1
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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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2
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Liu C, Ruppel KM, Spudich JA. Motility Assay to Probe the Calcium Sensitivity of Myosin and Regulated Thin Filaments. Methods Mol Biol 2024; 2735:169-189. [PMID: 38038849 PMCID: PMC10773985 DOI: 10.1007/978-1-0716-3527-8_10] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2023]
Abstract
Calcium-dependent activation of the thin filament mediated by the troponin-tropomyosin complex is key in the regulation of actin-myosin based muscle contraction. Perturbations to this system, either physiological (e.g., phosphorylation of myosin light chains) or pathological (e.g., mutations that cause familial cardiomyopathies), can alter calcium sensitivity and thus have important implications in human health and disease. The in vitro motility assay provides a quantitative and precise method to study the calcium sensitivity of the reconstituted myosin-thin filament motile system. Here we present a simple and robust protocol to perform calcium-dependent motility of β-cardiac myosin and regulated thin filaments. The experiment is done on a multichannel microfluidic slide requiring minimal amounts of proteins. A complete velocity vs. calcium concentration curve is produced from one experiment in under 1 h.
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Affiliation(s)
- Chao Liu
- Department of Biochemistry, Beckman Center B405, Stanford University School of Medicine, Stanford, CA, USA
- Cardiovascular Institute, Stanford University, Stanford, CA, USA
- Biosciences and Biotechnology Division, Lawrence Livermore National Laboratory, Livermore, CA, USA
| | - Kathleen M Ruppel
- Department of Biochemistry, Beckman Center B405, Stanford University School of Medicine, Stanford, CA, USA.
- Cardiovascular Institute, Stanford University, Stanford, CA, USA.
- Department of Pediatrics (Cardiology), Stanford University, Stanford, CA, USA.
| | - James A Spudich
- Department of Biochemistry, Beckman Center B405, Stanford University School of Medicine, Stanford, CA, USA.
- Cardiovascular Institute, Stanford University, Stanford, CA, USA.
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3
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Kopylova GV, Kochurova AM, Yampolskaya DS, Nefedova VV, Tsaturyan AK, Koubassova NA, Kleymenov SY, Levitsky DI, Bershitsky SY, Matyushenko AM, Shchepkin DV. Structural and Functional Properties of Kappa Tropomyosin. Int J Mol Sci 2023; 24:ijms24098340. [PMID: 37176047 PMCID: PMC10179609 DOI: 10.3390/ijms24098340] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2023] [Revised: 04/27/2023] [Accepted: 05/04/2023] [Indexed: 05/15/2023] Open
Abstract
In the myocardium, the TPM1 gene expresses two isoforms of tropomyosin (Tpm), alpha (αTpm; Tpm 1.1) and kappa (κTpm; Tpm 1.2). κTpm is the result of alternative splicing of the TPM1 gene. We studied the structural features of κTpm and its regulatory function in the atrial and ventricular myocardium using an in vitro motility assay. We tested the possibility of Tpm heterodimer formation from α- and κ-chains. Our result shows that the formation of ακTpm heterodimer is thermodynamically favorable, and in the myocardium, κTpm most likely exists as ακTpm heterodimer. Using circular dichroism, we compared the thermal unfolding of ααTpm, ακTpm, and κκTpm. κκTpm had the lowest stability, while the ακTpm was more stable than ααTpm. The differential scanning calorimetry results indicated that the thermal stability of the N-terminal part of κκTpm is much lower than that of ααTpm. The affinity of ααTpm and κκTpm to F-actin did not differ, and ακTpm interacted with F-actin significantly worse. The troponin T1 fragment enhanced the κκTpm and ακTpm affinity to F-actin. κκTpm differently affected the calcium regulation of the interaction of pig and rat ventricular myosin with the thin filament. With rat myosin, calcium sensitivity of thin filaments containing κκTpm was significantly lower than that with ααTpm and with pig myosin, and the sensitivity did not differ. Thin filaments containing κκTpm and ακTpm were better activated by pig atrial myosin than those containing ααTpm.
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Affiliation(s)
- Galina V Kopylova
- Institute of Immunology and Physiology, Russian Academy of Sciences, 620049 Yekaterinburg, Russia
| | - Anastasia M Kochurova
- Institute of Immunology and Physiology, Russian Academy of Sciences, 620049 Yekaterinburg, Russia
| | - Daria S Yampolskaya
- Research Center of Biotechnology, Russian Academy of Sciences, 119071 Moscow, Russia
| | - Victoria V Nefedova
- Research Center of Biotechnology, Russian Academy of Sciences, 119071 Moscow, Russia
| | | | | | - Sergey Y Kleymenov
- Research Center of Biotechnology, Russian Academy of Sciences, 119071 Moscow, Russia
- Koltzov Institute of Developmental Biology, Russian Academy of Sciences, 119334 Moscow, Russia
| | - Dmitrii I Levitsky
- Research Center of Biotechnology, Russian Academy of Sciences, 119071 Moscow, Russia
| | - Sergey Y Bershitsky
- Institute of Immunology and Physiology, Russian Academy of Sciences, 620049 Yekaterinburg, Russia
| | | | - Daniil V Shchepkin
- Institute of Immunology and Physiology, Russian Academy of Sciences, 620049 Yekaterinburg, Russia
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4
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Halder SS, Rynkiewicz MJ, Creso JG, Sewanan LR, Howland L, Moore JR, Lehman W, Campbell SG. Mechanisms of pathogenicity in the hypertrophic cardiomyopathy-associated TPM1 variant S215L. PNAS NEXUS 2023; 2:pgad011. [PMID: 36896133 PMCID: PMC9991458 DOI: 10.1093/pnasnexus/pgad011] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/10/2022] [Revised: 07/12/2022] [Accepted: 01/09/2023] [Indexed: 01/22/2023]
Abstract
Hypertrophic cardiomyopathy (HCM) is an inherited disorder often caused by mutations to sarcomeric genes. Many different HCM-associated TPM1 mutations have been identified but they vary in their degrees of severity, prevalence, and rate of disease progression. The pathogenicity of many TPM1 variants detected in the clinical population remains unknown. Our objective was to employ a computational modeling pipeline to assess pathogenicity of one such variant of unknown significance, TPM1 S215L, and validate predictions using experimental methods. Molecular dynamic simulations of tropomyosin on actin suggest that the S215L significantly destabilizes the blocked regulatory state while increasing flexibility of the tropomyosin chain. These changes were quantitatively represented in a Markov model of thin-filament activation to infer the impacts of S215L on myofilament function. Simulations of in vitro motility and isometric twitch force predicted that the mutation would increase Ca2+ sensitivity and twitch force while slowing twitch relaxation. In vitro motility experiments with thin filaments containing TPM1 S215L revealed higher Ca2+ sensitivity compared with wild type. Three-dimensional genetically engineered heart tissues expressing TPM1 S215L exhibited hypercontractility, upregulation of hypertrophic gene markers, and diastolic dysfunction. These data form a mechanistic description of TPM1 S215L pathogenicity that starts with disruption of the mechanical and regulatory properties of tropomyosin, leading thereafter to hypercontractility and finally induction of a hypertrophic phenotype. These simulations and experiments support the classification of S215L as a pathogenic mutation and support the hypothesis that an inability to adequately inhibit actomyosin interactions is the mechanism whereby thin-filament mutations cause HCM.
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Affiliation(s)
- Saiti S Halder
- Department of Biomedical Engineering, Yale University, New Haven, CT 06511
| | | | - Jenette G Creso
- Department of Biomedical Engineering, Yale University, New Haven, CT 06511
| | - Lorenzo R Sewanan
- Department of Biomedical Engineering, Yale University, New Haven, CT 06511
- Department of Internal Medicine, Columbia University, New York, NY 10032
| | - Lindsey Howland
- Department of Biological Sciences, University of Massachusetts Lowell, MA 01854
| | - Jeffrey R Moore
- Department of Biological Sciences, University of Massachusetts Lowell, MA 01854
| | - William Lehman
- Department of Physiology/Biophysics, Boston University, Boston, MA 02215
| | - Stuart G Campbell
- Department of Biomedical Engineering, Yale University, New Haven, CT 06511
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5
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Barrick SK, Garg A, Greenberg L, Zhang S, Lin CY, Stitziel NO, Greenberg MJ. Functional assays reveal the pathogenic mechanism of a de novo tropomyosin variant identified in patient with dilated cardiomyopathy. J Mol Cell Cardiol 2023; 176:58-67. [PMID: 36739943 PMCID: PMC11285302 DOI: 10.1016/j.yjmcc.2023.01.014] [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: 09/06/2022] [Revised: 01/09/2023] [Accepted: 01/31/2023] [Indexed: 02/05/2023]
Abstract
Dilated cardiomyopathy (DCM) is a leading cause of heart failure and a major indicator for heart transplant. Human genetic studies have identified over a thousand causal mutations for DCM in genes involved in a variety of cellular processes, including sarcomeric contraction. A substantial clinical challenge is determining the pathogenicity of novel variants in disease-associated genes. This challenge of connecting genotype and phenotype has frustrated attempts to develop effective, mechanism-based treatments for patients. Here, we identified a de novo mutation (T237S) in TPM1, the gene that encodes the thin filament protein tropomyosin, in a patient with DCM and conducted in vitro experiments to characterize the pathogenicity of this novel variant. We expressed recombinant mutant protein, reconstituted it into thin filaments, and examined the effects of the mutation on thin filament function. We show that the mutation reduces the calcium sensitivity of thin filament activation, as previously seen for known pathogenic mutations. Mechanistically, this shift is due to mutation-induced changes in tropomyosin positioning along the thin filament. We demonstrate that the thin filament activator omecamtiv mecarbil restores the calcium sensitivity of thin filaments regulated by the mutant tropomyosin, which lays the foundation for additional experiments to explore the therapeutic potential of this drug for patients harboring the T237S mutation. Taken together, our results suggest that the TPM1 T237S mutation is likely pathogenic and demonstrate how functional in vitro characterization of pathogenic protein variants in the lab might guide precision medicine in the clinic.
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Affiliation(s)
- Samantha K Barrick
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110, USA
| | - Ankit Garg
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110, USA; Center for Cardiovascular Research, Division of Cardiology, Department of Medicine, Washington University School of Medicine, St. Louis, MO 63110, USA
| | - Lina Greenberg
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110, USA
| | - Shanshan Zhang
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110, USA
| | - Chieh-Yu Lin
- Department of Pathology and Immunology, Washington University School of Medicine, St. Louis, MO 63110, USA
| | - Nathan O Stitziel
- Center for Cardiovascular Research, Division of Cardiology, Department of Medicine, Washington University School of Medicine, St. Louis, MO 63110, USA; Department of Genetics, Washington University School of Medicine, St. Louis, MO 63110, USA; McDonnell Genome Institute, Washington University School of Medicine, St. Louis, MO 63110, USA
| | - Michael J Greenberg
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110, USA.
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6
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Doran MH, Rynkiewicz MJ, Rassici D, Bodt SM, Barry ME, Bullitt E, Yengo CM, Moore JR, Lehman W. Conformational changes linked to ADP release from human cardiac myosin bound to actin-tropomyosin. J Gen Physiol 2023; 155:213802. [PMID: 36633586 PMCID: PMC9859928 DOI: 10.1085/jgp.202213267] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2022] [Revised: 11/11/2022] [Accepted: 12/14/2022] [Indexed: 01/13/2023] Open
Abstract
Following binding to the thin filament, β-cardiac myosin couples ATP-hydrolysis to conformational rearrangements in the myosin motor that drive myofilament sliding and cardiac ventricular contraction. However, key features of the cardiac-specific actin-myosin interaction remain uncertain, including the structural effect of ADP release from myosin, which is rate-limiting during force generation. In fact, ADP release slows under experimental load or in the intact heart due to the afterload, thereby adjusting cardiac muscle power output to meet physiological demands. To further elucidate the structural basis of this fundamental process, we used a combination of cryo-EM reconstruction methodologies to determine structures of the human cardiac actin-myosin-tropomyosin filament complex at better than 3.4 Å-resolution in the presence and in the absence of Mg2+·ADP. Focused refinements of the myosin motor head and its essential light chains in these reconstructions reveal that small changes in the nucleotide-binding site are coupled to significant rigid body movements of the myosin converter domain and a 16-degree lever arm swing. Our structures provide a mechanistic framework to understand the effect of ADP binding and release on human cardiac β-myosin, and offer insights into the force-sensing mechanism displayed by the cardiac myosin motor.
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Affiliation(s)
- Matthew H. Doran
- School of Medicine, Department of Physiology and Biophysics, Boston University, Boston, MA, USA,Department of Biological Chemistry and Molecular Pharmacology, Blavatnik Institute, Harvard Medical School, Boston, MA, USA
| | - Michael J. Rynkiewicz
- School of Medicine, Department of Physiology and Biophysics, Boston University, Boston, MA, USA
| | - David Rassici
- Department of Cellular and Molecular Physiology, Penn State College of Medicine, Hershey, PA, USA
| | - Skylar M.L. Bodt
- Department of Cellular and Molecular Physiology, Penn State College of Medicine, Hershey, PA, USA
| | - Meaghan E. Barry
- Department of Biological Science, University of Massachusetts Lowell, Lowell, MA, USA
| | - Esther Bullitt
- School of Medicine, Department of Physiology and Biophysics, Boston University, Boston, MA, USA
| | - Christopher M. Yengo
- Department of Cellular and Molecular Physiology, Penn State College of Medicine, Hershey, PA, USA
| | - Jeffrey R. Moore
- Department of Biological Science, University of Massachusetts Lowell, Lowell, MA, USA
| | - William Lehman
- School of Medicine, Department of Physiology and Biophysics, Boston University, Boston, MA, USA
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7
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Nefedova VV, Kopylova GV, Shchepkin DV, Kochurova AM, Kechko OI, Borzova VA, Ryabkova NS, Katrukha IA, Mitkevich VA, Bershitsky SY, Levitsky DI, Matyushenko AM. Impact of Troponin in Cardiomyopathy Development Caused by Mutations in Tropomyosin. Int J Mol Sci 2022; 23:ijms232415723. [PMID: 36555368 PMCID: PMC9779223 DOI: 10.3390/ijms232415723] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2022] [Revised: 12/07/2022] [Accepted: 12/08/2022] [Indexed: 12/14/2022] Open
Abstract
Tropomyosin (Tpm) mutations cause inherited cardiac diseases such as hypertrophic and dilated cardiomyopathies. We applied various approaches to investigate the role of cardiac troponin (Tn) and especially the troponin T (TnT) in the pathogenic effects of Tpm cardiomyopathy-associated mutations M8R, K15N, A277V, M281T, and I284V located in the overlap junction of neighboring Tpm dimers. Using co-sedimentation assay and viscosity measurements, we showed that TnT1 (fragment of TnT) stabilizes the overlap junction of Tpm WT and all Tpm mutants studied except Tpm M8R. However, isothermal titration calorimetry (ITC) indicated that TnT1 binds Tpm WT and all Tpm mutants similarly. By using ITC, we measured the direct KD of the Tpm overlap region, N-end, and C-end binding to TnT1. The ITC data revealed that the Tpm C-end binds to TnT1 independently from the N-end, while N-end does not bind. Therefore, we suppose that Tpm M8R binds to TnT1 without forming the overlap junction. We also demonstrated the possible role of Tn isoform composition in the cardiomyopathy development caused by M8R mutation. TnT1 dose-dependently reduced the velocity of F-actin-Tpm filaments containing Tpm WT, Tpm A277V, and Tpm M281T mutants in an in vitro motility assay. All mutations impaired the calcium regulation of the actin-myosin interaction. The M281T and I284V mutations increased the calcium sensitivity, while the K15N and A277V mutations reduced it. The Tpm M8R, M281T, and I284V mutations under-inhibited the velocity at low calcium concentrations. Our results demonstrate that Tpm mutations likely implement their pathogenic effects through Tpm interaction with Tn, cardiac myosin, or other protein partners.
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Affiliation(s)
- Victoria V. Nefedova
- Research Center of Biotechnology of the Russian Academy of Sciences, 119071 Moscow, Russia
- Correspondence:
| | - Galina V. Kopylova
- Institute of Immunology and Physiology of the Russian Academy of Sciences, 620049 Yekaterinburg, Russia
| | - Daniil V. Shchepkin
- Institute of Immunology and Physiology of the Russian Academy of Sciences, 620049 Yekaterinburg, Russia
| | - Anastasia M. Kochurova
- Institute of Immunology and Physiology of the Russian Academy of Sciences, 620049 Yekaterinburg, Russia
| | - Olga I. Kechko
- Center for Precision Genome Editing and Genetic Technologies for Biomedicine, Engelhardt Institute of Molecular Biology, Russian Academy of Science, 119991 Moscow, Russia
| | - Vera A. Borzova
- Research Center of Biotechnology of the Russian Academy of Sciences, 119071 Moscow, Russia
| | - Natalia S. Ryabkova
- Department of Biochemistry, Faculty of Biology, Lomonosov Moscow State University, 119234 Moscow, Russia
- HyTest Ltd., 20520 Turku, Finland
| | - Ivan A. Katrukha
- Department of Biochemistry, Faculty of Biology, Lomonosov Moscow State University, 119234 Moscow, Russia
- HyTest Ltd., 20520 Turku, Finland
| | - Vladimir A. Mitkevich
- Engelhardt Institute of Molecular Biology, Russian Academy of Science, 119991 Moscow, Russia
| | - Sergey Y. Bershitsky
- Institute of Immunology and Physiology of the Russian Academy of Sciences, 620049 Yekaterinburg, Russia
| | - Dmitrii I. Levitsky
- Research Center of Biotechnology of the Russian Academy of Sciences, 119071 Moscow, Russia
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8
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Sundar S, Rimkus B, Meemaduma PS, deLap S, LaFave N, Racca AW, Hettige P, Moore J, Gage M, Shehaj A, Konow N. Bridging the muscle genome to phenome across multiple biological scales. J Exp Biol 2022; 225:jeb243630. [PMID: 35288729 PMCID: PMC9080751 DOI: 10.1242/jeb.243630] [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: 10/05/2021] [Accepted: 03/08/2022] [Indexed: 11/20/2022]
Abstract
Muscle is highly hierarchically organized, with functions shaped by genetically controlled expression of protein ensembles with different isoform profiles at the sarcomere scale. However, it remains unclear how isoform profiles shape whole-muscle performance. We compared two mouse hindlimb muscles, the slow, relatively parallel-fibered soleus and the faster, more pennate-fibered tibialis anterior (TA), across scales: from gene regulation, isoform expression and translation speed, to force-length-velocity-power for intact muscles. Expression of myosin heavy-chain (MHC) isoforms directly corresponded with contraction velocity. The fast-twitch TA with fast MHC isoforms had faster unloaded velocities (actin sliding velocity, Vactin; peak fiber velocity, Vmax) than the slow-twitch soleus. For the soleus, Vactin was biased towards Vactin for purely slow MHC I, despite this muscle's even fast and slow MHC isoform composition. Our multi-scale results clearly identified a consistent and significant dampening in fiber shortening velocities for both muscles, underscoring an indirect correlation between Vactin and fiber Vmax that may be influenced by differences in fiber architecture, along with internal loading due to both passive and active effects. These influences correlate with the increased peak force and power in the slightly more pennate TA, leading to a broader length range of near-optimal force production. Conversely, a greater force-velocity curvature in the near-parallel fibered soleus highlights the fine-tuning by molecular-scale influences including myosin heavy and light chain expression along with whole-muscle characteristics. Our results demonstrate that the individual gene, protein and whole-fiber characteristics do not directly reflect overall muscle performance but that intricate fine-tuning across scales shapes specialized muscle function.
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Affiliation(s)
- SaiLavanyaa Sundar
- Department of Biological Sciences, University of Massachusetts, Lowell, MA 01854, USA
- UMass Movement Center, University of Massachusetts, Lowell, MA 01854, USA
| | - Barbora Rimkus
- Department of Biological Sciences, University of Massachusetts, Lowell, MA 01854, USA
- UMass Movement Center, University of Massachusetts, Lowell, MA 01854, USA
| | - Prabath S. Meemaduma
- UMass Movement Center, University of Massachusetts, Lowell, MA 01854, USA
- Department of Chemistry, University of Massachusetts, Lowell, MA 01854, USA
| | - Samuel deLap
- Department of Biological Sciences, University of Massachusetts, Lowell, MA 01854, USA
- UMass Movement Center, University of Massachusetts, Lowell, MA 01854, USA
| | - Nicholas LaFave
- Department of Biological Sciences, University of Massachusetts, Lowell, MA 01854, USA
- UMass Movement Center, University of Massachusetts, Lowell, MA 01854, USA
| | - Alice W. Racca
- Department of Biological Sciences, University of Massachusetts, Lowell, MA 01854, USA
- UMass Movement Center, University of Massachusetts, Lowell, MA 01854, USA
| | - Pabodha Hettige
- UMass Movement Center, University of Massachusetts, Lowell, MA 01854, USA
- Department of Chemistry, University of Massachusetts, Lowell, MA 01854, USA
| | - Jeffrey Moore
- Department of Biological Sciences, University of Massachusetts, Lowell, MA 01854, USA
- UMass Movement Center, University of Massachusetts, Lowell, MA 01854, USA
| | - Matthew Gage
- UMass Movement Center, University of Massachusetts, Lowell, MA 01854, USA
- Department of Chemistry, University of Massachusetts, Lowell, MA 01854, USA
| | - Andrea Shehaj
- Department of Biological Sciences, University of Massachusetts, Lowell, MA 01854, USA
- UMass Movement Center, University of Massachusetts, Lowell, MA 01854, USA
| | - Nicolai Konow
- Department of Biological Sciences, University of Massachusetts, Lowell, MA 01854, USA
- UMass Movement Center, University of Massachusetts, Lowell, MA 01854, USA
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9
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Racca AW, Rynkiewicz MJ, LaFave N, Ghosh A, Lehman W, Moore JR. M8R tropomyosin mutation disrupts actin binding and filament regulation: The beginning affects the middle and end. J Biol Chem 2020; 295:17128-17137. [PMID: 33020181 PMCID: PMC7863880 DOI: 10.1074/jbc.ra120.014713] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2020] [Revised: 09/28/2020] [Indexed: 11/06/2022] Open
Abstract
Dilated cardiomyopathy (DCM) is associated with mutations in cardiomyocyte sarcomeric proteins, including α-tropomyosin. In conjunction with troponin, tropomyosin shifts to regulate actomyosin interactions. Tropomyosin molecules overlap via tropomyosin-tropomyosin head-to-tail associations, forming a continuous strand along the thin filament. These associations are critical for propagation of tropomyosin's reconfiguration along the thin filament and key for the cooperative switching between heart muscle contraction and relaxation. Here, we tested perturbations in tropomyosin structure, biochemistry, and function caused by the DCM-linked mutation, M8R, which is located at the overlap junction. Localized and nonlocalized structural effects of the mutation were found in tropomyosin that ultimately perturb its thin filament regulatory function. Comparison of mutant and WT α-tropomyosin was carried out using in vitro motility assays, CD, actin co-sedimentation, and molecular dynamics simulations. Regulated thin filament velocity measurements showed that the presence of M8R tropomyosin decreased calcium sensitivity and thin filament cooperativity. The co-sedimentation of actin and tropomyosin showed weakening of actin-mutant tropomyosin binding. The binding of troponin T's N terminus to the actin-mutant tropomyosin complex was also weakened. CD and molecular dynamics indicate that the M8R mutation disrupts the four-helix bundle at the head-to-tail junction, leading to weaker tropomyosin-tropomyosin binding and weaker tropomyosin-actin binding. Molecular dynamics revealed that altered end-to-end bond formation has effects extending toward the central region of the tropomyosin molecule, which alter the azimuthal position of tropomyosin, likely disrupting the mutant thin filament response to calcium. These results demonstrate that mutation-induced alterations in tropomyosin-thin filament interactions underlie the altered regulatory phenotype and ultimately the pathogenesis of DCM.
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Affiliation(s)
- Alice Ward Racca
- Department of Biological Sciences, University of Massachusetts-Lowell, Lowell, Massachusetts, USA
| | - Michael J Rynkiewicz
- Department of Physiology & Biophysics, Boston University School of Medicine, Boston, Massachusetts, USA
| | - Nicholas LaFave
- Department of Biological Sciences, University of Massachusetts-Lowell, Lowell, Massachusetts, USA
| | - Anita Ghosh
- Department of Physiology & Biophysics, Boston University School of Medicine, Boston, Massachusetts, USA
| | - William Lehman
- Department of Physiology & Biophysics, Boston University School of Medicine, Boston, Massachusetts, USA
| | - Jeffrey R Moore
- Department of Biological Sciences, University of Massachusetts-Lowell, Lowell, Massachusetts, USA.
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