title: The Josephin domain determines the morphological and mechanical properties of ataxin-3 fibrils.
abstract: Fibrillar aggregation of the protein ataxin-3 is linked to the inherited neurodegenerative disorder Spinocerebellar ataxia type 3, a member of the polyQ expansion disease family. We previously reported that aggregation and stability of the nonpathological form of ataxin-3, carrying an unexpanded polyQ tract, are modulated by its N-terminal Josephin domain. It was also shown that expanded ataxin-3 aggregates via a two-stage mechanism initially involving Josephin self-association, followed by a polyQ-dependent step. Despite this recent progress, however, the exact mechanism of ataxin-3 fibrilization remains elusive. Here, we have used electron microscopy, atomic force microscopy, and other biophysical techniques to characterize the morphological and mechanical properties of nonexpanded ataxin-3 fibrils. By comparing aggregates of ataxin-3 and of the isolated Josephin domain, we show that the two proteins self-assemble into fibrils with markedly similar features over the temperature range 37-50°C. Estimates of persistence length and Young's modulus of the fibrils reveal a great flexibility. Our data indicate that, under physiological conditions, during early aggregation Josephin retains a nativelike secondary structure but loses its enzymatic activity. The results suggest a key role of Josephin in ataxin-3 fibrillar aggregation.
authors.affiliation: Division of Molecular Structure, Medical Research Council, National Institute for Medical Research, London, United Kingdom.
authors.forename: Laura
authors.initials: L
authors.lastname: Masino
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Nicastro
authors.forename: Alfonso
authors.initials: A
authors.lastname: De Simone
authors.forename: Lesley
authors.initials: L
authors.lastname: Calder
authors.forename: Justin
authors.initials: J
authors.lastname: Molloy
authors.forename: Annalisa
authors.initials: A
authors.lastname: Pastore
mesh_terms: D000067699:Ataxin-3; D001696:Biomechanical Phenomena; D004548:Elasticity; D006801:Humans; D055595:Mechanical Phenomena; D009419:Nerve Tissue Proteins / Q000737:chemistry* / Q000378:metabolism; D009687:Nuclear Proteins / Q000737:chemistry* / Q000378:metabolism; D055503:Protein Multimerization; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D012097:Repressor Proteins / Q000737:chemistry* / Q000378:metabolism; D013696:Temperature
chemical_list: D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D012097:Repressor Proteins; C092341:ATXN3 protein, human; D000067699:Ataxin-3