Recognition of ASF1 Using Hydrocarbon Constrained Peptides

Inhibition of the histone H3-ASF1 (anti-silencing function 1) protein-protein interaction (PPI) represents a potential approach for treatment of numerous cancers. As an α-helix mediated PPI, constraint of the key histone H3 helix (residues 118-135) represents a strategy through which chemical probes might be elaborated to test this hypothesis. In this work variant H3118-135 peptides bearing pentenyl glycine residues at i and i + 4 positions were constrained by olefin metathesis. Biophysical analyses revealed that promotion of a bioactive helical conformation depends on the position at which the constraint is introduced, but that potency of binding towards ASF1 is unaffected by the constraint and instead that enthalpy-entropy compensation occurs

Understanding p300-transcription factor interactions using sequence variation and hybridization

The hypoxic response is central to cell function and plays a significant role in the growth and survival of solid tumours. HIF-1 regulates the hypoxic response by activating over 100 genes responsible for adaptation to hypoxia, making it a potential target for anticancer drug discovery. Although there is significant structural and mechanistic understanding of the interaction between HIF-1α and p300 alongside negative regulators of HIF-1α such as CITED2, there remains a need to further understand the sequence determinants of binding. In this work we use a combination of protein expression, chemical synthesis, fluorescence anisotropy and isothermal titration calorimetry for HIF-1α sequence variants and a HIF-1α-CITED hybrid sequence which we term CITIF. We show the HIF-1α sequence is highly tolerant to sequence variation through reduced enthalpic and less unfavourable entropic contributions, These data imply backbone as opposed to side chain interactions and ligand folding control the binding interaction and that sequence variations are tolerated as a result of adopting a more disordered bound interaction or “fuzzy” complex

Cover Feature: Recognition of ASF1 by Using Hydrocarbon‐Constrained Peptides (ChemBioChem 7/2019)

The cover feature picture shows how inhibition of the histone H3‐ASF1 (anti‐silencing function 1) protein–protein interaction (PPI) represents a potential approach for the treatment of numerous cancers. To pursue this goal, a hydrocarbon constraint was used to pre‐organize the histone H3 peptide in α‐helical conformation; despite conferring protection against proteolysis, this constrained peptide unexpectedly exhibited enthalpy–entropy compensation in comparison to the natural sequence, in its binding of ASF1. More information can be found in the communication by F. Ochsenbein, A. J. Wilson et al. on page 891 in Issue 7, 2019 (DOI: 10.1002/cbic.201800633)

Query-Guided Protein-Protein Interaction Inhibitor Discovery

Protein–protein interactions (PPIs) are central to biological mechanisms, and can serve as compelling targets for drug discovery. Yet, the discovery of small molecule inhibitors of PPIs remains challenging given the large and typically shallow topography of the interacting protein surfaces. Here, we describe a general approach to the discovery of orthosteric PPI inhibitors that mimic specific secondary protein structures. Initially, hot residues at protein–protein interfaces are identified in silico or from experimental data, and incorporated into secondary structure-based queries. Virtual libraries of small molecules are then shape-matched against the queries, and promising ligands docked to target proteins. The approach is exemplified experimentally using two unrelated PPIs that are mediated by an α-helix (p53/hDM2) and a β-strand (GKAP/SHANK1-PDZ). In each case, selective PPI inhibitors are discovered with low μM activity as determined by a combination of fluorescence anisotropy and 1H–15N HSQC experiments. In addition, hit expansion yields a series of PPI inhibitors with defined structure–activity relationships. It is envisaged that the generality of the approach will enable discovery of inhibitors of a wide range of unrelated secondary structure-mediated PPIs