Journal: Nature / Year: 2010 Title: Direct visualization of secondary structures of F-actin by electron cryomicroscopy. Authors: Takashi Fujii / Atsuko H Iwane / Toshio Yanagida / Keiichi Namba / Abstract: F-actin is a helical assembly of actin, which is a component of muscle fibres essential for contraction and has a crucial role in numerous cellular processes, such as the formation of lamellipodia ...F-actin is a helical assembly of actin, which is a component of muscle fibres essential for contraction and has a crucial role in numerous cellular processes, such as the formation of lamellipodia and filopodia, as the most abundant component and regulator of cytoskeletons by dynamic assembly and disassembly (from G-actin to F-actin and vice versa). Actin is a ubiquitous protein and is involved in important biological functions, but the definitive high-resolution structure of F-actin remains unknown. Although a recent atomic model well reproduced X-ray fibre diffraction intensity data from a highly oriented liquid-crystalline sol specimen, its refinement without experimental phase information has certain limitations. Direct visualization of the structure by electron cryomicroscopy, however, has been difficult because it is relatively thin and flexible. Here we report the F-actin structure at 6.6 Å resolution, made obtainable by recent advances in electron cryomicroscopy. The density map clearly resolves all the secondary structures of G-actin, such as α-helices, β-structures and loops, and makes unambiguous modelling and refinement possible. Complex domain motions that open the nucleotide-binding pocket on F-actin formation, specific D-loop and terminal conformations, and relatively tight axial but markedly loose interprotofilament interactions hydrophilic in nature are revealed in the F-actin model, and all seem to be important for dynamic functions of actin.
Idetical with deposited unit in distinct coordinate
helical asymmetric unit
Type
Name
Symmetry operation
Number
helical symmetry operation
1
3
Idetical with deposited unit in distinct coordinate
helical asymmetric unit, std helical frame
Type
Name
Symmetry operation
Number
transform to helical frame
1
Symmetry
Helical symmetry: (Circular symmetry: 1 / Dyad axis: no / N subunits divisor: 1 / Num. of operations: 5 / Rise per n subunits: 27.6 Å / Rotation per n subunits: -166.656 °)
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