Torsional motion of eosin-labeled F-actin as detected in the time-resolved anisotropy decay of the probe in the sub-millisecond time range

Direct Measurement of the Torsional Rigidity of Single Actin Filaments

“…Optical anisotropy decays also gave much smaller k T than ours: 00.2 × 10 −26 N m for eosinlabeled F-Mg 2+ -actin in solution (Yoshimura et al, 1984), and 0.14 × 10 −26 N m for erythrosin-labeled F-Ca 2+ -actin in solution (Prochniewicz et al, 1996). These experimental estimates are difficult to reconcile with our new results.…”

“…However, we note in the literature, including the work of those groups reporting a very low torsional rigidity, that the effect of phalloidin on properties related to the filament rigidity is, at most, a factor of two: it is unlikely that phalloidin explains the order of magnitude difference between our rigidity values and the previous estimates. Thus, in the optical anisotropy decay measurements, phalloidin did not affect the decay characteristics (Yoshimura et al, 1984) or only slightly (40%) decreased the torsional rigidity (Prochniewicz et al, 1996). In the electron microscopic analysis (Orlova & Egelman, 1993), phalloidin did not increase the rigidity when added to normal actin filaments.…”

“…Because an actin filament sliding on myosin has been shown to undergo axial rotation (Nishizaka et al, 1993), as has also been shown for a microtubule driven by dynein (Vale & Toyoshima, 1988) or kinesin (Ray et al, 1993), the torsional rigidity of F-actin should also be a key factor for the actomyosin function. To date, however, the torsional rigidity has been measured only indirectly (Egelman et al, 1982;Egelman & DeRosier, 1992;Yoshimura et al, 1984;Prochniewicz et al, 1996). The values obtained in these studies are 1 to 2 orders of magnitude smaller than the flexural rigidity measured under an optical microscope (Yanagida et al, 1984;Ott et al, 1993;Gittes et al, 1993;Isambert et al, 1995), suggesting that the structure of an actin filament cannot be regarded as a homogenous isotropic rod.…”

“…In this sense, the elastic properties of F-actin on the scale of micrometers are not very different from those of a homogenous isotropic rod. However, experimental work (Egelman et al, 1982;Egelman & DeRosier, 1992;Yoshimura et al, 1984;Prochniewicz et al, 1996) has indicated a torsional rigidity one to two orders of magnitude smaller than the flexural rigidity. Thus, a torsional angular disorder Df of 5°t o 6°between two consecutive actin protomers in a filament has been suggested from electron microscopic images (Egelman et al, 1982;Egelman & DeRosier, 1992).…”

Modulation of actin mechanics by caldesmon and tropomyosin

“…Similarly, it has been shown using time-resolved phosphorescence anisotropy that cofilin [Prochniewicz et al, 2005] and gelsolin [Prochniewicz et al, 1996] increase the torsional flexibility of actin, whereas myosin decreases the torsional flexibility [Prochniewicz and Thomas, 1997] and phalloidin has no effect at all [Yoshimura et al, 1984]. Furthermore, EM data shows that cortactin binding to actin causes an increase in the variance in the angle of twist of actin [Pant et al, 2006] and thus an increase in the torsional flexibility [Yoshimura et al, 1984]. Thus it appears that different ABPs can affect the torsional and flexural properties of actin differently.…”