Structural analysis of muscle thin filament

Akihiro Tomioka, Hans O. Ribi, Makio Tokunaga, Taiji Furuno, Hiroyuki Sasabe, Kenjiro Miyano, Takeyuki Wakabayashi

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Abstract

Thin sheets of Ac-Tm-Tn paracrystals were prepared in the presence of high concentration of Ca2+ ion and three-dimensional image analysis was performed. The optical diffraction pattern of an electron micrograph showed spots up to 1/1.6 nm-1 in the radial direction and up to 1/2.5 nm-1 in the axial direction, the best resolution ever obtained so far. The translationally filtered image showed clear polarity of filament which looked like a "spearhead" per each crossover repeat of actin helix. The three-dimensionally reconstructed model looked very similar to the inner regions (A+B domains) of the Ac-Tm-S1 complex obtained by Toyoshima and Wakabayashi (14, 15) when they were placed so that the "spearhead" pattern of the Tc-Tm-Tn complex and the "arrowhead" pattern of the Ac-Tm-S1 complex pointed in the same direction. The myosin-binding site of actin was identified by comparison of two structures. The model of actin molecule cut out from the thin filament model had a low density region within itself, which was located about 2.5 nm from the helix axis. That low density region divided actin molecule into two domains, a large and a small domain. A dense "pillar" was detected which connected two neighboring actin molecules along a left-handed generic helix 1 nm from the helix axis. Two actin-actin binding sites which were responsible for the connection through the "pillar" were located on the inner surface of actin molecule. To obtain better crystalline arrays of actin, we tried a method utilizing adsorption to lipid. A positively-charged monolayer of lipids was formed on the surface of a small volume of buffer solution which was put in a microwell. Solution of negatively-charged F-actin was then injected into the buffer solution and was allowed to be joined to the lipid monolayer by electrostatic attraction. Fluidity of the lipid monolayer enabled the two-dimensional crystallization of actin. Electron microscopy revealed that larger paracrystalline arrays were formed more rapidly (< 1 hr) than those formed within solution, which demonstrated the advantage of this adsorption method.

Original languageEnglish
Pages (from-to)169-183
Number of pages15
JournalAdvances in Biophysics
Volume27
Issue numberC
DOIs
Publication statusPublished - 1991

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ASJC Scopus subject areas

  • Biophysics
  • Biochemistry

Cite this

Tomioka, A., Ribi, H. O., Tokunaga, M., Furuno, T., Sasabe, H., Miyano, K., & Wakabayashi, T. (1991). Structural analysis of muscle thin filament. Advances in Biophysics, 27(C), 169-183. https://doi.org/10.1016/0065-227X(91)90016-7