title: Molecular architecture of the Spire-actin nucleus and its implication for actin filament assembly.
abstract: The Spire protein is a multifunctional regulator of actin assembly. We studied the structures and properties of Spire-actin complexes by X-ray scattering, X-ray crystallography, total internal reflection fluorescence microscopy, and actin polymerization assays. We show that Spire-actin complexes in solution assume a unique, longitudinal-like shape, in which Wiskott-Aldrich syndrome protein homology 2 domains (WH2), in an extended configuration, line up actins along the long axis of the core of the Spire-actin particle. In the complex, the kinase noncatalytic C-lobe domain is positioned at the side of the first N-terminal Spire-actin module. In addition, we find that preformed, isolated Spire-actin complexes are very efficient nucleators of polymerization and afterward dissociate from the growing filament. However, under certain conditions, all Spire constructs--even a single WH2 repeat--sequester actin and disrupt existing filaments. This molecular and structural mechanism of actin polymerization by Spire should apply to other actin-binding proteins that contain WH2 domains in tandem.
authors: Max Planck Institute of Biochemistry, 82152 Martinsried, Germany. sitar@biochem.mpg.de
authors: Tomasz
authors: T
authors: Sitar
authors: Julia
authors: J
authors: Gallinger
authors: Anna M
authors: AM
authors: Ducka
authors: Teemu P
authors: TP
authors: Ikonen
authors: Michael
authors: M
authors: Wohlhoefler
authors: Kurt M
authors: KM
authors: Schmoller
authors: Andreas R
authors: AR
authors: Bausch
authors: Peteranne
authors: P
authors: Joel
authors: Kathleen M
authors: KM
authors: Trybus
authors: Angelika A
authors: AA
authors: Noegel
authors: Michael
authors: M
authors: Schleicher
authors: Robert
authors: R
authors: Huber
authors: Tad A
authors: TA
authors: Holak
mesh_terms: D008841:Actin Cytoskeleton / Q000737:chemistry* / Q000378:metabolism; D000199:Actins / Q000737:chemistry* / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D018360:Crystallography, X-Ray; D029721:Drosophila Proteins / Q000737:chemistry* / Q000378:metabolism; D004331:Drosophila melanogaster / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D008840:Microfilament Proteins / Q000737:chemistry* / Q000378:metabolism; D008856:Microscopy, Fluorescence; D008958:Models, Molecular; D046912:Multiprotein Complexes / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D053838:Scattering, Small Angle; D020080:Tandem Repeat Sequences; D051300:Wiskott-Aldrich Syndrome Protein Family / Q000737:chemistry / Q000378:metabolism; D014961:X-Ray Diffraction
chemical_list: D000199:Actins; D029721:Drosophila Proteins; D008840:Microfilament Proteins; D046912:Multiprotein Complexes; D051300:Wiskott-Aldrich Syndrome Protein Family; C402385:spir protein, Drosophila