scholarly journals Reconstitution of the equilibrium state of dynamic actin networks

2018 ◽  
Author(s):  
Angelika Manhart ◽  
Aleksandra Icheva ◽  
Christophe Guerin ◽  
Tobbias Klar ◽  
Rajaa Boujemaa-Paterski ◽  
...  
Keyword(s):  
Mathematical Model ◽  
Equilibrium State ◽  
Dynamic Equilibrium ◽  
Actin Network ◽  
Network Nodes ◽  
Actin Networks ◽  
Cell Functions ◽  
Dynamic Equilibrium State ◽  
Selective Disassembly

AbstractPrinciples of regulation of actin network dimensions, fundamentally important for cell functions, remain unclear. We studied in vitro and in silico the effect of key parameters, actin density, ADF/Cofilin concentration and network width on the network length. In the presence of ADF/Cofilin, networks reached equilibrium and became globally treadmilling. At the trailing edge, the network disintegrated into large fragments. A mathematical model predicts the network length as a function of width, actin and ADF/Cofilin concentrations. Local depletion of ADF/Cofilin by binding to actin is significant, leading to wider networks growing longer. A single rate of breaking network nodes, proportional to ADF/Cofilin density and inversely proportional to the square of the actin density, can account for the disassembly dynamics. Selective disassembly of heterogeneous networks by ADF/Cofilin controls steering during motility. Our results establish general principles on how the dynamic equilibrium state of actin network emerges from biochemical and structural feedbacks.

scholarly journals Quantitative regulation of the dynamic steady state of actin networks

eLife ◽  
2019 ◽  
Vol 8 ◽  
Author(s):  
Angelika Manhart ◽  
Téa Aleksandra Icheva ◽  
Christophe Guerin ◽  
Tobbias Klar ◽  
Rajaa Boujemaa-Paterski ◽  
...  
Keyword(s):  
Mathematical Model ◽  
Steady State ◽  
Heterogeneous Networks ◽  
In Silico ◽  
Actin Network ◽  
Network Nodes ◽  
Actin Networks ◽  
Cell Functions ◽  
Selective Disassembly

Principles of regulation of actin network dimensions are fundamentally important for cell functions, yet remain unclear. Using both in vitro and in silico approaches, we studied the effect of key parameters, such as actin density, ADF/Cofilin concentration and network width on the network length. In the presence of ADF/Cofilin, networks reached equilibrium and became treadmilling. At the trailing edge, the network disintegrated into large fragments. A mathematical model predicts the network length as a function of width, actin and ADF/Cofilin concentrations. Local depletion of ADF/Cofilin by binding to actin is significant, leading to wider networks growing longer. A single rate of breaking network nodes, proportional to ADF/Cofilin density and inversely proportional to the square of the actin density, can account for the disassembly dynamics. Selective disassembly of heterogeneous networks by ADF/Cofilin controls steering during motility. Our results establish general principles on how the dynamic steady state of actin network emerges from biochemical and structural feedbacks.

scholarly journals A unique internal ribosome entry site representing a dynamic equilibrium state of RNA tertiary structure in the 5′-UTR of Wheat yellow mosaic virus RNA1

2019 ◽  
Author(s):  
Guowei Geng ◽  
Chengming Yu ◽  
Xiangdong Li ◽  
Xuefeng Yuan
Keyword(s):  
Equilibrium State ◽  
Mosaic Virus ◽  
Dynamic Equilibrium ◽  
Yellow Mosaic Virus ◽  
Wheat Yellow Mosaic Virus ◽  
Long Distance ◽  
Internal Ribosome Entry ◽  
Interaction Sites ◽  
Dynamic Equilibrium State ◽  
Rna Interaction

Abstract Internal ribosome entry sites (IRESes) were first reported in RNA viruses and subsequently identified in cellular mRNAs. In this study, IRES activity of the 5′-UTR in Wheat yellow mosaic virus (WYMV) RNA1 was identified, and the 3′-UTR synergistically enhanced this IRES activity via long-distance RNA–RNA interaction between C80U81and A7574G7575. Within the 5′-UTR, the hairpin 1(H1), flexible hairpin 2 (H2) and linker region (LR1) between H1 and H2 played an essential role in cap-independent translation, which is associated with the structural stability of H1, length of discontinuous stems and nucleotide specificity of the H2 upper loop and the long-distance RNA–RNA interaction sites in LR1. The H2 upper loop is a target region of the eIF4E. Cytosines (C55, C66, C105 and C108) in H1 and H2 and guanines (G73, G79 and G85) in LR1 form discontinuous and alternative base pairing to maintain the dynamic equilibrium state, which is used to elaborately regulate translation at a suitable level. The WYMV RNA1 5′-UTR contains a novel IRES, which is different from reported IRESes because of the dynamic equilibrium state. It is also suggested that robustness not at the maximum level of translation is the selection target during evolution of WYMV RNA1.

Study on Tension Model of Running Deviation for Strip Rolling

2013 ◽  
Vol 779-780 ◽  
pp. 84-87
Author(s):  
Shen Bai Zheng ◽  
Xin Zhou Huo ◽  
Jin Zhi Yin ◽  
Gai Yan Yang ◽  
Wei Zhang
Keyword(s):  
Equilibrium State ◽  
Dynamic Equilibrium ◽  
Digital Simulation ◽  
Strip Rolling ◽  
Dynamic Equilibrium State ◽  
Two Sides ◽  
Roll Tilt

For running deviation of strip and camber deviation, a tension model was established on the discussion of the dynamic equilibrium state under tension. The friction difference of strips sides or workpiece wedge causes plain rolling camber, meanwhile housings elasticity inequality or roll tilt leads to axial shifting and camber deviation. In the digital simulation, the tension-drawing model is necessary to realize tension self-adjusting, and in the production, tension increments can be calculated for adjusting the two sides gaps.

scholarly journals MICAL2 acts through Arp3B isoform-specific Arp2/3 complexes to destabilize branched actin networks

2020 ◽  
Author(s):  
Chiara Galloni ◽  
Davide Carra ◽  
Jasmine V. G. Abella ◽  
Svend Kjær ◽  
Pavithra Singaravelu ◽  
...  
Keyword(s):  
Functional Properties ◽  
Actin Filament ◽  
Actin Assembly ◽  
Actin Network ◽  
Network Stability ◽  
Actin Networks ◽  
Cellular Processes ◽  
Actin Turnover ◽  
Filament Networks

AbstractThe Arp2/3 complex (Arp2, Arp3 and ARPC1-5) is essential to generate branched actin filament networks for many cellular processes. Human Arp3, ARPC1 and ARPC5 exist as two isoforms but the functional properties of Arp2/3 iso-complexes is largely unexplored. Here we show that Arp3B, but not Arp3 is subject to regulation by the methionine monooxygenase MICAL2, which is recruited to branched actin networks by coronin-1C. Although Arp3 and Arp3B iso-complexes promote actin assembly equally efficiently in vitro, they have different cellular properties. Arp3B turns over significantly faster than Arp3 within the network and upon its depletion actin turnover decreases. Substitution of Arp3B Met293 by Thr, the corresponding residue in Arp3 increases actin network stability, and conversely, replacing Arp3 Thr293 with Gln to mimic Met oxidation promotes network disassembly. Thus, MICAL2 regulates a subset of Arp2/3 complexes to control branched actin network disassembly.

scholarly journals Myosin 1b Flattens and Prunes Branched Actin Filaments

2020 ◽  
Author(s):  
Julien Pernier ◽  
Antoine Morchain ◽  
Valentina Caorsi ◽  
Aurélie Bertin ◽  
Hugo Bousquet ◽  
...  
Keyword(s):  
Total Internal Reflection ◽  
Molecular Motor ◽  
Internal Reflection ◽  
Total Internal Reflection Fluorescence ◽  
Actin Network ◽  
Tirf Microscopy ◽  
Actin Networks ◽  
Cellular Processes

AbstractMotile and morphological cellular processes require a spatially and temporally coordinated branched actin network that is controlled by the activity of various regulatory proteins including the Arp2/3 complex, profilin, cofilin and tropomyosin. We have previously reported that myosin 1b regulates the density of the actin network in the growth cone. Using in vitro F-actin gliding assays and total internal reflection fluorescence (TIRF) microscopy we show in this report that this molecular motor flattens the Arp2/3-dependent actin branches up to breaking them and reduces the probability to form new branches. This experiment reveals that myosin 1b can produce force sufficient enough to break up the Arp2/3-mediated actin junction. Together with the former in vivo studies, this work emphasizes the essential role played by myosins in the architecture and in the dynamics of actin networks in different cellular regions.Short summaryUsing in vitro F-actin gliding assays and total internal reflection fluorescence (TIRF) microscopy we show that myosin flattens the Arp2/3-dependent actin branches up to breaking them and reduces the probability to form new branches

scholarly journals Tropomyosin and α-actinin cooperation inhibits fimbrin association with actin filament networks in fission yeast

2017 ◽  
Author(s):  
Jenna R. Christensen ◽  
Kaitlin E. Homa ◽  
Meghan E. O’Connell ◽  
David R. Kovar
Keyword(s):  
Fission Yeast ◽  
Fluorescent Imaging ◽  
Actin Binding ◽  
Yeast Genetics ◽  
Actin Network ◽  
Contractile Ring ◽  
Actin Networks ◽  
Filament Networks ◽  
Actin Patch

ABSTRACTWe previously discovered that competition between fission yeast actin binding proteins (ABPs) for association with F-actin helps facilitate their sorting to different F-actin networks. Specifically, competition between actin patch ABPs fimbrin Fim1 and cofilin Adf1 enhances each other’s activities, and rapidly displaces tropomyosin Cdc8 from the F-actin network. However, these interactions don’t explain how Fim1, a robust competitor, is prevented from associating equally well with other F-actin networks. Here, with a combination of fission yeast genetics, live cell fluorescent imaging, and in vitro TIRF microscopy, we identified the contractile ring ABP α-actinin Ain1 as a key sorting factor. Fim1 competes with Ain1 for association with F-actin, which is dependent upon their residence time on F-actin. Remarkably, although Fim1 outcompetes both contractile ring ABPs Ain1 and Cdc8 individually, Cdc8 enhances the bundling activity of Ain1 10-fold, allowing the combination of Ain1 and Cdc8 to inhibit Fim1 association with contractile ring F-actin.

scholarly journals Synergy between Cyclase-associated protein and Cofilin accelerates actin filament depolymerization by two orders of magnitude

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Shashank Shekhar ◽  
Johnson Chung ◽  
Jane Kondev ◽  
Jeff Gelles ◽  
Bruce L. Goode
Keyword(s):  
Actin Filament ◽  
Single Molecule ◽  
Actin Filaments ◽  
Binding Protein ◽  
Actin Dynamics ◽  
Actin Network ◽  
Cellular Mechanisms ◽  
Actin Networks ◽  
Binding Event

AbstractCellular actin networks can be rapidly disassembled and remodeled in a few seconds, yet in vitro actin filaments depolymerize slowly over minutes. The cellular mechanisms enabling actin to depolymerize this fast have so far remained obscure. Using microfluidics-assisted TIRF, we show that Cyclase-associated protein (CAP) and Cofilin synergize to processively depolymerize actin filament pointed ends at a rate 330-fold faster than spontaneous depolymerization. Single molecule imaging further reveals that hexameric CAP molecules interact with the pointed ends of Cofilin-decorated filaments for several seconds at a time, removing approximately 100 actin subunits per binding event. These findings establish a paradigm, in which a filament end-binding protein and a side-binding protein work in concert to control actin dynamics, and help explain how rapid actin network depolymerization is achieved in cells.

scholarly journals A barbed end interference mechanism reveals how capping protein promotes nucleation in branched actin networks

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Johanna Funk ◽  
Felipe Merino ◽  
Matthias Schaks ◽  
Klemens Rottner ◽  
Stefan Raunser ◽  
...  
Keyword(s):  
Structural Biology ◽  
Actin Filaments ◽  
Actin Network ◽  
Essential Factor ◽  
Actin Networks ◽  
Capping Protein ◽  
Cellular Processes ◽  
In Vitro Reconstitution ◽  
Interference Mechanism

AbstractHeterodimeric capping protein (CP/CapZ) is an essential factor for the assembly of branched actin networks, which push against cellular membranes to drive a large variety of cellular processes. Aside from terminating filament growth, CP potentiates the nucleation of actin filaments by the Arp2/3 complex in branched actin networks through an unclear mechanism. Here, we combine structural biology with in vitro reconstitution to demonstrate that CP not only terminates filament elongation, but indirectly stimulates the activity of Arp2/3 activating nucleation promoting factors (NPFs) by preventing their association to filament barbed ends. Key to this function is one of CP’s C-terminal “tentacle” extensions, which sterically masks the main interaction site of the terminal actin protomer. Deletion of the β tentacle only modestly impairs capping. However, in the context of a growing branched actin network, its removal potently inhibits nucleation promoting factors by tethering them to capped filament ends. End tethering of NPFs prevents their loading with actin monomers required for activation of the Arp2/3 complex and thus strongly inhibits branched network assembly both in cells and reconstituted motility assays. Our results mechanistically explain how CP couples two opposed processes—capping and nucleation—in branched actin network assembly.

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