The Experts below are selected from a list of 74031 Experts worldwide ranked by ideXlab platform
Margaret L. Gardel - One of the best experts on this subject based on the ideXlab platform.
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coFilin drives rapid turnover and Fluidization oF entangled F Actin
Proceedings of the National Academy of Sciences of the United States of America, 2019Co-Authors: Patrick M Mccall, David R Kovar, F C Mackintosh, Margaret L. GardelAbstract:The shape oF most animal cells is controlled by the Actin cortex, a thin network oF dynamic Actin Filaments (F-Actin) situated just beneath the plasma membrane. The cortex is held Far From equilibrium by both active stresses and polymer turnover: Molecular motors drive deFormations required For cell morphogenesis, while Actin-Filament disassembly dynamics relax stress and Facilitate cortical remodeling. While many aspects oF Actin-cortex mechanics are well characterized, a mechanistic understanding oF how nonequilibrium Actin turnover contributes to stress relaxation is still lacking. To address this, we developed a reconstituted in vitro system oF entangled F-Actin, wherein the steady-state length and turnover rate oF F-Actin are controlled by the Actin regulatory proteins coFilin, proFilin, and Formin, which sever, recycle, and assemble Filaments, respectively. CoFilin-mediated severing accelerates the turnover and spatial reorganization oF F-Actin, without signiFicant changes to Filament length. We demonstrate that coFilin-mediated severing is a single-timescale mode oF stress relaxation that tunes the low-Frequency viscosity over two orders oF magnitude. These Findings serve as the Foundation For understanding the mechanics oF more physiological F-Actin networks with turnover and inForm an updated microscopic model oF single-Filament turnover. They also demonstrate that polymer activity, in the Form oF ATP hydrolysis on F-Actin coupled to nucleotide-dependent coFilin binding, is suFFicient to generate a Form oF active matter wherein asymmetric Filament disassembly preserves Filament number despite sustained severing.
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coFilin drives rapid turnover and Fluidization oF entangled F Actin
bioRxiv, 2017Co-Authors: Patrick M Mccall, David R Kovar, F C Mackintosh, Margaret L. GardelAbstract:The shape oF most animal cells is controlled by the Actin cortex, a thin, isotropic network oF dynamic Actin Filaments (F-Actin) situated just beneath the plasma membrane. The cortex is held Far From equilibrium by both active stresses and turnover: Myosin-II molecular motors drive deFormations required For cell division, migration, and tissue morphogenesis, while turnover oF the molecular components oF the Actin cortex relax stress and Facilitate network reorganization. While many aspects oF F-Actin network viscoelasticity are well-characterized in the presence and absence oF motor activity, a mechanistic understanding oF how non-equilibrium Actin turnover contributes to stress relaxation is still lacking. To address this, we developed a reconstituted in vitro system wherein the steady-state length and turnover rate oF F-Actin in entangled solutions are controlled by the Actin regulatory proteins coFilin, proFilin, and Formin, which sever, recycle, and nucleate Filaments, respectively. CoFilin-mediated severing accelerates the turnover and spatial reorganization oF F-Actin, without signiFicant changes to Filament length. Microrheology measurements demonstrate that coFilin-mediated severing is a single-timescale mode oF stress relaxation that tunes the low-Frequency viscosity over two orders oF magnitude. These Findings serve as the Foundation For understanding the mechanics oF more physiological F-Actin networks with turnover, and inForm an updated microscopic model oF single-Filament turnover. They also demonstrate that polymer activity, in the Form oF ATP hydrolysis on F-Actin coupled to nucleotide-dependent coFilin binding, is suFFicient to generate a Form oF active matter wherein asymmetric Filament disassembly preserves Filament number in spite oF sustained severing.
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F Actin buckling coordinates contractility and severing in a biomimetic actomyosin cortex
Proceedings of the National Academy of Sciences of the United States of America, 2012Co-Authors: Michael P Murrell, Margaret L. GardelAbstract:Here we develop a minimal model oF the cell actomyosin cortex by Forming a quasi-2D cross-linked Filamentous Actin (F-Actin) network adhered to a model cell membrane and contracted by myosin thick Filaments. Myosin motors generate both compressive and tensile stresses on F-Actin and consequently induce large bending Fluctuations, which reduces their eFFective persistence length to <1 μm. Over a large range oF conditions, we show the extent oF network contraction corresponds exactly to the extent oF individual F-Actin shortening via buckling. This demonstrates an essential role oF buckling in breaking the symmetry between tensile and compressive stresses to Facilitate mesoscale network contraction oF up to 80% strain. Portions oF buckled F-Actin with a radius oF curvature ~300 nm are prone to severing and thus compressive stresses mechanically coordinate contractility with F-Actin severing, the initial step oF F-Actin turnover. Finally, the F-Actin curvature acquired by myosin-induced stresses can be Further constrained by adhesion oF the network to a membrane, accelerating Filament severing but inhibiting the long-range transmission oF the stresses necessary For network contractility. Thus, the extent oF membrane adhesion can regulate the coupling between network contraction and F-Actin severing. These data demonstrate the essential role oF the nonlinear response oF F-Actin to compressive stresses in potentiating both myosin-mediated contractility and Filament severing. This may serve as a general mechanism to mechanically coordinate contractility and cortical dynamics across diverse actomyosin assemblies in smooth muscle and nonmuscle cells.
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conserved F Actin dynamics and Force transmission at cell adhesions
Current Opinion in Cell Biology, 2010Co-Authors: Venkat Maruthamuthu, Yvonne Aratynschaus, Margaret L. GardelAbstract:Adhesions are a central mechanism by which cells mechanically interact with the surrounding extracellular matrix (ECM) and neighboring cells. In both cell-ECM and cell-cell adhesions, Forces generated within the Actin cytoskeleton are transmitted to the surrounding environment and are essential For numerous morphogenic processes. Despite diFFerences in many molecular components that regulate cell-cell and cell-ECM adhesions, the roles oF F-Actin dynamics and mechanical Forces in adhesion regulation are surprisingly similar. Moreover, Force transmission at adhesions occurs concomitantly with dynamic F-Actin; proteins comprising the adhesion oF F-Actin to the plasma membrane must accommodate this movement while still Facilitating Force transmission. Thus, despite diFFerent molecular architectures, integrin and cadherin-mediated adhesions operate with common biophysical characteristics to transmit and respond to mechanical Forces in multicellular tissue.
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Mechanics oF the F-Actin cytoskeleton.
Journal of biomechanics, 2009Co-Authors: Jonathan Stricker, Tobias T. Falzone, Margaret L. GardelAbstract:Dynamic regulation oF the Filamentous Actin (F-Actin) cytoskeleton is critical to numerous physical cellular processes, including cell adhesion, migration and division. Each oF these processes require precise regulation oF cell shape and mechanical Force generation which, to a large degree, is regulated by the dynamic mechanical behaviors oF a diverse assortment oF F-Actin networks and bundles. In this review, we review the current understanding oF the mechanics oF F-Actin networks and identiFy areas oF Further research needed to establish physical models. We First review our understanding oF the mechanical behaviors oF F-Actin networks reconstituted in vitro, with a Focus on the nonlinear mechanical response and behavior oF "active" F-Actin networks. We then explore the types oF mechanical response measured oF cytoskeletal F-Actin networks and bundles Formed in living cells and identiFy how these measurements correspond to those perFormed on reconstituted F-Actin networks Formed in vitro. Together, these approaches identiFy the challenges and opportunities in the study oF living cytoskeletal matter.
Emil Reisler - One of the best experts on this subject based on the ideXlab platform.
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F Actin dismantling through a redox driven synergy between mical and coFilin
Nature Cell Biology, 2016Co-Authors: Elena E. Grintsevich, Jonathan R. Terman, Ruei Jiun Hung, Hunkar Gizem Yesilyurt, Shannon K. Rich, Emil ReislerAbstract:Numerous cellular Functions depend on Actin Filament (F-Actin) disassembly. The best-characterized disassembly proteins, the ADF (Actin-depolymerizing Factor)/coFilins (encoded by the twinstar gene in Drosophila), sever Filaments and recycle monomers to promote Actin assembly. CoFilin is also a relatively weak Actin disassembler, posing questions about mechanisms oF cellular F-Actin destabilization. Here we uncover a key link to targeted F-Actin disassembly by Finding that F-Actin is eFFiciently dismantled through a post-translational-mediated synergism between coFilin and the Actin-oxidizing enzyme Mical. We Find that Mical-mediated oxidation oF Actin improves coFilin binding to Filaments, where their combined eFFect dramatically accelerates F-Actin disassembly compared with either eFFector alone. This synergism is also necessary and suFFicient For F-Actin disassembly in vivo, magniFying the eFFects oF both Mical and coFilin on cellular remodelling, axon guidance and Semaphorin-Plexin repulsion. Mical and coFilin, thereFore, Form a redox-dependent synergistic pair that promotes F-Actin instability by rapidly dismantling F-Actin and generating post-translationally modiFied Actin that has altered assembly properties.
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Drebrin inhibits coFilin-induced severing oF F-Actin.
Cytoskeleton (Hoboken N.J.), 2014Co-Authors: Elena E. Grintsevich, Emil ReislerAbstract:Molecular cross-talk between neuronal drebrin A and coFilin is believed to be a part oF the activity-dependent cytoskeleton-modulating pathway in dendritic spines. Impairments in this pathway are implicated also in synaptic dysFunction in Alzheimer's disease, Down syndrome, epilepsy, and normal aging. However, up to now the molecular interplay between coFilin and drebrin has not been elucidated. TIRF microscopy and solution experiments revealed that Full length drebrin A or its Actin binding core (Drb1-300) inhibits, but do not abolish coFilin-induced severing oF Actin Filaments. Cosedimentation experiments showed that F-Actin can be Fully occupied with combination oF these two proteins. The dependence oF coFilin binding on Fractional saturation oF Actin Filaments with drebrin suggests direct competition between these two proteins For F-Actin binding. This implies that coFilin and drebrin can either overcome or reverse the allosteric changes in F-Actin induced by the competitor's binding. The ability oF coFilin to displace drebrin From Actin Filaments is pH dependent and is Facilitated at acidic pH (6.8). Pre-steady state kinetic experiments reveal that both binding and dissociation oF drebrin to/From Actin Filaments is Faster than that reported For cooperative binding oF coFilin. We Found, that drebrin displacement by coFilin is greatly inhibited when Actin severing is abolished, which might be linked to the cooperativity oF drebrin binding to Actin Filaments. Our results contribute to molecular understanding oF the competitive interactions oF drebrin and coFilin with Actin Filaments.
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F Actin structure destabilization and dnase i binding loop Fluctuations mutational cross linking and electron microscopy analysis oF loop states and eFFects on F Actin
Journal of Molecular Biology, 2010Co-Authors: Zeynep Oztug A Durer, Karthikeyan Diraviyam, David Sept, Dmitri S Kudryashov, Emil ReislerAbstract:The conFormational dynamics oF Filamentous Actin (F-Actin) is essential For the regulation and Functions oF cellular Actin networks. The main contribution to F-Actin dynamics and its multiple conFormational states arises From the mobility and Flexibility oF the DNase I binding loop (D-loop; residues 40-50) on subdomain 2. ThereFore, we explored the structural constraints on D-loop plasticity at the F-Actin interprotomer space by probing its dynamic interactions with the hydrophobic loop (H-loop), the C-terminus, and the W-loop via mutational disulFide cross-linking. To this end, residues oF the D-loop were mutated to cysteines on yeast Actin with a C374A background. These mutants showed no major changes in their polymerization and nucleotide exchange properties compared to wild-type Actin. Copper-catalyzed disulFide cross-linking was investigated in equimolar copolymers oF cysteine mutants From the D-loop with either wild-type (C374) Actin or mutant S265C/C374A (on the H-loop) or mutant F169C/C374A (on the W-loop). Remarkably, all tested residues oF the D-loop could be cross-linked to residues 374, 265, and 169 by disulFide bonds, demonstrating the plasticity oF the interprotomer region. However, each cross-link resulted in diFFerent eFFects on the Filament structure, as detected by electron microscopy and light-scattering measurements. DisulFide cross-linking in the longitudinal orientation produced mostly no visible changes in Filament morphology, whereas the cross-linking oF D-loop residues >45 to the H-loop, in the lateral direction, resulted in Filament disruption and the presence oF amorphous aggregates on electron microscopy images. A similar aggregation was also observed upon cross-linking the residues oF the D-loop (>41) to residue 169. The eFFects oF disulFide cross-links on F-Actin stability were only partially accounted For by the simulations oF current F-Actin models. Thus, our results present evidence For the high level oF conFormational plasticity in the interprotomer space and document the link between D-loop interactions and F-Actin stability.
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antagonistic eFFects oF coFilin beryllium Fluoride complex and phalloidin on subdomain 2 and nucleotide binding cleFt in F Actin
Biophysical Journal, 2006Co-Authors: Andras Muhlrad, Dmitry Pavlov, Israel Ringel, Michael Y Peyser, Emil ReislerAbstract:CoFilin/ADF, beryllium Fluoride complex (BeFx), and phalloidin have opposing eFFects on Actin Filament structure and dynamics. CoFilin/ADF decreases the stability oF F-Actin by enhancing disorder in subdomain 2, and by severing and accelerating the depolymerization oF the Filament. BeFx and phalloidin stabilize the subdomain 2 structure and decrease the critical concentration oF Actin, slowing the dissociation oF monomers. Yeast coFilin, unlike some other members oF the coFilin/ADF Family, binds to F-Actin in the presence oF BeFx; however, the rate oF its binding is strongly inhibited by BeFx and decreases with increasing pH. The inhibition oF the coFilin binding rate increases with the time oF BeFx incubation with F-Actin, indicating the existence oF two BeFx-F-Actin complexes. CoFilin dissociates BeFx From the Filament, while BeFx does not bind to F-Actin saturated with coFilin, presumably because oF the coFilin-induced changes in the nucleotide-binding cleFt oF F-Actin. These changes are apparent From the increase in the Fluorescence intensity oF F-Actin bound ɛ-ADP upon coFilin binding and a decrease in its accessibility to collisional quenchers. BeFx also aFFects the nucleotide-binding cleFt oF F-Actin, as indicated by an increase in the Fluorescence intensity oF ɛ-ADP-F-Actin. Phalloidin and coFilin inhibit, but do not exclude each other binding to their complexes with F-Actin. Phalloidin promotes the dissociation oF coFilin From F-Actin and slowly reverses the coFilin-induced disorder in the DNase I binding loop oF subdomain 2.
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conFormational dynamics oF loop 262 274 in g and F Actin
Biochemistry, 2006Co-Authors: Alexander Shvetsov, John D Stamm, Martin L Phillips, Dora Warshaviak, Christian Altenbach, Peter A Rubenstein, Kalman Hideg, Wayne L Hubbell, Emil ReislerAbstract:According to the original Holmes model oF F-Actin structure, the hydrophobic loop 262-274 stabilizes the Actin Filament by inserting into a pocket Formed at the interFace between two protomers on the opposing strand. Using a yeast Actin triple mutant, L180C/L269C/C374A [(LC)(2)CA], we showed previously that locking the hydrophobic loop to the G-Actin surFace by a disulFide bridge prevents Filament Formation. We report here that the hydrophobic loop is mobile in F- as well as in G-Actin, Fluctuating between the extended and parked conFormations. Copper-catalyzed, brieF air oxidation oF (LC)(2)CA F-Actin on electron microscopy grids resulted in the severing oF thin Filaments and their conversion to amorphous aggregates. DisulFide, bis(methanethiosulFonate) (MTS), and dibromobimane (DBB) cross-linking reactions proceeded in solution at a Faster rate with G- than with F-Actin. Cross-linking oF C180 to C269 by DBB (4.4 A) in either G- or F-Actin resulted in shorter and less stable Filaments. The cross-linking with a longer MTS-6 reagent (9.6 A) did not impair Actin polymerization or Filament structure. Myosin subFragment 1 (S1) and tropomyosin inhibited the disulFide cross-linking oF phalloidin-stabilized F-Actin. Electron paramagnetic resonance measurements with nitroxide spin-labeled Actin revealed strong spin-spin coupling and a similar mean interspin distance ( approximately 10 A) in G- and in F-Actin, with a broader distance distribution in G-Actin. These results show loop 262-274 Fluctuations in G- and F-Actin and correlate loop dynamics with Actin Filament Formation and stability.
Edward H Egelman - One of the best experts on this subject based on the ideXlab platform.
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Structural Polymorphism in F-Actin
Biophysical Journal, 2011Co-Authors: Vitold E Galkin, Gunnar F Schroder, Albina Orlova, Edward H EgelmanAbstract:Actin plays a major role in many cellular processes including motility, cell division, endocytosis, and exocytosis. Actin has also maintained an exquisite degree oF sequence conservation over large evolutionary distances For reasons that are not understood. Generating an atomic model oF the Actin Filament (F-Actin) has been driven by the desire to explain phenomena From muscle contraction to cytokinesis in mechanistic detail. To understand how key mobile elements oF Actin contribute to the intrinsic structural polymorphism oF F-Actin we carried out electron microscopic studies oF the Frozen-hydrated Actin Filaments. We show that Frozen-hydrated Actin Filaments possess substantial structural polymorphism. We demonstrate at higher resolution (∼ 10 A) that within the Actin Filament subdomain 2 oF Actin (SD2) can undergo signiFicant structural alterations From an ordered position to complete disorder, and that its dynamics is coupled with that oF the C- and N-termini oF Actin molecule. Our observations reconcile the multiplicity oF structural conFormations oF Actin observed by x-ray crystallography with the multiplicity oF conFormations seen within F-Actin. We link a number oF disease-causing mutations in the human ACTA1 gene to the most structurally dynamic elements oF Actin. Since F-Actin is structurally polymorphic it cannot be described using only one atomic model, and must be understood as an ensemble oF diFFerent states.
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Structural polymorphism in F-Actin
Nature Structural and Molecular Biology, 2010Co-Authors: Vitold E Galkin, Gunnar F Schroder, Albina Orlova, Edward H EgelmanAbstract:Actin has maintained an exquisite degree oF sequence conservation over large evolutionary distances For reasons that are not understood. The desire to explain phenomena From muscle contraction to cytokinesis in mechanistic detail has driven the generation oF an atomic model oF the Actin Filament (F-Actin). Here we use electron cryomicroscopy to show that Frozen-hydrated Actin Filaments contain a multiplicity oF diFFerent structural states. We show (at ∼10 Å resolution) that subdomain 2 can be disordered and can make multiple contacts with the C terminus oF a subunit above it. We link a number oF disease-causing mutations in the human ACTA1 gene to the most structurally dynamic elements oF Actin. Because F-Actin is structurally polymorphic, it cannot be described using only one atomic model and must be understood as an ensemble oF diFFerent states.
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high resolution cryo em structure oF the F Actin Fimbrin plastin abd2 complex
Proceedings of the National Academy of Sciences of the United States of America, 2008Co-Authors: Vitold E Galkin, Albina Orlova, Olga Cherepanova, Marie-christine Lebart, Edward H EgelmanAbstract:Many Actin binding proteins have a modular architecture, and calponin-homology (CH) domains are one such structurally conserved module Found in numerous proteins that interact with F-Actin. The manner in which CH-domains bind F-Actin has been controversial. Using cryo-EM and a single-particle approach to helical reconstruction, we have generated 12-A-resolution maps oF F-Actin alone and F-Actin decorated with a Fragment oF human Fimbrin (L-plastin) containing tandem CH-domains. The high resolution allows an unambiguous Fit oF the crystal structure oF Fimbrin into the map. The interaction between Fimbrin ABD2 (Actin binding domain 2) and F-Actin is diFFerent From any interaction previously observed or proposed For tandem CH-domain proteins, showing that the structural conservation oF the CH-domains does not lead to a conserved mode oF interaction with F-Actin. Both the stapling oF adjacent Actin protomers and the additional closure oF the nucleotide binding cleFt in F-Actin when the Fimbrin Fragment binds may explain how Fimbrin can stabilize Actin Filaments. A mechanism is proposed where ABD1 oF Fimbrin becomes activated For binding a second Actin Filament aFter ABD2 is bound to a First Filament, and this can explain how mutations oF residues buried in the interFace between ABD2 and ABD1 can rescue temperature-sensitive deFects in Actin.
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Actin depolymerizing Factor stabilizes an existing state oF F Actin and can change the tilt oF F Actin subunits
Journal of Cell Biology, 2001Co-Authors: Vitold E Galkin, Natalya Lukoyanova, Albina Orlova, Willy Wriggers, Edward H EgelmanAbstract:Proteins in the Actin depolymerizing Factor (ADF)/coFilin Family are essential For rapid F-Actin turnover, and most depolymerize Actin in a pH-dependent manner. Complexes oF human and plant ADF with F-Actin at diFFerent pH were examined using electron microscopy and a novel method oF image analysis For helical Filaments. Although ADF changes the mean twist oF Actin, we show that it does this by stabilizing a preexisting F-Actin angular conFormation. In addition, ADF induces a large (∼12°) tilt oF Actin subunits at high pH where Filaments are readily disrupted. A second ADF molecule binds to a site on the opposite side oF F-Actin From that oF the previously described ADF binding site, and this second site is only largely occupied at high pH. All oF these states display a high degree oF cooperativity that appears to be an integral part oF F-Actin.
David R Kovar - One of the best experts on this subject based on the ideXlab platform.
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F Actin cytoskeleton network selF organization through competition and cooperation
Annual Review of Cell and Developmental Biology, 2020Co-Authors: Rachel S Kadzik, Kaitlin E Homa, David R KovarAbstract:Many Fundamental cellular processes such as division, polarization, endocytosis, and motility require the assembly, maintenance, and disassembly oF Filamentous Actin (F-Actin) networks at speciFic locations and times within the cell. The particular Function oF each network is governed by F-Actin organization, size, and density as well as by its dynamics. The distinct characteristics oF diFFerent F-Actin networks are determined through the coordinated actions oF speciFic sets oF Actin-binding proteins (ABPs). Furthermore, a cell typically assembles and uses multiple F-Actin networks simultaneously within a common cytoplasm, so these networks must selF-organize From a common pool oF shared globular Actin (G-Actin) monomers and overlapping sets oF ABPs. Recent advances in multicolor imaging and analysis oF ABPs and their associated F-Actin networks in cells, as well as the development oF sophisticated in vitro reconstitutions oF networks with ensembles oF ABPs, have allowed the Field to start uncovering the underlying principles by which cells selF-organize diverse F-Actin networks to execute basic cellular Functions.
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coFilin drives rapid turnover and Fluidization oF entangled F Actin
Proceedings of the National Academy of Sciences of the United States of America, 2019Co-Authors: Patrick M Mccall, David R Kovar, F C Mackintosh, Margaret L. GardelAbstract:The shape oF most animal cells is controlled by the Actin cortex, a thin network oF dynamic Actin Filaments (F-Actin) situated just beneath the plasma membrane. The cortex is held Far From equilibrium by both active stresses and polymer turnover: Molecular motors drive deFormations required For cell morphogenesis, while Actin-Filament disassembly dynamics relax stress and Facilitate cortical remodeling. While many aspects oF Actin-cortex mechanics are well characterized, a mechanistic understanding oF how nonequilibrium Actin turnover contributes to stress relaxation is still lacking. To address this, we developed a reconstituted in vitro system oF entangled F-Actin, wherein the steady-state length and turnover rate oF F-Actin are controlled by the Actin regulatory proteins coFilin, proFilin, and Formin, which sever, recycle, and assemble Filaments, respectively. CoFilin-mediated severing accelerates the turnover and spatial reorganization oF F-Actin, without signiFicant changes to Filament length. We demonstrate that coFilin-mediated severing is a single-timescale mode oF stress relaxation that tunes the low-Frequency viscosity over two orders oF magnitude. These Findings serve as the Foundation For understanding the mechanics oF more physiological F-Actin networks with turnover and inForm an updated microscopic model oF single-Filament turnover. They also demonstrate that polymer activity, in the Form oF ATP hydrolysis on F-Actin coupled to nucleotide-dependent coFilin binding, is suFFicient to generate a Form oF active matter wherein asymmetric Filament disassembly preserves Filament number despite sustained severing.
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coFilin drives rapid turnover and Fluidization oF entangled F Actin
bioRxiv, 2017Co-Authors: Patrick M Mccall, David R Kovar, F C Mackintosh, Margaret L. GardelAbstract:The shape oF most animal cells is controlled by the Actin cortex, a thin, isotropic network oF dynamic Actin Filaments (F-Actin) situated just beneath the plasma membrane. The cortex is held Far From equilibrium by both active stresses and turnover: Myosin-II molecular motors drive deFormations required For cell division, migration, and tissue morphogenesis, while turnover oF the molecular components oF the Actin cortex relax stress and Facilitate network reorganization. While many aspects oF F-Actin network viscoelasticity are well-characterized in the presence and absence oF motor activity, a mechanistic understanding oF how non-equilibrium Actin turnover contributes to stress relaxation is still lacking. To address this, we developed a reconstituted in vitro system wherein the steady-state length and turnover rate oF F-Actin in entangled solutions are controlled by the Actin regulatory proteins coFilin, proFilin, and Formin, which sever, recycle, and nucleate Filaments, respectively. CoFilin-mediated severing accelerates the turnover and spatial reorganization oF F-Actin, without signiFicant changes to Filament length. Microrheology measurements demonstrate that coFilin-mediated severing is a single-timescale mode oF stress relaxation that tunes the low-Frequency viscosity over two orders oF magnitude. These Findings serve as the Foundation For understanding the mechanics oF more physiological F-Actin networks with turnover, and inForm an updated microscopic model oF single-Filament turnover. They also demonstrate that polymer activity, in the Form oF ATP hydrolysis on F-Actin coupled to nucleotide-dependent coFilin binding, is suFFicient to generate a Form oF active matter wherein asymmetric Filament disassembly preserves Filament number in spite oF sustained severing.
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proFilin regulates F Actin network homeostasis by Favoring Formin over arp2 3 complex
Developmental Cell, 2015Co-Authors: Cristian Suarez, Robert Carroll, Thomas A Burke, Jenna R Christensen, Andrew J Bestul, Jennifer A Sees, Michael L James, Vladimir Sirotkin, David R KovarAbstract: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.
Jonathan R. Terman - One of the best experts on this subject based on the ideXlab platform.
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the micals are a Family oF F Actin dismantling oxidoreductases conserved From drosophila to humans
Scientific Reports, 2018Co-Authors: Hunkar Gizem Yesilyurt, Jimok Yoon, Jonathan R. TermanAbstract:Cellular Form and Function - and thus normal development and physiology - are speciFied via proteins that control the organization and dynamic properties oF the Actin cytoskeleton. Using the Drosophila model, we have recently identiFied an unusual Actin regulatory enzyme, Mical, which is directly activated by F-Actin to selectively post-translationally oxidize and destabilize Filaments - regulating numerous cellular behaviors. Mical proteins are also present in mammals, but their Actin regulatory properties, including comparisons among diFFerent Family members, remain poorly deFined. We now Find that each human MICAL Family member, MICAL-1, MICAL-2, and MICAL-3, directly induces F-Actin dismantling and controls F-Actin-mediated cellular remodeling. SpeciFically, each human MICAL selectively associates with F-Actin, which directly induces MICALs catalytic activity. We also Find that each human MICAL uses an NADPH-dependent Redox activity to post-translationally oxidize Actin's methionine (M) M44/M47 residues, directly dismantling Filaments and limiting new polymerization. Genetic experiments also demonstrate that each human MICAL drives F-Actin disassembly in vivo, reshaping cells and their membranous extensions. Our results go on to reveal that MsrB/SelR reductase enzymes counteract each MICAL's eFFect on F-Actin in vitro and in vivo. Collectively, our results thereFore deFine the MICALs as an important phylogenetically-conserved Family oF catalytically-Acting F-Actin disassembly Factors.
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ampliFication oF F Actin disassembly and cellular repulsion by growth Factor signaling
Developmental Cell, 2017Co-Authors: Jimok Yoon, Giasuddin Ahmed, Jerry W Shay, Jonathan R. TermanAbstract:Summary Extracellular cues that regulate cellular shape, motility, and navigation are generally classiFied as growth promoting (i.e., growth Factors/chemoattractants and attractive guidance cues) or growth preventing (i.e., repellents and inhibitors). Yet, these designations are oFten based on complex assays and undeFined signaling pathways and thus may misrepresent direct roles oF speciFic cues. Here, we Find that a recognized growth-promoting signaling pathway ampliFies the F-Actin disassembly and repulsive eFFects oF a growth-preventing pathway. Focusing on Semaphorin/Plexin repulsion, we identiFied an interaction between the F-Actin-disassembly enzyme Mical and the Abl tyrosine kinase. Biochemical assays revealed Abl phosphorylates Mical to directly ampliFy Mical Redox-mediated F-Actin disassembly. Genetic assays revealed that Abl allows growth Factors and Semaphorin/Plexin repellents to combinatorially increase Mical-mediated F-Actin disassembly, cellular remodeling, and repulsive axon guidance. Similar roles For Mical in growth Factor/Abl-related cancer cell behaviors Further revealed contexts in which characterized positive eFFectors oF growth/guidance stimulate such negative cellular eFFects as F-Actin disassembly/repulsion.
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F Actin dismantling through a redox driven synergy between mical and coFilin
Nature Cell Biology, 2016Co-Authors: Elena E. Grintsevich, Jonathan R. Terman, Ruei Jiun Hung, Hunkar Gizem Yesilyurt, Shannon K. Rich, Emil ReislerAbstract:Numerous cellular Functions depend on Actin Filament (F-Actin) disassembly. The best-characterized disassembly proteins, the ADF (Actin-depolymerizing Factor)/coFilins (encoded by the twinstar gene in Drosophila), sever Filaments and recycle monomers to promote Actin assembly. CoFilin is also a relatively weak Actin disassembler, posing questions about mechanisms oF cellular F-Actin destabilization. Here we uncover a key link to targeted F-Actin disassembly by Finding that F-Actin is eFFiciently dismantled through a post-translational-mediated synergism between coFilin and the Actin-oxidizing enzyme Mical. We Find that Mical-mediated oxidation oF Actin improves coFilin binding to Filaments, where their combined eFFect dramatically accelerates F-Actin disassembly compared with either eFFector alone. This synergism is also necessary and suFFicient For F-Actin disassembly in vivo, magniFying the eFFects oF both Mical and coFilin on cellular remodelling, axon guidance and Semaphorin-Plexin repulsion. Mical and coFilin, thereFore, Form a redox-dependent synergistic pair that promotes F-Actin instability by rapidly dismantling F-Actin and generating post-translationally modiFied Actin that has altered assembly properties.
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Mical links semaphorins to F-Actin disassembly
Nature, 2010Co-Authors: Ruei Jiun Hung, Umar Yazdani, Jimok Yoon, Taehong Yang, Willem J.h. Van Berkel, Zhiyu Huang, Heng Wu, Nidhi Gupta, Jonathan R. TermanAbstract:How instructive cues present on the cell surFace have their precise eFFects on the Actin cytoskeleton is poorly understood. Semaphorins are one oF the largest Families oF these instructive cues and are widely studied For their eFFects on cell movement, navigation, angiogenesis, immunology and cancer. Semaphorins/collapsins were characterized in part on the basis oF their ability to drastically alter Actin cytoskeletal dynamics in neuronal processes, but despite considerable progress in the identiFication oF semaphorin receptors and their signalling pathways, the molecules linking them to the precise control oF cytoskeletal elements remain unknown. Recently, highly unusual proteins oF the Mical Family oF enzymes have been Found to associate with the cytoplasmic portion oF plexins, which are large cell-surFace semaphorin receptors, and to mediate axon guidance, synaptogenesis, dendritic pruning and other cell morphological changes. Mical enzymes perForm reduction-oxidation (redox) enzymatic reactions and also contain domains Found in proteins that regulate cell morphology. However, nothing is known oF the role oF Mical or its redox activity in mediating morphological changes. Here we report that Mical directly links semaphorins and their plexin receptors to the precise control oF Actin Filament (F-Actin) dynamics. We Found that Mical is both necessary and suFFicient For semaphorin-plexin-mediated F-Actin reorganization in vivo. Likewise, we puriFied Mical protein and Found that it directly binds F-Actin and disassembles both individual and bundled Actin Filaments. We also Found that Mical utilizes its redox activity to alter F-Actin dynamics in vivo and in vitro, indicating a previously unknown role For speciFic redox signalling events in Actin cytoskeletal regulation. Mical thereFore is a novel F-Actin-disassembly Factor that provides a molecular conduit through which Actin reorganization-a hallmark oF cell morphological changes including axon navigation-can be precisely achieved spatiotemporally in response to semaphorins.
