Targeting an interaction between two disordered domains using a designed peptide.

Intrinsically disordered regions in proteins (IDRs) mediate many disease-related protein-protein interactions. However, the unfolded character and continuous conformational changes of IDRs make them difficult to target for therapeutic purposes. Here we show that a designed peptide based on the disordered p53 linker domain can be used for targeting a partner IDR from the anti-apoptotic iASPP protein, promoting apoptosis of cancer cells. The p53 linker forms a hairpin-like structure with its two termini in close proximity. We designed a peptide derived from the disordered termini without the hairpin, termed p53 LinkTer. The LinkTer peptide bound the disordered RT loop of iASPP with the same affinity as the parent p53 Linker peptide, and inhibited the p53-iASPP interaction in vitro. The LinkTer peptide showed increased stability to proteolysis, penetrated cancer cells, caused nuclei shrinkage and decreased cells viability. We conclude that a designed peptide comprising only the IDR from a peptide sequence can be an improved inhibitor since it binds its target protein without the need for pre-folding, paving the way for therapeutic targeting of IDRs.