title: A conserved amphipathic helix in WASP/Scar proteins is essential for activation of Arp2/3 complex.
abstract: Members of the Wiskott-Aldrich syndrome protein (WASP) family link Rho GTPase signaling pathways to the cytoskeleton through a multiprotein assembly called Arp2/3 complex. The C-terminal VCA regions (verprolin-homology, central hydrophobic, and acidic regions) of WASP and its relatives stimulate Arp2/3 complex to nucleate actin filament branches. Here we show by differential line broadening in NMR spectra that the C (central) and A (acidic) segments of VCA domains from WASP, N-WASP and Scar bind Arp2/3 complex. The C regions of these proteins have a conserved sequence motif consisting of hydrophobic residues and an arginine residue. Point mutations in this conserved sequence motif suggest that it forms an amphipathic helix that is required in biochemical assays for activation of Arp2/3 complex. Key residues in this motif are buried through contacts with the GTPase binding domain in the autoinhibited structure of WASP and N-WASP, indicating that sequestration of these residues is an important aspect of autoinhibition.
authors.affiliation: Department of Biochemistry, University of Texas Southwestern Medical Center at Dallas, 5323 Harry Hines Boulevard, Dallas, Texas 75390, USA.
authors.forename: Sanjay C
authors.initials: SC
authors.lastname: Panchal
authors.forename: Donald A
authors.initials: DA
authors.lastname: Kaiser
authors.forename: Eduardo
authors.initials: E
authors.lastname: Torres
authors.forename: Thomas D
authors.initials: TD
authors.lastname: Pollard
authors.forename: Michael K
authors.initials: MK
authors.lastname: Rosen
mesh_terms: D051377:Actin-Related Protein 2; D051378:Actin-Related Protein 3; D000595:Amino Acid Sequence; D001665:Binding Sites; D003598:Cytoskeletal Proteins / Q000737:chemistry* / Q000378:metabolism*; D006801:Humans; D046911:Macromolecular Substances; D008958:Models, Molecular; D008969:Molecular Sequence Data; D046912:Multiprotein Complexes; D019906:Nuclear Magnetic Resonance, Biomolecular; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D051316:Wiskott-Aldrich Syndrome Protein
chemical_list: C495926:ACTR2 protein, human; C495928:ACTR3 protein, human; D051377:Actin-Related Protein 2; D051378:Actin-Related Protein 3; D003598:Cytoskeletal Proteins; D046911:Macromolecular Substances; D046912:Multiprotein Complexes; D011506:Proteins; C495767:WAS protein, human; D051316:Wiskott-Aldrich Syndrome Protein