1
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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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2
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Parijat P, Ponnam S, Attili S, Campbell KS, El-Mezgueldi M, Pfuhl M, Kampourakis T. Discovery of novel cardiac troponin activators using fluorescence polarization-based high throughput screening assays. Sci Rep 2023; 13:5216. [PMID: 36997544 PMCID: PMC10063609 DOI: 10.1038/s41598-023-32476-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2022] [Accepted: 03/28/2023] [Indexed: 04/03/2023] Open
Abstract
The large unmet demand for new heart failure therapeutics is widely acknowledged. Over the last decades the contractile myofilaments themselves have emerged as an attractive target for the development of new therapeutics for both systolic and diastolic heart failure. However, the clinical use of myofilament-directed drugs has been limited, and further progress has been hampered by incomplete understanding of myofilament function on the molecular level and screening technologies for small molecules that accurately reproduce this function in vitro. In this study we have designed, validated and characterized new high throughput screening platforms for small molecule effectors targeting the interactions between the troponin C and troponin I subunits of the cardiac troponin complex. Fluorescence polarization-based assays were used to screen commercially available compound libraries, and hits were validated using secondary screens and orthogonal assays. Hit compound-troponin interactions were characterized using isothermal titration calorimetry and NMR spectroscopy. We identified NS5806 as novel calcium sensitizer that stabilizes active troponin. In good agreement, NS5806 greatly increased the calcium sensitivity and maximal isometric force of demembranated human donor myocardium. Our results suggest that sarcomeric protein-directed screening platforms are suitable for the development of compounds that modulate cardiac myofilament function.
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Affiliation(s)
- Priyanka Parijat
- Randall Centre for Cell and Molecular Biophysics, King's College London, London, SE1 1UL, UK
- British Heart Foundation Centre of Research Excellence, King's College London, London, SE1 1UL, UK
| | - Saraswathi Ponnam
- Randall Centre for Cell and Molecular Biophysics, King's College London, London, SE1 1UL, UK
- British Heart Foundation Centre of Research Excellence, King's College London, London, SE1 1UL, UK
| | - Seetharamaiah Attili
- Randall Centre for Cell and Molecular Biophysics, King's College London, London, SE1 1UL, UK
- British Heart Foundation Centre of Research Excellence, King's College London, London, SE1 1UL, UK
| | - Kenneth S Campbell
- Division of Cardiovascular Medicine and Department of Physiology, University of Kentucky, Lexington, KY, USA
| | - Mohammed El-Mezgueldi
- Randall Centre for Cell and Molecular Biophysics, King's College London, London, SE1 1UL, UK
- British Heart Foundation Centre of Research Excellence, King's College London, London, SE1 1UL, UK
| | - Mark Pfuhl
- Randall Centre for Cell and Molecular Biophysics, King's College London, London, SE1 1UL, UK
- British Heart Foundation Centre of Research Excellence, King's College London, London, SE1 1UL, UK
| | - Thomas Kampourakis
- Randall Centre for Cell and Molecular Biophysics, King's College London, London, SE1 1UL, UK.
- British Heart Foundation Centre of Research Excellence, King's College London, London, SE1 1UL, UK.
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3
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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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4
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Poppe L, Hartman JJ, Romero A, Reagan JD. Structural and Thermodynamic Model for the Activation of Cardiac Troponin. Biochemistry 2022; 61:741-748. [PMID: 35349258 DOI: 10.1021/acs.biochem.2c00084] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Cardiac troponin is a regulatory protein complex located on the sarcomere that regulates the engagement of myosin on actin filaments. Low-molecular weight modulators of troponin that bind allosterically with the calcium ion have the potential to improve cardiac contractility in patients with reduced cardiac function. Here we propose an approach to the rational design of troponin modulators through the combined use of solution nuclear magnetic resonance and isothermal titration calorimetry methods. In contrast to traditional approaches limited to calcium and activator-bound troponin structures, here we analyzed the structural and thermodynamic impact of an activator in the context of the troponin functional cycle. This led us to propose a rationale for developing an efficacious troponin activator.
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Affiliation(s)
- Leszek Poppe
- Amgen, Inc., Thousand Oaks, California 91320, United States
| | - James J Hartman
- Cytokinetics, Inc., South San Francisco, California 94080, United States
| | - Antonio Romero
- Cytokinetics, Inc., South San Francisco, California 94080, United States
| | - Jeffrey D Reagan
- Amgen, Inc., South San Francisco, California 94080, United States
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5
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Yan C, Sack JS. X-ray structure of a human cardiac muscle troponin C/troponin I chimera in two crystal forms. Acta Crystallogr F Struct Biol Commun 2022; 78:17-24. [PMID: 34981771 PMCID: PMC8725003 DOI: 10.1107/s2053230x21012395] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2021] [Accepted: 11/22/2021] [Indexed: 01/03/2023] Open
Abstract
The X-ray crystal structure of a human cardiac muscle troponin C/troponin I chimera has been determined in two different crystal forms and shows a conformation of the complex that differs from that previously observed by NMR. The chimera consists of the N-terminal domain of troponin C (cTnC; residues 1-80) fused to the switch region of troponin I (cTnI; residues 138-162). In both crystal forms, the cTnI residues form a six-turn α-helix that lays across the hydrophobic groove of an adjacent cTnC molecule in the crystal structure. In contrast to previous models, the cTnI helix runs in a parallel direction relative to the cTnC groove and completely blocks the calcium desensitizer binding site of the cTnC-cTnI interface.
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Affiliation(s)
- Chunhong Yan
- Small Molecule Drug Discovery, Bristol Myers Squibb Research and Development, PO Box 4000, Princeton, NJ 08543-4000, USA
| | - John S. Sack
- Small Molecule Drug Discovery, Bristol Myers Squibb Research and Development, PO Box 4000, Princeton, NJ 08543-4000, USA,Correspondence e-mail:
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6
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Cai F, Kampourakis T, Klein BA, Sykes BD. A Potent Fluorescent Reversible-Covalent Inhibitor of Cardiac Muscle Contraction. ACS Med Chem Lett 2021; 12:1503-1507. [PMID: 34531960 DOI: 10.1021/acsmedchemlett.1c00366] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2021] [Accepted: 08/19/2021] [Indexed: 11/28/2022] Open
Abstract
Compounds that directly modulate the response of the cardiac sarcomere have potential in the treatment of cardiac disease. While a number of sarcomere activators have been discovered and extensively studied, very few inhibitors have been identified. We report a potent cardiac sarcomere inhibitor, DN-F01, targeting the cardiac muscle thin filament protein troponin complex. Functional studies show that DN-F01 has a strong inhibitory calcium-dependent effect on cardiac myofibrillar ATPase activity with an IC50 value of 11 ± 4 nmol/L. DN-F01 is shown to bind to a cardiac troponin C-troponin I chimera (cChimera) with a K D of ∼50 nM using fluorescence spectroscopy, indicating that troponin is the likely target for DN-F01. NMR titrations of DN-F01 to C35S and A-Cys cChimera show covalent and noncovalent binding of DN-F01 bound to the calcium-saturated cChimera.
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Affiliation(s)
- Fangze Cai
- Department of Biochemistry, University of Alberta, Edmonton AB T6G 2R3, Canada
| | - Thomas Kampourakis
- Randall Centre for Cell and Molecular Biophysics, King’s College London, London SE1 1UL, United Kingdom
| | - Brittney A. Klein
- Department of Biochemistry, University of Alberta, Edmonton AB T6G 2R3, Canada
| | - Brian D. Sykes
- Department of Biochemistry, University of Alberta, Edmonton AB T6G 2R3, Canada
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7
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Li MX, Mercier P, Hartman JJ, Sykes BD. Structural Basis of Tirasemtiv Activation of Fast Skeletal Muscle. J Med Chem 2021; 64:3026-3034. [PMID: 33703886 DOI: 10.1021/acs.jmedchem.0c01412] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Troponin regulates the calcium-mediated activation of skeletal muscle. Muscle weakness in diseases such as amyotrophic lateral sclerosis and spinal muscular atrophy occurs from diminished neuromuscular output. The first direct fast skeletal troponin activator, tirasemtiv, amplifies the response of muscle to neuromuscular input. Tirasemtiv binds selectively and strongly to fast skeletal troponin, slowing the rate of calcium release and sensitizing muscle to calcium. We report the solution NMR structure of tirasemtiv bound to a fast skeletal troponin C-troponin I chimera. The structure reveals that tirasemtiv binds in a hydrophobic pocket between the regulatory domain of troponin C and the switch region of troponin I, which overlaps with that of Anapoe in the X-ray structure of skeletal troponin. Multiple interactions stabilize the troponin C-troponin I interface, increase the affinity of troponin C for the switch region of fast skeletal troponin I, and drive the equilibrium toward the active state.
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Affiliation(s)
- Monica X Li
- Department of Biochemistry, University of Alberta, Edmonton, AB T6G 2H7, Canada
| | - Pascal Mercier
- National High Field NMR Centre, University of Alberta, Edmonton, AB T6G 2E1, Canada
| | - James J Hartman
- Cytokinetics, Inc., South San Francisco, California 94080, United States
| | - Brian D Sykes
- Department of Biochemistry, University of Alberta, Edmonton, AB T6G 2H7, Canada
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8
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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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9
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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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10
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Cai F, Hwang PM, Sykes BD. Structural Changes Induced by the Binding of the Calcium Desensitizer W7 to Cardiac Troponin. Biochemistry 2018; 57:6461-6469. [DOI: 10.1021/acs.biochem.8b00882] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Affiliation(s)
- Fangze Cai
- Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2H7
| | - Peter M. Hwang
- Department of Medicine, University of Alberta, Edmonton, Alberta, Canada T6G 2H7
| | - Brian D. Sykes
- Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2H7
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11
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Klein BA, Reiz B, Robertson IM, Irving M, Li L, Sun YB, Sykes BD. Reversible Covalent Reaction of Levosimendan with Cardiac Troponin C in Vitro and in Situ. Biochemistry 2018; 57:2256-2265. [DOI: 10.1021/acs.biochem.8b00109] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Affiliation(s)
- Brittney A. Klein
- Department of Biochemistry, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
| | - Béla Reiz
- Department of Chemistry, Faculty of Science, University of Alberta, Edmonton, Alberta T6H 2H7, Canada
| | - Ian M. Robertson
- Pharmaceutical and Health Benefits Branch, Ministry of Health, Government of Alberta, Edmonton, Alberta T5J 3Z5, Canada
| | - Malcolm Irving
- Randall Centre for Cell and Molecular Biophysics and British Heart Foundation Centre of Research Excellence, King’s College London, London SE1 1UL, U.K
| | - Liang Li
- Department of Chemistry, Faculty of Science, University of Alberta, Edmonton, Alberta T6H 2H7, Canada
| | - Yin-Biao Sun
- Randall Centre for Cell and Molecular Biophysics and British Heart Foundation Centre of Research Excellence, King’s College London, London SE1 1UL, U.K
| | - Brian D. Sykes
- Department of Biochemistry, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
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12
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Siddiqui JK, Tikunova SB, Walton SD, Liu B, Meyer M, de Tombe PP, Neilson N, Kekenes-Huskey PM, Salhi HE, Janssen PML, Biesiadecki BJ, Davis JP. Myofilament Calcium Sensitivity: Consequences of the Effective Concentration of Troponin I. Front Physiol 2016; 7:632. [PMID: 28066265 PMCID: PMC5175494 DOI: 10.3389/fphys.2016.00632] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2016] [Accepted: 12/05/2016] [Indexed: 12/04/2022] Open
Abstract
Control of calcium binding to and dissociation from cardiac troponin C (TnC) is essential to healthy cardiac muscle contraction/relaxation. There are numerous aberrant post-translational modifications and mutations within a plethora of contractile, and even non-contractile, proteins that appear to imbalance this delicate relationship. The direction and extent of the resulting change in calcium sensitivity is thought to drive the heart toward one type of disease or another. There are a number of molecular mechanisms that may be responsible for the altered calcium binding properties of TnC, potentially the most significant being the ability of the regulatory domain of TnC to bind the switch peptide region of TnI. Considering TnI is essentially tethered to TnC and cannot diffuse away in the absence of calcium, we suggest that the apparent calcium binding properties of TnC are highly dependent upon an “effective concentration” of TnI available to bind TnC. Based on our previous work, TnI peptide binding studies and the calcium binding properties of chimeric TnC-TnI fusion constructs, and building upon the concept of effective concentration, we have developed a mathematical model that can simulate the steady-state and kinetic calcium binding properties of a wide assortment of disease-related and post-translational protein modifications in the isolated troponin complex and reconstituted thin filament. We predict that several TnI and TnT modifications do not alter any of the intrinsic calcium or TnI binding constants of TnC, but rather alter the ability of TnC to “find” TnI in the presence of calcium. These studies demonstrate the apparent consequences of the effective TnI concentration in modulating the calcium binding properties of TnC.
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Affiliation(s)
- Jalal K Siddiqui
- Department of Physiology and Cell Biology and the Davis Heart and Lung Research Institute, The Ohio State University Columbus, OH, USA
| | - Svetlana B Tikunova
- Department of Physiology and Cell Biology and the Davis Heart and Lung Research Institute, The Ohio State University Columbus, OH, USA
| | - Shane D Walton
- Department of Physiology and Cell Biology and the Davis Heart and Lung Research Institute, The Ohio State University Columbus, OH, USA
| | - Bin Liu
- Department of Physiology and Cell Biology and the Davis Heart and Lung Research Institute, The Ohio State University Columbus, OH, USA
| | - Meredith Meyer
- Department of Physiology and Cell Biology and the Davis Heart and Lung Research Institute, The Ohio State University Columbus, OH, USA
| | - Pieter P de Tombe
- Cell and Molecular Physiology, Loyola University Chicago Maywood, IL, USA
| | - Nathan Neilson
- Department of Physiology and Cell Biology and the Davis Heart and Lung Research Institute, The Ohio State University Columbus, OH, USA
| | | | - Hussam E Salhi
- Department of Physiology and Cell Biology and the Davis Heart and Lung Research Institute, The Ohio State University Columbus, OH, USA
| | - Paul M L Janssen
- Department of Physiology and Cell Biology and the Davis Heart and Lung Research Institute, The Ohio State University Columbus, OH, USA
| | - Brandon J Biesiadecki
- Department of Physiology and Cell Biology and the Davis Heart and Lung Research Institute, The Ohio State University Columbus, OH, USA
| | - Jonathan P Davis
- Department of Physiology and Cell Biology and the Davis Heart and Lung Research Institute, The Ohio State University Columbus, OH, USA
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13
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Cai F, Li MX, Pineda-Sanabria SE, Gelozia S, Lindert S, West F, Sykes BD, Hwang PM. Structures reveal details of small molecule binding to cardiac troponin. J Mol Cell Cardiol 2016; 101:134-144. [PMID: 27825981 DOI: 10.1016/j.yjmcc.2016.10.016] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/09/2016] [Revised: 10/22/2016] [Accepted: 10/25/2016] [Indexed: 11/27/2022]
Abstract
In cardiac and skeletal muscle, the troponin complex turns muscle contraction on and off in a calcium-dependent manner. Many small molecules are known to bind to the troponin complex to modulate its calcium binding affinity, and this may be useful in a broad range of conditions in which striated muscle function is compromised, such as congestive heart failure. As a tool for developing drugs specific for the cardiac isoform of troponin, we have designed a chimeric construct (cChimera) consisting of the regulatory N-terminal domain of cardiac troponin C (cNTnC) fused to the switch region of cardiac troponin I (cTnI), mimicking the key binding event that turns on muscle contraction. We demonstrate by solution NMR spectroscopy that cChimera faithfully reproduces the native interface between cTnI and cNTnC. We determined that small molecules based on diphenylamine can bind to cChimera with a KD as low as 10μM. Solution NMR structures show that minimal structural perturbations in cChimera are needed to accommodate 3-methyldiphenylamine (3-mDPA), which is probably why it binds with higher affinity than previously studied compounds like bepridil, despite its significantly smaller size. The unsubstituted aromatic ring of 3-mDPA binds to an inner hydrophobic pocket adjacent to the central beta sheet of cNTnC. However, the methyl-substituted ring is able to bind in two different orientations, either inserting into the cNTnC-cTnI interface or "flipping out" to form contacts primarily with helix C of cNTnC. Our work suggests that preservation of the native interaction between cNTnC and cTnI is key to the development of a high affinity cardiac troponin-specific drug.
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Affiliation(s)
- Fangze Cai
- Department of Biochemistry, University of Alberta, Edmonton, AB, Canada
| | - Monica X Li
- Department of Medicine, University of Alberta, Edmonton, AB, Canada
| | | | - Shorena Gelozia
- Department of Chemistry, University of Alberta, Edmonton, AB, Canada
| | - Steffen Lindert
- Department of Chemistry and Biochemistry, Ohio State University, Columbus, OH, USA
| | - Frederick West
- Department of Chemistry, University of Alberta, Edmonton, AB, Canada
| | - Brian D Sykes
- Department of Biochemistry, University of Alberta, Edmonton, AB, Canada
| | - 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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14
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Marques MDA, de Oliveira GAP. Cardiac Troponin and Tropomyosin: Structural and Cellular Perspectives to Unveil the Hypertrophic Cardiomyopathy Phenotype. Front Physiol 2016; 7:429. [PMID: 27721798 PMCID: PMC5033975 DOI: 10.3389/fphys.2016.00429] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2016] [Accepted: 09/09/2016] [Indexed: 12/12/2022] Open
Abstract
Inherited myopathies affect both skeletal and cardiac muscle and are commonly associated with genetic dysfunctions, leading to the production of anomalous proteins. In cardiomyopathies, mutations frequently occur in sarcomeric genes, but the cause-effect scenario between genetic alterations and pathological processes remains elusive. Hypertrophic cardiomyopathy (HCM) was the first cardiac disease associated with a genetic background. Since the discovery of the first mutation in the β-myosin heavy chain, more than 1400 new mutations in 11 sarcomeric genes have been reported, awarding HCM the title of the “disease of the sarcomere.” The most common macroscopic phenotypes are left ventricle and interventricular septal thickening, but because the clinical profile of this disease is quite heterogeneous, these phenotypes are not suitable for an accurate diagnosis. The development of genomic approaches for clinical investigation allows for diagnostic progress and understanding at the molecular level. Meanwhile, the lack of accurate in vivo models to better comprehend the cellular events triggered by this pathology has become a challenge. Notwithstanding, the imbalance of Ca2+ concentrations, altered signaling pathways, induction of apoptotic factors, and heart remodeling leading to abnormal anatomy have already been reported. Of note, a misbalance of signaling biomolecules, such as kinases and tumor suppressors (e.g., Akt and p53), seems to participate in apoptotic and fibrotic events. In HCM, structural and cellular information about defective sarcomeric proteins and their altered interactome is emerging but still represents a bottleneck for developing new concepts in basic research and for future therapeutic interventions. This review focuses on the structural and cellular alterations triggered by HCM-causing mutations in troponin and tropomyosin proteins and how structural biology can aid in the discovery of new platforms for therapeutics. We highlight the importance of a better understanding of allosteric communications within these thin-filament proteins to decipher the HCM pathological state.
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Affiliation(s)
- Mayra de A Marques
- Programa de Biologia Estrutural, Centro Nacional de Ressonância Magnética Nuclear Jiri Jonas, Instituto de Bioquímica Médica Leopoldo de Meis, Instituto Nacional de Biologia Estrutural e Bioimagem, Universidade Federal do Rio de Janeiro Rio de Janeiro, Brazil
| | - Guilherme A P de Oliveira
- Programa de Biologia Estrutural, Centro Nacional de Ressonância Magnética Nuclear Jiri Jonas, Instituto de Bioquímica Médica Leopoldo de Meis, Instituto Nacional de Biologia Estrutural e Bioimagem, Universidade Federal do Rio de Janeiro Rio de Janeiro, Brazil
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15
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Pineda-Sanabria SE, Robertson IM, Sun YB, Irving M, Sykes BD. Probing the mechanism of cardiovascular drugs using a covalent levosimendan analog. J Mol Cell Cardiol 2016; 92:174-84. [PMID: 26853943 PMCID: PMC4831045 DOI: 10.1016/j.yjmcc.2016.02.003] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/01/2015] [Revised: 01/24/2016] [Accepted: 02/02/2016] [Indexed: 01/16/2023]
Abstract
One approach to improve contraction in the failing heart is the administration of calcium (Ca2 +) sensitizers. Although it is known that levosimendan and other sensitizers bind to troponin C (cTnC), their in vivo mechanism is not fully understood. Based on levosimendan, we designed a covalent Ca2 + sensitizer (i9) that targets C84 of cTnC and exchanged this complex into cardiac muscle. The NMR structure of the covalent complex showed that i9 binds deep in the hydrophobic pocket of cTnC. Despite slightly reducing troponin I affinity, i9 enhanced the Ca2 + sensitivity of cardiac muscle. We conclude that i9 enhances Ca2 + sensitivity by stabilizing the open conformation of cTnC. These findings provide new insights into the in vivo mechanism of Ca2 + sensitization and demonstrate that directly targeting cTnC has significant potential in cardiovascular therapy. A Ca2 + sensitizer, i9 was designed that forms a covalent bond with C84 of cTnC. i9 stabilized the open state of the N-domain of cTnC. The structure of the covalent cTnC-cTnI-i9 complex was solved by NMR. The structure showed that i9 binds deep in the hydrophobic pocket of cTnC. Despite slightly reducing cTnI affinity, i9 enhanced the Ca2 + sensitivity of cardiac muscle.
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Affiliation(s)
- Sandra E Pineda-Sanabria
- Department of Biochemistry, Faculty of Medicine & Dentistry, University of Alberta, Edmonton, AB T6G 2H7, Canada
| | - Ian M Robertson
- Randall Division of Cell and Molecular Biophysics and British Heart Foundation Centre of Research Excellence, New Hunt's House, Guy's Campus, King's College London, London SE1 1UL, UK
| | - Yin-Biao Sun
- Randall Division of Cell and Molecular Biophysics and British Heart Foundation Centre of Research Excellence, New Hunt's House, Guy's Campus, King's College London, London SE1 1UL, UK
| | - Malcolm Irving
- Randall Division of Cell and Molecular Biophysics and British Heart Foundation Centre of Research Excellence, New Hunt's House, Guy's Campus, King's College London, London SE1 1UL, UK
| | - Brian D Sykes
- Department of Biochemistry, Faculty of Medicine & Dentistry, University of Alberta, Edmonton, AB T6G 2H7, Canada.
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16
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Pineda-Sanabria SE, Robertson IM, Sykes BD. Structure and Dynamics of the Acidosis-Resistant A162H Mutant of the Switch Region of Troponin I Bound to the Regulatory Domain of Troponin C. Biochemistry 2015; 54:3583-93. [DOI: 10.1021/acs.biochem.5b00178] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Affiliation(s)
- Sandra E. Pineda-Sanabria
- Department of Biochemistry, ‡Department of Pediatrics, Faculty of Medicine & Dentistry, University of Alberta, Edmonton, AB T6G 2H7, Canada
| | - Ian M. Robertson
- Department of Biochemistry, ‡Department of Pediatrics, Faculty of Medicine & Dentistry, University of Alberta, Edmonton, AB T6G 2H7, Canada
| | - Brian D. Sykes
- Department of Biochemistry, ‡Department of Pediatrics, Faculty of Medicine & Dentistry, University of Alberta, Edmonton, AB T6G 2H7, Canada
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17
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Abstract
Various human diseases can disrupt the balance between muscle contraction and relaxation. Sarcomeric modulators can be used to readjust this balance either indirectly by intervening in signalling pathways or directly through interaction with the muscle proteins that control contraction. Such agents represent a novel approach to treating any condition in which striated muscle function is compromised, including heart failure, cardiomyopathies, skeletal myopathies and a wide range of neuromuscular conditions. Here, we review agents that modulate the mechanical function of the sarcomere, focusing on emerging compounds that target myosin or the troponin complex.
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