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Formation of Higher-order Actin Filaments

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...

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...

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...

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.

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...

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Related Experiment Video

Updated: Jun 8, 2026

In Vitro Polymerization of F-actin on Early Endosomes

In Vitro Polymerization of F-actin on Early Endosomes

Published on: August 28, 2017

Structural polymorphism in F-actin.

Vitold E Galkin¹, Albina Orlova, Gunnar F Schröder

¹Department of Biochemistry and Molecular Genetics, University of Virginia, Charlottesville, Virginia, USA. galkin@virginia.edu

Nature Structural & Molecular Biology

|October 12, 2010

Summary

This summary is machine-generated.

Actin filaments (F-actin) exhibit multiple structural states, challenging the single atomic model. This structural polymorphism is linked to disease-causing mutations in the ACTA1 gene.

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In Vitro Polymerization of F-actin on Early Endosomes

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Area of Science:

Biochemistry
Structural Biology
Molecular Biology

Background:

Actin's remarkable sequence conservation across evolution remains poorly understood.
Detailed mechanistic understanding of actin-dependent processes like muscle contraction and cytokinesis requires an atomic model of the actin filament (F-actin).

Purpose of the Study:

To investigate the structural heterogeneity of frozen-hydrated actin filaments using electron cryomicroscopy.
To correlate structural dynamics with disease-causing mutations in the human ACTA1 gene.

Main Methods:

Electron cryomicroscopy (cryo-EM) was employed to determine the structure of frozen-hydrated actin filaments at approximately 10 Å resolution.
Analysis focused on identifying different structural states within the filaments and characterizing dynamic elements.

Main Results:

Frozen-hydrated actin filaments were found to exist in a multiplicity of structural states.
Disordered subdomain 2 was observed, capable of multiple contacts with the C terminus of adjacent subunits.
Specific disease-causing mutations in the human ACTA1 gene were linked to the most structurally dynamic regions of actin.

Conclusions:

The actin filament (F-actin) is structurally polymorphic and cannot be accurately represented by a single atomic model.
Understanding F-actin requires considering it as an ensemble of various structural states.
Structural dynamics of actin are implicated in human diseases associated with ACTA1 mutations.