Abstract
α-Synuclein (αS) is an intrinsically disordered protein that is associated with Parkinson’s disease (PD) through its ability to self-assemble into oligomers and fibrils. Inhibition of this oligomerization cascade is an interesting approach to developing therapeutical strategies and β-synuclein (βS) has been described as a natural negative regulator of this process. However, the biological background and molecular mechanisms by which this inhibition occurs is unclear. Herein, we focused on assessing the effect of βS on the aggregation of five αS pathological mutants linked to early-onset PD (A30P, E46K, H50Q, G51D and A53T). By coupling single molecule fluorescence spectroscopy to a cell-free protein expression system, we validated the ability of βS to act as a chaperone of αS, effectively inhibiting its aggregation. Interestingly, we found that βS does so in a selective manner, i.e., is a more effective inhibitor for certain αS pathological mutants—A30P and G51D—as compared to E46K, H50Q and A53T. Moreover, two-color coincidence experiments proved that this discrepancy is due to a preferential incorporation of βS into smaller oligomers of αS. This was validated by showing that the chaperoning effect was lost when proteins were mixed after being expressed individually. This study highlights the potential of fluorescence spectroscopy to deconstruct αS aggregation cascade and its interplay with βS.
Highlights
Pathological protein aggregation is a poorly understood phenomenon that lies at the root of several neurodegenerative diseases including Parkinson’s, Alzheimer’s, Huntington’s and Creutzfeld–Jakob diseases
Α-Synuclein is amongst some of the most studied aggregation-prone proteins in neurodegeneration, mostly due to its involvement in the pathogenesis of Parkinson’s disease (PD) and other disorders such as Dementia with Lewy Bodies (DLB) or Multiple Systems Atrophy (MSA), all of which are generically designated as synucleinopathies [2]. αS is a small 140 amino-acid long protein, encoded by the gene SNCA, that predominantly localizes at the presynaptic terminals of neurons, where it comprises 1% of all cytosolic proteins
ΑS’s ability to self-assemble in PD is often depicted as an irreversible cascade of events that leads to the formation of different soluble oligomeric/protofibrillar species and culminates in the formation of insoluble fibrils that accumulate in Lewy Bodies [1]
Summary
Pathological protein aggregation is a poorly understood phenomenon that lies at the root of several neurodegenerative diseases including Parkinson’s, Alzheimer’s, Huntington’s and Creutzfeld–Jakob diseases. ΑS’s ability to self-assemble in PD is often depicted as an irreversible cascade of events that leads to the formation of different soluble oligomeric/protofibrillar species and culminates in the formation of insoluble fibrils that accumulate in Lewy Bodies [1]. Straightforward as this process may seem, it raises a multitude of questions. Recent studies have shown intermediate oligomeric states to be more toxic than the mature fibrils [6,7], challenging conventional views that have historically associated fibrils as the source of toxicity to neurons Whether this mechanism of toxicity is related to gain- or loss-of-function properties of αS aggregates is unclear
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