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Walklate J, Ujfalusi Z, Behrens V, King EJ, Geeves MA. A micro-volume adaptation of a stopped-flow system; use with μg quantities of muscle proteins. Anal Biochem 2019; 581:113338. [PMID: 31201789 DOI: 10.1016/j.ab.2019.06.009] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2019] [Revised: 06/07/2019] [Accepted: 06/10/2019] [Indexed: 11/29/2022]
Abstract
Stopped-flow spectroscopy is a powerful method for measuring very fast biological and chemical reactions. The technique however is often limited by the volumes of reactants needed to load the system. Here we present a simple adaptation of commercial stopped-flow system that reduces the volume needed by a factor of 4 to ≈120 μl. After evaluation the volume requirements of the system we show that many standard myosin based assays can be performed using <100 μg of myosin. This adaptation both reduces the volume and therefore mass of protein required and also produces data of similar quality to that produced using the standard set up. The 100 μg of myosin required for these assays is less than that which can be isolated from 100 mg of muscle tissue. With this reduced quantity of myosin, assays using biopsy samples become possible. This will allow assays to be used to assist diagnoses, to examine the effects of post translational modifications on muscle proteins and to test potential therapeutic drugs using patient derived samples.
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Affiliation(s)
- J Walklate
- School of Biosciences, University of Kent, Canterbury, Kent, CT2 7NJ, United Kingdom
| | - Zoltan Ujfalusi
- School of Biosciences, University of Kent, Canterbury, Kent, CT2 7NJ, United Kingdom; Department of Biophysics, University of Pécs, Medical School, Szigeti Street 12, H-7624, Pécs, Hungary
| | - Vincent Behrens
- Molecular and Cell Physiology, Hannover Medical School, Germany
| | - Edward J King
- TgK Scientific Limited, 7 Long's Yard, St. Margaret's Street, Bradford on Avon, BA15 1DH, United Kingdom
| | - Michael A Geeves
- School of Biosciences, University of Kent, Canterbury, Kent, CT2 7NJ, United Kingdom.
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2
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Philippe AG, Lionne C, Sanchez AMJ, Pagano AF, Candau R. Increase in muscle power is associated with myofibrillar ATPase adaptations during resistance training. Exp Physiol 2019; 104:1274-1285. [DOI: 10.1113/ep087071] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2018] [Accepted: 06/04/2019] [Indexed: 12/17/2022]
Affiliation(s)
- Antony G. Philippe
- Université de Montpellier INRA UMR866 Dynamique Musculaire et Métabolisme F‐34060 Montpellier France
| | - Corinne Lionne
- Centre de Biochimie Structurale CNRS UMR 5048 – UM – INSERM U 1054 Montpellier France
| | - Anthony M. J. Sanchez
- Laboratoire Européen Performance Santé AltitudeEA4604, University of Perpignan Via DomitiaFaculty of Sports Sciences Font‐Romeu France
| | - Allan F. Pagano
- Université de Montpellier INRA UMR866 Dynamique Musculaire et Métabolisme F‐34060 Montpellier France
| | - Robin Candau
- Université de Montpellier INRA UMR866 Dynamique Musculaire et Métabolisme F‐34060 Montpellier France
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3
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Tesi C, Barman T, Lionne C. Are there two different binding sites for ATP on the myosin head, or only one that switches between two conformers? J Muscle Res Cell Motil 2019; 38:137-142. [PMID: 28905159 DOI: 10.1007/s10974-017-9480-x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Chiara Tesi
- Division of Physiology, Department of Experimental and Clinical Medicine, University of Florence, Florence, Italy
| | - Tom Barman
- U128, 8 rue Dom Vaissette, Montpellier, France
| | - Corinne Lionne
- Centre de Biochimie Structurale (CBS), INSERM, CNRS, Université de Montpellier, Montpellier, France.
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4
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Gunther LK, Feng HZ, Wei H, Raupp J, Jin JP, Sakamoto T. Effect of N-Terminal Extension of Cardiac Troponin I on the Ca(2+) Regulation of ATP Binding and ADP Dissociation of Myosin II in Native Cardiac Myofibrils. Biochemistry 2016; 55:1887-97. [PMID: 26862665 DOI: 10.1021/acs.biochem.5b01059] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Cardiac troponin I (cTnI) has a unique N-terminal extension that plays a role in modifying the calcium regulation of cardiac muscle contraction. Restrictive cleavage of the N-terminal extension of cTnI occurs under stress conditions as a physiological adaptation. Recent studies have shown that in comparison with controls, transgenic mouse cardiac myofibrils containing cTnI lacking the N-terminal extension (cTnI-ND) had a lower sensitivity to calcium activation of ATPase, resulting in enhanced ventricular relaxation and cardiac function. To investigate which step(s) of the ATPase cycle is regulated by the N-terminal extension of cTnI, here we studied the calcium dependence of cardiac myosin II ATPase kinetics in isolated cardiac myofibrils. ATP binding and ADP dissociation rates were measured by using stopped-flow spectrofluorimetry with mant-dATP and mant-dADP, respectively. We found that the second-order mant-dATP binding rate of cTnI-ND mouse cardiac myofibrils was 3-fold faster than that of wild-type myofibrils at low Ca(2+) concentrations. The ADP dissociation rate of cTnI-ND myofibrils was positively dependent on calcium concentration, while the wild-type controls were not significantly affected. These data from experiments using native cardiac myofibrils under physiological conditions indicate that modification of the N-terminal extension of cTnI plays a role in the calcium regulation of the kinetics of actomyosin ATPase.
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Affiliation(s)
- Laura K Gunther
- Department of Physics and Astronomy, Wayne State University , Detroit, Michigan 48201, United States
| | - Han-Zhong Feng
- Department of Physiology, Wayne State University School of Medicine , Detroit, Michigan 48201, United States
| | - Hongguang Wei
- Department of Physiology, Wayne State University School of Medicine , Detroit, Michigan 48201, United States
| | - Justin Raupp
- Department of Physics and Astronomy, Wayne State University , Detroit, Michigan 48201, United States
| | - Jian-Ping Jin
- Department of Physiology, Wayne State University School of Medicine , Detroit, Michigan 48201, United States
| | - Takeshi Sakamoto
- Department of Physics and Astronomy, Wayne State University , Detroit, Michigan 48201, United States.,Department of Physiology, Wayne State University School of Medicine , Detroit, Michigan 48201, United States
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5
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Iorga B, Wang L, Stehle R, Pfitzer G, Kawai M. ATP binding and cross-bridge detachment steps during full Ca²⁺ activation: comparison of myofibril and muscle fibre mechanics by sinusoidal analysis. J Physiol 2012; 590:3361-73. [PMID: 22586213 DOI: 10.1113/jphysiol.2012.228379] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Single myofibrils 50–60 μm length and 2–3 μm diameter were isolated from rabbit psoas muscle fibres, and cross-bridge kinetics were studied by small perturbations of the length (∼0.2%) over a range of 15 frequencies (1–250 Hz). The experiments were performed at 15◦C in the presence of 0.05–10 mM MgATP, 8mM phosphate (Pi), 200 mM ionic strength with KAc (acetate), pCa 4.35–4.65, and pH 7.0. Two exponential processes, B and C, were resolved in tension transients. Their apparent rate constants (2πb and 2πc) increased as the [MgATP] was raised from 0.05 mM to 1mM, and then reached saturation at [MgATP] ≥ 1. Given that these rate constants were similar (c/b ∼1.7) at [Pi] ≥ 4 mM, they were combined to achieve an accurate estimate of the kinetic constants: their sum and product were analysed as functions of [MgATP]. These analyses yielded K1 =2.91 ± 0.31 mM −1, k2 =288 ± 36 s−1, and k−2 =10 ± 21 s−1 (±95% confidence limit, n =13 preparations), based on the cross-bridge model: AM+ATP ↔ (step 1) AM.ATP ↔ (step 2) A+M.ATP, where K1 is the ATP association constant (step 1), k2 is the rate constant of the cross-bridge detachment (step 2), and k−2 is the rate constant of its reversal step. These kinetic constants are respectively comparable to those observed in single fibres from rabbit psoas (K1 =2.35 ± 0.31 mM −1, k2 =243 ± 22 s−1, and k−2 =6 ± 14 s−1; n =8 preparations) when analysed by the same methods and under the same experimental conditions. These values are respectively not significantly different from those obtained in myofibrils, indicating that the same kinetic constants can be deduced from myofibril and muscle fibre studies, in terms of ATP binding and cross-bridge detachments steps. The fact that K1 in myofibrils is 1.2 times that in fibres (P≈0.05) may be explained by a small concentration gradient of ATP, ADP and/or Pi in single fibres.
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Affiliation(s)
- Bogdan Iorga
- Institute of Vegetative Physiology, University of Cologne, 50931 Cologne, Germany
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6
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Correlation between cross-bridge kinetics obtained from Trp fluorescence of myofibril suspensions and mechanical studies of single muscle fibers in rabbit psoas. J Muscle Res Cell Motil 2011; 32:315-26. [PMID: 22006015 DOI: 10.1007/s10974-011-9264-7] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2011] [Accepted: 09/13/2011] [Indexed: 10/16/2022]
Abstract
Our goal is to correlate kinetic constants obtained from fluorescence studies of myofibril suspension with those from mechanical studies of skinned muscle fibers from rabbit psoas. In myofibril studies, the stopped-flow technique with tryptophan fluorescence was used; in muscle fiber studies, tension transients with small amplitude sinusoidal length perturbations were used. All experiments were performed using the equivalent solution conditions (200 mM ionic strength, pH 7.00) at 10°C. The concentration of MgATP was varied to characterize kinetic constants of the ATP binding step 1 (K (1): dissociation constant), the binding induced cross-bridge detachment step 2 (k (2), k (-2): rate constants), and the ATP cleavage step 3 (k (3), k (-3)). In myofibrils we found that K (1) = 0.52 ± 0.08 mM (±95% confidence limits), k (2) = 242 ± 24 s(-1), and k (-2) ≈ 0; in muscle fibers, K (1) = 0.46 ± 0.06 mM, k (2) = 286 ± 32 s(-1), and k (-2) = 57 ± 21 s(-1). From these results, we conclude that myofibrils and muscle fibers exhibit nearly equal ATP binding step, and nearly equal ATP binding induced cross-bridge detachment step. Consequently, there is a good correlation between process C (phase 2 of step analysis) and the cross-bridge detachment step. The reverse detachment step is finite in fibers, but almost absent in myofibrils. We further studied partially cross-linked myofibrils and found little change in steps 2 and 3, indicating that cross-linking does not affect these steps. However, we found that K (1) is 2.5× of native myofibrils, indicating that MgATP binding is weakened by the presence of the extra load. We further studied the phosphate (Pi) effect in myofibrils, and found that Pi is a competitive inhibitor of MgATP, with the inhibitory dissociation constant of ~9 mM. Similar results were also deduced from fiber studies. To characterize the ATP cleavage step in myofibrils, we measured the slow rate constant in fluorescence, and found that k (3) + k (-3) = 16 ± 1 s(-1).
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7
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Interaction of human 3-phosphoglycerate kinase with its two substrates: is substrate antagonism a kinetic advantage? J Mol Biol 2011; 409:742-57. [PMID: 21549713 DOI: 10.1016/j.jmb.2011.04.048] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2011] [Revised: 04/17/2011] [Accepted: 04/20/2011] [Indexed: 11/22/2022]
Abstract
Substrate antagonism has been described for a variety of enzymes with more than one substrate and is characterized by a lowering of the affinity of one substrate in the presence of the other(s). 3-Phosphoglycerate kinase (PGK) catalyzes phosphotransfer from 1,3-bisphosphoglycerate (bPG) to ADP to give 3-phosphoglycerate (PG) and ATP, and is subject to substrate antagonism. Because of the instability of bPG, antagonism has only been described between PG and ATP or ADP. Here, we show that antagonism also occurs between bPG and ADP. Using the stopped-flow method, we show that the dissociation constant for one substrate increases in the presence of the other, and that this decrease in affinity is mainly due to an increase in the dissociation rate constant. As a consequence, there is an increase in the overall interaction kinetics. Interestingly, in the presence of the mirror image of natural d-ADP, l-ADP (a good substrate for PGK), antagonism is absent. Using rapid-quench-flow, we studied the kinetics of ATP formation. The time courses present the following: (1) a lag with l-ADP, but not with d-ADP, the kinetics of which were similar to the interaction kinetics measured by stopped-flow; (2) a burst that is directed by the phosphotransfer; and (3) a steady-state that is rate limited by the release of product kinetics. Structural explanations for these results are proposed by analyzing the crystallographic structure of the fully closed conformation of PGK in complex with l-ADP, PG, and the transition-state analogue AlF(4)(-) compared to previously determined structures.
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8
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Albet-Torres N, Bloemink MJ, Barman T, Candau R, Frölander K, Geeves MA, Golker K, Herrmann C, Lionne C, Piperio C, Schmitz S, Veigel C, Månsson A. Drug effect unveils inter-head cooperativity and strain-dependent ADP release in fast skeletal actomyosin. J Biol Chem 2009; 284:22926-37. [PMID: 19520847 PMCID: PMC2755700 DOI: 10.1074/jbc.m109.019232] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2009] [Revised: 05/09/2009] [Indexed: 11/06/2022] Open
Abstract
Amrinone is a bipyridine compound with characteristic effects on the force-velocity relationship of fast skeletal muscle, including a reduction in the maximum shortening velocity and increased maximum isometric force. Here we performed experiments to elucidate the molecular mechanisms for these effects, with the additional aim to gain insight into the molecular mechanisms underlying the force-velocity relationship. In vitro motility assays established that amrinone reduces the sliding velocity of heavy meromyosin-propelled actin filaments by 30% at different ionic strengths of the assay solution. Stopped-flow studies of myofibrils, heavy meromyosin and myosin subfragment 1, showed that the effects on sliding speed were not because of a reduced rate of ATP-induced actomyosin dissociation because the rate of this process was increased by amrinone. Moreover, optical tweezers studies could not detect any amrinone-induced changes in the working stroke length. In contrast, the ADP affinity of acto-heavy meromyosin was increased about 2-fold by 1 mm amrinone. Similar effects were not observed for acto-subfragment 1. Together with the other findings, this suggests that the amrinone-induced reduction in sliding velocity is attributed to inhibition of a strain-dependent ADP release step. Modeling results show that such an effect may account for the amrinone-induced changes of the force-velocity relationship. The data emphasize the importance of the rate of a strain-dependent ADP release step in influencing the maximum sliding velocity in fast skeletal muscle. The data also lead us to discuss the possible importance of cooperative interactions between the two myosin heads in muscle contraction.
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Affiliation(s)
- Nuria Albet-Torres
- From the School of Pure Applied Natural Science, University of Kalmar, SE-391 82 Kalmar, Sweden
| | - Marieke J. Bloemink
- the Department of Biosciences, University of Kent, Canterbury, Kent CT2 7NJ, United Kingdom
| | - Tom Barman
- Unité Mixte de Recherche 5236 CNRS, University of Montpellier I and II, Institut de Biologie, 34000 Montpellier, France
| | - Robin Candau
- Unité Mixte de Recherche 866 INRA, University of Montpellier I, 34060 Montpellier, France, and
| | - Kerstin Frölander
- From the School of Pure Applied Natural Science, University of Kalmar, SE-391 82 Kalmar, Sweden
| | - Michael A. Geeves
- the Department of Biosciences, University of Kent, Canterbury, Kent CT2 7NJ, United Kingdom
| | - Kerstin Golker
- From the School of Pure Applied Natural Science, University of Kalmar, SE-391 82 Kalmar, Sweden
| | - Christian Herrmann
- Unité Mixte de Recherche 5236 CNRS, University of Montpellier I and II, Institut de Biologie, 34000 Montpellier, France
| | - Corinne Lionne
- Unité Mixte de Recherche 5236 CNRS, University of Montpellier I and II, Institut de Biologie, 34000 Montpellier, France
| | - Claudia Piperio
- the National Institute for Medical Research, Mill Hill, London NW7 1AA, United Kingdom
| | - Stephan Schmitz
- the National Institute for Medical Research, Mill Hill, London NW7 1AA, United Kingdom
| | - Claudia Veigel
- the National Institute for Medical Research, Mill Hill, London NW7 1AA, United Kingdom
| | - Alf Månsson
- From the School of Pure Applied Natural Science, University of Kalmar, SE-391 82 Kalmar, Sweden
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9
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Insights into the kinetics of Ca2+-regulated contraction and relaxation from myofibril studies. Pflugers Arch 2009; 458:337-57. [PMID: 19165498 DOI: 10.1007/s00424-008-0630-2] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2008] [Accepted: 12/24/2008] [Indexed: 01/06/2023]
Abstract
Muscle contraction results from force-generating interactions between myosin cross-bridges on the thick filament and actin on the thin filament. The force-generating interactions are regulated by Ca(2+) via specialised proteins of the thin filament. It is controversial how the contractile and regulatory systems dynamically interact to determine the time course of muscle contraction and relaxation. Whereas kinetics of Ca(2+)-induced thin-filament regulation is often investigated with isolated proteins, force kinetics is usually studied in muscle fibres. The gap between studies on isolated proteins and structured fibres is now bridged by recent techniques that analyse the chemical and mechanical kinetics of small components of a muscle fibre, subcellular myofibrils isolated from skeletal and cardiac muscle. Formed of serially arranged repeating units called sarcomeres, myofibrils have a complete fully structured ensemble of contractile and Ca(2+) regulatory proteins. The small diameter of myofibrils (few micrometres) facilitates analysis of the kinetics of sarcomere contraction and relaxation induced by rapid changes of [ATP] or [Ca(2+)]. Among the processes studied on myofibrils are: (1) the Ca(2+)-regulated switch on/off of the troponin complex, (2) the chemical steps in the cross-bridge adenosine triphosphatase cycle, (3) the mechanics of force generation and (4) the length dynamics of individual sarcomeres. These studies give new insights into the kinetics of thin-filament regulation and of cross-bridge turnover, how cross-bridges transform chemical energy into mechanical work, and suggest that the cross-bridge ensembles of each half-sarcomere cooperate with each other across the half-sarcomere borders. Additionally, we now have a better understanding of muscle relaxation and its impairment in certain muscle diseases.
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Roels B, Reggiani C, Reboul C, Lionne C, Iorga B, Obert P, Tanguy S, Gibault A, Jougla A, Travers F, Millet GP, Candau R. Paradoxical effects of endurance training and chronic hypoxia on myofibrillar ATPase activity. Am J Physiol Regul Integr Comp Physiol 2008; 294:R1911-8. [PMID: 18417650 DOI: 10.1152/ajpregu.00210.2006] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
This study aimed to determine the changes in soleus myofibrillar ATPase (m-ATPase) activity and myosin heavy chain (MHC) isoform expression after endurance training and/or chronic hypoxic exposure. Dark Agouti rats were randomly divided into four groups: control, normoxic sedentary (N; n = 14), normoxic endurance trained (NT; n = 14), hypoxic sedentary (H; n = 10), and hypoxic endurance trained (HT; n = 14). Rats lived and trained in normoxia at 760 mmHg (N and NT) or hypobaric hypoxia at 550 mmHg (approximately 2,800 m) (H and HT). m-ATPase activity was measured by rapid flow quench technique; myosin subunits were analyzed with mono- and two-dimensional gel electrophoresis. Endurance training significantly increased m-ATPase (P < 0.01), although an increase in MHC-I content occurred (P < 0.01). In spite of slow-to-fast transitions in MHC isoform distribution in chronic hypoxia (P < 0.05) no increase in m-ATPase was observed. The rate constants of m-ATPase were 0.0350 +/- 0.0023 s(-1) and 0.047 +/- 0.0050 s(-1) for N and NT and 0.033 +/- 0.0021 s(-1) and 0.038 +/- 0.0032 s(-1) for H and HT. Thus, dissociation between variations in m-ATPase and changes in MHC isoform expression was observed. Changes in fraction of active myosin heads, in myosin light chain isoform (MLC) distribution or in MLC phosphorylation, could not explain the variations in m-ATPase. Myosin posttranslational modifications or changes in other myofibrillar proteins may therefore be responsible for the observed variations in m-ATPase activity.
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Affiliation(s)
- B Roels
- UMR 866 Institut National de la Recherche Agronomique, Faculty of Sport Sciences, University of Montpellier 1, Montpellier, France.
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11
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Solzin J, Iorga B, Sierakowski E, Gomez Alcazar DP, Ruess DF, Kubacki T, Zittrich S, Blaudeck N, Pfitzer G, Stehle R. Kinetic mechanism of the Ca2+-dependent switch-on and switch-off of cardiac troponin in myofibrils. Biophys J 2007; 93:3917-31. [PMID: 17704185 PMCID: PMC2099212 DOI: 10.1529/biophysj.107.111146] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The kinetics of Ca2+-dependent conformational changes of human cardiac troponin (cTn) were studied on isolated cTn and within the sarcomeric environment of myofibrils. Human cTnC was selectively labeled on cysteine 84 with N-((2-(iodoacetoxy)ethyl)-N-methyl)amino-7-nitrobenz-2-oxa-1,3-diazole and reconstituted with cTnI and cTnT to the cTn complex, which was incorporated into guinea pig cardiac myofibrils. These exchanged myofibrils, or the isolated cTn, were rapidly mixed in a stopped-flow apparatus with different [Ca2+] or the Ca2+-buffer 1,2-Bis(2-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid to determine the kinetics of the switch-on or switch-off, respectively, of cTn. Activation of myofibrils with high [Ca2+] (pCa 4.6) induced a biphasic fluorescence increase with rate constants of >2000 s−1 and ∼330 s−1, respectively. At low [Ca2+] (pCa 6.6), the slower rate was reduced to ∼25 s−1, but was still ∼50-fold higher than the rate constant of Ca2+-induced myofibrillar force development measured in a mechanical setup. Decreasing [Ca2+] from pCa 5.0–7.9 induced a fluorescence decay with a rate constant of 39 s−1, which was approximately fivefold faster than force relaxation. Modeling the data indicates two sequentially coupled conformational changes of cTnC in myofibrils: 1), rapid Ca2+-binding (kB ≈ 120 μM−1 s−1) and dissociation (kD ≈ 550 s−1); and 2), slower switch-on (kon = 390s−1) and switch-off (koff = 36s−1) kinetics. At high [Ca2+], ∼90% of cTnC is switched on. Both switch-on and switch-off kinetics of incorporated cTn were around fourfold faster than those of isolated cTn. In conclusion, the switch kinetics of cTn are sensitively changed by its structural integration in the sarcomere and directly rate-limit neither cardiac myofibrillar contraction nor relaxation.
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Affiliation(s)
- Johannes Solzin
- Institut fuer Vegetative Physiologie, University Cologne, Köln, Germany
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12
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Iorga B, Candau R, Travers F, Barman T, Lionne C. Does phosphate release limit the ATPases of soleus myofibrils? Evidence that (A)M. ADP.Pi states predominate on the cross-bridge cycle. J Muscle Res Cell Motil 2005; 25:367-78. [PMID: 15548866 DOI: 10.1007/s10974-004-0812-2] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The ATPases (+/-Ca2+) of myofibrils from rabbit soleus (a slow muscle) and psoas (a fast muscle) have different Ea: -Ca2+, 78 and 60 kJ/mol and +Ca2+, 155 and 71 kJ/mol, respectively. At physiological temperatures, the two types of myofibrillar ATPase are very similar and yet the mechanical properties of the muscles are different (Candau et al. (2003) Biophys J 85: 3132-3141). Muscle contraction relies on specific interactions of the different chemical states on the myosin head ATPase pathway with the thin filament. An explanation for the Ea data is that different states populate the pathways of the two types of myofibril because the rate limiting steps are different. Here, we put this to the test by a comparison of the transient kinetics of the initial steps of the ATPases of the two types of myofibril at 4 degrees C. We used two methods: rapid flow quench ('cold ATP chase': titration of active sites, ATP binding kinetics, k(cat); 'Pi burst': ATP cleavage kinetics) and fluorescence stopped-flow (MDCC-phosphate binding protein for free Pi; myofibrillar tryptophan fluorescence for myosin head-thin filament detachment and ATP cleavage kinetics). We find that, as with psoas myofibrils, the most populated state on the cross-bridge cycle of soleus myofibrils, whether relaxed or activated, is (A)M.ADP.Pi. We propose a reaction pathway that includes several (A)M.ADP.Pi sub-states that are either 'weak' or 'strong', depending on the mechanical condition.
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Affiliation(s)
- Bogdan Iorga
- UMR 5121, Université Montpellier, Montpellier, France
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13
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Lionne C, Iorga B, Candau R, Travers F. Why choose myofibrils to study muscle myosin ATPase? J Muscle Res Cell Motil 2004; 24:139-48. [PMID: 14609025 DOI: 10.1023/a:1026045328949] [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: 11/12/2022]
Abstract
Our objective is to propose an overview of the usefulness of skeletal myofibril as an experimental system for studying mechanochemical coupling of skeletal muscles and myosin ATPase activity. The myofibril is a true functional mini-muscle that is able to contract in the presence of ATP. It also contains the machinery necessary for the calcium sensitivity of the contraction. In the absence of calcium, myofibrillar ATPase activity is basal, no shortening occurs and no active force is developed. In the presence of calcium, myofibrillar ATPase is activated and myofibrils either shorten with no external load (native myofibrils) or contract isometrically (cross-linked myofibrils). With this organised system, both chemical and mechanical studies can be carried out. For a decade, our laboratory has been using rabbit psoas myofibrils for exploring myosin ATPase activity. The first challenge was to successfully apply rapid kinetic approaches, such as rapid-flow-quench, to this organised system. Another challenge was to work with myofibrils in cryoenzymic conditions, i.e. in the presence of organic solvents and at sub-zero temperatures. In this overview, we highlight differences between the myosin ATPase in organised systems (myofibrils or fibres) and that of contractile proteins in solution (S1 or actoS1) that we observed using these approaches. We discuss the importance of these differences in terms of mechanochemical coupling. It is concluded that great care should be taken when extrapolating mechanochemical properties of the contractile proteins in solution to the whole muscle.
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Affiliation(s)
- Corinne Lionne
- UMR 5121, CNRS-Université Montpellier I, Institut de Biologie, 4 boulevard Henri IV (CS89508), 34960 Montpellier 2, France.
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Krüger M, Pfitzer G, Stehle R. Expression and purification of human cardiac troponin subunits and their functional incorporation into isolated cardiac mouse myofibrils. J Chromatogr B Analyt Technol Biomed Life Sci 2003; 786:287-96. [PMID: 12651025 DOI: 10.1016/s1570-0232(02)00763-8] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The three subunits of the human cardiac troponin complex (hcTnC, hcTnI, hcTnT) were overexpressed in E. coli, purified and reconstituted to form the hcTn complex. This complex was then incorporated into subcellular bundles of mouse cardiac myofibrils whereby the native mcTn complex was replaced. On thus exchanged myofibrils, isometric force kinetics following sudden changes in free Ca(2+) concentration were measured using atomic force cantilevers. Following the exchange, the myofibrillar force remained fully Ca(2+) regulated, i.e. myofibrils were completely relaxed at pCa 7.5 and developed the same maximum Ca(2+)-activated isometric force upon increasing the pCa to 4.5 as unexchanged myofibrils. The replacement of endogenous mcTn by wild-type hcTn neither altered the kinetics of Ca(2+)-induced force development of the mouse myofibrils nor the kinetics of force relaxation induced by the sudden, complete removal of Ca(2+). Preparations of functional Tn reconstituted myofibrils provide a promising model to study the role of Tn in kinetic mechanisms of cardiac myofibrillar contraction and relaxation.
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Affiliation(s)
- Martina Krüger
- Institute of Vegetative Physiology, University of Cologne, Robert-Koch-Strasse 39, D-50931, Köln, Germany.
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