title: Ataxin-3 with an altered conformation that exposes the polyglutamine domain is associated with the nuclear matrix.
abstract: Spinocerebellar ataxia type-3 or Machado-Joseph disease (SCA3/MJD) is a member of the CAG/polyglutamine repeat disease family. In this family of disorders, a normally polymorphic CAG repeat becomes expanded, resulting in expression of an expanded polyglutamine domain in the disease gene product. Experimental models of polyglutamine disease implicate the nucleus in pathogenesis; however, the link between intranuclear expression of expanded polyglutamine and neuronal dysfunction remains unclear. Here we demonstrate that ataxin-3, the disease protein in SCA3/MJD, adopts a unique conformation when expressed within the nucleus of transfected cells. The monoclonal antibody 1C2 is known preferentially to bind expanded polyglutamine, but we find that it also binds a fragment of ataxin-3 containing a normal glutamine repeat. In addition, expression of ataxin-3 within the nucleus exposes the glutamine domain of the full-length non-pathological protein, allowing it to bind the monoclonal antibody 1C2. Fractionation and immunochemical experiments indicate that this novel conformation of intranuclear ataxin-3 is not due to proteolysis, suggesting instead that association with nuclear protein(s) alters the structure of full-length ataxin-3 which exposes the polyglutamine domain. This conformationally altered ataxin-3 is bound to the nuclear matrix. The pathological form of ataxin-3 with an expanded polyglutamine domain also associates with the nuclear matrix. These data suggest that an early event in the pathogenesis of SCA3/MJD may be an altered conformation of ataxin-3 within the nucleus that exposes the polyglutamine domain.
authors.affiliation: Department of Pharmacology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6084, USA.
authors.forename: M K
authors.initials: MK
authors.lastname: Perez
authors.forename: H L
authors.initials: HL
authors.lastname: Paulson
authors.forename: R N
authors.initials: RN
authors.lastname: Pittman
mesh_terms: D000911:Antibodies, Monoclonal; D000067699:Ataxin-3; D015153:Blotting, Western; D002460:Cell Line; D000939:Epitopes; D005455:Fluorescent Antibody Technique; D006801:Humans; D017827:Machado-Joseph Disease / Q000235:genetics; D018613:Microscopy, Confocal; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000378:metabolism*; D015530:Nuclear Matrix / Q000378:metabolism*; D009687:Nuclear Proteins; D010455:Peptides / Q000737:chemistry*; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D012097:Repressor Proteins; D014162:Transfection
chemical_list: D000911:Antibodies, Monoclonal; D000939:Epitopes; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D010455:Peptides; D012097:Repressor Proteins; C097188:polyglutamine; C092341:ATXN3 protein, human; D000067699:Ataxin-3