1
|
Codding SJ, Trudeau MC. Photoinhibition of the hERG potassium channel PAS domain by ultraviolet light speeds channel closing. Biophys J 2024:S0006-3495(24)00351-5. [PMID: 38796698 DOI: 10.1016/j.bpj.2024.05.024] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2024] [Revised: 04/30/2024] [Accepted: 05/22/2024] [Indexed: 05/28/2024] Open
Abstract
hERG potassium channels are critical for cardiac excitability. hERG channels have a Per-Arnt-Sim (PAS) domain at their N-terminus, and here, we examined the mechanism for PAS domain regulation of channel opening and closing (gating). We used TAG codon suppression to incorporate the noncanonical amino acid 4-benzoyl-L-phenylalanine (BZF), which is capable of forming covalent cross-links after photoactivation by ultraviolet (UV) light, at three locations (G47, F48, and E50) in the PAS domain. We found that hERG-G47BZF channels had faster closing (deactivation) when irradiated in the open state (at 0 mV) but showed no measurable changes when irradiated in the closed state (at -100 mV). hERG-F48BZF channels had slower activation, faster deactivation, and a marked rightward shift in the voltage dependence of activation when irradiated in the open (at 0 mV) or closed (at -100 mV) state. hERG-E50BZF channels had no measurable changes when irradiated in the open state (at 0 mV) but had slower activation, faster deactivation, and a rightward shift in the voltage dependence of activation when irradiated in the closed state (at -100mV), indicating that hERG-E50BZF had a state-dependent difference in UV photoactivation, which we interpret to mean that PAS underwent molecular motions between the open and closed states. Moreover, we propose that UV-dependent biophysical changes in hERG-G47BZF, F48BZF, and E50BZF were the direct result of photochemical cross-linking that reduced dynamic motions in the PAS domain and broadly stabilized the closed state relative to the open state of the channel.
Collapse
Affiliation(s)
- Sara J Codding
- Department of Physiology, University of Maryland School of Medicine, Baltimore, Maryland
| | - Matthew C Trudeau
- Department of Physiology, University of Maryland School of Medicine, Baltimore, Maryland.
| |
Collapse
|
2
|
Andreas MP, Giessen TW. The biosynthesis of the odorant 2-methylisoborneol is compartmentalized inside a protein shell. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.04.23.590730. [PMID: 38712110 PMCID: PMC11071394 DOI: 10.1101/2024.04.23.590730] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2024]
Abstract
Terpenoids are the largest class of natural products, found across all domains of life. One of the most abundant bacterial terpenoids is the volatile odorant 2-methylisoborneol (2-MIB), partially responsible for the earthy smell of soil and musty taste of contaminated water. Many bacterial 2-MIB biosynthetic gene clusters were thought to encode a conserved transcription factor, named EshA in the model soil bacterium Streptomyces griseus . Here, we revise the function of EshA, now referred to as Sg Enc, and show that it is a Family 2B encapsulin shell protein. Using cryo-electron microscopy, we find that Sg Enc forms an icosahedral protein shell and encapsulates 2-methylisoborneol synthase (2-MIBS) as a cargo protein. Sg Enc contains a cyclic adenosine monophosphate (cAMP) binding domain (CBD)-fold insertion and a unique metal-binding domain, both displayed on the shell exterior. We show that Sg Enc CBDs do not bind cAMP. We find that 2-MIBS cargo loading is mediated by an N-terminal disordered cargo-loading domain and that 2-MIBS activity and Sg Enc shell structure are not modulated by cAMP. Our work redefines the function of EshA and establishes Family 2B encapsulins as cargo-loaded protein nanocompartments involved in secondary metabolite biosynthesis.
Collapse
|
3
|
Ghorbani M, Wang ZJ, Chen X, Tiwari PB, Klauda JB, Brelidze TI. Chlorpromazine inhibits EAG1 channels by altering the coupling between the PAS, CNBH and pore domains. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.02.23.581826. [PMID: 38464246 PMCID: PMC10925124 DOI: 10.1101/2024.02.23.581826] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/12/2024]
Abstract
EAG1 depolarization-activated potassium selective channels are important targets for treatment of cancer and neurological disorders. EAG1 channels are formed by a tetrameric subunit assembly with each subunit containing an N-terminal Per-Arnt-Sim (PAS) domain and C-terminal cyclic nucleotide-binding homology (CNBH) domain. The PAS and CNBH domains from adjacent subunits interact and form an intracellular tetrameric ring that regulates the EAG1 channel gating, including the movement of the voltage sensor domain (VSD) from closed to open states. Small molecule ligands can inhibit EAG1 channels by binding to their PAS domains. However, the allosteric pathways of this inhibition are not known. Here we show that chlorpromazine, a PAS domain small molecule binder, alters interactions between the PAS and CNBH domains and decreases the coupling between the intracellular tetrameric ring and the pore of the channel, while having little effect on the coupling between the PAS and VSD domains. In addition, chlorpromazine binding to the PAS domain did not alter Cole-Moore shift characteristic of EAG1 channels, further indicating that chlorpromazine has no effect on VSD movement from the deep closed to opened states. Our study provides a framework for understanding global pathways of EAG1 channel regulation by small molecule PAS domain binders.
Collapse
|
4
|
Tiwari PB, Kamgar-Dayhoff P, Tiwari P, McKillop MI, Brelidze TI. Use of Surface Plasmon Resonance Technique for Studies of Inter-domain Interactions in Ion Channels. Methods Mol Biol 2024; 2796:105-118. [PMID: 38856898 PMCID: PMC11225882 DOI: 10.1007/978-1-0716-3818-7_7] [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] [Indexed: 06/11/2024]
Abstract
Ion channels are transmembrane proteins essential for cellular functions and are important drug targets. Surface plasmon resonance (SPR) is a powerful technique for investigating protein-protein and protein-small molecule ligand interactions. SPR has been underutilized for studies of ion channels, even though it could provide a wealth of information on the mechanisms of ion channel regulation and aid in ion channel drug discovery. Here we provide a detailed description of the use of SPR technology for investigating inter-domain interactions in KCNH potassium-selective and voltage-gated ion channels.
Collapse
Affiliation(s)
- Purushottam B Tiwari
- Department of Oncology, Georgetown University Medical Center, Washington, DC, USA
| | - Pareesa Kamgar-Dayhoff
- Department of Pharmacology and Physiology, Georgetown University Medical Center, Washington, DC, USA
| | - Prakriti Tiwari
- Department of Oncology, Georgetown University Medical Center, Washington, DC, USA
- Department of Biology, College of Arts & Sciences, Georgetown University, Washington, DC, USA
| | - Maria I McKillop
- Department of Pharmacology and Physiology, Georgetown University Medical Center, Washington, DC, USA
| | - Tinatin I Brelidze
- Department of Pharmacology and Physiology, Georgetown University Medical Center, Washington, DC, USA.
| |
Collapse
|
5
|
Galán-Vidal J, Socuéllamos PG, Baena-Nuevo M, Contreras L, González T, Pérez-Poyato MS, Valenzuela C, González-Lamuño D, Gandarillas A. A novel loss-of-function mutation of the voltage-gated potassium channel Kv10.2 involved in epilepsy and autism. Orphanet J Rare Dis 2022; 17:345. [PMID: 36068614 PMCID: PMC9446776 DOI: 10.1186/s13023-022-02499-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2022] [Accepted: 08/18/2022] [Indexed: 11/17/2022] Open
Abstract
Background Novel developmental mutations associated with disease are a continuous challenge in medicine. Clinical consequences caused by these mutations include neuron and cognitive alterations that can lead to epilepsy or autism spectrum disorders. Often, it is difficult to identify the physiological defects and the appropriate treatments. Results We have isolated and cultured primary cells from the skin of a patient with combined epilepsy and autism syndrome. A mutation in the potassium channel protein Kv10.2 was identified. We have characterised the alteration of the mutant channel and found that it causes loss of function (LOF). Primary cells from the skin displayed a very striking growth defect and increased differentiation. In vitro treatment with various carbonic anhydrase inhibitors with various degrees of specificity for potassium channels, (Brinzolamide, Acetazolamide, Retigabine) restored the activation capacity of the mutated channel. Interestingly, the drugs also recovered in vitro the expansion capacity of the mutated skin cells. Furthermore, treatment with Acetazolamide clearly improved the patient regarding epilepsy and cognitive skills. When the treatment was temporarily halted the syndrome worsened again. Conclusions By in vitro studying primary cells from the patient and the activation capacity of the mutated protein, we could first, find a readout for the cellular defects and second, test pharmaceutical treatments that proved to be beneficial. The results show the involvement of a novel LOF mutation of a Potassium channel in autism syndrome with epilepsy and the great potential of in vitro cultures of primary cells in personalised medicine of rare diseases.
Collapse
Affiliation(s)
- Jesús Galán-Vidal
- Cell Cycle, Stem Cell Fate and Cancer Laboratory, Institute for Research Marqués de Valdecilla (IDIVAL), 39011, Santander, Spain
| | - Paula G Socuéllamos
- Instituto de Investigaciones Biomédicas Alberto Sols, IIBM, CSIC-UAM, Madrid, Spain.,Spanish Network for Biomedical Research in Cardiovascular Research (CIBERCV), Instituto de Salud Carlos III, Madrid, Spain
| | - María Baena-Nuevo
- Instituto de Investigaciones Biomédicas Alberto Sols, IIBM, CSIC-UAM, Madrid, Spain.,Spanish Network for Biomedical Research in Cardiovascular Research (CIBERCV), Instituto de Salud Carlos III, Madrid, Spain
| | - Lizbeth Contreras
- Cell Cycle, Stem Cell Fate and Cancer Laboratory, Institute for Research Marqués de Valdecilla (IDIVAL), 39011, Santander, Spain
| | - Teresa González
- Instituto de Investigaciones Biomédicas Alberto Sols, IIBM, CSIC-UAM, Madrid, Spain.,Spanish Network for Biomedical Research in Cardiovascular Research (CIBERCV), Instituto de Salud Carlos III, Madrid, Spain
| | - María S Pérez-Poyato
- Neuropediatric, University Hospital Marqués de Valdecilla, 39008, Santander, Spain
| | - Carmen Valenzuela
- Instituto de Investigaciones Biomédicas Alberto Sols, IIBM, CSIC-UAM, Madrid, Spain. .,Spanish Network for Biomedical Research in Cardiovascular Research (CIBERCV), Instituto de Salud Carlos III, Madrid, Spain.
| | - Domingo González-Lamuño
- Cell Cycle, Stem Cell Fate and Cancer Laboratory, Institute for Research Marqués de Valdecilla (IDIVAL), 39011, Santander, Spain. .,Paediatric Department, University of Cantabria University, Marqués de Valdecilla Hospital, 39008, Santander, Spain.
| | - Alberto Gandarillas
- Cell Cycle, Stem Cell Fate and Cancer Laboratory, Institute for Research Marqués de Valdecilla (IDIVAL), 39011, Santander, Spain. .,INSERM, Occitanie Méditerranée, 34394, Montpellier, France.
| |
Collapse
|
6
|
Soohoo SM, Tiwari PB, Suzuki YJ, Brelidze TI. Investigation of PAS and CNBH domain interactions in hERG channels and effects of long-QT syndrome-causing mutations with surface plasmon resonance. J Biol Chem 2021; 298:101433. [PMID: 34801551 PMCID: PMC8693265 DOI: 10.1016/j.jbc.2021.101433] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2021] [Revised: 11/15/2021] [Accepted: 11/16/2021] [Indexed: 11/29/2022] Open
Abstract
Human ether-á-go-go-related gene (hERG) channels are key regulators of cardiac repolarization, neuronal excitability, and tumorigenesis. hERG channels contain N-terminal Per-Arnt-Sim (PAS) and C-terminal cyclic nucleotide-binding homology (CNBH) domains with many long-QT syndrome (LQTS)-causing mutations located at the interface between these domains. Despite the importance of PAS/CNBH domain interactions, little is known about their affinity. Here, we used the surface plasmon resonance (SPR) technique to investigate interactions between isolated PAS and CNBH domains and the effects of LQTS-causing mutations R20G, N33T, and E58D, located at the PAS/CNBH domain interface, on these interactions. We determined that the affinity of the PAS/CNBH domain interactions was ∼1.4 μM. R20G and E58D mutations had little effect on the domain interaction affinity, while N33T abolished the domain interactions. Interestingly, mutations in the intrinsic ligand, a conserved stretch of amino acids occupying the beta-roll cavity in the CNBH domain, had little effect on the affinity of PAS/CNBH domain interactions. Additionally, we determined that the isolated PAS domains formed oligomers with an interaction affinity of ∼1.6 μM. Coexpression of the isolated PAS domains with the full-length hERG channels or addition of the purified PAS protein inhibited hERG currents. These PAS/PAS interactions can have important implications for hERG function in normal and pathological conditions associated with increased surface density of channels or interaction with other PAS-domain-containing proteins. Taken together, our study provides the first account of the binding affinities for wild-type and mutant hERG PAS and CNBH domains and highlights the potential functional significance of PAS/PAS domain interactions.
Collapse
Affiliation(s)
- Stephanie M Soohoo
- Department of Pharmacology and Physiology, Georgetown University Medical Center, Washington, District of Columbia, USA
| | - Purushottam B Tiwari
- Department of Oncology, Georgetown University Medical Center, Washington, District of Columbia, USA
| | - Yuichiro J Suzuki
- Department of Pharmacology and Physiology, Georgetown University Medical Center, Washington, District of Columbia, USA
| | - Tinatin I Brelidze
- Department of Pharmacology and Physiology, Georgetown University Medical Center, Washington, District of Columbia, USA.
| |
Collapse
|
7
|
Conformation-sensitive antibody reveals an altered cytosolic PAS/CNBh assembly during hERG channel gating. Proc Natl Acad Sci U S A 2021; 118:2108796118. [PMID: 34716268 DOI: 10.1073/pnas.2108796118] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2021] [Accepted: 09/22/2021] [Indexed: 11/18/2022] Open
Abstract
The human ERG (hERG) K+ channel has a crucial function in cardiac repolarization, and mutations or channel block can give rise to long QT syndrome and catastrophic ventricular arrhythmias. The cytosolic assembly formed by the Per-Arnt-Sim (PAS) and cyclic nucleotide binding homology (CNBh) domains is the defining structural feature of hERG and related KCNH channels. However, the molecular role of these two domains in channel gating remains unclear. We have previously shown that single-chain variable fragment (scFv) antibodies can modulate hERG function by binding to the PAS domain. Here, we mapped the scFv2.12 epitope to a site overlapping with the PAS/CNBh domain interface using NMR spectroscopy and mutagenesis and show that scFv binding in vitro and in the cell is incompatible with the PAS interaction with CNBh. By generating a fluorescently labeled scFv2.12, we demonstrate that association with the full-length hERG channel is state dependent. We detect Förster resonance energy transfer (FRET) with scFv2.12 when the channel gate is open but not when it is closed. In addition, state dependence of scFv2.12 FRET signal disappears when the R56Q mutation, known to destabilize the PAS-CNBh interaction, is introduced in the channel. Altogether, these data are consistent with an extensive structural alteration of the PAS/CNBh assembly when the cytosolic gate opens, likely favoring PAS domain dissociation from the CNBh domain.
Collapse
|
8
|
Ben-Bassat A, Giladi M, Haitin Y. Structure of KCNH2 cyclic nucleotide-binding homology domain reveals a functionally vital salt-bridge. J Gen Physiol 2021; 152:151568. [PMID: 32191791 PMCID: PMC7141593 DOI: 10.1085/jgp.201912505] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2019] [Revised: 01/24/2020] [Accepted: 02/12/2020] [Indexed: 01/04/2023] Open
Abstract
Human KCNH2 channels (hKCNH2, ether-à-go-go [EAG]–related gene, hERG) are best known for their contribution to cardiac action potential repolarization and have key roles in various pathologies. Like other KCNH family members, hKCNH2 channels contain a unique intracellular complex, consisting of an N-terminal eag domain and a C-terminal cyclic nucleotide-binding homology domain (CNBHD), which is crucial for channel function. Previous studies demonstrated that the CNBHD is occupied by an intrinsic ligand motif, in a self-liganded conformation, providing a structural mechanism for the lack of KCNH channel regulation by cyclic nucleotides. While there have been significant advancements in the structural and functional characterization of the CNBHD of KCNH channels, a high-resolution structure of the hKCNH2 intracellular complex has been missing. Here, we report the 1.5 Å resolution structure of the hKCNH2 channel CNBHD. The structure reveals the canonical fold shared by other KCNH family members, where the spatial organization of the intrinsic ligand is preserved within the β-roll region. Moreover, measurements of small-angle x-ray scattering profile in solution, as well as comparison with a recent NMR analysis of hKCNH2, revealed high agreement with the crystallographic structure, indicating an overall low flexibility in solution. Importantly, we identified a novel salt-bridge (E807-R863) which was not previously resolved in the NMR and cryo-EM structures. Electrophysiological analysis of charge-reversal mutations revealed the bridge’s crucial role in hKCNH2 function. Moreover, comparison with other KCNH members revealed the structural conservation of this salt-bridge, consistent with its functional significance. Together with the available structure of the mouse KCNH1 intracellular complex and previous electrophysiological and spectroscopic studies of KCNH family members, we propose that this salt-bridge serves as a strategically positioned linchpin to support both the spatial organization of the intrinsic ligand and the maintenance of the intracellular complex interface.
Collapse
Affiliation(s)
- Ariel Ben-Bassat
- Department of Physiology and Pharmacology, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel
| | - Moshe Giladi
- Department of Physiology and Pharmacology, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel
| | - Yoni Haitin
- Department of Physiology and Pharmacology, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel.,Sagol School of Neuroscience, Tel Aviv University, Tel Aviv, Israel
| |
Collapse
|
9
|
Hernández-Meza JM, Mares-Sámano S, Garduño-Juárez R. Insights into the Molecular Inhibition of the Oncogenic Channel K V10.1 by Globular Toxins. J Chem Inf Model 2021; 61:2328-2340. [PMID: 33900765 DOI: 10.1021/acs.jcim.0c01353] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Inhibition of the expression of the human ether-à-go-go (hEAG1 or hKV10.1) channel is associated with a dramatic reduction in the growth of several cancerous tumors. The modulation of this channel's activity is a promising target for the development of new anticancer drugs. Although some small molecules have shown inhibitory activity against KV10.1, their lack of specificity has prevented their use in humans. In vitro studies have recently identified a limited number of peptide toxins with proven specificity in their hKV10.1 channel inhibitory effect. These peptide toxins have become desirable candidates to use as lead compounds to design more potent and specific hKV10.1 inhibitors. However, the currently available studies lack the atomic resolution needed to characterize the molecular features that favor their binding to hKV10.1. In this work, we present the first attempt to locate the possible hKV10.1 binding sites of the animal peptide toxins APETx4, Aa1a, Ap1a, and k-hefutoxin 1, all of which described as hKV10.1 inhibitors. Our studies incorporated homology modeling to construct a robust three-dimensional (3D) model of hKV10.1, applied protein docking, and multiscale molecular dynamics techniques to reveal in atomic resolution the toxin-channel interactions. Our approach suggests that some peptide toxins bind in the outer vestibule surrounding the pore of hKV10.1; it also identified the channel residues Met397 and Asp398 as possible anchors that stabilize the binding of the evaluated toxins. Finally, a description of the possible mechanism for inhibition and gating is presented.
Collapse
Affiliation(s)
- Juan M Hernández-Meza
- Instituto de Ciencias Físicas, Universidad Nacional Autónoma de México, Cuernavaca 62210, Morelos, México
| | - Sergio Mares-Sámano
- CONACYT - Instituto de Ciencias Físicas, Universidad Nacional Autónoma de México, Cuernavaca 62210, Morelos, México
| | - Ramón Garduño-Juárez
- Instituto de Ciencias Físicas, Universidad Nacional Autónoma de México, Cuernavaca 62210, Morelos, México
| |
Collapse
|
10
|
Wang ZJ, Soohoo SM, Tiwari PB, Piszczek G, Brelidze TI. Chlorpromazine binding to the PAS domains uncovers the effect of ligand modulation on EAG channel activity. J Biol Chem 2020; 295:4114-4123. [PMID: 32047112 PMCID: PMC7105296 DOI: 10.1074/jbc.ra119.012377] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2019] [Revised: 02/10/2020] [Indexed: 12/18/2022] Open
Abstract
Ether-a-go-go (EAG) potassium selective channels are major regulators of neuronal excitability and cancer progression. EAG channels contain a Per-Arnt-Sim (PAS) domain in their intracellular N-terminal region. The PAS domain is structurally similar to the PAS domains in non-ion channel proteins, where these domains frequently function as ligand-binding domains. Despite the structural similarity, it is not known whether the PAS domain can regulate EAG channel function via ligand binding. Here, using surface plasmon resonance, tryptophan fluorescence, and analysis of EAG currents recorded in Xenopus laevis oocytes, we show that a small molecule chlorpromazine (CH), widely used as an antipsychotic medication, binds to the isolated PAS domain of EAG channels and inhibits currents from these channels. Mutant EAG channels that lack the PAS domain show significantly lower inhibition by CH, suggesting that CH affects currents from EAG channels directly through the binding to the PAS domain. Our study lends support to the hypothesis that there are previously unaccounted steps in EAG channel gating that could be activated by ligand binding to the PAS domain. This has broad implications for understanding gating mechanisms of EAG and related ERG and ELK K+ channels and places the PAS domain as a new target for drug discovery in EAG and related channels. Up-regulation of EAG channel activity is linked to cancer and neurological disorders. Our study raises the possibility of repurposing the antipsychotic drug chlorpromazine for treatment of neurological disorders and cancer.
Collapse
Affiliation(s)
- Ze-Jun Wang
- Department of Pharmacology and Physiology, Georgetown University Medical Center, Washington, D. C., 20057
| | - Stephanie M Soohoo
- Department of Pharmacology and Physiology, Georgetown University Medical Center, Washington, D. C., 20057
| | - Purushottam B Tiwari
- Department of Oncology, Georgetown University Medical Center, Washington, D. C., 20057
| | - Grzegorz Piszczek
- Biophysics Core, NHLBI, National Institutes of Health, Bethesda, Maryland 20892
| | - Tinatin I Brelidze
- Department of Pharmacology and Physiology, Georgetown University Medical Center, Washington, D. C., 20057.
| |
Collapse
|
11
|
Shi YP, Thouta S, Claydon TW. Modulation of hERG K + Channel Deactivation by Voltage Sensor Relaxation. Front Pharmacol 2020; 11:139. [PMID: 32184724 PMCID: PMC7059196 DOI: 10.3389/fphar.2020.00139] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2019] [Accepted: 01/31/2020] [Indexed: 12/17/2022] Open
Abstract
The hERG (human-ether-à-go-go-related gene) channel underlies the rapid delayed rectifier current, Ikr, in the heart, which is essential for normal cardiac electrical activity and rhythm. Slow deactivation is one of the hallmark features of the unusual gating characteristics of hERG channels, and plays a crucial role in providing a robust current that aids repolarization of the cardiac action potential. As such, there is significant interest in elucidating the underlying mechanistic determinants of slow hERG channel deactivation. Recent work has shown that the hERG channel S4 voltage sensor is stabilized following activation in a process termed relaxation. Voltage sensor relaxation results in energetic separation of the activation and deactivation pathways, producing a hysteresis, which modulates the kinetics of deactivation gating. Despite widespread observation of relaxation behaviour in other voltage-gated K+ channels, such as Shaker, Kv1.2 and Kv3.1, as well as the voltage-sensing phosphatase Ci-VSP, the relationship between stabilization of the activated voltage sensor by the open pore and voltage sensor relaxation in the control of deactivation has only recently begun to be explored. In this review, we discuss present knowledge and questions raised related to the voltage sensor relaxation mechanism in hERG channels and compare structure-function aspects of relaxation with those observed in related ion channels. We focus discussion, in particular, on the mechanism of coupling between voltage sensor relaxation and deactivation gating to highlight the insight that these studies provide into the control of hERG channel deactivation gating during their physiological functioning.
Collapse
Affiliation(s)
- Yu Patrick Shi
- Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, Canada
| | - Samrat Thouta
- Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, Canada
| | - Thomas W Claydon
- Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, Canada
| |
Collapse
|
12
|
Robertson GA, Morais-Cabral JH. hERG Function in Light of Structure. Biophys J 2019; 118:790-797. [PMID: 31669064 DOI: 10.1016/j.bpj.2019.10.010] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2019] [Revised: 09/27/2019] [Accepted: 10/02/2019] [Indexed: 12/25/2022] Open
Abstract
The human ether-a-go-go-related gene1 (hERG) ion channel has been the subject of fascination since it was identified as a target of long QT syndrome more than 20 years ago. In this Biophysical Perspective, we look at what makes hERG intriguing and vexingly unique. By probing recent high-resolution structures in the context of functional and biochemical data, we attempt to summarize new insights into hERG-specific function and articulate important unanswered questions. X-ray crystallography and cryo-electron microscopy have revealed features not previously on the radar-the "nonswapped" transmembrane architecture, an "intrinsic ligand," and hydrophobic pockets off a pore cavity that is surprisingly small. Advances in our understanding of drug block and inactivation mechanisms are noted, but a full picture will require more investigation.
Collapse
Affiliation(s)
- Gail A Robertson
- Department of Neuroscience, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, Wisconsin.
| | - João H Morais-Cabral
- i3S, Instituto de Investigação e Inovação em Saúde, Universidade do Porto, Porto, Portugal; IBMC- Instituto de Biologia Molecular e Celular, Universidade do Porto, Porto, Portugal
| |
Collapse
|
13
|
Wang ZJ, Tiwari PB, Üren A, Brelidze TI. Identification of undecylenic acid as EAG channel inhibitor using surface plasmon resonance-based screen of KCNH channels. BMC Pharmacol Toxicol 2019; 20:42. [PMID: 31315662 PMCID: PMC6637479 DOI: 10.1186/s40360-019-0324-8] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2019] [Accepted: 07/11/2019] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND KCNH family of potassium channels is responsible for diverse physiological functions ranging from the regulation of neuronal excitability and cardiac contraction to the regulation of cancer progression. KCNH channels contain a Per-Arn-Sim (PAS) domain in their N-terminal and cyclic nucleotide-binding homology (CNBH) domain in their C-terminal regions. These intracellular domains shape the function of KCNH channels and are important targets for drug development. METHODS Here we describe a surface plasmon resonance (SPR)-based screening method aimed in identifying small molecule binders of PAS and CNBH domains for three KCNH channel subfamilies: ether-à-go-go (EAG), EAG-related gene (ERG), and EAG-like K+ (ELK). The method involves purification of the PAS and CNBH domains, immobilization of the purified domains on the SPR senor chip and screening small molecules in a chemical library for binding to the immobilized domains using changes in the SPR response as a reporter of the binding. The advantages of this method include low quantity of purified PAS and CNBH domains necessary for the implementation of the screen, direct assessment of the small molecule binding to the PAS and CNBH domains and easiness of assessing KCNH subfamily specificity of the small molecule binders. RESULTS Using the SPR-based method we screened the Spectrum Collection Library of 2560 compounds against the PAS and CNBH domains of the three KCNH channel subfamilies and identified a pool of small molecules that bind to the PAS or CNBH domains. To further evaluate the effectiveness of the screen we tested the functional effect of one of the identified mEAG PAS domain specific small molecule binders on currents recorded from EAG channels. Undecylenic acid inhibited currents recorded from EAG channels in a concentration-dependent manner with IC50 of ~ 1 μM. CONCLUSION Our results show that the SPR-based method is well suited for identifying small molecule binders of KCNH channels and can facilitate drug discovery for other ion channels as well.
Collapse
Affiliation(s)
- Ze-Jun Wang
- Department of Pharmacology and Physiology, Georgetown University Medical Center, Washington, DC USA
| | | | - Aykut Üren
- Department of Oncology, Georgetown University Medical Center, Washington, DC USA
| | - Tinatin I. Brelidze
- Department of Pharmacology and Physiology, Georgetown University Medical Center, Washington, DC USA
| |
Collapse
|
14
|
Brelidze TI. N- and C-terminal interactions in KCNH channels: The spotlight on the intrinsic ligand. J Gen Physiol 2019; 151:400-403. [PMID: 30782602 PMCID: PMC6445575 DOI: 10.1085/jgp.201812313] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Brelidze examines recent data revealing the new role of the intrinsic ligand in hERG potassium channel gating.
Collapse
Affiliation(s)
- Tinatin I Brelidze
- Department of Pharmacology and Physiology, Georgetown University Medical Center, Washington, DC
| |
Collapse
|
15
|
Dai G, James ZM, Zagotta WN. Dynamic rearrangement of the intrinsic ligand regulates KCNH potassium channels. J Gen Physiol 2018; 150:625-635. [PMID: 29567795 PMCID: PMC5881448 DOI: 10.1085/jgp.201711989] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2017] [Accepted: 02/28/2018] [Indexed: 12/27/2022] Open
Abstract
KCNH potassium channels possess an intrinsic ligand in their cyclic nucleotide-binding homology domain, located at the N- and C-terminal domain interface. Dai et al. show that this intrinsic ligand regulates voltage-dependent potentiation via a rearrangement between the ligand and its binding site. KCNH voltage-gated potassium channels (EAG, ERG, and ELK) play significant roles in neuronal and cardiac excitability. They contain cyclic nucleotide-binding homology domains (CNBHDs) but are not directly regulated by cyclic nucleotides. Instead, the CNBHD ligand-binding cavity is occupied by an intrinsic ligand, which resides at the intersubunit interface between the N-terminal eag domain and the C-terminal CNBHD. We show that, in Danio rerio ELK channels, this intrinsic ligand is critical for voltage-dependent potentiation (VDP), a process in which channel opening is stabilized by prior depolarization. We demonstrate that an exogenous peptide corresponding to the intrinsic ligand can bind to and regulate zebrafish ELK channels. This exogenous intrinsic ligand inhibits the channels before VDP and potentiates the channels after VDP. Furthermore, using transition metal ion fluorescence resonance energy transfer and a fluorescent noncanonical amino acid L-Anap, we show that there is a rearrangement of the intrinsic ligand relative to the CNBHD during VDP. We propose that the intrinsic ligand switches from antagonist to agonist as a result of a rearrangement of the eag domain–CNBHD interaction during VDP.
Collapse
Affiliation(s)
- Gucan Dai
- Department of Physiology and Biophysics, University of Washington, Seattle, WA
| | - 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
| |
Collapse
|
16
|
Abstract
Khoo and Pless examine new work that provides mechanistic insight into the role of the intrinsic ligand in KCNH ion channels.
Collapse
Affiliation(s)
- Keith K Khoo
- Department of Drug Design and Pharmacology, Center for Biopharmaceuticals, University of Copenhagen, Copenhagen, Denmark
| | - Stephan A Pless
- Department of Drug Design and Pharmacology, Center for Biopharmaceuticals, University of Copenhagen, Copenhagen, Denmark
| |
Collapse
|
17
|
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.
Collapse
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
| |
Collapse
|
18
|
Romero F, Santana-Calvo C, Sánchez-Guevara Y, Nishigaki T. FRET-based binding assay between a fluorescent cAMP analogue and a cyclic nucleotide-binding domain tagged with a CFP. FEBS Lett 2017; 591:2869-2878. [PMID: 28734016 DOI: 10.1002/1873-3468.12760] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2017] [Revised: 06/29/2017] [Accepted: 07/18/2017] [Indexed: 11/12/2022]
Abstract
The cyclic nucleotide-binding domain (CNBD) functions as a regulatory domain of many proteins involved in cyclic nucleotide signalling. We developed a straightforward and reliable binding assay based on intermolecular fluorescence resonance energy transfer (FRET) between an adenosine-3', 5'-cyclic monophosphate analogue labelled with fluorescein and a recombinant CNBD of human EPAC1 tagged with a cyan fluorescence protein (CFP). The high FRET efficiency of this method (~ 80%) allowed us to perform several types of binding experiments with nanomolar range of sample using conventional equipment. In addition, the CFP tag on the CNBD enabled us to perform a specific binding experiment using an unpurified protein. Considering these advantages, this technique is useful to study poorly characterized CNBDs.
Collapse
Affiliation(s)
- Francisco Romero
- Departamento de Genética del Desarrollo y Fisiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México (UNAM), Cuernavaca, Morelos, México
| | - Carmen Santana-Calvo
- Departamento de Genética del Desarrollo y Fisiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México (UNAM), Cuernavaca, Morelos, México
| | - Yoloxochitl Sánchez-Guevara
- Departamento de Genética del Desarrollo y Fisiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México (UNAM), Cuernavaca, Morelos, México
| | - Takuya Nishigaki
- Departamento de Genética del Desarrollo y Fisiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México (UNAM), Cuernavaca, Morelos, México
| |
Collapse
|
19
|
Dai G, Zagotta WN. Molecular mechanism of voltage-dependent potentiation of KCNH potassium channels. eLife 2017; 6. [PMID: 28443815 PMCID: PMC5440166 DOI: 10.7554/elife.26355] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2017] [Accepted: 04/24/2017] [Indexed: 12/11/2022] Open
Abstract
EAG-like (ELK) voltage-gated potassium channels are abundantly expressed in the brain. These channels exhibit a behavior called voltage-dependent potentiation (VDP), which appears to be a specialization to dampen the hyperexitability of neurons. VDP manifests as a potentiation of current amplitude, hyperpolarizing shift in voltage sensitivity, and slowing of deactivation in response to a depolarizing prepulse. Here we show that VDP of D. rerio ELK channels involves the structural interaction between the intracellular N-terminal eag domain and C-terminal CNBHD. Combining transition metal ion FRET, patch-clamp fluorometry, and incorporation of a fluorescent noncanonical amino acid, we show that there is a rearrangement in the eag domain-CNBHD interaction with the kinetics, voltage-dependence, and ATP-dependence of VDP. We propose that the activation of ELK channels involves a slow open-state dependent rearrangement of the direct interaction between the eag domain and CNBHD, which stabilizes the opening of the channel. DOI:http://dx.doi.org/10.7554/eLife.26355.001 In humans and other animals, electrical signals trigger the heart to beat and carry information around the brain and nervous system. Particular cells can generate these signals by regulating the flow of ions into and out of the cell via proteins called ion channels. These proteins sit in the membrane that surrounds the cell and will open or close in response to specific signals. For example, an ion channel in humans called hERG allows positively-charged potassium ions to flow out of a heart cell to help the cell return to its “resting” state after producing an electrical signal. Defects in hERG can alter the rhythm at which the heart beats, leading to a serious condition called Long QT syndrome. The human hERG channel is part of a family of related channels known as the KCNH channels. These channels are made of four protein subunits that assemble to form a pore that spans the cell membrane. When a cell is resting before producing an electrical signal, KCNH channels are generally closed. However, once an electrical signal starts, the flow of ions through other ion channels in the cell membrane changes an electrical property across the membrane known as the “voltage”. This change in voltage causes KCNH channels to open. Dai and Zagotta studied how a KCNH channel known as ELK from zebrafish responds to changes in membrane voltage. The experiments show that the manner in which ELK channels respond to the voltage is due to changes in how the subunits interact in the part of the channel that lies inside the cell. Further experiments using several new techniques reveal in much more detail how the shape of the channel alters as the voltage changes. These new techniques could also be used to observe how other KCNH channels in the heart and brain change shape in response to changes in voltage. This could lead to the design of new drugs to treat heart and neurological diseases. DOI:http://dx.doi.org/10.7554/eLife.26355.002
Collapse
Affiliation(s)
- Gucan Dai
- Department of Physiology and Biophysics, University of Washington, Seattle, United States
| | - William N Zagotta
- Department of Physiology and Biophysics, University of Washington, Seattle, United States
| |
Collapse
|
20
|
Abstract
Cyclic nucleotide-gated (CNG) and hyperpolarization-activated cyclic nucleotide-regulated (HCN) ion channels play crucial physiological roles in phototransduction, olfaction, and cardiac pace making. These channels are characterized by the presence of a carboxyl-terminal cyclic nucleotide-binding domain (CNBD) that connects to the channel pore via a C-linker domain. Although cyclic nucleotide binding has been shown to promote CNG and HCN channel opening, the precise mechanism underlying gating remains poorly understood. Here we used cryoEM to determine the structure of the intact LliK CNG channel isolated from Leptospira licerasiae-which shares sequence similarity to eukaryotic CNG and HCN channels-in the presence of a saturating concentration of cAMP. A short S4-S5 linker connects nearby voltage-sensing and pore domains to produce a non-domain-swapped transmembrane architecture, which appears to be a hallmark of this channel family. We also observe major conformational changes of the LliK C-linkers and CNBDs relative to the crystal structures of isolated C-linker/CNBD fragments and the cryoEM structures of related CNG, HCN, and KCNH channels. The conformation of our LliK structure may represent a functional state of this channel family not captured in previous studies.
Collapse
|
21
|
Eag1 Voltage-Dependent Potassium Channels: Structure, Electrophysiological Characteristics, and Function in Cancer. J Membr Biol 2017; 250:123-132. [DOI: 10.1007/s00232-016-9944-8] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2016] [Accepted: 12/19/2016] [Indexed: 01/07/2023]
|
22
|
Zhao Y, Goldschen-Ohm MP, Morais-Cabral JH, Chanda B, Robertson GA. The intrinsically liganded cyclic nucleotide-binding homology domain promotes KCNH channel activation. J Gen Physiol 2017; 149:249-260. [PMID: 28122815 PMCID: PMC5299623 DOI: 10.1085/jgp.201611701] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2016] [Revised: 11/29/2016] [Accepted: 12/21/2016] [Indexed: 12/17/2022] Open
Abstract
hEAG1 is a member of the KCNH family of ion channels, which are characterized by C-terminal regions with homology to cyclic nucleotide–binding domains (CNBhDs). Zhao et al. show that an “intrinsic ligand” occupying the CNBhD binding pocket promotes the activated and open state of the channel. Channels in the ether-à-go-go or KCNH family of potassium channels are characterized by a conserved, C-terminal domain with homology to cyclic nucleotide–binding homology domains (CNBhDs). Instead of cyclic nucleotides, two amino acid residues, Y699 and L701, occupy the binding pocket, forming an “intrinsic ligand.” The role of the CNBhD in KCNH channel gating is still unclear, however, and a detailed characterization of the intrinsic ligand is lacking. In this study, we show that mutating both Y699 and L701 to alanine, serine, aspartate, or glycine impairs human EAG1 channel function. These mutants slow channel activation and shift the conductance–voltage (G–V) relation to more depolarized potentials. The mutations affect activation and the G-V relation progressively, indicating that the gating machinery is sensitive to multiple conformations of the CNBhD. Substitution with glycine at both sites (GG), which eliminates the side chains that interact with the binding pocket, also reduces the ability of voltage prepulses to populate more preactivated states along the activation pathway (i.e., the Cole–Moore effect), as if stabilizing the voltage sensor in deep resting states. Notably, deletion of the entire CNBhD (577–708, ΔCNBhD) phenocopies the GG mutant, suggesting that GG is a loss-of-function mutation and the CNBhD requires an intrinsic ligand to exert its functional effects. We developed a kinetic model for both wild-type and ΔCNBhD mutant channels that describes all our observations on activation kinetics, the Cole–Moore shift, and G-V relations. These findings support a model in which the CNBhD both promotes voltage sensor activation and stabilizes the open pore. The intrinsic ligand is critical for these functional effects.
Collapse
Affiliation(s)
- Yaxian Zhao
- Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, WI 53705.,Cardiovascular Research Center, University of Wisconsin School of Medicine and Public Health, Madison, WI 53705
| | - Marcel P Goldschen-Ohm
- Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, WI 53705.,Cardiovascular Research Center, University of Wisconsin School of Medicine and Public Health, Madison, WI 53705
| | - João H Morais-Cabral
- Instituto de Biologia Molecular e Celular, Universidade do Porto, 4150 Porto, Portugal.,Instituto de Investigação e Inovação em Saúde, Universidade do Porto, 4150 Porto, Portugal
| | - Baron Chanda
- Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, WI 53705.,Cardiovascular Research Center, University of Wisconsin School of Medicine and Public Health, Madison, WI 53705
| | - Gail A Robertson
- Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, WI 53705 .,Cardiovascular Research Center, University of Wisconsin School of Medicine and Public Health, Madison, WI 53705
| |
Collapse
|
23
|
Bernsteiner H, Bründl M, Stary-Weinzinger A. Dynamics of the EAG1 K + channel selectivity filter assessed by molecular dynamics simulations. Biochem Biophys Res Commun 2017; 484:107-112. [PMID: 28109880 PMCID: PMC6531291 DOI: 10.1016/j.bbrc.2017.01.064] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2017] [Accepted: 01/13/2017] [Indexed: 01/14/2023]
Abstract
EAG1 channels belong to the KCNH family of voltage gated potassium channels. They are expressed in several brain regions and increased expression is linked to certain cancer types. Recent cryo-EM structure determination finally revealed the structure of these channels in atomic detail, allowing computational investigations. In this study, we performed molecular dynamics simulations to investigate the ion binding sites and the dynamical behavior of the selectivity filter. Our simulations suggest that sites S2 and S4 form stable ion binding sites, while ions placed at sites S1 and S3 rapidly switched to sites S2 and S4. Further, ions tended to dissociate away from S0 within less than 20 ns, due to increased filter flexibility. This was followed by water influx from the extracellular side, leading to a widening of the filter in this region, and likely non-conductive filter configurations. Simulations with the inactivation-enhancing mutant Y464A or Na+ ions lead to trapped water molecules behind the SF, suggesting that these simulations captured early conformational changes linked to C-type inactivation.
Collapse
Affiliation(s)
- Harald Bernsteiner
- Department of Pharmacology and Toxicology, University of Vienna, Althanstraße 14, 1090 Vienna, Austria
| | - Michael Bründl
- Department of Pharmacology and Toxicology, University of Vienna, Althanstraße 14, 1090 Vienna, Austria
| | - Anna Stary-Weinzinger
- Department of Pharmacology and Toxicology, University of Vienna, Althanstraße 14, 1090 Vienna, Austria.
| |
Collapse
|
24
|
Marques-Carvalho MJ, Oppermann J, Muñoz E, Fernandes AS, Gabant G, Cadene M, Heinemann SH, Schönherr R, Morais-Cabral JH. Molecular Insights into the Mechanism of Calmodulin Inhibition of the EAG1 Potassium Channel. Structure 2016; 24:1742-1754. [PMID: 27618660 DOI: 10.1016/j.str.2016.07.020] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2016] [Revised: 07/26/2016] [Accepted: 07/29/2016] [Indexed: 12/26/2022]
Abstract
The human EAG1 potassium channel belongs to the superfamily of KCNH voltage-gated potassium channels that have roles in cardiac repolarization and neuronal excitability. EAG1 is strongly inhibited by Ca2+/calmodulin (CaM) through a mechanism that is not understood. We determined the binding properties of CaM with each one of three previously identified binding sites (BDN, BDC1, and BDC2), analyzed binding to protein stretches that include more than one site, and determined the effect of neighboring globular domains on the binding properties. The determination of the crystal structure of CaM bound to BDC2 shows the channel fragment interacting with only the C lobe of calmodulin and adopting an unusual bent conformation. Based on this structure and on a functional and biochemical analysis of mutants, we propose a model for the mechanism of inhibition whereby the local conformational change induced by CaM binding at BDC2 lies at the basis of channel modulation.
Collapse
Affiliation(s)
- Maria João Marques-Carvalho
- Instituto de Biologia Molecular e Celular, Rua Alfredo Allen, 208, 4200-135 Porto, Portugal; Instituto de Investigação e Inovação em Saúde, Universidade do Porto, 4200-135 Porto, Portugal
| | - Johannes Oppermann
- Department of Biophysics, Center for Molecular Biomedicine, Friedrich Schiller University Jena and Jena University Hospital, 07745 Jena, Germany
| | - Eva Muñoz
- Software 4 Science Developments, 15782 Santiago de Compostela, Spain
| | - Andreia S Fernandes
- Instituto de Biologia Molecular e Celular, Rua Alfredo Allen, 208, 4200-135 Porto, Portugal; Instituto de Investigação e Inovação em Saúde, Universidade do Porto, 4200-135 Porto, Portugal
| | - Guillaume Gabant
- Centre de Biophysique Moléculaire, CNRS UPR430, 45071 Orléans, France
| | - Martine Cadene
- Centre de Biophysique Moléculaire, CNRS UPR430, 45071 Orléans, France
| | - Stefan H Heinemann
- Department of Biophysics, Center for Molecular Biomedicine, Friedrich Schiller University Jena and Jena University Hospital, 07745 Jena, Germany
| | - Roland Schönherr
- Department of Biophysics, Center for Molecular Biomedicine, Friedrich Schiller University Jena and Jena University Hospital, 07745 Jena, Germany
| | - João Henrique Morais-Cabral
- Instituto de Biologia Molecular e Celular, Rua Alfredo Allen, 208, 4200-135 Porto, Portugal; Instituto de Investigação e Inovação em Saúde, Universidade do Porto, 4200-135 Porto, Portugal.
| |
Collapse
|
25
|
Whicher JR, MacKinnon R. Structure of the voltage-gated K⁺ channel Eag1 reveals an alternative voltage sensing mechanism. Science 2016; 353:664-9. [PMID: 27516594 DOI: 10.1126/science.aaf8070] [Citation(s) in RCA: 232] [Impact Index Per Article: 29.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2016] [Accepted: 06/22/2016] [Indexed: 12/17/2022]
Abstract
Voltage-gated potassium (K(v)) channels are gated by the movement of the transmembrane voltage sensor, which is coupled, through the helical S4-S5 linker, to the potassium pore. We determined the single-particle cryo-electron microscopy structure of mammalian K(v)10.1, or Eag1, bound to the channel inhibitor calmodulin, at 3.78 angstrom resolution. Unlike previous K(v) structures, the S4-S5 linker of Eag1 is a five-residue loop and the transmembrane segments are not domain swapped, which suggest an alternative mechanism of voltage-dependent gating. Additionally, the structure and position of the S4-S5 linker allow calmodulin to bind to the intracellular domains and to close the potassium pore, independent of voltage-sensor position. The structure reveals an alternative gating mechanism for K(v) channels and provides a template to further understand the gating properties of Eag1 and related channels.
Collapse
Affiliation(s)
- Jonathan R Whicher
- 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.
| |
Collapse
|
26
|
Enhancement of hERG channel activity by scFv antibody fragments targeted to the PAS domain. Proc Natl Acad Sci U S A 2016; 113:9916-21. [PMID: 27516548 DOI: 10.1073/pnas.1601116113] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
The human human ether-à-go-go-related gene (hERG) potassium channel plays a critical role in the repolarization of the cardiac action potential. Changes in hERG channel function underlie long QT syndrome (LQTS) and are associated with cardiac arrhythmias and sudden death. A striking feature of this channel and KCNH channels in general is the presence of an N-terminal Per-Arnt-Sim (PAS) domain. In other proteins, PAS domains bind ligands and modulate effector domains. However, the PAS domains of KCNH channels are orphan receptors. We have uncovered a family of positive modulators of hERG that specifically bind to the PAS domain. We generated two single-chain variable fragments (scFvs) that recognize different epitopes on the PAS domain. Both antibodies increase the rate of deactivation but have different effects on channel activation and inactivation. Importantly, we show that both antibodies, on binding to the PAS domain, increase the total amount of current that permeates the channel during a ventricular action potential and significantly reduce the action potential duration recorded in human cardiomyocytes. Overall, these molecules constitute a previously unidentified class of positive modulators and establish that allosteric modulation of hERG channel function through ligand binding to the PAS domain can be attained.
Collapse
|
27
|
Tang X, Shao J, Qin X. Crystal structure of the PAS domain of the hEAG potassium channel. Acta Crystallogr F Struct Biol Commun 2016; 72:578-85. [PMID: 27487920 PMCID: PMC4973297 DOI: 10.1107/s2053230x16009419] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2016] [Accepted: 06/09/2016] [Indexed: 11/27/2022] Open
Abstract
KCNH voltage-gated potassium channels play critical roles in regulating cellular functions. The channel is composed of four subunits, each of which contains six transmembrane helices forming the central pore. The cytoplasmic parts of the subunits present a Per-Arnt-Sim (PAS) domain at the N-terminus and a cyclic nucleotide-binding homology domain at the C-terminus. PAS domains are conserved from prokaryotes to eukaryotes and are involved in sensing signals and cellular responses. To better understand the functional roles of PAS domains in KCNH channels, the structure of this domain from the human ether-à-go-go channel (hEAG channel) was determined. By comparing it with the structures of the Homo sapiens EAG-related gene (hERG) channel and the Drosophila EAG-like K(+) (dELK) channel and analyzing the structural features of the hEAG channel, it was identified that a hydrophobic patch on the β-sheet may mediate interaction between the PAS domain and other regions of the channel to regulate its functions.
Collapse
Affiliation(s)
- Xue Tang
- State Key Laboratory of Medicinal Chemical Biology, Nankai University, Tianjin 300071, People’s Republic of China
- Department of Biochemistry and Molecular Biology, College of Life Sciences, Nankai University, Tianjin 300071, People’s Republic of China
| | - Juan Shao
- State Key Laboratory of Medicinal Chemical Biology, Nankai University, Tianjin 300071, People’s Republic of China
- Department of Biochemistry and Molecular Biology, College of Life Sciences, Nankai University, Tianjin 300071, People’s Republic of China
| | - Xiaohong Qin
- State Key Laboratory of Medicinal Chemical Biology, Tianjin University, Tianjin 300071, People’s Republic of China
| |
Collapse
|
28
|
Lörinczi E, Helliwell M, Finch A, Stansfeld PJ, Davies NW, Mahaut-Smith M, Muskett FW, Mitcheson JS. Calmodulin Regulates Human Ether à Go-Go 1 (hEAG1) Potassium Channels through Interactions of the Eag Domain with the Cyclic Nucleotide Binding Homology Domain. J Biol Chem 2016; 291:17907-18. [PMID: 27325704 PMCID: PMC5016179 DOI: 10.1074/jbc.m116.733576] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2016] [Indexed: 11/24/2022] Open
Abstract
The ether à go-go family of voltage-gated potassium channels is structurally distinct. The N terminus contains an eag domain (eagD) that contains a Per-Arnt-Sim (PAS) domain that is preceded by a conserved sequence of 25–27 amino acids known as the PAS-cap. The C terminus contains a region with homology to cyclic nucleotide binding domains (cNBHD), which is directly linked to the channel pore. The human EAG1 (hEAG1) channel is remarkably sensitive to inhibition by intracellular calcium (Ca2+i) through binding of Ca2+-calmodulin to three sites adjacent to the eagD and cNBHD. Here, we show that the eagD and cNBHD interact to modulate Ca2+-calmodulin as well as voltage-dependent gating. Sustained elevation of Ca2+i resulted in an initial profound inhibition of hEAG1 currents, which was followed by a phase when current amplitudes partially recovered, but activation gating was slowed and shifted to depolarized potentials. Deletion of either the eagD or cNBHD abolished the inhibition by Ca2+i. However, deletion of just the PAS-cap resulted in a >15-fold potentiation in response to elevated Ca2+i. Mutations of residues at the interface between the eagD and cNBHD have been linked to human cancer. Glu-600 on the cNBHD, when substituted with residues with a larger volume, resulted in hEAG1 currents that were profoundly potentiated by Ca2+i in a manner similar to the ΔPAS-cap mutant. These findings provide the first evidence that eagD and cNBHD interactions are regulating Ca2+-dependent gating and indicate that the binding of the PAS-cap with the cNBHD is required for the closure of the channels upon CaM binding.
Collapse
Affiliation(s)
- Eva Lörinczi
- From the Department of Molecular and Cell Biology, University of Leicester, Leicester LE1 9HN
| | - Matthew Helliwell
- From the Department of Molecular and Cell Biology, University of Leicester, Leicester LE1 9HN, the School of Physiology and Pharmacology, University of Bristol, Bristol BS5 1TD, and
| | - Alina Finch
- From the Department of Molecular and Cell Biology, University of Leicester, Leicester LE1 9HN
| | - Phillip J Stansfeld
- the Department of Biochemistry, University of Oxford, Oxford OX1 3QU, United Kingdom
| | - Noel W Davies
- From the Department of Molecular and Cell Biology, University of Leicester, Leicester LE1 9HN
| | - Martyn Mahaut-Smith
- From the Department of Molecular and Cell Biology, University of Leicester, Leicester LE1 9HN
| | - Frederick W Muskett
- From the Department of Molecular and Cell Biology, University of Leicester, Leicester LE1 9HN
| | - John S Mitcheson
- From the Department of Molecular and Cell Biology, University of Leicester, Leicester LE1 9HN,
| |
Collapse
|
29
|
Fernandes AS, Morais-Cabral JH, Harley CA. Screening for Non-Pore-Binding Modulators of EAG K+ Channels. ACTA ACUST UNITED AC 2016; 21:758-65. [PMID: 26975997 DOI: 10.1177/1087057116636592] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2015] [Accepted: 02/08/2016] [Indexed: 11/15/2022]
Abstract
Members of the ether-à-go-go (EAG) family of voltage-gated K(+) channels are involved in several pathophysiological diseases, and there has been a great interest in screening for drugs that modulate the activity of these channels. Many drugs have been shown to bind in the pore of these channels, blocking ion flux and causing disease pathology. In this report, we present two independent screening campaigns in which we wanted to identify small molecules that bind to either the intracellular cytoplasmic amino terminal Per-Arnt-Sim (PAS) domain from the human EAG-related gene (ERG) channel or the amino or carboxy terminal globular domains from the mouse EAG1 channel, affecting their interaction. We report that in both cases, compounds were identified that showed weak, nonspecific binding. We suggest alternative routes should be pursued in future efforts to identify specific, high-affinity binders to these cytoplasmic domains.
Collapse
Affiliation(s)
- Andreia S Fernandes
- IBMC, Instituto de Biologia Molecular e Celular, Universidade do Porto, Porto, Portugal Instituto de Investigação e Inovação em Saúde, Universidade do Porto, Porto, Portugal
| | - João H Morais-Cabral
- IBMC, Instituto de Biologia Molecular e Celular, Universidade do Porto, Porto, Portugal Instituto de Investigação e Inovação em Saúde, Universidade do Porto, Porto, Portugal
| | - Carol A Harley
- IBMC, Instituto de Biologia Molecular e Celular, Universidade do Porto, Porto, Portugal Instituto de Investigação e Inovação em Saúde, Universidade do Porto, Porto, Portugal
| |
Collapse
|
30
|
Kv10.1 K+ channel: from physiology to cancer. Pflugers Arch 2016; 468:751-62. [DOI: 10.1007/s00424-015-1784-3] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2015] [Revised: 12/11/2015] [Accepted: 12/27/2015] [Indexed: 12/18/2022]
|
31
|
Mohanty S, Kennedy EJ, Herberg FW, Hui R, Taylor SS, Langsley G, Kannan N. Structural and evolutionary divergence of cyclic nucleotide binding domains in eukaryotic pathogens: Implications for drug design. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2015; 1854:1575-85. [PMID: 25847873 DOI: 10.1016/j.bbapap.2015.03.012] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 02/15/2015] [Accepted: 03/25/2015] [Indexed: 12/24/2022]
Abstract
Many cellular functions in eukaryotic pathogens are mediated by the cyclic nucleotide binding (CNB) domain, which senses second messengers such as cyclic AMP and cyclic GMP. Although CNB domain-containing proteins have been identified in many pathogenic organisms, an incomplete understanding of how CNB domains in pathogens differ from other eukaryotic hosts has hindered the development of selective inhibitors for CNB domains associated with infectious diseases. Here, we identify and classify CNB domain-containing proteins in eukaryotic genomes to understand the evolutionary basis for CNB domain functional divergence in pathogens. We identify 359 CNB domain-containing proteins in 31 pathogenic organisms and classify them into distinct subfamilies based on sequence similarity within the CNB domain as well as functional domains associated with the CNB domain. Our study reveals novel subfamilies with pathogen-specific variations in the phosphate-binding cassette. Analyzing these variations in light of existing structural and functional data provides new insights into ligand specificity and promiscuity and clues for drug design. This article is part of a Special Issue entitled: Inhibitors of Protein Kinases.
Collapse
Affiliation(s)
- Smita Mohanty
- Department of Biochemistry & Molecular Biology, University of Georgia, Athens, GA 30602, USA
| | - Eileen J Kennedy
- Department of Pharmaceutical and Biomedical Sciences, University of Georgia College of Pharmacy, Athens, GA 30602, USA
| | | | - Raymond Hui
- Structural Genomics Consortium, University of Toronto, Toronto, Ontario, Canada
| | - Susan S Taylor
- Department of Chemistry & Biochemistry and Pharmacology, University of CA, San Diego, USA
| | - Gordon Langsley
- INSERM U1016, CNRS UMR8104, Cochin Institute, Paris, 75014 France; Laboratoire de Biologie Cellulaire Comparative des Apicomplexes, Faculté de Médicine, Université Paris Descartes - Sorbonne Paris Cité, France
| | - Natarajan Kannan
- Department of Biochemistry & Molecular Biology, University of Georgia, Athens, GA 30602, USA; Institute of Bioinformatics, University of Georgia, Athens, GA 30602, USA.
| |
Collapse
|
32
|
Li Q, Ng HQ, Kang C. (1)H, (13)C and (15)N chemical shift assignments for the cyclic-nucleotide binding homology domain of a KCNH channel. BIOMOLECULAR NMR ASSIGNMENTS 2015; 9:55-58. [PMID: 24414223 DOI: 10.1007/s12104-014-9544-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/25/2013] [Accepted: 01/04/2014] [Indexed: 06/03/2023]
Abstract
The KCNH family of ion channels plays important roles in heart and nerve cells. The C-terminal region of the KCNH channel contains a cyclic-nucleotide binding homology domain (CNBHD) which is important for channel gating through interaction with the eag domain. To study the solution structure of CNBHD of the KCNH channel of zebrafish, we over-expressed and purified this domain from E. coli. We report the resonance assignments of the CNBHD. The assignments will allow us to perform structural and dynamic studies for this domain, which will shed light on its role in channel gating.
Collapse
Affiliation(s)
- Qingxin Li
- Institute of Chemical & Engineering Sciences, Agency for Science, Technology and Research, Singapore, Singapore
| | | | | |
Collapse
|
33
|
Kesters D, Brams M, Nys M, Wijckmans E, Spurny R, Voets T, Tytgat J, Kusch J, Ulens C. Structure of the SthK carboxy-terminal region reveals a gating mechanism for cyclic nucleotide-modulated ion channels. PLoS One 2015; 10:e0116369. [PMID: 25625648 PMCID: PMC4308110 DOI: 10.1371/journal.pone.0116369] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2014] [Accepted: 12/09/2014] [Indexed: 11/19/2022] Open
Abstract
Cyclic nucleotide-sensitive ion channels are molecular pores that open in response to cAMP or cGMP, which are universal second messengers. Binding of a cyclic nucleotide to the carboxyterminal cyclic nucleotide binding domain (CNBD) of these channels is thought to cause a conformational change that promotes channel opening. The C-linker domain, which connects the channel pore to this CNBD, plays an important role in coupling ligand binding to channel opening. Current structural insight into this mechanism mainly derives from X-ray crystal structures of the C-linker/CNBD from hyperpolarization-activated cyclic nucleotide-modulated (HCN) channels. However, these structures reveal little to no conformational changes upon comparison of the ligand-bound and unbound form. In this study, we take advantage of a recently identified prokaryote ion channel, SthK, which has functional properties that strongly resemble cyclic nucleotide-gated (CNG) channels and is activated by cAMP, but not by cGMP. We determined X-ray crystal structures of the C-linker/CNBD of SthK in the presence of cAMP or cGMP. We observe that the structure in complex with cGMP, which is an antagonist, is similar to previously determined HCN channel structures. In contrast, the structure in complex with cAMP, which is an agonist, is in a more open conformation. We observe that the CNBD makes an outward swinging movement, which is accompanied by an opening of the C-linker. This conformation mirrors the open gate structures of the Kv1.2 channel or MthK channel, which suggests that the cAMP-bound C-linker/CNBD from SthK represents an activated conformation. These results provide a structural framework for better understanding cyclic nucleotide modulation of ion channels, including HCN and CNG channels.
Collapse
Affiliation(s)
- Divya Kesters
- Laboratory of Structural Neurobiology, KU Leuven, Herestraat 49, PB601, Leuven, B-3000, Belgium
| | - Marijke Brams
- Laboratory of Structural Neurobiology, KU Leuven, Herestraat 49, PB601, Leuven, B-3000, Belgium
| | - Mieke Nys
- Laboratory of Structural Neurobiology, KU Leuven, Herestraat 49, PB601, Leuven, B-3000, Belgium
| | - Eveline Wijckmans
- Laboratory of Structural Neurobiology, KU Leuven, Herestraat 49, PB601, Leuven, B-3000, Belgium
| | - Radovan Spurny
- Laboratory of Structural Neurobiology, KU Leuven, Herestraat 49, PB601, Leuven, B-3000, Belgium
| | - Thomas Voets
- Laboratory of Ion Channel Research, KU Leuven, Herestraat 49, PB802, Leuven, B-3000, Belgium
| | - Jan Tytgat
- Laboratory of Toxicology and Pharmacology, KU Leuven, Herestraat 49, PB922, Leuven, B-3000, Belgium
| | - Jana Kusch
- University Hospital Jena, Institute of Physiologie II, Kollegiengasse 9, 07743, Jena, Germany
| | - Chris Ulens
- Laboratory of Structural Neurobiology, KU Leuven, Herestraat 49, PB601, Leuven, B-3000, Belgium
- * E-mail:
| |
Collapse
|
34
|
Shimizu N, Sato N, Kikuchi T, Ishizaki T, Kobayashi K, Kita K, Takimoto K. A sustained increase in the intracellular Ca²⁺ concentration induces proteolytic cleavage of EAG2 channel. Int J Biochem Cell Biol 2014; 59:126-34. [PMID: 25542181 DOI: 10.1016/j.biocel.2014.12.007] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2014] [Revised: 11/19/2014] [Accepted: 12/15/2014] [Indexed: 11/28/2022]
Abstract
Voltage-gated EAG2 channel is abundant in the brain and enhances cancer cell growth by controlling cell volume. The channel contains a cyclic nucleotide-binding homology (CNBH) domain and multiple calmodulin-binding motifs. Here we show that a raised intracellular Ca(2+) concentration causes proteolytic digestion of heterologously expressed and native EAG2 channels. A treatment of EAG2-expressing cells with the Ca(2+) ionophore A23187 for 1h reduces the full-length protein by ∼80% with a concomitant appearance of 30-35-kDa peptides. Similarly, a treatment with the Ca(2+)-ATPase inhibitor thapsigargin for 3h removes 30-35-kDa peptides from ∼1/3 of the channel protein. Moreover, an incubation of the isolated rat brain membrane with CaCl2 leads to the generation of fragments with similar sizes. This Ca(2+)-induced digestion is not seen with EAG1. Mutations in a C-terminal calmodulin-binding motif alter the degrees and positions of the cleavage. Truncated channels that mimic the digested proteins exhibit a reduced current density and altered channel gating. In particular, these shorter channels lack a rapid activation typical in EAG channels with more than 20-mV positive shifts in voltage dependence of activation. The truncation also eliminates the ability of EAG2 channel to reduce cell volume. These results suggest that a sustained increase in the intracellular Ca(2+) concentration leads to proteolytic cleavage at the C-terminal cytosolic region following the CNBH domain by altering its interaction with calmodulin. The observed Ca(2+)-induced proteolytic cleavage of EAG2 channel may act as an adaptive response under physiological and/or pathological conditions.
Collapse
Affiliation(s)
- Nobuhiro Shimizu
- Department of Bioengineering, Nagaoka University of Technology, 1603-1 Kamitomioka, Nagaoka, Niigata 940-2188, Japan
| | - Natsumi Sato
- Department of Bioengineering, Nagaoka University of Technology, 1603-1 Kamitomioka, Nagaoka, Niigata 940-2188, Japan
| | - Teppei Kikuchi
- Department of Bioengineering, Nagaoka University of Technology, 1603-1 Kamitomioka, Nagaoka, Niigata 940-2188, Japan
| | - Takuro Ishizaki
- Department of Bioengineering, Nagaoka University of Technology, 1603-1 Kamitomioka, Nagaoka, Niigata 940-2188, Japan
| | - Kazuto Kobayashi
- Department of Bioengineering, Nagaoka University of Technology, 1603-1 Kamitomioka, Nagaoka, Niigata 940-2188, Japan
| | - Kaori Kita
- Department of Environmental and Occupational Health, University of Pittsburgh, Pittsburgh, PA 15261, United States
| | - Koichi Takimoto
- Department of Bioengineering, Nagaoka University of Technology, 1603-1 Kamitomioka, Nagaoka, Niigata 940-2188, Japan; Department of Environmental and Occupational Health, University of Pittsburgh, Pittsburgh, PA 15261, United States.
| |
Collapse
|
35
|
Morais-Cabral JH, Robertson GA. The enigmatic cytoplasmic regions of KCNH channels. J Mol Biol 2014; 427:67-76. [PMID: 25158096 DOI: 10.1016/j.jmb.2014.08.008] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2014] [Revised: 08/14/2014] [Accepted: 08/15/2014] [Indexed: 01/09/2023]
Abstract
KCNH channels are expressed across a vast phylogenetic and evolutionary spectrum. In humans, they function in a wide range of tissues and serve as biomarkers and targets for diseases such as cancer and cardiac arrhythmias. These channels share a general architecture with other voltage-gated ion channels but are distinguished by the presence of an N-terminal PAS (Per-Arnt-Sim) domain and a C-terminal domain with homology to cyclic nucleotide binding domains (referred to as the CNBh domain). Cytosolic regions outside these domains show little conservation between KCNH families but are strongly conserved across species within a family, likely reflecting variability that confers specificity to individual channel types. PAS and CNBh domains participate in channel gating, but at least twice in evolutionary history, the PAS domain has been lost and it is omitted by alternate transcription to create a distinct channel subunit in one family. In this focused review, we present current knowledge of the structure and function of these cytosolic regions, discuss their evolution as modular domains and provide our perspective on the important questions moving forward.
Collapse
Affiliation(s)
- João H Morais-Cabral
- Instituto de Biologia Molecular e Celular, Universidade do Porto, 4150-180 Porto, Portugal.
| | - Gail A Robertson
- Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, WI 53705, USA
| |
Collapse
|
36
|
Ng CA, Phan K, Hill AP, Vandenberg JI, Perry MD. Multiple interactions between cytoplasmic domains regulate slow deactivation of Kv11.1 channels. J Biol Chem 2014; 289:25822-32. [PMID: 25074935 DOI: 10.1074/jbc.m114.558379] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The intracellular domains of many ion channels are important for fine-tuning their gating kinetics. In Kv11.1 channels, the slow kinetics of channel deactivation, which are critical for their function in the heart, are largely regulated by the N-terminal N-Cap and Per-Arnt-Sim (PAS) domains, as well as the C-terminal cyclic nucleotide-binding homology (cNBH) domain. Here, we use mutant cycle analysis to probe for functional interactions between the N-Cap/PAS domains and the cNBH domain. We identified a specific and stable charge-charge interaction between Arg(56) of the PAS domain and Asp(803) of the cNBH domain, as well an additional interaction between the cNBH domain and the N-Cap, both of which are critical for maintaining slow deactivation kinetics. Furthermore, we found that positively charged arginine residues within the disordered region of the N-Cap interact with negatively charged residues of the C-linker domain. Although this interaction is likely more transient than the PAS-cNBD interaction, it is strong enough to stabilize the open conformation of the channel and thus slow deactivation. These findings provide novel insights into the slow deactivation mechanism of Kv11.1 channels.
Collapse
Affiliation(s)
- Chai Ann Ng
- From the Victor Chang Cardiac Research Institute and St. Vincent's Clinical School, University of New South Wales, Darlinghurst, New South Wales 2010, Australia
| | - Kevin Phan
- From the Victor Chang Cardiac Research Institute and St. Vincent's Clinical School, University of New South Wales, Darlinghurst, New South Wales 2010, Australia
| | - Adam P Hill
- From the Victor Chang Cardiac Research Institute and St. Vincent's Clinical School, University of New South Wales, Darlinghurst, New South Wales 2010, Australia
| | - Jamie I Vandenberg
- From the Victor Chang Cardiac Research Institute and St. Vincent's Clinical School, University of New South Wales, Darlinghurst, New South Wales 2010, Australia
| | - Matthew D Perry
- From the Victor Chang Cardiac Research Institute and St. Vincent's Clinical School, University of New South Wales, Darlinghurst, New South Wales 2010, Australia
| |
Collapse
|
37
|
Insight into the molecular interaction between the cyclic nucleotide-binding homology domain and the eag domain of the hERG channel. FEBS Lett 2014; 588:2782-8. [PMID: 24931372 DOI: 10.1016/j.febslet.2014.05.056] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2014] [Revised: 05/14/2014] [Accepted: 05/27/2014] [Indexed: 12/18/2022]
Abstract
The gating of the hERG channel is regulated by its eag domain through molecular interaction with either the cyclic nucleotide-binding homology domain (CNBHD) or the linker between transmembrane segments 4 and 5. Our NMR study on the purified CNBHD demonstrated that it contains nine β-strands and does not bind cAMP. We show that the eag domain binds to the CBND through an interface containing several disease-associated mutations. The N-terminal cap domain and R56 in the eag domain are important for the interaction with the CNBHD. Residues from the CNBHD that were affected by the interaction with the eag domain were also identified. A R56Q mutation does not cause major structural changes in the eag domain and showed reduced interaction with the CNBHD.
Collapse
|
38
|
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.
Collapse
|
39
|
Kim YM, Li Q, Ng HQ, Yoon HS, Kang C. ¹H, ¹³C and ¹⁵N chemical shift assignments for the N-terminal PAS domain of the KCNH channel from zebrafish. BIOMOLECULAR NMR ASSIGNMENTS 2014; 8:165-168. [PMID: 23595857 DOI: 10.1007/s12104-013-9475-5] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/07/2013] [Accepted: 04/09/2013] [Indexed: 06/02/2023]
Abstract
The KCNH channels are voltage-gated potassium channels that play important roles in heart and nerve cells. The N-terminal region of the KCNH channel contains a Per-Arnt-Sim (PAS) domain which is important for the channel gating through interaction with other regions of the channel. To study the solution structure of the N-terminal PAS domain of the KCNH channel from Zebrafish (zNTD), we over-expressed and purified zNTD. We report the resonance assignments for zNTD. The data will allow us to perform structural studies for this domain, which will provide insight into its structural basis for the molecular interaction with other regions of the KCNH channel.
Collapse
Affiliation(s)
- Young Mee Kim
- Experimental Therapeutics Centre, Agency for Science, Technology and Research, 31 Biopolis Way Nanos, #03-01, Singapore, 138669, Singapore
| | | | | | | | | |
Collapse
|
40
|
Li Q, Ng HQ, Yoon HS, Kang C. Solution structure of the cyclic-nucleotide binding homology domain of a KCNH channel. J Struct Biol 2014; 186:68-74. [PMID: 24632450 DOI: 10.1016/j.jsb.2014.03.008] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2013] [Revised: 03/03/2014] [Accepted: 03/10/2014] [Indexed: 12/28/2022]
Abstract
The carboxy-terminal region of the KCNH family of potassium channels contains a cyclic-nucleotide binding homology domain (CNBHD) that is important for channel gating and trafficking. The solution structure of the CNBHD of the KCNH potassium of zebrafish was determined using solution NMR spectroscopy. This domain exists as a monomer under solution conditions and adopts a similar fold to that determined by X-ray crystallography. The CNBHD does not bind cAMP because residue Y740 blocks the entry of cyclic-nucleotide to the binding pocket. Relaxation results show that the CNBHD is rigid except that some residues in the loop between β6 and β7 are flexible. Our results will be useful to understand the gating mechanism of KCNH family members through the CNBHD.
Collapse
Affiliation(s)
- Qingxin Li
- Institute of Chemical & Engineering Sciences, Agency for Science, Technology and Research (A∗STAR), Singapore 627833, Singapore
| | - Hui Qi Ng
- Experimental Therapeutics Centre, Agency for Science, Technology and Research (A∗STAR), Singapore 138669, Singapore
| | - Ho Sup Yoon
- Division of Structural Biology and Biochemistry, School of Biological Sciences, Nanyang Technological University, 60 Nanyang Drive, Singapore 637511, Singapore
| | - Congbao Kang
- Experimental Therapeutics Centre, Agency for Science, Technology and Research (A∗STAR), Singapore 138669, Singapore.
| |
Collapse
|
41
|
Abstract
The voltage-gated, K+-selective ether á go-go 1 (EAG1) channel is expressed throughout the brain where it is thought to regulate neuronal excitability. Besides its normal physiological role in the brain, EAG1 is abnormally expressed in several cancer cell types and promotes tumor progression. Like all other channels in the KCNH family, EAG1 channels have a large intracellular carboxy-terminal region that shares structural similarity with cyclic nucleotide–binding homology domains (CNBHDs). EAG1 channels, however, are not regulated by the direct binding of cyclic nucleotides and have no known endogenous ligands. In a screen of biological metabolites, we have now identified four flavonoids as potentiators of EAG1 channels: fisetin, quercetin, luteolin, and kaempferol. These four flavonoids shifted the voltage dependence of activation toward more hyperpolarizing potentials and slowed channel deactivation. All four flavonoids regulated channel gating with half-maximal concentrations of 2–8 µM. The potentiation of gating did not require the amino-terminal or post-CNBHD regions of EAG1 channels. However, in fluorescence resonance energy transfer and anisotropy-based binding assays, flavonoids bound to the purified CNBHD of EAG1 channels. The CNBHD of KCNH channels contains an intrinsic ligand, a conserved stretch of residues that occupy the cyclic nucleotide–binding pocket. Mutations of the intrinsic ligand in EAG1 (Y699A) potentiated gating similar to flavonoids, and flavonoids did not further potentiate EAG1-Y699A channels. Furthermore, the Y699A mutant CNBHD bound to flavonoids with higher affinity than wild-type CNBHD. These results suggest that the flavonoids identified here potentiated EAG1 channels by binding to the CNBHD, possibly by displacing their intrinsic ligand. EAG1 channels should be considered as a possible target for the physiological effects of flavonoids.
Collapse
Affiliation(s)
- Anne E Carlson
- Department of Physiology and Biophysics, University of Washington School of Medicine, Seattle, WA 98195, USA
| | | | | |
Collapse
|
42
|
Huang GY, Kim JJ, Reger AS, Lorenz R, Moon EW, Zhao C, Casteel DE, Bertinetti D, Vanschouwen B, Selvaratnam R, Pflugrath JW, Sankaran B, Melacini G, Herberg FW, Kim C. Structural basis for cyclic-nucleotide selectivity and cGMP-selective activation of PKG I. Structure 2013; 22:116-24. [PMID: 24239458 DOI: 10.1016/j.str.2013.09.021] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2013] [Revised: 09/18/2013] [Accepted: 09/23/2013] [Indexed: 10/26/2022]
Abstract
Cyclic guanosine monophosphate (cGMP) and cyclic AMP (cAMP)-dependent protein kinases (PKG and PKA) are closely related homologs, and the cyclic nucleotide specificity of each kinase is crucial for keeping the two signaling pathways segregated, but the molecular mechanism of cyclic nucleotide selectivity is unknown. Here, we report that the PKG Iβ C-terminal cyclic nucleotide binding domain (CNB-B) is highly selective for cGMP binding, and we have solved crystal structures of CNB-B with and without bound cGMP. These structures, combined with a comprehensive mutagenic analysis, allowed us to identify Leu296 and Arg297 as key residues that mediate cGMP selectivity. In addition, by comparing the cGMP bound and unbound structures, we observed large conformational changes in the C-terminal helices in response to cGMP binding, which were stabilized by recruitment of Tyr351 as a "capping residue" for cGMP. The observed rearrangements of the C-terminal helices provide a mechanical insight into release of the catalytic domain and kinase activation.
Collapse
Affiliation(s)
- Gilbert Y Huang
- Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX 77030, USA
| | - Jeong Joo Kim
- Department of Pharmacology, Baylor College of Medicine, Houston, TX 77030, USA
| | - Albert S Reger
- Department of Pharmacology, Baylor College of Medicine, Houston, TX 77030, USA
| | - Robin Lorenz
- Department of Biochemistry, University of Kassel, Kassel 34132, Germany
| | - Eui-Whan Moon
- Department of Pharmacology, Baylor College of Medicine, Houston, TX 77030, USA
| | - Chi Zhao
- Department of Chemistry, Rice University, Houston, TX 77005, USA
| | - Darren E Casteel
- Department of Medicine, University of California, San Diego, La Jolla, CA 92093, USA
| | | | - Bryan Vanschouwen
- Department of Chemistry and Chemical Biology, McMaster University, Hamilton, ON L8S 4M1, Canada
| | - Rajeevan Selvaratnam
- Department of Chemistry and Chemical Biology, McMaster University, Hamilton, ON L8S 4M1, Canada
| | | | - Banumathi Sankaran
- Berkeley Center for Structural Biology, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Building 6R2100, Berkeley, CA 94720, USA
| | - Giuseppe Melacini
- Department of Chemistry and Chemical Biology, McMaster University, Hamilton, ON L8S 4M1, Canada
| | | | - Choel Kim
- Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX 77030, USA; Department of Pharmacology, Baylor College of Medicine, Houston, TX 77030, USA.
| |
Collapse
|
43
|
Ng CA, Ke Y, Perry MD, Tan PS, Hill AP, Vandenberg JI. C-terminal β9-strand of the cyclic nucleotide-binding homology domain stabilizes activated states of Kv11.1 channels. PLoS One 2013; 8:e77032. [PMID: 24204727 PMCID: PMC3808384 DOI: 10.1371/journal.pone.0077032] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2013] [Accepted: 09/06/2013] [Indexed: 12/25/2022] Open
Abstract
Kv11.1 potassium channels are important for regulation of the normal rhythm of the heartbeat. Reduced activity of Kv11.1 channels causes long QT syndrome type 2, a disorder that increases the risk of cardiac arrhythmias and sudden cardiac arrest. Kv11.1 channels are members of the KCNH subfamily of voltage-gated K+ channels. However, they also share many similarities with the cyclic nucleotide gated ion channel family, including having a cyclic nucleotide-binding homology (cNBH) domain. Kv11.1 channels, however, are not directly regulated by cyclic nucleotides. Recently, crystal structures of the cNBH domain from mEAG and zELK channels, both members of the KCNH family of voltage-gated potassium channels, revealed that a C-terminal β9-strand in the cNBH domain occupied the putative cyclic nucleotide-binding site thereby precluding binding of cyclic nucleotides. Here we show that mutations to residues in the β9-strand affect the stability of the open state relative to the closed state of Kv11.1 channels. We also show that disrupting the structure of the β9-strand reduces the stability of the inactivated state relative to the open state. Clinical mutations located in this β9-strand result in reduced trafficking efficiency, which suggests that binding of the C-terminal β9-strand to the putative cyclic nucleotide-binding pocket is also important for assembly and trafficking of Kv11.1 channels.
Collapse
Affiliation(s)
- Chai Ann Ng
- Molecular Cardiology and Biophysics Division, Victor Chang Cardiac Research Institute, Darlinghurst, New South Wales, Australia
- St Vincent's Clinical School, University of New South Wales, New South Wales, Australia
| | - Ying Ke
- Molecular Cardiology and Biophysics Division, Victor Chang Cardiac Research Institute, Darlinghurst, New South Wales, Australia
- St Vincent's Clinical School, University of New South Wales, New South Wales, Australia
| | - Matthew D. Perry
- Molecular Cardiology and Biophysics Division, Victor Chang Cardiac Research Institute, Darlinghurst, New South Wales, Australia
- St Vincent's Clinical School, University of New South Wales, New South Wales, Australia
| | - Peter S. Tan
- Molecular Cardiology and Biophysics Division, Victor Chang Cardiac Research Institute, Darlinghurst, New South Wales, Australia
| | - Adam P. Hill
- Molecular Cardiology and Biophysics Division, Victor Chang Cardiac Research Institute, Darlinghurst, New South Wales, Australia
- St Vincent's Clinical School, University of New South Wales, New South Wales, Australia
| | - Jamie I. Vandenberg
- Molecular Cardiology and Biophysics Division, Victor Chang Cardiac Research Institute, Darlinghurst, New South Wales, Australia
- St Vincent's Clinical School, University of New South Wales, New South Wales, Australia
- * E-mail:
| |
Collapse
|
44
|
Carlson AE, Rosenbaum JC, Brelidze TI, Klevit RE, Zagotta WN. Flavonoid regulation of HCN2 channels. J Biol Chem 2013; 288:33136-45. [PMID: 24085296 DOI: 10.1074/jbc.m113.501759] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
The hyperpolarization-activated cyclic nucleotide-modulated (HCN) channels are pacemaker channels whose currents contribute to rhythmic activity in the heart and brain. HCN channels open in response to hyperpolarizing voltages, and the binding of cAMP to their cyclic nucleotide-binding domain (CNBD) facilitates channel opening. Here, we report that, like cAMP, the flavonoid fisetin potentiates HCN2 channel gating. Fisetin sped HCN2 activation and shifted the conductance-voltage relationship to more depolarizing potentials with a half-maximal effective concentration (EC50) of 1.8 μM. When applied together, fisetin and cAMP regulated HCN2 gating in a nonadditive fashion. Fisetin did not potentiate HCN2 channels lacking their CNBD, and two independent fluorescence-based binding assays reported that fisetin bound to the purified CNBD. These data suggest that the CNBD mediates the fisetin potentiation of HCN2 channels. Moreover, binding assays suggest that fisetin and cAMP partially compete for binding to the CNBD. NMR experiments demonstrated that fisetin binds within the cAMP-binding pocket, interacting with some of the same residues as cAMP. Together, these data indicate that fisetin is a partial agonist for HCN2 channels.
Collapse
|
45
|
Haitin Y, Carlson AE, Zagotta WN. The structural mechanism of KCNH-channel regulation by the eag domain. Nature 2013; 501:444-8. [PMID: 23975098 PMCID: PMC3910112 DOI: 10.1038/nature12487] [Citation(s) in RCA: 84] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2013] [Accepted: 07/18/2013] [Indexed: 12/22/2022]
Abstract
The KCNH voltage-dependent potassium channels (ether-à-go-go, EAG; EAG-related gene, ERG; EAG-like channels, ELK) are important regulators of cellular excitability and have key roles in diseases such as cardiac long QT syndrome type 2 (LQT2), epilepsy, schizophrenia and cancer. The intracellular domains of KCNH channels are structurally distinct from other voltage-gated channels. The amino-terminal region contains an eag domain, which is composed of a Per-Arnt-Sim (PAS) domain and a PAS-cap domain, whereas the carboxy-terminal region contains a cyclic nucleotide-binding homology domain (CNBHD), which is connected to the pore through a C-linker domain. Many disease-causing mutations localize to these specialized intracellular domains, which underlie the unique gating and regulation of KCNH channels. It has been suggested that the eag domain may regulate the channel by interacting with either the S4-S5 linker or the CNBHD. Here we present a 2 Å resolution crystal structure of the eag domain-CNBHD complex of the mouse EAG1 (also known as KCNH1) channel. It displays extensive interactions between the eag domain and the CNBHD, indicating that the regulatory mechanism of the eag domain primarily involves the CNBHD. Notably, the structure reveals that a number of LQT2 mutations at homologous positions in human ERG, in addition to cancer-associated mutations in EAG channels, localize to the eag domain-CNBHD interface. Furthermore, mutations at the interface produced marked effects on channel gating, demonstrating the important physiological role of the eag domain-CNBHD interaction. Our structure of the eag domain-CNBHD complex of mouse EAG1 provides unique insights into the physiological and pathophysiological mechanisms of KCNH channels.
Collapse
Affiliation(s)
- Yoni Haitin
- Department of Physiology and Biophysics, University of Washington
School of Medicine, Seattle, WA 98195
| | - Anne E. Carlson
- Department of Physiology and Biophysics, University of Washington
School of Medicine, Seattle, WA 98195
| | - William N. Zagotta
- Department of Physiology and Biophysics, University of Washington
School of Medicine, Seattle, WA 98195
| |
Collapse
|
46
|
Gianulis EC, Liu Q, Trudeau MC. Direct interaction of eag domains and cyclic nucleotide-binding homology domains regulate deactivation gating in hERG channels. ACTA ACUST UNITED AC 2013; 142:351-66. [PMID: 24043860 PMCID: PMC3787778 DOI: 10.1085/jgp.201310995] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Human ether-á-go-go (eag)-related gene (hERG) potassium channels play a critical role in cardiac repolarization and are characterized by unusually slow closing (deactivation) kinetics. The N-terminal “eag” domain and a C-terminal C-linker/cyclic nucleotide–binding homology domain (CNBHD) are required for regulation of slow deactivation. The region between the S4 and S5 transmembrane domains (S4–S5 linker) is also implicated in this process, but the mechanism for regulation of slow deactivation is unclear. Here, using an eag domain–deleted channel (hERG Δeag) fused to Citrine fluorescent protein, we found that most channels bearing individual alanine mutations in the S4–S5 linker were directly regulated by recombinant eag domains fused to a cyan fluorescent protein (N-eag-CFP) and had robust Förster resonance energy transfer (FRET). Additionally, a channel bearing a group of eight alanine residues in the S4–S5 linker was not measurably regulated by N-eag-CFP domains, but robust FRET was measured. These findings demonstrate that the eag domain associated with all of the S4–S5 linker mutant channels. In contrast, channels that also lacked the CNBHD (hERG Δeag ΔCNBHD-Citrine) were not measurably regulated by N-eag-CFP nor was FRET detected, suggesting that the C-linker/CNBHD was required for eag domains to directly associate with the channel. In a FRET hybridization assay, N-eag-CFP had robust FRET with a C-linker/CNBHD-Citrine, suggesting a direct and specific interaction between the eag domain and the C-linker/CNBHD. Lastly, coexpression of a hERG subunit lacking the CNBHD and the distal C-terminal region (hERG ΔpCT-Citrine) with hERG Δeag-CFP subunits had FRET and partial restoration of slow deactivation. Collectively, these findings reveal that the C-linker/CNBHD, but not the S4–S5 linker, was necessary for the eag domain to associate with the channel, that the eag domain and the C-linker/CNBHD were sufficient for a direct interaction, and that an intersubunit interaction between the eag domain and the C-linker/CNBHD regulated slow deactivation in hERG channels at the plasma membrane.
Collapse
Affiliation(s)
- Elena C Gianulis
- Department of Physiology, University of Maryland School of Medicine, Baltimore, MD 21201
| | | | | |
Collapse
|
47
|
Structure of the C-terminal region of an ERG channel and functional implications. Proc Natl Acad Sci U S A 2013; 110:11648-53. [PMID: 23801759 DOI: 10.1073/pnas.1306887110] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
The human ether-à-go-go-related gene (hERG) encodes a K(+) channel crucial for repolarization of the cardiac action potential. EAG-related gene (ERG) channels contain a C-terminal cyclic nucleotide-binding homology domain coupled to the pore of the channel by a C-linker. Here, we report the structure of the C-linker/cyclic nucleotide-binding homology domain of a mosquito ERG channel at 2.5-Å resolution. The structure reveals that the region expected to form the cyclic nucleotide-binding pocket is negatively charged and is occupied by a short β-strand, referred to as the intrinsic ligand, explaining the lack of direct regulation of ERG channels by cyclic nucleotides. In hERG channels, the intrinsic ligand harbors hereditary mutations associated with long-QT syndrome (LQTS), a potentially lethal cardiac arrhythmia. Mutations in the intrinsic ligand affected hERG channel gating and LQTS mutations abolished hERG currents and altered trafficking of hERG channels, which explains the LQT phenotype. The structure also reveals a dramatically different conformation of the C-linker compared with the structures of the related ether-à-go-go-like K(+) and hyperpolarization-activated cyclic nucleotide-modulated channels, suggesting that the C-linker region may be highly dynamic in the KCNH, hyperpolarization-activated cyclic nucleotide-modulated, and cyclic nucleotide-gated channels.
Collapse
|
48
|
Puljung MC, Zagotta WN. A secondary structural transition in the C-helix promotes gating of cyclic nucleotide-regulated ion channels. J Biol Chem 2013; 288:12944-56. [PMID: 23525108 DOI: 10.1074/jbc.m113.464123] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
Cyclic nucleotide-regulated ion channels bind second messengers like cAMP to a C-terminal domain, consisting of a β-roll, followed by two α-helices (B- and C-helices). We monitored the cAMP-dependent changes in the structure of the C-helix of a C-terminal fragment of HCN2 channels using transition metal ion FRET between fluorophores on the C-helix and metal ions bound between histidine pairs on the same helix. cAMP induced a change in the dimensions of the C-helix and an increase in the metal binding affinity of the histidine pair. cAMP also caused an increase in the distance between a fluorophore on the C-helix and metal ions bound to the B-helix. Stabilizing the C-helix of intact CNGA1 channels by metal binding to a pair of histidines promoted channel opening. These data suggest that ordering of the C-helix is part of the gating conformational change in cyclic nucleotide-regulated channels.
Collapse
Affiliation(s)
- Michael C Puljung
- Department of Physiology and Biophysics, University of Washington, Seattle, Washington 98195-7290, USA
| | | |
Collapse
|
49
|
Adaixo R, Harley CA, Castro-Rodrigues AF, Morais-Cabral JH. Structural properties of PAS domains from the KCNH potassium channels. PLoS One 2013; 8:e59265. [PMID: 23555008 PMCID: PMC3598652 DOI: 10.1371/journal.pone.0059265] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2012] [Accepted: 02/13/2013] [Indexed: 11/19/2022] Open
Abstract
KCNH channels form an important family of voltage gated potassium channels. These channels include a N-terminal Per-Arnt-Sim (PAS) domain with unknown function. In other proteins PAS domains are implicated in cellular responses to environmental queues through small molecule binding or involvement in signaling cascades. To better understand their role we characterized the structural properties of several channel PAS domains. We determined high resolution structures of PAS domains from the mouse EAG (mEAG), drosophila ELK (dELK) and human ERG (hERG) channels and also of the hERG domain without the first nine amino acids. We analyzed these structures for features connected to ligand binding and signaling in other PAS domains. In particular, we have found cavities in the hERG and mEAG structures that share similarities with the ligand binding sites from other PAS domains. These cavities are lined by polar and apolar chemical groups and display potential flexibility in their volume. We have also found that the hydrophobic patch on the domain β-sheet is a conserved feature and appears to drive the formation of protein-protein contacts. In addition, the structures of the dELK domain and of the truncated hERG domain revealed the presence of N-terminal helices. These helices are equivalent to the helix described in the hERG NMR structures and are known to be important for channel function. Overall, these channel domains retain many of the PAS domain characteristics known to be important for cell signaling.
Collapse
Affiliation(s)
- Ricardo Adaixo
- IBMC, Instituto de Biologia Molecular e Celular, Universidade do Porto, Porto, Portugal
| | - Carol A. Harley
- IBMC, Instituto de Biologia Molecular e Celular, Universidade do Porto, Porto, Portugal
| | | | - João H. Morais-Cabral
- IBMC, Instituto de Biologia Molecular e Celular, Universidade do Porto, Porto, Portugal
- * E-mail:
| |
Collapse
|