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PubMed1994

Growth requirements of hyperthermophilic sulfur-dependent heterotrophic archaea isolated from a shallow submarine geothermal system with reference to their essential amino acids.

Three hyperthermophilic sulfur-dependent heterotrophs were isolated from a shallow submarine hydrothermal system at an inlet of Kodakara-jima island, Kagoshima, Japan. The isolates grew at 60 to 97 degrees C, with the optimum temperatures at 85 to 90 degrees C. Sensitivity to rifampin and the existence of ether lipids indicated that the isolates are hyperthermophilic archaea. Partial sequencing of the genes coding for 16S rRNA showed that the three isolates are closely related to the genus Thermococcus. They grew on proteinaceous mixtures, such as yeast extract, Casamino Acids, and purified proteins (e.g., casein and gelatin), but not on carbohydrates or organic acids as sole carbon and energy sources. Nine amino acids were essential for growth of isolate KS-1 (Thr, Leu, Ile, Val, Met, Phe, His, Tyr, and Arg). Isolate KS-2 required Lys in addition to the nine amino acids, and KS-8 required Lys instead of Tyr. In comparative studies, it was shown that Thermococcus celer DSM 2476 required 10 amino acids (Thr, Leu, Ile, Val, Met, Phe, Tyr, Trp, Lys, and Arg) while Pyrococcus furiosus DSM 3638 required only Ile and Val. The hyperthermophilic fermentative eubacterium Thermotoga neapolitana DSM 4359 did not require any amino acids for growth.

Amino Acids, Essential↗
PubMed1996

L-alanine production from glucose fermentation by hyperthermophilic members of the domains bacteria and Archaea: a remnant of an ancestral metabolism?

New members of the order Thermotogales were isolated from nonvolcanically heated geothermal environments, including oil fields and waters of the Great Artesian Basin of Australia, thereby extending their known habitats, previously recognized primarily as volcanic. The hyperthermophilic and thermophilic members of Thermotogales of volcanic origin, together with the recently described nonvolcanic species of this order and three new isolates described in this paper, were all found to produce L-alanine from glucose fermentation, in addition to acetate, lactate, CO2 and H2. L-alanine production from glucose is a trait in common with Pyrococcus furiosus and Thermococcus profundus. We propose that L-alanine production from sugar fermentation be regarded as an ancestral metabolic characteristic.

Alanine↗
PubMed1997

Stabilization of Enzymes against Thermal Stress and Freeze-Drying by Mannosylglycerate.

2-O-(beta)-Mannosylglycerate, a solute that accumulates in some (hyper)thermophilic organisms, was purified from Pyrococcus furiosus cells, and its effect on enzyme stabilization in vitro was assessed. Enzymes from hyperthermophilic, thermophilic, and mesophilic sources were examined. The thermostabilities of alcohol dehydrogenases from P. furiosus and Bacillus stearothermophilus and of glutamate dehydrogenases from Thermotoga maritima and Clostridium difficile were improved to a significant extent when enzyme solutions were incubated at supraoptimal temperatures in the presence of 2-O-(beta)-mannosylglycerate, but no effect on the thermostability of glutamate dehydrogenase from P. furiosus was detected. On the other hand, there was a remarkable effect on the thermal stabilities of rabbit muscle lactate dehydrogenase, baker's yeast alcohol dehydrogenase, and bovine liver glutamate dehydrogenase, which were used as model systems to evaluate stabilization of enzymes of mesophilic origin. For all of the enzymes examined and at the highest temperatures tested, 2-O-(beta)-mannosylglycerate was a better thermoprotectant than trehalose. The stabilizing effect exerted by 2-O-(beta)-mannosylglycerate on enzymes suggests a role for this compound as a protein thermostabilizer under physiological conditions. 2-O-(beta)-Mannosylglycerate was also effective in the protection of enzymes against stress imposed by freeze-drying, with its protecting effect being similar to or better than that exerted by trehalose. The data show 2-O-(beta)-mannosylglycerate to be a potential enzyme stabilizer in biotechnological applications.

Journal Article↗
PubMed1997

Organic solutes in hyperthermophilic archaea.

We examined the accumulation of organic solutes under optimum growth conditions in 12 species of thermophilic and hyperthermophilic Archaea belonging to the Crenarchaeota and Euryarchaeota. Pyrobaculum aerophilum, Thermoproteus tenax, Thermoplasma acidophilum, and members of the order Sulfolobales accumulated trehalose. Pyrococcus furiosus accumulated di-myo-inositol-1,1(prm1)(3,3(prm1))-phosphate and (beta)-mannosylglycerate, Methanothermus fervidus accumulated cyclic-2,3-bisphosphoglycerate and (beta)-mannosylglycerate, while the only solute detected in Pyrodictium occultum was di-myo-inositol-1,1(prm1)(3,3(prm1))-phosphate. Methanopyrus kandleri accumulated large concentrations of cyclic-2,3-bisphosphoglycerate. On the other hand, Archaeoglobus fulgidus accumulated three phosphorylated solutes; prominent among them was a compound identified as di-glycerol-phosphate. This solute increased in concentration as the salinity of the medium and the growth temperature were raised, suggesting that this compound serves as a general stress solute. Di-myo-inositol-1,1(prm1)(3,3(prm1))-phosphate accumulated at supraoptimal temperature only. The relationship between the accumulation of unusual solutes and high temperatures is also discussed.

Journal Article↗
PubMed1991

Distribution of folates and modified folates in extremely thermophilic bacteria.

Analyses were made of the structures and levels of folates and modified folates present in extremely thermophilic bacteria. These procedures involved the chemical analysis of products resulting from the oxidative cleavage of the 6-substituted, folatelike tetrahydropterins present in the cells. Air-oxidized cell extracts of extreme thermophiles from two members of the archaebacterial order Thermococcales, Thermococcus celer and Pyrococcus furiosus, contained only 7-methylpterin, indicating that these cells contain a modified folate with a methylated pterin. Cell extracts also contained 6-acetyl-7-methyl-7,8-dihydropterin, another product derived from the oxidative cleavage of a dimethylated folate, demonstrating that both the C-7 and C-9 carbons of the pterin were methylated. Extracts, however, contained neither p-aminobenzoylpolyglutamates nor methaniline, the oxidative cleavage products of folates and methanopterin, respectively, indicating that they contain a previously undescribed C1 carrier(s). On the basis of the level of the 7-methylpterin isolated, the levels of modified folate were 2 to 10 times higher than those typically found in mesophilic bacteria and 10 to 100 times less than the level of methanopterin found in the methanogenic bacteria. Oxidized cell extracts of Sulfolobus spp. of the archaebacterial order Sulfolobales contained only pterin, and, like members of the order Thermococcales, they contained neither-p-aminobenzoylpolyglutamates nor methaniline. Oxidized cell extracts of the extreme thermophiles Pyrobaculum sp. strain H10 and Pyrodictium occultum, from the archaebacterial orders Thermoproteales and Pyrodictiales, respectively, and Thermotoga maritima from the eubacterial order Thermotogales, contained pterin and p-aminobenzoylpolyglutamates, indicating that these cells contained unmodified folates. The levels of p-aminobenzoylpolyglutamates in these archaebacterial cell extracts indicate that the folates were present in the cells at levels 4 to 10 times higher than generally found in those mesophilic eubacteria which do not folates in energy metabolism. The levels and chain lengths of the of p-aminobenzoylpolyglutamates present in Thermotoga maritima were typical of those found in mesophilic eubacteria.

Archaea↗
PubMed1992

Hydrogen-oxidizing electron transport components in the hyperthermophilic archaebacterium Pyrodictium brockii.

The hyperthermophilic archaebacterium Pyrodictium brockii grows optimally at 105 degrees C by a form of metabolism known as hydrogen-sulfur autotrophy, which is characterized by the oxidation of H2 by S0 to produce ATP and H2S. UV-irradiated membranes were not able to carry out the hydrogen-dependent reduction of sulfur. However, the activity could be restored by the addition of ubiquinone Q10 or ubiquinone Q6 to the UV-damaged membranes. A quinone with thin-layer chromatography migration properties similar to those of Q6 was purified by thin-layer chromatography from membranes of P. brockii, but nuclear magnetic resonance analysis failed to confirm its identity as a ubiquinone. P. brockii quinone was capable of restoring hydrogen-dependent sulfur reduction to UV-irradiated membranes. Hydrogen-reduced-minus-air-oxidized absorption difference spectra on membranes revealed absorption peaks characteristic of c-type cytochromes. A c-type cytochrome with alpha, beta, and gamma peaks at 553, 522, and 421 nm, respectively, was solubilized from membranes with 0.5% Triton X-100. Pyridine ferrohemochrome spectra confirmed its identity as a c-type cytochrome, and heme staining of membranes loaded on sodium dodecyl sulfate gels revealed a single heme-containing component of 13 to 14 kDa. Studies with the ubiquinone analog 2-n-heptyl-4-hydroxyquinoline-N-oxide demonstrated that the P. brockii quinone is located on the substrate side of the electron transport chain with respect to the c-type cytochrome. These first characterizations of the strictly anaerobic, presumably primitive P. brockii electron transport chain suggest that the hydrogenase operates at a relatively high redox potential and that the H2-oxidizing chain more closely resembles those of aerobic eubacterial H2-oxidizing bacteria than those of the H2-metabolizing systems of anaerobes or the hyperthermophile Pyrococcus furiosus.

Archaea↗
PubMed1993

Structures of the modified folates in the extremely thermophilic archaebacterium Thermococcus litoralis.

The chemical structures of the two modified folates present in Thermococcus litoralis were established. These compounds, each containing a core structure of 1-[4-[[1-(2-amino-7-methyl- 4-oxo-6-pteridinyl)-ethyl]amino]phenyl]-1-deoxy-[1-alpha-D- ribofuranosyl]-ribitol, were characterized. The five position of the ribose in this core structure was beta-linked to the C-1 of a poly-beta (1-->4)N-acetylglucosamine having a chain length of four or five N-acetylglucosamine residues. Thus, these compounds are N-acetylglucosamine homologs of the modified folates found in Pyrococcus furiosus.

Acetylglucosamine↗
PubMed1995

Purification, characterization, and metabolic function of tungsten-containing aldehyde ferredoxin oxidoreductase from the hyperthermophilic and proteolytic archaeon Thermococcus strain ES-1.

Thermococcus strain ES-1 is a strictly anaerobic, hyperthermophilic archaeon that grows at temperatures up to 91 degrees C by the fermentation of peptides. It is obligately dependent upon elemental sulfur (S(o)) for growth, which it reduces to H2S. Cell extracts contain high aldehyde oxidation activity with viologen dyes as electron acceptors. The enzyme responsible, which we term aldehyde ferredoxin oxidoreductase (AOR), has been purified to electrophoretic homogeneity. AOR is a homodimeric protein with a subunit M(r) of approximately 67,000. It contains molybdopterin and one W, four to five Fe, one Mg, and two P atoms per subunit. Electron paramagnetic resonance analyses of the reduced enzyme indicated the presence of a single [4Fe-4S]+ cluster with an S = 3/2 ground state. While AOR oxidized a wide range of aliphatic and aromatic aldehydes, those with the highest apparent kcat/Km values (> 10 microM-1S-1) were acetaldehyde, isovalerylaldehyde, and phenylacetaldehyde (Km values of < 100 microM). The apparent Km value for Thermococcus strain ES-1 ferredoxin was 10 microM (with crotonaldehyde as the substrate). Thermococcus strain ES-1 AOR also catalyzed the reduction of acetate (apparent Km of 1.8 mM) below pH 6.0 (with reduced methyl viologen as the electron donor) but at much less than 1% of the rate of the oxidative reaction (with benzyl viologen as the electron acceptor at pH 6.0 to 10.0). The properties of Thermococcus strain ES-1 AOR are very similar to those of AOR previously purified from the saccharolytic hyperthermophile Pyrococcus furiosus, in which AOR was proposed to oxidize glyceraldehyde as part of a novel glycolytic pathway (S. Mukund and M. W. W. Adams, J. Biol. Chem. 266:14208-14216, 1991). However, Thermococcus strain ES-1 is not known to metabolize carbohydrates, and glyceraldehyde was a very poor substrate (kcat/Km of < 0.2 microM-1S-1) for its AOR. The most efficient substrates for Thermococcus strain ES-1 AOR were the aldehyde derivatives of transaminated amino acids. This suggests that the enzyme functions to oxidize aldehydes generated during amino acid catabolism, although the possibility that AOR generates aldehydes from organic acids produced by fermentation cannot be ruled out.

Aldehyde Oxidoreductases↗
PubMed2003

Metabolic enzymes from psychrophilic bacteria: challenge of adaptation to low temperatures in ornithine carbamoyltransferase from Moritella abyssi.

The enzyme ornithine carbamoyltransferase (OTCase) of Moritella abyssi (OTCase(Mab)), a new, strictly psychrophilic and piezophilic bacterial species, was purified. OTCase(Mab) displays maximal activity at rather low temperatures (23 to 25 degrees C) compared to other cold-active enzymes and is much less thermoresistant than its homologues from Escherichia coli or thermophilic procaryotes. In vitro the enzyme is in equilibrium between a trimeric state and a dodecameric, more stable state. The melting point and denaturation enthalpy changes for the two forms are considerably lower than the corresponding values for the dodecameric Pyrococcus furiosus OTCase and for a thermolabile trimeric mutant thereof. OTCase(Mab) displays higher K(m) values for ornithine and carbamoyl phosphate than mesophilic and thermophilic OTCases and is only weakly inhibited by the bisubstrate analogue delta-N-phosphonoacetyl-L-ornithine (PALO). OTCase(Mab) differs from other, nonpsychrophilic OTCases by substitutions in the most conserved motifs, which probably contribute to the comparatively high K(m) values and the lower sensitivity to PALO. The K(m) for ornithine, however, is substantially lower at low temperatures. A survey of the catalytic efficiencies (k(cat)/K(m)) of OTCases adapted to different temperatures showed that OTCase(Mab) activity remains suboptimal at low temperature despite the 4.5-fold decrease in the K(m) value for ornithine observed when the temperature is brought from 20 to 5 degrees C. OTCase(Mab) adaptation to cold indicates a trade-off between affinity and catalytic velocity, suggesting that optimization of key metabolic enzymes at low temperatures may be constrained by natural limits.

Adaptation, Biological↗
PubMed2005

Heat shock response of Archaeoglobus fulgidus.

The heat shock response of the hyperthermophilic archaeon Archaeoglobus fulgidus strain VC-16 was studied using whole-genome microarrays. On the basis of the resulting expression profiles, approximately 350 of the 2,410 open reading frames (ORFs) (ca. 14%) exhibited increased or decreased transcript abundance. These span a range of cell functions, including energy production, amino acid metabolism, and signal transduction, where the majority are uncharacterized. One ORF called AF1298 was identified that contains a putative helix-turn-helix DNA binding motif. The gene product, HSR1, was expressed and purified from Escherichia coli and was used to characterize specific DNA recognition regions upstream of two A. fulgidus genes, AF1298 and AF1971. The results indicate that AF1298 is autoregulated and is part of an operon with two downstream genes that encode a small heat shock protein, Hsp20, and cdc48, an AAA+ ATPase. The DNase I footprints using HSR1 suggest the presence of a cis-binding motif upstream of AF1298 consisting of CTAAC-N5-GTTAG. Since AF1298 is negatively regulated in response to heat shock and encodes a protein only distantly related to the N-terminal DNA binding domain of Phr of Pyrococcus furiosus, these results suggest that HSR1 and Phr may belong to an evolutionarily diverse protein family involved in heat shock regulation in hyperthermophilic and mesophilic Archaea organisms.

Amino Acid Sequence↗
PubMed1998

The euryarchaeotes, a subdomain of Archaea, survive on a single DNA polymerase: fact or farce?

Archaea is now recognized as the third domain of life. Since their discovery, much effort has been directed towards understanding the molecular biology and biochemistry of Archaea. The objective is to comprehend the complete structure and the depth of the phylogenetic tree of life. DNA replication is one of the most important events in living organisms and DNA polymerase is the key enzyme in the molecular machinery which drives the process. All archaeal DNA polymerases were thought to belong to family B. This was because all of the products of pol genes that had been cloned showed amino acid sequence similarities to those of this family, which includes three eukaryal DNA replicases and Escherichia coli DNA polymerase II. Recently, we found a new heterodimeric DNA polymerase from the hyperthermophilic archaeon, Pyrococcus furiosus. The genes coding for the subunits of this DNA polymerase are conserved in the euryarchaeotes whose genomes have been completely sequenced. The biochemical characteristics of the novel DNA polymerase family suggest that its members play an important role in DNA replication within euryarchaeal cells. We review here our current knowledge on DNA polymerases in Archaea with emphasis on the novel DNA polymerase discovered in Euryarchaeota.

Amino Acid Sequence↗
PubMed2002

Gene cloning and polymerase chain reaction with proliferating cell nuclear antigen from Thermococcus kodakaraensis KOD1.

The gene encoding the proliferating cell nuclear antigen (PCNA), a sliding clamp of DNA polymerases, was cloned from an euryarchaeote, Thermococcus kodakaraensis KOD1. The PCNA homologue, designated Tk-PCNA, contained 249 amino acid residues with a calculated molecular mass of 28,200 Da and was 84.3% identical to that from Pyrococcus furiosus. Tk-PCNA was overexpressed in Escherichia coli and purified. This protein stimulated the primer extension abilities of the DNA polymerase from T. kodakaraensis KOD1 'KOD DNA polymerase'. The stimulatory effect of Tk-PCNA was observed when a circular DNA template was used and was equally effective on both circular and linear DNA. The Tk-PCNA improved the sensitivity of PCR without adverse effects on fidelity with the KOD DNA polymerase. This is the first report in which a replication-related factor worked on PCR.

Cloning, Molecular↗
PubMed2006

Overexpression and characterization of a carboxypeptidase from the hyperthermophilic archaeon Thermococcus sp. NA1.

Genomic analysis of a hyperthermophilic archaeon, Thermococcus sp. NA1, revealed the presence of an 1,497 bp open reading frame, encoding a protein of 499 amino acids. The deduced amino acid sequence was similar to thermostable carboxypeptidase 1 from Pyrococcus furiosus, a member of peptidase family M32. Five motifs, including the HEXXH motif with two histidines coordinated with the active site metal, were conserved. The carboxypeptidase gene was cloned and overexpressed in Escherichia coli. Molecular masses assessed by SDS-PAGE and gel filtration were 61 kDa and 125 kDa respectively, which points to a dimeric structure for the recombinant enzyme, designated TNA1_CP. The enzyme showed optimum activity toward Z-Ala-Arg at pH 6.5 and 70-80 degrees C (k(cat)/K(m)=8.3 mM(-1) s(-1)). In comparison with that of P. furiosus CP (k(cat)/K(m)=667 mM(-1) s(-1)), TNA1_CP exhibited 80-fold lower catalytic efficiency. The enzyme showed broad substrate specificity with a preference for basic, aliphatic, and aromatic C-terminal amino acids. This broad specificity was confirmed by C-terminal ladder sequencing of porcine N-acetyl-renin substrate by TNA1_CP.

Amino Acid Motifs↗
PubMed1996

Evaluation of different amplification protocols for use in primer-extension preamplification.

Different amplification protocols were evaluated for use with primer-extension preamplification (PEP). We hypothesized that a protocol known to improve amplification of long DNA fragments would improve efficacy of PEP. Eight DNA samples were preamplified by PCR using different protocols. Treatments consisted of the use of Taq DNA polymerase (T), Taq plus a second polymerase obtained from Pyrococcus furiosus (E) or Stoffel fragment (S) in PEP. After preamplification, six genetic markers were genotyped, and the number of scorable genotypes was recorded. A control reaction (C) consisted of amplification using genomic DNA as template. A second experiment was performed to evaluate preamplification efficiency using Taq DNA polymerase (5 units) and exponential dilutions of Pfu DNA polymerase. After preamplification, the same procedure was used to obtain a number of scorable genotypes. In the first experiment, treatment E was the most reliable approach for amplifying genomic DNA in PEP. Treatments T and S produced fewer scorable genotypes than treatments E or C. In the second experiment, low concentrations of Pfu DNA polymerase produced a similar percentage of scorable genotypes as higher concentrations. Low concentrations of Pfu DNA polymerase combined with Taq DNA polymerase is the most cost-effective procedure to maximize amplification of limited DNA samples in PEP.

Animals↗
PubMed2002

Development of an ultrahigh-temperature process for the enzymatic hydrolysis of lactose. III. Utilization of two thermostable beta-glycosidases in a continuous ultrafiltration membrane reactor and galacto-oligosaccharide formation under steady-state conditions.

Hydrolysis of lactose by hyperthermophilic beta-glycosidases from the archaea Sulfolobus solfataricus (SsbetaGly) and Pyrococcus furiosus (CelB) was carried out at 70 degrees C in a continuous stirred-tank reactor (CSTR) coupled to a 10-kDa cross-flow ultrafiltration module to recycle the enzyme. Recirculation rates of > or =1 min(-1), reaction of proteins with reducing sugars, and enzyme adsorption onto the membrane are major "operational" factors of enzyme inactivation in the CSTR. They cause the half-life times of SsbetaGly and CelB to be reduced two- and eight-fold, respectively, the average value for both enzymes now being approximately 5 to 7 days. Using lactose at initial concentrations of 45 and 170 g/L, the CSTR was operated at a constant conversion level of approximately 80% for more than 2 weeks without the occurrence of microbial contamination. The productivities for the SsbetaGly-catalyzed conversion of lactose were determined at different dilution rates and initial substrate concentrations, and exceed by a factor of < or =2 those observed with CelB under otherwise identical conditions. This difference reflects the approximately eight-fold stronger product inhibition of CelB by D-glucose. While the maximum total galacto-oligosaccharide production (90-100 mM) at 170 g/L lactose in the CSTR was not different from that in the batch reactor (CelB) or was greater by approximately 25% (SsbetaGly), continuous and batchwise reactions with both enzymes differed markedly with regard to relative proportions of the individual saccharide components present at 80% substrate conversion. The CSTR yielded an up to four-fold greater ratio of disaccharides to trisaccharides concomitant with a 5- to 30-fold larger relative proportion of beta-D-Galp-(1-->3)-D-Glc in the product mixture. The results show that apart from continuous hydrolysis of lactose at 70 degrees C, a CSTR charged with SsbetaGly or CelB and operated at steady-state conditions could be a useful reaction system for the production of galacto-oligosaccharides in which composition is narrower and more easily programmable, in terms of the individual components contained, as compared to the batchwise reaction.

Bioreactors↗
PubMed1999

Cloning and Nucleotide Sequencing of Prolyl Endopeptidase Gene from Aeromonas punctata subsp. punctata.

Prolyl endopeptidase activity was found in Aeromonas punctata subsp. Punctata. The genomic DNA was partially digested with EcoRI and the recovered 8-16 kb DNA fragments were inserted into the EcoRI site of plasmid pUC19, and were transformated into Escherichia coli DH5alpha. The resulted clones were screened by using Benzyloxycarbonyl-Gly-Pro-beta-naphthylamide, the specific substrate of prolyl endopeptidase and a positive clone was obtained. The 12 kb insertion fragment of recombinant plasmid was digested with HincII and subcloned. The PEP gene was found in the 3.5 kb HincII/EcoRI fragment. Nucleotide sequence of the gene was completely sequenced by Auto Sequencer. The complete gene consisted of 2 073 bp corresponding to 690 amino acid residues with a calculated molecular weight of 76 467 Da. The amino acid sequence was 92.3% 53.2% 33.5% 33.2% and 20.5% homologous to those of Aeromonas hydrophila, Flavobacterium meningosepticum, porcine brain, human lymphocytes and Pyrococcus furiosus respectively. From a survey of sequence homology with other members of the prolyl endopeptidase family, the amino acid residues involved in the catalytic triad were deduced to be Ser(538) Asp(622) and His(657).

Journal Article↗
PubMed1995

Rapid differentiation of hyperthermophilic Archaea by restriction mapping of the intergenic spacer regions of the ribosomal RNA operons.

We report a sensitive and convenient method for rapid differentiation of new isolates of hyperthermophilic Archaea. Polymerase chain reaction (PCR) was used to amplify the intergenic spacer regions of the ribosomal RNA operons of eight Archaea. Spacer regions from one Euryarcheote, Pyrococcus furiosus, and one Crenarcheote, Pyrodictium brockii, were sequenced completely. Restriction fragment length polymorphism (RFLP) analyses were performed on the spacer regions from eight hyperthermophilic Archaea, and the restriction patterns were used as fingerprints for six known strains and two isolates. The PCR-RFLP method used in this study allowed the differentiation of seven of the eight strains tested and could be generally applicable to all the Archaea.

Archaea↗
PubMed1993

Characterization, cloning, and in vitro expression of the extremely thermostable glutamate dehydrogenase from the hyperthermophilic Archaeon, ES4.

Glutamate dehydrogenase (GDH) from the hyperthermophilic Archaeon ES4 (optimal growth temperature 98 degrees C and maximum growth temperature 110 degrees C) was purified to homogeneity. The purified native enzyme had an M(r) of 270,000 +/- 5,000 and was shown by gel filtration and SDS-polyacrylamide gel electrophoresis to be a hexamer with identical subunits of M(r) = 46,000 +/- 3,000. The hexameric subunit composition was also evident from electron micrographs, which show a triangular antiprism structure very similar to that of bovine GDH. The enzyme is exceptionally thermostable, with a half-time of inactivation of 3.5 h at 105 degrees C. Differential scanning calorimetry revealed a tm for denaturation of 113 degrees C, and a tm for activation at 60 degrees C. Antigenic cross-reaction with ES4 GDH was observed with the purified GDH from the thermophilic Archaea, Pyrococcus furiosus and Thermococcus litoralis as well as with bovine and yeast GDHs. The genome of ES4 was shown to contain a single copy of the gdhA gene, and this was cloned and sequenced. The deduced amino acid sequence of the GDH from ES4 corresponded to the NH2-terminal amino acid sequence obtained from the pure protein. From the nucleotide sequence the ES4 protein is composed of 420 residues. It has a relatively high hydrophobicity and a low number of sulfur-containing residues compared with mesophilic GDHs. Relatively high homology (52%) exists between the deduced amino acid sequence of ES4 GDH and Clostridium difficile GDH. Of the two distinct families of GDH sequences known, ES4 GDH belongs to the same family as vertebrates, C. difficile, and other Archaea. The gdhA gene of ES4 was expressed in vitro in a rabbit reticulocyte cell-free lysate, thus providing a system for structural studies of the mechanisms of thermostability in hyper-thermophilic proteins.

Amino Acid Sequence↗