Study of the mechano-chemical regulation in actin depolymerization kinetics
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A fundamental yet unresolved issue in cell biology is how force regulates actin dynamics and how this biophysical regulation is modulated by biochemical signaling molecules. Here we show, by atomic force microscopy (AFM) force-clamp experiments, that tensile force regulates the kinetics of G-actin/G-actin and G-actin/F-actin interactions by decelerating dissociation at low forces (catch bonds) and accelerating dissociation at high forces (slip bonds). The catch bonds can be structurally explained by force-induced formation of new interactions between actin subunits (Steered molecular dynamics (SMD) simulations performed by Dr. Jizhong Lou, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China). K113S mutation on yeast actin suppressed the actin catch-slip bonds, supporting the structural mechanism proposed by SMD simulations. Moreover, formin controlled by a RhoA-mediated auto-inhibitory module can serve as a "molecular switch", converting the catch-slip bonds to slip-only. These results imply anisotropic stability of the actin network in cells subjected to directional forces, possibly explaining force-induced cell and actin fiber alignment controlled by RhoA and formin. Our study suggests a molecular level crosstalk mechanism bridging the actin-mediated mechanotransduction and biochemical signal transduction pathways.