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

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


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acanthamoeba castellanii
  • Actin Cytoskeleton / chemistry*
  • Actin Cytoskeleton / ultrastructure*
  • Actin-Related Protein 2-3 Complex / chemistry*
  • Actin-Related Protein 2-3 Complex / ultrastructure*
  • Animals
  • Cattle
  • Computer Simulation
  • Cytoskeleton / chemistry*
  • Cytoskeleton / ultrastructure*
  • Dimerization
  • Macromolecular Substances / chemistry
  • Models, Molecular
  • Protein Binding / physiology
  • Protein Structure, Quaternary / physiology
  • Rabbits
  • Saccharomyces cerevisiae
  • Tomography, X-Ray Computed


  • Actin-Related Protein 2-3 Complex
  • Macromolecular Substances