Self-sufficient asymmetric reduction of β-ketoesters catalysed by a novel and robust thermophilic alcohol dehydrogenase co-immobilised with NADH

Region-Directed Enzyme Immobilization through Engineering Protein Surface with Histidine Clusters

Enzyme immobilization is a key enabling technology for a myriad of industrial applications, yet immobilization science is still too empirical to reach highly active and robust heterogeneous biocatalysts through a general approach. Conventional protein immobilization methods lack control over how enzymes are oriented on solid carriers, resulting in negative conformational changes that drive enzyme deactivation. Site-selective enzyme immobilization through peptide tags and protein domains addresses the orientation issue, but this approach limits the possible orientations to the N- and C-termini of the target enzyme. In this work, we engineer the surface of two model dehydrogenases to introduce histidine clusters into flexible regions not involved in catalysis, through which immobilization is driven. By varying the position and the histidine density of the clusters, we create a small library of enzyme variants to be immobilized on different carriers functionalized with different densities of various metal chelates (Co2+, Cu2+, Ni2+, and Fe3+). We first demonstrate that His-clusters can be as efficient as the conventional His-tags in immobilizing enzymes, recovering even more activity and gaining stability against some denaturing agents. Furthermore, we find that the enzyme orientation as well as the type and density of the metal chelates affect the immobilization parameters (immobilization yield and recovered activity) and the stability of the immobilized enzymes. According to proteomic studies, His-clusters enable a different enzyme orientation as compared to His-tag. Finally, these oriented heterogeneous biocatalysts are implemented in batch reactions, demonstrating that the stability achieved by an optimized orientation translates into increased operational stability.

Glycosylation of polyphenolic compounds: Design of a self-sufficient biocatalyst by co-immobilization of a glycosyltransferase, a sucrose synthase and the cofactor UDP

Glycosyltransferases catalyze the regioselective glycosylation of polyphenolic compounds, increasing their solubility without altering their antioxidant properties. Leloir-type glycosyltransferases require UDP-glucose as a cofactor to glycosylate a hydroxyl of the polyphenol, which is expensive and unstable. To simplify these processes for industrial implementation, the preparation of self-sufficient heterogeneous biocatalysts is needed. In this study, a glycosyltransferase and a sucrose synthase (as an UDP-regenerating enzyme) were co-immobilized onto porous agarose-based supports coated with polycationic polymers: polyethylenimine and polyallylamine. In addition, the UDP cofactor was strongly ionically adsorbed and co-immobilized with the enzymes, eliminating the need to add it separately. Thus, the optimal self-sufficient heterogeneous biocatalyst was able to catalyze the glycosylation of three polyphenolic compounds (piceid, phloretin and quercetin) with in situ regeneration of the UDP-glucose, allowing multiple consecutive reaction cycles without the addition of exogenous cofactor. A TTN value of 50 (theoretical maximum) was obtained in the reaction of piceid glycosylation, after 5 reaction cycles, using the self-sufficient biocatalyst based on an improved sucrose synthase variant. This result was 5-fold higher than the obtained using soluble cofactor and the co-immobilized enzymes, and much higher than those reported in the literature for similar processes.

Efficient asymmetric synthesis of ethyl (R)-3-hydroxybutyrate by recombinant Escherichia coli cells under high substrate loading using eco-friendly ionic liquids as cosolvent

Ionic liquids (ILs) which synthesized from bio-renewable materials have recently attracted much attention for their applications in biocatalysis. Ethyl (R)-3-hydroxybutyrate ((R)-EHB) as a versatile chiral intermediate is of great interest in pharmaceutical synthesis. This study focuses on evaluating the performances of choline chloride (ChCl)-based and tetramethylammonium (TMA)-based neoteric ILs in the efficient synthesis of (R)-EHB via the bioreduction of ethyl acetoacetate (EAA) at high substrate loading by recombinant Escherichia coli cells. It was found that choline chloride/glutathione (ChCl/GSH, molar ratio 1:1) and tetramethylammonium/cysteine ([TMA][Cys], molar ratio 1:1) as eco-friendly ILs not only enhanced the solubility of water-insoluble EAA in the aqueous buffer system, but also appropriately improved the membrane permeability of recombinant E. coli cells, thus boosting catalytic reduction efficiency of EAA to (R)-EHB. In the developed ChCl/GSH- or [TMA][Cys]-buffer systems, the space-time yields of (R)-EHB achieved 754.9 g/L/d and 726.3 g/L/d, respectively, which are much higher than neat aqueous buffer system (537.2 g/L/d space-time yield). Meanwhile, positive results have also been demonstrated in the bioreduction of other prochiral ketones in the established IL-buffer systems. This work exhibits an efficient bioprocess for (R)-EHB synthesis under 325 g/L (2.5 M) substrate loading, and provides promising ChCl/GSH- and [TMA][Cys]-buffer systems employed in the biocatalysis for hydrophobic substrate.

Immobilized short-chain dehydrogenase/reductase on Fe3O4 particles acts as a magnetically recoverable biocatalyst component in patulin bio-detoxification system

Patulin is one of the most important mycotoxins that contaminates fruit-derived products and causes acute or chronic toxicity in humans. In the present study, a novel patulin-degrading enzyme preparation was developed by taking a short-chain dehydrogenase/reductase and covalently linking it to dopamine/polyethyleneimine co-deposited magnetic Fe₃O₄ particles. Optimum immobilization provided 63% immobilization efficiency and 62% activity recovery. Moreover, the immobilization protocol substantially improved thermal and storage stabilities, proteolysis resistance, and reusability. Using reduced nicotinamide adenine dinucleotide phosphate as a cofactor, the immobilized enzyme exhibited a detoxification rate of 100% in phosphate-buffered saline and a detoxification rate of more than 80% in apple juice. The immobilized enzyme did not cause adverse effects on juice quality and could be magnetically separated quickly after detoxification to ensure convenient recycling. Moreover, it did not exhibit cytotoxicity against a human gastric mucosal epithelial cell line at a concentration of 100 mg/L. Consequently, the immobilized enzyme as a biocatalyst had the characteristics of high efficiency, stability, safety, and easy separation, establishing the first step in building a bio-detoxification system to control patulin contamination in juice and beverage products.

ATP-Independent and Cell-Free Biosynthesis of β-Hydroxy Acids Using Vinyl Esters as Smart Substrates

In vitro biosynthetic pathways that condense and reduce molecules through coenzyme A (CoASH) activation demand energy and redox power in the form of ATP and NAD(P)H, respectively. These coenzymes must be orthogonally recycled by ancillary reactions that consume chemicals, electricity, or light, impacting the atom economy and/or the energy consumption of the biosystem. In this work, we have exploited vinyl esters as dual acyl and electron donor substrates to synthesize β-hydroxy acids through a non-decarboxylating Claisen condensation, reduction and hydrolysis stepwise cascade, including a NADH recycling step, catalyzed by a total of 4 enzymes. Herein, the chemical energy to activate the acyl group with CoASH and the redox power for the reduction are embedded into the vinyl esters. Upon optimization, this self-sustaining cascade reached a titer of (S)-3-hydroxy butyrate of 24 mM without requiring ATP and simultaneously recycling CoASH and NADH. This work illustrates the potential of in vitro biocatalysis to transform simple molecules into multi-functional ones.

Lactate dehydrogenase encapsulated in a metal-organic framework: A novel stable and reusable biocatalyst for the synthesis of D-phenyllactic acid

In this study, we synthesized a novel biocatalyst by encapsulating lactate dehydrogenase (LDH) in the metal-organic framework ZIF-90 by one-pot embedding. It showed strong biological activity for efficient synthesis of D-phenyllactic acid (D-PLA). The morphology and structure of LDH@ZIF-90 was systematically characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, confocal laser scanning microscopy (CLSM) and gas sorption. According to thermogravimetric analysis (TGA), the enzyme loading of the biocatalyst was 3 %. The Michaelis-Menten constant (K_m) and maximal reaction rate (V_max) of LDH@ZIF-90 were similar to those of free LDH, which proved that ZIF-90 had good biocompatibility to encapsulate LDH. At the same time, LDH@ZIF-90 exhibited enhanced tolerance to temperature, pH and organic solvents, and its reusability was greatly improved with 68 % of initial enzyme activity remaining after 7 rounds of recylcing. Overall, LDH encapsulated in ZIF-90 may be an economically competitive and environmentally friendly novel biocatalyst for the synthesis of D-PLA.

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.

Coimmobilization of lipases exhibiting three very different stability ranges. Reuse of the active enzymes and selective discarding of the inactivated ones

Lipase B from Candida antarctica (CALB) and lipases from Candida rugosa (CRL) and Rhizomucor miehei (RML) have been coimmobilized on octyl and octyl-Asp agarose beads. CALB was much more stable than CRL, that was significantly more stable than RML. This forces the user to discard immobilized CALB and CRL when only RML has been inactivated, or immobilized CALB when CRL have been inactivated. To solve this problem, a new strategy has been proposed using three different immobilization protocols. CALB was covalently immobilized on octyl-vinyl sulfone agarose and blocked with Asp. Then, CRL was immobilized via interfacial activation. After coating both immobilized enzymes with polyethylenimine, RML could be immobilized via ion exchange. That way, by incubating in ammonium sulfate solutions, inactivated RML could be released enabling the reuse of coimmobilized CRL and CALB to build a new combi-lipase. Incubating in triton and ammonium sulfate solutions, it was possible to release inactivated CRL and RML, enabling the reuse of immobilized CALB when CRL was inactivated. These cycles could be repeated for 3 full cycles, maintaining the activity of the active and immobilized enzymes.

Selective Coimmobilization of His-Tagged Enzymes on Yttrium-Stabilized Zirconia-Based Membranes for Continuous Asymmetric Bioreductions

Scalability, process control, and modularity are some of the advantages that make flow biocatalysis a key-enabling technology for green and sustainable chemistry. In this context, rigid porous solid membranes hold the promise to expand the toolbox of flow biocatalysis due to their chemical stability and inertness. Yttrium-stabilized zirconia (YSZ) fulfills these properties; however, it has been scarcely exploited as a carrier for enzymes. Here, we discovered an unprecedented interaction between YSZ materials and His-tagged enzymes that enables the fabrication of multifunctional biocatalytic membranes for bioredox cascades. X-ray photoelectron spectroscopy suggests that enzyme immobilization is driven by coordination interactions between the imidazole groups of His-tags and both Zr and Y atoms. As model enzymes, we coimmobilized in-flow a thermophilic hydroxybutyryl-CoA dehydrogenase (TtHBDH-His) and a formate dehydrogenase (His-CbFDH) for the continuous asymmetric reduction of ethyl acetoacetate with in situ redox cofactor recycling. Fluorescence confocal microscopy deciphered the spatial organization of the two coimmobilized enzymes, pointing out the importance of the coimmobilization sequence. Finally, the coimmobilized system succeeded in situ, recycling the redox cofactor, maintaining the specific productivity using only 0.05 mM NADH, and accumulating a total enzyme turnover number of 4000 in 24 h. This work presents YSZ materials as ready-to-use carriers for the site-directed enzyme in-flow immobilization and the application of the resulting heterogeneous biocatalysts for continuous biomanufacturing.