Model for Probing Membrane-Cortex Adhesion by Micropipette Aspiration and Fluctuation Spectroscopy

Alert, Ricard; Casademunt, Jaume; Brugués, Jan; Sens, Pierre

doi:10.1016/j.bpj.2015.02.027

Cited by 46 publications

(82 citation statements)

References 54 publications

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“…Estimates of the confinement strength k te of biological membranes due to the interaction with the corresponding cell wall or cortex do not abound in the literature. In [29], the density of membrane-cortex linkers in eukaryotic cells was estimated to be around r m » -100 m rigidities k = 10-k T 100 B , and a typical cell radius ranging from from = R 1 to m 10 m, we find values for K ranging from2.5 10 4 up to2. 5 10 9 .…”

Section: Estimation and Control Of Model Parameters In Real Systemsmentioning

confidence: 78%

Pattern formation by curvature-inducing proteins on spherical membranes

Agudo-Canalejo

Golestanian

2017

New J. Phys.

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Spatial organisation is a hallmark of all living cells, and recreating it in model systems is a necessary step in the creation of synthetic cells. It is therefore of both fundamental and practical interest to better understand the basic mechanisms underlying spatial organisation in cells. In this work, we use a continuum model of membrane and protein dynamics to study the behaviour of curvature-inducing proteins on membranes of spherical shape, such as living cells or lipid vesicles. We show that the interplay between curvature energy, entropic forces, and the geometric constraints on the membrane can result in the formation of patterns of highly-curved/protein-rich and weakly-curved/proteinpoor domains on the membrane. The spontaneous formation of such patterns can be triggered either by an increase in the average density of curvature-inducing proteins, or by a relaxation of the geometric constraints on the membrane imposed by the membrane tension or by the tethering of the membrane to a rigid cell wall or cortex. These parameters can also be tuned to select the size and number of the protein-rich domains that arise upon pattern formation. The very general mechanism presented here could be related to protein self-organisation in many biological processes, ranging from (proto)cell division to the formation of membrane rafts. protein patterns on the surface of other types of cells, as well as in model systems consisting of lipid vesicles and proteins. In this work, we will explore in full generality and detail the predictions of such a model.The basic idea behind the model is presented in figure 1. A closed, initially spherical membrane contains proteins that impose a spontaneous curvature C p on the membrane (in general, the proteins might be attached to the membrane from the cytoplasmic or the exoplasmic sides, or they might be transmembrane proteins embedded in the membrane) [13,14]. If the proteins did not induce any curvature, a random, homogeneous distribution of proteins would be favoured by thermal fluctuations, that is, entropic forces (in the absence of direct attractive protein-protein interactions). However, if the curvature induced by the proteins is large enough, bending contributions to the free energy of the system can lead to an effective attraction between proteins and to the formation of spatially inhomogeneous patterns in protein distribution and membrane curvature. The details of membrane-mediated protein-protein interactions have been thoroughly studied in the past [15][16][17][18]. Furthermore, we will consider the possibility of geometric constraints on the membrane, such as the tethering of the membrane to a rigid cell wall/cortex or the existence of a membrane area reservoir at nonzero tension. Interestingly, it was recently shown that solid particles such as proteins can sense the local membrane curvature imposed by geometric constraints on the membrane [19].Here, we have found that, in realistic situations, spontaneous pattern formation can be induced either by an increase in the surfac...

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Section: Estimation and Control Of Model Parameters In Real Systemsmentioning

confidence: 78%

Pattern formation by curvature-inducing proteins on spherical membranes

Agudo-Canalejo

Golestanian

2017

New J. Phys.

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“…For a nearly planar lipid membrane in contact with a surrounding fluid, the z-component of the membrane velocity, ∂h/∂t, is assumed to match the z-component of the fluid velocity. Moreover, the force exerted on the fluid by the membrane is equal and opposite to the force exerted by the fluid on the membrane, which is captured by the internal membrane force per area p int (18). The dynamical equation governing passive membrane fluctuations is thus given by [6,13] ∂h(x, t)…”

Section: Dynamical Equation With Surrounding Fluidmentioning

confidence: 99%

Active Contact Forces Drive Nonequilibrium Fluctuations in Membrane Vesicles

Takatori

Sahu

2020

Phys. Rev. Lett.

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We analyze the non-equilibrium shape fluctuations of giant unilamellar vesicles encapsulating motile bacteria. Owing to bacteria-membrane collisions, we experimentally observe a significant increase in the magnitude of membrane fluctuations at low wave numbers, compared to the wellknown thermal fluctuation spectrum. We interrogate these results by numerically simulating membrane height fluctuations via a modified Langevin equation, which includes bacteria-membrane contact forces. Taking advantage of the length and time scale separation of these contact forces and thermal noise, we further corroborate our results with an approximate theoretical solution to the dynamical membrane equations. Our theory and simulations demonstrate excellent agreement with non-equilibrium fluctuations observed in experiments. Moreover, our theory reveals that the fluctuation-dissipation theorem is not broken by the bacteria; rather, membrane fluctuations can be decomposed into thermal and active components.arXiv:1911.01337v1 [cond-mat.soft]

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“…The scaffold in turn affects the hydrodynamic damping of the membrane reflected in changes of the time dependent correlation function and the associated power spectrum, the so-called power spectral density (PSD) [15,[22][23][24]. Moreover, in the cellular environment, active processes couple with the membrane fluctuations [23][24][25][26][27][28][29][30][31][32][33], resulting in the violation of the fluctuationdissipation theorem in the activated state of the cell [34][35][36].…”

Section: Introductionmentioning

confidence: 99%

Statistical Mechanics of an Elastically Pinned Membrane: Equilibrium Dynamics and Power Spectrum

Janeš

Schmidt

Blackwell

et al. 2019

Biophysical Journal

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In biological settings membranes typically interact locally with other membranes or the extracellular matrix in the exterior, as well as with internal cellular structures such as the cytoskeleton. Characterization of the dynamic properties of such interactions presents a difficult task. Significant progress has been achieved through simulations and experiments, yet analytical progress in modelling pinned membranes has been impeded by the complexity of governing equations. Here we circumvent these difficulties by calculating analytically the time-dependent Green's function of the operator governing the dynamics of an elastically pinned membrane in a hydrodynamic surrounding and subject to external forces. This enables us to calculate the equilibrium power spectral density for an overdamped membrane pinned by an elastic, permanently-attached spring subject to thermal excitations. By considering the effects of the finite experimental resolution on the measured spectra, we show that the elasticity of the pinning can be extracted from the experimentally measured spectrum. Membrane fluctuations can thus be used as a tool to probe mechanical properties of the underlying structures. Such a tool may be particularly relevant in the context of cell mechanics, where the elasticity of the membrane's attachment to the cytoskeleton could be measured.

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Model for Probing Membrane-Cortex Adhesion by Micropipette Aspiration and Fluctuation Spectroscopy

Cited by 46 publications

References 54 publications

Pattern formation by curvature-inducing proteins on spherical membranes

Pattern formation by curvature-inducing proteins on spherical membranes

Active Contact Forces Drive Nonequilibrium Fluctuations in Membrane Vesicles

Statistical Mechanics of an Elastically Pinned Membrane: Equilibrium Dynamics and Power Spectrum

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