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  • Articles  (1,702)
  • Springer  (1,702)
  • American Chemical Society
  • American Chemical Society (ACS)
  • American Geophysical Union
  • National Academy of Sciences
  • 2015-2019  (874)
  • 2005-2009  (682)
  • 1990-1994
  • 1980-1984  (146)
  • 2017  (874)
  • 2009  (682)
  • 1983  (146)
  • Applied Microbiology and Biotechnology  (231)
  • 843
  • Process Engineering, Biotechnology, Nutrition Technology  (1,702)
  • Physics
Collection
  • Articles  (1,702)
Source
Publisher
  • Springer  (1,702)
  • American Chemical Society
  • American Chemical Society (ACS)
  • American Geophysical Union
  • National Academy of Sciences
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  • 2015-2019  (874)
  • 2005-2009  (682)
  • 1990-1994
  • 1980-1984  (146)
Year
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  • Process Engineering, Biotechnology, Nutrition Technology  (1,702)
  • Physics
  • Biology  (1,702)
  • 1
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    Specific amino acids responsible for the cold adaptedness of Micrococcus antarcticus β-glucosidase BglU (2017)
    Springer
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    Publication Date: 2017-02-15
    Description: Psychrophilic enzymes display efficient activity at moderate or low temperatures (4–25 °C) and are therefore of great interest in biotechnological industries. We previously examined the crystal structure of BglU, a psychrophilic β-glucosidase from the bacterium Micrococcus antarcticus , at 2.2 Å resolution. In structural comparison and sequence alignment with mesophilic (BglB) and thermophilic (GlyTn) counterpart enzymes, BglU showed much lower contents of Pro residue and of charged amino acids (particularly positively charged) on the accessible surface area. In the present study, we investigated the roles of specific amino acid residues in the cold adaptedness of BglU. Mutagenesis assays showed that the mutations G261R and Q448P increased optimal temperature (from 25 to 40–45 °C) at the expense of low-temperature activity, but had no notable effects on maximal activity or heat lability. Mutations A368P, T383P, and A389E significantly increased optimal temperature (from 25 to 35–40 °C) and maximal activity (~1.5-fold relative to BglU). Thermostability of A368P and A389E increased slightly at 30 °C. Mutations K163P, N228P, and H301A greatly reduced enzymatic activity—almost completely in the case of H301A. Low contents of Pro, Arg, and Glu are important factors contributing to BglU’s psychrophilic properties. Our findings will be useful in structure-based engineering of psychrophilic enzymes and in production of mutants suitable for a variety of industrial processes (e.g., food production, sewage treatment) at cold or moderate temperatures.
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  • 2
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    Redesign of antifungal polyene glycosylation: engineered biosynthesis of disaccharide-modified NPP (2017)
    Springer
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    Publication Date: 2017-05-10
    Description: Polyene macrolides such as nystatin A1 and amphotericin B have been known to be potent antifungal antibiotics for several decades. Because the therapeutic application of polyenes is restricted by severe side effects such as nephrotoxicity, various chemical and biological studies to modify the polyene structure have been conducted to develop less-toxic polyene antifungals. A newly discovered nystatin-like polyene compound NPP was shown to contain an aglycone that was identical to nystatin but harbored a unique di-sugar moiety, mycosaminyl- N -acetyl-glucosamine, which led to higher solubility and reduced hemolytic toxicity. Additionally, a NPP-specific second sugar extending gene, nppY , was recently identified to be responsible for the transfer of a second sugar, N -acetyl-glucosamine, in NPP biosynthesis. In this study, we investigated biosynthesis of the glycoengineered NPP analog through genetic manipulation of the NPP A1 producer, Pseudonocardia autotrophica KCTC9441. NypY is another second sugar glycosyltransferase produced by Pseudonocardia sp. P1 that is responsible for the transfer of a mannose to the mycosaminyl sugar residue of nystatin. We blocked the transfer of a second sugar through nppY disruption, then expressed nypY in P. autotrophica △nppY mutant strain. When compared with nystain A1 and NPP A1, the newly engineered mannosylated NPP analog showed reduced in vitro antifungal activity, while exhibiting higher nephrotoxical activities against human hepatocytes. These results suggest for the first time that not only the number of sugar residues but also the type of extended second sugar moiety could affect biological activities of polyene macrolides.
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  • 3
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    Sucrose purification and repeated ethanol production from sugars remaining in sweet sorghum juice subjected to a membrane separation process (2017)
    Springer
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    Publication Date: 2017-05-11
    Description: The juice from sweet sorghum cultivar SIL-05 (harvested at physiological maturity) was extracted, and the component sucrose and reducing sugars (such as glucose and fructose) were subjected to a membrane separation process to purify the sucrose for subsequent sugar refining and to obtain a feedstock for repeated bioethanol production. Nanofiltration (NF) of an ultrafiltration (UF) permeate using an NTR-7450 membrane (Nitto Denko Corporation, Osaka, Japan) concentrated the juice and produced a sucrose-rich fraction (143.2 g L −1 sucrose, 8.5 g L −1 glucose, and 4.5 g L −1 fructose). In addition, the above NF permeate was concentrated using an ESNA3 NF membrane to provide concentrated permeated sugars (227.9 g L −1 ) and capture various amino acids in the juice, enabling subsequent ethanol fermentation without the addition of an exogenous nitrogen source. Sequential batch fermentation using the ESNA3 membrane concentrate provided an ethanol titer and theoretical ethanol yield of 102.5–109.5 g L −1 and 84.4–89.6%, respectively, throughout the five-cycle batch fermentation by Saccharomyces cerevisiae BY4741. Our results demonstrate that a membrane process using UF and two types of NF membranes has the potential to allow sucrose purification and repeated bioethanol production.
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  • 4
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    Fusion expression of the PGLa-AM1 with native structure and evaluation of its anti- Helicobacter pylori activity (2017)
    Springer
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    Publication Date: 2017-05-11
    Description: Helicobacter pylori ( H . pylori ) shows increasingly enhanced resistance to various antibiotics, and its eradication has become a major problem in medicine. The antimicrobial peptide PGLa-AM1 is a short peptide with 22 amino acids and exhibits strong antibacterial activity. In this study, we investigated whether it has anti- H . pylori activity for the further development of anti- H . pylori drugs to replace existing antibiotics. However, the natural antimicrobial peptide PGLa-AM1 shows a low yield and is difficult to separate, limiting its application. A good strategy to solve this problem is to express the antimicrobial peptide PGLa-AM1 using gene engineering at a high level and low cost. For getting PGLa-AM1 with native structure, in this study, a specific protease cleavage site of tobacco etch virus (TEV) was designed before the PGLa-AM1 peptide. For convenience to purify and identify high-efficiency expression PGLa-AM1, the PGLa-AM1 gene was fused with the polyhedrin gene of Bombyx mori ( B . mori ), and a 6 × His tag was designed to insert before the amino terminus of the fusion protein. The fusion antibacterial peptide PGLa-AM1 (FAMP) gene codon was optimized, and the gene was synthesized and cloned into the Escherichia coli ( E . coli ) pET-30a (+) expression vector. The results showed that the FAMP was successfully expressed in E . coli . Its molecular weight was approximately 34 kDa, and its expression level was approximately 30 mg/L. After the FAMP was purified, it was further digested with TEV protease. The acquired recombinant antimicrobial peptide PGLa-AM1 exerted strong anti- H . pylori activity and therapeutic effect in vitro and in vivo.
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  • 5
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    Polymers for enhanced oil recovery: fundamentals and selection criteria (2017)
    Springer
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    Publication Date: 2017-05-14
    Description: With a rising population, the demand for energy has increased over the years. As per the projections, both fossil fuel and renewables will remain as major energy source (678 quadrillion BTU) till 2030 with fossil fuel contributing 78% of total energy consumption. Hence, attempts are continuously made to make fossil fuel production more sustainable and cheaper. From the past 40 years, polymer flooding has been carried out in marginal oil fields and have proved to be successful in many cases. The common expectation from polymer flooding is to obtain 50% ultimate recovery with 15 to 20% incremental recovery over secondary water flooding. Both naturally derived polymers like xanthan gum and synthetic polymers like partially hydrolyzed polyacrylamide (HPAM) have been used for this purpose. Earlier laboratory and field trials revealed that salinity and temperature are the major issues with the synthetic polymers that lead to polymer degradation and adsorption on the rock surface. Microbial degradation and concentration are major issues with naturally derived polymers leading to loss of viscosity and pore throat plugging. Earlier studies also revealed that polymer flooding is successful in the fields where oil viscosity is quite higher (up to 126 cp) than injection water due to improvement in mobility ratio during polymer flooding. The largest successful polymer flood was reported in China in 1990 where both synthetic and naturally derived polymers were used in nearly 20 projects. The implementation of these projects provides valuable suggestions for further improving the available processes in future. This paper examines the selection criteria of polymer, field characteristics that support polymer floods and recommendation to design a large producing polymer flooding.
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  • 6
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    Enhancing H 2 O 2 resistance of an esterase from Pyrobaculum calidifontis by structure-guided engineering of the substrate binding site (2017)
    Springer
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    Publication Date: 2017-05-18
    Description: Green technologies are attracting increasing attention in industrial chemistry where enzymatic reactions can replace dangerous and environmentally unfriendly chemical processes. In situ enzymatic synthesis of peroxycarboxylic acid is an attractive alternative for several industrial applications although concentrated H 2 O 2 can denature the biocatalyst, limiting its usefulness. Herein, we report the structure-guided engineering of the Pyrobaculum calidifontis esterase (PestE) substrate binding site to increase its stability and perhydrolysis activity. The L89R/L40A PestE mutant showed better tolerance toward concentrated H 2 O 2 compared with wild-type PestE , and retained over 72% of its initial activity after 24-h incubation with 2 M H 2 O 2 . Surprisingly, the half-life ( t 1/2 , 80 °C) of PestE increased from 28 to 54 h. The k cat / K m values of the mutant increased 21- and 3.4-fold toward pentanoic acid and H 2 O 2, respectively. This work shows how protein engineering can be used to enhance the H 2 O 2 resistance and catalytic efficiency of an enzyme.
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  • 7
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    Identification, expression and characterization of an R -ω-transaminase from Capronia semiimmersa (2017)
    Springer
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    Publication Date: 2017-05-18
    Description: Chiral amines are essential precursors in the production of biologically active compounds, including several important drugs. Among the biocatalytic strategies that have been developed for their synthesis, the use of ω-transaminases (ω-TA) appears as an attractive alternative allowing the stereoselective amination of prochiral ketones. However, the problems associated with narrow substrate specificity, unfavourable reaction equilibrium and expensive amine donors still hamper its industrial application. The search for novel enzymes from nature can contribute to expand the catalytic repertoire of ω-TA and help to circumvent some of these problems. A genome mining approach, based on the work described by Höhne et al., was applied for selection of potential R -ω-TA. Additional criteria were used to select an enzyme that differs from previously described ones. A candidate R -ω-TA from Capronia semiimmersa was selected, cloned and expressed in Escherichia coli . Interestingly, alignment of this enzyme with previously reported TA sequences revealed the presence of two additional amino acid residues in a loop close to the active site. The impact of this change was analysed with a structural model based on crystallized R -ω-TAs. Analysis of the substrate specificity of R -ω-TA from C . semiimmersa indicates that it accepts a diversity of ketones as substrates yielding the corresponding amine with good yields and excellent enantioselectivity. The expressed enzyme accepts isopropylamine as amine donor what makes it suitable for industrial processes.
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  • 8
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    Effect of methyl-β-cyclodextrin on gene expression in microbial conversion of phytosterol (2017)
    Springer
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    Publication Date: 2017-05-24
    Description: Modified β-cyclodextrins are widely used for the enhancement of microbial conversions of lipophilic compounds such as steroids. Multiple mechanisms of cyclodextrin-mediated enhancement of phytosterol bioconversion by mycobacteria had previously been shown to include steroid solubilization, alterations in the cell wall permeability for both steroids and nutrients, facilitation of protein leaking, and activity suppression of some steroid-transforming enzymes.In this work, we studied whether cyclodextrins might affect expression of the genes involved in the steroid catabolic pathway. Phytosterol bioconversion with 9α-hydroxy-androst-4-ene-3,17-dione accumulation by Mycobacterium sp. VKM Ac-1817D in the presence of methylated β-cyclodextrin (MCD) was investigated. RNA sequencing of the whole transcriptomes in different combinations of phytosterol and MCD showed a similar expression level of the steroid catabolism genes related to the KstR-regulon and was responsible for side chain and initial steps of steroid core oxidation; whereas, induction levels of the genes related to the KstR2-regulon were attenuated in the presence of MCD in this strain. The data were attenuated with quantitative real-time PCR.The results contribute to the understanding of cyclodextrin effects on microbial steroid conversion and provide a basis for the use of cyclodextrins as expression enhancers for studies of sterol catabolism in actinobacteria.
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  • 9
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    Assessment of the horizontal transfer of functional genes as a suitable approach for evaluation of the bioremediation potential of petroleum-contaminated sites: a mini-review (2017)
    Springer
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    Publication Date: 2017-05-13
    Description: Petroleum sludge contains recalcitrant residuals. These compounds because of being toxic to humans and other organism are of the major concerns. Therefore, petroleum sludge should be safely disposed. Physicochemical methods which are used by this sector are mostly expensive and need complex devices. Bioremediation methods because of being eco-friendly and cost-effective overcome most of the limitations of physicochemical treatments. Microbial strains capable to degrade petroleum hydrocarbons are practically present in all soils and sediments and their population density increases in contact with contaminants. Bacterial strains cannot degrade alone all kinds of petroleum hydrocarbons, rather microbial consortium should collaborate with each other for degradation of petroleum hydrocarbon mixtures. Horizontal transfer of functional genes between bacteria plays an important role in increasing the metabolic potential of the microbial community. Therefore, selecting a suitable degrading gene and tracking its horizontal transfer would be a useful approach to evaluate the bioremediation process and to assess the bioremediation potential of contaminated sites.
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  • 10
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    Thermodynamics of enzyme-catalyzed esterifications: I. Succinic acid esterification with ethanol (2017)
    Springer
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    Publication Date: 2017-05-13
    Description: Succinic acid (SA) was esterified with ethanol using Candida antarctica lipase B immobilized on acrylic resin at 40 and 50 °C. Enzyme activity in the reaction medium was assured prior to reaction experiments. Reaction-equilibrium experiments were performed for varying initial molalities of SA and water in the reaction mixtures. This allowed calculating the molality-based apparent equilibrium constant K m as function of concentration and temperature. K m was shown to depend strongly on the molality of water and SA as well as on temperature. It could be concluded that increasing the molality of SA shifted the reaction equilibrium towards the products. Water had a strong effect on the activity of the enzyme and on K m . The concentration dependence of K m values was explained by the activity coefficients of the reacting agents. These were predicted with the thermodynamic models Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT), NRTL, and Universal Quasichemical Functional Group Activity Coefficients (UNIFAC), yielding the ratio of activity coefficients of products and reactants K γ . All model parameters were taken from literature. The models yielded K γ values between 25 and 115. Thus, activity coefficients have a huge impact on the consistent determination of the thermodynamic equilibrium constants K th . Combining K m and PC-SAFT-predicted K γ allowed determining K th and the standard Gibbs energy of reaction as function of temperature. This value was shown to be in very good agreement with results obtained from group contribution methods for Gibbs energy of formation. In contrast, inconsistencies were observed for K th using K γ values from the classical g E -models UNIFAC and NRTL. The importance of activity coefficients opens the door for an optimized reaction setup for enzymatic esterifications.
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