Cofilin increases the bending flexibility of actin filaments: implications for severing and cell mechanics

J Mol Biol. 2008 Sep 5;381(3):550-8. doi: 10.1016/j.jmb.2008.05.055. Epub 2008 May 29.


We determined the flexural (bending) rigidities of actin and cofilactin filaments from a cosine correlation function analysis of their thermally driven, two-dimensional fluctuations in shape. The persistence length of actin filaments is 9.8 microm, corresponding to a flexural rigidity of 0.040 pN microm(2). Cofilin binding lowers the persistence length approximately 5-fold to a value of 2.2 microm and the filament flexural rigidity to 0.0091 pN microm(2). That cofilin-decorated filaments are more flexible than native filaments despite an increased mass indicates that cofilin binding weakens and redistributes stabilizing subunit interactions of filaments. We favor a mechanism in which the increased flexibility of cofilin-decorated filaments results from the linked dissociation of filament-stabilizing ions and reorganization of actin subdomain 2 and as a consequence promotes severing due to a mechanical asymmetry. Knowledge of the effects of cofilin on actin filament bending mechanics, together with our previous analysis of torsional stiffness, provide a quantitative measure of the mechanical changes in actin filaments associated with cofilin binding, and suggest that the overall mechanical and force-producing properties of cells can be modulated by cofilin activity.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Actin Cytoskeleton / chemistry
  • Actin Cytoskeleton / physiology*
  • Animals
  • Biomechanical Phenomena
  • Cofilin 2 / physiology*
  • Computer Simulation
  • Cytoskeleton / physiology*
  • Microfilament Proteins / physiology*
  • Pliability
  • Rabbits


  • Cofilin 2
  • Microfilament Proteins