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Parry DAD. 50 Years of the steric-blocking mechanism in vertebrate skeletal muscle: a retrospective. J Muscle Res Cell Motil 2023; 44:133-141. [PMID: 35789471 PMCID: PMC10542282 DOI: 10.1007/s10974-022-09619-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2022] [Accepted: 05/12/2022] [Indexed: 11/27/2022]
Abstract
Fifty years have now passed since Parry and Squire proposed a detailed structural model that explained how tropomyosin, mediated by troponin, played a steric-blocking role in the regulation of vertebrate skeletal muscle. In this Special Issue dedicated to the memory of John Squire it is an opportune time to look back on this research and to appreciate John's key contributions. A review is also presented of a selection of the developments and insights into muscle regulation that have occurred in the years since this proposal was formulated.
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Affiliation(s)
- David A D Parry
- School of Natural Sciences, Massey University, Private Bag 11-222, Palmerston North, 4442, New Zealand.
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2
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Bradshaw M, Squire JM, Morris E, Atkinson G, Richardson R, Lees J, Caputo M, Bigotti GM, Paul DM. Zebrafish as a model for cardiac disease; Cryo-EM structure of native cardiac thin filaments from Danio Rerio. J Muscle Res Cell Motil 2023; 44:179-192. [PMID: 37480427 PMCID: PMC10542308 DOI: 10.1007/s10974-023-09653-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2022] [Accepted: 07/04/2023] [Indexed: 07/24/2023]
Abstract
Actin, tropomyosin and troponin, the proteins that comprise the contractile apparatus of the cardiac thin filament, are highly conserved across species. We have used cryo-EM to study the three-dimensional structure of the zebrafish cardiac thin and actin filaments. With 70% of human genes having an obvious zebrafish orthologue, and conservation of 85% of disease-causing genes, zebrafish are a good animal model for the study of human disease. Our structure of the zebrafish thin filament reveals the molecular interactions between the constituent proteins, showing that the fundamental organisation of the complex is the same as that reported in the human reconstituted thin filament. A reconstruction of zebrafish cardiac F-actin demonstrates no deviations from human cardiac actin over an extended length of 14 actin subunits. Modelling zebrafish homology models into our maps enabled us to compare, in detail, the similarity with human models. The structural similarities of troponin-T in particular, a region known to contain a hypertrophic cardiomyopathy 'hotspot', confirm the suitability of zebrafish to study these disease-causing mutations.
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Affiliation(s)
- Marston Bradshaw
- Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, UK
| | - John M Squire
- Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, UK
| | - Edward Morris
- University of Glasgow, Glasgow, UK
- Institute of Cancer Research, London, UK
| | - Georgia Atkinson
- Translational Health Sciences, University of Bristol, Bristol, UK
| | - Rebecca Richardson
- Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, UK
| | - Jon Lees
- Translational Health Sciences, University of Bristol, Bristol, UK
| | - Massimo Caputo
- Translational Health Sciences, University of Bristol, Bristol, UK
| | - Giulia M Bigotti
- Translational Health Sciences, University of Bristol, Bristol, UK
| | - Danielle M Paul
- Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, UK.
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3
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Deranek AE, Baldo AP, Lynn ML, Schwartz SD, Tardiff JC. Structure and Dynamics of the Flexible Cardiac Troponin T Linker Domain in a Fully Reconstituted Thin Filament. Biochemistry 2022; 61:1229-1242. [PMID: 35696530 DOI: 10.1021/acs.biochem.2c00091] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The structural analysis of large protein complexes has been greatly enhanced through the application of electron microscopy techniques. One such multiprotein complex, the cardiac thin filament (cTF), has cyclic interactions with thick filament proteins to drive contraction of the heart that has recently been the subject of such studies. As important as these studies are, they provide limited or no information on highly flexible regions that in isolation would be characterized as inherently disordered. One such region is the extended cardiac troponin T (cTnT) linker between the regions of cTnT which have been labeled TNT1 and TNT2. It comprises a hinge region (residues 158-166) and a highly flexible region (residues 167-203). Critically, this region modulates the troponin/tropomyosin complex's position across the actin filament. Thus, the cTnT linker structure and dynamics are central to the regulation of the function of cardiac muscles, but up to now, it was ill-understood. To establish the cTnT linker structure, we coupled an atomistic computational cTF model with time-resolved fluorescence resonance energy transfer measurements in both ±Ca2+ conditions utilizing fully reconstituted cTFs. We mapped the cTnT linker's positioning across the actin filament, and by coupling the experimental results to computation, we found mean structures and ranges of motion of this part of the complex. With this new insight, we can now address cTnT linker structural dynamics in both myofilament activation and disease.
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Affiliation(s)
- Andrea E Deranek
- Department of Biomedical Engineering, University of Arizona, Tucson, Arizona 85721, United States
| | - Anthony P Baldo
- Department of Chemistry and Biochemistry, University of Arizona, Tucson, Arizona 85721, United States
| | - Melissa L Lynn
- Department of Biomedical Engineering, University of Arizona, Tucson, Arizona 85721, United States
| | - Steven D Schwartz
- Department of Chemistry and Biochemistry, University of Arizona, Tucson, Arizona 85721, United States
| | - Jil C Tardiff
- Department of Biomedical Engineering, University of Arizona, Tucson, Arizona 85721, United States
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4
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Szikora S, Görög P, Mihály J. The Mechanisms of Thin Filament Assembly and Length Regulation in Muscles. Int J Mol Sci 2022; 23:5306. [PMID: 35628117 PMCID: PMC9140763 DOI: 10.3390/ijms23105306] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2022] [Revised: 05/05/2022] [Accepted: 05/06/2022] [Indexed: 02/01/2023] Open
Abstract
The actin containing tropomyosin and troponin decorated thin filaments form one of the crucial components of the contractile apparatus in muscles. The thin filaments are organized into densely packed lattices interdigitated with myosin-based thick filaments. The crossbridge interactions between these myofilaments drive muscle contraction, and the degree of myofilament overlap is a key factor of contractile force determination. As such, the optimal length of the thin filaments is critical for efficient activity, therefore, this parameter is precisely controlled according to the workload of a given muscle. Thin filament length is thought to be regulated by two major, but only partially understood mechanisms: it is set by (i) factors that mediate the assembly of filaments from monomers and catalyze their elongation, and (ii) by factors that specify their length and uniformity. Mutations affecting these factors can alter the length of thin filaments, and in human cases, many of them are linked to debilitating diseases such as nemaline myopathy and dilated cardiomyopathy.
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Affiliation(s)
- Szilárd Szikora
- Institute of Genetics, Biological Research Centre, H-6726 Szeged, Hungary;
| | - Péter Görög
- Institute of Genetics, Biological Research Centre, H-6726 Szeged, Hungary;
- Doctoral School of Multidisciplinary Medical Science, Faculty of Medicine, University of Szeged, H-6725 Szeged, Hungary
| | - József Mihály
- Institute of Genetics, Biological Research Centre, H-6726 Szeged, Hungary;
- Department of Genetics, University of Szeged, H-6726 Szeged, Hungary
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5
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Squire JM, Knupp C. Analysis methods and quality criteria for investigating muscle physiology using x-ray diffraction. J Gen Physiol 2021; 153:212538. [PMID: 34351359 PMCID: PMC8348228 DOI: 10.1085/jgp.202012778] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2020] [Revised: 12/23/2020] [Accepted: 07/12/2021] [Indexed: 12/20/2022] Open
Abstract
X-ray diffraction studies of muscle have been tremendously powerful in providing fundamental insights into the structures of, for example, the myosin and actin filaments in a variety of muscles and the physiology of the cross-bridge mechanism during the contractile cycle. However, interpretation of x-ray diffraction patterns is far from trivial, and if modeling of the observed diffraction intensities is required it needs to be performed carefully with full knowledge of the possible pitfalls. Here, we discuss (1) how x-ray diffraction can be used as a tool to monitor various specific muscle properties and (2) how to get the most out of the rest of the observed muscle x-ray diffraction patterns by modeling where the reliability of the modeling conclusions can be objectively tested. In other x-ray diffraction methods, such as protein crystallography, the reliability of every step of the process is estimated and quoted in published papers. In this way, the quality of the structure determination can be properly assessed. To be honest with ourselves in the muscle field, we need to do as near to the same as we can, within the limitations of the techniques that we are using. We discuss how this can be done. We also use test cases to reveal the dos and don’ts of using x-ray diffraction to study muscle physiology.
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Affiliation(s)
- John M Squire
- Muscle Contraction Group, School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, UK.,Faculty of Medicine, Imperial College, London, UK
| | - Carlo Knupp
- School of Optometry and Vision Sciences, Cardiff University, Cardiff, UK
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6
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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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7
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Solís C, Robinson JM. Cardiac troponin and tropomyosin bind to F-actin cooperatively, as revealed by fluorescence microscopy. FEBS Open Bio 2020; 10:1362-1372. [PMID: 32385956 PMCID: PMC7327902 DOI: 10.1002/2211-5463.12876] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2020] [Revised: 05/01/2020] [Accepted: 05/05/2020] [Indexed: 12/22/2022] Open
Abstract
In cardiac muscle, binding of troponin (Tn) and tropomyosin (Tpm) to filamentous (F)‐actin forms thin filaments capable of Ca2+‐dependent regulation of contraction. Tpm binds to F‐actin in a head‐to‐tail fashion, while Tn stabilizes these linkages. Valuable structural and functional information has come from biochemical, X‐ray, and electron microscopy data. However, the use of fluorescence microscopy to study thin filament assembly remains relatively underdeveloped. Here, triple fluorescent labeling of Tn, Tpm, and F‐actin allowed us to track thin filament assembly by fluorescence microscopy. It is shown here that Tn and Tpm molecules self‐organize on actin filaments and give rise to decorated and undecorated regions. Binding curves based on colocalization of Tn and Tpm on F‐actin exhibit cooperative binding with a dissociation constant Kd of ~ 0.5 µm that is independent of the Ca2+ concentration. Binding isotherms based on the intensity profile of fluorescently labeled Tn and Tpm on F‐actin show that binding of Tn is less cooperative relative to Tpm. Computational modeling of Tn‐Tpm binding to F‐actin suggests two equilibrium steps involving the binding of an initial Tn‐Tpm unit (nucleation) and subsequent recruitment of adjacent Tn‐Tpm units (elongation) that stabilize the assembly. The results presented here highlight the utility of employing fluorescence microscopy to study supramolecular protein assemblies.
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Affiliation(s)
- Christopher Solís
- Department of Chemistry and Biochemistry, South Dakota State University, Brookings, SD, USA
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8
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Cryo-EM structures of cardiac thin filaments reveal the 3D architecture of troponin. J Struct Biol 2020; 209:107450. [PMID: 31954841 DOI: 10.1016/j.jsb.2020.107450] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2019] [Revised: 01/06/2020] [Accepted: 01/12/2020] [Indexed: 02/06/2023]
Abstract
Troponin is an essential component of striated muscle and it regulates the sliding of actomyosin system in a calcium-dependent manner. Despite its importance, the structure of troponin has been elusive due to its high structural heterogeneity. In this study, we analyzed the 3D structures of murine cardiac thin filaments using a cryo-electron microscope equipped with a Volta phase plate (VPP). Contrast enhancement by a VPP enabled us to reconstruct the entire repeat of the thin filament. We determined the orientation of troponin relative to F-actin and tropomyosin, and characterized the interactions between troponin and tropomyosin. This study provides a structural basis for understanding the molecular mechanism of actomyosin system.
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9
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Yamada Y, Namba K, Fujii T. Cardiac muscle thin filament structures reveal calcium regulatory mechanism. Nat Commun 2020; 11:153. [PMID: 31919429 PMCID: PMC6952405 DOI: 10.1038/s41467-019-14008-1] [Citation(s) in RCA: 140] [Impact Index Per Article: 35.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2019] [Accepted: 12/12/2019] [Indexed: 01/04/2023] Open
Abstract
Contraction of striated muscles is driven by cyclic interactions of myosin head projecting from the thick filament with actin filament and is regulated by Ca2+ released from sarcoplasmic reticulum. Muscle thin filament consists of actin, tropomyosin and troponin, and Ca2+ binding to troponin triggers conformational changes of troponin and tropomyosin to allow actin-myosin interactions. However, the structural changes involved in this regulatory mechanism remain unknown. Here we report the structures of human cardiac muscle thin filament in the absence and presence of Ca2+ by electron cryomicroscopy. Molecular models in the two states built based on available crystal structures reveal the structures of a C-terminal region of troponin I and an N-terminal region of troponin T in complex with the head-to-tail junction of tropomyosin together with the troponin core on actin filament. Structural changes of the thin filament upon Ca2+ binding now reveal the mechanism of Ca2+ regulation of muscle contraction.
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Affiliation(s)
- Yurika Yamada
- Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka, 565-0871, Japan
| | - Keiichi Namba
- Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka, 565-0871, Japan.
- RIKEN Center for Biosystems Dynamics Research and SPring-8 Center, 1-3 Yamadaoka, Suita, Osaka, 565-0871, Japan.
- JEOL YOKOGUSHI Research Alliance Laboratories, Osaka University, 1-3 Yamadaoka, Suita, Osaka, 565-0871, Japan.
| | - Takashi Fujii
- Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka, 565-0871, Japan.
- JEOL YOKOGUSHI Research Alliance Laboratories, Osaka University, 1-3 Yamadaoka, Suita, Osaka, 565-0871, Japan.
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10
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Special Issue: The Actin-Myosin Interaction in Muscle: Background and Overview. Int J Mol Sci 2019; 20:ijms20225715. [PMID: 31739584 PMCID: PMC6887992 DOI: 10.3390/ijms20225715] [Citation(s) in RCA: 38] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2019] [Accepted: 10/15/2019] [Indexed: 12/12/2022] Open
Abstract
Muscular contraction is a fundamental phenomenon in all animals; without it life as we know it would be impossible. The basic mechanism in muscle, including heart muscle, involves the interaction of the protein filaments myosin and actin. Motility in all cells is also partly based on similar interactions of actin filaments with non-muscle myosins. Early studies of muscle contraction have informed later studies of these cellular actin-myosin systems. In muscles, projections on the myosin filaments, the so-called myosin heads or cross-bridges, interact with the nearby actin filaments and, in a mechanism powered by ATP-hydrolysis, they move the actin filaments past them in a kind of cyclic rowing action to produce the macroscopic muscular movements of which we are all aware. In this special issue the papers and reviews address different aspects of the actin-myosin interaction in muscle as studied by a plethora of complementary techniques. The present overview provides a brief and elementary introduction to muscle structure and function and the techniques used to study it. It goes on to give more detailed descriptions of what is known about muscle components and the cross-bridge cycle using structural biology techniques, particularly protein crystallography, electron microscopy and X-ray diffraction. It then has a quick look at muscle mechanics and it summarises what can be learnt about how muscle works based on the other studies covered in the different papers in the special issue. A picture emerges of the main molecular steps involved in the force-producing process; steps that are also likely to be seen in non-muscle myosin interactions with cellular actin filaments. Finally, the remarkable advances made in studying the effects of mutations in the contractile assembly in causing specific muscle diseases, particularly those in heart muscle, are outlined and discussed.
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11
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Abstract
Squire and Luther consider new evidence for a simple lattice structure in mammalian skeletal muscle.
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Affiliation(s)
- John M Squire
- Muscle Contraction Group, School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, UK .,Computational and Systems Medicine, Faculty of Medicine, Imperial College London, London, UK
| | - Pradeep K Luther
- Molecular Medicine Section, National Heart and Lung Institute, Imperial College London, London, UK
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12
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Kontziampasis D, Klebl DP, Iadanza MG, Scarff CA, Kopf F, Sobott F, Monteiro DCF, Trebbin M, Muench SP, White HD. A cryo-EM grid preparation device for time-resolved structural studies. IUCRJ 2019; 6:1024-1031. [PMID: 31709058 PMCID: PMC6830222 DOI: 10.1107/s2052252519011345] [Citation(s) in RCA: 57] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/16/2019] [Accepted: 08/13/2019] [Indexed: 05/28/2023]
Abstract
Structural biology generally provides static snapshots of protein conformations that can provide information on the functional mechanisms of biological systems. Time-resolved structural biology provides a means to visualize, at near-atomic resolution, the dynamic conformational changes that macromolecules undergo as they function. X-ray free-electron-laser technology has provided a powerful tool to study enzyme mechanisms at atomic resolution, typically in the femtosecond to picosecond timeframe. Complementary to this, recent advances in the resolution obtainable by electron microscopy and the broad range of samples that can be studied make it ideally suited to time-resolved approaches in the microsecond to millisecond timeframe to study large loop and domain motions in biomolecules. Here we describe a cryo-EM grid preparation device that permits rapid mixing, voltage-assisted spraying and vitrification of samples. It is shown that the device produces grids of sufficient ice quality to enable data collection from single grids that results in a sub-4 Å reconstruction. Rapid mixing can be achieved by blot-and-spray or mix-and-spray approaches with a delay of ∼10 ms, providing greater temporal resolution than previously reported mix-and-spray approaches.
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Affiliation(s)
- Dimitrios Kontziampasis
- School of Biomedical Sciences, University of Leeds, Leeds LS2 9JT, UK
- Astbury Centre for Structural and Molecular Biology, University of Leeds, Leeds LS2 9JT, UK
| | - David P. Klebl
- School of Biomedical Sciences, University of Leeds, Leeds LS2 9JT, UK
- Astbury Centre for Structural and Molecular Biology, University of Leeds, Leeds LS2 9JT, UK
| | - Matthew G. Iadanza
- Astbury Centre for Structural and Molecular Biology, University of Leeds, Leeds LS2 9JT, UK
- School of Molecular and Cellular Biology, University of Leeds, Leeds LS2 9JT, UK
| | - Charlotte A. Scarff
- Astbury Centre for Structural and Molecular Biology, University of Leeds, Leeds LS2 9JT, UK
- School of Molecular and Cellular Biology, University of Leeds, Leeds LS2 9JT, UK
| | - Florian Kopf
- The Hamburg Centre for Ultrafast Imaging, Universität Hamburg, Hamburg, Germany
| | - Frank Sobott
- Astbury Centre for Structural and Molecular Biology, University of Leeds, Leeds LS2 9JT, UK
- School of Molecular and Cellular Biology, University of Leeds, Leeds LS2 9JT, UK
- Department of Chemistry, Biomolecular and Analytical Mass Spectrometry group, University of Antwerp, Antwerp, Belgium
| | | | - Martin Trebbin
- Department of Chemistry,State University of New York at Buffalo, New York, USA
| | - Stephen P. Muench
- School of Biomedical Sciences, University of Leeds, Leeds LS2 9JT, UK
- Astbury Centre for Structural and Molecular Biology, University of Leeds, Leeds LS2 9JT, UK
| | - Howard D. White
- Department of Physiological Sciences, Eastern Virginia Medical School, Norfolk, Virginia USA
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13
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Matusovsky OS, Mansson A, Persson M, Cheng YS, Rassier DE. High-speed AFM reveals subsecond dynamics of cardiac thin filaments upon Ca 2+ activation and heavy meromyosin binding. Proc Natl Acad Sci U S A 2019; 116:16384-16393. [PMID: 31358631 PMCID: PMC6697793 DOI: 10.1073/pnas.1903228116] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
High-speed atomic force microscopy (HS-AFM) can be used to study dynamic processes with real-time imaging of molecules within 1- to 5-nm spatial resolution. In the current study, we evaluated the 3-state model of activation of cardiac thin filaments (cTFs) isolated as a complex and deposited on a mica-supported lipid bilayer. We studied this complex for dynamic conformational changes 1) at low and high [Ca2+] (pCa 9.0 and 4.5), and 2) upon myosin binding to the cTF in the nucleotide-free state or in the presence of ATP. HS-AFM was used to directly visualize the tropomyosin-troponin complex and Ca2+-induced tropomyosin movements accompanied by structural transitions of actin monomers within cTFs. Our data show that cTFs at relaxing or activating conditions are not ultimately in a blocked or activated state, respectively, but rather the combination of states with a prevalence that is dependent on the [Ca2+] and the presence of weakly or strongly bound myosin. The weakly and strongly bound myosin induce similar changes in the structure of cTFs as confirmed by the local dynamical displacement of individual tropomyosin strands in the center of a regulatory unit of cTF at the relaxed and activation conditions. The displacement of tropomyosin at the relaxed conditions had never been visualized directly and explains the ability of myosin binding to TF at the relaxed conditions. Based on the ratios of nonactivated and activated segments within cTFs, we proposed a mechanism of tropomyosin switching from different states that includes both weakly and strongly bound myosin.
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Affiliation(s)
- Oleg S Matusovsky
- Department of Kinesiology and Physical Education, McGill University, Montreal, QC H2W 1S4, Canada
| | - Alf Mansson
- Department of Chemistry and Biomedical Sciences, Linnaeus University, SE-391 82 Kalmar, Sweden
| | - Malin Persson
- Department of Kinesiology and Physical Education, McGill University, Montreal, QC H2W 1S4, Canada
- Department of Chemistry and Biomedical Sciences, Linnaeus University, SE-391 82 Kalmar, Sweden
| | - Yu-Shu Cheng
- Department of Kinesiology and Physical Education, McGill University, Montreal, QC H2W 1S4, Canada
| | - Dilson E Rassier
- Department of Kinesiology and Physical Education, McGill University, Montreal, QC H2W 1S4, Canada;
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14
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Bradshaw M, Paul DM. After the revolution: how is Cryo-EM contributing to muscle research? J Muscle Res Cell Motil 2019; 40:93-98. [PMID: 31302812 PMCID: PMC6726666 DOI: 10.1007/s10974-019-09537-7] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2019] [Accepted: 07/02/2019] [Indexed: 12/21/2022]
Abstract
The technique of electron microscopy (EM) has been fundamental to muscle research since the days of Huxley and Hanson. Direct observation of how proteins in the sarcomere are arranged and visualising the changes that occur upon activation have greatly increased our understanding of function. In the 1980s specimen preparation techniques for biological EM moved away from traditional fixing and staining. The technique known as cryo-electron microscopy (Cryo-EM) was developed, which involves rapidly freezing proteins in liquid ethane which maintains them in a near native state. Within the last 5 years there has been a step change in the achievable resolution using Cryo-EM. This ‘resolution revolution’ can be attributed to advances in detector technology, microscope automation and maximum likelihood image processing. In this article we look at how Cryo-EM has contributed to the field of muscle research in this post revolution era, focussing on recently published high resolution structures of sarcomeric proteins.
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Affiliation(s)
- Marston Bradshaw
- Department of Physiology & Pharmacology, University of Bristol, Bristol, BS8 1TD, UK
| | - Danielle M Paul
- Department of Physiology & Pharmacology, University of Bristol, Bristol, BS8 1TD, UK.
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15
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Eakins F, Knupp C, Squire JM. Monitoring the myosin crossbridge cycle in contracting muscle: steps towards 'Muscle-the Movie'. J Muscle Res Cell Motil 2019; 40:77-91. [PMID: 31327096 PMCID: PMC6726672 DOI: 10.1007/s10974-019-09543-9] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2019] [Accepted: 07/10/2019] [Indexed: 11/20/2022]
Abstract
Some vertebrate muscles (e.g. those in bony fish) have a simple lattice A-band which is so well ordered that low-angle X-ray diffraction patterns are sampled in a simple way amenable to crystallographic techniques. Time-resolved X-ray diffraction through the contractile cycle should provide a movie of the molecular movements involved in muscle contraction. Generation of 'Muscle-The Movie' was suggested in the 1990s and since then efforts have been made to work out how to achieve it. Here we discuss how a movie can be generated, we discuss the problems and opportunities, and present some new observations. Low angle X-ray diffraction patterns from bony fish muscles show myosin layer lines that are well sampled on row-lines expected from the simple hexagonal A-band lattice. The 1st, 2nd and 3rd myosin layer lines at d-spacings of around 42.9 nm, 21.5 nm and 14.3 nm respectively, get weaker in patterns from active muscle, but there is a well-sampled intensity remnant along the layer lines. We show here that the pattern from the tetanus plateau is not a residual resting pattern from fibres that have not been fully activated, but is a different well-sampled pattern showing the presence of a second, myosin-centred, arrangement of crossbridges within the active crossbridge population. We also show that the meridional M3 peak from active muscle has two components of different radial widths consistent with (i) active myosin-centred (probably weak-binding) heads giving a narrow peak and (ii) heads on actin in strong states giving a broad peak.
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Affiliation(s)
- Felicity Eakins
- Faculty of Medicine, Imperial College London, Exhibition Road, London, SW7 2AZ, UK
| | - Carlo Knupp
- School of Optometry and Vision Sciences, Cardiff University, Cardiff, CF10 3NB, UK
| | - John M Squire
- Faculty of Medicine, Imperial College London, Exhibition Road, London, SW7 2AZ, UK.
- Muscle Contraction Group, School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, BS8 1TD, UK.
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16
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Marston S, Zamora JE. Troponin structure and function: a view of recent progress. J Muscle Res Cell Motil 2019; 41:71-89. [PMID: 31030382 PMCID: PMC7109197 DOI: 10.1007/s10974-019-09513-1] [Citation(s) in RCA: 55] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2019] [Accepted: 04/12/2019] [Indexed: 12/15/2022]
Abstract
The molecular mechanism by which Ca2+ binding and phosphorylation regulate muscle contraction through Troponin is not yet fully understood. Revealing the differences between the relaxed and active structure of cTn, as well as the conformational changes that follow phosphorylation has remained a challenge for structural biologists over the years. Here we review the current understanding of how Ca2+, phosphorylation and disease-causing mutations affect the structure and dynamics of troponin to regulate the thin filament based on electron microscopy, X-ray diffraction, NMR and molecular dynamics methodologies.
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Affiliation(s)
- Steven Marston
- NHLI and Chemistry Departments, Imperial College London, W12 0NN, London, UK.
| | - Juan Eiros Zamora
- NHLI and Chemistry Departments, Imperial College London, W12 0NN, London, UK
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17
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Gong B, Wei X, Qian J, Lin Y. Modeling and Simulations of the Dynamic Behaviors of Actin-Based Cytoskeletal Networks. ACS Biomater Sci Eng 2019; 5:3720-3734. [DOI: 10.1021/acsbiomaterials.8b01228] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Affiliation(s)
- Bo Gong
- Department of Engineering Mechanics, Key Laboratory of Soft Machines and Smart Devices of Zhejiang Province, Zhejiang University, Hangzhou, Zhejiang 310027, China
| | - Xi Wei
- Department of Mechanical Engineering, The University of Hong Kong, Hong Kong, China
| | - Jin Qian
- Department of Engineering Mechanics, Key Laboratory of Soft Machines and Smart Devices of Zhejiang Province, Zhejiang University, Hangzhou, Zhejiang 310027, China
| | - Yuan Lin
- Department of Mechanical Engineering, The University of Hong Kong, Hong Kong, China
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18
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Ly T, Pappas CT, Johnson D, Schlecht W, Colpan M, Galkin VE, Gregorio CC, Dong WJ, Kostyukova AS. Effects of cardiomyopathy-linked mutations K15N and R21H in tropomyosin on thin-filament regulation and pointed-end dynamics. Mol Biol Cell 2018; 30:268-281. [PMID: 30462572 PMCID: PMC6589558 DOI: 10.1091/mbc.e18-06-0406] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Missense mutations K15N and R21H in striated muscle tropomyosin are linked to dilated cardiomyopathy (DCM) and hypertrophic cardiomyopathy (HCM), respectively. Tropomyosin, together with the troponin complex, regulates muscle contraction and, along with tropomodulin and leiomodin, controls the uniform thin-filament lengths crucial for normal sarcomere structure and function. We used Förster resonance energy transfer to study effects of the tropomyosin mutations on the structure and kinetics of the cardiac troponin core domain associated with the Ca2+-dependent regulation of cardiac thin filaments. We found that the K15N mutation desensitizes thin filaments to Ca2+ and slows the kinetics of structural changes in troponin induced by Ca2+ dissociation from troponin, while the R21H mutation has almost no effect on these parameters. Expression of the K15N mutant in cardiomyocytes decreases leiomodin’s thin-filament pointed-end assembly but does not affect tropomodulin’s assembly at the pointed end. Our in vitro assays show that the R21H mutation causes a twofold decrease in tropomyosin’s affinity for F-actin and affects leiomodin’s function. We suggest that the K15N mutation causes DCM by altering Ca2+-dependent thin-filament regulation and that one of the possible HCM-causing mechanisms by the R21H mutation is through alteration of leiomodin’s function.
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Affiliation(s)
- Thu Ly
- Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164
| | - Christopher T Pappas
- Department of Cellular and Molecular Medicine and Sarver Molecular Cardiovascular Research Program, University of Arizona, Tucson, AZ 85721
| | - Dylan Johnson
- Department of Biochemistry and Molecular Biology, Brody School of Medicine at East Carolina University, Greenville, NC 27834
| | - William Schlecht
- Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164.,Department of Integrative Physiology and Neuroscience, Washington State University, Pullman, WA 99164
| | - Mert Colpan
- Department of Cellular and Molecular Medicine and Sarver Molecular Cardiovascular Research Program, University of Arizona, Tucson, AZ 85721
| | - Vitold E Galkin
- Department of Physiological Sciences, Eastern Virginia Medical School, Norfolk, VA 23507
| | - Carol C Gregorio
- Department of Cellular and Molecular Medicine and Sarver Molecular Cardiovascular Research Program, University of Arizona, Tucson, AZ 85721
| | - Wen-Ji Dong
- Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164.,Department of Integrative Physiology and Neuroscience, Washington State University, Pullman, WA 99164
| | - Alla S Kostyukova
- Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164
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19
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Effects of an Interchain Disulfide Bond on Tropomyosin Structure: A Molecular Dynamics Study. Int J Mol Sci 2018; 19:ijms19113376. [PMID: 30373319 PMCID: PMC6274839 DOI: 10.3390/ijms19113376] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2018] [Revised: 10/24/2018] [Accepted: 10/25/2018] [Indexed: 11/24/2022] Open
Abstract
Tropomyosin (Tpm) is a coiled-coil actin-binding dimer protein that participates in the regulation of muscle contraction. Both Tpm chains contain Cys190 residues which are normally in the reduced state, but form an interchain disulfide bond in failing heart. Changes in structural and functional properties of Tpm and its complexes with actin upon disulfide cross-linking were studied using various experimental methods. To understand the molecular mechanism underlying these changes and to reveal the possible mechanism of the involvement of the cross-linking in heart failure, molecular dynamics (MD) simulations of the middle part of Tpm were performed in cross-linked and reduced states. The cross-linking increased bending stiffness of Tpm assessed from MD trajectories at 27 °C in agreement with previous experimental observations. However, at 40 °C, the cross-linking caused a decrease in Tpm stiffness and a significant reduction in the number of main chain hydrogen bonds in the vicinity of residues 133 and 134. These data are in line with observations showing enhanced thermal unfolding of the least stable part of Tpm at 30–40 °C and accelerated trypsin cleavage at residue 133 at 40 °C (but not at 27 °C) upon cross-linking. These results allow us to speculate about the possible mechanism of involvement of Tpm cross-linking to heart failure pathogenesis.
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20
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Different Myosin Head Conformations in Bony Fish Muscles Put into Rigor at Different Sarcomere Lengths. Int J Mol Sci 2018; 19:ijms19072091. [PMID: 30022010 PMCID: PMC6073893 DOI: 10.3390/ijms19072091] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2018] [Revised: 07/13/2018] [Accepted: 07/14/2018] [Indexed: 12/26/2022] Open
Abstract
At a resting sarcomere length of approximately 2.2 µm bony fish muscles put into rigor in the presence of BDM (2,3-butanedione monoxime) to reduce rigor tension generation show the normal arrangement of myosin head interactions with actin filaments as monitored by low-angle X-ray diffraction. However, if the muscles are put into rigor using the same protocol but stretched to 2.5 µm sarcomere length, a markedly different structure is observed. The X-ray diffraction pattern is not just a weaker version of the pattern at full overlap, as might be expected, but it is quite different. It is compatible with the actin-attached myosin heads being in a different conformation on actin, with the average centre of cross-bridge mass at a higher radius than in normal rigor and the myosin lever arms conforming less to the actin filament geometry, probably pointing back to their origins on their parent myosin filaments. The possible nature of this new rigor cross-bridge conformation is discussed in terms of other well-known states such as the weak binding state and the 'roll and lock' mechanism; we speculate that we may have trapped most myosin heads in an early attached strong actin-binding state in the cross-bridge cycle on actin.
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Abstract
In the last decade, improvements in electron microscopy and image processing have permitted significantly higher resolutions to be achieved (sometimes <1 nm) when studying isolated actin and myosin filaments. In the case of actin filaments the changing structure when troponin binds calcium ions can be followed using electron microscopy and single particle analysis to reveal what happens on each of the seven non-equivalent pseudo-repeats of the tropomyosin α-helical coiled-coil. In the case of the known family of myosin filaments not only are the myosin head arrangements under relaxing conditions being defined, but the latest analysis, also using single particle methods, is starting to reveal the way that the α-helical coiled-coil myosin rods are packed to give the filament backbones.
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Affiliation(s)
- John M Squire
- Muscle Contraction Group, School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, BS8 1TD, UK.
| | - Danielle M Paul
- Muscle Contraction Group, School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, BS8 1TD, UK
| | - Edward P Morris
- Division of Structural Biology, The Institute of Cancer Research, London, SW3 6JB, UK
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22
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Abstract
Tropomyosin is the archetypal-coiled coil, yet studies of its structure and function have proven it to be a dynamic regulator of actin filament function in muscle and non-muscle cells. Here we review aspects of its structure that deviate from canonical leucine zipper coiled coils that allow tropomyosin to bind to actin, regulate myosin, and interact directly and indirectly with actin-binding proteins. Four genes encode tropomyosins in vertebrates, with additional diversity that results from alternate promoters and alternatively spliced exons. At the same time that periodic motifs for binding actin and regulating myosin are conserved, isoform-specific domains allow for specific interaction with myosins and actin filament regulatory proteins, including troponin. Tropomyosin can be viewed as a universal regulator of the actin cytoskeleton that specifies actin filaments for cellular and intracellular functions.
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