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Peptide “cross-stitching” maintains binding affinity and can enhance helical and proteolytic stability.

“Stapled” peptides are typically designed to replace two non-interacting residues with a constraining, olefinic staple. To mimic interacting leucine and isoleucine residues, in this work we have created new amino acids that incorporate a methyl group in the γ-position of the stapling amino acid S5. We have incorporated them into a sequence derived from steroid receptor coactivator 2, which interacts with estrogen receptor α. The best peptide (IC₅₀=89 nm) replaces isoleucine 689 with an S-γ-methyl stapled amino acid, and has significantly higher affinity than unsubstituted peptides (390 and 760 nm). Through X- ray crystallography and molecular dynamics studies, we showmore » that the conformation taken up by the S-γ-methyl peptide minimizes the syn-pentane interactions between the α- and γ-methyl groups.« less