NADP-dependent mannitol dehydrogenase, a major allergen of Cladosporium herbarum

Cladosporium herbarum is an important allergenic fungal species that has been reported to cause allergic diseases in nearly all climatic zones. 5-30% of the allergic population displays IgE antibodies against molds. Sensitization to Cladosporium has often been associated with severe asthma and less frequently with chronic urticaria and atopic eczema. However, no dominant major allergen of this species has been found so far. We present cloning, production, and characterization of NADP-dependent mannitol dehydrogenase of C. herbarum (Cla h 8) and show that this protein is a major allergen that is recognized by IgE antibodies of approximately 57% of all Cladosporium allergic patients. This is the highest percentage of patients reacting with any Cladosporium allergen characterized so far. Cla h 8 was purified to homogeneity by standard chromatographic methods, and both N-terminal and internal amino acid sequences of protein fragments were determined. Enzymatic analysis of the purified natural protein revealed that this allergen represents a NADP-dependent mannitol dehydrogenase that interconverts mannitol and d-fructose. It is a soluble, non-glycosylated cytoplasmic protein. Two-dimensional protein analysis indicated that mannitol dehydrogenase is present as a single isoform. The cDNA encoding Cla h 8 was cloned from a lambda-ZAP library constructed from hyphae and spores. The recombinant non-fusion protein was expressed in Escherichia coli and purified to homogeneity. Its immunological and biochemical identity with the natural protein was shown by enzyme activity tests, CD spectroscopy, IgE immunoblots with sera of patients, and by skin prick testing of Cladosporium allergic patients. This protein therefore is a new major allergen of C. herbarum.

Genetic identification and host range of the Spanish strains of Echinococcus granulosus

Three strains of Echinococcus granulosus have been previously identified in Spain (namely 'sheep', 'horse' and 'pig'), but these Spanish strains have not been properly genotyped yet. The aim of the present research was to identify the genotype to which they correspond to. Cyst isolates were obtained from different host species, and the strain to which each belonged was established by analysis of its random amplified polymorphic DNA (RAPD) banding patterns. These results were compared to those obtained with the analysis of two mitochondrial fragment sequences (cytochrome oxidase 1 (CO1) and NADH dehydrogenase 1 (ND1)) from each isolate. The Spanish 'sheep' strain corresponded with the genotype 1 (G1) of the parasite, infecting Spanish sheep, cattle, goat, pig, wild boar and human; the Spanish 'horse' strain corresponded with the genotype 4 (G4), only infecting Spanish horses; and the Spanish 'pig' strain corresponded with the genotype 7 (G7), infecting Spanish goat, pig and wild boar. Goat, pig and wild boar can be infected by two genotypes, G1 and G7. This circumstance, and especially the possibility of sylvatic intermediate hosts serving as reservoirs of the G1 genotype of the parasite, must be taken into consideration by authorities in order to develop and evaluate effective anti-hydatidosis programmes.

On the role of Brønsted catalysis in Pseudomonas fluorescens mannitol 2-dehydrogenase

X-ray structure of the Pseudomonas fluorescens mannitol 2-dehydrogenase ternary complex with NAD+ and D-mannitol suggests that Lys-295 provides catalytic base assistance to secondary alcohol group oxidation. We have replaced Lys-295 by site-directed mutagenesis with alanine or methionine and evaluated the catalytic significance of side-chain substitution by kinetic analysis of restoration of activity with external amines, and from pH and solvent isotope effects on the reaction catalysed by K295A (Lys-295-->Ala mutant). K295A and K295M (Lys-295-->Met mutants) show 3x10(4)- and 2x10(6)-fold lower turnover numbers respectively for D-mannitol oxidation (kcatO) at pH 10.0 than the wild-type. The second-order rate constant for non-covalent rescue of activity (kB) by free methylamine base is 31 M(-1) x s(-1) for K295A, but only 0.021 M(-1) x s(-1) for K295M. A Brønsted relationship of log kB (corrected for molecular size effects) and pKa of the external amine is linear (slope beta=0.66+/-0.16; r2=0.99) for K295A-catalysed D-mannitol oxidation at pH 10.0. The kcatO values of K295A in H2O and 2H2O are linearly dependent on [OL-] in the pL range 7.5-10.5 (where L is 1H or 2H). The solvent isotope effect on kcatO is 0.69. The time course of D-fructose reduction by K295A at pH 8.2 displays a pre-steady-state burst of NADH consumption. These data support a mechanism in which the epsilon -NH2 group of Lys-295 participates in an obligatory pH-dependent, pre-catalytic equilibrium which may control alcohol/alkoxide equilibration of enzyme-bound D-mannitol and activates the C2 atom for subsequent catalytic oxidation by NAD+.

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.

A catalytic consensus motif for D-mannitol 2-dehydrogenase, a member of a polyol-specific long-chain dehydrogenase family, revealed by kinetic characterization of site-directed mutants of the enzyme from Pseudomonas fluorescens

Lys-295, Asn-300 and His-303 of D-mannitol 2-dehydrogenase from Pseudomonas fluorescens were mutated individually into alanine (K295A, N300A and H303A respectively). Purified mutants displayed catalytic efficiencies for NAD(+)-dependent oxidation of D-mannitol 300-fold (H303A), 1000-fold (N300A) and approx. 400000-fold (K295A) below the wild-type level. Comparison of primary kinetic isotope effects on kinetic parameters for D-fructose reduction by wild-type and mutants at pH 10.0 demonstrate that Asn-300 has an auxiliary role in stabilization of the transition state of hydride transfer, and His-303 contributes to substrate positioning. The large solvent isotope effect of 11+/-1 on k (cat) for mannitol oxidation by K295A at pH((2)H) 10.5 suggests a role for Lys-295 in general base enzymic catalysis. Positional conservation of Lys-295, Asn-300 and His-303 across a family of polyol-specific long-chain dehydrogenases suggests a unique catalytic signature: Lys-Xaa(4)-Asn-Xaa(2)-His (where 'Xaa' denotes 'any amino acid').

The crystallographic structure of the mannitol 2-dehydrogenase NADP+ binary complex from Agaricus bisporus

Mannitol, an acyclic six-carbon polyol, is one of the most abundant sugar alcohols occurring in nature. In the button mushroom, Agaricus bisporus, it is synthesized from fructose by the enzyme mannitol 2-dehydrogenase (MtDH; EC ) using NADPH as a cofactor. Mannitol serves as the main storage carbon (up to 50% of the fruit body dry weight) and plays a critical role in growth, fruit body development, osmoregulation, and salt tolerance. Furthermore, mannitol dehydrogenases are being evaluated for commercial mannitol production as alternatives to the less efficient chemical reduction of fructose. Given the importance of mannitol metabolism and mannitol dehydrogenases, MtDH was cloned into the pET28 expression system and overexpressed in Escherichia coli. Kinetic and physicochemical properties of the recombinant enzyme are indistinguishable from the natural enzyme. The crystal structure of its binary complex with NADP was solved at 1.5-A resolution and refined to an R value of 19.3%. It shows MtDH to be a tetramer and a member of the short chain dehydrogenase/reductase family of enzymes. The catalytic residues forming the so-called catalytic triad can be assigned to Ser(149), Tyr(169), and Lys(173).

Intestinal permeability increases with the severity of abdominal trauma: a comparison between gas liquid chromatographic and enzymatic method

BACKGROUND/AIMS

Increased intestinal permeability was found in humans after multiple trauma, burn injury and major vascular surgery. However, no data are reported regarding possible correlation between trauma and intestinal permeability degree. This study was undertaken to compare gas-liquid chromatographic and enzymatic method for the evaluation of intestinal permeability impairment in patients after severe abdominal trauma.

METHODOLOGY

Five traumatized patients with an injury severity score of more than 24 and 5 cross-matched healthy volunteers were studied. The intestinal permeability was performed using a test solution, containing 10 g lactulose and 5 g mannitol. Gas-liquid chromatographic method was applied to measure sugar standards and 5-hour urine samples and the results were compared with those obtained employing a specific enzymatic method.

RESULTS

Linearity of myoinositol, lactulose and mannitol measured by gas-liquid chromatographic method was from 0.2-1 microgram injected. Using the enzymatic method, the response was linear between mannitol concentrations of 0.34 and 5.49 mM. Linearity of lactulose standard was from 0.18-2.92 mM. The gas-liquid chromatographic and enzymatic methods showed a good agreement using the Bland-Altman procedure. The mean lactulose/mannitol ratio was 0.085 +/- 0.025 in patients and 0.009 +/- 0.001 in controls (P < 0.001). The higher the injury severity score (30.8 +/- 5) the larger the ratio of lactulose to mannitol (R2 = 0.74).

CONCLUSIONS

The enzymatic method--inexpensive, easy-to-perform and timesaving--is suitable for intestinal permeability studies. An abdominal trauma, without injury requiring surgical operation, modifies the intestinal mucosa permeability possibly favoring passage of bacteria and subsequent sepsis.

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.

MANNITOL AND MANNITOL DEHYDROGENASES IN CONIDIA OF ASPERGILLUS ORYZAE

Horikoshi, Koki (The Institute of Physical and Chemical Research, Tokyo, Japan), Shigeji Iida, and Yonosuke Ikeda. Mannitol and mannitol dehydrogenases in conidia of Aspergillus oryzae. J. Bacteriol. 89:326-330. 1965.-A sugar alcohol was isolated from the conidia of Aspergillus oryzae and identified as d-mannitol. Two types of d-mannitol dehydrogenases, nicotinamide adenine dinucleotide phosphate-linked and nicotinamide adenine dinucleotide-linked, were found in the conidia. Substrate specificities, pH optima, Michaelis-Menton constants, and the effects of inhibitors were studied. d-Mannitol was converted to fructose by the dehydrogenases. Synthesis of d-mannitol dehydrogenases was not observed during germination; the content of d-mannitol decreased at an early stage of germination. It was assumed, therefore, that d-mannitol might be used as the source of endogenous respiration and provide energy for the germination.

Rapid enzymatic method for the measurement of mannitol in urine

A previously described method for mannitol in urine has been modified and improved. End product inhibition by fructose in the mannitol dehydrogenase method for mannitol has been minimized; the assay is linear over a sample mannitol concentration range of 0-12 mmol/L; no significant interference from other sugars or sugar alcohols could be demonstrated. The method is precise (within-batch CV less than 1%), rapid and shows excellent recovery of mannitol in spiked samples. Comparison with gas liquid chromatography shows excellent correlation (r = 0.994) between the two methods.

Automated enzymatic assays for the determination of intestinal permeability probes in urine. 2. Mannitol

A need for a simple method for the determination of mannitol in urine has arisen because of the use of this monosaccharide in intestinal permeability tests. A rapid spectrophotometric assay for mannitol is presented based on the use of the bacterial enzyme mannitol dehydrogenase. The technique has been automated for use on the Cobas-Bio (Roche) centrifugal analyser. The assay has been shown to be highly specific for mannitol and was not affected by high concentrations of glucose, lactose or lactulose in samples. Within assay coefficient of variation was in the range 0.3 to 1.1% and 0.6 to 2.4% between assays. The technique represents a significant improvement in terms of time, simplicity and precision on existing methods.

Improved enzymatic method for determining mannitol and its application to dog serum after mannitol infusion

An enzymatic method for mannitol quantitation has been developed. Its application mannitol levels in serum samples from dogs after mannitol infusion is illustrated. The method is based on the spectrophotometric measurement of the initial rate of NADH formation in the reaction between mannitol and NAD catalyzed by mannitol dehydrogenase. A linear relationship between initial rates and mannitol concentration is seen between 17 mumol/l and 6.7 mmol/l mannitol. From the extent of dilution of the serum sample in the assay this corresponds to serum levels of 0.5 to 200 mmol/l. Because of the high degree of substrate specificity of mannitol dehydrogenase and the extensive dilution of the serum sample in the assay reaction mixture, serum proteins and glucose do not interfere with the reaction. As a result, pre-treatment of samples to remove glucose and deproteinization are necessary.