Molecular cloning of the mitochondrial aldehyde dehydrogenase gene of Saccharomyces cerevisiae by genetic complementation

Effect of Metschnikowia pulcherrima on Saccharomyces cerevisiae PDH By-Pass in MixedFermentation with Varied Sugar Concentrations of Synthetic Grape Juice and Inoculation Ratios

The effects of Metschnikowia pulcherrima and high glucose osmolality on S. cerevisiae pyruvate dehydrogenase pathway (PDH) by-pass were examined by varying the starting sugar concentration of synthetic grape juice and the inoculation ratio of S. cerevisiae to M. pulcherrima. The findings revealed that M. pulcherrima and osmolarity impacted S. cerevisiae’s PDH by-pass. The inoculation concentration of M. pulcherrima significantly affected pyruvate decarboxylase (PDC) activity and acs2 expression when the initial sugar concentration was 200 g L−1 and 290 g L−1. The osmolarity caused by the initial sugar (380 g L−1) significantly influenced the enzymatic activity of S. cerevisiae, which decreased PDC and acetaldehyde dehydrogenase (ALD) activities while increasing Acetyl-CoA synthetase (ACS) activity. The reduction in acetic acid in the wine was caused by M. pulcherrima altering the initial sugar concentration faced by S. cerevisiae, which in turn affected enzymatic activity. The alteration of enzyme activity and accumulation of primary metabolites revealed why mixed fermentation could reduce the acetic acid content in wine by altering the enzymatic activity and affecting the expression of several key genes. The M. pulcherrima inoculation levels had no significant effect on the acetic acid and glycerol concentration in the same fermentation medium.

Metschnikowia pulcherrima Influences the Expression of Genes Involved in PDH Bypass and Glyceropyruvic Fermentation in Saccharomyces cerevisiae

Previous studies reported that the use of Metschnikowia pulcherrima in sequential culture fermentation with Saccharomyces cerevisiae mainly induced a reduction of volatile acidity in wine. The impact of the presence of this yeast on the metabolic pathway involved in pyruvate dehydrogenase (PDH) bypass and glycerol production in S. cerevisiae has never been investigated. In this work, we compared acetic acid and glycerol production kinetics between pure S. cerevisiae culture and its sequential culture with M. pulcherrima during alcoholic fermentation. In parallel, the expression levels of the principal genes involved in PDH bypass and glyceropyruvic fermentation in S. cerevisiae were investigated. A sequential culture of M. pulcherrima/S. cerevisiae at an inoculation ratio of 10:1 produced 40% less acetic acid than pure S. cerevisiae culture and led to the enhancement of glycerol content (12% higher). High expression levels of pyruvate decarboxylase PDC1 and PDC5, acetaldehyde dehydrogenase ALD6, alcohol dehydrogenase ADH1 and glycerol-3-phosphate dehydrogenase PDC1 genes during the first 3 days of fermentation in sequential culture conditions are highlighted. Despite the complexity of correlating gene expression levels to acetic acid formation kinetics, we demonstrate that the acetic acid production pathway is altered by sequential culture conditions. Moreover, we show for the first time that the entire acetic acid and glycerol metabolic pathway can be modulated in S. cerevisiae by the presence of M. pulcherrima at the beginning of fermentation.

Different specificities of two aldehyde dehydrogenases from Saccharomyces cerevisiae var. boulardii

Aldehyde dehydrogenases play crucial roles in the detoxification of exogenous and endogenous aldehydes by catalysing their oxidation to carboxylic acid counterparts. The present study reports characterization of two such isoenzymes from the yeast Saccharomyces cerevisiae var. boulardii (NCYC 3264), one mitochondrial (Ald4p) and one cytosolic (Ald6p). Both Ald4p and Ald6p were oligomeric in solution and demonstrated positive kinetic cooperativity towards aldehyde substrates. Wild-type Ald6p showed activity only with aliphatic aldehydes. Ald4p, on the contrary, showed activity with benzaldehyde along with a limited range of aliphatic aldehydes. Inspection of modelled structure of Ald6p revealed that a bulky amino acid residue (Met177, compared with the equivalent residue Leu196 in Ald4p) might cause steric hindrance of cyclic substrates. Therefore, we hypothesized that specificities of the two isoenzymes towards aldehyde substrates were partly driven by steric hindrance in the active site. A variant of wild-type Ald6p with the Met177 residue replaced by a valine was also characterized to address to the hypothesis. It showed an increased specificity range and a gain of activity towards cyclohexanecarboxaldehyde. It also demonstrated an increased thermal stability when compared with both the wild-types. These data suggest that steric bulk in the active site of yeast aldehyde dehydrogenases is partially responsible for controlling specificity.

FOXD1-ALDH1A3 Signaling Is a Determinant for the Self-Renewal and Tumorigenicity of Mesenchymal Glioma Stem Cells

Glioma stem-like cells (GSC) with tumor-initiating activity orchestrate the cellular hierarchy in glioblastoma and engender therapeutic resistance. Recent work has divided GSC into two subtypes with a mesenchymal (MES) GSC population as the more malignant subtype. In this study, we identify the FOXD1-ALDH1A3 signaling axis as a determinant of the MES GSC phenotype. The transcription factor FOXD1 is expressed predominantly in patient-derived cultures enriched with MES, but not with the proneural GSC subtype. shRNA-mediated attenuation of FOXD1 in MES GSC ablates their clonogenicity in vitro and in vivo Mechanistically, FOXD1 regulates the transcriptional activity of ALDH1A3, an established functional marker for MES GSC. Indeed, the functional roles of FOXD1 and ALDH1A3 are likely evolutionally conserved, insofar as RNAi-mediated attenuation of their orthologous genes in Drosophila blocks formation of brain tumors engineered in that species. In clinical specimens of high-grade glioma, the levels of expression of both FOXD1 and ALDH1A3 are inversely correlated with patient prognosis. Finally, a novel small-molecule inhibitor of ALDH we developed, termed GA11, displays potent in vivo efficacy when administered systemically in a murine GSC-derived xenograft model of glioblastoma. Collectively, our findings define a FOXD1-ALDH1A3 pathway in controling the clonogenic and tumorigenic potential of MES GSC in glioblastoma tumors. Cancer Res; 76(24); 7219-30. ©2016 AACR.

Aldehyde dehydrogenase, Ald4p, is a major component of mitochondrial fluorescent inclusion bodies in the yeast Saccharomyces cerevisiae

When Saccharomyces cerevisiae strain 3626 was cultured to the stationary phase in a medium that contained glucose, needle-like structures that emitted autofluorescence were observed in almost all cells by fluorescence microscopy under UV excitation. The needle-like structures completely overlapped with the profile of straight elongated mitochondria. Therefore, these structures were designated as mitochondrial fluorescent inclusion bodies (MFIBs). The MFIB-enriched mitochondrial fractions were successfully isolated and 2D-gel electrophoresis revealed that a protein of 54 kDa was only highly concentrated in the fractions. Determination of the N-terminal amino acid sequence of the 54-kDa protein identified it as a mitochondrial aldehyde dehydrogenase, Ald4p. Immunofluorescence microscopy showed that anti-Ald4p antibody specifically stained MFIBs. Freeze-substitution electron microscopy demonstrated that cells that retained MFIBs had electron-dense filamentous structures with a diameter of 10 nm in straight elongated mitochondria. Immunoelectron microscopy showed that Ald4p was localized to the electron-dense filamentous structures in mitochondria. These results together showed that a major component of MFIBs is Ald4p. In addition, we demonstrate that MFIBs are common features that appear in mitochondria of many species of yeast.

cDNA cloning and characterization of the novel genes related to aldehyde dehydrogenase from wild Chinese grape (Vitis pseudoreticulata W. T. Wang)

mRNA differential display was employed to study the gene differential expression of wild Chinese grape (Vitis pseudoreticulata W. T. Wang) infected by Uncinula necator in different periods, a cDNA fragment of T11AC/B0319-456 coded by aldehyde dehydrogenase (ALDH) gene has been obtained. 5' RACE and 3' RACE have been used to clone the whole cDNA sequences of ALDH which consists of three cDNA sequences, whose sizes are 1887, 1956 and 1961 bp, and they encoded a polypeptide size of 537, 524 and 477 designated as VpALDH2a, VpALDH2b and VpALDH1a, respectively. The deduced amino acid sequence shared highly identity with other plants and Human ALDH. Both VpALDH2a and VpALDH2b protein contain putative mitochondrial targeting sequence except VpALDH1a, it indicates that VpALDH2a and VpALDH2b are mitochondrial enzymes, and VpALDH1a is cytosolic enzyme. The VpALDH2a was subcloned into the expression vector pGEX-4T-1, transformed into E.coli BL 21-coden plus induced by IPTG, and about Mr. 85 kD of GST-ALDH fusion protein displayed in SDS-PAGE gel.

Response to acetaldehyde stress in the yeast Saccharomyces cerevisiae involves a strain-dependent regulation of several ALD genes and is mediated by the general stress response pathway

One of the stress conditions that yeast may encounter is the presence of acetaldehyde. In a previous study we identified that, in response to this stress, several HSP genes are induced that are also involved in the response to other forms of stress. Aldehyde dehydrogenases (ALDH) play an important role in yeast acetaldehyde metabolism (e.g. when cells are growing in ethanol). In this work we analyse the expression of the genes encoding these enzymes (ALD) and also the corresponding enzymatic activities under several growth conditions. We investigate three kinds of yeast strains: laboratory strains, strains involved in the alcoholic fermentation stage of wine production and flor yeasts (responsible for the biological ageing of sherry wines). The latter are very important to consider because they grow in media containing high ethanol concentrations, and produce important amounts of acetaldehyde. Under several growth conditions, further addition of acetaldehyde or ethanol in flor yeasts induced the expression of some ALD genes and led to an increase in ALDH activity. This result is consistent with their need to obtain energy from ethanol during biological ageing processes. Our data also suggest that post-transcriptional and/or post-translational mechanisms are involved in regulating the activity of these enzymes. Finally, analyses indicate that the Msn2/4p and Hsf1p transcription factors are necessary for HSP26, ALD2/3 and ALD4 gene expression under acetaldehyde stress, while PKA represses the expression of these genes.

Engineering of the pyruvate dehydrogenase bypass in Saccharomyces cerevisiae: role of the cytosolic Mg(2+) and mitochondrial K(+) acetaldehyde dehydrogenases Ald6p and Ald4p in acetate formation during alcoholic fermentation

Acetic acid plays a crucial role in the organoleptic balance of many fermented products. We have investigated the factors controlling the production of acetate by Saccharomyces cerevisiae during alcoholic fermentation by metabolic engineering of the enzymatic steps involved in its formation and its utilization. The impact of reduced pyruvate decarboxylase (PDC), limited acetaldehyde dehydrogenase (ACDH), or increased acetoacetyl coenzyme A synthetase (ACS) levels in a strain derived from a wine yeast strain was studied during alcoholic fermentation. In the strain with the PDC1 gene deleted exhibiting 25% of the PDC activity of the wild type, no significant differences were observed in the acetate yield or in the amounts of secondary metabolites formed. A strain overexpressing ACS2 and displaying a four- to sevenfold increase in ACS activity did not produce reduced acetate levels. In contrast, strains with one or two disrupted copies of ALD6, encoding the cytosolic Mg(2+)-activated NADP-dependent ACDH and exhibiting 60 and 30% of wild-type ACDH activity, showed a substantial decrease in acetate yield (the acetate production was 75 and 40% of wild-type production, respectively). This decrease was associated with a rerouting of carbon flux towards the formation of glycerol, succinate, and butanediol. The deletion of ALD4, encoding the mitochondrial K(+)-activated NAD(P)-linked ACDH, had no effect on the amount of acetate formed. In contrast, a strain lacking both Ald6p and Ald4p exhibited a long delay in growth and acetate production, suggesting that Ald4p can partially replace the Ald6p isoform. Moreover, the ald6 ald4 double mutant was still able to ferment large amounts of sugar and to produce acetate, suggesting the contribution of another member(s) of the ALD family.

Molecular and cellular characterizations of a cDNA clone encoding a novel isozyme of aldehyde dehydrogenase from rice

Aldehyde dehydrogenases (ALDHs) are a group of enzymes catalyzing the conversion of aldehydes to the corresponding acids. In mammals and yeasts, at least two isozymes of ALDH are known to be involved in ethanol metabolism (cytosolic ALDH1 and mitochondrial ALDH2). Although mitochondrial ALDH isozymes have previously been identified in several plants, such as maize and tobacco, it is unclear whether cytosolic ALDH isozymes also exist in plants. In this study, we identified and characterized a cDNA clone encoding aldehyde dehydrogenase (ALDH1a) from rice (Oryza sativa L. cv. Nipponbare). The open reading frame of this clone did not contain a typical mitochondrial targeting signal. Analysis of the subcellular localization of ALDH1a using green fluorescent protein (GFP) suggested that ALDH1a is a cytosolic enzyme rather than a mitochondrial enzyme. A genomic Southern hybridization indicated that sequences homologous to the ALDH1a gene are present in at least two regions of the rice genome. Amplification by RT-PCR showed that ALDH1a is expressed strongly in roots, but not in leaves, of rice seedlings, suggesting that ALDH1a functions in roots.

Involvement of mitochondrial aldehyde dehydrogenase ALD5 in maintenance of the mitochondrial electron transport chain in Saccharomyces cerevisiae

The physiological role of mitochondrial aldehyde dehydrogenase (ALD5) was investigated by analysis of the ald5 mutant (AKD321) in Saccharomyces cerevisiae. K(+)-activated ALDH activity of the ald5 mutant was about 80% of the wild-type in the mitochondrial fraction, while the respiratory activity of the ald5 mutant was greatly reduced. Cytochrome content was also reduced in the ald5 mutant. Enzymatic analysis revealed that the alcohol dehydrogenase activity of the ald5 mutant was higher than that of the wild-type, while glycerol 3-phosphate dehydrogenase activity was the same in the two strains. Ethanol as a carbon source or addition of 1 M NaCl with glucose as the carbon source in the growth medium increased beta-galactosidase activity from an ALD5-lacZ fusion. Overexpression of another mitochondrial ALDH gene (ALD7) had no effect on increasing respiratory function of the ald5 mutant, but showed improved growth on ethanol. These observations show that mitochondrial ALD5 plays a role in regulation or biosynthesis of electron transport chain components.

Diethylcarbamoylating/nitroxylating agents as dual action inhibitors of aldehyde dehydrogenase: a disulfiram-cyanamide merger

Benzenesulfohydroxamic acid (Piloty's acid) was functionalized on the hydroxyl group with the N,N-diethylcarbamoyl group, and the hydroxylamine nitrogen was substituted with acetyl (1a), pivaloyl (1b), benzoyl (1c), and ethoxycarbonyl (1d) groups. Only compound 1d inhibited yeast aldehyde dehydrogenase (AlDH) in vitro (IC(50) 169 microM). When administered to rats, 1d significantly raised blood acetaldehyde levels following ethanol challenge, thus serving as a diethylcarbamoylating/nitroxylating, dual action inhibitor of AlDH in vivo. A more potent dual action agent was N-(N, N-diethylcarbamoyl)-O-methylbenzenesulfohydroxamic acid (5c), which was postulated to release diethylcarbamoylnitroxyl (9), a highly potent diethylcarbamoylating/nitroxylating agent, following metabolic O-demethylation in vivo. The dual action inhibition of AlDH exhibited by 1d, and especially 9, constitutes a merger of the mechanism of action of the alcohol deterrent agents, disulfiram and cyanamide.

A proposal for nomenclature of aldehyde dehydrogenases in Saccharomyces cerevisiae and characterization of the stress-inducible ALD2 and ALD3 genes

The complete sequencing of the genome of Saccharomyces cerevisiae indicated that this organism contains five genes encoding aldehyde dehydrogenases. YOR374w and YER073w correspond to the mitochondrial isoforms and we propose as gene names ALD4 and ALD5, respectively. YPL061w has been described as the cytoplasmic constitutive isoform and named ALD6. We characterize here the tandem-repeated ORFs YMR170c and YMR169c as the cytoplasmic stress-inducible isoforms, with gene names ALD2 and ALD3, respectively. The expression of ALD2 and ALD3 is dependent on the general-stress transcription factors Msn2,4 but independent of the HOG MAP kinase pathway. ALD3 is induced by a variety of stresses, including osmotic shock, heat shock, glucose exhaustion, oxidative stress and drugs. ALD2 is only induced by osmotic stress and glucose exhaustion. A double null mutant, ald2 ald3, exhibited unchanged sensitivity to any of the above stresses. The only phenotype detected in this mutant was a reduced growth rate in ethanol medium as compared to the wild type.

Transient mRNA responses in chemostat cultures as a method of defining putative regulatory elements: application to genes involved in Saccharomyces cerevisiae acetyl-coenzyme A metabolism

To identify common regulatory sequences in the promoters of genes, transcription of 31 genes of Saccharomyces cerevisiae was analysed during the transient response to a glucose pulse in a chemostat culture. mRNA levels were monitored during the subsequent excess glucose, ethanol and acetate phases, while other conditions were kept constant. This setup allowed a direct comparison between regulation by glucose, ethanol and acetate. Genes with identical regulation patterns were grouped to identify regulatory elements in the promoters. In respect to regulation on glucose four classes were identified: no transcription under any of the conditions tested, no difference in regulation on glucose, induced on glucose and repressed on glucose. In addition, genes were found that were repressed or induced on ethanol or acetate. Sequence alignment of genes with similar regulation patterns revealed five new, putative regulatory promoter elements. (i) The glucose-inducible fermentation genes PDC1 and ADH1 share the sequence ATACCTTCSTT. (ii) Acetate-repression might be mediated by the decamer CCCGAG RGGA, present in the promoters of ACS2 and ACR1. (iii) A specific element (CCWTTSRNCCG) for the glyoxylate cycle was present in seven genes studied: CIT2, ICL1, MLS1, MDH2, CAT2, ACR1 and ACH1. These genes were derepressed on ethanol or acetate. (iv) The sequence ACGTSCRGAATGA was found in the promoters of the partially ethanol-repressed genes ACS1 and YAT1. (v) Ethanol induction, as seen for ACS2, ADH3 and MDH1, might be mediated via the sequence CGGSGCCGRAG.

Purification and characterization of the coniferyl aldehyde dehydrogenase from Pseudomonas sp. Strain HR199 and molecular characterization of the gene

The coniferyl aldehyde dehydrogenase (CALDH) of Pseudomonas sp. strain HR199 (DSM7063), which catalyzes the NAD+-dependent oxidation of coniferyl aldehyde to ferulic acid and which is induced during growth with eugenol as the carbon source, was purified and characterized. The native protein exhibited an apparent molecular mass of 86,000 +/- 5,000 Da, and the subunit mass was 49.5 +/- 2.5 kDa, indicating an alpha2 structure of the native enzyme. The optimal oxidation of coniferyl aldehyde to ferulic acid was obtained at a pH of 8.8 and a temperature of 26 degreesC. The Km values for coniferyl aldehyde and NAD+ were about 7 to 12 microM and 334 microM, respectively. The enzyme also accepted other aromatic aldehydes as substrates, whereas aliphatic aldehydes were not accepted. The NH2-terminal amino acid sequence of CALDH was determined in order to clone the encoding gene (calB). The corresponding nucleotide sequence was localized on a 9.4-kbp EcoRI fragment (E94), which was subcloned from a Pseudomonas sp. strain HR199 genomic library in the cosmid pVK100. The partial sequencing of this fragment revealed an open reading frame of 1,446 bp encoding a protein with a relative molecular weight of 51,822. The deduced amino acid sequence, which is reported for the first time for a structural gene of a CALDH, exhibited up to 38.5% amino acid identity (60% similarity) to NAD+-dependent aldehyde dehydrogenases from different sources.

Identification and disruption of the gene encoding the K(+)-activated acetaldehyde dehydrogenase of Saccharomyces cerevisiae

The identity of the gene encoding the mitochondrial K(+)-activated acetaldehyde dehydrogenase (K(+)-ACDH) of Saccharomyces cerevisiae has been confirmed. The gene is situated on the right arm of chromosome XV, bears the systematic name YOR374w and the deduced product shows significant homology to other members of the S. cerevisiae aldehyde dehydrogenase (ALDH) family. YOR374w has now been assigned the gene name ALD7. The N-terminal amino acid sequences of K(+)-ACDHs purified from several diverse strains of S. cerevisiae were determined, and found to have 81-100% identity in alignments with the product of ALD7. Haploid mutants containing a deletion of ALD7 were constructed and, in these strains, the K(+)-ACDH was not detectable under any growth conditions examined. The activity of the Mg(2+)-activated acetaldehyde dehydrogenase (Mg(2+)-ACDH), encoded by ALD6, remained at wild-type levels in the mutants. Growth on glucose was not affected in the mutants lacking ALD7 (in contrast to the behaviour of ald6 mutants), whereas growth on ethanol was severely impaired. This observation, together with previous work by our group, shows that both the Mg(2+)- and K(+)-ACDHs are required for growth on ethanol, whilst only the former plays a role during growth on glucose.

Mechanisms of inhibition of aldehyde dehydrogenase by nitroxyl, the active metabolite of the alcohol deterrent agent cyanamide

Nitroxyl, produced in the bioactivation of the alcohol deterrent agent cyanamide, is a potent inhibitor of aldehyde dehydrogenase (AIDH); however, the mechanism of inhibition of AlDH by nitroxyl has not been described previously. Nitroxyl is also generated from Angeli's salt (Na2N2O3) at physiological pH, and, indeed, Angeli's salt inhibited yeast AlDH in a time- and concentration-dependent manner, with IC50 values under anaerobic conditions with and without NAD+ of 1.3 and 1.8 microM, respectively. Benzaldehyde, a substrate for AlDH, competitively blocked the inhibition of this enzyme by nitroxyl in the presence of NAD+, but not in its absence, in accord with the ordered mechanism of this reaction. The sulfhydryl reagents dithiothreitol (5 mM) and reduced glutathione (10 mM) completely blocked the inhibition of AlDH by Angeli's salt. These thiols were also able to partially restore activity to the nitroxyl-inhibited enzyme, the extent of reactivation being dependent on the pH at which the inactivation occurred. This pH dependency indicates the formation of two inhibited forms of the enzyme, with an irreversible form predominant at pH 7.5 and below, and a reversible form predominant at pH 8.5 and above. The reversible form of the inhibited enzyme is postulated to be an intra-subunit disulfide, while the irreversible form is postulated to be a sulfinamide. Both forms of the inhibited enzyme are derived via a common N-hydroxysulfenamide intermediate produced by the addition of nitroxyl to active site cysteine thiol(s).

Molecular cloning, characterization, and potential roles of cytosolic and mitochondrial aldehyde dehydrogenases in ethanol metabolism in Saccharomyces cerevisiae

The full-length DNAs for two Saccharomyces cerevisiae aldehyde dehydrogenase (ALDH) genes were cloned and expressed in Escherichia coli. A 2,744-bp DNA fragment contained an open reading frame encoding cytosolic ALDH1, with 500 amino acids, which was located on chromosome XVI. A 2,661-bp DNA fragment contained an open reading frame encoding mitochondrial ALDH5, with 519 amino acids, of which the N-terminal 23 amino acids were identified as the putative leader sequence. The ALDH5 gene was located on chromosome V. The commercial ALDH (designated ALDH2) was partially sequenced and appears to be a mitochondrial enzyme encoded by a gene located on chromosome XV. The recombinant ALDH1 enzyme was found to be essentially NADP dependent, while the ALDH5 enzyme could utilize either NADP or NAD as a cofactor. The activity of ALDH1 was stimulated two- to fourfold by divalent cations but was unaffected by K+ ions. In contrast, the activity of ALDH5 increased in the presence of K+ ions: 15-fold with NADP and 40-fold with NAD, respectively. Activity staining of isoelectric focusing gels showed that cytosolic ALDH1 contributed 30 to 70% of the overall activity, depending on the cofactor used, while mitochondrial ALDH2 contributed the rest. Neither ALDH5 nor the other ALDH-like proteins identified from the genomic sequence contributed to the in vitro oxidation of acetaldehyde. To evaluate the physiological roles of these three ALDH isoenzymes, the genes encoding cytosolic ALDH1 and mitochondrial ALDH2 and ALDH5 were disrupted in the genome of strain TWY397 separately or simultaneously. The growth of single-disruption delta ald1 and delta ald2 strains on ethanol was marginally slower than that of the parent strain. The delta ald1 delta ald2 double-disruption strain failed to grow on glucose alone, but growth was restored by the addition of acetate, indicating that both ALDHs might catalyze the oxidation of acetaldehyde produced during fermentation. The double-disruption strain grew very slowly on ethanol. The role of mitochondrial ALDH5 in acetaldehyde metabolism has not been defined but appears to be unimportant.

The ALD6 gene of Saccharomyces cerevisiae encodes a cytosolic, Mg(2+)-activated acetaldehyde dehydrogenase

The deduced translation product of an open reading frame on the left arm of chromosome XVI of Saccharomyces cerevisiae, with the systematic name of YPL061w, is 500 amino acids in length and shares significant homology with aldehyde dehydrogenases. Amino acids 2 to 16 of the protein encoded by YPL061w were found to be identical to the N-terminal 15 amino acids of the purified cytosolic, Mg(2+)-activated acetaldehyde dehydrogenase (ACDH) of S. cerevisiae. This enzyme is thought to be involved in the production of acetate from which cytosolic acetyl-CoA is then synthesized. Deletion of YPL061w was detrimental to the growth of haploid strains of yeast; an analysis of one deletion mutant revealed a maximum specific growth rate (in complex medium containing glucose) of one-third of that displayed by the wild-type strain. Mutants deleted in YPL061w were also unable to use ethanol as a carbon source. As expected, the cytosolic, Mg(2+)-activated ACDH activity had been lost from the mutants, although the mitochondrial, K(+)-activated ACDH was readily detected.

Mechanism for the inhibition of aldehyde dehydrogenase by nitric oxide

The inhibition of Saccharomyces cerevisiae aldehyde dehydrogenase (AlDH) by gaseous nitric oxide (NO) in solution and by NO generated from diethylamine nonoate was time and concentration dependent. The presence of oxygen significantly reduced the extent of inhibition by NO, indicating that NO itself rather than an oxidation product of NO such as N2O3 is the inhibitory species under physiological conditions. A cysteine residue at the active site of the enzyme was implicated in this inhibition based on the following observations: a) NAD+ and NADP+, but not reduced cofactors, significantly enhanced inhibition of AlDH by NO; b) the aldehyde substrate, benzaldehyde, blocked inhibition; and c) inhibition was accompanied by loss of free sulfhydryl groups on the enzyme. Activity of the NO-inactivated enzyme was readily restored by treatment with dithiothreitol (DTT), but not with GSH. This difference was attributed, in part, to a redox process leading to the formation of a cyclic DTT disulfide. Based on the chemistry deduced from model systems, the reaction of NO with AlDH sulfhydryls was shown to produce intramolecular disulfides and N2O. These disulfides were shown to be intrasubunit disulfides by nonreducing SDS-PAGE analysis of the NO- inhibited enzyme. Following complete inhibition of AlDH by NO, four of the eight titratable (Ellman's reagent) sulfhydryl groups of AlDH were found to be oxidized to disulfides. These results suggest that a) the sulfhydryl group of active site Cys-302 and a proximal cysteine are oxidized to form an intrasubunit disulfide by NO; b) only two of the four subunits of AlDH are catalytically active; and c) NO preferentially oxidizes sulfhydryl groups of the catalytically active subunits. A detailed mechanism for the inhibition of AlDH by NO is presented.

Inhibition of aldehyde dehydrogenase by disulfiram and its metabolite methyl diethylthiocarbamoyl-sulfoxide

Disulfiram (DSF) is presently the only available drug used in the aversion therapy of recovering alcoholics. It acts by inhibiting aldehyde dehydrogenase (ALDH), leading to high blood levels of acetaldehyde. The in vitro inhibition of ALDH by DSF and its metabolites was systematically studied by combined enzyme inhibition assay with direct molecular weight determination of the same sample using electrospray ionization-mass spectrometry (ESI-MS). Enzyme activity was measured after incubating yeast ALDH (yALDH) with excess concentrations of DSF, methyl diethyldithiocarbamate (MeDDC) and methyl diethylthiocarbamoyl-sulfoxide (MeDTC-SO) and then subjected to analysis by ESI-MS. Addition of DSF resulted in complete enzyme inhibition; however, ESI-MS analysis demonstrated no discernible shift in molecular weight, indicating that no intermolecular adduct was formed with the protein. Treatment of yALDH with MeDTC-SO also completely abolished yALDH activity with a concomitant increase of + approximately 100 Da in the molecular mass of the enzyme. This indicated formation of a covalent carbamoyl protein adduct. Furthermore, the effects of dithiothreitol (DTT) were examined on samples of inhibited protein in vitro. At pH 7.5, DTT completely reversed inhibition after DSF treatment. yALDH inhibited by MeDTC-SO could not be recovered by DTT at pH 7.5, but at pH 9 the enzymic activity was fully restored and a mass loss of approximately 100 Da was noted. This observations are consistent with mechanisms where inhibition of yALDH by DSF in vitro involves oxidation of the active site, whereas MeDTC-SO forms a covalent adduct with the protein in vitro resulting in cessation of enzyme activity.

Two potential indole-3-acetaldehyde dehydrogenases in the phytopathogenic fungus Ustilago maydis

The phytopathogenic basidiomycetc Ustilago maydis produces indole-3-acetic acid (IndCH2COOH) and indole-3-pyruvic acid (Ind-Prv) from tryptophan. Indole-3-acetaldehyde (IndCH2CH2O) is the common intermediate in the conversion of Ind-Prv and tryptamine to IndCH2COOH. We purified an enzyme (Iad1) from U. maydis that catalyzes the NAD(+)-dependent conversion of IndCH2CH2O to IndCH2COOH and isolated corresponding cDNA and genomic clones. The identity of the cDNA clone was confirmed by expression in Escherichia coli and demonstration of enzymatic activity. In U. maydis, iad1-null mutants were generated by gene replacement. The ability to convert IndCH2CH2O to IndCH2COOH was at least 100-fold reduced in U. maydis iad1-null mutants grown in medium with glucose as carbon source. However, the iad1-null mutants were not diminished in their capacity to produce IndCH2COOH from tryptophan, indicating that IndCH2COOH formation from tryptophan apparently proceeds in the absence of IndCH2CH2O dehydrogenase activity under these conditions. Iad1 expression was strongly induced during growth on ethanol while under these conditions iad1-null mutants were unable to grow. This reveals that iad1 is primarily engaged in the conversion of ethanol to acetate. In iad1-null mutants we detected an additional NAD(+)-dependent IndCH2CH2O dehydrogenase activity that was induced during growth on L-arabinose but repressed in the presence of D-glucose. In arabinose-containing medium the conversion of tryptophan to IndCH2COOH was approximately 5-fold reduced in wild-type strains but 10-15-fold reduced in iad1-null mutant strains compared to IndCH2COOH formation in glucose-containing medium. In addition, the formation of Ind-Prv from tryptophan was abolished in wild-type and iad1-null mutant strains. During growth on arabinose, the conversion of tryptamine to IndCH2COOH was strongly favored suggesting that the glucose-repressible IndCH2CH2O dehydrogenase is required to convert IndCH2CH2O derived from tryptamine to IndCH2COOH.

Enzymatic and nonenzymatic ADP-ribosylation of cysteine

Mono-ADP-ribosylation is a protein modification that occurs at a number of different amino acids, dictated by the specificity of the individual ADP-ribosyltransferases. A specific cysteine in several guanine nucleotide-binding regulatory proteins is ADP-ribosylated by the bacterial protein pertussis toxin. Recent purification of an ADP-ribosylcysteine hydrolase and NAD:cysteine ADP-ribosyltransferase, and detection of ADP-ribose-cysteine linkages in tissue samples has raised hope that an endogenous regulatory cysteine-specific ADP-ribosylation pathway exists. A current goal is the identification of such a pathway for ADP-ribosylation of cysteine within animal cells. Interpretation of the data in this field has been complicated by recent reports that revealed several unforeseen chemical reactions of NAD and its metabolites with free cysteine and cysteine in proteins. This mini-review covers the latest understanding of the ADP-ribosylation reactions associated with cysteine, and provides a set of criteria for future research to establish positively the existence of an endogenous cysteine-specific mono-ADP-ribosyltransferase.

Identification of Chloroacetaldehyde Dehydrogenase Involved in 1,2-Dichloroethane Degradation

The degradation of 1,2-dichloroethane and 2-chloroethanol by Xanthobacter autotrophicus GJ10 proceeds via chloroacetaldehyde, a reactive and potentially toxic intermediate. The organism produced at least three different aldehyde dehydrogenases, of which one is plasmid encoded. Two mutants of strain GJ10, designated GJ10M30 and GJ10M41, could no longer grow on 2-chloroethanol and were found to lack the NAD-dependent aldehyde dehydrogenase that is the predominant protein in wild-type cells growing on 2-chloroethanol. Mutant GJ10M30, selected on the basis of its resistance to 1,2-dibromoethane, also had lost haloalkane dehalogenase activity and Hg 2+ resistance, indicating plasmid loss. From a gene bank of strain GJ10, different clones that complemented one of these mutants were isolated. In both transconjugants, the aldehyde dehydrogenase that was absent in the mutants was overexpressed. The enzyme was purified and was a tetrameric protein of 55-kDa subunits. The substrate range was rather broad, with the highest activity measured for acetaldehyde. The K m value for chloroacetaldehyde was 160 μM, higher than those for other aldehydes tested. It is concluded that the ability of GJ10 to grow with 2-chloroethanol is due to the high expression level of an aldehyde dehydrogenase with a rather low activity for chloroacetaldehyde.

Aldehyde dehydrogenases: widespread structural and functional diversity within a shared framework

Sequences of 16 NAD and/or NADP-linked aldehyde oxidoreductases are aligned, including representative examples of all aldehyde dehydrogenase forms with wide substrate preferences as well as additional types with distinct specificities for certain metabolic aldehyde intermediates, particularly semialdehydes, yielding pairwise identities from 15 to 83%. Eleven of 23 invariant residues are glycine and three are proline, indicating evolutionary restraint against alteration of peptide chain-bending points. Additionally, another 66 positions show high conservation of residue type, mostly hydrophobic residues. Ten of these occur in predicted beta-strands, suggesting important interior-packing interactions. A single invariant cysteine residue is found, further supporting its catalytic role. A previously identified essential glutamic acid residue is conserved in all but methyl malonyl semialdehyde dehydrogenase, which may relate to formation by that enzyme of a CoA ester as a product rather than a free carboxylate species. Earlier, similarity to a GXGXXG segment expected in the NAD-binding site was noted from alignments with fewer sequences. The same region continues to be indicated, although now only the first glycine residue is strictly conserved and the second (usually threonine) is not present at all, suggesting greater variance in coenzyme-binding interactions.

Metabolic activation of n-butyraldoxime by rat liver microsomal cytochrome P450. A requirement for the inhibition of aldehyde dehydrogenase

n-Butyraldoxime (n-BO) is known to cause a disulfiram/ethanol-like reaction in humans, a manifestation of the inhibition of hepatic aldehyde dehydrogenase (AIDH). As with a number of other in vivo inhibitors of AIDH, n-BO does not inhibit purified AIDH in vitro, suggesting that a metabolite of n-BO is the actual inhibitor of this enzyme. In re-examination of the effect of n-BO on blood acetaldehyde levels following ethanol in the Sprague-Dawley rat, we found that pretreatment with substrates and/or inhibitors of cytochrome P450 blocked the n-BO-induced rise in blood acetaldehyde in the following order of decreasing potency: 1-benzylimidazole (0.1 mmol/kg) > 3-amino-1,2,4-triazole (1.0 g/kg) > ethanol (3.0 g/kg) > phenobarbital (0.1% in the drinking water, 7 days) > SKF-525A (40 mg/kg). Rat liver microsomes were shown to catalyze the conversion of n-BO to an active metabolite that inhibited yeast AIDH. This reaction was dependent on NADPH and molecular oxygen and was inhibited by CO and 1-benzylimidazole. Hydroxylamine, postulated by others to be a metabolite of n-BO, inhibited AIDH via a catalase-mediated reaction and not through an NADPH-supported microsome-catalyzed reaction. Using GLC-mass spectrometry, 1-nitrobutane (an N-oxidation product) and butyronitrile (a dehydration product) were identified as metabolites from microsomal incubations of n-BO. However, neither of these metabolic products inhibited AIDH directly or in the presence of liver microsomes and NADPH. We conclude that another NADPH-dependent, cytochrome P450-catalyzed metabolic product of n-BO is responsible for the inhibition of AIDH by n-BO.

An N-hydroxylated derivative of cyanamide that inhibits yeast aldehyde dehydrogenase

A stable, N,O-dibenzoyl derivative (DBHC) of N-hydroxycyanamide, the latter the postulated bioactivation product of the alcohol deterrent agent, cyanamide, has been synthesized. DBHC was an effective inhibitor of yeast aldehyde dehydrogenase (AIDH) in vitro and inhibited this enzyme in a concentration-dependent manner with an IC50 of 25 microM. Hydrolysis of the benzoate moiety of DBHC with dilute NaOH gave rise to the formation of nitroxyl (HN = O), detected by gas chromatography as nitrous oxide (N2O), the end-product of nitroxyl dimerization and disproportionation. It is postulated that the nitroxyl liberated by esterase action on DBHC by yeast AIDH may be the reactive species that inhibits AIDH.

Identification and molecular characterization of the gene coding for acetaldehyde dehydrogenase II (acoD) of Alcaligenes eutrophus

The N-terminal amino acid sequence of purified acetaldehyde dehydrogenase II (AcDH-II) from ethanol-grown cells of Alcaligenes eutrophus was determined. By using oligonucleotides deduced from this sequence the structural gene for AcDH-II, which was referred to as acoD, was localized on a 7.2-kbp EcoRI restriction fragment (fragment D), which has been cloned recently (C. Fründ, H. Priefert, A. Steinbüchel, and H. G. Schlegel, J. Bacteriol. 171:6539-6548, 1989). A 2.8-kbp PstI subfragment of D, which harbored acoD, was sequenced. It revealed an open reading frame of 1,518 bp, encoding a protein with a relative molecular weight of 54,819. The insertions of Tn5::mob of two transposon-induced mutants of A. eutrophus, which were impaired in the catabolism of acetoin, were mapped 483 or 1,359 bp downstream from the translational start codon of acoD. The structural gene was preceded by a putative Shine-Dalgarno sequence. The transcriptional start site 57 bp upstream of acoD was identified and was preceded by a sequence which exhibited a striking homology to the enterobacterial sigma 54-dependent promoter consensus sequence. This was in accordance with the observation that the expression of acoD and of other acetoin-catabolic genes depended on the presence of an intact rpoN-like gene. Alignments of the amino acid sequence deduced from acoD with the primary structures of aldehyde dehydrogenases from other sources revealed high degrees of homology, amounting to 46.5% identical amino acids.