Structural basis for actin assembly, activation of ATP hydrolysis, and delayed phosphate release.
Assembled actin filaments support cellular signaling, intracellular trafficking, and cytokinesis. ATP hydrolysis triggered by actin assembly provides the structural cues for filament turnover in vivo. Here, we present the cryo-electron microscopic (cryo-EM) structure of filamentous actin (F-actin) in the presence of phosphate, with the visualization of some α-helical backbones and large side chains. A complete atomic model based on the EM map identified intermolecular interactions mediated by bound magnesium and phosphate ions. Comparison of the F-actin model with G-actin monomer crystal structures reveals a critical role for bending of the conserved proline-rich loop in triggering phosphate release following ATP hydrolysis. Crystal structures of G-actin show that mutations in this loop trap the catalytic site in two intermediate states of the ATPase cycle. The combined structural information allows us to propose a detailed molecular mechanism for the biochemical events, including actin polymerization and ATPase activation, critical for actin filament dynamics.
Department of Biosciences, School of Science and Engineering, Teikyo University, Toyosatodai 1-1, Utsunomiya 320-8551, Japan.
Kenji
K
Murakami
Takuo
T
Yasunaga
Taro Q P
TQ
Noguchi
Yuki
Y
Gomibuchi
Kien X
KX
Ngo
Taro Q P
TQ
Uyeda
Takeyuki
T
Wakabayashi
D000199:Actins / Q000737:chemistry* / Q000648:ultrastructure; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D020285:Cryoelectron Microscopy; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D018482:Muscle, Skeletal / Q000737:chemistry* / Q000378:metabolism; D010710:Phosphates / Q000378:metabolism*; D011817:Rabbits
D000199:Actins; D010710:Phosphates; D000255:Adenosine Triphosphate