Leveraging bioorthogonal conjugation for alpha synuclein fibril surveillance

Alpha synuclein (α-syn) amyloid fibrils are associated with various neurodegenerative diseases. To better understand the molecular and cellular basis for α-syn fibril persistence and spread, we implemented a fluorophore labeling strategy to surveil pre-formed α-syn fibrils in solution and in cells. We leveraged amber codon mediated incorporation of a tetrazine-based artificial amino acid (TetV2.0) to install a cyclooctene-conjugated Janeliaflour, JF549, at four sites on human α-syn: residues 4, 60, 96 and 136. Fast coupling occurred under mild buffer conditions and in the presence of the disease-associated cofactor and cytotoxic lipid, psychosine. Labeled fibrils retained their polymorphic features, seeded the growth of new fibrils in vitro , and induced the seeding of positive puncta in α-syn FRET biosensor HEK293T cells. This allowed simultaneous tracking of exogenous and endogenous α-syn aggregates in biosensor cells, and their localization within the cells. In doing so, our approach facilitates more detailed mechanistic investigation of α-syn aggregates.