Self-oligomerization and protein aggregation of α-synuclein in the presence of coomassie brilliant blue

Abstract

α-Synuclein has been implicated in various neuro-degenerative disorders, including Parkinson's and Alzheimer's diseases, by its participation in abnormal protein depositions. As the protein has been suggested to play a significant role in the formation of the deposits which might be responsible for neurodegeneration, there is a strong demand to screen for α-synuclein-interactive small molecules. In this report, Coomassie Brilliant Blue (CBB) interaction of α-synuclein has been investigated with respect to induction of protein self-oligomerization in the presence of the chemical coupling reagent N-(ethoxy-carbonyl)-2-ethoxy-1,2-dihydroquinoline. Both CBB-G and CBB-R, which differ by only two methyl groups, induced the self-oligomerization of α-synuclein in a biphasic manner with optimal dye concentrations of 250 μm and 150 μm, respectively. The protein aggregates of α-synuclein induced by the dyes in the absence of the coupling reagent were analysed by electron microscopy. Whereas CBB-G induced formation of protein aggregates with a worm-like structure, CBB-R induced clear fibrilization of α-synuclein on a background of granular structures. CBB-R interacted with α-synuclein approximately twice as effectively as CBB-G (dissociation constants 0.63 μm and 1.37 μm, respectively). These dye interactions were independent from the acidic C-terminus of α-synuclein, which was reminiscent of the Aβ25-35 interaction of α-synuclein. However, the metal-catalysed oxidative self-oligomerization of α-synuclein in the presence of Cu2+/H2O2, which was augmented synergistically by Aβ25-35, was not affected by the dyes. This indicates that the dye binding site is also distinctive from the Ab25-35 interaction site on α-synuclein. These biochemically specific interactions between α-synuclein and the dyes indicate that α-synuclein-interactive small molecules could provide a tool with which to approach development of diagnostic, preventive, or therapeutic strategies for various α-synuclein-related neurodegenerative disorders.