Glyoxyl agarose: A fully inert and hydrophilic support for immobilization and high stabilization of proteins

Designing mixed cationic/anionic supports to covalently immobilize/stabilize enzymes with high isoelectric point by enzyme adsorption and support-enzyme glutaraldehyde crosslinking

Ficin fully immobilized on Asp-agarose beads at pH 7 but not on an aminated support. This made enzyme adsorption plus glutaraldehyde modification non-viable for this enzyme. Modifying glyoxyl-agarose beads with mixtures of Asp and 1,6-hexamethylenediamine (HA) at different ratios, mixed anion/cation exchanger supports were built. Only if HA greatly exceed Asp in the support, immobilization did not work. While only using the Asp-agarose support immobilized enzyme molecules were only ionically adsorbed after glutaraldehyde treatment (visualized in SDS-PAGE analysis), the mixed supports gave covalent immobilization. The glutaraldehyde modification of these biocatalysts permitted to establish covalent bonds with the support, and this was more effective when using higher amounts of HA in the support. When around 60 % of the groups in the support were HA, the treatment with glutaraldehyde fully suppressed enzyme release from the support after boiling in SDS. The glutaraldehyde treated biocatalysts were more stable than just the adsorbed enzymes or the enzyme adsorbed only on Asp supports and then treated with glutaraldehyde (the optimal biocatalyst retained 90 % of the initial activity while the just adsorbed ficin retained 50 % of the initial activity). This strategy can be utilized to immobilize other proteins with high isoelectric points following this immobilization strategy.

Microtiter Plate Immobilization Screening for Prototyping Heterogeneous Enzyme Cascades

Immobilization is a key enabling technology in applied biocatalysis that facilitates the separation, recovery, and reuse of heterogeneous biocatalysts. However, finding a consensus immobilization protocol for several enzymes forming a multi-enzyme system is extremely difficult and relies on a combinatorial trial-and-error approach. Herein, we describe a protocol in which 17 different carriers functionalized with different reactive groups are tested in a 96-well microtiter plate to screen up to 21 immobilization protocols for up to 18 enzymes. This screening includes an activity and stability assay to select the optimal immobilization chemistry to achieve the most active and stable heterogeneous biocatalysts. The information retrieved from the screening can be rationalized using a Python-based application CapiPy. Finally, through scoring the screening results, we find the consensus immobilization protocol to assemble an immobilized four-enzyme system to transform vinyl acetate into (S)-3-hydroxybutyric acid. This methodology opens a path to speed up the prototyping of immobilized multi-enzyme pathways for chemical manufacturing.

Chitosanase-immobilized magnetite-agar gel particles as a highly stable and reusable biocatalyst for enhanced production of physiologically active chitosan oligosaccharides

A novel immobilized chitosanase was developed and utilized to produce chitosan oligosaccharides (COSs) via chitosan hydrolysis. Magnetite-agar gel particles (average particle diameter: 338 μm) were prepared by emulsifying an aqueous agar solution dispersing 200-nm magnetite particles with isooctane containing an emulsifier at 80 °C, followed by cooling the emulsified mixture. The chitosanase from Bacillus pumilus was immobilized on the magnetite-agar gel particles chemically activated by introducing glyoxyl groups with high immobilization yields (>80%), and the observed specific activity of the immobilized chitosanase was 16% of that of the free enzyme. This immobilized chitosanase could be rapidly recovered from aqueous solutions by applying magnetic force. The thermal stability of the immobilized chitosanase improved remarkably compared with that of free chitosanase: the deactivation rate constants at 35 °C of the free and immobilized enzymes were 8.1 × 10-5 and 3.9 × 10-8 s-1, respectively. This immobilized chitosanase could be reused for chitosan hydrolysis at 75 °C and pH 5.6, and 80% of its initial activity was maintained even after 10 cycles of use. COSs with a degree of polymerization (DP) of 2-7 were obtained using this immobilized chitosanase, and the product content of physiologically active COSs (DP ≥ 5) reached approximately 50%.

Pros and Cons in Various Immobilization Techniques and Carriers for Enzymes

In recent years, enzyme immobilization technology has been developed, and studies on immobilized enzyme materials have become very prominent. With the immobilization technique, enzymes and compatible carrier materials are combined or enzyme crystals/aggregates are used in a carrier-free fashion, by physical, chemical, or biochemical methods. As a kind of biocatalyst, immobilized enzymes can catalyze certain chemical reactions with high selectivity and high efficiency under relatively mild reaction conditions and eliminate pollution to the environment. Considering the current status and applications of immobilized enzyme technology and materials emerging in the last 5 years, this mini-review introduces the advantages and disadvantages of various enzyme immobilization techniques with carriers as well as the pros and cons of different materials for immobilization. The future prospects of immobilization technology and carrier materials are outlined, aiming to provide a reference for further research and applications of sustainable technology.

Overcoming Biochemical Limitations of Galactose Oxidase through the Design of a Solid-Supported Self-Sufficient Biocatalyst

Galactose Oxidase (GalOx) has gained significant interest in biocatalysis due to its ability for selective oxidation beyond the natural oxidation of galactose, enabling the production of valuable derivatives. However, the practical application of GalOx has been hindered by the limited availability of active and stable biocatalysts, as well as the inherent biochemical limitations such as oxygen (O2 ) dependency and the need for activation. In this study, we addressed these challenges by immobilizing GalOx into agarose-based and Purolite supports to enhance its activity and stability. Additionally, we identified and quantified the oxygen supply limitation into solid catalysts by intraparticle oxygen sensing showing a trade-off between the amount of protein loaded onto the solid support and the catalytic effectiveness of the immobilized enzyme. Furthermore, we coimmobilized a heme-containing protein along with the enzyme to function as an activator. To evaluate the practical application of the immobilized GalOx, we conducted the oxidation of galactose in an instrumented aerated reactor. The results showcased the efficient performance of the immobilized enzyme in the 8 h reaction cycle. Notably, the GalOx immobilized into dextran sulfate-activated agarose exhibited improved stability, overcoming the need for a soluble activator supply, and demonstrated exceptional performance in galactose oxidation. These findings offer promising prospects for the utilization of GalOx in technical biocatalytic applications.

Grafting of proteins onto polymeric surfaces: A synthesis and characterization challenge

This review aims at answering the following question: how can a researcher be sure to succeed in grafting a protein onto a polymer surface? Even if protein immobilization on solid supports has been used industrially for a long time, hence enabling natural enzymes to serve as a powerful tool, emergence of new supports such as polymeric surfaces for the development of so-called intelligent materials requires new approaches. In this review, we introduce the challenges in grafting protein on synthetic polymers, mainly because compared to hard surfaces, polymers may be sensitive to various aqueous media, depending on the pH or reductive molecules, or may exhibit state transitions with temperature. Then, the specificity of grafting on synthetic polymers due to difference of chemical functions availability or difference of physical properties are summarized. We present next the various available routes to covalently bond the protein onto the polymeric substrates considering the functional groups coming from the monomers used during polymerization reaction or post-modification of the surfaces. We also focus our review on a major concern of grafting protein, which is avoiding the potential loss of function of the immobilized protein. Meanwhile, this review considers the different methods of characterization used to determine the grafting efficiency but also the behavior of enzymes once grafted. We finally dedicate the last part of this review to industrial application and future prospective, considering the sustainable processes based on green chemistry.

l-Theanine Goes Greener: A Highly Efficient Bioprocess Catalyzed by the Immobilized γ-Glutamyl Transferase from Bacillus subtilis

l-Theanine (l-Th) was synthesized by simply mixing the reactants (l-glutamine and ethylamine in water) at 25 °C and Bacillus subtilis γ-glutamyl transferase (BsGGT) covalently immobilized on glyoxyl-agarose according to a methodology previously reported by our research group; neither buffers, nor other additives were needed. Ratio of l-glutamine (donor) to ethylamine (acceptor), pH, enzymatic units (IU), and reaction time were optimized (molar ratio of donor/acceptor=1 : 8, pH 11.6, 1 IU mL^-1 , 6 h), furnishing l-Th in 93 % isolated yield (485 mg, 32.3 g L^-1 ) and high purity (99 %), after a simple filtration of the immobilized biocatalyst, distillation of the volatiles (unreacted ethylamine) and direct lyophilization. Immobilized BsGGT was re-used (four reaction cycles) with 100 % activity retention. This enzymatic synthesis represents a straightforward, fast, high-yielding, and easily scalable approach to l-Th preparation, besides having a favorable green chemistry metrics.

Laccase multi-point covalent immobilization: characterization, kinetics, and its hydrophobicity applications

Laccase from Myceliophthora thermophila was immobilized using one-point and multi-point covalent attachment on both a native and a modified new commercial epoxy carrier (Immobead 150P). After 10 cycles of operation at pH 3.0 and temperature 70 °C, the multi-point covalently immobilized laccase on the modified Immobead 150P performed best in terms of immobilization characteristics, retaining 95% of its initial activity. Thermodynamic parameters of thermal inactivation emphasized the positive impact of the immobilization procedure. At 50 °C, the immobilized and free enzyme activity levels dropped by 27 and 73%, respectively, after 48 h of incubation. The immobilized enzyme enhanced its stability in alkaline conditions, resuming 95% of its original activity after 3 h at pH 9.0. Immobilization reduced substrate affinity because the free laccase's K_m value was lower than that of the immobilized laccase. Finally, the application of immobilized laccase in an innovative wood treatment process was tested by grafting lauryl gallate (LG) in order to provide hydrophobic properties to the wood. The results showed a relative water contact angle of 85.7% for treated wood, whereas the control showed only 26.6%, after 4 min of contact between water and beechwood surface. KEY POINTS: • Multi-point covalent immobilization of a commercial laccase on a commercial support. • Enzymatic parameters generally improved by immobilization process. • New application of immobilized laccase: enzymatic-assisted wood hydrophobization.

Is enzyme immobilization a mature discipline? Some critical considerations to capitalize on the benefits of immobilization

Enzyme immobilization has been developing since the 1960s and although many industrial biocatalytic processes use the technology to improve enzyme performance, still today we are far from full exploitation of the field. One clear reason is that many evaluate immobilization based on only a few experiments that are not always well-designed. In contrast to many other reviews on the subject, here we highlight the pitfalls of using incorrectly designed immobilization protocols and explain why in many cases sub-optimal results are obtained. We also describe solutions to overcome these challenges and come to the conclusion that recent developments in material science, bioprocess engineering and protein science continue to open new opportunities for the future. In this way, enzyme immobilization, far from being a mature discipline, remains as a subject of high interest and where intense research is still necessary to take full advantage of the possibilities.

A review on the immobilization of pepsin: A Lys-poor enzyme that is unstable at alkaline pH values

Pepsin is a protease used in many different applications, and in many instances, it is utilized in an immobilized form to prevent contamination of the reaction product. This enzyme has two peculiarities that make its immobilization complex. The first one is related to the poor presence of primary amino groups on its surface (just one Lys and the terminal amino group). The second one is its poor stability at alkaline pH values. Both features make the immobilization of this enzyme to be considered a complicated goal, as most of the immobilization protocols utilize primary amino groups for immobilization. This review presents some of the attempts to get immobilized pepsin biocatalyst and their applications. The high density of anionic groups (Asp and Glu) make the anion exchange of the enzyme simpler, but this makes many of the strategies utilized to immobilize the enzyme (e.g., amino-glutaraldehyde supports) more related to a mixed ion exchange/hydrophobic adsorption than to real covalent immobilization. Finally, we propose some possibilities that can permit not only the covalent immobilization of this enzyme, but also their stabilization via multipoint covalent attachment.

Multipoint Immobilization at the Inert Center of Urease on Homofunctional Diazo-Activated Silica Gel: A Way of Restoring Room-Temperature Catalytic Sustainability for Perennial Utilization

At present, enzyme immobilization is a big issue. It improves enzyme stability, activity, specificity, or selectivity, particularly the enantioselectivity compared to the native enzymes, and by solving the separation problem, it helps in recovering the catalyst with good reusability as desired in vitro. Motivated by these facts, in this work, Jack bean urease (JBU) is immobilized on three-dimensional (3D)-network silica gel (SG) via multipoint covalent bonding employing dimethyldichlorosilane (DMDCS) and p-nitrophenol, respectively, as the second-generation silane-coupling reagent and spacer. The homofunctional diazo group appearing at the functionalized SG unit cell makes a diazo linkage at the inert center, the ortho position of the phenolic-OH of the tyrosine moiety, where all of the amino, thiol, phenol, imidazole, carboxy, etc., groups of the enzyme residues, including those that belong to the active site, remain intact. The coupling process, analyzed using field emission scanning electron microscopy (FESEM), energy-dispersive X-ray analysis (EDX), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy, ultraviolet-visible spectroscopy (UV-vis), and fluorescence spectroscopy, occurs without molecular aggregation in borate buffer at pH 8.8 ± 0.4, which is much higher than the iso-electric point (pH 5.1) of the macromolecule where it becomes soluble. Eventually, the immobilization is maximize and also the native-enzyme activities are restored remarkably. The immobilized catalyst converts urea (0.0625-0.15 mmol L^-1) to ammonia appreciably (94.50 ± 1.5%) at 27 °C, and the efficiency is well comparable to that of the native enzyme (93.0 ± 0.4%). The efficiency gradually diminishes, coming down to 50% at the 40th cycle, and the enzyme returns to its native conformation within 72 h in tris-EDTA borate buffer at 27 °C for the next 40 cycles of reuse and so on. The efficiency becomes hindered by 8-10% in every 5th subsequent reuse to reach 50% on the 30th reuse, resulting in room-temperature catalytic sustainability of 90 days. The catalytic performances are well restored in rice extract and coconut water.

Cell-Free Biosynthesis of ω-Hydroxy Acids Boosted by a Synergistic Combination of Alcohol Dehydrogenases

The activity orchestration of an unprecedented cell-free enzyme system with self-sufficient cofactor recycling enables the stepwise transformation of aliphatic diols into ω-hydroxy acids at the expense of molecular oxygen as electron acceptor. The efficiency of the biosynthetic route was maximized when two compatible alcohol dehydrogenases were selected as specialist biocatalysts for each one of the oxidative steps required for the oxidative lactonization of diols. The cell-free system reached up to 100 % conversion using 100 mM of linear C₅ diols and performed the desymmetrization of prochiral branched diols into the corresponding ω-hydroxy acids with an exquisite enantioselectivity (ee>99 %). Green metrics demonstrate superior sustainability of this system compared to traditional metal catalysts and even to whole cells for the synthesis of 5-hydroxypetanoic acid. Finally, the cell-free system was assembled into a consortium of heterogeneous biocatalysts that allowed the enzyme reutilization. This cascade illustrates the potential of systems biocatalysis to access new heterofunctional molecules such as ω-hydroxy acids.

Evaluation of MxOy/fucoidan hybrid system and their application in lipase immobilization process

In this work, new M_xO_y/fucoidan hybrid systems were fabricated and applied in lipase immobilization. Magnesium (MgO) and zirconium (ZrO₂) oxides were used as M_xO_y inorganic matrices. In the first step, the proposed oxides were functionalized with fucoidan from Fucus vesiculosus (Fuc). The obtained MgO/Fuc and ZrO₂/Fuc hybrids were characterized by means of spectroscopic analyses, including Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and nuclear magnetic resonance. Additionally, thermogravimetric analysis was performed to determine the thermal stability of the hybrids. Based on the results, the mechanism of interaction between the oxide supports and fucoidan was also determined. Furthermore, the fabricated M_xO_y/fucoidan hybrid materials were used as supports for the immobilization of lipase from Aspergillus niger, and a model reaction (transformation of p-nitrophenyl palmitate to p-nitrophenol) was performed to determine the catalytic activity of the proposed biocatalytic system. In that reaction, the immobilized lipase exhibited high apparent and specific activity (145.5 U/g_catalyst and 1.58 U/mg_enzyme for lipase immobilized on MgO/Fuc; 144.0 U/g_catalyst and 2.03 U/mg_enzyme for lipase immobilized on ZrO₂/Fuc). The immobilization efficiency was also confirmed using spectroscopic analyses (FTIR and XPS) and confocal microscopy.

Grapefruit Debittering by Simultaneous Naringin Hydrolysis and Limonin Adsorption Using Naringinase Immobilized in Agarose Supports

Naringin and limonin are the two main bitter compounds of citrus products such as grapefruit juice. The aim of this investigation was to evaluate the reduction in both bitter components simultaneously using a combined biochemical and physical approach. The proposed strategy was based on the use of heterofunctional supports with glyoxyl groups that allow for the covalent immobilization of naringinase, which hydrolyses naringin and alkyl groups that allow for the adsorption of limonin. The supports were butyl-glyoxyl agarose (BGA) and octyl-glyoxyl agarose (OGA), which were characterized in terms of aldehyde group quantification and FTIR analysis. The optimal pH and temperature of free and immobilized enzymes were assessed. The maximum enzyme loading capacity of supports was analyzed. Debittering of grapefruit juice was evaluated using soluble enzyme, enzyme-free supports, and immobilized catalysts. Enzyme immobilized in BGA reduced naringin and limonin concentrations by 54 and 100%, respectively, while the use of catalyst immobilized in OGA allowed a reduction of 74 and 76%, respectively, obtaining a final concentration of both bitter components under their detection threshold. The use of OGA biocatalyst presented better results than when soluble enzyme or enzyme-free support was utilized. Biocatalyst was successfully applied in juice debittering in five repeated batches.

Immobilization-Stabilization of β-Glucosidase for Implementation of Intensified Hydrolysis of Cellobiose in Continuous Flow Reactors

Cellulose saccharification to glucose is an operation of paramount importance in the bioenergy sector and the chemical and food industries, while glucose is a critical platform chemical in the integrated biorefinery. Among the cellulose degrading enzymes, β-glucosidases are responsible for cellobiose hydrolysis, the final step in cellulose saccharification, which is usually the critical bottleneck for the whole cellulose saccharification process. The design of very active and stable β-glucosidase-based biocatalysts is a key strategy to implement an efficient saccharification process. Enzyme immobilization and reaction engineering are two fundamental tools for its understanding and implementation. Here, we have designed an immobilized-stabilized solid-supported β-glucosidase based on the glyoxyl immobilization chemistry applied in porous solid particles. The biocatalyst was stable at operational temperature and highly active, which allowed us to implement 25 °C as working temperature with a catalyst productivity of 109 mmol/min/gsupport. Cellobiose degradation was implemented in discontinuous stirred tank reactors, following which a simplified kinetic model was applied to assess the process limitations due to substrate and product inhibition. Finally, the reactive process was driven in a continuous flow fixed-bed reactor, achieving reaction intensification under mild operation conditions, reaching full cellobiose conversion of 34 g/L in a reaction time span of 20 min.

β-Galactosidase from Kluyveromyces lactis: Characterization, production, immobilization and applications - A review

A review on the enzyme β-galactosidase from Kluyveromyces lactis is presented, from the perspective of its structure and mechanisms of action, the main catalyzed reactions, the key factors influencing its activity, and selectivity, as well as the main techniques used for improving the biocatalyst functionality. Particular attention was given to the discussion of hydrolysis, transglycosylation, and galactosylation reactions, which are commonly mediated by this enzyme. In addition, the products generated from these processes were highlighted. Finally, biocatalyst improvement techniques are also discussed, such as enzyme immobilization and protein engineering. On these topics, the most recent immobilization strategies are presented, emphasizing processes that not only allow the recovery of the biocatalyst but also deliver enzymes that show better resistance to high temperatures, chemicals, and inhibitors. In addition, genetic engineering techniques to improve the catalytic properties of the β-galactosidases were reported. This review gathers information to allow the development of biocatalysts based on the β-galactosidase enzyme from K. lactis, aiming to improve existing bioprocesses or develop new ones.

Stabilization of enzymes via immobilization: Multipoint covalent attachment and other stabilization strategies

The use of enzymes in industrial processes requires the improvement of their features in many instances. Enzyme immobilization, a requirement to facilitate the recovery and reuse of these water-soluble catalysts, is one of the tools that researchers may utilize to improve many of their properties. This review is focused on how enzyme immobilization may improve enzyme stability. Starting from the stabilization effects that an enzyme may experience by the mere fact of being inside a solid particle, we detail other possibilities to stabilize enzymes: generation of favorable enzyme environments, prevention of enzyme subunit dissociation in multimeric enzymes, generation of more stable enzyme conformations, or enzyme rigidification via multipoint covalent attachment. In this last point, we will discuss the features of an "ideal" immobilization protocol to maximize the intensity of the enzyme-support interactions. The most interesting active groups in the support (glutaraldehyde, epoxide, glyoxyl and vinyl sulfone) will be also presented, discussing their main properties and uses. Some instances in which the number of enzyme-support bonds is not directly related to a higher stabilization will be also presented. Finally, the possibility of coupling site-directed mutagenesis or chemical modification to get a more intense multipoint covalent immobilization will be discussed.

An overview on biocatalysts immobilization on textiles: Preparation, progress and application in wastewater treatment

The immobilization of biocatalysts or other bioactive components often means their transformation from a soluble to an insoluble state by attaching them to a solid support material. Various types of fibrous textiles from both natural and synthetic sources have been studied as suitable support material for biocatalysts immobilization. Strength, inexpensiveness, high surface area, high porosity, pore size, availability in various forms, and simple preparation/functionalization techniques have made textiles a primary choice for various applications. This led to the concept of a new domain called-biocatalysts immobilization on textiles. By addressing the growing advancement in biocatalysts immobilization on textile, this study provides the first detailed overview on this topic based on the terms of preparation, progress, and application in wastewater treatment. The fundamental reason behind the necessity of biocatalysts immobilized textile as well as the potential preparation methods has been identified and discussed. The overall progress and performances of biocatalysts immobilized textile have been scrutinized and summarized based on the form of textile, catalytic activity, and various influencing factors. This review also highlighted the potential challenges and future considerations that can enhance the pervasive use of such immobilized biocatalysts in various sustainable and green chemistry applications.

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.

Chitosan/Cellulose-Based Porous Nanofilm Delivering C-Phycocyanin: A Novel Platform for the Production of Cost-Effective Cultured Meat

Cultured meat is artificial meat produced via the mass culture of cells without slaughtering livestock. In the production process of cultured meat, the mass proliferation for preparing abundant cells is a strenuous and time-consuming procedure requiring expensive and excess serum. Herein, C-phycocyanin (C-PC) extracted from blue algae was selected as a substitute for animal-derived serum and a polysaccharide film-based platform was developed to effectively deliver C-PC to myoblast while reducing the cost of cell medium. The polysaccharide platform has a sophisticated structure in which an agarose layer is capped on a porous multilayer film formed by molecular reassembly between chitosan and carboxymethylcellulose (CMC). The porous multilayer film provides an inner structure in which C-PC can be incorporated, and the agarose layer protects and stabilizes the C-PC. The completed platform was easily applied to a cell culture plate to efficiently release C-PC, thereby improving myoblast proliferation in a serum-reduced environment during long-term culture. We developed a cell sheet-based meat model using this polysaccharide platform to evaluate the improved cost-efficiency by the platform method in the mass proliferation of cells. This strategy and innovative technology can simplify the production system and secure price competitiveness to commercialize cultured meat.

Challenges and perspectives of the β-galactosidase enzyme

The enzyme β-galactosidase has great potential for application in the food and pharmaceutical industries due to its ability to perform the hydrolysis of lactose, a disaccharide present in milk and in dairy by-products. It can be used in free form, in batch processes, or in immobilized form, which allows continuous operation and provides greater enzymatic stability. The choice of method and support for enzyme immobilization is essential, as the performance of the biocatalyst is strongly influenced by the properties of the material used and by the interaction mechanisms between support and enzyme. Therefore, this review showed the main enzyme immobilization techniques, and the most used supports for the constitution of biocatalysts. Also, materials with the potential for immobilization of β-galactosidases and the importance of their biotechnological application are presented. KEY POINTS: • The main methods of immobilization are physical adsorption, covalent bonding, and crosslinking. • The structural conditions of the supports are determining factors in the performance of the biocatalysts. • Enzymatic hydrolysis plays an important role in the biotechnology industry.

Effect of Tris Buffer in the Intensity of the Multipoint Covalent Immobilization of Enzymes in Glyoxyl-Agarose Beads

Tris is an extensively used buffer that presents a primary amine group on its structure. In the present work trypsin, chymotrypsin and penicillin G acylase (PGA) were immobilized/stabilized on glyoxyl agarose in presence of different concentrations of Tris (from 0 to 20 mM). The effects of the presence of Tris during immobilization were studied analyzing the thermal stability of the obtained immobilized biocatalysts. The results indicate a reduction of the enzyme stability when immobilized in the presence of Tris. This effect can be observed in inactivations carried out at pH 5, 7, and 9 with all the enzymes assayed. The reduction of enzyme stability increased with the Tris concentration. Another interesting result is that the stability reduction was more noticeable for immobilized PGA than in the other immobilized enzymes, the biocatalysts prepared in presence of 20 mM Tris lost totally the activity at pH 7 just after 1 h of inactivation, while the reference at this time still kept around 61 % of the residual activity. These differences are most likely due to the homogeneous distribution of the Lys groups in PGA compared to trypsin and chymotrypsin (where almost 50% of Lys group are in a small percentage of the protein surface). The results suggest that Tris could be affecting the multipoint covalent immobilization in two different ways, on one hand, reducing the number of available glyoxyl groups of the support during immobilization, and on the other hand, generating some steric hindrances that difficult the formation of covalent bonds.

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.

Solid-phase XRN1 reactions for RNA cleavage: application in single-molecule sequencing

Modifications in RNA are numerous (∼170) and in higher numbers compared to DNA (∼5) making the ability to sequence an RNA molecule to identify these modifications highly tenuous using next generation sequencing (NGS). The ability to immobilize an exoribonuclease enzyme, such as XRN1, to a solid support while maintaining its activity and capability to cleave both the canonical and modified ribonucleotides from an intact RNA molecule can be a viable approach for single-molecule RNA sequencing. In this study, we report an enzymatic reactor consisting of covalently attached XRN1 to a solid support as the groundwork for a novel RNA exosequencing technique. The covalent attachment of XRN1 to a plastic solid support was achieved using EDC/NHS coupling chemistry. Studies showed that the solid-phase digestion efficiency of model RNAs was 87.6 ± 2.8%, while the XRN1 solution-phase digestion for the same model was 78.3 ± 4.4%. The ability of immobilized XRN1 to digest methylated RNA containing m6A and m5C ribonucleotides was also demonstrated. The processivity and clipping rate of immobilized XRN1 secured using single-molecule fluorescence measurements of a single RNA transcript demonstrated a clipping rate of 26 ± 5 nt s-1 and a processivity of >10.5 kb at 25°C.

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.

Sugarcane Bagasse Saccharification by Enzymatic Hydrolysis Using Endocellulase and β-glucosidase Immobilized on Different Supports

The saccharification of sugarcane bagasse by enzymatic hydrolysis is one of the most promising processes for obtaining fermentable sugar to be used in the production of second-generation ethanol. The objective of this work was to study the immobilization and stabilization of two commercial enzymes: Endocellulase (E-CELBA) in dextran coated iron oxide magnetic nanoparticles activated with aldehyde groups (DIOMNP) and β-glucosidase (E-BGOSPC) in glyoxyl agarose (GLA) so that their immobilized derivatives could be applied in the saccharification of pretreated sugarcane bagasse. This was the first time that the pretreated sugarcane bagasse was saccharified by cascade reaction using a endocellulase immobilized on dextran coated Fe2O3 with aldehyde groups combined with a β-glucosidase immobilized on glyoxyl agarose. Both enzymes were successfully immobilized (more than 60% after reduction with sodium borohydride) and presented higher thermal stability than free enzymes at 60, 70, and 80 °C. The enzymatic hydrolysis of the sugarcane bagasse was carried out with 15 U of each enzyme per gram of bagasse in a solid-liquid ratio of 1:20 for 48 h at 50 °C. Under these conditions, 39.06 ± 1.18% of the cellulose present in the pretreated bagasse was hydrolyzed, producing 14.11 ± 0.47 g/L of reducing sugars (94.54% glucose). In addition, DIOMNP endo-cellulase derivative maintained 61.40 ± 1.17% of its enzymatic activity after seven reuse cycles, and GLA β-glucosidase derivative maintained up to 58.20 ± 1.55% of its enzymatic activity after nine reuse cycles.

Peptide-based electrochemical biosensors utilized for protein detection

Proteins are generally detected as biomarkers for tracing or determining various disorders in organisms. Biomarker proteins can be tracked in samples with various origins and in different concentrations, revealing whether an organism is in a healthy or unhealthy state. In regard to detection, electrochemical biosensors are a potential fusion of electronics, chemistry, and biology, allowing for fast and early point-of-care detection from a biological sample with the advantages of high sensitivity, simple construction, and easy operation. Peptides present a promising approach as a biorecognition element when connected with electrochemical biosensors. The benefits of short peptides lie mainly in their good stability and selective affinity to a target analyte. Therefore, peptide-based electrochemical biosensors (PBEBs) represent an alternative approach for the detection of different protein biomarkers. This review provides a summary of the past decade of recently proposed PBEBs designed for protein detection, dividing them according to different protein types: (i) enzyme detection, including proteases and kinases; (ii) antibody detection; and (iii) other protein detection. According to these protein types, different sensing mechanisms are discussed, such as the peptide cleavage by a proteases, phosphorylation by kinases, presence of antibodies, and exploiting of affinities; furthermore, measurements are obtained by different electrochemical methods. A discussion and comparison of various constructions, modifications, immobilization strategies and different sensing techniques in terms of high sensitivity, selectivity, repeatability, and potential for practical application are presented.

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.

Effect of Concentrated Salts Solutions on the Stability of Immobilized Enzymes: Influence of Inactivation Conditions and Immobilization Protocol

This paper aims to investigate the effects of some salts (NaCl, (NH₄)₂SO₄ and Na₂SO₄) at pH 5.0, 7.0 and 9.0 on the stability of 13 different immobilized enzymes: five lipases, three proteases, two glycosidases, and one laccase, penicillin G acylase and catalase. The enzymes were immobilized to prevent their aggregation. Lipases were immobilized via interfacial activation on octyl agarose or on glutaraldehyde-amino agarose beads, proteases on glyoxyl agarose or glutaraldehyde-amino agarose beads. The use of high concentrations of salts usually has some effects on enzyme stability, but the intensity and nature of these effects depends on the inactivation pH, nature and concentration of the salt, enzyme and immobilization protocol. The same salt can be a stabilizing or a destabilizing agent for a specific enzyme depending on its concentration, inactivation pH and immobilization protocol. Using lipases, (NH₄)₂SO₄ generally permits the highest stabilities (although this is not a universal rule), but using the other enzymes this salt is in many instances a destabilizing agent. At pH 9.0, it is more likely to find a salt destabilizing effect than at pH 7.0. Results confirm the difficulty of foreseeing the effect of high concentrations of salts in a specific immobilized enzyme.

Design of epidermal growth factor immobilization on 3D biocompatible scaffolds to promote tissue repair and regeneration

Exogenous application of human epidermal growth factor (hEGF) stimulates epidermal wound healing. The aim of this study was to develop bioconjugates based on hEGF mimicking the protein in its native state and thus suitable for tissue engineering applications, in particular for treating skin-related disorders as burns. Ribonuclease A (RNase A) was used to investigate a number of different activated-agarose carriers: cyanogen bromide (CNBr)-activated-agarose and glyoxyl-agarose showed to preserve the appropriate orientation of the protein for receptor binding. EGF was immobilized on these carriers and immobilization yield was evaluated (100% and 12%, respectively). A peptide mapping of unbound protein regions was carried out by LC-MS to take evidence of the residues involved in the immobilization and, consequently, the flexibility and surface accessibility of immobilized EGF. To assess cell proliferative activities, 10, 25, 50, and 100 ng/mL of each immobilized EGF sample were seeded on fibroblast cells and incubated for 24, 48 and 72 h. The immobilized growth factor showed significantly high cell proliferative activity at 50 and 100 ng/mL compared to control and soluble EGF. Although both of the immobilized samples show dose-dependency when seeded with high number of fibroblast cells, CNBr-agarose-EGF showed a significantly high activity at 100 ng/mL and 72 h incubation, compared to glyoxyl-agarose-EGF.

Single-Particle Kinetics of Immobilized Enzymes by Harnessing the Autofluorescence of Co-Immobilized Cofactors

The co-immobilized enzymes and cofactors onto porous microparticles work as self-sufficient heterogeneous biocatalysts whose catalytic activity can be easily monitored by means of the cofactors autofluorescence. The reduction step of some cofactors as NAD⁺ and FAD⁺ to NADH and FADH₂, respectively, involves an increase of its autofluorescence. This phenomenon is harnessed to image and analyze the enzymatic reactions catalyzed by cofactor-dependent enzymes at real time and single-particle level during the operational process. Due to the universality and highly accessibility of fluorescence microscopy, the strategy described here allows a straightforward and more accurate analysis at micro-scale of heterogeneous biocatalysts. These studies promote and support the rational design and optimization of biocatalysts toward highly efficient heterogeneous biocatalytic reactions.

Functionalization of Porous Cellulose with Glyoxyl Groups as a Carrier for Enzyme Immobilization and Stabilization

The functionalization of the internal surface of macroporous carriers with glyoxyl groups has proven to highly stabilize a large variety of enzymes through multipoint covalent immobilization. In this work, we have translated the surface chemistry developed for the fabrication of glyoxyl-agarose carriers to macroporous cellulose (CEL). To that aim, CEL-based microbeads were functionalized with glyoxyl groups through a stepwise alkoxylation (or alkylation)/oxidation synthetic scheme. This functionalization sequence was analyzed by solid-state NMR, while the scanning electron miscroscopy of CEL microbeads reveals that the mild oxidation conditions negligibly affect the morphological properties of the material. Through the optimal functionalization protocol using rac-glycidol, we introduce up to 200 μmols of aldehyde groups per gram of wet CEL, a similar density to the one obtained for the benchmarked agarose-glyoxyl carrier. This novel CEL-based carrier succeeds to immobilize and stabilize industrially relevant enzymes such as d-amino acid oxidase from Trigonopsis variabilis and xylanases from Trichoderma reseei. Remarkably, the xylanases immobilized on the optimal CEL-based materials present a half-life time of 51 h at 60 °C and convert up to 90% of the xylan after four operation cycles for the synthesis of xylooligosaccharides.

High stabilization and hyperactivation of a Recombinant β-Xylosidase through Immobilization Strategies

Attainment of a stable and highly active β-xylosidase is of major importance for the efficient and cost-competitive hydrolysis of hemicellulose xylan, as well as for its industrial conversion into biofuels and biochemicals. Here, a recombinant β-xylosidase of the glycoside hydrolase family (GH43) from Bacillus subtilis was produced in Escherichia coli culture, purified, and subsequently immobilized on agarose and chitosan. Glutaraldehyde and glyoxyl groups were evaluated as activating agents to select the most efficient derivative. Multi-point immobilization on agarose led to an extraordinary thermal stability (half-lives 3604 and 164-fold higher than the free enzyme, at 50° and 35 °C, respectively). Even for chitosan activated with glutaraldehyde, a low-cost support, thermal stability of the immobilized enzyme was 326 and 12-fold higher than the free enzyme at 50° and 35°C, respectively. Immobilized enzymes showed no release of any subunit for the agarose-glyoxyl derivative, and only a few ones for the support activated with glutaraldehyde. Most remarkably, the enzyme kinetic behavior after immobilization increased up to 4-fold in relation to the free one. β-xylosidase, a tetrameric enzyme with four identical subunits, exists in equilibrium between the monomeric and oligomeric forms in solution. Depending on the pH of immobilization, the enzyme oligomerization can be favored, thus explaining the hyperactivation phenomenon. Both glyoxyl-agarose and chitosan-glutaraldehyde derivatives were used to catalyze corncob xylan hydrolysis, reaching 72 % conversion, representing a xylose productivity of around 20 g L^-1 h^-1. After ten 4h-cycles (pH 6.0, 35 °C), the xylan-to-xylose conversion remained approximately unchanged. Therefore, the immobilized β-xylosidases prepared in this work can be of great interest as biocatalysts in a biorefinery context.

Developing a Library of Mannose-Based Mono- and Disaccharides: A General Chemoenzymatic Approach to Monohydroxylated Building Blocks

Regioselective deprotection of acetylated mannose-based mono- and disaccharides differently functionalized in anomeric position was achieved by enzymatic hydrolysis. Candida rugosa lipase (CRL) and Bacillus pumilus acetyl xylan esterase (AXE) were immobilized on octyl-Sepharose and glyoxyl-agarose, respectively. The regioselectivity of the biocatalysts was affected by the sugar structure and functionalization in anomeric position. Generally, CRL was able to catalyze regioselective deprotection of acetylated monosaccharides in C6 position. When acetylated disaccharides were used as substrates, AXE exhibited a marked preference for the C2, or C6 position when C2 was involved in the glycosidic bond. By selecting the best enzyme for each substrate in terms of activity and regioselectivity, we prepared a small library of differently monohydroxylated building blocks that could be used as intermediates for the synthesis of mannosylated glycoconjugate vaccines targeting mannose receptors of antigen presenting cells.

Capture of enzyme aggregates by covalent immobilization on solid supports. Relevant stabilization of enzymes by aggregation

In this paper, a novel procedure for the immobilization and stabilization of enzymes is proposed: the multipoint covalent attachment of bi-molecular enzyme aggregates. This immobilization protocol allows the "capture" and fixation of the enzyme aggregate on the support surface. In addition to stabilization by multipoint attachment, enzyme aggregation promotes very interesting stabilizing effects. In the presence of low concentrations of polyethylene glycol (30 %) the dimeric amine oxidase from Pisum sativum forms soluble bi-molecular aggregates. Enzyme aggregates were analyzed by Dynamic Light Scattering and by full chemical loading of a mesoporous support (10 % agarose gels activated with glyoxyl groups). The soluble aggregate was immobilized by multipoint attachment on glyoxyl- agarose at pH 8.5 though the four amino termini of the two dimeric molecules (Lys residues are not reactive at this pH). The immobilized aggregated structure cannot undergo any movement (translational or rotational) after multipoint attachment and the aggregate is "fixed" on the support surface even after the removal of PEG. The immobilized aggregate was further incubated at pH 10 in order to allow the Lys residues to react with the glyoxyl groups on the support. Enzyme aggregation has an important effect on enzyme stabilization: the aggregated derivative was 40 fold more stable than a similar derivative of the isolated enzyme and 200 fold more than native enzymes in experiments of thermal inactivation.

Immobilization of alcohol dehydrogenase from Saccharomyces cerevisiae onto carboxymethyl dextran-coated magnetic nanoparticles: a novel route for biocatalyst improvement via epoxy activation

A novel method is described for the immobilization of alcohol dehydrogenase (ADH) from Saccharomyces cerevisiae onto carboxymethyl dextran (CMD) coated magnetic nanoparticles (CMD-MNPs) activated with epoxy groups, using epichlorohydrin (EClH). EClH was used as an activating agent to bind ADH molecules on the surface of CMD-MNPs. Optimal immobilization conditions (activating agent concentration, temperature, rotation speed, medium pH, immobilization time and enzyme concentration) were set to obtain the highest expressed activity of the immobilized enzyme. ADH that was immobilized onto epoxy-activated CMD-MNPs (ADH-CMD-MNPs) maintained 90% of the expressed activity. Thermal stability of ADH-CMD-MNPS after 24 h at 20 °C and 40 °C yielded 79% and 80% of initial activity, respectively, while soluble enzyme activity was only 19% at 20 °C and the enzyme was non-active at 40 °C. Expressed activity of ADH-CMD-MNPs after 21 days of storage at 4 °C was 75%. Kinetic parameters (K_M, v_max) of soluble and immobilized ADH were determined, resulting in 125 mM and 1.2 µmol/min for soluble ADH, and in 73 mM and 4.7 µmol/min for immobilized ADH.

Enzyme-Coated Micro-Crystals: An Almost Forgotten but Very Simple and Elegant Immobilization Strategy

The immobilization of enzymes using protein coated micro-crystals (PCMCs) was reported for the first time in 2001 by Kreiner and coworkers. The strategy is very simple. First, an enzyme solution must be prepared in a concentrated solution of one compound (salt, sugar, amino acid) very soluble in water and poorly soluble in a water-soluble solvent. Then, the enzyme solution is added dropwise to the water soluble solvent under rapid stirring. The components accompanying the enzyme are called the crystal growing agents, the solvent being the dehydrating agent. This strategy permits the rapid dehydration of the enzyme solution drops, resulting in a crystallization of the crystal formation agent, and the enzyme is deposited on this crystal surface. The reaction medium where these biocatalysts can be used is marked by the solubility of the PCMC components, and usually these biocatalysts may be employed in water soluble organic solvents with a maximum of 20% water. The evolution of these PCMC was to chemically crosslink them and further improve their stabilities. Moreover, the PCMC strategy has been used to coimmobilize enzymes or enzymes and cofactors. The immobilization may permit the use of buffers as crystal growth agents, enabling control of the reaction pH in the enzyme environments. Usually, the PCMC biocatalysts are very stable and more active than other biocatalysts of the same enzyme. However, this simple (at least at laboratory scale) immobilization strategy is underutilized even when the publications using it systematically presented a better performance of them in organic solvents than that of many other immobilized biocatalysts. In fact, many possibilities and studies using this technique are lacking. This review tried to outline the possibilities of this useful immobilization strategy.

Co-Immobilization and Co-Localization of Oxidases and Catalases: Catalase from Bordetella Pertussis Fused with the Zbasic Domain

Oxidases catalyze selective oxidations by using molecular oxygen as an oxidizing agent. This process promotes the release of hydrogen peroxide, an undesirable byproduct. The instantaneous elimination of hydrogen peroxide can be achieved by co-immobilization and co-localization of the oxidase and an auxiliary catalase inside the porous structure of solid support. In this paper, we proposed that catalase from Bordetella pertussis fused with a small domain (Zbasic) as an excellent auxiliary enzyme. The enzyme had a specific activity of 23 U/mg, and this was almost six-fold higher than the one of the commercially available catalases from bovine liver. The Zbasic domain was fused to the four amino termini of this tetrameric enzyme. Two domains were close in one hemisphere of the enzyme molecule, and the other two were close in the opposite hemisphere. In this way, each hemisphere contained 24 residues with a positive charge that was very useful for the purification of the enzyme via cationic exchange chromatography. In addition to this, each hemisphere contained 10 Lys residues that were very useful for a rapid and intense multipoint covalent attachment on highly activated glyoxyl supports. In fact, 190 mg of the enzyme was immobilized on one gram of glyoxyl-10% agarose gel. The ratio catalase/oxidase able to instantaneously remove more than 93% of the released hydrogen peroxide was around 5–6 mg of catalase per mg of oxidase. Thirty milligrams of amine oxidase and 160 mg of catalase were co-immobilized and co-localized per gram of glyoxyl-agarose 10BCL (10% beads cross-linked) support. This biocatalyst eliminated biogenic amines (putrescine) 80-fold faster than a biocatalyst of the same oxidase co-localized with the commercial catalase from bovine liver.