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Updated: Jul 8, 2026

In Vitro Polymerization of F-actin on Early Endosomes
Published on: August 28, 2017
Pathway of actin filament branch formation by Arp2/3 complex
Christopher C Beltzner1, Thomas D Pollard
1Department of Molecular Cellular and Developmental Biology, Yale University, New Haven, Connecticut 06520-8103, USA.
Abstract:
A spectroscopic assay using pyrene-labeled fission yeast Arp2/3 complex revealed that the complex binds to and dissociates from actin filaments extremely slowly with or without the nucleation-promoting factor fission yeast Wsp1-VCA. Wsp1-VCA binds both Arp2/3 complex and actin monomers with high affinity. These two ligands have only modest impacts on the interaction of the other ligand with VCA. Simulations of a mathematical model based on the kinetic parameters determined in this study and elsewhere account for the full time course of actin polymerization in the presence of Arp2/3 complex and Wsp1-VCA and show that an activation step, postulated to follow binding of a ternary complex of Arp2/3 complex, a bound nucleation-promoting factor, and an actin monomer to an actin filament, has a rate constant at least 0.15 s(-1). Kinetic parameters determined in this study constrain the process of actin filament branch formation during cellular motility to one main pathway.
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