Full-length dimeric MCAK is a more efficient microtubule depolymerase than minimal domain monomeric MCAK

MCAK belongs to the Kinesin-13 family, whose members depolymerize microtubules rather than translocate along them. We defined the minimal functional unit of MCAK as the catalytic domain plus the class specific neck (MD-MCAK), which is consistent with previous reports. We used steady-state ATPase kinetics, microtubule depolymerization assays, and microtubule-MCAK cosedimentation assays to compare the activity of full-length MCAK, which is a dimer, with MD-MCAK, which is a monomer. Full-length MCAK exhibits higher ATPase activity, more efficient microtubule end binding, and reduced affinity for the tubulin heterodimer. Our studies suggest that MCAK dimerization is important for its catalytic cycle by promoting MCAK binding to microtubule ends, enhancing the ability of MCAK to recycle for multiple rounds of microtubule depolymerization, and preventing MCAK from being sequestered by tubulin heterodimers.