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Related Concept Videos

Assembly of Cytoskeletal Filaments01:18

Assembly of Cytoskeletal Filaments

Cytoskeletal filaments are polymeric forms of smaller protein subunits. However, individual cytoskeletal filaments may easily disassemble or associate with other similar filaments to form rigid structures. Microfilaments, made of actin monomers, rely on actin-binding proteins to form bundles and create networks of individual actin filaments. Microtubules rely on microtubule-associated proteins (MAPs) to form sturdy cylindrical structures. However, the proteins involved in forming complex...
Actin Polymerization01:42

Actin Polymerization

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.
The nucleation phase involves forming a stable nucleus consisting of three actin monomers to form a new actin filament. Actin-binding proteins such as formins and Arp2/3 complex help filament growth post-nucleation. The Formins form straight actin...
Generation of Straight or Branched Actin Filaments01:14

Generation of Straight or Branched Actin Filaments

The straight or branched structure formation of actin filaments is controlled by nucleating proteins such as the formins and Arp2/3 complex. Formin-mediated assembly results in straight filaments, whereas Arp2/3 protein complex-mediated assembly results in branched actin filaments.
Arp2/3 Complex
Arp2/3 complex is a seven-subunit complex consisting of two proteins similar to actin- Arp2 and Arp3, and five other subunits that help keep Arp2 and Arp3 inactive. When required, the complex is...
Actin Filament Depolymerization01:19

Actin Filament Depolymerization

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).
In F-actin, the ADF/cofilin proteins...
Formation of Higher-order Actin Filaments01:11

Formation of Higher-order Actin Filaments

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...
Disassembly of Intermediate Filaments01:35

Disassembly of Intermediate Filaments

Intermediate filaments (IFs) do not undergo spontaneous disassembly. Enzymes, kinases, and phosphatases add and remove phosphates from specific sites to regulate their disassembly. The IF concentration in the cytoplasm also regulates the disassembly. If the concentration crosses a threshold, it activates the protein kinases in the vicinity, allowing the phosphorylation of IFs.
Keratin proteins, found at the cell periphery near cell junctions, undergo a cycle of assembly and disassembly. In Type...

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Related Experiment Video

Updated: Jun 14, 2026

In Vitro Polymerization of F-actin on Early Endosomes
12:15

In Vitro Polymerization of F-actin on Early Endosomes

Published on: August 28, 2017

Depolymerization of F-actin by deoxyribonuclease I.

S E Hitchcock, L Carisson, U Lindberg

    Cell
    |April 1, 1976
    PubMed
    Summary

    Deoxyribonuclease I depolymerizes muscle actin filaments, forming a stable complex. Heavy meromyosin, in the absence of ATP, blocks this interaction, but ATP addition releases it, allowing actin depolymerization.

    Area of Science:

    • Biochemistry
    • Molecular Biology
    • Muscle Physiology

    Background:

    • Filamentous actin forms the backbone of muscle structure and function.
    • Deoxyribonuclease I (DNAase I) is an enzyme known to interact with actin.
    • Muscle regulatory proteins like tropomyosin and troponin modulate actin dynamics.

    Purpose of the Study:

    • To investigate the interaction between deoxyribonuclease I and filamentous muscle actin.
    • To elucidate the role of regulatory proteins and heavy meromyosin in modulating this interaction.
    • To understand the mechanism of actin depolymerization by DNAase I.

    Main Methods:

    • Biochemical assays to study protein-protein interactions.
    • Enzyme kinetics to measure depolymerization rates.

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    Using Microfluidics and Fluorescence Microscopy to Study the Assembly Dynamics of Single Actin Filaments and Bundles
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    Using Microfluidics and Fluorescence Microscopy to Study the Assembly Dynamics of Single Actin Filaments and Bundles

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    Reconstitution of Membrane-Tethered Minimal Actin Cortices on Supported Lipid Bilayers
    11:55

    Reconstitution of Membrane-Tethered Minimal Actin Cortices on Supported Lipid Bilayers

    Published on: July 12, 2022

    Related Experiment Videos

    Last Updated: Jun 14, 2026

    In Vitro Polymerization of F-actin on Early Endosomes
    12:15

    In Vitro Polymerization of F-actin on Early Endosomes

    Published on: August 28, 2017

    Using Microfluidics and Fluorescence Microscopy to Study the Assembly Dynamics of Single Actin Filaments and Bundles
    08:02

    Using Microfluidics and Fluorescence Microscopy to Study the Assembly Dynamics of Single Actin Filaments and Bundles

    Published on: May 5, 2022

    Reconstitution of Membrane-Tethered Minimal Actin Cortices on Supported Lipid Bilayers
    11:55

    Reconstitution of Membrane-Tethered Minimal Actin Cortices on Supported Lipid Bilayers

    Published on: July 12, 2022

  • Analysis of actin filament stability under various conditions.

    • Main Results:

    • Deoxyribonuclease I depolymerizes filamentous actin into a stable 1:1 DNAase I:actin complex.
    • Tropomyosin and troponin binding to actin slows, but does not prevent, DNAase I-mediated depolymerization.
    • Heavy meromyosin binding to actin filaments in the absence of ATP completely inhibits DNAase I activity.
    • ATP-induced release of heavy meromyosin restores DNAase I activity and allows actin depolymerization.

    Conclusions:

    • The interaction between DNAase I and actin is regulated by ATP-dependent binding of heavy meromyosin.
    • Muscle regulatory proteins influence, but do not abolish, DNAase I's effect on actin.
    • This study clarifies the molecular mechanisms governing actin filament stability and depolymerization.