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Related Concept Videos

Actin Treadmilling01:18

Actin Treadmilling

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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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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.
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...
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Generation of Straight or Branched Actin Filaments01:14

Generation of Straight or Branched Actin Filaments

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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...
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Actin Filament Depolymerization01:19

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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).
In F-actin, the ADF/cofilin proteins...
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Introduction to Actin01:26

Introduction to Actin

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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 Polymerization and Cell Motility01:13

Actin Polymerization and Cell Motility

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Actin is a family of globular proteins that are highly abundant in eukaryotic cells. It makes up approximately 1-5% of total cell protein concentration. Actin monomers polymerize to form a complex network of polarized filaments, the actin cytoskeleton, that plays a crucial role in many cellular processes, including cell motility, division, endocytosis, and metastasis of cancer cells.
Actin cytoskeleton dynamics can produce pushing, pulling, and resistance forces that help the cell to migrate....
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Using Microfluidics and Fluorescence Microscopy to Study the Assembly Dynamics of Single Actin Filaments and Bundles
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ATP-dependent actin barbed-end fluctuations at steady state.

Madhura Duttagupta1, Andrew T Riley1, William M Brieher1

  • 1Department of Cell and Developmental Biology, University of Illinois Urbana Champaign, Urbana, IL 61801.

Proceedings of the National Academy of Sciences of the United States of America
|November 20, 2025
PubMed
Summary
This summary is machine-generated.

Actin filament dynamics in vitro show frequent, small barbed-end fluctuations and rarer large ones, impacting length diffusivity. These fluctuations, dependent on ATP hydrolysis, offer new insights into actin network turnover.

Keywords:
ATPactindynamic instabilitydynamicstreadmilling

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Area of Science:

  • Biochemistry
  • Cell Biology
  • Biophysics

Background:

  • Actin networks are crucial for cellular processes and exhibit constant turnover.
  • The prevailing model for actin dynamics is treadmilling, predicting steady filament length.
  • Previous studies reported higher-than-expected length fluctuations (diffusivity) in actin filaments, with unclear origins.

Purpose of the Study:

  • To investigate the origin of high length diffusivity in pure actin filaments in vitro.
  • To characterize the nature and kinetics of barbed-end fluctuations in actin filaments.

Main Methods:

  • Imaging single actin filaments tethered to glass via α-actinin.
  • Observing and quantifying barbed-end fluctuations in real-time.
  • Analyzing the dependence of fluctuations on ATP hydrolysis, inorganic phosphate release, and capping agents.

Main Results:

  • Observed frequent, low-amplitude (±2-6 subunits) and rare, high-amplitude (±50-150 subunits) barbed-end fluctuations.
  • Demonstrated that fluctuations depend on ATP hydrolysis and Pi release, and are inhibited by phalloidin and capping agents.
  • Estimated that fluctuations consume one-third of ATP at steady state, contributing to length diffusivity exceeding pure treadmilling predictions but lower than previously reported.

Conclusions:

  • Actin filament dynamics exhibit a dampened form of dynamic instability, characterized by superimposed small and large barbed-end fluctuations.
  • These fluctuations explain observed length diffusivity, suggesting prior measurements included other variability sources.
  • Findings provide direct experimental support for kinetic models of actin dynamics.