Identification and functional analysis of fructosyl amino acid-binding protein from Gram-positive bacterium Arthrobacter sp.

AIM: Fructosyl amino acid-binding protein (FABP) is a substrate-binding protein (SBP), which recognizes fructosyl amino acids (FAs) as its ligands. Although FABP has been shown as a molecular recognition tool of biosensing for glycated proteins, the availability of FABP is still limited and no FABP was reported from Gram-positive bacteria. In this study, a novel FABP from Gram-positive bacteria, Arthrobacter spp., was reported. METHOD AND RESULTS: BLAST analysis revealed that FABP homologues exist in some of Arthrobacter species genomes. An FABP homologue cloned from Arthrobacter sp. FV1-1, FvcA, contained a putative lipoprotein signal sequence, suggesting that it is a lipoprotein anchored to the bacterial cytoplasmic membrane, which is a typical characteristic for SBPs from Gram-positive bacteria. In contrast, FvcA also exhibits high amino acid sequence similarity to a known Gram-negative bacterial FABP, which exists as a free periplasmic protein. FvcA, without the N-terminal anchoring region, was then recombinantly produced as soluble protein and was found to exhibit Nα-FA-specific binding activity by intrinsic fluorescent measurement. CONCLUSION: This study identified a novel FABP from a Gram-positive bacterium, Arthrobacter sp., which exhibited Nα-FA-specific binding ability. This is the first report concerning an FABP from a Gram-positive bacterium, suggesting that FABP-dependent FA catabolism system is also present in Gram-positive bacteria. SIGNIFICANCE AND IMPACT OF THE STUDY: The novel FABP exhibits the ability to specifically bind to Nα-FA with a high affinity. This selectivity is beneficial for applying FABP in HbA1c sensing. The successful preparation of water-soluble, functionally expressed Gram-negative bacterial FABP may make way for future applications for a variety of SBPs from Gram-positive bacteria employing the same expression strategy. The results obtained here enhance our understanding of bacterial FA catabolism and contribute to the improved development of FABP as Nα-FA-sensing molecules.

Isolation and identification of N-carbamoyl-beta-D-glucopyranosylamine from human serum.

N-carbamoyl-beta-D-glucopyranosylamine (NCG) is a compound, which can chemically be synthesized by the condensation of glucose and urea by heating under acidic condition. In this study, we isolated and identified NCG and its anomer from human serum. This is the first study showing the occurrence and isolation of NCG from a natural source. The NCG level in human serum was estimated to be 71+/-33 microM using a glucose-3-dehydrogenase-based assay. Because NCG is not commercially used in foods or drugs, we conclude that the NCG isolated from human serum is synthesized from blood glucose and urea in vivo.

Enzymatic synthesis of a novel trehalose derivative, 3,3'-diketotrehalose, and its potential application as the trehalase enzyme inhibitor.

We reported the preparation of a novel trehalose derivative based on enzymatic oxidation of trehalose by water-soluble glucose-3-dehydrogenase (G3DH) from marine bacterium Halomonas sp. alpha-15 cells. The product of G3DH enzymatic conversion was 3,3'-diketotrehalose (3,3'dkT), a novel trehalose derivative of which both third hydroxy groups of glucopyranosides were oxidized. 3,3'dkT was revealed to show an inhibitory effect toward pig-kidney and Bombyx mori trehalases. The IC(50) values of 3,3'dkT were 0.8 and 2.5 mM and K(i) values were 0.2 and 0.6 mM for pig-kidney and for B. mori trehalases, respectively. In addition, 3,3'dkT did not show any inhibitory effect on both maltase and mannosidase activities. Therefore, 3,3'dkT was a specific inhibitor of trehalases.

Cloning and expression of glucose 3-dehydrogenase from Halomonas sp. alpha-15 in Escherichia coli.

The gene encoding glucose 3-dehydrogenase (G3DH) from Halomonas sp. alpha-15 was cloned and expressed in Escherichia coli. An open reading frame of 1686 nucleotides was shown to encode G3DH. The flavine adenine dinucleotide binding motif was found in the N-terminal region of G3DH. The deduced primary structure of G3DH showed about 30% identity to sorbitol dehydrogenase from Gluconobacter oxydans and 2-keto-d-gluconate dehydrogenases from Erwinia herbicola and Pantoea citrea. The folding prediction of G3DH suggested that the 3D structure of G3DH was similar with cholesterol oxidase from Brevibacterium sterolicum or glucose oxidase from Aspergillus niger.

Screening and characterization of fructosyl-valine-utilizing marine microorganisms.

We describe the isolation of microorganisms utilizing fructosyl-amine (Amadori compound) from the marine environment and of fructosyl-amine oxidase from a marine yeast. Using fructosyl-valine (Fru-Val), a model Amadori compound for glycated hemoglobin, we isolated 12 microbial strains that grow aerobically in a minimal medium supplemented with Fru-Val as the sole nitrogen source. Among these strains, a yeast strain identified as Pichia sp. N1-1, produced a Fru-Val-oxidizing enzyme. The enzyme was purified in its active form, a single-polypeptide water-soluble protein of 54 kDa by gel electrophoresis, producing H(2)O(2) with the oxidation of Fru-Val. By its substrate specificity, the enzyme was categorized as a novel fructosyl-amine oxidase. This is the first study on the isolation of microorganisms utilizing fructosyl-amine in the marine environment and of fructosyl-amine oxidase from budding yeast.

Biodegradation of formaldehyde by a formaldehyde-resistant bacterium isolated from seawater.

A formaldehyde-tolerant bacterium designated as a DM-2 strain was used to biodegrade formaldehyde. The cells, precultivated in the presence of 400 ppm of formaldehyde, were able to degrade formaldehyde in a minimal medium supplemented with up to 400 ppm of formaldehyde in the presence of 3% NaCl. The rate of formaldehyde degradation achieved in this study was 45 ppm/h when the DM-2 culture's optical density at 660 nm was 1.2.

Improvement of enantioselectivity of chiral organophosphate insecticide hydrolysis by bacterial phosphotriesterase.

The bacterial phosphotriesterase (PTE) isolated from Flavobacterium sp. can catalyze the cleavage of the P-O bond in a variety of organophosphate triesters and has been shown to be an effective catalyst for the degradation of toxic organophosphate esters. Ethyl 4-nitrophenyl phenylphosphonothioate (EPN) is a chiral organophosphate. Optical isomers of EPN show differences in their toxicity. R-EPN is known to be more toxic to hens and houseflies than S-EPN. We determined the Ki value of each enantiomer toward electric eel acetylcholinesterase. R-EPN (Ki = 6 microM) inhibited acetylcholinesterase much more effectively than S-EPN (Ki = 52 microM) did in vitro. Since PTE has been found to hydrolyze only the S-isomer of EPN, we attempted to alter the enantioselectivity of PTE in order to degrade toxic EPN enantiomer effectively. When PTE hydrolyzed EPN in the presence of dimethyl sulfoxide (DMSO), enzymatic activity toward S-EPN decreased linearly, but enzymatic activity toward R-EPN increased as a function of DMSO concentration. At 20% DMSO, the maximum activity was observed. The kinetic parameters of PTE to EPN isomers clearly indicated that in the presence of 20% DMSO, the enantioselectivity of PTE changed. The Km value for R-EPN decreased from 0.24 to 0.03 mM, and the Vmax value increased from 0.25 to 0.60 U/mg of protein. Vmax/Km values indicated that PTE preferred R-EPN over S-EPN in the presence of DMSO by a factor of 2.

Enzyme electrochemical preparation of a 3-keto derivative of 1,5-anhydro-D-glucitol using glucose-3-dehydrogenase.

A novel enzymatic organic synthesis was reported, utilizing glucose-3-dehydrogenase (G3DH) and its regeneration via electrochemical methods. We combined the water-soluble G3DH prepared from a marine bacterium, Halomonas sp. alpha-15, and electron mediator with the electrode system in order to regenerate the enzyme. Using this system, the conversion of 1,5-anhydro-D-glucitol (1,5AG), a diabetes marker in human blood, was investigated. The final yield of the product, 3-keto anhydroglucitol (3-ketoAG), which was identified by 13C nuclear magnetic resonance, was 82% based on the initial amount of 1,5AG. The electrochemical yield of the reaction proceeded almost stoichiometrically. The electrochemical conversion rate of 1,5AG was 1.24 mmol/(L.h), and the electrochemical yield of 1,5AG consumption was 80%, whereas that for 3-ketoAG was 60%.

Effect of growth substrates on production of new soluble glucose 3-dehydrogenase in Halomonas (Deleya) sp. alpha-15.

Halomonas (Deleya) sp. alpha-15 produces new co-factor binding soluble glucose 3-dehydrogenase (G3DH), which oxidizes the third hydroxy group of pyranose. This study investigated the condition of efficient production of G3DH using Halomonas (Deleya) sp. alpha-15. This enzyme was inducible, and alpha-methyl-D-glucoside, isopropyl-thiogalactopyranoside (IPTG) and lactose were revealed to be suitable carbon sources for G3DH induction. Maximum G3DH production was achieved by using minimal medium containing 0.8% (w/v) lactose with a productivity of 470U/l.

Purification of a marine bacterial glucose dehydrogenase from Cytophaga marinoflava and its application for measurement of 1,5-anhydro-D-glucitol.

A novel glucose dehydrogenase (GDH) from a marine bacterium Cytophaga marinoflava IFO 14170 was isolated from its membrane fraction. This GDH catalyzes the oxidation of a hydroxy group of glucose, but does not react in its C-1 position. This enzyme is composed of a single peptide with a mol wt of 67,000. The GDH can react under high salinity. The optimum pH is around 8.0, showing typical property of marine bacterial enzymes. Using this novel enzyme, and enzymatic determination of 1,5-anhydro-D-glucitol (1,5AG) utilizing 2,6-dichrolophenolindophenol (DCIP) and phenazine methosulfate (PMS) as electron mediators was carried out. A good linear correlation was observed from 0.5 mM to 4 mM of 1,5AG.

Effect of PQQ glucose dehydrogenase overexpression in Escherichia coli on sugar-dependent respiration.

Pyrroloquinoline quinone glucose dehydrogenase (PQQGDH) was overexpressed in Escherichia coli, and its impact on sugar-dependent respiration was investigated. Sugar-dependent respiration patterns under PQQGDH overexpression can be devided into two types. The first type involves D-glucose and D-mannose, which are utilized by the phosphotransferase system (PTS) and are also the substrates of PQQGDH. As a result of PQQGDH overexpression, the apparent Km value of sugar-dependent respiration shifted to higher concentration compared with E. coli parental cells. The second type included D-xylose and D-galactose, which are the substrates of PQQGDH, but not the PTS sugars. PQQGDH overexpressing cells showed much higher respiration than parental cells. These results suggested that PQQGDH overexpression may alter sugar utilization preferences in E. coli, suggesting further possible applications in metabolic engineering for carbon source utilization.