Department of Cell and Molecular Biology, Northwestern University, Chicago, IL 60611, USA.
Kinesin-1 is a molecular motor protein that transports cargo along microtubules. Inside cells, the vast majority of kinesin-1 is regulated to conserve ATP and to ensure its proper intracellular distribution and coordination with other molecular motors. Regulated kinesin-1 folds in half at a hinge in its coiled-coil stalk. Interactions between coiled-coil regions near the enzymatically active heads at the N terminus and the regulatory tails at the C terminus bring these globular elements in proximity and stabilize the folded conformation. However, it has remained a mystery how kinesin-1's microtubule-stimulated ATPase activity is regulated in this folded conformation. Here, we present evidence for a direct interaction between the kinesin-1 head and tail. We photochemically cross-linked heads and tails and produced an 8-A cryoEM reconstruction of the cross-linked head-tail complex on microtubules. These data demonstrate that a conserved essential regulatory element in the kinesin-1 tail interacts directly and specifically with the enzymatically critical Switch I region of the head. This interaction suggests a mechanism for tail-mediated regulation of the ATPase activity of kinesin-1. In our structure, the tail makes simultaneous contacts with the kinesin-1 head and the microtubule, suggesting the tail may both regulate kinesin-1 in solution and hold it in a paused state with high ADP affinity on microtubules. The interaction of the Switch I region of the kinesin-1 head with the tail is strikingly similar to the interactions of small GTPases with their regulators, indicating that other kinesin motors may share similar regulatory mechanisms.