Engineering glucose oxidase for bioelectrochemical applications

Improving glucose oxidase catalysis in Aspergillus niger via Vitreoscilla hemoglobin fusion protein

Oxygen is crucial for converting glucose to gluconic acid catalyzed by glucose oxidase (Gox). However, industrial gluconic acid production faces oxygen supply limitations. To enhance Gox efficiency, Vitreoscilla hemoglobin (VHb) has been considered as an efficient oxygen transfer carrier. This study identified GoxA, a specific isoform of Gox in the industrial gluconic acid-producing strain of Aspergillus niger. Various forms of VHb expression in A. niger were tested to improve GoxA's catalytic efficiency. Surprisingly, the expression of free VHb, both intracellularly and extracellularly, did not promote gluconic acid production during shake flask fermentation. Then, five fusion proteins were constructed by linking Gox and VHb using various methods. Among these, VHb-GS1-GoxA, where VHb's C-terminus connected to GoxA's N-terminus via the flexible linker GS1, demonstrated a significantly higher Kcat/Km value (96% higher) than GoxA. Unfortunately, the expression of VHb-GS1-GoxA in A. niger was limited, resulting in a low gluconic acid production of 3.0 g/L. To overcome the low expression problem, single- and dual-strain systems were designed with tools of SpyCatcher/SpyTag and SnoopCatcher/SnoopTag. In these systems, Gox and VHb were separately expressed and then self-assembled into complex proteins. Impressively, the single-strain system outperformed the GoxA overexpression strain S1971, resulting in 23% and 9% higher gluconic acid production under 0.6 vvm and 1.2 vvm aeration conditions in the bioreactor fermentation, respectively. The successful construction of Gox and VHb fusion or complex proteins, as proposed in this study, presents promising approaches to enhance Gox catalytic efficiency and lower aerodynamic costs in gluconic acid production. KEY POINTS: • Overexpressing free VHb in A. niger did not improve the catalytic efficiency of Gox • The VHb-GS1-GoxA showed an increased Kcat/Km value by 96% than GoxA • The single-strain system worked better in the gluconic acid bioreactor fermentation.

An automatic glucose monitoring system based on periplasmic binding proteins for online bioprocess monitoring

Glucose is one of the most vital nutrients in all living organisms, so its monitoring is critical in healthcare and bioprocessing. Enzymatic sensors are more popular as a technology solution to meet the requirement. However, periplasmic binding proteins have been investigated extensively for their high sensitivity, enabling microdialysis sampling to replace existing complex and expensive glucose monitoring solutions based on enzymatic sensors. The binding proteins are used as optical biosensors by introducing an environment-sensitive fluorophore to the protein. The biosensor's construction, characterization, and potential application are well studied, but a complete glucose monitoring system based on it is yet to be reported. This work documents the development of the first glucose sensor prototype based on glucose binding protein (GBP) for automatic and continuous glucose measurements. The development includes immobilizing the protein into reusable chips and a low-cost solution for non-invasive glucose sampling in bioprocesses using microdialysis sampling technique. A program was written in LabVIEW to accompany the prototype for the complete automation of measurement. The sampling technique allowed glucose measurements of a few micromolar to 260 mM glucose levels. A thorough analysis of the sampling mode and the device's performance was conducted. The reported measurement accuracy was 81.78%, with an RSD of 1.83%. The prototype was also used in online glucose monitoring of E. coli cell culture. The mode of glucose sensing can be expanded to the measurement of other analytes by switching the binding proteins.

The Importance of Spin-Polarized Charge Reorganization in the Catalytic Activity of D-Glucose Oxidase

The reaction of D-glucose oxidase (GOx) with D- and L-glucose was investigated using confocal fluorescence microscopy and Hall voltage measurements, after the enzyme was adsorbed as a monolayer. By adsorbing the enzyme on a ferromagnetic substrate, we verified that the reaction is spin dependent. This conclusion was supported by monitoring the reaction when the enzyme is adsorbed on a Hall device that does not contain any magnetic elements. The spin dependence is consistent with the chiral-induced spin selectivity (CISS) effect; it can be explained by the improved fidelity of the electron transfer process through the chiral enzyme due to the coupling of the linear momentum of the electrons and their spin. Since the reaction studied often serve as a model system for enzymatic activity, the results may suggest the general importance of the spin-dependent electron transfer in bio-chemical processes.

Microbial electrosynthesis of valuable chemicals from the reduction of CO2: a review

The present energy demand of the world is increasing but the fossil fuels are gradually depleting. As a result, the need for alternative fuels and energy sources is growing. Fuel cells could be one alternative to address the challenge. The fuel cell can convert CO2 to value-added chemicals. The potential of bio-fuel cells, specifically enzymatic fuel cells and microbial fuel cells, and the importance of immobilization technology in bio-fuel cells are highlighted. The review paper also includes a detailed explanation of the microbial electrosynthesis system to reduce CO2 and the value-added products during microbial electrosynthesis. Future research in bio-electrochemical synthesis for CO2 conversion is expected to prioritize enhancing biocatalyst efficiency, refining reactor design, exploring novel electrode materials, understanding microbial interactions, integrating renewable energy sources, and investigating electrochemical processes for carbon capture and selective CO2 reduction. The challenges and perspectives of bio-electrochemical systems in the application of CO2 conversion are also discussed. Overall, this review paper provides valuable insights into the latest developments and criteria for effective research and implementation in bio-fuel cells, immobilization technology, and microbial electro-synthesis systems.

Emerging Trends of Bilirubin Oxidases at the Bioelectrochemical Interface: Paving the Way for Self-Powered Electrochemical Devices and Biosensors

Bilirubin oxidases (BODs) [EC 1.3.3.5 - bilirubin: oxygen oxido-reductase] are enzymes that belong to the multicopper oxidase family and can oxidize bilirubin, diphenols, and aryl amines and reduce the oxygen by direct four-electron transfer from the electrode with almost no electrochemical overpotential. Therefore, BOD is a promising bioelectrocatalyst for (self-powered) biosensors and/or enzymatic fuel cells. The advantages of electrochemically active BOD enzymes include selective biosensing, biocatalysis for efficient energy conversion, and electrosynthesis. Owing to the rise in publications and patents, as well as the expanding interest in BODs for a range of physiological conditions, this Review analyzes scientific literature reports on BOD enzymes and current hypotheses on their bioelectrocatalysis. This Review evaluates the specific research outcomes of the BOD in enzyme (protein) engineering, immobilization strategies, and challenges along with their bioelectrochemical properties, limitations, and applications in the fields of (i) biosensors, (ii) self-powered biosensors, and (iii) biofuel cells for powering bioelectronics.

Noninvasive glucose monitoring using portable GOx-Based biosensing system

Wearable biosensors have gained huge interest due to their potential for real-time physiological information. The development of a non-invasive blood glucose device is of great interests for health monitoring in reducing the diabetes incidence. Here, we report a sandwich-structured biosensor that is designed for glucose levels detection by using sweat as the means of monitoring. The Prussian blue nanoparticles (PBNPs) and carboxylated carbon nanotubes (MWCNT-COOH) were self-assembled on the electrode to improve the electrochemical performance and as the sensor unit, glucose oxidase (GOx) was immobilized by chitosan (CS) as the reaction catalysis unit, and finally encapsulated with Nafion to ensure a stable performance. As a result, the GOx/PBNPs/MWCNT-COOH sensor displays a low detection limit (7.0 μM), high sensitivity (11.87 μA mM-1 cm-2), and excellent interference resistance for a full sweat glucose application range (0.0-1.0 mM) for both healthy individuals and diabetic patients. Additionally, the glucose sensor exhibits stable stability for two weeks and can be successfully applied to screen-printed carbon electrodes (SPCE), demonstrating its great potential for personalized medical detection and chronic disease management.

Glucose oxidase virus-based nanoreactors for smart breast cancer therapy

BACKGROUND

Breast cancer is the most common malignant tumor disease and the leading cause of female mortality. The evolution of nanomaterials science opens the opportunity to improve traditional cancer therapies, enhancing therapy efficiency and reducing side effects.

METHODS AND MAJOR RESULTS

Herein, protein cages conceived as enzymatic nanoreactors were designed and produced by using virus-like nanoparticles (VLPs) from Brome mosaic virus (BMV) and containing the catalytic activity of glucose oxidase (GOx) enzyme. The GOx enzyme was encapsulated into the BMV capsid (VLP-GOx), and the resulting enzymatic nanoreactors were coated with human serum albumin (VLP-GOx@HSA) for breast tumor cell targeting. The effect of the synthesized GOx nanoreactors on breast tumor cell lines was studied in vitro. Both nanoreactor preparations VLP-GOx and VLP-GOx@HSA showed to be highly cytotoxic for breast tumor cell cultures. Cytotoxicity for human embryonic kidney cells was also found. The monitoring of nanoreactor treatment on triple-negative breast cancer cells showed an evident production of oxygen by the catalase antioxidant enzyme induced by the high production of hydrogen peroxide from GOx activity.

CONCLUSIONS AND IMPLICATIONS

The nanoreactors containing GOx activity are entirely suitable for cytotoxicity generation in tumor cells. The HSA functionalization of the VLP-GOx nanoreactors, a strategy designed for selective cancer targeting, showed no improvement in the cytotoxic effect. The GOx containing enzymatic nanoreactors seems to be an interesting alternative to improve the current cancer therapy. In vivo studies are ongoing to reinforce the effectiveness of this treatment strategy.

Untangling the Effects of Doping Carbon with Diverse Heteroatoms on the Bioelectrochemistry of Glucose Oxidase

Great enthusiasm for doping carbon materials with nonmetallic heteroatoms for promoting electrical contact of redox enzymes with electrodes in bioelectronics has been aroused. However, systematic studies of different heteroatoms on enzyme activities are still lacking. Herein, choosing glucose oxidase (GOD) as a model enzyme, carbon nanotubes (CNTs) are used as electron carriers to evaluate the effects of heteroatoms' species on the direct electron transfer and catalytic activities of GOD. Experimental data demonstrate that phosphorus (P)-doped CNTs provide the most intimate electrical contact with GOD compared to other elements (B, N, and S) doping, delivering a 3-fold increase in rate constant (k_s, 2.1 s^-1) and an enhanced turnover rate (k_cat, 2.74 × 10^-9 M cm^-2 s^-1) in comparison with CNTs. Meanwhile, theoretical modeling clarifies that the active center of GOD interacts more strongly with P-doped CNTs and maintains their conformation well compared to other CNTs. This study will help to understand the mechanism of heteroatom doping of carbon on the enzymatic electron transfer and shed light on the design of efficient bioelectrocatalytic interfaces.

Screen-Printable Functional Nanomaterials for Flexible and Wearable Single-Enzyme-Based Energy-Harvesting and Self-Powered Biosensing Devices

Developing flexible bioelectronics is essential to the realization of artificial intelligence devices and biomedical applications, such as wearables, but their potential is limited by sustainable energy supply. An enzymatic biofuel cell (BFC) is promising for power supply, but its use is limited by the challenges of incorporating multiple enzymes and rigid platforms. This paper shows the first example of screen-printable nanocomposite inks engineered for a single-enzyme-based energy-harvesting device and a self-powered biosensor driven by glucose on bioanode and biocathode. The anode ink is modified with naphthoquinone and multiwalled carbon nanotubes (MWCNTs), whereas the cathode ink is modified with Prussian blue/MWCNT hybrid before immobilizing with glucose oxidase. The flexible bioanode and the biocathode consume glucose. This BFC yields an open circuit voltage of 0.45 V and a maximum power density of 266 μW cm-2. The wearable device coupled with a wireless portable system can convert chemical energy into electric energy and detect glucose in artificial sweat. The self-powered sensor can detect glucose concentrations up to 10 mM. Common interfering substances, including lactate, uric acid, ascorbic acid, and creatinine, have no effect on this self-powered biosensor. Additionally, the device can endure multiple mechanical deformations. New advances in ink development and flexible platforms enable a wide range of applications, including on-body electronics, self-sustainable applications, and smart fabrics.

Molecular Dynamics Simulation of E412 Catalytic Residue Mutation of GOx-IPBCC

The enzyme glucose oxidase from Aspergillus niger has a homodimeric structure, consisting of two identical subunits with a molecular weight of 150,000 Daltons. In this study, we used the structure of the enzyme glucose oxidase from Aspergillus niger IPBCC.08.610 (GOx-IPBCC), this enzyme had a total activity of 92.87 U (μmol/min) and a Michaelis-Menten constant (Km) of 2.9 mM (millimolar). This study was conducted to predict the molecular dynamics of E412 (Glu412) residue catalytic mutation belonging to the GOx-IPBCC enzyme was determine the effect of changes in the catalytic residue on substrate binding (β-D-glucose). The results of molecular docking of 19 mutant structures, six E412 mutant homologous structures were selected (E412C, E412K, E412Q, E412T, E412, E412V, and E412W), which were evaluated using molecular dynamics simulation for 50 ns. The results showed a decrease in ∆G values in two mutant structures is E412C and E412T, and there is one mutant structure that increased ∆G values, namely E412W, these three mutant structures showed the best stability, bond interaction, and salt bridge profile according to molecular dynamics simulation.

Insights into the Structures, Inhibitors, and Improvement Strategies of Glucose Oxidase

Glucose oxidase, which uses molecular oxygen as an electron acceptor to specifically catalyze the conversion of β-d-glucose to gluconic acid and hydrogen peroxide (H₂O₂), has been considered an important enzyme in increasing environmental sustainability and food security. However, achieving the high yield, low price and high activity required for commercial viability remains challenging. In this review, we first present a brief introduction, looking at the sources, characteristics, catalytic process, and applications of glucose oxidase. Then, the predictive structures of glucose oxidase from two different sources are comparatively discussed. We summarize the inhibitors of glucose oxidase. Finally, we highlight how the production of glucose oxidase can be improved by optimizing the culture conditions and microbial metabolic engineering.

Wireless Lateral Flow Device for Biosensing

Many biosensing methods rely on signals produced by enzyme-catalyzed reactions and efficient methods to detect and record this activity. Herein, we report a wireless lateral flow device and demonstrate the conversion of oxidase reactions to changes in the resonance of radio frequency identification (RFID) circuits. The detection is triggered by polyoxometalate-catalyzed oxidative doping of polypyrrole (pPy) when exposed to oxidase-generated H₂O₂. We have integrated this transduction and RFID capability into a lateral flow device to create a low-cost, rapid, and portable method for quantitative biological signal detection. We further report a new method for creating functional coatings from pPy core-shell colloidal particles bioconjugated for streptavidin-biotin recognition with glucose oxidase or pyruvate oxidase. The biofunctionalized pPy particles coalesce on the nitrocellulose membrane to produce a chemiresistive band. Glucose or pyruvate solutions result in formation of H₂O₂ at the pPy bands, functionalized with the respective oxidase, to produce conductivity enhancements exceeding 7·10⁵%. Placing the pPy band in the RFID circuit converts the resistivity response to a change of RF resonance. The enzymatic response of glucose oxidase is recorded within 30 min with as low as 0.6 mM of glucose using this lateral flow device. Pyruvate is also shown to produce large responses. The oxidase enzymes/pPy transduction establishes a resistivity-based platform for the construction of a new family of lateral flow devices capable of detecting and quantifying biological targets.

The Impact of the Functional Layer Composition of Glucose Test-Strips on the Stability of Electrochemical Response

Herein, the impact of the chemical stability of RedOx mediator ferricyanide, K3[Fe(CN)6] (FC), a type of buffer solution used for bioreceptor preparation, gel composition (carboxymethylcellulose, CMC, Aerosile, AS, and alginate, ALG) on the long term stability of glucose test-strips and their analytical performance was examined. By simple addition of ALG to the functional gel aiming to improve its viscosity, we managed to enhance the sensitivity of conventional CMC-containing amperometric glucose test-strips from 3.3 µA/mM to 3.9 µA/mM and extend their shelf life from 8 months to 1.7 years. Moreover, during the course of investigations, it was revealed that the activity of enzyme in dependence with the used buffer did not linearly correlate with its activity in a dried functional layer, and the entire long-term electrochemical signal of glucose test-strips was determined by RedOx mediator FC chemical stability. The most stable and sensitive test-strips were obtained by the screen-printing approach from a gel containing 24 mg/mL GOx prepared in citrate buffer with pH 6, 200 mg/mL of FC and 10 mg/mL of CMC supplemented with 25 mg/mL of ALG.

Glucose oxidase converted into a general sugar-oxidase

Entrapment of glucose oxidase (GOx) within metallic gold converts this widely used enzyme into a general saccharide oxidase. The following sugar molecules were oxidized by the entrapped enzyme (in addition to D-glucose): fructose, xylose, L-glucose, glucose-6-phosphate, sucrose, lactose, methylglucoside, and the tri-saccharide raffinose. With the exception of raffinose, none of these sugars have a natural specific oxidase. The origin of this generalization of activity is attributed to the strong protein-gold 3D interactions and to the strong interactions of the co-entrapped CTAB with both the gold, and the protein. It is proposed that these interactions induce conformational changes in the channel leading to the active site, which is located at the interface between the two units of the dimeric GOx protein. The observations are compatible with affecting the specific conformation change of pulling apart and opening this gate-keeper, rendering the active site accessible to a variety of substrates. The entrapment methodology was also found to increase the thermal stability of GOx up to 100 °C and to allow its convenient reuse, two features of practical importance.

Review of glucose oxidase as a feed additive: production, engineering, applications, growth-promoting mechanisms, and outlook

The regulation and prohibition of antibiotics used as growth promoters (AGP) in the feed field are increasing because they cause antimicrobial resistance and drug residue issues and threaten community health. Recently, glucose oxidase (GOx) has attracted increasing interest in the feed industry as an alternative to antibiotics. GOx specifically catalyzes the production of gluconic acid (GA) and hydrogen peroxide (H₂O₂) by consuming molecular oxygen, and plays an important role in relieving oxidative stress, preserving health, and promoting animal growth. To expand the application of GOx in the feed field, considerable efforts have been made to mine new genetic resources. Efforts have also been made to heterologously overexpress relevant genes to reduce production costs and to engineer proteins by modifying enzyme properties, both of which are bottleneck problems that limit industrial feed applications. Herein, the: different sources, diverse biochemical properties, distinct structural features, and various strategies of GOx engineering and heterologous overexpression are summarized. The mechanism through which GOx promotes growth in animal production, including the improvement of antioxidant capacity, maintenance of intestinal microbiota homeostasis, and enhancement of gut function, are also systematically addressed. Finally, a new perspective is provided for the future development of GOx applications in the feed field.

Advances on Delivery of Cytotoxic Enzymes as Anticancer Agents

Cancer is one of the most serious human diseases, causing millions of deaths worldwide annually, and, therefore, it is one of the most investigated research disciplines. Developing efficient anticancer tools includes studying the effects of different natural enzymes of plant and microbial origin on tumor cells. The development of various smart delivery systems based on enzyme drugs has been conducted for more than two decades. Some of these delivery systems have been developed to the point that they have reached clinical stages, and a few have even found application in selected cancer treatments. Various biological, chemical, and physical approaches have been utilized to enhance their efficiencies by improving their delivery and targeting. In this paper, we review advanced delivery systems for enzyme drugs for use in cancer therapy. Their structure-based functions, mechanisms of action, fused forms with other peptides in terms of targeting and penetration, and other main results from in vivo and clinical studies of these advanced delivery systems are highlighted.

Acetylated Trifluoromethyl Diboronic Acid Anthracene with a Large Stokes Shift and Long Excitation Wavelength as a Glucose-Selective Probe

Continuous control of blood glucose levels is important for the effective treatment of diabetes. The short-term use of enzymatic continuous monitoring systems involves expensive maintenance and is inconvenient, which limits their widespread use by diabetes patients. The fluorescent diboronic anthracene-embedded system has demonstrated in vivo continuous glucose monitoring for 12 times longer than enzymatic systems by protecting the dye from reactive oxygen species. However, its small Stokes shift and low excitation and emission wavelength should be heavily considered for easy fabrication. We successfully synthesized a derivative of bis-phenyl boronate with a large Stokes shift and long excitation wavelength by adding an acetyl moiety to the anthracene ring. This resulted in a ~90-nm Stokes shift and 15-nm and 80-nm redshifts of the excitation and emission wavelengths, respectively. The fluorescence of the synthesized probe increased proportionally with the glucose concentration because the formation of the boronic acid-glucose complex prevented photoinduced electron transfer. The association constant and quantum yield for acetyl-substituted diboronic anthracene with glucose was 20% and 13% higher than that of the analog, respectively. While keeping resistance to the oxidation by reactive oxygen species, the improved optical properties and glucose-detecting performances of the newly synthesized dye will allow better pairing of the source and detecting unit for in vivo continuous glucose monitoring, leading to easy fabrication and then contributing more to utilization by diabetes patients.

Reversible Regulating the Substrate Specificity of Enzymes in Microgels by a Phase Transition in Polymer Networks

Here, we report a distinct approach for regulating the substrate specificity of enzymes immobilized in microgels by a phase transition in polymer networks. The finding is demonstrated on glucose oxidase that is immobilized in thermoresponsive poly(N-isopropylacrylamide)-based microgels. Laser light scattering and enzymatic oxidation tests indicate that the broadened specificity appears at low temperatures, at which the gel matrix is in the relatively swollen state relative to its state at microgel synthesis temperature; upon heating to the relative higher temperatures, the gel matrix is not able to shrink further that offers a tight space in which the enzyme resides to retain high glucose specificity. It is proposed that polymer phase transition in the gel matrix mainly alter protein gates that control passage of substrates into active sites, making them open or close to a certain extent that enable reversible regulating the substrate specificity. The finding is also observed on bulk gels under a rational design, making it of potential interest in enzymatic biofuel cell applications.

Bio-electron transfer modulated localized surface plasmon resonance biosensing with charge density monitoring

The analysis of reactant at different regions of the bioreaction interface is significant for the study on the influence of interface condition on bioreaction. In this study, we proposed a localized surface plasmon resonance (LSPR) biosensing platform for local charge density monitoring and corresponding analytes detection based on the bio-electron transfer modulation of plasmon resonance. Core-shell nanocomposites of polyaniline coated gold nanoparticles were synthesized for the enhanced sensitivity of plasmon resonance to applied electric potential. Tin-doped indium oxide (ITO) substrates modified with the nanocomposites were used as LSPR chip for optical and electrochemical measurements simultaneously. The charge sensitivity of LSPR was verified with external electric potential modulation theoretically and experimentally. Through layer-by-layer self-assembly immobilization of glucose oxidase (GOD) on the LSPR chips, the charge transfer monitoring during the bioreaction of glucose catalysis was further demonstrated based on the bio-electron transfer modulation of LSPR. By equivalent circuit method, the charge density of the LSPR chip were detected with optical extinction peak shifts, and the limit of detection was about 0.51 μC/cm². This bio-electron transfer modulated LSPR provides a promising approach for the detection of spatial charge densities and the evaluation of bioreaction substances at different region of single chip.

Immobilization of glucose oxidase on bioinspired polyphenol coatings as a high-throughput glucose assay platform

Glucose oxidase (GOx) is an enzyme with important industrial and biochemical applications, particularly in glucose detection. Here we leveraged the oxidative self-polymerization phenomenon of simple polyphenols (pyrogallol or catechol) in the presence of polyethylenimine (PEI) to form adhesive coatings that enabled GOx immobilization on conventional multi-well plates. Immobilization was verified and optimized by directly measuring GOx activity inside the coated wells. Our results showed that incorporating PEI in polyphenol coatings enhanced their enzyme immobilization efficiency, with pyrogallol (PG)-based coatings displaying the greatest enzyme activity. The immobilized enzyme maintained similar affinity to glucose compared to the free enzyme. GOx-immobilized PG/PEI-coated wells exhibited intermediate recycling ability but excellent resistance to urea as a denaturing agent compared to the free enzyme. GOx-immobilized 96-well plates allowed the construction of a linear glucose calibration curve upon adding glucose standards, with a detection limit of 0.4–112.6 mg dL⁻¹, which was comparable to commercially available enzymatic glucose assay kits. The assay platform was also capable of effectively detecting glucose in rat plasma samples. Our findings present a simple enzyme immobilization technique that can be used to construct a glucose assay platform in a convenient multi-well format for high-throughput glucose quantification.

Glucose oxidase was immobilized on conventional multi-well plates via bioinspired polyphenol chemistry for convenient colorimetric quantitation of glucose.

In Silico Analysis of Glucose Oxidase from Aspergillus niger: Potential Cysteine Mutation Sites for Enhancing Protein Stability

Glucose oxidase (GOx) holds considerable advantages for various applications. Nevertheless, the thermal instability of the enzyme remains a grand challenge, impeding the success in applications outside the well-controlled laboratories, particularly in practical bioelectronics. Many strategies to modify GOx to achieve better thermal stability have been proposed. However, modification of this enzyme by adding extra disulfide bonds is yet to be explored. This work describes the in silico bioengineering of GOx from Aspergillus niger by judiciously analyzing characteristics of disulfide bonds found in the Top8000 protein database, then scanning for amino acid residue pairs that are suitable to be replaced with cysteines in order to establish disulfide bonds. Next, we predicted and assessed the mutant GOx models in terms of disulfide bond quality (bond length and α angles), functional impact by means of residue conservation, and structural impact as indicated by Gibbs free energy. We found eight putative residue pairs that can be engineered to form disulfide bonds. Five of these are located in less conserved regions and, therefore, are unlikely to have a deleterious impact on functionality. Finally, two mutations, Pro149Cys and His158Cys, showed potential for stabilizing the protein structure as confirmed by a structure-based stability analysis tool. The findings in this study highlight the opportunity of using disulfide bond modification as a new alternative technique to enhance the thermal stability of GOx.

Synthetic Silica Nano-Organelles for Regulation of Cascade Reactions in Multi-Compartmentalized Systems

In eukaryotic cells, enzymes are compartmentalized into specific organelles so that different reactions and processes can be performed efficiently and with a high degree of control. In this work, we show that these features can be artificially emulated in robust synthetic organelles constructed using an enzyme co-compartmentalization strategy. We describe an in-situ encapsulation approach that allows enzymes to be loaded into silica nanoreactors in well-defined compositions. The nanoreactors can be combined into integrated systems to produce a desired reaction outcome. We used the selective enzyme co-compartmentalization and nanoreactor integration to regulate competitive cascade reactions and to modulate the kinetics of sequential reactions involving multiple nanoreactors. Furthermore, we show that the nanoreactors can be efficiently loaded into giant polymer vesicles, resulting in multi-compartmentalized microreactors.

A molecularly imprinted nanoreactor with spatially confined effect fabricated with nano-caged cascaded enzymatic system for specific detection of monosaccharides

Glucose oxidase (GOx), traditionally regarded as an oxidoreductase with high β-D-glucose specificity, has been widely applied as sensing probe for β-D-glucose detection. However, it is found that the specificity of GOx is not absolute and GOx cannot decern β-D-glucose among its isomers such as xylose, mannose and galactose. The existence of the other monosaccharides in sensing system could compromise the sensitivity for β-D-glucose, therefore, it is of great urgency to achieve the highly specific catalytic performance of GOx. Herein, porous metal-organic frameworks (MOF) are prepared as the host matrix for immobilization of both GOx and bovine hemoglobin (BHb), obtained a cascaded catalytic system (MOF@GOx@BHb) with both enhanced GOx activity and peroxidase-like activity owing to the spatially confined effect. Then, using β-D-glucose as both template molecules and substances, hydroxyl radicals are produced continuously and applied for initiating the polymerization of molecular imprinting polymers (MIPs) on the surface of MOF@GOx@BHb. Impressively, the obtaining molecularly imprinted GOx (noted as MOF@GOx@BHb-MIPs) achieves the highly sensitive and specific detection of β-D-glucose in the concentration range of 0.5-20 μM with the LOD = 0.4 μM (S/N = 3) by colorimetry. Similarly, MOF@GOx@BHb-MIPs are subsequently obtained using mannose, xylose and galactose as template molecules, respectively, and also show satisfied specific catalytic activity towards corresponding templates, indicating the effectiveness of the proposed strategy to achieve highly specific catalytic performance of GOx.

The Impact of Recent Developments in Electrochemical POC Sensor for Blood Sugar Care

Rapid glucose testing is very important in the care of diabetes. Monitoring of blood glucose is the most critical indicator of disease control in diabetic patients. The invention and popularity of electrochemical sensors have made glucose detection fast and inexpensive. The first generation of glucose sensors had limitations in terms of sensitivity and selectivity. In order to overcome these problems, scientists have used a range of new materials to produce new glucose electrochemical sensors with higher sensitivity, selectivity and lower cost. A variety of different electrochemical sensors including enzymatic electrochemical sensors and enzyme-free electrochemical sensors have been extensively investigated. We discussed the development process of electrochemical glucose sensors in this review. We focused on describing the benefits of carbon materials in nanomaterials, specially graphene for sensors. In addition, we discussed the limitations of the sensors and challenges in future research.

Electrochemical Response of Glucose Oxidase Adsorbed on Laser-Induced Graphene

Carbon-based electrodes have demonstrated great promise as electrochemical transducers in the development of biosensors. More recently, laser-induced graphene (LIG), a graphene derivative, appears as a great candidate due to its superior electron transfer characteristics, high surface area and simplicity in its synthesis. The continuous interest in the development of cost-effective, more stable and reliable biosensors for glucose detection make them the most studied and explored within the academic and industry community. In this work, the electrochemistry of glucose oxidase (GOx) adsorbed on LIG electrodes is studied in detail. In addition to the well-known electroactivity of free flavin adenine dinucleotide (FAD), the cofactor of GOx, at the expected half-wave potential of -0.490 V vs. Ag/AgCl (1 M KCl), a new well-defined redox pair at 0.155 V is observed and shown to be related to LIG/GOx interaction. A systematic study was undertaken in order to understand the origin of this activity, including scan rate and pH dependence, along with glucose detection tests. Two protons and two electrons are involved in this reaction, which is shown to be sensitive to the concentration of glucose, restraining its origin to the electron transfer from FAD in the active site of GOx to the electrode via direct or mediated by quinone derivatives acting as mediators.

Flexible Enzymatic Glucose Electrochemical Sensor Based on Polystyrene-Gold Electrodes

Metabolic disorders such as the highly prevalent disease diabetes require constant monitoring. The health status of patients is linked to glucose levels in blood, which are typically measured invasively, but can also be correlated to other body fluids such as sweat. Aiming at a reliable glucose biosensor, an enzymatic sensing layer was fabricated on flexible polystyrene foil, for which a versatile nanoimprinting process for microfluidics was presented. For the sensing layer, a gold electrode was modified with a cysteine layer and glutaraldehyde cross-linker for enzyme conformal immobilization. Chronoamperometric measurements were conducted in PBS buffered glucose solution at two potentials (0.65 V and 0.7 V) and demonstrated a linear range between 0.025 mM to 2mM and an operational range of 0.025 mM to 25 mM. The sensitivity was calculated as 1.76µA/mM/cm² and the limit of detection (LOD) was calculated as 0.055 mM at 0.7 V. An apparent Michaelis–Menten constant of 3.34 mM (0.7 V) and 0.445 mM (0.65 V) was computed. The wide operational range allows the application for point-of-care testing for a variety of body fluids. Yet, the linear range and low LOD make this biosensor especially suitable for non-invasive sweat sensing wearables.

Prebiotic Peptides Based on the Glycocodon Theory Analyzed with FRET

In modern protein–carbohydrate interactions, carbohydrate–aromatic contact with CH–π interactions are used. Currently, they are considered driving forces of this complexation. In these contacts, tryptophan, tyrosine, and histidine are preferred. In this study, we focus on primary prebiotic chemistry when only glycine, alanine, aspartic acid, and valine are available in polypeptides. In this situation, when the aromatic acids are not available, hydrogen-bonding aspartic acid must be used for monosaccharide complexation. It is shown here that (DAA)n polypeptides play important roles in primary “protein”–glucose recognition, that (DGG)n plays an important role in “protein”–ribose recognition, and that (DGA)n plays an important role in “protein”–galactose recognition. Glucose oxidase from Aspergillus niger, which still has some ancient prebiotic sequences, is chosen here as an example for discussion.

From Enzyme Stability to Enzymatic Bioelectrode Stabilization Processes

Bioelectrocatalysis using redox enzymes appears as a sustainable way for biosensing, electricity production, or biosynthesis of fine products. Despite advances in the knowledge of parameters that drive the efficiency of enzymatic electrocatalysis, the weak stability of bioelectrodes prevents large scale development of bioelectrocatalysis. In this review, starting from the understanding of the parameters that drive protein instability, we will discuss the main strategies available to improve all enzyme stability, including use of chemicals, protein engineering and immobilization. Considering in a second step the additional requirements for use of redox enzymes, we will evaluate how far these general strategies can be applied to bioelectrocatalysis.

Highly sensitive and stable fructose self-powered biosensor based on a self-charging biosupercapacitor

Herein, we present an alternative approach to obtain a highly sensitive and stable self-powered biosensor that was used to detect D-fructose as proof of concept.In this platform, we perform a two-step process, viz. self-charging the biosupercapacitor for a constant time by using D-fructose as fuel and using the stored charge to realize the detection of D-fructose by performing several polarization curves at different D-fructose concentrations. The proposed BSC shows an instantaneous power density release of 17.6 mW cm^-2 and 3.8 mW cm^-2 in pulse mode and at constant load, respectively. Moreover, the power density achieved for the self-charging BSC in pulse mode or under constant load allows for an enhancement of the sensitivity of the device up to 10 times (3.82 ± 0.01 mW cm^-2 mM^-1, charging time = 70 min) compared to the BSC in continuous operation mode and 100 times compared to the normal enzymatic fuel cell. The platform can potentially be employed as a self-powered biosensor in food or biomedical applications.

Rational design of electroactive redox enzyme nanocapsules for high-performance biosensors and enzymatic biofuel cell

The potential application of biodevices based on enzymatic bioelectrocatalysis are limited by poor stability and electrochemical performance. To solve the limitation, modifying enzyme with functional polymer to tailor enzyme function is highly desirable. Herein, glucose oxidase (GOx) was chosen as a model enzyme, and according to the chemical structure of GOx cofactor (flavin adenine dinucleotide, FAD), we customize a biomimetic cofactor containing vinyl group (SFAD) for GOx, and prepared an GOx nanocapsule via in-situ polymerization. The characterization of particle size distribution, TEM, fluorescence and electrochemical performance indicated the successful formation of electroactive GOx nanocapsule with SFAD-containing polymeric network (n (GOx-SFAD-PAM)). The network can act as an electronic "highway" to link the active site with electrode, with capability to accelerate electron transfer as well as enhanced GOx stability. Further investigation of bioelectrocatalysis shows that n (GOx-SFAD-PAM)-based biosensor has low detection potential (-0.4 vs. Ag/AgCl), high sensitivity (64.97 μAmM^-1cm^-2), good anti-interference performance, quick response (3⁓5s) and excellent stability, and that n (GOx-SFAD-PAM)-based enzymatic biofuel cell (EBFC) has the high maximum power density (1011.21 μWcm^-2), which is a 385-fold increase over that of native GOx-based EBFC (2.62 μWcm^-2). This study suggests that novel enzyme nanocapsule with electroactive polymeric shell might provide a prospective solution for the performance improvement of enzymatic bioelectrocatalysis-based biodevices.

Enzymatic Glucose-Based Bio-batteries: Bioenergy to Fuel Next-Generation Devices

This article consists of a review of the main concepts and paradigms established in the field of biological fuel cells or biofuel cells. The aim is to provide an overview of the current panorama, basic concepts, and methodologies used in the field of enzymatic biofuel cells, as well as the applications of these bio-systems in flexible electronics and implantable or portable devices. Finally, the challenges needing to be addressed in the development of biofuel cells capable of supplying power to small size devices with applications in areas related to health and well-being or next-generation portable devices are analyzed. The aim of this study is to contribute to biofuel cell technology development; this is a multidisciplinary topic about which review articles related to different scientific areas, from Materials Science to technology applications, can be found. With this article, the authors intend to reach a wide readership in order to spread biofuel cell technology for different scientific profiles and boost new contributions and developments to overcome future challenges.

High-level production of glucose oxidase in Pichia pastoris: Effects of Hac1p overexpression on cell physiology and enzyme expression

Secretion is a common bottleneck in the production of industrial proteins. Although overexpression of the unfolded protein response regulator Hac1p has been widely used to enhance protein secretion, its effects on the physiology of host cells were often overlooked, which would attenuate and even neutralize its beneficial effects on overall protein production. In order to achieve high-level glucose oxidase (GOX) production in Pichia pastoris, we used a set of Hac1p homologues from Saccharomyces cerevisiae (ScHac1p), P. pastoris (PpHac1p), Trichoderma reesei (TrHac1p) and Homo sapiens (HsXbp1), to evaluate the effects of Hac1p overexpression on the secretion capacity, cell physiology and overall enzyme production in P. pastoris strains containing different copies of the GOX gene. Results showed that overexpression of Hac1ps was able to remarkably alleviate the secretion bottleneck in the 3-copy strain, to improve its GOX secretion capacity by 21.2-140.2 % and its overall enzyme production by 23.7-69.2 %. However, overexpression of ScHac1p, PpHac1p and TrHac1p led to reduced cell growth in GS-3GOX, possibly due to increased oxidative stress. Overexpression of ScHac1p and PpHac1p in the 6-copy strain (resulting in GS-6GOX-Sc and GS-6GOX-Pp, respectively) further increased the overall GOX production levels by 88.9-103.3 %, and GS-6GOX-Pp exhibited the highest overall GOX production and GOX secretion capacity among all constructed strains. Nevertheless, in addition of significantly reduced growth, loss of GOX gene was also observed for GS-6GOX-Pp and GS-6GOX-Sc during the fermentation process. With higher induction cell density and co-feeding of yeast extract, the GOX titer of GS-6GOX-Pp reached 2125.3 U/mL on 1-liter fermentor. This study not only achieves a record high GOX production level but also provides new insights into secretion pathway engineering using Hac1p overexpression strategy.

Electrochemical glucose sensors in diabetes management: an updated review (2010-2020)

While over half a century has passed since the introduction of enzyme glucose biosensors by Clark and Lyons, this important field has continued to be the focus of immense research activity. Extensive efforts during the past decade have led to major scientific and technological innovations towards tight monitoring of diabetes. Such continued progress toward advanced continuous glucose monitoring platforms, either minimal- or non-invasive, holds considerable promise for addressing the limitations of finger-prick blood testing toward tracking glucose trends over time, optimal therapeutic interventions, and improving the life of diabetes patients. However, despite these major developments, the field of glucose biosensors is still facing major challenges. The scope of this review is to present the key scientific and technological advances in electrochemical glucose biosensing over the past decade (2010-present), along with current obstacles and prospects towards the ultimate goal of highly stable and reliable real-time minimally-invasive or non-invasive glucose monitoring. After an introduction to electrochemical glucose biosensors, we highlight recent progress based on using advanced nanomaterials at the electrode-enzyme interface of three generations of glucose sensors. Subsequently, we cover recent activity and challenges towards next-generation wearable non-invasive glucose monitoring devices based on innovative sensing principles, alternative body fluids, advanced flexible materials, and novel platforms. This is followed by highlighting the latest progress in the field of minimally-invasive continuous glucose monitoring (CGM) which offers real-time information about interstitial glucose levels, by focusing on the challenges toward developing biocompatible membrane coatings to protect electrochemical glucose sensors against surface biofouling. Subsequent sections cover new analytical concepts of self-powered glucose sensors, paper-based glucose sensing and multiplexed detection of diabetes-related biomarkers. Finally, we will cover the latest advances in commercially available devices along with the upcoming future technologies.

The vast repertoire of carbohydrate oxidases: An overview

Carbohydrates are widely abundant molecules present in a variety of forms. For their biosynthesis and modification, nature has evolved a plethora of carbohydrate-acting enzymes. Many of these enzymes are of particular interest for biotechnological applications, where they can be used as biocatalysts or biosensors. Among the enzymes catalysing conversions of carbohydrates are the carbohydrate oxidases. These oxidative enzymes belong to different structural families and use different cofactors to perform the oxidation reaction of CH-OH bonds in carbohydrates. The variety of carbohydrate oxidases available in nature reflects their specificity towards different sugars and selectivity of the oxidation site. Thanks to their properties, carbohydrate oxidases have received a lot of attention in basic and applied research, such that nowadays their role in biotechnological processes is of paramount importance. In this review we provide an overview of the available knowledge concerning the known carbohydrate oxidases. The oxidases are first classified according to their structural features. After a description on their mechanism of action, substrate acceptance and characterisation, we report on the engineering of the different carbohydrate oxidases to enhance their employment in biocatalysis and biotechnology. In the last part of the review we highlight some practical applications for which such enzymes have been exploited.

Phylogeny and Structure of Fatty Acid Photodecarboxylases and Glucose-Methanol-Choline Oxidoreductases

Glucose-methanol-choline (GMC) oxidoreductases are a large and diverse family of flavin-binding enzymes found in all kingdoms of life. Recently, a new related family of proteins has been discovered in algae named fatty acid photodecarboxylases (FAPs). These enzymes use the energy of light to convert fatty acids to the corresponding Cn-1 alkanes or alkenes, and hold great potential for biotechnological application. In this work, we aimed at uncovering the natural diversity of FAPs and their relations with other GMC oxidoreductases. We reviewed the available GMC structures, assembled a large dataset of GMC sequences, and found that one active site amino acid, a histidine, is extremely well conserved among the GMC proteins but not among FAPs, where it is replaced with alanine. Using this criterion, we found several new potential FAP genes, both in genomic and metagenomic databases, and showed that related bacterial, archaeal and fungal genes are unlikely to be FAPs. We also identified several uncharacterized clusters of GMC-like proteins as well as subfamilies of proteins that lack the conserved histidine but are not FAPs. Finally, the analysis of the collected dataset of potential photodecarboxylase sequences revealed the key active site residues that are strictly conserved, whereas other residues in the vicinity of the flavin adenine dinucleotide (FAD) cofactor and in the fatty acid-binding pocket are more variable. The identified variants may have different FAP activity and selectivity and consequently may prove useful for new biotechnological applications, thereby fostering the transition from a fossil carbon-based economy to a bio-economy by enabling the sustainable production of hydrocarbon fuels.

A thermostable glucose oxidase from Aspergillus heteromophus CBS 117.55 with broad pH stability and digestive enzyme resistance

In this study, the heterologous expression of an engineered thermostablle glucose oxidase from Aspergillus heteromophus CBS 117.55 was achieved in P. pastoris. This recombinant GoxAh was thermostable, with an optimal temperature range 25 °C-65 °C, and it was capable of retaining greater than 90% of its initial activity following a 10-min incubation at 75 °C. This enzyme had an optimum pH of 6.0, and it could retain above 80% of its initial activity following a 2-h incubation at a broad pH range (2.0-8.0). Moreover, GoxAh displayed excellent pepsin and trypsin resistance, and highly resistant to a range of tested metal ions and chemical reagents. These good properties make GoxAh a promising candidate for feed additive. The K_m and k_cat/K_m values of GoxAh were 187 mM and 1.09/mM/s, which limited its widespread application to some degree. However, due to its excellent characteristics, GoxAh is still of potential economic value for high value-added areas, as well as a good initial enzyme for developing applicable feed enzyme by protein engineering.

Expression of Aspergillus niger glucose oxidase in Pichia pastoris and its antimicrobial activity against Agrobacterium and Escherichia coli

The gene encoding glucose oxidase from Aspergillus niger ZM-8 was cloned and transferred to Pichia pastoris GS115, a transgenic strain P. pastoris GS115-His-GOD constructed. The growth curve of P. pastoris GS115-His-GOD was consistent with that of Pichia pastoris GS115-pPIC9K under non-induced culture conditions. Under methanol induction conditions, the growth of the GOD-transgenic strain was significantly lowered than P. pastoris GS115-pPIC9K with the induced-culture time increase, and the optical densities of GOD-transgenic strain reached one-third of that of the P. pastoris GS115-pPIC9K at 51 h. The activity of glucose oxidase in the cell-free supernatant, the supernatant of cell lysate, and the precipitation of cell lysate was 14.3 U/mL, 18.2 U/mL and 0.48 U/mL, respectively. The specific activity of glucose oxidase was 8.3 U/mg, 6.52 U/mg and 0.73 U/mg, respectively. The concentration of hydrogen peroxide formed by glucose oxidase from supernatant of the fermentation medium, the supernatant of the cell lysate, and the precipitation of cell lysate catalyzing 0.2 M glucose was 14.3 μg/mL, 18.2 μg/mL, 0.48 μg/mL, respectively. The combination of different concentrations of glucose oxidase and glucose could significantly inhibit the growth of Agrobacterium and Escherichia coli in logarithmic phase. The filter article containing supernatant of the fermentation medium, supernatant of the cell lysate, and precipitation of cell lysate had no inhibitory effect on Agrobacterium and E. coli. The minimum inhibitory concentration of hydrogen peroxide on the plate culture of Agrobacterium and E. coli was 5.6 × 10³ μg/mL and 6.0 × 10³ μg/mL, respectively.

Glucose oxidase modified Fenton reactions for in-situ ROS generation and potential application in groundwater remediation

Catalyzed H₂O₂ propagations (CHP) have demonstrated great potential in the remediation of chlorinated aliphatic hydrocarbons (CAHs) like trichloroethene (TCE) contaminated groundwater. However, the importation of highly unstable H₂O₂ into subsurface environment remains challenging. In this work, the in-situ H₂O₂ generation reaction between glucose oxidase (GOD) and glucose was applied in combination with Fe(II) to form the modified Fenton system (GMFs) and its performance in TCE oxidative degradation was investigated. The influence of reactant concentration as well as environmental factors like temperature and pH on the kinetics of TCE oxidation in GMFs were studied. At optimized conditions, about 78% TCE were removed within 8 h in GMFs, which remained effective over the temperature range of 15-30 °C and pH range of 3.6-6.0 (in acetate buffer). The in-situ H₂O₂ and OH generation capacity of GMFs were further investigated to elucidate their functional mechanism on TCE oxidation. Intermediate and product analysis indicated the near-complete release of chloride ion by TCE oxidation with few organic chlorinated intermediates detected. This work reveals the potential of GMFs for CAHs contaminated groundwater remediation through in-situ generation of reactive oxygen species.

Structure and function relationships of sugar oxidases and their potential use in biocatalysis

Several sugar oxidases that catalyze the oxidation of sugars have been isolated and characterized. These enzymes can be classified as flavoenzyme due to the presence of flavin adenine dinucleotide (FAD) as a cofactor. Sugar oxidases have been proposed to be the key biocatalyst in biotransformation of carbohydrates which can potentially convert sugars to provide a pool of intermediates for synthesis of rare sugars, fine chemicals and drugs. Moreover, sugar oxidases have been applied in biosensing of various biomolecules in food industries, diagnosis of diseases and environmental pollutant detection. This review provides the discussions on general properties, current mechanistic understanding, structural determination, biocatalytic application, and biosensor integration of representative sugar oxidase enzymes, namely pyranose 2-oxidase (P2O), glucose oxidase (GO), hexose oxidase (HO), and oligosaccharide oxidase. The information regarding the relationship between structure and function of these sugar oxidases points out the key properties of this particular group of enzymes that can be modified by engineering, which had resulted in a remarkable economic importance.

Engineering a diaphorase via directed evolution for enzymatic biofuel cell application

Background

Diaphorase (DI) has received wide attention as the key anodic enzyme mediating the electron transfer and electric energy generation in enzymatic biofuel cells (EBFCs). Lowering the anodic pH may be a useful strategy for constructing high-performance in EBFCs. However, most DI suffered from the poor activity at low pHs. Therefore, it is necessary to modify the activity and its acidic tolerance to further improve the performance of the EBFC.

Results

This paper attempts to improve the enzyme activity of DI originated from Geobacillus stearothermophilus under acidic conditions through directed evolution. Three rounds of random mutagenesis by error-prone PCR of the GsDI gene followed by high-throughput screening allowed the identification of the mutant 3–8 (H37Q, S73T, F105L, S68T, G61S, D74V) exhibiting a 4- or 7-fold increase in the catalytic activity at pH 5.4 or 4.5 compared to that of the wild type. And the pH stability of mutant 3–8 was significantly better than that of wild type and showed a 1.3 times higher in the stability at pH 5.4. The EBFC anode equipped with 0.5 mg of mutant 3–8 achieved a maximum current of 40 μA at pH 5.4, much higher than that with the same loading of the wild type enzyme.

Conclusion

The GsDI has been improved in the specific activity and pH stability by directed evolution which leads to the improvement of the EBFC performance. Also, the enlarged catalytic channel of mutant and decreased B-factor may be beneficial for the activity and stability. These results suggest that this engineered DI will be a useful candidate for the construction of enhanced EBFCs.