Purification, crystallization and structural elucidation of D-galactaro-1,4-lactone cycloisomerase from Agrobacterium tumefaciens involved in pectin degradation

Pectin is found in the cell wall of plants and is often discarded as waste. A number of research groups are interested in redirecting this biomass waste stream for the production of fuel and bulk chemicals. The primary monomeric subunit of this polysaccharide is D-galacturonate, a six-carbon acid sugar that is degraded in a five-step pathway to central metabolic intermediates by some bacteria, including Agrobacterium tumefaciens. In the third step of the pathway, D-galactaro-1,4-lactone is converted to 2-keto-3-deoxy-L-threo-hexarate by a member of the mandelate racemase subgroup of the enolase superfamily with a novel activity for the superfamily. The 1.6 Å resolution structure of this enzyme was determined, revealing an overall modified (β/α)7β TIM-barrel domain, a hallmark of the superfamily. D-Galactaro-1,4-lactone was manually docked into the active site located at the interface between the N-terminal lid domain and the C-terminal barrel domain. On the basis of the position of the lactone in the active site, Lys166 is predicted to be the active-site base responsible for abstraction of the α proton. His296 on the opposite side of the active site is predicted to be the general acid that donates a proton to the β carbon as the lactone ring opens. The lactone ring appears to be oriented within the active site by stacking interactions with Trp298.

Crystal structures of Physcomitrella patens AOC1 and AOC2: insights into the enzyme mechanism and differences in substrate specificity

In plants, oxylipins regulate developmental processes and defense responses. The first specific step in the biosynthesis of the cyclopentanone class of oxylipins is catalyzed by allene oxide cyclase (AOC) that forms cis(+)-12-oxo-phytodienoic acid. The moss Physcomitrella patens has two AOCs (PpAOC1 and PpAOC2) with different substrate specificities for C₁₈- and C₂₀-derived substrates, respectively. To better understand AOC's catalytic mechanism and to elucidate the structural properties that explain the differences in substrate specificity, we solved and analyzed the crystal structures of 36 monomers of both apo and ligand complexes of PpAOC1 and PpAOC2. From these data, we propose the following intermediates in AOC catalysis: (1) a resting state of the apo enzyme with a closed conformation, (2) a first shallow binding mode, followed by (3) a tight binding of the substrate accompanied by conformational changes in the binding pocket, and (4) initiation of the catalytic cycle by opening of the epoxide ring. As expected, the substrate dihydro analog cis-12,13S-epoxy-9Z,15Z-octadecadienoic acid did not cyclize in the presence of PpAOC1; however, when bound to the enzyme, it underwent isomerization into the corresponding trans-epoxide. By comparing complex structures of the C₁₈ substrate analog with in silico modeling of the C₂₀ substrate analog bound to the enzyme allowed us to identify three major molecular determinants responsible for the different substrate specificities (i.e. larger active site diameter, an elongated cavity of PpAOC2, and two nonidentical residues at the entrance of the active site).

The moss Physcomitrella patens contains cyclopentenones but no jasmonates: mutations in allene oxide cyclase lead to reduced fertility and altered sporophyte morphology

• Two cDNAs encoding allene oxide cyclases (PpAOC1, PpAOC2), key enzymes in the formation of jasmonic acid (JA) and its precursor (9S,13S)-12-oxo-phytodienoic acid (cis-(+)-OPDA), were isolated from the moss Physcomitrella patens. • Recombinant PpAOC1 and PpAOC2 show substrate specificity against the allene oxide derived from 13-hydroperoxy linolenic acid (13-HPOTE); PpAOC2 also shows substrate specificity against the allene oxide derived from 12-hydroperoxy arachidonic acid (12-HPETE). • In protonema and gametophores the occurrence of cis-(+)-OPDA, but neither JA nor the isoleucine conjugate of JA nor that of cis-(+)-OPDA was detected. • Targeted knockout mutants for PpAOC1 and for PpAOC2 were generated, while double mutants could not be obtained. The ΔPpAOC1 and ΔPpAOC2 mutants showed reduced fertility, aberrant sporophyte morphology and interrupted sporogenesis.

Large-scale expression, purification, and characterization of an engineered prostacyclin-synthesizing enzyme with therapeutic potential

Recently, we reported that a novel hybrid enzyme (TriCat enzyme), engineered by linking human cyclooxygenase-2 (COX-2) with prostacyclin (PGI(2)) synthase (PGIS) together through a transmembrane domain, was able to directly integrate the triple catalytic (TripCat) functions of COX-2 and PGIS and effectively convert arachidonic acid (AA) into the vascular protector, PGI(2) [K.H. Ruan, H. Deng, S.P. So, Biochemistry 45 (2006) 14003-14011]. In order to confirm the important biological activity and evaluate its therapeutic potential, it is critical to characterize the properties of the enzyme using the purified protein. The TriCat enzyme cDNA was subcloned into a baculovirus vector and its protein was expressed in Sf-9 cells in large-scale with a high-yield ( approximately 4% of the total membrane protein), as confirmed by Western blot and protein staining. The Sf-9 cells' membrane fraction, rich in TriCat enzyme, exhibited strong TriCat functions (K(m)=3 microM and K(cat)=100 molecules/min) for the TriCat enzyme and was 3-folds faster in converting AA to PGI(2) than the combination of the individual COX-2 and PGIS. Another superiority of the TriCat enzyme is its dual effect on platelet aggregation: it completely inhibited platelet aggregation at the low concentration of 2 microg/ml and then displayed the ability to reverse the initially aggregated platelets to their non-aggregated state. Furthermore, multiple substrate-binding sites were confirmed in the single protein by high-resolution NMR spectroscopy, using partially purified TriCat enzyme. These studies have clearly demonstrated that the isolated TriCat enzyme protein functions in the selective biosynthesis of the vascular protector, PGI(2), and revealed its potential for anti-thrombosis therapeutics.

Crystallization and preliminary X-ray analysis of allene oxide synthase, cytochrome P450 CYP74A2, from Parthenium argentatum

Oxylipins are oxygenated derivatives of fatty acids and pivotal signaling molecules in plants and animals. Allene oxide synthase (AOS) is a key cytochrome P450 CYP74 enzyme involved in the biosynthesis of plant oxylipin jasmonates to convert 13(S)-hydroperoxide to allene oxide. Guayule (Parthenium argentatum) AOS, CYP74A2, was expressed in Escherichia coli. Protein was purified using affinity chromatography and size exclusion chromatography, and then crystallized. Two different crystal forms were obtained from 0.2 M (NH(4))H(2)PO(4), 50% MPD, 0.1 M Tris, pH 8.5 at 277 K using the hanging-drop vapor-diffusion method. Preliminary X-ray analysis was carried out, and the crystals were found to belong to the tetragonal space group I422 with cell parameters a = b = 126.5, c = 163.9 A, and the monoclinic space group C2 with cell parameters a = 336.5, b = 184.2, c = 159.0 A, beta = 118.6 degrees . Diffraction data were collected to 2.4 A resolution from a tetragonal form of crystal using a home X-ray source.

Expression and purification of cysteine mutation isoforms of rat lipocalin-type prostaglandin D synthase for nuclear magnetic resonance study

Lipocalin-type prostaglandin (PG) D synthase (L-PGDS) is the only member of the lipocalin superfamily that displays enzymatic activity. It binds lipophilic ligands with high affinity and also can catalyze PGH2 to produce PGD2. Three cysteine residues, Cys65, Cys89, and Cys186 in L-PGDS, are conserved among all species, of which Cys89 and Cys186 residues form a disulfide bridge. In this study, we clarified the effects of thiol groups on the structure of the protein and investigated the structural significance of Cys residues of rat L-PGDS by site-directed mutagenesis. Four mutants were constructed by substituting Cys residues with alanine to identify the correct formation of disulfide bonds among these three residues. The effects of thiol groups on the structure of rat L-PGDS were also identified by these mutants. Analysis of HSQC experiments indicated that these enzymes were all properly folded with well defined tertiary structures. As the first step towards the 3-D nuclear magnetic resonance solution structure, we optimized expression of recombinant rat L-PGDS in Escherichia coli and established an efficient and economic purification protocol yielding large amounts of pure isotopically labeled rat L-PGDS. The results of assignments indicated that the wild-type rat L-PGDS obtained using this expression system was suitable for determination of 3-D nuclear magnetic resonance solution structure.

Proteomic analysis of N-glycosylation in mosquito dopachrome conversion enzyme

A novel dopachrome conversion enzyme (DCE) is present in insects and involved in their melanization pathway. DCE shares no sequence homology with any noninsect species from bacteria to humans. Several DCE sequences have been available, but enzyme structure and catalytic mechanism are unclear. This study concerns DCE PTMs, especially glycosylation. A mosquito DCE was purified and its monosaccharide composition, N-glycosylation site, and oligosaccharide structures were determined. Results showed that N-acetyl D-glucosamine and D-mannose are the major monosaccharides and L-fucose, D-xylose, and D-arabinose are the minor ones in mosquito DCE. Glycosylation site and oligosaccharide structures were elucidated from MS and MS/MS spectra of trypsin-digested DCE glycopeptides. A single N-glycosylation site (Asn285 -Glu-Thr) was identified in DCE and was proven to be fully glycosylated. Man3GlcNAc2, Man3(Fuc)1-2GlcNAc2, and their truncated structures were the dominant oligosaccharides. In addition, high mannose-type structures (Man4-7(Fuc)GlcNAc2) were also identified. Removal of DCE N-oligosaccharides with peptide N-glycosidase (PNGase F) decreased its activity and thermal stability. However, partial DCE deglycosylation with alpha-mannosidase or alpha-fucosidase somewhat stimulated its activity and improved its thermal stability. During mass spectrometric analysis of DCE glycopeptides, their CID patterns were highly intriguing, in that some glycopeptides underwent both C-terminal rearrangement and formation of dimeric structures during CID. Results of this study provide an interesting example in terms of potential complexity of the glycopeptide CID fragmentation pattern.

Production of Delta(1)-tetrahydrocannabinolic acid by the biosynthetic enzyme secreted from transgenic Pichia pastoris

Delta(1)-Tetrahydrocannabinolic acid (THCA) synthase is the enzyme that catalyzes the oxidative cyclization of cannabigerolic acid into THCA, the acidic precursor of Delta(1)-tetrahydrocannabinol. We developed a novel expression system for THCA synthase using a methylotrophic yeast Pichia pastoris as a host. Under optimized conditions, the transgenic P. pastoris secreted approximately 1.32nkat/l of THCA synthase activity, and the culture medium, from which the cells were removed, effectively synthesized THCA from cannabigerolic acid with a approximately 98% conversion rate. The secreted THCA synthase was readily purified to homogeneity. Interestingly, endoglycosidase treatment afforded a deglycosylated THCA synthase with more catalytic activity than that of the glycosylated form. The non-glycosylated THCA synthase should be suitable for structure-function studies because it displayed much more activity than the previously reported native enzyme from Cannabis sativa as well as the recombinant enzyme from insect cell cultures.

Reaction mechanisms of 15-hydroperoxyeicosatetraenoic acid catalyzed by human prostacyclin and thromboxane synthases

Prostacyclin synthase (PGIS) and thromboxane synthase (TXAS) are atypical cytochrome P450s. They do not require NADPH or dioxygen for isomerization of prostaglandin H(2) (PGH(2)) to produce prostacyclin (PGI(2)) and thromboxane A(2) (TXA(2)). PGI(2) and TXA(2) have opposing actions on platelet aggregation and blood vessel tone. In this report, we use a lipid hydroperoxide, 15-hydroperoxyeicosatetraenoic acid (15-HPETE), to explore the active site characteristics of PGIS and TXAS. The two enzymes transformed 15-HPETE not only into 13-hydroxy-14,15-epoxy-5,8,11-eicosatrienoic acid (13-OH-14,15-EET), like many microsomal P450s, but also to 15-ketoeicosatetraenoic acid (15-KETE) and 15-hydroxyeicosatetraenoic acid (15-HETE). 13-OH-14,15-EET and 15-KETE result from homolytic cleavage of the O-O bond, whereas 15-HETE results from heterolytic cleavage, a common peroxidase pathway. About 80% of 15-HPETE was homolytically cleaved by PGIS and 60% was homolytically cleaved by TXAS. The V(max) of homolytic cleavage is 3.5-fold faster than heterolytic cleavage for PGIS-catalyzed reactions (1100 min(-1)vs. 320 min(-1)) and 1.4-fold faster for TXAS (170 min(-1)vs. 120 min(-1)). Similar K(M) values for homolytic and heterolytic cleavages were found for PGIS ( approximately 60 microM 15-HPETE) and TXAS ( approximately 80 microM 15-HPETE), making PGIS a more efficient catalyst for the 15-HPETE reaction.

Characterization of a Plasmodium falciparum macrophage-migration inhibitory factor homologue

BACKGROUND

Macrophage-migration inhibitory factor (MIF), one of the first cytokines described, has a broad range of proinflammatory properties. The genome sequencing project of Plasmodium falciparum identified a parasite homologue of MIF. The protein is expressed during the asexual blood stages of the parasite life cycle that cause malarial disease. The identification of a parasite homologue of MIF raised the question of whether it affects monocyte function in a manner similar to its human counterpart.

METHODS

Recombinant P. falciparum MIF (PfMIF) was generated and used in vitro to assess its influence on monocyte function. Antibodies generated against PfMIF were used to determine the expression profile and localization of the protein in blood-stage parasites. Antibody responses to PfMIF were determined in Kenyan children with acute malaria and in control subjects.

RESULTS

PfMIF protein was expressed in asexual blood-stage parasites, localized to the Maurer's cleft. In vitro treatment of monocytes with PfMIF inhibited random migration and reduced the surface expression of Toll-like receptor (TLR) 2, TLR4, and CD86.

CONCLUSIONS

These results indicate that PfMIF is released during blood-stage malaria and potentially modulates the function of monocytes during acute P. falciparum infection.

The crystal structure of Arabidopsis thaliana allene oxide cyclase: insights into the oxylipin cyclization reaction

We describe the crystallization and structure elucidation of Arabidopsis thaliana allene oxide cyclase 2 (AOC2), a key enzyme in the biosynthesis of jasmonates. In a coupled reaction with allene oxide synthase, AOC2 releases the first cyclic and biologically active metabolite, 12-oxo-phytodienoic acid (OPDA). AOC2 (AT3G25770) folds into an eight-stranded antiparallel beta-barrel with a C-terminal partial helical extension. The protein forms a hydrophobic binding cavity with two distinct polar patches. AOC2 is trimeric in crystals, in vitro and in planta. Based on the observed folding pattern, we assigned AOC2 as a low molecular weight member of the lipocalin family with enzymatic activity in plants. We determined the binding position of the competitive inhibitor vernolic acid (a substrate analog) in the binding pocket. Based on models for bound substrate 12,13-epoxy-9,11,15-octadecatrienoic acid and product OPDA, we propose a reaction scheme that explains the influence of the C15 double bond on reactivity. Reaction is promoted by anchimeric assistance through a conserved Glu residue. The transition state with a pentadienyl carbocation and an oxyanion is stabilized by a strongly bound water molecule and favorable pi-pi interactions with aromatic residues in the cavity. Stereoselectivity results from steric restrictions to the necessary substrate isomerizations imposed by the protein.

Purification of prostaglandin D synthase by ceramic- and size exclusion chromatography

Prostaglandin D synthase (L-PGDS) is a major glycosylated polypeptide in cerebrospinal fluid (CSF). The overexpression of L-PGDS in inflamed bovine mammary glands indicates its role as biomarker. No diagnostic tool for the quantitative detection of L-PGDS in cows has been reported. Immunometric ELISA tests might help to identify inflamed bovine tissue. The isolation of pure bovine L-PGDS, which is required for the generation of monoclonal antibodies, is an important prerequisite for a diagnostic ELISA test. Our goal was to identify a suitable technique to generate pure L-PGDS from bovine substrates. In the present study a two-step method for the purification of bovine CSF using ceramic hydroxyapatite chromatography followed by size exclusion chromatography is described. Subsequently, the identification of bovine L-PGDS was demonstrated by Western blot analysis and the high grade of the pure product was shown by 2-D PAGE. The yield of purified L-PGDS was 6.8 mg/l bovine CSF. L-PGDS from bovine CSF is shown to consist of multiple isoforms identical in molecular mass and pI values to those in previously described secretions of inflamed bovine mammary glands. In addition, the method was successfully applied to the purification of L-PGDS from human CSF.

Human Follicular Dendritic Cells Express Prostacyclin Synthase: A Novel Mechanism to Control T Cell Numbers in the Germinal Center

Stromal cells in the lymphoid organs provide a microenvironment where lymphocytes undergo various biological processes such as development, homing, clonal expansion, and differentiation. Follicular dendritic cells (FDCs) in the primary and secondary follicles of the peripheral lymphoid tissues interact with lymphocytes by contacting directly or producing diffusible molecules. To understand the biological role of human FDC at the molecular level, we developed a mAb, 3C8, that recognizes FDC but not bone marrow-derived cells. Through expression cloning and proteome analysis, we identified the protein that is recognized by 3C8 mAb, which revealed that FDC expresses prostacyclin synthase. The 3C8 protein purified from FDC-like cells indeed displayed the enzymatic activity of prostacyclin synthase and converted PGH2 into prostacyclin. In addition, prostacyclin significantly inhibited proliferation of T cells but delayed their spontaneous apoptosis. These findings may help explain why T cells constitute only a minor population compared with B cells in the germinal center.

Purification and characterization of recombinant human prostacyclin synthase

Prostacyclin synthase (PGIS), which catalyzes the conversion of prostaglandin (PG) H(2) to prostacyclin (PGI(2)), is a member of the cytochrome P-450 (P450) superfamily, CYP8A1. To study the enzymatic and protein characteristics of human PGIS, the enzyme was overexpressed in Spodoptera frugiperda 21 (Sf21) cells using the baculovirus expression system. PGIS was expressed in the microsomes of the infected Sf21 cells after culture in 5 microg/ml hematin-supplemented medium for 72 h. The holoenzyme was isolated from the solubilized microsomal fraction by calcium phosphate gel absorption and purified to homogeneity by DEAE-Sepharose and hydroxyapatite column chromatography. The K(m) and V(max) values of the purified human PGIS for PGH(2) were 30 microM and 15 micromol/min/mg of protein at 24 degrees C, respectively. The optical absorption and EPR spectra of the enzyme revealed the characteristics of a low-spin form of P450 in the oxidized state. The carbon monoxide-reduced difference spectrum, however, exhibited a peak at 418 nm rather than 450 nm. The addition of a PGH(2) analogue, U46619, to the enzyme produced an oxygen-ligand type of the difference spectrum with maximum absorption at 407 nm and minimum absorption at 430 nm. Treatment with another PGH(2) analogue, U44069, produced a peak at 387 nm and a trough at 432 nm in the spectrum (Type I), while treatment with tranylcypromine, a PGIS inhibitor, produced a peak at 434 nm and a trough at 412 nm (Type II). A Cys441His mutant of the enzyme possessed no heme-binding ability or enzyme activity. Thus, we succeeded in obtaining a sufficient amount of the purified recombinant human PGIS from infected insect cells for spectral analyses that has high specific activity and the characteristics of a P450, indicating substrate specificity.

Phytochrome-Mediated Transcriptional Up-regulation of ALLENE OXIDE SYNTHASE in Rice Seedlings

Allene oxide synthase (AOS) is a key enzyme for the biosynthesis of jasmonic acid (JA). We identified four AOS gene homologs, named OsAOS1-4, in the database of a japonica rice genome and cloned a full-length cDNA of OsAOS1. The analysis of deduced amino acid sequences indicated that only OsAOS1 has a chloroplast transit peptide among all the identified monocot AOSs including OsAOSs. We found that the transcripts of OsAOS1 and OsAOS4 are up-regulated by red and far-red light in seedling shoots. The response in OsAOS1 transcripts occurred rapidly and transiently, while the response in OsAOS4 transcripts was slower and more sustainable; the maximal enhancement was greater in OsAOS1 transcripts than in OsAOS4 transcripts. The transcript of OsAOS1 was also up-regulated transiently in response to wounding, as reported for dicot AOSs. No wound-induced enhancement occurred, however, in OsAOS4 transcripts. Our results also indicated that OsAOS1, responding to both light and wounding, is the most highly expressed of all the OsAOSs in seedling shoots. By using phyA mutants of rice, it was demonstrated that the photoregulation of the AOS transcript level is mediated by phytochrome. It is suggested that this transcriptional photoregulation participates in the phytochrome-mediated inhibition of rice coleoptile growth.

Involvement of two cytosolic enzymes and a novel intermediate, 5'-oxoaverantin, in the pathway from 5'-hydroxyaverantin to averufin in aflatoxin biosynthesis

During aflatoxin biosynthesis, 5'-hydroxyaverantin (HAVN) is converted to averufin (AVR). Although we had previously suggested that this occurs in one enzymatic step, we demonstrate here that this conversion is composed of two enzymatic steps by showing that the two enzyme activities in the cytosol fraction of Aspergillus parasiticus were clearly separated by Mono Q column chromatography. An enzyme, HAVN dehydrogenase, catalyzes the first reaction from HAVN to a novel intermediate, another new enzyme catalyzes the next reaction from the intermediate to AVR, and the intermediate is a novel substance, 5'-oxoaverantin (OAVN), which was determined by physicochemical methods. We also purified both of the enzymes, HAVN dehydrogenase and OAVN cyclase, from the cytosol fraction of A. parasiticus by using ammonium sulfate fractionation and successive chromatographic steps. The HAVN dehydrogenase is a homodimer composed of 28-kDa subunits, and it requires NAD, but not NADP, as a cofactor for its activity. Matrix-assisted laser desorption ionization-time of flight mass spectrometry analysis of tryptic peptides of the purified HAVN dehydrogenase revealed that this enzyme coincides with a protein deduced from the adhA gene in the aflatoxin gene cluster of A. parasiticus. Also, the OAVN cyclase enzyme is a homodimer composed of 79-kDa subunits which does not require any cofactor for its activity. Further characterizations of both enzymes were performed.

Human microsomal prostaglandin E synthase-1: purification, functional characterization, and projection structure determination

Human, microsomal, and glutathione-dependent prostaglandin (PG) E synthase-1 (mPGES-1) was expressed with a histidine tag in Escherichia coli. mPGES-1 was purified to apparent homogeneity from Triton X-100-solubilized bacterial extracts by a combination of hydroxyapatite and immobilized metal affinity chromatography. The purified enzyme displayed rapid glutathione-dependent conversion of PGH2 to PGE2 (Vmax; 170 micromol min-1 mg-1) and high kcat/Km (310 mm-1 s-1). Purified mPGES-1 also catalyzed glutathione-dependent conversion of PGG2 to 15-hydroperoxy-PGE2 (Vmax; 250 micromol min-1 mg-1). The formation of 15-hydroperoxy-PGE2 represents an alternative pathway for the synthesis of PGE2, which requires further investigation. Purified mPGES-1 also catalyzed glutathione-dependent peroxidase activity toward cumene hydroperoxide (0.17 micromol min-1 mg-1), 5-hydroperoxyeicosatetraenoic acid (0.043 micromol min-1 mg-1), and 15-hydroperoxy-PGE2 (0.04 micromol min-1 mg-1). In addition, purified mPGES-1 catalyzed slow but significant conjugation of 1-chloro-2,4-dinitrobenzene to glutathione (0.8 micromol min-1 mg-1). These activities likely represent the evolutionary relationship to microsomal glutathione transferases. Two-dimensional crystals of purified mPGES-1 were prepared, and the projection map determined by electron crystallography demonstrated that microsomal PGES-1 constitutes a trimer in the crystal, i.e. an organization similar to the microsomal glutathione transferase 1. Hydrodynamic studies of the mPGES-1-Triton X-100 complex demonstrated a sedimentation coefficient of 4.1 S, a partial specific volume of 0.891 cm3/g, and a Stokes radius of 5.09 nm corresponding to a calculated molecular weight of 215,000. This molecular weight, including bound Triton X-100 (2.8 g/g protein), is fully consistent with a trimeric organization of mPGES-1.

Specific nitration at tyrosine 430 revealed by high resolution mass spectrometry as basis for redox regulation of bovine prostacyclin synthase

Treatment of bovine aortic microsomes containing active prostacyclin synthase (PGI(2) synthase) with increasing concentrations of peroxynitrite (PN) up to 250 microm of PN yielded specific staining of this enzyme on Western blots with antibodies against 3-nitrotyrosine (3-NT), whereas above 500 microm PN staining of additional proteins was also observed. Following treatment of aortic microsomes with 25 microm PN, PGI(2) synthase was about half-maximally nitrated and about half-inhibited. It was then isolated by gel electrophoresis and subjected to proteolytic digestion with several proteases. Digestion with thermolysin for 24 h provided a single specific peptide that was isolated by high performance liquid chromatography and identified as a tetrapeptide Leu-Lys-Asn-Tyr(3-nitro)-COOH corresponding to positions 427-430 of PGI(2) synthase. Its structure was established by precise mass determination using Fourier transform-ion cyclotron resonance-nanoelectrospray mass spectrometry and Edman microsequencing and ascertained by synthesis and mass spectrometric characterization of the authentic Tyr-nitrated peptide. Complete digestion by Pronase to 3-nitrotyrosine was obtained only after 72 h, suggesting that the nitrated Tyr-430 residue may be embedded in a tight fold around the heme binding site. These results provide evidence for the specific inhibition of PGI(2) synthase by nitration at Tyr-430 that may occur already at low levels of PN as a consequence of endothelial co-generation of nitric oxide and superoxide.

Purification and characterization of recombinant microsomal prostaglandin E synthase-1

Recombinant human microsomal prostaglandin E(2) synthase-1 (mPGES-1) was expressed in a baculovirus-Sf9 cell system. The mPGES-1 was solubilized from Sf9 cell membranes with diheptanoylphosphatidylcholine and purified in the presence of octylglucoside using hydroxyapatite column chromatography. The K(m) values of the substrates PGH(2) and GSH were 14 microM and 0.75 mM, respectively, with the purified enzyme. The specific activity (4 micromol/min/mg) was increased 3-5-fold by non-ionic and zwitterionic detergents. Kinetic analysis showed that dodecylmaltoside increases V(max) but does not affect the K(m) values of either substrate. Several other thiol-containing compounds were tested as glutathione replacements, none of which yielded detectable enzyme activity. During enzyme catalysis, glutathione was not oxidized and therefore can be considered an enzyme cofactor. No glutathione transferase or peroxidase activity could be determined with a range of potential substrates. The results show that purified mPGES-1 has a specific activity similar to Cox-2, consistent with its postulated role in Cox-2 mediated PGE(2) formation.

Identification of Drosophila melanogaster yellow-f and yellow-f2 proteins as dopachrome-conversion enzymes

This study describes the identification of Drosophila yellow-f and yellow-f2 as dopachrome-conversion enzymes responsible for catalysing the conversion of dopachrome into 5,6-dihydroxyindole in the melanization pathway. Drosophila yellow -y gene and yellow -b, -c, -f and -f2 genes were expressed in an insect cell/baculovirus expression system and their corresponding recombinant proteins were screened for dopachrome-conversion enzyme activity. Among the yellow and yellow -related genes, the yellow -f and yellow -f2 genes were identified as the genes coding for Drosophila dopachrome-conversion enzyme based on the high activity of their recombinant proteins in catalysing the production of 5,6-dihydroxyindole from dopachrome. Both yellow-f and yellow-f2 are capable of mediating a decarboxylative structural rearrangement of dopachrome, as well as an isomerization/tautomerization of dopamine chrome and dopa methyl ester chrome. Northern hybridization revealed the transcription of yellow -f in larvae and pupae, but a high abundance of mRNA was observed in later larval and early pupal stages. In contrast, yellow-f2 transcripts were present at all stages, but high abundance of its mRNA was observed in later-stage pupae and adults. These data indicate that yellow-f and yellow-f2 complement each other during Drosophila development and that the yellow-f is involved in larval and pupal melanization, and yellow-f2 plays a major role in melanization reactions in Drosophila during later pupal and adult development. Results from this study provide the groundwork towards a better understanding of the physiological roles of the Drosophila yellow gene family.

Biochemical characterization of mouse microsomal prostaglandin E synthase-1 and its colocalization with cyclooxygenase-2 in peritoneal macrophages

We cloned the cDNA for mouse microsomal prostaglandin (PG) E synthase-1 (mPGES-1) and expressed the recombinant enzyme in Escherichia coli. The membrane fraction containing recombinant mPGES-1 catalyzed the isomerization of PGH2 to PGE2 in the presence of GSH with K(m) values of 130 microM for PGH2 and 37 microM for GSH, a turnover number of 600 min(-1), and a k(cat)/K(m) ratio of 4.6 min(-1) microM(-1). Recombinant mPGES-1 was purified and used to generate a polyclonal antibody highly specific for mPGES-1. The antibody showed a single band on Western blotting of microsomal fractions from lipopolysaccharide-treated mouse peritoneal macrophages. Northern and Western blotting analyses revealed that mPGES-1 was induced together with cyclooxygenase-2 in mouse macrophages after treatment of the cells with lipopolysaccharide. Confocal immunofluorescence microscopy revealed that both mPGES-1 and cyclooxygenase-2 were colocalized in the lipopolysaccharide-treated macrophages. Taken together, these results demonstrate that mPGES-1 is an efficient downstream enzyme for the production of PGE2 in the activated macrophages treated by lipopolysaccharide.

Functional expression and characterization of Aedes aegypti dopachrome conversion enzyme

A full-length mosquito dopachrome conversion enzyme (DCE) and its truncated form lacking the last 54 carboxyl-terminal amino acid residues are expressed using a baculovirus/insect cell expression system. The full-length recombinant DCE displayed multiple bands during native PAGE with substrate staining, but only one active band was detected when the truncated recombinant DCE was analyzed under identical analysis conditions. Our data suggest that the last 50 some carboxyl-terminal residues are involved in the polymerization of the DCE molecules and that the proposed DCE isozymes likely reflect the presence of multimers of the same DCE molecules. The significance of the recombinant DCE in accelerating the melanization pathway is demonstrated by a rapid production of melanin in a dopa and tyrosinase reaction mixture in the presence of recombinant DCE. The DCE sequence data obtained in our previous study, together with results of functional expression and biochemical characterization achieved in this study, provide a necessary reference for the study of other insect DCEs.

Cloning and characterization of a dopachrome conversion enzyme from the yellow fever mosquito, Aedes aegypti

In this study we describe the purification and molecular cloning of a dopachrome conversion enzyme (DCE) from the yellow fever mosquito, Aedes aegypti. DCE catalyzes the conversion of L-dopachrome to 5,6-dihydroxyindole in the melanization pathway. Melanin biosynthesis is involved with crucial protective phenomena in mosquitoes, including egg chorion and cuticular tanning, wound healing, and the melanotic encapsulation immune response. The enzyme was purified to homogeneity by various chromatographic techniques from A. aegypti larvae and has a relative molecular mass of 51 kDa as-revealed by SDS-PAGE analysis. Physiochemical analysis of DCE revealed a pH optimum of 7.5-8.0 and substrate activity for L-dopachrome and aminochromes generated from dopa methyl ester, alpha-methyl dopa and dopamine. Trypsin digestion of the isolated DCE and subsequent reverse-phase separation resulted in the isolation of several polypeptide fragments, from which two partial internal amino acid sequences were obtained by Edman degradation. PCR amplification, using a degenerate primer based on one internal amino acid sequence and an oligo-dT primer, produced a 650 bp DNA fragment. Subsequent screening of an A. aegypti pupal cDNA library resulted in the isolation of a 1.6 kb clone containing coding sequence for both internal DCE amino acid sequences, thereby confirming the identity of the isolated gene product (pAaDce1) as DCE. Northern analysis revealed the constitutive expression of DCE message in developmental stages and adults, with the majority of transcript localized in the fat body and ovaries of adult females. AaDce1 mRNA increased in abundance above constitutive levels in adult females when a melanotic encapsulation immune response was initiated by the intrathoracic inoculation of Dirofilaria immitis microfilariae.

Partial characterization of an abundant human skin melanosomal 66 kDa protein (MP 66) and investigation to purify a similar protein from B16 murine melanoma tumours

A single polypeptide protein of molecular weight 66kDa (MP 66), purified to homogeneity from melanosomes of normal human cadaver skin epidermal melanocytes, was further characterized. Based on the yield in the present investigation, the intracellular concentration of this protein was calculated to be 4.2 microM. It was shown to be a glycoprotein on gel electrophoresis. Based on its partial N-terminal amino acid sequence, it was shown to be distinct from known melanosomal proteins such as gp 75, tyrosinase-related protein-2 (TRP-2) and Pmel 17. Investigation to purify a similar type of protein from B16 murine melanoma tumours by following the same purification procedure resulted in a partially purified protein with a molecular weight of 66 kDa. However, unlike MP 66, this protein did not show inhibition of the monophenolase activity of tyrosinase at pH 6.8. Finally, the effects of 0.5 mM each of CaCl2, ZnSO4 and FeSO4 together, and of human skin epidermal melanosomal proteins, were studied on melanin polymerization at pH 4.7. The metal cations failed to initiate melanin polymerization, while melanosomal proteins did in a dose-dependent manner.

A new mechanism for the control of phenoloxidase activity: inhibition and complex formation with quinone isomerase

Insect phenoloxidases participate in three physiologically important processes, viz., cuticular hardening (sclerotization), defense reactions (immune reaction), and wound healing. Arrest or even delay of any of these processes compromises the survival of insects. Since the products of phenoloxidase action, viz., quinones, are cytotoxic, uncontrolled phenoloxidase action is deleterious to the insects. Therefore, the activity of this important enzyme has to be finely controlled. A novel inhibition of insect phenoloxidases, which serves as a new regulatory mechanism for control of its activity, is described. The activity of phenoloxidases isolated from both Sarcophaga bullata and Manduca sexta is drastically inhibited by quinone isomerase (isolated from Calliphora), an enzyme that utilizes the phenoloxidase-generated 4-alkylquinones. In turn, phenoloxidase reciprocated the inhibition of isomerase. By forming a complex and controlling each other's activity, these two enzymes seem to regulate the levels of endogenously quinones. In support of this contention, an endogenous complex consisting of phenoloxidase, quinone isomerase, and quinone methide isomerase was characterized from the insect, Calliphora. This sclerotinogenic complex was isolated and purified by borate extraction of the larval cuticle, ammonium sulfate precipitation, and Sepharose 6B column chromatography. The complex exhibited a molecular mass of about 620-680 kDa, as judged by size-exclusion chromatography on Sepharose 6B and HPLC and did not even enter 3% polyacrylamide gel during electrophoresis. The phenoloxidase activity of the complex exhibited a wide substrate specificity. Incubation of the complex with N-acetyldopamine rapidly generated N-acetylnorepinephrine, dehydro-N-acetyldopamine, and its dimers. In addition, transient accumulation of N-acetyldopamine quinone was also observed. These results confirm the presence of phenoloxidase, quinone isomerase, and quinone methide isomerase in the complex. Attempts to dissociate the complex with even trace amounts of SDS ended in the total loss of quinone isomerase activity. The complex does not seems to be made up of stoichiometric amounts of individual enzymes as the ratio of phenoloxidase to quinone isomerase varied from preparation to preparation. It is proposed that the complex formation between sequential enzymes of sclerotinogenic pathway is advantageous for the organism to effectively channel various reactive intermediates during cuticular hardening.

Human melanocytes and melanomas express novel mRNA isoforms of the tyrosinase-related protein-2/DOPAchrome tautomerase gene: molecular and functional characterization

We previously reported that a melanoma antigen, recognized by tumor-specific cytotoxic T lymphocytes, was encoded by intron sequences retained in a partially spliced transcript of the tyrosinase-related protein-2/DOPAchrome tautomerase gene. At difference with the mRNA encoding tyrosinase-related protein-2, this anomalous transcript was not expressed in melanocytes. This study examined whether neoplastic and/or normal cells of the melanocytic lineage could express additional forms of tyrosinase-related protein-2 mRNA. Screening of a melanoma-derived cDNA library with a tyrosinase-related protein-2 probe allowed identification of two novel isoforms. The first, tyrosinase-related protein-2-long tail, corresponds to the dominant transcript detected on melanomas and melanocytes by northern blot analysis. Tyrosinase-related protein-2-long tail is identical to the tyrosinase-related protein-2-encoding published cDNA sequence except for an extended 3'-untranslated region and is originated by alternative polyadenylation. This novel 3'-untranslated region contains an alternatively spliced, tyrosinase-related protein-2 last exon in the second isoform (tyrosinase-related protein-2-8b). The protein encoded by tyrosinase-related protein-2-8b is identical to tyrosinase-related protein-2 in its first 460 amino acids but possesses a different carboxyl-terminus devoid of transmembrane domain. Tyrosinase-related protein-2-long tail exhibited DOPA-chrome tautomerase activity, when transiently transfected into COS-7 cells. On the contrary, no detectable activity was exhibited by tyrosinase-related protein-2-8b. Reverse transcription-polymerase chain reaction analysis indicated that tyrosinase-related protein-2-long tail and tyrosinase-related protein-2-8b are expressed by tyrosinase-related protein-2-positive melanomas and normal melanocytes. Moreover all cell lines positive for tyrosinase-related protein-2 isoforms expressed tyrosinase and, all but one, tyrosinase-related protein-1. These data show that the human tyrosinase-related protein-2/DOPAchrome tautomerase gene can yield different isoforms by alternative poly(A) site usage or by alternative splicing. The pattern of expression of these isoforms suggest that they might play a part in the normal pathway of melanin biosynthesis.

Comparative study of the asparagine-linked sugar chains of human lipocalin-type prostaglandin D synthase purified from urine and amniotic fluid, and recombinantly expressed in Chinese hamster ovary cells

Lipocalin-type prostaglandin D synthase (L-PGDS) is a highly glycosylated member of the lipocalin gene family and is secreted into various human body fluids. We comparatively analyzed the structures of asparagine-linked sugar chains of human L-PGDS produced by recombinant Chinese hamster ovary cells and naturally occurring human urine and amniotic fluid. After the sugar chains were liberated by hydrazinolysis followed by N-acetylation, they were derivatized with 2-aminobenzamide. All of the sugar chains of three L-PGDSs occur as biantennary complex-type sugar chains. Most of the sugar chains of three samples were fucosylated on the inner most N-acetylglucosamine residue. Although the sugar chains of the recombinant L-PGDS do not contain any bisecting N-acetylglucosamine residues, 58% and 34% of the fucosylated-sugar chains of amniotic fluid and urine L-PGDSs, respectively, contain bisecting N-acetylglucosamine residues. The sialic acid residues occur solely as Siaalpha2-->3Gal groups of the recombinant L-PGDS; the sialic acid residues of other L-PGDS occur as both Siaalpha2-->3Gal and Siaalpha2-->6Gal groups. Variations in L-PGDS glycosylation may prove useful as markers to further elucidate the role of L-PGDS glycoforms in different tissues.

Purification and inactivation by substrate of an allene oxide synthase (CYP74) from corn (Zea mays L.) seeds

The allene oxide synthase (AOS) was purified from corn (Zea mays) seeds to homogeneity and characterized partially. The corn AOS was a hemoprotein cytochrome P450 with a molecular weight and pI of 53,000 and 6.0, respectively. The corn AOS was found to be irreversibly inactivated by a substrate, 13-hydroperoxyoctadienoic acid. The rate of the enzyme inactivation was higher at low pHs.

Altered N-glycosylation in macrophage x melanoma fusion hybrids

It was recently reported that a majority of hybrids generated in vitro between weakly metastatic mouse Cloudman S91 melanoma cells and human or mouse macrophages showed enhanced metastatic potential (Rachkovsky et al., 1998). With few exceptions, hybrids with enhanced metastatic potential also had elevated basal melanin content, enhanced chemotactic responses to fibroblast-conditioned media, and stronger responsiveness to MSH compared to parental cells. Analyses revealed that altered N-glycosylation in metastatic hybrids could explain the multiple phenotypic changes. Tyrosinase, TRP-2 and LAMP-1 from hybrids migrated more slowly on gels compared to the same proteins from parental melanoma cells, consistent with increased glycosylation. Migration of LAMP-1 from hybrids was similar to that from peritoneal macrophages which also appeared to be more heavily glycosylated than LAMP-1 from Cloudman cells. The incorporation of 3H-glucosamine, as a marker of N-glycosylation, into tyrosinase and LAMP-1 was found to be elevated in hybrids, suppressed by N-glycosylation inhibitors and stimulated by MSH to a greater degree in hybrids compared to parental cells. These results indicate N-glycosylation as an important regulatory pathway for MSH-induced melanogenesis, and further suggest that altered N-linked glycosylation may be an underlying mechanism for regulation of both melanogenesis and metastasis in macrophage x melanoma hybrids.

Purification and characterization of membrane-bound prostaglandin E synthase from bovine heart

Prostaglandin (PG) E synthase was solubilized with 6 mM sodium deoxycholate from the microsomal fraction of bovine hearts. The enzyme was purified by about 800-fold to apparent homogeneity. The specific activity of the purified enzyme was about 830 mU/mg of protein, and the K(m) value for PGH(2) was 24 microM. The molecular weight of the enzyme was about 31000 on SDS-polyacrylamide gel electrophoresis and was about 60000 by gel filtration. The enzyme was separated from glutathione (GSH) S-transferase by DEAE-Toyopearl column chromatography, and did not exhibit any GSH S-transferase activity towards four different substrates. The purified enzyme was active in the absence of GSH, but it was activated by various SH-reducing reagents including dithiothreitol, GSH, or beta-mercaptoethanol. This is the first reported purification of membrane-bound PGE synthase to apparent homogeneity.

Rapid purification and characterization of L-dopachrome-methyl ester tautomerase (macrophage-migration-inhibitory factor) from Trichinella spiralis, Trichuris muris and Brugia pahangi

Macrophage-migration-inhibition factor (MIF) is an essential stimulator of mammalian T-lymphocyte-dependent adaptive immunity, hence MIF orthologues might be expressed by infectious organisms as an immunosubversive stratagem. Since MIF actively catalyses the tautomerization of the methyl ester of l-dopachrome (using dopachrome tautomerase), the occurrence of MIF orthologues in several parasitic helminths was investigated by assaying and characterizing such activity. Evidence of MIF orthologues (dopachrome tautomerase) was found in the soluble fraction of the nematodes Trichinella spiralis (stage 4 larvae) and Trichuris muris (adults), and the filarial nematode Brugia pahangi (adults). The MIF orthologues of Tr. muris (TmMIF) and B. pahangi (BpMIF) were purified to homogeneity using phenyl-agarose chromatography, that of T. spiralis (TsMIF) required a further step: cation-exchange FPLC. Retention time on reverse-phase HPLC and Mr on SDS/PAGE of the nematode MIFs were similar to those of human MIF. N-terminal sequences (19 residues) of TsMIF and TmMIF showed 47 and 36% identity, respectively, with human MIF. The N-terminal sequence of BpMIF (14 residues) was identical to that of an MIF orthologue in the genome of B. malayi (Swiss-Prot, P91850) and showed 43% identity to either human or TsMIF. TsMIF had 10-fold higher dopachrome tautomerase activity than MIF from the other sources. The enzyme activities of TsMIF, BpMIF and TmMIF were less sensitive to inhibition by haematin (I50: >15 microM, >15 microM and 2.6 microM, respectively) than that of human MIF (I50 0.2 microM). Significant dopachrome tautomerase or phenyl-agarose-purifiable MIF-like protein was not detected in the soluble fraction of the nematodes Heligmosomoides polygyrus and Nippostrongylus brasiliensis, the cestode Hymenolepis diminuta, or the trematodes Schistosoma mansoni, S. japonicum and S. haematobium, or the free-living nematode, Caenorhabditis elegans, which does contain an MIF-related gene.

Quantification of prostaglandin D synthetase in cerebrospinal fluid: a potential marker for brain tumor

Prostaglandin D synthetase (PGD-S; prostaglandin-H2 D-isomerase, EC 5,3,99,2), a 30 kDa glycoprotein also known as beta-trace protein that catalyzes the formation of prostaglandin D2 (PGD2) from PGH2, was purified to apparent homogeneity from human cerebrospinal fluid (CSF) using a two-step procedure involving HPLC on a Vydac C8 reversed-phase column and high performance electrophoresis chromatography (HPEC) using a 10% T SDS-polyacrylamide gel. The purity of PGD-S isolated from CSF was confirmed by silver stained SDS-polyacrylamide gel and direct protein microsequencing (NH2-APEAQVSVQPNFQ). A highly specific polyclonal antibody was prepared against this protein for immunoassay development. Using an ELISA, it was found that the concentration of PGD-S in CSF did not alter significantly in different pathological conditions of the central nervous system (CNS). These include dementia (n = 9), hydrocephalus (n = 4), neuropathy (n = 11), optic neuritis (n = 4), multiple sclerosis (n = 11), and demyelinating syndrome (n = 11), when compared to normal individuals (n = 12); however, the level of PGD-S in the CSF obtained from patients with brain tumor (n = 11), was reduced by as much as 2-fold when compared to control samples (n = 12) illustrating PGD-S is a potentially useful marker for brain tumor.

Purification and some properties of 2-hydroxychromene-2-carboxylate isomerase from naphthalenesulfonate-assimilating Pseudomonas sp. TA-2

A 2-hydroxychromene-2-carboxylate isomerase was purified from a cell-free extract of naphthalenesulfonate-assimilating Pseudomonas sp. TA-2 to an electrophoretically homogeneous state by successive column chromatography on DEAE-cellulose, DEAE-Toyopearl 650M, Sephadex G-75, Hydroxyapatite, and Mono Q. The enzyme had a molecular mass of 25 and 27 kDa as estimated by SDS-PAGE and Superdex 200, respectively. Its N-terminal 30 amino acid sequence had high homology with the deduced amino acid sequences of the 2HC2CA isomerase of nahD (a gene of naphthalene metabolism), pahD (a gene of naphthalene and phenanthrene metabolism), and doxJ (a gene of dibenzothiophene metabolism). The enzymatic product was a trans isomer. The isomerase activity was inhibited in the presence of monoiodoacetate or Hg2+, but not by preincubation with monoiodoacetate or N-ethylmaleimide. GSH functioned as a cofactor and activated the enzyme at above 0.15 mM.

Enzymatic activity and partial purification of solanapyrone synthase: first enzyme catalyzing Diels-Alder reaction

In cell-free extracts of Alternaria solani, an enzymatic activity converting prosolanapyrone II to solanapyrones A and D via oxidation and subsequent Diels-Alder reaction has been found. Chromatography with DEAE-Sepharose provided two active fractions, pools 1 and 2. The former fraction converted prosolanapyrone II to solanapyrones A and D in a ratio of 2.2:1 with optical purities of 99% and 45% ee, respectively. The latter fraction did so in a ratio of 7.6:1 with 99% and nearly 0% ee, respectively. The enzyme partially purified from pool 2 native molecular weight of 40-62 kD and a pl of 4.25. The high reactivity of prosolanapyrone III in aqueous solution and the chromatographic behavior of the enzyme in pool 2 suggest that a single enzyme catalyzes both the oxidation and Diels-Alder reaction.

Properties of prostacyclin synthase

Prostacyclin synthase (PGIS) was isolated from bovine aortic microsomes after detergent solubilisation following purification by DEAE-Sephacel, immobilized metal affinity, and hydroxy apatite chromatography. The homogenous protein exhibited spectral characteristics of a heme-thiolate protein (P450) like the enzyme purified earlier from porcine microsomes and had an apparent mass of 52 kDa on SDS/PAGE. Three peptides from an endoproteinase Lys-C digest were isolated and sequenced. An antiserum was prepared from rabbits and purified by affinity chromatography. This allowed Western blots of microsomes from cultured endothelial cells. After treatment with IL-1 the activity of the cells in producing 6-keto-PGF1 alpha increased about threefold over 27 h which was accompanied by an increase in PGIS mass. A monoclonal antibody was used to set up an ELISA which served for the quantitation of PGIS in bovine tissues.

Lipocalin-type prostaglandin D synthase in human male reproductive organs and seminal plasma

Prostaglandin D synthase (PGDS) activity was detected in human seminal plasma (0.05-1.83 nmol/min per milligram protein). The enzyme was purified from human seminal plasma by immunoaffinity chromatography and found to be 27 kDa in size and N-glycosylated, similar to PGDS in the cerebrospinal fluid. The N-terminal amino acid sequence of 16 residues of the seminal enzyme, APEAQVSVQPNFQQDK, was identical to that of the cerebrospinal fluid PGDS. Although PGDS activity and the content determined by the immunoassay each highly varied in the seminal plasma, the concentration was significantly (p < 0.001) lower in the oligozoospermic group (2.47 +/- 0.51 microg/ml) than in the normozoospermic group (9.75 +/- 1.49 microg/ml). Prostaglandin (PG) D2 was detected in the seminal plasma (5.00 +/- 0.65 ng/ml) with a positive correlation to the PGDS concentration (p < 0.05). PGD2 was converted to the J series of PGs in the seminal plasma with a half-life of 6.5 h. Northern blot analysis revealed that mRNA for PGDS was expressed in the testis, prostate, and epididymis. Through immunohistochemistry, PGDS was localized in Leydig cells of the testis and in epithelial cells of the prostate and ductus epididymidis.

Crystallization and preliminary X-ray analysis of human D-dopachrome tautomerase

D-Dopachrome tautomerase catalyzes the conversion of D-dopachrome to 5,6-dihydroxyindole. This protein has amino acid sequence homology with that of macrophage migration inhibitory factor (MIF), suggesting a pathophysiological role of this protein in inflammatory and immunological events. We previously determined the tertiary structure of MIF and revealed the functional and evolutional relationships of this protein to isomerase. However, the reaction mechanism of both proteins associated with the inflammatory response, immune system, or tautomerase activities in vitro have not yet been clarified. The tertiary structure of D-dopachrome tautomerase would provide insight into the molecular function and the mechanism of these proteins. In this study, we crystallized human D-dopachrome tautomerase by a hanging-drop vapor diffusion method. The crystals belong to the trigonal space group P3, with unit cell dimensions a = b = 84.2 A and c = 41.0 A. They contain three (or two) monomers in the asymmetric unit, corresponding to a VM value of 2.21 (or 3.32) A3 Da-1. The best crystals diffract X-ray to 1.6 A resolution using a synchrotron radiation source. Crystallization of the selenomethionyl derivative of the protein for applying the multiwavelength anomalous diffraction method was also successful.