Role of Residues Undergoing Hereditary Spastic Paraplegias Mutations: Insights from Simulating the Spiral to Ring Transition in Katanin.

Several dozen mutations in the M87 isoform of the spastin enzyme have been associated with mobility impairment in hereditary spastic paraplegias. Some of them impact the structural determinants of two functional conformations of the protein: spiral and ring. Here we investigate the possible patterns between these disease-related residues in spastin and aligned regions in the closely related protein katanin toward their role in the transition of the two conformations, which is essential for both enzymes' function. By performing a variety of molecular simulations (including metadynamics) on katanin, we suggest that about one-fourth of the known M87 spastin disease-associated mutations also affect the interconversion and/or the stability of a previously unrecognized intermediate of the katanin transition. The protocol used here can be applied to the study of conformational changes in other large biomolecular complexes.