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Structure of Arp2/3 Complex in Its Activated State and in Actin Filament Branch Junctions

Science  28 Sep 2001:
Vol. 293, Issue 5539, pp. 2456-2459
DOI: 10.1126/science.1063025

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Abstract

The seven-subunit Arp2/3 complex choreographs the formation of branched actin networks at the leading edge of migrating cells. When activated by Wiskott-Aldrich Syndrome protein (WASp), the Arp2/3 complex initiates actin filament branches from the sides of existing filaments. Electron cryomicroscopy and three-dimensional reconstruction of Acanthamoeba castellanii andSaccharomyces cerevisiae Arp2/3 complexes bound to the WASp carboxy-terminal domain reveal asymmetric, oblate ellipsoids. Image analysis of actin branches indicates that the complex binds the side of the mother filament, and Arp2 and Arp3 (for actin-related protein) are the first two subunits of the daughter filament. Comparison to the actin-free, WASp-activated complexes suggests that branch initiation involves large-scale structural rearrangements within Arp2/3.

  • * To whom correspondence should be addressed. E-mail: dorit{at}burnham.org

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