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Heeley DH, Belknap B, Atherton JL, Hasan SC, White HD. Effect of the N-terminal extension in myosin essential light chain A1 on the mechanism of actomyosin ATP hydrolysis. J Biol Chem 2024; 300:105521. [PMID: 38042484 PMCID: PMC10777021 DOI: 10.1016/j.jbc.2023.105521] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2023] [Revised: 11/22/2023] [Accepted: 11/24/2023] [Indexed: 12/04/2023] Open
Abstract
Myosin essential light chains A1 and A2 are identical isoforms except for an extension of ∼40 amino acids at the N terminus of A1 that binds F-actin. The extension has no bearing on the burst hydrolysis rate (M-ATP → M-ADP-Pi) as determined by chemical quench flow (100 μM isoenzyme). Whereas actomyosin-S1A2 steady state MgATPase (low ionic strength, 20 °C) is hyperbolically dependent on concentration: Vmax 7.6 s-1, Kapp 6.4 μM (F-actin) and Vmax 10.1 s-1, Kapp 5.5 μM (native thin filaments, pCa 4), the relationship for myosin-S1A1 is bimodal; an initial rise at low concentration followed by a decline to one-third the Vmax of S1A2, indicative of more than one rate-limiting step and A1-enforced flux through the slower actomyosin-limited hydrolysis pathway. In double-mixing stopped-flow with an indicator, Ca(II)-mediated activation of Pi dissociation (regulatedAM-ADP-Pi → regulatedAM-ADP + Pi) is attenuated by A1 attachment to thin filaments (pCa 4). The maximum accelerated rates of Pi dissociation are: 81 s-1 (S1A1, Kapp 8.9 μM) versus 129 s-1 (S1A2, Kapp 58 μM). To investigate apomyosin-S1-mediated activation, thin filaments (EGTA) are premixed with a given isomyosin-S1 and double-mixing is repeated with myosin-S1A1 in the first mix. Similar maximum rates of Pi dissociation are observed, 44.5 s-1 (S1A1) and 47.1 s-1 (S1A2), which are lower than for Ca(II) activation. Overall, these results biochemically demonstrate how the longer light chain A1 can contribute to slower contraction and higher force and the shorter version A2 to faster contraction and lower force, consistent with their distribution in different types of striated muscle.
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Affiliation(s)
- David H Heeley
- Department of Biochemistry, Memorial University, St John's, Newfoundland, Canada.
| | - Betty Belknap
- Department of Physiological Sciences, Eastern Virginia Medical School, Norfolk, Virginia, USA
| | - Jennifer L Atherton
- Department of Physiological Sciences, Eastern Virginia Medical School, Norfolk, Virginia, USA
| | - Stephanie C Hasan
- Department of Biochemistry, Memorial University, St John's, Newfoundland, Canada
| | - Howard D White
- Department of Physiological Sciences, Eastern Virginia Medical School, Norfolk, Virginia, USA
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2
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Ishii S, Oyama K, Kobirumaki-Shimozawa F, Nakanishi T, Nakahara N, Suzuki M, Ishiwata S, Fukuda N. Myosin and tropomyosin-troponin complementarily regulate thermal activation of muscles. J Gen Physiol 2023; 155:e202313414. [PMID: 37870863 PMCID: PMC10591409 DOI: 10.1085/jgp.202313414] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2023] [Revised: 09/04/2023] [Accepted: 10/03/2023] [Indexed: 10/24/2023] Open
Abstract
Contraction of striated muscles is initiated by an increase in cytosolic Ca2+ concentration, which is regulated by tropomyosin and troponin acting on actin filaments at the sarcomere level. Namely, Ca2+-binding to troponin C shifts the "on-off" equilibrium of the thin filament state toward the "on" state, promoting actomyosin interaction; likewise, an increase in temperature to within the body temperature range shifts the equilibrium to the on state, even in the absence of Ca2+. Here, we investigated the temperature dependence of sarcomere shortening along isolated fast skeletal myofibrils using optical heating microscopy. Rapid heating (25 to 41.5°C) within 2 s induced reversible sarcomere shortening in relaxing solution. Further, we investigated the temperature-dependence of the sliding velocity of reconstituted fast skeletal or cardiac thin filaments on fast skeletal or β-cardiac myosin in an in vitro motility assay within the body temperature range. We found that (a) with fast skeletal thin filaments on fast skeletal myosin, the temperature dependence was comparable to that obtained for sarcomere shortening in fast skeletal myofibrils (Q10 ∼8), (b) both types of thin filaments started to slide at lower temperatures on fast skeletal myosin than on β-cardiac myosin, and (c) cardiac thin filaments slid at lower temperatures compared with fast skeletal thin filaments on either type of myosin. Therefore, the mammalian striated muscle may be fine-tuned to contract efficiently via complementary regulation of myosin and tropomyosin-troponin within the body temperature range, depending on the physiological demands of various circumstances.
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Affiliation(s)
- Shuya Ishii
- Foundational Quantum Technology Research Directorate, National Institutes for Quantum Science and Technology, Gunma, Japan
- Department of Cell Physiology, The Jikei University School of Medicine, Tokyo, Japan
| | - Kotaro Oyama
- Foundational Quantum Technology Research Directorate, National Institutes for Quantum Science and Technology, Gunma, Japan
- Department of Cell Physiology, The Jikei University School of Medicine, Tokyo, Japan
| | | | - Tomohiro Nakanishi
- Department of Cell Physiology, The Jikei University School of Medicine, Tokyo, Japan
- Department of Anesthesiology, The Jikei University School of Medicine, Tokyo, Japan
| | - Naoya Nakahara
- Department of Molecular Physiology, The Jikei University School of Medicine, Tokyo, Japan
| | - Madoka Suzuki
- Institute for Protein Research, Osaka University, Osaka, Japan
| | - Shin’ichi Ishiwata
- Department of Physics, Faculty of Science and Engineering, Waseda University, Tokyo, Japan
| | - Norio Fukuda
- Department of Cell Physiology, The Jikei University School of Medicine, Tokyo, Japan
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Chalovich JM, Zhu L, Johnson D. Hypertrophic Cardiomyopathy Mutations of Troponin Reveal Details of Striated Muscle Regulation. Front Physiol 2022; 13:902079. [PMID: 35694406 PMCID: PMC9178916 DOI: 10.3389/fphys.2022.902079] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2022] [Accepted: 05/05/2022] [Indexed: 11/13/2022] Open
Abstract
Striated muscle contraction is inhibited by the actin associated proteins tropomyosin, troponin T, troponin I and troponin C. Binding of Ca2+ to troponin C relieves this inhibition by changing contacts among the regulatory components and ultimately repositioning tropomyosin on the actin filament creating a state that is permissive for contraction. Several lines of evidence suggest that there are three possible positions of tropomyosin on actin commonly called Blocked, Closed/Calcium and Open or Myosin states. These states are thought to correlate with different functional states of the contractile system: inactive-Ca2+-free, inactive-Ca2+-bound and active. The inactive-Ca2+-free state is highly occupied at low free Ca2+ levels. However, saturating Ca2+ produces a mixture of inactive and active states making study of the individual states difficult. Disease causing mutations of troponin, as well as phosphomimetic mutations change the stabilities of the states of the regulatory complex thus providing tools for studying individual states. Mutants of troponin are available to stabilize each of three structural states. Particular attention is given to the hypertrophic cardiomyopathy causing mutation, Δ14 of TnT, that is missing the last 14 C-terminal residues of cardiac troponin T. Removal of the basic residues in this region eliminates the inactive-Ca2+-free state. The major state occupied with Δ14 TnT at inactivating Ca2+ levels resembles the inactive-Ca2+-bound state in function and in displacement of TnI from actin-tropomyosin. Addition of Ca2+, with Δ14TnT, shifts the equilibrium between the inactive-Ca2+-bound and the active state to favor that latter state. These mutants suggest a unique role for the C-terminal region of Troponin T as a brake to limit Ca2+ activation.
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Solís C, Solaro RJ. Novel insights into sarcomere regulatory systems control of cardiac thin filament activation. J Gen Physiol 2021; 153:211903. [PMID: 33740037 PMCID: PMC7988513 DOI: 10.1085/jgp.202012777] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2020] [Accepted: 02/23/2021] [Indexed: 12/11/2022] Open
Abstract
Our review focuses on sarcomere regulatory mechanisms with a discussion of cardiac-specific modifications to the three-state model of thin filament activation from a blocked to closed to open state. We discuss modulation of these thin filament transitions by Ca2+, by crossbridge interactions, and by thick filament–associated proteins, cardiac myosin–binding protein C (cMyBP-C), cardiac regulatory light chain (cRLC), and titin. Emerging evidence supports the idea that the cooperative activation of the thin filaments despite a single Ca2+ triggering regulatory site on troponin C (cTnC) cannot be considered in isolation of other functional domains of the sarcomere. We discuss long- and short-range interactions among these domains with the regulatory units of thin filaments, including proteins at the barbed end at the Z-disc and the pointed end near the M-band. Important to these discussions is the ever-increasing understanding of the role of cMyBP-C, cRLC, and titin filaments. Detailed knowledge of these control processes is critical to the understanding of mechanisms sustaining physiological cardiac state with varying hemodynamic load, to better defining genetic and acquired cardiac disorders, and to developing targets for therapies at the level of the sarcomeres.
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Affiliation(s)
- Christopher Solís
- University of Illinois at Chicago, College of Medicine, Department of Physiology and Biophysics and Center for Cardiovascular Research, Chicago, IL
| | - R John Solaro
- University of Illinois at Chicago, College of Medicine, Department of Physiology and Biophysics and Center for Cardiovascular Research, Chicago, IL
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Tobacman LS. Troponin Revealed: Uncovering the Structure of the Thin Filament On-Off Switch in Striated Muscle. Biophys J 2021; 120:1-9. [PMID: 33221250 PMCID: PMC7820733 DOI: 10.1016/j.bpj.2020.11.014] [Citation(s) in RCA: 31] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2020] [Revised: 11/06/2020] [Accepted: 11/11/2020] [Indexed: 12/25/2022] Open
Abstract
Recently, our understanding of the structural basis of troponin-tropomyosin's Ca2+-triggered regulation of striated muscle contraction has advanced greatly, particularly via cryo-electron microscopy data. Compelling atomic models of troponin-tropomyosin-actin were published for both apo- and Ca2+-saturated states of the cardiac thin filament. Subsequent electron microscopy and computational analyses have supported and further elaborated the findings. Per cryo-electron microscopy, each troponin is highly extended and contacts both tropomyosin strands, which lie on opposite sides of the actin filament. In the apo-state characteristic of relaxed muscle, troponin and tropomyosin hinder strong myosin-actin binding in several different ways, apparently barricading the actin more substantially than does tropomyosin alone. The troponin core domain, the C-terminal third of TnI, and tropomyosin under the influence of a 64-residue helix of TnT located at the overlap of adjacent tropomyosins are all in positions that would hinder strong myosin binding to actin. In the Ca2+-saturated state, the TnI C-terminus dissociates from actin and binds in part to TnC; the core domain pivots significantly; the N-lobe of TnC binds specifically to actin and tropomyosin; and tropomyosin rotates partially away from myosin's binding site on actin. At the overlap domain, Ca2+ causes much less tropomyosin movement, so a more inhibitory orientation persists. In the myosin-saturated state of the thin filament, there is a large additional shift in tropomyosin, with molecular interactions now identified between tropomyosin and both actin and myosin. A new era has arrived for investigation of the thin filament and for functional understandings that increasingly accommodate the recent structural results.
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Affiliation(s)
- Larry S Tobacman
- Departments of Medicine and of Physiology and Biophysics, University of Illinois at Chicago, Chicago, Illinois.
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Silva AMM, Goonasekara CL, Hayley M, Heeley DH. Further Investigation into the Biochemical Effects of Phosphorylation of Tropomyosin Tpm1.1(α). Serine-283 Is in Communication with the Midregion. Biochemistry 2020; 59:4725-4734. [PMID: 33290064 DOI: 10.1021/acs.biochem.0c00882] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The phosphorylated and unphosphorylated forms of tropomyosin Tpm1.1(α) are prepared from adult rabbit heart and compared biochemically. Electrophoresis confirms the high level of enrichment of the chromatography fractions and is consistent with a single site of phosphorylation. Covalently bound phosphate groups at position 283 of Tpm1.1(α) increase the rate of digestion at Leu-169, suggestive of a conformational rearrangement that extends to the midregion. Such a rearrangement, which is supported by ellipticity measurements between 25 and 42 °C, is consistent with a phosphorylation-mediated tightening of the interaction between various myofilament components. In a nonradioactive, co-sedimentation assay [30 mM KCl, 1 mM Mg(II), and 4 °C], phosphorylated Tpm1.1(α) displays a higher affinity for F-actin compared to that of the unphosphorylated control (Kd, 0.16 μM vs 0.26 μM). Phosphorylation decreases the concentration of thin filaments (pCa 4 plus ATP) required to attain a half-maximal rate of release of product from a pre-power stroke complex [myosin-S1-2-deoxy-3-O-(N-methylanthraniloyl)ADP-Pi], as investigated by double-mixing stopped-flow fluorescence, suggestive of a change in the proportion of active (turned on) and inactive (turned off) conformers, but similar maximum rates of product release are observed with either type of reconstituted thin filament. Phosphorylated thin filaments (pCa 4 and 8) display a higher affinity for myosin-S1(ADP) versus the control scenario without affecting isotherm steepness. Specific activities of ATP and Tpm1.1(α) are determined during an in vitro incubation of rat cardiac tissue [12 day-old, 50% phosphorylated Tpm1.1(α)] with [32P]orthophosphate. The incorporation of an isotope into tropomyosin lags behind that of ATP by a factor of approximately 10, indicating that transfer is a comparatively slow process.
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Affiliation(s)
- A Madhushika M Silva
- Department of Biochemistry, Memorial University of Newfoundland, St. John's, Newfoundland A1B 3X9, Canada
| | - Charitha L Goonasekara
- Department of Biochemistry, Faculty of Medicine, Kotelawala University, Colombo 10390, Sri Lanka
| | - Michael Hayley
- Department of Biochemistry, Memorial University of Newfoundland, St. John's, Newfoundland A1B 3X9, Canada
| | - David H Heeley
- Department of Biochemistry, Memorial University of Newfoundland, St. John's, Newfoundland A1B 3X9, Canada
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7
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Lopez Davila AJ, Zhu L, Fritz L, Kraft T, Chalovich JM. The Positively Charged C-Terminal Region of Human Skeletal Troponin T Retards Activation and Decreases Calcium Sensitivity. Biochemistry 2020; 59:4189-4201. [PMID: 33074652 DOI: 10.1021/acs.biochem.0c00499] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Calcium binding to troponin C (TnC) activates striated muscle contraction by removing TnI (troponin I) from its inhibitory site on actin. Troponin T (TnT) links TnI with tropomyosin, causing tropomyosin to move from an inhibitory position on actin to an activating position. Positive charges within the C-terminal region of human cardiac TnT limit Ca2+ activation. We now show that the positively charged region of TnT has an even larger impact on skeletal muscle regulation. We prepared one variant of human skeletal TnT that had the C-terminal 16 residues truncated (Δ16) and another with an added C-terminal Cys residue and Ala substituted for the last 6 basic residues (251C-HAHA). Both mutants reduced (based on S1 binding kinetics) or eliminated (based on acrylodan-tropomyosin fluorescence) the first inactive state of actin at <10 nM free Ca2+. 251C-HAHA-TnT and Δ16-TnT mutants greatly increased ATPase activation at 0.2 mM Ca2+, even without high-affinity cross-bridge binding. They also shifted the force-pCa curve of muscle fibers to lower Ca2+ by 0.8-1.2 pCa units (the larger shift for 251C-HAHA-TnT). Shifts in force-pCa were maintained in the presence of para-aminoblebbistatin. The effects of modification of the C-terminal region of TnT on the kinetics of S1 binding to actin were somewhat different from those observed earlier with the cardiac analogue. In general, the C-terminal region of human skeletal TnT is critical to regulation, just as it is in the cardiac system, and is a potential target for modulating activity.
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Affiliation(s)
- Alfredo Jesus Lopez Davila
- Institute of Molecular and Cell Physiology, Hannover Medical School, Carl-Neuberg-Street 1, 103-Block 1-Ebene 03-1010, Hannover 30625, Germany
| | - Li Zhu
- Department of Biochemistry & Molecular Biology, Brody School of Medicine at East Carolina University, Greenville, North Carolina 27834, United States
| | - Leon Fritz
- Institute of Molecular and Cell Physiology, Hannover Medical School, Carl-Neuberg-Street 1, 103-Block 1-Ebene 03-1010, Hannover 30625, Germany
| | - Theresia Kraft
- Institute of Molecular and Cell Physiology, Hannover Medical School, Carl-Neuberg-Street 1, 103-Block 1-Ebene 03-1010, Hannover 30625, Germany
| | - Joseph M Chalovich
- Department of Biochemistry & Molecular Biology, Brody School of Medicine at East Carolina University, Greenville, North Carolina 27834, United States
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Johnson D, Landim-Vieira M, Solı S C, Zhu L, Robinson JM, Pinto JR, Chalovich JM. Eliminating the First Inactive State and Stabilizing the Active State of the Cardiac Regulatory System Alters Behavior in Solution and in Ordered Systems. Biochemistry 2020; 59:3487-3497. [PMID: 32840354 DOI: 10.1021/acs.biochem.0c00430] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Calcium binding to troponin C (TnC) is insufficient for full activation of myosin ATPase activity by actin-tropomyosin-troponin. Previous attempts to investigate full activation utilized ATP-free myosin or chemically modified myosin to stabilize the active state of regulated actin. We utilized the Δ14-TnT and the A8V-TnC mutants to stabilize the activated state at saturating Ca2+ and to eliminate one of the inactive states at low Ca2+. The observed effects differed in solution studies and in the more ordered in vitro motility assay and in skinned cardiac muscle preparations. At saturating Ca2+, full activation with Δ14-TnT·A8V-TnC decreased the apparent KM for actin-activated ATPase activity compared to bare actin filaments. Rates of in vitro motility increased at both high and low Ca2+ with Δ14-TnT; the maximum shortening speed at high Ca2+ increased 1.8-fold. Cardiac muscle preparations exhibited increased Ca2+ sensitivity and large increases in resting force with either Δ14-TnT or Δ14-TnT·A8V-TnC. We also observed a significant increase in the maximal rate of tension redevelopment. The results of full activation with Ca2+ and Δ14-TnT·A8V-TnC confirmed and extended several earlier observations using other means of reaching full activation. Furthermore, at low Ca2+, elimination of the first inactive state led to partial activation. This work also confirms, in three distinct experimental systems, that troponin is able to stabilize the active state of actin-tropomyosin-troponin without the need for high-affinity myosin binding. The results are relevant to the reason for two inactive states and for the role of force producing myosin in regulation.
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Affiliation(s)
- Dylan Johnson
- Department of Biochemistry & Molecular Biology, Brody School of Medicine at East Carolina University, Greenville, North Carolina, United States
| | - Maicon Landim-Vieira
- Department of Biomedical Sciences, College of Medicine, Florida State University, Tallahassee, Florida, United States
| | - Christopher Solı S
- Department of Chemistry and Biochemistry, South Dakota State University, Brookings, South Dakota 57007, United States
| | - Li Zhu
- Department of Biochemistry & Molecular Biology, Brody School of Medicine at East Carolina University, Greenville, North Carolina, United States
| | - John M Robinson
- Department of Chemistry and Biochemistry, South Dakota State University, Brookings, South Dakota 57007, United States
| | - Jose R Pinto
- Department of Biomedical Sciences, College of Medicine, Florida State University, Tallahassee, Florida, United States
| | - Joseph M Chalovich
- Department of Biochemistry & Molecular Biology, Brody School of Medicine at East Carolina University, Greenville, North Carolina, United States
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Geeves MA, Lehrer SS, Lehman W. The mechanism of thin filament regulation: Models in conflict? J Gen Physiol 2019; 151:1265-1271. [PMID: 31570503 PMCID: PMC6829557 DOI: 10.1085/jgp.201912446] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2019] [Accepted: 09/05/2019] [Indexed: 01/29/2023] Open
Abstract
Evidence on two- and three-state models of the calcium regulation models of muscle contractions remain in favor of three-state models. In a recent JGP article, Heeley et al. (2019. J. Gen. Physiol. https://doi.org/10.1085/jgp.201812198) reopened the debate about two- versus three-state models of thin filament regulation. The authors review their work, which measures the rate constant of Pi release from myosin.ADP.Pi activated by actin or thin filaments under a variety of conditions. They conclude that their data can be described by a two-state model and raise doubts about the generally accepted three-state model as originally formulated by McKillop and Geeves (1993. Biophys. J.https://doi.org/10.1016/S0006-3495(93)81110-X). However, in the following article, we follow Plato’s dictum that “twice and thrice over, as they say, good it is to repeat and review what is good.” We have therefore reviewed the evidence for the three- and two-state models and present our view that the evidence is overwhelmingly in favor of three structural states of the thin filament, which regulate access of myosin to its binding sites on actin and, hence, muscle contractility.
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Affiliation(s)
| | | | - William Lehman
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, MA
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Abstract
The second of two special issues on contractile systems charts further progress towards an understanding of myofilament regulation.
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Affiliation(s)
- Henk L Granzier
- Department of Cellular and Molecular Medicine, University of Arizona, Tucson, AZ
| | - Richard L Moss
- Department of Cell and Regenerative Biology, University of Wisconsin, Madison, WI
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