Context contribution to the intermolecular recognition of human ACE2-derived peptides by SARS-CoV-2 spike protein: implications for improving the peptide affinity but not altering the peptide specificity by optimizing indirect readout

The C-terminal self-binding helical peptide of human estrogen-related receptor γ can be druggably targeted by a novel class of rationally designed peptidic antagonists

Orphan nuclear estrogen-related receptor γ (ERRγ) has been recognized as a potential therapeutic target for cancer, inflammation and metabolic disorder. The ERRγ contains a regulatory AF2 helical tail linked C-terminally to its ligand-binding domain (LBD), which is a self-binding peptide (SBP) and serves as molecular switch to dynamically regulate the receptor alternation between active and inactive states by binding to and unbinding from the AF2-binding site on ERRγ LBD surface, respectively. Traditional ERRγ modulators are all small-molecule chemical ligands that can be classified into agonists and inverse agonists in terms of their action mechanism; the agonists stabilize the AF2 in ABS site with an agonist conformation, while the inverse agonists lock the AF2 out of the site to largely abolish ERRγ transcriptional activity. Here, a class of ERRγ peptidic antagonists was described to compete with native AF2 for the ABS site, thus blocking the active state of AF2 binding to ERRγ LBD domain. Self-inhibitory peptide was derived from the SBP-covering AF2 region and we expected it can rebind potently to the ABS site by reducing its intrinsic disorder and entropy cost upon the rebinding. Hydrocarbon stapling was employed to do so, which employed an all-hydrocarbon bridge across the [i, i + 4]-anchor residue pair in the N-terminal, middle or C-terminal region of the self-inhibitory peptide. As might be expected, it is revealed that the stapled peptides are good binders of ERRγ LBD domain and can effectively compete with the native AF2 helical tail for ERRγ ABS site, which exhibit a basically similar binding mode with AF2 to the site and form diverse noncovalent interactions with the site, thus conferring stability and specificity to the domain-peptide complexes.

Facilitating the drug repurposing with iC/E strategy: A practice on novel nNOS inhibitor discovery

Over the past decades, many existing drugs and clinical/preclinical compounds have been repositioned as new therapeutic indication from which they were originally intended and to treat off-target diseases by targeting their noncognate protein receptors, such as Sildenafil and Paxlovid, termed drug repurposing (DRP). Despite its significant attraction in the current medicinal community, the DRP is usually considered as a matter of accidents that cannot be fulfilled reliably by traditional drug discovery protocol. In this study, we proposed an integrated computational/experimental (iC/E) strategy to facilitate the DRP within a framework of rational drug design, which was practiced on the identification of new neuronal nitric oxide synthase (nNOS) inhibitors from a structurally diverse, functionally distinct drug pool. We demonstrated that the iC/E strategy is very efficient and readily feasible, which confirmed that the phosphodiesterase inhibitor DB06237 showed a high inhibitory potency against nNOS synthase domain, while other two general drugs, i.e. DB02302 and DB08258, can also inhibit the synthase at nanomolar level. Structural bioinformatics analysis revealed diverse noncovalent interactions such as hydrogen bonds, hydrophobic forces and van der Waals contacts across the complex interface of nNOS active site with these identified drugs, conferring both stability and specificity for the complex recognition and association.

Importance of Magnesium Status in COVID-19

A large amount of published research points to the interesting concept (hypothesis) that magnesium (Mg) status may have relevance for the outcome of COVID-19 and that Mg could be protective during the COVID disease course. As an essential element, Mg plays basic biochemical, cellular, and physiological roles required for cardiovascular, immunological, respiratory, and neurological functions. Both low serum and dietary Mg have been associated with the severity of COVID-19 outcomes, including mortality; both are also associated with COVID-19 risk factors such as older age, obesity, type 2 diabetes, kidney disease, cardiovascular disease, hypertension, and asthma. In addition, populations with high rates of COVID-19 mortality and hospitalization tend to consume diets high in modern processed foods, which are generally low in Mg. In this review, we review the research to describe and consider the possible impact of Mg and Mg status on COVID-19 showing that (1) serum Mg between 2.19 and 2.26 mg/dL and dietary Mg intakes > 329 mg/day could be protective during the disease course and (2) inhaled Mg may improve oxygenation of hypoxic COVID-19 patients. In spite of such promise, oral Mg for COVID-19 has thus far been studied only in combination with other nutrients. Mg deficiency is involved in the occurrence and aggravation of neuropsychiatric complications of COVID-19, including memory loss, cognition, loss of taste and smell, ataxia, confusion, dizziness, and headache. Potential of zinc and/or Mg as useful for increasing drug therapy effectiveness or reducing adverse effect of anti-COVID-19 drugs is reviewed. Oral Mg trials of patients with COVID-19 are warranted.

Systematic analysis and comparison of peptide specificity and selectivity between their cognate receptors and noncognate decoys

Protein-peptide interactions (PpIs) play an important role in cell signaling networks and have been exploited as new and attractive therapeutic targets. The affinity and specificity are two unity-of-opposite aspects of PpIs (and other biomolecular interactions); the former indicates the absolute binding strength between the peptide ligand and its cognate protein receptor in a PpI, while the latter represents the relative recognition selectivity of the peptide ligand for its cognate protein receptor in a PpI over those noncognate decoys that could be potentially encountered by the peptide in cell. Although the PpI binding affinity has been widely investigated over the past decades, the peptide recognition specificity (and selectivity) still remains largely unexplored to date. In this study, we classified PpI specificity into three types: (i) class-I specificity: peptide selectivity for its cognate wild-type protein receptor over the noncognate mutant decoys of this receptor, (ii) class-II specificity: peptide selectivity for its cognate protein receptor over other noncognate decoys that are homologous with this receptor, and (iii) class-III specificity: peptide selectivity for its cognate protein receptor over other noncognate decoys that are the cognate receptors of other peptides. We performed affinity and selectivity analysis for the three types of PpI specificity and revealed that the PpIs generally exhibit a moderate or modest specificity; peptide selectivity increases in the order: class-I < class-II < class-III. All the three types of PpI specificity were observed to have no statistically significant correlation with peptide length and hydrophobicity, but the class-I and class-II specificities can be influenced considerably by peptide secondary structures; the high specificity is preferentially associated with ordered structure types as compared to undefined structure types. In addition, the mutation distribution (for class-I specificity), sequence conservation (for class-II specificity), and structural similarity (for class-III specificity) seem also to address effects on peptide selectivity.

Targeting peptide-mediated interactions in omics

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.

The binding affinity of human pediatric respiratory syncytial virus Phosphoprotein's C-terminal tail to nucleocapsid can be improved by a rationally designed halogen-bonded system

Human respiratory syncytial virus (hRSV) is a common contagious virus that causes infections of pediatric pneumonia and specifically impacts infants and small children. The hRSV phosphoprotein is a key component of the viral RNA polymerase, which can interact with nucleocapsid and other partners through its C-terminal tail (CTT) to promote the formation of viral transcriptase complex, where the Phe241 is a key anchor residue. Based on the crystal template-modeled complex structure of hRSV nucleocapsid with a peptidic segment derived from the phosphoprotein's CTT, we successfully introduced a rationally designed halogen-bonded system to the complex interface by substituting para (p)-position of the side-chain phenyl moiety of CTT Phe241 residue with a halogen atom X (X = F, Cl, Br or I). The halogen-bonded system consists of a halogen bond (X-bond) between nucleocapsid Ser131 residue and CTT Phe241 residue as well as a hydrogen bond (H-bond) between nucleocapsid Ser131 residue and nucleocapsid Glu128 residue; the X-bond and H-bond share a common hydroxyl group of nucleocapsid Ser131 residue. High-level theoretical calculations suggested that bromine Br is the best choice that can render strong potency for the X-bond and can confer high affinity to the nucleocapsid-CTT binding. Affinity analysis revealed that the p-brominated CTT ([p]bCTT) exhibited 6.3-fold affinity improvement relative to its nonhalogenated counterpart. In contrast, the Br-substitutions at ortho (o)- and meta (m)-positions, which resulted in two negative controls of o-brominated [o]bCTT and m-brominated [m]bCTT, respectively, were unable to form effective X-bond with nucleocapsid according to theoretical investigation and did not improve the binding affinity essentially relative to native CTT.

Structural modeling, energetic analysis and molecular design of a π-stacking system at the complex interface of pediatric respiratory syncytial virus nucleocapsid with the C-terminal peptide of phosphoprotein

Human respiratory syncytial virus (RSV) is a primary cause of lower respiratory tract infections and hospital visits during infancy and childhood. The RSV phosphoprotein (P) is a major polymerase cofactor that interacts with nucleoprotein (N) to promote the recognition of ribonucleoprotein complex (RNP) by viral RNA polymerase. The binding pocket of N protein is chemically diverse, in or around which a number of aromatic and charged amino acid residues are observed. Previously, a nonapeptide segment (P peptide, ²³³DNDLSLEDF²⁴¹) representing the C-terminal tail of P protein was identified to mediate the N-P interaction with a moderate affinity, in which the Phe241 at the end of P's C-terminus plays a critical role in the binding of P peptide to N protein. Here, we found that the side-chain aromatic phenyl moiety of P Phe241 residue can form short- and long-range cation-π interactions with N Arg132 and Arg150 residues, respectively, as well as T-shaped and parallel-displaced π-π stackings with N Tyr135 and His151 residues, respectively, which co-define a geometrically satisfactory π-stacking system at the complex interface of N protein with P peptide, thus largely stabilizing the complex architecture. The stacking effect was further optimized by systematically mutating the P Phe241 residue to other natural and non-natural aromatic amino acids with diverse chemical substitutions at the phenyl moiety to examine their structural and energetic effects on π-stacking system and on protein-peptide binding. The electron-donating mutations at the phenyl moiety of P Phe241 residue can effectively enhance the π-stacking system and then promote peptide binding, whereas the bulky and positively charged mutations would considerably impair the peptide potency by introducing steric hindrance and electrostatic repulsion. The [Tyr]P, [Thp]P and [Fph]P mutants were determined to have an increased affinity relative to wild-type P peptide, which could be used as self-inhibitory peptides to competitively disrupt the native interaction between N and P proteins.

Human genome-wide analysis and identification of the hyperphosphorylation-elicited interactions between subarachnoid tau protein and phosphoprotein-binding domains

Abnormally hyperphosphorylated tau can be recognized by a variety of phosphoprotein-binding domains (PBDs) to elicit downstream tau signaling in neuropathology, which has been found to have a potential association with subarachnoid hemorrhage. In this study, the genome-wide binding behavior of tau phosphorylation sites (p-sites) to PBDs involved in subarachnoid hyperphosphorylation events was systematically profiled at molecular level by integrating peptide docking, structural minimization, affinity scoring, and binding assay, from which a number of potent PBD-p-site interaction pairs were identified. It was revealed that the PBD domains exhibit distinct binding preferences for phosphotyrosine, phosphoserine, and phosphothreonine p-sites; the PBD-recognition specificity of different tau p-sites is not overlapped with each other, and their phosphorylations would therefore regulate varying biological functions in tau signaling. A number of PBD-p-site pairs were identified to have potent binding potency as compared to others. The KCIP-pS[393-399] pair was found as a strong binder, which was further optimized with a rational peptide design protocol to derive a number of affinity-improved phosphopeptides. Structural analysis revealed diverse noncovalent chemical forces across the complex interface of KCIP domain with a designed high-affinity pS[393-399]-d4, which confers both stability and specificity to the domain-peptide complex system, with affinity improved by 10.9-fold relative to the native pS[393-399].

Molecular design and rational optimization of synergistic effect between the two wings of a roughly orthogonal cation-π-π stacking system at nasopharyngeal carcinoma YAP1-TEAD4 parallel Helix-Helix interaction interface

The Yes-associated protein-1 (YAP1) is an essential regulator of human Hippo signaling pathway and functions through interaction with TEA domain-4 (TEAD4) transcription factor involved in the tumorigenesis of nasopharyngeal cancer. Previously, a parallel helix-helix interaction (PHHI) was identified as the key hotspot at YAP1-TEAD4 complex interface and has been exploited as an attractive druggable target to disrupt the complex. In this study, we investigated a roughly orthogonal cation-π-π stacking system across the crystal PHHI packing interface by integrating computational modeling and binding assay, which forms between one YAP1 helical residue Phe69 and two TEAD4 helical residues Phe373/Lys376. A synergistic effect between cation-π and π-π interactions was observed; they separately represent two wings of the stacking system. The π-electron is primarily responsible for the synergistic effect. Combination between diverse aromatic/charged amino acids. as well as neutral alanine on the cation-π-π stacking, revealed that the presence of aromatic tryptophan and charged arginine at, respectively, the residues 373 and 376 of TEAD4 helix can considerably improve PHHI binding affinity by ~6-fold, whereas neutral alanine substitution on each residue and on both would reduce the affinity significantly, confirming a strong synergistic effect involved in the roughly orthogonal cation-π-π stacking system at YAP1-TEAD4 PHHI interface.

Comprehensive binary interaction mapping of τ phosphotyrosine sites with SH2 domains in the human genome: Implications for the rational design of self-inhibitory phosphopeptides to target τ hyperphosphorylation signaling in Alzheimer's Disease

Human microtubule-associated protein Tau (τ) is abundant in the axons of neurons where it stabilizes microtubule bundles; abnormally hyperphosphorylated τ is a hallmark of Alzheimer's disease (AD) and related tauopathies. The hyperphosphorylation events can be recognized by phosphotyrosine-recognition domain SH2 (Src homology 2) to elicit downstream τ signaling in AD pathology. In this study, a comprehensive binary interaction map (CBIM) of all the 6 τ phosphotyrosine sites with 120 SH2 domains in the human genome was systematically created at structural level using computational analyses and binding assays, from which we were able to identify those of strong and moderate binding pairs of sites to domains. It is found that the SH2-recognition specificity of different τ phosphotyrosine sites has been evolutionally optimized to become roughly orthogonal to each other, and thus these site phosphorylations would regulate different but probably partially overlapped biological functions in τ signaling. Some SH2 groups such as SRC, RIN, PLCG, SOCS and SH2D were revealed to have effective binding potency as compared to others; they could be regarded as potential τ-associated proteins to transduce the downstream signaling. We further determined the systematic binding affinities of 6 τ-phosphopeptides to the 11 SH2 domains in SRC group, from which the FYN-τ¹⁸ and YES-τ²⁹ pairs were identified as strong binders. Subsequently, rational molecular design was performed on τ¹⁸ and τ²⁹ to derive a number of τ-phosphopeptide mutants with increased affinity; they are self-inhibitory candidates to competitively target τ hyperphosphorylation events in AD. In addition, it is revealed that the primary anchor pY₀ and secondary anchor X₊₃ of τ-phosphopeptides play an important role in SRC-group SH2 recognition, which confer stability and specificity to the SH2-phosphopeptide binding, respectively.

Interleukin-1α, Interleukin-1β and Interleukin-1 Receptor Antagonist Share a Common U-shaped Recognition Epitope on Interleukin-1 Receptor Surface

Interleukin-1 (IL-1) plays a central role in the regulation of immune and inflammatory responses. There are two forms of IL-1 agonists (IL-1α and IL-1β) and one form of IL-1 antagonist (IL-1Ra); they share a similar binding mode to IL-1 receptor (IL-1R) but exhibit opposite biological functions on the receptor. In this study, the intermolecular interactions of IL-1R receptor with IL-1α, IL-1β and IL-1Ra ligands were systematically investigated at structural, energetic and dynamic levels. It was found that the receptor primarily adopts a U-shaped, double-stranded and linear/conformational-hybrid epitope to commonly interact with the three ligands. The epitope covers a common protein segment (residues 107-127), which is fully located within in the C2T2 subsdomain of IL-1R extracellular domain (ECD) and contributes ~40% to the total binding energy of IL-1R/ligand association. The epitope is natively folded into an ordered conformation in IL-1R protein context but would become largely disordered out of the context. Here, we adopted a disulfide bridge to staple U-shaped epitope-derived peptides, which can be effectively constrained into a native-like conformation and thus exhibit an improved affinity to ligands as compared to their unstapled counterpart, with affinity increase by up to ~15-fold. These disulfide bridges were designed to point out of ligand/peptide complex interface and thus would not disrupt the direct complex interaction. Energetic decomposition imparted that the stapling has only a modest influence on the interaction enthalpy and desolvation effect of ligand/peptide binding, but can substantially reduce entropy penalty upon the binding. For a peptide, the stapling-addressed entropic reduction can be roughly regarded as a constant, which only improves peptide affinity to these ligands, but does not change peptide selectivity over different ligands. This article is protected by copyright. All rights reserved.

Structural Mapping of BMP Conformational Epitopes and Bioengineering Design of Osteogenic Peptides to Specifically Target the Epitope-Binding Sites

Introduction

Human bone morphogenetic proteins (BMPs) constitute a large family of cytokines related to members of the transforming growth factor-β superfamily, which fulfill biological functions by specificity binding to their cognate type I (BRI) and type II (BRII) receptors through conformational wrist and linear knuckle epitopes, respectively.

Methods and Results

We systematically examined the intermolecular recognition and interaction between the BMP proteins and BRI receptor at structural, energetic and dynamic levels. The BRI-binding site consists of three hotspot regions on BMP surface, which totally contribute ~70% potency to the BMP-BRI binding events and represent the core sections of BMP conformational wrist epitope; the contribution increases in the order: hotspot 2 (~ 8%) < hotspot 3 (~ 20%) < hotspot 1 (~ 40%). Multiple sequence alignment and structural superposition revealed a consensus sequence pattern and a similar binding mode of the three hotspots shared by most BMP members, indicating a high conservation of wrist epitope in BMP family. The three hotspots are natively folded into wellstructured U-shaped,, loop and double-stranded conformations in BMP proteins, which, however, would become largely disordered when splitting from the protein context to derive osteogenic peptides in free state, thus largely impairing their rebinding capability to BRI receptor. In this respect, cyclization strategy was employed to constrain hotspot 1/3-derived peptides into a native-like conformation, which was conducted by adding a disulfide bond across the ending arms of linear peptides based on their native conformations. Fluorescence-based assays substantiated that the cyclization can effectively improve the binding affinities of osteogenic peptides to BRI receptor by 3-6-fold. The cyclic peptides also exhibit a good selectivity for BRI over BRII (> 5-fold), confirming that they can specifically target the wrist epitope-binding site of BRI receptor.

Conclusion

The rationally designed cyclic peptides can be regarded as the promising lead entities that should be further chemically modified to enhance their in vivo biological stability for further bioengineering therapeutic osteogenic peptides against chondrocyte senescence and bone disorder.

Quantitative structure-activity relationship modeling reveals the minimal sequence requirement and amino acid preference of sirtuin-1's deacetylation substrates in diabetes mellitus

Sirtuin 1 (SIRT1) is a nicotinamide adenine dinucleotide (NAD[Formula: see text]-dependent deacetylase involved in multiple glucose metabolism pathways and plays an important role in the pathogenesis of diabetes mellitus (DM). The enzyme specifically recognizes its deacetylation substrates' peptide segments containing a central acetyl-lysine residue as well as a number of amino acids flanking the central residue. In this study, we attempted to ascertain the minimal sequence requirement (MSR) around the central acetyl-lysine residue of SIRT1 substrate-recognition sites as well as the amino acid preference (AAP) at different residues of the MSR window through quantitative structure-activity relationship (QSAR) strategy, which would benefit our understanding of SIRT1 substrate specificity at the molecular level and is also helpful to rationally design substrate-mimicking peptidic agents against DM by competitively targeting SIRT1 active site. In this procedure, a large-scale dataset containing 6801 13-mer acetyl-lysine peptides (and their SIRT1-catalyized deacetylation activities) were compiled to train 10 QSAR regression models developed by systematic combination of machine learning methods (PLS and SVM) and five amino acids descriptors (DPPS, T-scale, MolSurf, [Formula: see text]-score, and FASGAI). The two best QSAR models (PLS+FASGAI and SVM+DPPS) were then employed to statistically examine the contribution of residue positions to the deacetylation activity of acetyl-lysine peptide substrates, revealing that the MSR can be represented by 5-mer acetyl-lysine peptides that meet a consensus motif X[Formula: see text]X[Formula: see text]X[Formula: see text](AcK)₀X[Formula: see text]. Structural analysis found that the X[Formula: see text] and (AcK)₀ residues are tightly packed against the enzyme active site and confer both stability and specificity for the enzyme-substrate complex, whereas the X[Formula: see text], X[Formula: see text] and X[Formula: see text] residues are partially exposed to solvent but can also effectively stabilize the complex system. Subsequently, a systematic deacetylation activity change profile (SDACP) was created based on QSAR modeling, from which the AAP for each residue position of MSR was depicted. With the profile, we were able to rationally design an SDACP combinatorial library with promising deacetylation activity, from which nine MSR acetyl-lysine peptides as well as two known SIRT1 acetyl-lysine peptide substrates were tested by using SIRT1 deacetylation assay. It is revealed that the designed peptides exhibit a comparable or even higher activity than the controls, although the former is considerably shorter than the latter.

Systematic analysis and molecular profiling of EGFR allosteric inhibitor cross-reactivity across the proto-oncogenic ErbB family kinases by integrating dynamics simulation, energetics calculation and biochemical assay

Human ErbB family of proteins contains four receptor tyrosine kinases (EGFR, Her2, Her3 and Her4) and has been established as a group of attractive druggable targets against diverse cancers. Over the past decades, a variety of ATP-competitive inhibitors have been discovered to target the orthosteric site of EGFR, which, however, would eventually develop acquired drug resistance due to the missense mutations T790M/C797S occurring in orthosteric site. In recent years, a number of forth-generation inhibitors have been successfully designed to overcome the T790M/C797S-induced drug resistance by targeting EGFR allosteric site instead of orthosteric site. Considering that the four proto-oncogenic ErbB kinases share a high conservation in sequence, structure and function, we herein attempted to investigate the binding potency and cross-reactivity of cognate EGFR allosteric inhibitors over noncognate Her2, Her3 and Her4 kinases--they are closely related to gynecological tumors such as ovarian cancer but no allosteric inhibitors have been reported specifically for them to date. A systematic affinity profile of 12 allosteric inhibitors and 4 orthosteric inhibitors to the 4 ErbB kinases was created by integrating dynamics simulations, energetics calculations and biochemical assays, which was then used to derive a systematic inhibitor selectivity profile for EGFR over other three kinases. It is found that allosteric and orthosteric inhibitors exhibit moderate and modest cross-reactivity across the ErbB family, respectively, but the former generally has a higher binding potency than the latter due to the additional energy cost used for inducing kinase conformational change. Moreover, most allosteric inhibitors can be sensitized by Her2 T798M gatekeeper mutation, a counterpart of EGFR T790M gatekeeper mutation that has been previously reported to cause generic drug resistance for orthosteric inhibitors.

Integrated unsupervised-supervised modeling and prediction of protein-peptide affinities at structural level

Cell signal networks are orchestrated directly or indirectly by various peptide-mediated protein-protein interactions, which are normally weak and transient and thus ideal for biological regulation and medicinal intervention. Here, we develop a general-purpose method for modeling and predicting the binding affinities of protein-peptide interactions (PpIs) at the structural level. The method is a hybrid strategy that employs an unsupervised approach to derive a layered PpI atom-residue interaction (ulPpI[a-r]) potential between different protein atom types and peptide residue types from thousands of solved PpI complex structures and then statistically correlates the potential descriptors with experimental affinities (KD values) over hundreds of known PpI samples in a supervised manner to create an integrated unsupervised-supervised PpI affinity (usPpIA) predictor. Although both the ulPpI[a-r] potential and usPpIA predictor can be used to calculate PpI affinities from their complex structures, the latter seems to perform much better than the former, suggesting that the unsupervised potential can be improved substantially with a further correction by supervised statistical learning. We examine the robustness and fault-tolerance of usPpIA predictor when applied to treat the coarse-grained PpI complex structures modeled computationally by sophisticated peptide docking and dynamics simulation. It is revealed that, despite developed solely based on solved structures, the integrated unsupervised-supervised method is also applicable for locally docked structures to reach a quantitative prediction but can only give a qualitative prediction on globally docked structures. The dynamics refinement seems not to change (or improve) the predictive results essentially, although it is computationally expensive and time-consuming relative to peptide docking. We also perform extrapolation of usPpIA predictor to the indirect affinity quantities of HLA-A*0201 binding epitope peptides and NHERF PDZ binding scaffold peptides, consequently resulting in a good and moderate correlation of the predicted KD with experimental IC50 and BLU on the two peptide sets, with Pearson's correlation coefficients Rp = 0.635 and 0.406, respectively.

Systematic profiling and identification of the peptide-mediated interactions between human Yes-associated protein and its partners in esophageal cancer

Human Yes-associated protein (YAP) is involved in the Hippo signaling pathway and serves as a coactivator to modulate gene expression, which contains a transactivation domain (TD) responsible for binding to the downstream TEA domain family (TEAD) of transcription factors and two WW1/2 domains that recognize the proline-rich motifs (PRMs) present in a variety of upstream protein partners through peptide-mediated interactions (PMIs). The downstream YAP TD-TEAD interactions are closely associated with gastric cancer, and a number of therapeutic agents have been developed to target the interactions. In contrast, the upstream YAP WW1/2-partner interactions are thought to be involved in esophageal cancer but still remain largely unexplored. Here, we attempted to elucidate the complicated PMIs between the YAP WW1/2 domains and various PRMs of YAP-interacting proteins. A total of 106 peptide segments carrying the class I WW-binding motif [P/L]Px[Y/P] were extracted from 22 partner candidates, which are potential recognition sites of YAP WW1/2 domains. Structural and energetic analyses of the intermolecular interactions between the domains and peptides created a systematic domain-peptide binding profile, from which a number of biologically functional PMIs were identified and then substantiated in vitro using fluorescence spectroscopy assays. It is revealed that: (a) The sequence requirement for the partner recognition site binding to YAP WW1/2 domains is a decapeptide segment that contains a core PRM motif as well as two three-residue extensions from each side of the motif; the core motif and extended sections are responsible for the binding stability and recognition specificity of domain-peptide interaction, respectively. (b) There is an exquisite difference in the recognition specificity of the two domains; the LPxP and PPxP appear to more prefer WW1 than WW2, whereas the WW2 can bind more effectively to LPxY and PPxY than WW1. (c) WW2 generally exhibits a higher affinity to the panel of recognition site candidates than WW1. In addition, a number of partner peptides were found as promising recognition sites of the two domains and/or to have a good selectivity between the two domains. For example, the DVL1 peptide was determined to have moderate affinity to WW2 and strong selectivity for WW2 over WW1. Hydrogen bonds play a central role in selectivity.

Interleukin-25 recognition by its unique receptor IL-17Rb via two discrete linear and cyclic epitopes

Interleukin-17 (IL-17) is a family of pro-inflammatory cytokines and has been involved in the pathogenesis of chronic inflammatory and autoimmune diseases. The IL-17E, also known as IL-25, is a distinct member of this family that binds to its unique receptor IL-17Rb to induce the activation of nuclear factor kappa-light-chain enhancer of activated B cells. Here, we systematically examined the intermolecular recognition and association of IL-25 with IL-17Rb and demonstrated that the IL-25 primarily adopts two discrete linear and cyclic epitopes to interact with IL-17Rb. The two epitopes are separately located in the monomers 1 and 2 of IL-25 homodimer and cover sequences ¹²⁵ DPRGNSELLYHN¹³⁶ and ⁷⁷ ELDRDLNRLPQDLY⁹⁰ . They totally contribute 71.6% binding energy to the full-length IL-25. The linear epitope targets a site spanning over the extracellular fnIIID1 and fnIIID2 domains of IL-17Rb, while the cyclic epitope primarily binds at the fnIIID1 domain. In addition, we also found that the linear and cyclic epitopes are natively folded into ordered single-stranded and double-stranded conformations in IL-25 protein context, respectively, but would become largely disordered when splitting from the context to be free peptides, which, however, cannot bind effectively to IL-17Rb as them in the native state. In this respect, we extended the cyclic epitope to cover the whole IL-25 double-stranded region and added a disulfide bridge across its two strands at three selected anchor residue pairs. It is revealed that the disulfide-stapled peptides can be constrained into a native-like conformation and thus exhibit an improved binding potency to IL-17Rb as compared to their unstapled counterpart.

Structural definition of the discrete hotspot sites of BMP-2 conformational wrist epitope and rational design of the hotspot-derived osteogenic peptides against chondrocyte senescence

The bone morphogenetic protein-2 (BMP-2) is an essential regulator of bone formation and remodeling, which has also been implicated in the pathogenesis of osteoarthritis and its closely related chondrocyte senescence. The BMP-2 uses a conformational wrist epitope and a linear knuckle epitope to interact with type-I (BMPR-I) and type-II (BMPR-II) receptors, respectively. Previously, the knuckle epitope has been intensely studied, but the wrist epitope still remains largely unexplored due to its discontinuous nature. In the present work, the intermolecular interaction of BMP-2 with BMPR-I was investigated systematically at structural, energetic and dynamic levels. Three discrete hotspots that represent the key BMPR-I recognition sites of BMP-2 were identified; they are spatially dispersed over the two monomers of BMP-2 dimer and totally account for 83.5 % binding potency of BMP-2 to BMPR-I (hotspot 1: residues 49-70 in monomer 1; hotspot 2: residues 24-31 in monomer 2; hotspot 3: residues 88-107 in monomer 2). Therefore, we defined the three discrete hotspot sites as the core region of wrist epitope; their contribution to the binding increases in the order: hotspot 2 < hotspot 3 < hotspot 1. We demonstrated that the primary hotspot 1 site has a native U-shaped conformation in the full-length BMP-2 protein context, but it cannot maintain in the native conformation when split from the context to obtain a free hotspot-1 peptide, thus largely impairing its binding potency to BMPR-I. We further employed disulfide-bonded cyclization and head-to-tail cyclization to constrain the peptide conformation, and found that only the former can effectively constrain the peptide into native conformation, thus considerably improving its binding affinity to BMPR-I, whereas the latter totally disorders the native conformation, thus rendering the peptide as a full nonbinder of BMPR-I.

Molecular conversion of MIG6 hotspot-3 peptide from the nonbinder to a moderate binder of HER2 by rational design of an orthogonal interaction system at the HER2-peptide interface

Human epidermal growth factor receptor 2 (HER2) has been established as an approved druggable target for the treatment of patients with diverse gynecological tumors such as ovarian, cervical and breast cancers. The mitogen-inducible gene 6 (MIG6) protein is a negative regulator of HER2 signaling by using its Seg1 segment to disrupt the allosteric dimerization of HER2 kinase domain. Previous studies found that the Seg1 adopts three separated hotspots to interact with the HER2 dimerization interface, in which the third hotspot (H3) is located at the core region of the interface but its derived H3 peptide (356PKYVS360) and Tyr358Phe mutant (356PKFVS360) cannot bind effectively to the interface in an independent manner. In this study, we demonstrate that the H3 peptide can be converted from nonbinder to a moderate binder of HER2 by just adding an orthogonal noncovalent interaction system (X⋯O┄H) between a halogen bond (X⋯O) and a hydrogen bond (H┄O) involving peptide Phe358 residue and HER2 Val948/Trp951 residues. High-level calculations are utilized to rigorously characterize and rationally design the X⋯O┄H system, which is then optimized with different halogen atoms and at different substituting positions. It is revealed that there is a synergistic effect between the X⋯O and H┄O of the orthogonal interaction system; formation of the halogen bond can enhance the interaction strength of the hydrogen bond. In silico analysis and in vitro assay reach a consistence that Br-substitution at the m-position of peptide Phe358 phenyl moiety is the best choice that can render strong interaction for the X⋯O┄H system, which also makes the peptide 'bindable' to HER2 kinase domain, while F/Cl/I-substitution at the same position can only improve the peptide affinity moderately or modestly. In contrast, the Br-substitution at the o- and p-positions of peptide Phe358 phenyl moiety cannot define effective X⋯O┄H interaction and thus does not confer additional affinity to the HER2-peptide complex.

Mig6 not only inhibits EGFR and HER2 but also targets HER3 and HER4 in a differential specificity: Implications for targeted esophageal cancer therapy

The human EGF receptor family plays pivotal roles in physiology and cancer, which contains four closely-related members: HER1/EGFR, HER2, HER3 and HER4. Previously, it was found that the mitogen-inducible gene 6 (Mig6) protein is a negative regulator of EGFR and HER2 by using its S1 segment to bind at the kinase dimerization interface. However, it is still unclear whether the S1 segment can also effectively target HER3 and HER4? Here, we performed a systematic investigation to address this issue. The segment can bind to all the four HER kinases with a varying affinity and moderate selectivity; breaking of the segment into shorter hotspot peptides would largely impair the affinity and selectivity, indicating that the full-length sequence is required for the effective binding of S1 to these kinases. The hs2 peptide, which corresponds to the middle hotspot region of S1 segment, can partially retain the affinity to HER kinases, can moderately compete with S1 segment at the dimerization interfaces, and can mimic the biological function of Mig6 protein to suppress HER4+ esophageal cancer at cellular level. In addition, we also analyzed the binding potency of S1 segment and hs2 peptide to the kinase domains of other five widely documented growth factor receptors (GFRs). It was showed that both the S1 and hs2 cannot effectively interact with these receptors. Overall, the Mig6 is suggested as a specific pan-HER inhibitor, which can target and suppress HER family members with a broad selectivity, but exhibits weak or no activity towards other GFRs.

Disulfide-stapled design of α-helical bundles to target the trimer-of-hairpins motif of human respiratory syncytial virus fusion protein

Human respiratory syncytial virus (RSV) is the major cause of acute lower respiratory tract infections worldwide in infants and young children. The RSV F glycoprotein is a class I fusion protein that mediates viral entry into host cells and is a major target of neutralizing antibodies. Targeting F glycoprotein has been recognized as a promising antiviral therapeutic strategy against RSV infection. Here, we reported the disulfide-stapled design of α-helical bundle to target the trimer-of-hairpins (TOH) motif of RSV F glycoprotein, which is the central regulatory module that triggers viral membrane fusion event. In TOH motif, three N-terminal heptad repeat (NtHR) helices form a trimeric coiled-coil core and other three C-terminal heptad repeat (CtHR) helices add to the core in an antiparallel manner. Interaction analysis between NtHR and CtHR revealed that the C-terminal tail of CtHR packs tightly against NtHR as compared to the N-terminal and middle regions of CtHR. A core binding site in CtHR C-terminus was identified, which represents a 13-mer chp peptide and can effectively interact with NtHR helix in native ordered conformation but would become largely disordered when splitting from the protein context of CtHR helix. Two chp helices were stapled together in a parallel manner with single, double or triple disulfide bridges, thus systematically resulting in seven disulfide-stapled α-helical bundles. Molecular simulations revealed that the double and triple stapling can effectively stabilize the structured conformation of α-helical bundles, whereas the free conformation of single-stapled bundles still remain intrinsically disordered in solvent. The double-stapled bundle chp-ds[508,516] and the triple-stapled bundle chp-ts[508,512,516] were rationally designed to have high potency; they can form a tight three-helix bundle with NtHR helix, thus potently targeting NtHR-CtHR interactions involved in RSV-F TOH motif through a competitive disruption mechanism.

Targeting the membrane fusion event of human respiratory syncytial virus with rationally designed α-helical hairpin traps

AIMS

Rational design of protein scaffolds with specific biological functions/activities has attracted much attention over the past decades. In the present study, we systematically examine the trimer-of-hairpins (TOH) motif of human respiratory syncytial virus (RSV) F protein, which plays a central role in viral membrane fusion and is a coiled-coil six-helix bundle formed by the antiparallel intermolecular interaction between three N-terminal heptad-repeat (HRN) helices and three C-terminal heptad-repeat (HRC) helices.

MAIN METHODS

A rational strategy that integrates dynamics simulation, thermodynamics calculation, fluorescence polarization and circular dichroism is proposed to design HRC-targeted α-helical hairpin traps based on the crystal template of HRN core.

KEY FINDINGS

The designed hairpin traps possess a typical helix-turn-helix scaffold that can be stabilized by stapling a disulfide bridge across its helical arms, which are highly structured (helicity >60%) and can mimic the native spatial arrangement of HRN helices in TOH motif to trap the hotspot sites of HRC with effective affinity (K_d is up to 6.4 μM).

SIGNIFICANCE

The designed α-helical hairpin traps can be used as lead entities for further developing TOH-disrupting agents to target RSV membrane fusion event and the proposed rational design strategy can be readily modified to apply for other type I viruses.

Scaffold-based analysis of nonpeptide oncogenic FTase inhibitors using multiple similarity matching, binding affinity scoring and enzyme inhibition assay

Oncogenic protein farnesyltransferase (FTase) is a key enzyme responsible for the lipid modification of a large and important number of proteins including Ras, which has been recognized as a druggable target of diverse cancers. Here, we report a systematic scaffold-based analysis to investigate the affinity, selectivity and cross-reactivity of nonpeptide inhibitors across ontology-enriched, disease-associated FTase mutants, by integrating multiple similarity matching, binding affinity scoring and enzyme inhibition assay. It is revealed that nonpeptide inhibitors are generally insensitive to FTase mutations; many of them cannot definitely select for wild-type target over mutant enzymes. Therefore, off-target is observed as a common phenomenon for the untargeted consequence of targeted therapies with FTase inhibition. This is not unexpected if considering that the enzyme active site is highly conserved in composition, configuration and function. The off-target, on the one hand, causes nonpeptide inhibitors with adverse drug reactions and, on the other hand, makes the inhibitors as promising candidates for the new use of old drugs. To practice the latter, a number of unexpected mutant-inhibitor interactions involved in cancer signaling pathways are uncovered in the created profile, from which several nonpeptide inhibitors are identified as insensitive to a drug-resistant mutation. Structural analysis suggests that the inhibitor ligands can bind to the mutant active site in a similar manner with wild-type target, although their nonbonded interactions appear to be impaired moderately upon the mutation.

Systematic inhibitor selectivity between PARP1 and PARP2 enzymes: Molecular implications for ovarian cancer personalized therapy

Human poly(ADP-ribose) polymerases (PARPs) are a class of nuclear enzymes involved in the pathogenesis of diverse gynecologic tumors. The PARP1 and PARP2 are the two most documented members in PARP family, which have been approved as the druggable targets of ovarian and cervical cancers. Selective targeting of the two enzymes with small-molecule inhibitors is a great challenge due to the high conservation in catalytic domain and active site. Here, we investigate the systematic selectivity profile of sophisticated PARP inhibitors between the two enzymes. Computational methods are used to model/optimize the complex structures of inhibitor ligands with PARP1/2 catalytic domains and then to estimate the theoretical Fenzymatic assays exhibit a good consistence with theoretical selectivity over six tested inhibitor samples (r_c ²  = 0.857). It is revealed that the inhibitor selectivity is conferred from the exquisite difference in the residue composition and structural architecture of both the local activity sites and the whole catalytic domains of the two enzymes. In particular, the TMZ50 and ME0328 show strong selectivity between PARP1 and PARP2, but only the former has a potent activity on the two enzymes, whereas the latter can only inhibit the enzymes moderately. These compounds can be considered as potential lead molecular entities to develop new specific PARP-selective inhibitor drugs for personalized therapy combating gynecologic cancers.

Integrative identification of human serpin PAI-1 inhibitors from Dracaena dragon blood and molecular implications for inhibitor-induced PAI-1 allosterism

Human plasminogen activator inhibitor-1 (PAI-1) is an important component of the coagulation system and has been recognized as a potential therapeutic target of diverse cardiovascular disorders. Previously, it was found that the extracts from the Chinese medicine Dracaena dragon blood have potent inhibitory activity against PAI-1, but it is unclear which constituents directly participate in the inhibition and how do they regulate PAI-1 at molecular level. Here, we describe an integrated strategy to identify the dragon blood's chemical constituents that can directly target PAI-1. With the strategy, five compounds 1-5 are hit as promising PAI-1 inhibitor candidates, from which three are measured to have high or moderate activity against PAI-1. In particular, the compound 3 is determined to exhibit the highest potency; this value is roughly comparable with the widely used PAI-1 inhibitor Tiplaxtinin. We further examine the molecular effect of compound 3 on PAI-1 conformation at structural level. It is supposed that small-molecule inhibitor regulates the reactive center loop (RCL) of PAI-1 through an allosterism, that is, binding of compound 3 to PAI-1 can allosterically stabilize RCL in latent form, thus promoting PAI-1 conformational conversion from metastable active form to the inactive latent form. Long-term atomistic simulations also demonstrate that removal of compound 3 can destabilize the structured β-stranded conformation of RCL in latent form, although the current simulations are still not sufficient to characterize the full conversion dynamics trajectory.