Aggregation of α-synuclein monomers and engineered oligomers in solution

Abstract

α-Synuclein is a protein that has been found as fibrillar aggregates in Lewy bodies in the brain of Parkinson’s disease patients. Though the cause of the Parkinson’s disease is unknown, previous research suggest that there is a close association between the disease and the toxicity of the intermediary α-synuclein oligomers in human neurons. Therefore, it is important to investigate the aggregation behaviour of intermediary oligomers. To do this we investigate aggregation of protein constructs that are monomers (Snca1), or engineered dimers (Snca2), tetramers (Snca4), and octamers (Snca8) of α-synuclein with a C terminal cysteine. Single-molecule fluorescence methods were used to study the molecular interactions between pairs of these oligomers under “physiological” aggregation conditions (10 mM PBS at pH = 7.4 at 37 °C). To be specific, we applied dual-color fluorescence cross correlation spectroscopy (dual-color FCCS) to study the self-aggregation (aggregation of one kind of α-synuclein) and the cross-aggregation (aggregation between the monomeric and oligomeric α-synuclein) of α-synuclein. The engineered α-synuclein monomers, dimers, tetramers and octamers were labelled with either Oregon Green 488 maleimide (green dye) or Cy5-tetrazine (red dye). A green dye labelled protein was incubated with a red dye labelled protein at micromolar concentrations with continuous shaking at 250 rpm and diluted aliquots of the aggregation mixture was measured by dual-color FCCS at nanomolar concentrations after different incubation times. The experimental results indicate that the engineered α-synuclein octamers aggregate faster and to a greater extent than monomers and dimers, with the tetramers being intermediate. The engineered oligomers preferred to incorporate themselves rather than the monomer into aggregates. Therefore, these oligomer constructs do not appear to seed the aggregation of monomers.