Optimal Stapling of a Helical Peptide-Foldamer Hybrid Using a C-terminal 4-Mercaptoproline Enhances Protein Surface Recognition and Cellular Activity.

Structural analysis of a co-crystal of a helically-folded peptide-foldamer hybrid in complex with hDM2 E3 ubiquitin ligase, revealed a unique orientation for the C-terminal proline with the pyrrolidine ring pointing backwards in the sequence, and suggested new opportunities for macrocyclization. In particular, we found that the C-terminal prolyl residue could be replaced by its (2S,4S)-4-mercaptoprolyl analogue for optimal bisthioether crosslinking with a cysteine residue installed at position 4 in the sequence. The resulting i,i+7 stapled peptide-foldamer is a high-affinity binder to hDM2, is cell permeable and restores the p53 signalling pathway in p53wt cancer cells. The co-crystal structure of hDM2 and the stapled peptide-foldamer hybrid was determined at 1.84 Å, fully validating the original design and further highlighting the potential of cis-4-mercaptoproline in the context of peptide and foldamer stapling.