The glyoxalase system of malaria parasites—Implications for cell biology and general glyoxalase research

Cytoprotective role of pyruvate in mitigating abiotic stress response in Arabidopsis thaliana

Pyruvate is a central metabolite in cellular respiration and metabolism. It can neutralize reactive oxygen species (ROS), safeguard mitochondrial membrane potential, and regulate gene expression under oxidative stress. However, its role in abiotic stress tolerance in plants needs to be explored. Therefore, the current study investigated the role of pyruvate and its metabolism in response to different abiotic stresses in the model plant Arabidopsis thaliana. We retrieved transcript profiling data for pyruvate metabolism and transportation genes (D-LDH, AlaAT, PK, MPC, PDC, PDH, NAD-ME) from public databases. The study's findings indicate that these genes' expression is regulated in response to different abiotic stresses. Moreover, the promoter region of these genes contained multiple cis-acting elements like ABRE, ARE, P-box, and MBS, which are associated with plants' abiotic stress response. Furthermore, colorimetric analysis showed higher pyruvate content under different abiotic stresses. Therefore, exogenous pyruvate treatment was given before and after different abiotic stresses, which could combat the toxicity of pro-oxidant molecules by pyruvate intake. The semiquantitative RT-PCR analysis revealed that exogenous pyruvate treatment enhances the expression of important transcription factors WRKY2, GH3.3, DREB2A, and bZIP1, and stress-responsive genes e.g., APX1, ERD5, ADC2, and HSP70 in addition to abiotic stresses. Moreover, Arabidopsis plants pre-treated with pyruvate before oxidative stress showed less RBOHD expression. Additionally, pyruvate's cytoprotective role was compared to other well-known antioxidants such as NAC, Trolox, and GSH. Finally, untargeted GC-MS/MS analysis of abiotic stress-treated Arabidopsis plants showed a higher metabolite level of β-hydroxy-pyruvic acid, indicating the crucial role of pyruvate during abiotic stress.

Pyramiding D-lactate dehydrogenase with the glyoxalase pathway enhances abiotic stress tolerance in plants

Methylglyoxal is a common cytotoxic metabolite produced in plants during multiple biotic and abiotic stress. To mitigate the toxicity of MG, plants utilize the glyoxalase pathway comprising glyoxalase I (GLYI), glyoxalase II (GLYII), or glyoxalase III (GLYIII). GLYI and GLYII are the key enzymes of glyoxalase pathways that play an important role in abiotic stress tolerance. Earlier research showed that MG level is lower when both GLYI and GLYII are overexpressed together, compared to GLYI or GLYII single gene overexpressed transgenic plants. D-lactate dehydrogenase (D-LDH) is an integral part of MG detoxification which metabolizes the end product (D-lactate) of the glyoxalase pathway. In this study, two Arabidopsis transgenic lines were constructed using gene pyramiding technique: GLYI and GLYII overexpressed (G-I + II), and GLYI, GLYII, and D-LDH overexpressed (G-I + II + D) plants. G-I + II + D exhibits lower MG and D-lactate levels and enhanced abiotic stress tolerance than the G-I + II and wild-type plants. Further study explores the stress tolerance mechanism of G-I + II + D plants through the interplay of different regulators and plant hormones. This, in turn, modulates the expression of ABA-dependent stress-responsive genes like RAB18, RD22, and RD29B to generate adaptive responses during stress. Therefore, there might be a potential correlation between ABA and MG detoxification pathways. Furthermore, higher STY46, GPX3, and CAMTA1 transcripts were observed in G-I + II + D plants during abiotic stress. Thus, our findings suggest that G-I + II + D has significantly improved MG detoxification, reduced oxidative stress-induced damage, and provided a better protective mechanism against abiotic stresses than G-I + II or wild-type plants.

Unexpected alkyl isomerization at the silicon ligand of an unsaturated Rh complex: combined experiment and theory

The formation of dimer [(μ-Cl)Rh-(κ3(P,Si,Si)PhP(o-C6H4CH2SiiPr2)(o-C6H4CH2SiiPrnPr))]2 (Rh-3) with an n-propyl group on one of the silicon atoms as a minor product was affected by the reaction of [RhCl(COD)]2 with proligand PhP(o-C6H4CH2SiHiPr2)2, L1. The major product of the reaction was monomeric 14-electron Rh(III) complex [ClRh(κ3(P,Si,Si)PhP(o-C6H4CH2SiiPr2)2)] (Rh-1). Computations revealed that the monomer-dimer equilibrium is shifted toward the monomer with four isopropyl substituents on the two Si atoms of the ligand as in Rh-1; conversely, the dimer is favored with only one n-propyl as in Rh-3, and with less bulky alkyl substituents such as in [ClRh(κ3(P,Si,Si)PhP(o-C6H4CH2SiMe2)2]2 (Rh-2). Computations on the mechanism of formation of Rh-3 directly from [RhCl(COD)]2 are in agreement with the experimental findings and it is found to be less energetic than if stemming from Rh-1. Additionally, a Si-O-Si complex, [μ-Cl-Rh{κ3(P,Si,C)PPh(o-C6H4CH2SiiPrO SiiPr2CH-o-C6H4)}]2, Rh-4, is generated from the reaction of Rh-1 with adventitious water as a result of intramolecular C-H activation.

Catalytic Reaction Mechanism of Glyoxalase II: A Quantum Mechanics/Molecular Mechanics Study

Methylglyoxal (MG) is a reactive and toxic compound produced in carbohydrate, lipid, and amino acid metabolism. The glyoxalase system is the main detoxifying route for MG and consists of two enzymes, glyoxalase I (GlxI) and glyoxalase II (GlxII). GlxI catalyzes the formation of S-d-lactoylglutathione from hemithioacetal, and GlxII converts this intermediate to d-lactate. A relationship between the glyoxalase system and some diseases like diabetes has been shown, and inhibiting enzymes of this system may be an effective means of controlling certain diseases. A detailed understanding of the reaction mechanism of an enzyme is essential to the rational design of competitive inhibitors. In this work, we use quantum mechanics/molecular mechanics (QM/MM) calculations and energy refinement utilizing the big-QM and QM/MM thermodynamic cycle perturbation methods to propose a mechanism for the GlxII reaction that starts with a nucleophilic attack of the bridging OH^- group on the substrate. The coordination of the substrate to the Zn ions places its electrophilic center close to the hydroxide group, enabling the reaction to proceed. Our estimated reaction energies are in excellent agreement with experimental data, thus demonstrating the reliability of our approach and the proposed mechanism. Additionally, we examined alternative protonation states of Asp-29, Asp-58, Asp-134, and the bridging hydroxide ion in the catalytic process. However, these give less favorable reactions, a poorer reproduction of the crystal structure geometry of the active site, and higher root-mean-squared deviations of the active site residues in molecular dynamics simulations.

Metabolic Shades of S-D-Lactoylglutathione

S-D-lactoylglutathione (SDL) is an intermediate of the glutathione-dependent metabolism of methylglyoxal (MGO) by glyoxalases. MGO is an electrophilic compound that is inevitably produced in conjunction with glucose breakdown and is essentially metabolized via the glyoxalase route. In the last decades, MGO metabolism and its cytotoxic effects have been under active investigation, while almost nothing is known about SDL. This article seeks to fill the gap by presenting an overview of the chemistry, biochemistry, physiological role and clinical importance of SDL. The effects of intracellular SDL are investigated in three main directions: as a substrate for post-translational protein modifications, as a reservoir for mitochondrial reduced glutathione and as an energy currency. In essence, all three approaches point to one direction, namely, a metabolism-related regulatory role, enhancing the cellular defense against insults. It is also suggested that an increased plasma concentration of SDL or its metabolites may possibly serve as marker molecules in hemolytic states, particularly when the cause of hemolysis is a disturbance of the pay-off phase of the glycolytic chain. Finally, SDL could also represent a useful marker in such metabolic disorders as diabetes mellitus or ketotic states, in which its formation is expected to be enhanced. Despite the lack of clear-cut evidence underlying the clinical and experimental findings, the investigation of SDL metabolism is a promising field of research.

The Role of Glyoxalase in Glycation and Carbonyl Stress Induced Metabolic Disorders

Glycation refers to the covalent binding of sugar molecules to macromolecules, such as DNA, proteins, and lipids in a non-enzymatic reaction, resulting in the formation of irreversibly bound products known as advanced glycation end products (AGEs). AGEs are synthesized in high amounts both in pathological conditions, such as diabetes and under physiological conditions resulting in aging. The body's anti-glycation defense mechanisms play a critical role in removing glycated products. However, if this defense system fails, AGEs start accumulating, which results in pathological conditions. Studies have been shown that increased accumulation of AGEs acts as key mediators in multiple diseases, such as diabetes, obesity, arthritis, cancer, atherosclerosis, decreased skin elasticity, male erectile dysfunction, pulmonary fibrosis, aging, and Alzheimer's disease. Furthermore, glycation of nucleotides, proteins, and phospholipids by α-oxoaldehyde metabolites, such as glyoxal (GO) and methylglyoxal (MGO), causes potential damage to the genome, proteome, and lipidome. Glyoxalase-1 (GLO-1) acts as a part of the anti-glycation defense system by carrying out detoxification of GO and MGO. It has been demonstrated that GLO-1 protects dicarbonyl modifications of the proteome and lipidome, thereby impeding the cell signaling and affecting age-related diseases. Its relationship with detoxification and anti-glycation defense is well established. Glycation of proteins by MGO and GO results in protein misfolding, thereby affecting their structure and function. These findings provide evidence for the rationale that the functional modulation of the GLO pathway could be used as a potential therapeutic target. In the present review, we summarized the newly emerged literature on the GLO pathway, including enzymes regulating the process. In addition, we described small bioactive molecules with the potential to modulate the GLO pathway, thereby providing a basis for the development of new treatment strategies against age-related complications.

Glyoxalase pathway is required for normal liver-stage proliferation of Plasmodium berghei

The glyoxalase system is a ubiquitous detoxification pathway of methylglyoxal, a cytotoxic byproduct of glycolysis. Actively proliferating cells, such as cancer cells, depend on their energy metabolism for glycolysis. Therefore, the glyoxalase system has been evaluated as a target of anticancer drugs. The malaria sporozoite, which is the infective stage of the malaria parasite, actively proliferates and produces thousands of merozoites within 2-3 days in hepatocytes. This is the first step of infection in mammalian hosts. The glyoxalase system appears to play an important role in this active proliferation stage of the malaria parasite in hepatocytes. In this study, we aimed to dissect the role of the glyoxalase system in malaria parasite proliferation in hepatocytes to examine its potential as a target of malaria prevention using a reverse genetics approach. The malaria parasite possesses a glyoxalase system, comprised of glyoxalases and GloI-like protein, in the cytosol and apicoplast. We generated cytosolic glyoxalase II (cgloII) knockout, apicoplast targeted glyoxalase gloII (tgloII) knockout, and cgloII and tgloII double-knockout parasites and performed their phenotypic analysis. We did not observe any defects in the cgloII or tgloII knockout parasites. In contrast, we observed approximately 90% inhibition of the liver-stage proliferation of cgloII and tgloII double-knockout parasites in vivo. These findings suggest that although the glyoxalase system is dispensable, it plays an important role in parasite proliferation in hepatocytes. Additionally, the results indicate a complementary relationship between the cytosolic and apicoplast glyoxalase pathways. We expect that the parasite utilizes a system similar to that observed in cancer cells to enable its rapid proliferation in hepatocytes; this process could be targeted in the development of novel strategies to prevent malaria.

Carbonyl Stress in Red Blood Cells and Hemoglobin

The paper overviews the peculiarities of carbonyl stress in nucleus-free mammal red blood cells (RBCs). Some functional features of RBCs make them exceptionally susceptible to reactive carbonyl compounds (RCC) from both blood plasma and the intracellular environment. In the first case, these compounds arise from the increased concentrations of glucose or ketone bodies in blood plasma, and in the second-from a misbalance in the glycolysis regulation. RBCs are normally exposed to RCC-methylglyoxal (MG), triglycerides-in blood plasma of diabetes patients. MG modifies lipoproteins and membrane proteins of RBCs and endothelial cells both on its own and with reactive oxygen species (ROS). Together, these phenomena may lead to arterial hypertension, atherosclerosis, hemolytic anemia, vascular occlusion, local ischemia, and hypercoagulation phenotype formation. ROS, reactive nitrogen species (RNS), and RCC might also damage hemoglobin (Hb), the most common protein in the RBC cytoplasm. It was Hb with which non-enzymatic glycation was first shown in living systems under physiological conditions. Glycated HbA1c is used as a very reliable and useful diagnostic marker. Studying the impacts of MG, ROS, and RNS on the physiological state of RBCs and Hb is of undisputed importance for basic and applied science.

Effects of Curcumin and Its Analogues on Infectious Diseases

Infectious diseases (IDs) are life-threatening illnesses, which result from the spread of pathogenic microorganisms such as bacteria, viruses, fungi, and parasites. IDs are a major challenge for the healthcare systems around the world, leading to a wide variety of clinical manifestations and complications. Despite the capability of frontline-approved medications to partially prevent or mitigate the invasion and subsequent damage of IDs to host tissues and cells, problems such as drug resistance, insufficient efficacy, unpleasant side effects, and high expenses stand in the way of their beneficial applications. One strategy is to evaluate currently explored and available bioactive compounds as possible anti-microbial agents. The natural polyphenol curcumin has been postulated to possess various properties including anti-microbial activities. Studies have shown that it possess pleiotropic effects against bacterial- and parasitic-associating IDs including drug-resistant strains. Curcumin can also potentiate the efficacy of available anti-bacterial and anti-parasitic drugs in a synergistic fashion. In this review, we summarize the findings of these studies along with reported controversies of native curcumin and its analogues, alone and in combination, toward its application in future studies as a natural anti-bacterial and anti-parasitic agent.

The Glyoxalase System-New Insights into an Ancient Metabolism

The glyoxalase system was discovered over a hundred years ago and since then it has been claimed to provide the role of an indispensable enzyme system in order to protect cells from a toxic byproduct of glycolysis. This review gives a broad overview of what has been postulated in the last 30 years of glyoxalase research, but within this context it also challenges the concept that the glyoxalase system is an exclusive tool of detoxification and that its substrate, methylglyoxal, is solely a detrimental burden for every living cell due to its toxicity. An overview of consequences of a complete loss of the glyoxalase system in various model organisms is presented with an emphasis on the role of alternative detoxification pathways of methylglyoxal. Furthermore, this review focuses on the overlooked posttranslational modification of Glyoxalase 1 and its possible implications for cellular maintenance under various (patho-)physiological conditions. As a final note, an intriguing point of view for the substrate methylglyoxal is offered, the concept of methylglyoxal (MG)-mediated hormesis.

Recent advances in the discovery and development of glyoxalase I inhibitors

Glyoxalase I (GLO1) is a homodimeric Zn²⁺-metalloenzyme that catalyses the transformation of methylglyoxal (MG) to d-lacate through the intermediate S-d-lactoylglutathione. Growing evidence indicates that GLO1 has been identified as a potential target for the treatment cancer and other diseases. Various inhibitors of GLO1 have been discovered or developed over the past several decades including natural or natural product-based inhibitors, GSH-based inhibitors, non-GSH-based inhibitors, etc. The aim of this review is to summarize recent achievements of concerning discovery, design strategies, as well as pharmacological aspects of GLO1 inhibitors with the target of promoting their development toward clinical application.

The Incomplete Glutathione Puzzle: Just Guessing at Numbers and Figures?

SIGNIFICANCE

Glutathione metabolism is comparable to a jigsaw puzzle with too many pieces. It is supposed to comprise (i) the reduction of disulfides, hydroperoxides, sulfenic acids, and nitrosothiols, (ii) the detoxification of aldehydes, xenobiotics, and heavy metals, and (iii) the synthesis of eicosanoids, steroids, and iron-sulfur clusters. In addition, glutathione affects oxidative protein folding and redox signaling. Here, I try to provide an overview on the relevance of glutathione-dependent pathways with an emphasis on quantitative data. Recent Advances: Intracellular redox measurements reveal that the cytosol, the nucleus, and mitochondria contain very little glutathione disulfide and that oxidative challenges are rapidly counterbalanced. Genetic approaches suggest that iron metabolism is the centerpiece of the glutathione puzzle in yeast. Furthermore, recent biochemical studies provide novel insights on glutathione transport processes and uncoupling mechanisms.

CRITICAL ISSUES

Which parts of the glutathione puzzle are most relevant? Does this explain the high intracellular concentrations of reduced glutathione? How can iron-sulfur cluster biogenesis, oxidative protein folding, or redox signaling occur at high glutathione concentrations? Answers to these questions not only seem to depend on the organism, cell type, and subcellular compartment but also on different ideologies among researchers.

FUTURE DIRECTIONS

A rational approach to compare the relevance of glutathione-dependent pathways is to combine genetic and quantitative kinetic data. However, there are still many missing pieces and too little is known about the compartment-specific repertoire and concentration of numerous metabolites, substrates, enzymes, and transporters as well as rate constants and enzyme kinetic patterns. Gathering this information might require the development of novel tools but is crucial to address potential kinetic competitions and to decipher uncoupling mechanisms to solve the glutathione puzzle. Antioxid. Redox Signal. 27, 1130-1161.

The cytosolic glyoxalases of Plasmodium falciparum are dispensable during asexual blood-stage development

The enzymes glyoxalase 1 and 2 (Glo1 and Glo2) are found in most eukaryotes and catalyze the glutathione-dependent conversion of 2-oxoaldehydes to 2-hydroxycarboxylic acids. Four glyoxalases are encoded in the genome of the malaria parasite Plasmodium falciparum, the cytosolic enzymes PfGlo1 and PfcGlo2, the apicoplast enzyme PftGlo2, and an inactive Glo1-like protein that also carries an apicoplast-targeting sequence. Inhibition or knockout of the Plasmodium glyoxalases was hypothesized to lead to an accumulation of 2-oxoaldehydes and advanced glycation end-products (AGE) in the host-parasite unit and to result in parasite death. Here, we generated clonal P. falciparum strain 3D7 knockout lines for PFGLO1 and PFcGLO2 using the CRISPR-Cas9 system. Although 3D7Δglo1 knockout clones had an increased susceptibility to external glyoxal, all 3D7Δglo1 and 3D7Δcglo2 knockout lines were viable and showed no significant growth phenotype under standard growth conditions. Furthermore, the lack of PfcGlo2, but not PfGlo1, increased gametocyte commitment in the knockout lines. In summary, PfGlo1 and PfcGlo2 are dispensable during asexual blood-stage development while the loss of PfcGlo2 may induce the formation of transmissible gametocytes. These combined data show that PfGlo1 and PfcGlo2 are most likely not suited as targets for selective drug development.

Methylglyoxal-induced dicarbonyl stress in aging and disease: first steps towards glyoxalase 1-based treatments

Dicarbonyl stress is the abnormal accumulation of dicarbonyl metabolites leading to increased protein and DNA modification contributing to cell and tissue dysfunction in aging and disease. It is produced by increased formation and/or decreased metabolism of dicarbonyl metabolites. MG (methylglyoxal) is a dicarbonyl metabolite of relatively high flux of formation and precursor of the most quantitatively and functionally important spontaneous modifications of protein and DNA clinically. Major MG-derived adducts are arginine-derived hydroimidazolones of protein and deoxyguanosine-derived imidazopurinones of DNA. These are formed non-oxidatively. The glyoxalase system provides an efficient and essential basal and stress-response-inducible enzymatic defence against dicarbonyl stress by the reduced glutathione-dependent metabolism of methylglyoxal by glyoxalase 1. The GLO1 gene encoding glyoxalase 1 has low prevalence duplication and high prevalence amplification in some tumours. Dicarbonyl stress contributes to aging, disease and activity of cytotoxic chemotherapeutic agents. It is found at a low, moderate and severe level in obesity, diabetes and renal failure respectively, where it contributes to the development of metabolic and vascular complications. Increased glyoxalase 1 expression confers multidrug resistance to cancer chemotherapy and has relatively high prevalence in liver, lung and breast cancers. Studies of dicarbonyl stress are providing improved understanding of aging and disease and the basis for rational design of novel pharmaceuticals: glyoxalase 1 inducers for obesity, diabetes and cardiovascular disease and glyoxalase 1 inhibitors for multidrug-resistant tumours. The first clinical trial of a glyoxalase 1 inducer in overweight and obese subjects showed improved glycaemic control, insulin resistance and vascular function.

Simultaneous ATR-FTIR Based Determination of Malaria Parasitemia, Glucose and Urea in Whole Blood Dried onto a Glass Slide

New diagnostic tools that can detect malaria parasites in conjunction with other diagnostic parameters are urgently required. In this study, Attenuated Total Reflection Fourier transform infrared (ATR-FTIR) spectroscopy in combination with Partial Least Square Discriminant Analysis (PLS-DA) and Partial Least Square Regression (PLS-R) have been applied as a point-of-care test for identifying malaria parasites, blood glucose, and urea levels in whole blood samples from thick blood films on glass slides. The specificity for the PLS-DA was found to be 98% for parasitemia levels >0.5%, but a rather low sensitivity of 70% was achieved because of the small number of negative samples in the model. In PLS-R the Root Mean Square Error of Cross Validation (RMSECV) for parasite concentration (0-5%) was 0.58%. Similarly, for glucose (0-400 mg/dL) and urea (0-250 mg/dL) spiked samples, relative RMSECVs were 16% and 17%, respectively. The method reported here is the first example of multianalyte/disease diagnosis using ATR-FTIR spectroscopy, which in this case, enabled the simultaneous quantification of glucose and urea analytes along with malaria parasitemia quantification using one spectrum obtained from a single drop of blood on a glass microscope slide.

Hemolytic and antimalarial effects of tight-binding glyoxalase 1 inhibitors on the host-parasite unit of erythrocytes infected with Plasmodium falciparum

Glyoxalases prevent the formation of advanced glycation end products by converting glycolysis-derived methylglyoxal to d-lactate with the help of glutathione. Vander Jagt and colleagues previously showed that erythrocytes release about thirty times more d-lactate after infection with the human malaria parasite Plasmodium falciparum. Functional glyoxalases in the host-parasite unit might therefore be crucial for parasite survival. Here, we determined the antimalarial and hemolytic activity of two tight-binding glyoxalase inhibitors using infected and uninfected erythrocytes. In addition, we synthesized and analyzed a set of diester derivates of both tight-binding inhibitors resulting in up to threefold lower IC₅₀ values and an altered methemoglobin formation and hemolytic activity depending on the type of ester. Inhibitor treatments of uninfected erythrocytes revealed an extremely slow inactivation of the host cell glyoxalase, irrespective of inhibitor modifications, and a potential dispensability of the host cell enzyme for parasite survival. Our study highlights the benefits and drawbacks of different esterifications of glutathione-derived inhibitors and demonstrates the suitability of glyoxalase inhibitors as a tool for deciphering the relevance and mode of action of different glyoxalase systems in a host-parasite unit.

Plasmodiumfalciparum infection induces dynamic changes in the erythrocyte phospho-proteome

The phosphorylation status of red blood cell proteins is strongly altered during the infection by the malaria parasite Plasmodium falciparum. We identify the key phosphorylation events that occur in the erythrocyte membrane and cytoskeleton during infection, by a comparative analysis of global phospho-proteome screens between infected (obtained at schizont stage) and uninfected RBCs. The meta-analysis of reported mass spectrometry studies revealed a novel compendium of 495 phosphorylation sites in 182 human proteins with regulatory roles in red cell morphology and stability, with about 25% of these sites specific to infected cells. A phosphorylation motif analysis detected 7 unique motifs that were largely mapped to kinase consensus sequences of casein kinase II and of protein kinase A/protein kinase C. This analysis highlighted prominent roles for PKA/PKC involving 78 phosphorylation sites. We then compared the phosphorylation status of PKA (PKC) specific sites in adducin, dematin, Band 3 and GLUT-1 in uninfected RBC stimulated or not by cAMP to their phosphorylation status in iRBC. We showed cAMP-induced phosphorylation of adducin S59 by immunoblotting and we were able to demonstrate parasite-induced phosphorylation for adducin S726, Band 3 and GLUT-1, corroborating the protein phosphorylation status in our erythrocyte phosphorylation site compendium.

Presence of unique glyoxalase III proteins in plants indicates the existence of shorter route for methylglyoxal detoxification

Glyoxalase pathway, comprising glyoxalase I (GLY I) and glyoxalase II (GLY II) enzymes, is the major pathway for detoxification of methylglyoxal (MG) into D-lactate involving reduced glutathione (GSH). However, in bacteria, glyoxalase III (GLY III) with DJ-1/PfpI domain(s) can do the same conversion in a single step without GSH. Our investigations for the presence of DJ-1/PfpI domain containing proteins in plants have indicated the existence of GLY III-like proteins in monocots, dicots, lycopods, gymnosperm and bryophytes. A deeper in silico analysis of rice genome identified twelve DJ-1 proteins encoded by six genes. Detailed analysis has been carried out including their chromosomal distribution, genomic architecture and localization. Transcript profiling under multiple stress conditions indicated strong induction of OsDJ-1 in response to exogenous MG. A member of OsDJ-1 family, OsDJ-1C, showed high constitutive expression at all developmental stages and tissues of rice. MG depletion study complemented by simultaneous formation of D-lactate proved OsDJ-1C to be a GLY III enzyme that converts MG directly into D-lactate in a GSH-independent manner. Site directed mutagenesis of Cys-119 to Alanine significantly reduces its GLY III activity indicating towards the existence of functional GLY III enzyme in rice—a shorter route for MG detoxification.

Characterization of Toxoplasma gondii glyoxalase 1 and evaluation of inhibitory effects of curcumin on the enzyme and parasite cultures

BACKGROUND

The glyoxalase pathway, which includes two enzymes, glyoxalase 1 and 2 (Glo1 and Glo2), is a ubiquitous cellular system responsible for the removal of cytotoxic methylglyoxal produced during glycolysis. Protozoan parasites, including Toxoplasma gondii (T. gondii) tachyzoites, produce methylglyoxal because of increased glycolytic fluxes. A Glo1 inhibitor such as curcumin could be considered a drug candidate for anti-protozoan, anti-inflammatory, and anti-cancer therapy.

METHODS

The T. gondii Glo1 gene (TgGlo1) was cloned and the recombinant protein was produced. Enzyme kinetics of TgGlo1 and five mutants were evaluated by adding methylglyoxal and glutathione to a reaction mixture. Finally, the inhibitory effects of various concentrations of curcumin on recombinant TgGlo1 were evaluated using in vitro cultures of T. gondii.

RESULTS

Active recombinant TgGlo1 was successfully produced and the active sites (E166 and E251) of TgGlo1 were verified by point mutagenesis. Curcumin at the tested doses inhibited the enzymatic activity of recombinant TgGlo1 as well as the parasitic propagation of in vitro-cultured T. gondii. The Ki and IC50 were 12.9 ± 0.5 μM and 38.3 ± 0.9 μM, respectively.

CONCLUSION

The inhibitory effect of curcumin on the enzymatic activity of TgGlo1 and parasitic propagation of T. gondii could be explored in the potential development of a potent drug for the treatment of toxoplasmosis. However, considering the fact that curcumin is known to have many effects on other molecules in the micromolar range, further elucidation of curcumin's direct inhibition of the glyoxalase system of T. gondii will be needed.

Role and Regulation of Glutathione Metabolism in Plasmodium falciparum

Malaria in humans is caused by one of five species of obligate intracellular protozoan parasites of the genus Plasmodium. P. falciparum causes the most severe disease and is responsible for 600,000 deaths annually, primarily in Sub-Saharan Africa. It has long been suggested that during their development, malaria parasites are exposed to environmental and metabolic stresses. One strategy to drug discovery was to increase these stresses by interfering with the parasites’ antioxidant and redox systems, which may be a valuable approach to disease intervention. Plasmodium possesses two redox systems—the thioredoxin and the glutathione system—with overlapping but also distinct functions. Glutathione is the most abundant low molecular weight redox active thiol in the parasites existing primarily in its reduced form representing an excellent thiol redox buffer. This allows for an efficient maintenance of the intracellular reducing environment of the parasite cytoplasm and its organelles. This review will highlight the mechanisms that are responsible for sustaining an adequate concentration of glutathione and maintaining its redox state in Plasmodium. It will provide a summary of the functions of the tripeptide and will discuss the potential of glutathione metabolism for drug discovery against human malaria parasites.

Bacterial glyoxalase I enzymes: structural and biochemical investigations

A number of bacterial glyoxalase I enzymes are maximally activated by Ni2+ and Co2+ ions, but are inactive in the presence of Zn2+, yet these enzymes will also bind this metal ion. The structure-activity relationships between these two classes of glyoxalase I serve as important clues as to how the molecular structures of these proteins control metal-activation profiles.

A glutathione responsive rice glyoxalase II, OsGLYII-2, functions in salinity adaptation by maintaining better photosynthesis efficiency and anti-oxidant pool

Glyoxalase II (GLY II), the second enzyme of glyoxalase pathway that detoxifies cytotoxic metabolite methylglyoxal (MG), belongs to the superfamily of metallo-β-lactamases. Here, detailed analysis of one of the uncharacterized rice glyoxalase II family members, OsGLYII-2 was conducted in terms of its metal content, enzyme kinetics and stress tolerance potential. Functional complementation of yeast GLY II mutant (∆GLO2) and enzyme kinetics data suggested that OsGLYII-2 possesses characteristic GLY II activity using S-lactoylglutathione (SLG) as the substrate. Further, Inductively Coupled Plasma Atomic Emission spectroscopy and modelled structure revealed that OsGLYII-2 contains a binuclear Zn/Fe centre in its active site and chelation studies indicated that these are essential for its activity. Interestingly, reconstitution of chelated enzyme with Zn(2+), and/or Fe(2+) could not reactivate the enzyme, while addition of Co(2+) was able to do so. End product inhibition study provides insight into the kinetics of GLY II enzyme and assigns hitherto unknown function to reduced glutathione (GSH). Ectopic expression of OsGLYII-2 in Escherichia coli and tobacco provides improved tolerance against salinity and dicarbonyl stress indicating towards its role in abiotic stress tolerance. Maintained levels of MG and GSH as well as better photosynthesis rate and reduced oxidative damage in transgenic plants under stress conditions seems to be the possible mechanism facilitating enhanced stress tolerance.

A unique Ni2+ -dependent and methylglyoxal-inducible rice glyoxalase I possesses a single active site and functions in abiotic stress response

The glyoxalase system constitutes the major pathway for the detoxification of metabolically produced cytotoxin methylglyoxal (MG) into a non-toxic metabolite D-lactate. Glyoxalase I (GLY I) is an evolutionarily conserved metalloenzyme requiring divalent metal ions for its activity: Zn(2+) in the case of eukaryotes or Ni(2+) for enzymes of prokaryotic origin. Plant GLY I proteins are part of a multimember family; however, not much is known about their physiological function, structure and metal dependency. In this study, we report a unique GLY I (OsGLYI-11.2) from Oryza sativa (rice) that requires Ni(2+) for its activity. Its biochemical, structural and functional characterization revealed it to be a monomeric enzyme, possessing a single Ni(2+) coordination site despite containing two GLY I domains. The requirement of Ni(2+) as a cofactor by an enzyme involved in cellular detoxification suggests an essential role for this otherwise toxic heavy metal in the stress response. Intriguingly, the expression of OsGLYI-11.2 was found to be highly substrate inducible, suggesting an important mode of regulation for its cellular levels. Heterologous expression of OsGLYI-11.2 in Escherichia coli and model plant Nicotiana tabacum (tobacco) resulted in improved adaptation to various abiotic stresses caused by increased scavenging of MG, lower Na(+) /K(+) ratio and maintenance of reduced glutathione levels. Together, our results suggest interesting links between MG cellular levels, its detoxification by GLY I, and Ni(2+) - the heavy metal cofactor of OsGLYI-11.2, in relation to stress response and adaptation in plants.

Glyoxalase diversity in parasitic protists

Our current knowledge of the isomerase glyoxalase I and the thioesterase glyoxalase II is based on a variety of prokaryotic and eukaryotic (model) systems with an emphasis on human glyoxalases. During the last decade, important insights on glyoxalase catalysis and structure–function relationships have also been obtained from parasitic protists. These organisms, including kinetoplastid and apicomplexan parasites, are particularly interesting, both because of their relevance as pathogens and because of their phylogenetic diversity and host–parasite co-evolution which has led to specialized organellar and metabolic adaptations. Accordingly, the glyoxalase repertoire and properties vary significantly among parasitic protists of different major eukaryotic lineages (and even between closely related organisms). For example, several protists have an insular or non-canonical glyoxalase. Furthermore, the structures and the substrate specificities of glyoxalases display drastic variations. The aim of the present review is to highlight such differences as well as similarities between the glyoxalases of parasitic protists and to emphasize the power of comparative studies for gaining insights into fundamental principles and alternative glyoxalase functions.

The glyoxalase pathway: the first hundred years... and beyond

The discovery of the enzymatic formation of lactic acid from methylglyoxal dates back to 1913 and was believed to be associated with one enzyme termed ketonaldehydemutase or glyoxalase, the latter designation prevailed. However, in 1951 it was shown that two enzymes were needed and that glutathione was the required catalytic co-factor. The concept of a metabolic pathway defined by two enzymes emerged at this time. Its association to detoxification and anti-glycation defence are its presently accepted roles, since methylglyoxal exerts irreversible effects on protein structure and function, associated with misfolding. This functional defence role has been the rationale behind the possible use of the glyoxalase pathway as a therapeutic target, since its inhibition might lead to an increased methylglyoxal concentration and cellular damage. However, metabolic pathway analysis showed that glyoxalase effects on methylglyoxal concentration are likely to be negligible and several organisms, from mammals to yeast and protozoan parasites, show no phenotype in the absence of one or both glyoxalase enzymes. The aim of the present review is to show the evolution of thought regarding the glyoxalase pathway since its discovery 100 years ago, the current knowledge on the glyoxalase enzymes and their recognized role in the control of glycation processes.

Genetic and genomic approaches for the discovery of parasite genes involved in antimalarial drug resistance

The biggest threat to the war on malaria is the continued evolution of drug resistance by the parasite. Resistance to almost all currently available antimalarials now exists in Plasmodium falciparum which causes the most suffering among all human malaria parasites. Monitoring of antimalarial efficacy and the development and subsequent spread of resistance has become an important part in the treatment and control of malaria. With recent reports of reduced efficacy of artemisinin, the current recommended treatment for uncomplicated malaria, there is urgent need for better methods to recognize and monitor drug resistance for effective treatment. Molecular markers have become a welcome addition to complement the more laborious and costly in vitro and in vivo methods that have traditionally been used to monitor drug resistance. However, there are currently no molecular markers for resistance to some antimalarials. This review highlights the role of the various genetic and genomic approaches that have been used in identifying the molecular markers that underlie drug resistance in P. falciparum. These approaches include; candidate genes, genetic linkage and genome-wide association studies. We discuss the requirements and limitations of each approach and use various examples to illustrate their contributions in identifying genomic regions of the parasite associated with antimalarial drug responses.

Low-molecular-mass antioxidants in parasites

SIGNIFICANCE

Parasitic infections continue to be a major problem for global human health. Vaccines are practically not available and chemotherapy is highly unsatisfactory. One approach toward a novel antiparasitic drug development is to unravel pathways that may be suited as future targets. Parasitic organisms show a remarkable diversity with respect to the nature and functions of their main low-molecular-mass antioxidants and many of them developed pathways that do not have a counterpart in their mammalian hosts.

RECENT ADVANCES

Work of the last years disclosed the individual antioxidants employed by parasites and their distinct pathways. Entamoeba, Trichomonas, and Giardia directly use cysteine as main low-molecular-mass thiol but have divergent cysteine metabolisms. Malarial parasites rely exclusively on cysteine uptake and generate glutathione (GSH) as main free thiol as do metazoan parasites. Trypanosomes and Leishmania have a unique trypanothione-based thiol metabolism but employ individual mechanisms for their cysteine supply. In addition, some trypanosomatids synthesize ovothiol A and/or ascorbate. Various essential parasite enzymes such as trypanothione synthetase and trypanothione reductase in Trypanosomatids and the Schistosoma thioredoxin GSH reductase are currently intensively explored as drug target molecules.

CRITICAL ISSUES

Essentiality is a prerequisite but not a sufficient property of an enzyme to become a suited drug target. The availability of an appropriate in vivo screening system and many other factors are equally important.

FUTURE DIRECTIONS

The current organism-wide RNA-interference and proteome analyses are supposed to reveal many more interesting candidates for future drug development approaches directed against the parasite antioxidant defense systems.

Large-scale proteome comparative analysis of developing rhizomes of the ancient vascular plant equisetum hyemale

Horsetail (Equisetum hyemale) is a widespread vascular plant species, whose reproduction is mainly dependent on the growth and development of the rhizomes. Due to its key evolutionary position, the identification of factors that could be involved in the existence of the rhizomatous trait may contribute to a better understanding of the role of this underground organ for the successful propagation of this and other plant species. In the present work, we characterized the proteome of E. hyemale rhizomes using a GeLC-MS spectral-counting proteomics strategy. A total of 1,911 and 1,860 non-redundant proteins were identified in the rhizomes apical tip and elongation zone, respectively. Rhizome-characteristic proteins were determined by comparisons of the developing rhizome tissues to developing roots. A total of 87 proteins were found to be up-regulated in both horsetail rhizome tissues in relation to developing roots. Hierarchical clustering indicated a vast dynamic range in the regulation of the 87 characteristic proteins and revealed, based on the regulation profile, the existence of nine major protein groups. Gene ontology analyses suggested an over-representation of the terms involved in macromolecular and protein biosynthetic processes, gene expression, and nucleotide and protein binding functions. Spatial difference analysis between the rhizome apical tip and the elongation zone revealed that only eight proteins were up-regulated in the apical tip including RNA-binding proteins and an acyl carrier protein, as well as a KH domain protein and a T-complex subunit; while only seven proteins were up-regulated in the elongation zone including phosphomannomutase, galactomannan galactosyltransferase, endoglucanase 10 and 25, and mannose-1-phosphate guanyltransferase subunits alpha and beta. This is the first large-scale characterization of the proteome of a plant rhizome. Implications of the findings were discussed in relation to other underground organs and related species.