BPS2026 – Chiral motion in actomyosin systems: Exploring structural determinants through myosin protein engineering

The power stroke of myosin motor proteins is understood to play a central role in force generation by producing directed motion along the axis of the actin filament. However, off-axis components of myosin’s power stroke may also contribute to directional off-axis force generation, leading to torque accumulation in actin filaments, chiral actin rotation, and chiral bending of actin gliding trajectories. These chiral aspects of actomyosin motor function may have important roles in symmetry breaking at higher orders of biological organization, including up to the organismal-scale. In this work, we demonstrate that by manipulating the lever arm geometry of myosin XI, we can alter the magnitude and direction (clockwise vs. counterclockwise) of actin filament curvature in gliding assays. Myosin lever arm variants produce a range of actin gliding curvatures, inspiring the use of structural models to explore the connection between power stroke geometry and off-axis force generation. By introducing optogenetic modules into myosin’s lever arm, we are able to dynamically change the curvature of actin filament trajectories in response to blue-light stimulation. Finally, we characterize the relationships between lever arm geometry, filament gliding curvature, and higher order symmetry breaking in active actomyosin materials such as crosslinked actin disks and dense actin chiral rings. These results provide insight into poorly understood dimensions of myosin motor activity, and contribute to an understanding of how symmetry breaking at the individual myosin scale can produce handed actomyosin network structures.