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Schmidt W, Madan A, Foster DB, Cammarato A. Lysine acetylation of F-actin decreases tropomyosin-based inhibition of actomyosin activity. J Biol Chem 2020; 295:15527-15539. [PMID: 32873710 DOI: 10.1074/jbc.ra120.015277] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2020] [Revised: 08/18/2020] [Indexed: 12/17/2022] Open
Abstract
Recent proteomics studies of vertebrate striated muscle have identified lysine acetylation at several sites on actin. Acetylation is a reversible post-translational modification that neutralizes lysine's positive charge. Positively charged residues on actin, particularly Lys326 and Lys328, are predicted to form critical electrostatic interactions with tropomyosin (Tpm) that promote its binding to filamentous (F)-actin and bias Tpm to an azimuthal location where it impedes myosin attachment. The troponin (Tn) complex also influences Tpm's position along F-actin as a function of Ca2+ to regulate exposure of myosin-binding sites and, thus, myosin cross-bridge recruitment and force production. Interestingly, Lys326 and Lys328 are among the documented acetylated residues. Using an acetic anhydride-based labeling approach, we showed that excessive, nonspecific actin acetylation did not disrupt characteristic F-actin-Tpm binding. However, it significantly reduced Tpm-mediated inhibition of myosin attachment, as reflected by increased F-actin-Tpm motility that persisted in the presence of Tn and submaximal Ca2+ Furthermore, decreasing the extent of chemical acetylation, to presumptively target highly reactive Lys326 and Lys328, also resulted in less inhibited F-actin-Tpm, implying that modifying only these residues influences Tpm's location and, potentially, thin filament regulation. To unequivocally determine the residue-specific consequences of acetylation on Tn-Tpm-based regulation of actomyosin activity, we assessed the effects of K326Q and K328Q acetyl (Ac)-mimetic actin on Ca2+-dependent, in vitro motility parameters of reconstituted thin filaments (RTFs). Incorporation of K328Q actin significantly enhanced Ca2+ sensitivity of RTF activation relative to control. Together, our findings suggest that actin acetylation, especially Lys328, modulates muscle contraction via disrupting inhibitory Tpm positioning.
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Affiliation(s)
- William Schmidt
- Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Aditi Madan
- Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - D Brian Foster
- Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Anthony Cammarato
- Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
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2
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Sundar S, Rynkiewicz MJ, Ghosh A, Lehman W, Moore JR. Cardiomyopathy Mutation Alters End-to-End Junction of Tropomyosin and Reduces Calcium Sensitivity. Biophys J 2019; 118:303-312. [PMID: 31882250 DOI: 10.1016/j.bpj.2019.11.3396] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2019] [Revised: 10/30/2019] [Accepted: 11/18/2019] [Indexed: 12/24/2022] Open
Abstract
Muscle contraction is governed by tropomyosin (Tpm) shifting azimuthally between three states on F-actin (B-, C-, and M-states) in response to calcium binding to troponin and actomyosin cross-bridge formation. The Tpm coiled coil polymerizes head to tail along the long-pitch helix of F-actin to form continuous superhelical cables that wrap around the actin filaments. The end-to-end bonds formed between the N- and C-terminus of adjacent Tpm molecules define Tpm continuity and play a critical role in the ability of Tpm to cooperatively bind to actin, thus facilitating Tpm conformational switching to cooperatively propagate along F-actin. We expect that a missense mutation in this critical overlap region associated with dilated cardiomyopathy, A277V, will alter Tpm binding and thin filament activation by altering the overlap structure. Here, we used cosedimentation assays and in vitro motility assays to determine how the mutation alters Tpm binding to actin and its ability to regulate actomyosin interactions. Analytical viscometry coupled with molecular dynamics simulations showed that the A277V mutation results in enhanced Tpm end-to-end bond strength and a reduced curvature of the Tpm overlap domain. The mutant Tpm exhibited enhanced actin-Tpm binding affinity, consistent with overlap stabilization. The observed A277V-induced decrease in cooperative activation observed with regulated thin filament motility indicates that increased overlap stabilization is not correlated with Tpm-Tpm overlap binding strength or mechanical rigidity as is often assumed. Instead, A277V-induced structural changes result in local and delocalized increases in Tpm flexibility and prominent coiled-coil twisting in pseudorepeat 4. An A277V-induced decrease in Ca2+ sensitivity, consistent with a mutation-induced bolstering of the B-state Tpm-actin electrostatic contacts and an increased Tpm troponin T1 binding affinity, was also observed.
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Affiliation(s)
- SaiLavanyaa Sundar
- Department of Biological Sciences, University of Massachusetts-Lowell, Lowell, Massachusetts
| | - Michael J Rynkiewicz
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, Massachusetts
| | - Anita Ghosh
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, Massachusetts
| | - 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.
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3
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Kopylova GV, Matyushenko AM, Koubassova NA, Shchepkin DV, Bershitsky SY, Levitsky DI, Tsaturyan AK. Functional outcomes of structural peculiarities of striated muscle tropomyosin. J Muscle Res Cell Motil 2019; 41:55-70. [DOI: 10.1007/s10974-019-09552-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2019] [Accepted: 08/17/2019] [Indexed: 12/27/2022]
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4
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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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5
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Lehman W, Li X, Kiani FA, Moore JR, Campbell SG, Fischer S, Rynkiewicz MJ. Precise Binding of Tropomyosin on Actin Involves Sequence-Dependent Variance in Coiled-Coil Twisting. Biophys J 2018; 115:1082-1092. [PMID: 30195938 DOI: 10.1016/j.bpj.2018.08.017] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2018] [Revised: 08/08/2018] [Accepted: 08/15/2018] [Indexed: 11/17/2022] Open
Abstract
Often considered an archetypal dimeric coiled coil, tropomyosin nonetheless exhibits distinctive "noncanonical" core residues located at the hydrophobic interface between its component α-helices. Notably, a charged aspartate, D137, takes the place of nonpolar residues otherwise present. Much speculation has been offered to rationalize potential local coiled-coil instability stemming from D137 and its effect on regulatory transitions of tropomyosin over actin filaments. Although experimental approaches such as electron cryomicroscopy reconstruction are optimal for defining average tropomyosin positions on actin filaments, to date, these methods have not captured the dynamics of tropomyosin residues clustered around position 137 or elsewhere. In contrast, computational biochemistry, involving molecular dynamics simulation, is a compelling choice to extend the understanding of local and global tropomyosin behavior on actin filaments at high resolution. Here, we report on molecular dynamics simulation of actin-free and actin-associated tropomyosin, showing noncanonical residue D137 as a locus for tropomyosin twist variation, with marked effects on actin-tropomyosin interactions. We conclude that D137-sponsored coiled-coil twisting is likely to optimize electrostatic side-chain contacts between tropomyosin and actin on the assembled thin filament, while offsetting disparities between tropomyosin pseudorepeat and actin subunit periodicities. We find that D137 has only minor local effects on tropomyosin coiled-coil flexibility, (i.e., on its flexural mobility). Indeed, D137-associated overtwisting may actually augment tropomyosin stiffness on actin filaments. Accordingly, such twisting-induced stiffness of tropomyosin is expected to enhance cooperative regulatory translocation of the tropomyosin cable over actin.
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Affiliation(s)
- William Lehman
- Department of Physiology & Biophysics, Boston University School of Medicine, Boston, Massachusetts.
| | - Xiaochuan Li
- Department of Physiology & Biophysics, Boston University School of Medicine, Boston, Massachusetts
| | - Farooq A Kiani
- Department of Physiology & 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 & Cellular and Molecular Physiology, Yale University, New Haven, Connecticut
| | - Stefan Fischer
- Interdisciplinary Center for Scientific Computing, University of Heidelberg, Heidelberg, Baden-Württemberg, Germany
| | - Michael J Rynkiewicz
- Department of Physiology & Biophysics, Boston University School of Medicine, Boston, Massachusetts
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6
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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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7
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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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8
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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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9
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Fischer S, Rynkiewicz MJ, Moore JR, Lehman W. Tropomyosin diffusion over actin subunits facilitates thin filament assembly. STRUCTURAL DYNAMICS (MELVILLE, N.Y.) 2016; 3:012002. [PMID: 26798831 PMCID: PMC4714992 DOI: 10.1063/1.4940223] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/08/2015] [Accepted: 01/07/2016] [Indexed: 06/05/2023]
Abstract
Coiled-coil tropomyosin binds to consecutive actin-subunits along actin-containing thin filaments. Tropomyosin molecules then polymerize head-to-tail to form cables that wrap helically around the filaments. Little is known about the assembly process that leads to continuous, gap-free tropomyosin cable formation. We propose that tropomyosin molecules diffuse over the actin-filament surface to connect head-to-tail to partners. This possibility is likely because (1) tropomyosin hovers loosely over the actin-filament, thus binding weakly to F-actin and (2) low energy-barriers provide tropomyosin freedom for 1D axial translation on F-actin. We consider that these unique features of the actin-tropomyosin interaction are the basis of tropomyosin cable formation.
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Affiliation(s)
- Stefan Fischer
- Computational Biochemistry Group, Interdisciplinary Center for Scientific Computing (IWR), University of Heidelberg , Im Neuenheimer Feld 368, D69120 Heidelberg, Germany
| | - Michael J Rynkiewicz
- Department of Physiology and Biophysics, Boston University School of Medicine , 72 East Concord Street, Boston, Massachusetts 02118, USA
| | - Jeffrey R Moore
- Department of Biological Sciences, University of Massachusetts Lowell , One University Avenue, Lowell, Massachusetts 01854, USA
| | - William Lehman
- Department of Physiology and Biophysics, Boston University School of Medicine , 72 East Concord Street, Boston, Massachusetts 02118, USA
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10
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Alamo L, Li XE, Espinoza-Fonseca LM, Pinto A, Thomas DD, Lehman W, Padrón R. Tarantula myosin free head regulatory light chain phosphorylation stiffens N-terminal extension, releasing it and blocking its docking back. MOLECULAR BIOSYSTEMS 2015; 11:2180-9. [PMID: 26038302 PMCID: PMC4503497 DOI: 10.1039/c5mb00163c] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Molecular dynamics simulations of smooth and striated muscle myosin regulatory light chain (RLC) N-terminal extension (NTE) showed that diphosphorylation induces a disorder-to-order transition. Our goal here was to further explore the effects of mono- and diphosphorylation on the straightening and rigidification of the tarantula myosin RLC NTE. For that we used MD simulations followed by persistence length analysis to explore the consequences of secondary and tertiary structure changes occurring on RLC NTE following phosphorylation. Static and dynamic persistence length analysis of tarantula RLC NTE peptides suggest that diphosphorylation produces an important 24-fold straightening and a 16-fold rigidification of the RLC NTE, while monophosphorylation has a less profound effect. This new information on myosin structural mechanics, not fully revealed by previous EM and MD studies, add support to a cooperative phosphorylation-dependent activation mechanism as proposed for the tarantula thick filament. Our results suggest that the RLC NTE straightening and rigidification after Ser45 phosphorylation leads to a release of the constitutively Ser35 monophosphorylated free head swaying away from the thick filament shaft. This is so because the stiffened diphosphorylated RLC NTE would hinder the docking back of the free head after swaying away, becoming released and mobile and unable to recover its original interacting position on activation.
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Affiliation(s)
- Lorenzo Alamo
- Centro de Biología Estructural, Instituto Venezolano de Investigaciones Científicas (IVIC), Apdo. 20632, Caracas 1020, Venezuela.
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11
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Fudge KR, Heeley DH. Biochemical Characterization of the Roles of Glycines 24 and 27 and Threonine 179 in Tropomyosin from the Fast Skeletal Trunk Muscle of the Atlantic Salmon. Biochemistry 2015; 54:2769-76. [DOI: 10.1021/acs.biochem.5b00156] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Affiliation(s)
- Korrina R. Fudge
- Department
of Biochemistry, Memorial University of Newfoundland, St. John’s, Newfoundland A1B 3X9, Canada
| | - David H. Heeley
- Department
of Biochemistry, Memorial University of Newfoundland, St. John’s, Newfoundland A1B 3X9, Canada
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12
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Convergently-evolved structural anomalies in the coiled coil domains of insect silk proteins. J Struct Biol 2014; 186:402-11. [DOI: 10.1016/j.jsb.2014.01.002] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2013] [Revised: 01/07/2014] [Accepted: 01/08/2014] [Indexed: 01/16/2023]
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13
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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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14
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Metalnikova NA, Tsaturyan AK. A mechanistic model of Ca regulation of thin filaments in cardiac muscle. Biophys J 2014; 105:941-50. [PMID: 23972846 DOI: 10.1016/j.bpj.2013.06.044] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2013] [Revised: 04/20/2013] [Accepted: 06/19/2013] [Indexed: 01/05/2023] Open
Abstract
We present a model of Ca-regulated thin filaments in cardiac muscle where tropomyosin is treated as a continuous elastic chain confined in the closed position on the actin helix by electrostatic forces. The main distinction from previous works is that the intrinsic stress-free helical shape of the tropomyosin chain was taken into account explicitly. This results in the appearance of a new, to our knowledge, tension-like term in the energy functional and the equilibrium equation. The competitive binding of calcium and the mobile segment of troponin-I to troponin-C were described by a simple kinetic scheme. The values of dimensionless model parameters were estimated from published data. A stochastic Monte Carlo simulation of calcium curves has been performed and its results were compared to published data. The model explains the high cooperativity of calcium response of the regulated thin filaments even in the absence of myosin heads. The binding of myosin heads to actin increases the calcium sensitivity while not affecting its cooperativity significantly. When the presence of calcium-insensitive troponin-C was simulated in the model, both calcium sensitivity and cooperativity decreased. All these features were previously observed experimentally.
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15
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Li XE, Orzechowski M, Lehman W, Fischer S. Structure and flexibility of the tropomyosin overlap junction. Biochem Biophys Res Commun 2014; 446:304-8. [PMID: 24607906 DOI: 10.1016/j.bbrc.2014.02.097] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2014] [Accepted: 02/23/2014] [Indexed: 12/12/2022]
Abstract
To be effective as a gatekeeper regulating the access of binding proteins to the actin filament, adjacent tropomyosin molecules associate head-to-tail to form a continuous super-helical cable running along the filament surface. Chimeric head-to-tail structures have been solved by NMR and X-ray crystallography for N- and C-terminal segments of smooth and striated muscle tropomyosin spliced onto non-native coiled-coil forming peptides. The resulting 4-helix complexes have a tight coiled-coil N-terminus inserted into a separated pair of C-terminal helices, with some helical unfolding of the terminal chains in the striated muscle peptides. These overlap complexes are distinctly curved, much more so than elsewhere along the superhelical tropomyosin cable. To verify whether the non-native protein adducts (needed to stabilize the coiled-coil chimeras) perturb the overlap, we carried out Molecular Dynamics simulations of head-to-tail structures having only native tropomyosin sequences. We observe that the splayed chains all refold and become helical. Significantly, the curvature of both the smooth and the striated muscle overlap domain is reduced and becomes comparable to that of the rest of the tropomyosin cable. Moreover, the measured flexibility across the junction is small. This and the reduced curvature ensure that the super-helical cable matches the contours of F-actin without manifesting localized kinking and excessive flexibility, thus enabling the high degree of cooperativity in the regulation of myosin accessibility to actin filaments.
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Affiliation(s)
- Xiaochuan Edward Li
- Department of Physiology and Biophysics, Boston University School of Medicine, 72 East Concord Street, Boston, MA 02118, USA; Computational Biochemistry Group, Interdisciplinary Center for Scientific Computing (IWR), University of Heidelberg, Im Neuenheimer Feld 368, Heidelberg D69120, Germany
| | - Marek Orzechowski
- Department of Physiology and Biophysics, Boston University School of Medicine, 72 East Concord Street, Boston, MA 02118, USA; Computational Biochemistry Group, Interdisciplinary Center for Scientific Computing (IWR), University of Heidelberg, Im Neuenheimer Feld 368, Heidelberg D69120, Germany
| | - William Lehman
- Department of Physiology and Biophysics, Boston University School of Medicine, 72 East Concord Street, Boston, MA 02118, USA.
| | - Stefan Fischer
- Computational Biochemistry Group, Interdisciplinary Center for Scientific Computing (IWR), University of Heidelberg, Im Neuenheimer Feld 368, Heidelberg D69120, Germany.
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16
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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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17
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Kirwan JP, Hodges RS. Transmission of stability information through the N-domain of tropomyosin is interrupted by a stabilizing mutation (A109L) in the hydrophobic core of the stability control region (residues 97-118). J Biol Chem 2013; 289:4356-66. [PMID: 24362038 PMCID: PMC3924298 DOI: 10.1074/jbc.m113.507236] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Tropomyosin (Tm) is an actin-binding, thin filament, two-stranded α-helical coiled-coil critical for muscle contraction and cytoskeletal function. We made the first identification of a stability control region (SCR), residues 97-118, in the Tm sequence that controls overall protein stability but is not required for folding. We also showed that the individual α-helical strands of the coiled-coil are stabilized by Leu-110, whereas the hydrophobic core is destabilized in the SCR by Ala residues at three consecutive d positions. Our hypothesis is that the stabilization of the individual α-helices provides an optimum stability and allows functionally beneficial dynamic motion between the α-helices that is critical for the transmission of stabilizing information along the coiled-coil from the SCR. We prepared three recombinant (rat) Tm(1-131) proteins, including the wild type sequence, a destabilizing mutation L110A, and a stabilizing mutation A109L. These proteins were evaluated by circular dichroism (CD) and differential scanning calorimetry. The single mutation L110A destabilizes the entire Tm(1-131) molecule, showing that the effect of this mutation is transmitted 165 Å along the coiled-coil in the N-terminal direction. The single mutation A109L prevents the SCR from transmitting stabilizing information and separates the coiled-coil into two domains, one that is ∼9 °C more stable than wild type and one that is ∼16 °C less stable. We know of no other example of the substitution of a stabilizing Leu residue in a coiled-coil hydrophobic core position d that causes this dramatic effect. We demonstrate the importance of the SCR in controlling and transmitting the stability signal along this rodlike molecule.
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Affiliation(s)
- J Paul Kirwan
- From the Program in Structural Biology and Biophysics, Department of Biochemistry and Molecular Genetics, School of Medicine, University of Colorado Denver, Aurora, Colorado 80045
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18
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Ly S, Lehrer SS. Long-range effects of familial hypertrophic cardiomyopathy mutations E180G and D175N on the properties of tropomyosin. Biochemistry 2012; 51:6413-20. [PMID: 22794249 PMCID: PMC3447992 DOI: 10.1021/bi3006835] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Cardiac α-tropomyosin (Tm) single-site mutations D175N and E180G cause familial hypertrophic cardiomyopathy (FHC). Previous studies have shown that these mutations increase both Ca(2+) sensitivity and residual contractile activity at low Ca(2+) concentrations, which causes incomplete relaxation during diastole resulting in hypertrophy and sarcomeric disarray. However, the molecular basis for the cause and the difference in the severity of the manifested phenotypes of disease are not known. In this work we have (1) used ATPase studies using reconstituted thin filaments in solution to show that these FHC mutants result in an increase in Ca(2+) sensitivity and an increased residual level of ATPase, (2) shown that both FHC mutants increase the rate of cleavage at R133, ~45 residues N-terminal to the mutations, when free and bound to actin, (3) shown that for Tm-E180G, the increase in the rate of cleavage is greater than that for D175N, and (4) shown that for E180G, cleavage also occurs at a new site 53 residues C-terminal to E180G, in parallel with cleavage at R133. The long-range decreases in dynamic stability due to these two single-site mutations suggest increases in flexibility that may weaken the ability of Tm to inhibit activity at low Ca(2+) concentrations for D175N and to a greater degree for E180G, which may contribute to differences in the severity of FHC.
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Affiliation(s)
- Socheata Ly
- Cardiovascular Program, Boston Biomedical Research Institute, 64 Grove Street, Watertown, MA 02472
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Nevzorov IA, Levitsky DI. Tropomyosin: double helix from the protein world. BIOCHEMISTRY (MOSCOW) 2012; 76:1507-27. [PMID: 22339601 DOI: 10.1134/s0006297911130098] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
This review concerns the structure and functions of tropomyosin (TM), an actin-binding protein that plays a key role in the regulation of muscle contraction. The TM molecule is a dimer of α-helices, which form a coiled-coil. Recent views on the TM structure are analyzed, and special attention is concentrated on those structural traits of the TM molecule that distinguish it from the other coiled-coil proteins. Modern data are presented on TM functional properties, such as its interaction with actin and ability to move on the surface of actin filaments, which underlies the regulation of the actin-myosin interaction upon contraction of skeletal and cardiac muscles. Also, part of the review is devoted to analysis of the effects of mutations in TM genes associated with muscle diseases (myopathies) on the structure and functions of TM.
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Affiliation(s)
- I A Nevzorov
- Bach Institute of Biochemistry, Russian Academy of Sciences, Moscow, Russia.
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Structural basis for myopathic defects engendered by alterations in the myosin rod. J Mol Biol 2011; 414:477-84. [PMID: 22037585 DOI: 10.1016/j.jmb.2011.10.019] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2011] [Revised: 10/03/2011] [Accepted: 10/12/2011] [Indexed: 12/12/2022]
Abstract
While mutations in the myosin subfragment 1 motor domain can directly disrupt the generation and transmission of force along myofibrils and lead to myopathy, the mechanism whereby mutations in the myosin rod influences mechanical function is less clear. Here, we used a combination of various imaging techniques and molecular dynamics simulations to test the hypothesis that perturbations in the myosin rod can disturb normal sarcomeric uniformity and, like motor domain lesions, would influence force production and propagation. We show that disrupting the rod can alter its nanomechanical properties and, in vivo, can drive asymmetric myofilament and sarcomere formation. Our imaging results indicate that myosin rod mutations likely disturb production and/or propagation of contractile force. This provides a unifying theory where common pathological cascades accompany both myosin motor and specific rod domain mutations. Finally, we suggest that sarcomeric inhomogeneity, caused by asymmetric thick filaments, could be a useful index of myopathic dysfunction.
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Li XE, Tobacman LS, Mun JY, Craig R, Fischer S, Lehman W. Tropomyosin position on F-actin revealed by EM reconstruction and computational chemistry. Biophys J 2011; 100:1005-13. [PMID: 21320445 DOI: 10.1016/j.bpj.2010.12.3697] [Citation(s) in RCA: 144] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2010] [Revised: 12/03/2010] [Accepted: 12/09/2010] [Indexed: 12/18/2022] Open
Abstract
Electron microscopy and fiber diffraction studies of reconstituted F-actin-tropomyosin filaments reveal the azimuthal position of end-to-end linked tropomyosin molecules on the surface of actin. However, the longitudinal z-position of tropomyosin along F-actin is still uncertain. Without this information, atomic models of F-actin-tropomyosin filaments, free of constraints imposed by troponin or other actin-binding proteins, cannot be formulated, and thus optimal interfacial contacts between actin and tropomyosin remain unknown. Here, a computational search assessing electrostatic interactions for multiple azimuthal locations, z-positions, and pseudo-rotations of tropomyosin on F-actin was performed. The information gleaned was used to localize tropomyosin on F-actin, yielding an atomic model characterized by protein-protein contacts that primarily involve clusters of basic amino acids on actin subdomains 1 and 3 juxtaposed against acidic residues on the successive quasi-repeating units of tropomyosin. A virtually identical model generated by docking F-actin and tropomyosin atomic structures into electron microscopy reconstructions of F-actin-tropomyosin validated the above solution. Here, the z-position of tropomyosin alongside F-actin was defined by matching the seven broad and narrow motifs that typify tropomyosin's twisting superhelical coiled-coil to the wide and tapering tropomyosin densities seen in surface views of F-actin-tropomyosin reconstructions. The functional implications of the F-actin-tropomyosin models determined in this work are discussed.
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Affiliation(s)
- Xiaochuan Edward Li
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, Massachusetts, USA
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Frye J, Klenchin VA, Rayment I. Structure of the tropomyosin overlap complex from chicken smooth muscle: insight into the diversity of N-terminal recognition. Biochemistry 2010; 49:4908-20. [PMID: 20465283 DOI: 10.1021/bi100349a] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Tropomyosin is a stereotypical alpha-helical coiled coil that polymerizes to form a filamentous macromolecular assembly that lies on the surface of F-actin. The interaction between the C-terminal and N-terminal segments on adjacent molecules is known as the overlap region. We report here two X-ray structures of the chicken smooth muscle tropomyosin overlap complex. A novel approach was used to stabilize the C-terminal and N-terminal fragments. Globular domains from both the human DNA ligase binding protein XRCC4 and bacteriophage varphi29 scaffolding protein Gp7 were fused to 37 and 28 C-terminal amino acid residues of tropomyosin, respectively, whereas the 29 N-terminal amino acids of tropomyosin were fused to the C-terminal helix bundle of microtubule binding protein EB1. The structures of both the XRCC4 and Gp7 fusion proteins complexed with the N-terminal EB1 fusion contain a very similar helix bundle in the overlap region that encompasses approximately 15 residues. The C-terminal coiled coil opens to allow formation of the helix bundle, which is stabilized by hydrophobic interactions. These structures are similar to that observed in the NMR structure of the rat skeletal overlap complex [Greenfield, N. J., et al. (2006) J. Mol. Biol. 364, 80-96]. The interactions between the N- and C-terminal coiled coils of smooth muscle tropomyosin show significant curvature, which differs somewhat between the two structures and implies flexibility in the overlap complex, at least in solution. This is likely an important attribute that allows tropomyosin to assemble around the actin filaments. These structures provide a molecular explanation for the role of N-acetylation in the assembly of native tropomyosin.
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Affiliation(s)
- Jeremiah Frye
- Department of Biochemistry, University of Wisconsin, Madison, Wisconsin 53706, USA
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