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J Cell Biol. 2008 Mar 10;180(5):887-95. doi: 10.1083/jcb.200709092. Epub 2008 Mar 3.

The structural basis of actin filament branching by the Arp2/3 complex.

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1
Burnham Institute for Medical Research, La Jolla, CA 92037, USA.

Abstract

The actin-related protein 2/3 (Arp2/3) complex mediates the formation of branched actin filaments at the leading edge of motile cells and in the comet tails moving certain intracellular pathogens. Crystal structures of the Arp2/3 complex are available, but the architecture of the junction formed by the Arp2/3 complex at the base of the branch was not known. In this study, we use electron tomography to reconstruct the branch junction with sufficient resolution to show how the Arp2/3 complex interacts with the mother filament. Our analysis reveals conformational changes in both the mother filament and Arp2/3 complex upon branch formation. The Arp2 and Arp3 subunits reorganize into a dimer, providing a short-pitch template for elongation of the daughter filament. Two subunits of the mother filament undergo conformational changes that increase stability of the branch. These data provide a rationale for why branch formation requires cooperative interactions among the Arp2/3 complex, nucleation-promoting factors, an actin monomer, and the mother filament.

PMID:
18316411
PMCID:
PMC2265399
DOI:
10.1083/jcb.200709092
[Indexed for MEDLINE]
Free PMC Article
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