Protein Binding Sites Research Articles

Key saltiness-enhancing substances in Maillard reaction products derived from chicken breast hydrolysate: Identification, saltiness-enhancing ability and mechanism

This work employs a saltiness-guided separation combined with UPLC-QTOF-MS to identify the key saltiness-enhancing substances in Maillard reaction products derived from chicken breast hydrolysate (CBH–MRPs). Thirteen compounds in the U3 fraction exhibited significant saltiness-enhancing abilities, which increased the saltiness intensity of NaCl (3 g/L) from 2.80 to 3.35–3.88. Interactions between the compounds and NaCl were evaluated using the S-curve method. The results showed that five compounds (5′-GMP, 5′-IMP, L-glutamic acid, L-lactic acid, and L-carnosine) and one compound (glutamine) exhibited synergistic and additive effects with NaCl, respectively, at tested concentrations. Notably, 5′-GMP/5′-IMP/glutamine and L-carnosine/L-lactic acid demonstrated better saltiness-enhancing abilities at their suprathreshold and subthreshold levels, respectively. Molecular docking results showed that hydrogen bonding was the key force for docking. Residues Cys475, Glu378, and Trp236 were the primary binding sites of the transmembrane channel-like protein 4 (TMC4). These results contribute to a better understanding of the saltiness modulating mechanisms of CBH–MRPs.

Unbiased MD simulations identify lipid binding sites in lipid transfer proteins.

The characterization of lipid binding to lipid transfer proteins (LTPs) is fundamental to understand their molecular mechanism. However, several structures of LTPs, and notably those proposed to act as bridges between membranes, do not provide the precise location of their endogenous lipid ligands. To address this limitation, computational approaches are a powerful alternative methodology, but they are often limited by the high flexibility of lipid substrates. Here, we develop a protocol based on unbiased coarse-grain molecular dynamics simulations in which lipids placed away from the protein can spontaneously bind to LTPs. This approach accurately determines binding pockets in LTPs and provides a working hypothesis for the lipid entry pathway. We apply this approach to characterize lipid binding to bridge LTPs of the Vps13-Atg2 family, for which the lipid localization inside the protein is currently unknown. Overall, our work paves the way to determine binding pockets and entry pathways for several LTPs in an inexpensive, fast, and accurate manner.

A Bioinformatic Analysis Predicts That Cannabidiol Could Function as a Potential Inhibitor of the MAPK Pathway in Colorectal Cancer.

Colorectal cancer (CRC), found in the intestinal tract, is initiated and progresses through various mechanisms, including the dysregulation of signaling pathways. Several signaling pathways, such as EGFR and MAPK, involved in cell proliferation, migration, and apoptosis, are often dysregulated in CRC. Although cannabidiol (CBD) has previously induced apoptosis and cell cycle arrest in vitro in CRC cell lines, its effects on signaling pathways have not yet been determined. An in silico analysis was used here to assess partner proteins that can bind to CBD, and docking simulations were used to predict precisely where CBD would bind to these selected proteins. A survey of the current literature was used to hypothesize the effect of CBD binding on such proteins. The results predict that CBD could interact with EGFR, RAS/RAF isoforms, MEK1/2, and ERK1/2. The predicted CBD-induced inhibition might be due to CBD binding to the ATP binding site of the target proteins. This prevents the required phosphoryl transfer to activate substrate proteins and/or CBD binding to the DFG motif from taking place, thus reducing catalytic activity.

The FXR1 network acts as a signaling scaffold for actomyosin remodeling

It is currently not known whether mRNAs fulfill structural roles in the cytoplasm. Here, we report the fragile X-related protein 1 (FXR1) network, an mRNA-protein (mRNP) network present throughout the cytoplasm, formed by FXR1-mediated packaging of exceptionally long mRNAs. These mRNAs serve as an underlying condensate scaffold and concentrate FXR1 molecules. The FXR1 network contains multiple protein binding sites and functions as a signaling scaffold for interacting proteins. We show that it is necessary for RhoA signaling-induced actomyosin reorganization to provide spatial proximity between kinases and their substrates. Point mutations in FXR1, found in its homolog FMR1, where they cause fragile X syndrome, disrupt the network. FXR1 network disruption prevents actomyosin remodeling-an essential and ubiquitous process for the regulation of cell shape, migration, and synaptic function. Our findings uncover a structural role for cytoplasmic mRNA and show how the FXR1 RNA-binding protein as part of the FXR1 network acts as an organizer of signaling reactions.

Mapping protein binding sites by photoreactive fragment pharmacophores

Fragment screening is a popular strategy of generating viable chemical starting points especially for challenging targets. Although fragments provide a better coverage of chemical space and they have typically higher chance of binding, their weak affinity necessitates highly sensitive biophysical assays. Here, we introduce a screening concept that combines evolutionary optimized fragment pharmacophores with the use of a photoaffinity handle that enables high hit rates by LC-MS-based detection. The sensitivity of our screening protocol was further improved by a target-conjugated photocatalyst. We have designed, synthesized, and screened 100 diazirine-tagged fragments against three benchmark and three therapeutically relevant protein targets of different tractability. Our therapeutic targets included a conventional enzyme, the first bromodomain of BRD4, a protein-protein interaction represented by the oncogenic KRasG12D protein, and the yet unliganded N-terminal domain of the STAT5B transcription factor. We have discovered several fragment hits against all three targets and identified their binding sites via enzymatic digestion, structural studies and modeling. Our results revealed that this protocol outperforms screening traditional fully functionalized and photoaffinity fragments in better exploration of the available binding sites and higher hit rates observed for even difficult targets.

Real-Time Measurement of a Weak Interaction of a Transcription Factor Motif with a Protein Hub at Single-Molecule Precision.

Transcription factors often interact with other protein cofactors, regulating gene expression. Direct detection of these brief events using existing technologies remains challenging due to their transient nature. In addition, intrinsically disordered domains, intranuclear location, and lack of cofactor-dependent active sites of transcription factors further complicate the quantitative analysis of these critical processes. Here, we create a genetically encoded label-free sensor to identify the interaction between a motif of the MYC transcription factor, a primary cancer driver, and WDR5, a chromatin-associated protein hub. Using an engineered nanopore equipped with this motif, WDR5 is probed through reversible captures and releases in a one-by-one and time-resolved fashion. Our single-molecule kinetic measurements indicate a weak-affinity interaction arising from a relatively slow complex association and a fast dissociation of WDR5 from the tethered motif. Further, we validate this subtle interaction by determinations in an ensemble using single nanodisc-wrapped nanopores immobilized on a biolayer interferometry sensor. This study also provides the proof-of-concept for a sensor that reveals unique recognition signatures of different protein binding sites. Our foundational work may be further developed to produce sensing elements for analytical proteomics and cancer nanomedicine.

CavitOmiX Drug Discovery: Engineering Antivirals with Enhanced Spectrum and Reduced Side Effects for Arboviral Diseases.

Advancing climate change increases the risk of future infectious disease outbreaks, particularly of zoonotic diseases, by affecting the abundance and spread of viral vectors. Concerningly, there are currently no approved drugs for some relevant diseases, such as the arboviral diseases chikungunya, dengue or zika. The development of novel inhibitors takes 10-15 years to reach the market and faces critical challenges in preclinical and clinical trials, with approximately 30% of trials failing due to side effects. As an early response to emerging infectious diseases, CavitOmiX allows for a rapid computational screening of databases containing 3D point-clouds representing binding sites of approved drugs to identify candidates for off-label use. This process, known as drug repurposing, reduces the time and cost of regulatory approval. Here, we present potential approved drug candidates for off-label use, targeting the ADP-ribose binding site of Alphavirus chikungunya non-structural protein 3. Additionally, we demonstrate a novel in silico drug design approach, considering potential side effects at the earliest stages of drug development. We use a genetic algorithm to iteratively refine potential inhibitors for (i) reduced off-target activity and (ii) improved binding to different viral variants or across related viral species, to provide broad-spectrum and safe antivirals for the future.

Investigation on synergistic inhibition of protein-bound heterocyclic amines in sarcoplasmic and myofibrillar model systems by amino acid combinations

The inhibition of amino acids on the formation of protein-bound HAs was assessed in both model systems and roast beef patties, and the synergism between these amino acids was also investigated. The amino acids can promote the formation of protein-bound HAs at low addition amount, and the total content of protein-bound HAs increased from 444.05 ± 4.98 ng/g of the control group to 517.36 ± 16.51 ng/g when 0.05 % cysteine was added. Amino acid combinations exhibited stable inhibitory effects, with the maximum inhibitory rate of 64 % in the treatment with histidine-proline combination (1:4). The synergistic inhibition may be caused by simultaneously scavenging intermediates and competing for the binding sites of muscle proteins, and the reaction with protein-bound HAs to form adduct can serve as supporting factors to co-mitigate the promotion in protein-bound HAs from increased protein solubility. These findings proposed the potential mitigation strategies against protein-bound HAs formation.

Exploring an Intracellular Allosteric Site of CC-Chemokine Receptor4 from 3D Models, Probe Simulations, and Mutagenesis.

We applied our previously developed probe confined dynamic mapping protocol, which combines enhanced sampling molecular dynamics (MD) simulations and fragment-based approaches, to identify the binding site of GSK2239633A (N-[[3-[[3-[(5-chlorothiophen-2-yl)sulfonylamino]-4-methoxyindazol-1-yl]methyl]phenyl]methyl]-2-hydroxy-2-methylpropanamide), a selective CC-chemokine receptor type 4 (CCR4) negative allosteric modulator, using CCR4 homology and AlphaFold models. By comparing the performance across five computational models, we identified conserved (K3108.49 and Y3047.53) and non-conserved (M2436.36) residue hotspots for GSK2239633A binding, which were validated by mutagenesis and bioluminescence resonance energy transfer assay. Further analysis of 3D models and MD simulations highlighted the pair of residues 6.36 and 7.56 that might account for antagonist selectivity among chemokine receptors. Our in silico protocol provides a promising approach for characterizing ligand binding sites in membrane proteins, considering receptor dynamics and adaptability and guiding protein template selection for ligand design.

Complex Formation and Hydrolytic Processes of Protected Peptides Containing the -SXH- Motif in the Presence of Nickel(II) Ion.

Interactions between metal ions and proteins are considered reversible, such as the coordination of a metal ion to a protein or enzyme, but irreversible processes like the oxidative reactions, aggregation or hydrolytic processes may occur. In the presence of Ni(II)-ions selective hydrolysis of the peptides containing the -SXH- or -TXH- motif was observed. Since the side chain of histidine serves as the metal ion binding site for many native proteins, and very often histidine is present in a -SXH- or -TXH- sequence, to study the complex formation and hydrolytic processes in presence of nickel(II) ion four peptides were synthesised: Ac-SKHM-NH2, A3SSH-NH2, A4SSH-NH2, AAAϵKSH-NH2. The Ni(II)-induced hydrolysis of Ac-SKHM-NH2 peptide occurs rapidly in alkaline medium already at room temperature. In two peptides containing -SSH- sequence on the C-termini, the N-terminal part is the major binding site for the nickel(II) ion, but the formation of dinuclear complexes was also observed. In the [Ni2LH-6]2- complex of hexapeptide, the coordination sphere of the metal ions is saturated with deprotonated Ser-O-, which does not result in hydrolysis of the peptide. For A4SSH-NH2, both Ni(II) ions fulfill the conditions for hydrolysis, which was confirmed by HPLC analyses at pH ≈8.2 and 25 °C.

Complete combinatorial mutational enumeration of a protein functional site enables sequence-landscape mapping and identifies highly-mutated variants that retain activity.

Understanding how proteins evolve under selective pressure is a longstanding challenge. The immensity of the search space has limited efforts to systematically evaluate the impact of multiple simultaneous mutations, so mutations have typically been assessed individually. However, epistasis, or the way in which mutations interact, prevents accurate prediction of combinatorial mutations based on measurements of individual mutations. Here, we use artificial intelligence to define the entire functional sequence landscape of a protein binding site in silico, and we call this approach Complete Combinatorial Mutational Enumeration (CCME). By leveraging CCME, we are able to construct a comprehensive map of the evolutionary connectivity within this functional sequence landscape. As a proof of concept, we applied CCME to the ACE2 binding site of the SARS-CoV-2 spike protein receptor binding domain. We selected representative variants from across the functional sequence landscape for testing in the laboratory. We identified variants that retained functionality to bind ACE2 despite changing over 40% of evaluated residue positions, and the variants now escape binding and neutralization by monoclonal antibodies. This work represents a crucial initial stride toward achieving precise predictions of pathogen evolution, opening avenues for proactive mitigation.

Studies on N-(6-Indazolyl) benzenesulfonamide Derivatives as Potential Anticancer Agents: Integrating Synthesis, In silico Docking, and Molecular Dynamics Simulations

A new series of benzenesulfonamide derivatives, namely N-(1-(2-chloropyrimidin-4-yl)-1[Formula: see text]-indazol-5-yl) compounds (4a-i) and N-(1-(2-chloropyrimidin-4-yl)-6-ethoxy-1[Formula: see text]-indazol-5-yl) derivatives (5a-i), were synthesized. This was achieved by reducing 1-(2-halopyrimidin-4-yl)-5-nitro-1[Formula: see text]-indazole (3) with SnCl2, followed by reacting with various aryl sulphonyl chlorides in pyridine. Structural confirmation was carried out through IR, 1H-NMR, [Formula: see text]C-NMR and mass spectral methods. Anticancer activity evaluation of compounds 4a-i and 5a-i revealed that N-(1-(2-chloropyrimidin-4-yl)-6-ethoxy-1H-indazol-5-yl)-2-nitrobenzenesulfonamide (5b) displayed exceptional efficacy. Molecular dynamics simulations were employed to rigorously assess the stability of ligand–protein complexes, highlighting a consistent and robust binding of the most potent compound within the binding sites of target proteins. The results unequivocally affirmed the remarkable anticancer activity, supported by comprehensive molecular docking analyses uncovering intricate interactions involving hydrogen bonds, electrostatic forces and hydrophobic contacts. These findings collectively offer invaluable insights into the complex molecular structure and dynamics of receptor target sites, establishing a robust foundation for the development of novel and potent anticancer agents with promising pharmaceutical implications.

Oligonucleotide-Based Photoaffinity Probes: Chemical Tools and Applications for Protein Labeling.

A variety of proteins interact with DNA and RNA, including polymerases, histones, ribosomes, transcription factors, and repair enzymes. However, the transient non-covalent nature of these interactions poses challenges for analysis. Introducing a covalent bond between proteins and DNA via photochemical activation of a photosensitive functional group introduced onto nucleic acids offers a means to stabilize these often weak interactions without significantly altering the binding interface. Consequently, photoactivatable oligonucleotides are powerful tools for investigating nucleic acid-protein interactions involved in numerous biological and pathological processes. In this review, we provide a comprehensive overview of the chemical tools developed so far and the different strategies used for incorporating the most commonly used photoreactive reagents into oligonucleotide probes or nucleic acids. Furthermore, we illustrate their application with several examples including protein binding site mapping, identification of protein binding partners, and in cell studies.

Mudskipper detects combinatorial RNA binding protein interactions in multiplexed CLIP data

The uncovering of protein-RNA interactions enables a deeper understanding of RNA processing. Recent multiplexed crosslinking and immunoprecipitation (CLIP) technologies such as antibody-barcoded eCLIP (ABC) dramatically increase the throughput of mapping RNA binding protein (RBP) binding sites. However, multiplex CLIP datasets are multivariate, and each RBP suffers non-uniform signal-to-noise ratio. To address this, we developed Mudskipper, a versatile computational suite comprising two components: a Dirichlet multinomial mixture model to account for the multivariate nature of ABC datasets and a softmasking approach that identifies and removes non-specific protein-RNA interactions in RBPs with low signal-to-noise ratio. Mudskipper demonstrates superior precision and recall over existing tools on multiplex datasets and supports analysis of repetitive elements and small non-coding RNAs. Our findings unravel splicing outcomes and variant-associated disruptions, enabling higher-throughput investigations into diseases and regulation mediated by RBPs.

Genetic variant rs11568818 of matrix metalloproteinase MMP7 associated with newborn weight in pregnant women with fetal growth restriction

Background: Fetal growth restriction is a common complication of pregnancy that has been associated with a variety of adverse perinatal outcomes. The condition carries significant risks of neonatal mortality, major and minor morbidity, and long term health sequelae. The aim of the study: The aim of the study was to study the associations of matrix metalloproteinases gene polymorphism with newborn weight in pregnant women with fetal growth restriction and to evaluate their functional effects. Materials and methods: 98 cases of women with fetal growth restriction were selected as the experimental group. All pregnant women were performed genotyping of 5 SNPs of genes of matrix metalloproteinase (rs1799750 MMP-1, rs243865 MMP-2, rs3025058 MMP-3, rs11568818 MMP-7, rs17577 MMP-9). Results: We found associations of the rs11568818 polymorphism of the MMP-7 gene with newborn weight in women with fetal growth restriction within a recessive model (β = 0.32±0.13, p=0.016 pperm=0.022). This polymorphic locus possesses important functional effects. It is localized in an evolutionarily conserved region, a binding site for regulatory proteins (TBP, CFOS, CJUN), a region of DNase hypersensitivity, and a site of modified histones marking enhancers and promoters in mesenchymal and hematopoietic stem cells, osteoblast cells, adipocytes, and fibroblast cell line lungs, various parts of the brain, lungs, etc., determines the sensitivity of DNA to four transcription factors (Foxa, GR, PLZF, Pou5f1), is associated with the level of mRNA expression of the MMP-7 gene in the lungs, liver, and skeletal muscles. Conclusion: The rs11568818 polymorphism of the MMP-7 gene is associated with a newborn weight.

Regulation of RHOV signaling by interaction with SH3 domain-containing adaptor proteins and phosphorylation by PKA

RHOV and RHOU are considered atypical Rho-family small GTPases because of the existence of N- and C-terminal extension regions, abnormal GDP/GTP cycling, and post-translational modification. Particularly, RHOV and RHOU both have a proline-rich (PR) motif in the N-terminal region. It has been reported that the PR motif of RHOU interacts with GRB2, a SH3 domain-containing adaptor protein, and regulates its activity through EGF receptor signaling. However, it is unknown whether RHOV, like RHOU, interacts with SH3 domain-containing adaptor proteins. In this study, we investigated the interactions between RHOV and SH3 domain-containing adaptor proteins, including GRB2 and NCK2. The RHOV-induced serum response factor (SRF)-dependent gene transcriptional activity was attenuated in cells co-expressing either GRB2 or NCK2 compared to cells expressing RHOV alone. From the results of experiments using various gene mutants of RHOV and GRB2, it appears that the PR motif of the N-terminal region of RHOV is the crucial binding site for the SH3 domain-containing proteins. Furthermore, we found that Ser25 in the N-terminal region of RHOV is phosphorylated by PKA and that its phosphorylation is suppressed by interaction with NCK2 but not GRB2. We have found a novel regulatory mechanism for the phosphorylation of RHOV and its interaction with SH3 domain-containing adaptor proteins.

Structural analysis of the FERM domain of human protein tyrosine phosphatase non-receptor type 21.

Protein tyrosine phosphatase non-receptor type 21 (PTPN21) is a cytosolic protein tyrosine phosphatase that regulates cell growth and invasion. Due to its oncogenic properties, PTPN21 has recently emerged as a potential therapeutic target for cancer. In this study, the three-dimensional structure of the PTPN21 FERM domain was determined at 2.1 Å resolution by X-ray crystallography. The crystal structure showed that this domain harbors canonical FERM folding and consists of three subdomains that are tightly packed via highly conserved intramolecular hydrophobic interactions. Consistent with this, the PTPN21 FERM domain shares high structural homology with several other FERM domains. Moreover, structural superimposition demonstrated two putative protein-binding sites of the PTPN21 FERM domain, which are presumed to be associated with interaction with its binding partner, kinesin family member 1C. Thus, these data suggest that the FERM domain of PTPN21 serves as a module that mediates protein-protein interaction, like other FERM domains.

Splicing-specific transcriptome-wide association uncovers genetic mechanisms for schizophrenia

Recent studies have highlighted the essential role of RNA splicing, a key mechanism of alternative RNA processing, in establishing connections between genetic variations and disease. Genetic loci influencing RNA splicing variations show considerable influence on complex traits, possibly surpassing those affecting total gene expression. Dysregulated RNA splicing has emerged as a major potential contributor to neurological and psychiatric disorders, likely due to the exceptionally high prevalence of alternatively spliced genes in the human brain. Nevertheless, establishing direct associations between genetically altered splicing and complex traits has remained an enduring challenge. We introduce Spliced-Transcriptome-Wide Associations (SpliTWAS) to integrate alternative splicing information with genome-wide association studies to pinpoint genes linked to traits through exon splicing events. We applied SpliTWAS to two schizophrenia (SCZ) RNA-sequencing datasets, BrainGVEX and CommonMind, revealing 137 and 88 trait-associated exons (in 84 and 67 genes), respectively. Enriched biological functions in the associated gene sets converged on neuronal function and development, immune cell activation, and cellular transport, which are highly relevant to SCZ. SpliTWAS variants impacted RNA-binding protein binding sites, revealing potential disruption of RNA-protein interactions affecting splicing. We extended the probabilistic fine-mapping method FOCUS to the exon level, identifying 36 genes and 48 exons as putatively causal for SCZ. We highlight VPS45 and APOPT1, where splicing of specific exons was associated with disease risk, eluding detection by conventional gene expression analysis. Collectively, this study supports the substantial role of alternative splicing in shaping the genetic basis of SCZ, providing a valuable approach for future investigations in this area.

Exploration of Potential Broad-Spectrum Antiviral Targets in the Enterovirus Replication Element: Identification of Six Distinct 5' Cloverleaves.

Enterovirus genomic replication initiates at a predicted RNA cloverleaf (5'CL) at the 5' end of the RNA genome. The 5'CL contains one stem (SA) and three stem-loops (SLB, SLC, SLD). Here, we present an analysis of 5'CL conservation and divergence for 209 human health-related serotypes from the enterovirus genus, including enterovirus and rhinovirus species. Phylogenetic analysis indicates six distinct 5'CL serotypes that only partially correlate with the species definition. Additional findings include that 5'CL sequence conservation is higher between the EV species than between the RV species, the 5'CL of EVA and EVB are nearly identical, and RVC has the lowest 5'CL conservation. Regions of high conservation throughout all species include SA and the loop and nearby bases of SLB, which is consistent with known protein interactions at these sites. In addition to the known protein binding site for the Poly-C binding protein in the loop of SLB, other conserved consecutive cytosines in the stems of SLB and SLC provide additional potential interaction sites that have not yet been explored. Other sites of conservation, including the predicted bulge of SLD and other conserved stem, loop, and junction regions, are more difficult to explain and suggest additional interactions or structural requirements that are not yet fully understood. This more intricate understanding of sequence and structure conservation and variability in the 5'CL may assist in the development of broad-spectrum antivirals against a wide range of enteroviruses, while better defining the range of virus isotypes expected to be affected by a particular antiviral.

Efficient synthesis and in-silico studies of pyrano[3,2-c]pyrones based glycohybrids

This work is comprising of designing, efficient synthesis and molecular docking studies of pyrano[3,2-c]pyrones based stereodivergent glycohybrids. The diverse pyrano[3,2-c]pyrones based glycohybrids were efficiently prepared through condensation of 4-hydroxycoumarin derivatives and 4‑hydroxy-6-methyl-2H-pyran-2-ones with various enantiopure 2,3-dideoxy-α,β-unsaturated carbohydrate enals using organo-catalyst, l-proline, in EtOAc at room temperature. 3,4,6-tri-O-acetyl-D-glucal derived acetyl-protected carbohydrate enals yielded highly diastereoselective glycohybrid products. Whereas, poor selectivity was observed with α,β-unsaturated carbohydrate enals obtained from 3,4,6-tri-O-acetyl-d-galactal. The in-silico investigations show the significant binding activity of the selected compounds in the active binding site of HCK protein (PDB:1QCF) with the better docking score of −7.13 kcal/mol as compared to the co-crystallized ligand PP1 (−6.77 kcal/mol). Additionally, MM/GBSA was calculated using the Prime module to determine the binding energy of the ligands. Selected compounds showed the maximum binding affinity of −74.18 kcal/mol compared to the co-crystallized ligand PP1 (−70.40 kcal/mol). ADMET screening of these compounds predicts the low toxicity and better metabolic profile of the synthesized compounds inside the body.