5m5m | pdb_00005m5m
Pseudo-atomic model of microtubule-bound S.pombe kinesin-5 motor domain in the AMPPNP state (based on cryo-electron microscopy experiment): the N-terminus adopts multiple conformations.
Structural highlights
Function[TBA1D_BOVIN] Tubulin is the major constituent of microtubules. It binds two moles of GTP, one at an exchangeable site on the beta chain and one at a non-exchangeable site on the alpha chain (By similarity). [CUT7_SCHPO] Could be a spindle pole body motor. On transition from G2 to M phase of the cell cycle, the spindle pole body duplicates; the daughter pole bodies seed microtubules which interdigitate to form a short spindle that elongates to span the nucleus at metaphase. Mutations at cut7 block spindle formation. [TBB2B_BOVIN] Tubulin is the major constituent of microtubules. It binds two moles of GTP, one at an exchangeable site on the beta chain and one at a non-exchangeable site on the alpha chain (By similarity). Publication Abstract from PubMedCut7, 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. Schizosaccharomyces pombe kinesin-5 switches direction using a steric blocking mechanism.,Britto M, Goulet A, Rizvi S, von Loeffelholz O, Moores CA, Cross RA Proc Natl Acad Sci U S A. 2016 Nov 22;113(47):E7483-E7489. Epub 2016 Nov 9. PMID:27834216[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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