Kinesin-14: A League of their Own

Abstract

Kinesin-14 represents a subfamily of kinesins that are nonprocessive, promote microtubule (MT) minus-end-directed force generation, and contain C-terminal motor domains that are dimerized through an N-terminal coiled-coil. Unlike the well-known N-terminal motor domain kinesins that use an asymmetric hand-over-hand mechanism for MT plus-end-directed processive stepping, Kinesin-14s use a MT minus-end-directed powerstroke to generate force to crosslink and slide one MT relative to another. While most Kinesin-14s are homodimers like Drosophila Ncd, S. cerevisiae Kar3Vik1 is a heterodimer. The C-terminal domain of Vik1 exhibits the structural fold of a kinesin motor domain, binds MTs independent of Kar3, yet lacks a nucleotide-binding site. Furthermore, Kar3Vik1 binds across adjacent MT protofilaments, a non-canonical MT binding configuration. The results indicate that Kar3Vik1 collides with the MT through Vik1, promoting MT binding by Kar3. The tight binding of Kar3 destabilizes the Vik1 interaction with the MT, positioning Kar3Vik1 for the start of the powerstroke. Rapid ATP binding to Kar3 is associated with the rotation of the coiled-coil stalk, and post-powerstroke ATP hydrolysis is independent of Vik1 providing additional evidence that Vik1 rotates with the coiled-coil during the powerstroke. Detachment of Kar3Vik1 from the MT completes the cycle and allows the motor to return to its initial conformation. Supported by NIH GM54141.