Cross-Linked Enzyme-Adhered Nanoparticles (CLEANs) for Continuous-Flow Bioproduction

Nanostructured but micro-sized biocatalysts were created by bottom-up technology using multi-functionalized silica nanoparticles (NPs) as nano-sized building blocks to form cross-linked enzyme-adhered nanoparticles (CLEANs) as robust micro-sized particles with beneficial internal structure and good mechanical properties. Systematic surface modification of NPs with a grafting mixture consisting of organosilanes with reactive (aminopropyl) and inert (e. g., vinyl, propyl, phenyl, or octyl) functions resulted in functional NPs enabling cross-linking agents, such as glutardialdehyde or bisepoxides (glycerol diglycidyl ether, neopentylglycol diglycidyl ether, and poly(propylene glycol) diglycidyl ether), to bind and cross-link enzymes covalently and to form macroporous microparticles. These CLEANs were able to diminish several weaknesses of traditional cross-linked enzyme aggregates as biocatalysts, such as poor mechanical resistance, difficult recovery, and storage, strengthening their use for packed-bed enzyme reactors. Lipase B from Candida antarctica (CaLB) was selected as model enzyme for development of robust CLEANs, which were successfully tested for various industrially relevant applications including a kinetic resolution of a racemic alcohol and the production of various natural fragrance compounds under continuous-flow conditions.

Lipase Immobilized on a Novel Rigid-Flexible Dendrimer-Grafted Hierarchically Porous Magnetic Microspheres for Effective Resolution of (R,S)-1-Phenylethanol

With the rapid development of biotechnological industry, there is an urgent need for exploiting new materials to immobilize enzymes to improve the performance of biocatalysts. In this paper, hierarchically porous magnetic microspheres (PFMMs) were prepared through solvothermal method and rapidly grafted with a novel rigid-flexible dendrimer first synthesized from monomers of trimesoyl chloride (TMC) and 1,6-hexanediamine (HDA) via interfacial polymerization process for covalent immobilization of Pseudomonas fluorescens lipase (PFL). The maximum PFL loading of the synthesized support reaches 87.5 mg_protein/g_support, and 864% activity recovery of PFMMs-G_3.0-PFL can be achieved at pH 9.0. Then, it was used to catalyze the resolution of (R,S)-1-phenylethanol with vinyl acetate. Under the optimized conditions, 50.0% conversion with 99.0% ee_s can be reached within 1.5 h. In addition, a conversion of 49.2% and ee_s of 96.9% can be retained after 10 batches of running, displaying an excellent operational stability. Importantly, a further investigation shows that the obviously improved reusability of the immobilized PFL is ascribed to the increased rigidity in comparison to fully flexible dendrimer. Thus, the newly constructed protocol for lipase immobilization exhibits a great prospect in biochemical engineering.

"Fishing and Hunting"-Selective Immobilization of a Recombinant Phenylalanine Ammonia-Lyase from Fermentation Media

This article overviews the numerous immobilization methods available for various biocatalysts such as whole-cells, cell fragments, lysates or enzymes which do not require preliminary enzyme purification and introduces an advanced approach avoiding the costly and time consuming downstream processes required by immobilization of purified enzyme-based biocatalysts (such as enzyme purification by chromatographic methods and dialysis). Our approach is based on silica shell coated magnetic nanoparticles as solid carriers decorated with mixed functions having either coordinative binding ability (a metal ion complexed by a chelator anchored to the surface) or covalent bond-forming ability (an epoxide attached to the surface via a proper linker) enabling a single operation enrichment and immobilization of a recombinant phenylalanine ammonia-lyase from parsley fused to a polyhistidine affinity tag.

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.