Polyglutamine expansion in ataxin-3 does not affect protein stability: implications for misfolding and disease.
Polyglutamine proteins that cause neurodegenerative disease are known to form proteinaceous aggregates, such as nuclear inclusions, in the neurons of affected patients. Although polyglutamine proteins have been shown to form fibrillar aggregates in a variety of contexts, the mechanisms underlying the aberrant conformational changes and aggregation are still not well understood. In this study, we have investigated the hypothesis that polyglutamine expansion in the protein ataxin-3 destabilizes the native protein, leading to the accumulation of a partially unfolded, aggregation-prone intermediate. To examine the relationship between polyglutamine length and native state stability, we produced and analyzed three ataxin-3 variants containing 15, 28, and 50 residues in their respective glutamine tracts. At pH 7.4 and 37 degrees C, Atax3(Q50), which lies within the pathological range, formed fibrils significantly faster than the other proteins. Somewhat surprisingly, we observed no difference in the acid-induced equilibrium and kinetic un/folding transitions of all three proteins, which indicates that the stability of the native conformation was not affected by polyglutamine tract extension. This has led us to reconsider the mechanisms and factors involved in ataxin-3 misfolding, and we have developed a new model for the aggregation process in which the pathways of un/folding and misfolding are distinct and separate. Furthermore, given that native state stability is unaffected by polyglutamine length, we consider the possible role and influence of other factors in the fibrillization of ataxin-3.
Chow
Michelle K M
MK
Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria 3800, Australia.
Ellisdon
Andrew M
AM
Cabrita
Lisa D
LD
Bottomley
Stephen P
SP
D000067699:Ataxin-3; D002942:Circular Dichroism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D009419:Nerve Tissue Proteins / Q000235:genetics* / Q000378:metabolism*; D019636:Neurodegenerative Diseases / Q000378:metabolism; D009687:Nuclear Proteins; D010455:Peptides / Q000378:metabolism*; D011487:Protein Conformation; D011489:Protein Denaturation; D017510:Protein Folding; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins
D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D010455:Peptides; D020033:Protein Isoforms; D012097:Repressor Proteins; C097188:polyglutamine; C092341:ATXN3 protein, human; D000067699:Ataxin-3