Spastin pulls tubulin out of shape

It's easier to snap a twig with two hands than one, and the same goes for snapping microtubules. By binding to tubulin in two places, a microtubule-severing protein can exert the force necessary to pull the polymer apart, according to White et al. (page 995).

Microtubule-severing spastin is a member of the AAA ATPase family, which often breaks down multiprotein complexes. The team now shows that spastin, like other AAAs, forms ring-shaped hexamers. They find that spastin must use two different binding domains—one on the outside of the ring and one on the loop domains inside the ring—to lock onto tubulin and cause severing.

The spastin ring is too small to fit around the whole microtubule. Instead, the team shows, spastin binds to two spots on the...