Site-Specific Dynamics of Aβ1-23 Amyloid Formation and Fibrillar Configuration using an Unnatural Amino Acid

Amyloid diseases, such as Alzheimer's and Parkinson's, are linked to a poorly understood progression of protein misfolding and aggregation that form tissue-selective fibrillar deposits. Elucidation of site-specific dynamics of protein aggregation is crucial for understanding the mechanistic details of protein amyloidogenesis. Hence, using Aβ1-23 as a model molecule, we identified distinct site-specific dynamics over the course of the aggregation and amyloid formation, and defined the structural characteristics of amyloid fibrils by using an unnatural amino acid, p-cyanophenylalanine, as a sensitive fluorescent and Raman probe. Our results reveal distinct local environmental changes of specific residues during the aggregation of Aβ1-23. In addition, our results suggest that an edge-to-face aromatic interaction between the Phe4 and Phe19 residues from the adjacent in-register β-strands plays a key role in the conformational conversion to form and stabilize β-sheet structure. Moreover, the alignment of the flip-over antiparallel pattern of β-sheet in the amyloid fibrils at the molecular level is proposed on the basis of the PheCN probing results.