Cloning, purification and biochemical characterization of two glutathione S-transferase isoforms from Rutilus frisii kutum.

Glutathione S-transferases are an important multifunctional family of intracellular enzymes that their detoxification function has been reported in fishes since 1970, but no studies have been conducted on Rutilus frisii kutum GSTs yet. In the present study, RkGSTA and RkGSTM encoding genes were cloned and sequenced and their nucleotide sequences were submitted to NCBI GenBank. In order to reduce the expression challenges of recombinant proteins including low solubility, low yield and insufficient purity issues in E. coli, the pKJE7 chaperone plasmid was used to increase the recovery of expressed proteins in the soluble fractions. Best expression clone was selected for purification by Ni-NTA affinity chromatography. The three-dimensional structural models were constructed by I-TASSER. The optimum temperature of purified RkGSTA and RkGSTM was 35 and 30 °C, with optimum activity at pH 9.0 and 8.5, respectively. The thermostability and pH stability results indicated that RkGSTA is more heat-tolerant than RkGSTM though both of them retained more than 80% of their activities at pH 6.5 to 9.0. Overall, this study represents a comprehensive perspective on the structural and biochemical aspects of this enzyme that would be even used in further researches such as drug design studies in order to eliminate toxicant compounds from the body and environment of fishes to protect them against undesired harmful damages.

Functional Expression, Purification and Identification of Interaction Partners of PACRG.

PACRG (Parkin co-regulated gene) shares a bi-directional promoter with the Parkinson's disease-associated gene Parkin, but the physiological roles of PACRG have not yet been fully elucidated. Recombinant expression methods are indispensable for protein structural and functional studies. In this study, the coding region of PACRG was cloned to a conventional vector pQE80L, as well as two cold-shock vectors pCold II and pCold-GST, respectively. The constructs were transformed into Escherichia coli (DE3), and the target proteins were overexpressed. The results showed that the cold-shock vectors are more suitable for PACRG expression. The soluble recombinant proteins were purified with Ni2+ chelating column, glutathione S-transferase (GST) affinity chromatography and gel filtration. His6 pull down assay and LC-MS/MS were carried out for identification of PACRG-binding proteins in HEK293T cell lysates, and a total number of 74 proteins were identified as potential interaction partners of PACRG. GO (Gene ontology) enrichment analysis (FunRich) of the 74 proteins revealed multiple molecular functions and biological processes. The highest proportion of the 74 proteins functioned as transcription regulator and transcription factor activity, suggesting that PACRG may play important roles in regulation of gene transcription.

Cloning, characterization and expression analysis of glutathione S-transferase from the Antarctic yeast Rhodotorula mucilaginosa AN5.

The gene for glutathione S-transferase (GST) in Antarctic sea-ice yeast Rhodotorula mucilaginosa AN5 was cloned and expressed in Escherichia coli and named RmGST. Sequence analysis showed that the RmGST gene contained a 843 bp open reading frame, which encoded 280 amino acid residues with a calculated molecular mass of 30.4 kDa and isoelectric point of 5.40. RmGST has the typical C- and N-terminal double domains of glutathione S-transferase. Recombinant RmGST (rRmGST) was expressed in E. coli to produce heterologous protein that had a high specific activity of 60.2 U/mg after purification. The apparent Km values of rRmGST for glutathione and 1-chloro-2,4-dinitrobenzene were 0.35 mM and 0.40 mM, respectively. Optimum enzyme activity was measured at 35 °C and at pH 7.0 and complete inactivation was observed after incubation at 55 °C for 60 min rRmGST tolerated high salt concentrations (1.0 M NaCl) and was stable at pH 3.0. Additionally, the recombinant protein nearly kept whole activity in Hg2+ and Mn2+, and could tolerate Ca2+, Cu2+, Mg2+, Cd2+, EDTA, thiourea, urea, Tween-80, H2O2 and Triton X-100. Real-time quantitative PCR showed that relative expression of the GST gene was significantly increased under Cu2+ and low temperature stress. These results indicate that rRmGST is a typical low thermostable enzyme, while its other characteristics, heavy metal and low temperature tolerance, might be related to its Antarctic home environment.

Structure of a serine-type glutathione S-transferase of Ceriporiopsis subvermispora and identification of the enzymatically important non-canonical residues by functional mutagenesis.

Ceriporiopsis subvermispora (C. subvermispora), one of the white-rot fungi, is known as a selective lignin degrader of the woody biomass. Glutathione S-transferases (GSTs) are multifunctional enzymes that are capable of catalyzing the reactions involved in detoxification and metabolic pathways. In this study, a GST of C. subvermispora, named CsGST63524, was overexpressed in E. coli, and then purified by affinity, anion exchange, and size exclusion column chromatography. The crystal structures of the CsGST63524 in ligand-free and complex with GSH were refined at 2.45 and 2.50 Šresolutions, respectively. The sulfur atom of glutathione forms a hydrogen bond with Ser21 of CsGST63524, indicating it is a serine-type GST. Mutagenesis of Ser21 unexpectedly indicated that this serine residue is not essential for the enzymatic activity of CsGST63524. Comparative sequence and structural analyses, together with functional mutagenesis, newly identified the enzymatically important non-canonical amino acid residues, Asn23 and Tyr45, other than the serine residue.

Cold-Adapted Glutathione S-Transferases from Antarctic Psychrophilic Bacterium Halomonas sp. ANT108: Heterologous Expression, Characterization, and Oxidative Resistance.

Glutathione S-transferases are one of the most important antioxidant enzymes to protect against oxidative damage induced by reactive oxygen species. In this study, a novel gst gene, designated as hsgst, was derived from Antarctic sea ice bacterium Halomonas sp. ANT108 and expressed in Escherichia coli (E. coli) BL21. The hsgst gene was 603 bp in length and encoded a protein of 200 amino acids. Compared with the mesophilic EcGST, homology modeling indicated HsGST had some structural characteristics of cold-adapted enzymes, such as higher frequency of glycine residues, lower frequency of proline and arginine residues, and reduced electrostatic interactions, which might be in relation to the high catalytic efficiency at low temperature. The recombinant HsGST (rHsGST) was purified to apparent homogeneity with Ni-affinity chromatography and its biochemical properties were investigated. The specific activity of the purified rHsGST was 254.20 nmol/min/mg. The optimum temperature and pH of enzyme were 25 °C and 7.5, respectively. Most importantly, rHsGST retained 41.67% of its maximal activity at 0 °C. 2.0 M NaCl and 0.2% H2O2 had no effect on the enzyme activity. Moreover, rHsGST exhibited its protective effects against oxidative stresses in E. coli cells. Due to its high catalytic efficiency and oxidative resistance at low temperature, rHsGST may be a potential candidate as antioxidant in low temperature health foods.

Isoenzymes of Aedes albopictus (Diptera: Culicidae) Glutathione S-transferases: Isolation and expression after acute insecticide treatment.

Glutathione S-transferases (GSTs) from susceptible Aedes albopictus larvae were partially isolated using two different purification strategies (GSTrap™ HP and GSH-agarose affinity columns) and the effects of permethrin and DDT on expression of the GSTs were investigated. Distinct double bands on SDS-PAGE with molecular weights between 20 and 25 kDa were successfully purified using GSTrap™ HP while a single band of 24.5 kDa was purified using GSH-agarose. The isolated GSTs belonged to the Delta, Sigma and Theta GST classes. When exposed to permethrin, one isoform of Theta, four isoforms of Sigma and thirteen isoforms of Delta GSTs showed an increased expression between 1.4-fold and 2.5-fold while DDT treatment resulted in between 1.4-fold and 3.2-fold increased expression in one isoform of Theta, four isoforms of Sigma and eleven isoforms of Delta GSTs (p < .05). This study indicated that GSTrap™ HP was more competent in isolating Ae. albopictus GSTs compared to GSH-agarose and also variable expression of GST isoforms occur in response to different insecticides. This information may be useful for improving insecticide resistance management strategies in aspect of molecular resistant and evolutionary tolerant detoxification enzyme.

Systematic analysis of the expression, solubility and purification of a passenger protein in fusion with different tags.

Purification of recombinant proteins is often achieved using a purification tag which can be located either at the N- or C-terminus of a passenger protein of interest. Many purification tags exist and their advantages and limitations are well documented. However, designing fusion proteins can be a challenging task to get a fully expressed, soluble and highly purified passenger protein. Besides, there is a lack of systematic studies on the use of a single tag versus combined tags and on the effect of the position of the tags in the construct. In the present study, 9 different fusion proteins were expressed in Escherichia coli using some of the most commonly used purification tags: maltose-binding protein (MBP), glutathione S-transferase (GST) and polyHis tag. The expression and purification of N-terminus single-tagged fusion proteins (MBP, GST and polyHis) and fusion proteins with combined tags at different positions have been tested. Both the identity of the tag(s) and its position were found to have a strong effect on the expression, solubility and purification yields of the fusion proteins. Consequently, the different fusion proteins assayed have shown varying expression, solubility and purification yields, which were also dependent on the passenger protein. Therefore, there is a compelling need to design various fusion proteins with different single or combined tags to identify optimized constructions allowing to achieve high levels of expression, solubility and purification of the passenger protein.

Evaluation of chalcones as inhibitors of glutathione S-transferase.

Glutathione S-transferases (GSTs) are the superfamily of multifunctional detoxification isoenzymes and play an important role in cellular signaling. In the present study, potential inhibition effects of chalcones were tested against human GST. For this purpose, GST was purified from human erythrocytes with 5.381 EU⋅mg-1 specific activity and 51.95% yield using a GSH-agarose affinity chromatographic method. The effects of chalcones on in vitro GST activity were tested at various concentrations. Ki constants of chalcones were found in the range of 7.76-41.93 µM. According to the results, 4-fluorochalcone showed a better inhibitory effect compared with the other compounds. The inhibition mechanisms of 2'-hydroxy-4-methoxychalcone and 4-methoxychalcone were noncompetitive, whereas the inhibition mechanisms of 4'- hydroxychalcone, 4- fluorochalcone, and 4,4'- diflurochalcone were competitive.

The toxicological impact of some avermectins on human erythrocytes glutathione S-transferase enzyme.

The drugs of the class avermectins are antiparasitic agents, which are widely used in medical and agricultural fields, especially in veterinary medicine. The aim of this study was to investigate the inhibitory effects of avermectin derivatives such as abamectin, doramectin, eprinomectin, ivermectin, and moxidectin, which are used for internal and external mammalian parasites. Glutathione S-transferase (GST, E.C. 2.5.1.18) was purified from fresh human erythrocytes. The purification of the GST enzyme was performed separately by affinity chromatography with a yield of 34.81% and 117.94-fold purification. The control of the pure GST enzyme was performed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis, and a single band was obtained. The IC50 values were approximately 0.31, 0.39, 0.13, 0.44, and 0.73 mM for abamectin, doramectin, eprinomectin, ivermectin, and moxidectin, and the Ki values were 0.32 ± 0.06, 0.39 ± 0.09, 0.13 ± 0.03, 0.44 ± 0.02, 0.73 ± 0.04 mM, respectively. This data revealed that the tested avermectins showed significant inhibitory effects on the GST enzyme.

Purification of glutathione S-transferase enzyme from quail liver tissue and inhibition effects of (3aR,4S,7R,7aS)-2-(4-((E)-3-(aryl)acryloyl)phenyl)-3a,4,7,7a-tetrahydro-1H-4,7-methanoisoindole-1,3(2H)-dione derivatives on the enzyme activity.

The use of quail meat and eggs has made this animal important in recent years, with its low cost and high yields. Glutathione S-transferases (GST, E.C.2.5.1.18) are an important enzyme family, which play a critical role in detoxification system. In our study, GST was purified from quail liver tissue with 47.88-fold purification and 12.33% recovery by glutathione agarose affinity chromatography. The purity of enzyme was checked by SDS-PAGE method and showed a single band. In addition, inhibition effects of (3aR,4S,7R,7aS)-2-(4-((E)-3-(aryl)acryloyl)phenyl)-3a,4,7,7a-tetrahydro-1H-4,7methanoisoindole-1,3(2H)-dion derivatives (1a-g) were investigated on the enzyme activity. The inhibition parameters (IC50 and Ki values) were calculated for these compounds. IC50 values of these derivatives (1a-e) were found as 23.00, 15.75, 115.50, 10.00, and 28.75 µM, respectively. Ki values of these derivatives (1a-e) were calculated in the range of 3.04 ± 0.50 to 131.50 ± 32.50 µM. However, for f and g compounds, the inhibition effects on the enzyme were not found.

Inhibition effects of pesticides on glutathione-S-transferase enzyme activity of Van Lake fish liver.

Glutathione-S-transferases (GSTs) have a function in xenobiotic metabolism. They are a significant multifunctional family with a wide variety of catalytic activities. In the current study, we determined in vitro inhibition effects of 2,4-dichlorophenoxyacetic acid dimethylamine salt (2,4-D DMA), haloxyfop-P-methyl, glyphosate isopropylamine, dichlorvos, and λ-cyhalothrin on purified GST. For this purpose, GST were purified from Van Lake fish (Chalcalburnus tarichii Pallas) liver with 29.25 EU mg-1 specific activity and 10.76% yield using GSH-agarose affinity chromatographic method. The pesticides were tested at various concentrations on in vitro GST activity. Ki constants were calculated as 0.17 ± 0.01, 0.25 ± 0.05, 3.72 ± 0.32, 0.42 ± 0.06, and 0.025 ± 0.004 mM, for 2,4-D DMA, haloxyfop-P-methyl, glyphosate isopropylamine, dichlorvos, and λ-cyhalothrin, respectively. λ-Cyhalothrin showed a better inhibitory effect compared to the other pesticides. The inhibition mechanisms of λ-cyhalothrin were competitive, while the other pesticides were noncompetitive.

Enzymatic characterization of two epsilon-class glutathione S-transferases of Spodoptera litura.

Two cDNAs encoding glutathione S-transferase (GST) of the tobacco cutworm, Spodoptera litura, were cloned by reverse transcriptase-polymerase chain reaction. The deduced amino acid sequences of the resulting clones revealed 32-51% identities to the epsilon-class GSTs from other organisms. The recombinant proteins were functionally overexpressed in Escherichia coli cells in soluble form and were purified to homogeneity. The enzymes were capable of catalyzing the bioconjugation of glutathione with 1-chloro-2,4-dinitrobenzene, 1,2-epoxy-3-(4-nitrophenoxy)-propane, and ethacrynic acid. A competition assay revealed that the GST activity was inhibited by insecticides, suggesting that it could be conducive to insecticide tolerance in the tobacco cutworm.

Two glutathione transferase isoforms isolated from juvenile cysts of Taenia crassiceps: identification, purification and characterization.

We identified and characterized the first two glutathione transferases (GSTs) isolated from juvenile cysts of Taenia crassiceps (EC 2.5.1.18). The two glutathione transferases (TcGST1 and TcGST2) were purified in a single-step protocol using glutathione (GSH)-sepharose chromatography in combination with a GSH gradient. The specific activities of TcGST1 and TcGST2 were 26 U mg-1 and 19 U mg-1, respectively, both at 25°C and pH 6.5 with 1-chloro-2,4-dinitrobenzene (CDNB) and GSH as substrates. The Km(CDNB) and Kcat(CDNB) values for TcGST1 and TcGST2 (0.86 µm and 62 s-1; 1.03 µm and 1.97 s-1, respectively) and Km(GSH) and Kcat(GSH) values for TcGST1 and TcGST2 (0.55 µm and 11.61 s-1; 0.3 µm and 32.3 s-1, respectively) were similar to those reported for mammalian and helminth GSTs. Mass spectrometry analysis showed that eight peptides from each of the two parasite transferases were a match for gi|29825896 glutathione transferase (Taenia solium), confirming that both enzymes are GSTs. The relative molecular masses were 54,000 ± 0.9 for the native enzymes and 27,500 ± 0.5 for the enzyme subunits. Thus, TcGST1 and TcGST2 are dimeric proteins. Optimal TcGST1 and TcGST2 activities were observed at pH 8.5 in the range of 20-55°C and pH 7.5 at 35-40°C, respectively. TcGST1 and TcGST2 were inhibited by cibacron blue (CB), bromosulphophthalein (BST), rose bengal (RB), indomethacin and haematin (Hm) with 50% inhibitory concentrations (IC50) in the µm range. TcGST1 was inhibited in a non-competitive manner by all tested inhibitors with the exception of indomethacin, which was uncompetitive. The discovery of these new GSTs facilitates the potential use of T. crassiceps as a model to investigate multifunctional GSTs.

Molecular cloning, identification of GSTs family in sunflower and their regulatory roles in biotic and abiotic stress.

Glutathione-S-transferase (GST) genes exist widely in plants and play major role in metabolic detoxification of exogenous chemical substances and oxidative stress. In this study, 14 sunflower GST genes (HaGSTs) were identified based on the sunflower transcriptome database that we had constructed. Full-length cDNA of 14 HaGTSs were isolated from total RNA by reverse transcription PCR (RT-PCR). Sunflower was received biotic stress (Sclerotinia sclerotiorum) and abiotic stress (NaCl, low-temperature, drought and wound). GST activity was measured by using the universal substrate. The results showed that most of the HaGSTs were up-regulated after NaCl and PEG6000-induced stresses, while a few HaGSTs were up-regulated after S. sclerotiorum, hypothermia and wound-induced stressed, and there was correlation between the changes of GST activity and the expression of HaGSTs, indicating that HaGSTs may play regulatory role in the biotic and abiotic stress responses. 14 HaGSTs from sunflower were identified, and the expression of HaGSTs were tissue-specific and played regulatory roles in both stress and abiotic stress.

Acrolein-detoxifying isozymes of glutathione transferase in plants.

MAIN CONCLUSION: Acrolein is a lipid-derived highly reactive aldehyde, mediating oxidative signal and damage in plants. We found acrolein-scavenging glutathione transferase activity in plants and purified a low K M isozyme from spinach. Various environmental stressors on plants cause the generation of acrolein, a highly toxic aldehyde produced from lipid peroxides, via the promotion of the formation of reactive oxygen species, which oxidize membrane lipids. In mammals, acrolein is scavenged by glutathione transferase (GST; EC 2.5.1.18) isozymes of Alpha, Pi, and Mu classes, but plants lack these GST classes. We detected the acrolein-scavenging GST activity in four species of plants, and purified an isozyme showing this activity from spinach (Spinacia oleracea L.) leaves. The isozyme (GST-Acr), obtained after an affinity chromatography and two ion exchange chromatography steps, showed the K M value for acrolein 93 µM, the smallest value known for acrolein-detoxifying enzymes in plants. Peptide sequence homology search revealed that GST-Acr belongs to the GST Tau, a plant-specific class. The Arabidopsis thaliana GST Tau19, which has the closest sequence similar to spinach GST-Acr, also showed a high catalytic efficiency for acrolein. These results suggest that GST plays as a scavenger for acrolein in plants.

Electrophoretic pattern of glutathione S-transferase (GST) in antibiotic resistance Gram-positive bacteria from poultry litter.

The present study is aimed to assess the role of glutathione S-transferase (GST) in antibiotic resistance among the bacteria isolated from the poultry litter and to identify the effect of GST to reduce the antimicrobial activity of antibiotics. Induction of various antibiotics to Staphylococcus, Streptococcus and Micrococcus sp. isolated from the poultry litter showed that the activity of GST was three to four folds higher than those of control. Analysis of the isozyme pattern of GST revealed that variation in the expression may be due to antibiotic resistance. The results concluded that GST might play an important role in the protection against the toxic effect of the antimicrobial agents which leads bacteria to become resistant to antibiotics.

Production of monoclonal antibodies and development of a quantitative immuno-polymerase chain reaction assay to detect and quantify recombinant Glutathione S-transferase.

GST-tagged proteins are important tools for the production of recombinant proteins. Removal of GST tag from its fusion protein, frequently by harsh chemical treatments or proteolytic methods, is often required. Thus, the monitoring of the proteins in tag-free form requires a significant effort to determine the remnants of GST during purification process. In the present study, we developed both a conventional enzyme-linked immunosorbent assay (ELISA) and an immuno-polymerase chain reaction (IPCR) assay, both specific for detection of recombinant GST (rGST). rGST was expressed in Escherichia coli JM109, using a pGEX4T-3 vector, and several anti-rGST monoclonal antibodies were generated using hybridoma technology. Two of these were rationally selected as capture and detection antibodies, allowing the development of a sandwich ELISA with a limit of detection (LOD) of 0.01 µg/ml. To develop the rGST-IPCR assay, we selected "Universal-IPCR" format, comprising the biotin-avidin binding as the coupling system. In addition, the rGST-IPCR was developed in standard PCR tubes, and the surface adsorption of antibodies on PCR tubes, the optimal neutravidin concentrations, the generation of a reporter DNA and the concentration effect were studied and determined. Under optimized assay conditions, the rGST-IPCR assay provided a 100-fold increase in the LOD as well as an expanded working range, in comparison with rGST-ELISA. The proposed method exhibited great potentiality for application in several fields in which measurement of very low levels of GST is necessary, and might provide a model for other IPCR assays.

Two-step chromatographic purification of glutathione S-transferase-tagged human papillomavirus type 16 E6 protein and its application for serology.

Human papillomavirus (HPV) E6 protein is an oncoprotein with a pivotal role in cervical carcinogenesis. Expression and purification of HPV E6 from Escherichia coli (E. coli) has been difficult because of its strong hydrophobicity even when expressed as a fusion protein with glutathione S-transferase (GST). There has been no protocol suggested for purifying GST-tagged HPV E6 protein with high purity so far. Herein, we provide efficient protocol for purifying GST-HPV16 E6 protein for the first time. In the current study, the GST-tagged protein was expressed in E. coli and a purification method was designed using cation-exchange chromatography followed by GST-affinity chromatography. Using physiological pH buffer during cell lysis and first cation-exchange chromatography significantly reduced yield of full-length GST-HPV16 E6 protein. It was found that using an alkaline buffer during cation-exchange chromatography was needed to obtain full length GST-HPV16 E6 protein. GST-HPV16 E6 protein recovered from the purification using alkaline condition retained its inherent p53-binding ability. Moreover, we were able to detect anti-HPV16 E6 antibodies with high sensitivity in sera from patients with cervical cancer using the GST-HPV16 E6 protein. It was found that the GST-HPV16 E6 protein could be used as a coating agent to enhance the sensitivity of detection of serum anti-HPV16 E6 antibodies when treated with ethylene glycol-bis (ß-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA). These results indicate that the two-step chromatographic purification allows obtaining high purity of GST-HPV16 E6 protein and the GST-HPV16 E6 is suitable to be used as an antigen of serology assay.

Crystal structure of a class-mu glutathione S-transferase from whiteleg shrimp Litopenaeus vannamei: structural changes in the xenobiotic binding H-site may alter the spectra of molecules bound.

Glutathione S-transferases (GSTs) are dimeric proteins that play a key role in phase II cellular detoxification. Here, the first crystal structure of a GST class-mu from marine crustacean shrimp Litopenaeus vannamei is reported at a resolution of 2.0 Å. The coordinates reported here have the lowest sequence identity with previously reported GSTs class-mu deposited at the Protein Data Bank (PDB), although they have subtle conformational differences. One key feature of GST class-mu from L. vannamei is the active site crevice markedly reduced when it is compared with other GSTs class-mu. This finding together with the chemical change of residues into the cavity (F112 and Y210) points to a particular specialization in which smallest xenobiotics with nonstandard chemical characteristics can be bound to the H-site. This suggests that marine organisms have evolved structural strategies to provide efficient selectivity toward xenobiotics to be disposed of by the phase II detoxification process.

A novel glutathione-S transferase immunosensor based on horseradish peroxidase and double-layer gold nanoparticles.

GSTs, a biotransformation enzyme group, can perform metabolism, drug transfer and detoxification functions. Rapid detection of the GSTs with more sensitive approaches is of great importance. In the current study, a novel double-layer gold nanoparticles-electrochemical immunosensor electrode (DGN-EIE) immobilized with Glutathione S-Transferase (GST) antibody derived from Balb/c mice was developed. To increase the fixed quantity of antibodies and electrochemical signal, an electrochemical biosensing signal amplification system was utilized with gold nanoparticles-thionine-chitosan absorbing horseradish peroxidase (HRP). In addition, transmission electron microscope (TEM) was used to characterize the nanogold solution. To evaluate the quality of DGN-EIE, the amperometric I-t curve method was applied to determine the GST in PBS. The results showed that the response current had a good linear correlation with the GST concentration ranged from 0.1-10(4) pg/mL. The lowest detection limit was found at 0.03 pg/mL(S/N = 3). The linear equation was deduced as △I/% = 7.386lgC + 22.36 (R(2) = 0.998). Moreover, it was validated with high sensitivity and reproducibility. Apparently, DGN-EIE may be a very useful tool for monitoring the GST.