Optimized heterologous expression of the human zinc enzyme glyoxalase I

Crystal structures of human glyoxalase I and its complex with TLSC702 reveal inhibitor binding mode and substrate preference

Human glyoxalase I (hGLO I) is an enzyme for detoxification of methylglyoxal (MG), and has been considered an attractive target for the development of new anti-cancer drugs. In our previous report, the GLO I inhibitor TLSC702 induced apoptosis in tumor cells. Here, we determined the crystal structures of hGLO I and its complex with TLSC702. In the complex, the carboxy O atom of TLSC702 is coordinated to Zn²⁺ , and TLSC702 mainly shows van der Waals interaction with hydrophobic residues. In the inhibitor-unbound structure, glycerol, which has similar functional groups to MG, was bound to Zn²⁺ , indicating that GLO I can easily bind to MG. This study provides a structural basis to develop better anticancer drugs.

Evolutionary Aspects of the Oxido-Reductive Network of Methylglyoxal

In the chemoautotrophic theory for the origin of life, offered as an alternative to broth theory, the archaic reductive citric acid cycle operating without enzymes is in the center. The non-enzymatic (methyl)glyoxalase pathway has been suggested to be the anaplerotic route for the reductive citric acid cycle. In the recent years, much has been learned about methylglyoxal, but its importance in the metabolic machinery is still uncovered. If methylglyoxal had been essential participant of the early stage of evolution, then it is a legitimate question whether it might have played a role in the early oxido-reduction network, too. Therefore, an oxido-reduction network of methylglyoxal that might have functioned under ancient circumstances without enzymes was constructed and analyzed by virtue of group contribution method. Taking methylglyoxal as input material, it turned out that the evolutionary value of reactions and biomolecules were not similar. Glycerol, glycerate, and tartonate, the output components, were conserved to different degrees. Although the tartonate route was similarly favorable from energetic point of view, its intermediates are almost not present in extant biochemistry. The presence of two carboxyl or aldehyde groups, or their combination in tricarbons of the constructed network seemed disadvantageous for selection, and the inductive effect, resulting in an asymmetry in electron cloud of chemicals, might have been important. The evolutionary role for cysteine, H₂S, and formaldehyde in the emergence of high-energy bonds in the form of thioesters and in Fe-S cluster formation as well as in imidazole synthesis was shown to bridge the gap between prebiotic chemistry and contemporary biochemistry. Overall, the ideas developed here represent an approach fitting to chemoautotrophic origin of life and implying to the role of methylglyoxal in triose formation. The proposed network is expected to have an impact upon how one may think of prebiological chemical processes on methylglyoxal, too. Finally, along the evolutionary time line, the network functioning without enzymes is situated between the formation of simple organic compounds and primeval cells, being closer to the former and well preceding the last common metabolic ancestor developed after primitive cells emerged.

Quantum Mechanics/Molecular Mechanics Study of the Reaction Mechanism of Glyoxalase I

Glyoxalase I (GlxI) is a member of the glyoxalase system, which is important in cell detoxification and converts hemithioacetals of methylglyoxal (a cytotoxic byproduct of sugar metabolism that may react with DNA or proteins and introduce nucleic acid strand breaks, elevated mutation frequencies, and structural or functional changes of the proteins) and glutathione into d-lactate. GlxI accepts both the S and R enantiomers of hemithioacetal, but converts them to only the S-d enantiomer of lactoylglutathione. Interestingly, the enzyme shows this unusual specificity with a rather symmetric active site (a Zn ion coordinated to two glutamate residues; Glu-99 and Glu-172), making the investigation of its reaction mechanism challenging. Herein, we have performed a series of combined quantum mechanics and molecular mechanics calculations to study the reaction mechanism of GlxI. The substrate can bind to the enzyme in two different modes, depending on the direction of its alcoholic proton (H2; toward Glu-99 or Glu-172). Our results show that the S substrate can react only if H2 is directed toward Glu-99 and the R substrate only if H2 is directed toward Glu-172. In both cases, the reactions lead to the experimentally observed S-d enantiomer of the product. In addition, the results do not show any low-energy paths to the wrong enantiomer of the product from neither the S nor the R substrate. Previous studies have presented several opposing mechanisms for the conversion of R and S enantiomers of the substrate to the correct enantiomer of the product. Our results confirm one of them for the S substrate, but propose a new one for the R substrate.

Targeting Metalloenzymes for Therapeutic Intervention

Metalloenzymes are central to a wide range of essential biological activities, including nucleic acid modification, protein degradation, and many others. The role of metalloenzymes in these processes also makes them central for the progression of many diseases and, as such, makes metalloenzymes attractive targets for therapeutic intervention. Increasing awareness of the role metalloenzymes play in disease and their importance as a class of targets has amplified interest in the development of new strategies to develop inhibitors and ultimately useful drugs. In this Review, we provide a broad overview of several drug discovery efforts focused on metalloenzymes and attempt to map out the current landscape of high-value metalloenzyme targets.

Heterologous expression of a Glyoxalase I gene from sugarcane confers tolerance to several environmental stresses in bacteria

Glyoxalase I belongs to the glyoxalase system that detoxifies methylglyoxal (MG), a cytotoxic by-product produced mainly from triose phosphates. The concentration of MG increases rapidly under stress conditions. In this study, a novel glyoxalase I gene, designated as SoGloI was identified from sugarcane. SoGloI had a size of 1,091 bp with one open reading frame (ORF) of 885 bp encoding a protein of 294 amino acids. SoGloI was predicted as a Ni2+-dependent GLOI protein with two typical glyoxalase domains at positions 28-149 and 159-283, respectively. SoGloI was cloned into an expression plasmid vector, and the Trx-His-S-tag SoGloI protein produced in Escherichia coli was about 51 kDa. The recombinant E. coli cells expressing SoGloI compared to the control grew faster and tolerated higher concentrations of NaCl, CuCl2, CdCl2, or ZnSO4. SoGloI ubiquitously expressed in various sugarcane tissues. The expression was up-regulated under the treatments of NaCl, CuCl2, CdCl2, ZnSO4 and abscisic acid (ABA), or under simulated biotic stress conditions upon exposure to salicylic acid (SA) and methyl jasmonate (MeJA). SoGloI activity steadily increased when sugarcane was subjected to NaCl, CuCl2, CdCl2, or ZnSO4 treatments. Sub-cellular observations indicated that the SoGloI protein was located in both cytosol and nucleus. These results suggest that the SoGloI gene may play an important role in sugarcane's response to various biotic and abiotic stresses.

Higher Flexibility of Glu-172 Explains the Unusual Stereospecificity of Glyoxalase I

Despite many studies during the latest two decades, the reason for the unusual stereospecificity of glyoxalase I (GlxI) is still unknown. This metalloenzyme converts both enantiomers of its natural substrate to only one enantiomer of its product. In addition, GlxI catalyzes reactions involving some substrate and product analogues with a stereospecificity similar to that of its natural substrate reaction. For example, the enzyme exchanges the pro- S, but not the pro- R, hydroxymethyl proton of glutathiohydroxyacetone (HOC-SG) with a deuterium from D₂O. To find some clues to the unusual stereospecificity of GlxI, we have studied the stereospecific proton exchange of the hydroxymethyl proton of HOC-SG by this enzyme. We employed density functional theory and molecular dynamics (MD) simulations to study the proton exchange mechanism and origin of the stereospecificity. The results show that a rigid cluster model with the same flexibility for the two active-site glutamate residues cannot explain the unusual stereospecificity of GlxI. However, using a cluster model with full flexibility of Glu-172 or a larger model with the entire glutamates, extending the backbone into the neighboring residues, the results showed that there is no way for HOC-SG to exchange its protons if the alcoholic proton is directed toward Glu-99. However, if the hydroxymethyl proton instead is directed toward the more flexible Glu-172, we find a catalytic reaction mechanism for the exchange of the H_S proton by a deuterium, in accordance with experimental findings. Thus, our results indicate that the special stereospecificity of GlxI is caused by the more flexible environment of Glu-172 in comparison to that of Glu-99. This higher flexibility of Glu-172 is also confirmed by MD simulations. We propose a reaction mechanism for the stereospecific proton exchange of the hydroxymethyl proton of HOC-SG by GlxI with an overall energy barrier of 15 kcal/mol.

Defense against Reactive Carbonyl Species Involves at Least Three Subcellular Compartments Where Individual Components of the System Respond to Cellular Sugar Status

Methylglyoxal (MGO) and glyoxal (GO) are toxic reactive carbonyl species generated as by-products of glycolysis. The pre-emption pathway for detoxification of these products, the glyoxalase (GLX) system, involves two consecutive reactions catalyzed by GLXI and GLXII. In Arabidopsis thaliana, the GLX system is encoded by three homologs of GLXI and three homologs of GLXII, from which several predicted GLXI and GLXII isoforms can be derived through alternative splicing. We identified the physiologically relevant splice forms using sequencing data and demonstrated that the resulting isoforms have different subcellular localizations. All three GLXI homologs are functional in vivo, as they complemented a yeast GLXI loss-of-function mutant. Efficient MGO and GO detoxification can be controlled by a switch in metal cofactor usage. MGO formation is closely connected to the flux through glycolysis and through the Calvin Benson cycle; accordingly, expression analysis indicated that GLXI is transcriptionally regulated by endogenous sugar levels. Analyses of Arabidopsis loss-of-function lines revealed that the elimination of toxic reactive carbonyl species during germination and seedling establishment depends on the activity of the cytosolic GLXI;3 isoform. The Arabidopsis GLX system involves the cytosol, chloroplasts, and mitochondria, which harbor individual components that might be used at specific developmental stages and respond differentially to cellular sugar status.

A nuclear-localized rice glyoxalase I enzyme, OsGLYI-8, functions in the detoxification of methylglyoxal in the nucleus

The cellular levels of methylglyoxal (MG), a toxic byproduct of glycolysis, rise under various abiotic stresses in plants. Detoxification of MG is primarily through the glyoxalase pathway. The first enzyme of the pathway, glyoxalase I (GLYI), is a cytosolic metalloenzyme requiring either Ni²⁺ or Zn²⁺ for its activity. Plants possess multiple GLYI genes, of which only some have been partially characterized; hence, the precise molecular mechanism, subcellular localization and physiological relevance of these diverse isoforms remain enigmatic. Here, we report the biochemical properties and physiological role of a putative chloroplast-localized GLYI enzyme, OsGLYI-8, from rice, which is strikingly different from all hitherto studied GLYI enzymes in terms of its intracellular localization, metal dependency and kinetics. In contrast to its predicted localization, OsGLYI-8 was found to localize in the nucleus along with its substrate, MG. Further, OsGLYI-8 does not show a strict requirement for metal ions for its activity, is functional as a dimer and exhibits unusual biphasic steady-state kinetics with a low-affinity and a high-affinity substrate-binding component. Loss of AtGLYI-2, the closest Arabidopsis ortholog of OsGLYI-8, results in severe germination defects in the presence of MG and growth retardation under salinity stress conditions. These defects were rescued upon complementation with AtGLYI-2 or OsGLYI-8. Our findings thus provide evidence for the presence of a GLYI enzyme and MG detoxification in the nucleus.

Arabidopsis thaliana Contains Both Ni2+ and Zn2+ Dependent Glyoxalase I Enzymes and Ectopic Expression of the Latter Contributes More towards Abiotic Stress Tolerance in E. coli

The glyoxalase pathway is ubiquitously found in all the organisms ranging from prokaryotes to eukaryotes. It acts as a major pathway for detoxification of methylglyoxal (MG), which deleteriously affects the biological system in stress conditions. The first important enzyme of this system is Glyoxalase I (GLYI). It is a metalloenzyme which requires divalent metal ions for its activity. This divalent metal ion can be either Zn²⁺ as found in most of eukaryotes or Ni²⁺ as seen in prokaryotes. In the present study, we have found three active GLYI enzymes (AtGLYI2, AtGLYI3 and AtGLYI6) belonging to different metal activation classes coexisting in Arabidopsis thaliana. These enzymes have been found to efficiently complement the GLYI yeast mutants. These three enzymes have been characterized in terms of their activity, metal dependency, kinetic parameters and their role in conferring tolerance to multiple abiotic stresses in E. coli and yeast. AtGLYI2 was found to be Zn²⁺ dependent whereas AtGLYI3 and AtGLYI6 were Ni²⁺ dependent. Enzyme activity of Zn²⁺ dependent enzyme, AtGLYI2, was observed to be exceptionally high (~250–670 fold) as compared to Ni²⁺ dependent enzymes, AtGLYI3 and AtGLYI6. The activity of these GLYI enzymes correlated well to their role in stress tolerance. Heterologous expression of these enzymes in E. coli led to better tolerance against various stress conditions. This is the first report of a higher eukaryotic species having multiple active GLYI enzymes belonging to different metal activation classes.

Genome-wide analysis and expression profiling of glyoxalase gene families in soybean (Glycine max) indicate their development and abiotic stress specific response

BACKGROUND

Glyoxalase pathway consists of two enzymes, glyoxalase I (GLYI) and glyoxalase II (GLYII) which detoxifies a highly cytotoxic metabolite methylglyoxal (MG) to its non-toxic form. MG may form advanced glycation end products with various cellular macro-molecules such as proteins, DNA and RNA; that ultimately lead to their inactivation. Role of glyoxalase enzymes has been extensively investigated in various plant species which showed their crucial role in salinity, drought and heavy metal stress tolerance. Previously genome-wide analysis of glyoxalase genes has been conducted in model plants Arabidopsis and rice, but no such study was performed in any legume species.

RESULTS

In the present study, a comprehensive genome database analysis of soybean was performed and identified a total of putative 41 GLYI and 23 GLYII proteins encoded by 24 and 12 genes, respectively. Detailed analysis of these identified members was conducted including their nomenclature and classification, chromosomal distribution and duplication, exon-intron organization, and protein domain(s) and motifs identification. Expression profiling of these genes has been performed in different tissues and developmental stages as well as under salinity and drought stresses using publicly available RNAseq and microarray data. The study revealed that GmGLYI-7 and GmGLYII-8 have been expressed intensively in all the developmental stages and tissues; while GmGLYI-6, GmGLYI-9, GmGLYI-20, GmGLYII-5 and GmGLYII-10 were highly abiotic stress responsive members.

CONCLUSIONS

The present study identifies the largest family of glyoxalase proteins to date with 41 GmGLYI and 23 GmGLYII members in soybean. Detailed analysis of GmGLYI and GmGLYII genes strongly indicates the genome-wide segmental and tandem duplication of the glyoxalase members. Moreover, this study provides a strong basis about the biological role and function of GmGLYI and GmGLYII members in soybean growth, development and stress physiology.

Proteomic analysis indicates that overexpression and nuclear translocation of lactoylglutathione lyase (GLO1) is associated with tumor progression in murine fibrosarcoma

Lactoylglutathione lyase (GLO1), a ubiquitously expressed methylglyoxal (MG) detoxification enzyme, is implicated in the progression of various human malignant diseases. However, the role of GLO1 in the development or progression of murine fibrosarcoma is still unclear. We performed proteomic analysis to identify differences in the intracellular proteins of the regressive tumor cell line QR-32 and the inflammatory cell-promoting progressive tumor cell line QRsP-11 of murine fibrosarcoma by 2DE combined with MS. Seven upregulated proteins were identified in QRsP-11 compared to QR-32 cells, namely, GLO1, annexin A1, adenylate kinase isoenzyme 1, transcription factor BTF3, myosin light polypeptide 6, low molecular weight phosphotyrosine protein phosphatase and nucleoside diphosphate kinase B. Heat shock protein beta-1 (HspB1), a methylglyoxal-adducted protein, is concomitantly over-expressed in QRsP-11 as compared to QR-32 cells. We also found out that GLO1 is translocated into the nucleus to a higher extent in QRsP-11 compared to QR-32 cells, which can be reversed by using a MEK inhibitor (U0126). Moreover, U0126 and GLO1 siRNA can inhibit cell proliferation and migration in QRsP-11 cells. Our data suggest that overexpression and nuclear translocation of GLO1 might be associated with tumor progression in murine fibrosarcoma.

Methylglyoxal in cells elicits a negative feedback loop entailing transglutaminase 2 and glyoxalase 1

Glyoxalase 1 (GlxI) is the key enzyme that converts the highly reactive α-oxo-aldehydes into the corresponding α-hydroxy acids using l-glutathione as a cofactor. In our preliminary data, GlxI was identified as a substrate of transglutaminase 2 (TG2), a ubiquitous enzyme with multiple functions. According to the catalytic properties of TG2, protein cross-linking, polyamine conjugation, and/or deamidation are potential post-translational modifications. In this article, we have demonstrated that TG2 catalyzes either polyamine conjugation or deamidation to GlxI depending on the presence of polyamines or not. Deamidation leads to activation of GlxI while polyamine conjugation results in activation of GlxI as well as stabilization of GlxI against denaturation treatment. In cultured HeLa cells, methylglyoxal challenge causes increase in intracellular levels of reactive oxygen species (ROS) and calcium leading to TG2 activation and subsequent transamidation and activation of GlxI. The inhibition of TG2 significantly weakens the cell resistance to the methylglyoxal challenge. Thus, GlxI is a novel substrate of TG2 and is activated by TG2 in vitro and in cellulo. Exposure to methylglyoxal elicits a negative feedback loop entailing ROS, calcium, TG2 and GlxI, thus leading to attenuation of the increase in the methylglyoxal level. The results imply that cancer cells highly express TG2 or GlxI can endure the oxidative stress derived from higher glycolytic flux and may gain extra growth advantage from the aerobic glycolysis.

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We have demonstrated novel modifications of glyoxalase I by transglutaminase 2.

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The modifications mediated by transglutaminse 2 modulate the glyoxalase I activities.

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Methylglyoxal treatment in cells induces increases in the levels of endogenous reactive oxygen species and activation transglutaminase 2 and glyoxalase I.

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Cells dispose the accumulated intracellular methylglyoxal by a negative feedback loop consisting of reactive oxygen species, calcium, transglutaminase 2 and glyoxalase I.

Structural variation in bacterial glyoxalase I enzymes: investigation of the metalloenzyme glyoxalase I from Clostridium acetobutylicum

The glyoxalase system catalyzes the conversion of toxic, metabolically produced α-ketoaldehydes, such as methylglyoxal, into their corresponding nontoxic 2-hydroxycarboxylic acids, leading to detoxification of these cellular metabolites. Previous studies on the first enzyme in the glyoxalase system, glyoxalase I (GlxI), from yeast, protozoa, animals, humans, plants, and Gram-negative bacteria, have suggested two metal activation classes, Zn(2+) and non-Zn(2+) activation. Here, we report a biochemical and structural investigation of the GlxI from Clostridium acetobutylicum, which is the first GlxI enzyme from Gram-positive bacteria that has been fully characterized as to its three-dimensional structure and its detailed metal specificity. It is a Ni(2+)/Co(2+)-activated enzyme, in which the active site geometry forms an octahedral coordination with one metal atom, two water molecules, and four metal-binding ligands, although its inactive Zn(2+)-bound form possesses a trigonal bipyramidal geometry with only one water molecule liganded to the metal center. This enzyme also possesses a unique dimeric molecular structure. Unlike other small homodimeric GlxI where two active sites are located at the dimeric interface, the C. acetobutylicum dimeric GlxI enzyme also forms two active sites but each within single subunits. Interestingly, even though this enzyme possesses a different dimeric structure from previously studied GlxI, its metal activation characteristics are consistent with properties of other GlxI. These findings indicate that metal activation profiles in this class of enzyme hold true across diverse quaternary structure arrangements.

Posttranslational modification of human glyoxalase 1 indicates redox-dependent regulation

BACKGROUND

Glyoxalase 1 (Glo1) and glyoxalase 2 (Glo2) are ubiquitously expressed cytosolic enzymes that catalyze the conversion of toxic alpha-oxo-aldehydes into the corresponding alpha-hydroxy acids using L-glutathione (GSH) as a cofactor. Human Glo1 exists in various isoforms; however, the nature of its modifications and their distinct functional assignment is mostly unknown.

METHODOLOGY/PRINCIPAL FINDINGS

We characterized native Glo1 purified from human erythrocytes by mass spectrometry. The enzyme was found to undergo four so far unidentified posttranslational modifications: (i) removal of the N-terminal methionine 1, (ii) N-terminal acetylation at alanine 2, (iii) a vicinal disulfide bridge between cysteine residues 19 and 20, and (iv) a mixed disulfide with glutathione on cysteine 139. Glutathionylation of Glo1 was confirmed by immunological methods. Both, N-acetylation and the oxidation state of Cys(19/20), did not impact enzyme activity. In contrast, glutathionylation strongly inhibited Glo1 activity in vitro. The discussed mechanism for enzyme inhibition by glutathionylation was validated by molecular dynamics simulation.

CONCLUSION/SIGNIFICANCE

It is shown for the first time that Glo1 activity directly can be regulated by an oxidative posttranslational modification that was found in the native enzyme, i.e., glutathionylation. Inhibition of Glo1 by chemical reaction with its co-factor and the role of its intramolecular disulfides are expected to be important factors within the context of redox-dependent regulation of glucose metabolism in cells.

Comparative genomic analyses of nickel, cobalt and vitamin B12 utilization

BACKGROUND

Nickel (Ni) and cobalt (Co) are trace elements required for a variety of biological processes. Ni is directly coordinated by proteins, whereas Co is mainly used as a component of vitamin B12. Although a number of Ni and Co-dependent enzymes have been characterized, systematic evolutionary analyses of utilization of these metals are limited.

RESULTS

We carried out comparative genomic analyses to examine occurrence and evolutionary dynamics of the use of Ni and Co at the level of (i) transport systems, and (ii) metalloproteomes. Our data show that both metals are widely used in bacteria and archaea. Cbi/NikMNQO is the most common prokaryotic Ni/Co transporter, while Ni-dependent urease and Ni-Fe hydrogenase, and B12-dependent methionine synthase (MetH), ribonucleotide reductase and methylmalonyl-CoA mutase are the most widespread metalloproteins for Ni and Co, respectively. Occurrence of other metalloenzymes showed a mosaic distribution and a new B12-dependent protein family was predicted. Deltaproteobacteria and Methanosarcina generally have larger Ni- and Co-dependent proteomes. On the other hand, utilization of these two metals is limited in eukaryotes, and very few of these organisms utilize both of them. The Ni-utilizing eukaryotes are mostly fungi (except saccharomycotina) and plants, whereas most B12-utilizing organisms are animals. The NiCoT transporter family is the most widespread eukaryotic Ni transporter, and eukaryotic urease and MetH are the most common Ni- and B12-dependent enzymes, respectively. Finally, investigation of environmental and other conditions and identity of organisms that show dependence on Ni or Co revealed that host-associated organisms (particularly obligate intracellular parasites and endosymbionts) have a tendency for loss of Ni/Co utilization.

CONCLUSION

Our data provide information on the evolutionary dynamics of Ni and Co utilization and highlight widespread use of these metals in the three domains of life, yet only a limited number of user proteins.

Distribution of glyoxalase I polymorphism among Zuni Indians: the Zuni Kidney Project

Zuni Indians are experiencing simultaneous epidemics of type 2 diabetes mellitus (T2DM) and renal disease [Scavini, M., Stidley, C. A., Shah, V. O., Narva, A. S., Tentori, F., Kessler, D. S., et al. (2003). Prevalence of diabetes is higher among female than male Zuni Indians: Diabetes among Zuni Indians. Diabetes Care, 26 (1), 55-60; Shah, V. O., Scavini, M., Stidley, C., Tentori, F., Welty, T., Maccluer, J. W., et al. (2003). Epidemic of diabetic and nondiabetic renal disease among the Zuni Indians: The Zuni Kidney Project. Journal of the American Society of Nephrology, 14, 1320-1329]. Methylglyoxal (MG), a highly reactive, cytotoxic, cross-linking endogenous aldehyde involved in the modification of biologic macromolecules, is elevated among patients with T2DM. Glyoxalase I (Glo1) is the initial enzyme involved in the detoxification of MG. Glo1 is a dimeric enzyme with three isoforms Glo1-1, Glo2-1, and Glo2-2, resulting from a point mutation (A-->C) at position 332 of cDNA. The present study was conducted to explore the hypothesis that specific polymorphisms of the Glo1 gene are associated with diabetes and/or albuminuria in Zuni Indians. We studied four groups of Zuni Indians stratified by diabetes status and albuminuria, as assessed by the urinary albumin:creatinine ratio (UACR): Group I--normal controls; Group II--T2DM and UACR<0.03; Group III--T2DM and UACR>or=0.03; and Group IV--nondiabetic participants with UACR>or=0.03. Genomic DNA was used as template for polymerase chain reaction amplification of the Glo1 gene. Products were digested to yield 110-bp bands (homozygous, CC); 54- and 45-bp bands (homozygous, AA); or all three bands (heterozygous CA). Data on age, gender, UACR, serum creatinine, hemoglobin A1(c), serum glucose, systolic and diastolic blood pressures, and the duration of T2DM among participants in Groups II and III were analyzed using analysis of variance. A generalized linear model logistic regression analysis was used to assess the relationships between specific Glo1 polymorphisms to T2DM and UACR. All three Glo1 genotypes were present among Zuni Indians. There were no significant differences in the distributions of Glo1 genotypes among the study groups (chi-square test, P=.5590). The prevalence of Glo1 A allele was higher among diabetic participants (Groups II and III combined) than among nondiabetic participants (Groups I and IV combined) (chi-square test, P=.0233). There was an association (odds ratio=2.9; 95% confidence interval=1.3-7.2) between the Glo1 A allele and T2DM.

Enhancing salt tolerance in a crop plant by overexpression of glyoxalase II

Earlier we have shown the role of glyoxalase overexpression in conferring salinity tolerance in transgenic tobacco. We now demonstrate the feasibility of same in a crop like rice through overproduction of glyoxalase II. The rice glyoxalase II was cloned in pCAMBIA1304 and transformed into rice (Oryza sativa cv PB1) via Agrobacterium. The transgenic plants showed higher constitutive activity of glyoxalase II that increased further upon salt stress, reflecting the upregulation of endogenous glyoxalase II. The transgenic rice showed higher tolerance to toxic concentrations of methylglyoxal (MG) and NaCl. Compared with non-transgenics, transgenic plants at the T1 generation exhibited sustained growth and more favorable ion balance under salt stress conditions.

Distinct classes of glyoxalase I: metal specificity of the Yersinia pestis, Pseudomonas aeruginosa and Neisseria meningitidis enzymes

The metalloisomerase glyoxalase I (GlxI) catalyses the conversion of methylglyoxal-glutathione hemithioacetal and related derivatives into the corresponding thioesters. In contrast with the previously characterized GlxI enzymes of Homo sapiens, Pseudomonas putida and Saccharomyces cerevisiae, we recently determined that Escherichia coli GlxI surprisingly did not display Zn2+-activation, but instead exhibited maximal activity with Ni2+. To investigate whether non-Zn2+ activation defines a distinct, previously undocumented class of GlxI enzymes, or whether the E. coli GlxI is an exception to the previously established Zn2+-activated GlxI, we have cloned and characterized the bacterial GlxI from Yersinia pestis, Pseudomonas aeruginosa and Neisseria meningitidis. The metal-activation profiles for these additional GlxIs firmly establish the existence of a non-Zn2+-dependent grouping within the general category of GlxI enzymes. This second, established class of metal activation was formerly unidentified for this metalloenzyme. Amino acid sequence comparisons indicate a more extended peptide chain in the Zn2+-dependent forms of GlxI (H. sapiens, P. putida and S. cerevisiae), compared with the GlxI enzymes of E. coli, Y. pestis, P. aeruginosa and N. meningitidis. The longer sequence is due in part to the presence of additional regions situated fairly close to the metal ligands in the Zn2+-dependent forms of the lyase. With respect to sequence alignments, these inserts may potentially contribute to defining the metal specificity of GlxI at a structural level.

Optimizing the Heterologous Expression of Glutathione Transferase

The heterologous expression of a protein may be enhanced by silent mutations in the coding region of its corresponding DNA. This simple approach has been successfully used for optimized production of a number of glutathione-linked enzymes. For example, the yield of human glutathione transferase M2-2 was elevated by 140-fold in a clone isolated by immunoscreening of a library of plasmids with randomized synonymous codons in the 5'-segment of the region encoding the enzyme.

Characterization of the glyoxalases of the malarial parasite Plasmodium falciparum and comparison with their human counterparts

The glyoxalase system consisting of glyoxalase I (GloI) and glyoxalase II (GloII) constitutes a glutathione-dependent intracellular pathway converting toxic 2-oxoaldehydes, such as methylglyoxal, to the corresponding 2-hydroxyacids. Here we describe a complete glyoxalase system in the malarial parasitePlasmodium falciparum. The biochemical, kinetic and structural properties of cytosolic GloI (cGloI) and two GloIIs (cytosolic GloII named cGloII, and tGloII preceded by a targeting sequence) were directly compared with the respective isofunctional host enzymes. cGloI and cGloII exhibit lowerKmvalues and higher catalytic efficiencies (kcat/Km) than the human counterparts, pointing to the importance of the system in malarial parasites. A Tyr185Phe mutant of cGloII shows a 2.5-fold increase inKm, proving the contribution of Tyr185 to substrate binding. Molecular models suggest very similar active sites/metal binding sites of parasite and host cell enzymes. However, a fourth protein, which has highest similarities to GloI, was found to be unique for malarial parasites; it is likely to act in the apicoplast, and has as yet undefined substrate specificity. Various S-(N-hydroxy-N-arylcarbamoyl)glutathiones tested asP. falciparumGlo inhibitors were active in the lower nanomolar range. The Glo system ofPlasmodiumwill be further evaluated as a target for the development of antimalarial drugs.

A trypanothione-dependent glyoxalase I with a prokaryotic ancestry in Leishmania major

Glyoxalase I forms part of the glyoxalase pathway that detoxifies reactive aldehydes such as methylglyoxal, using the spontaneously formed glutathione hemithioacetal as substrate. All known eukaryotic enzymes contain zinc as their metal cofactor, whereas the Escherichia coli glyoxalase I contains nickel. Database mining and sequence analysis identified putative glyoxalase I genes in the eukaryotic human parasites Leishmania major, Leishmania infantum, and Trypanosoma cruzi, with highest similarity to the cyanobacterial enzymes. Characterization of recombinant L. major glyoxalase I showed it to be unique among the eukaryotic enzymes in sharing the dependence of the E. coli enzyme on nickel. The parasite enzyme showed little activity with glutathione hemithioacetal substrates but was 200-fold more active with hemithioacetals formed from the unique trypanosomatid thiol trypanothione. L. major glyoxalase I also was insensitive to glutathione derivatives that are potent inhibitors of all other characterized glyoxalase I enzymes. This substrate specificity is distinct from that of the human enzyme and is reflected in the modification in the L. major sequence of a region of the human protein that interacts with the glycyl-carboxyl moiety of glutathione, a group that is conjugated to spermidine in trypanothione. This trypanothione-dependent glyoxalase I is therefore an attractive focus for additional biochemical and genetic investigation as a possible target for rational drug design.

Investigation of metal binding and activation of Escherichia coli glyoxalase I: kinetic, thermodynamic and mutagenesis studies

GlxI (glyoxalase I) isomerizes the hemithioacetal formed between glutathione and methylglyoxal. Unlike other GlxI enzymes, Escherichia coli GlxI exhibits no activity with Zn(2+) but maximal activation with Ni(2+). To elucidate further the metal site in E. coli GlxI, several approaches were undertaken. Kinetic studies indicate that the catalytic metal ion affects the k (cat) without significantly affecting the K (m) for the substrate. Inductively coupled plasma analysis and isothermal titration calorimetry confirmed one metal ion bound to the enzyme, including Zn(2+), which produces an inactive enzyme. Isothermal titration calorimetry was utilized to determine the relative binding affinity of GlxI for various bivalent metals. Each metal ion examined bound very tightly to GlxI with an association constant ( K (a))>10(7) M(-1), with the exception of Mn(2+) ( K (a) of the order of 10(6) M(-1)). One of the ligands to the catalytic metal, His(5), was altered to glutamine, a side chain found in the Zn(2+)-active Homo sapiens GlxI. The affinity of the mutant protein for all bivalent metals was drastically decreased. However, low levels of activity were now observed for Zn(2+)-bound GlxI. Although this residue has a marked effect on metal binding and activation, it is not the sole factor determining the differential metal activation between the human and E. coli GlxI enzymes.

Improved heterologous expression of human glutathione transferase A4-4 by random silent mutagenesis of codons in the 5' region

Glutathione transferase A4-4 (GST A4-4) is involved in the detoxication of lipid peroxidation products such as alkenals. The human enzyme has been heterologously expressed in Escherichia coli, but for more extensive characterization of the enzyme the expression level had to be elevated. A clone providing up to 8-fold higher yields was created, by screening an expression library with random silent mutations in the 5' region of the cDNA encoding GST A4-4.

A stress-responsive glyoxalase I from the parasitic nematode Onchocerca volvulus

Glyoxal, methylglyoxal and other physiological alpha-oxoaldehydes are formed by the lipid peroxidation, glycation and degradation of glycolytic intermediates. They are detoxified enzymically by the glyoxalase system. To investigate the physiological function of glyoxalase I in parasitic organisms, the cDNA for glyoxalase I from the filarial nematode Onchocerca volvulus (designated Ov-GloI) has been cloned and characterized. The isolated cDNA contains an open reading frame of 579 bp encoding a protein with a calculated molecular mass of 21930 Da. Owing to the high degree of sequence identity (60%) with human glyoxalase I, for which the X-ray structure is available, it has been possible to build a three-dimensional model of Ov-GloI. The modelled core of Ov-GloI is conserved compared with the human glyoxalase I; however, there are critical differences in the residues lining the hydrophobic substrate-binding pocket of Ov-GloI. A 22 kDa protein was obtained by heterologous expression in Escherichia coli. A homogeneous enzyme preparation was obtained by affinity purification and functional characterization of the recombinant enzyme included the determination of kinetic constants for methylglyoxal and phenylglyoxal as well as inhibition studies. Gel filtration demonstrated a dimeric structure. To assess the role of Ov-GloI as a potential vaccine candidate or serodiagnostic tool, the serological reactivity of the recombinant Ov-GloI was analysed with sera from microfilaria carriers and specific IgG1 antibodies were detected. The effects of oxidative insult, namely plumbagin and xanthine/xanthine oxidase, on the gene transcript level of Ov-GloI were investigated. By using a semi-quantitative PCR ELISA it was shown that Ov-GloI is expressed at elevated levels under conditions of oxidative stress.

The human glutathione transferase P1-1 specific inhibitor TER 117 designed for overcoming cytostatic-drug resistance is also a strong inhibitor of glyoxalase I

gamma-L-Glutamyl-S-(benzyl)-L-cysteinyl-R-(-)-phenylglycine (TER 117) has previously been developed for selective inhibition of human glutathione S-transferase P1-1 (GST P1-1) based on the postulated contribution of this isoenzyme to the development of drug resistance in cancer cells. In the present investigation, the inhibitory effect of TER 117 on the human glyoxalase system was studied. Although designed as an inhibitor specific for GST P1-1, TER 117 also competitively inhibits glyoxalase I (K(I) = 0.56 microM). In contrast, no inhibition of glyoxalase II was detected. Reduced glyoxalase activity is expected to raise intracellular levels of toxic 2-oxoaldehydes otherwise eliminated by glyoxalase I. The resulting toxicity would accompany the potentiation of cytostatic drugs, caused by inhibition of the detoxication effected by GST P1-1. TER 117 was designed for efficient inhibition of the most abundant form GST P1-1/Ile105. Therefore, the inhibitory effect of TER 117 on a second allelic variant GST P1-1/Val105 was also studied. TER 117 was shown to competitively inhibit both GST P1-1 variants. The apparent K(I) values at glutathione concentrations relevant to the intracellular milieu were in the micromolar range for both enzyme forms. Extrapolation to free enzyme produced K(I) values of approximately 0.1 microM for both isoenzymes, reflecting the high affinity of GST P1-1 for the inhibitor. Thus, the allelic variation in position 105 of GST P1-1 does not affect the inhibitory potency of TER 117. The inhibitory effects of TER 117 on GST P1-1 and glyoxalase I activities may act in synergy in the cell and improve the effectiveness of chemotherapy.

Cloning and characterization of glyoxalase I from soybean

Glyoxalase I and glutathione transferase (GST) are two glutathione-dependent enzymes which are enhanced in plants during cell division and in response to diverse stress treatments. In soybean, a further connection between these two enzymes has been suggested by a clone (Accession No. X68819) resembling a GST being described as a glyoxalase I. To characterize glyoxalase I in soybean, GmGlyox I resembling the dimeric enzyme from animals has been cloned from a cDNA library prepared from soybean suspension cultures. When expressed in Escherichia coli, GmGlyox I was found to be a 38-kDa dimer composed of 21-kDa subunits and unlike the enzyme from mammals showed activity in the absence of metal ions. GmGlyox I was active toward the hemithioacetal adducts formed by reacting methylglyoxal, or phenylglyoxal, with glutathione, homoglutathione, or gamma-glutamylcysteine, showing no preference for homoglutathione adducts over glutathione adducts, even though homoglutathione is the dominant thiol in soybean. When the clone X68819 was expressed in E. coli, the respective recombinant enzyme was active as a GST rather than a glyoxalase and was termed GmGST 3. GmGST 3 was active as a homodimer (45 kDa) composed of 26-kDa subunits and showed a preference for glutathione over homoglutathione when conjugating 1-chloro-2,4-dinitrobenzene. Both enzymes are associated with cell division in soybean cultures, but GmGST 3 (0.4% total protein) was 40 times more abundant than GmGlyox I (0.01%).

Genomic sequence of human glyoxalase-I: analysis of promoter activity and its regulation

Glyoxalase-I is a glutathione-binding protein involved in the detoxification of methylglyoxal, a by-product of glycolysis. Aberrations in the expression of human glyoxalase in cancer and diabetes have been reported. To gain a better understanding of the glyoxalase-I regulation under normal physiological conditions and in disease processes, we have cloned 12kb of genomic sequence, comprising five exons, separated by four introns. A fragment comprising 982bp of 5' flanking region was used in the pSEAP reporter system to identify the minimal promoter and to locate any cis-acting functional elements. This region contained a minimal promoter between -20 and -160bp. Cells transfected with a construct containing the 5' flanking sequence exhibited a 45-fold higher activity over vector transfected cells. A twofold reproducible increase in reporter activity was seen with insulin and ZnCl(2) treatments, indicating a functionally operative insulin response element (IRE) and metal response element (MRE). Knowledge regarding the regulation of glyoxalase-I may provide insights into the importance of this enzyme in human diseases.

Identification of candidate coding region single nucleotide polymorphisms in 165 human genes using assembled expressed sequence tags

Using assembled expressed sequence tags (ESTs) from 50 different cDNA libraries, we have identified contigs that represent the complete coding sequences of 850 known human genes, and have scanned these for high quality sequence substitutions. We report the identification and characteristics of 201 candidate single nucleotide polymorphisms found in the coding sequences (cSNPs) of 165 of these genes. Using a conservative calculation, coding region nucleotide diversity (the average number of differences between any pair of chromosomes) was found to be 3 per 10,000 bp based on this data. This analysis reveals that assembled ESTs from multiple libraries may provide a rich source of comparative sequences to search for cSNPs in the human genome.

Use of silent mutations in cDNA encoding human glutathione transferase M2-2 for optimized expression in Escherichia coli

Heterologous expression of human glutathione transferase M2-2 (GST M2-2) using Escherichia coli was improved 140-fold by mutating the cDNA expressing the enzyme. Expression of GST M2-2 from this cDNA clone, pKHXhGM2, generated approximately 190 mg protein per liter of bacterial culture, corresponding to approximately 12% of the total amount of soluble protein. The high-level-expressing cDNA was generated by oligonucleotide-directed mutagenesis introducing alternative silent mutations into the third nucleotide of codons 2, 4-7, and 10-14 in the 5' end of the cDNA coding region. The choice of alternative codons was restricted to those naturally occurring in highly biased genes in E. coli. Furthermore, the wild-type TAG stop codon at the 3' end was replaced with the two stop codons TAA and TGA in tandem to increase translation termination efficiency. The resulting partially randomized cDNA library was assayed for high-level expression using immunoscreening. Sequence similarities between the constructed high-level-expressing GST M2-2 cDNA and a similarly designed cDNA encoding the closely related human GST M1-1 suggest that the codons in the region immediately following the start codon are influential in achieving high-level expression. Pyrimidines seem to be more favorable than purines in the third position of codons in optimizing the expression of these enzymes in E. coli.

Optimized heterologous expression of glutathione reductase from Cyanobacterium anabaena PCC 7120 and characterization of the recombinant protein

Glutathione reductase (GR) from the cyanobacterium Anabaena PCC 7120 was heterologously expressed in Escherichia coli SG5. Silent random mutations were introduced in the 5' region of DNA encoding the enzyme in order to generate a high-level expression clone. To maximize protein expression, the culture conditions were also optimized. In the high-level expression clones selected, E. coli-preferred codons were selectively used at certain positions. Under the optimal expression conditions, a yield of 17 mg recombinant protein per liter was obtained, which is about 10-fold higher than that of the wild-type enzyme. A hexahistidine tag was added at the C-terminal of the protein in order to allow IMAC affinity purification. This strategy simplified the purification process and provided a homogeneous enzyme for functional characterization. Anabaena GR uses NADPH as a coenzyme, like most of the GRs from other sources, but the KM values for NADPH and GSSG are higher than those of enzymes previously studied. The Anabaena enzyme also shows significant activity when NADH is used as a reductant.

Glyoxalase I from Brassica juncea: molecular cloning, regulation and its over-expression confer tolerance in transgenic tobacco under stress

Despite its ubiquitous presence, the role of glyoxalase I has not been well investigated in plants. In order to find out its physiological functions, we have cloned and characterized a cDNA from Brassica juncea encoding glyoxalase I (Gly I) and made transgenic tobacco plants harbouring Gly I in both sense and antisense orientation. The transgenic nature of the plants was confirmed by Southern blotting, and the estimated number of genes inserted ranged from one to six. The transcript and protein levels of glyoxalase I were also monitored in transgenic plants. The expression of glyoxalase I in B. juncea was upregulated in response to salt, water and heavy metal stresses. In response to a high concentration of salt, the transcript level averaged threefold higher in 72 h, and an increase in the protein was also seen by immunoblotting. The transgenic plants over-expressing glyoxalase I showed significant tolerance to methylglyoxal and high salt, as tested in detached leaf disc senescence assay. A comparison of plants expressing high and low levels of glyoxalase I showed that the tolerance to different salt concentrations was correlated with the degree of glyoxalase I expression. Our results suggest an important role of glyoxalase I in conferring tolerance to plants under stress conditions.

Involvement of an active-site Zn2+ ligand in the catalytic mechanism of human glyoxalase I

The Zn2+ ligands glutamate 99 and glutamate 172 in the active site of human glyoxalase I were replaced, each in turn, by glutamines by site-directed mutagenesis to elucidate their potential significance for the catalytic properties of the enzyme. To compensate for the loss of the charged amino acid residue, another of the metal ligands, glutamine 33, was simultaneously mutated into glutamate. The double mutants and the single mutants Q33E, E99Q, and E172Q were expressed in Escherichia coli, purified on an S-hexylglutathione matrix, and characterized. Metal analysis demonstrated that mutant Q33E/E172Q contained 1.0 mol of zinc/mol of enzyme subunit, whereas mutant Q33E/E99Q contained only 0.3 mol of zinc/mol of subunit. No catalytic activity could be detected with the double mutant Q33E/E172Q (<10(-8) of the wild-type activity). The second double mutant Q33E/E99Q had 1.5% of the specific activity of the wild-type enzyme, whereas the values for mutants Q33E and E99Q were 1.3 and 0. 1%, respectively; the E172Q mutant had less than 10(-5) times the specific activity of the wild-type. The crystal structure of the catalytically inactive double mutant Q33E/E172Q demonstrated that Zn2+ was bound without any gross changes or perturbations. The results suggest that the metal ligand glutamate 172 is directly involved in the catalytic mechanism of the enzyme, presumably serving as the base that abstracts a proton from the hemithioacetal substrate.

Mutagenesis of residue 157 in the active site of human glyoxalase I

Met-157 in the active site of human glyoxalase I was changed by site-directed mutagenesis into alanine, glutamine or histidine in order to evaluate its possible role in catalysis. The glyoxalase I mutants were expressed in Escherichia coli and purified on an S-hexylglutathione affinity gel. The physicochemical properties of the mutant proteins were similar to those of the wild-type enzyme. The glutamine mutant exhibited the same high specific activity as wild-type glyoxalase I, whereas the alanine and histidine mutants had approx. 20% of wild-type activity. The kcat/Km values of the mutant glyoxalase I determined with the hemithioacetal adduct of glutathione and methylglyoxal were reduced to between 10 and 40% of the wild-type value. This reduction was due to lower kcat values for the alanine and histidine mutants and a twofold increase in the Km value for the glutamine mutant. With the hemithioacetal of glutathione and phenylglyoxal, the kinetic parameters of the mutants were also of the same magnitude as those of wild-type glyoxalase I. Studies with the competitive inhibitors S-hexyl- and S-benzyl-glutathione revealed that the affinity was reduced to 7-11% of the wild-type affinity for the glutamine and alanine mutants and to 30-40% for the histidine mutant, as measured by a comparison of Ki values. The results show that Met-157 has no direct role in catalysis, but is rather involved in forming the substrate-binding site of human glyoxalase I. The high activity of the glutamine mutant suggests that a structurally equivalent glutamine residue in the N-terminal half of Saccharomyces cerevisiae glyoxalase I may be part of a catalytically competent active site.

Crystal structure of human glyoxalase I--evidence for gene duplication and 3D domain swapping

The zinc metalloenzyme glyoxalase I catalyses the glutathione-dependent inactivation of toxic methylglyoxal. The structure of the dimeric human enzyme in complex with S-benzyl-glutathione has been determined by multiple isomorphous replacement (MIR) and refined at 2.2 A resolution. Each monomer consists of two domains. Despite only low sequence homology between them, these domains are structurally equivalent and appear to have arisen by a gene duplication. On the other hand, there is no structural homology to the 'glutathione binding domain' found in other glutathione-linked proteins. 3D domain swapping of the N- and C-terminal domains has resulted in the active site being situated in the dimer interface, with the inhibitor and essential zinc ion interacting with side chains from both subunits. Two structurally equivalent residues from each domain contribute to a square pyramidal coordination of the zinc ion, rarely seen in zinc enzymes. Comparison of glyoxalase I with other known structures shows the enzyme to belong to a new structural family which includes the Fe2+-dependent dihydroxybiphenyl dioxygenase and the bleomycin resistance protein. This structural family appears to allow members to form with or without domain swapping.

Molecular cloning and characterization of the thiolesterase glyoxalase II from Arabidopsis thaliana

cDNA encoding glyoxalase II from Arabidopsis thaliana has been cloned and sequenced. The isolated 894 bp segment included a sequence of 774 bp encoding a protein with a calculated molecular mass of 28,791 Da. The amino acid sequence deduced from the A. thaliana cDNA showed 54% identity with that of the human enzyme. Searches in databanks identified seven additional DNA sequences from different species with high similarity to glyoxalase II. Certain limited regions, one rich in histidine residues, shared 100% identity. A 29 kDa protein with an isoelectric point of 6.2 was obtained by heterologous expression of the A. thaliana cDNA in Escherichia coli. Homogeneous enzyme was obtained by affinity purification and its catalytic parameters with thiolesters of glutathione were similar to those for human glyoxalase II. The structural and functional similarities between glyoxalase II from A. thaliana and from human tissues suggest a common evolutionary origin.

Isolation and sequencing of a gene coding for glyoxalase I activity from Salmonella typhimurium and comparison with other glyoxalase I sequences

The glyoxalase I gene (gloA) from Salmonella typhimurium has been isolated in Escherichia coli on a multi-copy pBR322-derived plasmid, selecting for resistance to 3 mM methylglyoxal on Luria-Bertani agar. The region of the plasmid which confers the methylglyoxal resistance in E. coli was sequenced. The deduced protein sequence was compared to the known sequences of the Homo sapiens and Pseudomonas putida glyoxalase I (GlxI) enzymes, and regions of strong homology were used to probe the National Center for Biotechnology Information protein database. This search identified several previously known glyoxalase I sequences and other open reading frames with unassigned function. The clustal alignments of the sequences are presented, indicating possible Zn2+ ligands and active site regions. In addition, the S. typhimurium sequence aligns with both the N-terminal half and the C-terminal half of the proposed GlxI sequences from Saccharomyces cerevisiae and Schizosaccharomyces pombe, suggesting that the structures of the yeast enzymes are those of fused dimers.