Nucleotide sequence of the membrane-bound aldehyde dehydrogenase gene from Acetobacter polyoxogenes

Transcriptome Analysis Reveals Genes Contributed to Min Pig Villi Hair Follicle in Different Seasons

The Min pig, a local pig breed in China, has a special trait which has intermittent villus and coat hair regeneration. However, the regulation and mechanism of villus in Min pigs have not yet been described. We observed and described the phenotype of Min pig dermal villi in detail and sequenced the mRNA transcriptome of Min pig hair follicles. A total of 1520 differentially expressed genes (DEG) were obtained.K-means hierarchical clustering showed that there was a significant expression pattern difference in winter compared with summer. Gene enrichment and network analysis results showed that the hair growth in Min pigs was closely related to the composition of desmosomes and regulated by an interaction network composed of eight core genes, namely DSP, DSC3, DSG4, PKP1, TGM1, KRT4, KRT15, and KRT84. Methylation analysis of promoters of target genes showed that the PKP1 gene was demethylated. Our study will help to supplement current knowledge of the growth mechanism of different types of hair.

Shifting the metallocentric molybdoenzyme paradigm: the importance of pyranopterin coordination

In this review, we test the hypothesis that pyranopterin coordination plays a critical role in defining substrate reactivities in the four families of mononuclear molybdenum and tungsten enzymes (Mo/W-enzymes). Enzyme families containing a single pyranopterin dithiolene chelate have been demonstrated to have reactivity towards two (sulfite oxidase, SUOX-fold) and five (xanthine dehydrogenase, XDH-fold) types of substrate, whereas the major family of enzymes containing a bis-pyranopterin dithiolene chelate (dimethylsulfoxide reductase, DMSOR-fold) is reactive towards eight types of substrate. A second bis-pyranopterin enzyme (aldehyde oxidoreductase, AOR-fold) family catalyzes a single type of reaction. The diversity of reactions catalyzed by each family correlates with active site variability, and also with the number of pyranopterins and their coordination by the protein. In the case of the AOR-fold enzymes, inflexibility of pyranopterin coordination correlates with their limited substrate specificity (oxidation of aldehydes). In examples of the SUOX-fold and DMSOR-fold enzymes, we observe three types of histidine-containing charge-transfer relays that can: (1) connect the piperazine ring of the pyranopterin to the substrate-binding site (SUOX-fold enzymes); (2) provide inter-pyranopterin communication (DMSOR-fold enzymes); and (3) connect a pyran ring oxygen to deeply buried water molecules (the DMSOR-fold NarGHI-type nitrate reductases). Finally, sequence data mining reveals a number of bacterial species whose predicted proteomes contain large numbers (up to 64) of Mo/W-enzymes, with the DMSOR-fold enzymes being dominant. These analyses also reveal an inverse correlation between Mo/W-enzyme content and pathogenicity.

Identification and characterization of genes from Streptomyces sp. strain K30 responsible for clear zone formation on natural rubber latex and poly(cis-1,4-isoprene) rubber degradation

Streptomyces sp. strain K30 was isolated from soil next to a city high way in Münster (Germany) according to its ability to degrade natural and synthetic poly(cis-1,4-isoprene) rubber and to form clear zones on natural rubber latex agar plates. The clear zone forming phenotype was used to clone the responsible gene by phenotypic complementation of a clear zone negative mutant. An open reading frame (lcp) of 1,191 bp was identified, which was preceded by a putative signal sequence and restored the capability to form clear zones on natural rubber latex in the mutant. The putative translation product exhibited strong homologies (50% aa identity) to a putative secreted protein from Streptomyces coelicolor strain A3(2), another clear zone forming strain. Heterologous expression of lcp of Streptomyces sp. strain K30 in Streptomyces lividans strain TK23 enabled the latter to form clear zones on latex-overlay agar plates and to accumulate a degradation product of about 12 kDa containing aldehyde groups. Two ORFs putatively encoding a heterodimeric molybdenum hydroxylase (oxiAB) were identified downstream of lcp in Streptomyces sp. strain K30 strain which exerted a positive effect on clear zone formation and enabled the strain to oxidize the resulting aldehydes. Heterologous expression of a fragment harboring lcp plus oxiAB in S. lividans TK23 resulted in accumulation of aldehydes only in the presence of 10 mM tungstate. Determination of protein content during cultivation on poly(cis-1,4-isoprene) revealed an increase of the cellular protein, and gel permeation chromatography analysis indicated a shift of the molecular weight distribution of the rubber to lower values in the transgenic S. lividans strains and in the wild type, thus confirming utilization and degradation of rubber. Therefore, for the first time, genes responsible for clear zone formation on natural rubber latex and synthetic cis-1,4-polyisoprene degradation in Gram-positive bacteria were identified and characterized.

The biochemistry, physiology and genetics of PQQ and PQQ-containing enzymes

Pyrrolo-quinoline quinone (PQQ) is the non-covalently bound prosthetic group of many quinoproteins catalysing reactions in the periplasm of Gram-negative bacteria. Most of these involve the oxidation of alcohols or aldose sugars. PQQ is formed by fusion of glutamate and tyrosine, but details of the biosynthetic pathway are not known; a polypeptide precursor in the cytoplasm is probably involved, the completed PQQ being transported into the periplasm. In addition to the soluble methanol dehydrogenase of methylotrophs, there are three classes of alcohol dehydrogenases; type I is similar to methanol dehydrogenase; type II is a soluble quinohaemoprotein, having a C-terminal extension containing haem C; type III is similar but it has two additional subunits (one of which is a multihaem cytochrome c), bound in an unusual way to the periplasmic membrane. There are two types of glucose dehydrogenase; one is an atypical soluble quinoprotein which is probably not involved in energy transduction. The more widely distributed glucose dehydrogenases are integral membrane proteins, bound to the membrane by transmembrane helices at the N-terminus. The structures of the catalytic domains of type III alcohol dehydrogenase and membrane glucose dehydrogenase have been modelled successfully on the methanol dehydrogenase structure (determined by X-ray crystallography). Their mechanisms are likely to be similar in many ways and probably always involve a calcium ion (or other divalent cation) at the active site. The electron transport chains involving the soluble alcohol dehydrogenases usually consist only of soluble c-type cytochromes and the appropriate terminal oxidases. The membrane-bound quinohaemoprotein alcohol dehydrogenases pass electrons to membrane ubiquinone which is then oxidized directly by ubiquinol oxidases. The electron acceptor for membrane glucose dehydrogenase is ubiquinone which is subsequently oxidized directly by ubiquinol oxidases or by electron transfer chains involving cytochrome bc1, cytochrome c and cytochrome c oxidases. The function of most of these systems is to produce energy for growth on alcohol or aldose substrates, but there is some debate about the function of glucose dehydrogenases in those bacteria which contain one or more alternative pathways for glucose utilization. Synthesis of the quinoprotein respiratory systems requires production of PQQ, haem and the dehydrogenase subunits, transport of these into the periplasm, and incorporation together with divalent cations, into active quinoproteins and quinohaemoproteins. Six genes required for regulation of synthesis of methanol dehydrogenase have been identified in Methylobacterium, and there is evidence that two, two-component regulatory systems are involved.

Cloning of genes coding for L-sorbose and L-sorbosone dehydrogenases from Gluconobacter oxydans and microbial production of 2-keto-L-gulonate, a precursor of L-ascorbic acid, in a recombinant G. oxydans strain

We have purified L-sorbose dehydrogenase (SDH) and L-sorbosone dehydrogenase (SNDH) from Gluconobacter oxydans T-100 that showed an ability to convert D-sorbitol to 2-keto-L-gulonate (2-KLGA). A genomic library of Gluconobacter oxydans T-100 was screened with a probe, a 180-bp PCR product which was obtained from degenerate oligodeoxyribonucleotides based on the elucidated sequence of the purified SDH (used as primers) and the genomic DNA of G. oxydans T-100 (used as a template). From sequencing of the DNA from a clone positive to the probe, the SNDH and the SDH were estimated to be coded in sequential open reading frames with 1,497 and 1,599 nucleotides, respectively, which was confirmed by expression of the DNA in Escherichia coli that showed both enzymatic activities. The DNA was introduced to a shuttle vector which was prepared from a plasmid of G. oxydans T-100 and pHSG298 to obtain an expression vector designated pSDH155. The production of 2-KLGA by pSDH155 in G. oxydans G624, an L-sorbose-accumulating strain, was improved to 230% compared to that of G. oxydans T-100. Chemical mutation of the host strain to suppress the L-idonate pathway and replacement of the original promoter with that of E. coli tufB resulted in improving the production of 2-KLGA. Consequently, high-level production from D-sorbitol to 2-KLGA (130 mg/ml) was achieved by simple fermentation of the recombinant Gluconobacter.

Cloning, expression, and sequence analysis of the three genes encoding quinoline 2-oxidoreductase, a molybdenum-containing hydroxylase from Pseudomonas putida 86

The three genes coding for quinoline 2-oxidoreductase (Qor) of Pseudomonas putida 86 were cloned and sequenced. The qor genes are clustered in the transcriptional order medium (M) small (S), large (L) and code for three subunits of 288 (QorM), 168 (QorS), and 788 (QorL) amino acids, respectively. Formation of active quinoline 2-oxidoreductase and degradation of quinoline occurred in a recombinant P. putida KT2440 clone. The amino acid sequences of Qor show significant homology to various prokaryotic molybdenum containing hydroxylases and to eukaryotic xanthine dehydrogenases. QorS contains two conserved motifs for [2Fe-2S] clusters. The binding motif for the N-terminal [2Fe-2S] cluster corresponds to the binding site of bacterial and chloroplast-type [2Fe-2S] ferredoxins, whereas the amino acid pattern of the internal [2Fe-2S] center apparently is a distinct feature of molybdenum-containing hydroxylases, showing no homology to any other described [2Fe-2S] binding motif. The medium subunit QorM presumably contains the FAD, but no conserved sequence areas or described motifs of FAD, NAD, NADP, or ATP binding were detected. Putative binding sites of the molybdopterin cytosine dinucleotide cofactor were detected in QorL by comparison with "contacting segments" recently described in aldehyde oxidoreductase from Desulfovibrio gigas (Romão, M. J., Archer, M., Moura, I., Moura, J. J. G., LeGall, J., Engh, R., Schneider, M., Hof, P., and Huber, R. (1995) Science 270, 1170-1176).

Quinaldine 4-oxidase from Arthrobacter sp. Rü61a, a versatile procaryotic molybdenum-containing hydroxylase active towards N-containing heterocyclic compounds and aromatic aldehydes

Quinaldine 4-oxidase from Arthrobacter sp. Rü61a, an inducible molybdenum-containing hydroxylase, was purified to homogeneity by an optimized five-step procedure. Molecular oxygen is proposed as physiological electron acceptor. Electrons are also transferred to artificial electron acceptors with E'o > -8 mV. The molybdo-iron/sulfur flavoprotein regiospecifically attacks its N-heterocyclic substrates: isoquinoline and phthalazine are hydroxylated adjacent to the N-heteroatom at Cl, whereas quinaldine, quinoline, cinnoline and quinazoline are hydroxylated at C4. Additionally, the aromatic aldehydes benzaldehyde, salicylaldehyde, vanillin and cinnamaldehyde are oxidized to the corresponding carboxylic acids, whereas short-chain aliphatic aldehydes are not. Quinaldine 4-oxidase is compared to the two molybdenum-containing hydroxylases quinoline 2-oxidoreductase from Pseudomonas putida 86 [Tshisuaka, B., Kappl, R., Hüttermann, J. & Lingens, F. (1993) Biochemistry 32, 12928-12934] and isoquinoline 1-oxidoreductase from Pseudomonas diminuta 7 [Lehmann, M., Tshisuaka, B., Fetzner, S., Röger, P. & Lingens, F. (1994) J. Biol. Chem. 269, 11254-11260] with respect to the substrates converted and the electron-acceptor specificities. These dehydrogenases hydroxylate their N-heterocyclic substrates exclusively adjacent to the heteroatom. Whereas the aldehydes tested are scarcely oxidized by quinoline 2-oxidoreductase, isoquinoline 1-oxidoreductase catalyzes the oxidation of the aromatic aldehydes, although being progressively inhibited. Neither quinoline 2-oxidoreductase nor isoquinoline 1-oxidoreductase transfer electrons to oxygen. Otherwise, the spectrum of electron acceptors used by quinoline 2-oxidoreductase and quinaldine 4-oxidase is identical. However, isoquinoline 1-oxidoreductase differs in its electron-acceptor specificity. Quinaldine 4-oxidase is unusual in its substrate and electron-acceptor specificity. This enzyme is able to function as oxidase or dehydrogenase, it oxidizes aldehydes, and it catalyzes the nucleophilic attack of N-containing heterocyclic compounds at two varying positions depending on the substrate.

Molecular cloning of the isoquinoline 1-oxidoreductase genes from Pseudomonas diminuta 7, structural analysis of iorA and iorB, and sequence comparisons with other molybdenum-containing hydroxylases

The iorA and iorB genes from the isoquinoline-degrading bacterium Pseudomonas diminuta 7, encoding the heterodimeric molybdo-iron-sulfur-protein isoquinoline 1-oxidoreductase, were cloned and sequenced. The deduced amino acid sequences IorA and IorB showed homologies (i) to the small (gamma) and large (alpha) subunits of complex molybdenum-containing hydroxylases (alpha beta gamma/alpha 2 beta 2 gamma 2) possessing a pterin molybdenum cofactor with a monooxo-monosulfido-type molybdenum center, (ii) to the N- and C-terminal regions of aldehyde oxidoreductase from Desulfovibrio gigas, and (iii) to the N- and C-terminal domains of eucaryotic xanthine dehydrogenases, respectively. The closest similarity to IorB was shown by aldehyde dehydrogenase (Adh) from the acetic acid bacterium Acetobacter polyoxogenes. Five conserved domains of IorB were identified by multiple sequence alignments. Whereas IorB and Adh showed an identical sequential arrangement of these conserved domains, in all other molybdenum-containing hydroxylases the relative position of "domain A" differed. IorA contained eight conserved cysteine residues. The amino acid pattern harboring the four cysteine residues proposed to ligate the Fe/S I cluster was homologous to the consensus binding site of bacterial and chloroplast-type [2Fe-2S] ferredoxins, whereas the pattern including the four cysteines assumed to ligate the Fe/S II center showed no similarities to any described [2Fe-2S] binding motif. The N-terminal region of IorB comprised a putative signal peptide similar to typical leader peptides, indicating that isoquinoline 1-oxidoreductase is associated with the cell membrane.

Cloning and molecular characterization of hxA, the gene coding for the xanthine dehydrogenase (purine hydroxylase I) of Aspergillus nidulans

We have cloned and sequenced the hxA gene coding for the xanthine dehydrogenase (purine hydroxylase I) of Aspergillus nidulans. The gene codes for a polypeptide of 1363 amino acids. The sequencing of a nonsense mutation, hxA5, proves formally that the clones isolated correspond to the hxA gene. The gene sequence is interrupted by three introns. Similarity searches reveal two iron-sulfur centers and a NAD/FAD-binding domain and have enabled a consensus sequence to be determined for the molybdenum cofactor-binding domain. The A. nidulans sequence is a useful outclass for the other known sequences, which are all from metazoans. In particular, it gives added significance to the missense mutations sequenced in Drosophila melanogaster and leads to the conclusion that while one of the recently sequenced human genes codes for a xanthine dehydrogenase, the other one must code for a different molybdenum-containing hydroxylase, possibly an aldehyde oxidase. The transcription of the hxA gene is induced by the uric acid analogue 2-thiouric acid and repressed by ammonium. Induction necessitates the product of the uaY regulatory gene.

Cloning and nucleotide sequencing of the membrane-bound L-sorbosone dehydrogenase gene of Acetobacter liquefaciens IFO 12258 and its expression in Gluconobacter oxydans

Cloning and expression of the gene encoding Acetobacter liquefaciens IFO 12258 membrane-bound L-sorbosone dehydrogenase (SNDH) were studied. A genomic library of A. liquefaciens IFO 12258 was constructed with the mobilizable cosmid vector pVK102 (mob+) in Escherichia coli S17-1 (Tra+). The library was transferred by conjugal mating into Gluconobacter oxydans OX4, a mutant of G. oxydans IFO 3293 that accumulates L-sorbosone in the presence of L-sorbose. The transconjugants were screened for SNDH activity by performing a direct expression assay. One clone harboring plasmid p7A6 converted L-sorbosone to 2-keto-L-gulonic acid (2KGA) more rapidly than its host did and also converted L-sorbose to 2KGA with no accumulation of L-sorbosone. The insert (25 kb) of p7A6 was shortened to a 3.1-kb fragment, in which one open reading frame (1,347 bp) was found and was shown to encode a polypeptide with a molecular weight of 48,222. The SNDH gene was introduced into the 2KGA-producing strain G. oxydans IFO 3293 and its derivatives, which contained membrane-bound L-sorbose dehydrogenase. The cloned SNDH was correctly located in the membrane of the host. The membrane fraction of the clone exhibited almost stoichiometric formation of 2KGA from L-sorbosone and L-sorbose. Resting cells of the clones produced 2KGA very efficiently from L-sorbosone and L-sorbose, but not from D-sorbitol; the conversion yield from L-sorbosone was improved from approximately 25 to 83%, whereas the yield from L-sorbose was increased from 68 to 81%. Under fermentation conditions, cloning did not obviously improve the yield of 2KGA from L-sorbose.

The pca-pob supraoperonic cluster of Acinetobacter calcoaceticus contains quiA, the structural gene for quinate-shikimate dehydrogenase

An 18-kbp Acinetobacter calcoaceticus chromosomal segment contains the pcaIJFBDKCHG operon, which is required for catabolism of protocatechuate, and pobSRA, genes associated with conversion of p-hydroxybenzoate to protocatechuate. The genetic function of the 6.5 kbp of DNA between pcaG and pobS was unknown. Deletions in this DNA were designed by removal of fragments between restriction sites, and the deletion mutations were introduced into A. calcoaceticus by natural transformation. The mutations prevented growth with either quinate or shikimate, growth substrates that depend upon qui gene function for their catabolism to protocatechuate. The location of quiA, a gene encoding quinate-shikimate dehydrogenase, was indicated by its expression in one of the deletion mutants, and the position of the gene was confirmed by determination of its 2,427-bp nucleotide sequence. The deduced amino acid sequence of QuiA confirmed that it is a member of a family of membrane-associated, pyrrolo-quinoline quinone-dependent dehydrogenases, as had been suggested by earlier biochemical investigations. Catabolism of quinate and skikimate is initiated by NAD(+)-dependent dehydrogenases in other microorganisms, so it is evident that different gene pools were called upon to provide the ancestral enzyme for this metabolic step.

Genetic organization of Acetobacter for acetic acid fermentation

Plasmid vectors for the acetic acid-producing strains of Acetobacter and Gluconobacter were constructed from their cryptic plasmids and the efficient transformation conditions were established. The systems allowed to reveal the genetic background of the strains used in the acetic acid fermentation. Genes encoding indispensable components in the acetic acid fermentation, such as alcohol dehydrogenase, aldehyde dehydrogenase and terminal oxidase, were cloned and characterized. Spontaneous mutations at high frequencies in the acetic acid bacteria to cause the deficiency in ethanol oxidation were analyzed. A new insertion sequence element, IS1380, was identified as a major factor of the genetic instability, which causes insertional inactivation of the gene encoding cytochrome c, an essential component of the functional alcohol dehydrogenase complex. Several genes including the citrate synthase gene of A. aceti were identified to confer acetic acid resistance, and the histidinolphosphate aminotransferase gene was cloned as a multicopy suppressor of an ethanol sensitive mutant. Improvement of the acetic acid productivity of an A. aceti strain was achieved through amplification of the aldehyde dehydrogenase gene with a multicopy vector. In addition, spheroplast fusion of the Acetobacter strains was developed and applied to improve their properties.

Characterization of a cytochrome a1 that functions as a ubiquinol oxidase in Acetobacter aceti

The terminal oxidase for ethanol oxidation in Acetobacter aceti was purified as a complex consisting of four subunits (subunits I, II, III, and IV) with molecular masses of 72, 34, 21, and 13 kDa, respectively. Spectrophotometric analysis and catalytic properties determined with the purified enzyme showed that it belonged to a family of cytochrome a1 (ba)-type ubiquinol oxidases. A polymerase chain reaction with two oligonucleotides designed for amino acid sequences that are conserved in subunit I of the aa3-type cytochrome c oxidases from various origins and of an Escherichia coli o (bo)-type ubiquinol oxidase was used for cloning the cytochrome a1 gene. A 0.5-kb fragment thus amplified was used as the probe to clone a 4.5-kb KpnI fragment that contained a putative open reading frame for the whole subunit I gene. The molecular weight and amino acid composition of the product of this open reading frame (cyaA) were the same as those of the purified protein from A. aceti. The amino acid sequence of CyaA was homologous to that of subunit I of the E. coli o-type ubiquinol oxidase. Nucleotide sequence analysis of the region neighboring the cyaA gene revealed that the genes (cyaB, cyaC, and cyaD) encoding the other three subunits (subunits II, III, and IV) were clustered upstream and downstream of the cyaA gene in the order cyaB, cyaA, cyaC, and cyaD and with the same transcription polarity, forming an operon. As expected from the enzymatic properties, CyaB, CyaC, and CyaD showed great similarity in amino acid sequence to the corresponding sununits of the E. coli o-type ubiquinol oxidase and as(3)-type cytochrome c oxidases.

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.

Quinoproteins: enzymes containing the quinonoid cofactor pyrroloquinoline quinone, topaquinone or tryptophan-tryptophan quinone

The presently best known and largest group of quinoproteins consists of enzymes using the cofactor 2,7,9-tricarboxy-1H-pyrrolo[2,3-f]quinoline- 4,5-dione (PQQ), a compound having a pyrrole ring fused to a quinoline ring with an o-quinone group in it. Representatives of this group are found among the bacterial, NAD(P)-independent, periplasmic dehydrogenases. Despite their high midpoint redox potential, the overall behaviour of quinoprotein dehydrogenases is similar to that of their counterparts, those using a flavin cofactor or a nicotinamide coenzyme. Apart from an exceptional Gram-positive one, the sole organisms where the presence of PQQ has really been established are Gram-negative bacteria. Evidence for the occurrence of covalently bound PQQ is lacking since it has now been shown that several enzymes previously considered to contain this prosthetic group do not in fact do so. Another group of quinoproteins, consisting of amine oxidoreductases, has a protein chain containing one of the following quinonoid aromatic amino acids: 6-hydroxy-phenylalanine-3,4-dione (TPQ) or 4-(2'-tryptophyl)-tryptophan-6,7-dione (TTQ). There is no doubt that these o-quinones play a role as cofactor, in the case of TPQ in prokaryotic as well as eukaryotic amine oxidases. It appears, therefore, that a novel class of amino-acid-derived cofactors is emerging, ranging from the free radical form of tyrosine and tryptophan to those containing a dicarbonyl group (like the already known pyryvoyl group and the o-quinones here described.

Cloning an Escherichia coli gene encoding a protein remarkably similar to mammalian aldehyde dehydrogenases

The nucleotide (nt) sequence of 2.9 kb of Escherichia coli genomic DNA that encompasses a gene encoding a putative aldehyde dehydrogenase (ALDH) has been determined. The presence of an open reading frame beginning 2 nt downstream from the ALDH-coding sequence indicates that this gene may be part of a larger operon. An extended upstream nt sequence displays striking similarity to sequences found upstream or in intergenic regions of a number of other bacterial genes. Crude cell extracts from E. coli grown under several different conditions show weak but measurable ALDH enzyme activity that prefers NADP+ over NAD+ as coenzyme; however, aldH gene expression appears to be very low, since no specific transcripts derived from the novel gene can be detected on Northern blots of RNA isolated from these cells. The deduced E. coli protein contains 495 amino acid (aa) residues with a calculated Mr of 53418. Its aa sequence showed marked similarity to NAD(+)-dependent ALDHs of eukaryotes. About 40% aa sequence identity, and over 60% similarity, are detected between the E. coli protein and both the cytosolic (class-1) and the mitochondrial (class-2) forms of mammalian ALDHs. In contrast to the mammalian enzymes, which contain eight to eleven Cys residues, only four Cys are present in the E. coli protein, and of these only Cys302, corresponding to the disulfiram-sensitive residue in the mammalian enzymes, is found at a conserved position in both the prokaryotic and the eukaryotic ALDHs. The availability of a bacterial ALDH with a high degree of similarity to mammalian ALDHs promises to facilitate future structural studies on these enzymes.

Cloning and sequencing of the gene cluster encoding two subunits of membrane-bound alcohol dehydrogenase from Acetobacter polyoxogenes

The membrane-bound alcohol dehydrogenase (ADH) from Acetobacter polyoxogenes NBI1028 is composed of a 72 kDa subunit and a 44 kDa cytochrome c subunit. The amino acid sequences of the two regions of the 72 kDa subunit were determined to prepare oligonucleotides for the purpose of amplification of a DNA fragment corresponding to the intermediate region by the polymerase chain reaction. A 0.5 kb DNA fragment thus amplified was used as the probe to clone a 7.0 kb PstI fragment coding for the whole 72 kDa subunit. Nucleotide sequencing and immunoblot analysis revealed that the cloned fragment contained the full structural genes for the 72 kDa and the 44 kDa subunits and they were clustered with the same transcription polarity. The predicted amino acid sequence of the gene for the 72 kDa subunit showed homology with that of the 72 kDa subunit from ADH of A. aceti and those of methanol dehydrogenase from methylotrophic bacteria. The 72 and 44 kDa subunits contained one and three typical haem binding sequences, respectively.

Genetic organization of the cellulose synthase operon in Acetobacter xylinum

An operon encoding four proteins required for bacterial cellulose biosynthesis (bcs) in Acetobacter xylinum was isolated via genetic complementation with strains lacking cellulose synthase activity. Nucleotide sequence analysis indicated that the cellulose synthase operon is 9217 base pairs long and consists of four genes. The four genes--bcsA, bcsB, bcsC, and bcsD--appear to be translationally coupled and transcribed as a polycistronic mRNA with an initiation site 97 bases upstream of the coding region of the first gene (bcsA) in the operon. Results from genetic complementation tests and gene disruption analyses demonstrate that all four genes in the operon are required for maximal bacterial cellulose synthesis in A. xylinum. The calculated molecular masses of the proteins encoded by bcsA, bcsB, bcsC, and bcsD are 84.4, 85.3, 141.0, and 17.3 kDa, respectively. The second gene in the operon (bcsB) encodes the catalytic subunit of cellulose synthase. The functions of the bcsA, bcsC, and bcsD gene products are unknown. Bacterial strains mutated in the bcsA locus were found to be deficient in cellulose synthesis due to the lack of cellulose synthase and diguanylate cyclase activities. Mutants in the bcsC and bcsD genes were impaired in cellulose production in vivo, even though they had the capacity to make all the necessary metabolic precursors and cyclic diguanylic acid, the activator of cellulose synthase, and exhibit cellulose synthase activity in vitro. When the entire operon was present on a multicopy plasmid in the bacterial cell, both cellulose synthase activity and cellulose biosynthesis increased. When the promoter of the cellulose synthase operon was replaced on the chromosome by E. coli tac or lac promoters, cellulose production was reduced in parallel with decreased cellulose synthase activity. These observations suggest that the expression of the bcs operon is rate-limiting for cellulose synthesis in A. xylinum.