Faculty Opinions recommendation of Rotational movement of the formin mDia1 along the double helical strand of an actin filament.

An understanding of the specific interactions of actin with regulatory proteins has been limited by the lack of information about the structure of the actin filament. Molecular actin has been studied in actin-DNase I complexes by single crystal X-ray analysis, to a resolution of about 0.6nm, and in the electron microscope where two dimensional actin sheets have been reconstructed to a maximum resolution of 1.5nm. While these studies have shown something of the structure of individual actin molecules, essential information about the orientation of actin in the filament is still unavailable.The work of Egelman & DeRosier has, however, suggested a method which could be used to provide an initial quantitative estimate of the orientation of actin within the filament. This method involves the quantitative comparison of computed diffraction data from single actin filaments with diffraction data derived from synthetic filaments constructed using the molecular model of actin as a building block. Their preliminary work was conducted using a model consisting of two juxtaposed spheres of equal size.

Download Full-text

The 3-Dimensional Molecular Structure of the Actin Filament Revisited

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100119223 ◽

1985 ◽

Vol 43 ◽

pp. 480-481

Author(s):

U. Aebi ◽

R. Millonig ◽

H. Salvo

Keyword(s):

Actin Filament ◽

Supramolecular Assembly ◽

Specimen Preparation ◽

X Ray Diffraction ◽

Single Filament ◽

X Ray ◽

3 Dimensional ◽

Filament Diameter ◽

Preparation Conditions ◽

Apparent Diameter

To date, most 3-D reconstructions of undecorated actin filaments have been obtained from actin filament paracrystal data (for refs, see 1,2). However, due to the fact that (a) the paracrystals may be several filament layers thick, and (b) adjacent filaments may sustantially interdigitate, these reconstructions may be subject to significant artifacts. None of these reconstructions has permitted unambiguous tracing or orientation of the actin subunits within the filament. Furthermore, measured values for the maximal filament diameter both determined by EM and by X-ray diffraction analysis, vary between 6 and 10 nm. Obviously, the apparent diameter of the actin filament revealed in the EM will critically depend on specimen preparation, since it is a rather flexible supramolecular assembly which can easily be bent or distorted. To resolve some of these ambiguities, we have explored specimen preparation conditions which may preserve single filaments sufficiently straight and helically ordered to be suitable for single filament 3-D reconstructions, possibly revealing molecular detail.

Download Full-text