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Cubuk J, Greenberg L, Greenberg AE, Emenecker RJ, Stuchell-Brereton MD, Holehouse AS, Soranno A, Greenberg MJ. Structural dynamics of the intrinsically disordered linker region of cardiac troponin T. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.05.30.596451. [PMID: 38853835 PMCID: PMC11160775 DOI: 10.1101/2024.05.30.596451] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2024]
Abstract
The cardiac troponin complex, composed of troponins I, T, and C, plays a central role in regulating the calcium-dependent interactions between myosin and the thin filament. Mutations in troponin can cause cardiomyopathies; however, it is still a major challenge for the field to connect how changes in sequence affect troponin's function. Recent high-resolution structures of the thin filament revealed critical insights into the structure-function relationship of the troponin complex, but there remain large, unresolved segments of troponin, including the troponin-T linker region that is a hotspot for several cardiomyopathy mutations. This unresolved yet functionally-significant linker region has been proposed to be intrinsically disordered, with behaviors that are not well described by traditional structural approaches; however, this proposal has not been experimentally verified. Here, we used a combination of single-molecule Förster resonance energy transfer (FRET), molecular dynamics simulations, and functional reconstitution assays to investigate the troponin-T linker region. We experimentally and computationally show that in the context of both isolated troponin and the fully regulated troponin complex, the linker behaves as a dynamic, intrinsically disordered region. This region undergoes polyampholyte expansion in the presence of high salt and distinct conformational changes during the assembly of the troponin complex. We also examine the ΔE160 hypertrophic cardiomyopathy mutation in the linker, and we demonstrate that this mutation does not affect the conformational dynamics of the linker, rather it allosterically affects interactions with other subunits of the troponin complex, leading to increased molecular contractility. Taken together, our data clearly demonstrate the importance of disorder within the troponin-T linker and provide new insights into the molecular mechanisms controlling the pathogenesis of cardiomyopathies.
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Affiliation(s)
- Jasmine Cubuk
- Department of Biochemistry and Molecular Biophysics, Washington University in St Louis, 660 Euclid Ave, 63110, Saint Louis, MO, USA
- Center for Biomolecular Condensates, Washington University in St Louis, 1 Brookings Drive, 63130, Saint Louis, MO, USA
| | - Lina Greenberg
- Department of Biochemistry and Molecular Biophysics, Washington University in St Louis, 660 Euclid Ave, 63110, Saint Louis, MO, USA
| | - Akiva E. Greenberg
- Department of Biochemistry and Molecular Biophysics, Washington University in St Louis, 660 Euclid Ave, 63110, Saint Louis, MO, USA
| | - Ryan J. Emenecker
- Department of Biochemistry and Molecular Biophysics, Washington University in St Louis, 660 Euclid Ave, 63110, Saint Louis, MO, USA
- Center for Biomolecular Condensates, Washington University in St Louis, 1 Brookings Drive, 63130, Saint Louis, MO, USA
| | - Melissa D. Stuchell-Brereton
- Department of Biochemistry and Molecular Biophysics, Washington University in St Louis, 660 Euclid Ave, 63110, Saint Louis, MO, USA
- Center for Biomolecular Condensates, Washington University in St Louis, 1 Brookings Drive, 63130, Saint Louis, MO, USA
| | - Alex S. Holehouse
- Department of Biochemistry and Molecular Biophysics, Washington University in St Louis, 660 Euclid Ave, 63110, Saint Louis, MO, USA
- Center for Biomolecular Condensates, Washington University in St Louis, 1 Brookings Drive, 63130, Saint Louis, MO, USA
| | - Andrea Soranno
- Department of Biochemistry and Molecular Biophysics, Washington University in St Louis, 660 Euclid Ave, 63110, Saint Louis, MO, USA
- Center for Biomolecular Condensates, Washington University in St Louis, 1 Brookings Drive, 63130, Saint Louis, MO, USA
| | - Michael J. Greenberg
- Department of Biochemistry and Molecular Biophysics, Washington University in St Louis, 660 Euclid Ave, 63110, Saint Louis, MO, USA
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2
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Arts T, Lyon A, Delhaas T, Kuster DWD, van der Velden J, Lumens J. Translating myosin-binding protein C and titin abnormalities to whole-heart function using a novel calcium-contraction coupling model. J Mol Cell Cardiol 2024; 190:13-23. [PMID: 38462126 DOI: 10.1016/j.yjmcc.2024.03.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/01/2023] [Revised: 01/15/2024] [Accepted: 03/01/2024] [Indexed: 03/12/2024]
Abstract
Mutations in cardiac myosin-binding protein C (cMyBP-C) or titin may respectively lead to hypertrophic (HCM) or dilated (DCM) cardiomyopathies. The mechanisms leading to these phenotypes remain unclear because of the challenge of translating cellular abnormalities to whole-heart and system function. We developed and validated a novel computer model of calcium-contraction coupling incorporating the role of cMyBP-C and titin based on the key assumptions: 1) tension in the thick filament promotes cross-bridge attachment mechanochemically, 2) with increasing titin tension, more myosin heads are unlocked for attachment, and 3) cMyBP-C suppresses cross-bridge attachment. Simulated stationary calcium-tension curves, isotonic and isometric contractions, and quick release agreed with experimental data. The model predicted that a loss of cMyBP-C function decreases the steepness of the calcium-tension curve, and that more compliant titin decreases the level of passive and active tension and its dependency on sarcomere length. Integrating this cellular model in the CircAdapt model of the human heart and circulation showed that a loss of cMyBP-C function resulted in HCM-like hemodynamics with higher left ventricular end-diastolic pressures and smaller volumes. More compliant titin led to higher diastolic pressures and ventricular dilation, suggesting DCM-like hemodynamics. The novel model of calcium-contraction coupling incorporates the role of cMyBP-C and titin. Its coupling to whole-heart mechanics translates changes in cellular calcium-contraction coupling to changes in cardiac pump and circulatory function and identifies potential mechanisms by which cMyBP-C and titin abnormalities may develop into HCM and DCM phenotypes. This modeling platform may help identify distinct mechanisms underlying clinical phenotypes in cardiac diseases.
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Affiliation(s)
- Theo Arts
- Department of Biomedical Engineering, Cardiovascular Research Center Maastricht (CARIM), Maastricht University, 6200MD Maastricht, the Netherlands.
| | - Aurore Lyon
- Department of Biomedical Engineering, Cardiovascular Research Center Maastricht (CARIM), Maastricht University, 6200MD Maastricht, the Netherlands
| | - Tammo Delhaas
- Department of Biomedical Engineering, Cardiovascular Research Center Maastricht (CARIM), Maastricht University, 6200MD Maastricht, the Netherlands
| | - Diederik W D Kuster
- Department of Physiology, Amsterdam University Medical Center, 1081HZ Amsterdam, the Netherlands
| | - Jolanda van der Velden
- Department of Physiology, Amsterdam University Medical Center, 1081HZ Amsterdam, the Netherlands
| | - Joost Lumens
- Department of Biomedical Engineering, Cardiovascular Research Center Maastricht (CARIM), Maastricht University, 6200MD Maastricht, the Netherlands
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3
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Chapman EA, Roberts DS, Tiambeng TN, Andrews J, Wang MD, Reasoner EA, Melby JA, Li BH, Kim D, Alpert AJ, Jin S, Ge Y. Structure and dynamics of endogenous cardiac troponin complex in human heart tissue captured by native nanoproteomics. Nat Commun 2023; 14:8400. [PMID: 38110393 PMCID: PMC10728164 DOI: 10.1038/s41467-023-43321-z] [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: 07/04/2023] [Accepted: 11/07/2023] [Indexed: 12/20/2023] Open
Abstract
Protein complexes are highly dynamic entities that display substantial diversity in their assembly, post-translational modifications, and non-covalent interactions, allowing them to play critical roles in various biological processes. The heterogeneity, dynamic nature, and low abundance of protein complexes in their native states present challenges to study using conventional structural biology techniques. Here we develop a native nanoproteomics strategy for the enrichment and subsequent native top-down mass spectrometry (nTDMS) analysis of endogenous cardiac troponin (cTn) complex directly from human heart tissue. The cTn complex is enriched and purified using peptide-functionalized superparamagnetic nanoparticles under non-denaturing conditions to enable the isotopic resolution of cTn complex, revealing their complex structure and assembly. Moreover, nTDMS elucidates the stoichiometry and composition of the cTn complex, localizes Ca2+ binding domains, defines cTn-Ca2+ binding dynamics, and provides high-resolution mapping of the proteoform landscape. This native nanoproteomics strategy opens a paradigm for structural characterization of endogenous native protein complexes.
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Affiliation(s)
- Emily A Chapman
- Department of Chemistry, University of Wisconsin-Madison, Madison, WI, 53706, USA
| | - David S Roberts
- Department of Chemistry, University of Wisconsin-Madison, Madison, WI, 53706, USA
| | - Timothy N Tiambeng
- Department of Chemistry, University of Wisconsin-Madison, Madison, WI, 53706, USA
| | - Jãán Andrews
- Department of Chemistry, University of Wisconsin-Madison, Madison, WI, 53706, USA
| | - Man-Di Wang
- Department of Chemistry, University of Wisconsin-Madison, Madison, WI, 53706, USA
| | - Emily A Reasoner
- Department of Chemistry, University of Wisconsin-Madison, Madison, WI, 53706, USA
| | - Jake A Melby
- Department of Chemistry, University of Wisconsin-Madison, Madison, WI, 53706, USA
| | - Brad H Li
- Department of Biochemistry, University of Wisconsin-Madison, Madison, WI, 53706, USA
| | - Donguk Kim
- Department of Chemical and Biological Engineering, University of Wisconsin-Madison, Madison, WI, 53706, USA
| | | | - Song Jin
- Department of Chemistry, University of Wisconsin-Madison, Madison, WI, 53706, USA.
| | - Ying Ge
- Department of Chemistry, University of Wisconsin-Madison, Madison, WI, 53706, USA.
- Department of Cell and Regenerative Biology, University of Wisconsin-Madison, Madison, WI, 53705, USA.
- Human Proteomics Program, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI, 53705, USA.
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4
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Dowrick JM, Taberner AJ, Han JC, Tran K. Methods for assessing cardiac myofilament calcium sensitivity. Front Physiol 2023; 14:1323768. [PMID: 38116581 PMCID: PMC10728676 DOI: 10.3389/fphys.2023.1323768] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2023] [Accepted: 11/23/2023] [Indexed: 12/21/2023] Open
Abstract
Myofilament calcium (Ca2+) sensitivity is one of several mechanisms by which force production of cardiac muscle is modulated to meet the ever-changing demands placed on the heart. Compromised Ca2+ sensitivity is associated with pathologies, which makes it a parameter of interest for researchers. Ca2+ Sensitivity is the ratio of the association and dissociation rates between troponin C (TnC) and Ca2+. As it is not currently possible to measure these rates in tissue preparations directly, methods have been developed to infer myofilament sensitivity, typically using some combination of force and Ca2+ measurements. The current gold-standard approach constructs a steady-state force-Ca2+ relation by exposing permeabilised muscle samples to a range of Ca2+ concentrations and uses the half-maximal concentration as a proxy for sensitivity. While a valuable method for steady-state investigations, the permeabilisation process makes the method unsuitable when examining dynamic, i.e., twitch-to-twitch, changes in myofilament sensitivity. The ability of the heart to transiently adapt to changes in load is an important consideration when evaluating the impact of disease states. Alternative methods have been proffered, including force-Ca2+ phase loops, potassium contracture, hybrid experimental-modelling and conformation-based fluorophore approaches. This review provides an overview of the mechanisms underlying myofilament Ca2+ sensitivity, summarises existing methods, and explores, with modelling, whether any of them are suited to investigating dynamic changes in sensitivity. We conclude that a method that equips researchers to investigate the transient change of myofilament Ca2+ sensitivity is still needed. We propose that such a method will involve simultaneous measurements of cytosolic Ca2+ and TnC activation in actively twitching muscle and a biophysical model to interpret these data.
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Affiliation(s)
- Jarrah M. Dowrick
- Auckland Bioengineering Institute, University of Auckland, Auckland, New Zealand
| | - Andrew J. Taberner
- Auckland Bioengineering Institute, University of Auckland, Auckland, New Zealand
- Department of Engineering Science and Biomedical Engineering, University of Auckland, Auckland, New Zealand
| | - June-Chiew Han
- Auckland Bioengineering Institute, University of Auckland, Auckland, New Zealand
| | - Kenneth Tran
- Auckland Bioengineering Institute, University of Auckland, Auckland, New Zealand
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5
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Eisner D, Neher E, Taschenberger H, Smith G. Physiology of intracellular calcium buffering. Physiol Rev 2023; 103:2767-2845. [PMID: 37326298 DOI: 10.1152/physrev.00042.2022] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2022] [Revised: 05/08/2023] [Accepted: 06/11/2023] [Indexed: 06/17/2023] Open
Abstract
Calcium signaling underlies much of physiology. Almost all the Ca2+ in the cytoplasm is bound to buffers, with typically only ∼1% being freely ionized at resting levels in most cells. Physiological Ca2+ buffers include small molecules and proteins, and experimentally Ca2+ indicators will also buffer calcium. The chemistry of interactions between Ca2+ and buffers determines the extent and speed of Ca2+ binding. The physiological effects of Ca2+ buffers are determined by the kinetics with which they bind Ca2+ and their mobility within the cell. The degree of buffering depends on factors such as the affinity for Ca2+, the Ca2+ concentration, and whether Ca2+ ions bind cooperatively. Buffering affects both the amplitude and time course of cytoplasmic Ca2+ signals as well as changes of Ca2+ concentration in organelles. It can also facilitate Ca2+ diffusion inside the cell. Ca2+ buffering affects synaptic transmission, muscle contraction, Ca2+ transport across epithelia, and the killing of bacteria. Saturation of buffers leads to synaptic facilitation and tetanic contraction in skeletal muscle and may play a role in inotropy in the heart. This review focuses on the link between buffer chemistry and function and how Ca2+ buffering affects normal physiology and the consequences of changes in disease. As well as summarizing what is known, we point out the many areas where further work is required.
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Affiliation(s)
- David Eisner
- Division of Cardiovascular Sciences, University of Manchester, Manchester, United Kingdom
| | - Erwin Neher
- Membrane Biophysics Laboratory, Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany
- Cluster of Excellence "Multiscale Bioimaging: from Molecular Machines to Networks of Excitable Cells" (MBExC), University of Göttingen, Göttingen, Germany
| | - Holger Taschenberger
- Department of Molecular Neurobiology, Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany
| | - Godfrey Smith
- School of Cardiovascular and Metabolic Health, College of Medical, Veterinary, and Life Sciences, University of Glasgow, Glasgow, United Kingdom
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6
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Kooiker KB, Mohran S, Turner KL, Ma W, Martinson A, Flint G, Qi L, Gao C, Zheng Y, McMillen TS, Mandrycky C, Mahoney-Schaefer M, Freeman JC, Costales Arenas EG, Tu AY, Irving TC, Geeves MA, Tanner BC, Regnier M, Davis J, Moussavi-Harami F. Danicamtiv Increases Myosin Recruitment and Alters Cross-Bridge Cycling in Cardiac Muscle. Circ Res 2023; 133:430-443. [PMID: 37470183 PMCID: PMC10434831 DOI: 10.1161/circresaha.123.322629] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/04/2023] [Revised: 07/10/2023] [Accepted: 07/13/2023] [Indexed: 07/21/2023]
Abstract
BACKGROUND Modulating myosin function is a novel therapeutic approach in patients with cardiomyopathy. Danicamtiv is a novel myosin activator with promising preclinical data that is currently in clinical trials. While it is known that danicamtiv increases force and cardiomyocyte contractility without affecting calcium levels, detailed mechanistic studies regarding its mode of action are lacking. METHODS Permeabilized porcine cardiac tissue and myofibrils were used for X-ray diffraction and mechanical measurements. A mouse model of genetic dilated cardiomyopathy was used to evaluate the ability of danicamtiv to correct the contractile deficit. RESULTS Danicamtiv increased force and calcium sensitivity via increasing the number of myosins in the ON state and slowing cross-bridge turnover. Our detailed analysis showed that inhibition of ADP release results in decreased cross-bridge turnover with cross bridges staying attached longer and prolonging myofibril relaxation. Danicamtiv corrected decreased calcium sensitivity in demembranated tissue, abnormal twitch magnitude and kinetics in intact cardiac tissue, and reduced ejection fraction in the whole organ. CONCLUSIONS As demonstrated by the detailed studies of Danicamtiv, increasing myosin recruitment and altering cross-bridge cycling are 2 mechanisms to increase force and calcium sensitivity in cardiac muscle. Myosin activators such as Danicamtiv can treat the causative hypocontractile phenotype in genetic dilated cardiomyopathy.
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Affiliation(s)
- Kristina B. Kooiker
- Division of Cardiology, Medicine (K.B.K., M.M.-S., J.C.F., E.G.C.A., F.M.-H.), University of Washington
- Center of Translational Muscle Research (K.B.K., S.M., G.F., T.S.M., C.M., A.-Y.T., M.R., J.D., F.M.-H.), University of Washington
- Center for Cardiovascular Biology (K.B.K., A.M., M.R., J.D., F.M.-H.), University of Washington
- Institute for Stem Cell & Regenerative Medicine (K.B.K., S.M., A.M., T.S.M., A.-Y.T., M.R., J.D., F.M.-H.), University of Washington
| | - Saffie Mohran
- Center of Translational Muscle Research (K.B.K., S.M., G.F., T.S.M., C.M., A.-Y.T., M.R., J.D., F.M.-H.), University of Washington
- Institute for Stem Cell & Regenerative Medicine (K.B.K., S.M., A.M., T.S.M., A.-Y.T., M.R., J.D., F.M.-H.), University of Washington
- Department of Bioengineering (S.M., A.M., G.F., C.M., A.-Y.T., M.R., J.D.), University of Washington
| | - Kyrah L. Turner
- School of Molecular Biosciences, Washington State University (K.L.T.)
| | - Weikang Ma
- Department of Biology, Illinois Institute of Technology, Chicago (W.M., L.Q., T.C.I.)
| | - Amy Martinson
- Center for Cardiovascular Biology (K.B.K., A.M., M.R., J.D., F.M.-H.), University of Washington
- Department of Laboratory Medicine and Pathology (A.M., J.D., F.M.-H.), University of Washington
- Institute for Stem Cell & Regenerative Medicine (K.B.K., S.M., A.M., T.S.M., A.-Y.T., M.R., J.D., F.M.-H.), University of Washington
- Department of Bioengineering (S.M., A.M., G.F., C.M., A.-Y.T., M.R., J.D.), University of Washington
| | - Galina Flint
- Center of Translational Muscle Research (K.B.K., S.M., G.F., T.S.M., C.M., A.-Y.T., M.R., J.D., F.M.-H.), University of Washington
- Department of Bioengineering (S.M., A.M., G.F., C.M., A.-Y.T., M.R., J.D.), University of Washington
| | - Lin Qi
- Department of Biology, Illinois Institute of Technology, Chicago (W.M., L.Q., T.C.I.)
| | - Chengqian Gao
- College of Basic Medical Sciences, Dalian Medical University, Liaoning, China (C.G., Y.Z.)
| | - Yahan Zheng
- College of Basic Medical Sciences, Dalian Medical University, Liaoning, China (C.G., Y.Z.)
| | - Timothy S. McMillen
- Center of Translational Muscle Research (K.B.K., S.M., G.F., T.S.M., C.M., A.-Y.T., M.R., J.D., F.M.-H.), University of Washington
- Institute for Stem Cell & Regenerative Medicine (K.B.K., S.M., A.M., T.S.M., A.-Y.T., M.R., J.D., F.M.-H.), University of Washington
- Department of Anesthesiology and Pain Medicine (T.S.M.), University of Washington
| | - Christian Mandrycky
- Center of Translational Muscle Research (K.B.K., S.M., G.F., T.S.M., C.M., A.-Y.T., M.R., J.D., F.M.-H.), University of Washington
- Department of Bioengineering (S.M., A.M., G.F., C.M., A.-Y.T., M.R., J.D.), University of Washington
| | - Max Mahoney-Schaefer
- Division of Cardiology, Medicine (K.B.K., M.M.-S., J.C.F., E.G.C.A., F.M.-H.), University of Washington
| | - Jeremy C. Freeman
- Division of Cardiology, Medicine (K.B.K., M.M.-S., J.C.F., E.G.C.A., F.M.-H.), University of Washington
| | | | - An-Yu Tu
- Center of Translational Muscle Research (K.B.K., S.M., G.F., T.S.M., C.M., A.-Y.T., M.R., J.D., F.M.-H.), University of Washington
- Institute for Stem Cell & Regenerative Medicine (K.B.K., S.M., A.M., T.S.M., A.-Y.T., M.R., J.D., F.M.-H.), University of Washington
- Department of Bioengineering (S.M., A.M., G.F., C.M., A.-Y.T., M.R., J.D.), University of Washington
| | - Thomas C. Irving
- Department of Biology, Illinois Institute of Technology, Chicago (W.M., L.Q., T.C.I.)
| | - Michael A. Geeves
- School of Biosciences, Division of Natural Sciences, University of Kent, Canterbury, United Kingdom (M.A.G.)
| | - Bertrand C.W. Tanner
- Department of Integrative Physiology and Neuroscience, Washington State University (B.C.W.T.)
| | - Michael Regnier
- Center of Translational Muscle Research (K.B.K., S.M., G.F., T.S.M., C.M., A.-Y.T., M.R., J.D., F.M.-H.), University of Washington
- Center for Cardiovascular Biology (K.B.K., A.M., M.R., J.D., F.M.-H.), University of Washington
- Institute for Stem Cell & Regenerative Medicine (K.B.K., S.M., A.M., T.S.M., A.-Y.T., M.R., J.D., F.M.-H.), University of Washington
- Department of Bioengineering (S.M., A.M., G.F., C.M., A.-Y.T., M.R., J.D.), University of Washington
| | - Jennifer Davis
- Center of Translational Muscle Research (K.B.K., S.M., G.F., T.S.M., C.M., A.-Y.T., M.R., J.D., F.M.-H.), University of Washington
- Center for Cardiovascular Biology (K.B.K., A.M., M.R., J.D., F.M.-H.), University of Washington
- Department of Laboratory Medicine and Pathology (A.M., J.D., F.M.-H.), University of Washington
- Institute for Stem Cell & Regenerative Medicine (K.B.K., S.M., A.M., T.S.M., A.-Y.T., M.R., J.D., F.M.-H.), University of Washington
- Department of Bioengineering (S.M., A.M., G.F., C.M., A.-Y.T., M.R., J.D.), University of Washington
| | - Farid Moussavi-Harami
- Division of Cardiology, Medicine (K.B.K., M.M.-S., J.C.F., E.G.C.A., F.M.-H.), University of Washington
- Center of Translational Muscle Research (K.B.K., S.M., G.F., T.S.M., C.M., A.-Y.T., M.R., J.D., F.M.-H.), University of Washington
- Center for Cardiovascular Biology (K.B.K., A.M., M.R., J.D., F.M.-H.), University of Washington
- Department of Laboratory Medicine and Pathology (A.M., J.D., F.M.-H.), University of Washington
- Institute for Stem Cell & Regenerative Medicine (K.B.K., S.M., A.M., T.S.M., A.-Y.T., M.R., J.D., F.M.-H.), University of Washington
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7
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Shafaattalab S, Li AY, Jayousi F, Maaref Y, Dababneh S, Hamledari H, Baygi DH, Barszczewski T, Ruprai B, Jannati S, Nagalingam R, Cool AM, Langa P, Chiao M, Roston T, Solaro RJ, Sanatani S, Toepfer C, Lindert S, Lange P, Tibbits GF. Mechanisms of Pathogenicity of Hypertrophic Cardiomyopathy-Associated Troponin T (TNNT2) Variant R278C +/- During Development. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.06.06.542948. [PMID: 37609317 PMCID: PMC10441323 DOI: 10.1101/2023.06.06.542948] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/24/2023]
Abstract
Hypertrophic cardiomyopathy (HCM) is one of the most common heritable cardiovascular diseases and variants of TNNT2 (cardiac troponin T) are linked to increased risk of sudden cardiac arrest despite causing limited hypertrophy. In this study, a TNNT2 variant, R278C+/-, was generated in both human cardiac recombinant/reconstituted thin filaments (hcRTF) and human- induced pluripotent stem cells (hiPSCs) to investigate the mechanisms by which the R278C+/- variant affects cardiomyocytes at the proteomic and functional levels. The results of proteomics analysis showed a significant upregulation of markers of cardiac hypertrophy and remodeling in R278C+/- vs. the isogenic control. Functional measurements showed that R278C+/- variant enhances the myofilament sensitivity to Ca2+, increases the kinetics of contraction, and causes arrhythmia at frequencies >75 bpm. This study uniquely shows the profound impact of the TNNT2 R278C+/- variant on the cardiomyocyte proteomic profile, cardiac electrical and contractile function in the early stages of cardiac development.
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Affiliation(s)
- Sanam Shafaattalab
- Cellular and Regenerative Medicine Centre, BC Children’s Hospital Research Institute, Vancouver, BC, V5Z 4H4, Canada
- Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, V5A 1S6, Canada
| | - Alison Y Li
- Cellular and Regenerative Medicine Centre, BC Children’s Hospital Research Institute, Vancouver, BC, V5Z 4H4, Canada
- Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, V5A 1S6, Canada
| | - Farah Jayousi
- Cellular and Regenerative Medicine Centre, BC Children’s Hospital Research Institute, Vancouver, BC, V5Z 4H4, Canada
- Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, V5A 1S6, Canada
| | - Yasaman Maaref
- Cellular and Regenerative Medicine Centre, BC Children’s Hospital Research Institute, Vancouver, BC, V5Z 4H4, Canada
- Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, V5A 1S6, Canada
| | - Saif Dababneh
- Cellular and Regenerative Medicine Centre, BC Children’s Hospital Research Institute, Vancouver, BC, V5Z 4H4, Canada
- Department of Cellular and Physiological Sciences, Faculty of Medicine, University of British Columbia, Vancouver, BC, V6T 1Z3, Canada
| | - Homa Hamledari
- Cellular and Regenerative Medicine Centre, BC Children’s Hospital Research Institute, Vancouver, BC, V5Z 4H4, Canada
- Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, V5A 1S6, Canada
| | - Dina Hosseini Baygi
- Cellular and Regenerative Medicine Centre, BC Children’s Hospital Research Institute, Vancouver, BC, V5Z 4H4, Canada
- Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, V5A 1S6, Canada
| | - Tiffany Barszczewski
- Cellular and Regenerative Medicine Centre, BC Children’s Hospital Research Institute, Vancouver, BC, V5Z 4H4, Canada
- Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, V5A 1S6, Canada
| | - Balwinder Ruprai
- Cellular and Regenerative Medicine Centre, BC Children’s Hospital Research Institute, Vancouver, BC, V5Z 4H4, Canada
- Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, V5A 1S6, Canada
| | - Shayan Jannati
- Cellular and Regenerative Medicine Centre, BC Children’s Hospital Research Institute, Vancouver, BC, V5Z 4H4, Canada
- Mechanical Engineering, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada
| | - Raghu Nagalingam
- Cellular and Regenerative Medicine Centre, BC Children’s Hospital Research Institute, Vancouver, BC, V5Z 4H4, Canada
- Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, V5A 1S6, Canada
| | - Austin M Cool
- Department of Chemistry and Biochemistry, Ohio State University, Columbus, OH, USA
| | - Paulina Langa
- Department of Physiology and Biophysics, College of Medicine, University of Illinois at Chicago, Chicago, IL, 60612, USA
| | - Mu Chiao
- Mechanical Engineering, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada
| | - Thomas Roston
- Division of Cardiology and Centre for Cardiovascular Innovation, The University of British Columbia 1081 Burrard Street, Level 4 Cardiology Vancouver, BC, V6Z 1Y6, Canada
| | - R John Solaro
- Department of Physiology and Biophysics, College of Medicine, University of Illinois at Chicago, Chicago, IL, 60612, USA
| | - Shubhayan Sanatani
- Cellular and Regenerative Medicine Centre, BC Children’s Hospital Research Institute, Vancouver, BC, V5Z 4H4, Canada
| | | | - Steffen Lindert
- Mechanical Engineering, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada
| | - Philipp Lange
- Pathology and Laboratory Medicine, University of British Columbia, Vancouver, BC
- Michael Cuccione Childhood Cancer Research Program, BC Children’s Hospital Research Institute, Vancouver, BC, V5Z 4H4, Canada
| | - Glen F Tibbits
- Cellular and Regenerative Medicine Centre, BC Children’s Hospital Research Institute, Vancouver, BC, V5Z 4H4, Canada
- Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, V5A 1S6, Canada
- Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, BC, V5A 1S6, Canada
- School of Biomedical Engineering, University of British Columbia, Vancouver, BC, V6T 1Z3, Canada
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8
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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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9
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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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10
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Chapman EA, Roberts DS, Tiambeng TN, Andrews J, Wang MD, Reasoner EA, Melby JA, Li BH, Kim D, Alpert AJ, Jin S, Ge Y. Structure and dynamics of endogenous protein complexes in human heart tissue captured by native nanoproteomics. RESEARCH SQUARE 2023:rs.3.rs-3108087. [PMID: 37461709 PMCID: PMC10350235 DOI: 10.21203/rs.3.rs-3108087/v1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/25/2023]
Abstract
Protein complexes are highly dynamic entities that display substantial diversity in their assembly, post-translational modifications, and non-covalent interactions, allowing them to play critical roles in various biological processes. The heterogeneity, dynamic nature, and low abundance of protein complexes in their native states present tremendous challenges to study using conventional structural biology techniques. Here we develop a "native nanoproteomics" strategy for the native enrichment and subsequent native top-down mass spectrometry (nTDMS) of low-abundance protein complexes. Specifically, we demonstrate the first comprehensive characterization of the structure and dynamics of cardiac troponin (cTn) complexes directly from human heart tissue. The endogenous cTn complex is effectively enriched and purified using peptide-functionalized superparamagnetic nanoparticles under non-denaturing conditions to enable the isotopic resolution of cTn complexes, revealing their complex structure and assembly. Moreover, nTDMS elucidates the stoichiometry and composition of the heterotrimeric cTn complex, localizes Ca2+ binding domains (II-IV), defines cTn-Ca2+ binding dynamics, and provides high-resolution mapping of the proteoform landscape. This native nanoproteomics strategy opens a new paradigm for structural characterization of low-abundance native protein complexes.
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Affiliation(s)
- Emily A. Chapman
- Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
| | - David S. Roberts
- Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
| | - Timothy N. Tiambeng
- Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
| | - Jãán Andrews
- Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
| | - Man-Di Wang
- Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
| | - Emily A. Reasoner
- Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
| | - Jake A. Melby
- Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
| | - Brad H. Li
- Department of Biochemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
| | - Donguk Kim
- Department of Chemical and Biological Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
| | | | - Song Jin
- Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
| | - Ying Ge
- Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
- Department of Cell and Regenerative Biology, University of Wisconsin-Madison, Madison, Wisconsin 53705, USA
- Human Proteomics Program, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, Wisconsin 53705, USA
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11
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Chapman EA, Roberts DS, Tiambeng TN, Andrews J, Wang MD, Reasoner EA, Melby JA, Li BH, Kim D, Alpert AJ, Jin S, Ge Y. Structure and dynamics of endogenous protein complexes in human heart tissue captured by native nanoproteomics. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.06.13.544817. [PMID: 37398031 PMCID: PMC10312745 DOI: 10.1101/2023.06.13.544817] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/04/2023]
Abstract
Protein complexes are highly dynamic entities that display substantial diversity in their assembly, post-translational modifications, and non-covalent interactions, allowing them to play critical roles in various biological processes. The heterogeneity, dynamic nature, and low abundance of protein complexes in their native states present tremendous challenges to study using conventional structural biology techniques. Here we develop a "native nanoproteomics" strategy for the native enrichment and subsequent native top-down mass spectrometry (nTDMS) of low-abundance protein complexes. Specifically, we demonstrate the first comprehensive characterization of the structure and dynamics of cardiac troponin (cTn) complexes directly from human heart tissue. The endogenous cTn complex is effectively enriched and purified using peptide-functionalized superparamagnetic nanoparticles under non-denaturing conditions to enable the isotopic resolution of cTn complexes, revealing their complex structure and assembly. Moreover, nTDMS elucidates the stoichiometry and composition of the heterotrimeric cTn complex, localizes Ca2+ binding domains (II-IV), defines cTn-Ca2+ binding dynamics, and provides high-resolution mapping of the proteoform landscape. This native nanoproteomics strategy opens a new paradigm for structural characterization of low-abundance native protein complexes.
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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 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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13
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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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14
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Dvornikov AV, Bunch TA, Lepak VC, Colson BA. Fluorescence lifetime-based assay reports structural changes in cardiac muscle mediated by effectors of contractile regulation. J Gen Physiol 2023; 155:e202113054. [PMID: 36633587 PMCID: PMC9859762 DOI: 10.1085/jgp.202113054] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2021] [Revised: 09/23/2022] [Accepted: 12/20/2022] [Indexed: 01/13/2023] Open
Abstract
Cardiac muscle contraction is regulated by Ca2+-induced structural changes of the thin filaments to permit myosin cross-bridge cycling driven by ATP hydrolysis in the sarcomere. In congestive heart failure, contraction is weakened, and thus targeting the contractile proteins of the sarcomere is a promising approach to therapy. However, development of novel therapeutic interventions has been challenging due to a lack of precise discovery tools. We have developed a fluorescence lifetime-based assay using an existing site-directed probe, N,N'-dimethyl-N-(iodoacetyl)-N'-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)ethylenediamine (IANBD) attached to human cardiac troponin C (cTnC) mutant cTnCT53C, exchanged into porcine cardiac myofibrils. We hypothesized that IANBD-cTnCT53C fluorescence lifetime measurements provide insight into the activation state of the thin filament. The sensitivity and precision of detecting structural changes in cTnC due to physiological and therapeutic modulators of thick and thin filament functions were determined. The effects of Ca2+ binding to cTnC and myosin binding to the thin filament were readily detected by this assay in mock high-throughput screen tests using a fluorescence lifetime plate reader. We then evaluated known effectors of altered cTnC-Ca2+ binding, W7 and pimobendan, and myosin-binding drugs, mavacamten and omecamtiv mecarbil, used to treat cardiac diseases. Screening assays were determined to be of high quality as indicated by the Z' factor. We conclude that cTnC lifetime-based probes allow for precise evaluation of the thin filament activation in functioning myofibrils that can be used in future high-throughput screens of small-molecule modulators of function of the thin and thick filaments.
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Affiliation(s)
- Alexey V. Dvornikov
- Department of Cellular and Molecular Medicine, University of Arizona, Tucson, AZ, USA
| | - Thomas A. Bunch
- Department of Cellular and Molecular Medicine, University of Arizona, Tucson, AZ, USA
| | - Victoria C. Lepak
- Department of Cellular and Molecular Medicine, University of Arizona, Tucson, AZ, USA
| | - Brett A. Colson
- Department of Cellular and Molecular Medicine, University of Arizona, Tucson, AZ, USA
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15
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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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16
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Kooiker KB, Mohran S, Turner KL, Ma W, Flint G, Qi L, Gao C, Zheng Y, McMillen TS, Mandrycky C, Martinson A, Mahoney-Schaefer M, Freeman JC, Costales Arenas EG, Tu AY, Irving TC, Geeves MA, Tanner BCW, Regnier M, Davis J, Moussavi-Harami F. Danicamtiv increases myosin recruitment and alters the chemomechanical cross bridge cycle in cardiac muscle. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.01.31.526380. [PMID: 36778318 PMCID: PMC9915609 DOI: 10.1101/2023.01.31.526380] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Modulating myosin function is a novel therapeutic approach in patients with cardiomyopathy. Detailed mechanism of action of these agents can help predict potential unwanted affects and identify patient populations that can benefit most from them. Danicamtiv is a novel myosin activator with promising preclinical data that is currently in clinical trials. While it is known danicamtiv increases force and cardiomyocyte contractility without affecting calcium levels, detailed mechanistic studies regarding its mode of action are lacking. Using porcine cardiac tissue and myofibrils we demonstrate that Danicamtiv increases force and calcium sensitivity via increasing the number of myosin in the "on" state and slowing cross bridge turnover. Our detailed analysis shows that inhibition of ADP release results in decreased cross bridge turnover with cross bridges staying on longer and prolonging myofibril relaxation. Using a mouse model of genetic dilated cardiomyopathy, we demonstrated that Danicamtiv corrected calcium sensitivity in demembranated and abnormal twitch magnitude and kinetics in intact cardiac tissue. Significance Statement Directly augmenting sarcomere function has potential to overcome limitations of currently used inotropic agents to improve cardiac contractility. Myosin modulation is a novel mechanism for increased contraction in cardiomyopathies. Danicamtiv is a myosin activator that is currently under investigation for use in cardiomyopathy patients. Our study is the first detailed mechanism of how Danicamtiv increases force and alters kinetics of cardiac activation and relaxation. This new understanding of the mechanism of action of Danicamtiv can be used to help identify patients that could benefit most from this treatment.
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17
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Chung CS. Pressing Physiology to Move Our Understanding of Cytosolic Calcium Dynamics. J Appl Physiol (1985) 2022; 133:661-662. [PMID: 35981731 DOI: 10.1152/japplphysiol.00453.2022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Affiliation(s)
- Charles S Chung
- Department of Physiology, Wayne State University, Detroit MI, United States
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18
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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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19
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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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20
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Liang HF, Li XD. Locusta migratoria flight muscle troponin partially activates thin filament in a calcium-dependent manner. INSECT MOLECULAR BIOLOGY 2022; 31:346-355. [PMID: 35084070 DOI: 10.1111/imb.12763] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/07/2021] [Revised: 10/16/2021] [Accepted: 01/17/2022] [Indexed: 06/14/2023]
Abstract
The troponin (Tn) complex, the sensor for Ca2+ to regulate contraction of striated muscle, is composed of three subunits, that is, TnT, TnI and TnC. Different isoforms of TnI and TnC are expressed in the thorax dorsal longitudinal muscle (flight muscle) and the hind leg extensor tibiae muscle (jump muscle) of the migratory locust, Locusta migratoria. The major Tn complexes in the flight muscle and the jump muscle are Tn-171 (TnT1/TnI7/TnC1) and Tn-153 (TnT1/TnI5/TnC3), respectively. Here, we prepared a number of recombinant Tn complexes and the reconstituted thin filaments, and investigated their regulation on thin filament. Although both Tn-171 and Tn-153 regulate thin filament in a Ca2+ -dependent manner, the extent of Ca2+ activation mediated by Tn-171 was significantly lower than that by Tn-153. We demonstrated that TnC1 and TnC3, rather than TnI5 and TnI7, are responsible for the different levels of the thin filament activation. Mutagenesis of TnC1 and TnC3 shows that the low level of TnC1-mediated thin filament activation can be attributed to the noncanonical residue Leu60 in the EF-hand-II of TnC1. We therefore propose that, in addition to Ca2+ , other regulatory mechanism(s) is required for the full activation of locust flight muscle.
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Affiliation(s)
- Hui-Fang Liang
- State Key Laboratory of Integrated Management of Insect Pests and Rodents, Institute of Zoology, Chinese Academy of Sciences, Beijing, China
- University of Chinese Academy of Sciences, Beijing, China
| | - Xiang-Dong Li
- State Key Laboratory of Integrated Management of Insect Pests and Rodents, Institute of Zoology, Chinese Academy of Sciences, Beijing, China
- University of Chinese Academy of Sciences, Beijing, China
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21
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Barrick SK, Greenberg L, Greenberg MJ. A troponin T variant linked with pediatric dilated cardiomyopathy reduces the coupling of thin filament activation to myosin and calcium binding. Mol Biol Cell 2021; 32:1677-1689. [PMID: 34161147 PMCID: PMC8684737 DOI: 10.1091/mbc.e21-02-0082] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Dilated cardiomyopathy (DCM) is a significant cause of pediatric heart failure. Mutations in proteins that regulate cardiac muscle contraction can cause DCM; however, the mechanisms by which molecular-level mutations contribute to cellular dysfunction are not well understood. Better understanding of these mechanisms might enable the development of targeted therapeutics that benefit patient subpopulations with mutations that cause common biophysical defects. We examined the molecular- and cellular-level impacts of a troponin T variant associated with pediatric-onset DCM, R134G. The R134G variant decreased calcium sensitivity in an in vitro motility assay. Using stopped-flow and steady-state fluorescence measurements, we determined the molecular mechanism of the altered calcium sensitivity: R134G decouples calcium binding by troponin from the closed-to-open transition of the thin filament and decreases the cooperativity of myosin binding to regulated thin filaments. Consistent with the prediction that these effects would cause reduced force per sarcomere, cardiomyocytes carrying the R134G mutation are hypocontractile. They also show hallmarks of DCM that lie downstream of the initial insult, including disorganized sarcomeres and cellular hypertrophy. These results reinforce the importance of multiscale studies to fully understand mechanisms underlying human disease and highlight the value of mechanism-based precision medicine approaches for DCM.
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Affiliation(s)
- Samantha K Barrick
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110
| | - Lina Greenberg
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110
| | - Michael J Greenberg
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110
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22
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Clippinger SR, Cloonan PE, Wang W, Greenberg L, Stump WT, Angsutararux P, Nerbonne JM, Greenberg MJ. Mechanical dysfunction of the sarcomere induced by a pathogenic mutation in troponin T drives cellular adaptation. J Gen Physiol 2021; 153:211992. [PMID: 33856419 PMCID: PMC8054178 DOI: 10.1085/jgp.202012787] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2020] [Accepted: 03/18/2021] [Indexed: 12/15/2022] Open
Abstract
Familial hypertrophic cardiomyopathy (HCM), a leading cause of sudden cardiac death, is primarily caused by mutations in sarcomeric proteins. The pathogenesis of HCM is complex, with functional changes that span scales, from molecules to tissues. This makes it challenging to deconvolve the biophysical molecular defect that drives the disease pathogenesis from downstream changes in cellular function. In this study, we examine an HCM mutation in troponin T, R92Q, for which several models explaining its effects in disease have been put forward. We demonstrate that the primary molecular insult driving disease pathogenesis is mutation-induced alterations in tropomyosin positioning, which causes increased molecular and cellular force generation during calcium-based activation. Computational modeling shows that the increased cellular force is consistent with the molecular mechanism. These changes in cellular contractility cause downstream alterations in gene expression, calcium handling, and electrophysiology. Taken together, our results demonstrate that molecularly driven changes in mechanical tension drive the early disease pathogenesis of familial HCM, leading to activation of adaptive mechanobiological signaling pathways.
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Affiliation(s)
- Sarah R Clippinger
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO
| | - Paige E Cloonan
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO
| | - Wei Wang
- Cardiovascular Division, Department of Medicine, Washington University School of Medicine, St. Louis, MO
| | - Lina Greenberg
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO
| | - W Tom Stump
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO
| | | | - Jeanne M Nerbonne
- Cardiovascular Division, Department of Medicine, Washington University School of Medicine, St. Louis, MO
| | - Michael J Greenberg
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO
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23
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Solís C, Solaro RJ. Novel insights into sarcomere regulatory systems control of cardiac thin filament activation. J Gen Physiol 2021; 153:211903. [PMID: 33740037 PMCID: PMC7988513 DOI: 10.1085/jgp.202012777] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2020] [Accepted: 02/23/2021] [Indexed: 12/11/2022] Open
Abstract
Our review focuses on sarcomere regulatory mechanisms with a discussion of cardiac-specific modifications to the three-state model of thin filament activation from a blocked to closed to open state. We discuss modulation of these thin filament transitions by Ca2+, by crossbridge interactions, and by thick filament–associated proteins, cardiac myosin–binding protein C (cMyBP-C), cardiac regulatory light chain (cRLC), and titin. Emerging evidence supports the idea that the cooperative activation of the thin filaments despite a single Ca2+ triggering regulatory site on troponin C (cTnC) cannot be considered in isolation of other functional domains of the sarcomere. We discuss long- and short-range interactions among these domains with the regulatory units of thin filaments, including proteins at the barbed end at the Z-disc and the pointed end near the M-band. Important to these discussions is the ever-increasing understanding of the role of cMyBP-C, cRLC, and titin filaments. Detailed knowledge of these control processes is critical to the understanding of mechanisms sustaining physiological cardiac state with varying hemodynamic load, to better defining genetic and acquired cardiac disorders, and to developing targets for therapies at the level of the sarcomeres.
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Affiliation(s)
- Christopher Solís
- University of Illinois at Chicago, College of Medicine, Department of Physiology and Biophysics and Center for Cardiovascular Research, Chicago, IL
| | - R John Solaro
- University of Illinois at Chicago, College of Medicine, Department of Physiology and Biophysics and Center for Cardiovascular Research, Chicago, IL
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24
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Mijailovich SM, Prodanovic M, Poggesi C, Powers JD, Davis J, Geeves MA, Regnier M. The effect of variable troponin C mutation thin filament incorporation on cardiac muscle twitch contractions. J Mol Cell Cardiol 2021; 155:112-124. [PMID: 33636222 DOI: 10.1016/j.yjmcc.2021.02.009] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/11/2020] [Revised: 02/17/2021] [Accepted: 02/19/2021] [Indexed: 11/19/2022]
Abstract
One of the complexities of understanding the pathology of familial forms of cardiac diseases is the level of mutation incorporation in sarcomeres. Computational models of the sarcomere that are spatially explicit offer an approach to study aspects of mutational incorporation into myofilaments that are more challenging to get at experimentally. We studied two well characterized mutations of cardiac TnC, L48Q and I61Q, that decrease or increase the release rate of Ca2+ from cTnC, k-Ca, resulting in HCM and DCM respectively [1]. Expression of these mutations in transgenic mice was used to provide experimental data for incorporation of 30 and 50% (respectively) into sarcomeres. Here we demonstrate that fixed length twitch contractions of trabeculae from mice containing mutant differ from WT; L48Q trabeculae have slower relaxation while I61Q trabeculae have markedly reduced peak tension. Using our multiscale modelling approach [2] we were able to describe the tension transients of WT mouse myocardium. Tension transients for the mutant cTnCs were simulated with changes in k-Ca, measured experimentally for each cTnC mutant in whole troponin complex, a change in the affinity of cTnC for cTnI, and a reduction in the number of detached crossbridges available for binding. A major advantage of the multiscale explicit 3-D model is that it predicts the effects of variable mutation incorporation, and the effects of variations in mutation distribution within thin filaments in sarcomeres. Such effects are currently impossible to explore experimentally. We explored random and clustered distributions of mutant cTnCs in thin filaments, as well as distributions of individual thin filaments with only WT or mutant cTnCs present. The effects of variable amounts of incorporation and non-random distribution of mutant cTnCs are more marked for I61Q than L48Q cTnC. We conclude that this approach can be effective for study on mutations in multiple proteins of the sarcomere. SUMMARY: A challenge in experimental studies of diseases is accounting for the effect of variable mutation incorporation into myofilaments. Here we use a spatially explicit computational approach, informed by experimental data from transgenic mice expressing one of two mutations in cardiac Troponin C that increase or decrease calcium sensitivity. We demonstrate that the model can accurately describe twitch contractions for the data and go on to explore the effect of variable mutant incorporation and localization on simulated cardiac muscle twitches.
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Affiliation(s)
| | - Momcilo Prodanovic
- Bioengineering Research and Development Center (BioIRC), Kragujevac 34000, Serbia; Faculty of Engineering, University of Kragujevac, Kragujevac 34000, Serbia
| | - Corrado Poggesi
- Department of Experimental & Clinical Medicine, University of Florence, Florence 50134, Italy
| | - Joseph D Powers
- Department of Bioengineering, University of Washington, Seattle, WA 98105, USA; Dept. of Bioengineering, University of California, San Diego, CA 92093, USA
| | - Jennifer Davis
- Department of Bioengineering, University of Washington, Seattle, WA 98105, USA
| | - Michael A Geeves
- Dept. of Biosciences, University of Kent, Canterbury, Kent CT2 7NJ, UK
| | - Michael Regnier
- Department of Bioengineering, University of Washington, Seattle, WA 98105, USA
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25
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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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26
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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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27
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Karbassi E, Fenix A, Marchiano S, Muraoka N, Nakamura K, Yang X, Murry CE. Cardiomyocyte maturation: advances in knowledge and implications for regenerative medicine. Nat Rev Cardiol 2020; 17:341-359. [PMID: 32015528 DOI: 10.1038/s41569-019-0331-x] [Citation(s) in RCA: 386] [Impact Index Per Article: 96.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 12/12/2019] [Indexed: 12/20/2022]
Abstract
Our knowledge of pluripotent stem cell (PSC) biology has advanced to the point where we now can generate most cells of the human body in the laboratory. PSC-derived cardiomyocytes can be generated routinely with high yield and purity for disease research and drug development, and these cells are now gradually entering the clinical research phase for the testing of heart regeneration therapies. However, a major hurdle for their applications is the immature state of these cardiomyocytes. In this Review, we describe the structural and functional properties of cardiomyocytes and present the current approaches to mature PSC-derived cardiomyocytes. To date, the greatest success in maturation of PSC-derived cardiomyocytes has been with transplantation into the heart in animal models and the engineering of 3D heart tissues with electromechanical conditioning. In conventional 2D cell culture, biophysical stimuli such as mechanical loading, electrical stimulation and nanotopology cues all induce substantial maturation, particularly of the contractile cytoskeleton. Metabolism has emerged as a potent means to control maturation with unexpected effects on electrical and mechanical function. Different interventions induce distinct facets of maturation, suggesting that activating multiple signalling networks might lead to increased maturation. Despite considerable progress, we are still far from being able to generate PSC-derived cardiomyocytes with adult-like phenotypes in vitro. Future progress will come from identifying the developmental drivers of maturation and leveraging them to create more mature cardiomyocytes for research and regenerative medicine.
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Affiliation(s)
- Elaheh Karbassi
- Institute for Stem Cell and Regenerative Medicine, University of Washington, Seattle, WA, USA.,Center for Cardiovascular Biology, University of Washington, Seattle, WA, USA.,Department of Pathology, University of Washington, Seattle, WA, USA
| | - Aidan Fenix
- Institute for Stem Cell and Regenerative Medicine, University of Washington, Seattle, WA, USA.,Center for Cardiovascular Biology, University of Washington, Seattle, WA, USA.,Department of Pathology, University of Washington, Seattle, WA, USA
| | - Silvia Marchiano
- Institute for Stem Cell and Regenerative Medicine, University of Washington, Seattle, WA, USA.,Center for Cardiovascular Biology, University of Washington, Seattle, WA, USA.,Department of Pathology, University of Washington, Seattle, WA, USA
| | - Naoto Muraoka
- Institute for Stem Cell and Regenerative Medicine, University of Washington, Seattle, WA, USA.,Center for Cardiovascular Biology, University of Washington, Seattle, WA, USA.,Department of Pathology, University of Washington, Seattle, WA, USA
| | - Kenta Nakamura
- Institute for Stem Cell and Regenerative Medicine, University of Washington, Seattle, WA, USA.,Center for Cardiovascular Biology, University of Washington, Seattle, WA, USA.,Division of Cardiology, Department of Medicine, University of Washington, Seattle, WA, USA
| | - Xiulan Yang
- Institute for Stem Cell and Regenerative Medicine, University of Washington, Seattle, WA, USA.,Center for Cardiovascular Biology, University of Washington, Seattle, WA, USA.,Department of Pathology, University of Washington, Seattle, WA, USA
| | - Charles E Murry
- Institute for Stem Cell and Regenerative Medicine, University of Washington, Seattle, WA, USA. .,Center for Cardiovascular Biology, University of Washington, Seattle, WA, USA. .,Department of Pathology, University of Washington, Seattle, WA, USA. .,Division of Cardiology, Department of Medicine, University of Washington, Seattle, WA, USA. .,Department of Bioengineering, University of Washington, Seattle, WA, USA.
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28
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Affiliation(s)
- Stuart G Campbell
- From the Department of Biomedical Engineering (S.G.C.), Yale University, New Haven, CT.,Department of Cellular and Molecular Physiology (S.G.C.), Yale School of Medicine, New Haven, CT
| | - Yibing Qyang
- From the Department of Biomedical Engineering (S.G.C.), Yale University, New Haven, CT.,Yale Stem Cell Center (Y.Q.), Yale University, New Haven, CT.,Vascular Biology and Therapeutics Program (Y.Q.), Yale University, New Haven, CT.,Yale Cardiovascular Research Center, Section of Cardiovascular Medicine, Department of Internal Medicine (Y.Q.), Yale School of Medicine, New Haven, CT
| | - J Travis Hinson
- The Jackson Laboratory for Genomic Medicine, Farmington, CT (J.T.H.).,Department of Cardiology, UConn Health, Farmington, CT (J.T.H.)
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29
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Structure and proteolytic susceptibility of the inhibitory C-terminal tail of cardiac troponin I. Biochim Biophys Acta Gen Subj 2019; 1863:661-671. [DOI: 10.1016/j.bbagen.2019.01.008] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2018] [Revised: 11/22/2018] [Accepted: 01/14/2019] [Indexed: 01/17/2023]
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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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Solís C, Kim GH, Moutsoglou ME, Robinson JM. Ca 2+ and Myosin Cycle States Work as Allosteric Effectors of Troponin Activation. Biophys J 2018; 115:1762-1769. [PMID: 30249400 DOI: 10.1016/j.bpj.2018.08.033] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2017] [Revised: 08/22/2018] [Accepted: 08/24/2018] [Indexed: 10/28/2022] Open
Abstract
In cardiac muscle, troponin (Tn) and tropomyosin inhibit actin and myosin interactions through the steric blocking of myosin binding to F-actin. Ca2+ binding to Tn C modulates this inhibition. Thin filaments become activated upon Ca2+ binding, which enables strong binding of myosin with a concomitant release of ATP hydrolysis products and level arm swinging responsible for force generation. Despite this level of description, the current cross-bridge cycle model does not fully define the structural events that take place within Tn during combinatorial myosin and Ca2+ interventions. Here, we studied conformational changes within Tn bound to F-actin and tropomyosin by fluorescence lifetime imaging combined with Förster resonance energy transfer. Fluorescent dye molecules covalently bound to the Tn C C-lobe and Tn I C-terminal domain report Ca2+- and myosin-induced activation of Tn. Reconstituted thin filaments were deposited on a myosin-coated surface similar to an in vitro motility assay setup without filament sliding involved. Under all the tested conditions, Ca2+ was responsible for the most significant changes in Tn activation. Rigor myosin activated Tn at subsaturated Ca2+ conditions but not to the degree seen in thin filaments with Ca2+. ATP-γ-S did not affect Tn activation significantly; however, blebbistatin induced significant activation at subsaturating Ca2+ levels. The relation between the extent of Tn activation and its conformational flexibility suggests that active/inactive Tn states coexist in different proportions that depend on the combination of effectors. These results satisfy an allosteric activation model of the thin filament as a function of Ca2+ and the myosin catalytic cycle state.
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Affiliation(s)
- Christopher Solís
- Department of Chemistry and Biochemistry, South Dakota State University, Brookings, South Dakota.
| | - Giho H Kim
- Department of Chemistry and Biochemistry, South Dakota State University, Brookings, South Dakota
| | - Maria E Moutsoglou
- Department of Chemistry and Biochemistry, South Dakota State University, Brookings, South Dakota
| | - John M Robinson
- Department of Chemistry and Biochemistry, South Dakota State University, Brookings, South Dakota
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32
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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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33
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Stevens CM, Rayani K, Singh G, Lotfalisalmasi B, Tieleman DP, Tibbits GF. Changes in the dynamics of the cardiac troponin C molecule explain the effects of Ca 2+-sensitizing mutations. J Biol Chem 2017; 292:11915-11926. [PMID: 28533433 DOI: 10.1074/jbc.m116.770776] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2016] [Revised: 05/07/2017] [Indexed: 12/31/2022] Open
Abstract
Cardiac troponin C (cTnC) is the regulatory protein that initiates cardiac contraction in response to Ca2+ TnC binding Ca2+ initiates a cascade of protein-protein interactions that begins with the opening of the N-terminal domain of cTnC, followed by cTnC binding the troponin I switch peptide (TnISW). We have evaluated, through isothermal titration calorimetry and molecular-dynamics simulation, the effect of several clinically relevant mutations (A8V, L29Q, A31S, L48Q, Q50R, and C84Y) on the Ca2+ affinity, structural dynamics, and calculated interaction strengths between cTnC and each of Ca2+ and TnISW Surprisingly the Ca2+ affinity measured by isothermal titration calorimetry was only significantly affected by half of these mutations including L48Q, which had a 10-fold higher affinity than WT, and the Q50R and C84Y mutants, each of which had affinities 3-fold higher than wild type. This suggests that Ca2+ affinity of the N-terminal domain of cTnC in isolation is insufficient to explain the pathogenicity of these mutations. Molecular-dynamics simulation was used to evaluate the effects of these mutations on Ca2+ binding, structural dynamics, and TnI interaction independently. Many of the mutations had a pronounced effect on the balance between the open and closed conformations of the TnC molecule, which provides an indirect mechanism for their pathogenic properties. Our data demonstrate that the structural dynamics of the cTnC molecule are key in determining myofilament Ca2+ sensitivity. Our data further suggest that modulation of the structural dynamics is the underlying molecular mechanism for many disease mutations that are far from the regulatory Ca2+-binding site of cTnC.
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Affiliation(s)
- Charles M Stevens
- Cardiovascular Sciences, British Columbia Children's Hospital Research Institute, Vancouver, British Columbia V5Z 4H4, Canada; Departments of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada
| | - Kaveh Rayani
- Departments of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada
| | - Gurpreet Singh
- Centre for Molecular Simulation and Department of Biological Sciences, University of Calgary, Calgary, Alberta T2N 1N4, Canada
| | - Bairam Lotfalisalmasi
- Departments of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada
| | - D Peter Tieleman
- Centre for Molecular Simulation and Department of Biological Sciences, University of Calgary, Calgary, Alberta T2N 1N4, Canada
| | - Glen F Tibbits
- Cardiovascular Sciences, British Columbia Children's Hospital Research Institute, Vancouver, British Columbia V5Z 4H4, Canada; Departments of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada; Departments of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada.
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34
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Veltri T, de Oliveira GAP, Bienkiewicz EA, Palhano FL, Marques MDA, Moraes AH, Silva JL, Sorenson MM, Pinto JR. Amide hydrogens reveal a temperature-dependent structural transition that enhances site-II Ca 2+-binding affinity in a C-domain mutant of cardiac troponin C. Sci Rep 2017; 7:691. [PMID: 28386062 PMCID: PMC5429600 DOI: 10.1038/s41598-017-00777-6] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2016] [Accepted: 03/14/2017] [Indexed: 01/07/2023] Open
Abstract
The hypertrophic cardiomyopathy-associated mutant D145E, in cardiac troponin C (cTnC) C-domain, causes generalised instability at multiple sites in the isolated protein. As a result, structure and function of the mutant are more susceptible to higher temperatures. Above 25 °C there are large, progressive increases in N-domain Ca2+-binding affinity for D145E but only small changes for the wild-type protein. NMR-derived backbone amide temperature coefficients for many residues show a sharp transition above 30–40 °C, indicating a temperature-dependent conformational change that is most prominent around the mutated EF-hand IV, as well as throughout the C-domain. Smaller, isolated changes occur in the N-domain. Cardiac skinned fibres reconstituted with D145E are more sensitive to Ca2+ than fibres reconstituted with wild-type, and this defect is amplified near body-temperature. We speculate that the D145E mutation destabilises the native conformation of EF-hand IV, leading to a transient unfolding and dissociation of helix H that becomes more prominent at higher temperatures. This creates exposed hydrophobic surfaces that may be capable of binding unnaturally to a variety of targets, possibly including the N-domain of cTnC when it is in its open Ca2+-saturated state. This would constitute a potential route for propagating signals from one end of TnC to the other.
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Affiliation(s)
- Tiago Veltri
- Department of Biomedical Sciences, Florida State University College of Medicine, 1115 West Call Street, Tallahassee, FL, 32306-4300, USA.,Instituto de Bioquímica Médica, Universidade Federal do Rio de Janeiro, Av. Carlos Chagas F° 373, Cidade Universitária, Rio de Janeiro, 21941-902, RJ, Brazil
| | - Guilherme A P de Oliveira
- Programa de Biologia Estrutural, Instituto de Bioquímica Médica, Instituto Nacional de Biologia Estrutural e Bioimagem, Centro Nacional de Ressonância Magnética Nuclear Jiri Jonas, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Ewa A Bienkiewicz
- Department of Biomedical Sciences, Florida State University College of Medicine, 1115 West Call Street, Tallahassee, FL, 32306-4300, USA
| | - Fernando L Palhano
- Instituto de Bioquímica Médica, Universidade Federal do Rio de Janeiro, Av. Carlos Chagas F° 373, Cidade Universitária, Rio de Janeiro, 21941-902, RJ, Brazil
| | - Mayra de A Marques
- Programa de Biologia Estrutural, Instituto de Bioquímica Médica, Instituto Nacional de Biologia Estrutural e Bioimagem, Centro Nacional de Ressonância Magnética Nuclear Jiri Jonas, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Adolfo H Moraes
- Programa de Biologia Estrutural, Instituto de Bioquímica Médica, Instituto Nacional de Biologia Estrutural e Bioimagem, Centro Nacional de Ressonância Magnética Nuclear Jiri Jonas, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil.,Departamento de Química, Instituto de Ciências Exatas, Universidade Federal de Minas Gerais, Brazil
| | - Jerson L Silva
- Programa de Biologia Estrutural, Instituto de Bioquímica Médica, Instituto Nacional de Biologia Estrutural e Bioimagem, Centro Nacional de Ressonância Magnética Nuclear Jiri Jonas, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Martha M Sorenson
- Instituto de Bioquímica Médica, Universidade Federal do Rio de Janeiro, Av. Carlos Chagas F° 373, Cidade Universitária, Rio de Janeiro, 21941-902, RJ, Brazil
| | - Jose R Pinto
- Department of Biomedical Sciences, Florida State University College of Medicine, 1115 West Call Street, Tallahassee, FL, 32306-4300, USA.
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35
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Walton SD, Chakravarthy H, Shettigar V, O’Neil AJ, Siddiqui JK, Jones BR, Tikunova SB, Davis JP. Divergent Soybean Calmodulins Respond Similarly to Calcium Transients: Insight into Differential Target Regulation. FRONTIERS IN PLANT SCIENCE 2017; 8:208. [PMID: 28261258 PMCID: PMC5309217 DOI: 10.3389/fpls.2017.00208] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/02/2016] [Accepted: 02/03/2017] [Indexed: 05/07/2023]
Abstract
Plants commonly respond to stressors by modulating the expression of a large family of calcium binding proteins including isoforms of the ubiquitous signaling protein calmodulin (CaM). The various plant CaM isoforms are thought to differentially regulate the activity of specific target proteins to modulate cellular stress responses. The mechanism(s) behind differential target activation by the plant CaMs is unknown. In this study, we used steady-state and stopped-flow fluorescence spectroscopy to investigate the strategy by which two soybean CaMs (sCaM1 and sCaM4) have evolved to differentially regulate NAD kinase (NADK), which is activated by sCaM1 but inhibited by sCaM4. Although the isolated proteins have different cation binding properties, in the presence of Mg2+ and the CaM binding domains from proteins that are differentially regulated, the two plant CaMs respond nearly identically to rapid and slow Ca2+ transients. Our data suggest that the plant CaMs have evolved to bind certain targets with comparable affinities, respond similarly to a particular Ca2+ signature, but achieve different structural states, only one of which can activate the enzyme. Understanding the basis for differential enzyme regulation by the plant CaMs is the first step to engineering a vertebrate CaM that will selectively alter the CaM signaling network.
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Affiliation(s)
| | | | | | | | | | | | | | - Jonathan P. Davis
- Department of Physiology and Cell Biology, The Ohio State UniversityColumbus, OH, USA
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36
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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: 36] [Impact Index Per Article: 4.5] [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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37
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Gresham KS, Stelzer JE. The contributions of cardiac myosin binding protein C and troponin I phosphorylation to β-adrenergic enhancement of in vivo cardiac function. J Physiol 2016; 594:669-86. [PMID: 26635197 DOI: 10.1113/jp270959] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2015] [Accepted: 11/30/2015] [Indexed: 01/12/2023] Open
Abstract
KEY POINTS β-adrenergic stimulation increases cardiac myosin binding protein C (MyBP-C) and troponin I phosphorylation to accelerate pressure development and relaxation in vivo, although their relative contributions remain unknown. Using a novel mouse model lacking protein kinase A-phosphorylatable troponin I (TnI) and MyBP-C, we examined in vivo haemodynamic function before and after infusion of the β-agonist dobutamine. Mice expressing phospho-ablated MyBP-C displayed cardiac hypertrophy and prevented full acceleration of pressure development and relaxation in response to dobutamine, whereas expression of phosphor-ablated TnI alone had little effect on the acceleration of contractile function in response to dobutamine. Our data demonstrate that MyBP-C phosphorylation is the principal mediator of the contractile response to increased β-agonist stimulation in vivo. These results help us understand why MyBP-C dephosphorylation in the failing heart contributes to contractile dysfunction and decreased adrenergic reserve in response to acute stress. β-adrenergic stimulation plays a critical role in accelerating ventricular contraction and speeding relaxation to match cardiac output to changing circulatory demands. Two key myofilaments proteins, troponin I (TnI) and myosin binding protein-C (MyBP-C), are phosphorylated following β-adrenergic stimulation; however, their relative contributions to the enhancement of in vivo cardiac contractility are unknown. To examine the roles of TnI and MyBP-C phosphorylation in β-adrenergic-mediated enhancement of cardiac function, transgenic (TG) mice expressing non-phosphorylatable TnI protein kinase A (PKA) residues (i.e. serine to alanine substitution at Ser23/24; TnI(PKA-)) were bred with mice expressing non-phosphorylatable MyBP-C PKA residues (i.e. serine to alanine substitution at Ser273, Ser282 and Ser302; MyBPC(PKA-)) to generate a novel mouse model expressing non-phosphorylatable PKA residues in TnI and MyBP-C (DBL(PKA-)). MyBP-C dephosphorylation produced cardiac hypertrophy and increased wall thickness in MyBPC(PKA-) and DBL(PKA-) mice, and in vivo echocardiography and pressure-volume catheterization studies revealed impaired systolic function and prolonged diastolic relaxation compared to wild-type and TnI(PKA-) mice. Infusion of the β-agonist dobutamine resulted in accelerated rates of pressure development and relaxation in all mice; however, MyBPC(PKA-) and DBL(PKA-) mice displayed a blunted contractile response compared to wild-type and TnI(PKA-) mice. Furthermore, unanaesthesized MyBPC(PKA-) and DBL(PKA-) mice displayed depressed maximum systolic pressure in response to dobutamine as measured using implantable telemetry devices. Taken together, our data show that MyBP-C phosphorylation is a critical modulator of the in vivo acceleration of pressure development and relaxation as a result of enhanced β-adrenergic stimulation, and reduced MyBP-C phosphorylation may underlie depressed adrenergic reserve in heart failure.
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Affiliation(s)
- Kenneth S Gresham
- Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, OH, USA
| | - Julian E Stelzer
- Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, OH, USA
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38
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Aboelkassem Y, Bonilla JA, McCabe KJ, Campbell SG. Contributions of Ca2+-Independent Thin Filament Activation to Cardiac Muscle Function. Biophys J 2016; 109:2101-12. [PMID: 26588569 DOI: 10.1016/j.bpj.2015.09.028] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2015] [Revised: 09/03/2015] [Accepted: 09/11/2015] [Indexed: 12/29/2022] Open
Abstract
Although Ca2+ is the principal regulator of contraction in striated muscle, in vitro evidence suggests that some actin-myosin interaction is still possible even in its absence. Whether this Ca2+-independent activation (CIA) occurs under physiological conditions remains unclear, as does its potential impact on the function of intact cardiac muscle. The purpose of this study was to investigate CIA using computational analysis. We added a structurally motivated representation of this phenomenon to an existing myofilament model, which allowed predictions of CIA-dependent muscle behavior. We found that a certain amount of CIA was essential for the model to reproduce reported effects of nonfunctional troponin C on myofilament force generation. Consequently, those data enabled estimation of ΔGCIA, the energy barrier for activating a thin filament regulatory unit in the absence of Ca2+. Using this estimate of ΔGCIA as a point of reference (∼7 kJ mol(-1)), we examined its impact on various aspects of muscle function through additional simulations. CIA decreased the Hill coefficient of steady-state force while increasing myofilament Ca2+ sensitivity. At the same time, CIA had minimal effect on the rate of force redevelopment after slack/restretch. Simulations of twitch tension show that the presence of CIA increases peak tension while profoundly delaying relaxation. We tested the model's ability to represent perturbations to the Ca2+ regulatory mechanism by analyzing twitch records measured in transgenic mice expressing a cardiac troponin I mutation (R145G). The effects of the mutation on twitch dynamics were fully reproduced by a single parameter change, namely lowering ΔGCIA by 2.3 kJ mol(-1) relative to its wild-type value. Our analyses suggest that CIA is present in cardiac muscle under normal conditions and that its modulation by gene mutations or other factors can alter both systolic and diastolic function.
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Affiliation(s)
- Yasser Aboelkassem
- Department of Biomedical Engineering, Yale University, New Haven, Connecticut
| | - Jordan A Bonilla
- Department of Computing and Mathematical Sciences, California Institute of Technology, Pasadena, California
| | - Kimberly J McCabe
- Department of Biomedical Engineering, Yale University, New Haven, Connecticut
| | - Stuart G Campbell
- Department of Biomedical Engineering, Yale University, New Haven, Connecticut.
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39
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Sears EJ, Gillis TE. A functional comparison of cardiac troponin C from representatives of three vertebrate taxa: Linking phylogeny and protein function. Comp Biochem Physiol B Biochem Mol Biol 2016; 202:8-15. [PMID: 27453566 DOI: 10.1016/j.cbpb.2016.07.004] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2016] [Revised: 07/18/2016] [Accepted: 07/19/2016] [Indexed: 11/25/2022]
Abstract
The Ca2+ affinity of cardiac troponin C (cTnC) from rainbow trout is significantly greater than that of cTnC from mammalian species. This high affinity is thought to enable cardiac function in trout at low physiological temperatures and is due to residues Asn2, Ile28, Gln29, and Asp30 (Gillis et al., 2005, Physiol Genomics, 22, 1-7). Interestingly, the cTnC of the African clawed frog Xenopus laevis (frog cTnC) contains Gln29 and Asp30 but the residues at positions 2 and 28 are those found in all mammalian cTnC isoforms (Asp2 and Val28). The purpose of this study was to determine the Ca2+ affinity of frog cTnC, and to determine how these three protein orthologs influence the function of complete troponin complexes. Measurements of Ca2+ affinity and the rate of Ca2+ dissociation from the cTnC isoforms and cTn complexes were made by monitoring the fluorescence of anilinonapthalenesulfote iodoacetamide (IAANS) engineered into the cTnC isoforms to report changes in protein conformation. The results demonstrate that the Ca2+ affinity of frog cTnC is greater than that of trout cTnC and human cTnC. We also found that replacing human cTnC with frog cTnC in a mammalian cTn complex increased the Ca2+ affinity of the complex by 5-fold, which is also greater than complexes containing trout cTnC. Together these results suggest that frog cTnC has the potential to increase the Ca2+ sensitivity of force generation by the mammalian heart.
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Affiliation(s)
- Elizabeth J Sears
- Department of Integrative Biology, University of Guelph, Guelph, ON N1G 2W1, Canada; Cardiovasclar Research Center, University of Guelph, Canada
| | - Todd E Gillis
- Department of Integrative Biology, University of Guelph, Guelph, ON N1G 2W1, Canada; Cardiovasclar Research Center, University of Guelph, Canada.
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Abstract
Calcium binding and dissociation within the cardiac thin filament (CTF) is a fundamental regulator of normal contraction and relaxation. Although the disruption of this complex, allosterically mediated process has long been implicated in human disease, the precise atomic-level mechanisms remain opaque, greatly hampering the development of novel targeted therapies. To address this question, we used a fully atomistic CTF model to test both Ca(2+) binding strength and the energy required to remove Ca(2+) from the N-lobe binding site in WT and mutant troponin complexes that have been linked to genetic cardiomyopathies. This computational approach is combined with measurements of in vitro Ca(2+) dissociation rates in fully reconstituted WT and cardiac troponin T R92L and R92W thin filaments. These human disease mutations represent known substitutions at the same residue, reside at a significant distance from the calcium binding site in cardiac troponin C, and do not affect either the binding pocket affinity or EF-hand structure of the binding domain. Both have been shown to have significantly different effects on cardiac function in vivo. We now show that these mutations independently alter the interaction between the Ca(2+) ion and cardiac troponin I subunit. This interaction is a previously unidentified mechanism, in which mutations in one protein of a complex indirectly affect a third via structural and dynamic changes in a second to yield a pathogenic change in thin filament function that results in mutation-specific disease states. We can now provide atom-level insight that is potentially highly actionable in drug design.
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Designing proteins to combat disease: Cardiac troponin C as an example. Arch Biochem Biophys 2016; 601:4-10. [PMID: 26901433 DOI: 10.1016/j.abb.2016.02.007] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2016] [Accepted: 02/04/2016] [Indexed: 01/18/2023]
Abstract
Throughout history, muscle research has led to numerous scientific breakthroughs that have brought insight to a more general understanding of all biological processes. Potentially one of the most influential discoveries was the role of the second messenger calcium and its myriad of handling and sensing systems that mechanistically control muscle contraction. In this review we will briefly discuss the significance of calcium as a universal second messenger along with some of the most common calcium binding motifs in proteins, focusing on the EF-hand. We will also describe some of our approaches to rationally design calcium binding proteins to palliate, or potentially even cure cardiovascular disease. Considering not all failing hearts have the same etiology, genetic background and co-morbidities, personalized therapies will need to be developed. We predict designer proteins will open doors for unprecedented personalized, and potentially, even generalized medicines as gene therapy or protein delivery techniques come to fruition.
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Hwang PM. '(De-)sensitization' vs. 'Uncoupling': what drives cardiomyopathies in the thin filament? Cardiovasc Res 2016; 109:185-6. [PMID: 26464330 DOI: 10.1093/cvr/cvv232] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Peter M Hwang
- University of Alberta, 5-112 Clinical Sciences Building, Edmonton T6G 2G3, Canada
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Pan S, Sommese RF, Sallam KI, Nag S, Sutton S, Miller SM, Spudich JA, Ruppel KM, Ashley EA. Establishing disease causality for a novel gene variant in familial dilated cardiomyopathy using a functional in-vitro assay of regulated thin filaments and human cardiac myosin. BMC MEDICAL GENETICS 2015; 16:97. [PMID: 26498512 PMCID: PMC4620603 DOI: 10.1186/s12881-015-0243-5] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/28/2014] [Accepted: 10/16/2015] [Indexed: 11/10/2022]
Abstract
Background As next generation sequencing for the genetic diagnosis of cardiovascular disorders becomes more widely used, establishing causality for putative disease causing variants becomes increasingly relevant. Diseases of the cardiac sarcomere provide a particular challenge in this regard because of the complexity of assaying the effect of genetic variants in human cardiac contractile proteins. Results In this study we identified a novel variant R205Q in the cardiac troponin T gene (TNNT2). Carriers of the variant allele exhibited increased chamber volumes associated with decreased left ventricular ejection fraction. To clarify the causal role of this variant, we generated recombinant variant human protein and examined its calcium kinetics as well as the maximally activated ADP release of human β-cardiac myosin with regulated thin filaments containing the mutant troponin T. We found that the R205Q mutation significantly decreased the calcium sensitivity of the thin filament by altering the effective calcium dissociation kinetics. Conclusions The development of moderate throughput post-genomic assays is an essential step in the realization of the potential of next generation sequencing. Although technically challenging, biochemical and functional assays of human cardiac contractile proteins of the thin filament can be achieved and provide an orthogonal source of information to inform the question of causality for individual variants.
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Affiliation(s)
- Stephen Pan
- Leon H. Charney Division of Cardiology, NYU Langone Medical Center, New York, NY, USA.
| | - Ruth F Sommese
- Department of Genetics, Cell Biology, and Development, University of Minnesota, Minneapolis, MN, USA.
| | - Karim I Sallam
- Departments of Medicine (Cardiovascular Medicine), Stanford University School of Medicine, Stanford, CA, USA.
| | - Suman Nag
- Department of Biochemistry, Stanford University School of Medicine, Stanford, CA, USA.
| | - Shirley Sutton
- Department of Biochemistry, Stanford University School of Medicine, Stanford, CA, USA.
| | - Susan M Miller
- Department of Pharmaceutical Chemistry, University of California San Francisco, San Francisco, CA, USA.
| | - James A Spudich
- Department of Biochemistry, Stanford University School of Medicine, Stanford, CA, USA.
| | - Kathleen M Ruppel
- Department of Biochemistry, Stanford University School of Medicine, Stanford, CA, USA. .,Department of Pediatrics (Cardiology), Stanford University School of Medicine, Stanford, CA, USA.
| | - Euan A Ashley
- Departments of Medicine (Cardiovascular Medicine), Stanford University School of Medicine, Stanford, CA, USA.
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Rao V, Cheng Y, Lindert S, Wang D, Oxenford L, McCulloch AD, McCammon JA, Regnier M. PKA phosphorylation of cardiac troponin I modulates activation and relaxation kinetics of ventricular myofibrils. Biophys J 2015; 107:1196-1204. [PMID: 25185555 DOI: 10.1016/j.bpj.2014.07.027] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2014] [Revised: 07/10/2014] [Accepted: 07/15/2014] [Indexed: 10/24/2022] Open
Abstract
Protein kinase A (PKA) phosphorylation of myofibril proteins constitutes an important pathway for β-adrenergic modulation of cardiac contractility and relaxation. PKA targets the N-terminus (Ser-23/24) of cardiac troponin I (cTnI), cardiac myosin-binding protein C (cMyBP-C) and titin. The effect of PKA-mediated phosphorylation on the magnitude of contraction has been studied in some detail, but little is known about how it modulates the kinetics of thin filament activation and myofibril relaxation as Ca(2+) levels vary. Troponin C (cTnC) interaction with cTnI (C-I interaction) is a critical step in contractile activation that can be modulated by cTnI phosphorylation. We tested the hypothesis that altering C-I interactions by PKA, or by cTnI phosphomimetic mutations (S23D/S24D-cTnI), directly affects thin filament activation and myofilament relaxation kinetics. Rat ventricular myofibrils were isolated and endogenous cTn was exchanged with either wild-type cTnI, or S23D/S24D-cTnI recombinant cTn. Contractile mechanics were monitored at maximum and submaximal Ca(2+) concentrations. PKA treatment of wild-type cTn or exchange of cTn containing S23D/S24D-cTnI resulted in an increase in the rate of early, slow phase of relaxation (kREL,slow) and a decrease in its duration (tREL,slow). These effects were greater for submaximal Ca(2+) activated contractions. PKA treatment also reduced the rate of contractile activation (kACT) at maximal, but not submaximal Ca(2+), and reduced the Ca(2+) sensitivity of contraction. Using a fluorescent probe coupled to cTnC (C35S-IANBD), the Ca(2+)-cTn binding affinity and C-I interaction were monitored. Ca(2+) binding to cTn (pCa50) was significantly decreased when cTnI was phosphorylated by PKA (ΔpCa50 = 0.31). PKA phosphorylation of cTnI also weakened C-I interaction in the presence of Ca(2+). These data suggest that weakened C-I interaction, via PKA phosphorylation of cTnI, may slow thin filament activation and result in increased myofilament relaxation kinetics, the latter of which could enhance early phase diastolic relaxation during β-adrenergic stimulation.
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Affiliation(s)
- Vijay Rao
- University of Washington, Department of Bioengineering, Seattle, Washington
| | - Yuanhua Cheng
- University of Washington, Department of Bioengineering, Seattle, Washington; National Biomedical Computational Resource, La Jolla, California
| | - Steffen Lindert
- University of California San Diego, Department of Pharmacology, La Jolla, California
| | - Dan Wang
- University of Washington, Department of Bioengineering, Seattle, Washington
| | - Lucas Oxenford
- University of Washington, Department of Bioengineering, Seattle, Washington
| | - Andrew D McCulloch
- University of California San Diego, Department of Bioengineering, La Jolla, California; National Biomedical Computational Resource, La Jolla, California
| | - J Andrew McCammon
- University of California San Diego, Department of Pharmacology, La Jolla, California; National Biomedical Computational Resource, La Jolla, California
| | - Michael Regnier
- University of Washington, Department of Bioengineering, Seattle, Washington.
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McConnell BK, Singh S, Fan Q, Hernandez A, Portillo JP, Reiser PJ, Tikunova SB. Knock-in mice harboring a Ca(2+) desensitizing mutation in cardiac troponin C develop early onset dilated cardiomyopathy. Front Physiol 2015; 6:242. [PMID: 26379556 PMCID: PMC4550777 DOI: 10.3389/fphys.2015.00242] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2015] [Accepted: 08/11/2015] [Indexed: 12/05/2022] Open
Abstract
The physiological consequences of aberrant Ca(2+) binding and exchange with cardiac myofilaments are not clearly understood. In order to examine the effect of decreasing Ca(2+) sensitivity of cTnC on cardiac function, we generated knock-in mice carrying a D73N mutation (not known to be associated with heart disease in human patients) in cTnC. The D73N mutation was engineered into the regulatory N-domain of cTnC in order to reduce Ca(2+) sensitivity of reconstituted thin filaments by increasing the rate of Ca(2+) dissociation. In addition, the D73N mutation drastically blunted the extent of Ca(2+) desensitization of reconstituted thin filaments induced by cTnI pseudo-phosphorylation. Compared to wild-type mice, heterozygous knock-in mice carrying the D73N mutation exhibited a substantially decreased Ca(2+) sensitivity of force development in skinned ventricular trabeculae. Kaplan-Meier survival analysis revealed that median survival time for knock-in mice was 12 weeks. Echocardiographic analysis revealed that knock-in mice exhibited increased left ventricular dimensions with thinner walls. Echocardiographic analysis also revealed that measures of systolic function, such as ejection fraction (EF) and fractional shortening (FS), were dramatically reduced in knock-in mice. In addition, knock-in mice displayed electrophysiological abnormalities, namely prolonged QRS and QT intervals. Furthermore, ventricular myocytes isolated from knock-in mice did not respond to β-adrenergic stimulation. Thus, knock-in mice developed pathological features similar to those observed in human patients with dilated cardiomyopathy (DCM). In conclusion, our results suggest that decreasing Ca(2+) sensitivity of the regulatory N-domain of cTnC is sufficient to trigger the development of DCM.
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Affiliation(s)
- Bradley K. McConnell
- Department of Pharmacological and Pharmaceutical Sciences, University of HoustonHouston, TX, USA
| | - Sonal Singh
- Department of Pharmacological and Pharmaceutical Sciences, University of HoustonHouston, TX, USA
| | - Qiying Fan
- Department of Pharmacological and Pharmaceutical Sciences, University of HoustonHouston, TX, USA
| | - Adriana Hernandez
- Department of Pharmacological and Pharmaceutical Sciences, University of HoustonHouston, TX, USA
| | - Jesus P. Portillo
- Department of Pharmacological and Pharmaceutical Sciences, University of HoustonHouston, TX, USA
| | - Peter J. Reiser
- Division of Biosciences, College of Dentistry, The Ohio State UniversityColumbus, OH, USA
| | - Svetlana B. Tikunova
- Department of Pharmacological and Pharmaceutical Sciences, University of HoustonHouston, TX, USA
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46
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In situ time-resolved FRET reveals effects of sarcomere length on cardiac thin-filament activation. Biophys J 2015; 107:682-693. [PMID: 25099807 DOI: 10.1016/j.bpj.2014.05.044] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2013] [Revised: 05/10/2014] [Accepted: 05/13/2014] [Indexed: 02/07/2023] Open
Abstract
During cardiac thin-filament activation, the N-domain of cardiac troponin C (N-cTnC) binds to Ca(2+) and interacts with the actomyosin inhibitory troponin I (cTnI). The interaction between N-cTnC and cTnI stabilizes the Ca(2+)-induced opening of N-cTnC and is presumed to also destabilize cTnI-actin interactions that work together with steric effects of tropomyosin to inhibit force generation. Recently, our in situ steady-state FRET measurements based on N-cTnC opening suggested that at long sarcomere length, strongly bound cross-bridges indirectly stabilize this Ca(2+)-sensitizing N-cTnC-cTnI interaction through structural effects on tropomyosin and cTnI. However, the method previously used was unable to determine whether N-cTnC opening depends on sarcomere length. In this study, we used time-resolved FRET to monitor the effects of cross-bridge state and sarcomere length on the Ca(2+)-dependent conformational behavior of N-cTnC in skinned cardiac muscle fibers. FRET donor (AEDANS) and acceptor (DDPM)-labeled double-cysteine mutant cTnC(T13C/N51C)AEDANS-DDPM was incorporated into skinned muscle fibers to monitor N-cTnC opening. To study the structural effects of sarcomere length on N-cTnC, we monitored N-cTnC opening at relaxing and saturating levels of Ca(2+) and 1.80 and 2.2-μm sarcomere length. Mg(2+)-ADP and orthovanadate were used to examine the structural effects of noncycling strong-binding and weak-binding cross-bridges, respectively. We found that the stabilizing effect of strongly bound cross-bridges on N-cTnC opening (which we interpret as transmitted through related changes in cTnI and tropomyosin) become diminished by decreases in sarcomere length. Additionally, orthovanadate blunted the effect of sarcomere length on N-cTnC conformational behavior such that weak-binding cross-bridges had no effect on N-cTnC opening at any tested [Ca(2+)] or sarcomere length. Based on our findings, we conclude that the observed sarcomere length-dependent positive feedback regulation is a key determinant in the length-dependent Ca(2+) sensitivity of myofilament activation and consequently the mechanism underlying the Frank-Starling law of the heart.
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47
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Land S, Niederer SA. A Spatially Detailed Model of Isometric Contraction Based on Competitive Binding of Troponin I Explains Cooperative Interactions between Tropomyosin and Crossbridges. PLoS Comput Biol 2015; 11:e1004376. [PMID: 26262582 PMCID: PMC4532474 DOI: 10.1371/journal.pcbi.1004376] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2015] [Accepted: 06/03/2015] [Indexed: 01/20/2023] Open
Abstract
Biophysical models of cardiac tension development provide a succinct representation of our understanding of force generation in the heart. The link between protein kinetics and interactions that gives rise to high cooperativity is not yet fully explained from experiments or previous biophysical models. We propose a biophysical ODE-based representation of cross-bridge (XB), tropomyosin and troponin within a contractile regulatory unit (RU) to investigate the mechanisms behind cooperative activation, as well as the role of cooperativity in dynamic tension generation across different species. The model includes cooperative interactions between regulatory units (RU-RU), between crossbridges (XB-XB), as well more complex interactions between crossbridges and regulatory units (XB-RU interactions). For the steady-state force-calcium relationship, our framework predicts that: (1) XB-RU effects are key in shifting the half-activation value of the force-calcium relationship towards lower [Ca2+], but have only small effects on cooperativity. (2) XB-XB effects approximately double the duty ratio of myosin, but do not significantly affect cooperativity. (3) RU-RU effects derived from the long-range action of tropomyosin are a major factor in cooperative activation, with each additional unblocked RU increasing the rate of additional RU’s unblocking. (4) Myosin affinity for short (1–4 RU) unblocked stretches of actin of is very low, and the resulting suppression of force at low [Ca2+] is a major contributor in the biphasic force-calcium relationship. We also reproduce isometric tension development across mouse, rat and human at physiological temperature and pacing rate, and conclude that species differences require only changes in myosin affinity and troponin I/troponin C affinity. Furthermore, we show that the calcium dependence of the rate of tension redevelopment ktr is explained by transient blocking of RU’s by a temporary decrease in XB-RU effects. Force generation in cardiac muscle cells is driven by changes in calcium concentration. Relatively small changes in the calcium concentration over the course of a heart beat lead to the large changes in force required to fully contract and relax the heart. This is known as ‘cooperative activation’, and involves a complex interaction of several proteins involved in contraction. Current computer models which reproduce force generation often do not represent these processes explicitly, and stochastic approaches that do tend to require large amounts of computational power to solve, which limit the range of investigations in which they can be used. We have created an new computational model that captures the underlying physiological processes in more detail, and is more efficient than stochastic approaches, while still being able to run a large range of simulations. The model is able to explain the biological processes leading to the cooperative activation of muscle. In addition, the model reproduces how this cooperative activation translates to normal muscle function to generate force from changes in calcium across three different species.
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Affiliation(s)
- Sander Land
- Department of Biomedical Engineering, King’s College London, United Kingdom
- * E-mail:
| | - Steven A. Niederer
- Department of Biomedical Engineering, King’s College London, United Kingdom
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48
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Li MX, Hwang PM. Structure and function of cardiac troponin C (TNNC1): Implications for heart failure, cardiomyopathies, and troponin modulating drugs. Gene 2015; 571:153-66. [PMID: 26232335 DOI: 10.1016/j.gene.2015.07.074] [Citation(s) in RCA: 83] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2015] [Revised: 06/24/2015] [Accepted: 07/21/2015] [Indexed: 10/23/2022]
Abstract
In striated muscle, the protein troponin complex turns contraction on and off in a calcium-dependent manner. The calcium-sensing component of the complex is troponin C, which is expressed from the TNNC1 gene in both cardiac muscle and slow-twitch skeletal muscle (identical transcript in both tissues) and the TNNC2 gene in fast-twitch skeletal muscle. Cardiac troponin C (cTnC) is made up of two globular EF-hand domains connected by a flexible linker. The structural C-domain (cCTnC) contains two high affinity calcium-binding sites that are always occupied by Ca(2+) or Mg(2+) under physiologic conditions, stabilizing an open conformation that remains anchored to the rest of the troponin complex. In contrast, the regulatory N-domain (cNTnC) contains a single low affinity site that is largely unoccupied at resting calcium concentrations. During muscle activation, calcium binding to cNTnC favors an open conformation that binds to the switch region of troponin I, removing adjacent inhibitory regions of troponin I from actin and allowing muscle contraction to proceed. Regulation of the calcium binding affinity of cNTnC is physiologically important, because it directly impacts the calcium sensitivity of muscle contraction. Calcium sensitivity can be modified by drugs that stabilize the open form of cNTnC, post-translational modifications like phosphorylation of troponin I, or downstream thin filament protein interactions that impact the availability of the troponin I switch region. Recently, mutations in cTnC have been associated with hypertrophic or dilated cardiomyopathy. A detailed understanding of how calcium sensitivity is regulated through the troponin complex is necessary for explaining how mutations perturb its function to promote cardiomyopathy and how post-translational modifications in the thin filament affect heart function and heart failure. Troponin modulating drugs are being developed for the treatment of cardiomyopathies and heart failure.
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Affiliation(s)
- Monica X Li
- Department of Medicine, University of Alberta, Edmonton, AB T6G 2G3, Canada; Department of Biochemistry, University of Alberta, Edmonton, AB T6G 2H7, Canada
| | - Peter M Hwang
- Department of Medicine, University of Alberta, Edmonton, AB T6G 2G3, Canada; Department of Biochemistry, University of Alberta, Edmonton, AB T6G 2H7, Canada.
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49
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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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50
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Gupte TM, Haque F, Gangadharan B, Sunitha MS, Mukherjee S, Anandhan S, Rani DS, Mukundan N, Jambekar A, Thangaraj K, Sowdhamini R, Sommese RF, Nag S, Spudich JA, Mercer JA. Mechanistic heterogeneity in contractile properties of α-tropomyosin (TPM1) mutants associated with inherited cardiomyopathies. J Biol Chem 2014; 290:7003-15. [PMID: 25548289 DOI: 10.1074/jbc.m114.596676] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The most frequent known causes of primary cardiomyopathies are mutations in the genes encoding sarcomeric proteins. Among those are 30 single-residue mutations in TPM1, the gene encoding α-tropomyosin. We examined seven mutant tropomyosins, E62Q, D84N, I172T, L185R, S215L, D230N, and M281T, that were chosen based on their clinical severity and locations along the molecule. The goal of our study was to determine how the biochemical characteristics of each of these mutant proteins are altered, which in turn could provide a structural rationale for treatment of the cardiomyopathies they produce. Measurements of Ca(2+) sensitivity of human β-cardiac myosin ATPase activity are consistent with the hypothesis that hypertrophic cardiomyopathies are hypersensitive to Ca(2+) activation, and dilated cardiomyopathies are hyposensitive. We also report correlations between ATPase activity at maximum Ca(2+) concentrations and conformational changes in TnC measured using a fluorescent probe, which provide evidence that different substitutions perturb the structure of the regulatory complex in different ways. Moreover, we observed changes in protein stability and protein-protein interactions in these mutants. Our results suggest multiple mechanistic pathways to hypertrophic and dilated cardiomyopathies. Finally, we examined a computationally designed mutant, E181K, that is hypersensitive, confirming predictions derived from in silico structural analysis.
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Affiliation(s)
- Tejas M Gupte
- From the Institute for Stem Cell Biology and Regenerative Medicine, Bangalore 560065, India
| | - Farah Haque
- From the Institute for Stem Cell Biology and Regenerative Medicine, Bangalore 560065, India, the National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore 560065, India
| | - Binnu Gangadharan
- From the Institute for Stem Cell Biology and Regenerative Medicine, Bangalore 560065, India, the Manipal University, Madhav Nagar, Manipal 576104, India
| | - Margaret S Sunitha
- From the Institute for Stem Cell Biology and Regenerative Medicine, Bangalore 560065, India, the National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore 560065, India
| | - Souhrid Mukherjee
- From the Institute for Stem Cell Biology and Regenerative Medicine, Bangalore 560065, India
| | - Swetha Anandhan
- From the Institute for Stem Cell Biology and Regenerative Medicine, Bangalore 560065, India
| | - Deepa Selvi Rani
- the Council for Scientific and Industrial Research-Centre for Cellular and Molecular Biology, Hyderabad 500007, India
| | - Namita Mukundan
- the National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore 560065, India
| | - Amruta Jambekar
- From the Institute for Stem Cell Biology and Regenerative Medicine, Bangalore 560065, India
| | - Kumarasamy Thangaraj
- the Council for Scientific and Industrial Research-Centre for Cellular and Molecular Biology, Hyderabad 500007, India
| | - Ramanathan Sowdhamini
- the National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore 560065, India
| | - Ruth F Sommese
- the Department of Biochemistry, Stanford University School of Medicine, Stanford, California 94305, and
| | - Suman Nag
- the Department of Biochemistry, Stanford University School of Medicine, Stanford, California 94305, and
| | - James A Spudich
- From the Institute for Stem Cell Biology and Regenerative Medicine, Bangalore 560065, India, the Department of Biochemistry, Stanford University School of Medicine, Stanford, California 94305, and
| | - John A Mercer
- From the Institute for Stem Cell Biology and Regenerative Medicine, Bangalore 560065, India, the McLaughlin Research Institute, Great Falls, Montana 59405
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