| 1. |
- Christenson, Andreas, et al.
(författare)
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Direct electron transfer between ligninolytic redox enzymes and electrodes
- 2004
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Ingår i: Electroanalysis. - : Wiley. - 1040-0397 .- 1521-4109. ; 16:13-14, s. 1074-1092
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Forskningsöversikt (refereegranskat)abstract
- The electrochemistry of the ligninolytic redox enzymes, which include lignin peroxidase, manganese peroxidase and laccase and possibly also cellobiose dehydrogenase, is reviewed and discussed in conjunction with their basic biochemical characteristics. It is shown that long-range electron transfer between these enzymes and electrodes can be established and their ability to degrade lignin through a direct electron transfer mechanism is discussed.
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| 2. |
- Stoica, L., et al.
(författare)
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Membrane-Less Biofuel Cell Based on Cellobiose Dehydrogenase (Anode)/Laccase (Cathode) Wired via Specific Os-Redox Polymers
- 2009
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Ingår i: Fuel Cells. - : Wiley. - 1615-6854 .- 1615-6846. ; 9:1, s. 53-62
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Tidskriftsartikel (refereegranskat)abstract
- A membrane-free biofuel cell (BFC) is reported based on enzymes wired to graphite electrodes by means of Os-complex modified redox polymers. For the anode cellobiose dehydrogenase (CDH) is used as a biocatalyst whereas for the cathode a laccase was applied. This laccase is a high-potential laccase and hence able to reduce O-2 to H2O at a formal potential higher than +500 mV versus Ag/AgCl. In order to establish efficient electrochemical contact between the enzymes and graphite electrodes electrodeposition polymers containing Os-complex with specifically designed monomer compositions and formal potentials of the coordinatively bound Os-complex were synthesised and used to wire the enzymes to the electrodes. The newly designed CDH/Os-redox polymer anode was characterised at different pH values and optimised with respect to the nature of the polymer and the enzyme-to-polymer ratio. The resulting BFC was evaluated running on beta-lactose as a fuel and air/O-2 as an oxidising agent. The power output, the maximum current density and the electromotor force (E-emf) were found to be affected by the pH value, resulting in a maximum power output of 1.9 mu W cm(-2) reached at pH 4.3, a maximum current density of about 13 mu A cm(-2) at pH 3.5, and the highest E-emf approaching 600 mV at pH 4.0.
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| 3. |
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| 4. |
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| 5. |
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| 6. |
- Coman, Vasile, et al.
(författare)
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A Direct Electron Transfer-Based Glucose/Oxygen Biofuel Cell Operating in Human Serum
- 2010
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Ingår i: Fuel Cells. - : Wiley. - 1615-6854 .- 1615-6846. ; 10:1, s. 9-16
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Tidskriftsartikel (refereegranskat)abstract
- We report on the fabrication and characterisation of the very first direct electron transfer-based glucose/oxygen biofuel cell (BFC) operating in neutral glucose-containing buffer and human serum. Corynascus thermophilus cellobiose dehydrogenase and Myrothecium verrucaria bilirubin oxidase were used as anodic and cathodic bioelements, respectively. The following characteristics of the mediator-, separator- and membrane-less, a priori, non-toxic and simple miniature BFC, was obtained: an open-circuit voltage of 0.62 and 0.58 V, a maximum power density of ca. 3 and 4 mu W cm(-2) at 0.37 and 0.19 V of cell voltage, in phosphate buffer and human serum, respectively.
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| 7. |
- Hallberg, Martin, et al.
(författare)
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Crystal structure of the 270 kDa homotetrameric lignin-degrading enzyme pyranose 2-oxidase
- 2004
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Ingår i: Journal of Molecular Biology. - : Elsevier BV. - 0022-2836 .- 1089-8638. ; 341:3, s. 781-796
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Tidskriftsartikel (refereegranskat)abstract
- Pyranose 2-oxidase (P2Ox) is a 270 kDa homotetramer localized preferentially in the hyphal periplasmic space of lignocellulolytic fungi and has a proposed role in lignocellulose degradation to produce the essential co-substrate, hydrogen peroxide, for lignin peroxidases. P2Ox oxidizes D-glucose and other aldopyranoses regioselectively at C2 to the corresponding 2-keto sugars; however, for some substrates, the enzyme also displays specificity for oxidation at C3. The crystal structure of P2Ox from Trametes multicolor has been determined using single anomalous dispersion with mercury as anomalous scatterer. The model was refined at 1.8 Angstrom resolution to R and R-free values of 0.134 and 0.171, respectively. The overall fold of the P2Ox subunit resembles that of members of the glucose-methanol-choline family of long-chain oxidoreductases, featuring a flavin-binding Rossmann domain of class alpha/beta and a substrate-binding subdomain with a six-stranded central beta sheet and three U helices. The homotetramer buries a large internal cavity of roughly 15,000 Angstrom(3), from which the four active sites are accessible. Four solvent channels lead from the surface into the cavity through which substrate must enter before accessing the active site. The present structure shows an acetate molecule bound in the active site with the carboxylate group positioned immediately below the flavin N5 atom, and with one carboxylate oxygen atom interacting with the catalytic residues His548 and Asn593. The entrance to the active site is blocked by a loop (residues 452 to 461) with excellent electron density but elevated temperature factors. We predict that this loop is dynamic and opens to allow substrate entry and exit. In silico docking of D-glucose in the P2Ox active site shows that with the active-site loop in the closed conformation, monosaccharides cannot be accommodated; however, after removing the loop from the model, a tentative set of protein-substrate interactions for beta-D-glucose have been outlined.
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| 8. |
- Hassan, Noor, et al.
(författare)
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Biochemical and structural characterization of a thermostable beta-glucosidase from Halothermothrix orenii for galacto-oligosaccharide synthesis
- 2015
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Ingår i: Applied Microbiology and Biotechnology. - : Springer Science and Business Media LLC. - 0175-7598 .- 1432-0614. ; 99:4, s. 1731-1744
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Tidskriftsartikel (refereegranskat)abstract
- Lactose is a major disaccharide by-product from the dairy industries, and production of whey alone amounts to about 200 million tons globally each year. Thus, it is of particular interest to identify improved enzymatic processes for lactose utilization. Microbial beta-glucosidases (BGL) with significant beta-galactosidase (BGAL) activity can be used to convert lactose to glucose (Glc) and galactose (Gal), and most retaining BGLs also synthesizemore complex sugars from the monosaccharides by transglycosylation, such as galacto-oligosaccharides (GOS), which are prebiotic compounds that stimulate growth of beneficial gut bacteria. In this work, a BGL from the thermophilic and halophilic bacterium Halothermothrix orenii, HoBGLA, was characterized biochemically and structurally. It is an unspecific beta-glucosidase with mixed activities for different substrates and prominent activity with various galactosidases such as lactose. We show that HoBGLA is an attractive candidate for industrial lactose conversion based on its high activity and stability within a broad pH range (4.5-7.5), with maximal beta-galactosidase activity at pH 6.0. The temperature optimum is in the range of 65-70 degrees C, and HoBGLA also shows excellent thermostability at this temperature range. The main GOS products from HoBGLA transgalactosylation are beta-D-Galp-(1 -> 6)-D-Lac (6GALA) and beta-D-Galp-(1 -> 3)-D-Lac (3GALA), indicating that D-lactose is a better galactosyl acceptor than either of the monosaccharides. To evaluate ligand binding and guide GOS modeling, crystal structures of HoBGLA were determined in complex with thiocellobiose, 2-deoxy-2-fluoro-D-glucose and glucose. The two major GOS products, 3GALA and 6GALA, were modeled in the substrate-binding cleft of wild-type HoBGLA and shown to be favorably accommodated.
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| 9. |
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| 10. |
- Hassan, Noor, et al.
(författare)
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Crystal structures of Phanerochaete chrysosporium pyranose 2-oxidase suggest that the N-terminus acts as a propeptide that assists in homotetramer assembly
- 2013
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Ingår i: FEBS Open Bio. - : Wiley. - 2211-5463. ; 3, s. 496-504
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Tidskriftsartikel (refereegranskat)abstract
- The flavin-dependent homotetrameric enzyme pyranose 2-oxidase (P2O) is found mostly, but not exclusively, in lignocellulose-degrading fungi where it catalyzes the oxidation of β-. d-glucose to the corresponding 2-keto sugar concomitantly with hydrogen peroxide formation during lignin solubilization. Here, we present crystal structures of P2O from the efficient lignocellulolytic basidiomycete Phanerochaete chrysosporium. Structures were determined of wild-type PcP2O from the natural fungal source, and two variants of recombinant full-length PcP2O, both in complex with the slow substrate 3-deoxy-3-fluoro-. β-. d-glucose. The active sites in PcP2O and P2O from Trametes multicolor (TmP2O) are highly conserved with identical substrate binding. Our structural analysis suggests that the 17°C higher melting temperature of PcP2O compared to TmP2O is due to an increased number of intersubunit salt bridges. The structure of recombinant PcP2O expressed with its natural N-terminal sequence, including a proposed propeptide segment, reveals that the first five residues of the propeptide intercalate at the interface between A and B subunits to form stabilizing, mainly hydrophobic, interactions. In the structure of mature PcP2O purified from the natural source, the propeptide segment in subunit A has been replaced by a nearby loop in the B subunit. We propose that the propeptide in subunit A stabilizes the A/B interface of essential dimers in the homotetramer and that, upon maturation, it is replaced by the loop in the B subunit to form the mature subunit interface. This would imply that the propeptide segment of PcP2O acts as an intramolecular chaperone for oligomerization at the A/B interface of the essential dimer.
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