Electron tomography of the Arp2/3 complex branch junction reveals conformational changes in both the mother filament and Arp2/3 complex upon branch formation.
This study provides the structural rationale for how the Arp2/3 complex interacts with the mother filament to form branched actin networks.
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.
Rouiller et al. (Mon,) reported a other. Electron tomography of the Arp2/3 complex branch junction reveals conformational changes in both the mother filament and Arp2/3 complex upon branch formation.
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