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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.

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...

Role of Myosin in Cell Migration

Role of Myosin in Cell Migration

Myosins are multimeric motor proteins involved in various cellular processes such as migration, adhesion, and proliferation. Myosin II is the most common type in animal cells, which binds and cross-links actin filaments.
Myosin II is a hexamer comprising two heavy chains with globular heads and coiled-coil tails, two regulatory light chains, and two essential light chains. The ATPase sites on the myosin heads hydrolyze ATP, and the released phosphate generates the force for contraction. It is...

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...

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Related Experiment Video

Updated: Jul 7, 2026

Aip1p Dynamics Are Altered by the R256H Mutation in Actin

Aip1p Dynamics Are Altered by the R256H Mutation in Actin

Published on: July 30, 2014

Mechanism of actin-based motility.

D Pantaloni¹, C Le Clainche, M F Carlier

¹Dynamique du Cytosquelette, Laboratoire d'Enzymologie et Biochimie Structurales, CNRS, Avenue de la Terrasse, 91198 Gif-sur-Yvette, France.

Science (New York, N.Y.)

|May 31, 2001

Summary

Cell motility and protrusions are driven by actin polymerization. Researchers reconstituted this process in vitro using five proteins, revealing regulated actin filament treadmilling as the key mechanism.

Area of Science:

Cell Biology
Biophysics

Background:

Spatially controlled actin polymerization drives cell motility and the formation of cellular protrusions, such as lamellipodia.
Pathogens like Listeria monocytogenes and Shigella flexneri utilize actin-based propulsion, serving as models for lamellipodia dynamics.

Purpose of the Study:

To reconstitute and analyze the minimal protein requirements for actin-based motility in vitro.
To elucidate the mechanism underlying actin-based propulsion using a simplified system.

Main Methods:

Reconstitution of actin-based motility using five purified proteins.
Observation and analysis of actin filament dynamics and bacterial or microsphere movement in vitro.

Main Results:

Actin-based motility was successfully reconstituted in vitro using only five pure proteins.

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Reconstitution of Actin-Based Motility with Commercially Available Proteins

Reconstitution of Actin-Based Motility with Commercially Available Proteins

Published on: October 28, 2022

Related Experiment Videos

Last Updated: Jul 7, 2026

Aip1p Dynamics Are Altered by the R256H Mutation in Actin

Aip1p Dynamics Are Altered by the R256H Mutation in Actin

Published on: July 30, 2014

Measuring Cell-Edge Protrusion Dynamics during Spreading using Live-Cell Microscopy

Measuring Cell-Edge Protrusion Dynamics during Spreading using Live-Cell Microscopy

Published on: November 1, 2021

Reconstitution of Actin-Based Motility with Commercially Available Proteins

Reconstitution of Actin-Based Motility with Commercially Available Proteins

Published on: October 28, 2022

The reconstituted system demonstrated regulated, site-directed treadmilling of actin filaments.

Observed actin dynamics align with those in living motile cells and the properties of the synthetic medium components.

Conclusions:

A minimal set of five proteins is sufficient to drive actin-based motility.
Regulated actin filament treadmilling is the fundamental mechanism for actin-based propulsion.
This in vitro system provides a powerful model for studying cell motility and pathogen invasion.