1
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Risi CM, Belknap B, Atherton J, Coscarella IL, White HD, Bryant Chase P, Pinto JR, Galkin VE. Troponin Structural Dynamics in the Native Cardiac Thin Filament Revealed by Cryo Electron Microscopy. J Mol Biol 2024; 436:168498. [PMID: 38387550 PMCID: PMC11007730 DOI: 10.1016/j.jmb.2024.168498] [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: 01/04/2024] [Revised: 02/07/2024] [Accepted: 02/15/2024] [Indexed: 02/24/2024]
Abstract
Cardiac muscle contraction occurs due to repetitive interactions between myosin thick and actin thin filaments (TF) regulated by Ca2+ levels, active cross-bridges, and cardiac myosin-binding protein C (cMyBP-C). The cardiac TF (cTF) has two nonequivalent strands, each comprised of actin, tropomyosin (Tm), and troponin (Tn). Tn shifts Tm away from myosin-binding sites on actin at elevated Ca2+ levels to allow formation of force-producing actomyosin cross-bridges. The Tn complex is comprised of three distinct polypeptides - Ca2+-binding TnC, inhibitory TnI, and Tm-binding TnT. The molecular mechanism of their collective action is unresolved due to lack of comprehensive structural information on Tn region of cTF. C1 domain of cMyBP-C activates cTF in the absence of Ca2+ to the same extent as rigor myosin. Here we used cryo-EM of native cTFs to show that cTF Tn core adopts multiple structural conformations at high and low Ca2+ levels and that the two strands are structurally distinct. At high Ca2+ levels, cTF is not entirely activated by Ca2+ but exists in either partially or fully activated state. Complete dissociation of TnI C-terminus is required for full activation. In presence of cMyBP-C C1 domain, Tn core adopts a fully activated conformation, even in absence of Ca2+. Our data provide a structural description for the requirement of myosin to fully activate cTFs and explain increased affinity of TnC to Ca2+ in presence of active cross-bridges. We suggest that allosteric coupling between Tn subunits and Tm is required to control actomyosin interactions.
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Affiliation(s)
- Cristina M Risi
- Department of Physiological Sciences, Eastern Virginia Medical School, Norfolk, VA 23507, USA
| | - Betty Belknap
- Department of Physiological Sciences, Eastern Virginia Medical School, Norfolk, VA 23507, USA
| | - Jennifer Atherton
- Department of Physiological Sciences, Eastern Virginia Medical School, Norfolk, VA 23507, USA
| | - Isabella Leite Coscarella
- Department of Biomedical Sciences, Florida State University College of Medicine, Tallahassee, FL, USA
| | - Howard D White
- Department of Physiological Sciences, Eastern Virginia Medical School, Norfolk, VA 23507, USA
| | - P Bryant Chase
- Department of Biological Science, Florida State University, Tallahassee, FL, USA
| | - Jose R Pinto
- Department of Biomedical Sciences, Florida State University College of Medicine, Tallahassee, FL, USA
| | - Vitold E Galkin
- Department of Physiological Sciences, Eastern Virginia Medical School, Norfolk, VA 23507, USA.
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2
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Oikonomidis IL, Theodorou K, Papaioannou E, Xenoulis PG, Adamama-Moraitou KK, Steiner JM, Kritsepi-Konstantinou M, Suchodolski JS, Rallis T, Soubasis N. Serial measurement of cardiac troponin I in hospitalised dogs with canine parvoviral enteritis: Association with outcome and canine pancreas-specific lipase concentration. Res Vet Sci 2023; 157:1-5. [PMID: 36827790 DOI: 10.1016/j.rvsc.2023.02.004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2022] [Revised: 01/19/2023] [Accepted: 02/14/2023] [Indexed: 02/19/2023]
Abstract
The aim of this study was to serially evaluate serum cardiac troponin I (cTnI) concentrations in dogs with parvoviral enteritis (CPVE), and investigate the association with outcome and serum pancreas-specific lipase (Spec cPL) concentrations. Dogs with CPVE that were hospitalised for at least 5 days were included. cTnI and Spec cPL concentrations were measured on days 1, 3 and 5 of hospitalisation. Twenty-nine dogs (20 survivors, 9 non-survivors) were included. Spec cPL was indicative of pancreatitis (>400 μg/L) on at least one day in 10/29 (34.5%) dogs. Serum median (range) cTnI concentration was higher (P = 0.021) in non-survivors on day 5 [0.032 (0.001-0.395) ng/mL] compared to day 1 [0.012 (0.003-0.196) ng/mL]. Non-survivors had higher (P = 0.014) cTnI concentrations on day 5 [0.032 (0.001-0.395) ng/mL] compared to survivors [0.001 (0.001-0.042) ng/mL], but not at admission or on day 3 (P > 0.05). Serum cTnI concentrations were not significantly different (P = 0.465) between the three Spec cPL groups [group 1 (Spec cPL ≤ 200 μg/L): 0.007 (0.001-0.527) ng/mL; group 2 (Spec cPL: 201-399 μg/L): 0.0045 (0.001-0.196) ng/mL; group 3 (Spec cPL ≥ 400 μg/L): 0.011 (0.001-0.278) ng/mL]. cTnI and Spec cPL concentrations were not significantly correlated (rho = -0.043, P = 0.703). Serial measurement of cTnI had prognostic value in the examined cohort. However, cTnI was not correlated with spec cPL.
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Affiliation(s)
- I L Oikonomidis
- Diagnostic Laboratory, School of Veterinary Medicine, Faculty of Health Sciences, Aristotle University of Thessaloniki, Thessaloniki, Greece.
| | - K Theodorou
- Companion Animal Clinic, School of Veterinary Medicine, Faculty of Health Sciences, Aristotle University of Thessaloniki, Thessaloniki, Greece
| | - E Papaioannou
- Companion Animal Clinic, School of Veterinary Medicine, Faculty of Health Sciences, Aristotle University of Thessaloniki, Thessaloniki, Greece
| | - P G Xenoulis
- Clinic of Medicine, Faculty of Veterinary Science, University of Thessaly, Karditsa, Greece; Gastrointestinal Laboratory, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, TX, USA
| | - K K Adamama-Moraitou
- Companion Animal Clinic, School of Veterinary Medicine, Faculty of Health Sciences, Aristotle University of Thessaloniki, Thessaloniki, Greece
| | - J M Steiner
- Gastrointestinal Laboratory, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, TX, USA
| | - M Kritsepi-Konstantinou
- Diagnostic Laboratory, School of Veterinary Medicine, Faculty of Health Sciences, Aristotle University of Thessaloniki, Thessaloniki, Greece
| | - J S Suchodolski
- Gastrointestinal Laboratory, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, TX, USA
| | - T Rallis
- Companion Animal Clinic, School of Veterinary Medicine, Faculty of Health Sciences, Aristotle University of Thessaloniki, Thessaloniki, Greece
| | - N Soubasis
- Companion Animal Clinic, School of Veterinary Medicine, Faculty of Health Sciences, Aristotle University of Thessaloniki, Thessaloniki, Greece
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3
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Ji K, Jiao D, Yang G, Degen AA, Zhou J, Liu H, Wang W, Cong H. Transcriptome analysis revealed potential genes involved in thermogenesis in muscle tissue in cold-exposed lambs. Front Genet 2022; 13:1017458. [PMID: 36338953 PMCID: PMC9634817 DOI: 10.3389/fgene.2022.1017458] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2022] [Accepted: 10/05/2022] [Indexed: 11/28/2022] Open
Abstract
Cold tolerance is an important trait for sheep raised at high altitudes. Muscle tissue, comprising 30–40% of the total body mass, produces heat during cold exposure. However, little is known about the genetic mechanisms of this tissue and its role in thermogenesis in lambs. We examined genes in skeletal muscle tissue in a cold-adapted sheep breed, Altay, and a cold-intolerant sheep breed, Hu, when exposed to low air temperature. Three ewe-lambs of each breed were maintained at −5°C and three ewe-lambs of each breed were maintained at 20°C. After cold exposure for 25 days, the longissimus dorsi of each lamb was collected, and transcriptome profiles were sequenced and analyzed. The results of RNA-seq showed that the average reads among the four groups were 11.0 Gbase. The genome mapping rate averaged 88.1% and the gene mapping rate averaged 82.5%. The analysis of differentially expressed genes (DEGs) indicated that the peroxisome proliferator-activated receptors (PPAR), cAMP, and calcium signaling pathways and muscle contraction in muscle tissue were linked to thermogenesis in cold-exposed lambs. Furthermore, PCK1 (phosphoenolpyruvate carboxykinase1) increased glyceroneogenesis in cold-exposed Altay lambs, and APOC3 (apolipoprotein C3), LPL (lipoprotein lipase), and FABP4 (fatty acid binding protein 4, adipocyte) were involved in the intake and transport of free fatty acids. In Hu sheep, cAMP biosynthesis from ATP hydrolysis was regulated by ADCY10 (adenylate cyclase) and ADORA2a (adenosine A2a receptor). Skeletal muscle contraction was regulated by MYL2 (myosin light chain 2). In conclusion, cold exposure altered the expression level of genes involved in heat production in muscle tissue. Some potential mechanisms were revealed, including calcium ion transport in the calcium signaling pathway, fatty acid metabolism in the PPAR signaling pathway, and cAMP biosynthesis in the cAMP signaling pathway. This study implied that skeletal muscle plays an important role in thermoregulation in lambs.
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Affiliation(s)
- Kaixi Ji
- Key Laboratory of Stress Physiology and Ecology of Gansu Province, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou, China
- University of Chinese Academy of Sciences, Beijing, China
| | - Dan Jiao
- Key Laboratory of Stress Physiology and Ecology of Gansu Province, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou, China
| | - Guo Yang
- Key Laboratory of Stress Physiology and Ecology of Gansu Province, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou, China
- *Correspondence: Guo Yang,
| | - Abraham Allan Degen
- Desert Animal Adaptations and Husbandry, Wyler Department of Dryland Agriculture, Blaustein Institutes for Desert Research, Ben-Gurion University of Negev, Beer Sheva, Israel
| | - Jianwei Zhou
- State Key Laboratory of Grassland and Agro-Ecosystems, College of Pastoral Agriculture Science and Technology, Lanzhou University, Lanzhou, China
| | - Hu Liu
- College of Ecology, Lanzhou University, Lanzhou, China
| | - Wenqiang Wang
- College of Ecology, Lanzhou University, Lanzhou, China
| | - Haitao Cong
- Dongying Modern Animal Husbandry Development Service Center, Dongying, China
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4
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Keyt LK, Duran JM, Bui QM, Chen C, Miyamoto MI, Silva Enciso J, Tardiff JC, Adler ED. Thin filament cardiomyopathies: A review of genetics, disease mechanisms, and emerging therapeutics. Front Cardiovasc Med 2022; 9:972301. [PMID: 36158814 PMCID: PMC9489950 DOI: 10.3389/fcvm.2022.972301] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2022] [Accepted: 07/28/2022] [Indexed: 11/17/2022] Open
Abstract
All muscle contraction occurs due to the cyclical interaction between sarcomeric thin and thick filament proteins within the myocyte. The thin filament consists of the proteins actin, tropomyosin, Troponin C, Troponin I, and Troponin T. Mutations in these proteins can result in various forms of cardiomyopathy, including hypertrophic, restrictive, and dilated phenotypes and account for as many as 30% of all cases of inherited cardiomyopathy. There is significant evidence that thin filament mutations contribute to dysregulation of Ca2+ within the sarcomere and may have a distinct pathomechanism of disease from cardiomyopathy associated with thick filament mutations. A number of distinct clinical findings appear to be correlated with thin-filament mutations: greater degrees of restrictive cardiomyopathy and relatively less left ventricular (LV) hypertrophy and LV outflow tract obstruction than that seen with thick filament mutations, increased morbidity associated with heart failure, increased arrhythmia burden and potentially higher mortality. Most therapies that improve outcomes in heart failure blunt the neurohormonal pathways involved in cardiac remodeling, while most therapies for hypertrophic cardiomyopathy involve use of negative inotropes to reduce LV hypertrophy or septal reduction therapies to reduce LV outflow tract obstruction. None of these therapies directly address the underlying sarcomeric dysfunction associated with thin-filament mutations. With mounting evidence that thin filament cardiomyopathies occur through a distinct mechanism, there is need for therapies targeting the unique, underlying mechanisms tailored for each patient depending on a given mutation.
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Affiliation(s)
- Lucas K. Keyt
- Department of Internal Medicine, University of California, San Diego, San Diego, CA, United States
| | - Jason M. Duran
- Department of Cardiology, University of California, San Diego, San Diego, CA, United States
| | - Quan M. Bui
- Department of Cardiology, University of California, San Diego, San Diego, CA, United States
| | - Chao Chen
- Department of Cardiology, University of California, San Diego, San Diego, CA, United States
| | | | - Jorge Silva Enciso
- Department of Cardiology, University of California, San Diego, San Diego, CA, United States
| | - Jil C. Tardiff
- Department of Medicine and Biomedical Engineering, University of Arizona, Tucson, AZ, United States
| | - Eric D. Adler
- Department of Cardiology, University of California, San Diego, San Diego, CA, United States
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5
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Mahmud Z, Tikunova S, Belevych N, Wagg CS, Zhabyeyev P, Liu PB, Rasicci DV, Yengo CM, Oudit GY, Lopaschuk GD, Reiser PJ, Davis JP, Hwang PM. Small Molecule RPI-194 Stabilizes Activated Troponin to Increase the Calcium Sensitivity of Striated Muscle Contraction. Front Physiol 2022; 13:892979. [PMID: 35755445 PMCID: PMC9213791 DOI: 10.3389/fphys.2022.892979] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2022] [Accepted: 05/10/2022] [Indexed: 11/13/2022] Open
Abstract
Small molecule cardiac troponin activators could potentially enhance cardiac muscle contraction in the treatment of systolic heart failure. We designed a small molecule, RPI-194, to bind cardiac/slow skeletal muscle troponin (Cardiac muscle and slow skeletal muscle share a common isoform of the troponin C subunit.) Using solution NMR and stopped flow fluorescence spectroscopy, we determined that RPI-194 binds to cardiac troponin with a dissociation constant KD of 6-24 μM, stabilizing the activated complex between troponin C and the switch region of troponin I. The interaction between RPI-194 and troponin C is weak (KD 311 μM) in the absence of the switch region. RPI-194 acts as a calcium sensitizer, shifting the pCa50 of isometric contraction from 6.28 to 6.99 in mouse slow skeletal muscle fibers and from 5.68 to 5.96 in skinned cardiac trabeculae at 100 μM concentration. There is also some cross-reactivity with fast skeletal muscle fibers (pCa50 increases from 6.27 to 6.52). In the slack test performed on the same skinned skeletal muscle fibers, RPI-194 slowed the velocity of unloaded shortening at saturating calcium concentrations, suggesting that it slows the rate of actin-myosin cross-bridge cycling under these conditions. However, RPI-194 had no effect on the ATPase activity of purified actin-myosin. In isolated unloaded mouse cardiomyocytes, RPI-194 markedly decreased the velocity and amplitude of contractions. In contrast, cardiac function was preserved in mouse isolated perfused working hearts. In summary, the novel troponin activator RPI-194 acts as a calcium sensitizer in all striated muscle types. Surprisingly, it also slows the velocity of unloaded contraction, but the cause and significance of this is uncertain at this time. RPI-194 represents a new class of non-specific troponin activator that could potentially be used either to enhance cardiac muscle contractility in the setting of systolic heart failure or to enhance skeletal muscle contraction in neuromuscular disorders.
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Affiliation(s)
- Zabed Mahmud
- Department of Biochemistry, University of Alberta, Edmonton, AB, Canada
| | - Svetlana Tikunova
- Department of Physiology and Cell Biology, The Ohio State University, Columbus, OH, United States
| | - Natalya Belevych
- Division of Biosciences, College of Dentistry, The Ohio State University, Columbus, OH, United States
| | - Cory S Wagg
- Department of Pediatrics, University of Alberta, Edmonton, AB, Canada
| | - Pavel Zhabyeyev
- Department of Medicine, University of Alberta, Edmonton, AB, Canada
| | - Philip B Liu
- Department of Medicine, University of Alberta, Edmonton, AB, Canada
| | - David V Rasicci
- Department of Cellular and Molecular Physiology, College of Medicine, Pennsylvania State University, University Park, PA, United States
| | - Christopher M Yengo
- Department of Cellular and Molecular Physiology, College of Medicine, Pennsylvania State University, University Park, PA, United States
| | - Gavin Y Oudit
- Department of Medicine, University of Alberta, Edmonton, AB, Canada
| | - Gary D Lopaschuk
- Department of Pediatrics, University of Alberta, Edmonton, AB, Canada
| | - Peter J Reiser
- Division of Biosciences, College of Dentistry, The Ohio State University, Columbus, OH, United States
| | - Jonathan P Davis
- Department of Physiology and Cell Biology, The Ohio State University, Columbus, OH, United States
| | - Peter M Hwang
- Department of Biochemistry, University of Alberta, Edmonton, AB, Canada.,Department of Medicine, University of Alberta, Edmonton, AB, Canada
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6
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Cai F, Kampourakis T, Cockburn KT, Sykes BD. Drugging the Sarcomere, a Delicate Balance: Position of N-Terminal Charge of the Inhibitor W7. ACS Chem Biol 2022; 17:1495-1504. [PMID: 35649123 DOI: 10.1021/acschembio.2c00126] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
W7 is a sarcomere inhibitor that decreases the calcium sensitivity of force development in cardiac muscle. W7 binds to the interface of the regulatory domain of cardiac troponin C (cNTnC) and the switch region of troponin I (cTnI), decreasing the binding of cTnI to cNTnC, presumably by electrostatic repulsion between the -NH3+ group of W7 and basic amino acids in cTnI. W7 analogs with a -CO2- tail are inactive. To evaluate the importance of the location of the charged -NH3+, we used a series of compounds W4, W6, W8, and W9, which have three less, one less, one more, and two more methylene groups in the tail region than W7. W6, W8, and W9 all bind tighter to cNTnC-cTnI chimera (cChimera) than W7, while W4 binds weaker. W4 and, strikingly, W6 have no effect on calcium sensitivity of force generation, while W8 and W9 decrease calcium sensitivity, but less than W7. The structures of the cChimera-W6 and cChimera-W8 complexes reveal that W6 and W8 bind to the same hydrophobic cleft as W7, with the aliphatic tail taking a similar route to the surface. NMR relaxation data show that internal flexibility in the tail of W7 is very limited. Alignment of the cChimera-W7 structure with the recent cryoEM structures of the cardiac sarcomere in the diastolic and systolic states reveals the critical location of the amino group. Small molecule induced structural changes can therefore affect the tightly balanced equilibrium between tethered components required for rapid contraction.
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Affiliation(s)
- Fangze Cai
- Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2R3, Canada
| | - Thomas Kampourakis
- Randall Centre for Cell and Molecular Biophysics, King's College London, London SE1 1UL, United Kingdom
| | - Kieran T Cockburn
- Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2R3, Canada
| | - Brian D Sykes
- Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2R3, Canada
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7
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Fujiwara S. Dynamical Behavior of Disordered Regions in Disease-Related Proteins Revealed by Quasielastic Neutron Scattering. MEDICINA (KAUNAS, LITHUANIA) 2022; 58:795. [PMID: 35744058 PMCID: PMC9230977 DOI: 10.3390/medicina58060795] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/27/2022] [Accepted: 06/08/2022] [Indexed: 06/15/2023]
Abstract
Background and Objectives: Intrinsically disordered proteins (IDPs) and proteins containing intrinsically disordered regions (IDRs) are known to be involved in various human diseases. Since the IDPs/IDRs are fluctuating between many structural substrates, the dynamical behavior of the disease-related IDPs/IDRs needs to be characterized to elucidate the mechanisms of the pathogenesis of the diseases. As protein motions have a hierarchy ranging from local side-chain motions, through segmental motions of loops or disordered regions, to diffusive motions of entire molecules, segmental motions, as well as local motions, need to be characterized. Materials and Methods: Combined analysis of quasielastic neutron scattering (QENS) spectra with the structural data provides information on both the segmental motions and the local motions of the IDPs/IDRs. Here, this method is applied to re-analyze the QENS spectra of the troponin core domain (Tn-CD), various mutants of which cause the pathogenesis of familial cardiomyopathy (FCM), and α-synuclein (αSyn), amyloid fibril formation of which is closely related to the pathogenesis of Parkinson's disease, collected in the previous studies. The dynamical behavior of wild-type Tn-CD, FCM-related mutant Tn-CD, and αSyn in the different propensity states for fibril formation is characterized. Results: In the Tn-CD, the behavior of the segmental motions is shown to be different between the wild type and the mutant. This difference is likely to arise from changes in the intramolecular interactions, which are suggested to be related to the functional aberration of the mutant Tn-CD. In αSyn, concerted enhancement of the segmental motions and the local motions is observed with an increased propensity for fibril formation, suggesting the importance of these motions in fibril formation. Conclusions: Characterization of the segmental motions as well as the local motions is thus useful for discussing how the changes in dynamical behavior caused by the disease-related mutations and/or environmental changes could be related to the functional and/or behavioral aberrations of these proteins.
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Affiliation(s)
- Satoru Fujiwara
- Institute for Quantum Biology, National Institutes for Quantum Science and Technology, 2-4 Shirakata, Tokai, Ibaraki 319-1106, Japan
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8
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Deranek AE, Baldo AP, Lynn ML, Schwartz SD, Tardiff JC. Structure and Dynamics of the Flexible Cardiac Troponin T Linker Domain in a Fully Reconstituted Thin Filament. Biochemistry 2022; 61:1229-1242. [PMID: 35696530 DOI: 10.1021/acs.biochem.2c00091] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The structural analysis of large protein complexes has been greatly enhanced through the application of electron microscopy techniques. One such multiprotein complex, the cardiac thin filament (cTF), has cyclic interactions with thick filament proteins to drive contraction of the heart that has recently been the subject of such studies. As important as these studies are, they provide limited or no information on highly flexible regions that in isolation would be characterized as inherently disordered. One such region is the extended cardiac troponin T (cTnT) linker between the regions of cTnT which have been labeled TNT1 and TNT2. It comprises a hinge region (residues 158-166) and a highly flexible region (residues 167-203). Critically, this region modulates the troponin/tropomyosin complex's position across the actin filament. Thus, the cTnT linker structure and dynamics are central to the regulation of the function of cardiac muscles, but up to now, it was ill-understood. To establish the cTnT linker structure, we coupled an atomistic computational cTF model with time-resolved fluorescence resonance energy transfer measurements in both ±Ca2+ conditions utilizing fully reconstituted cTFs. We mapped the cTnT linker's positioning across the actin filament, and by coupling the experimental results to computation, we found mean structures and ranges of motion of this part of the complex. With this new insight, we can now address cTnT linker structural dynamics in both myofilament activation and disease.
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Affiliation(s)
- Andrea E Deranek
- Department of Biomedical Engineering, University of Arizona, Tucson, Arizona 85721, United States
| | - Anthony P Baldo
- Department of Chemistry and Biochemistry, University of Arizona, Tucson, Arizona 85721, United States
| | - Melissa L Lynn
- Department of Biomedical Engineering, University of Arizona, Tucson, Arizona 85721, United States
| | - Steven D Schwartz
- Department of Chemistry and Biochemistry, University of Arizona, Tucson, Arizona 85721, United States
| | - Jil C Tardiff
- Department of Biomedical Engineering, University of Arizona, Tucson, Arizona 85721, United States
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9
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Mason AB, Tardiff JC, Schwartz SD. Free-Energy Surfaces of Two Cardiac Thin Filament Conformational Changes during Muscle Contraction. J Phys Chem B 2022; 126:3844-3851. [PMID: 35584206 DOI: 10.1021/acs.jpcb.2c01337] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The troponin core is an important regulatory complex in cardiac sarcomeres. Contraction is initiated by a calcium ion binding to cardiac troponin C (cTnC), initiating a conformational shift within the protein, altering its interactions with cardiac troponin I (cTnI). The change in cTnC-cTnI interactions prompts the C-terminal domain of cTnI to dissociate from actin, allowing tropomyosin to reveal myosin-binding sites on actin. Each of the concerted movements in the cardiac thin filament (CTF) is crucial for allowing the contraction of cardiomyocytes, yet little is known about the free energy associated with each transition, which is vital for understanding contraction on a molecular level. Using metadynamics, we calculated the free-energy surface of two transitions in the CTF: cTnC opening in the presence and absence of Ca2+ and cTnI dissociating from actin with both open and closed cTnC. These results not only provide the free-energy surface of the transitions but will also be shown to determine if the order of transitions in the contraction cycle is important. From our calculations, we found that the calcium ion helps stabilize the open conformation of cTnC and that the C-terminus of cTnI is stabilized by cTnC in the open conformation when dissociating from the actin surface.
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Affiliation(s)
- Allison B Mason
- Department of Chemistry and Biochemistry, University of Arizona, 1306 E. University Blvd. Room 221, Tucson, Arizona 85721, United States
| | - Jil C Tardiff
- Department of Biomedical Engineering, University of Arizona, Tucson, Arizona 85721, United States
| | - Steven D Schwartz
- Department of Chemistry and Biochemistry, University of Arizona, 1306 E. University Blvd. Room 221, Tucson, Arizona 85721, United States
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10
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Cai F, Kampourakis T, Klein BA, Sykes BD. A Potent Fluorescent Reversible-Covalent Inhibitor of Cardiac Muscle Contraction. ACS Med Chem Lett 2021; 12:1503-1507. [PMID: 34531960 DOI: 10.1021/acsmedchemlett.1c00366] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2021] [Accepted: 08/19/2021] [Indexed: 11/28/2022] Open
Abstract
Compounds that directly modulate the response of the cardiac sarcomere have potential in the treatment of cardiac disease. While a number of sarcomere activators have been discovered and extensively studied, very few inhibitors have been identified. We report a potent cardiac sarcomere inhibitor, DN-F01, targeting the cardiac muscle thin filament protein troponin complex. Functional studies show that DN-F01 has a strong inhibitory calcium-dependent effect on cardiac myofibrillar ATPase activity with an IC50 value of 11 ± 4 nmol/L. DN-F01 is shown to bind to a cardiac troponin C-troponin I chimera (cChimera) with a K D of ∼50 nM using fluorescence spectroscopy, indicating that troponin is the likely target for DN-F01. NMR titrations of DN-F01 to C35S and A-Cys cChimera show covalent and noncovalent binding of DN-F01 bound to the calcium-saturated cChimera.
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Affiliation(s)
- Fangze Cai
- Department of Biochemistry, University of Alberta, Edmonton AB T6G 2R3, Canada
| | - Thomas Kampourakis
- Randall Centre for Cell and Molecular Biophysics, King’s College London, London SE1 1UL, United Kingdom
| | - Brittney A. Klein
- Department of Biochemistry, University of Alberta, Edmonton AB T6G 2R3, Canada
| | - Brian D. Sykes
- Department of Biochemistry, University of Alberta, Edmonton AB T6G 2R3, Canada
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11
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Na V1.5 knockout in iPSCs: a novel approach to study Na V1.5 variants in a human cardiomyocyte environment. Sci Rep 2021; 11:17168. [PMID: 34433864 PMCID: PMC8387439 DOI: 10.1038/s41598-021-96474-6] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2021] [Accepted: 08/10/2021] [Indexed: 11/18/2022] Open
Abstract
Cardiomyocytes derived from patient-specific induced pluripotent stem cells (iPSC-CMs) successfully reproduce the mechanisms of several channelopathies. However, this approach involve cell reprogramming from somatic tissue biopsies or genomic editing in healthy iPSCs for every mutation found and to be investigated. We aim to knockout (KO) NaV1.5, the cardiac sodium channel, in a healthy human iPSC line, characterize the model and then, use it to express variants of NaV1.5. We develop a homozygous NaV1.5 KO iPSC line able to differentiate into cardiomyocytes with CRISPR/Cas9 tool. The NaV1.5 KO iPSC-CMs exhibited an organized contractile apparatus, spontaneous contractile activity, and electrophysiological recordings confirmed the major reduction in total Na+ currents. The action potentials (APs) exhibited a reduction in their amplitude and in their maximal rate of rise. Voltage optical mapping recordings revealed that the conduction velocity Ca2+ transient waves propagation velocities were slow. A wild-type (WT) NaV1.5 channel expressed by transient transfection in the KO iPSC-CMs restored Na+ channel expression and AP properties. The expression of NaV1.5/delQKP, a long QT type 3 (LQT3) variant, in the NaV1.5 KO iPSC-CMs showed that dysfunctional Na+ channels exhibited a persistent Na+ current and caused prolonged AP duration that led to arrhythmic events, characteristics of LQT3.
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Li MX, Mercier P, Hartman JJ, Sykes BD. Structural Basis of Tirasemtiv Activation of Fast Skeletal Muscle. J Med Chem 2021; 64:3026-3034. [PMID: 33703886 DOI: 10.1021/acs.jmedchem.0c01412] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Troponin regulates the calcium-mediated activation of skeletal muscle. Muscle weakness in diseases such as amyotrophic lateral sclerosis and spinal muscular atrophy occurs from diminished neuromuscular output. The first direct fast skeletal troponin activator, tirasemtiv, amplifies the response of muscle to neuromuscular input. Tirasemtiv binds selectively and strongly to fast skeletal troponin, slowing the rate of calcium release and sensitizing muscle to calcium. We report the solution NMR structure of tirasemtiv bound to a fast skeletal troponin C-troponin I chimera. The structure reveals that tirasemtiv binds in a hydrophobic pocket between the regulatory domain of troponin C and the switch region of troponin I, which overlaps with that of Anapoe in the X-ray structure of skeletal troponin. Multiple interactions stabilize the troponin C-troponin I interface, increase the affinity of troponin C for the switch region of fast skeletal troponin I, and drive the equilibrium toward the active state.
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Affiliation(s)
- Monica X Li
- Department of Biochemistry, University of Alberta, Edmonton, AB T6G 2H7, Canada
| | - Pascal Mercier
- National High Field NMR Centre, University of Alberta, Edmonton, AB T6G 2E1, Canada
| | - James J Hartman
- Cytokinetics, Inc., South San Francisco, California 94080, United States
| | - Brian D Sykes
- Department of Biochemistry, University of Alberta, Edmonton, AB T6G 2H7, Canada
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Abstract
The measurement of cardiac troponin (cTn) is recommended by all guidelines as the gold standard for the differential diagnosis of Acute Coronary Syndromes. The aim of this review is to discuss in details some key issues regarding both analytical and clinical characteristics of the high-sensitivity methods for cTn (hs-cTn), which are still considered controversial or unresolved. In particular, the major clinical concern regarding hs-cTn methods is the difficulty to differentiate the pathophysiological mechanism responsible for biomarker release from cardiomyocytes after reversible or irreversible injury, respectively. Indeed, recent experimental and clinical studies have demonstrated that different circulating forms of cTnI and cTnT can be respectively measured in plasma samples of patients with reversible or irreversible myocardial injury. Accordingly, a new generation of hs-Tn methods should be set up, based on immunometric immunoassays or chromatographic techniques, specific for circulating peptide forms more characteristics for reversible or irreversible myocardial injury. It is conceivable that this new generation of hs-cTn methods will complete the mission regarding the laboratory tests for specific cardiac biomarkers, started more than 20 years ago, which has already revolutionized the diagnosis, prognosis and management of patients with cardiac diseases.
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Cai F, Robertson IM, Kampourakis T, Klein BA, Sykes BD. The Role of Electrostatics in the Mechanism of Cardiac Thin Filament Based Sensitizers. ACS Chem Biol 2020; 15:2289-2298. [PMID: 32633482 DOI: 10.1021/acschembio.0c00519] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Heart muscle contraction is regulated by calcium binding to cardiac troponin C. This induces troponin I (cTnI) switch region binding to the regulatory domain of troponin C (cNTnC), pulling the cTnI inhibitory region off actin and triggering muscle contraction. Small molecules targeting this cNTnC-cTnI interface have potential in the treatment of heart disease. Most of these have an aromatic core which binds to the hydrophobic core of cNTnC, and a polar and often charged 'tail'. The calmodulin antagonist W7 is unique in that it acts as calcium desensitizer. W7 binds to the interface of cNTnC and cTnI switch region and weakens cTnI binding, possibly by electrostatic repulsion between the positively charged terminal amino group of W7 and the positively charged RRVR144-147 region of cTnI. To evaluate the role of electrostatics, we synthesized A7, where the amino group of W7 was replaced with a carboxyl group. We determined the high-resolution solution NMR structure of A7 bound to a cNTnC-cTnI chimera. The structure shows that A7 does not change the overall conformation of the cNTnC-cTnI interface, and the naphthalene ring of A7 sits in the same hydrophobic pocket as that of W7, but the charged tail takes a different route to the surface of the complex, especially with respect to the position of the switch region of cTnI. We measured the affinities of A7 for cNTnC and the cNTnC-cTnI complex and that of the cTnI switch peptide for the cNTnC-A7 complex. We also compared the binding of W7 and A7 for two cNTnC-cTnI chimeras, differing in the presence or absence of the RRVR region of cTnI. A7 decreased the binding affinity of cTnI to cNTnC substantially less than W7 and bound more tightly to the more positively charged chimera. We tested the effects of W7 and A7 on the force-calcium relation of demembranated rat right ventricular trabeculae and demonstrated that A7 has a much weaker desensitization effect than W7. We also synthesized A6, which has one less methylene group on the hydrocarbon chain than A7. A6 did not affect binding of cTnI switch peptide nor change the calcium sensitivity of ventricular trabeculae. These results suggest that the negative inotropic effect of W7 may result from a combination of electrostatic repulsion and steric hindrance with cTnI.
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Affiliation(s)
- Fangze Cai
- Department of Biochemistry, University of Alberta, Edmonton, AB T6G 2R3, Canada
| | - Ian M. Robertson
- Ministry of Health, Government of Alberta, Edmonton, AB T5J 1S6, Canada
| | - Thomas Kampourakis
- Randall Centre for Cell and Molecular Biophysics, King’s College London, London SE1 1UL, United Kingdom
| | - Brittney A. Klein
- Department of Biochemistry, University of Alberta, Edmonton, AB T6G 2R3, Canada
| | - Brian D. Sykes
- Department of Biochemistry, University of Alberta, Edmonton, AB T6G 2R3, Canada
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15
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Coldren WH, Tikunova SB, Davis JP, Lindert S. Discovery of Novel Small-Molecule Calcium Sensitizers for Cardiac Troponin C: A Combined Virtual and Experimental Screening Approach. J Chem Inf Model 2020; 60:3648-3661. [PMID: 32633957 DOI: 10.1021/acs.jcim.0c00452] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Heart failure is a leading cause of death throughout the world and is triggered by a disruption of the cardiac contractile machinery. This machinery is regulated in a calcium-dependent manner by the protein complex troponin. Calcium binds to the N-terminal domain of cardiac troponin C (cNTnC) setting into motion the cascade of events leading to muscle contraction. Because of the severity and prevalence of heart failure, there is a strong need to develop small-molecule therapeutics designed to increase the calcium sensitivity of cardiac troponin in order to treat this devastating condition. Molecules that are able to stabilize an open configuration of cNTnC and additionally facilitate the binding of the cardiac troponin I (cTnI) switch peptide have the potential to enable increased calcium sensitization and strengthened cardiac function. Here, we employed a high throughput virtual screening methodology built upon the ability of computational docking to reproduce known experimental results and to accurately recognize cNTnC conformations conducive to small molecule binding using a receiver operator characteristic curve analysis. This approach combined with concurrent stopped-flow kinetic experimental verification led to the identification of a number of sensitizers, which slowed the calcium off-rate. An initial hit, compound 4, was identified with medium affinity (84 ± 30 μM). Through refinement, a calcium sensitizing agent, compound 5, with an apparent affinity of 1.45 ± 0.09 μM was discovered. This molecule is one of the highest affinity calcium sensitizers known to date.
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Affiliation(s)
- William H Coldren
- Department of Chemistry and Biochemistry, Ohio State University, Columbus, Ohio 43210, United States
| | - Svetlana B Tikunova
- Davis Heart and Lung Research Institute and Department of Physiology and Cell Biology, Ohio State University, Columbus, Ohio 43210, United States
| | - Jonathan P Davis
- Davis Heart and Lung Research Institute and Department of Physiology and Cell Biology, Ohio State University, Columbus, Ohio 43210, United States
| | - Steffen Lindert
- Department of Chemistry and Biochemistry, Ohio State University, Columbus, Ohio 43210, United States
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Arata T. Myosin and Other Energy-Transducing ATPases: Structural Dynamics Studied by Electron Paramagnetic Resonance. Int J Mol Sci 2020; 21:E672. [PMID: 31968570 PMCID: PMC7014194 DOI: 10.3390/ijms21020672] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2019] [Revised: 01/05/2020] [Accepted: 01/06/2020] [Indexed: 02/07/2023] Open
Abstract
The objective of this article was to document the energy-transducing and regulatory interactions in supramolecular complexes such as motor, pump, and clock ATPases. The dynamics and structural features were characterized by motion and distance measurements using spin-labeling electron paramagnetic resonance (EPR) spectroscopy. In particular, we focused on myosin ATPase with actin-troponin-tropomyosin, neural kinesin ATPase with microtubule, P-type ion-motive ATPase, and cyanobacterial clock ATPase. Finally, we have described the relationships or common principles among the molecular mechanisms of various energy-transducing systems and how the large-scale thermal structural transition of flexible elements from one state to the other precedes the subsequent irreversible chemical reactions.
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Affiliation(s)
- Toshiaki Arata
- Department of Biology, Graduate School of Science, Osaka City University, Osaka 558-8585, Japan
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17
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Negahdary M, Heli H. An electrochemical troponin I peptisensor using a triangular icicle-like gold nanostructure. Biochem Eng J 2019. [DOI: 10.1016/j.bej.2019.107326] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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18
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Zhao C, Somiya T, Takai S, Ueki S, Arata T. Structural Dynamics of the N-Extension of Cardiac Troponin I Complexed with Troponin C by Site-Directed Spin Labeling Electron Paramagnetic Resonance. Sci Rep 2019; 9:15259. [PMID: 31649274 PMCID: PMC6813352 DOI: 10.1038/s41598-019-51740-6] [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: 05/19/2016] [Accepted: 10/07/2019] [Indexed: 11/29/2022] Open
Abstract
The secondary structure of the N-extension of cardiac troponin I (cTnI) was determined by measuring the distance distribution between spin labels attached to the i and i + 4 residues: 15/19, 23/27, 27/31, 35/39, and 43/47. All of the EPR spectra of these regions in the monomeric state were broadened and had a amplitude that was reduced by two-thirds of that of the single spin-labeled spectra and was fit by two residual distance distributions, with a major distribution one spreading over the range from 1 to 2.5 nm and the other minor peak at 0.9 nm. Only slight or no obvious changes were observed when the extension was bound to cTnC in the cTnI-cTnC complex at 0.2 M KCl. However, at 0.1 M KCl, residues 43/47, located at the PKC phosphorylation sites Ser42/44 on the boundary of the extension, exclusively exhibited a 0.9 nm peak, as expected from α-helix in the crystal structure, in the complex. Furthermore, 23/27, which is located on the PKA phosphorylation sites Ser23/24, showed that the major distribution was markedly narrowed, centered at 1.4 nm and 0.5 nm wide, accompanying the spin label immobilization of residue 27. Residues 35 and 69 at site 1 and 2 of cTnC exhibited partial immobilization of the attached spin labels upon complex formation. The results show that the extension exhibited a primarily partially folded or unfolded structure equilibrated with a transiently formed α-helix-like short structure over the length. We hypothesize that the structure binds at least near sites 1 and 2 of cTnC and that the specific secondary structure of the extension on cTnC becomes uncovered when decreasing the ionic strength demonstrating that only the phosphorylation regions of cTnI interact stereospecifically with cTnC.
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Affiliation(s)
- Chenchao Zhao
- Department of Biological Sciences, Graduate School of Science, Osaka University, Machikaneyama-cho 1-1, Toyonaka, Osaka, 560-0043, Japan
| | - Takayasu Somiya
- Department of Biological Sciences, Graduate School of Science, Osaka University, Machikaneyama-cho 1-1, Toyonaka, Osaka, 560-0043, Japan
| | - Shinji Takai
- Department of Biological Sciences, Graduate School of Science, Osaka University, Machikaneyama-cho 1-1, Toyonaka, Osaka, 560-0043, Japan
| | - Shoji Ueki
- Kagawa School of Pharmaceutical Sciences, Tokushima Bunri University, Shido 1314-1, Samuki, Kagawa, 769-2193, Japan
| | - Toshiaki Arata
- Department of Biological Sciences, Graduate School of Science, Osaka University, Machikaneyama-cho 1-1, Toyonaka, Osaka, 560-0043, Japan. .,Center for Advanced High Magnetic Field Science, Graduate School of Science, Osaka University, Machikaneyama-cho 1-1, Toyonaka, Osaka, 560-0043, Japan. .,Department of Biology, Graduate School of Science, Osaka City University, Sugimoto 3-3-138, Osaka, Osaka, 558-8585, Japan.
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Klein BA, Robertson IM, Reiz B, Kampourakis T, Li L, Sykes BD. Thioimidate Bond Formation between Cardiac Troponin C and Nitrile-containing Compounds. ACS Med Chem Lett 2019; 10:1007-1012. [PMID: 32426091 PMCID: PMC7227049 DOI: 10.1021/acsmedchemlett.9b00168] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2019] [Accepted: 05/15/2019] [Indexed: 12/16/2022] Open
Abstract
We have investigated the mechanism and reactivity of covalent bond formation between cysteine-84 of the regulatory domain of cardiac troponin C and compounds containing a nitrile moiety similar to the calcium sensitizer levosimendan. The results of modifications to the levosimendan framework ranged from a large increase in covalent bond formation to complete inactivity. We present the biological activity of one of the most potent compounds. Limitations, including compound solubility and degradation at acidic pH, have prevented thorough investigation of the potential of these compounds. Our studies reveal the efficacious nature of the malononitrile moiety in targeting cNTnC and its potential in future cardiotonic drug design.
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Affiliation(s)
- Brittney A. Klein
- Department of Biochemistry, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
| | - Ian M. Robertson
- Ministry of Health, Government of Alberta, Edmonton, Alberta T5J 1S6, Canada
| | - Béla Reiz
- Department of Chemistry, Faculty of Science, University of Alberta, Edmonton, Alberta T6G 2G2, Canada
| | - Thomas Kampourakis
- Randall Division of Cell and Molecular Biophysics, King’s College London, New Hunt’s House, London, SE1 1UL, U.K
| | - Liang Li
- Department of Chemistry, Faculty of Science, University of Alberta, Edmonton, Alberta T6G 2G2, Canada
| | - Brian D. Sykes
- Department of Biochemistry, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
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20
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Moving beyond simple answers to complex disorders in sarcomeric cardiomyopathies: the role of integrated systems. Pflugers Arch 2019; 471:661-671. [PMID: 30848350 DOI: 10.1007/s00424-019-02269-0] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2019] [Accepted: 03/01/2019] [Indexed: 12/26/2022]
Abstract
The classic clinical definition of hypertrophic cardiomyopathy (HCM) as originally described by Teare is deceptively simple, "left ventricular hypertrophy in the absence of any identifiable cause." Longitudinal studies, however, including a seminal study performed by Frank and Braunwald in 1968, clearly described the disorder much as we know it today, a complex, progressive, and highly variable cardiomyopathy affecting ~ 1/500 individuals worldwide. Subsequent genetic linkage studies in the early 1990s identified mutations in virtually all of the protein components of the cardiac sarcomere as the primary molecular cause of HCM. In addition, a substantial proportion of inherited dilated cardiomyopathy (DCM) has also been linked to sarcomeric protein mutations. Despite our deep understanding of the overall function of the sarcomere as the primary driver of cardiac contractility, the ability to use genotype in patient management remains elusive. A persistent challenge in the field from both the biophysical and clinical standpoints is how to rigorously link high-resolution protein dynamics and mechanics to the long-term cardiovascular remodeling process that characterizes these complex disorders. In this review, we will explore the depth of the problem from both the standpoint of a multi-subunit, highly conserved and dynamic "machine" to the resultant clinical and structural human phenotype with an emphasis on new, integrative approaches that can be widely applied to identify both novel disease mechanisms and new therapeutic targets for these primary biophysical disorders of the cardiac sarcomere.
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Cai F, Hwang PM, Sykes BD. Structural Changes Induced by the Binding of the Calcium Desensitizer W7 to Cardiac Troponin. Biochemistry 2018; 57:6461-6469. [DOI: 10.1021/acs.biochem.8b00882] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Affiliation(s)
- Fangze Cai
- Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2H7
| | - Peter M. Hwang
- Department of Medicine, University of Alberta, Edmonton, Alberta, Canada T6G 2H7
| | - Brian D. Sykes
- Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2H7
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Zou L, Zhang J, Han J, Li W, Su F, Xu X, Zhai Z, Xiao F. cGMP interacts with tropomyosin and downregulates actin-tropomyosin-myosin complex interaction. Respir Res 2018; 19:201. [PMID: 30314482 PMCID: PMC6186101 DOI: 10.1186/s12931-018-0903-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2018] [Accepted: 09/27/2018] [Indexed: 11/10/2022] Open
Abstract
Background The nitric oxide-soluble guanylate cyclase-cyclic guanosine monophosphate (NO-sGC-cGMP) signaling pathway, plays a critical role in the pathogenesis of pulmonary arterial hypertension (PAH); however, its exact molecular mechanism remains undefined. Methods Biotin-cGMP pull-down assay was performed to search for proteins regulated by cGMP. The interaction between cGMP and tropomyosin was analyzed with antibody dependent pull-down in vivo. Tropomyosin fragments were constructed to explore the tropomyosin-cGMP binding sites. The expression level and subcellular localization of tropomyosin were detected with Real-time PCR, Western blot and immunofluorescence assay after the 8-Br-cGMP treatment. Finally, isothermal titration calorimetry (ITC) was utilized to detect the binding affinity of actin-tropomyosin-myosin in the existence of cGMP-tropomyosin interaction. Results cGMP interacted with tropomyosin. Isoform 4 of TPM1 gene was identified as the only isoform expressed in the human pulmonary artery smooth muscle cells (HPASMCs). The region of 68-208aa of tropomyosin was necessary for the interaction between tropomyosin and cGMP. The expression level and subcellular localization of tropomyosin showed no change after the stimulation of NO-sGC-cGMP pathway. However, cGMP-tropomyosin interaction decreased the affinity of tropomyosin to actin. Conclusions We elucidate the downstream signal pathway of NO-sGC-cGMP. This work will contribute to the detection of innovative targeted agents and provide novel insights into the development of new therapies for PAH.
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Affiliation(s)
- Lihui Zou
- The MOH Key Laboratory of Geriatrics, Beijing Hospital, National Center of Gerontology, Beijing, 100730, People's Republic of China
| | - Junhua Zhang
- The MOH Key Laboratory of Geriatrics, Beijing Hospital, National Center of Gerontology, Beijing, 100730, People's Republic of China
| | - Jingli Han
- The MOH Key Laboratory of Geriatrics, Beijing Hospital, National Center of Gerontology, Beijing, 100730, People's Republic of China
| | - Wenqing Li
- The MOH Key Laboratory of Geriatrics, Beijing Hospital, National Center of Gerontology, Beijing, 100730, People's Republic of China
| | - Fei Su
- Department of Pathology, Beijing Hospital, National Center of Gerontology, Beijing, 100730, People's Republic of China
| | - Xiaomao Xu
- Department of Respiratory and Critical Care Medicine, Beijing Hospital, National Center of Gerontology, Beijing, 100730, People's Republic of China
| | - Zhenguo Zhai
- Department of Respiratory and Critical Care Medicine, China-Japan Friendship Hospital, Beijing, 100029, People's Republic of China.
| | - Fei Xiao
- The MOH Key Laboratory of Geriatrics, Beijing Hospital, National Center of Gerontology, Beijing, 100730, People's Republic of China.
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Klein BA, Reiz B, Robertson IM, Irving M, Li L, Sun YB, Sykes BD. Reversible Covalent Reaction of Levosimendan with Cardiac Troponin C in Vitro and in Situ. Biochemistry 2018; 57:2256-2265. [DOI: 10.1021/acs.biochem.8b00109] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Affiliation(s)
- Brittney A. Klein
- Department of Biochemistry, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
| | - Béla Reiz
- Department of Chemistry, Faculty of Science, University of Alberta, Edmonton, Alberta T6H 2H7, Canada
| | - Ian M. Robertson
- Pharmaceutical and Health Benefits Branch, Ministry of Health, Government of Alberta, Edmonton, Alberta T5J 3Z5, Canada
| | - Malcolm Irving
- Randall Centre for Cell and Molecular Biophysics and British Heart Foundation Centre of Research Excellence, King’s College London, London SE1 1UL, U.K
| | - Liang Li
- Department of Chemistry, Faculty of Science, University of Alberta, Edmonton, Alberta T6H 2H7, Canada
| | - Yin-Biao Sun
- Randall Centre for Cell and Molecular Biophysics and British Heart Foundation Centre of Research Excellence, King’s College London, London SE1 1UL, U.K
| | - Brian D. Sykes
- Department of Biochemistry, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
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Potluri PR, Chamoun J, Cooke JA, Badr M, Guse JA, Rayes R, Cordina NM, McCamey D, Fajer PG, Brown LJ. The concerted movement of the switch region of Troponin I in cardiac muscle thin filaments as tracked by conventional and pulsed (DEER) EPR. J Struct Biol 2017; 200:376-387. [DOI: 10.1016/j.jsb.2017.08.007] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2017] [Revised: 08/03/2017] [Accepted: 08/28/2017] [Indexed: 10/18/2022]
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25
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Matsuo T, Tominaga T, Kono F, Shibata K, Fujiwara S. Modulation of the picosecond dynamics of troponin by the cardiomyopathy-causing mutation K247R of troponin T observed by quasielastic neutron scattering. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2017; 1865:1781-1789. [PMID: 28923663 DOI: 10.1016/j.bbapap.2017.09.007] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/31/2017] [Revised: 08/18/2017] [Accepted: 09/14/2017] [Indexed: 11/16/2022]
Abstract
Troponin (Tn), consisting of three subunits (TnC, TnI, and TnT), regulates cardiac muscle contraction in a Ca2+-dependent manner. Various point mutations of human cardiac Tn are known to cause familial hypertrophic cardiomyopathy due to aberration of the regulatory function. In this study, we investigated the effects of one of these mutations, K247R of TnT, on the picosecond dynamics of the Tn core domain (Tn-CD), consisting of TnC, TnI and TnT2 (183-288 residues of TnT), by carrying out the quasielastic neutron scattering measurements on the reconstituted Tn-CD containing either the wild-type TnT2 (wtTn-CD) or the mutant TnT2 (K247R-Tn-CD) in the absence and presence of Ca2+. It was found that Ca2+-binding to the wtTn-CD decreases the residence time of atomic motions in the Tn-CD with slight changes in amplitudes, suggesting that the regulatory function mainly requires modulation of frequency of atomic motions. On the other hand, the K247R-Tn-CD shows different dynamic behavior from that of the wtTn-CD both in the absence and presence of Ca2+. In particular, the K247R-Tn-CD exhibits a larger amplitude than the wtTn-CD in the presence of Ca2+, suggesting that the mutant can explore larger conformational space than the wild-type. This increased flexibility should be relevant to the functional aberration of this mutant.
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Affiliation(s)
- Tatsuhito Matsuo
- Quantum Beam Science Research Directorate, National Institutes for Quantum and Radiological Science and Technology, Tokai, Ibaraki 319-1106, Japan
| | - Taiki Tominaga
- Neutron Science and Technology Center, Comprehensive Research Organization for Science and Society, Tokai, Ibaraki 319-1106, Japan
| | - Fumiaki Kono
- Quantum Beam Science Research Directorate, National Institutes for Quantum and Radiological Science and Technology, Tokai, Ibaraki 319-1106, Japan
| | - Kaoru Shibata
- Neutron Science Section, J-PARC Center, Tokai, Ibaraki 319-1195, Japan
| | - Satoru Fujiwara
- Quantum Beam Science Research Directorate, National Institutes for Quantum and Radiological Science and Technology, Tokai, Ibaraki 319-1106, Japan.
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Ngkelo A, Richart A, Kirk JA, Bonnin P, Vilar J, Lemitre M, Marck P, Branchereau M, Le Gall S, Renault N, Guerin C, Ranek MJ, Kervadec A, Danelli L, Gautier G, Blank U, Launay P, Camerer E, Bruneval P, Menasche P, Heymes C, Luche E, Casteilla L, Cousin B, Rodewald HR, Kass DA, Silvestre JS. Mast cells regulate myofilament calcium sensitization and heart function after myocardial infarction. J Exp Med 2017; 213:1353-74. [PMID: 27353089 PMCID: PMC4925026 DOI: 10.1084/jem.20160081] [Citation(s) in RCA: 85] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2016] [Accepted: 05/12/2016] [Indexed: 11/24/2022] Open
Abstract
Ngkelo et al. use a mast cell–deficient mouse model to reveal a protective role of mast cells in myocardial infarction, through regulation of the cardiac contractile machinery. Acute myocardial infarction (MI) is a severe ischemic disease responsible for heart failure and sudden death. Inflammatory cells orchestrate postischemic cardiac remodeling after MI. Studies using mice with defective mast/stem cell growth factor receptor c-Kit have suggested key roles for mast cells (MCs) in postischemic cardiac remodeling. Because c-Kit mutations affect multiple cell types of both immune and nonimmune origin, we addressed the impact of MCs on cardiac function after MI, using the c-Kit–independent MC-deficient (Cpa3Cre/+) mice. In response to MI, MC progenitors originated primarily from white adipose tissue, infiltrated the heart, and differentiated into mature MCs. MC deficiency led to reduced postischemic cardiac function and depressed cardiomyocyte contractility caused by myofilament Ca2+ desensitization. This effect correlated with increased protein kinase A (PKA) activity and hyperphosphorylation of its targets, troponin I and myosin-binding protein C. MC-specific tryptase was identified to regulate PKA activity in cardiomyocytes via protease-activated receptor 2 proteolysis. This work reveals a novel function for cardiac MCs modulating cardiomyocyte contractility via alteration of PKA-regulated force–Ca2+ interactions in response to MI. Identification of this MC-cardiomyocyte cross-talk provides new insights on the cellular and molecular mechanisms regulating the cardiac contractile machinery and a novel platform for therapeutically addressable regulators.
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Affiliation(s)
- Anta Ngkelo
- Institut National de la Santé et de la Recherche Médicale (INSERM), UMRS-970, Centre de Recherche Cardiovasculaire, Université Paris Descartes, Sorbonne Paris Cité, F-75015 Paris, France
| | - Adèle Richart
- Institut National de la Santé et de la Recherche Médicale (INSERM), UMRS-970, Centre de Recherche Cardiovasculaire, Université Paris Descartes, Sorbonne Paris Cité, F-75015 Paris, France
| | - Jonathan A Kirk
- Division of Cardiology, Johns Hopkins Medical Institutions, Baltimore, MD 212015
| | - Philippe Bonnin
- INSERM, U965, Hôpital Lariboisière-Fernand-Widal, Assistance Publique Hôpitaux de Paris, F-75010 Paris, France
| | - Jose Vilar
- Institut National de la Santé et de la Recherche Médicale (INSERM), UMRS-970, Centre de Recherche Cardiovasculaire, Université Paris Descartes, Sorbonne Paris Cité, F-75015 Paris, France
| | - Mathilde Lemitre
- Institut National de la Santé et de la Recherche Médicale (INSERM), UMRS-970, Centre de Recherche Cardiovasculaire, Université Paris Descartes, Sorbonne Paris Cité, F-75015 Paris, France
| | - Pauline Marck
- INSERM, UMR-1048, Institut des Maladies Métaboliques et Cardiovasculaires, F-31004 Toulouse, France
| | - Maxime Branchereau
- INSERM, UMR-1048, Institut des Maladies Métaboliques et Cardiovasculaires, F-31004 Toulouse, France
| | - Sylvain Le Gall
- Institut National de la Santé et de la Recherche Médicale (INSERM), UMRS-970, Centre de Recherche Cardiovasculaire, Université Paris Descartes, Sorbonne Paris Cité, F-75015 Paris, France
| | - Nisa Renault
- Institut National de la Santé et de la Recherche Médicale (INSERM), UMRS-970, Centre de Recherche Cardiovasculaire, Université Paris Descartes, Sorbonne Paris Cité, F-75015 Paris, France
| | - Coralie Guerin
- National Cytometry Platform, Department of Infection and Immunity, Luxembourg Institute of Health, L-4354 Esch-sur-Alzette, Luxembourg
| | - Mark J Ranek
- Division of Cardiology, Johns Hopkins Medical Institutions, Baltimore, MD 212015
| | - Anaïs Kervadec
- Institut National de la Santé et de la Recherche Médicale (INSERM), UMRS-970, Centre de Recherche Cardiovasculaire, Université Paris Descartes, Sorbonne Paris Cité, F-75015 Paris, France
| | - Luca Danelli
- Laboratoire d'Excellence INFLAMEX, Université Paris Diderot, Sorbonne Paris Cité, F-75018 Paris, France INSERM, U1149, F-75018 Paris, France Centre National de la Recherche Scientifique (CNRS) ERL 8252, F-75018 Paris, France
| | - Gregory Gautier
- Laboratoire d'Excellence INFLAMEX, Université Paris Diderot, Sorbonne Paris Cité, F-75018 Paris, France INSERM, U1149, F-75018 Paris, France
| | - Ulrich Blank
- Laboratoire d'Excellence INFLAMEX, Université Paris Diderot, Sorbonne Paris Cité, F-75018 Paris, France INSERM, U1149, F-75018 Paris, France Centre National de la Recherche Scientifique (CNRS) ERL 8252, F-75018 Paris, France
| | - Pierre Launay
- Laboratoire d'Excellence INFLAMEX, Université Paris Diderot, Sorbonne Paris Cité, F-75018 Paris, France INSERM, U1149, F-75018 Paris, France
| | - Eric Camerer
- Institut National de la Santé et de la Recherche Médicale (INSERM), UMRS-970, Centre de Recherche Cardiovasculaire, Université Paris Descartes, Sorbonne Paris Cité, F-75015 Paris, France
| | - Patrick Bruneval
- Institut National de la Santé et de la Recherche Médicale (INSERM), UMRS-970, Centre de Recherche Cardiovasculaire, Université Paris Descartes, Sorbonne Paris Cité, F-75015 Paris, France Hôpital European George Pompidou, Assistance Publique Hôpitaux de Paris, F-75015 Paris, France
| | - Philippe Menasche
- Institut National de la Santé et de la Recherche Médicale (INSERM), UMRS-970, Centre de Recherche Cardiovasculaire, Université Paris Descartes, Sorbonne Paris Cité, F-75015 Paris, France Hôpital European George Pompidou, Assistance Publique Hôpitaux de Paris, F-75015 Paris, France
| | - Christophe Heymes
- INSERM, UMR-1048, Institut des Maladies Métaboliques et Cardiovasculaires, F-31004 Toulouse, France
| | - Elodie Luche
- STROMALab, Etablissement Français du Sang, INSERM U1031, CNRS ERL 5311, Université de Toulouse, F-31004 Toulouse, France
| | - Louis Casteilla
- STROMALab, Etablissement Français du Sang, INSERM U1031, CNRS ERL 5311, Université de Toulouse, F-31004 Toulouse, France
| | - Béatrice Cousin
- STROMALab, Etablissement Français du Sang, INSERM U1031, CNRS ERL 5311, Université de Toulouse, F-31004 Toulouse, France
| | - Hans-Reimer Rodewald
- Division of Cellular Immunology, German Cancer Research Center, D-69120 Heidelberg, Germany
| | - David A Kass
- Division of Cardiology, Johns Hopkins Medical Institutions, Baltimore, MD 212015
| | - Jean-Sébastien Silvestre
- Institut National de la Santé et de la Recherche Médicale (INSERM), UMRS-970, Centre de Recherche Cardiovasculaire, Université Paris Descartes, Sorbonne Paris Cité, F-75015 Paris, France
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Liu Q, Jiang C, Xu J, Zhao MT, Van Bortle K, Cheng X, Wang G, Chang HY, Wu JC, Snyder MP. Genome-Wide Temporal Profiling of Transcriptome and Open Chromatin of Early Cardiomyocyte Differentiation Derived From hiPSCs and hESCs. Circ Res 2017; 121:376-391. [PMID: 28663367 DOI: 10.1161/circresaha.116.310456] [Citation(s) in RCA: 80] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/11/2016] [Revised: 06/21/2017] [Accepted: 06/28/2017] [Indexed: 01/13/2023]
Abstract
RATIONALE Recent advances have improved our ability to generate cardiomyocytes from human induced pluripotent stem cells (hiPSCs) and human embryonic stem cells (hESCs). However, our understanding of the transcriptional regulatory networks underlying early stages (ie, from mesoderm to cardiac mesoderm) of cardiomyocyte differentiation remains limited. OBJECTIVE To characterize transcriptome and chromatin accessibility during early cardiomyocyte differentiation from hiPSCs and hESCs. METHODS AND RESULTS We profiled the temporal changes in transcriptome and chromatin accessibility at genome-wide levels during cardiomyocyte differentiation derived from 2 hiPSC lines and 2 hESC lines at 4 stages: pluripotent stem cells, mesoderm, cardiac mesoderm, and differentiated cardiomyocytes. Overall, RNA sequencing analysis revealed that transcriptomes during early cardiomyocyte differentiation were highly concordant between hiPSCs and hESCs, and clustering of 4 cell lines within each time point demonstrated that changes in genome-wide chromatin accessibility were similar across hiPSC and hESC cell lines. Weighted gene co-expression network analysis (WGCNA) identified several modules that were strongly correlated with different stages of cardiomyocyte differentiation. Several novel genes were identified with high weighted connectivity within modules and exhibited coexpression patterns with other genes, including noncoding RNA LINC01124 and uncharacterized RNA AK127400 in the module related to the mesoderm stage; E-box-binding homeobox 1 (ZEB1) in the module correlated with postcardiac mesoderm. We further demonstrated that ZEB1 is required for early cardiomyocyte differentiation. In addition, based on integrative analysis of both WGCNA and transcription factor motif enrichment analysis, we determined numerous transcription factors likely to play important roles at different stages during cardiomyocyte differentiation, such as T and eomesodermin (EOMES; mesoderm), lymphoid enhancer-binding factor 1 (LEF1) and mesoderm posterior BHLH transcription factor 1 (MESP1; from mesoderm to cardiac mesoderm), meis homeobox 1 (MEIS1) and GATA-binding protein 4 (GATA4) (postcardiac mesoderm), JUN and FOS families, and MEIS2 (cardiomyocyte). CONCLUSIONS Both hiPSCs and hESCs share similar transcriptional regulatory mechanisms underlying early cardiac differentiation, and our results have revealed transcriptional regulatory networks and new factors (eg, ZEB1) controlling early stages of cardiomyocyte differentiation.
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Affiliation(s)
- Qing Liu
- From the Department of Genetics (Q.L., C.J., K.V.B., M.P.S.), Center for Personal Dynamic Regulomes (J.X., H.Y.C.), Stanford Cardiovascular Institute (M.T.Z., J.C.W.), and Stem Cell Core Facility, Department of Genetics (X.C., G.W.), Stanford University School of Medicine, CA
| | - Chao Jiang
- From the Department of Genetics (Q.L., C.J., K.V.B., M.P.S.), Center for Personal Dynamic Regulomes (J.X., H.Y.C.), Stanford Cardiovascular Institute (M.T.Z., J.C.W.), and Stem Cell Core Facility, Department of Genetics (X.C., G.W.), Stanford University School of Medicine, CA
| | - Jin Xu
- From the Department of Genetics (Q.L., C.J., K.V.B., M.P.S.), Center for Personal Dynamic Regulomes (J.X., H.Y.C.), Stanford Cardiovascular Institute (M.T.Z., J.C.W.), and Stem Cell Core Facility, Department of Genetics (X.C., G.W.), Stanford University School of Medicine, CA
| | - Ming-Tao Zhao
- From the Department of Genetics (Q.L., C.J., K.V.B., M.P.S.), Center for Personal Dynamic Regulomes (J.X., H.Y.C.), Stanford Cardiovascular Institute (M.T.Z., J.C.W.), and Stem Cell Core Facility, Department of Genetics (X.C., G.W.), Stanford University School of Medicine, CA
| | - Kevin Van Bortle
- From the Department of Genetics (Q.L., C.J., K.V.B., M.P.S.), Center for Personal Dynamic Regulomes (J.X., H.Y.C.), Stanford Cardiovascular Institute (M.T.Z., J.C.W.), and Stem Cell Core Facility, Department of Genetics (X.C., G.W.), Stanford University School of Medicine, CA
| | - Xun Cheng
- From the Department of Genetics (Q.L., C.J., K.V.B., M.P.S.), Center for Personal Dynamic Regulomes (J.X., H.Y.C.), Stanford Cardiovascular Institute (M.T.Z., J.C.W.), and Stem Cell Core Facility, Department of Genetics (X.C., G.W.), Stanford University School of Medicine, CA
| | - Guangwen Wang
- From the Department of Genetics (Q.L., C.J., K.V.B., M.P.S.), Center for Personal Dynamic Regulomes (J.X., H.Y.C.), Stanford Cardiovascular Institute (M.T.Z., J.C.W.), and Stem Cell Core Facility, Department of Genetics (X.C., G.W.), Stanford University School of Medicine, CA
| | - Howard Y Chang
- From the Department of Genetics (Q.L., C.J., K.V.B., M.P.S.), Center for Personal Dynamic Regulomes (J.X., H.Y.C.), Stanford Cardiovascular Institute (M.T.Z., J.C.W.), and Stem Cell Core Facility, Department of Genetics (X.C., G.W.), Stanford University School of Medicine, CA
| | - Joseph C Wu
- From the Department of Genetics (Q.L., C.J., K.V.B., M.P.S.), Center for Personal Dynamic Regulomes (J.X., H.Y.C.), Stanford Cardiovascular Institute (M.T.Z., J.C.W.), and Stem Cell Core Facility, Department of Genetics (X.C., G.W.), Stanford University School of Medicine, CA
| | - Michael P Snyder
- From the Department of Genetics (Q.L., C.J., K.V.B., M.P.S.), Center for Personal Dynamic Regulomes (J.X., H.Y.C.), Stanford Cardiovascular Institute (M.T.Z., J.C.W.), and Stem Cell Core Facility, Department of Genetics (X.C., G.W.), Stanford University School of Medicine, CA.
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28
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Derivation of Inhibitory Peptides to Target the Cardiac Troponin C–I Interaction as Potential Therapeutics for Heart Failure. Int J Pept Res Ther 2017. [DOI: 10.1007/s10989-017-9576-6] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
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29
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Robertson IM, Pineda-Sanabria SE, Yan Z, Kampourakis T, Sun YB, Sykes BD, Irving M. Reversible Covalent Binding to Cardiac Troponin C by the Ca2+-Sensitizer Levosimendan. Biochemistry 2016; 55:6032-6045. [DOI: 10.1021/acs.biochem.6b00758] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Ian M. Robertson
- Randall
Division of Cell and Molecular Biophysics and British Heart Foundation
Centre of Research Excellence, King’s College London, New Hunt’s
House, Guy’s Campus, London, SE1 1UL, U.K
- Department
of Biochemistry, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
| | - Sandra E. Pineda-Sanabria
- Department
of Biochemistry, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
| | - Ziqian Yan
- Randall
Division of Cell and Molecular Biophysics and British Heart Foundation
Centre of Research Excellence, King’s College London, New Hunt’s
House, Guy’s Campus, London, SE1 1UL, U.K
| | - Thomas Kampourakis
- Randall
Division of Cell and Molecular Biophysics and British Heart Foundation
Centre of Research Excellence, King’s College London, New Hunt’s
House, Guy’s Campus, London, SE1 1UL, U.K
| | - Yin-Biao Sun
- Randall
Division of Cell and Molecular Biophysics and British Heart Foundation
Centre of Research Excellence, King’s College London, New Hunt’s
House, Guy’s Campus, London, SE1 1UL, U.K
| | - Brian D. Sykes
- Department
of Biochemistry, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
| | - Malcolm Irving
- Randall
Division of Cell and Molecular Biophysics and British Heart Foundation
Centre of Research Excellence, King’s College London, New Hunt’s
House, Guy’s Campus, London, SE1 1UL, U.K
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30
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Marques MDA, de Oliveira GAP. Cardiac Troponin and Tropomyosin: Structural and Cellular Perspectives to Unveil the Hypertrophic Cardiomyopathy Phenotype. Front Physiol 2016; 7:429. [PMID: 27721798 PMCID: PMC5033975 DOI: 10.3389/fphys.2016.00429] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2016] [Accepted: 09/09/2016] [Indexed: 12/12/2022] Open
Abstract
Inherited myopathies affect both skeletal and cardiac muscle and are commonly associated with genetic dysfunctions, leading to the production of anomalous proteins. In cardiomyopathies, mutations frequently occur in sarcomeric genes, but the cause-effect scenario between genetic alterations and pathological processes remains elusive. Hypertrophic cardiomyopathy (HCM) was the first cardiac disease associated with a genetic background. Since the discovery of the first mutation in the β-myosin heavy chain, more than 1400 new mutations in 11 sarcomeric genes have been reported, awarding HCM the title of the “disease of the sarcomere.” The most common macroscopic phenotypes are left ventricle and interventricular septal thickening, but because the clinical profile of this disease is quite heterogeneous, these phenotypes are not suitable for an accurate diagnosis. The development of genomic approaches for clinical investigation allows for diagnostic progress and understanding at the molecular level. Meanwhile, the lack of accurate in vivo models to better comprehend the cellular events triggered by this pathology has become a challenge. Notwithstanding, the imbalance of Ca2+ concentrations, altered signaling pathways, induction of apoptotic factors, and heart remodeling leading to abnormal anatomy have already been reported. Of note, a misbalance of signaling biomolecules, such as kinases and tumor suppressors (e.g., Akt and p53), seems to participate in apoptotic and fibrotic events. In HCM, structural and cellular information about defective sarcomeric proteins and their altered interactome is emerging but still represents a bottleneck for developing new concepts in basic research and for future therapeutic interventions. This review focuses on the structural and cellular alterations triggered by HCM-causing mutations in troponin and tropomyosin proteins and how structural biology can aid in the discovery of new platforms for therapeutics. We highlight the importance of a better understanding of allosteric communications within these thin-filament proteins to decipher the HCM pathological state.
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Affiliation(s)
- Mayra de A Marques
- Programa de Biologia Estrutural, Centro Nacional de Ressonância Magnética Nuclear Jiri Jonas, Instituto de Bioquímica Médica Leopoldo de Meis, Instituto Nacional de Biologia Estrutural e Bioimagem, Universidade Federal do Rio de Janeiro Rio de Janeiro, Brazil
| | - Guilherme A P de Oliveira
- Programa de Biologia Estrutural, Centro Nacional de Ressonância Magnética Nuclear Jiri Jonas, Instituto de Bioquímica Médica Leopoldo de Meis, Instituto Nacional de Biologia Estrutural e Bioimagem, Universidade Federal do Rio de Janeiro Rio de Janeiro, Brazil
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31
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Dewan S, McCabe KJ, Regnier M, McCulloch AD, Lindert S. Molecular Effects of cTnC DCM Mutations on Calcium Sensitivity and Myofilament Activation-An Integrated Multiscale Modeling Study. J Phys Chem B 2016; 120:8264-75. [PMID: 27133568 PMCID: PMC5001916 DOI: 10.1021/acs.jpcb.6b01950] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Mutations in cardiac troponin C (D75Y, E59D, and G159D), a key regulatory protein of myofilament contraction, have been associated with dilated cardiomyopathy (DCM). Despite reports of altered myofilament function in these mutants, the underlying molecular alterations caused by these mutations remain elusive. Here we investigate in silico the intramolecular mechanisms by which these mutations affect myofilament contraction. On the basis of the location of cardiac troponin C (cTnC) mutations, we tested the hypothesis that intramolecular effects can explain the altered myofilament calcium sensitivity of force development for D75Y and E59D cTnC, whereas altered cardiac troponin C-troponin I (cTnC-cTnI) interaction contributes to the reported contractile effects of the G159D mutation. We employed a multiscale approach combining molecular dynamics (MD) and Brownian dynamics (BD) simulations to estimate cTnC calcium association and hydrophobic patch opening. We then integrated these parameters into a Markov model of myofilament activation to compute the steady-state force-pCa relationship. The analysis showed that myofilament calcium sensitivity with D75Y and E59D can be explained by changes in calcium binding affinity of cTnC and the rate of hydrophobic patch opening, if a partial cTnC interhelical opening angle (110°) is sufficient for cTnI switch peptide association to cTnC. In contrast, interactions between cTnC and cTnI within the cardiac troponin complex must also be accounted for to explain contractile alterations due to G159D. In conclusion, this is the first multiscale in silico study to elucidate how direct molecular effects of genetic mutations in cTnC translate to altered myofilament contractile function.
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Affiliation(s)
- Sukriti Dewan
- Department of Bioengineering, University of California at San Diego, La Jolla, CA, 92093
| | - Kimberly J. McCabe
- Department of Bioengineering, University of California at San Diego, La Jolla, CA, 92093
| | - Michael Regnier
- Dept. of Bioengineering, University of Washington, Seattle, WA 98195
- Center for Cardiovascular Biology, University of Washington, Seattle, WA 98109
| | - Andrew D. McCulloch
- Department of Bioengineering, University of California at San Diego, La Jolla, CA, 92093
| | - Steffen Lindert
- Department of Chemistry & Biochemistry, Ohio State University, Columbus, OH, 43210
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32
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Cheng Y, Regnier M. Cardiac troponin structure-function and the influence of hypertrophic cardiomyopathy associated mutations on modulation of contractility. Arch Biochem Biophys 2016; 601:11-21. [PMID: 26851561 PMCID: PMC4899195 DOI: 10.1016/j.abb.2016.02.004] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2015] [Revised: 01/30/2016] [Accepted: 02/02/2016] [Indexed: 11/29/2022]
Abstract
Cardiac troponin (cTn) acts as a pivotal regulator of muscle contraction and relaxation and is composed of three distinct subunits (cTnC: a highly conserved Ca(2+) binding subunit, cTnI: an actomyosin ATPase inhibitory subunit, and cTnT: a tropomyosin binding subunit). In this mini-review, we briefly summarize the structure-function relationship of cTn and its subunits, its modulation by PKA-mediated phosphorylation of cTnI, and what is known about how these properties are altered by hypertrophic cardiomyopathy (HCM) associated mutations of cTnI. This includes recent work using computational modeling approaches to understand the atomic-based structural level basis of disease-associated mutations. We propose a viewpoint that it is alteration of cTnC-cTnI interaction (rather than the Ca(2+) binding properties of cTn) per se that disrupt the ability of PKA-mediated phosphorylation at cTnI Ser-23/24 to alter contraction and relaxation in at least some HCM-associated mutations. The combination of state of the art biophysical approaches can provide new insight on the structure-function mechanisms of contractile dysfunction resulting cTnI mutations and exciting new avenues for the diagnosis, prevention, and even treatment of heart diseases.
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Affiliation(s)
- Yuanhua Cheng
- University of Washington, Department of Bioengineering, Seattle, WA, USA
| | - Michael Regnier
- University of Washington, Department of Bioengineering, Seattle, WA, USA.
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33
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Pineda-Sanabria SE, Robertson IM, Sun YB, Irving M, Sykes BD. Probing the mechanism of cardiovascular drugs using a covalent levosimendan analog. J Mol Cell Cardiol 2016; 92:174-84. [PMID: 26853943 PMCID: PMC4831045 DOI: 10.1016/j.yjmcc.2016.02.003] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/01/2015] [Revised: 01/24/2016] [Accepted: 02/02/2016] [Indexed: 01/16/2023]
Abstract
One approach to improve contraction in the failing heart is the administration of calcium (Ca2 +) sensitizers. Although it is known that levosimendan and other sensitizers bind to troponin C (cTnC), their in vivo mechanism is not fully understood. Based on levosimendan, we designed a covalent Ca2 + sensitizer (i9) that targets C84 of cTnC and exchanged this complex into cardiac muscle. The NMR structure of the covalent complex showed that i9 binds deep in the hydrophobic pocket of cTnC. Despite slightly reducing troponin I affinity, i9 enhanced the Ca2 + sensitivity of cardiac muscle. We conclude that i9 enhances Ca2 + sensitivity by stabilizing the open conformation of cTnC. These findings provide new insights into the in vivo mechanism of Ca2 + sensitization and demonstrate that directly targeting cTnC has significant potential in cardiovascular therapy. A Ca2 + sensitizer, i9 was designed that forms a covalent bond with C84 of cTnC. i9 stabilized the open state of the N-domain of cTnC. The structure of the covalent cTnC-cTnI-i9 complex was solved by NMR. The structure showed that i9 binds deep in the hydrophobic pocket of cTnC. Despite slightly reducing cTnI affinity, i9 enhanced the Ca2 + sensitivity of cardiac muscle.
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Affiliation(s)
- Sandra E Pineda-Sanabria
- Department of Biochemistry, Faculty of Medicine & Dentistry, University of Alberta, Edmonton, AB T6G 2H7, Canada
| | - Ian M Robertson
- Randall Division of Cell and Molecular Biophysics and British Heart Foundation Centre of Research Excellence, New Hunt's House, Guy's Campus, King's College London, London SE1 1UL, UK
| | - Yin-Biao Sun
- Randall Division of Cell and Molecular Biophysics and British Heart Foundation Centre of Research Excellence, New Hunt's House, Guy's Campus, King's College London, London SE1 1UL, UK
| | - Malcolm Irving
- Randall Division of Cell and Molecular Biophysics and British Heart Foundation Centre of Research Excellence, New Hunt's House, Guy's Campus, King's College London, London SE1 1UL, UK
| | - Brian D Sykes
- Department of Biochemistry, Faculty of Medicine & Dentistry, University of Alberta, Edmonton, AB T6G 2H7, Canada.
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34
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Matsuo T, Takeda S, Oda T, Fujiwara S. Structures of the troponin core domain containing the cardiomyopathy-causing mutants studied by small-angle X-ray scattering. Biophys Physicobiol 2015; 12:145-58. [PMID: 27493864 PMCID: PMC4736830 DOI: 10.2142/biophysico.12.0_145] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2015] [Accepted: 12/01/2015] [Indexed: 12/01/2022] Open
Abstract
Troponin (Tn), consisting of three subunits, TnC, TnI, and TnT, is a protein in the thin filaments in muscle, and, together with another thin-filament protein tropomyosin (Tm), plays a major role in regulation of muscle contraction. Various mutations of Tn cause familial hypertrophic cardiomyopathy. These mutations are directly related to aberrations in this regulatory mechanism. Here we focus on the mutations E244D and K247R of TnT, which reside in the middle of the pathway of the Ca(2+)-binding signal from TnC to Tm. These mutations induce an increase in the maximum tension of cardiac muscle without changes in Ca(2+)-sensitivity. As a first step toward elucidating the molecular mechanism underlying this functional aberration, we carried out small-angle X-ray scattering experiments on the Tn core domain containing the wild type subunits and those containing the mutant TnT in the absence and presence of Ca(2+). Changes in the overall shape induced by the mutations were detected for the first time by the changes in the radius of gyration and the maximum dimension between the wild type and the mutants. Analysis of the scattering curves by model calculations shows that TnC adopts a dumbbell structure regardless of the mutations, and that the mutations change the distributions of the conformational ensembles so that the flexible N- and C-terminal regions of TnT become close to the center of the whole moelcule. This suggests, since these regions are related to the Tn-Tm interactions, that alteration of the Tn-Tm interactions induced by the mutations causes the functional aberration.
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Affiliation(s)
- Tatsuhito Matsuo
- Quantum Beam Science Center, Japan Atomic Energy Agency, Tokai-mura, Naka-gun, Ibaraki 319-1195, Japan
| | - Soichi Takeda
- National Cerebral and Cardiovascular Center Research Institute, Suita, Osaka 565-8565, Japan
| | - Toshiro Oda
- RIKEN SPring-8 center, RIKEN Harima Institute, Sayo, Hyogo 679-5148, Japan
| | - Satoru Fujiwara
- Quantum Beam Science Center, Japan Atomic Energy Agency, Tokai-mura, Naka-gun, Ibaraki 319-1195, Japan
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35
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Langhorn R, Willesen JL. Cardiac Troponins in Dogs and Cats. J Vet Intern Med 2015; 30:36-50. [PMID: 26681537 PMCID: PMC4913658 DOI: 10.1111/jvim.13801] [Citation(s) in RCA: 70] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2015] [Revised: 09/04/2015] [Accepted: 11/03/2015] [Indexed: 11/26/2022] Open
Abstract
Cardiac troponins are sensitive and specific markers of myocardial injury. The troponin concentration can be thought of as a quantitative measure of the degree of injury sustained by the heart, however, it provides no information on the cause of injury or the mechanism of troponin release. Conventionally, the cardiac troponins have been used for diagnosis of acute myocardial infarction in humans and have become the gold standard biomarkers for this indication. They have become increasingly recognized as an objective measure of cardiomyocyte status in both cardiac and noncardiac disease, supplying additional information to that provided by echocardiography and ECG. Injury to cardiomyocytes can occur through a variety of mechanisms with subsequent release of troponins. Independent of the underlying disease or the mechanism of troponin release, the presence of myocardial injury is associated with an increased risk of death. As increasingly sensitive assays are introduced, the frequent occurrence of myocardial injury is becoming apparent, and our understanding of its causes and importance is constantly evolving. Presently troponins are valuable for detecting a subgroup of patients with higher risk of death. Future research is needed to clarify whether troponins can serve as monitoring tools guiding treatment, whether administering more aggressive treatment to patients with evidence of myocardial injury is beneficial, and whether normalizing of troponin concentrations in patients presenting with evidence of myocardial injury is associated with reduced risk of death.
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Affiliation(s)
- R Langhorn
- Department of Veterinary Clinical and Animal Sciences, University of Copenhagen, Frederiksberg C, Denmark
| | - J L Willesen
- Department of Veterinary Clinical and Animal Sciences, University of Copenhagen, Frederiksberg C, Denmark
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Sheng JJ, Jin JP. TNNI1, TNNI2 and TNNI3: Evolution, regulation, and protein structure-function relationships. Gene 2015; 576:385-94. [PMID: 26526134 DOI: 10.1016/j.gene.2015.10.052] [Citation(s) in RCA: 66] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2015] [Revised: 09/21/2015] [Accepted: 10/20/2015] [Indexed: 12/11/2022]
Abstract
Troponin I (TnI) is the inhibitory subunit of the troponin complex in the sarcomeric thin filament of striated muscle and plays a central role in the calcium regulation of contraction and relaxation. Vertebrate TnI has evolved into three isoforms encoded by three homologous genes: TNNI1 for slow skeletal muscle TnI, TNNI2 for fast skeletal muscle TnI and TNNI3 for cardiac TnI, which are expressed under muscle type-specific and developmental regulations. To summarize the current knowledge on the TnI isoform genes and products, this review focuses on the evolution, gene regulation, posttranslational modifications, and structure-function relationship of TnI isoform proteins. Their physiological and medical significances are also discussed.
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Affiliation(s)
- Juan-Juan Sheng
- Department of Physiology, Wayne State University School of Medicine, Detroit, MI 48201, USA
| | - Jian-Ping Jin
- Department of Physiology, Wayne State University School of Medicine, Detroit, MI 48201, USA.
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Lindert S, Cheng Y, Kekenes-Huskey P, Regnier M, McCammon JA. Effects of HCM cTnI mutation R145G on troponin structure and modulation by PKA phosphorylation elucidated by molecular dynamics simulations. Biophys J 2015; 108:395-407. [PMID: 25606687 DOI: 10.1016/j.bpj.2014.11.3461] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2014] [Revised: 11/21/2014] [Accepted: 11/21/2014] [Indexed: 10/24/2022] Open
Abstract
Cardiac troponin (cTn) is a key molecule in the regulation of human cardiac muscle contraction. The N-terminal cardiac-specific peptide of the inhibitory subunit of troponin, cTnI (cTnI(1-39)), is a target for phosphorylation by protein kinase A (PKA) during β-adrenergic stimulation. We recently presented evidence indicating that this peptide interacts with the inhibitory peptide (cTnl(137-147)) when S23 and S24 are phosphorylated. The inhibitory peptide is also the target of the point mutation cTnI-R145G, which is associated with hypertrophic cardiomyopathy (HCM), a disease associated with sudden death in apparently healthy young adults. It has been shown that both phosphorylation and this mutation alter the cTnC-cTnI (C-I) interaction, which plays a crucial role in modulating contractile activation. However, little is known about the molecular-level events underlying this modulation. Here, we computationally investigated the effects of the cTnI-R145G mutation on the dynamics of cTn, cTnC Ca(2+) handling, and the C-I interaction. Comparisons were made with the cTnI-R145G/S23D/S24D phosphomimic mutation, which has been used both experimentally and computationally to study the cTnI N-terminal specific effects of PKA phosphorylation. Additional comparisons between the phosphomimic mutations and the real phosphorylations were made. For this purpose, we ran triplicate 150 ns molecular dynamics simulations of cTnI-R145G Ca(2+)-bound cTnC(1-161)-cTnI(1-172)-cTnT(236-285), cTnI-R145G/S23D/S24D Ca(2+)-bound cTnC(1-161)-cTnI(1-172)-cTnT(236-285), and cTnI-R145G/PS23/PS24 Ca(2+)-bound cTnC(1-161)-cTnI(1-172)-cTnT(236-285), respectively. We found that the cTnI-R145G mutation did not impact the overall dynamics of cTn, but stabilized crucial Ca(2+)-coordinating interactions. However, the phosphomimic mutations increased overall cTn fluctuations and destabilized Ca(2+) coordination. Interestingly, cTnI-R145G blunted the intrasubunit interactions between the cTnI N-terminal extension and the cTnI inhibitory peptide, which have been suggested to play a crucial role in modulating troponin function during β-adrenergic stimulation. These findings offer a molecular-level explanation for how the HCM mutation cTnI-R145G reduces the modulation of cTn by phosphorylation of S23/S24 during β-adrenergic stimulation.
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Affiliation(s)
- Steffen Lindert
- Department of Pharmacology, University of California San Diego, La Jolla, California; NSF Center for Theoretical Biological Physics, La Jolla, California.
| | - Yuanhua Cheng
- Department of Bioengineering, University of Washington, Seattle, Washington
| | - Peter Kekenes-Huskey
- Department of Pharmacology, University of California San Diego, La Jolla, California; Department of Chemistry, University of Kentucky, Lexington, Kentucky
| | - Michael Regnier
- Department of Bioengineering, University of Washington, Seattle, Washington
| | - J Andrew McCammon
- Department of Pharmacology, University of California San Diego, La Jolla, California; Howard Hughes Medical Institute, University of California San Diego, La Jolla, California; Department of Chemistry and Biochemistry, National Biomedical Computation Resource, University of California San Diego, La Jolla, California; NSF Center for Theoretical Biological Physics, La Jolla, California
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Votapka LW, Amaro RE. Multiscale Estimation of Binding Kinetics Using Brownian Dynamics, Molecular Dynamics and Milestoning. PLoS Comput Biol 2015; 11:e1004381. [PMID: 26505480 PMCID: PMC4624728 DOI: 10.1371/journal.pcbi.1004381] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2015] [Accepted: 06/04/2015] [Indexed: 12/16/2022] Open
Abstract
The kinetic rate constants of binding were estimated for four biochemically relevant molecular systems by a method that uses milestoning theory to combine Brownian dynamics simulations with more detailed molecular dynamics simulations. The rate constants found using this method agreed well with experimentally and theoretically obtained values. We predicted the association rate of a small charged molecule toward both a charged and an uncharged spherical receptor and verified the estimated value with Smoluchowski theory. We also calculated the kon rate constant for superoxide dismutase with its natural substrate, O2-, in a validation of a previous experiment using similar methods but with a number of important improvements. We also calculated the kon for a new system: the N-terminal domain of Troponin C with its natural substrate Ca2+. The kon calculated for the latter two systems closely resemble experimentally obtained values. This novel multiscale approach is computationally cheaper and more parallelizable when compared to other methods of similar accuracy. We anticipate that this methodology will be useful for predicting kinetic rate constants and for understanding the process of binding between a small molecule and a protein receptor.
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Affiliation(s)
- Lane W. Votapka
- Department of Chemistry and Biochemistry and National Biomedical Computation Resource, University of California, San Diego, San Diego, California, United States of America
| | - Rommie E. Amaro
- Department of Chemistry and Biochemistry and National Biomedical Computation Resource, University of California, San Diego, San Diego, California, United States of America
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The structural and functional effects of the familial hypertrophic cardiomyopathy-linked cardiac troponin C mutation, L29Q. J Mol Cell Cardiol 2015; 87:257-69. [PMID: 26341255 PMCID: PMC4640586 DOI: 10.1016/j.yjmcc.2015.08.017] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/31/2015] [Revised: 08/09/2015] [Accepted: 08/23/2015] [Indexed: 01/02/2023]
Abstract
Familial hypertrophic cardiomyopathy (FHC) is characterized by severe abnormal cardiac muscle growth. The traditional view of disease progression in FHC is that an increase in the Ca2 +-sensitivity of cardiac muscle contraction ultimately leads to pathogenic myocardial remodeling, though recent studies suggest this may be an oversimplification. For example, FHC may be developed through altered signaling that prevents downstream regulation of contraction. The mutation L29Q, found in the Ca2 +-binding regulatory protein in heart muscle, cardiac troponin C (cTnC), has been linked to cardiac hypertrophy. However, reports on the functional effects of this mutation are conflicting, and our goal was to combine in vitro and in situ structural and functional data to elucidate its mechanism of action. We used nuclear magnetic resonance and circular dichroism to solve the structure and characterize the backbone dynamics and stability of the regulatory domain of cTnC with the L29Q mutation. The overall structure and dynamics of cTnC were unperturbed, although a slight rearrangement of site 1, an increase in backbone flexibility, and a small decrease in protein stability were observed. The structure and function of cTnC was also assessed in demembranated ventricular trabeculae using fluorescence for in situ structure. L29Q reduced the cooperativity of the Ca2 +-dependent structural change in cTnC in trabeculae under basal conditions and abolished the effect of force-generating myosin cross-bridges on this structural change. These effects could contribute to the pathogenesis of this mutation. The cTnC L29Q mutation causes a small change in the NMR structure of site 1 in cTnC. L29Q reduces the cooperativity of Ca2 +-dependent structural changes in cTnC in situ. L29Q removes the impact of force-generating myosin heads on cTnC structural changes.
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Yang Y, Shi C, Hou X, Zhao Y, Chen B, Tan B, Deng Z, Li Q, Liu J, Xiao Z, Miao Q, Dai J. Modified VEGF targets the ischemic myocardium and promotes functional recovery after myocardial infarction. J Control Release 2015; 213:27-35. [PMID: 26144351 DOI: 10.1016/j.jconrel.2015.06.036] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2015] [Revised: 06/25/2015] [Accepted: 06/29/2015] [Indexed: 02/07/2023]
Abstract
Vascular endothelial growth factor (VEGF) promotes angiogenesis and improves cardiac function after myocardial infarction (MI). However, the non-targeted delivery of VEGF decreases its therapeutic efficacy due to an insufficient local concentration in the ischemic myocardium. In this study, we used a specific peptide to modify VEGF and determined that this modified VEGF (IMT-VEGF) localized to the ischemic myocardium through intravenous injection by interacting with cardiac troponin I (cTnI). When IMT-VEGF was used to mediate cardiac repair in a rat model of ischemia-reperfusion (I-R) injury, we observed a decreased scar size, enhanced angiogenesis and improved cardiac function. Moreover, an alternative treatment using the repeated administration of a low-dose IMT-VEGF also promoted angiogenesis and functional recovery. The therapeutic effects of IMT-VEGF were further confirmed in a pig model of MI as the result of the conserved properties of its interacting protein, cTnI. These results suggest a promising therapeutic strategy for MI based on the targeted delivery of IMT-VEGF.
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Affiliation(s)
- Yun Yang
- State Key Laboratory of Molecular Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, 3 Nanyitiao, Zhongguancun, Beijing, 100190, China; Graduate School, Chinese Academy of Sciences, 3 Nanyitiao, Zhongguancun, Beijing, 100190, China
| | - Chunying Shi
- State Key Laboratory of Molecular Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, 3 Nanyitiao, Zhongguancun, Beijing, 100190, China; Institute for Translational Medicine, College of Medicine, Qingdao University, 308 Ningxia Road, Qingdao, 266021, China
| | - Xianglin Hou
- State Key Laboratory of Molecular Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, 3 Nanyitiao, Zhongguancun, Beijing, 100190, China; Institute of Combined Injury, State Key Laboratory of Trauma, Burns and Combined Injury, College of Preventive Medicine, Third Military Medical University, 30 Gaotanyan Road, Chongqing, 400038, China
| | - Yannan Zhao
- State Key Laboratory of Molecular Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, 3 Nanyitiao, Zhongguancun, Beijing, 100190, China; Institute of Combined Injury, State Key Laboratory of Trauma, Burns and Combined Injury, College of Preventive Medicine, Third Military Medical University, 30 Gaotanyan Road, Chongqing, 400038, China
| | - Bing Chen
- State Key Laboratory of Molecular Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, 3 Nanyitiao, Zhongguancun, Beijing, 100190, China; Institute of Combined Injury, State Key Laboratory of Trauma, Burns and Combined Injury, College of Preventive Medicine, Third Military Medical University, 30 Gaotanyan Road, Chongqing, 400038, China
| | - Bo Tan
- Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, 398 Ruoshui Road, Suzhou, 215123, China
| | - Zongwu Deng
- Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, 398 Ruoshui Road, Suzhou, 215123, China
| | - Qingguo Li
- Department of Cardiothoracic Surgery, the affiliated Drum Tower Hospital of Nanjing University Medical School, 321 Zhongshan Road, Nanjing, 210008, China
| | - Jianzhou Liu
- Department of Cardiac Surgery, Peking Union Medical College Hospital, Peking Union Medical College, 1 Shuaifuyuan, Beijing, 100730, China
| | - Zhifeng Xiao
- State Key Laboratory of Molecular Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, 3 Nanyitiao, Zhongguancun, Beijing, 100190, China; Institute of Combined Injury, State Key Laboratory of Trauma, Burns and Combined Injury, College of Preventive Medicine, Third Military Medical University, 30 Gaotanyan Road, Chongqing, 400038, China
| | - Qi Miao
- Department of Cardiac Surgery, Peking Union Medical College Hospital, Peking Union Medical College, 1 Shuaifuyuan, Beijing, 100730, China
| | - Jianwu Dai
- State Key Laboratory of Molecular Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, 3 Nanyitiao, Zhongguancun, Beijing, 100190, China; Institute of Combined Injury, State Key Laboratory of Trauma, Burns and Combined Injury, College of Preventive Medicine, Third Military Medical University, 30 Gaotanyan Road, Chongqing, 400038, China.
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41
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Pineda-Sanabria SE, Robertson IM, Sykes BD. Structure and Dynamics of the Acidosis-Resistant A162H Mutant of the Switch Region of Troponin I Bound to the Regulatory Domain of Troponin C. Biochemistry 2015; 54:3583-93. [DOI: 10.1021/acs.biochem.5b00178] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Affiliation(s)
- Sandra E. Pineda-Sanabria
- Department of Biochemistry, ‡Department of Pediatrics, Faculty of Medicine & Dentistry, University of Alberta, Edmonton, AB T6G 2H7, Canada
| | - Ian M. Robertson
- Department of Biochemistry, ‡Department of Pediatrics, Faculty of Medicine & Dentistry, University of Alberta, Edmonton, AB T6G 2H7, Canada
| | - Brian D. Sykes
- Department of Biochemistry, ‡Department of Pediatrics, Faculty of Medicine & Dentistry, University of Alberta, Edmonton, AB T6G 2H7, Canada
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42
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Cordina NM, Liew CK, Potluri PR, Curmi PM, Fajer PG, Logan TM, Mackay JP, Brown LJ. Ca2+-induced PRE-NMR changes in the troponin complex reveal the possessive nature of the cardiac isoform for its regulatory switch. PLoS One 2014; 9:e112976. [PMID: 25392916 PMCID: PMC4231091 DOI: 10.1371/journal.pone.0112976] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2014] [Accepted: 10/17/2014] [Indexed: 11/19/2022] Open
Abstract
The interaction between myosin and actin in cardiac muscle, modulated by the calcium (Ca2+) sensor Troponin complex (Tn), is a complex process which is yet to be fully resolved at the molecular level. Our understanding of how the binding of Ca2+ triggers conformational changes within Tn that are subsequently propagated through the contractile apparatus to initiate muscle activation is hampered by a lack of an atomic structure for the Ca2+-free state of the cardiac isoform. We have used paramagnetic relaxation enhancement (PRE)-NMR to obtain a description of the Ca2+-free state of cardiac Tn by describing the movement of key regions of the troponin I (cTnI) subunit upon the release of Ca2+ from Troponin C (cTnC). Site-directed spin-labeling was used to position paramagnetic spin labels in cTnI and the changes in the interaction between cTnI and cTnC subunits were then mapped by PRE-NMR. The functionally important regions of cTnI targeted in this study included the cTnC-binding N-region (cTnI57), the inhibitory region (cTnI143), and two sites on the regulatory switch region (cTnI151 and cTnI159). Comparison of 1H-15N-TROSY spectra of Ca2+-bound and free states for the spin labeled cTnC-cTnI binary constructs demonstrated the release and modest movement of the cTnI switch region (∼10 Å) away from the hydrophobic N-lobe of troponin C (cTnC) upon the removal of Ca2+. Our data supports a model where the non-bound regulatory switch region of cTnI is highly flexible in the absence of Ca2+ but remains in close vicinity to cTnC. We speculate that the close proximity of TnI to TnC in the cardiac complex is favourable for increasing the frequency of collisions between the N-lobe of cTnC and the regulatory switch region, counterbalancing the reduction in collision probability that results from the incomplete opening of the N-lobe of TnC that is unique to the cardiac isoform.
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Affiliation(s)
- Nicole M. Cordina
- Department of Chemistry and Biomolecular Sciences, Macquarie University, Sydney, New South Wales, Australia
| | - Chu K. Liew
- Department of Molecular Cardiology and Biophysics, The Victor Chang Cardiac Research Institute, Darlinghurst, New South Wales, Australia
| | - Phani R. Potluri
- Department of Chemistry and Biomolecular Sciences, Macquarie University, Sydney, New South Wales, Australia
| | - Paul M. Curmi
- School of Physics, The University of New South Wales, Sydney, New South Wales, Australia
| | - Piotr G. Fajer
- Institute of Molecular Biophysics, Florida State University, Tallahassee, Florida, United States of America
| | - Timothy M. Logan
- Institute of Molecular Biophysics, Florida State University, Tallahassee, Florida, United States of America
| | - Joel P. Mackay
- School of Molecular and Microbial Biosciences, University of Sydney, Sydney, New South Wales, Australia
| | - Louise J. Brown
- Department of Chemistry and Biomolecular Sciences, Macquarie University, Sydney, New South Wales, Australia
- * E-mail:
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43
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Pineda-Sanabria SE, Julien O, Sykes BD. Versatile cardiac troponin chimera for muscle protein structural biology and drug discovery. ACS Chem Biol 2014; 9:2121-30. [PMID: 25010113 DOI: 10.1021/cb500249j] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Investigation of the molecular interactions within and between subunits of the heterotrimeric troponin complex, and with other proteins in the sarcomere, has revealed salient structural elements involved in regulation of muscle contraction. The discovery of new cardiotonic drugs and structural studies utilizing intact troponin, or regulatory complexes formed between the key regions identified in troponin C and troponin I, face intrinsic and technical difficulties associated with weak protein-protein interactions and with solubility, aggregation, stability of the overall architecture, isotope labeling, and size, respectively. We have designed and characterized a chimeric troponin C-troponin I hybrid protein with a cleavable linker that is useful for producing isotopically labeled troponin peptides, stabilizes their interaction, and has proven to be a faithful representation of the original complex in the systolic state, but lacking its disadvantages, making it particularly suitable for drug screening and structural studies.
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Affiliation(s)
- Sandra E. Pineda-Sanabria
- Department of Biochemistry, University of Alberta, 4-19 Medical
Sciences Building, Edmonton, Alberta Canada, T6G 2H7
| | - Olivier Julien
- Department of Biochemistry, University of Alberta, 4-19 Medical
Sciences Building, Edmonton, Alberta Canada, T6G 2H7
| | - Brian D. Sykes
- Department of Biochemistry, University of Alberta, 4-19 Medical
Sciences Building, Edmonton, Alberta Canada, T6G 2H7
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44
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Lindert S, Li MX, Sykes BD, McCammon JA. Computer-aided drug discovery approach finds calcium sensitizer of cardiac troponin. Chem Biol Drug Des 2014; 85:99-106. [PMID: 24954187 DOI: 10.1111/cbdd.12381] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2014] [Revised: 05/27/2014] [Accepted: 06/04/2014] [Indexed: 11/28/2022]
Abstract
In the fight against heart failure, therapeutics that have the ability to increase the contractile power of the heart are urgently needed. One possible route of action to improve heart contractile power is increasing the calcium sensitivity of the thin filament. From a pharmaceutical standpoint, calcium sensitizers have the distinct advantage of not altering cardiomyocyte calcium levels and thus have lower potential for side-effects. Small chemical molecules have been shown to bind to the interface between cTnC and the cTnI switch peptide and exhibit calcium-sensitizing properties, possibly by stabilizing cTnC in an open conformation. Building on existing structural data of a known calcium sensitizer bound to cardiac troponin, we combined computational structure-based virtual screening drug discovery methods and solution NMR titration assays to identify a novel calcium sensitizer 4-(4-(2,5-dimethylphenyl)-1-piperazinyl)-3-pyridinamine (NSC147866) which binds to cTnC and the cTnC-cTnI147-163 complex. Its presence increases the affinity of switch peptide to cTnC by approximately a factor of two. This action is comparable to that of known levosimendan analogues.
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Affiliation(s)
- Steffen Lindert
- Department of Pharmacology, University of California San Diego, La Jolla, CA, 92093, USA; NSF Center for Theoretical Biological Physics, La Jolla, CA, 92093, USA
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45
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Ueda K, Kimura-Sakiyama C, Aihara T, Miki M, Arata T. Calcium-dependent interaction sites of tropomyosin on reconstituted muscle thin filaments with bound Myosin heads as studied by site-directed spin-labeling. Biophys J 2014; 105:2366-73. [PMID: 24268148 DOI: 10.1016/j.bpj.2013.10.002] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2013] [Revised: 09/09/2013] [Accepted: 10/01/2013] [Indexed: 11/29/2022] Open
Abstract
To identify the interaction sites of Tm, we measured the rotational motion of a spin-label covalently bound to the side chain of a cysteine that was genetically incorporated into rabbit skeletal muscle tropomyosin (Tm) at positions 13, 36, 146, 160, 174, 190, 209, 230, 271, or 279. Most of the Tm residues were immobilized on actin filaments with myosin-S1 bound to them. The residues in the mid-portion of Tm, namely, 146, 174, 190, 209, and 230, were mobilized when the troponin (Tn) complex bound to the actin-Tm-S1 filaments. The addition of Ca(2+) ions partially reversed the Tn-induced mobilization. In contrast, residues at the joint region of Tm, 13, 36, 271, and 279 were unchanged or oppositely changed. All of these changes were detected using a maleimide spin label and less obviously using a methanesulfonate label. These results indicated that Tm was fixed on thin filaments with myosin bound to them, although a small change in the flexibility of the side chains of Tm residues, presumably interfaced with Tn, actin and myosin, was induced by the binding of Tn and Ca(2+). These findings suggest that even in the myosin-bound (open) state, Ca(2+) may regulate actomyosin contractile properties via Tm.
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Affiliation(s)
- Keisuke Ueda
- Department of Biological Sciences, Graduate School of Science, Osaka University, Osaka, Japan
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46
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Robertson IM, Pineda-Sanabria SE, Holmes PC, Sykes BD. Conformation of the critical pH sensitive region of troponin depends upon a single residue in troponin I. Arch Biochem Biophys 2014; 552-553:40-9. [DOI: 10.1016/j.abb.2013.12.003] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2013] [Revised: 11/18/2013] [Accepted: 12/05/2013] [Indexed: 12/20/2022]
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47
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Sheng JJ, Jin JP. Gene regulation, alternative splicing, and posttranslational modification of troponin subunits in cardiac development and adaptation: a focused review. Front Physiol 2014; 5:165. [PMID: 24817852 PMCID: PMC4012202 DOI: 10.3389/fphys.2014.00165] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2014] [Accepted: 04/10/2014] [Indexed: 12/19/2022] Open
Abstract
Troponin plays a central role in regulating the contraction and relaxation of vertebrate striated muscles. This review focuses on the isoform gene regulation, alternative RNA splicing, and posttranslational modifications of troponin subunits in cardiac development and adaptation. Transcriptional and posttranscriptional regulations such as phosphorylation and proteolysis modifications, and structure-function relationships of troponin subunit proteins are summarized. The physiological and pathophysiological significances are discussed for impacts on cardiac muscle contractility, heart function, and adaptations in health and diseases.
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Affiliation(s)
- Juan-Juan Sheng
- Department of Physiology, Wayne State University School of Medicine Detroit, MI, USA
| | - Jian-Ping Jin
- Department of Physiology, Wayne State University School of Medicine Detroit, MI, USA
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48
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Swindle N, Albury ANJ, Baroud B, Burney M, Tikunova SB. Molecular and functional consequences of mutations in the central helix of cardiac troponin C. Arch Biochem Biophys 2014; 548:46-53. [PMID: 24650606 DOI: 10.1016/j.abb.2014.03.004] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2014] [Revised: 03/04/2014] [Accepted: 03/05/2014] [Indexed: 01/28/2023]
Abstract
The objective of this work was to investigate the role of acidic residues within the exposed middle segment of the central helix of cTnC in (1) cTnC-cTnI interactions, (2) Ca(2+) binding and exchange with the regulatory N-domain of cTnC in increasingly complex biochemical systems, and (3) ability of the cTn complex to regulate actomyosin ATPase. In order to achieve this objective, we introduced the D87A/D88A and E94A/E95A/E96A mutations into the central helix of cTnC. The D87A/D88A and E94A/E95A/E96A mutations decreased affinity of cTnC for the regulatory region of cTnI. The Ca(2+) sensitivity of the regulatory N-domain of isolated cTnC was decreased by the D87A/D88A, but not E94A/E95A/E96A mutation. However, both the D87A/D88A and E94A/E95A/E96A mutations desensitized the cTn complex and reconstituted thin filaments to Ca(2+). Decreases in the Ca(2+) sensitivity of the cTn complex and reconstituted thin filaments were, at least in part, due to faster rates of Ca(2+) dissociation. In addition, the D87A/D88A and E94A/E95A/E96A mutations desensitized actomyosin ATPase to Ca(2+), and decreased maximal actomyosin ATPase activity. Thus, our results indicate that conserved acidic residues within the exposed middle segment of the central helix of cTnC are important for the proper regulatory function of the cTn complex.
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Affiliation(s)
- Nicholas Swindle
- Department of Pharmacological and Pharmaceutical Sciences, University of Houston, Houston, TX 77004, United States
| | - Acchia N J Albury
- Department of Biology, Wingate University, Wingate, NC 28174, United States
| | - Belal Baroud
- Department of Pharmacological and Pharmaceutical Sciences, University of Houston, Houston, TX 77004, United States
| | - Maryam Burney
- Department of Pharmacological and Pharmaceutical Sciences, University of Houston, Houston, TX 77004, United States
| | - Svetlana B Tikunova
- Department of Pharmacological and Pharmaceutical Sciences, University of Houston, Houston, TX 77004, United States.
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49
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Posttranslational modifications of cardiac troponin T: An overview. J Mol Cell Cardiol 2013; 63:47-56. [DOI: 10.1016/j.yjmcc.2013.07.004] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/21/2013] [Revised: 06/18/2013] [Accepted: 07/08/2013] [Indexed: 12/22/2022]
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50
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Structural basis for the in situ Ca(2+) sensitization of cardiac troponin C by positive feedback from force-generating myosin cross-bridges. Arch Biochem Biophys 2013; 537:198-209. [PMID: 23896515 DOI: 10.1016/j.abb.2013.07.013] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2013] [Revised: 07/10/2013] [Accepted: 07/11/2013] [Indexed: 11/21/2022]
Abstract
The in situ structural coupling between the cardiac troponin (cTn) Ca(2+)-sensitive regulatory switch (CRS) and strong myosin cross-bridges was investigated using Förster resonance energy transfer (FRET). The double cysteine mutant cTnC(T13C/N51C) was fluorescently labeled with the FRET pair 5-(iodoacetamidoethyl)aminonaphthelene-1-sulfonic acid (IAEDENS) and N-(4-dimethylamino-3,5-dinitrophenyl)maleimide (DDPM) and then incorporated into detergent skinned left ventricular papillary fiber bundles. Ca(2+) titrations of cTnC(T13C/N51C)AEDENS/DDPM-reconstituted fibers showed that the Ca(2+)-dependence of the opening of the N-domain of cTnC (N-cTnC) statistically matched the force-Ca(2+) relationship. N-cTnC opening still occurred steeply during Ca(2+) titrations in the presence of 1mM vanadate, but the maximal extent of ensemble-averaged N-cTnC opening and the Ca(2+)-sensitivity of the CRS were significantly reduced. At nanomolar, resting Ca(2+) levels, treatment with ADP·Mg in the absence of ATP caused a partial opening of N-cTnC. During subsequent Ca(2+) titrations in the presence of ADP·Mg and absence of ATP, further N-cTnC opening was stimulated as the CRS responded to Ca(2+) with increased Ca(2+)-sensitivity and reduced steepness. These findings supported our hypothesis here that strong cross-bridge interactions with the cardiac thin filament exert a Ca(2+)-sensitizing effect on the CRS by stabilizing the interaction between the exposed hydrophobic patch of N-cTnC and the switch region of cTnI.
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