Singh, B. P. | bioRxiv Science

bioRxiv2022

Structural conversion of α-synuclein at the mitochondria induces neuronal toxicity

Aggregation of -Synuclein (-Syn) drives Parkinsons disease, although the initial stages of self-assembly and structural conversion have not been captured inside neurons. We track the intracellular conformational states of -Syn utilizing a single-molecule FRET biosensor, and show that -Syn converts from its monomeric state to form two distinct oligomeric states in neurons in a concentration dependent, and sequence specific manner. 3D FRET-CLEM reveals the structural organization, and location of aggregation hotspots inside the cell. Notably multiple intracellular seeding events occur preferentially on membrane surfaces, especially mitochondrial membranes. The mitochondrial lipid, cardiolipin triggers rapid oligomerization of A53T -Syn, and cardiolipin is sequestered within aggregating lipid-protein complexes. Mitochondrial aggregates impair complex I activity and increase mitochondrial ROS generation, which accelerates the oligomerization of A53T -Syn, and ultimately causes permeabilization of mitochondrial membranes, and cell death. Patient iPSC derived neurons harboring A53T mutations exhibit accelerated oligomerization that is dependent on mitochondrial ROS, early mitochondrial permeabilization and neuronal death. Our study highlights a mechanism of de novo oligomerization at the mitochondria and its induction of neuronal toxicity.

neuroscience↗

bioRxiv2021

Lipid-induced polymorphic amyloid fibrils formation by α-synuclein.

Many proteins that self-assemble into amyloid and amyloid-like fibres can adopt polymorphic forms. These forms have been observed both in vitro and in vivo and can arise through variations in the steric-zipper interactions between {beta}-sheets, variations in the arrangements between protofilaments, and differences in the number of protofilaments that make up a given fibre class. Different polymorphs which arise from the same precursor molecule not only exhibit different levels of toxicity, but importantly can contribute to different disease conditions. In this work, we show that in the presence of 1,2-dimyristoyl-sn-glycero-3-phospho-L-serine, a highly abundant lipid in the plasma membrane of neurons, the aggregation of -synuclein is markedly accelerated and yields a diversity of polymorphic forms under identical experimental conditions. This morphological diversity includes thin and curly amyloid fibrils, helical and twisted ribbons, nanotubes and flat sheets. TEM analysis of fibrils sampled from the early stage of the growth phase shows the presence of helical and twisted ribbons, indicating that these morphological variants form at the early stages of aggregation. Total internal reflection fluorescence microscopy (TIRFM) indicated the presence of lipids collocated with the mature fibrils. This finding has important implication as the presence of -synuclein with co-localized high lipid content has been reported in Lewy bodies, the pathological hallmark of Parkinsons disease and other synucleinopathies. Thus, the present study demonstrates that an interface, such as that provided by a lipid membrane, can not only modulate the kinetics of -synuclein amyloid aggregation but also plays an important role in the formation of morphological variants by incorporating lipid molecules in the process of amyloid fibril formation.

biophysics↗