Peptide‐mediated interactions (PMIs) play a crucial role in cell signaling network, which are responsible for about half of cellular protein–protein associations in the human interactome and have recently been recognized as a new kind of promising druggable target for drug development and disease therapy. In this article, we give a systematic review regarding the proteome‐wide discovery of PMIs and targeting druggable PMIs (dPMIs) with chemical drugs, self‐inhibitory peptides (SIPs) and protein agents, particularly focusing on their implications and applications for therapeutic purpose in omics. We also introduce computational peptidology strategies used to model, analyze, and design PMI‐targeted molecular entities and further extend the concepts of protein context, direct/indirect readout, and enthalpy/entropy effect involved in PMIs. Current issues and future perspective on this topic are discussed. There is still a long way to go before establishment of efficient therapeutic strategies to target PMIs on the omics scale.

Targeting peptide‐mediated interactions in omics

Ehrlichia chaffeensis (E. chaffeensis) has evolved eukaryotic ligand mimicry to repurposes multiple cellular signaling pathways for immune evasion. In this investigation, we demonstrate that TRP120 has a novel repetitive short liner motif (SLiM) that activates the evolutionarily conserved Hedgehog (Hh) signaling pathway to inhibit apoptosis. In silico analysis revealed that TRP120 has sequence and functional similarity with Hh ligands and a candidate Hh ligand SLiM was identified. siRNA knockdown of Hh signaling and transcriptional components significantly reduced infection. Co-immunoprecipitation and surface plasmon resonance demonstrated that rTRP120-TR interacted directly with Hh receptor Patched-2 (PTCH2). E. chaffeensis infection resulted in early activation of Hh transcription factor GLI-1 and upregulation of Hh target genes. Moreover, soluble recombinant TRP120 (rTRP120) activated Hh and induced gene expression consistent with the eukaryotic Hh ligand. The TRP120 Hh SLiM (NPEVLIKD) induced nuclear translocation of GLI-1 in THP-1 cells and primary human monocytes and induced a rapid and expansive activation of Hh pathway target genes. Furthermore, Hh activation was blocked by an α-TRP120 Hh SLiM antibody. TRP120 Hh SLiM significantly increased levels of Hh target, anti-apoptotic protein B-cell lymphoma 2 (BCL-2), and siRNA knockdown of BCL-2 dramatically inhibited infection. Blocking Hh signaling with the inhibitor Vismodegib, induced a pro-apoptotic cellular program defined by decreased mitochondria membrane potential, significant reductions in BCL-2, activation of caspase 3 and 9, and increased apoptotic cells. This study reveals a novel E. chaffeensis SLiM ligand mimetic that activates Hh signaling to maintain E. chaffeensis infection by engaging a BCL-2 anti-apoptotic cellular program. Author summary Ehrlichia chaffeensis is an obligately intracellular bacterium that preferentially infects and replicates within mononuclear phagocytes and survives intracellularly by modulating cellular signaling pathways to subvert innate immune defenses. This investigation reveals the complex and expanding role that the E. chaffeensis TRP120 moonlighting effector and SLiM ligand mimetics have on immune subversion and infection through activation and regulation of evolutionarily conserved signaling pathways. Herein, we define a TRP120 Hh SLiM mimetic that induces Hh signaling and regulates the anti-apoptotic protein BCL-2 to prevent sequential activation of caspase 9 and 3, promoting E. chaffeensis infection. This study defines a novel prokaryotic SLiM mimetic that repurposes evolutionarily conserved eukaryotic signaling pathways to promote survival of an intracellular bacterium.

/pdf/ehrlichia-slim-ligand-mimetic-activates-hedgehog-signaling-312tbahg.pdf

Ehrlichia SLiM ligand mimetic activates Hedgehog signaling to engage a BCL-2 anti-apoptotic cellular program

Abstract Ehrlichia chaffeensis (E. chaffeensis) has evolved eukaryotic ligand mimicry to repurposes multiple cellular signaling pathways for immune evasion. In this investigation, we demonstrate that TRP120 has a novel repetitive s hort li ner m otif (SLiM) that activates the evolutionarily conserved Hedgehog (Hh) signaling pathway to inhibit apoptosis. In silico analysis revealed that TRP120 has sequence and functional similarity with Hh ligands and a candidate Hh ligand SLiM was identified. siRNA knockdown of Hh signaling and transcriptional components significantly reduced infection. Co-immunoprecipitation and surface plasmon resonance demonstrated that rTRP120-TR interacted directly with Hh receptor Patched-2 (PTCH2). E. chaffeensis infection resulted in early activation of Hh transcription factor GLI-1 and upregulation of Hh target genes. Moreover, soluble recombinant TRP120 (rTRP120) activated Hh and induced gene expression consistent with the eukaryotic Hh ligand. The TRP120 Hh SLiM (NPEVLIKD) induced nuclear translocation of GLI-1 in THP-1 cells and primary human monocytes and induced a rapid and expansive activation of Hh pathway target genes. Furthermore, Hh activation was blocked by an α-TRP120 Hh SLiM antibody. TRP120 Hh SLiM significantly increased levels of Hh target, anti-apoptotic protein B-cell lymphoma 2 (BCL-2), and siRNA knockdown of BCL-2 dramatically inhibited infection. Blocking Hh signaling with the inhibitor Vismodegib, induced a pro-apoptotic cellular program defined by decreased mitochondria membrane potential, significant reductions in BCL-2, activation of caspase 3 and 9, and increased apoptotic cells. This study reveals a novel E. chaffeensis SLiM ligand mimetic that activates Hh signaling to maintain E. chaffeensis infection by engaging a BCL-2 anti-apoptotic cellular program. Author summary Ehrlichia chaffeensis is an obligately intracellular bacterium that preferentially infects and replicates within mononuclear phagocytes and survives intracellularly by modulating cellular signaling pathways to subvert innate immune defenses. This investigation reveals the complex and expanding role that the E. chaffeensis TRP120 moonlighting effector and SLiM ligand mimetics have on immune subversion and infection through activation and regulation of evolutionarily conserved signaling pathways. Herein, we define a TRP120 Hh SLiM mimetic that induces Hh signaling and regulates the anti-apoptotic protein BCL-2 to prevent sequential activation of caspase 9 and 3, promoting E. chaffeensis infection. This study defines a novel prokaryotic SLiM mimetic that repurposes evolutionarily conserved eukaryotic signaling pathways to promote survival of an intracellular bacterium. 

Ehrlichia chaffeensis TRP120 effector has evolved short linear motif (SLiM) ligand mimicry to repurpose multiple evolutionarily conserved cellular signaling pathways including Wnt, Notch and Hedgehog. In this investigation, we demonstrate that E. chaffeensis and recombinant TRP120 deactivate Hippo signaling resulting in activation of Hippo transcription coactivator Yap and target gene expression. Moreover, a homologous 6 amino acid (QDVASH) SLiM shared by TRP120 and Wnt3a/5a ligands phenocopied Yap and β-catenin activation induced by E. chaffeensis, rTRP120 and Wnt5a. Similar Hippo gene expression profiles were also stimulated by E. chaffeensis, rTRP120, SLiM and Wnt5a. Single siRNA knockdown of Hippo transcription co-activator/factors (Yap and TEAD) significantly decreased E. chaffeensis infection. Yap activation was abolished in THP-1 Wnt Frizzled-5 (Fzd5) receptor knockout cells (KO), demonstrating Fzd5 receptor dependence. In addition, TRP120 Wnt-SLiM antibody blocked Hippo deactivation (Yap activation). Expression of anti-apoptotic Hippo target gene SLC2A1 (encodes glucose transporter 1; GLUT1) was upregulated by E. chaffeensis and corresponded to increased levels of GLUT1. Conversely, siRNA knockdown of SLC2A1 significantly inhibited infection. Higher GLUT1 levels correlated with increased BCL-xL and decreased Bax levels. Moreover, blocking Yap activation with the inhibitor Verteporfin induced apoptosis that corresponded to significant reductions in levels of GLUT1 and BCL-xL, and activation of Bax and Caspase-3 and -9. This study identifies a novel shared Wnt/Hippo SLiM ligand mimetic and demonstrates that E. chaffeensis deactivates the Hippo pathway to engage the anti-apoptotic Yap-GLUT1-BCL-xL axis.

/pdf/ehrlichia-wnt-short-linear-motif-ligand-mimetic-deactivates-3cufraxc.pdf

Ehrlichia Wnt short linear motif ligand mimetic deactivates the Hippo pathway to engage the anti-apoptotic Yap-GLUT1-BCL-xL axis

Viruses are obligate intracellular parasites that depend on host cellular machinery for performing even basic biological functions. One of the many ways they achieve this is through molecular mimicry, wherein the virus mimics a host sequence or structure, thereby being able to hijack the host's physiological interactions for its pathogenesis. Such adaptations are specific recognitions that often confer tissue and species-specific tropisms to the virus, and enable the virus to utilise previously existing host signalling networks, which ultimately aid in further steps of viral infection, such as entry, immune evasion and spread. A common form of sequence mimicry utilises short linear motifs (SLiMs). SLiMs are short-peptide sequences that mediate transient interactions and are major elements in host protein interaction networks. This work is aimed at providing a comprehensive review of current literature of some well-characterised SLiMs that play a role in the attachment and entry of viruses into host cells, which mimic physiological receptor-ligand interactions already present in the host. Considering recent trends in emerging diseases, further research on such motifs involved in viral entry can help in the discovery of previously unknown cellular receptors utilised by viruses, as well as help in the designing of targeted therapeutics such as vaccines or inhibitors directed towards these interactions. 

/pdf/molecular-mimicry-of-host-short-linear-motif-mediated-1mipqrze.pdf

Molecular mimicry of host short linear motif-mediated interactions utilised by viruses for entry

Linear motifs have an integral role in dynamic cell functions including cell signalling, the cell cycle and others. However, due to their small size, low complexity, degenerate nature, and frequent mutations, identifying novel functional motifs is a challenging task. Viral proteins rely extensively on the molecular mimicry of cellular linear motifs for modifying cell signalling and other processes in ways that favour viral infection. This study aims to discover human linear motifs convergently evolved also in disordered regions of viral proteins, under the hypothesis that these will result in enrichment in functional motif instances. We systematically apply computational motif prediction, combined with implementation of several functional and structural filters to the most recent publicly available human-viral and human-human protein interaction network. By limiting the search space to the sequences of viral proteins, we observed an increase in the sensitivity of motif prediction, as well as improved enrichment in known instances compared to the same analysis using only human protein interactions. We identified > 8,400 motif instances at various confidence levels, 105 of which were supported by all functional and structural filters applied. Overall, we provide a pipeline to improve the identification of functional linear motifs from interactomics datasets and a comprehensive catalogue of putative human motifs that can contribute to our understanding of the human domain-linear motif code and the mechanisms of viral interference with this.

https://www.biorxiv.org/content/biorxiv/early/2021/06/26/2021.06.25.449930.full.pdf

Use of viral motif mimicry improves the proteome-wide discovery of human linear motifs

Synthetic lethal interactions are of paramount importance both in biology and in medicine, and hence increasing efforts have been devoted to their systematic identification. A recent computational study found that synthetic lethal genes tend to be further away in chromosomes than random (i.e. repulsion), which was shown to provide bacterial genomes with greater robustness to large-scale DNA deletions. To evaluate this observation using published experimental data and to test its generalizability in eukaryotic genomes, we leveraged the wealth of experimentally determined synthetic lethal genetic interactions curated in BioGRID (Biological General Repository for Interaction Datasets) and CGIdb (Cancer Genetic Interaction db) databases. In support of the previous study, we observed repulsion of synthetic lethal gene pairs, manifested as striking depletion of closely located synthetic lethal gene pairs (i.e. with genomic distance

/pdf/chromosomal-arrangement-of-synthetic-lethal-gene-pairs-1g9cnt3oqk.pdf

Wadie B

Papers

Use of viral motif mimicry improves the proteome-wide discovery of human linear motifs

Chromosomal arrangement of synthetic lethal gene pairs: repulsion or attraction?