title: Mechanisms of ataxin-3 misfolding and fibril formation: kinetic analysis of a disease-associated polyglutamine protein.
abstract: The polyglutamine diseases are a family of nine proteins where intracellular protein misfolding and amyloid-like fibril formation are intrinsically coupled to disease. Previously, we identified a complex two-step mechanism of fibril formation of pathologically expanded ataxin-3, the causative protein of spinocerebellar ataxia type-3 (Machado-Joseph disease). Strikingly, ataxin-3 lacking a polyglutamine tract also formed fibrils, although this occurred only via a single-step that was homologous to the first step of expanded ataxin-3 fibril formation. Here, we present the first kinetic analysis of a disease-associated polyglutamine repeat protein. We show that ataxin-3 forms amyloid-like fibrils by a nucleation-dependent polymerization mechanism. We kinetically model the nucleating event in ataxin-3 fibrillogenesis to the formation of a monomeric thermodynamic nucleus. Fibril elongation then proceeds by a mechanism of monomer addition. The presence of an expanded polyglutamine tract leads subsequently to rapid inter-fibril association and formation of large, highly stable amyloid-like fibrils. These results enhance our general understanding of polyglutamine fibrillogenesis and highlights the role of non-poly(Q) domains in modulating the kinetics of misfolding in this family.
authors.affiliation: Department of Biochemistry and Molecular Biology, PO Box 13D Monash University, 3800, Australia.
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Ellisdon
authors.forename: Mary C
authors.initials: MC
authors.lastname: Pearce
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Bottomley
mesh_terms: D000682:Amyloid / Q000378:metabolism*; D007700:Kinetics; D008027:Light; D017827:Machado-Joseph Disease / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000737:chemistry* / Q000378:metabolism*; D010455:Peptides / Q000378:metabolism*; D017510:Protein Folding; D020836:Protein Structure, Quaternary; D012542:Scattering, Radiation; D012967:Sodium Dodecyl Sulfate / Q000494:pharmacology; D012995:Solubility / Q000187:drug effects / Q000528:radiation effects; D013816:Thermodynamics; D014461:Ultracentrifugation
chemical_list: D000682:Amyloid; D009419:Nerve Tissue Proteins; D010455:Peptides; C097188:polyglutamine; D012967:Sodium Dodecyl Sulfate