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Related Concept Videos

Formation of Higher-order Actin Filaments01:11

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 Polymerization01:42

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...
Assembly of Cytoskeletal Filaments01:18

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...
Actin Filament Depolymerization01:19

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...
Actin Polymerization and Cell Motility01:13

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 Filaments01:14

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...

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Updated: Jun 3, 2026

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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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

Polycation induced actin bundles.

Andras Muhlrad1, Elena E Grintsevich, Emil Reisler

  • 1Institute of Dental Sciences, School of Dental Medicine, The Hebrew University, Jerusalem 91120, Israel. muhlrad@cc.huji.ac.il

Biophysical Chemistry
|March 18, 2011
PubMed
Summary
This summary is machine-generated.

Polycations like polylysine and lysozyme rapidly induce actin bundle formation through electrostatic attraction. These bundles, crucial in cystic fibrosis mucus, can be stabilized or disassembled by varying polycation concentration and ionic strength.

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Area of Science:

  • Biochemistry
  • Cell Biology
  • Biophysics

Background:

  • Actin filaments form essential cellular structures.
  • Polycations are known to interact with nucleic acids and proteins.
  • The role of polycation-actin interactions in bundle formation and disease is not fully understood.

Purpose of the Study:

  • To investigate the formation, structure, and stability of polycation-induced actin bundles.
  • To explore the influence of ionic strength and polycation concentration on actin bundle dynamics.
  • To assess the pathological significance of actin-lysozyme bundles in cystic fibrosis.

Main Methods:

  • Studied bundle formation using polylysine, spermine, and lysozyme with MgATP-G-actins.
  • Assessed bundle sensitivity to ionic strength (NaCl) and polycation concentration.
  • Utilized MTS-1 cross-linker to probe filament packing and interfilament cross-links.
  • Investigated bundle disassembly using cofilin and heparin.

Main Results:

  • Polycations rapidly induced actin bundle formation at low ionic strength via electrostatic attraction.
  • Bundles exhibited sensitivity to ionic strength but could be stabilized by higher polycation concentrations.
  • MTS-1 cross-linking indicated tight filament packing within bundles.
  • Actin-lysozyme bundles are pathologically relevant to cystic fibrosis mucus.

Conclusions:

  • Polycations are potent inducers of actin bundle formation.
  • Actin bundle stability is modulated by ionic strength and polycation concentration.
  • Actin-lysozyme bundles contribute to the pathophysiology of cystic fibrosis by increasing mucus viscosity.