title: Three-dimensional reconstructions of actin filaments capped by Arp2/3 complex.
abstract: The primary function of Arp2/3 complex is the generation of free barbed ends by nucleating new filaments from the sides of pre-existing filaments. The pathway of branch formation is complex and involves nucleation promoting factors, actin monomers and nucleotides. A less prominent function of Arp2/3 complex is capping of actin filament pointed ends. Here we show, using electron microscopy, electron tomography, and image reconstruction of negatively-stained samples at ∼2-3nm resolution, that Arp2/3 complex bound to the pointed ends of actin filaments has a conformation similar to that in the branch junction with the Arps arranged in an actin-filament like configuration. This is direct evidence for the existence of two distinct activation pathways for Arp2/3 complex, one in the context of branch formation, one in the context of pointed-end capping, with essentially the same conformational end point.
authors.affiliation: Sanford-Burnham Medical Research Institute, 10901 North Torrey Pines Road, La Jolla, CA 92037, USA. Electronic address: niels@burnham.org.
authors.forename: Niels
authors.initials: N
authors.lastname: Volkmann
authors.affiliation: Sanford-Burnham Medical Research Institute, 10901 North Torrey Pines Road, La Jolla, CA 92037, USA.
authors.forename: Christopher
authors.initials: C
authors.lastname: Page
authors.affiliation: The Stowers Institute for Medical Research, 1000 East 50th Street, Kansas City, MO 64110, USA; Department of Molecular and Integrative Physiology, University of Kansas Medical Center, 3901 Rainbow Boulevard, Kansas City, KS 66160, USA.
authors.forename: Rong
authors.initials: R
authors.lastname: Li
authors.affiliation: Sanford-Burnham Medical Research Institute, 10901 North Torrey Pines Road, La Jolla, CA 92037, USA.
authors.forename: Dorit
authors.initials: D
authors.lastname: Hanein
mesh_terms: D048248:Acanthamoeba castellanii; D051344:Actin Capping Proteins / Q000378:metabolism; D008841:Actin Cytoskeleton / Q000737:chemistry* / Q000378:metabolism; D051376:Actin-Related Protein 2-3 Complex / Q000737:chemistry* / Q000378:metabolism; D011487:Protein Conformation; D055503:Protein Multimerization
chemical_list: D051344:Actin Capping Proteins; D051376:Actin-Related Protein 2-3 Complex
keywords: Actin cytoskeleton; Cell motility; Electron microscopy; Fitting; Image analysis