title: Three-color single molecule imaging shows WASP detachment from Arp2/3 complex triggers actin filament branch formation.
abstract: During cell locomotion and endocytosis, membrane-tethered WASP proteins stimulate actin filament nucleation by the Arp2/3 complex. This process generates highly branched arrays of filaments that grow toward the membrane to which they are tethered, a conflict that seemingly would restrict filament growth. Using three-color single-molecule imaging in vitro we revealed how the dynamic associations of Arp2/3 complex with mother filament and WASP are temporally coordinated with initiation of daughter filament growth. We found that WASP proteins dissociated from filament-bound Arp2/3 complex prior to new filament growth. Further, mutations that accelerated release of WASP from filament-bound Arp2/3 complex proportionally accelerated branch formation. These data suggest that while WASP promotes formation of pre-nucleation complexes, filament growth cannot occur until it is triggered by WASP release. This provides a mechanism by which membrane-bound WASP proteins can stimulate network growth without restraining it. DOI:http://dx.doi.org/10.7554/eLife.01008.001.
authors.affiliation: Department of Biochemistry , Brandeis University , Waltham , United States.
authors.forename: Benjamin A
authors.initials: BA
authors.lastname: Smith
authors.forename: Shae B
authors.initials: SB
authors.lastname: Padrick
authors.forename: Lynda K
authors.initials: LK
authors.lastname: Doolittle
authors.forename: Karen
authors.initials: K
authors.lastname: Daugherty-Clarke
authors.forename: Ivan R
authors.initials: IR
authors.lastname: Corrêa
authors.forename: Ming-Qun
authors.initials: MQ
authors.lastname: Xu
authors.forename: Bruce L
authors.initials: BL
authors.lastname: Goode
authors.forename: Michael K
authors.initials: MK
authors.lastname: Rosen
authors.forename: Jeff
authors.initials: J
authors.lastname: Gelles
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism*; D051376:Actin-Related Protein 2-3 Complex / Q000378:metabolism*; D003116:Color; D007700:Kinetics; D051316:Wiskott-Aldrich Syndrome Protein / Q000378:metabolism*
chemical_list: D051376:Actin-Related Protein 2-3 Complex; D051316:Wiskott-Aldrich Syndrome Protein
keywords: Human; S. cerevisiae; TIRF; WH2; Wiskott-Aldrich syndrome protein; activation; nucleation; verprolin homology