The mechanism of inactivation of glucose oxidase from Penicillium amagasakiense under ambient storage conditions

Evaluation of the operational conditions of the glucose oxidase and catalase multienzymatic system through enzyme co-immobilization on amino hierarchical porous silica

Hexaric acids have attracted attention lately because they are platform chemicals for synthesizing pharmaceuticals. In particular, gluconic acid is one of the most studied because it is readily available in nature. In this work, operational conditions like temperature and pH were evaluated for the enzymatic production of gluconic acid. For this purpose, glucose oxidase (GOx) and catalase (CAT) were individually immobilized and co-immobilized using amino-silica as support. The catalytic performance of the enzymes both as separate biocatalysts (GOx or CAT) and as an enzymatic complex (GOx-CAT) was assessed in terms of enzymatic activity and stability at temperatures 45 °C and 50 °C and pH 6 to 8. The results show that CAT is a key enzyme for gluconic acid production as it prevents GOx from being inhibited by H2O2. However, CAT was found to be less stable than GOx. Therefore, different GOx to CAT enzymatic ratios were studied, and a ratio of 1-3 was determined to be the best. The highest glucose conversion conditions were 45 °C and pH 7.0 for 24 h. Regarding the biocatalyst reuse, GOx-CAT retained more than 70% of its activity after 6 reaction cycles. These results contribute to further knowledge and application of oxidases for hexaric acid production and shed greater light on the role of the glucose oxidase/catalase pair in better catalytic performance. Both enzymes were immobilized in one pot, which is relevant for their potential use in industry; an enzyme system was obtained in a single step.

Comparison of the stability of Mucor-derived flavin adenine dinucleotide-dependent glucose dehydrogenase and glucose oxidase

Long-term stability at near-body temperature is important for continuous glucose monitoring (CGM) sensors. However, the stability of enzymes used in CGM sensors has often been evaluated by measuring their melting temperature (T_m) values and by short heat treatment but not at around 37 °C. Glucose oxidase (GOD) is used in current CGM sensors. In this study, we evaluated the stability of modified Mucor-derived flavin adenine dinucleotide-dependent glucose dehydrogenase (designated Mr144-297) with improved thermal stability at medium to high temperatures and compared it with that of GOD. The T_m value of Mr144-297 was 61.6 ± 0.3 °C and was similar to that of GOD (61.4 ± 1.2 °C). However, Mr144-297 was clearly more stable than GOD at 40 °C and 55 °C. At 37 °C, the stability of a carbon electrode with immobilized Mr144-297 was higher than that of an electrode with GOD. Our data indicate that Mr144-297 is a more suitable enzyme for CGM sensors than is GOD.

A handheld 3D-printed microchip for simple integration of the H2O2-producing enzymatic reactions with subsequent chemiluminescence detection: Application for sugars

Herein, a novel lab-on-a-chip (LoC) device fabricated by 3D printing based on H₂O₂-producing enzymatic reactions with sensitive chemiluminescence (CL) detection was developed to measure different sugars, including glucose, fructose, sucrose, and maltose, in honey, juice, and rice flour samples. The pumpless microchip included two main parts, separated by new cone-shape blocking valves; part A for sample introduction and subsequent enzymatic reaction, besides the CL reagent (luminol) container, and part B for detection. The specific enzyme(s) were embedded into the pores of the zinc zeolite-imidazole framework (ZIF-8) to improve their storage stability. By opening the valves, H₂O₂ produced by enzymatic reaction and luminol could flow through the designed channels into the detection zone on part B, where a 2D cobalt-imidazole framework was embedded to improve the luminol-H₂O₂ CL emission. The obtained signal was proportional to the considered sugar concentration, with the detection limits range of 20-268 µM.

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.

Transient, Implantable, Ultrathin Biofuel Cells Enabled by Laser-Induced Graphene and Gold Nanoparticles Composite

Transient power sources with excellent biocompatibility and bioresorablility have attracted significant attention. Here, we report high-performance, transient glucose enzymatic biofuel cells (TEBFCs) based on the laser-induced graphene (LIG)/gold nanoparticles (Au NPs) composite electrodes. Such LIG electrodes can be easily fabricated from polyimide (PI) with an infrared CO₂ laser and exhibit a low impedance (16 Ω). The resulted TEBFC yields a high open circuit potential (OCP) of 0.77 V and a maximum power density of 483.1 μW/cm². The TEBFC not only exhibits a quick response time that enables reaching the maximum OCP within 1 min but also owns a long lifetime over 28 days in vitro. The excellent biocompatibility and transient performance from in vitro and in vivo tests allow long-term implantation of TEBFCs in rats for energy harvesting. The TEBFCs with advanced processing methods provide a promising power solution for transient electronics.

Extracellular Oxidase from the Neonothopanus nambi Fungus as a Promising Enzyme for Analytical Applications

The extracellular enzyme with oxidase function was extracted from the Neonothopanus nambi luminescent fungus by using mild processing of mycelium with β-glucosidase and then isolated by gel-filtration chromatography. The extracted enzyme is found to be a FAD-containing protein, catalyzing phenol co-oxidation with 4-aminoantipyrine without addition of H₂O₂, which distinguishes it from peroxidases. This fact allowed us to assume that this enzyme may be a mixed-function oxidase. According to gel-filtration chromatography and SDS-PAGE, the oxidase has molecular weight of 60 kDa. The enzyme exhibits maximum activity at 55-70 °C and pH 5.0. Kinetic parameters K_m and V_max of the oxidase for phenol were 0.21 mM and 0.40 µM min^-1. We suggest that the extracted enzyme can be useful to develop a simplified biosensor for colorimetric detection of phenol in aqueous media, which does not require using hydrogen peroxide.

Methionine-Based pH and Oxidation Dual-Responsive Block Copolymer: Synthesis and Fabrication of Protein Nanogels

In this paper, we synthesized a block copolymer containing pendent thioether functionalities by reversible addition-fragmentation chain transfer polymerization of a tert-butyloxycarbonyl (Boc)-l-methionine-(2-methacryloylethyl)ester (Boc-METMA) monomer using a poly(ethylene glycol) (PEG)-based chain transfer agent. The deprotection of Boc groups resulted in an oxidation and pH dual-responsive cationic block copolymer PEG-b-P(METMA). The block copolymer PEG-b-P(METMA) possessing protonable amine groups was water-soluble at pH < 6.0 and self-assembled to form spherical micelles at pH > 6.0. In the presence of H₂O₂, the micelles first became highly swollen with time and completely disassembled at last, demonstrating the H₂O₂-responsive feature because of the oxidation of hydrophobic thioether to hydrophilic sulfoxide. The anticancer drug curcumin (Cur) was entrapped in the polymeric micelles and the Cur-loaded micelles displayed a H₂O₂-triggered release profile as well as a pH-dependent release behavior, making PEG-b-P(METMA) micelles promising nanocarriers for reactive oxygen species-responsive drug delivery. Taking advantage of the protonated amine groups, the cationic polyelectrolyte PEG-b-P(METMA) formed polyion complex micelles with glucose oxidase (GOx) through electrostatic interactions at pH 5.8. By cross-linking the cores of PIC micelles with glutaraldehyde, the PIC micelles were fixed to generate stable GOx nanogels under physiological conditions. The GOx nanogels were glucose-responsive and exhibited glucose-dependent H₂O₂-generation activity in vitro and improved storage and thermal stability of GOx. Cur can be encapsulated in the GOx nanogels, and the Cur-loaded GOx nanogels demonstrate the glucose-responsive release profile. The GOx nanogels displayed high cytotoxicity to 4T1 cells and were effectively internalized by the cells. Therefore, these GOx nanogels have potential applications in the areas of cancer starvation and oxidation therapy.

Exploiting the activity-stability trade-off of glucose oxidase from Aspergillus niger using a simple approach to calculate thermostability of mutants

Glucose oxidase (Gox) is a biocatalyst that is widely applied in the food industry, as well as other biotechnological industries. However, the industrial application of Gox is hampered by its low thermostability and activity. Here, we aimed to improve the thermostability of GoxM4 from Aspergillus niger without reducing its activity due to the activity-stability trade-off. A simple and effective approach combining enzyme activity and structure stability was adopted to evaluate the thermostability of GoxM4 and its mutants. After four rounds of computer-aided rational design, the best mutant, GoxM8, was obtained. The melting temperature (T_m) of GoxM8 was increased by 9 °C compared with GoxM4. The catalytic efficiency of GoxM8 was similar to GoxM4, suggesting that the enzyme activity-stability trade-off was counteracted. To explore its mechanism, we performed molecular dynamics simulations of GoxM4 and its mutants. Our findings provided a typical example for researching the enzyme activity-stability trade-off.

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.

Enhanced Thermostability of Glucose Oxidase through Computer-Aided Molecular Design

Glucose oxidase (GOD, EC.1.1.3.4) specifically catalyzes the reaction of β-d-glucose to gluconic acid and hydrogen peroxide in the presence of oxygen, which has become widely used in the food industry, gluconic acid production and the feed industry. However, the poor thermostability of the current commercial GOD is a key limiting factor preventing its widespread application. In the present study, amino acids closely related to the thermostability of glucose oxidase from Penicillium notatum were predicted with a computer-aided molecular simulation analysis, and mutant libraries were established following a saturation mutagenesis strategy. Two mutants with significantly improved thermostabilities, S100A and D408W, were subsequently obtained. Their protein denaturing temperatures were enhanced by about 4.4 °C and 1.2 °C, respectively, compared with the wild-type enzyme. Treated at 55 °C for 3 h, the residual activities of the mutants were greater than 72%, while that of the wild-type enzyme was only 20%. The half-lives of S100A and D408W were 5.13- and 4.41-fold greater, respectively, than that of the wild-type enzyme at the same temperature. This work provides novel and efficient approaches for enhancing the thermostability of GOD by reducing the protein free unfolding energy or increasing the interaction of amino acids with the coenzyme.

Fabrication of Biobased Polyelectrolyte Capsules and Their Application for Glucose-Triggered Insulin Delivery

To enhance the glucose sensitivity and self-regulated release of insulin, biobased capsules with glucose-responsive and competitive properties were fabricated based on poly(γ-glutamic acid) (γ-PGA) and chitosan oligosaccharide (CS) polyelectrolytes. First, poly(γ-glutamic acid)-g-3-aminophenylboronic acid) (γ-PGA-g-APBA) and galactosylated chitosan oligosaccharide (GC) were synthesized by grafting APBA and lactobionic acid (LA) to γ-PGA and CS, respectively. The (γ-PGA-g-APBA/GC)5 capsules were then prepared by layer-by-layer (LBL) assembly of γ-PGA-g-APBA and GC via electrostatic interaction. The size and morphology of the particles and capsules were investigated by DLS, SEM, and TEM. The size of the (γ-PGA-g-APBA/GC)5 capsules increased with increasing glucose concentration due to the swelling of the capsules. The capsules could be dissociated at high glucose concentration due to the breaking of the cross-linking bonds between APBA and LA by the competitive reaction of APBA with glucose. The encapsulated insulin was able to undergo self-regulated release from the capsules depending on the glucose level and APBA composition. The amount of insulin release increased with incubation in higher glucose concentration and decreased with higher APBA composition. Moreover, the on-off regulation of insulin release from the (γ-PGA-g-APBA/GC)5 capsules could be triggered with a synchronizing and variation of the external glucose concentration, whereas the capsules without the LA functional groups did not show the on-off regulated release. Furthermore, the (γ-PGA-g-APBA/GC)5 capsules are biocompatible. These (γ-PGA-g-APBA/GC)5 with good stability, glucose response, and controlled insulin delivery are expected to be used for future applications to glucose-triggered insulin delivery.

pH and heat-dependent behaviour of glucose oxidase down to single molecule level by combined fluorescence spectroscopy and molecular modelling

BACKGROUND

In the food industry, glucose oxidase (GOX) is used to improve the shelf life of food materials. The pH- and heat-induced conformational changes of glucose oxidase from Aspergillus niger were quantified by means of fluorescence spectroscopy and molecular dynamics simulations.

RESULTS

The phase diagram showed an all-or-none transition process, indicating that pH and temperature largely influence the conformational state of GOX. Shifts in maximum wavelength of Trp, Tyr were registered as the protein encounters a lower pH (pH 4.0), suggesting significant changes of the polarity around the chromophore molecule. Quenching experiments using KI showed higher quenching constants of Trp and flavin adenine dinucleotide upon heating or by changing pH value, and were mainly correlated with the conformational changes upon protein matrix. Finally, valuable insights into the thermal behaviour of GOX were obtained from molecular modelling results.

CONCLUSIONS

The conformation and structure of GOX protein is dependent upon the pH and heat treatment applied. Molecular dynamics simulation indicated significant changes in the substrate binding region at temperatures over 60 °C that might affect enzyme activity. Moreover, an important alteration of the small pocket hosting the positively charged His(516) residue responsible for oxygen activation appears evident at high temperatures.

Biocontrol of tomato plant diseases caused by Fusarium solani using a new isolated Aspergillus tubingensis CTM 507 glucose oxidase

The present study focuses on the potential of glucose oxidase (GOD) as a promising biocontrol agent for fungal plant pathogens. In fact, a new GOD producing fungus was isolated and identified as an Aspergillus tubingensis. GOD (125 AU) has been found to inhibit Fusarium solani growth and spore production. Indeed, GOD caused the reduction of spores, the formation of chlamydospores, the induction of mycelial cords and the vacuolization of mycelium. In vivo assays, GOD acted as a curative treatment capable of protecting the tomato plants against F. solani diseases. In fact, the incidence was null in the curative treatment with GOD and it is around 45% for the preventive treatment. The optimization of media composition and culture conditions led to a 2.6-fold enhancement in enzyme activity, reaching 81.48U/mL. This study has demonstrated that GOD is a potent antifungal agent that could be used as a new biofungicide to protect plants from diseases.

Glucose monitoring using a polymer brush modified polypropylene hollow fiber-based hydraulic flow sensor

Tight regulation of blood glucose levels of diabetic patients requires durable and robust continuous glucose sensing schemes. This manuscript reports the fabrication of ultrathin, phenylboronic acid (PBA) functionalized polymer brushes that swell upon glucose binding and which were integrated as the sensing interface in a new polypropylene hollow fiber (PPHF)-based hydraulic flow glucose sensor prototype. The polymer brushes were prepared via surface-initiated atom transfer radical polymerization of sodium methacrylate followed by postpolymerization modification with 3-aminophenyl boronic acid. In a first series of experiments, the glucose-response of PBA-functionalized poly(methacrylic acid) (PMAA) brushes grafted from planar silicon surfaces was investigated by quartz crystal microbalance with dissipation (QCM-D) and atomic force microscopy (AFM) experiments. The QCM-D experiments revealed a more or less linear change of the frequency shift for glucose concentrations up to ∼10 mM and demonstrated that glucose binding was completely reversible for up to seven switching cycles. The AFM experiments indicated that glucose binding was accompanied by an increase in the film thickness of the PBA functionalized PMAA brushes. The PBA functionalized PMAA brushes were subsequently grafted from the surface of PPHF membranes. The hydraulic permeability of these porous fibers depends on the thickness and swelling of the PMAA brush coating. PBA functionalized brush-coated PPHFs showed a decrease in flux upon exposure to glucose, which is consistent with swelling of the brush coating. Because they avoid the use of enzymes and do not rely on an electrochemical transduction scheme, these PPHF-based hydraulic flow sensors could represent an interesting alternative class of continuous glucose sensors.

Glucose oxidase from Penicillium amagasakiense: characterization of the transition state of its denaturation from molecular dynamics simulations

Glucose oxidase (GOx) is a flavoenzyme having applications in food and medical industries. However, GOx, as many other enzymes when extracted from the cells, has relatively short operational lifetimes. Several recent studies (both experimental and theoretical), carried out on small proteins (or small fractions of large proteins), show that a detailed knowledge of how the breakdown process starts and proceeds on molecular level could be of significant help to artificially improve the stability of fragile proteins. We have performed extended molecular dynamics (MD) simulations to study the denaturation of GOx (a protein dimer containing nearly 1200 amino acids) to identify weak points in its structure and in this way gather information to later make it more stable, for example, by mutations. A denaturation of a protein can be simulated by increasing the temperature far above physiological temperature. We have performed a series of MD simulations at different temperatures (300, 400, 500, and 600 K). The exit from the protein's native state has been successfully identified with the clustering method and supported by other methods used to analyze the simulation data. A common set of amino acids is regularly found to initiate the denaturation, suggesting a moiety where the enzyme could be strengthened by a suitable amino acid based modification.

Thermal inactivation of uricase (urate oxidase): mechanism and effects of additives

Uricase (Urc) is an oxidoreductase enzyme of both general and commercial interest, the former because of its lack of a cofactor and the latter because of its use in the treatment of hyperuricemic disorders. Results of fluorometry and circular dichroism (CD) spectroscopy indicate that the main phase of thermal Urc inactivation follows an irreversible two-state mechanism, with loss of ~20% of the helical structure, loss of the majority of the tertiary structure, and partial exposure of tryptophan residues to solution being approximately concurrent with activity loss. Results of size exclusion chromatography and 8-anilinonaphthalene-1-sulfonate binding studies confirm that this process results in the formation of aggregated molten globules. In addition to this process, CD studies indicate the presence of a rapid reversible denaturation phase that is not completely coupled to the main phase. Urc inactivation is inhibited by the presence of glycerol and trimethylamine oxide, stabilizers of hydrophobic interactions and backbone structure respectively, confirming that loss of hydrophobic bonding and loss of helical structure are key events in the loss of Urc activity. NaCl, however, destabilizes the enzyme at elevated temperature, emphasizing the importance of ionic interactions to Urc stability. A model is developed in which interfacial disruption, involving local loss of hydrophobic interactions, ionic bonds, and helical structure, leads to Urc inactivation and aggregation. Additional studies of Urc inactivation at a more ambient temperature indicate that the inactivation process followed under such conditions is different from that followed at higher temperatures, highlighting the limitations of high-temperature enzyme stability studies.

Engineering the interface between glucose oxidase and nanoparticles

The behavior of glucose oxidase (GOx) on gold nanoparticles (NPs) was investigated as a function of (1) NP surface chemistry, (2) stabilizing protein additives, and (3) protein microenvironment. GOx secondary structure and unfolding was probed by circular dichroism (CD) spectroscopy and fluorescence, and GOx enzymatic activity was measured by a colorimetric assay. We also examined the activity and structure of GOx after displacement from the NP surface. Generally, GOx behavior was negatively impacted by conjugation to the NP, and conjugation conditions could vary the influence of the NP. Surface chemistry and protein microenvironment could improve behavior, but addition of stabilizing proteins negatively influenced activity. After displacement from the NPs, GOx tended to remain unfolded, indicating that the interactions with the NP were irreversible.