Cloning, nucleotide sequence and expression of a mannitol dehydrogenase gene from Pseudomonas fluorescens DSM 50106 in Escherichia coli

Sugar alcohol degradation in Archaea: uptake and degradation of mannitol and sorbitol in Haloarcula hispanica

The halophilic archaeon Haloarcula hispanica utilizes the sugar alcohols mannitol and sorbitol as carbon and energy sources. Genes, enzymes, and transcriptional regulators involved in uptake and degradation of these sugar alcohols were identified by growth experiments with deletion mutants and enzyme characterization. It is shown that both mannitol and sorbitol are taken up via a single ABC transporter of the CUT1 transporter family. Then, mannitol and sorbitol are oxidized to fructose by two distinct dehydrogenases. Fructose is further phosphorylated to fructose-1-phosphate by a haloarchaeal ketohexokinase, providing the first evidence for a physiological function of ketohexokinase in prokaryotes. Finally, fructose-1-phosphate is phosphorylated via fructose-1-phosphate kinase to fructose-1,6-bisphosphate, which is cleaved to triosephosphates by a Class I fructose-1,6-bisphosphate aldolase. Two distinct transcriptional regulators, acting as activators, have been identified: an IclR-like regulator involved in activating genes for sugar alcohol uptake and oxidation to fructose, and a GfcR-like regulator that likely activates genes involved in the degradation of fructose to pyruvate. This is the first comprehensive analysis of a sugar alcohol degradation pathway in Archaea.

Mannitol as a Growth Substrate for Facultative Methylotroph Methylobrevis pamukkalensis PK2

Biochemistry of carbon assimilation in aerobic methylotrophs growing on reduced C1 compounds has been intensively studied due to the vital role of these microorganisms in nature. The biochemical pathways of carbon assimilation in methylotrophs growing on multi-carbon substrates are insufficiently explored. Here we elucidated the metabolic route of mannitol assimilation in the alphaproteobacterial facultative methylotroph Methylobrevis pamukkalensis PK2. Two key enzymes of mannitol metabolism, mannitol-2-dehydrogenase (MTD) and fructokinase (FruK), were obtained as His-tagged proteins by cloning and expression of mtd and fruK genes in Escherichia coli and characterized. Genomic analysis revealed that further transformation of fructose-6-phosphate proceeds via the Entner-Doudoroff pathway. During growth on mannitol + methanol mixture, the strain PK2 consumed both substrates simultaneously demonstrating independence of C1 and C6 metabolic pathways. Genome screening showed that genes for mannitol utilization enzymes are present in other alphaproteobacterial methylotrophs predominantly capable of living in association with plants. The capability to utilize a variety of carbohydrates (sorbitol, glucose, fructose, arabinose and xylose) suggests a broad adaptability of the strain PK2 to live in environments where availability of carbon substrate dynamically changes.

Promising Pathway of Thermostable Mannitol Dehydrogenase (MtDH) from Caldicellulosiruptor hydrothermalis 108 for D-Mannitol Synthesis

In this study, we conducted the characterization and purification of the thermostable mannitol dehydrogenase (MtDH) from Caldicellulosiruptor hydrothermalis 108. Furthermore, a coupling-enzyme system was designed using (MtDH) from Caldicellulosiruptor hydrothermalis 108 and formate dehydrogenase (FDH) from Ogataea parapolymorpha. The biotransformation system was constructed using Escherichia coli whole cells. The purified enzyme native and subunit molecular masses were 76.7 and 38 kDa, respectively, demonstrating that the enzyme was a dimer. The purified and couple enzyme system results were as follows; the optimum pH for the reduction and the oxidation was 7.0 and 8.0, the optimum temperature was 60 °C, the enzyme activity was inhibited by EDTA and restored by zinc. Additionally, no activity was detected with NADPH and NADP. The purified enzyme showed high catalytic efficiency Kcat 385 s−1, Km 31.8 mM, and kcat/Km 12.1 mM−1 s−1 for D-fructose reduction. Moreover, the purified enzyme retained 80%, 75%, 60%, and 10% of its initial activity after 4 h at 55, 60, 65, and 75 °C, respectively. D-mannitol yield was achieved via HPLC. Escherichia coli are the efficient biotransformation mediator to produce D-mannitol (byproducts free) at high temperature and staple pH, resulting in a significant D-mannitol conversation (41 mg/mL) from 5% D-fructose.

Archaeal hyperthermostable mannitol dehydrogenases: A promising industrial enzymes for d-mannitol synthesis

Recently, the term healthy lifestyle connected to low-calorie diets, although it is not possible to get rid of added sugars as a source of energy, despite the close relation of added sugars to some diseases such as obesity, diabetes, etc. As a result, the sweetener market has flourished, which has led to increased demand for natural sweeteners such as polyols, including d-mannitol. Various methods have been developed to produce d-mannitol to achieve high productivity and low cost. In particular, metabolic engineering for d-mannitol considers one of the most promising approaches for d-mannitol production on the industrial scale. To date, the chemical process is not ideal for large-scale production because of its multistep mechanism involving hydrogenation and high cost. In this review, we highlight and present a comparative evaluation of the biochemical parameters that affecting d-mannitol synthesis from Thermotoga neapolitana and Thermotoga maritima mannitol dehydrogenase (MtDH) as a potential contribution for d-mannitol bio-synthesis. These species were selected because purified mannitol dehydrogenases from both strains have been reported to produce d-mannitol with no sorbitol formation under temperatures (90-120 °C).

Does the mode of dispersion determine the properties of dispersed Pseudomonas aeruginosa biofilm cells?

INTRODUCTION

Actively dispersed Pseudomonas aeruginosa biofilm cells differ from planktonic cells, as they have a lower intracellular cyclic di-guanosine monophosphate (c-di-GMP) concentration and show increased virulence. In addition, the nature of the dispersion trigger has been shown to influence the antibiotic susceptibility of dispersed cells. However, properties of passively-dispersed cells, in which the dispersion trigger directly releases cells from the biofilm, have not been described. The present study determined c-di-GMP concentration, virulence in Galleria mellonella and antibiotic susceptibility of P. aeruginosa cells dispersed from biofilm using various triggers.

MATERIALS AND METHODS

P. aeruginosa biofilms grown in flow-cells were dispersed actively [exposure to the nitric oxide (NO)-donor sodium nitroprusside (SNP) or to glutamate] or passively [by stopping and restarting the flow or exposure to laser-induced vapor nanobubbles (VNB)], and properties of these dispersed cells were compared to those of spontaneously-dispersed cells.

RESULTS

The passively dispersed P. aeruginosa biofilm cells had significantly lower intracellular c-di-GMP levels than actively-dispersed cells. However, this did not result in differences in virulence in Galleria mellonella, nor in tobramycin and ciprofloxacin susceptibility. Passively-dispersed cells were more susceptible to colistin than actively- and spontaneously-dispersed cells. In cells dispersed by interrupting the flow, increased susceptibility to colistin was immediate, whereas this was delayed for VNB-dispersed cells.

CONCLUSION

Passively-dispersed P. aeruginosa biofilm cells have a decreased intracellular c-di-GMP concentration and an increased colistin susceptibility compared to actively-dispersed cells. No differences in virulence or susceptibility to tobramycin or colistin were observed.

Traversing the "Omic" landscape of microbial halotolerance for key molecular processes and new insights

Post-2005, the biology of the salt afflicted habitats is predominantly studied employing high throughput "Omic" approaches comprising metagenomics, transcriptomics, metatranscriptomics, metabolomics, and proteomics. Such "Omic-based" studies have deciphered the unfamiliar details about microbial salt-stress biology. The MAGs (Metagenome-assembled genomes) of uncultured halophilic microbial lineages such as Nanohaloarchaea and haloalkaliphilic members within CPR (Candidate Phyla Radiation) have been reconstructed from diverse hypersaline habitats. The study of MAGs of such uncultured halophilic microbial lineages has unveiled the genomic basis of salt stress tolerance in "yet to culture" microbial lineages. Furthermore, functional metagenomic approaches have been used to decipher the novel genes from uncultured microbes and their possible role in microbial salt-stress tolerance. The present review focuses on the new insights into microbial salt-stress biology gained through different "Omic" approaches. This review also summarizes the key molecular processes that underlie microbial salt-stress response, and their role in microbial salt-stress tolerance has been confirmed at more than one "Omic" levels.

Recent advances in microbial production of mannitol: utilization of low-cost substrates, strain development and regulation strategies

Mannitol has been widely used in fine chemicals, pharmaceutical industries, as well as functional foods due to its excellent characteristics, such as antioxidant protecting, regulation of osmotic pressure and non-metabolizable feature. Mannitol can be naturally produced by microorganisms. Compared with chemical manufacturing, microbial production of mannitol provides high yield and convenience in products separation; however the fermentative process has not been widely adopted yet. A major obstacle to microbial production of mannitol under industrial-scale lies in the low economical efficiency, owing to the high cost of fermentation medium, leakage of fructose, low mannitol productivity. In this review, recent advances in improving the economical efficiency of microbial production of mannitol were reviewed, including utilization of low-cost substrates, strain development for high mannitol yield and process regulation strategies for high productivity.

Improved xylitol production by expressing a novel d-arabitol dehydrogenase from isolated Gluconobacter sp. JX-05 and co-biotransformation of whole cells

In the present study, a novel ardh gene encoding d-arabitol dehydrogenase (ArDH) was cloned and expressed in Escherichia coli from a new isolated strain of Gluconobacter sp. JX-05. Sequence analysis revealed that ArDH containing a NAD(P)-binding motif and a classical active site motif belongs to the short-chain dehydrogenase family. Subsequently, the optimal pH and temperature, specific activities and kinetic parameter of ArDH were determined. In the co-biotransformation by the whole cells of BL21-ardh and BL21-xdh, 26.1g/L xylitol was produced from 30g/L d-arabitol in 22h with a yield of 0.87g/g. The xylitol production was increased by more than two times as compared with that of Gluconobacter sp. alone, and was improved 10.1% than that of Gluconobacter sp. mixed with BL21-xdh.

Global Analysis of Mannitol 2-Dehydrogenase in Lactobacillus reuteri CRL 1101 during Mannitol Production through Enzymatic, Genetic and Proteomic Approaches

Several plants, fungi, algae, and certain bacteria produce mannitol, a polyol derived from fructose. Mannitol has multiple industrial applications in the food, pharmaceutical, and medical industries, being mainly used as a non-metabolizable sweetener in foods. Many heterofermentative lactic acid bacteria synthesize mannitol when an alternative electron acceptor such as fructose is present in the medium. In previous work, we reported the ability of Lactobacillus reuteri CRL 1101 to efficiently produce mannitol from sugarcane molasses as carbon source at constant pH of 5.0; the activity of the enzyme mannitol 2-dehydrogenase (MDH) responsible for the fructose conversion into mannitol being highest during the log cell growth phase. Here, a detailed assessment of the MDH activity and relative expression of the mdh gene during the growth of L. reuteri CRL 1101 in the presence of fructose is presented. It was observed that MDH was markedly induced by the presence of fructose. A direct correlation between the maximum MDH enzyme activity and a high level of mdh transcript expression during the log-phase of cells grown in a fructose-containing chemically defined medium was detected. Furthermore, two proteomic approaches (2DE and shotgun proteomics) applied in this study confirmed the inducible expression of MDH in L. reuteri. A global study of the effect of fructose on activity, mdh gene, and protein expressions of MDH in L. reuteri is thus for the first time presented. This work represents a deep insight into the polyol formation by a Lactobacillus strain with biotechnological potential in the nutraceutics and pharmaceutical areas.

Controlled Orientation of Active Sites in a Nanostructured Multienzyme Complex

Multistep cascade reactions in nature maximize reaction efficiency by co-assembling related enzymes. Such organization facilitates the processing of intermediates by downstream enzymes. Previously, the studies on multienzyme nanocomplexes assembled on DNA scaffolds demonstrated that closer interenzyme distance enhances the overall reaction efficiency. However, it remains unknown how the active site orientation controlled at nanoscale can have an effect on multienzyme reaction. Here, we show that controlled alignment of active sites promotes the multienzyme reaction efficiency. By genetic incorporation of a non-natural amino acid and two compatible bioorthogonal chemistries, we conjugated mannitol dehydrogenase to formate dehydrogenase with the defined active site arrangement with the residue-level accuracy. The study revealed that the multienzyme complex with the active sites directed towards each other exhibits four-fold higher relative efficiency enhancement in the cascade reaction and produces 60% more D-mannitol than the other complex with active sites directed away from each other.

Transport and Catabolism of Pentitols by Listeria monocytogenes

Transposon insertion into Listeria monocytogenes lmo2665, which encodes an EIIC of the phosphoenolpyruvate:carbohydrate phosphotransferase system (PTS), was found to prevent D-arabitol utilization. We confirm this result with a deletion mutant and show that Lmo2665 is also required for D-xylitol utilization. We therefore called this protein EIICAxl. Both pentitols are probably catabolized via the pentose phosphate pathway (PPP) because lmo2665 belongs to an operon, which encodes the three PTSAxl components, two sugar-P dehydrogenases, and most PPP enzymes. The two dehydrogenases oxidize the pentitol-phosphates produced during PTS-catalyzed transport to the PPP intermediate xylulose-5-P. L. monocytogenes contains another PTS, which exhibits significant sequence identity to PTSAxl. Its genes are also part of an operon encoding PPP enzymes. Deletion of the EIIC-encoding gene (lmo0508) affected neither D-arabitol nor D-xylitol utilization, although D-arabitol induces the expression of this operon. Both operons are controlled by MtlR/LicR-type transcription activators (Lmo2668 and Lmo0501, respectively). Phosphorylation of Lmo0501 by the soluble PTSAxl components probably explains why D-arabitol also induces the second pentitol operon. Listerial virulence genes are submitted to strong repression by PTS sugars, such as glucose. However, D-arabitol inhibited virulence gene expression only at high concentrations, probably owing to its less efficient utilization compared to glucose.

Double clicking for site-specific coupling of multiple enzymes

Herein, we report a novel strategy to site-specifically couple multiple enzymes using two compatible click chemistries and site-specific incorporation of a clickable non-natural amino acid.

The mannitol utilization system of the marine bacterium Zobellia galactanivorans

Mannitol is a polyol that occurs in a wide range of living organisms, where it fulfills different physiological roles. In particular, mannitol can account for as much as 20 to 30% of the dry weight of brown algae and is likely to be an important source of carbon for marine heterotrophic bacteria. Zobellia galactanivorans (Flavobacteriia) is a model for the study of pathways involved in the degradation of seaweed carbohydrates. Annotation of its genome revealed the presence of genes potentially involved in mannitol catabolism, and we describe here the biochemical characterization of a recombinant mannitol-2-dehydrogenase (M2DH) and a fructokinase (FK). Among the observations, the M2DH of Z. galactanivorans was active as a monomer, did not require metal ions for catalysis, and featured a narrow substrate specificity. The FK characterized was active on fructose and mannose in the presence of a monocation, preferentially K(+). Furthermore, the genes coding for these two proteins were adjacent in the genome and were located directly downstream of three loci likely to encode an ATP binding cassette (ABC) transporter complex, suggesting organization into an operon. Gene expression analysis supported this hypothesis and showed the induction of these five genes after culture of Z. galactanivorans in the presence of mannitol as the sole source of carbon. This operon for mannitol catabolism was identified in only 6 genomes of Flavobacteriaceae among the 76 publicly available at the time of the analysis. It is not conserved in all Bacteroidetes; some species contain a predicted mannitol permease instead of a putative ABC transporter complex upstream of M2DH and FK ortholog genes.

Arabitol metabolism of Corynebacterium glutamicum and its regulation by AtlR

Expression profiling of Corynebacterium glutamicum in comparison to a derivative deficient in the transcriptional regulator AtlR (previously known as SucR or MtlR) revealed eight genes showing more than 4-fold higher mRNA levels in the mutant. Four of these genes are located in the direct vicinity of the atlR gene, i.e., xylB, rbtT, mtlD, and sixA, annotated as encoding xylulokinase, the ribitol transporter, mannitol 2-dehydrogenase, and phosphohistidine phosphatase, respectively. Transcriptional analysis indicated that atlR and the four genes are organized as atlR-xylB and rbtT-mtlD-sixA operons. Growth experiments with C. glutamicum and C. glutamicum ΔatlR, ΔxylB, ΔrbtT, ΔmtlD, and ΔsixA derivatives with sugar alcohols revealed that (i) wild-type C. glutamicum grows on D-arabitol but not on other sugar alcohols, (ii) growth in the presence of D-arabitol allows subsequent growth on D-mannitol, (iii) D-arabitol is cometabolized with glucose and preferentially utilized over D-mannitol, (iv) RbtT and XylB are involved in D-arabitol but not in D-mannitol metabolism, (v) MtlD is required for D-arabitol and D-mannitol metabolism, and (vi) SixA is not required for growth on any of the substrates tested. Furthermore, we show that MtlD confers D-arabitol and D-mannitol dehydrogenase activities, that the levels of these and also xylulokinase activities are generally high in the C. glutamicum ΔatlR mutant, whereas in the parental strain, they were high when cells were grown in the presence of D-arabitol and very low when cells were grown in its absence. Our results show that the XylB, RbtT, and MtlD proteins allow the growth of C. glutamicum on D-arabitol and that D-arabitol metabolism is subject to arabitol-dependent derepression by AtlR.

Architecture and characterization of sarcosine oxidase from Thermococcus kodakarensis KOD1

Sarcosine oxidase (SOX) catalyzes the oxidation of the methyl group in sarcosine and transfer of the oxidized methyl group into the one-carbon metabolic pool. Here, we separately cloned and expressed α and β subunit of SOX from Thermococcus kodakarensis KOD1 (TkSOX) in Escherichia coli and the recombinant proteins were purified to homogeneity. Gel filtration chromatography and transmission electron microscopy analysis showed that the α subunit formed a dimeric structure and behaved as an NADH dehydrogenase; β subunit was a tetramer that had sarcosine oxidase and L: -proline dehydrogenase activity. The TkSOX complex assembled into the hetero-octameric (αβ)(4) form and had NADH dehydrogenase activity. Gold-label analysis indicated that α and β subunits were oriented in the alternative form. Based on these results, we suggested that TkSOX was a multifunctional enzyme and that each subunit and (αβ)(4) complex may separately exist as a function enzyme in different conditions.

Molecular cloning and characterization of mannitol-1-phosphate dehydrogenase from Vibrio cholerae

Vibrio cholerae utilizes mannitol through an operon of the phosphoenolpyruvate-dependent phosphotransferase (PTS) type. A gene, mtlD, encoding mannitol-1-phosphate dehydrogenase was identified within the 3.9 kb mannitol operon of V. cholerae. The mtlD gene was cloned from V. cholerae O395, and the recombinant enzyme was functionally expressed in E. coli as a 6×His-tagged protein and purified to homogeneity. The recombinant protein is a monomer with a molecular mass of 42.35 kDa. The purified recombinant MtlD reduced fructose 6-phosphate (F6P) using NADH as a cofactor with a K(m) of 1.54 +/- 0.1 mM and V(max) of 320.8 +/- 7.81 micronmol/min/mg protein. The pH and temperature optima for F6P reduction were determined to be 7.5 and 37°C, respectively. Using quantitative real-time PCR analysis, mtlD was found to be constitutively expressed in V. cholerae, but the expression was up-regulated when grown in the presence of mannitol. The MtlD expression levels were not significantly different between V. cholerae O1 and non-O1 strains.

Biotechnological production of mannitol and its applications

Mannitol, a naturally occurring polyol (sugar alcohol), is widely used in the food, pharmaceutical, medical, and chemical industries. The production of mannitol by fermentation has become attractive because of the problems associated with its production chemically. A number of homo- and heterofermentative lactic acid bacteria (LAB), yeasts, and filamentous fungi are known to produce mannitol. In particular, several heterofermentative LAB are excellent producers of mannitol from fructose. These bacteria convert fructose to mannitol with 100% yields from a mixture of glucose and fructose (1:2). Glucose is converted to lactic acid and acetic acid, and fructose is converted to mannitol. The enzyme responsible for conversion of fructose to mannitol is NADPH- or NADH-dependent mannitol dehydrogenase (MDH). Fructose can also be converted to mannitol by using MDH in the presence of the cofactor NADPH or NADH. A two enzyme system can be used for cofactor regeneration with simultaneous conversion of two substrates into two products. Mannitol at 180 g l(-1) can be crystallized out from the fermentation broth by cooling crystallization. This paper reviews progress to date in the production of mannitol by fermentation and using enzyme technology, downstream processing, and applications of mannitol.

Proteins involved in difference of sorbitol fermentation rates of the toxigenic and nontoxigenic Vibrio cholerae El Tor strains revealed by comparative proteome analysis

BACKGROUND

The nontoxigenic V. cholerae El Tor strains ferment sorbitol faster than the toxigenic strains, hence fast-fermenting and slow-fermenting strains are defined by sorbitol fermentation test. This test has been used for more than 40 years in cholera surveillance and strain analysis in China. Understanding of the mechanisms of sorbitol metabolism of the toxigenic and nontoxigenic strains may help to explore the genome and metabolism divergence in these strains. Here we used comparative proteomic analysis to find the proteins which may be involved in such metabolic difference.

RESULTS

We found the production of formate and lactic acid in the sorbitol fermentation medium of the nontoxigenic strain was earlier than of the toxigenic strain. We compared the protein expression profiles of the toxigenic strain N16961 and nontoxigenic strain JS32 cultured in sorbitol fermentation medium, by using fructose fermentation medium as the control. Seventy-three differential protein spots were found and further identified by MALDI-MS. The difference of product of fructose-specific IIA/FPR component gene and mannitol-1-P dehydrogenase, may be involved in the difference of sorbitol transportation and dehydrogenation in the sorbitol fast- and slow-fermenting strains. The difference of the relative transcription levels of pyruvate formate-lyase to pyruvate dehydrogenase between the toxigenic and nontoxigenic strains may be also responsible for the time and ability difference of formate production between these strains.

CONCLUSION

Multiple factors involved in different metabolism steps may affect the sorbitol fermentation in the toxigenic and nontoxigenic strains of V. cholerae El Tor.

Thermotoga maritima TM0298 is a highly thermostable mannitol dehydrogenase

Thermotoga maritima TM0298 is annotated as an alcohol dehydrogenase, yet it shows high identity and similarity to mesophilic mannitol dehydrogenases. To investigate this enzyme further, its gene was cloned and expressed in Escherichia coli. The purified recombinant enzyme was most active on fructose and mannitol, making it the first known hyperthermophilic mannitol dehydrogenase. T. maritima mannitol dehydrogenase (TmMtDH) is optimally active between 90 and 100 degrees C and retains 63% of its activity at 120 degrees C but shows no detectable activity at room temperature. Its kinetic inactivation follows a first-order mechanism, with half-lives of 57 min at 80 degrees C and 6 min at 95 degrees C. Although TmMtDH has a higher V (max) with NADPH than with NADH, its catalytic efficiency is 2.2 times higher with NADH than with NADPH and 33 times higher with NAD(+) than with NADP(+). This cofactor specificity can be explained by the high density of negatively charged residues (Glu193, Asp195, and Glu196) downstream of the NAD(P) interaction site, the glycine motif. We demonstrate that TmMtDH contains a single catalytic zinc per subunit. Finally, we provide the first proof of concept that mannitol can be produced directly from glucose in a two-step enzymatic process, using a Thermotoga neapolitana xylose isomerase mutant and TmMtDH at 60 degrees C.

Structure-guided engineering of the coenzyme specificity of Pseudomonas fluorescens mannitol 2-dehydrogenase to enable efficient utilization of NAD(H) and NADP(H)

The structure of Pseudomonas fluorescens mannitol 2-dehydrogenase with bound NAD+ leads to the suggestion that the carboxylate group of Asp(69) forms a bifurcated hydrogen bond with the 2' and 3' hydroxyl groups of the adenosine of NAD+ and contributes to the 400-fold preference of the enzyme for NAD+ as compared to NADP+. Accordingly, the enzyme with the Asp(69)-->Ala substitution was found to use NADP(H) almost as well as wild-type enzyme uses NAD(H). The Glu(68)-->Lys substitution was expected to enhance the electrostatic interaction of the enzyme with the 2'-phosphate of NADP+. The Glu(68)-->Lys:Asp(69)-->Ala doubly mutated enzyme showed about a 10-fold preference for NADP(H) over NAD(H), accompanied by a small decrease in catalytic efficiency for NAD(H)-dependent reactions as compared to wild-type enzyme.

Microbial biochemistry, physiology, and biotechnology of hyperthermophilic Thermotoga species

High-throughput sequencing of microbial genomes has allowed the application of functional genomics methods to species lacking well-developed genetic systems. For the model hyperthermophile Thermotoga maritima, microarrays have been used in comparative genomic hybridization studies to investigate diversity among Thermotoga species. Transcriptional data have assisted in prediction of pathways for carbohydrate utilization, iron-sulfur cluster synthesis and repair, expolysaccharide formation, and quorum sensing. Structural genomics efforts aimed at the T. maritima proteome have yielded hundreds of high-resolution datasets and predicted functions for uncharacterized proteins. The information gained from genomics studies will be particularly useful for developing new biotechnology applications for T. maritima enzymes.

Expression and characterization of a thermostable sarcosine oxidase (SOX) from Bacillus sp. in Escherichia coli

A heat-stable sarcosine oxidase produced by Bacillus sp. BSD-8 (SOX) had been studied and its complete gene sequence, which contained 1,164 bp nucleotides and encoded a protein of 387 amino acids, was obtained by DNA Walking method. The sox gene was cloned and functionally overexpressed in E. coli and the recombinant SOX (rSOX) was purified to homogeneity, its properties was studied and compared with the wild type of SOX. The rSOX as well as SOX was stable at 60 degrees C and at pH 7.0 approximately 10.0, respectively. The optimal temperature for this enzyme was 60 degrees C and at pH 8.5, it showed its highest activity. The Km and Kcat of the enzyme was 3.1 mM and 20.3/s, respectively. The difference between the properties of the SOX and rSOX was that the SOX contained noncovalent FAD, whereas the rSOX contained covalent FAD. The study also showed that an increased number of alanine residues in the rSOX might have some contribution in the enzymatic thermostability.

Molecular cloning and functional expression of d-arabitol dehydrogenase gene from Gluconobacter oxydans in Escherichia coli

A NADP-dependent d-arabitol dehydrogenase gene was cloned from Gluconobacter oxydans CGMCC 1.110 and functionally expressed in Escherichia coli. With d-arabitol as sole carbon source, E. coli transformants grew rapidly in minimal medium, and produced d-xylulose. The enzymatic properties of the 29kDa enzyme were documented. The DNA sequence surrounding the gene suggested that it is part of an operon with several components of a sugar alcohol transporter system, and the d-arabitol dehydrogenase gene belongs to the short-chain dehydrogenase family.

Purification and characterization of a novel mannitol dehydrogenase from Lactobacillus intermedius

Mannitol 2-dehydrogenase (MDH) catalyzes the pyridine nucleotide dependent reduction of fructose to mannitol. Lactobacillus intermedius (NRRL B-3693), a heterofermentative lactic acid bacterium (LAB), was found to be an excellent producer of mannitol. The MDH from this bacterium was purified from the cell extract to homogeneity by DEAE Bio-Gel column chromatography, gel filtration on Bio-Gel A-0.5m gel, octyl-Sepharose hydrophobic interaction chromatography, and Bio-Gel Hydroxyapatite HTP column chromatography. The purified enzyme (specific activity, 331 U/mg protein) was a heterotetrameric protein with a native molecular weight (MW) of about 170 000 and subunit MWs of 43 000 and 34 500. The isoelectric point of the enzyme was at pH 4.7. Both subunits had the same N-terminal amino acid sequence. The optimum temperature for the reductive action of the purified MDH was at 35 degrees C with 44% activity at 50 degrees C and only 15% activity at 60 degrees C. The enzyme was optimally active at pH 5.5 with 50% activity at pH 6.5 and only 35% activity at pH 5.0 for reduction of fructose. The optimum pH for the oxidation of mannitol to fructose was 7.0. The purified enzyme was quite stable at pH 4.5-8.0 and temperature up to 35 degrees C. The K(m) and V(max) values of the enzyme for the reduction of fructose to mannitol were 20 mM and 396 micromol/min/mg protein, respectively. It did not have any reductive activity on glucose, xylose, and arabinose. The activity of the enzyme on fructose was 4.27 times greater with NADPH than NADH as cofactor. This is the first highly NADPH-dependent MDH (EC 1.1.1.138) from a LAB. Comparative properties of the enzyme with other microbial MDHs are presented.

Purification and characterization of a novel mannitol dehydrogenase from a newly isolated strain of Candida magnoliae

Mannitol biosynthesis in Candida magnoliae HH-01 (KCCM-10252), a yeast strain that is currently used for the industrial production of mannitol, is catalyzed by mannitol dehydrogenase (MDH) (EC 1.1.1.138). In this study, NAD(P)H-dependent MDH was purified to homogeneity from C. magnoliae HH-01 by ion-exchange chromatography, hydrophobic interaction chromatography, and affinity chromatography. The relative molecular masses of C. magnoliae MDH, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and size-exclusion chromatography, were 35 and 142 kDa, respectively, indicating that the enzyme is a tetramer. This enzyme catalyzed both fructose reduction and mannitol oxidation. The pH and temperature optima for fructose reduction and mannitol oxidation were 7.5 and 37 degrees C and 10.0 and 40 degrees C, respectively. C. magnoliae MDH showed high substrate specificity and high catalytic efficiency (k(cat) = 823 s(-1), K(m) = 28.0 mM, and k(cat)/K(m) = 29.4 mM(-1) s(-1)) for fructose, which may explain the high mannitol production observed in this strain. Initial velocity and product inhibition studies suggest that the reaction proceeds via a sequential ordered Bi Bi mechanism, and C. magnoliae MDH is specific for transferring the 4-pro-S hydrogen of NADPH, which is typical of a short-chain dehydrogenase reductase (SDR). The internal amino acid sequences of C. magnoliae MDH showed a significant homology with SDRs from various sources, indicating that the C. magnoliae MDH is an NAD(P)H-dependent tetrameric SDR. Although MDHs have been purified and characterized from several other sources, C. magnoliae MDH is distinguished from other MDHs by its high substrate specificity and catalytic efficiency for fructose only, which makes C. magnoliae MDH the ideal choice for industrial applications, including enzymatic synthesis of mannitol and salt-tolerant plants.

Purification and characterisation of mannitol dehydrogenase from Lactobacillus sanfranciscensis

Mannitol dehydrogenase (MDH) was purified and characterised from Lactobacillus sanfranciscensis. Two peptide fragments of MDH were N-terminally sequenced for the first time in the genus Lactobacillus. The purified enzyme had an apparent molecular mass of 44 kDa and catalysed both the reduction of fructose to mannitol and the oxidation of mannitol to fructose. The K(m) value for the reduction reaction was 24 mM fructose and that for the oxidation 78 mM mannitol. The optimum temperature was 35 degrees C, the pH optima for the reduction or oxidation were 5.8 and 8, respectively.

Pseudomonas fluorescens mannitol 2-dehydrogenase and the family of polyol-specific long-chain dehydrogenases/reductases: sequence-based classification and analysis of structure-function relationships

Multiple sequence alignment and analysis of evolutionary relationships have been used to characterize a family of polyol-specific long-chain dehydrogenases/reductases (PSLDRs). At the present time, 66 known and putative NAD(P)H-dependent oxidoreductases of mainly prokaryotic origin and between 357 and 544 amino acids in length constitute this family. The family is shown to include D-mannitol 2-dehydrogenase, D-mannonate 5-oxidoreductase, D-altronate 5-oxidoreductase, D-arabinitol 4-dehydrogenase, and D-mannitol-1-phosphate 5-dehydrogenase which form individual sub-families (defined by internal sequence identity of >/=30%) having distant origin and divergent substrate specificity but clearly displaying entire-chain relationship. When all forms are aligned, only three residues, Gly-33, Asp-230, and Lys-295 (in the numbering of Pseudomonas fluorescens D-mannitol 2-dehydrogenase (PsM2DH)) are strictly conserved. By combining sequence alignment with the known structure of PsM2DH and results from site-directed mutagenesis, we have developed a structure/function analysis for the family. Gly-33 is in the N-terminal coenzyme-binding domain and part of a nucleotide fingerprint region for the family, and Asp-230 and Lys-295 are at an interdomain segment contributing to the active site in which the lysine likely functions as the catalytic general acid/base. PSLDRs do not require a metal cofactor for activity and are specific for transferring the 4-pro-S hydrogen from NAD(P)H. Comparisons reveal that the core part of the two-domain fold has been conserved throughout all family members, perhaps reflecting the recruitment of a stable oxidoreductase structure and extensive trimming thereof to acquire functional properties specific to each sub-family. They also identify interactions that define the chemical mechanism of oxidoreduction and likely contribute to substrate and co-substrate specificities and are thus relevant for protein engineering.

Crystal structure of Pseudomonas fluorescens mannitol 2-dehydrogenase: evidence for a very divergent long-chain dehydrogenase family

Mannitol 2-dehydrogenase from Pseudomonas fluorescens (pfMDH) is a secondary alcohol dehydrogenase that catalyzes the reversible NAD(P)-dependent oxidation of D-mannitol to D-fructose, D-arabinitol to D-xylulose, and D-sorbitol to L-sorbose. It is a member of the mostly prokaryotic family of long-chain mannitol dehydrogenases that so far includes 66 members. Unlike other alcohol and polyol dehydrogenases that utilize metal cofactors or a conserved active-site tyrosine for catalysis, an invariant lysine is the general base. The crystal structure of pfMDH in a binary complex with NAD(H) and a ternary complex with NAD(H) and D-mannitol have been determined to 1.7 and 1.8 A resolution respectively. Comparison of secondary structure assignment to sequence alignments suggest the shortest members of this family, mannitol-1-phosphate 5-dehydrogenases, retain core elements but lack secondary structural components found on the surface of pfMDH. The elements predicted to be absent are distributed throughout the primary sequence, implying that a simple truncation or fusion did not occur. The closest structural neighbors are 6-phosphogluconate dehydrogenase, UDP-glucose dehydrogenase, N-(1-D-carboxyethyl)-L-norvaline dehydrogenase, and glycerol-3-phosphate dehydrogenase. Although sequence identity is only a barely recognizable 7-10%, conservation of secondary structural elements as well as homologous residues that are contributed to the active site indicates they may be related by divergent evolution.

A zinc-containing mannitol-2-dehydrogenase from Leuconostoc pseudomesenteroides ATCC 12291: purification of the enzyme and cloning of the gene

Mannitol-2-dehydrogenase (EC 1.1.1.67) of Leuconostoc pseudomesenteroides ATCC 12291 catalyzing the NADH-dependent reduction of d-fructose to d-mannitol was purified to homogeneity. Native mannitol-2-dehydrogenase has a molecular mass of 155 kDa as determined by gel filtration chromatography. In SDS-PAGE, a single band appeared corresponding to a molecular mass of 43 kDa which indicated that the enzyme was composed of four identical subunits. Enzyme activity was completely inhibited by EDTA and could be restored by zinc ions, but not by Mn(2+) or Mg(2+) which demonstrated that zinc is a cofactor. Purified mannitol-2-dehydrogenase exhibited a maximal specific activity of 400 micromol fructose reduced min(-1) x (mg protein)(-1), using NADH as electron donor. The enzyme showed a high substrate specificity for d-fructose and d-mannitol, however it accepted NADPH as a cofactor with 32% activity ( V(max)) relative to NADPH (100%). The mdh gene, encoding mannitol-2-dehydrogenase, was identified by hybridization with a degenerate gene probe complementary to the nucleotide sequence encoding the first eight N-terminal amino acids of the enzyme. The mdh gene was cloned on a 4.2-kb DNA fragment, subcloned, and expressed in Escherichia coli. Sequencing of the gene revealed an open reading frame of 1017 bp, encoding a protein of 338 amino acids with a predicted molecular mass of 36.0 kDa. Plasmid-encoded mdh was functionally expressed, with 70 U/mg of cell-free protein in E. coli. Multiple sequence alignments showed that mannitol-2-dehydrogenase was affiliated with members of the Zn(2+)-containing medium-chain alcohol/polyol dehydrogenase/reductase protein family (MDR).

Crystal structure of Pseudomonas fluorescens mannitol 2-dehydrogenase binary and ternary complexes. Specificity and catalytic mechanism

Long-chain mannitol dehydrogenases are secondary alcohol dehydrogenases that are of wide interest because of their involvement in metabolism and potential applications in agriculture, medicine, and industry. They differ from other alcohol and polyol dehydrogenases because they do not contain a conserved tyrosine and are not dependent on Zn(2+) or other metal cofactors. The structures of the long-chain mannitol 2-dehydrogenase (54 kDa) from Pseudomonas fluorescens in a binary complex with NAD(+) and ternary complex with NAD(+) and d-mannitol have been determined to resolutions of 1.7 and 1.8 A and R-factors of 0.171 and 0.176, respectively. These results show an N-terminal domain that includes a typical Rossmann fold. The C-terminal domain is primarily alpha-helical and mediates mannitol binding. The electron lone pair of Lys-295 is steered by hydrogen-bonding interactions with the amide oxygen of Asn-300 and the main-chain carbonyl oxygen of Val-229 to act as the general base. Asn-191 and Asn-300 are involved in a web of hydrogen bonding, which precisely orients the mannitol O2 proton for abstraction. These residues also aid in stabilizing a negative charge in the intermediate state and in preventing the formation of nonproductive complexes with the substrate. The catalytic lysine may be returned to its unprotonated state using a rectifying proton tunnel driven by Glu-292 oscillating among different environments. Despite low sequence homology, the closest structural neighbors are glycerol-3-phosphate dehydrogenase, N-(1-d-carboxylethyl)-l-norvaline dehydrogenase, UDP-glucose dehydrogenase, and 6-phosphogluconate dehydrogenase, indicating a possible evolutionary relationship among these enzymes.

Cloning of a gene for d-sorbitol dehydrogenase from Gluconobacter oxydans G624 and expression of the gene in Pseudomonas putida IFO3738

We have cloned a novel gene for d-sorbitol dehydrogenase (SLDH), which efficiently converted D-sorbitol to L-sorbose, from Gluconobacter oxydans G624 (FERM BP-4415). A cosmid library of the genomic DNA was screened by assaying SLDH activity. The inserted DNA from a positive clone was downsized by subcloning into charomid and pUCP plasmid, successively. Sequencing analysis of the DNA responsible for SLDH activity revealed an open reading frame of 1455 bp coding for 485 amino acid residues with a calculated molecular mass of 53,642 Da. The amino acid sequence showed 42.2% identity with a NAD+-dependent mannitol dehydrogenase (MDH), which catalyzed conversion of d-sorbitol to d-fructose, from Pseudomonas fluorescens DSM50106. Since the intact SLDH was found to be very unstable during isolation and purification, this SLDH fused to 6 x His-tag was expressed in Pseudomonas putida IFO3738 and purified by immobilized metal affinity chromatography using cobalt-based resins. The 6 x His-tag SLDH catalyzed the oxidation of D-sorbitol to L-sorbose and exhibited 15 times higher activity in the presence of NADP+ than that of NAD+. These results indicate that the SLDH is a novel kind of dehydrogenase distinct from MDH previously reported.

Cloning and characterization of NADP-mannitol dehydrogenase cDNA from the button mushroom, Agaricus bisporus, and its expression in response to NaCl stress

Mannitol, a six-carbon sugar alcohol, is the main storage carbon in the button mushroom, Agaricus bisporus. Given the physiological importance of mannitol metabolism in growth, fruit body development, and salt tolerance of A. bisporus, the enzyme responsible for mannitol biosynthesis, NADP-dependent mannitol dehydrogenase (MtDH) (EC 1.1.1.138), was purified to homogeneity, and MtDH cDNA was cloned, sequenced, and characterized. To our knowledge, this represents the first report on the isolation of a cDNA encoding an NADP-dependent mannitol dehydrogenase. The MtDH cDNA contains an open reading frame of 789 bp encoding a protein of approximately 28 kDa. The N-terminal and internal amino acid sequences of the deduced protein exactly matched the ones determined from the purified MtDH subunit, whereas the amino acid composition of the deduced protein was nearly identical to that of the purified MtDH. The MtDH cDNA showed high homology with a plant-induced short-chain dehydrogenase from Uromyces fabae. Phylogenetic analysis based on amino acid sequences from mannitol(-1-phosphate) dehydrogenases indicated a close relationship between the substrate specificity of the enzymes and phylogenetic differentiation. Salt-stressed fruit bodies showed an overall increase in mannitol biosynthesis, as was evident from the increase in MtDH activity, MtDH abundance, and MtDH RNA accumulation. Furthermore, the MtDH transcript level seems to be under developmental control, as MtDH RNA accumulated during maturation of the fruit body.

The mannitol utilization genes of Pseudomonas fluorescens are regulated by an activator: cloning, nucleotide sequence and expression of the mtlR gene

A plasmid with the galK gene under control of the promoter of the mannitol utilization genes (mtl) from Pseudomonas fluorescens DSM 50106 was constructed to isolate the mtl regulatory gene. An Escherichia coli galK- mtl- strain with this plasmid was used to screen a genomic library of P. fluorescens for the presence of the regulatory gene by plating on McConkey agar plates supplemented with galactose and mannitol. Clones carrying the regulatory gene were isolated and by complemention assays, deletion analysis and DNA sequencing an open reading frame (mtlR) of 906nt identified encoding the regulator. The deduced protein MtlR with a calculated molecular mass of 34.7kDa showed a low overall similarity to several other regulatory proteins of the XylS/AraC family. When mtlR was cloned and expressed in E. coli, the protein was produced as inclusion bodies. Complete denaturation followed by subsequent slow refolding led to low amounts of active protein. The activity was shown in gel mobility shift assays by binding of MtlR to a DNA fragment containing the promoter/operator region of the P. fluorescens mtl genes.

Structure and function of the genes involved in mannitol, arabitol and glucitol utilization from Pseudomonas fluorescens DSM50106

A DNA fragment from Pseudomonas fluorescens DSM50106 containing the genes for the uptake and utilization of mannitol, arabitol and glucitol was cloned in Escherichia coli and sequenced. Seven open reading frames (mtlEFGKDYZ) were identified on the 10031 bp fragment. The deduced amino acid sequences of the first four open reading frames (mtlEFGK) revealed significant similarity to the components of the maltose transport system in E. coli and Salmonella typhimurium. The gene mtlD encoding a polyol dehydrogenase was located downstream of mtlK. The deduced proteins of the last two genes on the fragment showed a high similarity to a fructokinase from Vibrio alginolyticus (MtlZ) and a xylulose kinase from Streptomyces rubiginosus (MtlY), respectively. Both genes were expressed in E. coli. MtlZ phosphorylated fructose, glucose and glucitol whereas MtlY was highly specific for xylulose. Upstream of mtlE, a putative promoter/operator region was identified by promoter probe studies which was active in P. fluorescens but not in E. coli.