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Related Concept Videos

Actin Filament Depolymerization01:19

Actin Filament Depolymerization

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Actin filaments (F-actin) are composed of actin subunits. The dissociation of actin monomers can occur from either end of F-actin. The rate of dissociation is faster from the minus-end or the pointed end, where the actin subunits exist with a bound ADP, together known as ADP-actin. The depolymerization of F-actin is aided by proteins, including the actin-depolymerizing factor (ADF) and cofilin family of proteins, gelsolin, and glia maturation factor (GMF).
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Actin Treadmilling01:18

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Actin filaments undergo polymerization and depolymerization from either end. The polymerization and depolymerization rates depend on the cytosolic concentration of free G-actins. The polymerization rate is generally higher at the plus or barbed end, while the depolymerization rate is higher at the minus or pointed end. At a steady state, critical concentration describes the concentration of free G-actin monomers at which the polymerization rate at the plus end is equal to that of the...
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Introduction to Actin01:26

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Actin is a highly conserved cytoskeletal protein found abundantly in eukaryotic cells. It constitutes 10% weight of the total cellular protein in muscle cells, while in non-muscle cells, it is lower and makes up around 1–5 percent of the total cell protein. Actin found in the unicellular amoebae and complex multicellular animals is around 80% similar, demonstrating their conservation over a billion years of evolution.  Actin coding genes are conserved within species and across...
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Actin Polymerization01:42

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Actin polymerization occurs through the head-to-tail association of binding sites on monomeric actin or G-actin to form filamentous or F-actin. The polymerization can be divided into three phases ̶  nucleation, elongation, and steady-state phase.
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Formation of Higher-order Actin Filaments01:11

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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.
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The Role of Actin and Myosin in Non-muscle Cells01:10

The Role of Actin and Myosin in Non-muscle Cells

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Actin and myosin or actomyosin filaments also play a significant role in cells other than those involved in muscle contraction (which occurs within the sarcomere of muscle cells). The mechanism of non-muscle cell contractile bundles was first observed in Dictyostelium and Acanthamoeba. In non-muscle cells, two bundles are commonly found: stress fibers and actomyosin adherence belts. These contractile bundles are smaller and less organized than the ones found in muscle cells. They  are held...
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An actin-depolymerizing protein (depactin) from starfish oocytes: properties and interaction with actin.

I Mabuchi

    The Journal of Cell Biology
    |November 1, 1983
    PubMed
    Summary

    Starfish depactin, an actin-depolymerizing protein, fragments newly formed actin filaments, increasing polymerization rates. It interacts with actin at a 1:1 molar ratio, affecting a significant portion of oocyte actin.

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    Area of Science:

    • Biochemistry
    • Cell Biology
    • Molecular Biology

    Background:

    • Actin dynamics are crucial for cellular processes.
    • Actin-depolymerizing proteins regulate actin polymerization.
    • Starfish oocytes provide a model for studying cytoskeletal proteins.

    Purpose of the Study:

    • To characterize the physico-chemical properties of starfish depactin.
    • To investigate the interaction between depactin and actin.
    • To elucidate the mechanism by which depactin affects actin polymerization.

    Main Methods:

    • Spectrophotometry to measure actin polymerization rates.
    • Viscometry and flow birefringence to determine critical actin concentration.
    • Cross-linking experiments to estimate molar ratios.
    • Affinity chromatography (DNase I-Sepharose) to study protein interactions.

    Main Results:

    • Depactin exists as a monomer with a molecular weight of approximately 20,000 Da.
    • Depactin reduces the extent but accelerates the rate of actin polymerization by fragmenting filaments.
    • The apparent critical concentration of actin increases with depactin presence.
    • Depactin interacts with actin at a 1:1 molar ratio with an association constant of 2-3 X 10^6 M^-1.
    • Depactin constitutes 1% of the high-speed supernatant in oocyte extracts, affecting 63% of the actin.

    Conclusions:

    • Depactin is a potent actin-binding protein that modulates actin dynamics.
    • Its filament-fragmenting activity suggests a significant role in regulating the actin cytoskeleton in starfish oocytes.
    • The interaction is specific and occurs at a defined stoichiometry.