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Formation of Higher-order Actin Filaments

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...

Assembly of Cytoskeletal Filaments

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...

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...

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.

Introduction to Actin

Introduction to Actin

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 different species.

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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Reconstitution of Actin-Based Motility with Commercially Available Proteins

Reconstitution of Actin-Based Motility with Commercially Available Proteins

Published on: October 28, 2022

Actin cytoskeleton: a team effort during actin assembly.

Laurent Blanchoin¹, Alphée Michelot

¹Laboratoire de Physiologie Cellulaire et Végétale, institut de Recherches en Technologies et Sciences pour le Vivant, iRTSV, CNRS/CEA/INRA/UJF, Grenoble 38054, France. laurent.blanchoin@cea.fr

Current Biology : CB

|August 25, 2012

Summary

Two studies reveal how actin nucleators work together to create new actin filaments. Formin acts as a key modulator, controlling the speed of filament elongation.

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Using Microfluidics and Fluorescence Microscopy to Study the Assembly Dynamics of Single Actin Filaments and Bundles

Using Microfluidics and Fluorescence Microscopy to Study the Assembly Dynamics of Single Actin Filaments and Bundles

Published on: May 5, 2022

Area of Science:

Cell Biology
Biochemistry
Molecular Biology

Background:

Actin filaments are essential for cell structure and function.
Actin nucleation is the rate-limiting step in filament formation.
Multiple actin nucleators exist, but their collaborative roles are not fully understood.

Purpose of the Study:

To investigate the collaborative mechanisms of actin nucleators.
To elucidate the specific role of formin in actin filament production.

Main Methods:

Utilized advanced microscopy techniques.
Employed biochemical assays to study protein interactions.
Performed genetic manipulation to analyze nucleator function.

Main Results:

Demonstrated that specific pairs of actin nucleators cooperate to initiate filament assembly.
Showed that formin proteins regulate the elongation rate of newly formed actin filaments.
Identified distinct roles for different nucleators within collaborative tandems.

Conclusions:

Actin filament formation is a coordinated process involving multiple nucleators.
Formin plays a crucial regulatory role in controlling actin filament length.
Understanding these collaborations provides insights into cellular processes regulated by the actin cytoskeleton.