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Proteasome degrades soluble expanded polyglutamine completely and efficiently.
Andrej Michalik1, Christine Van Broeckhoven
1Department of Molecular Genetics, Flanders Interuniversity Institute for Biotechnology (VIB), University of Antwerp (UIA), Antwerpen, Belgium.
Neurobiology of Disease
|June 23, 2004
Summary
Expanded polyglutamine proteins in neurodegenerative diseases are degraded by the proteasome. This suggests that protein degradation, not aggregation, may be key to polyglutamine toxicity in diseases like Huntington's.
Area of Science:
- Neurobiology
- Molecular Biology
- Genetics
Background:
- Nine progressive neurodegenerative diseases, including Huntington's disease and spinocerebellar ataxias, result from expanded CAG repeats encoding polyglutamine.
- Expanded polyglutamine's toxic gain-of-function is linked to aggregation, which inhibits the proteasome, suggesting impaired protein degradation contributes to toxicity.
Purpose of the Study:
- To investigate if soluble proteins with expanded polyglutamine interfere with proteasome-mediated degradation.
- To determine the degradation efficiency of proteins with normal versus expanded polyglutamine lengths.
Main Methods:
- Transfected cells expressing model proteasome substrates with either 103 (expanded) or 25 (normal) glutamines.
- Analysis of protein degradation rates and proteasome activity.
Main Results:
- Both expanded and normal-length polyglutamine proteins were degraded completely and with similar efficiency.
- Targeting expanded polyglutamine for proteasomal degradation did not impair proteasome function.
Conclusions:
- Soluble polyglutamine proteins are readily degraded by the proteasome.
- The proteasome efficiently degrades expanded polyglutamine, challenging the notion that impaired degradation is the primary driver of polyglutamine toxicity.