Phase Segregation of Passive Advective Particles in an Active Medium

Das, Amit; Polley, Anirban; Rao, Madan

doi:10.1103/physrevlett.116.068306

Cited by 35 publications

(69 citation statements)

References 44 publications

(62 reference statements)

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“…The influence of F-actin on domain dynamics is expected to be much stronger in a freestanding membrane system such as observed in GUVs (40,43) or support-free planar bilayers (62). Recent theoretical work from the laboratory of one of us suggests that the phase-segregating active composite membrane will exhibit specific characteristics in the distribution of domain sizes and its scaling behavior (63), and the experiments shown here exemplify the number of effects that such an active composite system can have on their dynamics.…”

Section: Discussionmentioning

confidence: 99%

Actomyosin dynamics drive local membrane component organization in an in vitro active composite layer

Köster

Husain

Iljazi

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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142

152

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The surface of a living cell provides a platform for receptor signaling, protein sorting, transport, and endocytosis, whose regulation requires the local control of membrane organization. Previous work has revealed a role for dynamic actomyosin in membrane protein and lipid organization, suggesting that the cell surface behaves as an active composite composed of a fluid bilayer and a thin film of active actomyosin. We reconstitute an analogous system in vitro that consists of a fluid lipid bilayer coupled via membrane-associated actinbinding proteins to dynamic actin filaments and myosin motors. Upon complete consumption of ATP, this system settles into distinct phases of actin organization, namely bundled filaments, linked apolar asters, and a lattice of polar asters. These depend on actin concentration, filament length, and actin/myosin ratio. During formation of the polar aster phase, advection of the self-organizing actomyosin network drives transient clustering of actin-associated membrane components. Regeneration of ATP supports a constitutively remodeling actomyosin state, which in turn drives active fluctuations of coupled membrane components, resembling those observed at the cell surface. In a multicomponent membrane bilayer, this remodeling actomyosin layer contributes to changes in the extent and dynamics of phasesegregating domains. These results show how local membrane composition can be driven by active processes arising from actomyosin, highlighting the fundamental basis of the active composite model of the cell surface, and indicate its relevance to the study of membrane organization.T he cell surface mediates interactions between the cell and the outside world by serving as the site for signal transduction. It also facilitates the uptake and release of cargo and supports adhesion to substrates. These diverse roles require that the cell surface components involved in each function are spatially and temporally organized into domains spanning a few nanometers (nanoclusters) to several micrometers (microdomains). The cell surface itself may be considered as a fluid-lipid bilayer wherein proteins are embedded (1). In the living cell, this multicomponent system is supported by an actin cortex, composed of a branched network of actin and a collection of filaments (2-4).Current models of membrane organization fall into three categories: those invoking lipid-lipid and lipid-protein interactions in the plasma membrane [e.g., the fluid mosaic model (1, 5) and the lipid raft hypothesis (6)], or those that appeal to the membrane-associated actin cortex (e.g., the picket fence model) (7), or a combination of these (8, 9). Although these models based on thermodynamic equilibrium principles have successfully explained the organization and dynamics of a range of membrane components and molecules, there is a growing class of phenomena that appears inconsistent with chemical and thermal equilibrium, which might warrant a different explanation. These include aspects of the organization and dynamics of outer leaflet...

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Section: Discussionmentioning

confidence: 99%

Actomyosin dynamics drive local membrane component organization in an in vitro active composite layer

Köster

Husain

Iljazi

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

142

152

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“…The exponents, χ = 1/2 and z 2 = 3/2, are the same as in the second class particle problem [16], which, due to the well-known mapping between the totally antisymmetric simple exclusion process and a discrete interface model in the KPZ class, corresponds to setting p ± = p(1 ± λ) uniformly over the interface instead of on the particle site only. The exponent z 2 = 3/2, there, reflects the dynamic exponent of the interface and the value χ = 1/2 yields η through (6). In this case the exponents obey the scaling relation (8).…”

Section: Fluctuating Metadynamics At ω ≤mentioning

confidence: 99%

Statistical mechanics of a single active slider on a fluctuating interface

2019

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We study the statistical mechanics of a single active slider on a fluctuating interface, by means of numerical simulations and theoretical arguments. The slider, which moves by definition towards the interface minima, is active as it also stimulates growth of the interface. Even though such a particle has no counterpart in thermodynamic systems, active sliders may provide a simple model for ATP-dependent membrane proteins that activate cytoskeletal growth. We find a wide range of dynamical regimes according to the ratio between the timescales associated with the slider motion and the interface relaxation. If the interface dynamics is slow, the slider behaves like a random walker in a random envinronment which, furthermore, is able to escape environmental troughs by making them grow. This results in different dynamic exponens to the interface and the particle: the former behaves as an Edward-Wilkinson surface with dynamic exponent 2 whereas the latter has dynamic exponent 3/2. When the interface is fast, we get sustained ballistic motion with the particle surfing a membrane wave created by itself. However, if the interface relaxes immediately (i.e., it is infinitely fast), particle motion becomes symmetric and goes back to diffusive. Due to such a rich phenomenology, we propose the active slider as a toy model of fundamental interest in the field of active membranes and, generally, whenever the system constituent can alter the environment by spending energy.

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“…Even more interesting are mixtures of active and passive particles [13], which provide, for example, an novel route for switchable self-assembly [14], microrheological measurements [15], or even shed light on the active dynamical processes within the cell [16]. By now, only structural properties, like phase behaviour, in mixtures with different activities [13,[17][18][19], temperatures [20][21][22], or diameters [23] have been investigated.…”

Section: Introductionmentioning

confidence: 99%

Propagating interfaces in mixtures of active and passive Brownian particles

2016

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The emergent collective dynamics in phase-separated mixtures of isometric active and passive Brownian particles is studied numerically in two-dimensions. A novel steady-state of well-defined propagating interfaces is observed, where the interface between the dense and the dilute phase propagates and the bulk of both phases is (nearly) at rest. Two kind of interfaces, advancing and receding, are formed by spontaneous symmetry breaking, induced by an instability of a planar interface due to the formation of localized vortices. The propagation arises due to flux imbalance at the interface, resembling the growth behavior of rough surfaces far from equilibrium. Above a threshold, the interface velocity decreases linearly with increasing fraction of active particles.

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Phase Segregation of Passive Advective Particles in an Active Medium

Cited by 35 publications

References 44 publications

Actomyosin dynamics drive local membrane component organization in an in vitro active composite layer

Actomyosin dynamics drive local membrane component organization in an in vitro active composite layer

Statistical mechanics of a single active slider on a fluctuating interface

Propagating interfaces in mixtures of active and passive Brownian particles

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