title: Expansion of polyglutamine induces the formation of quasi-aggregate in the early stage of protein fibrillization.
abstract: We examined the effects of the expansion of glutamine repeats on the early stage of protein fibrillization. Small-angle x-ray scattering (SAXS) and electron microscopic studies revealed that the elongation of polyglutamine from 35 to 50 repeats in protein induced a large assembly of the protein upon incubation at 37 degrees C and that its formation was completed in approximately 3 h. A bead modeling procedure based on SAXS spectra indicated that the largely assembled species of the protein, quasi-aggregate, is composed of 80 to approximately 90 monomers and a bowl-like structure with long and short axes of 400 and 190 A, respectively. Contrary to fibril, the quasi-aggregate did not show a peak at S = 0.21 A-1 corresponding to the 4.8-A spacing of beta-pleated sheets in SAXS spectra, and reacted with a monoclonal antibody specific to expanded polyglutamine. These results imply that beta-sheets of expanded polyglutamines in the quasi-aggregate are not orderly aligned and are partially exposed, in contrast to regularly oriented and buried beta-pleated sheets in fibril. The formation of non-fibrillary quasi-aggregate in the early phase of fibril formation would be one of the major characteristics of the protein containing an expanded polyglutamine.
authors.affiliation: Laboratory for Structural Neuropathology, RIKEN Brain Science Institute, Saitama 351-0198, Japan.
authors.forename: Motomasa
authors.initials: M
authors.lastname: Tanaka
authors.forename: Yoko
authors.initials: Y
authors.lastname: Machida
authors.forename: Yukihiro
authors.initials: Y
authors.lastname: Nishikawa
authors.forename: Takumi
authors.initials: T
authors.lastname: Akagi
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Hashikawa
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Fujisawa
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Nukina
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000378:metabolism; D002645:Chickens; D002845:Chromatography; D003224:Congo Red / Q000494:pharmacology; D004926:Escherichia coli / Q000378:metabolism; D015151:Immunoblotting; D008854:Microscopy, Electron; D008958:Models, Molecular; D010455:Peptides / Q000737:chemistry*; D011485:Protein Binding; D017433:Protein Structure, Secondary; D011506:Proteins / Q000737:chemistry*; D011994:Recombinant Proteins / Q000737:chemistry; D012542:Scattering, Radiation; D013696:Temperature; D013997:Time Factors; D014466:Ultraviolet Rays; D014961:X-Ray Diffraction; D014965:X-Rays
chemical_list: D000911:Antibodies, Monoclonal; D010455:Peptides; D011506:Proteins; D011994:Recombinant Proteins; C097188:polyglutamine; D003224:Congo Red