1
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Lehrer SS. The molecular basis for diminished muscle function in acidosis: a proposal. J Muscle Res Cell Motil 2020; 41:259-263. [PMID: 32048111 DOI: 10.1007/s10974-020-09576-5] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2019] [Revised: 01/24/2020] [Accepted: 02/05/2020] [Indexed: 11/25/2022]
Abstract
A testable molecular proposal for the effects of acidosis on skeletal and cardiac muscle is presented. It is based on fluorescence studies published in 1974, which provided evidence for carboxylates in an EF-hand Ca2+ binding site having an abnormal pKa. This results in an H+-bound Blocked substate in the 3-state model of muscle regulation whose contribution inhibits myosin binding in the pH 7 to 6 range. A schematic cartoon illustrates the substate within the 3-state model.
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2
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Solís C, Kim GH, Moutsoglou ME, Robinson JM. Ca 2+ and Myosin Cycle States Work as Allosteric Effectors of Troponin Activation. Biophys J 2018; 115:1762-1769. [PMID: 30249400 DOI: 10.1016/j.bpj.2018.08.033] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2017] [Revised: 08/22/2018] [Accepted: 08/24/2018] [Indexed: 10/28/2022] Open
Abstract
In cardiac muscle, troponin (Tn) and tropomyosin inhibit actin and myosin interactions through the steric blocking of myosin binding to F-actin. Ca2+ binding to Tn C modulates this inhibition. Thin filaments become activated upon Ca2+ binding, which enables strong binding of myosin with a concomitant release of ATP hydrolysis products and level arm swinging responsible for force generation. Despite this level of description, the current cross-bridge cycle model does not fully define the structural events that take place within Tn during combinatorial myosin and Ca2+ interventions. Here, we studied conformational changes within Tn bound to F-actin and tropomyosin by fluorescence lifetime imaging combined with Förster resonance energy transfer. Fluorescent dye molecules covalently bound to the Tn C C-lobe and Tn I C-terminal domain report Ca2+- and myosin-induced activation of Tn. Reconstituted thin filaments were deposited on a myosin-coated surface similar to an in vitro motility assay setup without filament sliding involved. Under all the tested conditions, Ca2+ was responsible for the most significant changes in Tn activation. Rigor myosin activated Tn at subsaturated Ca2+ conditions but not to the degree seen in thin filaments with Ca2+. ATP-γ-S did not affect Tn activation significantly; however, blebbistatin induced significant activation at subsaturating Ca2+ levels. The relation between the extent of Tn activation and its conformational flexibility suggests that active/inactive Tn states coexist in different proportions that depend on the combination of effectors. These results satisfy an allosteric activation model of the thin filament as a function of Ca2+ and the myosin catalytic cycle state.
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Affiliation(s)
- Christopher Solís
- Department of Chemistry and Biochemistry, South Dakota State University, Brookings, South Dakota.
| | - Giho H Kim
- Department of Chemistry and Biochemistry, South Dakota State University, Brookings, South Dakota
| | - Maria E Moutsoglou
- Department of Chemistry and Biochemistry, South Dakota State University, Brookings, South Dakota
| | - John M Robinson
- Department of Chemistry and Biochemistry, South Dakota State University, Brookings, South Dakota
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3
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Klein BA, Reiz B, Robertson IM, Irving M, Li L, Sun YB, Sykes BD. Reversible Covalent Reaction of Levosimendan with Cardiac Troponin C in Vitro and in Situ. Biochemistry 2018; 57:2256-2265. [DOI: 10.1021/acs.biochem.8b00109] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Affiliation(s)
- Brittney A. Klein
- Department of Biochemistry, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
| | - Béla Reiz
- Department of Chemistry, Faculty of Science, University of Alberta, Edmonton, Alberta T6H 2H7, Canada
| | - Ian M. Robertson
- Pharmaceutical and Health Benefits Branch, Ministry of Health, Government of Alberta, Edmonton, Alberta T5J 3Z5, Canada
| | - Malcolm Irving
- Randall Centre for Cell and Molecular Biophysics and British Heart Foundation Centre of Research Excellence, King’s College London, London SE1 1UL, U.K
| | - Liang Li
- Department of Chemistry, Faculty of Science, University of Alberta, Edmonton, Alberta T6H 2H7, Canada
| | - Yin-Biao Sun
- Randall Centre for Cell and Molecular Biophysics and British Heart Foundation Centre of Research Excellence, King’s College London, London SE1 1UL, U.K
| | - Brian D. Sykes
- Department of Biochemistry, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
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4
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Schlecht W, Dong WJ. Dynamic Equilibrium of Cardiac Troponin C's Hydrophobic Cleft and Its Modulation by Ca 2+ Sensitizers and a Ca 2+ Sensitivity Blunting Phosphomimic, cTnT(T204E). Bioconjug Chem 2017; 28:2581-2590. [PMID: 28876897 DOI: 10.1021/acs.bioconjchem.7b00418] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Several studies have suggested that conformational dynamics are important in the regulation of thin filament activation in cardiac troponin C (cTnC); however, little direct evidence has been offered to support these claims. In this study, a dye homodimerization approach is developed and implemented that allows the determination of the dynamic equilibrium between open and closed conformations in cTnC's hydrophobic cleft. Modulation of this equilibrium by Ca2+, cardiac troponin I (cTnI), cardiac troponin T (cTnT), Ca2+-sensitizers, and a Ca2+-desensitizing phosphomimic of cTnT (cTnT(T204E) is characterized. Isolated cTnC contained a small open conformation population in the absence of Ca2+ that increased significantly upon the addition of saturating levels of Ca2+. This suggests that the Ca2+-induced activation of thin filament arises from an increase in the probability of hydrophobic cleft opening. The inclusion of cTnI increased the population of open cTnC, and the inclusion of cTnT had the opposite effect. Samples containing Ca2+-desensitizing cTnT(T204E) showed a slight but insignificant decrease in open conformation probability compared to samples with cardiac troponin T, wild type [cTnT(wt)], while Ca2+ sensitizer treated samples generally increased open conformation probability. These findings show that an equilibrium between the open and closed conformations of cTnC's hydrophobic cleft play a significant role in tuning the Ca2+ sensitivity of the heart.
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Affiliation(s)
- William Schlecht
- The Voiland School of Chemical Engineering and Bioengineering and ‡The Department of Integrated Neuroscience and Physiology, Washington State University , Pullman, Washington 99164, United States
| | - Wen-Ji Dong
- The Voiland School of Chemical Engineering and Bioengineering and ‡The Department of Integrated Neuroscience and Physiology, Washington State University , Pullman, Washington 99164, United States
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5
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Pineda-Sanabria SE, Robertson IM, Sun YB, Irving M, Sykes BD. Probing the mechanism of cardiovascular drugs using a covalent levosimendan analog. J Mol Cell Cardiol 2016; 92:174-84. [PMID: 26853943 PMCID: PMC4831045 DOI: 10.1016/j.yjmcc.2016.02.003] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/01/2015] [Revised: 01/24/2016] [Accepted: 02/02/2016] [Indexed: 01/16/2023]
Abstract
One approach to improve contraction in the failing heart is the administration of calcium (Ca2 +) sensitizers. Although it is known that levosimendan and other sensitizers bind to troponin C (cTnC), their in vivo mechanism is not fully understood. Based on levosimendan, we designed a covalent Ca2 + sensitizer (i9) that targets C84 of cTnC and exchanged this complex into cardiac muscle. The NMR structure of the covalent complex showed that i9 binds deep in the hydrophobic pocket of cTnC. Despite slightly reducing troponin I affinity, i9 enhanced the Ca2 + sensitivity of cardiac muscle. We conclude that i9 enhances Ca2 + sensitivity by stabilizing the open conformation of cTnC. These findings provide new insights into the in vivo mechanism of Ca2 + sensitization and demonstrate that directly targeting cTnC has significant potential in cardiovascular therapy. A Ca2 + sensitizer, i9 was designed that forms a covalent bond with C84 of cTnC. i9 stabilized the open state of the N-domain of cTnC. The structure of the covalent cTnC-cTnI-i9 complex was solved by NMR. The structure showed that i9 binds deep in the hydrophobic pocket of cTnC. Despite slightly reducing cTnI affinity, i9 enhanced the Ca2 + sensitivity of cardiac muscle.
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Affiliation(s)
- Sandra E Pineda-Sanabria
- Department of Biochemistry, Faculty of Medicine & Dentistry, University of Alberta, Edmonton, AB T6G 2H7, Canada
| | - Ian M Robertson
- Randall Division of Cell and Molecular Biophysics and British Heart Foundation Centre of Research Excellence, New Hunt's House, Guy's Campus, King's College London, London SE1 1UL, UK
| | - Yin-Biao Sun
- Randall Division of Cell and Molecular Biophysics and British Heart Foundation Centre of Research Excellence, New Hunt's House, Guy's Campus, King's College London, London SE1 1UL, UK
| | - Malcolm Irving
- Randall Division of Cell and Molecular Biophysics and British Heart Foundation Centre of Research Excellence, New Hunt's House, Guy's Campus, King's College London, London SE1 1UL, UK
| | - Brian D Sykes
- Department of Biochemistry, Faculty of Medicine & Dentistry, University of Alberta, Edmonton, AB T6G 2H7, Canada.
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6
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In situ time-resolved FRET reveals effects of sarcomere length on cardiac thin-filament activation. Biophys J 2015; 107:682-693. [PMID: 25099807 DOI: 10.1016/j.bpj.2014.05.044] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2013] [Revised: 05/10/2014] [Accepted: 05/13/2014] [Indexed: 02/07/2023] Open
Abstract
During cardiac thin-filament activation, the N-domain of cardiac troponin C (N-cTnC) binds to Ca(2+) and interacts with the actomyosin inhibitory troponin I (cTnI). The interaction between N-cTnC and cTnI stabilizes the Ca(2+)-induced opening of N-cTnC and is presumed to also destabilize cTnI-actin interactions that work together with steric effects of tropomyosin to inhibit force generation. Recently, our in situ steady-state FRET measurements based on N-cTnC opening suggested that at long sarcomere length, strongly bound cross-bridges indirectly stabilize this Ca(2+)-sensitizing N-cTnC-cTnI interaction through structural effects on tropomyosin and cTnI. However, the method previously used was unable to determine whether N-cTnC opening depends on sarcomere length. In this study, we used time-resolved FRET to monitor the effects of cross-bridge state and sarcomere length on the Ca(2+)-dependent conformational behavior of N-cTnC in skinned cardiac muscle fibers. FRET donor (AEDANS) and acceptor (DDPM)-labeled double-cysteine mutant cTnC(T13C/N51C)AEDANS-DDPM was incorporated into skinned muscle fibers to monitor N-cTnC opening. To study the structural effects of sarcomere length on N-cTnC, we monitored N-cTnC opening at relaxing and saturating levels of Ca(2+) and 1.80 and 2.2-μm sarcomere length. Mg(2+)-ADP and orthovanadate were used to examine the structural effects of noncycling strong-binding and weak-binding cross-bridges, respectively. We found that the stabilizing effect of strongly bound cross-bridges on N-cTnC opening (which we interpret as transmitted through related changes in cTnI and tropomyosin) become diminished by decreases in sarcomere length. Additionally, orthovanadate blunted the effect of sarcomere length on N-cTnC conformational behavior such that weak-binding cross-bridges had no effect on N-cTnC opening at any tested [Ca(2+)] or sarcomere length. Based on our findings, we conclude that the observed sarcomere length-dependent positive feedback regulation is a key determinant in the length-dependent Ca(2+) sensitivity of myofilament activation and consequently the mechanism underlying the Frank-Starling law of the heart.
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7
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Lerner E, Orevi T, Ben Ishay E, Amir D, Haas E. Kinetics of fast changing intramolecular distance distributions obtained by combined analysis of FRET efficiency kinetics and time-resolved FRET equilibrium measurements. Biophys J 2014; 106:667-76. [PMID: 24507607 DOI: 10.1016/j.bpj.2013.11.4500] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2013] [Revised: 10/13/2013] [Accepted: 11/05/2013] [Indexed: 10/25/2022] Open
Abstract
Detailed studies of the mechanisms of macromolecular conformational transitions such as protein folding are enhanced by analysis of changes of distributions for intramolecular distances during the transitions. Time-resolved Förster resonance energy transfer (FRET) measurements yield such data, but the more readily available kinetics of mean FRET efficiency changes cannot be analyzed in terms of changes in distances because of the sixth-power dependence on the mean distance. To enhance the information obtained from mean FRET efficiency kinetics, we combined the analyses of FRET efficiency kinetics and equilibrium trFRET experiments. The joint analysis enabled determination of transient distance distributions along the folding reaction both in cases where a two-state transition is valid and in some cases consisting of a three-state scenario. The procedure and its limits were tested by simulations. Experimental data obtained from stopped-flow measurements of the refolding of Escherichia coli adenylate kinase were analyzed. The distance distributions between three double-labeled mutants, in the collapsed transient state, were determined and compared to those obtained experimentally using the double-kinetics technique. The proposed method effectively provides information on distance distributions of kinetically accessed intermediates of fast conformational transitions induced by common relaxation methods.
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Affiliation(s)
- E Lerner
- The Mina and Everard Goodman Faculty of Life Sciences, Bar Ilan University, Ramat Gan, Israel 52900
| | - T Orevi
- The Mina and Everard Goodman Faculty of Life Sciences, Bar Ilan University, Ramat Gan, Israel 52900
| | - E Ben Ishay
- The Mina and Everard Goodman Faculty of Life Sciences, Bar Ilan University, Ramat Gan, Israel 52900
| | - D Amir
- The Mina and Everard Goodman Faculty of Life Sciences, Bar Ilan University, Ramat Gan, Israel 52900
| | - E Haas
- The Mina and Everard Goodman Faculty of Life Sciences, Bar Ilan University, Ramat Gan, Israel 52900.
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8
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Pineda-Sanabria SE, Julien O, Sykes BD. Versatile cardiac troponin chimera for muscle protein structural biology and drug discovery. ACS Chem Biol 2014; 9:2121-30. [PMID: 25010113 DOI: 10.1021/cb500249j] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Investigation of the molecular interactions within and between subunits of the heterotrimeric troponin complex, and with other proteins in the sarcomere, has revealed salient structural elements involved in regulation of muscle contraction. The discovery of new cardiotonic drugs and structural studies utilizing intact troponin, or regulatory complexes formed between the key regions identified in troponin C and troponin I, face intrinsic and technical difficulties associated with weak protein-protein interactions and with solubility, aggregation, stability of the overall architecture, isotope labeling, and size, respectively. We have designed and characterized a chimeric troponin C-troponin I hybrid protein with a cleavable linker that is useful for producing isotopically labeled troponin peptides, stabilizes their interaction, and has proven to be a faithful representation of the original complex in the systolic state, but lacking its disadvantages, making it particularly suitable for drug screening and structural studies.
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Affiliation(s)
- Sandra E. Pineda-Sanabria
- Department of Biochemistry, University of Alberta, 4-19 Medical
Sciences Building, Edmonton, Alberta Canada, T6G 2H7
| | - Olivier Julien
- Department of Biochemistry, University of Alberta, 4-19 Medical
Sciences Building, Edmonton, Alberta Canada, T6G 2H7
| | - Brian D. Sykes
- Department of Biochemistry, University of Alberta, 4-19 Medical
Sciences Building, Edmonton, Alberta Canada, T6G 2H7
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9
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Sevrieva I, Knowles AC, Kampourakis T, Sun YB. Regulatory domain of troponin moves dynamically during activation of cardiac muscle. J Mol Cell Cardiol 2014; 75:181-7. [PMID: 25101951 PMCID: PMC4169182 DOI: 10.1016/j.yjmcc.2014.07.015] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/01/2014] [Revised: 07/09/2014] [Accepted: 07/26/2014] [Indexed: 11/24/2022]
Abstract
Heart muscle is activated by Ca2+ to generate force and shortening, and the signaling pathway involves allosteric mechanisms in the thin filament. Knowledge about the structure-function relationship among proteins in the thin filament is critical in understanding the physiology and pathology of the cardiac function, but remains obscure. We investigate the conformation of the cardiac troponin (Tn) on the thin filament and its response to Ca2+ activation and propose a molecular mechanism for the regulation of cardiac muscle contraction by Tn based uniquely on information from in situ protein domain orientation. Polarized fluorescence from bifunctional rhodamine is used to determine the orientation of the major component of Tn core domain on the thin filaments of cardiac muscle. We show that the C-terminal lobe of TnC (CTnC) does not move during activation, suggesting that CTnC, together with the coiled coil formed by the TnI and TnT chains (IT arm), acts as a scaffold that holds N-terminal lobe of TnC (NTnC) and the actin binding regions of troponin I. The NTnC, on the other hand, exhibits multiple orientations during both diastole and systole. By combining the in situ orientation data with published in vitro measurements of intermolecular distances, we construct a model for the in situ structure of the thin filament. The conformational dynamics of NTnC plays an important role in the regulation of cardiac muscle contraction by moving the C-terminal region of TnI from its actin-binding inhibitory location and enhancing the movement of tropomyosin away from its inhibitory position. In situ conformational changes of troponin in myocardium were investigated. A model for the cardiac thin filament was constructed based on the in situ data. The IT arm of cardiac troponin acts as a scaffold that holds the regulatory domain. The regulatory domain of cardiac troponin moves dynamically during activation. The dynamics of regulatory domain is important in cardiac muscle regulation.
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Affiliation(s)
- Ivanka Sevrieva
- Randall Division of Cell and Molecular Biophysics and British Heart Foundation Centre of Research Excellence, King's College London, London, SE1 1UL, UK
| | - Andrea C Knowles
- Randall Division of Cell and Molecular Biophysics and British Heart Foundation Centre of Research Excellence, King's College London, London, SE1 1UL, UK
| | - Thomas Kampourakis
- Randall Division of Cell and Molecular Biophysics and British Heart Foundation Centre of Research Excellence, King's College London, London, SE1 1UL, UK
| | - Yin-Biao Sun
- Randall Division of Cell and Molecular Biophysics and British Heart Foundation Centre of Research Excellence, King's College London, London, SE1 1UL, UK.
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10
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Defective Dynamic Properties of Human Cardiac Troponin Mutations. Biosci Biotechnol Biochem 2014; 74:82-91. [DOI: 10.1271/bbb.90586] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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11
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Structural basis for the in situ Ca(2+) sensitization of cardiac troponin C by positive feedback from force-generating myosin cross-bridges. Arch Biochem Biophys 2013; 537:198-209. [PMID: 23896515 DOI: 10.1016/j.abb.2013.07.013] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2013] [Revised: 07/10/2013] [Accepted: 07/11/2013] [Indexed: 11/21/2022]
Abstract
The in situ structural coupling between the cardiac troponin (cTn) Ca(2+)-sensitive regulatory switch (CRS) and strong myosin cross-bridges was investigated using Förster resonance energy transfer (FRET). The double cysteine mutant cTnC(T13C/N51C) was fluorescently labeled with the FRET pair 5-(iodoacetamidoethyl)aminonaphthelene-1-sulfonic acid (IAEDENS) and N-(4-dimethylamino-3,5-dinitrophenyl)maleimide (DDPM) and then incorporated into detergent skinned left ventricular papillary fiber bundles. Ca(2+) titrations of cTnC(T13C/N51C)AEDENS/DDPM-reconstituted fibers showed that the Ca(2+)-dependence of the opening of the N-domain of cTnC (N-cTnC) statistically matched the force-Ca(2+) relationship. N-cTnC opening still occurred steeply during Ca(2+) titrations in the presence of 1mM vanadate, but the maximal extent of ensemble-averaged N-cTnC opening and the Ca(2+)-sensitivity of the CRS were significantly reduced. At nanomolar, resting Ca(2+) levels, treatment with ADP·Mg in the absence of ATP caused a partial opening of N-cTnC. During subsequent Ca(2+) titrations in the presence of ADP·Mg and absence of ATP, further N-cTnC opening was stimulated as the CRS responded to Ca(2+) with increased Ca(2+)-sensitivity and reduced steepness. These findings supported our hypothesis here that strong cross-bridge interactions with the cardiac thin filament exert a Ca(2+)-sensitizing effect on the CRS by stabilizing the interaction between the exposed hydrophobic patch of N-cTnC and the switch region of cTnI.
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12
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Protein mechanics: how force regulates molecular function. Biochim Biophys Acta Gen Subj 2013; 1830:4762-8. [PMID: 23791949 DOI: 10.1016/j.bbagen.2013.06.005] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2012] [Revised: 05/26/2013] [Accepted: 06/04/2013] [Indexed: 12/13/2022]
Abstract
BACKGROUND Regulation of proteins is ubiquitous and vital for any organism. Protein activity can be altered chemically, by covalent modifications or non-covalent binding of co-factors. Mechanical forces are emerging as an additional way of regulating proteins, by inducing a conformational change or by partial unfolding. SCOPE We review some advances in experimental and theoretical techniques to study protein allostery driven by mechanical forces, as opposed to the more conventional ligand driven allostery. In this respect, we discuss recent single molecule pulling experiments as they have substantially augmented our view on the protein allostery by mechanical signals in recent years. Finally, we present a computational analysis technique, Force Distribution Analysis, that we developed to reveal allosteric pathways in proteins. MAJOR CONCLUSIONS Any kind of external perturbation, being it ligand binding or mechanical stretching, can be viewed as an external force acting on the macromolecule, rendering force-based experimental or computational techniques, a very general approach to the mechanics involved in protein allostery. GENERAL SIGNIFICANCE This unifying view might aid to decipher how complex allosteric protein machineries are regulated on the single molecular level.
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13
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Lopez-Davila AJ, Elhamine F, Ruess DF, Papadopoulos S, Iorga B, Kulozik FP, Zittrich S, Solzin J, Pfitzer G, Stehle R. Kinetic mechanism of Ca²⁺-controlled changes of skeletal troponin I in psoas myofibrils. Biophys J 2013; 103:1254-64. [PMID: 22995498 DOI: 10.1016/j.bpj.2012.08.022] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2012] [Revised: 07/12/2012] [Accepted: 08/08/2012] [Indexed: 10/27/2022] Open
Abstract
Conformational changes in the skeletal troponin complex (sTn) induced by rapidly increasing or decreasing the [Ca(2+)] were probed by 5-iodoacetamidofluorescein covalently bound to Cys-133 of skeletal troponin I (sTnI). Kinetics of conformational changes was determined for the isolated complex and after incorporating the complex into rabbit psoas myofibrils. Isolated and incorporated sTn exhibited biphasic Ca(2+)-activation kinetics. Whereas the fast phase (k(obs)∼1000 s(-1)) is only observed in this study, where kinetics were induced by Ca(2+), the slower phase resembles the monophasic kinetics of sTnI switching observed in another study (Brenner and Chalovich. 1999. Biophys. J. 77:2692-2708) that investigated the sTnI switching induced by releasing the feedback of force-generating cross-bridges on thin filament activation. Therefore, the slower conformational change likely reflects the sTnI switch that regulates force development. Modeling reveals that the fast conformational change can occur after the first Ca(2+) ion binds to skeletal troponin C (sTnC), whereas the slower change requires Ca(2+) binding to both regulatory sites of sTnC. Incorporating sTn into myofibrils increased the off-rate and lowered the Ca(2+) sensitivity of sTnI switching. Comparison of switch-off kinetics with myofibril force relaxation kinetics measured in a mechanical setup indicates that sTnI switching might limit the rate of fast skeletal muscle relaxation.
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Affiliation(s)
- A J Lopez-Davila
- Institute of Vegetative Physiology, University Cologne, Köln, Germany
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14
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Lassalle MW. Expression and assembly of active human cardiac troponin in Escherichia coli. Protein Expr Purif 2012; 87:61-6. [PMID: 23116770 DOI: 10.1016/j.pep.2012.10.005] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2012] [Revised: 10/18/2012] [Accepted: 10/19/2012] [Indexed: 10/27/2022]
Abstract
Cardiomyopathy-related mutations in human cardiac troponin subunits, including troponin C (hcTnC), troponin I (hcTnI), and troponin T (hcTnT), are well-documented. Recently, it has been recognised that human cardiac troponin (hcTn) is a sophisticated allosteric system. Therefore, the effect of drugs on this protein complex should be studied with assembled hcTn rather than a short fragment of a subunit or the subunit itself. Here, we describe the expression and assembly of active hcTn in Escherichia coli, a novel method that is rapid and simple, and produces large amounts of functional hcTn.
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Affiliation(s)
- Michael W Lassalle
- Senior Research Fellow Center, Ehime University, 3 Bunkyo-cho, Matsuyama, Ehime 790-8577, Japan.
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15
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Wen Y, Xu Y, Wang Y, Pinto JR, Potter JD, Kerrick WGL. Functional effects of a restrictive-cardiomyopathy-linked cardiac troponin I mutation (R145W) in transgenic mice. J Mol Biol 2009; 392:1158-67. [PMID: 19651143 DOI: 10.1016/j.jmb.2009.07.080] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2009] [Revised: 06/22/2009] [Accepted: 07/28/2009] [Indexed: 02/05/2023]
Abstract
The human cardiac troponin I (hcTnI) mutation R145W has been associated with restrictive cardiomyopathy. In this study, simultaneous measurements of ATPase activity and force in skinned papillary fibers from hcTnI R145W transgenic mice (Tg-R145W) were explored. Tg-R145W fibers showed an approximately 13-16% increase in maximal Ca(2+)-activated force and ATPase activity compared to hcTnI wild-type transgenic mice. The force-generating cross-bridge turnover rate (g) and the energy cost (ATPase/force) were the same in all groups of fibers. Also, the Tg-R145W fibers showed a large increase in the Ca(2+) sensitivity of both force development and ATPase. In intact fibers, the mutation caused prolonged force and intracellular [Ca(2+)] transients and increased time to peak force. Analysis of force and Ca(2+) transients showed that there was a 40% increase in peak force in Tg-R145W muscles, which was likely due to the increased Ca(2+) transient duration. The above cited results suggest that: (1) there would be an increase in resistance to ventricular filling during diastole resulting from the prolonged force and Ca(2+) transients that would result in a decrease in ventricular filling (diastolic dysfunction); and (2) there would be a large (approximately 53%) increase in force during systole, which may help to partly compensate for diastolic dysfunction. These functional results help to explain the mechanisms by which these mutations give rise to a restrictive phenotype.
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Affiliation(s)
- Yuhui Wen
- Department of Physiology and Biophysics, Miller School of Medicine, University of Miami, Miami, FL 33136, USA
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16
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Kobayashi T, Patrick SE, Kobayashi M. Ala scanning of the inhibitory region of cardiac troponin I. J Biol Chem 2009; 284:20052-60. [PMID: 19483081 DOI: 10.1074/jbc.m109.001396] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In skeletal and cardiac muscles, troponin (Tn), which resides on the thin filament, senses a change in intracellular Ca(2+) concentration. Tn is composed of TnC, TnI, and TnT. Ca(2+) binding to the regulatory domain of TnC removes the inhibitory effect by TnI on the contraction. The inhibitory region of cardiac TnI spans from residue 138 to 149. Upon Ca(2+) activation, the inhibitory region is believed to be released from actin, thus triggering actin-activation of myosin ATPase. In this study, we created a series of Ala-substitution mutants of cTnI to delineate the functional contribution of each amino acid in the inhibitory region to myofilament regulation. We found that most of the point mutations in the inhibitory region reduced the ATPase activity in the presence of Ca(2+), which suggests the same region also acts as an activator of the ATPase. The thin filaments can also be activated by strong myosin head (S1)-actin interactions. The binding of N-ethylmaleimide-treated myosin subfragment 1 (NEM-S1) to actin filaments mimics such strong interactions. Interestingly, in the absence of Ca(2+) NEM-S1-induced activation of S1 ATPase was significantly less with the thin filaments containing TnI(T144A) than that with the wild-type TnI. However, in the presence of Ca(2+), there was little difference in the activation of ATPase activity between these preparations.
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Affiliation(s)
- Tomoyoshi Kobayashi
- Department of Physiology and Biophysics and the Center for Cardiovascular Research, University of Illinois at Chicago, Chicago, Illinois 60612, USA.
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