Related Experiment Video

Updated: Oct 2, 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

Fimbrin is a cytoskeletal protein that crosslinks F-actin in vitro

A Bretscher

    Proceedings of the National Academy of Sciences of the United States of America
    |November 1, 1981
    PubMed

    Insights

    Fimbrin, a cytoskeletal protein, crosslinks actin filaments (F-actin) into rigid bundles. This structural role explains its presence in cellular projections like microvilli.

    Area of Science:

    • Cell Biology
    • Biochemistry
    • Biophysics

    Background:

    • Fimbrin is a cytoskeletal protein found in various cellular structures, including microvilli and microspikes.
    • It is associated with actin microfilaments, which are crucial for cell shape and movement.

    Purpose of the Study:

    • To investigate the biochemical properties of fimbrin and its interaction with F-actin.
    • To elucidate the structural role of fimbrin in organizing actin filaments.

    Main Methods:

    • Purification of fimbrin from intestinal epithelial cell brush borders.
    • Sedimentation assays to study fimbrin-actin binding under varying salt concentrations (KCl, Mg2+, Ca2+).
    • Electron microscopy to visualize fimbrin-crosslinked F-actin structures.

    Main Results:

    • Purified fimbrin is a monomeric protein of 68,000 molecular weight.
    • Fimbrin binds to F-actin in a salt-dependent manner, with optimal binding at 30 mM KCl and inhibition at higher concentrations.
    • Fimbrin stabilizes F-actin interactions, forming relatively straight bundles, with bundle length dependent on the fimbrin-to-actin ratio.

    Conclusions:

    • Fimbrin acts as an actin-crosslinking protein, conferring rigidity to the resulting bundles.
    • This crosslinking function supports fimbrin's role in maintaining the structure of cellular projections like microvilli and stereocilia.

    More Related Videos

    A Time-Efficient Fluorescence Spectroscopy-Based Assay for Evaluating Actin Polymerization Status in Rodent and Human Brain Tissues06:54

    A Time-Efficient Fluorescence Spectroscopy-Based Assay for Evaluating Actin Polymerization Status in Rodent and Human Brain Tissues

    Published on: June 3, 2021

    Using Microfluidics and Fluorescence Microscopy to Study the Assembly Dynamics of Single Actin Filaments and Bundles08:02

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

    Published on: May 5, 2022

    Related Concept Videos

    Studying the Cytoskeleton01:17

    Studying the Cytoskeleton

    The cytoskeletal architecture can be studied using different microscopic and biochemical techniques. Electron microscopy was instrumental in discovering the cytoskeletal architecture around the 1960s, which allowed obtaining structural information at a high-resolution level. However, the sample preparation procedure often limits this ability in biological samples. Several protocols have been developed over the years to optimize sample preparation. In one of the protocols known as rotary...
    Introduction to Actin01:26

    Introduction to Actin

    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 different species.
    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...
    Fibronectins Connect Cells with ECM01:25

    Fibronectins Connect Cells with ECM

    Fibronectin is an adhesive glycoprotein present in the extracellular matrix of embryogenic and adult tissue. These molecules primarily aid in regulating cell motility and attachment. A fibronectin molecule is composed of two identical polypeptide chains attached to each other by a pair of disulfide bonds at the C-terminal.
    Both proteoglycans and collagen are attached to fibronectin proteins, which, in turn, are attached to integrin proteins. These integrin proteins interact with transmembrane...