Nucleotide Exchange in Dimeric MCAK Induces Longitudinal and Lateral Stress at Microtubule Ends to Support Depolymerization

•Hydrolysis relaxes MCAK dimers for effective lattice engagement and diffusion•Dimeric MCAK returns to a closed form upon nucleotide exchange at microtubule ends•HX and EM support dimeric MCAK engaging two tubulin dimers, lateral to each other•The closed form imparts outward curvature and lateral separation, via the N termini

SummaryMembers of the kinesin-13 subfamily use motor domains in an unconventional fashion to initiate microtubule (MT) depolymerization at MT ends, suggesting unique conformational transitions for lattice engagement, end adaptation, or both. Using hydrogen-deuterium exchange and electron microscopy, we explored conformational changes in free dimeric mitotic centromere-associated kinesin (MCAK) and when bound to a depolymerization intermediate. ATP hydrolysis relaxes the conformation of the dimer, notably in the neck and N-terminal domain. Exchanging ADP in dimeric MCAK with ATP at the MT plus end induces outward curvature in α/β-tubulin, accompanied by a restructuring of the MCAK neck and N terminus, as it returns to a closed state. Reestablishing a closed dimer induces lateral separation of paired tubulin dimers, which may assist in depolymerization. Thus, full-length ADP-MCAK transitions from an open diffusion-competent configuration to a closed state upon plus end-mediated nucleotide exchange, which is mediated by conformational changes in the N-terminal domains of the dimer.

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