Biased localization of actin binding proteins by actin filament conformation

The assembly of actin filaments into distinct cytoskeletal structures plays a critical role in cell movement, shape change, and mechanics, but how different sets of proteins localize to these structures within a shared cytoplasm remains unclear. Here, we show that the actin-binding domains of accessory proteins can be sensitive to filament conformational changes induced by perturbations that include other binding proteins, stabilizing drugs, and physical constraints on the filament. Using a combination of live cell imaging and in vitro single molecule binding measurements, we demonstrate that the affinity of tandem calponin homology domain (CH1-CH2) mutants varies as actin filament twist is altered, and we show differential localization of native and mutant CH1-CH2 domains to actin networks at the front and rear of motile cells. These findings suggest that conformational heterogeneity of actin filaments in cells could influence the biochemical composition of cytoskeletal structures through a biophysical feedback loop.