Amino acid sequences flanking polyglutamine stretches influence their potential for aggregate formation

Expanded polyglutamine stretches have been shown to form aggregates and to be toxic to cells. In this study, we hypothesized that amino acid sequences flanking the polyglutamine stretches influence the aggregate formation pot ential of these stretches. Green fluorescent protein (GFP) fusion proteins containing glutamine repeats of various lengths and a fixed number of flank ing amino acids of ataxin-2, huntingtin, clentatorubral-pallidoluysian atro phy protein (DRPLAP) or ataxin-3 were transiently expressed in COS-7 cells. The aggregate formation potential of ataxin-2 and DRPLAP increased in a CA G-repeat-length-dependent manner, with a threshold between 34 and 36. Trunc ated ataxin-2-Q56-GFP and truncated huntingtin-Q56-GFP showed a significant ly higher aggregate formation potential than truncated DRPLAP-Q56-GFP or tr uncated ataxin-3-Q56-GFP. These results are in agreement with the clinical observation that ages of disease onset in patients with spinocerebellar ata xia type 2 or Huntington's disease are lower than those in patients with DR PLA or Machado-Joseph disease having expanded CAG repeats of the same lengt h. Furthermore, mutagenesis of the flanking sequence of ataxin-2 markedly r educed its aggregate formation potential. These results indicate that the a mino acid sequences flanking the polyglutamine stretches significantly infl uence their aggregate formation potential. NeuroReport 12:3357-3364 (C) 200 1 Lippincott Williams & Wilkins.