Pathway of actin filament branch formation by Arp2/3 complex revealed by single-molecule imaging.

Actin filament nucleation by actin-related protein (Arp) 2/3 complex is a critical process in cell motility and endocytosis, yet key aspects of its mechanism are unknown due to a lack of real-time observations of Arp2/3 complex through the nucleation process. Triggered by the verprolin homology, central, and acidic (VCA) region ...
of proteins in the Wiskott-Aldrich syndrome protein (WASp) family, Arp2/3 complex produces new (daughter) filaments as branches from the sides of preexisting (mother) filaments. We visualized individual fluorescently labeled Arp2/3 complexes dynamically interacting with and producing branches on growing actin filaments in vitro. Branch formation was strikingly inefficient, even in the presence of VCA: only ~1% of filament-bound Arp2/3 complexes yielded a daughter filament. VCA acted at multiple steps, increasing both the association rate of Arp2/3 complexes with mother filament and the fraction of filament-bound complexes that nucleated a daughter. The results lead to a quantitative kinetic mechanism for branched actin assembly, revealing the steps that can be stimulated by additional cellular factors.
Mesh Terms:
Actin-Related Protein 2-3 Complex, Actins, Animals, Kinetics, Microscopy, Fluorescence, Multiphoton, Models, Molecular, Protein Interaction Domains and Motifs, Protein Multimerization, Saccharomyces cerevisiae Proteins, Wiskott-Aldrich Syndrome Protein Family
Proc. Natl. Acad. Sci. U.S.A.
Date: Jan. 22, 2013
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