Enzyme stabilization by nano/microsized hybrid materials

Application of iron magnetic nanoparticles in protein immobilization

Due to their properties such as superparamagnetism, high surface area, large surface-to-volume ratio, easy separation under external magnetic fields, iron magnetic nanoparticles have attracted much attention in the past few decades. Various modification methods have been developed to produce biocompatible magnetic nanoparticles for protein immobilization. This review provides an updated and integrated focus on the fabrication and characterization of suitable magnetic iron nanoparticle-based nano-active materials for protein immobilization.

Preparation of polyphosphazene hydrogels for enzyme immobilization

We report on the synthesis and application of a new hydrogel based on a methacrylate substituted polyphosphazene. Through ring-opening polymerization and nucleophilic substitution, poly[bis(methacrylate)phosphazene] (PBMAP) was successfully synthesized from hexachlorocyclotriphosphazene. By adding PBMAP to methacrylic acid solution and then treating with UV light, we could obtain a cross-linked polyphosphazene network, which showed an ultra-high absorbency for distilled water. Lipase from Candida rugosa was used as the model lipase for entrapment immobilization in the hydrogel. The influence of methacrylic acid concentration on immobilization efficiency was studied. Results showed that enzyme loading reached a maximum of 24.02 mg/g with an activity retention of 67.25% when the methacrylic acid concentration was 20% (w/w).

Modification of PEGylated enzyme with glutaraldehyde can enhance stability while avoiding intermolecular crosslinking

We demonstrate an enzyme stabilization approach whereby a model enzyme is PEGylated, followed by controlled chemical modification with glutaraldehyde. Using this stabilization strategy, size increases and aggregation due to intermolecular crosslinking are avoided. Immediately following synthesis, the PEGylated enzyme with and without glutaraldehyde modification possessed specific activities of 372.9 ± 20.68 U/mg and 373.9 ± 15.14 U/mg, respectively (vs. 317.7 ± 19.31 U/mg for the native enzyme). The glutaraldehyde-modified PEGylated enzyme retains 73% original activity after 4 weeks at 37 °C (vs. 2% retention for control).

Immobilization of Trichoderma harzianum α-amylase on treated wool: optimization and characterization

α-Amylase from Trichoderma harzianum was covalently immobilized on activated wool by cyanuric chloride. Immobilized α-amylase exhibited 75% of its initial activity after 10 runs. The soluble and immobilized α-amylases exhibited maximum activity at pH values 6.0 and 6.5, respectively. The immobilized enzyme was more thermally stable than the soluble one. Various substrates were hydrolyzed by immobilized α-amylase with high efficiencies compared to those of soluble α-amylase. The inhibition of the immobilized α-amylase by metal ions was low as compared with soluble enzyme. On the basis of the results obtained, immobilized α-amylase could be employed in the saccharification of starch processing.

Evaluation of styrene-divinylbenzene beads as a support to immobilize lipases

A commercial and very hydrophobic styrene-divinylbenzene matrix, MCI GEL^® CHP20P, has been compared to octyl-Sepharose^® beads as support to immobilize three different enzymes: lipases from Thermomyces lanuginosus (TLL) and from Rhizomucor miehie (RML) and Lecitase^® Ultra, a commercial artificial phospholipase. The immobilization mechanism on both supports was similar: interfacial activation of the enzymes versus the hydrophobic surface of the supports. Immobilization rate and loading capacity is much higher using MCI GEL^® CHP20P compared to octyl-Sepharose^® (87.2 mg protein/g of support using TLL, 310 mg/g using RML and 180 mg/g using Lecitase^® Ultra). The thermal stability of all new preparations is much lower than that of the standard octyl-Sepharose^® immobilized preparations, while the opposite occurs when the inactivations were performed in the presence of organic co-solvents. Regarding the hydrolytic activities, the results were strongly dependent on the substrate and pH of measurement. Octyl-Sepharose^® immobilized enzymes were more active versus p-NPB than the enzymes immobilized on MCI GEL^® CHP20P, while RML became 700-fold less active versus methyl phenylacetate. Thus, the immobilization of a lipase on this matrix needs to be empirically evaluated, since it may present very positive effects in some cases while in other cases it may have very negative ones.

Homologous yeast lipases/acyltransferases exhibit remarkable cold-active properties

Lipases/acyltransferases catalyse acyltransfer to various nucleophiles preferentially to hydrolysis even in aqueous media with high thermodynamic activity of water (a w >0.9). Characterization of hydrolysis and acyltransfer activities in a large range of temperature (5 to 80 °C) of secreted recombinant homologous lipases of the Pseudozyma antarctica lipase A superfamily (CaLA) expressed in Pichia pastoris, enlighten the exceptional cold-activity of two remarkable lipases/acyltransferases: CpLIP2 from Candida parapsilosis and CtroL4 from Candida tropicalis. The activation energy of the reactions catalysed by CpLIP2 and CtroL4 was 18-23 kJ mol(-1) for hydrolysis and less than 15 kJ mol(-1) for transesterification between 5 and 35 °C, while it was respectively 43 and 47 kJ mol(-1) with the thermostable CaLA. A remarkable consequence is the high rate of the reactions catalysed by CpLIP2 and CtroL4 at very low temperatures, with CpLIP2 displaying at 5 °C 65 % of its alcoholysis activity and 45 % of its hydrolysis activity at 30 °C. These results suggest that, within the CaLA superfamily and its homologous subgroups, common structural determinants might allow both acyltransfer and cold-active properties. Such biocatalysts are of great interest for the efficient synthesis or functionalization of temperature-sensitive lipid derivatives, or more generally to lessen the environmental impact of biocatalytic processes.

Enzymatic resolution of ibuprofen in an organic solvent under ultrasound irradiation

Ultrasound has been successfully adopted to improve the biocatalytic properties of APE1547 (a novel esterase from the archaeon Aeropyrum pernix K1) in the resolution of ibuprofen. After optimizing the conditions (ultrasound power, 200 W; temperature, 35 °C), the best biocatalytic performance of APE1547 (enzyme activity, 5.39 µmol/H/mg; E value, 130.8) was obtained. Compared with the conventional reaction in an orbital shaker, the enzyme activity was significantly enhanced about 90-fold, and the enantioselectivity was enhanced about fourfold after an ultrasound. The results of scanning electron microscopy clearly indicated that the activation effect of ultrasound on APE1547 originated mainly in the morphological change of the enzyme powder. Both lower particle size and conformational change of APE1547 under ultrasound might be helpful to enhance the enantioselectivity. In addition, APE1547 kept its best performance under the low-power ultrasound for at least five reaction cycles.

Preparation of robust biocatalyst based on cross-linked enzyme aggregates entrapped in three-dimensionally ordered macroporous silica

With the aim to provide a highly stable and active biocatalyst, cross-linked enzyme aggregates (CLEAs) of lipase Candida sp. 99-125 were prepared in three-dimensionally ordered macroporous silica materials (CLEAs-LP@3DOM-SiO2). Lipase Candida sp. 99-125 was first precipitated in the pores of 3DOM SiO2 (named EAs-LP@3DOM-SiO2), and further cross-linked by glutaraldehyde to form CLEAs-LP@3DOM-SiO2. Saturated ammonium sulfate was used as a precipitant and glutaraldehyde with a concentration of 0.25% (w/w) was employed as a cross-linker. Compared with EAs-LP@3DOM-SiO2 and native lipase, CLEAs-LP@3DOM-SiO2 exhibited excellent thermal and mechanical stability, and could maintain more than 85% of initial activity after 16 days of shaking in organic and aqueous phase. When CLEAs-LP@3DOM-SiO2 was applied in esterification and transesterification reactions, improved activity and reusability were achieved. This method can be used for the immobilization of other enzymes of interest.

Combined electrochemical and microscopic study of porous enzymatic electrodes with direct electron transfer mechanism

In the present work electrochemical and microscopic methods have been utilized to get more insight into the complex relationship between the preparation route, structure and activity of porous enzymatic electrodes.

Probing structural and catalytic characteristics of galactose oxidase confined in nanoscale chemical environments

Synopsis: structural and catalytic features of a complex enzyme galactose oxidase confined in nanoscale chemical environments were investigated to show the catalytic efficiency of the enzyme depending on both the degree of space confinement and immobilization method.

Penicillium expansum lipase-coated magnetic Fe3O4–polymer hybrid hollow nanoparticles: a highly recoverable and magnetically separable catalyst for the synthesis of 1,3-dibutylurea

Amino-epoxy supports were innovatively imported onto magnetic nanoparticles for immobilizing enzyme which represents a novel class of heterogeneous catalyst for the synthesis of 1,3-dibutylurea from ethylene carbonate and butylamine.

Activity of laccase immobilized on TiO2-montmorillonite complexes

The TiO₂-montmorillonite (TiO₂-MMT) complex was prepared by blending TiO₂ sol and MMT with certain ratio, and its properties as an enzyme immobilization support were investigated. The pristine MMT and TiO₂-MMT calcined at 800 °C (TiO₂-MMT800) were used for comparison to better understand the immobilization mechanism. The structures of the pristine MMT, TiO₂-MMT, and TiO₂-MMT800 were examined by HR-TEM, XRD and BET. SEM was employed to study different morphologies before and after laccase immobilization. Activity and kinetic parameters of the immobilized laccase were also determined. It was found that the TiO₂ nanoparticles were successfully introduced into the MMT layer structure, and this intercalation enlarged the “d value” of two adjacent MMT layers and increased the surface area, while the calcination process led to a complete collapse of the MMT layers. SEM results showed that the clays were well coated with adsorbed enzymes. The study of laccase activity revealed that the optimum pH and temperature were pH = 3 and 60 °C, respectively. In addition, the storage stability for the immobilized laccase was satisfactory. The kinetic properties indicated that laccase immobilized on TiO₂-MMT complexes had a good affinity to the substrate. It has been proved that TiO₂-MMT complex is a good candidate for enzyme immobilization.

Cell-free Biosystems in the Production of Electricity and Bioenergy

: Increasing needs of green energy and concerns of climate change are motivating intensive R&D efforts toward the low-cost production of electricity and bioenergy, such as hydrogen, alcohols, and jet fuel, from renewable sugars. Cell-free biosystems for biomanufacturing (CFB2) have been suggested as an emerging platform to replace mainstream microbial fermentation for the cost-effective production of some biocommodities. As compared to whole-cell factories, cell-free biosystems comprised of synthetic enzymatic pathways have numerous advantages, such as high product yield, fast reaction rate, broad reaction condition, easy process control and regulation, tolerance of toxic compound/product, and an unmatched capability of performing unnatural reactions. However, issues pertaining to high costs and low stabilities of enzymes and cofactors as well as compromised optimal conditions for different source enzymes need to be solved before cell-free biosystems are scaled up for biomanufacturing. Here, we review the current status of cell-free technology, update recent advances, and focus on its applications in the production of electricity and bioenergy.