1
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Pliushcheuskaya P, Kesh S, Kaufmann E, Wucherpfennig S, Schwede F, Künze G, Nache V. Similar Binding Modes of cGMP Analogues Limit Selectivity in Modulating Retinal CNG Channels via the Cyclic Nucleotide-Binding Domain. ACS Chem Neurosci 2024; 15:1652-1668. [PMID: 38579109 PMCID: PMC11027099 DOI: 10.1021/acschemneuro.3c00665] [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: 10/16/2023] [Revised: 02/28/2024] [Accepted: 03/19/2024] [Indexed: 04/07/2024] Open
Abstract
In treating retinitis pigmentosa, a genetic disorder causing progressive vision loss, selective inhibition of rod cyclic nucleotide-gated (CNG) channels holds promise. Blocking the increased Ca2+-influx in rod photoreceptors through CNG channels can potentially delay disease progression and improve the quality of life for patients. To find inhibitors for rod CNG channels, we investigated the impact of 16 cGMP analogues on both rod and cone CNG channels using the patch-clamp technique. Although modifications at the C8 position of the guanine ring did not change the ligand efficacy, modifications at the N1 and N2 positions rendered cGMP largely ineffective in activating retinal CNG channels. Notably, PET-cGMP displayed selective potential, favoring rod over cone, whereas Rp-cGMPS showed greater efficiency in activating cone over rod CNG channels. Ligand docking and molecular dynamics simulations on cyclic nucleotide-binding domains showed comparable binding energies and binding modes for cGMP and its analogues in both rod and cone CNG channels (CNGA1 vs CNGA3 subunits). Computational experiments on CNGB1a vs CNGB3 subunits showed similar binding modes albeit with fewer amino acid interactions with cGMP due to an inactivated conformation of their C-helix. In addition, no clear correlation could be observed between the computational scores and the CNG channel efficacy values, suggesting additional factors beyond binding strength determining ligand selectivity and potency. This study highlights the importance of looking beyond the cyclic nucleotide-binding domain and toward the gating mechanism when searching for selective modulators. Future efforts in developing selective modulators for CNG channels should prioritize targeting alternative channel domains.
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Affiliation(s)
- Palina Pliushcheuskaya
- Institute
for Drug Discovery, Medical Faculty, University
of Leipzig, Leipzig 04103, Germany
| | - Sandeep Kesh
- Institute
of Physiology II, University Hospital Jena, Friedrich Schiller University
Jena, Jena 07743, Germany
| | - Emma Kaufmann
- Institute
of Physiology II, University Hospital Jena, Friedrich Schiller University
Jena, Jena 07743, Germany
| | - Sophie Wucherpfennig
- Institute
of Physiology II, University Hospital Jena, Friedrich Schiller University
Jena, Jena 07743, Germany
| | - Frank Schwede
- BIOLOG
Life Science Institute GmbH & Co KG, Bremen 28199, Germany
| | - Georg Künze
- Institute
for Drug Discovery, Medical Faculty, University
of Leipzig, Leipzig 04103, Germany
- Interdisciplinary
Center for Bioinformatics, University of
Leipzig, Leipzig 04107, Germany
- Center
for Scalable Data Analytics and Artificial Intelligence, University of Leipzig, Leipzig 04105, Germany
| | - Vasilica Nache
- Institute
of Physiology II, University Hospital Jena, Friedrich Schiller University
Jena, Jena 07743, Germany
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2
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Hu Z, Yang J. Structural basis of properties, mechanisms, and channelopathy of cyclic nucleotide-gated channels. Channels (Austin) 2023; 17:2273165. [PMID: 37905307 PMCID: PMC10761061 DOI: 10.1080/19336950.2023.2273165] [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: 09/07/2023] [Accepted: 10/07/2023] [Indexed: 11/02/2023] Open
Abstract
Recent years have seen an outpouring of atomic or near atomic resolution structures of cyclic nucleotide-gated (CNG) channels, captured in closed, transition, pre-open, partially open, and fully open states. These structures provide unprecedented molecular insights into the activation, assembly, architecture, regulation, and channelopathy of CNG channels, as well as mechanistic explanations for CNG channel biophysical and pharmacological properties. This article summarizes recent advances in CNG channel structural biology, describes key structural features and elements, and illuminates a detailed conformational landscape of activation by cyclic nucleotides. The review also correlates structures with findings and properties delineated in functional studies, including nonselective monovalent cation selectivity, Ca2+ permeation and block, block by L-cis-diltiazem, location of the activation gate, lack of voltage-dependent gating, and modulation by lipids and calmodulin. A perspective on future research is also offered.
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Affiliation(s)
- Zhengshan Hu
- Department of Biological Sciences, Columbia University, New York, NY, USA
| | - Jian Yang
- Department of Biological Sciences, Columbia University, New York, NY, USA
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3
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Sharma A, Kumar R, Varadwaj P. Developing human olfactory network and exploring olfactory receptor-odorant interaction. J Biomol Struct Dyn 2023; 41:8941-8960. [PMID: 36310099 DOI: 10.1080/07391102.2022.2138976] [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: 07/26/2022] [Accepted: 10/17/2022] [Indexed: 06/16/2023]
Abstract
The Olfactory receptor (OR)-odorant interactions are perplexed. ORs can bind to structurally diverse odorants associated with one or more odor percepts. Various attempts have been made to understand the intricacies of OR-odorant interaction. In this study, experimentally documented OR-odorant interactions are investigated comprehensively to; (a) suggest potential odor percepts for ORs based on the OR-OR network; (b) determine how odorants interacting with specific ORs differ in terms of inherent pharmacophoric features and molecular properties, (c) identify molecular interactions that explained OR-odorant interactions of selective ORs; and (d) predict the probable role of ORs other than olfaction. Human olfactory receptor network (hORnet) is developed to study possible odor percepts for ORs. We identified six molecular properties which showed variation and significant patterns to differentiate odorants binding with five ORs. The pharmacophore analysis revealed that odorants subset of five ORs follow similar pharmacophore hypothesis, (one hydrogen acceptor and two hydrophobic regions) but differ in terms of distance and orientation of pharmacophoric features. To ascertain the binding site residues and key interactions between the selected ORs and their interacting odorants, 3D-structure modelling, docking and molecular dynamics studies were carried out. Lastly, the potential role of ORs beyond olfaction is explored. A human OR-OR network was developed to suggest possible odor percepts for ORs using empirically proven OR-odorant interactions. We sought to find out significant characteristics, molecular properties, and molecular interactions that could explain OR-odorant interactions and add to the understanding of the complex issue of odor perception.Communicated by Ramaswamy H. Sarma.
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Affiliation(s)
- Anju Sharma
- Department of Applied Sciences, Indian Institute of Information Technology, Allahabad, Uttar Pradesh, India
| | - Rajnish Kumar
- Amity Institute of Biotechnology, Amity University Uttar Pradesh, Lucknow, Uttar Pradesh, India
| | - Pritish Varadwaj
- Department of Applied Sciences, Indian Institute of Information Technology, Allahabad, Uttar Pradesh, India
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4
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Hu Z, Zheng X, Yang J. Conformational trajectory of allosteric gating of the human cone photoreceptor cyclic nucleotide-gated channel. Nat Commun 2023; 14:4284. [PMID: 37463923 DOI: 10.1038/s41467-023-39971-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2023] [Accepted: 07/05/2023] [Indexed: 07/20/2023] Open
Abstract
Cyclic nucleotide-gated (CNG) channels transduce chemical signals into electrical signals in sensory receptors and neurons. They are activated by cGMP or cAMP, which bind to the cyclic nucleotide-binding domain (CNBD) to open a gate located 50-60 Å away in the central cavity. Structures of closed and open vertebrate CNG channels have been solved, but the conformational landscape of this allosteric gating remains to be elucidated and enriched. Here, we report structures of the cGMP-activated human cone photoreceptor CNGA3/CNGB3 channel in closed, intermediate, pre-open and open states in detergent or lipid nanodisc, all with fully bound cGMP. The pre-open and open states are obtained only in the lipid nanodisc, suggesting a critical role of lipids in tuning the energetic landscape of CNGA3/CNGB3 activation. The different states exhibit subunit-unique, incremental and distinct conformational rearrangements that originate in the CNBD, propagate through the gating ring to the transmembrane domain, and gradually open the S6 cavity gate. Our work illustrates a spatial conformational-change wave of allosteric gating of a vertebrate CNG channel by its natural ligand and provides an expanded framework for studying CNG properties and channelopathy.
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Affiliation(s)
- Zhengshan Hu
- Department of Biological Sciences, Columbia University, New York, NY, 10027, USA
| | - Xiangdong Zheng
- Department of Biological Sciences, Columbia University, New York, NY, 10027, USA
| | - Jian Yang
- Department of Biological Sciences, Columbia University, New York, NY, 10027, USA.
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5
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Barret D, Schuster D, Rodrigues M, Leitner A, Picotti P, Schertler G, Kaupp U, Korkhov V, Marino J. Structural basis of calmodulin modulation of the rod cyclic nucleotide-gated channel. Proc Natl Acad Sci U S A 2023; 120:e2300309120. [PMID: 37011209 PMCID: PMC10104587 DOI: 10.1073/pnas.2300309120] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2023] [Accepted: 03/06/2023] [Indexed: 04/05/2023] Open
Abstract
Calmodulin (CaM) regulates many ion channels to control calcium entry into cells, and mutations that alter this interaction are linked to fatal diseases. The structural basis of CaM regulation remains largely unexplored. In retinal photoreceptors, CaM binds to the CNGB subunit of cyclic nucleotide-gated (CNG) channels and, thereby, adjusts the channel's Cyclic guanosine monophosphate (cGMP) sensitivity in response to changes in ambient light conditions. Here, we provide the structural characterization for CaM regulation of a CNG channel by using a combination of single-particle cryo-electron microscopy and structural proteomics. CaM connects the CNGA and CNGB subunits, resulting in structural changes both in the cytosolic and transmembrane regions of the channel. Cross-linking and limited proteolysis-coupled mass spectrometry mapped the conformational changes induced by CaM in vitro and in the native membrane. We propose that CaM is a constitutive subunit of the rod channel to ensure high sensitivity in dim light. Our mass spectrometry-based approach is generally relevant for studying the effect of CaM on ion channels in tissues of medical interest, where only minute quantities are available.
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Affiliation(s)
- Diane C. A. Barret
- Laboratory of Biomolecular Research, Paul Scherrer Institute, 5232Villigen, Switzerland
| | - Dina Schuster
- Laboratory of Biomolecular Research, Paul Scherrer Institute, 5232Villigen, Switzerland
- Institute of Molecular Systems Biology, Department of Biology, ETH Zurich, 8049Zürich, Switzerland
- Institute of Molecular Biology and Biophysics, ETH Zürich, 8049Zurich, Switzerland
| | - Matthew J. Rodrigues
- Laboratory of Biomolecular Research, Paul Scherrer Institute, 5232Villigen, Switzerland
| | - Alexander Leitner
- Institute of Molecular Systems Biology, Department of Biology, ETH Zurich, 8049Zürich, Switzerland
| | - Paola Picotti
- Institute of Molecular Systems Biology, Department of Biology, ETH Zurich, 8049Zürich, Switzerland
| | | | - U. Benjamin Kaupp
- Life and Medical Sciences Institute, University of Bonn, 53115Bonn, Germany
- Max Planck Institute for Multidisciplinary Sciences, 37077Göttingen, Germany
| | - Volodymyr M. Korkhov
- Laboratory of Biomolecular Research, Paul Scherrer Institute, 5232Villigen, Switzerland
- Institute of Molecular Biology and Biophysics, ETH Zürich, 8049Zurich, Switzerland
| | - Jacopo Marino
- Laboratory of Biomolecular Research, Paul Scherrer Institute, 5232Villigen, Switzerland
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6
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Hofmann KP, Lamb TD. Rhodopsin, light-sensor of vision. Prog Retin Eye Res 2023; 93:101116. [PMID: 36273969 DOI: 10.1016/j.preteyeres.2022.101116] [Citation(s) in RCA: 21] [Impact Index Per Article: 21.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2022] [Revised: 08/20/2022] [Accepted: 08/22/2022] [Indexed: 11/06/2022]
Abstract
The light sensor of vertebrate scotopic (low-light) vision, rhodopsin, is a G-protein-coupled receptor comprising a polypeptide chain with bound chromophore, 11-cis-retinal, that exhibits remarkable physicochemical properties. This photopigment is extremely stable in the dark, yet its chromophore isomerises upon photon absorption with 70% efficiency, enabling the activation of its G-protein, transducin, with high efficiency. Rhodopsin's photochemical and biochemical activities occur over very different time-scales: the energy of retinaldehyde's excited state is stored in <1 ps in retinal-protein interactions, but it takes milliseconds for the catalytically active state to form, and many tens of minutes for the resting state to be restored. In this review, we describe the properties of rhodopsin and its role in rod phototransduction. We first introduce rhodopsin's gross structural features, its evolution, and the basic mechanisms of its activation. We then discuss light absorption and spectral sensitivity, photoreceptor electrical responses that result from the activity of individual rhodopsin molecules, and recovery of rhodopsin and the visual system from intense bleaching exposures. We then provide a detailed examination of rhodopsin's molecular structure and function, first in its dark state, and then in the active Meta states that govern its interactions with transducin, rhodopsin kinase and arrestin. While it is clear that rhodopsin's molecular properties are exquisitely honed for phototransduction, from starlight to dawn/dusk intensity levels, our understanding of how its molecular interactions determine the properties of scotopic vision remains incomplete. We describe potential future directions of research, and outline several major problems that remain to be solved.
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Affiliation(s)
- Klaus Peter Hofmann
- Institut für Medizinische Physik und Biophysik (CC2), Charité, and, Zentrum für Biophysik und Bioinformatik, Humboldt-Unversität zu Berlin, Berlin, 10117, Germany.
| | - Trevor D Lamb
- Eccles Institute of Neuroscience, John Curtin School of Medical Research, The Australian National University, Canberra, ACT 2600, Australia.
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7
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Abstract
PURPOSE Mutations in the cyclic nucleotide-gated (CNG) channel beta subunit (CNGB1) are an important cause of recessive retinitis pigmentosa. We identified a large animal model with a truncating mutation of CNGB1. This study reports the persistence of small, desensitized rod ERG responses in this model. METHODS Dark-, light-adapted and chromatic ERGs were recorded in CNGB1 mutant dogs and age and breed matched controls. Comparisons were made with a dog model known to completely lack rod function; young dogs with a mutation in the rod phosphodiesterase 6 alpha subunit (PDE6A-/-). Immunohistochemistry (IHC) to label the rod CNG alpha (CNGA1) and CNGB1 subunits was performed. RESULTS The dark-adapted ERG of CNGB1 mutant dogs had a raised response threshold with lack of normal rod response and a remaining cone response. Increasing stimulus strength resulted in the appearance of a separate, slower positive waveform following the dark-adapted cone b-wave. With increasing stimulus strength this increased in amplitude and became faster to merge with the initial b-wave. Comparison of responses from PDE6A-/- (cone only dogs) with CNGB1 mutant dogs to red and blue flashes and between dark-adapted and light-adapted responses supported the hypothesis that the CNGB1 mutant dog had residual desensitized rod responses. CNGB1 mutant dogs had a small amount of CNGA1 detectable in the outer segments. CONCLUSIONS CNGB1 mutant dogs have a residual ERG response from desensitized rods. This may be due to low levels of CNGA1 in outer segments.
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8
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Retinal Cyclic Nucleotide-Gated Channel Regulation by Calmodulin. Int J Mol Sci 2022; 23:ijms232214143. [PMID: 36430626 PMCID: PMC9694239 DOI: 10.3390/ijms232214143] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2022] [Revised: 11/10/2022] [Accepted: 11/12/2022] [Indexed: 11/19/2022] Open
Abstract
Retinal cyclic nucleotide-gated (CNG) ion channels bind to intracellular cGMP and mediate visual phototransduction in photoreceptor rod and cone cells. Retinal rod CNG channels form hetero-tetramers comprised of three CNGA1 and one CNGB1 protein subunits. Cone CNG channels are similar tetramers consisting of three CNGA3 and one CNGB3 subunits. Calmodulin (CaM) binds to two distinct sites (CaM1: residues 565-587 and CaM2: residues 1120-1147) within the cytosolic domains of rod CNGB1. The binding of Ca2+-bound CaM to CNGB1 promotes the Ca2+-induced desensitization of CNG channels in retinal rods that may be important for photoreceptor light adaptation. Mutations that affect Ca2+-dependent CNG channel function are responsible for inherited forms of blindness. In this review, we propose structural models of the rod CNG channel bound to CaM that suggest how CaM might cause channel desensitization and how dysregulation of the channel may lead to retinal disease.
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9
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Schirmeyer J, Eick T, Schulz E, Hummert S, Sattler C, Schmauder R, Benndorf K. Subunit promotion energies for channel opening in heterotetrameric olfactory CNG channels. PLoS Comput Biol 2022; 18:e1010376. [PMID: 35998156 PMCID: PMC9512249 DOI: 10.1371/journal.pcbi.1010376] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2022] [Revised: 09/26/2022] [Accepted: 07/11/2022] [Indexed: 11/18/2022] Open
Abstract
Cyclic nucleotide-gated (CNG) ion channels of olfactory sensory neurons contain three types of homologue subunits, two CNGA2 subunits, one CNGA4 subunit and one CNGB1b subunit. Each subunit carries an intracellular cyclic nucleotide binding domain (CNBD) whose occupation by up to four cyclic nucleotides evokes channel activation. Thereby, the subunits interact in a cooperative fashion. Here we studied 16 concatamers with systematically disabled, but still functional, binding sites and quantified channel activation by systems of intimately coupled state models transferred to 4D hypercubes, thereby exploiting a weak voltage dependence of the channels. We provide the complete landscape of free energies for the complex activation process of heterotetrameric channels, including 32 binding steps, in both the closed and open channel, as well as 16 closed-open isomerizations. The binding steps are specific for the subunits and show pronounced positive cooperativity for the binding of the second and the third ligand. The energetics of the closed-open isomerizations were disassembled to elementary subunit promotion energies for channel opening, ΔΔGfpn, adding to the free energy of the closed-open isomerization of the empty channel, E0. The ΔΔGfpn values are specific for the four subunits and presumably invariant for the specific patterns of liganding. In conclusion, subunit cooperativity is confined to the CNBD whereas the subunit promotion energies for channel opening are independent. Olfactory sensory neurons (OSNs) in the nose transmit the information of odor molecules to electrical signals that are conducted to central parts of the brain. Olfactory cyclic nucleotide-gated (CNG) ion channels, located in the cell membrane of the OSNs, are relevant proteins in this process. These olfactory CNG channels are formed by three types of homologue subunits and each of these subunits contains a cyclic nucleotide binding domain (CNBD). A channel is activated by the binding of up to four cyclic nucleotides. The process of channel activation is only poorly understood. Herein we analyzed this activation process in great detail by concatenating these four subunits, disabling the CNBDs by mutations and performing extended computational fit analyses providing all 32 constants for the different binding steps at different degrees of liganding and, in addition, elementary subunit promotion energies for channel opening for all subunits. Our data suggest that subunit cooperativity is confined to the action of the CNBD.
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Affiliation(s)
- Jana Schirmeyer
- Institute of Physiology II, Jena University Hospital, Friedrich Schiller University Jena, Jena, Germany
| | - Thomas Eick
- Institute of Physiology II, Jena University Hospital, Friedrich Schiller University Jena, Jena, Germany
| | - Eckhard Schulz
- Schmalkalden University of Applied Sciences, Faculty of Electrical Engineering, Blechhammer, Schmalkalden, Germany
| | - Sabine Hummert
- Institute of Physiology II, Jena University Hospital, Friedrich Schiller University Jena, Jena, Germany
- Schmalkalden University of Applied Sciences, Faculty of Electrical Engineering, Blechhammer, Schmalkalden, Germany
| | - Christian Sattler
- Institute of Physiology II, Jena University Hospital, Friedrich Schiller University Jena, Jena, Germany
| | - Ralf Schmauder
- Institute of Physiology II, Jena University Hospital, Friedrich Schiller University Jena, Jena, Germany
| | - Klaus Benndorf
- Institute of Physiology II, Jena University Hospital, Friedrich Schiller University Jena, Jena, Germany
- * E-mail:
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10
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Barret DC, Kaupp UB, Marino J. The structure of cyclic nucleotide-gated channels in rod and cone photoreceptors. Trends Neurosci 2022; 45:763-776. [DOI: 10.1016/j.tins.2022.07.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2022] [Revised: 07/06/2022] [Accepted: 07/19/2022] [Indexed: 10/16/2022]
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11
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Das S, Popp V, Power M, Groeneveld K, Yan J, Melle C, Rogerson L, Achury M, Schwede F, Strasser T, Euler T, Paquet-Durand F, Nache V. Redefining the role of Ca 2+-permeable channels in photoreceptor degeneration using diltiazem. Cell Death Dis 2022; 13:47. [PMID: 35013127 PMCID: PMC8748460 DOI: 10.1038/s41419-021-04482-1] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2021] [Revised: 10/07/2021] [Accepted: 11/23/2021] [Indexed: 12/18/2022]
Abstract
Hereditary degeneration of photoreceptors has been linked to over-activation of Ca2+-permeable channels, excessive Ca2+-influx, and downstream activation of Ca2+-dependent calpain-type proteases. Unfortunately, after more than 20 years of pertinent research, unequivocal evidence proving significant and reproducible photoreceptor protection with Ca2+-channel blockers is still lacking. Here, we show that both D- and L-cis enantiomers of the anti-hypertensive drug diltiazem were very effective at blocking photoreceptor Ca2+-influx, most probably by blocking the pore of Ca2+-permeable channels. Yet, unexpectedly, this block neither reduced the activity of calpain-type proteases, nor did it result in photoreceptor protection. Remarkably, application of the L-cis enantiomer of diltiazem even led to a strong increase in photoreceptor cell death. These findings shed doubt on the previously proposed links between Ca2+ and retinal degeneration and are highly relevant for future therapy development as they may serve to refocus research efforts towards alternative, Ca2+-independent degenerative mechanisms.
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Affiliation(s)
- Soumyaparna Das
- Institute for Ophthalmic Research, University of Tübingen, 72076, Tübingen, Germany
| | - Valerie Popp
- Institute of Physiology II, University Hospital Jena, Friedrich Schiller University Jena, 07743, Jena, Germany
| | - Michael Power
- Institute for Ophthalmic Research, University of Tübingen, 72076, Tübingen, Germany.,Werner Reichardt Centre for Integrative Neuroscience (CIN), University of Tübingen, 72076, Tübingen, Germany
| | - Kathrin Groeneveld
- Institute of Physiology II, University Hospital Jena, Friedrich Schiller University Jena, 07743, Jena, Germany.,Biomolecular Photonics Group, University Hospital Jena, Friedrich Schiller University Jena, 07743, Jena, Germany
| | - Jie Yan
- Institute for Ophthalmic Research, University of Tübingen, 72076, Tübingen, Germany
| | - Christian Melle
- Biomolecular Photonics Group, University Hospital Jena, Friedrich Schiller University Jena, 07743, Jena, Germany
| | - Luke Rogerson
- Werner Reichardt Centre for Integrative Neuroscience (CIN), University of Tübingen, 72076, Tübingen, Germany
| | - Marlly Achury
- Institute for Ophthalmic Research, University of Tübingen, 72076, Tübingen, Germany
| | - Frank Schwede
- BIOLOG Life Science Institute GmbH & Co KG, 28199, Bremen, Germany
| | - Torsten Strasser
- Institute for Ophthalmic Research, University of Tübingen, 72076, Tübingen, Germany
| | - Thomas Euler
- Institute for Ophthalmic Research, University of Tübingen, 72076, Tübingen, Germany.,Werner Reichardt Centre for Integrative Neuroscience (CIN), University of Tübingen, 72076, Tübingen, Germany
| | | | - Vasilica Nache
- Institute of Physiology II, University Hospital Jena, Friedrich Schiller University Jena, 07743, Jena, Germany.
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12
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Xue J, Han Y, Zeng W, Jiang Y. Structural mechanisms of assembly, permeation, gating, and pharmacology of native human rod CNG channel. Neuron 2022; 110:86-95.e5. [PMID: 34699778 PMCID: PMC8738139 DOI: 10.1016/j.neuron.2021.10.006] [Citation(s) in RCA: 20] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2021] [Revised: 09/15/2021] [Accepted: 10/01/2021] [Indexed: 01/07/2023]
Abstract
Mammalian cyclic nucleotide-gated (CNG) channels are nonselective cation channels activated by cGMP or cAMP and play essential roles in the signal transduction of the visual and olfactory sensory systems. CNGA1, the principal component of the CNG channel from rod photoreceptors, can by itself form a functional homotetrameric channel and has been used as the model system in the majority of rod CNG studies. However, the native rod CNG functions as a heterotetramer consisting of three A1 and one B1 subunits and exhibits different functional properties than the CNGA1 homomer. Here we present the functional analysis of human rod CNGA1/B1 heterotetramer and its cryo-EM structures in apo, cGMP-bound, cAMP-bound, and L-cis-Diltiazem-blocked states. These structures, with resolution ranging from 2.6 to 3.3 Å, elucidate the structural mechanisms underlying the 3:1 subunit stoichiometry, the asymmetrical gating upon cGMP activation, and the unique pharmacological property of the native rod CNG channel.
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Affiliation(s)
- Jing Xue
- Howard Hughes Medical Institute and Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas, USA,Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, Texas, USA
| | - Yan Han
- Howard Hughes Medical Institute and Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas, USA,Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, Texas, USA
| | - Weizhong Zeng
- Howard Hughes Medical Institute and Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas, USA,Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, Texas, USA
| | - Youxing Jiang
- Howard Hughes Medical Institute and Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas, USA,Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, Texas, USA,Lead Contact: Youxing Jiang, Ph.D., Department of Physiology, UT Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, Texas 75390-9040, Tel. 214 645-6027; Fax. 214 645-6042;
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13
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Barret DCA, Schertler GFX, Kaupp UB, Marino J. The structure of the native CNGA1/CNGB1 CNG channel from bovine retinal rods. Nat Struct Mol Biol 2022; 29:32-39. [PMID: 34969975 DOI: 10.1038/s41594-021-00700-8] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2021] [Accepted: 11/09/2021] [Indexed: 11/09/2022]
Abstract
In rod photoreceptors of the retina, the cyclic nucleotide-gated (CNG) channel is composed of three CNGA and one CNGB subunits, and it closes in response to light activation to generate an electrical signal that is conveyed to the brain. Here we report the cryo-EM structure of the closed state of the native rod CNG channel isolated from bovine retina. The structure reveals differences between CNGA1 and CNGB1 subunits. Three CNGA1 subunits are tethered at their C terminus by a coiled-coil region. The C-helix in the cyclic nucleotide-binding domain of CNGB1 features a different orientation from that in the three CNGA1 subunits. The arginine residue R994 of CNGB1 reaches into the ionic pathway and blocks the pore, thus introducing an additional gate, which is different from the central hydrophobic gate known from homomeric CNGA channels. These results address the long-standing question of how CNGB1 subunits contribute to the function of CNG channels in visual and olfactory neurons.
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Affiliation(s)
- Diane C A Barret
- Laboratory of Biomolecular Research, Paul Scherrer Institut, Villigen, Switzerland
| | - Gebhard F X Schertler
- Laboratory of Biomolecular Research, Paul Scherrer Institut, Villigen, Switzerland.,Department of Biology, ETH-Zurich, Zurich, Switzerland
| | - U Benjamin Kaupp
- Center for Advanced European Studies and Research (CAESAR), Bonn, Germany.,Life and Medical Sciences Institute LIMES, University of Bonn, Bonn, Germany
| | - Jacopo Marino
- Laboratory of Biomolecular Research, Paul Scherrer Institut, Villigen, Switzerland.
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14
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Structure of the human cone photoreceptor cyclic nucleotide-gated channel. Nat Struct Mol Biol 2022; 29:40-46. [PMID: 34969976 PMCID: PMC8776609 DOI: 10.1038/s41594-021-00699-y] [Citation(s) in RCA: 22] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2021] [Accepted: 11/09/2021] [Indexed: 11/08/2022]
Abstract
Cyclic nucleotide-gated (CNG) channels transduce light-induced chemical signals into electrical signals in retinal cone and rod photoreceptors. Structures of native CNG channels, which are heterotetramers formed by CNGA and CNGB subunits, have not been obtained. In the present study, we report a high-resolution cryo-electron microscopy structure of the human cone CNG channel in the apo closed state. The channel contains three CNGA3 and one CNGB3 subunits. Arg403 in the pore helix of CNGB3 projects into an asymmetric selectivity filter and forms hydrogen bonds with two pore-lining backbone carbonyl oxygens. Arg442 in S6 of CNGB3 protrudes into and occludes the pore below the hydrophobic cavity gate previously observed in homotetrameric CNGA channels. It is interesting that Arg403Gln is a disease mutation, and Arg442 is replaced by glutamine in some animal species with dichromatic or monochromatic vision. These and other unique structural features and the disease link conferred by CNGB3 indicate a critical role of CNGB3 in shaping cone photoresponses.
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15
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Cyclic Nucleotide (cNMP) Analogues: Past, Present and Future. Int J Mol Sci 2021; 22:ijms222312879. [PMID: 34884683 PMCID: PMC8657615 DOI: 10.3390/ijms222312879] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2021] [Revised: 11/22/2021] [Accepted: 11/25/2021] [Indexed: 11/17/2022] Open
Abstract
Cyclic nucleotides are important second messengers involved in cellular events, and analogues of this type of molecules are promising drug candidates. Some cyclic nucleotide analogues have become standard tools for the investigation of biochemical and physiological signal transduction pathways, such as the Rp-diastereomers of adenosine and guanosine 3′,5′-cyclic monophosphorothioate, which are competitive inhibitors of cAMP- and cGMP-dependent protein kinases. Next generation analogues exhibit a higher membrane permeability, increased resistance against degradation, and improved target specificity, or are caged or photoactivatable for fast and/or targeted cellular imaging. Novel specific nucleotide analogues activating or inhibiting cyclic nucleotide-dependent ion channels, EPAC/GEF proteins, and bacterial target molecules have been developed, opening new avenues for basic and applied research. This review provides an overview of the current state of the field, what can be expected in the future and some practical considerations for the use of cyclic nucleotide analogues in biological systems.
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16
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Montell C. Drosophila sensory receptors-a set of molecular Swiss Army Knives. Genetics 2021; 217:1-34. [PMID: 33683373 DOI: 10.1093/genetics/iyaa011] [Citation(s) in RCA: 46] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2020] [Accepted: 11/17/2020] [Indexed: 01/01/2023] Open
Abstract
Genetic approaches in the fruit fly, Drosophila melanogaster, have led to a major triumph in the field of sensory biology-the discovery of multiple large families of sensory receptors and channels. Some of these families, such as transient receptor potential channels, are conserved from animals ranging from worms to humans, while others, such as "gustatory receptors," "olfactory receptors," and "ionotropic receptors," are restricted to invertebrates. Prior to the identification of sensory receptors in flies, it was widely assumed that these proteins function in just one modality such as vision, smell, taste, hearing, and somatosensation, which includes thermosensation, light, and noxious mechanical touch. By employing a vast combination of genetic, behavioral, electrophysiological, and other approaches in flies, a major concept to emerge is that many sensory receptors are multitaskers. The earliest example of this idea was the discovery that individual transient receptor potential channels function in multiple senses. It is now clear that multitasking is exhibited by other large receptor families including gustatory receptors, ionotropic receptors, epithelial Na+ channels (also referred to as Pickpockets), and even opsins, which were formerly thought to function exclusively as light sensors. Genetic characterizations of these Drosophila receptors and the neurons that express them also reveal the mechanisms through which flies can accurately differentiate between different stimuli even when they activate the same receptor, as well as mechanisms of adaptation, amplification, and sensory integration. The insights gleaned from studies in flies have been highly influential in directing investigations in many other animal models.
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Affiliation(s)
- Craig Montell
- Department of Molecular, Cellular, and Developmental Biology, The Neuroscience Research Institute, University of California, Santa Barbara, CA 93106, USA
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17
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CNG channel structure, function, and gating: a tale of conformational flexibility. Pflugers Arch 2021; 473:1423-1435. [PMID: 34357442 DOI: 10.1007/s00424-021-02610-6] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2020] [Revised: 03/10/2021] [Accepted: 03/11/2021] [Indexed: 10/20/2022]
Abstract
Cyclic nucleotide-gated (CNG) channels are key to the signal transduction machinery of certain sensory modalities both in vertebrate and invertebrate organisms. They translate a chemical change in cyclic nucleotide concentration into an electrical signal that can spread through sensory cells. Despite CNG and voltage-gated potassium channels sharing a remarkable amino acid sequence homology and basic architectural plan, their functional properties are dramatically different. While voltage-gated potassium channels are highly selective and require membrane depolarization to open, CNG channels have low ion selectivity and are not very sensitive to voltage. In the last few years, many high-resolution structures of intact CNG channels have been released. This wealth of new structural information has provided enormous progress toward the understanding of the molecular mechanisms and driving forces underpinning CNG channel activation. In this review, we report on the current understanding and controversies surrounding the gating mechanism in CNG channels, as well as the deep intertwining existing between gating, the ion permeation process, and its modulation by membrane voltage. While the existence of this powerful coupling was recognized many decades ago, its direct structural demonstration, and ties to the CNG channel inherent pore flexibility, is a recent achievement.
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18
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Weidinger D, Jovancevic N, Zwanziger D, Theurer S, Hönes J, Führer D, Hatt H. Functional Characterization of Olfactory Receptors in the Thyroid Gland. Front Physiol 2021; 12:676907. [PMID: 34385931 PMCID: PMC8353271 DOI: 10.3389/fphys.2021.676907] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2021] [Accepted: 07/02/2021] [Indexed: 11/13/2022] Open
Abstract
Olfactory receptors (ORs) are almost ubiquitously expressed in the human body. However, information about their functions in these tissues is lacking. To date, no functional characterization of expressed ORs in the human thyroid has been performed. In this study, we detected and compared the expression of OR2H2 and OR2W3 in healthy and malignant cell lines and their corresponding tissues, respectively. We demonstrated that stimulation of ORs by their specific ligand resulted in a transient increase in intracellular calcium and cAMP concentrations. In the case of OR2H2, the downstream signaling cascade analysis revealed that adenylate cyclase (AC) and phosphoinositide phospholipase C (PLC) were involved. Furthermore, OR2H2 and OR2W3 activation affected migration, proliferation, and invasion. These are the first insights that ORs influence physiology-relevant processes in the healthy and malignant thyroid.
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Affiliation(s)
- Daniel Weidinger
- Department of Cell Physiology, Ruhr-University Bochum, Bochum, Germany
| | | | - Denise Zwanziger
- Department of Endocrinology, Diabetes and Metabolism, University Hospital Essen, University of Duisburg-Essen, Essen, Germany
| | - Sarah Theurer
- Institute of Pathology, University Hospital Essen, University of Duisburg-Essen, Essen, Germany
| | - Judith Hönes
- Department of Endocrinology, Diabetes and Metabolism, University Hospital Essen, University of Duisburg-Essen, Essen, Germany
| | - Dagmar Führer
- Department of Endocrinology, Diabetes and Metabolism, University Hospital Essen, University of Duisburg-Essen, Essen, Germany
| | - Hanns Hatt
- Department of Cell Physiology, Ruhr-University Bochum, Bochum, Germany
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19
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Barravecchia I, Demontis GC. HCN1 channels: A versatile tool for signal processing by primary sensory neurons. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2021; 166:133-146. [PMID: 34197835 DOI: 10.1016/j.pbiomolbio.2021.06.009] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/08/2021] [Revised: 06/11/2021] [Accepted: 06/25/2021] [Indexed: 12/20/2022]
Abstract
Most primary sensory neurons (PSNs) generate a slowly-activating inward current in response to membrane hyperpolarization (Ih) and express HCN1 along with additional isoforms coding for hyperpolarization-activated channels (HCN). Changes in HCN expression may affect the excitability and firing patterns of PSNs, but retinal and inner ear PSNs do not fire action potentials, suggesting HCN channel roles may extend beyond excitability and cell firing control. In patients taking Ih blockers, photopsia triggered in response to abrupt changes in luminance correlates with impaired visual signal processing via parallel rod and cone pathways. Furthermore, in a mouse model of inherited retinal degeneration, HCN blockers or Hcn1 genetic ablation may worsen photoreceptors' demise. PSN's use of HCN channels to adjust either their firing rate or process signals generated by sensory transduction in non-spiking PSNs indicates HCN1 channels as a versatile tool with a novel role in sensory processing beyond firing control.
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Affiliation(s)
- Ivana Barravecchia
- Department of Pharmacy, Università di Pisa, Italy, Via Bonanno, 6, 56126, Pisa, Italy; Istitute of Life Science, Scuola Superiore Sant' Anna, 56127, Pisa, Italy.
| | - Gian Carlo Demontis
- Department of Pharmacy, Università di Pisa, Italy, Via Bonanno, 6, 56126, Pisa, Italy.
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20
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Das S, Chen Y, Yan J, Christensen G, Belhadj S, Tolone A, Paquet-Durand F. The role of cGMP-signalling and calcium-signalling in photoreceptor cell death: perspectives for therapy development. Pflugers Arch 2021; 473:1411-1421. [PMID: 33864120 PMCID: PMC8370896 DOI: 10.1007/s00424-021-02556-9] [Citation(s) in RCA: 26] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2020] [Revised: 03/04/2021] [Accepted: 03/10/2021] [Indexed: 12/12/2022]
Abstract
The second messengers, cGMP and Ca2+, have both been implicated in retinal degeneration; however, it is still unclear which of the two is most relevant for photoreceptor cell death. This problem is exacerbated by the close connections and crosstalk between cGMP-signalling and calcium (Ca2+)-signalling in photoreceptors. In this review, we summarize key aspects of cGMP-signalling and Ca2+-signalling relevant for hereditary photoreceptor degeneration. The topics covered include cGMP-signalling targets, the role of Ca2+ permeable channels, relation to energy metabolism, calpain-type proteases, and how the related metabolic processes may trigger and execute photoreceptor cell death. A focus is then put on cGMP-dependent mechanisms and how exceedingly high photoreceptor cGMP levels set in motion cascades of Ca2+-dependent and independent processes that eventually bring about photoreceptor cell death. Finally, an outlook is given into mutation-independent therapeutic approaches that exploit specific features of cGMP-signalling. Such approaches might be combined with suitable drug delivery systems for translation into clinical applications.
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Affiliation(s)
- Soumyaparna Das
- Institute for Ophthalmic Research, University of Tübingen, Elfriede-Aulhorn-Strasse 7, 72076, Tübingen, Germany
| | - Yiyi Chen
- Institute for Ophthalmic Research, University of Tübingen, Elfriede-Aulhorn-Strasse 7, 72076, Tübingen, Germany
| | - Jie Yan
- Institute for Ophthalmic Research, University of Tübingen, Elfriede-Aulhorn-Strasse 7, 72076, Tübingen, Germany
| | - Gustav Christensen
- Institute for Ophthalmic Research, University of Tübingen, Elfriede-Aulhorn-Strasse 7, 72076, Tübingen, Germany
| | - Soumaya Belhadj
- Institute for Ophthalmic Research, University of Tübingen, Elfriede-Aulhorn-Strasse 7, 72076, Tübingen, Germany
| | - Arianna Tolone
- Institute for Ophthalmic Research, University of Tübingen, Elfriede-Aulhorn-Strasse 7, 72076, Tübingen, Germany
| | - François Paquet-Durand
- Institute for Ophthalmic Research, University of Tübingen, Elfriede-Aulhorn-Strasse 7, 72076, Tübingen, Germany.
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21
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The GARP Domain of the Rod CNG Channel's β1-Subunit Contains Distinct Sites for Outer Segment Targeting and Connecting to the Photoreceptor Disk Rim. J Neurosci 2021; 41:3094-3104. [PMID: 33637563 DOI: 10.1523/jneurosci.2609-20.2021] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2020] [Revised: 01/15/2021] [Accepted: 02/18/2021] [Indexed: 11/21/2022] Open
Abstract
Vision begins when light is captured by the outer segment organelle of photoreceptor cells in the retina. Outer segments are modified cilia filled with hundreds of flattened disk-shaped membranes. Disk membranes are separated from the surrounding plasma membrane, and each membrane type has unique protein components. The mechanisms underlying this protein sorting remain entirely unknown. In this study, we investigated the outer segment delivery of the rod cyclic nucleotide-gated (CNG) channel, which is located in the outer segment plasma membrane, where it mediates the electrical response to light. Using Xenopus and mouse models of both sexes, we now show that the targeted delivery of the CNG channel to the outer segment uses the conventional secretory pathway, including protein processing in both ER and Golgi, and requires preassembly of its constituent α1 and β1 subunits. We further demonstrate that the N-terminal glutamic acid-rich protein (GARP) domain of CNGβ1 contains two distinct functional regions. The glutamic acid-rich region encodes specific information targeting the channel to rod outer segments. The adjacent proline-enriched region connects the CNG channel to photoreceptor disk rims, likely through an interaction with peripherin-2. These data reveal fine functional specializations within the structural domains of the CNG channel and suggest that its sequestration to the outer segment plasma membrane requires an interaction with peripherin-2.SIGNIFICANCE STATEMENT Neurons and other differentiated cells have a remarkable ability to deliver and organize signaling proteins at precise subcellular locations. We now report that the CNG channel, mediating the electrical response to light in rod photoreceptors, contains two specialized regions within the N terminus of its β-subunit: one responsible for delivery of this channel to the ciliary outer segment organelle and another for subsequent channel sequestration into the outer segment plasma membrane. These findings expand our understanding of the molecular specializations used by neurons to populate their critical functional compartments.
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22
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Structural mechanisms of gating and selectivity of human rod CNGA1 channel. Neuron 2021; 109:1302-1313.e4. [PMID: 33651975 DOI: 10.1016/j.neuron.2021.02.007] [Citation(s) in RCA: 30] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2020] [Revised: 01/22/2021] [Accepted: 02/03/2021] [Indexed: 11/22/2022]
Abstract
Mammalian cyclic nucleotide-gated (CNG) channels play an essential role in the signal transduction of the visual and olfactory sensory systems. Here we reveal the structural mechanism of ligand gating in human rod CNGA1 channel by determining its cryo-EM structures in both the apo closed and cGMP-bound open states. Distinct from most other members of voltage-gated tetrameric cation channels, CNGA1 forms a central channel gate in the middle of the membrane, occluding the central cavity. Structural analyses of ion binding profiles in the selectivity filters of the wild-type channel and the E365Q filter mutant allow us to unambiguously define the two Ca2+ binding sites inside the selectivity filter, providing structural insights into Ca2+ blockage and permeation in CNG channels. The structure of the E365Q mutant also reveals two alternative side-chain conformations at Q365, providing a plausible explanation for the voltage-dependent gating of CNG channel acquired upon E365 mutation.
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23
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Raka RN, Wu H, Xiao J, Hossen I, Cao Y, Huang M, Jin J. Human ectopic olfactory receptors and their food originated ligands: a review. Crit Rev Food Sci Nutr 2021; 62:5424-5443. [PMID: 33605814 DOI: 10.1080/10408398.2021.1885007] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Ectopic olfactory receptors (EORs) are expressed in non-nasal tissues of human body. They belong to the G-protein coupled receptor (GPCR) superfamily. EORs may not be capable of differentiating odorants as nasal olfactory receptors (ORs), but still can be triggered by odorants and are involved in different biological processes such as anti-inflammation, energy metabolism, apoptosis etc. Consumption of strong flavored foods like celery, oranges, onions, and spices, is a good aid to attenuate inflammation and boost our immune system. During the digestion of these foods in human digestive system and the metabolization by gut microbiota, the odorants closely interacting with EORs, may play important roles in various bio-functions like serotonin release, appetite regulation etc., and ultimately impact health and diseases. Thus, EORs could be a potential target linking the ligands from food and their bioactivities. There have been related studies in different research fields of medicine and physiology, but still no systematic food oriented review. Our review portrays that EORs could be a potential target for functional food development. In this review, we summarized the EORs found in human tissues, their impacts on health and disease, ligands interacting with EORs exerting specific biological effects, and the mechanisms involved.
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Affiliation(s)
- Rifat Nowshin Raka
- Beijing Technology and Business University, Beijing, China.,Key Laboratory of Brewing Molecular Engineering of China Light Industry, Beijing, China.,Beijing Engineering and Technology Research Center of Food Additives, Beijing, China.,Beijing Laboratory for Food Quality and Safety, Beijing, China.,Beijing Advanced Innovation Center for Food Nutrition and Human Health, Beijing, China
| | - Hua Wu
- Beijing Technology and Business University, Beijing, China.,Key Laboratory of Brewing Molecular Engineering of China Light Industry, Beijing, China.,Beijing Key Lab of Plant Resource Research and Development, Beijing, China
| | - Junsong Xiao
- Beijing Technology and Business University, Beijing, China.,Key Laboratory of Brewing Molecular Engineering of China Light Industry, Beijing, China.,Beijing Engineering and Technology Research Center of Food Additives, Beijing, China.,Beijing Laboratory for Food Quality and Safety, Beijing, China.,Beijing Advanced Innovation Center for Food Nutrition and Human Health, Beijing, China
| | - Imam Hossen
- Beijing Technology and Business University, Beijing, China.,Key Laboratory of Brewing Molecular Engineering of China Light Industry, Beijing, China.,Beijing Engineering and Technology Research Center of Food Additives, Beijing, China.,Beijing Laboratory for Food Quality and Safety, Beijing, China.,Beijing Advanced Innovation Center for Food Nutrition and Human Health, Beijing, China
| | - Yanping Cao
- Beijing Technology and Business University, Beijing, China.,Beijing Engineering and Technology Research Center of Food Additives, Beijing, China
| | - Mingquan Huang
- Beijing Technology and Business University, Beijing, China.,Key Laboratory of Brewing Molecular Engineering of China Light Industry, Beijing, China
| | - Jianming Jin
- Beijing Technology and Business University, Beijing, China.,Beijing Key Lab of Plant Resource Research and Development, Beijing, China
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24
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Bang J, Zippin JH. Cyclic adenosine monophosphate (cAMP) signaling in melanocyte pigmentation and melanomagenesis. Pigment Cell Melanoma Res 2020; 34:28-43. [PMID: 32777162 DOI: 10.1111/pcmr.12920] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2020] [Revised: 07/24/2020] [Accepted: 08/07/2020] [Indexed: 12/12/2022]
Abstract
The second messenger cyclic adenosine monophosphate (cAMP) regulates numerous functions in both benign melanocytes and melanoma cells. cAMP is generated from two distinct sources, transmembrane and soluble adenylyl cyclases (tmAC and sAC, respectively), and is degraded by a family of proteins called phosphodiesterases (PDEs). cAMP signaling can be regulated in many different ways and can lead to varied effects in melanocytes. It was recently revealed that distinct cAMP signaling pathways regulate pigmentation by either altering pigment gene expression or the pH of melanosomes. In the context of melanoma, many studies report seemingly contradictory roles for cAMP in tumorigenesis. For example, cAMP signaling has been implicated in both cancer promotion and suppression, as well as both therapy resistance and sensitization. This conundrum in the field may be explained by the fact that cAMP signals in discrete microdomains and each microdomain can mediate differential cellular functions. Here, we review the role of cAMP signaling microdomains in benign melanocyte biology, focusing on pigmentation, and in melanomagenesis.
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Affiliation(s)
- Jakyung Bang
- Department of Dermatology, Joan and Sanford I. Weill Medical College of Cornell University, New York, NY, USA
| | - Jonathan H Zippin
- Department of Dermatology, Joan and Sanford I. Weill Medical College of Cornell University, New York, NY, USA
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25
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Zheng X, Fu Z, Su D, Zhang Y, Li M, Pan Y, Li H, Li S, Grassucci RA, Ren Z, Hu Z, Li X, Zhou M, Li G, Frank J, Yang J. Mechanism of ligand activation of a eukaryotic cyclic nucleotide-gated channel. Nat Struct Mol Biol 2020; 27:625-634. [PMID: 32483338 PMCID: PMC7354226 DOI: 10.1038/s41594-020-0433-5] [Citation(s) in RCA: 33] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2020] [Accepted: 04/10/2020] [Indexed: 01/21/2023]
Abstract
Cyclic nucleotide-gated (CNG) channels convert cyclic nucleotide (CN) binding and unbinding into electrical signals in sensory receptors and neurons. The molecular conformational changes underpinning ligand activation are largely undefined. We report both closed- and open-state atomic cryo-EM structures of a full-length Caenorhabditis elegans cyclic GMP-activated channel TAX-4, reconstituted in lipid nanodiscs. These structures, together with computational and functional analyses and a mutant channel structure, reveal a double-barrier hydrophobic gate formed by two S6 amino acids in the central cavity. cGMP binding produces global conformational changes that open the cavity gate located ~52 Å away but do not alter the structure of the selectivity filter-the commonly presumed activation gate. Our work provides mechanistic insights into the allosteric gating and regulation of CN-gated and nucleotide-modulated channels and CNG channel-related channelopathies.
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Affiliation(s)
- Xiangdong Zheng
- Department of Biological Sciences, Columbia University, New York, NY 10027, USA,These authors contributed equally to this work
| | - Ziao Fu
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA,These authors contributed equally to this work
| | - Deyuan Su
- Key Laboratory of Animal Models and Human Disease Mechanisms of Chinese Academy of Sciences/Key Laboratory of Bioactive Peptides of Yunnan Province, Chinese Academy of Sciences, Kunming 650223, China,These authors contributed equally to this work
| | - Yuebin Zhang
- State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China
| | - Minghui Li
- Department of Biological Sciences, Columbia University, New York, NY 10027, USA,Current address: HIT Center for Life Sciences, School of Life Science and Technology, Harbin Institute of Technology, Harbin 150001, China
| | - Yaping Pan
- Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX 77030, USA
| | - Huan Li
- Department of Biological Sciences, Columbia University, New York, NY 10027, USA
| | - Shufang Li
- Department of Biological Sciences, Columbia University, New York, NY 10027, USA,Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
| | - Robert A. Grassucci
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
| | - Zhenning Ren
- Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX 77030, USA
| | - Zhengshan Hu
- Department of Biological Sciences, Columbia University, New York, NY 10027, USA
| | - Xueming Li
- Beijing Advanced Innovation Center for Structural Biology, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - Ming Zhou
- Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX 77030, USA
| | - Guohui Li
- State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China
| | - Joachim Frank
- Department of Biological Sciences, Columbia University, New York, NY 10027, USA,Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
| | - Jian Yang
- Department of Biological Sciences, Columbia University, New York, NY 10027, USA,Key Laboratory of Animal Models and Human Disease Mechanisms of Chinese Academy of Sciences/Key Laboratory of Bioactive Peptides of Yunnan Province, Chinese Academy of Sciences, Kunming 650223, China
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26
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Activation of Rod Input in a Model of Retinal Degeneration Reverses Retinal Remodeling and Induces Formation of Functional Synapses and Recovery of Visual Signaling in the Adult Retina. J Neurosci 2019; 39:6798-6810. [PMID: 31285302 DOI: 10.1523/jneurosci.2902-18.2019] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2018] [Revised: 05/28/2019] [Accepted: 06/18/2019] [Indexed: 12/31/2022] Open
Abstract
A major cause of human blindness is the death of rod photoreceptors. As rods degenerate, synaptic structures between rod and rod bipolar cells disappear and the rod bipolar cells extend their dendrites and occasionally make aberrant contacts. Such changes are broadly observed in blinding disorders caused by photoreceptor cell death and are thought to occur in response to deafferentation. How the remodeled retinal circuit affects visual processing following rod rescue is not known. To address this question, we generated male and female transgenic mice wherein a disrupted cGMP-gated channel (CNG) gene can be repaired at the endogenous locus and at different stages of degeneration by tamoxifen-inducible cre-mediated recombination. In normal rods, light-induced closure of CNG channels leads to hyperpolarization of the cell, reducing neurotransmitter release at the synapse. Similarly, rods lacking CNG channels exhibit a resting membrane potential that was ~10 mV hyperpolarized compared to WT rods, indicating diminished glutamate release. Retinas from these mice undergo stereotypic retinal remodeling as a consequence of rod malfunction and degeneration. Upon tamoxifen-induced expression of CNG channels, rods recovered their structure and exhibited normal light responses. Moreover, we show that the adult mouse retina displays a surprising degree of plasticity upon activation of rod input. Wayward bipolar cell dendrites establish contact with rods to support normal synaptic transmission, which is propagated to the retinal ganglion cells. These findings demonstrate remarkable plasticity extending beyond the developmental period and support efforts to repair or replace defective rods in patients blinded by rod degeneration.SIGNIFICANCE STATEMENT Current strategies for treatment of neurodegenerative disorders are focused on the repair of the primary affected cell type. However, the defective neurons function within a complex neural circuitry, which also becomes degraded during disease. It is not known whether rescued neurons and the remodeled circuit will establish communication to regain normal function. We show that the adult mammalian neural retina exhibits a surprising degree of plasticity following rescue of rod photoreceptors. The wayward dendrites of rod bipolar cells re-establish contact with rods to support normal synaptic transmission, which is propagated to the retinal ganglion cells. These findings support efforts to repair or replace defective rods in patients blinded by rod cell loss.
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27
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Clinical findings of end-stage retinitis pigmentosa with a homozygous PDE6A variant (p.R653X). Am J Ophthalmol Case Rep 2018; 13:110-115. [PMID: 30619975 PMCID: PMC6307093 DOI: 10.1016/j.ajoc.2018.12.019] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2018] [Revised: 11/24/2018] [Accepted: 12/17/2018] [Indexed: 12/16/2022] Open
Abstract
Purpose To report clinical and genetic features of a Japanese patient with end-stage retinitis pigmentosa (RP) caused by a homozygous PDE6A variant. Methods We performed comprehensive ophthalmic examinations. Whole exome sequencing analysis was used to investigate the RP patient with parental consanguinity. The pedigree included 4 RP patients in the two generations, which suggests presumed pseudo-autosomal dominant inheritance. Results A PDE6A variant (p.R653X) was identified to be homozygous and disease-causing in the patient. Homozygosity mapping revealed the homozygous region including the variant and confirmation of autosomal recessive inheritance. The patient reported night blindness at 4 years of age and exhibited typical RP fundus appearance with macula involvement during the follow-up period from at the age of 52–69 years. At the age of 52, the patient exhibited a loss of visual acuity and had severely constricted visual fields, with a further gradual deterioration of her vision until she was 69 years old. At the age of 69, funduscopy showed severe chorioretinal degeneration in the area from the posterior pole to the peripheral retina. Conclusions and Importance This is the first report that the PDE6A variant (p.R653X) has been identified as one of the causes of autosomal recessive RP in the Japanese population. Longitudinal natural history/end-stage findings demonstrated early-onset and a severe RP phenotype with macula involvement when the patient was in her 50s and severe chorioretinal degenerations in her late 60s.
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Maßberg D, Hatt H. Human Olfactory Receptors: Novel Cellular Functions Outside of the Nose. Physiol Rev 2018; 98:1739-1763. [PMID: 29897292 DOI: 10.1152/physrev.00013.2017] [Citation(s) in RCA: 126] [Impact Index Per Article: 21.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Olfactory receptors (ORs) are not exclusively expressed in the olfactory sensory neurons; they are also observed outside of the olfactory system in all other human tissues tested to date, including the testis, lung, intestine, skin, heart, and blood. Within these tissues, certain ORs have been determined to be exclusively expressed in only one tissue, whereas other ORs are more widely distributed in many different tissues throughout the human body. For most of the ectopically expressed ORs, limited data are available for their functional roles. They have been shown to be involved in the modulation of cell-cell recognition, migration, proliferation, the apoptotic cycle, exocytosis, and pathfinding processes. Additionally, there is a growing body of evidence that they have the potential to serve as diagnostic and therapeutic tools, as ORs are highly expressed in different cancer tissues. Interestingly, in addition to the canonical signaling pathways activated by ORs in olfactory sensory neurons, alternative pathways have been demonstrated in nonolfactory tissues. In this review, the existing data concerning the expression, as well as the physiological and pathophysiological functions, of ORs outside of the nose are highlighted to provide insights into future lines of research.
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Affiliation(s)
- Désirée Maßberg
- Ruhr-University Bochum, Department of Cell Physiology , Bochum , Germany
| | - Hanns Hatt
- Ruhr-University Bochum, Department of Cell Physiology , Bochum , Germany
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29
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Hydrophobic alkyl chains substituted to the 8-position of cyclic nucleotides enhance activation of CNG and HCN channels by an intricate enthalpy - entropy compensation. Sci Rep 2018; 8:14960. [PMID: 30297855 PMCID: PMC6175941 DOI: 10.1038/s41598-018-33050-5] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2018] [Accepted: 09/19/2018] [Indexed: 01/01/2023] Open
Abstract
Cyclic nucleotide-gated (CNG) and hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are tetrameric non-specific cation channels in the plasma membrane that are activated by either cAMP or cGMP binding to specific binding domains incorporated in each subunit. Typical apparent affinities of these channels for these cyclic nucleotides range from several hundred nanomolar to tens of micromolar. Here we synthesized and characterized novel cAMP and cGMP derivatives by substituting either hydrophobic alkyl chains or similar-sized more hydrophilic heteroalkyl chains to the 8-position of the purine ring with the aim to obtain full agonists of higher potency. The compounds were tested in homotetrameric CNGA2, heterotetrameric CNGA2:CNGA4:CNGB1b and homotetrameric HCN2 channels. We show that nearly all compounds are full agonists and that longer alkyl chains systematically increase the apparent affinity, at the best more than 30 times. The effects are stronger in CNG than HCN2 channels which, however, are constitutively more sensitive to cAMP. Kinetic analyses reveal that the off-rate is significantly slowed by the hydrophobic alkyl chains. Molecular dynamics simulations and free energy calculations suggest that an intricate enthalpy - entropy compensation underlies the higher apparent affinity of the derivatives with the longer alkyl chains, which is shown to result from a reduced loss of configurational entropy upon binding.
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30
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Rheinberger J, Gao X, Schmidpeter PA, Nimigean CM. Ligand discrimination and gating in cyclic nucleotide-gated ion channels from apo and partial agonist-bound cryo-EM structures. eLife 2018; 7:39775. [PMID: 30028291 PMCID: PMC6093708 DOI: 10.7554/elife.39775] [Citation(s) in RCA: 37] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2018] [Accepted: 07/19/2018] [Indexed: 12/11/2022] Open
Abstract
Cyclic nucleotide-modulated channels have important roles in visual signal transduction and pacemaking. Binding of cyclic nucleotides (cAMP/cGMP) elicits diverse functional responses in different channels within the family despite their high sequence and structure homology. The molecular mechanisms responsible for ligand discrimination and gating are unknown due to lack of correspondence between structural information and functional states. Using single particle cryo-electron microscopy and single-channel recording, we assigned functional states to high-resolution structures of SthK, a prokaryotic cyclic nucleotide-gated channel. The structures for apo, cAMP-bound, and cGMP-bound SthK in lipid nanodiscs, correspond to no, moderate, and low single-channel activity, respectively, consistent with the observation that all structures are in resting, closed states. The similarity between apo and ligand-bound structures indicates that ligand-binding domains are strongly coupled to pore and SthK gates in an allosteric, concerted fashion. The different orientations of cAMP and cGMP in the ‘resting’ and ‘activated’ structures suggest a mechanism for ligand discrimination. Ion channels are essential for transmitting signals in the nervous system and brain. One large group of ion channels includes members that are activated by cyclic nucleotides, small molecules used to transmit signals within cells. These cyclic nucleotide-gated channels play an important role in regulating our ability to see and smell. The activity of these ion channels has been studied for years, but scientists have only recently been able to look into their structure. Since structural biology methods require purified, well-behaved proteins, the members of this ion channel family selected for structural studies do not necessarily match those whose activity has been well established. There is a need for a good model that would allow both the structure and activity of a cyclic nucleotide-gated ion channel to be characterized. The cyclic nucleotide-gated ion channel, SthK, from bacteria called Spirochaeta thermophila, was identified as such model because both its activity and its structure are accessible. Rheinberger et al. have used cryo electron microscopy to solve several high-resolution structures of SthK channels. In two of the structures, SthK was bound to either one of two types of activating cyclic nucleotides – cAMP or cGMP – and in another structure, no cyclic nucleotides were bound. Separately recording the activity of individual channels allowed the activity states likely to be represented by these structures to be identified. Combining the results of the experiments revealed no activity from channels in an unbound state, low levels of activity for channels bound to cGMP, and moderate activity for channels bound to cAMP. Rheinberger et al. show that the channel, under the conditions experienced in cryo electron microscopy, is closed in all of the states studied. Unexpectedly, the binding of cyclic nucleotides produced no structural change even in the cyclic nucleotide-binding pocket of the channel, a region that was previously observed to undergo such changes when this region alone was crystallized. Rheinberger et al. deduce from this that the four subunits that make up the channel likely undergo the conformational change towards an open state all at once, rather than one by one. The structures and the basic functional characterization of SthK channels provide a strong starting point for future research into determining the entire opening and closing cycle for a cyclic nucleotide-gated channel. Human equivalents of the channel are likely to work in similar ways. The results presented by Rheinberger et al. could therefore be built upon to help address diseases that result from deficiencies in cyclic nucleotide-gated channels, such as loss of vision due to retinal degradation (retinitis pigmentosa or progressive cone dystrophy) and achromatopsia.
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Affiliation(s)
- Jan Rheinberger
- Departments of Anesthesiology, Weill Cornell Medical College, New York, United States
| | - Xiaolong Gao
- Departments of Anesthesiology, Weill Cornell Medical College, New York, United States
| | | | - Crina M Nimigean
- Departments of Anesthesiology, Weill Cornell Medical College, New York, United States.,Department of Physiology and Biophysics, Weill Cornell Medical College, New York, United States.,Department of Biochemistry, Weill Cornell Medical College, New York, United States
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31
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Schmidpeter PAM, Gao X, Uphadyay V, Rheinberger J, Nimigean CM. Ligand binding and activation properties of the purified bacterial cyclic nucleotide-gated channel SthK. J Gen Physiol 2018; 150:821-834. [PMID: 29752414 PMCID: PMC5987880 DOI: 10.1085/jgp.201812023] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2018] [Accepted: 04/09/2018] [Indexed: 11/20/2022] Open
Abstract
SthK is a bacterial cyclic nucleotide–gated ion channel from Spirochaeta thermophila. By optimizing the expression and purification of SthK, Schmidpeter et al. show that cAMP and cGMP bind to the channel with similar affinity but activate it with different efficacy. Cyclic nucleotide–modulated ion channels play several essential physiological roles. They are involved in signal transduction in photoreceptors and olfactory sensory neurons as well as pacemaking activity in the heart and brain. Investigations of the molecular mechanism of their actions, including structural and electrophysiological characterization, are restricted by the availability of stable, purified protein obtained from accessible systems. Here, we establish that SthK, a cyclic nucleotide–gated (CNG) channel from Spirochaeta thermophila, is an excellent model for investigating the gating of eukaryotic CNG channels at the molecular level. The channel has high sequence similarity with its eukaryotic counterparts and was previously reported to be activated by cyclic nucleotides in patch-clamp experiments with Xenopus laevis oocytes. We optimized protein expression and purification to obtain large quantities of pure, homogeneous, and active recombinant SthK protein from Escherichia coli. A negative-stain electron microscopy (EM) single-particle analysis indicated that this channel is a promising candidate for structural studies with cryo-EM. Using radioactivity and fluorescence flux assays, as well as single-channel recordings in lipid bilayers, we show that the protein is partially activated by micromolar concentrations of cyclic adenosine monophosphate (cAMP) and that channel activity is increased by depolarization. Unlike previous studies, we find that cyclic guanosine monophosphate (cGMP) is also able to activate SthK, but with much lower efficiency than cAMP. The distinct sensitivities to different ligands resemble eukaryotic CNG and hyperpolarization-activated and cyclic nucleotide–modulated channels. Using a fluorescence binding assay, we show that cGMP and cAMP bind to SthK with similar apparent affinities, suggesting that the large difference in channel activation by cAMP or cGMP is caused by the efficacy with which each ligand promotes the conformational changes toward the open state. We conclude that the functional characteristics of SthK reported here will permit future studies to analyze ligand gating and discrimination in CNG channels.
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Affiliation(s)
| | - Xiaolong Gao
- Department of Anesthesiology, Weill Cornell Medicine, New York, NY
| | - Vikrant Uphadyay
- Department of Anesthesiology, Weill Cornell Medicine, New York, NY
| | - Jan Rheinberger
- Department of Anesthesiology, Weill Cornell Medicine, New York, NY
| | - Crina M Nimigean
- Department of Anesthesiology, Weill Cornell Medicine, New York, NY .,Department of Biochemistry, Weill Cornell Medicine, New York, NY.,Department of Physiology and Biophysics, Weill Cornell Medicine, New York, NY
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32
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Mazzolini M, Arcangeletti M, Marchesi A, Napolitano LMR, Grosa D, Maity S, Anselmi C, Torre V. The gating mechanism in cyclic nucleotide-gated ion channels. Sci Rep 2018; 8:45. [PMID: 29311674 PMCID: PMC5758780 DOI: 10.1038/s41598-017-18499-0] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2017] [Accepted: 12/04/2017] [Indexed: 11/09/2022] Open
Abstract
Cyclic nucleotide-gated (CNG) channels mediate transduction in several sensory neurons. These channels use the free energy of CNs' binding to open the pore, a process referred to as gating. CNG channels belong to the superfamily of voltage-gated channels, where the motion of the α-helix S6 controls gating in most of its members. To date, only the open, cGMP-bound, structure of a CNG channel has been determined at atomic resolution, which is inadequate to determine the molecular events underlying gating. By using electrophysiology, site-directed mutagenesis, chemical modification, and Single Molecule Force Spectroscopy, we demonstrate that opening of CNGA1 channels is initiated by the formation of salt bridges between residues in the C-linker and S5 helix. These events trigger conformational changes of the α-helix S5, transmitted to the P-helix and leading to channel opening. Therefore, the superfamily of voltage-gated channels shares a similar molecular architecture but has evolved divergent gating mechanisms.
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Affiliation(s)
- Monica Mazzolini
- International School for Advanced Studies, Trieste, 34136, Italy.
| | | | - Arin Marchesi
- INSERM U1006, Aix-Marseille Université, Parc Scientifique et Technologique de Luminy, Marseille, 13009, France
| | - Luisa M R Napolitano
- International School for Advanced Studies, Trieste, 34136, Italy
- Structural Biology Laboratory, Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Trieste, 34149, Italy
| | - Debora Grosa
- International School for Advanced Studies, Trieste, 34136, Italy
| | - Sourav Maity
- International School for Advanced Studies, Trieste, 34136, Italy
| | - Claudio Anselmi
- National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland, 20892, USA
| | - Vincent Torre
- International School for Advanced Studies, Trieste, 34136, Italy.
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33
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James ZM, Zagotta WN. Structural insights into the mechanisms of CNBD channel function. J Gen Physiol 2017; 150:225-244. [PMID: 29233886 PMCID: PMC5806680 DOI: 10.1085/jgp.201711898] [Citation(s) in RCA: 64] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2017] [Accepted: 11/28/2017] [Indexed: 12/28/2022] Open
Abstract
James and Zagotta discuss how recent cryoEM structures inform our understanding of cyclic nucleotide–binding domain channels. Cyclic nucleotide-binding domain (CNBD) channels are a family of ion channels in the voltage-gated K+ channel superfamily that play crucial roles in many physiological processes. CNBD channels are structurally similar but functionally very diverse. This family includes three subfamilies: (1) the cyclic nucleotide-gated (CNG) channels, which are cation-nonselective, voltage-independent, and cyclic nucleotide-gated; (2) the hyperpolarization-activated cyclic nucleotide-gated (HCN) channels, which are weakly K+ selective, hyperpolarization-activated, and cyclic nucleotide-gated; and (3) the ether-à-go-go-type (KCNH) channels, which are strongly K+ selective, depolarization-activated, and cyclic nucleotide-independent. Recently, several high-resolution structures have been reported for intact CNBD channels, providing a structural framework to better understand their diverse function. In this review, we compare and contrast the recent structures and discuss how they inform our understanding of ion selectivity, voltage-dependent gating, and cyclic nucleotide–dependent gating within this channel family.
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Affiliation(s)
- Zachary M James
- Department of Physiology and Biophysics, University of Washington, Seattle, WA
| | - William N Zagotta
- Department of Physiology and Biophysics, University of Washington, Seattle, WA
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34
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Maity S, Ilieva N, Laio A, Torre V, Mazzolini M. New views on phototransduction from atomic force microscopy and single molecule force spectroscopy on native rods. Sci Rep 2017; 7:12000. [PMID: 28931892 PMCID: PMC5607320 DOI: 10.1038/s41598-017-11912-8] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2017] [Accepted: 08/25/2017] [Indexed: 12/11/2022] Open
Abstract
By combining atomic force microscopy (AFM) imaging and single-molecule force spectroscopy (SMFS), we analyzed membrane proteins of the rod outer segments (OS). With this combined approach we were able to study the membrane proteins in their natural environment. In the plasma membrane we identified native cyclic nucleotide-gated (CNG) channels which are organized in single file strings. We also identified rhodopsin located both in the discs and in the plasma membrane. SMFS reveals strikingly different mechanical properties of rhodopsin unfolding in the two environments. Molecular dynamic simulations suggest that this difference is likely to be related to the higher hydrophobicity of the plasma membrane, due to the higher cholesterol concentration. This increases rhodopsin mechanical stability lowering the rate of transition towards its active form, hindering, in this manner, phototransduction.
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Affiliation(s)
- Sourav Maity
- International School for Advanced Studies (SISSA-ISAS) via Bonomea 265, 34136, Trieste, Italy
| | - Nina Ilieva
- International School for Advanced Studies (SISSA-ISAS) via Bonomea 265, 34136, Trieste, Italy
| | - Alessandro Laio
- International School for Advanced Studies (SISSA-ISAS) via Bonomea 265, 34136, Trieste, Italy
| | - Vincent Torre
- International School for Advanced Studies (SISSA-ISAS) via Bonomea 265, 34136, Trieste, Italy.
| | - Monica Mazzolini
- International School for Advanced Studies (SISSA-ISAS) via Bonomea 265, 34136, Trieste, Italy.
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35
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Rose K, Walston ST, Chen J. Separation of photoreceptor cell compartments in mouse retina for protein analysis. Mol Neurodegener 2017; 12:28. [PMID: 28399904 PMCID: PMC5387348 DOI: 10.1186/s13024-017-0171-2] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2016] [Accepted: 03/30/2017] [Indexed: 02/02/2023] Open
Abstract
BACKGROUND Light exposure triggers movement of certain signaling proteins within the cellular compartments of the highly polarized rod photoreceptor cell. This redistribution of proteins between the inner and outer segment compartments affects the performance and physiology of the rod cell. In addition, newly synthesized phototransduction proteins traverse from the site of their synthesis in the inner segment, through the thin connecting cilium, to reach their destination in the outer segment. Processes that impede normal trafficking of these abundant proteins lead to cell death. The study of movement and unique localization of biomolecules within the different compartments of the rod cell would be greatly facilitated by techniques that reliably separate these compartments. Ideally, these methods can be applied to the mouse retina due to the widespread usage of transgenic mouse models in the investigation of basic visual processes and disease mechanisms that affect vision. Although the retina is organized in distinct layers, the small and highly curved mouse retina makes physical separation of retinal layers a challenge. We introduce two peeling methods that efficiently and reliably isolate the rod outer segment and other cell compartments for Western blots to examine protein movement across these compartments. METHODS The first separation method employs Whatman® filter paper to successively remove the rod outer segments from isolated, live mouse retinas. The second method utilizes ScotchTM tape to peel the rod outer segment layer and the rod inner segment layer from lyophilized mouse retinas. Both procedures can be completed within one hour. RESULTS We utilize these two protocols on dark-adapted and light-exposed retinas of C57BL/6 mice and subject the isolated tissue layers to Western blots to demonstrate their effectiveness in detecting light-induced translocation of transducin (GNAT1) and rod arrestin (ARR1). Furthermore, we provide evidence that RGS9 does not undergo light-induced translocation. CONCLUSIONS These results demonstrate the effectiveness of the two different peeling protocols for the separation of the layered compartments of the mouse retina and their utility for investigations of protein compositions within these compartments.
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Affiliation(s)
- Kasey Rose
- Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California, USA
| | - Steven T Walston
- Department of Biomedical Engineering, Viterbi School of Engineering, University of Southern California, Los Angeles, California, USA
| | - Jeannie Chen
- Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California, USA. .,Department of Cell & Neurobiology, Keck School of Medicine, University of Southern California, Los Angeles, California, USA.
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36
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Li M, Zhou X, Wang S, Michailidis I, Gong Y, Su D, Li H, Li X, Yang J. Structure of a eukaryotic cyclic-nucleotide-gated channel. Nature 2017; 542:60-65. [PMID: 28099415 DOI: 10.1038/nature20819] [Citation(s) in RCA: 99] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2016] [Accepted: 11/23/2016] [Indexed: 12/11/2022]
Abstract
Cyclic-nucleotide-gated channels are essential for vision and olfaction. They belong to the voltage-gated ion channel superfamily but their activities are controlled by intracellular cyclic nucleotides instead of transmembrane voltage. Here we report a 3.5-Å-resolution single-particle electron cryo-microscopy structure of a cyclic-nucleotide-gated channel from Caenorhabditis elegans in the cyclic guanosine monophosphate (cGMP)-bound open state. The channel has an unusual voltage-sensor-like domain, accounting for its deficient voltage dependence. A carboxy-terminal linker connecting S6 and the cyclic-nucleotide-binding domain interacts directly with both the voltage-sensor-like domain and the pore domain, forming a gating ring that couples conformational changes triggered by cyclic nucleotide binding to the gate. The selectivity filter is lined by the carboxylate side chains of a functionally important glutamate and three rings of backbone carbonyls. This structure provides a new framework for understanding mechanisms of ion permeation, gating and channelopathy of cyclic-nucleotide-gated channels and cyclic nucleotide modulation of related channels.
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Affiliation(s)
- Minghui Li
- Department of Biological Sciences, Columbia University, New York, New York 10027, USA
| | - Xiaoyuan Zhou
- Beijing Advanced Innovation Center for Structural Biology, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - Shu Wang
- Key Laboratory of Animal Models and Human Disease Mechanisms of the Chinese Academy of Sciences, Chinese Academy of Sciences, Kunming 650223, China.,Key Laboratory of Bioactive Peptides of Yunnan Province, Chinese Academy of Sciences, Kunming 650223, China.,Ion Channel Research and Drug Development Center, Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming 650223, China.,Kunming College of Life Science, University of Chinese Academy of Sciences, Kunming 650204, China
| | - Ioannis Michailidis
- Department of Biological Sciences, Columbia University, New York, New York 10027, USA
| | - Ye Gong
- Key Laboratory of Animal Models and Human Disease Mechanisms of the Chinese Academy of Sciences, Chinese Academy of Sciences, Kunming 650223, China.,Key Laboratory of Bioactive Peptides of Yunnan Province, Chinese Academy of Sciences, Kunming 650223, China.,Ion Channel Research and Drug Development Center, Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming 650223, China
| | - Deyuan Su
- Key Laboratory of Animal Models and Human Disease Mechanisms of the Chinese Academy of Sciences, Chinese Academy of Sciences, Kunming 650223, China.,Key Laboratory of Bioactive Peptides of Yunnan Province, Chinese Academy of Sciences, Kunming 650223, China.,Ion Channel Research and Drug Development Center, Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming 650223, China.,Kunming College of Life Science, University of Chinese Academy of Sciences, Kunming 650204, China
| | - Huan Li
- Key Laboratory of Animal Models and Human Disease Mechanisms of the Chinese Academy of Sciences, Chinese Academy of Sciences, Kunming 650223, China.,Key Laboratory of Bioactive Peptides of Yunnan Province, Chinese Academy of Sciences, Kunming 650223, China.,Ion Channel Research and Drug Development Center, Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming 650223, China.,Kunming College of Life Science, University of Chinese Academy of Sciences, Kunming 650204, China
| | - Xueming Li
- Beijing Advanced Innovation Center for Structural Biology, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - Jian Yang
- Department of Biological Sciences, Columbia University, New York, New York 10027, USA.,Key Laboratory of Animal Models and Human Disease Mechanisms of the Chinese Academy of Sciences, Chinese Academy of Sciences, Kunming 650223, China.,Key Laboratory of Bioactive Peptides of Yunnan Province, Chinese Academy of Sciences, Kunming 650223, China.,Ion Channel Research and Drug Development Center, Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming 650223, China
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37
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Lee CH, MacKinnon R. Structures of the Human HCN1 Hyperpolarization-Activated Channel. Cell 2017; 168:111-120.e11. [PMID: 28086084 DOI: 10.1016/j.cell.2016.12.023] [Citation(s) in RCA: 259] [Impact Index Per Article: 37.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2016] [Revised: 11/29/2016] [Accepted: 12/15/2016] [Indexed: 01/23/2023]
Abstract
Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels underlie the control of rhythmic activity in cardiac and neuronal pacemaker cells. In HCN, the polarity of voltage dependence is uniquely reversed. Intracellular cyclic adenosine monophosphate (cAMP) levels tune the voltage response, enabling sympathetic nerve stimulation to increase the heart rate. We present cryo-electron microscopy structures of the human HCN channel in the absence and presence of cAMP at 3.5 Å resolution. HCN channels contain a K+ channel selectivity filter-forming sequence from which the amino acids create a unique structure that explains Na+ and K+ permeability. The voltage sensor adopts a depolarized conformation, and the pore is closed. An S4 helix of unprecedented length extends into the cytoplasm, contacts the C-linker, and twists the inner helical gate shut. cAMP binding rotates cytoplasmic domains to favor opening of the inner helical gate. These structures advance understanding of ion selectivity, reversed polarity gating, and cAMP regulation in HCN channels.
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Affiliation(s)
- Chia-Hsueh Lee
- Laboratory of Molecular Neurobiology and Biophysics, The Rockefeller University, Howard Hughes Medical Institute, 1230 York Avenue, New York, NY 10065, USA
| | - Roderick MacKinnon
- Laboratory of Molecular Neurobiology and Biophysics, The Rockefeller University, Howard Hughes Medical Institute, 1230 York Avenue, New York, NY 10065, USA.
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Maity S, Marchesi A, Torre V, Mazzolini M. Structural Heterogeneity of CNGA1 Channels Revealed by Electrophysiology and Single-Molecule Force Spectroscopy. ACS OMEGA 2016; 1:1205-1219. [PMID: 31457189 PMCID: PMC6640748 DOI: 10.1021/acsomega.6b00202] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/22/2016] [Accepted: 10/14/2016] [Indexed: 06/10/2023]
Abstract
The determination at atomic resolution of the three-dimensional molecular structure of membrane proteins such as receptors and several ion channels has been a major breakthrough in structural biology. The molecular structure of several members of the superfamily of voltage-gated ionic channels such as K+ and Na+ is now available. However, despite several attempts, the molecular structure at atomic resolution of the full cyclic nucleotide-gated (CNG) ion channel, although a member of the same superfamily of voltage-gated ion channels, has not been obtained yet, neither by X-ray crystallography nor by electron cryomicroscopy (cryo-EM). It is possible that CNG channels have a high structural heterogeneity, making difficult crystallization and single-particle analysis. To address this issue, we have combined single-molecule force spectroscopy (SMFS) and electrophysiological experiments to characterize the structural heterogeneity of CNGA1 channels expressed in Xenopus laevis oocytes. The unfolding of the cytoplasmic domain had force peaks, occurring with a probability from 0.2 to 0.96. Force peaks during the unfolding of the transmembrane domain had a probability close to 1, but the distribution of the increase in contour length between two successive force peaks had multiple maxima differing by tens of nanometers. Concomitant electrophysiological experiments showed that the rundown in mutant channels S399C is highly variable and that the effect of thiol reagents when specific residues were mutated was consistent with a dynamic structural heterogeneity. These results show that CNGA1 channels have a wide spectrum of native conformations that are difficult to detect with X-ray crystallography and cryo-EM.
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Jha SK, Sharma M, Pandey GK. Role of Cyclic Nucleotide Gated Channels in Stress Management in Plants. Curr Genomics 2016; 17:315-29. [PMID: 27499681 PMCID: PMC4955031 DOI: 10.2174/1389202917666160331202125] [Citation(s) in RCA: 52] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2015] [Revised: 09/04/2015] [Accepted: 09/08/2015] [Indexed: 11/22/2022] Open
Abstract
Tolerance of plants to a number of biotic and abiotic stresses such as pathogen and herbivore attack, drought, salinity, cold and nutritional limitations is ensued by complex multimodule signaling pathways. The outcome of this complex signaling pathways results in adaptive responses by restoring the cellular homeostasis and thus promoting survival. Functions of many plant cation transporter and channel protein families such as glutamate receptor homologs (GLRs), cyclic nucleotide-gated ion channel (CNGC) have been implicated in providing biotic and abiotic stress tolerance. Ion homeostasis regulated by several transporters and channels is one of the crucial parameters for the optimal growth, development and survival of all living organisms. The CNGC family members are known to be involved in the uptake of cations such as Na(+), K(+) and Ca(2+) and regulate plant growth and development. Detail functional genomics approaches have given an emerging picture of CNGCs wherein these protein are believed to play crucial role in pathways related to cellular ion homeostasis, development and as a 'guard' in defense against biotic and abiotic challenges. Here, we discuss the current knowledge of role of CNGCs in mediating stress management and how they aid plants in survival under adverse conditions.
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Affiliation(s)
- Saroj K. Jha
- Department of Plant Molecular Biology, University of Delhi South Campus, Benito Juarez Road, Dhaula Kuan, New Delhi-110021, India
| | - Manisha Sharma
- Department of Plant Molecular Biology, University of Delhi South Campus, Benito Juarez Road, Dhaula Kuan, New Delhi-110021, India
| | - Girdhar K. Pandey
- Department of Plant Molecular Biology, University of Delhi South Campus, Benito Juarez Road, Dhaula Kuan, New Delhi-110021, India
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40
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Ding XQ, Thapa A, Ma H, Xu J, Elliott MH, Rodgers KK, Smith ML, Wang JS, Pittler SJ, Kefalov VJ. The B3 Subunit of the Cone Cyclic Nucleotide-gated Channel Regulates the Light Responses of Cones and Contributes to the Channel Structural Flexibility. J Biol Chem 2016; 291:8721-34. [PMID: 26893377 DOI: 10.1074/jbc.m115.696138] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2015] [Indexed: 11/06/2022] Open
Abstract
Cone photoreceptor cyclic nucleotide-gated (CNG) channels play a pivotal role in cone phototransduction, which is a process essential for daylight vision, color vision, and visual acuity. Mutations in the cone channel subunits CNGA3 and CNGB3 are associated with human cone diseases, including achromatopsia, cone dystrophies, and early onset macular degeneration. Mutations in CNGB3 alone account for 50% of reported cases of achromatopsia. This work investigated the role of CNGB3 in cone light response and cone channel structural stability. As cones comprise only 2-3% of the total photoreceptor population in the wild-type mouse retina, we used Cngb3(-/-)/Nrl(-/-) mice with CNGB3 deficiency on a cone-dominant background in our study. We found that, in the absence of CNGB3, CNGA3 was able to travel to the outer segments, co-localize with cone opsin, and form tetrameric complexes. Electroretinogram analyses revealed reduced cone light response amplitude/sensitivity and slower response recovery in Cngb3(-/-)/Nrl(-/-) mice compared with Nrl(-/-) mice. Absence of CNGB3 expression altered the adaptation capacity of cones and severely compromised function in bright light. Biochemical analysis demonstrated that CNGA3 channels lacking CNGB3 were more resilient to proteolysis than CNGA3/CNGB3 channels, suggesting a hindered structural flexibility. Thus, CNGB3 regulates cone light response kinetics and the channel structural flexibility. This work advances our understanding of the biochemical and functional role of CNGB3 in cone photoreceptors.
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Affiliation(s)
| | | | - Hongwei Ma
- From the Departments of Cell Biology and
| | - Jianhua Xu
- From the Departments of Cell Biology and
| | - Michael H Elliott
- Ophthalmology and Dean McGee Eye Institute, Oklahoma City, Oklahoma 73104
| | - Karla K Rodgers
- Biochemistry, University of Oklahoma Health Sciences Center and
| | - Marci L Smith
- Department of Vision Sciences, University of Alabama, Birmingham, Alabama 35924, and
| | - Jin-Shan Wang
- Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, Saint Louis, Missouri 63110
| | - Steven J Pittler
- Department of Vision Sciences, University of Alabama, Birmingham, Alabama 35924, and
| | - Vladimir J Kefalov
- Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, Saint Louis, Missouri 63110
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41
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Giblin JP, Comes N, Strauss O, Gasull X. Ion Channels in the Eye: Involvement in Ocular Pathologies. ADVANCES IN PROTEIN CHEMISTRY AND STRUCTURAL BIOLOGY 2015; 104:157-231. [PMID: 27038375 DOI: 10.1016/bs.apcsb.2015.11.006] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The eye is the sensory organ of vision. There, the retina transforms photons into electrical signals that are sent to higher brain areas to produce visual sensations. In the light path to the retina, different types of cells and tissues are involved in maintaining the transparency of avascular structures like the cornea or lens, while others, like the retinal pigment epithelium, have a critical role in the maintenance of photoreceptor function by regenerating the visual pigment. Here, we have reviewed the roles of different ion channels expressed in ocular tissues (cornea, conjunctiva and neurons innervating the ocular surface, lens, retina, retinal pigment epithelium, and the inflow and outflow systems of the aqueous humor) that are involved in ocular disease pathophysiologies and those whose deletion or pharmacological modulation leads to specific diseases of the eye. These include pathologies such as retinitis pigmentosa, macular degeneration, achromatopsia, glaucoma, cataracts, dry eye, or keratoconjunctivitis among others. Several disease-associated ion channels are potential targets for pharmacological intervention or other therapeutic approaches, thus highlighting the importance of these channels in ocular physiology and pathophysiology.
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Affiliation(s)
- Jonathan P Giblin
- Universitat de Barcelona, Barcelona, Spain; Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), Barcelona, Spain
| | - Nuria Comes
- Universitat de Barcelona, Barcelona, Spain; Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), Barcelona, Spain
| | | | - Xavier Gasull
- Universitat de Barcelona, Barcelona, Spain; Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), Barcelona, Spain.
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Conformational rearrangements in the transmembrane domain of CNGA1 channels revealed by single-molecule force spectroscopy. Nat Commun 2015; 6:7093. [PMID: 25963832 PMCID: PMC4432583 DOI: 10.1038/ncomms8093] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2014] [Accepted: 04/01/2015] [Indexed: 11/12/2022] Open
Abstract
Cyclic nucleotide-gated (CNG) channels are activated by binding of cyclic nucleotides. Although structural studies have identified the channel pore and selectivity filter, conformation changes associated with gating remain poorly understood. Here we combine single-molecule force spectroscopy (SMFS) with mutagenesis, bioinformatics and electrophysiology to study conformational changes associated with gating. By expressing functional channels with SMFS fingerprints in Xenopus laevis oocytes, we were able to investigate gating of CNGA1 in a physiological-like membrane. Force spectra determined that the S4 transmembrane domain is mechanically coupled to S5 in the open state, but S3 in the closed state. We also show there are multiple pathways for the unfolding of the transmembrane domains, probably caused by a different degree of α-helix folding. This approach demonstrates that CNG transmembrane domains have dynamic structure and establishes SMFS as a tool for probing conformational change in ion channels. Cyclic nucleotide gated channels are activated after binding cyclic nucleotides. Here, using single molecule force spectroscopy, the authors reveal that cyclic nucleotide binding causes conformational changes and tighter coupling of the S4 helix to the pore forming domain.
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43
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Strünker T, Kaupp UB. Larry Cohen-50 ways to DYE your science. NEUROPHOTONICS 2015; 2:021004. [PMID: 26157995 PMCID: PMC4487647 DOI: 10.1117/1.nph.2.2.021004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Affiliation(s)
- Timo Strünker
- Center of Advanced European Studies and Research, Department of Molecular Sensory Systems, Ludwig-Erhard-Allee 2, 53175 Bonn, Germany
| | - U. Benjamin Kaupp
- Center of Advanced European Studies and Research, Department of Molecular Sensory Systems, Ludwig-Erhard-Allee 2, 53175 Bonn, Germany
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Marchesi A, Arcangeletti M, Mazzolini M, Torre V. Proton transfer unlocks inactivation in cyclic nucleotide-gated A1 channels. J Physiol 2015; 593:857-70. [PMID: 25480799 DOI: 10.1113/jphysiol.2014.284216] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2014] [Accepted: 11/28/2014] [Indexed: 01/12/2023] Open
Abstract
KEY POINTS Desensitization and inactivation provide a form of short-term memory controlling the firing patterns of excitable cells and adaptation in sensory systems. Unlike many of their cousin K(+) channels, cyclic nucleotide-gated (CNG) channels are thought not to desensitize or inactivate. Here we report that CNG channels do inactivate and that inactivation is controlled by extracellular protons. Titration of a glutamate residue within the selectivity filter destabilizes the pore architecture, which collapses towards a non-conductive, inactivated state in a process reminiscent of the usual C-type inactivation observed in many K(+) channels. These results indicate that inactivation in CNG channels represents a regulatory mechanism that has been neglected thus far, with possible implications in several physiological processes ranging from signal transduction to growth cone navigation. ABSTRACT Ion channels control ionic fluxes across biological membranes by residing in any of three functionally distinct states: deactivated (closed), activated (open) or inactivated (closed). Unlike many of their cousin K(+) channels, cyclic nucleotide-gated (CNG) channels do not desensitize or inactivate. Using patch recording techniques, we show that when extracellular pH (pHo ) is decreased from 7.4 to 6 or lower, wild-type CNGA1 channels inactivate in a voltage-dependent manner. pHo titration experiments show that at pHo < 7 the I-V relationships are outwardly rectifying and that inactivation is coupled to current rectification. Single-channel recordings indicate that a fast mechanism of proton blockage underlines current rectification while inactivation arises from conformational changes downstream from protonation. Furthermore, mutagenesis and ionic substitution experiments highlight the role of the selectivity filter in current decline, suggesting analogies with the C-type inactivation observed in K(+) channels. Analysis with Markovian models indicates that the non-independent binding of two protons within the transmembrane electrical field explains both the voltage-dependent blockage and the inactivation. Low pH, by inhibiting the CNGA1 channels in a state-dependent manner, may represent an unrecognized endogenous signal regulating CNG physiological functions in diverse tissues.
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Affiliation(s)
- Arin Marchesi
- Neurobiology Sector, International School for Advanced Studies (SISSA), Trieste, Italy
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Moran Y, Barzilai MG, Liebeskind BJ, Zakon HH. Evolution of voltage-gated ion channels at the emergence of Metazoa. J Exp Biol 2015; 218:515-25. [DOI: 10.1242/jeb.110270] [Citation(s) in RCA: 85] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Voltage-gated ion channels are large transmembrane proteins that enable the passage of ions through their pore across the cell membrane. These channels belong to one superfamily and carry pivotal roles such as the propagation of neuronal and muscular action potentials and the promotion of neurotransmitter secretion in synapses. In this review, we describe in detail the current state of knowledge regarding the evolution of these channels with a special emphasis on the metazoan lineage. We highlight the contribution of the genomic revolution to the understanding of ion channel evolution and for revealing that these channels appeared long before the appearance of the first animal. We also explain how the elucidation of channel selectivity properties and function in non-bilaterian animals such as cnidarians (sea anemones, corals, jellyfish and hydroids) can contribute to the study of channel evolution. Finally, we point to open questions and future directions in this field of research.
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Affiliation(s)
- Yehu Moran
- Department of Ecology, Evolution and Behavior, Alexander Silberman Institute of Life Sciences, Faculty of Science, Hebrew University of Jerusalem, Jerusalem 91904, Israel
| | - Maya Gur Barzilai
- Department of Molecular Biology and Ecology of Plants, George S. Wise Faculty of Life Sciences, Tel-Aviv University, Tel-Aviv 69978, Israel
| | - Benjamin J. Liebeskind
- Department of Integrative Biology and Center for Computational Biology and Bioinformatics, University of Texas, Austin, TX 78712, USA
| | - Harold H. Zakon
- Department of Integrative Biology and Center for Computational Biology and Bioinformatics, University of Texas, Austin, TX 78712, USA
- Department of Neuroscience, University of Texas at Austin, TX 78712, USA
- Josephine Bay Paul Center for Molecular Biology and Evolution, Marine Biological Laboratory, Woods Hole, MA 02543, USA
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Submembrane assembly and renewal of rod photoreceptor cGMP-gated channel: insight into the actin-dependent process of outer segment morphogenesis. J Neurosci 2014; 34:8164-74. [PMID: 24920621 DOI: 10.1523/jneurosci.1282-14.2014] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
The photoreceptor outer segment (OS) is comprised of two compartments: plasma membrane (PM) and disk membranes. It is unknown how the PM renewal is coordinated with that of the disk membranes. Here we visualized the localization and trafficking process of rod cyclic nucleotide-gated channel α-subunit (CNGA1), a PM component essential for phototransduction. The localization was visualized by fusing CNGA1 to a fluorescent protein Dendra2 and expressing in Xenopus laevis rod photoreceptors. Dendra2 allowed us to label CNGA1 in a spatiotemporal manner and therefore discriminate between old and newly trafficked CNGA1-Dendra2 in the OS PM. Newly synthesized CNGA1 was preferentially trafficked to the basal region of the lateral OS PM where newly formed and matured disks are also added. Unique trafficking pattern and diffusion barrier excluded CNGA1 from the PM domains, which are the proposed site of disk membrane maturation. Such distinct compartmentalization allows the confinement of cyclic nucleotide-gated channel in the PM, while preventing the disk membrane incorporation. Cytochalasin D and latrunculin A treatments, which are known to disrupt F-actin-dependent disk membrane morphogenesis, prevented the entrance of newly synthesized CNGA1 to the OS PM, but did not prevent the entrance of rhodopsin and peripherin/rds to the membrane evaginations believed to be disk membrane precursors. Uptake of rhodopsin and peripherin/rds coincided with the overgrowth of the evaginations at the base of the OS. Thus F-actin is essential for the trafficking of CNGA1 to the ciliary PM, and coordinates the formations of disk membrane rim region and OS PM.
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47
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Family of prokaryote cyclic nucleotide-modulated ion channels. Proc Natl Acad Sci U S A 2014; 111:7855-60. [PMID: 24821777 DOI: 10.1073/pnas.1401917111] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Cyclic nucleotide-modulated ion channels are molecular pores that mediate the passage of ions across the cell membrane in response to cAMP or GMP. Structural insight into this class of ion channels currently comes from a related homolog, MloK1, that contains six transmembrane domains and a cytoplasmic cyclic nucleotide binding domain. However, unlike eukaryote hyperpolarization-activated cyclic nucleotide-modulated (HCN) and cyclic nucleotide-gated (CNG) channels, MloK1 lacks a C-linker region, which critically contributes to the molecular coupling between ligand binding and channel opening. In this study, we report the identification and characterization of five previously unidentified prokaryote homologs with high sequence similarity (24-32%) to eukaryote HCN and CNG channels and that contain a C-linker region. Biochemical characterization shows that two homologs, termed AmaK and SthK, can be expressed and purified as detergent-solubilized protein from Escherichia coli membranes. Expression of SthK channels in Xenopus laevis oocytes and functional characterization using the patch-clamp technique revealed that the channels are gated by cAMP, but not cGMP, are highly selective for K(+) ions over Na(+) ions, generate a large unitary conductance, and are only weakly voltage dependent. These properties resemble essential properties of various eukaryote HCN or CNG channels. Our results contribute to an understanding of the evolutionary origin of cyclic nucleotide-modulated ion channels and pave the way for future structural and functional studies.
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48
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CRIS-a novel cAMP-binding protein controlling spermiogenesis and the development of flagellar bending. PLoS Genet 2013; 9:e1003960. [PMID: 24339785 PMCID: PMC3854790 DOI: 10.1371/journal.pgen.1003960] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2013] [Accepted: 09/30/2013] [Indexed: 12/17/2022] Open
Abstract
The second messengers cAMP and cGMP activate their target proteins by binding to a conserved cyclic nucleotide-binding domain (CNBD). Here, we identify and characterize an entirely novel CNBD-containing protein called CRIS (cyclic nucleotide receptor involved in sperm function) that is unrelated to any of the other members of this protein family. CRIS is exclusively expressed in sperm precursor cells. Cris-deficient male mice are either infertile due to a lack of sperm resulting from spermatogenic arrest, or subfertile due to impaired sperm motility. The motility defect is caused by altered Ca(2+) regulation of flagellar beat asymmetry, leading to a beating pattern that is reminiscent of sperm hyperactivation. Our results suggest that CRIS interacts during spermiogenesis with Ca(2+)-regulated proteins that--in mature sperm--are involved in flagellar bending.
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49
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Alexander SPH, Benson HE, Faccenda E, Pawson AJ, Sharman JL, Catterall WA, Spedding M, Peters JA, Harmar AJ. The Concise Guide to PHARMACOLOGY 2013/14: ion channels. Br J Pharmacol 2013; 170:1607-51. [PMID: 24528239 PMCID: PMC3892289 DOI: 10.1111/bph.12447] [Citation(s) in RCA: 225] [Impact Index Per Article: 20.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
The Concise Guide to PHARMACOLOGY 2013/14 provides concise overviews of the key properties of over 2000 human drug targets with their pharmacology, plus links to an open access knowledgebase of drug targets and their ligands (www.guidetopharmacology.org), which provides more detailed views of target and ligand properties. The full contents can be found at http://onlinelibrary.wiley.com/doi/10.1111/bph.12444/full. Ion channels are one of the seven major pharmacological targets into which the Guide is divided, with the others being G protein-coupled receptors, ligand-gated ion channels, catalytic receptors, nuclear hormone receptors, transporters and enzymes. These are presented with nomenclature guidance and summary information on the best available pharmacological tools, alongside key references and suggestions for further reading. A new landscape format has easy to use tables comparing related targets. It is a condensed version of material contemporary to late 2013, which is presented in greater detail and constantly updated on the website www.guidetopharmacology.org, superseding data presented in previous Guides to Receptors and Channels. It is produced in conjunction with NC-IUPHAR and provides the official IUPHAR classification and nomenclature for human drug targets, where appropriate. It consolidates information previously curated and displayed separately in IUPHAR-DB and the Guide to Receptors and Channels, providing a permanent, citable, point-in-time record that will survive database updates.
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Affiliation(s)
- Stephen PH Alexander
- School of Life Sciences, University of Nottingham Medical SchoolNottingham, NG7 2UH, UK
- *
Author for correspondence;
| | - Helen E Benson
- The University/BHF Centre for Cardiovascular Science, University of EdinburghEdinburgh, EH16 4TJ, UK
| | - Elena Faccenda
- The University/BHF Centre for Cardiovascular Science, University of EdinburghEdinburgh, EH16 4TJ, UK
| | - Adam J Pawson
- The University/BHF Centre for Cardiovascular Science, University of EdinburghEdinburgh, EH16 4TJ, UK
| | - Joanna L Sharman
- The University/BHF Centre for Cardiovascular Science, University of EdinburghEdinburgh, EH16 4TJ, UK
| | - William A Catterall
- University of Washington, School of Medicine, Department of PharmacologyBox 357280, Seattle, WA 98195-7280, USA
| | | | - John A Peters
- Neuroscience Division, Medical Education Institute, Ninewells Hospital and Medical School, University of DundeeDundee, DD1 9SY, UK
| | - Anthony J Harmar
- The University/BHF Centre for Cardiovascular Science, University of EdinburghEdinburgh, EH16 4TJ, UK
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50
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Winkler PA, Ekenstedt KJ, Occelli LM, Frattaroli AV, Bartoe JT, Venta PJ, Petersen-Jones SM. A large animal model for CNGB1 autosomal recessive retinitis pigmentosa. PLoS One 2013; 8:e72229. [PMID: 23977260 PMCID: PMC3747135 DOI: 10.1371/journal.pone.0072229] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2013] [Accepted: 07/08/2013] [Indexed: 11/25/2022] Open
Abstract
Retinal dystrophies in dogs are invaluable models of human disease. Progressive retinal atrophy (PRA) is the canine equivalent of retinitis pigmentosa (RP). Similar to RP, PRA is a genetically heterogenous condition. We investigated PRA in the Papillon breed of dog using homozygosity mapping and haplotype construction of single nucleotide polymorphisms within a small family group to identify potential positional candidate genes. Based on the phenotypic similarities between the PRA-affected Papillons, mouse models and human patients, CNGB1 was selected as the most promising positional candidate gene. CNGB1 was sequenced and a complex mutation consisting of the combination of a one basepair deletion and a 6 basepair insertion was identified in exon 26 (c.2387delA;2389_2390insAGCTAC) leading to a frameshift and premature stop codon. Immunohistochemistry (IHC) of pre-degenerate retinal sections from a young affected dog showed absence of labeling using a C-terminal CNGB1 antibody. Whereas an antibody directed against the N-terminus of the protein, which also recognizes the glutamic acid rich proteins arising from alternative splicing of the CNGB1 transcript (upstream of the premature stop codon), labeled rod outer segments. CNGB1 combines with CNGA1 to form the rod cyclic nucleotide gated channel and previous studies have shown the requirement of CNGB1 for normal targeting of CNGA1 to the rod outer segment. In keeping with these previous observations, IHC showed a lack of detectable CNGA1 protein in the rod outer segments of the affected dog. A population study did not identify the CNGB1 mutation in PRA-affected dogs in other breeds and documented that the CNGB1 mutation accounts for ∼70% of cases of Papillon PRA in our PRA-affected canine DNA bank. CNGB1 mutations are one cause of autosomal recessive RP making the CNGB1 mutant dog a valuable large animal model of the condition.
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Affiliation(s)
- Paige A. Winkler
- Department of Small Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, Michigan, United States of America
- Genetics Program, Michigan State University, East Lansing, Michigan, United States of America
| | - Kari J. Ekenstedt
- Department of Animal and Food Sciences, University of Wisconsin-River Falls, River Falls, Wisconsin, United States of America
| | - Laurence M. Occelli
- Department of Small Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, Michigan, United States of America
| | - Anton V. Frattaroli
- Health Information Technology, Michigan State University, East Lansing, Michigan, United States of America
| | - Joshua T. Bartoe
- Department of Small Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, Michigan, United States of America
| | - Patrick J. Venta
- Department of Small Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, Michigan, United States of America
- Genetics Program, Michigan State University, East Lansing, Michigan, United States of America
- Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan, United States of America
| | - Simon M. Petersen-Jones
- Department of Small Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, Michigan, United States of America
- Genetics Program, Michigan State University, East Lansing, Michigan, United States of America
- * E-mail:
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