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Roopnarine O, Thomas DD. Structural Dynamics of Protein Interactions Using Site-Directed Spin Labeling of Cysteines to Measure Distances and Rotational Dynamics with EPR Spectroscopy. APPLIED MAGNETIC RESONANCE 2024; 55:79-100. [PMID: 38371230 PMCID: PMC10868710 DOI: 10.1007/s00723-023-01623-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/14/2023] [Revised: 09/19/2023] [Accepted: 09/22/2023] [Indexed: 02/20/2024]
Abstract
Here we review applications of site-directed spin labeling (SDSL) with engineered cysteines in proteins, to study the structural dynamics of muscle and non-muscle proteins, using and developing the electron paramagnetic resonance (EPR) spectroscopic techniques of dipolar EPR, double electron electron resonance (DEER), saturation transfer EPR (STEPR), and orientation measured by EPR. The SDSL technology pioneered by Wayne Hubbell and collaborators has greatly expanded the use of EPR, including the measurement of distances between spin labels covalently attached to proteins and peptides. The Thomas lab and collaborators have applied these techniques to elucidate dynamic interactions in the myosin-actin complex, myosin-binding protein C, calmodulin, ryanodine receptor, phospholamban, utrophin, dystrophin, β-III-spectrin, and Aurora kinase. The ability to design and engineer cysteines in proteins for site-directed covalent labeling has enabled the use of these powerful EPR techniques to measure distances, while showing that they are complementary with optical spectroscopy measurements.
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Affiliation(s)
- Osha Roopnarine
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, MN 55455, USA
| | - David D. Thomas
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, MN 55455, USA
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2
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Szwec S, Kapłucha Z, Chamberlain JS, Konieczny P. Dystrophin- and Utrophin-Based Therapeutic Approaches for Treatment of Duchenne Muscular Dystrophy: A Comparative Review. BioDrugs 2024; 38:95-119. [PMID: 37917377 PMCID: PMC10789850 DOI: 10.1007/s40259-023-00632-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/10/2023] [Indexed: 11/04/2023]
Abstract
Duchenne muscular dystrophy is a devastating disease that leads to progressive muscle loss and premature death. While medical management focuses mostly on symptomatic treatment, decades of research have resulted in first therapeutics able to restore the affected reading frame of dystrophin transcripts or induce synthesis of a truncated dystrophin protein from a vector, with other strategies based on gene therapy and cell signaling in preclinical or clinical development. Nevertheless, recent reports show that potentially therapeutic dystrophins can be immunogenic in patients. This raises the question of whether a dystrophin paralog, utrophin, could be a more suitable therapeutic protein. Here, we compare dystrophin and utrophin amino acid sequences and structures, combining published data with our extended in silico analyses. We then discuss these results in the context of therapeutic approaches for Duchenne muscular dystrophy. Specifically, we focus on strategies based on delivery of micro-dystrophin and micro-utrophin genes with recombinant adeno-associated viral vectors, exon skipping of the mutated dystrophin pre-mRNAs, reading through termination codons with small molecules that mask premature stop codons, dystrophin gene repair by clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (CRISPR/Cas9)-mediated genetic engineering, and increasing utrophin levels. Our analyses highlight the importance of various dystrophin and utrophin domains in Duchenne muscular dystrophy treatment, providing insights into designing novel therapeutic compounds with improved efficacy and decreased immunoreactivity. While the necessary actin and β-dystroglycan binding sites are present in both proteins, important functional distinctions can be identified in these domains and some other parts of truncated dystrophins might need redesigning due to their potentially immunogenic qualities. Alternatively, therapies based on utrophins might provide a safer and more effective approach.
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Affiliation(s)
- Sylwia Szwec
- Institute of Human Biology and Evolution, Faculty of Biology, Adam Mickiewicz University, ul. Uniwersytetu Poznańskiego 6, 61-614, Poznań, Poland
| | - Zuzanna Kapłucha
- Institute of Human Biology and Evolution, Faculty of Biology, Adam Mickiewicz University, ul. Uniwersytetu Poznańskiego 6, 61-614, Poznań, Poland
| | - Jeffrey S Chamberlain
- Department of Neurology, University of Washington School of Medicine, Seattle, WA, 98109-8055, USA
- Senator Paul D. Wellstone Muscular Dystrophy Specialized Research Center, University of Washington School of Medicine, Seattle, WA, 98109-8055, USA
- Department of Biochemistry, University of Washington School of Medicine, Seattle, WA, 98109-8055, USA
- Department of Medicine, University of Washington School of Medicine, Seattle, WA, 98109-8055, USA
| | - Patryk Konieczny
- Institute of Human Biology and Evolution, Faculty of Biology, Adam Mickiewicz University, ul. Uniwersytetu Poznańskiego 6, 61-614, Poznań, Poland.
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3
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Dong S, Zheng W, Pinkerton N, Hansen J, Tikunova SB, Davis JP, Heissler SM, Kudryashova E, Egelman EH, Kudryashov DS. Photorhabdus luminescens TccC3 Toxin Targets the Dynamic Population of F-Actin and Impairs Cell Cortex Integrity. Int J Mol Sci 2022; 23:7026. [PMID: 35806028 PMCID: PMC9266650 DOI: 10.3390/ijms23137026] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2022] [Revised: 06/17/2022] [Accepted: 06/22/2022] [Indexed: 12/30/2022] Open
Abstract
Due to its essential role in cellular processes, actin is a common target for bacterial toxins. One such toxin, TccC3, is an effector domain of the ABC-toxin produced by entomopathogenic bacteria of Photorhabdus spp. Unlike other actin-targeting toxins, TccC3 uniquely ADP-ribosylates actin at Thr-148, resulting in the formation of actin aggregates and inhibition of phagocytosis. It has been shown that the fully modified F-actin is resistant to depolymerization by cofilin and gelsolin, but their effects on partially modified actin were not explored. We found that only F-actin unprotected by tropomyosin is the physiological TccC3 substrate. Yet, ADP-ribosylated G-actin can be produced upon cofilin-accelerated F-actin depolymerization, which was only mildly inhibited in partially modified actin. The affinity of TccC3-ADP-ribosylated G-actin for profilin and thymosin-β4 was weakened moderately but sufficiently to potentiate spontaneous polymerization in their presence. Interestingly, the Arp2/3-mediated nucleation was also potentiated by T148-ADP-ribosylation. Notably, even partially modified actin showed reduced bundling by plastins and α-actinin. In agreement with the role of these and other tandem calponin-homology domain actin organizers in the assembly of the cortical actin network, TccC3 induced intense membrane blebbing in cultured cells. Overall, our data suggest that TccC3 imposes a complex action on the cytoskeleton by affecting F-actin nucleation, recycling, and interaction with actin-binding proteins involved in the integration of actin filaments with each other and cellular elements.
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Affiliation(s)
- Songyu Dong
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA; (S.D.); (N.P.); (J.H.); (E.K.)
- The Ohio State Biochemistry Program, The Ohio State University, Columbus, OH 43210, USA
| | - Weili Zheng
- Department of Biochemistry and Molecular Genetics, University of Virginia, Charlottesville, VA 22903, USA; (W.Z.); (E.H.E.)
| | - Nicholas Pinkerton
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA; (S.D.); (N.P.); (J.H.); (E.K.)
| | - Jacob Hansen
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA; (S.D.); (N.P.); (J.H.); (E.K.)
| | - Svetlana B. Tikunova
- Department of Physiology and Cell Biology, Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH 43210, USA; (S.B.T.); (J.P.D.); (S.M.H.)
| | - Jonathan P. Davis
- Department of Physiology and Cell Biology, Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH 43210, USA; (S.B.T.); (J.P.D.); (S.M.H.)
| | - Sarah M. Heissler
- Department of Physiology and Cell Biology, Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH 43210, USA; (S.B.T.); (J.P.D.); (S.M.H.)
| | - Elena Kudryashova
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA; (S.D.); (N.P.); (J.H.); (E.K.)
| | - Edward H. Egelman
- Department of Biochemistry and Molecular Genetics, University of Virginia, Charlottesville, VA 22903, USA; (W.Z.); (E.H.E.)
| | - Dmitri S. Kudryashov
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA; (S.D.); (N.P.); (J.H.); (E.K.)
- The Ohio State Biochemistry Program, The Ohio State University, Columbus, OH 43210, USA
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4
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Abstract
Actin is a highly conserved protein in mammals. The actin dynamics is regulated by actin-binding proteins and actin-related proteins. Nuclear actin and these regulatory proteins participate in multiple nuclear processes, including chromosome architecture organization, chromatin remodeling, transcription machinery regulation, and DNA repair. It is well known that the dysfunctions of these processes contribute to the development of cancer. Moreover, emerging evidence has shown that the deregulated actin dynamics is also related to cancer. This chapter discusses how the deregulation of nuclear actin dynamics contributes to tumorigenesis via such various nuclear events.
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Affiliation(s)
- Yuanjian Huang
- Department of Experimental Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, USA
- Department of General Surgery, The First Affiliated Hospital of Nanjing Medical University, Nanjing, Jiangsu, China
| | - Shengzhe Zhang
- Department of Experimental Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, USA
| | - Jae-Il Park
- Department of Experimental Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, USA.
- Graduate School of Biomedical Sciences, The University of Texas MD Anderson Cancer Center and Health Science Center, Houston, TX, USA.
- Program in Genetics and Epigenetics, The University of Texas MD Anderson Cancer Center, Houston, TX, USA.
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5
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Hurst V, Challa K, Shimada K, Gasser SM. Cytoskeleton integrity influences XRCC1 and PCNA dynamics at DNA damage. Mol Biol Cell 2021; 32:br6. [PMID: 34379448 PMCID: PMC8684753 DOI: 10.1091/mbc.e20-10-0680] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
On induction of DNA damage with 405-nm laser light, proteins involved in base excision repair (BER) are recruited to DNA lesions. We find that the dynamics of factors typical of either short-patch (XRCC1) or long-patch (PCNA) BER are altered by chemicals that perturb actin or tubulin polymerization in human cells. Whereas the destabilization of actin filaments by latrunculin B, cytochalasin B, or Jasplakinolide decreases BER factor accumulation at laser-induced damage, inhibition of tubulin polymerization by nocodazole increases it. We detect no recruitment of actin to sites of laser-induced DNA damage, yet the depolymerization of cytoplasmic actin filaments elevates both actin and tubulin signals in the nucleus. While published evidence suggested a positive role for F-actin in double-strand break repair in mammals, the enrichment of actin in budding yeast nuclei interferes with BER, augmenting sensitivity to Zeocin. Our quantitative imaging results suggest that the depolymerization of cytoplasmic actin may compromise BER efficiency in mammals not only due to elevated levels of nuclear actin but also of tubulin, linking cytoskeletal integrity to BER.
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Affiliation(s)
- Verena Hurst
- Friedrich Miescher Institute for Biomedical Research, Maulbeerstrasse 66, CH-4058 Basel, Switzerland.,Faculty of Natural Sciences, University of Basel, Klingelbergstrasse 90, CH-4056 Basel, Switzerland
| | - Kiran Challa
- Friedrich Miescher Institute for Biomedical Research, Maulbeerstrasse 66, CH-4058 Basel, Switzerland
| | - Kenji Shimada
- Friedrich Miescher Institute for Biomedical Research, Maulbeerstrasse 66, CH-4058 Basel, Switzerland
| | - Susan M Gasser
- Friedrich Miescher Institute for Biomedical Research, Maulbeerstrasse 66, CH-4058 Basel, Switzerland.,Faculty of Natural Sciences, University of Basel, Klingelbergstrasse 90, CH-4056 Basel, Switzerland
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6
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Morita R, Nakano K, Shigeta Y, Harada R. Molecular Mechanism for the Actin-Binding Domain of α-Actinin Ain1 Elucidated by Molecular Dynamics Simulations and Mutagenesis Experiments. J Phys Chem B 2020; 124:8495-8503. [DOI: 10.1021/acs.jpcb.0c04623] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Rikuri Morita
- Department of Biological Sciences, Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennohdai, Tsukuba, Ibaraki 305-8572, Japan
- Center for Computational Sciences, University of Tsukuba, 1-1-1 Tennohdai, Tsukuba, Ibaraki 305-8577, Japan
| | - Kentaro Nakano
- Department of Biological Sciences, Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennohdai, Tsukuba, Ibaraki 305-8572, Japan
| | - Yasuteru Shigeta
- Center for Computational Sciences, University of Tsukuba, 1-1-1 Tennohdai, Tsukuba, Ibaraki 305-8577, Japan
| | - Ryuhei Harada
- Center for Computational Sciences, University of Tsukuba, 1-1-1 Tennohdai, Tsukuba, Ibaraki 305-8577, Japan
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7
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Kumari A, Kesarwani S, Javoor MG, Vinothkumar KR, Sirajuddin M. Structural insights into actin filament recognition by commonly used cellular actin markers. EMBO J 2020; 39:e104006. [PMID: 32567727 PMCID: PMC7360965 DOI: 10.15252/embj.2019104006] [Citation(s) in RCA: 38] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2019] [Revised: 05/11/2020] [Accepted: 05/18/2020] [Indexed: 01/16/2023] Open
Abstract
Cellular studies of filamentous actin (F‐actin) processes commonly utilize fluorescent versions of toxins, peptides, and proteins that bind actin. While the choice of these markers has been largely based on availability and ease, there is a severe dearth of structural data for an informed judgment in employing suitable F‐actin markers for a particular requirement. Here, we describe the electron cryomicroscopy structures of phalloidin, lifeAct, and utrophin bound to F‐actin, providing a comprehensive high‐resolution structural comparison of widely used actin markers and their influence towards F‐actin. Our results show that phalloidin binding does not induce specific conformational change and lifeAct specifically recognizes closed D‐loop conformation, i.e., ADP‐Pi or ADP states of F‐actin. The structural models aided designing of minimal utrophin and a shorter lifeAct, which can be utilized as F‐actin marker. Together, our study provides a structural perspective, where the binding sites of utrophin and lifeAct overlap with majority of actin‐binding proteins and thus offering an invaluable resource for researchers in choosing appropriate actin markers and generating new marker variants.
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Affiliation(s)
- Archana Kumari
- Center for Cardiovascular Biology and Diseases, Institute for Stem Cell Science and Regenerative Medicine, Bengaluru, India
| | - Shubham Kesarwani
- Center for Cardiovascular Biology and Diseases, Institute for Stem Cell Science and Regenerative Medicine, Bengaluru, India.,Manipal Academy of Higher Education, Manipal, India
| | - Manjunath G Javoor
- Center for Cardiovascular Biology and Diseases, Institute for Stem Cell Science and Regenerative Medicine, Bengaluru, India.,Manipal Academy of Higher Education, Manipal, India
| | | | - Minhajuddin Sirajuddin
- Center for Cardiovascular Biology and Diseases, Institute for Stem Cell Science and Regenerative Medicine, Bengaluru, India
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8
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Bernadzki KM, Daszczuk P, Rojek KO, Pęziński M, Gawor M, Pradhan BS, de Cicco T, Bijata M, Bijata K, Włodarczyk J, Prószyński TJ, Niewiadomski P. Arhgef5 Binds α-Dystrobrevin 1 and Regulates Neuromuscular Junction Integrity. Front Mol Neurosci 2020; 13:104. [PMID: 32587503 PMCID: PMC7299196 DOI: 10.3389/fnmol.2020.00104] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2020] [Accepted: 05/13/2020] [Indexed: 01/09/2023] Open
Abstract
The neuromuscular junctions (NMJs) connect muscle fibers with motor neurons and enable the coordinated contraction of skeletal muscles. The dystrophin-associated glycoprotein complex (DGC) is an essential component of the postsynaptic machinery of the NMJ and is important for the maintenance of NMJ structural integrity. To identify novel proteins that are important for NMJ organization, we performed a mass spectrometry-based screen for interactors of α-dystrobrevin 1 (aDB1), one of the components of the DGC. The guanidine nucleotide exchange factor (GEF) Arhgef5 was found to be one of the aDB1 binding partners that is recruited to Tyr-713 in a phospho-dependent manner. We show here that Arhgef5 localizes to the NMJ and that its genetic depletion in the muscle causes the fragmentation of the synapses in conditional knockout mice. Arhgef5 loss in vivo is associated with a reduction in the levels of active GTP-bound RhoA and Cdc42 GTPases, highlighting the importance of actin dynamics regulation for the maintenance of NMJ integrity.
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Affiliation(s)
- Krzysztof M Bernadzki
- Laboratory of Synaptogenesis, Nencki Institute of Experimental Biology, Warsaw, Poland
| | - Patrycja Daszczuk
- Laboratory of Synaptogenesis, Nencki Institute of Experimental Biology, Warsaw, Poland
| | - Katarzyna O Rojek
- Laboratory of Synaptogenesis, Nencki Institute of Experimental Biology, Warsaw, Poland.,Institute of Physical Chemistry, Polish Academy of Sciences, Warsaw, Poland
| | - Marcin Pęziński
- Laboratory of Synaptogenesis, Nencki Institute of Experimental Biology, Warsaw, Poland
| | - Marta Gawor
- Laboratory of Synaptogenesis, Nencki Institute of Experimental Biology, Warsaw, Poland
| | - Bhola S Pradhan
- Laboratory of Synaptogenesis, Nencki Institute of Experimental Biology, Warsaw, Poland
| | - Teresa de Cicco
- Laboratory of Synaptogenesis, Nencki Institute of Experimental Biology, Warsaw, Poland
| | - Monika Bijata
- Laboratory of Cell Biophysics, Nencki Institute of Experimental Biology, Warsaw, Poland
| | - Krystian Bijata
- Laboratory of Cell Biophysics, Nencki Institute of Experimental Biology, Warsaw, Poland
| | - Jakub Włodarczyk
- Laboratory of Cell Biophysics, Nencki Institute of Experimental Biology, Warsaw, Poland
| | - Tomasz J Prószyński
- Laboratory of Synaptogenesis, Nencki Institute of Experimental Biology, Warsaw, Poland.,Łukasiewicz Research Network - PORT Polish Center for Technology Development, Wrocław, Poland
| | - Paweł Niewiadomski
- Laboratory of Synaptogenesis, Nencki Institute of Experimental Biology, Warsaw, Poland.,Laboratory of Molecular and Cellular Signaling, Centre of New Technologies, University of Warsaw, Warsaw, Poland
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9
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Balasanyan V, Watanabe K, Dempsey WP, Lewis TL, Trinh LA, Arnold DB. Structure and Function of an Actin-Based Filter in the Proximal Axon. Cell Rep 2018; 21:2696-2705. [PMID: 29212018 DOI: 10.1016/j.celrep.2017.11.046] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2017] [Revised: 08/24/2017] [Accepted: 11/13/2017] [Indexed: 10/18/2022] Open
Abstract
The essential organization of microtubules within neurons has been described; however, less is known about how neuronal actin is arranged and the functional implications of its arrangement. Here, we describe, in live cells, an actin-based structure in the proximal axon that selectively prevents some proteins from entering the axon while allowing the passage of others. Concentrated patches of actin in proximal axons are present shortly after axonal specification in rat and zebrafish neurons imaged live, and they mark positions where anterogradely traveling vesicles carrying dendritic proteins halt and reverse. Patches colocalize with the ARP2/3 complex, and when ARP2/3-mediated nucleation is blocked, a dendritic protein mislocalizes to the axon. Patches are highly dynamic, with few persisting longer than 30 min. In neurons in culture and in vivo, actin appears to form a contiguous, semipermeable barrier, despite its apparently sparse distribution, preventing axonal localization of constitutively active myosin Va but not myosin VI.
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Affiliation(s)
- Varuzhan Balasanyan
- Department of Biology, Division of Molecular and Computational Biology, University of Southern California, Los Angeles, CA 90089, USA
| | - Kaori Watanabe
- Department of Biology, Division of Molecular and Computational Biology, University of Southern California, Los Angeles, CA 90089, USA
| | - William P Dempsey
- Department of Biology, Division of Molecular and Computational Biology, University of Southern California, Los Angeles, CA 90089, USA
| | - Tommy L Lewis
- Department of Biology, Division of Molecular and Computational Biology, University of Southern California, Los Angeles, CA 90089, USA
| | - Le A Trinh
- Department of Biology, Division of Molecular and Computational Biology, University of Southern California, Los Angeles, CA 90089, USA
| | - Don B Arnold
- Department of Biology, Division of Molecular and Computational Biology, University of Southern California, Los Angeles, CA 90089, USA.
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10
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Grintsevich EE. Remodeling of Actin Filaments by Drebrin A and Its Implications. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2017; 1006:61-82. [DOI: 10.1007/978-4-431-56550-5_5] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
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11
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Zhang R, Chang M, Zhang M, Wu Y, Qu X, Huang S. The Structurally Plastic CH2 Domain Is Linked to Distinct Functions of Fimbrins/Plastins. J Biol Chem 2016; 291:17881-96. [PMID: 27261463 DOI: 10.1074/jbc.m116.730069] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2016] [Indexed: 01/08/2023] Open
Abstract
Fimbrins/plastins have been implicated in the generation of distinct actin structures, which are linked to different cellular processes. Historically, fimbrins/plastins were mainly considered as generating tight actin bundles. Here, we demonstrate that different members of the fimbrin/plastin family have diverged biochemically during evolution to generate either tight actin bundles or loose networks with distinct biochemical and biophysical properties. Using the phylogenetically and functionally distinct Arabidopsis fimbrins FIM4 and FIM5 we found that FIM4 generates both actin bundles and cross-linked actin filaments, whereas FIM5 only generates actin bundles. The distinct functions of FIM4 and FIM5 are clearly observed at single-filament resolution. Domain swapping experiments showed that cooperation between the conformationally plastic calponin-homology domain 2 (CH2) and the N-terminal headpiece determines the function of the full-length protein. Our study suggests that the structural plasticity of fimbrins/plastins has biologically meaningful consequences, and provides novel insights into the structure-function relationship of fimbrins/plastins as well as shedding light on how cells generate distinct actin structures.
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Affiliation(s)
- Ruihui Zhang
- From the Key Laboratory of Plant Molecular Physiology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, the University of Chinese Academy of Sciences, Beijing 100049, China
| | - Ming Chang
- the Center for Plant Biology, School of Life Sciences, Tsinghua University, Beijing 100084
| | - Meng Zhang
- From the Key Laboratory of Plant Molecular Physiology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, the University of Chinese Academy of Sciences, Beijing 100049, China
| | - Youjun Wu
- From the Key Laboratory of Plant Molecular Physiology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093
| | - Xiaolu Qu
- the Center for Plant Biology, School of Life Sciences, Tsinghua University, Beijing 100084, the Tsinghua-Peking Joint Center for Life Sciences, Beijing 100084, and
| | - Shanjin Huang
- From the Key Laboratory of Plant Molecular Physiology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, the Center for Plant Biology, School of Life Sciences, Tsinghua University, Beijing 100084,
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12
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Anatomy of the red cell membrane skeleton: unanswered questions. Blood 2015; 127:187-99. [PMID: 26537302 DOI: 10.1182/blood-2014-12-512772] [Citation(s) in RCA: 221] [Impact Index Per Article: 24.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2014] [Accepted: 03/30/2015] [Indexed: 11/20/2022] Open
Abstract
The red cell membrane skeleton is a pseudohexagonal meshwork of spectrin, actin, protein 4.1R, ankyrin, and actin-associated proteins that laminates the inner membrane surface and attaches to the overlying lipid bilayer via band 3-containing multiprotein complexes at the ankyrin- and actin-binding ends of spectrin. The membrane skeleton strengthens the lipid bilayer and endows the membrane with the durability and flexibility to survive in the circulation. In the 36 years since the first primitive model of the red cell skeleton was proposed, many additional proteins have been discovered, and their structures and interactions have been defined. However, almost nothing is known of the skeleton's physiology, and myriad questions about its structure remain, including questions concerning the structure of spectrin in situ, the way spectrin and other proteins bind to actin, how the membrane is assembled, the dynamics of the skeleton when the membrane is deformed or perturbed by parasites, the role lipids play, and variations in membrane structure in unique regions like lipid rafts. This knowledge is important because the red cell membrane skeleton is the model for spectrin-based membrane skeletons in all cells, and because defects in the red cell membrane skeleton underlie multiple hemolytic anemias.
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13
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Smith C, Dolat L, Angelis D, Forgacs E, Spiliotis ET, Galkin VE. Septin 9 Exhibits Polymorphic Binding to F-Actin and Inhibits Myosin and Cofilin Activity. J Mol Biol 2015; 427:3273-3284. [PMID: 26297986 DOI: 10.1016/j.jmb.2015.07.026] [Citation(s) in RCA: 57] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2015] [Revised: 07/29/2015] [Accepted: 07/31/2015] [Indexed: 02/06/2023]
Abstract
Septins are a highly conserved family of proteins in eukaryotes that is recognized as a novel component of the cytoskeleton. Septin 9 (SEPT9) interacts directly with actin filaments and functions as an actin stress fiber cross-linking protein that promotes the maturation of nascent focal adhesions and cell migration. However, the molecular details of how SEPT9 interacts with F-actin remain unknown. Here, we use electron microscopy and image analysis to show that SEPT9 binds to F-actin in a highly polymorphic fashion. We demonstrate that the basic domain (B-domain) of the N-terminal tail of SEPT9 is responsible for actin cross-linking, while the GTP-binding domain (G-domain) does not bundle F-actin. We show that the B-domain of SEPT9 binds to three sites on F-actin, and the two of these sites overlap with the binding regions of myosin and cofilin. SEPT9 inhibits actin-dependent ATPase activity of myosin and competes with the weakly bound state of myosin for binding to F-actin. At the same time, SEPT9 significantly reduces the extent of F-actin depolymerization by cofilin. Taken together, these data suggest that SEPT9 protects actin filaments from depolymerization by cofilin and myosin and indicate a mechanism by which SEPT9 could maintain the integrity of growing and contracting actin filaments.
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Affiliation(s)
- Clayton Smith
- Department of Physiological Sciences, Eastern Virginia Medical School, Norfolk, VA 23507, USA
| | - Lee Dolat
- Department of Biology, Drexel University, Philadelphia, PA 19104, USA
| | - Dimitrios Angelis
- Department of Biology, Drexel University, Philadelphia, PA 19104, USA
| | - Eva Forgacs
- Department of Physiological Sciences, Eastern Virginia Medical School, Norfolk, VA 23507, USA
| | - Elias T Spiliotis
- Department of Biology, Drexel University, Philadelphia, PA 19104, USA.
| | - Vitold E Galkin
- Department of Physiological Sciences, Eastern Virginia Medical School, Norfolk, VA 23507, USA.
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14
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Blunk AD, Akbergenova Y, Cho RW, Lee J, Walldorf U, Xu K, Zhong G, Zhuang X, Littleton JT. Postsynaptic actin regulates active zone spacing and glutamate receptor apposition at the Drosophila neuromuscular junction. Mol Cell Neurosci 2014; 61:241-54. [PMID: 25066865 PMCID: PMC4134997 DOI: 10.1016/j.mcn.2014.07.005] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2014] [Revised: 07/14/2014] [Accepted: 07/23/2014] [Indexed: 12/26/2022] Open
Abstract
Synaptic communication requires precise alignment of presynaptic active zones with postsynaptic receptors to enable rapid and efficient neurotransmitter release. How transsynaptic signaling between connected partners organizes this synaptic apparatus is poorly understood. To further define the mechanisms that mediate synapse assembly, we carried out a chemical mutagenesis screen in Drosophila to identify mutants defective in the alignment of active zones with postsynaptic glutamate receptor fields at the larval neuromuscular junction. From this screen we identified a mutation in Actin 57B that disrupted synaptic morphology and presynaptic active zone organization. Actin 57B, one of six actin genes in Drosophila, is expressed within the postsynaptic bodywall musculature. The isolated allele, act(E84K), harbors a point mutation in a highly conserved glutamate residue in subdomain 1 that binds members of the Calponin Homology protein family, including spectrin. Homozygous act(E84K) mutants show impaired alignment and spacing of presynaptic active zones, as well as defects in apposition of active zones to postsynaptic glutamate receptor fields. act(E84K) mutants have disrupted postsynaptic actin networks surrounding presynaptic boutons, with the formation of aberrant actin swirls previously observed following disruption of postsynaptic spectrin. Consistent with a disruption of the postsynaptic actin cytoskeleton, spectrin, adducin and the PSD-95 homolog Discs-Large are all mislocalized in act(E84K) mutants. Genetic interactions between act(E84K) and neurexin mutants suggest that the postsynaptic actin cytoskeleton may function together with the Neurexin-Neuroligin transsynaptic signaling complex to mediate normal synapse development and presynaptic active zone organization.
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Affiliation(s)
- Aline D Blunk
- The Picower Institute for Learning and Memory, Massachusetts Institute of Technology, Cambridge, MA 02139, United States; Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, United States; Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, United States
| | - Yulia Akbergenova
- The Picower Institute for Learning and Memory, Massachusetts Institute of Technology, Cambridge, MA 02139, United States; Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, United States; Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, United States
| | - Richard W Cho
- The Picower Institute for Learning and Memory, Massachusetts Institute of Technology, Cambridge, MA 02139, United States; Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, United States; Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, United States
| | - Jihye Lee
- The Picower Institute for Learning and Memory, Massachusetts Institute of Technology, Cambridge, MA 02139, United States; Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, United States; Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, United States; The Department of Oral Pathology, School of Dentistry, Pusan National University, Republic of Korea
| | - Uwe Walldorf
- Department of Developmental Biology, University of Saarland, Homburg, Saar, Germany
| | - Ke Xu
- Howard Hughes Medical Institute (HHMI), Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138, United States
| | - Guisheng Zhong
- Howard Hughes Medical Institute (HHMI), Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138, United States
| | - Xiaowei Zhuang
- Howard Hughes Medical Institute (HHMI), Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138, United States; Department of Physics, Harvard University, Cambridge, MA 02138, United States
| | - J Troy Littleton
- The Picower Institute for Learning and Memory, Massachusetts Institute of Technology, Cambridge, MA 02139, United States; Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, United States; Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, United States.
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15
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Zschätzsch M, Oliva C, Langen M, De Geest N, Ozel MN, Williamson WR, Lemon WC, Soldano A, Munck S, Hiesinger PR, Sanchez-Soriano N, Hassan BA. Regulation of branching dynamics by axon-intrinsic asymmetries in Tyrosine Kinase Receptor signaling. eLife 2014; 3:e01699. [PMID: 24755286 PMCID: PMC3990184 DOI: 10.7554/elife.01699] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Axonal branching allows a neuron to connect to several targets, increasing neuronal circuit complexity. While axonal branching is well described, the mechanisms that control it remain largely unknown. We find that in the Drosophila CNS branches develop through a process of excessive growth followed by pruning. In vivo high-resolution live imaging of developing brains as well as loss and gain of function experiments show that activation of Epidermal Growth Factor Receptor (EGFR) is necessary for branch dynamics and the final branching pattern. Live imaging also reveals that intrinsic asymmetry in EGFR localization regulates the balance between dynamic and static filopodia. Elimination of signaling asymmetry by either loss or gain of EGFR function results in reduced dynamics leading to excessive branch formation. In summary, we propose that the dynamic process of axon branch development is mediated by differential local distribution of signaling receptors. DOI:http://dx.doi.org/10.7554/eLife.01699.001 In the human brain, 100 billion neurons form 100 trillion connections. Each neuron consists of a cell body with numerous small branch-like projections known as dendrites (from the Greek word for ‘tree’), plus a long cable-like structure called the axon. Neurons receive electrical inputs from neighboring cells via their dendrites, and then relay these signals onto other cells in their network via their axons. The development of the brain relies on new neurons integrating successfully into existing networks. Axon branching helps with this by enabling a single neuron to establish connections with several cells, but it is unclear how individual neurons decide when and where to form branches. Now, Zschätzsch et al. have revealed the mechanism behind this process in the fruit fly, Drosophila. Mutant flies that lack a protein called EGFR produce abnormal numbers of axon branches, suggesting that this molecule regulates branch formation. Indeed in fruit flies, just as in mammals, the developing brain initially produces excessive numbers of branches, which are subsequently pruned to leave only those that have formed appropriate connections. In Drosophila, an uneven distribution of EGFR between branches belonging to the same axon acts as a signal to regulate this pruning process. To examine this mechanism in more detail, high-resolution four-dimensional imaging was used to study brains that had been removed from Drosophila pupae and kept alive in special culture chambers. Axon branching and loss could now be followed in real time, and were found to occur more slowly in brains that lacked EGFR. The receptor controlled the branching of axons by influencing the distribution of another protein called actin, which is a key component of the internal skeleton that gives cells their structure. In addition to providing new insights into a fundamental aspect of brain development, the work of Zschätzsch et al. also highlights the importance of stochastic events in shaping the network of connections within the developing brain. These findings may well be relevant to ongoing efforts to map the human brain ‘connectome’. DOI:http://dx.doi.org/10.7554/eLife.01699.002
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Affiliation(s)
- Marlen Zschätzsch
- Center for the Biology of Disease, Vlaams Instituut voor Biotechnologie, Leuven, Belgium
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16
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Singh SM, Bandi S, Winder SJ, Mallela KMG. The actin binding affinity of the utrophin tandem calponin-homology domain is primarily determined by its N-terminal domain. Biochemistry 2014; 53:1801-9. [PMID: 24628267 DOI: 10.1021/bi500149q] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The structural determinants of the actin binding function of tandem calponin-homology (CH) domains are poorly understood, particularly the role of individual domains. We determined the actin binding affinity of isolated CH domains from human utrophin and compared them with the affinity of the full-length tandem CH domain. Traditional cosedimentation assays indicate that the C-terminal CH2 domain binds to F-actin much weaker than the full-length tandem CH domain. The N-terminal CH1 domain is less stable and undergoes severe protein aggregation; therefore, traditional actin cosedimentation assays could not be used. To address this, we have developed a folding-upon-binding method. We refolded the CH1 domain from its unfolded state in the presence of F-actin. This results in a competition between actin binding and aggregation. A differential centrifugation technique was used to distinguish actin binding from aggregation. Low-speed centrifugation pelleted CH1 aggregates, but not F-actin or its bound protein. Subsequent high-speed centrifugation resulted in the cosedimentation of bound CH1 along with F-actin. The CH1 domain binds to F-actin with an affinity similar to that of the full-length tandem CH domain, unlike the CH2 domain. The actin binding cooperativity between the two domains was quantitatively calculated from the association constants of the full-length tandem CH domain and its CH domains, and found to be much smaller than the association constant of the CH1 domain alone. These results indicate that the actin binding affinity of the utrophin tandem CH domain is primarily determined by its CH1 domain, when compared to that of its CH2 domain or the cooperativity between the two CH domains.
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Affiliation(s)
- Surinder M Singh
- Department of Pharmaceutical Sciences, Skaggs School of Pharmacy and Pharmaceutical Sciences, University of Colorado Anschutz Medical Campus , Aurora, Colorado 80045, United States
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17
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Gokhin DS, Tierney MT, Sui Z, Sacco A, Fowler VM. Calpain-mediated proteolysis of tropomodulin isoforms leads to thin filament elongation in dystrophic skeletal muscle. Mol Biol Cell 2014; 25:852-65. [PMID: 24430868 PMCID: PMC3952854 DOI: 10.1091/mbc.e13-10-0608] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Calpain-mediated proteolysis of the thin filament pointed-end–capping protein tropomodulin results in actin subunit association onto pointed ends and increased thin filament lengths in two different murine models of Duchenne muscular dystrophy. This mechanism affects different skeletal muscles in a use- and disease severity–dependent manner. Duchenne muscular dystrophy (DMD) induces sarcolemmal mechanical instability and rupture, hyperactivity of intracellular calpains, and proteolytic breakdown of muscle structural proteins. Here we identify the two sarcomeric tropomodulin (Tmod) isoforms, Tmod1 and Tmod4, as novel proteolytic targets of m-calpain, with Tmod1 exhibiting ∼10-fold greater sensitivity to calpain-mediated cleavage than Tmod4 in situ. In mdx mice, increased m-calpain levels in dystrophic soleus muscle are associated with loss of Tmod1 from the thin filament pointed ends, resulting in ∼11% increase in thin filament lengths. In mdx/mTR mice, a more severe model of DMD, Tmod1 disappears from the thin filament pointed ends in both tibialis anterior (TA) and soleus muscles, whereas Tmod4 additionally disappears from soleus muscle, resulting in thin filament length increases of ∼10 and ∼12% in TA and soleus muscles, respectively. In both mdx and mdx/mTR mice, both TA and soleus muscles exhibit normal localization of α-actinin, the nebulin M1M2M3 domain, Tmod3, and cytoplasmic γ-actin, indicating that m-calpain does not cause wholesale proteolysis of other sarcomeric and actin cytoskeletal proteins in dystrophic skeletal muscle. These results implicate Tmod proteolysis and resultant thin filament length misspecification as novel mechanisms that may contribute to DMD pathology, affecting muscles in a use- and disease severity–dependent manner.
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Affiliation(s)
- David S Gokhin
- Department of Cell and Molecular Biology, The Scripps Research Institute, La Jolla, CA 92037 Sanford Children's Health Research Center, Sanford-Burnham Medical Research Institute, La Jolla, CA 92037
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18
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Sharma S, Zhu H, Grintsevich EE, Reisler E, Gimzewski JK. Correlative nanoscale imaging of actin filaments and their complexes. NANOSCALE 2013; 5:5692-702. [PMID: 23727693 PMCID: PMC4030708 DOI: 10.1039/c3nr01039b] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
Actin remodeling is an area of interest in biology in which correlative microscopy can bring a new way to analyze protein complexes at the nanoscale. Advances in EM, X-ray diffraction, fluorescence, and single molecule techniques have provided a wealth of information about the modulation of the F-actin structure and its regulation by actin binding proteins (ABPs). Yet, there are technological limitations of these approaches to achieving quantitative molecular level information on the structural and biophysical changes resulting from ABPs interaction with F-actin. Fundamental questions about the actin structure and dynamics and how these determine the function of ABPs remain unanswered. Specifically, how local and long-range structural and conformational changes result in ABPs induced remodeling of F-actin needs to be addressed at the single filament level. Advanced, sensitive and accurate experimental tools for detailed understanding of ABP-actin interactions are much needed. This article discusses the current understanding of nanoscale structural and mechanical modulation of F-actin by ABPs at the single filament level using several correlative microscopic techniques, focusing mainly on results obtained by Atomic Force Microscopy (AFM) analysis of ABP-actin complexes.
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Affiliation(s)
- Shivani Sharma
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California, USA. Fax: +1 310 206 4038; +1 310 206 4038; Tel: +1 310 794 7514; +1 310 983 1027
- California NanoSystems Institute, University of California, Los Angeles, California, USA
| | - Huanqi Zhu
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California, USA. Fax: +1 310 206 4038; +1 310 206 4038; Tel: +1 310 794 7514; +1 310 983 1027
| | - Elena E. Grintsevich
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California, USA. Fax: +1 310 206 4038; +1 310 206 4038; Tel: +1 310 794 7514; +1 310 983 1027
| | - Emil Reisler
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California, USA. Fax: +1 310 206 4038; +1 310 206 4038; Tel: +1 310 794 7514; +1 310 983 1027
- Molecular Biology Institute, University of California, Los Angeles, California, USA
| | - James K. Gimzewski
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California, USA. Fax: +1 310 206 4038; +1 310 206 4038; Tel: +1 310 794 7514; +1 310 983 1027
- California NanoSystems Institute, University of California, Los Angeles, California, USA
- International Center for Materials Nanoarchitectonics Satellite (MANA), National Institute for Materials Science (NIMS), Tsukuba, Japan
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19
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The N-terminal actin-binding tandem calponin-homology (CH) domain of dystrophin is in a closed conformation in solution and when bound to F-actin. Biophys J 2013. [PMID: 23199925 DOI: 10.1016/j.bpj.2012.08.066] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Deficiency of the vital muscle protein dystrophin triggers Duchenne/Becker muscular dystrophy, but the structure-function relationship of dystrophin is poorly understood. To date, molecular structures of three dystrophin domains have been determined, of which the N-terminal actin-binding domain (N-ABD or ABD1) is of particular interest. This domain is composed of two calponin-homology (CH) domains, which form an important class of ABDs in muscle proteins. A previously determined x-ray structure indicates that the dystrophin N-ABD is a domain-swapped dimer, with each monomer adopting an extended, open conformation in which the two CH domains do not interact. This structure is controversial because it contradicts functional studies and known structures of similar ABDs from other muscle proteins. Here, we investigated the solution conformation of the dystrophin N-ABD using a very simple and elegant technique of pyrene excimer fluorescence. Using the wild-type protein, which contains two cysteines, and the corresponding single-cysteine mutants, we show that the protein is a monomer in solution and is in a closed conformation in which the two CH domains seem to interact, as observed from the excimer fluorescence of pyrene-labeled wild-type protein. Excimer fluorescence was also observed in its actin-bound form, indicating that the dystrophin N-ABD binds to F-actin in a closed conformation. Comparison of the dystrophin N-ABD conformation with other ABDs indicates that the tandem CH domains in general may be monomeric in solution and predominantly occur in closed conformation, whereas their actin-bound conformations may differ.
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20
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MacGrath SM, Koleske AJ. Arg/Abl2 modulates the affinity and stoichiometry of binding of cortactin to F-actin. Biochemistry 2012; 51:6644-53. [PMID: 22849492 DOI: 10.1021/bi300722t] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The Abl family nonreceptor tyrosine kinase Arg/Abl2 interacts with cortactin, an Arp2/3 complex activator, to promote actin-driven cell edge protrusion. Both Arg and cortactin bind directly to filamentous actin (F-actin). While protein-protein interactions between Arg and cortactin have well-characterized downstream effects on the actin cytoskeleton, it is unclear whether and how Arg and cortactin affect each other's actin binding properties. We employ actin cosedimentation assays to show that Arg increases the stoichiometry of binding of cortactin to F-actin at saturation. Using a series of Arg deletion mutants and fragments, we demonstrate that the Arg C-terminal calponin homology domain is necessary and sufficient to increase the stoichiometry of binding of cortactin to F-actin. We also show that interactions between Arg and cortactin are required for optimal affinity between cortactin and the actin filament. Our data suggest a mechanism for Arg-dependent stimulation of binding of cortactin to F-actin, which may facilitate the recruitment of cortactin to sites of local actin network assembly.
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Affiliation(s)
- Stacey M MacGrath
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520, USA
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21
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Broderick MJF, Bobkov A, Winder SJ. Utrophin ABD binds to F-actin in an open conformation. FEBS Open Bio 2012; 2:6-11. [PMID: 23650574 PMCID: PMC3642092 DOI: 10.1016/j.fob.2012.01.001] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2012] [Accepted: 01/18/2012] [Indexed: 11/20/2022] Open
Abstract
Structural analyses of actin binding regions comprising tandem calponin homology domains alone and when bound to F-actin have revealed a number of different conformations with calponin homology domains in ‘open’ and ‘closed’ positions. In an attempt to resolve these issues we have examined the properties of the utrophin actin binding domain in open and closed conformations in order to verify the conformation when bound to F-actin. Locking the actin binding domain in a closed conformation using engineered cysteine residues in each calponin homology domain reduced the affinity for F-actin without affecting the stoichiometry furthermore differential scanning calorimetry experiments revealed a reduction in melting temperature on binding to actin. The data suggest the amino-terminal utrophin actin binding domain is in an open conformation in solution and when bound to F-actin.
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Key Words
- ABD, actin binding domain
- Actin binding domain
- CD, circular dichroism
- CH, calponin homology
- Calponin homology domain
- DSC, differential scanning calorimetry
- Differential scanning calorimetry
- Dystrophin
- EM, electron microscopy
- F-actin, filamentous actin
- NTCB, 2-nitro-5-thiocyanobenzoic acid
- SDS-PAGE, sodium dodecyl sulphate poly-acrylamide electrophoresis
- Spectrin
- Tm, melting temperature
- UTR261, utrophin residues 1-261
- α-Actinin
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Affiliation(s)
- Mike J F Broderick
- Department of Biomedical Science, University of Sheffield, Firth Court, Western Bank, Sheffield S10 2TN, UK ; IBLS, University of Glasgow, Glasgow G12 8QQ, UK
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22
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Large-scale opening of utrophin's tandem calponin homology (CH) domains upon actin binding by an induced-fit mechanism. Proc Natl Acad Sci U S A 2011; 108:12729-33. [PMID: 21768337 DOI: 10.1073/pnas.1106453108] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
We have used site-directed spin labeling and pulsed electron paramagnetic resonance to resolve a controversy concerning the structure of the utrophin-actin complex, with implications for the pathophysiology of muscular dystrophy. Utrophin is a homolog of dystrophin, the defective protein in Duchenne and Becker muscular dystrophies, and therapeutic utrophin derivatives are currently being developed. Both proteins have a pair of N-terminal calponin homology (CH) domains that are important for actin binding. Although there is a crystal structure of the utrophin actin-binding domain, electron microscopy of the actin-bound complexes has produced two very different structural models, in which the CH domains are in open or closed conformations. We engineered a pair of labeling sites in the CH domains of utrophin and used dipolar electron-electron resonance to determine the distribution of interdomain distances with high resolution. We found that the two domains are flexibly connected in solution, indicating a dynamic equilibrium between two distinct open structures. Upon actin binding, the two domains become dramatically separated and ordered, indicating a transition to a single open and extended conformation. There is no trace of this open conformation of utrophin in the absence of actin, providing strong support for an induced-fit model of actin binding.
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23
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Nestor MW, Cai X, Stone MR, Bloch RJ, Thompson SM. The actin binding domain of βI-spectrin regulates the morphological and functional dynamics of dendritic spines. PLoS One 2011; 6:e16197. [PMID: 21297961 PMCID: PMC3031527 DOI: 10.1371/journal.pone.0016197] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2010] [Accepted: 12/07/2010] [Indexed: 01/30/2023] Open
Abstract
Actin microfilaments regulate the size, shape and mobility of dendritic spines and are in turn regulated by actin binding proteins and small GTPases. The βI isoform of spectrin, a protein that links the actin cytoskeleton to membrane proteins, is present in spines. To understand its function, we expressed its actin-binding domain (ABD) in CA1 pyramidal neurons in hippocampal slice cultures. The ABD of βI-spectrin bundled actin in principal dendrites and was concentrated in dendritic spines, where it significantly increased the size of the spine head. These effects were not observed after expression of homologous ABDs of utrophin, dystrophin, and α-actinin. Treatment of slice cultures with latrunculin-B significantly decreased spine head size and decreased actin-GFP fluorescence in cells expressing the ABD of α-actinin, but not the ABD of βI-spectrin, suggesting that its presence inhibits actin depolymerization. We also observed an increase in the area of GFP-tagged PSD-95 in the spine head and an increase in the amplitude of mEPSCs at spines expressing the ABD of βI-spectrin. The effects of the βI-spectrin ABD on spine size and mEPSC amplitude were mimicked by expressing wild-type Rac3, a small GTPase that co-immunoprecipitates specifically with βI-spectrin in extracts of cultured cortical neurons. Spine size was normal in cells co-expressing a dominant negative Rac3 construct with the βI-spectrin ABD. We suggest that βI-spectrin is a synaptic protein that can modulate both the morphological and functional dynamics of dendritic spines, perhaps via interaction with actin and Rac3.
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Affiliation(s)
- Michael W. Nestor
- Department of Physiology, University of Maryland School of Medicine, Baltimore, Maryland, United States of America
- Program in Neuroscience, University of Maryland School of Medicine, Baltimore, Maryland, United States of America
- Training Program in Integrative Membrane Biology, University of Maryland School of Medicine, Baltimore, Maryland, United States of America
| | - Xiang Cai
- Department of Physiology, University of Maryland School of Medicine, Baltimore, Maryland, United States of America
| | - Michele R. Stone
- Department of Physiology, University of Maryland School of Medicine, Baltimore, Maryland, United States of America
| | - Robert J. Bloch
- Department of Physiology, University of Maryland School of Medicine, Baltimore, Maryland, United States of America
- Program in Neuroscience, University of Maryland School of Medicine, Baltimore, Maryland, United States of America
- Training Program in Integrative Membrane Biology, University of Maryland School of Medicine, Baltimore, Maryland, United States of America
| | - Scott M. Thompson
- Department of Physiology, University of Maryland School of Medicine, Baltimore, Maryland, United States of America
- Program in Neuroscience, University of Maryland School of Medicine, Baltimore, Maryland, United States of America
- Training Program in Integrative Membrane Biology, University of Maryland School of Medicine, Baltimore, Maryland, United States of America
- * E-mail:
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24
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The carboxyterminal EF domain of erythroid alpha-spectrin is necessary for optimal spectrin-actin binding. Blood 2010; 116:2600-7. [PMID: 20585040 DOI: 10.1182/blood-2009-12-260612] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Spectrin and protein 4.1R crosslink F-actin, forming the membrane skeleton. Actin and 4.1R bind to one end of β-spectrin. The adjacent end of α-spectrin, called the EF domain, is calmodulin-like, with calcium-dependent and calcium-independent EF hands. The severely anemic sph(1J)/sph(1J) mouse has very fragile red cells and lacks the last 13 amino acids in the EF domain, implying that the domain is critical for skeletal integrity. To test this, we constructed a minispectrin heterodimer from the actin-binding domain, the EF domain, and 4 adjacent spectrin repeats in each chain. The minispectrin bound to F-actin in the presence of native human protein 4.1R. Formation of the spectrin-actin-4.1R complex was markedly attenuated when the minispectrin contained the shortened sph(1J) α-spectrin. The α-spectrin deletion did not interfere with spectrin heterodimer assembly or 4.1R binding but abolished the binary interaction between spectrin and F-actin. The data show that the α-spectrin EF domain greatly amplifies the function of the β-spectrin actin-binding domain (ABD) in forming the spectrin-actin-4.1R complex. A model, based on the structure of α-actinin, suggests that the EF domain modulates the function of the ABD and that the C-terminal EF hands (EF(34)) may bind to the linker that connects the ABD to the first spectrin repeat.
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25
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Abstract
The dynamic remolding of the actin cytoskeleton is a critical part of most cellular activities, and malfunction of cytoskeletal proteins results in various human diseases. The transition between two forms of actin, monomeric or G-actin and filamentous or F-actin, is tightly regulated in time and space by a large number of signaling, scaffolding and actin-binding proteins (ABPs). New ABPs are constantly being discovered in the post-genomic era. Most of these proteins are modular, integrating actin binding, protein-protein interaction, membrane-binding, and signaling domains. In response to extracellular signals, often mediated by Rho family GTPases, ABPs control different steps of actin cytoskeleton assembly, including filament nucleation, elongation, severing, capping, and depolymerization. This review summarizes structure-function relationships among ABPs in the regulation of actin cytoskeleton assembly.
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Affiliation(s)
- Sung Haeng Lee
- Chosun University School of Medicine, Department of Cellular and Molecular Medicine, Gwangju 501-759, Korea.
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26
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Grintsevich EE, Galkin VE, Orlova A, Ytterberg AJ, Mikati MM, Kudryashov DS, Loo JA, Egelman EH, Reisler E. Mapping of drebrin binding site on F-actin. J Mol Biol 2010; 398:542-54. [PMID: 20347847 DOI: 10.1016/j.jmb.2010.03.039] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2009] [Revised: 03/18/2010] [Accepted: 03/19/2010] [Indexed: 01/09/2023]
Abstract
Drebrin is a filament-binding protein involved in organizing the dendritic pool of actin. Previous in vivo studies identified the actin-binding domain of drebrin (DrABD), which causes the same rearrangements in the cytoskeleton as the full-length protein. Site-directed mutagenesis, electron microscopic reconstruction, and chemical cross-linking combined with mass spectrometry analysis were employed here to map the DrABD binding interface on actin filaments. DrABD could be simultaneously attached to two adjacent actin protomers using the combination of 2-iminothiolane (Traut's reagent) and MTS1 [1,1-methanediyl bis(methanethiosulfonate)]. Site-directed mutagenesis combined with chemical cross-linking revealed that residue 238 of DrABD is located within 5.4 A from C374 of actin protomer 1 and that native cysteine 308 of drebrin is near C374 of actin protomer 2. Mass spectrometry analysis revealed that a zero-length cross-linker, 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide, can link the N-terminal G-S extension of the recombinant DrABD to E99 and/or E100 on actin. Efficient cross-linking of drebrin residues 238, 248, 252, 270, and 271 to actin residue 51 was achieved with reagents of different lengths (5.4-19 A). These results suggest that the "core" DrABD is centered on actin subdomain 2 and may adopt a folded conformation upon binding to F-actin. The results of electron microscopic reconstruction, which are in a good agreement with the cross-linking data, revealed polymorphism in DrABD binding to F-actin and suggested the existence of two binding sites. These results provide new structural insight into the previously observed competition between drebrin and several other F-actin-binding proteins.
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Affiliation(s)
- Elena E Grintsevich
- Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095, USA
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27
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The RecB nuclease domain binds to RecA-DNA filaments: implications for filament loading. J Mol Biol 2009; 391:269-74. [PMID: 19540850 DOI: 10.1016/j.jmb.2009.06.042] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2009] [Revised: 05/29/2009] [Accepted: 06/16/2009] [Indexed: 11/23/2022]
Abstract
The E. coli RecBCD enzyme facilitates the loading of RecA onto single-stranded DNA produced by the combined helicase/nuclease activity of RecBCD. The nuclease domain of RecB protein, RecB(nuc), has been previously shown to bind RecA. Surprisingly, RecB(nuc) also binds to phage and eukaryotic homologs of RecA, leading to the suggestion that RecB(nuc) interacts with the polymerization motif that is present in all three proteins. This mode of interaction could only be with monomeric RecA, as this motif would be buried in filaments. We show that RecB(nuc) binds extensively to the outside of RecA-DNA filaments. Three-dimensional reconstructions suggest that RecB(nuc) binds to the ATP-binding core of RecA, with a displacement of the C-terminal domain of RecA. Solution experiments confirm that the interaction of RecB(nuc) is only with the RecA core. Since the RecA C-terminal domain has been shown to be regulatory, the interaction observed may be part of the loading mechanism where RecB displaces the RecA C-terminal domain and activates a RecA monomer for polymerization.
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28
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Sawyer GM, Clark AR, Robertson SP, Sutherland-Smith AJ. Disease-associated substitutions in the filamin B actin binding domain confer enhanced actin binding affinity in the absence of major structural disturbance: Insights from the crystal structures of filamin B actin binding domains. J Mol Biol 2009; 390:1030-47. [PMID: 19505475 DOI: 10.1016/j.jmb.2009.06.009] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2009] [Revised: 05/29/2009] [Accepted: 06/03/2009] [Indexed: 10/20/2022]
Abstract
Missense mutations in filamin B (FLNB) are associated with the autosomal dominant atelosteogenesis (AO) and the Larsen group of skeletal malformation disorders. These mutations cluster in particular FLNB protein domains and act in a presumptive gain-of-function mechanism. In contrast the loss-of-function disorder, spondylocarpotarsal synostosis syndrome, is characterised by the complete absence of FLNB. One cluster of AO missense mutations is found within the second of two calponin homology (CH) domains that create a functional actin-binding domain (ABD). This N-terminal ABD is required for filamin F-actin crosslinking activity, a crucial aspect of filamin's role of integrating cell-signalling events with cellular scaffolding and mechanoprotection. This study characterises the wild type FLNB ABD and investigates the effects of two disease-associated mutations on the structure and function of the FLNB ABD that could explain a gain-of-function mechanism for the AO diseases. We have determined high-resolution X-ray crystal structures of the human filamin B wild type ABD, plus W148R and M202V mutants. All three structures display the classic compact monomeric conformation for the ABD with the CH1 and CH2 domains in close contact. The conservation of tertiary structure in the presence of these mutations shows that the compact ABD conformation is stable to the sequence substitutions. In solution the mutant ABDs display reduced melting temperatures (by 6-7 degrees C) as determined by differential scanning fluorimetry. Characterisation of the wild type and mutant ABD F-actin binding activities via co-sedimentation assays shows that the mutant FLNB ABDs have increased F-actin binding affinities, with dissociation constants of 2.0 microM (W148R) and 0.56 microM (M202V), compared to the wild type ABD K(d) of 7.0 microM. The increased F-actin binding affinity of the mutants presents a biochemical mechanism that differentiates the autosomal dominant gain-of-function FLNB disorders from those that arise through the complete loss of FLNB protein.
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Affiliation(s)
- Gregory M Sawyer
- Institute of Molecular BioSciences, Massey University, Palmerston North, New Zealand
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29
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Dystrophin and utrophin have distinct effects on the structural dynamics of actin. Proc Natl Acad Sci U S A 2009; 106:7822-7. [PMID: 19416869 DOI: 10.1073/pnas.0812007106] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We have used time-resolved spectroscopy to investigate the structural dynamics of actin interaction with dystrophin and utrophin in relationship to the pathology of muscular dystrophy. Dystrophin and utrophin bind actin in vitro with similar affinities, but the molecular contacts of these two proteins with actin are different. It has been hypothesized that the presence of two low-affinity actin-binding sites in dystrophin allows more elastic response of the actin-dystrophin-sarcolemma linkage to muscle stretches, compared with utrophin, which binds via one contiguous actin-binding domain. We have directly tested this hypothesis by determining the effects of dystrophin and utrophin on the microsecond rotational dynamics of a phosphorescent dye attached to C374 on actin, as detected by transient phosphorescence anisotropy (TPA). Binding of dystrophin or utrophin to actin resulted in significant changes in the TPA decay, increasing the final anisotropy (restricting the rotational amplitude) and decreasing the rotational correlation times (increasing the rotational rates and the torsional flexibility). This paradoxical combination of effects on actin dynamics (decreased amplitude but increased rate) has not been observed for other actin-binding proteins. Thus, when dystrophin or utrophin binds, actin becomes less like cast iron (strong but brittle) and more like steel (stronger and more resilient). At low levels of saturation, the binding of dystrophin and utrophin has similar effects, but at higher levels, utrophin caused much greater restrictions in amplitude and increases in rate. The effects of dystrophin and utrophin on actin dynamics provide molecular insight into the pathology of muscular dystrophy.
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30
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Sjöblom B, Ylänne J, Djinović-Carugo K. Novel structural insights into F-actin-binding and novel functions of calponin homology domains. Curr Opin Struct Biol 2008; 18:702-8. [PMID: 18952167 DOI: 10.1016/j.sbi.2008.10.003] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2008] [Revised: 10/14/2008] [Accepted: 10/14/2008] [Indexed: 12/23/2022]
Abstract
Tandem calponin homology (CH) domains are well-known actin filaments (F-actin) binding motifs. There has been a continuous debate about the details of CH domain-actin interaction, mainly because atomic level structures of F-actin are not available. A recent electron microscopy study has considerably advanced our structural understanding of CH domain:F-actin complex. On the contrary, it has recently also been shown that CH domains can bind other macromolecular systems: two CH domains from separate polypeptides Ncd80, Nuf2 can form a microtubule-binding site, as well as tandem CH domains in the EB1 dimer, while the single C-terminal CH domain of alpha-parvin has been observed to bind to a alpha-helical leucin-aspartate rich motif from paxillin.
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Affiliation(s)
- Björn Sjöblom
- Department for Biomolecular Structural Chemistry, Max F. Perutz Laboratories, University of Vienna, Campus Vienna Biocenter 5, A-1030 Vienna, Austria
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31
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Egelman EH. Problems in fitting high resolution structures into electron microscopic reconstructions. HFSP JOURNAL 2008; 2:324-31. [PMID: 19436497 DOI: 10.2976/1.2992221] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/13/2008] [Indexed: 11/19/2022]
Abstract
Great advances have been made in electron microscopy (EM) over the past decade, with the result that a number of protein complexes have been solved at near-atomic resolution using EM imaging. However, only a limited number of such complexes are expected to have the high degree of internal order needed to achieve this type of resolution. Many other complexes and polymers will be visualized and reconstructed by EM at an intermediate level of resolution, where the polypeptide chain cannot be directly traced. Crystal and nuclear magnetic resonance structures for components or subunits of these higher-order assemblies are frequently available. One of the greatest strengths of EM continues to be the ability to dock high-resolution structures of components into low or intermediate resolution reconstructions of assemblies to build pseudoatomic models for quaternary structure. This review discusses the strengths and limitations of this approach, with particular emphasis on protein polymers. I discuss how limitations in resolution can lead to ambiguities in building models, and these cannot be always be resolved with available data. The use of homology models for quaternary structure are particularly problematic, given accumulating evidence for the divergence of quaternary structures at the same time that tertiary structure can be conserved.
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Affiliation(s)
- Edward H Egelman
- Department of Biochemistry and Molecular Genetics, University of Virginia, Charlottesville, Virginia 22908-0733
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32
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Lee SH, Weins A, Hayes DB, Pollak MR, Dominguez R. Crystal structure of the actin-binding domain of alpha-actinin-4 Lys255Glu mutant implicated in focal segmental glomerulosclerosis. J Mol Biol 2008; 376:317-24. [PMID: 18164029 PMCID: PMC2255586 DOI: 10.1016/j.jmb.2007.11.084] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2007] [Revised: 11/22/2007] [Accepted: 11/28/2007] [Indexed: 11/28/2022]
Abstract
Mutations in alpha-actinin-4 have been linked to familial focal segmental glomerulosclerosis (FSGS), a common renal disorder in humans, and produce an apparent increase in the actin-binding affinity of alpha-actinin-4 in vitro. One of the mutations, in particular, Lys255Glu, falls in the middle of the actin-binding interface of the actin-binding domain (ABD). The ABD consists of tandem calponin homology (CH) domains (CH1 and CH2). The crystal structures of most ABDs display a compact conformation, characterized by extensive inter-CH interactions. However, the conformation of F-actin-bound ABDs is unsettled. Some electron microscopy studies find that the compact conformation is preserved upon binding to F-actin, whereas other studies suggest that the CHs separate and the ABD becomes extended. The Lys255Glu mutation in CH2 is significant in this regard since it removes a crucial inter-CH interaction with Trp147 of CH1, thought to stabilize the compact conformation. Together, the increased actin-binding affinity and the removal of this important inter-CH contact suggested that the Lys255Glu mutation might facilitate the transition toward the open ABD conformation proposed by some of the electron microscopy studies. However, the crystal structure of the ABD of alpha-actinin-4 Lys255Glu mutant described here displays the canonical compact conformation. Furthermore, the sedimentation coefficients by analytical ultracentrifugation of wild-type and FSGS mutant ABDs (Lys255Glu, Ser262Pro, and Thr259Ile) are nearly identical (2.50+/-0.03 S) and are in good agreement with the theoretical value calculated from the crystal structure (2.382 S), implying that the compact conformation is retained in solution. The absence of a structural change suggests that the compact ABD conformation observed in the majority of the structures is highly stable and is preserved in solution, even in FSGS mutant ABDs.
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Affiliation(s)
- Sung Haeng Lee
- University of Pennsylvania School of Medicine, Department of Physiology, 3700 Hamilton Walk, Philadelphia, PA 19104−6085
| | - Astrid Weins
- Renal and Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, USA
| | - David B. Hayes
- Boston Biomedical Research Institute, 64 Grove Street, Watertown, MA 02472
| | - Martin R. Pollak
- Renal and Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, USA
| | - Roberto Dominguez
- University of Pennsylvania School of Medicine, Department of Physiology, 3700 Hamilton Walk, Philadelphia, PA 19104−6085
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33
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High-resolution cryo-EM structure of the F-actin-fimbrin/plastin ABD2 complex. Proc Natl Acad Sci U S A 2008; 105:1494-8. [PMID: 18234857 DOI: 10.1073/pnas.0708667105] [Citation(s) in RCA: 96] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Many actin binding proteins have a modular architecture, and calponin-homology (CH) domains are one such structurally conserved module found in numerous proteins that interact with F-actin. The manner in which CH-domains bind F-actin has been controversial. Using cryo-EM and a single-particle approach to helical reconstruction, we have generated 12-A-resolution maps of F-actin alone and F-actin decorated with a fragment of human fimbrin (L-plastin) containing tandem CH-domains. The high resolution allows an unambiguous fit of the crystal structure of fimbrin into the map. The interaction between fimbrin ABD2 (actin binding domain 2) and F-actin is different from any interaction previously observed or proposed for tandem CH-domain proteins, showing that the structural conservation of the CH-domains does not lead to a conserved mode of interaction with F-actin. Both the stapling of adjacent actin protomers and the additional closure of the nucleotide binding cleft in F-actin when the fimbrin fragment binds may explain how fimbrin can stabilize actin filaments. A mechanism is proposed where ABD1 of fimbrin becomes activated for binding a second actin filament after ABD2 is bound to a first filament, and this can explain how mutations of residues buried in the interface between ABD2 and ABD1 can rescue temperature-sensitive defects in actin.
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34
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Bruneau EG, Brenner DS, Kuwada JY, Akaaboune M. Acetylcholine Receptor Clustering Is Required for the Accumulation and Maintenance of Scaffolding Proteins. Curr Biol 2008; 18:109-15. [DOI: 10.1016/j.cub.2007.12.029] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2007] [Revised: 12/06/2007] [Accepted: 12/07/2007] [Indexed: 11/29/2022]
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35
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Dobbins GC, Zhang B, Xiong WC, Mei L. The role of the cytoskeleton in neuromuscular junction formation. J Mol Neurosci 2007; 30:115-8. [PMID: 17192654 DOI: 10.1385/jmn:30:1:115] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/1999] [Revised: 11/30/1999] [Accepted: 11/30/1999] [Indexed: 11/11/2022]
Abstract
The cytoskeleton plays a vital role in neuromuscular junction (NMJ) formation. It is responsible for shaping synaptic membrane into folds opposed to presynaptic active zones and anchoring acetylcholine receptors (AChRs) to the crest of the junctional folds. Acetylcholine receptors (AChRs) associate with the actin cytoskeleton, the disruption of which affects spontaneous and agrin-induced AChR clusters (Prives et al., 1982; Connolly, 1984; Peng and Phelan, 1984; Bloch, 1986; Dai et al., 2000). How AChRs are tethered to the actin cytoskeleton remains unclear.
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Affiliation(s)
- G Clement Dobbins
- Program of Developmental Neurobiology, Institute of Molecular Medicine and Genetics, Department of Neurology, Medical College of Georgia, Augusta, GA 30912, USA
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36
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Egelman EH. The iterative helical real space reconstruction method: surmounting the problems posed by real polymers. J Struct Biol 2007; 157:83-94. [PMID: 16919474 DOI: 10.1016/j.jsb.2006.05.015] [Citation(s) in RCA: 186] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2006] [Revised: 05/02/2006] [Accepted: 05/16/2006] [Indexed: 11/20/2022]
Abstract
Many important biological macromolecules exist as helical polymers. Examples are actin, tubulin, myosin, RecA, Rad51, flagellin, pili, and filamentous bacteriophage. The first application of three-dimensional reconstruction from electron microscopic images was to a helical polymer, and a number of laboratories today are using helical tubes of integral membrane proteins for solving the structure of these proteins in the electron microscope at near atomic resolution. We have developed a method to analyze and reconstruct electron microscopic images of macromolecular helical polymers, the iterative helical real space reconstruction (IHRSR) algorithm. We can show that when there is disorder or heterogeneity, when the specimens diffract weakly, or when Bessel functions overlap, we can do far better with our method than can be done using traditional Fourier-Bessel approaches. In many cases, structures that were not even amenable to analysis can be solved at fairly high resolution using our method. The problems inherent in the traditional approach are discussed, and examples are presented illustrating how the IHRSR approach surmounts these problems.
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Affiliation(s)
- Edward H Egelman
- Department of Biochemistry and Molecular Genetics, University of Virginia Health Sciences, P.O. Box 800733, Charlottesville, VA 22908-0733, USA.
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37
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Ervasti JM. Dystrophin, its interactions with other proteins, and implications for muscular dystrophy. Biochim Biophys Acta Mol Basis Dis 2006; 1772:108-17. [PMID: 16829057 DOI: 10.1016/j.bbadis.2006.05.010] [Citation(s) in RCA: 221] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2006] [Revised: 05/31/2006] [Accepted: 05/31/2006] [Indexed: 11/27/2022]
Abstract
Duchenne muscular dystrophy is the most prevalent and severe form of human muscular dystrophy. Investigations into the molecular basis for Duchenne muscular dystrophy were greatly facilitated by seminal studies in the 1980s that identified the defective gene and its major protein product, dystrophin. Biochemical studies revealed its tight association with a multi-subunit complex, the so-named dystrophin-glycoprotein complex. Since its description, the dystrophin-glycoprotein complex has emerged as an important structural unit of muscle and also as a critical nexus for understanding a diverse array of muscular dystrophies arising from defects in several distinct genes. The dystrophin homologue utrophin can compensate at the cell/tissue level for dystrophin deficiency, but functions through distinct molecular mechanisms of protein-protein interaction.
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Affiliation(s)
- James M Ervasti
- Department of Physiology, 127 Service Memorial Institute, University of Wisconsin Medical School, 1300 University Avenue, Madison, WI 53706, USA.
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38
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Galkin VE, Orlova A, Fattoum A, Walsh MP, Egelman EH. The CH-domain of calponin does not determine the modes of calponin binding to F-actin. J Mol Biol 2006; 359:478-85. [PMID: 16626733 DOI: 10.1016/j.jmb.2006.03.044] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2006] [Revised: 03/15/2006] [Accepted: 03/20/2006] [Indexed: 11/30/2022]
Abstract
Many actin-binding proteins have been observed to have a modular architecture. One of the most abundant modules is the calponin-homology (CH) domain, found as tandem repeats in proteins that cross-link actin filaments (such as fimbrin, spectrin and alpha-actinin) or link the actin cytoskeleton to intermediate filaments (such as plectin). In proteins such as the eponymous calponin, IQGAP1, and Scp1, a single CH-domain exists, but there has been some controversy over whether this domain binds to actin filaments. A previous three-dimensional reconstruction of the calponin-F-actin complex has led to the conclusion that the visualized portion of calponin bound to actin belongs to its amino-terminal homology (CH) domain. We show, using a calponin fragment lacking the CH-domain, that this domain is not bound to F-actin, and cannot be positioning calponin on F-actin as hypothesized. Further, using classification methods, we show a multiplicity in cooperative modes of binding of calponin to F-actin, similar to what has been observed for other actin-binding proteins such as tropomyosin and cofilin. Our results suggest that the form and function of the structurally conserved CH-domain found in many other actin-binding proteins have diverged. This has broad implications for inferring function from the presence of structurally conserved domains.
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Affiliation(s)
- Vitold E Galkin
- Department of Biochemistry and Molecular Genetics, University of Virginia, Charlottesville, VA 22908-0733, USA
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39
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Borrego-Diaz E, Kerff F, Lee SH, Ferron F, Li Y, Dominguez R. Crystal structure of the actin-binding domain of alpha-actinin 1: evaluating two competing actin-binding models. J Struct Biol 2006; 155:230-8. [PMID: 16698282 DOI: 10.1016/j.jsb.2006.01.013] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2005] [Accepted: 01/29/2006] [Indexed: 11/28/2022]
Abstract
Alpha-actinin belongs to the spectrin family of actin crosslinking and bundling proteins that function as key regulators of cell motility, morphology and adhesion. The actin-binding domain (ABD) of these proteins consists of two consecutive calponin homology (CH) domains. Electron microscopy studies on ABDs appear to support two competing actin-binding models, extended and compact, whereas the crystal structures typically display a compact conformation. We have determined the 1.7A resolution structure of the ABD of alpha-actinin 1, a ubiquitously expressed isoform. The structure displays the classical compact conformation. We evaluated the two binding models by surface conservation analysis. The results show a conserved surface that spans both domains and corresponds to two previously identified actin-binding sites (ABS2 and ABS3). A third, and probably less important site, ABS1, is mostly buried in the compact conformation. However, a thorough examination of existing structures suggests a weak and semi-polar binding interface between the two CHs, leaving open the possibility of domain reorientation or opening. Our results are consistent with a two-step binding mechanism in which the ABD interacts first in the compact form observed in the structures, and then transitions toward a higher affinity state, possibly through minor rearrangement of the domains.
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Affiliation(s)
- Emma Borrego-Diaz
- Boston Biomedical Research Institute, 64 Grove Street, Watertown, MA 02472, USA
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40
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Cherepanova O, Orlova A, Galkin VE, van der Ven PFM, Fürst DO, Jin JP, Egelman EH. Xin-repeats and nebulin-like repeats bind to F-actin in a similar manner. J Mol Biol 2005; 356:714-23. [PMID: 16384582 DOI: 10.1016/j.jmb.2005.11.082] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2005] [Revised: 11/16/2005] [Accepted: 11/26/2005] [Indexed: 10/25/2022]
Abstract
Xin and nebulette are striated muscle-specific actin-binding proteins that both contain multiple actin-binding repeats. The nature of these repeats is different: nebulette has nebulin-like repeats, while Xin contains its own unique repeats. However, the suggestion was made from biochemical data that the Xin-repeats may bind to multiple sites on the actin molecule as was found for nebulin. We have used electron microscopy and the iterative helical real space reconstruction to visualize complexes of F-actin with Xin fragments containing either three or six Xin-repeats, and with the CN5-nebulette fragment, containing five nebulin-like repeats. Our results indicate that Xin and nebulette fragments bind to F-actin in a similar manner and in two distinct modes: in one mode actin subdomain 1 is bound, while in the second mode the binding bridges between a different site on actin subdomains 1/2 of one protomer and subdomains 3/4 of an adjacent actin protomer. Taken together with published data about nebulin, tropomyosin and ADF/cofilin, our results suggest that the ability to bind in multiple modes to the actin protomer is a general property of many actin-binding proteins.
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Affiliation(s)
- Olga Cherepanova
- Department of Biochemistry and Molecular Genetics, University of Virginia Health Sciences Center, Charlottesville, VA 22908-0733, USA
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41
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Volkmann N, Liu H, Hazelwood L, Krementsova EB, Lowey S, Trybus KM, Hanein D. The structural basis of myosin V processive movement as revealed by electron cryomicroscopy. Mol Cell 2005; 19:595-605. [PMID: 16137617 DOI: 10.1016/j.molcel.2005.07.015] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2005] [Revised: 06/20/2005] [Accepted: 07/14/2005] [Indexed: 11/24/2022]
Abstract
The processive motor myosin V has a relatively high affinity for actin in the presence of ATP and, thus, offers the unique opportunity to visualize some of the weaker, hitherto inaccessible, actin bound states of the ATPase cycle. Here, electron cryomicroscopy together with computer-based docking of crystal structures into three-dimensional (3D) reconstructions provide the atomic models of myosin V in both weak and strong actin bound states. One structure shows that ATP binding opens the long cleft dividing the actin binding region of the motor domain, thus destroying the strong binding actomyosin interface while rearranging loop 2 as a tether. Nucleotide analogs showed a second new state in which the lever arm points upward, in a prepower-stroke configuration (lever arm up) bound to actin before phosphate release. Our findings reveal how the structural elements of myosin V work together to allow myosin V to step along actin for multiple ATPase cycles without dissociating.
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Affiliation(s)
- Niels Volkmann
- The Program of Cell Adhesion, The Burnham Institute, La Jolla, California 92037, USA
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42
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Abstract
Actin participates in more protein-protein interactions than any other known protein, including the interaction of actin with itself to form the helical polymer F-actin. The vast majority of actin-binding proteins (ABPs) can be grouped into conserved families. Only a handful of structures of complexes of actin with ABPs have been determined so far. These structures are starting to reveal how certain ABPs, including gelsolin, vitamin D-binding protein and Wiskott-Aldrich syndrome protein (WASP)-homology domain-2-related proteins, share a common actin-binding motif. It is proposed here that other ABPs, including actin itself, might share this motif, providing a mechanism whereby ABPs and actin compete for a common binding site. Of particular interest is a hydrophobic pocket that mediates important interactions in five of the existing structures of actin complexes. As the pocket remains accessible in F-actin, it is proposed that this pocket represents a primary target for F-actin-binding proteins, such as calponin-homology-related proteins and myosin.
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Affiliation(s)
- Roberto Dominguez
- Boston Biomedical Research Institute, 64 Grove Street, Watertown, MA 02472, USA.
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43
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Stone MR, O'Neill A, Catino D, Bloch RJ. Specific interaction of the actin-binding domain of dystrophin with intermediate filaments containing keratin 19. Mol Biol Cell 2005; 16:4280-93. [PMID: 16000376 PMCID: PMC1196337 DOI: 10.1091/mbc.e05-02-0112] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Cytokeratins 8 and 19 concentrate at costameres of striated muscle and copurify with the dystrophin-glycoprotein complex, perhaps through the interaction of the cytokeratins with the actin-binding domain of dystrophin. We overexpressed dystrophin's actin-binding domain (Dys-ABD), K8 and K19, as well as closely related proteins, in COS-7 cells to assess the basis and specificity of their interaction. Dys-ABD alone associated with actin microfilaments. Expressed with K8 and K19, which form filaments, Dys-ABD associated preferentially with the cytokeratins. This interaction was specific, as the homologous ABD of betaI-spectrin failed to interact with K8/K19 filaments, and Dys-ABD did not associate with desmin or K8/K18 filaments. Studies in COS-7 cells and in vitro showed that Dys-ABD binds directly and specifically to K19. Expressed in muscle fibers in vivo, K19 accumulated in the myoplasm in structures that contained dystrophin and spectrin and disrupted the organization of the sarcolemma. K8 incorporated into sarcomeres, with no effect on the sarcolemma. Our results show that dystrophin interacts through its ABD with K19 specifically and are consistent with the idea that cytokeratins associate with dystrophin at the sarcolemma of striated muscle.
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Affiliation(s)
- Michele R Stone
- Department of Physiology, University of Maryland School of Medicine, Baltimore, MD 21201, USA
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44
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Rybakova IN, Ervasti JM. Identification of spectrin-like repeats required for high affinity utrophin-actin interaction. J Biol Chem 2005; 280:23018-23. [PMID: 15826935 DOI: 10.1074/jbc.m502530200] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Most studies aimed at characterizing the utrophinactin interaction have focused on the amino-terminal tandem calponin homology domain. However, we recently reported evidence suggesting that spectrin-like repeats of utrophin also participate in binding to actin. Here we expressed several recombinant fragments encoding the utrophin amino-terminal domain alone or in combination with various numbers of spectrin-like repeats. We further quantitatively characterized the actin binding properties of each recombinant utrophin fragment using a high-speed sedimentation assay. To evaluate the capacity of each protein to stabilize actin filaments, we compared the effect of utrophin recombinant fragments and full-length utrophin on 6-propionyl-2-(N,N-dimethylamino)naphthalene actin depolymerization. Our results suggest that, whereas the amino-terminal domain is essential for primary interaction between utrophin and actin, spectrin-like repeats have additive effects on the affinity and stoichiometry of binding. Our data indicate that the amino-terminal domain and first 10 consecutive spectrin-like repeats recapitulate the actin binding activity of full-length utrophin more faithfully than the amino-terminal domain alone. These findings support the model for lateral association of utrophin along the actin filament and provide the molecular basis for designing the most effective utrophin "mini-genes" for treatment of dystrophinopathies.
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Affiliation(s)
- Inna N Rybakova
- Department of Physiology, University of Wisconsin Medical School, Madison, 53706, USA
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Franzot G, Sjöblom B, Gautel M, Djinović Carugo K. The Crystal Structure of the Actin Binding Domain from α-Actinin in its Closed Conformation: Structural Insight into Phospholipid Regulation of α-Actinin. J Mol Biol 2005; 348:151-65. [PMID: 15808860 DOI: 10.1016/j.jmb.2005.01.002] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2004] [Revised: 12/22/2004] [Accepted: 01/03/2005] [Indexed: 10/25/2022]
Abstract
Alpha-actinin is the major F-actin crosslinking protein in both muscle and non-muscle cells. We report the crystal structure of the actin binding domain of human muscle alpha-actinin-3, which is formed by two consecutive calponin homology domains arranged in a "closed" conformation. Structural studies and available biochemical data on actin binding domains suggest that two calponin homology domains come in a closed conformation in the native apo-form, and that conformational changes involving the relative orientation of the two calponin homology domains are required for efficient binding to actin filaments. The actin binding activity of muscle isoforms is supposed to be regulated by phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2), which binds to the second calponin homology domain. On the basis of structural analysis we propose a distinct binding site for PtdIns(4,5)P2, where the fatty acid moiety would be oriented in a direction that allows it to interact with the linker sequence between the actin binding domain and the first spectrin-like repeat, regulating thereby the binding of the C-terminal calmodulin-like domain to this linker.
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Affiliation(s)
- Giacomo Franzot
- Structural Biology Laboratory, Elettra-Sincrotrone Trieste in Area Science Park, S.S. 14 Km 163,5 34012 Trieste, Italy
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Abstract
Spectrin family proteins represent an important group of actin-bundling and membrane-anchoring proteins found in diverse structures from yeast to man. Arising from a common ancestral alpha-actinin gene through duplications and rearrangements, the family has increased to include the spectrins and dystrophin/utrophin. The spectrin family is characterized by the presence of spectrin repeats, actin binding domains, and EF hands. With increasing divergence, new domains and functions have been added such that spectrin and dystrophin also contain specialized protein-protein interaction motifs and regions for interaction with membranes and phospholipids. The acquisition of new domains also increased the functional complexity of the family such that the proteins perform a range of tasks way beyond the simple bundling of actin filaments by alpha-actinin in S. pombe. We discuss the evolutionary, structural, functional, and regulatory roles of the spectrin family of proteins and describe some of the disease traits associated with loss of spectrin family protein function.
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Affiliation(s)
- M J F Broderick
- Department of Biomedical Science, University of Sheffield, Sheffield S10 2TN, United Kingdom
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Trachtenberg S, Galkin VE, Egelman EH. Refining the structure of the Halobacterium salinarum flagellar filament using the iterative helical real space reconstruction method: insights into polymorphism. J Mol Biol 2005; 346:665-76. [PMID: 15713454 DOI: 10.1016/j.jmb.2004.12.010] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2004] [Revised: 11/30/2004] [Accepted: 12/07/2004] [Indexed: 11/20/2022]
Abstract
The eubacterial flagellar filament is an external, self-assembling, helical polymer approximately 220 A in diameter constructed from a highly conserved monomer, flagellin, which polymerizes externally at the distal end. The archaeal filament is only approximately 100 A in diameter, assembles at the proximal end and is constructed from different, glycosylated flagellins. Although the phenomenology of swimming is similar to that of eubacteria, the symmetry of the archebacterial filament is entirely different. Here, we extend our previous study on the flagellar coiled filament structure of strain R1M1 of Halobacterium salinarum. We use strain M175 of H.salinarum, which forms poly-flagellar bundles at high yield which, under conditions of relatively low ionic-strength (0.8 M versus 5 M) and low pH ( approximately 2.5 versus approximately 6.8), form straight filaments. We demonstrated previously that a single-particle approach to helical reconstruction has many advantages over conventional Fourier-Bessel methods when dealing with variable helical symmetry and heterogeneity. We show here that when this method is applied to the ordered helical structure of the archebacterial uncoiled flagellar filament, significant extensions in resolution can be obtained readily when compared to applying traditional helical techniques. The filament population can be separated into classes of different morphologies, which may represent polymorphic states. Using cryo-negatively stained images, a resolution of approximately 10-15 A has been achieved. Single alpha-helices can be fit into the reconstruction, supporting the proposed similarity of the structure to that of type IV bacterial pili.
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Affiliation(s)
- Shlomo Trachtenberg
- Department of Membrane and Ultrastructural Research, The Hebrew University of Jerusalem-Hadassah Medical School, P.O. Box 12272, Jerusalem 91120, Israel.
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Galkin VE, Orlova A, Koleske AJ, Egelman EH. The Arg non-receptor tyrosine kinase modifies F-actin structure. J Mol Biol 2004; 346:565-75. [PMID: 15670605 DOI: 10.1016/j.jmb.2004.11.078] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2004] [Revised: 11/28/2004] [Accepted: 11/30/2004] [Indexed: 11/29/2022]
Abstract
The Arg (Abl-related gene) protein belongs to the Abl family of non-receptor tyrosine kinases that regulate cell motility and morphogenesis. It contains two actin-binding domains, one containing the talin-like I/LWEQ motif, and a C-terminal calponin homology (CH) domain. We used electron microscopy and single particle image analysis to reconstruct complexes of F-actin with full-length Arg, and fragments lacking either the I/LWEQ or CH domains. The Arg CH domain binds to actin's subdomain-1 (SD1) and induces a tilt of actin protomers. The I/LWEQ domain binds to either SD1 or SD4, closing the nucleotide binding cleft of actin. Although Arg can use either its CH or ILWEQ domains to bind an actin filament, both domains within Arg cannot bind simultaneously to adjacent protomers in the filament, consistent with its F-actin-bundling activity. The conformational changes in the filament introduced by Arg can explain the cooperative binding of Arg to F-actin and might prevent other actin binding proteins from binding to actin filaments.
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Affiliation(s)
- Vitold E Galkin
- Department of Biochemistry and Molecular Genetics, University of Virginia Health Sciences Center, Charlottesville, VA 22908-0733, USA
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Schmid MF, Sherman MB, Matsudaira P, Chiu W. Structure of the acrosomal bundle. Nature 2004; 431:104-7. [PMID: 15343340 DOI: 10.1038/nature02881] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2004] [Accepted: 07/20/2004] [Indexed: 11/08/2022]
Abstract
In the unactivated Limulus sperm, a 60- micro m-long bundle of actin filaments crosslinked by the protein scruin is bent and twisted into a coil around the base of the nucleus. At fertilization, the bundle uncoils and fully extends in five seconds to support a finger of membrane known as the acrosomal process. This biological spring is powered by stored elastic energy and does not require the action of motor proteins or actin polymerization. In a 9.5-A electron cryomicroscopic structure of the extended bundle, we show that twist, tilt and rotation of actin-scruin subunits deviate widely from a 'standard' F-actin filament. This variability in structural organization allows filaments to pack into a highly ordered and rigid bundle in the extended state and suggests a mechanism for storing and releasing energy between coiled and extended states without disassembly.
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Affiliation(s)
- Michael F Schmid
- National Center for Macromolecular Imaging, Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas 77030, USA
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