Aggregation of polyQ proteins is increased upon yeast aging and affected by Sir2 and Hsf1: novel quantitative biochemical and microscopic assays

PLoS One. 2012;7(9):e44785. doi: 10.1371/journal.pone.0044785. Epub 2012 Sep 6.


Aging-related neurodegenerative disorders, such as Parkinson's, Alzheimer's and Huntington's diseases, are characterized by accumulation of protein aggregates in distinct neuronal cells that eventually die. In Huntington's disease, the protein huntingtin forms aggregates, and the age of disease onset is inversely correlated to the length of the protein's poly-glutamine tract. Using quantitative assays to estimate microscopically and capture biochemically protein aggregates, here we study in Saccharomyces cerevisiae aging-related aggregation of GFP-tagged, huntingtin-derived proteins with different polyQ lengths. We find that the short 25Q protein never aggregates whereas the long 103Q version always aggregates. However, the mid-size 47Q protein is soluble in young logarithmically growing yeast but aggregates as the yeast cells enter the stationary phase and age, allowing us to plot an "aggregation timeline". This aging-dependent aggregation was associated with increased cytotoxicity. We also show that two aging-related genes, SIR2 and HSF1, affect aggregation of the polyQ proteins. In Δsir2 strain the aging-dependent aggregation of the 47Q protein is aggravated, while overexpression of the transcription factor Hsf1 attenuates aggregation. Thus, the mid-size 47Q protein and our quantitative aggregation assays provide valuable tools to unravel the roles of genes and environmental conditions that affect aging-related aggregation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Blotting, Western
  • DNA-Binding Proteins / metabolism
  • DNA-Binding Proteins / physiology*
  • Heat-Shock Proteins / metabolism
  • Heat-Shock Proteins / physiology*
  • Microscopy, Fluorescence
  • Peptides / metabolism*
  • Saccharomyces cerevisiae / cytology
  • Saccharomyces cerevisiae / physiology*
  • Saccharomyces cerevisiae Proteins / metabolism
  • Saccharomyces cerevisiae Proteins / physiology*
  • Silent Information Regulator Proteins, Saccharomyces cerevisiae / metabolism
  • Silent Information Regulator Proteins, Saccharomyces cerevisiae / physiology*
  • Sirtuin 2 / metabolism
  • Sirtuin 2 / physiology*
  • Transcription Factors / metabolism
  • Transcription Factors / physiology*


  • DNA-Binding Proteins
  • HSF1 protein, S cerevisiae
  • Heat-Shock Proteins
  • Peptides
  • Saccharomyces cerevisiae Proteins
  • Silent Information Regulator Proteins, Saccharomyces cerevisiae
  • Transcription Factors
  • polyglutamine
  • SIR2 protein, S cerevisiae
  • Sirtuin 2

Grants and funding

Initial stages of this study were supported by a grant from the Chief Scientist Office of the Ministry of Health, Israel (grant no. 3–3211 to SB) and later by a grant from The Israel Science Foundation (grant no. 384/11 to SB). IN is supported in part by the Edmond J. Safra Center for Bioinformatics at Tel Aviv University. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.