Katanin P60 Targets Microtubules with Defects

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Microtubules form and reorganize a variety of networks in cells, including the mitotic spindle, cilia, and neuronal processes. The organization and remodeling of microtubule architecture is regulated by microtubule-associated proteins (MAPs). Microtubule severing enzymes are a novel class of MAPs that regulate filaments by cutting them anywhere along their length. Microtubule severing enzymes, such as Katanin, oligomerize into hexamers and hydrolyze ATP to sever microtubules. Previous work has shown that Katanin specifically targets defects in the microtubules. Using in vitro single molecule assays with GFP labeled Katanin p60, the catalytic subunit of Katanin, we show that Katanin severs microtubules made in high salt more frequently. High salt microtubules have been shown to have fewer than the typical 13 protofilaments and a high incidence of protofilament shifts. We also measured the activity of Katanin on subtilisin treated microtubules (normal and high-salt) which have the c-terminal tails of alpha and beta tubulin cleaved off. Using these types of microtubules has given us insight into what types of defects Katanin might target and a better understanding of its mechanism of severing.