1
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Smith QM, Inchingolo AV, Mihailescu MD, Dai H, Kad NM. Single-molecule imaging reveals the concerted release of myosin from regulated thin filaments. eLife 2021; 10:69184. [PMID: 34569933 PMCID: PMC8476120 DOI: 10.7554/elife.69184] [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: 04/07/2021] [Accepted: 09/11/2021] [Indexed: 11/13/2022] Open
Abstract
Regulated thin filaments (RTFs) tightly control striated muscle contraction through calcium binding to troponin, which enables tropomyosin to expose myosin-binding sites on actin. Myosin binding holds tropomyosin in an open position, exposing more myosin-binding sites on actin, leading to cooperative activation. At lower calcium levels, troponin and tropomyosin turn off the thin filament; however, this is antagonised by the high local concentration of myosin, questioning how the thin filament relaxes. To provide molecular details of deactivation, we used single-molecule imaging of green fluorescent protein (GFP)-tagged myosin-S1 (S1-GFP) to follow the activation of RTF tightropes. In sub-maximal activation conditions, RTFs are not fully active, enabling direct observation of deactivation in real time. We observed that myosin binding occurs in a stochastic step-wise fashion; however, an unexpectedly large probability of multiple contemporaneous detachments is observed. This suggests that deactivation of the thin filament is a coordinated active process.
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Affiliation(s)
- Quentin M Smith
- School of Biosciences, University of Kent, Canterbury, United Kingdom
| | | | | | - Hongsheng Dai
- Department of Mathematical Sciences, University of Essex, Colchester, United Kingdom
| | - Neil M Kad
- School of Biosciences, University of Kent, Canterbury, United Kingdom
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2
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Sewanan LR, Park J, Rynkiewicz MJ, Racca AW, Papoutsidakis N, Schwan J, Jacoby DL, Moore JR, Lehman W, Qyang Y, Campbell SG. Loss of crossbridge inhibition drives pathological cardiac hypertrophy in patients harboring the TPM1 E192K mutation. J Gen Physiol 2021; 153:212516. [PMID: 34319370 PMCID: PMC8321830 DOI: 10.1085/jgp.202012640] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2020] [Revised: 06/14/2021] [Accepted: 07/09/2021] [Indexed: 01/10/2023] Open
Abstract
Hypertrophic cardiomyopathy (HCM) is an inherited disorder caused primarily by mutations to thick and thinfilament proteins. Although thin filament mutations are less prevalent than their oft-studied thick filament counterparts, they are frequently associated with severe patient phenotypes and can offer important insight into fundamental disease mechanisms. We have performed a detailed study of tropomyosin (TPM1) E192K, a variant of uncertain significance associated with HCM. Molecular dynamics revealed that E192K results in a more flexible TPM1 molecule, which could affect its ability to regulate crossbridges. In vitro motility assays of regulated actin filaments containing TPM1 E192K showed an overall loss of Ca2+ sensitivity. To understand these effects, we used multiscale computational models that suggested a subtle phenotype in which E192K leads to an inability to completely inhibit actin-myosin crossbridge activity at low Ca2+. To assess the physiological impact of the mutation, we generated patient-derived engineered heart tissues expressing E192K. These tissues showed disease features similar to those of the patients, including cellular hypertrophy, hypercontractility, and diastolic dysfunction. We hypothesized that excess residual crossbridge activity could be triggering cellular hypertrophy, even if the overall Ca2+ sensitivity was reduced by E192K. To test this hypothesis, the cardiac myosin-specific inhibitor mavacamten was applied to patient-derived engineered heart tissues for 4 d followed by 24 h of washout. Chronic mavacamten treatment abolished contractile differences between control and TPM1 E192K engineered heart tissues and reversed hypertrophy in cardiomyocytes. These results suggest that the TPM1 E192K mutation triggers cardiomyocyte hypertrophy by permitting excess residual crossbridge activity. These studies also provide direct evidence that myosin inhibition by mavacamten can counteract the hypertrophic effects of mutant tropomyosin.
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Affiliation(s)
- Lorenzo R Sewanan
- Department of Biomedical Engineering, Yale University, New Haven, CT
| | - Jinkyu Park
- Department of Internal Medicine, Section of Cardiovascular Medicine, Yale Cardiovascular Research Center, Yale School of Medicine, New Haven, CT.,Yale Stem Cell Center, Yale School of Medicine, New Haven, CT
| | - Michael J Rynkiewicz
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, MA
| | - Alice W Racca
- Department of Biological Sciences, University of Massachusetts, Lowell, MA
| | - Nikolaos Papoutsidakis
- Department of Internal Medicine, Section of Cardiovascular Medicine, Yale School of Medicine, New Haven, CT
| | - Jonas Schwan
- Department of Biomedical Engineering, Yale University, New Haven, CT
| | - Daniel L Jacoby
- Department of Internal Medicine, Section of Cardiovascular Medicine, Yale School of Medicine, New Haven, CT
| | - Jeffrey R Moore
- Department of Biological Sciences, University of Massachusetts, Lowell, MA
| | - William Lehman
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, MA
| | - Yibing Qyang
- Department of Internal Medicine, Section of Cardiovascular Medicine, Yale Cardiovascular Research Center, Yale School of Medicine, New Haven, CT.,Yale Stem Cell Center, Yale School of Medicine, New Haven, CT.,Vascular Biology and Therapeutics Program, Yale University, New Haven, CT.,Department of Pathology, Yale University, New Haven, CT
| | - Stuart G Campbell
- Department of Biomedical Engineering, Yale University, New Haven, CT.,Department of Cellular and Molecular Physiology, Yale School of Medicine, New Haven, CT
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3
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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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4
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Aboelkassem Y, Powers JD, McCabe KJ, McCulloch AD. Multiscale Models of Cardiac Muscle Biophysics and Tissue Remodeling in Hypertrophic Cardiomyopathies. CURRENT OPINION IN BIOMEDICAL ENGINEERING 2019; 11:35-44. [PMID: 31886450 DOI: 10.1016/j.cobme.2019.09.005] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Myocardial hypertrophy is the result of sustained perturbations to the mechanical and/or neurohormonal homeostasis of cardiac cells and is driven by integrated, multiscale biophysical and biochemical processes that are currently not well defined. In this brief review, we highlight recent computational and experimental models of cardiac hypertrophy that span mechanisms from the molecular level to the tissue level. Specifically, we focus on: (i) molecular-level models of the structural dynamics of sarcomere proteins in hypertrophic hearts, (ii) cellular-level models of excitation-contraction coupling and mechanosensitive signaling in disease-state myocytes, and (iii) organ-level models of myocardial growth kinematics and predictors thereof. Finally, we discuss how spanning these scales and combining multiple experimental/computational models will provide new information about the processes governing hypertrophy and potential methods to prevent or reverse them.
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Affiliation(s)
- Yasser Aboelkassem
- Department of Bioengineering, University of California San Diego, La Jolla, CA 92093, USA
| | - Joseph D Powers
- Department of Bioengineering, University of California San Diego, La Jolla, CA 92093, USA
| | - Kimberly J McCabe
- Department of Computational Physiology, Simula Research Laboratory, Lysaker, Norway
| | - Andrew D McCulloch
- Department of Bioengineering, University of California San Diego, La Jolla, CA 92093, USA
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5
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Aboelkassem Y, McCabe KJ, Huber GA, Regnier M, McCammon JA, McCulloch AD. A Stochastic Multiscale Model of Cardiac Thin Filament Activation Using Brownian-Langevin Dynamics. Biophys J 2019; 117:2255-2272. [PMID: 31547973 DOI: 10.1016/j.bpj.2019.08.003] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2019] [Revised: 07/31/2019] [Accepted: 08/02/2019] [Indexed: 11/16/2022] Open
Abstract
We use Brownian-Langevin dynamics principles to derive a coarse-graining multiscale myofilament model that can describe the thin-filament activation process during contraction. The model links atomistic molecular simulations of protein-protein interactions in the thin-filament regulatory unit to sarcomere-level activation dynamics. We first calculate the molecular interaction energy between tropomyosin and actin surface using Brownian dynamics simulations. This energy profile is then generalized to account for the observed tropomyosin transitions between its regulatory stable states. The generalized energy landscape then served as a basis for developing a filament-scale model using Langevin dynamics. This integrated analysis, spanning molecular to thin-filament scales, is capable of tracking the events of the tropomyosin conformational changes as it moves over the actin surface. The tropomyosin coil with flexible overlap regions between adjacent tropomyosins is represented in the model as a system of coupled stochastic ordinary differential equations. The proposed multiscale approach provides a more detailed molecular connection between tropomyosin dynamics, the trompomyosin-actin interaction-energy landscape, and the generated force by the sarcomere.
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Affiliation(s)
- Yasser Aboelkassem
- Department of Bioengineering, University of California San Diego, La Jolla, California.
| | - Kimberly J McCabe
- Department of Bioengineering, University of California San Diego, La Jolla, California
| | - Gary A Huber
- Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, California
| | - Michael Regnier
- Department of Bioengineering, University of Washington, Seattle, Washington
| | - J Andrew McCammon
- Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, California
| | - Andrew D McCulloch
- Department of Bioengineering, University of California San Diego, La Jolla, California
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6
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Thin filament dysfunctions caused by mutations in tropomyosin Tpm3.12 and Tpm1.1. J Muscle Res Cell Motil 2019; 41:39-53. [PMID: 31270709 PMCID: PMC7109180 DOI: 10.1007/s10974-019-09532-y] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2019] [Accepted: 06/26/2019] [Indexed: 12/14/2022]
Abstract
Tropomyosin is the major regulator of the thin filament. In striated muscle its function is to bind troponin complex and control the access of myosin heads to actin in a Ca2+-dependent manner. It also participates in the maintenance of thin filament length by regulation of tropomodulin and leiomodin, the pointed end-binding proteins. Because the size of the overlap between actin and myosin filaments affects the number of myosin heads which interact with actin, the filament length is one of the determinants of force development. Numerous point mutations in genes encoding tropomyosin lead to single amino acid substitutions along the entire length of the coiled coil that are associated with various types of cardiomyopathy and skeletal muscle disease. Specific regions of tropomyosin interact with different binding partners; therefore, the mutations affect diverse tropomyosin functions. In this review, results of studies on mutations in the genes TPM1 and TPM3, encoding Tpm1.1 and Tpm3.12, are described. The paper is particularly focused on mutation-dependent alterations in the mechanisms of actin-myosin interactions and dynamics of the thin filament at the pointed end.
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7
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Lehman W, Moore JR, Campbell SG, Rynkiewicz MJ. The Effect of Tropomyosin Mutations on Actin-Tropomyosin Binding: In Search of Lost Time. Biophys J 2019; 116:2275-2284. [PMID: 31130236 PMCID: PMC6588729 DOI: 10.1016/j.bpj.2019.05.009] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2019] [Revised: 05/06/2019] [Accepted: 05/09/2019] [Indexed: 12/14/2022] Open
Abstract
The initial binding of tropomyosin onto actin filaments and then its polymerization into continuous cables on the filament surface must be precisely tuned to overall thin-filament structure, function, and performance. Low-affinity interaction of tropomyosin with actin has to be sufficiently strong to localize the tropomyosin on actin, yet not so tight that regulatory movement on filaments is curtailed. Likewise, head-to-tail association of tropomyosin molecules must be favorable enough to promote tropomyosin cable formation but not so tenacious that polymerization precedes filament binding. Arguably, little molecular detail on early tropomyosin binding steps has been revealed since Wegner's seminal studies on filament assembly almost 40 years ago. Thus, interpretation of mutation-based actin-tropomyosin binding anomalies leading to cardiomyopathies cannot be described fully. In vitro, tropomyosin binding is masked by explosive tropomyosin polymerization once cable formation is initiated on actin filaments. In contrast, in silico analysis, characterizing molecular dynamics simulations of single wild-type and mutant tropomyosin molecules on F-actin, is not complicated by tropomyosin polymerization at all. In fact, molecular dynamics performed here demonstrates that a midpiece tropomyosin domain is essential for normal actin-tropomyosin interaction and that this interaction is strictly conserved in a number of tropomyosin mutant species. Elsewhere along these mutant molecules, twisting and bending corrupts the tropomyosin superhelices as they "lose their grip" on F-actin. We propose that residual interactions displayed by these mutant tropomyosin structures with actin mimic ones that occur in early stages of thin-filament generation, as if the mutants are recapitulating the assembly process but in reverse. We conclude therefore that an initial binding step in tropomyosin assembly onto actin involves interaction of the essential centrally located domain.
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Affiliation(s)
- William Lehman
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, Massachusetts.
| | - Jeffrey R Moore
- Department of Biological Sciences, University of Massachusetts-Lowell, Lowell, Massachusetts
| | - Stuart G Campbell
- Departments of Biomedical Engineering and Cellular and Molecular Physiology, Yale University, New Haven, Connecticut
| | - Michael J Rynkiewicz
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, Massachusetts
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8
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Zheng W, Wen H. Molecular dynamics simulation of tropomyosin bound to actins/myosin in the closed and open states. Proteins 2019; 87:805-814. [PMID: 31090107 DOI: 10.1002/prot.25707] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2018] [Revised: 04/22/2019] [Accepted: 05/05/2019] [Indexed: 11/09/2022]
Abstract
Tropomyosin (Tpm) is a dimeric coiled-coil protein that binds to filamentous actin, and regulates actin-myosin interaction by moving between three positions corresponding to the blocked, closed, and open states. To elucidate how Tpm undergoes transitions between these functional states, we have built structural models and conducted extensive molecular dynamics simulations of the Tpm-actins/myosin complex in the closed and open states (total simulation time >1.4 μs). Based on the simulation trajectories, we have analyzed the dynamics and energetics of a truncated Tpm interacting with actins/myosin under the physiological conditions. Our simulations have shown distinct dynamics of four Tpm periods (P3-P6), featuring pronounced biased fluctuations of P4 and P5 toward the open position in the closed state, which is consistent with a conformational selection mechanism for Tpm-regulated myosin binding. Additionally, we have identified key residues of Tpm specifically binding to actins/myosin in the closed and open state. Some of them were validated as functionally important in comparison with past functional/clinical studies, and the rest will make promising targets for future mutational experiments.
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Affiliation(s)
- Wenjun Zheng
- Department of Physics, University at Buffalo, Buffalo, New York
| | - Han Wen
- Department of Physics, University at Buffalo, Buffalo, New York
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9
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Szatkowski L, Lynn ML, Holeman T, Williams MR, Baldo AP, Tardiff JC, Schwartz SD. Proof of Principle that Molecular Modeling Followed by a Biophysical Experiment Can Develop Small Molecules that Restore Function to the Cardiac Thin Filament in the Presence of Cardiomyopathic Mutations. ACS OMEGA 2019; 4:6492-6501. [PMID: 31342001 PMCID: PMC6649307 DOI: 10.1021/acsomega.8b03340] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/29/2018] [Accepted: 03/28/2019] [Indexed: 06/10/2023]
Abstract
This article reports a coupled computational experimental approach to design small molecules aimed at targeting genetic cardiomyopathies. We begin with a fully atomistic model of the cardiac thin filament. To this we dock molecules using accepted computational drug binding methodologies. The candidates are screened for their ability to repair alterations in biophysical properties caused by mutation. Hypertrophic and dilated cardiomyopathies caused by mutation are initially biophysical in nature, and the approach we take is to correct the biophysical insult prior to irreversible cardiac damage. Candidate molecules are then tested experimentally for both binding and biophysical properties. This is a proof of concept study-eventually candidate molecules will be tested in transgenic animal models of genetic (sarcomeric) cardiomyopathies.
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Affiliation(s)
- Lukasz Szatkowski
- Department
of Chemistry and Biochemistry, University
of Arizona, Tucson, Arizona 85721, United States
| | - Melissa L. Lynn
- Department of Physiological
Sciences and Department of Medicine, University of Arizona, Tucson, Arizona 85724, United States
| | - Teryn Holeman
- Department of Physiological
Sciences and Department of Medicine, University of Arizona, Tucson, Arizona 85724, United States
| | - Michael R. Williams
- Department
of Chemistry and Biochemistry, University
of Arizona, Tucson, Arizona 85721, United States
| | - Anthony P. Baldo
- Department
of Chemistry and Biochemistry, University
of Arizona, Tucson, Arizona 85721, United States
| | - Jil C. Tardiff
- Department of Physiological
Sciences and Department of Medicine, University of Arizona, Tucson, Arizona 85724, United States
| | - Steven D. Schwartz
- Department
of Chemistry and Biochemistry, University
of Arizona, Tucson, Arizona 85721, United States
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10
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Farman GP, Rynkiewicz MJ, Orzechowski M, Lehman W, Moore JR. HCM and DCM cardiomyopathy-linked α-tropomyosin mutations influence off-state stability and crossbridge interaction on thin filaments. Arch Biochem Biophys 2018; 647:84-92. [PMID: 29626422 DOI: 10.1016/j.abb.2018.04.002] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2017] [Revised: 04/02/2018] [Accepted: 04/03/2018] [Indexed: 12/19/2022]
Abstract
Calcium regulation of cardiac muscle contraction is controlled by the thin-filament proteins troponin and tropomyosin bound to actin. In the absence of calcium, troponin-tropomyosin inhibits myosin-interactions on actin and induces muscle relaxation, whereas the addition of calcium relieves the inhibitory constraint to initiate contraction. Many mutations in thin filament proteins linked to cardiomyopathy appear to disrupt this regulatory switching. Here, we tested perturbations caused by mutant tropomyosins (E40K, DCM; and E62Q, HCM) on intra-filament interactions affecting acto-myosin interactions including those induced further by myosin association. Comparison of wild-type and mutant human α-tropomyosin (Tpm1.1) behavior was carried out using in vitro motility assays and molecular dynamics simulations. Our results show that E62Q tropomyosin destabilizes thin filament off-state function by increasing calcium-sensitivity, but without apparent affect on global tropomyosin structure by modifying coiled-coil rigidity. In contrast, the E40K mutant tropomyosin appears to stabilize the off-state, demonstrates increased tropomyosin flexibility, while also decreasing calcium-sensitivity. In addition, the E40K mutation reduces thin filament velocity at low myosin concentration while the E62Q mutant tropomyosin increases velocity. Corresponding molecular dynamics simulations indicate specific residue interactions that are likely to redefine underlying molecular regulatory mechanisms, which we propose explain the altered contractility evoked by the disease-causing mutations.
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Affiliation(s)
- Gerrie P Farman
- Department of Biological Sciences, University of Massachusetts-Lowell, One University Avenue, Lowell, MA 01854, USA; Department of Physiology & Biophysics, Boston University School of Medicine, 700 Albany Street, Boston, MA 02118, USA.
| | - Michael J Rynkiewicz
- Department of Physiology & Biophysics, Boston University School of Medicine, 700 Albany Street, Boston, MA 02118, USA.
| | - Marek Orzechowski
- Department of Physiology & Biophysics, Boston University School of Medicine, 700 Albany Street, Boston, MA 02118, USA.
| | - William Lehman
- Department of Physiology & Biophysics, Boston University School of Medicine, 700 Albany Street, Boston, MA 02118, USA.
| | - Jeffrey R Moore
- Department of Biological Sciences, University of Massachusetts-Lowell, One University Avenue, Lowell, MA 01854, USA.
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11
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Ozawa H, Umezawa K, Takano M, Ishizaki S, Watabe S, Ochiai Y. Structural and dynamical characteristics of tropomyosin epitopes as the major allergens in shrimp. Biochem Biophys Res Commun 2018; 498:119-124. [DOI: 10.1016/j.bbrc.2018.02.172] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2018] [Accepted: 02/22/2018] [Indexed: 12/16/2022]
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12
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McConnell M, Tal Grinspan L, Williams MR, Lynn ML, Schwartz BA, Fass OZ, Schwartz SD, Tardiff JC. Clinically Divergent Mutation Effects on the Structure and Function of the Human Cardiac Tropomyosin Overlap. Biochemistry 2017; 56:3403-3413. [PMID: 28603979 DOI: 10.1021/acs.biochem.7b00266] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
The progression of genetically inherited cardiomyopathies from an altered protein structure to clinical presentation of disease is not well understood. One of the main roadblocks to mechanistic insight remains a lack of high-resolution structural information about multiprotein complexes within the cardiac sarcomere. One example is the tropomyosin (Tm) overlap region of the thin filament that is crucial for the function of the cardiac sarcomere. To address this central question, we devised coupled experimental and computational modalities to characterize the baseline function and structure of the Tm overlap, as well as the effects of mutations causing divergent patterns of ventricular remodeling on both structure and function. Because the Tm overlap contributes to the cooperativity of myofilament activation, we hypothesized that mutations that enhance the interactions between overlap proteins result in more cooperativity, and conversely, those that weaken interaction between these elements lower cooperativity. Our results suggest that the Tm overlap region is affected differentially by dilated cardiomyopathy-associated Tm D230N and hypertrophic cardiomyopathy-associated human cardiac troponin T (cTnT) R92L. The Tm D230N mutation compacts the Tm overlap region, increasing the cooperativity of the Tm filament, contributing to a dilated cardiomyopathy phenotype. The cTnT R92L mutation causes weakened interactions closer to the N-terminal end of the overlap, resulting in decreased cooperativity. These studies demonstrate that mutations with differential phenotypes exert opposite effects on the Tm-Tn overlap, and that these effects can be directly correlated to a molecular level understanding of the structure and dynamics of the component proteins.
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Affiliation(s)
- Mark McConnell
- Department of Biomedical Engineering, University of Arizona , Tucson, Arizona 85721, United States
| | - Lauren Tal Grinspan
- Department of Medicine, Columbia University Medical Center , New York, New York 10032, United States
| | - Michael R Williams
- Department of Chemistry and Biochemistry, University of Arizona , Tucson, Arizona 85721, United States
| | - Melissa L Lynn
- Department of Physiological Sciences, University of Arizona , Tucson, Arizona 85724, United States
| | - Benjamin A Schwartz
- Graduate Interdisciplinary Program in Neuroscience, University of Arizona , Tucson, Arizona 85721, United States
| | - Ofer Z Fass
- Department of Physiological Sciences, University of Arizona , Tucson, Arizona 85724, 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.,Department of Physiological Sciences, University of Arizona , Tucson, Arizona 85724, United States.,Department of Medicine, University of Arizona , Tucson, Arizona 85724, United States
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13
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Dewan S, McCabe KJ, Regnier M, McCulloch AD. Insights and Challenges of Multi-Scale Modeling of Sarcomere Mechanics in cTn and Tm DCM Mutants-Genotype to Cellular Phenotype. Front Physiol 2017; 8:151. [PMID: 28352236 PMCID: PMC5348544 DOI: 10.3389/fphys.2017.00151] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2016] [Accepted: 02/24/2017] [Indexed: 01/18/2023] Open
Abstract
Dilated Cardiomyopathy (DCM) is a leading cause of sudden cardiac death characterized by impaired pump function and dilatation of cardiac ventricles. In this review we discuss various in silico approaches to elucidating the mechanisms of genetic mutations leading to DCM. The approaches covered in this review focus on bridging the spatial and temporal gaps that exist between molecular and cellular processes. Mutations in sarcomeric regulatory thin filament proteins such as the troponin complex (cTn) and Tropomyosin (Tm) have been associated with DCM. Despite the experimentally-observed myofilament measures of contractility in the case of these mutations, the mechanisms by which the underlying molecular changes and protein interactions scale up to organ failure by these mutations remains elusive. The review highlights multi-scale modeling approaches and their applicability to study the effects of sarcomeric gene mutations in-silico. We discuss some of the insights that can be gained from computational models of cardiac biomechanics when scaling from molecular states to cellular level.
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Affiliation(s)
- Sukriti Dewan
- Departments of Bioengineering and Medicine, University of California San Diego, La Jolla, CA, USA
| | - Kimberly J McCabe
- Departments of Bioengineering and Medicine, University of California San Diego, La Jolla, CA, USA
| | - Michael Regnier
- Departments of Bioengineering and Medicine, University of Washington Seattle, WA, USA
| | - Andrew D McCulloch
- Departments of Bioengineering and Medicine, University of California San Diego, La Jolla, CA, USA
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14
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Borovikov YS, Rysev NA, Avrova SV, Karpicheva OE, Borys D, Moraczewska J. Molecular mechanisms of deregulation of the thin filament associated with the R167H and K168E substitutions in tropomyosin Tpm1.1. Arch Biochem Biophys 2016; 614:28-40. [PMID: 27956029 DOI: 10.1016/j.abb.2016.12.004] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2016] [Revised: 12/06/2016] [Accepted: 12/08/2016] [Indexed: 12/01/2022]
Abstract
Point mutations R167H and K168E in tropomyosin Tpm1.1 (TM) disturb Ca2+-dependent regulation of the actomyosin ATPase. To understand mechanisms of this defect we studied multistep changes in mobility and spatial arrangement of tropomyosin, actin and myosin heads during the ATPase cycle in reconstituted ghost fibres using the polarized fluorescence microscopy. It was found that both mutations disturbed the mode of troponin operation in the fibres. At high Ca2+, troponin increased the fraction of actin monomers that were in the "switched on" state, but both mutant tropomyosins were shifted toward the outer actin domains, which decreased the fraction of strongly bound myosin heads throughout the ATPase cycle. At low Ca2+, the R167H-TM was located close to the outer actin domains, which reduced the number of strongly-bound myosin heads. However, under these conditions troponin increased the number of actin monomers that were switched on. The K168E-TM was displaced far to the outer actin domains and troponin binding decreased the fraction of switched on actin monomers, but the proportion of the strongly bound myosin heads was abnormally high. Thus, the mutations differently disturbed transmission of conformational changes between troponin, tropomyosin and actin, which is essential for the Са2+-dependent regulation of the thin filament.
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Affiliation(s)
- Yurii S Borovikov
- Institute of Cytology, Tikhoretsky Pr., 4, Saint Petersburg, 194064, Russia.
| | - Nikita A Rysev
- Institute of Cytology, Tikhoretsky Pr., 4, Saint Petersburg, 194064, Russia
| | | | - Olga E Karpicheva
- Institute of Cytology, Tikhoretsky Pr., 4, Saint Petersburg, 194064, Russia
| | - Danuta Borys
- Kazimierz Wielki University in Bydgoszcz, Ks. J. Poniatowski 12, Str., 85-671 Bydgoszcz, Poland
| | - Joanna Moraczewska
- Kazimierz Wielki University in Bydgoszcz, Ks. J. Poniatowski 12, Str., 85-671 Bydgoszcz, Poland
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15
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Sewanan LR, Moore JR, Lehman W, Campbell SG. Predicting Effects of Tropomyosin Mutations on Cardiac Muscle Contraction through Myofilament Modeling. Front Physiol 2016; 7:473. [PMID: 27833562 PMCID: PMC5081029 DOI: 10.3389/fphys.2016.00473] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2016] [Accepted: 10/03/2016] [Indexed: 12/23/2022] Open
Abstract
Point mutations to the human gene TPM1 have been implicated in the development of both hypertrophic and dilated cardiomyopathies. Such observations have led to studies investigating the link between single residue changes and the biophysical behavior of the tropomyosin molecule. However, the degree to which these molecular perturbations explain the performance of intact sarcomeres containing mutant tropomyosin remains uncertain. Here, we present a modeling approach that integrates various aspects of tropomyosin's molecular properties into a cohesive paradigm representing their impact on muscle function. In particular, we considered the effects of tropomyosin mutations on (1) persistence length, (2) equilibrium between thin filament blocked and closed regulatory states, and (3) the crossbridge duty cycle. After demonstrating the ability of the new model to capture Ca-dependent myofilament responses during both dynamic and steady-state activation, we used it to capture the effects of hypertrophic cardiomyopathy (HCM) related E180G and D175N mutations on skinned myofiber mechanics. Our analysis indicates that the fiber-level effects of the two mutations can be accurately described by a combination of changes to the three tropomyosin properties represented in the model. Subsequently, we used the model to predict mutation effects on muscle twitch. Both mutations led to increased twitch contractility as a consequence of diminished cooperative inhibition between thin filament regulatory units. Overall, simulations suggest that a common twitch phenotype for HCM-linked tropomyosin mutations includes both increased contractility and elevated diastolic tension.
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Affiliation(s)
- Lorenzo R Sewanan
- Department of Biomedical Engineering, Yale UniversityNew Haven, CT, USA; Yale School of Medicine, Yale UniversityNew Haven, CT, USA
| | - Jeffrey R Moore
- Department of Biological Sciences, University of Massachusetts Lowell Lowell, MA, USA
| | - William Lehman
- Department of Physiology and Biophysics, Boston University School of Medicine Boston, MA, USA
| | - Stuart G Campbell
- Department of Biomedical Engineering, Yale UniversityNew Haven, CT, USA; Department of Cellular and Molecular Physiology, Yale School of MedicineNew Haven, CT, USA
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16
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Zheng W, Hitchcock-DeGregori SE, Barua B. Investigating the effects of tropomyosin mutations on its flexibility and interactions with filamentous actin using molecular dynamics simulation. J Muscle Res Cell Motil 2016; 37:131-147. [DOI: 10.1007/s10974-016-9447-3] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2016] [Accepted: 06/24/2016] [Indexed: 12/15/2022]
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17
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Nabiev SR, Ovsyannikov DA, Kopylova GV, Shchepkin DV, Matyushenko AM, Koubassova NA, Levitsky DI, Tsaturyan AK, Bershitsky SY. Stabilizing the central part of tropomyosin increases the bending stiffness of the thin filament. Biophys J 2016. [PMID: 26200873 DOI: 10.1016/j.bpj.2015.06.006] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022] Open
Abstract
A two-beam optical trap was used to measure the bending stiffness of F-actin and reconstructed thin filaments. A dumbbell was formed by a filament segment attached to two beads that were held in the two optical traps. One trap was static and held a bead used as a force transducer, whereas an acoustooptical deflector moved the beam holding the second bead, causing stretch of the dumbbell. The distance between the beads was measured using image analysis of micrographs. An exact solution to the problem of bending of an elastic filament attached to two beads and subjected to a stretch was used for data analysis. Substitution of noncanonical residues in the central part of tropomyosin with canonical ones, G126R and D137L, and especially their combination, caused an increase in the bending stiffness of the thin filaments. The data confirm that the effect of these mutations on the regulation of actin-myosin interactions may be caused by an increase in tropomyosin stiffness.
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Affiliation(s)
- Salavat R Nabiev
- Institute of Immunology and Physiology, Russian Academy of Sciences, Yekaterinburg, Russia
| | - Denis A Ovsyannikov
- Institute of Immunology and Physiology, Russian Academy of Sciences, Yekaterinburg, Russia
| | - Galina V Kopylova
- Institute of Immunology and Physiology, Russian Academy of Sciences, Yekaterinburg, Russia
| | - Daniil V Shchepkin
- Institute of Immunology and Physiology, Russian Academy of Sciences, Yekaterinburg, Russia
| | - Alexander M Matyushenko
- A.N. Bach Institute of Biochemistry, Russian Academy of Sciences, Moscow, Russia; Department of Biochemistry, School of Biology, Moscow State University, Moscow, Russia
| | | | - Dmitrii I Levitsky
- A.N. Bach Institute of Biochemistry, Russian Academy of Sciences, Moscow, Russia; A.N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow, Russia
| | | | - Sergey Y Bershitsky
- Institute of Immunology and Physiology, Russian Academy of Sciences, Yekaterinburg, Russia.
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18
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Abstract
By interacting with the troponin-tropomyosin complex on myofibrillar thin filaments, Ca2+ and myosin govern the regulatory switching processes influencing contractile activity of mammalian cardiac and skeletal muscles. A possible explanation of the roles played by Ca2+ and myosin emerged in the early 1970s when a compelling "steric model" began to gain traction as a likely mechanism accounting for muscle regulation. In its most simple form, the model holds that, under the control of Ca2+ binding to troponin and myosin binding to actin, tropomyosin strands running along thin filaments either block myosin-binding sites on actin when muscles are relaxed or move away from them when muscles are activated. Evidence for the steric model was initially based on interpretation of subtle changes observed in X-ray fiber diffraction patterns of intact skeletal muscle preparations. Over the past 25 years, electron microscopy coupled with three-dimensional reconstruction directly resolved thin filament organization under many experimental conditions and at increasingly higher resolution. At low-Ca2+, tropomyosin was shown to occupy a "blocked-state" position on the filament, and switched-on in a two-step process, involving first a movement of tropomyosin away from the majority of the myosin-binding site as Ca2+ binds to troponin and then a further movement to fully expose the site when small numbers of myosin heads bind to actin. In this contribution, basic information on Ca2+-regulation of muscle contraction is provided. A description is then given relating the voyage of discovery taken to arrive at the present understanding of the steric regulatory model.
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Affiliation(s)
- William Lehman
- Department of Physiology & Biophysics, Boston University School of Medicine, Boston, Massachusetts, U.S.A
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19
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Eeftens JM, Katan AJ, Kschonsak M, Hassler M, de Wilde L, Dief EM, Haering CH, Dekker C. Condensin Smc2-Smc4 Dimers Are Flexible and Dynamic. Cell Rep 2016; 14:1813-8. [PMID: 26904946 PMCID: PMC4785793 DOI: 10.1016/j.celrep.2016.01.063] [Citation(s) in RCA: 73] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2015] [Revised: 12/21/2015] [Accepted: 01/20/2016] [Indexed: 12/20/2022] Open
Abstract
Structural maintenance of chromosomes (SMC) protein complexes, including cohesin and condensin, play key roles in the regulation of higher-order chromosome organization. Even though SMC proteins are thought to mechanistically determine the function of the complexes, their native conformations and dynamics have remained unclear. Here, we probe the topology of Smc2-Smc4 dimers of the S. cerevisiae condensin complex with high-speed atomic force microscopy (AFM) in liquid. We show that the Smc2-Smc4 coiled coils are highly flexible polymers with a persistence length of only ∼ 4 nm. Moreover, we demonstrate that the SMC dimers can adopt various architectures that interconvert dynamically over time, and we find that the SMC head domains engage not only with each other, but also with the hinge domain situated at the other end of the ∼ 45-nm-long coiled coil. Our findings reveal structural properties that provide insights into the molecular mechanics of condensin complexes.
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Affiliation(s)
- Jorine M Eeftens
- Department of Bionanoscience, Kavli Institute of Nanoscience Delft, Delft University of Technology, Delft 2628 CJ, the Netherlands
| | - Allard J Katan
- Department of Bionanoscience, Kavli Institute of Nanoscience Delft, Delft University of Technology, Delft 2628 CJ, the Netherlands
| | - Marc Kschonsak
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory (EMBL), 69117 Heidelberg, Germany
| | - Markus Hassler
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory (EMBL), 69117 Heidelberg, Germany
| | - Liza de Wilde
- Department of Bionanoscience, Kavli Institute of Nanoscience Delft, Delft University of Technology, Delft 2628 CJ, the Netherlands
| | - Essam M Dief
- Department of Bionanoscience, Kavli Institute of Nanoscience Delft, Delft University of Technology, Delft 2628 CJ, the Netherlands
| | - Christian H Haering
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory (EMBL), 69117 Heidelberg, Germany.
| | - Cees Dekker
- Department of Bionanoscience, Kavli Institute of Nanoscience Delft, Delft University of Technology, Delft 2628 CJ, the Netherlands.
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20
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Duncker DJ, Bakkers J, Brundel BJ, Robbins J, Tardiff JC, Carrier L. Animal and in silico models for the study of sarcomeric cardiomyopathies. Cardiovasc Res 2015; 105:439-48. [PMID: 25600962 DOI: 10.1093/cvr/cvv006] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Over the past decade, our understanding of cardiomyopathies has improved dramatically, due to improvements in screening and detection of gene defects in the human genome as well as a variety of novel animal models (mouse, zebrafish, and drosophila) and in silico computational models. These novel experimental tools have created a platform that is highly complementary to the naturally occurring cardiomyopathies in cats and dogs that had been available for some time. A fully integrative approach, which incorporates all these modalities, is likely required for significant steps forward in understanding the molecular underpinnings and pathogenesis of cardiomyopathies. Finally, novel technologies, including CRISPR/Cas9, which have already been proved to work in zebrafish, are currently being employed to engineer sarcomeric cardiomyopathy in larger animals, including pigs and non-human primates. In the mouse, the increased speed with which these techniques can be employed to engineer precise 'knock-in' models that previously took years to make via multiple rounds of homologous recombination-based gene targeting promises multiple and precise models of human cardiac disease for future study. Such novel genetically engineered animal models recapitulating human sarcomeric protein defects will help bridging the gap to translate therapeutic targets from small animal and in silico models to the human patient with sarcomeric cardiomyopathy.
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Affiliation(s)
- Dirk J Duncker
- Division of Experimental Cardiology, Department of Cardiology, Thoraxcenter, Erasmus University Medical Center, Rotterdam, The Netherlands
| | - Jeroen Bakkers
- Hubrecht Institute-KNAW and University Medical Center Utrecht, Utrecht, The Netherlands
| | - Bianca J Brundel
- Department of Clinical Pharmacy and Pharmacology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands
| | - Jeff Robbins
- Division of Molecular Cardiovascular Biology, Cincinnati Children's Hospital, Cincinnati, OH, USA
| | - Jil C Tardiff
- Department of Medicine and Department of Cellular and Molecular Medicine, University of Arizona, Tucson, AZ, USA
| | - Lucie Carrier
- Department of Experimental Pharmacology and Toxicology, Cardiovascular Research Center, University Medical Center Hamburg-Eppendorf, Hamburg, Germany DZHK (German Centre for Cardiovascular Research), partner site Hamburg/Kiel/Lübeck, Hamburg, Germany
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21
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Robaszkiewicz K, Ostrowska Z, Cyranka-Czaja A, Moraczewska J. Impaired tropomyosin-troponin interactions reduce activation of the actin thin filament. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2015; 1854:381-90. [PMID: 25603119 DOI: 10.1016/j.bbapap.2015.01.004] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/15/2014] [Revised: 01/09/2015] [Accepted: 01/13/2015] [Indexed: 01/23/2023]
Abstract
Tropomyosin and troponin are bound to the actin filament to control the contraction of striated muscle in the Ca-dependent manner. The interactions between both regulatory proteins important for the regulation process are not fully understood. To gain more insight into the mechanisms of the thin filament regulation by skeletal α-tropomyosin and troponin, we analyzed effects of seven myopathy-related substitutions: Leu99Met, Ala155Thr, Arg167Gly, Arg167Cys, Arg167His, Lys168Glu, and Arg244Gly. All substitutions reduced Ca-dependent activation of the actomyosin ATPase. The effects of mutations in Arg167 and Lys168 were the most severe. The amino acid substitutions did not significantly affect troponin binding to the whole filament, but reduced 1.2-2.8 fold the affinity of troponin to tropomyosin alone. The excimer fluorescence of N-(1-pyrene)iodoacetamide, a probe attached to the central Cys190, demonstrated that substitutions located near the troponin core domain-binding region strongly affected conformational changes accompanying the tropomyosin-troponin interactions. The thermal stability of all tropomyosin mutants was lower than the stability of the wild type tropomyosin, with TM reduced by 5.3-8.5°C. Together the analyses demonstrated that the myopathy-causing mutations affected tropomyosin structure and led to changes in interactions between tropomyosin and troponin, which impaired the transition of the thin filament from the inactive off to the active on state.
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Affiliation(s)
- Katarzyna Robaszkiewicz
- Department of Biochemistry and Cell Biology, Faculty of Natural Sciences, Kazimierz Wielki University in Bydgoszcz, Chodkiewicz 30, Str., 85-064 Bydgoszcz, Poland
| | - Zofia Ostrowska
- Department of Biochemistry and Cell Biology, Faculty of Natural Sciences, Kazimierz Wielki University in Bydgoszcz, Chodkiewicz 30, Str., 85-064 Bydgoszcz, Poland
| | | | - Joanna Moraczewska
- Department of Biochemistry and Cell Biology, Faculty of Natural Sciences, Kazimierz Wielki University in Bydgoszcz, Chodkiewicz 30, Str., 85-064 Bydgoszcz, Poland.
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22
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Gupte TM, Haque F, Gangadharan B, Sunitha MS, Mukherjee S, Anandhan S, Rani DS, Mukundan N, Jambekar A, Thangaraj K, Sowdhamini R, Sommese RF, Nag S, Spudich JA, Mercer JA. Mechanistic heterogeneity in contractile properties of α-tropomyosin (TPM1) mutants associated with inherited cardiomyopathies. J Biol Chem 2014; 290:7003-15. [PMID: 25548289 DOI: 10.1074/jbc.m114.596676] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The most frequent known causes of primary cardiomyopathies are mutations in the genes encoding sarcomeric proteins. Among those are 30 single-residue mutations in TPM1, the gene encoding α-tropomyosin. We examined seven mutant tropomyosins, E62Q, D84N, I172T, L185R, S215L, D230N, and M281T, that were chosen based on their clinical severity and locations along the molecule. The goal of our study was to determine how the biochemical characteristics of each of these mutant proteins are altered, which in turn could provide a structural rationale for treatment of the cardiomyopathies they produce. Measurements of Ca(2+) sensitivity of human β-cardiac myosin ATPase activity are consistent with the hypothesis that hypertrophic cardiomyopathies are hypersensitive to Ca(2+) activation, and dilated cardiomyopathies are hyposensitive. We also report correlations between ATPase activity at maximum Ca(2+) concentrations and conformational changes in TnC measured using a fluorescent probe, which provide evidence that different substitutions perturb the structure of the regulatory complex in different ways. Moreover, we observed changes in protein stability and protein-protein interactions in these mutants. Our results suggest multiple mechanistic pathways to hypertrophic and dilated cardiomyopathies. Finally, we examined a computationally designed mutant, E181K, that is hypersensitive, confirming predictions derived from in silico structural analysis.
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Affiliation(s)
- Tejas M Gupte
- From the Institute for Stem Cell Biology and Regenerative Medicine, Bangalore 560065, India
| | - Farah Haque
- From the Institute for Stem Cell Biology and Regenerative Medicine, Bangalore 560065, India, the National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore 560065, India
| | - Binnu Gangadharan
- From the Institute for Stem Cell Biology and Regenerative Medicine, Bangalore 560065, India, the Manipal University, Madhav Nagar, Manipal 576104, India
| | - Margaret S Sunitha
- From the Institute for Stem Cell Biology and Regenerative Medicine, Bangalore 560065, India, the National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore 560065, India
| | - Souhrid Mukherjee
- From the Institute for Stem Cell Biology and Regenerative Medicine, Bangalore 560065, India
| | - Swetha Anandhan
- From the Institute for Stem Cell Biology and Regenerative Medicine, Bangalore 560065, India
| | - Deepa Selvi Rani
- the Council for Scientific and Industrial Research-Centre for Cellular and Molecular Biology, Hyderabad 500007, India
| | - Namita Mukundan
- the National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore 560065, India
| | - Amruta Jambekar
- From the Institute for Stem Cell Biology and Regenerative Medicine, Bangalore 560065, India
| | - Kumarasamy Thangaraj
- the Council for Scientific and Industrial Research-Centre for Cellular and Molecular Biology, Hyderabad 500007, India
| | - Ramanathan Sowdhamini
- the National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore 560065, India
| | - Ruth F Sommese
- the Department of Biochemistry, Stanford University School of Medicine, Stanford, California 94305, and
| | - Suman Nag
- the Department of Biochemistry, Stanford University School of Medicine, Stanford, California 94305, and
| | - James A Spudich
- From the Institute for Stem Cell Biology and Regenerative Medicine, Bangalore 560065, India, the Department of Biochemistry, Stanford University School of Medicine, Stanford, California 94305, and
| | - John A Mercer
- From the Institute for Stem Cell Biology and Regenerative Medicine, Bangalore 560065, India, the McLaughlin Research Institute, Great Falls, Montana 59405
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23
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Chang AN, Greenfield NJ, Singh A, Potter JD, Pinto JR. Structural and protein interaction effects of hypertrophic and dilated cardiomyopathic mutations in alpha-tropomyosin. Front Physiol 2014; 5:460. [PMID: 25520664 PMCID: PMC4251307 DOI: 10.3389/fphys.2014.00460] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2014] [Accepted: 11/10/2014] [Indexed: 12/16/2022] Open
Abstract
The potential alterations to structure and associations with thin filament proteins caused by the dilated cardiomyopathy (DCM) associated tropomyosin (Tm) mutants E40K and E54K, and the hypertrophic cardiomyopathy (HCM) associated Tm mutants E62Q and L185R, were investigated. In order to ascertain what the cause of the known functional effects may be, structural and protein-protein interaction studies were conducted utilizing actomyosin ATPase activity measurements and spectroscopy. In actomyosin ATPase measurements, both HCM mutants and the DCM mutant E54K caused increases in Ca2+-induced maximal ATPase activities, while E40K caused a decrease. Investigation of Tm's ability to inhibit actomyosin ATPase in the absence of troponin showed that HCM-associated mutant Tms did not inhibit as well as wildtype, whereas the DCM associated mutant E40K inhibited better. E54K did not inhibit the actomyosin ATPase activity at any concentration of Tm tested. Thermal denaturation studies by circular dichroism and molecular modeling of the mutations in Tm showed that in general, the DCM mutants caused localized destabilization of the Tm dimers, while the HCM mutants resulted in increased stability. These findings demonstrate that the structural alterations in Tm observed here may affect the regulatory function of Tm on actin, thereby directly altering the ATPase rates of myosin.
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Affiliation(s)
- Audrey N Chang
- Department of Molecular and Cellular Pharmacology, Leonard Miller School of Medicine, University of Miami Miami, FL, USA
| | - Norma J Greenfield
- Department of Neuroscience and Cell Biology, Robert Wood Johnson Medical School, Rutgers University New Jersey, NJ, USA
| | - Abhishek Singh
- Department of Neuroscience and Cell Biology, Robert Wood Johnson Medical School, Rutgers University New Jersey, NJ, USA ; Department of Cardiology, UCSF Medical Center, University of California, San Francisco San Francisco, CA, USA
| | - James D Potter
- Department of Molecular and Cellular Pharmacology, Leonard Miller School of Medicine, University of Miami Miami, FL, USA
| | - Jose R Pinto
- Department of Biomedical Sciences, Florida State University College of Medicine Tallahassee, FL, USA
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24
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Parvatiyar MS, Pinto JR. Pathogenesis associated with a restrictive cardiomyopathy mutant in cardiac troponin T is due to reduced protein stability and greatly increased myofilament Ca2+ sensitivity. Biochim Biophys Acta Gen Subj 2014; 1850:365-72. [PMID: 25450489 DOI: 10.1016/j.bbagen.2014.09.029] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2014] [Revised: 09/12/2014] [Accepted: 09/15/2014] [Indexed: 01/21/2023]
Abstract
BACKGROUND Dilated and hypertrophic cardiomyopathy mutations in troponin can blunt effects of protein kinase A (PKA) phosphorylation of cardiac troponin I (cTnI), decreasing myofilament Ca2+-sensitivity; however this effect has never been tested for restrictive cardiomyopathy (RCM) mutants. This study explores whether an RCM cardiac troponin T mutant (cTnT-ΔE96) interferes with convergent PKA regulation and if TnT instability contributes to greatly enhanced Ca2+-sensitivity in skinned fibers. METHODS Force of contraction in skinned cardiac porcine fiber and spectroscopic studies were performed. RESULTS A decrease of -0.26 and -0.25 pCa units in Ca2+-sensitivity of contraction after PKA incubation was observed for skinned fibers incorporated with WT or cTnT-ΔE96, respectively. To further assess whether cTnT-ΔE96 interferes solely with transmission of cTnI phosphorylation effects, skinned fibers were reconstituted with PKA pseudo-phosphorylated cTnI (cTnI-SS/DD.cTnC). Fibers displaced with cTnT-WT, reconstituted with cTnI-SS/DD.cTnC decreased Ca2+-sensitivity of force (pCa50=5.61) compared to control cTnI-WT.cTnC (pCa50=5.75), similarly affecting cTnT-ΔE96 (pCa50=6.03) compared to control \cTnI-WT.cTnC (pCa50=6.14). Fluorescence studies measuring cTnC(IAANS) Ca2+-affinity changes due to cTnT-ΔE96 indicated that higher complexity (thin filament) better recapitulates skinned fiber Ca2+ sensitive changes. Circular dichroism revealed reduced α-helicity and earlier thermal unfolding for cTnT-ΔE96 compared to WT. CONCLUSIONS Although ineffective in decreasing myofilament Ca2+-sensitivity to normal levels, cTnT-ΔE96 does not interfere with PKA cTnI phosphorylation mediated effects; 2) cTnT-ΔE96 requires actin to increase cTnC Ca2+-affinity; and 3) deletion of E96 reduces cTnT stability, likely disrupting crucial thin filament interactions. GENERAL SIGNIFICANCE The pathological effect of cTnT-ΔE96 is largely manifested by dramatic myofilament Ca2+-sensitization which still persists even after PKA phosphorylation mediated Ca2+-desensitization.
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Affiliation(s)
- Michelle S Parvatiyar
- Department of Molecular and Cellular Pharmacology, University of Miami Miller School of Medicine, Miami, FL 33136, USA
| | - Jose Renato Pinto
- Department of Biomedical Sciences, Florida State University, Tallahassee, FL 32306, USA.
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25
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Energy landscapes reveal the myopathic effects of tropomyosin mutations. Arch Biochem Biophys 2014; 564:89-99. [PMID: 25241052 DOI: 10.1016/j.abb.2014.09.007] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2014] [Revised: 09/03/2014] [Accepted: 09/09/2014] [Indexed: 11/24/2022]
Abstract
Striated muscle contraction is regulated by an interaction network connecting the effects of troponin, Ca(2+), and myosin-heads to the azimuthal positioning of tropomyosin along thin filaments. Many missense mutations, located at the actin-tropomyosin interface, however, reset the regulatory switching mechanism either by weakening or strengthening residue-specific interactions, leading to hyper- or hypo-contractile pathologies. Here, we compute energy landscapes for the actin-tropomyosin interface and quantify contributions of single amino acid residues to actin-tropomyosin binding. The method is a useful tool to assess effects of actin and tropomyosin mutations, potentially relating initial stages of myopathy to alterations in thin filament stability and regulation. Landscapes for mutant filaments linked to hyper-contractility provide a simple picture that describes a decrease in actin-tropomyosin interaction energy. Destabilizing the blocked (relaxed)-state parallels previously noted enhanced Ca(2+)-sensitivity conferred by these mutants. Energy landscapes also identify post-translational modifications that can rescue regulatory imbalances. For example, cardiomyopathy-associated E62Q tropomyosin mutation weakens actin-tropomyosin interaction, but phosphorylation of neighboring S61 rescues the binding-deficit, results confirmed experimentally by in vitro motility assays. Unlike results on hyper-contractility-related mutants, landscapes for tropomyosin mutants tied to hypo-contractility do not present a straightforward picture. These mutations may affect other components of the regulatory network, e.g., troponin-tropomyosin signaling.
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26
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Instability in the central region of tropomyosin modulates the function of its overlapping ends. Biophys J 2014; 105:2104-13. [PMID: 24209855 DOI: 10.1016/j.bpj.2013.09.026] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2013] [Revised: 08/20/2013] [Accepted: 09/17/2013] [Indexed: 12/14/2022] Open
Abstract
The causal link between disparate tropomyosin (Tm) functions and the structural instability in Tm is unknown. To test the hypothesis that the structural instability in the central region of Tm modulates the function of the overlapping ends of contiguous Tm dimers, we used transgenic mice (Tm(DM)) that expressed a mutant α-Tm in the heart; S229E and H276N substitutions induce structural instability in the central region and the overlapping ends of Tm, respectively. In addition, two mouse cardiac troponin T mutants (TnT(1-44Δ) and TnT(45-74Δ)) that have a divergent effect on the overlapping ends of Tm were employed. The S229E-induced instability in the central region of Tm(DM) altered the overlapping ends of Tm(DM), thereby it negated the attenuating effect of H276N on Ca(2+)-activated maximal tension. The rate of cross-bridge detachment (g) decreased in Tm(DM)+TnT(WT) and Tm(H276N)+TnT(WT) fibers but increased in Tm(DM)+TnT(45-74Δ) fibers; however, TnT(45-74Δ) did not alter g, demonstrating that S229E in Tm(DM) had divergent effects on g. The S229E substitution in Tm(DM) ablated the H276N-induced desensitization of myofilament Ca(2+) sensitivity in Tm(DM)+TnT(1-44Δ) fibers. To our knowledge, novel findings from this study show that the structural instability in the central region of Tm modifies cardiac contractile function via its effect on the overlapping ends of contiguous Tm.
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Zheng W, Barua B, Hitchcock-DeGregori SE. Probing the flexibility of tropomyosin and its binding to filamentous actin using molecular dynamics simulations. Biophys J 2014; 105:1882-92. [PMID: 24138864 DOI: 10.1016/j.bpj.2013.09.003] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2013] [Revised: 08/24/2013] [Accepted: 09/04/2013] [Indexed: 01/17/2023] Open
Abstract
Tropomyosin (Tm) is a coiled-coil protein that binds to filamentous actin (F-actin) and regulates its interactions with actin-binding proteins like myosin by moving between three positions on F-actin (the blocked, closed, and open positions). To elucidate the molecular details of Tm flexibility in relation to its binding to F-actin, we conducted extensive molecular dynamics simulations for both Tm alone and Tm-F-actin complex in the presence of explicit solvent (total simulation time >400 ns). Based on the simulations, we systematically analyzed the local flexibility of the Tm coiled coil using multiple parameters. We found a good correlation between the regions with high local flexibility and a number of destabilizing regions in Tm, including six clusters of core alanines. Despite the stabilization by F-actin binding, the distribution of local flexibility in Tm is largely unchanged in the absence and presence of F-actin. Our simulations showed variable fluctuations of individual Tm periods from the closed position toward the open position. In addition, we performed Tm-F-actin binding calculations based on the simulation trajectories, which support the importance of Tm flexibility to Tm-F-actin binding. We identified key residues of Tm involved in its dynamic interactions with F-actin, many of which have been found in recent mutational studies to be functionally important, and the rest of which will make promising targets for future mutational experiments.
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Affiliation(s)
- Wenjun Zheng
- Department of Physics, University at Buffalo, Buffalo, New York.
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28
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El-Mezgueldi M. Tropomyosin dynamics. J Muscle Res Cell Motil 2014; 35:203-10. [PMID: 24510226 DOI: 10.1007/s10974-014-9377-x] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2013] [Accepted: 01/28/2014] [Indexed: 12/28/2022]
Abstract
Tropomyosin is a two chained α-helical coiled coil protein that binds actin filaments and interacts with various actin binding proteins. Tropomyosin function depends on its ability to move to distinct locations on the surface of actin in response to the binding of different thin filament effectors. Tropomyosin dynamics plays an important role in these fluctuating interactions with actin and is thought to be fundamental to many of its biological activities. For example tropomyosin concerted movement on the surface of actin triggered by Ca(2+) binding to troponin or myosin head binding to actin has been argued to be key to the cooperative allosteric regulation of muscle contraction. These large-scale motions are affected by tropomyosin internal dynamics and mechanical properties. Tropomyosin internal dynamics corresponding to smaller and more localised structural fluctuations are increasingly recognised to play an important role in its function. A thorough understanding of the coupling between local and global structural fluctuations in tropomyosin is required to understand how time dependent structural fluctuations in tropomyosin contribute to the overall thin filament dynamics and dictate their various biological activities.
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Affiliation(s)
- Mohammed El-Mezgueldi
- Department of Biochemistry, Faculty of Medicine and Biological Sciences, University of Leicester, Henry Wellcome Building, Lancaster Road, Leicester, LE1 9HN, UK,
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Rysev NA, Nevzorov IA, Avrova SV, Karpicheva OE, Redwood CS, Levitsky DI, Borovikov YS. Gly126Arg substitution causes anomalous behaviour of α-skeletal and β-smooth tropomyosins during the ATPase cycle. Arch Biochem Biophys 2013; 543:57-66. [PMID: 24374033 DOI: 10.1016/j.abb.2013.12.016] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2013] [Revised: 12/13/2013] [Accepted: 12/16/2013] [Indexed: 12/26/2022]
Abstract
To investigate how TM stabilization induced by the Gly126Arg mutation in skeletal α-TM or in smooth muscle β-TM affects the flexibility of TMs and their position on troponin-free thin filaments, we labelled the recombinant wild type and mutant TMs with 5-IAF and F-actin with FITC-phalloidin, incorporated them into ghost muscle fibres and studied polarized fluorescence at different stages of the ATPase cycle. It has been shown that in the myosin- and troponin-free filaments the Gly126Arg mutation causes a shift of TM strands towards the outer domain of actin, reduces the number of switched on actin monomers and decreases the rigidity of the C-terminus of α-TM and increases the rigidity of the N-terminus of β-TMs. The binding of myosin subfragment-1 to the filaments shifted the wild type TMs towards the inner domain of actin, decreased the flexibility of both terminal parts of TMs, and increased the number of switched on actin monomers. Multistep alterations in the position of α- and β-TMs and actin monomers in the filaments and in the flexibility of TMs and F-actin during the ATPase cycle were observed. The Gly126Arg mutation uncouples a correlation between the position of TM and the number of the switched on actin monomers in the filaments.
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Affiliation(s)
- Nikita A Rysev
- Laboratory of Mechanisms of Cell Motility, Institute of Cytology, Russian Academy of Sciences, 4 Tikhoretsky Avenue, St. Petersburg 194064, Russia
| | - Ilya A Nevzorov
- Institute of Biotechnology, University of Helsinki, Viikinkaari 9, 00014 Helsinki, Finland
| | - Stanislava V Avrova
- Laboratory of Mechanisms of Cell Motility, Institute of Cytology, Russian Academy of Sciences, 4 Tikhoretsky Avenue, St. Petersburg 194064, Russia
| | - Olga E Karpicheva
- Laboratory of Mechanisms of Cell Motility, Institute of Cytology, Russian Academy of Sciences, 4 Tikhoretsky Avenue, St. Petersburg 194064, Russia
| | - Charles S Redwood
- Department of Cardiovascular Medicine, University of Oxford, John Radcliffe Hospital, Oxford OX3 9DU, UK
| | - Dmitrii I Levitsky
- A.N. Bach Institute of Biochemistry, Russian Academy of Sciences, Moscow 119071, Russia
| | - Yurii S Borovikov
- Laboratory of Mechanisms of Cell Motility, Institute of Cytology, Russian Academy of Sciences, 4 Tikhoretsky Avenue, St. Petersburg 194064, Russia.
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30
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Redwood C, Robinson P. Alpha-tropomyosin mutations in inherited cardiomyopathies. J Muscle Res Cell Motil 2013; 34:285-94. [DOI: 10.1007/s10974-013-9358-5] [Citation(s) in RCA: 61] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2013] [Accepted: 08/23/2013] [Indexed: 10/26/2022]
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31
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Schulz EM, Wilder T, Chowdhury SAK, Sheikh HN, Wolska BM, Solaro RJ, Wieczorek DF. Decreasing tropomyosin phosphorylation rescues tropomyosin-induced familial hypertrophic cardiomyopathy. J Biol Chem 2013; 288:28925-35. [PMID: 23960072 DOI: 10.1074/jbc.m113.466466] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Studies indicate that tropomyosin (Tm) phosphorylation status varies in different mouse models of cardiac disease. Investigation of basal and acute cardiac function utilizing a mouse model expressing an α-Tm protein that cannot be phosphorylated (S283A) shows a compensated hypertrophic phenotype with significant increases in SERCA2a expression and phosphorylation of phospholamban Ser-16 (Schulz, E. M., Correll, R. N., Sheikh, H. N., Lofrano-Alves, M. S., Engel, P. L., Newman, G., Schultz Jel, J., Molkentin, J. D., Wolska, B. M., Solaro, R. J., and Wieczorek, D. F. (2012) J. Biol. Chem. 287, 44478-44489). With these results, we hypothesized that decreasing α-Tm phosphorylation may be beneficial in the context of a chronic, intrinsic stressor. To test this hypothesis, we utilized the familial hypertrophic cardiomyopathy (FHC) α-Tm E180G model (Prabhakar, R., Boivin, G. P., Grupp, I. L., Hoit, B., Arteaga, G., Solaro, R. J., and Wieczorek, D. F. (2001) J. Mol. Cell. Cardiol. 33, 1815-1828). These FHC hearts are characterized by increased heart:body weight ratios, fibrosis, increased myofilament Ca(2+) sensitivity, and contractile defects. The FHC mice die by 6-8 months of age. We generated mice expressing both the E180G and S283A mutations and found that the hypertrophic phenotype was rescued in the α-Tm E180G/S283A double mutant transgenic animals; these mice exhibited no signs of cardiac hypertrophy and displayed improved cardiac function. These double mutant transgenic hearts showed increased phosphorylation of phospholamban Ser-16 and Thr-17 compared with the α-Tm E180G mice. This is the first study to demonstrate that decreasing phosphorylation of tropomyosin can rescue a hypertrophic cardiomyopathic phenotype.
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Affiliation(s)
- Emily M Schulz
- From the Department of Molecular Genetics, Biochemistry, and Microbiology, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267
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32
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Nuclear tropomyosin and troponin in striated muscle: new roles in a new locale? J Muscle Res Cell Motil 2013; 34:275-84. [DOI: 10.1007/s10974-013-9356-7] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2013] [Accepted: 07/23/2013] [Indexed: 01/03/2023]
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33
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Janco M, Suphamungmee W, Li X, Lehman W, Lehrer SS, Geeves MA. Polymorphism in tropomyosin structure and function. J Muscle Res Cell Motil 2013; 34:177-87. [PMID: 23832280 PMCID: PMC4509547 DOI: 10.1007/s10974-013-9353-x] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2013] [Accepted: 06/28/2013] [Indexed: 12/18/2022]
Abstract
Tropomyosins (Tm) in humans are expressed from four distinct genes and by alternate splicing >40 different Tm polypeptide chains can be made. The functional Tm unit is a dimer of two parallel polypeptide chains and these can be assembled from identical (homodimer) or different (heterodimer) polypeptide chains provided both chains are of the same length. Since most cells express multiple isoforms of Tm, the number of different homo and heterodimers that can be assembled becomes very large. We review the mechanism of dimer assembly and how preferential assembly of some heterodimers is driven by thermodynamic stability. We examine how in vitro studies can reveal functional differences between Tm homo and heterodimers (stability, actin affinity, flexibility) and the implication for how there could be selection of Tm isomers in the assembly on to an actin filament. The role of Tm heterodimers becomes more complex when mutations in Tm are considered, such as those associated with cardiomyopathies, since mutations can appear in only one of the chains.
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Affiliation(s)
- Miro Janco
- School of Biosciences, University of Kent, Canterbury, Kent, UK
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34
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Schulz EM, Wieczorek DF. Tropomyosin de-phosphorylation in the heart: What are the consequences? J Muscle Res Cell Motil 2013; 34:239-46. [DOI: 10.1007/s10974-013-9348-7] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2013] [Accepted: 05/24/2013] [Indexed: 11/30/2022]
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35
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Gestalt-binding of tropomyosin on actin during thin filament activation. J Muscle Res Cell Motil 2013; 34:155-63. [PMID: 23666668 DOI: 10.1007/s10974-013-9342-0] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2013] [Accepted: 04/17/2013] [Indexed: 01/07/2023]
Abstract
Our thesis is that thin filament function can only be fully understood and muscle regulation then elucidated if atomic structures of the thin filament are available to reveal the positions of tropomyosin on actin in all physiological states. After all, it is tropomyosin influenced by troponin that regulates myosin-crossbridge cycling on actin and therefore controls contraction in all muscles. In addition, we maintain that a complete appreciation of thin filament activation also requires that the mechanical properties of tropomyosin itself are recognized and then related to the effect of myosin-association on actin. Taking the Gestalt-binding of tropomyosin into account, coupled with our electron microscopy structures and computational chemistry, we propose a comprehensive mechanism for tropomyosin regulatory movement over the actin filament surface that explains the cooperative muscle activation process. In fact, well-known point mutations of critical amino acids on the actin-tropomyosin binding interface disrupt Gestalt-binding and are associated with a number of inherited myopathies. Moreover, dysregulation of tropomyosin may also be a factor that interferes with the gatekeeping operation of non-muscle tropomyosin in the controlling interactions of a wide variety of cellular actin-binding proteins. The clinical relevance of Gestalt-binding is discussed in articles by the Marston and the Gunning groups in this special journal issue devoted to the impact of tropomyosin on biological systems.
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36
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Abstract
We focus here on the modulation of thin filament activity by cardiac troponin I phosphorylation as an integral and adaptive mechanism in cardiac homeostasis and as a mechanism vulnerable to maladaptive response to stress. We discuss a current concept of cardiac troponin I function in the A-band region of the sarcomere and potential signaling to cardiac troponin I in a network involving the ends of the thin filaments at the Z-disk and the M-band regions. The cardiac sarcomere represents a remarkable set of interacting proteins that functions not only as a molecular machine generating the heartbeat but also as a hub of signaling. We review how phosphorylation signaling to cardiac troponin I is integrated, with parallel signals controlling excitation-contraction coupling, hypertrophy, and metabolism.
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Affiliation(s)
- R John Solaro
- Department of Physiology and Biophysics and Center for Cardiovascular Research, University of Illinois at Chicago, College of Medicine, Chicago, IL 60612, USA.
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37
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Mamidi R, Mallampalli SL, Wieczorek DF, Chandra M. Identification of two new regions in the N-terminus of cardiac troponin T that have divergent effects on cardiac contractile function. J Physiol 2012. [PMID: 23207592 DOI: 10.1113/jphysiol.2012.243394] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Abstract Cardiac troponin T (cTnT) has a highly acidic extended N-terminus, the physiological role of which remains poorly understood. To decipher the physiological role of this unique region, we deleted specific regions within the N-terminus of mouse cTnT (McTnT) to create McTnT1-44 and McTnT45-74 proteins. Contractile function and dynamic force-length measurements were made after reconstituting the McTnT deletion proteins into detergent-skinned cardiac papillary fibres harvested from non-transgenic mice that expressed α-tropomyosin (Tm). To further understand how the functional effects of the N-terminus of cTnT are modulated by Tm isoforms, McTnT deletion proteins were reconstituted into detergent-skinned cardiac papillary fibres harvested from transgenic mice that expressed both α- and β-Tm. McTnT1-44, but not McTnT45-74, attenuated maximal activation of the thin filament. Myofilament Ca(2+) sensitivity, as measured by pCa50 (-log of [Ca(2+)]free required for half-maximal activation), decreased in McTnT1-44 (α-Tm) fibres. The desensitizing effect of McTnT1-44 on pCa50 was ablated in β-Tm fibres. McTnT45-74 enhanced pCa50 in both α- and β-Tm fibres, with β-Tm having a bigger effect. The Hill coefficient of tension development was significantly attenuated by McTnT45-74, suggesting an effect on thin-filament cooperativity. The rate of cross-bridge (XB) detachment and the strained XB-mediated impact on other XBs were augmented by McTnT1-44 in β-Tm fibres. The magnitude of the length-mediated recruitment of XBs was attenuated by McTnT1-44 in β-Tm fibres. Our data demonstrate that the 1-44 region of McTnT is essential for maximal activation, whereas the cardiac-specific 45-74 region of McTnT is essential for augmenting cooperativity. Moreover, our data show that α- and β-Tm isoforms have divergent effects on McTnT deletion mutant's ability to modulate cardiac thin-filament activation and Ca(2+) sensitivity. Our results not only provide the first explicit evidence for the existence of two distinct functional regions within the N-terminus of cTnT, but also offer mechanistic insights into the divergent physiological roles of these regions in mediating cardiac contractile activation.
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Affiliation(s)
- Ranganath Mamidi
- Department of Veterinary and Comparative Anatomy, Pharmacology and Physiology, Washington State University, Pullman, WA-99164, USA.
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Janco M, Kalyva A, Scellini B, Piroddi N, Tesi C, Poggesi C, Geeves MA. α-Tropomyosin with a D175N or E180G mutation in only one chain differs from tropomyosin with mutations in both chains. Biochemistry 2012; 51:9880-90. [PMID: 23170982 PMCID: PMC3711130 DOI: 10.1021/bi301323n] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
α-Tropomyosin (Tm) carrying hypertrophic cardiomyopathy mutation D175N or E180G was expressed in Escherichia coli. We have assembled dimers of two polypeptide chains in vitro that carry one (αα*) or two (α*α*) copies of the mutation. We found that the presence of the mutation has little effect on dimer assembly, thereby predicting that individuals heterozygous for the Tm mutations are likely to express both αα* and α*α* Tm. Depending on the expression level, the heterodimer may be the predominant form in individuals carrying the mutation. Thus, it is important to define differences in the properties of Tm molecules carrying one or two copies of the mutation. We examined the Tm homo- and heterodimer properties: actin affinity, thermal stability, calcium regulation of myosin subfragment 1 binding, and calcium regulation of myofibril force. We report that the properties of the heterodimer may be similar to those of the wild-type homodimer (actin affinity, thermal stability, D175N αα*), similar to those of the mutant homodimer (calcium sensitivity, D175N αα*), intermediate between the two (actin affinity, E180G αα*), or different from both (thermal stability, E180G αα*). Thus, the properties of the homodimer are not a completely reliable guide to the properties of the heterodimer.
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Affiliation(s)
- Miro Janco
- School of Biosciences, University of Kent, Canterbury, Kent, United Kingdom
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DCM-related tropomyosin mutants E40K/E54K over-inhibit the actomyosin interaction and lead to a decrease in the number of cycling cross-bridges. PLoS One 2012; 7:e47471. [PMID: 23077624 PMCID: PMC3471818 DOI: 10.1371/journal.pone.0047471] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2012] [Accepted: 09/11/2012] [Indexed: 11/19/2022] Open
Abstract
Two DCM mutants (E40K and E54K) of tropomyosin (Tm) were examined using the thin-filament extraction/reconstitution technique. The effects of the Ca2+, ATP, phosphate (Pi), and ADP concentrations on isometric tension and its transients were studied at 25°C, and the results were compared to those for the WT protein. Our results indicate that both E40K and E54K have a significantly lower THC (high Ca2+ tension at pCa 4.66) (E40K: 1.21±0.06 Ta, ±SEM, N = 34; E54K: 1.24±0.07 Ta, N = 28), a significantly lower TLC (low- Ca2+ tension at pCa 7.0) (E40K: 0.07±0.02 Ta, N = 34; E54K: 0.06±0.02 Ta, N = 28), and a significantly lower Tact (Ca2+ activatable tension) (Tact = THC–TLC, E40K: 1.15±0.08 Ta, N = 34; E54K: 1.18±0.06 Ta, N = 28) than WT (THC = 1.53±0.07 Ta, TLC = 0.12±0.01 Ta, Tact = 1.40±0.07 Ta, N = 25). All tensions were normalized to Ta ( = 13.9±0.8 kPa, N = 57), the tension of actin-filament reconstituted cardiac fibers (myocardium) under the standard activating conditions. The Ca2+ sensitivity (pCa50) of E40K (5.23±0.02, N = 34) and E54K (5.24±0.03, N = 28) was similar to that of the WT protein (5.26±0.03, N = 25). The cooperativity increased significantly in E54K (3.73±0.25, N = 28) compared to WT (2.80±0.17, N = 25). Seven kinetic constants were deduced using sinusoidal analysis at pCa 4.66. These results enabled us to calculate the cross-bridge distribution in the strongly attached states, and thereby deduce the force/cross-bridge. The results indicate that the force/cross-bridge is ∼15% less in E54K than WT, but remains similar to that of the WT protein in the case of E40K. We conclude that over-inhibition of the actomyosin interaction by E40K and E54K Tm mutants leads to a decreased force-generating ability at systole, which is the main mechanism underlying the early pathogenesis of DCM.
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Mijailovich SM, Kayser-Herold O, Li X, Griffiths H, Geeves MA. Cooperative regulation of myosin-S1 binding to actin filaments by a continuous flexible Tm-Tn chain. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2012; 41:1015-32. [PMID: 23052974 PMCID: PMC3509328 DOI: 10.1007/s00249-012-0859-8] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/04/2012] [Revised: 08/30/2012] [Accepted: 09/06/2012] [Indexed: 12/20/2022]
Abstract
The regulation of striated muscle contraction involves cooperative interactions between actin filaments, myosin-S1 (S1), tropomyosin (Tm), troponin (Tn), and calcium. These interactions are modeled by treating overlapping tropomyosins as a continuous flexible chain (CFC), weakly confined by electrostatic interactions with actin. The CFC is displaced locally in opposite directions on the actin surface by the binding of either S1 or Troponin I (TnI) to actin. The apparent rate constants for myosin and TnI binding to and detachment from actin are then intrinsically coupled via the CFC model to the presence of neighboring bound S1s and TnIs. Monte Carlo simulations at prescribed values of the CFC stiffness, the CFC’s degree of azimuthal confinement, and the angular displacements caused by the bound proteins were able to predict the stopped-flow transients of S1 binding to regulated F-actin. The transients collected over a large range of calcium concentrations could be well described by adjusting a single calcium-dependent parameter, the rate constant of TnI detachment from actin, k−I. The resulting equilibrium constant \documentclass[12pt]{minimal}
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\begin{document}$$ K_{\text{B}} \equiv 1/K_{\text{I}} $$\end{document} varied sigmoidally with the free calcium, increasing from 0.12 at low calcium (pCa >7) to 12 at high calcium (pCa <5.5) with a Hill coefficient of ~2.15. The similarity of the curves for excess-actin and excess-myosin data confirms their allosteric relationship. The spatially explicit calculations confirmed variable sizes for the cooperative units and clustering of bound myosins at low calcium concentrations. Moreover, inclusion of negative cooperativity between myosin units predicted the observed slowing of myosin binding at excess-myosin concentrations.
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Affiliation(s)
- Srboljub M Mijailovich
- Department of Environmental Health, Harvard School of Public Health, Boston, MA 02115, USA.
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41
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Tuning the calcium sensitivity of cardiac muscle. Biophys J 2012; 103:849-50. [PMID: 23009833 DOI: 10.1016/j.bpj.2012.07.039] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2012] [Revised: 07/20/2012] [Accepted: 07/23/2012] [Indexed: 11/24/2022] Open
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