Backbone Thioamide Substitution Enhances the Activity of Short Peptides in Modulating the Aggregation of α-Synuclein

The non-amyloid-β component (NAC) region of the Parkinson’s-associated protein α-synuclein plays a key role in its pathogenic aggregation, motivating the development of molecules that target this critical region. Here, we show that a minimal NAC-derived motif, ⁶⁶ VGGAVVT ⁷² , can be reprogrammed through backbone engineering to modulate α-synuclein aggregation. Backbone thioamide substitution of this peptide enhances its interactions with α-synuclein fibrils and accelerates aggregation, whereas N -methylation disrupts β-sheet hydrogen bonding and inhibits fibrillization. Strikingly, combining these modifications yields hybrid peptides that inhibit the fibrillization of full-length α-synuclein at sub-stoichiometric concentrations. Consistent with in vitro results, these backbone-modified peptides can also reduce seeded α-synuclein aggregation in cells. These results establish that minimal amyloidogenic sequences can be systematically tuned from aggregation promoters to inhibitors through backbone-level perturbations, particularly thioamide incorporation.