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Mechanisms of KCNQ1 channel dysfunction in long QT syndrome involving voltage sensor domain mutations.
Huang H, Kuenze G, Smith JA, Taylor KC, Duran AM, Hadziselimovic A, Meiler J, Vanoye CG, George AL, Sanders CR
(2018) Sci Adv 4: eaar2631
MeSH Terms: Cell Membrane, HEK293 Cells, Humans, KCNQ1 Potassium Channel, Leupeptins, Long QT Syndrome, Loss of Function Mutation, Magnetic Resonance Spectroscopy, Mutant Proteins, Mutation, Proteasome Endopeptidase Complex, Proteasome Inhibitors, Protein Domains, Protein Folding, Protein Structure, Secondary, Proteolysis
Show Abstract · Added March 14, 2018
Mutations that induce loss of function (LOF) or dysfunction of the human KCNQ1 channel are responsible for susceptibility to a life-threatening heart rhythm disorder, the congenital long QT syndrome (LQTS). Hundreds of mutations have been identified, but the molecular mechanisms responsible for impaired function are poorly understood. We investigated the impact of 51 KCNQ1 variants with mutations located within the voltage sensor domain (VSD), with an emphasis on elucidating effects on cell surface expression, protein folding, and structure. For each variant, the efficiency of trafficking to the plasma membrane, the impact of proteasome inhibition, and protein stability were assayed. The results of these experiments combined with channel functional data provided the basis for classifying each mutation into one of six mechanistic categories, highlighting heterogeneity in the mechanisms resulting in channel dysfunction or LOF. More than half of the KCNQ1 LOF mutations examined were seen to destabilize the structure of the VSD, generally accompanied by mistrafficking and degradation by the proteasome, an observation that underscores the growing appreciation that mutation-induced destabilization of membrane proteins may be a common human disease mechanism. Finally, we observed that five of the folding-defective LQTS mutant sites are located in the VSD S0 helix, where they interact with a number of other LOF mutation sites in other segments of the VSD. These observations reveal a critical role for the S0 helix as a central scaffold to help organize and stabilize the KCNQ1 VSD and, most likely, the corresponding domain of many other ion channels.
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16 MeSH Terms
Exploiting ion channel structure to assess rare variant pathogenicity.
Kroncke BM, Yang T, Kannankeril P, Shoemaker MB, Roden DM
(2018) Heart Rhythm 15: 890-894
MeSH Terms: Adolescent, Adult, Body Surface Potential Mapping, DNA, DNA Mutational Analysis, ERG1 Potassium Channel, Female, Humans, KCNQ1 Potassium Channel, Long QT Syndrome, Mutation, Pedigree, Phenotype
Show Abstract · Added March 26, 2019
BACKGROUND - A 27-year-old woman was seen for long QT syndrome. She was found to be a carrier of 2 variants, KCNQ1 Val162Met and KCNH2 Ser55Leu, and both were classified as "pathogenic" by a diagnostic laboratory, in part because of sequence proximity to other known pathogenic variants.
OBJECTIVE - The purpose of this study was to assess the relationship between both the KCNQ1 and KCNH2 variants and clinical significance using protein structure, in vitro functional assays, and familial segregation.
METHODS - We used co-segregation analysis of family, patch clamp in vitro electrophysiology, and structural analysis using recently released cryo-electron microscopy structures of both channels.
RESULTS - The structural analysis indicates that KCNQ1 Val162Met is oriented away from functionally important regions while Ser55Leu is positioned at domains critical for KCNH2 fast inactivation. Clinical phenotyping and electrophysiology study further support the conclusion that KCNH2 Ser55Leu is correctly classified as pathogenic but KCNQ1 Val162Met is benign.
CONCLUSION - Proximity in sequence space does not always translate accurately to proximity in 3-dimensional space. Emerging structural methods will add value to pathogenicity prediction.
Copyright © 2018 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.
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Predicting the Functional Impact of KCNQ1 Variants of Unknown Significance.
Li B, Mendenhall JL, Kroncke BM, Taylor KC, Huang H, Smith DK, Vanoye CG, Blume JD, George AL, Sanders CR, Meiler J
(2017) Circ Cardiovasc Genet 10:
MeSH Terms: Databases, Genetic, Female, Genetic Variation, Humans, KCNQ1 Potassium Channel, Long QT Syndrome, Male, Predictive Value of Tests, Protein Domains
Show Abstract · Added March 14, 2018
BACKGROUND - An emerging standard-of-care for long-QT syndrome uses clinical genetic testing to identify genetic variants of the KCNQ1 potassium channel. However, interpreting results from genetic testing is confounded by the presence of variants of unknown significance for which there is inadequate evidence of pathogenicity.
METHODS AND RESULTS - In this study, we curated from the literature a high-quality set of 107 functionally characterized KCNQ1 variants. Based on this data set, we completed a detailed quantitative analysis on the sequence conservation patterns of subdomains of KCNQ1 and the distribution of pathogenic variants therein. We found that conserved subdomains generally are critical for channel function and are enriched with dysfunctional variants. Using this experimentally validated data set, we trained a neural network, designated Q1VarPred, specifically for predicting the functional impact of KCNQ1 variants of unknown significance. The estimated predictive performance of Q1VarPred in terms of Matthew's correlation coefficient and area under the receiver operating characteristic curve were 0.581 and 0.884, respectively, superior to the performance of 8 previous methods tested in parallel. Q1VarPred is publicly available as a web server at http://meilerlab.org/q1varpred.
CONCLUSIONS - Although a plethora of tools are available for making pathogenicity predictions over a genome-wide scale, previous tools fail to perform in a robust manner when applied to KCNQ1. The contrasting and favorable results for Q1VarPred suggest a promising approach, where a machine-learning algorithm is tailored to a specific protein target and trained with a functionally validated data set to calibrate informatics tools.
© 2017 American Heart Association, Inc.
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9 MeSH Terms
Azithromycin Causes a Novel Proarrhythmic Syndrome.
Yang Z, Prinsen JK, Bersell KR, Shen W, Yermalitskaya L, Sidorova T, Luis PB, Hall L, Zhang W, Du L, Milne G, Tucker P, George AL, Campbell CM, Pickett RA, Shaffer CM, Chopra N, Yang T, Knollmann BC, Roden DM, Murray KT
(2017) Circ Arrhythm Electrophysiol 10:
MeSH Terms: Action Potentials, Animals, Anti-Bacterial Agents, Arrhythmias, Cardiac, Azithromycin, CHO Cells, Calcium Channel Blockers, Calcium Channels, L-Type, Cricetulus, Dose-Response Relationship, Drug, Electrocardiography, Ambulatory, Female, HEK293 Cells, Heart Rate, Humans, KCNQ1 Potassium Channel, Mice, Inbred C57BL, Myocytes, Cardiac, NAV1.5 Voltage-Gated Sodium Channel, Potassium Channel Blockers, Potassium Channels, Inwardly Rectifying, Potassium Channels, Voltage-Gated, Rabbits, Sodium Channel Blockers, Telemetry, Time Factors, Transfection, Young Adult
Show Abstract · Added July 6, 2017
BACKGROUND - The widely used macrolide antibiotic azithromycin increases risk of cardiovascular and sudden cardiac death, although the underlying mechanisms are unclear. Case reports, including the one we document here, demonstrate that azithromycin can cause rapid, polymorphic ventricular tachycardia in the absence of QT prolongation, indicating a novel proarrhythmic syndrome. We investigated the electrophysiological effects of azithromycin in vivo and in vitro using mice, cardiomyocytes, and human ion channels heterologously expressed in human embryonic kidney (HEK 293) and Chinese hamster ovary (CHO) cells.
METHODS AND RESULTS - In conscious telemetered mice, acute intraperitoneal and oral administration of azithromycin caused effects consistent with multi-ion channel block, with significant sinus slowing and increased PR, QRS, QT, and QTc intervals, as seen with azithromycin overdose. Similarly, in HL-1 cardiomyocytes, the drug slowed sinus automaticity, reduced phase 0 upstroke slope, and prolonged action potential duration. Acute exposure to azithromycin reduced peak SCN5A currents in HEK cells (IC=110±3 μmol/L) and Na current in mouse ventricular myocytes. However, with chronic (24 hour) exposure, azithromycin caused a ≈2-fold increase in both peak and late SCN5A currents, with findings confirmed for I in cardiomyocytes. Mild block occurred for K currents representing I (CHO cells expressing hERG; IC=219±21 μmol/L) and I (CHO cells expressing KCNQ1+KCNE1; IC=184±12 μmol/L), whereas azithromycin suppressed L-type Ca currents (rabbit ventricular myocytes, IC=66.5±4 μmol/L) and I (HEK cells expressing Kir2.1, IC=44±3 μmol/L).
CONCLUSIONS - Chronic exposure to azithromycin increases cardiac Na current to promote intracellular Na loading, providing a potential mechanistic basis for the novel form of proarrhythmia seen with this macrolide antibiotic.
© 2017 American Heart Association, Inc.
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28 MeSH Terms
Regulation of KCNQ/Kv7 family voltage-gated K channels by lipids.
Taylor KC, Sanders CR
(2017) Biochim Biophys Acta Biomembr 1859: 586-597
MeSH Terms: Amino Acid Sequence, Binding Sites, Cell Membrane, Epilepsy, Benign Neonatal, Fatty Acids, Unsaturated, Hearing Loss, Bilateral, Humans, Hydrophobic and Hydrophilic Interactions, KCNQ1 Potassium Channel, Long QT Syndrome, Membrane Lipids, Models, Molecular, Phosphatidylinositol 4,5-Diphosphate, Protein Binding, Protein Isoforms, Protein Structure, Secondary
Show Abstract · Added November 21, 2018
Many years of studies have established that lipids can impact membrane protein structure and function through bulk membrane effects, by direct but transient annular interactions with the bilayer-exposed surface of protein transmembrane domains, and by specific binding to protein sites. Here, we focus on how phosphatidylinositol 4,5-bisphosphate (PIP) and polyunsaturated fatty acids (PUFAs) impact ion channel function and how the structural details of the interactions of these lipids with ion channels are beginning to emerge. We focus on the Kv7 (KCNQ) subfamily of voltage-gated K channels, which are regulated by both PIP and PUFAs and play a variety of important roles in human health and disease. This article is part of a Special Issue entitled: Lipid order/lipid defects and lipid-control of protein activity edited by Dirk Schneider.
Copyright © 2016 Elsevier B.V. All rights reserved.
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Structural basis for KCNE3 modulation of potassium recycling in epithelia.
Kroncke BM, Van Horn WD, Smith J, Kang C, Welch RC, Song Y, Nannemann DP, Taylor KC, Sisco NJ, George AL, Meiler J, Vanoye CG, Sanders CR
(2016) Sci Adv 2: e1501228
MeSH Terms: Animals, Chloride Channels, Computational Biology, Cystic Fibrosis, Electrophysiological Phenomena, Epithelial Cells, Humans, KCNQ1 Potassium Channel, Multiprotein Complexes, Potassium, Potassium Channels, Voltage-Gated, Protein Domains
Show Abstract · Added April 7, 2017
The single-span membrane protein KCNE3 modulates a variety of voltage-gated ion channels in diverse biological contexts. In epithelial cells, KCNE3 regulates the function of the KCNQ1 potassium ion (K(+)) channel to enable K(+) recycling coupled to transepithelial chloride ion (Cl(-)) secretion, a physiologically critical cellular transport process in various organs and whose malfunction causes diseases, such as cystic fibrosis (CF), cholera, and pulmonary edema. Structural, computational, biochemical, and electrophysiological studies lead to an atomically explicit integrative structural model of the KCNE3-KCNQ1 complex that explains how KCNE3 induces the constitutive activation of KCNQ1 channel activity, a crucial component in K(+) recycling. Central to this mechanism are direct interactions of KCNE3 residues at both ends of its transmembrane domain with residues on the intra- and extracellular ends of the KCNQ1 voltage-sensing domain S4 helix. These interactions appear to stabilize the activated "up" state configuration of S4, a prerequisite for full opening of the KCNQ1 channel gate. In addition, the integrative structural model was used to guide electrophysiological studies that illuminate the molecular basis for how estrogen exacerbates CF lung disease in female patients, a phenomenon known as the "CF gender gap."
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12 MeSH Terms
Influence of Pathogenic Mutations on the Energetics of Translocon-Mediated Bilayer Integration of Transmembrane Helices.
Schlebach JP, Sanders CR
(2015) J Membr Biol 248: 371-81
MeSH Terms: Amino Acid Sequence, Animals, Cattle, Conserved Sequence, Cystic Fibrosis Transmembrane Conductance Regulator, Humans, KCNQ1 Potassium Channel, Lipid Bilayers, Mutation, Mutation, Missense, Myelin Proteins, Protein Structure, Secondary, Protein Transport, Receptors, Vasopressin, Rhodopsin, Thermodynamics
Show Abstract · Added November 21, 2018
Aberrant protein folding and assembly contribute to a number of diseases, and efforts to rationalize how pathogenic mutations cause this phenomenon represent an important imperative in biochemical research. However, for α-helical membrane proteins, this task is complicated by the fact that membrane proteins require intricate machinery to achieve structural and functional maturity under cellular conditions. In this work, we utilized the ΔG predictor algorithm ( www.dgpred.cbr.su.se ) to survey 470 known pathogenic mutations occurring in five misfolding-prone α-helical membrane proteins for their predicted effects on the translocon-mediated membrane integration of transmembrane helices, a critical step in biosynthesis and folding of nascent membrane proteins. The results suggest that about 10 % of these mutations are likely to have adverse effects on the topogenesis of nascent membrane proteins. These results suggest that the misfolding of a modest but nonetheless significant subset of pathogenic variants may begin at the translocon. Potential implications for therapeutic design and personalized medicine are discussed.
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Meta-analysis of genome-wide association studies in African Americans provides insights into the genetic architecture of type 2 diabetes.
Ng MC, Shriner D, Chen BH, Li J, Chen WM, Guo X, Liu J, Bielinski SJ, Yanek LR, Nalls MA, Comeau ME, Rasmussen-Torvik LJ, Jensen RA, Evans DS, Sun YV, An P, Patel SR, Lu Y, Long J, Armstrong LL, Wagenknecht L, Yang L, Snively BM, Palmer ND, Mudgal P, Langefeld CD, Keene KL, Freedman BI, Mychaleckyj JC, Nayak U, Raffel LJ, Goodarzi MO, Chen YD, Taylor HA, Correa A, Sims M, Couper D, Pankow JS, Boerwinkle E, Adeyemo A, Doumatey A, Chen G, Mathias RA, Vaidya D, Singleton AB, Zonderman AB, Igo RP, Sedor JR, FIND Consortium, Kabagambe EK, Siscovick DS, McKnight B, Rice K, Liu Y, Hsueh WC, Zhao W, Bielak LF, Kraja A, Province MA, Bottinger EP, Gottesman O, Cai Q, Zheng W, Blot WJ, Lowe WL, Pacheco JA, Crawford DC, eMERGE Consortium, DIAGRAM Consortium, Grundberg E, MuTHER Consortium, Rich SS, Hayes MG, Shu XO, Loos RJ, Borecki IB, Peyser PA, Cummings SR, Psaty BM, Fornage M, Iyengar SK, Evans MK, Becker DM, Kao WH, Wilson JG, Rotter JI, Sale MM, Liu S, Rotimi CN, Bowden DW, MEta-analysis of type 2 DIabetes in African Americans Consortium
(2014) PLoS Genet 10: e1004517
MeSH Terms: African Americans, Diabetes Mellitus, Type 2, Genome-Wide Association Study, HLA-B27 Antigen, HMGA2 Protein, Humans, KCNQ1 Potassium Channel, Mutant Chimeric Proteins, Polymorphism, Single Nucleotide, Transcription Factor 7-Like 2 Protein
Show Abstract · Added January 20, 2015
Type 2 diabetes (T2D) is more prevalent in African Americans than in Europeans. However, little is known about the genetic risk in African Americans despite the recent identification of more than 70 T2D loci primarily by genome-wide association studies (GWAS) in individuals of European ancestry. In order to investigate the genetic architecture of T2D in African Americans, the MEta-analysis of type 2 DIabetes in African Americans (MEDIA) Consortium examined 17 GWAS on T2D comprising 8,284 cases and 15,543 controls in African Americans in stage 1 analysis. Single nucleotide polymorphisms (SNPs) association analysis was conducted in each study under the additive model after adjustment for age, sex, study site, and principal components. Meta-analysis of approximately 2.6 million genotyped and imputed SNPs in all studies was conducted using an inverse variance-weighted fixed effect model. Replications were performed to follow up 21 loci in up to 6,061 cases and 5,483 controls in African Americans, and 8,130 cases and 38,987 controls of European ancestry. We identified three known loci (TCF7L2, HMGA2 and KCNQ1) and two novel loci (HLA-B and INS-IGF2) at genome-wide significance (4.15 × 10(-94)
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10 MeSH Terms
Meta-analysis of genome-wide association studies in East Asian-ancestry populations identifies four new loci for body mass index.
Wen W, Zheng W, Okada Y, Takeuchi F, Tabara Y, Hwang JY, Dorajoo R, Li H, Tsai FJ, Yang X, He J, Wu Y, He M, Zhang Y, Liang J, Guo X, Sheu WH, Delahanty R, Guo X, Kubo M, Yamamoto K, Ohkubo T, Go MJ, Liu JJ, Gan W, Chen CC, Gao Y, Li S, Lee NR, Wu C, Zhou X, Song H, Yao J, Lee IT, Long J, Tsunoda T, Akiyama K, Takashima N, Cho YS, Ong RT, Lu L, Chen CH, Tan A, Rice TK, Adair LS, Gui L, Allison M, Lee WJ, Cai Q, Isomura M, Umemura S, Kim YJ, Seielstad M, Hixson J, Xiang YB, Isono M, Kim BJ, Sim X, Lu W, Nabika T, Lee J, Lim WY, Gao YT, Takayanagi R, Kang DH, Wong TY, Hsiung CA, Wu IC, Juang JM, Shi J, Choi BY, Aung T, Hu F, Kim MK, Lim WY, Wang TD, Shin MH, Lee J, Ji BT, Lee YH, Young TL, Shin DH, Chun BY, Cho MC, Han BG, Hwu CM, Assimes TL, Absher D, Yan X, Kim E, Kuo JZ, Kwon S, Taylor KD, Chen YD, Rotter JI, Qi L, Zhu D, Wu T, Mohlke KL, Gu D, Mo Z, Wu JY, Lin X, Miki T, Tai ES, Lee JY, Kato N, Shu XO, Tanaka T
(2014) Hum Mol Genet 23: 5492-504
MeSH Terms: 5'-Nucleotidase, Aldehyde Dehydrogenase, Aldehyde Dehydrogenase, Mitochondrial, Asian Continental Ancestry Group, Blood Proteins, Body Mass Index, Cardiac Myosins, Far East, Female, Genetic Predisposition to Disease, Genome-Wide Association Study, Glycoproteins, Humans, KCNQ1 Potassium Channel, Male, Myosin Light Chains, Obesity, Polymorphism, Single Nucleotide, Proteinase Inhibitory Proteins, Secretory
Show Abstract · Added June 26, 2014
Recent genetic association studies have identified 55 genetic loci associated with obesity or body mass index (BMI). The vast majority, 51 loci, however, were identified in European-ancestry populations. We conducted a meta-analysis of associations between BMI and ∼2.5 million genotyped or imputed single nucleotide polymorphisms among 86 757 individuals of Asian ancestry, followed by in silico and de novo replication among 7488-47 352 additional Asian-ancestry individuals. We identified four novel BMI-associated loci near the KCNQ1 (rs2237892, P = 9.29 × 10(-13)), ALDH2/MYL2 (rs671, P = 3.40 × 10(-11); rs12229654, P = 4.56 × 10(-9)), ITIH4 (rs2535633, P = 1.77 × 10(-10)) and NT5C2 (rs11191580, P = 3.83 × 10(-8)) genes. The association of BMI with rs2237892, rs671 and rs12229654 was significantly stronger among men than among women. Of the 51 BMI-associated loci initially identified in European-ancestry populations, we confirmed eight loci at the genome-wide significance level (P < 5.0 × 10(-8)) and an additional 14 at P < 1.0 × 10(-3) with the same direction of effect as reported previously. Findings from this analysis expand our knowledge of the genetic basis of obesity.
© The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.
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19 MeSH Terms
Purification and structural study of the voltage-sensor domain of the human KCNQ1 potassium ion channel.
Peng D, Kim JH, Kroncke BM, Law CL, Xia Y, Droege KD, Van Horn WD, Vanoye CG, Sanders CR
(2014) Biochemistry 53: 2032-42
MeSH Terms: Amino Acid Sequence, Deuterium Exchange Measurement, Humans, KCNQ1 Potassium Channel, Molecular Sequence Data, Protein Structure, Tertiary, Structure-Activity Relationship
Show Abstract · Added November 21, 2018
KCNQ1 (also known as KV7.1 or KVLQT1) is a voltage-gated potassium channel modulated by members of the KCNE protein family. Among multiple functions, KCNQ1 plays a critical role in the cardiac action potential. This channel is also subject to inherited mutations that cause certain cardiac arrhythmias and deafness. In this study, we report the overexpression, purification, and preliminary structural characterization of the voltage-sensor domain (VSD) of human KCNQ1 (Q1-VSD). Q1-VSD was expressed in Escherichia coli and purified into lyso-palmitoylphosphatidylglycerol micelles, conditions under which this tetraspan membrane protein yields excellent nuclear magnetic resonance (NMR) spectra. NMR studies reveal that Q1-VSD shares a common overall topology with other channel VSDs, with an S0 helix followed by transmembrane helices S1-S4. The exact sequential locations of the helical spans do, however, show significant variations from those of the homologous segments of previously characterized VSDs. The S4 segment of Q1-VSD was seen to be α-helical (with no 310 component) and underwent rapid backbone amide H-D exchange over most of its length. These results lay the foundation for more advanced structural studies and can be used to generate testable hypotheses for future structure-function experiments.
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