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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...

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...

Mechanism of Filopodia Formation

Mechanism of Filopodia Formation

Filopodia are thin, actin-rich cellular protrusions that play an important role in many fundamental cellular functions. They vary in their occurrence, length, and positioning in different cell types, suggesting their diverse roles.
Their main function is to guide migrating cells during normal tissue morphogenesis or cancer metastasis by recognizing and making initial contacts with the extracellular matrix. However, they can also act as stationary cell anchors or help to establish communication...

Mechanism of Lamellipodia Formation

Mechanism of Lamellipodia Formation

Cells migrating in response to external stimuli form lamellipodia, which are thin membrane protrusions supported by a mesh of linked, branched, or unbranched actin filaments. These actin filaments interact with myosin motor proteins, creating the dynamic actomyosin complex within the cytoskeleton. Contractility, or the ability to generate contractile stress, is inherent to the actomyosin complex. It helps cells detect the stiffness of the surrounding ECM and exert contractile force for...

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...

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: Jul 18, 2026

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

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

Published on: May 5, 2022

Actin polymerization upon processive capping by formin: a model for slowing and acceleration.

Tom Shemesh¹, Michael M Kozlov

¹Department of Physiology and Pharmacology, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel.

Biophysical Journal

|December 13, 2006

Summary

Formin proteins cap actin filaments, influencing cell dynamics. A new model shows a single physical parameter, effective elastic energy, explains diverse actin polymerization rates observed with different formins and profilin.

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

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In Vitro Polymerization of F-actin on Early Endosomes

In Vitro Polymerization of F-actin on Early Endosomes

Published on: August 28, 2017

Area of Science:

Cell Biology
Biophysics
Molecular Dynamics

Background:

Formin proteins are crucial regulators of actin filament dynamics.
Actin polymerization underlies many essential intracellular processes.
Formin's interaction with actin filaments affects polymerization rates, influenced by profilin.

Purpose of the Study:

To elucidate the physical mechanism behind formin-mediated processive capping of actin filaments.
To explain the wide range of actin polymerization rates observed with different formins and profilin.
To develop a predictive model for formin-actin interactions.

Main Methods:

Development of a theoretical model based on physical parameters.
Analysis of experimental data on actin polymerization rates.
Fitting theoretical predictions to experimental curves to derive physical parameter values.

Main Results:

A single physical parameter, the effective elastic energy of the formin-capped barbed end, predicts polymerization rates.
The model successfully explains both the slowing of polymerization by FH2 domains and acceleration by FH1-FH2 domains with profilin.
Effective elastic energies for various formin-barbed end complexes were determined.

Conclusions:

The effective elastic energy is a key determinant of formin's influence on actin polymerization.
This model provides a unified framework for understanding formin capping mechanisms.
The findings are vital for comprehending intracellular actin dynamics.