Carbonyl reductase activity exhibited by pig testicular 20 beta-hydroxysteroid dehydrogenase

Characterization of a novel porcine carbonyl reductase activated by glutathione: Relationship to carbonyl reductase 1, 3α/β-hydroxysteroid dehydrogenase and prostaglandin 9-ketoreductase

A porcine gene, LOC100622246, encodes carbonyl reductase [NADPH] 1 (pCBR-N1), whose function remains unknown. Previously, three porcine carbonyl reductases, carbonyl reductase 1 (pCBR1), 3α/β-hydroxysteroid dehydrogenase (p3α/β-HSD) and prostaglandine-9-keto reductase (pPG-9-KR), were purified from neonatal testis, adult testis and adult kidney, respectively. However, the relationship of pCBR-N1 with the three enzymes is still unknown. Here, we compare the properties of the recombinant pCBR-N1 and pCBR1. The two enzymes reduced various carbonyl compounds including 5α-dihydrotestosterone, which was converted to its 3α- and 3β-hydroxy-metabolites. Compared to pCBR1, pCBR-N1 exhibited higher Km and kcat values for most substrates, but more efficiently reduced prostaglandin E2. pCBR-N1 was inhibited by known inhibitors of p3α/β-HSD (hexestrol and indomethacin), but not by pCBR1 inhibitors. pCBR-N1 was highly expressed than pCBR1 in the several tissues of adult domestic and microminiature pigs. The results, together with partial amino acid sequence match between pCBR-N1 and pPG-9-KR, reveal that pCBR-N1 is identical to p3α/β-HSD and pPG-9-KR. Notably, pCBR-N1, but not pCBR1, reduced S-nitrosoglutathione and glutathione-adducts of alkenals including 4-oxo-2-nonenal with Km of 8.3-32 μM, and its activity toward non-glutathionylated substrates was activated 2- to 9-fold by 1 mM glutathione. Similar activation by glutathione was also observed for human CBR1. Site-directed mutagenesis revealed that the differences in kinetic constants and glutathione-mediated activation between pCBR-N1 and pCBR1 are due to differences in residue 236 and two glutathione-binding residues (at positions 97 and 193), respectively. Thus, pCBR-N1 is a glutathione-activated carbonyl reductase that functions in the metabolism of endogenous and xenobiotic carbonyl compounds.

Differential expression of subunits of 20β-hydroxysteroid dehydrogenase during gametogenesis in rainbow trout (Oncorhychus mykiss)

The patterns of expression of two subunits of 20β-hydroxysteroid dehydrogenase (20β-HSD), key enzyme involved in the biosynthesis and activation of steroid hormones, were examined in rainbow trout by using a combination of quantitative real-time PCR and in-situ hybridization. The expression of targeted genes was examined in mRNA extracted from different tissues at different gonadal stages in male and female trout. Both subunits of 20β-HSD were found to be widely distributed in tissues. The highest expression of 20β-HSD A was found in intestine followed by skin, stomach, liver and gills, whereas, the highest expression of 20β-HSD B was observed in stomach followed by head kidney, ovary - at late vitellogenesis stage- and trunk kidney. In ovarian tissue 20β-HSD A was highly expressed in mature oocytes, and the highest expression of 20β-HSD B was in ovary at late vitellogenesis stage. There were no differences in the level of expression of either subunit among groups of rainbow trout at different stages of maturational competence. In male fish, 20β-HSD A was highly expressed in testis stage I in contrast to 20β-HSD B which was highly expressed in testis stage VIII. In situ- hybridization results showed that the 20β-HSD gene was highly expressed in gastrointestinal organs, while only slightly expressed in the gonadal tissue of fish at stage 62day-post-fertilization (dpf). Overall, the results confirm the ubiquitous presence of 20β-HSD among tissues in rainbow trout with relatively minor fluctuations in expression associated with reproductive cycles which collectively suggests a wider metabolic role of these enzymes than just an association with the synthesis of control hormones for reproduction.

Functional mechanism of C-terminal tail in the enzymatic role of porcine testicular carbonyl reductase: a combined experiment and molecular dynamics simulation study of the C-terminal tail in the enzymatic role of PTCR

Porcine testicular carbonyl reductase, PTCR which is one of the short chain dehydrogenases/reductases (SDR) superfamily catalyzes the NADPH-dependent reduction of carbonyl compounds including steroids and prostaglandins. Previously we reported C- terminal tail of PTCR was deleted due to a nonsynonymous single nucleotide variation (nsSNV). Here we identified from kinetic studies that the enzymatic properties for 5α-dihydrotestosterone (5α-DHT) were different between wild-type and C-terminal-deleted PTCRs. Compared to wild-type PTCR, C-terminal-deleted PTCR has much higher reduction rate. To investigate structural difference between wild-type and C-terminal-deleted PTCRs upon 5α-DHT binding, we performed molecular dynamics simulations for two complexes. Using trajectories, molecular interactions including hydrogen bonding patterns, distance between 5α-DHT and catalytic Tyr193, and interaction energies are analyzed and compared. During the MD simulation time, the dynamic behavior of C-terminal tail in wild-type PTCR is also examined using essential dynamics analysis. The results of our simulations reveal that the binding conformation of 5α-DHT in C-terminal-deleted PTCR is more favorable for reduction reaction in PTCR, which shows strong agreement with kinetic data. These structural findings provide valuable information to understand substrate specificity of PTCR and further kinetic properties of enzymes belonging to the SDR superfamily.

Carbonyl Reductases and Pluripotent Hydroxysteroid Dehydrogenases of the Short-chain Dehydrogenase/reductase Superfamily

Carbonyl reduction of aldehydes, ketones, and quinones to their corresponding hydroxy derivatives plays an important role in the phase I metabolism of many endogenous (biogenic aldehydes, steroids, prostaglandins, reactive lipid peroxidation products) and xenobiotic (pharmacologic drugs, carcinogens, toxicants) compounds. Carbonyl-reducing enzymes are grouped into two large protein superfamilies: the aldo-keto reductases (AKR) and the short-chain dehydrogenases/reductases (SDR). Whereas aldehyde reductase and aldose reductase are AKRs, several forms of carbonyl reductase belong to the SDRs. In addition, there exist a variety of pluripotent hydroxysteroid dehydrogenases (HSDs) of both superfamilies that specifically catalyze the oxidoreduction at different positions of the steroid nucleus and also catalyze, rather nonspecifically, the reductive metabolism of a great number of nonsteroidal carbonyl compounds. The present review summarizes recent findings on carbonyl reductases and pluripotent HSDs of the SDR protein superfamily.

Molecular modeling and site-directed mutagenesis reveal the benzylisoquinoline binding site of the short-chain dehydrogenase/reductase salutaridine reductase

Recently, the NADPH-dependent short-chain dehydrogenase/reductase (SDR) salutaridine reductase (E.C. 1.1.1.248) implicated in morphine biosynthesis was cloned from Papaver somniferum. In this report, a homology model of the Papaver bracteatum homolog was created based on the x-ray structure of human carbonyl reductase 1. The model shows the typical alpha/beta-folding pattern of SDRs, including the four additional helices alphaF'-1 to alphaF'-4 assumed to prevent the dimerization of the monomeric short-chain dehydrogenases/reductases. Site-directed mutagenesis of asparagine-152, serine-180, tyrosine-236, and lysine-240 resulted in enzyme variants with strongly reduced performance or inactive enzymes, showing the involvement of these residues in the proton transfer system for the reduction of salutaridine. The strong preference for NADPH over NADH could be abolished by replacement of arginine residues 44 and 48 by glutamic acid, confirming the interaction between the arginines and the 2'-phosphate group. Docking of salutaridine into the active site revealed nine amino acids presumably responsible for the high substrate specificity of salutaridine reductase. Some of these residues are arranged in the right position by an additional alphaE' helix, which is not present in SDRs analyzed so far. Enzyme kinetic data from mutagenic replacement emphasize the critical role of these residues in salutaridine binding and provide the first data on the molecular interaction of benzylisoquinoline alkaloids with enzymes.

Multiplicity of mammalian reductases for xenobiotic carbonyl compounds

A variety of carbonyl compounds are present in foods, environmental pollutants, and drugs. These xenobiotic carbonyl compounds are metabolized into the corresponding alcohols by many mammalian NAD(P)H-dependent reductases, which belong to the short-chain dehydrogenase/reductase (SDR) and aldo-keto reductase superfamilies. Recent genomic analysis, cDNA isolation and characterization of the recombinant enzymes suggested that, in humans, the six members of each of the two superfamilies, i.e., total of 12 enzymes, are involved in the reductive metabolism of xenobiotic carbonyl compounds. They comprise three types of carbonyl reductase, dehydrogenase/reductase (SDR family) member 4, 11beta-hydroxysteroid dehydrogenase type 1, L-xylulose reductase, two types of aflatoxin B1 aldehyde reductase, 20alpha-hydroxysteroid dehydrogenase, and three types of 3alpha-hydroxysteroid dehydrogenase. Accumulating data on the human enzymes provide new insights into their roles in cellular and molecular reactions including xenobiotic metabolism. On the other hand, mice and rats lack the gene for a protein corresponding to human 3alpha-hydroxysteroid dehydrogenase type 3, but instead possess additional five or six genes encoding proteins that are structurally related to human hydroxysteroid dehydrogenases. Characterization of the additional enzymes suggested their involvement in species-specific biological events and species differences in the metabolism of xenobiotic carbonyl compounds.

Inhibition of 3 alpha/beta,20 beta-hydroxysteroid dehydrogenase by dexamethasone, glycyrrhetinic acid and spironolactone is attenuated by deletion of 12 carboxyl-terminal residues

We constructed a pig 3alpha/beta,20beta-hydroxysteroid dehydrogenase (3alpha/beta,20beta-HSD) mutant, which lacks 12 carboxyl-terminal amino acids residues. Enzyme activity studies indicated that the deleted amino acids have a role in steroid metabolism and may assist in substrate binding in wild-type 3alpha/beta,20beta-HSD. Furthermore, substrate binding likely induces a conformational change allowing the 12 carboxyl-terminal amino acids interact with the steroid substrate [Nakajin S. et al., Biochim. Biophys. Acta, 1550, 175-182 (2001)]. In this paper, we clarified that although pig 3alpha/beta,20beta-HSD is potently inhibited by dexamethasone, glycyrrhetinic acid and spironolactone, this inhibition is remarkably attenuated by deleting the 12 carboxyl-terminal residues. The inhibition constant (Ki) of pig 3alpha/beta,20beta-HSD for dexamethasone increased 115-fold. These observations also indicate that these amino acid residues interact with steroid substrates or steroid inhibitors and have an important role in substrate or inhibitor binding to the active site.

Sperm-zona pellucida interaction involves a carbonyl reductase activity in the hamster

For successful fertilization to occur, the spermatozoa must transit through an egg-specific extracellular matrix or zona pellucida (zp) to reach and ultimately fuse with the oocyte plasma membrane. This process involves ligand-receptor recognition between the zp and the acrosomal cap of the sperm. The hamster sperm protein P26h, a receptor which is acquired during epididymal transit, has been suggested to act in sperm-zp binding. The cloning and characterization of the full-length cDNA-encoding hamster P26h revealed 85% identity with a porcine lung carbonyl reductase. To better understand the mechanism by which P26h interacts with zp proteins, we investigated carbonyl reductase activity during gamete interactions. In the present study, we show that specific inhibitors of carbonyl reductase such as diclofenac and phenylbutazone decreases sperm-zp binding without affecting the motility, progressivity or acrosome integrity of sperm. We also detected, and partly purified, carbonyl reductase activities from cauda epididymal sperm protein extract and this activity was associated with an enriched fraction of P26h. Removing P26h from the partly purified protein fractions by immunoaffinity chromatography led to the loss of carbonyl reductase activity. The findings that sperm-zp binding is blocked by carbonyl reductase inhibitors and that P26h is active in mature sperm suggest that P26h could play an important role in the fertilization process.

Hormonal regulation of male-specific 20beta-hydroxysteroid dehydrogenase with carbonyl reductase-like activity present in kidney microsomes of rats

Progesterone, 17alpha-hydroxyprogesterone, cortisone and cortisol, which are C(21)-steroids with a ketone group at the 20-position, potently inhibited the activity of enzyme acetohexamide reductase (AHR) responsible for the reductive metabolism of acetohexamide in kidney microsomes of male rats. Furthermore, progesterone was a competitive inhibitor of AHR. In the case of progesterone usage as the substrate, 20beta-hydroxysteroid dehydrogenase (20beta-HSD) activity was much higher than 20alpha-hydroxysteroid dehydrogenase (20alpha-HSD) activity in kidney microsomes of male rats. These results indicate that AHR present in kidney microsomes of male rats, functions as 20beta-HSD with carbonyl reductase-like activity. In male rats, both testectomy and hypophysectomy decreased the renal microsomal 20beta-HSD activity, but the decreased enzyme activities were increased by the treatment with testosterone propionate (TP). We propose the possibility that TP treatment regulates the renal microsomal 20beta-HSD activity by acting directly on the kidney of male rats. This is supported from the fact that when TP was given to ovariectomized and hypophysectomized female rats, the male-specific 20beta-HSD activity was detected in their kidney microsomes.

Porcine carbonyl reductase. structural basis for a functional monomer in short chain dehydrogenases/reductases

Porcine testicular carbonyl reductase (PTCR) belongs to the short chain dehydrogenases/reductases (SDR) superfamily and catalyzes the NADPH-dependent reduction of ketones on steroids and prostaglandins. The enzyme shares nearly 85% sequence identity with the NADPH-dependent human 15-hydroxyprostaglandin dehydrogenase/carbonyl reductase. The tertiary structure of the enzyme at 2.3 A reveals a fold characteristic of the SDR superfamily that uses a Tyr-Lys-Ser triad as catalytic residues, but exhibits neither the functional homotetramer nor the homodimer that distinguish all SDRs. It is the first known monomeric structure in the SDR superfamily. In PTCR, which is also active as a monomer, a 41-residue insertion immediately before the catalytic Tyr describes an all-helix subdomain that packs against interfacial helices, eliminating the four-helix bundle interface conserved in the superfamily. An additional anti-parallel strand in the PTCR structure also blocks the other strand-mediated interface. These novel structural features provide the basis for the scaffolding of one catalytic site within a single molecule of the enzyme.

Characterization of ovarian carbonyl reductase gene expression during ovulation in the gonadotropin-primed immature Rat

In this differential-display polymerase chain reaction-based study, four different primer sets generated cDNA fragments of ovarian carbonyl reductase genes that were uniquely expressed during the ovulatory process in eCG-primed immature rats. The temporal pattern of expression of this aldo-keto reductase gene was delineated by extracting ovarian RNA at 0, 2, 4, 8, 12, and 24 h after induction of ovulation via injection of the primed animals with hCG. The results showed that at least four homologous forms of this gene were transcribed during ovulation. Northern blot analyses indicated a 14-fold increase in ovarian mRNA for carbonyl reductase, with expression reaching a peak at 8 h after hCG treatment and then declining to negligible levels during the next 16 h. In situ hybridization revealed that most of the transcription was in the thecal connective tissue of the ovary and was absent from the granulosa layer of ovarian follicles. Treatment of the animals with ovulation-blocking doses of epostane (an inhibitor of progesterone synthesis) or indomethacin (an inhibitor of prostanoid synthesis) did not reduce the expression of ovarian carbonyl reductase. Nevertheless, the temporal pattern of expression of carbonyl reductase after the induction of ovulation suggests that this enzyme activity is at least indirectly associated with the ovulatory process.

Cloning and expression of two carbonyl reductase-like 20beta-hydroxysteroid dehydrogenase cDNAs in ovarian follicles of rainbow trout (Oncorhynchus mykiss)

In salmonid fish, 20beta-hydroxysteroid dehydrogenase (20beta-HSD) is a key enzyme involved in the production of oocyte maturation-inducing hormone (MIH), 17alpha, 20beta-dihydroxy-4-pregnen-3-one. Here we report the isolation of two cDNAs which encode proteins with high homology to carbonyl reductase-like 20beta-HSD (CR/20beta-HSD) from rainbow trout (Oncorhynchus mykiss) ovarian follicles. Genomic DNA analysis showed that the two CR/20beta-HSD cDNAs are derived from two different genes. Northern blot and RT PCR analysis demonstrated that trout CR/20beta-HSDs are broadly expressed in various tissues. Enzymatic characterization using recombinant CR/20beta-HSD proteins produced in E. coli showed that the product of one of the two cDNAs had both 20beta-HSD and CR activity, but the other had neither activity. Although the functional significance of the two genes remains unresolved, these results clearly demonstrate the presence of two distinct CR/20beta-HSD transcripts in the trout ovary.

Mutation of tyrosine-194 and lysine-198 in the catalytic site of pig 3alpha/beta,20beta-hydroxysteroid dehydrogenase

Pig 3alpha/beta,20beta-hydroxysteroid dehydrogenase is an NADPH-dependent enzyme that catalyses the reduction of ketones on steroids and aldehydes and ketones on various xenobiotics, like its homologue carbonyl reductase. 3alpha/beta,20beta-Hydroxysteroid dehydrogenase and carbonyl reductase are members of the short-chain dehydrogenases/reductase family, in which a tyrosine residue and a lysine residue have been identified as catalytically important. In pig 20beta-hydroxysteroid dehydrogenase these residues are tyrosine-194 and lysine-198. Here we report the effect on the reduction of two ketone and two aldehyde substrates by pig 3alpha/beta,20beta-hydroxysteroid dehydrogenase in which tyrosine-194 has been mutated to phenylalanine and cysteine, and lysine-198 has been mutated to isoleucine and arginine. Mutants with phenylalanine-194 or isoleucine-198 are inactive. Depending on the substrate, the mutant with cysteine-194 has a catalytic efficiency of 0.4-1% and the mutant with arginine-198 has a catalytic efficiency of 4-23% of the wild-type enzyme. We also mutated tyrosine-81 and tyrosine-253 to phenylalanine. Although both tyrosines are conserved in 3alpha/beta,20beta-hydroxysteroid dehydrogenase and carbonyl reductase, depending on the substrate, the mutant enzymes are as active as, or more active than, wild-type enzyme.