1: J Mol Biol  1996 Oct 25;263(2):227-36 

Direct measurement of the torsional rigidity of single actin filaments.

Yasuda R, Miyata H, Kinosita K Jr.

Department of Physics, Faculty of Science and Technology, Keio University
Hiyoshi, Yokohama, Japan.

Flexural and torsional rigidities of actin filaments are important factors in
cell motility and muscle contraction, where actin filaments serve as mechanical
elements. The flexural rigidity has already been determined by directly
observing the bending of individual filaments under a microscope, but
measurement of the torsional rigidity has been relatively scarce and indirect,
because torsion of an actin filament is difficult to visualize. This paper shows
that the torsional rigidity can be measured directly by visualizing the
torsional Brownian motion of a single actin filament with a novel methodology
based on an optical trapping technique. Actin filaments (F-actin) were prepared
by polymerizing actin monomers binding Ca2+ ion or Mg2+ ion at the high affinity
site. The torsional rigidity of F-Ca(2+)-actin ((8.5(+/- 1.3)) x 10(-26) N m2)
was about three times as large as that of F-Mg(2+)-actin ((2.8(+/- 0.3)) x
10(-26) N m2), whereas the flexural rigidity ((6.0(+/- 0.2)) x 10(-26) N m2) was
almost independent of the kind of the bound cation. The dynamic structure of
F-actin is regulated by the bound metal in an anisotropic manner. The torsional
rigidities above, whether of F-Ca(2+)-actin or F-Mg(2+)-actin, are one to two
orders of magnitude greater than previous experimental estimates.

PMID: 8913303 [PubMed - indexed for MEDLINE]