1
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Iwamuro T, Itohara K, Furukawa Y. Stability of N-type inactivation and the coupling between N-type and C-type inactivation in the Aplysia Kv1 channel. Pflugers Arch 2024; 476:1493-1516. [PMID: 39008084 DOI: 10.1007/s00424-024-02982-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2024] [Revised: 05/28/2024] [Accepted: 06/19/2024] [Indexed: 07/16/2024]
Abstract
The voltage-dependent potassium channels (Kv channels) show several different types of inactivation. N-type inactivation is a fast inactivating mechanism, which is essentially an open pore blockade by the amino-terminal structure of the channel itself or the auxiliary subunit. There are several functionally discriminatable slow inactivation (C-type, P-type, U-type), the mechanism of which is supposed to include rearrangement of the pore region. In some Kv1 channels, the actual inactivation is brought about by coupling of N-type and C-type inactivation (N-C coupling). In the present study, we focused on the N-C coupling of the Aplysia Kv1 channel (AKv1). AKv1 shows a robust N-type inactivation, but its recovery is almost thoroughly from C-type inactivated state owing to the efficient N-C coupling. In the I8Q mutant of AKv1, we found that the inactivation as well as its recovery showed two kinetic components apparently correspond to N-type and C-type inactivation. Also, the cumulative inactivation which depends on N-type mechanism in AKv1 was hindered in I8Q, suggesting that N-type inactivation of I8Q is less stable. We also found that Zn2 + specifically accelerates C-type inactivation of AKv1 and that H382 in the pore turret is involved in the Zn2 + binding. Because the region around Ile8 (I8) in AKv1 has been suggested to be involved in the pre-block binding of the amino-terminal structure, our results strengthen a hypothesis that the stability of the pre-block state is important for stable N-type inactivation as well as the N-C coupling in the Kv1 channel inactivation.
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Affiliation(s)
- Tokunari Iwamuro
- Laboratory of Neurobiology, Graduate School of Integrated Sciences of Life, Hiroshima University, Kagamiyama 1-7-1, 739-8521, Higashi-Hiroshima, Japan
| | - Kazuki Itohara
- Laboratory of Neurobiology, Graduate School of Integrated Sciences of Life, Hiroshima University, Kagamiyama 1-7-1, 739-8521, Higashi-Hiroshima, Japan
| | - Yasuo Furukawa
- Laboratory of Neurobiology, Graduate School of Integrated Sciences of Life, Hiroshima University, Kagamiyama 1-7-1, 739-8521, Higashi-Hiroshima, Japan.
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2
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Palmisano VF, Anguita-Ortiz N, Faraji S, Nogueira JJ. Voltage-Gated Ion Channels: Structure, Pharmacology and Photopharmacology. Chemphyschem 2024; 25:e202400162. [PMID: 38649320 DOI: 10.1002/cphc.202400162] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2024] [Revised: 04/21/2024] [Accepted: 04/22/2024] [Indexed: 04/25/2024]
Abstract
Voltage-gated ion channels are transmembrane proteins responsible for the generation and propagation of action potentials in excitable cells. Over the last decade, advancements have enabled the elucidation of crystal structures of ion channels. This progress in structural understanding, particularly in identifying the binding sites of local anesthetics, opens avenues for the design of novel compounds capable of modulating ion conduction. However, many traditional drugs lack selectivity and come with adverse side effects. The emergence of photopharmacology has provided an orthogonal way of controlling the activity of compounds, enabling the regulation of ion conduction with light. In this review, we explore the central pore region of voltage-gated sodium and potassium channels, providing insights from both structural and pharmacological perspectives. We discuss the different binding modes of synthetic compounds that can physically occlude the pore and, therefore, block ion conduction. Moreover, we examine recent advances in the photopharmacology of voltage-gated ion channels, introducing molecular approaches aimed at controlling their activity by using photosensitive drugs.
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Affiliation(s)
- Vito F Palmisano
- Department of Chemistry, Universidad Autónoma de Madrid, 28049, Madrid, Spain
- Theoretical Chemistry Group, Zernike Institute for Advanced Materials, University of Groningen, 9747 AG, Groningen, The Netherlands
| | - Nuria Anguita-Ortiz
- Department of Chemistry, Universidad Autónoma de Madrid, 28049, Madrid, Spain
| | - Shirin Faraji
- Theoretical Chemistry Group, Zernike Institute for Advanced Materials, University of Groningen, 9747 AG, Groningen, The Netherlands
| | - Juan J Nogueira
- Department of Chemistry, Universidad Autónoma de Madrid, 28049, Madrid, Spain
- IADCHEM, Institute for Advanced Research in Chemistry, Universidad Autónoma de Madrid, 28049, Madrid, Spain
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3
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Aman TK, Raman IM. Resurgent current in context: Insights from the structure and function of Na and K channels. Biophys J 2024; 123:1924-1941. [PMID: 38130058 PMCID: PMC11309984 DOI: 10.1016/j.bpj.2023.12.016] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2023] [Revised: 12/07/2023] [Accepted: 12/18/2023] [Indexed: 12/23/2023] Open
Abstract
Discovered just over 25 years ago in cerebellar Purkinje neurons, resurgent Na current was originally described operationally as a component of voltage-gated Na current that flows upon repolarization from relatively depolarized potentials and speeds recovery from inactivation, increasing excitability. Its presence in many excitable cells and absence from others has raised questions regarding its biophysical and molecular mechanisms. Early studies proposed that Na channels capable of generating resurgent current are subject to a rapid open-channel block by an endogenous blocking protein, which binds upon depolarization and unblocks upon repolarization. Since the time that this mechanism was suggested, many physiological and structural studies of both Na and K channels have revealed aspects of gating and conformational states that provide insights into resurgent current. These include descriptions of domain movements for activation and inactivation, solution of cryo-EM structures with pore-blocking compounds, and identification of native blocking domains, proteins, and modulatory subunits. Such results not only allow the open-channel block hypothesis to be refined but also link it more clearly to research that preceded it. This review considers possible mechanisms for resurgent Na current in the context of earlier and later studies of ion channels and suggests a framework for future research.
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Affiliation(s)
- Teresa K Aman
- Department of Neurobiology, Northwestern University, Evanston, Illinois
| | - Indira M Raman
- Department of Neurobiology, Northwestern University, Evanston, Illinois.
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4
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Iqbal S, Atiq M, Sahi ST, Akbar N, Rajput NA. Progressive alterations in mineral contents in citrus genotypes toward Alternaria citri causing brown spot of citrus. PLoS One 2024; 19:e0306031. [PMID: 38959268 PMCID: PMC11221669 DOI: 10.1371/journal.pone.0306031] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2023] [Accepted: 06/10/2024] [Indexed: 07/05/2024] Open
Abstract
Brown spot of citrus caused by Alternaria citri is one of the emerging threats to the successful production of citrus crops. The present study, conducted with a substantial sample size of 50 leaf samples for statistical reliability, aimed to determine the change in mineral content in citrus leaves after brown spot disease attack. Leaf samples from a diverse range of susceptible citrus varieties (Valentia late, Washington navel, and Kinnow) and resistant varieties (Citron, Eruka lemon, and Mayer lemon) were analyzed. Significant variations (p ≤ 0.05) in mineral contents were observed across reaction groups (inoculated and un-inoculated), types (resistant and susceptible), and varieties of citrus in response to infection of Alternaria citri. The analysis of variance showed significant changes in mineral levels of citrus leaves, including nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), zinc (Zn), sodium (Na), iron (Fe), and copper (Cu). The results indicate that the concentration of N and P differed by 6.63% and 1.44%, respectively, in resistant plants, while susceptible plants showed a difference of 6.07% and 1.19%. Moreover, resistant plants showed a higher concentrations of K, Ca, Mg, Zn, Na, Fe, and Cu at 8.40, 2.1, 1.83, 2.21, 1.58, 2.89, and 0.36 ppm respectively, compared to susceptible plants which showed concentrations of 5.99, 1.93, 1.47, 1.09, 1.24, 1.81, and 0.31 ppm respectively. Amounts of mineral contents were reduced in both resistant as well as susceptible plants of citrus after inoculation. Amount of N (8.56), P (1.87) % while K (10.74), Ca (2.71), Mg (2.62), Zn (2.20), Na (2.08), Fe (3.57) and Cu (0.20) ppm were recorded in un-inoculated group of citrus plants that reduced to 3.15 and 0.76% and 3.66, 1.40, 0.63,0.42, 0.74, 1.13 and 0.13 ppm in inoculated group respectively. It was accomplished that susceptible varieties contained lower ionic contents than resistant varieties. The higher concentrations of ionic contents in resistant citrus varieties build up the biochemical and physiological processes of the citrus plant, which help to restrict spread of pathogens. Further research could explore the interplay between mineral nutrition and disease resistance in citrus, potentially leading to the development of new disease-resistant varieties.
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Affiliation(s)
- Shahid Iqbal
- Department of Plant Pathology, University of Agriculture Faisalabad, Faisalabad, Pakistan
- National Agriculture Research Center, Crop Disease Research Institute, PARC, Islamabad, Pakistan
| | - Muhammad Atiq
- Department of Plant Pathology, University of Agriculture Faisalabad, Faisalabad, Pakistan
| | - Shahbaz Talib Sahi
- Department of Plant Pathology, University of Agriculture Faisalabad, Faisalabad, Pakistan
| | - Nadeem Akbar
- Department of Agronomy, University of Agriculture Faisalabad, Faisalabad, Pakistan
| | - Nasir Ahmed Rajput
- Department of Plant Pathology, University of Agriculture Faisalabad, Faisalabad, Pakistan
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5
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Rönnelid O, Elinder F. Carboxyl-group compounds activate voltage-gated potassium channels via a distinct mechanism. J Gen Physiol 2024; 156:e202313516. [PMID: 38832889 PMCID: PMC11148469 DOI: 10.1085/jgp.202313516] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2023] [Revised: 03/14/2024] [Accepted: 05/21/2024] [Indexed: 06/06/2024] Open
Abstract
Voltage-gated ion channels are responsible for the electrical excitability of neurons and cardiomyocytes. Thus, they are obvious targets for pharmaceuticals aimed to modulate excitability. Compounds activating voltage-gated potassium (KV) channels are expected to reduce excitability. To search for new KV-channel activators, we performed a high-throughput screen of 10,000 compounds on a specially designed Shaker KV channel. Here, we report on a large family of channel-activating compounds with a carboxyl (COOH) group as the common motif. The most potent COOH activators are lipophilic (4 < LogP <7) and are suggested to bind at the interface between the lipid bilayer and the channel's positively charged voltage sensor. The negatively charged form of the COOH-group compounds is suggested to open the channel by electrostatically pulling the voltage sensor to an activated state. Several of the COOH-group compounds also activate the therapeutically important KV7.2/7.3 channel and can thus potentially be developed into antiseizure drugs. The COOH-group compounds identified in this study are suggested to act via the same site and mechanism of action as previously studied COOH-group compounds, such as polyunsaturated fatty acids and resin acids, but distinct from sites for several other types of potassium channel-activating compounds.
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Affiliation(s)
- Olle Rönnelid
- Department of Biomedical and Clinical Sciences, Linköping University, Linköping, Sweden
| | - Fredrik Elinder
- Department of Biomedical and Clinical Sciences, Linköping University, Linköping, Sweden
- Science for Life Laboratory, Linköping University, Linköping, Sweden
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6
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Renart ML, Giudici AM, González-Ros JM, Poveda JA. Steady-state and time-resolved fluorescent methodologies to characterize the conformational landscape of the selectivity filter of K + channels. Methods 2024; 225:89-99. [PMID: 38508347 DOI: 10.1016/j.ymeth.2024.02.010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2023] [Revised: 02/02/2024] [Accepted: 02/23/2024] [Indexed: 03/22/2024] Open
Abstract
A variety of equilibrium and non-equilibrium methods have been used in a multidisciplinary approach to study the conformational landscape associated with the binding of different cations to the pore of potassium channels. These binding processes, and the conformational changes resulting therefrom, modulate the functional properties of such integral membrane properties, revealing these permeant and blocking cations as true effectors of such integral membrane proteins. KcsA, a prototypic K+ channel from Streptomyces lividans, has been extensively characterized in this regard. Here, we revise several fluorescence-based approaches to monitor cation binding under different experimental conditions in diluted samples, analyzing the advantages and disadvantages of each approach. These studies have contributed to explain the selectivity, conduction, and inactivation properties of K+ channels at the molecular level, together with the allosteric communication between the two gates that control the ion channel flux, and how they are modulated by lipids.
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Affiliation(s)
- María Lourdes Renart
- IDiBE-Instituto de Investigación, Desarrollo e Innovación en Biotecnología Sanitaria de Elche, Universidad Miguel Hernández, 03202 Elche, Spain.
| | - Ana Marcela Giudici
- IDiBE-Instituto de Investigación, Desarrollo e Innovación en Biotecnología Sanitaria de Elche, Universidad Miguel Hernández, 03202 Elche, Spain.
| | - José M González-Ros
- IDiBE-Instituto de Investigación, Desarrollo e Innovación en Biotecnología Sanitaria de Elche, Universidad Miguel Hernández, 03202 Elche, Spain.
| | - José A Poveda
- IDiBE-Instituto de Investigación, Desarrollo e Innovación en Biotecnología Sanitaria de Elche, Universidad Miguel Hernández, 03202 Elche, Spain.
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7
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Jagielnicki M, Kucharska I, Bennett BC, Harris AL, Yeager M. Connexin Gap Junction Channels and Hemichannels: Insights from High-Resolution Structures. BIOLOGY 2024; 13:298. [PMID: 38785780 PMCID: PMC11117596 DOI: 10.3390/biology13050298] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/26/2024] [Revised: 03/29/2024] [Accepted: 04/08/2024] [Indexed: 05/25/2024]
Abstract
Connexins (Cxs) are a family of integral membrane proteins, which function as both hexameric hemichannels (HCs) and dodecameric gap junction channels (GJCs), behaving as conduits for the electrical and molecular communication between cells and between cells and the extracellular environment, respectively. Their proper functioning is crucial for many processes, including development, physiology, and response to disease and trauma. Abnormal GJC and HC communication can lead to numerous pathological states including inflammation, skin diseases, deafness, nervous system disorders, and cardiac arrhythmias. Over the last 15 years, high-resolution X-ray and electron cryomicroscopy (cryoEM) structures for seven Cx isoforms have revealed conservation in the four-helix transmembrane (TM) bundle of each subunit; an αβ fold in the disulfide-bonded extracellular loops and inter-subunit hydrogen bonding across the extracellular gap that mediates end-to-end docking to form a tight seal between hexamers in the GJC. Tissue injury is associated with cellular Ca2+ overload. Surprisingly, the binding of 12 Ca2+ ions in the Cx26 GJC results in a novel electrostatic gating mechanism that blocks cation permeation. In contrast, acidic pH during tissue injury elicits association of the N-terminal (NT) domains that sterically blocks the pore in a "ball-and-chain" fashion. The NT domains under physiologic conditions display multiple conformational states, stabilized by protein-protein and protein-lipid interactions, which may relate to gating mechanisms. The cryoEM maps also revealed putative lipid densities within the pore, intercalated among transmembrane α-helices and between protomers, the functions of which are unknown. For the future, time-resolved cryoEM of isolated Cx channels as well as cryotomography of GJCs and HCs in cells and tissues will yield a deeper insight into the mechanisms for channel regulation. The cytoplasmic loop (CL) and C-terminal (CT) domains are divergent in sequence and length, are likely involved in channel regulation, but are not visualized in the high-resolution X-ray and cryoEM maps presumably due to conformational flexibility. We expect that the integrated use of synergistic physicochemical, spectroscopic, biophysical, and computational methods will reveal conformational dynamics relevant to functional states. We anticipate that such a wealth of results under different pathologic conditions will accelerate drug discovery related to Cx channel modulation.
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Affiliation(s)
- Maciej Jagielnicki
- The Phillip and Patricia Frost Institute for Chemistry and Molecular Science, Department of Chemistry, University of Miami, 1201 Memorial Drive, Miami, FL 33146, USA; (M.J.); (I.K.)
| | - Iga Kucharska
- The Phillip and Patricia Frost Institute for Chemistry and Molecular Science, Department of Chemistry, University of Miami, 1201 Memorial Drive, Miami, FL 33146, USA; (M.J.); (I.K.)
| | - Brad C. Bennett
- Department of Biological and Environmental Sciences, Howard College of Arts and Sciences, Samford University, Birmingham, AL 35229, USA;
| | - Andrew L. Harris
- Rutgers New Jersey Medical School, Department of Pharmacology, Physiology and Neuroscience, Newark, NJ 07103, USA;
| | - Mark Yeager
- The Phillip and Patricia Frost Institute for Chemistry and Molecular Science, Department of Chemistry, University of Miami, 1201 Memorial Drive, Miami, FL 33146, USA; (M.J.); (I.K.)
- The Phillip and Patricia Frost Institute for Chemistry and Molecular Science, Department of Biochemistry and Molecular Biology, University of Miami, Miami, FL 33146, USA
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8
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Kwon HC, Fairclough RH, Chen TY. Biophysical and Pharmacological Insights to CLC Chloride Channels. Handb Exp Pharmacol 2024; 283:1-34. [PMID: 35768555 DOI: 10.1007/164_2022_594] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
The CLC family encompasses two functional categories of transmembrane proteins: chloride conducting channels and proton-chloride antiporters. All members in this chloride channel/transporter family consist of two identical protein subunits, and each subunit forms an independent ion-transport pathway, a structural architecture known as "double barrel." These CLC proteins serve biological functions ranging from membrane excitability and cell volume regulation to acidification of endosomes. Despite their ubiquitous expression, physiological significance, and resolved molecular structures of some of the family members, the mechanisms governing these molecules' biophysical functions are still not completely settled. However, a series of functional and structural studies have brought insights into interesting questions related to these proteins. This chapter explores the functional peculiarities underlying CLC channels aided by information observed from the chloride-proton antiporters in the CLC family. The overall structural features of these CLC proteins will be presented, and the biophysical functions will be addressed. Finally, the mechanism of pharmacological agents that interact with CLC channels will also be discussed.
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Affiliation(s)
- Hwoi Chan Kwon
- Center for Neuroscience and Biophysics Graduate Group, University of California, Davis, CA, USA
| | - Robert H Fairclough
- Department of Neurology and the Biophysics Graduate Group, University of California, Davis, CA, USA
| | - Tsung-Yu Chen
- Center for Neuroscience, Department of Neurology, and Biophysics Graduate Group, University of California, Davis, CA, USA.
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9
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Reddi R, Chatterjee S, Matulef K, Gustafson A, Gao L, Valiyaveetil FI. A facile approach for incorporating tyrosine esters to probe ion-binding sites and backbone hydrogen bonds. J Biol Chem 2024; 300:105517. [PMID: 38042487 PMCID: PMC10790091 DOI: 10.1016/j.jbc.2023.105517] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2023] [Revised: 11/06/2023] [Accepted: 11/22/2023] [Indexed: 12/04/2023] Open
Abstract
Amide-to-ester substitutions are used to study the role of the amide bonds of the protein backbone in protein structure, function, and folding. An amber suppressor tRNA/synthetase pair has been reported for incorporation of p-hydroxy-phenyl-L-lactic acid (HPLA), thereby introducing ester substitution at tyrosine residues. However, the application of this approach was limited due to the low yields of the modified proteins and the high cost of HPLA. Here we report the in vivo generation of HPLA from the significantly cheaper phenyl-L-lactic acid. We also construct an optimized plasmid with the HPLA suppressor tRNA/synthetase pair that provides higher yields of the modified proteins. The combination of the new plasmid and the in-situ generation of HPLA provides a facile and economical approach for introducing tyrosine ester substitutions. We demonstrate the utility of this approach by introducing tyrosine ester substitutions into the K+ channel KcsA and the integral membrane enzyme GlpG. We introduce the tyrosine ester in the selectivity filter of the M96V mutant of the KcsA to probe the role of the second ion binding site in the conformation of the selectivity filter and the process of inactivation. We use tyrosine ester substitutions in GlpG to perturb backbone H-bonds to investigate the contribution of these H-bonds to membrane protein stability. We anticipate that the approach developed in this study will facilitate further investigations using tyrosine ester substitutions.
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Affiliation(s)
- Ravikumar Reddi
- Department of Chemical Physiology and Biochemistry, Oregon Health and Science University, Multnomah County, Portland, Oregon, USA
| | - Satyaki Chatterjee
- Department of Chemical Physiology and Biochemistry, Oregon Health and Science University, Multnomah County, Portland, Oregon, USA
| | - Kimberly Matulef
- Department of Chemical Physiology and Biochemistry, Oregon Health and Science University, Multnomah County, Portland, Oregon, USA
| | - Andrew Gustafson
- Department of Chemical Physiology and Biochemistry, Oregon Health and Science University, Multnomah County, Portland, Oregon, USA
| | - Lujia Gao
- Department of Chemical Physiology and Biochemistry, Oregon Health and Science University, Multnomah County, Portland, Oregon, USA
| | - Francis I Valiyaveetil
- Department of Chemical Physiology and Biochemistry, Oregon Health and Science University, Multnomah County, Portland, Oregon, USA.
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10
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Stix R, Tan XF, Bae C, Fernández-Mariño AI, Swartz KJ, Faraldo-Gómez JD. Eukaryotic Kv channel Shaker inactivates through selectivity filter dilation rather than collapse. SCIENCE ADVANCES 2023; 9:eadj5539. [PMID: 38064553 PMCID: PMC10708196 DOI: 10.1126/sciadv.adj5539] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/04/2023] [Accepted: 11/09/2023] [Indexed: 12/18/2023]
Abstract
Eukaryotic voltage-gated K+ channels have been extensively studied, but the structural bases for some of their most salient functional features remain to be established. C-type inactivation, for example, is an auto-inhibitory mechanism that confers temporal resolution to their signal-firing activity. In a recent breakthrough, studies of a mutant of Shaker that is prone to inactivate indicated that this process entails a dilation of the selectivity filter, the narrowest part of the ion conduction pathway. Here, we report an atomic-resolution cryo-electron microscopy structure that demonstrates that the wild-type channel can also adopt this dilated state. All-atom simulations corroborate this conformation is congruent with the electrophysiological characteristics of the C-type inactivated state, namely, residual K+ conductance and altered ion specificity, and help rationalize why inactivation is accelerated or impeded by certain mutations. In summary, this study establishes the molecular basis for an important self-regulatory mechanism in eukaryotic K+ channels, laying a solid foundation for further studies.
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Affiliation(s)
- Robyn Stix
- Theoretical Molecular Biophysics Laboratory, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA
- Department of Biology, Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD 21218, USA
| | - Xiao-Feng Tan
- Molecular Physiology and Biophysics Section, Porter Neuroscience Research Center, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA
| | - Chanhyung Bae
- Molecular Physiology and Biophysics Section, Porter Neuroscience Research Center, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA
| | - Ana I. Fernández-Mariño
- Molecular Physiology and Biophysics Section, Porter Neuroscience Research Center, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA
| | - Kenton J. Swartz
- Molecular Physiology and Biophysics Section, Porter Neuroscience Research Center, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA
| | - José D. Faraldo-Gómez
- Theoretical Molecular Biophysics Laboratory, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA
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11
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Nsasra E, Dahan I, Eichler J, Yifrach O. It's Time for Entropic Clocks: The Roles of Random Chain Protein Sequences in Timing Ion Channel Processes Underlying Action Potential Properties. ENTROPY (BASEL, SWITZERLAND) 2023; 25:1351. [PMID: 37761650 PMCID: PMC10527868 DOI: 10.3390/e25091351] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/30/2023] [Revised: 09/10/2023] [Accepted: 09/13/2023] [Indexed: 09/29/2023]
Abstract
In recent years, it has become clear that intrinsically disordered protein segments play diverse functional roles in many cellular processes, thus leading to a reassessment of the classical structure-function paradigm. One class of intrinsically disordered protein segments is entropic clocks, corresponding to unstructured random protein chains involved in timing cellular processes. Such clocks were shown to modulate ion channel processes underlying action potential generation, propagation, and transmission. In this review, we survey the role of entropic clocks in timing intra- and inter-molecular binding events of voltage-activated potassium channels involved in gating and clustering processes, respectively, and where both are known to occur according to a similar 'ball and chain' mechanism. We begin by delineating the thermodynamic and timing signatures of a 'ball and chain'-based binding mechanism involving entropic clocks, followed by a detailed analysis of the use of such a mechanism in the prototypical Shaker voltage-activated K+ channel model protein, with particular emphasis on ion channel clustering. We demonstrate how 'chain'-level alternative splicing of the Kv channel gene modulates entropic clock-based 'ball and chain' inactivation and clustering channel functions. As such, the Kv channel model system exemplifies how linkage between alternative splicing and intrinsic disorder enables the functional diversity underlying changes in electrical signaling.
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Affiliation(s)
| | | | | | - Ofer Yifrach
- Department of Life Sciences, School of Brain Sciences and Cognition, Ben-Gurion University of the Negev, P.O. Box 653, Beer Sheva 84105, Israel; (E.N.); (J.E.)
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12
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Noh Y, Aluru NR. Ion transport in two-dimensional flexible nanoporous membranes. NANOSCALE 2023. [PMID: 37337690 DOI: 10.1039/d3nr00875d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/21/2023]
Abstract
Ion transport is a fundamental mechanism in living systems that plays a role in cell proliferation, energy conversion, and maintaining homeostasis. This has inspired various nanofluidic applications such as electricity harvesting, molecular sensors, and molecular separation. Two dimensional (2D) nanoporous membranes are particularly promising for these applications due to their ultralow transport barriers. We investigated ion conduction across flexible 2D membranes via extensive molecular dynamics simulations. We found that the microscopic fluctuations of these membranes can significantly increase ion conductance, for example, by 320% in Cu-HAB with 0.5 M KCl. Our analysis of ion dynamics near the flexible membranes revealed that ion hydration is destabilized when the membrane fluctuated within a specific frequency range leading to improved ion conduction. Our results show that the dynamic coupling between the fluctuating membrane and ions can play a crucial role in ion conduction across 2D nanoporous membranes.
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Affiliation(s)
- Yechan Noh
- Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
| | - Narayana R Aluru
- Walker Department of Mechanical Engineering, Oden Institute for Computational Engineering & Sciences, University of Texas at Austin, Austin 78712, USA.
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13
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Burakova E, Vasa SK, Linser R. Characterization of conformational heterogeneity via higher-dimensionality, proton-detected solid-state NMR. JOURNAL OF BIOMOLECULAR NMR 2022; 76:197-212. [PMID: 36149571 PMCID: PMC9712413 DOI: 10.1007/s10858-022-00405-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/17/2022] [Accepted: 09/07/2022] [Indexed: 06/16/2023]
Abstract
Site-specific heterogeneity of solid protein samples can be exploited as valuable information to answer biological questions ranging from thermodynamic properties determining fibril formation to protein folding and conformational stability upon stress. In particular, for proteins of increasing molecular weight, however, site-resolved assessment without residue-specific labeling is challenging using established methodology, which tends to rely on carbon-detected 2D correlations. Here we develop purely chemical-shift-based approaches for assessment of relative conformational heterogeneity that allows identification of each residue via four chemical-shift dimensions. High dimensionality diminishes the probability of peak overlap in the presence of multiple, heterogeneously broadened resonances. Utilizing backbone dihedral-angle reconstruction from individual contributions to the peak shape either via suitably adapted prediction routines or direct association with a relational database, the methods may in future studies afford assessment of site-specific heterogeneity of proteins without site-specific labeling.
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Affiliation(s)
- Ekaterina Burakova
- Department of Chemistry and Chemical Biology, Technical University Dortmund, Otto-Hahn-Str. 4a, 44227, Dortmund, Germany
- Department of Chemistry and Pharmacy, Ludwig-Maximilians-University Munich, Butenandtstr. 5-13, 81377, Munich, Germany
| | - Suresh K Vasa
- Department of Chemistry and Chemical Biology, Technical University Dortmund, Otto-Hahn-Str. 4a, 44227, Dortmund, Germany
- Department of Chemistry and Pharmacy, Ludwig-Maximilians-University Munich, Butenandtstr. 5-13, 81377, Munich, Germany
| | - Rasmus Linser
- Department of Chemistry and Chemical Biology, Technical University Dortmund, Otto-Hahn-Str. 4a, 44227, Dortmund, Germany.
- Department of Chemistry and Pharmacy, Ludwig-Maximilians-University Munich, Butenandtstr. 5-13, 81377, Munich, Germany.
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14
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Coonen L, Martinez-Morales E, Van De Sande DV, Snyders DJ, Cortes DM, Cuello LG, Labro AJ. The nonconducting W434F mutant adopts upon membrane depolarization an inactivated-like state that differs from wild-type Shaker-IR potassium channels. SCIENCE ADVANCES 2022; 8:eabn1731. [PMID: 36112676 PMCID: PMC9481120 DOI: 10.1126/sciadv.abn1731] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/08/2021] [Accepted: 08/01/2022] [Indexed: 06/15/2023]
Abstract
Voltage-gated K+ (Kv) channels mediate the flow of K+ across the cell membrane by regulating the conductive state of their activation gate (AG). Several Kv channels display slow C-type inactivation, a process whereby their selectivity filter (SF) becomes less or nonconductive. It has been proposed that, in the fast inactivation-removed Shaker-IR channel, the W434F mutation epitomizes the C-type inactivated state because it functionally accelerates this process. By introducing another pore mutation that prevents AG closure, P475D, we found a way to record ionic currents of the Shaker-IR-W434F-P475D mutant at hyperpolarized membrane potentials as the W434F-mutant SF recovers from its inactivated state. This W434F conductive state lost its high K+ over Na+ selectivity, and even NMDG+ can permeate, features not observed in a wild-type SF. This indicates that, at least during recovery from inactivation, the W434F-mutant SF transitions to a widened and noncationic specific conformation.
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Affiliation(s)
- Laura Coonen
- Department of Biomedical Sciences, Faculty of Pharmaceutical, Biomedical and Veterinary Sciences, University of Antwerp, 2610 Antwerp, Belgium
| | - Evelyn Martinez-Morales
- Department of Biomedical Sciences, Faculty of Pharmaceutical, Biomedical and Veterinary Sciences, University of Antwerp, 2610 Antwerp, Belgium
| | - Dieter V. Van De Sande
- Department of Biomedical Sciences, Faculty of Pharmaceutical, Biomedical and Veterinary Sciences, University of Antwerp, 2610 Antwerp, Belgium
| | - Dirk J. Snyders
- Department of Biomedical Sciences, Faculty of Pharmaceutical, Biomedical and Veterinary Sciences, University of Antwerp, 2610 Antwerp, Belgium
| | - D. Marien Cortes
- Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, TX 79430, USA
| | - Luis G. Cuello
- Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, TX 79430, USA
| | - Alain J. Labro
- Department of Biomedical Sciences, Faculty of Pharmaceutical, Biomedical and Veterinary Sciences, University of Antwerp, 2610 Antwerp, Belgium
- Department of Basic and Applied Medical Sciences, Faculty of Medicine, Ghent University, 9000 Ghent, Belgium
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15
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Maly J, Emigh AM, DeMarco KR, Furutani K, Sack JT, Clancy CE, Vorobyov I, Yarov-Yarovoy V. Structural modeling of the hERG potassium channel and associated drug interactions. Front Pharmacol 2022; 13:966463. [PMID: 36188564 PMCID: PMC9523588 DOI: 10.3389/fphar.2022.966463] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2022] [Accepted: 08/25/2022] [Indexed: 11/13/2022] Open
Abstract
The voltage-gated potassium channel, KV11.1, encoded by the human Ether-à-go-go-Related Gene (hERG), is expressed in cardiac myocytes, where it is crucial for the membrane repolarization of the action potential. Gating of the hERG channel is characterized by rapid, voltage-dependent, C-type inactivation, which blocks ion conduction and is suggested to involve constriction of the selectivity filter. Mutations S620T and S641A/T within the selectivity filter region of hERG have been shown to alter the voltage dependence of channel inactivation. Because hERG channel blockade is implicated in drug-induced arrhythmias associated with both the open and inactivated states, we used Rosetta to simulate the effects of hERG S620T and S641A/T mutations to elucidate conformational changes associated with hERG channel inactivation and differences in drug binding between the two states. Rosetta modeling of the S641A fast-inactivating mutation revealed a lateral shift of the F627 side chain in the selectivity filter into the central channel axis along the ion conduction pathway and the formation of four lateral fenestrations in the pore. Rosetta modeling of the non-inactivating mutations S620T and S641T suggested a potential molecular mechanism preventing F627 side chain from shifting into the ion conduction pathway during the proposed inactivation process. Furthermore, we used Rosetta docking to explore the binding mechanism of highly selective and potent hERG blockers - dofetilide, terfenadine, and E4031. Our structural modeling correlates well with much, but not all, existing experimental evidence involving interactions of hERG blockers with key residues in hERG pore and reveals potential molecular mechanisms of ligand interactions with hERG in an inactivated state.
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Affiliation(s)
- Jan Maly
- Department of Physiology and Membrane Biology, University of California, Davis, Davis, CA, United States
- Biophysics Graduate Group, University of California, Davis, Davis, CA, United States
| | - Aiyana M. Emigh
- Department of Physiology and Membrane Biology, University of California, Davis, Davis, CA, United States
- Biophysics Graduate Group, University of California, Davis, Davis, CA, United States
| | - Kevin R. DeMarco
- Department of Physiology and Membrane Biology, University of California, Davis, Davis, CA, United States
- Biophysics Graduate Group, University of California, Davis, Davis, CA, United States
| | - Kazuharu Furutani
- Department of Pharmacology, Tokushima Bunri University, Tokushima, Japan
| | - Jon T. Sack
- Department of Physiology and Membrane Biology, University of California, Davis, Davis, CA, United States
| | - Colleen E. Clancy
- Department of Physiology and Membrane Biology, University of California, Davis, Davis, CA, United States
- Department of Pharmacology, University of California, Davis, Davis, CA, United States
| | - Igor Vorobyov
- Department of Physiology and Membrane Biology, University of California, Davis, Davis, CA, United States
- Department of Pharmacology, University of California, Davis, Davis, CA, United States
| | - Vladimir Yarov-Yarovoy
- Department of Physiology and Membrane Biology, University of California, Davis, Davis, CA, United States
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16
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Li S. Detergents and alternatives in cryo-EM studies of membrane proteins. Acta Biochim Biophys Sin (Shanghai) 2022; 54:1049-1056. [PMID: 35866608 PMCID: PMC9828306 DOI: 10.3724/abbs.2022088] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2021] [Accepted: 05/28/2022] [Indexed: 11/25/2022] Open
Abstract
Structure determination of membrane proteins has been a long-standing challenge to understand the molecular basis of life processes. Detergents are widely used to study the structure and function of membrane proteins by various experimental methods, and the application of membrane mimetics is also a prevalent trend in the field of cryo-EM analysis. This review focuses on the widely-used detergents and corresponding properties and structures, and also discusses the growing interests in membrane mimetic systems used in cryo-EM studies, providing insights into the role of detergent alternatives in structure determination.
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Affiliation(s)
- Shuo Li
- />Department of Life ScienceNational Natural Science Foundation of ChinaBeijing100085China
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17
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Molecular Events behind the Selectivity and Inactivation Properties of Model NaK-Derived Ion Channels. Int J Mol Sci 2022; 23:ijms23169246. [PMID: 36012519 PMCID: PMC9409022 DOI: 10.3390/ijms23169246] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2022] [Revised: 08/10/2022] [Accepted: 08/14/2022] [Indexed: 11/17/2022] Open
Abstract
Y55W mutants of non-selective NaK and partly K+-selective NaK2K channels have been used to explore the conformational dynamics at the pore region of these channels as they interact with either Na+ or K+. A major conclusion is that these channels exhibit a remarkable pore conformational flexibility. Homo-FRET measurements reveal a large change in W55–W55 intersubunit distances, enabling the selectivity filter (SF) to admit different species, thus, favoring poor or no selectivity. Depending on the cation, these channels exhibit wide-open conformations of the SF in Na+, or tight induced-fit conformations in K+, most favored in the four binding sites containing NaK2K channels. Such conformational flexibility seems to arise from an altered pattern of restricting interactions between the SF and the protein scaffold behind it. Additionally, binding experiments provide clues to explain such poor selectivity. Compared to the K+-selective KcsA channel, these channels lack a high affinity K+ binding component and do not collapse in Na+. Thus, they cannot properly select K+ over competing cations, nor reject Na+ by collapsing, as K+-selective channels do. Finally, these channels do not show C-type inactivation, likely because their submillimolar K+ binding affinities prevent an efficient K+ loss from their SF, thus favoring permanently open channel states.
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18
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Marquis MJ, Sack JT. Mechanism of use-dependent Kv2 channel inhibition by RY785. J Gen Physiol 2022; 154:e202112981. [PMID: 35435946 PMCID: PMC9195051 DOI: 10.1085/jgp.202112981] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2021] [Revised: 03/01/2022] [Accepted: 03/30/2022] [Indexed: 01/21/2023] Open
Abstract
Understanding the mechanism by which ion channel modulators act is critical for interpretation of their physiological effects and can provide insight into mechanisms of ion channel gating. The small molecule RY785 is a potent and selective inhibitor of Kv2 voltage-gated K+ channels that has a use-dependent onset of inhibition. Here, we investigate the mechanism of RY785 inhibition of rat Kv2.1 (Kcnb1) channels heterologously expressed in CHO-K1 cells. We find that 1 µM RY785 block eliminates Kv2.1 current at all physiologically relevant voltages, inhibiting ≥98% of the Kv2.1 conductance. Both onset of and recovery from RY785 inhibition require voltage sensor activation. Intracellular tetraethylammonium, a classic open-channel blocker, competes with RY785 inhibition. However, channel opening itself does not appear to alter RY785 access. Gating current measurements reveal that RY785 inhibits a component of voltage sensor activation and accelerates voltage sensor deactivation. We propose that voltage sensor activation opens a path into the central cavity of Kv2.1 where RY785 binds and promotes voltage sensor deactivation, trapping itself inside. This gated-access mechanism in conjunction with slow kinetics of unblock supports simple interpretation of RY785 effects: channel activation is required for block by RY785 to equilibrate, after which trapped RY785 will simply decrease the Kv2 conductance density.
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Affiliation(s)
- Matthew James Marquis
- Department of Physiology & Membrane Biology, University of California, Davis, Davis, CA
| | - Jon T. Sack
- Department of Physiology & Membrane Biology, University of California, Davis, Davis, CA
- Department of Anesthesiology and Pain Medicine, University of California, Davis, Davis, CA
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19
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Hussain S, De Waele J, Lammens M, Bosmans F. N-Type Inactivation Variances in Honeybee and Asian Giant Hornet Kv Channels. Bioelectricity 2022. [DOI: 10.1089/bioe.2022.0006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Affiliation(s)
- Shahid Hussain
- Department of Basic and Applied Medical Sciences, Ghent University, Ghent, Belgium
| | - Jolien De Waele
- Department of Basic and Applied Medical Sciences, Ghent University, Ghent, Belgium
| | - Maxime Lammens
- Department of Basic and Applied Medical Sciences, Ghent University, Ghent, Belgium
| | - Frank Bosmans
- Department of Basic and Applied Medical Sciences, Ghent University, Ghent, Belgium
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20
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N-type fast inactivation of a eukaryotic voltage-gated sodium channel. Nat Commun 2022; 13:2713. [PMID: 35581266 PMCID: PMC9114117 DOI: 10.1038/s41467-022-30400-w] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2022] [Accepted: 04/28/2022] [Indexed: 12/19/2022] Open
Abstract
Voltage-gated sodium (NaV) channels initiate action potentials. Fast inactivation of NaV channels, mediated by an Ile-Phe-Met motif, is crucial for preventing hyperexcitability and regulating firing frequency. Here we present cryo-electron microscopy structure of NaVEh from the coccolithophore Emiliania huxleyi, which reveals an unexpected molecular gating mechanism for NaV channel fast inactivation independent of the Ile-Phe-Met motif. An N-terminal helix of NaVEh plugs into the open activation gate and blocks it. The binding pose of the helix is stabilized by multiple electrostatic interactions. Deletion of the helix or mutations blocking the electrostatic interactions completely abolished the fast inactivation. These strong interactions enable rapid inactivation, but also delay recovery from fast inactivation, which is ~160-fold slower than human NaV channels. Together, our results provide mechanistic insights into fast inactivation of NaVEh that fundamentally differs from the conventional local allosteric inhibition, revealing both surprising structural diversity and functional conservation of ion channel inactivation.
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21
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Reddi R, Matulef K, Riederer EA, Whorton MR, Valiyaveetil FI. Structural basis for C-type inactivation in a Shaker family voltage-gated K + channel. SCIENCE ADVANCES 2022; 8:eabm8804. [PMID: 35452285 PMCID: PMC9032944 DOI: 10.1126/sciadv.abm8804] [Citation(s) in RCA: 19] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/20/2021] [Accepted: 03/08/2022] [Indexed: 06/14/2023]
Abstract
C-type inactivation is a process by which ion flux through a voltage-gated K+ (Kv) channel is regulated at the selectivity filter. While prior studies have indicated that C-type inactivation involves structural changes at the selectivity filter, the nature of the changes has not been resolved. Here, we report the crystal structure of the Kv1.2 channel in a C-type inactivated state. The structure shows that C-type inactivation involves changes in the selectivity filter that disrupt the outer two ion binding sites in the filter. The changes at the selectivity filter propagate to the extracellular mouth and the turret regions of the channel pore. The structural changes observed are consistent with the functional hallmarks of C-type inactivation. This study highlights the intricate interplay between K+ occupancy at the ion binding sites and the interactions of the selectivity filter in determining the balance between the conductive and the inactivated conformations of the filter.
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Affiliation(s)
- Ravikumar Reddi
- Program in Chemical Biology, Department of Chemical Physiology and Biochemistry, Oregon Health & Science University, 3181 SW Sam Jackson Park Rd, Portland, OR 97239, USA
| | - Kimberly Matulef
- Program in Chemical Biology, Department of Chemical Physiology and Biochemistry, Oregon Health & Science University, 3181 SW Sam Jackson Park Rd, Portland, OR 97239, USA
| | - Erika A. Riederer
- Program in Chemical Biology, Department of Chemical Physiology and Biochemistry, Oregon Health & Science University, 3181 SW Sam Jackson Park Rd, Portland, OR 97239, USA
| | - Matthew R. Whorton
- Vollum Institute, Oregon Health & Science University, 3181 SW Sam Jackson Park Rd, Portland, OR 97239, USA
| | - Francis I. Valiyaveetil
- Program in Chemical Biology, Department of Chemical Physiology and Biochemistry, Oregon Health & Science University, 3181 SW Sam Jackson Park Rd, Portland, OR 97239, USA
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22
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Puthenveetil R, Christenson ET, Vinogradova O. New Horizons in Structural Biology of Membrane Proteins: Experimental Evaluation of the Role of Conformational Dynamics and Intrinsic Flexibility. MEMBRANES 2022; 12:227. [PMID: 35207148 PMCID: PMC8877495 DOI: 10.3390/membranes12020227] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/01/2022] [Revised: 02/13/2022] [Accepted: 02/14/2022] [Indexed: 02/08/2023]
Abstract
A plethora of membrane proteins are found along the cell surface and on the convoluted labyrinth of membranes surrounding organelles. Since the advent of various structural biology techniques, a sub-population of these proteins has become accessible to investigation at near-atomic resolutions. The predominant bona fide methods for structure solution, X-ray crystallography and cryo-EM, provide high resolution in three-dimensional space at the cost of neglecting protein motions through time. Though structures provide various rigid snapshots, only an amorphous mechanistic understanding can be inferred from interpolations between these different static states. In this review, we discuss various techniques that have been utilized in observing dynamic conformational intermediaries that remain elusive from rigid structures. More specifically we discuss the application of structural techniques such as NMR, cryo-EM and X-ray crystallography in studying protein dynamics along with complementation by conformational trapping by specific binders such as antibodies. We finally showcase the strength of various biophysical techniques including FRET, EPR and computational approaches using a multitude of succinct examples from GPCRs, transporters and ion channels.
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Affiliation(s)
- Robbins Puthenveetil
- Section on Structural and Chemical Biology of Membrane Proteins, Neurosciences and Cellular and Structural Biology Division, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, 35A Convent Dr., Bethesda, MD 20892, USA
| | | | - Olga Vinogradova
- Department of Pharmaceutical Sciences, School of Pharmacy, University of Connecticut, Storrs, CT 06269, USA
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23
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Guardiani C, Cecconi F, Chiodo L, Cottone G, Malgaretti P, Maragliano L, Barabash ML, Camisasca G, Ceccarelli M, Corry B, Roth R, Giacomello A, Roux B. Computational methods and theory for ion channel research. ADVANCES IN PHYSICS: X 2022; 7:2080587. [PMID: 35874965 PMCID: PMC9302924 DOI: 10.1080/23746149.2022.2080587] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2022] [Accepted: 05/15/2022] [Indexed: 06/15/2023] Open
Abstract
Ion channels are fundamental biological devices that act as gates in order to ensure selective ion transport across cellular membranes; their operation constitutes the molecular mechanism through which basic biological functions, such as nerve signal transmission and muscle contraction, are carried out. Here, we review recent results in the field of computational research on ion channels, covering theoretical advances, state-of-the-art simulation approaches, and frontline modeling techniques. We also report on few selected applications of continuum and atomistic methods to characterize the mechanisms of permeation, selectivity, and gating in biological and model channels.
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Affiliation(s)
- C. Guardiani
- Dipartimento di Ingegneria Meccanica e Aerospaziale, Sapienza Università di Roma, Rome, Italy
| | - F. Cecconi
- CNR - Istituto dei Sistemi Complessi, Rome, Italy and Istituto Nazionale di Fisica Nucleare, INFN, Roma1 section. 00185, Roma, Italy
| | - L. Chiodo
- Department of Engineering, Campus Bio-Medico University, Rome, Italy
| | - G. Cottone
- Department of Physics and Chemistry-Emilio Segrè, University of Palermo, Palermo, Italy
| | - P. Malgaretti
- Helmholtz Institute Erlangen-Nürnberg for Renewable Energy (IEK-11), Forschungszentrum Jülich, Erlangen, Germany
| | - L. Maragliano
- Department of Life and Environmental Sciences, Polytechnic University of Marche, Ancona, Italy, and Center for Synaptic Neuroscience and Technology, Istituto Italiano di Tecnologia, Genova, Italy
| | - M. L. Barabash
- Department of Materials Science and Nanoengineering, Rice University, Houston, TX 77005, USA
| | - G. Camisasca
- Dipartimento di Ingegneria Meccanica e Aerospaziale, Sapienza Università di Roma, Rome, Italy
- Dipartimento di Fisica, Università Roma Tre, Rome, Italy
| | - M. Ceccarelli
- Department of Physics and CNR-IOM, University of Cagliari, Monserrato 09042-IT, Italy
| | - B. Corry
- Research School of Biology, The Australian National University, Canberra, ACT 2600, Australia
| | - R. Roth
- Institut Für Theoretische Physik, Eberhard Karls Universität Tübingen, Tübingen, Germany
| | - A. Giacomello
- Dipartimento di Ingegneria Meccanica e Aerospaziale, Sapienza Università di Roma, Rome, Italy
| | - B. Roux
- Department of Biochemistry & Molecular Biology, University of Chicago, Chicago IL, USA
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24
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Lefoulon C. The bare necessities of plant K+ channel regulation. PLANT PHYSIOLOGY 2021; 187:2092-2109. [PMID: 34618033 PMCID: PMC8644596 DOI: 10.1093/plphys/kiab266] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/29/2021] [Accepted: 05/11/2021] [Indexed: 05/29/2023]
Abstract
Potassium (K+) channels serve a wide range of functions in plants from mineral nutrition and osmotic balance to turgor generation for cell expansion and guard cell aperture control. Plant K+ channels are members of the superfamily of voltage-dependent K+ channels, or Kv channels, that include the Shaker channels first identified in fruit flies (Drosophila melanogaster). Kv channels have been studied in depth over the past half century and are the best-known of the voltage-dependent channels in plants. Like the Kv channels of animals, the plant Kv channels are regulated over timescales of milliseconds by conformational mechanisms that are commonly referred to as gating. Many aspects of gating are now well established, but these channels still hold some secrets, especially when it comes to the control of gating. How this control is achieved is especially important, as it holds substantial prospects for solutions to plant breeding with improved growth and water use efficiencies. Resolution of the structure for the KAT1 K+ channel, the first channel from plants to be crystallized, shows that many previous assumptions about how the channels function need now to be revisited. Here, I strip the plant Kv channels bare to understand how they work, how they are gated by voltage and, in some cases, by K+ itself, and how the gating of these channels can be regulated by the binding with other protein partners. Each of these features of plant Kv channels has important implications for plant physiology.
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Affiliation(s)
- Cécile Lefoulon
- Laboratory of Plant Physiology and Biophysics, Bower Building, University of Glasgow, Glasgow G12 8QQ, Scotland
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25
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Mechanisms underlying drug-mediated regulation of membrane protein function. Proc Natl Acad Sci U S A 2021; 118:2113229118. [PMID: 34753824 DOI: 10.1073/pnas.2113229118] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/20/2021] [Indexed: 11/18/2022] Open
Abstract
The hydrophobic coupling between membrane proteins and their host lipid bilayer provides a mechanism by which bilayer-modifying drugs may alter protein function. Drug regulation of membrane protein function thus may be mediated by both direct interactions with the protein and drug-induced alterations of bilayer properties, in which the latter will alter the energetics of protein conformational changes. To tease apart these mechanisms, we examine how the prototypical, proton-gated bacterial potassium channel KcsA is regulated by bilayer-modifying drugs using a fluorescence-based approach to quantify changes in both KcsA function and lipid bilayer properties (using gramicidin channels as probes). All tested drugs inhibited KcsA activity, and the changes in the different gating steps varied with bilayer thickness, suggesting a coupling to the bilayer. Examining the correlations between changes in KcsA gating steps and bilayer properties reveals that drug-induced regulation of membrane protein function indeed involves bilayer-mediated mechanisms. Both direct, either specific or nonspecific, binding and bilayer-mediated mechanisms therefore are likely to be important whenever there is overlap between the concentration ranges at which a drug alters membrane protein function and bilayer properties. Because changes in bilayer properties will impact many diverse membrane proteins, they may cause indiscriminate changes in protein function.
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26
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Abstract
K+ channels enable potassium to flow across the membrane with great selectivity. There are four K+ channel families: voltage-gated K (Kv), calcium-activated (KCa), inwardly rectifying K (Kir), and two-pore domain potassium (K2P) channels. All four K+ channels are formed by subunits assembling into a classic tetrameric (4x1P = 4P for the Kv, KCa, and Kir channels) or tetramer-like (2x2P = 4P for the K2P channels) architecture. These subunits can either be the same (homomers) or different (heteromers), conferring great diversity to these channels. They share a highly conserved selectivity filter within the pore but show different gating mechanisms adapted for their function. K+ channels play essential roles in controlling neuronal excitability by shaping action potentials, influencing the resting membrane potential, and responding to diverse physicochemical stimuli, such as a voltage change (Kv), intracellular calcium oscillations (KCa), cellular mediators (Kir), or temperature (K2P).
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27
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Control of Biophysical and Pharmacological Properties of Potassium Channels by Ancillary Subunits. Handb Exp Pharmacol 2021; 267:445-480. [PMID: 34247280 DOI: 10.1007/164_2021_512] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Abstract
Potassium channels facilitate and regulate physiological processes as diverse as electrical signaling, ion, solute and hormone secretion, fluid homeostasis, hearing, pain sensation, muscular contraction, and the heartbeat. Potassium channels are each formed by either a tetramer or dimer of pore-forming α subunits that co-assemble to create a multimer with a K+-selective pore that in most cases is capable of functioning as a discrete unit to pass K+ ions across the cell membrane. The reality in vivo, however, is that the potassium channel α subunit multimers co-assemble with ancillary subunits to serve specific physiological functions. The ancillary subunits impart specific physiological properties that are often required for a particular activity in vivo; in addition, ancillary subunit interaction often alters the pharmacology of the resultant complex. In this chapter the modes of action of ancillary subunits on K+ channel physiology and pharmacology are described and categorized into various mechanistic classes.
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Broichhagen J, Kilian N. Chemical Biology Tools To Investigate Malaria Parasites. Chembiochem 2021; 22:2219-2236. [PMID: 33570245 PMCID: PMC8360121 DOI: 10.1002/cbic.202000882] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2020] [Revised: 02/10/2021] [Indexed: 02/06/2023]
Abstract
Parasitic diseases like malaria tropica have been shaping human evolution and history since the beginning of mankind. After infection, the response of the human host ranges from asymptomatic to severe and may culminate in death. Therefore, proper examination of the parasite's biology is pivotal to deciphering unique molecular, biochemical and cell biological processes, which in turn ensure the identification of treatment strategies, such as potent drug targets and vaccine candidates. However, implementing molecular biology methods for genetic manipulation proves to be difficult for many parasite model organisms. The development of fast and straightforward applicable alternatives, for instance small-molecule probes from the field of chemical biology, is essential. In this review, we will recapitulate the highlights of previous molecular and chemical biology approaches that have already created insight and understanding of the malaria parasite Plasmodium falciparum. We discuss current developments from the field of chemical biology and explore how their application could advance research into this parasite in the future. We anticipate that the described approaches will help to close knowledge gaps in the biology of P. falciparum and we hope that researchers will be inspired to use these methods to gain knowledge - with the aim of ending this devastating disease.
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Affiliation(s)
- Johannes Broichhagen
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP)Robert-Roessle-Strasse 1013125BerlinGermany
| | - Nicole Kilian
- Centre for Infectious DiseasesParasitologyHeidelberg University HospitalIm Neuenheimer Feld 32469120HeidelbergGermany
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29
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Cao E. Structural mechanisms of transient receptor potential ion channels. J Gen Physiol 2021; 152:133640. [PMID: 31972006 PMCID: PMC7054860 DOI: 10.1085/jgp.201811998] [Citation(s) in RCA: 52] [Impact Index Per Article: 17.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2019] [Accepted: 01/03/2020] [Indexed: 12/26/2022] Open
Abstract
Transient receptor potential (TRP) ion channels are evolutionarily ancient sensory proteins that detect and integrate a wide range of physical and chemical stimuli. TRP channels are fundamental for numerous biological processes and are therefore associated with a multitude of inherited and acquired human disorders. In contrast to many other major ion channel families, high-resolution structures of TRP channels were not available before 2013. Remarkably, however, the subsequent “resolution revolution” in cryo-EM has led to an explosion of TRP structures in the last few years. These structures have confirmed that TRP channels assemble as tetramers and resemble voltage-gated ion channels in their overall architecture. But beyond the relatively conserved transmembrane core embedded within the lipid bilayer, each TRP subtype appears to be endowed with a unique set of soluble domains that may confer diverse regulatory mechanisms. Importantly, TRP channel structures have revealed sites and mechanisms of action of numerous synthetic and natural compounds, as well as those for endogenous ligands such as lipids, Ca2+, and calmodulin. Here, I discuss these recent findings with a particular focus on the conserved transmembrane region and how these structures may help to rationally target this important class of ion channels for the treatment of numerous human conditions.
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Affiliation(s)
- Erhu Cao
- Department of Biochemistry, University of Utah School of Medicine, Salt Lake City, UT
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30
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Johnston J. Pharmacology of A-Type K + Channels. Handb Exp Pharmacol 2021; 267:167-183. [PMID: 33907894 DOI: 10.1007/164_2021_456] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/19/2023]
Abstract
Transient outward potassium currents were first described nearly 60 years ago, since then major strides have been made in understanding their molecular basis and physiological roles. From the large family of voltage-gated potassium channels members of 3 subfamilies can produce such fast-inactivating A-type potassium currents. Each subfamily gives rise to currents with distinct biophysical properties and pharmacological profiles and a simple workflow is provided to aid the identification of channels mediating A-type currents in native cells. Their unique properties and regulation enable A-type K+ channels to perform varied roles in excitable cells including repolarisation of the cardiac action potential, controlling spike and synaptic timing, regulating dendritic integration and long-term potentiation as well as being a locus of neural plasticity.
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Affiliation(s)
- Jamie Johnston
- Faculty of Biological Sciences, University of Leeds, Leeds, UK.
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31
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Natale AM, Deal PE, Minor DL. Structural Insights into the Mechanisms and Pharmacology of K 2P Potassium Channels. J Mol Biol 2021; 433:166995. [PMID: 33887333 PMCID: PMC8436263 DOI: 10.1016/j.jmb.2021.166995] [Citation(s) in RCA: 26] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2021] [Revised: 04/08/2021] [Accepted: 04/09/2021] [Indexed: 01/10/2023]
Abstract
Leak currents, defined as voltage and time independent flows of ions across cell membranes, are central to cellular electrical excitability control. The K2P (KCNK) potassium channel class comprises an ion channel family that produces potassium leak currents that oppose excitation and stabilize the resting membrane potential in cells in the brain, cardiovascular system, immune system, and sensory organs. Due to their widespread tissue distribution, K2Ps contribute to many physiological and pathophysiological processes including anesthesia, pain, arrythmias, ischemia, hypertension, migraine, intraocular pressure regulation, and lung injury responses. Structural studies of six homomeric K2Ps have established the basic architecture of this channel family, revealed key moving parts involved in K2P function, uncovered the importance of asymmetric pinching and dilation motions in the K2P selectivity filter (SF) C-type gate, and defined two K2P structural classes based on the absence or presence of an intracellular gate. Further, a series of structures characterizing K2P:modulator interactions have revealed a striking polysite pharmacology housed within a relatively modestly sized (~70 kDa) channel. Binding sites for small molecules or lipids that control channel function are found at every layer of the channel structure, starting from its extracellular side through the portion that interacts with the membrane bilayer inner leaflet. This framework provides the basis for understanding how gating cues sensed by different channel parts control function and how small molecules and lipids modulate K2P activity. Such knowledge should catalyze development of new K2P modulators to probe function and treat a wide range of disorders.
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Affiliation(s)
- Andrew M Natale
- Cardiovascular Research Institute, University of California, San Francisco, CA 94158, USA
| | - Parker E Deal
- Cardiovascular Research Institute, University of California, San Francisco, CA 94158, USA
| | - Daniel L Minor
- Cardiovascular Research Institute, University of California, San Francisco, CA 94158, USA; Departments of Biochemistry and Biophysics, and Cellular and Molecular Pharmacology, University of California, San Francisco, CA 94158, USA; California Institute for Quantitative Biomedical Research, University of California, San Francisco, CA 94158, USA; Kavli Institute for Fundamental Neuroscience University of California, San Francisco, CA 94158, USA; Molecular Biophysics and Integrated Bio-imaging Division Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
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32
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Stautz J, Hellmich Y, Fuss MF, Silberberg JM, Devlin JR, Stockbridge RB, Hänelt I. Molecular Mechanisms for Bacterial Potassium Homeostasis. J Mol Biol 2021; 433:166968. [PMID: 33798529 DOI: 10.1016/j.jmb.2021.166968] [Citation(s) in RCA: 55] [Impact Index Per Article: 18.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2021] [Revised: 03/11/2021] [Accepted: 03/22/2021] [Indexed: 10/21/2022]
Abstract
Potassium ion homeostasis is essential for bacterial survival, playing roles in osmoregulation, pH homeostasis, regulation of protein synthesis, enzyme activation, membrane potential adjustment and electrical signaling. To accomplish such diverse physiological tasks, it is not surprising that a single bacterium typically encodes several potassium uptake and release systems. To understand the role each individual protein fulfills and how these proteins work in concert, it is important to identify the molecular details of their function. One needs to understand whether the systems transport ions actively or passively, and what mechanisms or ligands lead to the activation or inactivation of individual systems. Combining mechanistic information with knowledge about the physiology under different stress situations, such as osmostress, pH stress or nutrient limitation, one can identify the task of each system and deduce how they are coordinated with each other. By reviewing the general principles of bacterial membrane physiology and describing the molecular architecture and function of several bacterial K+-transporting systems, we aim to provide a framework for microbiologists studying bacterial potassium homeostasis and the many K+-translocating systems that are still poorly understood.
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Affiliation(s)
- Janina Stautz
- Institute of Biochemistry, Goethe University Frankfurt, Frankfurt am Main, Germany
| | - Yvonne Hellmich
- Institute of Biochemistry, Goethe University Frankfurt, Frankfurt am Main, Germany
| | - Michael F Fuss
- Institute of Biochemistry, Goethe University Frankfurt, Frankfurt am Main, Germany
| | - Jakob M Silberberg
- Institute of Biochemistry, Goethe University Frankfurt, Frankfurt am Main, Germany
| | - Jason R Devlin
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI, United States
| | - Randy B Stockbridge
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI, United States.
| | - Inga Hänelt
- Institute of Biochemistry, Goethe University Frankfurt, Frankfurt am Main, Germany.
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33
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Gutzeit VA, Acosta-Ruiz A, Munguba H, Häfner S, Landra-Willm A, Mathes B, Mony J, Yarotski D, Börjesson K, Liston C, Sandoz G, Levitz J, Broichhagen J. A fine-tuned azobenzene for enhanced photopharmacology in vivo. Cell Chem Biol 2021; 28:1648-1663.e16. [PMID: 33735619 DOI: 10.1016/j.chembiol.2021.02.020] [Citation(s) in RCA: 29] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2020] [Revised: 12/23/2020] [Accepted: 02/23/2021] [Indexed: 12/15/2022]
Abstract
Despite the power of photopharmacology for interrogating signaling proteins, many photopharmacological systems are limited by their efficiency, speed, or spectral properties. Here, we screen a library of azobenzene photoswitches and identify a urea-substituted "azobenzene-400" core that offers bistable switching between cis and trans with improved kinetics, light sensitivity, and a red-shift. We then focus on the metabotropic glutamate receptors (mGluRs), neuromodulatory receptors that are major pharmacological targets. Synthesis of "BGAG12,400," a photoswitchable orthogonal, remotely tethered ligand (PORTL), enables highly efficient, rapid optical agonism following conjugation to SNAP-tagged mGluR2 and permits robust optical control of mGluR1 and mGluR5 signaling. We then produce fluorophore-conjugated branched PORTLs to enable dual imaging and manipulation of mGluRs and highlight their power in ex vivo slice and in vivo behavioral experiments in the mouse prefrontal cortex. Finally, we demonstrate the generalizability of our strategy by developing an improved soluble, photoswitchable pore blocker for potassium channels.
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Affiliation(s)
- Vanessa A Gutzeit
- Neuroscience Graduate Program, Weill Cornell Medicine, New York, NY 10065, USA
| | - Amanda Acosta-Ruiz
- Biochemistry, Cell and Molecular Biology Graduate Program, Weill Cornell Medicine, New York, NY 10065, USA
| | - Hermany Munguba
- Department of Biochemistry, Weill Cornell Medicine, New York, NY 10065, USA
| | - Stephanie Häfner
- Université Cote d'Azur, CNRS, INSERM, iBV, Nice, France; Laboratories of Excellence, Ion Channel Science and Therapeutics, Nice, France
| | - Arnaud Landra-Willm
- Université Cote d'Azur, CNRS, INSERM, iBV, Nice, France; Laboratories of Excellence, Ion Channel Science and Therapeutics, Nice, France
| | - Bettina Mathes
- Department of Chemical Biology, Max Planck Institute for Medical Research, 69120 Heidelberg, Germany
| | - Jürgen Mony
- Department of Chemistry and Molecular Biology, University of Gothenburg, 41296 Gothenburg, Sweden
| | - Dzianis Yarotski
- Department of Chemical Biology, Max Planck Institute for Medical Research, 69120 Heidelberg, Germany
| | - Karl Börjesson
- Department of Chemistry and Molecular Biology, University of Gothenburg, 41296 Gothenburg, Sweden
| | - Conor Liston
- Department of Psychiatry and Brain and Mind Research Institute, Weill Cornell Medicine, New York, NY 10065, USA
| | - Guillaume Sandoz
- Université Cote d'Azur, CNRS, INSERM, iBV, Nice, France; Laboratories of Excellence, Ion Channel Science and Therapeutics, Nice, France
| | - Joshua Levitz
- Neuroscience Graduate Program, Weill Cornell Medicine, New York, NY 10065, USA; Biochemistry, Cell and Molecular Biology Graduate Program, Weill Cornell Medicine, New York, NY 10065, USA; Department of Biochemistry, Weill Cornell Medicine, New York, NY 10065, USA.
| | - Johannes Broichhagen
- Department of Chemical Biology, Max Planck Institute for Medical Research, 69120 Heidelberg, Germany; Department of Chemical Biology, Leibniz-Forschungsinstitut für Molekulare Pharmakologie, 13125 Berlin, Germany.
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34
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Palmisano VF, Gómez-Rodellar C, Pollak H, Cárdenas G, Corry B, Faraji S, Nogueira JJ. Binding of azobenzene and p-diaminoazobenzene to the human voltage-gated sodium channel Na v1.4. Phys Chem Chem Phys 2021; 23:3552-3564. [PMID: 33514952 DOI: 10.1039/d0cp06140a] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The activity of voltage-gated ion channels can be controlled by the binding of photoswitches inside their internal cavity and subsequent light irradiation. We investigated the binding of azobenzene and p-diaminoazobenzene to the human Nav1.4 channel in the inactivated state by means of Gaussian accelerated molecular dynamics simulations and free-energy computations. Three stable binding pockets were identified for each of the two photoswitches. In all the cases, the binding is controlled by the balance between the favorable hydrophobic interactions of the ligands with the nonpolar residues of the protein and the unfavorable polar solvation energy. In addition, electrostatic interactions between the ligand and the polar aminoacids are also relevant for p-diaminoazobenzene due to the presence of the amino groups on the benzene moieties. These groups participate in hydrogen bonding in the most favorable binding pocket and in long-range electrostatic interactions in the other pockets. The thermodinamically preferred binding sites found for both photoswitches are close to the selectivity filter of the channel. Therefore, it is very likely that the binding of these ligands will induce alterations in the ion conduction through the channel.
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Affiliation(s)
- Vito F Palmisano
- Department of Chemistry, Universidad Autónoma de Madrid, Calle Francisco Tomás y Valiente, 7, 28049, Madrid, Spain.
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35
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Giudici AM, Díaz-García C, Renart ML, Coutinho A, Prieto M, González-Ros JM, Poveda JA. Tetraoctylammonium, a Long Chain Quaternary Ammonium Blocker, Promotes a Noncollapsed, Resting-Like Inactivated State in KcsA. Int J Mol Sci 2021; 22:ijms22020490. [PMID: 33419017 PMCID: PMC7825302 DOI: 10.3390/ijms22020490] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2020] [Revised: 12/28/2020] [Accepted: 01/01/2021] [Indexed: 02/06/2023] Open
Abstract
Alkylammonium salts have been used extensively to study the structure and function of potassium channels. Here, we use the hydrophobic tetraoctylammonium (TOA+) to shed light on the structure of the inactivated state of KcsA, a tetrameric prokaryotic potassium channel that serves as a model to its homologous eukaryotic counterparts. By the combined use of a thermal denaturation assay and the analysis of homo-Förster resonance energy transfer in a mutant channel containing a single tryptophan (W67) per subunit, we found that TOA+ binds the channel cavity with high affinity, either with the inner gate open or closed. Moreover, TOA+ bound at the cavity allosterically shifts the equilibrium of the channel's selectivity filter conformation from conductive to an inactivated-like form. The inactivated TOA+-KcsA complex exhibits a loss in the affinity towards permeant K+ at pH 7.0, when the channel is in its closed state, but maintains the two sets of K+ binding sites and the W67-W67 intersubunit distances characteristic of the selectivity filter in the channel resting state. Thus, the TOA+-bound state differs clearly from the collapsed channel state described by X-ray crystallography and claimed to represent the inactivated form of KcsA.
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Affiliation(s)
- Ana Marcela Giudici
- Instituto de Investigación, Desarrollo e Innovación en Biotecnología Sanitaria de Elche (IDiBE), Instituto de Biología Molecular y Celular (IBMC), Universidad Miguel Hernández, E-03202 Elche, Spain; (A.M.G.); (M.L.R.)
| | - Clara Díaz-García
- Institute for Bioengineering and Bioscience (IBB), Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal; (C.D.-G.); (A.C.); (M.P.)
| | - Maria Lourdes Renart
- Instituto de Investigación, Desarrollo e Innovación en Biotecnología Sanitaria de Elche (IDiBE), Instituto de Biología Molecular y Celular (IBMC), Universidad Miguel Hernández, E-03202 Elche, Spain; (A.M.G.); (M.L.R.)
| | - Ana Coutinho
- Institute for Bioengineering and Bioscience (IBB), Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal; (C.D.-G.); (A.C.); (M.P.)
- Departamento de Química e Bioquímica, Faculty of Sciences, Universidade de Lisboa, 1749-016 Lisboa, Portugal
| | - Manuel Prieto
- Institute for Bioengineering and Bioscience (IBB), Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal; (C.D.-G.); (A.C.); (M.P.)
| | - José M. González-Ros
- Instituto de Investigación, Desarrollo e Innovación en Biotecnología Sanitaria de Elche (IDiBE), Instituto de Biología Molecular y Celular (IBMC), Universidad Miguel Hernández, E-03202 Elche, Spain; (A.M.G.); (M.L.R.)
- Correspondence: (J.M.G.-R.); (J.A.P.); Tel.: +34-966-658-757 (J.M.G.-R.); +34-966-658-466 (J.A.P.)
| | - José Antonio Poveda
- Instituto de Investigación, Desarrollo e Innovación en Biotecnología Sanitaria de Elche (IDiBE), Instituto de Biología Molecular y Celular (IBMC), Universidad Miguel Hernández, E-03202 Elche, Spain; (A.M.G.); (M.L.R.)
- Correspondence: (J.M.G.-R.); (J.A.P.); Tel.: +34-966-658-757 (J.M.G.-R.); +34-966-658-466 (J.A.P.)
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36
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Cosseddu SM, Choe EJ, Khovanov IA. Unraveling of a Strongly Correlated Dynamical Network of Residues Controlling the Permeation of Potassium in KcsA Ion Channel. ENTROPY (BASEL, SWITZERLAND) 2021; 23:E72. [PMID: 33418985 PMCID: PMC7825352 DOI: 10.3390/e23010072] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/10/2020] [Revised: 12/23/2020] [Accepted: 01/02/2021] [Indexed: 12/26/2022]
Abstract
The complicated patterns of the single-channel currents in potassium ion channel KcsA are governed by the structural variability of the selectivity filter. A comparative analysis of the dynamics of the wild type KcsA channel and several of its mutants showing different conducting patterns was performed. A strongly correlated dynamical network of interacting residues is found to play a key role in regulating the state of the wild type channel. The network is centered on the aspartate D80 which plays the role of a hub by strong interacting via hydrogen bonds with residues E71, R64, R89, and W67. Residue D80 also affects the selectivity filter via its backbones. This network further compromises ions and water molecules located inside the channel that results in the mutual influence: the permeation depends on the configuration of residues in the network, and the dynamics of network's residues depends on locations of ions and water molecules inside the selectivity filter. Some features of the network provide a further understanding of experimental results describing the KcsA activity. In particular, the necessity of anionic lipids to be present for functioning the channel is explained by the interaction between the lipids and the arginine residues R64 and R89 that prevents destabilizing the structure of the selectivity filter.
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Affiliation(s)
| | | | - Igor A. Khovanov
- School of Engineering, University of Warwick, Coventry CV4 7AL, UK; (S.M.C.); (E.J.C.)
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37
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Lipinsky M, Tobelaim WS, Peretz A, Simhaev L, Yeheskel A, Yakubovich D, Lebel G, Paas Y, Hirsch JA, Attali B. A unique mechanism of inactivation gating of the Kv channel family member Kv7.1 and its modulation by PIP2 and calmodulin. SCIENCE ADVANCES 2020; 6:eabd6922. [PMID: 33355140 PMCID: PMC11206195 DOI: 10.1126/sciadv.abd6922] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/06/2020] [Accepted: 11/06/2020] [Indexed: 06/12/2023]
Abstract
Inactivation of voltage-gated K+ (Kv) channels mostly occurs by fast N-type or/and slow C-type mechanisms. Here, we characterized a unique mechanism of inactivation gating comprising two inactivation states in a member of the Kv channel superfamily, Kv7.1. Removal of external Ca2+ in wild-type Kv7.1 channels produced a large, voltage-dependent inactivation, which differed from N- or C-type mechanisms. Glu295 and Asp317 located, respectively, in the turret and pore entrance are involved in Ca2+ coordination, allowing Asp317 to form H-bonding with the pore helix Trp304, which stabilizes the selectivity filter and prevents inactivation. Phosphatidylinositol 4,5-bisphosphate (PIP2) and Ca2+-calmodulin prevented Kv7.1 inactivation triggered by Ca2+-free external solutions, where Ser182 at the S2-S3 linker relays the calmodulin signal from its inner boundary to the external pore to allow proper channel conduction. Thus, we revealed a unique mechanism of inactivation gating in Kv7.1, exquisitely controlled by external Ca2+ and allosterically coupled by internal PIP2 and Ca2+-calmodulin.
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Affiliation(s)
- Maya Lipinsky
- Department of Physiology and Pharmacology, Sackler Faculty of Medicine and Sagol School of Neurosciences, Tel Aviv University, Tel Aviv 69978, Israel
| | - William Sam Tobelaim
- Department of Physiology and Pharmacology, Sackler Faculty of Medicine and Sagol School of Neurosciences, Tel Aviv University, Tel Aviv 69978, Israel
| | - Asher Peretz
- Department of Physiology and Pharmacology, Sackler Faculty of Medicine and Sagol School of Neurosciences, Tel Aviv University, Tel Aviv 69978, Israel
| | - Luba Simhaev
- The Blavatnik Center for Drug Discovery, Tel Aviv University, Tel Aviv 69978, Israel
| | - Adva Yeheskel
- The Blavatnik Center for Drug Discovery, Tel Aviv University, Tel Aviv 69978, Israel
| | - Daniel Yakubovich
- Department of Physiology and Pharmacology, Sackler Faculty of Medicine and Sagol School of Neurosciences, Tel Aviv University, Tel Aviv 69978, Israel
| | - Guy Lebel
- Department of Biochemistry and Molecular Biology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel
| | - Yoav Paas
- The Mina and Everard Goodman Faculty of Life Sciences, Bar-Ilan University, Ramat-Gan 52900, Israel
| | - Joel A Hirsch
- Department of Biochemistry and Molecular Biology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel
| | - Bernard Attali
- Department of Physiology and Pharmacology, Sackler Faculty of Medicine and Sagol School of Neurosciences, Tel Aviv University, Tel Aviv 69978, Israel.
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38
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Abstract
The opening and closing of voltage-gated ion channels are regulated by voltage sensors coupled to a gate that controls the ion flux across the cellular membrane. Modulation of any part of gating constitutes an entry point for pharmacologically regulating channel function. Here, we report on the discovery of a large family of warfarin-like compounds that open the two voltage-gated type 1 potassium (KV1) channels KV1.5 and Shaker, but not the related KV2-, KV4-, or KV7-type channels. These negatively charged compounds bind in the open state to positively charged arginines and lysines between the intracellular ends of the voltage-sensor domains and the pore domain. This mechanism of action resembles that of endogenous channel-opening lipids and opens up an avenue for the development of ion-channel modulators.
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39
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Leveraging a gain-of-function allele of Caenorhabditis elegans paqr-1 to elucidate membrane homeostasis by PAQR proteins. PLoS Genet 2020; 16:e1008975. [PMID: 32750056 PMCID: PMC7428288 DOI: 10.1371/journal.pgen.1008975] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2020] [Revised: 08/14/2020] [Accepted: 07/01/2020] [Indexed: 12/12/2022] Open
Abstract
The C. elegans proteins PAQR-2 (a homolog of the human seven-transmembrane domain AdipoR1 and AdipoR2 proteins) and IGLR-2 (a homolog of the mammalian LRIG proteins characterized by a single transmembrane domain and the presence of immunoglobulin domains and leucine-rich repeats in their extracellular portion) form a complex that protects against plasma membrane rigidification by promoting the expression of fatty acid desaturases and the incorporation of polyunsaturated fatty acids into phospholipids, hence increasing membrane fluidity. In the present study, we leveraged a novel gain-of-function allele of PAQR-1, a PAQR-2 paralog, to carry out structure-function studies. We found that the transmembrane domains of PAQR-2 are responsible for its functional requirement for IGLR-2, that PAQR-1 does not require IGLR-2 but acts via the same pathway as PAQR-2, and that the divergent N-terminal cytoplasmic domains of the PAQR-1 and PAQR-2 proteins serve a regulatory function and may regulate access to the catalytic site of these proteins. We also show that overexpression of human AdipoR1 or AdipoR2 alone is sufficient to confer increased palmitic acid resistance in HEK293 cells, and thus act in a manner analogous to the PAQR-1 gain-of-function allele.
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40
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Wang Y, Eldstrom J, Fedida D. Gating and Regulation of KCNQ1 and KCNQ1 + KCNE1 Channel Complexes. Front Physiol 2020; 11:504. [PMID: 32581825 PMCID: PMC7287213 DOI: 10.3389/fphys.2020.00504] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2020] [Accepted: 04/24/2020] [Indexed: 12/20/2022] Open
Abstract
The IKs channel complex is formed by the co-assembly of Kv7.1 (KCNQ1), a voltage-gated potassium channel, with its β-subunit, KCNE1 and the association of numerous accessory regulatory molecules such as PIP2, calmodulin, and yotiao. As a result, the IKs potassium current shows kinetic and regulatory flexibility, which not only allows IKs to fulfill physiological roles as disparate as cardiac repolarization and the maintenance of endolymph K+ homeostasis, but also to cause significant disease when it malfunctions. Here, we review new areas of understanding in the assembly, kinetics of activation and inactivation, voltage-sensor pore coupling, unitary events and regulation of this important ion channel complex, all of which have been given further impetus by the recent solution of cryo-EM structural representations of KCNQ1 alone and KCNQ1+KCNE3. Recently, the stoichiometric ratio of KCNE1 to KCNQ1 subunits has been confirmed to be variable up to a ratio of 4:4, rather than fixed at 2:4, and we will review the results and new methodologies that support this conclusion. Significant advances have been made in understanding differences between KCNQ1 and IKs gating using voltage clamp fluorimetry and mutational analysis to illuminate voltage sensor activation and inactivation, and the relationship between voltage sensor translation and pore domain opening. We now understand that the KCNQ1 pore can open with different permeabilities and conductance when the voltage sensor is in partially or fully activated positions, and the ability to make robust single channel recordings from IKs channels has also revealed the complicated pore subconductance architecture during these opening steps, during inactivation, and regulation by 1−4 associated KCNE1 subunits. Experiments placing mutations into individual voltage sensors to drastically change voltage dependence or prevent their movement altogether have demonstrated that the activation of KCNQ1 alone and IKs can best be explained using allosteric models of channel gating. Finally, we discuss how the intrinsic gating properties of KCNQ1 and IKs are highly modulated through the impact of intracellular signaling molecules and co-factors such as PIP2, protein kinase A, calmodulin and ATP, all of which modulate IKs current kinetics and contribute to diverse IKs channel complex function.
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Affiliation(s)
- Yundi Wang
- Department of Anesthesiology, Pharmacology & Therapeutics, The University of British Columbia, Vancouver, BC, Canada
| | - Jodene Eldstrom
- Department of Anesthesiology, Pharmacology & Therapeutics, The University of British Columbia, Vancouver, BC, Canada
| | - David Fedida
- Department of Anesthesiology, Pharmacology & Therapeutics, The University of British Columbia, Vancouver, BC, Canada
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41
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New Structural insights into Kir channel gating from molecular simulations, HDX-MS and functional studies. Sci Rep 2020; 10:8392. [PMID: 32439887 PMCID: PMC7242327 DOI: 10.1038/s41598-020-65246-z] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2019] [Accepted: 04/29/2020] [Indexed: 11/25/2022] Open
Abstract
Inward rectifier potassium (Kir) channels play diverse and important roles in shaping action potentials in biological membranes. An increasing number of diseases are now known to be directly associated with abnormal Kir function. However, the gating of Kir still remains unknown. To increase our understanding of its gating mechanism, a dynamical view of the entire channel is essential. Here the gating activation was studied using a recent developped in silico method, MDeNM, which combines normal mode analysis and molecular dynamics simulations that showed for the very first time the importance of interrelated collective and localized conformational movements. In particular, we highlighted the role played by concerted movements of the different regions throughout the entire protein, such as the cytoplasmic and transmembrane domains and the slide helices. In addition, the HDX-MS analysis achieved in these studies provided a comprehensive and detailed view of the dynamics associated with open/closed transition of the Kir channel in coherence with the theoretical results. MDeNM gives access to the probability of the different opening states that are in agreement with our electrophysiological experiments. The investigations presented in this article are important to remedy dysfunctional channels and are of interest for designing new pharmacological compounds.
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42
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Khan AK, Jagielnicki M, McIntire WE, Purdy MD, Dharmarajan V, Griffin PR, Yeager M. A Steric “Ball-and-Chain” Mechanism for pH-Mediated Regulation of Gap Junction Channels. Cell Rep 2020; 31:107482. [PMID: 32320665 DOI: 10.1016/j.celrep.2020.03.046] [Citation(s) in RCA: 27] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2019] [Revised: 09/10/2019] [Accepted: 03/13/2020] [Indexed: 12/21/2022] Open
Abstract
Gap junction channels (GJCs) mediate intercellular communication and are gated by numerous conditions such as pH. The electron cryomicroscopy (cryo-EM) structure of Cx26 GJC at physiological pH recapitulates previous GJC structures in lipid bilayers. At pH 6.4, we identify two conformational states, one resembling the open physiological-pH structure and a closed conformation that displays six threads of density, that join to form a pore-occluding density. Crosslinking and hydrogen-deuterium exchange mass spectrometry reveal closer association between the N-terminal (NT) domains and the cytoplasmic loops (CL) at acidic pH. Previous electrophysiologic studies suggest an association between NT residue N14 and H100 near M2, which may trigger the observed movement of M2 toward M1 in our cryo-EM maps, thereby accounting for additional NT-CL crosslinks at acidic pH. We propose that these pH-induced interactions and conformational changes result in extension, ordering, and association of the acetylated NT domains to form a hexameric "ball-and-chain" gating particle.
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43
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Siemer AB. Advances in studying protein disorder with solid-state NMR. SOLID STATE NUCLEAR MAGNETIC RESONANCE 2020; 106:101643. [PMID: 31972419 PMCID: PMC7202078 DOI: 10.1016/j.ssnmr.2020.101643] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/18/2019] [Revised: 01/06/2020] [Accepted: 01/07/2020] [Indexed: 05/26/2023]
Abstract
Solution NMR is a key tool to study intrinsically disordered proteins (IDPs), whose importance for biological function is widely accepted. However, disordered proteins are not limited to solution and are also found in non-soluble systems such as fibrils and membrane proteins. In this Trends article, I will discuss how solid-state NMR can be used to study disorder in non-soluble proteins. Techniques based on dipolar couplings can study static protein disorder which either occurs naturally as e.g. in spider silk or can be induced by freeze trapping IDPs or unfolded proteins. In this case, structural ensembles are directly reflected by a static distribution of dihedral angels that can be determined by the distribution of chemical shifts or other methods. Techniques based on J-couplings can detect dynamic protein disorder under MAS. In this case, only average chemical shifts are measured but disorder can be characterized with a variety of data including secondary chemical shifts, relaxation rates, paramagnetic relaxation enhancements, or residual dipolar couplings. I describe both technical aspects and examples of solid-state NMR on protein disorder and end the article with a discussion of challenges and opportunities of this emerging field.
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Affiliation(s)
- Ansgar B Siemer
- Department of Physiology and Neuroscience, Zilkha Neurogenetic Institute, Univeristy of Southern California, 1501 San Pablo Street, Los Angeles, CA, 90033, USA.
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44
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Fan C, Sukomon N, Flood E, Rheinberger J, Allen TW, Nimigean CM. Ball-and-chain inactivation in a calcium-gated potassium channel. Nature 2020; 580:288-293. [PMID: 32269335 PMCID: PMC7153497 DOI: 10.1038/s41586-020-2116-0] [Citation(s) in RCA: 36] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2019] [Accepted: 01/15/2020] [Indexed: 01/21/2023]
Abstract
Inactivation is the process by which ion channels terminate ion flux through their pores while the opening stimulus is still present1. In neurons, inactivation of both sodium and potassium channels is crucial for the generation of action potentials and regulation of firing frequency1,2. A cytoplasmic domain of either the channel or an accessory subunit is thought to plug the open pore to inactivate the channel via a 'ball-and-chain' mechanism3-7. Here we use cryo-electron microscopy to identify the molecular gating mechanism in calcium-activated potassium channels by obtaining structures of the MthK channel from Methanobacterium thermoautotrophicum-a purely calcium-gated and inactivating channel-in a lipid environment. In the absence of Ca2+, we obtained a single structure in a closed state, which was shown by atomistic simulations to be highly flexible in lipid bilayers at ambient temperature, with large rocking motions of the gating ring and bending of pore-lining helices. In Ca2+-bound conditions, we obtained several structures, including multiple open-inactivated conformations, further indication of a highly dynamic protein. These different channel conformations are distinguished by rocking of the gating rings with respect to the transmembrane region, indicating symmetry breakage across the channel. Furthermore, in all conformations displaying open channel pores, the N terminus of one subunit of the channel tetramer sticks into the pore and plugs it, with free energy simulations showing that this is a strong interaction. Deletion of this N terminus leads to functionally non-inactivating channels and structures of open states without a pore plug, indicating that this previously unresolved N-terminal peptide is responsible for a ball-and-chain inactivation mechanism.
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Affiliation(s)
- Chen Fan
- Department of Anesthesiology, Weill Cornell Medical College, New York, NY, USA
| | - Nattakan Sukomon
- Department of Anesthesiology, Weill Cornell Medical College, New York, NY, USA
| | - Emelie Flood
- School of Science, RMIT University, Melbourne, Victoria, Australia
| | - Jan Rheinberger
- Department of Anesthesiology, Weill Cornell Medical College, New York, NY, USA
- Department of Structural Biology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Groningen, The Netherlands
| | - Toby W Allen
- School of Science, RMIT University, Melbourne, Victoria, Australia
| | - Crina M Nimigean
- Department of Anesthesiology, Weill Cornell Medical College, New York, NY, USA.
- Department of Physiology and Biophysics, Weill Cornell Medical College, New York, NY, USA.
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45
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Núñez E, Muguruza-Montero A, Villarroel A. Atomistic Insights of Calmodulin Gating of Complete Ion Channels. Int J Mol Sci 2020; 21:ijms21041285. [PMID: 32075037 PMCID: PMC7072864 DOI: 10.3390/ijms21041285] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2019] [Revised: 02/07/2020] [Accepted: 02/12/2020] [Indexed: 12/13/2022] Open
Abstract
Intracellular calcium is essential for many physiological processes, from neuronal signaling and exocytosis to muscle contraction and bone formation. Ca2+ signaling from the extracellular medium depends both on membrane potential, especially controlled by ion channels selective to K+, and direct permeation of this cation through specialized channels. Calmodulin (CaM), through direct binding to these proteins, participates in setting the membrane potential and the overall permeability to Ca2+. Over the past years many structures of complete channels in complex with CaM at near atomic resolution have been resolved. In combination with mutagenesis-function, structural information of individual domains and functional studies, different mechanisms employed by CaM to control channel gating are starting to be understood at atomic detail. Here, new insights regarding four types of tetrameric channels with six transmembrane (6TM) architecture, Eag1, SK2/SK4, TRPV5/TRPV6 and KCNQ1–5, and its regulation by CaM are described structurally. Different CaM regions, N-lobe, C-lobe and EF3/EF4-linker play prominent signaling roles in different complexes, emerging the realization of crucial non-canonical interactions between CaM and its target that are only evidenced in the full-channel structure. Different mechanisms to control gating are used, including direct and indirect mechanical actuation over the pore, allosteric control, indirect effect through lipid binding, as well as direct plugging of the pore. Although each CaM lobe engages through apparently similar alpha-helices, they do so using different docking strategies. We discuss how this allows selective action of drugs with great therapeutic potential.
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Meisel E, Tobelaim W, Dvir M, Haitin Y, Peretz A, Attali B. Inactivation gating of Kv7.1 channels does not involve concerted cooperative subunit interactions. Channels (Austin) 2019; 12:89-99. [PMID: 29451064 PMCID: PMC5972808 DOI: 10.1080/19336950.2018.1441649] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Inactivation is an intrinsic property of numerous voltage-gated K+ (Kv) channels and can occur by N-type or/and C-type mechanisms. N-type inactivation is a fast, voltage independent process, coupled to activation, with each inactivation particle of a tetrameric channel acting independently. In N-type inactivation, a single inactivation particle is necessary and sufficient to occlude the pore. C-type inactivation is a slower process, involving the outermost region of the pore and is mediated by a concerted, highly cooperative interaction between all four subunits. Inactivation of Kv7.1 channels does not exhibit the hallmarks of N- and C-type inactivation. Inactivation of WT Kv7.1 channels can be revealed by hooked tail currents that reflects the recovery from a fast and voltage-independent inactivation process. However, several Kv7.1 mutants such as the pore mutant L273F generate an additional voltage-dependent slow inactivation. The subunit interactions during this slow inactivation gating remain unexplored. The goal of the present study was to study the nature of subunit interactions along Kv7.1 inactivation gating, using concatenated tetrameric Kv7.1 channel and introducing sequentially into each of the four subunits the slow inactivating pore mutation L273F. Incorporating an incremental number of inactivating mutant subunits did not affect the inactivation kinetics but slowed down the recovery kinetics from inactivation. Results indicate that Kv7.1 inactivation gating is not compatible with a concerted cooperative process. Instead, adding an inactivating subunit L273F into the Kv7.1 tetramer incrementally stabilizes the inactivated state, which suggests that like for activation gating, Kv7.1 slow inactivation gating is not a concerted process.
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Affiliation(s)
- Eshcar Meisel
- a Department of Physiology & Pharmacology , the Sackler Faculty of Medicine and Sagol School of Neurosciences, Tel Aviv University , Tel Aviv , Israel
| | - William Tobelaim
- a Department of Physiology & Pharmacology , the Sackler Faculty of Medicine and Sagol School of Neurosciences, Tel Aviv University , Tel Aviv , Israel
| | - Meidan Dvir
- a Department of Physiology & Pharmacology , the Sackler Faculty of Medicine and Sagol School of Neurosciences, Tel Aviv University , Tel Aviv , Israel
| | - Yoni Haitin
- a Department of Physiology & Pharmacology , the Sackler Faculty of Medicine and Sagol School of Neurosciences, Tel Aviv University , Tel Aviv , Israel
| | - Asher Peretz
- a Department of Physiology & Pharmacology , the Sackler Faculty of Medicine and Sagol School of Neurosciences, Tel Aviv University , Tel Aviv , Israel
| | - Bernard Attali
- a Department of Physiology & Pharmacology , the Sackler Faculty of Medicine and Sagol School of Neurosciences, Tel Aviv University , Tel Aviv , Israel
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Structure, function, and ion-binding properties of a K + channel stabilized in the 2,4-ion-bound configuration. Proc Natl Acad Sci U S A 2019; 116:16829-16834. [PMID: 31387976 DOI: 10.1073/pnas.1901888116] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Here, we present the atomic resolution crystallographic structure, the function, and the ion-binding properties of the KcsA mutants, G77A and G77C, that stabilize the 2,4-ion-bound configuration (i.e., water, K+, water, K+-ion-bound configuration) of the K+ channel's selectivity filter. A full functional and thermodynamic characterization of the G77A mutant revealed wild-type-like ion selectivity and apparent K+-binding affinity, in addition to showing a lack of C-type inactivation gating and a marked reduction in its single-channel conductance. These structures validate, from a structural point of view, the notion that 2 isoenergetic ion-bound configurations coexist within a K+ channel's selectivity filter, which fully agrees with the water-K+-ion-coupled transport detected by streaming potential measurements.
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48
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A Structural Model of the Inactivation Gate of Voltage-Activated Potassium Channels. Biophys J 2019; 117:377-387. [PMID: 31278002 DOI: 10.1016/j.bpj.2019.06.008] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2019] [Revised: 05/21/2019] [Accepted: 06/07/2019] [Indexed: 11/24/2022] Open
Abstract
After opening, the Shaker voltage-gated potassium (KV) channel rapidly inactivates when one of its four N-termini enters and occludes the channel pore. Although it is known that the tip of the N-terminus reaches deep into the central cavity, the conformation adopted by this domain during inactivation and the nature of its interactions with the rest of the channel remain unclear. Here, we use molecular dynamics simulations coupled with electrophysiology experiments to reveal the atomic-scale mechanisms of inactivation. We find that the first six amino acids of the N-terminus spontaneously enter the central cavity in an extended conformation, establishing hydrophobic contacts with residues lining the pore. A second portion of the N-terminus, consisting of a long 24 amino acid α-helix, forms numerous polar contacts with residues in the intracellular entryway of the T1 domain. Double mutant cycle analysis revealed a strong relationship between predicted interatomic distances and empirically observed thermodynamic coupling, establishing a plausible model of the transition of KV channels to the inactivated state.
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49
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Diffracted X-ray tracking method for recording single-molecule protein motions. Biochim Biophys Acta Gen Subj 2019; 1864:129361. [PMID: 31077793 DOI: 10.1016/j.bbagen.2019.05.004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2018] [Revised: 04/25/2019] [Accepted: 05/05/2019] [Indexed: 11/24/2022]
Abstract
BACKGROUND Proteins change their conformation depending on function. Although a vast number of static pictures of proteins have been accumulated, information regarding their dynamics in function is limited. Diffracted X-ray tracking (DXT) is a good candidate to obtain the missing data. SCOPE OF REVIEW A gold nanocrystal was attached to the target protein as a probe and the motion of the X-ray diffraction spots from the crystal corresponded to the motion of the target. Although it has advantages of high temporal (sub-millisecond) and spatial (approximately 0.1°) resolutions, it is not extensively utilized. This review focused on its effective application from a user's perspective. We also present an example with the KcsA channel and the status of recent developments to show the future possibilities of the method. MAJOR CONCLUSIONS DXT is a powerful method to investigate intramolecular structural changes. For instance, in the KcsA channel, the method revealed a wave of conformational changes transmitted from the gate region to the end of the molecule. The method is continuously being developed, and users can choose an appropriate measurement system depending on the condition of their sample. GENERAL SIGNIFICANCE Revealing the protein structural changes with respect to function is an important frontier. The most distinctive feature of the DXT method is that both high temporal and spatial resolutions are achievable, and it is possible to track the motions of multiple molecules at the same time. This feature is an advantage for screening molecules associated with the target proteins (e.g., ligands and medicines).
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50
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Guidelli R, Becucci L. Merging Shaker K+ channel electrophysiology with structural data by a nucleation and growth mechanism. Electrochim Acta 2019. [DOI: 10.1016/j.electacta.2019.01.183] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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