title: Activation of the Arp2/3 complex by the actin filament binding protein Abp1p.
abstract: 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.
authors.affiliation: Department of Molecular and Cell Biology, University of California Berkeley, Berkeley, California 94720-3202, USA.
authors.forename: B L
authors.initials: BL
authors.lastname: Goode
authors.forename: A A
authors.initials: AA
authors.lastname: Rodal
authors.forename: G
authors.initials: G
authors.lastname: Barnes
authors.forename: D G
authors.initials: DG
authors.lastname: Drubin
mesh_terms: D051377:Actin-Related Protein 2; D051378:Actin-Related Protein 3; D000199:Actins / Q000378:metabolism*; D001665:Binding Sites; D003598:Cytoskeletal Proteins; D004705:Endocytosis / Q000502:physiology*; D005656:Fungal Proteins / Q000378:metabolism*; D008840:Microfilament Proteins / Q000378:metabolism*; D011485:Protein Binding; D029701:Saccharomyces cerevisiae Proteins; D015003:Yeasts
chemical_list: C062612:ABP1 protein, S cerevisiae; D051377:Actin-Related Protein 2; D051378:Actin-Related Protein 3; D000199:Actins; D003598:Cytoskeletal Proteins; D005656:Fungal Proteins; D008840:Microfilament Proteins; D029701:Saccharomyces cerevisiae Proteins