Structure of Arp2/3 complex at a branched actin filament junction resolved by single-particle cryo-electron microscopy

Bojian Ding, Heidy Y. Narvaez-Ortiz, Yuvraj Singh, Glen M. Hocky, Saikat Chowdhury, Brad J. Nolen

Research output: Contribution to journalArticlepeer-review


Arp2/3 complex nucleates branched actin filaments that provide pushing forces to drive cellular processes such as lamellipodial protrusion and endocytosis. Arp2/3 complex is intrinsically inactive, and multiple classes of nucleation promoting factors (NPFs) stimulate its nucleation activity. When activated by WASP family NPFs, the complex must bind to the side of a preexisting (mother) filament of actin to complete the nucleation process, ensuring that WASP-mediated activation creates branched rather than linear actin filaments. How actin filaments contribute to activation is currently not understood, largely due to the lack of high-resolution structures of activated Arp2/3 complex bound to the side of a filament. Here, we present the 3.9-Å cryo-electron microscopy structure of the Arp2/3 complex at a branch junction. The structure reveals contacts between Arp2/3 complex and the side of the mother actin filament that likely stimulate subunit flattening, a conformational change that allows the actin-related protein subunits in the complex (Arp2 and Arp3) to mimic filamentous actin subunits. In contrast, limited contact between the bottom half of the complex and the mother filament suggests that clamp twisting, a second major conformational change observed in the active state, is not stimulated by actin filaments, potentially explaining why actin filaments are required but insufficient to trigger nucleation during WASP-mediated activation. Along with biochemical and live-cell imaging data and molecular dynamics simulations, the structure reveals features critical for the interaction of Arp2/3 complex with actin filaments and regulated assembly of branched actin filament networks in cells.

Original languageEnglish (US)
Article numbere2202723119
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number22
StatePublished - May 31 2022


  • Arp2/3
  • actin
  • cryo-electron microscopy
  • cytoskeleton
  • nucleation
  • Cryoelectron Microscopy
  • Wiskott-Aldrich Syndrome Protein/metabolism
  • Actin-Related Protein 2-3 Complex/chemistry
  • Cytoskeleton/metabolism
  • Protein Conformation
  • Actin Cytoskeleton/chemistry
  • Molecular Dynamics Simulation

ASJC Scopus subject areas

  • General


Dive into the research topics of 'Structure of Arp2/3 complex at a branched actin filament junction resolved by single-particle cryo-electron microscopy'. Together they form a unique fingerprint.

Cite this