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Journal Articles Biophysical Journal Year : 2005

The Interplay between Viscoelastic and Thermodynamic Properties Determines the Birefringence of F-Actin Gels

Abstract

F-actin gels of increasing concentrations (25-300 µM) display in vitro a progressive onset of birefringence due to orientational ordering of actin filaments. At F-actin concentrations <100 µM, this birefringence can be erased and restored at will by sonication and gentle flow, respectively. Hence, the orientational ordering does not result from a thermodynamic transition to a nematic phase but instead is due to mechanical stresses stored in the gels. In contrast, at F-actin concentrations >=100 µM, gels display spontaneous birefringence recovery, at rest, which is the sign of true nematic ordering, in good agreement with statistical physics models of the isotropic/nematic transition. Well-aligned samples of F-actin gels could be produced and their small-angle x-ray scattering patterns are quite anisotropic. These patterns show no sign of filament positional short-range order and could be modeled by averaging the form factor with the Maier-Saupe nematic distribution function. The derived nematic order parameter S of the gels ranged from S = 0.7 at 300 µM to S = 0.4 at 25 µM. Both birefringence and small-angle x-ray scattering data indicate that, even in absence of cross-linking proteins, spontaneous cooperative alignment of actin filaments may arise in motile regions of living cells where F-actin concentrations can reach values of a few 100 µM.

Dates and versions

hal-01960784 , version 1 (11-01-2019)

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Emmanuèle Helfer, Pierre Panine, Marie-France Carlier, Patrick Davidson. The Interplay between Viscoelastic and Thermodynamic Properties Determines the Birefringence of F-Actin Gels. Biophysical Journal, 2005, 89 (1), pp.543-553. ⟨10.1529/biophysj.104.050245⟩. ⟨hal-01960784⟩
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