Modified Peptide Inhibitors of the Keap1–Nrf2 Protein–Protein Interaction Incorporating Unnatural Amino Acids

Abstract

Noncovalent inhibitors of the Keap1–Nrf2 protein–protein interaction (PPI) have therapeutic potential in a range of disease states including neurodegenerative diseases (Parkinson's and Alzheimer's diseases), chronic obstructive pulmonary disease and various inflammatory conditions. By stalling Keap1‐mediated ubiquitination of Nrf2, such compounds can enhance Nrf2 transcriptional activity and activate the expression of a range of genes with antioxidant response elements in their promoter regions. Keap1 inhibitors based on peptide and small‐molecule templates have been identified. In this paper we develop the structure–activity relationships of the peptide series and identify a group of ligands incorporating unnatural amino acids that demonstrate improved binding affinity in fluorescence polarisation, differential scanning fluorimetry and isothermal titration calorimetry assays. These modified peptides have the potential for further development into peptidomimetic chemical probes to explore the role of Nrf2 in disease and as potential lead structures for drug development.

Recent advances in the development of protein–protein interactions modulators: mechanisms and clinical trials

“…180 The study of the Keap1/Nrf2 inhibitors begins with the investigation of the polypeptides that inhibits the Keap1/Nrf2 interaction. Up to date, a number of the inhibitive polypeptides have been reported [181][182][183][184] (Table 4). Hu et al 185 developed a series of fluorescent probes to verify when the peptide chain length is 9 amino acids it has the best activity to inhibit the Keap1/Nrf2 interaction.…”

Structure of the BRK domain of the SWI/SNF chromatin remodeling complex subunit BRG1 reveals a potential role in protein–protein interactions

“…The highly context-dependent roles of SWI/SNF complexes makes chemical biology approaches a particularly attractive strategy for this endeavor. The use of peptidomimetic chemical probes, [30][31][32] for example, would help to elucidate the role of the domain and assess the potential of targeting it for therapeutic intervention. With regard to druggability with small molecules, an analysis of the structure using the program GHECOM 33 identifies two pockets for small-molecule binding within the putative peptide binding site: one shallow pocket adjacent to the conserved AP motif in loop between the second beta strand and the helix and a deeper pocket around the highly conserved tryptophan residue in the helix (W642).…”

Flavolignans from Silymarin as Nrf2 Bioactivators and Their Therapeutic Applications

“…As previously mentioned, although several other mechanisms of action are suggested for the action of SM [12], the effects on Nrf2 activity appear to be crucial. Recent works describe the action of compounds on this system by direct interaction or by the disruption of proteins linked to Nrf2 activity [166,167], with Keap1 as the main target [168],due to that, under basal conditions, the Nrf2 protein is constitutively trapped by Keap1 and retained in the cytoplasm for ubiquitin conjugation and subsequent proteasome degradation. In this regard, 178 phytochemicals proven to possess good antioxidant properties were selected and tested in silico by Li et al, suggesting that phenylethanoid glycosides, tocopherols, flavones, flavanols, anthocyanins, and flavonols have entertained high affinity with Keap1 and have potential as inhibitors of the inactivator action on Nrf2 [169].…”

“…In this regard, 178 phytochemicals proven to possess good antioxidant properties were selected and tested in silico by Li et al, suggesting that phenylethanoid glycosides, tocopherols, flavones, flavanols, anthocyanins, and flavonols have entertained high affinity with Keap1 and have potential as inhibitors of the inactivator action on Nrf2 [169]. In a complementary manner, itis noteworthy that several research workgroups have developed and tested compounds to disrupt Keap1:Nrf2 interaction [168,170,171]. The main aim of these approaches is the design of potential drugs for numerous pathologies, but also for deciphering molecular disease mechanisms [170].…”

“…The main aim of these approaches is the design of potential drugs for numerous pathologies, but also for deciphering molecular disease mechanisms [170]. Interestingly, the binding site shares several residues conserved for ligands with various aromatic rings (often 3 or 4, as several bioactive compounds from SM), albeit that tested compounds exhibit notable differences, such as those identified from a peptide series that demonstrated improved binding affinity in fluorescence polarization, differential scanning fluorimetry, and isothermal titration calorimetry assays [168]. In the meanwhile, other potent inhibitors were synthesized strategically by means of the exploration and optimization of protein-ligand interactions in three energetic "hot-spots" identified by fragment screening [170].…”