Slow and steady wins the race: encounters of myosin-5 and myosin-6 on shared actin filaments

In the cellular environment multiple myosins use the same filamentous actin (F-actin) tracks, yet little is known about how this track sharing is achieved and maintained. To assess the influence that different myosin classes have on each other, we developed an assay that combines two dynamic elements: elongating actin filaments with identified barbed and pointed ends, and myosins moving along these filaments. We studied two different myosins, myosin-5 and myosin-6. These myosins have distinct functions in the cell and are known to travel in opposite directions along actin filaments. Myosin-5 walks towards the barbed end of F-actin and generally into dynamically rearranging actin at the cell periphery. Myosin-6 is a pointed-end directed myosin that generally walks towards the cell center. We successfully reconstituted simultaneous bidirectional motility of myosin-5 and myosin-6 on single polymerizing filaments of actin. We report and provide statistical analysis of encounters between myosin-5 and myosin-6 walking along the single filaments. When myosin-5 and myosin-6 collide, myosin-5 detaches more frequently than myosin-6. The experimental observations are consistent with a stochastic stepping model based upon known myosin kinetics, which suggests that faster motors are more likely to detach.