LAUSR

β‐Sheet conformation is promoted in peptides with amphiphilic design, and stable β‐turn formation is favored with the unnatural amino acid d‐Pro followed by a flexible residue such as Gly. A 19‐residue peptide (B3) was synthesized with alternating hydrophobic and hydrophilic residues connected by symmetrical d‐Pro‐Gly and Gly‐d‐Pro turns. B3 forms an oligomeric aggregate, rich in β‐sheet conformation, that reversibly transforms into an unordered structure on heating, as evidenced by its temperature‐dependent IR spectra. When a dansyl moiety was added to the N terminus of B3, the resulting peptide (B3D) can convert into a fibrillar structure after higher temperature incubation, as detected spectroscopically as well as by TEM. The fibrillization process involves an initial unfolding step monitored by the quenching of dansyl emission; in contrast, subsequent enhanced thioflavin T emission is seen on its binding to the fibril. A possible mechanism is proposed: B3D forms a low‐temperature oligomer, which is at least partially unfolded by heat and subsequently reassembles more slowly as a fibril.