miranda V, Sepúlveda RV, Valencia I, Díaz-Franulic I, González-Nilo F, Naranjo D. K⁺ conduction and Mg²⁺ blockade in a shaker Kv-channel single point mutant with an unusually high conductance. Biophys J 2013; 103:1198-207. [PMID: 22995492 DOI: 10.1016/j.bpj.2012.08.015] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2012] [Revised: 07/30/2012] [Accepted: 08/01/2012] [Indexed: 12/27/2022] Open
Abstract
Potassium channels exhibit a large diversity of single-channel conductances. Shaker is a low-conductance K-channel in which Pro475→Asp, a single-point mutation near the internal pore entrance, promotes 6- to 8-fold higher unitary current. To assess the mechanism for this higher conductance, we measured Shaker-P475D single-channel current in a wide range of symmetrical K(+) concentrations and voltages. Below 300 mM K(+), the current-to-voltage relations (i-V) showed inward rectification that disappeared at 1000 mM K(+). Single-channel conductance reached a maximum of ∼190 pS at saturating [K(+)], a value 4- to 5-fold larger than that estimated for the native channel. Intracellular Mg(2+) blocked this variant with ∼100-fold higher affinity. Near zero voltage, blockade was competitively antagonized by K(+); however, at voltages >100 mV, it was enhanced by K(+). This result is consistent with a lock-in effect in a single-file diffusion regime of Mg(2+) and K(+) along the pore. Molecular-dynamics simulations revealed higher K(+) density in the pore, especially near the Asp-475 side chains, as in the high-conductance MthK bacterial channel. The molecular dynamics also showed that K(+) ions bound distally can coexist with other K(+) or Mg(2+) in the cavity, supporting a lock-in mechanism. The maximal K(+) transport rate and higher occupancy could be due to a decrease in the electrostatic energy profile for K(+) throughout the pore, reducing the energy wells and barriers differentially by ∼0.7 and ∼2 kT, respectively.
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Affiliation(s)
- Cristian Moscoso
- Centro Interdisciplinario de Neurociencias de Valparaíso, Universidad de Valparaíso, Valparaíso, Chile
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82
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Transfer of Kv3.1 voltage sensor features to the isolated Ci-VSP voltage-sensing domain. Biophys J 2013; 103:669-76. [PMID: 22947928 DOI: 10.1016/j.bpj.2012.07.031] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2012] [Revised: 07/16/2012] [Accepted: 07/23/2012] [Indexed: 11/21/2022] Open
Abstract
Membrane proteins that respond to changes in transmembrane voltage are critical in regulating the function of living cells. The voltage-sensing domains (VSDs) of voltage-gated ion channels are extensively studied to elucidate voltage-sensing mechanisms, and yet many aspects of their structure-function relationship remain elusive. Here, we transplanted homologous amino acid motifs from the tetrameric voltage-activated potassium channel Kv3.1 to the monomeric VSD of Ciona intestinalis voltage-sensitive phosphatase (Ci-VSP) to explore which portions of Kv3.1 subunits depend on the tetrameric structure of Kv channels and which properties of Kv3.1 can be transferred to the monomeric Ci-VSP scaffold. By attaching fluorescent proteins to these chimeric VSDs, we obtained an optical readout to establish membrane trafficking and kinetics of voltage-dependent structural rearrangements. We found that motifs extending from 10 to roughly 100 amino acids can be readily transplanted from Kv3.1 into Ci-VSP to form engineered VSDs that efficiently incorporate into the plasma membrane and sense voltage. Some of the functional features of these engineered VSDs are reminiscent of Kv3.1 channels, indicating that these properties do not require interactions between Kv subunits or between the voltage sensing and the pore domains of Kv channels.
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83
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Mapder T, Adhya S, Adhya L. Electrostatic interaction between dipoles and side chains in the voltage sensor domain of K(+) channel. J Nat Sci Biol Med 2013; 4:45-50. [PMID: 23633834 PMCID: PMC3633302 DOI: 10.4103/0976-9668.107259] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2022] Open
Abstract
Background: It is well known that α-helices of protein, possessing equal and opposite charged ends, behaves like a macrodipole, but the relative importance of such macrodipoles to the aggregation of a pair of helix in the voltage sensor domain (VSD) of K+ ion channel, has not been assessed. In the VSD, importance has been given primarily to the helically arranged Arginine residues of helix, but the role of the charged residues of S3b is less focused. Method and Objective: Applying electrostatic theory, we have studied the interaction between the charges of S3b-S4 α-helix pair of KvAP through virtual mutagenesis. Result and Conclusion: We have shown that the terminal charges arising from the inherent dipolar property of α-helices play an important role in affecting the stability of the S3b-S4 pair, and in determining its spatial position at zero transmembrane potential. Moreover, the negatively charged side chain of S3b was found to be the primary stabilizing factor in holding S3b-S4 pair together as a “paddle”. Comparison of sequences of S3b helix of K+ channels from different species showed a previously unreported positional conservation of negative residues, highlighting their functional importance. These charges may contribute to the energetic of α-helix movements in an electric field.
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Affiliation(s)
- Tarunendu Mapder
- Department of Engineering Physics, B. P. Poddar Institute of Management and Technology, 137, V.I.P. Road, Kolkata, India
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84
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A conserved threonine in the S1-S2 loop of KV7.2 and K V7.3 channels regulates voltage-dependent activation. Pflugers Arch 2012; 465:797-804. [PMID: 23271449 DOI: 10.1007/s00424-012-1184-x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2012] [Revised: 11/02/2012] [Accepted: 11/09/2012] [Indexed: 12/12/2022]
Abstract
The voltage-gated potassium channels KV7.2 and KV7.3 (KCNQ2/3 genes) play an important role in regulating neuronal excitability. More than 50 KCNQ2/3 mutations have been identified to cause an inherited form of epilepsy in newborns. For two of those (E119G and S122L) found in the S1-S2 region of KV7.2, we previously showed a decreased channel availability mainly at action potential subthreshold voltages caused by a slight depolarizing shift of the activation curve. Interestingly, recent studies revealed that a threonine residue within the S1-S2 loop, highly conserved among different classes of KV channels, is crucial for both their function and surface expression. To investigate the functional role of the homologous threonine residues in KV7.2 (T114) and KV7.3 (T144) channels, we replaced them with alanine and examined the electrophysiological properties using heterologous expression in CHO cells and whole cell patch clamping. Channels comprising mutant subunits yielded decreased potassium currents with slowed activation and accelerated deactivation kinetics. However, the most striking effect was a depolarizing shift in the voltage dependence of activation reaching +30 mV upon co-expression of both mutant subunits. Potential interactions of T114 within the channel were analyzed by creating a 3D homology model of KV7.2 in an open state suggesting that this residue plays a central role in the formation of a stable interface between the S1-S2 and the S5 segment helices. This could be the explanation why substitution of the conserved threonine in KV7.2 and KV7.3 channels destabilizes the open and favors the closed state of these channels.
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85
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Boukalova S, Teisinger J, Vlachova V. Protons stabilize the closed conformation of gain-of-function mutants of the TRPV1 channel. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2012; 1833:520-8. [PMID: 23220012 DOI: 10.1016/j.bbamcr.2012.11.017] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/27/2012] [Revised: 10/29/2012] [Accepted: 11/20/2012] [Indexed: 12/29/2022]
Abstract
The vanilloid transient receptor potential channel TRPV1 is a molecular integrator of noxious stimuli, including capsaicin, heat and protons. Despite clear similarities between the overall architecture of TRPV1 and voltage-dependent potassium (Kv) channels, the extent of conservation in the molecular logic for gating is unknown. In Kv channels, a small contact surface between S1 and the pore-helix is required for channel functioning. To explore the function of S1 in TRPV1, we used tryptophan-scanning mutagenesis and characterized the responses to capsaicin and protons. Wild-type-like currents were generated in 9 out of 17 mutants; three mutants (M445W, A452W, R455W) were non-functional. The conservative mutation R455K in the extracellular extent of S1 slowed down capsaicin-induced activation and prevented normal channel closure. This mutant was neither activated nor potentiated by protons, on the contrary, protons promoted a rapid deactivation of its currents. Similar phenotypes were found in two other gain-of-function mutants and also in the pore-helix mutant T633A, known to uncouple proton activation. We propose that the S1 domain contains a functionally important region that may be specifically involved in TRPV1 channel gating, and thus be important for the energetic coupling between S1-S4 sensor activation and gate opening. Analogous to Kv channels, the S1-pore interface might serve to stabilize conformations associated with TRPV1 channel gating.
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Affiliation(s)
- Stepana Boukalova
- Institute of Physiology, Academy of Sciences of the Czech Republic, Videnska 1083, 142 20 Prague 4, Czech Republic
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86
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Balijepalli SY, Lim E, Concannon SP, Chew CL, Holzem KE, Tester DJ, Ackerman MJ, Delisle BP, Balijepalli RC, January CT. Mechanism of loss of Kv11.1 K+ current in mutant T421M-Kv11.1-expressing rat ventricular myocytes: interaction of trafficking and gating. Circulation 2012; 126:2809-18. [PMID: 23136156 DOI: 10.1161/circulationaha.112.118018] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND Type 2 long QT syndrome involves mutations in the human ether a-go-go-related gene (hERG or KCNH2). T421M, an S1 domain mutation in the Kv11.1 channel protein, was identified in a resuscitated patient. We assessed its biophysical, protein trafficking, and pharmacological mechanisms in adult rat ventricular myocytes. METHODS AND RESULTS Isolated adult rat ventricular myocytes were infected with wild-type (WT)-Kv11.1- and T421M-Kv11.1-expressing adenovirus and analyzed with the use of patch clamp, Western blot, and confocal imaging techniques. Expression of WT-Kv11.1 or T421M-Kv11.1 produced peak tail current (I(Kv11.1)) of 8.78±1.18 and 1.91±0.22 pA/pF, respectively. Loss of mutant I(Kv11.1) resulted from (1) a partially trafficking-deficient channel protein with reduced cell surface expression and (2) altered channel gating with a positive shift in the voltage dependence of activation and altered kinetics of activation and deactivation. Coexpression of WT+T421M-Kv11.1 resulted in heterotetrameric channels that remained partially trafficking deficient with only a minimal increase in peak I(Kv11.1) density, whereas the voltage dependence of channel gating became WT-like. In the adult rat ventricular myocyte model, both WT-Kv11.1 and T421M-Kv11.1 channels responded to β-adrenergic stimulation by increasing I(Kv11.1). CONCLUSIONS The T421M-Kv11.1 mutation caused a loss of I(Kv11.1) through interactions of abnormal protein trafficking and channel gating. Furthermore, for coexpressed WT+T421M-Kv11.1 channels, different dominant-negative interactions govern protein trafficking and ion channel gating, and these are likely to be reflected in the clinical phenotype. Our results also show that WT and mutant Kv11.1 channels responded to β-adrenergic stimulation.
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87
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Yang H, Gao Z, Li P, Yu K, Yu Y, Xu TL, Li M, Jiang H. A theoretical model for calculating voltage sensitivity of ion channels and the application on Kv1.2 potassium channel. Biophys J 2012; 102:1815-25. [PMID: 22768937 DOI: 10.1016/j.bpj.2012.03.032] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2011] [Revised: 02/11/2012] [Accepted: 03/15/2012] [Indexed: 01/03/2023] Open
Abstract
Voltage sensing confers conversion of a change in membrane potential to signaling activities underlying the physiological processes. For an ion channel, voltage sensitivity is usually experimentally measured by fitting electrophysiological data to Boltzmann distributions. In our study, a two-state model of the ion channel and equilibrium statistical mechanics principle were used to test the hypothesis of empirically calculating the overall voltage sensitivity of an ion channel on the basis of its closed and open conformations, and determine the contribution of individual residues to the voltage sensing. We examined the theoretical paradigm by performing experimental measurements with Kv1.2 channel and a series of mutants. The correlation between the calculated values and the experimental values is at respective level, R(2) = 0.73. Our report therefore provides in silico prediction of key conformations and has identified additional residues critical for voltage sensing.
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Affiliation(s)
- Huaiyu Yang
- Drug Discovery and Design Center, State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China
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88
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Zhang J, Qu X, Covarrubias M, Germann MW. Insight into the modulation of Shaw2 Kv channels by general anesthetics: structural and functional studies of S4-S5 linker and S6 C-terminal peptides in micelles by NMR. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2012; 1828:595-601. [PMID: 23031574 DOI: 10.1016/j.bbamem.2012.09.025] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/20/2012] [Revised: 09/23/2012] [Accepted: 09/24/2012] [Indexed: 12/20/2022]
Abstract
The modulation of the Drosophila Shaw2 Kv channel by 1-alkanols and inhaled anesthetics is correlated with the involvement of the S4-S5 linker and C-terminus of S6, and consistent with stabilization of the channel's closed state. Structural analysis of peptides from S4-S5 (L45) and S6 (S6c), by nuclear magnetic resonance and circular dichroism spectroscopy supports that an α-helical conformation was adopted by L45, while S6c was only in an unstable/dynamic partially folded α-helix in dodecylphosphocholine micelles. Solvent accessibility and paramagnetic probing of L45 revealed that L45 lies parallel to the surface of micelles with charged and polar residues pointing towards the solution while hydrophobic residues are buried inside the micelles. Chemical shift perturbation introduced by 1-butanol on residues Gln320, Thr321, Phe322 and Arg323 of L45, as well as Thr423 and Gln424 of S6c indicates possible anesthetic binding sites on these two important components in the channel activation apparatus. Diffusion measurements confirmed the association of L45, S6c and 1-butanol with micelles which suggests the capability of 1-butanol to influence a possible interaction of L45 and S6c in the micelle environment.
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Affiliation(s)
- Jin Zhang
- Department of Chemistry, Georgia State University, Atlanta, GA 30303, USA
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89
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Tetrameric assembly of KvLm K+ channels with defined numbers of voltage sensors. Proc Natl Acad Sci U S A 2012; 109:16917-22. [PMID: 23019583 DOI: 10.1073/pnas.1205592109] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Voltage-gated K(+) (Kv) channels are tetrameric assemblies in which each modular subunit consists of a voltage sensor and a pore domain. KvLm, the voltage-gated K(+) channel from Listeria monocytogenes, differs from other Kv channels in that its voltage sensor contains only three out of the eight charged residues previously implicated in voltage gating. Here, we ask how many sensors are required to produce a functional Kv channel by investigating heterotetramers comprising combinations of full-length KvLm (FL) and its sensorless pore module. KvLm heterotetramers were produced by cell-free expression, purified by electrophoresis, and shown to yield functional channels after reconstitution in droplet interface bilayers. We studied the properties of KvLm channels with zero, one, two, three, and four voltage sensors. Three sensors suffice to promote channel opening with FL(4)-like voltage dependence at depolarizing potentials, but all four sensors are required to keep the channel closed during membrane hyperpolarization.
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90
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Blunck R, Batulan Z. Mechanism of electromechanical coupling in voltage-gated potassium channels. Front Pharmacol 2012; 3:166. [PMID: 22988442 PMCID: PMC3439648 DOI: 10.3389/fphar.2012.00166] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2012] [Accepted: 08/24/2012] [Indexed: 01/10/2023] Open
Abstract
Voltage-gated ion channels play a central role in the generation of action potentials in the nervous system. They are selective for one type of ion - sodium, calcium, or potassium. Voltage-gated ion channels are composed of a central pore that allows ions to pass through the membrane and four peripheral voltage sensing domains that respond to changes in the membrane potential. Upon depolarization, voltage sensors in voltage-gated potassium channels (Kv) undergo conformational changes driven by positive charges in the S4 segment and aided by pairwise electrostatic interactions with the surrounding voltage sensor. Structure-function relations of Kv channels have been investigated in detail, and the resulting models on the movement of the voltage sensors now converge to a consensus; the S4 segment undergoes a combined movement of rotation, tilt, and vertical displacement in order to bring 3-4e(+) each through the electric field focused in this region. Nevertheless, the mechanism by which the voltage sensor movement leads to pore opening, the electromechanical coupling, is still not fully understood. Thus, recently, electromechanical coupling in different Kv channels has been investigated with a multitude of techniques including electrophysiology, 3D crystal structures, fluorescence spectroscopy, and molecular dynamics simulations. Evidently, the S4-S5 linker, the covalent link between the voltage sensor and pore, plays a crucial role. The linker transfers the energy from the voltage sensor movement to the pore domain via an interaction with the S6 C-termini, which are pulled open during gating. In addition, other contact regions have been proposed. This review aims to provide (i) an in-depth comparison of the molecular mechanisms of electromechanical coupling in different Kv channels; (ii) insight as to how the voltage sensor and pore domain influence one another; and (iii) theoretical predictions on the movement of the cytosolic face of the Kv channels during gating.
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Affiliation(s)
- Rikard Blunck
- Groupe d’étude des protéines membranairesMontreal, QC, Canada
- Department of Physiology, Université de MontréalMontreal, QC, Canada
- Department of Physics, Université de MontréalMontreal, QC, Canada
| | - Zarah Batulan
- Groupe d’étude des protéines membranairesMontreal, QC, Canada
- Department of Physiology, Université de MontréalMontreal, QC, Canada
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91
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Vardanyan V, Pongs O. Coupling of voltage-sensors to the channel pore: a comparative view. Front Pharmacol 2012; 3:145. [PMID: 22866036 PMCID: PMC3406610 DOI: 10.3389/fphar.2012.00145] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2012] [Accepted: 07/07/2012] [Indexed: 12/11/2022] Open
Abstract
The activation of voltage-dependent ion channels is initiated by potential-induced conformational rearrangements in the voltage-sensor domains that propagates to the pore domain (PD) and finally opens the ion conduction pathway. In potassium channels voltage-sensors are covalently linked to the pore via S4-S5 linkers at the cytoplasmic site of the PD. Transformation of membrane electric energy into the mechanical work required for the opening or closing of the channel pore is achieved through an electromechanical coupling mechanism, which involves local interaction between residues in S4-S5 linker and pore-forming alpha helices. In this review we discuss present knowledge and open questions related to the electromechanical coupling mechanism in most intensively studied voltage-gated Shaker potassium channel and compare structure-functional aspects of coupling with those observed in distantly related ion channels. We focus particularly on the role of electromechanical coupling in modulation of the constitutive conductance of ion channels.
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Affiliation(s)
- Vitya Vardanyan
- Ion Channel Research Group, Institute of Molecular Biology, National Academy of Sciences of the Republic of Armenia Yerevan, Armenia
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92
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Gating of cyclic nucleotide-gated channels is voltage dependent. Nat Commun 2012; 3:973. [PMID: 22828633 DOI: 10.1038/ncomms1972] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2012] [Accepted: 06/25/2012] [Indexed: 01/09/2023] Open
Abstract
Cyclic nucleotide-gated channels belong to the family of voltage-gated ion channels, but pore opening requires the presence of intracellular cyclic nucleotides. In the presence of a saturating agonist, cyclic nucleotide-gated channel gating is voltage independent and it is not known why cyclic nucleotide-gated channels are voltage-insensitive despite harbouring the S4-type voltage sensor. Here we report that, in the presence of Li(+), Na(+) and K(+), the gating of wild-type cyclic nucleotide-gated A1 and native cyclic nucleotide-gated channels is voltage independent, whereas their gating is highly voltage-dependent in the presence of Rb(+), Cs(+) and organic cations. Mutagenesis experiments show that voltage sensing occurs through a voltage sensor composed of charged/polar residues in the pore and of the S4-type voltage sensor. During evolution, cyclic nucleotide-gated channels lose their voltage-sensing ability when Na(+) or K(+) permeate so that the vertebrate photoreceptor cyclic nucleotide-gated channels are open at negative voltages, a necessary condition for phototransduction.
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93
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Choveau FS, Abderemane-Ali F, Coyan FC, Es-Salah-Lamoureux Z, Baró I, Loussouarn G. Opposite Effects of the S4-S5 Linker and PIP(2) on Voltage-Gated Channel Function: KCNQ1/KCNE1 and Other Channels. Front Pharmacol 2012; 3:125. [PMID: 22787448 PMCID: PMC3389672 DOI: 10.3389/fphar.2012.00125] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2012] [Accepted: 06/14/2012] [Indexed: 01/16/2023] Open
Abstract
Voltage-gated potassium (Kv) channels are tetramers, each subunit presenting six transmembrane segments (S1-S6), with each S1-S4 segments forming a voltage-sensing domain (VSD) and the four S5-S6 forming both the conduction pathway and its gate. S4 segments control the opening of the intracellular activation gate in response to changes in membrane potential. Crystal structures of several voltage-gated ion channels in combination with biophysical and mutagenesis studies highlighted the critical role of the S4-S5 linker (S4S5(L)) and of the S6 C-terminal part (S6(T)) in the coupling between the VSD and the activation gate. Several mechanisms have been proposed to describe the coupling at a molecular scale. This review summarizes the mechanisms suggested for various voltage-gated ion channels, including a mechanism that we described for KCNQ1, in which S4S5(L) is acting like a ligand binding to S6(T) to stabilize the channel in a closed state. As discussed in this review, this mechanism may explain the reverse response to depolarization in HCN-like channels. As opposed to S4S5(L), the phosphoinositide, phosphatidylinositol 4,5-bisphosphate (PIP(2)), stabilizes KCNQ1 channel in an open state. Many other ion channels (not only voltage-gated) require PIP(2) to function properly, confirming its crucial importance as an ion channel cofactor. This is highlighted in cases in which an altered regulation of ion channels by PIP(2) leads to channelopathies, as observed for KCNQ1. This review summarizes the state of the art on the two regulatory mechanisms that are critical for KCNQ1 and other voltage-gated channels function (PIP(2) and S4S5(L)), and assesses their potential physiological and pathophysiological roles.
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Affiliation(s)
- Frank S Choveau
- UMR 1087, Institut National de la Santé et de la Recherche Médicale Nantes, France
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94
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Goodchild SJ, Fedida D. Contributions of intracellular ions to kv channel voltage sensor dynamics. Front Pharmacol 2012; 3:114. [PMID: 22719727 PMCID: PMC3376422 DOI: 10.3389/fphar.2012.00114] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2012] [Accepted: 05/25/2012] [Indexed: 11/13/2022] Open
Abstract
Voltage-sensing domains (VSDs) of Kv channels control ionic conductance through coupling of the movement of charged residues in the S4 segment to conformational changes at the cytoplasmic region of the pore domain, that allow K(+) ions to flow. Conformational transitions within the VSD are induced by changes in the applied voltage across the membrane field. However, several other factors not directly linked to the voltage-dependent movement of charged residues within the voltage sensor impact the dynamics of the voltage sensor, such as inactivation, ionic conductance, intracellular ion identity, and block of the channel by intracellular ligands. The effect of intracellular ions on voltage sensor dynamics is of importance in the interpretation of gating current measurements and the physiology of pore/voltage sensor coupling. There is a significant amount of variability in the reported kinetics of voltage sensor deactivation kinetics of Kv channels attributed to different mechanisms such as open state stabilization, immobilization, and relaxation processes of the voltage sensor. Here we separate these factors and focus on the causal role that intracellular ions can play in allosterically modulating the dynamics of Kv voltage sensor deactivation kinetics. These considerations are of critical importance in understanding the molecular determinants of the complete channel gating cycle from activation to deactivation.
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Affiliation(s)
- Samuel J Goodchild
- Department of Anesthesiology, Pharmacology and Therapeutics, University of British Columbia Vancouver, BC, Canada
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95
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Sun X, Zaydman MA, Cui J. Regulation of Voltage-Activated K(+) Channel Gating by Transmembrane β Subunits. Front Pharmacol 2012; 3:63. [PMID: 22529812 PMCID: PMC3328208 DOI: 10.3389/fphar.2012.00063] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2012] [Accepted: 03/29/2012] [Indexed: 01/15/2023] Open
Abstract
Voltage-activated K+ (KV) channels are important for shaping action potentials and maintaining resting membrane potential in excitable cells. KV channels contain a central pore-gate domain (PGD) surrounded by four voltage-sensing domains (VSDs). The VSDs will change conformation in response to alterations of the membrane potential thereby inducing the opening of the PGD. Many KV channels are heteromeric protein complexes containing auxiliary β subunits. These β subunits modulate channel expression and activity to increase functional diversity and render tissue specific phenotypes. This review focuses on the KV β subunits that contain transmembrane (TM) segments including the KCNE family and the β subunits of large conductance, Ca2+- and voltage-activated K+ (BK) channels. These TM β subunits affect the voltage-dependent activation of KV α subunits. Experimental and computational studies have described the structural location of these β subunits in the channel complexes and the biophysical effects on VSD activation, PGD opening, and VSD–PGD coupling. These results reveal some common characteristics and mechanistic insights into KV channel modulation by TM β subunits.
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Affiliation(s)
- Xiaohui Sun
- Department of Biomedical Engineering, Washington University Saint Louis, MO, USA
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96
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Tikhonov DB, Zhorov BS. Architecture and Pore Block of Eukaryotic Voltage-Gated Sodium Channels in View of NavAb Bacterial Sodium Channel Structure. Mol Pharmacol 2012; 82:97-104. [DOI: 10.1124/mol.112.078212] [Citation(s) in RCA: 86] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
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97
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98
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Hot spots for allosteric regulation on protein surfaces. Cell 2012; 147:1564-75. [PMID: 22196731 DOI: 10.1016/j.cell.2011.10.049] [Citation(s) in RCA: 263] [Impact Index Per Article: 21.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2011] [Revised: 08/10/2011] [Accepted: 10/19/2011] [Indexed: 11/22/2022]
Abstract
Recent work indicates a general architecture for proteins in which sparse networks of physically contiguous and coevolving amino acids underlie basic aspects of structure and function. These networks, termed sectors, are spatially organized such that active sites are linked to many surface sites distributed throughout the structure. Using the metabolic enzyme dihydrofolate reductase as a model system, we show that: (1) the sector is strongly correlated to a network of residues undergoing millisecond conformational fluctuations associated with enzyme catalysis, and (2) sector-connected surface sites are statistically preferred locations for the emergence of allosteric control in vivo. Thus, sectors represent an evolutionarily conserved "wiring" mechanism that can enable perturbations at specific surface positions to rapidly initiate conformational control over protein function. These findings suggest that sectors enable the evolution of intermolecular communication and regulation.
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99
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Molecular mapping of general anesthetic sites in a voltage-gated ion channel. Biophys J 2012; 101:1613-22. [PMID: 21961587 DOI: 10.1016/j.bpj.2011.08.026] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2011] [Revised: 08/11/2011] [Accepted: 08/15/2011] [Indexed: 12/20/2022] Open
Abstract
Several voltage-gated ion channels are modulated by clinically relevant doses of general anesthetics. However, the structural basis of this modulation is not well understood. Previous work suggested that n-alcohols and inhaled anesthetics stabilize the closed state of the Shaw2 voltage-gated (Kv) channel (K-Shaw2) by directly interacting with a discrete channel site. We hypothesize that the inhibition of K-Shaw2 channels by general anesthetics is governed by interactions between binding and effector sites involving components of the channel's activation gate. To investigate this hypothesis, we applied Ala/Val scanning mutagenesis to the S4-S5 linker and the post-PVP S6 segment, and conducted electrophysiological analysis to evaluate the energetic impact of the mutations on the inhibition of the K-Shaw2 channel by 1-butanol and halothane. These analyses identified residues that determine an apparent binding cooperativity and residue pairs that act in concert to modulate gating upon anesthetic binding. In some instances, due to their critical location, key residues also influence channel gating. Complementing these results, molecular dynamics simulations and in silico docking experiments helped us visualize possible anesthetic sites and interactions. We conclude that the inhibition of K-Shaw2 by general anesthetics results from allosteric interactions between distinct but contiguous binding and effector sites involving inter- and intrasubunit interfaces.
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Wood ML, Schow EV, Freites JA, White SH, Tombola F, Tobias DJ. Water wires in atomistic models of the Hv1 proton channel. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2011; 1818:286-93. [PMID: 21843503 DOI: 10.1016/j.bbamem.2011.07.045] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/03/2011] [Revised: 07/28/2011] [Accepted: 07/29/2011] [Indexed: 01/06/2023]
Abstract
The voltage-gated proton channel (Hv1) is homologous to the voltage-sensing domain (VSD) of voltage-gated potassium (Kv) channels but lacks a separate pore domain. The Hv1 monomer has dual functions: it gates the proton current and also serves as the proton conduction pathway. To gain insight into the structure and dynamics of the yet unresolved proton permeation pathway, we performed all-atom molecular dynamics simulations of two different Hv1 homology models in a lipid bilayer in excess water. The structure of the Kv1.2-Kv2.1 paddle-chimera VSD was used as template to generate both models, but they differ in the sequence alignment of the S4 segment. In both models, we observe a water wire that extends through the membrane, whereas the corresponding region is dry in simulations of the Kv1.2-Kv2.1 paddle-chimera. We find that the kinetic stability of the water wire is dependent upon the identity and location of the residues lining the permeation pathway, in particular, the S4 arginines. A measurement of water transport kinetics indicates that the water wire is a relatively static feature of the permeation pathway. Taken together, our results suggest that proton conduction in Hv1 may occur via Grotthuss hopping along a robust water wire, with exchange of water molecules between inner and outer ends of the permeation pathway minimized by specific water-protein interactions. This article is part of a Special Issue entitled: Membrane protein structure and function.
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Affiliation(s)
- Mona L Wood
- Department of Chemistry, University of California, Irvine, CA 92697-2025, USA
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