Targeting an interaction between two disordered domains using a designed peptide

Intrinsically disordered proteins (IDPs) and regions (IDRs) mediate numerous protein-protein interactions that play roles in many human diseases. However, despite being important potential drug targets, the unfolded character of IDPs and IDRs makes them difficult to target for therapeutic purposes. The main challenge is to design molecules for binding targets that continually change their structure. Here we show that a designed peptide based on an IDR can be used for targeting a partner IDR. iASPP is an anti-apoptotic protein that is upregulated in many cancers and is therefore an emerging anti-cancer drug target. iASPP inhibits the activity of p53, one of the major tumor suppressor proteins in the cell that has a central part in the anti-cancer defense mechanisms of the cell. The intrinsically disordered linker domain of p53 (p53 289-322) interacts with one of the disordered loops of iASPP, and thus promotes cancer cell death. We describe the development of a peptide derived from the p53 linker domain, which inhibits the iASPP-p53 interaction and promotes apoptosis of cancer cells. We show that the p53 linker forms a hairpin-like structure that brings the two termini of the peptide close to each other. We designed a peptide derived from the N and the C termini of the p53 linker, without the hairpin, p53 289-297,313-322 (p53 linkTer), which binds iASPP with the same affinity as the parent p53 linker peptide. Using peptide array screening and computational simulations, we showed that the p53 linkTer peptide binds the disordered RT loop region in iASPP, thus inhibiting the interaction between iASPP and p53 in vitro. Our results present a shorter peptide, p53 linkTer, comprising only the intrinsically disordered part of the parent peptide that inhibits the interaction between two disordered domains, paving the way for using such peptides for therapeutic purposes.