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Guo J, Jiang H, Schuftan D, Moreno JD, Ramahdita G, Aryan L, Bhagavan D, Silva J, Huebsch N. Substrate mechanics unveil early structural and functional pathology in iPSC micro-tissue models of hypertrophic cardiomyopathy. iScience 2024; 27:109954. [PMID: 38827401 PMCID: PMC11141149 DOI: 10.1016/j.isci.2024.109954] [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: 12/06/2023] [Revised: 03/22/2024] [Accepted: 05/08/2024] [Indexed: 06/04/2024] Open
Abstract
Hypertension is a major cause of morbidity and mortality in patients with hypertrophic cardiomyopathy (HCM), suggesting a potential role for mechanics in HCM pathogenesis. Here, we developed an in vitro physiological model to investigate how mechanics acts together with HCM-linked myosin binding protein C (MYBPC3) mutations to trigger disease. Micro-heart muscles (μHM) were engineered from induced pluripotent stem cell (iPSC)-derived cardiomyocytes bearing MYBPC3+/- mutations and challenged to contract against substrates of different elasticity. μHMs that worked against substrates with stiffness at or exceeding the stiffness of healthy adult heart muscle exhibited several hallmarks of HCM, including cellular hypertrophy, impaired contractile energetics, and maladaptive calcium handling. Remarkably, we discovered changes in troponin C and T localization in MYBPC3+/- μHM that were entirely absent in 2D culture. Pharmacologic studies suggested that excessive Ca2+ intake through membrane-embedded channels underlie the observed electrophysiological abnormalities. These results illustrate the power of physiologically relevant engineered tissue models to study inherited disease with iPSC technology.
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Affiliation(s)
- Jingxuan Guo
- Department of Mechanical Engineering and Material Science, Washington University in Saint Louis, Saint Louis, MO 63130, USA
| | - Huanzhu Jiang
- Department of Biomedical Engineering, Washington University in Saint Louis, Saint Louis, MO 63130, USA
| | - David Schuftan
- Department of Biomedical Engineering, Washington University in Saint Louis, Saint Louis, MO 63130, USA
| | - Jonathan D. Moreno
- Division of Cardiology, Department of Medicine, Washington University in Saint Louis, Saint Louis, MO 63130, USA
| | - Ghiska Ramahdita
- Department of Mechanical Engineering and Material Science, Washington University in Saint Louis, Saint Louis, MO 63130, USA
- NSF Science and Technology Center for Engineering Mechanobiology, Washington University in Saint Louis, Saint Louis, MO 63130, USA
| | - Lavanya Aryan
- Department of Biomedical Engineering, Washington University in Saint Louis, Saint Louis, MO 63130, USA
| | - Druv Bhagavan
- Department of Biomedical Engineering, Washington University in Saint Louis, Saint Louis, MO 63130, USA
| | - Jonathan Silva
- Department of Biomedical Engineering, Washington University in Saint Louis, Saint Louis, MO 63130, USA
| | - Nathaniel Huebsch
- Department of Biomedical Engineering, Washington University in Saint Louis, Saint Louis, MO 63130, USA
- NSF Science and Technology Center for Engineering Mechanobiology, Washington University in Saint Louis, Saint Louis, MO 63130, USA
- Center for Cardiovascular Research, Center for Regenerative Medicine, Center for Investigation of Membrane Excitability Diseases, Washington University in Saint Louis, Saint Louis, MO 63130, USA
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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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3
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Barry ME, Rynkiewicz MJ, Pavadai E, Viana A, Lehman W, Moore JR. Glutamate 139 of tropomyosin is critical for cardiac thin filament blocked-state stabilization. J Mol Cell Cardiol 2024; 188:30-37. [PMID: 38266978 DOI: 10.1016/j.yjmcc.2024.01.004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/16/2023] [Revised: 12/14/2023] [Accepted: 01/20/2024] [Indexed: 01/26/2024]
Abstract
The cardiac thin filament proteins troponin and tropomyosin control actomyosin formation and thus cardiac contractility. Calcium binding to troponin changes tropomyosin position along the thin filament, allowing myosin head binding to actin required for heart muscle contraction. The thin filament regulatory proteins are hot spots for genetic mutations causing heart muscle dysfunction. While much of the thin filament structure has been characterized, critical regions of troponin and tropomyosin involved in triggering conformational changes remain unresolved. A poorly resolved region, helix-4 (H4) of troponin I, is thought to stabilize tropomyosin in a position on actin that blocks actomyosin interactions at low calcium concentrations during muscle relaxation. We have proposed that contact between glutamate 139 on tropomyosin and positively charged residues on H4 leads to blocking-state stabilization. In this study, we attempted to disrupt these interactions by replacing E139 with lysine (E139K) to define the importance of this residue in thin filament regulation. Comparison of mutant and wild-type tropomyosin was carried out using in-vitro motility assays, actin co-sedimentation, and molecular dynamics simulations to determine perturbations in troponin-tropomyosin function caused by the tropomyosin mutation. Motility assays revealed that mutant thin filaments moved at higher velocity at low calcium with increased calcium sensitivity demonstrating that tropomyosin residue 139 is vital for proper tropomyosin-mediated inhibition during relaxation. Similarly, molecular dynamic simulations revealed a mutation-induced decrease in interaction energy between tropomyosin-E139K and troponin I (R170 and K174). These results suggest that salt-bridge stabilization of tropomyosin position by troponin IH4 is essential to prevent actomyosin interactions during cardiac muscle relaxation.
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Affiliation(s)
- Meaghan E Barry
- Department of Biological Sciences, University of Massachusetts Lowell, One University Ave, Lowell, MA 01854, United States of America
| | - Michael J Rynkiewicz
- Department of Pharmacology, Physiology & Biophysics, Boston University Chobanian and Avedisan School of Medicine, 700 Albany Street, W-408E, Boston, MA 02118, United States of America
| | - Elumalai Pavadai
- Department of Pharmacology, Physiology & Biophysics, Boston University Chobanian and Avedisan School of Medicine, 700 Albany Street, W-408E, Boston, MA 02118, United States of America
| | - Alex Viana
- Department of Biological Sciences, University of Massachusetts Lowell, One University Ave, Lowell, MA 01854, United States of America
| | - William Lehman
- Department of Pharmacology, Physiology & Biophysics, Boston University Chobanian and Avedisan School of Medicine, 700 Albany Street, W-408E, Boston, MA 02118, United States of America
| | - Jeffrey R Moore
- Department of Biological Sciences, University of Massachusetts Lowell, One University Ave, Lowell, MA 01854, United States of America.
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Lea TA, Panizza PM, Arthur PG, Bakker AJ, Pinniger GJ. Hypochlorous acid exposure impairs skeletal muscle function and Ca 2+ signalling: implications for Duchenne muscular dystrophy pathology. J Physiol 2023; 601:5257-5275. [PMID: 37864413 DOI: 10.1113/jp285263] [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: 07/11/2023] [Accepted: 10/09/2023] [Indexed: 10/22/2023] Open
Abstract
Duchenne muscular dystrophy (DMD) is a fatal X-linked disease characterised by severe muscle wasting. The mechanisms underlying the DMD pathology likely involve the interaction between inflammation, oxidative stress and impaired Ca2+ signalling. Hypochlorous acid (HOCl) is a highly reactive oxidant produced endogenously via myeloperoxidase; an enzyme secreted by neutrophils that is significantly elevated in dystrophic muscle. Oxidation of Ca2+ -handling proteins by HOCl may impair Ca2+ signalling. This study aimed to determine the effects of HOCl on skeletal muscle function and its potential contribution to the dystrophic pathology. Extensor digitorum longus (EDL), soleus and interosseous muscles were surgically isolated from anaesthetised C57 (wild-type) and mdx (dystrophic) mice for measurement of ex vivo force production and intracellular Ca2+ concentration. In whole EDL muscle, HOCl (200 μM) significantly decreased maximal force and increased resting muscle tension which was only partially reversible by dithiothreitol. The effects of HOCl (200 μM) on maximal force in slow-twitch soleus were lower than found in the fast-twitch EDL muscle. In single interosseous myofibres, HOCl (10 μM) significantly increased resting intracellular Ca2+ concentration and decreased Ca2+ transient amplitude. These effects of HOCl were reduced by the application of tetracaine, Gd3+ or streptomycin, implicating involvement of ryanodine receptors and transient receptor potential channels. These results demonstrate the potent effects of HOCl on skeletal muscle function potentially mediated by HOCl-induced oxidation to Ca2+ signalling proteins. Hence, HOCl may provide a link between chronic inflammation, oxidative stress and impaired Ca2+ handling that is characteristic of DMD and presents a potential therapeutic target for DMD. KEY POINTS: Duchenne muscular dystrophy is a fatal genetic disease with pathological mechanisms which involve the complex interaction of chronic inflammation, increased reactive oxygen species production and increased cytosolic Ca2+ concentrations. Hypochlorous acid can be endogenously produced by neutrophils via the enzyme myeloperoxidase. Both neutrophil and myeloperoxidase activity are increased in dystrophic mice. This study found that hypochlorous acid decreased muscle force production and increased cytosolic Ca2+ concentrations in isolated muscles from wild-type and dystrophic mice at relatively low concentrations of hypochlorous acid. These results indicate that hypochlorous acid may be key in the Duchenne muscular dystrophy disease pathology and may provide a unifying link between the chronic inflammation, increased reactive oxygen species production and increased cytosolic Ca2+ concentrations observed in Duchenne muscular dystrophy. Hypochlorous acid production may be a potential target for therapeutic treatments of Duchenne muscular dystrophy.
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Affiliation(s)
- Thomas A Lea
- School of Human Sciences, University of Western Australia, Perth, Western Australia, Australia
| | - Peter M Panizza
- School of Human Sciences, University of Western Australia, Perth, Western Australia, Australia
| | - Peter G Arthur
- School of Molecular Sciences, University of Western Australia, Perth, Western Australia, Australia
| | - Anthony J Bakker
- School of Human Sciences, University of Western Australia, Perth, Western Australia, Australia
| | - Gavin J Pinniger
- School of Human Sciences, University of Western Australia, Perth, Western Australia, Australia
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Guo J, Jiang H, Schuftan D, Moreno JD, Ramahdita G, Aryan L, Bhagavan D, Silva J, Huebsch N. Mechanical Resistance to Micro-Heart Tissue Contractility unveils early Structural and Functional Pathology in iPSC Models of Hypertrophic Cardiomyopathy. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.10.30.564856. [PMID: 37961198 PMCID: PMC10634965 DOI: 10.1101/2023.10.30.564856] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/15/2023]
Abstract
Hypertrophic cardiomyopathy is the most common cause of sudden death in the young. Because the disease exhibits variable penetrance, there are likely nongenetic factors that contribute to the manifestation of the disease phenotype. Clinically, hypertension is a major cause of morbidity and mortality in patients with HCM, suggesting a potential synergistic role for the sarcomeric mutations associated with HCM and mechanical stress on the heart. We developed an in vitro physiological model to investigate how the afterload that the heart muscle works against during contraction acts together with HCM-linked MYBPC3 mutations to trigger a disease phenotype. Micro-heart muscle arrays (μHM) were engineered from iPSC-derived cardiomyocytes bearing MYBPC3 loss-of-function mutations and challenged to contract against mechanical resistance with substrates stiffnesses ranging from the of embryonic hearts (0.4 kPa) up to the stiffness of fibrotic adult hearts (114 kPa). Whereas MYBPC3 +/- iPSC-cardiomyocytes showed little signs of disease pathology in standard 2D culture, μHMs that included components of afterload revealed several hallmarks of HCM, including cellular hypertrophy, impaired contractile energetics, and maladaptive calcium handling. Remarkably, we discovered changes in troponin C and T localization in the MYBPC3 +/- μHM that were entirely absent in 2D culture. Pharmacologic studies suggested that excessive Ca 2+ intake through membrane-embedded channels, rather than sarcoplasmic reticulum Ca 2+ ATPase (SERCA) dysfunction or Ca 2+ buffering at myofilaments underlie the observed electrophysiological abnormalities. These results illustrate the power of physiologically relevant engineered tissue models to study inherited disease mechanisms with iPSC technology.
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Tikunova SB, Thuma J, Davis JP. Mouse Models of Cardiomyopathies Caused by Mutations in Troponin C. Int J Mol Sci 2023; 24:12349. [PMID: 37569724 PMCID: PMC10419064 DOI: 10.3390/ijms241512349] [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: 07/01/2023] [Revised: 07/27/2023] [Accepted: 08/01/2023] [Indexed: 08/13/2023] Open
Abstract
Cardiac muscle contraction is regulated via Ca2+ exchange with the hetero-trimeric troponin complex located on the thin filament. Binding of Ca2+ to cardiac troponin C, a Ca2+ sensing subunit within the troponin complex, results in a series of conformational re-arrangements among the thin filament components, leading to an increase in the formation of actomyosin cross-bridges and muscle contraction. Ultimately, a decline in intracellular Ca2+ leads to the dissociation of Ca2+ from troponin C, inhibiting cross-bridge cycling and initiating muscle relaxation. Therefore, troponin C plays a crucial role in the regulation of cardiac muscle contraction and relaxation. Naturally occurring and engineered mutations in troponin C can lead to altered interactions among components of the thin filament and to aberrant Ca2+ binding and exchange with the thin filament. Mutations in troponin C have been associated with various forms of cardiac disease, including hypertrophic, restrictive, dilated, and left ventricular noncompaction cardiomyopathies. Despite progress made to date, more information from human studies, biophysical characterizations, and animal models is required for a clearer understanding of disease drivers that lead to cardiomyopathies. The unique use of engineered cardiac troponin C with the L48Q mutation that had been thoroughly characterized and genetically introduced into mouse myocardium clearly demonstrates that Ca2+ sensitization in and of itself should not necessarily be considered a disease driver. This opens the door for small molecule and protein engineering strategies to help boost impaired systolic function. On the other hand, the engineered troponin C mutants (I61Q and D73N), genetically introduced into mouse myocardium, demonstrate that Ca2+ desensitization under basal conditions may be a driving factor for dilated cardiomyopathy. In addition to enhancing our knowledge of molecular mechanisms that trigger hypertrophy, dilation, morbidity, and mortality, these cardiomyopathy mouse models could be used to test novel treatment strategies for cardiovascular diseases. In this review, we will discuss (1) the various ways mutations in cardiac troponin C might lead to disease; (2) relevant data on mutations in cardiac troponin C linked to human disease, and (3) all currently existing mouse models containing cardiac troponin C mutations (disease-associated and engineered).
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Affiliation(s)
- Svetlana B. Tikunova
- Department of Physiology and Cell Biology, Dorothy M. Davis Heart and Lung Research Institute, College of Medicine, The Ohio State University, Columbus, OH 43210, USA (J.P.D.)
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7
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Lynn ML, Jimenez J, Castillo RL, Klass MM, Vasquez C, Baldo A, Gibson C, Murphy AM, Tardiff JC. The HCM - Linked Mutation Arg92Leu in TNNT2 Allosterically Alters the cTnC - cTnI Interface and Disrupts the PKA-mediated Regulation of Myofilament Relaxation. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.07.18.549569. [PMID: 37503299 PMCID: PMC10370115 DOI: 10.1101/2023.07.18.549569] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/29/2023]
Abstract
Background Impaired left ventricular relaxation, high filling pressures, and dysregulation of Ca 2+ homeostasis are common findings contributing to diastolic dysfunction in hypertrophic cardiomyopathy (HCM). Studies have shown that impaired relaxation is an early observation in the sarcomere-gene-positive preclinical HCM cohort which suggests potential involvement of myofilament regulators of relaxation. Yet, a molecular level understanding of mechanism(s) at the level of the myofilament is lacking. We hypothesized that mutation-specific, allosterically mediated, changes to the cardiac troponin C-cardiac troponin I (cTnC-cTnI) interface can account for the development of early-onset diastolic dysfunction via decreased PKA accessibility to cTnI. Methods HCM mutations R92L-cTnT (Arg92Leu) and Δ160E-cTnT (Glu160 deletion) were studied in vivo , in vitro, and in silico via 2D echocardiography, western blotting, ex vivo hemodynamics, stopped-flow kinetics, time resolved fluorescence resonance energy transfer (TR-FRET), and molecular dynamics simulations. Results The HCM-causative mutations R92L-cTnT and Δ160E-cTnT result in different time-of-onset of diastolic dysfunction. R92L-cTnT demonstrated early-onset diastolic dysfunction accompanied by a localized decrease in phosphorylation of cTnI. Constitutive phosphorylation of cTnI (cTnI-D 23 D 24 ) was sufficient to recover diastolic function to Non-Tg levels only for R92L-cTnT. Mutation-specific changes in Ca 2+ dissociation rates associated with R92L-cTnT reconstituted with cTnI-D 23 D 24 led us to investigate potential involvement of structural changes in the cTnC-cTnI interface as an explanation for these observations. We probed the interface via TR-FRET revealing a repositioning of the N-terminus of cTnI, closer to cTnC, and concomitant decreases in distance distributions at sites flanking the PKA consensus sequence. Implementing TR-FRET distances as constraints into our atomistic model identified additional electrostatic interactions at the consensus sequence. Conclusion These data indicate that the early diastolic dysfunction observed in a subset of HCM is likely attributable to structural changes at the cTnC-cTnI interface that impair accessibility of PKA thereby blunting β-adrenergic responsiveness and identifying a potential molecular target for therapeutic intervention.
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Hantz ER, Tikunova SB, Belevych N, Davis JP, Reiser PJ, Lindert S. Targeting Troponin C with Small Molecules Containing Diphenyl Moieties: Calcium Sensitivity Effects on Striated Muscles and Structure-Activity Relationship. J Chem Inf Model 2023; 63:3462-3473. [PMID: 37204863 PMCID: PMC10496875 DOI: 10.1021/acs.jcim.3c00196] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
Despite large investments from academia and industry, heart failure, which results from a disruption of the contractile apparatus, remains a leading cause of death. Cardiac muscle contraction is a calcium-dependent mechanism, which is regulated by the troponin protein complex (cTn) and specifically by the N-terminal domain of its calcium-binding subunit (cNTnC). There is an increasing need for the development of small molecules that increase calcium sensitivity without altering the systolic calcium concentration, thereby strengthening the cardiac function. Here, we examined the effect of our previously identified calcium-sensitizing small molecule, ChemBridge compound 7930079, in the context of several homologous muscle systems. The effect of this molecule on force generation in isolated cardiac trabeculae and slow skeletal muscle fibers was measured. Furthermore, we explored the use of Gaussian accelerated molecular dynamics in sampling highly predictive receptor conformations based on NMR-derived starting structures. Additionally, we took a rational computational approach for lead optimization based on lipophilic diphenyl moieties. This integrated structural-biochemical-physiological approach led to the identification of three novel low-affinity binders, which had similar binding affinities to the known positive inotrope trifluoperazine. The most potent identified calcium sensitizer was compound 16 with an apparent affinity of 117 ± 17 μM.
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Affiliation(s)
- Eric R. Hantz
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH, 43210
| | - Svetlana B. Tikunova
- Davis Heart and Lung Research Institute and Department of Physiology and Cell Biology, The Ohio State University, Columbus, OH, 43210
| | - Natalya Belevych
- Division of Biosciences, College of Dentistry, The Ohio State University, Columbus, OH 43210
| | - Jonathan P. Davis
- Davis Heart and Lung Research Institute and Department of Physiology and Cell Biology, The Ohio State University, Columbus, OH, 43210
| | - Peter J. Reiser
- Division of Biosciences, College of Dentistry, The Ohio State University, Columbus, OH 43210
| | - Steffen Lindert
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH, 43210
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Cool AM, Lindert S. Umbrella Sampling Simulations of Cardiac Thin Filament Reveal Thermodynamic Consequences of Troponin I Inhibitory Peptide Mutations. J Chem Inf Model 2023; 63:3534-3543. [PMID: 37261389 PMCID: PMC10506665 DOI: 10.1021/acs.jcim.3c00388] [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: 06/02/2023]
Abstract
The cardiac thin filament comprises F-actin, tropomyosin, and troponin (cTn). cTn is composed of three subunits: troponin C (cTnC), troponin I (cTnI), and troponin T (cTnT). To computationally study the effect of the thin filament on cTn activation events, we employed targeted molecular dynamics followed by umbrella sampling using a model of the thin filament to measure the thermodynamics of cTn transition events. Our simulations revealed that the thin filament causes an increase in the free energy required to open the cTnC hydrophobic patch and causes a more favorable interaction between this region and the cTnI switch peptide. Mutations to the cTn complex can lead to cardiomyopathy, a collection of diseases that present clinically with symptoms of hypertrophy or dilation of the cardiac muscle, leading to impairment of the heart's ability to function normally and ultimately myocardial infarction or heart failure. Upon introduction of cardiomyopathic mutations to R145 of cTnI, we observed a general decrease in the free energy of opening the cTnC hydrophobic patch, which is on par with previous experimental results. These mutations also exhibited a decrease in electrostatic interactions between cTnI-R145 and actin-E334. After introduction of a small molecule to the wild-type cTnI-actin interface to intentionally disrupt intersubunit contacts, we successfully observed similar thermodynamic consequences and disruptions to the same protein-protein contacts as observed with the cardiomyopathic mutations. Computational studies utilizing the cTn complex in isolation would have been unable to observe these effects, highlighting the importance of using a more physiologically relevant thin-filament model to investigate the global consequences of cardiomyopathic mutations to the cTn complex.
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Affiliation(s)
- Austin M. Cool
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH, 43210
| | - Steffen Lindert
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH, 43210
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Asencio A, Malingen S, Kooiker KB, Powers JD, Davis J, Daniel T, Moussavi-Harami F. Machine learning meets Monte Carlo methods for models of muscle's molecular machinery to classify mutations. J Gen Physiol 2023; 155:e202213291. [PMID: 37000171 PMCID: PMC10067704 DOI: 10.1085/jgp.202213291] [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] [Received: 10/31/2022] [Revised: 02/14/2023] [Accepted: 03/14/2023] [Indexed: 04/01/2023] Open
Abstract
The timing and magnitude of force generation by a muscle depend on complex interactions in a compliant, contractile filament lattice. Perturbations in these interactions can result in cardiac muscle diseases. In this study, we address the fundamental challenge of connecting the temporal features of cardiac twitches to underlying rate constants and their perturbations associated with genetic cardiomyopathies. Current state-of-the-art metrics for characterizing the mechanical consequence of cardiac muscle disease do not utilize information embedded in the complete time course of twitch force. We pair dimension reduction techniques and machine learning methods to classify underlying perturbations that shape the timing of twitch force. To do this, we created a large twitch dataset using a spatially explicit Monte Carlo model of muscle contraction. Uniquely, we modified the rate constants of this model in line with mouse models of cardiac muscle disease and varied mutation penetrance. Ultimately, the results of this study show that machine learning models combined with biologically informed dimension reduction techniques can yield excellent classification accuracy of underlying muscle perturbations.
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Affiliation(s)
- Anthony Asencio
- Department of Biology, University of Washington, Seattle, WA, USA
- Department of Bioengineering, University of Washington, Seattle, WA, USA
- Division of Cardiology, University of Washington, Seattle, WA, USA
- Center for Transnational Muscle Research, University of Washington, Seattle, WA, USA
| | - Sage Malingen
- Department of Bioengineering, University of Washington, Seattle, WA, USA
- Center for Transnational Muscle Research, University of Washington, Seattle, WA, USA
| | - Kristina B. Kooiker
- Division of Cardiology, University of Washington, Seattle, WA, USA
- Center for Transnational Muscle Research, University of Washington, Seattle, WA, USA
- Center for Cardiovascular Biology, University of Washington, Seattle, WA, USA
| | - Joseph D. Powers
- Department of Bioengineering, University of California, San Diego, San Diego, CA, USA
| | - Jennifer Davis
- Department of Bioengineering, University of Washington, Seattle, WA, USA
- Center for Transnational Muscle Research, University of Washington, Seattle, WA, USA
- Department of Laboratory Medicine Pathology, University of Washington, Seattle, WA, USA
- Center for Cardiovascular Biology, University of Washington, Seattle, WA, USA
| | - Thomas Daniel
- Department of Biology, University of Washington, Seattle, WA, USA
- Department of Bioengineering, University of Washington, Seattle, WA, USA
- Center for Transnational Muscle Research, University of Washington, Seattle, WA, USA
| | - Farid Moussavi-Harami
- Division of Cardiology, University of Washington, Seattle, WA, USA
- Center for Transnational Muscle Research, University of Washington, Seattle, WA, USA
- Department of Laboratory Medicine Pathology, University of Washington, Seattle, WA, USA
- Center for Cardiovascular Biology, University of Washington, Seattle, WA, USA
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11
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Salhi HE, Shettigar V, Salyer L, Sturgill S, Brundage EA, Robinett J, Xu Z, Abay E, Lowe J, Janssen PML, Rafael-Fortney JA, Weisleder N, Ziolo MT, Biesiadecki BJ. The lack of Troponin I Ser-23/24 phosphorylation is detrimental to in vivo cardiac function and exacerbates cardiac disease. J Mol Cell Cardiol 2023; 176:84-96. [PMID: 36724829 PMCID: PMC10074981 DOI: 10.1016/j.yjmcc.2023.01.010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/08/2022] [Revised: 01/11/2023] [Accepted: 01/24/2023] [Indexed: 01/30/2023]
Abstract
Troponin I (TnI) is a key regulator of cardiac contraction and relaxation with TnI Ser-23/24 phosphorylation serving as a myofilament mechanism to modulate cardiac function. Basal cardiac TnI Ser-23/24 phosphorylation is high such that both increased and decreased TnI phosphorylation may modulate cardiac function. While the effects of increasing TnI Ser-23/24 phosphorylation on heart function are well established, the effects of decreasing TnI Ser-23/24 phosphorylation are not clear. To understand the in vivo role of decreased TnI Ser-23/24 phosphorylation, mice expressing TnI with Ser-23/24 mutated to alanine (TnI S23/24A) that lack the ability to be phosphorylated at these residues were subjected to echocardiography and pressure-volume hemodynamic measurements in the absence or presence of physiological (pacing increasing heart rate or adrenergic stimulation) or pathological (transverse aortic constriction (TAC)) stress. In the absence of pathological stress, the lack of TnI Ser-23/24 phosphorylation impaired systolic and diastolic function. TnI S23/24A mice also had an impaired systolic and diastolic response upon stimulation increased heart rate and an impaired adrenergic response upon dobutamine infusion. Following pathological cardiac stress induced by TAC, TnI S23/24A mice had a greater increase in ventricular mass, worse diastolic function, and impaired systolic and diastolic function upon increasing heart rate. These findings demonstrate that mice lacking the ability to phosphorylate TnI at Ser-23/24 have impaired in vivo systolic and diastolic cardiac function, a blunted cardiac reserve and a worse response to pathological stress supporting decreased TnI Ser23/24 phosphorylation is a modulator of these processes in vivo.
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Affiliation(s)
- Hussam E Salhi
- Department of Physiology and Cell Biology and Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH, United States of America
| | - Vikram Shettigar
- Department of Physiology and Cell Biology and Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH, United States of America
| | - Lorien Salyer
- Department of Physiology and Cell Biology and Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH, United States of America
| | - Sarah Sturgill
- Department of Physiology and Cell Biology and Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH, United States of America
| | - Elizabeth A Brundage
- Department of Physiology and Cell Biology and Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH, United States of America
| | - Joel Robinett
- Department of Physiology and Cell Biology and Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH, United States of America
| | - Zhaobin Xu
- Department of Physiology and Cell Biology and Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH, United States of America
| | - Eaman Abay
- Department of Physiology and Cell Biology and Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH, United States of America
| | - Jeovanna Lowe
- Department of Physiology and Cell Biology and Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH, United States of America
| | - Paul M L Janssen
- Department of Physiology and Cell Biology and Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH, United States of America
| | - Jill A Rafael-Fortney
- Department of Physiology and Cell Biology and Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH, United States of America
| | - Noah Weisleder
- Department of Physiology and Cell Biology and Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH, United States of America
| | - Mark T Ziolo
- Department of Physiology and Cell Biology and Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH, United States of America
| | - Brandon J Biesiadecki
- Department of Physiology and Cell Biology and Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH, United States of America.
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12
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Hantz ER, Tikunova SB, Belevych N, Davis JP, Reiser PJ, Lindert S. Targeting Troponin C with Small Molecules Containing Diphenyl Moieties: Calcium Sensitivity Effects on Striated Muscle and Structure Activity Relationship. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.02.06.527323. [PMID: 36798160 PMCID: PMC9934531 DOI: 10.1101/2023.02.06.527323] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 02/09/2023]
Abstract
Despite large investments from academia and industry, heart failure, which results from a disruption of the contractile apparatus, remains a leading cause of death. Cardiac muscle contraction is a calcium-dependent mechanism, which is regulated by the troponin protein complex (cTn) and specifically by the N-terminal domain of its calcium binding subunit (cNTnC). There is an increasing need for the development of small molecules that increase calcium sensitivity without altering systolic calcium concentration, thereby strengthening cardiac function. Here, we examined the effect of our previously identified calcium sensitizing small molecule, ChemBridge compound 7930079, in the context of several homologous muscle systems. The effect of this molecule on force generation in isolated cardiac trabeculae and slow skeletal muscle fibers was measured. Furthermore, we explored the use of Gaussian accelerated molecular dynamics in sampling highly predictive receptor conformations based on NMR derived starting structures. Additionally, we took a rational computational approach for lead optimization based on lipophilic diphenyl moieties. This led to the identification of three novel low affinity binders, which had similar binding affinities to known positive inotrope trifluoperazine. The most potent identified calcium sensitizer was compound 16 with an apparent affinity of 117 ± 17 μM .
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Affiliation(s)
- Eric R. Hantz
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH, 43210
| | - Svetlana B. Tikunova
- Davis Heart and Lung Research Institute and Department of Physiology and Cell Biology, The Ohio State University, Columbus, OH, 43210
| | - Natalya Belevych
- Division of Biosciences, College of Dentistry, The Ohio State University, Columbus, OH 43210
| | - Jonathan P. Davis
- Davis Heart and Lung Research Institute and Department of Physiology and Cell Biology, The Ohio State University, Columbus, OH, 43210
| | - Peter J. Reiser
- Division of Biosciences, College of Dentistry, The Ohio State University, Columbus, OH 43210
| | - Steffen Lindert
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH, 43210,Correspondence to: Department of Chemistry and Biochemistry, Ohio State University, 2114 Newman & Wolfrom Laboratory, 100 W. 18th Avenue, Columbus, OH 43210, 614-292-8284 (office), 614-292-1685 (fax),
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13
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Sun B, Kekenes-Huskey PM. Myofilament-associated proteins with intrinsic disorder (MAPIDs) and their resolution by computational modeling. Q Rev Biophys 2023; 56:e2. [PMID: 36628457 PMCID: PMC11070111 DOI: 10.1017/s003358352300001x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
The cardiac sarcomere is a cellular structure in the heart that enables muscle cells to contract. Dozens of proteins belong to the cardiac sarcomere, which work in tandem to generate force and adapt to demands on cardiac output. Intriguingly, the majority of these proteins have significant intrinsic disorder that contributes to their functions, yet the biophysics of these intrinsically disordered regions (IDRs) have been characterized in limited detail. In this review, we first enumerate these myofilament-associated proteins with intrinsic disorder (MAPIDs) and recent biophysical studies to characterize their IDRs. We secondly summarize the biophysics governing IDR properties and the state-of-the-art in computational tools toward MAPID identification and characterization of their conformation ensembles. We conclude with an overview of future computational approaches toward broadening the understanding of intrinsic disorder in the cardiac sarcomere.
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Affiliation(s)
- Bin Sun
- Research Center for Pharmacoinformatics (The State-Province Key Laboratories of Biomedicine-Pharmaceutics of China), Department of Medicinal Chemistry and Natural Medicine Chemistry, College of Pharmacy, Harbin Medical University, Harbin 150081, China
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14
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Hong X, Cholko T, Chang CEA, Wheeldon I. Multiscale simulation-guided design of enzyme bioconjugates with enhanced catalysis. CHEM CATALYSIS 2022; 2:2691-2703. [PMID: 36569428 PMCID: PMC9784400 DOI: 10.1016/j.checat.2022.09.018] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Biopolymer-scaffold modification is widely used to enhance enzyme catalysis. A central challenge is predicting the effects of scaffold position on enzyme properties. Here, we use a computational-experimental approach to develop a model for the effects of DNA scaffold position on enzyme kinetics. Using phosphotriesterase modified with a 20bp dsDNA, we demonstrate that conjugation position is as important as the scaffold's chemistry and structure. Multiscale simulations predict the effective substrate concentration increases close to the scaffold, which has μM-strength binding to the substrate. Kinetic analysis shows that the effective concentration that the scaffold provides is best utilized when positioned next to, but not blocking, the active site. At ~5Å distance between scaffold and active site a 7-fold increase in k cat /K M was achieved. A model that accounts for the substrate concentration as well PTE-DNA geometry accurately captures the kinetic enhancements, enabling prediction of the effect across a range of DNA positions.
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Affiliation(s)
- Xiao Hong
- Department of Biochemistry, University of California-Riverside, Riverside, CA, 92521
| | - Timothy Cholko
- Department of Chemistry, University of California-Riverside, Riverside, CA, 92521
| | - Chia-en A. Chang
- Department of Chemistry, University of California-Riverside, Riverside, CA, 92521
| | - Ian Wheeldon
- Department of Chemical and Environmental Engineering, University of California-Riverside, Riverside, CA, 92521
- Center for Industrial Biotechnology, University of California-Riverside, Riverside, CA, 92521
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15
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Sun B, Kekenes-Huskey PM. Calmodulin's Interdomain Linker Is Optimized for Dynamics Signal Transmission and Calcium Binding. J Chem Inf Model 2022; 62:4210-4221. [PMID: 35994621 DOI: 10.1021/acs.jcim.2c00587] [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
Linkers are ubiquitous in multidomain proteins. These linkers are integral to protein functions, and accumulating evidence suggests that the linkers' versatile roles are encoded in their sequences. However, a molecular picture of how amino acid differences in the linker influence protein function is still lacking. By using extensive Gaussian-accelerated MD coupled with dynamic network analysis, we reveal the molecular bases underlying the linker's role in Calmodulin (CaM), a highly conserved Ca2+-signaling hub in eukaryotes. Three CaM constructs comprising a wild-type linker, a flexible linker (four glycines at position D78-S81), and a rigid linker (four prolines at position D78-S81) were simulated. We show that the flexible linker resembles the wild type in allowing CaM to sample a large ensemble of conformations while the rigid linker confines the sampling. Our simulations recapture experimental observations that target binding enhances the Ca2+ affinity to CaM's EF-hand sites at the N-domain. However, only the wild-type linker can both correctly capture the Ca2+ binding order and maintain the α-helical structure of the domain. The other two constructs either bind Ca2+ in an incorrect order or exhibit unfolding of an N-domain helix. We demonstrate that the wild-type linker achieves these outcomes by transmitting interdomain dynamics efficiently. This was evidenced by stronger (anti)correlations among the linker residues, decoupling of the hydrogen bonds between A1-A15 and V35-E45, and structuring of the N-domain for Ca2+ binding. This decoupling was not evident for the other two constructs. Lastly, we show that the wild-type linker's optimal transmission stems from its thermodynamically favorable strain and solvation relative to the other two constructs. Our results show how the linker sequence tunes CaM function, suggesting possible mechanisms for changes in linker properties such as mutations or post-translational modifications to modulate protein/substrate binding.
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Affiliation(s)
- Bin Sun
- Department of Pharmacology, Harbin Medical University, Harbin 150081, China
| | - Peter M Kekenes-Huskey
- Department of Cell and Molecular Physiology, Loyola University, Chicago, Illinois 60153, United States
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16
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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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17
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Dong S, Zheng W, Pinkerton N, Hansen J, Tikunova SB, Davis JP, Heissler SM, Kudryashova E, Egelman EH, Kudryashov DS. Photorhabdus luminescens TccC3 Toxin Targets the Dynamic Population of F-Actin and Impairs Cell Cortex Integrity. Int J Mol Sci 2022; 23:7026. [PMID: 35806028 PMCID: PMC9266650 DOI: 10.3390/ijms23137026] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2022] [Revised: 06/17/2022] [Accepted: 06/22/2022] [Indexed: 12/30/2022] Open
Abstract
Due to its essential role in cellular processes, actin is a common target for bacterial toxins. One such toxin, TccC3, is an effector domain of the ABC-toxin produced by entomopathogenic bacteria of Photorhabdus spp. Unlike other actin-targeting toxins, TccC3 uniquely ADP-ribosylates actin at Thr-148, resulting in the formation of actin aggregates and inhibition of phagocytosis. It has been shown that the fully modified F-actin is resistant to depolymerization by cofilin and gelsolin, but their effects on partially modified actin were not explored. We found that only F-actin unprotected by tropomyosin is the physiological TccC3 substrate. Yet, ADP-ribosylated G-actin can be produced upon cofilin-accelerated F-actin depolymerization, which was only mildly inhibited in partially modified actin. The affinity of TccC3-ADP-ribosylated G-actin for profilin and thymosin-β4 was weakened moderately but sufficiently to potentiate spontaneous polymerization in their presence. Interestingly, the Arp2/3-mediated nucleation was also potentiated by T148-ADP-ribosylation. Notably, even partially modified actin showed reduced bundling by plastins and α-actinin. In agreement with the role of these and other tandem calponin-homology domain actin organizers in the assembly of the cortical actin network, TccC3 induced intense membrane blebbing in cultured cells. Overall, our data suggest that TccC3 imposes a complex action on the cytoskeleton by affecting F-actin nucleation, recycling, and interaction with actin-binding proteins involved in the integration of actin filaments with each other and cellular elements.
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Affiliation(s)
- Songyu Dong
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA; (S.D.); (N.P.); (J.H.); (E.K.)
- The Ohio State Biochemistry Program, The Ohio State University, Columbus, OH 43210, USA
| | - Weili Zheng
- Department of Biochemistry and Molecular Genetics, University of Virginia, Charlottesville, VA 22903, USA; (W.Z.); (E.H.E.)
| | - Nicholas Pinkerton
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA; (S.D.); (N.P.); (J.H.); (E.K.)
| | - Jacob Hansen
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA; (S.D.); (N.P.); (J.H.); (E.K.)
| | - Svetlana B. Tikunova
- Department of Physiology and Cell Biology, Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH 43210, USA; (S.B.T.); (J.P.D.); (S.M.H.)
| | - Jonathan P. Davis
- Department of Physiology and Cell Biology, Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH 43210, USA; (S.B.T.); (J.P.D.); (S.M.H.)
| | - Sarah M. Heissler
- Department of Physiology and Cell Biology, Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH 43210, USA; (S.B.T.); (J.P.D.); (S.M.H.)
| | - Elena Kudryashova
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA; (S.D.); (N.P.); (J.H.); (E.K.)
| | - Edward H. Egelman
- Department of Biochemistry and Molecular Genetics, University of Virginia, Charlottesville, VA 22903, USA; (W.Z.); (E.H.E.)
| | - Dmitri S. Kudryashov
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA; (S.D.); (N.P.); (J.H.); (E.K.)
- The Ohio State Biochemistry Program, The Ohio State University, Columbus, OH 43210, USA
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18
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Lertwanakarn T, Suntravat M, Sánchez EE, Wolska BM, Solaro RJ, de Tombe PP, Tachampa K. Negative inotropic mechanisms of β-cardiotoxin in cardiomyocytes by depression of myofilament ATPase activity without activation of the classical β-adrenergic pathway. Sci Rep 2021; 11:21154. [PMID: 34707114 PMCID: PMC8551325 DOI: 10.1038/s41598-021-00282-x] [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: 06/08/2021] [Accepted: 10/06/2021] [Indexed: 11/09/2022] Open
Abstract
Beta-cardiotoxin (β-CTX) from the king cobra venom (Ophiophagus hannah) was previously proposed as a novel β-adrenergic blocker. However, the involvement of β-adrenergic signaling by this compound has never been elucidated. The objectives of this study were to investigate the underlying mechanisms of β-CTX as a β-blocker and its association with the β-adrenergic pathway. The effects of β-CTX on isolated cardiac myocyte functions, calcium homeostasis, the phosphorylation level of targeted proteins, and the myofibrillar ATPase activity were studied. Healthy Sprague Dawley rats were used for cardiomyocytes isolation. Like propranolol, β-CTX attenuated the cardiomyocyte inotropy and calcium transient alterations as induced by isoproterenol stimulation. In contrast, these effects were not observed in forskolin-treated cells. Interestingly, cardiomyocytes treated with β-CTX showed no changes in phosphorylation level at any PKA-targeted sites in the myofilaments as demonstrated in Western blot analysis. The skinned fibers study revealed no change in myofilament kinetics by β-CTX. However, this protein exhibited the direct inhibition of myofibrillar ATPase activity with calcium de-sensitization of the enzyme. In summary, the negative inotropic mechanism of β-CTX was discovered. β-CTX exhibits an atypical β-blocker mechanism. These properties of β-CTX may benefit in developing a novel agent aid to treat hypertrophic cardiomyopathy.
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Affiliation(s)
- Tuchakorn Lertwanakarn
- Department of Physiology, Faculty of Veterinary Science, Chulalongkorn University, Bangkok, Thailand
| | - Montamas Suntravat
- National Natural Toxins Research Center, Texas-A&M University-Kingsville, Kingsville, TX, USA.,Department of Chemistry, Texas A&M University-Kingsville, Kingsville, TX, USA
| | - Elda E Sánchez
- National Natural Toxins Research Center, Texas-A&M University-Kingsville, Kingsville, TX, USA.,Department of Chemistry, Texas A&M University-Kingsville, Kingsville, TX, USA
| | - Beata M Wolska
- Department of Physiology and Biophysics, the University of Illinois at Chicago, Chicago, IL, USA.,Department of Medicine, the University of Illinois at Chicago, Chicago, IL, USA
| | - R John Solaro
- Department of Physiology and Biophysics, the University of Illinois at Chicago, Chicago, IL, USA
| | - Pieter P de Tombe
- Department of Physiology and Biophysics, the University of Illinois at Chicago, Chicago, IL, USA.,Phymedexp, Université de Montpellier, Inserm, CNRS, Montpellier, France
| | - Kittipong Tachampa
- Department of Physiology, Faculty of Veterinary Science, Chulalongkorn University, Bangkok, Thailand.
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19
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Cool AM, Lindert S. Computational Methods Elucidate Consequences of Mutations and Post-translational Modifications on Troponin I Effective Concentration to Troponin C. J Phys Chem B 2021; 125:7388-7396. [PMID: 34213339 DOI: 10.1021/acs.jpcb.1c03844] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Ca2+ binding to cardiac troponin C (cTnC) causes a conformational shift that exposes a hydrophobic patch (cTnCHP) for binding of the cTnI switch peptide (cTnISP), ultimately resulting in contraction of the heart. The inhibitory peptide (cTnIIP), attached at the N-terminal end of the cTnISP, serves as a tether for the cTnISP to the rest of the troponin complex. Due to this tethered nature, the cTnISP remains within proximity of the hydrophobic patch region, resulting in the cTnCHP experiencing an elevated "effective concentration" of the cTnISP. Mutations to the cTnIIP region have been hypothesized to cause disease by affecting the ability of the cTnISP to "find" the hydrophobic patch, resulting in alterations to the heart's ability to contract normally. We tested this hypothesis using molecular dynamics (MD) simulations of the troponin complex using a model that contained all three subunits of troponin: C, I, and T. We developed methods that allowed us to quantitatively measure the effective concentration of the cTnISP from the simulations. A significant reduction in the cTnISP effective concentration was observed when the cTnIIP was removed from the system, showcasing the importance of a tethered cTnISP. Through accelerated MD methods, we proposed the minimum effective concentration of a tethered cTnISP to be approximately 21 mM. Modification of the cTnIIP via PKC-mediated phosphorylation of T143 was shown to significantly increase the estimated effective concentration of cTnISP, help the cTnISP find the cTnCHP more effectively, and maintain the relative shape of the cTnIIP when compared to the native model. All of these data indicate that pT143 may be able to help promote binding of cTnISP to the cTnCHP. We then tested six mutations within the cTnIIP region that are known cTnC Ca2+-sensitizing mutations and have been linked with cardiomyopathy. We did not observe a significant reduction in the effective concentration upon the introduction of these mutations; however, we did observe increased variability in the flexibility and dynamics of the cTnIIP region when compared to native. Our observations led us to hypothesize that the mechanism by which these cardiomyopathic mutations affect Ca2+ sensitivity is by altering the off rate of cTnISP from the hydrophobic patch.
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Affiliation(s)
- Austin M Cool
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio 43210, United States
| | - Steffen Lindert
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio 43210, United States
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20
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Tobacman LS, Cammarato A. Cardiomyopathic troponin mutations predominantly occur at its interface with actin and tropomyosin. J Gen Physiol 2021; 153:e202012815. [PMID: 33492345 PMCID: PMC7836260 DOI: 10.1085/jgp.202012815] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2020] [Accepted: 12/23/2020] [Indexed: 01/09/2023] Open
Abstract
Reversible Ca2+ binding to troponin is the primary on-off switch of the contractile apparatus of striated muscles, including the heart. Dominant missense mutations in human cardiac troponin genes are among the causes of hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy. Structural understanding of troponin action has recently advanced considerably via electron microscopy and molecular dynamics studies of the thin filament. As a result, it is now possible to examine cardiomyopathy-inducing troponin mutations in thin-filament structural context, and from that to seek new insight into pathogenesis and into the troponin regulatory mechanism. We compiled from consortium reports a representative set of troponin mutation sites whose pathogenicity was determined using standardized clinical genetics criteria. Another set of sites, apparently tolerant of amino acid substitutions, was compiled from the gnomAD v2 database. Pathogenic substitutions occurred predominantly in the areas of troponin that contact actin or tropomyosin, including, but not limited to, two regions of newly proposed structure and long-known implication in cardiomyopathy: the C-terminal third of troponin I and a part of the troponin T N terminus. The pathogenic mutations were located in troponin regions that prevent contraction under low Ca2+ concentration conditions. These regions contribute to Ca2+-regulated steric hindrance of myosin by the combined effects of troponin and tropomyosin. Loss-of-function mutations within these parts of troponin result in loss of inhibition, consistent with the hypercontractile phenotype characteristic of HCM. Notably, pathogenic mutations are absent in our dataset from the Ca2+-binding, activation-producing troponin C (TnC) N-lobe, which controls contraction by a multi-faceted mechanism. Apparently benign mutations are also diminished in the TnC N-lobe, suggesting mutations are poorly tolerated in that critical domain.
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Affiliation(s)
- Larry S. Tobacman
- Departments of Medicine and of Physiology and Biophysics, University of Illinois at Chicago, Chicago, IL
| | - Anthony Cammarato
- Departments of Medicine and of Physiology, Johns Hopkins University, Baltimore, MD
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21
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Rayani K, Seffernick J, Li AY, Davis JP, Spuches AM, Van Petegem F, Solaro RJ, Lindert S, Tibbits GF. Binding of calcium and magnesium to human cardiac troponin C. J Biol Chem 2021; 296:100350. [PMID: 33548225 PMCID: PMC7961095 DOI: 10.1016/j.jbc.2021.100350] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2020] [Revised: 01/25/2021] [Accepted: 01/27/2021] [Indexed: 01/03/2023] Open
Abstract
Cardiac muscle thin filaments are composed of actin, tropomyosin, and troponin that change conformation in response to Ca2+ binding, triggering muscle contraction. Human cardiac troponin C (cTnC) is the Ca2+-sensing component of the thin filament. It contains structural sites (III/IV) that bind both Ca2+ and Mg2+ and a regulatory site (II) that has been thought to bind only Ca2+. Binding of Ca2+ at this site initiates a series of conformational changes that culminate in force production. However, the mechanisms that underpin the regulation of binding at site II remain unclear. Here, we have quantified the interaction between site II and Ca2+/Mg2+ through isothermal titration calorimetry and thermodynamic integration simulations. Direct and competitive binding titrations with WT N-terminal cTnC and full-length cTnC indicate that physiologically relevant concentrations of both Ca2+/Mg2+ interacted with the same locus. Moreover, the D67A/D73A N-terminal cTnC construct in which two coordinating residues within site II were removed was found to have significantly reduced affinity for both cations. In addition, 1 mM Mg2+ caused a 1.4-fold lower affinity for Ca2+. These experiments strongly suggest that cytosolic-free Mg2+ occupies a significant population of the available site II. Interaction of Mg2+ with site II of cTnC likely has important functional consequences for the heart both at baseline as well as in diseased states that decrease or increase the availability of Mg2+, such as secondary hyperparathyroidism or ischemia, respectively.
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Affiliation(s)
- Kaveh Rayani
- Molecular Cardiac Physiology Group, Simon Fraser University, Burnaby, British Columbia, Canada
| | - Justin Seffernick
- Department of Chemistry and Biochemistry, Ohio State University, Columbus, Ohio, USA
| | - Alison Yueh Li
- Molecular Cardiac Physiology Group, Simon Fraser University, Burnaby, British Columbia, Canada; Department of Biochemistry and Molecular Biology, The University of British Columbia, Vancouver, British Columbia, Canada
| | - Jonathan P Davis
- Department of Physiology and Cell Biology, The Ohio State University, Columbus, Ohio, USA
| | - Anne Marie Spuches
- Department of Chemistry, East Carolina University, 300 Science and Technology Building, Greenville, North Carolina, USA
| | - Filip Van Petegem
- Department of Biochemistry and Molecular Biology, The University of British Columbia, Vancouver, British Columbia, Canada
| | - R John Solaro
- Department of Physiology and Biophysics and the Center for Cardiovascular Research, College of Medicine, University of Illinois at Chicago, Chicago, Illinois, USA
| | - Steffen Lindert
- Department of Chemistry and Biochemistry, Ohio State University, Columbus, Ohio, USA
| | - Glen F Tibbits
- Molecular Cardiac Physiology Group, Simon Fraser University, Burnaby, British Columbia, Canada; Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia, Canada; Cardiac Group, BC Children's Hospital Research Institute, Vancouver, British Columbia, Canada.
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22
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Parijat P, Kondacs L, Alexandrovich A, Gautel M, Cobb AJA, Kampourakis T. High Throughput Screen Identifies Small Molecule Effectors That Modulate Thin Filament Activation in Cardiac Muscle. ACS Chem Biol 2021; 16:225-235. [PMID: 33315370 DOI: 10.1021/acschembio.0c00908] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Current therapeutic interventions for both heart disease and heart failure are largely insufficient and associated with undesired side effects. Biomedical research has emphasized the role of sarcomeric protein function for the normal performance and energy efficiency of the heart, suggesting that directly targeting the contractile myofilaments themselves using small molecule effectors has therapeutic potential and will likely result in greater drug efficacy and selectivity. In this study, we developed a robust and highly reproducible fluorescence polarization-based high throughput screening (HTS) assay that directly targets the calcium-dependent interaction between cardiac troponin C (cTnC) and the switch region of cardiac troponin I (cTnISP), with the aim of identifying small molecule effectors of the cardiac thin filament activation pathway. We screened a commercially available small molecule library and identified several hit compounds with both inhibitory and activating effects. We used a range of biophysical and biochemical methods to characterize hit compounds and identified fingolimod, a sphingosin-1-phosphate receptor modulator, as a new troponin-based small molecule effector. Fingolimod decreased the ATPase activity and calcium sensitivity of demembranated cardiac muscle fibers in a dose-dependent manner, suggesting that the compound acts as a calcium desensitizer. We investigated fingolimod's mechanism of action using a combination of computational studies, biophysical methods, and synthetic chemistry, showing that fingolimod bound to cTnC repels cTnISP via mainly electrostatic repulsion of its positively charged tail. These results suggest that fingolimod is a potential new lead compound/scaffold for the development of troponin-directed heart failure therapeutics.
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Affiliation(s)
- Priyanka Parijat
- Randall Centre for Cell and Molecular Biophysics, King’s College London, and British Heart Foundation Centre of Research Excellence, London SE1 1UL, United Kingdom
| | - Laszlo Kondacs
- Department of Chemistry, King’s College London, 7 Trinity Street, London, SE1 1DB, United Kingdom
| | - Alexander Alexandrovich
- Randall Centre for Cell and Molecular Biophysics, King’s College London, and British Heart Foundation Centre of Research Excellence, London SE1 1UL, United Kingdom
| | - Mathias Gautel
- Randall Centre for Cell and Molecular Biophysics, King’s College London, and British Heart Foundation Centre of Research Excellence, London SE1 1UL, United Kingdom
| | - Alexander J. A. Cobb
- Department of Chemistry, King’s College London, 7 Trinity Street, London, SE1 1DB, United Kingdom
| | - Thomas Kampourakis
- Randall Centre for Cell and Molecular Biophysics, King’s College London, and British Heart Foundation Centre of Research Excellence, London SE1 1UL, United Kingdom
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23
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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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24
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Abstract
Changes of intracellular Ca2+ concentration regulate many aspects of cardiac myocyte function. About 99% of the cytoplasmic calcium in cardiac myocytes is bound to buffers, and their properties will therefore have a major influence on Ca2+ signaling. This article considers the fundamental properties and identities of the buffers and how to measure them. It reviews the effects of buffering on the systolic Ca2+ transient and how this may change physiologically, and in heart failure and both atrial and ventricular arrhythmias, as well. It is concluded that the consequences of this strong buffering may be more significant than currently appreciated, and a fuller understanding is needed for proper understanding of cardiac calcium cycling and contractility.
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Affiliation(s)
- Godfrey L Smith
- Institute of Cardiovascular and Medical Sciences, College of Medical, Veterinary, and Life Sciences, University of Glasgow, UK (G.L.S.)
| | - David A Eisner
- Unit of Cardiac Physiology, Division of Cardiovascular Sciences, University of Manchester, UK (D.A.E.)
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25
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Sun B, Vaughan D, Tikunova S, Creamer TP, Davis JP, Kekenes-Huskey PM. Calmodulin-Calcineurin Interaction beyond the Calmodulin-Binding Region Contributes to Calcineurin Activation. Biochemistry 2019; 58:4070-4085. [PMID: 31483613 DOI: 10.1021/acs.biochem.9b00626] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Calcineurin (CaN) is a calcium-dependent phosphatase involved in numerous signaling pathways. Its activation is in part driven by the binding of calmodulin (CaM) to a CaM recognition region (CaMBR) within CaN's regulatory domain (RD). However, secondary interactions between CaM and the CaN RD may be necessary to fully activate CaN. Specifically, it is established that the CaN RD folds upon CaM binding and a region C-terminal to CaMBR, the "distal helix", assumes an α-helix fold and contributes to activation [Dunlap, T. B., et al. (2013) Biochemistry 52, 8643-8651]. We hypothesized in that previous study that this distal helix can bind CaM in a region distinct from the canonical CaMBR. To test this hypothesis, we utilized molecular simulations, including replica-exchange molecular dynamics, protein-protein docking, and computational mutagenesis, to determine potential distal helix-binding sites on CaM's surface. We isolated a potential binding site on CaM (site D) that facilitates moderate-affinity interprotein interactions and predicted that mutation of site D residues K30 and G40 on CaM would weaken CaN distal helix binding. We experimentally confirmed that two variants (K30E and G40D) indicate weaker binding of a phosphate substrate p-nitrophenyl phosphate to the CaN catalytic site by a phosphatase assay. This weakened substrate affinity is consistent with competitive binding of the CaN autoinhibition domain to the catalytic site, which we suggest is due to the weakened distal helix-CaM interactions. This study therefore suggests a novel mechanism for CaM regulation of CaN that may extend to other CaM targets.
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Affiliation(s)
- Bin Sun
- Department of Chemistry , University of Kentucky , Lexington , Kentucky 40506 , United States
| | - Darin Vaughan
- Department of Chemistry , University of Kentucky , Lexington , Kentucky 40506 , United States
| | - Svetlana Tikunova
- Department of Physiology and Cell Biology , The Ohio State University , Columbus , Ohio 43210 , United States
| | - Trevor P Creamer
- Center for Structural Biology and Department of Molecular & Cellular Biochemistry , University of Kentucky , Lexington , Kentucky 40536 , United States
| | - Jonathan P Davis
- Department of Physiology and Cell Biology , The Ohio State University , Columbus , Ohio 43210 , United States
| | - P M Kekenes-Huskey
- Department of Chemical and Materials Engineering , University of Kentucky , Lexington , Kentucky 40506 , United States.,Department of Cell and Molecular Physiology , Loyola University Chicago , Maywood , Illinois 60153 , United States
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26
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Bowman JD, Lindert S. Computational Studies of Cardiac and Skeletal Troponin. Front Mol Biosci 2019; 6:68. [PMID: 31448287 PMCID: PMC6696891 DOI: 10.3389/fmolb.2019.00068] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2019] [Accepted: 07/25/2019] [Indexed: 12/16/2022] Open
Abstract
Troponin is a key regulatory protein in muscle contraction, consisting of three subunits troponin C (TnC), troponin I (TnI), and troponin T (TnT). Calcium association to TnC initiates contraction by causing a series of dynamic and conformational changes that allow the switch peptide of TnI to bind and subsequently cross bridges to form between the thin and thick filament of the sarcomere. Owing to its pivotal role in contraction regulation, troponin has been the focus of numerous computational studies over the last decade. These studies elegantly supplemented a large volume of experimental work and focused on the structure, dynamics and function of the whole troponin complex, individual subunits, and even on segments of the thin filament. Molecular dynamics, Brownian dynamics, and free energy simulations have been used to elucidate the conformational dynamics and underlying free energy landscape of troponin, calcium, and switch peptide binding, as well as the effect of disease mutations, small molecules and post-translational modifications such as phosphorylation. Frequently, simulations have been used to confirm or explain experimental observations. Computer-aided drug discovery tools have been employed to identify novel potential calcium sensitizing agents binding to the TnC-TnI interface. Finally, Markov modeling has contributed to simulating contraction within the sarcomere on the mesoscale. Here we are reviewing and classifying the existing computational work on troponin and its subunits, outline current gaps in simulations elucidating troponin's role in contraction and suggest potential future developments in the field.
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Affiliation(s)
- Jacob D Bowman
- Department of Chemistry and Biochemistry, Ohio State University, Columbus, OH, United States
| | - Steffen Lindert
- Department of Chemistry and Biochemistry, Ohio State University, Columbus, OH, United States
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27
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Johnson CN, Pattanayek R, Potet F, Rebbeck RT, Blackwell DJ, Nikolaienko R, Sequeira V, Le Meur R, Radwański PB, Davis JP, Zima AV, Cornea RL, Damo SM, Györke S, George AL, Knollmann BC. The CaMKII inhibitor KN93-calmodulin interaction and implications for calmodulin tuning of Na V1.5 and RyR2 function. Cell Calcium 2019; 82:102063. [PMID: 31401388 DOI: 10.1016/j.ceca.2019.102063] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2019] [Revised: 07/15/2019] [Accepted: 07/26/2019] [Indexed: 02/06/2023]
Abstract
Here we report the structure of the widely utilized calmodulin (CaM)-dependent protein kinase II (CaMKII) inhibitor KN93 bound to the Ca2+-sensing protein CaM. KN93 is widely believed to inhibit CaMKII by binding to the kinase. The CaM-KN93 interaction is significant as it can interfere with the interaction between CaM and it's physiological targets, thereby raising the possibility of ascribing modified protein function to CaMKII phosphorylation while concealing a CaM-protein interaction. NMR spectroscopy, stopped-flow kinetic measurements, and x-ray crystallography were used to characterize the structure and biophysical properties of the CaM-KN93 interaction. We then investigated the functional properties of the cardiac Na+ channel (NaV1.5) and ryanodine receptor (RyR2). We find that KN93 disrupts a high affinity CaM-NaV1.5 interaction and alters channel function independent of CaMKII. Moreover, KN93 increases RyR2 Ca2+ release in cardiomyocytes independent of CaMKII. Therefore, when interpreting KN93 data, targets other than CaMKII need to be considered.
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Affiliation(s)
- Christopher N Johnson
- Center for Arrhythmia Research and Therapeutics, Vanderbilt University Medical Center, Nashville, TN 37240, USA; Dorothy M. Davis Heart and Lung Research Institute, College of Medicine, The Ohio State University Wexner Medical Center, Columbus, OH, USA.
| | - Rekha Pattanayek
- Department of Life and Physical Sciences, Fisk University, Nashville, TN 37208, USA
| | - Franck Potet
- Department of Pharmacology Feinberg School of Medicine, Northwestern University, Chicago IL, 60611, USA
| | - Robyn T Rebbeck
- Department of Biochemistry, Molecular Biology and Biophysics University of Minnesota, Minneapolis, MN 55455, USA
| | - Daniel J Blackwell
- Center for Arrhythmia Research and Therapeutics, Vanderbilt University Medical Center, Nashville, TN 37240, USA
| | - Roman Nikolaienko
- Department of Cell and Molecular Physiology, Stritch School of Medicine, Loyola University, Maywood IL, 60153, USA
| | - Vasco Sequeira
- Department of Translational Science Universitätsklinikum, Würzburg, Germany
| | - Remy Le Meur
- Department of Biochemistry, Vanderbilt University, Nashville TN 37204, USA
| | - Przemysław B Radwański
- Dorothy M. Davis Heart and Lung Research Institute, College of Medicine, The Ohio State University Wexner Medical Center, Columbus, OH, USA
| | - Jonathan P Davis
- Dorothy M. Davis Heart and Lung Research Institute, College of Medicine, The Ohio State University Wexner Medical Center, Columbus, OH, USA
| | - Aleksey V Zima
- Department of Cell and Molecular Physiology, Stritch School of Medicine, Loyola University, Maywood IL, 60153, USA
| | - Razvan L Cornea
- Department of Biochemistry, Molecular Biology and Biophysics University of Minnesota, Minneapolis, MN 55455, USA
| | - Steven M Damo
- Department of Life and Physical Sciences, Fisk University, Nashville, TN 37208, USA
| | - Sandor Györke
- Dorothy M. Davis Heart and Lung Research Institute, College of Medicine, The Ohio State University Wexner Medical Center, Columbus, OH, USA
| | - Alfred L George
- Department of Pharmacology Feinberg School of Medicine, Northwestern University, Chicago IL, 60611, USA
| | - Björn C Knollmann
- Center for Arrhythmia Research and Therapeutics, Vanderbilt University Medical Center, Nashville, TN 37240, USA
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28
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TnI Structural Interface with the N-Terminal Lobe of TnC as a Determinant of Cardiac Contractility. Biophys J 2019; 114:1646-1656. [PMID: 29642034 DOI: 10.1016/j.bpj.2018.02.015] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2017] [Revised: 01/26/2018] [Accepted: 02/02/2018] [Indexed: 12/24/2022] Open
Abstract
The heterotrimeric cardiac troponin complex is a key regulator of contraction and plays an essential role in conferring Ca2+ sensitivity to the sarcomere. During ischemic injury, rapidly accumulating protons acidify the myoplasm, resulting in markedly reduced Ca2+ sensitivity of the sarcomere. Unlike the adult heart, sarcomeric Ca2+ sensitivity in fetal cardiac tissue is comparatively pH insensitive. Replacement of the adult cardiac troponin I (cTnI) isoform with the fetal troponin I (ssTnI) isoform renders adult cardiac contractile machinery relatively insensitive to acidification. Alignment and functional studies have determined histidine 132 of ssTnI to be the predominant source of this pH insensitivity. Substitution of histidine at the cognate position 164 in cTnI confers the same pH insensitivity to adult cardiac myocytes. An alanine at position 164 of cTnI is conserved in all mammals, with the exception of the platypus, which expresses a proline. Prolines are biophysically unique because of their innate conformational rigidity and helix-disrupting function. To provide deeper structure-function insight into the role of the TnC-TnI interface in determining contractility, we employed a live-cell approach alongside molecular dynamics simulations to ascertain the chemo-mechanical implications of the disrupted helix 4 of cTnI where position 164 exists. This important motif belongs to the critical switch region of cTnI. Substitution of a proline at position 164 of cTnI in adult rat cardiac myocytes causes increased contractility independent of alterations in the Ca2+ transient. Free-energy perturbation calculations of cTnC-Ca2+ binding indicate no difference in cTnC-Ca2+ affinity. Rather, we propose the enhanced contractility is derived from new salt bridge interactions between cTnI helix 4 and cTnC helix A, which are critical in determining pH sensitivity and contractility. Molecular dynamics simulations demonstrate that cTnI A164P structurally phenocopies ssTnI under baseline but not acidotic conditions. These findings highlight the evolutionarily directed role of the TnI-cTnC interface in determining cardiac contractility.
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29
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Campbell KS, Yengo CM, Lee LC, Kotter J, Sorrell VL, Guglin M, Wenk JF. Closing the therapeutic loop. Arch Biochem Biophys 2019; 663:129-131. [PMID: 30639169 DOI: 10.1016/j.abb.2019.01.006] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2018] [Revised: 12/12/2018] [Accepted: 01/08/2019] [Indexed: 11/28/2022]
Affiliation(s)
- Kenneth S Campbell
- Department of Physiology, University of Kentucky, United States; Division of Cardiovascular Medicine, University of Kentucky, United States.
| | - Christopher M Yengo
- Department of Cellular and Molecular Physiology, Penn State College of Medicine, United States
| | - Lik-Chuan Lee
- Department of Mechanical Engineering, Michigan State University, United States
| | - John Kotter
- Division of Cardiovascular Medicine, University of Kentucky, United States
| | - Vincent L Sorrell
- Division of Cardiovascular Medicine, University of Kentucky, United States
| | - Maya Guglin
- Division of Cardiovascular Medicine, University of Kentucky, United States
| | - Jonathan F Wenk
- Department of Mechanical Engineering and Department of Surgery, University of Kentucky, United States
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30
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Tikunova SB, Cuesta A, Price M, Li MX, Belevych N, Biesiadecki BJ, Reiser PJ, Hwang PM, Davis JP. 3-Chlorodiphenylamine activates cardiac troponin by a mechanism distinct from bepridil or TFP. J Gen Physiol 2018; 151:9-17. [PMID: 30442775 PMCID: PMC6314390 DOI: 10.1085/jgp.201812131] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2018] [Accepted: 10/02/2018] [Indexed: 01/14/2023] Open
Abstract
Cardiac troponin activators could be beneficial in systolic heart failure. Tikunova et al. demonstrate that, unlike previously known calcium sensitizers, the small molecule 3-chlorodiphenylamine does not activate isolated cardiac troponin C but instead activates the intact troponin complex. Despite extensive efforts spanning multiple decades, the development of highly effective Ca2+ sensitizers for the heart remains an elusive goal. Existing Ca2+ sensitizers have other targets in addition to cardiac troponin (cTn), which can lead to adverse side effects, such as hypotension or arrhythmias. Thus, there is a need to design Ca2+-sensitizing drugs with higher affinity and selectivity for cTn. Previously, we determined that many compounds based on diphenylamine (DPA) were able to bind to a cTnC–cTnI chimera with moderate affinity (Kd ∼10–120 µM). Of these compounds, 3-chlorodiphenylamine (3-Cl-DPA) bound most tightly (Kd of 10 µM). Here, we investigate 3-Cl-DPA further and find that it increases the Ca2+ sensitivity of force development in skinned cardiac muscle. Using NMR, we show that, like the known Ca2+ sensitizers, trifluoperazine (TFP) and bepridil, 3-Cl-DPA is able to bind to the isolated N-terminal domain (N-domain) of cTnC (Kd of 6 µM). However, while the bulky molecules of TFP and bepridil stabilize the open state of the N-domain of cTnC, the small and flexible 3-Cl-DPA molecule is able to bind without stabilizing this open state. Thus, unlike TFP, which drastically slows the rate of Ca2+ dissociation from the N-domain of isolated cTnC in a dose-dependent manner, 3-Cl-DPA has no effect on the rate of Ca2+ dissociation. On the other hand, the affinity of 3-Cl-DPA for a cTnC–TnI chimera is at least an order of magnitude higher than that of TFP or bepridil, likely because 3-Cl-DPA is less disruptive of cTnI binding to cTnC. Therefore, 3-Cl-DPA has a bigger effect on the rate of Ca2+ dissociation from the entire cTn complex than TFP and bepridil. Our data suggest that 3-Cl-DPA activates the cTn complex via a unique mechanism and could be a suitable scaffold for the development of novel treatments for systolic heart failure.
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Affiliation(s)
- Svetlana B Tikunova
- Department of Physiology and Cell Biology, The Ohio State University, Columbus, OH
| | - Andres Cuesta
- Department of Physiology and Cell Biology, The Ohio State University, Columbus, OH
| | - Morgan Price
- Department of Physiology and Cell Biology, The Ohio State University, Columbus, OH
| | - Monica X Li
- Departments of Medicine and Biochemistry, University of Alberta, Edmonton, AB, Canada
| | - Natalya Belevych
- Division of Biosciences, College of Dentistry, The Ohio State University, Columbus, OH
| | | | - Peter J Reiser
- Division of Biosciences, College of Dentistry, The Ohio State University, Columbus, OH
| | - Peter M Hwang
- Departments of Medicine and Biochemistry, University of Alberta, Edmonton, AB, Canada
| | - Jonathan P Davis
- Department of Physiology and Cell Biology, The Ohio State University, Columbus, OH
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31
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Bowman JD, Lindert S. Molecular Dynamics and Umbrella Sampling Simulations Elucidate Differences in Troponin C Isoform and Mutant Hydrophobic Patch Exposure. J Phys Chem B 2018; 122:7874-7883. [PMID: 30070845 DOI: 10.1021/acs.jpcb.8b05435] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Troponin C (TnC) facilitates muscle contraction through calcium-binding within its N-terminal region (NTnC). As previously observed using molecular dynamics (MD) simulations, this calcium-binding event leads to an increase in the dynamics of helices lining a hydrophobic patch on TnC. Simulation times of multiple microseconds were required to even see a partial opening of the hydrophobic patch, limiting the ability to thoroughly and quantitatively investigate these rare events. Here we describe the application of umbrella sampling to probe the TnC hydrophobic patch opening in a more targeted and quantitative fashion. Umbrella sampling was utilized to investigate the differences in the free energy of opening between cardiac (cTnC) and fast skeletal TnC (sTnC). We found that, in agreement with previous reports, holo (calcium-bound) sTnC had a lower free energy of opening compared with holo cTnC. Additionally, differences in the free energy of opening of hypertrophic (HCM) and dilated cardiomyopathy (DCM) cTnC systems were investigated. MD simulations and umbrella sampling revealed a lower free energy of opening for the HCM mutations A8V and A31S, as well as the calcium-sensitizing mutation L48Q. The DCM mutations, Y5H, Q50R, and E59D/D75Y, all exhibited a higher free energy of opening. An umbrella sampling simulation of cTnI-bound holo cTnC exhibited the lowest free energy in the open configuration, in agreement with experimental data. In conclusion, this study presents a novel and successful protocol for applying umbrella sampling simulations to quantitatively study the molecular basis of muscle contraction and proposes a mechanism by which HCM and DCM-associated mutations influence contraction.
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Affiliation(s)
- Jacob D Bowman
- Department of Chemistry and Biochemistry , 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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32
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Force-Dependent Recruitment from the Myosin Off State Contributes to Length-Dependent Activation. Biophys J 2018; 115:543-553. [PMID: 30054031 DOI: 10.1016/j.bpj.2018.07.006] [Citation(s) in RCA: 39] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2018] [Accepted: 07/02/2018] [Indexed: 11/21/2022] Open
Abstract
Cardiac muscle develops more force when it is activated at longer lengths. The concentration of Ca2+ required to develop half-maximal force also decreases. These effects are known as length-dependent activation and are thought to play critical roles in the Frank-Starling relationship and cardiovascular homeostasis. The molecular mechanisms underpinning length-dependent activation remain unclear, but recent experiments suggest that they may include recruitment of myosin heads from the off (sometimes called super-relaxed) state. This manuscript presents a mathematical model of muscle contraction that was developed to investigate this hypothesis. Myosin heads in the model transitioned between an off state (that could not interact with actin), an on state (that could bind to actin), and a single attached state. Simulations were fitted to experimental data using multidimensional parameter optimization. Statistical analysis showed that a model in which the rate of the off-to-on transition increased linearly with force reproduced the length-dependent behavior of chemically permeabilized myocardium better than a model with a constant off-to-on transition rate (F-test, p < 0.001). This result suggests that the thick-filament transitions are modulated by force. Additional calculations showed that the model incorporating a mechanosensitive thick filament could also reproduce twitch responses measured in a trabecula stretched to different lengths. A final set of simulations was then used to test the model. These calculations predicted how reducing passive stiffness would impact the length dependence of the calcium sensitivity of contractile force. The prediction (a 60% reduction in ΔpCa50) mimicked the 58% reduction in ΔpCa50 in myocardium from rats that expressed a giant isoform of titin and had low resting tension. Together, these computational results suggest that force-dependent recruitment of myosin heads from the thick-filament off state contributes to length-dependent activation and the Frank-Starling relationship.
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33
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Abstract
This article focuses on three "bins" that comprise sets of biophysical derangements elicited by cardiomyopathy-associated mutations in the myofilament. Current therapies focus on symptom palliation and do not address the disease at its core. We and others have proposed that a more nuanced classification could lead to direct interventions based on early dysregulation changing the trajectory of disease progression in the preclinical cohort. Continued research is necessary to address the complexity of cardiomyopathic progression and develop efficacious therapeutics.
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Affiliation(s)
- Melissa L Lynn
- Department of Medicine, University of Arizona, Room 317, 1656 East Mabel Street, Tucson, AZ 85724, USA
| | - Sarah J Lehman
- Department of Physiological Sciences, University of Arizona, Room 317, 1656 East Mabel Street, Tucson, AZ 85724, USA
| | - Jil C Tardiff
- Department of Medicine, University of Arizona, Room 312, 1656 East Mabel Street, Tucson, AZ 85724, USA.
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Aprahamian ML, Tikunova SB, Price MV, Cuesta AF, Davis JP, Lindert S. Successful Identification of Cardiac Troponin Calcium Sensitizers Using a Combination of Virtual Screening and ROC Analysis of Known Troponin C Binders. J Chem Inf Model 2017; 57:3056-3069. [PMID: 29144742 DOI: 10.1021/acs.jcim.7b00536] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Calcium-dependent cardiac muscle contraction is regulated by the protein complex troponin. Calcium binds to the N-terminal domain of troponin C (cNTnC) which initiates the process of contraction. Heart failure is a consequence of a disruption of this process. With the prevalence of this condition, a strong need exists to find novel compounds to increase the calcium sensitivity of cNTnC. Desirable are small chemical molecules that bind to the interface between cTnC and the cTnI switch peptide and exhibit calcium sensitizing properties by possibly stabilizing cTnC in an open conformation. To identify novel drug candidates, we employed a structure-based drug discovery protocol that incorporated the use of a relaxed complex scheme (RCS). In preparation for the virtual screening, cNTnC conformations were identified based on their ability to correctly predict known cNTnC binders using a receiver operating characteristics analysis. Following a virtual screen of the National Cancer Institute's Developmental Therapeutic Program database, a small number of molecules were experimentally tested using stopped-flow kinetics and steady-state fluorescence titrations. We identified two novel compounds, 3-(4-methoxyphenyl)-6,7-chromanediol (NSC600285) and 3-(4-methylphenyl)-7,8-chromanediol (NSC611817), that show increased calcium sensitivity of cTnC in the presence of the regulatory domain of cTnI. The effects of NSC600285 and NSC611817 on the calcium dissociation rate was stronger than that of the known calcium sensitizer bepridil. Thus, we identified a 3-phenylchromane group as a possible key pharmacophore in the sensitization of cardiac muscle contraction. Building on this finding is of interest to researchers working on development of drugs for calcium sensitization.
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Affiliation(s)
- Melanie L Aprahamian
- 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
| | - Morgan V Price
- Davis Heart and Lung Research Institute and Department of Physiology and Cell Biology, Ohio State University , Columbus, Ohio 43210, United States
| | - Andres F Cuesta
- 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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35
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Chung JH, Biesiadecki BJ, Ziolo MT, Davis JP, Janssen PML. Myofilament Calcium Sensitivity: Role in Regulation of In vivo Cardiac Contraction and Relaxation. Front Physiol 2016; 7:562. [PMID: 28018228 PMCID: PMC5159616 DOI: 10.3389/fphys.2016.00562] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2016] [Accepted: 11/07/2016] [Indexed: 11/13/2022] Open
Abstract
Myofilament calcium sensitivity is an often-used indicator of cardiac muscle function, often assessed in disease states such as hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy (DCM). While assessment of calcium sensitivity provides important insights into the mechanical force-generating capability of a muscle at steady-state, the dynamic behavior of the muscle cannot be sufficiently assessed with a force-pCa curve alone. The equilibrium dissociation constant (Kd) of the force-pCa curve depends on the ratio of the apparent calcium association rate constant (kon) and apparent calcium dissociation rate constant (koff) of calcium on TnC and as a stand-alone parameter cannot provide an accurate description of the dynamic contraction and relaxation behavior without the additional quantification of kon or koff, or actually measuring dynamic twitch kinetic parameters in an intact muscle. In this review, we examine the effect of length, frequency, and beta-adrenergic stimulation on myofilament calcium sensitivity and dynamic contraction in the myocardium, the effect of membrane permeabilization/mechanical- or chemical skinning on calcium sensitivity, and the dynamic consequences of various myofilament protein mutations with potential implications in contractile and relaxation behavior.
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Affiliation(s)
- Jae-Hoon Chung
- Department of Physiology and Cell Biology, The Ohio State University Wexner Medical CenterColumbus, OH, USA; Dorothy M. Davis Heart and Lung Research Institute, The Ohio State University Wexner Medical CenterColumbus, OH, USA; Medical Scientist Training Program and Biomedical Sciences Graduate Program, The Ohio State University Wexner Medical CenterColumbus, OH, USA
| | - Brandon J Biesiadecki
- Department of Physiology and Cell Biology, The Ohio State University Wexner Medical CenterColumbus, OH, USA; Dorothy M. Davis Heart and Lung Research Institute, The Ohio State University Wexner Medical CenterColumbus, OH, USA
| | - Mark T Ziolo
- Department of Physiology and Cell Biology, The Ohio State University Wexner Medical CenterColumbus, OH, USA; Dorothy M. Davis Heart and Lung Research Institute, The Ohio State University Wexner Medical CenterColumbus, OH, USA
| | - Jonathan P Davis
- Department of Physiology and Cell Biology, The Ohio State University Wexner Medical CenterColumbus, OH, USA; Dorothy M. Davis Heart and Lung Research Institute, The Ohio State University Wexner Medical CenterColumbus, OH, USA
| | - Paul M L Janssen
- Department of Physiology and Cell Biology, The Ohio State University Wexner Medical CenterColumbus, OH, USA; Dorothy M. Davis Heart and Lung Research Institute, The Ohio State University Wexner Medical CenterColumbus, OH, USA; Department of Internal Medicine, The Ohio State University Wexner Medical CenterColumbus, OH, USA
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36
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Salhi HE, Hassel NC, Siddiqui JK, Brundage EA, Ziolo MT, Janssen PML, Davis JP, Biesiadecki BJ. Myofilament Calcium Sensitivity: Mechanistic Insight into TnI Ser-23/24 and Ser-150 Phosphorylation Integration. Front Physiol 2016; 7:567. [PMID: 28018230 PMCID: PMC5156683 DOI: 10.3389/fphys.2016.00567] [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: 08/12/2016] [Accepted: 11/08/2016] [Indexed: 11/14/2022] Open
Abstract
Troponin I (TnI) is a major regulator of cardiac muscle contraction and relaxation. During physiological and pathological stress, TnI is differentially phosphorylated at multiple residues through different signaling pathways to match cardiac function to demand. The combination of these TnI phosphorylations can exhibit an expected or unexpected functional integration, whereby the function of two phosphorylations are different than that predicted from the combined function of each individual phosphorylation alone. We have shown that TnI Ser-23/24 and Ser-150 phosphorylation exhibit functional integration and are simultaneously increased in response to cardiac stress. In the current study, we investigated the functional integration of TnI Ser-23/24 and Ser-150 to alter cardiac contraction. We hypothesized that Ser-23/24 and Ser-150 phosphorylation each utilize distinct molecular mechanisms to alter the TnI binding affinity within the thin filament. Mathematical modeling predicts that Ser-23/24 and Ser-150 phosphorylation affect different TnI affinities within the thin filament to distinctly alter the Ca2+-binding properties of troponin. Protein binding experiments validate this assertion by demonstrating pseudo-phosphorylated Ser-150 decreases the affinity of isolated TnI for actin, whereas Ser-23/24 pseudo-phosphorylation is not different from unphosphorylated. Thus, our data supports that TnI Ser-23/24 affects TnI-TnC binding, while Ser-150 phosphorylation alters TnI-actin binding. By measuring force development in troponin-exchanged skinned myocytes, we demonstrate that the Ca2+ sensitivity of force is directly related to the amount of phosphate present on TnI. Furthermore, we demonstrate that Ser-150 pseudo-phosphorylation blunts Ser-23/24-mediated decreased Ca2+-sensitive force development whether on the same or different TnI molecule. Therefore, TnI phosphorylations can integrate across troponins along the myofilament. These data demonstrate that TnI Ser-23/24 and Ser-150 phosphorylation regulates muscle contraction in part by modulating different TnI interactions in the thin filament and it is the combination of these differential mechanisms that provides understanding of their functional integration.
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Affiliation(s)
- Hussam E Salhi
- Department of Physiology and Cell Biology and Davis Heart and Lung Research Institute, Ohio State University Columbus, OH, USA
| | - Nathan C Hassel
- Department of Physiology and Cell Biology and Davis Heart and Lung Research Institute, Ohio State University Columbus, OH, USA
| | - Jalal K Siddiqui
- Department of Physiology and Cell Biology and Davis Heart and Lung Research Institute, Ohio State University Columbus, OH, USA
| | - Elizabeth A Brundage
- Department of Physiology and Cell Biology and Davis Heart and Lung Research Institute, Ohio State University Columbus, OH, USA
| | - Mark T Ziolo
- Department of Physiology and Cell Biology and Davis Heart and Lung Research Institute, Ohio State University Columbus, OH, USA
| | - Paul M L Janssen
- Department of Physiology and Cell Biology and Davis Heart and Lung Research Institute, Ohio State University Columbus, OH, USA
| | - Jonathan P Davis
- Department of Physiology and Cell Biology and Davis Heart and Lung Research Institute, Ohio State University Columbus, OH, USA
| | - Brandon J Biesiadecki
- Department of Physiology and Cell Biology and Davis Heart and Lung Research Institute, Ohio State University Columbus, OH, USA
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