ATP-dependent microtubule severing protein. Stimulates microtubule minus-end depolymerization and poleward microtubule flux in the mitotic spindle (PubMed:15242610, PubMed:15562320, PubMed:15823537, PubMed:16276413, PubMed:17452528, PubMed:25875445, PubMed:18202664, PubMed:19341724). Regulates microtubule stability in the neuromuscular junction synapse (PubMed:15242610, PubMed:15562320, PubMed:19341724). Involved in lipid metabolism by regulating the size and distribution of lipid droplets (PubMed:25875445). Involved in axon regeneration by regulating microtubule severing (PubMed:23122959). n ATP + n H2O + a microtubule = n ADP + n phosphate + (n+1) alpha/beta tubulin heterodimers. Homohexamer. The homohexamer is stabilized by ATP-binding. The homohexamer may adopt a ring conformation through which microtubules pass prior to being severed (PubMed:18202664). Interacts with microtubules (PubMed:15823537, PubMed:18202664). Interacts with atl; may be involved in microtubule dynamics (PubMed:19341724). Forms a intramembrane hairpin-like structure in the membrane (By similarity). Colocalizes with cellular microtubule arrays. Localizes to chromosomes from prometaphase/metaphase to anaphase, and this requires microtubules (PubMed:17452528). Localizes to discrete punctate cytoplasmic foci which may correspond to secretory vesicles (PubMed:15823537). Maternally expressed in early embryogenesis with high expression until blastoderm. At the cell formation stage, strongly expressed near the basal part of the cell layer underlying the surface. During germband extension and stomodeal plate formation, expressed in the ventral head and trunk ectoderm, as well as in cells near the cephalic furrow and in the invaginating hindgut and midgut primordia. After germband retraction and delamination of neuroblasts at stage 13, expressed in subsets of cells in all neuromeres of the CNS including those of the supraesophageal and subesophageal ganglia. In later embryonic stages expressed in cell clusters throughout the supraesophageal ganglion, with pronounced expression also seen in the subesophageal ganglion. In the ventral nerve cord (VNC), expressed in two broad longitudinal stripes located laterally, and weakly expressed in some midline cells. Also expressed in some sensory head organs of the peripheral nervous system (PNS), most probably the Bolwigs organs and/or the dorsal organs. Expressed in the developing larval neuromusculature, muscles and neuronal axons. Enriched in neuromuscular junctions throughout the muscles of the body wall. Enriched in punctate domains of synaptic boutons and excluded from interbouton axonal connections. Colocalizes with the synaptic vesicle pools. Loss of protein expression throughout the embryo leads to pupal lethality. Loss of protein expression specifically in the nervous system causes synaptic undergrowth and a reduction in total synaptic area. Neuromuscular junction boutons are smaller and more numerous. Microtubule stability appears to be enhanced within neuronal axons and at neuromuscular junctions and synaptic currents are increased. Older flies exhibit numerous vacuoles in the neuropil and cortex. Adult coordination and locomotory behavior are compromised and lifespan is reduced. RNAi-mediated knockdown results in climbing defects, which can be rescued following exposure to the drugs methylene blue, phenazine, or N-acetyl-L-cysteine (PubMed:26744324). RNAi-mediated knockdown results in increased oxidative stress, which can be rescued following exposure to the drug methylene blue (PubMed:26744324). Belongs to the AAA ATPase family. Spastin subfamily.