C-Terminal Truncated α-Synuclein Fibrils Contain Strongly Twisted β-Sheets

C-terminal truncations of monomeric wild-type alpha-synuclein (henceforth WT-alpha S) have been shown to enhance the formation of amyloid aggregates both in vivo and in vitro and have been associated with accelerated progression of Parkinson's disease (PD). The correlation with PD may not solely be a result of faster aggregation, but also of which fibril polymorphs are preferentially formed when the C-terminal residues are deleted. Considering that different polymorphs are known to result in distinct pathologies, it is important to understand how these truncations affect the organization of alpha S into fibrils. Here we present high-resolution microscopy and advanced vibrational spectroscopy studies that indicate that the C-terminal truncation variant of alpha S, lacking residues 109-140 (henceforth referred to as 1-108-alpha S), forms amyloid fibrils with a distinct structure and morphology. The 1-108-alpha S fibrils have a unique negative circular dichroism band at similar to 230 nm, a feature that differs from the canonical similar to 218 nm band usually observed for amyloid fibrils. We show evidence that 1-108-alpha S fibrils consist of strongly twisted beta-sheets with an increased inter-beta-sheet distance and a higher solvent exposure than WT-alpha S fibrils, which is also indicated by the pronounced differences in the 1D-IR (FTIR), 2D-IR, and vibrational circular dichroism spectra. As a result of their distinct beta-sheet structure, 1-108-alpha S fibrils resist incorporation of WT-alpha S monomers.