51
|
Fernández A, Pupo A, Mena-Ulecia K, Gonzalez C. Pharmacological Modulation of Proton Channel Hv1 in Cancer Therapy: Future Perspectives. Mol Pharmacol 2016; 90:385-402. [PMID: 27260771 DOI: 10.1124/mol.116.103804] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2016] [Accepted: 06/02/2016] [Indexed: 12/23/2022] Open
Abstract
The pharmacological modulation of the immunosuppressive tumor microenvironment has emerged as a relevant component for cancer therapy. Several approaches aiming to deplete innate and adaptive suppressive populations, to circumvent the impairment in antigen presentation, and to ultimately increase the frequency of activated tumor-specific T cells are currently being explored. In this review, we address the potentiality of targeting the voltage-gated proton channel, Hv1, as a novel strategy to modulate the tumor microenvironment. The function of Hv1 in immune cells such as macrophages, neutrophils, dendritic cells, and T cells has been associated with the maintenance of NADPH oxidase activity and the generation of reactive oxygen species, which are required for the host defense against pathogens. We discuss evidence suggesting that the Hv1 proton channel could also be important for the function of these cells within the tumor microenvironment. Furthermore, as summarized here, tumor cells express Hv1 as a primary mechanism to extrude the increased amount of protons generated metabolically, thus maintaining physiologic values for the intracellular pH. Therefore, because this channel might be relevant for both tumor cells and immune cells supporting tumor growth, the pharmacological inhibition of Hv1 could be an innovative approach for cancer therapy. With that focus, we analyzed the available compounds that inhibit Hv1, highlighted the need to develop better drugs suitable for patients, and commented on the future perspectives of targeting Hv1 in the context of cancer therapy.
Collapse
Affiliation(s)
- Audry Fernández
- Interdisciplinary Center for Neurosciences of Valparaíso, Faculty of Sciences, University of Valparaíso, Chile
| | - Amaury Pupo
- Interdisciplinary Center for Neurosciences of Valparaíso, Faculty of Sciences, University of Valparaíso, Chile
| | - Karel Mena-Ulecia
- Interdisciplinary Center for Neurosciences of Valparaíso, Faculty of Sciences, University of Valparaíso, Chile
| | - Carlos Gonzalez
- Interdisciplinary Center for Neurosciences of Valparaíso, Faculty of Sciences, University of Valparaíso, Chile
| |
Collapse
|
52
|
Thioxanthenes, chlorprothixene and flupentixol inhibit proton currents in BV2 microglial cells. Eur J Pharmacol 2016; 779:31-7. [PMID: 26945819 DOI: 10.1016/j.ejphar.2016.03.009] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2015] [Revised: 03/02/2016] [Accepted: 03/02/2016] [Indexed: 01/28/2023]
Abstract
The thioxanthene antipsychotic drugs chlorprothixene and flupentixol have anti-inflammatory and antioxidant properties. The reactive oxygen species produced by NADPH oxidase during microglia-mediated inflammatory responses cause neuronal damage, thereby contributing to various neurodegenerative diseases. Voltage-gated proton channels sustain the NADPH oxidase activity, and inhibition of the channels' activity reduces the production of reactive oxygen species. Herein, the effects of chlorprothixene and flupentixol on proton currents were investigated in BV2 microglial cells using the whole-cell patch-clamp method. Both drugs inhibited the proton currents in a concentration-dependent manner (IC50=1.7μM and 6.6μM, respectively). Chlorprothixene at 3μM slightly shifted the activation voltage toward depolarization. Both the activation and the deactivation kinetics of the proton currents were slowed by chlorprothixene 1.2- and 3.5-fold, respectively. Thus, the inhibition of proton currents may be partly responsible for the antioxidant effects of thioxanthene antipsychotic drugs.
Collapse
|
53
|
Abstract
Hv1 is a voltage-gated proton-selective channel that plays critical parts in host defense, sperm motility, and cancer progression. Hv1 contains a conserved voltage-sensor domain (VSD) that is shared by a large family of voltage-gated ion channels, but it lacks a pore domain. Voltage sensitivity and proton conductivity are conferred by a unitary VSD that consists of four transmembrane helices. The architecture of Hv1 differs from that of cation channels that form a pore in the center among multiple subunits (as in most cation channels) or homologous repeats (as in voltage-gated sodium and calcium channels). Hv1 forms a dimer in which a cytoplasmic coiled coil underpins the two protomers and forms a single, long helix that is contiguous with S4, the transmembrane voltage-sensing segment. The closed-state structure of Hv1 was recently solved using X-ray crystallography. In this article, we discuss the gating mechanism of Hv1 and focus on cooperativity within dimers and their sensitivity to metal ions.
Collapse
Affiliation(s)
- Yasushi Okamura
- Department of Integrative Physiology, Graduate School of Medicine, Osaka University, Osaka 565-0871, Japan; , ,
| | | | | |
Collapse
|
54
|
Rajapaksha SP, Pal N, Zheng D, Lu HP. Protein-fluctuation-induced water-pore formation in ion channel voltage-sensor translocation across a lipid bilayer membrane. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2015; 92:052719. [PMID: 26651735 DOI: 10.1103/physreve.92.052719] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/24/2015] [Indexed: 06/05/2023]
Abstract
We have applied a combined fluorescence microscopy and single-ion-channel electric current recording approach, correlating with molecular dynamics (MD) simulations, to study the mechanism of voltage-sensor domain translocation across a lipid bilayer. We use the colicin Ia ion channel as a model system, and our experimental and simulation results show the following: (1) The open-close activity of an activated colicin Ia is not necessarily sensitive to the amplitude of the applied cross-membrane voltage when the cross-membrane voltage is around the resting potential of excitable membranes; and (2) there is a significant probability that the activation of colicin Ia occurs by forming a transient and fluctuating water pore of ∼15 Å diameter in the lipid bilayer membrane. The location of the water-pore formation is nonrandom and highly specific, right at the insertion site of colicin Ia charged residues in the lipid bilayer membrane, and the formation is intrinsically associated with the polypeptide conformational fluctuations and solvation dynamics. Our results suggest an interesting mechanistic pathway for voltage-sensitive ion channel activation, and specifically for translocation of charged polypeptide chains across the lipid membrane under a transmembrane electric field: the charged polypeptide domain facilitates the formation of hydrophilic water pore in the membrane and diffuses through the hydrophilic pathway across the membrane; i.e., the charged polypeptide chain can cross a lipid membrane without entering into the hydrophobic core of the lipid membrane but entirely through the aqueous and hydrophilic environment to achieve a cross-membrane translocation. This mechanism sheds light on the intensive and fundamental debate on how a hydrophilic and charged peptide domain diffuses across the biologically inaccessible high-energy barrier of the hydrophobic core of a lipid bilayer: The peptide domain does not need to cross the hydrophobic core to move across a lipid bilayer.
Collapse
Affiliation(s)
- Suneth P Rajapaksha
- Department of Chemistry and Center for Photochemical Sciences, Bowling Green State University, Bowling Green, Ohio 43403, USA
| | - Nibedita Pal
- Department of Chemistry and Center for Photochemical Sciences, Bowling Green State University, Bowling Green, Ohio 43403, USA
| | - Desheng Zheng
- Department of Chemistry and Center for Photochemical Sciences, Bowling Green State University, Bowling Green, Ohio 43403, USA
| | - H Peter Lu
- Department of Chemistry and Center for Photochemical Sciences, Bowling Green State University, Bowling Green, Ohio 43403, USA
| |
Collapse
|
55
|
Li Q, Shen R, Treger JS, Wanderling SS, Milewski W, Siwowska K, Bezanilla F, Perozo E. Resting state of the human proton channel dimer in a lipid bilayer. Proc Natl Acad Sci U S A 2015; 112:E5926-35. [PMID: 26443860 PMCID: PMC4640771 DOI: 10.1073/pnas.1515043112] [Citation(s) in RCA: 57] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
The voltage-gated proton channel Hv1 plays a critical role in the fast proton translocation that underlies a wide range of physiological functions, including the phagocytic respiratory burst, sperm motility, apoptosis, and metastatic cancer. Both voltage activation and proton conduction are carried out by a voltage-sensing domain (VSD) with strong similarity to canonical VSDs in voltage-dependent cation channels and enzymes. We set out to determine the structural properties of membrane-reconstituted human proton channel (hHv1) in its resting conformation using electron paramagnetic resonance spectroscopy together with biochemical and computational methods. We evaluated existing structural templates and generated a spectroscopically constrained model of the hHv1 dimer based on the Ci-VSD structure at resting state. Mapped accessibility data revealed deep water penetration through hHv1, suggesting a highly focused electric field, comprising two turns of helix along the fourth transmembrane segment. This region likely contains the H(+) selectivity filter and the conduction pore. Our 3D model offers plausible explanations for existing electrophysiological and biochemical data, offering an explicit mechanism for voltage activation based on a one-click sliding helix conformational rearrangement.
Collapse
Affiliation(s)
- Qufei Li
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL 60637
| | - Rong Shen
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL 60637
| | - Jeremy S Treger
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL 60637
| | - Sherry S Wanderling
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL 60637
| | - Wieslawa Milewski
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL 60637
| | - Klaudia Siwowska
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL 60637
| | - Francisco Bezanilla
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL 60637
| | - Eduardo Perozo
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL 60637
| |
Collapse
|
56
|
Interrogation of the intersubunit interface of the open Hv1 proton channel with a probe of allosteric coupling. Sci Rep 2015; 5:14077. [PMID: 26365828 PMCID: PMC4568520 DOI: 10.1038/srep14077] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2015] [Accepted: 08/14/2015] [Indexed: 12/15/2022] Open
Abstract
The Hv1 voltage-gated proton channel is a dimeric complex consisting of two voltage-sensing domains (VSDs), each containing a gated proton permeation pathway. Dimerization is controlled by a cytoplasmic coiled-coil domain. The transitions from the closed to the open state in the two VSDs are known to occur cooperatively; however, the underlying mechanism is poorly understood. Intersubunit interfaces play a critical role in allosteric processes; but, such interfaces have not been determined in the open Hv1 channel. Here we show that 2-guanidinothiazole derivatives block the two Hv1 VSDs in a cooperative way, and use one of the compounds as a probe of allosteric coupling between open subunits. We find that the extracellular ends of the first transmembrane segments of the VSDs form the intersubunit interface that mediates coupling between binding sites, while the coiled-coil domain does not directly participate in the process. We also find strong evidence that the channel’s proton selectivity filter controls blocker binding cooperativity.
Collapse
|
57
|
Morera FJ, Saravia J, Pontigo JP, Vargas-Chacoff L, Contreras GF, Pupo A, Lorenzo Y, Castillo K, Tilegenova C, Cuello LG, Gonzalez C. Voltage-dependent BK and Hv1 channels expressed in non-excitable tissues: New therapeutics opportunities as targets in human diseases. Pharmacol Res 2015; 101:56-64. [PMID: 26305431 DOI: 10.1016/j.phrs.2015.08.011] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/15/2015] [Revised: 08/14/2015] [Accepted: 08/14/2015] [Indexed: 11/28/2022]
Abstract
Voltage-gated ion channels are the molecular determinants of cellular excitability. This group of ion channels is one of the most important pharmacological targets in excitable tissues such as nervous system, cardiac and skeletal muscle. Moreover, voltage-gated ion channels are expressed in non-excitable cells, where they mediate key cellular functions through intracellular biochemical mechanisms rather than rapid electrical signaling. This review aims at illustrating the pharmacological impact of these ion channels, highlighting in particular the structural details and physiological functions of two of them - the high conductance voltage- and Ca(2+)-gated K(+) (BK) channels and voltage-gated proton (Hv1) channels- in non-excitable cells. BK channels have been implicated in a variety of physiological processes ranging from regulation of smooth muscle tone to modulation of hormone and neurotransmitter release. Interestingly, BK channels are also involved in modulating K(+) transport in the mammalian kidney and colon epithelium with a potential role in the hyperkalemic phenotype observed in patients with familial hyperkalemic hypertension type 2, and in the pathophysiology of hypertension. In addition, BK channels are responsible for resting and stimulated Ca(2+)-activated K(+) secretion in the distal colon. Hv1 channels have been detected in many cell types, including macrophages, blood cells, lung epithelia, skeletal muscle and microglia. These channels have a central role in the phagocytic system. In macrophages, Hv1 channels participate in the generation of reactive oxygen species in the respiratory burst during the process of phagocytosis.
Collapse
Affiliation(s)
- Francisco J Morera
- Institute of Pharmacology and Morphophysiology, Faculty of Veterinary Sciences, Universidad Austral de Chile, Valdivia, Chile.
| | - Julia Saravia
- Institute of Pharmacology and Morphophysiology, Faculty of Veterinary Sciences, Universidad Austral de Chile, Valdivia, Chile
| | - Juan Pablo Pontigo
- Institute of Marine Sciences and Limnology, Faculty of Sciences, Universidad Austral de Chile, Valdivia, Chile
| | - Luis Vargas-Chacoff
- Institute of Marine Sciences and Limnology, Faculty of Sciences, Universidad Austral de Chile, Valdivia, Chile
| | - Gustavo F Contreras
- Interdisciplinary Center for Neuroscience of Valparaiso, Faculty of Sciences, Universidad de Valparaiso, Valparaiso, Chile
| | - Amaury Pupo
- Interdisciplinary Center for Neuroscience of Valparaiso, Faculty of Sciences, Universidad de Valparaiso, Valparaiso, Chile
| | - Yenisleidy Lorenzo
- Interdisciplinary Center for Neuroscience of Valparaiso, Faculty of Sciences, Universidad de Valparaiso, Valparaiso, Chile
| | - Karen Castillo
- Interdisciplinary Center for Neuroscience of Valparaiso, Faculty of Sciences, Universidad de Valparaiso, Valparaiso, Chile
| | - Cholpon Tilegenova
- Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubcock, TX, USA
| | - Luis G Cuello
- Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubcock, TX, USA.
| | - Carlos Gonzalez
- Interdisciplinary Center for Neuroscience of Valparaiso, Faculty of Sciences, Universidad de Valparaiso, Valparaiso, Chile.
| |
Collapse
|
58
|
Castillo K, Pupo A, Baez-Nieto D, Contreras GF, Morera FJ, Neely A, Latorre R, Gonzalez C. Voltage-gated proton (H(v)1) channels, a singular voltage sensing domain. FEBS Lett 2015; 589:3471-8. [PMID: 26296320 DOI: 10.1016/j.febslet.2015.08.003] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2015] [Revised: 08/10/2015] [Accepted: 08/11/2015] [Indexed: 12/28/2022]
Abstract
The main role of voltage-gated proton channels (Hv1) is to extrude protons from the intracellular milieu when, mediated by different cellular processes, the H(+) concentration increases. Hv1 are exquisitely selective for protons and their structure is homologous to the voltage sensing domain (VSD) of other voltage-gated ion channels like sodium, potassium, and calcium channels. In clear contrast to the classical voltage-dependent channels, Hv1 lacks a pore domain and thus permeation necessarily occurs through the voltage sensing domain. Hv1 channels are activated by depolarizing voltages, and increases in internal proton concentration. It has been proposed that local conformational changes of the transmembrane segment S4, driven by depolarization, trigger the molecular rearrangements that open Hv1. However, it is still unclear how the electromechanical coupling is achieved between the VSD and the potential pore, allowing the proton flux from the intracellular to the extracellular side. Here we provide a revised view of voltage activation in Hv1 channels, offering a comparative scenario with other voltage sensing channels domains.
Collapse
Affiliation(s)
- Karen Castillo
- Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso 2360103, Chile
| | - Amaury Pupo
- Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso 2360103, Chile
| | - David Baez-Nieto
- Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso 2360103, Chile
| | - Gustavo F Contreras
- Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso 2360103, Chile
| | - Francisco J Morera
- Institute of Pharmacology and Morphophysiology, Faculty of Veterinary Sciences, Universidad Austral de Chile, Valdivia, Chile
| | - Alan Neely
- Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso 2360103, Chile
| | - Ramon Latorre
- Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso 2360103, Chile.
| | - Carlos Gonzalez
- Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso 2360103, Chile.
| |
Collapse
|
59
|
Seredenina T, Demaurex N, Krause KH. Voltage-Gated Proton Channels as Novel Drug Targets: From NADPH Oxidase Regulation to Sperm Biology. Antioxid Redox Signal 2015; 23:490-513. [PMID: 24483328 PMCID: PMC4543398 DOI: 10.1089/ars.2013.5806] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
SIGNIFICANCE Voltage-gated proton channels are increasingly implicated in cellular proton homeostasis. Proton currents were originally identified in snail neurons less than 40 years ago, and subsequently shown to play an important auxiliary role in the functioning of reactive oxygen species (ROS)-generating nicotinamide adenine dinucleotide phosphate (NADPH) oxidases. Molecular identification of voltage-gated proton channels was achieved less than 10 years ago. Interestingly, so far, only one gene coding for voltage-gated proton channels has been identified, namely hydrogen voltage-gated channel 1 (HVCN1), which codes for the HV1 proton channel protein. Over the last years, the first picture of putative physiological functions of HV1 has been emerging. RECENT ADVANCES The best-studied role remains charge and pH compensation during the respiratory burst of the phagocyte NADPH oxidase (NOX). Strong evidence for a role of HV1 is also emerging in sperm biology, but the relationship with the sperm NOX5 remains unclear. Probably in many instances, HV1 functions independently of NOX: for example in snail neurons, basophils, osteoclasts, and cancer cells. CRITICAL ISSUES Generally, ion channels are good drug targets; however, this feature has so far not been exploited for HV1, and hitherto no inhibitors compatible with clinical use exist. However, there are emerging indications for HV1 inhibitors, ranging from diseases with a strong activation of the phagocyte NOX (e.g., stroke) to infertility, osteoporosis, and cancer. FUTURE DIRECTIONS Clinically useful HV1-active drugs should be developed and might become interesting drugs of the future.
Collapse
Affiliation(s)
- Tamara Seredenina
- 1 Department of Pathology and Immunology, Geneva University Medical Faculty , Centre Médical Universitaire, Geneva, Switzerland
| | - Nicolas Demaurex
- 2 Department of Cellular Physiology and Metabolism, Geneva University Medical Faculty , Centre Médical Universitaire, Geneva, Switzerland
| | - Karl-Heinz Krause
- 1 Department of Pathology and Immunology, Geneva University Medical Faculty , Centre Médical Universitaire, Geneva, Switzerland .,3 Department of Genetic and Laboratory Medicine, Geneva University Hospitals , Centre Médical Universitaire, Geneva, Switzerland
| |
Collapse
|
60
|
Miller MR, Mansell SA, Meyers SA, Lishko PV. Flagellar ion channels of sperm: similarities and differences between species. Cell Calcium 2015; 58:105-13. [DOI: 10.1016/j.ceca.2014.10.009] [Citation(s) in RCA: 58] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2014] [Revised: 10/16/2014] [Accepted: 10/20/2014] [Indexed: 10/24/2022]
|
61
|
Abstract
The voltage sensitive domain (VSD) is a pivotal structure of voltage-gated ion channels (VGICs) and plays an essential role in the generation of electrochemical signals by neurons, striated muscle cells, and endocrine cells. The VSD is not unique to VGICs. Recent studies have shown that a VSD regulates a phosphatase. Similarly, Hv1, a voltage-sensitive protein that lacks an apparent pore domain, is a self-contained voltage sensor that operates as an H⁺ channel. VSDs are formed by four transmembrane helices (S1-S4). The S4 helix is positively charged due to the presence of arginine and lysine residues. It is surrounded by two water crevices that extend into the membrane from both the extracellular and intracellular milieus. A hydrophobic septum disrupts communication between these water crevices thus preventing the permeation of ions. The septum is maintained by interactions between the charged residues of the S4 segment and the gating charge transfer center. Mutating the charged residue of the S4 segment allows the water crevices to communicate and generate gating pore or omega pore. Gating pore currents have been reported to underlie several neuronal and striated muscle channelopathies. Depending on which charged residue on the S4 segment is mutated, gating pores are permeant either at depolarized or hyperpolarized voltages. Gating pores are cation selective and seem to converge toward Eisenmann's first or second selectivity sequences. Most gating pores are blocked by guanidine derivatives as well as trivalent and quadrivalent cations. Gating pores can be used to study the movement of the voltage sensor and could serve as targets for novel small therapeutic molecules.
Collapse
|
62
|
Pupo A, Baez-Nieto D, Martínez A, Latorre R, González C. Proton channel models filling the gap between experimental data and the structural rationale. Channels (Austin) 2015; 8:180-92. [PMID: 24755912 PMCID: PMC4203746 DOI: 10.4161/chan.28665] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Voltage-gated proton channels are integral membrane proteins with the capacity to permeate elementary particles in a voltage and pH dependent manner. These proteins have been found in several species and are involved in various physiological processes. Although their primary topology is known, lack of details regarding their structures in the open conformation has limited analyses toward a deeper understanding of the molecular determinants of their function and regulation. Consequently, the function-structure relationships have been inferred based on homology models. In the present work, we review the existing proton channel models, their assumptions, predictions and the experimental facts that support them. Modeling proton channels is not a trivial task due to the lack of a close homolog template. Hence, there are important differences between published models. This work attempts to critically review existing proton channel models toward the aim of contributing to a better understanding of the structural features of these proteins.
Collapse
|
63
|
Abstract
The main properties of the voltage-gated proton channel (HV1) are described in this review, along with what is known about how the channel protein structure accomplishes its functions. Just as protons are unique among ions, proton channels are unique among ion channels. Their four transmembrane helices sense voltage and the pH gradient and conduct protons exclusively. Selectivity is achieved by the unique ability of H3O(+) to protonate an Asp-Arg salt bridge. Pathognomonic sensitivity of gating to the pH gradient ensures HV1 channel opening only when acid extrusion will result, which is crucial to most of its biological functions. An exception occurs in dinoflagellates in which influx of H(+) through HV1 triggers the bioluminescent flash. Pharmacological interventions that promise to ameliorate cancer, asthma, brain damage in ischemic stroke, Alzheimer's disease, autoimmune diseases, and numerous other conditions await future progress.
Collapse
Affiliation(s)
- Thomas E. DeCoursey
- Department of Molecular Biophysics and Physiology, Rush University, 1750 West Harrison, Chicago IL, 60612 USA
| |
Collapse
|
64
|
Shin H, Kim J, Song JH. Clozapine and olanzapine inhibit proton currents in BV2 microglial cells. Eur J Pharmacol 2015; 755:74-9. [PMID: 25771455 DOI: 10.1016/j.ejphar.2015.03.003] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2014] [Revised: 02/23/2015] [Accepted: 03/01/2015] [Indexed: 01/21/2023]
Abstract
Excessive reactive oxygen species produced by NADPH oxidase in over-activated microglia can lead to neuronal death. Some atypical antipsychotic drugs possibly have anti-inflammatory properties and suppress the production of pro-inflammatory cytokines and reactive oxygen species from microglia. Voltage-gated proton channels (Hv1) are expressed in microglia and are required for NADPH oxidase-dependent reactive oxygen species generation, which could contribute to neuronal death and ischemic brain damage. In the present study, we examined the effects of the atypical antipsychotics clozapine, olanzapine and risperidone on proton currents in microglial BV2 cells. Clozapine and olanzapine inhibited proton currents with IC50 values of 9.8 μM and 84 μM, respectively. Risperidone, however, showed very weak inhibition of proton currents. Clozapine-induced inhibition of proton currents was not accompanied by a positive shift in the activation voltage or reversal potential, indicating that the inhibition was not mediated through an increase in the intracellular pH. Clozapine binds to a multitude of receptors, including serotonin, dopamine and muscarinic receptors. Serotonin receptors, however, were not responsible for the proton current inhibition by clozapine. Of the three drugs, only clozapine could reach concentrations to inhibit microglial proton currents in the brain at therapeutic doses. Thus, the anti-inflammatory activity of clozapine may be partly attributable to its inhibition of microglial proton currents.
Collapse
Affiliation(s)
- Hyewon Shin
- Department of Pharmacology, College of Medicine, Chung-Ang University, 84 Heukseok-Ro, Dongjak-Gu, Seoul 156-756, Republic of Korea
| | - Jiwon Kim
- Department of Pharmacology, College of Medicine, Chung-Ang University, 84 Heukseok-Ro, Dongjak-Gu, Seoul 156-756, Republic of Korea
| | - Jin-Ho Song
- Department of Pharmacology, College of Medicine, Chung-Ang University, 84 Heukseok-Ro, Dongjak-Gu, Seoul 156-756, Republic of Korea.
| |
Collapse
|
65
|
A specialized molecular motion opens the Hv1 voltage-gated proton channel. Nat Struct Mol Biol 2015; 22:283-290. [PMID: 25730777 PMCID: PMC4385474 DOI: 10.1038/nsmb.2978] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2014] [Accepted: 01/30/2015] [Indexed: 12/22/2022]
Abstract
The Hv1 proton channel is unique among voltage-gated channels for containing the pore and gate within its voltage-sensing domain. Pore opening has been proposed to include assembly of the selectivity filter between an arginine (R3) of segment S4 and an aspartate (D1) of segment S1. We determined whether gating involves motion of S1, using Ciona intestinalis Hv1. We found that channel opening is concomitant with solution access to the pore-lining face of S1, from the cytoplasm to deep inside the pore. Voltage- and patch-clamp fluorometry showed that this involves a motion of S1 relative to its surroundings. S1 motion and the S4 motion that precedes it are each influenced by residues on the other helix, thus suggesting a dynamic interaction between S1 and S4. Our findings suggest that the S1 of Hv1 has specialized to function as part of the channel's gate.
Collapse
|
66
|
Kim IH, Hevezi P, Varga C, Pathak MM, Hong L, Ta D, Tran CT, Zlotnik A, Soltesz I, Tombola F. Evidence for functional diversity between the voltage-gated proton channel Hv1 and its closest related protein HVRP1. PLoS One 2014; 9:e105926. [PMID: 25165868 PMCID: PMC4148356 DOI: 10.1371/journal.pone.0105926] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2014] [Accepted: 07/25/2014] [Indexed: 11/18/2022] Open
Abstract
The Hv1 channel and voltage-sensitive phosphatases share with voltage-gated sodium, potassium, and calcium channels the ability to detect changes in membrane potential through voltage-sensing domains (VSDs). However, they lack the pore domain typical of these other channels. NaV, KV, and CaV proteins can be found in neurons and muscles, where they play important roles in electrical excitability. In contrast, VSD-containing proteins lacking a pore domain are found in non-excitable cells and are not involved in neuronal signaling. Here, we report the identification of HVRP1, a protein related to the Hv1 channel (from which the name Hv1 Related Protein 1 is derived), which we find to be expressed primarily in the central nervous system, and particularly in the cerebellum. Within the cerebellar tissue, HVRP1 is specifically expressed in granule neurons, as determined by in situ hybridization and immunohistochemistry. Analysis of subcellular distribution via electron microscopy and immunogold labeling reveals that the protein localizes on the post-synaptic side of contacts between glutamatergic mossy fibers and the granule cells. We also find that, despite the similarities in amino acid sequence and structural organization between Hv1 and HVRP1, the two proteins have distinct functional properties. The high conservation of HVRP1 in vertebrates and its cellular and subcellular localizations suggest an important function in the nervous system.
Collapse
Affiliation(s)
- Iris H. Kim
- Department of Physiology and Biophysics, University of California Irvine, Irvine, California, United States of America
| | - Peter Hevezi
- Department of Physiology and Biophysics, University of California Irvine, Irvine, California, United States of America
| | - Csaba Varga
- Department of Anatomy and Neurobiology, University of California Irvine, Irvine, California, United States of America
| | - Medha M. Pathak
- Department of Physiology and Biophysics, University of California Irvine, Irvine, California, United States of America
| | - Liang Hong
- Department of Physiology and Biophysics, University of California Irvine, Irvine, California, United States of America
| | - Dennis Ta
- Department of Physiology and Biophysics, University of California Irvine, Irvine, California, United States of America
| | - Chau T. Tran
- Department of Physiology and Biophysics, University of California Irvine, Irvine, California, United States of America
| | - Albert Zlotnik
- Department of Physiology and Biophysics, University of California Irvine, Irvine, California, United States of America
| | - Ivan Soltesz
- Department of Anatomy and Neurobiology, University of California Irvine, Irvine, California, United States of America
| | - Francesco Tombola
- Department of Physiology and Biophysics, University of California Irvine, Irvine, California, United States of America
- * E-mail:
| |
Collapse
|
67
|
|
68
|
Molecular determinants of Hv1 proton channel inhibition by guanidine derivatives. Proc Natl Acad Sci U S A 2014; 111:9971-6. [PMID: 24912149 DOI: 10.1073/pnas.1324012111] [Citation(s) in RCA: 80] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
The voltage-gated proton channel Hv1 plays important roles in proton extrusion, pH homeostasis, and production of reactive oxygen species in a variety of cell types. Excessive Hv1 activity increases proliferation and invasiveness in cancer cells and worsens brain damage in ischemic stroke. The channel is composed of two subunits, each containing a proton-permeable voltage-sensing domain (VSD) and lacking the pore domain typical of other voltage-gated ion channels. We have previously shown that the compound 2-guanidinobenzimidazole (2GBI) inhibits Hv1 proton conduction by binding to the VSD from its intracellular side. Here, we examine the binding affinities of a series of 2GBI derivatives on human Hv1 channels mutated at positions located in the core of the VSD and apply mutant cycle analysis to determine how the inhibitor interacts with the channel. We identify four Hv1 residues involved in the binding: aspartate 112, phenylalanine 150, serine 181, and arginine 211. 2GBI appears to be oriented in the binding site with its benzo ring pointing to F150, its imidazole ring inserted between residue D112 and residues S181 and R211, and the guanidine group positioned in the proximity of R211. We also identify a modified version of 2GBI that is able to reach the binding site on Hv1 from the extracellular side of the membrane. Understanding how compounds like 2GBI interact with the Hv1 channel is an important step to the development of pharmacological treatments for diseases caused by Hv1 hyperactivity.
Collapse
|
69
|
Takeshita K, Sakata S, Yamashita E, Fujiwara Y, Kawanabe A, Kurokawa T, Okochi Y, Matsuda M, Narita H, Okamura Y, Nakagawa A. X-ray crystal structure of voltage-gated proton channel. Nat Struct Mol Biol 2014; 21:352-7. [DOI: 10.1038/nsmb.2783] [Citation(s) in RCA: 144] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2013] [Accepted: 02/03/2014] [Indexed: 12/12/2022]
|
70
|
Abstract
Microglia are brain resident immune cells and their functions are implicated in both the normal and diseased brain. Microglia express a plethora of ion channels, including K(+) channels, Na(+) channels, TRP channels, Cl(-) channels, and proton channels. These ion channels play critical roles in microglial proliferation, migration, and production/release of cytokines, chemokines, and neurotoxic or neurotrophic substances. Among microglial ion channels, the voltage-gated proton channel HV1 is a recently cloned ion channel that rapidly removes protons from depolarized cytoplasm and is highly expressed in the immune system. However, the function of microglial HV1 in the brain is poorly understood. Recent studies showed that HV1 is selectively expressed in microglia but not neurons in the brain. At the cellular level, microglial HV1 regulates intracellular pH and aids in NADPH oxidase-dependent generation of reactive oxygen species. In a mouse model of middle cerebral artery occlusion, microglial HV1 contributes to neuronal cell death and ischemic brain damage. This review discusses the discovery, properties, regulation, and pathophysiology of microglial HV1 proton channel in the brain.
Collapse
Affiliation(s)
- Long-Jun Wu
- Department of Cell Biology and Neuroscience, Rutgers University, Piscataway, NJ, USA
| |
Collapse
|
71
|
Fujiwara Y, Okamura Y. Temperature-sensitive gating of voltage-gated proton channels. CURRENT TOPICS IN MEMBRANES 2014; 74:259-92. [PMID: 25366240 DOI: 10.1016/b978-0-12-800181-3.00010-5] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
The voltage-gated proton channel (Hv) mediates robust proton transport down the proton electrochemical gradient. Hv is mainly expressed in immune cells, including neutrophils and macrophages, the physiological functions of which are temperature sensitive. In those cells, Hv plays key roles in the regulation of reactive oxygen species production and pH homeostasis. Proton transport through Hv is regulated by both the membrane potential and the pH difference across the cell membrane. Earlier studies showed that the properties of Hv, including proton conductance and gating, are highly temperature dependent. Hv consists of a voltage sensor domain involved in both voltage sensing and proton permeation and a C-terminal coiled coil region. Although the channel's activities are innate to the protomers, normally two protomers assemble as a dimer via interaction between C-terminal coiled coils. We recently discovered that the coiled-coil region of Hv dissociates at around room temperature, and that subtle changes in the coiled-coil region affect temperature-sensitive gating. In this chapter, we describe the physiological functions and molecular mechanisms of Hv, focusing mainly on the structure and thermosensitive properties of Hv.
Collapse
Affiliation(s)
- Yuichiro Fujiwara
- Laboratory of Integrative Physiology, Graduate School of Medicine, Osaka University, Suita, Japan
| | - Yasushi Okamura
- Laboratory of Integrative Physiology, Graduate School of Medicine, Osaka University, Suita, Japan
| |
Collapse
|
72
|
Abstract
Voltage-gated proton (Hv1) channels play important roles in the respiratory burst, in pH regulation, in spermatozoa, in apoptosis, and in cancer metastasis. Unlike other voltage-gated cation channels, the Hv1 channel lacks a centrally located pore formed by the assembly of subunits. Instead, the proton permeation pathway in the Hv1 channel is within the voltage-sensing domain of each subunit. The gating mechanism of this pathway is still unclear. Mutagenic and fluorescence studies suggest that the fourth transmembrane (TM) segment (S4) functions as a voltage sensor and that there is an outward movement of S4 during channel activation. Using thermodynamic mutant cycle analysis, we find that the conserved positively charged residues in S4 are stabilized by countercharges in the other TM segments both in the closed and open states. We constructed models of both the closed and open states of Hv1 channels that are consistent with the mutant cycle analysis. These structural models suggest that electrostatic interactions between TM segments in the closed state pull hydrophobic residues together to form a hydrophobic plug in the center of the voltage-sensing domain. Outward S4 movement during channel activation induces conformational changes that remove this hydrophobic plug and instead insert protonatable residues in the center of the channel that, together with water molecules, can form a hydrogen bond chain across the channel for proton permeation. This suggests that salt bridge networks and the hydrophobic plug function as the gate in Hv1 channels and that outward movement of S4 leads to the opening of this gate.
Collapse
|
73
|
Kurokawa T, Okamura Y. Mapping of sites facing aqueous environment of voltage-gated proton channel at resting state: a study with PEGylation protection. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2013; 1838:382-7. [PMID: 24140009 DOI: 10.1016/j.bbamem.2013.10.001] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/26/2013] [Revised: 09/30/2013] [Accepted: 10/01/2013] [Indexed: 12/19/2022]
Abstract
Hv1 (also named, voltage-sensor only protein, VSOP) lacks an authentic pore domain, and its voltage sensor domain plays both roles in voltage sensing and proton permeation. The activities of a proton channel are intrinsic to protomers of Hv1, while Hv1 is dimeric in biological membranes; cooperative gating is exerted by interaction between two protomers. As the signature pattern conserved among voltage-gated channels and voltage-sensing phosphatase, Hv1 has multiple arginines intervened by two hydrophobic residues on the fourth transmembrane segment, S4. S4 moves upward relative to other helices upon depolarization, causing conformational change possibly leading to the formation of a proton-selective conduction pathway. However, detailed mechanisms of proton-selectivity and gating of Hv1 are unknown. Here we took an approach of PEGylation protection assay to define residues facing the aqueous environment of mouse Hv1 (mHv1). Accessibilities of two maleimide molecules, N-ethylmaleimide (NEM) and 4-acetamido-4'-maleimidylstilbene-2,2'-disulfonic acid (AMS), were examined on cysteine introduced into individual sites. Only the first arginine on S4 (R1: R201) was inaccessible by NEM and AMS in mHv1. This is consistent with previous results of electrophysiology on the resting state channel, suggesting that the accessibility profile represents the resting state of mHv1. D108, critical for proton selectivity, was accessible by AMS and NEM, suggesting that D108 faces the vestibule. F146, a site critical for blocking by a guanidinium-reagent, was accessible by NEM, suggesting that F146 also faces the inner vestibule. These findings suggest an inner vestibule lined by several residues on S2 including F146, D108 on S1, and the C-terminal half of S4.
Collapse
Affiliation(s)
- Tatsuki Kurokawa
- Laboratory of Integrative Physiology, Department of Physiology, Graduate School of Medicine, Osaka University, Yamada-oka 2-2, Suita, Osaka 565-0871, Japan
| | | |
Collapse
|
74
|
Microglial voltage-gated proton channel Hv1 in ischemic stroke. Transl Stroke Res 2013; 5:99-108. [PMID: 24323712 DOI: 10.1007/s12975-013-0289-7] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2013] [Revised: 09/11/2013] [Accepted: 09/19/2013] [Indexed: 12/22/2022]
Abstract
Microglia, resident immune cells in the brain, contribute both to the damage and resolution of ischemic stroke. However, the mechanisms of microglia's detrimental or beneficial role in the disease are poorly understood. The voltage-gated proton channel, Hv1, rapidly removes protons from depolarized cytoplasm, and is highly expressed in the immune system. In the brain, Hv1 is selectively and functionally expressed in microglia but not neurons. Although the physiological function of microglial Hv1 is still not clear, Hv1 is one of major ion channels expressed in resting microglia. Under pathological conditions, microglial Hv1 is required for NADPH oxidase (NOX)-dependent generation of reactive oxygen species (ROS) by providing charge compensation for exported electrons and relieving intracellular acidosis. In a mouse model of cerebral middle artery occlusion, Hv1 knockout mice are protected from ischemic damage, showing reduced NOX-dependent ROS production, microglial activation and neuronal cell death. Therefore, microglial Hv1 aids in NOX-dependent ROS generation, which subsequently induces neuronal cell death and a significant fraction of brain damage after ischemic stroke. These studies illuminate a critical role of microglial Hv1 in ischemic brain injury, providing a rationale for Hv1 as a potential therapeutic target for the treatment of ischemic stroke. The current understanding of Hv1 in ischemic injury through NOX-dependent ROS production may serve as a common model to reveal the deleterious role of microglia in neurological diseases other than ischemic stroke, such as multiple sclerosis, amyotrophic lateral sclerosis, Alzheimer's disease, and neuropathic pain.
Collapse
|
75
|
Subunit interactions during cooperative opening of voltage-gated proton channels. Neuron 2013; 77:288-98. [PMID: 23352165 DOI: 10.1016/j.neuron.2012.12.021] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/14/2012] [Indexed: 11/24/2022]
Abstract
Voltage-gated proton (Hv1) channels are dimers, where each subunit has a separate permeation pathway. However, opening of the two pathways is highly cooperative. It is unclear how Hv1 channels open their permeation pathways, because Hv1 channels lack a classic pore domain. Using voltage-clamp fluorometry, we here detect two conformational changes reported by a fluorophore attached to the voltage sensor S4 in Hv1 channels. The first is voltage dependent and precedes channel opening, with properties consistent with reporting on independent S4 charge movements in the two subunits. The second is less voltage dependent and closely correlates with channel opening. Mutations that reduce dimerization or alter the intersubunit interface affect both the second conformational change and channel opening. These observations suggest that, following an initial S4 charge movement in the two subunits, there is a second, cooperative conformational change, involving interactions between subunits, that opens both pathways in Hv1 channels.
Collapse
|
76
|
Abstract
Voltage-activated proton (Hv1) channels are relatives of classical voltage-activated cation channels. In this issue of Neuron, Hong et al. (2013) and Qiu et al. (2013) investigate the functional mechanisms of Hv1 gating and uncover key relationships with Kv channels.
Collapse
Affiliation(s)
- Jeet Kalia
- Molecular Physiology and Biophysics Section, NINDS, Porter Neuroscience Research Center, Bethesda, MD 20892-3701, USA
| | | |
Collapse
|