Coupling protein scaffold and biosilicification: A sustainable and recyclable approach for d-mannitol production via one-step purification and immobilization of multienzymes.

Enzymatic synthesis of biochemicals in vitro is vital in synthetic biology for its efficiency, minimal by-products, and easy product separation. However, challenges like enzyme preparation, stability, and reusability persist. Here, we introduced a protein scaffold and biosilicification coupled system, providing a singular process for the purification and immobilization of multiple enzymes. Using d-mannitol as a model, we initially constructed a self-assembling EE/KK protein scaffold for the co-immobilization of glucose dehydrogenase and mannitol dehydrogenase. Under an enzyme-to-scaffold ratio of 1:8, a d-mannitol yield of 0.692 mol/mol was achieved within 4 h, 2.16-fold higher than the free enzymes. The immobilized enzymes retained 70.9 % of the initial joint activity while the free ones diminished nearly to inactivity after 8 h. Furthermore, we incorporated the biosilicification peptide CotB into the EE/KK scaffold, inducing silica deposition, which enabled the one-step purification and immobilization process assisted by Spy/Snoop protein-peptide pairs. The coupled system demonstrated a comparable d-mannitol yield to that of EE/KK scaffold and 1.34-fold higher remaining activities after 36 h. Following 6 cycles of reaction, the immobilized system retained the capability to synthesize 56.4 % of the initial d-mannitol titer. The self-assembly co-immobilization platform offers an effective approach for enzymatic synthesis of d-mannitol and other biochemicals.

Does Acinetobacter calcoaceticus glucose dehydrogenase produce self-damaging H2O2?

The soluble glucose dehydrogenase (sGDH) from Acinetobacter calcoaceticus has been widely studied and is used, in biosensors, to detect the presence of glucose, taking advantage of its high turnover and insensitivity to molecular oxygen. This approach, however, presents two drawbacks: the enzyme has broad substrate specificity (leading to imprecise blood glucose measurements) and shows instability over time (inferior to other oxidizing glucose enzymes). We report the characterization of two sGDH mutants: the single mutant Y343F and the double mutant D143E/Y343F. The mutants present enzyme selectivity and specificity of 1.2 (Y343F) and 5.7 (D143E/Y343F) times higher for glucose compared with that of the wild-type. Crystallographic experiments, designed to characterize these mutants, surprisingly revealed that the prosthetic group PQQ (pyrroloquinoline quinone), essential for the enzymatic activity, is in a cleaved form for both wild-type and mutant structures. We provide evidence suggesting that the sGDH produces H2O2, the level of production depending on the mutation. In addition, spectroscopic experiments allowed us to follow the self-degradation of the prosthetic group and the disappearance of sGDH's glucose oxidation activity. These studies suggest that the enzyme is sensitive to its self-production of H2O2. We show that the premature aging of sGDH can be slowed down by adding catalase to consume the H2O2 produced, allowing the design of a more stable biosensor over time. Our research opens questions about the mechanism of H2O2 production and the physiological role of this activity by sGDH.

Catalytic Synthesis of (S)-CHBE by Directional Coupling and Immobilization of Carbonyl Reductase and Glucose Dehydrogenase.

Ethyl (S)-4-chloro-3-hydroxybutyrate ((S)-CHBE) is an important chiral intermediate in the synthesis of the cholesterol-lowering drug atorvastatin. Studying the use of SpyTag/SpyCatcher and SnoopTag/SnoopCatcher systems for the asymmetric reduction reaction and directed coupling coenzyme regeneration is practical for efficiently synthesizing (S)-CHBE. In this study, Spy and Snoop systems were used to construct a double-enzyme directed fixation system of carbonyl reductase (BsCR) and glucose dehydrogenase (BsGDH) for converting 4-chloroacetoacetate (COBE) to (S)-CHBE and achieving coenzyme regeneration. We discussed the enzymatic properties of the immobilized enzyme and the optimal catalytic conditions and reusability of the double-enzyme immobilization system. Compared to the free enzyme, the immobilized enzyme showed an improved optimal pH and temperature, maintaining higher relative activity across a wider range. The double-enzyme immobilization system was applied to catalyze the asymmetric reduction reaction of COBE, and the yield of (S)-CHBE reached 60.1% at 30 °C and pH 8.0. In addition, the double-enzyme immobilization system possessed better operational stability than the free enzyme, and maintained about 50% of the initial yield after six cycles. In summary, we show a simple and effective strategy for self-assembling SpyCatcher/SnoopCatcher and SpyTag/SnoopTag fusion proteins, which inspires building more cascade systems at the interface. It provides a new method for facilitating the rapid construction of in vitro immobilized multi-enzyme complexes from crude cell lysate.

Development of an Enzyme Cascade System for the Synthesis of Enantiomerically Pure D-Amino Acids Utilizing Ancestral L-Amino Acid Oxidase.

Enantiomerically pure D-amino acids hold significant potential as precursors for synthesizing various fine chemicals, including peptide-based drugs and other pharmaceuticals. This study focuses on establishing an enzymatic cascade system capable of converting various L-amino acids into their D-isomers. The system integrates four enzymes: ancestral L-amino acid oxidase (AncLAAO-N4), D-amino acid dehydrogenase (DAADH), D-glucose dehydrogenase (GDH), and catalase. AncLAAO-N4 initiates the process by converting L-amino acids to corresponding keto acids, which are then stereo-selectively aminated to D-amino acids by DAADH using NADPH and NH4Cl. Concurrently, any generated H2O2 is decomposed into O2 and H2O by catalase, while GDH regenerates NADPH from D-glucose. Optimization of reaction conditions and substrate concentrations enabled the successful synthesis of five D-amino acids, including a D-Phe derivative, three D-Trp derivatives, and D-phenylglycine, all with high enantiopurity (>99 % ee) at a preparative scale (>100 mg). This system demonstrates a versatile approach for producing a diverse array of D-amino acids.

Development of Direct Electron Transfer-Type Extended Gate Field Effect Transistor Enzymatic Sensors for Metabolite Detection.

In this work, direct electron transfer (DET)-type extended gate field effect transistor (EGFET) enzymatic sensors were developed by employing DET-type or quasi-DET-type enzymes to detect glucose or lactate in both 100 mM potassium phosphate buffer and artificial sweat. The system employed either a DET-type glucose dehydrogenase or a quasi-DET-type lactate oxidase, the latter of which was a mutant enzyme with suppressed oxidase activity and modified with amine-reactive phenazine ethosulfate. These enzymes were immobilized on the extended gate electrodes. Changes in the measured transistor drain current (ID) resulting from changes to the working electrode junction potential (φ) were observed as glucose and lactate concentrations were varied. Calibration curves were generated for both absolute measured ID and ΔID (normalized to a blank solution containing no substrate) to account for variations in enzyme immobilization and conjugation to the mediator and variations in reference electrode potential. This work resulted in a limit of detection of 53.9 µM (based on ID) for glucose and 2.12 mM (based on ID) for lactate, respectively. The DET-type and Quasi-DET-type EGFET enzymatic sensor was then modeled using the case of the lactate sensor as an equivalent circuit to validate the principle of sensor operation being driven through OCP changes caused by the substrate-enzyme interaction. The model showed slight deviation from collected empirical data with 7.3% error for the slope and 8.6% error for the y-intercept.

Enzymatic Galvanic Redox Potentiometry for In Vivo Biosensing.

Redox potentiometry has emerged as a new platform for in vivo sensing, with improved neuronal compatibility and strong tolerance against sensitivity variation caused by protein fouling. Although enzymes show great possibilities in the fabrication of selective redox potentiometry, the fabrication of an enzyme electrode to output open-circuit voltage (EOC) with fast response remains challenging. Herein, we report a concept of novel enzymatic galvanic redox potentiometry (GRP) with improved time response coupling the merits of the high selectivity of enzyme electrodes with the excellent biocompatibility and reliability of GRP sensors. With a glucose biosensor as an illustration, we use flavin adenine dinucleotide-dependent glucose dehydrogenase as the recognition element and carbon black as the potential relay station to improve the response time. We find that the enzymatic GRP biosensor rapidly responds to glucose with a good linear relationship between EOC and the logarithm of glucose concentration within a range from 100 µM to 2.65 mM. The GRP biosensor shows high selectivity over O2 and coexisting neurochemicals, good reversibility, and sensitivity and can in vivo monitor glucose dynamics in rat brain. We believe that this study will pave a new platform for the in vivo potentiometric biosensing of chemical events with high reliability.

Ketogluconate production by Gluconobacter strains: enzymes and biotechnological applications.

Gluconobacter strains perform incomplete oxidation of various sugars and alcohols, employing regio- and stereoselective membrane-bound dehydrogenases oriented toward the periplasmic space. This oxidative fermentation process is utilized industrially. The ketogluconate production pathway, characteristic of these strains, begins with the conversion of d-glucose to d-gluconate, which then diverges and splits into 2 pathways producing 5-keto-d-gluconate and 2-keto-d-gluconate and subsequently 2,5-diketo-d-gluconate. These transformations are facilitated by membrane-bound d-glucose dehydrogenase, glycerol dehydrogenase, d-gluconate dehydrogenase, and 2-keto-d-gluconate dehydrogenase. The variance in end products across Gluconobacter strains stems from the diversity of enzymes and their activities. This review synthesizes biochemical and genetic knowledge with biotechnological applications, highlighting recent advances in metabolic engineering and the development of an efficient production process focusing on enzymes relevant to the ketogluconate production pathway in Gluconobacter strains.

3D Carbon-Based Conductive Network Printed for Glucose Sensors on Curved and Flexible Substrates.

The rising prevalence of diabetes has led to an increased focus on real-time glucose monitoring. Wearable glucose sensor patches allow noninvasive, real-time monitoring, reducing patient discomfort compared to invasive sensors. However, most existing glucose sensor patches rely on complex and contaminating metal vapor deposition technologies, which pose limitations in practical production. In this study, we propose a novel approach for preparing graphite/multiwall carbon nanotubes (MWCNT)/reduced graphene oxide (rGO) using a high-viscosity ink, which can be easily obtained through simple mechanical stirring. To create intricate patterns and enable printing on curved substrates, we employed a 3D printer equipped with an infrared laser ranging system. The ink served as a working electrode, and we developed a three-electrode system patch with a concentric circle structure. Subsequently, the working electrode underwent enzymatic modification with glucose dehydrogenase with flavin adenine dinucleotide (GDH-FAD) using a polymer embedding method. The resulting wearable glucose sensor exhibited a sensitivity of 2.42 µA mM-1 and a linear detection range of 1-12 mM. In addition, the glucose sensor has excellent anti-interference capability and demonstrates good repeatability in simulated real human wear scenarios, which meets the requirements for accurate human detection. These findings provide valuable insights into the development of human health monitoring technologies.

Immobilization of Thermoplasma acidophilum Glucose Dehydrogenase and Isocitrate Dehydrogenase Through Enzyme-Inorganic Hybrid Nanocrystal Formation.

The development of green catalysts, specifically biocatalysts, is crucial for building a sustainable society. To enhance the versatility of biocatalysts, the immobilization of enzymes plays a vital role as it improves their recyclability and robustness. As target enzymes to immobilize, glucose dehydrogenases and carboxylases are particularly important among various kinds of enzymes due to their involvement in two significant reactions: regeneration of the reduced form of coenzyme required for various reactions, and carboxylation reactions utilizing CO2 as a substrate, respectively. In this study, we immobilized Thermoplasma acidophilum glucose dehydrogenase (TaGDH) and T. acidophilum isocitrate dehydrogenase (TaIDH) using a previously reported method involving the formation of enzyme-inorganic hybrid nanocrystals, in the course of our continuing study focusing on carboxylation catalyzed by the free form of TaGDH and TaIDH. Subsequently, we investigated the properties of the resulting immobilized enzymes. Our results indicate the successful immobilization of TaGDH and TaIDH through the formation of hybrid nanocrystals utilizing Mn2+. The immobilization process enhanced TaIDH activity, up to 211%, while TaGDH retained 71% of its original activity. Notably, the immobilized TaGDH exhibited higher activity at temperatures exceeding 87 °C than the free TaGDH. Moreover, these immobilized enzymes could be recycled. Finally, we successfully utilized the immobilized enzymes for the carboxylation of 2-ketoglutaric acid under 1 MPa CO2. In conclusion, this study represents the first immobilization of TaGDH and TaIDH using the hybrid nanocrystal forming method. Furthermore, we achieved significant activity enhancement of TaIDH through immobilization and demonstrated the recyclability of the immobilized enzymes.

The application of bacteria-derived dehydrogenases and oxidases in the synthesis of gold nanoparticles.

In this work the green synthesis of gold nanoparticles (Au-NPs) using the oxidoreductive enzymes Myriococcum thermophilum cellobiose dehydrogenase (Mt CDH), Glomerella cingulata glucose dehydrogenase (Gc GDH), and Aspergillus niger glucose oxidase (An GOX)) as bioreductants was investigated. The influence of reaction conditions on the synthesis of Au-NPs was examined and optimised. The reaction kinetics and the influence of Au ions on the reaction rate were determined. Based on the kinetic study, the mechanism of Au-NP synthesis was proposed. The Au-NPs were characterized by UV-Vis spectroscopy and transmission electron microscopy (TEM). The surface plasmon resonance (SPR) absorption peaks of the Au-NPs synthesised with Mt CDH and Gc GDH were observed at 535 nm, indicating an average size of around 50 nm. According to the image analysis performed on a TEM micrograph, the Au-NPs synthesized with Gc GDH have a spherical shape with an average size of 2.83 and 6.63 nm after 24 and 48 h of the reaction, respectively. KEY POINTS: • The Au NPs were synthesised by the action of enzymes CDH and GDH. • The synthesis of Au-NPs by CDH is related to the oxidation of cellobiose. • The synthesis of Au-NPs by GDH was not driven by the reaction kinetic.

Identification of a novel thermostable transaminase and its application in L-phosphinothricin biosynthesis.

Transaminase (TA) is a crucial biocatalyst for enantioselective production of the herbicide L-phosphinothricin (L-PPT). The use of enzymatic cascades has been shown to effectively overcome the unfavorable thermodynamic equilibrium of TA-catalyzed transamination reaction, also increasing demand for TA stability. In this work, a novel thermostable transaminase (PtTA) from Pseudomonas thermotolerans was mined and characterized. The PtTA showed a high specific activity (28.63 U/mg) towards 2-oxo-4-[(hydroxy)(methyl)phosphinoyl]butyric acid (PPO), with excellent thermostability and substrate tolerance. Two cascade systems driven by PtTA were developed for L-PPT biosynthesis, including asymmetric synthesis of L-PPT from PPO and deracemization of D, L-PPT. For the asymmetric synthesis of L-PPT from PPO, a three-enzyme cascade was constructed as a recombinant Escherichia coli (E. coli G), by co-expressing PtTA, glutamate dehydrogenase (GluDH) and D-glucose dehydrogenase (GDH). Complete conversion of 400 mM PPO was achieved using only 40 mM amino donor L-glutamate. Furthermore, by coupling D-amino acid aminotransferase (Ym DAAT) from Bacillus sp. YM-1 and PtTA, a two-transaminase cascade was developed for the one-pot deracemization of D, L-PPT. Under the highest reported substrate concentration (800 mM D, L-PPT), a 90.43% L-PPT yield was realized. The superior catalytic performance of the PtTA-driven cascade demonstrated that the thermodynamic limitation was overcome, highlighting its application prospect for L-PPT biosynthesis. KEY POINTS: • A novel thermostable transaminase was mined for L-phosphinothricin biosynthesis. • The asymmetric synthesis of L-phosphinothricin was achieved via a three-enzyme cascade. • Development of a two-transaminase cascade for D, L-phosphinothricin deracemization.

Sustainable asymmetric synthesis of diltiazem precursor enabled by recombinant Escherichia coli whole cells co-expressing an engineered ketoreductase and glucose dehydrogenase.

As a key synthetic intermediate of the cardiovascular drug diltiazem, methyl (2R,3S)-3-(4-methoxyphenyl) glycidate ((2R,3S)-MPGM) (1) is accessible via the ring closure of chlorohydrin (3S)-methyl 2-chloro-3-hydroxy-3-(4-methoxyphenyl)propanoate ((3S)-2). We report the efficient reduction of methyl 2-chloro-3-(4-methoxyphenyl)-3-oxo-propanoate (3) to (3S)-2 using an engineered enzyme SSCRM2 possessing 4.5-fold improved specific activity, which was obtained through the structure-guided site-saturation mutagenesis of the ketoreductase SSCR by reliving steric hindrance and undesired interactions. With the combined use of the co-expression fine-tuning strategy, a recombinant E. coli (pET28a-RBS-SSCRM2 /pACYCDuet-GDH), co-expressing SSCRM2 and glucose dehydrogenase, was constructed and optimized for protein expression. After optimizing the reaction conditions, whole-cell-catalyzed complete reduction of industrially relevant 300 g L-1 of 3 was realized, affording (3S)-2 with 99% ee and a space-time yield of 519.1 g∙L-1 ∙d-1 , representing the highest record for the biocatalytic synthesis of (3S)-2 reported to date. The E-factor of this biocatalytic synthesis was 24.5 (including water). Chiral alcohol (3S)-2 generated in this atom-economic synthesis was transformed to (2R,3S)-MPGM in 95% yield with 99% ee.

A nationwide survey of adenovirus-associated encephalitis/encephalopathy in Japan.

BACKGROUND: Adenovirus is a major pathogen causing febrile illness among children. It may also cause acute encephalitis/encephalopathy. This study aimed to elucidate the clinical features of adenovirus-associated encephalitis/encephalopathy (AdVE) among children in Japan. METHODS: A nationwide survey of children with AdVE was conducted. An initial survey was distributed among pediatricians to obtain information about children with AdVE treated between January 2014 and March 2019. A second survey was used to obtain the clinical information of children with AdVE from hospitals that responded to the initial survey and those identified from a literature search of the reported cases. We collected demographic data and information about symptoms of infection, neurological symptoms, laboratory parameters, treatment, and outcomes. Outcomes were determined using the Pediatric Cerebral Performance Category Score. RESULTS: Clinical information was available for 23 children with a median age of 39 months. Two had preexisting neurological disorders and six had a history of febrile seizures. The outcome was good in 15 patients and poor in eight patients. Serum lactate dehydrogenase, glucose, and ammonia levels were higher among children with a poor outcome compared to those with a good outcome. Clinically mild encephalitis/encephalopathy with a reversible splenial lesion was the most common type (n = 8), followed by acute encephalopathy with biphasic seizures and late reduced diffusion (n = 7). CONCLUSION: A prior history of febrile seizures was frequent in children with AdVE. Several different subtypes of acute encephalopathy were seen in children with AdVE, and the outcome was poor in those with acute encephalopathy with biphasic seizures and late reduced diffusion and hemorrhagic shock and encephalopathy syndrome. Elevated lactate dehydrogenase, glucose, and ammonia levels on admission were found to correlate with a poor outcome.

Reduced Graphene Oxide/Organic Dye Composites for Bioelectroconversion of Saccharides: Application for Detection of Saccharides and α-Amylase Assessments.

In this study, PQQ-dependent glucose dehydrogenase (PQQ-GDH) was immobilized onto reduced graphene oxide (rGO) modified with organic dyes from three different classes (acridine, arylmethane, and diazo); namely, neutral red (NR), malachite green (MG), and congo red (CR) formed three types of biosensors. All three rGO/organic dye composites were characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. The impact of three rGO/organic dye modifications employed in bioelectrocatalytic systems on changes in enzyme activity and substrate selectivity was investigated. The highest sensitivity of 39 µA/cm2 was obtained for 1 mM of glucose when a rGO_MG/PQQ-GDH biosensor was used. A significant improvement in the electrochemical response of biosensors was attributed to the higher amount of pyrrolic nitrogen groups on the surface of the rGO/organic dye composites. Modifications of rGO by NR and MG not only improved the surfaces for efficient direct electron transfer (DET) but also influenced the enzyme selectivity through proper binding and orientation of the enzyme. The accuracy of the biosensor's action was confirmed by the spectrophotometric analysis. Perspectives for using the proposed bioelectrocatalytic systems operating on DET principles for total or single monosaccharide and/or disaccharide determination/bioconversion systems or for diagnoses have been presented through examples of bioconversion of D-glucose, D-xylose, and maltose.

IL-6/JAK2-dependent G6PD phosphorylation promotes nucleotide synthesis and supports tumor growth.

OBJECTIVE: Tumor cells hijack inflammatory mechanisms to promote their own growth. IL-6 is one of the major cytokines, and is frequently upregulated in tumors. The pentose phosphate pathway (PPP) generates the indispensable building blocks to produce various nucleotides. Here we aimed to determine whether and how PPP is timely tuned in response to IL-6 to support tumor growth. METHODS: Protein expression was examined by immunoblot. Protein interaction was examined by immunoprecipitation. Tumor cell proliferation in in vitro culture was examined by BrdU assay and colony formation assay. Tumor cell proliferation in mouse xenograft model was examined by Ki-67 staining. RESULTS: Here we show that the metabolic flux of PPP and enzymatic activity of glucose-6-phosphate dehydrogenase (G6PD) is rapidly induced under IL-6 treatment, without obvious changes in G6PD expression level. Mechanistically, Janus kinase 2 (JAK2) phosphorylates G6PD Y437 under IL-6 treatment, which accentuates G6PD enzymatic activity by promoting G6PD binding with its substrate G6P. Further, JAK2-dependent G6PD Y437 phosphorylation is required for IL-6-induced nucleotide biosynthesis and tumor cell proliferation, and is associated with the progression of oral squamous cell carcinoma. CONCLUSIONS: Our findings report a new mechanism implicated in the crosstalk between tumor cells and inflammatory microenvironment, by which JAK2-dependent activation of G6PD governs nucleotide synthesis to support tumor cell proliferation, thereby highlighting its value as a potential anti-tumor target.

Smart enzyme catalysts capable of self-separation by sensing the reaction extent.

A smart biocatalyst should dissolve homogeneously for catalysis and recover spontaneously at the end of the reaction. In this study, we present a strategy for preparing self-precipitating enzyme catalysts by exploiting reaction-induced pH decreases, which connect the reaction extent to the catalyst aggregation state. Using poly(methacrylic acid)-functionalized gold nanoparticles as carriers, we construct smart catalysts with three model systems, including the glucose oxidase (GOx)-catalase (CAT) cascade, the alcohol dehydrogenase (ADH)-glucose dehydrogenase (GDH) cascade, and a combination of two lipases. All smart catalysts can self-separate with a nearly 100% recovery efficiency when a certain conversion threshold is reached. The threshold can be adjusted depending on the reaction demand and buffer capacity. By monitoring the optical signals caused by the dissolution/precipitation of smart catalysts, we propose a prototypic automation system that may enable unsupervised batch/fed-batch bioprocessing.

Orientation-Controllable Enzyme Cascade on Electrode for Bioelectrocatalytic Chain Reaction.

The accomplishment of concurrent interenzyme chain reaction and direct electric communication in a multienzyme-electrode is challenging since the required condition of multienzymatic binding conformation is quite complex. In this study, an enzyme cascade-induced bioelectrocatalytic system has been constructed using solid binding peptide (SBP) as a molecular binder that coimmobilizes the invertase (INV) and flavin adenine dinucleotide (FAD)-dependent glucose dehydrogenase gamma-alpha complex (GDHγα) cascade system on a single electrode surface. The SBP-fused enzyme cascade was strategically designed to induce diverse relative orientations of coupling enzymes while enabling efficient direct electron transfer (DET) at the FAD cofactor of GDHγα and the electrode interface. The interenzyme relative orientation was found to determine the intermediate delivery route and affect overall chain reaction efficiency. Moreover, interfacial DET between the fusion GDHγα and the electrode was altered by the binding conformation of the coimmobilized enzyme and fusion INVs. Collectively, this work emphasizes the importance of interenzyme orientation when incorporating enzymatic cascade in an electrocatalytic system and demonstrates the efficacy of SBP fusion technology as a generic tool for developing cascade-induced direct bioelectrocatalytic systems. The proposed approach is applicable to enzyme cascade-based bioelectronics such as biofuel cells, biosensors, and bioeletrosynthetic systems utilizing or producing complex biomolecules.

Multi-Enzymatic Cascade for Efficient Deracemization of dl-Pantolactone into d-Pantolactone.

d-pantolactone is an intermediate in the synthesis of d-pantothenic acid, which is known as vitamin B5. The commercial synthesis of d-pantolactone is carried out through the selective resolution of dl-pantolactone catalyzed by lactone hydrolase. In contrast to a kinetic resolution approach, the deracemization of dl-pantolactone is a simpler, greener, and more sustainable way to obtain d-pantolactone with high optical purity. Herein, an efficient three-enzyme cascade was developed for the deracemization of dl-pantolactone, using l-pantolactone dehydrogenase from Amycolatopsis methanolica (AmeLPLDH), conjugated polyketone reductase from Zygosaccharomyces parabailii (ZpaCPR), and glucose dehydrogenase from Bacillus subtilis (BsGDH). The AmeLPLDH was used to catalyze the dehydrogenated l-pantolactone into ketopantolactone; the ZpaCPR was used to further catalyze the ketopantolactone into d-pantolactone; and glucose dehydrogenase together with glucose fulfilled the function of coenzyme regeneration. All three enzymes were co-expressed in E. coli strain BL21(DE3), which served as the whole-cell biocatalyst. Under optimized conditions, 36 h deracemization of 1.25 M dl-pantolactone d-pantolactone led to an e.e.p value of 98.6%, corresponding to productivity of 107.7 g/(l·d).

Electrochemical and biosensing properties of an FAD-dependent glucose dehydrogenase from Trichoderma virens.

We investigated the bioelectrochemical properties of an FAD-dependent glucose dehydrogenase from Trichoderma virens (TvGDH) and its electrochemical behaviour when immobilized on a graphite electrode. TvGDH was recently shown to have an unusual substrate spectrum and to prefer maltose over glucose as substrate, and hence could be of interest as recognition element in a maltose sensor. In this study, we determined the redox potential of TvGDH, which is -0.268 ± 0.007 V vs. SHE, and advantageously low to be used with many redox mediators or redox polymers. The enzyme was entrapped in, and wired by an osmium redox polymer (poly(1-vinylimidazole-co-allylamine)-{[Os(2,2'-bipyridine)2Cl]Cl}) with formal redox potential of +0.275 V vs. Ag|AgCl via poly(ethylene glycol) diglycidyl ether crosslinking onto a graphite electrode. When the TvGDH-based biosensor was tested with maltose it showed a sensitivity of 1.7 µA mM-1cm-2, a linear range of 0.5-15 mM, and a detection limit of 0.45 mM. Furthermore, it gave the lowest apparent Michaelis-Menten constant (KM app) of 19.2 ± 1.5 mM towards maltose when compared to other sugars. The biosensor is also able to detect other saccharides including glucose, maltotriose and galactose, these however also interfere with maltose sensing.

Engineering Glucose Dehydrogenase to Favor Totally Synthetic Biomimetic Cofactors Containing Carboxyl Group.

The utilization of unnatural nicotinamide cofactors for reactions catalyzed by oxidoreductases has gained increasing interest. Totally synthetic nicotinamide cofactor biomimetics (NCBs) are cost-effective and convenient to synthesize. Thus, it has become increasingly important to develop enzymes that accept NCBs. Here, we have engineered SsGDH to favor a newly synthesized unnatural cofactor 3-carbamoyl-1-(4-carboxybenzyl) pyridin-1-ium (BANA+ ). Using in situ ligand minimization tool, sites 44 and 114 were identified as hotspots for mutagenesis. All the double mutants demonstrated 2.7-7.7-fold improvements in catalytic activity, and the best double mutant E44D/E114 L exhibited 10.6-fold increased catalytic efficiency toward BANA+ . These results provide valuable information for the rational engineering of oxidoreductases with versatile NCBs-dependency, as well as the design of novel biomimetic cofactors.