MCAK Recognizes the Nucleotide-Dependent Feature at Growing Microtubule Ends

The growing plus-end is a key regulatory site for microtubule dynamics. MCAK (mitotic centromere-associated kinesin), a microtubule depolymerizing kinesin, is an end-binding regulator of catastrophe frequency. It is intriguing how MCAK specifically binds to growing microtubule ends. Here, we measure the end-binding kinetics of MCAK using single-molecule imaging, and reveal that MCAK binds to the entire GTP cap, including the region where EB1 preferentially binds and the distalmost tip. Further analysis shows that MCAK strongly binds to GTPγS microtubules, and this binding preference is dependent on the nucleotide state of MCAK. This finding suggests that MCAK recognizes the nucleotide-dependent feature of microtubules. Moreover, we show that although MCAK and XMAP215 partly share binding regions at the distalmost ends, their regulatory effects can be additive, highlighting a simple rule of how the end-binding regulators coordinate their activities. Overall, our findings provide new insights into how MCAK regulates microtubule end dynamics.