Cross-Linked Enzyme Aggregates of Chloroperoxidase: Synthesis, Optimization and Characterization

Recent developments in the use of peroxygenases - Exploring their high potential in selective oxyfunctionalisations

Peroxygenases are an emerging new class of enzymes allowing selective oxyfunctionalisation reactions in a cofactor-independent way different from well-known P450 monooxygenases. Herein, we focused on recent developments from organic synthesis, molecular biotechnology and reaction engineering viewpoints that are devoted to bring these enzymes in industrial applications. This covers natural diversity from different sources, protein engineering strategies for expression, substrate scope, activity and selectivity, stabilisation of enzymes via immobilisation, and the use of peroxygenases in low water media. We believe that peroxygenases have much to offer for selective oxyfunctionalisations and we have much to study to explore the full potential of these versatile biocatalysts in organic synthesis.

CLEAs, Combi-CLEAs and ‘Smart’ Magnetic CLEAs: Biocatalysis in a Bio-Based Economy

Biocatalysis has emerged in the last decade as a pre-eminent technology for enabling the envisaged transition to a more sustainable bio-based economy. For industrial viability it is essential that enzymes can be readily recovered and recycled by immobilization as solid, recyclable catalysts. One method to achieve this is via carrier-free immobilization as cross-linked enzyme aggregates (CLEAs). This methodology proved to be very effective with a broad selection of enzymes, in particular carbohydrate-converting enzymes. Methods for optimizing CLEA preparations by, for example, adding proteic feeders to promote cross-linking, and strategies for making the pores accessible for macromolecular substrates are critically reviewed and compared. Co-immobilization of two or more enzymes in combi-CLEAs enables the cost-effective use of multiple enzymes in biocatalytic cascade processes and the use of “smart” magnetic CLEAs to separate the immobilized enzyme from other solids has raised the CLEA technology to a new level of industrial and environmental relevance. Magnetic-CLEAs of polysaccharide-converting enzymes, for example, are eminently suitable for use in the conversion of first and second generation biomass.

Improved Biodegradation of Synthetic Azo Dye by Anionic Cross-Linking of Chloroperoxidase on ZnO/SiO2 Nanocomposite Support

A novel ZnO nanowire/macroporous SiO₂ composite was used as a support to immobilize chloroperoxidase (CPO) by in situ cross-linking method. An anionic bi-epoxy compound was synthesized and used as a long-chained anionic cross-linker, and it was adsorbed on the surface of ZnO nanowires through static interaction before reaction with CPO, creating a new approach to change the structure, property, and catalytic performance of the produced cross-linking enzyme aggregates (CLEAs) of CPO. The immobilized CPO showed high activity in the decolorization of three azo dyes. The effect of various conditions such as the loading amount of CPO, solution pH, temperature, and dye concentration was optimized on the decolorization. Under optimized conditions, the decolorization percentage of Acid Blue 113, Direct Black 38, and Acid Black 10 BX reached as high as 95.4, 92.3, and 89.1%, respectively. The immobilized CPO exhibited much better thermostability and resistance to pH inactivation than free CPO. The storage stability and reusability were greatly improved through the immobilization. It was found from the decolorization of Acid Blue 113 that 83.6% of initial activity retained after incubation at 4 °C for 60 days and that 80.9% of decolorization efficiency retained after 12 cycles of reuses.

The taming of oxygen: biocatalytic oxyfunctionalisations

The scope and limitations of oxygenases as catalysts for preparative organic synthesis is discussed.

Specific oxyfunctionalisations catalysed by peroxygenases: opportunities, challenges and solutions

Peroxygenases are promising oxyfunctionalisation catalysts for organic synthesis.

Cross-linked enzyme aggregates of β-glucosidase from Prunus domestica seeds

Cross-linked enzyme aggregates (CLEAs) of β-glucosidase were prepared and characterized. Under the optimum conditions, the activity recovery of CLEAs reached 84 %. The reduction by NaBH(4) resulted in slightly lower activities of CLEAs, while their thermostability was enhanced. CLEAs were more thermally stable than free enzyme (half lives, 973 vs. 518 min at 50 °C), while less stable than seed meal (half life, 1,090 min). In 90 % (v/v) t-butanol, the half lives of CLEAs and free enzyme were 53 and 6.7 h, respectively. Besides, the catalytic efficiency (V (max)/K (m)) of CLEAs was comparable to free enzyme (0.42 vs. 0.47 min(-1) mg(-1)). This carrier-free immobilized enzyme had a network structure with multiple layers. The productivity of salidroside using CLEAs reached 150 g/l g catalyst, while being 6.3 g/l g with seed meal.

Characteristic features and biotechnological applications of cross-linked enzyme aggregates (CLEAs)

Cross-linked enzyme aggregates (CLEAs) have many economic and environmental benefits in the context of industrial biocatalysis. They are easily prepared from crude enzyme extracts, and the costs of (often expensive) carriers are circumvented. They generally exhibit improved storage and operational stability towards denaturation by heat, organic solvents, and autoproteolysis and are stable towards leaching in aqueous media. Furthermore, they have high catalyst productivities (kilograms product per kilogram biocatalyst) and are easy to recover and recycle. Yet another advantage derives from the possibility to co-immobilize two or more enzymes to provide CLEAs that are capable of catalyzing multiple biotransformations, independently or in sequence as catalytic cascade processes.

Conformation and Activity of Sol-Gels Encapsulated Cross-Linked Enzyme Aggregates of Lipase from Burkholderia cepacia

Cross-linked enzyme aggregates (CLEAs) of lipase from Burkholderia cepacia (BCL) were explored using different precipitants and different amount of glutaraldehyde as cross-linkers. The ‘fresh’ and ‘mature’ CLEAs-BCL was successfully encapsulated with sol-gel support. The latter showed the highest specific enzyme activity, which was 1.7 and 13.2-fold over CLEAs-BCL before encapsulation with sol-gel and free BCL, respectively. It performed high transesterification activity with the biodiesel yield of 88.5%. The ‘mature’ CLEAs-BCL presented high stability in the ranges of temperature (30-70 ºС) and pH (pH = 5-10). Scanning electron microscopy (SEM) and circular dichroism (CD) studies showed that the morph secondary structure of ‘fresh’ and ‘mature’ CLEAs-BCL was variant to some extent, which may be responsible for the catalytic activity variance.