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The polymerization of G-actin monomers into filamentous F-actin is a multi-step process. Once the F-actins are formed, they can bundle together in different arrangements to form higher-order networks and regulate cellular functions. Common examples include the formation of lamellipodia and filopodia at the cell's leading edge by actin reorganization in a migrating cell. The microvilli on the brush border epithelial cells are also formed through the F-actin network.

The high-order actin networks with straight F-actins are formed either through their bundled arrangement or by cross-linking them into gel-like networks. The dendritic networks are formed with the help of the branched F-actins. Actin binding proteins like fimbrin, fascin, and alpha-actinin form different types of actin filament bundles. Contrastingly filamin protein help in cross-linking the actin filaments into a gel-like network.

Actin bundling proteins

Actin-bundling proteins can arrange F-actins in either parallel or anti-parallel linear arrays. The bundles can be loose or tight depending on cellular functional requirements and the bundle's accessory protein. Monomeric proteins like fimbrin have two actin-binding domains and tightly bind to parallelly arranged adjacent actin filaments. These bundles can be found in microvilli in the small intestine. Contrastingly α-actinin is a dimeric protein having one actin-binding domain on each monomer. A helical spacer separates these actin-binding domains to form loose bundles with anti-parallelly arranged F-actins.

Actin cross-linking protein

Filamin is an actin cross-linking protein having two long flexible forms with one actin-binding domain on each arm. This allows flexible movement of filamin to form perpendicularly arranged actin filaments into a gel-like network. Some small proteins like transgelin have been reported to form dense meshworks.

Tags
FormationHigher order Actin FilamentsPolymerizationG actin MonomersF actinBundlingNetworksCellular FunctionsLamellipodiaFilopodiaActin ReorganizationMigrating CellMicrovilliBrush Border Epithelial CellsBundled ArrangementGel like NetworksDendritic NetworksBranched F actinsActin Binding ProteinsFimbrinFascinAlpha actininFilamin ProteinActin Bundling ProteinsParallel ArraysAnti parallel Linear ArraysLoose BundlesTight BundlesAccessory Protein

Aus Kapitel 25:

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25.15 : Bildung von Aktinfilamenten höherer Ordnung

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25.1 : Einführung in das Zytoskelett

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25.2 : Anpassungsfähigkeit von Zytoskelettfilamenten

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25.3 : Polarität des Zytoskeletts

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25.4 : Assemblierung von Zytoskelett-Filamenten

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25.5 : Linkerproteine des Zytoskeletts - Plakins

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25.6 : Akzessorische Proteine des Zytoskeletts

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25.7 : Proteine des Zytoskeletts in Bakterien

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25.8 : Intrazelluläre Bewegung von Viren und Bakterien

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25.9 : Untersuchung des Zytoskeletts

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25.10 : Einführung in Actin

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25.11 : Aktin-Polymerisation

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25.12 : Aktin-Treadmilling

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25.13 : Bildung von geraden oder verzweigten Aktinfilamenten

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25.14 : Depolymerisation von Aktinfilamenten

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