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Related Concept Videos

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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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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Introduction to Actin01:26

Introduction to Actin

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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...
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Actin Polymerization01:42

Actin Polymerization

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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 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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Related Experiment Video

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Aip1p Dynamics Are Altered by the R256H Mutation in Actin
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Aip1p Dynamics Are Altered by the R256H Mutation in Actin

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D-Loop Mutation G42A/G46A Decreases Actin Dynamics.

Mizuki Matsuzaki1, Ikuko Fujiwara2, Sae Kashima1

  • 1Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan.

Biomolecules
|May 14, 2020
PubMed
Summary
This summary is machine-generated.

Two glycines in the actin filament's DNase I binding loop (D-loop) are crucial for its dynamics. Mutations restricting this loop's flexibility reduced polymerization and depolymerization rates and inhibited cofilin binding.

Keywords:
cofilindepolymerizationintrinsically disorderedpolymerization

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Area of Science:

  • Biochemistry
  • Cell Biology
  • Biophysics

Background:

  • Actin filament dynamics, including polymerization and depolymerization, are essential for eukaryotic cellular functions.
  • The DNase I binding loop (D-loop) of actin is intrinsically disordered and contributes to filament stability and dynamics.
  • Understanding the role of specific residues within the D-loop is key to elucidating actin's mechanical properties.

Purpose of the Study:

  • To investigate the functional significance of glycine residues at positions 42 and 46 within the D-loop of beta-cytoskeletal mammalian actin.
  • To determine how mutations affecting D-loop conformational freedom impact actin polymerization, depolymerization, and interactions with regulatory proteins like cofilin.

Main Methods:

  • Site-directed mutagenesis was used to introduce a double mutation (G42A/G46A) into the D-loop of mammalian actin.
  • Actin polymerization and depolymerization kinetics were measured at both filament ends.
  • Cofilin binding assays were performed to assess the impact of the mutation on protein-actin interactions.

Main Results:

  • The G42A/G46A double mutation significantly restricted the conformational freedom of the D-loop.
  • While critical concentration changes were minimal and no major structural alterations were observed, polymerization and depolymerization rates were reduced.
  • The double mutation led to inhibited binding of cofilin to the actin filament.

Conclusions:

  • The two glycine residues at the tip of the D-loop play a critical role in regulating actin filament dynamics.
  • Restricting the conformational flexibility of the D-loop impairs actin polymerization/depolymerization and cofilin-mediated actin disassembly.
  • These findings highlight the importance of intrinsic disorder and conformational freedom in the D-loop for normal actin function.