What pathological mutants tell us about synuclein aggregation pathways

Abstract

Misfolding and pathological aggregation of proteins is a hallmark of many neurodegenerative diseases. α‐synuclein (α‐Syn) is one of the major components of the Lewy bodies associated with Parkinson's disease and other neurodegenerative disorders called synucleinopathies. Mutations in the SNCA gene were the first reported links between familial sporadic Parkinson's disease and perturbations at the molecular level.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 and denaturation steps, in completely undisturbed samples. In these conditions, α‐Syn oligomerisation and aggregation is a rapid process that occurred co‐translationally, at nM concentrations.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. Therefore, the different mutants could provide access to different species formed along the fibrillation path of α‐Syn.We then examined the effects of a variety of chaperones on the aggregation propensity of the different mutants. This uncovers the specificty of the different chaperones for specific species in the aggregation pathway and identifies new therapeutic targets in Parkinson's disease and multiple sceloris atrophy (MSA).