Glutathione turnover in human cell lines in the presence of agents with glutathione influencing potential with and without acivicin inhibition of γ-glutamyltranspeptidase

Fucosyltransferase 2 inhibitors: Identification via docking and STD-NMR studies

Fucosyltransferase 2 (FUT2) catalyzes the biosynthesis of A, B, and H antigens and other important glycans, such as (Sialyl Lewisx) sLex, and (Sialyl Lewisy) sLey. The production of these glycans is increased in various cancers, hence to design and develop specific inhibitors of FUT2 is a therapeutic strategy. The current study was designed to identify the inhibitors for FUT2. In silico screening of 300 synthetic compounds was performed. Molecular docking studies highlighted the interactions of ligands with critical amino acid residues, present in the active site of FUT2. The epitope mapping in ligands was performed using the STD-NMR experiments to identify the interactions between ligands, and receptor protein. Finally, we have identified 5 lead compounds 4, 5, 26, 27, and 28 that can be studied for further development as cancer therapeutic agents.

Statistical optimization of culture conditions of mesophillic gamma-glutamyl transpeptidase from Bacillus altitudinis IHB B1644

Microbial gamma-glutamyl transpeptidase (GGT) is a key enzyme in production of several γ-glutamyl compounds with food and pharmaceutical applications. Bacterial GGTs are not commercially available in the market owing to their low production from various sources. Thus, the study was focused on achieving the higher GGT production from B. altitudinis IHB B1644 by optimizing the culture conditions using one-variable-at-a-time (OVAT) strategy. A mesophillic temperature of 28 °C, agitation 200 rpm and neutral pH 7 were found to be optimal for higher GGT titre. Among the medium components, the monosaccharide glucose served as the best carbon source over disaccharides, and yeast extract was the preferred organic nitrogen source over inorganic nitrogen sources. The statistical approaches (Plakett-Burman and response surface methodology) were further employed for the optimization of medium components. Medium composition: 0.1% w/v glucose, 0.3% w/v yeast extract, 0.03% w/v magnesium sulphate, 0.20% w/v potassium dihydrogen phosphate and 2.5% w/v sodium chloride with inoculum size (1% v/v) was suitable for higher GGT titres (449 U ml^-1). Time kinetics showed the stability of enzyme up to 96 h of incubation suggesting its application in the industrial use. The proposed strategy resulted in 2.6-fold increase in the GGT production compared to that obtained in the unoptimized medium. The results demonstrated that RSM was fitting to identify the optimum production conditions and this finding should be of great importance for commercial GGT production.

Mutational Analysis of a Highly Conserved PLSSMXP Sequence in the Small Subunit of Bacillus licheniformis γ-Glutamyltranspeptidase

A highly conserved ⁴⁵⁸PLSSMXP⁴⁶⁴ sequence in the small subunit (S-subunit) of an industrially important Bacillus licheniformis γ-glutamyltranspeptidase (BlGGT) was identified by sequence alignment. Molecular structures of the precursor mimic and the mature form of BlGGT clearly reveal that this peptide sequence is in close spatial proximity to the self-processing and catalytic sites of the enzyme. To probe the role of this conserved sequence, ten mutant enzymes of BlGGT were created through a series of deletion and alanine-scanning mutagenesis. SDS-PAGE and densitometric analyses showed that the intrinsic ability of BlGGT to undergo autocatalytic processing was detrimentally affected by the deletion-associated mutations. However, loss of self-activating capacity was not obviously observed in most of the Ala-replacement mutants. The Ala-replacement mutants had a specific activity comparable to or greater than that of the wild-type enzyme; conversely, all deletion mutants completely lost their enzymatic activity. As compared with BlGGT, S460A and S461S showed greatly enhanced k_cat/K_m values by 2.73- and 2.67-fold, respectively. The intrinsic tryptophan fluorescence and circular dichroism spectral profiles of Ala-replacement and deletion mutants were typically similar to those of BlGGT. However, heat and guanidine hydrochloride-induced unfolding transitions of the deletion-associated mutant proteins were severely reduced as compared with the wild-type enzyme. The predictive mutant models suggest that the microenvironments required for both self-activation and catalytic reaction of BlGGT can be altered upon mutations.

Influence of signal-peptide truncations on the functional expression of Escherichia coli gamma -glutamyltranspeptidase

The full-length Escherichia coli gamma -glutamyltranspeptidase (EcGGT) gene and five truncations lacking 33, 51, 54, 60, and 78 bp respectively at the 5' end were prepared by polymerase chain reaction and cloned into the expression vector pQE-30. Isopropyl-beta -D-thiogalactopyranoside induction of E. coli M15 cells bearing the recombinant plasmids resulted in the intracellular production of the expressed proteins, EcGGT, EcGGT/DeltaN11, EcGGT/DeltaN17, EcGGT/DeltaN18, EcGGT/DeltaN20, and EcGGT/DeltaN26. The overexpressed enzymes were purified to near homogeneity by Ni(2+)-NTA resin. The specific activity for EcGGT, EcGGT/DeltaN11 and EcGGT/DeltaN17 was 5.3, 4.9, and 4.8 U/mg protein respectively, whereas the rest three enzymes had shown no GGT activity under the enzyme assay conditions. More than 94% of the activity was found in the cytoplasmic fraction of E. coli M15 cells harboring pQE-EcGGT, pQE-EcGGT/DeltaN11 or pQE-EcGGT/DeltaN17. Western blot analysis confirmed that the majority of N-terminally truncated enzymes were present in the cytoplasm.

Cysteine turnover in human cell lines is influenced by glyphosate

Pesticides are widely spread in the environment and there is a lack of knowledge concerning the impact of these substances on the human cell. In the present study the effect of low doses of the pesticides bentazon, metalaxyl and glyphosate on the cellular metabolism of glutathione and cysteine was examined in HeLa and hepatoma cell cultures. No effect was observed when the cells were exposed to bentazon or metalaxyl. However, significant changes in the intra- and extracellular concentration of cysteine, a precursor for glutathione synthesis, were detected when glyphosate was added to the medium. This finding was observed in the presence of micromolar concentration range of glyphosate, and is relevant when compared to concentrations observed in monitoring programmes.

Effect of enlarged glutathione on zinc-mediated toxicity in lung-derived cell lines

Zinc-mediated toxicity has been linked to cellular glutathione content in isolated cells. In addition, treatment of alveolar epithelial type II cells with glucocorticoids diminishes cellular glutathione content, and this is followed by an increase in zinc-mediated toxicity. The question arises whether an increase in glutathione synthesis might decrease zinc-mediated toxicity. For this purpose an administration of 200 micromol/l N-acetyl-L-cysteine (NAC) was given to the cells, while cysteine was used up to 100 micromol/l. Zinc-mediated toxicity was assessed by measuring protein synthesis inhibition and glutathione dependent parameters. De novo synthesis of glutathione was assessed as compared to controls by N-acetyl-D-cysteine (NADC) treatment. Comparing NAC and NADC treatment no differences in zinc-mediated toxicity were found. Furthermore only in one (of three) cell line tested a significant increase in GSH content by NAC as compared to NADC treatment was achieved. But even in this cell line no changes by zinc-mediated toxicity were found. It is concluded that the cell lines tested can use other sources of cys for glutathione synthesis. Furthermore the increased zinc-mediated toxicity due to hydrocortisone was abolished in the alveolar epithelial cell lines by the NADC/NAC treatment. It is therefore discussed that additionally to glutathione some other antioxidative defence mechanisms can influence zinc-mediated toxicity as well.

The effects of modulation of γ-glutamyl transpeptidase activity in HepG2 cells on thiol homeostasis and caspase-3-activity

The present studies aimed to elucidate how the modulation of gamma-glutamyl transpeptidase (gammaGT) activity in human hepatoma (HepG2) cell line influences H(2)O(2) production, caspase 3 activity, protein S-thiolation by glutathione (GSH), cysteinyl-glycine (Cys-Gly) and cysteine (Cys), and the level of other redox forms of these thiols. The experiments showed that 1-h stimulation of gammaGT elevated H(2)O(2) production, leading to prooxidant conditions. After 24-h stimulation, H(2)O(2) concentration was at the control level, while Cys-Gly-, Cys- and GSH-dependent S-thiolation was markedly increased, which was accompanied by a drop in caspase-3 activity. The inhibition of gammaGT activity by acivicin led to H(2)O(2) decrease after 1-h incubation which still persisted after 24 h. The inhibition of gammaGT activity in HepG2 cells was also connected with the lowering of S-thiolation with Cys and Cys-Gly and with increasing of caspase-3 activity. The results of our studies indicate that the modulation of gammaGT activity can be used to change cellular redox status, and can affect Cys- and Cys-Gly-dependent S-thiolation and caspase-3 activity. We suggest that the role of high gammaGT activity in HepG2 cells can be connected with production of reactive oxygen species and with S-thiolation with Cys and Cys-Gly that can influence activity of caspase 3.