Intrinsically disordered domain of kinesin-3 Kif14 enables unique functional diversity

In addition to their force-generating motor domains, kinesin motor proteins feature various accessory domains enabling them to fulfil a variety of functions in the cell. Human kinesin-3, Kif14, localizes to the midbody of the mitotic spindle and is involved in the progression of cytokinesis. The specific motor properties enabling Kif14s cellular functions, however, remain unknown. Here, we show in vitro that it is the intrinsically disordered N-terminal domain of Kif14 that enables unique functional diversity of the motor. Using single molecule TIRF microscopy we observed that the presence of the disordered domain i) increased the Kif14 run-length by an order of magnitude, rendering the motor super-processive and enabling the motor to pass through highly crowded microtubule areas shielded by cohesive layers of microtubule-associated protein tau, which blocks less processive motors ii) enabled robust, autonomous Kif14 tracking of growing microtubule tips, independent of microtubule end-binding (EB) proteins and iii) enabled Kif14 to crosslink parallel microtubules and to drive the relative sliding of antiparallel ones. We explain these features of Kif14 by the observed increased affinity of the disordered domain for GTP-like tubulin and the observed diffusible interaction of the disordered domain with the microtubule lattice. We hypothesize that the disordered domain tethers the motor domain to the microtubule forming a diffusible foothold. We suggest that the intrinsically disordered N-terminal anchoring domain of Kif14 is a regulatory hub supporting the various cellular functions of Kif14 by tuning the motors interaction with microtubules.