Aim: Glutathione transferase P1-1 (GST P1-1) plays a crucial role in the human phase II detoxication system and is implicated in drug resistance in certain cancer cells. Analogs of drugs used in Hormone Replacement Therapy (HRT) have been reported to exhibit inhibition of various GSTs. This study aims to investigate the inhibitory potential of several HRT drugs on GST P1-1 for the possible use of counteracting drug resistance and for other therapeutic purposes. Materials and Methods: GST P1-1 was expressed and then purified in a single step using Nickel Sepharose affinity chromatography. Synthetic drugs that are used in HRT were screened for inhibition of GST P1-1 using 1-chloro-2,4-dinitrobenzene as the substrate. The IC50 value of the most potent compound was calculated and binding location and formation of bonds to GST P1-1 were identified through docking analysis. Results: Screening the inhibitory effect of eight synthetic estrogenic drugs reveals that estradiol valerate is the most potent inhibitor, showing 72 ± 4% inhibition of GST P1-1. This effect is followed by estradiol cypionate 53 ± 5%, mestranol 39 ± 4%, and estradiol propionate 35 ± 2%. The most potent compound estradiol valerate has an IC50 value of 30 ± 2 μM. According to docking analysis, it binds to the H-site of the enzyme where the residues Phe9, Arg14, Val36, Trp39, Ile105, Tyr109, Pro203, Asn207, and Gln210 were within 5 Å proximity of the ligand. Estradiol valerate forms Pi-alkyl interactions with Phe9 and Val36, as well as an alkyl interaction with Ile104. Conclusion: Estradiol valerate is a modest inhibitor for hGST P1-1, however it fits in the area of H-site of the enzyme and forms bonds with critical key residues. Understanding its binding site on the enzyme is critical for designing other inhibitors targeting GSTs or possibility for the potential use as a substrate with other GSTs.

Glutathione is an important antioxidant that plays a crucial role in the cellular protection against oxidative stress and detoxification of electrophilic mutagens, and carcinogens. Glutathione transferases are enzymes catalyzing glutathione-dependent reactions that lead to inactivation and conjugation of toxic compounds, processes followed by subsequent excretion of the detoxified products. Degeneration and loss of neuromelanin-containing dopaminergic neurons in the nigrostriatal neurons generally involves oxidative stress, neuroinflammation, alpha-synuclein aggregation to neurotoxic oligomers, mitochondrial dysfunction, protein degradation dysfunction, and endoplasmic reticulum stress. However, it is still unclear what triggers these neurodegenerative processes. It has been reported that aminochrome may elicit all of these mechanisms and, interestingly, aminochrome is formed inside neuromelanin-containing dopaminergic neurons during neuromelanin synthesis. Aminochrome is a neurotoxic ortho-quinone formed in neuromelanin synthesis. However, it seems paradoxical that the neurotoxin aminochrome is generated during neuromelanin synthesis, even though healthy seniors have these neurons intact when they die. The explanation of this paradox is the existence of protective tools against aminochrome neurotoxicity composed of the enzymes DT-diaphorase, expressed in these neurons, and glutathione transferase M2-2, expressed in astrocytes. Recently, it has been reported that dopaminergic neurons can be protected by glutathione transferase M2-2 from astrocytes, which secrete exosomes containing the protective enzyme.

Recently, the glutathione transferase A3-3 (GST A3-3) enzyme was identified as the most efficient enzyme that catalyzes isomerization of the precursors of testosterone, estradiol, and progesterone ...

Equine glutathione transferase A3-3 (EcaGST A3-3) belongs to the superfamily of detoxifying enzymes found in all organisms. However it is also the most efficient steroid double-bond isomerase known ...

Inhibitory effects of ethacrynic acid on glutathione S-transferase A1-1 from Callithrix jacchus

The previously uncharacterized Drosophila melanogaster Epsilon-class glutathione transferases E6 and E7 were immobilized on nanoporous alumina. The nanoporous anodized alumina membranes were derivatized with 3-aminopropyl-triethoxysilane, and the amino groups were activated with carbonyldiimidazole to allow coupling of the enzymes via ε-amino groups. Kinetic analyses of the immobilized enzymes were carried out in a circulating flow system using CDNB (1-chloro-2,4-dinitrobenzene) as substrate, followed by specificity screening with alternative substrates. A good correlation was observed between the substrate screening data for immobilized enzyme and corresponding data for the enzyme in solution. A limited kinetic study was also carried out on immobilized human GST S1-1 (also known as hematopoietic prostaglandin D synthase). The stability of the immobilized enzymes was virtually identical to that of enzymes in solution, and no leakage of enzyme from the matrix could be observed.

The prodrug azathioprine is primarily used for maintaining remission in inflammatory bowel disease, but approximately 30% of the patients suffer adverse side effects. The prodrug is activated by glutathione conjugation and release of 6-mercaptopurine, a reaction most efficiently catalyzed by glutathione transferase (GST) A2-2. Among five genotypes of GST A2-2, the variant A2* E has threefold-fourfold higher catalytic efficiency with azathioprine, suggesting that the expression of A2*E could boost 6-mercaptopurine release and adverse side effects in treated patients.Structure-activity studies of the GST A2-2 variants and homologous alpha class GSTs were made to delineate the determinants of high catalytic efficiency compared to other alpha class GSTs. Engineered chimeras identified GST peptide segments of importance, and replacing the corresponding regions in low-activity GSTs by these short segments produced chimeras with higher azathioprine activity. By contrast, H-site mutagenesis led to decreased azathioprine activity when active-site positions 208 and 213 in these favored segments were mutagenized. Alternative substitutions indicated that hydrophobic residues were favored.A pertinent question is whether variant A2* E represents the highest azathioprine activity achievable within the GST structural framework. This issue was addressed by mutagenesis of H-site residues assumed to interact with the substrate based on molecular modeling. The mutants with notably enhanced activities had small or polar residues in the mutated positions. The most active mutant L107G/L108D/F222H displayed a 70-fold enhanced catalytic efficiency with azathioprine. The determination of its structure by X-ray crystallography showed an expanded H-site, suggesting improved accommodation of the transition state for catalysis.

Organic isothiocyanates (ITCs) are allelochemicals produced by plants in order to combat insects and other herbivores. The compounds are toxic electrophiles that can be inactivated and conjugated w ...

Glutathione transferases (GSTs) are important enzymes in the metabolism of electrophilic xenobiotic and endobiotic toxic compounds. In addition, human GST A3-3 also catalyzes the double bond isomerization of Δ5-androstene-3,17-dione (Δ(5)-AD) and Δ(5)-pregnene-3,20-dione (Δ(5)-PD), which are the immediate precursors of testosterone and progesterone. In fact, GST A3-3 is the most efficient human enzyme known to exist in the catalysis of these reactions. In this work, we have used density functional theory (DFT) calculations to propose a refined mechanism for the isomerization of Δ(5)-AD catalyzed by GST A3-3. In this mechanism the glutathione (GSH) thiol and Tyr9 catalyze the proton transfer from the Δ(5)-AD C4 atom to the Δ(5)-AD C6 atom, with a rate limiting activation energy of 15.8 kcal · mol(-1). GSH has a dual function, because it is also responsible for stabilizing the negative charge that is formed in the O3 atom of the enolate intermediate. The catalytic role of Tyr9 depends on significant conformational rearrangements of its side chain. Neither of these contributions to catalysis has been observed before. Residues Phe10, Leu111, Ala 208, and Ala 216 complete the list of the important catalytic residues. The mechanism detailed here is based on the GST A3-3:GSH:Δ(4)-AD crystal structure and is consistent with all available experimental data.

We have synthesized a series of 4-substituted-2-nitrobenzene-sulfonyl compounds for caged fluorogenic probes and conducted a Hammett plot analysis using the steady-state kinetic parameters. The results revealed that the glutathione transferase (GST) alpha catalyzed reaction was dependent on the σ value in the same way as the non-enzymatic reaction, whereas the dependence of the σ value of the GST mu and pi was not as pronounced as that of GST alpha.

Lecture 1: Glutathione transferases, detoxication, cancer and longevity Glutathione transferases (GSTs) were discovered 50 years ago as enzymes capable of conjugating electrophilic organic substances with the thiol group of glutathione. Early on GSTs were identified as prominent detoxication enzymes that protect cells against mutagens and carcinogens. Our research established that products of lipid peroxidation and other oxidative processes are natural substrates of the enzymes. In humans GST...

Lecture 1: Glutathione transferases, detoxication, cancer and longevity Glutathione transferases (GSTs) were discovered 50 years ago as enzymes capable of conjugating electrophilic organic substances with the thiol group of glutathione. Early on GSTs were identified as prominent detoxication enzymes that protect cells against mutagens and carcinogens. Our research established that products of lipid peroxidation and other oxidative processes are natural substrates of the enzymes. In humans GST...

Canfosfamide (TLK286, TELCYTA) is a prodrug that upon activation by glutathione transferase P1-1 (GST P1-1) yields an anticancer alkylating agent and a glutathione derivative. The rationale underlying the use of TLK286 in chemotherapy is that tumor cells overexpressing GST P1-1 will be locally exposed to the released alkylating agent with limited collateral toxicity to the surrounding normal tissues. TLK286 has demonstrated clinical effects in phase II and III clinical trials for the treatment of malignancies, such as ovarian cancer, nonsmall cell lung cancer, and breast cancer, as a single agent and in combination with other chemotherapeutic agents. In spite of these promising results, the detailed mechanism of GST P1-1 activation of the prodrug has not been elucidated. Here, we propose a mechanism for the TLK286 activation by GST P1-1 on the basis of density functional theory (DFT) and on potential of mean force (PMF) calculations. A catalytic water molecule is instrumental to the activation by forming a network of intermolecular interactions between the active-site Tyr7 hydroxyl and the sulfone and COO(-) groups of TLK286. The results obtained are consistent with the available experimental kinetic data and provide an atomistic understanding of the TLK286 activation mechanism.

Background: Microbial multidrug resistance is a major global problem. Results: Evolution of enhanced β-lactamase activity in engineered metalloenzyme mutants was demonstrated with seven different β-lactam antibiotics and cross-resistance to alternative antibiotics was observed. Conclusion: Resistance against a single antibiotic can develop with collateral resistance to additional drugs. Significance: Cataloging the substrate specificity of enzyme variants could lead to a more tailored use of antibiotics in clinical settings. The extensive use and misuse of antibiotics during the last seven decades has led to the evolution and global spread of a variety of resistance mechanisms in bacteria. Of high medical importance are β-lactamases, a group of enzymes inactivating β-lactam antibiotics. Metallo-β-lactamases (MBLs) are particularly problematic because of their ability to act on virtually all classes of β-lactam antibiotics. An engineered MBL (evMBL9) characterized by low level activity with several β-lactam antibiotics was constructed and employed as a parental MBL in an experiment to examine how an enzyme can evolve toward increased activity with a variety of β-lactam antibiotics. We designed and synthesized a mutant library in which the substrate activity profile was varied by randomizing six active site amino acid residues. The library was expressed in Salmonella typhimurium, clones with increased resistance against seven different β-lactam antibiotics (penicillin G, ampicillin, cephalothin, cefaclor, cefuroxime, cefoperazone, and cefotaxime) were isolated, and the MBL variants were characterized. For the majority of the mutants, bacterial resistance was significantly increased despite marked reductions in both mRNA and protein levels relative to those of parental evMBL9, indicating that the catalytic activities of these mutant MBLs were highly increased. Multivariate analysis showed that the majority of the mutant enzymes were generalists, conferring increased resistance against most of the examined β-lactams.