Design of nanoscale enzyme complexes based on various scaffolding materials for biomass conversion and immobilization

Enhancing Phycocyanobilin Production Efficiency in Engineered Corynebacterium glutamicum: Strategies and Potential Application

Phycocyanobilin, an algae-originated light-harvesting pigment known for its antioxidant properties, has gained attention as it plays important roles in the food and medication industries and has surged in demand owing to its low-yield extraction from natural resources. In this study, engineered Corynebacterium glutamicum was developed to achieve high PCB production, and three strategies were proposed: reinforcement of the heme biosynthesis pathway with the introduction of two PCB-related enzymes, strengthening of the pentose phosphate pathway to generate an efficient cycle of NADPH, and fed-batch fermentation to maximize PCB production. Each approach increased PCB synthesis, and the final engineered strain successfully produced 78.19 mg/L in a flask and 259.63 mg/L in a 5 L bioreactor, representing the highest bacterial production of PCB reported to date, to our knowledge. The strategies applied in this study will be useful for the synthesis of PCB derivatives and can be applied in the food and pharmaceutical industries.

Enzyme Cascade Electrode Reactions with Nanomaterials and Their Applicability towards Biosensor and Biofuel Cells

Nanomaterials, including carbon nanotubes, graphene oxide, metal-organic frameworks, metal nanoparticles, and porous carbon, play a crucial role as efficient carriers to enhance enzyme activity through substrate channeling while improving enzyme stability and reusability. However, there are significant debates surrounding aspects such as enzyme orientation, enzyme loading, retention of enzyme activity, and immobilization techniques. Consequently, these subjects have become the focus of intensive research in the realm of multi-enzyme cascade reactions. Researchers have undertaken the challenge of creating functional in vitro multi-enzyme systems, drawing inspiration from natural multi-enzyme processes within living organisms. Substantial progress has been achieved in designing multi-step reactions that harness the synthetic capabilities of various enzymes, particularly in applications such as biomarker detection (e.g., biosensors) and the development of biofuel cells. This review provides an overview of recent developments in concurrent and sequential approaches involving two or more enzymes in sequence. It delves into the intricacies of multi-enzyme cascade reactions conducted on nanostructured electrodes, addressing both the challenges encountered and the innovative solutions devised in this field.

Bionanofabrication of Cupric oxide catalyst from Water hyacinth based carbohydrate and its impact on cellulose deconstructing enzymes production under solid state fermentation

One of the most important properties of cellulolytic enzyme is its ability to convert cellulosic polymer into monomeric fermentable sugars which are carbohydrate by nature can efficiently convert into biofuels. However, higher production costs of these enzymes with moderate activity-based stability are the main obstacles to making cellulase-based applications sustainably viable, and this has necessitated rigorous research for the economical availability of this process. Using water hyacinth (WH) waste leaves as the substrate for cellulase production under solid state fermentation (SSF) while treating the fermentation production medium with CuO (cupric oxide oxide) bionanocatalyst have been examined as ways to make fungal cellulase production economically feasible. Herein, a sustainable green synthesis of CuO bionanocatalyst has been performed by using waste leaves of WH. Through XRD, FT-IR, SEM, and TEM analysis, the prepared CuO bionanocatalyst's physicochemical properties have been evaluated. Furthermore, the effect of CuO bionanocatalyst on the temperature stability of raw cellulases was observed, and its half-life stability was found to be up to 9 h at 65 °C. The results presented in the current investigation may have broad scope for mass trials for various industrial applications, such as cellulosic biomass conversion.

Study of the inhibition effects on glutathione peroxidase immobilized on MNPs using a stopped-flow microfluidic system

A stopped-flow microfluidic system to monitor glutathione peroxidase (GPx) activity and evaluate potential inhibitors of the enzyme has been developed based on the integration of the microfluidic chip in the reaction/detection zone. This integration supposes the physical alignment at the optimal location of the microfluidic channel, both the magnetically retained enzyme microreactor (MREµR) and the remote luminescence detection using a focused bifurcated fiber optic bundle (BFOB) connected to a conventional spectrofluorometer detector. The method is based on the coupling of two competitive oxidative chemical reactions, in which glutathione (GSH) and homovanillic acid (HVA) competed for their interaction with hydrogen peroxide in the presence of the magnetically retained GPx-MNPs. The biocatalytic reaction was followed by monitoring the fluorescence of the biphenyl-HVA dimer formed. The dynamic range of the calibration graph was 0.45-10 µmol L^-1, expressed as GSH concentration with a detection limit of 0.1 µmol L^-1 (r² = 0.9954, n = 10, r = 3). The precision expressed as the relative standard deviation (RSD%) was between 0.5 and 3.9%. The stopped-flow microfluidic system showed a sampling frequency of 25 h^-1. The method was applied to the study of GPx inhibition provided by three inhibitory compounds, two metallic ions Hg(II) and Cu(II) and t-butyl hydroperoxide, and their presence in liquid samples, as water, milk, and edible oil. Recovery values between 88.7 and 99.4% were achieved in all instances.

Recent trends using natural polymeric nanofibers as supports for enzyme immobilization and catalysis

All the disciplines of science, especially biotechnology, have given continuous attention to the area of enzyme immobilization. However, the structural support made by material science intervention determines the performance of immobilized enzymes. Studies have proven that nanostructured supports can maintain better catalytic performance and improve immobilization efficiency. The recent trends in the application of nanofibers using natural polymers for enzyme immobilization have been addressed in this review article. A comprehensive survey about the immobilization strategies and their characteristics are highlighted. The natural polymers, e.g., chitin, chitosan, silk fibroin, gelatin, cellulose, and their blends with other synthetic polymers capable of immobilizing enzymes in their 1D nanofibrous form, are discussed. The multiple applications of enzymes immobilized on nanofibers in biocatalysis, biosensors, biofuels, antifouling, regenerative medicine, biomolecule degradation, etc.; some of these are discussed in this review article.

Boosting Hydrolysis of Cellulose at High Temperature by β-Glucosidase Induced Metal-Organic Framework In-Situ Co-Precipitation Encapsulation

Due to the poor enzyme thermal stability, the efficient conversion of high crystallinity cellulose into glucose in aqueous phase over 50 °C is challenging. Herein, an enzyme-induced MOFs encapsulation of β-glucosidase (β-G) strategy was proposed for the first time. By using various methods, including SEM, XRD, XPS, NMR, FTIR and BET, the successful preparation of a porous channel-type flower-like enzyme complex (β-G@MOFs) was confirmed. The prepared enzyme complex (β-G@MOFs) materials showed improved thermal stability (from 50 °C to 100 °C in the aqueous phase) and excellent resistance to ionic liquids (the reaction temperature was as high as 110 °C) compared to the free enzyme (β-G). Not only the catalytic hydrolysis of cellulose by single enzyme (β-G) in ionic liquid was realized, but also the high-temperature continuous reaction performance of the enzyme was significantly improved. Benefiting from the significantly improved heat resistance, the β-G@MOFs exhibited 32.1 times and 34.2 times higher enzymatic hydrolysis rate compared to β-G for cellobiose and cellulose substrates, respectively. Besides, the catalytic activity of β-G@MOFs was retained up to 86 % after five cycles at 110 °C. This was remarkable because the fixation of the enzyme by the MOFs ensured that the folded structure of the enzyme would not expand at high temperatures, allowing the native conformation of the encapsulated protein well-maintained. Furthermore, we believe that this structural stability was caused by the confinement of flower-like porous MOFs.

Sustainable green approach to synthesize Fe3O4/α-Fe2O3 nanocomposite using waste pulp of Syzygium cumini and its application in functional stability of microbial cellulases

Synthesis of nanomaterials following green routes have drawn much attention in recent years due to the low cost, easy and eco-friendly approaches involved therein. Therefore, the current study is focused towards the synthesis of Fe3O4/α-Fe2O3 nanocomposite using waste pulp of Jamun (Syzygium cumini) and iron nitrate as the precursor of iron in an eco-friendly way. The synthesized Fe3O4/α-Fe2O3 nanocomposite has been extensively characterized through numerous techniques to explore the physicochemical properties, including X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, Ultraviolet-Vis spectroscopy, field emission scanning electron microscope, high resolution transmission electron microscope and vibrating sample magnetometer. Further, efficiency of the Fe3O4/α-Fe2O3 nanocomposite has been evaluated to improve the incubation temperature, thermal/pH stability of the crude cellulase enzymes obtained from the lab isolate fungal strain Cladosporium cladosporioides NS2 via solid state fermentation. It is found that the presence of 0.5% Fe3O4/α-Fe2O3 nanocomposite showed optimum incubation temperature and thermal stability in the long temperature range of 50-60 °C for 15 h along with improved pH stability in the range of pH 3.5-6.0. The presented study may have potential application in bioconversion of waste biomass at high temperature and broad pH range.

Current perspective on production and applications of microbial cellulases: a review

The potential of cellulolytic enzymes has been widely studied and explored for bioconversion processes and plays a key role in various industrial applications. Cellulase, a key enzyme for cellulose-rich waste feedstock-based biorefinery, has increasing demand in various industries, e.g., paper and pulp, juice clarification, etc. Also, there has been constant progress in developing new strategies to enhance its production, such as the application of waste feedstock as the substrate for the production of individual or enzyme cocktails, process parameters control, and genetic manipulations for enzyme production with enhanced yield, efficiency, and specificity. Further, an insight into immobilization techniques has also been presented for improved reusability of cellulase, a critical factor that controls the cost of the enzyme at an industrial scale. In addition, the review also gives an insight into the status of the significant application of cellulase in the industrial sector, with its techno-economic analysis for future applications. The present review gives a complete overview of current perspectives on the production of microbial cellulases as a promising tool to develop a sustainable and greener concept for industrial applications.

Cell-surface engineering of yeasts for whole-cell biocatalysts

Due to the unique advantages comparing with traditional free enzymes and chemical catalysis, whole-cell biocatalysts have been widely used to catalyze reactions effectively, simply and environment friendly. Cell-surface display technology provides a novel and effective approach for improved whole-cell biocatalysts expressing heterologous enzymes on the cell surface. They can overcome the substrate transport limitation of the intracellular expression and provide the enzymes with enhanced properties. Among all the host surface-displaying microorganisms, yeast is ideally suitable for constructing whole cell-surface-displaying biocatalyst, because of the large cell size, the generally regarded as safe (GRAS) status, and the perfect post-translational processing of secreted proteins. Yeast cell-surface display system has been a promising and powerful method for development of novel and improved engineered biocatalysts. In this review, the characterization and principles of yeast cell-surface display and the applications of yeast cell-surface display in engineered whole-cell biocatalysts as well as the improvement of the enzyme efficiency are summarized and discussed.

Selective ene-reductase immobilization to magnetic nanoparticles through a novel affinity tag

BACKGROUND

Magnetic nanoparticles (MNPs) are becoming more important as carriers, because of their large specific surface area and easy separability. They are increasingly used in enzyme technology, diagnostics, and drug delivery.

MAJOR RESULTS

For the directed and almost irreversible immobilization of proteins on MNPs, we have developed a new selective (His-Arg)₄ peptide-tag, that binds fusion proteins directly from an E. coli cell lysate to non-functionalized, low-cost MNPs. Using the immobilization of an ene-reductase as an example, we could demonstrate that the fusion with this tag increases thermostability without reducing overall activity (ER w/o tag: t_1/2  = 3.7 h, (HR)₄ -ER: t_1/2  = 9.9 h). Immobilization by adsorption in Tris buffer resulted in very high enzyme loads with approx. 380 mg g^-1 and 67% residual activity. The immobilization on the MNPs allowed a fast concentration, buffer exchange, and reuse. While about 50% of the activity was lost after the first reuse, we were able to show that the activity did not decrease further and was stable for another nine cycles.

CONCLUSION

According to our studies, our tag highly works for any kind of immobilization on MNPs and holds the potential for enzyme immobilizations as well as for drug delivery and sensors.

Progress in Ameliorating Beneficial Characteristics of Microbial Cellulases by Genetic Engineering Approaches for Cellulose Saccharification

Lignocellulosic biomass is a renewable and sustainable energy source. Cellulases are the enzymes that cleave β-1, 4-glycosidic linkages in cellulose to liberate sugars that can be fermented to ethanol, butanol, and other products. Low enzyme activity and yield, and thermostability are, however, some of the limitations posing hurdles in saccharification of lignocellulosic residues. Recent advancements in synthetic and systems biology have generated immense interest in metabolic and genetic engineering that has led to the development of sustainable technology for saccharification of lignocellulosics in the last couple of decades. There have been several attempts in applying genetic engineering in the production of a repertoire of cellulases at a low cost with a high biomass saccharification. A diverse range of cellulases are produced by different microbes, some of which are being engineered to evolve robust cellulases. This review summarizes various successful genetic engineering strategies employed for improving cellulase kinetics and cellulolytic efficiency.

Trienzymatic Complex System for Isomerization of Agar-Derived d-Galactose into d-Tagatose as a Low-Calorie Sweetener

d-Tagatose is a rare monosaccharide that is used in products in the food industry as a low-calorie sweetener. To facilitate biological conversion of d-tagatose, the agarolytic enzyme complexes based on the principle of the cellulosome structure were constructed through dockerin-cohesin interaction with the scaffoldin. The construction of agarolytic complexes composed of l-arabinose isomerase caused efficient isomerization activity on the agar-derived sugars. In a trienzymatic complex, the chimeric β-agarase (cAgaB) and anhydro-galactosidase (cAhgA) from Zobellia galactanivorans could synergistically hydrolyze natural agar substrates and l-arabinose isomerase (LsAraA Doc) from Lactobacillus sakei 23K could convert d-galactose into d-tagatose. The trienzymatic complex increased the concentration of d-tagatose from the agar substrate to 4.2 g/L. Compared with the monomeric enzyme, the multimeric enzyme showed a 1.4-fold increase in tagatose production, good thermostability, and reusability. A residual activity of 75% remained, and 52% of conversion was noted after five recycles. These results indicated that the dockerin-fused chimeric enzymes on the scaffoldin successfully isomerized d-galactose into d-tagatose with synergistic activity. Thus, the results demonstrated the possibility of advancing efficient strategies for utilizing red algae as a biomass source to produce d-tagatose in the industrial food field that uses marine biomass as the feedstock.

Immobilization of Enzymes in Protein Films

Heterogeneous biocatalysis usually involves the use of immobilized enzymes on solid supports. Enzymes have suitable properties in terms of efficiency and selectivity for use as immobilized catalysts. Different approaches have been developed for effective immobilization, including adsorption, covalent binding, entrapment, encapsulation, and cross-linking. Those systems offer some advantages with regard to homogeneous catalysts in solution, such as low costs, easy separation and recovery of the catalyst, reusability, and enzymatic stability. Here, we describe a new approach for the immobilization of active enzymes into homogenous films composed solely of scaffolding proteins that differs from the standard methods of enzyme immobilization on solid supports.

Layered Co-Immobilization of β-Glucosidase and Cellulase on Polymer Film by Visible-Light-Induced Graft Polymerization

Exploring a suitable immobilization strategy to improve catalytic efficiency and reusability of cellulase is of great importance to lowering the cost and promoting the industrialization of cellulose-derived bioethanol. In this work, a layered structure with a thin PEG hydrogel as the inner layer and sodium polyacrylate (PAANa) brush as the outer layer was fabricated on low density polyethylene (LDPE) film by visible-light-induced graft polymerization. Two enzymes, β-glucosidase (BG) and cellulase, were separately coimmobilized onto this hierarchical film. As supplementary to cellulase for improving catalytic efficiency, BG was in situ entrapped into the inner PEG hydrogel layer during the graft polymerization from the LDPE surface. After graft polymerization of sodium acrylate on the PEG hydrogel layer was reinitiated, cellulase was covalently attached on the outer PAANa brush layer. Owing to the mild reaction condition (visible-light irradiation and room temperature), the immobilized BG could retain a high activity after the graft polymerization. The immobilization did not alter the optimal pH and temperature of BG or the optimal temperature of cellulase. However, the optimal pH of cellulase shifts to 5.0 after immobilization. Compared with the original activity of single cellulase system and isolated BG/cellulase immobilization system, the dual-enzyme system exhibited 82% and 20% increase in catalytic activity, respectively. The dual-enzyme system could maintain 93% of carboxymethylcellulose sodium salt (CMC) activity after repeating 10 cycles of hydrolysis and 89% of filter paper activity after 6 cycles relative to original activity, exhibiting excellent reusability. This layer coimmobilization system of BG and cellulase on the polymer film displays tremendous potential for practical application in a biorefinery.

Stable cellulase immobilized on graphene oxide@CMC-g-poly(AMPS-co-AAm) hydrogel for enhanced enzymatic hydrolysis of lignocellulosic biomass

This study indicated tailoring efficient polymer-enzyme bioconjugates with superb stability and activity for practical utilization of cellulase enzyme in hydrolyzing lignocellulosic biomass. To this goal, a dual crosslinking (DC) strategy was presented to synthesize novel 3D networks of carboxymethyl cellulose grafted copolymers of 2-acrylamido-2methyl propane sulfonate and acrylamide (CMC-g-poly(AMPS-co-AAm)) hydrogels. Graphene oxide (GO) nano-sheets were utilized as nano-filler and physical cross-linker making H-bondings between polymeric chains to prepare GO@CMC-g-poly(AMPS-co-AAm) networks. The GO content effects on the performance of as-synthesized architectures in conjugation to a model enzyme (PersiCel1) were examined. PersiCel1 immobilization on the GO reinforced hydrogels resulted in noticeable retaining near 60 % of its maximum activity at 90 °C, along with the remarkable enhancement of its specific activity and storage stability. Compared with the free PersiCel1, the immobilized enzyme on the GO containing hydrogels showed 154.8 % increase in conversion of alkalin-treated sugar beet pulp, while the PersiCel1/neat-Hydrogel indicated an increment of 66.7 %, under the same conditions.

Stabilizing displayed proteins on vegetative Bacillus subtilis cells

Microbes engineered to display heterologous proteins could be useful biotechnological tools for protein engineering, lignocellulose degradation, biocatalysis, bioremediation, and biosensing. Bacillus subtilis is a promising host to display proteins, as this model Gram-positive bacterium is genetically tractable and already used industrially to produce enzymes. To gain insight into the factors that affect displayed protein stability and copy number, we systematically compared the ability of different protease-deficient B. subtilis strains (WB800, BRB07, BRB08, and BRB14) to display a Cel8A-LysM reporter protein in which the Clostridium thermocellum Cel8A endoglucanase is fused to LysM cell wall binding modules. Whole-cell cellulase measurements and fractionation experiments demonstrate that genetically eliminating extracytoplasmic bacterial proteases improves Cel8A-LysM display levels. However, upon entering stationary phase, for all protease-deficient strains, the amount of displayed reporter dramatically decreases, presumably as a result of cellular autolysis. This problem can be partially overcome by adding chemical protease inhibitors, which significantly increase protein display levels. We conclude that strain BRB08 is well suited for stably displaying our reporter protein, as genetic removal of its extracellular and cell wall-associated proteases leads to the highest levels of surface-accumulated Cel8A-LysM without causing secretion stress or impairing growth. A two-step procedure is presented that enables the construction of enzyme-coated vegetative B. subtilis cells that retain stable cell-associated enzyme activity for nearly 3 days. The results of this work could aid the development of whole-cell display systems that have useful biotechnological applications.