Dynamic actin cross-linking governs the cytoplasm’s transition to fluid-like behavior

Cells constantly adapt their mechanics in response to mechanical and biochemical cues to migrate, divide, and organize into tissues. We developed new methods to probe the viscoelasticity of the cytoplasm and found that the binding kinetics of proteins that cross-link actin filaments control the transition from an elastic to a fluid-like network.

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Viscometric analysis of the gelation of Acanthamoeba extracts and purification of two gelation factors.

The Journal of Cell Biology ◽

10.1083/jcb.85.2.414 ◽

1980 ◽

Vol 85 (2) ◽

pp. 414-428 ◽

Cited By ~ 214

Author(s):

S D MacLean-Fletcher ◽

T D Pollard

Keyword(s):

Crude Extract ◽

Cross Linking ◽

Cross Link ◽

Gelation Process ◽

Optimum Ph ◽

Kinetics Of ◽

Low Shear

We have studied the kinetics of the gelation process that occurs upon warming cold extracts of Acanthamoeba using a low-shear falling ball assay. We find that the reaction has at least two steps, requires 0.5 mM ATP and 1.5 mM MgCl2, and is inhibited by micromolar Ca++. The optimum pH is 7.0 and temperature, 25 degrees-30 degrees C. The rate of the reaction is increased by cold preincubation with both MgCl2 and ATP. Nonhydrolyzable analogues of ATP will not substitute for ATP either in this "potentiation reaction" or in the gelation process. Either of two purified or any one of four partially purified Acanthamoeba proteins will cross-link purified actin to form a gel, but none can account for the dependence of the reaction in the crude extract on Mg-ATP or its regulation by Ca++. This suggests that the extract contains, in addition to actin-cross-linking proteins, factors dependent on Mg-ATP and Ca++ that regulate the gelation process.

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Why Are Two Different Cross-linkers Necessary for Actin Bundle Formation In Vivo and What Does Each Cross-link Contribute?

The Journal of Cell Biology ◽

10.1083/jcb.143.1.121 ◽

1998 ◽

Vol 143 (1) ◽

pp. 121-133 ◽

Cited By ~ 83

Author(s):

Lewis G. Tilney ◽

Patricia S. Connelly ◽

Kelly A. Vranich ◽

Michael K. Shaw ◽

Gregory M. Guild

Keyword(s):

Potassium Iodide ◽

Actin Filaments ◽

Cross Linking ◽

Wild Type ◽

Cross Link ◽

Actin Bundle ◽

Cross Linker ◽

Three Phases

In developing Drosophila bristles two species of cross-linker, the forked proteins and fascin, connect adjacent actin filaments into bundles. Bundles form in three phases: (a) tiny bundles appear; (b) these bundles aggregate into larger bundles; and (c) the filaments become maximally cross-linked by fascin. In mutants that completely lack forked, aggregation of the bundles does not occur so that the mature bundles consist of <50 filaments versus ∼700 for wild type. If the forked concentration is genetically reduced to half the wild type, aggregation of the tiny bundles occurs but the filaments are poorly ordered albeit with small patches of fascin cross-linked filaments. In mutants containing an excess of forked, all the bundles tend to aggregate and the filaments are maximally crossbridged by fascin. Alternatively, if fascin is absent, phases 1 and 2 occur normally but the resultant bundles are twisted and the filaments within them are poorly ordered. By extracting fully elongated bristles with potassium iodide which removes fascin but leaves forked, the bundles change from being straight to twisted and the filaments within them become poorly ordered. From these observations we conclude that (a) forked is used early in development to aggregate the tiny bundles into larger bundles; and (b) forked facilitates fascin entry into the bundles to maximally cross-link the actin filaments into straight, compact, rigid bundles. Thus, forked aligns the filaments and then directs fascin binding so that inappropriate cross-linking does not occur.

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Ionic Liquids Applied to Improve the Dispersion of Coagent Particles in an Elastomer

Journal of Composites ◽

10.1155/2013/286534 ◽

2013 ◽

Vol 2013 ◽

pp. 1-8 ◽

Cited By ~ 6

Author(s):

Magdalena Maciejewska ◽

Marian Zaborski

Keyword(s):

Ionic Liquids ◽

Alkyl Chain ◽

Cross Linking ◽

Cross Link ◽

Rubber Compounds ◽

Link Density ◽

Vulcanization Kinetics ◽

Cross Link Density ◽

The Cross ◽

Kinetics Of

The aim of this work was to study the activity of several ionic liquids (alkylimidazolium salts) that are used to improve the dispersion of coagent particles in peroxide-cross-linked hydrogenated acrylonitrile butadiene elastomer (HNBR). Hydrotalcite grafted with monoallyl maleate was applied as a coagent for the HNBR vulcanization. In this paper, we discuss the effect of the ionic liquids (alkylimidazolium salts) with respect to their anion (bromide, chloride, tetrafluoroborate, and hexafluorophosphate) and the length of alkyl chain in the cation (allyl-, ethyl-, butyl-, hexyl-, and octyl-) on the vulcanization kinetics of rubber compounds. The influence of ionic liquids on the cross-link density, the mechanical properties of the vulcanizates, and their resistance to weather ageing were also studied. Alkylimidazolium salts seem to improve the dispersion of the coagent particles and to be active in the cross-linking of HNBR with peroxide. The type of ionic liquid considerably influences the activity of the coagent particles toward the HNBR. The application of ionic liquids increases the cross-link density of the vulcanizates and improves their resistance to weather aging.

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Damage to actin filaments by glutaraldehyde: protection by tropomyosin.

The Journal of Cell Biology ◽

10.1083/jcb.90.2.459 ◽

1981 ◽

Vol 90 (2) ◽

pp. 459-466 ◽

Cited By ~ 46

Author(s):

S S Lehrer

Keyword(s):

Sodium Dodecyl Sulfate ◽

Gel Electrophoresis ◽

Actin Filaments ◽

Polyacrylamide Gel Electrophoresis ◽

Sodium Dodecyl ◽

Cross Linking ◽

Cross Link ◽

Reaction Conditions ◽

Cross Links ◽

Link Formation

Reaction of F-actin and the F-actin-tropomyosin complex with 20 mM glutaraldehyde for 19-22 h at 0 degrees C and 25 degrees C results in extensively cross-linked filaments, as judged by sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis. Electron micrographs show shorter, more irregular filaments for glutaraldehyde-treated F-actin in the absence of tropomyosin as compared to the presence of tropomyosin or untreated controls. There was a 40% drop in viscosity of glutaraldehyde-treated F-actin solutions but a 90% increase in viscosity for the glutaraldehyde-treated F-actin-tropomyosin complex in solution, as compared to the untreated controls, indicating different effects of cross-linking. SDS gels indicate that intrasubunit cross-links are introduced into F-actin and that when tropomyosin is present, intramolecular cross-link formation is inhibited. Inhibition of the salt-induced G leads to F polymerization results when intramolecular cross-links are introduced into G-actin under similar or milder reaction conditions. These data indicate that, under conditions for which extensive F-actin filament cross-linking (fixing) occurs, the filaments become damaged due to the concurrent formation of intrasubunit cross-links that cause local depolymerization and distortion and that tropomyosin protects against this damage.

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Chimeric Platinum-Polyamines and DNA Binding. Kinetics of DNA Interstrand Cross-Link Formation by Dinuclear Platinum Complexes with Polyamine Linkers

Journal of the American Chemical Society ◽

10.1021/ja301397h ◽

2012 ◽

Vol 134 (16) ◽

pp. 7135-7146 ◽

Cited By ~ 22

Author(s):

Rasha A. Ruhayel ◽

Janina S. Langner ◽

Matilda-Jane Oke ◽

Susan J. Berners-Price ◽

Ibrahim Zgani ◽

...

Keyword(s):

Dna Binding ◽

Platinum Complexes ◽

Binding Kinetics ◽

Cross Link ◽

Dinuclear Platinum ◽

Kinetics Of ◽

Dinuclear Platinum Complexes ◽

Link Formation

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Binding kinetics of fluorescent bisphosphonates as a tool for monitoring bone dynamics in vivo

Bone Abstracts ◽

10.1530/boneabs.1.pp318 ◽

2013 ◽

Author(s):

Robert Tower ◽

Graeme Campbell ◽

Marc Muller ◽

Olga Will ◽

Frederieka Grundmann ◽

...

Keyword(s):

Binding Kinetics ◽

Kinetics Of ◽

Bone Dynamics

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Influence of Brain Gangliosides on the Formation and Properties of Supported Lipid Bilayers for Binding Kinetics Studies

10.26434/chemrxiv.7505330 ◽

2018 ◽

Author(s):

Luke Jordan ◽

Nathan Wittenberg

Keyword(s):

Lipid Bilayers ◽

Binding Kinetics ◽

Supported Lipid Bilayers ◽

Dependent Manner ◽

Concentration Dependent Manner ◽

Supported Lipid Bilayer ◽

Head Groups ◽

Lipid Diffusion ◽

Kinetics Of ◽

Brain Gangliosides

This is a comprehensive study of the effects of the four major brain gangliosides (GM1, GD1b, GD1a, and GT1b) on the adsorption and rupture of phospholipid vesicles on SiO2 surfaces for the formation of supported lipid bilayer (SLB) membranes. Using quartz crystal microbalance with dissipation monitoring (QCM-D) we show that gangliosides GD1a and GT1b significantly slow the SLB formation process, whereas GM1 and GD1b have smaller effects. This is likely due to the net ganglioside charge as well as the positions of acidic sugar groups on ganglioside glycan head groups. Data is included that shows calcium can accelerate the formation of ganglioside-rich SLBs. Using fluorescence recovery after photobleaching (FRAP) we also show that the presence of gangliosides significantly reduces lipid diffusion coefficients in SLBs in a concentration-dependent manner. Finally, using QCM-D and GD1a-rich SLB membranes we measure the binding kinetics of an anti-GD1a antibody that has similarities to a monoclonal antibody that is a hallmark of a variant of Guillain-Barre syndrome.

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