Submolecular Resolution Imaging of Amyloid Aggregation: An STM Approach to Decipher Missense Mutation Effects in α-Synuclein.

Intrinsically disordered regions (IDRs) are critical regulators of cellular function, and their aberrant phase transitions into amyloid fibrils underlie the pathogenesis of amyloidosis. Missense mutations modulate IDR aggregation, but mechanisms remain unclear. Here, we investigate the impact of Parkinson's disease-associated mutations (A53V and T72M) on the aggregation dynamics of α-synuclein (α-Syn), a prototype protein containing IDRs, using scanning tunneling microscopy (STM). We focused on two disease-associated mutations, A53V and T72M, in the fibril-forming fragment (residues 42-78) of α-Syn, and we compared their aggregation behaviors with the wild-type truncated α-Syn. As demonstrated by the STM imaging, mutations remodel the coexisting conformational substates as well as the inter-β-strand interactions in the aggregates. The A53V and T72M mutations reduce the specific inter-β-strand recognitions, which are correlated with the altered aggregation kinetics. This study mechanistically explains how mutations regulate IDR aggregation through changing the conformational diversity, advancing our understanding of the molecular basis of amyloidosis.