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Chen L, Chen DF, Dong HL, Liu GL, Wu ZY. A novel frameshift ACTN2 variant causes a rare adult-onset distal myopathy with multi-minicores. CNS Neurosci Ther 2021; 27:1198-1205. [PMID: 34170073 PMCID: PMC8446211 DOI: 10.1111/cns.13697] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2021] [Revised: 06/03/2021] [Accepted: 06/07/2021] [Indexed: 02/07/2023] Open
Abstract
Introduction Distal myopathies are a group of rare muscle disorders characterized by selective or predominant weakness in the feet and/or hands. In 2019, ACTN2 gene was firstly identified to be a cause of a new adult‐onset distal muscular dystrophy calling actininopathy and another distinctly different myopathy, named multiple structured core disease (MsCD). Thus, the various phenotypes and limited mutations in ACTN2‐related myopathy make the genotype‐phenotype correlation hard to understand. Aims To investigate the clinical features and histological findings in a Chinese family with distal myopathy. Whole exome sequencing and several functional studies were performed to explore the pathogenesis of the disease. Results We firstly identified a novel frameshift variant (c.2504delT, p.Phe835Serfs*66) within ACTN2 in a family including three patients. The patients exhibited adult‐onset distal myopathy with multi‐minicores, which, interestingly, was more like a combination of MsCD and actininopathy. Moreover, functional analysis using muscle samples revealed that the variant significantly increased the expression level of α‐actinin‐2 and resulted in abnormal Z‐line organization of muscle fiber. Vitro studies suggested aggregate formations might be involved in the pathogenesis of the disease. Conclusion Our results expanded the phenotypes of ACTN2‐related myopathy and provided helpful information to clarify the molecular mechanisms.
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Affiliation(s)
- Lei Chen
- Department of Neurology and Research Center of Neurology in Second Affiliated Hospital, and Key Laboratory of Medical Neurobiology of Zhejiang Province, Zhejiang University School of Medicine, Hangzhou, China
| | - Dian-Fu Chen
- Department of Neurology and Research Center of Neurology in Second Affiliated Hospital, and Key Laboratory of Medical Neurobiology of Zhejiang Province, Zhejiang University School of Medicine, Hangzhou, China
| | - Hai-Lin Dong
- Department of Neurology and Research Center of Neurology in Second Affiliated Hospital, and Key Laboratory of Medical Neurobiology of Zhejiang Province, Zhejiang University School of Medicine, Hangzhou, China
| | - Gong-Lu Liu
- Department of Neurology and Research Center of Neurology in Second Affiliated Hospital, and Key Laboratory of Medical Neurobiology of Zhejiang Province, Zhejiang University School of Medicine, Hangzhou, China
| | - Zhi-Ying Wu
- Department of Neurology and Research Center of Neurology in Second Affiliated Hospital, and Key Laboratory of Medical Neurobiology of Zhejiang Province, Zhejiang University School of Medicine, Hangzhou, China
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2
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Persson K, Backman L. Structural and functional characterization of a plant alpha-actinin. FEBS Open Bio 2021. [PMID: 34110107 PMCID: PMC8329775 DOI: 10.1002/2211-5463.13222] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2021] [Revised: 06/01/2021] [Accepted: 06/09/2021] [Indexed: 11/08/2022] Open
Abstract
The Australian tree malletwood (Rhodamnia argentea) is unique. The genome of malletwood is the only known plant genome that contains a gene coding for an α‐actinin‐like protein. Several organisms predating the animal‐plant bifurcation express an α‐actinin or α‐actinin‐like protein. Therefore, it appears that plants in general, but not malletwood, have lost the α‐actinin or α‐actinin‐like gene during evolution. In order to characterize its structure and function, we synthesized the gene and expressed the recombinant R. argentea protein. The results clearly show that this protein has all properties of genuine α‐actinin. The N‐terminal actin‐binding domain (ABD), with two calponin homology motifs, is very similar to the ABD of any α‐actinin. The C‐terminal calmodulin‐like domain, as well as the intervening rod domain, are also similar to the corresponding regions in other α‐actinins. The R. argentea α‐actinin‐like protein dimerises in solution and thereby can cross‐link actin filaments. Based on these results, we believe the R. argentea protein represents a genuine α‐actinin, making R. argentea unique in the plant world.
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Affiliation(s)
| | - Lars Backman
- Department of Chemistry, Umeå University, Sweden
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3
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Shams H, Golji J, Garakani K, Mofrad MRK. Dynamic Regulation of α-Actinin's Calponin Homology Domains on F-Actin. Biophys J 2016; 110:1444-55. [PMID: 27028653 PMCID: PMC4816760 DOI: 10.1016/j.bpj.2016.02.024] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2015] [Revised: 01/22/2016] [Accepted: 02/01/2016] [Indexed: 11/24/2022] Open
Abstract
α-Actinin is an essential actin cross-linker involved in cytoskeletal organization and dynamics. The molecular conformation of α-actinin's actin-binding domain (ABD) regulates its association with actin and thus mutations in this domain can lead to severe pathogenic conditions. A point mutation at lysine 255 in human α-actinin-4 to glutamate increases the binding affinity resulting in stiffer cytoskeletal structures. The role of different ABD conformations and the effect of K255E mutation on ABD conformations remain elusive. To evaluate the impact of K255E mutation on ABD binding to actin we use all-atom molecular dynamics and free energy calculation methods and study the molecular mechanism of actin association in both wild-type α-actinin and in the K225E mutant. Our models illustrate that the strength of actin association is indeed sensitive to the ABD conformation, predict the effect of K255E mutation--based on simulations with the K237E mutant chicken α-actinin--and evaluate the mechanism of α-actinin binding to actin. Furthermore, our simulations showed that the calmodulin domain binding to the linker region was important for regulating the distance between actin and ABD. Our results provide valuable insights into the molecular details of this critical cellular phenomenon and further contribute to an understanding of cytoskeletal dynamics in health and disease.
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Affiliation(s)
- Hengameh Shams
- Molecular Cell Biomechanics Laboratory, Departments of Bioengineering and Mechanical Engineering, University of California, Berkeley, Berkeley, California
| | - Javad Golji
- Molecular Cell Biomechanics Laboratory, Departments of Bioengineering and Mechanical Engineering, University of California, Berkeley, Berkeley, California
| | - Kiavash Garakani
- Molecular Cell Biomechanics Laboratory, Departments of Bioengineering and Mechanical Engineering, University of California, Berkeley, Berkeley, California
| | - Mohammad R K Mofrad
- Molecular Cell Biomechanics Laboratory, Departments of Bioengineering and Mechanical Engineering, University of California, Berkeley, Berkeley, California; Molecular Biophysics and Integrative Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, California.
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4
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Addario B, Sandblad L, Persson K, Backman L. Characterisation of Schizosaccharomyces pombe α-actinin. PeerJ 2016; 4:e1858. [PMID: 27069798 PMCID: PMC4824898 DOI: 10.7717/peerj.1858] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2015] [Accepted: 03/08/2016] [Indexed: 11/27/2022] Open
Abstract
The actin cytoskeleton plays a fundamental role in eukaryotic cells. Its reorganization is regulated by a plethora of actin-modulating proteins, such as a-actinin. In higher organisms, α-actinin is characterized by the presence of three distinct structural domains: an N-terminal actin-binding domain and a C-terminal region with EF-hand motif separated by a central rod domain with four spectrin repeats. Sequence analysis has revealed that the central rod domain of α-actinin from the fission yeast Schizosaccharomyces pombe consists of only two spectrin repeats. To obtain a firmer understanding of the structure and function of this unconventional α-actinin, we have cloned and characterized each structural domain. Our results show that this a-actinin isoform is capable of forming dimers and that the rod domain is required for this. However, its actin-binding and cross-linking activity appears less efficient compared to conventional α-actinins. The solved crystal structure of the actin-binding domain indicates that the closed state is stabilised by hydrogen bonds and a salt bridge not present in other α-actinins, which may reduce the affinity for actin.
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Affiliation(s)
- Barbara Addario
- Cell Biology Laboratory, School of Biochemistry and Cell Biology, BioScience Institute, University College Cork , Cork , Ireland
| | - Linda Sandblad
- Department of Molecular Biology, UmeåUniversity , Umeå , Sweden
| | - Karina Persson
- Department of Chemistry, Biological Chemistry , Umeå , Sweden
| | - Lars Backman
- Department of Chemistry, Biological Chemistry , Umeå , Sweden
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5
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Low SH, Mukhina S, Srinivas V, Ng CZ, Murata-Hori M. Domain analysis of α-actinin reveals new aspects of its association with F-actin during cytokinesis. Exp Cell Res 2010; 316:1925-34. [DOI: 10.1016/j.yexcr.2010.03.004] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2010] [Revised: 03/02/2010] [Accepted: 03/06/2010] [Indexed: 10/19/2022]
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6
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Hampton CM, Taylor DW, Taylor KA. Novel structures for alpha-actinin:F-actin interactions and their implications for actin-membrane attachment and tension sensing in the cytoskeleton. J Mol Biol 2007; 368:92-104. [PMID: 17331538 PMCID: PMC1919418 DOI: 10.1016/j.jmb.2007.01.071] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2006] [Revised: 01/22/2007] [Accepted: 01/25/2007] [Indexed: 01/25/2023]
Abstract
We have applied correspondence analysis to electron micrographs of 2-D rafts of F-actin cross-linked with alpha-actinin on a lipid monolayer to investigate alpha-actinin:F-actin binding and cross-linking. More than 8000 actin crossover repeats, each with one to five alpha-actinin molecules bound, were selected, aligned, and grouped to produce class averages of alpha-actinin cross-links with approximately 9-fold improvement in the stochastic signal-to-noise ratio. Measurements and comparative molecular models show variation in the distance separating actin-binding domains and the angle of the alpha-actinin cross-links. Rafts of F-actin and alpha-actinin formed predominantly polar 2-D arrays of actin filaments, with occasional insertion of filaments of opposite polarity. Unique to this study are the numbers of alpha-actinin molecules bound to successive crossovers on the same actin filament. These "monofilament"-bound alpha-actinin molecules may reflect a new mode of interaction for alpha-actinin, particularly in protein-dense actin-membrane attachments in focal adhesions. These results suggest that alpha-actinin is not simply a rigid spacer between actin filaments, but rather a flexible cross-linking, scaffolding, and anchoring protein. We suggest these properties of alpha-actinin may contribute to tension sensing in actin bundles.
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Affiliation(s)
| | | | - Kenneth A. Taylor
- *Corresponding Author Phone: (850)644-3357, Fax: (850)644-7244, e-mail:
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7
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Kelly DF, Taylor DW, Bakolitsa C, Bobkov AA, Bankston L, Liddington RC, Taylor KA. Structure of the alpha-actinin-vinculin head domain complex determined by cryo-electron microscopy. J Mol Biol 2006; 357:562-73. [PMID: 16430917 DOI: 10.1016/j.jmb.2005.12.076] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2005] [Revised: 12/21/2005] [Accepted: 12/23/2005] [Indexed: 10/25/2022]
Abstract
The vinculin binding site on alpha-actinin was determined by cryo-electron microscopy of 2D arrays formed on phospholipid monolayers doped with a nickel chelating lipid. Chicken smooth muscle alpha-actinin was cocrystallized with the beta1-integrin cytoplasmic domain and a vinculin fragment containing residues 1-258 (vinculin(D1)). Vinculin(D1) was located at a single site on alpha-actinin with 60-70% occupancy. In these arrays, alpha-actinin lacks molecular 2-fold symmetry and the two ends of the molecule, which contain the calmodulin-like and actin binding domains, are held in distinctly different environments. The vinculin(D1) difference density has a shape very suggestive of the atomic structure. The atomic model of the complex juxtaposes the alpha-actinin binding site on vinculin(D1) with the N-terminal lobe of the calmodulin-like domain on alpha-actinin. The results show that the interaction between two species with weak affinity can be visualized in a membrane-like environment.
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Affiliation(s)
- Deborah F Kelly
- Institute of Molecular Biophysics, Florida State University, Tallahassee, FL 32306-4380, USA
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8
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Liu J, Taylor DW, Taylor KA. A 3-D reconstruction of smooth muscle alpha-actinin by CryoEm reveals two different conformations at the actin-binding region. J Mol Biol 2004; 338:115-25. [PMID: 15050827 DOI: 10.1016/j.jmb.2004.02.034] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2003] [Revised: 02/05/2004] [Accepted: 02/11/2004] [Indexed: 11/20/2022]
Abstract
Cryoelectron microscopy was used to obtain a 3-D image at 2.0 nm resolution of 2-D arrays of smooth muscle alpha-actinin. The reconstruction reveals a well-resolved long central domain with 90 degrees of left-handed twist and near 2-fold symmetry. However, the molecular ends which contain the actin binding and calmodulin-like domains, have different structures oriented approximately 90 degrees to each other. Atomic structures for the alpha-actinin domains were built by homology modeling and assembled into an atomic model. Model building suggests that in the 2-D arrays, the two calponin homology domains that comprise the actin-binding domain have a closed conformation at one end and an open conformation at the other end due to domain swapping. The open and closed conformations of the actin-binding domain suggests flexibility that may underlie Ca2+ regulation. The approximately 90 degrees orientation difference at the molecular ends may underlie alpha-actinin's ability to crosslink actin filaments in nearly any orientation.
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Affiliation(s)
- Jun Liu
- Institute of Molecular Biophysics, Florida State University, Tallahassee, FL 32306-4380, USA
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9
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Tang J, Taylor DW, Taylor KA. The three-dimensional structure of alpha-actinin obtained by cryoelectron microscopy suggests a model for Ca(2+)-dependent actin binding. J Mol Biol 2001; 310:845-58. [PMID: 11453692 DOI: 10.1006/jmbi.2001.4789] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The three-dimensional structure of alpha-actinin from rabbit skeletal muscle was determined by cryoelectron microscopy in combination with homology modeling of the separate domain structures based on results previously determined by X-ray crystallography and nuclear magnetic resonance spectroscopy. alpha-Actinin was induced to form two-dimensional arrays on a positively charged lipid monolayer and micrographs were collected from unstained, frozen hydrated specimens at tilt angles from 0 degrees to 60 degrees. Interpretation of the 15 A-resolution three-dimensional structure was done by manually docking homologous models of the three key domains, actin-binding, three-helix motif and the C-terminal calmodulin-like domains. The initial model was refined quantitatively to improve its fit to the experimental reconstruction. The molecular model of alpha-actinin provides the first view of the overall structure of a complete actin cross-linking protein. The structure is characterized by close proximity of the C-terminal, calmodulin-like domain to the linker between the two calponin-homology domains that comprise the actin-binding domain. This location suggests a hypothesis to explain the involvement of the C-terminal domain in Ca(2+)-dependent actin binding of non-muscle isoforms.
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Affiliation(s)
- J Tang
- Institute of Molecular Biophysics, Florida State University, Tallahassee, FL 32306-4380, USA
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10
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Young P, Gautel M. The interaction of titin and alpha-actinin is controlled by a phospholipid-regulated intramolecular pseudoligand mechanism. EMBO J 2000; 19:6331-40. [PMID: 11101506 PMCID: PMC305858 DOI: 10.1093/emboj/19.23.6331] [Citation(s) in RCA: 77] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The assembly of stable cytoskeletal structures from dynamically recycled molecules requires developmental and spatial regulation of protein interactions. In muscle, titin acts as a molecular ruler organizing the actin cytoskeleton via interactions with many sarcomeric proteins, including the crosslinking protein alpha-actinin. An interaction between the C-terminal domain of alpha-actinin and titin Z-repeat motifs targets alpha-actinin to the Z-disk. Here we investigate the cellular regulation of this interaction. alpha-actinin is a rod shaped head-to-tail homodimer. In contrast to C-terminal fragments, full-length alpha-actinin does not bind Z-repeats. We identify a 30-residue Z-repeat homologous sequence between the actin-binding and rod regions of alpha-actinin that binds the C-terminal domain with nanomolar affinity. Thus, Z-repeat binding is prevented by this 'pseudoligand' interaction between the subunits of the alpha-actinin dimer. This autoinhibition is relieved upon binding of the Z-disk lipid phosphatidylinositol-bisphosphate to the actin-binding domain. We suggest that this novel mechanism is relevant to control the site-specific interactions of alpha-actinin during sarcomere assembly and turnover. The intramolecular contacts defined here also constrain a structural model for intrasterical regulation of all alpha-actinin isoforms.
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Affiliation(s)
- P Young
- European Molecular Biology Laboratory, Structural Biology Division, 69012 Heidelberg, Germany
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11
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Abstract
We have prepared two fragments of the human dystrophin rod domain, each containing eight spectrin-like repeating units, by expression in Escherichia coli. The first corresponds to the central portion of the rod, the other to three repeats from the N-terminal end, fused to five repeats from the C-terminal end. The latter makes up the entire mutant rod, found in a patient with mild (Becker-type) muscular dystrophy. Both fragments were found to possess an ordered, stable structure, and had the form of short rod-like particles in the electron microscope. Molecular weight determinations by sedimentation equilibrium revealed that both polypeptides were monomeric in solution, suggesting that the dystrophin rod domain is incapable of forming an antiparallel homodimer. This supports the inference from sequence analyses [Winder et al., 1995: FEBS Lett. 369:27-33, 1996: Biochem. Soc. Trans. 24:2805] that the dystrophin rod domain lacks the arrangement of sites required for lateral self-association, and that dystrophin, unlike the other known proteins of the spectrin superfamily, may thus exist as a monomer.
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Affiliation(s)
- E Kahana
- Medical Research Council Muscle and Cell Motility Unit, King's College, London, England
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12
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Ojima K, Lin ZX, Zhang ZQ, Hijikata T, Holtzer S, Labeit S, Sweeney HL, Holtzer H. Initiation and maturation of I-Z-I bodies in the growth tips of transfected myotubes. J Cell Sci 1999; 112 ( Pt 22):4101-12. [PMID: 10547369 DOI: 10.1242/jcs.112.22.4101] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
While over a dozen I-Z-I proteins are expressed in postmitotic myoblasts and myotubes it is unclear how, when, or where these first assemble into transitory I-Z-I bodies (thin filament/Z-band precursors) and, a short time later, into definitive I-Z-I bands. By double-staining the growth tips of transfected myotubes expressing (a) MYC-tagged s-alpha-actinins (MYC/s-alpha-actinins) or (b) green fluorescent protein-tagged titin cap (GFP/T-cap) with antibodies against MYC and I-Z-I band proteins, we found that the de novo assembly of I-Z-I bodies and their maturation into I-Z-I bands involved relatively concurrent, cooperative binding and reconfiguration of, at a minimum, 5 integral Z-band molecules. These included s-alpha-actinin, nebulin, titin, T-cap and alpha-actin. Resolution of the approximately 1.0 microm polarized alpha-actin/nebulin/tropomyosin/troponin thin filament complexes occurred subsequent to the maturation of Z-bands into a dense tetragonal configuration. Of particular interest is finding that mutant MYC/s-alpha-actinin peptides (a) lacking spectrin-like repeats 1–4, or consisting of spectrin-like repeats 1–4 only, as well as (b) mutants/fragments lacking titin or alpha-actin binding sites, were promptly and exclusively incorporated into de novo assembling I-Z-I bodies and definitive I-Z-I bands as was exogenous full length MYC/s-alpha-actinin or GFP/T-cap.
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Affiliation(s)
- K Ojima
- Department of Physiology and Cell and Developmental Biology, The School of Medicine, University of Pennsylvania, Philadelphia, PA l9l04, USA
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13
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Djinović-Carugo K, Young P, Gautel M, Saraste M. Structure of the alpha-actinin rod: molecular basis for cross-linking of actin filaments. Cell 1999; 98:537-46. [PMID: 10481917 DOI: 10.1016/s0092-8674(00)81981-9] [Citation(s) in RCA: 206] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
We have determined the crystal structure of the two central repeats in the alpha-actinin rod at 2.5 A resolution. The repeats are connected by a helical linker and form a symmetric, antiparallel dimer in which the repeats are aligned rather than staggered. Using this structure, which reveals the structural principle that governs the architecture of alpha-actinin, we have devised a plausible model of the entire alpha-actinin rod. The electrostatic properties explain how the two alpha-actinin subunits assemble in an antiparallel fashion, placing the actin-binding sites at both ends of the rod. This molecular architecture results in a protein that is able to form cross-links between actin filaments.
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Affiliation(s)
- K Djinović-Carugo
- Structural Biology Programme, European Molecular Biology Laboratory, Heidelberg, Germany
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14
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Chan Y, Tong HQ, Beggs AH, Kunkel LM. Human skeletal muscle-specific alpha-actinin-2 and -3 isoforms form homodimers and heterodimers in vitro and in vivo. Biochem Biophys Res Commun 1998; 248:134-9. [PMID: 9675099 DOI: 10.1006/bbrc.1998.8920] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Alpha-actinins belong to a family of actin-binding and crosslinking proteins and are expressed in many different cell types. Multiple isoforms of alpha-actinin are found in humans and are encoded by at least four distinct genes. Human skeletal muscle contains two sarcomeric isoforms, alpha-actinin-2 and -3. Previous studies have shown that the alpha-actinins function as anti-parallel homodimers but the question of heterodimer formation between two different isoforms expressed in the same cell type has not been explored. To address this issue, we expressed both alpha-actinin-2 and -3 in vitro and were able to detect their interaction by both blot overlay and co-immunoprecipitation methods. We were also able to demonstrate the presence of heterodimers in vivo in human skeletal muscle and in COS-1 cells transiently transfected with both isoforms. Our results clearly demonstrate the potential for alpha-actinin isoforms to form heterodimers which might have unique functional characteristics.
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Affiliation(s)
- Y Chan
- Howard Hughes Medical Institute, Children's Hospital, Boston, Massachusetts, USA
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15
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Young P, Ferguson C, Bañuelos S, Gautel M. Molecular structure of the sarcomeric Z-disk: two types of titin interactions lead to an asymmetrical sorting of alpha-actinin. EMBO J 1998; 17:1614-24. [PMID: 9501083 PMCID: PMC1170509 DOI: 10.1093/emboj/17.6.1614] [Citation(s) in RCA: 192] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
The sarcomeric Z-disk, the anchoring plane of thin (actin) filaments, links titin (also called connectin) and actin filaments from opposing sarcomere halves in a lattice connected by alpha-actinin. We demonstrate by protein interaction analysis that two types of titin interactions are involved in the assembly of alpha-actinin into the Z-disk. Titin interacts via a single binding site with the two central spectrin-like repeats of the outermost pair of alpha-actinin molecules. In the central Z-disk, titin can interact with multiple alpha-actinin molecules via their C-terminal domains. These interactions allow the assembly of a ternary complex of titin, actin and alpha-actinin in vitro, and are expected to constrain the path of titin in the Z-disk. In thick skeletal muscle Z-disks, titin filaments cross over the Z-disk centre by approximately 30 nm, suggesting that their alpha-actinin-binding sites overlap in an antiparallel fashion. The combination of our biochemical and ultrastructural data now allows a molecular model of the sarcomeric Z-disk, where overlapping titin filaments and their interactions with the alpha-actinin rod and C-terminal domain can account for the essential ultrastructural features.
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Affiliation(s)
- P Young
- European Molecular Biology Laboratory, Postfach 10 22 09, 69012 Heidelberg, Germany
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16
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Abstract
Dystrophin, a component of the muscle membrane cytoskeleton, is the protein altered in Duchenne Muscular Dystrophy (DMD) and Becker Muscular Dystrophy (BMD). Dystrophin shares significant homology with other cytoskeletal proteins, such as alpha-actinin and spectrin. On the basis of its sequence similarity with alpha-actinin and spectrin, dystrophin has been proposed to function as dimer. However, the existence of both dimers and monomers have been observed by electron microscopy. To address this apparent discrepancy, we expressed dystrophin fragments composed of different domains in an in vitro translation system. The expressed fragments were tested for their ability to interact with each other and full-length dystrophin by both immunoprecipitation and blot overlay assays. These assays were successfully used to demonstrate the dimerization of alpha-actinin and spectrin, yet failed to detect any interaction between dystrophin fragments. Although these in vitro results do not prove that dystrophin is not a dimer in vivo, they do indicate that this interaction is not like that of the alpha-actinin and spectrin.
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Affiliation(s)
- Y Chan
- Howard Hughes Medical Institute, and Division of Genetics at Children's Hospital, Boston, MA 02115, USA
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17
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Affiliation(s)
- W D Kohn
- Department of Biochemistry, MRC Group in Protein Structure and Function, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
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18
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Gilmore AP, Parr T, Patel B, Gratzer WB, Critchley DR. Analysis of the phasing of four spectrin-like repeats in alpha-actinin. EUROPEAN JOURNAL OF BIOCHEMISTRY 1994; 225:235-42. [PMID: 7925443 DOI: 10.1111/j.1432-1033.1994.00235.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Selected fragments of the central rod of chicken gizzard alpha-actinin were expressed as fusion proteins in Escherichia coli, with the aim of determining the positions in the sequence of the four successive spectrin-like repeats that make up this domain. The criteria for an independently folding unit were resistance to proteolysis and the high alpha helicity characteristic of the native protein. Sequences containing repeats 1-4, 2-4, 3-4 and 4 all generated stable fragments on digestion with trypsin and/or thermolysin and N-terminal sequencing gave the most probable starting position of each repeat. The sequences of all four inferred repeats and the sequences of the entire rod, were separately expressed and were shown to assume a stable, protease-resistant fold in solution. The repeat boundaries established in this way differed from those originally deduced from sequence alignments; the N-terminal boundaries of the repeats were 14-24 residues nearer the C-terminus than predicted. The ability to express individual repeats should facilitate identification of the binding sites for the cytoplasmic domains of beta 1 integrins and intercellular cell adhesion molecule-1 which have been localised to the rod domain of alpha-actinin.
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Affiliation(s)
- A P Gilmore
- Department of Biochemistry, University of Leicester, England
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19
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Abstract
The crystal structure of the three-helix-bundle spectrin motif provides new insights into the structure of the large proteins that constitute the spectrin superfamily, which includes dystrophin and alpha-actinin.
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Affiliation(s)
- D W Speicher
- Wistar Institute, Philadelphia, Pennsylvania 19104
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Wachsstock DH, Schwartz WH, Pollard TD. Affinity of alpha-actinin for actin determines the structure and mechanical properties of actin filament gels. Biophys J 1993; 65:205-14. [PMID: 8369430 PMCID: PMC1225716 DOI: 10.1016/s0006-3495(93)81059-2] [Citation(s) in RCA: 178] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Proteins that cross-link actin filaments can either form bundles of parallel filaments or isotropic networks of individual filaments. We have found that mixtures of actin filaments with alpha-actinin purified from either Acanthamoeba castellanii or chicken smooth muscle can form bundles or isotropic networks depending on their concentration. Low concentrations of alpha-actinin and actin filaments form networks indistinguishable in electron micrographs from gels of actin alone. Higher concentrations of alpha-actinin and actin filaments form bundles. The threshold for bundling depends on the affinity of the alpha-actinin for actin. The complex of Acanthamoeba alpha-actinin with actin filaments has a Kd of 4.7 microM and a bundling threshold of 0.1 microM; chicken smooth muscle has a Kd of 0.6 microM and a bundling threshold of 1 microM. The physical properties of isotropic networks of cross-linked actin filaments are very different from a gel of bundles: the network behaves like a solid because each actin filament is part of a single structure that encompasses all the filaments. Bundles of filaments behave more like a very viscous fluid because each bundle, while very long and stiff, can slip past other bundles. We have developed a computer model that predicts the bundling threshold based on four variables: the length of the actin filaments, the affinity of the alpha-actinin for actin, and the concentrations of actin and alpha-actinin.
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Affiliation(s)
- D H Wachsstock
- Department of Cell Biology and Anatomy, Johns Hopkins University, Baltimore, Maryland 21205
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