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Cell Biology International (2010) 34, 933–942 (Printed in Great Britain)

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The composition of the polyglutamine-containing proteins influences their co-aggregation properties

Daniel Bąk*† and Michał Milewski*¹

*Laboratory of Cell Biology, Department of Medical Genetics, Institute of Mother and Child, Kasprzaka 17a, 01211 Warsaw, Poland, and †Postgraduate School of Molecular Medicine, wirki i Wigury 61, 02091 Warsaw, Poland

The sequestration of crucial cellular proteins into insoluble aggregates formed by the polypeptides containing expanded polyglutamine tracts has been proposed to be the key mechanism responsible for the abnormal cell functioning in the so-called polyglutamine diseases. To evaluate to what extent the ability of polyglutamine sequences to recruit other proteins into the intracellular aggregates depends on the composition of the aggregating peptide, we analysed the co-aggregation properties of the N-terminal fragment of huntingtin fused with unrelated non-aggregating and/or self-aggregating peptides. We show that the ability of the mutated N-terminal huntingtin fragment to sequester non-related proteins can be significantly increased by fusion with the non-aggregating reporter protein [GFP (green fluorescence protein)]. By contrast, fusion with the self-aggregating C-terminal fragment of the CFTR (cystic fibrosis transmembrane conductance regulator) dramatically reduces the sequestration of related non-fused huntingtin fragments. We also demonstrate that the co-aggregation of different non-fused N-terminal huntingtin fragments depends on their length, with long fragments of the wild-type huntingtin not only excluded from the nuclear inclusions, but also very inefficiently sequestered into the cytoplasmic aggregates formed by the short fragments of mutant protein. Additionally, our results suggest that atypical intracellular aggregation patterns, which include unusual distribution and/or morphology of protein aggregates, are associated with altered ability of accumulating proteins to co-aggregate with other peptides.

Key words: co-aggregation, huntingtin, Huntington's disease, polyglutamine, protein aggregation

Abbreviations: CFTR, cystic fibrosis transmembrane conductance regulator, DAPI, 4, 6-diamidino-2-phenylindole, GFP, green fluorescence protein, HA, haemagglutinin

¹To whom correspondence should be addressed (email milewski@imid.med.pl).

Received 8 December 2009/6 May 2010; accepted 1 June 2010

Published as Cell Biology International Immediate Publication 1 June 2010, doi:10.1042/CBI20090474

© The Author(s) Journal compilation © 2010 Portland Press Limited