scholarly journals Side-binding proteins modulate actin filament dynamics

2014 ◽  
Author(s):  
Alvaro H. Crevenna ◽  
Marcelino Arciniega ◽  
Aurelie Dupont ◽  
Kaja Kowalska ◽  
Oliver Lange ◽  
...  
Keyword(s):  
Actin Filament ◽  
Brownian Dynamics ◽  
Actin Polymerization ◽  
Actin Dynamics ◽  
Central Feature ◽  
Filament Dynamics ◽  
Filament Structure ◽  
The Rich ◽  
Dynamics Simulations ◽  
Pointed End

Actin filament dynamics govern many key physiological processes from cell motility to tissue morphogenesis. A central feature of actin dynamics is the capacity of the filament to polymerize and depolymerize at its ends in response to cellular conditions. It is currently thought that filament kinetics can be described by a single rate constant for each end. Here, using direct visualization of single actin filament elongation, we show that actin polymerization kinetics at both filament ends are strongly influenced by proteins that bind to the lateral filament surface. We also show that the less dynamic end, called the pointed-end, has a non-elongating state that dominates the observed filament kinetic asymmetry. Estimates of filament flexibility and Brownian dynamics simulations suggest that the observed kinetic diversity arises from structural alteration. Tuning filament kinetics by exploiting the natural malleability of the actin filament structure may be a ubiquitous mechanism to generate the rich variety of observed cellular actin dynamics.

scholarly journals Side-binding proteins modulate actin filament dynamics

eLife ◽  
2015 ◽  
Vol 4 ◽  
Author(s):  
Alvaro H Crevenna ◽  
Marcelino Arciniega ◽  
Aurélie Dupont ◽  
Naoko Mizuno ◽  
Kaja Kowalska ◽  
...  
Keyword(s):  
Actin Filament ◽  
Actin Polymerization ◽  
Actin Dynamics ◽  
Central Feature ◽  
Filament Dynamics ◽  
Physiological Processes ◽  
Filament Structure ◽  
Pointed End ◽  
Filament Surface ◽  
As Effects

Actin filament dynamics govern many key physiological processes from cell motility to tissue morphogenesis. A central feature of actin dynamics is the capacity of filaments to polymerize and depolymerize at their ends in response to cellular conditions. It is currently thought that filament kinetics can be described by a single rate constant for each end. In this study, using direct visualization of single actin filament elongation, we show that actin polymerization kinetics at both filament ends are strongly influenced by the binding of proteins to the lateral filament surface. We also show that the pointed-end has a non-elongating state that dominates the observed filament kinetic asymmetry. Estimates of flexibility as well as effects on fragmentation and growth suggest that the observed kinetic diversity arises from structural alteration. Tuning elongation kinetics by exploiting the malleability of the filament structure may be a ubiquitous mechanism to generate a rich variety of cellular actin dynamics.

scholarly journals Tropomyosin inhibits ADF/cofilin-dependent actin filament dynamics

2002 ◽  
Vol 156 (6) ◽  
pp. 1065-1076 ◽  
Author(s):  
Shoichiro Ono ◽  
Kanako Ono
Keyword(s):  
Actin Filament ◽  
Actin Filaments ◽  
Actin Polymerization ◽  
Biological Properties ◽  
Actin Dynamics ◽  
Background Suppression ◽  
Thin Filaments ◽  
Actin Organization ◽  
C Elegans ◽  
Filament Dynamics

Tropomyosin binds to actin filaments and is implicated in stabilization of actin cytoskeleton. We examined biochemical and cell biological properties of Caenorhabditis elegans tropomyosin (CeTM) and obtained evidence that CeTM is antagonistic to ADF/cofilin-dependent actin filament dynamics. We purified CeTM, actin, and UNC-60B (a muscle-specific ADF/cofilin isoform), all of which are derived from C. elegans, and showed that CeTM and UNC-60B bound to F-actin in a mutually exclusive manner. CeTM inhibited UNC-60B–induced actin depolymerization and enhancement of actin polymerization. Within isolated native thin filaments, actin and CeTM were detected as major components, whereas UNC-60B was present at a trace amount. Purified UNC-60B was unable to interact with the native thin filaments unless CeTM and other associated proteins were removed by high-salt extraction. Purified CeTM was sufficient to restore the resistance of the salt-extracted filaments from UNC-60B. In muscle cells, CeTM and UNC-60B were localized in different patterns. Suppression of CeTM by RNA interference resulted in disorganized actin filaments and paralyzed worms in wild-type background. However, in an ADF/cofilin mutant background, suppression of CeTM did not worsen actin organization and worm motility. These results suggest that tropomyosin is a physiological inhibitor of ADF/cofilin-dependent actin dynamics.

scholarly journals Insights into actin polymerization and nucleation using a coarse grained model

2019 ◽  
Author(s):  
Brandon G. Horan ◽  
Aaron R. Hall ◽  
Dimitrios Vavylonis
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulations ◽  
Actin Filament ◽  
Actin Polymerization ◽  
Activation Barrier ◽  
Computational Cost ◽  
Coarse Grained ◽  
Coarse Grained Model ◽  
Dynamics Simulations ◽  
Pointed End

ABSTRACTWe studied actin filament polymerization and nucleation with molecular dynamics simulations and a previously established coarse-grained model having each residue represented by a single interaction site located at the Cα atom. We approximate each actin protein as a fully or partially rigid unit to identify the equilibrium structural ensemble of interprotein complexes. Monomers in the F-actin configuration bound to both barbed and pointed ends of a short F-actin filament at the anticipated locations for polymerization. Binding at both ends occurred with similar affinity. Contacts between residues of the incoming subunit and the short filament were consistent with expectation from models based on crystallography, X-ray diffraction and cryo-electron microscopy. Binding at the barbed and pointed end also occurred at an angle with respect to the polymerizable bound structure, and the angle range depended on the flexibility of the D-loop. Additional barbed end bound states were seen when the incoming subunit was in the G-actin form. Consistent with an activation barrier for pointed end polymerization, G-actin did not bind at an F-actin pointed end. In all cases, binding at the barbed end also occurred in a configuration similar to the antiparallel (lower) dimer. Individual monomers bound each other in a short-pitch helix complex in addition to other configurations, with several of them apparently non-productive for polymerization. Simulations with multiple monomers in the F-actin form show assembly into filaments as well as transient aggregates at the barbed end. We discuss the implications of these observations on the kinetic pathway of actin filament nucleation and polymerization and possibilities for future improvements of the coarse-grained model.SIGNIFICANCEControl of actin filament nucleation and elongation has crucial importance to cellular life. We show that coarse-grained molecular dynamics simulations are a powerful tool which can gauge involved mechanisms at reasonable computational cost, while retaining essential features of the fully atomic, yet less computationally tractable, system. Using a knowledge-based potential demonstrates the power of these methods for explaining and reproducing polymerization. Intermediate actin complexes identified in the simulations may play critical roles in the kinetic pathways of actin polymerization which may have been difficult to observe in prior experiments. These methods have been sparsely applied to the actin system, yet have potential to answer many important questions in the field.

scholarly journals Cofilin is a pH sensor for actin free barbed end formation: role of phosphoinositide binding

2008 ◽  
Vol 183 (5) ◽  
pp. 865-879 ◽  
Author(s):  
Christian Frantz ◽  
Gabriela Barreiro ◽  
Laura Dominguez ◽  
Xiaoming Chen ◽  
Robert Eddy ◽  
...  
Keyword(s):  
Actin Filament ◽  
Structural Changes ◽  
Ph Sensor ◽  
Ph Sensitive ◽  
Actin Binding ◽  
Filamentous Actin ◽  
Filament Dynamics ◽  
Ph Dependent ◽  
Dynamics Simulations

Newly generated actin free barbed ends at the front of motile cells provide sites for actin filament assembly driving membrane protrusion. Growth factors induce a rapid biphasic increase in actin free barbed ends, and we found both phases absent in fibroblasts lacking H+ efflux by the Na-H exchanger NHE1. The first phase is restored by expression of mutant cofilin-H133A but not unphosphorylated cofilin-S3A. Constant pH molecular dynamics simulations and nuclear magnetic resonance (NMR) reveal pH-sensitive structural changes in the cofilin C-terminal filamentous actin binding site dependent on His133. However, cofilin-H133A retains pH-sensitive changes in NMR spectra and severing activity in vitro, which suggests that it has a more complex behavior in cells. Cofilin activity is inhibited by phosphoinositide binding, and we found that phosphoinositide binding is pH-dependent for wild-type cofilin, with decreased binding at a higher pH. In contrast, phosphoinositide binding by cofilin-H133A is attenuated and pH insensitive. These data suggest a molecular mechanism whereby cofilin acts as a pH sensor to mediate a pH-dependent actin filament dynamics.

scholarly journals EGF stimulates an increase in actin nucleation and filament number at the leading edge of the lamellipod in mammary adenocarcinoma cells

1998 ◽  
Vol 111 (2) ◽  
pp. 199-211 ◽  
Author(s):  
A.Y. Chan ◽  
S. Raft ◽  
M. Bailly ◽  
J.B. Wyckoff ◽  
J.E. Segall ◽  
...  
Keyword(s):  
Actin Polymerization ◽  
De Novo ◽  
Leading Edge ◽  
Mammary Adenocarcinoma ◽  
Actin Dynamics ◽  
Actin Nucleation ◽  
Nucleation Sites ◽  
Nucleation Activity ◽  
Pointed End ◽  
Stimulation Of

Stimulation of metastatic MTLn3 cells with EGF causes the rapid extension of lamellipods, which contain a zone of F-actin at the leading edge. In order to establish the mechanism for accumulation of F-actin at the leading edge and its relationship to lamellipod extension in response to EGF, we have studied the kinetics and location of EGF-induced actin nucleation activity in MTLn3 cells and characterized the actin dynamics at the leading edge by measuring the changes at the pointed and barbed ends of actin filaments upon EGF stimulation of MTLn3 cells. The major result of this study is that stimulation of MTLn3 cells with EGF causes a transient increase in actin nucleation activity resulting from the appearance of free barbed ends very close to the leading edge of extending lamellipods. In addition, cytochalasin D causes a significant decrease in the total F-actin content in EGF-stimulated cells, indicating that both actin polymerization and depolymerization are stimulated by EGF. Pointed end incorporation of rhodamine-labeled actin by the EGF stimulated cells is 2.12+/−0.47 times higher than that of control cells. Since EGF stimulation causes an increase in both barbed and pointed end incorporation of rhodamine-labeled actin in the same location, the EGF-stimulated nucleation sites are more likely due either to severing of pre-existing filaments or de novo nucleation of filaments at the leading edge thereby creating new barbed and pointed ends. The timing and location of EGF-induced actin nucleation activity in MTLn3 cells can account for the observed accumulation of F-actin at the leading edge and demonstrate that this F-actin rich zone is the primary actin polymerization zone after stimulation.

scholarly journals Insights into the evolution of regulated actin dynamics via characterization of primitive gelsolin/cofilin proteins from Asgard archaea

2020 ◽  
Vol 117 (33) ◽  
pp. 19904-19913 ◽  
Author(s):  
Caner Akıl ◽  
Linh T. Tran ◽  
Magali Orhant-Prioux ◽  
Yohendran Baskaran ◽  
Edward Manser ◽  
...  
Keyword(s):  
Actin Cytoskeleton ◽  
Actin Filament ◽  
Calcium Binding ◽  
Mammalian Cells ◽  
Actin Polymerization ◽  
Calcium Release ◽  
Duplication Event ◽  
Cellular Level ◽  
Actin Dynamics

Asgard archaea genomes contain potential eukaryotic-like genes that provide intriguing insight for the evolution of eukaryotes. The eukaryotic actin polymerization/depolymerization cycle is critical for providing force and structure in many processes, including membrane remodeling. In general, Asgard genomes encode two classes of actin-regulating proteins from sequence analysis, profilins and gelsolins. Asgard profilins were demonstrated to regulate actin filament nucleation. Here, we identify actin filament severing, capping, annealing and bundling, and monomer sequestration activities by gelsolin proteins from Thorarchaeota (Thor), which complete a eukaryotic-like actin depolymerization cycle, and indicate complex actin cytoskeleton regulation in Asgard organisms. Thor gelsolins have homologs in other Asgard archaea and comprise one or two copies of the prototypical gelsolin domain. This appears to be a record of an initial preeukaryotic gene duplication event, since eukaryotic gelsolins are generally comprise three to six domains. X-ray structures of these proteins in complex with mammalian actin revealed similar interactions to the first domain of human gelsolin or cofilin with actin. Asgard two-domain, but not one-domain, gelsolins contain calcium-binding sites, which is manifested in calcium-controlled activities. Expression of two-domain gelsolins in mammalian cells enhanced actin filament disassembly on ionomycin-triggered calcium release. This functional demonstration, at the cellular level, provides evidence for a calcium-controlled Asgard actin cytoskeleton, indicating that the calcium-regulated actin cytoskeleton predates eukaryotes. In eukaryotes, dynamic bundled actin filaments are responsible for shaping filopodia and microvilli. By correlation, we hypothesize that the formation of the protrusions observed from Lokiarchaeota cell bodies may involve the gelsolin-regulated actin structures.

scholarly journals EPLIN regulates actin dynamics by cross-linking and stabilizing filaments

2003 ◽  
Vol 160 (3) ◽  
pp. 399-407 ◽  
Author(s):  
Raymond S. Maul ◽  
Yuhong Song ◽  
Kurt J. Amann ◽  
Sachi C. Gerbin ◽  
Thomas D. Pollard ◽  
...  
Keyword(s):  
Actin Filament ◽  
Actin Polymerization ◽  
Binding Activity ◽  
Stress Fibers ◽  
Actin Dynamics ◽  
Actin Binding ◽  
Membrane Ruffling ◽  
Cross Links ◽  
As Stress ◽  
Kinetics Of

Epithelial protein lost in neoplasm (EPLIN) is a cytoskeleton-associated protein encoded by a gene that is down-regulated in transformed cells. EPLIN increases the number and size of actin stress fibers and inhibits membrane ruffling induced by Rac. EPLIN has at least two actin binding sites. Purified recombinant EPLIN inhibits actin filament depolymerization and cross-links filaments in bundles. EPLIN does not affect the kinetics of spontaneous actin polymerization or elongation at the barbed end, but inhibits branching nucleation of actin filaments by Arp2/3 complex. Side binding activity may stabilize filaments and account for the inhibition of nucleation mediated by Arp2/3 complex. We propose that EPLIN promotes the formation of stable actin filament structures such as stress fibers at the expense of more dynamic actin filament structures such as membrane ruffles. Reduced expression of EPLIN may contribute to the motility of invasive tumor cells.

scholarly journals Actin filament dynamics are dominated by rapid growth and severing activity in the Arabidopsis cortical array

2009 ◽  
Vol 184 (2) ◽  
pp. 269-280 ◽  
Author(s):  
Christopher J. Staiger ◽  
Michael B. Sheahan ◽  
Parul Khurana ◽  
Xia Wang ◽  
David W. McCurdy ◽  
...  
Keyword(s):  
Actin Filament ◽  
Actin Filaments ◽  
Stochastic Dynamics ◽  
Actin Dynamics ◽  
Epifluorescence Microscopy ◽  
Actin Assembly ◽  
Cortical Actin ◽  
Filament Dynamics ◽  
Cortical Array

Metazoan cells harness the power of actin dynamics to create cytoskeletal arrays that stimulate protrusions and drive intracellular organelle movements. In plant cells, the actin cytoskeleton is understood to participate in cell elongation; however, a detailed description and molecular mechanism(s) underpinning filament nucleation, growth, and turnover are lacking. Here, we use variable-angle epifluorescence microscopy (VAEM) to examine the organization and dynamics of the cortical cytoskeleton in growing and nongrowing epidermal cells. One population of filaments in the cortical array, which most likely represent single actin filaments, is randomly oriented and highly dynamic. These filaments grow at rates of 1.7 µm/s, but are generally short-lived. Instead of depolymerization at their ends, actin filaments are disassembled by severing activity. Remodeling of the cortical actin array also features filament buckling and straightening events. These observations indicate a mechanism inconsistent with treadmilling. Instead, cortical actin filament dynamics resemble the stochastic dynamics of an in vitro biomimetic system for actin assembly.

scholarly journals Crosslinking actin networks produces compressive force

2019 ◽  
Author(s):  
Rui Ma ◽  
Julien Berro
Keyword(s):  
Actin Filaments ◽  
Brownian Dynamics ◽  
Actin Polymerization ◽  
Turgor Pressure ◽  
Compressive Force ◽  
Yeast Cells ◽  
Actin Networks ◽  
Dynamics Simulations ◽  
Brownian Dynamics Simulations ◽  
Over Time

AbstractActin has been shown to be essential for clathrin-mediated endocytosis in yeast. However, actin polymerization alone is likely insufficient to produce enough force to deform the membrane against the huge turgor pressure of yeast cells. In this paper, we used Brownian dynamics simulations to demonstrate that crosslinking of a meshwork of non-polymerizing actin filaments is able to produce compressive forces. We show that the force can be up to thousands of piconewtons if the crosslinker has a high stiffness. The force decays over time as a result of crosslinker turnover, and is a result of converting chemical binding energy into elastic energy.

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