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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.

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.
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Microtubules in Cell Motility

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Microtubules are thick hollow cylindrical proteins that help form the cytoskeleton. Microtubules have varied roles in the cell. These filaments help form cellular appendages like cilia and flagella, which are responsible for locomotion. The cilia arise from basal bodies, separated from the main body by a membrane-like structure forming the transition zone. This zone is the gate for the entry of lipids and proteins, creating a unique composition of lipids and proteins in the ciliary membrane and...

Microtubules in Cell Motility

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Microtubules are thick hollow cylindrical proteins that help form the cytoskeleton. Microtubules have varied roles in the cell. These filaments help form cellular appendages like cilia and flagella, which are responsible for locomotion. The cilia arise from basal bodies, separated from the main body by a membrane-like structure forming the transition zone. This zone is the gate for the entry of lipids and proteins, creating a unique composition of lipids and proteins in the ciliary membrane and...

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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...

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Related Experiment Video

Updated: Jun 5, 2026

Reconstitution of Actin-Based Motility with Commercially Available Proteins

Reconstitution of Actin-Based Motility with Commercially Available Proteins

Published on: October 28, 2022

Actin motility: formin a SCAry tail.

Art Alberts¹, Michael Way

¹Laboratory of Cell Structure & Signal Integration, Van Andel Research Institute, Grand Rapids, MI 49503, USA. Art.Alberts@vai.org

Current Biology : CB

|January 11, 2011

Summary

The Rickettsia bacterial protein Sca2 assembles actin filaments. This process is crucial for bacterial virulence and motility, mimicking formin tactics.

Area of Science:

Microbiology
Biochemistry
Cell Biology

Background:

The Rickettsia bacterial protein Sca2 is essential for virulence.
Sca2 mediates actin-dependent motility in Rickettsia species.

Purpose of the Study:

To elucidate the biochemical mechanism by which Sca2 assembles actin filaments.
To compare the actin assembly mechanism of Sca2 with known actin-binding proteins.

Main Methods:

Biochemical analysis of Sca2's interaction with actin.
In vitro actin polymerization assays.
Comparison of Sca2-mediated actin assembly with formin-mediated assembly.

Main Results:

Sca2 directly promotes actin filament assembly.

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Last Updated: Jun 5, 2026

Reconstitution of Actin-Based Motility with Commercially Available Proteins

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Published on: October 28, 2022

Probing Myosin Ensemble Mechanics in Actin Filament Bundles Using Optical Tweezers

Probing Myosin Ensemble Mechanics in Actin Filament Bundles Using Optical Tweezers

Published on: May 4, 2022

Analyses of Actin Dynamics, Clutch Coupling and Traction Force for Growth Cone Advance

Analyses of Actin Dynamics, Clutch Coupling and Traction Force for Growth Cone Advance

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The mechanism of actin assembly by Sca2 is processive, similar to formins.

Sca2's actin assembly function is critical for Rickettsia virulence and motility.

Conclusions:

Rickettsia Sca2 utilizes a formin-like mechanism for processive actin filament elongation.
This actin assembly capability is a key virulence factor for Rickettsia.
Understanding Sca2's mechanism provides insights into bacterial pathogenesis and actin dynamics.