Amyloid fibrils are a pathological hallmark of several neurodegenerative diseases, including Parkinson, Huntington, and Alzheimer diseases. Though there is much interest in understanding the role amyloid fibrils play in disease progression, collecting detailed structural information on these protein aggregates is inherently difficult due to their insoluble, noncrystalline nature. In this work, we use Raman spectroscopy to characterize structural details of α-synuclein (α-syn) fibrils prepared under different buffer conditions. Raman spectroscopy is sensitive to intrinsic molecular vibrations and can therefore directly report on protein secondary structure without need of additional probes. Raman spectroscopy is particularly advantageous because it can be used to easily study liquids or insoluble precipitates, like amyloid fibrils. Experimentally, the technique is fast and nondestructive, and requires minimal sample volumes (&lt;10 μL of ~15 μM protein fibrils in solution). Many literature examples have shown the amount of β-sheet content of amyloid fibrils can be characterized using the amide-I region of the spectrum, but here we extend our analysis beyond this region and consider more carefully the amide-III and the CH2,CH3 deformation stretching regions of the spectrum to gain insight into fibril structural details. Specifically, we use Raman spectroscopy to show WT-α-syn fibrils formed under different buffer conditions (pH 5 vs pH 7.4) display differences in the amide-I, amide-III, and CH2,CH3 deformation stretches, indicating differences in secondary structure and tertiary contacts by aliphatic sidechains, respectively. Further, we have interrogated solvation effects using H2O/D2O solvent exchange experiments. Because fibrils provide a direct structural link of α-syn to Parkinson's disease, this work provides an important step in establishing Raman spectroscopy as a sensitive technique for structurally characterizing the end-product of aggregation and detecting fibril structural features that may be important in disease progression.

Structural features and solvation effects of α-synuclein amyloid fibrils probed by Raman spectroscopy

254th National Meeting (2017)

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