Direct Observation of the Interconversion of Normal and Toxic Forms of α-Synuclein

Summary

Here, we use single-molecule techniques to study the aggregation of α-synuclein, the protein whose misfolding and deposition is associated with Parkinson's disease. We identify a conformational change from the initially formed oligomers to stable, more compact proteinase-K-resistant oligomers as the key step that leads ultimately to fibril formation. The oligomers formed as a result of the structural conversion generate much higher levels of oxidative stress in rat primary neurons than do the oligomers formed initially, showing that they are more damaging to cells. The structural conversion is remarkably slow, indicating a high kinetic barrier for the conversion and suggesting that there is a significant period of time for the cellular protective machinery to operate and potentially for therapeutic intervention, prior to the onset of cellular damage. In the absence of added soluble protein, the assembly process is reversed and fibrils disaggregate to form stable oligomers, hence acting as a source of cytotoxic species.

Abstract

Graphical Abstract

Highlights

► A variety of oligomers form during αS amyloid fibril assembly and disaggregation ► A slow process converts early oligomers to stable, proteinase-K-resistant forms ► Oligomers arising from the conversion reaction are more toxic than the early species ► Mature amyloid fibrils can either sequester or release potentially cytotoxic oligomers

Abstract

Single-molecule fluorescence reveals that the cytotoxic species of α-synuclein associated with Parkinson's disease forms via the slow structural conversion of disordered, nontoxic oligomers into a stable form that is toxic to primary neurons and that precedes fibril formation.