Hee-Jung Moon

Konkuk University, Seoul, Seoul, South Korea

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Publications (21)64.21 Total impact

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    ABSTRACT: Ribitol dehydrogenase from Zymomonas mobilis (ZmRDH) catalyzes the conversion of ribitol to d-ribulose and concomitantly reduces NAD(P)(+) to NAD(P)H. A systematic approach involving an initial sequence alignment-based residue screening, followed by a homology model-based screening and site-directed mutagenesis of the screened residues, was used to study the molecular determinants of the cofactor specificity of ZmRDH. A homologous conserved amino acid, Ser156, in the substrate-binding pocket of the wild-type ZmRDH was identified as an important residue affecting the cofactor specificity of ZmRDH. Further insights into the function of the Ser156 residue were obtained by substituting it with other hydrophobic nonpolar or polar amino acids. Substituting Ser156 with the negatively charged amino acids (Asp and Glu) altered the cofactor specificity of ZmRDH toward NAD(+) (S156D, [k(cat)/K(m)(,NAD)]/[k(cat)/K(m)(,NADP)] = 10.9, where K(m)(,NAD) is the K(m) for NAD(+) and K(m)(,NADP) is the K(m) for NADP(+)). In contrast, the mutants containing positively charged amino acids (His, Lys, or Arg) at position 156 showed a higher efficiency with NADP(+) as the cofactor (S156H, [k(cat)/K(m)(,NAD)]/[k(cat)/K(m)(,NADP)] = 0.11). These data, in addition to those of molecular dynamics and isothermal titration calorimetry studies, suggest that the cofactor specificity of ZmRDH can be modulated by manipulating the amino acid residue at position 156.
    Applied and environmental microbiology 02/2012; 78(9):3079-86. · 3.69 Impact Factor
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    ABSTRACT: Glycopeptide antibiotics, vancomycin and teicoplanin, inhibit cell wall synthesis in Gram-positive bacteria by interacting with peptidoglycan D-Ala-D-Ala peptide stem termini of the pentapeptide side chains of the peptidoglycan precursors. In glycopeptide-resistant bacteria, multiresistance poses major therapeutic problems. New potent antibacterial agents are needed to combat these resistance problems, resulting in the explosion of novel glycopeptides in recent years. The glycosylation patterns of glycopeptides and the chemical modifications of the glycosyl moieties greatly influence their antibiotic activity, and certain combinations have resulted in highly active new compounds. Considerable efforts have been made to produce semisynthetic glycopeptides with improved pharmacokinetic and pharmacodynamic properties and activity towards resistant strains. This review provides an overview of the chemistry, the antimicrobial activity, the pharmacokinetics and the toxicology of teicoplanin and other glycopeptide antibiotic derivatives.
    Current Pharmaceutical Biotechnology 07/2011; 12(8):1194-1204. · 2.69 Impact Factor
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    ABSTRACT: A highly efficient cellobiohydrolase (CBH)-secreting basidiomycetous fungus, Agaricus arvensis KMJ623, was isolated and identified based on its morphological features and sequence analysis of internal transcribed spacer rDNA. An extracellular CBH was purified to homogeneity from A. arvencis culture supernatant using sequential chromatography. The relative molecular mass of A. arvencis CBH was determined to be 65 kDa by SDSPAGE and 130 kDa by size-exclusion chromatography, indicating that the enzyme is a dimer. A. arvencis CBH showed a catalytic efficiency (kcat/Km) of 31.8 mM⁻¹ s⁻¹ for p-nitrophenyl-beta-D-cellobioside, the highest level seen for CBH-producing microorganisms. Its internal amino acid sequences showed significant homology with CBHs from glycoside hydrolase family 7. Although CBHs have been purified and characterized from other sources, A. arvencis CBH is distinguished from other CBHs by its high catalytic efficiency.
    Journal of Microbiology and Biotechnology 07/2011; 21(7):711-8. · 1.40 Impact Factor
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    ABSTRACT: Active site modeling of dimerization interface in combination with site-directed mutagenesis indicates that the electron in the PrnD Rieske oxygenase can be transferred by either of two pathways, one involving Asp183' and the other involving Asn180'. In addition, the overexpression of the isc operon involved in the assembly of iron-sulfur clusters increased the catalytic activity of PrnD in Escherichia coli by a factor of at least 4.
    Bioorganic & medicinal chemistry letters 05/2011; 21(10):2873-6. · 2.65 Impact Factor
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    ABSTRACT: Glycopeptide antibiotics, vancomycin and teicoplanin, inhibit cell wall synthesis in Gram-positive bacteria by interacting with peptidoglycan D-Ala-D-Ala peptide stem termini of the pentapeptide side chains of the peptidoglycan precursors. In glycopeptide-resistant bacteria, multiresistance poses major therapeutic problems. New potent antibacterial agents are needed to combat these resistance problems, resulting in the explosion of novel glycopeptides in recent years. The glycosylation patterns of glycopeptides and the chemical modifications of the glycosyl moieties greatly influence their antibiotic activity, and certain combinations have resulted in highly active new compounds. Considerable efforts have been made to produce semisynthetic glycopeptides with improved pharmacokinetic and pharmacodynamic properties and activity towards resistant strains. This review provides an overview of the chemistry, the antimicrobial activity, the pharmacokinetics and the toxicology of teicoplanin and other glycopeptide antibiotic derivatives.
    Current pharmaceutical biotechnology 04/2011; 12(8):1194-204. · 3.40 Impact Factor
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    ABSTRACT: A high cellobiohydrolase (CBH)-producing strain was isolated and identified as Penicillium purpurogenum KJS506 according to the morphology and comparison of internal transcribed spacer rDNA gene sequence. When rice straw and corn steep powder were used as carbon and nitrogen sources, respectively, a maximum CBH activity of 2.6 U mg-protein(-1), one of the highest among CBH-producing microorganisms, was obtained. The optimum temperature and pH for CBH production were 30 °C and 4.0, respectively. The increased production of CBH in P. purpurogenum culture at 30 °C was confirmed by two-dimensional electrophoresis followed by MS/MS sequencing of the partial peptide. The internal amino acid sequences of P. purpurogenum CBH showed a significant homology with hydrolases from glycoside hydrolase family 7. The extracellular CBH was purified to homogeneity by sequential chromatography of P. purpurogenum culture supernatants on a DEAE-sepharose column, a gel filtration column, and then on a Mono Q column with fast-protein liquid chromatography. The purified CBH was a monomeric protein with a molecular weight of 60 kDa and showed broad substrate specificity with maximum activity towards p-nitrophenyl β-D: -cellobiopyranoside. P. purpurogenum CBH showed t (1/2) value of 4 h at 60 °C and V (max) value of 11.9 μmol min(-1) mg-protein(-1) for p-nitrophenyl-D: -cellobiopyranoside. Although CBHs have been reported, the high specific activity distinguishes P. purpurogenum CBH.
    Applied biochemistry and biotechnology 01/2011; 163(1):25-39. · 1.94 Impact Factor
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    ABSTRACT: Agaricus arvensis, a newly isolated basidiomycetous fungus, was found to secrete efficient cellulases. The strain produced the highest endoglucanase (EG), cellobiohydrolase (CBH) and beta-glucosidase (BGL) activities of 0.3, 3.2 and 8U/mg-protein, respectively, with rice straw as the carbon source. Saccharification of the woody biomass with A. arvensis cellulase as the enzyme source released a high level of fermentable sugars. Enzymatic hydrolysis of the poplar biomass was optimized using the response surface methodology in order to study the influence of the variables (pH, temperature, cellulases concentration and substrate concentration). The enzyme and substrate concentrations were identified as the limiting factors for the saccharification of poplar wood biomass. A total reducing sugar level of 29g/L (293mg/g-substrate) was obtained at an enzyme concentration of 65FPU/g-substrate after optimization of the hydrolysis parameters. The model validation showed a good agreement between the experimental results and the predicted responses. A. arvensis could be a good candidate for the production of reducing sugars from a cellulosic biomass.
    Bioresource Technology 11/2010; 101(22):8742-9. · 4.75 Impact Factor
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    ABSTRACT: Ribitol dehydrogenase (RDH) catalyzes the conversion of ribitol to D-ribulose. A novel RDH gene was cloned from Zymomonas mobilis subsp. mobilis ZM4 and overexpressed in Escherichia coli BL21(DE3). DNA sequence analysis revealed an open reading frame of 795 bp, capable of encoding a polypeptide of 266 amino acid residues with a calculated molecular mass of 28,426 Da. The gene was overexpressed in E. coli BL21(DE3) and the protein was purified as an active soluble form using glutathione S-transferase affinity chromatography. The molecular mass of the purified enzyme was estimated to be approximately 28 kDa by sodium dodecyl sulfate-polyacrylamide gel and approximately 58 KDa with gel filtration chromatography, suggesting that the enzyme is a homodimer. The enzyme had an optimal pH and temperature of 9.5 and 65 degrees C, respectively. Unlike previously characterized RDHs, Z. mobilis RDH (ZmRDH) showed an unusual dual coenzyme specificity, with a k(cat) of 4.83 s(-1) for NADH (k(cat)/K(m) = 27.3 s(-1) mM(-1)) and k(cat) of 2.79 s(-1) for NADPH (k(cat)/K(m) = 10.8 s(-1) mM(-1)). Homology modeling and docking studies of NAD+ and NADP+ into the active site of ZmRDH shed light on the dual coenzyme specificity of ZmRDH.
    Applied Microbiology and Biotechnology 06/2010; 87(1):205-14. · 3.69 Impact Factor
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    ABSTRACT: Methylan polysaccharide derivatives were prepared by dialkylaminoalkylation and reductive amination followed by quaternization. Their antitumor activity was investigated and a relationship between structure and activity is suggested. For quaternized DEAE-methylan at only 75 mug ml(-1), tumor cell proliferation was suppressed by 58-84% in three cell lines tested in the order Colo < Hela < HepG2.
    Biotechnology Letters 03/2010; 32(7):891-5. · 1.85 Impact Factor
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    ABSTRACT: An NAD(+)-dependent xylitol dehydrogenase from Rhizobium etli CFN42 (ReXDH) was cloned and overexpressed in Escherichia coli. The DNA sequence analysis revealed an open reading frame of 1,044 bp, capable of encoding a polypeptide of 347 amino acid residues with a calculated molecular mass of 35,858 Da. The ReXDH protein was purified as an active soluble form using GST affinity chromatography. The molecular mass of the purified enzyme was estimated to be approximately 34 kDa by sodium dodecyl sulfate-polyacrylamide gel and approximately 135 kDa with gel filtration chromatography, suggesting that the enzyme is a homotetramer. Among various polyols, xylitol was the preferred substrate of ReXDH with a K (m) = 17.9 mM and k(cat) /K (m) = 0.5 mM(-1) s(-1) for xylitol. The enzyme had an optimal pH and temperature of 9.5 and 70 degrees C, respectively. Heat inactivation studies revealed a half life of the ReXDH at 40 degrees C of 120 min and a half denaturation temperature (T (1/2)) of 53.1 degrees C. ReXDH showed the highest optimum temperature and thermal stability among the known XDHs. Homology modeling and sequence analysis of ReXDH shed light on the factors contributing to the high thermostability of ReXDH. Although XDHs have been characterized from several other sources, ReXDH is distinguished from other XDHs by its high thermostability.
    Applied Microbiology and Biotechnology 02/2010; 87(2):571-81. · 3.69 Impact Factor
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    ABSTRACT: Erythritol, a four-carbon polyol, is a biological sweetener with applications in food and pharmaceutical industries. It is also used as a functional sugar substitute in special foods for people with diabetes and obesity because of its unique nutritional properties. Erythritol is produced by microbial methods using mostly osmophilic yeasts and has been produced commercially using mutant strains of Aureobasidium sp. and Pseudozyma tsukubaensis. Due to the high yield and productivity in the industrial scale of production, erythritol serves as an inexpensive starting material for the production of other sugars. This review focuses on the approaches for the efficient erythritol production, strategies used to enhance erythritol productivity in microbes, and the potential biotechnological applications of erythritol.
    Applied Microbiology and Biotechnology 02/2010; 86(4):1017-25. · 3.69 Impact Factor
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    ABSTRACT: A high β-glucosidase (BGL)-producing strain was isolated and identified as Penicillium pinophilum KMJ601 based on its morphology and internal transcribed spacer rDNA gene sequence. Under the optimal culture conditions, a maximum BGL specific activity of 3.2 U ml−1 (83 U mg-protein−1), one of the highest levels among BGL-producing microorganisms was obtained. An extracellular BGL was purified to homogeneity by sequential chromatography of P. pinophilum culture supernatants on a DEAE-Sepharose column, a gel filtration column, and then on a Mono Q column. The relative molecular weight of P. pinophilum BGL was determined to be 120 kDa by SDS-PAGE and size exclusion chromatography, indicating that the enzyme is a monomer. The hydrolytic activity of the BGL had a pH optimum of 3.5 and a temperature optimum of 32 °C. P. pinophilum BGL showed a higher activity (Vmax = 1120 U mg-protein−1) than most BGLs purified from other sources. The internal amino acid sequences of P. pinophilum BGL showed a significant homology with hydrolases from glycoside hydrolase family 3. Although BGLs have been purified and characterized from several other sources, P. pinophilum BGL is distinguished from other BGLs by its high activity.
    Process Biochemistry. 01/2010;
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    ABSTRACT: Coenzyme Q(10) (CoQ(10)), an obligatory cofactor in the aerobic respiratory electron transfer for energy generation, is formed from the conjugation of a benzoquinone ring with a hydrophobic isoprenoid chain. CoQ(10) is now used as a nutritional supplement because of its antioxidant properties and is beneficial in the treatment of several human diseases when administered orally. Bioprocesses have been developed for the commercial production of CoQ(10) because of its increased demand, and these bioprocesses depend on microbes that produce high levels of CoQ(10) naturally. However, as knowledge of the biosynthetic enzymes and the regulatory mechanisms modulating CoQ(10) production increases, approaches arise for the genetic engineering of CoQ(10) production in Escherichia coli and Agrobacterium tumefaciens. This review focused on approaches for CoQ(10) production, strategies used to engineer CoQ(10) production in microbes, and potential applications of CoQ(10).
    Applied Microbiology and Biotechnology 12/2009; 85(6):1653-63. · 3.69 Impact Factor
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    ABSTRACT: An isolated gene from Bacillus subtilis str. 168 encoding a putative isomerase was proposed as an L-arabinose isomerase (L-AI), cloned into Escherichia coli, and its nucleotide sequence was determined. DNA sequence analysis revealed an open reading frame of 1,491 bp, capable of encoding a polypeptide of 496 amino acid residues. The gene was overexpressed in E. coli and the protein was purified using nickel-nitrilotriacetic acid chromatography. The purified enzyme showed the highest catalytic efficiency ever reported, with a k(cat) of 14,504 min(-1) and a k(cat)/K(m) of 121 min(-1) mM(-1) for L-arabinose. A homology model of B. subtilis L-AI was constructed based on the X-ray crystal structure of E. coli L-AI. Molecular dynamics simulation studies of the enzyme with the natural substrate, L-arabinose, and an analogue, D-galactose, shed light on the unique substrate specificity displayed by B. subtilis L-AI only towards L-arabinose. Although L-AIs have been characterized from several other sources, B. subtilis L-AI is distinguished from other L-AIs by its high substrate specificity and catalytic efficiency for L-arabinose.
    Applied Microbiology and Biotechnology 10/2009; 85(6):1839-47. · 3.69 Impact Factor
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    ABSTRACT: The glycopeptide teicoplanin isolated from the fermentation broth of Actinoplanes teichomyceticus is used to treat serious Gram-positive bacterial infections that are resistant to other antibiotics, e.g. beta-lactams. The long time frame and progressively broader clinical use of teicoplanin has eventually led to the emergence and spreading of resistance in enterococci and staphylococci towards the antibiotics. Given the structural complexity of the natural product, only fermentative routes are available for bulk production of teicoplanin even though the total synthesis of the antibiotic has been accomplished. Because the low productivity (0.1-3.1 g/L) is a limitation to the commercial production of teicoplanin, substantial effort has been devoted to the strain improvement and process development for enhancing the productivity. This review summarizes the current state of the action mechanism, antibacterial activity, resistance mechanism, biotechnological production, and application of teicoplanin.
    Applied Microbiology and Biotechnology 08/2009; 84(3):417-28. · 3.69 Impact Factor
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    ABSTRACT: Alpha-lipoic acid (LA), a naturally occurring cofactor reported to be present in a diverse group of microorganisms, plants, and animal tissues, has been widely and successfully used as a therapy for a variety of diseases, including diabetes and heart disease. However, to date, recombinant DNA technology has not been applied for higher LA production due mainly to difficulties in the functional expression of key enzymes involved in LA production. Here, we report a study for higher LA production with the aid of chaperone plasmids, DnaKJE and trigger factor (Tf). The lipA and lplA genes encoding lipoate synthase and lipoate protein ligase in Pseudomonas fluorescens, respectively, were cloned and transformed into Escherichia coli K12. When they were overexpressed in E. coli, both LipA and LplA were expressed as inclusion bodies leading to no increase in LA production. However, when chaperone plasmids DnaKJE and Tf were coexpressed with lipA and lplA, the resulting recombinant E. coli strains showed higher LA production than the wild-type E. coli by 32-111%, respectively.
    Applied Microbiology and Biotechnology 03/2009; 83(2):329-37. · 3.69 Impact Factor
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    ABSTRACT: Nitrile groups are catabolized to the corresponding acid and ammonia through one-step reaction involving a nitrilase. Here, we report the use of bioinformatic and biochemical tools to identify and characterize the nitrilase (NitPf5) from Pseudomonas fluorescens Pf-5. The nitPf5 gene was identified via sequence analysis of the whole genome of P. fluorescens Pf-5 and subsequently cloned and overexpressed in Escherichia coli. DNA sequence analysis revealed an open-reading frame of 921 bp, capable of encoding a polypeptide of 307 amino acids residues with a calculated isoelectric point of pH 5.4. The enzyme had an optimal pH and temperature of 7.0 degrees C and 45 degrees C, respectively, with a specific activity of 1.7 and 1.9 micromol min(-1) mg protein(-1) for succinonitrile and fumaronitrile, respectively. The molecular weight of the nitrilase as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and gel filtration chromatography was 33,000 and 138,000 Da, respectively, suggesting that the enzyme is homotetrameric. Among various nitriles, dinitriles were the preferred substrate of NitPf5 with a K (m) = 17.9 mM and k (cat)/K (m) = 0.5 mM(-1) s(-1) for succinonitrile. Homology modeling and docking studies of dinitrile and mononitrile substrate into the active site of NitPf5 shed light on the substrate specificity of NitPf5. Although nitrilases have been characterized from several other sources, P. fluorescens Pf-5 nitrilase NitPf5 is distinguished from other nitrilases by its high specific activity toward dinitriles, which make P. fluorescens NitPf5 useful for industrial applications, including enzymatic synthesis of various cyanocarboxylic acids.
    Applied Microbiology and Biotechnology 02/2009; 83(2):273-83. · 3.69 Impact Factor
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    ABSTRACT: This report describes the optimization of culture conditions for teicoplanin production by Actinoplanes teichomyceticus KCCM-10601, an identified high-teicoplanin-producing strain (US 2006/0134757 A1). Among the conditions tested, temperature, pH, and the dissolved oxygen tension (DOT) were key factors affecting teicoplanin production. When the temperature, pH, and DOT were controlled at 34 degrees C, 7.0 and 20-30%, respectively, a dry-cell weight of 42.8 g l(-1) and a teicoplanin production of 2.9 g l(-1) were obtained after 120 h of batch culture, corresponding to a specific teicoplanin content of 67.8 mg g-DCW(-1). Teicoplanin production was scaled-up from a laboratory scale (7-l fermenter) to a pilot scale (300 l) and a plant scale (5,000 l) using the impeller tip velocity (V tip) as a scale-up parameter. Teicoplanin production at the laboratory scale was similar to those at the pilot and plant scales. This is the highest report of pilot- and plant-scale production of teicoplanin.
    Applied Microbiology and Biotechnology 09/2008; 80(1):21-7. · 3.69 Impact Factor
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    ABSTRACT: This report describes the optimization of culture conditions for vancomycin production by Amycolatopsis orientalis KCCM-10836P, an identified high-vancomycin-producing strain (US11/712,494). Among the conditions tested, pH and the dissolved oxygen tension (DOT) were key factors affecting vancomycin production. When the pH and DOT were controlled at 7.0 and 20-30%, respectively, a dry-cell weight (DCW) of 62.0 g l(-1) and a vancomycin production of 11.5 g l(-1) were obtained after 120 h of batch culture, corresponding to a specific vancomycin content of 185.4 mg g-DCW(-1). Vancomycin production was scaled up from a laboratory scale (7-l fermentor) to a pilot scale (300 l) and a plant scale (5,000 l) using the impeller tip velocity (V (tip)) as a scale-up parameter. Vancomycin production at the laboratory scale was similar to those at the pilot and plant scales.
    Applied Microbiology and Biotechnology 01/2008; 77(4):789-95. · 3.69 Impact Factor
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    ABSTRACT: By the optimization of nitrogen source for coenzyme Q10 (ubiquinone, CoQ10) production in Agrobacterium tumefaciens KCCM 10413 culture, the highest CoQ10 production was achieved in medium containing corn steep powder (CSP). Components for a stimulatory effect on the production of CoQ10 in CSP were screened, and lactate was found to increase dry cell weight (DCW) and the specific CoQ10 content. In a fed-batch culture of A. tumefaciens, supplementation with 1.5 g of lactate l−1 further improved DCW, the specific CoQ10 content, and CoQ10 production by 16.0, 5.8, and 22.8%, respectively. It has been reported that lactate stimulates cell growth and acts as an accelerator driving the tricarboxylic acid (TCA) cycle (Roberto et al. 2002, Biotechnol Let 24:427–431; Matsuoka et al. 1996, Biosci Biotechnol Biochem 60:575–579). In this study, lactate supplementation increased DCW and the specific CoQ10 content in A. tumefaciens culture, probably by accelerating TCA cycle and energy production as reported previously, leading to the increase of CoQ10 production.
    World Journal of Microbiology and Biotechnology 01/2008; 24(6):887-890. · 1.26 Impact Factor