Expansion of Polyglutamine Induces the Formation of Quasi-aggregate in the Early Stage of Protein Fibrillization*
- Motomasa Tanaka‡,
- Yoko Machida‡,
- Yukihiro Nishikawa§,
- Takumi Akagi¶,
- Tsutomu Hashikawa¶,
- Tetsuro Fujisawa§ and
- Nobuyuki Nukina‡∥
- ‡Laboratory for Structural Neuropathology, RIKEN Brain Science Institute, Saitama 351-0198, Japan, the §Laboratory for Structural Biology, RIKEN Harima Institute/SPring-8, Hyogo 351-0198, Japan, and the ¶Laboratory for Neural Architecture, RIKEN Brain Science Institute, Saitama 351-0198, Japan
- ∥ To whom correspondence should be addressed: Laboratory for Structural Neuropathology, RIKEN Brain Science Institute, 2-1 Hirosawa, Wako-City, Saitama 351-0198, Japan. Tel.: 81-48-467-9702; Fax: 81-48-462-4796; E-mail: nukina{at}brain.riken.go.jp.
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 °C and that its formation was completed in ∼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 ∼90 monomers and a bowl-like structure with long and short axes of 400 and 190 Å, respectively. Contrary to fibril, the quasi-aggregate did not show a peak at S = 0.21 Å–1 corresponding to the 4.8-Å spacing of β-pleated sheets in SAXS spectra, and reacted with a monoclonal antibody specific to expanded polyglutamine. These results imply that β-sheets of expanded polyglutamines in the quasi-aggregate are not orderly aligned and are partially exposed, in contrast to regularly oriented and buried β-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.
Footnotes
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↵1 The abbreviations used are: Mb, myoglobin; WT, wild type; SAXS, small-angle X-ray scattering; MOPS, 4-morpholinepropanesulfonic acid; SVD, singular value deconvolution; DAMMIN, dummy atom minimization.
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↵2 Y. Nishikawa and T. Fujisawa, unpublished results.
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↵* This study was partly supported by grants-in-aid from the Ministry of Health, Labor and Welfare (to N. N.) and from the Ministry of Education, Culture, Sports, Science and Technology (to M. T., T. F., and N. N.), Japan. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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- Received September 25, 2002.
- Revision received June 16, 2003.
- The American Society for Biochemistry and Molecular Biology, Inc.
