Promotion of sheet formation in α-peptide strands by a β-peptide reverse turn

[GRAPHICS] We show that a tetrapeptide with a heterogeneous backbone, i.e., with two different classes of amino acid residues, adopts a hairpin conformation in which each type of residue plays a different structural role. The alpha residues at the ends form hydrogen bonds characteristic of antiparallel beta-sheet secondary structure, while the central di-beta-peptide segment forms a reverse turn. The configuration of the turn residues is critical to sheet formation.