Homologies between enzymes involved in steroid and xenobiotic carbonyl reduction in vertebrates, invertebrates and procaryonts

Insights into the evolution of sorbitol metabolism: phylogenetic analysis of SDR196C family

Background

Short chain dehydrogenases/reductases (SDR) are NAD(P)(H)-dependent oxidoreductases with a highly conserved 3D structure and of an early origin, which has allowed them to diverge into several families and enzymatic activities. The SDR196C family (http://www.sdr-enzymes.org) groups bacterial sorbitol dehydrogenases (SDH), which are of great industrial interest. In this study, we examine the phylogenetic relationship between the members of this family, and based on the findings and some sequence conserved blocks, a new and a more accurate classification is proposed.

Results

The distribution of the 66 bacterial SDH species analyzed was limited to Gram-negative bacteria. Six different bacterial families were found, encompassing α-, β- and γ-proteobacteria. This broad distribution in terms of bacteria and niches agrees with that of SDR, which are found in all forms of life. A cluster analysis of sorbitol dehydrogenase revealed different types of gene organization, although with a common pattern in which the SDH gene is surrounded by sugar ABC transporter proteins, another SDR, a kinase, and several gene regulators.

According to the obtained trees, six different lineages and three sublineages can be discerned. The phylogenetic analysis also suggested two different origins for SDH in β-proteobacteria and four origins for γ-proteobacteria.

Finally, this subdivision was further confirmed by the differences observed in the sequence of the conserved blocks described for SDR and some specific blocks of SDH, and by a functional divergence analysis, which made it possible to establish new consensus sequences and specific fingerprints for the lineages and sub lineages.

Conclusion

SDH distribution agrees with that observed for SDR, indicating the importance of the polyol metabolism, as an alternative source of carbon and energy. The phylogenetic analysis pointed to six clearly defined lineages and three sub lineages, and great variability in the origin of this gene, despite its well conserved 3D structure. This suggests that SDH are very old and emerged early during the evolution. This study also opens up a new and more accurate classification of SDR196C family, introducing two numbers at the end of the family name, which indicate the lineage and the sublineage of each member, i.e, SDR196C6.3.

Recent advances in 17beta-hydroxysteroid dehydrogenases

The metabolism of steroids at position 17 is catalysed by a growing number of 17beta-hydroxysteroid dehydrogenases (17beta-HSDs). Several human diseases like breast or prostate cancer, endometriosis,metabolic syndrome and mental diseases were associated with dysfunctions of 17beta-HSDs, which consequently became drug targets. This review will focus on identities of 17beta-HSDs and recent advances in analyses of their physiological roles in steroid and lipid metabolism. It will also address the potential of metabolomics in drug development.

Medium- and short-chain dehydrogenase/reductase gene and protein families : the SDR superfamily: functional and structural diversity within a family of metabolic and regulatory enzymes

Short-chain dehydrogenases/reductases (SDRs) constitute a large family of NAD(P)(H)-dependent oxidoreductases, sharing sequence motifs and displaying similar mechanisms. SDR enzymes have critical roles in lipid, amino acid, carbohydrate, cofactor, hormone and xenobiotic metabolism as well as in redox sensor mechanisms. Sequence identities are low, and the most conserved feature is an α/β folding pattern with a central beta sheet flanked by 2–3 α-helices from each side, thus a classical Rossmannfold motif for nucleotide binding. The conservation of this element and an active site, often with an Asn-Ser-Tyr-Lys tetrad, provides a platform for enzymatic activities encompassing several EC classes, including oxidoreductases, epimerases and lyases. The common mechanism is an underlying hydride and proton transfer involving the nicotinamide and typically an active site tyrosine residue, whereas substrate specificity is determined by a variable C-terminal segment. Relationships exist with bacterial haloalcohol dehalogenases, which lack cofactor binding but have the active site architecture, emphasizing the versatility of the basic fold in also generating hydride transfer-independent lyases. The conserved fold and nucleotide binding emphasize the role of SDRs as scaffolds for an NAD(P)(H) redox sensor system, of importance to control metabolic routes, transcription and signalling.

Steroids in aquatic invertebrates

Steroid molecules are present in all invertebrates, and some of them have established hormonal roles: this is the case for ecdysteroids in arthropods and, to a lesser extent, for vertebrate-type steroids in molluscs. Steroids are not only hormones, they may also fulfill many other functions in chemical communication, chemical defense or even digestive physiology. The increasing occurrence of endocrine disruption problems caused by environmental pollutants, which interfere in particular with reproductive physiology of vertebrates but also of invertebrates has made necessary to better understand the endocrine physiology of the latter and the role of steroids in these processes. So many attempts are being made to better understand the endocrine roles of steroids in arthropods and molluscs, and to establish whether they also fulfill similar functions in other invertebrate phyla. At the moment, both the precise identification of these steroids, the determination of their origin (endogenous versus exogenous) and of their mechanism of action are under active investigation. This research takes profit of the development of genome sequencing programs on many invertebrate species, which allow the identification of receptors and/or biosynthetic enzymes, when related to their vertebrate counterparts, but the story is not so simple, as will be exemplified by estrogen receptors of molluscs.

Comparative enzymology of 11 beta -hydroxysteroid dehydrogenase type 1 from glucocorticoid resistant (Guinea pig) versus sensitive (human) species

Type 1 11 beta-hydroxysteroid dehydrogenase constitutes a prereceptor control mechanism through its ability to reduce dehydroglucocorticoids to the receptor ligands cortisol and corticosterone in vivo. We compared kinetic characteristics of the human and guinea pig 11 beta-hydroxysteroid dehydrogenase isozymes derived from species differing in glucocorticoid sensitivity. Both orthologs were successfully expressed as full-length enzymes in yeast and COS7 cells and as soluble transmembrane-deleted constructs in Escherichia coli. Both isozymes display Michaelis-Menten kinetics in intact cells and homogenates and show low apparent micromolar K(m) values in homogenates, which are lowered by approximately one order of magnitude in intact cells, allowing corticosteroid activation at physiological glucocorticoid levels. Recombinant soluble proteins were expressed and purified with high specific dehydrogenase and reductase activities, revealing several hundred-fold higher specificity constants than those reported earlier for the purified native enzyme. Importantly, these purified soluble enzymes also display a hyperbolic dependence of reaction velocity versus substrate concentration in 11-oxoreduction with K(m) values of 0.8 microm (human) and 0.6 microm (guinea pig), close to the values obtained from intact cells. Active site titration was carried out with the human enzyme using a novel inhibitor compound and reveals a fraction of 40-50% active sites/mol total enzyme. The kinetic data obtained argue against the involvement of 11 beta-hydroxysteroid dehydrogenase as a modulating factor for the glucocorticoid resistance observed in guinea pigs. Instead, the expression of 11 beta-hydroxysteroid dehydrogenase type 1 in the Zona glomerulosa of the guinea pig adrenal gland suggests a role of this enzyme in mineralocorticoid synthesis in this hypercortisolic species.

Novel enzymological profiles of human 11beta-hydroxysteroid dehydrogenase type 1

The human enzyme 11beta-hydroxysteroid dehydrogenase (11beta-HSD) catalyzes the reversible oxidoreduction of 11beta-OH/11-oxo groups of glucocorticoid hormones. Besides this important endocrinological property, the type 1 isozyme (11beta-HSD1) mediates reductive phase I reactions of several carbonyl group bearing xenobiotics, including drugs, insecticides and carcinogens. The aim of this study was to explore novel substrate specificities of human 11beta-HSD1, using heterologously expressed protein in the yeast system Pichia pastoris. In addition to established phase I xenobiotic substrates, it is now demonstrated that transformed yeast strains catalyze the reduction of ketoprofen to its hydroxy metabolite, and the oxidation of the prodrug DFU-lactol to the pharmacologically active lactone compound. Purified recombinant 11beta-HSD1 mediated oxidative reactions, however, the labile reductive activity component could not be maintained. In conclusion, evidence is provided that human 11beta-HSD1 in vitro is involved in phase I reactions of anti-inflammatory non-steroidal drugs like ketoprofen and DFU-lactol.

Heterogeneity of 11beta-hydroxysteroid dehydrogenase type 1/microsomal carbonyl reductase (11beta-HSD/CR) in guinea pig tissues. Purification of the liver form suggests modification in the cosubstrate binding site

11beta-hydroxysteroid dehydrogenase (11beta-HSD) and xenobiotic carbonyl reductase activities were determined in guinea pig tissue microsomes. The data indicate the presence of a NADP(H) dependent form, distinct from the known type I isozyme. Purification of 11beta-HSD-1 from liver microsomes resulted in two distinct peaks, resolved by dye-ligand chromatography, indicating differences in the cosubstrate binding site. Immunoblot analysis using anti 11beta-HSD-1 antibodies reveals the presence of similar structural determinants between the enzyme forms. Both have an apparent molecular mass of 32 kDa, suggesting protein modifications occurring in the type 1 isozyme which account for the differences in chromatographic behaviour.

Carbonyl reduction of an anti-insect agent imidazole analogue of metyrapone in soil bacteria, invertebrate and vertebrate species

Carbonyl reduction to the respective alcohol metabolites of the anti-insect agent imidazole analogue of metyrapone, NKI 42255 (2-(1-imidazolyl)-1-(4-methoxyphenyl)-2-methyl-1-propanone) and its parent compound metyrapone was characterized in subcellular fractions previously described bacterial and mammalian hydroxysteroid dehydrogenases/carbonyl from soil bacteria, as well as insect, invertebrate and teleost species. The enzymes involved in this metabolic step were characterized with respect to their cosubstrate specificities, inhibitor susceptibilities, and immunological crossreactivities with antibodies directed against reductases (HSD/CR). All fractions investigated rapidly reduced metyrapone, with highest specific activities found in insect, invertebrate and vertebrate fractions. Except for the insect fractions, all species examined reduced the NKI compound. Cosubstrate dependence and inhibitor specificities suggest that the enzymes described belong to the protein superfamilies of short-chain dehydrogenases/reductases (SDR) or aldo-keto reductases (AKR). Immunological crossreactions to the previously established subgroup of HSD/CRs were found in trout liver microsomes and insect homogenates, but not in all bacterial extracts or earthworm microsomes. These findings suggest that the high CR activities found in these fractions belong to different subgroups of SDR or AKR.

Characterization of a 3 alpha-hydroxysteroid dehydrogenase/carbonyl reductase from the gram-negative bacterium Comamonas testosteroni

A new form of the NAD(P)-dependent 3 alpha-hydroxysteroid dehydrogenases (3 alpha-HSDs), present in the gram-negative bacterium Comamonas testosteroni ATCC 11996, was isolated from a testosterone-induced bacterial extract and characterized. The enzyme (HSD 28) has a monomeric molecular mass of 28 kDa. It belongs to the protein superfamily of short-chain dehydrogenases/reductases (SDR) as established by N-terminal sequence analysis. Along with the 3 alpha-hydroxysteroid dehydrogenase and 3-oxo-reductase activities towards a variety of cis or trans fused A/B ring steroids, it also reduces several xenobiotic carbonyl compounds, including a metyrapone-based class of insecticides, to the respective alcohol metabolites. No dihydrodiol dehydrogenase activity towards trans- or cis-benzene-dihydrodiols could be detected, thus distinguishing it from the indomethacine-sensitive, mammalian liver type 3 alpha-HSDs. Subcellular fractionation revealed that the enzyme is localized in the cytoplasm of the bacterial cell. Proteins similar to the 3 alpha-HSD were detected and characterized from Comamonas testosteroni strain ATCC 17454 and from a commercially available steroid-induced extract of a patent Pseudomonas strain. The N-terminal amino acid sequence of the 3 alpha-HSD from the latter strain (HSD 29) is highly similar (94% identity over 15 residues) to a previously determined primary structure of a Pseudomonas species 3 alpha-HSD. However, no similarities could be detected between HSD 28 and a recently determined 3 alpha-HSD sequence from the ATCC 11996 Comamonas strain. The specific crossreaction of antibodies directed against mammalian liver type I 11 beta-hydroxysteroid dehydrogenase (11 beta-HSD I) with the isolated 3 alpha-HSDs suggests the existence of a functionally and structurally related subgroup within the SDR superfamily. The broad substrate specificities of the characterized 3 alpha-HSD enzymes lead to the conclusion that they might participate in the intestinal bioactivation or inactivation of hormones, bile acids and xenobiotics since Comamonas testosteroni and related species are found in the intestinal tract of vertebrates including man.

Cloning and primary structure of murine 11 beta-hydroxysteroid dehydrogenase/microsomal carbonyl reductase

Screening of a mouse liver lambda gt 11 cDNA library with a rat liver 11 beta-hydroxysteroid dehydrogenase cDNA (11 beta-HSDr1A) and subsequent screening with an isolated mouse probe, resulted in the isolation and structure determination of a mouse cDNA encoding an amino acid sequence which is very similar to human and rat 11 beta-hydroxysteroid dehydrogenases (78% and 86% similar, respectively), and also to other known vertebrate 11 beta-hydroxysteroid dehydrogenase structures. Open-reading-frame analysis and the deduced amino acid sequence predict a protein with a molecular mass of 32.3 kDa which belongs to the superfamily of the short-chain dehydrogenase proteins. The amino acid sequence contains two potential glycosylation sites. These data are in agreement with information on the glycoprotein character of the native enzyme. This kind of post-translational modification seems to be a determining factor concerning the equilibrium of the catalyzed 11 beta-dehydrogenation/11-oxo reduction step [Obeid, J., Curnow, K. M., Aisenberg, J. & White, P.C. (1993) Mol. Endocrinol. 7, 154-160; Agarwal, A.K., Tusie-Luna, M.T., Monder, C. & White, P.C. (1990) Mol. Endocrinol. 4, 1827-1832]. After in vitro transcription/translation of the mouse cDNA, immunoprecipitation with anti-(microsomal carbonyl reductase) serum and N-terminal sequence analysis of the purified protein confirms the identity of microsomal 11 beta-hydroxysteroid dehydrogenase with the previously described, microsomal-bound xenobiotic carbonyl reductase [Maser, E. & Bannenberg, G. (1994) Biochem. Pharmacol. 47, 1805-1812], and points to an involvement of the 11 beta-HSD1A isoform in the reductive phase-I metabolism of xenobiotic compounds, besides its endocrinological functions. The alignment and comparison to other hydroxysteroid dehydrogenase forms of the same protein superfamily allows the identification of important residues in the 11 beta-HSD primary structure.

11 beta-hydroxysteroid dehydrogenase mediates reductive metabolism of xenobiotic carbonyl compounds

The enzyme 11 beta-hydroxysteroid dehydrogenase (11 beta-HSD) is considered to confer mineralocorticoid specificity on the non-selective Type I adrenocorticoid receptor by converting active 11-hydroxyglucocorticoids to receptor-inactive 11-oxo metabolites, in mineralocorticoid target tissues like the kidney. However, 11 beta-HSD is also present in the liver, where it may regulate steroid exposure to the glucocorticoid Type II receptor. Because of the much higher activities compared to that in kidney, liver 11 beta-HSD possibly has additional functions besides the metabolism of glucocorticoids. In the present investigation we have isolated 11 beta-HSD from mouse liver microsomes and demonstrate that the homogeneously purified enzyme is also capable of catalyzing the reductive metabolism of xenobiotic carbonyl compounds such as metyrapone, p-nitroacetophenone and p-nitrobenzaldehyde. Enzyme kinetic studies revealed that, in addition to NADP+, mouse liver 11 beta-HSD also accepts NAD+ as cosubstrate for glucocorticoid 11 beta-dehydrogenation. NADH as cosubstrate for 11-oxoreduction plays only a minor role compared to that with NADPH, a fact which is also true for xenobiotic carbonyl reduction. Inhibition experiments revealed strong sensitivity of xenobiotic carbonyl reduction to glucocorticoids. The competitive nature of this inhibition suggests that both glucocorticoids and xenobiotic carbonyl substances bind to the same catalytically active site of 11 beta-HSD. High enzyme activities were also found in microsomal fractions of the ovary and adrenal gland but, although expressing considerable glucocorticoid 11-dehydrogenation activity (one third that of liver), almost no carbonyl reduction was detectable in kidney microsomes. Immunoblot analysis with polyclonal antibodies directed against the liver 11 beta-HSD did not yield an immunological crossreaction in the same tissues. In conclusion, corresponding to the cytosolic aldo-keto reductases, microsomal 11 beta-HSD of liver may be considered to play a role in the phase I biotransformation of pharmacologically relevant carbonyl substances as well as protecting organisms against toxic carbonyl compounds by converting them to less lipophilic and more soluble and conjugatable metabolites. Discrepancies in bioactivity together with the lack of response to anti-liver 11 beta-HSD antibodies strongly indicate the existence of distinct forms of 11 beta-HSD to be present in kidney, adrenal gland and ovary. The ability of xenobiotic carbonyl reduction might be another distinguishing feature among the various 11 beta-HSD isozymes.