1
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Genchev GZ, Kobayashi M, Kobayashi T, Lu H. Molecular dynamics provides new insights into the mechanism of calcium signal transduction and interdomain interactions in cardiac troponin. FEBS Open Bio 2021; 11:1841-1853. [PMID: 33085832 PMCID: PMC8255835 DOI: 10.1002/2211-5463.13009] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2020] [Revised: 10/05/2020] [Accepted: 10/17/2020] [Indexed: 12/16/2022] Open
Abstract
Understanding the regulation of cardiac muscle contraction at a molecular level is crucial for the development of therapeutics for heart conditions. Despite the availability of atomic structures of the protein components of cardiac muscle thin filaments, detailed insights into their dynamics and response to calcium are yet to be fully depicted. In this study, we used molecular dynamics simulations of the core domains of the cardiac muscle protein troponin to characterize the equilibrium dynamics of its calcium-bound and calcium-free forms, with a focus on elements of cardiac muscle contraction activation and deactivation, that is, calcium binding to the cardiac troponin Ca2+ -binding subunit (TnC) and the release of the switch region of the troponin inhibitory subunit (TnI) from TnC. The process of calcium binding to the TnC binding site is described as a three-step process commencing with calcium capture by the binding site residues, followed by cooperative residue interplay bringing the calcium ion to the binding site, and finally, calcium-water exchange. Furthermore, we uncovered a set of TnC-TnI interdomain interactions that are critical for TnC N-lobe hydrophobic pocket dynamics. Absence of these interactions allows the closure of the TnC N-lobe hydrophobic pocket while the TnI switch region remains expelled, whereas if the interactions are maintained, the hydrophobic pocket remains open. Modification of these interactions may fine-tune the ability of the TnC N-lobe hydrophobic pocket to close or remain open, modulate cardiac contractility and present potential therapy-relevant targets.
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Affiliation(s)
- Georgi Z Genchev
- Center for Biomedical Informatics, Shanghai Children's Hospital, Shanghai, China.,SJTU-Yale Joint Center for Biostatistics, Shanghai Jiao Tong University, Shanghai, China.,Bulgarian Institute for Genomics and Precision Medicine, Sofia, Bulgaria.,Bioinformatics Program, Department of Bioengineering, University of Illinois at Chicago, Chicago, IL, USA
| | - Minae Kobayashi
- Department of Physiology and Biophysics and Center for Cardiovascular Research, University of Illinois at Chicago College of Medicine, Chicago, IL, USA
| | - Tomoyoshi Kobayashi
- Department of Physiology and Biophysics and Center for Cardiovascular Research, University of Illinois at Chicago College of Medicine, Chicago, IL, USA
| | - Hui Lu
- Center for Biomedical Informatics, Shanghai Children's Hospital, Shanghai, China.,SJTU-Yale Joint Center for Biostatistics, Shanghai Jiao Tong University, Shanghai, China.,Department of Bioinformatics and Biostatistics, Shanghai Jiao Tong University, Shanghai, China
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2
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Powers JD, Malingen SA, Regnier M, Daniel TL. The Sliding Filament Theory Since Andrew Huxley: Multiscale and Multidisciplinary Muscle Research. Annu Rev Biophys 2021; 50:373-400. [PMID: 33637009 DOI: 10.1146/annurev-biophys-110320-062613] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Two groundbreaking papers published in 1954 laid out the theory of the mechanism of muscle contraction based on force-generating interactions between myofilaments in the sarcomere that cause filaments to slide past one another during muscle contraction. The succeeding decades of research in muscle physiology have revealed a unifying interest: to understand the multiscale processes-from atom to organ-that govern muscle function. Such an understanding would have profound consequences for a vast array of applications, from developing new biomimetic technologies to treating heart disease. However, connecting structural and functional properties that are relevant at one spatiotemporal scale to those that are relevant at other scales remains a great challenge. Through a lens of multiscale dynamics, we review in this article current and historical research in muscle physiology sparked by the sliding filament theory.
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Affiliation(s)
- Joseph D Powers
- Department of Bioengineering, University of California San Diego, La Jolla, California 92093, USA
| | - Sage A Malingen
- Department of Biology, University of Washington, Seattle, Washington 98195, USA;
| | - Michael Regnier
- Department of Bioengineering, University of Washington, Seattle, Washington 98185, USA
- Center for Translational Muscle Research, University of Washington, Seattle, Washington 98185, USA
| | - Thomas L Daniel
- Department of Biology, University of Washington, Seattle, Washington 98195, USA;
- Department of Bioengineering, University of Washington, Seattle, Washington 98185, USA
- Center for Translational Muscle Research, University of Washington, Seattle, Washington 98185, USA
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3
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van de Locht M, Donkervoort S, de Winter JM, Conijn S, Begthel L, Kusters B, Mohassel P, Hu Y, Medne L, Quinn C, Moore SA, Foley AR, Seo G, Hwee DT, Malik FI, Irving T, Ma W, Granzier HL, Kamsteeg EJ, Immadisetty K, Kekenes-Huskey P, Pinto JR, Voermans N, Bönnemann CG, Ottenheijm CA. Pathogenic variants in TNNC2 cause congenital myopathy due to an impaired force response to calcium. J Clin Invest 2021; 131:145700. [PMID: 33755597 DOI: 10.1172/jci145700] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2020] [Accepted: 03/18/2021] [Indexed: 12/11/2022] Open
Abstract
Troponin C (TnC) is a critical regulator of skeletal muscle contraction; it binds Ca2+ to activate muscle contraction. Surprisingly, the gene encoding fast skeletal TnC (TNNC2) has not yet been implicated in muscle disease. Here, we report 2 families with pathogenic variants in TNNC2. Patients present with a distinct, dominantly inherited congenital muscle disease. Molecular dynamics simulations suggested that the pathomechanisms by which the variants cause muscle disease include disruption of the binding sites for Ca2+ and for troponin I. In line with these findings, physiological studies in myofibers isolated from patients' biopsies revealed a markedly reduced force response of the sarcomeres to [Ca2+]. This pathomechanism was further confirmed in experiments in which contractile dysfunction was evoked by replacing TnC in myofibers from healthy control subjects with recombinant, mutant TnC. Conversely, the contractile dysfunction of myofibers from patients was repaired by replacing endogenous, mutant TnC with recombinant, wild-type TnC. Finally, we tested the therapeutic potential of the fast skeletal muscle troponin activator tirasemtiv in patients' myofibers and showed that the contractile dysfunction was repaired. Thus, our data reveal that pathogenic variants in TNNC2 cause congenital muscle disease, and they provide therapeutic angles to repair muscle contractility.
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Affiliation(s)
- Martijn van de Locht
- Deptartment of Physiology, Amsterdam UMC (location VUmc), Amsterdam, Netherlands
| | - Sandra Donkervoort
- Neuromuscular and Neurogenetic Disorders of Childhood Section, National Institute of Neurological Disorders and Stroke, NIH, Bethesda, Maryland, USA
| | - Josine M de Winter
- Deptartment of Physiology, Amsterdam UMC (location VUmc), Amsterdam, Netherlands
| | - Stefan Conijn
- Deptartment of Physiology, Amsterdam UMC (location VUmc), Amsterdam, Netherlands
| | - Leon Begthel
- Deptartment of Physiology, Amsterdam UMC (location VUmc), Amsterdam, Netherlands
| | - Benno Kusters
- Department of Neurology and Human Genetics, Radboud University Medical Center, Nijmegen, Netherlands
| | - Payam Mohassel
- Neuromuscular and Neurogenetic Disorders of Childhood Section, National Institute of Neurological Disorders and Stroke, NIH, Bethesda, Maryland, USA
| | - Ying Hu
- Neuromuscular and Neurogenetic Disorders of Childhood Section, National Institute of Neurological Disorders and Stroke, NIH, Bethesda, Maryland, USA
| | - Livija Medne
- Division of Human Genetics, Department of Pediatrics, Individualized Medical Genetics Center, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania, USA
| | - Colin Quinn
- Department of Neurology, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Steven A Moore
- Department of Pathology, University of Iowa Carver College of Medicine, Iowa City, Iowa, USA
| | - A Reghan Foley
- Neuromuscular and Neurogenetic Disorders of Childhood Section, National Institute of Neurological Disorders and Stroke, NIH, Bethesda, Maryland, USA
| | - Gwimoon Seo
- Protein Expression Facility, Institute of Molecular Biophysics, The Florida State University, Tallahassee, Florida, USA
| | - Darren T Hwee
- Research and Early Development, Cytokinetics Inc., South San Francisco, California, USA
| | - Fady I Malik
- Research and Early Development, Cytokinetics Inc., South San Francisco, California, USA
| | - Thomas Irving
- BioCAT, Illinois Institute of Technology, Chicago, Illinois, USA
| | - Weikang Ma
- BioCAT, Illinois Institute of Technology, Chicago, Illinois, USA
| | - Henk L Granzier
- Department of Cellular and Molecular Medicine, University of Arizona, Tucson, Arizona, USA
| | - Erik-Jan Kamsteeg
- Department of Neurology and Human Genetics, Radboud University Medical Center, Nijmegen, Netherlands
| | - Kalyan Immadisetty
- Department of Cell and Molecular Physiology, Loyola University, Chicago, Illinois, USA
| | - Peter Kekenes-Huskey
- Department of Cell and Molecular Physiology, Loyola University, Chicago, Illinois, USA
| | - José R Pinto
- Department of Biomedical Sciences, The Florida State University College of Medicine, Tallahassee, Florida, USA
| | - Nicol Voermans
- Department of Neurology and Human Genetics, Radboud University Medical Center, Nijmegen, Netherlands
| | - Carsten G Bönnemann
- Neuromuscular and Neurogenetic Disorders of Childhood Section, National Institute of Neurological Disorders and Stroke, NIH, Bethesda, Maryland, USA
| | - Coen Ac Ottenheijm
- Deptartment of Physiology, Amsterdam UMC (location VUmc), Amsterdam, Netherlands.,Department of Cellular and Molecular Medicine, University of Arizona, Tucson, Arizona, USA
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4
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Rayani K, Seffernick J, Li AY, Davis JP, Spuches AM, Van Petegem F, Solaro RJ, Lindert S, Tibbits GF. Binding of calcium and magnesium to human cardiac troponin C. J Biol Chem 2021; 296:100350. [PMID: 33548225 PMCID: PMC7961095 DOI: 10.1016/j.jbc.2021.100350] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2020] [Revised: 01/25/2021] [Accepted: 01/27/2021] [Indexed: 01/03/2023] Open
Abstract
Cardiac muscle thin filaments are composed of actin, tropomyosin, and troponin that change conformation in response to Ca2+ binding, triggering muscle contraction. Human cardiac troponin C (cTnC) is the Ca2+-sensing component of the thin filament. It contains structural sites (III/IV) that bind both Ca2+ and Mg2+ and a regulatory site (II) that has been thought to bind only Ca2+. Binding of Ca2+ at this site initiates a series of conformational changes that culminate in force production. However, the mechanisms that underpin the regulation of binding at site II remain unclear. Here, we have quantified the interaction between site II and Ca2+/Mg2+ through isothermal titration calorimetry and thermodynamic integration simulations. Direct and competitive binding titrations with WT N-terminal cTnC and full-length cTnC indicate that physiologically relevant concentrations of both Ca2+/Mg2+ interacted with the same locus. Moreover, the D67A/D73A N-terminal cTnC construct in which two coordinating residues within site II were removed was found to have significantly reduced affinity for both cations. In addition, 1 mM Mg2+ caused a 1.4-fold lower affinity for Ca2+. These experiments strongly suggest that cytosolic-free Mg2+ occupies a significant population of the available site II. Interaction of Mg2+ with site II of cTnC likely has important functional consequences for the heart both at baseline as well as in diseased states that decrease or increase the availability of Mg2+, such as secondary hyperparathyroidism or ischemia, respectively.
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Affiliation(s)
- Kaveh Rayani
- Molecular Cardiac Physiology Group, Simon Fraser University, Burnaby, British Columbia, Canada
| | - Justin Seffernick
- Department of Chemistry and Biochemistry, Ohio State University, Columbus, Ohio, USA
| | - Alison Yueh Li
- Molecular Cardiac Physiology Group, Simon Fraser University, Burnaby, British Columbia, Canada; Department of Biochemistry and Molecular Biology, The University of British Columbia, Vancouver, British Columbia, Canada
| | - Jonathan P Davis
- Department of Physiology and Cell Biology, The Ohio State University, Columbus, Ohio, USA
| | - Anne Marie Spuches
- Department of Chemistry, East Carolina University, 300 Science and Technology Building, Greenville, North Carolina, USA
| | - Filip Van Petegem
- Department of Biochemistry and Molecular Biology, The University of British Columbia, Vancouver, British Columbia, Canada
| | - R John Solaro
- Department of Physiology and Biophysics and the Center for Cardiovascular Research, College of Medicine, University of Illinois at Chicago, Chicago, Illinois, USA
| | - Steffen Lindert
- Department of Chemistry and Biochemistry, Ohio State University, Columbus, Ohio, USA
| | - Glen F Tibbits
- Molecular Cardiac Physiology Group, Simon Fraser University, Burnaby, British Columbia, Canada; Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia, Canada; Cardiac Group, BC Children's Hospital Research Institute, Vancouver, British Columbia, Canada.
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5
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Through thick and thin: dual regulation of insect flight muscle and cardiac muscle compared. J Muscle Res Cell Motil 2019; 40:99-110. [PMID: 31292801 PMCID: PMC6726838 DOI: 10.1007/s10974-019-09536-8] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2019] [Accepted: 07/02/2019] [Indexed: 01/15/2023]
Abstract
Both insect flight muscle and cardiac muscle contract rhythmically, but the way in which repetitive contractions are controlled is different in the two types of muscle. We have compared the flight muscle of the water bug, Lethocerus, with cardiac muscle. Both have relatively high resting elasticity and are activated by an increase in sarcomere length or a quick stretch. The larger response of flight muscle is attributed to the highly ordered lattice of thick and thin filaments and to an isoform of troponin C that has no exchangeable Ca2+-binding site. The Ca2+ sensitivity of cardiac muscle and flight muscle can be manipulated so that cardiac muscle responds to Ca2+ like flight muscle, and flight muscle responds like cardiac muscle, showing the malleability of regulation. The interactions of the subunits in flight muscle troponin are described; a model of the complex, using the structure of cardiac troponin as a template, shows an overall similarity of cardiac and flight muscle troponin complexes. The dual regulation by thick and thin filaments in skeletal and cardiac muscle is thought to operate in flight muscle. The structure of inhibited myosin heads folded back on the thick filament in relaxed Lethocerus fibres has not been seen in other species and may be an adaptation to the rapid contractions of flight muscle. A scheme for regulation by thick and thin filaments during oscillatory contraction is described. Cardiac and flight muscle have much in common, but the differing mechanical requirements mean that regulation by both thick and thin filaments is adapted to the particular muscle.
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6
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Solution structure of TbCentrin4 from Trypanosoma brucei and its interactions with Ca 2+ and other centrins. Biochem J 2018; 475:3763-3778. [PMID: 30389845 DOI: 10.1042/bcj20180752] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2018] [Revised: 10/30/2018] [Accepted: 11/01/2018] [Indexed: 12/17/2022]
Abstract
Centrin is a conserved calcium-binding protein that plays an important role in diverse cellular biological processes such as ciliogenesis, gene expression, DNA repair and signal transduction. In Trypanosoma brucei, TbCentrin4 is mainly localized in basal bodies and bi-lobe structure, and is involved in the processes coordinating karyokinesis and cytokinesis. In the present study, we solved the solution structure of TbCentrin4 using NMR (nuclear magnetic resonance) spectroscopy. TbCentrin4 contains four EF-hand motifs consisting of eight α-helices. Isothermal titration calorimetry experiment showed that TbCentrin4 has a strong Ca2+ binding ability. NMR chemical shift perturbation indicated that TbCentrin4 binds to Ca2+ through its C-terminal domain composed of EF-hand 3 and 4. Meanwhile, we revealed that TbCentrin4 undergoes a conformational change and self-assembly induced by high concentration of Ca2+ Intriguingly, localization of TbCentrin4 was dispersed or disappeared from basal bodies and the bi-lobe structure when the cells were treated with Ca2+ in vivo, implying the influence of Ca2+ on the cellular functions of TbCentrin4. Besides, we observed the interactions between TbCentrin4 and other Tbcentrins and revealed that the interactions are Ca2+ dependent. Our findings provide a structural basis for better understanding the biological functions of TbCentrin4 in the relevant cellular processes.
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7
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Molecular Basis of S100A1 Activation at Saturating and Subsaturating Calcium Concentrations. Biophys J 2016; 110:1052-63. [PMID: 26958883 DOI: 10.1016/j.bpj.2015.12.040] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2015] [Revised: 11/30/2015] [Accepted: 12/14/2015] [Indexed: 10/22/2022] Open
Abstract
The S100A1 protein mediates a wide variety of physiological processes through its binding of calcium (Ca(2+)) and endogenous target proteins. S100A1 presents two Ca(2+)-binding domains: a high-affinity "canonical" EF (cEF) hand and a low-affinity "pseudo" EF (pEF) hand. Accumulating evidence suggests that both Ca(2+)-binding sites must be saturated to stabilize an open state conducive to peptide recognition, yet the pEF hand's low affinity limits Ca(2+) binding at normal physiological concentrations. To understand the molecular basis of Ca(2+) binding and open-state stabilization, we performed 100 ns molecular dynamics simulations of S100A1 in the apo/holo (Ca(2+)-free/bound) states and a half-saturated state, for which only the cEF sites are Ca(2+)-bound. Our simulations indicate that the pattern of oxygen coordination about Ca(2+) in the cEF relative to the pEF site contributes to the former's higher affinity, whereas Ca(2+) binding strongly reshapes the protein's conformational dynamics by disrupting β-sheet coupling between EF hands. Moreover, modeling of the half-saturated configuration suggests that the open state is unstable and reverts toward a closed state in the absence of the pEF Ca(2+) ion. These findings indicate that Ca(2+) binding at the cEF site alone is insufficient to stabilize opening; thus, posttranslational modification of the protein may be required for target peptide binding at subsaturating intracellular Ca(2+) levels.
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8
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Badr MA, Pinto JR, Davidson MW, Chase PB. Fluorescent Protein-Based Ca2+ Sensor Reveals Global, Divalent Cation-Dependent Conformational Changes in Cardiac Troponin C. PLoS One 2016; 11:e0164222. [PMID: 27736894 PMCID: PMC5063504 DOI: 10.1371/journal.pone.0164222] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2016] [Accepted: 09/21/2016] [Indexed: 12/12/2022] Open
Abstract
Cardiac troponin C (cTnC) is a key effector in cardiac muscle excitation-contraction coupling as the Ca2+ sensing subunit responsible for controlling contraction. In this study, we generated several FRET sensors for divalent cations based on cTnC flanked by a donor fluorescent protein (CFP) and an acceptor fluorescent protein (YFP). The sensors report Ca2+ and Mg2+ binding, and relay global structural information about the structural relationship between cTnC’s N- and C-domains. The sensors were first characterized using end point titrations to decipher the response to Ca2+ binding in the presence or absence of Mg2+. The sensor that exhibited the largest responses in end point titrations, CTV-TnC, (Cerulean, TnC, and Venus) was characterized more extensively. Most of the divalent cation-dependent FRET signal originates from the high affinity C-terminal EF hands. CTV-TnC reconstitutes into skinned fiber preparations indicating proper assembly of troponin complex, with only ~0.2 pCa unit rightward shift of Ca2+-sensitive force development compared to WT-cTnC. Affinity of CTV-TnC for divalent cations is in agreement with known values for WT-cTnC. Analytical ultracentrifugation indicates that CTV-TnC undergoes compaction as divalent cations bind. C-terminal sites induce ion-specific (Ca2+ versus Mg2+) conformational changes in cTnC. Our data also provide support for the presence of additional, non-EF-hand sites on cTnC for Mg2+ binding. In conclusion, we successfully generated a novel FRET-Ca2+ sensor based on full length cTnC with a variety of cellular applications. Our sensor reveals global structural information about cTnC upon divalent cation binding.
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Affiliation(s)
- Myriam A. Badr
- Department of Biological Science, Florida State University, Tallahassee, Florida, United States of America
- Institute of Molecular Biophysics, Florida State University, Tallahassee, Florida, United States of America
- * E-mail:
| | - Jose R. Pinto
- Department of Biomedical Sciences, College of Medicine, Florida State University, Tallahassee, Florida, United States of America
| | - Michael W. Davidson
- Department of Biological Science, Florida State University, Tallahassee, Florida, United States of America
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida, United States of America
| | - P. Bryant Chase
- Department of Biological Science, Florida State University, Tallahassee, Florida, United States of America
- Institute of Molecular Biophysics, Florida State University, Tallahassee, Florida, United States of America
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9
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Marques MDA, de Oliveira GAP. Cardiac Troponin and Tropomyosin: Structural and Cellular Perspectives to Unveil the Hypertrophic Cardiomyopathy Phenotype. Front Physiol 2016; 7:429. [PMID: 27721798 PMCID: PMC5033975 DOI: 10.3389/fphys.2016.00429] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2016] [Accepted: 09/09/2016] [Indexed: 12/12/2022] Open
Abstract
Inherited myopathies affect both skeletal and cardiac muscle and are commonly associated with genetic dysfunctions, leading to the production of anomalous proteins. In cardiomyopathies, mutations frequently occur in sarcomeric genes, but the cause-effect scenario between genetic alterations and pathological processes remains elusive. Hypertrophic cardiomyopathy (HCM) was the first cardiac disease associated with a genetic background. Since the discovery of the first mutation in the β-myosin heavy chain, more than 1400 new mutations in 11 sarcomeric genes have been reported, awarding HCM the title of the “disease of the sarcomere.” The most common macroscopic phenotypes are left ventricle and interventricular septal thickening, but because the clinical profile of this disease is quite heterogeneous, these phenotypes are not suitable for an accurate diagnosis. The development of genomic approaches for clinical investigation allows for diagnostic progress and understanding at the molecular level. Meanwhile, the lack of accurate in vivo models to better comprehend the cellular events triggered by this pathology has become a challenge. Notwithstanding, the imbalance of Ca2+ concentrations, altered signaling pathways, induction of apoptotic factors, and heart remodeling leading to abnormal anatomy have already been reported. Of note, a misbalance of signaling biomolecules, such as kinases and tumor suppressors (e.g., Akt and p53), seems to participate in apoptotic and fibrotic events. In HCM, structural and cellular information about defective sarcomeric proteins and their altered interactome is emerging but still represents a bottleneck for developing new concepts in basic research and for future therapeutic interventions. This review focuses on the structural and cellular alterations triggered by HCM-causing mutations in troponin and tropomyosin proteins and how structural biology can aid in the discovery of new platforms for therapeutics. We highlight the importance of a better understanding of allosteric communications within these thin-filament proteins to decipher the HCM pathological state.
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Affiliation(s)
- Mayra de A Marques
- Programa de Biologia Estrutural, Centro Nacional de Ressonância Magnética Nuclear Jiri Jonas, Instituto de Bioquímica Médica Leopoldo de Meis, Instituto Nacional de Biologia Estrutural e Bioimagem, Universidade Federal do Rio de Janeiro Rio de Janeiro, Brazil
| | - Guilherme A P de Oliveira
- Programa de Biologia Estrutural, Centro Nacional de Ressonância Magnética Nuclear Jiri Jonas, Instituto de Bioquímica Médica Leopoldo de Meis, Instituto Nacional de Biologia Estrutural e Bioimagem, Universidade Federal do Rio de Janeiro Rio de Janeiro, Brazil
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10
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Nara M, Morii H, Tanokura M. Infrared study of synthetic peptide analogues of the calcium-binding site III of troponin C: The role of helix F of an EF-hand motif. Biopolymers 2016; 99:342-7. [PMID: 23426577 DOI: 10.1002/bip.22176] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2012] [Revised: 10/13/2012] [Accepted: 10/14/2012] [Indexed: 11/10/2022]
Abstract
The EF-hand motif (helix-loop-helix) is a Ca(2+)-binding domain that is common among many intracellular Ca(2+)-binding proteins. We applied Fourier-transform infrared spectroscopy to study the synthetic peptide analogues of site III of rabbit skeletal muscle troponin C (helix E-loop-helix F). The 17-residue peptides corresponding to loop-helix F (DRDADGYIDAEELAEIF), where one residue is substituted by the D-type amino acid, were investigated to disturb the α-helical conformation of helix F systematically. These D-type-substituted peptides showed no band at about 1555 cm(-1) even in the Ca(2+)-loaded state although the native peptide (L-type only) showed a band at about 1555 cm(-1) in the Ca(2+)-loaded state, which is assigned to the side-chain COO(-) group of Glu at the 12th position, serving as the ligand for Ca(2+) in the bidentate coordination mode. Therefore, helix F is vital to the interaction between the Ca(2+) and the side-chain COO(-) group of Glu at the 12th position. Implications of the COO(-) antisymmetric stretch and the amide-I' of the synthetic peptide analogues of the Ca(2+)-binding sites are discussed.
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Affiliation(s)
- Masayuki Nara
- Department of Chemistry, College of Liberal Arts and Sciences, Tokyo Medical and Dental University, Chiba 272-0827, Japan.
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11
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Sikdar S, Chakrabarti J, Ghosh M. Conformational thermodynamics guided structural reconstruction of biomolecular fragments. MOLECULAR BIOSYSTEMS 2016; 12:444-53. [DOI: 10.1039/c5mb00529a] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Conformational thermodynamics compares the modeling protocols to identify the conformation of the missing region leading to a suitable model for metal ion free (apo) skeletal muscle Troponin C.
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Affiliation(s)
- Samapan Sikdar
- Department of Chemical
- Biological and Macromolecular Sciences
- S. N. Bose National Centre for Basic Sciences
- Salt Lake
- India
| | - J. Chakrabarti
- Department of Chemical
- Biological and Macromolecular Sciences
- S. N. Bose National Centre for Basic Sciences
- Salt Lake
- India
| | - Mahua Ghosh
- Department of Chemical
- Biological and Macromolecular Sciences
- S. N. Bose National Centre for Basic Sciences
- Salt Lake
- India
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12
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Matsuo T, Takeda S, Oda T, Fujiwara S. Structures of the troponin core domain containing the cardiomyopathy-causing mutants studied by small-angle X-ray scattering. Biophys Physicobiol 2015; 12:145-58. [PMID: 27493864 PMCID: PMC4736830 DOI: 10.2142/biophysico.12.0_145] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2015] [Accepted: 12/01/2015] [Indexed: 12/01/2022] Open
Abstract
Troponin (Tn), consisting of three subunits, TnC, TnI, and TnT, is a protein in the thin filaments in muscle, and, together with another thin-filament protein tropomyosin (Tm), plays a major role in regulation of muscle contraction. Various mutations of Tn cause familial hypertrophic cardiomyopathy. These mutations are directly related to aberrations in this regulatory mechanism. Here we focus on the mutations E244D and K247R of TnT, which reside in the middle of the pathway of the Ca(2+)-binding signal from TnC to Tm. These mutations induce an increase in the maximum tension of cardiac muscle without changes in Ca(2+)-sensitivity. As a first step toward elucidating the molecular mechanism underlying this functional aberration, we carried out small-angle X-ray scattering experiments on the Tn core domain containing the wild type subunits and those containing the mutant TnT in the absence and presence of Ca(2+). Changes in the overall shape induced by the mutations were detected for the first time by the changes in the radius of gyration and the maximum dimension between the wild type and the mutants. Analysis of the scattering curves by model calculations shows that TnC adopts a dumbbell structure regardless of the mutations, and that the mutations change the distributions of the conformational ensembles so that the flexible N- and C-terminal regions of TnT become close to the center of the whole moelcule. This suggests, since these regions are related to the Tn-Tm interactions, that alteration of the Tn-Tm interactions induced by the mutations causes the functional aberration.
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Affiliation(s)
- Tatsuhito Matsuo
- Quantum Beam Science Center, Japan Atomic Energy Agency, Tokai-mura, Naka-gun, Ibaraki 319-1195, Japan
| | - Soichi Takeda
- National Cerebral and Cardiovascular Center Research Institute, Suita, Osaka 565-8565, Japan
| | - Toshiro Oda
- RIKEN SPring-8 center, RIKEN Harima Institute, Sayo, Hyogo 679-5148, Japan
| | - Satoru Fujiwara
- Quantum Beam Science Center, Japan Atomic Energy Agency, Tokai-mura, Naka-gun, Ibaraki 319-1195, Japan
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13
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Li MX, Hwang PM. Structure and function of cardiac troponin C (TNNC1): Implications for heart failure, cardiomyopathies, and troponin modulating drugs. Gene 2015; 571:153-66. [PMID: 26232335 DOI: 10.1016/j.gene.2015.07.074] [Citation(s) in RCA: 83] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2015] [Revised: 06/24/2015] [Accepted: 07/21/2015] [Indexed: 10/23/2022]
Abstract
In striated muscle, the protein troponin complex turns contraction on and off in a calcium-dependent manner. The calcium-sensing component of the complex is troponin C, which is expressed from the TNNC1 gene in both cardiac muscle and slow-twitch skeletal muscle (identical transcript in both tissues) and the TNNC2 gene in fast-twitch skeletal muscle. Cardiac troponin C (cTnC) is made up of two globular EF-hand domains connected by a flexible linker. The structural C-domain (cCTnC) contains two high affinity calcium-binding sites that are always occupied by Ca(2+) or Mg(2+) under physiologic conditions, stabilizing an open conformation that remains anchored to the rest of the troponin complex. In contrast, the regulatory N-domain (cNTnC) contains a single low affinity site that is largely unoccupied at resting calcium concentrations. During muscle activation, calcium binding to cNTnC favors an open conformation that binds to the switch region of troponin I, removing adjacent inhibitory regions of troponin I from actin and allowing muscle contraction to proceed. Regulation of the calcium binding affinity of cNTnC is physiologically important, because it directly impacts the calcium sensitivity of muscle contraction. Calcium sensitivity can be modified by drugs that stabilize the open form of cNTnC, post-translational modifications like phosphorylation of troponin I, or downstream thin filament protein interactions that impact the availability of the troponin I switch region. Recently, mutations in cTnC have been associated with hypertrophic or dilated cardiomyopathy. A detailed understanding of how calcium sensitivity is regulated through the troponin complex is necessary for explaining how mutations perturb its function to promote cardiomyopathy and how post-translational modifications in the thin filament affect heart function and heart failure. Troponin modulating drugs are being developed for the treatment of cardiomyopathies and heart failure.
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Affiliation(s)
- Monica X Li
- Department of Medicine, University of Alberta, Edmonton, AB T6G 2G3, Canada; Department of Biochemistry, University of Alberta, Edmonton, AB T6G 2H7, Canada
| | - Peter M Hwang
- Department of Medicine, University of Alberta, Edmonton, AB T6G 2G3, Canada; Department of Biochemistry, University of Alberta, Edmonton, AB T6G 2H7, Canada.
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14
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Wabik J, Kurcinski M, Kolinski A. Coarse-Grained Modeling of Peptide Docking Associated with Large Conformation Transitions of the Binding Protein: Troponin I Fragment-Troponin C System. Molecules 2015; 20:10763-80. [PMID: 26111167 PMCID: PMC6272278 DOI: 10.3390/molecules200610763] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2015] [Revised: 05/14/2015] [Accepted: 05/21/2015] [Indexed: 11/25/2022] Open
Abstract
Most of the current docking procedures are focused on fine conformational adjustments of assembled complexes and fail to reproduce large-scale protein motion. In this paper, we test a new modeling approach developed to address this problem. CABS-dock is a versatile and efficient tool for modeling the structure, dynamics and interactions of protein complexes. The docking protocol employs a coarse-grained representation of proteins, a simplified model of interactions and advanced protocols for conformational sampling. CABS-dock is one of the very few tools that allow unrestrained docking with large conformational freedom of the receptor. In an example application we modeled the process of complex assembly between two proteins: Troponin C (TnC) and the N-terminal helix of Troponin I (TnI N-helix), which occurs in vivo during muscle contraction. Docking simulations illustrated how the TnC molecule undergoes significant conformational transition on complex formation, a phenomenon that can be modeled only when protein flexibility is properly accounted for. This way our procedure opens up a new possibility for studying mechanisms of protein complex assembly, which may be a supporting tool for rational drug design.
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Affiliation(s)
- Jacek Wabik
- Laboratory of Theory of Biopolymers, Faculty of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland.
| | - Mateusz Kurcinski
- Laboratory of Theory of Biopolymers, Faculty of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland.
| | - Andrzej Kolinski
- Laboratory of Theory of Biopolymers, Faculty of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland.
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15
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Webb M, Jackson DR, Stewart TJ, Dugan SP, Carter MS, Cremo CR, Baker JE. The myosin duty ratio tunes the calcium sensitivity and cooperative activation of the thin filament. Biochemistry 2013; 52:6437-44. [PMID: 23947752 DOI: 10.1021/bi400262h] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
In striated muscle, calcium binding to the thin filament (TF) regulatory complex activates actin-myosin ATPase activity, and actin-myosin kinetics in turn regulates TF activation. However, a quantitative description of the effects of actin-myosin kinetics on the calcium sensitivity (pCa50) and cooperativity (nH) of TF activation is lacking. With the assumption that TF structural transitions and TF-myosin binding transitions are inextricably coupled, we advanced the principles established by Kad et al. [Kad, N., et al. (2005) Proc. Natl. Acad. Sci. U.S.A. 102, 16990-16995] and Sich et al. [Sich, N. M., et al. (2011) J. Biol. Chem. 285, 39150-39159] to develop a simple model of TF regulation, which predicts that pCa50 varies linearly with duty ratio and that nH is maximal near physiological duty ratios. Using in vitro motility to determine the calcium sensitivity of TF sliding velocities, we measured pCa50 and nH at different myosin densities and in the presence of ATPase inhibitors. The observed effects of myosin density and actin-myosin duty ratio on pCa50 and nH are consistent with our model predictions. In striated muscle, pCa50 must match cytosolic calcium concentrations and a maximal nH optimizes calcium responsiveness. Our results indicate that pCa50 and nH can be predictably tuned through TF-myosin ATPase kinetics and that drugs and disease states that alter ATPase kinetics can, through their effects on calcium sensitivity, alter the efficiency of muscle contraction.
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Affiliation(s)
- Milad Webb
- Department of Electrical and Biomedical Engineering, University of Nevada, Reno , Reno, Nevada 89557, United States
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16
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Genchev GZ, Kobayashi T, Lu H. Calcium induced regulation of skeletal troponin--computational insights from molecular dynamics simulations. PLoS One 2013; 8:e58313. [PMID: 23554884 PMCID: PMC3598806 DOI: 10.1371/journal.pone.0058313] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2012] [Accepted: 02/01/2013] [Indexed: 01/11/2023] Open
Abstract
The interaction between calcium and the regulatory site(s) of striated muscle regulatory protein troponin switches on and off muscle contraction. In skeletal troponin binding of calcium to sites I and II of the TnC subunit results in a set of structural changes in the troponin complex, displaces tropomyosin along the actin filament and allows myosin-actin interaction to produce mechanical force. In this study, we used molecular dynamics simulations to characterize the calcium dependent dynamics of the fast skeletal troponin molecule and its TnC subunit in the calcium saturated and depleted states. We focused on the N-lobe and on describing the atomic level events that take place subsequent to removal of the calcium ion from the regulatory sites I and II. A main structural event - a closure of the A/B helix hydrophobic pocket results from the integrated effect of the following conformational changes: the breakage of H-bond interactions between the backbone nitrogen atoms of the residues at positions 2, 9 and sidechain oxygen atoms of the residue at position 12 (N2-OE12/N9-OE12) in sites I and II; expansion of sites I and II and increased site II N-terminal end-segment flexibility; strengthening of the β-sheet scaffold; and the subsequent re-packing of the N-lobe hydrophobic residues. Additionally, the calcium release allows the N-lobe to rotate relative to the rest of the Tn molecule. Based on the findings presented herein we propose a novel model of skeletal thin filament regulation.
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Affiliation(s)
- Georgi Z. Genchev
- Bioinformatics Program, Department of Bioengineering, University of Illinois at Chicago, Chicago, Illinois, United States of America
| | - Tomoyoshi Kobayashi
- Department of Physiology and Biophysics and Center for Cardiovascular Research, University of Illinois at Chicago, Chicago, Illinois, United States of America
- * E-mail: (HL); (TK)
| | - Hui Lu
- Bioinformatics Program, Department of Bioengineering, University of Illinois at Chicago, Chicago, Illinois, United States of America
- Shanghai Institute of Medical Genetics, Children’s Hospital of Shanghai, Shanghai, China
- Key Lab of Embryo Molecular Biology, Ministry of Health, Shanghai, China
- Shanghai Lab of Embryo and Reproduction Engineering, Shanghai, China
- * E-mail: (HL); (TK)
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17
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de Oliveira GAP, Rocha CB, Marques MDA, Cordeiro Y, Sorenson MM, Foguel D, Silva JL, Suarez MC. Insights into the Intramolecular Coupling between the N- and C-Domains of Troponin C Derived from High-Pressure, Fluorescence, Nuclear Magnetic Resonance, and Small-Angle X-ray Scattering Studies. Biochemistry 2012; 52:28-40. [DOI: 10.1021/bi301139d] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- 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, 21941-902 Rio de Janeiro, Brazil
| | - Cristiane B. Rocha
- UNIRIO-Universidade Federal do Estado do Rio de Janeiro, CCBS-Centro de
Ciências Biológicas e da Saúde, Instituto Biomédico-IB,
Departamento de Bioquímica, Rua Frei Caneca 94-Centro, Rio
de Janeiro, Brazil
| | - Mayra de A. Marques
- Programa de
Biologia Estrutural,
Instituto de Bioquímica Médica, Instituto Nacional de
Biologia Estrutural e Bioimagem, Centro Nacional de Ressonância
Magnética Nuclear Jiri Jonas, Universidade Federal do Rio de Janeiro, 21941-902 Rio de Janeiro, Brazil
| | - Yraima Cordeiro
- Faculdade
de Farmácia, Universidade Federal do Rio de Janeiro, Rio de Janeiro,
Brazil
| | - Martha M. Sorenson
- 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, 21941-902 Rio de Janeiro, Brazil
| | - Débora Foguel
- 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, 21941-902 Rio de Janeiro, Brazil
| | - Jerson L. Silva
- Programa de
Biologia Estrutural,
Instituto de Bioquímica Médica, Instituto Nacional de
Biologia Estrutural e Bioimagem, Centro Nacional de Ressonância
Magnética Nuclear Jiri Jonas, Universidade Federal do Rio de Janeiro, 21941-902 Rio de Janeiro, Brazil
| | - Marisa C. Suarez
- 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, 21941-902 Rio de Janeiro, Brazil
- Programa de Biologia
Estrutural,
Instituto de Bioquímica Médica-Polo Xerém, Universidade Federal do Rio de Janeiro, Xerém,
Brazil
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18
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Geiger A, Russo L, Gensch T, Thestrup T, Becker S, Hopfner KP, Griesinger C, Witte G, Griesbeck O. Correlating calcium binding, Förster resonance energy transfer, and conformational change in the biosensor TN-XXL. Biophys J 2012; 102:2401-10. [PMID: 22677394 PMCID: PMC3353025 DOI: 10.1016/j.bpj.2012.03.065] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2012] [Revised: 03/21/2012] [Accepted: 03/27/2012] [Indexed: 11/23/2022] Open
Abstract
Genetically encoded calcium indicators have become instrumental in imaging signaling in complex tissues and neuronal circuits in vivo. Despite their importance, structure-function relationships of these sensors often remain largely uncharacterized due to their artificial and multimodular composition. Here, we describe a combination of protein engineering and kinetic, spectroscopic, and biophysical analysis of the Förster resonance energy transfer (FRET)-based calcium biosensor TN-XXL. Using fluorescence spectroscopy of engineered tyrosines, we show that two of the four calcium binding EF-hands dominate the FRET output of TN-XXL and that local conformational changes of these hands match the kinetics of FRET change. Using small-angle x-ray scattering and NMR spectroscopy, we show that TN-XXL changes from a flexible elongated to a rigid globular shape upon binding calcium, thus resulting in FRET signal output. Furthermore, we compare calcium titrations using fluorescence lifetime spectroscopy with the ratiometric approach and investigate potential non-FRET effects that may affect the fluorophores. Thus, our data characterize the biophysics of TN-XXL in detail and may form a basis for further rational engineering of FRET-based biosensors.
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Affiliation(s)
- Anselm Geiger
- Max-Planck-Institut für Neurobiologie, Martinsried, Germany
| | - Luigi Russo
- Max-Planck-Institut für biophysikalische Chemie, Göttingen, Germany
| | | | | | - Stefan Becker
- Max-Planck-Institut für biophysikalische Chemie, Göttingen, Germany
| | - Karl-Peter Hopfner
- Genzentrum und Department Biochemie, Ludwig-Maximilians-Universität, Munich, Germany
| | | | - Gregor Witte
- Genzentrum und Department Biochemie, Ludwig-Maximilians-Universität, Munich, Germany
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19
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20
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Zhang H, Wen J, Huang RYC, Blankenship RE, Gross ML. Mass spectrometry-based carboxyl footprinting of proteins: method evaluation. INTERNATIONAL JOURNAL OF MASS SPECTROMETRY 2012; 312:78-86. [PMID: 22408386 PMCID: PMC3293472 DOI: 10.1016/j.ijms.2011.07.015] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
Protein structure determines function in biology, and a variety of approaches have been employed to obtain structural information about proteins. Mass spectrometry-based protein footprinting is one fast-growing approach. One labeling-based footprinting approach is the use of a water-soluble carbodiimide, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) and glycine ethyl ester (GEE) to modify solvent-accessible carboxyl groups on glutamate (E) and aspartate (D). This paper describes method development of carboxyl-group modification in protein footprinting. The modification protocol was evaluated by using the protein calmodulin as a model. Because carboxyl-group modification is a slow reaction relative to protein folding and unfolding, there is an issue that modifications at certain sites may induce protein unfolding and lead to additional modification at sites that are not solvent-accessible in the wild-type protein. We investigated this possibility by using hydrogen deuterium amide exchange (H/DX). The study demonstrated that application of carboxyl group modification in probing conformational changes in calmodulin induced by Ca(2+) binding provides useful information that is not compromised by modification-induced protein unfolding.
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Affiliation(s)
- Hao Zhang
- Department of Chemistry, Washington University in St. Louis, MO 63130
| | - Jianzhong Wen
- Department of Chemistry, Washington University in St. Louis, MO 63130
- Department of Biology, Washington University in St. Louis, MO 63130
| | - Richard Y-C Huang
- Department of Chemistry, Washington University in St. Louis, MO 63130
| | - Robert E. Blankenship
- Department of Chemistry, Washington University in St. Louis, MO 63130
- Department of Biology, Washington University in St. Louis, MO 63130
| | - Michael L. Gross
- Department of Chemistry, Washington University in St. Louis, MO 63130
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21
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Identification of the critical structural determinants of the EF-hand domain arrangements in calcium binding proteins. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2012; 1824:608-19. [PMID: 22285364 DOI: 10.1016/j.bbapap.2012.01.005] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/29/2011] [Revised: 12/02/2011] [Accepted: 01/04/2012] [Indexed: 11/22/2022]
Abstract
EF-hand calcium binding proteins (CaBPs) share strong sequence homology, but exhibit great diversity in structure and function. Thus although calmodulin (CaM) and calcineurin B (CNB) both consist of four EF hands, their domain arrangements are quite distinct. CaM and the CaM-like proteins are characterized by an extended architecture, whereas CNB and the CNB-like proteins have a more compact form. In this study, we performed structural alignments and molecular dynamics (MD) simulations on 3 CaM-like proteins and 6 CNB-like proteins, and quantified their distinct structural and dynamical features in an effort to establish how their sequences specify their structures and dynamics. Alignments of the EF2-EF3 region of these proteins revealed that several residues (not restricted to the linker between the EF2 and EF3 motifs) differed between the two groups of proteins. A customized inverse folding approach followed by structural assessments and MD simulations established the critical role of these residues in determining the structure of the proteins. Identification of the critical determinants of the two different EF-hand domain arrangements and the distinct dynamical features relevant to their respective functions provides insight into the relationships between sequence, structure, dynamics and function among these EF-hand CaBPs.
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22
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Little SC, Tikunova SB, Norman C, Swartz DR, Davis JP. Measurement of calcium dissociation rates from troponin C in rigor skeletal myofibrils. Front Physiol 2011; 2:70. [PMID: 22013424 PMCID: PMC3190119 DOI: 10.3389/fphys.2011.00070] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2011] [Accepted: 09/19/2011] [Indexed: 11/28/2022] Open
Abstract
Ca2+ dissociation from the regulatory domain of troponin C may influence the rate of striated muscle relaxation. However, Ca2+ dissociation from troponin C has not been measured within the geometric and stoichiometric constraints of the muscle fiber. Here we report the rates of Ca2+ dissociation from the N-terminal regulatory and C-terminal structural domains of fluorescent troponin C constructs reconstituted into rabbit rigor psoas myofibrils using stopped-flow technology. Chicken skeletal troponin C fluorescently labeled at Cys 101, troponin CIAEDANS, reported Ca2+ dissociation exclusively from the structural domain of troponin C at ∼0.37, 0.06, and 0.07/s in isolation, in the presence of troponin I and in myofibrils at 15°C, respectively. Ca2+ dissociation from the regulatory domain was observed utilizing fluorescently labeled troponin C containing the T54C and C101S mutations. Troponin CMIANST54C,C101S reported Ca2+ dissociation exclusively from the regulatory domain of troponin C at >1000, 8.8, and 15/s in isolation, in the presence of troponin I and in myofibrils at 15°C, respectively. Interestingly, troponin CIAANST54C,C101S reported a biphasic fluorescence change upon Ca2+ dissociation from the N- and C-terminal domains of troponin C with rates that were similar to those reported by troponin CMIANST54C,C101S and troponin CIAEDANS at all levels of the troponin C systems. Furthermore, the rate of Ca2+ dissociation from troponin C in the myofibrils was similar to the rate of Ca2+ dissociation measured from the troponin C-troponin I complexes. Since the rate of Ca2+ dissociation from the regulatory domain of TnC in myofibrils is similar to the rate of skeletal muscle relaxation, Ca2+ dissociation from troponin C may influence relaxation.
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Affiliation(s)
- Sean C Little
- Department of Physiology and Cell Biology, The Ohio State University Columbus, OH, USA
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23
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Geeves M, Griffiths H, Mijailovich S, Smith D. Cooperative [Ca²+]-dependent regulation of the rate of myosin binding to actin: solution data and the tropomyosin chain model. Biophys J 2011; 100:2679-87. [PMID: 21641313 DOI: 10.1016/j.bpj.2011.04.020] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2011] [Revised: 03/26/2011] [Accepted: 04/07/2011] [Indexed: 01/15/2023] Open
Abstract
The regulation of muscle contraction by calcium involves interactions among actin filaments, myosin-S1, tropomyosin (Tm), and troponin (Tn). We have extended our previous model in which the TmTn regulatory units are treated as a continuous flexible chain, and applied it to transient kinetic data. We have measured the time course of myosin-S1 binding to actin-Tm-Tn filaments in solution at various calcium levels with [actin]/[myosin] ratios of 10 and 0.1, which exhibit modest slowing as [Ca(2+)] is reduced and a lag phase at low calcium. These observations can be explained if myosin binds to actin in two steps, where the first step is rate-limiting and blocked by TmTnI at low calcium, and the second step is fast, reversible, and controlled by the neighboring configuration of coupled tropomyosin-troponin units. The model can describe the calcium dependence of the observed myosin binding reactions and predicts cooperative calcium binding to TnC with competition between actin and Ca-TnC for the binding of TnI. Implications for theories of thin-filament regulation in muscle are discussed.
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Affiliation(s)
- Michael Geeves
- Department of Biosciences, University of Kent, Canterbury, Kent, United Kingdom.
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24
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Huang RYC, Rempel DL, Gross ML. HD exchange and PLIMSTEX determine the affinities and order of binding of Ca2+ with troponin C. Biochemistry 2011; 50:5426-35. [PMID: 21574565 PMCID: PMC3115450 DOI: 10.1021/bi200377c] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Troponin C (TnC), present in all striated muscle, is the Ca(2+)-activated trigger that initiates myocyte contraction. The binding of Ca(2+) to TnC initiates a cascade of conformational changes involving the constituent proteins of the thin filament. The functional properties of TnC and its ability to bind Ca(2+) have significant regulatory influence on the contractile reaction of muscle. Changes in TnC may also correlate with cardiac and various other muscle-related diseases. We report here the implementation of the PLIMSTEX strategy (protein ligand interaction by mass spectrometry, titration, and H/D exchange) to elucidate the binding affinity of TnC with Ca(2+) and, more importantly, to determine the order of Ca(2+) binding of the four EF hands of the protein. The four equilibrium constants, K(1) = (5 ± 5) × 10(7) M(-1), K(2) = (1.8 ± 0.8) × 10(7) M(-1), K(3) = (4.2 ± 0.9) × 10(6) M(-1), and K(4) = (1.6 ± 0.6) × 10(6) M(-1), agree well with determinations by other methods and serve to increase our confidence in the PLIMSTEX approach. We determined the order of binding to the four EF hands to be III, IV, II, and I by extracting from the H/DX results the deuterium patterns for each EF hand for each state of the protein (apo through fully Ca(2+) bound). This approach, demonstrated for the first time, may be general for determining binding orders of metal ions and other ligands to proteins.
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Affiliation(s)
- Richard Y-C. Huang
- Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130
| | - Don L. Rempel
- Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130
| | - Michael L. Gross
- Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130
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25
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Lu Y, Jeffries CM, Trewhella J. Invited review: probing the structures of muscle regulatory proteins using small-angle solution scattering. Biopolymers 2011; 95:505-16. [PMID: 21442605 DOI: 10.1002/bip.21624] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2011] [Revised: 02/03/2011] [Accepted: 02/03/2011] [Indexed: 11/09/2022]
Abstract
Small-angle X-ray and neutron scattering with contrast variation have made important contributions in advancing our understanding of muscle regulatory protein structures in the context of the dynamic molecular processes governing muscle action. The contributions of the scattering investigations have depended upon the results of key crystallographic, NMR, and electron microscopy experiments that have provided detailed structural information that has aided in the interpretation of the scattering data. This review will cover the advances made using small-angle scattering techniques, in combination with the results from these complementary techniques, in probing the structures of troponin and myosin binding protein C. A focus of the troponin work has been to understand the isoform differences between the skeletal and cardiac isoforms of this major calcium receptor in muscle. In the case of myosin binding protein C, significant data are accumulating, indicating that this protein may act to modulate the primary calcium signals from troponin, and interest in its biological role has grown because of linkages between gene mutations in the cardiac isoform and serious heart disease.
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Affiliation(s)
- Yanling Lu
- School of Molecular Bioscience, University of Sydney, NSW 2006, Australia
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26
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Martin SR, Avella G, Adrover M, de Nicola GF, Bullard B, Pastore A. Binding properties of the calcium-activated F2 isoform of Lethocerus troponin C. Biochemistry 2011; 50:1839-47. [PMID: 21250664 PMCID: PMC3057471 DOI: 10.1021/bi102076s] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
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While in most muscles contraction is triggered by calcium effluxes, insect flight muscles are also activated by mechanical stretch. We are interested in understanding the role that the troponin C protein, usually the calcium sensor, plays in stretch activation. In the flight muscles of Lethocerus, a giant water bug often used as a model system, there are two isoforms of TnC, F1 and F2, present in an approximately 10:1 ratio. F1 TnC is responsible for activating the muscle following a stretch, whereas F2 TnC produces a sustained contraction, the magnitude of which depends on the concentration of Ca2+ in the fiber. We have previously shown that F1 TnC binds only one Ca2+ ion in its C-terminal domain and that interaction with troponin H, the insect ortholog of troponin I, is insensitive to Ca2+. Here, we have studied the effect of Ca2+ and Mg2+ on the affinities of the interaction of F2 TnC with troponin H peptides. We show that the presence of two Ca2+ ions, one in each of the globular domains, increases the affinity for TnH by at least 1 order of magnitude. The N lobe has a lower affinity for Ca2+, but it is also sensitive to Mg2+. The C lobe is insensitive to Mg2+ as previously demonstrated by mutations of the individual EF-hands. The interaction with TnH seems also to have significant structural differences from that observed for the F1 TnC isoform. We discuss how our findings could account for stretch activation.
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Affiliation(s)
- Stephen R Martin
- National Institute for Medical Research, The Ridgeway, London NW71AA, U.K
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27
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Kowlessur D, Tobacman LS. Troponin regulatory function and dynamics revealed by H/D exchange-mass spectrometry. J Biol Chem 2009; 285:2686-94. [PMID: 19920153 DOI: 10.1074/jbc.m109.062349] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Muscle contraction is tightly regulated by Ca(2+) binding to the thin filament protein troponin. The mechanism of this regulation was investigated by detailed mapping of the dynamic properties of cardiac troponin using amide hydrogen exchange-mass spectrometry. Results were obtained in the presence of either saturation or non-saturation of the regulatory Ca(2+) binding site in the NH(2) domain of subunit TnC. Troponin was found to be highly dynamic, with 60% of amides exchanging H for D within seconds of exposure to D(2)O. In contrast, portions of the TnT-TnI coiled-coil exhibited high protection from exchange, despite 6 h in D(2)O. The data indicate that the most stable portion of the trimeric troponin complex is the coiled-coil. Regulatory site Ca(2+) binding altered dynamic properties (i.e. H/D exchange protection) locally, near the binding site and in the TnI switch helix that attaches to the Ca(2+)-saturated TnC NH(2) domain. More notably, Ca(2+) also altered the dynamic properties of other parts of troponin: the TnI inhibitory peptide region that binds to actin, the TnT-TnI coiled-coil, and the TnC COOH domain that contains the regulatory Ca(2+) sites in many invertebrate as opposed to vertebrate troponins. Mapping of these affected regions onto the troponin highly extended structure suggests that cardiac troponin switches between alternative sets of intramolecular interactions, similar to previous intermediate resolution x-ray data of skeletal muscle troponin.
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Affiliation(s)
- Devanand Kowlessur
- Department of Medicine, University of Illinois at Chicago, Chicago, Illinois 60612, USA
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Robertson IM, Li MX, Sykes BD. Solution structure of human cardiac troponin C in complex with the green tea polyphenol, (-)-epigallocatechin 3-gallate. J Biol Chem 2009; 284:23012-23. [PMID: 19542563 DOI: 10.1074/jbc.m109.021352] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
Heart muscle contraction is regulated by Ca(2+) binding to the thin filament protein troponin C. In cardiovascular disease, the myofilament response to Ca(2+) is often altered. Compounds that rectify this perturbation are of considerable interest as therapeutics. Plant flavonoids have been found to provide protection against a variety of human illnesses such as cancer, infection, and heart disease. (-)-Epigallocatechin gallate (EGCg), the prevalent flavonoid in green tea, modulates force generation in isolated guinea pig hearts (Hotta, Y., Huang, L., Muto, T., Yajima, M., Miyazeki, K., Ishikawa, N., Fukuzawa, Y., Wakida, Y., Tushima, H., Ando, H., and Nonogaki, T. (2006) Eur. J. Pharmacol. 552, 123-130) and in skinned cardiac muscle fibers (Liou, Y. M., Kuo, S. C., and Hsieh, S. R. (2008) Pflugers Arch. 456, 787-800; and Tadano, N., Yumoto, F., Tanokura, M., Ohtsuki, I., and Morimoto, S. (2005) Biophys. J. 88, 314a). In this study we describe the solution structure of the Ca(2+)-saturated C-terminal domain of troponin C in complex with EGCg. Moreover, we show that EGCg forms a ternary complex with the C-terminal domain of troponin C and the anchoring region of troponin I. The structural evidence indicates that the binding site of EGCg on the C-terminal domain of troponin C is in the hydrophobic pocket in the absence of troponin I, akin to EMD 57033. Based on chemical shift mapping, the binding of EGCg to the C-terminal domain of troponin C in the presence of troponin I may be to a new site formed by the troponin C.troponin I complex. This interaction of EGCg with the C-terminal domain of troponin C.troponin I complex has not been shown with other cardiotonic molecules and illustrates the potential mechanism by which EGCg modulates heart contraction.
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Affiliation(s)
- Ian M Robertson
- Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
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Li J, Jia Z, Zhou W, Wei Q. Calcineurin regulatory subunit B is a unique calcium sensor that regulates calcineurin in both calcium-dependent and calcium-independent manner. Proteins 2009; 77:612-23. [DOI: 10.1002/prot.22474] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
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Xu X, Zhang L, Shen D, Wu H, Peng L, Li J. Effect of metal ion substitutions in anticoagulation factor I from the venom of Agkistrodon acutus on the binding of activated coagulation factor X and on structural stability. J Biol Inorg Chem 2009; 14:559-71. [PMID: 19184130 DOI: 10.1007/s00775-009-0470-3] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2008] [Accepted: 01/11/2009] [Indexed: 11/29/2022]
Abstract
Anticoagulation factor I (ACF I) isolated from the venom of Agkistrodon acutus is an activated coagulation factor X (FXa)-binding protein that binds in a Ca(2+)-dependent fashion with marked anticoagulant activity. The thermodynamics of the binding of alkaline earth metal ions to ACF I and the effects of alkaline earth metal ions on the guanidine hydrochloride (GdnHCl)-induced unfolding of ACF I and the binding of ACF I to FXa were studied by isothermal titration calorimetry, fluorescence, circular dichroism, and surface plasmon resonance, respectively. The results indicate that the ionic radii of the cations occupying Ca(2+)-binding sites in ACF I crucially affect the binding affinity of ACF I for alkaline earth metal ions as well as the structural stability of ACF I against GdnHCl denaturation. Sr(2+) and Ba(2+), with ionic radii larger than the ionic radius of Ca(2+), can bind to Ca(2+)-free ACF I (apo-ACF I), while Mg(2+), with an ionic radius smaller than that of Ca(2+), shows significantly low affinity for the binding to apo-ACF I. All bindings of Ca(2+), Sr(2+), and Ba(2+) ions in two sites of ACF I are mainly enthalpy-driven and the entropy is unfavorable for them. Sr(2+)-stabilized ACF I exhibits slightly lower resistance to GdnHCl denaturation than Ca(2+)-ACF I, while Ba(2+)-stabilized ACF I exhibits much lower resistance to GdnHCl denaturation than Ca(2+)-ACF I. Mg(2+) and Sr(2+), with ionic radii close to that of Ca(2+), can bind to FXa and therefore also induce the binding of ACF I to FXa, whereas Ba(2+), with a much larger ionic radius than Ca(2+), cannot support the binding of ACF I with FXa. Our observations suggest that bindings of Ca(2+), Sr(2+), and Ba(2+) ions in two sites of ACF I increase the structural stability of ACF I, but these bindings are not essential for the binding of ACF I with FXa, and that the binding of Mg(2+), Ca(2+), and Sr(2+) ions to FXa may be essential for the recognition between FXa and ACF I.
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Affiliation(s)
- Xiaolong Xu
- Department of Chemistry, University of Science and Technology of China, Hefei, People's Republic of China.
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31
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Mouawad L, Isvoran A, Quiniou E, Craescu CT. What determines the degree of compactness of a calcium-binding protein? FEBS J 2009; 276:1082-93. [DOI: 10.1111/j.1742-4658.2008.06851.x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Ribeiro MMB, Franquelim HG, Castanho MARB, Veiga AS. Molecular interaction studies of peptides using steady-state fluorescence intensity. Static (de)quenching revisited. J Pept Sci 2008; 14:401-6. [PMID: 17994617 DOI: 10.1002/psc.939] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Protein-protein interactions, as well as peptide-peptide and peptide-protein interactions are fields of study of growing importance as molecular-level detail is avidly pursued in drug design, metabolic regulation and molecular dynamics, among other classes of studies. In membranes, this issue is particularly relevant because lipid bilayers potentiate molecular interactions due to the high local concentration of peptides and other solutes.However, experimental techniques and methodologies to detect and quantify such interactions are not abundant. A reliable, fast and inexpensive alternative methodology is revisited in this work. Considering the interaction of two molecules, at least one of them being fluorescent, either intrinsically (e.g. Trp residues) or by grafting a specific probe, changes in their aggregation state may be reported, as long as the fluorophore is sensitive to local changes in polarity, conformation and/or exposure to the solvent. The interaction will probably lead to modifications in fluorescence intensity resulting in a decrease ('quenching') or enhancement ('dequenching'). Although the presented methodology is based on static quenching methodologies, the concept is extended from quenching to any kind of interference with the fluorophore. Equations for data analysis are shown and their applications are illustrated by calculating the binding constant for several data-sets.
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Affiliation(s)
- Marta M B Ribeiro
- Centro de Química e Bioquímica, Faculdade de Ciências da Universidade de Lisboa, Campo Grande, Ed C8, 1749-016 Lisboa, Portugal
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Rocha CB, Suarez MC, Yu A, Ballard L, Sorenson MM, Foguel D, Silva JL. Volume and free energy of folding for troponin C C-domain: linkage to ion binding and N-domain interaction. Biochemistry 2008; 47:5047-58. [PMID: 18393534 DOI: 10.1021/bi702058t] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Troponin C (TnC) is an 18-kDa acidic protein of the EF-hand family that serves as the trigger for muscle contraction. In this study, we investigated the thermodynamic stability of the C-domain of TnC in all its occupancy states (apo, Mg (2+)-, and Ca (2+)-bound states) using a fluorescent mutant with Phe 105 replaced by Trp (F105W/C-domain, residues 88-162) and (1)H NMR spectroscopy. High hydrostatic pressure was employed as a perturbing agent, in combination with urea or without it. On the basis of changes in Trp emission, the C-domain apo state was denatured by pressure (in the range of 1-1000 bar) in the absence of urea. The fluorescence data were corroborated by following the changes in the (1)H NMR signal of Histidine 128. Addition of Ca (2+) or Mg (2+) increased the C-domain stability so that complete denaturation was attained only by the combined use of high hydrostatic pressure and either 7-8 M or 1.5-2 M urea, respectively. The (1)H NMR spectra in the presence of Ca (2+) was typical of a highly structured protein and allowed us to follow the changes in the local environment of several amino-acid residues as a function of pressure at 4 M Urea. Different residues presented different volume changes, but those that are in the hydrophobic core portrayed values very similar to that obtained for tryptophan 105 as measured by fluorescence, indicating that it is indeed a good probe for the overall tertiary structure. From these experiments, we calculated the thermodynamic parameters (Delta G degrees atm and Delta V) that govern the folding of the C-domain in all its possible physiological states and constructed a thermodynamic cycle. Furthermore, a comparison of the volume and free-energy changes of folding of isolated C-domain with those of intact TnC (F105W) revealed that the N-domain has little effect on the structure of the C-domain, even in the presence of Ca (2+). The volume and free-energy diagrams reveal a landscape of different conformations from the less structured, denatured apo form to the highly structured, Ca (2+)-bound form. The large change in folding free energy of the C-domain that takes place when Ca (2+) binds may explain the much higher Ca (2+) affinity of sites III and IV, 2 orders of magnitude higher than the affinity of sites I and II.
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Affiliation(s)
- Cristiane Barbosa Rocha
- Instituto de Bioquímica Médica, Centro Nacional de Ressonância Magnética Nuclear Jiri Jonas, Universidade Federal do Rio de Janeiro 21941-590, Rio de Janeiro, RJ, Brazil
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Trojan P, Krauss N, Choe HW, Giessl A, Pulvermüller A, Wolfrum U. Centrins in retinal photoreceptor cells: regulators in the connecting cilium. Prog Retin Eye Res 2008; 27:237-59. [PMID: 18329314 DOI: 10.1016/j.preteyeres.2008.01.003] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Changes in the intracellular Ca2+ concentration regulate the visual signal transduction cascade directly or more often indirectly through Ca2+-binding proteins. Here we focus on centrins, which are members of a highly conserved subgroup of the EF-hand superfamily of Ca2+-binding proteins in photoreceptor cells of the vertebrate retina. Centrins are commonly associated with centrosome-related structures. In mammalian retinal photoreceptor cells, four centrin isoforms are expressed as prominent components in the connecting cilium linking the light-sensitive outer segment compartment with the metabolically active inner segment compartment. Our data indicate that Ca2+-activated centrin isoforms assemble into protein complexes with the visual heterotrimeric G-protein transducin. This interaction of centrins with transducin is mediated by binding to the betagamma-dimer of the heterotrimeric G-protein. More recent findings show that these interactions of centrins with transducin are reciprocally regulated via site-specific phosphorylations mediated by the protein kinase CK2. The assembly of centrin/G-protein complexes is a novel aspect of translocation regulation of signalling proteins in sensory cells, and represents a potential link between molecular trafficking and signal transduction in general.
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Affiliation(s)
- Philipp Trojan
- Institut für Zoologie, Johannes Gutenberg-Universität Mainz, 55099 Mainz, Germany
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Differential effects of a green tea-derived polyphenol (-)-epigallocatechin-3-gallate on the acidosis-induced decrease in the Ca(2+) sensitivity of cardiac and skeletal muscle. Pflugers Arch 2008; 456:787-800. [PMID: 18231806 DOI: 10.1007/s00424-008-0456-y] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2007] [Revised: 01/12/2008] [Accepted: 01/14/2008] [Indexed: 10/22/2022]
Abstract
(-)-Epigallocatechin-3-gallate (EGCg), a green tea-derived polyphenol, has received much attention as a protective agent against cardiovascular diseases. In this study, we determined its effects on the acidosis-induced change in the Ca(2+) sensitivity of myofilaments in myofibrils prepared from porcine ventricular myocardium and chicken pectoral muscle. EGCg (0.1 mM) significantly inhibited the decrease caused by lowering the pH from 7.0 to 6.0 in the Ca(2+) sensitivity of myofibrillar ATPase activity in cardiac muscle, but not in skeletal muscle. Studies on recombinant mouse cardiac troponin C (cTnC) and chicken fast skeletal troponin C (sTnC) using circular dichroism and intrinsic and extrinsic fluorescence spectroscopy showed that EGCg bound to cTnC with a dissociation constant of approximately 3-4 muM, but did not bind to sTnC. By presumably binding to the cTnC C-lobe, EGCg decreased Ca(2+) binding to cTnC and overcame the depressant effect of protons on the Ca(2+) sensitivity of the cardiac contractile response. To demonstrate isoform-specific effects of the action of EGCg, the pH sensitivity of the Ca(2+) response was examined in cardiac myofibrils in which endogenous cTnC was replaced with exogenous sTnC or cTnC and in skeletal myofibrils in which the endogenous sTn complex was replaced with whole cardiac Tn complex (cTn). The results suggest that the binding of EGCg to the cardiac isoform-specific TnC or Tn complex alters the effect of pH on myofilament Ca(2+) sensitivity in striated muscle.
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36
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Nara M, Tanokura M. Infrared spectroscopic study of the metal-coordination structures of calcium-binding proteins. Biochem Biophys Res Commun 2008; 369:225-39. [PMID: 18182161 DOI: 10.1016/j.bbrc.2007.11.188] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2007] [Accepted: 11/15/2007] [Indexed: 11/30/2022]
Abstract
Carboxylate (COO(-)) groups can coordinate to metal ions in of the following four modes: 'unidentate', 'bidentate', 'bridging' and 'pseudo-bridging' modes. COO(-) stretching frequencies provide information about the coordination modes of COO(-) groups to metal ions. We review the Fourier-transform infrared spectroscopy (FTIR) of side-chain COO(-) groups of Ca(2+)-binding proteins: pike parvalbumin pI 4.10, bovine calmodulin and Akazara scallop troponin C. FTIR spectroscopy of Akazara scallop troponin C has demonstrated that the coordination structure of Mg(2+) is distinctly different from that of Ca(2+) in the Ca(2+)-binding site. The assignments of the COO(-) antisymmetric stretch have been ensured on the basis of the spectra of calcium-binding peptide analogues. The downshift of the COO(-) antisymmetric stretching mode from 1565 cm(-1) to 1555-1540 cm(-1) upon Ca(2+) binding is a commonly observed feature of FTIR spectra for EF-hand proteins.
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Affiliation(s)
- Masayuki Nara
- Laboratory of Chemistry, College of Liberal Arts and Sciences, Tokyo Medical and Dental University, Chiba 272-0827, Japan
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Li MX, Robertson IM, Sykes BD. Interaction of cardiac troponin with cardiotonic drugs: a structural perspective. Biochem Biophys Res Commun 2007; 369:88-99. [PMID: 18162171 DOI: 10.1016/j.bbrc.2007.12.108] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2007] [Accepted: 12/11/2007] [Indexed: 11/29/2022]
Abstract
Over the 40 years since its discovery, many studies have focused on understanding the role of troponin as a myofilament based molecular switch in regulating the Ca(2+)-dependent activation of striated muscle contraction. Recently, studies have explored the role of cardiac troponin as a target for cardiotonic agents. These drugs are clinically useful for treating heart failure, a condition in which the heart is no longer able to pump enough blood to other organs. These agents act via a mechanism that modulates the Ca(2+)-sensitivity of troponin; such a mode of action is therapeutically desirable because intracellular Ca(2+) concentration is not perturbed, preserving the regulation of other Ca(2+)-based signaling pathways. This review describes molecular details of the interaction of cardiac troponin with a variety of cardiotonic drugs. We present recent structural work that has identified the docking sites of several cardiotonic drugs in the troponin C-troponin I interface and discuss their relevance in the design of troponin based drugs for the treatment of heart disease.
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Affiliation(s)
- Monica X Li
- Department of Biochemistry, University of Alberta, Edmonton, Alta., Canada
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De Nicola G, Burkart C, Qiu F, Agianian B, Labeit S, Martin S, Bullard B, Pastore A. The Structure of Lethocerus Troponin C: Insights into the Mechanism of Stretch Activation in Muscles. Structure 2007; 15:813-24. [PMID: 17637342 DOI: 10.1016/j.str.2007.05.007] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2007] [Revised: 05/07/2007] [Accepted: 05/07/2007] [Indexed: 10/23/2022]
Abstract
To gain a molecular description of how muscles can be activated by mechanical stretch, we have solved the structure of the calcium-loaded F1 isoform of troponin C (TnC) from Lethocerus and characterized its interactions with troponin I (TnI). We show that the presence of only one calcium cation in the fourth EF hand motif is sufficient to induce an open conformation in the C-terminal lobe of F1 TnC, in contrast with what is observed in vertebrate muscle. This lobe interacts in a calcium-independent way both with the N terminus of TnI and, with lower affinity, with a region of TnI equivalent to the switch and inhibitory peptides of vertebrate muscles. Using both synthetic peptides and recombinant proteins, we show that the N lobe of F1 TnC is not engaged in interactions with TnI, excluding a regulatory role of this domain. These findings provide insights into mechanically stimulated muscle contraction.
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Affiliation(s)
- Gianfelice De Nicola
- Molecular Structure Division, National Institute for Medical Research, The Ridgeway, Mill Hill, London NW7 1AA, United Kingdom
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Vinogradova MV, Stone DB, Malanina GG, Mendelson RA, Fletterick RJ. Ca ion and the troponin switch. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2007; 592:47-57. [PMID: 17278355 DOI: 10.1007/978-4-431-38453-3_6] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
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40
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Yang L, Gao YQ. An Approximate Method in Using Molecular Mechanics Simulations To Study Slow Protein Conformational Changes. J Phys Chem B 2007; 111:2969-75. [PMID: 17319713 DOI: 10.1021/jp066289+] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The broad range of characteristic motions in proteins has limited the applicability of molecular dynamics simulations in studying large-scale conformational transitions. We present an approximate method, making use of standard MD simulations and using a much larger integration time step, to obtain the structural changes for slow systematic motions of large complex systems. We show the applicability of this method by simulating the open to closed Calmodulin calcium binding domain conformational changes. Starting with the Ca2+-bound X-ray structure, and after the removal of the Ca2+ ions, our calculation yielded intermediate conformations during the rearrangement of helices in each Ca2+ binding pocket, leading to a structure with a lowest rmsd of 1.56 A compared to the NMR apo-calmodulin structure.
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Affiliation(s)
- Lijiang Yang
- Department of Chemistry, Texas A and M University, College Station, Texas 77843, USA
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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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Babini E, Bertini I, Capozzi F, Chirivino E, Luchinat C. A structural and dynamic characterization of the EF-hand protein CLSP. Structure 2006; 14:1029-38. [PMID: 16765896 DOI: 10.1016/j.str.2006.04.004] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2006] [Revised: 04/04/2006] [Accepted: 04/06/2006] [Indexed: 11/21/2022]
Abstract
The structure and dynamics of human calmodulin-like skin protein (CLSP) have been characterized by NMR spectroscopy. The mobility of CLSP has been found to be different for the N-terminal and C-terminal domains. The isolated domains were also expressed and analyzed. The structure of the isolated C-terminal domain is presented. The N-terminal domain is characterized by four stable helices, which experience large fluctuations. This is shown to be due to mutations in the hydrophobic core. The overall N-terminal domain behavior is similar both in the full-length protein and in the isolated domain. By exploiting the capability of Tb3+ bound to CLSP to induce partial orientation of the molecule in a magnetic field, restricted motion of one domain with respect to the other was proved. By using NMR, ITC, and ESI-MS, the calcium and magnesium binding properties were investigated. Finally, CLSP is framed into the evolutionary scheme of the calmodulin-like family.
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Affiliation(s)
- Elena Babini
- Centro Risonanze Magnetiche, University of Florence, Via Sacconi 6, 50019 Sesto Fiorentino, Florence, Italy
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43
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Nara M, Morii H, Yumoto F, Kagi H, Tanokura M. Fourier transform infrared spectroscopic study on the Ca2+ -bound coordination structures of synthetic peptide analogues of the calcium-binding site III of troponin C. Biopolymers 2006; 82:339-43. [PMID: 16475158 DOI: 10.1002/bip.20477] [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: 11/06/2022]
Abstract
The coordination structures of Ca(2+) ion bound to synthetic peptide analogues of the calcium-binding site III of rabbit skeletal muscle troponin C (TnC) were investigated by Fourier transform infrared (FTIR) spectroscopy. The region of the COO(-) antisymmetric stretching vibration provides information about the coordination modes of a COO(-) group to a metal ion. The 34-residue peptide corresponding to the EF hand motif (helix-loop-helix) showed a band at 1552 cm(-1) in the Ca(2+)-loaded state, indicating that the side-chain COO(-) group of Glu at the 12th position serves as a ligand for Ca(2+) in the bidentate coordination mode. On the other hand, the 13-residue peptide (Ac-DRDADGYIDAEEL-NH(2)) containing the Ca(2+)-binding site III (DRDADGYIDAEE) did not show such spectral patterns in the Ca(2+)-loaded state, meaning that shorter synthetic peptide corresponding to the site III has less or no affinity for Ca(2+). It was found that the 17-residue peptide (Ac-DRDADGYIDAEELAEIF-NH(2)) is the minimum peptide necessary for the interaction of side-chain COO(-)of Glu at the 12th position with Ca(2+) in the bidentate coordination mode. We discuss the relationship between the amino acid length of synthetic peptide analogues and the formation of Ca(2+)-bound coordination structure.
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Affiliation(s)
- Masayuki Nara
- Laboratory of Chemistry, College of Liberal Arts and Sciences, Tokyo Medical and Dental University, 2-8-30 Kohnodai, Ichikawa, Chiba 272-0827, Japan.
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Grabarek Z. Structural basis for diversity of the EF-hand calcium-binding proteins. J Mol Biol 2006; 359:509-25. [PMID: 16678204 DOI: 10.1016/j.jmb.2006.03.066] [Citation(s) in RCA: 277] [Impact Index Per Article: 15.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2006] [Revised: 03/25/2006] [Accepted: 03/30/2006] [Indexed: 12/31/2022]
Abstract
The calcium binding proteins of the EF-hand super-family are involved in the regulation of all aspects of cell function. These proteins exhibit a great diversity of composition, structure, Ca2+-binding and target interaction properties. Here, our current understanding of the Ca2+-binding mechanism is assessed. The structures of the EF-hand motifs containing 11-14 amino acid residues in the Ca2+-binding loop are analyzed within the framework of the recently proposed two-step Ca2+-binding mechanism. A hypothesis is put forward that in all EF-hand proteins the Ca2+-binding and the resultant conformational responses are governed by the central structure connecting the Ca2+-binding loops in the two-EF-hand domain. This structure, named EFbeta-scaffold, defines the position of the bound Ca2+, and coordinates the function of the N-terminal (variable and flexible) with the C-terminal (invariable and rigid) parts of the Ca2+-binding loop. It is proposed that the nature of the first ligand of the Ca2+-binding loop is an important determinant of the conformational change. Additional factors, including the interhelical contacts, the length, structure and flexibility of the linker connecting the EF-hand motifs, and the overall energy balance provide the fine-tuning of the Ca2+-induced conformational change in the EF-hand proteins.
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Affiliation(s)
- Zenon Grabarek
- Boston Biomedical Research Institute, Watertown, MA 02472, USA.
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Babini E, Bertini I, Capozzi F, Luchinat C, Quattrone A, Turano M. Principal Component Analysis of the Conformational Freedom within the EF-Hand Superfamily. J Proteome Res 2005; 4:1961-71. [PMID: 16335940 DOI: 10.1021/pr050148n] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
A database of nonredundant structures of EF-hand domains--i.e., pairs of helix-loop-helix motifs--has been assembled, and the six angles among the four helices re-determined. A principal component analysis of these angles allows us to use two such components (PC1 and PC2) to describe the system retaining 80% of the total variance. A PC2 against PC1 plot representation allows us to represent in a compact way the full range of structural diversity of EF-hand domains, their grouping into protein families, and the variation for each family upon calcium and peptide binding.
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Affiliation(s)
- Elena Babini
- Department of Food Science, University of Bologna, 47023 Cesena, Italy
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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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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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Abstract
Although well known as the location of the mechanism by which the cardiac sarcomere is activated by Ca2+ to generate force and shortening, the thin filament is now also recognized as a vital component determining the dynamics of contraction and relaxation. Molecular signaling in the thin filament involves steric, allosteric, and cooperative mechanisms that are modified by protein phosphorylation, sarcomere length and load, the chemical environment, and isoform composition. Approaches employing transgenesis and mutagenesis now permit investigation of these processes at the level of the systems biology of the heart. These studies reveal that the thin filaments are not merely slaves to the levels of Ca2+ determined by membrane channels, transporters and exchangers, but are actively involved in beat to beat control of cardiac function by neural and hormonal factors and by the Frank-Starling mechanism.
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Affiliation(s)
- Tomoyoshi Kobayashi
- Department of Physiology and Biophysics, College of Medicine, University of Illinois at Chicago, Chicago, Illinois 60612, USA.
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Vinogradova MV, Stone DB, Malanina GG, Karatzaferi C, Cooke R, Mendelson RA, Fletterick RJ. Ca(2+)-regulated structural changes in troponin. Proc Natl Acad Sci U S A 2005; 102:5038-43. [PMID: 15784741 PMCID: PMC555973 DOI: 10.1073/pnas.0408882102] [Citation(s) in RCA: 249] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2004] [Indexed: 11/18/2022] Open
Abstract
Troponin senses Ca2+ to regulate contraction in striated muscle. Structures of skeletal muscle troponin composed of TnC (the sensor), TnI (the regulator), and TnT (the link to the muscle thin filament) have been determined. The structure of troponin in the Ca(2+)-activated state features a nearly twofold symmetrical assembly of TnI and TnT subunits penetrated asymmetrically by the dumbbell-shaped TnC subunit. Ca ions are thought to regulate contraction by controlling the presentation to and withdrawal of the TnI inhibitory segment from the thin filament. Here, we show that the rigid central helix of the sensor binds the inhibitory segment of TnI in the Ca(2+)-activated state. Comparison of crystal structures of troponin in the Ca(2+)-activated state at 3.0 angstroms resolution and in the Ca(2+)-free state at 7.0 angstroms resolution shows that the long framework helices of TnI and TnT, presumed to be a Ca(2+)-independent structural domain of troponin are unchanged. Loss of Ca ions causes the rigid central helix of the sensor to collapse and to release the inhibitory segment of TnI. The inhibitory segment of TnI changes conformation from an extended loop in the presence of Ca2+ to a short alpha-helix in its absence. We also show that Anapoe, a detergent molecule, increases the contractile force of muscle fibers and binds specifically, together with the TnI switch helix, in a hydrophobic pocket of TnC upon activation by Ca ions.
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Affiliation(s)
- Maia V Vinogradova
- Department of Biochemistry and Biophysics, University of California, San Francisco, CA 94143-2240, USA
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