title: Early nucleation events in the polymerization of actin, probed by time-resolved small-angle x-ray scattering.
abstract: Nucleators generating new F-actin filaments play important roles in cell activities. Detailed information concerning the events involved in nucleation of actin alone in vitro is fundamental to understanding these processes, but such information has been hard to come by. We addressed the early process of salt-induced polymerization of actin using the time-resolved synchrotron small-angle X-ray scattering (SAXS). Actin molecules in low salt solution maintain a monomeric state by an electrostatic repulsive force between molecules. On mixing with salts, the repulsive force was rapidly screened, causing an immediate formation of many of non-polymerizable dimers. SAXS kinetic analysis revealed that tetramerization gives the highest energetic barrier to further polymerization, and the major nucleation is the formation of helical tetramers. Filaments start to grow rapidly with the formation of pentamers. These findings suggest an acceleration mechanism of actin assembly by a variety of nucleators in cells.
authors: X-ray Structural Analysis Research Team, RIKEN SPring-8 Center, RIKEN Harima Institute, Kouto 1-1, Sayo, Hyogo 679-5148, Japan.
authors: Toshiro
authors: T
authors: Oda
authors: X-ray Structural Analysis Research Team, RIKEN SPring-8 Center, RIKEN Harima Institute, Kouto 1-1, Sayo, Hyogo 679-5148, Japan.
authors: Tomoki
authors: T
authors: Aihara
authors: X-ray Structural Analysis Research Team, RIKEN SPring-8 Center, RIKEN Harima Institute, Kouto 1-1, Sayo, Hyogo 679-5148, Japan.|Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan.
authors: Katsuzo
authors: K
authors: Wakabayashi
mesh_terms: D008841:Actin Cytoskeleton / Q000737:chemistry / Q000378:metabolism; D000199:Actins / Q000737:chemistry*; D000465:Algorithms; D000818:Animals; D002645:Chickens; D007700:Kinetics; D009124:Muscle Proteins / Q000737:chemistry*; D058105:Polymerization; D055503:Protein Multimerization; D053838:Scattering, Small Angle; D013816:Thermodynamics; D014961:X-Ray Diffraction / Q000379:methods*
chemical_list: D000199:Actins; D009124:Muscle Proteins