Using the flexibility of disordered protein domains to promote cancer cell death

Intrinsically disordered proteins (IDPs) and regions (IDRs) play a major role in controlling protein-protein interactions. A disordered region can form multiple conformations and therefore can form high-specificity/low-affinity interactionsthat play crucial roles in many human diseases. The design of drugs that target IDPs should take into consideration the dynamic structure of that target. iASPP is an anti-apoptotic protein thatis upregulated in many cancers and is therefore an emerging anti-cancer drug target. iASPP binds the linker domain of the tumor suppressor p53, resulting in antiapoptotic activity. Thus, inhibiting the iASPP-p53 interaction should promote apoptosis of cancer cells. Here we show using CD and simulations that the p53 linker is disordered with beta turn motif, forming a hairpin-like structure. A peptide derived from the N and C termini of the p53 linker, without the hairpin, binds iASPP with the same affinity. Using peptide array screening and Piper-Flex Doc simulations we showed that both variants of the disordered linker bind the RT loop region in iASPP, a disordered region that has been previously shown to play an important role in iASPP activation and interactions. Peptides derived from both variants of the p53 linker inhibited the interaction between iASPP and p53 in vitro and caused a decrease of 20-40% in the viability of p53WT cancer cell lines after 24 h using 10uM of both variants. Our results show that it is possible to target the interaction between two disordered domains.