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Belyy A, Raoux-Barbot D, Saveanu C, Namane A, Ogryzko V, Worpenberg L, David V, Henriot V, Fellous S, Merrifield C, Assayag E, Ladant D, Renault L, Mechold U. Actin activates Pseudomonas aeruginosa ExoY nucleotidyl cyclase toxin and ExoY-like effector domains from MARTX toxins. Nat Commun 2016; 7:13582. [PMID: 27917880 PMCID: PMC5150216 DOI: 10.1038/ncomms13582] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2016] [Accepted: 10/13/2016] [Indexed: 12/15/2022] Open
Abstract
The nucleotidyl cyclase toxin ExoY is one of the virulence factors injected by the Pseudomonas aeruginosa type III secretion system into host cells. Inside cells, it is activated by an unknown eukaryotic cofactor to synthesize various cyclic nucleotide monophosphates. ExoY-like adenylate cyclases are also found in Multifunctional-Autoprocessing Repeats-in-ToXin (MARTX) toxins produced by various Gram-negative pathogens. Here we demonstrate that filamentous actin (F-actin) is the hitherto unknown cofactor of ExoY. Association with F-actin stimulates ExoY activity more than 10,000 fold in vitro and results in stabilization of actin filaments. ExoY is recruited to actin filaments in transfected cells and alters F-actin turnover. Actin also activates an ExoY-like adenylate cyclase MARTX effector domain from Vibrio nigripulchritudo. Finally, using a yeast genetic screen, we identify actin mutants that no longer activate ExoY. Our results thus reveal a new sub-group within the class II adenylyl cyclase family, namely actin-activated nucleotidyl cyclase (AA-NC) toxins.
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Affiliation(s)
- Alexander Belyy
- Institut Pasteur, CNRS UMR3528, Unité de Biochimie des Interactions Macromoléculaires, Département de Biologie Structurale et Chimie, 25-28 rue du Docteur Roux, 75724 Paris cedex 15, France
- Department of Bacterial Infections, Gamaleya Research Center, Moscow 123098, Russia
| | - Dorothée Raoux-Barbot
- Institut Pasteur, CNRS UMR3528, Unité de Biochimie des Interactions Macromoléculaires, Département de Biologie Structurale et Chimie, 25-28 rue du Docteur Roux, 75724 Paris cedex 15, France
| | - Cosmin Saveanu
- Institut Pasteur, CNRS UMR3525, Génétique des Interactions Macromoléculaires, Département de Génomes et Génétique, 25-28 rue du Docteur Roux, 75724 Paris cedex 15, France
| | - Abdelkader Namane
- Institut Pasteur, CNRS UMR3525, Génétique des Interactions Macromoléculaires, Département de Génomes et Génétique, 25-28 rue du Docteur Roux, 75724 Paris cedex 15, France
| | - Vasily Ogryzko
- Institut Gustave Roussy, CNRS UMR 8126, Unité de Signaling, Nuclei and Innovations in Oncology, 94805 Villejuif, France
| | - Lina Worpenberg
- Institut Pasteur, CNRS UMR3528, Unité de Biochimie des Interactions Macromoléculaires, Département de Biologie Structurale et Chimie, 25-28 rue du Docteur Roux, 75724 Paris cedex 15, France
| | - Violaine David
- Institute for Integrative Biology of the Cell (I2BC), CEA, CNRS, Univ. Paris-Sud, Université Paris-Saclay, 91198 Gif-sur-Yvette cedex, France
| | - Veronique Henriot
- Institute for Integrative Biology of the Cell (I2BC), CEA, CNRS, Univ. Paris-Sud, Université Paris-Saclay, 91198 Gif-sur-Yvette cedex, France
| | - Souad Fellous
- Institute for Integrative Biology of the Cell (I2BC), CEA, CNRS, Univ. Paris-Sud, Université Paris-Saclay, 91198 Gif-sur-Yvette cedex, France
| | - Christien Merrifield
- Institute for Integrative Biology of the Cell (I2BC), CEA, CNRS, Univ. Paris-Sud, Université Paris-Saclay, 91198 Gif-sur-Yvette cedex, France
| | - Elodie Assayag
- Institut Pasteur, CNRS UMR3528, Unité de Biochimie des Interactions Macromoléculaires, Département de Biologie Structurale et Chimie, 25-28 rue du Docteur Roux, 75724 Paris cedex 15, France
| | - Daniel Ladant
- Institut Pasteur, CNRS UMR3528, Unité de Biochimie des Interactions Macromoléculaires, Département de Biologie Structurale et Chimie, 25-28 rue du Docteur Roux, 75724 Paris cedex 15, France
| | - Louis Renault
- Institute for Integrative Biology of the Cell (I2BC), CEA, CNRS, Univ. Paris-Sud, Université Paris-Saclay, 91198 Gif-sur-Yvette cedex, France
| | - Undine Mechold
- Institut Pasteur, CNRS UMR3528, Unité de Biochimie des Interactions Macromoléculaires, Département de Biologie Structurale et Chimie, 25-28 rue du Docteur Roux, 75724 Paris cedex 15, France
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Oda T, Aihara T, Wakabayashi K. Early nucleation events in the polymerization of actin, probed by time-resolved small-angle x-ray scattering. Sci Rep 2016; 6:34539. [PMID: 27775032 PMCID: PMC5075782 DOI: 10.1038/srep34539] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2014] [Accepted: 09/15/2016] [Indexed: 11/30/2022] Open
Abstract
Nucleators generating new F-actin filaments play important roles in cell activities. Detailed information concerning the events involved in nucleation of actin alone in vitro is fundamental to understanding these processes, but such information has been hard to come by. We addressed the early process of salt-induced polymerization of actin using the time-resolved synchrotron small-angle X-ray scattering (SAXS). Actin molecules in low salt solution maintain a monomeric state by an electrostatic repulsive force between molecules. On mixing with salts, the repulsive force was rapidly screened, causing an immediate formation of many of non-polymerizable dimers. SAXS kinetic analysis revealed that tetramerization gives the highest energetic barrier to further polymerization, and the major nucleation is the formation of helical tetramers. Filaments start to grow rapidly with the formation of pentamers. These findings suggest an acceleration mechanism of actin assembly by a variety of nucleators in cells.
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Affiliation(s)
- Toshiro Oda
- X-ray Structural Analysis Research Team, RIKEN SPring-8 Center, RIKEN Harima Institute, Kouto 1-1, Sayo, Hyogo 679-5148, Japan
| | - Tomoki Aihara
- X-ray Structural Analysis Research Team, RIKEN SPring-8 Center, RIKEN Harima Institute, Kouto 1-1, Sayo, Hyogo 679-5148, Japan
| | - Katsuzo Wakabayashi
- X-ray Structural Analysis Research Team, RIKEN SPring-8 Center, RIKEN Harima Institute, Kouto 1-1, Sayo, Hyogo 679-5148, Japan.,Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan
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53
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Tyler JJ, Allwood EG, Ayscough KR. WASP family proteins, more than Arp2/3 activators. Biochem Soc Trans 2016; 44:1339-1345. [PMID: 27911716 PMCID: PMC5095904 DOI: 10.1042/bst20160176] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2016] [Revised: 07/14/2016] [Accepted: 07/21/2016] [Indexed: 01/19/2023]
Abstract
Wiskott-Aldrich syndrome protein (WASP) family proteins have been extensively characterized as factors that promote the nucleation of actin through the activation of the protein complex Arp2/3. While yeast mostly have a single member of the family, mammalian cells have at least six different members, often with multiple isoforms. Members of the family are characterized by a common structure. Their N-termini are varied and are considered to confer spatial and temporal regulation of Arp2/3-activating activity, whereas their C-terminal half contains a polyproline-rich region, one or more WASP homology-2 (WH2) actin-binding domains and motifs that bind directly to Arp2/3. Recent studies, however, indicate that the yeast WASP homologue Las17 is able to nucleate actin independently of Arp2/3 through the function of novel G-actin-binding activities in its polyproline region. This allows Las17 to generate the mother filaments that are needed for subsequent Arp2/3 recruitment and activation during the actin polymerization that drives endocytic invagination in yeast. In this review, we consider how motifs within the polyproline region of Las17 support nucleation of actin filaments, and whether similar mechanisms might exist among other family members.
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Affiliation(s)
- Joe J Tyler
- Department of Biomedical Science, Firth Court, University of Sheffield, Sheffield S10 2TN, U.K
| | - Ellen G Allwood
- Department of Biomedical Science, Firth Court, University of Sheffield, Sheffield S10 2TN, U.K
| | - Kathryn R Ayscough
- Department of Biomedical Science, Firth Court, University of Sheffield, Sheffield S10 2TN, U.K
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Hamp J, Löwer A, Dottermusch-Heidel C, Beck L, Moussian B, Flötenmeyer M, Önel SF. Drosophila Kette coordinates myoblast junction dissolution and the ratio of Scar-to-WASp during myoblast fusion. J Cell Sci 2016; 129:3426-36. [PMID: 27521427 PMCID: PMC5047678 DOI: 10.1242/jcs.175638] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2015] [Accepted: 07/25/2016] [Indexed: 12/31/2022] Open
Abstract
The fusion of founder cells and fusion-competent myoblasts (FCMs) is crucial for muscle formation in Drosophila. Characteristic events of myoblast fusion include the recognition and adhesion of myoblasts, and the formation of branched F-actin by the Arp2/3 complex at the site of cell–cell contact. At the ultrastructural level, these events are reflected by the appearance of finger-like protrusions and electron-dense plaques that appear prior to fusion. Severe defects in myoblast fusion are caused by the loss of Kette (a homolog of Nap1 and Hem-2, also known as NCKAP1 and NCKAP1L, respectively), a member of the regulatory complex formed by Scar or WAVE proteins (represented by the single protein, Scar, in flies). kette mutants form finger-like protrusions, but the electron-dense plaques are extended. Here, we show that the electron-dense plaques in wild-type and kette mutant myoblasts resemble other electron-dense structures that are known to function as cellular junctions. Furthermore, analysis of double mutants and attempts to rescue the kette mutant phenotype with N-cadherin, wasp and genes of members of the regulatory Scar complex revealed that Kette has two functions during myoblast fusion. First, Kette controls the dissolution of electron-dense plaques. Second, Kette controls the ratio of the Arp2/3 activators Scar and WASp in FCMs. Summary: The Drosophila protein Kette is essential for myoblast fusion. It controls the dissolution of electron-dense plaques and the ratio of Scar and WASp proteins in fusion-competent myoblasts during fusion pore formation.
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Affiliation(s)
- Julia Hamp
- Philipps-Universität Marburg, FB Biologie, Entwicklungsbiologie, Karl-von-Frisch Str. 8, Marburg 35043, Germany
| | - Andreas Löwer
- Philipps-Universität Marburg, FB Biologie, Entwicklungsbiologie, Karl-von-Frisch Str. 8, Marburg 35043, Germany
| | | | - Lothar Beck
- Fachbereich Biologie, Spezielle Zoologie, Philipps-Universität Marburg, Karl-von-Frisch Str. 8, Marburg 35043, Germany
| | - Bernard Moussian
- Interfaculty Institute for Cell Biology, Section Animal Genetics, University of Tübingen, Tübingen 72076, Germany
| | - Matthias Flötenmeyer
- Max Planck Institute for Developmental Biology, Section Electron Microscopy, Tübingen 72076, Germany
| | - Susanne-Filiz Önel
- Philipps-Universität Marburg, FB Biologie, Entwicklungsbiologie, Karl-von-Frisch Str. 8, Marburg 35043, Germany
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55
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Abstract
Organisms from all domains of life depend on filaments of the protein actin to provide structure and to support internal movements. Many eukaryotic cells use forces produced by actin polymerization for their motility, and myosin motor proteins use ATP hydrolysis to produce force on actin filaments. Actin polymerizes spontaneously, followed by hydrolysis of a bound adenosine triphosphate (ATP). Dissociation of the γ-phosphate prepares the polymer for disassembly. This review provides an overview of the properties of actin and shows how dozens of proteins control both the assembly and disassembly of actin filaments. These players catalyze nucleotide exchange on actin monomers, initiate polymerization, promote phosphate dissociation, cap the ends of polymers, cross-link filaments to each other and other cellular components, and sever filaments.
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56
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Rodnick-Smith M, Liu SL, Balzer CJ, Luan Q, Nolen BJ. Identification of an ATP-controlled allosteric switch that controls actin filament nucleation by Arp2/3 complex. Nat Commun 2016; 7:12226. [PMID: 27417392 PMCID: PMC4947185 DOI: 10.1038/ncomms12226] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2015] [Accepted: 06/10/2016] [Indexed: 01/07/2023] Open
Abstract
Nucleation of branched actin filaments by Arp2/3 complex is tightly regulated to control actin assembly in cells. Arp2/3 complex activation involves conformational changes brought about by ATP, Nucleation Promoting Factor (NPF) proteins, actin filaments and NPF-recruited actin monomers. To understand how these factors promote activation, we must first understand how the complex is held inactive in their absence. Here we demonstrate that the Arp3 C-terminal tail is a structural switch that prevents Arp2/3 complex from adopting an active conformation. The interaction between the tail and a hydrophobic groove in Arp3 blocks movement of Arp2 and Arp3 into an activated filament-like (short pitch) conformation. Our data indicate ATP binding destabilizes this interaction via an allosteric link between the Arp3 nucleotide cleft and the hydrophobic groove, thereby promoting the short-pitch conformation. Our results help explain how Arp2/3 complex is locked in an inactive state without activators and how autoinhibition is relieved.
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Affiliation(s)
- Max Rodnick-Smith
- Institute of Molecular Biology and Department of Chemistry and Biochemistry, University of Oregon, Eugene, Oregon 97403, USA
| | - Su-Ling Liu
- Institute of Molecular Biology, University of Oregon, Eugene, Oregon 97403, USA
| | - Connor J Balzer
- Institute of Molecular Biology and Department of Chemistry and Biochemistry, University of Oregon, Eugene, Oregon 97403, USA
| | - Qing Luan
- Institute of Molecular Biology, University of Oregon, Eugene, Oregon 97403, USA
| | - Brad J Nolen
- Institute of Molecular Biology and Department of Chemistry and Biochemistry, University of Oregon, Eugene, Oregon 97403, USA
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57
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Role and structural mechanism of WASP-triggered conformational changes in branched actin filament nucleation by Arp2/3 complex. Proc Natl Acad Sci U S A 2016; 113:E3834-43. [PMID: 27325766 DOI: 10.1073/pnas.1517798113] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
The Arp2/3 (Actin-related proteins 2/3) complex is activated by WASP (Wiskott-Aldrich syndrome protein) family proteins to nucleate branched actin filaments that are important for cellular motility. WASP recruits actin monomers to the complex and stimulates movement of Arp2 and Arp3 into a "short-pitch" conformation that mimics the arrangement of actin subunits within filaments. The relative contribution of these functions in Arp2/3 complex activation and the mechanism by which WASP stimulates the conformational change have been unknown. We purified budding yeast Arp2/3 complex held in or near the short-pitch conformation by an engineered covalent cross-link to determine if the WASP-induced conformational change is sufficient for activity. Remarkably, cross-linked Arp2/3 complex bypasses the need for WASP in activation and is more active than WASP-activated Arp2/3 complex. These data indicate that stimulation of the short-pitch conformation is the critical activating function of WASP and that monomer delivery is not a fundamental requirement for nucleation but is a specific requirement for WASP-mediated activation. During activation, WASP limits nucleation rates by releasing slowly from nascent branches. The cross-linked complex is inhibited by WASP's CA region, even though CA potently stimulates cross-linking, suggesting that slow WASP detachment masks the activating potential of the short-pitch conformational switch. We use structure-based mutations and WASP-Arp fusion chimeras to determine how WASP stimulates movement toward the short-pitch conformation. Our data indicate that WASP displaces the autoinhibitory Arp3 C-terminal tail from a hydrophobic groove at Arp3's barbed end to destabilize the inactive state, providing a mechanism by which WASP stimulates the short-pitch conformation and activates Arp2/3 complex.
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58
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Namgoong S, Kim NH. Roles of actin binding proteins in mammalian oocyte maturation and beyond. Cell Cycle 2016; 15:1830-43. [PMID: 27152960 DOI: 10.1080/15384101.2016.1181239] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022] Open
Abstract
Actin nucleation factors, which promote the formation of new actin filaments, have emerged in the last decade as key regulatory factors controlling asymmetric division in mammalian oocytes. Actin nucleators such as formin-2, spire, and the ARP2/3 complex have been found to be important regulators of actin remodeling during oocyte maturation. Another class of actin-binding proteins including cofilin, tropomyosin, myosin motors, capping proteins, tropomodulin, and Ezrin-Radixin-Moesin proteins are thought to control actin cytoskeleton dynamics at various steps of oocyte maturation. In addition, actin dynamics controlling asymmetric-symmetric transitions after fertilization is a new area of investigation. Taken together, defining the mechanisms by which actin-binding proteins regulate actin cytoskeletons is crucial for understanding the basic biology of mammalian gamete formation and pre-implantation development.
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Affiliation(s)
- Suk Namgoong
- a Department of Animal Sciences , Chungbuk National University , Cheong-Ju , ChungChungBuk-do , Republic of Korea
| | - Nam-Hyung Kim
- a Department of Animal Sciences , Chungbuk National University , Cheong-Ju , ChungChungBuk-do , Republic of Korea
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59
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The WH2 Domain and Actin Nucleation: Necessary but Insufficient. Trends Biochem Sci 2016; 41:478-490. [PMID: 27068179 DOI: 10.1016/j.tibs.2016.03.004] [Citation(s) in RCA: 95] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2015] [Revised: 02/18/2016] [Accepted: 03/11/2016] [Indexed: 11/22/2022]
Abstract
Two types of sequences, proline-rich domains (PRDs) and the WASP-homology 2 (WH2) domain, are found in most actin filament nucleation and elongation factors discovered thus far. PRDs serve as a platform for protein-protein interactions, often mediating the binding of profilin-actin. The WH2 domain is an abundant actin monomer-binding motif comprising ∼17 amino acids. It frequently occurs in tandem repeats, and functions in nucleation by recruiting actin subunits to form the polymerization nucleus. It is found in Spire, Cordon Bleu (Cobl), Leiomodin (Lmod), Arp2/3 complex activators (WASP, WHAMM, WAVE, etc.), the bacterial nucleators VopL/VopF and Sca2, and some formins. Yet, it is argued here that the WH2 domain plays only an auxiliary role in nucleation, always synergizing with other domains or proteins for this activity.
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60
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Abstract
The light chains (KLCs) of the microtubule motor kinesin-1 bind cargoes and regulate its activity. Through their tetratricopeptide repeat domain (KLC(TPR)), they can recognize short linear peptide motifs found in many cargo proteins characterized by a central tryptophan flanked by aspartic/glutamic acid residues (W-acidic). Using a fluorescence resonance energy transfer biosensor in combination with X-ray crystallographic, biochemical, and biophysical approaches, we describe how an intramolecular interaction between the KLC2(TPR) domain and a conserved peptide motif within an unstructured region of the molecule, partly occludes the W-acidic binding site on the TPR domain. Cargo binding displaces this interaction, effecting a global conformational change in KLCs resulting in a more extended conformation. Thus, like the motor-bearing kinesin heavy chains, KLCs exist in a dynamic conformational state that is regulated by self-interaction and cargo binding. We propose a model by which, via this molecular switch, W-acidic cargo binding regulates the activity of the holoenzyme.
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61
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Fetics S, Thureau A, Campanacci V, Aumont-Nicaise M, Dang I, Gautreau A, Pérez J, Cherfils J. Hybrid Structural Analysis of the Arp2/3 Regulator Arpin Identifies Its Acidic Tail as a Primary Binding Epitope. Structure 2016; 24:252-60. [PMID: 26774128 DOI: 10.1016/j.str.2015.12.001] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2015] [Revised: 11/24/2015] [Accepted: 12/01/2015] [Indexed: 01/25/2023]
Abstract
Arpin is a newly discovered regulator of actin polymerization at the cell leading edge, which steers cell migration by exerting a negative control on the Arp2/3 complex. Arpin proteins have an acidic tail homologous to the acidic motif of the VCA domain of nucleation-promoting factors (NPFs). This tail is predicted to compete with the VCA of NPFs for binding to the Arp2/3 complex, thereby mitigating activation and/or tethering of the complex to sites of actin branching. Here, we investigated the structure of full-length Arpin using synchrotron small-angle X-ray scattering, and of its acidic tail in complex with an ankyrin repeats domain using X-ray crystallography. The data were combined in a hybrid model in which the acidic tail extends from the globular core as a linear peptide and forms a primary epitope that is readily accessible in unbound Arpin and suffices to tether Arpin to interacting proteins with high affinity.
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Affiliation(s)
- Susan Fetics
- Laboratoire de Pharmacologie et Biologie Appliquée, UMR 8113, CNRS-Ecole Normale Supérieure de Cachan, 61 Avenue du Président Wilson, 94235 Cachan Cedex, France; Laboratoire d'Enzymologie et Biochimie Structurales, CNRS UPR3082, 91190 Gif-sur-Yvette, France
| | | | - Valérie Campanacci
- Laboratoire d'Enzymologie et Biochimie Structurales, CNRS UPR3082, 91190 Gif-sur-Yvette, France
| | - Magali Aumont-Nicaise
- Institut de Biochimie et Biophysique Moléculaire et Cellulaire, CNRS-Université Paris-Sud UMR 8619, 91400 Orsay, France
| | - Irène Dang
- Laboratoire d'Enzymologie et Biochimie Structurales, CNRS UPR3082, 91190 Gif-sur-Yvette, France; Ecole Polytechnique-CNRS UMR7654, 91120 Palaiseau, France
| | - Alexis Gautreau
- Laboratoire d'Enzymologie et Biochimie Structurales, CNRS UPR3082, 91190 Gif-sur-Yvette, France; Ecole Polytechnique-CNRS UMR7654, 91120 Palaiseau, France
| | - Javier Pérez
- Synchrotron SOLEIL, 91190 Gif-sur-Yvette, France
| | - Jacqueline Cherfils
- Laboratoire de Pharmacologie et Biologie Appliquée, UMR 8113, CNRS-Ecole Normale Supérieure de Cachan, 61 Avenue du Président Wilson, 94235 Cachan Cedex, France; Laboratoire d'Enzymologie et Biochimie Structurales, CNRS UPR3082, 91190 Gif-sur-Yvette, France.
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62
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Abstract
Seven decades of research have revealed much about actin structure, assembly, regulatory proteins, and cellular functions. However, some key information is still missing, so we do not understand the mechanisms of most processes that depend on actin. This chapter summarizes our current knowledge and explains some examples of work that will be required to fill these gaps and arrive at a mechanistic understanding of actin biology.
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Affiliation(s)
- Thomas D Pollard
- Department of Molecular Cellular and Developmental Biology, Yale University, 208103, New Haven, CT, 06520-8103, USA. .,Department of Molecular Biophysics and Biochemistry, Yale University, 208103, New Haven, CT, 06520-8103, USA. .,Department of Cell Biology, Yale University, 208103, New Haven, CT, 06520-8103, USA.
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63
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Abella JVG, Galloni C, Pernier J, Barry DJ, Kjær S, Carlier MF, Way M. Isoform diversity in the Arp2/3 complex determines actin filament dynamics. Nat Cell Biol 2015; 18:76-86. [PMID: 26655834 DOI: 10.1038/ncb3286] [Citation(s) in RCA: 142] [Impact Index Per Article: 15.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2015] [Accepted: 11/09/2015] [Indexed: 12/16/2022]
Abstract
The Arp2/3 complex consists of seven evolutionarily conserved subunits (Arp2, Arp3 and ARPC1-5) and plays an essential role in generating branched actin filament networks during many different cellular processes. In mammals, however, the ARPC1 and ARPC5 subunits are each encoded by two isoforms that are 67% identical. This raises the possibility that Arp2/3 complexes with different properties may exist. We found that Arp2/3 complexes containing ARPC1B and ARPC5L are significantly better at promoting actin assembly than those with ARPC1A and ARPC5, both in cells and in vitro. Branched actin networks induced by complexes containing ARPC1B or ARPC5L are also disassembled ∼2-fold slower than those formed by their counterparts. This difference reflects the ability of cortactin to stabilize ARPC1B- and ARPC5L- but not ARPC1A- and ARPC5-containing complexes against coronin-mediated disassembly. Our observations demonstrate that the Arp2/3 complex in higher eukaryotes is actually a family of complexes with different properties.
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Affiliation(s)
- Jasmine V G Abella
- Cellular Signalling and Cytoskeletal Function, The Francis Crick Institute, Lincoln's Inn Fields Laboratory, 44 Lincoln's Inn Fields, London, WC2A 3LY, UK
| | - Chiara Galloni
- Cellular Signalling and Cytoskeletal Function, The Francis Crick Institute, Lincoln's Inn Fields Laboratory, 44 Lincoln's Inn Fields, London, WC2A 3LY, UK
| | - Julien Pernier
- Laboratoire d'Enzymologie et Biochimie Structurale, I2BC, CNRS, 91198 Gif-sur-Yvette, France
| | - David J Barry
- Cellular Signalling and Cytoskeletal Function, The Francis Crick Institute, Lincoln's Inn Fields Laboratory, 44 Lincoln's Inn Fields, London, WC2A 3LY, UK
| | - Svend Kjær
- The Structural Biology Science Technology Platform, The Francis Crick Institute, Lincoln's Inn Fields Laboratory, 44 Lincoln's Inn Fields, London, WC2A 3LY, UK
| | - Marie-France Carlier
- Laboratoire d'Enzymologie et Biochimie Structurale, I2BC, CNRS, 91198 Gif-sur-Yvette, France
| | - Michael Way
- Cellular Signalling and Cytoskeletal Function, The Francis Crick Institute, Lincoln's Inn Fields Laboratory, 44 Lincoln's Inn Fields, London, WC2A 3LY, UK
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64
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Van Roey K, Davey NE. Motif co-regulation and co-operativity are common mechanisms in transcriptional, post-transcriptional and post-translational regulation. Cell Commun Signal 2015; 13:45. [PMID: 26626130 PMCID: PMC4666095 DOI: 10.1186/s12964-015-0123-9] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2015] [Accepted: 11/24/2015] [Indexed: 01/01/2023] Open
Abstract
A substantial portion of the regulatory interactions in the higher eukaryotic cell are mediated by simple sequence motifs in the regulatory segments of genes and (pre-)mRNAs, and in the intrinsically disordered regions of proteins. Although these regulatory modules are physicochemically distinct, they share an evolutionary plasticity that has facilitated a rapid growth of their use and resulted in their ubiquity in complex organisms. The ease of motif acquisition simplifies access to basal housekeeping functions, facilitates the co-regulation of multiple biomolecules allowing them to respond in a coordinated manner to changes in the cell state, and supports the integration of multiple signals for combinatorial decision-making. Consequently, motifs are indispensable for temporal, spatial, conditional and basal regulation at the transcriptional, post-transcriptional and post-translational level. In this review, we highlight that many of the key regulatory pathways of the cell are recruited by motifs and that the ease of motif acquisition has resulted in large networks of co-regulated biomolecules. We discuss how co-operativity allows simple static motifs to perform the conditional regulation that underlies decision-making in higher eukaryotic biological systems. We observe that each gene and its products have a unique set of DNA, RNA or protein motifs that encode a regulatory program to define the logical circuitry that guides the life cycle of these biomolecules, from transcription to degradation. Finally, we contrast the regulatory properties of protein motifs and the regulatory elements of DNA and (pre-)mRNAs, advocating that co-regulation, co-operativity, and motif-driven regulatory programs are common mechanisms that emerge from the use of simple, evolutionarily plastic regulatory modules.
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Affiliation(s)
- Kim Van Roey
- Structural and Computational Biology Unit, European Molecular Biology Laboratory (EMBL), 69117, Heidelberg, Germany.
- Health Services Research Unit, Operational Direction Public Health and Surveillance, Scientific Institute of Public Health (WIV-ISP), 1050, Brussels, Belgium.
| | - Norman E Davey
- Conway Institute of Biomolecular and Biomedical Sciences, University College Dublin, Dublin 4, Ireland.
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65
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Abstract
Actin filament networks assemble on cellular membranes in response to signals that locally activate neural Wiskott-Aldrich-syndrome protein (N-WASP) and the Arp2/3 complex. An inactive conformation of N-WASP is stabilized by intramolecular contacts between the GTPase binding domain (GBD) and the C helix of the verprolin-homology, connector-helix, acidic motif (VCA) segment. Multiple SH3 domain-containing adapter proteins can bind and possibly activate N-WASP, but it remains unclear how such binding events relieve autoinhibition to unmask the VCA segment and activate the Arp2/3 complex. Here, we have used purified components to reconstitute a signaling cascade driven by membrane-localized Src homology 3 (SH3) adapters and N-WASP, resulting in the assembly of dynamic actin networks. Among six SH3 adapters tested, Nck was the most potent activator of N-WASP-driven actin assembly. We identify within Nck a previously unrecognized activation motif in a linker between the first two SH3 domains. This linker sequence, reminiscent of bacterial virulence factors, directly engages the N-WASP GBD and competes with VCA binding. Our results suggest that animals, like pathogenic bacteria, have evolved peptide motifs that allosterically activate N-WASP, leading to localized actin nucleation on cellular membranes.
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66
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Filteau M, Hamel V, Pouliot MC, Gagnon-Arsenault I, Dubé AK, Landry CR. Evolutionary rescue by compensatory mutations is constrained by genomic and environmental backgrounds. Mol Syst Biol 2015; 11:832. [PMID: 26459777 PMCID: PMC4631203 DOI: 10.15252/msb.20156444] [Citation(s) in RCA: 49] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Since deleterious mutations may be rescued by secondary mutations during evolution, compensatory evolution could identify genetic solutions leading to therapeutic targets. Here, we tested this hypothesis and examined whether these solutions would be universal or would need to be adapted to one's genetic and environmental makeups. We performed experimental evolutionary rescue in a yeast disease model for the Wiskott–Aldrich syndrome in two genetic backgrounds and carbon sources. We found that multiple aspects of the evolutionary rescue outcome depend on the genotype, the environment, or a combination thereof. Specifically, the compensatory mutation rate and type, the molecular rescue mechanism, the genetic target, and the associated fitness cost varied across contexts. The course of compensatory evolution is therefore highly contingent on the initial conditions in which the deleterious mutation occurs. In addition, these results reveal biologically favored therapeutic targets for the Wiskott–Aldrich syndrome, including the target of an unrelated clinically approved drug. Our results experimentally illustrate the importance of epistasis and environmental evolutionary constraints that shape the adaptive landscape and evolutionary rate of molecular networks.
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Affiliation(s)
- Marie Filteau
- Département de Biologie, PROTEO and Institut de Biologie Intégrative et des Systèmes (IBIS) Université Laval, Québec, Qc, Canada
| | - Véronique Hamel
- Département de Biologie, PROTEO and Institut de Biologie Intégrative et des Systèmes (IBIS) Université Laval, Québec, Qc, Canada
| | - Marie-Christine Pouliot
- Département de Biologie, PROTEO and Institut de Biologie Intégrative et des Systèmes (IBIS) Université Laval, Québec, Qc, Canada
| | - Isabelle Gagnon-Arsenault
- Département de Biologie, PROTEO and Institut de Biologie Intégrative et des Systèmes (IBIS) Université Laval, Québec, Qc, Canada
| | - Alexandre K Dubé
- Département de Biologie, PROTEO and Institut de Biologie Intégrative et des Systèmes (IBIS) Université Laval, Québec, Qc, Canada
| | - Christian R Landry
- Département de Biologie, PROTEO and Institut de Biologie Intégrative et des Systèmes (IBIS) Université Laval, Québec, Qc, Canada
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67
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Structural analysis of the transitional state of Arp2/3 complex activation by two actin-bound WCAs. Nat Commun 2015; 5:3308. [PMID: 24518936 DOI: 10.1038/ncomms4308] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2013] [Accepted: 01/22/2014] [Indexed: 11/08/2022] Open
Abstract
Actin filament nucleation and branching by Arp2/3 complex is activated by nucleation-promoting factors (NPFs), whose C-terminal WCA region contains binding sites for actin (W) and Arp2/3 complex (CA). It is debated whether one or two NPFs are required for activation. Here we present evidence in support of the two-NPF model and show that actin plays a crucial role in the interactions of two mammalian NPFs, N-WASP and WAVE2, with Arp2/3 complex. Competition between actin-WCA and glia maturation factor (GMF) for binding to Arp2/3 complex suggests that during activation the first actin monomer binds at the barbed end of Arp2. Based on distance constraints obtained by time-resolved fluorescence resonance energy transfer, we define the relative position of the two actin-WCAs on Arp2/3 complex and propose an atomic model of the 11-subunit transitional complex.
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68
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Jurgenson CT, Pollard TD. Crystals of the Arp2/3 complex in two new space groups with structural information about actin-related protein 2 and potential WASP binding sites. Acta Crystallogr F Struct Biol Commun 2015; 71:1161-8. [PMID: 26323303 PMCID: PMC4555924 DOI: 10.1107/s2053230x15013515] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2015] [Accepted: 07/14/2015] [Indexed: 02/06/2023] Open
Abstract
Co-crystals of the bovine Arp2/3 complex with the CA motif from N-WASP in two new space groups were analyzed by X-ray diffraction. The crystals in the orthorhombic space group P212121 contained one complex per asymmetric unit, with unit-cell parameters a = 105.48, b = 156.71, c = 177.84 Å, and diffracted to 3.9 Å resolution. The crystals in the tetragonal space group P41 contained two complexes per asymmetric unit, with unit-cell parameters a = b = 149.93, c = 265.91 Å, and diffracted to 5.0 Å resolution. The electron-density maps of both new crystal forms had densities for small segments of subdomains 1 and 2 of Arp2. Both maps had density at the binding site on Arp3 for the C-terminal EWE tripeptide from N-WASP and a binding site proposed for the C motif of N-WASP in the barbed-end groove of Arp2. The map from the tetragonal crystal form had density near the barbed end of Arp3 that may correspond to the C helix of N-WASP. The noise levels and the low resolution of the maps made the assignment of specific molecular structures for any of these CA peptides impossible.
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Affiliation(s)
- Christopher T. Jurgenson
- Department of Chemistry and Physics, Delta State University, 1003 West Sunflower Road, Cleveland, MS 38733, USA
| | - Thomas D. Pollard
- Departments of Molecular, Cellular and Developmental Biology and Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520, USA
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69
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Freeman SA, Grinstein S. Phagocytosis: receptors, signal integration, and the cytoskeleton. Immunol Rev 2015; 262:193-215. [PMID: 25319336 DOI: 10.1111/imr.12212] [Citation(s) in RCA: 363] [Impact Index Per Article: 40.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Phagocytosis is a remarkably complex and versatile process: it contributes to innate immunity through the ingestion and elimination of pathogens, while also being central to tissue homeostasis and remodeling by clearing effete cells. The ability of phagocytes to perform such diverse functions rests, in large part, on their vast repertoire of receptors. In this review, we address the various receptor types, their mobility in the plane of the membrane, and two modes of receptor crosstalk: priming and synergy. A major section is devoted to the actin cytoskeleton, which not only governs receptor mobility and clustering but also is instrumental in particle engulfment. Four stages of the actin remodeling process are identified and discussed: (i) the 'resting' stage that precedes receptor engagement, (ii) the disruption of the cortical actin prior to formation of the phagocytic cup, (iii) the actin polymerization that propels pseudopod extension, and (iv) the termination of polymerization and removal of preassembled actin that are required for focal delivery of endomembranes and phagosomal sealing. These topics are viewed in the larger context of the differentiation and polarization of the phagocytic cells.
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Affiliation(s)
- Spencer A Freeman
- Program in Cell Biology, The Hospital for Sick Children, Toronto, Ontario, Canada
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70
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Mooren OL, Kim J, Li J, Cooper JA. Role of N-WASP in Endothelial Monolayer Formation and Integrity. J Biol Chem 2015; 290:18796-805. [PMID: 26070569 DOI: 10.1074/jbc.m115.668285] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2015] [Indexed: 11/06/2022] Open
Abstract
Endothelial cells (ECs) form a monolayer that serves as a barrier between the blood and the underlying tissue. ECs tightly regulate their cell-cell junctions, controlling the passage of soluble materials and immune cells across the monolayer barrier. We studied the role of N-WASP, a key regulator of Arp2/3 complex and actin assembly, in EC monolayers. We report that N-WASP regulates endothelial monolayer integrity by affecting the organization of cell junctions. Depletion of N-WASP resulted in an increase in transendothelial electrical resistance, a measure of monolayer integrity. N-WASP depletion increased the width of cell-cell junctions and altered the organization of F-actin and VE-cadherin at junctions. N-WASP was not present at cell-cell junctions in monolayers under resting conditions, but it was recruited following treatment with sphingosine-1-phosphate. Taken together, our results reveal a novel role for N-WASP in remodeling EC junctions, which is critical for monolayer integrity and function.
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Affiliation(s)
- Olivia L Mooren
- From the Department of Cell Biology and Physiology, Washington University, St. Louis, Missouri 63110
| | - Joanna Kim
- From the Department of Cell Biology and Physiology, Washington University, St. Louis, Missouri 63110
| | - Jinmei Li
- From the Department of Cell Biology and Physiology, Washington University, St. Louis, Missouri 63110
| | - John A Cooper
- From the Department of Cell Biology and Physiology, Washington University, St. Louis, Missouri 63110
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71
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Control of polarized assembly of actin filaments in cell motility. Cell Mol Life Sci 2015; 72:3051-67. [PMID: 25948416 PMCID: PMC4506460 DOI: 10.1007/s00018-015-1914-2] [Citation(s) in RCA: 66] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2015] [Revised: 04/02/2015] [Accepted: 04/23/2015] [Indexed: 10/25/2022]
Abstract
Actin cytoskeleton remodeling, which drives changes in cell shape and motility, is orchestrated by a coordinated control of polarized assembly of actin filaments. Signal responsive, membrane-bound protein machineries initiate and regulate polarized growth of actin filaments by mediating transient links with their barbed ends, which elongate from polymerizable actin monomers. The barbed end of an actin filament thus stands out as a hotspot of regulation of filament assembly. It is the target of both soluble and membrane-bound agonists as well as antagonists of filament assembly. Here, we review the molecular mechanisms by which various regulators of actin dynamics bind, synergize or compete at filament barbed ends. Two proteins can compete for the barbed end via a mutually exclusive binding scheme. Alternatively, two regulators acting individually at barbed ends may be bound together transiently to terminal actin subunits at barbed ends, leading to the displacement of one by the other. The kinetics of these reactions is a key in understanding how filament length and membrane-filament linkage are controlled. It is also essential for understanding how force is produced to shape membranes by mechano-sensitive, processive barbed end tracking machineries like formins and by WASP-Arp2/3 branched filament arrays. A combination of biochemical and biophysical approaches, including bulk solution assembly measurements using pyrenyl-actin fluorescence, single filament dynamics, single molecule fluorescence imaging and reconstituted self-organized filament assemblies, have provided mechanistic insight into the role of actin polymerization in motile processes.
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72
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Deng WS, Zhang J, Ju H, Zheng HM, Wang J, Wang S, Zhang DL. Arpin contributes to bacterial translocation and development of severe acute pancreatitis. World J Gastroenterol 2015; 21:4293-4301. [PMID: 25892881 PMCID: PMC4394092 DOI: 10.3748/wjg.v21.i14.4293] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/10/2014] [Revised: 01/11/2015] [Accepted: 02/05/2015] [Indexed: 02/07/2023] Open
Abstract
AIM: To assess the impact of Arpin protein and tight junction (TJ) proteins in the intestinal mucosa on bacterial translocation in patients with severe acute pancreatitis (SAP).
METHODS: Fifty SAP patients were identified as study objects and then classified into two groups according to the presence of bacterial translocation (BT) in the blood [i.e., BT(+) and BT(-)]. Twenty healthy individuals were included in the control group. BT was analyzed by polymerase chain reaction, colonic mucosal tissue was obtained by endoscopy and the expression of TJ proteins and Arpin protein was determined using immunofluorescence and western blotting.
RESULTS: Bacterial DNA was detected in the peripheral blood of 62.0% of patients (31/50) with SAP. The expression of TJ proteins in SAP patients was lower than that in healthy controls. In contrast, Arpin protein expression in SAP patients was higher than in healthy controls (0.38 ± 0.19 vs 0.28 ± 0.16, P < 0.05). Among SAP patients, those positive for BT showed a higher level of claudin-2 expression (0.64 ± 0.27 vs 0.32 ± 0.21, P < 0.05) and a lower level of occludin (OC) (0.61 ± 0.28 vs 0.73 ± 0.32, P < 0.05) and zonula occludens-1 (0.42 ± 0.26 vs 0.58 ± 0.17, P = 0.038) expression in comparison with BT (-) patients. Moreover, the level of Arpin expression in BT (+) patients was higher than in BT (-) patients (0.61 ± 0.28 vs 0.31 ± 0.24, P < 0.05).
CONCLUSION: Arpin protein affects the expression of tight junction proteins and may have an impact on BT. These results contribute to a better understanding of the factors involved in bacterial translocation during acute pancreatitis.
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73
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Mukherjee S, Kim J, Mooren OL, Shahan ST, Cohan M, Cooper JA. Role of cortactin homolog HS1 in transendothelial migration of natural killer cells. PLoS One 2015; 10:e0118153. [PMID: 25723543 PMCID: PMC4344232 DOI: 10.1371/journal.pone.0118153] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2014] [Accepted: 01/08/2015] [Indexed: 12/28/2022] Open
Abstract
Natural Killer (NK) cells perform many functions that depend on actin assembly, including adhesion, chemotaxis, lytic synapse assembly and cytolysis. HS1, the hematopoietic homolog of cortactin, binds to Arp2/3 complex and promotes actin assembly by helping to form and stabilize actin filament branches. We investigated the role of HS1 in transendothelial migration (TEM) by NK cells. Depletion of HS1 led to a decrease in the efficiency of TEM by NK cells, as measured by transwell assays with endothelial cell monolayers on porous filters. Transwell assays involve chemotaxis of NK cells across the filter, so to examine TEM more specifically, we imaged live-cell preparations and antibody-stained fixed preparations, with and without the chemoattractant SDF-1α. We found small to moderate effects of HS1 depletion on TEM, including whether the NK cells migrated via the transcellular or paracellular route. Expression of HS1 mutants indicated that phosphorylation of HS1 tyrosines at positions 222, 378 and 397 was required for rescue in the transwell assay, but HS1 mutations affecting interaction with Arp2/3 complex or SH3-domain ligands had no effect. The GEF Vav1, a ligand of HS1 phosphotyrosine, influenced NK cell transendothelial migration. HS1 and Vav1 also affected the speed of NK cells migrating across the surface of the endothelium. We conclude that HS1 has a role in transendothelial migration of NK cells and that HS1 tyrosine phosphorylation may signal through Vav1.
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Affiliation(s)
- Suranjana Mukherjee
- Department of Cell Biology & Physiology, Washington University School of Medicine, St. Louis, Missouri, United States of America
| | - Joanna Kim
- Department of Cell Biology & Physiology, Washington University School of Medicine, St. Louis, Missouri, United States of America
| | - Olivia L. Mooren
- Department of Cell Biology & Physiology, Washington University School of Medicine, St. Louis, Missouri, United States of America
| | - Stefanie T. Shahan
- Department of Cell Biology & Physiology, Washington University School of Medicine, St. Louis, Missouri, United States of America
| | - Megan Cohan
- Department of Cell Biology & Physiology, Washington University School of Medicine, St. Louis, Missouri, United States of America
| | - John A. Cooper
- Department of Cell Biology & Physiology, Washington University School of Medicine, St. Louis, Missouri, United States of America
- * E-mail:
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74
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Feliciano D, Tolsma TO, Farrell KB, Aradi A, Di Pietro SM. A second Las17 monomeric actin-binding motif functions in Arp2/3-dependent actin polymerization during endocytosis. Traffic 2015; 16:379-97. [PMID: 25615019 DOI: 10.1111/tra.12259] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2014] [Revised: 01/03/2015] [Accepted: 01/05/2015] [Indexed: 12/16/2022]
Abstract
During clathrin-mediated endocytosis (CME), actin assembly provides force to drive vesicle internalization. Members of the Wiskott-Aldrich syndrome protein (WASP) family play a fundamental role stimulating actin assembly. WASP family proteins contain a WH2 motif that binds globular actin (G-actin) and a central-acidic motif that binds the Arp2/3 complex, thus promoting the formation of branched actin filaments. Yeast WASP (Las17) is the strongest of five factors promoting Arp2/3-dependent actin polymerization during CME. It was suggested that this strong activity may be caused by a putative second G-actin-binding motif in Las17. Here, we describe the in vitro and in vivo characterization of such Las17 G-actin-binding motif (LGM) and its dependence on a group of conserved arginine residues. Using the yeast two-hybrid system, GST-pulldown, fluorescence polarization and pyrene-actin polymerization assays, we show that LGM binds G-actin and is necessary for normal Arp2/3-mediated actin polymerization in vitro. Live-cell fluorescence microscopy experiments demonstrate that LGM is required for normal dynamics of actin polymerization during CME. Further, LGM is necessary for normal dynamics of endocytic machinery components that are recruited at early, intermediate and late stages of endocytosis, as well as for optimal endocytosis of native CME cargo. Both in vitro and in vivo experiments show that LGM has relatively lower potency compared to the previously known Las17 G-actin-binding motif, WH2. These results establish a second G-actin-binding motif in Las17 and advance our knowledge on the mechanism of actin assembly during CME.
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Affiliation(s)
- Daniel Feliciano
- Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, CO 80523, USA
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75
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Madasu Y, Yang C, Boczkowska M, Bethoney KA, Zwolak A, Rebowski G, Svitkina T, Dominguez R. PICK1 is implicated in organelle motility in an Arp2/3 complex-independent manner. Mol Biol Cell 2015; 26:1308-22. [PMID: 25657323 PMCID: PMC4454178 DOI: 10.1091/mbc.e14-10-1448] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
A SAXS-based structural model is described for PICK1, a key player in AMPA receptor trafficking. It is shown that the acidic C-terminal tail of PICK1 is involved in autoinhibition and motility of PICK1-associated vesicle-like structures, but, contrary to previous reports, PICK1 neither binds nor inhibits Arp2/3 complex. PICK1 is a modular scaffold implicated in synaptic receptor trafficking. It features a PDZ domain, a BAR domain, and an acidic C-terminal tail (ACT). Analysis by small- angle x-ray scattering suggests a structural model that places the receptor-binding site of the PDZ domain and membrane-binding surfaces of the BAR and PDZ domains adjacent to each other on the concave side of the banana-shaped PICK1 dimer. In the model, the ACT of one subunit of the dimer interacts with the PDZ and BAR domains of the other subunit, possibly accounting for autoinhibition. Consistently, full-length PICK1 shows diffuse cytoplasmic localization, but it clusters on vesicle-like structures that colocalize with the trans-Golgi network marker TGN38 upon deletion of either the ACT or PDZ domain. This localization is driven by the BAR domain. Live-cell imaging further reveals that PICK1-associated vesicles undergo fast, nondirectional motility in an F-actin–dependent manner, but deleting the ACT dramatically reduces vesicle speed. Thus the ACT links PICK1-associated vesicles to a motility factor, likely myosin, but, contrary to previous reports, PICK1 neither binds nor inhibits Arp2/3 complex.
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Affiliation(s)
- Yadaiah Madasu
- Department of Physiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104
| | - Changsong Yang
- Department of Biology, University of Pennsylvania, Philadelphia, PA 19104
| | - Malgorzata Boczkowska
- Department of Physiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104
| | - Kelley A Bethoney
- Department of Physiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104
| | - Adam Zwolak
- Department of Physiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104
| | - Grzegorz Rebowski
- Department of Physiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104
| | - Tatyana Svitkina
- Department of Biology, University of Pennsylvania, Philadelphia, PA 19104
| | - Roberto Dominguez
- Department of Physiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104
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76
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Abstract
Endocytosis, the process whereby the plasma membrane invaginates to form vesicles, is essential for bringing many substances into the cell and for membrane turnover. The mechanism driving clathrin-mediated endocytosis (CME) involves > 50 different protein components assembling at a single location on the plasma membrane in a temporally ordered and hierarchal pathway. These proteins perform precisely choreographed steps that promote receptor recognition and clustering, membrane remodeling, and force-generating actin-filament assembly and turnover to drive membrane invagination and vesicle scission. Many critical aspects of the CME mechanism are conserved from yeast to mammals and were first elucidated in yeast, demonstrating that it is a powerful system for studying endocytosis. In this review, we describe our current mechanistic understanding of each step in the process of yeast CME, and the essential roles played by actin polymerization at these sites, while providing a historical perspective of how the landscape has changed since the preceding version of the YeastBook was published 17 years ago (1997). Finally, we discuss the key unresolved issues and where future studies might be headed.
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Affiliation(s)
- Bruce L Goode
- Brandeis University, Department of Biology, Rosenstiel Center, Waltham, Massachusetts 02454
| | - Julian A Eskin
- Brandeis University, Department of Biology, Rosenstiel Center, Waltham, Massachusetts 02454
| | - Beverly Wendland
- The Johns Hopkins University, Department of Biology, Baltimore, Maryland 21218
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77
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Suarez C, Carroll RT, Burke TA, Christensen JR, Bestul AJ, Sees JA, James ML, Sirotkin V, Kovar DR. Profilin regulates F-actin network homeostasis by favoring formin over Arp2/3 complex. Dev Cell 2014; 32:43-53. [PMID: 25543282 DOI: 10.1016/j.devcel.2014.10.027] [Citation(s) in RCA: 188] [Impact Index Per Article: 18.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2014] [Revised: 09/12/2014] [Accepted: 10/30/2014] [Indexed: 10/24/2022]
Abstract
Fission yeast cells use Arp2/3 complex and formin to assemble diverse filamentous actin (F-actin) networks within a common cytoplasm for endocytosis, division, and polarization. Although these homeostatic F-actin networks are usually investigated separately, competition for a limited pool of actin monomers (G-actin) helps to regulate their size and density. However, the mechanism by which G-actin is correctly distributed between rival F-actin networks is not clear. Using a combination of cell biological approaches and in vitro reconstitution of competition between actin assembly factors, we found that the small G-actin binding protein profilin directly inhibits Arp2/3 complex-mediated actin assembly. Profilin is therefore required for formin to compete effectively with excess Arp2/3 complex for limited G-actin and to assemble F-actin for contractile ring formation in dividing cells.
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Affiliation(s)
- Cristian Suarez
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, IL 60637, USA
| | - Robert T Carroll
- Department of Cell and Developmental Biology, State University of New York (SUNY) Upstate Medical University, 750 East Adams Street, Syracuse, NY 13210, USA
| | - Thomas A Burke
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, IL 60637, USA
| | - Jenna R Christensen
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, IL 60637, USA
| | - Andrew J Bestul
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, IL 60637, USA
| | - Jennifer A Sees
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, IL 60637, USA
| | - Michael L James
- Department of Cell and Developmental Biology, State University of New York (SUNY) Upstate Medical University, 750 East Adams Street, Syracuse, NY 13210, USA
| | - Vladimir Sirotkin
- Department of Cell and Developmental Biology, State University of New York (SUNY) Upstate Medical University, 750 East Adams Street, Syracuse, NY 13210, USA.
| | - David R Kovar
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, IL 60637, USA; Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL 60637, USA.
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78
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Mooren OL, Li J, Nawas J, Cooper JA. Endothelial cells use dynamic actin to facilitate lymphocyte transendothelial migration and maintain the monolayer barrier. Mol Biol Cell 2014; 25:4115-29. [PMID: 25355948 PMCID: PMC4263454 DOI: 10.1091/mbc.e14-05-0976] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Actin assembly downstream of WAVE2 in endothelial cells is necessary to engage transmigrating lymphocytes, promote the transcellular route of migration, and close junctional pores after the lymphocyte moves away. In addition, WAVE2 is necessary for endothelial monolayer integrity. The vascular endothelium is a highly dynamic structure, and the integrity of its barrier function is tightly regulated. Normally impenetrable to cells, the endothelium actively assists lymphocytes to exit the bloodstream during inflammation. The actin cytoskeleton of the endothelial cell (EC) is known to facilitate transmigration, but the cellular and molecular mechanisms are not well understood. Here we report that actin assembly in the EC, induced by Arp2/3 complex under control of WAVE2, is important for several steps in the process of transmigration. To begin transmigration, ECs deploy actin-based membrane protrusions that create a cup-shaped docking structure for the lymphocyte. We found that docking structure formation involves the localization and activation of Arp2/3 complex by WAVE2. The next step in transmigration is creation of a migratory pore, and we found that endothelial WAVE2 is needed for lymphocytes to follow a transcellular route through an EC. Later, ECs use actin-based protrusions to close the gap behind the lymphocyte, which we discovered is also driven by WAVE2. Finally, we found that ECs in resting endothelial monolayers use lamellipodial protrusions dependent on WAVE2 to form and maintain contacts and junctions between cells.
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Affiliation(s)
- Olivia L Mooren
- Department of Cell Biology and Physiology, Washington University, St. Louis, MO 63110
| | - Jinmei Li
- Department of Cell Biology and Physiology, Washington University, St. Louis, MO 63110
| | - Julie Nawas
- Department of Cell Biology and Physiology, Washington University, St. Louis, MO 63110
| | - John A Cooper
- Department of Cell Biology and Physiology, Washington University, St. Louis, MO 63110
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79
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Steering cell migration: lamellipodium dynamics and the regulation of directional persistence. Nat Rev Mol Cell Biol 2014; 15:577-90. [PMID: 25145849 DOI: 10.1038/nrm3861] [Citation(s) in RCA: 394] [Impact Index Per Article: 39.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Membrane protrusions at the leading edge of cells, known as lamellipodia, drive cell migration in many normal and pathological situations. Lamellipodial protrusion is powered by actin polymerization, which is mediated by the actin-related protein 2/3 (ARP2/3)-induced nucleation of branched actin networks and the elongation of actin filaments. Recently, advances have been made in our understanding of positive and negative ARP2/3 regulators (such as the SCAR/WAVE (SCAR/WASP family verprolin-homologous protein) complex and Arpin, respectively) and of proteins that control actin branch stability (such as glial maturation factor (GMF)) or actin filament elongation (such as ENA/VASP proteins) in lamellipodium dynamics and cell migration. This Review highlights how the balance between actin filament branching and elongation, and between the positive and negative feedback loops that regulate these activities, determines lamellipodial persistence. Importantly, directional persistence, which results from lamellipodial persistence, emerges as a critical factor in steering cell migration.
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80
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Helgeson LA, Prendergast JG, Wagner AR, Rodnick-Smith M, Nolen BJ. Interactions with actin monomers, actin filaments, and Arp2/3 complex define the roles of WASP family proteins and cortactin in coordinately regulating branched actin networks. J Biol Chem 2014; 289:28856-69. [PMID: 25160634 DOI: 10.1074/jbc.m114.587527] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Arp2/3 complex is an important actin filament nucleator that creates branched actin filament networks required for formation of lamellipodia and endocytic actin structures. Cellular assembly of branched actin networks frequently requires multiple Arp2/3 complex activators, called nucleation promoting factors (NPFs). We recently presented a mechanism by which cortactin, a weak NPF, can displace a more potent NPF, N-WASP, from nascent branch junctions to synergistically accelerate nucleation. The distinct roles of these NPFs in branching nucleation are surprising given their similarities. We biochemically dissected these two classes of NPFs to determine how their Arp2/3 complex and actin interacting segments modulate their influences on branched actin networks. We find that the Arp2/3 complex-interacting N-terminal acidic sequence (NtA) of cortactin has structural features distinct from WASP acidic regions (A) that are required for synergy between the two NPFs. Our mutational analysis shows that differences between NtA and A do not explain the weak intrinsic NPF activity of cortactin, but instead that cortactin is a weak NPF because it cannot recruit actin monomers to Arp2/3 complex. We use TIRF microscopy to show that cortactin bundles branched actin filaments using actin filament binding repeats within a single cortactin molecule, but that N-WASP antagonizes cortactin-mediated bundling. Finally, we demonstrate that multiple WASP family proteins synergistically activate Arp2/3 complex and determine the biochemical requirements in WASP proteins for synergy. Our data indicate that synergy between WASP proteins and cortactin may play a general role in assembling diverse actin-based structures, including lamellipodia, podosomes, and endocytic actin networks.
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Affiliation(s)
- Luke A Helgeson
- From the Institute of Molecular Biology and Department of Chemistry and Biochemistry, University of Oregon, Eugene, Oregon 97403-1229
| | - Julianna G Prendergast
- From the Institute of Molecular Biology and Department of Chemistry and Biochemistry, University of Oregon, Eugene, Oregon 97403-1229
| | - Andrew R Wagner
- From the Institute of Molecular Biology and Department of Chemistry and Biochemistry, University of Oregon, Eugene, Oregon 97403-1229
| | - Max Rodnick-Smith
- From the Institute of Molecular Biology and Department of Chemistry and Biochemistry, University of Oregon, Eugene, Oregon 97403-1229
| | - Brad J Nolen
- From the Institute of Molecular Biology and Department of Chemistry and Biochemistry, University of Oregon, Eugene, Oregon 97403-1229
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81
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Abstract
Accurate cell migration requires intricate control over the actin cytoskeleton. Recent work has identified an Arp2/3-interacting protein called Arpin, which restricts the rate of actin polymerization and is the latest component in the steadily expanding protein repertoire that controls cell migration.
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Affiliation(s)
- Douwe Veltman
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge Biomedical Campus, Cambridge CB2 0QH, UK.
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82
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Tania N, Condeelis J, Edelstein-Keshet L. Modeling the synergy of cofilin and Arp2/3 in lamellipodial protrusive activity. Biophys J 2014; 105:1946-55. [PMID: 24209839 DOI: 10.1016/j.bpj.2013.09.013] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2013] [Revised: 09/10/2013] [Accepted: 09/16/2013] [Indexed: 12/13/2022] Open
Abstract
Rapid polymerization of actin filament barbed ends generates protrusive forces at the cell edge, leading to cell migration. Two important regulators of free barbed ends, cofilin and Arp2/3, have been shown to work in synergy (net effect greater than additive). To explore this synergy, we model the dynamics of F-actin at the leading edge, motivated by data from EGF-stimulated mammary carcinoma cells. We study how synergy depends on the localized rates and relative timing of cofilin and Arp2/3 activation at the cell edge. The model incorporates diffusion of cofilin, membrane protrusion, F-actin capping, aging, and severing by cofilin and branch nucleation by Arp2/3 (but not G-actin recycling). In a well-mixed system, cofilin and Arp2/3 can each generate a large pulse of barbed ends on their own, but have little synergy; high synergy occurs only at low activation rates, when few barbed ends are produced. In the full spatially distributed model, both synergy and barbed-end production are significant over a range of activation rates. Furthermore, barbed-end production is greatest when Arp2/3 activation is delayed relative to cofilin. Our model supports a direct role for cofilin-mediated actin polymerization in stimulated cell migration, including chemotaxis and cancer invasion.
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Affiliation(s)
- Nessy Tania
- Department of Mathematics, University of British Columbia, Vancouver, Canada; Department of Mathematics and Statistics, Smith College, Northampton, Massachusetts
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83
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Truong D, Copeland JW, Brumell JH. Bacterial subversion of host cytoskeletal machinery: hijacking formins and the Arp2/3 complex. Bioessays 2014; 36:687-96. [PMID: 24849003 DOI: 10.1002/bies.201400038] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The host actin nucleation machinery is subverted by many bacterial pathogens to facilitate their entry, motility, replication, and survival. The majority of research conducted in the past primarily focused on exploitation of a host actin nucleator, the Arp2/3 complex, by bacterial pathogens. Recently, new studies have begun to explore the role of formins, another family of host actin nucleators, in bacterial pathogenesis. This review provides an overview of recent advances in the study of the exploitation of the Arp2/3 complex and formins by bacterial pathogens. Secreted bacterial effector proteins seem to manipulate the regulation of these actin nucleators or functionally mimic them to drive bacterial entry, motility and survival within host cells. An enhanced understanding of how formins are exploited will provide us with greater insight into how a fundamental eurkaryotic cellular process is utilized by bacteria and will also advance our knowledge of host-pathogen interactions.
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Affiliation(s)
- Dorothy Truong
- Cell Biology Program, The Hospital for Sick Children, Toronto, ON, Canada; Department of Molecular Genetics, University of Toronto, Toronto, ON, Canada
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84
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McCormick CD, Akamatsu MS, Ti SC, Pollard TD. Measuring affinities of fission yeast spindle pole body proteins in live cells across the cell cycle. Biophys J 2014; 105:1324-35. [PMID: 24047983 DOI: 10.1016/j.bpj.2013.08.017] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2013] [Revised: 08/12/2013] [Accepted: 08/14/2013] [Indexed: 12/22/2022] Open
Abstract
Characterizing protein-protein interactions is essential for understanding molecular mechanisms, although reproducing cellular conditions in vitro is challenging and some proteins are difficult to purify. We developed a method to measure binding to cellular structures using fission yeast cells as reaction vessels. We varied the concentrations of Sid2p and Mob1p (proteins of the septation initiation network) and measured their binding to spindle pole bodies (SPBs), the centrosome equivalent of yeast. From our measurements we infer that Sid2p and Mob1p both exist as monomeric, heterodimeric, and homodimeric species throughout the cell cycle. During interphase these species have widely different affinities for their common receptor Cdc11p on the SPB. The data support a model with a subset of Cdc11p binding the heterodimeric species with a Kd < 0.1 μM when Sid2p binds Mob1p-Cdc11p and Kd in the micromolar range when Mob1p binds Sid2p-Cdc11p. During mitosis an additional species presumed to be the phosphorylated Sid2p-Mob1p heterodimer binds SPBs with a lower affinity. Homodimers of Sid2p or Mob1p bind to the rest of Cdc11p at SPBs with lower affinity: Kds > 10 μM during interphase and somewhat stronger during mitosis. These measurements allowed us to account for the fluctuations in Sid2p binding to SPBs throughout the cell cycle.
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Affiliation(s)
- Chad D McCormick
- Departments of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut
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85
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Three-dimensional reconstructions of actin filaments capped by Arp2/3 complex. Eur J Cell Biol 2014; 93:179-83. [PMID: 24552843 DOI: 10.1016/j.ejcb.2014.01.003] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2013] [Revised: 01/01/2014] [Accepted: 01/09/2014] [Indexed: 11/20/2022] Open
Abstract
The primary function of Arp2/3 complex is the generation of free barbed ends by nucleating new filaments from the sides of pre-existing filaments. The pathway of branch formation is complex and involves nucleation promoting factors, actin monomers and nucleotides. A less prominent function of Arp2/3 complex is capping of actin filament pointed ends. Here we show, using electron microscopy, electron tomography, and image reconstruction of negatively-stained samples at ∼2-3nm resolution, that Arp2/3 complex bound to the pointed ends of actin filaments has a conformation similar to that in the branch junction with the Arps arranged in an actin-filament like configuration. This is direct evidence for the existence of two distinct activation pathways for Arp2/3 complex, one in the context of branch formation, one in the context of pointed-end capping, with essentially the same conformational end point.
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86
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Zahm JA, Padrick SB, Chen Z, Pak CW, Yunus AA, Henry L, Tomchick DR, Chen Z, Rosen MK. The bacterial effector VopL organizes actin into filament-like structures. Cell 2013; 155:423-34. [PMID: 24120140 DOI: 10.1016/j.cell.2013.09.019] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2013] [Revised: 07/22/2013] [Accepted: 09/11/2013] [Indexed: 12/28/2022]
Abstract
VopL is an effector protein from Vibrio parahaemolyticus that nucleates actin filaments. VopL consists of a VopL C-terminal domain (VCD) and an array of three WASP homology 2 (WH2) motifs. Here, we report the crystal structure of the VCD dimer bound to actin. The VCD organizes three actin monomers in a spatial arrangement close to that found in the canonical actin filament. In this arrangement, WH2 motifs can be modeled into the binding site of each actin without steric clashes. The data suggest a mechanism of nucleation wherein VopL creates filament-like structures, organized by the VCD with monomers delivered by the WH2 array, that can template addition of new subunits. Similarities with Arp2/3 complex and formin proteins suggest that organization of monomers into filament-like structures is a general and central feature of actin nucleation.
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Affiliation(s)
- Jacob A Zahm
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA; Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
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87
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Matalon O, Reicher B, Barda-Saad M. Wiskott-Aldrich syndrome protein - dynamic regulation of actin homeostasis: from activation through function and signal termination in T lymphocytes. Immunol Rev 2013; 256:10-29. [DOI: 10.1111/imr.12112] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Affiliation(s)
- Omri Matalon
- The Mina and Everard Goodman Faculty of Life Sciences; Bar-Ilan University; Ramat-Gan Israel
| | - Barak Reicher
- The Mina and Everard Goodman Faculty of Life Sciences; Bar-Ilan University; Ramat-Gan Israel
| | - Mira Barda-Saad
- The Mina and Everard Goodman Faculty of Life Sciences; Bar-Ilan University; Ramat-Gan Israel
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88
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Wagner AR, Luan Q, Liu SL, Nolen BJ. Dip1 defines a class of Arp2/3 complex activators that function without preformed actin filaments. Curr Biol 2013; 23:1990-8. [PMID: 24120641 DOI: 10.1016/j.cub.2013.08.029] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2013] [Revised: 07/01/2013] [Accepted: 08/08/2013] [Indexed: 11/29/2022]
Abstract
BACKGROUND Arp2/3 complex is a key actin cytoskeletal regulator that creates branched actin filament networks in response to cellular signals. WASP-activated Arp2/3 complex assembles branched actin networks by nucleating new filaments from the sides of pre-existing ones. WASP-mediated activation requires seed filaments, to which the WASP-bound Arp2/3 complex can bind to form branches, but the source of the first substrate filaments for branching is unknown. RESULTS Here we show that Dip1, a member of the WISH/DIP/SPIN90 family of actin regulators, potently activates Arp2/3 complex without preformed filaments. Unlike other Arp2/3 complex activators, Dip1 does not bind actin monomers or filaments, and it interacts with the complex using a non-WASP-like binding mode. In addition, Dip1-activated Arp2/3 complex creates linear instead of branched actin filament networks. CONCLUSIONS Our data show the mechanism by which Dip1 and other WISH/DIP/SPIN90 proteins can provide seed filaments to Arp2/3 complex to serve as master switches in initiating branched actin assembly. This mechanism is distinct from other known activators of Arp2/3 complex.
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Affiliation(s)
- Andrew R Wagner
- Institute of Molecular Biology and Department of Chemistry and Biochemistry, University of Oregon, Eugene, OR 97403, USA
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89
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Park M, Kim HJ, Lim B, Wylegala A, Toborek M. Methamphetamine-induced occludin endocytosis is mediated by the Arp2/3 complex-regulated actin rearrangement. J Biol Chem 2013; 288:33324-34. [PMID: 24081143 PMCID: PMC3829179 DOI: 10.1074/jbc.m113.483487] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Methamphetamine (METH) is a drug of abuse with neurotoxic and neuroinflammatory effects, which include disruption of the blood-brain barrier (BBB) and alterations of tight junction protein expression. This study focused on the actin cytoskeletal rearrangement as a modulator of METH-induced redistribution of tight junction protein occludin in brain endothelial cells. Exposure to METH resulted in a shift of occludin localization from plasma membranes to endosomes. These changes were accompanied by activation of the actin-related protein 2/3 (Arp2/3) complex, which stimulates actin polymerization by promoting actin nucleation. In addition, METH-induced coronin-1b phosphorylation diminishes the inhibitory effect of nonphosphorylated coronin-1b on actin nucleation. Blocking actin nucleation with CK-666, a specific inhibitor of the Arp2/3 complex, protected against METH-induced occludin internalization and increased transendothelial monocyte migration. Importantly, treatment with CK-666 attenuated a decrease in occludin levels in brain microvessels and BBB permeability of METH-injected mice. These findings indicate that actin cytoskeletal dynamics is detrimental to METH-induced BBB dysfunction by increasing internalization of occludin.
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Affiliation(s)
- Minseon Park
- From the Department of Biochemistry and Molecular Biology, Miller School of Medicine, University of Miami, Miami, Florida 33136 and
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90
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Helgeson LA, Nolen BJ. Mechanism of synergistic activation of Arp2/3 complex by cortactin and N-WASP. eLife 2013; 2:e00884. [PMID: 24015358 PMCID: PMC3762189 DOI: 10.7554/elife.00884] [Citation(s) in RCA: 94] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2013] [Accepted: 07/31/2013] [Indexed: 01/06/2023] Open
Abstract
Nucleation promoting factors (NPFs) initiate branched actin network assembly by activating Arp2/3 complex, a branched actin filament nucleator. Cellular actin networks contain multiple NPFs, but how they coordinately regulate Arp2/3 complex is unclear. Cortactin is an NPF that activates Arp2/3 complex weakly on its own, but with WASP/N-WASP, another class of NPFs, potently activates. We dissect the mechanism of synergy and propose a model in which cortactin displaces N-WASP from nascent branches as a prerequisite for nucleation. Single-molecule imaging revealed that unlike WASP/N-WASP, cortactin remains bound to junctions during nucleation, and specifically targets junctions with a ∼160-fold increased on rate over filament sides. N-WASP must be dimerized for potent synergy, and targeted mutations indicate release of dimeric N-WASP from nascent branches limits nucleation. Mathematical modeling shows cortactin-mediated displacement but not N-WASP recycling or filament recruitment models can explain synergy. Our results provide a molecular basis for coordinate Arp2/3 complex regulation. DOI:http://dx.doi.org/10.7554/eLife.00884.001.
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Affiliation(s)
- Luke A Helgeson
- Institute of Molecular Biology , University of Oregon , Eugene , United States ; Department of Chemistry and Biochemistry , University of Oregon , Eugene , United States
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91
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Smith BA, Padrick SB, Doolittle LK, Daugherty-Clarke K, Corrêa IR, Xu MQ, Goode BL, Rosen MK, Gelles J. Three-color single molecule imaging shows WASP detachment from Arp2/3 complex triggers actin filament branch formation. eLife 2013; 2:e01008. [PMID: 24015360 PMCID: PMC3762362 DOI: 10.7554/elife.01008] [Citation(s) in RCA: 84] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2013] [Accepted: 07/29/2013] [Indexed: 01/22/2023] Open
Abstract
During cell locomotion and endocytosis, membrane-tethered WASP proteins stimulate actin filament nucleation by the Arp2/3 complex. This process generates highly branched arrays of filaments that grow toward the membrane to which they are tethered, a conflict that seemingly would restrict filament growth. Using three-color single-molecule imaging in vitro we revealed how the dynamic associations of Arp2/3 complex with mother filament and WASP are temporally coordinated with initiation of daughter filament growth. We found that WASP proteins dissociated from filament-bound Arp2/3 complex prior to new filament growth. Further, mutations that accelerated release of WASP from filament-bound Arp2/3 complex proportionally accelerated branch formation. These data suggest that while WASP promotes formation of pre-nucleation complexes, filament growth cannot occur until it is triggered by WASP release. This provides a mechanism by which membrane-bound WASP proteins can stimulate network growth without restraining it. DOI:http://dx.doi.org/10.7554/eLife.01008.001.
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Affiliation(s)
- Benjamin A Smith
- Department of Biochemistry, Brandeis University, Waltham, United States
| | - Shae B Padrick
- Department of Biophysics, Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, United States
| | - Lynda K Doolittle
- Department of Biophysics, Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, United States
| | - Karen Daugherty-Clarke
- Rosenstiel Basic Medical Sciences Research Center, Brandeis University, Waltham, United States
- Department of Biology, Brandeis University, Waltham, United States
| | | | | | - Bruce L Goode
- Rosenstiel Basic Medical Sciences Research Center, Brandeis University, Waltham, United States
- Department of Biology, Brandeis University, Waltham, United States
| | - Michael K Rosen
- Department of Biophysics, Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, United States
| | - Jeff Gelles
- Department of Biochemistry, Brandeis University, Waltham, United States
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92
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Boczkowska M, Rebowski G, Dominguez R. Glia maturation factor (GMF) interacts with Arp2/3 complex in a nucleotide state-dependent manner. J Biol Chem 2013; 288:25683-25688. [PMID: 23897816 DOI: 10.1074/jbc.c113.493338] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
Glia maturation factor (GMF) is a member of the actin-depolymerizing factor (ADF)/cofilin family. ADF/cofilin promotes disassembly of aged actin filaments, whereas GMF interacts specifically with Arp2/3 complex at branch junctions and promotes debranching. A distinguishing feature of ADF/cofilin is that it binds tighter to ADP-bound than to ATP-bound monomeric or filamentous actin. The interaction is also regulated by phosphorylation at Ser-3 of mammalian cofilin, which inhibits binding to actin. However, it is unknown whether these two factors play a role in the interaction of GMF with Arp2/3 complex. Here we show using isothermal titration calorimetry that mammalian GMF has very low affinity for ATP-bound Arp2/3 complex but binds ADP-bound Arp2/3 complex with 0.7 μM affinity. The phosphomimetic mutation S2E in GMF inhibits this interaction. GMF does not bind monomeric ATP- or ADP-actin, confirming its specificity for Arp2/3 complex. We further show that mammalian Arp2/3 complex nucleation activated by the WCA region of the nucleation-promoting factor N-WASP is not affected by GMF, whereas nucleation activated by the WCA region of WAVE2 is slightly inhibited at high GMF concentrations. Together, the results suggest that GMF functions by a mechanism similar to that of other ADF/cofilin family members, displaying a preference for ADP-Arp2/3 complex and undergoing inhibition by phosphorylation of a serine residue near the N terminus. Arp2/3 complex nucleation occurs in the ATP state, and nucleotide hydrolysis promotes debranching, suggesting that the higher affinity of GMF for ADP-Arp2/3 complex plays a physiological role by promoting debranching of aged branch junctions without interfering with Arp2/3 complex nucleation.
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Affiliation(s)
- Malgorzata Boczkowska
- From the Department of Physiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104
| | - Grzegorz Rebowski
- From the Department of Physiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104
| | - Roberto Dominguez
- From the Department of Physiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104.
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93
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Structural basis for regulation of Arp2/3 complex by GMF. Nat Struct Mol Biol 2013; 20:1062-8. [PMID: 23893131 PMCID: PMC3766443 DOI: 10.1038/nsmb.2628] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2013] [Accepted: 06/05/2013] [Indexed: 01/15/2023]
Abstract
Arp2/3 complex mediates formation of complex cellular structures such as lamellapodia by nucleating branched actin filaments. Arp2/3 complex activity is precisely controlled by more than a dozen regulators, yet the structural mechanism by which regulators interact with the complex is unknown. GMF is a recently discovered regulator of Arp2/3 complex that can inhibit nucleation and dissemble branches. We solved the structure of the 240 kDa complex of Mus musculus GMF and Bos taurus Arp2/3 and found GMF binds to the barbed end of Arp2, overlapping with the proposed binding site of WASP family proteins. The structure suggests GMF can bind branch junctions like cofilin binds filament sides, consistent with a modified cofilin-like mechanism for debranching by GMF. The GMF-Arp2 interface reveals how the ADF-H actin-binding domain in GMF is exploited to specifically recognize Arp2/3 complex and not actin.
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94
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Chen Q, Pollard T. Actin filament severing by cofilin dismantles actin patches and produces mother filaments for new patches. Curr Biol 2013; 23:1154-62. [PMID: 23727096 PMCID: PMC4131202 DOI: 10.1016/j.cub.2013.05.005] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2012] [Revised: 04/02/2013] [Accepted: 05/02/2013] [Indexed: 12/12/2022]
Abstract
BACKGROUND Yeast cells depend on Arp2/3 complex to assemble actin filaments at sites of endocytosis, but the source of the initial filaments required to activate Arp2/3 complex is not known. RESULTS We tested the proposal that cofilin severs actin filaments during endocytosis in fission yeast cells using a mutant cofilin defective in severing. We used quantitative fluorescence microscopy to track mGFP-tagged proteins, including early endocytic adaptor proteins, activators of Arp2/3 complex, and actin filaments. Consistent with the hypothesis, actin patches disassembled far more slowly in cells depending on severing-deficient cofilin than in wild-type cells. Even more interesting, actin patches assembled slowly in these cofilin mutant cells. Adaptor proteins End4p and Pan1p accumulated and persisted at endocytic sites more than ten times longer than in wild-type cells, followed by slow but persistent recruitment of activators of Arp2/3 complex, including WASP and myosin-I. Mutations revealed that actin filament binding sites on adaptor proteins Pan1p and End4p contribute to initiating actin polymerization in actin patches. CONCLUSIONS We propose a "sever, diffuse, and trigger" model for the nucleation of actin filaments at sites of endocytosis, whereby cofilin generates actin filament fragments that diffuse through the cytoplasm, bind adaptor proteins at nascent sites of endocytosis, and serve as mother filaments to initiate the autocatalytic assembly of the branched actin filament network of each new patch. This hypothesis explains the source of the "mother filaments" that are absolutely required for Arp2/3 complex to nucleate actin polymerization.
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Affiliation(s)
- Qian Chen
- Departments of Molecular Cellular and Developmental Biology, Yale University, PO Box 208103, New Haven, CT 06520-8103 USA
| | - Thomas Pollard
- Departments of Molecular Cellular and Developmental Biology, Yale University, PO Box 208103, New Haven, CT 06520-8103 USA
- Departments of Molecular Biophysics and Biochemistry, Yale University, PO Box 208103, New Haven, CT 06520-8103 USA
- Department of Cell Biology, Yale University, PO Box 208103, New Haven, CT 06520-8103 USA
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95
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Johnson ME, Hummer G. Evolutionary pressure on the topology of protein interface interaction networks. J Phys Chem B 2013; 117:13098-106. [PMID: 23701316 DOI: 10.1021/jp402944e] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The densely connected structure of protein-protein interaction (PPI) networks reflects the functional need of proteins to cooperate in cellular processes. However, PPI networks do not adequately capture the competition in protein binding. By contrast, the interface interaction network (IIN) studied here resolves the modular character of protein-protein binding and distinguishes between simultaneous and exclusive interactions that underlie both cooperation and competition. We show that the topology of the IIN is under evolutionary pressure, and we connect topological features of the IIN to specific biological functions. To reveal the forces shaping the network topology, we use a sequence-based computational model of interface binding along with network analysis. We find that the more fragmented structure of IINs, in contrast to the dense PPI networks, arises in large part from the competition between specific and nonspecific binding. The need to minimize nonspecific binding favors specific network motifs, including a minimal number of cliques (i.e., fully connected subgraphs) and many disconnected fragments. Validating the model, we find that these network characteristics are closely mirrored in the IIN of clathrin-mediated endocytosis. Features unexpected on the basis of our motif analysis are found to indicate either exceptional binding selectivity or important regulatory functions.
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Affiliation(s)
- Margaret E Johnson
- Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health , Bethesda, Maryland 20892-0520, United States
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96
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Ydenberg CA, Padrick SB, Sweeney MO, Gandhi M, Sokolova O, Goode BL. GMF severs actin-Arp2/3 complex branch junctions by a cofilin-like mechanism. Curr Biol 2013; 23:1037-45. [PMID: 23727094 DOI: 10.1016/j.cub.2013.04.058] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2013] [Revised: 03/27/2013] [Accepted: 04/19/2013] [Indexed: 12/31/2022]
Abstract
BACKGROUND Branched actin filament networks driving cell motility, endocytosis, and intracellular transport are assembled in seconds by the Arp2/3 complex and must be equally rapidly debranched and turned over. One of the only factors known to promote debranching of actin networks is the yeast homolog of glia maturation factor (GMF), which is structurally related to the actin filament-severing protein cofilin. However, the identity of the molecular mechanism underlying debranching and whether this activity extends to mammalian GMF have remained open questions. RESULTS Using scanning mutagenesis and total internal reflection fluorescence microscopy, we show that GMF depends on two separate surfaces for debranching. One is analogous to the G-actin and F-actin binding site on cofilin, but we show using fluorescence anisotropy and chemical crosslinking that it instead interacts with actin-related proteins in the Arp2/3 complex. The other is analogous to a second F-actin binding site on cofilin, which in GMF appears to contact the first actin subunit in the daughter filament. We further show that GMF binds to the Arp2/3 complex with low nanomolar affinity and promotes the open conformation. Finally, we show that this debranching activity and mechanism are conserved for mammalian GMF. CONCLUSIONS GMF debranches filaments by a mechanism related to cofilin-mediated severing, but in which GMF has evolved to target molecular junctions between actin-related proteins in the Arp2/3 complex and actin subunits in the daughter filament of the branch. This activity and mechanism are conserved in GMF homologs from evolutionarily distant species.
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Affiliation(s)
- Casey A Ydenberg
- Rosenstiel Center for Basic Biomedical Research, Brandeis University, Waltham, MA 02453, USA
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97
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Interface-resolved network of protein-protein interactions. PLoS Comput Biol 2013; 9:e1003065. [PMID: 23696724 PMCID: PMC3656101 DOI: 10.1371/journal.pcbi.1003065] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2012] [Accepted: 04/08/2013] [Indexed: 12/01/2022] Open
Abstract
We define an interface-interaction network (IIN) to capture the specificity and competition between protein-protein interactions (PPI). This new type of network represents interactions between individual interfaces used in functional protein binding and thereby contains the detail necessary to describe the competition and cooperation between any pair of binding partners. Here we establish a general framework for the construction of IINs that merges computational structure-based interface assignment with careful curation of available literature. To complement limited structural data, the inclusion of biochemical data is critical for achieving the accuracy and completeness necessary to analyze the specificity and competition between the protein interactions. Firstly, this procedure provides a means to clarify the information content of existing data on purported protein interactions and to remove indirect and spurious interactions. Secondly, the IIN we have constructed here for proteins involved in clathrin-mediated endocytosis (CME) exhibits distinctive topological properties. In contrast to PPI networks with their global and relatively dense connectivity, the fragmentation of the IIN into distinctive network modules suggests that different functional pressures act on the evolution of its topology. Large modules in the IIN are formed by interfaces sharing specificity for certain domain types, such as SH3 domains distributed across different proteins. The shared and distinct specificity of an interface is necessary for effective negative and positive design of highly selective binding targets. Lastly, the organization of detailed structural data in a network format allows one to identify pathways of specific binding interactions and thereby predict effects of mutations at specific surfaces on a protein and of specific binding inhibitors, as we explore in several examples. Overall, the endocytosis IIN is remarkably complex and rich in features masked in the coarser PPI, and collects relevant detail of protein association in a readily interpretable format. Much of the work inside the cell is carried out by proteins interacting with other proteins. Each edge in a protein-protein interaction network reflects these functional interactions and each node a separate protein, creating a complex structure that nevertheless follows well-established global and local patterns related to robust protein function. However, this network is not detailed enough to assess whether a particular protein can bind multiple interaction partners simultaneously through distinct interfaces, or whether the partners targeting a specific interface share similar structural or chemical properties. By breaking each protein node into its constituent interface nodes, we generate and assess such a detailed new network. To sample protein binding interactions broadly and accurately beyond those seen in crystal structures, our method combines computational interface assignment with data from biochemical studies. Using this approach we are able to assign interfaces to the majority of known interactions between proteins involved in the clathrin-mediated endocytosis pathway in yeast. Analysis of this interface-interaction network provides novel insights into the functional specificity of protein interactions, and highlights elements of cooperativity and competition among the proteins. By identifying diverse multi-protein complexes, interface-interaction networks also provide a map for targeted drug development.
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98
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Small molecules CK-666 and CK-869 inhibit actin-related protein 2/3 complex by blocking an activating conformational change. ACTA ACUST UNITED AC 2013; 20:701-12. [PMID: 23623350 DOI: 10.1016/j.chembiol.2013.03.019] [Citation(s) in RCA: 238] [Impact Index Per Article: 21.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2012] [Revised: 02/27/2013] [Accepted: 03/19/2013] [Indexed: 11/24/2022]
Abstract
Actin-related protein 2/3 (Arp2/3) complex is a seven-subunit assembly that nucleates branched actin filaments. Small molecule inhibitors CK-666 and CK-869 bind to Arp2/3 complex and inhibit nucleation, but their modes of action are unknown. Here, we use biochemical and structural methods to determine the mechanism of each inhibitor. Our data indicate that CK-666 stabilizes the inactive state of the complex, blocking movement of the Arp2 and Arp3 subunits into the activated filament-like (short pitch) conformation, while CK-869 binds to a serendipitous pocket on Arp3 and allosterically destabilizes the short pitch Arp3-Arp2 interface. These results provide key insights into the relationship between conformation and activity in Arp2/3 complex and will be critical for interpreting the influence of the inhibitors on actin filament networks in vivo.
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99
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Weichsel J, Baczynski K, Schwarz US. Unifying autocatalytic and zeroth-order branching models for growing actin networks. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2013; 87:040701. [PMID: 23679361 DOI: 10.1103/physreve.87.040701] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/17/2012] [Revised: 12/06/2012] [Indexed: 06/02/2023]
Abstract
The directed polymerization of actin networks is an essential element of many biological processes, including cell migration. Different theoretical models considering the interplay between the underlying processes of polymerization, capping, and branching have resulted in conflicting predictions. One of the main reasons for this discrepancy is the assumption of a branching reaction that is either first order (autocatalytic) or zeroth order in the number of existing filaments. Here we introduce a unifying framework from which the two established scenarios emerge as limiting cases for low and high filament numbers. A smooth transition between the two cases is found at intermediate conditions. We also derive a threshold for the capping rate above which autocatalytic growth is predicted at sufficiently low filament number. Below the threshold, zeroth-order characteristics are predicted to dominate the dynamics of the network for all accessible filament numbers. Together, these mechanisms allow cells to grow stable actin networks over a large range of different conditions.
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Affiliation(s)
- Julian Weichsel
- Bioquant and Institute for Theoretical Physics, University of Heidelberg, Germany.
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100
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Shen QT, Hsiue PP, Sindelar CV, Welch MD, Campellone KG, Wang HW. Structural insights into WHAMM-mediated cytoskeletal coordination during membrane remodeling. ACTA ACUST UNITED AC 2013; 199:111-24. [PMID: 23027905 PMCID: PMC3461504 DOI: 10.1083/jcb.201204010] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Structural analysis of the WHAMM–microtubule interaction provides insight into WHAMM’s coordination of microtubule binding, membrane association, and actin nucleation. The microtubule (MT) and actin cytoskeletons drive many essential cellular processes, yet fairly little is known about how their functions are coordinated. One factor that mediates important cross talk between these two systems is WHAMM, a Golgi-associated protein that utilizes MT binding and actin nucleation activities to promote membrane tubulation during intracellular transport. Using cryoelectron microscopy and other biophysical and biochemical approaches, we unveil the underlying mechanisms for how these activities are coordinated. We find that WHAMM bound to the outer surface of MT protofilaments via a novel interaction between its central coiled-coil region and tubulin heterodimers. Upon the assembly of WHAMM onto MTs, its N-terminal membrane-binding domain was exposed at the MT periphery, where it can recruit vesicles and remodel them into tubular structures. In contrast, MT binding masked the C-terminal portion of WHAMM and prevented it from promoting actin nucleation. These results give rise to a model whereby distinct MT-bound and actin-nucleating populations of WHAMM collaborate during membrane tubulation.
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Affiliation(s)
- Qing-Tao Shen
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520, USA
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