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Related Concept Videos

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.
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Actin Filament Depolymerization01:19

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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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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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Generation of Straight or Branched Actin Filaments01:14

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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 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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Formation of Higher-order Actin Filaments01:11

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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.
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Aip1p Dynamics Are Altered by the R256H Mutation in Actin
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Two Deafness-Causing Actin Mutations (DFNA20/26) Have Allosteric Effects on the Actin Structure.

Lauren Jepsen1, Karina A Kruth2, Peter A Rubenstein2

  • 1Bioinformatics Graduate Program, University of Michigan, Ann Arbor, Michigan; Department of Biomedical Engineering, University of Michigan, Ann Arbor, Michigan; Center for Computational Medicine and Bioinformatics, University of Michigan, Ann Arbor, Michigan.

Biophysical Journal
|July 28, 2016
PubMed
Summary

Point mutations in gamma-cytoplasmic actin (γ-actin) cause early-onset deafness. This study compares two mutations, K118M and K118N, revealing how they alter actin structure, dynamics, and polymerization, leading to hearing loss.

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Area of Science:

  • Molecular Biology
  • Biochemistry
  • Genetics

Background:

  • Point mutations in γ-cytoplasmic actin are linked to autosomal-dominant, early-onset deafness.
  • Two distinct mutations at the K118 site (K118M and K118N) offer a model to study structure-phenotype relationships.

Purpose of the Study:

  • To investigate the molecular mechanisms by which K118M and K118N mutations in γ-actin affect actin structure, dynamics, and polymerization.
  • To compare the effects of two different amino acid substitutions at the same site that lead to a similar human phenotype.

Main Methods:

  • Computational and experimental studies utilizing yeast actin.
  • Analysis of structural and dynamic changes in actin monomers.
  • In vitro polymerization assays.

Main Results:

  • Mutations at K118 alter the DNase-I loop and H73 loop structures, affecting nucleotide exchange rates.
  • Significant shifts in monomer twist were observed, with K118N mimicking the F-actin protomer twist.
  • K118N mutation accelerated in vitro actin polymerization.

Conclusions:

  • Subtle structural and dynamic alterations in actin monomers can lead to misregulation of actin assembly and dynamics.
  • These changes, though tolerated in vivo, contribute to the pathogenesis of hearing loss.