Takenori Satomura

ADP-dependent glucokinase/phosphofructokinase, a novel bifunctional enzyme from the hyperthermophilic archaeon Methanococcus jannaschii.

A gene encoding an ADP-dependent phosphofructokinase homologue has been identified in the hyperthermophilic archaeon Methanococcus jannaschii via genome sequencing. The gene encoded a protein of 462 amino acids with a molecular weight of 53,361. The deduced amino acid sequence of the gene showed 52 and 29% identities to the ADP-dependent phosphofructokinase and glucokinase from Pyrococcus furiosus, respectively. The gene was overexpressed inEscherichia coli, and the produced enzyme was purified and characterized. To our surprise, the enzyme showed high ADP-dependent activities for both glucokinase and phosphofructokinase. A native molecular mass was estimated to be 55 kDa, and this indicates the enzyme is monomeric. The reaction rate for the phosphorylation of d-glucose was almost 3 times that for d-fructose 6-phosphate. The K m values for d-fructose 6-phosphate and d-glucose were calculated to be 0.010 and 1.6 mm, respectively. TheK m values for ADP were 0.032 and 0.63 mm when d-glucose and d-fructose 6-phosphate were used as a phosphoryl group acceptor, respectively. The gene encoding the enzyme is proposed to be an ancestral gene of an ADP-dependent phosphofructokinase and glucokinase. A gene duplication event might lead to the two enzymatic activities.

Dye-linked d-Proline Dehydrogenase from Hyperthermophilic Archaeon Pyrobaculum islandicum Is a Novel FAD-dependent Amino Acid Dehydrogenase

The activity of dye-linkedd-proline dehydrogenase was found in the crude extract of a hyperthermophilic archaeon, Pyrobaculum islandicum JCM 9189. The dye-linked d-proline dehydrogenase was a membrane associated enzyme and was solubilized from the membrane fractions by treatment with Tween 20. The solubilized enzyme was purified 34-fold in the presence of 0.1% Tween 20 by four sequential chromatographies. The enzyme has a molecular mass of about 145 kDa and consisted of homotetrameric subunits with a molecular mass of about 42 kDa. The N-terminal amino acid sequence of the subunit was MKVAIVGGGIIGLFTAYHLRQQGADVVI. The enzyme retained its full activity both after incubation at 80 °C for 10 min and after incubation in the range of pH 4.0–10.0 at 50 °C for 10 min. The enzyme-catalyzed dehydrogenation of several d-amino acids was carried out using 2,6-dichloroindophenol as an electron acceptor, andd-proline was the most preferred substrate among thed-amino acids. The Michaelis constants ford-proline and 2,6-dichloroindophenol were determined to be 4.2 and 0.14 mm, respectively. Δ1-Pyrroline-2-carboxylate was identified as the reaction product from d-proline by thin layer chromatography. The prosthetic group of the enzyme was identified to be FAD by high-performance liquid chromatography. The gene encoding the enzyme was cloned and expressed in Escherichia coli. The nucleotide sequence of the dye-linked d-proline dehydrogenase gene was determined and encoded a peptide of 363 amino acids with a calculated molecular weight of 40,341. The amino acid sequence of the Pb. islandicum enzyme showed the highest similarity (38%) with that of the probable oxidoreductase inSulfolobus solfataricus, but low similarity with those ofd-alanine dehydrogenases from the mesophiles so far reported. This shows that the membrane-bound d-proline dehydrogenase from Pb. islandicum is a novel FAD-dependent amino acid dehydrogenase.

Purification, Characterization, and Application of a Novel Dye-Linked l-Proline Dehydrogenase from a Hyperthermophilic Archaeon, Thermococcus profundus

ABSTRACT The distribution of dye-linked l-amino acid dehydrogenases was investigated in several hyperthermophiles, and the activity of dye-linked l-proline dehydrogenase (dye-l-proDH, l-proline:acceptor oxidoreductase) was found in the crude extract of someThermococcales strains. The enzyme was purified to homogeneity from a hyperthermophilic archaeon, Thermococcus profundus DSM 9503, which exhibited the highest specific activity in the crude extract. The molecular mass of the enzyme was about 160 kDa, and the enzyme consisted of heterotetrameric subunits (α2 β2) with two different molecular masses of about 50 and 40 kDa. The N-terminal amino acid sequences of the α-subunit (50-kDa subunit) and the β-subunit (40-kDa subunit) were MRLTEHPILDFSERRGRKVTIHF and XRSEAKTVIIGGGIIGLSIAYNLAK, respectively. Dye-l-proDH was extraordinarily stable among the dye-linked dehydrogenases under various conditions: the enzyme retained its full activity upon incubation at 70°C for 10 min, and ca. 40% of the activity still remained after heating at 80°C for 120 min. The enzyme did not lose the activity upon incubation over a wide range of pHs from 4.0 to 10.0 at 50°C for 10 min. The enzyme exclusively catalyzed l-proline dehydrogenation using 2,6-dichloroindophenol (Cl2Ind) as an electron acceptor. The Michaelis constants for l-proline and Cl2Ind were determined to be 2.05 and 0.073 mM, respectively. The reaction product was identified as Δ1-pyrroline-5-carboxylate by thin-layer chromatography. The prosthetic group of the enzyme was identified as flavin adenine dinucleotide by high-pressure liquid chromatography. In addition, the simple and specific determination of l-proline at concentrations from 0.10 to 2.5 mM using the stable dye-l-proDH was achieved.

L-aspartate oxidase is present in the anaerobic hyperthermophilic archaeon Pyrococcus horikoshii OT-3: characteristics and role in the de novo biosynthesis of nicotinamide adenine dinucleotide proposed by genome sequencing.

A gene encoding the L-aspartate oxidase homologue was identified via genome sequencing in the anaerobic hyperthermophilic archaeon Pyrococcus horikoshii OT-3. We succeeded in expressing the encoding gene in Escherichia coli and purified the product to homogeneity. Characterization of the protein revealed that it is the most thermostable L-aspartate oxidase detected so far. In addition to the oxidase activity, the enzyme catalyzed L-aspartate dehydrogenation in the presence of an artificial electron acceptor such as phenazine methosulfate, 2,6-dichlorophenol-indophenol, and ferricyanide. L-Aspartate oxidase is known to function as the first enzyme in the de novo NAD biosynthetic pathway in prokaryotes. By a similarity search in public databases, the genes that encode the homologue of all other enzymes involved in the pathway were identified in the P. horikoshii OT-3 genome. This suggests that P. horikoshii OT-3 may use the de novo NAD biosynthetic pathway under anaerobic conditions.

Catalytic properties and crystal structure of quinoprotein aldose sugar dehydrogenase from hyperthermophilic archaeon Pyrobaculum aerophilum

We identified a gene encoding a soluble quinoprotein glucose dehydrogenase homologue in the hyperthermophilic archaeon Pyrobaculum aerophilum. The gene was overexpressed in Escherichia coli, after which its product was purified and characterized. The enzyme was extremely thermostable, and the activity of the pyrroloquinoline quinone (PQQ)-bound holoenzyme was not lost after incubation at 100 degrees C for 10 min. The crystal structure of the enzyme was determined in both the apoform and as the PQQ-bound holoenzyme. The overall fold of the P. aerophilum enzyme showed significant similarity to that of soluble quinoprotein aldose sugar dehydrogenase (Asd) from E. coli. However, clear topological differences were observed in the two long loops around the PQQ-binding sites of the two enzymes. Structural comparison revealed that the hyperthermostability of the P. aerophilum enzyme is likely attributable to the presence of an extensive aromatic pair network located around a beta-sheet involving N- and C-terminal beta-strands.

A novel flavin adenine dinucleotide (FAD) containing D-lactate dehydrogenase from the thermoacidophilic crenarchaeota Sulfolobus tokodaii strain 7: Purification, characterization and expression in Escherichia coli

Dye-linked D-lactate dehydrogenase activity was found in the crude extract of a continental thermoacidophilic crenarchaeota, Sulfolobus tokodaii strain 7, and was purified 375-fold through four sequential chromatography steps. With a molecular mass of about 93 kDa, this enzyme was a homodimer comprised of identical subunits with molecular masses of about 48 kDa. The enzyme retained its full activity after incubation at 80 degrees C for 10 min and after incubation at pHs ranging from 6.5 to 10.0 for 30 min at 50 degrees C. The preferred substrate for this enzyme was D-lactate, with 2,6-dichloroindophenol serving as the electron acceptor. Using high-performance liquid chromatography (HPLC), the enzymes prosthetic group was determined to be flavin adenine dinucleotide (FAD). Its N-terminal amino acid sequence was MLEGIEYSQGEEREDFVGFKIKPKI. Using that sequence and previously reported genome information, the gene encoding the enzyme (ST0649) was identified. It was subsequently cloned and expressed in Escherichia coli and found to encode a polypeptide of 440 amino acids with a calculated molecular weight of 49,715. The amino acid sequence of this dye-linked D-lactate dehydrogenase showed higher homology (39% identity) with that of a glycolate oxidase subunit homologue from Archaeoglobus fulgidus, but less similarity (32% identity) to D-lactate dehydrogenase from A. fulgidus. Taken together, our findings indicate that the dye-linked D-lactate dehydrogenase from S. tokodaii is a novel type of FAD containing D-lactate dehydrogenase.

l-Proline dehydrogenases in hyperthermophilic archaea: distribution, function, structure, and application

Dye-linked l-proline dehydrogenase (ProDH) catalyzes the oxidation of l-proline to ∆1-pyrroline-5-carboxylate (P5C) in the presence of artificial electron acceptors. The enzyme is known to be widely distributed in bacteria and eukarya, together with nicotinamide adenine dinucleotide (phosphate)-dependent P5C dehydrogenase, and to function in the metabolism of l-proline to l-glutamate. In addition, over the course of the last decade, three other types of ProDH with molecular compositions completely different from previously known ones have been identified in hyperthermophilic archaea. The first is a heterotetrameric αβγδ-type ProDH, which exhibits both ProDH and reduced nicotinamide adenine dinucleotide dehydrogenase activity and includes two electron transfer proteins. The second is a heterooctameric α4β4-type ProDH, which uses flavin adenine dinucleotide, flavin mononucleotide, adenosine triphosphate, and Fe as cofactors and creates a new electron transfer pathway. The third is a recently identified homodimeric ProDH, which exhibits the greatest thermostability among these archaeal ProDHs. This minireview focuses on the functional and structural properties of these three types of archaeal ProDH and their distribution in archaea. In addition, we will describe the specific application of hyperthermostable ProDH for use in a biosensor and for DNA sensing.

Structure of a D-tagatose 3-epimerase-related protein from the hyperthermophilic bacterium Thermotoga maritima

The crystal structure of a D-tagatose 3-epimerase-related protein (TM0416p) encoded by the hypothetical open reading frame TM0416 in the genome of the hyperthermophilic bacterium Thermotoga maritima was determined at a resolution of 2.2 A. The asymmetric unit contained two homologous subunits and a dimer was generated by twofold symmetry. The main-chain coordinates of the enzyme monomer proved to be similar to those of D-tagatose 3-epimerase from Pseudomonas cichorii and D-psicose 3-epimerase from Agrobacterium tumefaciens; however, TM0416p exhibited a unique solvent-accessible substrate-binding pocket that reflected the absence of an alpha-helix that covers the active-site cleft in the two aforementioned ketohexose 3-epimerases. In addition, the residues responsible for creating a hydrophobic environment around the substrate in TM0416p differ entirely from those in the other two enzymes. Collectively, these findings suggest that the substrate specificity of TM0416p is likely to differ substantially from those of other D-tagatose 3-epimerase family enzymes.

Efficient Direct Electron Transfer for a Highly Oriented PQQ-GDH Immobilized Electrode for Bioanode

A bioanode with improved enzyme orientation was developed to achieve an efficient enzyme reaction and electron transfer on an electrode surface. A highly stable PQQ-dependent glucose dehydrogenase (PQQ-GDH) isolated from a hyper-thermophilic archaeon was employed as an electron conversion element. PQQ-GDH is expected to maintain battery properties and to have a long battery life. To immobilize the enzyme onto the electrode with appropriate orientation, we introduced a His-tag to the N-terminal of PQQ-GDH by a genetic technique and utilized the affinity bond between His-tag and Cu atoms. The catalytic current density in the presence of substrate was 18.6 μA/cm2 without a mediator. The current density of the oriented electrode was approximately 90 times higher than that of the non-oriented electrode. By immobilizing the enzyme with orientation, the accessibility between the enzyme and substrate for enzyme reaction increased because the active site of PQQ-GDH is located opposite the electrode. Because enzymes have different orientations at the surface of the non-orientated electrode, the efficiency of the electrode was lower than that of the high-orientation electrode. The results of the present study present a potentially promising finding for application to practical bioelectric devices, such as bio-fuel cells and biosensors.

Crystallization and preliminary X-ray analysis of a novel dye-linked L-proline dehydrogenase from the aerobic hyperthermophilic archaeon Aeropyrum pernix.

A novel dye-linked L-proline dehydrogenase from the aerobic hyperthermophilic archaeon Aeropyrum pernix was crystallized using the sitting-drop vapour-diffusion method with polyethylene glycol 8000 as the precipitant. The crystals belonged to the tetragonal space group P4(1)2(1)2 or its enantiomorph P4(3)2(1)2, with unit-cell parameters a = b = 61.1, c = 276.3 Å, and diffracted to 2.87 Å resolution using a Cu Kα rotating-anode generator with an R-AXIS VII detector. The asymmetric unit contained one protein molecule, giving a crystal volume per enzyme mass (V(M)) of 2.75 Å(3) Da(-1) and a solvent content of 55.3%.