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Reiser PJ. Current understanding of conventional and novel co-expression patterns of mammalian sarcomeric myosin heavy chains and light chains. Arch Biochem Biophys 2018; 662:129-133. [PMID: 30528779 DOI: 10.1016/j.abb.2018.12.009] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2018] [Revised: 10/31/2018] [Accepted: 12/04/2018] [Indexed: 10/27/2022]
Abstract
A central tenet of muscle physiology that has accrued from several decades of intense investigations is that myosin, and the vast set of isoforms that constitute its six subunits, is a major regulator of contractile properties of smooth, cardiac and skeletal muscle. Two frequent questions are (1) how many myosin heavy chain (MyHC) isoforms and myosin light chain (MLC) isoforms are expressed in mammalian striated muscles and (2) which isoforms of MyHC and MLC are expressed, at the protein level, with each other - that is, what patterns of co-expression exist in single striated muscle fibers? The answer to the former question is straightforward: eleven MyHC isoforms and nine MLC isoforms, are expressed in a developmentally-regulated and muscle-specific manner. The answer to the latter question, on the other hand, is not clear-cut. The observed number of MyHC and MLC isoform combinations among single fibers is far less than the total number of potential permutations, indicating strict regulation of expression in individual muscle cells. This article provides a review of the current and still evolving understanding of the complexity of muscle fiber types defined on the basis of expression patterns of MyHC and MLC isoforms that constitute an intact functioning molecule.
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Affiliation(s)
- Peter J Reiser
- Division of Biosciences, College of Dentistry, The Ohio State University, 305 West 12th Avenue, Columbus, OH, 43210, USA.
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2
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Abstract
The myosin holoenzyme is a multimeric protein complex consisting of heavy chains and light chains. Myosin light chains are calmodulin family members which are crucially involved in the mechanoenzymatic function of the myosin holoenzyme. This review examines the diversity of light chains within the myosin superfamily, discusses interactions between the light chain and the myosin heavy chain as well as regulatory and structural functions of the light chain as a subunit of the myosin holoenzyme. It covers aspects of the myosin light chain in the localization of the myosin holoenzyme, protein-protein interactions and light chain binding to non-myosin binding partners. Finally, this review challenges the dogma that myosin regulatory and essential light chain exclusively associate with conventional myosin heavy chains while unconventional myosin heavy chains usually associate with calmodulin.
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Affiliation(s)
- Sarah M Heissler
- a Laboratory of Molecular Physiology; National Heart, Lung, and Blood Institute; National Institutes of Health ; Bethesda , MD USA
| | - James R Sellers
- a Laboratory of Molecular Physiology; National Heart, Lung, and Blood Institute; National Institutes of Health ; Bethesda , MD USA
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3
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Martin C, Gunning P. Isoform sorting of tropomyosins. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2008; 644:187-200. [PMID: 19209823 DOI: 10.1007/978-0-387-85766-4_15] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Cytoskeletal tropomyosin (Tm) isoforms show extensive intracellular sorting, resulting in spatially distinct actin-filament populations. Sorting of Tm isoforms has been observed in a number of cell types, including fibroblasts, epithelial cells, osteoclasts, neurons and muscle cells. Different Tm isoforms have differential impact on the activity of a number of actin-binding proteins and can therefore differentially regulate actin filament function. Functionally distinct sub-populations of actin filaments can therefore be defined on the basis of the Tm isoforms associated with the filaments. The mechanisms that underlie Tm sorting are not yet well understood, but it is clear that Tm sorting is a very fluid and dynamic process, with changes in sorting occurring throughout development and cell differentiation. For this reason, it is unlikely that Tm localization is determined by an intrinsic sorting signal that directs particular isoforms to a single geographical location. Rather, a molecular sink model where isoforms accumulate in actin-based structures where they have the highest affinity, is most consistent with current data. This model would predict Tm sorting to be influenced by changes to actin filament dynamics and organization and collaboration with other actin-binding proteins.
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Affiliation(s)
- Claire Martin
- Oncology Research Unit, The Children's Hospital at Westmead, Westmead, New South Wales, Australia
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4
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Schoenauer R, Lange S, Hirschy A, Ehler E, Perriard JC, Agarkova I. Myomesin 3, a novel structural component of the M-band in striated muscle. J Mol Biol 2007; 376:338-51. [PMID: 18177667 DOI: 10.1016/j.jmb.2007.11.048] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2007] [Revised: 11/12/2007] [Accepted: 11/13/2007] [Indexed: 10/22/2022]
Abstract
The M-band is the cytoskeletal structure that cross-links the myosin and titin filaments in the middle of the sarcomere. Apart from the myosin tails and the C-termini of titin, only two closely related structural proteins had been detected at the M-band so far, myomesin and M-protein. However, electron microscopy studies revealed structural features that do not correlate with the expression of these two proteins, indicating the presence of unknown constituents in the M-band. Using comparative sequence analysis, we have identified a third member of this gene family, myomesin 3, and characterised its biological properties. Myomesin 3 is predicted to consist of a unique head domain followed by a conserved sequence of either fibronectin- or immunoglobulin-like domains, similarly to myomesin 3 and M-protein. While all three members of the myomesin family are localised to the M-band of the sarcomere, each member shows its specific expression pattern. In contrast to myomesin, which is ubiquitously expressed in all striated muscles, and M-protein, whose expression is restricted to adult heart and fast-twitch skeletal muscle, myomesin 3 can be detected mainly in intermediate speed fibers of skeletal muscle. In analogy to myomesin, myomesin 3 targets to the M-band region of the sarcomere via its N-terminal part and forms homodimers via its C-terminal domain. However, despite the high degree of homology, no heterodimer between distinct members of the myomesin gene family can be detected. We propose that each member of the myomesin family is a component of one of the distinct ultrastructures, the M-lines, which modulate the mechanical properties of the M-bands in different muscle types.
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Affiliation(s)
- Roman Schoenauer
- Institute of Cell Biology, Swiss Federal Institute of Technology, ETH-Hönggerberg, CH-8093 Zurich, Switzerland
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5
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Hernandez OM, Jones M, Guzman G, Szczesna-Cordary D. Myosin essential light chain in health and disease. Am J Physiol Heart Circ Physiol 2006; 292:H1643-54. [PMID: 17142342 DOI: 10.1152/ajpheart.00931.2006] [Citation(s) in RCA: 92] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The essential light chain of myosin (ELC) is known to be important for structural stability of the alpha-helical lever arm domain of the myosin head, but its function in striated muscle contraction is poorly understood. Two ELC isoforms are expressed in fast skeletal muscle, a long isoform and its NH(2)-terminal approximately 40 amino acid shorter counterpart, whereas only the long ELC is observed in the heart. Biochemical and structural studies revealed that the NH(2)-terminus of the long ELC can make direct contacts with actin, but the effects of the ELC on the affinity of myosin for actin, ATPase, force, and the kinetics of force generating myosin cross-bridges are inconclusive. Myosin containing the long ELC has been shown to have slower cross-bridge kinetics than myosin with the short isoform. A difference was also reported among myosins with long isoforms. Increased shortening velocity was observed in atrial compared with ventricular muscle fibers. The common findings suggest that ELC provides the fine tuning of the myosin motor function, which is regulated in an isoform and tissue-dependent manner. The functional importance of the ELC is further implicated by the discovery of ELC mutations associated with Familial Hypertrophic Cardiomyopathy. The pathological phenotypes vary in severity, but more notably, almost all ELC mutations result in sudden cardiac death at a young age. This review summarizes the functional roles of striated muscle ELC in normal healthy muscle and in disease. Transgenic animal models and phenotypic characterization of ELC-mediated remodeling of the heart are also discussed.
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Affiliation(s)
- Olga M Hernandez
- Department of Molecular and Cellular Pharmacology, University of Miami, Leonard M. Miller School of Medicine, Miami Florida 33136, USA
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6
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Khan MM, Komiyama M. The second EF-hand is responsible for the isoform-specific sorting of myosin essential light chain. Cell Struct Funct 2001; 26:243-51. [PMID: 11699641 DOI: 10.1247/csf.26.243] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
It has been known that isoforms of myosin essential light chain (LC) exhibit the isoform-specific sorting within cardiac myocytes and fibroblasts. In order to analyze which domain of LC is responsible for the sorting, various chimeric cDNA constructs between human nonmuscle isoform (LC3nm) and chicken fast skeletal muscle isoform (LC3f) were generated and expressed in cultured chicken cardiac myocytes. If chimeras contained LC3f sequence at the place that was restricted by BssHII and PstI, they were preferentially sorted to sarcomeres and precisely localized at A-bands, and their incorporation levels into the A-bands were identical with that of the wild type LC3f. However, other chimeras were distributed throughout the cytoplasm like the wild type LC3nm. Comparison of amino acid sequences revealed that 12 amino acids are different between chicken LC3f and human LC3nm in the BssHII-PstI fragment, and these amino acids are located within the second EF-hand of LC. These results indicated that the second EF-hand is responsible for the isoform-specific sorting of LC. Although the second EF-hand is not included in the key contacts with myosin heavy chain, it is supposed that this domain is important for the relative disposition of neighboring domains. Thus, the 12 amino acids in the second EF-hand might play a key role for modulation of overall configuration of LC, thereby influencing the precise association of the key contacts.
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Affiliation(s)
- M M Khan
- Department of Bioenvironmental Medicine, Graduate School of Medicine, Chiba University, Japan
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7
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Young P, Ehler E, Gautel M. Obscurin, a giant sarcomeric Rho guanine nucleotide exchange factor protein involved in sarcomere assembly. J Cell Biol 2001; 154:123-36. [PMID: 11448995 PMCID: PMC2196875 DOI: 10.1083/jcb.200102110] [Citation(s) in RCA: 230] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Vertebrate-striated muscle is assumed to owe its remarkable order to the molecular ruler functions of the giant modular signaling proteins, titin and nebulin. It was believed that these two proteins represented unique results of protein evolution in vertebrate muscle. In this paper we report the identification of a third giant protein from vertebrate muscle, obscurin, encoded on chromosome 1q42. Obscurin is approximately 800 kD and is expressed specifically in skeletal and cardiac muscle. The complete cDNA sequence of obscurin reveals a modular architecture, consisting of >67 intracellular immunoglobulin (Ig)- or fibronectin-3-like domains with multiple splice variants. A large region of obscurin shows a modular architecture of tandem Ig domains reminiscent of the elastic region of titin. The COOH-terminal region of obscurin interacts via two specific Ig-like domains with the NH(2)-terminal Z-disk region of titin. Both proteins coassemble during myofibrillogenesis. During the progression of myofibrillogenesis, all obscurin epitopes become detectable at the M band. The presence of a calmodulin-binding IQ motif, and a Rho guanine nucleotide exchange factor domain in the COOH-terminal region suggest that obscurin is involved in Ca(2+)/calmodulin, as well as G protein-coupled signal transduction in the sarcomere.
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MESH Headings
- Amino Acid Motifs
- Amino Acid Sequence
- Animals
- Blotting, Western
- Calmodulin/metabolism
- Cell Adhesion
- Cells, Cultured
- Chick Embryo
- Chromosomes, Human, Pair 1
- Cloning, Molecular
- DNA, Complementary/metabolism
- Epitopes
- Gene Library
- Guanine Nucleotide Exchange Factors/chemistry
- Guanine Nucleotide Exchange Factors/physiology
- Humans
- Immunoglobulins/metabolism
- Microscopy, Confocal
- Models, Genetic
- Molecular Sequence Data
- Muscle Proteins/chemistry
- Muscle Proteins/physiology
- Muscle, Skeletal/metabolism
- Myocardium/metabolism
- Phylogeny
- Protein Binding
- Protein Serine-Threonine Kinases
- Protein Structure, Tertiary
- Rats
- Rats, Wistar
- Rho Guanine Nucleotide Exchange Factors
- Sarcomeres/chemistry
- Sequence Homology, Amino Acid
- Signal Transduction
- Tissue Distribution
- Transfection
- rho GTP-Binding Proteins/chemistry
- rho GTP-Binding Proteins/physiology
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Affiliation(s)
- P Young
- European Molecular Biology Laboratory, Structural Biology Division, 69117 Heidelberg, Germany
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8
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van der Ven PF, Wiesner S, Salmikangas P, Auerbach D, Himmel M, Kempa S, Hayess K, Pacholsky D, Taivainen A, Schröder R, Carpén O, Fürst DO. Indications for a novel muscular dystrophy pathway. gamma-filamin, the muscle-specific filamin isoform, interacts with myotilin. J Cell Biol 2000; 151:235-48. [PMID: 11038172 PMCID: PMC2192634 DOI: 10.1083/jcb.151.2.235] [Citation(s) in RCA: 149] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
gamma-Filamin, also called ABP-L, is a filamin isoform that is specifically expressed in striated muscles, where it is predominantly localized in myofibrillar Z-discs. A minor fraction of the protein shows subsarcolemmal localization. Although gamma-filamin has the same overall structure as the two other known isoforms, it is the only isoform that carries a unique insertion in its immunoglobulin (Ig)-like domain 20. Sequencing of the genomic region encoding this part of the molecule shows that this insert is encoded by an extra exon. Transient transfections of the insert-bearing domain in skeletal muscle cells and cardiomyocytes show that this single domain is sufficient for targeting to developing and mature Z-discs. The yeast two-hybrid method was used to identify possible binding partners for the insert-bearing Ig-like domain 20 of gamma-filamin. The two Ig-like domains of the recently described alpha-actinin-binding Z-disc protein myotilin were found to interact directly with this filamin domain, indicating that the amino-terminal end of gamma-filamin may be indirectly anchored to alpha-actinin in the Z-disc via myotilin. Since defects in the myotilin gene were recently reported to cause a form of autosomal dominant limb-girdle muscular dystrophy, our findings provide a further contribution to the molecular understanding of this disease.
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Affiliation(s)
- P F van der Ven
- Department of Cell Biology, University of Potsdam, D-14471 Potsdam, Germany.
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9
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Komiyama M, Khan MM, Toyota N, Shimada Y. Fast skeletal muscle isoforms exhibit the highest incorporation level into myofibrils and stress fibers among members of myosin alkali light chain isoform family. Cell Struct Funct 2000; 25:141-8. [PMID: 10984097 DOI: 10.1247/csf.25.141] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Isoproteins of myosin alkali light chain (LC) were co-expressed in cultured chicken cardiomyocytes and fibroblasts and their incorporation levels into myofibrils and stress fibers were compared among members of the LC isoform family. In order to distinguish each isoform from the other, cDNAs of LC isoforms were tagged with different epitopes. Expressed LCs were detected with antibodies to the tags and their distribution was analyzed by confocal microscopy. In cardiomyocytes, the incorporation level of LC into myofibrils was shown to increase in the order from nonmuscle isoform (LC3nm), to slow skeletal muscle isoform (LC1sa), to slow skeletal/ventricular muscle isoform (LC1sb), and to fast skeletal muscle isoforms (LC1f and LC3f). Thus, the hierarchal order of the LC affinity for the cardiac myosin heavy chain (MHC) is identical to that obtained in the rat (Komiyama et al., 1996. J. Cell Sci., 109: 2089-2099), suggesting that this order may be common for taxonomic animal classes. In fibroblasts, the affinity of LC for the nonmuscle MHC in stress fibers was found to increase in the order from LC3nm, to LC1sb, to LC1sa, and to LC1f and LC3f. This order for the nonmuscle MHC is partly different from that for the cardiac MHC. This indicates that the order of the affinity of LC isoproteins for MHC varies depending on the MHC isoform. Further, for both the cardiac and nonmuscle MHCs, the fast skeletal muscle LCs exhibited the highest affinity. This suggests that the fast skeletal muscle LCs may be evolved isoforms possessing the ability to associate tightly with a variety of MHC isoforms.
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Affiliation(s)
- M Komiyama
- Department of Anatomy and Cell Biology, School of Medicine, Chiba University, Japan.
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10
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Zuppinger C, Schaub MC, Eppenberger HM. Dynamics of early contact formation in cultured adult rat cardiomyocytes studied by N-cadherin fused to green fluorescent protein. J Mol Cell Cardiol 2000; 32:539-55. [PMID: 10756112 DOI: 10.1006/jmcc.1999.1086] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We investigated dynamic events during the formation of intercalated disc-like structures of adult rat cardiomyocytes (ARC) in long-term culture. Given the complexity of ARC cytoIarchitecture after de- and re-differentiation, and the non-uniform morphological development of individual cells, green fluorescent protein (GFP) technology was used to track N-cadherin in living cells. Sorting and functionality of the GFP fusion protein was tested in ARC. Isolated ARC were micro-injected with the expression construct at the onset of spreading in culture, and the fluorescence signals were tracked during contact formation and in fully redifferentiated living cells. The first contact sites were found to be established by cellular protrusions, which were marked by an ultrastructure similar to microspikes and probably have a role as exploratory units in the spreading phase. Subsequently, initial contact sites served as anchorage for the most prominent stress fibre-like structures. The fusion protein appeared before connexin-43 at newly established cell-cell contacts. Membrane invaginations at the sarcolemma facing the substratum of cultured ARC may be responsible for the appearance of a striped pattern of N-cadherin and other adherens junction proteins away from intercalated disc-like structures. The stripes were immobile in redifferentiated cells, while the distinct small fluorescent particles in the cell body were found to move directionally at speeds around 10 micro m/min. These results contribute to the understanding of the mechanisms of cell-cell contact formation of adult cardiomyocytes, which is a prerequisite for any future implantation technology.
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Affiliation(s)
- C Zuppinger
- Institute of Cell Biology, Federal Institute of Technology (ETH), Zurich, CH-8093, Switzerland
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11
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Weiss A, Schiaffino S, Leinwand LA. Comparative sequence analysis of the complete human sarcomeric myosin heavy chain family: implications for functional diversity. J Mol Biol 1999; 290:61-75. [PMID: 10388558 DOI: 10.1006/jmbi.1999.2865] [Citation(s) in RCA: 160] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The conventional myosin motor proteins that drive mammalian skeletal and cardiac muscle contraction include eight sarcomeric myosin heavy chain (MyHC) isoforms. Six skeletal MyHCs are encoded by genes found in tightly linked clusters on human and mouse chromosomes 17 and 11, respectively. The full coding regions of only two out of six mammalian skeletal MyHCs had been sequenced prior to this work. In an effort to assess the extent of sequence diversity within the human MyHC family we present new full-length coding sequences corresponding to four additional human genes: MyHC-IIb, MyHC-extraocular, MyHC-IIa and MyHC-IIx/d. This represents the first opportunity to compare the full coding sequences of all eight sarcomeric MyHC isoforms within a vertebrate organism. Sequence variability has been analyzed in the context of available structure/function data with an emphasis on potential functional diversity within the family. Results indicate that functional diversity among MyHCs is likely to be accomplished by having small pockets of sequence diversity in an otherwise highly conserved molecule.
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Affiliation(s)
- A Weiss
- Department of Microbiology and Immunology, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, 10461, USA
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12
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Auerbach D, Bantle S, Keller S, Hinderling V, Leu M, Ehler E, Perriard JC. Different domains of the M-band protein myomesin are involved in myosin binding and M-band targeting. Mol Biol Cell 1999; 10:1297-308. [PMID: 10233145 PMCID: PMC25262 DOI: 10.1091/mbc.10.5.1297] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Myomesin is a 185-kDa protein located in the M-band of striated muscle where it interacts with myosin and titin, possibly connecting thick filaments with the third filament system. By using expression of epitope-tagged myomesin fragments in cultured cardiomyocytes and biochemical binding assays, we could demonstrate that the M-band targeting activity and the myosin-binding site are located in different domains of the molecule. An N-terminal immunoglobulin-like domain is sufficient for targeting to the M-band, but solid-phase overlay assays between individual N-terminal domains and the thick filament protein myosin revealed that the unique head domain contains the myosin-binding site. When expressed in cardiomyocytes, the head domains of rat and chicken myomesin showed species-specific differences in their incorporation pattern. The head domain of rat myomesin localized to a central area within the A-band, whereas the head domain of chicken myomesin was diffusely distributed in the cytoplasm. We therefore conclude that the head domain of myomesin binds to myosin but that this affinity is not sufficient for the restriction of the domain to the M-band in vivo. Instead, the neighboring immunoglobulin-like domain is essential for the precise incorporation of myomesin into the M-band, possibly because of interaction with a yet unknown protein of the sarcomere.
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Affiliation(s)
- D Auerbach
- Institute of Cell Biology, Swiss Federal Institute of Technology, ETH Hönggerberg, CH-8093 Zürich
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13
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Gruen M, Gautel M. Mutations in beta-myosin S2 that cause familial hypertrophic cardiomyopathy (FHC) abolish the interaction with the regulatory domain of myosin-binding protein-C. J Mol Biol 1999; 286:933-49. [PMID: 10024460 DOI: 10.1006/jmbi.1998.2522] [Citation(s) in RCA: 185] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The myosin filaments of striated muscle contain a family of enigmatic myosin-binding proteins (MyBP), MyBP-C and MyBP-H. These modular proteins of the intracellular immunoglobulin superfamily contain unique domains near their N termini. The N-terminal domain of cardiac MyBP-C, the MyBP-C motif, contains additional phosphorylation sites and may regulate contraction in a phosphorylation dependent way. In contrast to the C terminus, which binds to the light meromyosin portion of the myosin rod, the interactions of this domain are unknown. We demonstrate that fragments of MyBP-C containing the MyBP-C motif localise to the sarcomeric A-band in cardiomyocytes and isolated myofibrils, without affecting sarcomere structure. The binding site for the MyBP-C motif resides in the N-terminal 126 residues of the S2 segment of the myosin rod. In this region, several mutations in beta-myosin are associated with FHC; however, their molecular implications remained unclear. We show that two representative FHC mutations in beta-myosin S2, R870H and E924K, drastically reduce MyBP-C binding (Kd approximately 60 microM for R870H compared with a Kd of approximately 5 microM for the wild-type) down to undetectable levels (E924K). These mutations do not affect the coiled-coil structure of myosin. We suggest that the regulatory function of MyBP-C is mediated by the interaction with S2, and that mutations in beta-myosin S2 may act by altering the interactions with MyBP-C.
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Affiliation(s)
- M Gruen
- Max-Planck-Institut für Molekulare Physiologie, Rheinlanddamm 201, Dortmund, 44139, Germany
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14
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Suomalainen M, Nakano MY, Keller S, Boucke K, Stidwill RP, Greber UF. Microtubule-dependent plus- and minus end-directed motilities are competing processes for nuclear targeting of adenovirus. J Cell Biol 1999; 144:657-72. [PMID: 10037788 PMCID: PMC2132937 DOI: 10.1083/jcb.144.4.657] [Citation(s) in RCA: 351] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
Adenovirus (Ad) enters target cells by receptor-mediated endocytosis, escapes to the cytosol, and then delivers its DNA genome into the nucleus. Here we analyzed the trafficking of fluorophore-tagged viruses in HeLa and TC7 cells by time-lapse microscopy. Our results show that native or taxol-stabilized microtubules (MTs) support alternating minus- and plus end-directed movements of cytosolic virus with elementary speeds up to 2.6 micrometer/s. No directed movement was observed in nocodazole-treated cells. Switching between plus- and minus end-directed elementary speeds at frequencies up to 1 Hz was observed in the periphery and near the MT organizing center (MTOC) after recovery from nocodazole treatment. MT-dependent motilities allowed virus accumulation near the MTOC at population speeds of 1-10 micrometer/min, depending on the cell type. Overexpression of p50/dynamitin, which is known to affect dynein-dependent minus end-directed vesicular transport, significantly reduced the extent and the frequency of minus end-directed migration of cytosolic virus, and increased the frequency, but not the extent of plus end-directed motility. The data imply that a single cytosolic Ad particle engages with two types of MT-dependent motor activities, the minus end- directed cytoplasmic dynein and an unknown plus end- directed activity.
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Affiliation(s)
- M Suomalainen
- Institute of Zoology, University of Zürich, CH-8057 Zürich, Switzerland
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15
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Abstract
Epitope tagging is a recombinant DNA method by which a protein encoded by a cloned gene is made immunoreactive to a known antibody. This review discusses the major advantages and limitations of epitope tagging and describes a number of recent applications. Major areas of application include monitoring protein expression, localizing proteins at the cellular and subcellular levels, and protein purification, as well as the analysis of protein topology, dynamics and interactions. Recently the method has also found use in transgenic and gene therapy studies and in the emerging fields of functional genomics and proteomics.
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Affiliation(s)
- J W Jarvik
- Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA.
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16
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Helfman DM, Berthier C, Grossman J, Leu M, Ehler E, Perriard E, Perriard JC. Nonmuscle tropomyosin-4 requires coexpression with other low molecular weight isoforms for binding to thin filaments in cardiomyocytes. J Cell Sci 1999; 112 ( Pt 3):371-80. [PMID: 9885290 DOI: 10.1242/jcs.112.3.371] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
Vertebrate tropomyosins (TMs) are expressed from four genes, and at least 18 distinct isoforms are generated via a complex pattern of alternative RNA splicing and alternative promoters. The functional significance of this isoform diversity is largely unknown and it remains to be determined whether specific isoforms are required for assembly and integration into distinct actin-containing structures. The ability of nonmuscle (TM-1, -2, -3, -4, -5(NM1), -5a or -5b) and striated muscle (skeletal muscle (α)-TM) isoforms to incorporate into actin filaments of neonatal rat cardiomyocytes (NRCs) was studied using expression plasmids containing TM-fusions with GFP (green fluorescent protein) as well as with VSV- or HA-epitope tags. All isoforms, except of fibroblast TM-4, were able to incorporate into the I-band of NRCs. When TM-4 was co-transfected with other low molecular weight (LMW) isoforms of TM (TM-5, TM-5a and TM-5b), it was able to incorporate into sarcomeres of NRCs. This result was not obtained when TM-4 was co-transfected with high molecular weight (HMW) TMs (TM-1, TM-2 or skeletal muscle (α)-TM). These data demonstrate that the ability of TM-4 to bind to actin filaments can be specifically influenced by its interaction with other LMW TM isoforms. In addition, cells that incorporated the muscle or nonmuscle GFP-TMs into their sarcomeres continued to beat and exhibited sarcomeric contraction. These studies provide the first in vivo demonstration of synergistic effects between TM isoforms for binding to actin filaments. These results have important implications in understanding actin filament dynamics in nonmuscle cell systems, especially during development and in transformed cells, where alterations in the ratio of different LMW isoforms might lead to changes in their interactions with actin filaments. Furthermore, these studies demonstrate that GFP-TM can be used to study thin-filament dynamics in muscle cells and actin filament dynamics in nonmuscle cells.
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Affiliation(s)
- D M Helfman
- Cold Spring Harbor Laboratory, PO Box 100, Cold Spring Harbor, New York, USA.
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Gunning P, Weinberger R, Jeffrey P, Hardeman E. Isoform sorting and the creation of intracellular compartments. Annu Rev Cell Dev Biol 1999; 14:339-72. [PMID: 9891787 DOI: 10.1146/annurev.cellbio.14.1.339] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
The generation of isoforms via gene duplication and alternative splicing has been a valuable evolutionary tool for the creation of biological diversity. In addition to the formation of molecules with related but different functional characteristics, it is now apparent that isoforms can be segregated into different intracellular sites within the same cell. Sorting has been observed in a wide range of genes, including those encoding structural molecules, receptors, channels, enzymes, and signaling molecules. This results in the creation of intracellular compartments that (a) can be independently controlled and (b) have different functional properties. The sorting mechanisms are likely to operate at the level of both proteins and mRNAs. Isoform sorting may be an important consequence of the evolution of isoforms and is likely to have contributed to the diversity of functional properties within groups of isoforms.
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Affiliation(s)
- P Gunning
- Oncology Research Unit, New Children's Hospital, Parramatta, NSW, Australia.
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Becker KD, Gottshall KR, Hickey R, Perriard JC, Chien KR. Point mutations in human beta cardiac myosin heavy chain have differential effects on sarcomeric structure and assembly: an ATP binding site change disrupts both thick and thin filaments, whereas hypertrophic cardiomyopathy mutations display normal assembly. J Cell Biol 1997; 137:131-40. [PMID: 9105042 PMCID: PMC2139848 DOI: 10.1083/jcb.137.1.131] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/1996] [Revised: 01/14/1997] [Indexed: 02/04/2023] Open
Abstract
Hypertrophic cardiomyopathy is a human heart disease characterized by increased ventricular mass, focal areas of fibrosis, myocyte, and myofibrillar disorganization. This genetically dominant disease can be caused by mutations in any one of several contractile proteins, including beta cardiac myosin heavy chain (beta MHC). To determine whether point mutations in human beta MHC have direct effects on interfering with filament assembly and sarcomeric structure, full-length wild-type and mutant human beta MHC cDNAs were cloned and expressed in primary cultures of neonatal rat ventricular cardiomyocytes (NRC) under conditions that promote myofibrillogenesis. A lysine to arginine change at amino acid 184 in the consensus ATP binding sequence of human beta MHC resulted in abnormal subcellular localization and disrupted both thick and thin filament structure in transfected NRC. Diffuse beta MHC K184R protein appeared to colocalize with actin throughout the myocyte, suggesting a tight interaction of these two proteins. Human beta MHC with S472V mutation assembled normally into thick filaments and did not affect sarcomeric structure. Two mutant myosins previously described as causing human hypertrophic cardiomyopathy, R249Q and R403Q, were competent to assemble into thick filaments producing myofibrils with well defined I bands, A bands, and H zones. Coexpression and detection of wild-type beta MHC and either R249Q or R403Q proteins in the same myocyte showed these proteins are equally able to assemble into the sarcomere and provided no discernible differences in subcellular localization. Thus, human beta MHC R249Q and R403Q mutant proteins were readily incorporated into NRC sarcomeres and did not disrupt myofilament formation. This study indicates that the phenotype of myofibrillar disarray seen in HCM patients which harbor either of these two mutations may not be directly due to the failure of the mutant myosin heavy chain protein to assemble and form normal sarcomeres, but may rather be a secondary effect possibly resulting from the chronic stress of decreased beta MHC function.
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Affiliation(s)
- K D Becker
- Department of Medicine, American Heart Association Bugher Foundation Center for Molecular Biology, University of California, San Diego, La Jolla 92093, USA.
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