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] [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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Yin X, Guo S, Gao J, Luo L, Liao X, Li M, Su H, Huang Z, Xu J, Pei J, Chen S. Kinetic analysis of effects of temperature and time on the regulation of venom expression in Bungarus multicinctus. Sci Rep 2020; 10:14142. [PMID: 32839510 PMCID: PMC7445180 DOI: 10.1038/s41598-020-70565-2] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2020] [Accepted: 07/20/2020] [Indexed: 01/25/2023] Open
Abstract
Venom gland is a highly efficient venom production system to maintain their predatory arsenal. Venom toxins mRNA has been shown to increase abruptly in snake after venom expenditure, while the dynamics of venom accumulation during synthesis are poorly understood. Here, PacBio long-read sequencing, Illumina RNA sequencing (RNA-seq), and label-free proteome quantification were used to investigate the composition landscape and time- and temperature-dependent dynamics changes of the Bungarus multicinctus venom gland system. Transcriptome data (19.5223 Gb) from six adult B. multicinctus tissues were sequenced using PacBio RS II to generate a reference assembly, and average 7.28 Gb of clean RNA-seq data was obtained from venom glands by Illumina sequencing. Differentially expressed genes (DEGs) mainly were protein processing rather than venom toxins. Post-translational modifications provided the evidence of the significantly different proportions of toxins in the venom proteome with the changing of replenishment time and temperature, but constant of venom toxins mRNA in the venom gland transcriptome. Dynamic of toxins and genes involved in venom gland contraction suggesting the formation of the mature venom gland system would take at least 9 days. In addition, 59 toxin processing genes were identified, peptidylprolyl isomerase B of which underwent positive selection in Toxicofera. These results provide a reference for determining the extraction time of venom, production of polyclonal and monoclonal antibody for precise treatment plans of venomous snakebites, and construction of an in vitro synthesis system for snake venom protein.
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Affiliation(s)
- Xianmei Yin
- Key Laboratory of Distinctive Chinese Medicine Resources in Southwest China, Pharmacy College, Chengdu University of Traditional Chinese Medicine, Chengdu, 611137, People's Republic of China
| | - Shuai Guo
- Key Laboratory of Distinctive Chinese Medicine Resources in Southwest China, Pharmacy College, Chengdu University of Traditional Chinese Medicine, Chengdu, 611137, People's Republic of China
| | - Jihai Gao
- Key Laboratory of Distinctive Chinese Medicine Resources in Southwest China, Pharmacy College, Chengdu University of Traditional Chinese Medicine, Chengdu, 611137, People's Republic of China
| | - Lu Luo
- Key Laboratory of Beijing for Identification and Safety Evaluation of Chinese Medicine, Institution of Chinese Materia Medica, China Academy of Chinese Medical Sciences, Beijing, 100700, China
| | - Xuejiao Liao
- Key Laboratory of Distinctive Chinese Medicine Resources in Southwest China, Pharmacy College, Chengdu University of Traditional Chinese Medicine, Chengdu, 611137, People's Republic of China
| | - Mingqian Li
- Cancer Institute of Integrated Traditional Chinese and Western Medicine, Zhejiang Academy of Traditional Chinese Medicine, Tongde Hospital of Zhejiang Province, Hangzhou, 310012, Zhejiang, China
| | - He Su
- The Second Clinical College, Guangzhou University of Chinese Medicine, Guangzhou, 510006, China
| | - Zhihai Huang
- The Second Clinical College, Guangzhou University of Chinese Medicine, Guangzhou, 510006, China
| | - Jiang Xu
- Key Laboratory of Beijing for Identification and Safety Evaluation of Chinese Medicine, Institution of Chinese Materia Medica, China Academy of Chinese Medical Sciences, Beijing, 100700, China.
| | - Jin Pei
- Key Laboratory of Distinctive Chinese Medicine Resources in Southwest China, Pharmacy College, Chengdu University of Traditional Chinese Medicine, Chengdu, 611137, People's Republic of China.
| | - Shilin Chen
- Key Laboratory of Beijing for Identification and Safety Evaluation of Chinese Medicine, Institution of Chinese Materia Medica, China Academy of Chinese Medical Sciences, Beijing, 100700, China.
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3
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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: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [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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4
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Marston S, Zamora JE. Troponin structure and function: a view of recent progress. J Muscle Res Cell Motil 2019; 41:71-89. [PMID: 31030382 PMCID: PMC7109197 DOI: 10.1007/s10974-019-09513-1] [Citation(s) in RCA: 55] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2019] [Accepted: 04/12/2019] [Indexed: 12/15/2022]
Abstract
The molecular mechanism by which Ca2+ binding and phosphorylation regulate muscle contraction through Troponin is not yet fully understood. Revealing the differences between the relaxed and active structure of cTn, as well as the conformational changes that follow phosphorylation has remained a challenge for structural biologists over the years. Here we review the current understanding of how Ca2+, phosphorylation and disease-causing mutations affect the structure and dynamics of troponin to regulate the thin filament based on electron microscopy, X-ray diffraction, NMR and molecular dynamics methodologies.
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Affiliation(s)
- Steven Marston
- NHLI and Chemistry Departments, Imperial College London, W12 0NN, London, UK.
| | - Juan Eiros Zamora
- NHLI and Chemistry Departments, Imperial College London, W12 0NN, London, UK
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5
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Baxley T, Johnson D, Pinto JR, Chalovich JM. Troponin C Mutations Partially Stabilize the Active State of Regulated Actin and Fully Stabilize the Active State When Paired with Δ14 TnT. Biochemistry 2017; 56:2928-2937. [PMID: 28530094 DOI: 10.1021/acs.biochem.6b01092] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Striated muscle contraction is regulated by the actin-associated proteins tropomyosin and troponin. The extent of activation of myosin ATPase activity is lowest in the absence of both Ca2+ and activating cross-bridges (i.e., S1-ADP or rigor S1). Binding of activating species of myosin to actin at a saturating Ca2+ concentration stabilizes the most active state (M state) of the actin-tropomyosin-troponin complex (regulated actin). Ca2+ binding alone produces partial stabilization of the active state. The extent of stabilization at a saturating Ca2+ concentration depends on the isoform of the troponin subunits, the phosphorylation state of troponin, and, in the case of cardiac muscle, the presence of hypertrophic cardiomyopathy-producing mutants of troponin T and troponin I. Cardiac dysfunction is also associated with mutations of troponin C (TnC). Troponin C mutants A8V, C84Y, and D145E increase the Ca2+ sensitivity of ATPase activity. We show that these mutants change the distribution of regulated actin states. The A8V and C84Y TnC mutants decreased the inactive B state distribution slightly at low Ca2+ concentrations, but the D145E mutants had no effect on that state. All TnC mutants increased the level of the active M state compared to that of the wild type, at a saturating Ca2+ concentration. Troponin complexes that contained two mutations that stabilize the active M state, A8V TnC and Δ14 TnT, appeared to be completely in the active state in the presence of only Ca2+. Because Ca2+ gives full activation, in this situation, troponin must be capable of positioning tropomyosin in the active M state without the need for rigor myosin binding.
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Affiliation(s)
- Tamatha Baxley
- Department of Biochemistry & Molecular Biology, Brody School of Medicine at East Carolina University , Greenville, North Carolina 27858, United States
| | - Dylan Johnson
- Department of Biochemistry & Molecular Biology, Brody School of Medicine at East Carolina University , Greenville, North Carolina 27858, 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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6
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Ronca F, Raggi A. Role of troponin T and AMP deaminase in the modulation of skeletal muscle contraction. RENDICONTI LINCEI 2016. [DOI: 10.1007/s12210-016-0586-7] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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7
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Amarasinghe C, Hossain MM, Jin JP. Functional Basis of Three New Recessive Mutations of Slow Skeletal Muscle Troponin T Found in Non-Amish TNNT1 Nemaline Myopathies. Biochemistry 2016; 55:4560-7. [DOI: 10.1021/acs.biochem.6b00577] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Affiliation(s)
- Chinthaka Amarasinghe
- Department
of Physiology, Wayne State University School of Medicine, Detroit, Michigan 48201, United States
| | - M. Moazzem Hossain
- Department
of Physiology, Wayne State University School of Medicine, Detroit, Michigan 48201, United States
| | - J.-P. Jin
- Department
of Physiology, Wayne State University School of Medicine, Detroit, Michigan 48201, United States
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8
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TNNT1, TNNT2, and TNNT3: Isoform genes, regulation, and structure-function relationships. Gene 2016; 582:1-13. [PMID: 26774798 DOI: 10.1016/j.gene.2016.01.006] [Citation(s) in RCA: 135] [Impact Index Per Article: 16.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2015] [Revised: 12/31/2015] [Accepted: 01/05/2016] [Indexed: 12/18/2022]
Abstract
Troponin T (TnT) is a central player in the calcium regulation of actin thin filament function and is essential for the contraction of striated muscles. Three homologous genes have evolved in vertebrates to encode three muscle type-specific TnT isoforms: TNNT1 for slow skeletal muscle TnT, TNNT2 for cardiac muscle TnT, and TNNT3 for fast skeletal muscle TnT. Alternative splicing and posttranslational modifications confer additional structural and functional variations of TnT during development and muscle adaptation to various physiological and pathological conditions. This review focuses on the TnT isoform genes and their molecular evolution, alternative splicing, developmental regulation, structure-function relationships of TnT proteins, posttranslational modifications, and myopathic mutations and abnormal splicing. The goal is to provide a concise summary of the current knowledge and some perspectives for future research and translational applications.
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9
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Chandra V, Gollapudi SK, Chandra M. Rat cardiac troponin T mutation (F72L)-mediated impact on thin filament cooperativity is divergently modulated by α- and β-myosin heavy chain isoforms. Am J Physiol Heart Circ Physiol 2015; 309:H1260-70. [PMID: 26342069 DOI: 10.1152/ajpheart.00519.2015] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/06/2015] [Accepted: 08/31/2015] [Indexed: 11/22/2022]
Abstract
The primary causal link between disparate effects of human hypertrophic cardiomyopathy (HCM)-related mutations in troponin T (TnT) and α- and β-myosin heavy chain (MHC) isoforms on cardiac contractile phenotype remains poorly understood. Given the divergent impact of α- and β-MHC on the NH2-terminal extension (44-73 residues) of TnT, we tested if the effects of the HCM-linked mutation (TnTF70L) were differentially altered by α- and β-MHC. We hypothesized that the emergence of divergent thin filament cooperativity would lead to contrasting effects of TnTF70L on contractile function in the presence of α- and β-MHC. The rat TnT analog of the human F70L mutation (TnTF72L) or the wild-type rat TnT (TnTWT) was reconstituted into demembranated muscle fibers from normal (α-MHC) and propylthiouracil-treated (β-MHC) rat hearts to measure steady-state and dynamic contractile function. TnTF72L-mediated effects on tension, myofilament Ca(2+) sensitivity, myofilament cooperativity, rate constants of cross-bridge (XB) recruitment dynamics, and force redevelopment were divergently modulated by α- and β-MHC. TnTF72L increased the rate of XB distortion dynamics by 49% in α-MHC fibers but had no effect in β-MHC fibers; these observations suggest that TnTF72L augmented XB detachment kinetics in α-MHC, but not β-MHC, fibers. TnTF72L increased the negative impact of strained XBs on the force-bearing XBs by 39% in α-MHC fibers but had no effect in β-MHC fibers. Therefore, TnTF72L leads to contractile changes that are linked to dilated cardiomyopathy in the presence of α-MHC. On the other hand, TnTF72L leads to contractile changes that are linked to HCM in the presence of β-MHC.
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Affiliation(s)
- Vikram Chandra
- Department of Integrative Physiology and Neuroscience, Washington State University, Pullman, Washington
| | - Sampath K Gollapudi
- Department of Integrative Physiology and Neuroscience, Washington State University, Pullman, Washington
| | - Murali Chandra
- Department of Integrative Physiology and Neuroscience, Washington State University, Pullman, Washington
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10
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Chen H, Zhang J, Yu B, Li L, Shang Y. Molecular cloning, structural analysis, and tissue expression of the TNNT3 gene in Guizhou black goat. Gene 2015; 573:123-8. [PMID: 26187066 DOI: 10.1016/j.gene.2015.07.038] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2014] [Revised: 07/08/2015] [Accepted: 07/11/2015] [Indexed: 10/23/2022]
Abstract
The vertebrate fast skeletal troponin T (TNNT3) protein is an important regulatory and structural component of thin filaments in skeletal muscle, which improves meat quality traits of livestock and poultry. In this study, the troponin T isoforms from adult goat (skeletal muscle mRNA) were identified. We isolated the full-length coding sequence of the goat TNNT3 gene (GenBank: KM042888), analyzed its structure, and investigated its expression in different tissues from different aged goats (10, 30, 90, 180, and 360 days old). Real-time quantitative reverse transcription-polymerase chain reaction analyses revealed that Guizhou black goat TNNT3 was highly expressed in the biceps femoris muscle, abdominal muscle, and longissimus dorsi muscle (P<0.01), and lowly expressed in the cardiac muscle, masseter muscle, and rumen tissue (P>0.05). Western blotting confirmed that the TNNT3 protein was expressed in the muscle tissues listed above, with the highest level found in the longissimus dorsi muscle, and the lowest level in the masseter muscle. In the 10 to 360day study period the TNNT3 protein expression level was the highest when the goats were 30 days old. A peptide, ASPPPAEVPEVHEEVH that may contribute to improved goat meat tenderness was identified. This study provides an insight into the molecular structure of the vertebrate TNNT3 gene.
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Affiliation(s)
- Haolin Chen
- Guizhou Animal Husbandry and Veterinary Research Institute, 2 Laolipo Street, Nanming District, Guiyang, Guizhou 550000, China
| | - Jinhua Zhang
- Guizhou Animal Husbandry and Veterinary Research Institute, 2 Laolipo Street, Nanming District, Guiyang, Guizhou 550000, China
| | - Bo Yu
- Guizhou Animal Husbandry and Veterinary Research Institute, 2 Laolipo Street, Nanming District, Guiyang, Guizhou 550000, China
| | - Liang Li
- Guizhou Animal Husbandry and Veterinary Research Institute, 2 Laolipo Street, Nanming District, Guiyang, Guizhou 550000, China
| | - Yishun Shang
- Guizhou Animal Husbandry and Veterinary Research Institute, 2 Laolipo Street, Nanming District, Guiyang, Guizhou 550000, China.
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11
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Schlecht W, Zhou Z, Li KL, Rieck D, Ouyang Y, Dong WJ. FRET study of the structural and kinetic effects of PKC phosphomimetic cardiac troponin T mutants on thin filament regulation. Arch Biochem Biophys 2014; 550-551:1-11. [PMID: 24708997 DOI: 10.1016/j.abb.2014.03.013] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2014] [Revised: 03/27/2014] [Accepted: 03/28/2014] [Indexed: 01/31/2023]
Abstract
FRET was used to investigate the structural and kinetic effects that PKC phosphorylations exert on Ca(2+) and myosin subfragment-1 dependent conformational transitions of the cardiac thin filament. PKC phosphorylations of cTnT were mimicked by glutamate substitution. Ca(2+) and S1-induced distance changes between the central linker of cTnC and the switch region of cTnI (cTnI-Sr) were monitored in reconstituted thin filaments using steady state and time resolved FRET, while kinetics of structural transitions were determined using stopped flow. Thin filament Ca(2+) sensitivity was found to be significantly blunted by the presence of the cTnT(T204E) mutant, whereas pseudo-phosphorylation at additional sites increased the Ca(2+)-sensitivity. The rate of Ca(2+)-dissociation induced structural changes was decreased in the C-terminal end of cTnI-Sr in the presence of pseudo-phosphorylations while remaining unchanged at the N-terminal end of this region. Additionally, the distance between cTnI-Sr and cTnC was decreased significantly for the triple and quadruple phosphomimetic mutants cTnT(T195E/S199E/T204E) and cTnT(T195E/S199E/T204E/T285E), which correlated with the Ca(2+)-sensitivity increase seen in these same mutants. We conclude that significant changes in thin filament Ca(2+)-sensitivity, structure and kinetics are brought about through PKC phosphorylation of cTnT. These changes can either decrease or increase Ca(2+)-sensitivity and likely play an important role in cardiac regulation.
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Affiliation(s)
- William Schlecht
- The Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164, USA
| | - Zhiqun Zhou
- The Department of Integrated Neuroscience and Physiology, Washington State University, Pullman, WA 99164, USA
| | - King-Lun Li
- The Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164, USA
| | - Daniel Rieck
- The Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164, USA
| | - Yexin Ouyang
- The Department of Integrated Neuroscience and Physiology, Washington State University, Pullman, WA 99164, USA
| | - Wen-Ji Dong
- The Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164, USA; The Department of Integrated Neuroscience and Physiology, Washington State University, Pullman, WA 99164, USA.
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12
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Ramachandran G, Kumar M, Selvi Rani D, Annanthapur V, Calambur N, Nallari P, Kaur P. An in silico analysis of troponin I mutations in hypertrophic cardiomyopathy of Indian origin. PLoS One 2013; 8:e70704. [PMID: 23967088 PMCID: PMC3742764 DOI: 10.1371/journal.pone.0070704] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2013] [Accepted: 06/21/2013] [Indexed: 12/03/2022] Open
Abstract
Hypertrophic Cardiomyopathy (HCM) is an autosomal dominant disorder of the myocardium which is hypertrophied resulting in arrhythmias and heart failure leading to sudden cardiac death (SCD). Several sarcomeric proteins and modifier genes have been implicated in this disease. Troponin I, being a part of the Troponin complex (troponin I, troponin C, troponin T), is an important gene for sarcomeric function. Four mutations (1 novel) were identified in Indian HCM cases, namely, Pro82Ser, Arg98Gln, Arg141Gln and Arg162Gln in Troponin I protein, which are in functionally significant domains. In order to analyse the effect of the mutations on protein stability and protein-protein interactions within the Troponin complex, an in silico study was carried out. The freely available X-ray crystal structure (PDB ID: 1JIE) was used as the template to model the protein followed by loop generation and development of troponin complex for both the troponin I wild type and four mutants (NCBI ID: PRJNA194382). The structural study was carried out to determine the effect of mutation on the structural stability and protein-protein interactions between three subunits in the complex. These mutations, especially the arginine to glutamine substitutions were found to result in local perturbations within the troponin complex by creating/removing inter/intra molecular hydrogen bonds with troponin T and troponin C. This has led to a decrease in the protein stability and loss of important interactions between the three subunits. It could have a significant impact on the disease progression when coupled with allelic heterogeneity which was observed in the cases carrying these mutations. However, this can be further confirmed by functional studies on protein levels in the identified cases.
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Affiliation(s)
| | - Manoj Kumar
- Department of Biophysics, All India Institute of Medical Sciences, New Delhi, India
| | - Deepa Selvi Rani
- Centre for Cellular and Molecular Biology, Hyderabad, Andhra Pradesh, India
| | | | - Narasimhan Calambur
- Department of Cardiology, CARE Hospital, Nampally, Hyderabad, Andhra Pradesh, India
| | - Pratibha Nallari
- Department of Genetics, Osmania University, Hyderabad, Andhra Pradesh, India
- * E-mail:
| | - Punit Kaur
- Department of Biophysics, All India Institute of Medical Sciences, New Delhi, India
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13
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The tropomyosin binding region of cardiac troponin T modulates crossbridge recruitment dynamics in rat cardiac muscle fibers. J Mol Biol 2013; 425:1565-81. [PMID: 23357173 DOI: 10.1016/j.jmb.2013.01.028] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2012] [Revised: 01/15/2013] [Accepted: 01/17/2013] [Indexed: 11/22/2022]
Abstract
The cardiac muscle comprises dynamically interacting components that use allosteric/cooperative mechanisms to yield unique heart-specific properties. An essential protein in this allosteric/cooperative mechanism is cardiac muscle troponin T (cTnT), the central region (CR) and the T2 region of which differ significantly from those of fast skeletal muscle troponin T (fsTnT). To understand the biological significance of such sequence heterogeneity, we replaced the T1 or T2 domain of rat cTnT (RcT1 or RcT2) with its counterpart from rat fsTnT (RfsT1or RfsT2) to generate RfsT1-RcT2 and RcT1-RfsT2 recombinant proteins. In addition to contractile function measurements, dynamic features of RfsT1-RcT2- and RcT1-RfsT2-reconstituted rat cardiac muscle fibers were captured by fitting the recruitment-distortion model to the force response of small-amplitude (0.5%) muscle length changes. RfsT1-RcT2 fibers showed a 40% decrease in tension and a 44% decrease in ATPase activity, but RcT1-RfsT2 fibers were unaffected. The magnitude of length-mediated increase in crossbridge (XB) recruitment (E0) decreased by ~33% and the speed of XB recruitment (b) increased by ~100% in RfsT1-RcT2 fibers. Our data suggest the following: (1) the CR of cTnT modulates XB recruitment dynamics; (2) the N-terminal end region of cTnT has a synergistic effect on the ability of the CR to modulate XB recruitment dynamics; (3) the T2 region is important for tuning the Ca(2+) regulation of cardiac thin filaments. The combined effects of CR-tropomyosin interactions and the modulating effect of the N-terminal end of cTnT on CR-tropomyosin interactions may lead to the emergence of a unique property that tunes contractile dynamics to heart rates.
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Mamidi R, Mallampalli SL, Wieczorek DF, Chandra M. Identification of two new regions in the N-terminus of cardiac troponin T that have divergent effects on cardiac contractile function. J Physiol 2012. [PMID: 23207592 DOI: 10.1113/jphysiol.2012.243394] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Abstract Cardiac troponin T (cTnT) has a highly acidic extended N-terminus, the physiological role of which remains poorly understood. To decipher the physiological role of this unique region, we deleted specific regions within the N-terminus of mouse cTnT (McTnT) to create McTnT1-44 and McTnT45-74 proteins. Contractile function and dynamic force-length measurements were made after reconstituting the McTnT deletion proteins into detergent-skinned cardiac papillary fibres harvested from non-transgenic mice that expressed α-tropomyosin (Tm). To further understand how the functional effects of the N-terminus of cTnT are modulated by Tm isoforms, McTnT deletion proteins were reconstituted into detergent-skinned cardiac papillary fibres harvested from transgenic mice that expressed both α- and β-Tm. McTnT1-44, but not McTnT45-74, attenuated maximal activation of the thin filament. Myofilament Ca(2+) sensitivity, as measured by pCa50 (-log of [Ca(2+)]free required for half-maximal activation), decreased in McTnT1-44 (α-Tm) fibres. The desensitizing effect of McTnT1-44 on pCa50 was ablated in β-Tm fibres. McTnT45-74 enhanced pCa50 in both α- and β-Tm fibres, with β-Tm having a bigger effect. The Hill coefficient of tension development was significantly attenuated by McTnT45-74, suggesting an effect on thin-filament cooperativity. The rate of cross-bridge (XB) detachment and the strained XB-mediated impact on other XBs were augmented by McTnT1-44 in β-Tm fibres. The magnitude of the length-mediated recruitment of XBs was attenuated by McTnT1-44 in β-Tm fibres. Our data demonstrate that the 1-44 region of McTnT is essential for maximal activation, whereas the cardiac-specific 45-74 region of McTnT is essential for augmenting cooperativity. Moreover, our data show that α- and β-Tm isoforms have divergent effects on McTnT deletion mutant's ability to modulate cardiac thin-filament activation and Ca(2+) sensitivity. Our results not only provide the first explicit evidence for the existence of two distinct functional regions within the N-terminus of cTnT, but also offer mechanistic insights into the divergent physiological roles of these regions in mediating cardiac contractile activation.
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Affiliation(s)
- Ranganath Mamidi
- Department of Veterinary and Comparative Anatomy, Pharmacology and Physiology, Washington State University, Pullman, WA-99164, USA.
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15
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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] [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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Ohshiro K, Obinata T, Dennisson JG, Ogasawara M, Sato N. Troponin in both Smooth and Striated Muscles of Ascidian Ciona intestinalis Functions as a Ca2+-Dependent Accelerator of Actin−Myosin Interaction. Biochemistry 2010; 49:9563-71. [DOI: 10.1021/bi101295m] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Katsushi Ohshiro
- Department of Nanobiology, Graduate School of Advanced Integration Science, Chiba University, Yayoi-cho, Inage-ku, Chiba 263-8522, Japan
| | - Takashi Obinata
- Department of Nanobiology, Graduate School of Advanced Integration Science, Chiba University, Yayoi-cho, Inage-ku, Chiba 263-8522, Japan
- Department of Health and Nutrition, Teikyo-Heisei University, Higashi Ikebukuro 2-51-4, Toshima-ku, Tokyo 170-8445, Japan
| | - Jeanette G. Dennisson
- Department of Nanobiology, Graduate School of Advanced Integration Science, Chiba University, Yayoi-cho, Inage-ku, Chiba 263-8522, Japan
| | - Michio Ogasawara
- Department of Nanobiology, Graduate School of Advanced Integration Science, Chiba University, Yayoi-cho, Inage-ku, Chiba 263-8522, Japan
| | - Naruki Sato
- Department of Nanobiology, Graduate School of Advanced Integration Science, Chiba University, Yayoi-cho, Inage-ku, Chiba 263-8522, Japan
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17
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Parvatiyar MS, Pinto JR, Liang J, Potter JD. Predicting cardiomyopathic phenotypes by altering Ca2+ affinity of cardiac troponin C. J Biol Chem 2010; 285:27785-97. [PMID: 20566645 DOI: 10.1074/jbc.m110.112326] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Cardiac diseases associated with mutations in troponin subunits include hypertrophic cardiomyopathy (HCM), dilated cardiomyopathy (DCM), and restrictive cardiomyopathy (RCM). Altered calcium handling in these diseases is evidenced by changes in the Ca(2+) sensitivity of contraction. Mutations in the Ca(2+) sensor, troponin C (TnC), were generated to increase/decrease the Ca(2+) sensitivity of cardiac skinned fibers to create the characteristic effects of DCM, HCM, and RCM. We also used a reconstituted assay to determine the mutation effects on ATPase activation and inhibition. One mutant (A23Q) was found with HCM-like properties (increased Ca(2+) sensitivity of force and normal levels of ATPase inhibition). Three mutants (S37G, V44Q, and L48Q) were identified with RCM-like properties (a large increase in Ca(2+) sensitivity, partial loss of ATPase inhibition, and increased basal force). Two mutations were identified (E40A and I61Q) with DCM properties (decreased Ca(2+) sensitivity, maximal force recovery, and activation of the ATPase at high [Ca(2+)]). Steady-state fluorescence was utilized to assess Ca(2+) affinity in isolated cardiac (c)TnCs containing F27W and did not necessarily mirror the fiber Ca(2+) sensitivity. Circular dichroism of mutant cTnCs revealed a trend where increased alpha-helical content correlated with increased Ca(2+) sensitivity in skinned fibers and vice versa. The main findings from this study were as follows: 1) cTnC mutants demonstrated distinct functional phenotypes reminiscent of bona fide HCM, RCM, and DCM mutations; 2) a region in cTnC associated with increased Ca(2+) sensitivity in skinned fibers was identified; and 3) the F27W reporter mutation affected Ca(2+) sensitivity, maximal force, and ATPase activation of some mutants.
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Affiliation(s)
- Michelle S Parvatiyar
- Department of Molecular and Cellular Pharmacology, University of Miami Miller School of Medicine, Miami, Florida 33136, USA
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Stefancsik R, Randall JD, Mao C, Sarkar S. Structure and sequence of the human fast skeletal troponin T (TNNT3) gene: insight into the evolution of the gene and the origin of the developmentally regulated isoforms. Comp Funct Genomics 2010; 4:609-25. [PMID: 18629027 PMCID: PMC2447309 DOI: 10.1002/cfg.343] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2003] [Revised: 09/24/2003] [Accepted: 10/06/2003] [Indexed: 11/21/2022] Open
Abstract
We describe the cloning, sequencing and structure of the human fast skeletal troponin T (TNNT3) gene located on chromosome 11p15.5. The single-copy gene encodes 19
exons and 18 introns. Eleven of these exons, 1–3, 9–15 and 18, are constitutively
spliced, whereas exons 4–8 are alternatively spliced. The gene contains an additional
subset of developmentally regulated and alternatively spliced exons, including a foetal
exon located between exon 8 and 9 and exon 16 or α (adult) and 17 or β (foetal and
neonatal). Exon phasing suggests that the majority of the alternatively spliced exons
located at the 5′ end of the gene may have evolved as a result of exon shuffling, because
they are of the same phase class. In contrast, the 3′ exons encoding an evolutionarily
conserved heptad repeat domain, shared by both TnT and troponin I (TnI), may be
remnants of an ancient ancestral gene. The sequence of the 5′ flanking region shows
that the putative promoter contains motifs including binding sites for MyoD, MEF-2
and several transcription factors which may play a role in transcriptional regulation
and tissue-specific expression of TnT. The coding region of TNNT3 exhibits strong
similarity to the corresponding rat sequence. However, unlike the rat TnT gene,
TNNT3 possesses two repeat regions of CCA and TC. The exclusive presence of
these repetitive elements in the human gene indicates divergence in the evolutionary
dynamics of mammalian TnT genes. Homologous muscle-specific splicing enhancer
motifs are present in the introns upstream and downstream of the foetal exon, and
may play a role in the developmental pattern of alternative splicing of the gene. The
genomic correlates of TNNT3 are relevant to our understanding of the evolution and
regulation of expression of the gene, as well as the structure and function of the protein
isoforms. The nucleotide sequence of TNNT3 has been submitted to EMBL/GenBank
under Accession No. AF026276.
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Affiliation(s)
- Raymund Stefancsik
- Department of Anatomy and Cellular Biology, Tufts University, Health Science Campus, 136 Harrison Avenue, Boston, MA 02111, USA
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19
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Cardiac troponin mutations and restrictive cardiomyopathy. J Biomed Biotechnol 2010; 2010:350706. [PMID: 20617149 PMCID: PMC2896668 DOI: 10.1155/2010/350706] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2009] [Accepted: 02/22/2010] [Indexed: 11/19/2022] Open
Abstract
Mutations in sarcomeric proteins have recently been established as heritable causes of Restrictive Cardiomyopathy (RCM). RCM is clinically characterized as a defect in cardiac diastolic function, such as, impaired ventricular relaxation, reduced diastolic volume and increased end-diastolic pressure. To date, mutations have been identified in the cardiac genes for desmin, α-actin, troponin I and troponin T. Functional studies in skinned muscle fibers reconstituted with troponin mutants have established phenotypes consistent with the clinical findings which include an increase in myofilament Ca2+ sensitivity and basal force. Moreover, when RCM mutants are incorporated into reconstituted myofilaments, the ability to inhibit the ATPase activity is reduced. A majority of the mutations cluster in specific regions of cardiac troponin and appear to be mutational “hot spots”. This paper highlights the functional and clinical characteristics of RCM linked mutations within the troponin complex.
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20
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Boda U, Vadapalli S, Calambur N, Nallari P. Novel mutations in beta-myosin heavy chain, actin and troponin-I genes associated with dilated cardiomyopathy in Indian population. J Genet 2010; 88:373-7. [PMID: 20086309 DOI: 10.1007/s12041-009-0057-3] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Affiliation(s)
- Ushasree Boda
- Department of Genetics, Osmania University, Hyderabad 500 001, India
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21
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Kobayashi T, Patrick SE, Kobayashi M. Ala scanning of the inhibitory region of cardiac troponin I. J Biol Chem 2009; 284:20052-60. [PMID: 19483081 DOI: 10.1074/jbc.m109.001396] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In skeletal and cardiac muscles, troponin (Tn), which resides on the thin filament, senses a change in intracellular Ca(2+) concentration. Tn is composed of TnC, TnI, and TnT. Ca(2+) binding to the regulatory domain of TnC removes the inhibitory effect by TnI on the contraction. The inhibitory region of cardiac TnI spans from residue 138 to 149. Upon Ca(2+) activation, the inhibitory region is believed to be released from actin, thus triggering actin-activation of myosin ATPase. In this study, we created a series of Ala-substitution mutants of cTnI to delineate the functional contribution of each amino acid in the inhibitory region to myofilament regulation. We found that most of the point mutations in the inhibitory region reduced the ATPase activity in the presence of Ca(2+), which suggests the same region also acts as an activator of the ATPase. The thin filaments can also be activated by strong myosin head (S1)-actin interactions. The binding of N-ethylmaleimide-treated myosin subfragment 1 (NEM-S1) to actin filaments mimics such strong interactions. Interestingly, in the absence of Ca(2+) NEM-S1-induced activation of S1 ATPase was significantly less with the thin filaments containing TnI(T144A) than that with the wild-type TnI. However, in the presence of Ca(2+), there was little difference in the activation of ATPase activity between these preparations.
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Affiliation(s)
- Tomoyoshi Kobayashi
- Department of Physiology and Biophysics and the Center for Cardiovascular Research, University of Illinois at Chicago, Chicago, Illinois 60612, USA.
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22
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Tanaka H, Suzuki H, Ohtsuki I, Ojima T. Structure-function relationships of molluscan troponin T revealed by limited proteolysis. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2008; 1784:1037-42. [PMID: 18454947 DOI: 10.1016/j.bbapap.2008.04.001] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/14/2007] [Revised: 03/17/2008] [Accepted: 04/01/2008] [Indexed: 10/22/2022]
Abstract
Molluscan troponin regulates muscle contraction through a novel Ca(2+)-dependent activating mechanism associated with Ca(2+)-binding to the C-terminal domain of troponin C. To elucidate the further details of this regulation, we performed limited chymotryptic digestion of the troponin complex from akazara scallop striated muscle. The results indicated that troponin T is very susceptible to the protease, compared to troponin C or troponin I. The cleavage occurred at the C-terminal extension, producing an N-terminal 33-kDa fragment and a C-terminal 6-kDa fragment. This extension is conserved in various invertebrate troponin T proteins, but not in vertebrate troponin T. A ternary complex composed of the 33-kDa fragment of troponin T, troponin I, and troponin C could be separated from the 6-kDa troponin T fragment by gel filtration. This complex did not show any Ca(2+)-dependent activation of the Mg-ATPase activity of rabbit-actomyosin-scallop-tropomyosin. In addition, the actin-tropomyosin-binding affinity of this complex was significantly decreased with increasing Ca(2+) concentration. These results indicate that the C-terminal extension of molluscan troponin T plays a role in anchoring the troponin complex to actin-tropomyosin filaments and is essential for regulation.
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Affiliation(s)
- Hiroyuki Tanaka
- Laboratory of Marine Biotechnology and Microbiology, Graduate School of Fisheries Sciences, Hokkaido University, Japan
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23
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Coulton AT, Koka K, Lehrer SS, Geeves MA. Role of the Head-to-Tail Overlap Region in Smooth and Skeletal Muscle β-Tropomyosin. Biochemistry 2007; 47:388-97. [DOI: 10.1021/bi701144g] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Affiliation(s)
- Arthur T. Coulton
- Department of Biosciences, University of Kent, Canterbury CT2 7NY, U.K., and Cardiovascular Program, Boston Biomedical Research Institute, Watertown, Massachusetts 02472-2829
| | - Kezia Koka
- Department of Biosciences, University of Kent, Canterbury CT2 7NY, U.K., and Cardiovascular Program, Boston Biomedical Research Institute, Watertown, Massachusetts 02472-2829
| | - Sherwin S. Lehrer
- Department of Biosciences, University of Kent, Canterbury CT2 7NY, U.K., and Cardiovascular Program, Boston Biomedical Research Institute, Watertown, Massachusetts 02472-2829
| | - Michael A. Geeves
- Department of Biosciences, University of Kent, Canterbury CT2 7NY, U.K., and Cardiovascular Program, Boston Biomedical Research Institute, Watertown, Massachusetts 02472-2829
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Murakami K, Yumoto F, Ohki SY, Yasunaga T, Tanokura M, Wakabayashi T. Structural basis for calcium-regulated relaxation of striated muscles at interaction sites of troponin with actin and tropomyosin. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2007; 592:71-86. [PMID: 17278357 DOI: 10.1007/978-4-431-38453-3_8] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
In summary, we have shown that the TnI-TnC-TnT2 ternary complex (-52 kDa) has a mobile actin-binding domain (-6.1 kDa) that tumbles independently of the core domain. By docking the mobile domain and the core domain into the cryo-EM map obtained for thin filaments at low Ca2+, a model for actin-troponin interaction has been obtained. This model shows the atomic details of interactions of actin with the mobile domain and suggests the mechanism by which troponin generates a shift in the azimuthal position of tropomyosin in response to changes in Ca2+ levels. In this model the mobile domain of troponin interacts with three actins and one troponin interacts with four actin molecules. The relationship between myosin and the mobile domain suggests that the latter may work as a fail-safe latch to secure a relaxed state. The model also provides insights into many mutations associated with human cardiomyopathy and has implications for the function of other actin-binding proteins. Coordinates of the mobile domain have been deposited in the Protein Data Bank under accession codes 1VDI (low Ca2+) and 1VDJ (high Ca2+). Chemical shifts of the mobile domain have been deposited in the BMRB under accession ID 18140.
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Affiliation(s)
- Kenji Murakami
- Department of Biosciences, School of Science and Engineering, Teikyo University, Toyosatodai 1-1, Utsunomiya 320-8551, Japan
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25
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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. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 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] [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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26
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Frey N, Brixius K, Schwinger RHG, Benis T, Karpowski A, Lorenzen HP, Luedde M, Katus HA, Franz WM. Alterations of tension-dependent ATP utilization in a transgenic rat model of hypertrophic cardiomyopathy. J Biol Chem 2006; 281:29575-82. [PMID: 16882671 DOI: 10.1074/jbc.m507740200] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Although it is established that familial hypertrophic cardiomyopathy (FHC) is caused by mutations in several sarcomeric proteins, including cardiac troponin T (TnT), its pathogenesis is still not completely understood. Previously, we established a transgenic rat model of FHC expressing a human TnT molecule with a truncation mutation (DEL-TnT). This study investigated whether contractile dysfunction and electrical vulnerability observed in DEL-TnT rats might be due to alterations of intracellular Ca(2+) homeostasis, myofibrillar Ca(2+) sensitivity, and/or myofibrillar ATP utilization. Simultaneous measurements of the force of contraction and intracellular Ca(2+) transients were performed in right ventricular trabeculae of DEL-TnT hearts at 0.25 and 1.0 Hz. Rats expressing wild-type human TnT as well as nontransgenic rats served as controls. In addition, calcium-dependent ATPase activity and tension development were investigated in skinned cardiac muscle fibers. Force of contraction was significantly decreased in DEL-TnT compared with nontransgenic rats and TnT. Time parameters of Ca(2+) transients were unchanged at 0.25 Hz but prolonged at 1.0 Hz in DEL-TnT. The amplitude of the fura-2 transient was similar in all groups investigated, whereas diastolic and systolic fura-2 ratios were found elevated in rats expressing nontruncated human troponin T. In DEL-TnT rats, myofibrillar Ca(2+)-dependent tension development as well as Ca(2+) sensitivity of tension were significantly decreased, whereas tension-dependent ATP consumption ("tension cost") was markedly increased. Thus, a C-terminal truncation of the cardiac TnT molecule impairs the force-generating capacity of the cycling cross-bridges resulting in increased tension-dependent ATP utilization. Taken together, our data support the hypothesis of energy compromise as a contributing factor in the pathogenesis of FHC.
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Affiliation(s)
- Norbert Frey
- Department of Medicine III, University of Heidelberg, 69120 Heidelberg, Germany.
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27
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Gallon CE, Tschirgi ML, Chandra M. Differences in myofilament calcium sensitivity in rat psoas fibers reconstituted with troponin T isoforms containing the alpha- and beta-exons. Arch Biochem Biophys 2006; 456:127-34. [PMID: 16839517 DOI: 10.1016/j.abb.2006.06.008] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2006] [Revised: 04/19/2006] [Accepted: 06/08/2006] [Indexed: 11/25/2022]
Abstract
The carboxy terminus of fast skeletal muscle troponin T (fsTnT) is highly conserved. However, mutually exclusive splicing of exons 16 and 17 in the fsTnT gene results in the expression of either the alpha- or beta-fsTnT isoform. The alpha-isoform is expressed only in adult fast skeletal muscle, whereas the beta-isoform is expressed in varying quantities throughout muscle development. Reconstitution of detergent-skinned adult rat psoas muscle fibers with rat fast skeletal troponin complexes containing either fsTnT isoform demonstrated that reconstitution with alpha-fsTnT resulted in greater myofilament Ca(2+) sensitivity than reconstitution with beta-fsTnT, without changes to Ca(2+)-activated maximal tension, ATPase activity or tension cost. The observed isoform-specific differences in myofilament Ca(2+) sensitivity may be due to changes in the transition of the thin-filament regulatory unit from the off to the on state, possibly due to altered interactions of the C-terminus of fsTnT with troponins I and/or C.
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Affiliation(s)
- Clare E Gallon
- Department of Veterinary Comparative Anatomy, Pharmacology and Physiology, Washington State University, Pullman, WA 99164-6520, USA
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28
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Mizuno H, Honda H. Troponin Is a Potential Regulator for Actomyosin Interactions. ACTA ACUST UNITED AC 2006; 139:289-93. [PMID: 16452317 DOI: 10.1093/jb/mvj030] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
Abstract
Troponin extracted from rabbit skeletal muscle directly binds to an actin filament in a molar ratio of 1:1 even in the absence of tropomyosin. An actin filament decorated with troponin did not exhibit significant difference from pure actin filaments in the maximum rate of actomyosin ATP hydrolysis and the sliding velocity of the filament examined by means of an in vitro motility assay. However, the relative number of troponin-bound actin filaments moving in the absence of calcium ions decreased to half that in their presence. The amount of HMM bound to the filaments was less than 4% of actin monomers in the presence of TNs. In addition, actin filaments could not move when Tn molecules were bound in the molar ratio of about 1:1 although they sufficiently bind to myosin heads. These results indicate that troponin can transform an actin monomer within a filament into an Off-state without sterically blocking of the myosin-binding sites with tropomyosin molecules.
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Affiliation(s)
- Hiroaki Mizuno
- Department of BioEngineering, Nagaoka University of Technology, Nagaoka, Niigata, 940-2188, Japan
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Murakami K, Yumoto F, Ohki SY, Yasunaga T, Tanokura M, Wakabayashi T. Structural basis for Ca2+-regulated muscle relaxation at interaction sites of troponin with actin and tropomyosin. J Mol Biol 2005; 352:178-201. [PMID: 16061251 DOI: 10.1016/j.jmb.2005.06.067] [Citation(s) in RCA: 96] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2005] [Revised: 06/17/2005] [Accepted: 06/29/2005] [Indexed: 10/25/2022]
Abstract
Troponin and tropomyosin on actin filaments constitute a Ca2+-sensitive switch that regulates the contraction of vertebrate striated muscle through a series of conformational changes within the actin-based thin filament. Troponin consists of three subunits: an inhibitory subunit (TnI), a Ca2+-binding subunit (TnC), and a tropomyosin-binding subunit (TnT). Ca2+-binding to TnC is believed to weaken interactions between troponin and actin, and triggers a large conformational change of the troponin complex. However, the atomic details of the actin-binding sites of troponin have not been determined. Ternary troponin complexes have been reconstituted from recombinant chicken skeletal TnI, TnC, and TnT2 (the C-terminal region of TnT), among which only TnI was uniformly labelled with 15N and/or 13C. By applying NMR spectroscopy, the solution structures of a "mobile" actin-binding domain (approximately 6.1 kDa) in the troponin ternary complex (approximately 52 kDa) were determined. The mobile domain appears to tumble independently of the core domain of troponin. Ca2+-induced changes in the chemical shift and line shape suggested that its tumbling was more restricted at high Ca2+ concentrations. The atomic details of interactions between actin and the mobile domain of troponin were defined by docking the mobile domain into the cryo-electron microscopy (cryo-EM) density map of thin filament at low [Ca2+]. This allowed the determination of the 3D position of residue 133 of TnI, which has been an important landmark to incorporate the available information. This enabled unique docking of the entire globular head region of troponin into the thin filament cryo-EM map at a low Ca2+ concentration. The resultant atomic model suggests that troponin interacted electrostatically with actin and caused the shift of tropomyosin to achieve muscle relaxation. An important feature is that the coiled-coil region of troponin pushed tropomyosin at a low Ca2+ concentration. Moreover, the relationship between myosin and the mobile domain on actin filaments suggests that the latter works as a fail-safe latch.
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Affiliation(s)
- Kenji Murakami
- Department of Biosciences, School of Science and Engineering, Teikyo University, Toyosatodai 1-1, Utsunomiya 320-8551, Japan
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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] [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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31
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Tanaka H, Takeya Y, Doi T, Yumoto F, Tanokura M, Ohtsuki I, Nishita K, Ojima T. Comparative studies on the functional roles of N- and C-terminal regions of molluskan and vertebrate troponin-I. FEBS J 2005; 272:4475-86. [PMID: 16128816 DOI: 10.1111/j.1742-4658.2005.04866.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Vertebrate troponin regulates muscle contraction through alternative binding of the C-terminal region of the inhibitory subunit, troponin-I (TnI), to actin or troponin-C (TnC) in a Ca(2+)-dependent manner. To elucidate the molecular mechanisms of this regulation by molluskan troponin, we compared the functional properties of the recombinant fragments of Akazara scallop TnI and rabbit fast skeletal TnI. The C-terminal fragment of Akazara scallop TnI (ATnI(232-292)), which contains the inhibitory region (residues 104-115 of rabbit TnI) and the regulatory TnC-binding site (residues 116-131), bound actin-tropomyosin and inhibited actomyosin-tropomyosin Mg-ATPase. However, it did not interact with TnC, even in the presence of Ca(2+). These results indicated that the mechanism involved in the alternative binding of this region was not observed in molluskan troponin. On the other hand, ATnI(130-252), which contains the structural TnC-binding site (residues 1-30 of rabbit TnI) and the inhibitory region, bound strongly to both actin and TnC. Moreover, the ternary complex consisting of this fragment, troponin-T, and TnC activated the ATPase in a Ca(2+)-dependent manner almost as effectively as intact Akazara scallop troponin. Therefore, Akazara scallop troponin regulates the contraction through the activating mechanisms that involve the region spanning from the structural TnC-binding site to the inhibitory region of TnI. Together with the observation that corresponding rabbit TnI-fragment (RTnI(1-116)) shows similar activating effects, these findings suggest the importance of the TnI N-terminal region not only for maintaining the structural integrity of troponin complex but also for Ca(2+)-dependent activation.
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Affiliation(s)
- Hiroyuki Tanaka
- Laboratory of Biotechnology and Microbiology, Graduate School of Fisheries Sciences, Hokkaido University, Japan
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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] [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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Blumenschein TMA, Stone DB, Fletterick RJ, Mendelson RA, Sykes BD. Calcium-dependent Changes in the Flexibility of the Regulatory Domain of Troponin C in the Troponin Complex. J Biol Chem 2005; 280:21924-32. [PMID: 15826946 DOI: 10.1074/jbc.m500574200] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
With the recent advances in structure determination of the troponin complex, it becomes even more important to understand the dynamics of its components and how they are affected by the presence or absence of Ca(2+). We used NMR techniques to study the backbone dynamics of skeletal troponin C (TnC) in the complex. Transverse relaxation-optimized spectroscopy pulse sequences and deuteration of TnC were essential to assign most of the TnC residues in the complex. Backbone amide (15)N relaxation times were measured in the presence of Ca(2+) or EGTA/Mg(2+). T(1) relaxation times could not be interpreted precisely, because for a molecule of this size, the longitudinal backbone amide (15)N relaxation rate due to chemical shift anisotropy and dipole-dipole interactions becomes too small, and other relaxation mechanisms become relevant. T(2) relaxation times were of the expected magnitude for a complex of this size, and most of the variation of T(2) times in the presence of Ca(2+) could be explained by the anisotropy of the complex, suggesting a relatively rigid molecule. The only exception was EF-hand site III and helix F immediately after, which are more flexible than the rest of the molecule. In the presence of EGTA/Mg(2+), relaxation times for residues in the C-domain of TnC are very similar to values in the presence of Ca(2+), whereas the N-domain becomes more flexible. Taken together with the high flexibility of the linker between the two domains, we concluded that in the absence of Ca(2+), the N-domain of TnC moves independently from the rest of the complex.
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Affiliation(s)
- Tharin M A Blumenschein
- Canadian Institutes of Health Research Group in Structure and Function and Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
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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] [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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Venkatraman G, Gomes AV, Kerrick WGL, Potter JD. Characterization of Troponin T Dilated Cardiomyopathy Mutations in the Fetal Troponin Isoform. J Biol Chem 2005; 280:17584-92. [PMID: 15623536 DOI: 10.1074/jbc.m409337200] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The major goal of this study was to elucidate how troponin T (TnT) dilated cardiomyopathy (DCM) mutations in fetal TnT and fetal troponin affect the functional properties of the fetal heart that lead to infantile cardiomyopathy. The DCM mutations R141W and DeltaK210 were created in the TnT1 isoform, the primary isoform of cardiac TnT in the embryonic heart. In addition to a different TnT isoform, a different troponin I (TnI) isoform, slow skeletal TnI (ssTnI), is the dominant isoform in the embryonic heart. In skinned fiber studies, TnT1-wild-type (WT)-treated fibers reconstituted with cardiac TnI.troponin C (TnC) or ssTnI.TnC significantly increased Ca(2+) sensitivity of force development when compared with TnT3-WT-treated fibers at both pH 7.0 and pH 6.5. Porcine cardiac fibers treated with TnT1 that contained the DCM mutations (R141W and DeltaK210), when reconstituted with either cardiac TnI.TnC or ssTnI.TnC, significantly decreased Ca(2+) sensitivity of force development compared with TnT1-WT at both pH values. The R141W mutation, which showed no significant change in the Ca(2+) sensitivity of force development in the TnT3 isoform, caused a significant decrease in the TnT1 isoform. The DeltaK210 mutation caused a greater decrease in Ca(2+) sensitivity and maximal isometric force development compared with the R141W mutation in both the fetal and adult TnT isoforms. When complexed with cardiac TnI.TnC or ssTnI.TnC, both TnT1 DCM mutations strongly decreased maximal actomyosin ATPase activity as compared with TnT1-WT. Our results suggest that a decrease in maximal actomyosin ATPase activity in conjunction with decreased Ca(2+) sensitivity of force development may cause a severe DCM phenotype in infants with the mutations.
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Affiliation(s)
- Gayathri Venkatraman
- Department of Molecular and Cellular Pharmacology and Physiology and Biophysics, University of Miami School of Medicine, Miami, Florida 33101, USA
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Li MX, Wang X, Sykes BD. Structural based insights into the role of troponin in cardiac muscle pathophysiology. J Muscle Res Cell Motil 2005; 25:559-79. [PMID: 15711886 DOI: 10.1007/s10974-004-5879-2] [Citation(s) in RCA: 117] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2004] [Accepted: 10/25/2004] [Indexed: 10/25/2022]
Abstract
Troponin is a molecular switch, directly regulating the Ca2+-dependent activation of myofilament in striated muscle contraction. Cardiac troponin is subject to covalent and noncovalent modifications; phosphorylation modulates myofilament physiology, mutations are linked to familial hypertrophic cardiomyopathy, intracellular acidification causes myocardial infarction, and cardiotonic drugs modify myofilament response to Ca2+. The structure of troponin provides insights into the mechanism of this molecular switch and an understanding of the effects of protein modification under pathophysiological conditions. Although the structure of troponin C has been solved in various Ca2+-bound states for some time, structural information on troponin I and troponin T has only emerged recently. This review summarizes recent advances on the structure of complexes of troponin subunits with the aim of assessing how these proteins interact with each other to execute its role as a molecular switch and how covalent and noncovalent modifications affect the structure of troponin and the switch mechanism. We focus on pinpointing the specific amino acid residues involved in phosphorylation and mutation and the pH sensitive regions in the structure of troponin. We also present recent structural work that have identified the docking sites of several cardiotonic drugs on cardiac troponin C and discuss their relevance in the direction of troponin based drug design in the therapy of heart disease.
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Affiliation(s)
- Monica X Li
- CIHR Group in Protein Structure and Function, Department of Biochemistry, University of Alberta, Edmonton, Alberta, T6G 2H7, Canada
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King WA, Stone DB, Timmins PA, Narayanan T, von Brasch AAM, Mendelson RA, Curmi PMG. Solution Structure of the Chicken Skeletal Muscle Troponin Complex Via Small-angle Neutron and X-ray Scattering. J Mol Biol 2005; 345:797-815. [PMID: 15588827 DOI: 10.1016/j.jmb.2004.10.090] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2004] [Revised: 10/29/2004] [Accepted: 10/29/2004] [Indexed: 10/26/2022]
Abstract
Troponin is a Ca2+-sensitive switch that regulates the contraction of vertebrate striated muscle by participating in a series of conformational events within the actin-based thin filament. Troponin is a heterotrimeric complex consisting of a Ca2+-binding subunit (TnC), an inhibitory subunit (TnI), and a tropomyosin-binding subunit (TnT). Ternary troponin complexes have been produced by assembling recombinant chicken skeletal muscle TnC, TnI and the C-terminal portion of TnT known as TnT2. A full set of small-angle neutron scattering data has been collected from TnC-TnI-TnT2 ternary complexes, in which all possible combinations of the subunits have been deuterated, in both the +Ca2+ and -Ca2+ states. Small-angle X-ray scattering data were also collected from the same troponin TnC-TnI-TnT2 complex. Guinier analysis shows that the complex is monomeric in solution and that there is a large change in the radius of gyration of TnI when it goes from the +Ca2+ to the -Ca2+ state. Starting with a model based on the human cardiac troponin crystal structure, a rigid-body Monte Carlo optimization procedure was used to yield models of chicken skeletal muscle troponin, in solution, in the presence and in the absence of regulatory calcium. The optimization was carried out simultaneously against all of the scattering data sets. The optimized models show significant differences when compared to the cardiac troponin crystal structure in the +Ca2+ state and provide a structural model for the switch between +Ca2+ and -Ca2+ states. A key feature is that TnC adopts a dumbbell conformation in both the +Ca2+ and -Ca2+ states. More importantly, the data for the -Ca2+ state suggest a long extension of the troponin IT arm, consisting mainly of TnI. Thus, the troponin complex undergoes a large structural change triggered by Ca2+ binding.
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Affiliation(s)
- William A King
- School of Physics, University of New South Wales, Sydney NSW 2052, Australia
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Gafurov B, Fredricksen S, Cai A, Brenner B, Chase PB, Chalovich JM. The Delta 14 mutation of human cardiac troponin T enhances ATPase activity and alters the cooperative binding of S1-ADP to regulated actin. Biochemistry 2004; 43:15276-85. [PMID: 15568820 PMCID: PMC1351011 DOI: 10.1021/bi048646h] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The complex of tropomyosin and troponin binds to actin and inhibits activation of myosin ATPase activity and force production of striated muscles at low free Ca(2+) concentrations. Ca(2+) stimulates ATP activity, and at subsaturating actin concentrations, the binding of NEM-modified S1 to actin-tropomyosin-troponin increases the rate of ATP hydrolysis even further. We show here that the Delta14 mutation of troponin T, associated with familial hypertrophic cardiomyopathy, results in an increase in ATPase rate like that seen with wild-type troponin in the presence of NEM-S1. The enhanced ATPase activity was not due to a decreased incorporation of mutant troponin T with troponin I and troponin C to form an active troponin complex. The activating effect was more prominent with a hybrid troponin (skeletal TnI, TnC, and cardiac TnT) than with all cardiac troponin. Thus it appears that changes in the troponin-troponin contacts that result from mutations or from forming hybrids stabilize a more active state of regulated actin. An analysis of the effect of the Delta14 mutation on the equilibrium binding of S1-ADP to actin was consistent with stabilization of an active state of actin. This change in activation may be important in the development of cardiac disease.
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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] [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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Burkeen AK, Maday SL, Rybicka KK, Sulcove JA, Ward J, Huang MM, Barstead R, Franzini-Armstrong C, Allen TS. Disruption of Caenorhabditis elegans muscle structure and function caused by mutation of troponin I. Biophys J 2004; 86:991-1001. [PMID: 14747334 PMCID: PMC1303946 DOI: 10.1016/s0006-3495(04)74174-0] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
Caenorhabditis elegans strains mutant for the unc-27 gene show abnormal locomotion and muscle structure. Experiments revealed that unc-27 is one of four C. elegans troponin I genes and that three mutant alleles truncate the protein: recessive and presumed null allele e155 terminates after nine codons; semidominant su142sd eliminates the inhibitory and C-terminal regions; and semidominant su195sd abbreviates the extreme C-terminus. Assays of in vivo muscular performance at high and low loads indicated that su142sd is most deleterious, with e155 least and su195sd intermediate. Microscopy revealed in mutant muscle a prevalent disorder of dense body positioning and a less well defined sarcomeric structure, with small islands of thin filaments interspersed within the overlap region of A bands and even within the H zone. The mutants' rigid paralysis and sarcomeric disarray are consistent with unregulated contraction of the sarcomeres, in which small portions of each myofibril shorten irregularly and independently of one another, thereby distorting the disposition of filaments. The exacerbated deficits of su142sd worms are compatible with involvement in vivo of the N-terminal portion of troponin I in enhancing force production, and the severe impairment associated with su195sd highlights importance of the extreme C-terminus in the protein's inhibitory function.
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Affiliation(s)
- A K Burkeen
- Biology Department, Oberlin College, Oberlin, Ohio 44074-1097, USA
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Stefanelli CB, Rosenthal A, Borisov AB, Ensing GJ, Russell MW. Novel troponin T mutation in familial dilated cardiomyopathy with gender-dependant severity. Mol Genet Metab 2004; 83:188-96. [PMID: 15464434 DOI: 10.1016/j.ymgme.2004.04.013] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/24/2004] [Revised: 04/27/2004] [Accepted: 04/27/2004] [Indexed: 10/26/2022]
Abstract
Mutations in sarcomeric proteins can lead to either hypertrophic or dilated cardiomyopathy depending on their effects on the structural and functional properties of the contractile unit of the heart. Mutations in cardiac troponin T, which binds the calcium-responsive troponin complex to alpha-tropomyosin, have been shown to result in cardiac hypertrophy or cardiac dilatation and heart failure, depending on the nature of the specific mutation. In this study, we report the identification of a novel cardiac troponin T mutation (A171S) leading to dilated cardiomyopathy and sudden cardiac death. In contrast to prior described mutations, the A171S mutation results in a significant gender difference in the severity of the observed phenotype with adult males (over 20 years of age) demonstrating more severe ventricular dilatation [left ventricular end diastolic dimension (LVEDD) 7.1 vs. 5.1cm; P=0.01, t test] and left ventricular dysfunction [left ventricular shortening fraction (LVSF) 21 vs. 34%; P=0.04, t test] than adult females. The described mutation substitutes a hydrophilic amino acid for a hydrophobic one in a highly conserved domain involved in the interaction between troponin T and alpha-tropomyosin. Interestingly, four previously described mutations within 12 amino acids of A171 lead to a hypertrophic phenotype, suggesting that further characterization of the functional consequences of the A171S mutation may lead to a better understanding of the pathophysiology of DCM and of the functional differences between HCM- and DCM-causing mutations in cardiac troponin T.
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Affiliation(s)
- Christopher B Stefanelli
- Department of Pediatrics and Communicable Diseases, Division of Pediatric Cardiology, University of Michigan, Ann Arbor, MI 48109, USA
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42
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Stelzer JE, Patel JR, Olsson MC, Fitzsimons DP, Leinwand LA, Moss RL. Expression of cardiac troponin T with COOH-terminal truncation accelerates cross-bridge interaction kinetics in mouse myocardium. Am J Physiol Heart Circ Physiol 2004; 287:H1756-61. [PMID: 15165990 DOI: 10.1152/ajpheart.00172.2004] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Transgenic mice expressing an allele of cardiac troponin T (cTnT) with a COOH-terminal truncation (cTnT(trunc)) exhibit severe diastolic and mild systolic dysfunction. We tested the hypothesis that contractile dysfunction in myocardium expressing low levels of cTnT(trunc) (i.e., <5%) is due to slowed cross-bridge kinetics and reduced thin filament activation as a consequence of reduced cross-bridge binding. We measured the Ca(2+) sensitivity of force development [pCa for half-maximal tension generation (pCa(50))] and the rate constant of force redevelopment (k(tr)) in cTnT(trunc) and wild-type (WT) skinned myocardium both in the absence and in the presence of a strong-binding, non-force-generating derivative of myosin subfragment-1 (NEM-S1). Compared with WT mice, cTnT(trunc) mice exhibited greater pCa(50), reduced steepness of the force-pCa relationship [Hill coefficient (n(H))], and faster k(tr) at submaximal Ca(2+) concentration ([Ca(2+)]), i.e., reduced activation dependence of k(tr). Treatment with NEM-S1 elicited similar increases in pCa(50) and similar reductions in n(H) in WT and cTnT(trunc) myocardium but elicited greater increases in k(tr) at submaximal activation in cTnT(trunc) myocardium. Contrary to our initial hypothesis, cTnT(trunc) appears to enhance thin filament activation in myocardium, which is manifested as significant increases in Ca(2+)-activated force and the rate of cross-bridge attachment at submaximal [Ca(2+)]. Although these mechanisms would not be expected to depress systolic function per se in cTnT(trunc) hearts, they would account for slowed rates of myocardial relaxation during early diastole.
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Affiliation(s)
- Julian E Stelzer
- Dept. of Physiology, University of Wisconsin School of Medicine, 1300 University Avenue, Madison, WI 53706, USA.
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43
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Holthauzen LMF, Corrêa F, Farah CS. Ca2+-induced Rolling of Tropomyosin in Muscle Thin Filaments. J Biol Chem 2004; 279:15204-13. [PMID: 14724287 DOI: 10.1074/jbc.m308904200] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Tropomyosin is a filamentous coiled-coil protein directly involved in the regulation of the actomyosin interaction responsible for muscle contraction: it transmits the local calcium-induced conformational change in troponin to the helical array of myosin-binding sites on the surface of the actin filament. McLachlan and Stewart (McLachlan, A. D., and Stewart, M. (1976) J. Mol. Biol. 103, 271-298) proposed that the tropomyosin coiled-coil structure can be divided into 14 alternating 19- to 20-residue "alpha- and beta-bands," which could act as alternate 7-fold sets of sites for specific binding to actin in the different conformational states of the regulated thin filament. Here we present the first direct experimental evidence in support of the alpha- and beta-band hypothesis: we analyze the acrylamide quenching of the fluorescence of mutant tropomyosins containing 5-hydroxytryptophan residues at different positions along the coiled-coil structure under a variety of conditions (alone, complexed with actin, and complexed with actin and troponin with or without Ca(2+)). We show that fluorescent probes placed in the alpha-bands become less solvent-exposed in the absence of calcium, whereas those in the beta-bands become less solvent-exposed in the presence of calcium. A model in which the tropomyosin coiled-coil rolls across the actin surface in response to Ca(2+)-binding to troponin most easily explains these observations.
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Affiliation(s)
- Luis M F Holthauzen
- Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, Av. Prof. Lineu Prestes 748, CEP 05508-900, São Paulo, SP, Brazil.
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44
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Sumandea MP, Pyle WG, Kobayashi T, de Tombe PP, Solaro RJ. Identification of a functionally critical protein kinase C phosphorylation residue of cardiac troponin T. J Biol Chem 2003; 278:35135-44. [PMID: 12832403 DOI: 10.1074/jbc.m306325200] [Citation(s) in RCA: 155] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Cardiac Troponin T (cTnT) is one prominent substrate through which protein kinase C (PKC) exerts its effect on cardiomyocyte function. To determine the specific functional effects of the cTnT PKC-dependent phosphorylation sites (Thr197, Ser201, Thr206, and Thr287) we first mutated these residues to glutamate (E) or alanine (A). cTnT was selectively mutated to generate single, double, triple, and quadruple mutants. Bacterially expressed mutants were evaluated in detergent-treated mouse left ventricular papillary muscle fiber bundles where the endogenous troponin was replaced with a recombinant troponin complex containing either cTnT phosphorylated by PKC-alpha or a mutant cTnT. We simultaneously determined isometric tension development and actomyosin Mg-ATPase activity of the exchanged fiber bundles as a function of Ca2+ concentration. Our systematic analysis of the functional role of the multiple PKC phosphorylation sites on cTnT identified a localized region that controls maximum tension, ATPase activity, and Ca2+ sensitivity of the myofilaments. An important and novel finding of our study was that Thr206 is a functionally critical cTnT PKC phosphorylation residue. Its exclusive phosphorylation by PKC-alpha or replacement by Glu (mimicking phosphorylation) significantly decreased maximum tension, actomyosin Mg-ATPase activity, myofilament Ca2+ sensitivity, and cooperativity. On the other hand the charge modification of the other three residues together (T197/S201/T287-E) had no functional effect. Fibers bundles containing phosphorylated cTnT-wt (but not the T197/S201/T206/T287-E) exhibited a significant decrease of tension cost as compared with cTnT-wt.
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Affiliation(s)
- Marius P Sumandea
- Department of Physiology and Biophysics, Program in Cardiovascular Sciences, College of Medicine, University of Illinois at Chicago, Chicago, Illinois 60612, USA
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Liou YM, Chen MW. Calcium-dependent protein-protein interactions induce changes in proximity relationships of Cys48 and Cys64 in chicken skeletal troponin I. EUROPEAN JOURNAL OF BIOCHEMISTRY 2003; 270:3092-100. [PMID: 12846843 DOI: 10.1046/j.1432-1033.2003.03700.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The goal of this study was to relate conformational changes in the N-terminal domain of chicken troponin I (TnI) to Ca2+ activation of the actin-myosin interaction. The two cysteine residues in this region (Cys48 and Cys64) were labeled with two sulfhydryl-reactive pyrene-containing fluorophores [N-(1-pyrene)maleimide, and N-(1-pyrene)iodoacetamide]. The labeled TnI showed a typical fluorescence spectrum: two sharp peaks of monomer fluorescence and a broad peak of excimer fluorescence arising from the formation of an excited dimer (excimer). Results obtained show that forming a binary complex of labeled TnI with skeletal TnC (sTnC) in the absence of Ca2+ decreases the excimer fluorescence, indicating a separation of the two residues. This reduction in excimer fluorescence does not occur when labeled TnI is complexed with cardiac TnC (cTnC). The latter causes only partial activation of the Ca2+-dependent myofibrillar ATPase. The binding of Ca2+ to the two N-terminal sites of sTnC causes a significant decrease in excimer fluorescence and an increase in monomer fluorescence in complexes of labeled TnI with skeletal TnC or TnC/TnT, while Ca2+ binding to site II of cTnC only causes an increase in monomer fluorescence but no change in excimer fluorescence. Thus a conformational change in the N-terminal region of TnI may be necessary for full activation of muscle contraction.
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Affiliation(s)
- Ying-Ming Liou
- Department of Life Science, Institute of Biochemistry, National Chung-Hsing University, Taichung, Taiwan.
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Heller WT, Finley NL, Dong WJ, Timmins P, Cheung HC, Rosevear PR, Trewhella J. Small-angle neutron scattering with contrast variation reveals spatial relationships between the three subunits in the ternary cardiac troponin complex and the effects of troponin I phosphorylation. Biochemistry 2003; 42:7790-800. [PMID: 12820888 DOI: 10.1021/bi0341509] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Small-angle neutron scattering with contrast variation has been used to determine the shapes and dispositions of the three subunits of cardiac troponin and to study the influence of phosphorylation on the structure. Three contrast variation series were collected on three different isotopically labeled variants of the cTnC/cTnI/cTnT(198-298) complex, one of which contained deuterated and bisphosphorylated cTnI. Analysis of the scattering data shows cTnT(198-298) interacting with a single lobe of a somewhat compacted cTnC that sits at one end of an elongated rodlike cTnI, covering about one-third of its length. The cTnT(198-298) sits near the center of the long cTnI axis. The components undergo significant conformational changes and reorientations in response to protein kinase A phosphorylation of cTnI. The rodlike cTnI bends sharply at the end interacting with the cTnC/cTnT(198-298) component, which reorients so as to maintain its contacts with cTnI while undergoing only a relatively small change in shape.
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Affiliation(s)
- William T Heller
- Bioscience Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
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Oliveira DCSG, Reinach FC. The calcium-induced switch in the troponin complex probed by fluorescent mutants of troponin I. EUROPEAN JOURNAL OF BIOCHEMISTRY 2003; 270:2937-44. [PMID: 12846826 DOI: 10.1046/j.1432-1033.2003.03659.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The Ca2+-induced transition in the troponin complex (Tn) regulates vertebrate striated muscle contraction. Tn was reconstituted with recombinant forms of troponin I (TnI) containing a single intrinsic 5-hydroxytryptophan (5HW). Fluorescence analysis of these mutants of TnI demonstrate that the regions in TnI that respond to Ca2+ binding to the regulatory N-domain of TnC are the inhibitory region (residues 96-116) and a neighboring region that includes position 121. Our data confirms the role of TnI as a modulator of the Ca2+ affinity of TnC; we show that point mutations and incorporation of 5HW in TnI can affect both the affinity and the cooperativity of Ca2+ binding to TnC. We also discuss the possibility that the regulatory sites in the N-terminal domain of TnC might be the high affinity Ca2+-binding sites in the troponin complex.
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Jozaki M, Hosoda K, Miyazaki JI. Differential expression of mutually exclusive exons of the fast skeletal muscle troponin T gene in the chicken wing and leg muscles. J Muscle Res Cell Motil 2003; 23:235-43. [PMID: 12500903 DOI: 10.1023/a:1020956216423] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
To determine the physiological significance of developmentally regulated and muscle tissue-specific expression of troponin T (TnT) isoforms and also to elucidate mechanisms of alternative splicing, we investigated splicing patterns of fast skeletal muscle TnT by sequencing cDNAs obtained from the chicken wing and leg muscles. The chicken fast skeletal muscle TnT gene has 27 exons, and produces potentially 2(15) transcripts if alternative exons are randomly spliced. For the fourteen alternative exons in the 5'-region of the gene, we found 7 and 12 splice variants in the wing biceps brachii and leg gastrocnemius, respectively. Out of 19, 12 variants were newly found in this study. Twenty two different splice variants were reported by the previous studies, but this number has now increased to 34 in the chicken TnT gene, suggesting that alternative splicing is not random, but strictly regulated. We also investigated splicing patterns of mutually exclusive exons 16 and 17 in the 3'-region of the gene. Approximately equal amounts of cDNAs containing exons 16 and 17 were detected in proximal regions of adult biceps brachii and gastrocnemius, respectively, whereas cDNA with exon 17 dominated in distal regions. Only cDNA containing exon 17 was found in both proximal and distal regions of 5-day-old gastrocnemius. The inclusion of exon 16 into cDNAs was detected in the proximal region of 15-day-old gastrocnemius and increased during development.
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Affiliation(s)
- Miho Jozaki
- Institute of Biological Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8572, Japan
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Marston S. Random walks with thin filaments: application of in vitro motility assay to the study of actomyosin regulation. J Muscle Res Cell Motil 2003; 24:149-56. [PMID: 14609026 DOI: 10.1023/a:1026097313020] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The in vitro motility devised by Kron and Spudich (Kron and Spudich, 1986; Kron et al., 1991) has proved a very valuable technique for studying the motor properties of myosin of all kinds but it is equally useful for the study of the thin filaments of muscle and their regulation. The movement of a population of thin filaments over immobilised myosin appears to be random but it does in fact yield a large amount of information about contractility and its regulation. The key to extracting useful information from in vitro motility assay experiments is the logical and comprehensive analysis of filament movements.
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Affiliation(s)
- Steven Marston
- Imperial College London, NHLI Doverhouse Street, London SW3 6LY, UK.
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50
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Martins SM, Chapeaurouge A, Ferreira ST. Equilibrium unfolding and conformational plasticity of troponin I and T. EUROPEAN JOURNAL OF BIOCHEMISTRY 2002; 269:5484-91. [PMID: 12423346 DOI: 10.1046/j.1432-1033.2002.03248.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The structures and stabilities of recombinant chicken muscle troponin I (TnI) and T (TnT) were investigated by a combination of bis-ANS binding and equilibrium unfolding studies. Unlike most folded proteins, isolated TnI and TnT bind the hydrophobic fluorescent probe bis-ANS, indicating the existence of solvent-exposed hydrophobic domains in their structures. Bis-ANS binding to binary or ternary mixtures of TnI, TnT and troponin C (TnC) in solution is significantly lower than binding to the isolated subunits, which can be explained by burial of previously exposed hydrophobic domains upon association of the subunits to form the native troponin complex. Equilibrium unfolding studies of TnT and TnI by guanidine hydrochloride and urea monitored by changes in far-UV CD and bis-ANS fluorescence revealed noncooperative folding transitions for both proteins and the existence of partially folded intermediate states. Taken together, these results indicate that isolated TnI and TnT are partially unstructured proteins, and suggest that conformational plasticity of the isolated subunits may play an important role in macromolecular recognition for the assembly of the troponin complex.
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Affiliation(s)
- Samantha M Martins
- Departamento de Bioquímica Médica, Universidade Federal do Rio de Janeiro, Brazil
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