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Related Concept Videos

Actin Polymerization01:42

Actin Polymerization

6.3K
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...
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Generation of Straight or Branched Actin Filaments01:14

Generation of Straight or Branched Actin Filaments

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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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Actin Filament Depolymerization01:19

Actin Filament Depolymerization

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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...
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Formation of Higher-order Actin Filaments01:11

Formation of Higher-order Actin Filaments

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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...
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Actin Polymerization and Cell Motility01:13

Actin Polymerization and Cell Motility

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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....
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Actin Treadmilling01:18

Actin Treadmilling

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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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Using Microfluidics and Fluorescence Microscopy to Study the Assembly Dynamics of Single Actin Filaments and Bundles
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Energy-based modelling of single actin filament polymerization using bond graphs.

Peter J Gawthrop1, Michael Pan2,3,4, Vijay Rajagopal1,5,6

  • 1Department of Biomedical Engineering, Faculty of Engineering & Information Technology, University of Melbourne, Melbourne, Victoria 3010, Australia.

Journal of the Royal Society, Interface
|January 30, 2025
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Summary

Bond graphs now model chemomechanical transduction in biological systems. This energy-based method offers a simpler alternative to existing approaches for actin filament dynamics.

Keywords:
Brownian ratchetSystems Biologyactin dynamicsbond graphchemomechanical transductionenergy-based modelling

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Area of Science:

  • Systems biology
  • Biophysics
  • Computational biology

Background:

  • Bond graphs offer a hierarchical, energy-based modeling approach for complex systems.
  • Current methods allow modeling of biological systems with chemical and electrical subsystems.
  • Chemomechanical transduction is crucial in biological processes like muscle contraction and cell motility.

Purpose of the Study:

  • To extend the bond graph methodology to include chemomechanical transduction.
  • To model actin filament polymerization and force generation using bond graphs.
  • To provide a simpler, energy-based alternative to the Brownian ratchet model.

Main Methods:

  • Utilized the bond graph approach, incorporating the transformer (TF) component.
  • Modeled actin filament polymerization and force generation as a chemomechanical system.
  • Extended the model to include flexibility, non-normal incidence, and compliance.

Main Results:

  • Demonstrated that the TF bond graph component effectively models chemomechanical transduction.
  • Showed the bond graph approach yields equivalent equations to the Brownian ratchet model in simple cases.
  • Illustrated how additional bond graph components can model system complexities like flexibility and non-normal incidence.
  • Revealed that compliance leads to non-convexity in the force-velocity curve.

Conclusions:

  • The bond graph approach provides a versatile and conceptually simple framework for modeling chemomechanical transduction in biological systems.
  • This energy-based methodology facilitates the investigation of power transmission and efficiency in systems like actin filaments.
  • The bond graph model can be fitted to experimental data by adjusting physical parameters, enabling quantitative analysis.