title: The structural basis of actin filament branching by the Arp2/3 complex.
abstract: The actin-related protein 2/3 (Arp2/3) complex mediates the formation of branched actin filaments at the leading edge of motile cells and in the comet tails moving certain intracellular pathogens. Crystal structures of the Arp2/3 complex are available, but the architecture of the junction formed by the Arp2/3 complex at the base of the branch was not known. In this study, we use electron tomography to reconstruct the branch junction with sufficient resolution to show how the Arp2/3 complex interacts with the mother filament. Our analysis reveals conformational changes in both the mother filament and Arp2/3 complex upon branch formation. The Arp2 and Arp3 subunits reorganize into a dimer, providing a short-pitch template for elongation of the daughter filament. Two subunits of the mother filament undergo conformational changes that increase stability of the branch. These data provide a rationale for why branch formation requires cooperative interactions among the Arp2/3 complex, nucleation-promoting factors, an actin monomer, and the mother filament.
authors.affiliation: Burnham Institute for Medical Research, La Jolla, CA 92037, USA.
authors.forename: Isabelle
authors.initials: I
authors.lastname: Rouiller
authors.forename: Xiao-Ping
authors.initials: XP
authors.lastname: Xu
authors.forename: Kurt J
authors.initials: KJ
authors.lastname: Amann
authors.forename: Coumaran
authors.initials: C
authors.lastname: Egile
authors.forename: Stephan
authors.initials: S
authors.lastname: Nickell
authors.forename: Daniela
authors.initials: D
authors.lastname: Nicastro
authors.forename: Rong
authors.initials: R
authors.lastname: Li
authors.forename: Thomas D
authors.initials: TD
authors.lastname: Pollard
authors.forename: Niels
authors.initials: N
authors.lastname: Volkmann
authors.forename: Dorit
authors.initials: D
authors.lastname: Hanein
mesh_terms: D048248:Acanthamoeba castellanii; D008841:Actin Cytoskeleton / Q000737:chemistry* / Q000648:ultrastructure*; D051376:Actin-Related Protein 2-3 Complex / Q000737:chemistry* / Q000648:ultrastructure*; D000818:Animals; D002417:Cattle; D003198:Computer Simulation; D003599:Cytoskeleton / Q000737:chemistry* / Q000648:ultrastructure*; D019281:Dimerization; D046911:Macromolecular Substances / Q000737:chemistry; D008958:Models, Molecular; D011485:Protein Binding / Q000502:physiology; D020836:Protein Structure, Quaternary / Q000502:physiology; D011817:Rabbits; D012441:Saccharomyces cerevisiae; D014057:Tomography, X-Ray Computed
chemical_list: D051376:Actin-Related Protein 2-3 Complex; D046911:Macromolecular Substances