Isotropic to Nematic Liquid Crystalline Phase Transition of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>F</mml:mi></mml:math>-Actin Varies from Continuous to First Order

Viamontes, Jorge; Oakes, Patrick W.; Tang, Jay X.

doi:10.1103/physrevlett.97.118103

Cited by 49 publications

(41 citation statements)

References 30 publications

(47 reference statements)

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“…2b), indicating its properties as a nematic liquid crystal. It has already been shown that F-actin forms a nematic phase at high concentrations 15,[27][28][29] . From observations in the bulk solution, it has been reported that the nematic liquid crystallization of F-actin depends on its concentration and length like many other rod-like molecules, and the liquid crystal phase tends to appear at 50 μM or higher concentrations of F-actin 29,30 .…”

Section: Resultsmentioning

confidence: 99%

Repetitive stretching of giant liposomes utilizing the nematic alignment of confined actin

2018

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Giant liposomes encapsulating cytoskeletons have been constructed to further understand the mechanisms of cell movement and develop cell-sized chemical machineries. Innovative studies demonstrating liposomal movements using microtubules and the molecular motors kinesin/dynein have been reported. However, no one has succeeded in generating repetitive motions controlled by external stimuli. Here we show that if the actin concentration in liposomes is comparable to that of cytoplasm of living cells, the liposomes can be deformed into spindle shapes by encapsulating only actin filaments, even without the molecular motor myosin. Furthermore, their shapes can be changed reversibly between spindle and sphere shapes by adjusting osmotic pressure or by light irradiation of fluorescent-labeled actin. In the latter case, the repetitive shape changes are accompanied with stretching and shrinking of filopodia-or acrosome projection-like extensions. Our results indicate that filamentous polymer of variable length like actin filament is a potential material for the reproduction of cell-like movement.

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Section: Resultsmentioning

confidence: 99%

Repetitive stretching of giant liposomes utilizing the nematic alignment of confined actin

2018

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“…This actin concentration (3.75 mg/ml) is much lower than the measured isotropic-nematic (I-N) transition concentration (> 7 mg/ml) for 1 µm F-actin under similar ionic conditions [14]. SAXS experiments were performed both at 9KeV at BL4-2 of the Stanford Synchrotron Radiation Laboratory and at 12KeV the BESSRC-CAT (BL12-ID) at the Advanced Photon Source.…”

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confidence: 84%

Structural Polymorphism of the Actin-Espin System: A Prototypical System of Filaments and Linkers in Stereocilia

2007

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We examine the interaction between cytoskeletal F-actin and espin 3A, a prototypical actin bundling protein found in sensory cell microvilli, including cochlear cell stereocilia. Espin induces twist distortions in F-actin as well as facilitates bundle formation. Mutations in one of the two F-actin binding sites of espin, which have been implicated in deafness, can tune espin-actin inter-actions and radically transform the system's phase behavior. These results are compared to recent theoretical work on the general phase behavior linker-rod systems.Filamentous actin (F-actin), a biological rod-like polyelectrolyte, is a principal component of the eukaryotic cytoskeleton. The organization of F-actin is controlled predominantly by actin binding proteins (ABP's), which crosslink actin into a polymorphism of bundle and network phases [1][2][3], through a process that has recently been examined theoretically [4,5]. Espins are a recently discovered class of ABP's responsible for the formation of parallel actin bundles in vivo and in vitro [6][7][8]. A specific isoform, espin 3A, is found in actin bundles in sensory cell microvilli, such as the stereocilia of cochlear hair cells, which are vital for the transduction of sound in hearing [9][10][11]. Genetic mutations in espin's F-actin binding sites are linked to malformed stereocilia, deafness and vestibular dysfunction in humans and mice [11][12][13]. Such 'deafness' mutations allow us to assess the role of linker 'stickiness' in the organization of actin bundles.In this Letter we describe the first measurements of self-assembled espin-actin bundle structure, and examine how interactions between F-actin and different espin linkers are expressed in the system's phase behavior. Small angle x-ray scattering (SAXS) shows that as espin concentration increases, the system evolves directly from an isotropic phase to hexagonally coordinated paracrystalline bundles of hyper-twisted filaments. As the ability of a given espin to crosslink F-actin is decreased by using two different genetically modified 'deafness' mutants of espin with progressively more severe damage to one of the two actin binding sites, an unanticipated nematic actin-espin network is observed. By mixing wild type (wt) and mutant espin, which allows us to continuously tune this crosslinking affinity between espin and actin (as well as mimic heterozygous expression of mutant espins), we find that the onset of this nematic-network phase is a strong function of espin crosslinking affinity and concentration. We hypothesize that this unexpected isotropic to nematic network transition, which has strong implications for stereocilia formation and hearing, is due to the way weak espin linkers crosslink actin rods. F-actin was prepared from lyophilized rabbit skeletal muscle G-actin monomer (42 kDa, Cytoskeleton, Inc). G-actin was resuspended in 5 mM Tris, with 0.2 mM CaCl 2 , 0.5 mM ATP, 0.2 mM Dithotreithol (DTT) and 0.01% NaN 3 at pH 8.0 and polymerized into F-actin upon the addition of 100 mM KCl. F-actin is t...

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“…On the other hand, numerous experimental and numerical studies have been recently devoted to the analysis of equilibrium properties in systems of non-spherical particles [18,19,20,21,22,23,24,25,26]. Of special interest are those studies dealing with lattice versions of the present problem, where the situation is much less clear than in the continuum case.…”

Section: Introductionmentioning

confidence: 99%

Nonmonotonic size dependence of the critical concentration in 2D percolation of straight rigid rods under equilibrium conditions

2012

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Numerical simulations and finite-size scaling analysis have been carried out to study the percolation behavior of straight rigid rods of length k (k-mers) on twodimensional square lattices. The k-mers, containing k identical units (each one occupying a lattice site), were adsorbed at equilibrium on the lattice. The process was monitored by following the probability R L,k (θ) that a lattice composed of L × L sites percolates at a concentration θ of sites occupied by particles of size k. A nonmonotonic size dependence was observed for the percolation threshold, which decreases for small particles sizes, goes through a minimum, and finally asymptotically converges towards a definite value for large segments. This striking behavior has been interpreted as a consequence of the isotropic-nematic phase transition occurring in the system for large values of k. Finally, the universality class of the model was found to be the same as for the random percolation model.

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Isotropic to Nematic Liquid Crystalline Phase Transition ofF-Actin Varies from Continuous to First Order

Cited by 49 publications

References 30 publications

Repetitive stretching of giant liposomes utilizing the nematic alignment of confined actin

Repetitive stretching of giant liposomes utilizing the nematic alignment of confined actin

Structural Polymorphism of the Actin-Espin System: A Prototypical System of Filaments and Linkers in Stereocilia

Nonmonotonic size dependence of the critical concentration in 2D percolation of straight rigid rods under equilibrium conditions

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