1
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Ando T. Functional Implications of Dynamic Structures of Intrinsically Disordered Proteins Revealed by High-Speed AFM Imaging. Biomolecules 2022; 12:biom12121876. [PMID: 36551304 PMCID: PMC9776203 DOI: 10.3390/biom12121876] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2022] [Revised: 12/09/2022] [Accepted: 12/11/2022] [Indexed: 12/15/2022] Open
Abstract
The unique functions of intrinsically disordered proteins (IDPs) depend on their dynamic protean structure that often eludes analysis. High-speed atomic force microscopy (HS-AFM) can conduct this difficult analysis by directly visualizing individual IDP molecules in dynamic motion at sub-molecular resolution. After brief descriptions of the microscopy technique, this review first shows that the intermittent tip-sample contact does not alter the dynamic structure of IDPs and then describes how the number of amino acids contained in a fully disordered region can be estimated from its HS-AFM images. Next, the functional relevance of a dumbbell-like structure that has often been observed on IDPs is discussed. Finally, the dynamic structural information of two measles virus IDPs acquired from their HS-AFM and NMR analyses is described together with its functional implications.
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Affiliation(s)
- Toshio Ando
- Nano Life Science Institute, Kanazawa University, Kanazawa 920-1192, Japan
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2
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Klebba PE, Newton SMC, Six DA, Kumar A, Yang T, Nairn BL, Munger C, Chakravorty S. Iron Acquisition Systems of Gram-negative Bacterial Pathogens Define TonB-Dependent Pathways to Novel Antibiotics. Chem Rev 2021; 121:5193-5239. [PMID: 33724814 PMCID: PMC8687107 DOI: 10.1021/acs.chemrev.0c01005] [Citation(s) in RCA: 50] [Impact Index Per Article: 16.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Iron is an indispensable metabolic cofactor in both pro- and eukaryotes, which engenders a natural competition for the metal between bacterial pathogens and their human or animal hosts. Bacteria secrete siderophores that extract Fe3+ from tissues, fluids, cells, and proteins; the ligand gated porins of the Gram-negative bacterial outer membrane actively acquire the resulting ferric siderophores, as well as other iron-containing molecules like heme. Conversely, eukaryotic hosts combat bacterial iron scavenging by sequestering Fe3+ in binding proteins and ferritin. The variety of iron uptake systems in Gram-negative bacterial pathogens illustrates a range of chemical and biochemical mechanisms that facilitate microbial pathogenesis. This document attempts to summarize and understand these processes, to guide discovery of immunological or chemical interventions that may thwart infectious disease.
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Affiliation(s)
- Phillip E Klebba
- Department of Biochemistry and Molecular Biophysics, Kansas State University, Manhattan, Kansas 66506, United States
| | - Salete M C Newton
- Department of Biochemistry and Molecular Biophysics, Kansas State University, Manhattan, Kansas 66506, United States
| | - David A Six
- Venatorx Pharmaceuticals, Inc., 30 Spring Mill Drive, Malvern, Pennsylvania 19355, United States
| | - Ashish Kumar
- Department of Biochemistry and Molecular Biophysics, Kansas State University, Manhattan, Kansas 66506, United States
| | - Taihao Yang
- Department of Biochemistry and Molecular Biophysics, Kansas State University, Manhattan, Kansas 66506, United States
| | - Brittany L Nairn
- Department of Biological Sciences, Bethel University, 3900 Bethel Drive, St. Paul, Minnesota 55112, United States
| | - Colton Munger
- Department of Biochemistry and Molecular Biophysics, Kansas State University, Manhattan, Kansas 66506, United States
| | - Somnath Chakravorty
- Jacobs School of Medicine and Biomedical Sciences, SUNY Buffalo, Buffalo, New York 14203, United States
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3
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Marques MA, Landim-Vieira M, Moraes AH, Sun B, Johnston JR, Dieseldorff Jones KM, Cino EA, Parvatiyar MS, Valera IC, Silva JL, Galkin VE, Chase PB, Kekenes-Huskey PM, de Oliveira GAP, Pinto JR. Anomalous structural dynamics of minimally frustrated residues in cardiac troponin C triggers hypertrophic cardiomyopathy. Chem Sci 2021; 12:7308-7323. [PMID: 34163821 PMCID: PMC8171346 DOI: 10.1039/d1sc01886h] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2021] [Accepted: 04/11/2021] [Indexed: 12/13/2022] Open
Abstract
Cardiac TnC (cTnC) is highly conserved among mammals, and genetic variants can result in disease by perturbing Ca2+-regulation of myocardial contraction. Here, we report the molecular basis of a human mutation in cTnC's αD-helix (TNNC1-p.C84Y) that impacts conformational dynamics of the D/E central-linker and sampling of discrete states in the N-domain, favoring the "primed" state associated with Ca2+ binding. We demonstrate cTnC's αD-helix normally functions as a central hub that controls minimally frustrated interactions, maintaining evolutionarily conserved rigidity of the N-domain. αD-helix perturbation remotely alters conformational dynamics of the N-domain, compromising its structural rigidity. Transgenic mice carrying this cTnC mutation exhibit altered dynamics of sarcomere function and hypertrophic cardiomyopathy. Together, our data suggest that disruption of evolutionary conserved molecular frustration networks by a myofilament protein mutation may ultimately compromise contractile performance and trigger hypertrophic cardiomyopathy.
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Affiliation(s)
- Mayra A Marques
- Institute of Medical Biochemistry Leopoldo de Meis, National Institute of Structural Biology and Bioimaging, National Center of Nuclear Magnetic Resonance Jiri Jonas, Federal University of Rio de Janeiro 373 Carlos Chagas Filho Av, Room: E-10 Rio de Janeiro RJ 21941-902 Brazil +55-21-3938-6756
| | - Maicon Landim-Vieira
- Department of Biomedical Sciences, Florida State University, College of Medicine 1115 West Call Street, Room: 1370 (lab) - 1350-H (office) Tallahassee FL 32306 USA +1-850-645-0016
| | - Adolfo H Moraes
- Department of Chemistry, Federal University of Minas Gerais Belo Horizonte MG Brazil
| | - Bin Sun
- Department of Cell and Molecular Physiology, Loyola University Chicago Maywood IL USA
| | - Jamie R Johnston
- Department of Biomedical Sciences, Florida State University, College of Medicine 1115 West Call Street, Room: 1370 (lab) - 1350-H (office) Tallahassee FL 32306 USA +1-850-645-0016
| | - Karissa M Dieseldorff Jones
- Department of Biomedical Sciences, Florida State University, College of Medicine 1115 West Call Street, Room: 1370 (lab) - 1350-H (office) Tallahassee FL 32306 USA +1-850-645-0016
| | - Elio A Cino
- Department of Biochemistry and Immunology, Federal University of Minas Gerais Belo Horizonte MG Brazil
| | - Michelle S Parvatiyar
- Department of Nutrition, Food and Exercise Sciences, Florida State University Tallahassee FL USA
| | - Isela C Valera
- Department of Nutrition, Food and Exercise Sciences, Florida State University Tallahassee FL USA
| | - Jerson L Silva
- Institute of Medical Biochemistry Leopoldo de Meis, National Institute of Structural Biology and Bioimaging, National Center of Nuclear Magnetic Resonance Jiri Jonas, Federal University of Rio de Janeiro 373 Carlos Chagas Filho Av, Room: E-10 Rio de Janeiro RJ 21941-902 Brazil +55-21-3938-6756
| | - Vitold E Galkin
- Department of Physiological Sciences, Eastern Virginia Medical School Norfolk VA USA
| | - P Bryant Chase
- Department of Biological Science, Florida State University Tallahassee FL USA
| | | | - Guilherme A P de Oliveira
- Institute of Medical Biochemistry Leopoldo de Meis, National Institute of Structural Biology and Bioimaging, National Center of Nuclear Magnetic Resonance Jiri Jonas, Federal University of Rio de Janeiro 373 Carlos Chagas Filho Av, Room: E-10 Rio de Janeiro RJ 21941-902 Brazil +55-21-3938-6756
| | - Jose Renato Pinto
- Department of Biomedical Sciences, Florida State University, College of Medicine 1115 West Call Street, Room: 1370 (lab) - 1350-H (office) Tallahassee FL 32306 USA +1-850-645-0016
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4
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Kachooei E, Cordina NM, Potluri PR, Guse JA, McCamey D, Brown LJ. Phosphorylation of Troponin I finely controls the positioning of Troponin for the optimal regulation of cardiac muscle contraction. J Mol Cell Cardiol 2020; 150:44-53. [PMID: 33080242 DOI: 10.1016/j.yjmcc.2020.10.007] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/23/2020] [Revised: 09/22/2020] [Accepted: 10/14/2020] [Indexed: 12/01/2022]
Abstract
Troponin is the Ca2+ molecular switch that regulates striated muscle contraction. In the heart, troponin Ca2+ sensitivity is also modulated by the PKA-dependent phosphorylation of a unique 31-residue N-terminal extension region of the Troponin I subunit (NH2-TnI). However, the detailed mechanism for the propagation of the phosphorylation signal through Tn, which results in the enhancement of the myocardial relaxation rate, is difficult to examine within whole Tn. Several models exist for how phosphorylation modulates the troponin response in cardiac cells but these are mostly built from peptide-NMR studies and molecular dynamics simulations. Here we used a paramagnetic spin labeling approach to position and track the movement of the NH2-TnI region within whole Tn. Through paramagnetic relaxation enhancement (PRE)-NMR experiments, we show that the NH2-TnI region interacts with a broad surface area on the N-domain of the Troponin C subunit. This region includes the Ca2+ regulatory Site II and the TnI switch-binding site. Phosphorylation of the NH2-TnI both weakens and shifts this region to an adjacent site on TnC. Interspin EPR distances between NH2-TnI and TnC further reveal a phosphorylation induced re-orientation of the TnC N-domain under saturating Ca2+ conditions. We propose an allosteric model where phosphorylation triggered cooperative changes in both the interaction of the NH2-TnI region with TnC, and the re-orientation of the TnC interdomain orientation, together promote the release of the TnI switch-peptide. Enhancement of the myocardial relaxation rate then occurs. Knowledge of this unique role of phosphorylation in whole Tn is important for understanding pathological processes affecting the heart.
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Affiliation(s)
- Ehsan Kachooei
- Department of Molecular Sciences, Macquarie University, Sydney, New South Wales 2109, Australia
| | - Nicole M Cordina
- Department of Molecular Sciences, Macquarie University, Sydney, New South Wales 2109, Australia
| | - Phani R Potluri
- Department of Molecular Sciences, Macquarie University, Sydney, New South Wales 2109, Australia
| | - Joanna A Guse
- School of Physics, The University of New South Wales, Sydney, New South Wales 2052, Australia
| | - Dane McCamey
- School of Physics, The University of New South Wales, Sydney, New South Wales 2052, Australia
| | - Louise J Brown
- Department of Molecular Sciences, Macquarie University, Sydney, New South Wales 2109, Australia.
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5
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Arata T. Myosin and Other Energy-Transducing ATPases: Structural Dynamics Studied by Electron Paramagnetic Resonance. Int J Mol Sci 2020; 21:E672. [PMID: 31968570 PMCID: PMC7014194 DOI: 10.3390/ijms21020672] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2019] [Revised: 01/05/2020] [Accepted: 01/06/2020] [Indexed: 02/07/2023] Open
Abstract
The objective of this article was to document the energy-transducing and regulatory interactions in supramolecular complexes such as motor, pump, and clock ATPases. The dynamics and structural features were characterized by motion and distance measurements using spin-labeling electron paramagnetic resonance (EPR) spectroscopy. In particular, we focused on myosin ATPase with actin-troponin-tropomyosin, neural kinesin ATPase with microtubule, P-type ion-motive ATPase, and cyanobacterial clock ATPase. Finally, we have described the relationships or common principles among the molecular mechanisms of various energy-transducing systems and how the large-scale thermal structural transition of flexible elements from one state to the other precedes the subsequent irreversible chemical reactions.
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Affiliation(s)
- Toshiaki Arata
- Department of Biology, Graduate School of Science, Osaka City University, Osaka 558-8585, Japan
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6
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Gutiérrez-Mejía FA, Moerland CP, van IJzendoorn LJ, Prins MWJ. Conformation switching of single native proteins revealed by nanomechanical probing without a pulling force. NANOSCALE 2019; 11:19933-19942. [PMID: 31599908 DOI: 10.1039/c9nr01448a] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Protein conformational changes are essential to biological function, and the heterogeneous nature of the corresponding protein states provokes an interest to measure conformational changes at the single molecule level. Here we demonstrate that conformational changes in single native proteins can be revealed by non-covalent antibody-targeting of specific domains within the protein, using nanomechanical probing without an applied pulling force. The protein of interest was captured between a particle and a substrate and three properties were quantified: the twist amplitude related to an applied torque, torsional compliance related to rotational Brownian motion, and translational Brownian displacement. Calcium-dependent conformation switching was studied in native human cardiac troponin, a heterotrimer protein complex that regulates the contraction and relaxation of heart muscle cells and is also a key biomarker for diagnosing myocardial infarction. The data reveal a change in mechanical properties upon conformation switching from the non-saturated to the calcium-saturated state, which in cardiomyocytes gives myosin motor proteins access to actin filaments. A clear increase was observed in the molecular stiffness for the calcium-saturated protein conformation. Using libraries of monoclonal antibodies, the nanomechanical probing of conformation by antibody targeting opens avenues for characterizing single native protein complexes for research as well as for diagnostic applications.
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Affiliation(s)
- Fabiola A Gutiérrez-Mejía
- Department of Applied Physics, Eindhoven University of Technology (TU/e), Eindhoven, The Netherlands. and Institute for Complex Molecular Systems (ICMS), TU/e, Eindhoven, The Netherlands
| | - Christian P Moerland
- Department of Applied Physics, Eindhoven University of Technology (TU/e), Eindhoven, The Netherlands. and Institute for Complex Molecular Systems (ICMS), TU/e, Eindhoven, The Netherlands
| | - Leo J van IJzendoorn
- Department of Applied Physics, Eindhoven University of Technology (TU/e), Eindhoven, The Netherlands. and Institute for Complex Molecular Systems (ICMS), TU/e, Eindhoven, The Netherlands
| | - Menno W J Prins
- Department of Applied Physics, Eindhoven University of Technology (TU/e), Eindhoven, The Netherlands. and Institute for Complex Molecular Systems (ICMS), TU/e, Eindhoven, The Netherlands and Department of Biomedical Engineering, TU/e, Eindhoven, The Netherlands
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7
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Zhao C, Somiya T, Takai S, Ueki S, Arata T. Structural Dynamics of the N-Extension of Cardiac Troponin I Complexed with Troponin C by Site-Directed Spin Labeling Electron Paramagnetic Resonance. Sci Rep 2019; 9:15259. [PMID: 31649274 PMCID: PMC6813352 DOI: 10.1038/s41598-019-51740-6] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2016] [Accepted: 10/07/2019] [Indexed: 11/29/2022] Open
Abstract
The secondary structure of the N-extension of cardiac troponin I (cTnI) was determined by measuring the distance distribution between spin labels attached to the i and i + 4 residues: 15/19, 23/27, 27/31, 35/39, and 43/47. All of the EPR spectra of these regions in the monomeric state were broadened and had a amplitude that was reduced by two-thirds of that of the single spin-labeled spectra and was fit by two residual distance distributions, with a major distribution one spreading over the range from 1 to 2.5 nm and the other minor peak at 0.9 nm. Only slight or no obvious changes were observed when the extension was bound to cTnC in the cTnI-cTnC complex at 0.2 M KCl. However, at 0.1 M KCl, residues 43/47, located at the PKC phosphorylation sites Ser42/44 on the boundary of the extension, exclusively exhibited a 0.9 nm peak, as expected from α-helix in the crystal structure, in the complex. Furthermore, 23/27, which is located on the PKA phosphorylation sites Ser23/24, showed that the major distribution was markedly narrowed, centered at 1.4 nm and 0.5 nm wide, accompanying the spin label immobilization of residue 27. Residues 35 and 69 at site 1 and 2 of cTnC exhibited partial immobilization of the attached spin labels upon complex formation. The results show that the extension exhibited a primarily partially folded or unfolded structure equilibrated with a transiently formed α-helix-like short structure over the length. We hypothesize that the structure binds at least near sites 1 and 2 of cTnC and that the specific secondary structure of the extension on cTnC becomes uncovered when decreasing the ionic strength demonstrating that only the phosphorylation regions of cTnI interact stereospecifically with cTnC.
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Affiliation(s)
- Chenchao Zhao
- Department of Biological Sciences, Graduate School of Science, Osaka University, Machikaneyama-cho 1-1, Toyonaka, Osaka, 560-0043, Japan
| | - Takayasu Somiya
- Department of Biological Sciences, Graduate School of Science, Osaka University, Machikaneyama-cho 1-1, Toyonaka, Osaka, 560-0043, Japan
| | - Shinji Takai
- Department of Biological Sciences, Graduate School of Science, Osaka University, Machikaneyama-cho 1-1, Toyonaka, Osaka, 560-0043, Japan
| | - Shoji Ueki
- Kagawa School of Pharmaceutical Sciences, Tokushima Bunri University, Shido 1314-1, Samuki, Kagawa, 769-2193, Japan
| | - Toshiaki Arata
- Department of Biological Sciences, Graduate School of Science, Osaka University, Machikaneyama-cho 1-1, Toyonaka, Osaka, 560-0043, Japan. .,Center for Advanced High Magnetic Field Science, Graduate School of Science, Osaka University, Machikaneyama-cho 1-1, Toyonaka, Osaka, 560-0043, Japan. .,Department of Biology, Graduate School of Science, Osaka City University, Sugimoto 3-3-138, Osaka, Osaka, 558-8585, Japan.
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8
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Johns CW, Finley NL. Site I Inactivation Impacts Calmodulin Calcium Binding and Activation of Bordetella pertussis Adenylate Cyclase Toxin. Toxins (Basel) 2017; 9:toxins9120389. [PMID: 29189743 PMCID: PMC5744109 DOI: 10.3390/toxins9120389] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2017] [Revised: 11/26/2017] [Accepted: 11/27/2017] [Indexed: 12/20/2022] Open
Abstract
Site I inactivation of calmodulin (CaM) was used to examine the importance of aspartic acid 22 at position 3 in CaM calcium binding, protein folding, and activation of the Bordetella pertussis adenylate cyclase toxin domain (CyaA-ACD). NMR calcium titration experiments showed that site I in the CaM mutant (D22A) remained largely unperturbed, while sites II, III, and IV exhibited calcium-induced conformational changes similar to wild-type CaM (CaMWt). Circular dichroism analyses revealed that D22A had comparable α-helical content to CaMWt, and only modest differences in α-helical composition were detected between CaMWt-CyaA-ACD and D22A-CyaA-ACD complexes. However, the thermal stability of the D22A-CyaA-ACD complex was reduced, as compared to the CaMWt-CyaA-ACD complex. Moreover, CaM-dependent activity of CyaA-ACD decreased 87% in the presence of D22A. Taken together, our findings provide evidence that D22A engages CyaA-ACD, likely through C-terminal mediated binding, and that site I inactivation exerts functional effects through the modification of stabilizing interactions that occur between N-terminal CaM and CyaA-ACD.
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Affiliation(s)
- Christian W Johns
- Cell, Molecular, and Structural Biology Program, Miami University, Oxford, OH 45056, USA.
| | - Natosha L Finley
- Cell, Molecular, and Structural Biology Program, Miami University, Oxford, OH 45056, USA.
- Department of Microbiology, Miami University, Oxford, OH 45056, USA.
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9
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Soler MA, Fortuna S. Influence of Linker Flexibility on the Binding Affinity of Bidentate Binders. J Phys Chem B 2017; 121:3918-3924. [PMID: 28379693 DOI: 10.1021/acs.jpcb.6b12627] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The design of responsive nanosensors typically relies on the availability of probes capable of capturing their target with high affinity and specificity. This can be achieved by coupling two or more binding units through a linker. In this work, we study the dependence on the binder architecture of the binding affinity between a target molecule and a semirigid bidentate binder. Using two different binder architectures, central-rigid and extreme-rigid, and modifying the length and the flexibility degree of the linker we generated 153 different architectures. We computed their dissociation free energies by means of Monte Carlo simulations and thermodynamic integration. We found that central-rigid bidentate binders are a poor choice, as they dissociate more easily than analogous fully flexible bidentate binders. On the other hand, molecular architectures presenting extreme-rigid units were shown effective for a wide range of set-ups.
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Affiliation(s)
- Miguel A Soler
- Molecular Nanotechnology for Life Science Applications Theory Group, Department of Medical and Biological Sciences, University of Udine , Udine, 33100, Italy.,SISSA , Via Bonomea 265, Trieste, Italy
| | - Sara Fortuna
- Molecular Nanotechnology for Life Science Applications Theory Group, Department of Medical and Biological Sciences, University of Udine , Udine, 33100, Italy.,SISSA , Via Bonomea 265, Trieste, Italy.,Center for Biomedical Sciences and Engineering, University of Nova Gorica , Nova Gorica, Goriška 5000, Slovenia
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10
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Badr MA, Pinto JR, Davidson MW, Chase PB. Fluorescent Protein-Based Ca2+ Sensor Reveals Global, Divalent Cation-Dependent Conformational Changes in Cardiac Troponin C. PLoS One 2016; 11:e0164222. [PMID: 27736894 PMCID: PMC5063504 DOI: 10.1371/journal.pone.0164222] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2016] [Accepted: 09/21/2016] [Indexed: 12/12/2022] Open
Abstract
Cardiac troponin C (cTnC) is a key effector in cardiac muscle excitation-contraction coupling as the Ca2+ sensing subunit responsible for controlling contraction. In this study, we generated several FRET sensors for divalent cations based on cTnC flanked by a donor fluorescent protein (CFP) and an acceptor fluorescent protein (YFP). The sensors report Ca2+ and Mg2+ binding, and relay global structural information about the structural relationship between cTnC’s N- and C-domains. The sensors were first characterized using end point titrations to decipher the response to Ca2+ binding in the presence or absence of Mg2+. The sensor that exhibited the largest responses in end point titrations, CTV-TnC, (Cerulean, TnC, and Venus) was characterized more extensively. Most of the divalent cation-dependent FRET signal originates from the high affinity C-terminal EF hands. CTV-TnC reconstitutes into skinned fiber preparations indicating proper assembly of troponin complex, with only ~0.2 pCa unit rightward shift of Ca2+-sensitive force development compared to WT-cTnC. Affinity of CTV-TnC for divalent cations is in agreement with known values for WT-cTnC. Analytical ultracentrifugation indicates that CTV-TnC undergoes compaction as divalent cations bind. C-terminal sites induce ion-specific (Ca2+ versus Mg2+) conformational changes in cTnC. Our data also provide support for the presence of additional, non-EF-hand sites on cTnC for Mg2+ binding. In conclusion, we successfully generated a novel FRET-Ca2+ sensor based on full length cTnC with a variety of cellular applications. Our sensor reveals global structural information about cTnC upon divalent cation binding.
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Affiliation(s)
- Myriam A. Badr
- Department of Biological Science, Florida State University, Tallahassee, Florida, United States of America
- Institute of Molecular Biophysics, Florida State University, Tallahassee, Florida, United States of America
- * E-mail:
| | - Jose R. Pinto
- Department of Biomedical Sciences, College of Medicine, Florida State University, Tallahassee, Florida, United States of America
| | - Michael W. Davidson
- Department of Biological Science, Florida State University, Tallahassee, Florida, United States of America
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida, United States of America
| | - P. Bryant Chase
- Department of Biological Science, Florida State University, Tallahassee, Florida, United States of America
- Institute of Molecular Biophysics, Florida State University, Tallahassee, Florida, United States of America
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11
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Wabik J, Kurcinski M, Kolinski A. Coarse-Grained Modeling of Peptide Docking Associated with Large Conformation Transitions of the Binding Protein: Troponin I Fragment-Troponin C System. Molecules 2015; 20:10763-80. [PMID: 26111167 PMCID: PMC6272278 DOI: 10.3390/molecules200610763] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2015] [Revised: 05/14/2015] [Accepted: 05/21/2015] [Indexed: 11/25/2022] Open
Abstract
Most of the current docking procedures are focused on fine conformational adjustments of assembled complexes and fail to reproduce large-scale protein motion. In this paper, we test a new modeling approach developed to address this problem. CABS-dock is a versatile and efficient tool for modeling the structure, dynamics and interactions of protein complexes. The docking protocol employs a coarse-grained representation of proteins, a simplified model of interactions and advanced protocols for conformational sampling. CABS-dock is one of the very few tools that allow unrestrained docking with large conformational freedom of the receptor. In an example application we modeled the process of complex assembly between two proteins: Troponin C (TnC) and the N-terminal helix of Troponin I (TnI N-helix), which occurs in vivo during muscle contraction. Docking simulations illustrated how the TnC molecule undergoes significant conformational transition on complex formation, a phenomenon that can be modeled only when protein flexibility is properly accounted for. This way our procedure opens up a new possibility for studying mechanisms of protein complex assembly, which may be a supporting tool for rational drug design.
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Affiliation(s)
- Jacek Wabik
- Laboratory of Theory of Biopolymers, Faculty of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland.
| | - Mateusz Kurcinski
- Laboratory of Theory of Biopolymers, Faculty of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland.
| | - Andrzej Kolinski
- Laboratory of Theory of Biopolymers, Faculty of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland.
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12
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Cordina NM, Liew CK, Potluri PR, Curmi PM, Fajer PG, Logan TM, Mackay JP, Brown LJ. Ca2+-induced PRE-NMR changes in the troponin complex reveal the possessive nature of the cardiac isoform for its regulatory switch. PLoS One 2014; 9:e112976. [PMID: 25392916 PMCID: PMC4231091 DOI: 10.1371/journal.pone.0112976] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2014] [Accepted: 10/17/2014] [Indexed: 11/19/2022] Open
Abstract
The interaction between myosin and actin in cardiac muscle, modulated by the calcium (Ca2+) sensor Troponin complex (Tn), is a complex process which is yet to be fully resolved at the molecular level. Our understanding of how the binding of Ca2+ triggers conformational changes within Tn that are subsequently propagated through the contractile apparatus to initiate muscle activation is hampered by a lack of an atomic structure for the Ca2+-free state of the cardiac isoform. We have used paramagnetic relaxation enhancement (PRE)-NMR to obtain a description of the Ca2+-free state of cardiac Tn by describing the movement of key regions of the troponin I (cTnI) subunit upon the release of Ca2+ from Troponin C (cTnC). Site-directed spin-labeling was used to position paramagnetic spin labels in cTnI and the changes in the interaction between cTnI and cTnC subunits were then mapped by PRE-NMR. The functionally important regions of cTnI targeted in this study included the cTnC-binding N-region (cTnI57), the inhibitory region (cTnI143), and two sites on the regulatory switch region (cTnI151 and cTnI159). Comparison of 1H-15N-TROSY spectra of Ca2+-bound and free states for the spin labeled cTnC-cTnI binary constructs demonstrated the release and modest movement of the cTnI switch region (∼10 Å) away from the hydrophobic N-lobe of troponin C (cTnC) upon the removal of Ca2+. Our data supports a model where the non-bound regulatory switch region of cTnI is highly flexible in the absence of Ca2+ but remains in close vicinity to cTnC. We speculate that the close proximity of TnI to TnC in the cardiac complex is favourable for increasing the frequency of collisions between the N-lobe of cTnC and the regulatory switch region, counterbalancing the reduction in collision probability that results from the incomplete opening of the N-lobe of TnC that is unique to the cardiac isoform.
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Affiliation(s)
- Nicole M. Cordina
- Department of Chemistry and Biomolecular Sciences, Macquarie University, Sydney, New South Wales, Australia
| | - Chu K. Liew
- Department of Molecular Cardiology and Biophysics, The Victor Chang Cardiac Research Institute, Darlinghurst, New South Wales, Australia
| | - Phani R. Potluri
- Department of Chemistry and Biomolecular Sciences, Macquarie University, Sydney, New South Wales, Australia
| | - Paul M. Curmi
- School of Physics, The University of New South Wales, Sydney, New South Wales, Australia
| | - Piotr G. Fajer
- Institute of Molecular Biophysics, Florida State University, Tallahassee, Florida, United States of America
| | - Timothy M. Logan
- Institute of Molecular Biophysics, Florida State University, Tallahassee, Florida, United States of America
| | - Joel P. Mackay
- School of Molecular and Microbial Biosciences, University of Sydney, Sydney, New South Wales, Australia
| | - Louise J. Brown
- Department of Chemistry and Biomolecular Sciences, Macquarie University, Sydney, New South Wales, Australia
- * E-mail:
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13
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Jayasundar JJ, Xing J, Robinson JM, Cheung HC, Dong WJ. Molecular dynamics simulations of the cardiac troponin complex performed with FRET distances as restraints. PLoS One 2014; 9:e87135. [PMID: 24558365 PMCID: PMC3928104 DOI: 10.1371/journal.pone.0087135] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2013] [Accepted: 12/18/2013] [Indexed: 11/22/2022] Open
Abstract
Cardiac troponin (cTn) is the Ca2+-sensitive molecular switch that controls cardiac muscle activation and relaxation. However, the molecular detail of the switching mechanism and how the Ca2+ signal received at cardiac troponin C (cTnC) is communicated to cardiac troponin I (cTnI) are still elusive. To unravel the structural details of troponin switching, we performed ensemble Förster resonance energy transfer (FRET) measurements and molecular dynamic (MD) simulations of the cardiac troponin core domain complex. The distance distributions of forty five inter-residue pairs were obtained under Ca2+-free and saturating Ca2+ conditions from time-resolved FRET measurements. These distances were incorporated as restraints during the MD simulations of the cardiac troponin core domain. Compared to the Ca2+-saturated structure, the absence of regulatory Ca2+ perturbed the cTnC N-domain hydrophobic pocket which assumed a closed conformation. This event partially unfolded the cTnI regulatory region/switch. The absence of Ca2+, induced flexibility to the D/E linker and the cTnI inhibitory region, and rotated the cTnC N-domain with respect to rest of the troponin core domain. In the presence of saturating Ca2+ the above said phenomenon were absent. We postulate that the secondary structure perturbations experienced by the cTnI regulatory region held within the cTnC N-domain hydrophobic pocket, coupled with the rotation of the cTnC N-domain would control the cTnI mobile domain interaction with actin. Concomitantly the rotation of the cTnC N-domain and perturbation of the D/E linker rigidity would control the cTnI inhibitory region interaction with actin to effect muscle relaxation.
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Affiliation(s)
- Jayant James Jayasundar
- Voiland School of Chemical Engineering and Bioengineering and The Department of Integrated Physiology and Neuroscience, Washington State University, Pullman, Washington, United States of America
| | - Jun Xing
- Voiland School of Chemical Engineering and Bioengineering and The Department of Integrated Physiology and Neuroscience, Washington State University, Pullman, Washington, United States of America
| | - John M. Robinson
- Department of Chemistry and Biochemistry, South Dakota State University, Brookings, South Dakota, United States of America
| | - Herbert C. Cheung
- The Department of Biochemistry and Molecular Genetics, University of Alabama at Birmingham, Birmingham, Alabama, United States of America
| | - Wen-Ji Dong
- Voiland School of Chemical Engineering and Bioengineering and The Department of Integrated Physiology and Neuroscience, Washington State University, Pullman, Washington, United States of America
- * E-mail:
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14
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Bhaskara RM, de Brevern AG, Srinivasan N. Understanding the role of domain–domain linkers in the spatial orientation of domains in multi-domain proteins. J Biomol Struct Dyn 2013; 31:1467-80. [DOI: 10.1080/07391102.2012.743438] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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15
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NMR spectroscopy on domain dynamics in biomacromolecules. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2013; 112:58-117. [DOI: 10.1016/j.pbiomolbio.2013.05.001] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/03/2013] [Revised: 05/06/2013] [Accepted: 05/07/2013] [Indexed: 12/22/2022]
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16
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Abstract
We focus here on the modulation of thin filament activity by cardiac troponin I phosphorylation as an integral and adaptive mechanism in cardiac homeostasis and as a mechanism vulnerable to maladaptive response to stress. We discuss a current concept of cardiac troponin I function in the A-band region of the sarcomere and potential signaling to cardiac troponin I in a network involving the ends of the thin filaments at the Z-disk and the M-band regions. The cardiac sarcomere represents a remarkable set of interacting proteins that functions not only as a molecular machine generating the heartbeat but also as a hub of signaling. We review how phosphorylation signaling to cardiac troponin I is integrated, with parallel signals controlling excitation-contraction coupling, hypertrophy, and metabolism.
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Affiliation(s)
- R John Solaro
- Department of Physiology and Biophysics and Center for Cardiovascular Research, University of Illinois at Chicago, College of Medicine, Chicago, IL 60612, USA.
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17
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Cordina NM, Liew CK, Gell DA, Fajer PG, Mackay JP, Brown LJ. Interdomain orientation of cardiac troponin C characterized by paramagnetic relaxation enhancement NMR reveals a compact state. Protein Sci 2013; 21:1376-87. [PMID: 22811351 DOI: 10.1002/pro.2124] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Cardiac troponin C (cTnC) is the calcium binding subunit of the troponin complex that triggers the thin filament response to calcium influx into the sarcomere. cTnC consists of two globular EF-hand domains (termed the N- and C-domains) connected by a flexible linker. While the conformation of each domain of cTnC has been thoroughly characterized through NMR studies involving either the isolated N-domain (N-cTnC) or C-domain (C-cTnC), little attention has been paid to the range of interdomain orientations possible in full-length cTnC that arises as a consequence of the flexibility of the domain linker. Flexibility in the domain linker of cTnC is essential for effective regulatory function of troponin. We have therefore utilized paramagnetic relaxation enhancement (PRE) NMR to assess the interdomain orientation of cTnC. Ensemble fitting of our interdomain PRE measurements reveals that isolated cTnC has considerable interdomain flexibility and preferentially adopts a bent conformation in solution, with a defined range of relative domain orientations.
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Affiliation(s)
- Nicole M Cordina
- Department of Chemistry and Biomolecular Sciences, Macquarie University, Sydney, New South Wales 2109, Australia
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18
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Solaro RJ, Kobayashi T. Protein phosphorylation and signal transduction in cardiac thin filaments. J Biol Chem 2011; 286:9935-40. [PMID: 21257760 DOI: 10.1074/jbc.r110.197731] [Citation(s) in RCA: 83] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Affiliation(s)
- R John Solaro
- Department of Physiology and Biophysics and Center for Cardiovascular Research, University of Illinois at Chicago, Chicago, Illinois 60612, USA.
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19
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Li MX, Robertson IM, Sykes BD. Interaction of cardiac troponin with cardiotonic drugs: a structural perspective. Biochem Biophys Res Commun 2007; 369:88-99. [PMID: 18162171 DOI: 10.1016/j.bbrc.2007.12.108] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2007] [Accepted: 12/11/2007] [Indexed: 11/29/2022]
Abstract
Over the 40 years since its discovery, many studies have focused on understanding the role of troponin as a myofilament based molecular switch in regulating the Ca(2+)-dependent activation of striated muscle contraction. Recently, studies have explored the role of cardiac troponin as a target for cardiotonic agents. These drugs are clinically useful for treating heart failure, a condition in which the heart is no longer able to pump enough blood to other organs. These agents act via a mechanism that modulates the Ca(2+)-sensitivity of troponin; such a mode of action is therapeutically desirable because intracellular Ca(2+) concentration is not perturbed, preserving the regulation of other Ca(2+)-based signaling pathways. This review describes molecular details of the interaction of cardiac troponin with a variety of cardiotonic drugs. We present recent structural work that has identified the docking sites of several cardiotonic drugs in the troponin C-troponin I interface and discuss their relevance in the design of troponin based drugs for the treatment of heart disease.
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Affiliation(s)
- Monica X Li
- Department of Biochemistry, University of Alberta, Edmonton, Alta., Canada
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20
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Dong WJ, Xing J, Ouyang Y, An J, Cheung HC. Structural kinetics of cardiac troponin C mutants linked to familial hypertrophic and dilated cardiomyopathy in troponin complexes. J Biol Chem 2007; 283:3424-3432. [PMID: 18063575 DOI: 10.1074/jbc.m703822200] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The key events in regulating cardiac muscle contraction involve Ca(2+) binding to and release from cTnC (troponin C) and structural changes in cTnC and other thin filament proteins triggered by Ca(2+) movement. Single mutations L29Q and G159D in human cTnC have been reported to associate with familial hypertrophic and dilated cardiomyopathy, respectively. We have examined the effects of these individual mutations on structural transitions in the regulatory N-domain of cTnC triggered by Ca(2+) binding and dissociation. This study was carried out with a double mutant or triple mutants of cTnC, reconstituted into troponin with tryptophanless cTnI and cTnT. The double mutant, cTnC(L12W/N51C) labeled with 1,5-IAEDANS at Cys-51, served as a control to monitor Ca(2+)-induced opening and closing of the N-domain by Förster resonance energy transfer (FRET). The triple mutants contained both L12W and N51C labeled with 1,5-IAEDANS, and either L29Q or G159D. Both mutations had minimal effects on the equilibrium distance between Trp-12 and Cys-51-AEDANS in the absence or presence of bound Ca(2+). L29Q had no effect on the closing rate of the N-domain triggered by release of Ca(2+), but reduced the Ca(2+)-induced opening rate. G159D reduced both the closing and opening rates. Previous results showed that the closing rate of cTnC N-domain triggered by Ca(2+) dissociation was substantially enhanced by PKA phosphorylation of cTnI. This rate enhancement was abolished by L29Q or G159D. These mutations alter the kinetics of structural transitions in the regulatory N-domain of cTnC that are involved in either activation (L29Q) or deactivation (G159D). Both mutations appear to be antagonistic toward phosphorylation signaling between cTnI and cTnC.
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Affiliation(s)
- Wen-Ji Dong
- School of Chemical Engineering and Bioengineering, Washington State University, Pullman, Washington 99164; Department of Veterinary and Comparative Anatomy, Pharmacology, and Physiology, Washington State University, Pullman, Washington 99164.
| | - Jun Xing
- Department of Biochemistry and Molecular Genetics, University of Alabama at Birmingham, Alabama 35294
| | - Yexin Ouyang
- Department of Veterinary and Comparative Anatomy, Pharmacology, and Physiology, Washington State University, Pullman, Washington 99164
| | - Jianli An
- Department of Biochemistry and Molecular Genetics, University of Alabama at Birmingham, Alabama 35294
| | - Herbert C Cheung
- Department of Biochemistry and Molecular Genetics, University of Alabama at Birmingham, Alabama 35294
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21
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Sadayappan S, Finley N, Howarth JW, Osinska H, Klevitsky R, Lorenz JN, Rosevear PR, Robbins J. Role of the acidic N' region of cardiac troponin I in regulating myocardial function. FASEB J 2007; 22:1246-57. [PMID: 17984178 DOI: 10.1096/fj.07-9458com] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Cardiac troponin I (cTnI) phosphorylation modulates myocardial contractility and relaxation during beta-adrenergic stimulation. cTnI differs from the skeletal isoform in that it has a cardiac specific N' extension of 32 residues (N' extension). The role of the acidic N' region in modulating cardiac contractility has not been fully defined. To test the hypothesis that the acidic N' region of cTnI helps regulate myocardial function, we generated cardiac-specific transgenic mice in which residues 2-11 (cTnI(Delta2-11)) were deleted. The hearts displayed significantly decreased contraction and relaxation under basal and beta-adrenergic stress compared to nontransgenic hearts, with a reduction in maximal Ca(2+)-dependent force and maximal Ca(2+)-activated Mg(2+)-ATPase activity. However, Ca(2+) sensitivity of force development and cTnI-Ser(23/24) phosphorylation were not affected. Chemical shift mapping shows that both cTnI and cTnI(Delta2-11) interact with the N lobe of cardiac troponin C (cTnC) and that phosphorylation at Ser(23/24) weakens these interactions. These observations suggest that residues 2-11 of cTnI, comprising the acidic N' region, do not play a direct role in the calcium-induced transition in the cardiac regulatory or N lobe of cTnC. We hypothesized that phosphorylation at Ser(23/24) induces a large conformational change positioning the conserved acidic N region to compete with actin for the inhibitory region of cTnI. Consistent with this hypothesis, deletion of the conserved acidic N' region results in a decrease in myocardial contractility in the cTnI(Delta2-11) mice demonstrating the importance of acidic N' region in regulating myocardial contractility and mediating the response of the heart to beta-AR stimulation.
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Affiliation(s)
- Sakthivel Sadayappan
- Division of Molecular Cardiovascular Biology, Cincinnati Children's Hospital Medical Center, 3333 Burnet Ave., Cincinnati, OH 45229-3039, USA
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22
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Howarth JW, Meller J, Solaro RJ, Trewhella J, Rosevear PR. Phosphorylation-dependent conformational transition of the cardiac specific N-extension of troponin I in cardiac troponin. J Mol Biol 2007; 373:706-22. [PMID: 17854829 DOI: 10.1016/j.jmb.2007.08.035] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2007] [Revised: 08/08/2007] [Accepted: 08/14/2007] [Indexed: 10/22/2022]
Abstract
We present here the solution structure for the bisphosphorylated form of the cardiac N-extension of troponin I (cTnI(1-32)), a region for which there are no previous high-resolution data. Using this structure, the X-ray crystal structure of the cardiac troponin core, and uniform density models of the troponin components derived from neutron contrast variation data, we built atomic models for troponin that show the conformational transition in cardiac troponin induced by bisphosphorylation. In the absence of phosphorylation, our NMR data and sequence analyses indicate a less structured cardiac N-extension with a propensity for a helical region surrounding the phosphorylation motif, followed by a helical C-terminal region (residues 25-30). In this conformation, TnI(1-32) interacts with the N-lobe of cardiac troponin C (cTnC) and thus is positioned to modulate myofilament Ca2+-sensitivity. Bisphosphorylation at Ser23/24 extends the C-terminal helix (residues 21-30) which results in weakening interactions with the N-lobe of cTnC and a re-positioning of the acidic amino terminus of cTnI(1-32) for favorable interactions with basic regions, likely the inhibitory region of cTnI. An extended poly(L-proline)II helix between residues 11 and 19 serves as the rigid linker that aids in re-positioning the amino terminus of cTnI(1-32) upon bisphosphorylation at Ser23/24. We propose that it is these electrostatic interactions between the acidic amino terminus of cTnI(1-32) and the basic inhibitory region of troponin I that induces a bending of cTnI at the end that interacts with cTnC. This model provides a molecular mechanism for the observed changes in cross-bridge kinetics upon TnI phosphorylation.
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Affiliation(s)
- Jack W Howarth
- Department of Molecular Genetics, Biochemistry, and Microbiology, University of Cincinnati College of Medicine, 231 Albert Sabin Way, Cincinnati, Ohio, 45267, USA
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23
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Vinogradova MV, Stone DB, Malanina GG, Mendelson RA, Fletterick RJ. Ca ion and the troponin switch. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2007; 592:47-57. [PMID: 17278355 DOI: 10.1007/978-4-431-38453-3_6] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
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24
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Umeki N, Mitsui T, Kondo K, Maruta S. Conformational change of the loop L5 in rice kinesin motor domain induced by nucleotide binding. J Biochem 2006; 139:857-64. [PMID: 16751593 DOI: 10.1093/jb/mvj102] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022] Open
Abstract
Loop L5 of kinesin is located near the ATPase site, in common with kinesins of various animal species. The rice plant-specific kinesin K16 also has a corresponding loop that is slightly shorter than that of mouse brain kinesin. The present study was designed to monitor conformational changes in loop L5 during ATP hydrolysis. For this purpose, we introduced one reactive cysteine into the L5 of rice kinesin and modified it with fluorescent probes. The cysteine in L5 was labeled with a fluorescent probe 2-(4'(iodoacetamide) anilino-naphthalene-6-sulfonic acid sodium salt) [IAANS]. IAANS was incorporated into L5 at an almost equimolar ratio in the absence of nucleotides. In contrast, the incorporated amount was reduced to 0.62 and 0.32 mol IAANS/mol motor domain in the presence of ATP and ADP, respectively. Upon nucleotide addition, the fluorescent intensity of IAANS incorporated into L5 was significantly reduced to 63% and 51% for ATP and ADP, respectively. These results suggest that L5 of rice kinesin significantly changes its conformation during ATP hydrolysis.
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Affiliation(s)
- Nobuhisa Umeki
- Laboratories of Plant and Microbial Genome Control, Graduate School of Science and Technology, Niigata University, Niigata 950-2181
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25
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Cho M, Chung S, Heo SD, Ku J, Ban C. A simple fluorescent method for detecting mismatched DNAs using a MutS-fluorophore conjugate. Biosens Bioelectron 2006; 22:1376-81. [PMID: 16876990 DOI: 10.1016/j.bios.2006.06.010] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2006] [Revised: 03/16/2006] [Accepted: 06/14/2006] [Indexed: 11/20/2022]
Abstract
A fluorescent method was developed for the detection of unpaired and mismatched DNAs using a MutS-fluorophore conjugate. The fluorophore, 2-(4'-(iodoacetoamido)anilino) naphthalene-6-sulfonic acid (IAANS), was site-specifically attached to the 469 position of Thermus aquaticus (Taq.) MutS mutant (C42A/T469C). The fluorophore labeled residue located at the dimer interface of the protein undergoes a drastic conformational change upon binding with mismatched DNA. The close proximity of the two identical fluorescent molecules presumably causes the self-quenching of the fluorophore, since fluorescence emission of the biosensor decreases with increasing concentrations of mismatched DNA. The order of binding affinity for each unpaired and mismatched DNA obtained by this method was DeltaT (Kd=52 nM)>GT (62 nM)>DeltaC (130 nM)>CT (160 nM)>DeltaG (170 nM)>DeltaA (250 nM)>CC (720 nM)>AT (950 nM). This order is comparable to the previous results of the gel mobility shift assay. Thus, this method can be a simple, useful tool for elucidating the mechanism of DNA mismatch repair as well as a novel probe for detecting of genetic mutation.
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Affiliation(s)
- Minseon Cho
- Department of Chemistry and Division of Molecular and Life Sciences (BK21), Pohang University of Science and Technology, San 31, Hyojadong, Pohang, Gyungbuk 790-784, Republic of Korea
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26
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Hoffman RMB, Li MX, Sykes BD. The Binding of W7, an Inhibitor of Striated Muscle Contraction, to Cardiac Troponin C. Biochemistry 2005; 44:15750-9. [PMID: 16313178 DOI: 10.1021/bi051583y] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
W7 is a well-characterized calmodulin antagonist. It decreases the maximal tension and rate of ATP hydrolysis in cardiac muscle fibers. Cardiac troponin C (cTnC) has been previously implicated as the mechanistically significant target for W7 in the myofilament. Two-dimensional NMR spectra ({1H,15N}- and {1H,13C}-HSQCs) were used to monitor the Ca2+-dependent binding of W7 to cTnC. Titration of cTnC x 3Ca2+ with W7 indicated binding to both domains of the protein. We examined the binding of W7 to the separated domains of cTnC to simplify the spectral analysis. In the titration of the C-terminal domain (cCTnC x 2Ca2+), the spectral peaks originating from a subset of residues changed nonuniformly, and could not be well-described as single-site binding. A global fit of the cCTnC x 2Ca2+ titration data to a two-site, sequential binding model (47 residues simultaneously fit) yielded a dissociation constant (Kd1) of 0.85-0.91 mM for the singly bound state, with the second dissociation constant fit to 3.40-3.65 mM (> or = 4 x Kd1). The titration data for the N-terminal domain (cNTnC x Ca2+) was globally fit to single-site binding model with a Kd of 0.15-0.30 mM (41 residues fit). The data are consistent with W7 binding to each domain's major hydrophobic pocket, coordinating side chains responsible for liganding cTnI. When in muscle fibers, W7 may compete with cTnI for target sites on cTnC.
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Affiliation(s)
- Ryan M B Hoffman
- CIHR Group in Protein Structure and Function, Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2H7
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27
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Eichmüller C, Skrynnikov NR. A new amide proton R1rho experiment permits accurate characterization of microsecond time-scale conformational exchange. JOURNAL OF BIOMOLECULAR NMR 2005; 32:281-93. [PMID: 16211482 DOI: 10.1007/s10858-005-0658-y] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/04/2005] [Accepted: 06/19/2005] [Indexed: 05/04/2023]
Abstract
A new off-resonance spin-lock experiment to record relaxation dispersion profiles of amide protons is presented. The sensitivity-enhanced HSQC-type sequence is designed to minimize the interference from cross-relaxation effects and ensure that the dispersion profiles in the absence of micros-ms time-scale dynamics are flat. Toward this end (i) the proton background is eliminated by sample deuteration (Ishima et al., 1998), (ii) 1H spin lock is applied to two-spin modes 2(H(x)Sin theta + H(z)Cos theta) N(z), and (iii) the tilt angle theta approximately 35 degrees is maintained throughout the series of measurements (Desvaux et al. Mol. Phys., 86 (1995) 1059). The relaxation dispersion profiles recorded in this manner sample a wide range of effective rf field strengths (up to and in excess of 20 kHz) which makes them particularly suitable for studies of motions on the time scale < or = 100 micros. The new experiment has been tested on the Ca2+-loaded regulatory domain of cardiac troponin C. Many residues show pronounced dispersions with remarkably similar correlation times of approximately 30 micros. Furthermore, these residues are localized in the regions that have been previously implicated in conformational changes (Spyracopoulos et al. Biochemistry, 36 (1997) 12138).
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Affiliation(s)
- Christian Eichmüller
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, IN 47907-2084, USA
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28
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Vinogradova MV, Stone DB, Malanina GG, Karatzaferi C, Cooke R, Mendelson RA, Fletterick RJ. Ca(2+)-regulated structural changes in troponin. Proc Natl Acad Sci U S A 2005; 102:5038-43. [PMID: 15784741 PMCID: PMC555973 DOI: 10.1073/pnas.0408882102] [Citation(s) in RCA: 249] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2004] [Indexed: 11/18/2022] Open
Abstract
Troponin senses Ca2+ to regulate contraction in striated muscle. Structures of skeletal muscle troponin composed of TnC (the sensor), TnI (the regulator), and TnT (the link to the muscle thin filament) have been determined. The structure of troponin in the Ca(2+)-activated state features a nearly twofold symmetrical assembly of TnI and TnT subunits penetrated asymmetrically by the dumbbell-shaped TnC subunit. Ca ions are thought to regulate contraction by controlling the presentation to and withdrawal of the TnI inhibitory segment from the thin filament. Here, we show that the rigid central helix of the sensor binds the inhibitory segment of TnI in the Ca(2+)-activated state. Comparison of crystal structures of troponin in the Ca(2+)-activated state at 3.0 angstroms resolution and in the Ca(2+)-free state at 7.0 angstroms resolution shows that the long framework helices of TnI and TnT, presumed to be a Ca(2+)-independent structural domain of troponin are unchanged. Loss of Ca ions causes the rigid central helix of the sensor to collapse and to release the inhibitory segment of TnI. The inhibitory segment of TnI changes conformation from an extended loop in the presence of Ca2+ to a short alpha-helix in its absence. We also show that Anapoe, a detergent molecule, increases the contractile force of muscle fibers and binds specifically, together with the TnI switch helix, in a hydrophobic pocket of TnC upon activation by Ca ions.
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Affiliation(s)
- Maia V Vinogradova
- Department of Biochemistry and Biophysics, University of California, San Francisco, CA 94143-2240, USA
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29
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Sakthivel S, Finley NL, Rosevear PR, Lorenz JN, Gulick J, Kim S, VanBuren P, Martin LA, Robbins J. In Vivo and in Vitro Analysis of Cardiac Troponin I Phosphorylation. J Biol Chem 2005; 280:703-14. [PMID: 15507454 DOI: 10.1074/jbc.m409513200] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Adrenergic stimulation induces positive changes in cardiac contractility and relaxation. Cardiac troponin I is phosphorylated at different sites by protein kinase A and protein kinase C, but the effects of these post-translational modifications on the rate and extent of contractility and relaxation during beta-adrenergic stimulation in the intact animal remain obscure. To investigate the effect(s) of complete and chronic cTnI phosphorylation on cardiac function, we generated transgenic animals in which the five possible phosphorylation sites were replaced with aspartic acid, mimicking a constant state of complete phosphorylation (cTnI-AllP). We hypothesized that chronic and complete phosphorylation of cTnI might result in increased morbidity or mortality, but complete replacement with the transgenic protein was benign with no detectable pathology. To differentiate the effects of the different phosphorylation sites, we generated another mouse model, cTnI-PP, in which only the protein kinase A phosphorylation sites (Ser(23)/Ser(24)) were mutated to aspartic acid. In contrast to the cTnIAllP, the cTnI-PP mice showed enhanced diastolic function under basal conditions. The cTnI-PP animals also showed augmented relaxation and contraction at higher heart rates compared with the nontransgenic controls. Nuclear magnetic resonance amide proton/nitrogen chemical shift analysis of cardiac troponin C showed that, in the presence of cTnI-AllP and cTnI-PP, the N terminus exhibits a more closed conformation, respectively. The data show that protein kinase C phosphorylation of cTnI plays a dominant role in depressing contractility and exerts an antithetic role on the ability of protein kinase A to increase relaxation.
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Affiliation(s)
- Sadayappan Sakthivel
- Division of Molecular Cardiovascular Biology, Department of Pediatrics, The Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio 45229, USA
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30
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Finley NL, Rosevear PR. Introduction of negative charge mimicking protein kinase C phosphorylation of cardiac troponin I. Effects on cardiac troponin C. J Biol Chem 2004; 279:54833-40. [PMID: 15485824 DOI: 10.1074/jbc.m408304200] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Protein kinase C phosphorylation of cardiac troponin, the Ca(2+)-sensing switch in muscle contraction, is capable of modulating the response of cardiac muscle to a Ca(2+) ion concentration. The N-domain of cardiac troponin I contains two protein kinase C phosphorylation sites. Although the physiological consequences of phosphorylation at Ser(43)/Ser(45) are known, the molecular mechanisms responsible for these functional changes have yet to be established. In this work, NMR was used to identify conformational and dynamic changes in cardiac troponin C upon binding a phosphomimetic troponin I, having Ser(43)/Ser(45) mutated to Asp. Chemical shift perturbation mapping indicated that residues in helix G were most affected. Smaller chemical shift changes were observed in residues located in the Ca(2+)/Mg(2+)-binding loops. Amide hydrogen/deuterium exchange rates in the C-lobe of troponin C were compared in complexes containing either the wild-type or phosphomimetic N-domain of troponin I. In the presence of a phosphomimetic domain, exchange rates in helix G increased, whereas a decrease in exchange rates for residues mapping to Ca(2+)/Mg(2+)-binding loops III and IV was observed. Increased exchange rates are consistent with destabilization of the Thr(129)-Asp(132) helix capping box previously characterized in helix G. The perturbation of helix G and metal binding loops III and IV suggests that phosphorylation alters metal ion affinity and inter-subunit interactions. Our studies support a novel mechanism for protein kinase C signal transduction, emphasizing the importance of C-lobe Ca(2+)/Mg(2+)-dependent troponin interactions.
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Affiliation(s)
- Natosha L Finley
- Department of Molecular Genetics, University of Cincinnati, College of Medicine, Cincinnati, Ohio 45267-0524, USA
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31
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Tong CW, Gaffin RD, Zawieja DC, Muthuchamy M. Roles of phosphorylation of myosin binding protein-C and troponin I in mouse cardiac muscle twitch dynamics. J Physiol 2004; 558:927-41. [PMID: 15194741 PMCID: PMC1665013 DOI: 10.1113/jphysiol.2004.062539] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
A normal heart increases its contractile force with increasing heart rate. Although calcium handling and myofibrillar proteins have been implicated in maintaining this positive force-frequency relationship (FFR), the exact mechanisms by which it occurs have not been addressed. In this study, we have developed an analytical method to define the calcium-force loop data, which characterizes the function of the contractile proteins in response to calcium that is independent of the calcium handling proteins. Results demonstrate that increasing the stimulation frequency causes increased force production per unit calcium concentration and decreased frequency-dependent calcium sensitivity during the relaxation phase. We hypothesize that phosphorylation of myosin binding protein-C (MyBP-C) and troponin I (TnI) acts coordinately to change the rates of force generation and relaxation, respectively. To test this hypothesis, we performed simultaneous calcium and force measurements on stimulated intact mouse papillary bundles before and after inhibition of MyBP-C and TnI phosphorylation using the calcium/calmodulin kinase II (CaMK2) inhibitor autocamtide-2 related inhibitory peptide, or the protein kinase A (PKA) inhibitor 14-22 amide. CaMK2 inhibition reduced both MyBP-C and TnI phosphorylation and decreased active force without changing the magnitude of the [Ca(2+)](i) transient. This reduced the normalized change in force per change in calcium by 19-39%. Data analyses demonstrated that CaMK2 inhibition changed the myofilament characteristics via a crossbridge feedback mechanism. These results strongly suggest that the phosphorylation of MyBP-C and TnI contributes significantly to the rates of force development and relaxation.
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Affiliation(s)
- Carl W Tong
- 336 Reynolds Medical Building, Cardiovascular Research Institute and Department of Medical Physiology, College of Medicine, Texas A & M University System Health Science Center, College Station, TX 77843-1114, USA
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32
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Sorsa T, Pollesello P, Rosevear PR, Drakenberg T, Kilpeläinen I. Stereoselective binding of levosimendan to cardiac troponin C causes Ca2+-sensitization. Eur J Pharmacol 2004; 486:1-8. [PMID: 14751401 DOI: 10.1016/j.ejphar.2003.12.006] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The effects of the Ca(2+) sensitizer levosimendan and that of its stereoisomer dextrosimendan on the cardiac contractile apparatus were studied using skinned fibers obtained from guinea pig hearts. Levosimendan was found to be more effective than dextrosimendan in this model. The respective concentrations of levosimendan and dextrosimendan at EC(50) were 0.3 and 3 microM. In order to explain the difference in efficacy as Ca(2+) sensitizers, the binding of the two stereoisomers on cardiac troponin C was studied by nuclear magnetic resonance in the absence and presence of two peptides of cardiac troponin I. The two stereoisomers interacted with both domains of cardiac troponin C in the absence of cardiac troponin I. In the presence of cardiac troponin I-(32-79) and cardiac troponin I-(128-180), the binding of both levosimendan and dextrosimendan to the C-terminal domain of cardiac troponin C was blocked and only the binding to the N-terminal domain was observable. Differences in the overall binding behavior of the two isomers to cardiac troponin C were highlighted in order to discuss their structure to activity relation. Our data are consistent with the notion that the action of levosimendan as a Ca(2+) sensitizer and positive inotrope relates to its stereoselective binding to Ca(2+)-saturated cardiac troponin C.
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Affiliation(s)
- Tia Sorsa
- Discovery Biology, Orion Pharma, P.O. Box 65, FIN-02101 Espoo, Finland.
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33
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Heller WT, Finley NL, Dong WJ, Timmins P, Cheung HC, Rosevear PR, Trewhella J. Small-angle neutron scattering with contrast variation reveals spatial relationships between the three subunits in the ternary cardiac troponin complex and the effects of troponin I phosphorylation. Biochemistry 2003; 42:7790-800. [PMID: 12820888 DOI: 10.1021/bi0341509] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Small-angle neutron scattering with contrast variation has been used to determine the shapes and dispositions of the three subunits of cardiac troponin and to study the influence of phosphorylation on the structure. Three contrast variation series were collected on three different isotopically labeled variants of the cTnC/cTnI/cTnT(198-298) complex, one of which contained deuterated and bisphosphorylated cTnI. Analysis of the scattering data shows cTnT(198-298) interacting with a single lobe of a somewhat compacted cTnC that sits at one end of an elongated rodlike cTnI, covering about one-third of its length. The cTnT(198-298) sits near the center of the long cTnI axis. The components undergo significant conformational changes and reorientations in response to protein kinase A phosphorylation of cTnI. The rodlike cTnI bends sharply at the end interacting with the cTnC/cTnT(198-298) component, which reorients so as to maintain its contacts with cTnI while undergoing only a relatively small change in shape.
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Affiliation(s)
- William T Heller
- Bioscience Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
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34
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Heller WT, Abusamhadneh E, Finley N, Rosevear PR, Trewhella J. The solution structure of a cardiac troponin C-troponin I-troponin T complex shows a somewhat compact troponin C interacting with an extended troponin I-troponin T component. Biochemistry 2002; 41:15654-63. [PMID: 12501194 DOI: 10.1021/bi026687c] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We have investigated the structure of the cTnC-cTnI-cTnT(198-298) calcium-saturated, ternary cardiac troponin complex by small-angle scattering with contrast variation. Shape restoration was also applied to the scattering information resulting from the deuterated cTnC subunit, the unlabeled cTnI-cTnT(198-298) subunits, and the entire complex. The experimental results and modeling indicate that cTnC adopts a partially collapsed conformation, while the cTnI-cTnT(198-298) components have an extended, rod-like structure. Shape restoration applied to the X-ray scattering data and the entire contrast variation series suggest that cTnC and the cTnI-cTnT(198-298) component lie with their long axes roughly parallel to one another with a relatively small surface area for interaction. Our findings indicate that the nature of the interactions between TnC and the TnI-TnT component differs significantly between the cardiac and skeletal isoforms as evidenced by the different degrees of compactness between the cardiac TnC and skeletal TnC in their respective ternary complexes and the fact that the cTnC subunit is not highly intertwined with the other subunits, as observed in the binary complex of the skeletal isoforms [Olah, G. A., and Trewhella, J. (1994) Biochemistry 33, 12800-12806].
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Affiliation(s)
- William T Heller
- Bioscience Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA
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35
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36
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Dvoretsky A, Abusamhadneh EM, Howarth JW, Rosevear PR. Solution structure of calcium-saturated cardiac troponin C bound to cardiac troponin I. J Biol Chem 2002; 277:38565-70. [PMID: 12147696 DOI: 10.1074/jbc.m205306200] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Cardiac troponin C (TnC) is composed of two globular domains connected by a flexible linker. In solution, linker flexibility results in an ill defined orientation of the two globular domains relative to one another. We have previously shown a decrease in linker flexibility in response to cardiac troponin I (cTnI) binding. To investigate the relative orientation of calcium-saturated TnC domains when bound to cTnI, (1)H-(15)N residual dipolar couplings were measured in two different alignment media. Similarity in alignment tensor orientation for the two TnC domains supports restriction of domain motion in the presence of cTnI. The relative spatial orientation of TnC domains bound to TnI was calculated from measured residual dipolar couplings and long-range distance restraints utilizing a rigid body molecular dynamics protocol. The relative domain orientation is such that hydrophobic pockets face each other, forming a latch to constrain separate helical segments of TnI. We have utilized this structure to successfully explain the observed functional consequences of linker region deletion mutants. Together, these studies suggest that, although linker plasticity is important, the ability of TnC to function in muscle contraction can be correlated with a preferred domain orientation and interdomain distance.
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Affiliation(s)
- Alex Dvoretsky
- Department of Molecular Genetics, Biochemistry, and Microbiology, University of Cincinnati, College of Medicine, Cincinnati, Ohio 45267, USA
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37
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Lindhout DA, Li MX, Schieve D, Sykes BD. Effects of T142 phosphorylation and mutation R145G on the interaction of the inhibitory region of human cardiac troponin I with the C-domain of human cardiac troponin C. Biochemistry 2002; 41:7267-74. [PMID: 12044157 DOI: 10.1021/bi020100c] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Cardiac troponin I (cTnI) is the inhibitory component of the troponin complex, and its interaction with cardiac troponin C (cTnC) plays a critical role in transmitting the Ca(2+) signal to the other myofilament proteins in heart muscle contraction. The switch between contraction and relaxation involves a movement of the inhibitory region of cTnI (cIp) from cTnC to actin-tropomyosin. This region of cTnI is prone to missense mutations in heart disease, and a specific mutation, R145G, has been associated with familial hypertrophic cardiomyopathy. It also contains the unique cardiac PKC phosphorylation site at residue T142. To determine the structural consequences of the mutation R145G and the T142 phosphorylation on the interaction of cIp with cTnC, we have utilized 2D [(1)H, (15)N]-HSQC NMR spectroscopy to monitor the binding of native cIp, cIp-R (R145G), and cIp-P (phosphorylated T142), respectively, to the Ca(2+)-saturated C-domain of cTnC (cCTnC.2Ca(2+)). We also report a strategy for cloning, expression, and purification of cTnI peptide, and both synthetic and recombinant peptides are used in this study. NMR chemical shift mapping indicates that the binding epitope of cIp on cCTnC.2Ca(2+) is not greatly affected, but the affinity is reduced by approximately 14-fold by the T142 phosphorylation and approximately 4-fold by the mutation R145G, respectively. This suggests that these modifications of cIp have an adverse effect on the binding of cIp to cCTnC.2Ca(2+). These perturbations may correlate with the impairment or loss of cTnI function in heart muscle contraction.
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Affiliation(s)
- Darrin A Lindhout
- CIHR Group in Protein Structure and Function, Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2H7
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38
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Abstract
Ca(2+)-sensitizers are inotropic agents that modify the response of myofilaments to Ca2+, and are potentially valuable drugs in the treatment of heart failure. These agents have diverse chemical structures, and in some cases also have effects as inhibitors of phosphodiesterase activity. Advantages of their actions include vasodilation combined with inotropic effects. Reduction in the amounts of Ca2+ required to activate the myofilaments also lowers the oxygen consumption required for Ca2+ transport, lowers the threat of arrhythmias, and may blunt Ca(2+)-dependent transcriptional and translational mechanisms leading to hypertrophy and failure. Although diastolic abnormalities and impaired relaxation were thought to be potential undesirable effects of Ca(2+)-sensitizers, studies of hearts beating in situ indicate that this may not be a major problem. We focus here on Ca(2+)-sensitizers that act on cardiac troponin C, the Ca2+ receptor that triggers activation of the actin-myosin interaction. Structural studies have identified a unique mode of Ca2+ signaling in cardiac troponin C that should aid in targeting drugs to the heart. Moreover, identification of docking sites of Ca(2+)-sensitizers on troponin C suggest new directions for rational drug design.
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Affiliation(s)
- Grace M Arteaga
- Department of Physiology and Biophysics, College of Medicine, University of Illinois at Chicago, 60612-7342, USA
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39
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Abusamhadneh E, Abbott MB, Dvoretsky A, Finley N, Sasi S, Rosevear PR. Interaction of bepridil with the cardiac troponin C/troponin I complex. FEBS Lett 2001; 506:51-4. [PMID: 11591369 DOI: 10.1016/s0014-5793(01)02790-9] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
We have investigated the binding of bepridil to calcium-saturated cardiac troponin C in a cardiac troponin C/troponin I complex. Nuclear magnetic resonance spectroscopy and [(15)N,(2)H]cardiac troponin C permitted the mapping of bepridil-induced amide proton chemical shifts. A single bepridil-binding site in the regulatory domain was found with an affinity constant of approximately 140 microM(-1). In the presence of cardiac troponin I, bepridil binding to the C domain of cardiac troponin C was not detected. The pattern of bepridil-induced chemical shifts is consistent with stabilization of more open regulatory domain conformational states. A similar pattern of chemical shift perturbations was observed for interaction of the troponin I cardiac-specific amino-terminus with the cardiac troponin C regulatory domain. These results suggest that both bepridil and the cardiac-specific amino-terminus may mediate an increase in calcium affinity by interacting with and stabilizing open regulatory domain conformations. Chemical shift mapping suggests a possible role for inactive calcium-binding site I in the modulation of calcium affinity.
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Affiliation(s)
- E Abusamhadneh
- Department of Molecular Genetics, Biochemistry, and Microbiology, University of Cincinnati, College of Medicine, 231 Albert B. Sabin Way, Cincinnati, OH 45267, USA
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40
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Abbott MB, Dong WJ, Dvoretsky A, DaGue B, Caprioli RM, Cheung HC, Rosevear PR. Modulation of cardiac troponin C-cardiac troponin I regulatory interactions by the amino-terminus of cardiac troponin I. Biochemistry 2001; 40:5992-6001. [PMID: 11352734 DOI: 10.1021/bi0100642] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Multidimensional heteronuclear magnetic resonance studies of the cardiac troponin C/troponin I(1-80)/troponin I(129-166) complex demonstrated that cardiac troponin I(129-166), corresponding to the adjacent inhibitory and regulatory regions, interacts with and induces an opening of the cardiac troponin C regulatory domain. Chemical shift perturbation mapping and (15)N transverse relaxation rates for intact cardiac troponin C bound to either cardiac troponin I(1-80)/troponin I(129-166) or troponin I(1-167) suggested that troponin I residues 81-128 do not interact strongly with troponin C but likely serve to modulate the interaction of troponin I(129-166) with the cardiac troponin C regulatory domain. Chemical shift perturbations due to troponin I(129-166) binding the cardiac troponin C/troponin I(1-80) complex correlate with partial opening of the cardiac troponin C regulatory domain previously demonstrated by distance measurements using fluorescence methodologies. Fluorescence emission from cardiac troponin C(F20W/N51C)(AEDANS) complexed to cardiac troponin I(1-80) was used to monitor binding of cardiac troponin I(129-166) to the regulatory domain of cardiac troponin C. The apparent K(d) for cardiac troponin I(129-166) binding to cardiac troponin C/troponin I(1-80) was 43.3 +/- 3.2 microM. After bisphosphorylation of cardiac troponin I(1-80) the apparent K(d) increased to 59.1 +/- 1.3 microM. Thus, phosphorylation of the cardiac-specific N-terminus of troponin I reduces the apparent binding affinity of the regulatory domain of cardiac troponin C for cardiac troponin I(129-166) and provides further evidence for beta-adrenergic modulation of troponin Ca(2+) sensitivity through a direct interaction between the cardiac-specific amino-terminus of troponin I and the cardiac troponin C regulatory domain.
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Affiliation(s)
- M B Abbott
- Department of Molecular Genetics, Biochemistry, and Microbiology, College of Medicine, University of Cincinnati, Cincinnati, Ohio 45267, USA
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41
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Ngai SM, Pearlstone JR, Farah CS, Reinach FC, Smillie LB, Hodges RS. Structural and functional studies on Troponin I and Troponin C interactions. J Cell Biochem 2001; 83:33-46. [PMID: 11500952 DOI: 10.1002/jcb.1204] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Troponin I (TnI) peptides (TnI inhibitory peptide residues 104-115, Ip; TnI regulatory peptide resides 1-30, TnI1-30), recombinant Troponin C (TnC) and Troponin I mutants were used to study the structural and functional relationship between TnI and TnC. Our results reveal that an intact central D/E helix in TnC is required to maintain the ability of TnC to release the TnI inhibition of the acto-S1-TM ATPase activity. Ca(2+)-titration of the TnC-TnI1-30 complex was monitored by circular dichroism. The results show that binding of TnI1-30 to TnC caused a three-folded increase in Ca(2+) affinity in the high affinity sites (III and IV) of TnC. Gel electrophoresis and high performance liquid chromatography (HPLC) studies demonstrate that the sequences of the N- and C-terminal regions of TnI interact in an anti-parallel fashion with the corresponding N- and C-domain of TnC. Our results also indicate that the N- and C-terminal domains of TnI which flank the TnI inhibitory region (residues 104 to 115) play a vital role in modulating the Ca(2+)- sensitive release of the TnI inhibitory region by TnC within the muscle filament. A modified schematic diagram of the TnC/TnI interaction is proposed.
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Affiliation(s)
- S M Ngai
- Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada.
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