title: The role of spartin and its novel ubiquitin binding region in DALIS occurrence.
abstract: Troyer syndrome is an autosomal recessive hereditary spastic paraplegia (HSP) caused by frameshift mutations in the SPG20 gene that results in a lack of expression of the truncated protein. Spartin is a multifunctional protein, yet only two conserved domains--a microtubule-interacting and trafficking domain and a plant-related senescence domain involved in cytokinesis and mitochondrial physiology, respectively--have been defined. We have shown that overexpressed spartin binds to the Ile44 hydrophobic pocket of ubiquitin, suggesting spartin might contain a ubiquitin-binding domain. In the present study, we demonstrate that spartin contributes to the formation of dendritic aggresome-like induced structures (DALIS) through a unique ubiquitin-binding region (UBR). Using short hairpin RNA, we knocked down spartin in RAW264.7 cells and found that DALIS frequency decreased; conversely, overexpression of spartin increased the percentage of cells containing DALIS. Using nuclear magnetic resonance spectroscopy, we characterized spartin's UBR and defined the UBR's amino acids that are key for ubiquitin binding. We also found that spartin, via the UBR, binds Lys-63-linked ubiquitin chains but does not bind Lys-48-linked ubiquitin chains. Finally, we demonstrate that spartin's role in DALIS formation depends on key residues within its UBR.
authors: Department of Molecular Pharmacology and Therapeutics, Loyola University Chicago, Maywood, IL 60153 Department of Chemistry, State University of New York at Albany, Albany, NY 12222 Department of Physiology, University of Pennsylvania, Philadelphia, PA 19104 Department of Oncology, University of Wisconsin-Madison, Madison, WI 53705.
authors: Amelia B
authors: AB
authors: Karlsson
authors: Jacqueline
authors: J
authors: Washington
authors: Valentina
authors: V
authors: Dimitrova
authors: Christopher
authors: C
authors: Hooper
authors: Alexander
authors: A
authors: Shekhtman
authors: Joanna C
authors: JC
authors: Bakowska
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism*; D002460:Cell Line; D022083:Cytoplasmic Structures / Q000276:immunology / Q000378:metabolism*; D003713:Dendritic Cells / Q000166:cytology* / Q000276:immunology; D005982:Glutathione Transferase / Q000235:genetics; D006801:Humans; D051379:Mice; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D034622:RNA Interference; D034741:RNA, Small Interfering; D015419:Spastic Paraplegia, Hereditary / Q000235:genetics; D025801:Ubiquitin / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; D034741:RNA, Small Interfering; C562344:SPG20 protein, mouse; D025801:Ubiquitin; D005982:Glutathione Transferase