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Ji W, Shi D, Shi S, Yang X, Chen Y, An H, Pang C. TMEM16A protein: calcium binding site and its activation mechanism. Protein Pept Lett 2021; 28:1338-1348. [PMID: 34749600 DOI: 10.2174/0929866528666211105112131] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2021] [Revised: 09/08/2021] [Accepted: 09/18/2021] [Indexed: 11/22/2022]
Abstract
TMEM16A mediates calcium-activated transmembrane flow of chloride ion and a variety of physiological functions. The binding of cytoplasmic calcium ions of TMEM16A and the consequent conformational changes of it are the key issues to explore the relationship between its structure and function. In recent years, researchers have explored this issue through electrophysiological experiment, structure resolving, molecular dynamic simulation and other methods. The structures of TMEM16 family members resolved by cryo-Electron microscopy (cryo-EM) and X-ray crystallization provide the primarily basis for the investigation of the molecular mechanism of TMEM16A. However, the binding and activation mechanism of calcium ions in TMEM16A are still unclear and controversial. This review discusses four Ca2+ sensing sites of TMEM16A and analyze activation properties of TMEM16A by them, which will help to understand the structure-function relationship of TMEM16A and throw light on the molecular design targeting TMEM16A channel.
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Affiliation(s)
- Wanying Ji
- Institute of Biophysics, School of Science, Hebei University of Technology, Tianjin 300401. China
| | - Donghong Shi
- Institute of Biophysics, School of Science, Hebei University of Technology, Tianjin 300401. China
| | - Sai Shi
- Institute of Biophysics, School of Science, Hebei University of Technology, Tianjin 300401. China
| | - Xiao Yang
- Institute of Biophysics, School of Science, Hebei University of Technology, Tianjin 300401. China
| | - Yafei Chen
- Institute of Biophysics, School of Science, Hebei University of Technology, Tianjin 300401. China
| | - Hailong An
- Institute of Biophysics, School of Science, Hebei University of Technology, Tianjin 300401. China
| | - Chunli Pang
- Institute of Biophysics, School of Science, Hebei University of Technology, Tianjin 300401. China
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2
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Mäki-Marttunen T, Devor A, Phillips WA, Dale AM, Andreassen OA, Einevoll GT. Computational Modeling of Genetic Contributions to Excitability and Neural Coding in Layer V Pyramidal Cells: Applications to Schizophrenia Pathology. Front Comput Neurosci 2019; 13:66. [PMID: 31616272 PMCID: PMC6775251 DOI: 10.3389/fncom.2019.00066] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2019] [Accepted: 09/09/2019] [Indexed: 11/13/2022] Open
Abstract
Pyramidal cells in layer V of the neocortex are one of the most widely studied neuron types in the mammalian brain. Due to their role as integrators of feedforward and cortical feedback inputs, they are well-positioned to contribute to the symptoms and pathology in mental disorders-such as schizophrenia-that are characterized by a mismatch between the internal perception and external inputs. In this modeling study, we analyze the input/output properties of layer V pyramidal cells and their sensitivity to modeled genetic variants in schizophrenia-associated genes. We show that the excitability of layer V pyramidal cells and the way they integrate inputs in space and time are altered by many types of variants in ion-channel and Ca2+ transporter-encoding genes that have been identified as risk genes by recent genome-wide association studies. We also show that the variability in the output patterns of spiking and Ca2+ transients in layer V pyramidal cells is altered by these model variants. Importantly, we show that many of the predicted effects are robust to noise and qualitatively similar across different computational models of layer V pyramidal cells. Our modeling framework reveals several aspects of single-neuron excitability that can be linked to known schizophrenia-related phenotypes and existing hypotheses on disease mechanisms. In particular, our models predict that single-cell steady-state firing rate is positively correlated with the coding capacity of the neuron and negatively correlated with the amplitude of a prepulse-mediated adaptation and sensitivity to coincidence of stimuli in the apical dendrite and the perisomatic region of a layer V pyramidal cell. These results help to uncover the voltage-gated ion-channel and Ca2+ transporter-associated genetic underpinnings of schizophrenia phenotypes and biomarkers.
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Affiliation(s)
| | - Anna Devor
- Department of Neurosciences, University of California San Diego, La Jolla, CA, United States.,Department of Radiology, University of California San Diego, La Jolla, CA, United States.,Martinos Center for Biomedical Imaging, Harvard Medical School, Massachusetts General Hospital, Charlestown, MA, United States
| | - William A Phillips
- Psychology, Faculty of Natural Sciences, University of Stirling, Stirling, United Kingdom
| | - Anders M Dale
- Department of Neurosciences, University of California San Diego, La Jolla, CA, United States.,Department of Radiology, University of California San Diego, La Jolla, CA, United States
| | - Ole A Andreassen
- NORMENT, Division of Mental Health and Addiction, Oslo University Hospital and Institute of Clinical Medicine, University of Oslo, Oslo, Norway
| | - Gaute T Einevoll
- Faculty of Science and Technology, Norwegian University of Life Sciences, Ås, Norway.,Department of Physics, University of Oslo, Oslo, Norway
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3
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Stowe DF, Yang M, Heisner JS, Camara AK. Endogenous and Agonist-induced Opening of Mitochondrial Big Versus Small Ca2+-sensitive K+ Channels on Cardiac Cell and Mitochondrial Protection. J Cardiovasc Pharmacol 2017; 70:314-328. [PMID: 28777255 PMCID: PMC5726766 DOI: 10.1097/fjc.0000000000000524] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Both big (BKCa) and small (SKCa) conductance Ca-sensitive K channels are present in mammalian cardiac cell mitochondria (m). We used pharmacological agonists and antagonists of BKCa and SKCa channels to examine the importance of endogenous opening of these channels and the relative contribution of either or both of these channels to protect against contractile dysfunction and reduce infarct size after ischemia reperfusion (IR) injury through a mitochondrial protective mechanism. After global cardiac IR injury of ex vivo perfused Guinea pig hearts, we found the following: both agonists NS1619 (for BKCa) and DCEB (for SKCa) improved contractility; BKCa antagonist paxilline (PAX) alone or with SKCa antagonist NS8593 worsened contractility and enhanced infarct size; both antagonists PAX and NS8593 obliterated protection by their respective agonists; BKCa and SKCa antagonists did not block protection afforded by SKCa and BKCa agonists, respectively; and all protective effects by the agonists were blocked by scavenging superoxide anions (O2) with Mn(III) tetrakis (4-benzoic acid) porphyrin (TBAP). Contractile function was inversely associated with global infarct size. In in vivo rats, infusion of NS8593, PAX, or both antagonists enhanced regional infarct size while infusion of either NS1619 or DCEB reduced infarct size. In cardiac mitochondria isolated from ex vivo hearts after IR, combined SKCa and BKCa agonists improved respiratory control index and Ca retention capacity compared with IR alone, whereas the combined antagonists did not alter respiratory control index but worsened Ca retention capacity. Although the differential protective bioenergetics effects of endogenous or exogenous BKCa and SKCa channel opening remain unclear, each channel likely responds to different sensing Ca concentrations and voltage gradients over time during oxidative stress-induced injury to individually or together protect cardiac mitochondria and myocytes.
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Affiliation(s)
- David F. Stowe
- Department of Anesthesiology, Medical College of Wisconsin, Milwaukee, WI, USA
- Department of Physiology, Medical College of Wisconsin, Milwaukee, WI, USA
- Department of Biomedical Engineering, Marquette University and Medical College of Wisconsin, Milwaukee, WI, USA
- Cardiovascular Center, The Medical College of Wisconsin, Milwaukee, WI, USA
- Research Service, Zablocki VA Medical Center, Milwaukee, WI, USA
| | - Meiying Yang
- Department of Anesthesiology, Medical College of Wisconsin, Milwaukee, WI, USA
| | - James S. Heisner
- Department of Anesthesiology, Medical College of Wisconsin, Milwaukee, WI, USA
| | - Amadou K.S. Camara
- Department of Anesthesiology, Medical College of Wisconsin, Milwaukee, WI, USA
- Cardiovascular Center, The Medical College of Wisconsin, Milwaukee, WI, USA
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4
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Functional Interactions between BK Caα-Subunit and Annexin A5: Implications in Apoptosis. OXIDATIVE MEDICINE AND CELLULAR LONGEVITY 2016; 2016:1607092. [PMID: 27738490 PMCID: PMC5055951 DOI: 10.1155/2016/1607092] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/14/2016] [Revised: 07/04/2016] [Accepted: 07/10/2016] [Indexed: 12/26/2022]
Abstract
Proteomic studies have suggested a biochemical interaction between α subunit of the large conductance, voltage- and Ca2+-activated potassium channel (BKCaα), and annexin A5 (ANXA5), which we verify here by coimmunoprecipitation and double labelling immunocytochemistry. The observation that annexin is flipped to the outer membrane leaflet of the plasma membrane during apoptosis, together with the knowledge that the intracellular C-terminal of BKCaα contains both Ca2+-binding and a putative annexin-binding motif, prompted us to investigate the functional consequences of this protein partnership to cell death. Membrane biotinylation demonstrated that ANXA5 was flipped to the outer membrane leaflet of HEK 293 cells early in serum deprivation-evoked apoptosis. As expected, serum deprivation caused caspase-3/7 activation and this was accentuated in BKCaα expressing HEK 293 cells. The functional consequences of ANXA5 partnership with BKCaα were striking, with ANXA5 knockdown causing an increase and ANXA5 overexpression causing a decrease, in single BKCa channel Ca2+-sensitivity, measured in inside-out membrane patches by patch-clamp. Taken together, these data suggest a novel model of the early stages of apoptosis where membrane flippage results in removal of the inhibitory effect of ANXA5 on K+ channel activity with the consequent amplification of Ca2+ influx and augmented activation of caspases.
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Abeyrathne PD, Chami M, Stahlberg H. Biochemical and biophysical approaches to study the structure and function of the chloride channel (ClC) family of proteins. Biochimie 2016; 128-129:154-62. [PMID: 27554851 DOI: 10.1016/j.biochi.2016.08.008] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2016] [Accepted: 08/19/2016] [Indexed: 11/30/2022]
Abstract
The chloride channel (ClC) protein family comprises both chloride (Cl(-)) channels and chloride/proton (Cl(-)/H(+)) antiporters. In prokaryotes and eukaryotes, these proteins mediate the movement of Cl(-) ions across the membrane. In eukaryotes, ClC proteins play a role in the stabilization of membrane potential, epithelial ion transport, hippocampal neuroprotection, cardiac pacemaker activity and vesicular acidification. Moreover, mutations in the genes encoding ClC proteins can cause genetic disease in humans. In prokaryotes, the Cl(-)/H(+) antiporters, such as ClC-ec1 found in Escherichia coli promote proton expulsion in the extreme acid-resistance response common to enteric bacteria. To date, structural and functional studies of the prokaryotic protein have revealed unique structural features, including complicated transmembrane topology with 18 α-helices in each subunit and an anion-coordinating region in each subunit. Several different approaches such as X-ray crystallography, NMR, biochemical studies, and molecular dynamics simulations have been applied to the study of ClC proteins. Continued study of the unique structure and function of this diverse family of proteins has the potential to lead to the development of novel therapeutic targets for neuronal, renal, bone, and food-borne diseases.
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Affiliation(s)
- Priyanka D Abeyrathne
- Center for Cellular Imaging and NanoAnalytics, Biozentrum, University of Basel, WRO-1508 Mattenstrasse 26, CH-4058, Basel, Switzerland.
| | - Mohamed Chami
- Center for Cellular Imaging and NanoAnalytics, Biozentrum, University of Basel, WRO-1508 Mattenstrasse 26, CH-4058, Basel, Switzerland
| | - Henning Stahlberg
- Center for Cellular Imaging and NanoAnalytics, Biozentrum, University of Basel, WRO-1508 Mattenstrasse 26, CH-4058, Basel, Switzerland
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6
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Gaburjakova J, Gaburjakova M. Cardiac ryanodine receptor: Selectivity for alkaline earth metal cations points to the EF-hand nature of luminal binding sites. Bioelectrochemistry 2016; 109:49-56. [PMID: 26849106 DOI: 10.1016/j.bioelechem.2016.01.002] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2015] [Revised: 01/21/2016] [Accepted: 01/24/2016] [Indexed: 11/18/2022]
Abstract
A growing body of evidence suggests that the regulation of cardiac ryanodine receptor (RYR2) by luminal Ca(2+) is mediated by luminal binding sites located on the RYR2 channel itself and/or its auxiliary protein, calsequestrin. The localization and structure of RYR2-resident binding sites are not known because of the lack of a high-resolution structure of RYR2 luminal regions. To obtain the first structural insight, we probed the RYR2 luminal face stripped of calsequestrin by alkaline earth metal divalents (M(2+): Mg(2+), Ca(2+), Sr(2+) or Ba(2+)). We show that the RYR2 response to caffeine at the single-channel level is significantly modified by the nature of luminal M(2+). Moreover, we performed competition experiments by varying the concentration of luminal M(2+) (Mg(2+), Sr(2+) or Ba(2+)) from 8 mM to 53 mM and investigated its ability to compete with 1mM luminal Ca(2+). We demonstrate that all tested M(2+) bind to exactly the same RYR2 luminal binding sites. Their affinities decrease in the order: Ca(2+)>Sr(2+)>Mg(2+)~Ba(2+), showing a strong correlation with the M(2+) affinity of the EF-hand motif. This indicates that the RYR2 luminal binding regions and the EF-hand motif likely share some structural similarities because the structure ties directly to the function.
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Affiliation(s)
- Jana Gaburjakova
- Institute of Molecular Physiology and Genetics, Slovak Academy of Sciences, Health Sciences Pavilion, 840 05, Bratislava, Slovak Republic.
| | - Marta Gaburjakova
- Institute of Molecular Physiology and Genetics, Slovak Academy of Sciences, Health Sciences Pavilion, 840 05, Bratislava, Slovak Republic.
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7
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Stowe DF, Gadicherla AK, Zhou Y, Aldakkak M, Cheng Q, Kwok WM, Jiang MT, Heisner JS, Yang M, Camara AKS. Protection against cardiac injury by small Ca(2+)-sensitive K(+) channels identified in guinea pig cardiac inner mitochondrial membrane. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2012; 1828:427-42. [PMID: 22982251 DOI: 10.1016/j.bbamem.2012.08.031] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/25/2012] [Revised: 08/29/2012] [Accepted: 08/30/2012] [Indexed: 11/24/2022]
Abstract
We tested if small conductance, Ca(2+)-sensitive K(+) channels (SK(Ca)) precondition hearts against ischemia reperfusion (IR) injury by improving mitochondrial (m) bioenergetics, if O(2)-derived free radicals are required to initiate protection via SK(Ca) channels, and, importantly, if SK(Ca) channels are present in cardiac cell inner mitochondrial membrane (IMM). NADH and FAD, superoxide (O(2)(-)), and m[Ca(2+)] were measured in guinea pig isolated hearts by fluorescence spectrophotometry. SK(Ca) and IK(Ca) channel opener DCEBIO (DCEB) was given for 10 min and ended 20 min before IR. Either TBAP, a dismutator of O(2)()(-), NS8593, an antagonist of SK(Ca) isoforms, or other K(Ca) and K(ATP) channel antagonists, were given before DCEB and before ischemia. DCEB treatment resulted in a 2-fold increase in LV pressure on reperfusion and a 2.5 fold decrease in infarct size vs. non-treated hearts associated with reduced O(2)(-) and m[Ca(2+)], and more normalized NADH and FAD during IR. Only NS8593 and TBAP antagonized protection by DCEB. Localization of SK(Ca) channels to mitochondria and IMM was evidenced by a) identification of purified mSK(Ca) protein by Western blotting, immuno-histochemical staining, confocal microscopy, and immuno-gold electron microscopy, b) 2-D gel electrophoresis and mass spectroscopy of IMM protein, c) [Ca(2+)]-dependence of mSK(Ca) channels in planar lipid bilayers, and d) matrix K(+) influx induced by DCEB and blocked by SK(Ca) antagonist UCL1684. This study shows that 1) SK(Ca) channels are located and functional in IMM, 2) mSK(Ca) channel opening by DCEB leads to protection that is O(2)(-) dependent, and 3) protection by DCEB is evident beginning during ischemia.
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Affiliation(s)
- David F Stowe
- Department of Anesthesiology, Medical College of Wisconsin, Milwaukee, WI, USA.
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Savalli N, Pantazis A, Yusifov T, Sigg D, Olcese R. The contribution of RCK domains to human BK channel allosteric activation. J Biol Chem 2012; 287:21741-50. [PMID: 22556415 PMCID: PMC3381136 DOI: 10.1074/jbc.m112.346171] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2012] [Revised: 04/10/2012] [Indexed: 11/06/2022] Open
Abstract
Large conductance voltage- and Ca(2+)-activated K(+) (BK) channels are potent regulators of cellular processes including neuronal firing, synaptic transmission, cochlear hair cell tuning, insulin release, and smooth muscle tone. Their unique activation pathway relies on structurally distinct regulatory domains including one transmembrane voltage-sensing domain (VSD) and two intracellular high affinity Ca(2+)-sensing sites per subunit (located in the RCK1 and RCK2 domains). Four pairs of RCK1 and RCK2 domains form a Ca(2+)-sensing apparatus known as the "gating ring." The allosteric interplay between voltage- and Ca(2+)-sensing apparati is a fundamental mechanism of BK channel function. Using voltage-clamp fluorometry and UV photolysis of intracellular caged Ca(2+), we optically resolved VSD activation prompted by Ca(2+) binding to the gating ring. The sudden increase of intracellular Ca(2+) concentration ([Ca(2+)](i)) induced a hyperpolarizing shift in the voltage dependence of both channel opening and VSD activation, reported by a fluorophore labeling position 202, located in the upper side of the S4 transmembrane segment. The neutralization of the Ca(2+) sensor located in the RCK2 domain abolished the effect of [Ca(2+)](i) increase on the VSD rearrangements. On the other hand, the mutation of RCK1 residues involved in Ca(2+) sensing did not prevent the effect of Ca(2+) release on the VSD, revealing a functionally distinct interaction between RCK1 and RCK2 and the VSD. A statistical-mechanical model quantifies the complex thermodynamics interplay between Ca(2+) association in two distinct sites, voltage sensor activation, and BK channel opening.
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Affiliation(s)
- Nicoletta Savalli
- From the Department of Anesthesiology, Division of Molecular Medicine
| | - Antonios Pantazis
- From the Department of Anesthesiology, Division of Molecular Medicine
| | - Taleh Yusifov
- From the Department of Anesthesiology, Division of Molecular Medicine
| | - Daniel Sigg
- From the Department of Anesthesiology, Division of Molecular Medicine
| | - Riccardo Olcese
- From the Department of Anesthesiology, Division of Molecular Medicine
- the Brain Research Institute, and
- the Cardiovascular Research Laboratories, David Geffen School of Medicine, University of California at Los Angeles, Los Angeles, California 90075
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Javaherian AD, Yusifov T, Pantazis A, Franklin S, Gandhi CS, Olcese R. Metal-driven operation of the human large-conductance voltage- and Ca2+-dependent potassium channel (BK) gating ring apparatus. J Biol Chem 2011; 286:20701-9. [PMID: 21471215 DOI: 10.1074/jbc.m111.235234] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Large-conductance voltage- and Ca(2+)-dependent K(+) (BK, also known as MaxiK) channels are homo-tetrameric proteins with a broad expression pattern that potently regulate cellular excitability and Ca(2+) homeostasis. Their activation results from the complex synergy between the transmembrane voltage sensors and a large (>300 kDa) C-terminal, cytoplasmic complex (the "gating ring"), which confers sensitivity to intracellular Ca(2+) and other ligands. However, the molecular and biophysical operation of the gating ring remains unclear. We have used spectroscopic and particle-scale optical approaches to probe the metal-sensing properties of the human BK gating ring under physiologically relevant conditions. This functional molecular sensor undergoes Ca(2+)- and Mg(2+)-dependent conformational changes at physiologically relevant concentrations, detected by time-resolved and steady-state fluorescence spectroscopy. The lack of detectable Ba(2+)-evoked structural changes defined the metal selectivity of the gating ring. Neutralization of a high-affinity Ca(2+)-binding site (the "calcium bowl") reduced the Ca(2+) and abolished the Mg(2+) dependence of structural rearrangements. In congruence with electrophysiological investigations, these findings provide biochemical evidence that the gating ring possesses an additional high-affinity Ca(2+)-binding site and that Mg(2+) can bind to the calcium bowl with less affinity than Ca(2+). Dynamic light scattering analysis revealed a reversible Ca(2+)-dependent decrease of the hydrodynamic radius of the gating ring, consistent with a more compact overall shape. These structural changes, resolved under physiologically relevant conditions, likely represent the molecular transitions that initiate the ligand-induced activation of the human BK channel.
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Affiliation(s)
- Anoosh D Javaherian
- Division of Molecular Medicine, Department of Anesthesiology, David Geffen School of Medicine, UCLA, Los Angeles, California 90095-7115, USA
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Liu B, Sun X, Zhu Y, Gan L, Xu H, Yang X. Biphasic effects of H(2)O(2) on BK(Ca) channels. Free Radic Res 2011; 44:1004-12. [PMID: 20560834 DOI: 10.3109/10715762.2010.495126] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
The inhibitory or activating effect of H(2)O(2) on large conductance calcium and voltage-dependent potassium (BK(Ca)) channels has been reported. However, the mechanism by which this occurs is unclear. In this paper, BK(Ca) channels encoded by mouse Slo were expressed in HEK 293 cells and BK(Ca) channel activity was measured by electrophysiology. The results showed that H(2)O(2) inhibited BK(Ca) channel activity in inside-out patches but enhanced BK(Ca) channel activity in cell-attached patches. The inhibition by H(2)O(2) in inside-out patches may be due to oxidative modification of cysteine residues in BK(Ca) channels or other membrane proteins that regulate BK(Ca) channel function. PI3K/AKT signaling modulates the H(2)O(2)-induced BK(Ca) channel activation in cell-attached patches. BK(Ca) channels and PI3K signaling pathway were involved in H(2)O(2)-induced vasodilation and H(2)O(2)-induced vasodilation by PI3K pathway was mainly due to modulation of BK(Ca) channel activity.
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Affiliation(s)
- Bo Liu
- Huazhong University of Science and Technology, Wuhan, PR China
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Pantazis A, Kohanteb AP, Olcese R. Relative motion of transmembrane segments S0 and S4 during voltage sensor activation in the human BK(Ca) channel. J Gen Physiol 2010; 136:645-57. [PMID: 21078868 PMCID: PMC2995153 DOI: 10.1085/jgp.201010503] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2010] [Accepted: 11/01/2010] [Indexed: 01/06/2023] Open
Abstract
Large-conductance voltage- and Ca(2+)-activated K(+) (BK(Ca)) channel α subunits possess a unique transmembrane helix referred to as S0 at their N terminus, which is absent in other members of the voltage-gated channel superfamily. Recently, S0 was found to pack close to transmembrane segments S3 and S4, which are important components of the BK(Ca) voltage-sensing apparatus. To assess the role of S0 in voltage sensitivity, we optically tracked protein conformational rearrangements from its extracellular flank by site-specific labeling with an environment-sensitive fluorophore, tetramethylrhodamine maleimide (TMRM). The structural transitions resolved from the S0 region exhibited voltage dependence similar to that of charge-bearing transmembrane domains S2 and S4. The molecular determinant of the fluorescence changes was identified in W203 at the extracellular tip of S4: at hyperpolarized potential, W203 quenches the fluorescence of TMRM labeling positions at the N-terminal flank of S0. We provide evidence that upon depolarization, W203 (in S4) moves away from the extracellular region of S0, lifting its quenching effect on TMRM fluorescence. We suggest that S0 acts as a pivot component against which the voltage-sensitive S4 moves upon depolarization to facilitate channel activation.
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Affiliation(s)
- Antonios Pantazis
- Department of Anesthesiology, Division of Molecular Medicine, Brain Research Institute, and Cardiovascular Research Laboratories, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90075
| | - Azadeh P. Kohanteb
- Department of Anesthesiology, Division of Molecular Medicine, Brain Research Institute, and Cardiovascular Research Laboratories, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90075
| | - Riccardo Olcese
- Department of Anesthesiology, Division of Molecular Medicine, Brain Research Institute, and Cardiovascular Research Laboratories, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90075
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Yusifov T, Javaherian AD, Pantazis A, Gandhi CS, Olcese R. The RCK1 domain of the human BKCa channel transduces Ca2+ binding into structural rearrangements. ACTA ACUST UNITED AC 2010; 136:189-202. [PMID: 20624858 PMCID: PMC2912072 DOI: 10.1085/jgp.200910374] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Large-conductance voltage- and Ca2+-activated K+ (BKCa) channels play a fundamental role in cellular function by integrating information from their voltage and Ca2+ sensors to control membrane potential and Ca2+ homeostasis. The molecular mechanism of Ca2+-dependent regulation of BKCa channels is unknown, but likely relies on the operation of two cytosolic domains, regulator of K+ conductance (RCK)1 and RCK2. Using solution-based investigations, we demonstrate that the purified BKCa RCK1 domain adopts an α/β fold, binds Ca2+, and assembles into an octameric superstructure similar to prokaryotic RCK domains. Results from steady-state and time-resolved spectroscopy reveal Ca2+-induced conformational changes in physiologically relevant [Ca2+]. The neutralization of residues known to be involved in high-affinity Ca2+ sensing (D362 and D367) prevented Ca2+-induced structural transitions in RCK1 but did not abolish Ca2+ binding. We provide evidence that the RCK1 domain is a high-affinity Ca2+ sensor that transduces Ca2+ binding into structural rearrangements, likely representing elementary steps in the Ca2+-dependent activation of human BKCa channels.
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Affiliation(s)
- Taleh Yusifov
- Division of Molecular Medicine, Department of Anesthesiology, David Geffen School of Medicine at University of California, Los Angeles, CA 90095, USA
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Yuan P, Leonetti MD, Pico AR, Hsiung Y, MacKinnon R. Structure of the human BK channel Ca2+-activation apparatus at 3.0 A resolution. Science 2010; 329:182-6. [PMID: 20508092 DOI: 10.1126/science.1190414] [Citation(s) in RCA: 232] [Impact Index Per Article: 16.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
High-conductance voltage- and Ca2+-activated K+ (BK) channels encode negative feedback regulation of membrane voltage and Ca2+ signaling, playing a central role in numerous physiological processes. We determined the x-ray structure of the human BK Ca2+ gating apparatus at a resolution of 3.0 angstroms and deduced its tetrameric assembly by solving a 6 angstrom resolution structure of a Na+-activated homolog. Two tandem C-terminal regulator of K+ conductance (RCK) domains from each of four channel subunits form a 350-kilodalton gating ring at the intracellular membrane surface. A sequence of aspartic amino acids that is known as the Ca2+ bowl, and is located within the second of the tandem RCK domains, creates four Ca2+ binding sites on the outer perimeter of the gating ring at the "assembly interface" between RCK domains. Functionally important mutations cluster near the Ca2+ bowl, near the "flexible interface" between RCK domains, and on the surface of the gating ring that faces the voltage sensors. The structure suggests that the Ca2+ gating ring, in addition to regulating the pore directly, may also modulate the voltage sensor.
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Affiliation(s)
- Peng Yuan
- Laboratory of Molecular Neurobiology and Biophysics, Rockefeller University, Howard Hughes Medical Institute, 1230 York Avenue, New York, NY 10065, USA
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Kranjc A, Grillo FW, Rievaj J, Boccaccio A, Pietrucci F, Menini A, Carloni P, Anselmi C. Regulation of bestrophins by Ca2+: a theoretical and experimental study. PLoS One 2009; 4:e4672. [PMID: 19262692 PMCID: PMC2650406 DOI: 10.1371/journal.pone.0004672] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2008] [Accepted: 01/26/2009] [Indexed: 01/06/2023] Open
Abstract
Bestrophins are a recently discovered family of Cl(-) channels, for which no structural information is available. Some family members are activated by increased intracellular Ca2+ concentration. Bestrophins feature a well conserved Asp-rich tract in their COOH terminus (Asp-rich domain), which is homologous to Ca2+-binding motifs in human thrombospondins and in human big-conductance Ca2+- and voltage-gated K+ channels (BK(Ca)). Consequently, the Asp-rich domain is also a candidate for Ca2+ binding in bestrophins. Based on these considerations, we constructed homology models of human bestrophin-1 (Best1) Asp-rich domain using human thrombospondin-1 X-ray structure as a template. Molecular dynamics simulations were used to identify Asp and Glu residues binding Ca2+ and to predict the effects of their mutations to alanine. We then proceeded to test selected mutations in the Asp-rich domain of the highly homologous mouse bestrophin-2. The mutants expressed in HEK-293 cells were investigated by electrophysiological experiments using the whole-cell voltage-clamp technique. Based on our molecular modeling results, we predicted that Asp-rich domain has two defined binding sites and that D301A and D304A mutations may impact the binding of the metal ions. The experiments confirmed that these mutations do actually affect the function of the protein causing a large decrease in the Ca2+-activated Cl(-) current, fully consistent with our predictions. In addition, other studied mutations (E306A, D312A) did not decrease Ca2+-activated Cl(-) current in agreement with modeling results.
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Affiliation(s)
- Agata Kranjc
- International School for Advanced Studies (SISSA/ISAS), Trieste, Italy
| | | | - Juraj Rievaj
- International School for Advanced Studies (SISSA/ISAS), Trieste, Italy
| | - Anna Boccaccio
- International School for Advanced Studies (SISSA/ISAS), Trieste, Italy
- Italian Institute of Technology (IIT), SISSA-Unit, Trieste, Italy
| | - Fabio Pietrucci
- International School for Advanced Studies (SISSA/ISAS), Trieste, Italy
| | - Anna Menini
- International School for Advanced Studies (SISSA/ISAS), Trieste, Italy
- Italian Institute of Technology (IIT), SISSA-Unit, Trieste, Italy
| | - Paolo Carloni
- International School for Advanced Studies (SISSA/ISAS), Trieste, Italy
- Italian Institute of Technology (IIT), SISSA-Unit, Trieste, Italy
- CNR-INFM-DEMOCRITOS Modeling Center for Research in Atomistic Simulation, Trieste, Italy
| | - Claudio Anselmi
- International School for Advanced Studies (SISSA/ISAS), Trieste, Italy
- CNR-INFM-DEMOCRITOS Modeling Center for Research in Atomistic Simulation, Trieste, Italy
- * E-mail:
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15
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Xiao Q, Prussia A, Yu K, Cui YY, Hartzell HC. Regulation of bestrophin Cl channels by calcium: role of the C terminus. ACTA ACUST UNITED AC 2009; 132:681-92. [PMID: 19029375 PMCID: PMC2585866 DOI: 10.1085/jgp.200810056] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Human bestrophin-1 (hBest1), which is genetically linked to several kinds of retinopathy and macular degeneration in both humans and dogs, is the founding member of a family of Cl− ion channels that are activated by intracellular Ca2+. At present, the structures and mechanisms responsible for Ca2+ sensing remain unknown. Here, we have used a combination of molecular modeling, density functional–binding energy calculations, mutagenesis, and patch clamp to identify the regions of hBest1 involved in Ca2+ sensing. We identified a cluster of a five contiguous acidic amino acids in the C terminus immediately after the last transmembrane domain, followed by an EF hand and another regulatory domain that are essential for Ca2+ sensing by hBest1. The cluster of five amino acids (293–308) is crucial for normal channel gating by Ca2+ because all but two of the 35 mutations we made in this region rendered the channel incapable of being activated by Ca2+. Using homology models built on the crystal structure of calmodulin (CaM), an EF hand (EF1) was identified in hBest1. EF1 was predicted to bind Ca2+ with a slightly higher affinity than the third EF hand of CaM and lower affinity than the second EF hand of troponin C. As predicted by the model, the D312G mutation in the putative Ca2+-binding loop (312–323) reduced the apparent Ca2+ affinity by 20-fold. In addition, the D312G and D323N mutations abolished Ca2+-dependent rundown of the current. Furthermore, analysis of truncation mutants of hBest1 identified a domain adjacent to EF1 that is rich in acidic amino acids (350–390) that is required for Ca2+ activation and plays a role in current rundown. These experiments identify a region of hBest1 (312–323) that is involved in the gating of hBest1 by Ca2+ and suggest a model in which Ca2+ binding to EF1 activates the channel in a process that requires the acidic domain (293–308) and another regulatory domain (350–390). Many of the ∼100 disease-causing mutations in hBest1 are located in this region that we have implicated in Ca2+ sensing, suggesting that these mutations disrupt hBest1 channel gating by Ca2+.
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Affiliation(s)
- Qinghuan Xiao
- Department of Cell Biology and Center for Neurodegenerative Disease, Emory University School of Medicine, Atlanta, GA 30322, USA
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16
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Korovkina VP, Stamnes SJ, Brainard AM, England SK. Nardilysin convertase regulates the function of the maxi-K channel isoform mK44 in human myometrium. Am J Physiol Cell Physiol 2008; 296:C433-40. [PMID: 19118164 DOI: 10.1152/ajpcell.00357.2008] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In smooth muscle, large-conductance Ca(2+)- and voltage-activated K(+) channels from the gene KCNMA (maxi-K channels) generate isoforms with disparate responses to contractile stimuli. We previously showed that the human myometrium expresses high levels of the splice variant of the maxi-K channel containing a 44-amino acid insertion (mK44). The studies presented here demonstrate that nardilysin convertase, a Zn(2+)-dependent metalloprotease of the insulinase family, regulates the plasma membrane expression of mK44 and its response to increases in intracellular Ca(2+). We show that nardilysin convertase isoform 1 is present in human myometrium and colocalizes with mK44. Studies indicate that nardilysin convertase regulates 1) retention of the mK44 COOH-terminal fragment in the endoplasmic reticulum in quiescent myometrial smooth muscle and 2) Ca(2+)-induced translocation of mK44 to the plasma membrane. In mouse fibroblasts, nardilysin convertase significantly attenuates mK44-dependent current. In human myometrial smooth muscle cells, inhibition of nardilysin convertase promotes membrane localization of mK44 and an increase in maxi-K current. Overall, our data indicate that, in human myometrium, nardilysin convertase and mK44 channels are a part of the molecular mechanism that regulates the excitability of smooth muscle cells.
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Affiliation(s)
- Victoria P Korovkina
- Dept. of Molecular Physiology and Biophysics, 6-432 BSB, Iowa City, IA 52242-1109, USA
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17
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Liu J, Vaithianathan T, Manivannan K, Parrill A, Dopico AM. Ethanol modulates BKCa channels by acting as an adjuvant of calcium. Mol Pharmacol 2008; 74:628-40. [PMID: 18552122 DOI: 10.1124/mol.108.048694] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Ethanol modulation of calcium- and voltage-gated potassium (slo1) channels alters neuronal excitability, cerebrovascular tone, brain function, and behavior, yet the mechanism of this modulation remains unknown. Using patch-clamp electrophysiology on recombinant BK(Ca) channels cloned from mouse brain and expressed in Xenopus laevis oocytes, we demonstrate that ethanol, even at concentrations maximally effective to modulate BK(Ca) channel function (100 mM), fails to gate the channel in absence of activating calcium. Moreover, ethanol does not modify intrinsic, voltage- or physiological magnesium-driven gating. The alcohol works as an adjuvant of calcium by selectively facilitating calcium-driven gating. This facilitation, however, renders differential ethanol effects on channel activity: potentiation at low (<10 microM) and inhibition at high (>10 microM) calcium, this dual pattern remaining largely unmodified by coexpression of brain slo1 channels with the neuronally abundant BK(Ca) channel beta(4) subunit. Calcium recognition by either of the slo1 high-affinity sensors (calcium bowl and RCK1 Asp362/Asp367) is required for ethanol to amplify channel activation by calcium. The Asp362/Asp367 site, however, is necessary and sufficient to sustain ethanol inhibition. This inhibition also results from ethanol facilitation of calcium action; in this case, ethanol favors channel dwelling in a calcium-driven, low-activity mode. The agonist-adjuvant mechanism that we advance from the calcium-ethanol interaction on slo1 might be applicable to data of ethanol action on a wide variety of ligand-gated channels.
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Affiliation(s)
- Jianxi Liu
- Department of Pharmacology, the University of Tennessee Health Science Center, 874 Union Ave., Memphis, TN 38163, USA
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18
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Yusifov T, Savalli N, Gandhi CS, Ottolia M, Olcese R. The RCK2 domain of the human BKCa channel is a calcium sensor. Proc Natl Acad Sci U S A 2008; 105:376-81. [PMID: 18162557 PMCID: PMC2224220 DOI: 10.1073/pnas.0705261105] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2007] [Indexed: 12/21/2022] Open
Abstract
Large conductance voltage and Ca(2+)-dependent K(+) channels (BK(Ca)) are activated by both membrane depolarization and intracellular Ca(2+). Recent studies on bacterial channels have proposed that a Ca(2+)-induced conformational change within specialized regulators of K(+) conductance (RCK) domains is responsible for channel gating. Each pore-forming alpha subunit of the homotetrameric BK(Ca) channel is expected to contain two intracellular RCK domains. The first RCK domain in BK(Ca) channels (RCK1) has been shown to contain residues critical for Ca(2+) sensitivity, possibly participating in the formation of a Ca(2+)-binding site. The location and structure of the second RCK domain in the BK(Ca) channel (RCK2) is still being examined, and the presence of a high-affinity Ca(2+)-binding site within this region is not yet established. Here, we present a structure-based alignment of the C terminus of BK(Ca) and prokaryotic RCK domains that reveal the location of a second RCK domain in human BK(Ca) channels (hSloRCK2). hSloRCK2 includes a high-affinity Ca(2+)-binding site (Ca bowl) and contains similar secondary structural elements as the bacterial RCK domains. Using CD spectroscopy, we provide evidence that hSloRCK2 undergoes a Ca(2+)-induced change in conformation, associated with an alpha-to-beta structural transition. We also show that the Ca bowl is an essential element for the Ca(2+)-induced rearrangement of hSloRCK2. We speculate that the molecular rearrangements of RCK2 likely underlie the Ca(2+)-dependent gating mechanism of BK(Ca) channels. A structural model of the heterodimeric complex of hSloRCK1 and hSloRCK2 domains is discussed.
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Affiliation(s)
- Taleh Yusifov
- *Division of Molecular Medicine, Department of Anesthesiology
| | | | - Chris S. Gandhi
- Division of Chemistry and Chemical Engineering, Howard Hughes Medical Institute, MC 114-96, California Institute of Technology, Pasadena, CA 91125
| | - Michela Ottolia
- Cardiovascular Research Laboratory, and
- Department of Physiology, David Geffen School of Medicine, University of California, Los Angeles, CA 90095-7115; and
| | - Riccardo Olcese
- *Division of Molecular Medicine, Department of Anesthesiology
- Brain Research Institute
- Cardiovascular Research Laboratory, and
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19
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Abstract
Intracellular Mg(2+) at physiological concentrations activates mSlo1 BK channels by binding to a metal-binding site in the cytosolic domain. Previous studies suggest that residues E374, Q397, and E399 are important in Mg(2+) binding. In the present study, we show that mutations of E374 or E399 to other amino acids, except for Asp, abolish Mg(2+) sensitivity. These results further support that the side chains of E374 and E399 are essential for Mg(2+) coordination. To the contrary, none of the Q397 mutations abolishes Mg(2+) sensitivity, suggesting that its side chain may not coordinate to Mg(2+). However, because Q397 is spatially close to E374 and E399, its mutations affect the Mg(2+) sensitivity of channel gating by either reducing or increasing the Mg(2+) binding affinity. The pattern of mutational effects and the effect of chemical modification of Q397C indicate that Q397 is involved in the Mg(2+)-dependent activation of BK channels and that mutations of Q397 alter Mg(2+) sensitivity by affecting the conformation of the Mg(2+) binding site as well as by electrostatic interactions with the bound Mg(2+) ion.
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Affiliation(s)
- Huanghe Yang
- Department of Biomedical Engineering and Cardiac Bioelectricity and Arrhythmia Center, Washington University, St. Louis, Missouri 63130, USA
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20
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Fodor AA, Aldrich RW. Statistical limits to the identification of ion channel domains by sequence similarity. ACTA ACUST UNITED AC 2006; 127:755-66. [PMID: 16735758 PMCID: PMC2151544 DOI: 10.1085/jgp.200509419] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The study of ion channel function is constrained by the availability of structures for only a small number of channels. A commonly used bioinformatics technique is to assert, based on sequence similarity, that a domain within a channel of interest has the same structure as a reference domain for which the structure is known. This technique, while useful, is often employed when there is only a slight similarity between the channel of interest and the domain of known structure. In this study, we exploit recent advances in structural genomics to calculate the sequence-based probability of the presence of putative domains in a number of ion channels. We find strong support for the presence of many domains that have been proposed in the literature. For example, eukaryotic and prokaryotic CLC proteins almost certainly share a common structure. A number of proposed domains, however, are not as well supported. In particular, for the COOH terminus of the BK channel we find a number of literature proposed domains for which the assertion of common structure based on common sequence has a nontrivial probability of error.
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Affiliation(s)
- Anthony A Fodor
- Department of Molecular and Cellular Physiology, Howard Hughes Medical Institute, Stanford University School of Medicine, CA 94305, USA.
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