title: Influence of phalloidin on the formation of actin filament branches by Arp2/3 complex.
abstract: The cyclic peptide phalloidin binds and stabilizes actin filaments. It is widely used in studies of actin filament assembly, including analysis of branch formation by Arp2/3 complex, but its influence on the branching reaction has not been considered. Here we show that rhodamine-phalloidin binds both Arp2/3 complex and the VCA domain of Arp2/3 complex activator, hWASp, with dissociation equilibrium constants of about 100 nM. Not only does phalloidin promote nucleation of pure actin monomers but it also dramatically stimulates branch formation by actin, Arp2/3 complex, and hWASp-VCA more than 10-fold and inhibits dissociation of branches. Therefore, the appearance of more branches in samples treated with rhodamine-phalloidin arises from multiple influences of the peptide on both the formation and dissociation of branches.
authors.affiliation: Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, Connecticut 06520-8103, USA.
authors.forename: Rachel E
authors.initials: RE
authors.lastname: Mahaffy
authors.forename: Thomas D
authors.initials: TD
authors.lastname: Pollard
mesh_terms: D051377:Actin-Related Protein 2 / Q000737:chemistry / Q000378:metabolism; D051376:Actin-Related Protein 2-3 Complex / Q000737:chemistry* / Q000378:metabolism*; D051378:Actin-Related Protein 3 / Q000737:chemistry / Q000378:metabolism; D000199:Actins / Q000737:chemistry / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D002417:Cattle; D002645:Chickens; D005454:Fluorescence Polarization; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D010590:Phalloidine / Q000737:chemistry* / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism; D051316:Wiskott-Aldrich Syndrome Protein / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism
chemical_list: D051377:Actin-Related Protein 2; D051376:Actin-Related Protein 2-3 Complex; D051378:Actin-Related Protein 3; D000199:Actins; D011993:Recombinant Fusion Proteins; D051316:Wiskott-Aldrich Syndrome Protein; D010590:Phalloidine