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Mechanisms of the modulation of actin-myosin interactions by A1-type myosin light chains. Biochim Biophys Acta Gen Subj 2022; 1866:130132. [PMID: 35307509 DOI: 10.1016/j.bbagen.2022.130132] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2021] [Revised: 03/04/2022] [Accepted: 03/13/2022] [Indexed: 10/18/2022]
Abstract
BACKGROUND The interaction of N-terminal extension of the myosin A1 essential light chain (A1 ELC) with actin is receiving increasing attention as a target in utilizing synthetic A1 ELC N-terminal-derived peptides in cardiac dysfunction therapy. METHODS To elucidate the mechanism by which these peptides regulate actin-myosin interaction, here we have investigated their effects on the myosin subfragment 1 (S1)-induced polymerization of G-actin. RESULTS The MLCFpep and MLCSpep peptides spanning the 3-12 of A1 ELC sequences from fast and slow skeletal muscle, respectively, increased the rate of actin polymerization not only by S1(A2) but also the rate of S1(A1)-induced actin polymerization, suggesting that they did not interfere with the direct binding of A1 ELC with actin. The efficiency of actin polymerization in the presence of the N-terminal ELC peptides depended on their sequence. Substitution of aspartic acid for neutral asparagine at position 5 of MLCFpep dramatically enhanced its ability to stimulate S1-induced polymerization and enabled it to initiate polymerization of G-actin in the absence of S1. CONCLUSIONS These and other results presented in this work suggest that the modulation of myosin motor activity by N-terminal ELC peptides is exerted through a change in actin filament conformation rather than through blocking the A1 ELC-actin interaction. GENERAL SIGNIFICANCE The results imply the possibility of enhancing therapeutic effects of these peptides by modifications of their sequence.
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2
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MacTaggart B, Kashina A. Posttranslational modifications of the cytoskeleton. Cytoskeleton (Hoboken) 2021; 78:142-173. [PMID: 34152688 DOI: 10.1002/cm.21679] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2021] [Revised: 06/13/2021] [Accepted: 06/16/2021] [Indexed: 12/12/2022]
Abstract
The cytoskeleton plays important roles in many essential processes at the cellular and organismal levels, including cell migration and motility, cell division, and the establishment and maintenance of cell and tissue architecture. In order to facilitate these varied functions, the main cytoskeletal components-microtubules, actin filaments, and intermediate filaments-must form highly diverse intracellular arrays in different subcellular areas and cell types. The question of how this diversity is conferred has been the focus of research for decades. One key mechanism is the addition of posttranslational modifications (PTMs) to the major cytoskeletal proteins. This posttranslational addition of various chemical groups dramatically increases the complexity of the cytoskeletal proteome and helps facilitate major global and local cytoskeletal functions. Cytoskeletal proteins undergo many PTMs, most of which are not well understood. Recent technological advances in proteomics and cell biology have allowed for the in-depth study of individual PTMs and their functions in the cytoskeleton. Here, we provide an overview of the major PTMs that occur on the main structural components of the three cytoskeletal systems-tubulin, actin, and intermediate filament proteins-and highlight the cellular function of these modifications.
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Affiliation(s)
- Brittany MacTaggart
- School of Veterinary Medicine, Department of Biomedical Sciences, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Anna Kashina
- School of Veterinary Medicine, Department of Biomedical Sciences, University of Pennsylvania, Philadelphia, Pennsylvania, USA
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3
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Das S, Ge P, Oztug Durer ZA, Grintsevich EE, Zhou ZH, Reisler E. D-loop Dynamics and Near-Atomic-Resolution Cryo-EM Structure of Phalloidin-Bound F-Actin. Structure 2020; 28:586-593.e3. [PMID: 32348747 DOI: 10.1016/j.str.2020.04.004] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2019] [Revised: 02/28/2020] [Accepted: 04/06/2020] [Indexed: 12/13/2022]
Abstract
Detailed molecular information on G-actin assembly into filaments (F-actin), and their structure, dynamics, and interactions, is essential for understanding their cellular functions. Previous studies indicate that a flexible DNase I binding loop (D-loop, residues 40-50) plays a major role in actin's conformational dynamics. Phalloidin, a "gold standard" for actin filament staining, stabilizes them and affects the D-loop. Using disulfide crosslinking in yeast actin D-loop mutant Q41C/V45C, light-scattering measurements, and cryoelectron microscopy reconstructions, we probed the constraints of D-loop dynamics and its contribution to F-actin formation/stability. Our data support a model of residues 41-45 distances that facilitate G- to F-actin transition. We report also a 3.3-Å resolution structure of phalloidin-bound F-actin in the ADP-Pi-like (ADP-BeFx) state. This shows the phalloidin-binding site on F-actin and how the relative movement between its two protofilaments is restricted by it. Together, our results provide molecular details of F-actin structure and D-loop dynamics.
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Affiliation(s)
- Sanchaita Das
- Department of Chemistry and Biochemistry, University of California, UCLA, Los Angeles, CA 90095, USA
| | - Peng Ge
- California NanoSystems Institute (CNSI), UCLA, Los Angeles, CA 90095, USA
| | - Zeynep A Oztug Durer
- Department of Chemistry and Biochemistry, University of California, UCLA, Los Angeles, CA 90095, USA
| | - Elena E Grintsevich
- Department of Chemistry and Biochemistry, University of California, UCLA, Los Angeles, CA 90095, USA
| | - Z Hong Zhou
- California NanoSystems Institute (CNSI), UCLA, Los Angeles, CA 90095, USA; Department of Microbiology, Immunology and Molecular Genetics, UCLA, Los Angeles, CA 90095, USA; Molecular Biology Institute, UCLA, Los Angeles, CA 90095, USA
| | - Emil Reisler
- Department of Chemistry and Biochemistry, University of California, UCLA, Los Angeles, CA 90095, USA; Molecular Biology Institute, UCLA, Los Angeles, CA 90095, USA.
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4
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Rubenstein PA, Wen KK. Insights into the effects of disease-causing mutations in human actins. Cytoskeleton (Hoboken) 2014; 71:211-29. [PMID: 24574087 DOI: 10.1002/cm.21169] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2013] [Revised: 02/13/2013] [Accepted: 02/19/2014] [Indexed: 01/04/2023]
Abstract
Mutations in all six actins in humans have now been shown to cause diseases. However, a number of factors have made it difficult to gain insight into how the changes in actin functions brought about by these pathogenic mutations result in the disease phenotype. These include the presence of multiple actins in the same cell, limited accessibility to pure mutant material, and complexities associated with the structures and their component cells that manifest the diseases. To try to circumvent these difficulties, investigators have turned to the use of model systems. This review describes these various approaches, the initial results obtained using them, and the insight they have provided into allosteric mechanisms that govern actin function. Although results so far have not explained a particular disease phenotype at the molecular level, they have provided valuable insight into actin function at the mechanistic level which can be utilized in the future to delineate the molecular bases of these different actinopathies.
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Affiliation(s)
- Peter A Rubenstein
- Department of Biochemistry, University of Iowa Carver College of Medicine, Iowa City, Iowa
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5
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Johnston JJ, Wen KK, Keppler-Noreuil K, McKane M, Maiers JL, Greiner A, Sapp JC, DeMali KA, Rubenstein PA, Biesecker LG. Functional analysis of a de novo ACTB mutation in a patient with atypical Baraitser-Winter syndrome. Hum Mutat 2013; 34:1242-9. [PMID: 23649928 PMCID: PMC3745514 DOI: 10.1002/humu.22350] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2013] [Accepted: 04/30/2013] [Indexed: 11/08/2022]
Abstract
Exome sequence analysis can be instrumental in identifying the genetic etiology behind atypical disease. We report a patient presenting with microcephaly, dysmorphic features, and intellectual disability with a tentative diagnosis of Dubowitz syndrome. Exome analysis was performed on the patient and both parents. A de novo missense variant was identified in ACTB, c.349G>A, p.E117K. Recent work in Baraitser-Winter syndrome has identified ACTB and ACTG1 mutations in a cohort of individuals, and we rediagnosed the patient with atypical Baraitser-Winter syndrome. We performed functional characterization of the variant actin and show that it alters cell adhesion and polymer formation supporting its role in disease. We present the clinical findings in the patient, comparison of this patient to other patients with ACTB/ACTG1 mutations, and results from actin functional studies that demonstrate novel functional attributes of this mutant protein.
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Affiliation(s)
- Jennifer J. Johnston
- Genetic Disease Research Branch, National Human Genome Research Institute, National Institutes of Health, Bethesda, MD, USA
| | | | - Kim Keppler-Noreuil
- Genetic Disease Research Branch, National Human Genome Research Institute, National Institutes of Health, Bethesda, MD, USA
| | | | | | | | - Julie C. Sapp
- Genetic Disease Research Branch, National Human Genome Research Institute, National Institutes of Health, Bethesda, MD, USA
| | | | | | | | - Leslie G. Biesecker
- Genetic Disease Research Branch, National Human Genome Research Institute, National Institutes of Health, Bethesda, MD, USA
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6
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Connecting actin monomers by iso-peptide bond is a toxicity mechanism of the Vibrio cholerae MARTX toxin. Proc Natl Acad Sci U S A 2008; 105:18537-42. [PMID: 19015515 DOI: 10.1073/pnas.0808082105] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The Gram-negative bacterium Vibrio cholerae is the causative agent of a severe diarrheal disease that afflicts three to five million persons annually, causing up to 200,000 deaths. Nearly all V. cholerae strains produce a large multifunctional-autoprocessing RTX toxin (MARTX(Vc)), which contributes significantly to the pathogenesis of cholera in model systems. The actin cross-linking domain (ACD) of MARTX(Vc) directly catalyzes a covalent cross-linking of monomeric G-actin into oligomeric chains and causes cell rounding, but the nature of the cross-linked bond and the mechanism of the actin cytoskeleton disruption remained elusive. To elucidate the mechanism of ACD action and effect on actin, we identified the covalent cross-link bond between actin protomers using limited proteolysis, X-ray crystallography, and mass spectrometry. We report here that ACD catalyzes the formation of an intermolecular iso-peptide bond between residues E270 and K50 located in the hydrophobic and the DNaseI-binding loops of actin, respectively. Mutagenesis studies confirm that no other residues on actin can be cross-linked by ACD both in vitro and in vivo. This cross-linking locks actin protomers into an orientation different from that of F-actin, resulting in strong inhibition of actin polymerization. This report describes a microbial toxin mechanism acting via iso-peptide bond cross-linking between host proteins and is, to the best of our knowledge, the only known example of a peptide linkage between nonterminal glutamate and lysine side chains.
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7
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Sawaya MR, Kudryashov DS, Pashkov I, Adisetiyo H, Reisler E, Yeates TO. Multiple crystal structures of actin dimers and their implications for interactions in the actin filament. ACTA CRYSTALLOGRAPHICA SECTION D: BIOLOGICAL CRYSTALLOGRAPHY 2008; 64:454-65. [PMID: 18391412 PMCID: PMC2631129 DOI: 10.1107/s0907444908003351] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/11/2007] [Accepted: 01/30/2008] [Indexed: 01/04/2023]
Abstract
Multiple crystal structures are reported of cross-linked actin dimers. Interactions that are conserved across crystal structures suggest detailed interactions that are likely to be present in F-actin filaments. The structure of actin in its monomeric form is known at high resolution, while the structure of filamentous F-actin is only understood at considerably lower resolution. Knowing precisely how the monomers of actin fit together would lead to a deeper understanding of the dynamic behavior of the actin filament. Here, a series of crystal structures of actin dimers are reported which were prepared by cross-linking in either the longitudinal or the lateral direction in the filament state. Laterally cross-linked dimers, comprised of monomers belonging to different protofilaments, are found to adopt configurations in crystals that are not related to the native structure of filamentous actin. In contrast, multiple structures of longitudinal dimers consistently reveal the same interface between monomers within a single protofilament. The reappearance of the same longitudinal interface in multiple crystal structures adds weight to arguments that the interface visualized is similar to that in actin filaments. Highly conserved atomic interactions involving residues 199–205 and 287–291 are highlighted.
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Affiliation(s)
- Michael R Sawaya
- UCLA Department of Chemistry and Biochemistry, Los Angeles, CA 90095-1569, USA
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8
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Kudryashov DS, Cordero CL, Reisler E, Satchell KJF. Characterization of the enzymatic activity of the actin cross-linking domain from the Vibrio cholerae MARTX Vc toxin. J Biol Chem 2008; 283:445-452. [PMID: 17951576 PMCID: PMC2365471 DOI: 10.1074/jbc.m703910200] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Vibrio cholerae is a Gram-negative bacterial pathogen that exports enterotoxins, which alter host cells through a number of mechanisms resulting in diarrheal disease. Among the secreted toxins is the multifunctional, autoprocessing RTX toxin (MARTX(Vc)), which disrupts actin cytoskeleton by covalently cross-linking actin monomers into oligomers. The region of the toxin responsible for cross-linking activity is the actin cross-linking domain (ACD). In this study, we demonstrate unambiguously that ACD utilizes G- and not F-actin as a substrate for the cross-linking reaction and hydrolyzes one molecule of ATP per cross-linking event. Furthermore, major actin-binding proteins that regulate actin cytoskeleton in vivo do not block the cross-linking reaction in vitro. Cofilin inhibits the cross-linking of G- and F-actin, at a high mole ratio to actin but accelerates F-actin cross-linking at low mole ratios. DNase I completely blocks the cross-linking of actin, likely due to steric hindrance with one of the cross-linking sites on actin. In the context of the holotoxin, the inhibition of Rho by the Rho-inactivating domain of MARTX(Vc) (Sheahan, K. L., and Satchell, K. J. F. (2007) Cell. Microbiol. 9, 1324-1335) would accelerate F-actin depolymerization and provide G-actin, alone or in complex with actin-binding proteins, for cross-linking by ACD, ultimately leading to the observed rapid cell rounding.
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Affiliation(s)
- Dmitri S Kudryashov
- Department of Chemistry and Biochemistry and the Molecular Biology Institute, University of California, Los Angeles, California 90095
| | - Christina L Cordero
- Department of Microbiology-Immunology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois 60611
| | - Emil Reisler
- Department of Chemistry and Biochemistry and the Molecular Biology Institute, University of California, Los Angeles, California 90095
| | - Karla J Fullner Satchell
- Department of Microbiology-Immunology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois 60611.
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9
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Actin hydrophobic loop 262-274 and filament nucleation and elongation. J Mol Biol 2007; 375:793-801. [PMID: 18037437 DOI: 10.1016/j.jmb.2007.10.076] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2007] [Revised: 10/15/2007] [Accepted: 10/28/2007] [Indexed: 11/21/2022]
Abstract
The importance of actin hydrophobic loop 262-274 dynamics to actin polymerization and filament stability has been shown recently with the use of the yeast mutant actin L180C/L269C/C374A, in which the hydrophobic loop could be locked in a "parked" conformation by a disulfide bond between C180 and C269. Such a cross-linked globular actin monomer does not form filaments, suggesting nucleation and/or elongation inhibition. To determine the role of loop dynamics in filament nucleation and/or elongation, we studied the polymerization of the cross-linked actin in the presence of cofilin, to assist with actin nucleation, and with phalloidin, to stabilize the elongating filament segments. We demonstrate here that together, but not individually, phalloidin and cofilin co-rescue the polymerization of cross-linked actin. The polymerization was also rescued by filament seeds added together with phalloidin but not with cofilin. Thus, loop immobilization via cross-linking inhibits both filament nucleation and elongation. Nevertheless, the conformational changes needed to catalyze ATP hydrolysis by actin occur in the cross-linked actin. When actin filaments are fully decorated by cofilin, the helical twist of filamentous actin (F-actin) changes by approximately 5 degrees per subunit. Electron microscopic analysis of filaments rescued by cofilin and phalloidin revealed a dense contact between opposite strands in F-actin and a change of twist by approximately 1 degrees per subunit, indicating either partial or disordered attachment of cofilin to F-actin and/or competition between cofilin and phalloidin to alter F-actin symmetry. Our findings show an importance of the hydrophobic loop conformational dynamics in both actin nucleation and elongation and reveal that the inhibition of these two steps in the cross-linked actin can be relieved by appropriate factors.
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10
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Kudryashov DS, Galkin VE, Orlova A, Phan M, Egelman EH, Reisler E. Cofilin cross-bridges adjacent actin protomers and replaces part of the longitudinal F-actin interface. J Mol Biol 2006; 358:785-97. [PMID: 16530787 DOI: 10.1016/j.jmb.2006.02.029] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2005] [Revised: 01/22/2006] [Accepted: 02/13/2006] [Indexed: 11/25/2022]
Abstract
ADF/cofilins are abundant actin binding proteins critical to the survival of eukaryotic cells. Most ADF/cofilins bind both G and F-actin, sever the filaments and accelerate their treadmilling. These effects are linked to rearrangements of interprotomer contacts, changes in the mean twist, and filament destabilization by ADF/cofilin. Paradoxically, it was reported that under certain in vitro and in vivo conditions cofilin may stabilize actin filaments and nucleate their formation. Here, we show that yeast cofilin and human muscle cofilin (cofilin-2) accelerate the nucleation and elongation of ADP-F-actin and stabilize such filaments. Moreover, cofilin rescues the polymerization of the assembly incompetent tethramethyl rhodamine (TMR)-actin and T203C/C374S yeast mutant actin. Filaments of cofilin-decorated TMR-actin and unlabeled actin are indistinguishable, as revealed by electron microscopy and three-dimensional reconstruction. Our data suggest that ADF/cofilins play an active role in establishing new interprotomer interfaces in F-actin that substitute for disrupted (as in TMR-actin and mutant actin) or weakened (as in ADP-actin) longitudinal contacts in filaments.
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Affiliation(s)
- D S Kudryashov
- Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095, USA.
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11
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Kudryashov DS, Sawaya MR, Adisetiyo H, Norcross T, Hegyi G, Reisler E, Yeates TO. The crystal structure of a cross-linked actin dimer suggests a detailed molecular interface in F-actin. Proc Natl Acad Sci U S A 2005; 102:13105-10. [PMID: 16141336 PMCID: PMC1196358 DOI: 10.1073/pnas.0506429102] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The 2.5-A resolution crystal structure is reported for an actin dimer, composed of two protomers cross-linked along the longitudinal (or vertical) direction of the F-actin filament. The crystal structure provides an atomic resolution view of a molecular interface between actin protomers, which we argue represents a near-native interaction in the F-actin filament. The interaction involves subdomains 3 and 4 from distinct protomers. The atomic positions in the interface visualized differ by 5-10 A from those suggested by previous models of F-actin. Such differences fall within the range of uncertainties allowed by the fiber diffraction and electron microscopy methods on which previous models have been based. In the crystal, the translational arrangement of protomers lacks the slow twist found in native filaments. A plausible model of F-actin can be constructed by reintroducing the known filament twist, without disturbing significantly the interface observed in the actin dimer crystal.
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Affiliation(s)
- Dmitry S Kudryashov
- Department of Chemistry and Biochemistry and Molecular Biology Institute, University of California, Los Angeles, CA 90095, USA
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12
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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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13
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Wawro B, Khaitlina SY, Galińska-Rakoczy A, Strzelecka-Gołaszewska H. Role of actin DNase-I-binding loop in myosin subfragment 1-induced polymerization of G-actin: implications for the mechanism of polymerization. Biophys J 2005; 88:2883-96. [PMID: 15665122 PMCID: PMC1305383 DOI: 10.1529/biophysj.104.049155] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2004] [Accepted: 12/29/2004] [Indexed: 11/18/2022] Open
Abstract
Proteolytic cleavage of actin between Gly(42) and Val(43) within its DNase-I-binding loop (D-loop) abolishes the ability of Ca-G-actin to spontaneously polymerize in the presence of KCl. Here we show that such modified actin is assembled into filaments, albeit at a lower rate than unmodified actin, by myosin subfragment 1 (S1) carrying the A1 essential light chain but not by S1(A2). S1 titration of pyrene-G-actin showed a diminished affinity of cleaved actin for S1, but this could be compensated for by using S1 in excess. The most significant effect of the cleavage, revealed by measuring the fluorescence of pyrene-actin and light-scattering intensities as a function of actin concentration at saturating concentrations of S1, is strong inhibition of association of G-actin-S1 complexes into oligomers. Measurements of the fluorescence of dansyl cadaverine attached to Gln(41) indicate substantial inhibition of the initial association of G-actin-S1 into longitudinal dimers. The data provide experimental evidence for the critical role of D-loop conformation in both longitudinal and lateral, cross-strand actin-actin contact formation in the nucleation reaction. Electron microscopic analysis of the changes in filament-length distribution during polymerization of actin by S1(A1) and S1(A2) suggests that the mechanism of S1-induced polymerization is not substantially different from the nucleation-elongation scheme of spontaneous actin polymerization.
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Affiliation(s)
- Barbara Wawro
- Department of Muscle Biochemistry, Nencki Institute of Experimental Biology, 02-093 Warsaw, Poland
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14
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Hild G, Nyitrai M, Somogyi B. Intermonomer flexibility of Ca- and Mg-actin filaments at different pH values. EUROPEAN JOURNAL OF BIOCHEMISTRY 2002; 269:842-9. [PMID: 11846785 DOI: 10.1046/j.0014-2956.2001.02716.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The fluorescence resonance energy transfer parameter, f, is defined as the efficiency of the energy transfer normalized by the quantum yield of the donor in the presence of acceptor. It is possible to characterize the flexibility of the protein matrix between the appropriate fluorescent probes by monitoring the temperature dependence of f. The intermonomer flexibility of the Ca-actin and Mg-actin filaments was characterized by using this method at pH values of 6.5 and 7.4. The protomers were labeled on Cys374 with donor [N-(((iodoacetyl)amino)ethyl)-5-naphthylamine-1-sulfonate; IAEDANS] or acceptor [5-(iodoacetamido)fluorescein; IAF] molecules. The temperature profile of f suggested that the intermonomer flexibility of actin filaments was larger at pH 7.4 than pH 6.5 in the case of Mg-F-actin while this difference was absent in the case of Ca-F-actin. More rigid intermonomer connection was identified at both pH values between the protomers of Mg-F-actin compared to the Ca-F-actin. The results were further supported by time dependent fluorescence measurements made on IAEDANS and IAF labeled Mg- and Ca-actin filaments at pH 6.5 and 7.4. Our spectroscopic results may suggest that the altered function of muscle following the change of pH within the muscle cells under physiological or pathological conditions might be affected by the modified dynamic properties of the magnesium saturated actin filaments. The change of the intracellular pH does not have an effect on the intermonomer flexibility of the Ca-actin filaments.
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Affiliation(s)
- Gábor Hild
- Department of Biophysics, University of Pécs, Faculty of Medicine, Hungary
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15
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Fullner KJ, Mekalanos JJ. In vivo covalent cross-linking of cellular actin by the Vibrio cholerae RTX toxin. EMBO J 2000; 19:5315-23. [PMID: 11032799 PMCID: PMC314022 DOI: 10.1093/emboj/19.20.5315] [Citation(s) in RCA: 116] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Enteric pathogens often export toxins that elicit diarrhea as a part of the etiology of disease, including toxins that affect cytoskeletal structure. Recently, we discovered that the intestinal pathogen Vibrio cholerae elicits rounding of epithelial cells that is dependent upon a gene we designated rtxA. Here we investigate the association of rtxA with the cell-rounding effect. We find that V. cholerae exports a large toxin, RTX (repeats-in-toxin) toxin, to culture supernatant fluids and that this toxin is responsible for cell rounding. Furthermore, we find that cell rounding is not due to necrosis, suggesting that RTX toxin is not a typical member of the RTX family of pore-forming toxins. Rather, RTX toxin causes depolymerization of actin stress fibers and covalent cross-linking of cellular actin into dimers, trimers and higher multimers. This RTX toxin-specific cross-linking occurs in cells previously rounded with cytochalasin D, indicating that G-actin is the toxin target. Although several models explain our observations, our simultaneous detection of actin cross-linking and depolymerization points toward a novel mechanism of action for RTX toxin, distinguishing it from all other known toxins.
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Affiliation(s)
- K J Fullner
- Department of Microbiology and Molecular Genetics, Harvard Medical School, 200 Longwood Avenue, D1-408, Boston, MA 02115, USA
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16
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Kim E, Wriggers W, Phillips M, Kokabi K, Rubenstein PA, Reisler E. Cross-linking constraints on F-actin structure. J Mol Biol 2000; 299:421-9. [PMID: 10860749 DOI: 10.1006/jmbi.2000.3727] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The DNase I binding loop (residues 38-52), the hydrophobic plug (residues 262-274), and the C terminus region are among the structural elements of monomeric (G-) actin proposed to form the intermonomer interface in F-actin. To test the proximity and interactions of these elements and to provide constraints on models of F-actin structure, cysteine residues were introduced into yeast actin either at residue 41 or 265. These mutations allowed for specific cross-linking of F-actin between C41 and C265, C265 and C374, and C41 and C265 using dibromobimane and disulfide bond formation. The cross-linked products were visualized on SDS-PAGE and by electron microscopy. Model calculations carried out for the cross-linked F-actins revealed that considerable flexibility or displacement of actin residues is required in the disulfide cross-linked segments to fit these filaments into model F-actin structures. The calculated, cross-linked structures showed a better fit to the Holmes rather than the refined Lorenz model of F-actin. It is predicted on the basis of such calculations that image reconstruction of electron micrographs of disulfide cross-linked C41-C374 F-actin should provide a conclusive test of these two similar models of F-actin structure.
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Affiliation(s)
- E Kim
- Department of Chemistry and Biochemistry and the Molecular Biology Institute, University of California, Los Angeles, CA, 90095, USA
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