Thermotoga maritima TM0298 is a highly thermostable mannitol dehydrogenase

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).

Metabolism Dealing with Thermal Degradation of NAD+ in the Hyperthermophilic Archaeon Thermococcus kodakarensis

NAD⁺ is an important cofactor for enzymatic oxidation reactions in all living organisms, including (hyper)thermophiles. However, NAD⁺ is susceptible to thermal degradation at high temperatures. It can thus be expected that (hyper)thermophiles harbor mechanisms that maintain in vivo NAD⁺ concentrations and possibly remove and/or reuse undesirable degradation products of NAD⁺ Here we confirmed that at 85°C, thermal degradation of NAD⁺ results mostly in the generation of nicotinamide and ADP-ribose, the latter known to display toxicity by spontaneously linking to proteins. The hyperthermophilic archaeon Thermococcus kodakarensis possesses a putative ADP-ribose pyrophosphatase (ADPR-PPase) encoded by the TK2284 gene. ADPR-PPase hydrolyzes ADP-ribose to ribose 5-phosphate (R5P) and AMP. The purified recombinant TK2284 protein exhibited activity toward ADP-ribose as well as ADP-glucose. Kinetic analyses revealed a much higher catalytic efficiency toward ADP-ribose, suggesting that ADP-ribose was the physiological substrate. To gain insight into the physiological function of TK2284, a TK2284 gene disruption strain was constructed and examined. Incubation of NAD⁺ in the cell extract of the mutant strain at 85°C resulted in higher ADP-ribose accumulation and lower AMP production compared with those in experiments with the host strain cell extract. The mutant strain also exhibited lower cell yield and specific growth rates in a synthetic amino acid medium compared with those of the host strain. The results obtained here suggest that the ADPR-PPase in T. kodakarensis is responsible for the cleavage of ADP-ribose to R5P and AMP, providing a means to utilize the otherwise dead-end product of NAD⁺ breakdown.IMPORTANCE Hyperthermophilic microorganisms living under high temperature conditions should have mechanisms that deal with the degradation of thermolabile molecules. NAD⁺ is an important cofactor for enzymatic oxidation reactions and is susceptible to thermal degradation to ADP-ribose and nicotinamide. Here we show that an ADP-ribose pyrophosphatase homolog from the hyperthermophilic archaeon Thermococcus kodakarensis converts the detrimental ADP-ribose to ribose 5-phosphate and AMP, compounds that can be directed to central carbon metabolism. This physiological role for ADP-ribose pyrophosphatases might be universal in hyperthermophiles, as their homologs are widely distributed among both hyperthermophilic bacteria and archaea.

Activity of select dehydrogenases with sepharose-immobilized N(6)-carboxymethyl-NAD

N⁶-carboxymethyl-NAD (N⁶-CM-NAD) can be used to immobilize NAD onto a substrate containing terminal primary amines. We previously immobilized N⁶-CM-NAD onto sepharose beads and showed that Thermotoga maritima glycerol dehydrogenase could use the immobilized cofactor with cofactor recycling. We now show that Saccharomyces cerevisiae alcohol dehydrogenase, rabbit muscle L-lactate dehydrogenase (type XI), bovine liver L-glutamic dehydrogenase (type III), Leuconostoc mesenteroides glucose-6-phosphate dehydro-genase, and Thermotoga maritima mannitol dehydrogenase are active with soluble N⁶-CM-NAD. The products of all enzymes but 6-phospho-D-glucono-1,5-lactone were formed when sepharose-immobilized N⁶-CM-NAD was recycled by T. maritima glycerol dehydrogenase, indicating that N⁶-immobilized NAD is suitable for use by a variety of different dehydrogenases. Observations of the enzyme active sites suggest that steric hindrance plays a greater role in limiting or allowing activity with the modified cofactor than do polarity and charge of the residues surrounding the N⁶-amine group on NAD.

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.

Characterization of Thermotoga maritima glycerol dehydrogenase for the enzymatic production of dihydroxyacetone

NAD-dependent Thermotoga maritima glycerol dehydrogenase (TmGlyDH) converts glycerol into dihydroxyacetone (DHA), a valuable synthetic precursor and sunless tanning agent. In this work, recombinant TmGlyDH was characterized to determine if it can be used to catalyze DHA production. The pH optima for glycerol oxidation and DHA reduction at 50 °C were 7.9 and 6.0, respectively. Under the conditions tested, TmGlyDH had a linear Arrhenius plot up to 80 °C. TmGlyDH was more thermostable than other glycerol dehydrogenases, remaining over 50 % active after 7 h at 50 °C. TmGlyDH was active on racemic 1,2-propanediol and produced (R)-1,2-propanediol from hydroxyacetone with an enantiomeric excess above 99 %, suggesting that TmGlyDH can also be used for chiral synthesis. (R)-1,2-propanediol production from hydroxyacetone was demonstrated for the first time in a one-enzyme cycling reaction using glycerol as the second substrate. Negative cooperativity was observed with glycerol and DHA, but not with the cofactor. Apparent kinetic parameters for glycerol, DHA, and NAD(H) were determined over a broad pH range. TmGlyDH showed little activity with N(6)-carboxymethyl-NAD(+) (N(6)-CM-NAD), an NAD(+) analog modified for easy immobilization to amino groups, but the double mutation V44A/K157G increased catalytic efficiency with N(6)-CM-NAD(+) ten-fold. Finally, we showed for the first time that a GlyDH is active with immobilized N(6)-CM-NAD(+), suggesting that N(6)-CM-NAD(+) can be immobilized on an electrode to allow TmGlyDH activity in a system that reoxidizes the cofactor electrocatalytically.

Challenges in enzymatic route of mannitol production

Mannitol is an important biochemical often used as medicine and in food sector, yet its biotechnological is not preffered in Industry for large scale production, which may be due to the multistep mechanism involved in hydrogenation and reduction. This paper is a comparative preview covering present chemical and biotechnological approaches existing today for mannitol production at industrial scale. Biotechnological routes are suitable for adaptation at industrial level for mannitol production, and whatever concerns are there had been discussed in detail, namely, raw materials, broad range of enzymes with high activity at elevated temperature suitable for use in reactor, cofactor limitation, reduced by-product formation, end product inhibition, and reduced utilization of mannitol for enhancing the yield with maximum volumetric productivity.

Diversity and versatility of the Thermotoga maritima sugar kinome

Sugar phosphorylation is an indispensable committed step in a large variety of sugar catabolic pathways, which are major suppliers of carbon and energy in heterotrophic species. Specialized sugar kinases that are indispensable for most of these pathways can be utilized as signature enzymes for the reconstruction of carbohydrate utilization machinery from microbial genomic and metagenomic data. Sugar kinases occur in several structurally distinct families with various partially overlapping as well as yet unknown substrate specificities that often cannot be accurately assigned by homology-based techniques. A subsystems-based metabolic reconstruction combined with the analysis of genome context and followed by experimental testing of predicted gene functions is a powerful approach of functional gene annotation. Here we applied this integrated approach for functional mapping of all sugar kinases constituting an extensive and diverse sugar kinome in the thermophilic bacterium Thermotoga maritima. Substrate preferences of 14 kinases mainly from the FGGY and PfkB families were inferred by bioinformatics analysis and biochemically characterized by screening with a panel of 45 different carbohydrates. Most of the analyzed enzymes displayed narrow substrate preferences corresponding to their predicted physiological roles in their respective catabolic pathways. The observed consistency supports the choice of kinases as signature enzymes for genomics-based identification and reconstruction of sugar utilization pathways. Use of the integrated genomic and experimental approach greatly speeds up the identification of the biochemical function of unknown proteins and improves the quality of reconstructed pathways.

The mechanisms of Mg2+ and Co2+ transport by the CorA family of divalent cation transporters

The metal ions Mg(2+) and Co(2+) are essential for life, although to different degree. They have similar chemical and physical properties, but their slight differences result in Mg(2+) to be the most abundant metal ion in living cells and the trace element Co(2+) being toxic at relatively low concentrations. Specialized transporters have evolved in living cells to supply and balance the Mg(2+) and Co(2+) need of the cells. The current knowledge of the molecular mechanisms of Mg(2+) and Co(2+) -specific transporters is very limited at this point. Recently, there has been remarkable advances to understand the CorA family, a family of transporters that are able to transport both ions. These new data have increased our insights in how Mg(2+) and Co(2+) are translocated across membranes. Presently, CorA is probably the best system to study the mechanisms of Mg(2+) and Co(2+) transport. This chapter discusses the mechanisms through which CorA selects, transports, and regulates the translocation of its substrate. In addition, we highlight the physical and chemical properties of the substrates, which are important parameters required for better understanding of the transporter action.

Co2+ selectivity of Thermotoga maritima CorA and its inability to regulate Mg2+ homeostasis present a new class of CorA proteins

CorA is a family of divalent cation transporters ubiquitously present in bacteria and archaea. Although CorA can transport both Mg(2+) and Co(2+) almost equally well, its main role has been suggested to be that of primary Mg(2+) transporter of prokaryotes and hence the regulator of Mg(2+) homeostasis. The reason is that the affinity of CorA for Co(2+) is relatively low and thus considered non-physiological. Here, we show that Thermotoga maritima CorA (TmCorA) is incapable of regulating the Mg(2+) homeostasis and therefore cannot be the primary Mg(2+) transporter of T. maritima. Further, our in vivo experiments confirm that TmCorA is a highly selective Co(2+) transporter, as it selects Co(2+) over Mg(2+) at >100 times lower concentrations. In addition, we present data that show TmCorA to be extremely thermostable in the presence of Co(2+). Mg(2+) could not stabilize the protein to the same extent, even at high concentrations. We also show that addition of Co(2+), but not Mg(2+), specifically induces structural changes to the protein. Altogether, these data show that TmCorA has the role of being the transporter of Co(2+) but not Mg(2+). The physiological relevance and requirements of Co(2+) in T. maritima is discussed and highlighted. We suggest that CorA may have different roles in different organisms. Such functional diversity is presumably a reflection of minor, but important structural differences within the CorA family that regulate the gating, substrate selection, and transport.

Properties of recombinant Strep-tagged and untagged hyperthermophilic D-arabitol dehydrogenase from Thermotoga maritima

The first hyperthermophilic D-arabitol dehydrogenase from Thermotoga maritima was heterologously purified from Escherichia coli. The protein was purified with and without a Strep-tag. The enzyme exclusively catalyzed the NAD(H)-dependent oxidoreduction of D-arabitol, D-xylitol, D-ribulose, or D-xylulose. A twofold increase of catalytic rates was observed upon addition of Mg(2+) or K(+). Interestingly, only the tag-less protein was thermostable, retaining 90% of its activity after 90 min at 85 °C. However, the tag-less form of D-arabitol dehydrogenase had similar kinetic parameters compared to the tagged enzyme, demonstrating that the Strep-tag was not deleterious to protein function but decreased protein stability. A single band at 27.6 kDa was observed on SDS-PAGE and native PAGE revealed that the protein formed a homohexamer and a homododecamer. The enzyme catalyzed oxidation of D-arabitol to D: -ribulose and therefore belongs to the class of D-arabitol 2-dehydrogenases, which are typically observed in yeast and not bacteria. The product D-ribulose is a rare ketopentose sugar that has numerous industrially applications. Given its thermostability and specificity, D-arabitol 2-dehydrogenase is a desirable biocatalyst for the production of rare sugar precursors.

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.