title: X-ray scattering study of activated Arp2/3 complex with bound actin-WCA.
abstract: Previous structures of Arp2/3 complex, determined in the absence of a nucleation-promoting factor and actin, reveal its inactive conformation. The study of the activated structure has been hampered by uncontrollable polymerization. We have engineered a stable activated complex consisting of Arp2/3 complex, the WCA activator region of N-WASP, and one actin monomer, and studied its structure in solution by small angle X-ray scattering (SAXS). The scattering data support a model in which the first actin subunit binds at the barbed end of Arp2, and disqualify an alternative model that places the first actin subunit at the barbed end of Arp3. This location of the first actin and bound W motif constrains the binding site of the C motif to subunits Arp2 and ARPC1, from where the A motif can reach subunits Arp3 and ARPC3. The results support a model of activation that is consistent with most of the biochemical observations.
authors.affiliation: Department of Physiology, University of Pennsylvania School of Medicine, 3700 Hamilton Walk, A507 Richards Building, Philadelphia, PA 19104-6085, USA.
authors.forename: Malgorzata
authors.initials: M
authors.lastname: Boczkowska
authors.forename: Grzegorz
authors.initials: G
authors.lastname: Rebowski
authors.forename: Maxim V
authors.initials: MV
authors.lastname: Petoukhov
authors.forename: David B
authors.initials: DB
authors.lastname: Hayes
authors.forename: Dmitri I
authors.initials: DI
authors.lastname: Svergun
authors.forename: Roberto
authors.initials: R
authors.lastname: Dominguez
mesh_terms: D051376:Actin-Related Protein 2-3 Complex / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D000199:Actins / Q000737:chemistry / Q000378:metabolism*; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D001923:Brain Chemistry; D002417:Cattle; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D053838:Scattering, Small Angle; D017386:Sequence Homology, Amino Acid; D051316:Wiskott-Aldrich Syndrome Protein / Q000737:chemistry* / Q000378:metabolism*; D014961:X-Ray Diffraction
chemical_list: D051376:Actin-Related Protein 2-3 Complex; D000199:Actins; D051316:Wiskott-Aldrich Syndrome Protein