SPAST

This gene encodes a member of the AAA (ATPases associated with a variety of cellular activities) protein family. Members of this protein family share an ATPase domain and have roles in diverse cellular processes including membrane trafficking, intracellular motility, organelle biogenesis, protein folding, and proteolysis. The encoded ATPase may be involved in the assembly or function of nuclear protein complexes. Two transcript variants encoding distinct isoforms have been identified for this gene. Other alternative splice variants have been described but their full length sequences have not been determined. Mutations associated with this gene cause the most frequent form of autosomal dominant spastic paraplegia 4. [provided by RefSeq, Jul 2008]

Spastin

ATP-dependent microtubule severing protein that specifically recognizes and cuts microtubules that are polyglutamylated (PubMed:11809724, PubMed:15716377, PubMed:16219033, PubMed:17389232, PubMed:20530212, PubMed:22637577, PubMed:26875866).
Preferentially recognizes and acts on microtubules decorated with short polyglutamate tails: severing activity increases as the number of glutamates per tubulin rises from one to eight, but decreases beyond this glutamylation threshold (PubMed:26875866).
Severing activity is not dependent on tubulin acetylation or detyrosination (PubMed:26875866).
Microtubule severing promotes reorganization of cellular microtubule arrays and the release of microtubules from the centrosome following nucleation. It is critical for the biogenesis and maintenance of complex microtubule arrays in axons, spindles and cilia. SPAST is involved in abscission step of cytokinesis and nuclear envelope reassembly during anaphase in cooperation with the ESCRT-III complex (PubMed:19000169, PubMed:21310966, PubMed:26040712).
Recruited at the midbody, probably by IST1, and participates in membrane fission during abscission together with the ESCRT-III complex (PubMed:21310966).
Recruited to the nuclear membrane by IST1 and mediates microtubule severing, promoting nuclear envelope sealing and mitotic spindle disassembly during late anaphase (PubMed:26040712).
Required for membrane traffic from the endoplasmic reticulum (ER) to the Golgi and endosome recycling (PubMed:23897888).
Recruited by IST1 to endosomes and regulates early endosomal tubulation and recycling by mediating microtubule severing (PubMed:23897888).
Probably plays a role in axon growth and the formation of axonal branches (PubMed:15716377).
Isoform 1
Involved in lipid metabolism by regulating the size and distribution of lipid droplets.

Biological Process anterograde axonal transportISS:UniProtKB
Biological Process axonal transport of mitochondrionISS:UniProtKB
Biological Process axonogenesisIEA:UniProtKB-UniRule
Biological Process cytokinetic processManual Assertion Based On ExperimentIMP:UniProtKB
Biological Process cytoskeleton-dependent cytokinesisManual Assertion Based On ExperimentTAS:ARUK-UCL
Biological Process endoplasmic reticulum to Golgi vesicle-mediated transportManual Assertion Based On ExperimentIMP:UniProtKB
Biological Process exit from mitosisManual Assertion Based On ExperimentIMP:UniProtKB
Biological Process membrane fissionManual Assertion Based On ExperimentIMP:UniProtKB
Biological Process metabolic processIEA:UniProtKB-KW
Biological Process microtubule bundle formationManual Assertion Based On ExperimentIDA:UniProtKB
Biological Process microtubule severingManual Assertion Based On ExperimentIDA:UniProtKB
Biological Process mitotic cytokinesisManual Assertion Based On ExperimentIMP:UniProtKB
Biological Process mitotic nuclear membrane reassemblyTAS:Reactome
Biological Process mitotic spindle disassemblyManual Assertion Based On ExperimentIMP:UniProtKB
Biological Process nuclear membrane reassemblyManual Assertion Based On ExperimentIMP:UniProtKB
Biological Process positive regulation of cytokinesisManual Assertion Based On ExperimentIMP:UniProtKB
Biological Process positive regulation of microtubule depolymerizationIEA:UniProtKB-UniRule
Biological Process protein hexamerizationManual Assertion Based On ExperimentIDA:UniProtKB
Biological Process protein homooligomerizationManual Assertion Based On ExperimentIDA:UniProtKB

Membrane
Endoplasmic reticulum
Midbody
Cytoplasm, cytoskeleton, microtubule organizing center, centrosome
Cytoplasm, cytoskeleton
Cytoplasm, perinuclear region
Nucleus
Cytoplasm, cytoskeleton, spindle
Cytoplasm
Cell projection, axon
Forms an intramembrane hairpin-like structure in the membrane (PubMed:20200447).
Localization to the centrosome is independent of microtubules (PubMed:15891913).
Localizes to the midbody of dividing cells, and this requires CHMP1B (PubMed:18997780).
Enriched in the distal axons and branches of postmitotic neurons (PubMed:15269182).
Mainly nuclear in interphase cells and becomes associated with the centrosomes, spindle microtubules, midzone and finally the midbody during cell division (PubMed:15269182).
Isoform 1
Endoplasmic reticulum membrane
Nucleus membrane
Lipid droplet
Cytoplasm, cytoskeleton
Endosome
Forms an intramembrane hairpin-like structure in the membrane (PubMed:20200447).
Recruited to nuclear membrane by IST1 during late anaphase (PubMed:26040712).
Localizes to endoplasmic reticulum tubular network (PubMed:23969831).
Isoform 3
Cytoplasm
Endosome
Nucleus membrane
Cytoplasm, cytoskeleton, microtubule organizing center, centrosome
Constitutes the main endosomal form (PubMed:19000169).
Recruited to nuclear membrane by IST1 during late anaphase (PubMed:26040712).

Spastic paraplegia 4, autosomal dominant (SPG4):
A form of spastic paraplegia, a neurodegenerative disorder characterized by a slow, gradual, progressive weakness and spasticity of the lower limbs. Rate of progression and the severity of symptoms are quite variable. Initial symptoms may include difficulty with balance, weakness and stiffness in the legs, muscle spasms, and dragging the toes when walking. In some forms of the disorder, bladder symptoms (such as incontinence) may appear, or the weakness and stiffness may spread to other parts of the body.

Cytoplasmic: 1-56
Helical: 57-77
Cytoplasmic: 78-616