β-Sheet Assembly Translates Conservative Single-Site Mutation into a Perturbation in Macroscopic Structure.

Transferring structural information from amino acid sequence to macroscale assembly is a challenging approach for designing protein quaternary structure. However, the pathway by which the slight variations in sequence result in a global perturbation effect on the assembled structure is unknown. Herein, we design two synthetic peptides, QNL-His and QNL-Arg, with one amino acid substitution and use scanning tunneling microscopy (STM) to image individual peptides in the assembled state. The submolecular resolution of STM enables us to determine the folding structure and β-sheet supramolecular organization of peptides. QNL-His and QNL-Arg differ in their β-strand length distribution in pleated β-sheet association. These structural variations lead to distinguishable outcomes in their β-sheet assembled fibrils and phase transitions. The comparison of QNL-His versus QNL-Arg structures and macroscopic properties unveils the role of assembly to amplify the structural variations associated with a single-site mutation from a single-molecule scale to a macroscopic scale.