Biophysical Studies Reveals the Specific Activities of Fidgetin, a Microtubule Severing AAA Enzyme

Abstract

Cell morphology, development, and differentiation rely on the spatio-temporal dynamics of microtubules. Microtubule dynamics and network remodeling are finely tuned in cells by the orchestrated activity of microtubule-associated proteins (MAPs). Reorganization of the microtubule network is performed by a novel class of MAPs called microtubule severing enzymes that are AAA+ (ATPases Associated with various cellular Activities) family of ATPases. The former member of this novel class of AAA+ enzymes is katanin p60, the catalytic subunit of katanin complex that regulates microtubule length and dynamics in cells during interphase and mitosis and targets to microtubule defects. The newest member of the severing enzyme family is fidgetin, which is involved in mammalian development. We have performed the first biophysical characterization of fidgetin in vitro. Interestingly, at a low concentration this enzyme removes tubulin dimers preferentially from the minus end of the microtubules, making microtubules appear to depolymerizing. At a higher concentration fidgetin severs microtubules. We find that fidgetin targets and severs GMPCPP microtubules better than taxol-stabilized microtubules. Further, fidgetin removes extended regions of protofilaments, in an activity we call “protofilament stripping”. Our results indicate that fidgetin is a microtubule severing enzyme with new and specific biophysical abilities and targeting on microtubules.