title: ER network formation and membrane fusion by atlastin1/SPG3A disease variants.
abstract: At least 38 distinct missense mutations in the neuronal atlastin1/SPG3A GTPase are implicated in an autosomal dominant form of hereditary spastic paraplegia (HSP), a motor-neurological disorder manifested by lower limb weakness and spasticity and length-dependent axonopathy of corticospinal motor neurons. Because the atlastin GTPase is sufficient to catalyze membrane fusion and required to form the ER network, at least in nonneuronal cells, it is logically assumed that defects in ER membrane morphogenesis due to impaired fusion activity are the primary drivers of SPG3A-associated HSP. Here we analyzed a subset of established atlastin1/SPG3A disease variants using cell-based assays for atlastin-mediated ER network formation and biochemical assays for atlastin-catalyzed GTP hydrolysis, dimer formation, and membrane fusion. As anticipated, some variants exhibited clear deficits. Surprisingly however, at least two disease variants, one of which represents that most frequently identified in SPG3A HSP patients, displayed wild-type levels of activity in all assays. The same variants were also capable of co-redistributing ER-localized REEP1, a recently identified function of atlastins that requires its catalytic activity. Taken together, these findings indicate that a deficit in the membrane fusion activity of atlastin1 may be a key contributor, but is not required, for HSP causation.
authors.affiliation: Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA 15213.
authors.forename: Idil
authors.initials: I
authors.lastname: Ulengin
authors.affiliation: Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA 15213.
authors.forename: John J
authors.initials: JJ
authors.lastname: Park
authors.affiliation: Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA 15213 thl@andrew.cmu.edu.
authors.forename: Tina H
authors.initials: TH
authors.lastname: Lee
mesh_terms: D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D029721:Drosophila Proteins / Q000502:physiology; D004331:Drosophila melanogaster; D004721:Endoplasmic Reticulum / Q000502:physiology*; D019204:GTP-Binding Proteins / Q000502:physiology*; D006367:HeLa Cells; D006801:Humans; D008561:Membrane Fusion; D008565:Membrane Proteins / Q000502:physiology*; D026901:Membrane Transport Proteins / Q000378:metabolism; D020125:Mutation, Missense; D016716:PC12 Cells; D055550:Protein Stability; D051381:Rats; D015419:Spastic Paraplegia, Hereditary / Q000235:genetics*
chemical_list: D029721:Drosophila Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; C495318:REEP1 protein, human; C440006:ATL1 protein, human; D019204:GTP-Binding Proteins