Defectos en la red de microtúbulos facilitan el corte mediado por espastina

The length regulation of microtubules and their organization into complex arrays inside cells occurs through the activity of polymerases, depolymerases as well as severing enzymes such as spastin and katanin. The latter hexamerize on the microtubule lattice, pull out single tubulin dimers in an ATP-dependent manner and eventually generate internal breaks in the microtubule. While spastin was shown to be regulated by posttranslational tubulin modifications, the impact of microtubule lattice defects on the severing characteristics of spastin has not been explored. To answer this question, we prepared GMPCPP-stabilized microtubules with varying defect densities - introduced either through specific polymerization conditions or by end-to-end annealing - for subsequent in vitro severing assays. We found that (i) the presence of defects accelerated the onset of the severing process and (ii) severing was twice as frequent in microtubule segments with defect sites as compared to random lattice segments. However, there was no evidence of preferential binding of spastin to defect sites. We therefore propose a severing mechanism in which defects do not actively promote microtubule severing but rather passively contribute to microtubule lattice instability, facilitating the process as fewer tubulin subunits are required to be removed for microtubule severing.