Activation of the Arp2/3 complex by the actin filament binding protein Abp1p

J Cell Biol. 2001 Apr 30;153(3):627-34. doi: 10.1083/jcb.153.3.627.


The actin-related protein (Arp) 2/3 complex plays a central role in assembly of actin networks. Because distinct actin-based structures mediate diverse processes, many proteins are likely to make spatially and temporally regulated interactions with the Arp2/3 complex. We have isolated a new activator, Abp1p, which associates tightly with the yeast Arp2/3 complex. Abp1p contains two acidic sequences (DDW) similar to those found in SCAR/WASp proteins. We demonstrate that mutation of these sequences abolishes Arp2/3 complex activation in vitro. Genetic studies indicate that this activity is important for Abp1p functions in vivo. In contrast to SCAR/WASp proteins, Abp1p binds specifically to actin filaments, not monomers. Actin filament binding is mediated by the ADF/cofilin homology (ADF-H) domain of Abp1p and is required for Arp2/3 complex activation in vitro. We demonstrate that Abp1p recruits Arp2/3 complex to the sides of filaments, suggesting a novel mechanism of activation. Studies in yeast and mammalian cells indicate that Abp1p is involved functionally in endocytosis. Based on these results, we speculate that Abp1p may link Arp2/3-mediated actin assembly to a specific step in endocytosis.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Actin-Related Protein 2
  • Actin-Related Protein 3
  • Actins / metabolism*
  • Binding Sites
  • Cytoskeletal Proteins*
  • Endocytosis / physiology*
  • Fungal Proteins / metabolism*
  • Microfilament Proteins / metabolism*
  • Protein Binding
  • Saccharomyces cerevisiae Proteins*
  • Yeasts


  • ABP1 protein, S cerevisiae
  • Actin-Related Protein 2
  • Actin-Related Protein 3
  • Actins
  • Cytoskeletal Proteins
  • Fungal Proteins
  • Microfilament Proteins
  • Saccharomyces cerevisiae Proteins