Screening and isolation of quorum sensing inhibitors of Pseudomonas aeruginosa from Phellodendron amurense extracts using bio-affinity chromatography.

Drug-resistant bacterial infections pose a significant challenge in the field of bacterial disease treatment. Finding new antibacterial pathways and targets to combat drug-resistant bacteria is crucial. The bacterial quorum sensing (QS) system regulates the expression of bacterial virulence factors. Inhibiting bacterial QS and reducing bacterial virulence can achieve antibacterial therapeutic effects, making QS inhibition an effective strategy to control bacterial pathogenicity. This article mainly focused on the PqsA protein in the QS system of Pseudomonas aeruginosa. An affinity chromatography medium was developed using the SpyTag/SpyCatcher heteropeptide bond system. Berberine, which can interact with the PqsA target, was screened from Phellodendron amurense by affinity chromatography. We characterized its structure, verified its inhibitory activity on P. aeruginosa, and preliminarily analyzed its mechanism using molecular docking technology. This method can also be widely applied to the immobilization of various protein targets and the effective screening of active substances.

Screening of inhibitors on successful covalent tyrosinase coupling with help from SpyBank.

Microbial metabolites are an important source of tyrosinase (TYR) inhibitors because of their rich chemical diversity. However, because of the complex metabolic environment of microbial products, it is difficult to rapidly locate and identify natural TYR inhibitors. Affinity-based ligand screening is an important method for capturing active ingredients in complex samples, but ligand immobilization is an important factor affecting the screening process. In this paper, TYR was used as ligand, and the SpyTag/SpyCatcher coupling system was used to rapidly construct affinity chromatography vectors for screening TYR inhibitors and separating active components from complex samples. We successfully expressed SpyTag-TYR fusion protein and SpyCatcher protein, and incubated SpyCatcher protein with epoxy-activated agarose. The SpyTag-TYR protein was spontaneously coupled with SpyCatcher to obtain an affinity chromatography filler for immobilization of TYR, and the performance of the packaging material was characterized. Finally, compound 1 with enzyme inhibitory activity was successfully obtained from the fermentation product of marine microorganism C. Through HPLC, MS, 1H NMR and 13C NMR analyses, its structure was deduced as azelaic acid, and its activity was analyzed. The results showed that this is a feasible method for screening TYR inhibitors in complex systems.

A new method based on dispersive liquid-liquid microextraction for fat-soluble vitamin determination in serum by LC-MS/MS.

A green and inexpensive pretreatment known as dispersive liquid-liquid microextraction (DLLME) was developed in this assay coupled with the LC-MS/MS method for routine analysis of fat soluble vitamins (FSVs). The technique was performed with methanol as the dispersive solvent and dichloromethane as the extraction solvent. The extraction phase containing FSVs was evaporated to dryness and reconstituted in a mixture of acetonitrile and water. The influence variables concerning the DLLME procedure were optimized. After that, the method was investigated for its applicability in LC-MS/MS analysis. As a result, the parameters were settled for the optimal conditions during the DLLME process. A cheap and lipid-free substance was found as an alternative to serum to eliminate the matrix effect while preparing the calibrators. The method validation indicated that it was suitable for determining FSVs in serum. Moreover, this method was applied successfully to determine serum samples, which was consistent with the literature. In summary, the DLLME method developed in this report was reliable and more cost-effective than the traditional LC-MS/MS method, and could be applied in the future.

Production of bilirubin by biotransformation of biliverdin using recombinant Escherichia coli cells.

Bilirubin, a natural intermediate in heme degradation, is a valuable Chinese medicine used in more than 50 traditional Chinese medicine (TCM) preparations. At present, bilirubin is mainly produced by extraction from pig bile, but a shortage of the raw material has increased the price, to about US$10,000/kg in the Chinese market. Biliverdin, the precursor of bilirubin, is more abundant and less expensive than bilirubin, but it is not used in TCM. Thus, the biotransformation of biliverdin by biliverdin reductase (BvdR) may be a practical way to produce bilirubin. In this study, the codon-optimized gene of biliverdin reductase (mbvdR) from the cyanobacterium Synechocystis was cloned into Escherichia coli BL21(DE3), and the conditions for BL21-mBvdR expressing BvdR were optimized. Resting BL21-mBvdR cells were employed as biocatalysts to biotransform biliverdin to bilirubin. At a concentration of biliverdin substrate of 450 mg/L in the reaction mixture, the bilirubin content in dry cells reached 20.8 ± 0.8 mg/g, with a conversion yield of 72.3%. Therefore, recombinant E. coli expressing BvdR can be applied to biotransform biliverdin to bilirubin, providing a potential alternative process for bilirubin production.

A structure-activity relationship of a thrombin-binding aptamer containing LNA in novel sites.

In this report, structural characterization, aptamer stability and thrombin of a new modified thrombin-ligand complex binding aptamer (TBA) containing anti-guanine bases and a loop position locked nucleic acid (LNA) are presented. NMR, circular dichroic spectroscopy and molecular modeling were used to characterize the three-dimensional structure of two G-quadruplexes. LNA-modification of the anti-guanosines yields G-quadruplexes that show affinity and inhibitory activity toward thrombin, whereas LNA-modification of a thymine nucleotide in the TGT loop increases the thermal stability of TBA. As assessed by denatured PAGE electrophoresis, all modified aptamers display an increase in environmental stability. The prothrombin time assay and fibrinogen assay showed that the aptamers still had good inhibitory activity, and 15 of them had the longest PT time. Therefore, the LNA modification is well suited to improve the physicochemical and biological properties of the native thrombin-binding aptamer.

Construction and application of an electrochemical biosensor based on an endotoxin aptamer.

An electrochemical biosensor that used an aptamer as a biological element was constructed to detect endotoxin. Biolayer interferometry was used to obtain the affinity constant of an aptamer for lipopolysaccharide, which had an equilibrium dissociation constant of 22.9 nM. The amine-terminated aptamer was then assembled on a gold electrode surface using 3-mercaptopropionic acid as an intermediate linker. The modification of the gold electrode was confirmed by cyclic voltammetry and electrochemical impedance spectroscopy. In the range of 0.001-1 EU/mL, the increase in electron transfer resistance of the biosensor was linear with the logarithmic value of the endotoxin concentration. The constructed biosensor exhibits sensitivity and a low limit of detection.

Preparation of recombinant human thymic stromal lymphopoietin protein.

Human thymic stromal lymphopoietin (hTSLP) protein plays a central role in inflammation. Characterizing properties of hTSLP requires a recombinant overexpression system that produces correctly folded, active hTSLP. In this report, an efficient overexpression system for the production of hTSLP was developed. We constructed expression plasmids of the full-length hTslp gene with or without the signal peptide and transformed the plasmids into Escherichia coli. The design of the recombinant proteins included an N-terminal His-tag, which facilitated purification. An affinity gradient elution method was used to improve recovery and concentration levels of denatured hTSLP, with 90% purity observed following affinity chromatography. Refolding of the denatured hTSLP was tested using four different protein refolding approaches. The optimal refolding conditions involved stepwise buffer exchanges to reduce the urea concentration from 4 to 0 M in 50 mM Tris (pH 8.0), 1 mM EDTA, 50 mM NaCl, 10% glycerol, 400 mM L-Arg, 0.2 mM oxidized glutathione, and 2 mM reduced glutathione. The activity of the refolded recombinant hTSLP protein was measured by an ELISA assay. Interestingly, the presence of N-terminal signal peptide inhibited the overexpression of hTSLP in E. coli. The amount of recombinant hTSLP protein purified reached a level of 2.52 × 10-3 mg/L.

A biotransformation process for the production of cucurbitacin B from its glycoside using a selected Streptomyces sp.

Cucurbitacin B (CuB) and its glycoside, cucurbitacin B 2-o-ß-D-glucoside (CuBg), abundantly occur in the pedicels of Cucumis melo. Compared with CuB, CuBg is not efficiently extracted from the pedicels. Furthermore, the anticancer activity of CuBg is lower than that of the aglycone. A process for CuBg biotransformation to CuB was developed for the first time. A strain of Streptomyces species that converts CuBg into CuB was isolated from an enrichment culture of C. melo pedicels. After optimization of conditions for enzyme production and biotransformation, a maximum conversion rate of 92.6 % was obtained at a CuBg concentration of 0.25 g/L. When biotransformation was performed on C. melo pedicel extracts, the CuB concentration in the extracts increased from 1.50 to 3.27 g/L. The conversion rate was almost 100 %. The developed process may be an effective biotransformation method for industrial production CuB from C. melo pedicels for pharmaceuticals.

Functions of thymic stromal lymphopoietin in non-allergic diseases.

Thymic stromal lymphopoietin (TSLP) is an interleukin 7-like cytokine produced mainly by epithelial cells. Many studies indicate that TSLP contributes to promote T helper (Th) 2 immune responses which are associated with the pathogenesis of allergic inflammatory diseases. Base on the cross-talk between Th2 inflammation and cancers, we will highlight the role of TSLP in the progression of cancers in this review. TSLP is involved in the increasing prevalence of Tregs in the cancer microenvironment. Besides, TSLP has an important role in promoting the growth of vascular endothelial cells and angiogenesis, which could further promote the development and progression of cervical cancer. It gives the evidence that TSLP could induce EMT to promote cancer metastasis. In addition, TSLP could be detected in some fibroblasts and may play a role in the pathogenesis of non-allergic diseases characterized by a type 2 immune response and organ fibrosis.

Selecting DNA aptamers for endotoxin separation.

OBJECTIVES: To select aptamers for endotoxin separation from a 75-nucleotide single-stranded DNA random library using systematic evolution of ligands by exponential enrichment. RESULTS: After 15 rounds of selection, the final pool of aptamers was specific to endotoxin. Structural analysis of aptamers that appeared more than once suggested that one aptamer can form a G-quartet structure. Tests for binding affinity and specificity showed that this aptamer exhibited a high affinity for endotoxin. Using this aptamer, aptamer-magnetic beads were designed to separate endotoxin. CONCLUSIONS: Using these aptamer-magnetic beads, a new method to separate endotoxin was developed to enable specific separation of endotoxin that can be applied to drug and food products.