1
|
Barrick SK, Greenberg L, Greenberg MJ. A troponin T variant linked with pediatric dilated cardiomyopathy reduces the coupling of thin filament activation to myosin and calcium binding. Mol Biol Cell 2021; 32:1677-1689. [PMID: 34161147 PMCID: PMC8684737 DOI: 10.1091/mbc.e21-02-0082] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Dilated cardiomyopathy (DCM) is a significant cause of pediatric heart failure. Mutations in proteins that regulate cardiac muscle contraction can cause DCM; however, the mechanisms by which molecular-level mutations contribute to cellular dysfunction are not well understood. Better understanding of these mechanisms might enable the development of targeted therapeutics that benefit patient subpopulations with mutations that cause common biophysical defects. We examined the molecular- and cellular-level impacts of a troponin T variant associated with pediatric-onset DCM, R134G. The R134G variant decreased calcium sensitivity in an in vitro motility assay. Using stopped-flow and steady-state fluorescence measurements, we determined the molecular mechanism of the altered calcium sensitivity: R134G decouples calcium binding by troponin from the closed-to-open transition of the thin filament and decreases the cooperativity of myosin binding to regulated thin filaments. Consistent with the prediction that these effects would cause reduced force per sarcomere, cardiomyocytes carrying the R134G mutation are hypocontractile. They also show hallmarks of DCM that lie downstream of the initial insult, including disorganized sarcomeres and cellular hypertrophy. These results reinforce the importance of multiscale studies to fully understand mechanisms underlying human disease and highlight the value of mechanism-based precision medicine approaches for DCM.
Collapse
Affiliation(s)
- Samantha K Barrick
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110
| | - Lina Greenberg
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110
| | - Michael J Greenberg
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110
| |
Collapse
|
2
|
Creso JG, Campbell SG. Potential impacts of the cardiac troponin I mobile domain on myofilament activation and relaxation. J Mol Cell Cardiol 2021; 155:50-57. [PMID: 33647310 DOI: 10.1016/j.yjmcc.2021.02.012] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/29/2020] [Revised: 01/13/2021] [Accepted: 02/22/2021] [Indexed: 10/22/2022]
Abstract
The cardiac thin filament is regulated in a Ca2+-dependent manner through conformational changes of troponin and tropomyosin (Tm). It has been generally understood that under conditions of low Ca2+ the inhibitory peptide domain (IP) of troponin I (TnI) binds to actin and holds Tm over the myosin binding sites on actin to prevent crossbridge formation. More recently, evidence that the C-terminal mobile domain (MD) of TnI also binds actin has made for a more complex scenario. This study uses a computational model to investigate the consequences of assuming that TnI regulates Tm movement via two actin-binding domains rather than one. First, a 16-state model of the cardiac thin filament regulatory unit was created with TnI-IP as the sole regulatory domain. Expansion of this to include TnI-MD formed a 24-state model. Comparison of these models showed that assumption of a second actin-binding site allows the individual domains to have a lower affinity for actin than would be required for IP acting alone. Indeed, setting actin affinities of the IP and MD to 25% of that assumed for the IP in the single-site model was sufficient to achieve precisely the same degree of Ca2+ regulation. We also tested the 24-state model's ability to represent steady-state experimental data in the case of disruption of either the IP or MD. We were able to capture qualitative changes in several properties that matched what was seen in the experimental data. Lastly, simulations were run to examine the effect of disruption of the IP or MD on twitch dynamics. Our results suggest that both domains are required to keep diastolic cross-bridge activity to a minimum and accelerate myofilament relaxation. Overall, our analyses support a paradigm in which two domains of TnI bind with moderate affinity to actin, working in tandem to complete Ca2+-dependent regulation of the thin filament.
Collapse
Affiliation(s)
- Jenette G Creso
- Department of Biomedical Engineering, Yale University, 55 Prospect St, New Haven, CT 06511, USA.
| | - Stuart G Campbell
- Department of Biomedical Engineering, Yale University, 55 Prospect St, New Haven, CT 06511, USA; Department of Cellular and Molecular Physiology, Yale School of Medicine, 333 Cedar St, New Haven, CT 06510, USA.
| |
Collapse
|
3
|
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.
Collapse
Affiliation(s)
- Larry S Tobacman
- Departments of Medicine and of Physiology and Biophysics, University of Illinois at Chicago, Chicago, Illinois.
| |
Collapse
|
4
|
Ezekian JE, Clippinger SR, Garcia JM, Yang Q, Denfield S, Jeewa A, Dreyer WJ, Zou W, Fan Y, Allen HD, Kim JJ, Greenberg MJ, Landstrom AP. Variant R94C in TNNT2-Encoded Troponin T Predisposes to Pediatric Restrictive Cardiomyopathy and Sudden Death Through Impaired Thin Filament Relaxation Resulting in Myocardial Diastolic Dysfunction. J Am Heart Assoc 2020; 9:e015111. [PMID: 32098556 PMCID: PMC7335540 DOI: 10.1161/jaha.119.015111] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Background Pediatric‐onset restrictive cardiomyopathy (RCM) is associated with high mortality, but underlying mechanisms of disease are under investigated. RCM‐associated diastolic dysfunction secondary to variants in TNNT2‐encoded cardiac troponin T (TNNT2) is poorly described. Methods and Results Genetic analysis of a proband and kindred with RCM identified TNNT2‐R94C, which cosegregated in a family with 2 generations of RCM, ventricular arrhythmias, and sudden death. TNNT2‐R94C was absent among large, population‐based cohorts Genome Aggregation Database (gnomAD) and predicted to be pathologic by in silico modeling. Biophysical experiments using recombinant human TNNT2‐R94C demonstrated impaired cardiac regulation at the molecular level attributed to reduced calcium‐dependent blocking of myosin's interaction with the thin filament. Computational modeling predicted a shift in the force‐calcium curve for the R94C mutant toward submaximal calcium activation compared within the wild type, suggesting low levels of muscle activation even at resting calcium concentrations and hypercontractility following activation by calcium. Conclusions The pathogenic TNNT2‐R94C variant activates thin‐filament–mediated sarcomeric contraction at submaximal calcium concentrations, likely resulting in increased muscle tension during diastole and hypercontractility during systole. This describes the proximal biophysical mechanism for development of RCM in this family.
Collapse
Affiliation(s)
- Jordan E Ezekian
- Division of Paediatric Cardiology Department of Pediatrics Duke University School of Medicine Durham NC
| | - Sarah R Clippinger
- Department of Biochemistry and Molecular Biophysics Washington University in St. Louis St. Louis MO
| | - Jaquelin M Garcia
- Department of Biochemistry and Molecular Biophysics Washington University in St. Louis St. Louis MO
| | - Qixin Yang
- Division of Paediatric Cardiology Department of Pediatrics Duke University School of Medicine Durham NC
| | - Susan Denfield
- Department of Pediatrics The Lillie Frank Abercrombie Section of Pediatric Cardiology Baylor College of Medicine Houston TX
| | - Aamir Jeewa
- Department of Pediatrics The Hospital for Sick Children Toronto Ontario Canada
| | - William J Dreyer
- Department of Pediatrics The Lillie Frank Abercrombie Section of Pediatric Cardiology Baylor College of Medicine Houston TX
| | - Wenxin Zou
- Department of Pediatrics The Lillie Frank Abercrombie Section of Pediatric Cardiology Baylor College of Medicine Houston TX
| | - Yuxin Fan
- Department of Pediatrics The Lillie Frank Abercrombie Section of Pediatric Cardiology Baylor College of Medicine Houston TX
| | - Hugh D Allen
- Department of Pediatrics The Lillie Frank Abercrombie Section of Pediatric Cardiology Baylor College of Medicine Houston TX
| | - Jeffrey J Kim
- Department of Pediatrics The Lillie Frank Abercrombie Section of Pediatric Cardiology Baylor College of Medicine Houston TX
| | - Michael J Greenberg
- Department of Biochemistry and Molecular Biophysics Washington University in St. Louis St. Louis MO
| | - Andrew P Landstrom
- Division of Paediatric Cardiology Department of Pediatrics Duke University School of Medicine Durham NC.,Department of Cell Biology Duke University School of Medicine Durham NC
| |
Collapse
|
5
|
Barrick SK, Clippinger SR, Greenberg L, Greenberg MJ. Computational Tool to Study Perturbations in Muscle Regulation and Its Application to Heart Disease. Biophys J 2019; 116:2246-2252. [PMID: 31126584 PMCID: PMC6588827 DOI: 10.1016/j.bpj.2019.05.002] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2019] [Revised: 04/29/2019] [Accepted: 05/01/2019] [Indexed: 11/21/2022] Open
Abstract
Striated muscle contraction occurs when myosin thick filaments bind to thin filaments in the sarcomere and generate pulling forces. This process is regulated by calcium, and it can be perturbed by pathological conditions (e.g., myopathies), physiological adaptations (e.g., β-adrenergic stimulation), and pharmacological interventions. Therefore, it is important to have a methodology to robustly determine the impact of these perturbations and statistically evaluate their effects. Here, we present an approach to measure the equilibrium constants that govern muscle activation, estimate uncertainty in these parameters, and statistically test the effects of perturbations. We provide a MATLAB-based computational tool for these analyses, along with easy-to-follow tutorials that make this approach accessible. The hypothesis testing and error estimation approaches described here are broadly applicable, and the provided tools work with other types of data, including cellular measurements. To demonstrate the utility of the approach, we apply it to elucidate the biophysical mechanism of a mutation that causes familial hypertrophic cardiomyopathy. This approach is generally useful for studying muscle diseases and therapeutic interventions that target muscle contraction.
Collapse
Affiliation(s)
- Samantha K Barrick
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, Missouri
| | - Sarah R Clippinger
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, Missouri
| | - Lina Greenberg
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, Missouri
| | - Michael J Greenberg
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, Missouri.
| |
Collapse
|
6
|
Johnson D, Mathur MC, Kobayashi T, Chalovich JM. The Cardiomyopathy Mutation, R146G Troponin I, Stabilizes the Intermediate “C” State of Regulated Actin under High- and Low-Free Ca2+ Conditions. Biochemistry 2016; 55:4533-40. [DOI: 10.1021/acs.biochem.5b01359] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Dylan Johnson
- Department
of Biochemistry and Molecular Biology, Brody School of Medicine, East Carolina University, Greenville, North Carolina 27834, United States
- Department
of Chemistry, East Carolina University, Greenville, North Carolina 27858-4353, United States
| | - Mohit C. Mathur
- Department
of Biochemistry and Molecular Biology, Brody School of Medicine, East Carolina University, Greenville, North Carolina 27834, United States
| | - Tomoyoshi Kobayashi
- Department
of Physiology and Biophysics and Center for Cardiovascular Research,
College of Medicine, University of Illinois, Chicago, Illinois 60612-7342, United States
| | - Joseph M. Chalovich
- Department
of Biochemistry and Molecular Biology, Brody School of Medicine, East Carolina University, Greenville, North Carolina 27834, United States
| |
Collapse
|
7
|
Order-Disorder Transitions in the Cardiac Troponin Complex. J Mol Biol 2016; 428:2965-77. [PMID: 27395017 DOI: 10.1016/j.jmb.2016.06.022] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2016] [Revised: 06/21/2016] [Accepted: 06/29/2016] [Indexed: 12/26/2022]
Abstract
The troponin complex is a molecular switch that ties shifting intracellular calcium concentration to association and dissociation of actin and myosin, effectively allowing excitation-contraction coupling in striated muscle. Although there is a long history of muscle biophysics and structural biology, many of the mechanistic details that enable troponin's function remain incompletely understood. This review summarizes the current structural understanding of the troponin complex on the muscle thin filament, focusing on conformational changes in flexible regions of the troponin I subunit. In particular, we focus on order-disorder transitions in the C-terminal domain of troponin I, which have important implications in cardiac disease and could also have potential as a model system for the study of coupled binding and folding.
Collapse
|
8
|
Meyer NL, Chase PB. Role of cardiac troponin I carboxy terminal mobile domain and linker sequence in regulating cardiac contraction. Arch Biochem Biophys 2016; 601:80-7. [PMID: 26971468 PMCID: PMC4899117 DOI: 10.1016/j.abb.2016.03.010] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2015] [Revised: 02/26/2016] [Accepted: 03/08/2016] [Indexed: 01/24/2023]
Abstract
Inhibition of striated muscle contraction at resting Ca(2+) depends on the C-terminal half of troponin I (TnI) in thin filaments. Much focus has been on a short inhibitory peptide (Ip) sequence within TnI, but structural studies and identification of disease-associated mutations broadened emphasis to include a larger mobile domain (Md) sequence at the C-terminus of TnI. For Md to function effectively in muscle relaxation, tight mechanical coupling to troponin's core-and thus tropomyosin-is presumably needed. We generated recombinant, human cardiac troponins containing one of two TnI constructs: either an 8-amino acid linker between Md and the rest of troponin (cTnILink8), or an Md deletion (cTnI1-163). Motility assays revealed that Ca(2+)-sensitivity of reconstituted thin filament sliding was markedly increased with cTnILink8 (∼0.9 pCa unit leftward shift of speed-pCa relation compared to WT), and increased further when Md was missing entirely (∼1.4 pCa unit shift). Cardiac Tn's ability to turn off filament sliding at diastolic Ca(2+) was mostly (61%), but not completely eliminated with cTnI1-163. TnI's Md is required for full inhibition of unloaded filament sliding, although other portions of troponin-presumably including Ip-are also necessary. We also confirm that TnI's Md is not responsible for superactivation of actomyosin cycling by troponin.
Collapse
Affiliation(s)
- Nancy L Meyer
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, OR, USA
| | - P Bryant Chase
- Department of Biological Science and Program in Molecular Biophysics, Florida State University, Tallahassee, FL, USA.
| |
Collapse
|
9
|
Solaro RJ, Kobayashi T. Protein phosphorylation and signal transduction in cardiac thin filaments. J Biol Chem 2011; 286:9935-40. [PMID: 21257760 DOI: 10.1074/jbc.r110.197731] [Citation(s) in RCA: 83] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Affiliation(s)
- R John Solaro
- Department of Physiology and Biophysics and Center for Cardiovascular Research, University of Illinois at Chicago, Chicago, Illinois 60612, USA.
| | | |
Collapse
|