Cryo-EM structure of amyloid fibril formed by α-synuclein hereditary A53E mutation reveals a distinct protofilament interface

Synucleinopathies like Parkinson's disease (PD), dementia have the same pathologic feature of misfolded alpha-synuclein protein (alpha-syn) accumulation in the brain. PD patients who carry alpha-syn hereditary mutations tend to have earlier onset and more severe clinical symptoms than sporadic PD patients. Therefore, revealing the effect of hereditary mutations to the alpha-syn fibril structure can help us understand these synucleinopathies' structural basis. Here, we present a 3.38 angstrom cryoelectron microscopy structure of alpha-synuclein fibrils containing the hereditary A53E mutation. The A53E fibril is symmetrically composed of two protofilaments, similar to other fibril structures of WT and mutant alpha-synuclein. The new structure is distinct from all other synuclein fibrils, not only at the interface between proto-filaments, but also between residues packed within the same proto-filament. A53E has the smallest interface with the least buried surface area among all alpha-syn fibrils, consisting of only two contacting residues. Within the same protofilament, A53E reveals distinct residue rearrangement and structural variation at a cavity near its fibril core. Moreover, the A53E fibrils exhibit slower fibril formation and lower stability compared to WT and other mutants like A53T and H50Q, while also demonstrate strong cellular seeding in alpha-synuclein biosensor cells and primary neurons. In summary, our study aims to highlight structural differences - both within and between the protofilaments of A53E fibrils - and interpret fibril formation and cellular seeding of alpha-synumutants.