PROJECT SUMMARY/ABSTRACT Intrinsically disordered proteins (IDPs) are a ubiquitous class of proteins whose structural plasticity allows them to function as hubs in protein-protein interaction (PPI) and signaling networks. IDP PPIs are therefore tightly regulated, and aberrant IDP PPIs are associated with many disease states. As IDP folding and activity are dependent on the conformations induced by its native binding partners, small molecules that induce native-like IDP conformations are highly desirable for studying IDP function. However, complex IDP PPI interfaces are difficult targets for traditional small molecules. Instead, non-traditional approaches using stabilized α-helical peptides, such as the hydrogen bond surrogate (HBS) approach developed in the Arora laboratory, are promising for creating small molecules that nucleate native-like IDP folding with both high affinity and high specificity. Thus, I hypothesize that HBS peptides can mimic key portions of IDP binding partners to nucleate IDP folding and competitively inhibit IDP PPIs in vitro and in vivo. The overall goal is to create HBS-derived artificial folders that induce IDPs to favor one fold over others. A classic IDP PPI example is the interaction of the general transcriptional coactivator p300 with the intrinsically disordered C-terminal transcription-activation domain of hypoxia-inducible factor 1 α (HIF1α CTAD). This interaction is critical for hypoxia-inducible transcription, leading to the upregulation of many cancer-associated genes involved in angiogenesis, invasion, and proliferation. The Arora lab has shown that mimicry of a HIF1α CTAD helical fragment downregulates hypoxia-inducible transcription and decreases xenograft tumor size in mice. However, targeting p300 may impair its ability to interact with its numerous binding partners. In the current proposal, I propose to develop a complementary strategy to use HBS peptides to induce HIF1α CTAD folding and competitively inhibit the p300-HIF1α CTAD interaction. To achieve this goal, I will first design and synthesize HBS peptides that mimic a p300 helical fragment that interacts with HIF1α CTAD. I will evaluate HBS peptide binding affinity and specificity for HIF1α CTAD in vitro. I will then characterize the structures of HIF1α CTAD-HBS complexes to evaluate HBS peptide-induced folding of HIF1α CTAD. I will also evaluate HBS peptides’ ability to modulate HIF1α-mediated transcription using cell-based assays. HBS peptides that induce native-like HIF1α CTAD folding with high affinity and specificity may serve as useful tools for studying HIF1α function and potential cancer therapeutic leads for HIF1α inhibition. This strategy for inducing IDP folding may also provide a specific application of a general approach to modulate IDP structures and activities using structured peptides.

PROJECT NARRATIVE Intrinsically disordered proteins (IDPs) are a diverse family of proteins, many of which undergo induced folding and concomitant changes in activity that are associated with disease. While it is difficult to induce IDP folding using traditional small molecules for functional studies and therapeutic intervention, non-traditional peptide approaches can use mimics of natural IDP binding partners to produce promising small molecules that specifically induce IDP folding and inhibit IDP protein-protein interactions (PPIs). The proposed research strategy involves the design, synthesis, and evaluation of stable, structured peptides to specifically induce the folding of an intrinsically disordered, cancer-associated HIF1α domain, serving as a specific example of a general approach for inducing IDP folding and generating potential therapeutic leads for inhibiting IDP PPIs in vivo.