The microtubule‐binding domain of spastin participates in microtubule severing through electrostatic interactions

Spastin is a microtubule‐severing enzyme and takes part in various microtubule‐based events, but its microtubule‐severing mechanism remains largely elusive. Spastin has an intrinsically unstructured microtubule‐binding domain (MTBD) N‐terminal to the AAA domain that is indispensable for the microtubule‐severing activity. By performing a series of mutagenesis studies, we find that spastin can tolerate the mutation of a small number of basic residues in the MTBD, but mutating half of the basic residues abolishes the basal and microtubule‐stimulated ATPase activities of spastin. The isolated MTBD pellets an equal molar amount of tubulin into curl and ring assemblies. Moreover, spastin with a sequence‐reversed MTBD is active in ATP hydrolysis and microtubule severing. These results suggest that the MTBD of spastin participates in microtubule severing by making electrostatic interactions with microtubule protofilaments.