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Related Concept Videos

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.
Actin Polymerization and Cell Motility01:13

Actin Polymerization and Cell Motility

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.
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...
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...
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...
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...

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Related Experiment Video

Updated: Jun 14, 2026

Aip1p Dynamics Are Altered by the R256H Mutation in Actin
08:57

Aip1p Dynamics Are Altered by the R256H Mutation in Actin

Published on: July 30, 2014

Ion-dependent polymerization differences between mammalian beta- and gamma-nonmuscle actin isoforms.

Sarah E Bergeron1, Mei Zhu, Suzanne M Thiem

  • 1Department of Biochemistry, Roy A and Lucille A Carver College of Medicine, University of Iowa, Iowa City, Iowa 52242, USA.

The Journal of Biological Chemistry
|March 24, 2010
PubMed
Summary

Beta- and gamma-nonmuscle actins, differing by only four amino acids, exhibit distinct polymerization dynamics and filament stability, particularly in the presence of calcium ions. These biochemical differences suggest specialized cellular roles for these actin isoforms.

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A Time-Efficient Fluorescence Spectroscopy-Based Assay for Evaluating Actin Polymerization Status in Rodent and Human Brain Tissues
06:54

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

Published on: June 3, 2021

Measuring Protein Binding to F-actin by Co-sedimentation
06:17

Measuring Protein Binding to F-actin by Co-sedimentation

Published on: May 18, 2017

Related Experiment Videos

Last Updated: Jun 14, 2026

Aip1p Dynamics Are Altered by the R256H Mutation in Actin
08:57

Aip1p Dynamics Are Altered by the R256H Mutation in Actin

Published on: July 30, 2014

A Time-Efficient Fluorescence Spectroscopy-Based Assay for Evaluating Actin Polymerization Status in Rodent and Human Brain Tissues
06:54

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

Published on: June 3, 2021

Measuring Protein Binding to F-actin by Co-sedimentation
06:17

Measuring Protein Binding to F-actin by Co-sedimentation

Published on: May 18, 2017

Area of Science:

  • Biochemistry
  • Cell Biology
  • Molecular Biology

Background:

  • Beta- and gamma-nonmuscle actins are highly conserved isoforms differing by four amino acids near the N-terminus.
  • Despite structural similarities, their differential cellular localization suggests distinct functional roles.
  • These roles may stem from subtle differences in their biochemical properties.

Purpose of the Study:

  • To investigate the biochemical differences between beta- and gamma-actin, focusing on polymerization kinetics and filament stability.
  • To test the hypothesis that amino acid variations lead to distinct functional properties.
  • To understand the impact of calcium on actin isoform behavior.

Main Methods:

  • Established a baculovirus-driven expression system for producing purified beta- and gamma-actin isoforms.
  • Utilized biochemical assays to measure monomeric nucleotide exchange rates, nucleation and elongation phases, and depolymerization rates.
  • Performed mixing experiments and analyzed phosphate release during polymerization and treadmilling under calcium and magnesium conditions.

Main Results:

  • In the presence of calcium (Ca-form), gamma-actin showed slower nucleotide exchange, a prolonged nucleation phase, and slower elongation compared to beta-actin.
  • Ca-gamma-actin exhibited half the depolymerization rate of beta-actin, indicating greater filament stability.
  • Phosphate release kinetics differed significantly, with beta-actin showing faster and more extensive release during polymerization and treadmilling in the Ca-form.
  • In the magnesium form (Mg-form), these differences were less pronounced.

Conclusions:

  • Calcium binding to gamma-actin may create an energy barrier, slowing G- to F-actin monomer conformation equilibration and enhancing filament stability.
  • These distinct biochemical properties, especially under varying calcium concentrations, support specialized roles for beta- and gamma-actin in cellular processes.
  • The findings are particularly relevant to calcium-sensitive structures like the stereocilium in cochlear hair cells.