Modulation of Transaminase Activity by Encapsulation in Temperature-Sensitive Poly(N-acryloyl glycinamide) Hydrogels

Smart hydrogels hold much potential for biocatalysis, not only for the immobilization of enzymes, but also for the control of enzyme activity. We investigated upper critical solution temperature‐type poly N‐acryloyl glycinamide (pNAGA) hydrogels as a smart matrix for the amine transaminase from Bacillus megaterium (BmTA). Physical entrapment of BmTA in pNAGA hydrogels results in high immobilization efficiency (>89 %) and high activity (97 %). The temperature‐sensitiveness of pNAGA is preserved upon immobilization of BmTA and shows a gradual deswelling upon temperature reduction. While enzyme activity is mainly controlled by temperature, deactivation tended to be higher for immobilized BmTA (≈62–68 %) than for free BmTA (≈44 %), suggesting a deactivating effect due to deswelling of the pNAGA gel. Although the deactivation in response to hydrogel deswelling is not yet suitable for controlling enzyme activity sufficiently, it is nevertheless a good starting point for further optimization.

Surface Modulation of Graphene Oxide for Amidase Immobilization with High Loadings for Efficient Biocatalysis

As a type of important and versatile biocatalyst, amidase immobilization on solid materials has received broad attention with its relatively easy procedure and available reusability. However, current porous supports have suffered from limited loadings, and it is highly desired to develop a new type of material with abundant space so as to ensure a high loading of amidase. Here, graphene oxide was adopted as the support for amidase immobilization, which showed the highest loading capacity for amidase (~3000 mg/g) to date. To the best of our knowledge, it is the first case of amidase immobilized on graphene oxide. Through surface modulation via reducing the contents of oxygen-containing functional groups, activity recovery of immobilized amidase increased from 67.8% to 85.3%. Moreover, surface-modulated graphene oxide can efficiently uptake amidase under a wide range of pH, and the maximum loading can reach ~3500 mg/g. The resultant biocomposites exhibit efficient biocatalytic performance for asymmetric synthesis of a chiral amino acid (i.e., L-4-fluorophenylglycine, an intermediate of aprepitant).

Catalytically active inclusion bodies (CatIBs) induced by terminally attached self-assembling coiled-coil domains: To enhance the stability of (R)-hydroxynitrile lyase

The catalytically-active inclusion bodies (CatIBs) represent a promising strategy for immobilizing enzyme without additional carriers and chemicals, which has aroused great attention in academic and industrial communities. In this work, we discovered two natural parallel right-handed coiled-coil tetramer peptides from PDB database by a structural mining strategy. The two self-assembling peptides, NSPdoT from rotavirus and HVdoT from human Vasodilator-stimulated phosphoprotein, efficiently induced the CatIBs formation of a (R)-Hydroxynitrile lyase from Arabidopsis thaliana (AtHNL) in Escherichia coli cells. This is convenient to simultaneously purify and immobilize the target proteins as biocatalysts. As expected, HVdoT-AtHNL and NSPdoT-AtHNL possessed drastically increased tolerance toward lower pH values, which will be very critical to synthesize cyanohydrins under acidic condition for suppressing the non-enzymatic side reaction. In addition. AtHNL-CatIBs are produced at high yield in host cells as bioactive microparticles, which exhibited high thermal and pH stabilities. Therefore, the CatIBs method represent a promising application for the immobilization of enzymes in the biocatalysis field.

Free and Immobilised β-Glucosidases in Oenology: Biotechnological Characterisation and Its Effect on Enhancement of Wine Aroma

In grapes, monoterpenes and norisoprenoids are in the form of non-volatile compounds, flavourless glycosides which could enhance the aroma of wines after its hydrolysis using β- glucosidases enzymes. It is known that the use of immobilised enzymes offers advantages such as reusability and easy recuperation. In this study, a commercial β-glucosidase was immobilised by absorption in sodium alginate. Biotechnological characteristics and terpen hydrolysis (hydrolysis aroma precursors) in muscat wines were studied after treatment with both free and immobilised commercial β- glucosidase with two different concentrations. It was revealed that both forms shared an optimal pH (4.5) and a maximum temperature (64°C), even an increment on the activity between 40and 60°C. A similar Km value has been determined while Vmax from the immobilised enzyme was higher than the free (3.35 and 2.52 μmol min^–1 mg^–1, respectively). Additionally, the immobilised enzyme showed a better hydrolytic activity during 24 h, and its reusability has been proven. Regarding enzymatic hydrolysis in grape must, the best results were observed for the highest concentration of free β-glucosidase although glucose release was also determined for the immobilised enzyme along the days. In contrast, maximum activity was reached by the immobilised β-glucosidase in less time but in no case equalled the free ones. Finally, volatile compound liberation in wines treated with free or immobilised enzymes was analysed using HRGC-MS. Liberation for both enzymes and the greatest concentrations of some volatiles were detected when a double dose of the free β-glucosidase was used. Nevertheless, the wines treated with the immobilised β-glucosidase showed a high concentration of some volatile compounds such as nerol or geraniol.

Sustainable Biological Ammonia Production towards a Carbon-Free Society

A sustainable society was proposed more than 50 years ago. However, it is yet to be realised. For example, the production of ammonia, an important chemical widely used in the agriculture, steel, chemical, textile, and pharmaceutical industries, still depends on fossil fuels. Recently, biological approaches to achieve sustainable ammonia production have been gaining attention. Moreover, unlike chemical methods, biological approaches have a lesser environmental impact because ammonia can be produced under mild conditions of normal temperature and pressure. Therefore, in previous studies, nitrogen fixation by nitrogenase, including enzymatic ammonia production using food waste, has been attempted. Additionally, the production of crops using nitrogen-fixing bacteria has been implemented in the industry as one of the most promising approaches to achieving a sustainable ammonia economy. Thus, in this review, we described previous studies on biological ammonia production and showed the prospects for realising a sustainable society.

Immobilization of papain: A review

Papain is a cysteine protease from papaya, with many applications due to its broad specificity. This paper reviews for first time the immobilization of papain on different supports (organic, inorganic or hybrid supports) presenting some of the features of the utilized immobilization strategies (e.g., epoxide, glutaraldehyde, genipin, glyoxyl for covalent immobilization). Special focus is placed on the preparation of magnetic biocatalysts, which will permit the simple recovery of the biocatalyst even if the medium is a suspension. Problems specific to the immobilization of proteases (e.g., steric problems when hydrolyzing large proteins) are also defined. The benefits of a proper immobilization (enzyme stabilization, widening of the operation window) are discussed, together with some artifacts that may suggest an enzyme stabilization that may be unrelated to enzyme rigidification.

Metal-Organic Frameworks as a Versatile Materials Platform for Unlocking New Potentials in Biocatalysis

Biocatalysts immobilization with nanomaterials has promoted the development of biocatalysis significantly and made it an indispensable part of catalysis industries nowadays. Metal-organic frameworks (MOFs), constructed from organic linkers and metal ions or clusters, have raised significant interests for biocatalysts immobilization in recent years. The diversity of building units, molecular-scale tunability, and modular synthetic routes of MOFs greatly expand its ability as the host to integrate with biocatalysts. In this review, the general synthetic strategies of MOFs with biocatalysts are first summarized. Then, the recent progress of MOFs as a versatile host for a series of biocatalysts, including natural enzymes, nanozymes, and organism-based biocatalysts, followed by the introduction of MOFs themselves as biocatalysts, is discussed. Furthermore, the stimuli-responsive properties of MOFs themselves or the additional functionalization of protein, polymer, and peptide within/on MOF that enable the biocatalysts with the controllable and tunable behavior are also summarized, which could unlock new potentials in biocatalysis. Finally, a perspective of the upcoming challenges, potential impacts, and future directions of biocatalytic MOFs is provided.

Protein Corona Hinders N-CQDs Oxidative Potential and Favors Their Application as Nanobiocatalytic System

The oxidative properties of nanomaterials arouse legitimate concerns about oxidative damage in biological systems. On the other hand, the undisputable benefits of nanomaterials promote them for biomedical applications; thus, the strategies to reduce oxidative potential are urgently needed. We aimed at analysis of nitrogen-containing carbon quantum dots (N-CQDs) in terms of their biocompatibility and internalization by different cells. Surprisingly, N-CQD uptake does not contribute to the increased oxidative stress inside cells and lacks cytotoxic influence even at high concentrations, primarily through protein corona formation. We proved experimentally that the protein coating effectively limits the oxidative capacity of N-CQDs. Thus, N-CQDs served as an immobilization support for three different enzymes with the potential to be used as therapeutics. Various kinetic parameters of immobilized enzymes were analyzed. Regardless of the enzyme structure and type of reaction catalyzed, adsorption on the nanocarrier resulted in increased catalytic efficiency. The enzymatic-protein-to-nanomaterial ratio is the pivotal factor determining the course of kinetic parameter changes that can be tailored for enzyme application. We conclude that the above properties of N-CQDs make them an ideal support for enzymatic drugs required for multiple biomedical applications, including personalized medical therapies.

Ferritin-catalyzed synthesis of ferrihydrite nanoparticles with high mimetic peroxidase activity for biomolecule detection

Natural enzymes are generally sophisticated structural proteins that catalyze biological reactions with high specificity and efficiency and thus offer great potential in various disciplines, but intrinsic proteinic features such as easy denaturation and digestion restrict their practical application. So far, many functional nanomaterials with robust structures have been advanced as enzyme-mimetic catalysts to replace natural enzymes, however, their synthesis processes are generally complicated and require harsh experimental conditions such as high temperature and pressure. Herein, we report the facile synthesis of nanoparticles with high peroxidase-like activity by enzymatic catalysis. Specifically, by utilizing the intrinsic ferroxidase activity and mineralization capability of ferritin, ferrihydrite nanoparticles can be easily prepared within the apoferritin cavity at room temperature in aqueous solution (pH ∼ 7.0). Notably, reconstituted ferrihydrite nanoparticles exhibited comparative catalytic activity with a natural enzyme, horse radish peroxidase. Notably, when coupled with another oxidase, a dual-enzyme sensor system can be constructed for the detection of biomolecules such as glucose, and xanthine. Due to the biocompatibility and easy modification of the ferritin shell using well-established chemical and genetic techniques, the nanoparticles encapsulated by a protein shell possess great potential application in theranostics and immunoassays.

Immobilization of PETase enzymes on magnetic iron oxide nanoparticles for the decomposition of microplastic PET

Polyethylene terephthalate (PET) is responsible for a large amount of environmental contamination with microplastics. Based on its high affinity, the PET degrading enzyme PETase can be immobilized on superparamagnetic iron oxide nanoparticles through a His-tag. The His-tag increases enzyme stability, and allows magnetic separation for recovery. Multiple recycling steps are possible and microplastic particles can be decomposed depending on the PET's crystallinity. The separation or decomposition of PET allows for a sustainable way to remove microplastic from water.

Nitrilase immobilization and transposition from a micro-scale batch to a continuous process increase the nicotinic acid productivity

In recent years, many biocatalytic processes have been developed for the production of chemicals and pharmaceuticals. In this context, enzyme immobilization methods have attracted attention for their advantages, such as continuous production and increased stability. Here, enzyme immobilization methods and a collection of nitrilases from biodiversity for the conversion of 3-cyanopyridine to nicotinic acid were screened. Substrate conversion over 10 conversion cycles was monitored to optimize the process. The best immobilization conditions were found with cross-linking using glutaraldehyde to modify the PMMA beads. This method showed good activity over 10 cycles in a batch reactor at 30 and 40°C. Finally, production with a new thermostable nitrilase was examined in a continuous packed bed reactor, showing very high stability of the biocatalytic process at a flow rate of 0.12 ml min^-1 and a temperature of 50°C. The complete conversion of 3-cyanopyridine was obtained over 30 days of operation. Future steps will concern reactor scale-up to increase the production rate with reasonable pressure drops.

Current Status of Mining, Modification, and Application of Cellulases in Bioactive Substance Extraction

Cellulases have been used to extract bioactive ingredients from medical plants; however, the poor enzymatic properties of current cellulases significantly limit their application. Two strategies are expected to address this concern: (1) new cellulase gene mining strategies have been promoted, optimized, and integrated, thanks to the improvement of gene sequencing, genomic data, and algorithm optimization, and (2) known cellulases are being modified, thanks to the development of protein engineering, crystal structure data, and computing power. Here, we focus on mining strategies and provide a systemic overview of two approaches based on sequencing and function. Strategies based on protein structure modification, such as introducing disulfide bonds, proline, salt bridges, N-glycosylation modification, and truncation of loop structures, have already been summarized. This review discusses four aspects of cellulase-assisted extraction. Initially, cellulase alone was used to extract bioactive substances, and later, mixed enzyme systems were developed. Physical methods such as ultrasound, microwave, and high hydrostatic pressure have assisted in improving extraction efficiency. Cellulase changes the structure of biomolecules during the extraction process to convert them into effective ingredients with better activity and bioavailability. The combination of cellulase with other enzymes and physical technologies is a promising strategy for future extraction applications.

Continuous process technology for glucoside production from sucrose using a whole cell-derived solid catalyst of sucrose phosphorylase

Advanced biotransformation processes typically involve the upstream processing part performed continuously and interlinked tightly with the product isolation. Key in their development is a catalyst that is highly active, operationally robust, conveniently produced, and recyclable. A promising strategy to obtain such catalyst is to encapsulate enzymes as permeabilized whole cells in porous polymer materials. Here, we show immobilization of the sucrose phosphorylase from Bifidobacterium adolescentis (P134Q-variant) by encapsulating the corresponding E. coli cells into polyacrylamide. Applying the solid catalyst, we demonstrate continuous production of the commercial extremolyte 2-α-D-glucosyl-glycerol (2-GG) from sucrose and glycerol. The solid catalyst exhibited similar activity (≥70%) as the cell-free extract (~800 U g-1 cell wet weight) and showed excellent in-operando stability (40 °C) over 6 weeks in a packed-bed reactor. Systematic study of immobilization parameters related to catalyst activity led to the identification of cell loading and catalyst particle size as important factors of process optimization. Using glycerol in excess (1.8 M), we analyzed sucrose conversion dependent on space velocity (0.075-0.750 h-1) and revealed conditions for full conversion of up to 900 mM sucrose. The maximum 2-GG space-time yield reached was 45 g L-1 h-1 for a product concentration of 120 g L-1. Collectively, our study establishes a step-economic route towards a practical whole cell-derived solid catalyst of sucrose phosphorylase, enabling continuous production of glucosides from sucrose. This strengthens the current biomanufacturing of 2-GG, but also has significant replication potential for other sucrose-derived glucosides, promoting their industrial scale production using sucrose phosphorylase. KEY POINTS: • Cells of sucrose phosphorylase fixed in polyacrylamide were highly active and stable. • Solid catalyst was integrated with continuous flow to reach high process efficiency. • Generic process technology to efficiently produce glucosides from sucrose is shown.

Bioactive peptides from fisheries residues: A review of use of papain in proteolysis reactions

Papain is a cysteine endopeptidase of vegetal origin (papaya (Carica papaya L.) with diverse applications in food technology. In this review we have focused our attention on its application in the production of bio-peptides by hydrolysis of proteins from fish residues. This way, a residual material, that can become a contaminant if dumped without control, is converted into highly interesting products. The main bioactivity of the produced peptides is their antioxidant activity, followed by their nutritional and functional activities, but peptides with many other bioactivities have been produced. Thera are also examples of production of hydrolysates with several bioactivities. The enzyme may be used alone, or in combination with other enzymes to increase the degree of hydrolysis.

Design of bioreactor based on immobilized laccase on silica-chitosan support for phenol removal in continuous mode

A silica-chitosan support was employed for laccase immobilization. The hybrid support was obtained using calcium ion as linking agent that coordinates silanol and hydroxyl groups of chitosan. The insoluble biocatalyst was then packed in a column and used in a flow system for phenol removal. The immobilized enzyme reactor (IMER) showed a good storage stability (70 % of activity in 70 days) and good reusability (90-50 % of catalytic activity at the 4th reuse in function of chitosan type). The best performance for the phenol removal was obtained with a low molecular weight chitosan from crab shells at pH 5 and with a flow rate of 0.7 mL/min. The apparent Michaelis-Menten (V_max^app, K_m^app) and the inherent (V_max^inh, K_m^inh) constants were also determined to evaluate the influence of the phenol structure on the performance of the system. The enzymatic oxidation of a phenol mixture (4-methylcatechol, catechol, caffeic acid, syringic acid, vanillic acid, p-coumaric acid, and tyrosol) was followed for 21 h in a continuous mode by HPLC. The phenol mixture removal of 90 % was also confirmed by Folin-Ciocalteu assay.

An overview to process design, simulation and sustainability evaluation of biodiesel production

The overwhelming concerns due to over exploitation of fossil resources necessitate the utilization of alternative energy resources. Biodiesel has been considered as one of the most adaptable alternative to fossil-derived diesel with similar properties and numerous environmental benefits. Although there are various approaches for biodiesel production, development of cost-effective and robust catalyst with efficient production methods and utilization of a variety of feedstock could be the optimum solution to bring down the production cost. Considering the complexity of biodiesel production processes, process design, quantitative evaluation and optimization of the biodiesel from whole systems perspectives is essential for unlocking the complexity and enhancing the system performances. Process systems engineering offers an efficient approach to design and optimize biodiesel manufacturing systems by using a variety of tools. This review reflects state-of-the-art biodiesel research in the field of process systems engineering with a particular focus on biodiesel production including process design and simulation, sustainability evaluation, optimization and supply chain management. This review also highlights the challenges and opportunities for the development of potentially sustainable and eco-friendly enzymatic biodiesel technology.

Enzyme-Loaded Flower-Shaped Nanomaterials: A Versatile Platform with Biosensing, Biocatalytic, and Environmental Promise

As a result of their unique structural and multifunctional characteristics, organic-inorganic hybrid nanoflowers (hNFs), a newly developed class of flower-like, well-structured and well-oriented materials has gained significant attention. The structural attributes along with the surface-engineered functional entities of hNFs, e.g., their size, shape, surface orientation, structural integrity, stability under reactive environments, enzyme stabilizing capability, and organic-inorganic ratio, all significantly contribute to and determine their applications. Although hNFs are still in their infancy and in the early stage of robust development, the recent hike in biotechnology at large and nanotechnology in particular is making hNFs a versatile platform for constructing enzyme-loaded/immobilized structures for different applications. For instance, detection- and sensing-based applications, environmental- and sustainability-based applications, and biocatalytic and biotransformation applications are of supreme interest. Considering the above points, herein we reviewed current advances in multifunctional hNFs, with particular emphasis on (1) critical factors, (2) different metal/non-metal-based synthesizing processes (i.e., (i) copper-based hNFs, (ii) calcium-based hNFs, (iii) manganese-based hNFs, (iv) zinc-based hNFs, (v) cobalt-based hNFs, (vi) iron-based hNFs, (vii) multi-metal-based hNFs, and (viii) non-metal-based hNFs), and (3) their applications. Moreover, the interfacial mechanism involved in hNF development is also discussed considering the following three critical points: (1) the combination of metal ions and organic matter, (2) petal formation, and (3) the generation of hNFs. In summary, the literature given herein could be used to engineer hNFs for multipurpose applications in the biosensing, biocatalysis, and other environmental sectors.

Enhanced Stability of Long-Living Immobilized Recombinant β-d-N-Acetyl-Hexosaminidase A on Polylactic Acid (PLA) Films for Potential Biomedical Applications

β-d-N-acetyl-hexosaminidase (Hex, EC 3.2.1.52) is an acid hydrolase that catalyzes the cleavage of the β-1,4 bond in N-acetyl-d-galactosamine (Gal-NAc) and N-acetyl-d-glucosamine (Glc-NAc) from the non-reducing end of oligosaccharides and glycoconjugates. It is widely expressed in both the prokaryotic and eukaryotic world, where it performs multiple and important functions. Hex has antifungal activity in plants, is capable of degrading many biological substrates, and can play an important role in the biomedical field for the treatment of Tay-Sachs and Sandhoff diseases. With the aim being able to obtain a device with a stable enzyme, a method of covalent immobilization on polylactic acid (PLA) films was developed for the A isoform of the β-d-N-acetyl-hexosaminidase enzyme (HexA), produced in a recombinant way from Human Embryonic Kidney-293 (HEK-293) cells and suitably purified. An in-depth biochemical characterization of the immobilized enzyme was carried out, evaluating the optimal temperature, thermal stability, pH parameters, and Km value. Moreover, the stability of the enzymatic activity over time was assessed. The results obtained showed an improvement in terms of kinetic parameters and stability to heat for the enzyme following immobilization and the presence of HexA in two distinct immobilized forms, with an unexpected ability for one of them to maintain its functionality for a long period of time (over a year). The stability and functionality of the enzyme in its immobilized form are therefore extremely promising for potential biotechnological and biomedical applications.

Laccase and Its Mutant Displayed on the Bacillus subtilis Spore Coat for Oxidation of Phenolic Compounds in Organic Solvents

Enzymes displayed on the Bacillus subtilis spore coat have several features that are useful for biocatalysis. The enzyme is preimmobilized on an inert surface of the spore coat, which is due to the natural sporulation process. As a result, protein stability can be increased, and they are resistant to environmental changes. Next, they would not lyse under extreme conditions, such as in organic solvents. Furthermore, they can be easily removed from the reaction solution and reused. The laboratory evolved CotA laccase variant T480A-CotA was used to oxidize the following phenolic substrates: (+)-catechin, (−)-epicatechin, and sinapic acid. The kinetic parameters were determined and T480A-CotA had a greater Vmax/Km than wt-CotA for all substrates. The Vmax/Km for T480A-CotA was 4.1, 5.6, and 1.4-fold greater than wt-CotA for (+)-catechin, (−)-epicatechin, and sinapic acid, respectively. The activity of wt-CotA and T480A-CotA was measured at different concentrations from 0–70% in organic solvents (dimethyl sulfoxide, ethanol, methanol, and acetonitrile). The Vmax for T480A-CotA was observed to be greater than the wt-CotA in all organic solvents. Finally, the T480A-CotA was recycled 7 times over a 23-h period and up to 60% activity for (+)-catechin remained. The product yield was up to 3.1-fold greater than the wild-type.

d-Glucose Isomerization with PAMAM Dendrimers as Environmentally Friendly Catalysts

The isomerization of d-glucose to d-fructose plays a key role in the biochemical and chemical conversion of biomass, and it is therefore desirable to develop and improve catalysts for this reaction. In this study, the environmentally friendly polymer poly(amidoamine) (PAMAM) dendrimer's properties as catalysts for this isomerization are investigated. The experimental results showed that the PAMAM dendrimers, which have basic terminal groups, can effectively promote the d-glucose isomerization reaction. Under the optimized reaction conditions, d-fructose was generated with a 20% maximum yield and above 90% selectivity. ¹³C and ²H isotope experiments by NMR were carried out to explore the reaction mechanism. When the reaction was performed in D₂O, the C1 signal of d-fructose changed to a triplet, which confirmed that the C1 carbon binds to a deuterium atom, i.e., isotopic exchange. It was also found that the deuterium atom at the C2 position of d-glucose-2-d₁ cannot transfer to d-fructose. These data indicate that PAMAM dendrimers catalyze d-glucose isomerization through a mechanism, which includes deprotonation, formation of ene-diol intermediate, and proton exchange with the solvent.

Immobilization of the Peroxygenase from Agrocybe aegerita. The Effect of the Immobilization pH on the Features of an Ionically Exchanged Dimeric Peroxygenase

This paper outlines the immobilization of the recombinant dimeric unspecific peroxygenase from Agrocybe aegerita (rAaeUPO). The enzyme was quite stable (remaining unaltered its activity after 35 h at 47 °C and pH 7.0). Phosphate destabilized the enzyme, while glycerol stabilized it. The enzyme was not immobilized on glyoxyl-agarose supports, while it was immobilized albeit in inactive form on vinyl-sulfone-activated supports. rAaeUPO immobilization on glutaraldehyde pre-activated supports gave almost quantitative immobilization yield and retained some activity, but the biocatalyst was very unstable. Its immobilization via anion exchange on PEI supports also produced good immobilization yields, but the rAaeUPO stability dropped. However, using aminated agarose, the enzyme retained stability and activity. The stability of the immobilized enzyme strongly depended on the immobilization pH, being much less stable when rAaeUPO was adsorbed at pH 9.0 than when it was immobilized at pH 7.0 or pH 5.0 (residual activity was almost 0 for the former and 80% for the other preparations), presenting stability very similar to that of the free enzyme. This is a very clear example of how the immobilization pH greatly affects the final biocatalyst performance.

Enzymatic characteristics of immobilized carbonic anhydrase and its applications in CO2 conversion

Native carbonic anhydrase (CA) has been widely used in several different applications due to its catalytic function in the interconversion of carbon dioxide (CO₂) and carbonic acid. However, subject to its stability and recyclability, native CA often deactivates when in harsh environments, which restricts its applications in the commercial market. Maintaining the stability and high catalytic activity of CA is challenging. Immobilization provides an effective route that can improve enzymatic stability. Through the interaction of covalent bonds and van der Waals forces, water-soluble CA can be combined with various insoluble supports to form water-insoluble immobilized CA so that CA stability and utilization can be greatly improved. However, if the immobilization method or immobilization condition is not suitable, it often leads to a decrease in CA activity, reducing the application effects on CO₂ conversion. In this review, we discuss existing immobilization methods and applications of immobilized CA in the environmental field, such as the mineralization of carbon dioxide and multienzyme cascade catalysis based on CA. Additionally, prospects in current development are outlined. Because of the many outstanding and superior properties after immobilization, CA is likely to be used in a wide variety of scientific and technical areas in the future.

Co-immobilized recombinant glycosyltransferases efficiently convert rebaudioside A to M in cascade

Rebaudioside M (Reb M), as a natural and healthy Stevia sweetener, is produced by two glycosyltransferases that catalyze the serial glycosylation of Rebaudioside A (Reb A) and Rebaudioside D (Reb D) in cascade. Meanwhile, it is of great importance in developing an immobilization strategy to improve the reusability of glycosyltransferases in reducing the production cost of Reb M. Here, the recombinant glycosyltransferases, i.e., OsEUGT11 (UGT1) and SrUGT76G1 (UGT2), were expressed in Escherichia coli and covalently immobilized onto chitosan beads. UGT1 and UGT2 were individually immobilized and co-immobilized onto the beads that catalyze Reb A to Reb M in one-pot. The co-immobilized enzymes system exhibited ∼3.2-fold higher activity than that of the mixed immobilized enzymes system. A fairly high Reb A conversion rate (97.3%) and a high Reb M yield of 72.2% (4.82 ± 0.11 g L-1) were obtained with a feeding Reb A concentration of 5 g L-1. Eventually, after 4 and 8 reused cycles, the co-immobilized enzymes retained 72.5% and 53.1% of their original activity, respectively, showing a high stability to minimize the total cost of enzymes and suggesting that the co-immobilized UGTs is of potentially signficant value for the production of Reb M.

Chemical and physical Chitosan modification for designing enzymatic industrial biocatalysts: How to choose the best strategy?

Chitosan is one of the most abundant natural polymer worldwide, and due to its inherent characteristics, its use in industrial processes has been extensively explored. Because it is biodegradable, biocompatible, non-toxic, hydrophilic, cheap, and has good physical-chemical stability, it is seen as an excellent alternative for the replacement of synthetic materials in the search for more sustainable production methodologies. Thus being, a possible biotechnological application of Chitosan is as a direct support for enzyme immobilization. However, its applicability is quite specific, and to overcome this issue, alternative pretreatments are required, such as chemical and physical modifications to its structure, enabling its use in a wider array of applications. This review aims to present the topic in detail, by exploring and discussing methods of employment of Chitosan in enzymatic immobilization processes with various enzymes, presenting its advantages and disadvantages, as well as listing possible chemical modifications and combinations with other compounds for formulating an ideal support for this purpose. First, we will present Chitosan emphasizing its characteristics that allow its use as enzyme support. Furthermore, we will discuss possible physicochemical modifications that can be made to Chitosan, mentioning the improvements obtained in each process. These discussions will enable a comprehensive comparison between, and an informed choice of, the best technologies concerning enzyme immobilization and the application conditions of the biocatalyst.

Immobilization of recombinant Escherichia coli cells expressing glucose isomerase using modified diatomite as a carrier for effective production of high fructose corn syrup in packed bed reactor

To improve the operational stability of glucose isomerase in E. coli TEGI-W139F/V186T, the immobilized cells were prepared with modified diatomite as a carrier and 74.1% activity of free cells was recovered after immobilization. Results showed that the immobilized cells still retained 86.2% of the initial transformational activity after intermittent reused 40 cycles and the yield of D-fructose reached above 42% yield at 60 °C. Moreover, the immobilized cells were employed in the continuous production of High Fructose Corn Syrup (HFCS) in a recirculating packed bed reactor for 603 h at a constant flow rate. It showed that the immobilized cells exhibited good operational stability and the yield of D-fructose retained above 42% within 603 h. The space-time yield of high fructose corn syrup reached 3.84 kg L^-1 day^-1. The investigation provided an efficient immobilization method for recombinant cells expressing glucose isomerase with higher stability, and the immobilized cells are a promising biocatalyst for HFCS production.

Two-step biosynthesis of d-allulose via a multienzyme cascade for the bioconversion of fruit juices

d-Allulose, a low-calorie rare sugar with potential as sucrose substitute for diabetics, can be produced using d-allulose 3-epimerase (DAE). Here, we characterized a putative thermostable DAE from Pirellula sp. SH-Sr6A (PsDAE), with a half-life of 6 h at 60 °C. Bioconversion of 500 g/L d-fructose using immobilized PsDAE on epoxy support yielded 152.7 g/L d-allulose, which maintained 80% of the initial activity after 11 reuse cycles. A multienzyme cascade system was developed to convert sucrose to d-allulose comprising sucrose invertase, d-glucose isomerase and PsDAE. Fruit juices were treated using this system to convert the high-calorie sugars, such as sucrose, d-glucose, and d-fructose, into d-allulose. The content of d-allulose among total monosaccharides in the treated fruit juice remained between 16 and 19% during 15 reaction cycles. This study provides an efficient strategy for the development of functional fruit juices containing d-allulose for diabetics and other special consumer categories.

Effect of confinement of horse heart cytochrome c and formate dehydrogenase from Candida boidinii on mesoporous carbons on their catalytic activity

This study reports the immobilization of two biocatalysts (e.g., cytochrome c-Cyt c-and the non-metalloenzyme formate dehydrogenase from Candida boidinii-cbFDH) on a series of mesoporous carbons with controlled pore sizes. The catalytic activity of the nanoconfined proteins was correlated with the pore size distribution of the carbon materials used as supports. The electrochemical behaviour of nanoconfined Cyt c showed direct electron transfer electroactivity in pore sizes matching tightly the protein dimension. The pseudo-peroxidase activity towards H₂O₂ reduction was enhanced at pH 4.0, due to the protein conformational changes. For cbFDH, the reduction of CO₂ towards formic acid was evaluated for the nanoconfined protein, in the presence of nicotinamide adenine dinucleotide (NADH). The carbons displayed different cbFDH uptake capacity, governed by the dimensions of the main mesopore cavities and their accessibility through narrow pore necks. The catalytic activity of nanoconfined cbFDH was largely improved, compared to its performance in free solution. Regardless of the carbon support used, the production of formic acid was higher upon immobilization with lower nominal cbFDH:NADH ratios.

Design of novel enzyme biocatalysts for industrial bioprocess: Harnessing the power of protein engineering, high throughput screening and synthetic biology

Biocatalysts have wider applications in various industries. Biocatalysts are generating bigger attention among researchers due to their unique catalytic properties like activity, specificity and stability. However the industrial use of many enzymes is hindered by low catalytic efficiency and stability during industrial processes. Properties of enzymes can be altered by protein engineering. Protein engineers are increasingly study the structure-function characteristics, engineering attributes, design of computational tools for enzyme engineering, and functional screening processes to improve the design and applications of enzymes. The potent and innovative techniques of enzyme engineering deliver outstanding opportunities for tailoring industrially important enzymes for the versatile production of biochemicals. An overview of the current trends in enzyme engineering is explored with important representative examples.

New insights into the degradation of synthetic pollutants in contaminated environments

The environment is contaminated by synthetic contaminants owing to their extensive applications globally. Hence, the removal of synthetic pollutants (SPs) from the environment has received widespread attention. Different remediation technologies have been investigated for their abilities to eliminate SPs from the ecosystem; these include photocatalysis, sonochemical techniques, nanoremediation, and bioremediation. SPs, which can be organic or inorganic, can be degraded by microbial metabolism at contaminated sites. Owing to their diverse metabolisms, microbes can adapt to a wide variety of environments. Several microbial strains have been reported for their bioremediation potential concerning synthetic chemical compounds. The selection of potential strains for large-scale removal of organic pollutants is an important research priority. Additionally, novel microbial consortia have been found to be capable of efficient degradation owing to their combined and co-metabolic activities. Microbial engineering is one of the most prominent and promising techniques for providing new opportunities to develop proficient microorganisms for various biological processes; here, we have targeted the SP-degrading mechanisms of microorganisms. This review provides an in-depth discussion of microbial engineering techniques that are used to enhance the removal of both organic and inorganic pollutants from different contaminated environments and under different conditions. The degradation of these pollutants is investigated using abiotic and biotic approaches; interestingly, biotic approaches based on microbial methods are preferable owing to their high potential for pollutant removal and cost-effectiveness.

Immobilization of horseradish peroxidase on cationic microporous starch: Physico-bio-chemical characterization and removal of phenolic compounds

In the present study, two different modified starches; microporous starch (MPS) and cationic microporous starch (CMPS) were synthesized. The granules of MPS that distributed regularly were destroyed after the etherification reaction. The data depicted that the immobilization of horseradish peroxidase (HRP) on CMPS revealed highest immobilization efficiency (86%) at 100 mg of CMPS at pH = 6.0 and 100 units of enzyme. After 10 reuses of the CMPS-HRP, it retained 66% of initial activity. The soluble HRP showed broad pH optimum of 6.0-7.0, which changed to sharp pH = 6.0 for CMPS-HRP. Soluble-HRP and CMPS-HRP showed temperature optima at 30 °C and 40 °C, respectively. The CMPS-HRP showed high thermal stability up to 50 °C compared to the soluble HRP (40 °C). The Km values of soluble HRP and CMPS-HRP were 6.6 and 10.8 mM for H₂O₂ and 34 and 41.6 mM for guaiacol, respectively. CMPS-HRP showed higher affinity toward various substrates than the soluble-HRP. CMPS-HRP showed more resistance against heavy metals, urea, isopropanol, Triton X-100 and trypsin than soluble enzyme. The CMPS-HRP showed higher ability to remove phenol and p-chlorophenol compared to soluble-HRP.

Trends in the development of innovative nanobiocatalysts and their application in biocatalytic transformations

The ever-growing demand for cost-effective and innocuous biocatalytic transformations has prompted the rational design and development of robust biocatalytic tools. Enzyme immobilization technology lies in the formation of cooperative interactions between the tailored surface of the support and the enzyme of choice, which result in the fabrication of tremendous biocatalytic tools with desirable properties, complying with the current demands even on an industrial level. Different nanoscale materials (organic, inorganic, and green) have attracted great attention as immobilization matrices for single or multi-enzymatic systems. Aiming to unveil the potentialities of nanobiocatalytic systems, we present distinct immobilization strategies and give a thorough insight into the effect of nanosupports specific properties on the biocatalysts' structure and catalytic performance. We also highlight the development of nanobiocatalysts for their incorporation in cascade enzymatic processes and various types of batch and continuous-flow reactor systems. Remarkable emphasis is given on the application of such nanobiocatalytic tools in several biocatalytic transformations including bioremediation processes, biofuel production, and synthesis of bioactive compounds and fine chemicals for the food and pharmaceutical industry.

Evaluation of the role of the DNA surface for enhancing the activity of scaffolded enzymes

The catalytic enhancements of enzymes loaded on DNA nanostructures have been attributed to the characteristics provided by highly negative charges on the surface of the DNA scaffold, such as the modulation of the local pH near enzymes. In this study, two types of enzymes with optimal activity at pH 6 and 8 equally displayed significant catalytic enhancements on the DNA scaffold surface. By using a ratiometric pH indicator, a lower local pH shift of 0.8 was observed near the DNA scaffold surface. The postulated local pH change near the DNA scaffold surface is unlikely to play a general role in enhancing the activity of the scaffolded enzymes.

Novel biotechnological formulations of cysteine proteases, immobilized on chitosan. Structure, stability and activity

Bromelain, papain, and ficin are studied the most for meat tenderization, but have limited application due to their short lifetime. The aim of this work is to identify the adsorption mechanisms of these cysteine proteases on chitosan to improve the enzymes' stability. It is known that immobilization can lead to a significant loss of enzyme activity, which we observed during the sorption of bromelain (protease activity compared to soluble enzyme is 49% for medium and 64% for high molecular weight chitosan), papain (34 and 28% respectively) and ficin (69 and 70% respectively). Immobilization on the chitosan matrix leads to a partial destruction of protein helical structure (from 5 to 19%). Using computer modelling, we have shown that the sorption of cysteine proteases on chitosan is carried out by molecule regions located on the border of domains L and R, including active cites of the enzymes, which explains the decrease in their catalytic activity upon immobilization. The immobilization on chitosan does not shift the optimal range of pH (7.5) and temperature values (60 °C for bromelain and papain, 37-60 °C for ficin), but significantly increases the stability of biocatalysts (from 5.8 times for bromelain to 7.6 times for papain).

Different strategies for the lipase immobilization on the chitosan based supports and their applications

Immobilized enzymes have received incredible interests in industry, pharmaceuticals, chemistry and biochemistry sectors due to their various advantages such as ease of separation, multiple reusability, non-toxicity, biocompatibility, high activity and resistant to environmental changes. This review in between various immobilized enzymes focuses on lipase as one of the most practical enzyme and chitosan as a preferred biosupport for lipase immobilization and provides a broad range of studies of recent decade. We highlight several aspects of lipase immobilization on the surface of chitosan support containing various types of lipase and immobilization techniques from physical adsorption to covalent bonding and cross-linking with their benefits and drawbacks. The recent advances and future perspectives that can improve the present problems with lipase and chitosan such as high-price of lipase and low mechanical resistance of chitosan are also discussed. According to the literature, optimization of immobilization methods, combination of these methods with other techniques, physical and chemical modifications of chitosan, co-immobilization and protein engineering can be useful as a solution to overcome the mentioned limitations.

Stabilization of β-Galactosidase on Modified Gold Nanoparticles: A Preliminary Biochemical Study to Obtain Lactose-Free Dairy Products for Lactose-Intolerant Individuals

The unique chemical, optical, and electrical characteristics of nanoparticles make their utilization highly successful in every field of biological sciences as compared to their bulk counterpart. These properties arise as a result of their miniature size, which provides them an excellent surface area-to-volume ratio, inner structure, and shape, and hence increases their surface characteristics. Therefore, this study was undertaken to engineer gold nanoparticles (AuNPs) for improving their catalytic activity and stability in biotechnological processes. The characterization of AuNPs was performed by XRD, UV spectra, and TEM. The synthesized AuNPs were surface-modified by polyvinyl alcohol (PVA) for binding the enzyme in excellent yield. The developed immobilized enzyme system (PVA-AuNPs-β-galactosidase) displayed pH optima at pH 7.0 and temperature optima at 40 °C. Moreover, the stability of PVA-AuNPs-β-galactosidase was significantly enhanced at wider pH and temperature ranges and at higher galactose concentrations, in contrast to the free enzyme. β-galactosidase bound to PVA-modified AuNPs exhibited greater operational activity, even after its sixth reuse. The developed nanosystem may prove useful in producing lactose-free dairy products for lactose-intolerant patients.

α-Cellulose Fibers of Paper-Waste Origin Surface-Modified with Fe3O4 and Thiolated-Chitosan for Efficacious Immobilization of Laccase

The utilization of waste-paper-biomass for extraction of important α-cellulose biopolymer, and modification of extracted α-cellulose for application in enzyme immobilization can be extremely vital for green circular bio-economy. Thus, in this study, α-cellulose fibers were super-magnetized (Fe3O4), grafted with chitosan (CTNs), and thiol (-SH) modified for laccase immobilization. The developed material was characterized by high-resolution transmission electron microscopy (HR-TEM), HR-TEM energy dispersive X-ray spectroscopy (HR-TEM-EDS), X-ray diffraction (XRD), vibrating sample magnetometer (VSM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FT-IR) analyses. Laccase immobilized on α-Cellulose-Fe3O4-CTNs (α-Cellulose-Fe3O4-CTNs-Laccase) gave significant activity recovery (99.16%) and laccase loading potential (169.36 mg/g). The α-Cellulose-Fe3O4-CTNs-Laccase displayed excellent stabilities for temperature, pH, and storage time. The α-Cellulose-Fe3O4-CTNs-Laccase applied in repeated cycles shown remarkable consistency of activity retention for 10 cycles. After the 10th cycle, α-Cellulose-Fe3O4-CTNs possessed 80.65% relative activity. Furthermore, α-Cellulose-Fe3O4-CTNs-Laccase shown excellent degradation of pharmaceutical contaminant sulfamethoxazole (SMX). The SMX degradation by α-Cellulose-Fe3O4-CTNs-Laccase was found optimum at incubation time (20 h), pH (3), temperatures (30 °C), and shaking conditions (200 rpm). Finally, α-Cellulose-Fe3O4-CTNs-Laccase gave repeated degradation of SMX. Thus, this study presents a novel, waste-derived, highly capable, and super-magnetic nanocomposite for enzyme immobilization applications.

Effect of amine length in the interference of the multipoint covalent immobilization of enzymes on glyoxyl agarose beads

Trypsin, chymotrypsin, penicillin G acylase and ficin extract have been stabilized by immobilization on glyoxyl agarose, adding different aliphatic compounds bearing a primary amine group during the immobilization: ethyl amine, butyl amine, hexyl amine (at concentrations ranging from 0 to 20 mM) and octyl amine (from 0 to 10 mM) to analyze their effects on the immobilized enzyme stability. As expected, the presence of amines reduced the intensity of the enzyme-support multipoint covalent attachment, and therefore the enzyme stability. However, it is clear that this effect is higher using octyl amine for all enzymes (in some cases the enzyme immobilized in the presence of 10 mM octyl amine was almost inactivated while the reference kept over 50 % of the initial activity). This way, it seems that the most important effect of the presence of aminated compounds came from the generation of steric hindrances to the enzyme/support multi-reaction promoted by the ammines that are interacting with the aldehyde groups. In some instances, just 1 mM of aminated compounds is enough to greatly decrease enzyme stability. The results suggested that, if the composition of the enzyme extract is unknown, to eliminate small aminated compounds may be necessary to maximize the enzyme-support reaction.

The β-galactosidase immobilization protocol determines its performance as catalysts in the kinetically controlled synthesis of lactulose

In this paper, 3 different biocatalysts of β-galactosidase from Kluyveromyces lactis have been prepared by immobilization in chitosan activated with glutaraldehyde (Chi_Glu_Gal), glyoxyl agarose (Aga_Gly_Gal) and agarose coated with polyethylenimine (Aga_PEI_Gal). These biocatalysts have been used to catalyze the synthesis of lactulose from lactose and fructose. Aga-PEI-Gal only produces lactulose at 50 °C, and not at 25 or 37 °C, Aga_Gly_Gal was unable to produce lactulose at any of the assayed temperatures while Chi_Glu_Gal produced lactulose at all assayed temperatures, although a lower yield was obtained at 25 or 37 °C. The pre-incubation of this biocatalyst at 50 °C permitted to obtain similar yields at 25 or 37 °C than at 50 °C. The use of milk whey instead of pure lactose and fructose produced an improvement in the yields using Aga_PEI_Gal and a decrease using Chi_Glu_Gal. The operational stability also depends on the reaction medium and of biocatalyst. This study reveals how enzyme immobilization may greatly alter the performance of β-galactosidase in a kinetically controlled manner, and how medium composition influences this performance due to the kinetic properties of β-galactosidase.

Magnetic Cross-Linked Enzyme Aggregates of a Transpeptidase-Specialized Variant (N450D) of Bacillus licheniformis γ-Glutamyl Transpeptidase: An Efficient and Stable Biocatalyst for l-Theanine Synthesis

γ-Glutamyl transpeptidase (GGT) catalyzes the transfer of glutathione’s γ-glutamyl group and related γ-glutamyl amides to water, amino acids or peptides, and utilizes a conserved Thr residue to process its own polypeptide chain into a large and a small subunit that then assemble to produce a catalytically competent enzyme. In this study, the magnetic cross-linked enzyme aggregates (mCLEAs) of a transpeptidase-specialized variant (N450D) of Bacillus licheniformis GGT were successfully prepared with optimized process parameters viz.1.25:1 (v/v) of isopropanol to N450D (0.3 mg/mL) ratio/0.02:1 (w/w) of enzyme to 3-aminopropyl triethoxysilane (APTES)-coated magnetic nanoparticle ratio/20 mM of glutaraldehyde. The prepared magnetic nanoparticles and immobilized enzyme (N450D-mCLEAs) were characterized by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy, field-emission scanning electron microscope integrated with energy dispersive X-ray spectroscopy (FESEM/EDS), and superparamagnetic analysis. As compared with free enzyme, N450D-mCLEAs displayed significantly higher heat resistance at temperatures of 55 and 60 °C, and had a greater stability over a storage period of one month. The immobilized enzyme could also be reused for 10 consecutive biocatalytic cycles with no significant reduction in the percent yield of l-theanine. Conclusively, this immobilization strategy surely provides a meaningful glance of developing N450D-mediated biocatalysis for the production of physiologically important γ-glutamyl compounds.

Fragmented α-Amylase into Microporous Metal-Organic Frameworks as Bioreactors

This work presents an efficient and facile strategy to prepare an α-amylase bioreactor. As enzymes are quite large to be immobilized inside metal-organic frameworks (MOFs), the tertiary and quaternary structures of α-amylase were first disrupted using a combination of urea, dithiothreitol (DTT), and iodoacetamide (IAA). After losing its tertiary structure, the unfolded proteins can now penetrate into the microporous MOFs, affording fragmented α-amylase@MOF bioreactors. Among the different MOFs evaluated, UiO-66 gave the most promising potential due to the size-matching effect of the α-helix of the fragmented α-amylase with the pore size of UiO-66. The prepared bioreactor exhibited high yields of small carbohydrate (maltose) even when reused up to 15 times (>80% conversion).

Evaluating enzyme stabilizations in calcium carbonate: Comparing in situ and crosslinking mediated immobilization

Enzyme immobilization using inorganic materials has been shown to preserve enzyme activity improving and improve their practical applications in biocatalytic process designs. Proper immobilization methods have been used to obtain high recycling and storage stability. In this study, we compared the activity and stability of in situ or crosslink-immobilized enzymes in a CaCO₃ biomineral carrier. More than 30% of the initial enzyme activity was preserved for both the systems after 180 days upon 15 activity measurements at room temperature, confirming the improved stability of these enzyme systems (100 mM phosphate buffer, pH 8.0); however, differences in enzyme loading, activity, and characteristics were observed for each of these methods. Each system exhibited efficacy of 80% and 20%, respectively. Based on the same amount of immobilized enzyme (0.2 mg), the specific activities of hydrolysis of p-nitrophenyl butyrate substrate at room temperature of in situ immobilized carboxyl esterase (CE) and crosslinked CE were 11.37 and 7.63 mM min^-1 mg^-1, respectively (100 mM phosphate buffer, pH 8.0). Moreover, based on the kinetic behavior, in situ immobilized CE exhibited improved catalytic efficiency (Vmax Km^-1) of the enzyme, exhibiting 4-fold higher activity and efficiency values than those of the CE immobilized in CaCO₃. This is the first study to describe the stabilization of enzymes in CaCO₃ and compare the enzyme kinetics and efficiencies between in situ immobilization and crosslinking in CaCO₃ carriers.

Three-dimensional ordered magnetic macroporous metal-organic frameworks for enzyme immobilization

Metal-organic frameworks (MOFs) have been emerged as a promising support for immobilizing enzymes owing to the tunable porosity, high surface area, and structural diversity. However, most of these possess nanometer size and small pores, which are difficult to recover them from the reaction medium and present low immobilization efficiency and protein loading capacity, and high substrate diffusion limitations. Herein, a novel magnetic amino-functionalized zeolitic imidazolate framework-8 (ZIF-8) with 3D highly ordered macroporous structure was synthesized using the assembled polystyrene (PS) nanosphere monoliths as a template. Subsequently, catalase (CAT) molecules were immobilized on the surface of macroporous magnetic ZIF-8 and inside the macropores by precipitation, covalent binding and cross-linking. The resultant immobilized CAT showed high immobilization efficiency (58%) and protein loading capacity (29%), leading to 500% higher activity than the immobilized CAT on ZIF-8 (CAT/ZIF-8). Meanwhile, the immobilized CAT could be easily recovered with a magnet without obvious activity loss. The traditional CAT/ZIF-8 lost its activity after 6 cycles, whereas, the immobilized CAT retained 90% activity of its initial activity after reusing for 8 cycles, indicating excellent reusability. In conclusion, this study provides a facile and efficient approach to immobilize enzymes on/in MOFs with enhanced activity and excellent recyclability.