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Actin Polymerization

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 Treadmilling

Actin Treadmilling

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...

Actin Filament Depolymerization

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 Filaments

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...

Introduction to Actin

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 Motility

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.

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Related Experiment Video

Updated: Jun 23, 2026

Micromanipulation Techniques Allowing Analysis of Morphogenetic Dynamics and Turnover of Cytoskeletal Regulators

Micromanipulation Techniques Allowing Analysis of Morphogenetic Dynamics and Turnover of Cytoskeletal Regulators

Published on: May 12, 2018

Nonequilibrium actin polymerization treated by a truncated rate-equation method.

F J Brooks¹, A E Carlsson

¹Department of Physics, Washington University, St. Louis, Missouri 63130, USA. fjbrooks@physics.wustl.edu

Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics

|April 28, 2009

Summary

Simplified actin polymerization models offer accessible deterministic rate equations for nonequilibrium dynamics. This approach accurately predicts actin concentrations and aids in parameter extraction from experimental data.

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Micromanipulation Techniques Allowing Analysis of Morphogenetic Dynamics and Turnover of Cytoskeletal Regulators

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Area of Science:

Biophysics
Cell Biology
Computational Biology

Background:

Actin polymerization exhibits complex nonequilibrium dynamics not fully captured by simplified rate equations.
Previous modeling relied on computationally intensive stochastic simulations or elaborate recursion schemes.
Accurate modeling is crucial for understanding cellular processes like motility.

Purpose of the Study:

To derive a set of simplified, accessible deterministic rate equations for actin polymerization dynamics.
To enable integration of actin polymerization modeling into whole-cell motility simulations.
To accurately predict actin concentrations across different nucleotide states and polymerization stages.

Main Methods:

Utilized a truncation approach to develop deterministic rate equations.
Modeled polymerization time courses nucleated via seed filaments.
Extended the model to incorporate the effects of capping protein.

Main Results:

Derived readily accessible deterministic rate equations significantly simpler than prior models.
Equations accurately predict relative concentrations of monomeric and polymerized actin in various nucleotide states.
Successfully extended the model to include capping protein effects.

Conclusions:

The developed rate equations provide a computationally tractable method for modeling actin polymerization.
This approach facilitates the incorporation of detailed actin dynamics into larger cellular models.
The method is applicable for extracting key kinetic parameters from experimental data.