Horizontal Magnetic Tweezers to Directly Measure the Force–Velocity Relationship for Multiple Kinesin Motors

Abstract Transport of intracellular cargo along cytoskeletal filaments is often achieved by the concerted action of multiple motor molecules. While single‐molecule studies have provided profound insight into the mechano‐chemical principles and force generation of individual motors, studies on multi‐motor systems are less advanced. Here, a horizontal magnetic‐tweezers setup is applied, capable of producing up to 150 pN of horizontal force onto 2.8 µm superparamagnetic beads, to motor‐propelled cytoskeletal filaments. It is found that kinesin‐1 driven microtubules decorated with individual beads display frequent transitions in their gliding velocities which we attribute to dynamic changes in the number of engaged motors. Applying defined temporal force‐ramps the force–velocity relationship is directly measured for multi‐motor transport. It is found that the stall forces of individual motors are approximately additive and collective backward motion of the transport system under super‐stall forces is observed. The magnetic‐tweezers apparatus is expected to be readily applicable to a wide range of molecular and cellular motility assays.