What are actin filaments? Actin filaments (F-actin) are linear polymers of globular actin (G-actin) subunits and occur as microfilaments in the cytoskeleton and as thin filaments, which are part of the contractile apparatus, in muscle and nonmuscle cells (see contractile bundles). They commonly underlie [...]

What are the functions of actin filaments? Several biological processes related to cell shape and movement depend on actin filaments (reviewed in [1]). Some keys functions are: To form the dynamic cytoskeleton, which gives structural support to cells and links the interior of the [...]

How are actin filaments distributed in cells and tissues? Actin filaments are widely distributed throughout cells, forming a range of cytoskeletal structures and contributing to an even broader range of processes. Some of the functions are widely observed across many cell types while in [...]

How do actin filaments act as a force-sensing conduit for both internal and external forces? Internal forces The orientation of individual actin filaments in the cytoskeleton is a force-driven evolutionary process [1] that contributes to the elastic behavior of the network and influences whether [...]

How do actin filaments depolymerize? Introduction to Actin Filament Depolymerization Whole cell motility and mechanosensing rely on the continual restructuring of the cytoskeleton, particularly within lamellipodia and filopodia; two dynamic structures that contribute to cell motility. Actin filament depolymerization ensures the turnover of actin [...]

What is actin nucleation? The first step in actin polymerization is known as ‘nucleation’. This step sees the formation of an actin nucleus, which is essentially a complex of three actin monomers, from which an actin filament may elongate. Although non-muscle cells have a [...]

How does Arp2/3-mediate the nucleation of branched filaments? The Arp2/3 complex is composed of 7 evolutionarily conserved subunits (Arp2, Arp3, ARPC1-C5) that are structurally similar to the barbed end of actin [1]. The complex is inherently inactive, however once activated it facilitates the nucleation [...]

How do actin filaments grow? Actin Filaments (F-actin) grow from the polymerization of G-actin monomers Actin is a highly abundant (10-100 micromolar on average),~42 kDa structural protein found in all eukaryotic cells (except for nematode sperm). With more than 95% conservation in the primary [...]

What factors influence actin filament length and treadmilling? Several factors influence actin filament length and treadmilling. ATP binding on G-actin and free ATP-G-actin concentration ATP-binding on actin subunits modulates the dynamics of filament assembly, with ATP-binding generally favoring intersubunit interactions and thereby filament assembly [...]

What factors regulate actin filament polymerization? Nucleation Promoting Factors (NPFs) (e.g. WASP, Scar/WAVE) modulate actin filament nucleation by bringing together actin monomers and pre-existing actin filaments, for example, during filopodial initiation where they recruit the Arp2/3 complex. NPFs compete with profilin for binding to [...]

Actin Crosslinking Crosslinking of actin filaments is a critical step in cell motility and is a fundamental process in filopodia protrusion and lamellipodia formation. Smaller cross-linking proteins that are more globular (e.g. fascin) or have more than one actin binding site (e.g. fimbrin, [...]

What is the role of cortactin in actin polymerization? Cortactin is a class II nucleation promoting factor (NPF) that binds to actin filaments and influences their stability. Cortactin specifically stabilizes Arp2/3-mediated branch points along actin filaments through its repetitive actin binding sites [1] (reviewed [...]