1
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Ngo K, Yarov-Yarovoy V, Clancy CE, Vorobyov I. Harnessing AlphaFold to reveal state secrets: Prediction of hERG closed and inactivated states. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.01.27.577468. [PMID: 38352360 PMCID: PMC10862728 DOI: 10.1101/2024.01.27.577468] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 02/20/2024]
Abstract
To design safe, selective, and effective new therapies, there must be a deep understanding of the structure and function of the drug target. One of the most difficult problems to solve has been resolution of discrete conformational states of transmembrane ion channel proteins. An example is KV11.1 (hERG), comprising the primary cardiac repolarizing current, IKr. hERG is a notorious drug anti-target against which all promising drugs are screened to determine potential for arrhythmia. Drug interactions with the hERG inactivated state are linked to elevated arrhythmia risk, and drugs may become trapped during channel closure. However, the structural details of multiple conformational states have remained elusive. Here, we guided AlphaFold2 to predict plausible hERG inactivated and closed conformations, obtaining results consistent with myriad available experimental data. Drug docking simulations demonstrated hERG state-specific drug interactions aligning well with experimental results, revealing that most drugs bind more effectively in the inactivated state and are trapped in the closed state. Molecular dynamics simulations demonstrated ion conduction that aligned with earlier studies. Finally, we identified key molecular determinants of state transitions by analyzing interaction networks across closed, open, and inactivated states in agreement with earlier mutagenesis studies. Here, we demonstrate a readily generalizable application of AlphaFold2 as a novel method to predict discrete protein conformations and novel linkages from structure to function.
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Affiliation(s)
- Khoa Ngo
- Biophysics Graduate Group, University of California, Davis, CA
- Department of Physiology and Membrane Biology, University of California, Davis, CA
- Center for Precision Medicine and Data Science, University of California, Davis, CA
| | - Vladimir Yarov-Yarovoy
- Department of Physiology and Membrane Biology, University of California, Davis, CA
- Department of Anesthesiology and Pain Medicine, University of California, Davis, CA
| | - Colleen E. Clancy
- Department of Physiology and Membrane Biology, University of California, Davis, CA
- Department of Pharmacology, University of California, Davis, CA
- Center for Precision Medicine and Data Science, University of California, Davis, CA
| | - Igor Vorobyov
- Department of Physiology and Membrane Biology, University of California, Davis, CA
- Department of Pharmacology, University of California, Davis, CA
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2
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Furutani K. Facilitation of hERG Activation by Its Blocker: A Mechanism to Reduce Drug-Induced Proarrhythmic Risk. Int J Mol Sci 2023; 24:16261. [PMID: 38003453 PMCID: PMC10671758 DOI: 10.3390/ijms242216261] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2023] [Revised: 11/08/2023] [Accepted: 11/12/2023] [Indexed: 11/26/2023] Open
Abstract
Modulation of the human Ether-à-go-go-Related Gene (hERG) channel, a crucial voltage-gated potassium channel in the repolarization of action potentials in ventricular myocytes of the heart, has significant implications on cardiac electrophysiology and can be either antiarrhythmic or proarrhythmic. For example, hERG channel blockade is a leading cause of long QT syndrome and potentially life-threatening arrhythmias, such as torsades de pointes. Conversely, hERG channel blockade is the mechanism of action of Class III antiarrhythmic agents in terminating ventricular tachycardia and fibrillation. In recent years, it has been recognized that less proarrhythmic hERG blockers with clinical potential or Class III antiarrhythmic agents exhibit, in addition to their hERG-blocking activity, a second action that facilitates the voltage-dependent activation of the hERG channel. This facilitation is believed to reduce the proarrhythmic potential by supporting the final repolarizing of action potentials. This review covers the pharmacological characteristics of hERG blockers/facilitators, the molecular mechanisms underlying facilitation, and their clinical significance, as well as unresolved issues and requirements for research in the fields of ion channel pharmacology and drug-induced arrhythmias.
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Affiliation(s)
- Kazuharu Furutani
- Department of Pharmacology, Faculty of Pharmaceutical Sciences, Tokushima Bunri University, 180 Nishihama-Boji, Yamashiro-cho, Tokushima 770-8514, Japan
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3
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Kudaibergenova M, Guo J, Khan HM, Lees-Miller J, Mousaei M, Miranda W, Ngo VA, Noskov SY, Tieleman DP, Duff HJ. The voltage-sensing domain of a hERG1 mutant is a cation-selective channel. Biophys J 2022; 121:4585-4599. [PMID: 36815709 PMCID: PMC9748372 DOI: 10.1016/j.bpj.2022.10.032] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2022] [Revised: 06/29/2022] [Accepted: 10/24/2022] [Indexed: 11/24/2022] Open
Abstract
A cationic leak current known as an "omega current" may arise from mutations of the first charged residue in the S4 of the voltage sensor domains of sodium and potassium voltage-gated channels. The voltage-sensing domains (VSDs) in these mutated channels act as pores allowing nonspecific passage of cations, such as Li+, K+, Cs+, and guanidinium. Interestingly, no omega currents have been previously detected in the nonswapped voltage-gated potassium channels such as the human-ether-a-go-go-related (hERG1), hyperpolarization-activated cyclic nucleotide-gated, and ether-a-go-go channels. In this work, we discovered a novel omega current by mutating the first charged residue of the S4 of the hERG1, K525 to serine. To characterize this omega current, we used various probes, including the hERG1 pore domain blocker, dofetilide, to show that the omega current does not require cation flux via the canonical pore domain. In addition, the omega flux does not cross the conventional selectivity filter. We also show that the mutated channel (K525S hERG1) conducts guanidinium. These data are indicative of the formation of an omega current channel within the VSD. Using molecular dynamics simulations with replica-exchange umbrella sampling simulations of the wild-type hERG1 and the K525S hERG1, we explored the molecular underpinnings governing the cation flow in the VSD of the mutant. We also show that the wild-type hERG1 may form water crevices supported by the biophysical surface accessibility data. Overall, our multidisciplinary study demonstrates that the VSD of hERG1 may act as a cation-selective channel wherein a mutation of the first charged residue in the S4 generates an omega current. Our simulation uncovers the atomistic underpinning of this mechanism.
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Affiliation(s)
- Meruyert Kudaibergenova
- Centre for Molecular Simulation and Department of Biological Sciences, University of Calgary, Calgary, AB, Canada
| | - Jiqing Guo
- Department of Cardiac Sciences, Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, AB, Canada
| | - Hanif M Khan
- Centre for Molecular Simulation and Department of Biological Sciences, University of Calgary, Calgary, AB, Canada
| | - James Lees-Miller
- Department of Cardiac Sciences, Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, AB, Canada
| | - Mahdi Mousaei
- Centre for Molecular Simulation and Department of Biological Sciences, University of Calgary, Calgary, AB, Canada
| | - Williams Miranda
- Centre for Molecular Simulation and Department of Biological Sciences, University of Calgary, Calgary, AB, Canada
| | - Van A Ngo
- Centre for Molecular Simulation and Department of Biological Sciences, University of Calgary, Calgary, AB, Canada
| | - Sergei Yu Noskov
- Centre for Molecular Simulation and Department of Biological Sciences, University of Calgary, Calgary, AB, Canada
| | - D Peter Tieleman
- Centre for Molecular Simulation and Department of Biological Sciences, University of Calgary, Calgary, AB, Canada.
| | - Henry J Duff
- Department of Cardiac Sciences, Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, AB, Canada.
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4
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Marquis MJ, Sack JT. Mechanism of use-dependent Kv2 channel inhibition by RY785. J Gen Physiol 2022; 154:e202112981. [PMID: 35435946 PMCID: PMC9195051 DOI: 10.1085/jgp.202112981] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2021] [Revised: 03/01/2022] [Accepted: 03/30/2022] [Indexed: 01/21/2023] Open
Abstract
Understanding the mechanism by which ion channel modulators act is critical for interpretation of their physiological effects and can provide insight into mechanisms of ion channel gating. The small molecule RY785 is a potent and selective inhibitor of Kv2 voltage-gated K+ channels that has a use-dependent onset of inhibition. Here, we investigate the mechanism of RY785 inhibition of rat Kv2.1 (Kcnb1) channels heterologously expressed in CHO-K1 cells. We find that 1 µM RY785 block eliminates Kv2.1 current at all physiologically relevant voltages, inhibiting ≥98% of the Kv2.1 conductance. Both onset of and recovery from RY785 inhibition require voltage sensor activation. Intracellular tetraethylammonium, a classic open-channel blocker, competes with RY785 inhibition. However, channel opening itself does not appear to alter RY785 access. Gating current measurements reveal that RY785 inhibits a component of voltage sensor activation and accelerates voltage sensor deactivation. We propose that voltage sensor activation opens a path into the central cavity of Kv2.1 where RY785 binds and promotes voltage sensor deactivation, trapping itself inside. This gated-access mechanism in conjunction with slow kinetics of unblock supports simple interpretation of RY785 effects: channel activation is required for block by RY785 to equilibrate, after which trapped RY785 will simply decrease the Kv2 conductance density.
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Affiliation(s)
- Matthew James Marquis
- Department of Physiology & Membrane Biology, University of California, Davis, Davis, CA
| | - Jon T. Sack
- Department of Physiology & Membrane Biology, University of California, Davis, Davis, CA
- Department of Anesthesiology and Pain Medicine, University of California, Davis, Davis, CA
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5
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Metabolic and electrolyte abnormalities as risk factors in drug-induced long QT syndrome. Biophys Rev 2022; 14:353-367. [PMID: 35103080 PMCID: PMC8792523 DOI: 10.1007/s12551-022-00929-7] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2021] [Accepted: 01/04/2022] [Indexed: 02/06/2023] Open
Abstract
Drug-induced long QT syndrome (diLQTS) is the phenomenon by which the administration of drugs causes prolongation of cardiac repolarisation and leads to an increased risk of the ventricular tachycardia known as torsades de pointes (TdP). In most cases of diLQTS, the primary molecular target is the human ether-à-go-go-related gene protein (hERG) potassium channel, which carries the rapid delayed rectifier current (IKr) in the heart. However, the proarrhythmic risk associated with drugs that block hERG can be modified in patients by a range of environmental- and disease-related factors, such as febrile temperatures, alterations in pH, dyselectrolytaemias such as hypokalaemia and hypomagnesemia and coadministration with other drugs. In this review, we will discuss the clinical occurrence of drug-induced LQTS in the context of these modifying factors as well as the mechanisms by which they contribute to altered hERG potency and proarrhythmic risk.
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6
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Yin Z, Peng J, Qiao Z, Zhang Y, Wei N. A fluorogenic probe for TRPA1 channel imaging based on a molecular rotation mechanism. NEW J CHEM 2022. [DOI: 10.1039/d2nj01728h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A fluorescent probe for selectively visualizing the TRPA1 channel and rapidly screening its regulators.
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Affiliation(s)
- Zhengji Yin
- Department of Pharmaceutical Analysis and Pharmacology, School of Pharmacy, Qingdao University Medical College, No. 1 Ningde Road, Qingdao 266073, China
| | - Junli Peng
- Department of Pharmaceutical Analysis and Pharmacology, School of Pharmacy, Qingdao University Medical College, No. 1 Ningde Road, Qingdao 266073, China
| | - Zhen Qiao
- Department of Pharmaceutical Analysis and Pharmacology, School of Pharmacy, Qingdao University Medical College, No. 1 Ningde Road, Qingdao 266073, China
| | - Yanru Zhang
- Department of Pharmaceutical Analysis and Pharmacology, School of Pharmacy, Qingdao University Medical College, No. 1 Ningde Road, Qingdao 266073, China
| | - Ningning Wei
- Department of Pharmaceutical Analysis and Pharmacology, School of Pharmacy, Qingdao University Medical College, No. 1 Ningde Road, Qingdao 266073, China
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7
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TeBay C, McArthur JR, Mangala M, Kerr N, Heitmann S, Perry MD, Windley MJ, Vandenberg JI, Hill AP. Pathophysiological metabolic changes associated with disease modify the proarrhythmic risk profile of drugs with potential to prolong repolarisation. Br J Pharmacol 2021; 179:2631-2646. [PMID: 34837219 DOI: 10.1111/bph.15757] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2021] [Revised: 11/16/2021] [Accepted: 11/18/2021] [Indexed: 11/27/2022] Open
Abstract
BACKGROUND AND PURPOSE Hydroxychloroquine, chloroquine and azithromycin are three drugs that were proposed to treat COVID-19. While concern already existed around their proarrhythmic potential there is little data regarding how altered physiological states encountered in patients such as febrile state, electrolyte imbalances or acidosis might change their risk profiles. EXPERIMENTAL APPROACH Potency of hERG block was measured using high-throughput electrophysiology in the presence of variable environmental factors. These potencies informed simulations to predict population risk profiles. Effects on cardiac repolarisation were verified in human induced pluripotent stem cell-derived cardiomyocytes from multiple individuals. KEY RESULTS Chloroquine and hydroxychloroquine blocked hERG with IC50 of 1.47±0.07 μM and 3.78±0.17 μM respectively, indicating proarrhythmic risk at concentrations effective against SARS-CoV-2 in vitro. Hypokalaemia and hypermagnesemia increased potency of chloroquine and hydroxychloroquine, indicating increased proarrhythmic risk. Acidosis significantly reduced potency of all drugs, whereas increased temperature decreased potency of chloroquine and hydroxychloroquine against hERG but increased potency for azithromycin. In silico simulations demonstrated that proarrhythmic risk was increased by female sex, hypokalaemia and heart failure, and identified specific genetic backgrounds associated with emergence of arrhythmia. CONCLUSION AND IMPLICATIONS Our study demonstrates how proarrhythmic risk can be exacerbated by metabolic changes and pre-existing disease. More broadly, the study acts as a blueprint for how high-throughput in vitro screening, combined with in silico simulations can help guide both preclinical screening and clinical management of patients in relation to drugs with potential to prolong repolarisation.
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Affiliation(s)
- Clifford TeBay
- Victor Chang Cardiac Research Institute, Sydney, Australia
| | - Jeffrey R McArthur
- Victor Chang Cardiac Research Institute, Sydney, Australia.,Illawarra Health and Medical Research Institute, University of Wollongong, Australia
| | - Melissa Mangala
- Victor Chang Cardiac Research Institute, Sydney, Australia.,St. Vincent's Clinical school, UNSW Sydney, Sydney, Australia
| | - Nicholas Kerr
- Victor Chang Cardiac Research Institute, Sydney, Australia.,St. Vincent's Clinical school, UNSW Sydney, Sydney, Australia
| | | | - Matthew D Perry
- Victor Chang Cardiac Research Institute, Sydney, Australia.,School of Medical Sciences, UNSW Sydney, Sydney, Australia
| | - Monique J Windley
- Victor Chang Cardiac Research Institute, Sydney, Australia.,St. Vincent's Clinical school, UNSW Sydney, Sydney, Australia
| | - Jamie I Vandenberg
- Victor Chang Cardiac Research Institute, Sydney, Australia.,St. Vincent's Clinical school, UNSW Sydney, Sydney, Australia
| | - Adam P Hill
- Victor Chang Cardiac Research Institute, Sydney, Australia.,St. Vincent's Clinical school, UNSW Sydney, Sydney, Australia
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8
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Refinement of a cryo-EM structure of hERG: Bridging structure and function. Biophys J 2021; 120:738-748. [PMID: 33476597 DOI: 10.1016/j.bpj.2021.01.011] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2020] [Revised: 12/22/2020] [Accepted: 01/11/2021] [Indexed: 01/16/2023] Open
Abstract
The human-ether-a-go-go-related gene (hERG) encodes the voltage-gated potassium channel (KCNH2 or Kv11.1, commonly known as hERG). This channel plays a pivotal role in the stability of phase 3 repolarization of the cardiac action potential. Although a high-resolution cryo-EM structure is available for its depolarized (open) state, the structure surprisingly did not feature many functionally important interactions established by previous biochemical and electrophysiology experiments. Using molecular dynamics flexible fitting (MDFF), we refined the structure and recovered the missing functionally relevant salt bridges in hERG in its depolarized state. We also performed electrophysiology experiments to confirm the functional relevance of a novel salt bridge predicted by our refinement protocol. Our work shows how refinement of a high-resolution cryo-EM structure helps to bridge the existing gap between the structure and function in the voltage-sensing domain (VSD) of hERG.
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9
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Pethő Z, Najder K, Carvalho T, McMorrow R, Todesca LM, Rugi M, Bulk E, Chan A, Löwik CWGM, Reshkin SJ, Schwab A. pH-Channeling in Cancer: How pH-Dependence of Cation Channels Shapes Cancer Pathophysiology. Cancers (Basel) 2020; 12:E2484. [PMID: 32887220 PMCID: PMC7565548 DOI: 10.3390/cancers12092484] [Citation(s) in RCA: 31] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2020] [Revised: 08/25/2020] [Accepted: 08/26/2020] [Indexed: 12/20/2022] Open
Abstract
Tissue acidosis plays a pivotal role in tumor progression: in particular, interstitial acidosis promotes tumor cell invasion, and is a major contributor to the dysregulation of tumor immunity and tumor stromal cells. The cell membrane and integral membrane proteins commonly act as important sensors and transducers of altered pH. Cell adhesion molecules and cation channels are prominent membrane proteins, the majority of which is regulated by protons. The pathophysiological consequences of proton-sensitive ion channel function in cancer, however, are scarcely considered in the literature. Thus, the main focus of this review is to highlight possible events in tumor progression and tumor immunity where the pH sensitivity of cation channels could be of great importance.
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Affiliation(s)
- Zoltán Pethő
- Institute of Physiology II, University Münster, 48147 Münster, Germany; (K.N.); (L.M.T.); (M.R.); (E.B.); (A.S.)
| | - Karolina Najder
- Institute of Physiology II, University Münster, 48147 Münster, Germany; (K.N.); (L.M.T.); (M.R.); (E.B.); (A.S.)
| | - Tiago Carvalho
- Department of Biosciences, Biotechnologies, and Biopharmaceutics, University of Bari, 90126 Bari, Italy; (T.C.); (S.J.R.)
| | - Roisin McMorrow
- Department of Radiology and Nuclear Medicine, Erasmus Medical Center, 3035 GD Rotterdam, The Netherlands; (R.M.); (C.W.G.M.L.)
| | - Luca Matteo Todesca
- Institute of Physiology II, University Münster, 48147 Münster, Germany; (K.N.); (L.M.T.); (M.R.); (E.B.); (A.S.)
| | - Micol Rugi
- Institute of Physiology II, University Münster, 48147 Münster, Germany; (K.N.); (L.M.T.); (M.R.); (E.B.); (A.S.)
| | - Etmar Bulk
- Institute of Physiology II, University Münster, 48147 Münster, Germany; (K.N.); (L.M.T.); (M.R.); (E.B.); (A.S.)
| | - Alan Chan
- Percuros B.V., 2333 CL Leiden, The Netherlands;
| | - Clemens W. G. M. Löwik
- Department of Radiology and Nuclear Medicine, Erasmus Medical Center, 3035 GD Rotterdam, The Netherlands; (R.M.); (C.W.G.M.L.)
- Department of Oncology CHUV, UNIL and Ludwig Cancer Center, 1011 Lausanne, Switzerland
| | - Stephan J. Reshkin
- Department of Biosciences, Biotechnologies, and Biopharmaceutics, University of Bari, 90126 Bari, Italy; (T.C.); (S.J.R.)
| | - Albrecht Schwab
- Institute of Physiology II, University Münster, 48147 Münster, Germany; (K.N.); (L.M.T.); (M.R.); (E.B.); (A.S.)
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10
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Liu Y, Li L, Liu X, Wang Y, Liu L, Peng L, Liu J, Zhang L, Wang G, Li H, Liu DX, Huang B, Lu J, Zhang Y. Arginine methylation of SHANK2 by PRMT7 promotes human breast cancer metastasis through activating endosomal FAK signalling. eLife 2020; 9:57617. [PMID: 32844749 PMCID: PMC7494359 DOI: 10.7554/elife.57617] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2020] [Accepted: 08/25/2020] [Indexed: 12/17/2022] Open
Abstract
Arginine methyltransferase PRMT7 is associated with human breast cancer metastasis. Endosomal FAK signalling is critical for cancer cell migration. Here we identified the pivotal roles of PRMT7 in promoting endosomal FAK signalling activation during breast cancer metastasis. PRMT7 exerted its functions through binding to scaffold protein SHANK2 and catalyzing di-methylation of SHANK2 at R240. SHANK2 R240 methylation exposed ANK domain by disrupting its SPN-ANK domain blockade, promoting in co-accumulation of dynamin2, talin, FAK, cortactin with SHANK2 on endosomes. In addition, SHANK2 R240 methylation activated endosomal FAK/cortactin signals in vitro and in vivo. Consistently, all the levels of PRMT7, methylated SHANK2, FAK Y397 phosphorylation and cortactin Y421 phosphorylation were correlated with aggressive clinical breast cancer tissues. These findings characterize the PRMT7-dependent SHANK2 methylation as a key player in mediating endosomal FAK signals activation, also point to the value of SHANK2 R240 methylation as a target for breast cancer metastasis.
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Affiliation(s)
- Yingqi Liu
- The Key Laboratory of Molecular Epigenetics of the Ministry of Education, Northeast Normal University, Changchun, China
| | - Lingling Li
- The Institute of Genetics and Cytology, Northeast Normal University, Changchun, China
| | - Xiaoqing Liu
- The Key Laboratory of Molecular Epigenetics of the Ministry of Education, Northeast Normal University, Changchun, China
| | - Yibo Wang
- Laboratory of Chemical Biology, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, China
| | - Lingxia Liu
- The Institute of Genetics and Cytology, Northeast Normal University, Changchun, China
| | - Lu Peng
- The Institute of Genetics and Cytology, Northeast Normal University, Changchun, China
| | - Jiayuan Liu
- The Institute of Genetics and Cytology, Northeast Normal University, Changchun, China
| | - Lian Zhang
- The Key Laboratory of Molecular Epigenetics of the Ministry of Education, Northeast Normal University, Changchun, China
| | - Guannan Wang
- The Key Laboratory of Molecular Epigenetics of the Ministry of Education, Northeast Normal University, Changchun, China
| | - Hongyuan Li
- Laboratory of Chemical Biology, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, China
| | - Dong-Xu Liu
- The Centre for Biomedical and Chemical Sciences, School of Science, Faculty of Health and Environmental Sciences, Auckland University of Technology, Auckland, New Zealand
| | - Baiqu Huang
- The Key Laboratory of Molecular Epigenetics of the Ministry of Education, Northeast Normal University, Changchun, China
| | - Jun Lu
- The Institute of Genetics and Cytology, Northeast Normal University, Changchun, China
| | - Yu Zhang
- The Key Laboratory of Molecular Epigenetics of the Ministry of Education, Northeast Normal University, Changchun, China
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11
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Kudaibergenova M, Guo J, Khan HM, Zahid F, Lees-Miller J, Noskov SY, Duff HJ. Allosteric Coupling Between Drug Binding and the Aromatic Cassette in the Pore Domain of the hERG1 Channel: Implications for a State-Dependent Blockade. Front Pharmacol 2020; 11:914. [PMID: 32694995 PMCID: PMC7338687 DOI: 10.3389/fphar.2020.00914] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2019] [Accepted: 06/04/2020] [Indexed: 12/18/2022] Open
Abstract
Human-ether-a-go-go-related channel (hERG1) is the pore-forming domain of the delayed rectifier K+ channel in the heart which underlies the IKr current. The channel has been extensively studied due to its propensity to bind chemically diverse group of drugs. The subsequent hERG1 block can lead to a prolongation of the QT interval potentially leading to an abnormal cardiac electrical activity. The recently solved cryo-EM structure featured a striking non-swapped topology of the Voltage-Sensor Domain (VSD) which is packed against the pore-domain as well as a small and hydrophobic intra-cavity space. The small size and hydrophobicity of the cavity was unexpected and challenges the already-established hypothesis of drugs binding to the wide cavity. Recently, we showed that an amphipathic drug, ivabradine, may favorably bind the channel from the lipid-facing surface and we discovered a mutant (M651T) on the lipid facing domain between the VSD and the PD which inhibited the blocking capacity of the drug. Using multi-microseconds Molecular Dynamics (MD) simulations of wild-type and M651T mutant hERG1, we suggested the block of the channel through the lipid mediated pathway, the opening of which is facilitated by the flexible phenylalanine ring (F656). In this study, we characterize the dynamic interaction of the methionine-aromatic cassette in the S5-S6 helices by combining data from electrophysiological experiments with MD simulations and molecular docking to elucidate the complex allosteric coupling between drug binding to lipid-facing and intra-cavity sites and aromatic cassette dynamics. We investigated two well-established hERG1 blockers (ivabradine and dofetilide) for M651 sensitivity through electrophysiology and mutagenesis techniques. Our electrophysiology data reveal insensitivity of dofetilide to the mutations at site M651 on the lipid facing side of the channel, mirroring our results obtained from docking experiments. Moreover, we show that the dofetilide-induced block of hERG1 occurs through the intracellular space, whereas little to no block of ivabradine is observed during the intracellular application of the drug. The dynamic conformational rearrangement of the F656 appears to regulate the translocation of ivabradine into the central cavity. M651T mutation appears to disrupt this entry pathway by altering the molecular conformation of F656.
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Affiliation(s)
- Meruyert Kudaibergenova
- Centre for Molecular Simulation, Department of Biological Sciences, University of Calgary, Calgary, AB, Canada.,Cumming School of Medicine, Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, AB, Canada
| | - Jiqing Guo
- Cumming School of Medicine, Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, AB, Canada
| | - Hanif M Khan
- Centre for Molecular Simulation, Department of Biological Sciences, University of Calgary, Calgary, AB, Canada
| | - Farhan Zahid
- Centre for Molecular Simulation, Department of Biological Sciences, University of Calgary, Calgary, AB, Canada
| | - James Lees-Miller
- Cumming School of Medicine, Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, AB, Canada
| | - Sergei Yu Noskov
- Centre for Molecular Simulation, Department of Biological Sciences, University of Calgary, Calgary, AB, Canada
| | - Henry J Duff
- Cumming School of Medicine, Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, AB, Canada
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12
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Tschirhart JN, Zhang S. Fentanyl-Induced Block of hERG Channels Is Exacerbated by Hypoxia, Hypokalemia, Alkalosis, and the Presence of hERG1b. Mol Pharmacol 2020; 98:508-517. [PMID: 32321735 DOI: 10.1124/mol.119.119271] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2019] [Accepted: 04/08/2020] [Indexed: 01/19/2023] Open
Abstract
Human ether-a-go-go-related gene (hERG) encodes the pore-forming subunit of the rapidly activating delayed rectifier potassium current (IKr) important for repolarization of cardiac action potentials. Drug-induced disruption of hERG channel function is a main cause of acquired long QT syndrome, which can lead to ventricular arrhythmias and sudden death. Illicit fentanyl use is associated with sudden death. We have demonstrated that fentanyl blocks hERG current (IhERG) at concentrations that overlap with the upper range of postmortem blood concentrations in fentanyl-related deaths. Since fentanyl can cause respiratory depression and electrolyte imbalances, in the present study we investigated whether certain pathologic circumstances exacerbate fentanyl-induced block of IhERG Our results show that chronic hypoxia or hypokalemia additively reduced IhERG with fentanyl. As well, high pH potentiated the fentanyl-mediated block of hERG channels, with an IC50 at pH 8.4 being 7-fold lower than that at pH 7.4. Furthermore, although the full-length hERG variant, hERG1a, has been widely used to study hERG channels, coexpression with the short variant, hERG1b (which does not produce current when expressed alone), produces functional hERG1a/1b channels, which gate more closely resembling native IKr Our results showed that fentanyl blocked hERG1a/1b channels with a 3-fold greater potency than hERG1a channels. Thus, in addition to a greater susceptibility due to the presence of hERG1b in the human heart, hERG channel block by fentanyl can be exacerbated by certain conditions, such as hypoxia, hypokalemia, or alkalosis, which may increase the risk of fentanyl-induced ventricular arrhythmias and sudden death. SIGNIFICANCE STATEMENT: This work demonstrates that heterologously expressed human ether a-go-go-related gene (hERG) 1a/1b channels, which more closely resemble rapidly activating delayed rectifier potassium current in the human heart, are blocked by fentanyl with a 3-fold greater potency than the previously studied hERG1a expressed alone. Additionally, chronic hypoxia, hypokalemia, and alkalosis can increase the block of hERG current by fentanyl, potentially increasing the risk of cardiac arrhythmias and sudden death.
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Affiliation(s)
- Jared N Tschirhart
- Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Ontario, Canada
| | - Shetuan Zhang
- Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Ontario, Canada
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13
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Yang PC, DeMarco KR, Aghasafari P, Jeng MT, Dawson JRD, Bekker S, Noskov SY, Yarov-Yarovoy V, Vorobyov I, Clancy CE. A Computational Pipeline to Predict Cardiotoxicity: From the Atom to the Rhythm. Circ Res 2020; 126:947-964. [PMID: 32091972 DOI: 10.1161/circresaha.119.316404] [Citation(s) in RCA: 42] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
RATIONALE Drug-induced proarrhythmia is so tightly associated with prolongation of the QT interval that QT prolongation is an accepted surrogate marker for arrhythmia. But QT interval is too sensitive a marker and not selective, resulting in many useful drugs eliminated in drug discovery. OBJECTIVE To predict the impact of a drug from the drug chemistry on the cardiac rhythm. METHODS AND RESULTS In a new linkage, we connected atomistic scale information to protein, cell, and tissue scales by predicting drug-binding affinities and rates from simulation of ion channel and drug structure interactions and then used these values to model drug effects on the hERG channel. Model components were integrated into predictive models at the cell and tissue scales to expose fundamental arrhythmia vulnerability mechanisms and complex interactions underlying emergent behaviors. Human clinical data were used for model framework validation and showed excellent agreement, demonstrating feasibility of a new approach for cardiotoxicity prediction. CONCLUSIONS We present a multiscale model framework to predict electrotoxicity in the heart from the atom to the rhythm. Novel mechanistic insights emerged at all scales of the system, from the specific nature of proarrhythmic drug interaction with the hERG channel, to the fundamental cellular and tissue-level arrhythmia mechanisms. Applications of machine learning indicate necessary and sufficient parameters that predict arrhythmia vulnerability. We expect that the model framework may be expanded to make an impact in drug discovery, drug safety screening for a variety of compounds and targets, and in a variety of regulatory processes.
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Affiliation(s)
- Pei-Chi Yang
- From the Department of Physiology and Membrane Biology (P.-C.Y., K.R.D., P.A., M.-T.J., J.R.D.D., V.Y.-Y., I.V., C.E.C.), University of California Davis
| | - Kevin R DeMarco
- From the Department of Physiology and Membrane Biology (P.-C.Y., K.R.D., P.A., M.-T.J., J.R.D.D., V.Y.-Y., I.V., C.E.C.), University of California Davis
| | - Parya Aghasafari
- From the Department of Physiology and Membrane Biology (P.-C.Y., K.R.D., P.A., M.-T.J., J.R.D.D., V.Y.-Y., I.V., C.E.C.), University of California Davis
| | - Mao-Tsuen Jeng
- From the Department of Physiology and Membrane Biology (P.-C.Y., K.R.D., P.A., M.-T.J., J.R.D.D., V.Y.-Y., I.V., C.E.C.), University of California Davis
| | - John R D Dawson
- From the Department of Physiology and Membrane Biology (P.-C.Y., K.R.D., P.A., M.-T.J., J.R.D.D., V.Y.-Y., I.V., C.E.C.), University of California Davis.,Biophysics Graduate Group (J.R.D.D.), University of California Davis
| | - Slava Bekker
- Department of Science and Engineering, American River College, Sacramento, CA (S.B.)
| | - Sergei Y Noskov
- Faculty of Science, Centre for Molecular Simulations and Department of Biological Sciences, University of Calgary, Alberta, Canada (S.Y.N.)
| | - Vladimir Yarov-Yarovoy
- From the Department of Physiology and Membrane Biology (P.-C.Y., K.R.D., P.A., M.-T.J., J.R.D.D., V.Y.-Y., I.V., C.E.C.), University of California Davis
| | - Igor Vorobyov
- From the Department of Physiology and Membrane Biology (P.-C.Y., K.R.D., P.A., M.-T.J., J.R.D.D., V.Y.-Y., I.V., C.E.C.), University of California Davis.,Department of Pharmacology (I.V., C.E.C.), University of California Davis
| | - Colleen E Clancy
- From the Department of Physiology and Membrane Biology (P.-C.Y., K.R.D., P.A., M.-T.J., J.R.D.D., V.Y.-Y., I.V., C.E.C.), University of California Davis.,Department of Pharmacology (I.V., C.E.C.), University of California Davis
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14
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Perissinotti L, Guo J, Kudaibergenova M, Lees-Miller J, Ol'khovich M, Sharapova A, Perlovich GL, Muruve DA, Gerull B, Noskov SY, Duff HJ. The Pore-Lipid Interface: Role of Amino-Acid Determinants of Lipophilic Access by Ivabradine to the hERG1 Pore Domain. Mol Pharmacol 2019; 96:259-271. [PMID: 31182542 DOI: 10.1124/mol.118.115642] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2018] [Accepted: 05/28/2019] [Indexed: 12/14/2022] Open
Abstract
Abnormal cardiac electrical activity is a common side effect caused by unintended block of the promiscuous drug target human ether-à-go-go-related gene (hERG1), the pore-forming domain of the delayed rectifier K+ channel in the heart. hERG1 block leads to a prolongation of the QT interval, a phase of the cardiac cycle that underlies myocyte repolarization detectable on the electrocardiogram. Even newly released drugs such as heart-rate lowering agent ivabradine block the rapid delayed rectifier current IKr, prolong action potential duration, and induce potentially lethal arrhythmia known as torsades de pointes. In this study, we describe a critical drug-binding pocket located at the lateral pore surface facing the cellular membrane. Mutations of the conserved M651 residue alter ivabradine-induced block but not by the common hERG1 blocker dofetilide. As revealed by molecular dynamics simulations, binding of ivabradine to a lipophilic pore access site is coupled to a state-dependent reorientation of aromatic residues F557 and F656 in the S5 and S6 helices. We show that the M651 mutation impedes state-dependent dynamics of F557 and F656 aromatic cassettes at the protein-lipid interface, which has a potential to disrupt drug-induced block of the channel. This fundamentally new mechanism coupling the channel dynamics and small-molecule access from the membrane into the hERG1 intracavitary site provides a simple rationale for the well established state-dependence of drug blockade. SIGNIFICANCE STATEMENT: The drug interference with the function of the cardiac hERG channels represents one of the major sources of drug-induced heart disturbances. We found a novel and a critical drug-binding pocket adjacent to a lipid-facing surface of the hERG1 channel, which furthers our molecular understanding of drug-induced QT syndrome.
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Affiliation(s)
- Laura Perissinotti
- Centre for Molecular Simulation, Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada (L.P., M.K., S.Y.N.); Libin Cardiovascular Institute of Alberta (J.G., J.-L.M., H.J.D.) and Snyder Institute for Chronic Diseases (D.A.M.), Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada; Institute of Solution Chemistry, Russian Academy of Sciences, Ivanovo, Russian Federation (M.O., A.S., G.L.P.); Department of Cardiac Sciences and Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Alberta, Canada (B.G.); and Comprehensive Heart Failure Center and Department of Internal Medicine I, University Hospital Würzburg, Würzburg, Germany (B.G.)
| | - Jiqing Guo
- Centre for Molecular Simulation, Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada (L.P., M.K., S.Y.N.); Libin Cardiovascular Institute of Alberta (J.G., J.-L.M., H.J.D.) and Snyder Institute for Chronic Diseases (D.A.M.), Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada; Institute of Solution Chemistry, Russian Academy of Sciences, Ivanovo, Russian Federation (M.O., A.S., G.L.P.); Department of Cardiac Sciences and Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Alberta, Canada (B.G.); and Comprehensive Heart Failure Center and Department of Internal Medicine I, University Hospital Würzburg, Würzburg, Germany (B.G.)
| | - Meruyert Kudaibergenova
- Centre for Molecular Simulation, Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada (L.P., M.K., S.Y.N.); Libin Cardiovascular Institute of Alberta (J.G., J.-L.M., H.J.D.) and Snyder Institute for Chronic Diseases (D.A.M.), Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada; Institute of Solution Chemistry, Russian Academy of Sciences, Ivanovo, Russian Federation (M.O., A.S., G.L.P.); Department of Cardiac Sciences and Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Alberta, Canada (B.G.); and Comprehensive Heart Failure Center and Department of Internal Medicine I, University Hospital Würzburg, Würzburg, Germany (B.G.)
| | - James Lees-Miller
- Centre for Molecular Simulation, Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada (L.P., M.K., S.Y.N.); Libin Cardiovascular Institute of Alberta (J.G., J.-L.M., H.J.D.) and Snyder Institute for Chronic Diseases (D.A.M.), Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada; Institute of Solution Chemistry, Russian Academy of Sciences, Ivanovo, Russian Federation (M.O., A.S., G.L.P.); Department of Cardiac Sciences and Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Alberta, Canada (B.G.); and Comprehensive Heart Failure Center and Department of Internal Medicine I, University Hospital Würzburg, Würzburg, Germany (B.G.)
| | - Marina Ol'khovich
- Centre for Molecular Simulation, Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada (L.P., M.K., S.Y.N.); Libin Cardiovascular Institute of Alberta (J.G., J.-L.M., H.J.D.) and Snyder Institute for Chronic Diseases (D.A.M.), Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada; Institute of Solution Chemistry, Russian Academy of Sciences, Ivanovo, Russian Federation (M.O., A.S., G.L.P.); Department of Cardiac Sciences and Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Alberta, Canada (B.G.); and Comprehensive Heart Failure Center and Department of Internal Medicine I, University Hospital Würzburg, Würzburg, Germany (B.G.)
| | - Angelica Sharapova
- Centre for Molecular Simulation, Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada (L.P., M.K., S.Y.N.); Libin Cardiovascular Institute of Alberta (J.G., J.-L.M., H.J.D.) and Snyder Institute for Chronic Diseases (D.A.M.), Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada; Institute of Solution Chemistry, Russian Academy of Sciences, Ivanovo, Russian Federation (M.O., A.S., G.L.P.); Department of Cardiac Sciences and Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Alberta, Canada (B.G.); and Comprehensive Heart Failure Center and Department of Internal Medicine I, University Hospital Würzburg, Würzburg, Germany (B.G.)
| | - German L Perlovich
- Centre for Molecular Simulation, Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada (L.P., M.K., S.Y.N.); Libin Cardiovascular Institute of Alberta (J.G., J.-L.M., H.J.D.) and Snyder Institute for Chronic Diseases (D.A.M.), Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada; Institute of Solution Chemistry, Russian Academy of Sciences, Ivanovo, Russian Federation (M.O., A.S., G.L.P.); Department of Cardiac Sciences and Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Alberta, Canada (B.G.); and Comprehensive Heart Failure Center and Department of Internal Medicine I, University Hospital Würzburg, Würzburg, Germany (B.G.)
| | - Daniel A Muruve
- Centre for Molecular Simulation, Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada (L.P., M.K., S.Y.N.); Libin Cardiovascular Institute of Alberta (J.G., J.-L.M., H.J.D.) and Snyder Institute for Chronic Diseases (D.A.M.), Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada; Institute of Solution Chemistry, Russian Academy of Sciences, Ivanovo, Russian Federation (M.O., A.S., G.L.P.); Department of Cardiac Sciences and Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Alberta, Canada (B.G.); and Comprehensive Heart Failure Center and Department of Internal Medicine I, University Hospital Würzburg, Würzburg, Germany (B.G.)
| | - Brenda Gerull
- Centre for Molecular Simulation, Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada (L.P., M.K., S.Y.N.); Libin Cardiovascular Institute of Alberta (J.G., J.-L.M., H.J.D.) and Snyder Institute for Chronic Diseases (D.A.M.), Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada; Institute of Solution Chemistry, Russian Academy of Sciences, Ivanovo, Russian Federation (M.O., A.S., G.L.P.); Department of Cardiac Sciences and Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Alberta, Canada (B.G.); and Comprehensive Heart Failure Center and Department of Internal Medicine I, University Hospital Würzburg, Würzburg, Germany (B.G.)
| | - Sergei Yu Noskov
- Centre for Molecular Simulation, Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada (L.P., M.K., S.Y.N.); Libin Cardiovascular Institute of Alberta (J.G., J.-L.M., H.J.D.) and Snyder Institute for Chronic Diseases (D.A.M.), Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada; Institute of Solution Chemistry, Russian Academy of Sciences, Ivanovo, Russian Federation (M.O., A.S., G.L.P.); Department of Cardiac Sciences and Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Alberta, Canada (B.G.); and Comprehensive Heart Failure Center and Department of Internal Medicine I, University Hospital Würzburg, Würzburg, Germany (B.G.)
| | - Henry J Duff
- Centre for Molecular Simulation, Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada (L.P., M.K., S.Y.N.); Libin Cardiovascular Institute of Alberta (J.G., J.-L.M., H.J.D.) and Snyder Institute for Chronic Diseases (D.A.M.), Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada; Institute of Solution Chemistry, Russian Academy of Sciences, Ivanovo, Russian Federation (M.O., A.S., G.L.P.); Department of Cardiac Sciences and Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Alberta, Canada (B.G.); and Comprehensive Heart Failure Center and Department of Internal Medicine I, University Hospital Würzburg, Würzburg, Germany (B.G.)
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15
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Qiao Z, Zhou Q, Zhang H, Wei N, Zhang Y, Wang K. The visualization of hERG channels in living cells via a fluorescent probe regulated by the synergy between solvatochromism and molecular rotation based on simple targeting of the group 4-benzylaniline. Chem Commun (Camb) 2019; 55:5515-5518. [PMID: 31020283 DOI: 10.1039/c9cc01735f] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A highly sensitive fluorescent probe CBH based on solvatochromism and molecular rotation was designed and developed for imaging of hERG channels by employing a novel targeting group 4-benzylaniline. More importantly, CBH has the potential for the quantitative analysis of the hERG channels expressed in tumor cells.
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Affiliation(s)
- Zhen Qiao
- Departments of Pharmacology and Medicinal Chemistry, Qingdao University School of Pharmacy, Qingdao 266021, China.
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16
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Corradi V, Sejdiu BI, Mesa-Galloso H, Abdizadeh H, Noskov SY, Marrink SJ, Tieleman DP. Emerging Diversity in Lipid-Protein Interactions. Chem Rev 2019; 119:5775-5848. [PMID: 30758191 PMCID: PMC6509647 DOI: 10.1021/acs.chemrev.8b00451] [Citation(s) in RCA: 245] [Impact Index Per Article: 49.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
![]()
Membrane
lipids interact with proteins in a variety of ways, ranging
from providing a stable membrane environment for proteins to being
embedded in to detailed roles in complicated and well-regulated protein
functions. Experimental and computational advances are converging
in a rapidly expanding research area of lipid–protein interactions.
Experimentally, the database of high-resolution membrane protein structures
is growing, as are capabilities to identify the complex lipid composition
of different membranes, to probe the challenging time and length scales
of lipid–protein interactions, and to link lipid–protein
interactions to protein function in a variety of proteins. Computationally,
more accurate membrane models and more powerful computers now enable
a detailed look at lipid–protein interactions and increasing
overlap with experimental observations for validation and joint interpretation
of simulation and experiment. Here we review papers that use computational
approaches to study detailed lipid–protein interactions, together
with brief experimental and physiological contexts, aiming at comprehensive
coverage of simulation papers in the last five years. Overall, a complex
picture of lipid–protein interactions emerges, through a range
of mechanisms including modulation of the physical properties of the
lipid environment, detailed chemical interactions between lipids and
proteins, and key functional roles of very specific lipids binding
to well-defined binding sites on proteins. Computationally, despite
important limitations, molecular dynamics simulations with current
computer power and theoretical models are now in an excellent position
to answer detailed questions about lipid–protein interactions.
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Affiliation(s)
- Valentina Corradi
- Centre for Molecular Simulation and Department of Biological Sciences , University of Calgary , 2500 University Drive NW , Calgary , Alberta T2N 1N4 , Canada
| | - Besian I Sejdiu
- Centre for Molecular Simulation and Department of Biological Sciences , University of Calgary , 2500 University Drive NW , Calgary , Alberta T2N 1N4 , Canada
| | - Haydee Mesa-Galloso
- Centre for Molecular Simulation and Department of Biological Sciences , University of Calgary , 2500 University Drive NW , Calgary , Alberta T2N 1N4 , Canada
| | - Haleh Abdizadeh
- Groningen Biomolecular Sciences and Biotechnology Institute and Zernike Institute for Advanced Materials , University of Groningen , Nijenborgh 7 , 9747 AG Groningen , The Netherlands
| | - Sergei Yu Noskov
- Centre for Molecular Simulation and Department of Biological Sciences , University of Calgary , 2500 University Drive NW , Calgary , Alberta T2N 1N4 , Canada
| | - Siewert J Marrink
- Groningen Biomolecular Sciences and Biotechnology Institute and Zernike Institute for Advanced Materials , University of Groningen , Nijenborgh 7 , 9747 AG Groningen , The Netherlands
| | - D Peter Tieleman
- Centre for Molecular Simulation and Department of Biological Sciences , University of Calgary , 2500 University Drive NW , Calgary , Alberta T2N 1N4 , Canada
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17
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Żołek T, Qile M, Kaźmierczak P, Bloothooft M, van der Heyden MAG, Maciejewska D. Drug-likeness of linear pentamidine analogues and their impact on the hERG K+channel – correlation with structural features. RSC Adv 2019; 9:38355-38371. [PMID: 35540224 PMCID: PMC9082326 DOI: 10.1039/c9ra08404e] [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] [Received: 10/14/2019] [Accepted: 11/15/2019] [Indexed: 01/08/2023] Open
Abstract
The pentamidines with S atoms or sulfanilide groups in the linker have favorable drug-likeness parameters and low toxicity.
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Affiliation(s)
- Teresa Żołek
- Department of Organic Chemistry
- Faculty of Pharmacy
- Medical University of Warsaw
- 02-097 Warsaw
- Poland
| | - Muge Qile
- Department of Medical Physiology
- Division Heart & Lungs
- University Medical Center Utrecht
- Utrecht
- The Netherlands
| | - Paweł Kaźmierczak
- Department of Organic Chemistry
- Faculty of Pharmacy
- Medical University of Warsaw
- 02-097 Warsaw
- Poland
| | - Meye Bloothooft
- Department of Medical Physiology
- Division Heart & Lungs
- University Medical Center Utrecht
- Utrecht
- The Netherlands
| | - Marcel A. G. van der Heyden
- Department of Medical Physiology
- Division Heart & Lungs
- University Medical Center Utrecht
- Utrecht
- The Netherlands
| | - Dorota Maciejewska
- Department of Organic Chemistry
- Faculty of Pharmacy
- Medical University of Warsaw
- 02-097 Warsaw
- Poland
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18
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Chen R, Chung SH. Inhibition of Voltage-Gated K + Channel Kv1.5 by Antiarrhythmic Drugs. Biochemistry 2018; 57:2704-2710. [PMID: 29652491 DOI: 10.1021/acs.biochem.8b00268] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Molecular dynamics simulations are employed to determine the inhibitory mechanisms of three drugs, 5-(4-phenoxybutoxy)psoralen (PAP-1), vernakalant, and flecainide, on the voltage-gated K+ channel Kv1.5, a target for the treatment of cardiac arrhythmia. At neutral pH, PAP-1 is neutral, whereas the other two molecules carry one positive charge. We show that PAP-1 forms stable dimers in water, primarily through hydrophobic interactions between aromatic rings. All three molecules bind to the cavity between the Ile508 and Val512 residues from the four subunits of the channel. Once bound, the drug molecules are flexible, with the average root-mean-square fluctuation being between 2 and 3 Å, which is larger than the radius of gyration of a bulky amino acid. The presence of a monomeric PAP-1 causes the permeating K+ ion to dehydrate, thereby creating a significant energy barrier. In contrast, vernakalant blocks the ion permeation primarily via an electrostatic mechanism and, therefore, must be in the protonated and charged form to be effective.
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Affiliation(s)
- Rong Chen
- Research School of Biology , Australian National University , Acton , ACT 2601 , Australia
| | - Shin-Ho Chung
- Research School of Biology , Australian National University , Acton , ACT 2601 , Australia
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19
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Yang XJ, Zhang K, Xu JJ, Chen HY. In Situ Visualization of hERG Potassium Channel via Dual Signal Amplification. Anal Chem 2018; 90:6199-6205. [DOI: 10.1021/acs.analchem.8b00725] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Affiliation(s)
- Xue-Jiao Yang
- State Key Laboratory of Analytical Chemistry for Life Science and Collaborative Innovation Center of Chemistry for Life Sciences, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023, China
| | - Kai Zhang
- State Key Laboratory of Analytical Chemistry for Life Science and Collaborative Innovation Center of Chemistry for Life Sciences, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023, China
| | - Jing-Juan Xu
- State Key Laboratory of Analytical Chemistry for Life Science and Collaborative Innovation Center of Chemistry for Life Sciences, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023, China
- Key Laboratory of Sensor Analysis of Tumor Marker, Ministry of Education, College of Chemistry and Molecular Engineering, Qingdao University of Science and Technology, Qingdao 266042, China
| | - Hong-Yuan Chen
- State Key Laboratory of Analytical Chemistry for Life Science and Collaborative Innovation Center of Chemistry for Life Sciences, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023, China
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20
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DeMarco KR, Bekker S, Clancy CE, Noskov SY, Vorobyov I. Digging into Lipid Membrane Permeation for Cardiac Ion Channel Blocker d-Sotalol with All-Atom Simulations. Front Pharmacol 2018; 9:26. [PMID: 29449809 PMCID: PMC5799612 DOI: 10.3389/fphar.2018.00026] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2017] [Accepted: 01/10/2018] [Indexed: 12/31/2022] Open
Abstract
Interactions of drug molecules with lipid membranes play crucial role in their accessibility of cellular targets and can be an important predictor of their therapeutic and safety profiles. Very little is known about spatial localization of various drugs in the lipid bilayers, their active form (ionization state) or translocation rates and therefore potency to bind to different sites in membrane proteins. All-atom molecular simulations may help to map drug partitioning kinetics and thermodynamics, thus providing in-depth assessment of drug lipophilicity. As a proof of principle, we evaluated extensively lipid membrane partitioning of d-sotalol, well-known blocker of a cardiac potassium channel Kv11.1 encoded by the hERG gene, with reported substantial proclivity for arrhythmogenesis. We developed the positively charged (cationic) and neutral d-sotalol models, compatible with the biomolecular CHARMM force field, and subjected them to all-atom molecular dynamics (MD) simulations of drug partitioning through hydrated lipid membranes, aiming to elucidate thermodynamics and kinetics of their translocation and thus putative propensities for hydrophobic and aqueous hERG access. We found that only a neutral form of d-sotalol accumulates in the membrane interior and can move across the bilayer within millisecond time scale, and can be relevant to a lipophilic channel access. The computed water-membrane partitioning coefficient for this form is in good agreement with experiment. There is a large energetic barrier for a cationic form of the drug, dominant in water, to cross the membrane, resulting in slow membrane translocation kinetics. However, this form of the drug can be important for an aqueous access pathway through the intracellular gate of hERG. This route will likely occur after a neutral form of a drug crosses the membrane and subsequently re-protonates. Our study serves to demonstrate a first step toward a framework for multi-scale in silico safety pharmacology, and identifies some of the challenges that lie therein.
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Affiliation(s)
- Kevin R DeMarco
- Department of Physiology and Membrane Biology, University of California, Davis, Davis, CA, United States.,Department of Pharmacology, University of California, Davis, Davis, CA, United States.,Biophysics Graduate Group, University of California, Davis, Davis, CA, United States
| | - Slava Bekker
- Department of Physiology and Membrane Biology, University of California, Davis, Davis, CA, United States.,Hartnell College, Salinas, CA, United States
| | - Colleen E Clancy
- Department of Physiology and Membrane Biology, University of California, Davis, Davis, CA, United States.,Department of Pharmacology, University of California, Davis, Davis, CA, United States
| | - Sergei Y Noskov
- Centre for Molecular Simulations, Department of Biological Sciences, Faculty of Science, University of Calgary, Calgary, AB, Canada
| | - Igor Vorobyov
- Department of Physiology and Membrane Biology, University of California, Davis, Davis, CA, United States.,Department of Pharmacology, University of California, Davis, Davis, CA, United States
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Kalyaanamoorthy S, Barakat KH. Binding modes of hERG blockers: an unsolved mystery in the drug design arena. Expert Opin Drug Discov 2017; 13:207-210. [DOI: 10.1080/17460441.2018.1418319] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Affiliation(s)
- Subha Kalyaanamoorthy
- Faculty Of Pharmacy And Pharmaceutical Sciences, University Of Alberta, Edmonton, AB, Canada
| | - Khaled H. Barakat
- Faculty Of Pharmacy And Pharmaceutical Sciences, University Of Alberta, Edmonton, AB, Canada
- Li Ka Shing Institute Of Virology, University Of Alberta, Edmonton, AB,Canada
- Li Ka Shing Applied Virology Institute, University Of Alberta, Edmonton, AB,Canada
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22
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Lee W, Windley MJ, Vandenberg JI, Hill AP. In Vitro and In Silico Risk Assessment in Acquired Long QT Syndrome: The Devil Is in the Details. Front Physiol 2017; 8:934. [PMID: 29201009 PMCID: PMC5696636 DOI: 10.3389/fphys.2017.00934] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2017] [Accepted: 11/03/2017] [Indexed: 12/16/2022] Open
Abstract
Acquired long QT syndrome, mostly as a result of drug block of the Kv11. 1 potassium channel in the heart, is characterized by delayed cardiac myocyte repolarization, prolongation of the T interval on the ECG, syncope and sudden cardiac death due to the polymorphic ventricular arrhythmia Torsade de Pointes (TdP). In recent years, efforts are underway through the Comprehensive in vitro proarrhythmic assay (CiPA) initiative, to develop better tests for this drug induced arrhythmia based in part on in silico simulations of pharmacological disruption of repolarization. However, drug binding to Kv11.1 is more complex than a simple binary molecular reaction, meaning simple steady state measures of potency are poor surrogates for risk. As a result, there is a plethora of mechanistic detail describing the drug/Kv11.1 interaction—such as drug binding kinetics, state preference, temperature dependence and trapping—that needs to be considered when developing in silico models for risk prediction. In addition to this, other factors, such as multichannel pharmacological profile and the nature of the ventricular cell models used in simulations also need to be considered in the search for the optimum in silico approach. Here we consider how much of mechanistic detail needs to be included for in silico models to accurately predict risk and further, how much of this detail can be retrieved from protocols that are practical to implement in high throughout screens as part of next generation of preclinical in silico drug screening approaches?
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Affiliation(s)
- William Lee
- Molecular Cardiology and Biophysics Division, Victor Chang Cardiac Research Institute, Darlinghurst, NSW, Australia.,St. Vincent's Clinical School, University of New South Wales, Sydney, NSW, Australia
| | - Monique J Windley
- Molecular Cardiology and Biophysics Division, Victor Chang Cardiac Research Institute, Darlinghurst, NSW, Australia.,St. Vincent's Clinical School, University of New South Wales, Sydney, NSW, Australia
| | - Jamie I Vandenberg
- Molecular Cardiology and Biophysics Division, Victor Chang Cardiac Research Institute, Darlinghurst, NSW, Australia.,St. Vincent's Clinical School, University of New South Wales, Sydney, NSW, Australia
| | - Adam P Hill
- Molecular Cardiology and Biophysics Division, Victor Chang Cardiac Research Institute, Darlinghurst, NSW, Australia.,St. Vincent's Clinical School, University of New South Wales, Sydney, NSW, Australia
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23
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Liu L, Yu H, Yang L, Zhao X, Huang X. Elucidating proton-mediated conformational changes in an acid-sensing ion channel 1a through molecular dynamics simulation. J Biomol Struct Dyn 2017; 36:2261-2267. [DOI: 10.1080/07391102.2017.1347524] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Affiliation(s)
- Lu Liu
- Laboratory of Theoretical and Computational Chemistry, Institute of Theoretical Chemistry, Jilin University, Changchun, China
| | - Hui Yu
- Chemistry Teaching Center, College of Chemistry and Biology, Beihua University, Jilin 132013, China
| | - Lianjuan Yang
- The Fungal Reference Laboratory of Shanghai Dermatology Hospital, Shanghai 200050, China
| | - Xi Zhao
- Laboratory of Theoretical and Computational Chemistry, Institute of Theoretical Chemistry, Jilin University, Changchun, China
| | - Xuri Huang
- Laboratory of Theoretical and Computational Chemistry, Institute of Theoretical Chemistry, Jilin University, Changchun, China
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24
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Yang PC, Perissinotti LL, López-Redondo F, Wang Y, DeMarco KR, Jeng MT, Vorobyov I, Harvey RD, Kurokawa J, Noskov SY, Clancy CE. A multiscale computational modelling approach predicts mechanisms of female sex risk in the setting of arousal-induced arrhythmias. J Physiol 2017; 595:4695-4723. [PMID: 28516454 PMCID: PMC5509858 DOI: 10.1113/jp273142] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2017] [Accepted: 04/24/2017] [Indexed: 01/10/2023] Open
Abstract
KEY POINTS This study represents a first step toward predicting mechanisms of sex-based arrhythmias that may lead to important developments in risk stratification and may inform future drug design and screening. We undertook simulations to reveal the conditions (i.e. pacing, drugs, sympathetic stimulation) required for triggering and sustaining reentrant arrhythmias. Using the recently solved cryo-EM structure for the Eag-family channel as a template, we revealed potential interactions of oestrogen with the pore loop hERG mutation (G604S). Molecular models suggest that oestrogen and dofetilide blockade can concur simultaneously in the hERG channel pore. ABSTRACT Female sex is a risk factor for inherited and acquired long-QT associated torsade de pointes (TdP) arrhythmias, and sympathetic discharge is a major factor in triggering TdP in female long-QT syndrome patients. We used a combined experimental and computational approach to predict 'the perfect storm' of hormone concentration, IKr block and sympathetic stimulation that induces arrhythmia in females with inherited and acquired long-QT. More specifically, we developed mathematical models of acquired and inherited long-QT syndrome in male and female ventricular human myocytes by combining effects of a hormone and a hERG blocker, dofetilide, or hERG mutations. These 'male' and 'female' model myocytes and tissues then were used to predict how various sex-based differences underlie arrhythmia risk in the setting of acute sympathetic nervous system discharge. The model predicted increased risk for arrhythmia in females when acute sympathetic nervous system discharge was applied in the settings of both inherited and acquired long-QT syndrome. Females were predicted to have protection from arrhythmia induction when progesterone is high. Males were protected by the presence of testosterone. Structural modelling points towards two plausible and distinct mechanisms of oestrogen action enhancing torsadogenic effects: oestradiol interaction with hERG mutations in the pore loop containing G604 or with common TdP-related blockers in the intra-cavity binding site. Our study presents findings that constitute the first evidence linking structure to function mechanisms underlying female dominance of arousal-induced arrhythmias.
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Affiliation(s)
- Pei-Chi Yang
- Department of Pharmacology, School of Medicine, University of California, Davis, CA, USA
| | - Laura L Perissinotti
- Centre for Molecular Simulation, Department of Biological Sciences, University of Calgary, Alberta, Canada
| | - Fernando López-Redondo
- Department of Bio-informational Pharmacology, Medical Research Institute, Tokyo Medical and Dental University
| | - Yibo Wang
- Centre for Molecular Simulation, Department of Biological Sciences, University of Calgary, Alberta, Canada
| | - Kevin R DeMarco
- Department of Pharmacology, School of Medicine, University of California, Davis, CA, USA
| | - Mao-Tsuen Jeng
- Department of Pharmacology, School of Medicine, University of California, Davis, CA, USA
| | - Igor Vorobyov
- Department of Pharmacology, School of Medicine, University of California, Davis, CA, USA
| | - Robert D Harvey
- Department of Pharmacology, University of Nevada, Reno, NV, USA
| | - Junko Kurokawa
- Department of Bio-informational Pharmacology, Medical Research Institute, Tokyo Medical and Dental University.,Department of Bio-informational Pharmacology, School of Pharmaceutical Sciences, University of Shizuoka, Shizuoka, Japan
| | - Sergei Y Noskov
- Centre for Molecular Simulation, Department of Biological Sciences, University of Calgary, Alberta, Canada
| | - Colleen E Clancy
- Department of Pharmacology, School of Medicine, University of California, Davis, CA, USA
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25
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Durdagi S, Erol I, Salmas RE, Patterson M, Noskov SY. First universal pharmacophore model for hERG1 K + channel activators: acthER. J Mol Graph Model 2017; 74:153-170. [PMID: 28499268 DOI: 10.1016/j.jmgm.2017.03.020] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2016] [Revised: 03/28/2017] [Accepted: 03/29/2017] [Indexed: 01/31/2023]
Abstract
The intra-cavitary drug blockade of hERG1 channel has been extensively studied, both experimentally and theoretically. Structurally diverse ligands inadvertently block the hERG1 K+ channel currents lead to drug induced Long QT Syndrome (LQTS). Accordingly, designing either hERG1 channel openers or current activators, with the potential to target other binding pockets of the channel, has been introduced as a viable approach in modern anti-arrhythmia drug development. However, reports and investigations on the molecular mechanisms underlying activators binding to the hERG1 channel remain sparse and the overall molecular design principles are largely unknown. Most of the hERG1 activators were discovered during mandatory screening for hERG1 blockade. To fill this apparent deficit, the first universal pharmacophore model for hERG1 K+ channel activators was developed using PHASE. 3D structures of 18 hERG1 K+ channel activators and their corresponding measured binding affinity values were used in the development of pharmacophore models. These compounds spanned a range of structurally different chemotypes with moderate variation in binding affinity. A five sites AAHRR (A, hydrogen-bond accepting, H, hydrophobic, R, aromatic) pharmacophore model has shown reasonable high statistical results compared to the other developed more than 1000 hypotheses. This model was used to construct steric and electrostatic contour maps. The predictive power of the model was tested with 3 external test set compounds as true unknowns. Finally, the pharmacophore model was combined with the previously developed receptor-based model of hERG1 K+ channel to develop and screen novel activators. The results are quite striking and it suggests a greater future role for pharmacophore modeling and virtual drug screening simulations in deciphering complex patterns of molecular mechanisms of hERG1 channel openers at the target sites. The developed model is available upon request and it may serve as basis for the synthesis of novel therapeutic hERG1 activators.
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Affiliation(s)
- Serdar Durdagi
- Computational Biology and Molecular Simulations Laboratory, Department of Biophysics, School of Medicine, Bahcesehir University, Istanbul, Turkey.
| | - Ismail Erol
- Computational Biology and Molecular Simulations Laboratory, Department of Biophysics, School of Medicine, Bahcesehir University, Istanbul, Turkey; Department of Chemistry, Gebze Technical University, Kocaeli, Turkey
| | - Ramin Ekhteiari Salmas
- Computational Biology and Molecular Simulations Laboratory, Department of Biophysics, School of Medicine, Bahcesehir University, Istanbul, Turkey
| | - Matthew Patterson
- Centre for Molecular Simulation, Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada
| | - Sergei Y Noskov
- Centre for Molecular Simulation, Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada.
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26
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Inhibitory effects of cholinesterase inhibitor donepezil on the Kv1.5 potassium channel. Sci Rep 2017; 7:41509. [PMID: 28198801 PMCID: PMC5304190 DOI: 10.1038/srep41509] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2016] [Accepted: 12/21/2016] [Indexed: 11/25/2022] Open
Abstract
Kv1.5 channels carry ultra-rapid delayed rectifier K+ currents in excitable cells, including neurons and cardiac myocytes. In the current study, the effects of cholinesterase inhibitor donepezil on cloned Kv1.5 channels expressed in HEK29 cells were explored using whole-cell recording technique. Exposure to donepezil resulted in a rapid and reversible block of Kv1.5 currents, with an IC50 value of 72.5 μM. The mutant R476V significantly reduced the binding affinity of donepezil to Kv1.5 channels, showing the target site in the outer mouth region. Donepezil produced a significant delay in the duration of activation and deactivation, and mutant R476V potentiated these effects without altering activation curves. In response to slowed deactivation time course, a typical crossover of Kv1.5 tail currents was clearly evident after bath application of donepezil. In addition, both this chemical and mutant R476V accelerated current decay during channel inactivation in a voltage-dependent way, but barely changed the inactivation and recovery curves. The presence of donepezil exhibited the use-dependent block of Kv1.5 currents in response to a series of depolarizing pulses. Our data indicate that donepezil can directly block Kv1.5 channels in its open and closed states.
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