Mechanics of F-actin characterized with microfabricated cantilevers

In this report we characterized the longitudinal elasticity of single actin filaments manipulated by novel silicon-nitride microfabricated levers. Single actin filaments were stretched from zero tension to maximal physiological tension, P-o. The obtained length-tension relation was nonlinear in the low-tension range (0-50 pN) with a resultant strain of similar to0.4-0.6% and then became linear at moderate to high tensions (similar to50-230 pN). In this region, the stretching stiffness of a single rhodamine-phalloidin-labeled, 1-mum-long F-actin is 34.5 +/- 3.5 pN/nm. Such a length-tension relation could be characterized by an entropic-enthalpic worm-like chain model, which ascribes most of the energy consumed in the nonlinear portion to overcoming thermal undulations. arising from the filament's interaction with surrounding solution and the linear portion to the intrinsic stretching elasticity. By fitting the experimental data with such a worm-like chain model, an estimation of persistence length of similar to8.75 mum was derived. These results suggest that F-actin is more compliant than previously thought and that thin filament compliance may account for a substantial fraction of the sarcomere's elasticity.