Probing the Mechanism of GSH Activation in Schistosoma haematobium Glutathione-S-transferase by Site-directed Mutagenesis and X-ray Crystallography

SINAPs: A Software Tool for Analysis and Visualization of Interaction Networks of Molecular Dynamics Simulations

As long as the structural study of molecular mechanisms requires multiple molecular dynamics reflecting contrasted bioactive states, the subsequent analysis of molecular interaction networks remains a bottleneck to be fairly treated and requires a user-friendly 3D view of key interactions. Structural Interaction Network Analysis Protocols (SINAPs) is a proprietary python tool developed to (i) quickly solve key interactions able to distinguish two protein states, either from two sets of molecular dynamics simulations or from two crystallographic structures, and (ii) render a user-friendly 3D view of these key interactions through a plugin of UCSF Chimera, one of the most popular open-source viewing software for biomolecular systems. Through two case studies, glucose transporter-1 (GLUT-1) and A2A adenosine receptor (A2AR), SINAPs easily pinpointed key interactions observed experimentally and relevant for their bioactivities. This very effective tool was thus applied to identify the amino acids involved in the molecular enzymatic mechanisms ruling the activation of an immunomodulator drug candidate, P28 glutathione-S-transferase (P28GST). SINAPs is freely available at https://github.com/ParImmune/SINAPs.

A comprehensive and critical overview of schistosomiasis vaccine candidates

A digenetic platyhelminth Schistosoma is the causative agent of schistosomiasis, one of the neglected tropical diseases that affect humans and animals in numerous countries in the Middle East, sub-Saharan Africa, South America and China. Several control methods were used for prevention of infection or treatment of acute and chronic disease. Mass drug administration led to reduction in heavy-intensity infections and morbidity, but failed to decrease schistosomiasis prevalence and eliminate transmission, indicating the need to develop anti-schistosome vaccine to prevent infection and parasite transmission. This review summarizes the efficacy and protective capacity of available schistosomiasis vaccine candidates with some insights and future prospects.

Chromatographic and computational studies of ligands associated with bilharziasis

OBJECTIVE

Rapid diagnostic techniques that do not depend on microscopic analysis are urgently needed for rapid diagnosis and management of bilharziasis. Specific ligands that are excreted through urine in bilharziasis may serve as rapid diagnostic biomarkers to replace microscopy, which is cumbersome and time-consuming. The aim of this study was to identify ligands associated with bilharziasis.

METHODS

Microscopy was employed to detect ova of Schistosoma haematobium in urine specimens obtained from 1032 subjects. Pooled positive urine samples and pooled normal urine samples were separately prepared in triplicates and analyzed by gas chromatography-mass spectrophotometry (GC-MS). Ligands identified in each pool were noted. Computational analysis was performed between the schistosome receptors and ligands.

RESULTS

GC-MS revealed that the level of indole in bilharziasis sample was higher than that in normal urine. Indole was the ligand with the highest (28.63%) concentration in the pooled positive urine sample, while ethyl phenazone level was the highest (69.64%) in the pooled normal sample. Computational analysis depicted perfect docking with indole and all other ligands identified in positive urine samples.

CONCLUSION

This study identified some ligands associated with bilharziasis some unique to normal (negative) urine samples.

X-ray structure of Fasciola hepatica Sigma class glutathione transferase 1 reveals a disulfide bond to support stability in gastro-intestinal environment

Sigma class GST (Prostaglandin D synthase), FhGST-S1, is present in the excretory–secretory products (ES) of the liver fluke parasite Fasciola hepatica as cargo of extracellular vesicles (EVs) released by the parasite. FhGST-S1 has a well characterised role in the modulation of the immune response; a key fluke intercession that allows for establishment and development within their hosts. We have resolved the three-dimensional structure of FhGST-S1 in complex with its co-factor glutathione, in complex with a glutathione-cysteine adduct, and in a glutathione disulfide complex in order to initiate a research pipeline to mechanistically understand how FhGST-S1 functions within the host environment and to rationally design selective inhibitors. The overall fold of FhGST-S1 shows high structural similarity to other Sigma class GSTs. However, a unique interdomain disulfide bond was found in the FhGST-S1 which could stabilise the structure within the host gastro-intestinal environment. The position of the two domains of the protein with respect to each other is seen to be crucial in the formation of the active site cleft of the enzyme. The interdomain disulfide bond raises the possibility of oxidative regulation of the active site of this GST protein.

Evaluation of glutathione S-transferase T1 deletion polymorphism on type 2 diabetes mellitus risk in Zoroastrian females in Yazd, Iran

BACKGROUND

There has been much interest in the role of free radicals and oxidative stress in the pathogenesis of diabetes mellitus (DM). The aim of this study was to assess the possible association between genetic polymorphisms of the glutathione S-transferase-Theta (GSTT1) and the risk of the development of DM in Zoroastrian females in Yazd, Iran.

MATERIALS AND METHODS

This was a case-control study in which GSTT1 polymorphism was genotyped in 51 randomly selected DM patients and 50 randomly selected healthy controls among Zoroastrian females whose ages ranged from 40 to 70.

RESULTS

The frequencies of GSTT1 null genotype and GSTT1 present were 72% and 28%, respectively, in control samples, while in patients with type 2 diabetes (T2DM), the frequencies of GSTT1 null genotype and GSTT1 present were 27.5% and 72.5%, respectively. There were higher levels of triglyceride (TG), fasting blood sugar (FBS), total cholesterol (TC), low-density lipoprotein (LDL), Urea, and high-density lipoprotein (HDL) in cases of GSTT1 null genotype compared to the GSTT1 present genotype in controls.

CONCLUSIONS

Our results indicated that healthy subjects had a higher frequency of the GSTT1 null genotype than patients with T2DM. However, we observed no significant association between the GSTT1 null genotype and T2DM in the current study.

The crystal structure of archaeal serine hydroxymethyltransferase reveals idiosyncratic features likely required to withstand high temperatures

Serine hydroxymethyltransferases (SHMTs) play an essential role in one-carbon unit metabolism and are used in biomimetic reactions. We determined the crystal structure of free (apo) and pyridoxal-5'-phosphate-bound (holo) SHMT from Methanocaldococcus jannaschii, the first from a hyperthermophile, from the archaea domain of life and that uses H₄MPT as a cofactor, at 2.83 and 3.0 Å resolution, respectively. Idiosyncratic features were observed that are likely to contribute to structure stabilization. At the dimer interface, the C-terminal region folds in a unique fashion with respect to SHMTs from eubacteria and eukarya. At the active site, the conserved tyrosine does not make a cation-π interaction with an arginine like that observed in all other SHMT structures, but establishes an amide-aromatic interaction with Asn257, at a different sequence position. This asparagine residue is conserved and occurs almost exclusively in (hyper)thermophile SHMTs. This led us to formulate the hypothesis that removal of frustrated interactions (such as the Arg-Tyr cation-π interaction occurring in mesophile SHMTs) is an additional strategy of adaptation to high temperature. Both peculiar features may be tested by designing enzyme variants potentially endowed with improved stability for applications in biomimetic processes.

Evaluation of Glutathione S-transferase T1 (GSTT1) deletion polymorphism on type 2 diabetes mellitus risk in a sample of Yazdian females in Yazd, Iran

Background:

There has been much interest in the role of free radicals and oxidative stress in the pathogenesis of diabetes mellitus (DM). The aim of this study was to assess the possible association between genetic polymorphisms of the glutathione S-transferase-mu (GSTT1) and the risk of the development of DM in a sample of Yazdian females in Yazd, Iran.

Methods:

This was a case-control study in which GSTT1 polymorphism was genotyped in 51 randomly selected DM patients and 50 randomly selected healthy controls among Yazdian females whose ages ranged from 40 to 70.

Results:

The frequencies of GSTT1 null genotype and GSTT1 present were 8 and 92%, respectively, in the control samples. In patients with type 2 diabetes (T2DM), the frequencies of GSTT1 null genotype and GSTT1 present were 14 and 86%, respectively. There were higher levels of triglycerides (TG), fasting blood sugar (FBS), total cholesterol (TC), low density lipoprotein (LDL), body mass index (BMI), and high density lipoprotein (HDL) in patients with GSTT1 null genotype than in patients with the GSTT1 present genotype.

Conclusions:

Our results indicated that the GSTT1 deletion polymorphism is a risk factor for T2DM. We did not determine any significant association between the GSTT1 null genotype and T2DM.

Cytokine responses to the anti-schistosome vaccine candidate antigen glutathione-S-transferase vary with host age and are boosted by praziquantel treatment

Background

Improved helminth control is required to alleviate the global burden of schistosomiasis and schistosome-associated pathologies. Current control efforts rely on the anti-helminthic drug praziquantel (PZQ), which enhances immune responses to crude schistosome antigens but does not prevent re-infection. An anti-schistosome vaccine based on Schistosoma haematobium glutathione-S-transferase (GST) is currently in Phase III clinical trials, but little is known about the immune responses directed against this antigen in humans naturally exposed to schistosomes or how these responses change following PZQ treatment.

Methodology

Blood samples from inhabitants of a Schistosoma haematobium-endemic area were incubated for 48 hours with or without GST before (n = 195) and six weeks after PZQ treatment (n = 107). Concentrations of cytokines associated with innate inflammatory (TNFα, IL-6, IL-8), type 1 (Th1; IFNγ, IL-2, IL-12p70), type 2 (IL-4, IL-5, IL-13), type 17 (IL-17A, IL-21, IL-23p19) and regulatory (IL-10) responses were quantified in culture supernatants via enzyme-linked immunosorbent assay (ELISA). Factor analysis and multidimensional scaling were used to analyse multiple cytokines simultaneously.

Principal Findings

A combination of GST-specific type 2 (IL-5 and IL-13) and regulatory (IL-10) cytokines was significantly lower in 10–12 year olds, the age group at which S. haematobium infection intensity and prevalence peak, than in 4–9 or 13+ year olds. Following PZQ treatment there was an increase in the number of participants producing detectable levels of GST-specific cytokines (TNFα, IL-6, IL-8, IFNγ, IL-12p70, IL-13 and IL-23p19) and also a shift in the GST-specific cytokine response towards a more pro-inflammatory phenotype than that observed before treatment. Participant age and pre-treatment infection status significantly influenced post-treatment cytokine profiles.

Conclusions/Significance

In areas where schistosomiasis is endemic host age, schistosome infection status and PZQ treatment affect the cellular cytokine response to GST. Thus the efficacy of a GST-based vaccine may also be shaped by the demographic and epidemiological characteristics of targeted populations.

Schistosomiasis is caused by infection with Schistosoma spp. parasites, for which the main treatment is the drug praziquantel (PZQ). Since PZQ does not prevent reinfection, an anti-schistosome vaccine based on the Schistosoma haematobium enzyme glutathione-S-transferase (GST) is being developed. In this study we investigated the GST-specific immune responses of people naturally exposed to schistosomes and the affect that PZQ has on these responses. We cultured blood samples from a schistosome-exposed community with GST before and six weeks after PZQ treatment and measured a range of soluble proteins (cytokines) in culture supernatants as indicators of blood cell activation and phenotype. Before treatment, GST-specific cytokine responses varied with host age, particularly in children with high intensity schistosome infections. Following treatment, GST activated blood samples from more individuals to produce a broader range of cytokines and the combination of GST-specific cytokine responses reflected a more pro-inflammatory immune phenotype than that observed pre-treatment. Post-treatment responses varied according to host age and pre-treatment infection status. Taken together, our study suggests that current and future GST-based vaccine trials should take host age, schistosome infection status and PZQ treatment history into account since these factors influence GST-specific immune activation.

Null genotypes of GSTM1 and GSTT1 contribute to increased risk of diabetes mellitus: a meta-analysis

Diabetes mellitus (DM) is a common disease which results from various causes including genetic and environmental factors. Glutathione S-Transferase M1 (GSTM1) and Glutathione S-Transferase T1 (GSTT1) genes are polymorphic in human and the null genotypes lead to the absence of enzyme function. Many studies assessed the associations between GSTM1/GSTT1 null genotypes and DM risk but reported conflicting results. In order to get a more precise estimate of the associations of GSTM1/GSTT1 null genotypes with DM risk, we performed this meta-analysis. Published literature from PubMed, Embase and China Biology Medicine (CBM) databases was searched for eligible studies. Pooled odds ratios (OR) and corresponding 95% confidence intervals (95%CI) were calculated using a fixed- or random-effects model. 11 publications (a total of 2577 cases and 4572 controls) were finally included into this meta-analysis. Meta-analyses indicated that null genotypes of GSTM1/GSTT1 and dual null genotype of GSTM1-GSTT1 were all associated with increased risk of DM (GSTM1: OR random-effects=1.60, 95%CI 1.10-2.34, POR=0.014; GSTT1: OR random-effects=1.47, 95%CI 1.12-1.92, POR=0.005; GSTM1-GSTT1: OR fixed-effects=1.83, 95%CI 1.30-2.59, POR=0.001). Subgroup by ethnicity suggested significant associations between null genotypes of GSTM1 and GSTT1 and DM risk among Asians (GSTM1: OR random-effects=1.77, 95%CI 1.24-2.53, POR=0.002; GSTT1: OR random-effects=1.58, 95%CI 1.09-2.27, POR=0.015). This meta-analysis suggests null genotypes of GSTM1/GSTT1 and dual null genotype of GSTM1-GSTT1 are all associated with increased risk of DM, and null genotypes of GSTM1/GSTT1 and dual null genotype of GSTM1-GSTT1 are potential biomarkers of DM.

Structure-based mechanism for early PLP-mediated steps of rabbit cytosolic serine hydroxymethyltransferase reaction

Serine hydroxymethyltransferase catalyzes the reversible interconversion of L-serine and glycine with transfer of one-carbon groups to and from tetrahydrofolate. Active site residue Thr254 is known to be involved in the transaldimination reaction, a crucial step in the catalytic mechanism of all pyridoxal 5'-phosphate- (PLP-) dependent enzymes, which determines binding of substrates and release of products. In order to better understand the role of Thr254, we have expressed, characterized, and determined the crystal structures of rabbit cytosolic serine hydroxymethyltransferase T254A and T254C mutant forms, in the absence and presence of substrates. These mutants accumulate a kinetically stable gem-diamine intermediate, and their crystal structures show differences in the active site with respect to wild type. The kinetic and crystallographic data acquired with mutant enzymes permit us to infer that conversion of gem-diamine to external aldimine is significantly slowed because intermediates are trapped into an anomalous position by a misorientation of the PLP ring, and a new energy barrier hampers the transaldimination reaction. This barrier likely arises from the loss of the stabilizing hydrogen bond between the hydroxymethyl group of Thr254 and the ε -amino group of active site Lys257, which stabilizes the external aldimine intermediate in wild type SHMTs.

Role of a conserved active site cation-pi interaction in Escherichia coli serine hydroxymethyltransferase

Serine hydroxymethyltransferase is a pyridoxal 5'-phosphate-dependent enzyme that catalyzes the interconversion of serine and glycine using tetrahydropteroylglutamate as the one-carbon carrier. In all pyridoxal phosphate-dependent enzymes, amino acid substrates are bound and released through a transaldimination process, in which an internal aldimine and an external aldimine are interconverted via gem-diamine intermediates. Bioinformatic analyses of serine hydroxymethyltransferase sequences and structures showed the presence of two highly conserved residues, a tyrosine and an arginine, engaged in a cation-pi interaction. In Escherichia coli serine hydroxymethyltranferase, the hydroxyl group of this conserved tyrosine (Tyr55) is located in a position compatible with a role as hydrogen exchanger in the transaldimination reaction. Because of the location of Tyr55 at the active site, the enhancement of its acidic properties caused by the cation-pi interaction with Arg235, and the hydrogen bonds established by its hydroxyl group, a role of this residue as acid-base catalyst in the transaldimination process was envisaged. The role played by this cation-pi interaction in the E. coli serine hydroxymethyltransferase was investigated by crystallography and site-directed mutagenesis using Y55F and three R235 mutant forms. The crystal structure of the Y55F mutant suggests that the presence of Tyr55 is indispensable for a correct positioning of the cofactor and for the maintenance of the structure of several loops involved in substrate and cofactor binding. The kinetic properties of all mutant enzymes are profoundly altered. Substrate binding and rapid kinetic experiments showed that both Y55 and R235 are required for a correct progress of the transaldimination reaction.

Molecular cloning and characterization of a glutathione S-transferase gene fromGinkgo biloba

Glutathione S-transferases (GSTs) play an important role in the response of plants to changing environmental conditions. Here, we report the cloning of the GST gene for GST from Ginkgo biloba, a native medicinal plant species in China, by rapid amplification of cDNA ends (RACE). The full-length cDNA (designated as GbGST) was 1008 bp and contained a 684 bp open reading frame (ORF) encoding a polypeptide of 228 amino acids. The genomic sequence of GbGST was also obtained. Semi-quantitative RT-PCR analysis revealed that GbGST expressed in all tested tissues of G. biloba, including leaf, root and stem and the expression of GbGST could be induced by UV, MJ and drought treatments, suggesting that GbGST was potentially involved in plant's stress tolerance. To our knowledge, this is the first GST cDNA cloned from Ginkgoaceae. Based on comparative analyses of amino acid sequence, phylogeny, predicted three-dimensional structure together with the gene structure, the GbGST should be classified into the tau class.

Glutathione transferases from parasites: a biochemical view

The glutathione transferase (GST) system of parasites represents the main detoxification mechanism of hydrophobic and electrophilic compounds. Parasites lack the CYP450 activity, hence part of its function has been taken over by other enzymes including GSTs. Cytosolic GSTs (cGSTs) are found in this system and constitute a versatile and numerous group that in parasites display many peculiarities in contrast to mammalian cGSTs. This review summarizes aspects of the biochemistry of parasite cGSTs such as substrate specificities, inhibitor sensitivities, classification, kinetics and catalysis, as well as some aspects of their protective role.