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.

中文翻译：

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Katanin螺旋和环形结构为微管切断提供了动力冲程的亮点

切断微管的酶katanin，spastin和fidgetin是AAA ATPase，对于轴突，纺锤体和纤毛中复杂的微管阵列的生物发生和维持至关重要。由于这些酶缺乏已知的3D结构，因此对其作用机理仍知之甚少。在这里我们报告秀丽隐杆线虫单体AAA katanin模块的X射线晶体结构和冷冻EM重建六聚体的两个构象。该结构揭示了由微管切割酶特有的结构元件介导的AAA结构域的意外非对称排列，并且对它们的功能至关重要。重建表明，katanin在开环螺旋和闭环构象之间循环，这取决于拉紧或放宽proprotomer界面的门protomer的ATP占有率。这些构象之间的六聚体循环将为微管切断提供动力。