Severing Enzymes Amplify Microtubule Arrays through Lattice GTP-Tubulin Incorporation

Abstract

Spastin and katanin sever and destabilize microtubules. Their mutation causes debilitating diseases. Paradoxically, despite their destructive activity they increase microtubule mass in spindles, plant cortical arrays and neurons. Combining electron and single-molecule TIRF microscopy we show that the elemental step in microtubule-severing is the generation of nanoscale damage throughout the microtubule by active extraction of tubulin heterodimers. These damage sites are repaired spontaneously by GTP-tubulin incorporation. As a result, the microtubule shaft is rejuvenated with GTP-tubulin islands that stabilize it against depolymerization and newly severed ends emerge with a high-density of GTP-tubulin that protects against depolymerization. Consequently, spastin and katanin increase microtubule rescue frequency without affecting growth rates and catastrophe. The stabilization of the newly severed plus-ends and the higher rescue frequency synergize to amplify microtubule number and mass. Thus, severing enzymes regulate microtubule architecture and dynamics by promoting GTP-tubulin incorporation within the microtubule shaft.