Two Opposing d‐Amino Acids Give Zigzag Hairpin Epitopes an Additional Kink to Create Antibody‐Selective Peptide Antigens

We have developed peptides that are able to distinguish between subgroups of polyclonal antibodies. These β‐hairpin peptides act as conformational epitopes with specific shape and flexibility; they have been analyzed by NMR and CD spectroscopy, and have been shown to identify known disease markers. As a standalone mini β‐sheet, a hairpin is stabilized by alternating pairs of hydrogen‐bonded and non‐bonded amino acids on its two opposing peptide strands. A single d mutation disrupts this secondary structure, the correlated double‐d mutation of two opposing amino acids compensates for this destabilizing effect. The designed kink was introduced into both hydrogen‐bonded and ‐non‐bonded positions of an all‐l hairpin that is a known conformational epitope in molecular recognition. Our peptides enabled the discrimination of different human rheumatoid arthritis autoantibodies in an ELISA assay.