Membrane interactions accelerate the self-aggregation of huntingtin exon 1 fragments in a polyglutamine length-dependent manner

Abstract

The accumulation of aggregated protein is a typical hallmark of many human neurodegenerative disorders including Huntington's disease. Misfolding of the amyloidogenic proteins gives rise to self-assembled complexes and fibers. The huntingtin protein is characterized by a segment of consecutive glutamines, which when exceeding a certain number of residues results in the occurrence of the disease.Furthermore, it has also been demonstrated that the 17-residue amino-terminal domain of the protein (htt17), located upstream of this polyglutamine tract, strongly correlates with aggregate formation and pathology. Here we demonstrate that membrane interactions strongly accelerate the oligomerization and β-amyloid fibril formation of htt17-polyglutamine segments. By using a combination of biophysical approaches the kinetics of fibre formation has been quantitatively investigated and found to be strongly dependent to the presence of lipids, the length of the polyQ expansion and the polypeptide-to-lipid ratio. Finally, the implications for therapeutic approaches are discussed. Statement of significance:The quantitative analysis of the aggregation kinetics of amino-terminal fragments of huntingtin demonstrate the importance of the 17residue amino-terminal membrane anchor and a resulting dominant effect of membranes in promoting the aggregation of polyglutamines. Other parameters further modulating the association kinetics are the length of the polyglutamine stretch and the peptide concentration. The findings can have important impact on finding new therapies to treat Huntington's and other polyglutamine related diseases.

Characterization of binding specificity using GST-conjugated mutant huntingtin epitopes in surface plasmon resonance (SPR)

“…These polyglutamine tracts are also prone to intracellular aggregation and inclusion formation. Aggregation of mutant huntingtin has been shown to be promoted by increasing the number of polyglutamine repeats (Cooper et al, 1998;Li and XJ, 1998;Marquette et al, 2021). The mechanism causing protein aggregation is unknown, but one possibility is that the normal protein conformation is destabilized in the presence of an expanded polyglutamine tract, which leads to abnormal proteinprotein interactions and the formation of aggregates.…”