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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...

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.
Their main function is to guide migrating cells during normal tissue morphogenesis or cancer metastasis by recognizing and making initial contacts with the extracellular matrix. However, they can also act as stationary cell anchors or help to establish communication...

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.

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...

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Aip1p Dynamics Are Altered by the R256H Mutation in Actin

Aip1p Dynamics Are Altered by the R256H Mutation in Actin

Published on: July 30, 2014

Hsp27-actin interaction.

Philip Graceffa¹

¹Boston Biomedical Research Institute, 64 Grove Street, Watertown, MA 02472, USA.

Biochemistry Research International

|October 19, 2011

Summary

This summary is machine-generated.

Heat shock protein 27 (Hsp27) weakly binds to the sides of filamentous actin (F-actin) as a monomer, not an end-capping protein. This finding challenges previous models of Hsp27

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Actin Co-Sedimentation Assay; for the Analysis of Protein Binding to F-Actin

Actin Co-Sedimentation Assay; for the Analysis of Protein Binding to F-Actin

Published on: March 28, 2008

Area of Science:

Biochemistry
Molecular Biology
Cellular Dynamics

Background:

Heat shock protein 27 (Hsp27) is known to interact with filamentous actin (F-actin).
Previous research suggested Hsp27 functions as a barbed-end-capping protein for F-actin.

Purpose of the Study:

To quantitatively determine the binding strength and stoichiometry of Hsp27 interaction with F-actin.
To elucidate the oligomeric state of Hsp27 during F-actin binding.
To clarify the mechanism of Hsp27-F-actin interaction.

Main Methods:

Fluorescence spectroscopy using acrylodan and pyrene probes attached to Hsp27 cysteine-137.
Determination of binding constants and stoichiometry via fluorescence titration with F-actin.
Electron microscopy (EM) to assess G-actin sequestration and F-actin binding patterns.

Main Results:

Acrylodan fluorescence increased upon F-actin interaction, indicating binding.
A weak apparent dissociation constant (K(D) (app) = 5.3 μM) and variable stoichiometry (<1 to 6) were observed.
Pyrene excimer fluorescence decreased upon F-actin interaction, suggesting monomeric Hsp27 binding.
EM showed Hsp27 is not a potent G-actin sequestrant.

Conclusions:

Hsp27 interacts with F-actin as a monomer, not an oligomer.
Hsp27 exhibits weak F-actin side-binding properties in vitro.
The study refutes the model of Hsp27 as a primary F-actin end-capping protein.