Isothermal titration calorimetry for characterization of recombinant proteins

A comprehensive survey of drug-target interaction analysis in allopathy and siddha medicine

Effective drug delivery is the cornerstone of modern healthcare, ensuring therapeutic compounds reach their intended targets efficiently. This paper explores the potential of personalized and holistic healthcare, driven by the synergy between traditional and allopathic medicine systems, with a specific focus on the vast reservoir of medicinal compounds found in plants rooted in the historical legacy of traditional medicine. Motivated by the desire to unlock the therapeutic potential of medicinal plants and bridge the gap between traditional and allopathic medicine, this survey delves into in-silico computational approaches for studying Drug-Target Interactions (DTI) within the contexts of allopathy and siddha medicine. The contributions of this survey are multifaceted: it offers a comprehensive overview of in-silico methods for DTI analysis in both systems, identifies common challenges in DTI studies, provides insights into future directions to advance DTI analysis, and includes a comparative analysis of DTI in allopathy and siddha medicine. The findings of this survey highlight the pivotal role of in-silico computational approaches in advancing drug research and development in both allopathy and siddha medicine, emphasizing the importance of integrating these methods to drive the future of personalized healthcare.

Prediction of the binding interactions between rosmarinic acid and cysteinyl leukotriene receptor type 1 by molecular docking and immobilized receptor chromatography

Drug-protein interaction analysis is still at the center of research efforts to illustrate binding mechanisms and provide valuable information for selecting drug candidates with ideal properties in the early drug discovery stage. We present the prediction of the binding of rosmarinic acid (RA) to cysteinyl leukotriene receptor type1 (CysLTR1) by molecular docking. According to our findings, CysLTR1 is a potential anti-inflammatory target of RA. Under this assumption, we prepared the immobilized CysLTR1 column via a one-step method and characterized the immobilized CysLTR1 by fluorescent and chromatographic analyses. Furthermore, we used the immobilized CysLTR1 column to evaluate the binding interactions between RA and the immobilized receptor. Molecular docking showed that Tyr 249, Phe 174, Thr 280, Pro 177, and Thr 100 are the main sites for RA to interact with CysLTR1. The main forces that drive the findings are hydrogen bonds and hydrophobic interactions. Characterization results show that CysLTR1 is successfully immobilized with high specificity and stability. Almost no non-specific binding is observed on the immobilized CysLTR1 gels. The association constant and the binding sites are calculated to be 7.268 × 105 L mol-1 and 1.237 × 10-8 mol L-1 by injection amount-dependent method. These results, taken together, confirm the potential target of RA on the anti-inflammatory effect. We believe that it can provide valuable reference information on the in-depth exploration of drug-protein interaction mechanisms, and lead compound screening by this method.

Recent advances and challenges in the interaction between myofibrillar proteins and flavor substances

Myofibrillar proteins are an important component of proteins. Flavor characteristics are the key attributes of food quality. The ability of proteins to bind flavor is one of their most fundamental functional properties. The dynamic balance of release and retention of volatile flavor compounds in protein-containing systems largely affects the sensory quality and consumer acceptability of foods. At present, research on flavor mainly focuses on the formation mechanism of flavor components, while there are few reports on the release and perception of flavor components. This review introduces the composition and structure of myofibrillar proteins, the classification of flavor substances, the physical binding and chemical adsorption of myofibrillar proteins and volatile flavor substances, as well as clarifies the regulation law of flavor substances from the viewpoint of endogenous flavor characteristics and exogenous environment factors, to provide a theoretical reference for the flavor regulation of meat products.

Factors affecting product association as a mechanism of host-cell protein persistence in bioprocessing

Product association of host-cell proteins (HCPs) to monoclonal antibodies (mAbs) is widely regarded as a mechanism that can enable HCP persistence through multiple purification steps and even into the final drug substance. Discussion of this mechanism often implies that the existence or extent of persistence is directly related to the strength of binding but actual measurements of the binding affinity of such interactions remain sparse. Two separate avenues of investigation of HCP-mAb binding are reported here. One is the measurement of the affinity of binding of individual, commonly persistent Chinese hamster ovary (CHO) HCPs to each of a set of mAbs, and the other uses quantitative proteomic measurements to assess binding of HCPs in a null CHO harvested cell culture fluid (HCCF) to mAbs produced in the same cell line. The individual HCP measurements show that the binding affinities of individual HCPs to different mAbs can vary appreciably but are rarely very high, with only weak pH dependence. The measurements on the null HCCF allow estimation of individual HCP-mAb affinities; these are typically weaker than those seen in affinity measurements on isolated HCPs. Instead, the extent of binding appears correlated with the initial abundance of individual HCPs in the HCCF and the forms of the HCPs in the solution, i.e., whether HCPs are present as free molecules or as parts of large aggregates. Separate protein A chromatography experiments performed by feeding different fractions of a mAb-containing HCCF obtained by size-exclusion chromatography (SEC) showed clear differences in the number and identity of HCPs found in the protein A eluate. These results indicate a significant role for HCP-mAb association in determining HCP persistence through protein A chromatography, presumably through binding of HCP-mAb complexes to the resin. Overall, the results illustrate the importance of considering more fully the biophysical context of HCP-product association in assessing the factors that may affect the phenomenon and determine its implications. Knowledge of the abundances and the forms of individual or aggregated HCPs in HCCF are particularly significant, emphasizing the integration of upstream and downstream bioprocessing and the importance of understanding the collective properties of HCPs in addition to just the biophysical properties of individual HCPs.

Novel role of peptidoglycan recognition protein 2 in activating NOD2-NFκB inflammatory axis in coronary artery disease

BACKGROUNDS AND AIMS

The role of inflammation in driving atherosclerosis is well-established. It exerts systemic effects beyond the local site of plaque formation. In the context of coronary artery disease (CAD), the proteins that show altered levels in the plasma, are potentially important for understanding the key regulatory mechanism in the pathogenesis of atherosclerosis. A case-control study revealed that plasma soluble Peptidoglycan Recognition Protein 2 (PGLYRP2) primarily produced by the liver, is increased in subjects with CAD. Furthermore, the concentration of PGLYRP2 in the blood correlates with the severity of coronary artery disease. Thus, it raises interest in understanding the exact role of the protein in aortic inflammation and plaque progression.

METHODS

We evaluated the plasma concentration of PGLYRP2 in three distinct groups: patients with CAD (N = 68), asymptomatic individuals (N = 34), and healthy volunteers (N = 20). Furthermore, we investigated the correlation between disease severity and PGLYRP2 levels in CAD patients. To identify potential binding partners of PGLYRP2, we employed computational analysis. We verified the PGLYRP2-NOD2 interaction in macrophage cells and elucidated the inflammatory pathways activated by PGLYRP2 within these cells. To assess the impact of PGLYRP2, we examined its effects in the atherosclerotic mice model (ApoE-/-).

RESULTS

In this study, we report for the first time that Nucleotide-binding Oligomerization domain 2 (NOD2) which is expressed on the surface of macrophages, is a receptor of PGLYRP2. The N-terminal domain of PGLYRP2 directly binds to NOD2 and activates the NOD2-RIP2-NFκB cascade that promotes the secretion of proinflammatory cytokines like TNFα, IL1β, and IL-8. In the atherosclerotic mice model (ApoE-/-) we demonstrate that elevated PGLYRP2 level is parallel with increased proinflammatory cytokines in the plasma when fed a High Cholesterol Diet (HCD). Immunohistochemical analysis reveals that PGLYRP2 is co-localized with NOD2 on the macrophages at the site of the lesion.

CONCLUSIONS

Taken together, our data demonstrate that NOD2 acts as a receptor of PGLYRP2 on macrophages, which mediates the activation of the NOD2-RIP2-NFκB pathway and promotes inflammation, thus significantly contributing to the development and progression of atherosclerosis.

Isothermal Titration Calorimetry for Fragment-Based Analysis of Ion Channel Interactions

Ion channels are membrane proteins that may also have intracellular and extracellular domains that interact with other ligands. In many cases, these interaction sites are highly mobile and may undergo changes in the configuration upon binding with regulatory signaling molecules. Isothermal titration calorimetry (ITC) is a powerful technique to quantify protein-ligand interactions of purified samples in solution. This chapter describes a fragment-based analysis method using ITC to quantify the interactions between a domain of the voltage-gated Kv7 channel and the calcium-regulated protein calmodulin. This example can be used to quantify the interactions between specific domains of other ion channels and their regulatory signaling proteins.

Probing the interactions between amyloidogenic proteins and bio-membranes

Protein misfolding diseases (PMDs) in humans are characterized by the deposition of protein aggregates in tissues, including Alzheimer's disease, Parkinson's disease, type 2 diabetes, and amyotrophic lateral sclerosis. Misfolding and aggregation of amyloidogenic proteins play a central role in the onset and progression of PMDs, and these processes are regulated by multiple factors, especially the interaction between proteins and bio-membranes. Bio-membranes induce conformational changes in amyloidogenic proteins and affect their aggregation; on the other hand, the aggregates of amyloidogenic proteins may cause membrane damage or dysfunction leading to cytotoxicity. In this review, we summarize the factors that affect the binding of amyloidogenic proteins and membranes, the effects of bio-membranes on the aggregation of amyloidogenic proteins, mechanisms of membrane disruption by amyloidogenic aggregates, technical approaches for detecting these interactions, and finally therapeutic strategies targeting membrane damage caused by amyloidogenic proteins.

Temperature dependent mechanical unfolding and refolding of a protein studied by thermo-regulated optical tweezers

Temperature is a useful system variable to gather kinetic and thermodynamic information from proteins. Usually, free energy and the associated entropic and enthalpic contributions are obtained by quantifying the conformational equilibrium based on melting experiments performed in bulk conditions. Such experiments are suitable only for those small single-domain proteins whose side reactions of irreversible aggregation are unlikely to occur. Here, we avoid aggregation by pulling single-protein molecules in a thermo-regulated optical tweezers. Thus, we are able to explore the temperature dependence of the thermodynamic and kinetic parameters of MJ0366 from Methanocaldococcus jannaschii at the single-molecule level. By performing force-ramp experiments between 2°C and 40°C, we found that MJ0366 has a nonlinear dependence of free energy with temperature and a specific heat change of 2.3 ± 1.2 kcal/mol∗K. These thermodynamic parameters are compatible with a two-state unfolding/refolding mechanism for MJ0366. However, the kinetics measured as a function of the temperature show a complex behavior, suggesting a three-state folding mechanism comprising a high-energy intermediate state. The combination of two perturbations, temperature and force, reveals a high-energy species in the folding mechanism of MJ0366 not detected in force-ramp experiments at constant temperature.

Cysteine protease domain of potato virus Y: The potential target for urea derivatives

The cysteine protease structural domain (CPD) encoded by the potato virus Y (PVY) accessory component protein helper component-proteinase (HC-Pro) is an auxiliary component of aphid virus transmission and plays an important role in virus infection and replication. Urea derivatives have potential antiviral activities. In this study, the PVY HC-Pro C-terminal truncated recombinant protein (residues 307-465) was expressed and purified. The interactions of PVY CPD with urea derivatives HD1-36 were investigated. Microscale thermophoresis experiments showed that HD6, -19, -21 and - 25 had the strongest binding forces to proteins, with K_d values of 2.16, 1.40, 1.97 and 1.12 μM, respectively. An experiment verified the microscale thermophoresis results, and the results were as expected, with K_d values of 6.10, 4.78, 5.32, and 4.52 μM for HD6, -19, -21, and - 25, respectively. Molecular docking studies indicated that the interaction sites between PVY CPD and HD6, -19, -21, and - 25, independently, were aspartic acid 121, asparagine 48, and tyrosine 38, which played important roles in their binding. In vivo experiments verified that HD25 inhibited PVY more than the control agents ningnanmycin and urea. These data have important implications for the design and synthesis of novel urea derivatives.

Disagreements Between Calorimetric and Van't Hoff Enthalpies of Adsorption II: Effect of pH and pH Buffers on Phenobarbital Adsorption to Activated Carbon

The reported inconsistencies between the van't Hoff equation and calorimetry hinder the utility of thermodynamics in biochemical and pharmaceutical research. A novel thermodynamic approach is developed herein for ligand adsorption with a focus on the interpretation of calorimetric data in the presence of concurrent proton exchange reactions. Such exchange reactions typically result in a pH-dependence of calorimetric measurements that obscures intrinsic binding enthalpies. It is shown that for the adsorption of phenobarbital to activated carbon, the measured calorimetric enthalpy is a result of three linked acid/base equilibria. A model was established to predict the intrinsic binding enthalpy using 1) the adsorbate's pKa and 2) the adsorbate's enthalpy of protonation. The observed calorimetric enthalpy of binding exhibited both pH and buffer-dependence and was between -5 and -42 kJ/mol. Meanwhile, the predicted intrinsic enthalpy (-25.1 kJ/mol) of binding was in excellent agreement with the measured intrinsic enthalpy (-25.6 kJ/mol). Corrections to the observed calorimetric enthalpies allowed comparisons with enthalpies obtained from the van't Hoff method. It is shown that the predicted intrinsic calorimetric enthalpy agrees well with the van't Hoff enthalpies in instances where observed enthalpies significantly deviated. This treatment is general and is not specific to phenobarbital or activated carbon.

An Optimized Microscale Thermophoresis Method for High-Throughput Screening of DNA Methyltransferase 2 Ligands

Developing methyltransferase inhibitors is challenging, since most of the currently used assays are time-consuming and cost-intensive. Therefore, efficient, fast, and reliable methods for screenings and affinity determinations are of utmost importance. Starting from a literature-known fluorescent S-adenosylhomocysteine derivative, 5-FAM-triazolyl-adenosyl-Dab, developed for a fluorescence polarization assay to investigate the histone methyltransferase mixed-lineage leukemia 1, we herein describe the applicability of this compound as a fluorescent tracer for the investigation of DNA-methyltransferase 2 (DNMT2), a human RNA methyltransferase. Based on these findings, we established a microscale thermophoresis (MST) assay for DNMT2. This displacement assay can circumvent various problems inherent to this method. Furthermore, we optimized a screening method via MST which even indicates if the detected binding is competitive and gives the opportunity to estimate the potency of a ligand, both of which are not possible with a direct binding assay.

Picomolar fluorescent probes for compound affinity determination to carbonic anhydrase IX expressed in live cancer cells

Numerous human cancers, especially hypoxic solid tumors, express carbonic anhydrase IX (CAIX), a transmembrane protein with its catalytic domain located in the extracellular space. CAIX acidifies the tumor microenvironment, promotes metastases and invasiveness, and is therefore considered a promising anticancer target. We have designed a series of high affinity and high selectivity fluorescein-labeled compounds targeting CAIX to visualize and quantify CAIX expression in cancer cells. The competitive binding model enabled the determination of common CA inhibitors' dissociation constants for CAIX expressed in exponentially growing cancer cells. All tested sulfonamide compounds bound the proliferating cells with similar affinity as to recombinantly purified CAIX. The probes are applicable for the design of selective drug-like compounds for CAIX and the competition strategy could be applied to other drug targets.

Comparative study of the binding between chlorogenic acid and four proteins by isothermal titration calorimetry, spectroscopy and docking methods

As a polyphenolic compound, chlorogenic acid has antioxidant, anti-inflammatory, antiviral, anti-obesity and other effects. Based on the interactions between chlorogenic acid and the proteins (human serum albumin (HSA), pepsin (Pep), trypsin (Try), fat mass and obesity-associated protein (FTO)), results will provide clues for screening effective inhibitors. The interaction between chlorogenic acid and the four proteins (HSA, Pep, Try, FTO) was analyzed by the aid of fluorescence quenching, synchronous fluorescence, three-dimensional fluorescence, isothermal titration calorimetry, and molecular docking. It can be concluded that there is no obvious interaction between chlorogenic acid and FTO. The binding affinity between chlorogenic acid and three proteins is HSA > Try > Pep. The binding process is spontaneous, and the quenching type is static quenching. Hydrophobic interaction and hydrogen bonding is observed in the binding process. This study provides valuable information for understanding the interaction mechanism between chlorogenic acid and proteins, and provides clues for screening inhibitors.

Non-synonymous substitution of evolutionarily conserved residue in Tau class glutathione transferases alters structural and catalytic features

Plant-specific tau glutathione transferases (GSTs) are basically involved in catalysing γ-glutathione (GSH)-dependent conjugation reactions with pesticides and herbicides, which play an important role in the detoxification of pollutants. Given the lack of systematic biochemical and structural information on tau GSTs, the study of their mediated defence mechanisms against toxic compounds has been greatly hindered. Here, we reveal the importance of the Ile residue closely interacting with GSH for the structural stability and catalytic function of GST. Evolutionary conservation analysis indicated that the crucial G-site Ile55 in the SbGSTU6 was converted to Thr53 of SbGSTU7. The comparative biochemical data on SbGSTU6, SbGSTU7 and their mutants showed that the substitution of Ile by Thr caused significant decrease in the affinity and catalytic efficiency of the GSTs. The unfavourable structural flexibility and pKa distribution of the active cavity residues were also demonstrated. Crystallography studies and molecular dynamics simulations showed that the conversion resulted in the hydrogen bond recombination with GSH and conformational rearrangement of GST active cavity, in which the Ile residue was more conducive to the formation of enzyme substrate complexes. The extensive biochemical and structural data not only reveal the critical role of the conserved G-site Ile residue in catalysing GSH-conjugate reactions but also provide valuable resources for the development of GST engineering in analytical and agricultural biotechnology.

Thrombopoietin receptor-based protein-protein interaction screening (THROPPIS)

As protein-protein interactions (PPIs) are involved in many cellular events, development of mammalian cytosolic PPI detection systems is important for drug discovery as well as understanding biological phenomena. We have previously reported a c-kit-based PPI screening (KIPPIS) system, in which proteins of interest were fused with a receptor tyrosine kinase c-kit, leading to intracellular PPI-dependent cell growth. However, it has not been investigated whether PPI can be detected using other receptors. In this study, we employed a thrombopoietin receptor, which belongs to the Type I cytokine receptor family, to develop a thrombopoietin receptor-based PPI screening (THROPPIS) system. To improve the sensitivity of THROPPIS, we examined two strategies of (i) localization of the chimeric receptors on the cell membrane, and (ii) addition of a helper module to the chimeric receptors. Intriguingly, the nonlocalized chimeric receptor showed the best performance of THROPPIS. Furthermore, the addition of the helper module dramatically improved the detection sensitivity. In total, 5 peptide-domain interactions were detected successfully, demonstrating the versatility of THROPPIS. In addition, a peptide-domain interaction was detected even when insulin receptor or epidermal growth factor receptor was used as a signaling domain, demonstrating that this PPI detection system can be extended to other receptors.

Tempol Reverses the Negative Effects of Morphine on Arterial Blood-Gas Chemistry and Tissue Oxygen Saturation in Freely-Moving Rats

We have reported that pretreatment with the clinically approved superoxide dismutase mimetic, Tempol (4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl), blunts the cardiorespiratory depressant responses elicited by a subsequent injection of fentanyl, in halothane-anesthetized rats. The objective of the present study was to determine whether Tempol is able to reverse the effects of morphine on arterial blood-gas (ABG) chemistry in freely-moving Sprague Dawley rats. The intravenous injection of morphine (10 mg/kg) elicited substantial decreases in pH, pO₂ and sO₂ that were accompanied by substantial increases in pCO₂ and Alveolar-arterial gradient, which results in diminished gas-exchange within the lungs. Intravenous injection of a 60 mg/kg dose of Tempol 15 min after the injection of morphine caused minor improvements in pO₂ and pCO₂ but not in other ABG parameters. In contrast, the 100 mg/kg dose of Tempol caused an immediate and sustained reversal of the negative effects of morphine on arterial blood pH, pCO₂, pO₂, sO₂ and Alveolar-arterial gradient. In other rats, we used pulse oximetry to determine that the 100 mg/kg dose of Tempol, but not the 60 mg/kg dose elicited a rapid and sustained reversal of the negative effects of morphine (10 mg/kg, IV) on tissue O₂ saturation (SpO₂). The injection of morphine caused a relatively minor fall in mean arterial blood pressure that was somewhat exacerbated by Tempol. These findings demonstrate that Tempol can reverse the negative effects of morphine on ABG chemistry in freely-moving rats paving the way of structure-activity and mechanisms of action studies with the host of Tempol analogues that are commercially available.

Glutamate Dehydrogenase as a Promising Target for Hyperinsulinism Hyperammonemia Syndrome Therapy

Hyperinsulinism-hyperammonemia syndrome (HHS) is a rare disease characterized by recurrent hypoglycemia and persistent elevation of plasma ammonia, and it can lead to severe epilepsy and permanent brain damage. It has been demonstrated that functional mutations of glutamate dehydrogenase (GDH), an enzyme in the mitochondrial matrix, are responsible for the HHS. Thus, GDH has become a promising target for the small molecule therapeutic intervention of HHS. Several medicinal chemistry studies are currently aimed at GDH, however, to date, none of the compounds reported has been entered clinical trials. This perspective summarizes the progress in the discovery and development of GDH inhibitors, including the pathogenesis of HHS, potential binding sites, screening methods, and research models. Future therapeutic perspectives are offered to provide a reference for discovering potent GDH modulators and encourage additional research that will provide more comprehensive guidance for drug development.

Allergens and their associated small molecule ligands-their dual role in sensitization

Many allergens feature hydrophobic cavities that allow the binding of primarily hydrophobic small‐molecule ligands. Ligand‐binding specificities can be strict or promiscuous. Serum albumins from mammals and birds can assume multiple conformations that facilitate the binding of a broad spectrum of compounds. Pollen and plant food allergens of the family 10 of pathogenesis‐related proteins bind a variety of small molecules such as glycosylated flavonoid derivatives, flavonoids, cytokinins, and steroids in vitro. However, their natural ligand binding was reported to be highly specific. Insect and mammalian lipocalins transport odorants, pheromones, catecholamines, and fatty acids with a similar level of specificity, while the food allergen β‐lactoglobulin from cow's milk is notably more promiscuous. Non‐specific lipid transfer proteins from pollen and plant foods bind a wide variety of lipids, from phospholipids to fatty acids, as well as sterols and prostaglandin B2, aided by the high plasticity and flexibility displayed by their lipid‐binding cavities. Ligands increase the stability of allergens to thermal and/or proteolytic degradation. They can also act as immunomodulatory agents that favor a Th2 polarization. In summary, ligand‐binding allergens expose the immune system to a variety of biologically active compounds whose impact on the sensitization process has not been well studied thus far.

Effect of a Good buffer on the fate of metastable protein-rich droplets near physiological composition

Metastable protein-rich microdroplets are produced from liquid-liquid phase separation (LLPS) of protein aqueous solutions. These globules can be intermediates for the formation of other protein-rich phases. Lysozyme aqueous solutions undergo LLPS around 0 °C in the presence of NaCl near physiological conditions. Here, it is shown that insertion of small amounts of 4-(2-hydroxyethyl)-1-piperazineethanesulfonate (HEPES, 0.1 M) as a second additive to lysozyme-NaCl-water solutions near physiological ionic strength (0.2 M) is an essential step for triggering conversion of protein-rich droplets into another phase. Specifically, LLPS induced by cooling reproducibly leads to a rapid and high-yield formation of compact tetragonal crystalline microparticles only in the presence of HEPES. These microcrystals exhibit small size (1-3 μm), narrow size distribution and guest-binding properties. The temperature-concentration phase diagram shows a characteristic topology with LLPS boundary metastable with respect to tetragonal microcrystals, which in turn become less stable than rod-shaped orthorhombic crystals above 40 °C. Interestingly, dynamic light scattering, hydrogen-ion titrations and isothermal titration calorimetry reveal that lysozyme-HEPES interactions were found to be weakly attractive and exothermic. Our findings indicate that additives of salting-in type can represent an important factor controlling the fate of metastable protein-rich microdroplets relevant to drug formulations, femtosecond crystallography, and potential implications in protein-driven cytoplasmic compartmentalization.

Systemic Administration of Tempol Attenuates the Cardiorespiratory Depressant Effects of Fentanyl

Fentanyl is a high-potency opioid receptor agonist that elicits profound analgesia and suppression of breathing in humans and animals. To date, there is limited evidence as to whether changes in oxidant stress are important factors in any of the actions of acutely administered fentanyl. This study determined whether the clinically approved superoxide dismutase mimetic, Tempol (4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl), or a potent antioxidant, N-acetyl-L-cysteine methyl ester (L-NACme), modify the cardiorespiratory and analgesic actions of fentanyl. We examined whether the prior systemic injection of Tempol or L-NACme affects the cardiorespiratory and/or analgesic responses elicited by the subsequent injection of fentanyl in isoflurane-anesthetized and/or freely moving male Sprague-Dawley rats. Bolus injections of Tempol (25, 50 or 100 mg/kg, IV) elicited minor increases in frequency of breathing, tidal volume and minute ventilation. The ventilatory-depressant effects of fentanyl (5 μg/kg, IV) given 15 min later were dose-dependently inhibited by prior injections of Tempol. Tempol elicited dose-dependent and transient hypotension that had (except for the highest dose) resolved when fentanyl was injected. The hypotensive responses elicited by fentanyl were markedly blunted after Tempol pretreatment. The analgesic actions of fentanyl (25 μg/kg, IV) were not affected by Tempol (100 mg/kg, IV). L-NACme did not modify any of the effects of fentanyl. We conclude that prior administration of Tempol attenuates the cardiorespiratory actions of fentanyl without affecting the analgesic effects of this potent opioid. As such, Tempol may not directly affect opioid-receptors that elicit the effects of fentanyl. Whether, the effects of Tempol are solely due to alterations in oxidative stress is in doubt since the powerful antioxidant, L-NACme, did not affect fentanyl-induced suppression of breathing.

Genetic design of co-expressed Mesorhizobium loti carbonic anhydrase and chaperone GroELS to enhancing carbon dioxide sequestration

Mesorhizobium loti carbonic anhydrase (MlCA), an intrinsically high catalytic enzyme, has been employed for carbon dioxide capture and sequestration. However, recombinant expression of MlCA in Escherichia coli often forms inclusion bodies. Hence, protein partners such as fusion-tags and molecular chaperones are involved in regarding reduce the harshness of protein folding. TrxA-tag and GroELS have been chosen to co-express with MlCA in E. coli under an inducible T7 promoter or a constitutive J23100 promoter to compare productivity and activity. The results possessed that coupling protein partners effectively increased soluble MlCA up to 2.9-folds under T7 promoter, thus enhancing the CA activity by 120% and achieving a 5.2-folds turnover rate. Besides, it has also shifted the optimum temperature from 40 °C to 50 °C, promoted stability in the broad pH range (4.5 to 9.5) and the presence of various metal ions. Based on the in vitro assay and isothermal titration calorimetry (ITC) analysis, GroELS enhancing CA activity was due to change the intrinsic thermodynamic properties of the enzyme from endothermic to exothermic reaction (i.e., ∆H = 89.8 to -121.8 kJ/mol). Therefore, the collaboration of TrxA-MlCA with GroELS successfully augmented CO₂ biomineralization.

Development of a Microscale Thermophoresis-Based Method for Screening and Characterizing Inhibitors of the Methyl-Lysine Reader Protein MRG15

MRG15 is a transcription factor containing the methyl-lysine reader chromodomain. Despite its involvement in different physiological and pathological states, to date the role of this protein has not been fully elucidated due to the lack of a specific and potent chemical probe.In this work, we report the development of a microscale thermophoresis (MST)-based assay for the study of MRG15-ligand binding interactions. After the development, the assay was validated using a small focused library and UNC1215 as the reference compound, to yield the identification of 10 MRG15 ligands with affinities ranging from 37.8 nM to 59.1 µM.Hence, our method is robust, convenient, and fast and could be applied to other methylation reader domain-containing proteins for the identification of new chemical probes.

An electrochemical impedimetric sensing platform based on a peptide aptamer identified by high-throughput molecular docking for sensitive l-arginine detection

As a primary building block for protein synthesis, l-arginine (l-Arg) is also a precursor for the synthesis of important metabolites, and is involved in various physiological and pathophysiological processes. l-Arg is a potential biomarker in clinical diagnosis and nutritional status assessment, making it valuable to quantify and monitor this biomolecule. In this study, peptide aptamers that specifically interact with l-Arg were identified by high-throughput molecular docking, and the binding capacities between the synthesized peptide aptamers and l-Arg were then measured by isothermal titration calorimetry. We hypothesized that the peptide aptamer with the greatest binding capacity could be used as the recognition element in a biosensor. A chemosynthetic peptide aptamer modified with mercaptan and spacer units (thioctic acid-GGGG-FGHIHEGY) was thus used to construct label-free electrochemical impedimetric biosensors for l-Arg based on gold electrodes. The optimum biosensor showed good sensitivity to l-Arg with a linear range of 0.1 pM-0.1 mM, and the calculated limit of detection (three times the signal-to-noise ratio) was 0.01 pM. Interference studies and assays of diluted serum samples were also carried out, and satisfactory results obtained. In conclusion, a potential method of peptide aptamer screening and biosensor fabrication for detecting small biological molecules was demonstrated.

The peptide PROTAC modality: a novel strategy for targeted protein ubiquitination

Despite dramatic advances in drug discovery over the decades, effective therapeutic strategies for cancers treatment are still in urgent demands. PROteolysis TArgeting Chimera (PROTAC), a novel therapeutic modality, has been vigorously promoted in preclinical and clinical applications. Unlike small molecule PROTAC, peptide PROTAC (p-PROTAC) with advantages of high specificity and low toxicity, while avoiding the limitations of shallow binding pockets through large interacting surfaces, provides promising substitutions for E3 ubiquitin ligase complex-mediated ubiquitination of "undruggable proteins". It is worth noting that successful applications of p-PROTAC still have some obstacles, including low stability and poor membrane permeability. Hence, we highlight that p-PROTAC combined with cell-penetrating peptides, constrained conformation technique, and targeted delivery systems could be the future efforts for potential translational research.