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Karpicheva OE, Avrova SV, Bogdanov AL, Sirenko VV, Redwood CS, Borovikov YS. Molecular Mechanisms of Deregulation of Muscle Contractility Caused by the R168H Mutation in TPM3 and Its Attenuation by Therapeutic Agents. Int J Mol Sci 2023; 24:ijms24065829. [PMID: 36982903 PMCID: PMC10051413 DOI: 10.3390/ijms24065829] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2023] [Revised: 03/13/2023] [Accepted: 03/13/2023] [Indexed: 03/30/2023] Open
Abstract
The substitution for Arg168His (R168H) in γ-tropomyosin (TPM3 gene, Tpm3.12 isoform) is associated with congenital muscle fiber type disproportion (CFTD) and muscle weakness. It is still unclear what molecular mechanisms underlie the muscle dysfunction seen in CFTD. The aim of this work was to study the effect of the R168H mutation in Tpm3.12 on the critical conformational changes that myosin, actin, troponin, and tropomyosin undergo during the ATPase cycle. We used polarized fluorescence microscopy and ghost muscle fibers containing regulated thin filaments and myosin heads (myosin subfragment-1) modified with the 1,5-IAEDANS fluorescent probe. Analysis of the data obtained revealed that a sequential interdependent conformational-functional rearrangement of tropomyosin, actin and myosin heads takes place when modeling the ATPase cycle in the presence of wild-type tropomyosin. A multistep shift of the tropomyosin strands from the outer to the inner domain of actin occurs during the transition from weak to strong binding of myosin to actin. Each tropomyosin position determines the corresponding balance between switched-on and switched-off actin monomers and between the strongly and weakly bound myosin heads. At low Ca2+, the R168H mutation was shown to switch some extra actin monomers on and increase the persistence length of tropomyosin, demonstrating the freezing of the R168HTpm strands close to the open position and disruption of the regulatory function of troponin. Instead of reducing the formation of strong bonds between myosin heads and F-actin, troponin activated it. However, at high Ca2+, troponin decreased the amount of strongly bound myosin heads instead of promoting their formation. Abnormally high sensitivity of thin filaments to Ca2+, inhibition of muscle fiber relaxation due to the appearance of the myosin heads strongly associated with F-actin, and distinct activation of the contractile system at submaximal concentrations of Ca2+ can lead to muscle inefficiency and weakness. Modulators of troponin (tirasemtiv and epigallocatechin-3-gallate) and myosin (omecamtiv mecarbil and 2,3-butanedione monoxime) have been shown to more or less attenuate the negative effects of the tropomyosin R168H mutant. Tirasemtiv and epigallocatechin-3-gallate may be used to prevent muscle dysfunction.
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Affiliation(s)
- Olga E Karpicheva
- Institute of Cytology, Russian Academy of Sciences, 4 Tikhoretsky Av., St. Petersburg 194064, Russia
| | - Stanislava V Avrova
- Institute of Cytology, Russian Academy of Sciences, 4 Tikhoretsky Av., St. Petersburg 194064, Russia
| | - Andrey L Bogdanov
- Institute of Cytology, Russian Academy of Sciences, 4 Tikhoretsky Av., St. Petersburg 194064, Russia
| | - Vladimir V Sirenko
- Institute of Cytology, Russian Academy of Sciences, 4 Tikhoretsky Av., St. Petersburg 194064, Russia
| | - Charles S Redwood
- Radcliffe Department of Medicine, University of Oxford, John Radcliffe Hospital, Oxford OX3 9DU, UK
| | - Yurii S Borovikov
- Institute of Cytology, Russian Academy of Sciences, 4 Tikhoretsky Av., St. Petersburg 194064, Russia
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Reindl T, Giese S, Greve JN, Reinke PY, Chizhov I, Latham SL, Mulvihill DP, Taft MH, Manstein DJ. Distinct actin–tropomyosin cofilament populations drive the functional diversification of cytoskeletal myosin motor complexes. iScience 2022; 25:104484. [PMID: 35720262 PMCID: PMC9204724 DOI: 10.1016/j.isci.2022.104484] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2022] [Revised: 05/02/2022] [Accepted: 05/24/2022] [Indexed: 11/02/2022] Open
Abstract
The effects of N-terminal acetylation of the high molecular weight tropomyosin isoforms Tpm1.6 and Tpm2.1 and the low molecular weight isoforms Tpm1.12, Tpm3.1, and Tpm4.2 on the actin affinity and the thermal stability of actin-tropomyosin cofilaments are described. Furthermore, we show how the exchange of cytoskeletal tropomyosin isoforms and their N-terminal acetylation affects the kinetic and chemomechanical properties of cytoskeletal actin-tropomyosin-myosin complexes. Our results reveal the extent to which the different actin-tropomyosin-myosin complexes differ in their kinetic and functional properties. The maximum sliding velocity of the actin filament as well as the optimal motor density for continuous unidirectional movement, parameters that were previously considered to be unique and invariant properties of each myosin isoform, are shown to be influenced by the exchange of the tropomyosin isoform and the N-terminal acetylation of tropomyosin. Tpm diversity is largely determined by sequences contributing to the overlap region Global sequence differences are of greater importance than variable exon 6 usage Tpm isoforms confer distinctly altered properties to cytoskeletal myosin motors Cytoskeletal myosins are differentially affected by N-terminal acetylation of Tpm
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Karpicheva OE. Hallmark Features of the Tropomyosin
Regulatory Function in Several Variants of Congenital Myopathy. J EVOL BIOCHEM PHYS+ 2021. [DOI: 10.1134/s0022093021030133] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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4
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Janco M, Rynkiewicz MJ, Li L, Hook J, Eiffe E, Ghosh A, Böcking T, Lehman WJ, Hardeman EC, Gunning PW. Molecular integration of the anti-tropomyosin compound ATM-3507 into the coiled coil overlap region of the cancer-associated Tpm3.1. Sci Rep 2019; 9:11262. [PMID: 31375704 PMCID: PMC6677793 DOI: 10.1038/s41598-019-47592-9] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2019] [Accepted: 07/19/2019] [Indexed: 11/30/2022] Open
Abstract
Tropomyosins (Tpm) determine the functional capacity of actin filaments in an isoform-specific manner. The primary isoform in cancer cells is Tpm3.1 and compounds that target Tpm3.1 show promising results as anti-cancer agents both in vivo and in vitro. We have determined the molecular mechanism of interaction of the lead compound ATM-3507 with Tpm3.1-containing actin filaments. When present during co-polymerization of Tpm3.1 with actin, 3H-ATM-3507 is incorporated into the filaments and saturates at approximately one molecule per Tpm3.1 dimer and with an apparent binding affinity of approximately 2 µM. In contrast, 3H-ATM-3507 is poorly incorporated into preformed Tpm3.1/actin co-polymers. CD spectroscopy and thermal melts using Tpm3.1 peptides containing the C-terminus, the N-terminus, and a combination of the two forming the overlap junction at the interface of adjacent Tpm3.1 dimers, show that ATM-3507 shifts the melting temperature of the C-terminus and the overlap junction, but not the N-terminus. Molecular dynamic simulation (MDS) analysis predicts that ATM-3507 integrates into the 4-helix coiled coil overlap junction and in doing so, likely changes the lateral movement of Tpm3.1 across the actin surface resulting in an alteration of filament interactions with actin binding proteins and myosin motors, consistent with the cellular impact of ATM-3507.
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Affiliation(s)
- Miro Janco
- School of Medical Sciences, University of New South Wales Sydney, Sydney, NSW, 2052, Australia
| | - Michael J Rynkiewicz
- Department of Physiology & Biophysics, Boston University School of Medicine, 72 East Concord Street, Boston, MA, 02118, USA
| | - Liang Li
- School of Medical Sciences, University of New South Wales Sydney, Sydney, NSW, 2052, Australia
| | - Jeff Hook
- School of Medical Sciences, University of New South Wales Sydney, Sydney, NSW, 2052, Australia
| | - Eleanor Eiffe
- School of Medical Sciences, University of New South Wales Sydney, Sydney, NSW, 2052, Australia
| | - Anita Ghosh
- Department of Physiology & Biophysics, Boston University School of Medicine, 72 East Concord Street, Boston, MA, 02118, USA
| | - Till Böcking
- Single Molecule Science and ARC Centre of Excellence in Advanced Molecular Imaging, University of New South Wales Sydney, Sydney, NSW, 2052, Australia
| | - William J Lehman
- Department of Physiology & Biophysics, Boston University School of Medicine, 72 East Concord Street, Boston, MA, 02118, USA
| | - Edna C Hardeman
- School of Medical Sciences, University of New South Wales Sydney, Sydney, NSW, 2052, Australia
| | - Peter W Gunning
- School of Medical Sciences, University of New South Wales Sydney, Sydney, NSW, 2052, Australia.
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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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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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Manjunathachar HV, Kumar B, Saravanan BC, Choudhary S, Mohanty AK, Nagar G, Chigure G, Ravi Kumar GVPPS, de la Fuente J, Ghosh S. Identification and characterization of vaccine candidates against Hyalomma anatolicum-Vector of Crimean-Congo haemorrhagic fever virus. Transbound Emerg Dis 2018; 66:422-434. [PMID: 30300470 DOI: 10.1111/tbed.13038] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2018] [Revised: 09/27/2018] [Accepted: 09/30/2018] [Indexed: 12/24/2022]
Abstract
Crimean-Congo haemorrhagic fever (CCHF) is a tick borne viral disease reported from different parts of the world. The distribution of the CCHF cases are linked with the distribution of the principal vector, Hyalomma anatolicum in the ecosystem. Presently, vector control is mainly dependent on repeated application of acaricides, results in partial efficacy and generated acaricide resistant tick strains. Amongst the different components of integrated management programme, immunization of hosts is considered as one of the sustainable component. To restrict CCHF virus spreading, use of anti-Hyalomma vaccines appears as a viable solution. Accordingly, present study was under taken to characterize and evaluate vaccine potential of two conserved molecules, ferritin2 (FER2) and tropomyosin (TPM). Silencing of the genes conferred a cumulative reduction (rejection + unable to engorge) of 61.3% in FER2 and 70.2% in TPM respectively. Furthermore, 44.2% and 72.7% reduction in engorgement weight, 63.6% and 94.9% reduction in egg masses in FER2 and TPM silenced ticks in comparison to LUC-control group was recorded. The recombinant protein, rHaFER2 was characterized as 35 kDa protein with pI of 5.84 and possesses iron binding domains. While rHaTPM is a 51kDa protein with pI of 4.94 having calcium binding domains. Immunization of cross-bred calves by rHaFER2 conferred 51.7% and 51.2% protection against larvae and adults of H. anatolicum challenge infestations. While rHaTPM conferred 63.7% and 66.4% protection against larvae and adults infestations, respectively. The results were comparable with the data generated by RNAi and it clearly showed the possibility for the development of anti-hyalomma vaccine to manage CCHF virus and Theileria annulata infection in human and animals.
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Affiliation(s)
| | - Binod Kumar
- Entomology Laboratory, Division of Parasitology, Indian Veterinary Research Institute (IVRI)-Izatnagar, Bareilly, India
| | | | - Suman Choudhary
- Animal Biotechnology Centre, National Dairy Research Institute, Karnal, Haryana, India
| | - Ashok K Mohanty
- Animal Biotechnology Centre, National Dairy Research Institute, Karnal, Haryana, India
| | - Gaurav Nagar
- Entomology Laboratory, Division of Parasitology, Indian Veterinary Research Institute (IVRI)-Izatnagar, Bareilly, India
| | - Gajanan Chigure
- Entomology Laboratory, Division of Parasitology, Indian Veterinary Research Institute (IVRI)-Izatnagar, Bareilly, India
| | | | - José de la Fuente
- SaBio, Instituto de Investigación en Recursos Cinegéticos IREC (CSIC-UCLM-JCCM), Ciudad Real, Spain.,Department of Veterinary Pathobiology, Center for Veterinary Health Sciences, Oklahoma State University, Stillwater, Oklahoma
| | - Srikant Ghosh
- Entomology Laboratory, Division of Parasitology, Indian Veterinary Research Institute (IVRI)-Izatnagar, Bareilly, India
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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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Rynkiewicz MJ, Prum T, Hollenberg S, Kiani FA, Fagnant PM, Marston SB, Trybus KM, Fischer S, Moore JR, Lehman W. Tropomyosin Must Interact Weakly with Actin to Effectively Regulate Thin Filament Function. Biophys J 2018; 113:2444-2451. [PMID: 29211998 DOI: 10.1016/j.bpj.2017.10.004] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2017] [Revised: 09/13/2017] [Accepted: 10/05/2017] [Indexed: 10/18/2022] Open
Abstract
Elongated tropomyosin, associated with actin-subunits along the surface of thin filaments, makes electrostatic interactions with clusters of conserved residues, K326, K328, and R147, on actin. The association is weak, permitting low-energy cost regulatory movement of tropomyosin across the filament during muscle activation. Interestingly, acidic D292 on actin, also evolutionarily conserved, lies adjacent to the three-residue cluster of basic amino acids and thus may moderate the combined local positive charge, diminishing tropomyosin-actin interaction and facilitating regulatory-switching. Indeed, charge neutralization of D292 is connected to muscle hypotonia in individuals with D292V actin mutations and linked to congenital fiber-type disproportion. Here, the D292V mutation may predispose tropomyosin-actin positioning to a myosin-blocking state, aberrantly favoring muscle relaxation, thus mimicking the low-Ca2+ effect of troponin even in activated muscles. To test this hypothesis, interaction energetics and in vitro function of wild-type and D292V filaments were measured. Energy landscapes based on F-actin-tropomyosin models show the mutation localizes tropomyosin in a blocked-state position on actin defined by a deeper energy minimum, consistent with augmented steric-interference of actin-myosin binding. In addition, whereas myosin-dependent motility of troponin/tropomyosin-free D292V F-actin is normal, motility is dramatically inhibited after addition of tropomyosin to the mutant actin. Thus, D292V-induced blocked-state stabilization appears to disrupt the delicately poised energy balance governing thin filament regulation. Our results validate the premise that stereospecific but necessarily weak binding of tropomyosin to F-actin is required for effective thin filament function.
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Affiliation(s)
- Michael J Rynkiewicz
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, Massachusetts
| | - Thavanareth Prum
- Department of Biological Sciences, University of Massachusetts-Lowell, Lowell, Massachusetts
| | - Stephen Hollenberg
- Department of Biological Sciences, University of Massachusetts-Lowell, Lowell, Massachusetts
| | - Farooq A Kiani
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, Massachusetts
| | - Patricia M Fagnant
- Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, Vermont
| | - Steven B Marston
- National Heart and Lung Institute, Imperial College London, London, United Kingdom
| | - Kathleen M Trybus
- Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, Vermont
| | - Stefan Fischer
- Computational Biochemistry Group, IWR, Heidelberg University, Heidelberg, Germany
| | - Jeffrey R Moore
- Department of Biological Sciences, University of Massachusetts-Lowell, Lowell, Massachusetts
| | - William Lehman
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, Massachusetts.
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Abstract
Tropomyosin is the archetypal-coiled coil, yet studies of its structure and function have proven it to be a dynamic regulator of actin filament function in muscle and non-muscle cells. Here we review aspects of its structure that deviate from canonical leucine zipper coiled coils that allow tropomyosin to bind to actin, regulate myosin, and interact directly and indirectly with actin-binding proteins. Four genes encode tropomyosins in vertebrates, with additional diversity that results from alternate promoters and alternatively spliced exons. At the same time that periodic motifs for binding actin and regulating myosin are conserved, isoform-specific domains allow for specific interaction with myosins and actin filament regulatory proteins, including troponin. Tropomyosin can be viewed as a universal regulator of the actin cytoskeleton that specifies actin filaments for cellular and intracellular functions.
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Rynkiewicz MJ, Fischer S, Lehman W. The propensity for tropomyosin twisting in the presence and absence of F-actin. Arch Biochem Biophys 2016; 609:51-58. [PMID: 27663225 DOI: 10.1016/j.abb.2016.09.008] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2016] [Revised: 09/14/2016] [Accepted: 09/19/2016] [Indexed: 12/15/2022]
Abstract
A canonical model of muscle α-tropomyosin (Tpm1.1), based on molecular-mechanics and electron microscopy of different contractile states, shows that the two-stranded coiled-coiled is pre-bent to present a specific molecular-face to the F-actin filament. This conformation is thought to facilitate both filament assembly and tropomyosin sliding across actin to modulate myosin-binding. However, to bind effectively to actin filaments, the 42 nm-long tropomyosin coiled-coil is not strictly canonical. Here, the mid-region of tropomyosin twists an additional ∼20° in order to better match the F-actin helix. In addition, the N- and C-terminal regions of tropomyosin polymerize head-to-tail to form continuous super-helical cables. In this case, 9 to 10 residue-long overlapping domains between adjacent molecules untwist relative to each other to accommodate orthogonal interactions between chains in the junctional four-helix nexus. Extensive molecular dynamics simulations show that the twisting and untwisting motions of tropomyosin vary appreciably along tropomyosin length, and in particular that substantial terminal domain winding and unwinding occurs whether tropomyosin is bound to F-actin or not. The local and regional twisting and untwisting do not appear to proceed in a concerted fashion, resembling more of a "wringing-type" behavior rather than a rotation.
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Affiliation(s)
- Michael J Rynkiewicz
- Department of Physiology & 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, D69120 Heidelberg, Germany.
| | - William Lehman
- Department of Physiology & Biophysics, Boston University School of Medicine, 72 East Concord Street, Boston, MA 02118, USA.
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12
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Phillips GN, Onuchic JN. Preface to Special Topic on Protein Dynamics: Beyond Static Snapshots in Structural Biology. Struct Dyn 2016; 3:011901. [PMID: 27042685 PMCID: PMC4803324 DOI: 10.1063/1.4942424] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2016] [Accepted: 02/08/2016] [Indexed: 12/02/2022] Open
Affiliation(s)
- George N. Phillips
- Department of BioSciences and Chemistry, Rice University, Houston, Texas 77005, USA
| | - José N. Onuchic
- Center for Theoretical Biological Physics and Department of Physics, Rice University, Houston, Texas 77005, USA
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13
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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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