Changes in interfacial properties of alpha-synuclein preceding its aggregation
Parkinson's disease (PD) is associated with the formation and deposition of amyloid fibrils of the protein alpha-synuclein (AS). It has been proposed that oligomeric intermediates on the pathway to fibrilization rather than the fibrils themselves are the pathogenic agents of PD, but efficient methods for their detection are lacking. We have studied the interfacial properties of wild-type AS and the course of its aggregation in vitro using electrochemical analysis and dynamic light scattering. The oxidation signals of tyrosine residues of AS at carbon electrodes and the ability of fibrils to adsorb and catalyze hydrogen evolution at hanging mercury drop electrodes (HMDEs) decreased during incubation. HMDEs were particularly sensitive to pre-aggregation changes in AS. Already after 1 h of a standard aggregation assay in vitro (stirring at 37 degrees C), the electrocatalytic peak H increased greatly and shifted to less negative potentials. Between 3 and 9 h of incubation, an interval during which dynamic light scattering indicated AS oligomerization, peak H diminished and shifted to more negative potentials, and AS adsorbability decreased. We tentatively attribute the very early changes in the interfacial behavior of the protein after the first few hours of incubation to protein destabilization with disruption of long-range interactions. The subsequent changes can be related to the onset of oligomerization. Our results demonstrate the utility of electrochemical methods as new and simple tools for the investigation of amyloid formation.