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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...

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...

Formation of Intermediate Filaments

Formation of Intermediate Filaments

Intermediate filaments are cytoskeletal proteins with higher tensile strength and flexibility than microfilaments and microtubules. Unlike the other two cytoskeletal proteins, intermediate filament formation lacks the enzymatic activity to hydrolyze nucleotides like ATP and GTP to generate energy for polymerization. Therefore, the formation of intermediate filaments is multistep self-assembly. The involvement of any accessory proteins in intermediate filament formation has not yet been reported.

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...

Polymer Classification: Architecture

Polymer Classification: Architecture

Polymers are classified as linear or branched on the basis of their chain architecture. The polymer chains in linear polymers have a long chain-like structure with minimal to no branching at all. Even if a polymer features large substituent groups on the monomer, which appear as branches to the skeleton, it is not considered a branched polymer. A branched polymer contains secondary polymer chains that arise from the main polymer chain. The branching occurs when the polymer growth shifts from...

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Related Experiment Video

Updated: May 19, 2026

Reconstituting and Characterizing Actin-Microtubule Composites with Tunable Motor-Driven Dynamics and Mechanics

Reconstituting and Characterizing Actin-Microtubule Composites with Tunable Motor-Driven Dynamics and Mechanics

Published on: August 25, 2022

Active compaction of crosslinked driven filament networks.

V Schaller¹, B Hammerich, A R Bausch

¹Lehrstuhl für Biophysik-E27, Technische Universität München, Garching, Germany.

The European Physical Journal. E, Soft Matter

|August 29, 2012

Summary

Active materials compact into long fibers through the interplay of actin filament transport and crosslinking. This minimal system offers control over active compaction structure and length scales.

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Area of Science:

Biophysics
Materials Science
Cellular Mechanics

Background:

Contractile active materials rely on complex interactions between force-exerting and force-bearing components.
Understanding fundamental principles is hindered by system complexity and limited parameter control.

Purpose of the Study:

To investigate the fundamental principles of active material contraction.
To analyze a minimal reconstituted system for controlled active compaction.

Main Methods:

Utilized a reconstituted system of concentrated actin filaments crosslinked by α-actinin.
Employed a two-dimensional motility assay for active transport analysis.

Main Results:

The minimal system actively compacted into highly organized fibers.
Observed fiber lengths exceeded individual filament lengths by two orders of magnitude.
Identified the interplay between active transport and crosslinking as the driver of compaction.

Conclusions:

The interplay between active transport and crosslinking governs active compaction in this minimal system.
This system provides a controllable platform for studying active material structure and length scales.