End-to-end Structural Restriction of α-Synuclein and Its Influence on Amyloid Fibril Formation

Relationship between molecular freedom of amyloidogenic protein and its self-assembly into amyloid fibrils has been evaluated with ${\alpha}$ -synuclein, an intrinsically unfolded protein related to Parkinson's disease, by restricting its structural plasticity through an end-to-end disulfide bond formation between two newly introduced cysteine residues on the N- and C-termini. Although the resulting circular form of ${\alpha}$ -synuclein exhibited an impaired fibrillation propensity, the restriction did not completely block the protein's interactive core since co-incubation with wild-type ${\alpha}$ -synuclein dramatically facilitated the fibrillation by producing distinctive forms of amyloid fibrils. The suppressed fibrillation propensity was instantly restored as the structural restriction was unleashed with ${\beta}$ -mercaptoethanol. Conformational flexibility of the accreting amyloi…