Structure and chromosomal localization of human and mouse genes for hematopoietic prostaglandin D synthase. Conservation of the ancestral genomic structure of sigma-class glutathione S-transferase

15d-PGJ2: the anti-inflammatory prostaglandin?

15-Deoxy-Delta-12,14-prostaglandin J2 (15d-PGJ2) is the most recently discovered prostaglandin. This cyclopentanone, the dehydration end product of PGD2, differs from other prostaglandins in several respects. There is no specific prostaglandin synthase (PGS) leading to 15d-PGJ2 production and no specific 15d-PGJ2 receptor has been identified to date. Instead, 15d-PGJ2 has been shown to act via PGD2 receptors (DP1 and DP2) and through interaction with intracellular targets. In particular, 15d-PGJ2 is recognized as the endogenous ligand for the intranuclear receptor PPARgamma. This property is responsible for many of the 15d-PGJ2 anti-inflammatory functions. In this review, we summarize the current understanding of 15d-PGJ2 synthesis, biology and main effects both in molecular physiology and pathological states.

Prostaglandins in non-insectan invertebrates: recent insights and unsolved problems

Prostaglandins (PG) are oxygenated derivatives of C20 polyunsaturated fatty acids including arachidonic and eicosapentaenoic acids. In mammals, these compounds have been shown to play key roles in haemostasis, sleep-wake regulation, smooth muscle tone, and vaso-, temperature and immune regulation. In invertebrates, PGs have been reported to perform similar roles and are involved in the control of oogenesis and spermatogenesis, ion transport and defence. Although there is often a detailed understanding of the actions of these compounds in invertebrates such as insects, knowledge of their mechanism of biosynthesis is often lacking. This account provides a critical review of our current knowledge on the structure and modes of biosynthesis of PGs in invertebrates, with particular reference to aquatic invertebrates. It emphasises some of the most recent findings, which suggest that some PGs have been misidentified.

Prostaglandins in invertebrates can be categorised into two main types; the classical forms, such as PGE2 and PGD2 that are found in mammals, and novel forms including clavulones, bromo- and iodo-vulones and various PGA2 and PGE2 esters. A significant number of reports of PG identification in invertebrates have relied upon methods such as enzyme immunoassay that do not have the necessary specificity to ensure the validity of the identification. For example, in the barnacle Balanus amphitrite, although there are PG-like compounds that bind to antibodies raised against PGE2, mass spectrometric analysis failed to confirm the presence of this and other classical PGs. Therefore, care should be taken in drawing conclusions about what PGs are formed in invertebrates without employing appropriate analytical methods. Finally, the recent publication of the Ciona genome should facilitate studies on the nature and mode of biosynthesis of PGs in this advanced deuterostomate invertebrate.

Gene and Protein Characterization of the Human Glutathione S-Transferase Kappa and Evidence for a Peroxisomal Localization

Kappa class glutathione S-transferase (GST) cDNA sequences have been identified in rat, mouse, and human. In the present study, we determined the structure and chromosomal location of the human GST Kappa 1 (hGSTK1) gene, characterized the protein, and demonstrated its subcellular localization. The human gene spans approximately 5 kb, has 8 exons, and maps onto chromosome 7q34. The 5'-flanking region lacks TATA or CCAAT boxes, but there is an initiator element overlapping the transcription start site. hGSTK1 amino acid sequence showed homology to bacterial 2-hydroxychromene-2-carboxylate isomerase, an enzyme involved in naphthalene degradation pathway. hGSTK1 mRNA was expressed in all of the organs examined. Subcellular fractionation of HepG2 cells showed that the protein was located in peroxisomes and mitochondria and was not detectable in cytoplasm. The peroxisomal localization was confirmed by transfection of HepG2 cells with a plasmid coding a green fluorescent protein fused inframe to the N terminus of hGSTK1. The C terminus of hGSTK1 was essential for localization of the protein to peroxisomes, and the C-terminal sequence Ala-Arg-Leu represents a peroxisome targeting signal. This is the first time that a human GST has been found in peroxisomes, suggesting a new function for this family of enzymes.

Prostaglandin synthases: recent developments and a novel hypothesis

Cells are continuously exposed to cues, which signal cell survival or death. Fine-tuning of these conflicting signals is essential for tissue development and homeostasis, and defective pathways are linked to many disease processes, especially cancer. It is well established that prostaglandins (PGs), as signalling molecules, are important regulators of cell proliferation, differentiation and apoptosis. PG production has been a focus of many researchers interested in the mechanisms of parturition. Previously, investigators have focussed on the committed step of PG biosynthesis, the conversion by prostaglandin H synthase (PGHS; also termed cyclo-oxygenase, COX) of arachidonic acid (AA) (substrate) to PGH2, the common precursor for biosynthesis of the various prostanoids. However, recently the genes encoding the terminal synthase enzymes involved in converting PGH2 to each of the bioactive PGs, including the major uterotonic PGs, PGE2 (PGE synthase) and PGF2alpha (PGF synthase), have been cloned and characterized. This review highlights how the regulation of the expression and balance of key enzymes can produce, from a single precursor, prostanoids with varied and often opposing effects.

[Functional analyses of lipocalin-type and hematopoietic prostaglandin D synthases]

Prostaglandin (PG) D synthase (PGDS) catalyzes the isomerization of PGH(2) to PGD(2), which acts as an endogenous somnogen and an allergic mediator. There are two distinct types of PGDS: one is lipocalin-type PGDS (L-PGDS) localized in the central nervous system, male genitals, and heart; and the other is hematopoietic PGDS (H-PGDS) in mast cells and Th2 lymphocytes. L-PGDS is the same as beta-trace, a major protein in human cerebrospinal fluid, and is also secreted into the seminal plasma and plasma. The L-PGDS concentration in various body fluids is useful as a marker for various diseases such as renal failure and coronary atherosclerosis. H-PGDS is a cytosolic enzyme and is a member of the Sigma class of glutathione S-transferase. We determined the X-ray crystallographic structures of H-PGDS and L-PGDS. We also generated the gene-knockout (KO) mice and the human enzyme-overexpressing transgenic mice for each PGDS. L-PGDS-KO mice lacked PGE(2)-induced tactile allodynia and rebound of non-rapid eye movement sleep after sleep deprivation. Human L-PGDS-overexpressing transgenic mice showed an increase in non-rapid eye movement sleep due to accumulation of PGD(2) in the brain after tail clipping. H-PGDS-KO mice showed an allergic reaction weaker than that of the wild-type mice.

Sigma-class glutathione transferase from Xenopus laevis: molecular cloning, expression, and site-directed mutagenesis

The structural gene for glutathione transferase (XlGSTS1-1) in the amphibia Xenopus laevis has been cloned from an embryo library and its nucleotide sequence has been determined. Open reading frame analysis indicated that xlgsts1 gene encodes the smallest protein of sigma class GST so far identified as being composed of only 194 amino acid residues. The recombinant XlGSTS1-1 shows a narrow range of substrate specificity as well as a significantly lower 1-chloro-2,4-dinitrobenzene conjugation capacity than that of squid sigma class GST. To compare the structural and functional differences between the squid and amphibian enzymes, several site-specific mutations were introduced in XlGSTS1-1, i.e., Ser100Asn, Phe102Tyr, Trp143Leu, Phe146Leu, and Trp148Cys. The results obtained indicate that Trp143 and Trp148 are more important determinants for the structural stability of XlGSTS1-1 rather than for its substrate specificity.

Hematopoietic prostaglandin D synthase

The biological actions of prostaglandin (PG) D(2) include vasodilatation, bronchoconstriction, inhibition of platelet aggregation, and recruitment of inflammatory cells. Characterization of DP receptor null mice in which antigen-induced airway and inflammatory responses are attenuated and identification of CRTH2 as a novel PGD(2) receptor have shed light on the role of PGD(2) in the immune and inflammatory responses. Hematopoietic PGD synthase (H-PGDS) is a cytosolic enzyme that isomerizes PGH(2), a common precursor for all PGs and thromboxanes, to PGD(2) in a glutathione-dependent manner. H-PGDS is expressed in mast cells, antigen-presenting cells, and Th2 cells, and is the only mammalian member of the Sigma class of cytosolic glutathione S-transferases. In this review, we focus on the molecular biology of H-PGDS, the determination of its three-dimensional structure, characterization of the regulation of its gene expression, and information gleaned from transgenic animals.

Biochemical and genetic characterization of a murine class Kappa glutathione S-transferase

The class Kappa family of glutathione S-transferases (GSTs) currently comprises a single rat subunit (rGSTK1), originally isolated from the matrix of liver mitochondria [Harris, Meyer, Coles and Ketterer (1991) Biochem. J. 278, 137-141; Pemble, Wardle and Taylor (1996) Biochem. J. 319, 749-754]. In the present study, an expressed sequence tag (EST) clone has been identified which encodes a mouse class Kappa GST (designated mGSTK1). The EST clone contains an open reading frame of 678 bp, encoding a protein composed of 226 amino acid residues with 86% sequence identity with the rGSTK1 polypeptide. The mGSTK1 and rGSTK1 proteins have been heterologously expressed in Escherichia coli and purified by affinity chromatography. Both mouse and rat transferases were found to exhibit GSH-conjugating and GSH-peroxidase activities towards model substrates. Analysis of expression levels in a range of mouse and rat tissues revealed that the mRNA encoding these enzymes is expressed predominantly in heart, kidney, liver and skeletal muscle. Although other soluble GST isoenzymes are believed to reside primarily within the cytosol, subcellular fractionation of mouse liver demonstrates that this novel murine class Kappa GST is associated with mitochondrial fractions. Through the use of bioinformatics, the genes encoding the mouse and rat class Kappa GSTs have been identified. Both genes comprise eight exons, the protein coding region of which spans approx. 4.3 kb and 4.1 kb of DNA for mGSTK1 and rGSTK1 respectively. This conservation in primary structure, catalytic properties, tissue-specific expression, subcellular localization and gene structure between mouse and rat class Kappa GSTs indicates that they perform similar physiological functions. Furthermore, the association of these enzymes with mitochondrial fractions is consistent with them performing a specific conserved biological role within this organelle.

Mechanism of metal activation of human hematopoietic prostaglandin D synthase

Here we report the crystal structures of human hematopoietic prostaglandin (PG) D synthase bound to glutathione (GSH) and Ca2+ or Mg2+. Using GSH as a cofactor, prostaglandin D synthase catalyzes the isomerization of PGH2 to PGD2, a mediator for allergy response. The enzyme is a homodimer, and Ca2+ or Mg2+ increases its activity to approximately 150% of the basal level, with half maximum effective concentrations of 400 microM for Ca2+ and 50 microM for Mg2+. In the Mg2+-bound form, the ion is octahedrally coordinated by six water molecules at the dimer interface. The water molecules are surrounded by pairs of Asp93, Asp96 and Asp97 from each subunit. Ca(2+) is coordinated by five water molecules and an Asp96 from one subunit. The Asp96 residue in the Ca2+-bound form makes hydrogen bonds with two guanidium nitrogen atoms of Arg14 in the GSH-binding pocket. Mg2+ alters the coordinating water structure and reduces one hydrogen bond between Asp96 and Arg14, thereby changing the interaction between Arg14 and GSH. This effect explains a four-fold reduction in the K(m) of the enzyme for GSH. The structure provides insights into how Ca2+ or Mg2+ binding activates human hematopoietic PGD synthase.

Cytokines, prostaglandins and parturition--a review

The elaboration of cytokines, chemokines and immunomodulatory proteins in the placenta and gestational membranes has been extensively investigated in the context of both normal and abnormal pregnancy and delivery. Patterns of expression of cytokines in the foetal membranes and decidua suggest that inflammatory activation occurs modestly with term labour, but much more robustly in preterm delivery, particularly in the presence of intrauterine infection. Enhanced chemokine expression, particularly evident in deliveries with an infected amniotic cavity, is presumably responsible for recruiting infiltrating leukocytes into the membranes thereby amplifying the inflammatory process and hastening membrane rupture and delivery. Anti-inflammatory cytokines suppress inflammatory reactions in the placenta, but under some circumstances may act in a pro-inflammatory fashion in the membranes. Intracellular signalling by cytokines is modulated by proteins such as SOCS (Silencer Of Cytokine Signalling)-1, -2 and -3. Changes in the abundance of these proteins occur with term labour, implicating them as modulators of cytokine actions around the time of parturition. Prostaglandins, released by the membranes in response to stretch and the actions of pro-inflammatory cytokines, act not only upon the myometrium and cervix, but may also exert paracrine/autocrine effects on cell viability and matrix protein integrity. The localization and regulation of prostanoid isomerases, responsible for converting PGH(2) (derived from prostaglandin H synthase-1 and -2) to bioactive prostanoids, are being studied in these tissues, particularly in the context of cytokine interactions. Although the gestational tissues are known to be sources of PGD(2), PGJ(2) and its derivatives, the regulation of production of these prostaglandins has yet to be studied in any detail and their actions, which may include apoptosis and suppression of inflammation, remain poorly defined. A more complete understanding of these aspects of cytokine-prostaglandin interactions in pregnancy and parturition will, no doubt, unfold as current studies come to fruition.

Structure of a Drosophila sigma class glutathione S-transferase reveals a novel active site topography suited for lipid peroxidation products

Insect glutathione-S-transferases (GSTs) are grouped in three classes, I, II and recently III; class I (Delta class) enzymes together with class III members are implicated in conferring resistance to insecticides. Class II (Sigma class) GSTs, however, are poorly characterized and their exact biological function remains elusive. Drosophila glutathione S-transferase-2 (GST-2) (DmGSTS1-1) is a class II enzyme previously found associated specifically with the insect indirect flight muscle. It was recently shown that GST-2 exhibits considerable conjugation activity for 4-hydroxynonenal (4-HNE), a lipid peroxidation product, raising the possibility that it has a major anti-oxidant role in the flight muscle. Here, we report the crystal structure of GST-2 at 1.75A resolution. The GST-2 dimer shows the canonical GST fold with glutathione (GSH) ordered in only one of the two binding sites. While the GSH-binding mode is similar to other GST structures, a distinct orientation of helix alpha6 creates a novel electrophilic substrate-binding site (H-site) topography, largely flat and without a prominent hydrophobic-binding pocket, which characterizes the H-sites of other GSTs. The H-site displays directionality in the distribution of charged/polar and hydrophobic residues creating a binding surface that explains the selectivity for amphipolar peroxidation products, with the polar-binding region formed by residues Y208, Y153 and R145 and the hydrophobic-binding region by residues V57, A59, Y211 and the C-terminal V249. A structure-based model of 4-HNE binding is presented. The model suggest that residues Y208, R145 and possibly Y153 may be key residues involved in catalysis.

Prostaglandin D2 synthase enzymes and PPARgamma are co-expressed in mouse 3T3-L1 adipocytes and human tissues

Peroxisome proliferator-activated receptor gamma (PPARgamma) is a critical regulator of adipocyte differentiation. Whilst 15-deoxy-delta(12,14)-prostaglandin J2 (15-d-PGJ2) has been identified as a putative endogenous ligand for this transcription factor, it is unclear whether the enzymes necessary for 15-d-PGJ2 biosynthesis are co-expressed with PPARgamma. Prostaglandin D2 synthase (PGDS) enzymes represent the terminal enzymatic components responsible for 15-d-PGJ2 production. Both glutathione (GSH)-dependent and GSH-independent PGDS isoenzymes exist. We have, therefore, examined the expression of PGDS isoenzymes in mouse 3T3-L1 adipocytes, and various human tissues. The GSH-independent PGDS was found to be expressed in 3T3-L1 cells both before and after their differentiation into adipocytes. By contrast, we were unable to detect expression of the GSH-dependent PGDS at any stage during the adipose conversion of 3T3-L1 cells. Quantitative analysis of mRNA levels for PPARgamma and each PGDS isoenzyme revealed their co-expression in a number of human tissues and cell types, including adipose tissue, placenta, prostate, and macrophages. These data reveal the potential for de novo 15-d-PGJ2 synthesis in the context of PPARgamma expression, suggesting that this prostaglandin may contribute to PPARgamma signalling in vivo.

Metabolism of the endocannabinoids, 2-arachidonylglycerol and anandamide, into prostaglandin, thromboxane, and prostacyclin glycerol esters and ethanolamides

Cyclooxygenase-2 (COX-2) action on the endocannabinoids, 2-arachidonylglycerol (2-AG) and anandamide (AEA), generates prostaglandin glycerol esters (PG-G) and ethanolamides (PG-EA), respectively. The diversity of PG-Gs and PG-EAs that can be formed enzymatically following COX-2 oxygenation of endocannabinoids was examined in cellular and subcellular systems. In cellular systems, glycerol esters and ethanolamides of PGE(2), PGD(2), and PGF(2alpha) were major products of the endocannabinoid-derived COX-2 products, PGH(2)-G and PGH(2)-EA. The sequential action of purified COX-2 and thromboxane synthase on AEA and 2-AG provided thromboxane A(2) ethanolamide and glycerol ester, respectively. Similarly, bovine prostacyclin synthase catalyzed the isomerization of the intermediate endoperoxides, PGH(2)-G and PGH(2)-EA, to the corresponding prostacyclin derivatives. Quantification of the efficiency of prostaglandin and thromboxane synthase-directed endoperoxide isomerization demonstrated that PGE, PGD, and PGI synthases catalyze the isomerization of PGH(2)-G at rates approaching those observed with PGH(2). In contrast, thromboxane synthase was far more efficient at catalyzing PGH(2) isomerization than at catalyzing the isomerization of PGH(2)-G. These results define the in vitro diversity of endocannabinoid-derived prostanoids and will permit focused investigations into their production and potential biological actions in vivo.

Lipocalin-type and hematopoietic prostaglandin D synthases as a novel example of functional convergence

Prostaglandin (PG) D2 is a major PG produced in the central nervous system and is involved in the regulation of sleep and pain responses through DP receptors. It is also actively produced by mast cells, basophils, and Th2 cells, acting as an allergic mediator through DP and CRTH2 receptors. PGD2 is further dehydrated to produce PGJ2, delta12-PGJ2, and 15-deoxy-delta(12,14)-PGJ2, the last being a ligand for the nuclear receptor PPARgamma. PGD synthase (PGDS) catalyzes the isomerization of PGH2 to PGD2 in the presence of sulfhydryl compounds. Two distinct types of PGDS have been identified: one is the lipocalin-type PGDS (L-PGDS); and the other, the hematopoietic PGDS (H-PGDS). We isolated the human and mouse cDNAs and genes for L-PGDS and H-PGDS, determined their X-ray crystallographic structures, examined their tissue distribution profiles and cellular localization, and generated gene-knockout mice and human enzyme-overexpressing transgenic mice. L-PGDS and H-PGDS are quite different from each other, in terms of their amino acid sequence, tertiary structure, evolutional origin, chromosomal and cellular localization, tissue distribution, and also functional relevance. Therefore, L-PGDS and H-PGDS are considered to be a novel example of functional convergence.

The human glutathione transferase alpha locus: genomic organization of the gene cluster and functional characterization of the genetic polymorphism in the hGSTA1 promoter

By searching the human genome sequence database with human hGSTA1 and hGSTA4 cDNA sequences, we identified three PAC and one BAC clones covering more than 400 kilobases and containing the entire GST alpha gene cluster. The cluster consists of five genes: hGSTA1, hGSTA2, hGSTA3, hGSTA4 and hGSTA5, and seven pseudogenes that are distinguished as such by single-base and/or complete exon deletions. Using gene-specific probes we demonstrated that hGSTA1, hGSTA2 and hGSTA4 mRNAs are widely expressed in human tissues, whereas hGSTA3 mRNA appears to be a rare message subject to splicing defects. Although examination of the hGSTA5 gene sequence suggests that it is a functional gene, hGSTA5 mRNA could not be detected in human tissues we studied. hGSTA1 expression has been shown to be influenced by a genetic polymorphism, that consists of two alleles hGSTA1*A and hGSTA1*B, containing three linked base substitutions in the proximal promoter, at positions -567, -69 and -52. Constructs consisting of the luciferase gene controlled by variant hGSTA1 promoters showed differential expression when transfected into HepG2, GLC4 and Caco-2 cells: hGSTA1*A > hGSTA1*B. Directed mutagenesis for each base substitution indicated that the base change -52G>A was responsible for the differential promoter activity of hGSTA1*A and hGSTA1*B. The base at position -52 also altered binding of the ubiquitous transcription factor Sp1, as determined by gel shift analysis. Thus it may be postulated that hGSTA1 genotyping will be of importance to determine individual susceptibility to certain cancers or the efficacy of chemotherapeutics via its effect on hGSTA1 expression.

Prostaglandin D2 and reproduction

This review highlights recent studies investigating the role of prostaglandin (PG)D2 in reproduction. PGD2 induces sleep, allergic responses, inhibition of platelet aggregation, and relaxation of vascular and non-vascular smooth muscle, and has some roles in reproduction. Two types of PGD2 synthase are known. Lipocalin-type PGD synthase is present in cerebrospinal fluid, seminal plasma and may play an important role in male reproduction. Another PGD synthase, hematopoietic PGD synthase is present in the spleen, fallopian tube, endometrial gland cells, extravillous trophoblasts and villous trophoblasts, and perhaps plays an important role in female reproduction. Recent studies demonstrate that PGD2 is probably involved in multiple aspects of inflammation through its dual receptor systems, DP and CRTH2. CRTH2 but not DP is a chemo-attractant receptor for PGD2. Interestingly, CRTH2 is a most reliable marker for the detection of human T helper type 2 (Th2) and T cytotoxic type 2 (Tc2) cells, and the percentages of CRTH expressing CD4+-T cells and CD8+-T cells were significantly higher in the decidua especially at the implantation site, suggesting that Th2 and Tc2 cells recruit into the materno-fetal interface, in a PGD2-mediated manner. PGD2 has a very unique effect to inhibit antigen presentation by inhibition of dendritic cell (DC) migration through DP but not CRTH2. PGD2 might appear to contribute to the maintenance of pregnancy by controlling the Th1/Th2 balance and antigen presentation by DCs through its dual receptor systems, CRTH2 and DP.

New polymorphisms of haematopoietic prostaglandin D synthase and human prostanoid DP receptor genes

BACKGROUND

Prostaglandin D2 (PGD2), a major cyclo-oxygenase metabolite of arachidonic acid in mast cells, induces bronchoconstriction in the human lung. It has been reported that mice lacking PGD receptor fail to develop the bronchial hyper-responsiveness upon ovalbumin challenge, suggesting that PGD2 functions as a mediator of allergic asthma.

OBJECTIVE

To determine if there are any mutations associated with the development of asthma in the haematopoietic prostaglandin D synthase (H-PGDS) gene and the human prostanoid DP receptor (PTGDR) gene.

METHODS AND RESULTS

We screened the 5'flanking and coding regions of the H-PGDS gene and the PTGDR gene by direct sequence. We identified one variant in intron 2 (IVS2 + 11 A > C) and one variant in intron 3 (IVS3 + 13T > C) of the H-PGDS gene, and two variants in the 5'flanking region of the PTGDR gene (-197T > C and -2C > T). The IVS3 + 13T > C and -197T > C variants were rare, appearing only once in 48 subjects. transmission disequilibrium test (TDT) analysis of 144 asthmatic families revealed that the IVS2 + 11 A allele of the H-PGDS gene was significantly transmitted preferentially to asthma-affected children (P = 0.0056), but no association was observed between -2C/T polymorphism of the PTGDR gene and asthma (P > 0.05).

CONCLUSION

Our results suggest that the IVS2 + 11A/C allele may be involved in the development of asthma in the Japanese population.

Catalytic function ofDrosophila melanogasterglutathioneS-transferase DmGSTS1-1 (GST-2) in conjugation of lipid peroxidation end products

Drosophila melanogaster glutathione S-transferase DmGSTS1-1 (earlier designated as GST-2) is related to sigma class GSTs and was previously described as an indirect flight muscle-associated protein with no known catalytic properties. We now report that DmGSTS1-1 isolated from Drosophila or expressed in Escherichia coli is essentially inactive toward the commonly used synthetic substrate 1-chloro-2,4-dinitrobenzene (CDNB), but has relatively high glutathione-conjugating activity for 4-hydroxynonenal (4-HNE), an electrophilic aldehyde derived from lipid peroxidation. 4-HNE is thought to have signaling functions and, at higher concentrations, has been shown to be cytotoxic and involved in the etiology of various degenerative diseases. Drosophila strains carrying P-element insertions in the GstS1 gene have a reduced capacity for glutathione conjugation of 4-HNE. In flies with both, one, or none of the GstS1 alleles disrupted by P-element insertion, there is a linear correlation between DmGSTS1-1 protein content and 4-HNE-conjugating activity. This correlation indicates that in adult Drosophila 70 +/- 6% of the capacity to conjugate 4-HNE is attributable to DmGSTS1-1. The high abundance of DmGSTS1-1 (approximately 2% of the soluble protein in adult flies) and its previously reported localization in tissues that are either highly aerobic (indirect flight muscle) or especially sensitive to oxidative damage (neuronal tissue) suggest that the enzyme may have a protective role against deleterious effects of oxidative stress. Such function in insects would be analogous to that carried out in mammals by specialized alpha class glutathione S-transferases (e.g. GSTA4-4). The independent emergence of 4-HNE-conjugating activity in more than one branch of the glutathione S-transferase superfamily suggests that 4-HNE catabolism may be essential for aerobic life.

Structure, function and evolution of glutathione transferases: implications for classification of non-mammalian members of an ancient enzyme superfamily

The glutathione transferases (GSTs; also known as glutathione S-transferases) are major phase II detoxification enzymes found mainly in the cytosol. In addition to their role in catalysing the conjugation of electrophilic substrates to glutathione (GSH), these enzymes also carry out a range of other functions. They have peroxidase and isomerase activities, they can inhibit the Jun N-terminal kinase (thus protecting cells against H(2)O(2)-induced cell death), and they are able to bind non-catalytically a wide range of endogenous and exogenous ligands. Cytosolic GSTs of mammals have been particularly well characterized, and were originally classified into Alpha, Mu, Pi and Theta classes on the basis of a combination of criteria such as substrate/inhibitor specificity, primary and tertiary structure similarities and immunological identity. Non-mammalian GSTs have been much less well characterized, but have provided a disproportionately large number of three-dimensional structures, thus extending our structure-function knowledge of the superfamily as a whole. Moreover, several novel classes identified in non-mammalian species have been subsequently identified in mammals, sometimes carrying out functions not previously associated with GSTs. These studies have revealed that the GSTs comprise a widespread and highly versatile superfamily which show similarities to non-GST stress-related proteins. Independent classification systems have arisen for groups of organisms such as plants and insects. This review surveys the classification of GSTs in non-mammalian sources, such as bacteria, fungi, plants, insects and helminths, and attempts to relate them to the more mainstream classification system for mammalian enzymes. The implications of this classification with regard to the evolution of GSTs are discussed.

Mammalian class Sigma glutathione S-transferases: catalytic properties and tissue-specific expression of human and rat GSH-dependent prostaglandin D2 synthases

GSH-dependent prostaglandin D(2) synthase (PGDS) enzymes represent the only vertebrate members of class Sigma glutathione S-transferases (GSTs) identified to date. Complementary DNA clones encoding the orthologous human and rat GSH-dependent PGDS (hPGDS and rPGDS, respectively) have been expressed in Escherichia coli, and the recombinant proteins isolated by affinity chromatography. The purified enzymes were both shown to catalyse specifically the isomerization of prostaglandin (PG) H(2) to PGD(2). Each transferase also exhibited GSH-conjugating and GSH-peroxidase activities. The ability of hPGDS to catalyse the conjugation of aryl halides and isothiocyanates with GSH was found to be less than that of the rat enzyme. Whilst there is no difference between the enzymes with respect to their K(m) values for 1-chloro-2,4-dinitrobenzene, marked differences were found to exist with respect to their K(m) for GSH (8 mM versus 0.3 mM for hPGDS and rPGDS, respectively). Using molecular modelling techniques, amino acid substitutions have been identified in the N-terminal domain of these enzymes that lie outside the proposed GSH-binding site, which may explain these catalytic differences. The tissue-specific expression of PGDS also varies significantly between human and rat; amongst the tissues examined, variation in expression between the two species was most apparent in spleen and bone marrow. Differences in catalytic properties and tissue-specific expression of hPGDS and rPGDS appears to reflect distinct physiological roles for class Sigma GST between species. The evolution of divergent functions for the hPGDS and rPGDS is discussed in the context of the orthologous enzyme from chicken.

The crystal structures of glutathione S-transferases isozymes 1-3 and 1-4 from Anopheles dirus species B

Glutathione S-transferases (GSTs) are dimeric proteins that play an important role in cellular detoxification. Four GSTs from the mosquito Anopheles dirus species B (Ad), an important malaria vector in South East Asia, are produced by alternate splicing of a single transcription product and were previously shown to have detoxifying activity towards pesticides such as DDT. We have determined the crystal structures for two of these alternatively spliced proteins, AdGST1-3 (complexed with glutathione) and AdGST1-4 (apo form), at 1.75 and 2.45 A resolution, respectively. These GST isozymes show differences from the related GST from the Australian sheep blowfly Lucilia cuprina; in particular, the presence of a C-terminal helix forming part of the active site. This helix causes the active site of the Anopheles GSTs to be enclosed. The glutathione-binding helix alpha2 and flanking residues are disordered in the AdGST1-4 (apo) structure, yet ordered in the AdGST1-3 (GSH-bound) structure, suggesting that insect GSTs operate with an induced fit mechanism similar to that found in the plant phi- and human pi-class GSTs. Despite the high overall sequence identities, the active site residues of AdGST1-4 and AdGST1-3 have different conformations.

Oxidation of prostaglandin H(2) and prostaglandin H(2) analogues by human cytochromes P450: analysis of omega-side chain hydroxy metabolites and four steroisomers of 5-hydroxyprostaglandin I(1) by mass spectrometry

The objective was to examine the NADPH-dependent oxygenation of prostaglandin H(2) (PGH(2)) and three PGH(2) analogues, 9,11-diazo-15-deoxy-PGH(2) (U51605), 9,11-epoxymethano-PGH(2) (U44069), and 11,9-epoxymethano-PGH(2) (U46619), by cytochromes P450, and to characterize the metabolites by mass spectrometry. CYP2C19, CYP4A11, CYP4F8, and liver and renal cortical microsomes oxidized the omega-side chain of U44069, U46619, and U51605, whereas only CYP4F8 oxidized the omega-side chain of PGH(2). PGH(2) was transformed to four stereoisomers of 5-hydroxy-PGI(1) by recombinant cytochromes P450. CYP4F8 formed the 5-hydroxy-PGI(1) isomers in small amounts compared to the 19-hydroxy metabolites of PGH(2). Isomers of 5-hydroxy-PGI(1) and 6-keto-PGF(1 alpha) were detectable when PGH(2) decomposed in the presence of hemin, hemoglobin, or heat-inactivated microsomes. 5-Hydroxy-PGI(1) is likely formed from PGH(2) in a pseudo-enzymatic reaction involving homolytic scission of the endoperoxide and formation of an ether between C-9 and C-6 and a carbon-centered radical at C-5, which reacts with molecular oxygen. CYP4F8 catalyzes 19-hydroxylation of PGH(2), but the absolute configuration of the 19-hydroxy group is unknown, whereas human seminal fluid contains (19R)-hydroxy-PGE(2). CYP4F8 was found to metabolize U51605 to 90% of the (19R)-hydroxy metabolite, providing further evidence in favor of a role of CYP4F8 in biosynthesis of (19R)-hydroxy PGE in human seminal vesicles. We conclude that omega-side chain hydroxylation of PGH(2) analogues may be catalyzed by many different cytochromes P450, but only CYP4F8 oxidizes the omega-side chain of PGH(2) efficiently.

Transcriptional activation of the human hematopoietic prostaglandin D synthase gene in megakaryoblastic cells. Roles of the oct-1 element in the 5'-flanking region and the AP-2 element in the untranslated exon 1

The human hematopoietic prostaglandin D synthase (H-PGDS) gene is highly expressed in human megakaryoblastic cells, in which phorbol ester induces its expression. We characterized the promoter activity of the 5'-flanking region and the untranslated exon 1 (-1044 to +290) of the human H-PGDS gene in human megakaryoblastic Dami cells. Transient expression analysis using the luciferase reporter gene revealed that the 5'-flanking region and the untranslated exon 1 were sufficient for efficient expression of the H-PGDS gene in Dami cells, but not in monocytic U937 cells. Deletion and site-directed mutagenesis of the Oct-1 element in the 5'-flanking region decreased the promoter activity by approximately 30% compared with that of the entire region from -1044 to +290. An electrophoretic mobility shift assay demonstrated that Oct-1 specifically bound to the promoter region. Interestingly, even only untranslated exon 1 (+1 to +290) showed approximately 60% of the promoter activity of the entire region from -1044 to +290. Site-directed mutagenesis of the AP-2 element within the untranslated exon 1 abolished the basal promoter activity as well as its phorbol ester-mediated up-regulation. In AP-2-deficient HepG2 cells, the H-PGDS promoter activity was enhanced by coexpression with AP-2alpha. These findings indicate that the Oct-1 element in the 5'-flanking region acts as a positive cis-acting element and that the AP-2 element in the untranslated exon 1 is crucial for both basal and phorbol ester-mediated up-regulation of human H-PGDS gene expression in megakaryoblastic Dami cells.

Biochemical, structural, genetic, physiological, and pathophysiological features of lipocalin-type prostaglandin D synthase

Lipocalin-type prostaglandin (PG) D synthase (PGDS) catalyzes the isomerization of PGH(2), a common precursor of various prostanoids, to produce PGD(2), a potent endogenous somnogen and nociceptive modulator, in the presence of sulfhydryl compounds. PGDS is an N-glycosylated monomeric protein with an M(r) of 20000-31000 depending on the size of the glycosyl moiety. PGDS is localized in the central nervous system and male genital organs of various mammals and in the human heart and is secreted into the cerebrospinal fluid, seminal plasma, and plasma, respectively, as beta-trace. The PGDS concentrations in these body fluids are useful for the diagnosis of several neurological disorders, dysfunction of sperm formation, and cardiovascular and renal diseases. The cDNA and gene for PGDS have been isolated from several animal species, and the tissue distribution and cellular localization have also been determined. This enzyme is considered to be a dual functional protein; i.e. it acts as a PGD(2)-producing enzyme and also as a lipophilic ligand-binding protein, because the enzyme binds biliverdin, bilirubin (K(d)=30 nM), retinaldehyde, retinoic acid (K(d)=80 nM) with high affinities. X-ray crystallographic analyses revealed that PGDS possesses a beta-barrel structure with a hydrophobic pocket in which an active thiol, Cys(65), the active center for the catalytic reaction, was located facing to the inside of the pocket. Gene-knockout and transgenic mice for PGDS were generated and found to have abnormalities in the regulation of nociception and sleep.