The metal ion requirements of Arabidopsis thaliana Glx2-2 for catalytic activity

Glyoxalase 2: Towards a Broader View of the Second Player of the Glyoxalase System

Glyoxalase 2 is a mitochondrial and cytoplasmic protein belonging to the metallo-β-lactamase family encoded by the hydroxyacylglutathione hydrolase (HAGH) gene. This enzyme is the second enzyme of the glyoxalase system that is responsible for detoxification of the α-ketothaldehyde methylglyoxal in cells. The two enzymes glyoxalase 1 (Glo1) and glyoxalase 2 (Glo2) form the complete glyoxalase pathway, which utilizes glutathione as cofactor in eukaryotic cells. The importance of Glo2 is highlighted by its ubiquitous distribution in prokaryotic and eukaryotic organisms. Its function in the system has been well defined, but in recent years, additional roles are emerging, especially those related to oxidative stress. This review focuses on Glo2 by considering its genetics, molecular and structural properties, its involvement in post-translational modifications and its interaction with specific metabolic pathways. The purpose of this review is to focus attention on an enzyme that, from the most recent studies, appears to play a role in multiple regulatory pathways that may be important in certain diseases such as cancer or oxidative stress-related diseases.

De novo transcriptome analysis of Rhizophora mucronata Lam. furnishes evidence for the existence of glyoxalase system correlated to glutathione metabolic enzymes and glutathione regulated transporter in salt tolerant mangroves

The accumulation of a metabolic by product - methylglyoxal above a minimal range can be highly toxic in all organisms. Stress induced elevation in methylglyoxal inactivates proteins and nucleic acids. Glutathione dependent glyoxalase enzymes like glyoxalase I and glyoxalase II together with glutathione independent glyoxalase III play inevitable role in methylglyoxal detoxification. Glyoxalase genes are generally conserved but with obvious exceptions. Mangroves being potent harsh land inhabitants, their internal organelles are constantly been exposed to elevated levels of methylglyoxal. First and foremost it is important to detect the presence of glyoxalases in mangroves. De novo transcriptome analysis of mangrove species Rhizophora mucronata Lam., identified eleven putative glyoxalase proteins (RmGLYI-1 to 5, RmGLYII-1 to 5 and RmGLYIII). Molecular characterization proposed PLN02300 or PLN02367 as the key domains of RmGLYI proteins. They possess molecular weight ranging from 26.45 to 32.53 kDa and may localize in cytosol or chloroplast. RmGLYII proteins of molecular weight 28.64-36 kDa, carrying PLN02398 or PLN02469 domains are expected to be localized in diverse cellular compartments. Cytosolic RmGLYIII with DJ-1/PfpI domain carries a molecular weight 26.4 kDa. Detailed structural analysis revealed monomeric nature of RmGLYI-1 and RmGLYII-1 whereas RmGLYIII is found to be homodimer. Molecular phylogenetic analysis and multiple sequence alignment specified conserved metal ion/substrate binding residues of RmGLY proteins. Estimation of relative expression of glyoxalases under salt stress indicated the prominence of RmGLYI and RmGLYII over RmGLYIII. The aforementioned prominence is supported by salt induced expression difference of glutathione metabolic enzymes and glutathione regulated transporter protein.

Structure, function, and regulation of thioesterases

Thioesterases are present in all living cells and perform a wide range of important biological functions by catalysing the cleavage of thioester bonds present in a diverse array of cellular substrates. Thioesterases are organised into 25 families based on their sequence conservation, tertiary and quaternary structure, active site configuration, and substrate specificity. Recent structural and functional characterisation of thioesterases has led to significant changes in our understanding of the regulatory mechanisms that govern enzyme activity and their respective cellular roles. The resulting dogma changes in thioesterase regulation include mechanistic insights into ATP and GDP-mediated regulation by oligomerisation, the role of new key regulatory regions, and new insights into a conserved quaternary structure within TE4 family members. Here we provide a current and comparative snapshot of our understanding of thioesterase structure, function, and regulation across the different thioesterase families.

Genome-wide analysis of glyoxalase-like gene families in grape (Vitis vinifera L.) and their expression profiling in response to downy mildew infection

BACKGROUND

The glyoxalase system usually comprises two enzymes, glyoxalase I (GLYI) and glyoxalase II (GLYII). This system converts cytotoxic methylglyoxal (MG) into non-toxic D-lactate in the presence of reduced glutathione (GSH) in two enzymatic steps. Recently, a novel type of glyoxalase III (GLYIII) activity has observed in Escherichia coli that can detoxify MG into D-lactate directly, in one step, without a cofactor. Investigation of the glyoxalase enzymes of a number of plant species shows the importance of their roles in response both to abiotic and to biotic stresses. Until now, glyoxalase gene families have been identified in the genomes of four plants, Arabidopsis, Oryza sativa, Glycine max and Medicago truncatula but no similar study has been done with the grapevine Vitis vinifera L.

RESULTS

In this study, four GLYI-like, two GLYII-like and three GLYIII-like genes are identified from the genome database of grape. All these genes were analysed in detail, including their chromosomal locations, phylogenetic relationships, exon-intron distributions, protein domain organisations and the presence of conserved binding sites. Using quantitative real-time PCR analysis (qRT-PCR), the expression profiles of these genes were analysed in different tissues of grape, and also when under infection stress from downy mildew (Plasmopara viticola). The study reveals that most VvGLY-like genes had higher expressions in stem, leaf, tendril and ovule but lower expressions in the flower. In addition, most of the VvGLY-like gene members were P. viticola responsive with high expressions 6-12 h and 96-120 h after inoculation. However, VvGLYI-like1 was highly expressed 48 h after inoculation, similar to VvPR1 and VvNPR1 which are involved in the defence response.

CONCLUSIONS

This study identified the GLYI-like, GLYII-like and GLYIII-like full gene families of the grapevine. Based on a phylogenetic analysis and the presence of conserved binding sites, we speculate that these glyoxalase-like genes in grape encode active glyoxalases. Moreover, our study provides a basis for discussing the roles of VvGLYI-like, VvGLYII-like and VvGLYIII-like genes in grape's response to downy mildew infection. Our results shed light on the selection of candidate genes for downy mildew tolerance in grape and lay the foundation for further functional investigations of these glyoxalase genes.

Glyoxalase Goes Green: The Expanding Roles of Glyoxalase in Plants

The ubiquitous glyoxalase enzymatic pathway is involved in the detoxification of methylglyoxal (MG), a cytotoxic byproduct of glycolysis. The glyoxalase system has been more extensively studied in animals versus plants. Plant glyoxalases have been primarily associated with stress responses and their overexpression is known to impart tolerance to various abiotic stresses. In plants, glyoxalases exist as multigene families, and new roles for glyoxalases in various developmental and signaling pathways have started to emerge. Glyoxalase-based MG detoxification has now been shown to be important for pollination responses. During self-incompatibility response in Brassicaceae, MG is required to target compatibility factors for proteasomal degradation, while accumulation of glyoxalase leads to MG detoxification and efficient pollination. In this review, we discuss the importance of glyoxalase systems and their emerging biological roles in plants.

Characteristic Variations and Similarities in Biochemical, Molecular, and Functional Properties of Glyoxalases across Prokaryotes and Eukaryotes

The glyoxalase system is the ubiquitous pathway for the detoxification of methylglyoxal (MG) in the biological systems. It comprises two enzymes, glyoxalase I (GLYI) and glyoxalase II (GLYII), which act sequentially to convert MG into d-lactate, thereby helping living systems get rid of this otherwise cytotoxic byproduct of metabolism. In addition, a glutathione-independent GLYIII enzyme activity also exists in the biological systems that can directly convert MG to d-lactate. Humans and Escherichia coli possess a single copy of GLYI (encoding either the Ni- or Zn-dependent form) and GLYII genes, which through MG detoxification provide protection against various pathological and disease conditions. By contrast, the plant genome possesses multiple GLYI and GLYII genes with a role in abiotic stress tolerance. Plants possess both Ni²⁺- and Zn²⁺-dependent forms of GLYI, and studies on plant glyoxalases reveal the various unique features of these enzymes distinguishing them from prokaryotic and other eukaryotic glyoxalases. Through this review, we provide an overview of the plant glyoxalase family along with a comparative analysis of glyoxalases across various species, highlighting similarities as well as differences in the biochemical, molecular, and physiological properties of these enzymes. We believe that the evolution of multiple glyoxalases isoforms in plants is an important component of their robust defense strategies.

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.

Activation of Escherichia coli UDP-3-O-[(R)-3-hydroxymyristoyl]-N-acetylglucosamine deacetylase by Fe2+ yields a more efficient enzyme with altered ligand affinity

The metal-dependent deacetylase UDP-3-O-[(R)-3-hydroxymyristoyl]-N-acetylglucosamine deacetylase (LpxC) catalyzes the first committed step in lipid A biosynthesis, the hydrolysis of UDP-3-O-myristoyl-N-acetylglucosamine to form UDP-3-O-myristoylglucosamine and acetate. Consequently, LpxC is a target for the development of antibiotics, nearly all of which coordinate the active site metal ion. Here we examine the ability of Fe(2+) to serve as a cofactor for wild-type Escherichia coli LpxC and a mutant enzyme (EcC63A), in which one of the ligands for the inhibitory metal binding site has been removed. LpxC exhibits higher activity (6-8-fold) with a single bound Fe(2+) as the cofactor compared to Zn(2+)-LpxC; both metalloenzymes have a bell-shaped dependence on pH with similar pK(a) values, indicating that at least two ionizations are important for maximal activity. X-ray absorption spectroscopy experiments suggest that the catalytic metal ion bound to Fe(2+)-EcLpxC is five-coordinate, suggesting that catalytic activity may correlate with coordination number. Furthermore, the ligand affinity of Fe(2+)-LpxC compared to the Zn(2+) enzyme is altered by up to 6-fold. In contrast to Zn(2+)-LpxC, the activity of Fe(2+)-LpxC is redox-sensitive, and a time-dependent decrease in activity is observed under aerobic conditions. The LpxC activity of crude E. coli cell lysates is also aerobically sensitive, consistent with the presence of Fe(2+)-LpxC. These data indicate that EcLpxC can use either Fe(2+) or Zn(2+) to activate catalysis in vitro and possibly in vivo, which may allow LpxC to function in E. coli grown under different environmental conditions.