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

Efficient and easible biocatalysts: Strategies for enzyme improvement. A review

Owing to the environmental friendliness and vast advantages that enzymes offer in the biotechnology and industry fields, biocatalysts are a prolific investigation field. However, the low catalytic activity, stability, and specific selectivity of the enzyme limit the range of the reaction enzymes involved in. A comprehensive understanding of the protein structure and dynamics in terms of molecular details enables us to tackle these limitations effectively and enhance the catalytic activity by enzyme engineering or modifying the supports and solvents. Along with different strategies including computational, enzyme engineering based on DNA recombination, enzyme immobilization, additives, chemical modification, and physicochemical modification approaches can be promising for the wide spread of industrial enzyme usage. This is attributed to the successful application of biocatalysts in industrial and synthetic processes requires a system that exhibits stability, activity, and reusability in a continuous flow process, thereby reducing the production cost. The main goal of this review is to display relevant approaches for improving enzyme characteristics to overcome their industrial application.

A review on the immobilization of bromelain

This review shows the endeavors performed to prepare immobilized formulations of bromelain extract, usually from pineapple, and their use in diverse applications. This extract has a potent proteolytic component that is based on thiol proteases, which differ depending on the location on the fruit. Stem and fruit are the areas where higher activity is found. The edible origin of this enzyme is one of the features that determines the applications of the immobilized bromelain to a more significant degree. The enzyme has been immobilized on a wide diversity of supports via different strategies (covalent bonds, ion exchange), and also forming ex novo solids (nanoflowers, CLEAs, trapping in alginate beads, etc.). The use of preexisting nanoparticles as immobilization supports is relevant, as this facilitates one of the main applications of the immobilized enzyme, in therapeutic applications (as wound dressing and healing components, antibacterial or anticancer, mucus mobility control, etc.). A curiosity is the immobilization of this enzyme on spores of probiotic microorganisms via adsorption, in order to have a perfect in vivo compatibility. Other outstanding applications of the immobilized enzyme are in the stabilization of wine versus haze during storage, mainly when immobilized on chitosan. Curiously, the immobilized bromelain has been scarcely applied in the production of bioactive peptides.

Immobilized Multi-Enzyme/Nanozyme Biomimetic Cascade Catalysis for Biosensing Applications

Multiple enzyme-induced cascade catalysis has an indispensable role in the process of complex life activities, and is widely used to construct robust biosensors for analyzing various targets. The immobilized multi-enzyme cascade catalysis system is a novel biomimetic catalysis strategy that immobilizes various enzymes with different functions in stable carriers to simulate the synergistic catalysis of multiple enzymes in biological systems, which enables high stability of enzymes and efficiency enzymatic cascade catalysis. Nanozymes, a type of nanomaterial with intrinsic enzyme-like characteristics and excellent stabilities, are also widely applied instead of enzymes to construct immobilized cascade systems, achieving better catalytic performance and reaction stability. Due to good stability, reusability, and remarkably high efficiency, the immobilized multi-enzyme/nanozyme biomimetic cascade catalysis systems show distinct advantages in promoting signal transduction and amplification, thereby attracting vast research interest in biosensing applications. This review focuses on the research progress of the immobilized multi-enzyme/nanozyme biomimetic cascade catalysis systems in recent years. The construction approaches, factors affecting the efficiency, and applications for sensitive biosensing are discussed in detail. Further, their challenges and outlooks for future study are also provided.

A New Approach in Lipase-Octyl-Agarose Biocatalysis of 2-Arylpropionic Acid Derivatives

The use of lipase immobilized on an octyl-agarose support to obtain the optically pure enantiomers of chiral drugs in reactions carried out in organic solvents is a great challenge for chemical and pharmaceutical sciences. Therefore, it is extremely important to develop optimal procedures to achieve a high enantioselectivity of the biocatalysts in the organic medium. Our paper describes a new approach to biocatalysis performed in an organic solvent with the use of CALB-octyl-agarose support including the application of a polypropylene reactor, an appropriate buffer for immobilization (Tris base-pH 9, 100 mM), a drying step, and then the storage of immobilized lipases in a climatic chamber or a refrigerator. An immobilized lipase B from Candida antarctica (CALB) was used in the kinetic resolution of (R,S)-flurbiprofen by enantioselective esterification with methanol, reaching a high enantiomeric excess (eep = 89.6 ± 2.0%). As part of the immobilization optimization, the influence of different buffers was investigated. The effect of the reactor material and the reaction medium on the lipase activity was also studied. Moreover, the stability of the immobilized lipases: lipase from Candida rugosa (CRL) and CALB during storage in various temperature and humidity conditions (climatic chamber and refrigerator) was tested. The application of the immobilized CALB in a polypropylene reactor allowed for receiving over 9-fold higher conversion values compared to the results achieved when conducting the reaction in a glass reactor, as well as approximately 30-fold higher conversion values in comparison with free lipase. The good stability of the CALB-octyl-agarose support was demonstrated. After 7 days of storage in a climatic chamber or refrigerator (with protection from humidity) approximately 60% higher conversion values were obtained compared to the results observed for the immobilized form that had not been stored. The new approach involving the application of the CALB-octyl-agarose support for reactions performed in organic solvents indicates a significant role of the polymer reactor material being used in achieving high catalytic activity.

Chemically Bonded Pepsin via Its Inert Center to Diazo Functionalized Silica Gel through Multipoint Attachment Mode: A Way of Restoring Biocatalytic Sustainability over "Wider pH" Range

Proteolytic enzymes play a pivotal role in the industry. Still, because of denaturation, the extensive applicability at their level of best catalytic efficiency over a more comprehensive pH range, particularly in alkaline conditions over pH 8, has not been fully developed. On the other hand, enzyme immobilization following a suitable protocol is a long pending issue that determines the conformational stability, specificity, selectivity, enantioselectivity, and activity of the native enzymes at long-range pH. As a bridge between these two findings, in an attempt at a freezing temperature 273-278 K at an alkaline pH, the diazo-functionalized silica gel (SG) surface has been used to rapidly diazo couple pepsin through its inert center, the O-carbon of the phenolic -OH of surface-occupied Tyr residues in a multipoint mode: when all the various protein groups, viz., amino, thiol, phenol, imidazole, carboxy, etc., in the molecular sequence including those belonging to the active sites, remain intact, the inherent inbuilt interactions among themselves remain. Thereby, the macromolecule's global conformation and helicity preserve the status quo. The dimension of the SG-enzyme conjugate confirms as {Si(OSi)4 (H2O)1.03}n {-O-Si(CH3)2-O-C6H4-N═N+}4·{pepsin}·yH2O; where the values of n and y have been determined respectively as 347 and 188. The material performs the catalytic activity much better at 7-8.5 than at pH 2-3.5 and continues for up to six months without any appreciable change.

Topochemical Design of Cellulose-Based Carriers for Immobilization of Endoxylanase

Xylooligosaccharides (XOSs) gained much attention for their use in food and animal feed, attributed to their prebiotic function. These short-chained carbohydrates can be enzymatically produced from xylan, one of the most prevalent forms of hemicellulose. In this work, endo-1,4-β-xylanase from Thermotoga maritima was immobilized on cellulose-based beads with the goal of producing xylooligosaccharides with degrees of polymerization (DPs) in the range of 4-6 monomeric units. More specifically, the impact of different spacer arms, tethers connecting the enzyme with the particle, on the expressed enzymatic activity and oligosaccharide yield was investigated. After surface functionalization of the cellulose beads, the presence of amines was confirmed with time of flight secondary ion mass spectrometry (TOF-SIMS), and the influence of different spacer arms on xylanase activity was established. Furthermore, XOSs (DPs 2-6) with up to 58.27 mg/g xylan were obtained, which were greatly enriched in longer oligosaccharides. Approximately 80% of these XOSs displayed DPs between 4 and 6. These findings highlight the importance of topochemical engineering of carriers to influence enzyme activity, and the work puts forward an enzymatic system focusing on the production of longer xylooligosaccharides.

3D Printed Porous Nanocellulose-Based Scaffolds As Carriers for Immobilization of Glycosyltransferases

Biocatalysis is increasingly becoming an alternative method for the synthesis of industrially relevant complex molecules. This can be realized by using enzyme immobilized polysaccharide-based 3D scaffolds as compatible carriers, with defined properties. Especially, immobilization of either single or multiple enzymes on a 3D printed polysaccharide scaffold, exhibiting well-organized interconnected porous structure and morphology, is a versatile approach to access the performance of industrially important enzymes. Here, we demonstrated the use of nanocellulose-based 3D porous scaffolds for the immobilization of glycosyltransferases, responsible for glycosylation in natural biosynthesis. The scaffolds were produced using an ink containing nanofibrillated cellulose (NFC), carboxymethyl cellulose (CMC), and citric acid. Direct-ink-writing 3D printing followed by freeze-drying and dehydrothermal treatment at elevated temperature resulted in chemically cross-linked scaffolds, featuring tunable negative charges (2.2-5.0 mmol/g), pore sizes (10-800 μm), fluid uptake capacity, and exceptional dimensional and mechanical stability in the wet state. The negatively charged scaffolds were applied to immobilize two sugar nucleotide-dependent glycosyltransferases (C-glycosyltransferase, Z_basic2-CGT; sucrose synthase, Z_basic2-SuSy), each harboring a cationic binding module (Z_basic2) to promote charge-based enzyme adsorption. Both enzymes were immobilized at ∼30 mg of protein/g of dry carrier (∼20% yield), independent of the scaffold used. Their specific activities were 0.50 U/mg (Z_basic2-CGT) and 0.19 U/mg (Z_basic2-SuSy), corresponding to an efficacy of 37 and 18%, respectively, compared to the soluble enzymes. The glycosyltransferases were coimmobilized and shown to be active in a cascade reaction to give the natural C-glycoside nothofagin from phloretin (1.0 mM; ∼95% conversion). All enzyme bound scaffolds showed reusability of a maximum of 5 consecutive reactions. These results suggest that the 3D printed and cross-linked NFC/CMC-based scaffolds could present a class of solid carriers for enzyme (co)-immobilization, with promising applications in glycosyltransferase-catalyzed synthesis and other fields of biocatalysis.

Influence of TEMPO oxidation on the properties of ethylene glycol methyl ether acrylate grafted cellulose sponges

In this study, cellulose nanofibers (CNF) obtained via high-pressure microfluidization were 2,6,6-tetra-methylpiperidine-1-oxyl (TEMPO) oxidized (TOCNF) in order to facilitate the grafting of ethylene glycol methyl ether acrylate (EGA). FTIR and XPS analyses revealed a more efficient grafting of EGA oligomers on the surface of TOCNF as compared to the original CNF. As a result, a consistent covering of the TOCNF fibers with EGA oligomers, an increased hydrophobicity and a reduction in porosity were noticed for TOCNF-EGA. However, the swelling ratio of TOCNF-EGA was similar to that of original CNF grafted with EGA and higher than that of TOCNF, because the higher amount of grafted EGA onto oxidized cellulose and the looser structure reduced the contacts between the fibrils and increased the absorption of water. All these results corroborated with a good cytocompatibility and compression strength recommend TOCNF-EGA for applications in regenerative medicine.

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.