Fused Enzyme Glucose-6-Phosphate Dehydrogenase::6-Phosphogluconolactonase (G6PD::6PGL) as a Potential Drug Target in Giardia lamblia, Trichomonas vaginalis, and Plasmodium falciparum.

Several microaerophilic parasites such as Giardia lamblia, Trichomonas vaginalis, and Plasmodium falciparum are major disease-causing organisms and are responsible for spreading infections worldwide. Despite significant progress made in understanding the metabolism and molecular biology of microaerophilic parasites, chemotherapeutic treatment to control it has seen limited progress. A current proposed strategy for drug discovery against parasitic diseases is the identification of essential key enzymes of metabolic pathways associated with the parasite's survival. In these organisms, glucose-6-phosphate dehydrogenase::6-phosphogluconolactonase (G6PD:: 6PGL), the first enzyme of the pentose phosphate pathway (PPP), is essential for its metabolism. Since G6PD:: 6PGL provides substrates for nucleotides synthesis and NADPH as a source of reducing equivalents, it could be considered an anti-parasite drug target. This review analyzes the anaerobic energy metabolism of G. lamblia, T. vaginalis, and P. falciparum, with a focus on glucose metabolism through the pentose phosphate pathway and the significance of the fused G6PD:: 6PGL enzyme as a therapeutic target in the search for new drugs.

An Overall View of the Functional and Structural Characterization of Glucose-6-Phosphate Dehydrogenase Variants in the Mexican Population.

Glucose-6-phosphate dehydrogenase (G6PD) deficiency, affecting an estimated 500 million people worldwide, is a genetic disorder that causes human enzymopathies. Biochemical and genetic studies have identified several variants that produce different ranges of phenotypes; thus, depending on its severity, this enzymopathy is classified from the mildest (Class IV) to the most severe (Class I). Therefore, understanding the correlation between the mutation sites of G6PD and the resulting phenotype greatly enhances the current knowledge of enzymopathies' phenotypic and genotypic heterogeneity, which will assist both clinical diagnoses and personalized treatments for patients with G6PD deficiency. In this review, we analyzed and compared the structural and functional data from 21 characterized G6PD variants found in the Mexican population that we previously characterized. In order to contribute to the knowledge regarding the function and structure of the variants associated with G6PD deficiency, this review aimed to determine the molecular basis of G6PD and identify how these mutations could impact the structure, stability, and function of the enzyme and its relation with the clinical manifestations of this disease.

Nitazoxanide Inhibits the Bifunctional Enzyme GlG6PD::6PGL of Giardia lamblia: Biochemical and In Silico Characterization of a New Druggable Target.

Giardiasis, which is caused by Giardia lamblia infection, is a relevant cause of morbidity and mortality worldwide. Because no vaccines are currently available to treat giardiasis, chemotherapeutic drugs are the main options for controlling infection. Evidence has shown that the nitro drug nitazoxanide (NTZ) is a commonly prescribed treatment for giardiasis; however, the mechanisms underlying NTZ's antigiardial activity are not well-understood. Herein, we identified the glucose-6-phosphate::6-phosphogluconate dehydrogenase (GlG6PD::6PGL) fused enzyme as a nitazoxanide target, as NTZ behaves as a GlG6PD::6PGL catalytic inhibitor. Furthermore, fluorescence assays suggest alterations in the stability of GlG6PD::6PGL protein, whereas the results indicate a loss of catalytic activity due to conformational and folding changes. Molecular docking and dynamic simulation studies suggest a model of NTZ binding on the active site of the G6PD domain and near the structural NADP+ binding site. The findings of this study provide a novel mechanistic basis and strategy for the antigiardial activity of the NTZ drug.

Pyridyl Methylsulfinyl Benzimidazole Derivatives as Promising Agents against Giardia lamblia and Trichomonas vaginalis.

Protozoan parasites, such as Giardia lamblia and Trichomonas vaginalis, cause the most prevalent infections in humans in developing countries and provoke significant morbidity and mortality in endemic countries. Despite its side-effects, metronidazole is still the drug of choice as a giardiacidal and trichomonacidal tissue-active agent. However, the emergence of metronidazole resistance and its evolved strategies of parasites to evade innate host defenses have hindered the identification and development of new therapeutic strategies against these parasites. Here, we tested five synthesized benzimidazole derivatives as possible drugs for treating giardiasis and trichomoniasis, probing the bifunctional enzyme glucose 6-phosphate dehydrogenase::6-phosphogluconolactone from G. lamblia (GlG6PD::6PGL) and T. vaginalis (TvG6PD::6PGL) as a drug target. The investigated benzimidazole derivatives were H-B2M1, H-B2M2, H2N-BZM6, O2N-BZM7, and O2N-BZM9. The recombinant enzymes were used in inhibition assays, and in silico computational predictions and spectroscopic studies were applied to follow the structural alteration of the enzymes and identify the possible mechanism of inhibition. We identified two potent benzimidazole compounds (O2N-BZM7 and O2N-BZM9), which are capable of inhibiting both protozoan G6PD::6PGL enzymes and in vitro assays with these parasites, showing that these compounds also affect their viability. These results demonstrate that other therapeutic targets of the compounds are the enzymes GlG6PD::6PGL and TvG6PD::6PGL, which contribute to their antiparasitic effect and their possible use in antigiardial and trichomonacidal therapies.

Giardia lamblia G6PD::6PGL Fused Protein Inhibitors Decrease Trophozoite Viability: A New Alternative against Giardiasis.

Treatments to combat giardiasis have been reported to have several drawbacks, partly due to the drug resistance and toxicity of current antiparasitic agents. These constraints have prompted many researchers to investigate new drugs that act against protozoan parasites. Enzyme inhibition is an important means of regulating pathogen metabolism and has recently been identified as a significant alternative target in the search for new treatments. Glucose-6-phosphate dehydrogenase and 6-phosphogluconolactonase (G6PD::6PGL) is a bifunctional enzyme involved in the pentose phosphate pathway (PPP) in Giardia lamblia (G. lamblia). The G. lamblia enzyme is unusual since, unlike the human enzyme, it is a fused enzyme. Here, we show, through inhibition assays, that an in-house chemical library of 120 compounds and four target compounds, named CNZ-7, CNZ-8, CMC-1, and FLP-2, are potent inhibitors of the G. lamblia G6PD::6PGL fused enzyme. With a constant (k2) of 2.3, 3.2, and 2.8 M−1 s−1, respectively, they provoke alterations in the secondary and tertiary protein structure and global stability. As a novel approach, target compounds show antigiardial activity, with IC50 values of 8.7, 15.2, 15.3, and 24.1 µM in trophozoites from G. lamblia. Moreover, these compounds show selectivity against G. lamblia, since, through counter-screening in Caco-2 and HT29 human cells, they were found to have low toxicity. This finding positions these compounds as a potential and attractive starting point for new antigiardial drugs.

Biochemical and Kinetic Characterization of the Glucose-6-Phosphate Dehydrogenase from Helicobacter pylori Strain 29CaP.

Helicobacter pylori (H. pylori) has been proposed as the foremost risk factor for the development of gastric cancer. We found that H. pylori express the enzyme glucose-6-phosphate dehydrogenase (HpG6PD), which participates in glucose metabolism via the pentose phosphate pathway. Thus, we hypothesized that if the biochemical and physicochemical characteristics of HpG6PD contrast with the host G6PD (human G6PD, HsG6PD), HpG6PD becomes a potential target for novel drugs against H. pylori. In this work, we characterized the biochemical properties of the HpG6PD from the H.pylori strain 29CaP and expressed the active recombinant protein, to analyze its steady-state kinetics, thermostability, and biophysical aspects. In addition, we analyzed the HpG6PD in silico structural properties to compare them with those of the HsG6PD. The optimal pH for enzyme activity was 7.5, with a T1/2 of 46.6 °C, at an optimum stability temperature of 37 °C. The apparent Km values calculated for G6P and NADP+ were 75.0 and 12.8 µM, respectively. G6P does not protect HpG6PD from trypsin digestion, but NADP+ does protect the enzyme from trypsin and guanidine hydrochloride (Gdn-HCl). The biochemical characterization of HpG6PD contributes to knowledge regarding H. pylori metabolism and opens up the possibility of using this enzyme as a potential target for specific and efficient treatment against this pathogen; structural alignment indicates that the three-dimensional (3D) homodimer model of the G6PD protein from H. pylori is different from the 3D G6PD of Homo sapiens.

Kinetic and Molecular Docking Studies to Determine the Effect of Inhibitors on the Activity and Structure of Fused G6PD::6PGL Protein from Trichomonas vaginalis.

Trichomoniasis is a sexually transmitted disease with a high incidence worldwide, affecting 270 million people. Despite the existence of a catalog of available drugs to combat this infection, their extensive use promotes the appearance of resistant Trichomonas vaginalis (T. vaginalis), and some side effects in treated people, which are reasons why it is necessary to find new alternatives to combat this infection. In this study, we investigated the impact of an in-house library comprising 55 compounds on the activity of the fused T. vaginalis G6PD::6PGL (TvG6PD::6PGL) protein, a protein mediating the first reaction step of the pentose phosphate pathway (PPP), a crucial pathway involved in the parasite's energy production. We found four compounds: JMM-3, CNZ-3, CNZ-17, and MCC-7, which inhibited the TvG6PD::6PGL protein by more than 50%. Furthermore, we determined the IC50, the inactivation constants, and the type of inhibition. Our results showed that these inhibitors induced catalytic function loss of the TvG6PD::6PGL enzyme by altering its secondary and tertiary structures. Finally, molecular docking was performed for the best inhibitors, JMM-3 and MCC-7. All our findings demonstrate the potential role of these selected hit compounds as TvG6PD::6PGL enzyme selective inhibitors.

Validation and Selection of New Reference Genes for RT-qPCR Analysis in Pediatric Glioma of Different Grades.

Gliomas are heterogeneous, solid, and intracranial tumors that originate from glial cells. Malignant cells from the tumor undergo metabolic alterations to obtain the energy required for proliferation and the invasion of the cerebral parenchyma. The alterations in the expression of the genes related to the metabolic pathways can be detected in biopsies of gliomas of different CNS WHO grades. In this study, we evaluated the expression of 16 candidate reference genes in the HMC3 microglia cell line. Then, statistical algorithms such as BestKeeper, the comparative ΔCT method, geNorm, NormFinder, and RefFinder were applied to obtain the genes most suitable to be considered as references for measuring the levels of expression in glioma samples. The results show that PKM and TPI1 are two novel genes suitable for genic expression studies on gliomas. Finally, we analyzed the expression of genes involved in metabolic pathways in clinical samples of brain gliomas of different CNS WHO grades. RT-qPCR analysis showed that in CNS WHO grade 3 and 4 gliomas, the expression levels of HK1, PFKM, GAPDH, G6PD, PGD1, IDH1, FASN, ACACA, and ELOVL2 were higher than those of CNS WHO grade 1 and 2 glioma biopsies. Hence, our results suggest that reference genes from metabolic pathways have different expression profiles depending on the stratification of gliomas and constitute a potential model for studying the development of this type of tumor and the search for molecular targets to treat gliomas.

Identification and In Silico Characterization of Novel Helicobacter pylori Glucose-6-Phosphate Dehydrogenase Inhibitors.

Helicobacter pylori (H. pylori) is a pathogen that can remain in the stomach of an infected person for their entire life. As a result, this leads to the development of severe gastric diseases such as gastric cancer. In addition, current therapies have several problems including antibiotics resistance. Therefore, new practical options to eliminate this bacterium, and its induced affections, are required to avoid morbidity and mortality worldwide. One strategy in the search for new drugs is to detect compounds that inhibit a limiting step in a central metabolic pathway of the pathogen of interest. In this work, we tested 55 compounds to gain insights into their possible use as new inhibitory drugs of H. pylori glucose-6-phosphate dehydrogenase (HpG6PD) activity. The compounds YGC-1; MGD-1, MGD-2; TDA-1; and JMM-3 with their respective scaffold 1,3-thiazolidine-2,4-dione; 1H-benzimidazole; 1,3-benzoxazole, morpholine, and biphenylcarbonitrile showed the best inhibitory activity (IC50 = 310, 465, 340, 204 and 304 µM, respectively). We then modeled the HpG6PD protein by homology modeling to conduct an in silico study of the chemical compounds and discovers its possible interactions with the HpG6PD enzyme. We found that compounds can be internalized at the NADP+ catalytic binding site. Hence, they probably exert a competitive inhibitory effect with NADP+ and a non-competitive or uncompetitive effect with G6P, that of the compounds binding far from the enzyme's active site. Based on these findings, the tested compounds inhibiting HpG6PD represent promising novel drug candidates against H. pylori.

Glucose-6-Phosphate Dehydrogenase::6-Phosphogluconolactonase from the Parasite Giardia lamblia. A Molecular and Biochemical Perspective of a Fused Enzyme.

Giardia lamblia is a single-celled eukaryotic parasite with a small genome and is considered an early divergent eukaryote. The pentose phosphate pathway (PPP) plays an essential role in the oxidative stress defense of the parasite and the production of ribose-5-phosphate. In this parasite, the glucose-6-phosphate dehydrogenase (G6PD) is fused with the 6-phosphogluconolactonase (6PGL) enzyme, generating the enzyme named G6PD::6PGL that catalyzes the first two steps of the PPP. Here, we report that the G6PD::6PGL is a bifunctional enzyme with two catalytically active sites. We performed the kinetic characterization of both domains in the fused G6PD::6PGL enzyme, as well as the individual cloned G6PD. The results suggest that the catalytic activity of G6PD and 6PGL domains in the G6PD::6PGL enzyme are more efficient than the individual proteins. Additionally, using enzymatic and mass spectrometry assays, we found that the final metabolites of the catalytic reaction of the G6PD::6PGL are 6-phosphoglucono-δ-lactone and 6-phosphogluconate. Finally, we propose the reaction mechanism in which the G6PD domain performs the catalysis, releasing 6-phosphoglucono-δ-lactone to the reaction medium. Then, this metabolite binds to the 6PGL domain catalyzing the hydrolysis reaction and generating 6-phosphogluconate. The structural difference between the G. lamblia fused enzyme G6PD::6PGL with the human G6PD indicate that the G6PD::6PGL is a potential drug target for the rational synthesis of novels anti-Giardia drugs.

Cloning, purification, and characterization of the 6-phosphogluconate dehydrogenase (6 PGDH) from Giardia lamblia.

Giardia lamblia, due to the habitat in which it develops, requires a continuous supply of intermediate compounds that allow it to survive in the host. The pentose phosphate pathway (PPP) provides essential molecules such as NADPH and ribulose-5-phosphate during the oxidative phase of the pathway. One of the key enzymes during this stage is 6-phosphogluconate dehydrogenase (6 PGDH) for generating NADPH. Given the relevance of the enzyme, in the present work, the 6pgdh gene from G. lamblia was amplified and cloned to produce the recombinant protein (Gl-6 PGDH) and characterize it functionally and structurally after the purification of Gl-6 PGDH by affinity chromatography. The results of the characterization showed that the protein has a molecular mass of 54 kDa, with an optimal pH of 7.0 and a temperature of 36-42 °C. The kinetic parameters of Gl-6 PGDH were Km = 49.2 and 139.9 µM (for NADP+ and 6-PG, respectively), Vmax =26.27 µmol*min-1*mg-1, and Kcat = 24.0 s-1. Finally, computational modeling studies were performed to obtain a structural visualization of the Gl-6 PGDH protein. The generation of the model and the characterization assays will allow us to expand our knowledge for future studies of the function of the protein in the metabolism of the parasite.

Novel inhibitors of human glucose-6-phosphate dehydrogenase (HsG6PD) affect the activity and stability of the protein.

BACKGROUND: The pentose phosphate pathway (PPP) has received significant attention because of the role of NADPH and R-5-P in the maintenance of cancer cells, which are necessary for the synthesis of fatty acids and contribute to uncontrollable proliferation. The HsG6PD enzyme is the rate-limiting step in the oxidative branch of the PPP, leading to an increase in the expression levels in tumor cells; therefore, the protein has been proposed as a target for the development of new molecules for use in cancer. METHODS: Through in vitro studies, we assayed the effects of 55 chemical compounds against recombinant HsG6PD. Here, we present the kinetic characterization of four new HsG6PD inhibitors as well as their functional and structural effects on the protein. Furthermore, molecular docking was performed to determine the interaction of the best hits with HsG6PD. RESULTS: Four compounds, JMM-2, CCM-4, CNZ-3, and CNZ-7, were capable of reducing HsG6PD activity and showed noncompetitive and uncompetitive inhibition. Moreover, experiments using circular dichroism and fluorescence spectroscopy showed that the molecules affect the structure (secondary and tertiary) of the protein as well as its thermal stability. Computational docking analysis revealed that the interaction of the compounds with the protein does not occur at the active site. CONCLUSIONS: We identified two new compounds (CNZ-3 and JMM-2) capable of inhibiting HsG6PD that, compared to other previously known HsG6PD inhibitors, showed different mechanisms of inhibition. GENERAL SIGNIFICANCE: Screening of new inhibitors for HsG6PD with a future pharmacological approach for the study and treatment of cancer.

Characterizing the Fused TvG6PD::6PGL Protein from the Protozoan Trichomonas vaginalis, and Effects of the NADP+ Molecule on Enzyme Stability.

This report describes a functional and structural analysis of fused glucose-6-phosphate dehydrogenase dehydrogenase-phosphogluconolactonase protein from the protozoan Trichomonas vaginalis (T. vaginalis). The glucose-6-phosphate dehydrogenase (g6pd) gene from T. vaginalis was isolated by PCR and the sequence of the product showed that is fused with 6pgl gene. The fused Tvg6pd::6pgl gene was cloned and overexpressed in a heterologous system. The recombinant protein was purified by affinity chromatography, and the oligomeric state of the TvG6PD::6PGL protein was found as tetramer, with an optimal pH of 8.0. The kinetic parameters for the G6PD domain were determined using glucose-6-phosphate (G6P) and nicotinamide adenine dinucleotide phosphate (NADP+) as substrates. Biochemical assays as the effects of temperature, susceptibility to trypsin digestion, and analysis of hydrochloride of guanidine on protein stability in the presence or absence of NADP+ were performed. These results revealed that the protein becomes more stable in the presence of the NADP+. In addition, we determined the dissociation constant for the binding (Kd) of NADP+ in the protein and suggests the possible structural site in the fused TvG6PD::6PGL protein. Finally, computational modeling studies were performed to obtain an approximation of the structure of TvG6PD::6PGL. The generated model showed differences with the GlG6PD::6PGL protein (even more so with human G6PD) despite both being fused.

Effects of Single and Double Mutants in Human Glucose-6-Phosphate Dehydrogenase Variants Present in the Mexican Population: Biochemical and Structural Analysis.

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is the most frequent human enzymopathy, affecting over 400 million people globally. Worldwide, 217 mutations have been reported at the genetic level, and only 19 have been found in Mexico. The objective of this work was to contribute to the knowledge of the function and structure of three single natural variants (G6PD A+, G6PD San Luis Potosi, and G6PD Guadalajara) and a double mutant (G6PD Mount Sinai), each localized in a different region of the three-dimensional (3D) structure. In the functional characterization of the mutants, we observed a decrease in specific activity, protein expression and purification, catalytic efficiency, and substrate affinity in comparison with wild-type (WT) G6PD. Moreover, the analysis of the effect of all mutations on the structural stability showed that its presence increases denaturation and lability with temperature and it is more sensible to trypsin digestion protease and guanidine hydrochloride compared with WT G6PD. This could be explained by accelerated degradation of the variant enzymes due to reduced stability of the protein, as is shown in patients with G6PD deficiency.

Molecular Cloning and Exploration of the Biochemical and Functional Analysis of Recombinant Glucose-6-Phosphate Dehydrogenase from Gluconoacetobacter diazotrophicus PAL5.

Gluconacetobacter diazotrophicus PAL5 (GDI) is an endophytic bacterium with potential biotechnological applications in industry and agronomy. The recent description of its complete genome and its principal metabolic enzymes suggests that glucose metabolism is accomplished through the pentose phosphate pathway (PPP); however, the enzymes participating in this pathway have not yet been characterized in detail. The objective of the present work was to clone, purify, and biochemically and physicochemically characterize glucose-6-phosphate dehydrogenase (G6PD) from GDI. The gene was cloned and expressed as a tagged protein in E. coli to be purified by affinity chromatography. The native state of the G6PD protein in the solution was found to be a tetramer with optimal activity at pH 8.8 and a temperature between 37 and 50 °C. The apparent Km values for G6P and nicotinamide adenine dinucleotide phosphate (NADP+) were 63 and 7.2 µM, respectively. Finally, from the amino acid sequence a three-dimensional (3D) model was obtained, which allowed the arrangement of the amino acids involved in the catalytic activity, which are conserved (RIDHYLGKE, GxGGDLT, and EKPxG) with those of other species, to be identified. This characterization of the enzyme could help to identify new environmental conditions for the knowledge of the plant-microorganism interactions and a better use of GDI in new technological applications.

Identification of the NADP+ Structural Binding Site and Coenzyme Effect on the Fused G6PD::6PGL Protein from Giardia lamblia.

Giardia lambia is a flagellated protozoan parasite that lives in the small intestine and is the causal agent of giardiasis. It has been reported that G. lamblia exhibits glucose-6-phosphate dehydrogenase (G6PD), the first enzyme in the pentose phosphate pathway (PPP). Our group work demonstrated that the g6pd and 6pgl genes are present in the open frame that gives rise to the fused G6PD::6PGL protein; where the G6PD region is similar to the 3D structure of G6PD in Homo sapiens. The objective of the present work was to show the presence of the structural NADP+ binding site on the fused G6PD::6PGL protein and evaluate the effect of the NADP+ molecule on protein stability using biochemical and computational analysis. A protective effect was observed on the thermal inactivation, thermal stability, and trypsin digestions assays when the protein was incubated with NADP+. By molecular docking, we determined the possible structural-NADP+ binding site, which is located between the Rossmann fold of G6PD and 6PGL. Finally, molecular dynamic (MD) simulation was used to test the stability of this complex; it was determined that the presence of both NADP+ structural and cofactor increased the stability of the enzyme, which is in agreement with our experimental results.

Biochemical Characterization and Structural Modeling of Fused Glucose-6-Phosphate Dehydrogenase-Phosphogluconolactonase from Giardia lamblia.

Glucose-6-phosphate dehydrogenase (G6PD) is the first enzyme in the pentose phosphate pathway and is highly relevant in the metabolism of Giardialamblia. Previous reports suggested that the G6PD gene is fused with the 6-phosphogluconolactonase (6PGL) gene (6pgl). Therefore, in this work, we decided to characterize the fused G6PD-6PGL protein in Giardialamblia. First, the gene of g6pd fused with the 6pgl gene (6gpd::6pgl) was isolated from trophozoites of Giardialamblia and the corresponding G6PD::6PGL protein was overexpressed and purified in Escherichia coli. Then, we characterized the native oligomeric state of the G6PD::6PGL protein in solution and we found a catalytic dimer with an optimum pH of 8.75. Furthermore, we determined the steady-state kinetic parameters for the G6PD domain and measured the thermal stability of the protein in both the presence and absence of guanidine hydrochloride (Gdn-HCl) and observed that the G6PD::6PGL protein showed alterations in the stability, secondary structure, and tertiary structure in the presence of Gdn-HCl. Finally, computer modeling studies revealed unique structural and functional features, which clearly established the differences between G6PD::6PGL protein from G. lamblia and the human G6PD enzyme, proving that the model can be used for the design of new drugs with antigiardiasic activity. These results broaden the perspective for future studies of the function of the protein and its effect on the metabolism of this parasite as a potential pharmacological target.