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Nat Struct Mol Biol. 2017 Sep;24(9):717-725. doi: 10.1038/nsmb.3448. Epub 2017 Aug 7.

Katanin spiral and ring structures shed light on power stroke for microtubule severing.

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Cell Biology and Biophysics Unit, Porter Neuroscience Research Center, National Institute of Neurological Disorders and Stroke, Bethesda, Maryland, USA.
Biophysics Core, National Heart, Lung and Blood Institute, Bethesda, Maryland, USA.
X-ray Science Division, Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois, USA.
Biochemistry and Biophysics Center, National Heart, Lung and Blood Institute, Bethesda, Maryland, USA.


Microtubule-severing enzymes katanin, spastin and fidgetin are AAA ATPases important for the biogenesis and maintenance of complex microtubule arrays in axons, spindles and cilia. Because of a lack of known 3D structures for these enzymes, their mechanism of action has remained poorly understood. Here we report the X-ray crystal structure of the monomeric AAA katanin module from Caenorhabditis elegans and cryo-EM reconstructions of the hexamer in two conformations. The structures reveal an unexpected asymmetric arrangement of the AAA domains mediated by structural elements unique to microtubule-severing enzymes and critical for their function. The reconstructions show that katanin cycles between open spiral and closed ring conformations, depending on the ATP occupancy of a gating protomer that tenses or relaxes interprotomer interfaces. Cycling of the hexamer between these conformations would provide the power stroke for microtubule severing.

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