Kinetic and Conformational Insights into Islet Amyloid Polypeptide Self-Assembly Using a Biarsenical Fluorogenic Probe.

Amyloid fibril formation and tissue deposition are associated with many diseases. Studies have shown that prefibrillar intermediates, such as oligomers, are the most toxic proteospecies of the amyloidogenic cascade. Thus, understanding the mechanisms of formation and the conformational ensemble of prefibrillar species is critical. Due to their transient and heterogeneous nature, detection and characterization of prefibrillar species remain challenging. The fluorogenic probe fluorescein arsenical hairpin (FlAsH), which recognizes a tetracysteine motif, has been recently used to detect the oligomerization of amyloidogenic peptides encompassing a Cys-Cys tag. In this study, we extended the FlAsH detection method to gain novel kinetic and conformational insights into the self-assembly of islet amyloid polypeptide (IAPP), a 37-residue peptide hormone whose deposition is associated with type II diabetes. By positional scanning of the Cys-Cys motif, the stability of the noncontiguous tetracysteine FlAsH-binding sites formed during self-assembly was evaluated and revealed rapid monomer self-recognition through the convergence of C-terminal domains. On the other hand, the N-terminal domains come close to each other only upon the formation of the cross-β-sheet amyloid structure. We demonstrated that this method is well-suited to detect thioflavin T-negative fibrils and to screen inhibitors of amyloid formation. This study highlights that with positional scanning of the split-tetracysteine motif (Cys-Cys), the FlAsH detection method offers unique time-dependent conformational insights on the proteospecies assembled throughout the amyloidogenic pathway.