Schizosaccharomyces pombe kinesin-5 switches direction using a steric blocking mechanism.Britto, M., Goulet, A., Rizvi, S., von Loeffelholz, O., Moores, C.A., Cross, R.A.
(2016) Proc. Natl. Acad. Sci. U.S.A. 113: E7483-E7489
- PubMed: 27834216
- DOI: 10.1073/pnas.1611581113
- Primary Citation of Related Structures:  5M5I, 5M5L, 5M5N, 5M5O
- PubMed Abstract:
Cut7, the sole kinesin-5 in Schizosaccharomyces pombe, is essential for mitosis. Like other yeast kinesin-5 motors, Cut7 can reverse its stepping direction, by mechanisms that are currently unclear. Here we show that for full-length Cut7, the key det ...
Cut7, the sole kinesin-5 in Schizosaccharomyces pombe, is essential for mitosis. Like other yeast kinesin-5 motors, Cut7 can reverse its stepping direction, by mechanisms that are currently unclear. Here we show that for full-length Cut7, the key determinant of stepping direction is the degree of motor crowding on the microtubule lattice, with greater crowding converting the motor from minus end-directed to plus end-directed stepping. To explain how high Cut7 occupancy causes this reversal, we postulate a simple proximity sensing mechanism that operates via steric blocking. We propose that the minus end-directed stepping action of Cut7 is selectively inhibited by collisions with neighbors under crowded conditions, whereas its plus end-directed action, being less space-hungry, is not. In support of this idea, we show that the direction of Cut7-driven microtubule sliding can be reversed by crowding it with non-Cut7 proteins. Thus, crowding by either dynein microtubule binding domain or Klp2, a kinesin-14, converts Cut7 from net minus end-directed to net plus end-directed stepping. Biochemical assays confirm that the Cut7 N terminus increases Cut7 occupancy by binding directly to microtubules. Direct observation by cryoEM reveals that this occupancy-enhancing N-terminal domain is partially ordered. Overall, our data point to a steric blocking mechanism for directional reversal through which collisions of Cut7 motor domains with their neighbors inhibit their minus end-directed stepping action, but not their plus end-directed stepping action. Our model can potentially reconcile a number of previous, apparently conflicting, observations and proposals for the reversal mechanism of yeast kinesins-5.
Centre for Mechanochemical Cell Biology, Warwick Medical School, University of Warwick, Coventry CV4 7AL, United Kingdom.