Multienzyme Cascade Reactions—Status and Recent Advances

Development of a Four-Enzyme Magnetic Nanobiocatalyst for Multi-Step Cascade Reactions

We report the preparation, characterization and application of a novel magnetic four-enzyme nanobiocatalyst prepared by the simultaneous covalent co-immobilization of cellulase (CelDZ1), β-glucosidase (bgl), glucose oxidase (GOx) and horseradish peroxidase (HRP) onto the surface of amino-functionalized magnetic nanoparticles (MNPs). This nanobiocatalyst was characterized by various spectroscopic techniques. The co-immobilization process yielded maximum recovered enzymatic activity (CelDZ1: 42%, bgl: 66%, GOx: 94% and HRP: 78%) at a 10% v/v cross-linker concentration, after 2 h incubation time and at 1:1 mass ratio of MNPs to total enzyme content. The immobilization process leads to an increase of Km and a decrease of Vmax values of co-immobilized enzymes. The thermal stability studies of the co-immobilized enzymes indicated up to 2-fold increase in half-life time constants and up to 1.5-fold increase in their deactivation energies compared to the native enzymes. The enhanced thermodynamic parameters of the four-enzyme co-immobilized MNPs also suggested increment in their thermal stability. Furthermore, the co-immobilized enzymes retained a significant part of their activity (up to 50%) after 5 reaction cycles at 50 °C and remained active even after 24 d of incubation at 5 °C. The nanobiocatalyst was successfully applied in a four-step cascade reaction involving the hydrolysis of cellulose.

Three-Enzyme Phosphorylase Cascade for Integrated Production of Short-Chain Cellodextrins

Cellodextrins are linear β-1,4-gluco-oligosaccharides that are soluble in water up to a degree of polymerization (DP) of ≈6. Soluble cellodextrins have promising applications as nutritional ingredients. A DP-controlled, bottom-up synthesis from expedient substrates is desired for their bulk production. Here, a three-enzyme glycoside phosphorylase cascade is developed for the conversion of sucrose and glucose into short-chain (soluble) cellodextrins (DP range 3-6). The cascade reaction involves iterative β-1,4-glucosylation of glucose from α-glucose 1-phosphate (αGlc1-P) donor that is formed in situ from sucrose and phosphate. With final concentration and yield of the soluble cellodextrins set as targets for biocatalytic synthesis, three major factors of reaction efficiency are identified and partly optimized: the ratio of enzyme activity, the ratio of sucrose and glucose, and the phosphate concentration used. The efficient use of the phosphate/αGlc1-P shuttle for cellodextrin production is demonstrated and the soluble product at 40 g L^-1 is obtained under near-complete utilization of the donor substrate offered (88 mol% from 200 mm sucrose). The productivity is 16 g (L h)^-1 . Through a simple two-step route, the soluble cellodextrins are recovered from the reaction mixture in ≥95% purity and ≈92% yield. Overall, this study provides the basis for their integrated production.

From stars to stripes: RNA-directed shaping of plant viral protein templates-structural synthetic virology for smart biohybrid nanostructures

The self-assembly of viral building blocks bears exciting prospects for fabricating new types of bionanoparticles with multivalent protein shells. These enable a spatially controlled immobilization of functionalities at highest surface densities-an increasing demand worldwide for applications from vaccination to tissue engineering, biocatalysis, and sensing. Certain plant viruses hold particular promise because they are sustainably available, biodegradable, nonpathogenic for mammals, and amenable to in vitro self-organization of virus-like particles. This offers great opportunities for their redesign into novel "green" carrier systems by spatial and structural synthetic biology approaches, as worked out here for the robust nanotubular tobacco mosaic virus (TMV) as prime example. Natural TMV of 300 x 18 nm is built from more than 2,100 identical coat proteins (CPs) helically arranged around a 6,395 nucleotides ssRNA. In vitro, TMV-like particles (TLPs) may self-assemble also from modified CPs and RNAs if the latter contain an Origin of Assembly structure, which initiates a bidirectional encapsidation. By way of tailored RNA, the process can be reprogrammed to yield uncommon shapes such as branched nanoobjects. The nonsymmetric mechanism also proceeds on 3'-terminally immobilized RNA and can integrate distinct CP types in blends or serially. Other emerging plant virus-deduced systems include the usually isometric cowpea chlorotic mottle virus (CCMV) with further strikingly altered structures up to "cherrybombs" with protruding nucleic acids. Cartoon strips and pictorial descriptions of major RNA-based strategies induct the reader into a rare field of nanoconstruction that can give rise to utile soft-matter architectures for complex tasks. This article is categorized under: Biology-Inspired Nanomaterials > Protein and Virus-Based Structures Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Biology-Inspired Nanomaterials > Nucleic Acid-Based Structures.

Electrostatic Interaction-Induced Formation of Enzyme-on-MOF as Chemo-Biocatalyst for Cascade Reaction with Unexpectedly Acid-Stable Catalytic Performance

Combining biocatalytic and chemocatalytic reactions in a one-pot reaction not only avoids the tedious isolation of intermediates during the reactions but also provides a desirable alternative to extend the range of catalytic reactions. Here, we report a facile strategy to immobilize an enzyme, glucose oxidase (GOx), on PCN-222(Fe) induced by electrostatic interaction in which PCN-222(Fe) serves as both a support and chemocatalyst. The immobilization was confirmed through ζ potential measurement, confocal laser scanning microscopy, Fourier transform infrared spectrometry, and UV-vis spectroscopy. This chemo-biocatalyst was applied to a cascade reaction to catalyze glucose oxidation and ABTS (ABTS = 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (or pyrogallol) oxidation. The catalytic kinetics studies show that these chemo-biocatalytic cascade reactions obey the Michaelis-Menten equation, which indicates that the cascade reactions follow the typical enzymatic dynamic regulation process. Interestingly, GOx/PCN-222(Fe) exhibits an exceptional acid-stable catalytic performance as evidenced by circular dichroism spectroscopy where no significant structure change was observed toward acidic solutions with different pH values. GOx/PCN-222(Fe) also displays desirable recyclability since no significant loss of conversion rates was found after six repeated reactions. This work presents a convenient strategy to construct metal-organic framework based chemo-biocatalysts, which may find potential applications in sensing and nanomachines.

Product solubility control in cellooligosaccharide production by coupled cellobiose and cellodextrin phosphorylase

Soluble cellodextrins (linear β-1,4-d-gluco-oligosaccharides) have interesting applications as ingredients for human and animal nutrition. Their bottom-up synthesis from glucose is promising for bulk production, but to ensure a completely water-soluble product via degree of polymerization (DP) control (DP ≤ 6) is challenging. Here, we show biocatalytic production of cellodextrins with DP centered at 3 to 6 (~96 wt.% of total product) using coupled cellobiose and cellodextrin phosphorylase. The cascade reaction, wherein glucose was elongated sequentially from α-d-glucose 1-phosphate (αGlc1-P), required optimization and control at two main points. First, kinetic and thermodynamic restrictions upon αGlc1-P utilization (200 mM; 45°C, pH 7.0) were effectively overcome (53% → ≥90% conversion after 10 hrs of reaction) by in situ removal of the phosphate released via precipitation with Mg2+ . Second, the product DP was controlled by the molar ratio of glucose/αGlc1-P (∼0.25; 50 mM glucose) used in the reaction. In optimized conversion, soluble cellodextrins in a total product concentration of 36 g/L were obtained through efficient utilization of the substrates used (glucose: 98%; αGlc1-P: ∼80%) after 1 hr of reaction. We also showed that, by keeping the glucose concentration low (i.e., 1-10 mM; 200 mM αGlc1-P), the reaction was shifted completely towards insoluble product formation (DP ∼9-10). In summary, this study provides the basis for an efficient and product DP-controlled biocatalytic synthesis of cellodextrins from expedient substrates.

Optimization of a reduced enzymatic reaction cascade for the production of L-alanine

Cell-free enzymatic reaction cascades combine the advantages of well-established in vitro biocatalysis with the power of multi-step in vivo pathways. The absence of a regulatory cell environment enables direct process control including methods for facile bottleneck identification and process optimization. Within this work, we developed a reduced, enzymatic reaction cascade for the direct production of L-alanine from D-glucose and ammonium sulfate. An efficient, activity based enzyme selection is demonstrated for the two branches of the cascade. The resulting redox neutral cascade is composed of a glucose dehydrogenase, two dihydroxyacid dehydratases, a keto-deoxy-aldolase, an aldehyde dehydrogenase and an L-alanine dehydrogenase. This artificial combination of purified biocatalysts eliminates the need for phosphorylation and only requires NAD as cofactor. We provide insight into in detail optimization of the process parameters applying a fluorescamine based L-alanine quantification assay. An optimized enzyme ratio and the necessary enzyme load were identified and together with the optimal concentrations of cofactor (NAD), ammonium and buffer yields of >95% for the main branch and of 8% for the side branch were achieved.

In vitro production of cysteine from glucose

Cysteine is a commercially valuable amino acid with an increasing demand in the food, cosmetic, and pharmaceutical industries. Although cysteine is conventionally manufactured by extraction from animal proteins, this method has several problems, such as troublesome waste-water treatment and incompatibility with some dietary restrictions. Fermentative production of cysteine from plant-derived substrates is a promising alternative for the industrial production of cysteine. However, it often suffers from low product yield as living organisms are equipped with various regulatory systems to control the intracellular cysteine concentration at a moderate level. In this study, we constructed an in vitro cysteine biosynthetic pathway by assembling 11 thermophilic enzymes. The in vitro pathway was designed to be insensitive to the feedback regulation by cysteine and to balance the intra-pathway consumption and regeneration of cofactors. A kinetic model for the in vitro pathway was built using rate equations of individual enzymes and used to optimize the loading ratio of each enzyme. Consequently, 10.5 mM cysteine could be produced from 20 mM glucose through the optimized pathway. However, the observed yield and production rate of the assay were considerably lower than those predicted by the model. Determination of cofactor concentrations in the reaction mixture indicated that the inconsistency between the model and experimental assay could be attributed to the depletion of ATP and ADP, likely due to host-derived, thermo-stable enzyme(s). Based on these observations, possible approaches to improve the feasibility of cysteine production through an in vitro pathway have been discussed.

Engineering a Seven Enzyme Biotransformation using Mathematical Modelling and Characterized Enzyme Parts

Multi-step enzyme reactions offer considerable cost and productivity benefits. Process models offer a route to understanding the complexity of these reactions, and allow for their optimization. Despite the increasing prevalence of multi-step biotransformations, there are few examples of process models for enzyme reactions. From a toolbox of characterized enzyme parts, we demonstrate the construction of a process model for a seven enzyme, three step biotransformation using isolated enzymes. Enzymes for cofactor regeneration were employed to make this in vitro reaction economical. Good modelling practice was critical in evaluating the impact of approximations and experimental error. We show that the use and validation of process models was instrumental in realizing and removing process bottlenecks, identifying divergent behavior, and for the optimization of the entire reaction using a genetic algorithm. We validated the optimized reaction to demonstrate that complex multi-step reactions with cofactor recycling involving at least seven enzymes can be reliably modelled and optimized.

Markov-State Transition Path Analysis of Electrostatic Channeling

Electrostatic channeling is a naturally occurring approach to control the flux of charged intermediates in catalytic cascades. Computational techniques have enabled quantitative understanding of such mechanisms, augmenting experimental approaches by modeling molecular interactions in atomic detail. In this work, we report the first utilization of a Markov-state model (MSM) to describe the surface diffusion of a reaction intermediate, glucose 6-phosphate, on an artificially modified cascade where hexokinase and glucose-6-phosphate dehydrogenase are covalently conjugated by a cationic oligopeptide bridge. Conformation space networks are used to represent intermediate transport on enzyme surfaces, along with committor probabilities that assess the desorption probability of the intermediate on each segment of the channeling pathway. For the region between the peptide bridge and downstream active site, the ionic strength dependence of desorption probability by MSM agreed well with that by transition state theory. A kinetic Monte Carlo model integrates parameters from different computational methods to evaluate the contribution of desorption during each step. The approach is validated by calculation of kinetic lag time, which agrees well with experimental results. These results further demonstrate the applicability of molecular simulations and advanced sampling techniques to the design of chemical networks.

A multi-enzyme cascade reaction for the production of 6-hydroxyhexanoic acid

Multi-enzyme cascade reactions capture the essence of nature's efficiency by increasing the productivity of a process. Here we describe one such three-enzyme cascade for the synthesis of 6-hydroxyhexanoic acid. Whole cells of Escherichia coli co-expressing an alcohol dehydrogenase and a Baeyer-Villiger monooxygenase (CHMO) for internal cofactor regeneration were used without the supply of external NADPH or NADP+. The product inhibition caused by the ε-caprolactone formed by the CHMO was overcome by the use of lipase CAL-B for in situ conversion into 6-hydroxyhexanoic acid. A stirred tank reactor under fed-batch mode was chosen for efficient catalysis. By using this setup, a product titre of >20 g L-1 was achieved in a 500 mL scale with an isolated yield of 81% 6-hydroxyhexanoic acid.

Linear enzyme cascade for the production of (-)-iso-isopulegol

Biocatalysis has developed enormously in the last decade and now offers solutions for the sustainable production of chiral and highly functionalised asset molecules. Products generated by enzymatic transformations are already being used in the food, feed, chemical, pharmaceutical and cosmetic industry, and the accessible compound panoply is expected to expand even further. In particular, the combination of stereo-selective enzymes in linear cascade reactions is an elegant strategy toward enantiomeric pure compounds, as it reduces the number of isolation and purification steps and avoids accumulation of potentially unstable intermediates. Here, we present the set-up of an enzyme cascade to selectively convert citral to (-)-iso-isopulegol by combining an ene reductase and a squalene hopene cyclase. In the initial reaction step, the ene reductase YqjM from Bacillus subtilis selectively transforms citral to (S)-citronellal, which is subsequently cyclised exclusively to (-)-iso-isopulegol by a mutant of the squalene hopene cyclase from Alicyclobacillus acidocaldarius (AacSHC). With this approach, we can convert citral to an enantiopure precursor for isomenthol derivatives.

Design of enzymatic cascade processes for the production of low-priced chemicals

While the application of enzymes to synthetic and industrial problems continues to grow, the major development today is focused on multi-enzymatic cascades. Such systems are particularly attractive, because many commercially available enzymes operate under relatively similar operating conditions. This opens the possibility of one-pot operation with multiple enzymes in a single reactor. In this paper the concept of modules is introduced whereby groups of enzymes are combined in modules, each operating in a single reactor, but with the option of various operating strategies to avoid any complications of nonproductive interactions between the enzymes, substrates or products in a given reactor. In this paper the selection of modules is illustrated using the synthesis of the bulk chemical, gluconic acid, from lignocellulosic waste.

Bienzymatic Cascade for the Synthesis of an Optically Active O-benzoyl Cyanohydrin

A concurrent bienzymatic cascade for the synthesis of optically pure (S)-4-methoxymandelonitrile benzoate ((S)-3) starting from 4-anisaldehyde (1) has been developed. The cascade involves an enantioselective Manihot esculenta hydroxynitrile lyase-catalyzed hydrocyanation of 1, and the subsequent benzoylation of the resulting cyanohydrin (S)-2 catalyzed by Candida antarctica lipase A in organic solvent. To accomplish this new direct synthesis of the protected enantiopure cyanohydrin, both enzymes were immobilized and each biocatalytic step was studied separately in search for a window of compatibility. In addition, potential cross-interactions between the two reactions were identified. Optimization of the cascade resulted in 81% conversion of the aldehyde to the corresponding benzoyl cyanohydrin with 98% enantiomeric excess.

Stimulus-Responsive Regulation of Enzyme Activity for One-Step and Multi-Step Syntheses

Multi-step biocatalytic reactions have gained increasing importance in recent years because the combination of different enzymes enables the synthesis of a broad variety of industrially relevant products. However, the more enzymes combined, the more crucial it is to avoid cross-reactivity in these cascade reactions and thus achieve high product yields and high purities. The selective control of enzyme activity, i.e., remote on-/off-switching of enzymes, might be a suitable tool to avoid the formation of unwanted by-products in multi-enzyme reactions. This review compiles a range of methods that are known to modulate enzyme activity in a stimulus-responsive manner. It focuses predominantly on in vitro systems and is subdivided into reversible and irreversible enzyme activity control. Furthermore, a discussion section provides indications as to which factors should be considered when designing and choosing activity control systems for biocatalysis. Finally, an outlook is given regarding the future prospects of the field.

Designing of a Cofactor Self-Sufficient Whole-Cell Biocatalyst System for Production of 1,2-Amino Alcohols from Epoxides

Optically pure 1,2-amino alcohols are highly valuable products as intermediates for chiral pharmaceutical products. Here we designed an environmentally friendly non-natural biocatalytic cascade for efficient synthesis of 1,2-amino alcohols from cheaper epoxides. A redesignated ω-transaminase PAKω-TA was tested and showed good bioactivity at a lower pH than other reported transaminases. The cascade was efficiently constructed as a single one-pot E. coli recombinant, by coupling SpEH (epoxide hydrolase), MnADH (alcohol dehydrogenase), and PAKω-TA. Furthermore, RBS regulation strategy was used to overcome the rate limiting step by increasing expression of MnADH. For cofactor regeneration and amino donor source, an interesting point was involved as that a cofactor self-sufficient system was designed by expression of GluDH. It established a "bridge" between the cofactor and the cosubstrate, such that the cofactor self-sufficient system could release cofactor (NADP⁺) and cosubstrate (l-Glutamine) regenerated simultaneously. The recombinant E. coli BL21 (SGMP) with cofactor self-sufficient whole-cell cascade biocatalysis showed high ee value (>99%) and high yield, with 99.6% conversion of epoxide ( S)-1a to 1,2-amino alcohol ( S)-1d in 10 h. It further converted ( S)-2a-5a to ( S)-2d-5d with varying conversion rates ranging between 65-96.4%. This study first provides one-step synthesis of optically pure 1,2-amino alcohols from ( S)-epoxides employing a synthetic redox-self-sufficient cascade.

Exploiting Designed Oxidase-Peroxygenase Mutual Benefit System for Asymmetric Cascade Reactions

A unique P450 monooxygenase–peroxygenase mutual benefit system was designed as the core element in the construction of a biocatalytic cascade reaction sequence leading from 3-phenyl propionic acid to (R)-phenyl glycol. In this system, P450 monooxygenase (P450-BM3) and P450 peroxygenase (OleT_JE) not only function as catalysts for the crucial initial reactions, they also ensure an internal in situ H₂O₂ recycle mechanism that avoids its accumulation and thus prevents possible toxic effects. By directed evolution of P450-BM3 as the catalyst in the enantioselective epoxidation of the styrene-intermediate, formed from 3-phenyl propionic acid, and the epoxide hydrolase ANEH for final hydrolytic ring opening, (R)-phenyl glycol and 9 derivatives thereof were synthesized from the respective carboxylic acids in one-pot processes with high enantioselectivity.

Improvement of lipase activity by synergistic immobilization on polyurethane and its application for large-scale synthesizing vitamin A palmitate

We have developed an improved and effective method to immobilize lipase on hydrophobic polyurethane foam (PUF) with different modifications. PUF was treated with hydrochloric acid to increase the active sites and then the active carboxyl groups and amino groups were exposed. Enzyme activity of lipase immobilized on PUF-HCL (8000 U/g) was 50% higher than that of lipase immobilized on PUF (5300 U/g). There is an increase in the activity of the immobilized lipase on AA/PEI-modified support (115,000 U/g), a 2.17-fold increase compared to lipase immobilized on the native support was observed. The activity of immobilized lipases was dependent on the PEI molecular weight, with best results from enzyme immobilized on PUF-HCL-AA/PEI (MW 70,000 Da, 12,800 U/g)), which was 2.41 times higher compared to that of the same enzyme immobilized on PUF. These results suggest that the activity of immobilized lipase is influenced by the support surface properties, and a moderate support surface micro-environment is crucial for improving enzyme activity. Finally, the immobilized lipase was used for the production of vitamin A palmitate. The immobilized lipase can be reused for up to 18 times with a conversion rate above 90% for 12 h in a 3 L bioreactor. Research highlights An efficient immobilization protocol on polyurethane foam was developed Polyethyleneimine and acetic acid were used to regulate the micro-environment concurrently The activity of lipase immobilized on PUF-HCL-AA/PEI was improved by 2.41 times Immobilized lipase exhibited excellent operational stability for vitamin A palmitate synthesis.

Artificial Metalloenzymes Based on the Biotin-Streptavidin Technology: Enzymatic Cascades and Directed Evolution

Artificial metalloenzymes (ArMs) result from anchoring a metal-containing moiety within a macromolecular scaffold (protein or oligonucleotide). The resulting hybrid catalyst combines attractive features of both homogeneous catalysts and enzymes. This strategy includes the possibility of optimizing the reaction by both chemical (catalyst design) and genetic means leading to achievement of a novel degree of (enantio)selectivity, broadening of the substrate scope, or increased activity, among others. In the past 20 years, the Ward group has exploited, among others, the biotin–(strept)avidin technology to localize a catalytic moiety within a well-defined protein environment. Streptavidin has proven versatile for the implementation of ArMs as it offers the following features: (i) it is an extremely robust protein scaffold, amenable to extensive genetic manipulation and mishandling, (ii) it can be expressed in E. coli to very high titers (up to >8 g·L^–1 in fed-batch cultures), and (iii) the cavity surrounding the biotinylated cofactor is commensurate with the size of a typical metal-catalyzed transition state. Relying on a chemogenetic optimization strategy, varying the orientation and the nature of the biotinylated cofactor within genetically engineered streptavidin, 12 reactions have been reported by the Ward group thus far. Recent efforts within our group have focused on extending the ArM technology to create complex systems for integration into biological cascade reactions and in vivo.

With the long-term goal of complementing in vivo natural enzymes with ArMs, we summarize herein three complementary research lines: (i) With the aim of mimicking complex cross-regulation mechanisms prevalent in metabolism, we have engineered enzyme cascades, including cross-regulated reactions, that rely on ArMs. These efforts highlight the remarkable (bio)compatibility and complementarity of ArMs with natural enzymes. (ii) Additionally, multiple-turnover catalysis in the cytoplasm of aerobic organisms was achieved with ArMs that are compatible with a glutathione-rich environment. This feat is demonstrated in HEK-293T cells that are engineered with a gene switch that is upregulated by an ArM equipped with a cell-penetrating module. (iii) Finally, ArMs offer the fascinating prospect of “endowing organometallic chemistry with a genetic memory.” With this goal in mind, we have identified E. coli’s periplasmic space and surface display to compartmentalize an ArM, while maintaining the critical phenotype–genotype linkage. This strategy offers a straightforward means to optimize by directed evolution the catalytic performance of ArMs. Five reactions have been optimized following these compartmentalization strategies: ruthenium-catalyzed olefin metathesis, ruthenium-catalyzed deallylation, iridium-catalyzed transfer hydrogenation, dirhodium-catalyzed cyclopropanation and carbene insertion in C–H bonds. Importantly, >100 turnovers were achieved with ArMs in E. coli whole cells, highlighting the multiple turnover catalytic nature of these systems.

Seven-enzyme in vitro cascade to (3R)-3-hydroxybutyryl-CoA

Economical and environmentally-friendly routes to convert feedstock chemicals like acetate into valuable chiral products such as (R)-3-hydroxybutyrate are in demand. Here, seven enzymes (CoaA, CoaD, CoaE, ACS, BktB, PhaB, and GDH) are employed in a one-pot, in vitro, biocatalytic synthesis of (3R)-3-hydroxybutyryl-CoA, which was readily isolated. This platform generates not only chiral diketide building blocks but also desirable CoA derivatives.

Biocatalytic selective functionalisation of alkenes via single-step and one-pot multi-step reactions

Alkenes are excellent starting materials for organic synthesis due to the versatile reactivity of C[double bond, length as m-dash]C bonds and the easy availability of many unfunctionalised alkenes. Direct regio- and/or enantioselective conversion of alkenes into functionalised (chiral) compounds has enormous potential for industrial applications, and thus has attracted the attention of researchers for extensive development using chemo-catalysis over the past few years. On the other hand, many enzymes have also been employed for conversion of alkenes in a highly selective and much greener manner to offer valuable products. Herein, we review recent advances in seven well-known types of biocatalytic conversion of alkenes. Remarkably, recent mechanism-guided directed evolution and enzyme cascades have enabled the development of seven novel types of single-step and one-pot multi-step functionalisation of alkenes, some of which are even unattainable via chemo-catalysis. These new reactions are particularly highlighted in this feature article. Overall, we present an ever-expanding enzyme toolbox for various alkene functionalisations inspiring further research in this fast-developing theme.

Metal-Organic-Framework-Based Enzymatic Microfluidic Biosensor via Surface Patterning and Biomineralization

Recently, the biomineralization of enzyme in metal-organic-framework (enzyme-MOF) composite have shown a great potential to increase enzymes stability without compromising their activity; hence, it is desirable for its applications in biosensing devices. Nonetheless, most of the enzyme-MOF research has been focusing on enzyme encapsulation in particle form, which limits its synthesis flexibility for practical applications because of its requirement for postsynthesis immobilization onto solid support. Therefore, to develop a diagnostic device out of the biomineralized enzyme, surface patterning and integration of microfluidic system offers many advantages. In this work, mussel-inspired polydopamine/polyethyleneimine (PDA/PEI) coating is employed to pattern enzyme-MOF in microfluidic channels and exploit the wettability gradient for "pumpless transportation" effect. As a proof of concept, we combine a cascade reaction of glucose oxidase (GOx) and horseradish peroxidase (HRP) enzymes to detect glucose into a patterned zeolitic imidazole framework-8 (ZIF-8) thin film on a flexible polymeric substrate. The results show that the ZIF-8/GOx&HRP in situ composites on PDA/PEI patterns have good acid and thermal stability compared with samples without ZIF-8. ZIF-8/GOx&HRP in situ shows high selectivity toward glucose, linear sensitivity of 0.00303 Abs/μM, and the limit of detection of 8 μM glucose concentration. An unexpected benefit of this approach is the ability of the ZIF-8 thin-film structure to provide a diffusion limiting effect for substrate influx, thus, producing high range of linear response range (8 μM to 5 mM of glucose). This work provides insights into the spatial location of the enzymes in MOF thin films and the potential of such patterning techniques for MOF-based biosensors using other types of biological elements such as antibodies and aptamers.

Enzyme Fusions in Biocatalysis: Coupling Reactions by Pairing Enzymes

One approach to bringing enzymes together for multienzyme biocatalysis is genetic fusion. This enables the production of multifunctional enzymes that can be used for whole-cell biotransformations or for in vitro (cascade) reactions. In some cases and in some aspects, such as expression and conversions, the fused enzymes outperform a combination of the individual enzymes. In contrast, some enzyme fusions are greatly compromised in activity and/or expression. In this Minireview, we give an overview of studies on fusions between two or more enzymes that were used for biocatalytic applications, with a focus on oxidative enzymes. Typically, the enzymes are paired to facilitate cofactor recycling or cosubstrate supply. In addition, different linker designs are briefly discussed. Although enzyme fusion is a promising tool for some biocatalytic applications, future studies could benefit from integrating the findings of previous studies in order to improve reliability and effectiveness.

Asymmetric ring opening of racemic epoxides for enantioselective synthesis of (S)-β-amino alcohols by a cofactor self-sufficient cascade biocatalysis system

Asymmetric ring opening of racemic epoxides to enantiopure β-amino alcohols via a cascade biocatalysis system.

Highly selective synthesis of d-amino acids from readily available l-amino acids by a one-pot biocatalytic stereoinversion cascade

d-Amino acids are key intermediates required for the synthesis of important pharmaceuticals. However, establishing a universal enzymatic method for the general synthesis of d-amino acids from cheap and readily available precursors with few by-products is challenging. In this study, we constructed and optimized a cascade enzymatic route involving l-amino acid deaminase and d-amino acid dehydrogenase for the biocatalytic stereoinversions of l-amino acids into d-amino acids. Using l-phenylalanine (l-Phe) as a model substrate, this artificial biocatalytic cascade stereoinversion route first deaminates l-Phe to phenylpyruvic acid (PPA) through catalysis involving recombinant Escherichia coli cells that express l-amino acid deaminase from Proteus mirabilis (PmLAAD), followed by stereoselective reductive amination with recombinant meso-diaminopimelate dehydrogenase from Symbiobacterium thermophilum (StDAPDH) to produce d-phenylalanine (d-Phe). By incorporating a formate dehydrogenase-based NADPH-recycling system, d-Phe was obtained in quantitative yield with an enantiomeric excess greater than 99%. In addition, the cascade reaction system was also used to stereoinvert a variety of aromatic and aliphatic l-amino acids to the corresponding d-amino acids by combining the PmLAAD whole-cell biocatalyst with the StDAPDH variant. Hence, this method represents a concise and efficient route for the asymmetric synthesis of d-amino acids from the corresponding l-amino acids.

An efficient one-pot biocatalytic cascade was developed for synthesis of d-amino acids from readily available l-amino acids via stereoinversion.

Chemoenzymatic cascade for stilbene production from cinnamic acid catalyzed by ferulic acid decarboxylase and an artificial metathease

We report a chemoenzymatic cascade reaction for stilbene production combining decarboxylation and olefin metathesis with efficient removal of metal contamination.

Tools and strategies for constructing cell-free enzyme pathways

Single enzyme systems or engineered microbial hosts have been used for decades but the notion of assembling multiple enzymes into cell-free synthetic pathways is a relatively new development. The extensive possibilities that stem from this synthetic concept makes it a fast growing and potentially high impact field for biomanufacturing fine and platform chemicals, pharmaceuticals and biofuels. However, the translation of individual single enzymatic reactions into cell-free multi-enzyme pathways is not trivial. In reality, the kinetics of an enzyme pathway can be very inadequate and the production of multiple enzymes can impose a great burden on the economics of the process. We examine here strategies for designing synthetic pathways and draw attention to the requirements of substrates, enzymes and cofactor regeneration systems for improving the effectiveness and sustainability of cell-free biocatalysis. In addition, we comment on methods for the immobilisation of members of a multi-enzyme pathway to enhance the viability of the system. Finally, we focus on the recent development of integrative tools such as in silico pathway modelling and high throughput flux analysis with the aim of reinforcing their indispensable role in the future of cell-free biocatalytic pathways for biomanufacturing.

Recent Advances in Catalyzed Sequential Reactions and the Potential Use of Tetrapyrrolic Macrocycles as Catalysts

Complexes of porphyrins and of other similar tetrapyrrolic macrocycles are extensively explored as catalysts for different chemical processes, and the development of solid catalysts for heterogeneous processes using molecules with the ability to act as multifunctional catalysts in one-pot reactions is increasing and can lead to the wider use of this class of molecules as catalysts. This mini review focuses on the application of this class of complexes as catalysts in a variety of sequential one-pot reactions.

Stereoselective Double Reduction of 3-Methyl-2-cyclohexenone, by Use of Palladium and Platinum Nanoparticles, in Tandem with Alcohol Dehydrogenase

The combination of metal nanoparticles (Pd or Pt NPs) with NAD-dependent thermostable alcohol dehydrogenase (TADH) resulted in the one-flask catalytic double reduction of 3-methyl-2-cyclohexenone to 3-(1S,3S)-methylcyclohexanol. In this article, some assumptions about the interactions between a chemocatalyst and a biocatalyst have been proposed. It was demonstrated that the size of the NPs was the critical parameter for the mutual inhibition: the bigger the NPs, the more harmful for the enzyme they were, even if the NPs themselves were only moderately inactivated. Conversely, the smaller the NPs, the more minimal the TADH denaturation, although they were dramatically inhibited. Resuming, the chemocatalysts were very sensitive to deactivation, which was not related to the amount of enzyme used, while the inhibition of the biocatalyst can be strongly reduced by minimizing the NPs/TADH ratio used to catalyze the reaction. Among some methods to avoid direct binding of NPs with TADH, we found that using large Pd NPs and protecting their surfaces with a silica shell, the overall yield of 3-(1S,3S)-methylcyclohexanol was maximized (36%).

Biomimetic cofactors and methods for their recycling

Nicotinamide cofactor biomimetics (NCBs) belong to a class of compounds that, as the name suggests, mimic the structures and functions of natural nicotinamide cofactors, namely nicotinamide adenine dinucleotide and nicotinamide adenine dinucleotide phosphate and their corresponding reduced forms. The first set of NCBs was discovered in the 1930s; these were initially used to study the chemical properties of this class of cofactors as well as understand nicotinamide binding of oxidoreductases. Since then, various NCBs, enzymes, and recycling systems have evolved and lately, new NCBs have been developed and used to run biocatalytic reactions.

Immobilized carbonic anhydrase: preparation, characteristics and biotechnological applications

Carbonic anhydrase (CA) is an essential metalloenzyme in living systems for accelerating the hydration and dehydration of carbon dioxide. CA-catalyzed reactions can be applied in vitro for capturing industrially emitted gaseous carbon dioxide in aqueous solutions. To facilitate this type of practical application, the immobilization of CA on or inside solid or soft support materials is of great importance because the immobilization of enzymes in general offers the opportunity for enzyme recycling or long-term use in bioreactors. Moreover, the thermal/storage stability and reactivity of immobilized CA can be modulated through the physicochemical nature and structural characteristics of the support material used. This review focuses on (i) immobilization methods which have been applied so far, (ii) some of the characteristic features of immobilized forms of CA, and (iii) biotechnological applications of immobilized CA. The applications described not only include the CA-assisted capturing and sequestration of carbon dioxide, but also the CA-supported bioelectrochemical conversion of CO₂ into organic molecules, and the detection of clinically important CA inhibitors. Furthermore, immobilized CA can be used in biomimetic materials synthesis involving cascade reactions, e.g. for bone regeneration based on calcium carbonate formation from urea with two consecutive reactions catalyzed by urease and CA.

Multienzyme One-Pot Cascade for the Stereoselective Hydroxyethyl Functionalization of Substituted Phenols

The operability and substrate scope of a redesigned vinylphenol hydratase as a single biocatalyst or as part of multienzyme cascades using either substituted coumaric acids or phenols as stable, cheap, and readily available substrates are reported.

Two-Component FAD-Dependent Monooxygenases: Current Knowledge and Biotechnological Opportunities

Flavoprotein monooxygenases create valuable compounds that are of high interest for the chemical, pharmaceutical, and agrochemical industries, among others. Monooxygenases that use flavin as cofactor are either single- or two-component systems. Here we summarize the current knowledge about two-component flavin adenine dinucleotide (FAD)-dependent monooxygenases and describe their biotechnological relevance. Two-component FAD-dependent monooxygenases catalyze hydroxylation, epoxidation, and halogenation reactions and are physiologically involved in amino acid metabolism, mineralization of aromatic compounds, and biosynthesis of secondary metabolites. The monooxygenase component of these enzymes is strictly dependent on reduced FAD, which is supplied by the reductase component. More and more representatives of two-component FAD-dependent monooxygenases have been discovered and characterized in recent years, which has resulted in the identification of novel physiological roles, functional properties, and a variety of biocatalytic opportunities.

Bioproduction of Benzylamine from Renewable Feedstocks via a Nine-Step Artificial Enzyme Cascade and Engineered Metabolic Pathways

Production of chemicals from renewable feedstocks has been an important task for sustainable chemical industry. Although microbial fermentation has been widely employed to produce many biochemicals, it is still very challenging to access non-natural chemicals. Two methods (biotransformation and fermentation) have been developed for the first bio-derived synthesis of benzylamine, a commodity non-natural amine with broad applications. Firstly, a nine-step artificial enzyme cascade was designed by biocatalytic retrosynthetic analysis and engineered in recombinant E. coli LZ243. Biotransformation of l-phenylalanine (60 mm) with the E. coli cells produced benzylamine (42 mm) in 70 % conversion. Importantly, the cascade biotransformation was scaled up to 100 mL and benzylamine was successfully isolated in 57 % yield. Secondly, an artificial biosynthesis pathway to benzylamine from glucose was developed by combining the nine-step cascade with an enhanced l-phenylalanine synthesis pathway in cells. Fermentation with E. coli LZ249 gave benzylamine in 4.3 mm concentration from glucose. In addition, one-pot syntheses of several useful benzylamines from the easily available styrenes were achieved, representing a new type of alkene transformation by formal oxidative cleavage and reductive amination.