Characterization of Di-myo-Inositol-1,1(prm1)-Phosphate in the Hyperthermophilic Bacterium Thermotoga maritima

Characterizing osmolyte chemical class hierarchies and functional group requirements for thermal stabilization of proteins

Osmolytes are naturally occurring organic compounds that protect cellular proteins and other macromolecules against various forms of stress including temperature extremes. While biological studies have correlated the accumulation of certain classes of osmolytes with specific forms of stress, including thermal stress, it remains unclear whether or not these observations reflect an intrinsic chemical class hierarchy amongst the osmolytes with respect to effects on protein stability. In addition, very little is known in regards to the molecular elements of the osmolytes themselves that are essential for their functions. In this study, we use differential scanning fluorimetry to quantify the thermal stabilizing effects of members from each of the three main classes of protecting osmolytes on two model protein systems, C-reactive protein and tumor necrosis factor alpha. Our data reveals the absence of a strict chemical class hierarchy amongst the osmolytes with respect to protein thermal stabilization, and indicates differential responses of these proteins to certain osmolytes. In the second part of this investigation we dissected the molecular elements of amino acid osmolytes required for thermal stabilization of myoglobin and C-reactive protein. We show that the complete amino acid zwitterion is required for thermal stabilization of myoglobin, whereas removal of the osmolyte amino group does not diminish stabilizing effects on C-reactive protein. These disparate responses of proteins to osmolytes and other small molecules are consistent with previous observations that osmolyte effects on protein stability are protein-specific. Moreover, the data reported in this study support the view that osmolyte effects cannot be fully explained by considering only the solvent accessibility of the polypeptide backbone in the native and denatured states, and corroborate the need for more complex models that take into account the entire protein fabric.

Combined transcriptomics-metabolomics profiling of the heat shock response in the hyperthermophilic archaeon Pyrococcus furiosus

Pyrococcus furiosus is a remarkable archaeon able to grow at temperatures around 100 °C. To gain insight into how this model hyperthermophile copes with heat stress, we compared transcriptomic and metabolomic data of cells subjected to a temperature shift from 90 °C to 97 °C. In this study, we used RNA-sequencing to characterize the global variation in gene expression levels, while nuclear magnetic resonance (NMR) and targeted ion exchange liquid chromatography-mass spectrometry (LC-MS) were used to determine changes in metabolite levels. Of the 552 differentially expressed genes in response to heat shock conditions, 257 were upregulated and 295 were downregulated. In particular, there was a significant downregulation of genes for synthesis and transport of amino acids. At the metabolite level, 37 compounds were quantified. The level of di-myo-inositol phosphate, a canonical heat stress solute among marine hyperthermophiles, increased considerably (5.4-fold) at elevated temperature. Also, the levels of mannosylglycerate, UDP-N-acetylglucosamine (UDPGlcNac) and UDP-N-acetylgalactosamine were enhanced. The increase in the pool of UDPGlcNac was concurrent with an increase in the transcript levels of the respective biosynthetic genes. This work provides the first metabolomic analysis of the heat shock response of a hyperthermophile.

Thermococcus kodakarensis mutants deficient in di-myo-inositol phosphate use aspartate to cope with heat stress

Many of the marine microorganisms which are adapted to grow at temperatures above 80 degrees C accumulate di-myo-inositol phosphate (DIP) in response to heat stress. This led to the hypothesis that the solute plays a role in thermoprotection, but there is a lack of definitive experimental evidence. Mutant strains of Thermococcus kodakarensis (formerly Thermococcus kodakaraensis), manipulated in their ability to synthesize DIP, were constructed and used to investigate the involvement of DIP in thermoadaptation of this archaeon. The solute pool of the parental strain comprised DIP, aspartate, and alpha-glutamate. Under heat stress the level of DIP increased 20-fold compared to optimal conditions, whereas the pool of aspartate increased 4.3-fold in response to osmotic stress. Deleting the gene encoding the key enzyme in DIP synthesis, CTP:inositol-1-phosphate cytidylyltransferase/CDP-inositol:inositol-1-phosphate transferase, abolished DIP synthesis. Conversely, overexpression of the same gene resulted in a mutant with restored ability to synthesize DIP. Despite the absence of DIP in the deletion mutant, this strain exhibited growth parameters similar to those of the parental strain, both at optimal (85 degrees C) and supraoptimal (93.7 degrees C) temperatures for growth. Analysis of the respective solute pools showed that DIP was replaced by aspartate. We conclude that DIP is part of the strategy used by T. kodakarensis to cope with heat stress, and aspartate can be used as an alternative solute of similar efficacy. This is the first study using mutants to demonstrate the involvement of compatible solutes in the thermoadaptation of (hyper)thermophilic organisms.

Di-myo-inositol phosphate and novel UDP-sugars accumulate in the extreme hyperthermophile Pyrolobus fumarii

The archaeon Pyrolobus fumarii, one of the most extreme members of hyperthermophiles known thus far, is able to grow at temperatures up to 113 degrees C. Over a decade after the description of this organism our knowledge about the structures and strategies underlying its remarkable thermal resistance remains incipient. The accumulation of a restricted number of charged organic solutes is a common response to heat stress in hyperthermophilic organisms and accordingly their role in thermoprotection has been often postulated. In this work, the organic solute pool of P. fumarii was characterized using 1H, 13C, and 31P NMR. Di-myo-inositol phosphate was the major solute (0.21 micromol/mg protein), reinforcing the correlation between the occurrence of this solute and hyperthermophily; in addition, UDP-sugars (total concentration 0.11 micromol/mg protein) were present. The structures of the two major UDP-sugars were identified as UDP-alpha-GlcNAc3NAc and UDP-alpha-GlcNAc3NAc-(4<--1)-beta-GlcpNAc3NAc. Interestingly, the latter compound appears to be derived from the first one by addition of a 2,3-N-acetylglucoronic acid unit, suggesting that these UDP-sugars are intermediates of an N-linked glycosylation pathway. To our knowledge the UDP-disaccharide has not been reported elsewhere. The physiological roles of these organic solutes are discussed.

Bifunctional CTP:inositol-1-phosphate cytidylyltransferase/CDP-inositol:inositol-1-phosphate transferase, the key enzyme for di-myo-inositol-phosphate synthesis in several (hyper)thermophiles

The pathway for the synthesis of di-myo-inositol-phosphate (DIP) was recently elucidated on the basis of the detection of the relevant activities in cell extracts of Archaeoglobus fulgidus and structural characterization of products by nuclear magnetic resonance (NMR) (N. Borges, L. G. Gonçalves, M. V. Rodrigues, F. Siopa, R. Ventura, C. Maycock, P. Lamosa, and H. Santos, J. Bacteriol. 188:8128-8135, 2006). Here, a genomic approach was used to identify the genes involved in the synthesis of DIP. Cloning and expression in Escherichia coli of the putative genes for CTP:l-myo-inositol-1-phosphate cytidylyltransferase and DIPP (di-myo-inositol-1,3'-phosphate-1'-phosphate, a phosphorylated form of DIP) synthase from several (hyper)thermophiles (A. fulgidus, Pyrococcus furiosus, Thermococcus kodakaraensis, Aquifex aeolicus, and Rubrobacter xylanophilus) confirmed the presence of those activities in the gene products. The DIPP synthase activity was part of a bifunctional enzyme that catalyzed the condensation of CTP and l-myo-inositol-1-phosphate into CDP-l-myo-inositol, as well as the synthesis of DIPP from CDP-l-myo-inositol and l-myo-inositol-1-phosphate. The cytidylyltransferase was absolutely specific for CTP and l-myo-inositol-1-P; the DIPP synthase domain used only l-myo-inositol-1-phosphate as an alcohol acceptor, but CDP-glycerol, as well as CDP-l-myo-inositol and CDP-d-myo-inositol, were recognized as alcohol donors. Genome analysis showed homologous genes in all organisms known to accumulate DIP and for which genome sequences were available. In most cases, the two activities (l-myo-inositol-1-P cytidylyltransferase and DIPP synthase) were fused in a single gene product, but separate genes were predicted in Aeropyrum pernix, Thermotoga maritima, and Hyperthermus butylicus. Additionally, using l-myo-inositol-1-phosphate labeled on C-1 with carbon 13, the stereochemical configuration of all the metabolites involved in DIP synthesis was established by NMR analysis. The two inositol moieties in DIP had different stereochemical configurations, in contradiction of previous reports. The use of the designation di-myo-inositol-1,3'-phosphate is recommended to facilitate tracing individual carbon atoms through metabolic pathways.

Biosynthetic pathways of inositol and glycerol phosphodiesters used by the hyperthermophile Archaeoglobus fulgidus in stress adaptation

Archaeoglobus fulgidus accumulates di-myo-inositol phosphate (DIP) and diglycerol phosphate (DGP) in response to heat and osmotic stresses, respectively, and the level of glycero-phospho-myo-inositol (GPI) increases primarily when the two stresses are combined. In this work, the pathways for the biosynthesis of these three compatible solutes were established based on the detection of the relevant enzymatic activities and characterization of the intermediate metabolites by nuclear magnetic resonance analysis. The synthesis of DIP proceeds from glucose-6-phosphate via four steps: (i) glucose-6-phosphate was converted into l-myo-inositol 1-phosphate by l-myo-inositol 1-phosphate synthase; (ii) l-myo-inositol 1-phosphate was activated to CDP-inositol at the expense of CTP; this is the first demonstration of CDP-inositol synthesis in a biological system; (iii) CDP-inositol was coupled with l-myo-inositol 1-phosphate to yield a phosphorylated intermediate, 1,1'-di-myo-inosityl phosphate 3-phosphate (DIPP); (iv) finally, DIPP was dephosphorylated into DIP by the action of a phosphatase. The synthesis of the two other polyol-phosphodiesters, DGP and GPI, proceeds via the condensation of CDP-glycerol with the respective phosphorylated polyol, glycerol 3-phosphate for DGP and l-myo-inositol 1-phosphate for GPI, yielding the respective phosphorylated intermediates, 1X,1'X-diglyceryl phosphate 3-phosphate (DGPP) and 1-(1X-glyceryl) myo-inosityl phosphate 3-phosphate (GPIP), which are subsequently dephosphorylated to form the final products. The results disclosed here represent an important step toward the elucidation of the regulatory mechanisms underlying the differential accumulation of these compounds in response to heat and osmotic stresses.

Genomics-based design of defined growth media for the plant pathogen Xylella fastidiosa

Based on the genetic analysis of the phytopathogen Xylella fastidiosa genome, five media with defined composition were developed and the growth abilities of this fastidious prokaryote were evaluated in liquid media and on solid plates. All media had a common salt composition and included the same amounts of glucose and vitamins but differed in their amino acid content. XDM(1) medium contained amino acids threonine, serine, glycine, alanine, aspartic acid and glutamic acid, for which complete degradation pathways occur in X. fastidiosa; XDM(2) included serine and methionine, amino acids for which biosynthetic enzymes are absent, plus asparagine and glutamine, which are abundant in the xylem sap; XDM(3) had the same composition as XDM(2) but with asparagine replaced by aspartic acid due to the presence of complete degradation pathway for aspartic acid; XDM(4) was a minimal medium with glutamine as a sole nitrogen source; XDM(5) had the same composition as XDM(4), plus methionine. The liquid and solidified XDM(2) and XDM(3) media were the most effective for the growth of X. fastidiosa. This work opens the opportunity for the in silico design of bacterial defined media once their genome is sequenced.

Compatible solutes of organisms that live in hot saline environments

The accumulation of organic solutes is a prerequisite for osmotic adjustment of all microorganisms. Thermophilic and hyperthermophilic organisms generally accumulate very unusual compatible solutes namely, di-myo-inositol-phosphate, di-mannosyl-di-myo-inositol-phosphate, di-glycerol-phosphate, mannosylglycerate and mannosylglyceramide, which have not been identified in bacteria or archaea that grow at low and moderate temperatures. There is also a growing awareness that some of these compatible solutes may have a role in the protection of cell components against thermal denaturation. Mannosylglycerate and di-glycerol-phosphate have been shown to protect enzymes and proteins from thermal denaturation in vitro as well, or better, than compatible solutes from mesophiles. The pathways leading to the synthesis of some of these compatible solutes from thermophiles and hyperthermophiles have been elucidated. However, large numbers of questions remain unanswered. Fundamental and applied interest in compatible -solutes and osmotic adjustment in these organisms, drives research that, will, in the near future, allow us to understand the role of compatible solutes in osmotic protection and thermoprotection of some of the most fascinating organisms known on Earth.

Purification and characterization of a cobalt-activated carboxypeptidase from the hyperthermophilic archaeon Pyrococcus furiosus

A novel metallocarboxypeptidase (PfuCP) has been purified to homogeneity from the hyperthermophilic archaeon, Pyrococcus furiosus, with its intended use in C-terminal ladder sequencing of proteins and peptides at elevated temperatures. PfuCP was purified in its inactive state by the addition of ethylenediaminetetraacetic acid (EDTA) and dithiothreitol (DTT) to purification buffers, and the activity was restored by the addition of divalent cobalt (K, = 24 +/- 4 microM at 80 degrees C). The serine protease inhibitor phenylmethylsulfonyl fluoride (PMSF) had no effect on the activity. The molecular mass of monomeric PfuCP is 59 kDa as determined by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) and 58 kDa by SDS-PAGE analysis. In solution, PfuCP exists as a homodimer of approximately 128 kDa as determined by gel filtration chromatography. The activity of PfuCP exhibits a temperature optimum exceeding 90 degrees C under ambient pressure, and a narrow pH optimum of 6.2-6.6. Addition of Co2+ to the apoPfuCP at room temperature does not alter its far-UV circular dichroism (CD) or its intrinsic fluorescence spectrum. Even when the CoPfuCP is heated to 80 degrees C, its far-UV CD shows a minimal change in the global conformation and the intrinsic fluorescence of aromatic residues shows only a partial quenching. Changes in the intrinsic fluorescence appear essentially reversible with temperature. Finally, the far-UV CD and intrinsic fluorescence data suggest that the overall structure of the holoenzyme is extremely thermostable. However, the activities of both the apo and holo enzyme exhibit a similar second-order decay over time, with 50% activity remaining after approximately 40 min at 80 degrees C. The N-blocked synthetic dipeptide, N-carbobenzoxy-Ala-Arg (ZAR), was used in the purification assay. The kinetic parameters at 80 degrees C with 0.4 mM CoCl2 were: Km, 0.9 +/- 0.1 mM; Vmax, 2,300 +/- 70 U mg(-1); and turn over number, 600 +/- 20 s(-1). Activity against other ZAX substrates (X = V, L, I, M, W, Y, F, N, A, S, H, K) revealed a broad specificity for neutral, aromatic, polar, and basic C-terminal residues. This broad specificity was confirmed by the C-terminal ladder sequencing of several synthetic and natural peptides, including porcine N-acetyl-renin substrate, for which we have observed (by MALDI-TOF MS) stepwise hydrolysis by PfuCP of up to seven residues from the C-terminus: Ac-Asp-Arg-Val-Tyr-Ile-His-Pro-Phe-His-Leu-Leu-Val-Tyr-Ser.

Characterization of a tetrameric inositol monophosphatase from the hyperthermophilic bacterium Thermotoga maritima

Inositol monophosphatase (I-1-Pase) catalyzes the dephosphorylation step in the de novo biosynthetic pathway of inositol and is crucial for all inositol-dependent processes. An extremely heat-stable tetrameric form of I-1-Pase from the hyperthermophilic bacterium Thermotoga maritima was overexpressed in Escherichia coli. In addition to its different quaternary structure (all other known I-1-Pases are dimers), this enzyme displayed a 20-fold higher rate of hydrolysis of D-inositol 1-phosphate than of the L isomer. The homogeneous recombinant T. maritima I-1-Pase (containing 256 amino acids with a subunit molecular mass of 28 kDa) possessed an unusually high V(max) (442 micromol min(-1) mg(-1)) that was much higher than the V(max) of the same enzyme from another hyperthermophile, Methanococcus jannaschii. Although T. maritima is a eubacterium, its I-1-Pase is more similar to archaeal I-1-Pases than to the other known bacterial or mammalian I-1-Pases with respect to substrate specificity, Li(+) inhibition, inhibition by high Mg(2+) concentrations, metal ion activation, heat stability, and activation energy. Possible reasons for the observed kinetic differences are discussed based on an active site sequence alignment of the human and T. maritima I-1-Pases.

Instability, stabilization, and formulation of liquid protein pharmaceuticals

One of the most challenging tasks in the development of protein pharmaceuticals is to deal with physical and chemical instabilities of proteins. Protein instability is one of the major reasons why protein pharmaceuticals are administered traditionally through injection rather than taken orally like most small chemical drugs. Protein pharmaceuticals usually have to be stored under cold conditions or freeze-dried to achieve an acceptable shelf life. To understand and maximize the stability of protein pharmaceuticals or any other usable proteins such as catalytic enzymes, many studies have been conducted, especially in the past two decades. These studies have covered many areas such as protein folding and unfolding/denaturation, mechanisms of chemical and physical instabilities of proteins, and various means of stabilizing proteins in aqueous or solid state and under various processing conditions such as freeze-thawing and drying. This article reviews these investigations and achievements in recent years and discusses the basic behavior of proteins, their instabilities, and stabilization in aqueous state in relation to the development of liquid protein pharmaceuticals.

Influence of polymolecular events on inactivation behavior of xylose isomerase from Thermotoga neapolitana 5068

The inactivation behavior of the xylose isomerase from Thermotoga neapolitana (TN5068 XI) was examined for both the soluble and immobilized enzyme. Polymolecular events were involved in the deactivation of the soluble enzyme. Inactivation was biphasic at 95 degrees C, pH 7.0 and 7.9, the second phase was concentration-dependent. The enzyme was most stable at low enzyme concentrations, however, the second phase of inactivation was 3- to 30-fold slower than the initial phase. Both phases of inactivation were more rapid at pH 7.9, relative to 7.0. Differential scanning calorimetry of the TN5068 XI revealed two distinct thermal transitions at 99 degrees and 109 degrees C. The relative magnitude of the second transition was dramatically reduced at pH 7.9 relative to pH 7.0. Approximately 24% and 11% activity were recoverable after the first transition at pH 7.0 and 7.9, respectively. When the TN5068 XI was immobilized by covalent attachment to glass beads, inactivation was monophasic with a rate corresponding to the initial phase of inactivation for the soluble enzyme. The immobilized enzyme inactivation rate corresponded closely to the rate of ammonia release, presumably from deamidation of labile asparagine and/or glutamine residues. A second, slower inactivation phase suggests the presence of an unfolding intermediate, which was not observed for the immobilized enzyme. The concentration dependence of the second phase of inactivation suggests that polymolecular events were involved. Formation of a reversible polymolecular aggregate capable of protecting the soluble enzyme from irreversible deactivation appears to be responsible for the second phase of inactivation seen for the soluble enzyme. Whether this characteristic is common to other hyperthermophilic enzymes remains to be seen.

Purification and molecular characterization of the tungsten-containing formaldehyde ferredoxin oxidoreductase from the hyperthermophilic archaeon Pyrococcus furiosus: the third of a putative five-member tungstoenzyme family

Pyrococcus furiosus is a hyperthermophilic archaeon which grows optimally near 100 degreesC by fermenting peptides and sugars to produce organic acids, CO2, and H2. Its growth requires tungsten, and two different tungsten-containing enzymes, aldehyde ferredoxin oxidoreductase (AOR) and glyceraldehyde-3-phosphate ferredoxin oxidoreductase (GAPOR), have been previously purified from P. furiosus. These two enzymes are thought to function in the metabolism of peptides and carbohydrates, respectively. A third type of tungsten-containing enzyme, formaldehyde ferredoxin oxidoreductase (FOR), has now been characterized. FOR is a homotetramer with a mass of 280 kDa and contains approximately 1 W atom, 4 Fe atoms, and 1 Ca atom per subunit, together with a pterin cofactor. The low recovery of FOR activity during purification was attributed to loss of sulfide, since the purified enzyme was activated up to fivefold by treatment with sulfide (HS-) under reducing conditions. FOR uses P. furiosus ferredoxin as an electron acceptor (Km = 100 microM) and oxidizes a range of aldehydes. Formaldehyde (Km = 15 mM for the sulfide-activated enzyme) was used in routine assays, but the physiological substrate is thought to be an aliphatic C5 semi- or dialdehyde, e.g., glutaric dialdehyde (Km = 1 mM). Based on its amino-terminal sequence, the gene encoding FOR (for) was identified in the genomic database, together with those encoding AOR and GAPOR. The amino acid sequence of FOR corresponded to a mass of 68.7 kDa and is highly similar to those of the subunits of AOR (61% similarity and 40% identity) and GAPOR (50% similarity and 23% identity). The three genes are not linked on the P. furiosus chromosome. Two additional (and nonlinked) genes (termed wor4 and wor5) that encode putative tungstoenzymes with 57% (WOR4) and 56% (WOR5) sequence similarity to FOR were also identified. Based on sequence motif similarities with FOR, both WOR4 and WOR5 are also proposed to contain a tungstobispterin site and one [4Fe-4S] cluster per subunit.

Cloning, sequencing, and expression of the gene encoding cyclic 2, 3-diphosphoglycerate synthetase, the key enzyme of cyclic 2, 3-diphosphoglycerate metabolism in Methanothermus fervidus

Cyclic 2,3-diphosphoglycerate synthetase (cDPGS) catalyzes the synthesis of cyclic 2,3-diphosphoglycerate (cDPG) by formation of an intramolecular phosphoanhydride bond in 2,3-diphosphoglycerate. cDPG is known to be accumulated to high intracellular concentrations (>300 mM) as a putative thermoadapter in some hyperthermophilic methanogens. For the first time, we have purified active cDPGS from a methanogen, the hyperthermophilic archaeon Methanothermus fervidus, sequenced the coding gene, and expressed it in Escherichia coli. cDPGS purification resulted in enzyme preparations containing two isoforms differing in their electrophoretic mobility under denaturing conditions. Since both polypeptides showed the same N-terminal amino acid sequence and Southern analyses indicate the presence of only one gene coding for cDPGS in M. fervidus, the two polypeptides originate from the same gene but differ by a not yet identified modification. The native cDPGS represents a dimer with an apparent molecular mass of 112 kDa and catalyzes the reversible formation of the intramolecular phosphoanhydride bond at the expense of ATP. The enzyme shows a clear preference for the synthetic reaction: the substrate affinity and the Vmax of the synthetic reaction are a factor of 8 to 10 higher than the corresponding values for the reverse reaction. Comparison with the kinetic properties of the electrophoretically homogeneous, apparently unmodified recombinant enzyme from E. coli revealed a twofold-higher Vmax of the enzyme from M. fervidus in the synthesizing direction.

Cloning and expression of the inositol monophosphatase gene from Methanococcus jannaschii and characterization of the enzyme

Inositol monophosphatase (EC 3.1.3.25) plays a pivotal role in the biosynthesis of di-myo-inositol-1,1'-phosphate, an osmolyte found in hyperthermophilic archaeal. Given the sequence homology between the MJ109 gene product of Methanococcus jannaschii and human inositol monophosphatase, the MJ109 gene was cloned and expressed in Escherichia coli and examined for inositol monophosphatase activity. The purified MJ109 gene product showed inositol monophosphatase activity with kinetic parameters (K(m) = 0.091 +/- 0.016 mM; Vmax = 9.3 +/- 0.45 mumol of Pi min-1 mg of protein-1) comparable to those of mammalian and E. coli enzymes. Its substrate specificity, Mg2+ requirement, Li+ inhibition, subunit association (dimerization), and heat stability were studied and compared to those of other inositol monophosphatases. The lack of inhibition by low concentrations of Li+ and high concentrations of Mg2+ and the high rates of hydrolysis of glucose-1-phosphate and p-nitrophenylphosphate are the most pronounced differences between the archaeal inositol monophosphatase and those from other sources. The possible causes of these kinetic differences are discussed, based on the active site sequence alignment between M. jannaschii and human inositol monophosphatase and the crystal structure of the mammalian enzyme.

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.

Characterization of UDP amino sugars as major phosphocompounds in the hyperthermophilic archaeon Pyrococcus furiosus

The archaeon Pyrococcus furiosus is a strictly anaerobic heterotroph that grows optimally at 100 degrees C by the fermentation of carbohydrates. It is known to contain high concentrations of novel intracellular solutes such as beta-mannosylglycerate and di-myo-inositol 1,1'-phosphate (DIP) (L. O. Martins and H. Santos, Appl. Environ. Microbiol. 61:3299-3303, 1995). Here, 31P nuclear magnetic resonance (NMR) spectroscopy was used to show that this organism also accumulates another type of phospho compound, as revealed by a major multiplet signal in the pyrophosphate region. The compounds were purified from cell extracts of P. furiosus by anion-exchange and gel filtration chromatographic procedures and were structurally analyzed by 1H, 13C, and 31P NMR spectroscopy. They were identified as two uridylated amino sugars, UDP N-acetylglucosamine and UDP N-acetylgalactosamine. Unambiguous characterizations and complete assignments of 1H and 13C resonances from such sugars have not been previously reported. In vitro 31P NMR spectroscopic analyses showed that, in contrast to DIP, which is maintained at a constant intracellular concentration (approximately 32 mM) throughout the growth phase of P. furiosus, the UDP amino sugars accumulated (to approximately 14 mM) only during the late log phase. The possible biochemical roles of these compounds in P. furiosus are discussed.