Demonstration of three dopamine molecules bound to <i>α</i>-Synuclein: Implication of oligomerization at the initial stage

α-Synuclein is the major component of the filamentous Lewy bodies and Lewy neurites that define neuropathological features and dementia with Lewy bodies. To investigate the role of dopamine (DA) in α-synuclein fibrillation, the structural propensities to form oligomers at the initial stage fibrillation were studied using size exclusion chromatography and various biophysical techniques. Interactions with DA were observed for wild-type α-synuclein and its mutants, A30P, E46K and A53T, using electrospray ionization mass spectrometry (ESI-MS). The results of ESI-MS indicate that an intact α-synuclein, which was not oxidized, had an ability to bind with three molecules of DA at the initial stage. Furthermore, upon binding to DA, α-synuclein oligomerizes to higher molecular weight species. These oligomers are structurally different from amyloid fibrils, as confirmed by thioflavin T and CD analysis.