Polyglutamine expansion mutation yields a pathological epitope linked to nucleation of protein aggregate: determinant of Huntington's disease onset

• Published in: PloS one Vol. 2; no. 7; p. e635
• Main Authors: Sugaya, Keizo, Matsubara, Shiro, Kagamihara, Yasuhiro, Kawata, Akihiro, Hayashi, Hideaki
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 25.07.2007; Public Library of Science (PLoS)
• Subjects: Age; Age of Onset; Agglomeration; Alzheimer Disease - genetics; Alzheimer's disease; Antigenic determinants; Apoptosis; Biochemistry/Protein Folding; Biocompatibility; Biophysics/Protein Folding; Cell Death; Diseases; DNA - blood; DNA - genetics; DNA - isolation & purification; DNA Primers; DNA Repeat Expansion; Drosophila; Epitopes; Expansion; Fibrils; Genes, Reporter; Genetic aspects; Glutamine; Glutamine - genetics; Humans; Huntingtin; Huntington Disease - genetics; Huntington Disease - metabolism; Huntington Disease - pathology; Huntington's disease; Huntingtons disease; Insects; Kinetics; Monoclonal antibodies; Monomers; Movement disorders; Mutation; Nervous system diseases; Neurodegeneration; Neurodegenerative diseases; Neurological diseases; Neurological Disorders; Neurological Disorders/Neurogenetics; Neurology; Nucleation; Parkinson Disease - genetics; Parkinson's disease; Pathogenesis; Peptides; Peptides - genetics; Peptides - metabolism; Plasmids; Polyglutamine diseases; Polyleucine; Polylysine - genetics; Polymerase Chain Reaction; Polymerization; Protein folding; Protein interaction; Protein structure; Proteins; Reaction kinetics; Surface structure; Toxicity; Transfection; Trinucleotide repeat diseases; β-Amyloid
• DOI: 10.1371/journal.pone.0000635
• ISSN: 1932-6203

Polyglutamine (polyQ) expansion mutation causes conformational, neurodegenerative diseases, such as Alzheimer's and Parkinson's diseases. These diseases are characterized by the aggregation of misfolded proteins, such as amyloid fibrils, which are toxic to cells. Amyloid fibrils are formed by a nucleated growth polymerization reaction. Unexpectedly, the critical nucleus of polyQ aggregation was found to be a monomer, suggesting that the rate-limiting nucleation process of polyQ aggregation involves the folding of mutated protein monomers. The monoclonal antibody 1C2 selectively recognizes expanded pathogenic and aggregate-prone glutamine repeats in polyQ diseases, including Huntington's disease (HD), as well as binding to polyleucine. We have therefore assayed the in vitro and in vivo aggregation kinetics of these monomeric proteins. We found that the repeat-length-dependent differences in aggregation lag times of variable lengths of polyQ and polyleucine tracts were consistently related to the integration of the length-dependent intensity of anti-1C2 signal on soluble monomers of these proteins. Surprisingly, the correlation between the aggregation lag times of polyQ tracts and the intensity of anti-1C2 signal on soluble monomers of huntingtin precisely reflected the repeat-length dependent age-of-onset of HD patients. These data suggest that the alterations in protein surface structure due to polyQ expansion mutation in soluble monomers of the mutated proteins act as an amyloid-precursor epitope. This, in turn, leads to nucleation, a key process in protein aggregation, thereby determining HD onset. These findings provide new insight into the gain-of-function mechanisms of polyQ diseases, in which polyQ expansion leads to nucleation rather than having toxic effects on the cells.