Aims
Alpha-synuclein is one of the major components of the Lewy bodies associated with Parkinson’s disease. Mutations in the SNCA gene were the first reported links between familial sporadic Parkinson’s disease and perturbations at the molecular level. The steps that alpha-synuclein undergoes to reach fibrillation are still poorly understood. An hypothesis was postulated that the different oligomeric species formed by these mutants could correspond to the different steps in the aggregation of alpha-synuclein.
Method
We compared the behavior of α-synuclein and five pathological mutants (A30P, E46K, H50Q, G51D and A53T). To gain insights into the aggregagtion behavior of these proteins, we developed a method coupling single molecule detection and cell-free expression to measure precisely the oligomerisation of proteins, without purification, labelling or denaturation steps, in completely undisturbed samples. In these conditions, we could detect the formation of oligomeric and pre-fibrillar species at very short time scale and low micromolar concentrations.
Results
Surprisingly, the pathogenic mutants segregated into two classes: one group forms large aggregates and fibrils while the other tends to form smaller oligomers and fewer fibrils. Strikingly, co-expression experiments reveal that members from the different groups tend to not interact with each other, both at the fibril and monomer levels. Further biochemical analyses revealed differences of structure between the aggregates.
Conclusion
Together, this data paints a completely different picture of alpha-synuclein aggregation, with two possible pathways leading to the development of fibrils. Further studies are being conducted to investigate the co-chaperoning of beta-synuclein and two of its mutants on the aggregation of alpha-synuclein.