title: Conformational changes in the Arp2/3 complex leading to actin nucleation.
abstract: The two actin-related subunits of the Arp2/3 complex, Arp2 and Arp3, are proposed to form a pseudo actin dimer that nucleates actin polymerization. However, in the crystal structure of the inactive complex, they are too far apart to form such a nucleus. Here, we show using EM that yeast and bovine Arp2/3 complexes exist in a distribution among open, intermediate and closed conformations. The crystal structure docks well into the open conformation. The activator WASp binds at the cleft between Arp2 and Arp3, and all WASp-bound complexes are closed. The inhibitor coronin binds near the p35 subunit, and all coronin-bound complexes are open. Activating and loss-of-function mutations in the p35 subunit skew conformational distribution in opposite directions, closed and open, respectively. We conclude that WASp stabilizes p35-dependent closure of the complex, holding Arp2 and Arp3 closer together to nucleate an actin filament.
authors.affiliation: Department of Biology, Rosenstiel Basic Medical Sciences Research Center, Brandeis University, Waltham, Massachusetts 02454, USA.
authors.forename: Avital A
authors.initials: AA
authors.lastname: Rodal
authors.forename: Olga
authors.initials: O
authors.lastname: Sokolova
authors.forename: Deborah B
authors.initials: DB
authors.lastname: Robins
authors.forename: Karen M
authors.initials: KM
authors.lastname: Daugherty
authors.forename: Simon
authors.initials: S
authors.lastname: Hippenmeyer
authors.forename: Howard
authors.initials: H
authors.lastname: Riezman
authors.forename: Nikolaus
authors.initials: N
authors.lastname: Grigorieff
authors.forename: Bruce L
authors.initials: BL
authors.lastname: Goode
mesh_terms: D051377:Actin-Related Protein 2; D051378:Actin-Related Protein 3; D000199:Actins / Q000737:chemistry* / Q000378:metabolism*; D000818:Animals; D002417:Cattle; D018360:Crystallography, X-Ray; D003598:Cytoskeletal Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D008840:Microfilament Proteins / Q000737:chemistry / Q000378:metabolism; D008854:Microscopy, Electron; D011485:Protein Binding; D011487:Protein Conformation; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000737:chemistry / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000378:metabolism; D051316:Wiskott-Aldrich Syndrome Protein
chemical_list: D051377:Actin-Related Protein 2; D051378:Actin-Related Protein 3; D000199:Actins; D003598:Cytoskeletal Proteins; C480361:LAS17 protein, S cerevisiae; D008840:Microfilament Proteins; D021122:Protein Subunits; D029701:Saccharomyces cerevisiae Proteins; D051316:Wiskott-Aldrich Syndrome Protein; C072061:coronin proteins