1
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Ronca F, Raggi A. Role of the interaction between troponin T and AMP deaminase by zinc bridge in modulating muscle contraction and ammonia production. Mol Cell Biochem 2024; 479:793-809. [PMID: 37184757 PMCID: PMC11016001 DOI: 10.1007/s11010-023-04763-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2023] [Accepted: 05/06/2023] [Indexed: 05/16/2023]
Abstract
The N-terminal region of troponin T (TnT) does not bind any protein of the contractile machinery and the role of its hypervariability remains uncertain. In this review we report the evidence of the interaction between TnT and AMP deaminase (AMPD), a regulated zinc enzyme localized on the myofibril. In periods of intense muscular activity, a decrease in the ATP/ADP ratio, together with a decrease in the tissue pH, is the stimulus for the activation of the enzyme that deaminating AMP to IMP and NH3 displaces the myokinase reaction towards the formation of ATP. In skeletal muscle subjected to strong tetanic contractions, a calpain-like proteolytic activity produces the removal in vivo of a 97-residue N-terminal fragment from the enzyme that becomes desensitized towards the inhibition by ATP, leading to an unrestrained production of NH3. When a 95-residue N-terminal fragment is removed from AMPD by trypsin, simulating in vitro the calpain action, rabbit fast TnT or its phosphorylated 50-residue N-terminal peptide binds AMPD restoring the inhibition by ATP. Taking in consideration that the N-terminus of TnT expressed in human as well as rabbit white muscle contains a zinc-binding motif, we suggest that TnT might mimic the regulatory action of the inhibitory N-terminal domain of AMPD due to the presence of a zinc ion connecting the N-terminal and C-terminal regions of the enzyme, indicating that the two proteins might physiologically associate to modulate muscle contraction and ammonia production in fast-twitching muscle under strenuous conditions.
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Affiliation(s)
- Francesca Ronca
- Laboratory of Biochemistry, Department of Pathology, University of Pisa, Via Roma 55, 56126, Pisa, Italy.
| | - Antonio Raggi
- Laboratory of Biochemistry, Department of Pathology, University of Pisa, Via Roma 55, 56126, Pisa, Italy
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2
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Zhu L, Landim-Vieira M, Garcia MR, Pinto JR, Chalovich JM. Negative Charges Introduced Near the IT Helix of Cardiac Troponin T Stabilize the Active State of Actin Filaments. Biochemistry 2023; 62:2137-2146. [PMID: 37379571 PMCID: PMC10576618 DOI: 10.1021/acs.biochem.3c00279] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/30/2023]
Abstract
The disordered and basic C-terminal 14 residues of human troponin T (TnT) are essential for full inhibition of actomyosin ATPase activity at low Ca2+ levels and for limiting activation at saturating Ca2+. In previous studies, stepwise truncation of the C-terminal region of TnT increased activity in proportion to the number of positive charges eliminated. To define key basic residues more closely, we generated phosphomimetic-like mutants of TnT. Phosphomimetic mutants were chosen because of reports that phosphorylation of TnT, including sites within the C terminal region, depressed activity, contrary to our expectations. Four constructs were made where one or more Ser and Thr residues were replaced with Asp residues. The S275D and T277D mutants, near the IT helix and adjacent to basic residues, produced the greatest activation of ATPase rates in solution; the effects of the S275D mutant were recapitulated in muscle fiber preparations with enhanced myofilament Ca2+ sensitivity. Actin filaments containing S275D TnT were also shown to be incapable of populating the inactive state at low Ca2+ levels. Actin filaments containing both S275D/T284D were not statistically different from those containing only S275D in both solution and cardiac muscle preparation studies. Finally, actin filaments containing T284D TnT, closer to the C-terminus and not adjacent to a basic residue, had the smallest effect on activity. Thus, the effects of negative charge placement in the C-terminal region of TnT were greatest near the IT helix and adjacent to a basic residue.
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Affiliation(s)
- Li Zhu
- Department of Biochemistry & Molecular Biology, Brody School of Medicine at East Carolina University, Greenville, North Carolina 27858, United States
| | - Maicon Landim-Vieira
- Department of Biomedical Sciences, Florida State University College of Medicine, Tallahassee, Florida 32304, United States
| | - Michelle Rodriguez Garcia
- Department of Biomedical Sciences, Florida State University College of Medicine, Tallahassee, Florida 32304, United States
| | - Jose R Pinto
- Department of Biomedical Sciences, Florida State University College of Medicine, Tallahassee, Florida 32304, United States
| | - Joseph M Chalovich
- Department of Biochemistry & Molecular Biology, Brody School of Medicine at East Carolina University, Greenville, North Carolina 27858, United States
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3
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Landim-Vieira M, Ma W, Song T, Rastegarpouyani H, Gong H, Coscarella IL, Bogaards SJP, Conijn SP, Ottenheijm CAC, Hwang HS, Papadaki M, Knollmann BC, Sadayappan S, Irving TC, Galkin VE, Chase PB, Pinto JR. Cardiac troponin T N-domain variant destabilizes the actin interface resulting in disturbed myofilament function. Proc Natl Acad Sci U S A 2023; 120:e2221244120. [PMID: 37252999 PMCID: PMC10265946 DOI: 10.1073/pnas.2221244120] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2022] [Accepted: 05/04/2023] [Indexed: 06/01/2023] Open
Abstract
Missense variant Ile79Asn in human cardiac troponin T (cTnT-I79N) has been associated with hypertrophic cardiomyopathy and sudden cardiac arrest in juveniles. cTnT-I79N is located in the cTnT N-terminal (TnT1) loop region and is known for its pathological and prognostic relevance. A recent structural study revealed that I79 is part of a hydrophobic interface between the TnT1 loop and actin, which stabilizes the relaxed (OFF) state of the cardiac thin filament. Given the importance of understanding the role of TnT1 loop region in Ca2+ regulation of the cardiac thin filament along with the underlying mechanisms of cTnT-I79N-linked pathogenesis, we investigated the effects of cTnT-I79N on cardiac myofilament function. Transgenic I79N (Tg-I79N) muscle bundles displayed increased myofilament Ca2+ sensitivity, smaller myofilament lattice spacing, and slower crossbridge kinetics. These findings can be attributed to destabilization of the cardiac thin filament's relaxed state resulting in an increased number of crossbridges during Ca2+ activation. Additionally, in the low Ca2+-relaxed state (pCa8), we showed that more myosin heads are in the disordered-relaxed state (DRX) that are more likely to interact with actin in cTnT-I79N muscle bundles. Dysregulation of the myosin super-relaxed state (SRX) and the SRX/DRX equilibrium in cTnT-I79N muscle bundles likely result in increased mobility of myosin heads at pCa8, enhanced actomyosin interactions as evidenced by increased active force at low Ca2+, and increased sinusoidal stiffness. These findings point to a mechanism whereby cTnT-I79N weakens the interaction of the TnT1 loop with the actin filament, which in turn destabilizes the relaxed state of the cardiac thin filament.
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Affiliation(s)
- Maicon Landim-Vieira
- Department of Biomedical Sciences, Florida State University College of Medicine, Tallahassee, FL32306
| | - Weikang Ma
- Department of Biology, Illinois Institute of Technology, Chicago, IL60616
| | - Taejeong Song
- Division of Cardiovascular Health and Disease, Department of Internal Medicine, University of Cincinnati College of Medicine, Cincinnati, OH45267
| | - Hosna Rastegarpouyani
- Department of Biological Science, Florida State University, Tallahassee, FL32306
- Institude of Molecular Biophysics, Florida State University, Tallahassee, FL32306
| | - Henry Gong
- Department of Biology, Illinois Institute of Technology, Chicago, IL60616
| | - Isabella Leite Coscarella
- Department of Biomedical Sciences, Florida State University College of Medicine, Tallahassee, FL32306
| | - Sylvia J. P. Bogaards
- Department of Physiology, Amsterdam University Medical Center, Amsterdam, De Boelelaan 1108, 1081 HZ Amsterdam, The Netherlands
| | - Stefan P. Conijn
- Department of Physiology, Amsterdam University Medical Center, Amsterdam, De Boelelaan 1108, 1081 HZ Amsterdam, The Netherlands
| | - Coen A. C. Ottenheijm
- Department of Physiology, Amsterdam University Medical Center, Amsterdam, De Boelelaan 1108, 1081 HZ Amsterdam, The Netherlands
| | - Hyun S. Hwang
- Department of Nutrition and Integrative Physiology, Florida State University, Tallahassee, FL32306
| | - Maria Papadaki
- Department of Cell and Molecular Physiology, Loyola University Chicago Stritch School of Medicine, Chicago, IL60153
| | - Bjorn C. Knollmann
- Department of Medicine, Vanderbilt University Medical Center, Nashville, TN37232
| | - Sakthivel Sadayappan
- Division of Cardiovascular Health and Disease, Department of Internal Medicine, University of Cincinnati College of Medicine, Cincinnati, OH45267
| | - Thomas C. Irving
- Department of Biology, Illinois Institute of Technology, Chicago, IL60616
| | - Vitold E. Galkin
- Department of Physiological Sciences, Eastern Virginia Medical School, Norfolk, VA23507
| | - P. Bryant Chase
- Department of Biological Science, Florida State University, Tallahassee, FL32306
| | - Jose Renato Pinto
- Department of Biomedical Sciences, Florida State University College of Medicine, Tallahassee, FL32306
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4
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Abstract
The movement of tropomyosin over filamentous actin regulates the cross-bridge cycle of the thick with thin filament of cardiac muscle by blocking and revealing myosin binding sites. Tropomyosin exists in three, distinct equilibrium states with one state blocking myosin-actin interactions (blocked position) and the remaining two allowing for weak (closed position) and strong myosin binding (open position). However, experimental information illuminating how myosin binds to the thin filament and influences tropomyosin's transition across the actin surface is lacking. Using metadynamics, we mimic the effect of a single myosin head binding by determining the work required to pull small segments of tropomyosin toward the open position in several distinct regions of the thin filament. We find differences in required work due to the influence of cardiac troponin T lead to preferential binding sites and determine the mechanism of further myosin head recruitment.
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Affiliation(s)
- Anthony P Baldo
- Department of Chemistry and Biochemistry, The University of Arizona, Tucson, Arizona 85721, United States
| | - Jil C Tardiff
- Department of Biomedical Engineering, The University of Arizona, Tucson, Arizona 85724, United States
| | - Steven D Schwartz
- Department of Chemistry and Biochemistry, The University of Arizona, Tucson, Arizona 85721, United States
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Kwon CW, Chang PS. Role of Endogenous Cathepsin L in Muscle Protein Degradation in Olive Flounder ( Paralichthys olivaceus) Surimi Gel. Molecules 2021; 26:molecules26071901. [PMID: 33800606 PMCID: PMC8037396 DOI: 10.3390/molecules26071901] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2021] [Revised: 03/11/2021] [Accepted: 03/22/2021] [Indexed: 11/16/2022] Open
Abstract
We investigated the effect of endogenous cathepsin L on surimi gel produced from olive flounder (Paralichthys olivaceus). The amino acid sequences of six proteins predicted or identified as cathepsin L were obtained from the olive flounder genome database, and a phylogenetic analysis was conducted. Next, cathepsin L activity toward N-α-benzyloxycarbonyl-l-phenylalanyl-l-arginine-(7-amino-4-methylcoumarin) (Z-F-R-AMC) was detected in crude olive flounder extract and a crude enzyme preparation. A considerable decrease in the level of myosin heavy chain (MHC) in surimi occurred during autolysis at 60 °C. In contrast, the levels of actin, troponin-T, and tropomyosin decreased only slightly. To prevent protein degradation by cathepsin L, a protease inhibitor was added to surimi. In the presence of 1.0% protease inhibitor, the autolysis of olive flounder surimi at 60 °C was inhibited by 12.2%; the degree of inhibition increased to 44.2% as the inhibitor concentration increased to 3.0%. In addition, the deformation and hardness of modori gel increased as the inhibitor concentration increased to 2.0%. Therefore, cathepsin L plays an important role in protein degradation in surimi, and the quality of surimi gel could be enhanced by inhibiting its activity.
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Affiliation(s)
- Chang Woo Kwon
- Research Institute of Agriculture and Life Sciences, Seoul National University, Seoul 08826, Korea;
| | - Pahn-Shick Chang
- Research Institute of Agriculture and Life Sciences, Seoul National University, Seoul 08826, Korea;
- Department of Agricultural Biotechnology, Seoul National University, Seoul 08826, Korea
- Center for Food and Bioconvergence, Seoul National University, Seoul 08826, Korea
- Center for Agricultural Microorganism and Enzyme, Seoul National University, Seoul 08826, Korea
- Correspondence: ; Tel.: +82-2-880-4852
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Madan A, Viswanathan MC, Woulfe KC, Schmidt W, Sidor A, Liu T, Nguyen TH, Trinh B, Wilson C, Madathil S, Vogler G, O'Rourke B, Biesiadecki BJ, Tobacman LS, Cammarato A. TNNT2 mutations in the tropomyosin binding region of TNT1 disrupt its role in contractile inhibition and stimulate cardiac dysfunction. Proc Natl Acad Sci U S A 2020; 117:18822-18831. [PMID: 32690703 PMCID: PMC7414051 DOI: 10.1073/pnas.2001692117] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Muscle contraction is regulated by the movement of end-to-end-linked troponin-tropomyosin complexes over the thin filament surface, which uncovers or blocks myosin binding sites along F-actin. The N-terminal half of troponin T (TnT), TNT1, independently promotes tropomyosin-based, steric inhibition of acto-myosin associations, in vitro. Recent structural models additionally suggest TNT1 may restrain the uniform, regulatory translocation of tropomyosin. Therefore, TnT potentially contributes to striated muscle relaxation; however, the in vivo functional relevance and molecular basis of this noncanonical role remain unclear. Impaired relaxation is a hallmark of hypertrophic and restrictive cardiomyopathies (HCM and RCM). Investigating the effects of cardiomyopathy-causing mutations could help clarify TNT1's enigmatic inhibitory property. We tested the hypothesis that coupling of TNT1 with tropomyosin's end-to-end overlap region helps anchor tropomyosin to an inhibitory position on F-actin, where it deters myosin binding at rest, and that, correspondingly, cross-bridge cycling is defectively suppressed under diastolic/low Ca2+ conditions in the presence of HCM/RCM lesions. The impact of TNT1 mutations on Drosophila cardiac performance, rat myofibrillar and cardiomyocyte properties, and human TNT1's propensity to inhibit myosin-driven, F-actin-tropomyosin motility were evaluated. Our data collectively demonstrate that removing conserved, charged residues in TNT1's tropomyosin-binding domain impairs TnT's contribution to inhibitory tropomyosin positioning and relaxation. Thus, TNT1 may modulate acto-myosin activity by optimizing F-actin-tropomyosin interfacial contacts and by binding to actin, which restrict tropomyosin's movement to activating configurations. HCM/RCM mutations, therefore, highlight TNT1's essential role in contractile regulation by diminishing its tropomyosin-anchoring effects, potentially serving as the initial trigger of pathology in our animal models and humans.
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Affiliation(s)
- Aditi Madan
- Department of Medicine, Division of Cardiology, Johns Hopkins University, Baltimore, MD 21205
| | - Meera C Viswanathan
- Department of Medicine, Division of Cardiology, Johns Hopkins University, Baltimore, MD 21205
| | - Kathleen C Woulfe
- Department of Medicine, Division of Cardiology, University of Colorado Denver, Aurora, CO 80045
| | - William Schmidt
- Department of Medicine, Division of Cardiology, Johns Hopkins University, Baltimore, MD 21205
| | - Agnes Sidor
- Department of Medicine, Division of Cardiology, Johns Hopkins University, Baltimore, MD 21205
| | - Ting Liu
- Department of Medicine, Division of Cardiology, Johns Hopkins University, Baltimore, MD 21205
| | - Tran H Nguyen
- Department of Medicine, Division of Cardiology, Johns Hopkins University, Baltimore, MD 21205
| | - Bosco Trinh
- Development, Aging and Regeneration Program, Sanford Burnham Prebys Medical Discovery Institute, La Jolla, CA 92037
| | - Cortney Wilson
- Department of Medicine, Division of Cardiology, University of Colorado Denver, Aurora, CO 80045
| | - Sineej Madathil
- Department of Medicine, University of Illinois College of Medicine, Chicago, IL 60612
| | - Georg Vogler
- Development, Aging and Regeneration Program, Sanford Burnham Prebys Medical Discovery Institute, La Jolla, CA 92037
| | - Brian O'Rourke
- Department of Medicine, Division of Cardiology, Johns Hopkins University, Baltimore, MD 21205
| | - Brandon J Biesiadecki
- Department of Physiology and Cell Biology, The Ohio State University, Columbus, OH 43210
- The Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH 43210
| | - Larry S Tobacman
- Department of Medicine, University of Illinois College of Medicine, Chicago, IL 60612
| | - Anthony Cammarato
- Department of Medicine, Division of Cardiology, Johns Hopkins University, Baltimore, MD 21205;
- Department of Physiology, Johns Hopkins University, Baltimore, MD 21205
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7
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Yamaguchi M, Kimura M, Ohno T, Nakahara N, Akiyama N, Takemori S, Yagi N. Crossbridge Recruitment Capacity of Wild-Type and Hypertrophic Cardiomyopathy-Related Mutant Troponin-T Evaluated by X-ray Diffraction and Mechanical Study of Cardiac Skinned Fibers. Int J Mol Sci 2020; 21:ijms21103520. [PMID: 32429250 PMCID: PMC7278983 DOI: 10.3390/ijms21103520] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2020] [Revised: 05/10/2020] [Accepted: 05/11/2020] [Indexed: 12/02/2022] Open
Abstract
X-ray diffraction and tension measurement experiments were conducted on rat left ventricular skinned fibers with or without “troponin-T treatment,” which exchanges the endogenous troponin T/I/C complex with exogenous troponin-T. These experiments were performed to observe the structural changes in troponin-T within a fiber elicited by contractile crossbridge formation and investigate the abnormality of hypertrophic cardiomyopathy-related troponin-T mutants. The intensity of the troponin reflection at 1/38.5 nm−1 was decreased significantly by ATP addition after treatment with wild-type or mutant troponin-T, indicating that crossbridge formation affected the conformation of troponin-T. In experiments on cardiac fibers treated with the hypertrophic cardiomyopathy-related mutants E244D- and K247R-troponin-T, treatment with K247R-troponin-T did not recruit contracting actomyosin to a greater extent than wild-type-troponin-T, although a similar drop in the intensity of the troponin reflection occurred. Therefore, the conformational change in K247R-troponin-T was suggested to be unable to fully recruit actomyosin interaction, which may be the cause of cardiomyopathy.
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Affiliation(s)
- Maki Yamaguchi
- Department of Physiology, The Jikei University School of Medicine, Tokyo 105-8461, Japan; (N.N.); (S.T.)
- Correspondence: ; Tel.: +81-33433-1111
| | - Masako Kimura
- Department of Integrated Physiology, Kagawa Nutrition University, Saitama 350-0288, Japan;
| | - Tetsuo Ohno
- Department of Sports Medicine, Teikyo Heisei University, Chiba 290-0193, Japan;
| | - Naoya Nakahara
- Department of Physiology, The Jikei University School of Medicine, Tokyo 105-8461, Japan; (N.N.); (S.T.)
| | - Nobutake Akiyama
- Core Research Facilities for Basic Science, The Jikei University School of Medicine, Tokyo 105-8461, Japan;
| | - Shigeru Takemori
- Department of Physiology, The Jikei University School of Medicine, Tokyo 105-8461, Japan; (N.N.); (S.T.)
| | - Naoto Yagi
- Spectroscopy and Imaging Division, Japan Synchrotron Radiation Research Institute, SPring-8, Hyogo 679-5198, Japan;
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Cao T, Sujkowski A, Cobb T, Wessells RJ, Jin JP. The glutamic acid-rich-long C-terminal extension of troponin T has a critical role in insect muscle functions. J Biol Chem 2020; 295:3794-3807. [PMID: 32024695 PMCID: PMC7086023 DOI: 10.1074/jbc.ra119.012014] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2019] [Revised: 02/03/2020] [Indexed: 12/12/2022] Open
Abstract
The troponin complex regulates the Ca2+ activation of myofilaments during striated muscle contraction and relaxation. Troponin genes emerged 500-700 million years ago during early animal evolution. Troponin T (TnT) is the thin-filament-anchoring subunit of troponin. Vertebrate and invertebrate TnTs have conserved core structures, reflecting conserved functions in regulating muscle contraction, and they also contain significantly diverged structures, reflecting muscle type- and species-specific adaptations. TnT in insects contains a highly-diverged structure consisting of a long glutamic acid-rich C-terminal extension of ∼70 residues with unknown function. We found here that C-terminally truncated Drosophila TnT (TpnT-CD70) retains binding of tropomyosin, troponin I, and troponin C, indicating a preserved core structure of TnT. However, the mutant TpnTCD70 gene residing on the X chromosome resulted in lethality in male flies. We demonstrate that this X-linked mutation produces dominant-negative phenotypes, including decreased flying and climbing abilities, in heterozygous female flies. Immunoblot quantification with a TpnT-specific mAb indicated expression of TpnT-CD70 in vivo and normal stoichiometry of total TnT in myofilaments of heterozygous female flies. Light and EM examinations revealed primarily normal sarcomere structures in female heterozygous animals, whereas Z-band streaming could be observed in the jump muscle of these flies. Although TpnT-CD70-expressing flies exhibited lower resistance to cardiac stress, their hearts were significantly more tolerant to Ca2+ overloading induced by high-frequency electrical pacing. Our findings suggest that the Glu-rich long C-terminal extension of insect TnT functions as a myofilament Ca2+ buffer/reservoir and is potentially critical to the high-frequency asynchronous contraction of flight muscles.
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Affiliation(s)
- Tianxin Cao
- Department of Physiology, Wayne State University School of Medicine, Detroit, Michigan 48201
| | - Alyson Sujkowski
- Department of Physiology, Wayne State University School of Medicine, Detroit, Michigan 48201
| | - Tyler Cobb
- Department of Physiology, Wayne State University School of Medicine, Detroit, Michigan 48201
| | - Robert J Wessells
- Department of Physiology, Wayne State University School of Medicine, Detroit, Michigan 48201
| | - Jian-Ping Jin
- Department of Physiology, Wayne State University School of Medicine, Detroit, Michigan 48201
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9
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Johnston JR, Landim-Vieira M, Marques MA, de Oliveira GAP, Gonzalez-Martinez D, Moraes AH, He H, Iqbal A, Wilnai Y, Birk E, Zucker N, Silva JL, Chase PB, Pinto JR. The intrinsically disordered C terminus of troponin T binds to troponin C to modulate myocardial force generation. J Biol Chem 2019; 294:20054-20069. [PMID: 31748410 PMCID: PMC6937556 DOI: 10.1074/jbc.ra119.011177] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2019] [Revised: 11/13/2019] [Indexed: 12/15/2022] Open
Abstract
Aberrant regulation of myocardial force production represents an early biomechanical defect associated with sarcomeric cardiomyopathies, but the molecular mechanisms remain poorly defined. Here, we evaluated the pathogenicity of a previously unreported sarcomeric gene variant identified in a pediatric patient with sporadic dilated cardiomyopathy, and we determined a molecular mechanism. Trio whole-exome sequencing revealed a de novo missense variant in TNNC1 that encodes a p.I4M substitution in the N-terminal helix of cardiac troponin C (cTnC). Reconstitution of this human cTnC variant into permeabilized porcine cardiac muscle preparations significantly decreases the magnitude and rate of isometric force generation at physiological Ca2+-activation levels. Computational modeling suggests that this inhibitory effect can be explained by a decrease in the rates of cross-bridge attachment and detachment. For the first time, we show that cardiac troponin T (cTnT), in part through its intrinsically disordered C terminus, directly binds to WT cTnC, and we find that this cardiomyopathic variant displays tighter binding to cTnT. Steady-state fluorescence and NMR spectroscopy studies suggest that this variant propagates perturbations in cTnC structural dynamics to distal regions of the molecule. We propose that the intrinsically disordered C terminus of cTnT directly interacts with the regulatory N-domain of cTnC to allosterically modulate Ca2+ activation of force, perhaps by controlling the troponin I switching mechanism of striated muscle contraction. Alterations in cTnC-cTnT binding may compromise contractile performance and trigger pathological remodeling of the myocardium.
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Affiliation(s)
- Jamie R Johnston
- Department of Biomedical Sciences, College of Medicine, Florida State University, Tallahassee, Florida 32306
| | - Maicon Landim-Vieira
- Department of Biomedical Sciences, College of Medicine, Florida State University, Tallahassee, Florida 32306
| | - Mayra 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 21941-902, 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 21941-902, Brazil
| | - David Gonzalez-Martinez
- Department of Biomedical Sciences, College of Medicine, Florida State University, Tallahassee, Florida 32306
| | - Adolfo H Moraes
- Departamento de Química, Instituto de Ciências Exatas, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais 31270-901, Brazil
| | - Huan He
- Department of Biomedical Sciences, College of Medicine, Florida State University, Tallahassee, Florida 32306
- Institute of Molecular Biophysics, Florida State University, Tallahassee, Florida 32306
| | - Anwar Iqbal
- 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 21941-902, Brazil
| | - Yael Wilnai
- Department of Pediatrics, Dana-Dwek ChildrenγÇÖs Hospital, Tel Aviv Sourasky Medical Center, Tel Aviv, Israel 6423906
| | - Einat Birk
- Department of Cardiology, Schneider ChildrenγÇÖs Medical Center, Tel Aviv University, Petah Tikva, Israel 4920235
| | - Nili Zucker
- Department of Cardiology, Schneider ChildrenγÇÖs Medical Center, Tel Aviv University, Petah Tikva, Israel 4920235
| | - 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 21941-902, Brazil
| | - P Bryant Chase
- Department of Biological Science, Florida State University, Tallahassee, Florida 32306
| | - Jose Renato Pinto
- Department of Biomedical Sciences, College of Medicine, Florida State University, Tallahassee, Florida 32306
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10
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Clippinger SR, Cloonan PE, Greenberg L, Ernst M, Stump WT, Greenberg MJ. Disrupted mechanobiology links the molecular and cellular phenotypes in familial dilated cardiomyopathy. Proc Natl Acad Sci U S A 2019; 116:17831-17840. [PMID: 31427533 PMCID: PMC6731759 DOI: 10.1073/pnas.1910962116] [Citation(s) in RCA: 33] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Familial dilated cardiomyopathy (DCM) is a leading cause of sudden cardiac death and a major indicator for heart transplant. The disease is frequently caused by mutations of sarcomeric proteins; however, it is not well understood how these molecular mutations lead to alterations in cellular organization and contractility. To address this critical gap in our knowledge, we studied the molecular and cellular consequences of a DCM mutation in troponin-T, ΔK210. We determined the molecular mechanism of ΔK210 and used computational modeling to predict that the mutation should reduce the force per sarcomere. In mutant cardiomyocytes, we found that ΔK210 not only reduces contractility but also causes cellular hypertrophy and impairs cardiomyocytes' ability to adapt to changes in substrate stiffness (e.g., heart tissue fibrosis that occurs with aging and disease). These results help link the molecular and cellular phenotypes and implicate alterations in mechanosensing as an important factor in the development of DCM.
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Affiliation(s)
- Sarah R Clippinger
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110
| | - Paige E Cloonan
- 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
| | - Melanie Ernst
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110
| | - W Tom Stump
- 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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11
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Lin Z, Guo F, Gregorich ZR, Sun R, Zhang H, Hu Y, Shanmuganayagam D, Ge Y. Comprehensive Characterization of Swine Cardiac Troponin T Proteoforms by Top-Down Mass Spectrometry. J Am Soc Mass Spectrom 2018; 29:1284-1294. [PMID: 29633223 PMCID: PMC6109964 DOI: 10.1007/s13361-018-1925-y] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/18/2018] [Revised: 02/14/2018] [Accepted: 02/14/2018] [Indexed: 05/12/2023]
Abstract
Cardiac troponin T (cTnT) regulates the Ca2+-mediated interaction between myosin thick filaments and actin thin filaments during cardiac contraction and relaxation. cTnT is released into the blood following injury, and increased serum levels of the protein are used clinically as a biomarker for myocardial infarction. Moreover, mutations in cTnT are causative in a number of familial cardiomyopathies. With the increasing use of large animal (swine) model to recapitulate human diseases, it is essential to characterize species-dependent protein sequence variants, alternative RNA splicing, and post-translational modifications (PTMs), but challenges remain due to the incomplete database and lack of validation of the predicted splicing isoforms. Herein, we integrated top-down mass spectrometry (MS) with online liquid chromatography (LC) and immunoaffinity purification to comprehensively characterize miniature swine cTnT proteoforms, including those arising from alternative RNA splicing and PTMs. A total of seven alternative splicing isoforms of cTnT were identified by LC/MS from swine left ventricular tissue, with each isoform containing un-phosphorylated and mono-phosphorylated proteoforms. The phosphorylation site was localized to Ser1 for the mono-phosphorylated proteoforms of cTnT1, 3, 4, and 6 by online MS/MS combining collisionally activated dissociation (CAD) and electron transfer dissociation (ETD). Offline MS/MS on Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometer with CAD and electron capture dissociation (ECD) was then utilized to achieve deep sequencing of mono-phosphorylated cTnT1 (35.2 kDa) with a high sequence coverage of 87%. Taken together, this study demonstrated the unique advantage of top-down MS in the comprehensive characterization of protein alternative splicing isoforms together with PTMs. Graphical Abstract ᅟ.
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Affiliation(s)
- Ziqing Lin
- Department of Cell and Regenerative Biology, University of Wisconsin-Madison, Madison, WI, 53705, USA
- Human Proteomics Program, University of Wisconsin-Madison, Madison, WI, 53705, USA
| | - Fang Guo
- Department of Cell and Regenerative Biology, University of Wisconsin-Madison, Madison, WI, 53705, USA
- Department of Cardiology, Shandong Provincial Hospital, Jinan, 250021, Shandong, People's Republic of China
| | - Zachery R Gregorich
- Department of Cell and Regenerative Biology, University of Wisconsin-Madison, Madison, WI, 53705, USA
| | - Ruixiang Sun
- Department of Cell and Regenerative Biology, University of Wisconsin-Madison, Madison, WI, 53705, USA
- Institute of Computing Technology, Chinese Academy of Sciences, Beijing, 100190, People's Republic of China
| | - Han Zhang
- Department of Chemistry, University of Wisconsin-Madison, Madison, WI, 53706, USA
| | - Yang Hu
- Department of Cell and Regenerative Biology, University of Wisconsin-Madison, Madison, WI, 53705, USA
| | | | - Ying Ge
- Department of Cell and Regenerative Biology, University of Wisconsin-Madison, Madison, WI, 53705, USA.
- Human Proteomics Program, University of Wisconsin-Madison, Madison, WI, 53705, USA.
- Department of Chemistry, University of Wisconsin-Madison, Madison, WI, 53706, USA.
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12
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Iwasaki T, Taniguchi H, Hasegawa Y, Maeda N, Yamamoto K. A novel method for monitoring troponin T fragment from rabbit skeletal muscle during aging using quartz crystal microbalance. J Sci Food Agric 2016; 96:3944-3949. [PMID: 26676372 DOI: 10.1002/jsfa.7558] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/25/2015] [Revised: 08/03/2015] [Accepted: 11/27/2015] [Indexed: 06/05/2023]
Abstract
BACKGROUND Troponin T (TnT) is degraded during aging of meat. The proteolytic fragment of TnT, especially the 30 kDa fragment, is used as one of indices for estimating aging of meat. We have tried to use quartz crystal microbalance (QCM), which is widely used to analyze interaction among macromolecules, to detect proteolytic fragments of TnT during aging of meat. RESULT The frequency of the QCM sensor with immobilized anti-TnT antibody in high-salt solution extracts of both myofibrils and whole meat decreased with time of aging. The staining intensity of the bands, including a 30 kDa fragment bound to anti-TnT antibody, also increased with time of aging in western blotting. These results confirm that TnT is degraded during aging and released from thin filaments, and QCM analysis is sufficiently sensitive to detect the TnT fragments. CONCLUSION The QCM analysis of muscle and myofibrillar extracts using anti-TnT antibody-immobilized sensor can be used as a convenient tool for monitoring the extent of aging of meat. © 2015 Society of Chemical Industry.
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Affiliation(s)
- Tomohito Iwasaki
- Department of Food Science and Human Wellness, Rakuno Gakuen University, Hokkaido, Japan
| | - Hironobu Taniguchi
- Department of Food Science and Human Wellness, Rakuno Gakuen University, Hokkaido, Japan
| | - Yasuhiro Hasegawa
- Department of Food Science and Human Wellness, Rakuno Gakuen University, Hokkaido, Japan
| | - Naoyuki Maeda
- Safety Research Institute for Chemical Compounds Co. Ltd, Hokkaido, Japan
| | - Katsuhiro Yamamoto
- Department of Food Science and Human Wellness, Rakuno Gakuen University, Hokkaido, Japan
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13
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Cheng Y, Regnier M. Cardiac troponin structure-function and the influence of hypertrophic cardiomyopathy associated mutations on modulation of contractility. Arch Biochem Biophys 2016; 601:11-21. [PMID: 26851561 PMCID: PMC4899195 DOI: 10.1016/j.abb.2016.02.004] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2015] [Revised: 01/30/2016] [Accepted: 02/02/2016] [Indexed: 11/29/2022]
Abstract
Cardiac troponin (cTn) acts as a pivotal regulator of muscle contraction and relaxation and is composed of three distinct subunits (cTnC: a highly conserved Ca(2+) binding subunit, cTnI: an actomyosin ATPase inhibitory subunit, and cTnT: a tropomyosin binding subunit). In this mini-review, we briefly summarize the structure-function relationship of cTn and its subunits, its modulation by PKA-mediated phosphorylation of cTnI, and what is known about how these properties are altered by hypertrophic cardiomyopathy (HCM) associated mutations of cTnI. This includes recent work using computational modeling approaches to understand the atomic-based structural level basis of disease-associated mutations. We propose a viewpoint that it is alteration of cTnC-cTnI interaction (rather than the Ca(2+) binding properties of cTn) per se that disrupt the ability of PKA-mediated phosphorylation at cTnI Ser-23/24 to alter contraction and relaxation in at least some HCM-associated mutations. The combination of state of the art biophysical approaches can provide new insight on the structure-function mechanisms of contractile dysfunction resulting cTnI mutations and exciting new avenues for the diagnosis, prevention, and even treatment of heart diseases.
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Affiliation(s)
- Yuanhua Cheng
- University of Washington, Department of Bioengineering, Seattle, WA, USA
| | - Michael Regnier
- University of Washington, Department of Bioengineering, Seattle, WA, USA.
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14
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Ahadian S, Yamada S, Ramón-Azcón J, Estili M, Liang X, Nakajima K, Shiku H, Khademhosseini A, Matsue T. Hybrid hydrogel-aligned carbon nanotube scaffolds to enhance cardiac differentiation of embryoid bodies. Acta Biomater 2016; 31:134-143. [PMID: 26621696 DOI: 10.1016/j.actbio.2015.11.047] [Citation(s) in RCA: 110] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2015] [Revised: 11/20/2015] [Accepted: 11/23/2015] [Indexed: 02/01/2023]
Abstract
Carbon nanotubes (CNTs) were aligned in gelatin methacryloyl (GelMA) hydrogels using dielectrophoresis approach. Mouse embryoid bodies (EBs) were cultured in the microwells fabricated on the aligned CNT-hydrogel scaffolds. The GelMA-dielectrophoretically aligned CNT hydrogels enhanced the cardiac differentiation of the EBs compared with the pure GelMA and GelMA-random CNT hydrogels. This result was confirmed by Troponin-T immunostaining, the expression of cardiac genes (i.e., Tnnt2, Nkx2-5, and Actc1), and beating analysis of the EBs. The effect on EB properties was significantly enhanced by applying an electrical pulse stimulation (frequency, 1Hz; voltage, 3V; duration, 10ms) to the EBs for two continuous days. Taken together, the fabricated hybrid hydrogel-aligned CNT scaffolds with tunable mechanical and electrical characteristics offer an efficient and controllable platform for electrically induced differentiation and stimulation of stem cells for potential tissue regeneration and cell therapy applications. STATEMENT OF SIGNIFICANCE Dielectrophoresis approach was used to rapidly align carbon nanotubes (CNTs) in gelatin methacryloyl (GelMA) hydrogels resulting in hybrid GelMA-CNT hydrogels with tunable and anisotropic electrical and mechanical properties. The GelMA-aligned CNT hydrogels may be used to apply accurate and controllable electrical pulses to cell and tissue constructs and thereby regulating their behavior and function. In this work, it was demonstrated that the GelMA hydrogels containing the aligned CNTs had superior performance in cardiac differentiation of stem cells upon applying electrical stimulation in contrast with control gels. Due to broad use of electrical stimulation in tissue engineering and stem cell differentiation, it is envisioned that the GelMA-aligned CNT hydrogels would find wide applications in tissue regeneration and stem cell therapy.
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Affiliation(s)
- Samad Ahadian
- WPI-Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
| | - Shukuyo Yamada
- Graduate School of Environmental Studies, Tohoku University, Sendai 980-8579, Japan
| | - Javier Ramón-Azcón
- Nanobiotechnology for Diagnostics (Nb4D) Group, IQAC-CSIC, Jordi Girona 18-26, Barcelona 08034, Spain; CIBER de Bioingenieria, Biomateriales y Nanomedicina (CIBER-BBN), Jordi Girona 18-26, Barcelona 08034, Spain
| | - Mehdi Estili
- Advanced Ceramics Group, Materials Processing Unit, National Institute for Materials Science (NIMS), Tsukuba 305-0047, Japan
| | - Xiaobin Liang
- WPI-Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
| | - Ken Nakajima
- WPI-Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
| | - Hitoshi Shiku
- Graduate School of Environmental Studies, Tohoku University, Sendai 980-8579, Japan
| | - Ali Khademhosseini
- WPI-Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan; Department of Medicine, Center for Biomedical Engineering, Brigham and Women's Hospital, Harvard Medical School, Cambridge, MA 02139, USA; Harvard-MIT Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA; Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA 02115, USA; College of Animal Bioscience and Technology, Department of Bioindustrial Technologies, Konkuk University, Hwayang-dong, Kwangjin-gu, Seoul 143-701, Republic of Korea; Department of Physics, Faculty of Science, King Abdulaziz University, Jeddah 21569, Saudi Arabia.
| | - Tomokazu Matsue
- WPI-Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan; Graduate School of Environmental Studies, Tohoku University, Sendai 980-8579, Japan.
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15
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Brunet NM, Chase PB, Mihajlović G, Schoffstall B. Ca(2+)-regulatory function of the inhibitory peptide region of cardiac troponin I is aided by the C-terminus of cardiac troponin T: Effects of familial hypertrophic cardiomyopathy mutations cTnI R145G and cTnT R278C, alone and in combination, on filament sliding. Arch Biochem Biophys 2014; 552-553:11-20. [PMID: 24418317 PMCID: PMC4043889 DOI: 10.1016/j.abb.2013.12.021] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2013] [Revised: 12/10/2013] [Accepted: 12/28/2013] [Indexed: 01/10/2023]
Abstract
Investigations of cardiomyopathy mutations in Ca(2+) regulatory proteins troponin and tropomyosin provide crucial information about cardiac disease mechanisms, and also provide insights into functional domains in the affected polypeptides. Hypertrophic cardiomyopathy-associated mutations TnI R145G, located within the inhibitory peptide (Ip) of human cardiac troponin I (hcTnI), and TnT R278C, located immediately C-terminal to the IT arm in human cardiac troponin T (hcTnT), share some remarkable features: structurally, biochemically, and pathologically. Using bioinformatics, we find compelling evidence that TnI and TnT, and more specifically the affected regions of hcTnI and hcTnT, may be related not just structurally but also evolutionarily. To test for functional interactions of these mutations on Ca(2+)-regulation, we generated and characterized Tn complexes containing either mutation alone, or both mutations simultaneously. The most important results from in vitro motility assays (varying [Ca(2+)], temperature or HMM density) show that the TnT mutant "rescued" some deleterious effects of the TnI mutant at high Ca(2+), but exacerbated the loss of function, i.e., switching off the actomyosin interaction, at low Ca(2+). Taken together, our experimental results suggest that the C-terminus of cTnT aids Ca(2+)-regulatory function of cTnI Ip within the troponin complex.
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Affiliation(s)
- Nicolas M Brunet
- Institute of Molecular Biophysics, Florida State University, Tallahassee, FL 32306, USA
| | - P Bryant Chase
- Institute of Molecular Biophysics, Florida State University, Tallahassee, FL 32306, USA; Department of Biological Science, Florida State University, Tallahassee, FL 32306, USA.
| | - Goran Mihajlović
- Department of Physics, Florida State University, Tallahassee, FL 32306, USA
| | - Brenda Schoffstall
- Institute of Molecular Biophysics, Florida State University, Tallahassee, FL 32306, USA
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16
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Abstract
In this study, 10 troponin T isoforms from adult porcine skeletal muscle messenger RNA were clarified. These were eight fast- and two slow-type isoforms. Fast-type isoforms had three and two variable exons in the N-terminal and the C-terminal region respectively. Slow-type isoforms had one variable exon in the N-terminal region.
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17
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Sommese RF, Nag S, Sutton S, Miller SM, Spudich JA, Ruppel KM. Effects of troponin T cardiomyopathy mutations on the calcium sensitivity of the regulated thin filament and the actomyosin cross-bridge kinetics of human β-cardiac myosin. PLoS One 2013; 8:e83403. [PMID: 24367593 PMCID: PMC3867432 DOI: 10.1371/journal.pone.0083403] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2013] [Accepted: 11/13/2013] [Indexed: 11/20/2022] Open
Abstract
Hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy (DCM) lead to significant cardiovascular morbidity and mortality worldwide. Mutations in the genes encoding the sarcomere, the force-generating unit in the cardiomyocyte, cause familial forms of both HCM and DCM. This study examines two HCM-causing (I79N, E163K) and two DCM-causing (R141W, R173W) mutations in the troponin T subunit of the troponin complex using human β-cardiac myosin. Unlike earlier reports using various myosin constructs, we found that none of these mutations affect the maximal sliding velocities or maximal Ca2+-activated ADP release rates involving the thin filament human β-cardiac myosin complex. Changes in Ca2+ sensitivity using the human myosin isoform do, however, mimic changes seen previously with non-human myosin isoforms. Transient kinetic measurements show that these mutations alter the kinetics of Ca2+ induced conformational changes in the regulatory thin filament proteins. These changes in calcium sensitivity are independent of active, cycling human β-cardiac myosin.
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Affiliation(s)
- Ruth F. Sommese
- Department of Biochemistry, Stanford University School of Medicine, Stanford, California, United States of America
| | - Suman Nag
- Department of Biochemistry, Stanford University School of Medicine, Stanford, California, United States of America
| | - Shirley Sutton
- Department of Biochemistry, Stanford University School of Medicine, Stanford, California, United States of America
| | - Susan M. Miller
- Department of Pharmaceutical Chemistry, University of California San Francisco, San Francisco, California, United States of America
| | - James A. Spudich
- Department of Biochemistry, Stanford University School of Medicine, Stanford, California, United States of America
- * E-mail: (KR); (JS)
| | - Kathleen M. Ruppel
- Department of Biochemistry, Stanford University School of Medicine, Stanford, California, United States of America
- Department of Pediatrics (Cardiology), Stanford University School of Medicine, Stanford, California, United States of America
- * E-mail: (KR); (JS)
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18
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Coffee Castro-Zena PG, Root DD. Asymmetric myosin binding to the thin filament as revealed by a fluorescent nanocircuit. Arch Biochem Biophys 2013; 535:14-21. [PMID: 23274408 PMCID: PMC3627744 DOI: 10.1016/j.abb.2012.12.014] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2012] [Revised: 12/07/2012] [Accepted: 12/11/2012] [Indexed: 11/15/2022]
Abstract
The interplay between myosin, actin, and striated muscle regulatory proteins involves complex cooperative interactions that propagate along the thin filament. A repeating unit of the tropomyosin dimer, troponin heterotrimer, and the actin protofilament heptamer is sometimes assumed to be able to bind myosin at any of its seven actins when activated even though the regulatory proteins are asymmetrically positioned along this repeating unit. Analysis of the impact of this asymmetry on actin and myosin interactions by sensitized emission luminescence resonance energy transfer spectroscopy and a unique fluorescent nanocircuit design reveals that the troponin affects the structure and function of myosin heads bound nearby in a different manner than myosin heads bound further away from the troponin. To test this hypothesis, a fluorescent nanocircuit reported the position of the myosin lever arm only when the myosin was bound adjacent to the troponin, or in controls, only when the myosin was bound distant from the troponin. Confirming the hypothesis, the myosin lever arm is predominantly in the pre powerstroke orientation when bound near troponin, but is predominantly in the post powerstroke orientation when bound distant from troponin. These data are consistent with the hypothesis that troponin is responsible for the formation of myosin binding target zones along the thin filament.
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19
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Zhang T, Birbrair A, Delbono O. Nonmyofilament-associated troponin T3 nuclear and nucleolar localization sequence and leucine zipper domain mediate muscle cell apoptosis. Cytoskeleton (Hoboken) 2013; 70:134-47. [PMID: 23378072 DOI: 10.1002/cm.21095] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2012] [Revised: 12/17/2012] [Accepted: 12/21/2012] [Indexed: 11/07/2022]
Abstract
Troponin T (TnT) plays a major role in striated muscle contraction. We recently demonstrated that the fast skeletal muscle TnT3 isoform is localized in the muscle nucleus, and either its full-length or COOH-terminus leads to muscle cell apoptosis. Here, we further explored the mechanism by which it enters the nucleus and promotes cytotoxicity. Amino acid truncation and substitution showed that its COOH-terminus contains a dominant nuclear/nucleolar localization sequence (KLKRQK) and the basic lysine and arginine residues might play an important role in the nuclear retention and nucleolar enrichment of KLKRQK-DsRed fusion proteins. Deleting this domain or substituting lysine and arginine residues (KLAAQK) resulted in a dramatic loss of TnT3 nuclear and nucleolar localization. In contrast, the GATAKGKVGGRWK domain-DsRed construct localized exclusively in the cytoplasm, indicating that a nuclear exporting sequence is possibly localized in this region. Additionally, we identified a classical DNA-binding leucine zipper domain (LZD) which is conserved among TnT isoforms and species. Deletion of LZD or KLKRQK sequence significantly reduced cell apoptosis compared to full-length TnT3. We conclude that TnT3 contains both a nuclear localization signal and a DNA-binding domain, which may mediate nuclear/nucleolar signaling and muscle cell apoptosis.
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Affiliation(s)
- Tan Zhang
- Department of Internal Medicine, Section on Gerontology and Geriatric Medicine, Wake Forest School of Medicine, 1 Medical Center Boulevard, Winston-Salem, NC 27157, USA
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20
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Pinto JR, Gomes AV, Jones MA, Liang J, Nguyen S, Miller T, Parvatiyar MS, Potter JD. The functional properties of human slow skeletal troponin T isoforms in cardiac muscle regulation. J Biol Chem 2012; 287:37362-70. [PMID: 22977240 PMCID: PMC3481333 DOI: 10.1074/jbc.m112.364927] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2012] [Revised: 08/17/2012] [Indexed: 11/06/2022] Open
Abstract
Human slow skeletal troponin T (HSSTnT) shares a high degree of homology with cardiac TnT (CTnT). Although the presence of HSSTnT has not been confirmed in the heart at the protein level, detectable levels of HSSTnT mRNA have been found. Whether HSSTnT isoforms are expressed transiently remains unknown. Because transient re-expression of HSSTnT may be a potential mechanism of regulating function, we explored the effect of HSSTnT on the regulation of cardiac muscle. At least three HSSTnT isoforms have been found to exist in slow skeletal muscle: HSSTnT1 (+exons 5 and 12), HSSTnT2 (+exon 5, -exon 12), and HSSTnT3 (-exons 5 and 12). Another isoform, HSSTnT hypothetical (Hyp) (-exon 5, +exon 12), has only been found at the mRNA level. Compared with HCTnT3 (adult isoform), Tn complexes containing HSSTnT1, -2, and -3 did not alter the actomyosin ATPase activation and inhibition in the presence and absence of Ca(2+), respectively. HSSTnTHyp was not evaluated as it did not form a Tn complex under a variety of conditions. Porcine papillary skinned fibers displaced with HSSTnT1, -2, or -3 and reconstituted with human cardiac troponin I and troponin C (HCTnI·TnC) complex showed a decrease in the Ca(2+) sensitivity of force development and an increase in maximal recovered force (HSSTnT1 and -3) compared with HCTnT3. In contrast, HSSTnTHyp showed an increase in the Ca(2+) sensitivity of force development. This suggests that re- or overexpression of specific SSTnT isoforms might have therapeutic potential in the failing heart because they increase the maximal force of contraction. In addition, circular dichroism and proteolytic digestion experiments revealed structural differences between HSSTnT isoforms and HCTnT3 and that HSSTnT1 is more susceptible to calpain and trypsin proteolysis than the other HSSTnTs. Overall, HSSTnT isoforms despite being homologues of CTnT may display distinct functional properties in muscle regulation.
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Affiliation(s)
- Jose Renato Pinto
- Department of Molecular and Cellular Pharmacology, University of Miami Miller School of Medicine, Miami, Florida 33136, USA.
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21
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Gollapudi S, Mamidi R, Mallampalli S, Chandra M. The N-terminal extension of cardiac troponin T stabilizes the blocked state of cardiac thin filament. Biophys J 2012; 103:940-8. [PMID: 23009843 PMCID: PMC3433604 DOI: 10.1016/j.bpj.2012.07.035] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2012] [Revised: 06/25/2012] [Accepted: 07/09/2012] [Indexed: 11/21/2022] Open
Abstract
Cardiac troponin T (cTnT) is a key component of contractile regulatory proteins. cTnT is characterized by a ∼32 amino acid N-terminal extension (NTE), the function of which remains unknown. To understand its function, we generated a transgenic (TG) mouse line that expressed a recombinant chimeric cTnT in which the NTE of mouse cTnT was removed by replacing its 1-73 residues with the corresponding 1-41 residues of mouse fast skeletal TnT. Detergent-skinned papillary muscle fibers from non-TG (NTG) and TG mouse hearts were used to measure tension, ATPase activity, Ca(2+) sensitivity (pCa(50)) of tension, rate of tension redevelopment, dynamic muscle fiber stiffness, and maximal fiber shortening velocity at sarcomere lengths (SLs) of 1.9 and 2.3 μm. Ca(2+) sensitivity increased significantly in TG fibers at both short SL (pCa(50) of 5.96 vs. 5.62 in NTG fibers) and long SL (pCa(50) of 6.10 vs. 5.76 in NTG fibers). Maximal cross-bridge turnover and detachment kinetics were unaltered in TG fibers. Our data suggest that the NTE constrains cardiac thin filament activation such that the transition of the thin filament from the blocked to the closed state becomes less responsive to Ca(2+). Our finding has implications regarding the effect of tissue- and disease-related changes in cTnT isoforms on cardiac muscle function.
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Affiliation(s)
| | | | | | - Murali Chandra
- Department of Veterinary and Comparative Anatomy, Pharmacology, and Physiology, Washington State University, Pullman, Washington
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22
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Franklin A, Baxley T, Kobayashi T, Chalovich J. The C-terminus of troponin T is essential for maintaining the inactive state of regulated actin. Biophys J 2012; 102:2536-44. [PMID: 22713569 PMCID: PMC3368147 DOI: 10.1016/j.bpj.2012.04.037] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2011] [Revised: 03/23/2012] [Accepted: 04/24/2012] [Indexed: 01/11/2023] Open
Abstract
Striated muscle contraction is regulated by the actin binding proteins tropomyosin and troponin. Defects in these proteins lead to myopathies and cardiomyopathies. Deletion of the 14 C-terminal residues of cardiac troponin T leads to hypertrophic cardiomyopathy. We showed earlier that regulated actin containing Δ14 TnT was more readily activated than wild-type regulated actin. We suggested that the equilibria among the inactive (blocked), intermediate (closed or calcium), and active (open or myosin) states was shifted to the active state. We now show that, in addition, such regulated actin filaments cannot enter the inactive or blocked state. Regulated actin containing Δ14 TnT had ATPase activities in the absence of Ca2+ that were higher than wild-type filaments but far below the fully active rate. The rapid dissociation of S1-ATP from regulated actin filaments containing Δ14 TnT and acrylodan-labeled tropomyosin did not show the fluorescence increase characteristic of moving to the inactive state. Replacing wild-type TnI with S45E TnI, that favors the inactive state, did not restore the fluorescence change. We conclude that TnT has a previously unrecognized role in forming the inactive state of regulated actin.
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Affiliation(s)
- Andrew J. Franklin
- Department of Biochemistry and Molecular Biology, Brody School of Medicine, East Carolina University, Greenville, North Carolina
| | - Tamatha Baxley
- Department of Biochemistry and Molecular Biology, Brody School of Medicine, East Carolina University, Greenville, North Carolina
| | - Tomoyoshi Kobayashi
- Department of Physiology and Biophysics and Center for Cardiovascular Research, College of Medicine, University of Illinois, Chicago, Illinois
| | - Joseph M. Chalovich
- Department of Biochemistry and Molecular Biology, Brody School of Medicine, East Carolina University, Greenville, North Carolina
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Morimoto S. Role of protein kinase C in thin filament activation by rigor-like cross-bridges under ischemic conditions. J Mol Cell Cardiol 2009; 47:350-1. [PMID: 19540843 DOI: 10.1016/j.yjmcc.2009.06.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/02/2009] [Accepted: 06/13/2009] [Indexed: 11/17/2022]
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Matsumoto F, Maeda K, Chatake T, Maéda Y, Fujiwara S. Functional aberration of myofibrils by cardiomyopathy-causing mutations in the coiled-coil region of the troponin-core domain. Biochem Biophys Res Commun 2009; 382:205-9. [PMID: 19275886 DOI: 10.1016/j.bbrc.2009.03.009] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2009] [Accepted: 03/04/2009] [Indexed: 11/19/2022]
Abstract
Two cardiomyopathy-causing mutations, E244D and K247R, in human cardiac troponin T (TnT) are located in the coiled-coil region of the Tn-core domain. To elucidate effects of mutations in this region on the regulatory function of Tn, we measured Ca(2+)-dependent ATPase activity of myofibrils containing various mutants of TnT at these residues. The results confirmed that the mutant E244D increases the maximum ATPase activity without changing the Ca(2+)-sensitivity. The mutant K247R was shown for the first time to have the effect similar to the mutant E244D. Furthermore, various TnT mutants (E244D, E244M, E244A, E244K, K247R, K247E, and K247A) showed various effects on the maximum ATPase activity while the Ca(2+)-sensitivity was unchanged. Molecular dynamics simulations of the Tn-core containing these TnT mutants suggested that the hydrogen-bond network formed by the side chains of neighboring residues around residues 244 and 247 is important for Tn to function properly.
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Affiliation(s)
- Fumiko Matsumoto
- Quantum Beam Science Directorate, Japan Atomic Energy Agency, 2-4 Shirakata-Shirane, Tokai-mura, Naka-gun, Ibaraki 319-1195, Japan
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25
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Abstract
The conserved central and COOH-terminal regions of troponin T (TnT) interact with troponin C, troponin I, and tropomyosin to regulate striated muscle contraction. Phylogenic data show that the NH2-terminal region has evolved as an addition to the conserved core structure of TnT. This NH2-terminal region does not bind other thin filament proteins, and its sequence is hypervariable between fiber type and developmental isoforms. Previous studies have demonstrated that NH2-terminal modifications alter the COOH-terminal conformation of TnT and thin filament Ca2+-activation, yet the functional core structure of TnT and the mechanism of NH2-terminal modulation are not well understood. To define the TnT core structure and investigate the regulatory role of the NH2-terminal variable region, we investigated two classes of model TnT molecules: (1) NH2-terminal truncated cardiac TnT and (2) chimera proteins consisting of an acidic or basic skeletal muscle TnT NH2-terminus spliced to the cardiac TnT core. Deletion of the TnT hypervariable NH2-terminus preserved binding to troponin I and tropomyosin and sustained cardiac muscle contraction in the heart of transgenic mice. Further deletion of the conserved central region diminished binding to tropomyosin. The reintroduction of differently charged NH2-terminal domains in the chimeric molecules produced long-range conformational changes in the central and COOH-terminal regions to alter troponin I and tropomyosin binding. Similar NH2-terminal charge effects are demonstrated in naturally occurring cardiac TnT isoforms, indicating a physiological significance. These results suggest that the hypervariable NH2-terminal region modulates the conformation and function of the TnT core structure to fine-tune muscle contractility.
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Affiliation(s)
- Brandon J. Biesiadecki
- From the Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, 10900 Euclid Ave., Cleveland, OH 44106; and
| | - Stephen M. Chong
- Section of Molecular Cardiology, Evanston Northwestern Healthcare and Northwestern University Fienberg School of Medicine, Evanston, Illinois 60201
| | - Thomas M. Nosek
- From the Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, 10900 Euclid Ave., Cleveland, OH 44106; and
| | - J.-P. Jin
- From the Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, 10900 Euclid Ave., Cleveland, OH 44106; and
- Section of Molecular Cardiology, Evanston Northwestern Healthcare and Northwestern University Fienberg School of Medicine, Evanston, Illinois 60201
- *To whom correspondence should be addressed: Tel.: 847-570-1960; Fax: 847-570-1865; e-mail:
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26
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Liou YM, Chao HL. Fluorescence spectroscopic analysis of the proximity changes between the central helix of troponin C and the C-terminus of troponin T from chicken skeletal muscle. Biochim Biophys Acta 2007; 1774:466-73. [PMID: 17350907 DOI: 10.1016/j.bbapap.2007.01.004] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/01/2006] [Revised: 01/29/2007] [Accepted: 01/29/2007] [Indexed: 11/24/2022]
Abstract
Recent structural studies of the troponin (Tn) core complex have shown that the regulatory head containing the N-lobe of TnC is connected to the IT arm by a flexible linker of TnC. The IT arm is a long coiled-coil formed by alpha-helices of TnI and TnT, plus the C-lobe of TnC. The TnT is thought to play a pivotal role in the linking of Ca(2+) -triggered conformational changes in thin filament regulatory proteins to the activation of cross-bridge cycling. However, a functional domain at the C-terminus of TnT is missing from the Tn core complex. In this study, we intended to determine the proximity relationship between the central helix of TnC and the TnT C-terminus in the binary and the ternary complex with and without Ca2+ by using pyrene excimer fluorescence spectroscopy and fluorescence resonance energy transfer. Chicken fast skeletal TnC contains a Cys102 at the E helix, while TnT has a Cys264 at its C-terminus. These two cysteines were specifically labeled with sulfhydryl-reactive fluorescence probes. The measured distance in the binary complex was about 19 Angstroms and slightly increased when they formed the ternary complex with TnI (20 Angstroms). Upon Ca2+ binding the distance was not affected in the binary complex but increased by approximately 4 Angstroms in the ternary complex. These results suggest that TnI plays an essential role in the Ca(2+) -mediated change in the spatial relationship between the C-lobe of TnC and the C-terminus of TnT.
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Affiliation(s)
- Ying-Ming Liou
- Department of Life Sciences, National Chung-Hsing University, Taichung, Taiwan.
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27
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Amin MZ, Bando T, Ruksana R, Anokye-Danso F, Takashima Y, Sakube Y, Kagawa H. Tissue-specific interactions of TNI isoforms with other TN subunits and tropomyosins in C. elegans: the role of the C- and N-terminal extensions. Biochim Biophys Acta 2007; 1774:456-65. [PMID: 17369112 DOI: 10.1016/j.bbapap.2007.01.003] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/21/2006] [Revised: 01/26/2007] [Accepted: 01/30/2007] [Indexed: 11/20/2022]
Abstract
The aim of this study is to investigate the function of the C-terminal extension of three troponin I isoforms, that are unique to the body wall muscles of Caenorhabditis elegans and to understand the molecular interactions within the TN complex between troponin I with troponin C/T, and tropomyosin. We constructed several expression vectors to generate recombinant proteins of three body wall and one pharyngeal troponin I isoforms in Escherichia coli. Protein overlay assays and Western blot analyses were performed using antibodies. We demonstrated that pharyngeal TNI-4 interacted with only the pharyngeal isoforms of troponin C/T and tropomyosin. In contrast, the body wall TNI-2 bound both the body wall and pharyngeal isoforms of these components. Similar to other invertebrates, the N-terminus of troponin I contributes to interactions with troponin C. Full-length troponin I was essential for interactions with tropomyosin isoforms. Deletion of the C-terminal extension had no direct effect on the binding of the body wall troponin I to other muscle thin filament troponin C/T and tropomyosin isoforms.
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Affiliation(s)
- Md Ziaul Amin
- Division of Bioscience, Graduate School of Natural Science and Technology, Okayama University, Okayama, Japan
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Eichmüller C, Skrynnikov NR. Observation of microsecond time-scale protein dynamics in the presence of Ln3+ ions: application to the N-terminal domain of cardiac troponin C. J Biomol NMR 2007; 37:79-95. [PMID: 17180551 DOI: 10.1007/s10858-006-9105-y] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/20/2006] [Accepted: 10/02/2006] [Indexed: 05/13/2023]
Abstract
The microsecond time-scale motions in the N-terminal domain of cardiac troponin C (NcTnC) loaded with lanthanide ions have been investigated by means of a (1)H(N) off-resonance spin-lock experiment. The observed relaxation dispersion effects strongly increase along the series of NcTnC samples containing La(3+), Ce(3+), and Pr(3+) ions. This rise in dispersion effects is due to modulation of long-range pseudocontact shifts by micros time-scale dynamics. Specifically, the motion in the coordination sphere of the lanthanide ion (i.e. in the NcTnC EF-hand motif) causes modulation of the paramagnetic susceptibility tensor which, in turn, causes modulation of pseudocontact shifts. It is also probable that opening/closing dynamics, previously identified in Ca(2+)-NcTnC, contributes to some of the observed dispersions. On the other hand, it is unlikely that monomer-dimer exchange in the solution of NcTnC is directly responsible for the dispersion effects. Finally, on-off exchange of the lanthanide ion does not seem to play any significant role. The amplification of dispersion effects by Ln(3+) ions is a potentially useful tool for studies of micros-ms motions in proteins. This approach makes it possible to observe the dispersions even when the local environment of the reporting spin does not change. This happens, for example, when the motion involves a 'rigid' structural unit such as individual alpha-helix. Even more significantly, the dispersions based on pseudocontact shifts offer better chances for structural characterization of the dynamic species. This method can be generalized for a large class of applications via the use of specially designed lanthanide-binding tags.
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29
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Zhang Z, Biesiadecki BJ, Jin JP. Selective deletion of the NH2-terminal variable region of cardiac troponin T in ischemia reperfusion by myofibril-associated mu-calpain cleavage. Biochemistry 2006; 45:11681-94. [PMID: 16981728 PMCID: PMC1762003 DOI: 10.1021/bi060273s] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
The structure of the NH2-terminal region of troponin T (TnT) is hypervariable among the muscle type-specific isoforms and is also regulated by alternative RNA splicing. This region does not contain binding sites for other thin filament proteins, but alteration of its structure affects the Ca2+ regulation of muscle contraction. Here we report a truncated cardiac TnT produced during myocardial ischemia reperfusion. Amino acid sequencing and protein fragment reconstruction determined that it is generated by a posttranslational modification selectively removing the NH2-terminal variable region and preserving the conserved core structure of TnT. Triton X-100 extraction of cardiac muscle fibers promoted production of the NH2-terminal truncated cardiac TnT (cTnT-ND), indicating a myofibril-associated proteolytic activity. Mu-calpain is a myofibril-associated protease and is known to degrade TnT. Supporting a role of mu-calpain in producing cTnT-ND in myocardial ischemia reperfusion, calpain inhibitors decreased the level of cTnT-ND in Triton-extracted myofibrils. Mu-calpain treatment of the cardiac myofibril and troponin complex specifically reproduced cTnT-ND. In contrast, mu-calpain treatment of isolated cardiac TnT resulted in nonspecific degradation, suggesting that this structural modification is relevant to physiological structures of the myofilament. Triton X-100 treatment of transgenic mouse cardiac myofibrils overexpressing fast skeletal muscle TnT produced similar NH2-terminal truncations of the endogenous and exogenous TnT, despite different amino acid sequences at the cleavage site. With the functional consequences of removing the NH2-terminal variable region of TnT, the mu-calpain-mediated proteolytic modification of TnT may act as an acute mechanism to adjust muscle contractility under stress conditions.
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Affiliation(s)
| | | | - Jian-Ping Jin
- * To whom correspondence should be addressed: Molecular Cardiology, Evanston Northwestern Healthcare, Evanston, Illinois 60201 Tel: (847) 570-1960. Fax: (847) 570-1865.
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30
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Messer AE, Jacques AM, Marston SB. Troponin phosphorylation and regulatory function in human heart muscle: dephosphorylation of Ser23/24 on troponin I could account for the contractile defect in end-stage heart failure. J Mol Cell Cardiol 2006; 42:247-59. [PMID: 17081561 DOI: 10.1016/j.yjmcc.2006.08.017] [Citation(s) in RCA: 146] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/20/2006] [Revised: 08/19/2006] [Accepted: 08/24/2006] [Indexed: 11/27/2022]
Abstract
We made quantitative measurements of phosphorylation in troponin isolated from 6 non-failing donor hearts and 6 explanted hearts with end-stage heart failure in SDS-PAGE gels using Pro-Q Diamond phosphoprotein stain. The troponin T phosphorylation level was the same in troponin from failing and non-failing heart (3.1 mol Pi/mol). However, troponin I phosphorylation was significantly lower in failing (0.37+/-0.18 mol Pi/mol) compared with non-failing heart troponin (2.25+/-0.36 mol Pi/mol). Levels of troponin I PKA-dependent phosphorylation, measured with a phosphoserine 23/24-specific antibody, were also significantly lower in failing heart troponin (0.19+/-0.06 mol Pi/mol) compared to non-failing troponin (1.14+/-0.09 mol Pi/mol). We calculate that there is phosphorylation in addition to serine 23/24 of 1.11+/-0.34 mol Pi/mol in non-failing reduced to 0.18+/-0.17 mol Pi/mol in failing heart troponin, attributed to phosphorylation on the PKC sites. To test for the functional role of troponin I phosphorylation, the native troponin I from either non-failing or failing heart troponin was exchanged for a recombinant (unphosphorylated) human cardiac troponin I. Thin filament Ca(2+)-regulatory function was studied with the quantitative in vitro motility assay: thin filaments containing the replaced troponin I resulted in a failing phenotype of a 17-26% reduced sliding speed and an increased Ca(2+)-sensitivity relative to non-failing troponin (EC(50) TnI-exchanged/non-failing=0.57, p<0.001). When exchanged with troponin I phosphorylated with PKA motility parameters reverted to a pattern indistinguishable from non-failing troponin (p=0.35-0.75). We suggest that changes in troponin function can account for the contractile abnormality in failing heart muscle and that the functional changes in troponin are due to reduced phosphorylation of troponin I at the PKA sites.
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Affiliation(s)
- Andrew E Messer
- National Heart and Lung Institute, Imperial College London, Dovehouse Street, London SW3 6LY, UK
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31
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Abstract
In agricultural sciences, proteomics has become the new hope for analyzing the meat quality traits that are closely related to the skeletal muscle traits. 2-DE muscle maps of many species have been recently reported and used to find molecular markers of meat quality traits. However, one limitation of 2-DE based analyses is due to the limited alkaline protein separation. Considering this problem, there is a need to use recent advances that have markedly improved the 2-DE based analysis of alkaline proteins. Hence, the present study provides additional information concerning the alkaline proteome of bovine skeletal muscle by using an appropriate protocol to characterize proteins over the entire range of pH 7-11. A total of 32 distinct gene products corresponding to 60 protein spots were identified by PMF and grouped in seven categories according to their main function. This 2-D map will contribute to muscle proteome studies since a significant portion of proteins is in the alkaline pH range.
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Affiliation(s)
- Thibault Chaze
- Herbivore Research Unit, Muscle Growth and Metabolism Group, INRA, France
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32
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Jideama NM, Crawford BH, Hussain AKMA, Raynor RL. Dephosphorylation specificities of protein phosphatase for cardiac troponin I, troponin T, and sites within troponin T. Int J Biol Sci 2006; 2:1-9. [PMID: 16585947 PMCID: PMC1415850 DOI: 10.7150/ijbs.2.1] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2006] [Accepted: 03/01/2006] [Indexed: 11/25/2022] Open
Abstract
Protein dephosphorylation by protein phosphatase 1 (PP1), acting in concert with protein kinase C (PKC) and protein kinase A (PKA), is a pivotal regulatory mechanism of protein phosphorylation. Isolated rat cardiac myofibrils phosphorylated by PKC/PKA and dephosphorylated by PP1 were used in determining dephosphorylation specificities, Ca2+-stimulated Mg2+ATPase activities, and Ca2+ sensitivities. In reconstituted troponin (Tn) complex, PP1 displayed distinct substrate specificity in dephosphorylation of TnT preferentially to TnI, in vitro. In situ phosphorylation of cardiomyocytes with calyculin A, a protein phosphatase inhibitor, resulted in an increase in the phosphorylation stiochiometry of TnT (0.3 to 0.5 (67%)), TnI (2.6 to 3.6 (38%)), and MLC2 (0.4 to 1.7 (325%)). These results further confirmed that though MLC2 is the preferred target substrate for protein phosphatase in the thick filament, the Tn complex (TnI and TnT) from thin filament and C-protein in the thick filament are also protein phosphatase substrates. Our in vitro dephosphorylation experiments revealed that while PP1 differentially dephosphorylated within TnT at multiple sites, TnI was uniformly dephosphorylated. Phosphopeptide maps from the in vitro experiments show that TnT phosphopeptides at spots 4A and 4B are much more resistant to PP1 dephosphorylation than other TnT phosphopeptides. Mg2+ATPase assays of myofibrils phosphorylated by PKC/PKA and dephosphorylated by PP1 delineated that while PKC and PKA phosphorylation decreased the Ca2+-stimulated Mg2+ATPase activities, dephosphorylation antagonistically restored it. PKC and PKA phosphorylation decreased Ca2+ sensitivity to 3.6 µM and 5.0 µM respectively. However, dephosphorylation restored the Mg2+ATPase activity of PKC (99%) and PKA (95%), along with the Ca2+ sensitivities (3.3 µM and 3.0 µM, respectively).
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Affiliation(s)
- Nathan M Jideama
- Department of Biological Sciences, Clark Atlanta University, Atlanta, GA 30314, USA.
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Michielsen ECHJ, Diris JHC, Kleijnen VWVC, Wodzig WKWH, Van Dieijen-Visser MP. Interpretation of cardiac troponin T behaviour in size-exclusion chromatography. Clin Chem Lab Med 2006; 44:1422-7. [PMID: 17163817 DOI: 10.1515/cclm.2006.265] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
AbstractClin Chem Lab Med 2006;44:1422–7.
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Affiliation(s)
- Etienne C H J Michielsen
- Department of Clinical Chemistry, University Hospital Maastricht, 6202 AZ Maastricht, The Netherlands
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Ertz-Berger BR, He H, Dowell C, Factor SM, Haim TE, Nunez S, Schwartz SD, Ingwall JS, Tardiff JC. Changes in the chemical and dynamic properties of cardiac troponin T cause discrete cardiomyopathies in transgenic mice. Proc Natl Acad Sci U S A 2005; 102:18219-24. [PMID: 16326803 PMCID: PMC1298915 DOI: 10.1073/pnas.0509181102] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Cardiac troponin T (cTnT) is a central component of the regulatory thin filament. Mutations in cTnT have been linked to severe forms of familial hypertrophic cardiomyopathy. A mutational "hotspot" that leads to distinct clinical phenotypes has been identified at codon 92. Although the basic functional and structural roles of cTnT in modulating contractility are relatively well understood, the mechanisms that link point mutations in cTnT to the development of this complex cardiomyopathy are unknown. To address this question, we have taken a highly interdisciplinary approach by first determining the effects of the residue 92 mutations on the molecular flexibility and stability of cTnT by means of molecular dynamics simulations. To test whether the predicted alterations in thin filament structure could lead to distinct cardiomyopathies in vivo, we developed transgenic mouse models expressing either the Arg-92-Trp or Arg-92-Leu cTnT proteins in the heart. Characterization of these models at the cellular and whole-heart levels has revealed mutation-specific early alterations in transcriptional activation that result in distinct pathways of ventricular remodeling and contractile performance. Thus, our computational and experimental results show that changes in thin filament structure caused by single amino acid substitutions lead to differences in the biophysical properties of cTnT and alter disease pathogenesis.
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Affiliation(s)
- Briar R Ertz-Berger
- Department of Physiology and Biophysics, Albert Einstein College of Medicine, Bronx, NY 10461, USA
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35
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Gaze DC, Collinson PO. Interpretation of cardiac troponin measurements in neonates--the devil is in the details. Commentary to trevisanuto et Al.: cardiac troponin I in asphyxiated neonates (biol neonate 2006;89:190-193). Neonatology 2005; 89:194-6. [PMID: 16276078 DOI: 10.1159/000089549] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Affiliation(s)
- David C Gaze
- Chemical Pathology, St. George's Healthcare NHS Trust, London, UK.
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Chaudhuri T, Mukherjea M, Sachdev S, Randall JD, Sarkar S. Role of the fetal and alpha/beta exons in the function of fast skeletal troponin T isoforms: correlation with altered Ca2+ regulation associated with development. J Mol Biol 2005; 352:58-71. [PMID: 16081096 DOI: 10.1016/j.jmb.2005.06.066] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2005] [Revised: 06/17/2005] [Accepted: 06/29/2005] [Indexed: 12/01/2022]
Abstract
In mammalian fast skeletal muscle, constitutive and alternative splicing from a single troponin T (TnT) gene produce multiple developmentally regulated and tissue specific TnT isoforms. Two exons, alpha (exon 16) and beta (exon 17), located near the 3' end of the gene and coding for two different 14 amino acid residue peptides are spliced in a mutually exclusive manner giving rise to the adult TnTalpha and the fetal TnTbeta isoforms. In addition, an acidic peptide coded by a fetal (f) exon located between exons 8 and 9 near the 5' end of the gene, is specifically present in TnTbeta and absent in the adult isoforms. To define the functional role of the f and alpha/beta exons, we constructed combinations of TnT cDNAs from a single human fetal fast skeletal TnTbeta cDNA clone in order to circumvent the problem of N-terminal sequence heterogeneity present in wild-type TnT isoforms, irrespective of the stage of development. Nucleotide sequences of these constructs, viz. TnTalpha, TnTalpha + f, TnTbeta - f and TnTbeta are identical, except for the presence or absence of the alpha or beta and f exons. Our results, using the recombinant TnT isoforms in different functional in vitro assays, show that the presence of the f peptide in the N-terminal T1 region of TnT, has a strong inhibitory effect on binary interactions between TnT and other thin filament proteins, TnI, TnC and Tm. The presence of the f peptide led to reduced Ca2+-dependent ATPase activity in a reconstituted thin filament, whereas the contribution of the alpha and beta peptides in the biological activity of TnT was primarily modulatory. These results indicate that the f peptide confers an inhibitory effect on the biological function of fast skeletal TnT and this can be correlated with changes in the Ca2+ regulation associated with development in fast skeletal muscle.
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Affiliation(s)
- Tathagata Chaudhuri
- Program in Cell, Molecular and Developmental Biology, Sackler School of Graduate Biomedical Sciences, Tufts University, Boston, MA 02111, USA
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37
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Abstract
Troponin plays a central role in the regulation of skeletal and cardiac muscle contraction. The protein consists of three polypeptide chains (TnT, TnI and TnC) and is located on polymerized actin together with tropomyosin, forming muscle thin filament. We have determined the molecular structures of the core domains (relative molecular mass of 46,000 and 52,000) of human cardiac troponin in the Ca2+-saturated form by X-ray crystallography. Analysis of the four structures derived from the two crystal forms reveals that the core domain is further divided into sub-domains, connected by linkers, making the entire molecule highly flexible. The structures of the troponin ternary complex suggests that the Ca2+-binding to the regulatory TnC site displaces the carboxyl-terminal portion of TnI from actin/tropomyosin, thereby altering mobility and/or flexibility of the troponin/tropomyosin strand on the actin filament. These Ca2+-dependent changes in the properties of the tropomyosin strand on the actin filament may in turn alter accessibility of myosin heads (motor protein) to the actin filament.
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Affiliation(s)
- Soichi Takeda
- Department of Cardiac Physiology, National Cardiovascular Center Research Institute, 5-7-1 Fujishiro-dai, Suita, Osaka 565-8565, Japan.
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38
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Kischel P, Bastide B, Muller M, Dubail F, Offredi F, Jin JP, Mounier Y, Martial J. Expression and functional properties of four slow skeletal troponin T isoforms in rat muscles. Am J Physiol Cell Physiol 2005; 289:C437-43. [PMID: 15788488 DOI: 10.1152/ajpcell.00365.2004] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We investigated the expression and functional properties of slow skeletal troponin T (sTnT) isoforms in rat skeletal muscles. Four sTnT cDNAs were cloned from the slow soleus muscle. Three isoforms were found to be similar to sTnT1, sTnT2, and sTnT3 isoforms described in mouse muscles. A new rat isoform, with a molecular weight slightly higher than that of sTnT3, was discovered. This fourth isoform had never been detected previously in any skeletal muscle and was therefore called sTnTx. From both expression pattern and functional measurements, it appears that sTnT isoforms can be separated into two classes, high-molecular-weight (sTnT1, sTnT2) and low-molecular-weight (sTnTx, sTnT3) isoforms. By comparison to the apparent migration pattern of the four recombinant sTnT isoforms, the newly described low-molecular-weight sTnTx isoform appeared predominantly and typically expressed in fast skeletal muscles, whereas the higher-molecular-weight isoforms were more abundant in slow soleus muscle. The relative proportion of the sTnT isoforms in the soleus was not modified after exposure to hindlimb unloading (HU), known to induce a functional atrophy and a slow-to-fast isoform transition of several myofibrillar proteins. Functional data gathered from replacement of endogenous troponin complexes in skinned muscle fibers showed that the sTnT isoforms modified the Ca2+activation characteristics of single skeletal muscle fibers, with sTnT2 and sTnT1 conferring a similar increase in Ca2+affinity higher than that caused by low-molecular-weight isoforms sTnTx and sTnT3. Thus we show for the first time the presence of sTnT in fast muscle fibers, and our data show that the changes in neuromuscular activity on HU are insufficient to alter the sTnT expression pattern.
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Affiliation(s)
- P Kischel
- Laboratoire de Biologie Moléculaire et Génie Génétique, Allée de la Chimie 3, Campus du Sart-Tilman, Bât. B6, 4000 Liège, Belgium.
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39
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Abstract
Myostatin plays a major role in muscle growth and development and animals with disruption of this gene display marked increases in muscle mass. Little is known about muscle physiological adaptations in relation to this muscle hypertrophy. To provide a more comprehensive view, we analyzed bovine muscles from control, heterozygote and homozygote young Belgian blue bulls for myostatin deletion, which results in a normal level of inactive myostatin. Heterozygote and homozygote animals were characterized by a higher proportion of fast-twitch glycolytic fibers in Semitendinosus muscle. Differential proteomic analysis of this muscle was performed using two-dimensional gel electrophoresis followed by mass spectrometry. Thirteen proteins, corresponding to 28 protein spots, were significantly altered in response to the myostatin deletion. The observed changes in protein expression are consistent with an increased fast muscle phenotype, suggesting that myostatin negatively controls mainly fast-twitch glycolytic fiber number. Finally, we demonstrated that differential mRNA splicing of fast troponin T is altered by the loss of myostatin function. The structure of mutually exclusive exon 16 appears predominantly expressed in muscles from heterozygote and homozygote animals. This suggests a role for exon 16 of fast troponin T in the physiological adaptation of the fast muscle phenotype.
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MESH Headings
- Animals
- Base Sequence
- Blotting, Western
- Cattle
- Electrophoresis, Gel, Two-Dimensional
- Exons
- Gene Deletion
- Gene Expression Regulation
- Glycolysis
- Heterozygote
- Homozygote
- Hypertrophy
- Immunohistochemistry
- Male
- Mass Spectrometry
- Muscle Fibers, Fast-Twitch/chemistry
- Muscle Fibers, Fast-Twitch/metabolism
- Muscle Fibers, Fast-Twitch/physiology
- Muscle, Skeletal/chemistry
- Muscle, Skeletal/physiology
- Myostatin
- Proteome/analysis
- Proteome/chemistry
- Proteome/physiology
- Proteomics
- RNA Splicing
- RNA, Messenger/metabolism
- Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
- Transforming Growth Factor beta/chemistry
- Transforming Growth Factor beta/genetics
- Transforming Growth Factor beta/metabolism
- Troponin T/chemistry
- Troponin T/genetics
- Trypsin/metabolism
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Affiliation(s)
- Julien Bouley
- Herbivore Research Unit, Muscle Growth and Metabolism Group, INRA, St-Genès-Champanelle, France
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40
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Mirza M, Marston S, Willott R, Ashley C, Mogensen J, McKenna W, Robinson P, Redwood C, Watkins H. Dilated cardiomyopathy mutations in three thin filament regulatory proteins result in a common functional phenotype. J Biol Chem 2005; 280:28498-506. [PMID: 15923195 DOI: 10.1074/jbc.m412281200] [Citation(s) in RCA: 126] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Dilated cardiomyopathy (DCM), characterized by cardiac dilatation and contractile dysfunction, is a major cause of heart failure. Inherited DCM can result from mutations in the genes encoding cardiac troponin T, troponin C, and alpha-tropomyosin; different mutations in the same genes cause hypertrophic cardiomyopathy. To understand how certain mutations lead specifically to DCM, we have investigated their effect on contractile function by comparing wild-type and mutant recombinant proteins. Because initial studies on two troponin T mutations have generated conflicting findings, we analyzed all eight published DCM mutations in troponin T, troponin C, and alpha-tropomyosin in a range of in vitro assays. Thin filaments, reconstituted with a 1:1 ratio of mutant/wild-type proteins (the likely in vivo ratio), all showed reduced Ca(2+) sensitivity of activation in ATPase and motility assays, and except for one alpha-tropomyosin mutant showed lower maximum Ca(2+) activation. Incorporation of either of two troponin T mutants in skinned cardiac trabeculae also decreased Ca(2+) sensitivity of force generation. Structure/function considerations imply that the diverse thin filament DCM mutations affect different aspects of regulatory function yet change contractility in a consistent manner. The DCM mutations depress myofibrillar function, an effect fundamentally opposite to that of hypertrophic cardiomyopathy-causing thin filament mutations, suggesting that decreased contractility may trigger pathways that ultimately lead to the clinical phenotype.
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Affiliation(s)
- Mahmooda Mirza
- National Heart and Lung Institute, Imperial College London, London SW3 6LY, United Kingdom
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41
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Kitamura SI, Muroya S, Tanabe S, Okumura T, Chikuni K, Nishimura T. Mechanism of production of troponin T fragments during postmortem aging of porcine muscle. J Agric Food Chem 2005; 53:4178-81. [PMID: 15884856 DOI: 10.1021/jf047974l] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
Troponin T (TnT) is one of the myofibrillar proteins that is easily degraded during postmortem aging of pork. In this study, we determined the N-terminal amino acid sequences of TnT degradation fragments produced during postmortem aging and by m-calpain hydrolysis. The N-terminal amino acid sequences of TnT fragments produced during postmortem aging were EVHEPEEKPRPKLTAP, EKPRPKLTAPKIPEG, and APKIPEGEKVDF. On the other hand, the N-terminal amino acid sequences of TnT fragments produced by the action of m-calpain were APPPPAEV, EVHEPEEK, and APK. These sequences of degradation fragments could be mapped on fast type TnT isoform 2. The peptide bonds of His37-Glu38 and Thr51-Ala52 in fTnT2 were cleaved during postmortem aging as well as by the calpain hydrolysis; therefore, calpain was concluded to have an important role in TnT degradation during postmortem aging. It was also found that the sourness-suppressing peptide APPPPAEVHEVHEEVH (Okumura et al. Biosci. Biotechnol. Biochem. 2004, 68, 1657-1662) derived from TnT degradation could be produced by the action of calpains on Glu21-Ala22 and His37-Glu38 sites.
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Affiliation(s)
- Shin-ichi Kitamura
- Graduate School of Biosphere Science, Hiroshima University, Higashi-Hiroshima 739-8528, Japan
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42
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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] [What about the content of this article? (0)] [Affiliation(s)] [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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43
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Doi T, Satoh A, Tanaka H, Inoue A, Yumoto F, Tanokura M, Ohtsuki I, Nishita K, Ojima T. Functional importance of Ca2+-deficient N-terminal lobe of molluscan troponin C in troponin regulation. Arch Biochem Biophys 2005; 436:83-90. [PMID: 15752712 DOI: 10.1016/j.abb.2005.01.004] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2004] [Revised: 01/11/2005] [Indexed: 11/16/2022]
Abstract
Ca(2+)-binding sites I and II in the N-terminal lobe of molluscan troponin C (TnC) have lost the ability to bind Ca(2+) due to substitutions of the amino acid residues responsible for Ca(2+) liganding. To evaluate the functional importance of the Ca(2+)-deficient N-terminal lobe in the Ca(2+)-regulatory function of molluscan troponin, we constructed chimeric TnCs comprising the N-terminal lobes from rabbit fast muscle and squid mantle muscle TnCs and the C-terminal lobe from akazara scallop TnC, TnC(RA), and TnC(SA), respectively. We characterized their biochemical properties as compared with those of akazara scallop wild-type TnC (TnC(AA)). According to equilibrium dialysis using (45)Ca(2+), TnC(RA), and TnC(SA) bound stoichiometrically 3 mol Ca(2+)/mol and 1 mol Ca(2+)/mol, respectively, as expected from their primary structures. All the chimeric TnCs exhibited difference-UV-absorption spectra at around 280-290 nm upon Ca(2+) binding and formed stable complexes with akazara scallop troponin I, even in the presence of 6M urea, if Ca(2+) was present. However, when the troponin complexes were constructed from chimeric TnCs and akazara scallop troponin T and troponin I, they showed different Ca(2+)-regulation abilities from each other depending on the TnC species. Thus, the troponin containing TnC(SA) conferred as high a Ca(2+) sensitivity to Mg-ATPase activity of rabbit actomyosin-akazara scallop tropomyosin as did the troponin containing TnC(AA), whereas the troponin containing TnC(RA) conferred virtually no Ca(2+) sensitivity. Our findings indicate that the N-terminal lobe of molluscan TnC plays important roles in molluscan troponin regulation, despite its inability to bind Ca(2+).
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Affiliation(s)
- Teppei Doi
- Laboratory of Biochemistry and Biotechnology, Graduate School of Fisheries Sciences, Hokkaido University, Hakodate, Hokkaido 041-8611, Japan
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44
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Abstract
Several striated muscle myopathies have been directly linked to mutations in contractile and associated proteins. Troponin T (TnT) is one of the three subunits that form troponin (Tn) which together with tropomyosin is responsible for the regulation of striated muscle contraction. All three subunits of cardiac Tn as well as tropomyosin have been associated with hypertrophic cardiomyopathy (HCM). However, TnT accounts for most of the mutations that cause HCM in these regulatory proteins. To date 30 mutations have been identified in the cardiac TnT (CTnT) gene that results in familial HCM (FHC). The CTnT gene has also been associated with familial dilated cardiomyopathy (DCM). CTnT deficiency is lethal due to impaired cardiac development. A recessive nonsense mutation in the gene encoding slow skeletal TnT has been associated with an unusual, severe form of nemaline myopathy among the Old Order Amish. How each mutation leads to the diverse clinical symptoms associated with FHC, DCM or nemaline myopathy is unclear. However, the use of animal model systems, in particular transgenic mice, has significantly increased our knowledge of normal and myopathic muscle physiology. In this review, we focus on the role of TnT in muscle physiology and disease.
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MESH Headings
- Amino Acid Sequence
- Animals
- Base Sequence
- Cardiomyopathy, Dilated/genetics
- Cardiomyopathy, Dilated/physiopathology
- Cardiomyopathy, Hypertrophic, Familial/genetics
- Cardiomyopathy, Hypertrophic, Familial/physiopathology
- DNA/genetics
- Humans
- Hydrogen-Ion Concentration
- In Vitro Techniques
- Mice
- Mice, Transgenic
- Models, Biological
- Molecular Sequence Data
- Muscle Contraction/physiology
- Muscular Diseases/genetics
- Muscular Diseases/physiopathology
- Mutation
- Myopathies, Nemaline/genetics
- Myopathies, Nemaline/physiopathology
- Phenotype
- Troponin T/chemistry
- Troponin T/genetics
- Troponin T/physiology
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Affiliation(s)
- Aldrin V Gomes
- Department of Molecular and Cellular Pharmacology, University of Miami School of Medicine, Miami, Florida 33136, USA.
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45
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Abstract
Background and Purpose—
The prognostic value of cardiac troponins and natriuretic peptide in acute ischemic stroke is uncertain. We measured cardiac troponin T (cTnT), cardiac troponin I (cTnI), and N-terminal pro-brain natriuretic peptide (NT-proBNP) at admission in acute ischemic stroke patients without evident myocardial damage.
Methods—
In 174 consecutive patients with MRI-confirmed ischemic stroke, serial measurements of cTnT, cTnI, and NT-proBNP were performed at 3 different time points in the hyperacute phase (at admission, on days 1 and 2). Relation of laboratory values to risk factors, stroke subtype classification, and clinical outcome after 3 months was analyzed.
Results—
The highest proportion of raised parameters was found at day 2 for cTnI in 8 of 103 (7.8%), at day 3 for cTnT in 8 of 174 (4.6%), and NT-proBNP in 114 of 174 (65.5%) patients. Proportion of patients with good outcome was significantly reduced in the group with highest NT-proBNP quartile. However, using multivariate regression analysis, no significant relation to morbidity and mortality was found for cTnT, cTnI, or NT-proBNP. Significant impact on the outcome was detected for lesion size, insular involvement, sex, age, and stroke severity.
Conclusions—
NT-proBNP is raised in nearly two thirds of acute stroke patients, whereas elevated cardiac troponins are found only in a small number of acute ischemic stroke patients. Neither NT-proBNP nor cardiac troponins influence clinical outcome if other risk factors are considered.
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Affiliation(s)
- Thorleif Etgen
- Department of Neurology, Technical University of Munich, Germany.
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46
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Michielsen ECHJ, Diris JHC, Hackeng CM, Wodzig WKWH, Van Dieijen-Visser MP. Highly Sensitive Immunoprecipitation Method for Extracting and Concentrating Low-Abundance Proteins from Human Serum. Clin Chem 2005; 51:222-4. [PMID: 15613717 DOI: 10.1373/clinchem.2004.036251] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Affiliation(s)
- Etienne C H J Michielsen
- Department of Clinical Chemistry, University Hospital Maastricht, Maastricht 6202 AZ, The Netherlands
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47
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Sorsa T, Pollesello P, Solaro RJ. The contractile apparatus as a target for drugs against heart failure: Interaction of levosimendan, a calcium sensitiser, with cardiac troponin c. Mol Cell Biochem 2004; 266:87-107. [PMID: 15646030 DOI: 10.1023/b:mcbi.0000049141.37823.19] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Cardiac failure is one of the leading causes of mortality in developed countries. As life expectancies of the populations of these countries grow, the number of patients suffering from cardiac insufficiency also increases. Effective treatments are being sought and recently a new class of drugs, the calcium sensitisers, was developed. These drugs cause a positive inotropic effect on cardio-myocytes by interacting directly with the contractile apparatus. Their mechanism of action is not accompanied by an increase in intracellular calcium concentration at therapeutic doses, as seen for the older generation of positive inotropic drugs, and thus does not induce calcium-related deleterious effects such as arrhythmias or apoptosis. Levosimendan is a novel calcium sensitiser which has been discovered by using cardiac troponin C (cTnC) as target protein. This drug has been proved to be a well-tolerated and effective treatment for patients with severe decompensated heart failure. This review describes the basic principles of muscle contraction, the main components of the contractile apparatus and their roles in the heart contraction. The regulatory proteins troponin C (cTnC), troponin I (cTnI), troponin T (cTnT), and tropomyosin (Tm) and their interactions are discussed in details. The concept of calcium sensitisation is thereafter explained and a few examples of calcium sensitisers and their putative mechanisms are discussed. Finally, the binding of levosimendan to cTnC and its mechanism of action are described and the results discussed under the light of the action of this drug in vitro and in vivo.
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Affiliation(s)
- Tia Sorsa
- Orion Pharma, Cardiovascular Research, Espoo, Finland
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48
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Liou YM, Chang JCH. Differential pH Effect on Calcium-Induced Conformational Changes of Cardiac Troponin C Complexed with Cardiac and Fast Skeletal Isoforms of Troponin I and Troponin T. J Biochem 2004; 136:683-92. [PMID: 15632309 DOI: 10.1093/jb/mvh175] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The aim of this study is to investigate the molecular events associated with the deleterious effects of acidosis on the contractile properties of cardiac muscle as in the ischemia of heart failure. We have conducted a study of the effects of increasing acidity on the Ca(2+) induced conformational changes of pyrene labelled cardiac troponin C (PIA-cTnC) in isolation and in complex with porcine cardiac or chicken pectoral skeletal muscle TnI and/or TnT. The pyrene label has been shown to serve as a useful fluorescence reporter group for conformational and interaction events of the N-terminal regulatory domain of TnC with only minimal fluorescence changes associated with C-terminal domain. Results obtained show that the significant decreases at pH 6.0 of site II Ca(2+) affinity of PIA-cTnC when complexed as a binary complex with either cTnI or cTnT are significantly reduced when cTnI is replaced with sTnI or cTnT with sTnT. However, this effect is appreciably diminished when the cTnI and cTnT in the ternary complex are replaced by sTnI and sTnT. The smaller effects in the ternary complex of replacing both cTnI and cTnT by their skeletal counterparts on depressing the Ca(2+) affinity from pH 7.0 to 6.0 arise from TnI replacement. Thus, changes in TnC conformation resulting from isoform-specific interactions with TnI and TnT could be an integral part of the effect of pH on myofilament Ca(2+)sensitivity.
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Affiliation(s)
- Y M Liou
- Department of Life Science, National Chung-Hsing University, Taichung, 402, Taiwan.
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49
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Mukhopadhyay S, Langsetmo K, Stafford WF, Henry GD, Baleja JD, Sarkar S. Identification of a region of fast skeletal troponin T required for stabilization of the coiled-coil formation with troponin I. J Biol Chem 2004; 280:538-47. [PMID: 15507453 DOI: 10.1074/jbc.m409537200] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We have previously identified evolutionarily conserved heptad hydrophobic repeat (HR) domains in all isoprotein members of troponin T (TnT) and troponin I (TnI), two subunits of the Ca(2+)-regulatory troponin complex. Our suggestion that the HR domains are involved in the formation of a coiled-coil heterodimer of TnT and TnI has been recently confirmed by the crystal structure of the core domain of the human cardiac troponin complex. Here we studied a series of recombinant deletion mutants of the fast skeletal TnT to determine the minimal sequence required for stable coiled-coil formation with the HR domain of the fast skeletal TnI. Using circular dichroism spectroscopy, we measured the alpha helical content of the coiled-coil formed by the various TnT peptides with TnI HR domain. Sedimentation equilibrium experiments confirmed that the individual peptides of TnT were monomeric but formed heterodimers when mixed with HR domain of TnI. Isothermal titration calorimetry was then used to directly measure the affinity of the TnT peptides for the TnI HR domain. Surprisingly we found that the HR regions alone of the fast skeletal TnT and TnI, as defined earlier, were insufficient to form a coiled-coil. Furthermore we showed that an additional 14 amino acid residues N-terminal to the conserved HR region (TnT residues 165-178) are essential for the stable coiled-coil formation. We discuss the implication of our finding in the fast skeletal troponin isoform in the light of the crystal structure of the cardiac isoform.
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Affiliation(s)
- Subhradip Mukhopadhyay
- Program in Cell, Molecular and Developmental Biology, Sackler School of Graduate Biomedical Sciences, Tufts University School of Medicine, Boston, MA 02111, USA
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50
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Jagatheesan G, Rajan S, Petrashevskaya N, Schwartz A, Boivin G, Arteaga G, de Tombe PP, Solaro RJ, Wieczorek DF. Physiological significance of troponin T binding domains in striated muscle tropomyosin. Am J Physiol Heart Circ Physiol 2004; 287:H1484-94. [PMID: 15191887 DOI: 10.1152/ajpheart.01112.2003] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Striated muscle tropomyosin (TM) plays an essential role in sarcomeric contraction and relaxation through its regulated movement on the thin filament. Previous work in our laboratory established that α- and β-TM isoforms elicit physiological differences in sarcomeric performance. To address the significance of isoform-specific troponin T binding regions in TM, in this present work we replaced α-TM amino acids 175–190 and 258–284 with the β-TM regions and expressed this chimeric protein in the hearts of transgenic mice. Hearts that express this chimeric protein exhibit significant decreases in rates of contraction and relaxation when assessed by ex vivo work-performing cardiac analyses. There are increases in time to peak pressure and in half-time to relaxation. These hearts respond appropriately to β-adrenergic stimulation but do not attain control rates of contraction or relaxation. With increased expression of the transgene, 70% of the mice die by 5 mo of age without exhibiting gross pathological changes in the heart. Myofilaments from these mice have no differences in Ca2+sensitivity of percent maximum force, but there is a decrease in maximum tension development. Our data are the first to demonstrate that the troponin T binding regions of specific TM isoforms can alter sarcomeric performance without changing the Ca2+sensitivity of the myofilaments.
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Affiliation(s)
- Ganapathy Jagatheesan
- Dept. of Molecular Genetics, Biochemistry, and Microbiology, University of Cincinnati College of Medicine, Cincinnati, OH 45267-0524, USA
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