Elucidating the Alpha-Synuclein Fibril Fold by Pulsed EPR

Abstract

Amyloid fibrils are constituents of the plaques that are the hallmarks of neurogdegenerative diseases. In Parkinson's disease, these plaques (Lewy bodies) consist predominantly of the α-synuclein (αS) protein. To understand and interfere with aggregation, the structure of the fibrils (right Fig., green) needs to be known. Here we study the molecular architecture of the fibrils of αS by measuring distances between pairs of residues in the protein using double electron-electron paramagnetic resonance (DEER). Site-specific spin labeling was employed to create nine doubly labeled αS-variants that were investigated in the fibrillar state. Diamagnetic dilution with wild-type αS suppressed intermolecular interactions. The intramolecular distances provide constraints for the fold of the protein inside the fibril. Intramolecular distances were unambiguously observed for four pairs (41/69, 56/69, 56/90 and 69/90). Three of these distances (arrows) provide the constraints to suggest a model for the fold between residues 56 and 90 in the fibril (light blue). Assuming that only parallel β-sheets occur (l.-blue arrows), a model of four adjacent β-strands results (II-V), in which the strands comprise of eight to twelve residues each.View Large Image | View Hi-Res Image | Download PowerPoint Slide