סמינר בכימיה פיזיקלית: Directionality of biological kinesin-5 nano-motors: old dogma new insights

Abstract:

Kinesin-related motor proteins are biological nano-machines that move along the microtubule filaments using ATP hydrolysis, thus performing essential roles in cell division, vesicle trafficking and cell locomotion. The bipolar kinesin-5 motors perform essential functions in mitotic spindle dynamics by crosslinking and sliding apart antiparallel microtubules of the spindle. 

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. The mechanism of this directionality switch and its physiological significance remain unclear. To understand the mechanism and regulation of the bi-directionality of Cin8 and Kip1, we examined their in vitro motile properties and in vivo functions by TIRF microscopy and live-cell imaging. 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 [3]. Clustering of Cin8 at the minus-end of the MTs serves as a primary site for capturing and antiparallel sliding of the MTs. Based on these results, we propose a revised model for activity of Cin8 and Kip1 during mitosis and propose a physiological role for their minus-end directed motility.

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, 2013. 126(Pt 18): p. 4147-59.

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, 2011. 30(24): p. 4942-54.

3. Shapira, O., et al., A potential physiological role for bi-directional motility and motor clustering of mitotic kinesin-5 Cin8 in yeast mitosis. J Cell Sci, 2017. 130(4): p. 725-734.

מארגני הסמינר: ד"ר שרלי פליישר וד"ר טל שוורץ