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HARASZTI TAMÁS, SCHULZ SIMON, UHRIG KAI, KURRE RAINER, ROOS WOUTER, SCHMITZ CHRISTIANHJ, CURTIS JENNIFERE, MAIER TIMO, CLEMEN ANABELEM, SPATZ JOACHIMP. BIOMIMETIC MODELS OF THE ACTIN CORTEX. ACTA ACUST UNITED AC 2011. [DOI: 10.1142/s1793048009001009] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The cytoskeleton is an actively regulated complex network in the cell. One of the most researched components is actin. In our work we developed and tested two microfluidic systems both being applicable to construct quasi 2-dimensional biomimetic actin networks. The first system uses polydimethylsiloxane micropillars, the other polystyrene microparticles held by holographic optical tweezers as anchoring points. Our devices provide actin networks with mesh sizes from a few micrometers up to the order of 10 micrometers. Qualitative analysis shows similar network formation in both systems. Crosslinking was tested using filamin, α-actinin, Ca and Mg ions. The crosslinking process is characterized by a zipping like event, which is limited only by the high stretching modulus of the actin filaments.
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Affiliation(s)
- TAMÁS HARASZTI
- Max-Planck Institute for Metals Research, Heisenbergstrasse 3, Stuttgart, 70569, Germany
- Biophysical Chemistry Group, Institute of Physical Chemistry, University of Heidelberg, Im Neuenhelmer Feld 253, Heidelberg, 69120, Germany
| | - SIMON SCHULZ
- Max-Planck Institute for Metals Research, Heisenbergstrasse 3, Stuttgart, 70569, Germany
- Biophysical Chemistry Group, Institute of Physical Chemistry, University of Heidelberg, Im Neuenhelmer Feld 253, Heidelberg, 69120, Germany
| | - KAI UHRIG
- Max-Planck Institute for Metals Research, Heisenbergstrasse 3, Stuttgart, 70569, Germany
- Biophysical Chemistry Group, Institute of Physical Chemistry, University of Heidelberg, Im Neuenhelmer Feld 253, Heidelberg, 69120, Germany
| | - RAINER KURRE
- Max-Planck Institute for Metals Research, Heisenbergstrasse 3, Stuttgart, 70569, Germany
- Biophysical Chemistry Group, Institute of Physical Chemistry, University of Heidelberg, Im Neuenhelmer Feld 253, Heidelberg, 69120, Germany
| | - WOUTER ROOS
- Max-Planck Institute for Metals Research, Heisenbergstrasse 3, Stuttgart, 70569, Germany
- Biophysical Chemistry Group, Institute of Physical Chemistry, University of Heidelberg, Im Neuenhelmer Feld 253, Heidelberg, 69120, Germany
| | - CHRISTIAN H. J. SCHMITZ
- Max-Planck Institute for Metals Research, Heisenbergstrasse 3, Stuttgart, 70569, Germany
- Biophysical Chemistry Group, Institute of Physical Chemistry, University of Heidelberg, Im Neuenhelmer Feld 253, Heidelberg, 69120, Germany
| | - JENNIFER E. CURTIS
- Max-Planck Institute for Metals Research, Heisenbergstrasse 3, Stuttgart, 70569, Germany
- Biophysical Chemistry Group, Institute of Physical Chemistry, University of Heidelberg, Im Neuenhelmer Feld 253, Heidelberg, 69120, Germany
| | - TIMO MAIER
- Max-Planck Institute for Metals Research, Heisenbergstrasse 3, Stuttgart, 70569, Germany
- Biophysical Chemistry Group, Institute of Physical Chemistry, University of Heidelberg, Im Neuenhelmer Feld 253, Heidelberg, 69120, Germany
| | - ANABEL E.-M. CLEMEN
- Max-Planck Institute for Metals Research, Heisenbergstrasse 3, Stuttgart, 70569, Germany
- Biophysical Chemistry Group, Institute of Physical Chemistry, University of Heidelberg, Im Neuenhelmer Feld 253, Heidelberg, 69120, Germany
| | - JOACHIM P. SPATZ
- Max-Planck Institute for Metals Research, Heisenbergstrasse 3, Stuttgart, 70569, Germany
- Biophysical Chemistry Group, Institute of Physical Chemistry, University of Heidelberg, Im Neuenhelmer Feld 253, Heidelberg, 69120, Germany
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Sutherland-Smith AJ. Filamin structure, function and mechanics: are altered filamin-mediated force responses associated with human disease? Biophys Rev 2011; 3:15-23. [PMID: 28510233 DOI: 10.1007/s12551-011-0042-y] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2010] [Accepted: 01/03/2011] [Indexed: 01/08/2023] Open
Abstract
The cytoskeleton framework is essential not only for cell structure and stability but also for dynamic processes such as cell migration, division and differentiation. The F-actin cytoskeleton is mechanically stabilised and regulated by various actin-binding proteins, one family of which are the filamins that cross-link F-actin into networks that greatly alter the elastic properties of the cytoskeleton. Filamins also interact with cell membrane-associated extracellular matrix receptors and intracellular signalling proteins providing a potential mechanism for cells to sense their external environment by linking these signalling systems. The stiffness of the external matrix to which cells are attached is an important environmental variable for cellular behaviour. In order for a cell to probe matrix stiffness, a mechanosensing mechanism functioning via alteration of protein structure and/or binding events in response to external tension is required. Current structural, mechanical, biochemical and human disease-associated evidence suggests filamins are good candidates for a role in mechanosensing.
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Affiliation(s)
- Andrew J Sutherland-Smith
- Institute of Molecular BioSciences, Massey University, Private Bag 11222, Palmerston North, 4442, New Zealand.
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Schüler H, Peti W. Structure-function analysis of the filamentous actin binding domain of the neuronal scaffolding protein spinophilin. FEBS J 2007; 275:59-68. [PMID: 18028445 DOI: 10.1111/j.1742-4658.2007.06171.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Spinophilin, a neuronal scaffolding protein, is essential for synaptic transmission, and functions to target protein phosphatase-1 to distinct subcellular locations in dendritic spines. It is vital for the regulation of dendritic spine formation and motility, and functions by regulating glutamatergic receptors and binding to filamentous actin. To investigate its role in regulating actin cytoskeletal structure, we initiated structural studies of the actin binding domain of spinophilin. We demonstrate that the spinophilin actin binding domain is intrinsically unstructured, and that, with increasing C-terminal length, the domain shows augmented secondary structure content. Further characterization confirmed the previously known crosslinking activity and uncovered a novel filamentous actin pointed-end capping activity. Both of these functions seem to be fully contained within residues 1-154 of spinophilin.
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Affiliation(s)
- Herwig Schüler
- Max Delbrück Center for Molecular Medicine, Berlin-Buch, Germany.
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Esue O, Tseng Y, Wirtz D. Mechanical shear can accelerate the gelation of actin filament networks. PHYSICAL REVIEW LETTERS 2005; 95:048301. [PMID: 16090845 DOI: 10.1103/physrevlett.95.048301] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/01/2004] [Indexed: 05/03/2023]
Abstract
Rearrangements of the filamentous actin cytoskeleton at the leading edge of motile cells occur under large mechanical stresses. Contrary to conventional wisdom, we show that mechanical deformations applied during gelation can accelerate the rate of gelation and produce F-actin networks that are stiffer and mechanically more resilient than those polymerized under low or high shear deformations. Above a threshold shear strain amplitude, F-actin networks collapse and become soft and liquidlike. This effect of shear-induced strengthening of polymerizing networks depends on the state of hydrolysis of the actin-bound adenosine triphosphate.
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Affiliation(s)
- Osigwe Esue
- Department of Chemical and Biomolecular Engineering, The Johns Hopkins University, Baltimore, Maryland 21218, USA
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Tseng Y, Wirtz D. Mechanics and multiple-particle tracking microheterogeneity of alpha-actinin-cross-linked actin filament networks. Biophys J 2001; 81:1643-56. [PMID: 11509377 PMCID: PMC1301642 DOI: 10.1016/s0006-3495(01)75818-3] [Citation(s) in RCA: 129] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
Abstract
Cell morphology is controlled by the actin cytoskeleton organization and mechanical properties, which are regulated by the available contents in actin and actin regulatory proteins. Using rheometry and the recently developed multiple-particle tracking method, we compare the mechanical properties and microheterogeneity of actin filament networks containing the F-actin cross-linking protein alpha-actinin. The elasticity of F-actin/alpha-actinin networks increases with actin concentration more rapidly for a fixed molar ratio of actin to alpha-actinin than in the absence of alpha-actinin, for networks of fixed alpha-actinin concentration and of fixed actin concentration, but more slowly than theoretically predicted for a homogeneous cross-linked semiflexible polymer network. These rheological measurements are complemented by multiple-particle tracking of fluorescent microspheres imbedded in the networks. The distribution of the mean squared displacements of these microspheres becomes progressively more asymmetric and wider for increasing concentration in alpha-actinin and, to a lesser extent, for increasing actin concentration, which suggests that F-actin networks become progressively heterogeneous for increasing protein content. This may explain the slower-than-predicted rise in elasticity of F-actin/alpha-actinin networks. Together these in vitro results suggest that actin and alpha-actinin provides the cell with an unsuspected range of regulatory pathways to modulate its cytoskeleton's micromechanics and local organization in vivo.
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Affiliation(s)
- Y Tseng
- Department of Chemical Engineering, The Johns Hopkins University, Baltimore, Maryland 21218, USA
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Goldmann WH, Tempel M, Sprenger I, Isenberg G, Ezzell RM. Viscoelasticity of actin-gelsolin networks in the presence of filamin. EUROPEAN JOURNAL OF BIOCHEMISTRY 1997; 246:373-9. [PMID: 9208927 DOI: 10.1111/j.1432-1033.1997.00373.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Cross-linking of actin filaments by filamin by means of frequency-dependent rheology yields an increase in the filament's elasticity and stiffness. Higher cross-linker (filamin) ratios are required for mean actin-filament lengths of 5-6 microm than for random-length distribution of actin filaments. The loss modulus (i.e. the viscous portion) in the region of the internal-chain dynamics [G"(omega) approximately omega(alpha)] is influenced by the cross-linking of filaments, and with an increasing molar ratio of filamin/actin a reduction of alpha is observed. Rheological measurements reveal that actin networks are already formed at the polymerizing stage at a molar ratio of filamin/actin of less than 1:100, and electron micrographs show phase separation of actin/filament networks of low density and of actin/filament bundles.
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Affiliation(s)
- W H Goldmann
- Surgery Research Laboratories, Massachusetts General Hospital, Harvard Medical School, Charlestown 02129, USA.
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Furukawa R, Fechheimer M. The structure, function, and assembly of actin filament bundles. INTERNATIONAL REVIEW OF CYTOLOGY 1997; 175:29-90. [PMID: 9203356 DOI: 10.1016/s0074-7696(08)62125-7] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The cellular organization, function, and molecular composition of selected biological systems with prominent actin filament bundles are reviewed. An overall picture of the great variety of functions served by actin bundles emerges from this overview. A unifying theme is that the actin cross-linking proteins are conserved throughout the eukaryotic kingdom and yet assembled in a variety of combinations to produce actin bundles of differing functions. Mechanisms of actin bundle formation in vitro are considered illustrating the variety of physical and chemical driving forces in this exceedingly complex process. Our limited knowledge regarding the formation of actin filament bundles in vivo is contrasted with the elegant biophysical studies performed in vitro but nonetheless reveals that interactions with membranes, nucleation sites, and other organizational components must contribute to formation of actin bundles in vivo.
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Affiliation(s)
- R Furukawa
- Department of Cellular Biology, University of Georgia, Athens 30602, USA
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Wachsstock DH, Schwarz WH, Pollard TD. Cross-linker dynamics determine the mechanical properties of actin gels. Biophys J 1994; 66:801-9. [PMID: 8011912 PMCID: PMC1275778 DOI: 10.1016/s0006-3495(94)80856-2] [Citation(s) in RCA: 173] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
To evaluate the contributions of cross-linker dynamics and polymer deformation to the frequency-dependent stiffness of actin filament gels, we compared the rheological properties of actin gels with three types of cross-linkers: a weak one, Acanthamoeba alpha-actinin (dissociation rate constant 5.2 s-1, association rate constant 1.1 x 10(6) M-1 s-1); a strong one, chicken smooth muscle alpha-actinin (dissociation rate constant 0.66 s-1, association rate constant 1.20 x 10(6) M-1 s-1); and an extremely strong one, biotin/avidin (dissociation rate constant approximately zero). The biotin/avidin cross-linked gel, whose behavior is determined by polymer bending alone, behaves like a solid and shows no frequency dependence. The amoeba alpha-actinin cross-linked gel behaves like a viscoelastic fluid, and the frequency dependence of the stiffness can be explained by a mathematical model for dynamically cross-linked gels. The stiffness of the chicken alpha-actinin cross-linked gel is independent of frequency, and has viscoelastic properties intermediate between the two. The two alpha-actinins have similar association rate constants for binding to actin filaments, consistent with a diffusion-limited reaction. Rigid cross-links make the gel stiff, but make it elastic without the ability to deform permanently. Dynamically cross-linked actin filaments should allow the cell to react passively to various outside forces without any sort of signaling. Slower, signal-mediated pathways, such as severing filaments or changing the affinity of cross-linkers, could alter the nature of these passive reactions.
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Affiliation(s)
- D H Wachsstock
- Department of Cell Biology and Anatomy, Johns Hopkins University, Baltimore, Maryland 21205
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Wachsstock DH, Schwartz WH, Pollard TD. Affinity of alpha-actinin for actin determines the structure and mechanical properties of actin filament gels. Biophys J 1993; 65:205-14. [PMID: 8369430 PMCID: PMC1225716 DOI: 10.1016/s0006-3495(93)81059-2] [Citation(s) in RCA: 178] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Proteins that cross-link actin filaments can either form bundles of parallel filaments or isotropic networks of individual filaments. We have found that mixtures of actin filaments with alpha-actinin purified from either Acanthamoeba castellanii or chicken smooth muscle can form bundles or isotropic networks depending on their concentration. Low concentrations of alpha-actinin and actin filaments form networks indistinguishable in electron micrographs from gels of actin alone. Higher concentrations of alpha-actinin and actin filaments form bundles. The threshold for bundling depends on the affinity of the alpha-actinin for actin. The complex of Acanthamoeba alpha-actinin with actin filaments has a Kd of 4.7 microM and a bundling threshold of 0.1 microM; chicken smooth muscle has a Kd of 0.6 microM and a bundling threshold of 1 microM. The physical properties of isotropic networks of cross-linked actin filaments are very different from a gel of bundles: the network behaves like a solid because each actin filament is part of a single structure that encompasses all the filaments. Bundles of filaments behave more like a very viscous fluid because each bundle, while very long and stiff, can slip past other bundles. We have developed a computer model that predicts the bundling threshold based on four variables: the length of the actin filaments, the affinity of the alpha-actinin for actin, and the concentrations of actin and alpha-actinin.
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Affiliation(s)
- D H Wachsstock
- Department of Cell Biology and Anatomy, Johns Hopkins University, Baltimore, Maryland 21205
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Kubler MD, Watt FM. Changes in the distribution of actin-associated proteins during epidermal wound healing. J Invest Dermatol 1993; 100:785-9. [PMID: 8388426 DOI: 10.1111/1523-1747.ep12476492] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
We have examined the distribution of actin filaments and a number of actin-associated proteins during human epidermal wound healing, using a suction blister model in which the epidermis is detached from the dermis, leaving the basement membrane intact. Filamentous actin was found in all the living epidermal layers before, during and after wound healing. alpha-actinin was also present in all the living layers of normal epidermis, but diffuse cytoplasmic staining was observed at the leading edge of migrating epidermis. Vinculin and talin were concentrated at the basement membrane prior to wounding, but were absent from the leading edge during wound healing. In normal epidermis, filamin and gelsolin showed a complementary distribution, with filamin most abundant in the basal layer and gelsolin most abundant suprabasally. The abundance of both proteins was reduced at the leading edge of migrating epidermis. All of the changes were transient, as the expression patterns returned to normal by 1 week after wounding, when the epidermis had reformed. The relevance of these changes to the process of keratinocyte migration is discussed.
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Affiliation(s)
- M D Kubler
- Keratinocyte Laboratory, Imperial Cancer Research Fund, London, England
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