Mechanism of Actin Network Stabilization by Changes in Polymer Flexibility by Calponin

Abstract

The cellular actin cytoskeleton plays a central role in the ability of cells to properly sense, propagate, and respond to external stresses and other mechanical stimuli. The actin binding protein calponin has been previously implicated in actin cytoskeletal regulation and is thought to act as an actin stabilizer, but the mechanism of its function is poorly understood.To investigate the underlying physical mechanism, we studied an in vitro model system of crosslinked actin using bulk rheology. Networks with basic calponin exhibited a delayed onset of strain stiffening (gamma crit) and were able to withstand higher strains (gamma max) and stresses (sigma max) before failing. Using fluorescence microscopy to study the mechanics of single actin filaments, we found that calponin increased the flexibility of actin filaments. Our data are consistent with current models of affine strain behavior in semiflexible polymer networks, suggesting that calponin stabilization of actin networks can be explained by changes in single filament mechanics. Comparisons to computational models indicate that a reduction of persistence length of individual actin filaments is the primary mechanism by which calponin stabilizes actin networks against shear.Representative stress-strain curve shown below:View Large Image | View Hi-Res Image | Download PowerPoint Slide