Kinesin-1 is a cytoskeletal motor that transports cargos toward the microtubule plus end. Optical trapping experiments have suggested that kinesin-1 behaves as a “slippery” motor, prone to rapid detachment and seemingly unable to work cooperatively to generate substantial collective forces. A likely explanation is that the radial ( z axis) forces present in standard bead-trapping assays accelerate motor dissociation from microtubules. To address this, we reduced the z-force by linking the trapped bead to the motor through a long DNA handle and then analyzed the motility and force output of both single and multiple kinesin-1 molecules. In this load regime, kinesin-1 withstands hindering loads without readily detaching, though it disengages rapidly under assisting loads even when z-forces are minimal. Moreover, we observe strong, nearly proportional force production by groups of kinesin-1. These results clarify how ensembles of kinesin-1 cooperate to perform functions that require more force than a single motor can produce.
Hensley et al. (Sun,) studied this question.