Glycerol protection and purification of Bacillus subtilis glucose dehydrogenase

Fluorescence Anisotropy Assay with Guanine Nucleotides Provides Access to Functional Analysis of Gαi1 Proteins

Gα proteins as part of heterotrimeric G proteins are molecular switches essential for G protein-coupled receptor- mediated intracellular signaling. The role of the Gα subunits has been examined for decades with various guanine nucleotides to elucidate the activation mechanism and Gα protein-dependent signal transduction. Several approaches describe fluorescent ligands mimicking the GTP function, yet lack the efficient estimation of the proteins' GTP binding activity and the fraction of active protein. Herein, we report the development of a reliable fluorescence anisotropy-based method to determine the affinity of ligands at the GTP-binding site and to quantify the fraction of active Gαi1 protein. An advanced bacterial expression protocol was applied to produce active human Gαi1 protein, whose GTP binding capability was determined with novel fluorescently labeled guanine nucleotides acting as high-affinity Gαi1 binders compared to the commonly used BODIPY FL GTPγS. This study thus contributes a new method for future investigations of the characterization of Gαi and other Gα protein subunits, exploring their corresponding signal transduction systems and potential for biomedical applications.

NAD(P)-dependent glucose dehydrogenase: Applications for biosensors, bioelectrodes, and biofuel cells

This review discusses the physical and chemical properties of nicotinamide redox cofactor dependent glucose dehydrogenase (NAD(P) dependent GDH) and its extensive application in biosensors and bio-fuel cells. GDHs from different organisms show diverse biochemical properties (e.g., activity and stability) and preferences towards cofactors, such as nicotinamide adenine dinucleotide (NAD⁺) and nicotinamide adenine dinucleotide phosphate (NADP⁺). The (NAD(P)⁺) play important roles in biological electron transfer, however, there are some difficulties related to their application in devices that originate from their chemical properties and labile binding to the GDH enzyme. This review discusses the electrode modifications aimed at immobilising NAD⁺ or NADP⁺ cofactors and GDH at electrodes. Binding of the enzyme was achieved by appropriate protein engineering techniques, including polymerisation, hydrophobisation or hydrophilisation processes. Various enzyme-modified electrodes applied in biosensors, enzymatic fuel cells, and biobatteries are compared. Importantly, GDH can operate alone or as part of an enzymatic cascade, which often improves the functional parameters of the biofuel cell or simply allows use of cheaper fuels. Overall, this review explores how NAD(P)-dependent GDH has recently demonstrated high potential for use in various systems to generate electricity from biological sources for applications in implantable biomedical devices, wireless sensors, and portable electronic devices.

Characterization and Application of a Robust Glucose Dehydrogenase from Paenibacillus pini for Cofactor Regeneration in Biocatalysis

Glucose dehydrogenases are important auxiliary enzymes in biocatalysis, employed in the regeneration of reduced nicotinamide cofactors for oxidoreductase catalysed reactions. Here we report the identification and characterization of a novel glucose-1-dehydrogenase (GDH) from Paenibacillus pini that prefers NAD⁺ as cofactor over NADP⁺. The purified recombinant P. pini GDH displayed a specific activity of 247.5 U/mg. The enzyme was stable in the pH range 4-8.5 and exhibited excellent thermostability till 50 °C for 24 h, even in the absence of NaCl or glycerol. Paenibacillus pini GDH was also tolerant to organic solvents, demonstrating its potential for recycling cofactors for biotransformation. The potential application of the enzyme was evaluated by coupling with a NAD⁺-dependent alcohol dehydrogenase for the reduction of acetophenone and ethyl-4-chloro-3-oxo-butanoate. Conversions higher than 95% were achieved within 2 h with low enzyme loading using lyophilized cell lysate, suggesting that P. pini GDH could be highly effective for recycling NADH in redox biocatalysis.

Discovery and evaluation of inhibitory activity and mechanism of arylcoumarin derivatives on Theileria annulata enolase by in vitro and molecular docking studies

In this study, the inhibition potential of 3- and 4-arylcoumarin derivatives on Theileria annulata enolase (TaENO) was assessed for the first time in the literature. Firstly, protein stabilization analyses of TaENO were performed and it was found that the enzyme remains stable with the addition of 6 M ethylene glycol at + 4 °C. Inhibitor screening analyses were carried out using 25 coumarin derivatives on highly purified TaENO (> 95%), and four coumarin derivatives [4-(3,4-dimethoxyphenyl)-6,7-dihydroxy-2H-chromen-2-one (C8); 4-(3,4-dihydroxyphenyl)-7,8 dihydroxy-2H-chromen-2-one (C9); 4-(3,4-dihydroxyphenyl)-6,7-dihydroxy-2H-chromen-2 one (C21); and 3-(3,4-dihydroxyphenyl)-7,8-dihydroxy-2H-chromen-2-one (C23)] showed the highest inhibitory effects with the IC₅₀ values of 10.450, 13.170, 8.871 and 10.863 µM, respectively. The kinetic results indicated that these compounds inhibited the enzyme by uncompetitive inhibition. In addition, the successful binding of the most potent inhibitor (C21) into TaENO was confirmed by using MALDI-TOF mass spectrophotometry. Molecular docking analyses have predicted that C8 and C21 coumarin derivatives which showed high inhibitory effects on TaENO were interacted with high affinity to the potential regions out of the active site. Taken together, these coumarin derivatives (C8, C9, C21 and C23) are first known potent, nonsubstrate, uncompetitive inhibitors of TaENO and these results will facilitate further in vitro and in vivo analysis toward structure-based drug design studies.

An enzyme-modified capillary as a platform for simultaneous fluorometric detection of d-glucose and l- lactate

The preparation of a glass capillary pattered with lipid layers　on which lactate dehydrogenase (LDH) and glucose dehydrogenase (GDH) were regionally adsorbed and its application for simultaneous detection of d-glucose and l-lactate in human serum is described. A lipid layer was formed on the surface of BSA-unabsorbed octadecyltrichlorosilane (OTS) inner wall of a glass capillary. The electrostatic charge of the lipid layer was a key factor for adsorbing the enzymes on the lipid layer. The fluorescence intensities were observed at each enzyme site in the presence of diaphorase (DIA), β-nicotinamide-adenine dinucleotide oxidized (NAD), resazurin, d-glucose and l-lactate. The fluorescence intensities at each enzyme site increased with an increase in the concentration of d-glucose and l-lactate=with the detection limits of 32 μM and 4.9 μM, respectively.

Biochemical and Computational Insights on a Novel Acid-Resistant and Thermal-Stable Glucose 1-Dehydrogenase

Due to the dual cofactor specificity, glucose 1-dehydrogenase (GDH) has been considered as a promising alternative for coenzyme regeneration in biocatalysis. To mine for potential GDHs for practical applications, several genes encoding for GDH had been heterogeneously expressed in Escherichia coli BL21 (DE3) for primary screening. Of all the candidates, GDH from Bacillus sp. ZJ (BzGDH) was one of the most robust enzymes. BzGDH was then purified to homogeneity by immobilized metal affinity chromatography and characterized biochemically. It displayed maximum activity at 45 °C and pH 9.0, and was stable at temperatures below 50 °C. BzGDH also exhibited a broad pH stability, especially in the acidic region, which could maintain around 80% of its initial activity at the pH range of 4.0–8.5 after incubating for 1 hour. Molecular dynamics simulation was conducted for better understanding the stability feature of BzGDH against the structural context. The in-silico simulation shows that BzGDH is stable and can maintain its overall structure against heat during the simulation at 323 K, which is consistent with the biochemical studies. In brief, the robust stability of BzGDH made it an attractive participant for cofactor regeneration on practical applications, especially for the catalysis implemented in acidic pH and high temperature.

Controlling Central Carbon Metabolism for Improved Pathway Yields in Saccharomyces cerevisiae

Engineering control of metabolic pathways is important to improving product titers and yields. Traditional methods such as overexpressing pathway enzymes and deleting competing ones are restricted by the interdependence of metabolic reactions and the finite nature of cellular resources. Here, we developed a metabolite valve that controls glycolytic flux through central carbon metabolism in Saccharomyces cerevisiae. In a Hexokinase 2 and Glucokinase 1 deleted strain (hxk2Δglk1Δ), glucose flux was diverted away from glycolysis and into a model pathway, gluconate, by controlling the transcription of Hexokinase 1 with the tetracycline transactivator protein (tTA). A maximum 10-fold decrease in hexokinase activity resulted in a 50-fold increase in gluconate yields, from 0.7% to 36% mol/mol of glucose. The reduction in glucose flux resulted in a significant decrease in ethanol byproduction that extended to semianaerobic conditions, as shown in the production of isobutanol. This proof-of-concept is one of the first demonstrations in S. cerevisiae of dynamic redirection of glucose from glycolysis and into a heterologous pathway.

Kinetic properties and stability of glucose dehydrogenase from Bacillus amyloliquefaciens SB5 and its potential for cofactor regeneration

Glucose dehydrogenases (GluDH) from Bacillus species offer several advantages over other NAD(P)H regeneration systems including high stability, inexpensive substrate, thermodynamically favorable reaction and flexibility to regenerate both NADH and NADPH. In this research, characteristics of GluDH from Bacillus amyloliquefaciens SB5 (GluDH-BA) was reported for the first time. Despite a highly similar amino acid sequence when comparing with GluDH from Bacillus subtilis (GluDH-BS), GluDH-BA exhibited significantly higher specific activity (4.7-fold) and stability when pH was higher than 6. While an optimum activity of GluDH-BA was observed at a temperature of 50 °C, the enzyme was stable only up to 42 °C. GluDH-BA exhibited an extreme tolerance towards n-hexane and its respective alcohols. The productivity of GluDH obtained in this study (8.42 mg-GluDH/g-wet cells; 1035 U/g-wet cells) was among the highest productivity reported for recombinant E. coli. With its low K_M-value towards glucose (5.5 mM) and NADP⁺ (0.05 mM), GluDH-BA was highly suitable for in vivo applications. In this work, a recombinant solvent-tolerant B. subtilis BA overexpressing GluDH-BA was developed and evaluated by coupling with B. subtilis overexpressing an enzyme P450 BM3 F87V for a whole-cell hydroxylation of n-hexane. Significantly higher products obtained clearly proved that B. subtilis BA was an effective cofactor regenerator, a valuable asset for bioproduction of value-added chemicals.

Functional expression of L-lysine α-oxidase from Scomber japonicus in Escherichia coli for one-pot synthesis of L-pipecolic acid from DL-lysine

L-Pipecolic acid is a key component of biologically active molecules and a pharmaceutically important chiral building block. It can be stereoselectively produced from L-lysine by a two-step bioconversion involving L-lysine α-oxidase and ∆(1)-piperideine-2-carboxylae (Pip2C) reductase. In this study, we focused on an L-lysine α-oxidase from Scomber japonicus that was originally identified as an apoptosis-inducing protein (AIP) and applied the enzyme to one-pot fermentation of L-pipecolic acid in Escherichia coli. A synthetic gene coding for an AIP was expressed in E. coli, and the recombinant enzyme was purified and characterized. The purified enzyme was determined to be a homodimer with a molecular mass of 133.9 kDa. The enzyme essentially exhibited the same substrate specificity as the native enzyme. Optimal temperature and pH for the enzymatic reaction were 70 °C and 7.4, respectively. The enzyme was stable below 60 °C and at a pH range of 5.5-7.5 but was markedly inhibited by Co(2+). To establish a one-pot fermentation system for the synthesis of optically pure L-pipecolic acid from DL-lysine, an E. coli strain carrying a plasmid encoding AIP, Pip2C reductase from Pseudomonas putida, lysine racemase from P. putida, and glucose dehydrogenase from Bacillus subtilis was constructed. The one-pot process produced 45.1 g/L of L-pipecolic acid (87.4 % yield from DL-lysine) after a 46-h reaction with high optical purity (>99.9 % enantiomeric excess).

Multi-enzymatic one-pot reduction of dehydrocholic acid to 12-keto-ursodeoxycholic acid with whole-cell biocatalysts

Ursodeoxycholic acid (UDCA) is a bile acid of industrial interest as it is used as an agent for the treatment of primary sclerosing cholangitis and the medicamentous, non-surgical dissolution of gallstones. Currently, it is prepared industrially from cholic acid following a seven-step chemical procedure with an overall yield of <30%. In this study, we investigated the key enzymatic steps in the chemo-enzymatic preparation of UDCA-the two-step reduction of dehydrocholic acid (DHCA) to 12-keto-ursodeoxycholic acid using a mutant of 7β-hydroxysteroid dehydrogenase (7β-HSDH) from Collinsella aerofaciens and 3α-hydroxysteroid dehydrogenase (3α-HSDH) from Comamonas testosteroni. Three different one-pot reaction approaches were investigated using whole-cell biocatalysts in simple batch processes. We applied one-biocatalyst systems, where 3α-HSDH, 7β-HSDH, and either a mutant of formate dehydrogenase (FDH) from Mycobacterium vaccae N10 or a glucose dehydrogenase (GDH) from Bacillus subtilis were expressed in a Escherichia coli BL21(DE3) based host strain. We also investigated two-biocatalyst systems, where 3α-HSDH and 7β-HSDH were expressed separately together with FDH enzymes for cofactor regeneration in two distinct E. coli hosts that were simultaneously applied in the one-pot reaction. The best result was achieved by the one-biocatalyst system with GDH for cofactor regeneration, which was able to completely convert 100 mM DHCA to >99.5 mM 12-keto-UDCA within 4.5 h in a simple batch process on a liter scale.

Cloning and expression in E. coli of an organic solvent-tolerant and alkali-resistant glucose 1-dehydrogenase from Lysinibacillus sphaericus G10

The gene gdh encoding an organic solvent-tolerant and alkaline-resistant NAD(P)-dependent glucose 1-dehydrogenase (LsGDH) was cloned from Lysinibacillus sphaericus G10 and expressed in Escherichia coli. The recombinant LsGDH exhibited maximum activity at pH 9.5 and 50 °C. LsGDH displayed high stability at a wide pH ranging from 6.5 to 10.0 and was stable after incubation at 30 °C for 1 week in 25 mM sodium phosphate buffer (pH 6.5) in the absence or presence of NaCl. The activity of LsGDH was enhanced by Li+, Na+, K+, NH4+, Mg2+, and EDTA at pH 8.0. LsGDH exhibited high tolerance to 60% DMSO, 30% acetone, 30% methanol, 30% ethanol, 10% n-propanol, 30% isopropanol, 60% n-hexanol and 30% n-hexane. The relationship between stability and chain length of the alcohols fit a Gaussian distribution model (R2≥0.94), and demonstrated lowest enzyme stability in C4-alcohol. The results suggested that LsGDH was potentially useful for coenzyme regeneration in organic solvents or under alkaline conditions.

Purification and characterization of a novel glucooligosaccharide oxidase from Acremonium strictum T1

A novel glucooligosaccharide oxidase was purified 495-fold from wheat bran culture of a soil-isolated Acremonium strictum strain T1 with an overall yield of 21%. This enzyme was composed of a single polypeptide chain with a molecular mass of 61 kDa as determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis and size-exclusion high-performance liquid chromatography. Its isoelectric point was pH 4.3-4.5. This enzyme contained 1 mol of FAD per mol of enzyme and showed absorption maxima at 274, 379 and 444 nm. This enzyme was stable in the pH range of 5.0 to 11.0 with an optimal reaction pH of 10.0. The optimal reaction temperature was 50 degrees C. It was stable up to 50 degrees C for 1 h at pH 7.8. This enzyme oxidized those oligosaccharides with glucose residue on the reducing end and each sugar residue jointed by alpha or beta-1,4 glucosidic bond. The relative activity of this enzyme toward maltose, maltotriose, maltotetraose, maltopentaose, maltohexaose, maltoheptaose, lactose, cellobiose and glucose was 100:94:74:46:66:56:64:47:59. To our knowledge, this is the first report on the discovery of an glucooligosaccharide oxidase as judged from enzyme substrate specificity.

Glucose dehydrogenase from Bacillus subtilis expressed in Escherichia coli. I: Purification, characterization and comparison with glucose dehydrogenase from Bacillus megaterium

Escherichia coli containing the Bacillus subtilis glucose dehydrogenase gene on a plasmid (prL7) was used to produce the enzyme in high quantities. Gluc-DH-S was purified from the cell extract by (NH4)2SO4-precipitation, ion-exchange chromatography and Triazine-dye chromatography to a specific activity of 375 U/mg. The enzyme was apparently homogenous on SDS-PAGE with a subunit molecular mass of 31.5 kDa. Investigation of Gluc-DH-S was performed for comparison with the corresponding properties of Gluc-DH-M. The limiting Michaelis constant at pH 8.0 for NAD+ is Ka = 0.11 mM and for D-glucose Kb = 8.7 mM. The dissociation constant for NAD+ is Kia = 17.1 mM. Similar to Gluc-DH-M, Gluc-DH-S is inactivated by dissociation under weak alkaline conditions at pH 9.0. Complete reactivation is attained by readjustment to pH 6.5. Ultraviolet absorption, fluorescence and CD-spectra of native Gluc-DH-S, as well as fluorescence- and CD-backbone-spectra of the dissociated enzyme were nearly identical to the corresponding spectra of Gluc-DH-M. The aromatic CD-spectrum of dissociated Gluc-DH-S was different, representing a residual ellipticity of tryptophyl moieties in the 290-310 nm region. Density gradient centrifugation proved that this behaviour is due to the formation of inactive dimers in equilibrium with monomers after dissociation. In comparison to Gluc-DH-M, the kinetics of inactivation as well as the time-dependent change of fluorescence intensity at pH 9.0 of Gluc-DH-S showed a higher velocity and a changed course of the dissociation process.

Purification and site-specific immobilization of genetically engineered glucose dehydrogenase on thiopropyl-Sepharose

The gene encoding glucose dehydrogenase (EC 1.1.1.47) from Bacillus subtilis was inserted in a plasmid 1.0 kb downstream from a lac promoter, resulting in a 70-fold higher production of the enzyme when expressed in Escherichia coli. A glucose dehydrogenase mutant containing a cysteine residue at position 44 could also be expressed at the same high level. This single cysteine residue was used as an 'affinity tag' to simplify the purification procedure as well as for site-specific immobilization of glucose dehydrogenase on Thiopropyl-Sepharose. This enzyme was purified to homogeneity with a final recovery of 65% and a specific activity of 240 U/mg. The oriented immobilization resulted in increased thermal stability.

Enzymatic properties of isozymes and variants of glucose dehydrogenase from Bacillus megaterium

Three glucose dehydrogenases (GlcDH) from Bacillus megaterium, GlcDH-I, GlcDH-II and GlcDH-IWG3, were purified from Escherichia coli cells harboring one of the hybrid plasmids, pGDK1, pGDK2 and pGDA3, respectively, pGDK1 and pGDK2 contain two isozyme genes, gdhI and gdhII, respectively, from B. megaterium IAM 1030 and pGDA3 contains an isozyme gene from B. megaterium IWG3; GlcDH-IWG3 is a variant of GlcDH-I. GlcDH-I and GlcDH-II have similar pH/activity profiles and the profile for GlcDH-IWG3 is identical to that of GlcDH-I. The pH/stability profiles of these enzymes show that GlcDH-IWG3 is the most stable enzyme in the acidic region, while GlcDH-II is the most stable in the alkaline region, and GlcDH-I is the most unstable throughout the entire pH range examined. As for thermostability, GlcDH-II is the most resistant against heat inactivation at pH 6.5. The values of the first-order rate constant for heat inactivation at 50 degrees C are 0.27 min-1, 0.05 min-1 and 0.11 min-1 for GlcDH-I, GlcDH-II and GlcDH-IWG3, respectively. Kinetic studies show that these enzymes have similar kinetic constant values except that there are some differences in Kia for NAD(P) and Ka (the limiting Michaelis constant) for NAD; the values of the ratio of Kia for NAD and NADP are 11,340 and 8.7 for GlcDH-I, GlcDH-II and GlcDH-IWG3, respectively. GlcDH-I and GlcDH-IWG3 have very similar substrate specificities and GlcDH-II has a slightly higher specificity for D-glucose and 2-deoxy-D-glucose than the others. The results are discussed on the basis of the amino acid substitutions between the enzymes.

Improved purification and properties of glucose dehydrogenase from Bacillus subtilis

Glucose dehydrogenase (EC 1.1.1.47) from Bacillus subtilis was purified about 5240-fold, using an aqueous two-phase system and triazine-dye affinity chromatography. The specific activity of the purified preparation was about 460 units/mg of protein with a final recovery of enzyme activity of about 75%. The affinity column could be regenerated and reused again several times. The purified enzyme appeared to be homogeneous when analyzed both on SDS-PAGE and native PAGE. The protein band on native PAGE coincided with the activity stain. ATP acts apparently as a competitive inhibitor for this enzyme with respect to NAD and protects the enzyme from dissociation into partially inactive dimers. In the absence of either glycerol or ATP, the enzyme dissociates into partially inactive dimers.

An improved method for the purification of Bacillus subtilis glucose dehydrogenase cloned in Escherichia coli

An improved and simplified purification procedure has been developed for the isolation of the Bacillus subtilis glucose dehydrogenase which has resulted in a 10 fold higher yield of pure enzyme. The purification procedure utilizes gene cloning and an additional ammonium sulfate step to facilitate the removal of contaminating proteins. The procedure requires fewer chromatographic steps than previously reported, thus simplifying the procedure. This improved and simplified purification of B. subtilis glucose dehydrogenase will facilitate further structure-function studies of this sporulation specific enzyme.

Sequence homologies of glucose-dehydrogenases of Bacillus megaterium and Bacillus subtilis

The sequence homologies of the glucose dehydrogenase subunits of B. megaterium and B. subtilis are compared. From the known B. megaterium aminoacid sequence and the base sequence of the cloned B. subtilis structural gene we predict the B. megaterium structural glucose dehydrogenase gene. Assuming the minimal mutational changes to convert one gene into the other 23 transitions, 30 transversions, 1 inversion, 3 insertion-deletions, but no frameshifts are postulated necessary to interconvert the structural genes. The homology of both enzyme subunits of 85% reflects the close evolutionary distance between B. subtilis and B. megaterium.

Characterization of the developmentally regulated Bacillus subtilis glucose dehydrogenase gene

The DNA sequence of the structural gene for glucose dehydrogenase (EC 1.1.1.47) of Bacillus subtilis was determined and comprises 780 base pairs. The subunit molecular weight of glucose dehydrogenase as deduced from the nucleotide sequence is 28,196, which agrees well with the subunit molecular weight of 31,500 as determined from sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The sequence of the 49 amino acids at the NH2 terminus of glucose dehydrogenase purified from sporulating B. subtilis cells matched the amino acid sequence derived from the DNA sequence. Glucose dehydrogenase was purified from an Escherichia coli strain harboring pEF1, a plasmid that contains the B. subtilis gene encoding glucose dehydrogenase. This enzyme has the identical amino acid sequence at the NH2 terminus as the B. subtilis enzyme. A putative ribosome-binding site, 5'-AGGAGG-3', which is complementary to the 3' end of the 16S rRNA of B. subtilis, was found 6 base pairs preceding the translational start codon of the structural gene of glucose dehydrogenase. No known promoterlike DNA sequences that are recognized by B. subtilis RNA polymerases were present immediately preceding the translational start site of the glucose dehydrogenase structural gene. The glucose dehydrogenase gene was found to be under sporulation control at the trancriptional level. A transcript of 1.6 kilobases hybridized to a DNA fragment within the structural gene of glucose dehydrogenase. This transcript was synthesized 3 h after the cessation of vegetative growth concomitant to the appearance of glucose dehydrogenase.

Possibility of association and activation of glucose dehydrogenase during germination and outgrowth of Bacillus subtilis spores

Both a salt-dependent form and an active form of glucose dehydrogenase [EC 1.1.1.47] were isolated from germinated spores of Bacillus subtilis disrupted in deionized water and 100 mM phosphate buffer (pH 6.6), and most of the enzyme isolated from young vegetative cells was the active form regardless of the conditions for breakage by sonication. The molecular weight of the salt-dependent form of the enzyme was about 55,000 and that of the active form was about 120,000. From the above results and the results on the glucose dehydrogenase extracted from resting spores disrupted in deionized water and 100 mM phosphate buffer (pH 6.6) reported in a previous paper, we propose that glucose dehydrogenase is present in resting spores as a monomeric form and is activated with association in vivo during germination and outgrowth.