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Assembly of Cytoskeletal Filaments

Assembly of Cytoskeletal Filaments

Cytoskeletal filaments are polymeric forms of smaller protein subunits. However, individual cytoskeletal filaments may easily disassemble or associate with other similar filaments to form rigid structures. Microfilaments, made of actin monomers, rely on actin-binding proteins to form bundles and create networks of individual actin filaments. Microtubules rely on microtubule-associated proteins (MAPs) to form sturdy cylindrical structures. However, the proteins involved in forming complex...

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.

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...

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...

Cytoskeletal Accessory Proteins

Cytoskeletal Accessory Proteins

The cytoskeleton is an essential cell component that plays several structural and functional roles. However, the filaments that make up the cytoskeleton cannot function independently and depend on the accessory or ancillary proteins to effectively carry out their function. Accessory proteins associate with cytoskeletal filaments and their monomers, aiding filament formation and function. They also help in the cross-communication among cytoskeletal filaments. Cytoskeletal accessory proteins are...

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Related Experiment Video

Updated: Jun 20, 2026

Tuning the Contractility and Deformation Modes of Active Actin-Based Assemblies In Vitro: From Two-Dimensional Active Networks to Liquid Crystal Drops

Tuning the Contractility and Deformation Modes of Active Actin-Based Assemblies In Vitro: From Two-Dimensional Active Networks to Liquid Crystal Drops

Published on: July 11, 2025

Cysteine engineering of actin self-assembly interfaces.

Kate Pengelly¹, Ana Loncar, Alex A Perieteanu

¹Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON N1G 2W1, Canada.

Biochemistry and Cell Biology = Biochimie Et Biologie Cellulaire

|September 22, 2009

Summary

Cysteine engineering of actin revealed that modifying specific sites inhibits filament formation. Chemical modification of introduced cysteine residues with large reagents blocks polymerization, supporting atomic interaction models.

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Tuning the Contractility and Deformation Modes of Active Actin-Based Assemblies In Vitro: From Two-Dimensional Active Networks to Liquid Crystal Drops

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Area of Science:

Biochemistry
Molecular Biology
Structural Biology

Background:

Filamentous actin (F-actin) structure and subunit interactions are crucial for cellular functions.
The Holmes model proposes specific atomic interactions governing F-actin polymerization.

Purpose of the Study:

To investigate atomic interactions between F-actin subunits using cysteine engineering.
To inhibit F-actin polymerization by introducing chemical groups at critical sites.

Main Methods:

Cysteine substitution of surface amino acids in actin.
Expression of engineered actin mutants in yeast.
Analysis of protein folding and polymerization characteristics.
Chemical modification of introduced cysteine residues.
Examination of polymerization inhibition and aggregate formation.
Chemical crosslinking studies to determine subunit proximity.

Main Results:

Modification of cysteine residues with large hydrophobic reagents inhibited actin polymerization.
D288C actin mutant showed impaired polymerization under oxidizing conditions and aggregate formation.
Crosslinking supported proximity between Asp288 and Ala204 in neighboring subunits, consistent with the Holmes model.

Conclusions:

Specific atomic interactions are critical for F-actin polymerization.
Cysteine engineering is a viable method to probe and potentially inhibit F-actin assembly.
Experimental data supports the proposed subunit interactions in the Holmes model of F-actin structure.