[Show abstract][Hide abstract] ABSTRACT: AKR1B10 is a human aldo-keto reductase (AKR) found to be elevated in several cancer types and in precancerous lesions. In vitro, AKR1B10 exhibits a much higher retinaldehyde reductase activity than any other human AKR, including AKR1B1 (aldose reductase). We here demonstrate that AKR1B10 also acts as a retinaldehyde reductase in vivo. This activity may be relevant in controlling the first step of retinoic acid synthesis. Up-regulation of AKR1B10, resulting in retinoic acid depletion, may lead to cellular proliferation. Both in vitro and in vivo activities of AKR1B10 were inhibited by tolrestat, an AKR1B1 inhibitor developed for diabetes treatment. The crystal structure of the ternary complex AKR1B10-NADP(+)-tolrestat was determined at 1.25-A resolution. Molecular dynamics models of AKR1B10 and AKR1B1 with retinaldehyde isomers and site-directed mutagenesis show that subtle differences at the entrance of the retinoid-binding site, especially at position 125, are determinant for the all-trans-retinaldehyde specificity of AKR1B10. Substitutions in the retinaldehyde cyclohexene ring also influence the specificity. These structural features should facilitate the design of specific inhibitors, with potential use in cancer and diabetes treatments.
Proceedings of the National Academy of Sciences 01/2008; 104(52):20764-9. DOI:10.1073/pnas.0705659105 · 9.67 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Zeta-crystallins constitute a family of proteins with NADPH:quinone reductase activity found initially in mammalian lenses but now known to be present in many other organisms and tissues. Few proteins from this family have been characterized, and their function remains unclear. In the present work, zeta-crystallins from human and yeast (Zta1p) were expressed, purified and characterized. Both enzymes are able to reduce ortho-quinones in the presence of NADPH but are not active with 2-alkenals. Deletion of the ZTA1 gene makes yeast more sensitive to menadione and hydrogen peroxide, suggesting a role in the oxidative stress response. The human and yeast enzymes specifically bind to adenine-uracil rich elements (ARE) in RNA, indicating that both enzymes are ARE-binding proteins and that this property has been conserved in zeta-crystallins throughout evolution. This supports a role for zeta-crystallins as trans-acting factors that could regulate the turnover of certain mRNAs.
Cellular and Molecular Life Sciences CMLS 07/2007; 64(11):1419-27. DOI:10.1007/s00018-007-7091-1 · 5.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The metabolism of all-trans- and 9-cis-retinol/ retinaldehyde has been investigated with focus on the activities of human, mouse and rat alcohol dehydrogenase 2 (ADH2), an intriguing enzyme with apparently different functions in human and rodents. Kinetic constants were determined with an HPLC method and a structural approach was implemented by in silico substrate dockings. For human ADH2, the determined K(m) values ranged from 0.05 to 0.3 microM and k(cat) values from 2.3 to 17.6 min(-1), while the catalytic efficiency for 9-cis-retinol showed the highest value for any substrate. In contrast, poor activities were detected for the rodent enzymes. A mouse ADH2 mutant (ADH2Pro47His) was studied that resembles the human ADH2 setup. This mutation increased the retinoid activity up to 100-fold. The K(m) values of human ADH2 are the lowest among all known human retinol dehydrogenases, which clearly support a role in hepatic retinol oxidation at physiological concentrations.
Cellular and Molecular Life Sciences CMLS 03/2007; 64(4):498-505. DOI:10.1007/s00018-007-6449-8 · 5.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Retinoic acid biosynthesis in vertebrates occurs in two consecutive steps: the oxidation of retinol to retinaldehyde followed by the oxidation of retinaldehyde to retinoic acid. Enzymes of the MDR (medium-chain dehydrogenase/reductase), SDR (short-chain dehydrogenase/reductase) and AKR (aldo-keto reductase) superfamilies have been reported to catalyse the conversion between retinol and retinaldehyde. Estimation of the relative contribution of enzymes of each type was difficult since kinetics were performed with different methodologies, but SDRs would supposedly play a major role because of their low K(m) values, and because they were found to be active with retinol bound to CRBPI (cellular retinol binding protein type I). In the present study we employed detergent-free assays and HPLC-based methodology to characterize side-by-side the retinoid-converting activities of human MDR [ADH (alcohol dehydrogenase) 1B2 and ADH4), SDR (RoDH (retinol dehydrogenase)-4 and RDH11] and AKR (AKR1B1 and AKR1B10) enzymes. Our results demonstrate that none of the enzymes, including the SDR members, are active with CRBPI-bound retinoids, which questions the previously suggested role of CRBPI as a retinol supplier in the retinoic acid synthesis pathway. The members of all three superfamilies exhibit similar and low K(m) values for retinoids (0.12-1.1 microM), whilst they strongly differ in their kcat values, which range from 0.35 min(-1) for AKR1B1 to 302 min(-1) for ADH4. ADHs appear to be more effective retinol dehydrogenases than SDRs because of their higher kcat values, whereas RDH11 and AKR1B10 are efficient retinaldehyde reductases. Cell culture studies support a role for RoDH-4 as a retinol dehydrogenase and for AKR1B1 as a retinaldehyde reductase in vivo.
[Show abstract][Hide abstract] ABSTRACT: (R)-all-trans-3-hydroxyretinal 1, (S)-all-trans-4-hydroxyretinal and (R)-all-trans-4-hydroxyretinal have been synthesized stereoselectively by Horner-Wadsworth-Emmons and Stille cross-coupling as bond-forming reactions. The CBS method of ketone reduction was used in the enantioface-differentiation step to provide the precursors for the synthesis of the 4-hydroxyretinal enantiomers. The kinetic constants of Xenopus laevis ADH8 with these retinoids have been determined.
[Show abstract][Hide abstract] ABSTRACT: Human stomach mucosa contains a characteristic alcohol dehydrogenase (ADH) enzyme, σσ-ADH. Its cDNA has been cloned from a human stomach library and sequenced. The deduced amino acid sequence shows 59–70% identities with the other human ADH classes, demonstrating that the stomach enzyme represents a distinct structure, constituting class IV, coded by a separate gene, ADH7. The amino acid identity with the rat stomach class IV ADH is 88%, which is intermediate between constant and variable dehydrogenases. This value reflects higher conservation than for the classical liver enzymes of class I, compatible with a separate functional significance of the class IV enzyme. Its enzymic features can be correlated with its structural characteristics. The residues lining the substrate-binding cleft are bulky and hydrophobic, similar to those of the class I enzyme; this explains the similar specificity of both classes, compatible with the origin of class IV from class I. Position 47 has Arg, in contrast to Gly in the rat class IV enzyme, but this Arg is still associated with an extremely high activity (kcat= 1510 min-1) and weak coenzyme binding (KiaNAD+= 1.6 mM). Thus, the strong interaction with coenzyme imposed by Arg47 in class I is probably compensated for in class IV by changes that may negatively affect coenzyme binding: Glu230, His271, Asn260, Asn261, Asn363. The still higher activity and weaker coenzyme binding of rat class IV (kcat= 2600 min-1, KiaNAD = 4 mM) can be correlated to the exchanges to Gly47, Gln230 and Tyr363. An important change at position 294, with Val in human and Ala in rat class IV, is probably responsible for the dramatic difference in Km values for ethanol between human (37 mM) and rat (2.4 M) class IV enzymes.
[Show abstract][Hide abstract] ABSTRACT: Ring-oxidized retinoids have been synthesized stereoselectively using the Stille cross-coupling reaction. Kinetic constants of mouse class I alcohol dehydrogenase (ADH1) with these retinoids were determined.
[Show abstract][Hide abstract] ABSTRACT: Human alcohol dehydrogenases (ADH1 and ADH4) actively use retinoids oxidized at the cyclohexenyl ring (4-oxo-, 4-hydroxy-, and 3,4-didehydro-retinoids), which are functional compounds in several cells and tissues (i.e., in human skin). Remarkably, activities with 4-oxo-retinal and 4-hydroxy-retinol (kcat = 2050 min(-1) for ADH4) are the highest among retinoids, similar to those of the best aliphatic alcohols. Thus, ADH1 and ADH4 provide a metabolic pathway for the synthesis of the corresponding retinoic acids. Tween 80, a widely used detergent in the retinoid activity assay, behaves as a competitive inhibitor. The Km values for all-trans-retinol (2-3 microM), estimated in the absence of detergent, are 10-fold lower than those obtained at the usual 0.02% Tween 80. This suggests a contribution of ADH to retinoid metabolism more relevant than previously expected. However, Tween 80 stabilizes retinoids in water solution and provides a reliable and reproducible assay, suitable for comparing different ADHs and different retinoid substrates.
Archives of Biochemistry and Biophysics 11/2004; 430(2):210-7. DOI:10.1016/j.abb.2004.07.002 · 3.02 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The crystal structure of Saccharomyces cerevisiae ScAdh6p has been solved using the anomalous signal from the two zinc atoms found per subunit, and it constitutes the first structure determined from a member of the cinnamyl alcohol dehydrogenase family. ScAdh6p subunits exhibit the general fold of the medium-chain dehydrogenases/reductases (MDR) but with distinct specific characteristics. In the three crystal structures solved (two trigonal and one monoclinic), ScAdh6p molecules appear to be structural heterodimers composed of one subunit in the apo and the second subunit in the holo conformation. Between the two conformations, the relative disposition of domains remains unchanged, while two loops, Cys250-Asn260 and Ile277-Lys292, experience large movements. The apo-apo structure is disfavoured because of steric impairment involving the loop Ile277-Lys292, while in the holo-holo conformation some of the hydrogen bonds between subunits would break apart. These suggest that the first NADPH molecule would bind to the enzyme much more tightly than the second. In addition, fluorimetric analysis of NADPH binding demonstrates that only one cofactor molecule binds per dimer. Therefore, ScAdh6p appears to function according to a half-of-the-sites reactivity mechanism, resulting from a pre-existing (prior to cofactor binding) tendency for the structural asymmetry in the dimer. The specificity of ScAdh6p towards NADPH is mainly due to the tripod-like interactions of the terminal phosphate group with Ser210, Arg211 and Lys215. The size and the shape of the substrate-binding pocket correlate well with the substrate specificity of ScAdh6p towards cinnamaldehyde and other aromatic compounds. The structural relationships of ScAdh6p with other MDR structures are analysed.
[Show abstract][Hide abstract] ABSTRACT: Studies in knockout mice support the involvement of alcohol dehydrogenases ADH1 and ADH4 in retinoid metabolism, although kinetics with retinoids are not known for the mouse enzymes. Moreover, a role of alcohol dehydrogenase (ADH) in the eye retinoid interconversions cannot be ascertained due to the lack of information on the kinetics with 11-cis-retinoids. We report here the kinetics of human ADH1B1, ADH1B2, ADH4, and mouse ADH1 and ADH4 with all-trans-, 7-cis-, 9-cis-, 11-cis- and 13-cis-isomers of retinol and retinal. These retinoids are substrates for all enzymes tested, except the 13-cis isomers which are not used by ADH1. In general, human and mouse ADH4 exhibit similar activity, higher than that of ADH1, while mouse ADH1 is more efficient than the homologous human enzymes. All tested ADHs use 11-cis-retinoids efficiently. ADH4 shows much higher k(cat)/K(m) values for 11-cis-retinol oxidation than for 11-cis-retinal reduction, a unique property among mammalian ADHs for any alcohol/aldehyde substrate pair. Docking simulations and the kinetic properties of the human ADH4 M141L mutant demonstrated that residue 141, in the middle region of the active site, is essential for such ADH4 specificity. The distinct kinetics of ADH4 with 11-cis-retinol, its wide specificity with retinol isomers and its immunolocalization in several retinal cell layers, including pigment epithelium, support a role of this enzyme in the various retinol oxidations that occur in the retina. Cytosolic ADH4 activity may complement the isomer-specific microsomal enzymes involved in photopigment regeneration and retinoic acid synthesis.
European Journal of Biochemistry 06/2004; 271(9):1660-70. DOI:10.1111/j.1432-1033.2004.04058.x · 3.58 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Gastric tissues from amphibian Rana perezi express the only vertebrate alcohol dehydrogenase (ADH8) that is specific for NADP(H) instead of NAD(H). In the crystallographic ADH8-NADP+ complex, a binding pocket for the extra phosphate group of coenzyme is formed by ADH8-specific residues Gly223-Thr224-His225, and the highly conserved Leu200 and Lys228. To investigate the minimal structural determinants for coenzyme specificity, several ADH8 mutants involving residues 223 to 225 were engineered and kinetically characterized. Computer-assisted modeling of the docked coenzymes was also performed with the mutant enzymes and compared with the wild-type crystallographic binary complex. The G223D mutant, having a negative charge in the phosphate-binding site, still preferred NADP(H) over NAD(H), as did the T224I and H225N mutants. Catalytic efficiency with NADP(H) dropped dramatically in the double mutants, G223D/T224I and T224I/H225N, and in the triple mutant, G223D/T224I/H225N (kcat/KmNADPH = 760 mm-1 min-1), as compared with the wild-type enzyme (kcat/KmNADPH = 133330 mm-1 min-1). This was associated with a lower binding affinity for NADP+ and a change in the rate-limiting step. Conversely, in the triple mutant, catalytic efficiency with NAD(H) increased, reaching values (kcat/KmNADH = 155000 mm-1 min-1) similar to those of the wild-type enzyme with NADP(H). The complete reversal of ADH8 coenzyme specificity was therefore attained by the substitution of only three consecutive residues in the phosphate-binding site, an unprecedented achievement within the ADH family.
[Show abstract][Hide abstract] ABSTRACT: To gain a better insight into the alterations of brain function after chronic ethanol, we measured the release of various neurotransmitters from nerve terminals of cortex and hippocampus isolated fm rats chronically fed with ethanol. The K+-evoked release of [3H]acetylcholine (ACh), f[H]dopamine (DA), [3H] glutamate(Glu) and [3H]noradrenaline (NA) was determined in superfused synaptosomes of brain cortex and hippocampus from rats exposed to the Lieber-DeCarli alcohol liquid diet for 5 weeks. In cortical synaptosomes, chronic ethanol administration did not affect the release of ACh and of DA, while significantly decreasing the release of Glu and NA. The endogenous levels of NA, DA and their metabolites were unchanged. In hippocampal synaptosomes the only effect of chronic alcohol was an increased release of Glu. It can be concluded that at presynaptic level chronic ethanol alters brain neurotransmitter systems selectively. Glutamatergic and noradrenergic nerve terminals from cortex are more vulnerable than those from hippocampus.
[Show abstract][Hide abstract] ABSTRACT: The ADH2 gene codes for the Arabidopsis glutathione-dependent formaldehyde dehydrogenase (FALDH), an enzyme involved in formaldehyde metabolism in eukaryotes. In the present work, we have investigated the potential role of FALDH in detoxification of exogenous formaldehyde. We have generated a yeast (Saccharomyces cerevisiae) mutant strain (sfa1Delta) by in vivo deletion of the SFA1 gene that codes for the endogenous FALDH. Overexpression of Arabidopsis FALDH in this mutant confers high resistance to formaldehyde added exogenously, which demonstrates the functional conservation of the enzyme through evolution and supports its essential role in formaldehyde metabolism. To investigate the role of the enzyme in plants, we have generated Arabidopsis transgenic lines with modified levels of FALDH. Plants overexpressing the enzyme show a 25% increase in their efficiency to take up exogenous formaldehyde, whereas plants with reduced levels of FALDH (due to either a cosuppression phenotype or to the expression of an antisense construct) show a marked slower rate and reduced ability for formaldehyde detoxification as compared with the wild-type Arabidopsis. These results show that the capacity to take up and detoxify high concentrations of formaldehyde is proportionally related to the FALDH activity in the plant, revealing the essential role of this enzyme in formaldehyde detoxification.
[Show abstract][Hide abstract] ABSTRACT: Aldo-keto reductases (AKRs) are NAD(P)H-dependent oxidoreductases that catalyse the reduction of a variety of carbonyl compounds, such as carbohydrates, aliphatic and aromatic aldehydes and steroids. We have studied the retinal reductase activity of human aldose reductase (AR), human small-intestine (HSI) AR and pig aldehyde reductase. Human AR and HSI AR were very efficient in the reduction of all- trans -, 9- cis - and 13- cis -retinal ( k (cat)/ K (m)=1100-10300 mM(-1).min(-1)), constituting the first cytosolic NADP(H)-dependent retinal reductases described in humans. Aldehyde reductase showed no activity with these retinal isomers. Glucose was a poor inhibitor ( K (i)=80 mM) of retinal reductase activity of human AR, whereas tolrestat, a classical AKR inhibitor used pharmacologically to treat diabetes, inhibited retinal reduction by human AR and HSI AR. All- trans -retinoic acid failed to inhibit both enzymes. In this paper we present the AKRs as an emergent superfamily of retinal-active enzymes, putatively involved in the regulation of retinoid biological activity through the assimilation of retinoids from beta-carotene and the control of retinal bioavailability.
[Show abstract][Hide abstract] ABSTRACT: ADH1 and ADH4 are the major alcohol dehydrogenases (ADH) in ethanol and retinol oxidation. ADH activity and protein expression were investigated in rat gastrointestinal tissue homogenates by enzymatic and Western blot analyses. In addition, sections of adult rat gastrointestinal tract were examined by in situ hybridization and immunohistochemistry. ADH1 and ADH4 were detected along the whole tract, changing their localization and relative content as a function of the area studied. While ADH4 was more abundant in the upper (esophagus and stomach) and lower (colorectal) regions, ADH1 was predominant in the intestine but also present in stomach. Both enzymes were detected in mucosa but, in general, ADH4 was found in outer cell layers, lining the lumen, while ADH1 was detected in the inner cell layers. Of interest were the sharp discontinuities in the expression found in the pyloric region (ADH1) and the gastroduodenal junction (ADH4), reflecting functional changes. The precise localization of ADH in the gut reveals the cell types where active alcohol oxidation occurs during ethanol ingestion, providing a molecular basis for the gastrointestinal alcohol pathology. Localization of ADH, acting as retinol dehydrogenase/retinal reductase, also indicates sites of active retinoid metabolism in the gut, essential for mucosa function and vitamin A absorption.
European Journal of Biochemistry 07/2003; 270(12):2652-62. DOI:10.1046/j.1432-1033.2003.03642.x · 3.58 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The amphibian enzyme ADH8, previously named class IV-like, is the only known vertebrate alcohol dehydrogenase (ADH) with specificity towards NADP(H). The three-dimensional structures of ADH8 and of the binary complex ADH8-NADP(+) have been now determined and refined to resolutions of 2.2A and 1.8A, respectively. The coenzyme and substrate specificity of ADH8, that has 50-65% sequence identity with vertebrate NAD(H)-dependent ADHs, suggest a role in aldehyde reduction probably as a retinal reductase. The large volume of the substrate-binding pocket can explain both the high catalytic efficiency of ADH8 with retinoids and the high K(m) value for ethanol. Preference of NADP(H) appears to be achieved by the presence in ADH8 of the triad Gly223-Thr224-His225 and the recruitment of conserved Lys228, which define a binding pocket for the terminal phosphate group of the cofactor. NADP(H) binds to ADH8 in an extended conformation that superimposes well with the NAD(H) molecules found in NAD(H)-dependent ADH complexes. No additional reshaping of the dinucleotide-binding site is observed which explains why NAD(H) can also be used as a cofactor by ADH8. The structural features support the classification of ADH8 as an independent ADH class.
[Show abstract][Hide abstract] ABSTRACT: S-nitrosoglutathione (GSNO) formation represents a mechanism for storage and transport of nitric oxide. Analysis of human liver and Saccharomyces cerevisiae extracts has revealed the presence of only one enzyme able to significantly reduce GSNO, identified as glutathione-dependent formaldehyde dehydrogenase (FALDH). GSNO is the best substrate known for the human and yeast enzymes (kcat/Km = 444,400 and 350,000 mM(-1) min(-1), respectively). Although NADH is the preferred cofactor, some activity with NADPH (Km = 460 microM) can be predicted in vivo. The subcellular localization demonstrates a cytosolic and nuclear distribution of FALDH in living yeast cells. This agrees with previous results in rat, and suggests a role in the regulation of GSNO levels in the cytoplasmic and nuclear compartments of the eukaryotic cell.
Cellular and Molecular Life Sciences CMLS 06/2003; 60(5):1013-8. DOI:10.1007/s00018-003-3025-x · 5.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The completion of the Saccharomyces cerevisiae genome project has provided the opportunity to explore for new genes of the medium-chain dehydrogenase/reductase enzyme superfamily. Our group has recently identified a new gene, the YMR318C open reading frame, which coded for a Zn-containing NADP(H)-dependent alcohol dehydrogenase (ADHVI). ADHVI has been purified to homogeneity from over expressing yeast cells, and found to be a homodimer of 40 kDa subunits. The enzyme showed a strict specificity for NADP(H) and high activity with a variety of long chain aliphatic and bulky substrates. Aldehydes exhibited 50-12000 times higher catalytic efficiency than the corresponding alcohols. Substrates with high k(cat)/K(m) were: pentanal, veratraldehyde and cinnamaldehyde. The ADHVI expression was strongly induced when galactose was the sole carbon source in the culture medium. Phylogenetic trees include ADHVI in the cinnamyl alcohol dehydrogenase (CADH) family. In contrast to the plant CADH, involved in lignin biosynthesis, this is not the function for ADHVI, since yeast does not synthesize lignin. ADHVI may be physiologically involved in several steps of the lignin degradation pathway, initiated by other microorganisms, in the synthesis of fusel alcohols, products derived from the aminoacidic metabolism, and in the homeostasis of NADP(H). Disruption of ADH6 was not lethal for the yeast, under laboratory conditions.
[Show abstract][Hide abstract] ABSTRACT: Different crystal forms diffracting to high resolution have been obtained for two NADP(H)-dependent alcohol dehydrogenases, members of the medium-chain dehydrogenase/reductase superfamily: ScADHVI from Saccharomyces cerevisiae and ADH8 from Rana perezi. ScADHVI is a broad-specificity enzyme, with a sequence identity lower than 25% with respect to all other ADHs of known structure. The best crystals of ScADHVI diffracted beyond 2.8 A resolution and belonged to the trigonal space group P3(1)21 (or to its enantiomorph P3(2)21), with unit-cell parameters a = b = 102.2, c = 149.7 A, gamma = 120 degrees. These crystals were produced by the hanging-drop vapour-diffusion method using ammonium sulfate as precipitant. Packing considerations together with the self-rotation function and the native Patterson map seem to indicate the presence of only one subunit per asymmetric unit, with a Volume solvent content of about 80%. ADH8 from R. perezi is the only NADP(H)-dependent ADH from vertebrates characterized to date. Crystals of ADH8 obtained both in the absence and in the presence of NADP(+) using polyethylene glycol and lithium sulfate as precipitants diffracted to 2.2 and 1.8 A, respectively, using synchrotron radiation. These crystals were isomorphous, space group C2, with approximate unit-cell parameters a = 122, b = 79, c = 91 A, beta = 113 degrees and contain one dimer per asymmetric unit, with a Volume solvent content of about 50%.
[Show abstract][Hide abstract] ABSTRACT: A new NADP(H)-dependent alcohol dehydrogenase (the YCR105W gene product, ADHVII) has been identified in Saccharomyces cerevisiae. The enzyme has been purified to homogeneity and found to be a homodimer of 40 kDa subunits and a pI of 6.2-6.4. ADHVII shows a broad substrate specificity similar to the recently characterized ADHVI (64% identity), although they show some differences in kinetic properties. ADHVI and ADHVII are the only members of the cinnamyl alcohol dehydrogenase family in yeast. Simultaneous deletion of ADH6 and ADH7 was not lethal for the yeast. Both enzymes could participate in the synthesis of fusel alcohols, ligninolysis and NADP(H) homeostasis.
European Journal of Biochemistry 12/2002; 269(22):5738-45. DOI:10.1046/j.1432-1033.2002.03296.x · 3.58 Impact Factor