Factors that Regulate the Directionality of the Kinesin-5 Nano-motor Cin8

Mary Popov mary.popov@gmail.com Mary Popov Sudhir Kumar Singh Leah Gheber
Department of Chemistry and Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev, Beer Sheva, Israel

Mitosis is an essential process by which duplicated genetic information is transmitted from mother to two daughter cells. Incorrect chromosome segregation during mitosis can lead to genetic diseases, chromosome instability and cancer. This process is mediated by a dynamic microtubule-based intracellular structure, the mitotic spindle. The homotetrameric bipolar kinesin-5 nano-motors perform essential functions in mitotic spindle dynamics by crosslinking and sliding apart antiparallel microtubules emanating from opposite poles. S. cerevisiae cells express two kinesin-5 homologues, Cin8 and Kip1, which partially overlap in function.

We have recently demonstrated that the S. cerevisiae kinesin-5 Cin8 and Kip1, are minus-end directed on the single-molecule level and can switch directionality in vitro under a number of conditions (1, 2). These findings broke twenty-five-years old dogma stating that kinesin motors that carry their catalytic domain at the N-terminus are exclusively plus-end directed.

To understand the mechanism, regulation and physiological role of the bi-directionality of Cin8, we examined its motile properties by in vitro single molecule fluorescence motility assay. We found that in vitro, Cin8 not only moves to- but also clusters at the minus-end of the MTs. This clustering causes Cin8 to reverse its directionality from fast minus- to slow plus-end directed motility. To understand the mechanism of this directionality switch, we characterized the dependence of velocity and directionality on the cluster size of Cin8. We also examined the influence of none-motor N-terminal sequences and the large loop-8 in the catalytic domain of Cin8 on its velocity and directionality. Based on these results, we propose a revised model for activity of Cin8 during mitosis and propose a physiological role for its minus-end directed and switchable motility.

  1. Gerson-Gurwitz A, et al. (2011). Embo J 30 (24):4942-4954.

2. Fridman V, et al. (2013). J Cell Sci 126 (18):4147-4159.









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