Sensitive electrochemical detection of native and aggregated α-synuclein protein involved in Parkinson's disease

The aggregation of alpha-synuclein, a 14 kDa protein, is involved in several human neurodegenerative disorders, including Parkinson's disease. We studied native and in vitro aggregated alpha-synuclein by circular dichroism (CD), atomic force microscopy (AFM) and electrochemical methods. We used constant current chronopotentiometric stripping analysis (CPSA) to measure hydrogen evolution catalyzed by alpha-synuclein (peak H) at hanging mercury drop electrodes (HMDE) and square-wave stripping voltammetry (SWSV) to monitor tyrosine oxidation at carbon paste electrodes (CPE). To decrease the volume of the analyte, most of the electrochemical measurements were performed by adsorptive transfer (medium exchange) from 3 - 6 muL drops of alpha-synuclein samples. With both CPE and HMDE we observed changes in electrochemical responses of alpha-synuclein corresponding to protein fibrillization detectable by CD, fluorescence and AFM. Aggregation-induced changes in peak H at HMDE were relatively large in strongly aggregated samples, suggesting that this electrochemical signal may find use in the analysis of early stages of alpha-synuclein aggregation. This assumption was documented by marked changes in the peak H potential and height in samples withdrawn at the end of the lag and the beginning of the elongation phase. Native alpha-synuclein can be detected down to subnanomolar concentrations by CPSA.