1
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Ragusa R, Caselli C. Focus on cardiac troponin complex: From gene expression to cardiomyopathy. Genes Dis 2024; 11:101263. [PMID: 39211905 PMCID: PMC11357864 DOI: 10.1016/j.gendis.2024.101263] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2023] [Revised: 01/26/2024] [Accepted: 02/21/2024] [Indexed: 09/04/2024] Open
Abstract
The cardiac troponin complex (cTn) is a regulatory component of sarcomere. cTn consists of three subunits: cardiac troponin C (cTnC), which confers Ca2+ sensitivity to muscle; cTnI, which inhibits the interaction of cross-bridge of myosin with thin filament during diastole; and cTnT, which has multiple roles in sarcomere, such as promoting the link between the cTnI-cTnC complex and tropomyosin within the thin filament and influencing Ca2+ sensitivity of cTn and force development during contraction. Conditions that interfere with interactions within cTn and/or other thin filament proteins can be key factors in the regulation of cardiac contraction. These conditions include alterations in myofilament Ca2+ sensitivity, direct changes in cTn function, and triggering downstream events that lead to adverse cardiac remodeling and impairment of heart function. This review describes gene expression and post-translational modifications of cTn as well as the conditions that can adversely affect the delicate balance among the components of cTn, thereby promoting contractile dysfunction.
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Affiliation(s)
- Rosetta Ragusa
- Institute of Clinical Physiology, CNR, via Moruzzi 1, Pisa 56124, Italy
| | - Chiara Caselli
- Institute of Clinical Physiology, CNR, via Moruzzi 1, Pisa 56124, Italy
- Fondazione Toscana Gabriele Monasterio, via Moruzzi 1, Pisa 56124, Italy
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2
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Barry ME, Rynkiewicz MJ, Pavadai E, Viana A, Lehman W, Moore JR. Glutamate 139 of tropomyosin is critical for cardiac thin filament blocked-state stabilization. J Mol Cell Cardiol 2024; 188:30-37. [PMID: 38266978 DOI: 10.1016/j.yjmcc.2024.01.004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/16/2023] [Revised: 12/14/2023] [Accepted: 01/20/2024] [Indexed: 01/26/2024]
Abstract
The cardiac thin filament proteins troponin and tropomyosin control actomyosin formation and thus cardiac contractility. Calcium binding to troponin changes tropomyosin position along the thin filament, allowing myosin head binding to actin required for heart muscle contraction. The thin filament regulatory proteins are hot spots for genetic mutations causing heart muscle dysfunction. While much of the thin filament structure has been characterized, critical regions of troponin and tropomyosin involved in triggering conformational changes remain unresolved. A poorly resolved region, helix-4 (H4) of troponin I, is thought to stabilize tropomyosin in a position on actin that blocks actomyosin interactions at low calcium concentrations during muscle relaxation. We have proposed that contact between glutamate 139 on tropomyosin and positively charged residues on H4 leads to blocking-state stabilization. In this study, we attempted to disrupt these interactions by replacing E139 with lysine (E139K) to define the importance of this residue in thin filament regulation. Comparison of mutant and wild-type tropomyosin was carried out using in-vitro motility assays, actin co-sedimentation, and molecular dynamics simulations to determine perturbations in troponin-tropomyosin function caused by the tropomyosin mutation. Motility assays revealed that mutant thin filaments moved at higher velocity at low calcium with increased calcium sensitivity demonstrating that tropomyosin residue 139 is vital for proper tropomyosin-mediated inhibition during relaxation. Similarly, molecular dynamic simulations revealed a mutation-induced decrease in interaction energy between tropomyosin-E139K and troponin I (R170 and K174). These results suggest that salt-bridge stabilization of tropomyosin position by troponin IH4 is essential to prevent actomyosin interactions during cardiac muscle relaxation.
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Affiliation(s)
- Meaghan E Barry
- Department of Biological Sciences, University of Massachusetts Lowell, One University Ave, Lowell, MA 01854, United States of America
| | - Michael J Rynkiewicz
- Department of Pharmacology, Physiology & Biophysics, Boston University Chobanian and Avedisan School of Medicine, 700 Albany Street, W-408E, Boston, MA 02118, United States of America
| | - Elumalai Pavadai
- Department of Pharmacology, Physiology & Biophysics, Boston University Chobanian and Avedisan School of Medicine, 700 Albany Street, W-408E, Boston, MA 02118, United States of America
| | - Alex Viana
- Department of Biological Sciences, University of Massachusetts Lowell, One University Ave, Lowell, MA 01854, United States of America
| | - William Lehman
- Department of Pharmacology, Physiology & Biophysics, Boston University Chobanian and Avedisan School of Medicine, 700 Albany Street, W-408E, Boston, MA 02118, United States of America
| | - Jeffrey R Moore
- Department of Biological Sciences, University of Massachusetts Lowell, One University Ave, Lowell, MA 01854, United States of America.
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3
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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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4
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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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5
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Lopez AJ, Andreadaki M, Vahokoski J, Deligianni E, Calder LJ, Camerini S, Freitag A, Bergmann U, Rosenthal PB, Sidén-Kiamos I, Kursula I. Structure and function of Plasmodium actin II in the parasite mosquito stages. PLoS Pathog 2023; 19:e1011174. [PMID: 36877739 PMCID: PMC10019781 DOI: 10.1371/journal.ppat.1011174] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2022] [Revised: 03/16/2023] [Accepted: 02/03/2023] [Indexed: 03/07/2023] Open
Abstract
Actins are filament-forming, highly-conserved proteins in eukaryotes. They are involved in essential processes in the cytoplasm and also have nuclear functions. Malaria parasites (Plasmodium spp.) have two actin isoforms that differ from each other and from canonical actins in structure and filament-forming properties. Actin I has an essential role in motility and is fairly well characterized. The structure and function of actin II are not as well understood, but mutational analyses have revealed two essential functions in male gametogenesis and in the oocyst. Here, we present expression analysis, high-resolution filament structures, and biochemical characterization of Plasmodium actin II. We confirm expression in male gametocytes and zygotes and show that actin II is associated with the nucleus in both stages in filament-like structures. Unlike actin I, actin II readily forms long filaments in vitro, and near-atomic structures in the presence or absence of jasplakinolide reveal very similar structures. Small but significant differences compared to other actins in the openness and twist, the active site, the D-loop, and the plug region contribute to filament stability. The function of actin II was investigated through mutational analysis, suggesting that long and stable filaments are necessary for male gametogenesis, while a second function in the oocyst stage also requires fine-tuned regulation by methylation of histidine 73. Actin II polymerizes via the classical nucleation-elongation mechanism and has a critical concentration of ~0.1 μM at the steady-state, like actin I and canonical actins. Similarly to actin I, dimers are a stable form of actin II at equilibrium.
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Affiliation(s)
- Andrea J. Lopez
- Department of Biomedicine, University of Bergen, Bergen, Norway
| | - Maria Andreadaki
- Institute of Molecular Biology and Biotechnology, Foundation for Research and Technology-Hellas, Heraklion, Greece
| | - Juha Vahokoski
- Department of Biomedicine, University of Bergen, Bergen, Norway
| | - Elena Deligianni
- Institute of Molecular Biology and Biotechnology, Foundation for Research and Technology-Hellas, Heraklion, Greece
| | - Lesley J. Calder
- Structural Biology of Cells and Viruses Laboratory, Francis Crick Institute, London, United Kingdom
| | | | - Anika Freitag
- Institute of Molecular Biology and Biotechnology, Foundation for Research and Technology-Hellas, Heraklion, Greece
| | - Ulrich Bergmann
- Faculty of Biochemistry and Molecular Medicine, University of Oulu, Oulu, Finland
| | - Peter B. Rosenthal
- Structural Biology of Cells and Viruses Laboratory, Francis Crick Institute, London, United Kingdom
| | - Inga Sidén-Kiamos
- Institute of Molecular Biology and Biotechnology, Foundation for Research and Technology-Hellas, Heraklion, Greece
- * E-mail: (ISK); (IK)
| | - Inari Kursula
- Department of Biomedicine, University of Bergen, Bergen, Norway
- Faculty of Biochemistry and Molecular Medicine, University of Oulu, Oulu, Finland
- * E-mail: (ISK); (IK)
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6
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Yamaguchi Y, Nishiyama M, Kai H, Kaneko T, Kaihara K, Iribe G, Takai A, Naruse K, Morimatsu M. High hydrostatic pressure induces slow contraction in mouse cardiomyocytes. Biophys J 2022; 121:3286-3294. [PMID: 35841143 PMCID: PMC9463647 DOI: 10.1016/j.bpj.2022.07.016] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2022] [Revised: 05/26/2022] [Accepted: 07/11/2022] [Indexed: 11/28/2022] Open
Abstract
Cardiomyocytes are contractile cells that regulate heart contraction. Ca2+ flux via Ca2+ channels activates actomyosin interactions, leading to cardiomyocyte contraction, which is modulated by physical factors (e.g., stretch, shear stress, and hydrostatic pressure). We evaluated the mechanism triggering slow contractions using a high-pressure microscope to characterize changes in cell morphology and intracellular Ca2+ concentration ([Ca2+]i) in mouse cardiomyocytes exposed to high hydrostatic pressures. We found that cardiomyocytes contracted slowly without an acute transient increase in [Ca2+]i, while a myosin ATPase inhibitor interrupted pressure-induced slow contractions. Furthermore, transmission electron microscopy showed that, although the sarcomere length was shortened upon the application of 20 MPa, this pressure did not collapse cellular structures such as the sarcolemma and sarcomeres. Our results suggest that pressure-induced slow contractions in cardiomyocytes are driven by the activation of actomyosin interactions without an acute transient increase in [Ca2+]i.
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Affiliation(s)
- Yohei Yamaguchi
- Department of Cardiovascular Physiology, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Okayama, Japan; Department of Physiology, Asahikawa Medical University, Asahikawa, Hokkaido, Japan.
| | - Masayoshi Nishiyama
- Department of Physics, Faculty of Science and Engineering, Kindai University, Higashiosaka, Osaka, Japan
| | - Hiroaki Kai
- Department of Cardiovascular Physiology, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Okayama, Japan
| | - Toshiyuki Kaneko
- Department of Physiology, Asahikawa Medical University, Asahikawa, Hokkaido, Japan
| | - Keiko Kaihara
- Department of Cardiovascular Physiology, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Okayama, Japan
| | - Gentaro Iribe
- Department of Cardiovascular Physiology, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Okayama, Japan; Department of Physiology, Asahikawa Medical University, Asahikawa, Hokkaido, Japan
| | - Akira Takai
- Department of Physiology, Asahikawa Medical University, Asahikawa, Hokkaido, Japan
| | - Keiji Naruse
- Department of Cardiovascular Physiology, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Okayama, Japan
| | - Masatoshi Morimatsu
- Department of Cardiovascular Physiology, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Okayama, Japan.
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7
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Mahmud Z, Tikunova S, Belevych N, Wagg CS, Zhabyeyev P, Liu PB, Rasicci DV, Yengo CM, Oudit GY, Lopaschuk GD, Reiser PJ, Davis JP, Hwang PM. Small Molecule RPI-194 Stabilizes Activated Troponin to Increase the Calcium Sensitivity of Striated Muscle Contraction. Front Physiol 2022; 13:892979. [PMID: 35755445 PMCID: PMC9213791 DOI: 10.3389/fphys.2022.892979] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2022] [Accepted: 05/10/2022] [Indexed: 11/13/2022] Open
Abstract
Small molecule cardiac troponin activators could potentially enhance cardiac muscle contraction in the treatment of systolic heart failure. We designed a small molecule, RPI-194, to bind cardiac/slow skeletal muscle troponin (Cardiac muscle and slow skeletal muscle share a common isoform of the troponin C subunit.) Using solution NMR and stopped flow fluorescence spectroscopy, we determined that RPI-194 binds to cardiac troponin with a dissociation constant KD of 6-24 μM, stabilizing the activated complex between troponin C and the switch region of troponin I. The interaction between RPI-194 and troponin C is weak (KD 311 μM) in the absence of the switch region. RPI-194 acts as a calcium sensitizer, shifting the pCa50 of isometric contraction from 6.28 to 6.99 in mouse slow skeletal muscle fibers and from 5.68 to 5.96 in skinned cardiac trabeculae at 100 μM concentration. There is also some cross-reactivity with fast skeletal muscle fibers (pCa50 increases from 6.27 to 6.52). In the slack test performed on the same skinned skeletal muscle fibers, RPI-194 slowed the velocity of unloaded shortening at saturating calcium concentrations, suggesting that it slows the rate of actin-myosin cross-bridge cycling under these conditions. However, RPI-194 had no effect on the ATPase activity of purified actin-myosin. In isolated unloaded mouse cardiomyocytes, RPI-194 markedly decreased the velocity and amplitude of contractions. In contrast, cardiac function was preserved in mouse isolated perfused working hearts. In summary, the novel troponin activator RPI-194 acts as a calcium sensitizer in all striated muscle types. Surprisingly, it also slows the velocity of unloaded contraction, but the cause and significance of this is uncertain at this time. RPI-194 represents a new class of non-specific troponin activator that could potentially be used either to enhance cardiac muscle contractility in the setting of systolic heart failure or to enhance skeletal muscle contraction in neuromuscular disorders.
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Affiliation(s)
- Zabed Mahmud
- Department of Biochemistry, University of Alberta, Edmonton, AB, Canada
| | - Svetlana Tikunova
- Department of Physiology and Cell Biology, The Ohio State University, Columbus, OH, United States
| | - Natalya Belevych
- Division of Biosciences, College of Dentistry, The Ohio State University, Columbus, OH, United States
| | - Cory S Wagg
- Department of Pediatrics, University of Alberta, Edmonton, AB, Canada
| | - Pavel Zhabyeyev
- Department of Medicine, University of Alberta, Edmonton, AB, Canada
| | - Philip B Liu
- Department of Medicine, University of Alberta, Edmonton, AB, Canada
| | - David V Rasicci
- Department of Cellular and Molecular Physiology, College of Medicine, Pennsylvania State University, University Park, PA, United States
| | - Christopher M Yengo
- Department of Cellular and Molecular Physiology, College of Medicine, Pennsylvania State University, University Park, PA, United States
| | - Gavin Y Oudit
- Department of Medicine, University of Alberta, Edmonton, AB, Canada
| | - Gary D Lopaschuk
- Department of Pediatrics, University of Alberta, Edmonton, AB, Canada
| | - Peter J Reiser
- Division of Biosciences, College of Dentistry, The Ohio State University, Columbus, OH, United States
| | - Jonathan P Davis
- Department of Physiology and Cell Biology, The Ohio State University, Columbus, OH, United States
| | - Peter M Hwang
- Department of Biochemistry, University of Alberta, Edmonton, AB, Canada.,Department of Medicine, University of Alberta, Edmonton, AB, Canada
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8
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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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9
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Vahokoski J, Calder LJ, Lopez AJ, Molloy JE, Kursula I, Rosenthal PB. High-resolution structures of malaria parasite actomyosin and actin filaments. PLoS Pathog 2022; 18:e1010408. [PMID: 35377914 PMCID: PMC9037914 DOI: 10.1371/journal.ppat.1010408] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2021] [Revised: 04/25/2022] [Accepted: 03/01/2022] [Indexed: 12/20/2022] Open
Abstract
Malaria is responsible for half a million deaths annually and poses a huge economic burden on the developing world. The mosquito-borne parasites (Plasmodium spp.) that cause the disease depend upon an unconventional actomyosin motor for both gliding motility and host cell invasion. The motor system, often referred to as the glideosome complex, remains to be understood in molecular terms and is an attractive target for new drugs that might block the infection pathway. Here, we present the high-resolution structure of the actomyosin motor complex from Plasmodium falciparum. The complex includes the malaria parasite actin filament (PfAct1) complexed with the class XIV myosin motor (PfMyoA) and its two associated light-chains. The high-resolution core structure reveals the PfAct1:PfMyoA interface in atomic detail, while at lower-resolution, we visualize the PfMyoA light-chain binding region, including the essential light chain (PfELC) and the myosin tail interacting protein (PfMTIP). Finally, we report a bare PfAct1 filament structure at improved resolution.
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Affiliation(s)
- Juha Vahokoski
- Department of Biomedicine, University of Bergen, Bergen, Norway
| | - Lesley J. Calder
- Structural Biology of Cells and Viruses Laboratory, Francis Crick Institute, London, United Kingdom
| | - Andrea J. Lopez
- Department of Biomedicine, University of Bergen, Bergen, Norway
| | - Justin E. Molloy
- Structural Biology of Cells and Viruses Laboratory, Francis Crick Institute, London, United Kingdom
| | - Inari Kursula
- Department of Biomedicine, University of Bergen, Bergen, Norway
- Biocenter Oulu and Faculty of Biochemistry and Molecular Medicine, University of Oulu, Oulu, Finland
| | - Peter B. Rosenthal
- Structural Biology of Cells and Viruses Laboratory, Francis Crick Institute, London, United Kingdom
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10
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Jeon YK, Kwon JW, Jang J, Choi SW, Woo J, Cho SH, Yu BI, Chun YS, Youm JB, Zhang YH, Kim SJ. Lower troponin expression in the right ventricle of rats explains interventricular differences in E-C coupling. J Gen Physiol 2022; 154:212990. [PMID: 35099502 PMCID: PMC8823606 DOI: 10.1085/jgp.202112949] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2021] [Accepted: 01/06/2022] [Indexed: 12/12/2022] Open
Abstract
Despite distinctive functional and anatomic differences, a precise understanding of the cardiac interventricular differences in excitation–contraction (E–C) coupling mechanisms is still lacking. Here, we directly compared rat right and left cardiomyocytes (RVCM and LVCM). Whole-cell patch clamp, the IonOptix system, and fura-2 fluorimetry were used to measure electrical properties (action potential and ionic currents), single-cell contractility, and cytosolic Ca2+ ([Ca2+]i), respectively. Myofilament proteins were analyzed by immunoblotting. RVCM showed significantly shorter action potential duration (APD) and higher density of transient outward K+ current (Ito). However, the triggered [Ca2+]i change (Ca2+ transient) was not different, while the decay rate of the Ca2+ transient was slower in RVCM. Although the relaxation speed was also slower, the sarcomere shortening amplitude (ΔSL) was smaller in RVCM. SERCA activity was ∼60% lower in RVCM, which is partly responsible for the slower decay of the Ca2+ transient. Immunoblot analysis revealed lower expression of the cardiac troponin complex (cTn) in RVCM, implying a smaller Ca2+ buffering capacity (κS), which was proved by in situ analysis. The introduction of these new levels of cTn, Ito, and SERCA into a mathematical model of rat LVCM reproduced the similar Ca2+ transient, slower Ca2+ decay, shorter APD, and smaller ΔSL of RVCM. Taken together, these data show reduced expression of cTn proteins in the RVCM, which provides an explanation for the interventricular difference in the E–C coupling kinetics.
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Affiliation(s)
- Young Keul Jeon
- Department of Physiology, Ischemic/Hypoxic Disease Institute, Seoul National University College of Medicine, Seoul, Republic of Korea
| | - Jae Won Kwon
- Department of Physiology, Ischemic/Hypoxic Disease Institute, Seoul National University College of Medicine, Seoul, Republic of Korea
| | - Jihyun Jang
- Department of Physiology, Ischemic/Hypoxic Disease Institute, Seoul National University College of Medicine, Seoul, Republic of Korea.,Department of Surgery, Center for Vascular and Inflammatory Disease, University of Maryland School of Medicine, Baltimore, MD
| | - Seong Woo Choi
- Department of Physiology and Ion Channel Disease Research Center, Dongguk University College of Medicine, Seoul, Republic of Korea.,Ischemic/Hypoxic Disease Institute, Seoul National University College of Medicine, Seoul, Republic of Korea
| | - Joohan Woo
- Department of Physiology and Ion Channel Disease Research Center, Dongguk University College of Medicine, Seoul, Republic of Korea
| | - Su Han Cho
- Department of Physiology, Ischemic/Hypoxic Disease Institute, Seoul National University College of Medicine, Seoul, Republic of Korea
| | - Byeong Il Yu
- Department of Physiology, Ischemic/Hypoxic Disease Institute, Seoul National University College of Medicine, Seoul, Republic of Korea
| | - Yang Sook Chun
- Department of Physiology, Ischemic/Hypoxic Disease Institute, Seoul National University College of Medicine, Seoul, Republic of Korea.,Ischemic/Hypoxic Disease Institute, Seoul National University College of Medicine, Seoul, Republic of Korea
| | - Jae Boum Youm
- Cardiovascular and Metabolic Disease Center, Department of Physiology, College of Medicine, Inje University, Busan, Republic of Korea
| | - Yin Hua Zhang
- Department of Physiology, Ischemic/Hypoxic Disease Institute, Seoul National University College of Medicine, Seoul, Republic of Korea.,Yanbian University Hospital, Yanji, China.,Institute of Cardiovascular Sciences, Faculty of Biology, Medicine and Health Sciences, University of Manchester, Manchester, UK
| | - Sung Joon Kim
- Department of Physiology, Ischemic/Hypoxic Disease Institute, Seoul National University College of Medicine, Seoul, Republic of Korea.,Ischemic/Hypoxic Disease Institute, Seoul National University College of Medicine, Seoul, Republic of Korea.,Wide River Institute of Immunology, Seoul National University College of Medicine, Hongcheon, Republic of Korea
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11
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Mason AB, Lynn ML, Baldo AP, Deranek AE, Tardiff JC, Schwartz SD. Computational and biophysical determination of pathogenicity of variants of unknown significance in cardiac thin filament. JCI Insight 2021; 6:154350. [PMID: 34699384 PMCID: PMC8675185 DOI: 10.1172/jci.insight.154350] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2021] [Accepted: 10/22/2021] [Indexed: 11/17/2022] Open
Abstract
Point mutations within sarcomeric proteins have been associated with altered function and cardiomyopathy development. Difficulties remain, however, in establishing the pathogenic potential of individual mutations, often limiting the use of genotype in management of affected families. To directly address this challenge, we utilized our all-atom computational model of the human full cardiac thin filament (CTF) to predict how sequence substitutions in CTF proteins might affect structure and dynamics on an atomistic level. Utilizing molecular dynamics calculations, we simulated 21 well-defined genetic pathogenic cardiac troponin T and tropomyosin variants to establish a baseline of pathogenic changes induced in computational observables. Computational results were verified via differential scanning calorimetry on a subset of variants to develop an experimental correlation. Calculations were performed on 9 independent variants of unknown significance (VUS), and results were compared with pathogenic variants to identify high-resolution pathogenic signatures. Results for VUS were compared with the baseline set to determine induced structural and dynamic changes, and potential variant reclassifications were proposed. This unbiased, high-resolution computational methodology can provide unique structural and dynamic information that can be incorporated into existing analyses to facilitate classification both for de novo variants and those where established approaches have provided conflicting information.
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Affiliation(s)
| | - Melissa L Lynn
- Department of Biomedical Engineering, University of Arizona, Tucson, Arizona, USA
| | | | - Andrea E Deranek
- Department of Biomedical Engineering, University of Arizona, Tucson, Arizona, USA
| | - Jil C Tardiff
- Department of Biomedical Engineering, University of Arizona, Tucson, Arizona, USA
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12
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Gaietta G, Swift MF, Volkmann N, Hanein D. Rapid tool for cell nanoarchitecture integrity assessment. J Struct Biol 2021; 213:107801. [PMID: 34582983 PMCID: PMC8665072 DOI: 10.1016/j.jsb.2021.107801] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2021] [Revised: 09/12/2021] [Accepted: 09/21/2021] [Indexed: 12/13/2022]
Abstract
With the rapid increase and accessibility of high-resolution imaging technologies of cells, the interpretation of results relies more and more on the assumption that the three-dimensional integrity of the surrounding cellular landscape is not compromised by the experimental setup. However, the only available technology for directly probing the structural integrity of whole-cell preparations at the nanoscale is electron cryo-tomography, which is time-consuming, costly, and complex. We devised an accessible, inexpensive and reliable screening assay to quickly report on the compatibility of experimental protocols with preserving the structural integrity of whole-cell preparations at the nanoscale. Our Rapid Cell Integrity Assessment (RCIA) assay is executed at room temperature and relies solely on light microscopy imaging. Using cellular electron cryo-tomography as a benchmark, we verify that RCIA accurately unveils the adverse impact of reagents and/or protocols such as those used for virus inactivation or to arrest dynamic processes on the cellular nanoarchitecture.
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Affiliation(s)
| | | | - Niels Volkmann
- Scintillon Institute, San Diego CA 92123, USA; Institut Pasteur, Université de Paris, CNRS UMR3528, Structural Image Analysis Unit, F-75015 Paris, France
| | - Dorit Hanein
- Scintillon Institute, San Diego CA 92123, USA; Institut Pasteur, CNRS UMR3528, Structural Studies of Macromolecular Machines in Cellulo Unit, F-75015 Paris, France.
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13
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Shi Y, Bethea JP, Hetzel-Ebben HL, Landim-Vieira M, Mayper RJ, Williams RL, Kessler LE, Ruiz AM, Gargiulo K, Rose JSM, Platt G, Pinto JR, Washburn BK, Chase PB. Mandibular muscle troponin of the Florida carpenter ant Camponotus floridanus: extending our insights into invertebrate Ca 2+ regulation. J Muscle Res Cell Motil 2021; 42:399-417. [PMID: 34255253 DOI: 10.1007/s10974-021-09606-w] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2020] [Accepted: 07/07/2021] [Indexed: 12/18/2022]
Abstract
Ants use their mandibles for a variety of functions and behaviors. We investigated mandibular muscle structure and function from major workers of the Florida carpenter ant Camponotus floridanus: force-pCa relation and velocity of unloaded shortening of single, permeabilized fibres, primary sequences of troponin subunits (TnC, TnI and TnT) from a mandibular muscle cDNA library, and muscle fibre ultrastructure. From the mechanical measurements, we found Ca2+-sensitivity of isometric force was markedly shifted rightward compared with vertebrate striated muscle. From the troponin sequence results, we identified features that could explain the rightward shift of Ca2+-activation: the N-helix of TnC is effectively absent and three of the four EF-hands of TnC (sites I, II and III) do not adhere to canonical sequence rules for divalent cation binding; two alternatively spliced isoforms of TnI were identified with the alternatively spliced exon occurring in the region of the IT-arm α-helical coiled-coil, and the N-terminal extension of TnI may be involved in modulation of regulation, as in mammalian cardiac muscle; and TnT has a Glu-rich C-terminus. In addition, a structural homology model was built of C. floridanus troponin on the thin filament. From analysis of electron micrographs, we found thick filaments are almost as long as the 6.8 μm sarcomeres, have diameter of ~ 16 nm, and typical center-to-center spacing of ~ 46 nm. These results have implications for the mechanisms by which mandibular muscle fibres perform such a variety of functions, and how the structure of the troponin complex aids in these tasks.
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Affiliation(s)
- Yun Shi
- Department of Biological Science, Florida State University, Tallahassee, FL, 32306, USA
| | - Julia P Bethea
- Department of Biological Science, Florida State University, Tallahassee, FL, 32306, USA
| | - Hannah L Hetzel-Ebben
- Department of Biological Science, Florida State University, Tallahassee, FL, 32306, USA
| | - Maicon Landim-Vieira
- Department of Biomedical Sciences, Florida State University College of Medicine, Tallahassee, FL, 32306, USA
| | - Ross J Mayper
- Department of Biological Science, Florida State University, Tallahassee, FL, 32306, USA
| | - Regan L Williams
- Department of Biological Science, Florida State University, Tallahassee, FL, 32306, USA
| | - Lauren E Kessler
- Department of Biological Science, Florida State University, Tallahassee, FL, 32306, USA
| | - Amanda M Ruiz
- Department of Biological Science, Florida State University, Tallahassee, FL, 32306, USA
| | - Kathryn Gargiulo
- Department of Biological Science, Florida State University, Tallahassee, FL, 32306, USA
| | - Jennifer S M Rose
- Department of Biological Science, Florida State University, Tallahassee, FL, 32306, USA
| | - Grayson Platt
- Department of Biological Science, Florida State University, Tallahassee, FL, 32306, USA
| | - Jose R Pinto
- Department of Biomedical Sciences, Florida State University College of Medicine, Tallahassee, FL, 32306, USA
| | - Brian K Washburn
- Department of Biological Science, Florida State University, Tallahassee, FL, 32306, USA
| | - P Bryant Chase
- Department of Biological Science, Florida State University, Tallahassee, FL, 32306, USA. .,Department of Biological Science, Florida State University, Biology Unit One, Box 3064370, Tallahassee, FL, 32306-4370, USA.
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14
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Lehman W, Pavadai E, Rynkiewicz MJ. C-terminal troponin-I residues trap tropomyosin in the muscle thin filament blocked-state. Biochem Biophys Res Commun 2021; 551:27-32. [PMID: 33714756 DOI: 10.1016/j.bbrc.2021.03.010] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2021] [Accepted: 03/02/2021] [Indexed: 12/16/2022]
Abstract
Tropomyosin and troponin regulate muscle contraction by participating in a macromolecular scale steric-mechanism to control myosin-crossbridge - actin interactions and consequently contraction. At low-Ca2+, the C-terminal 30% of troponin subunit-I (TnI) is proposed to trap tropomyosin in a position on thin filaments that sterically interferes with myosin-binding, thus causing muscle relaxation. In contrast, at high-Ca2+, inhibition is released after the C-terminal domains dissociate from F-actin-tropomyosin as its component switch-peptide domain binds to the N-lobe of troponin-C (TnC). Recent, paradigm-shifting, cryo-EM reconstructions by the Namba group have revealed density attributed to TnI along cardiac muscle thin filaments at both low- and high-Ca2+ concentration. Modeling the reconstructions showed expected high-Ca2+ hydrophobic interactions of the TnI switch-peptide and TnC. However, under low-Ca2+ conditions, sparse interactions of TnI and tropomyosin, and in particular juxtaposition of non-polar switch-peptide residues and charged tropomyosin amino acids in the published model seem difficult to reconcile with an expected steric-blocking conformation. This anomaly is likely due to inaccurate fitting of tropomyosin into the cryo-EM volume. In the current study, the low-Ca2+ cryo-EM volume was fitted with a more accurate tropomyosin model and representation of cardiac TnI. Our results show that at low-Ca2+ a cluster of hydrophobic residues at the TnI switch-peptide and adjacent H4 helix (Ala149, Ala151, Met 154, Leu159, Gly160, Ala161, Ala163, Leu167, Leu169, Ala171, Leu173) draw-in tropomyosin surface residues (Ile143, Ile146, Ala151, Ile154), presumably attracting the entire tropomyosin cable to its myosin-blocking position on actin. The modeling confirms that neighboring TnI "inhibitory domain" residues (Arg145, Arg148) bind to thin filaments at actin residue Asp25, as previously suggested. ClusPro docking of TnI residues 137-184 to actin-tropomyosin, including the TnI inhibitory-domain, switch-peptide and Helix H4, verified the modeled configuration. Our residue-to-residue contact-mapping of the TnI-tropomyosin association lends itself to experimental validation and functional localization of disease-bearing mutations.
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Affiliation(s)
- William Lehman
- Department of Physiology & Biophysics, Boston University School of Medicine, Boston, MA, 02118, USA.
| | - Elumalai Pavadai
- Department of Physiology & Biophysics, Boston University School of Medicine, Boston, MA, 02118, USA.
| | - Michael J Rynkiewicz
- Department of Physiology & Biophysics, Boston University School of Medicine, Boston, MA, 02118, USA.
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15
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Tobacman LS, Cammarato A. Cardiomyopathic troponin mutations predominantly occur at its interface with actin and tropomyosin. J Gen Physiol 2021; 153:e202012815. [PMID: 33492345 PMCID: PMC7836260 DOI: 10.1085/jgp.202012815] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2020] [Accepted: 12/23/2020] [Indexed: 01/09/2023] Open
Abstract
Reversible Ca2+ binding to troponin is the primary on-off switch of the contractile apparatus of striated muscles, including the heart. Dominant missense mutations in human cardiac troponin genes are among the causes of hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy. Structural understanding of troponin action has recently advanced considerably via electron microscopy and molecular dynamics studies of the thin filament. As a result, it is now possible to examine cardiomyopathy-inducing troponin mutations in thin-filament structural context, and from that to seek new insight into pathogenesis and into the troponin regulatory mechanism. We compiled from consortium reports a representative set of troponin mutation sites whose pathogenicity was determined using standardized clinical genetics criteria. Another set of sites, apparently tolerant of amino acid substitutions, was compiled from the gnomAD v2 database. Pathogenic substitutions occurred predominantly in the areas of troponin that contact actin or tropomyosin, including, but not limited to, two regions of newly proposed structure and long-known implication in cardiomyopathy: the C-terminal third of troponin I and a part of the troponin T N terminus. The pathogenic mutations were located in troponin regions that prevent contraction under low Ca2+ concentration conditions. These regions contribute to Ca2+-regulated steric hindrance of myosin by the combined effects of troponin and tropomyosin. Loss-of-function mutations within these parts of troponin result in loss of inhibition, consistent with the hypercontractile phenotype characteristic of HCM. Notably, pathogenic mutations are absent in our dataset from the Ca2+-binding, activation-producing troponin C (TnC) N-lobe, which controls contraction by a multi-faceted mechanism. Apparently benign mutations are also diminished in the TnC N-lobe, suggesting mutations are poorly tolerated in that critical domain.
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Affiliation(s)
- Larry S. Tobacman
- Departments of Medicine and of Physiology and Biophysics, University of Illinois at Chicago, Chicago, IL
| | - Anthony Cammarato
- Departments of Medicine and of Physiology, Johns Hopkins University, Baltimore, MD
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16
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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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17
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A comprehensive guide to genetic variants and post-translational modifications of cardiac troponin C. J Muscle Res Cell Motil 2020; 42:323-342. [PMID: 33179204 DOI: 10.1007/s10974-020-09592-5] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2020] [Accepted: 10/24/2020] [Indexed: 02/07/2023]
Abstract
Familial cardiomyopathy is an inherited disease that affects the structure and function of heart muscle and has an extreme range of phenotypes. Among the millions of affected individuals, patients with hypertrophic (HCM), dilated (DCM), or left ventricular non-compaction (LVNC) cardiomyopathy can experience morphologic changes of the heart which lead to sudden death in the most detrimental cases. TNNC1, the gene that codes for cardiac troponin C (cTnC), is a sarcomere gene associated with cardiomyopathies in which probands exhibit young age of presentation and high death, transplant or ventricular fibrillation events relative to TNNT2 and TNNI3 probands. Using GnomAD, ClinVar, UniProt and PhosphoSitePlus databases and published literature, an extensive list to date of identified genetic variants in TNNC1 and post-translational modifications (PTMs) in cTnC was compiled. Additionally, a recent cryo-EM structure of the cardiac thin filament regulatory unit was used to localize each functionally studied amino acid variant and each PTM (acetylation, glycation, s-nitrosylation, phosphorylation) in the structure of cTnC. TNNC1 has a large number of variants (> 100) relative to other genes of the same transcript size. Surprisingly, the mapped variant amino acids and PTMs are distributed throughout the cTnC structure. While many cardiomyopathy-associated variants are localized in α-helical regions of cTnC, this was not statistically significant χ2 (p = 0.72). Exploring the variants in TNNC1 and PTMs of cTnC in the contexts of cardiomyopathy association, physiological modulation and potential non-canonical roles provides insights into the normal function of cTnC along with the many facets of TNNC1 as a cardiomyopathic gene.
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18
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Oda T, Yanagisawa H. Cryo-electron tomography of cardiac myofibrils reveals a 3D lattice spring within the Z-discs. Commun Biol 2020; 3:585. [PMID: 33067529 PMCID: PMC7567829 DOI: 10.1038/s42003-020-01321-5] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2020] [Accepted: 09/25/2020] [Indexed: 01/29/2023] Open
Abstract
The Z-disc forms a boundary between sarcomeres, which constitute structural and functional units of striated muscle tissue. Actin filaments from adjacent sarcomeres are cross-bridged by α-actinin in the Z-disc, allowing transmission of tension across the myofibril. Despite decades of studies, the 3D structure of Z-disc has remained elusive due to the limited resolution of conventional electron microscopy. Here, we observed porcine cardiac myofibrils using cryo-electron tomography and reconstructed the 3D structures of the actin-actinin cross-bridging complexes within the Z-discs in relaxed and activated states. We found that the α-actinin dimers showed contraction-dependent swinging and sliding motions in response to a global twist in the F-actin lattice. Our observation suggests that the actin-actinin complex constitutes a molecular lattice spring, which maintains the integrity of the Z-disc during the muscle contraction cycle.
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Affiliation(s)
- Toshiyuki Oda
- Department of Anatomy and Structural Biology, Graduate School of Medicine, University of Yamanashi, 1110 Shimokato, Chuo, Yamanashi, 409-3898, Japan.
| | - Haruaki Yanagisawa
- Department of Cell Biology and Anatomy, Graduate School of Medicine, the University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan
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