REGULATION OF THE BI-DIRECTIONAL MOTILITY OF BIOLOGICAL NANO-MOTOR KINESIN-5 Cin8

The bipolar kinesin-5 biological nano-motors perform essential functions in mitotic spindle dynamics. Until recently, these motors were believed to move exclusively towards the plus-ends of the microtubules (MTs). We have demonstrated that in vitro, S. cerevisiae kinesin-5 motors Cin8 and Kip1 are minus-end directed as single-molecules and switch directionality when binding between antiparallel MTs (1-3). The mechanism of this switch and its physiological significance remain unclear.

Here we show by TIRF microscopy, that single molecules of Cin8 not only move to- but also cluster at the minus-ends of MTs. This clustering induces a directionality switch from fast minus- to slow plus-end directed motility. Clusters of two Cin8 molecules can switch directionality. Cin8 clusters at MT minus-ends are the primary sites for capture and crosslinking of antiparallel MTs leading to productive antiparallel sliding. In early mitotic cells, Cin8 localizes near the spindle poles, at the minus-end of the MTs. Based on these results, we propose a revised model for in vivo Cin8 function: by moving to- and clustering at minus-ends, Cin8 localizes near the spindle poles and promotes antiparallel MT sliding, which is essential to initiate mitotic spindle assembly.

1 Fridman, V. et al. Kinesin-5 Kip1 is a bi-directional motor that stabilizes microtubules and tracks their plus-ends in vivo. J Cell Sci 126, 4147-4159, doi:10.1242/jcs.125153 (2013).

2 Gerson-Gurwitz, A. et al. Directionality of individual kinesin-5 Cin8 motors is modulated by loop 8, ionic strength and microtubule geometry. Embo J 30, 4942-4954 (2011).

3 Duselder, A. et al. Deletion of the Tail Domain of the Kinesin-5 Cin8 affects its directionality. J Biol Chem 19, 620799 (2015).