1
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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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Månsson A. Changing face of contractile activation in striated muscle at physiological temperature. J Gen Physiol 2023; 155:e202313494. [PMID: 37934475 PMCID: PMC10630095 DOI: 10.1085/jgp.202313494] [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] [Indexed: 11/08/2023] Open
Abstract
Calcium binding to troponin, with subsequent displacement of its linked tropomyosin molecule on the thin filament surface, cooperates with myosin binding to actin in the contractile regulation of striated muscle. The intertwined role of these systems is studied in the present issue of JGP by Ishii et al. (https://doi.org/10.1085/jgp.202313414). A particularly interesting feature of the paper, except for studying both skeletal and cardiac muscle proteins, is that the experiments unlike most other similar studies are performed at physiological temperature (35-40°C).
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Affiliation(s)
- Alf Månsson
- Department of Chemistry and Biomedical Sciences, Linnaeus University, Kalmar, Sweden
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3
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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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4
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Matusovsky OS, Månsson A, Rassier DE. Cooperativity of myosin II motors in the non-regulated and regulated thin filaments investigated with high-speed AFM. J Gen Physiol 2023; 155:213801. [PMID: 36633585 PMCID: PMC9859764 DOI: 10.1085/jgp.202213190] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2022] [Revised: 09/09/2022] [Accepted: 11/23/2022] [Indexed: 01/13/2023] Open
Abstract
Skeletal myosins II are non-processive molecular motors that work in ensembles to produce muscle contraction while binding to the actin filament. Although the molecular properties of myosin II are well known, there is still debate about the collective work of the motors: is there cooperativity between myosin motors while binding to the actin filaments? In this study, we use high-speed AFM to evaluate this issue. We observed that the initial binding of small arrays of myosin heads to the non-regulated actin filaments did not affect the cooperative probability of subsequent bindings and did not lead to an increase in the fractional occupancy of the actin binding sites. These results suggest that myosin motors are independent force generators when connected in small arrays, and that the binding of one myosin does not alter the kinetics of other myosins. In contrast, the probability of binding of myosin heads to regulated thin filaments under activating conditions (at high Ca2+ concentration in the presence of 2 μM ATP) was increased with the initial binding of one myosin, leading to a larger occupancy of available binding sites at the next half-helical pitch of the filament. The result suggests that myosin cooperativity is observed over five pseudo-repeats and defined by the activation status of the thin filaments.
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Affiliation(s)
- Oleg S. Matusovsky
- Department of Kinesiology and Physical Education, McGill University, Montreal, Québec, Canada
| | - Alf Månsson
- Department of Chemistry and Biomedical Sciences, Linnaeus University, Kalmar, Sweden
| | - Dilson E. Rassier
- Department of Kinesiology and Physical Education, McGill University, Montreal, Québec, Canada,Correspondence to Dilson E. Rassier:
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5
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Risi CM, Villanueva E, Belknap B, Sadler RL, Harris SP, White HD, Galkin VE. Cryo-Electron Microscopy Reveals Cardiac Myosin Binding Protein-C M-Domain Interactions with the Thin Filament. J Mol Biol 2022; 434:167879. [PMID: 36370805 PMCID: PMC9771592 DOI: 10.1016/j.jmb.2022.167879] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2022] [Revised: 10/18/2022] [Accepted: 11/04/2022] [Indexed: 11/11/2022]
Abstract
Cardiac myosin binding protein C (cMyBP-C) modulates cardiac contraction via direct interactions with cardiac thick (myosin) and thin (actin) filaments (cTFs). While its C-terminal domains (e.g. C8-C10) anchor cMyBP-C to the backbone of the thick filament, its N-terminal domains (NTDs) (e.g. C0, C1, M, and C2) bind to both myosin and actin to accomplish its dual roles of inhibiting thick filaments and activating cTFs. While the positions of C0, C1 and C2 on cTF have been reported, the binding site of the M-domain on the surface of the cTF is unknown. Here, we used cryo-EM to reveal that the M-domain interacts with actin via helix 3 of its ordered tri-helix bundle region, while the unstructured part of the M-domain does not maintain extensive interactions with actin. We combined the recently obtained structure of the cTF with the positions of all the four NTDs on its surface to propose a complete model of the NTD binding to the cTF. The model predicts that the interactions of the NTDs with the cTF depend on the activation state of the cTF. At the peak of systole, when bound to the extensively activated cTF, NTDs would inhibit actomyosin interactions. In contrast, at falling Ca2+ levels, NTDs would not compete with the myosin heads for binding to the cTF, but would rather promote formation of active cross-bridges at the adjacent regulatory units located at the opposite cTF strand. Our structural data provides a testable model of the cTF regulation by the cMyBP-C.
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Affiliation(s)
- Cristina M Risi
- Department of Physiological Sciences, Eastern Virginia Medical School, Norfolk, VA 23507, USA
| | - Edwin Villanueva
- Department of Physiological Sciences, Eastern Virginia Medical School, Norfolk, VA 23507, USA
| | - Betty Belknap
- Department of Physiological Sciences, Eastern Virginia Medical School, Norfolk, VA 23507, USA
| | - Rachel L Sadler
- Department of Cellular and Molecular Medicine, University of Arizona, Tucson, AZ 85724, USA
| | - Samantha P Harris
- Department of Cellular and Molecular Medicine, University of Arizona, Tucson, AZ 85724, USA
| | - Howard D White
- Department of Physiological Sciences, Eastern Virginia Medical School, Norfolk, VA 23507, USA
| | - Vitold E Galkin
- Department of Physiological Sciences, Eastern Virginia Medical School, Norfolk, VA 23507, USA.
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6
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Barrick SK, Greenberg MJ. Cardiac myosin contraction and mechanotransduction in health and disease. J Biol Chem 2021; 297:101297. [PMID: 34634306 PMCID: PMC8559575 DOI: 10.1016/j.jbc.2021.101297] [Citation(s) in RCA: 38] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2021] [Revised: 10/06/2021] [Accepted: 10/07/2021] [Indexed: 12/17/2022] Open
Abstract
Cardiac myosin is the molecular motor that powers heart contraction by converting chemical energy from ATP hydrolysis into mechanical force. The power output of the heart is tightly regulated to meet the physiological needs of the body. Recent multiscale studies spanning from molecules to tissues have revealed complex regulatory mechanisms that fine-tune cardiac contraction, in which myosin not only generates power output but also plays an active role in its regulation. Thus, myosin is both shaped by and actively involved in shaping its mechanical environment. Moreover, these studies have shown that cardiac myosin-generated tension affects physiological processes beyond muscle contraction. Here, we review these novel regulatory mechanisms, as well as the roles that myosin-based force generation and mechanotransduction play in development and disease. We describe how key intra- and intermolecular interactions contribute to the regulation of myosin-based contractility and the role of mechanical forces in tuning myosin function. We also discuss the emergence of cardiac myosin as a drug target for diseases including heart failure, leading to the discovery of therapeutics that directly tune myosin contractility. Finally, we highlight some of the outstanding questions that must be addressed to better understand myosin's functions and regulation, and we discuss prospects for translating these discoveries into precision medicine therapeutics targeting contractility and mechanotransduction.
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Affiliation(s)
- Samantha K Barrick
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, Missouri, USA
| | - Michael J Greenberg
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, Missouri, USA.
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7
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Barrick SK, Greenberg L, Greenberg MJ. A troponin T variant linked with pediatric dilated cardiomyopathy reduces the coupling of thin filament activation to myosin and calcium binding. Mol Biol Cell 2021; 32:1677-1689. [PMID: 34161147 PMCID: PMC8684737 DOI: 10.1091/mbc.e21-02-0082] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Dilated cardiomyopathy (DCM) is a significant cause of pediatric heart failure. Mutations in proteins that regulate cardiac muscle contraction can cause DCM; however, the mechanisms by which molecular-level mutations contribute to cellular dysfunction are not well understood. Better understanding of these mechanisms might enable the development of targeted therapeutics that benefit patient subpopulations with mutations that cause common biophysical defects. We examined the molecular- and cellular-level impacts of a troponin T variant associated with pediatric-onset DCM, R134G. The R134G variant decreased calcium sensitivity in an in vitro motility assay. Using stopped-flow and steady-state fluorescence measurements, we determined the molecular mechanism of the altered calcium sensitivity: R134G decouples calcium binding by troponin from the closed-to-open transition of the thin filament and decreases the cooperativity of myosin binding to regulated thin filaments. Consistent with the prediction that these effects would cause reduced force per sarcomere, cardiomyocytes carrying the R134G mutation are hypocontractile. They also show hallmarks of DCM that lie downstream of the initial insult, including disorganized sarcomeres and cellular hypertrophy. These results reinforce the importance of multiscale studies to fully understand mechanisms underlying human disease and highlight the value of mechanism-based precision medicine approaches for DCM.
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Affiliation(s)
- Samantha K Barrick
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110
| | - Lina Greenberg
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110
| | - Michael J Greenberg
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110
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8
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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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9
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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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10
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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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11
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López-Dávila AJ, Chalovich JM, Zittrich S, Piep B, Matinmehr F, Málnási-Csizmadia A, Rauscher AÁ, Kraft T, Brenner B, Stehle R. Cycling Cross-Bridges Contribute to Thin Filament Activation in Human Slow-Twitch Fibers. Front Physiol 2020; 11:144. [PMID: 32265723 PMCID: PMC7105683 DOI: 10.3389/fphys.2020.00144] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2019] [Accepted: 02/11/2020] [Indexed: 11/13/2022] Open
Abstract
It has been shown that not only calcium but also strong binding myosin heads contribute to thin filament activation in isometrically contracting animal fast-twitch and cardiac muscle preparations. This behavior has not been studied in human muscle fibers or animal slow-twitch fibers. Human slow-twitch fibers are interesting since they contain the same myosin heavy chain isoform as the human heart. To explore myosin-induced activation of the thin filament in isometrically contracting human slow-twitch fibers, the endogenous troponin complex was exchanged for a well-characterized fast-twitch skeletal troponin complex labeled with the fluorescent dye N-((2-(Iodoacetoxy)ethyl)-N-methyl)amino-7-nitrobenz-2-oxa-1,3-diazole (fsTn-IANBD). The exchange was ≈70% complete (n = 8). The relative contributions of calcium and strong binding cross-bridges to thin filament activation were dissected by increasing the concentration of calcium from relaxing (pCa 7.5) to saturating levels (pCa 4.5) before and after incubating the exchanged fibers in the myosin inhibitor para-aminoblebbistatin (AmBleb). At pCa 4.5, the relative contributions of calcium and strong binding cross-bridges to thin filament activation were ≈69 and ≈31%, respectively. Additionally, switching from isometric to isotonic contraction at pCa 4.5 revealed that strong binding cross-bridges contributed ≈29% to thin filament activation (i.e., virtually the same magnitude obtained with AmBleb). Thus, we showed through two different approaches that lowering the number of strong binding cross-bridges, at saturating calcium, significantly reduced the activation of the thin filament in human slow-twitch fibers. The contribution of myosin to activation resembled that which was previously reported in rat cardiac and rabbit fast-twitch muscle preparations. This method could be applied to slow-twitch human fibers obtained from the soleus muscle of cardiomyopathy patients. Such studies could lead to a better understanding of the effect of point mutations of the cardiac myosin head on the regulation of muscle contraction and could lead to better management by pharmacological approaches.
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Affiliation(s)
| | - Joseph M Chalovich
- Department of Biochemistry and Molecular Biology, Brody School of Medicine, East Carolina University, Greenville, NC, United States
| | - Stefan Zittrich
- Institute of Vegetative Physiology, University of Cologne, Cologne, Germany
| | - Birgit Piep
- Institute of Molecular and Cell Physiology, Hannover Medical School, Hanover, Germany
| | - Faramarz Matinmehr
- Institute of Molecular and Cell Physiology, Hannover Medical School, Hanover, Germany
| | - Andras Málnási-Csizmadia
- MTA-ELTE Motor Pharmacology Research Group, Department of Biochemistry, Eötvös Loránd University, Budapest, Hungary
| | | | - Theresia Kraft
- Institute of Molecular and Cell Physiology, Hannover Medical School, Hanover, Germany
| | - Bernhard Brenner
- Institute of Molecular and Cell Physiology, Hannover Medical School, Hanover, Germany
| | - Robert Stehle
- Institute of Vegetative Physiology, University of Cologne, Cologne, Germany
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12
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Clippinger SR, Cloonan PE, Greenberg L, Ernst M, Stump WT, Greenberg MJ. Disrupted mechanobiology links the molecular and cellular phenotypes in familial dilated cardiomyopathy. Proc Natl Acad Sci U S A 2019; 116:17831-17840. [PMID: 31427533 PMCID: PMC6731759 DOI: 10.1073/pnas.1910962116] [Citation(s) in RCA: 33] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Familial dilated cardiomyopathy (DCM) is a leading cause of sudden cardiac death and a major indicator for heart transplant. The disease is frequently caused by mutations of sarcomeric proteins; however, it is not well understood how these molecular mutations lead to alterations in cellular organization and contractility. To address this critical gap in our knowledge, we studied the molecular and cellular consequences of a DCM mutation in troponin-T, ΔK210. We determined the molecular mechanism of ΔK210 and used computational modeling to predict that the mutation should reduce the force per sarcomere. In mutant cardiomyocytes, we found that ΔK210 not only reduces contractility but also causes cellular hypertrophy and impairs cardiomyocytes' ability to adapt to changes in substrate stiffness (e.g., heart tissue fibrosis that occurs with aging and disease). These results help link the molecular and cellular phenotypes and implicate alterations in mechanosensing as an important factor in the development of DCM.
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Affiliation(s)
- Sarah R Clippinger
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110
| | - Paige E Cloonan
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110
| | - Lina Greenberg
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110
| | - Melanie Ernst
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110
| | - W Tom Stump
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110
| | - Michael J Greenberg
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110
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13
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Barrick SK, Clippinger SR, Greenberg L, Greenberg MJ. Computational Tool to Study Perturbations in Muscle Regulation and Its Application to Heart Disease. Biophys J 2019; 116:2246-2252. [PMID: 31126584 PMCID: PMC6588827 DOI: 10.1016/j.bpj.2019.05.002] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2019] [Revised: 04/29/2019] [Accepted: 05/01/2019] [Indexed: 11/21/2022] Open
Abstract
Striated muscle contraction occurs when myosin thick filaments bind to thin filaments in the sarcomere and generate pulling forces. This process is regulated by calcium, and it can be perturbed by pathological conditions (e.g., myopathies), physiological adaptations (e.g., β-adrenergic stimulation), and pharmacological interventions. Therefore, it is important to have a methodology to robustly determine the impact of these perturbations and statistically evaluate their effects. Here, we present an approach to measure the equilibrium constants that govern muscle activation, estimate uncertainty in these parameters, and statistically test the effects of perturbations. We provide a MATLAB-based computational tool for these analyses, along with easy-to-follow tutorials that make this approach accessible. The hypothesis testing and error estimation approaches described here are broadly applicable, and the provided tools work with other types of data, including cellular measurements. To demonstrate the utility of the approach, we apply it to elucidate the biophysical mechanism of a mutation that causes familial hypertrophic cardiomyopathy. This approach is generally useful for studying muscle diseases and therapeutic interventions that target muscle contraction.
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Affiliation(s)
- Samantha K Barrick
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, Missouri
| | - Sarah R Clippinger
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, Missouri
| | - Lina Greenberg
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, Missouri
| | - Michael J Greenberg
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, Missouri.
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14
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Heeley DH, White HD, Taylor EW. Investigation into the mechanism of thin filament regulation by transient kinetics and equilibrium binding: Is there a conflict? J Gen Physiol 2019; 151:628-634. [PMID: 30824574 PMCID: PMC6504287 DOI: 10.1085/jgp.201812198] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2018] [Revised: 10/23/2018] [Accepted: 02/07/2019] [Indexed: 11/22/2022] Open
Abstract
The authors examine the apparent discrepancies from studies aimed at understanding the mechanism of thin filament regulation. Striated muscle contraction occurs when myosin undergoes a lever-type structural change. This process (the power stroke) requires ATP and is governed by the thin filament, a complex of actin, tropomyosin, and troponin. The authors have used a fast-mixing instrument to investigate the mechanism of regulation. Such (pre–steady-state kinetic) experiments allow biochemical intermediates in a working actomyosin cycle to be monitored. The regulatory focal point is demonstrated to be the step that involves the departure of inorganic phosphate (i.e., AM-ADP-Pi → AM-ADP). This part of the cycle, which lies on the main kinetic pathway and coincides with the drive stroke, is maximally accelerated ∼100-fold by the combined association of ligands (Ca[II] and rigor myosin heads) with the thin filament. However, the observed ligand dependencies of the rates of Pi dissociation that are reported herein are at variance with predictions of models derived from experiments where ATP hydrolysis is not taking place (and myosin exists in a nonphysiological form). It is concluded that the principal influence of the thin filament is in setting the rate of Pi dissociation and that physiological levels of regulation are dependent upon the liganded state of the thin filament as well as the conformation of myosin.
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Affiliation(s)
- David H Heeley
- Department of Biochemistry, Memorial University, St. John's, Canada
| | - Howard D White
- Department of Physiological Sciences, Eastern Virginia Medical School, Norfolk, VA
| | - Edwin W Taylor
- Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, IL
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15
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Risi C, Belknap B, Forgacs-Lonart E, Harris SP, Schröder GF, White HD, Galkin VE. N-Terminal Domains of Cardiac Myosin Binding Protein C Cooperatively Activate the Thin Filament. Structure 2018; 26:1604-1611.e4. [PMID: 30270174 PMCID: PMC6281772 DOI: 10.1016/j.str.2018.08.007] [Citation(s) in RCA: 53] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2018] [Revised: 06/25/2018] [Accepted: 08/09/2018] [Indexed: 10/28/2022]
Abstract
Muscle contraction relies on interaction between myosin-based thick filaments and actin-based thin filaments. Myosin binding protein C (MyBP-C) is a key regulator of actomyosin interactions. Recent studies established that the N'-terminal domains (NTDs) of MyBP-C can either activate or inhibit thin filaments, but the mechanism of their collective action is poorly understood. Cardiac MyBP-C (cMyBP-C) harbors an extra NTD, which is absent in skeletal isoforms of MyBP-C, and its role in regulation of cardiac contraction is unknown. Here we show that the first two domains of human cMyPB-C (i.e., C0 and C1) cooperate to activate the thin filament. We demonstrate that C1 interacts with tropomyosin via a positively charged loop and that this interaction, stabilized by the C0 domain, is required for thin filament activation by cMyBP-C. Our data reveal a mechanism by which cMyBP-C can modulate cardiac contraction and demonstrate a function of the C0 domain.
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Affiliation(s)
- Cristina Risi
- Department of Physiological Sciences, Eastern Virginia Medical School, 700 West Olney Road, Lewis Hall, Room 3126, Norfolk, VA 23507, USA
| | - Betty Belknap
- Department of Physiological Sciences, Eastern Virginia Medical School, 700 West Olney Road, Lewis Hall, Room 3126, Norfolk, VA 23507, USA
| | - Eva Forgacs-Lonart
- Department of Physiological Sciences, Eastern Virginia Medical School, 700 West Olney Road, Lewis Hall, Room 3126, Norfolk, VA 23507, USA
| | - Samantha P Harris
- Department of Cellular and Molecular Medicine, University of Arizona, Tucson, AZ 85724, USA
| | - Gunnar F Schröder
- Institute of Complex Systems ICS-6, Forschungszentrum Jülich, 52425 Jülich, Germany; Physics Department, Heinrich-Heine Universität Düsseldorf, 40225 Düsseldorf, Germany
| | - Howard D White
- Department of Physiological Sciences, Eastern Virginia Medical School, 700 West Olney Road, Lewis Hall, Room 3126, Norfolk, VA 23507, USA
| | - Vitold E Galkin
- Department of Physiological Sciences, Eastern Virginia Medical School, 700 West Olney Road, Lewis Hall, Room 3126, Norfolk, VA 23507, USA.
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16
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Johnson D, Angus CW, Chalovich JM. Stepwise C-Terminal Truncation of Cardiac Troponin T Alters Function at Low and Saturating Ca 2. Biophys J 2018; 115:702-712. [PMID: 30057009 DOI: 10.1016/j.bpj.2018.06.028] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2018] [Revised: 06/19/2018] [Accepted: 06/29/2018] [Indexed: 11/16/2022] Open
Abstract
Activation of striated muscle contraction occurs in response to Ca2+ binding to troponin C. The resulting reorganization of troponin repositions tropomyosin on actin and permits activation of myosin-catalyzed ATP hydrolysis. It now appears that the C-terminal 14 amino acids of cardiac troponin T (TnT) control the level of activity at both low and high Ca2+. We made a series of C-terminal truncation mutants of human cardiac troponin T, isoform 2, to determine if the same residues of TnT are involved in the low and high Ca2+ effects. We measured the effect of these mutations on the normalized ATPase activity at saturating Ca2+. Changes in acrylodan tropomyosin fluorescence and the degree of Ca2+ stimulation of the rate of binding of rigor myosin subfragment 1 to pyrene-labeled actin-tropomyosin-troponin were measured at low Ca2+. These measurements define the distribution of actin-tropomyosin-troponin among the three regulatory states. Residues SKTR and GRWK of TnT were required for the functioning of TnT at both low and high Ca2+. Thus, the effects on forming the inactive B-state and in retarding formation of the active M-state require the same regions of TnT. We also observed that the rate of binding of rigor subfragment 1 to pyrene-labeled regulated actin at saturating Ca2+ was higher for the truncation mutants than for wild-type TnT. This violated an assumption necessary for determining the B-state population by this kinetic method.
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Affiliation(s)
- Dylan Johnson
- Department of Biochemistry, Brody School of Medicine, East Carolina University, Greenville, North Carolina
| | - C William Angus
- Department of Biochemistry, Brody School of Medicine, East Carolina University, Greenville, North Carolina
| | - Joseph M Chalovich
- Department of Biochemistry, Brody School of Medicine, East Carolina University, Greenville, North Carolina.
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17
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Ca 2+-induced movement of tropomyosin on native cardiac thin filaments revealed by cryoelectron microscopy. Proc Natl Acad Sci U S A 2017; 114:6782-6787. [PMID: 28607071 DOI: 10.1073/pnas.1700868114] [Citation(s) in RCA: 54] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
Muscle contraction relies on the interaction of myosin motors with F-actin, which is regulated through a translocation of tropomyosin by the troponin complex in response to Ca2+ The current model of muscle regulation holds that at relaxing (low-Ca2+) conditions tropomyosin blocks myosin binding sites on F-actin, whereas at activating (high-Ca2+) conditions tropomyosin translocation only partially exposes myosin binding sites on F-actin so that binding of rigor myosin is required to fully activate the thin filament (TF). Here we used a single-particle approach to helical reconstruction of frozen hydrated native cardiac TFs under relaxing and activating conditions to reveal the azimuthal movement of the tropomyosin on the surface of the native cardiac TF upon Ca2+ activation. We demonstrate that at either relaxing or activating conditions tropomyosin is not constrained in one structural state, but rather is distributed between three structural positions on the surface of the TF. We show that two of these tropomyosin positions restrain actomyosin interactions, whereas in the third position, which is significantly enhanced at high Ca2+, tropomyosin does not block myosin binding sites on F-actin. Our data provide a structural framework for the enhanced activation of the cardiac TF over the skeletal TF by Ca2+ and lead to a mechanistic model for the regulation of the cardiac TF.
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18
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Baxley T, Johnson D, Pinto JR, Chalovich JM. Troponin C Mutations Partially Stabilize the Active State of Regulated Actin and Fully Stabilize the Active State When Paired with Δ14 TnT. Biochemistry 2017; 56:2928-2937. [PMID: 28530094 DOI: 10.1021/acs.biochem.6b01092] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Striated muscle contraction is regulated by the actin-associated proteins tropomyosin and troponin. The extent of activation of myosin ATPase activity is lowest in the absence of both Ca2+ and activating cross-bridges (i.e., S1-ADP or rigor S1). Binding of activating species of myosin to actin at a saturating Ca2+ concentration stabilizes the most active state (M state) of the actin-tropomyosin-troponin complex (regulated actin). Ca2+ binding alone produces partial stabilization of the active state. The extent of stabilization at a saturating Ca2+ concentration depends on the isoform of the troponin subunits, the phosphorylation state of troponin, and, in the case of cardiac muscle, the presence of hypertrophic cardiomyopathy-producing mutants of troponin T and troponin I. Cardiac dysfunction is also associated with mutations of troponin C (TnC). Troponin C mutants A8V, C84Y, and D145E increase the Ca2+ sensitivity of ATPase activity. We show that these mutants change the distribution of regulated actin states. The A8V and C84Y TnC mutants decreased the inactive B state distribution slightly at low Ca2+ concentrations, but the D145E mutants had no effect on that state. All TnC mutants increased the level of the active M state compared to that of the wild type, at a saturating Ca2+ concentration. Troponin complexes that contained two mutations that stabilize the active M state, A8V TnC and Δ14 TnT, appeared to be completely in the active state in the presence of only Ca2+. Because Ca2+ gives full activation, in this situation, troponin must be capable of positioning tropomyosin in the active M state without the need for rigor myosin binding.
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Affiliation(s)
- Tamatha Baxley
- Department of Biochemistry & Molecular Biology, Brody School of Medicine at East Carolina University , Greenville, North Carolina 27858, United States
| | - Dylan Johnson
- Department of Biochemistry & Molecular Biology, Brody School of Medicine at East Carolina University , Greenville, North Carolina 27858, United States
| | - Jose R Pinto
- Department of Biomedical Sciences, Florida State University College of Medicine , Tallahassee, Florida 32304, United States
| | - Joseph M Chalovich
- Department of Biochemistry & Molecular Biology, Brody School of Medicine at East Carolina University , Greenville, North Carolina 27858, United States
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19
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Johnson D, Mathur MC, Kobayashi T, Chalovich JM. The Cardiomyopathy Mutation, R146G Troponin I, Stabilizes the Intermediate “C” State of Regulated Actin under High- and Low-Free Ca2+ Conditions. Biochemistry 2016; 55:4533-40. [DOI: 10.1021/acs.biochem.5b01359] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Dylan Johnson
- Department
of Biochemistry and Molecular Biology, Brody School of Medicine, East Carolina University, Greenville, North Carolina 27834, United States
- Department
of Chemistry, East Carolina University, Greenville, North Carolina 27858-4353, United States
| | - Mohit C. Mathur
- Department
of Biochemistry and Molecular Biology, Brody School of Medicine, East Carolina University, Greenville, North Carolina 27834, United States
| | - Tomoyoshi Kobayashi
- Department
of Physiology and Biophysics and Center for Cardiovascular Research,
College of Medicine, University of Illinois, Chicago, Illinois 60612-7342, United States
| | - Joseph M. Chalovich
- Department
of Biochemistry and Molecular Biology, Brody School of Medicine, East Carolina University, Greenville, North Carolina 27834, United States
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20
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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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21
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Lohmeier-Vogel EM, Heeley DH. Biochemical Comparison of Tpm1.1 (α) and Tpm2.2 (β) Tropomyosins from Rabbit Skeletal Muscle. Biochemistry 2016; 55:1418-27. [DOI: 10.1021/acs.biochem.5b01140] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Affiliation(s)
- Elke M. Lohmeier-Vogel
- Department
of Biological Sciences, University of Calgary, Calgary, Alberta T2N1N4, Canada
| | - David H. Heeley
- Department
of Biochemistry, Memorial University of Newfoundland, St. John’s, Newfoundland A1B 3X9, Canada
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22
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Liu Y, White HD, Belknap B, Winkelmann DA, Forgacs E. Omecamtiv Mecarbil modulates the kinetic and motile properties of porcine β-cardiac myosin. Biochemistry 2015; 54:1963-75. [PMID: 25680381 DOI: 10.1021/bi5015166] [Citation(s) in RCA: 93] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
We determined the effect of Omecamtiv Mecarbil, a novel allosteric effector of cardiac muscle myosin, on the kinetic and "in vitro" motility properties of the porcine ventricular heavy meromyosin (PV-HMM). Omecamtiv Mecarbil increases the equilibrium constant of the hydrolysis step (M-ATP ⇄ M-ADP-Pi) from 2.4 to 6 as determined by quench flow, but the maximal rates of both the hydrolysis step and tryptophan fluorescence increase are unchanged by the drug. OM also increases the amplitude of the fast phase of phosphate dissociation (AM-ADP-Pi → AM-ADP + Pi) that is associated with force production in muscle by 4-fold. These results suggest a mechanism in which hydrolysis of M-ATP to M-ADP-Pi occurs both before and after the recovery stroke, but rapid acceleration of phosphate dissociation by actin occurs only on post-recovery stroke A-M-ADP-Pi. One of the more dramatic effects of OM on PV-HMM is a 14-fold decrease in the unloaded shortening velocity measured by the in vitro motility assay. The increase in flux through phosphate dissociation and the unchanged rate of ADP dissociation (AM-ADP → AM + ADP) by the drug produce a higher duty ratio motor in which a larger fraction of myosin heads are strongly bound to actin filaments. The increased internal load produced by a larger fraction of strongly attached crossbridges explains the reduced rate of in vitro motility velocity in the presence of OM and predicts that the drug will produce slower and stronger contraction of cardiac muscle.
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Affiliation(s)
- Yingying Liu
- †Department of Physiological Sciences, Eastern Virginia Medical School, Norfolk, Virginia 23507, United States
| | - Howard D White
- †Department of Physiological Sciences, Eastern Virginia Medical School, Norfolk, Virginia 23507, United States
| | - Betty Belknap
- †Department of Physiological Sciences, Eastern Virginia Medical School, Norfolk, Virginia 23507, United States
| | - Donald A Winkelmann
- ‡Department of Pathology and Laboratory Medicine, Robert Wood Johnson Medical School, Rutgers University, Piscataway, New Jersey 08854, United States
| | - Eva Forgacs
- †Department of Physiological Sciences, Eastern Virginia Medical School, Norfolk, Virginia 23507, United States
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23
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Yang S, Barbu-Tudoran L, Orzechowski M, Craig R, Trinick J, White H, Lehman W. Three-dimensional organization of troponin on cardiac muscle thin filaments in the relaxed state. Biophys J 2014; 106:855-64. [PMID: 24559988 DOI: 10.1016/j.bpj.2014.01.007] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2013] [Revised: 12/02/2013] [Accepted: 01/07/2014] [Indexed: 01/03/2023] Open
Abstract
Muscle contraction is regulated by troponin-tropomyosin, which blocks and unblocks myosin binding sites on actin. To elucidate this regulatory mechanism, the three-dimensional organization of troponin and tropomyosin on the thin filament must be determined. Although tropomyosin is well defined in electron microscopy helical reconstructions of thin filaments, troponin density is mostly lost. Here, we determined troponin organization on native relaxed cardiac muscle thin filaments by applying single particle reconstruction procedures to negatively stained specimens. Multiple reference models led to the same final structure, indicating absence of model bias in the procedure. The new reconstructions clearly showed F-actin, tropomyosin, and troponin densities. At the 25 Å resolution achieved, troponin was considerably better defined than in previous reconstructions. The troponin density closely resembled the shape of troponin crystallographic structures, facilitating detailed interpretation of the electron microscopy density map. The orientation of troponin-T and the troponin core domain established troponin polarity. Density attributable to the troponin-I mobile regulatory domain was positioned where it could hold tropomyosin in its blocking position on actin, thus suggesting the underlying structural basis of thin filament regulation. Our previous understanding of thin filament regulation had been limited to known movements of tropomyosin that sterically block and unblock myosin binding sites on actin. We now show how troponin, the Ca(2+) sensor, may control these movements, ultimately determining whether muscle contracts or relaxes.
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Affiliation(s)
- Shixin Yang
- Department of Cell and Developmental Biology, University of Massachusetts Medical School, Worcester, Massachusetts
| | | | - Marek Orzechowski
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, Massachusetts
| | - Roger Craig
- Department of Cell and Developmental Biology, University of Massachusetts Medical School, Worcester, Massachusetts
| | - John Trinick
- School of Molecular and Cellular Biology, University of Leeds, Leeds, United Kingdom
| | - Howard White
- Department of Physiological Sciences, Eastern Virginia Medical School, Norfolk, Virginia
| | - William Lehman
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, Massachusetts.
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24
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Belknap B, Harris SP, White HD. Modulation of thin filament activation of myosin ATP hydrolysis by N-terminal domains of cardiac myosin binding protein-C. Biochemistry 2014; 53:6717-24. [PMID: 25265574 PMCID: PMC4211651 DOI: 10.1021/bi500787f] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
![]()
We
have used enzyme kinetics to investigate the molecular mechanism
by which the N-terminal domains of human and mouse cardiac MyBP-C
(C0C1, C1C2, and C0C2) affect the activation of myosin ATP hydrolysis
by F-actin and by native porcine thin filaments. N-Terminal domains
of cMyBP-C inhibit the activation of myosin-S1 ATPase by F-actin.
However, mouse and human C1C2 and C0C2 produce biphasic activating
and inhibitory effects on the activation of myosin ATP hydrolysis
by native cardiac thin filaments. Low ratios of MyBP-C N-terminal
domains to thin filaments activate myosin-S1 ATP hydrolysis, but higher
ratios inhibit ATP hydrolysis, as is observed with F-actin alone.
These data suggest that low concentrations of C1C2 and C0C2 activate
thin filaments by a mechanism similar to that of rigor myosin-S1,
whereas higher concentrations inhibit the ATPase rate by competing
with myosin-S1-ADP-Pi for binding to actin and thin filaments.
In contrast to C0C2 and C1C2, the activating effects of the C0C1 domain
are species-dependent: human C0C1 activates actomyosin-S1 ATPase rates,
but mouse C0C1 does not produce significant activation or inhibition.
Phosphorylation of serine residues in the m-linker between the C1
and C2 domains by protein kinase-A decreases the activation of thin
filaments by huC0C2 at pCa > 8 but
has
little effect on the activation mechanism at pCa = 4. In sarcomeres, the low ratio of cMyBP-C to actin is
expected to favor the activating effects of cMyBP-C while minimizing
inhibition produced by competition with myosin heads.
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Affiliation(s)
- Betty Belknap
- Department of Physiological Sciences, Eastern Virginia Medical School , Norfolk, Virginia 23507, United States
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25
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Katrukha IA. Human cardiac troponin complex. Structure and functions. BIOCHEMISTRY (MOSCOW) 2014; 78:1447-65. [DOI: 10.1134/s0006297913130063] [Citation(s) in RCA: 104] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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26
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Korte FS, Feest ER, Razumova MV, Tu AY, Regnier M. Enhanced Ca2+ binding of cardiac troponin reduces sarcomere length dependence of contractile activation independently of strong crossbridges. Am J Physiol Heart Circ Physiol 2012; 303:H863-70. [PMID: 22865385 PMCID: PMC3469702 DOI: 10.1152/ajpheart.00395.2012] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/23/2012] [Accepted: 07/26/2012] [Indexed: 11/22/2022]
Abstract
Calcium sensitivity of the force-pCa relationship depends strongly on sarcomere length (SL) in cardiac muscle and is considered to be the cellular basis of the Frank-Starling law of the heart. SL dependence may involve changes in myofilament lattice spacing and/or myosin crossbridge orientation to increase probability of binding to actin at longer SLs. We used the L48Q cardiac troponin C (cTnC) variant, which has enhanced Ca(2+) binding affinity, to test the hypotheses that the intrinsic properties of cTnC are important in determining 1) thin filament binding site availability and responsiveness to crossbridge activation and 2) SL dependence of force in cardiac muscle. Trabeculae containing L48Q cTnC-cTn lost SL dependence of the Ca(2+) sensitivity of force. This occurred despite maintaining the typical SL-dependent changes in maximal force (F(max)). Osmotic compression of preparations at SL 2.0 μm with 3% dextran increased F(max) but not pCa(50) in L48Q cTnC-cTn exchanged trabeculae, whereas wild-type (WT)-cTnC-cTn exchanged trabeculae exhibited increases in both F(max) and pCa(50). Furthermore, crossbridge inhibition with 2,3-butanedione monoxime at SL 2.3 μm decreased F(max) and pCa(50) in WT cTnC-cTn trabeculae to levels measured at SL 2.0 μm, whereas only F(max) was decreased with L48Q cTnC-cTn. Overall, these results suggest that L48Q cTnC confers reduced crossbridge dependence of thin filament activation in cardiac muscle and that changes in the Ca(2+) sensitivity of force in response to changes in SL are at least partially dependent on properties of thin filament troponin.
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Affiliation(s)
- F Steven Korte
- Department of Bioengineering, University of Washington, Seattle, WA 98195-7962, USA
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27
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Rysev NA, Karpicheva OE, Redwood CS, Borovikov YS. The effect of the Asp175Asn and Glu180Gly TPM1 mutations on actin-myosin interaction during the ATPase cycle. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2011; 1824:366-73. [PMID: 22155441 DOI: 10.1016/j.bbapap.2011.11.004] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/14/2011] [Revised: 10/31/2011] [Accepted: 11/23/2011] [Indexed: 01/29/2023]
Abstract
Hypertrophic cardiomyopathy (HCM), characterized by cardiac hypertrophy and contractile dysfunction, is a major cause of heart failure. HCM can result from mutations in the gene encoding cardiac α-tropomyosin (TM). To understand how the HCM-causing Asp175Asn and Glu180Gly mutations in α-tropomyosin affect on actin-myosin interaction during the ATPase cycle, we labeled the SH1 helix of myosin subfragment-1 and the actin subdomain-1 with the fluorescent probe N-iodoacetyl-N'-(5-sulfo-1-naphtylo)ethylenediamine. These proteins were incorporated into ghost muscle fibers and their conformational states were monitored during the ATPase cycle by measuring polarized fluorescence. For the first time, the effect of these α-tropomyosins on the mobility and rotation of subdomain-1 of actin and the SH1 helix of myosin subfragment-1 during the ATP hydrolysis cycle have been demonstrated directly by polarized fluorimetry. Wild-type α-tropomyosin increases the amplitude of the SH1 helix and subdomain-1 movements during the ATPase cycle, indicating the enhancement of the efficiency of the work of cross-bridges. Both mutant TMs increase the proportion of the strong-binding sub-states, with the effect of the Glu180Gly mutation being greater than that of Asp175Asn. It is suggested that the alteration in the concerted conformational changes of actomyosin is likely to provide the structural basis for the altered cardiac muscle contraction.
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Affiliation(s)
- Nikita A Rysev
- Laboratory of Mechanisms of Cell Motility, Institute of Cytology, Russian Academy of Sciences, St. Petersburg, Russia
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The 3-state model of muscle regulation revisited: is a fourth state involved? J Muscle Res Cell Motil 2011; 32:203-8. [DOI: 10.1007/s10974-011-9263-8] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2011] [Accepted: 09/13/2011] [Indexed: 10/17/2022]
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