The human erythrocyte membrane skeleton may be an ionic gel

Stokke, Bjørn Torger; Mikkelsen, Arne; Elgsaeter, Arnljot

doi:10.1007/bf00260369

Cited by 36 publications

(9 citation statements)

References 33 publications

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“…3d). Gel collapse would enable a small change in the conditions (ion concentration, polymer concentration and number, and polymer elasticity) to drive important filament rearrangements (31).…”

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Actin polymerization induces a shape change in actin-containing vesicles.

Cortese

Schwab

Frieden

et al. 1989

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

112

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We have encapsulated actin rilaments in the presence and absence of various actin-binding proteins into lipid vesicles. These vesicles are approximately the same size as animal cells and can be characterized by the same optical microscopic and mechanical techniques used to study cells. We demonstrate that the initially spherical vesicles can be forced into asymmetric, irregular shapes by polymerization of the actin that they contain. Deformation of the vesicles requires that the actin filaments be on average at least =0.5 ,um long as shown by the effects of gelsolin, an actin rilament-nucleating protein. Filamin, a filament-crosslinking protein, caused the surfaces of the vesicles to have a smoother appearance. Heterogeneous distribution of actin filaments within the vesicles is caused by interfilament interactions and modulated by gelsolin and ifiamin. The vesicles provide a model system to study control ofcell shape and cytoskeletal organization, membranecytoskeleton interactions, and cytomechanics.The shapes and mechanical properties of animal cells are governed mainly by systems of cytoplasmic filaments collectively termed the cytoskeleton (1, 2). Ofthese systems, the actin microfilament system is the principal determinant of cellular viscoelastic properties (B.S. and E.L.E., in preparation) and is most directly involved in driving mechanical processes such as locomotion, cytokinesis, and phagocytosis (2, 3). As cells perform these functions, the organization of the actin cytoskeleton changes, probably under the control of actin-binding proteins that regulate the length and extent of crosslinking of the filaments (3-5). A model system in which cytoskeletal components could be reconstituted inside vesicles comparable in size to cells would be useful for studies of the regulation of cytoskeletal organization and the determination of cellular mechanical properties by the cytoskeleton.We have developed a model system of this kind for the actin filament system. Actin and actin-binding proteins have been encapsulated in lipid vesicles large enough (up to 20 jim in diameter) to be characterized by optical microscopy. The vesicles are large enough to be studied with biophysical techniques that measure, for example, actin diffusion by fluorescence photobleaching recovery (FPR) (6) or mechanical properties (1) ofindividual vesicles. The reconstitution of actin filaments with actin-binding proteins allows study of the effects of the latter on filament organization and distribution and the ability of the actin gel to drive morphological changes. In this work we have investigated the effects of gelsolin, which restricts the length of actin filaments, and of filamin, which crosslinks actin filaments (5). A striking observation is that vesicles are deformed when the actin inside them polymerizes. The extent of the deformation depends on the lengths of the resulting filaments. This observation provides experimental evidence for the speculation that actin filament polymerization can drive lamellar extension during ce...

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Section: Discussionmentioning

confidence: 99%

“…Spontaneous reorganization of filaments could be stabilized by actin-crosslinking proteins such as filamin (30) or a actinin (32). It is likely, however, that additional processes such as changes in gel osmotic pressure and interactions with the membrane are important (19,31,33,34). These could also depend critically on filament length (35).…”

Section: Discussionmentioning

confidence: 99%

Actin polymerization induces a shape change in actin-containing vesicles.

Cortese

Schwab

Frieden

et al. 1989

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

112

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“…A model treating the membrane as a pair of slightly compressible monolayers bound together with non-instantaneous lipid density relaxation has also been proposed [11]. A full sophisticated model for cytoskeleton fortified membranes has also been developed [26] and applied to erythrocyte deformation [27]. This model includes the shear elasticity of the cytoskeleton in combination with the Helfrich Hamiltonian.…”

Section: Methodsmentioning

confidence: 99%

Landscape of finite-temperature equilibrium behaviour of curvature-inducing proteins on a bilayer membrane explored using a linearized elastic free energy model

2008

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Using a recently developed multiscale simulation methodology, we describe the equilibrium behaviour of bilayer membranes under the influence of curvature-inducing proteins using a linearized elastic free energy model. In particular, we describe how the cooperativity associated with a multitude of protein-membrane interactions and protein diffusion on a membrane-mediated energy landscape elicits emergent behaviour in the membrane phase. Based on our model simulations, we predict that, depending on the density of membrane-bound proteins and the degree to which a single protein molecule can induce intrinsic mean curvature in the membrane, a range of membrane phase behaviour can be observed including two different modes of vesicle-bud nucleation and repressed membrane undulations. A state diagram as a function of experimentally tunable parameters to classify the underlying states is proposed.

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“…105 (2) A model for cytoskeleton fortified membranes has been developed 98 and applied to erythrocyte deformation. 99 This model includes shear elasticity of the cytoskeleton in combination with the Helfrich Hamiltonian. (3) The dynamics of the Helfrich membrane in the overdamped limit including hydrodynamic coupling to the surrounding solvent and arbitrary external forces have been introduced.…”

Section: Mechanism and Biophysical Model For Membrane Deformation mentioning

confidence: 99%

Systems biology and physical biology of clathrin-mediated endocytosis

et al. 2011

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In this review, we describe the application of experimental data and modeling of intracellular endocytic trafficking mechanisms with a focus on the process of clathrin-mediated endocytosis. A detailed parts-list for the protein–protein interactions in clathrin-mediated endocytosis has been available for some time. However, recent experimental, theoretical, and computational tools have proved to be critical in establishing a sequence of events, cooperative dynamics, and energetics of the intracellular process. On the experimental front, total internal reflection fluorescence microscopy, photo-activated localization microscopy, and spinning-disk confocal microscopy have focused on assembly and patterning of endocytic proteins at the membrane, while on the theory front, minimal theoretical models for clathrin nucleation, biophysical models for membrane curvature and bending elasticity, as well as methods from computational structural and systems biology, have proved insightful in describing membrane topologies, curvature mechanisms, and energetics.

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The human erythrocyte membrane skeleton may be an ionic gel

Cited by 36 publications

References 33 publications

Actin polymerization induces a shape change in actin-containing vesicles.

Actin polymerization induces a shape change in actin-containing vesicles.

Landscape of finite-temperature equilibrium behaviour of curvature-inducing proteins on a bilayer membrane explored using a linearized elastic free energy model

Systems biology and physical biology of clathrin-mediated endocytosis

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