A compact beta model of huntingtin toxicity

Area of Science:

• Neuroscience
• Molecular Biology
• Biochemistry

Background:

• Huntington disease (HD) is a neurodegenerative disorder caused by mutations in the huntingtin (HTT) gene.
• Pathology involves neuronal loss and protein aggregates of N-terminal HTT fragments with expanded polyglutamine (polyQ) regions.
• The specific structure of mutant HTT that drives toxicity remains poorly understood, though a beta-sheet conformation is hypothesized.

Purpose of the Study:

• To investigate the role of compact beta-sheet structures in the aggregation and toxicity of mutant huntingtin N-terminal fragments.
• To design and test cellular models expressing specific beta-rich variants of Htt exon 1.

Main Methods:

• Mammalian cell expression constructs encoding compact beta variants of Htt exon 1 were designed.
• Aggregation and toxicity assays were performed in cultured neuronal cells.
• Molecular dynamics simulations were used to analyze structural properties.
• An antibody (3B5H10) recognizing compact beta-rich hairpin structures was employed.

Main Results:

• Molecular dynamics simulations indicated that expanded polyQ beta-strands are stabilized by main-chain hydrogen bonding.
• A correlation was observed between reactivity to the 3B5H10 antibody and the induction of cell toxicity.
• Designed Htt exon 1 variants showed varying aggregation and toxicity profiles.

Conclusions:

• A compact beta-sheet structure plays a significant role in the cellular toxicity induced by mutant huntingtin.
• These findings provide structural insights into Huntington disease pathogenesis.
• Targeting these specific beta structures may offer therapeutic avenues for HD.