Purification, characterization and function of dihydrolipoamide dehydrogenase from the cyanobacterium Anabaena sp. strain P.C.C. 7119

Dihydrolipoamide dehydrogenase of Vibrio splendidus is involved in adhesion to Apostichopus japonicus

Vibrio splendidus is one of the most opportunistic marine pathogens and infects many important marine animals, including the sea cucumber Apostichopus japonicus. In this study, two genes named DLD1 and DLD2, encoding dihydrolipoamide dehydrogenase (DLD) homologues in pathogenic V. splendidus, were cloned, and conditionally expressed in Escherichia coli BL21 (DE3). The enzymatic activities of DLD1 and DLD2 showed that they both belonged to the NADH oxidase family. Both DLD1 and DLD2 were located on the outer membrane of V. splendidus as detected by whole-cell ELISA. To study the adhesion function of DLD1 and DLD2, polyclonal antibodies were prepared, and antibody block assay was performed to detect the normal function of the two proteins. DLD1 and DLD2 were determined to play important roles in adhesion to different matrices and the adhesive ability of V. splendidus reduced more than 50% when DLD1 or DLD2 was defective.

Enzymatic characterization of a NADH-dependent diaphorase from Lysinibacillus sp. strain PAD-91

Diaphorases are flavin-containing enzymes with potential applications in biotransfomation reactions, biosensor design and in vitro diagnostic tests. In this paper, we present recombinant expression, characterization and medium optimization of a lipoamide dehydrogenase (DLD) with NADH-dependent diaphorase activity from a Lysinibacillus sp. strain. DLD encoding sequence showed an open reading frame of 1413-bp encoding a 470 amino acid chain. Lysinibacillus sp. DLD catalyzed the NADH-dependent reduction of electron acceptors and exhibited diaphorase activity. The molecular mass of the isolated enzyme was found to be about 50 kDa, and determined to be a monomeric protein. The optimum pH and temperature for the catalytic activity of the enzyme was about pH 7.5 and 30 °C. The K_m and V_max values were estimated to be 0.025 mM and 1.33 μmol/min, respectively. Recombinant enzyme was optimally produced in fermentation medium containing 10 g/L sucrose, 25 g/L yeast extract, 5 g/L NaCl and 0.25 g/L MgSO₄. By Scaling up fermentation from flask to bioreactor, enzyme activity was increased to 487.5 U/ml. This study provides data on the identification, characterization and medium optimization of a NADH-dependent diaphorase from a newly isolated Lysinibacillus sp. PAD-91.

Medium Optimization for Improved Production of Dihydrolipohyl Dehydrogenase from Bacillus sphaericus PAD-91 in Escherichia coli

Dihydrolipohyl dehydrogenase (DLD) is a FAD-dependent enzyme that catalyzes the reversible oxidation of dihydrolipoamide. Herein, we report medium optimization for the production of a recombinant DLD with NADH-dependent diaphorase activity from a strain of Bacillus sphaericus PAD-91. The DLD gene that consisted of 1413 bp was expressed in Escherichia coli BL21 (DE3), and its enzymatic properties were studied. The composition of production medium was optimized using one-variable-at-a-time method followed by response surface methodology (RSM). B. sphaericus DLD catalyzed the reduction of lipoamide by NAD⁺ and exhibited diaphorase activity. The molecular weight of enzyme was about 50 kDa and determined to be a monomeric protein. Recombinant diaphorase showed its optimal activity at temperature of 30 °C and pH 8.5. K _m and V _max values with NADH were estimated to be 0.025 mM and 275.8 U/mL, respectively. Recombinant enzyme was optimally produced in fermentation medium containing 10 g/L sucrose, 25 g/L yeast extract, 5 g/L NaCl and 0.25 g/L MgSO₄. At these concentrations, the actual diaphorase activity was calculated to be 345.0 ± 4.1 U/mL. By scaling up fermentation from flask to bioreactor, enzyme activity was increased to 486.3 ± 5.5 U/mL. Briefly, a DLD with diaphorase activity from a newly isolated B. sphaericus PAD-91 was characterized and the production of recombinant enzyme was optimized using RSM technique.

Recombinant expression, characterization and application of a dihydrolipoamide dehydrogenase with diaphorase activity from Bacillus sphaericus

Diaphorases are flavin-containing enzymes with potential applications in biotransfomation reactions, biosensor design and in vitro diagnostic tests. In this communication, we describe recombinant expression, characterization and application of a lipoamide dehydrogenase (DLD) with diaphorase activity from a strain of Bacillus sphaericus. The DLD gene consisting of 1413 bp encoding a protein of 470 amino acids was expressed in Escherichia coli BL21 (DE3) and the recombinant enzyme was characterized. B. sphaericus DLD catalyzed the reduction of NAD⁺ by dihydrolipoamide and exhibited NADH-dependent diaphorase activity. The molecular weight of purified enzyme was about 50 kDa, and determined to be a monomeric protein. Diaphorase was active and stable from pH 7.0 to 9.0 with an optimal activity at pH 8.5. It showed its maximal activity at temperature of 30 °C and was almost stable at temperatures between 25 and 30 °C. Different metal ions and inhibitors showed no influence on the activity of target enzyme. The K _m and V _max values for NADH were estimated to be 0.33 mM and 200.0 U/ml, respectively. Moreover, recombinant B. sphaericus diaphorase exhibited considerable potential to be used as a component of diagnostic tests for the quantification of metabolites. In conclusion, considering the properties of diaphorase from B. sphaericus PAD-91, it can have potential application as a diagnostic enzyme.

Two strictly polyphosphate-dependent gluco(manno)kinases from diazotrophic Cyanobacteria with potential to phosphorylate hexoses from polyphosphates

The single-copy genes encoding putative polyphosphate-glucose phosphotransferases (PPGK, EC 2.7.1.63) from two nitrogen-fixing Cyanobacteria, Nostoc sp. PCC7120 and Nostoc punctiforme PCC73102, were cloned and functionally characterized. In contrast to their actinobacterial counterparts, the cyanobacterial PPGKs have shown the ability to phosphorylate glucose using strictly inorganic polyphosphates (polyP) as phosphoryl donors. This has proven to be an economically attractive reagent in contrast to the more costly ATP. Cyanobacterial PPGKs had a higher affinity for medium-long-sized polyP (greater than ten phosphoryl residues). Thus, longer polyP resulted in higher catalytic efficiency. Also in contrast to most their homologs in Actinobacteria, both cyanobacterial PPGKs exhibited a modest but significant polyP-mannokinase activity as well. Specific activities were in the range of 180-230 and 2-3 μmol min(-1) mg(-1) with glucose and mannose as substrates, respectively. No polyP-fructokinase activity was detected. Cyanobacterial PPGKs required a divalent metal cofactor and exhibited alkaline pH optima (approx. 9.0) and a remarkable thermostability (optimum temperature, 45 °C). The preference for Mg(2+) was noted with an affinity constant of 1.3 mM. Both recombinant PPGKs are homodimers with a subunit molecular mass of ca. 27 kDa. Based on database searches and experimental data from Southern blots and activity assays, closely related PPGK homologs appear to be widespread among unicellular and filamentous mostly nitrogen-fixing Cyanobacteria. Overall, these findings indicate that polyP may be metabolized in these photosynthetic prokaryotes to yield glucose (or mannose) 6-phosphate. They also provide evidence for a novel group-specific subfamily of strictly polyP-dependent gluco(manno)kinases with ancestral features and high biotechnological potential, capable of efficiently using polyP as an alternative and cheap source of energy-rich phosphate instead of costly ATP. Finally, these results could shed new light on the evolutionary origin of sugar kinases.

Histochemical staining and quantification of dihydrolipoamide dehydrogenase diaphorase activity using blue native PAGE

Mammalian mitochondrial dihydrolipoamide dehydrogenase (DLDH, EC 1.8.1.4) catalyzes NAD(+)-dependent oxidation of dihydrolipoamide in vivo and can also act as a diaphorase catalyzing in vitro nicotinamide adenine dinucleotide (reduced form) (NADH)-dependent reduction of electron-accepting molecules such as ubiquinone and nitroblue tetrazolium (NBT). In this paper, we report a gel-based method for histochemical staining and quantification of DLDH diaphorase activity using blue native PAGE (BN-PAGE). Rat brain mitochondrial extracts, used as the source of DLDH, were resolved by nongradient BN-PAGE (9%), which was followed by diaphorase activity staining using NADH as the electron donor and NBT as the electron acceptor. It was shown that activity staining of DLDH diaphorase was both protein amount- and time-dependent. Moreover, this in-gel activity-staining method was demonstrated to be in good agreement with the conventional spectrophotometric method that measures DLDH dehydrogenase activity using dihydrolipoamide as the substrate. The method was applied to determine levels of DLDH diaphorase activity in several rat tissues other than the brain, and the results indicated a similar level of DLDH diaphorase activity for all the tissues examined. Finally, the effects of thiol-reactive reagents such as N-ethylmaleimide (NEM) and nitric oxide donors on DLDH diaphorase activity were evaluated, demonstrating that, with this method, DLDH diaphorase activity can be determined without having to remove these thiol-reactive reagents that may otherwise interfere with spectrophotometric measurement of DLDH dehydrogenase activity. The gel-based method can also be used as a means to isolate mitochondrial DLDH that is to be analyzed by mass spectral techniques in studying DLDH post-translational modifications.

Selective identification of new therapeutic targets of Mycobacterium tuberculosis by IVIAT approach

The in vivo induced antigen technology (IVIAT)(1) has been used for the identification of open reading frames (ORFs) which could be possible therapeutic targets. A recombinant lambdagt11:: Mycobacterium tuberculosis H37Rv expression library was screened with pooled TB patient sera preabsorbed with in vitro grown M. tuberculosis H37Rv. Preabsorption of pooled TB patient sera allowed identification of antigens specifically expressed or upregulated during infection and growth in vivo. Six ORFs were identified, of which four (rv0287, rv2402, rv3878 and rv1045) were of hypothetical functions. Rv0287 is a probable regulatory protein. Rv3878 is present uniquely in M. tuberculosis H37Rv and is a part of RDI deletion region of M. bovis BCG, which includes esat 6 region. This could be exploited as a tool for diagnosis. Two ORFs were assigned function solely on the basis of homology, dnaQ (rv3711c) and lpdA (rv3303c). dnaQ codes for the epsilon subunit of DNA polymerase III, which is responsible for the proofreading activity of the complex. lpdA codes for dihydrolipoamide dehydrogenase, which is a part of many multienzyme complexes such as pyruvate dehydrogenase, keto-acid dehydrogenase and alpha-ketoglutarate dehydrogenase. These two enzymes appear to be potential targets for drug development.

Characterization of a gene encoding dihydrolipoamide dehydrogenase of the cyanobacterium Synechocystis sp. strain PCC 6803

The authors previously reported the isolation and partial characterization of a periplasmically located dihydrolipoamide dehydrogenase (LPD) from the cyanobacterium Synechocystis sp. strain PCC 6803. In the present work the gene (lpdA; database accession number Z48564) encoding the apoprotein of this LPD in Synechocystis PCC 6803 has been identified, sequenced and analysed. The lpdA gene codes for a protein starting with methionine, which is post-translationally removed. The mature protein contains an N-terminal serine and consists of 473 amino acids with a deduced molecular mass of 51421 Da (including one FAD). The LPD is an acidic protein with a calculated isoelectric point of 5.17. Comparison of the amino acid sequence of the Synechocystis LPD with protein sequences in the databases revealed that the enzyme shares identities of 31-35% with all 18 LPDs so far sequenced and published. As a first step in determining the role of this cyanobacterial LPD, attempts were made to generate an LPD-free Synechocystis mutant by insertionally inactivating the lpdA gene with a kanamycin-resistance cassette. However, the selected transformants appeared to be heteroallelic, containing both the intact lpdA gene and the lpdA gene inactivated by the drug-resistance cassette. The heteroallelic mutant studied, which had about 50% of the wild-type LPD activity, caused acidification of the growth medium. Growth over a prolonged time was only possible after an increased buffering of the medium. Since it is reported in the literature that inactivation of the pyruvate dehydrogenase complex (PDC) leads to acidosis, a function of the LPD in a cytoplasmic-membrane-associated PDC is conceivable.

Isolation, partial characterization and localization of a dihydrolipoamide dehydrogenase from the cyanobacterium Synechocystis PCC 6803

A dihydrolipoamide dehydrogenase (LPD; dihydrolipoamide:NAD oxidoreductase, EC 1.8.1.4.) activity has been detected in the cyanobacterium Synechocystis PCC 6803. The enzyme was isolated from the membraneous fraction after detergent solubilization and shown to be homogenous on the basis of SDS-PAGE and N-terminal sequencing. The isolated enzyme had a specific activity of 75 U (mg protein)(-1) and was shown to be a homodimer with an apparent molecular mass of 104 kDa for the dimer and 55 kDa for the subunits. The enzyme contains 1.75 mol noncovalently bound FAD (mol enzyme)(-1) suggesting that each subunit contains 1 mol FAD and that the FAD is fairly tightly associated with the enzyme. N-terminal sequencing gave a contiguous amino acid sequence of 17 residues and showed that the N-terminus of the LPD from Synechocystis PCC 6803 has significant homologies to other LPDs sequenced so far. Immunoblot experiments indicated that the enzyme is mainly present in the membrane fraction, and immunocytochemical investigations gave evidence that the LPD in Synechocystis PCC 6803 is located in the periplasma space between the cytoplasma membrane and the peptidoglycan layer. This is the first report on an extracellular, membrane-bound LPD in a cyanobacterium.

Evidence for a posttranslational covalent modification of liver glyceraldehyde-3-phosphate dehydrogenase in hibernating jerboa (Jaculus orientalis)

The specific activity of D-glyceraldehyde-3-phosphate (G3P) dehydrogenase (phosphorylating) (GPDH, EC 1.2.1.12) found in liver of induced hibernating jerboa (Jaculus orientalis) was 2-3-fold lower than in the euthermic animal. However, the comparative analysis of the soluble protein fraction of these tissues by SDS-PAGE and Western blotting showed no significant changes in the intensity of the 36 kDa protein band of the GPDH subunit. After using the same purification procedure, the GPDH from liver hibernating jerboa exhibited lower values for both apparent optimal temperature and specific activity than the enzyme from the euthermic animal. Similar non-linear Arrhenius plots were obtained, but the Ea values calculated for the GPDH from hibernating tissue were higher. Although in both purified enzyme preparations four isoelectric GPDH isoforms were resolved by chromatofocusing, those of hibernating liver exhibited more acidic pI values (pI 7.3-6.1) than the hepatic isoforms of euthermic animals (pI 8.7-8.1). However, all liver GPDH isoforms exhibited similar native and subunit molecular masses and cross-reacted with an antibody raised against muscle GPDH. The comparison of the kinetic parameters of both purified preparations and the main isoforms isolated from euthermic and hibernating tissues showed the decreased catalytic efficiency of hibernating enzyme being exclusively due to a lower Vmax for both substrates G3P and NAD+. Phosphodiesterase treatment of cell-free extracts increased GPDH activity in the case of hibernating liver only. The pI of the main isoform purified from this tissue, about 6.9, changed after this treatment to an alkaline value (pI 8.44) similar to those of the euthermic GPDH isoforms. Differential ultraviolet absorption spectra of these isoforms indicated that a substance absorbing at 260 nm, that was released by the phosphodiesterase digestion, was present in the enzyme of hibernating tissue. Incubation of purified GPDH with the NO-releasing agent sodium nitroprussite produced under conditions that promote mono-ADP-ribosylation a dramatic decrease of activity (up to 60%) of both euthermic and phosphodiesterase-treated hibernating preparations but only a marginal inhibition of the hibernating enzyme. These data suggest that the liver GPDH of hibernating jerboa exhibits a posttranslational covalent modification, being probably a mono-ADP-ribosylation. The resulting inhibition of enzyme activity could contribute to the wide depression of the glycolytic metabolic flow associated with mammalian hibernation.

A lipoamide dehydrogenase from Neisseria meningitidis has a lipoyl domain

A protein of molecular weight of 64 kDa (p64k) found in the outer membrane of Neisseria meningitidis shows a high degree of homology with both the lipoyl domain of the acetyltransferase and the entire sequence of the lipoamide dehydrogenase, the E2 and E3 components of the dehydrogenase multienzyme complexes, respectively. The alignment of the p64k with lipoyl domains and lipoamide dehydrogenases from different species is presented. The possible implications of this protein in binding protein-dependent transport are discussed. This is the first lipoamide dehydrogenase reported to have a lipoyl domain.