Covalent and Noncovalent Targeting of the Tcf4/β-Catenin Strand Interface with β-Hairpin Mimics

A high-throughput molecular dynamics screening (HTMDS) approach to the design of novel cyclopeptide inhibitors of ATAD2B based on the non-canonical combinatorial library

Cyclic peptides (CPs) are a promising class of drugs because of their high biological activity and specificity. However, the design of CP remains challenging due to their conformational flexibility and difficulties in designing stable binding conformation. Herein, we present a high-throughput MD screening (HTMDS) process for the iterative design of stable CP binders with a combinatorial CP library composed of canonical and non-canonical amino acids. As a proof of concept, we apply our methods to design CP inhibitors for the bromodomain (BrD) of ATAD2B. 698,800 CP candidates with a total of 25,570 ns MD simulations were performed to study the protein-ligand binding interactions. The binding free energies (ΔGbind) estimated by MM/PBSA approach for eight lead CP designs were found to be low. CP-1st.43 was the best CP candidate with an estimated ΔGbind of -28.48 kcal/mol when compared to the standard inhibitor C-38 which has been experimentally validated and shown to exhibit ΔGbind of -17.11 kcal/mol. The major contribution of binding sites for BrD of ATAD2B involved the hydrogen-bonding anchor within the Aly-binding pocket, salt bridging, and hydrogen-bonding mediated stabilization of the ZA loop and BC loop, and the complementary Van der Waals attraction. Our methods demonstrate encouraging results by yielding conformationally stable and high-potential CP binders that should have potential applicability in future CP drug development.Communicated by Ramaswamy H. Sarma.

Design of target specific peptide inhibitors using generative deep learning and molecular dynamics simulations

We introduce a computational approach for the design of target-specific peptides. Our method integrates a Gated Recurrent Unit-based Variational Autoencoder with Rosetta FlexPepDock for peptide sequence generation and binding affinity assessment. Subsequently, molecular dynamics simulations are employed to narrow down the selection of peptides for experimental assays. We apply this computational strategy to design peptide inhibitors that specifically target β-catenin and NF-κB essential modulator. Among the twelve β-catenin inhibitors, six exhibit improved binding affinity compared to the parent peptide. Notably, the best C-terminal peptide binds β-catenin with an IC50 of 0.010 ± 0.06 μM, which is 15-fold better than the parent peptide. For NF-κB essential modulator, two of the four tested peptides display substantially enhanced binding compared to the parent peptide. Collectively, this study underscores the successful integration of deep learning and structure-based modeling and simulation for target specific peptide design.

Macrocyclic β-Sheets Stabilized by Hydrogen Bond Surrogates

Mimics of protein secondary and tertiary structure offer rationally-designed inhibitors of biomolecular interactions. β-Sheet mimics have a storied history in bioorganic chemistry and are typically designed with synthetic or natural turn segments. We hypothesized that replacement of terminal inter-β-strand hydrogen bonds with hydrogen bond surrogates (HBS) may lead to conformationally-defined macrocyclic β-sheets without the requirement for natural or synthetic β-turns, thereby providing a minimal mimic of a protein β-sheet. To access turn-less antiparallel β-sheet mimics, we developed a facile solid phase synthesis protocol. We surveyed a dataset of protein β-sheets for naturally observed interstrand side chain interactions. This bioinformatics survey highlighted an over-abundance of aromatic-aromatic, cation-π and ionic interactions in β-sheets. In correspondence with natural β-sheets, we find that minimal HBS mimics show robust β-sheet formation when specific amino acid residue pairings are incorporated. In isolated β-sheets, aromatic interactions endow superior conformational stability over ionic or cation-π interactions. Circular dichroism and NMR spectroscopies, along with high-resolution X-ray crystallography, support our design principles.

Molecular Complementarity of Proteomimetic Materials for Target-Specific Recognition and Recognition-Mediated Complex Functions

As biomolecules essential for sustaining life, proteins are generated from long chains of 20 different α-amino acids that are folded into unique 3D structures. In particular, many proteins have molecular recognition functions owing to their binding pockets, which have complementary shapes, charges, and polarities for specific targets, making these biopolymers unique and highly valuable for biomedical and biocatalytic applications. Based on the understanding of protein structures and microenvironments, molecular complementarity can be exhibited by synthesizable and modifiable materials. This has prompted researchers to explore the proteomimetic potentials of a diverse range of materials, including biologically available peptides and oligonucleotides, synthetic supramolecules, inorganic molecules, and related coordination networks. To fully resemble a protein, proteomimetic materials perform the molecular recognition to mediate complex molecular functions, such as allosteric regulation, signal transduction, enzymatic reactions, and stimuli-responsive motions; this can also expand the landscape of their potential bio-applications. This review focuses on the recognitive aspects of proteomimetic designs derived for individual materials and their conformations. Recent progress provides insights to help guide the development of advanced protein mimicry with material heterogeneity, design modularity, and tailored functionality. The perspectives and challenges of current proteomimetic designs and tools are also discussed in relation to future applications.

Diagonal Interactions between Glutamate and Arginine Analogs with Varying Side-Chain Lengths in a β-Hairpin

Cross-strand interactions are important for the stability of β-sheet structures. Accordingly, cross-strand diagonal interactions between glutamate and arginine analogs with varying side-chain lengths were studied in a series of β-hairpin peptides. The peptides were analyzed by homonuclear two-dimensional nuclear magnetic resonance methods. The fraction folded population and folding free energy of the peptides were derived from the chemical shift data. The fraction folded population trends could be rationalized using the strand propensity of the constituting residues, which was not the case for the peptides with lysine analogs, highlighting the difference between the arginine analogs and lysine analogs. Double-mutant cycle analysis was used to derive the diagonal ion-pairing interaction energetics. The most stabilizing diagonal cross-strand interaction was between the shortest residues (i.e., Asp2-Agp9), most likely due to the least side-chain conformational penalty for ion-pair formation. The diagonal interaction energetics in this study involving the arginine analogs appears to be consistent with and extend beyond our understanding of diagonal ion-pairing interactions involving lysine analogs. The results should be useful for designing β-strand-containing molecules to affect biological processes such as amyloid formation and protein-protein interactions.

Peptide-based covalent inhibitors of protein-protein interactions

Protein-protein interactions (PPI) are involved in all cellular processes and many represent attractive therapeutic targets. However, the frequently rather flat and large interaction areas render the identification of small molecular PPI inhibitors very challenging. As an alternative, peptide interaction motifs derived from a PPI interface can serve as starting points for the development of inhibitors. However, certain proteins remain challenging targets when applying inhibitors with a competitive mode of action. For that reason, peptide-based ligands with an irreversible binding mode have gained attention in recent years. This review summarizes examples of covalent inhibitors that employ peptidic binders and have been tested in a biological context.

Cyclic Peptide Screening Methods for Preclinical Drug Discovery

Cyclic peptides are among the most diverse architectures for current drug discovery efforts. Their size, stability, and ease of synthesis provide attractive scaffolds to engage and modulate some of the most challenging targets, including protein-protein interactions and those considered to be "undruggable". With a variety of sophisticated screening technologies to produce libraries of cyclic peptides, including phage display, mRNA display, split intein circular ligation of peptides, and in silico screening, a new era of cyclic peptide drug discovery is at the forefront of modern medicine. In this perspective, we begin by discussing cyclic peptides approved for clinical use in the past two decades. Particular focus is placed around synthetic chemistries to generate de novo libraries of cyclic peptides and novel methods to screen them. The perspective culminates with future prospects for generating cyclic peptides as viable therapeutic options and discusses the advantages and disadvantages currently being faced with bringing them to market.

Covalent Proteomimetic Inhibitor of the Bacterial FtsQB Divisome Complex

The use of antibiotics is threatened by the emergence and spread of multidrug-resistant strains of bacteria. Thus, there is a need to develop antibiotics that address new targets. In this respect, the bacterial divisome, a multi-protein complex central to cell division, represents a potentially attractive target. Of particular interest is the FtsQB subcomplex that plays a decisive role in divisome assembly and peptidoglycan biogenesis in E. coli. Here, we report the structure-based design of a macrocyclic covalent inhibitor derived from a periplasmic region of FtsB that mediates its binding to FtsQ. The bioactive conformation of this motif was stabilized by a customized cross-link resulting in a tertiary structure mimetic with increased affinity for FtsQ. To increase activity, a covalent handle was incorporated, providing an inhibitor that impedes the interaction between FtsQ and FtsB irreversibly. The covalent inhibitor reduced the growth of an outer membrane-permeable E. coli strain, concurrent with the expected loss of FtsB localization, and also affected the infection of zebrafish larvae by a clinical E. coli strain. This first-in-class inhibitor of a divisome protein–protein interaction highlights the potential of proteomimetic molecules as inhibitors of challenging targets. In particular, the covalent mode-of-action can serve as an inspiration for future antibiotics that target protein–protein interactions.

Targeting the interaction of β-catenin and TCF/LEF transcription factors to inhibit oncogenic Wnt signaling

The Wnt/β-catenin signaling pathway is crucially involved in embryonic development, stem cell maintenance and tissue renewal. Hyperactivation of this pathway is associated with the development and progression of various types of cancers. The transcriptional coactivator β-catenin represents a pivotal component of the pathway and its interaction with transcription factors of the TCF/LEF family is central to pathway activation. Inhibition of this crucial protein-protein interaction via direct targeting of β-catenin is considered a promising strategy for the inactivation of oncogenic Wnt signaling. This review summarizes advances in the development of Wnt antagonists that have been shown to directly bind β-catenin.

The Effects of Charged Amino Acid Side-Chain Length on Diagonal Cross-Strand Interactions between Carboxylate- and Ammonium-Containing Residues in a β-Hairpin

The β-sheet is one of the common protein secondary structures, and the aberrant aggregation of β-sheets is implicated in various neurodegenerative diseases. Cross-strand interactions are an important determinant of β-sheet stability. Accordingly, both diagonal and lateral cross-strand interactions have been studied. Surprisingly, diagonal cross-strand ion-pairing interactions have yet to be investigated. Herein, we present a systematic study on the effects of charged amino acid side-chain length on a diagonal ion-pairing interaction between carboxylate- and ammonium-containing residues in a β-hairpin. To this end, 2D-NMR was used to investigate the conformation of the peptides. The fraction folded population and the folding free energy were derived from the chemical shift data. The fraction folded population for these peptides with potential diagonal ion pairs was mostly lower compared to the corresponding peptide with a potential lateral ion pair. The diagonal ion-pairing interaction energy was derived using double mutant cycle analysis. The Asp2-Dab9 (Asp: one methylene; Dab: two methylenes) interaction was the most stabilizing (−0.79 ± 0.14 kcal/mol), most likely representing an optimal balance between the entropic penalty to enable the ion-pairing interaction and the number of side-chain conformations that can accommodate the interaction. These results should be useful for designing β-sheet containing molecular entities for various applications.

Design of Protein Segments and Peptides for Binding to Protein Targets

Recent years have witnessed a rise in methods for accurate prediction of structure and design of novel functional proteins. Design of functional protein fragments and peptides occupy a small, albeit unique, space within the general field of protein design. While the smaller size of these peptides allows for more exhaustive computational methods, flexibility in their structure and sparsity of data compared to proteins, as well as presence of noncanonical building blocks, add additional challenges to their design. This review summarizes the current advances in the design of protein fragments and peptides for binding to targets and discusses the challenges in the field, with an eye toward future directions.

Covalent labeling of a chromatin reader domain using proximity-reactive cyclic peptides

Chemical probes for chromatin reader proteins are valuable tools for investigating epigenetic regulatory mechanisms and evaluating whether the target of interest holds therapeutic potential. Developing potent inhibitors for the plant homeodomain (PHD) family of methylation readers remains a difficult task due to the charged, shallow and extended nature of the histone binding site that precludes effective engagement of conventional small molecules. Herein, we describe the development of novel proximity-reactive cyclopeptide inhibitors for PHD3—a trimethyllysine reader domain of histone demethylase KDM5A. Guided by the PHD3–histone co-crystal structure, we designed a sidechain-to-sidechain linking strategy to improve peptide proteolytic stability whilst maintaining binding affinity. We have developed an operationally simple solid-phase macrocyclization pathway, capitalizing on the inherent reactivity of the dimethyllysine ε-amino group to generate scaffolds bearing charged tetraalkylammonium functionalities that effectively engage the shallow aromatic ‘groove’ of PHD3. Leveraging a surface-exposed lysine residue on PHD3 adjacent to the ligand binding site, cyclic peptides were rendered covalent through installation of an arylsulfonyl fluoride warhead. The resulting lysine-reactive cyclic peptides demonstrated rapid and efficient labeling of the PHD3 domain in HEK293T lysates, showcasing the feasibility of employing proximity-induced reactivity for covalent labeling of this challenging family of reader domains.

We describe the development of covalent cyclic peptide ligands which target a chromatin methylation reader domain using a proximity-reactive sulfonyl fluoride moiety.