Intramolecular interaction kinetically regulates fibril formation by human and mouse & alpha;-synuclein

Regulation of & alpha;-synuclein (& alpha;S) fibril formation is a potent therapeutic strategy for & alpha;S-related neurodegenerative disorders. & alpha;S, an intrinsically disordered 140-residue intraneural protein, comprises positively charged N-terminal, hydrophobic non-amyloid & beta; component (NAC), and negatively charged C-terminal regions. Although mouse and human & alpha;S share 95% sequence identity, mouse & alpha;S forms amyloid fibrils faster than human & alpha;S. To evaluate the kinetic regulation of & alpha;S fibrillation, we examined the effects of mismatched residues in human and mouse & alpha;S on fibril formation and intramolecular interactions. Thioflavin T fluorescence assay using domain-swapped or C-terminal-truncated & alpha;S variants revealed that mouse & alpha;S exhibited higher nucleation and fibril elongation than human & alpha;S. In mouse & alpha;S, S87N substitution in the NAC region rather than A53T substitution is dominant for enhanced fibril formation. Forester resonance energy transfer analysis demonstrated that the intramolecular interaction of the C-terminal region with the N-terminal and NAC regions observed in human & alpha;S is perturbed in mouse & alpha;S. In mouse & alpha;S, S87N substitution is responsible for the perturbed interaction. These results indicate that the interaction of the C-terminal region with the N-terminal and NAC regions suppresses & alpha;S fibril formation and that the human-to-mouse S87N substitution in the NAC region accelerates & alpha;S fibril formation by perturbing intramolecular interaction.

Automated summary

Regulation of α-synuclein (αS) fibril formation is important for treating αS-related neurodegenerative disorders. Mouse αS forms fibrils faster than human αS due to the S87N substitution in the non-amyloid β component (NAC) region. Interaction of the C-terminal region with the N-terminal and NAC regions suppresses αS fibril formation, while the human-to-mouse S87N substitution accelerates fibril formation by perturbing intramolecular interaction.