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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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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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Mechanism of Filopodia Formation01:39

Mechanism of Filopodia Formation

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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...
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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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Cytoskeletal Accessory Proteins01:13

Cytoskeletal Accessory Proteins

3.9K
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...
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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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Reconstitution of Actin-Based Motility with Commercially Available Proteins
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Kaptin Functions as a Barbed-End Binding Protein to Control Actin Filament Dynamics.

Priyanka Dutta1, Ipshita Maiti2, Krishna Chandra Mondal1

  • 1National Centre for Cell Science, NCCS Complex, S.P. Pune University Campus, Ganeshkhind, Pune 411007, India.

Journal of Molecular Biology
|November 22, 2025
PubMed
Summary

Kaptin (KPTN) is a novel protein regulating actin dynamics by binding filament barbed ends, suppressing elongation, and promoting stabilization and bundling. This discovery reveals KPTN

Keywords:
KPTN (Kaptin)WD-repeat proteinactin cytoskeletonbarbed-end bindingfilament dynamics

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Area of Science:

  • Cell Biology
  • Biochemistry
  • Structural Biology

Background:

  • Actin cytoskeleton regulation is crucial for cellular functions like morphology and motility.
  • While key actin-binding proteins are known, additional modulators are needed for precise control.
  • The spatial and temporal regulation of actin dynamics involves complex protein interactions.

Purpose of the Study:

  • To identify and characterize novel regulators of actin filament dynamics.
  • To elucidate the mechanism by which Kaptin (KPTN) influences actin cytoskeleton organization.
  • To determine the structural basis of KPTN's interaction with actin filaments.

Main Methods:

  • Biochemical reconstitution assays to study protein-actin interactions.
  • Single-molecule Total Internal Reflection Fluorescence (TIRF) microscopy to observe filament dynamics.
  • AlphaFold structural prediction to analyze KPTN protein structure and identify key residues.

Main Results:

  • Kaptin (KPTN) was identified as a novel actin-binding protein localized to the cell periphery.
  • KPTN binds to actin filament barbed ends, inhibiting filament elongation and promoting stabilization.
  • KPTN also contributes to filament bundling, indicating a dual role in actin architecture.
  • Structural analysis revealed KPTN belongs to the WD-repeat protein family, with a conserved residue essential for actin binding.

Conclusions:

  • Kaptin (KPTN) represents a novel regulator of actin dynamics with a dual function in filament stabilization and bundling.
  • KPTN acts as both a barbed-end and side-binding protein, contributing to the maintenance of actin cytoskeletal networks.
  • The findings provide new insights into the complex mechanisms governing actin cytoskeleton organization and cellular processes.