Recent progress in industrial biocatalysis

Biocatalytic, Stereoconvergent Alkylation of (Z/E)-Trisubstituted Silyl Enol Ethers

Alkene functionalization has garnered significant attention due to the versatile reactivity of C=C bonds. A major challenge is the selective conversion of isomeric alkenes into chiral products. Researchers have devised various biocatalytic strategies to transform isomeric alkenes into stereopure compounds; while selective, the enzymes often specifically convert one alkene isomer, thereby diminishing overall yield. To increase the overall yield, scientists have introduced additional driving forces to interconvert alkene isomers. This improves the yield of biocatalytic alkene functionalization at the cost of increased energy consumption and chemical waste. Developing a stereoconvergent enzyme for alkene functionalization offers an ideal solution, although such catalysts are rarely reported. Here we present engineered hemoproteins derived from a bacterial cytochrome P450 that efficiently catalyze the stereoconvergent α-carbonyl alkylation of isomeric silyl enol ethers, producing stereopure products. Through screening and directed evolution, we generated P450BM3 variant SCA-G2, which catalyzes stereoconvergent carbene transfer in E. coli, with high efficiency and stereoselectivity toward various Z/E mixtures of silyl enol ethers. In contrast to established stereospecific transformations that leave one isomer unreacted, SCA-G2 converts both isomers to a stereopure product. This biocatalytic approach simplifies the synthesis of chiral α-branched ketones by eliminating the need for stoichiometric chiral auxiliaries, strongly basic alkali-metal enolates, and harsh conditions, delivering products with high efficiency and excellent chemo- and stereoselectivities.

Optimization of asymmetric bioreduction conditions of 1-indanone by Leuconostoc mesenteroides N6 using a face-centered design-based multi-objective optimization model

There has been an increasing interest in biocatalysts over the past few decades in order to obtain high efficiency, high yield, and environmentally benign procedures aiming at the manufacture of pharmacologically relevant chemicals. Lactic Acid Bacteria (LAB), a microbial group, can be employed as biocatalysts while performing asymmetric reduction of prochiral ketones. In this study, Leuconostoc mesenteroides N6 was used for the asymmetric bioreduction 1-indanone. And then, a novel and innovative face-centered design-based multi-objective optimization model was used to optimize experimental conditions. Also, the experimental design factors were defined as agitation speed, incubation period, pH, and temperature for optimization to acquire the maximum enantiomeric excess (ee) and conversion rate (cr) values. When using the face-centered design-based multi-objective optimization model, the optimum culture conditions corresponded to 96.34 and 99.42%, ee and cr responses, respectively, were pH = 5.87, incubation temperature = 35 °C, incubation period = 50.88 h, and agitation speed = 152.60 rpm. Notably, the validation experiment under the optimum model conditions confirmed the model results. This study demonstrated the importance of the optimization and the efficiency of the face-centered design-based multi-objective model.

Enzymatic Bioconjugation: A Perspective from the Pharmaceutical Industry

Enzymes have firmly established themselves as bespoke catalysts for small molecule transformations in the pharmaceutical industry, from early research and development stages to large-scale production. In principle, their exquisite selectivity and rate acceleration can also be leveraged for modifying macromolecules to form bioconjugates. However, available catalysts face stiff competition from other bioorthogonal chemistries. In this Perspective, we seek to illuminate applications of enzymatic bioconjugation in the face of an expanding palette of new drug modalities. With these applications, we wish to highlight some examples of current successes and pitfalls of using enzymes for bioconjugation along the pipeline and try to illustrate opportunities for further development.

Biocatalysis: A smart and green tool for the preparation of chiral drugs

Over the last decades, biocatalysis has achieved growing interest thanks to its potential to enable high efficiency, high yield, and eco-friendly processes aimed at the production of pharmacologically relevant compounds. Particularly, biocatalysis proved an effective and potent tool in the preparation of chiral molecules, and the recent innovations of biotechnologies and nanotechnologies open up a new era of further developments in this field. Different strategies are now available for the synthesis of chiral drugs and their intermediates. Enzymes are green tools that offer several advantages, associated both to catalysis and environmentally friendly reactants. Specifically, the use of enzymes isolated from biological sources or of whole-cell represents a valuable approach to obtain pharmaceutical products. The sustainability, the higher efficiency, and cost-effectiveness of biocatalytic reactions result in improved performance and properties that can be translated from academia to industry. In this review, we focus on biocatalytic approaches for synthesizing chiral drugs or their intermediates. Aiming to unveil the potentialities of biocatalysis systems, we discuss different examples of innovative biocatalytic approaches and their applications in the pharmaceutical industry.

A multifunctional enzyme portfolio for α-chaconine and α-solanine degradation in the Phthorimaea operculella gut bacterium Glutamicibacter halophytocola S2 encoded in a trisaccharide utilization locus

Steroidal glycoalkaloids (SGAs) are secondary metabolites commonly found in members of the family Solanaceae, including potatoes, and are toxic to pests and humans. The predominant SGAs in potato are α-chaconine and α-solanine. We previously reported that Glutamicibacter halophytocola S2, a gut bacterium of the pest Phthorimaea operculella (potato tuber moth), can degrade α-chaconine and α-solanine in potatoes, which can improve the fitness of P. operculella to feed on potatoes with a high content of toxic SGAs. Glutamicibacter halophytocola S2 harbored a gene cluster containing three deglycosylase genes-GE000599, GE000600, and GE000601-that were predicted encode α-rhamnosidase (RhaA), β-glucosidase (GluA), and β-galactosidase (GalA). However, there is limited information is available on the enzyme activities of the three enzymes expressed by this gene cluster and how they degrade the major toxic α-chaconine and α-solanine. In the current study, each enzyme of this gene cluster was produced by a prokaryotic expression approach and the activity of the recombinant enzymes for their target substrate and α-chaconine and α-solanine were evaluated by EPOCH microplate spectrophotometer and liquid chromatography mass spectrometry (LC-MS). The three enzymes had multifunctional activities, with RhaA and GluA could hydrolyze α-rhamnose, β-glucose, and β-galactose, while GalA can hydrolyze β-glucose and β-galactose. The degradation of α-chaconine and α-solanine was consistent with the results of the enzyme activity assays. The final product solanidine could be generated by adding RhaA or GluA alone. In conclusion, this study characterized the multifunctional activity and specific degradation pathway of these three enzymes in G. halophytocola S2. The three multifunctional enzymes have high glycosidic hydrolysis activity and clear gene sequence information, which help facilitates understanding the detoxification mechanism of insect gut microbes. The enzymes have a broad application potential and may be valuable in the removal of toxic SGAs from for potato food consumption.

Exploring the Temperature Effect on Enantioselectivity of a Baeyer-Villiger Biooxidation by the 2,5-DKCMO Module: The SLM Approach

Temperature is a crucial parameter for biological and chemical processes. Its effect on enzymatically catalysed reactions has been known for decades, and stereo- and enantiopreference are often temperature-dependent. For the first time, we present the temperature effect on the Baeyer-Villiger oxidation of rac-bicyclo[3.2.0]hept-2-en-6-one by the type II Bayer-Villiger monooxygenase, 2,5-DKCMO. In the absence of a reductase and driven by the hydride-donation of a synthetic nicotinamide analogue, the clear trend for a decreasing enantioselectivity at higher temperatures was observed. "Traditional" approaches such as the determination of the enantiomeric ratio (E) appeared unsuitable due to the complexity of the system. To quantify the trend, we chose to use the 'Shape Language Modelling' (SLM), a tool that allows the reaction to be described at all points in a shape prescriptive manner. Thus, without knowing the equation of the reaction, the substrate ee can be estimated that at any conversion.

Chemoenzymatic Asymmetric Synthesis of Pyridine-Based α-Fluorinated Secondary Alcohols

Fluoro‐substituted and heteroaromatic compounds are valuable intermediates for a variety of applications in pharma‐ and agrochemistry and synthetic chemistry. This study investigates the chemoenzymatic preparation of chiral alcohols bearing a heteroaromatic ring with an increasing degree of fluorination in α‐position. Starting from readily available picoline derivatives prochiral α‐halogenated acyl moieties were introduced with excellent selectivity and 64–95 % yield. The formed carbonyl group was subsequently reduced to the corresponding alcohols using the alcohol dehydrogenase from Lactobacillus kefir, yielding an enantiomeric excess of 95–>99 % and up to 98 % yield.

Lipase-Catalyzed Kinetic Resolution of Dimethyl and Dibutyl 1-Butyryloxy-1-carboxymethylphosphonates

The main objective of this study is the enantioselective synthesis of carboxyhydroxyphosphonates by lipase-catalyzed reactions. For this purpose, racemic dimethyl and dibutyl 1-butyryloxy-1-carboxymethylphosphonates were synthesized and hydrolyzed, using a wide spectrum of commercially available lipases from different sources (e.g., fungi and bacteria). The best hydrolysis results of dimethyl 1-butyryloxy-1-carboxymethylphosphonate were obtained with the use of lipases from Candida rugosa, Candida antarctica, and Aspergillus niger, leading to optically active dimethyl 1-carboxy-1-hydroxymethylphosphonate (58%–98% enantiomeric excess) with high enantiomeric ratio (reaching up to 126). However, in the case of hydrolysis of dibutyl 1-butyryloxy-1-carboxymethylphosphonate, the best results were obtained by lipases from Burkholderia cepacia and Termomyces lanuginosus, leading to optically active dibutyl 1-carboxy-1-hydroxymethylphosphonate (66%–68% enantiomeric excess) with moderate enantiomeric ratio (reaching up to 8.6). The absolute configuration of the products after biotransformation was also determined. In most cases, lipases hydrolyzed (R) enantiomers of both compounds.

Programming Integrative Multienzyme Systems and Ionic Strength For Recyclable Synthesis of Glutathione

In the enzymatic cascade catalysis, it is a big challenge to construct a stable and reusable catalyst with targeted enzymes. The artificial multienzyme reactor has attracted great attention due to its potential for facilitating the performance of enzyme catalysis. In this study, we set up a reliable system that could assemble polyphosphate kinase (PPK) with bifunctional glutathione synthetase (GshF) via SpyCatcher/SpyTag to form multienzyme systems (MESs). Furthermore, MESs could assemble into nanoaggregates by altering the ionic strength, and the larger nanoaggregates could be applied in robust and reusable synthesis of glutathione (GSH). To enhance MES levels in vivo, gene duplication and different coexpression modes were performed. Finally, the optimized production of GSH and oxidized glutathione (GSSG) reached 102.6 and 6.7 mM within 2 h. Compared with the first round, the total yield only decreased by 9.4% after five continuous rounds of biocatalysis.

Immobilization of Aldoxime Dehydratases and Their Use as Biocatalysts in Aqueous Reaction Media

Immobilization of biocatalysts is a current topic in research enabling the easy recovery of catalysts from the reaction medium after the reaction, and it is often accompanied by a stabilization of the catalysts, which enables recycling. Within our ongoing research on the utilization of aldoxime dehydratases in the cyanide-free synthesis of nitriles through dehydration of readily available aldoximes, a screening of different immobilization methods for free enzymes was performed. The applied immobilization methods are based on covalent binding and hydrophobic interactions of the enzyme with the carrier material and whole-cell immobilization in calcium alginate beads with and without subsequent coating. In our study, we found that the immobilization with purified free aldoxime dehydratases from OxdRE (Rhodococcus erythropolis) and OxdB (Bacillus sp. strain OxB-1) leads to high immobilization efficiencies, but also to a strong loss of activity with a residual activity of <20%, regardless of the carrier material used. However, when using whole cells for immobilization instead of purified enzymes, we could increase the residual activity significantly. Escherichia coli BL21(DE3)-CodonPlus-RIL OxdRE and OxdB whole cells were entrapped in calcium alginate beads and coated with silica using tetraethylorthosilicate (TEOS), leading to immobilized catalysts with up to 75% residual activity and a higher stability compared to the free whole cells. Even after three rounds of recycling, which corresponds to a 3 d reaction time, the immobilized OxdB whole cells showed a residual activity of 85%.

A Simple Biosystem for the High-Yielding Cascade Conversion of Racemic Alcohols to Enantiopure Amines

The amination of racemic alcohols to produce enantiopure amines is an important green chemistry reaction for pharmaceutical manufacturing, requiring simple and efficient solutions. Herein, we report the development of a cascade biotransformation to aminate racemic alcohols. This cascade utilizes an ambidextrous alcohol dehydrogenase (ADH) to oxidize a racemic alcohol, an enantioselective transaminase (TA) to convert the ketone intermediate to chiral amine, and isopropylamine to recycle PMP and NAD⁺ cofactors via the reversed cascade reactions. The concept was proven by using an ambidextrous CpSADH-W286A engineered from (S)-enantioselective CpSADH as the first example of evolving ambidextrous ADHs, an enantioselective BmTA, and isopropylamine. A biosystem containing isopropylamine and E. coli (CpSADH-W286A/BmTA) expressing the two enzymes was developed for the amination of racemic alcohols to produce eight useful and high-value (S)-amines in 72-99 % yield and 98-99 % ee, providing with a simple and practical solution to this type of reaction.

Metals in Biotechnology: Cr-Driven Stereoselective Reduction of Conjugated C=C Double Bonds

Elemental metals are shown to be suitable sacrificial electron donors to drive the stereoselective reduction of conjugated C=C double bonds using Old Yellow Enzymes as catalysts. Both direct electron transfer from the metal to the enzyme as well as mediated electron transfer is feasible, although the latter excels by higher reaction rates. The general applicability of this new chemoenzymatic reduction method is demonstrated, and current limitations are outlined.

Detailed small-scale characterization and scale-up of active YFP inclusion body production with Escherichia coli induced by a tetrameric coiled coil domain

During heterologous protein production with Escherichia coli, the formation of inclusion bodies (IBs) is often a major drawback as these aggregated proteins are usually inactive. However, different strategies for the generation of IBs consisting of catalytically active proteins have recently been described. In this study, the archaeal tetrameric coiled-coil domain of the cell-surface protein tetrabrachion was fused to a target reporter protein to produce fluorescent IBs (FIBs). As the cultivation conditions severely influence IB formation, the entire cultivation process resulting in the production of FIBs were thoroughly studied. First, the cultivation process was scaled down based on the maximum oxygen transfer capacity, combining online monitoring technologies for shake flasks and microtiter plates with offline sampling. The evaluation of culture conditions in complex terrific broth autoinduction medium showed strong oxygen limitation and leaky expression. Furthermore, strong acetate formation and pH changes from 6.5 to 8.8 led to sub-optimal cultivation conditions. However, in minimal Wilms-MOPS autoinduction medium, defined culture conditions and a tightly controlled expression were achieved. The production of FIBs is strongly influenced by the induction strength. Increasing induction strengths result in lower total amounts of functional protein. However, the amount of functional FIBs increases. Furthermore, to prevent the formation of conventional inactive IBs, a temperature shift from 37 °C to 15 °C is crucial to generate FIBs. Finally, the gained insights were transferred to a stirred tank reactor batch fermentation. Hereby, 12 g/L FIBs were produced, making up 43 % (w/w) of the total generated biomass.

Accelerating the implementation of biocatalysis in industry

Despite enormous progress in protein engineering, complemented by bioprocess engineering, the revolution awaiting the application of biocatalysis in the fine chemical industry has still not been fully realized. In order to achieve that, further research is required on several topics, including (1) rapid methods for protein engineering using machine learning, (2) mathematical modelling of multi-enzyme cascade processes, (3) process standardization, (4) continuous process technology, (5) methods to identify improvements required to achieve industrial implementation, (6) downstream processing, (7) enzyme stability modelling and prediction, as well as (8) new reactor technology. In this brief mini-review, the status of each of these topics will be briefly discussed.

Facile fabrication of a recyclable nanobiocatalyst: immobilization of Burkholderia cepacia lipase on carbon nanofibers for the kinetic resolution of a racemic atenolol intermediate

Immobilization of surfactant treated Burkholderia cepacia lipase on the surface of carbon nanofibers was performed via two different methods: adsorption and covalent attachment. Simple adsorption of lipase on carbon nanofibers turned out to be a poor strategy, exhibiting an immobilization efficiency of 36%, while covalent coupling using 1-ethyl-3-[3-dimethylaminopropyl] carbodiimide (EDC)/N-hydroxysuccinimide (NHS) showed better immobilization efficiency (56%). The nanobioconjugate fabricated using the latter method showed an eleven-fold increase in enzyme activity towards the hydrolysis of p-nitrophenyl palmitate and enhanced dispersion in organic solvents. At 80 °C, the half-life of lipase in the nanobioconjugate was almost 20 fold higher than that of free lipase, demonstrating its thermal stability. The as-prepared nanobioconjugate was reused for nine consecutive reaction cycles achieving 100% yield in the hydrolysis of p-nitrophenol palmitate but losing almost 50% of the initial activity after seven operational cycles. Finally, this heterogeneous nanobioconjugate was more active and enantioselective [C = 47.8, eep = 97.0 and E = 194] than free lipase [C = 35.4, eep = 97.1 and E = 88] towards the kinetic resolution of a racemic intermediate of atenolol yielding the S enantiomer, which signifies its importance as a nanobiocatalyst.

Recent developments in biocatalysis in multiphasic ionic liquid reaction systems

Ionic liquids are well known and frequently used 'designer solvents' for biocatalytic reactions. This review highlights recent achievements in the field of multiphasic ionic liquid-based reaction concepts. It covers classical biphasic systems including supported ionic liquid phases, thermo-regulated multi-component solvent systems (TMS) and polymerized ionic liquids. These powerful concepts combine unique reaction conditions with a high potential for future applications on a laboratory and industrial scale. The presence of a multiphasic system simplifies downstream processing due to the distribution of the catalyst and reactants in different phases.

Fungal synthesis of chiral phosphonic synthetic platform - Scope and limitations of the method

Chiral hydroxyphosphonates due to their wide range of biological properties are industrially important chemicals. Chemical synthesis of their optical isomers is expensive, time consuming and not friendly to the environment, so biotransformations are under consideration. Among others, these compounds act as enzymes inhibitors. This makes the bioconversions of phosphonates, especially scaling experiments, hard to perform. Biocatalysis is one of the methods that can be applied in synthesis of optically pure compounds. To increase the efficiency of the process with whole cell biocatalysts, it is essential to ensure optimal reaction conditions that minimize cellular stress and can enhance the metabolic activity of cells. The present investigation focuses on the scaling up of the kinetic resolution of racemic mixture of 2-butyryloxy-2-(ethoxy-P-phenylphosphinyl)acetic acid, applying free and immobilized form of the fungal biocatalysts and two operation systems: shake flask and recirculated fixed-bed batch reactor. Protocols of effective mycelium immobilization on polyurethane foams were set for T. purpurogenus IAFB 2512, F. oxysporum, P. commune. The best results of biotransformation were obtained with the immobilized P. commune in the column recirculated fixed-bed batch reactor. The conversion reaches 56% (maximal for the kinetic process) and the enantiomeric enrichment of the isomers mixture ranges between 82 and 93% (93% for ester of R_P,R conformation). All biocatalysts exhibit S_P-preference toward tested compound, what is essential because of importance of the phosphorus atom chirality for its biological activity.

Mycobacterial F420H2-Dependent Reductases Promiscuously Reduce Diverse Compounds through a Common Mechanism

An unusual aspect of actinobacterial metabolism is the use of the redox cofactor F₄₂₀. Studies have shown that actinobacterial F₄₂₀H₂-dependent reductases promiscuously hydrogenate diverse organic compounds in biodegradative and biosynthetic processes. These enzymes therefore represent promising candidates for next-generation industrial biocatalysts. In this work, we undertook the first broad survey of these enzymes as potential industrial biocatalysts by exploring the extent, as well as mechanistic and structural bases, of their substrate promiscuity. We expressed and purified 11 enzymes from seven subgroups of the flavin/deazaflavin oxidoreductase (FDOR) superfamily (A1, A2, A3, B1, B2, B3, B4) from the model soil actinobacterium Mycobacterium smegmatis. These enzymes reduced compounds from six chemical classes, including fundamental monocycles such as a cyclohexenone, a dihydropyran, and pyrones, as well as more complex quinone, coumarin, and arylmethane compounds. Substrate range and reduction rates varied between the enzymes, with the A1, A3, and B1 groups exhibiting greatest promiscuity. Molecular docking studies suggested that structurally diverse compounds are accommodated in the large substrate-binding pocket of the most promiscuous FDOR through hydrophobic interactions with conserved aromatic residues and the isoalloxazine headgroup of F₄₂₀H₂. Liquid chromatography-mass spectrometry (LC/MS) and gas chromatography-mass spectrometry (GC/MS) analysis of derivatized reaction products showed reduction occurred through a common mechanism involving hydride transfer from F₄₂₀H^- to the electron-deficient alkene groups of substrates. Reduction occurs when the hydride donor (C5 of F₄₂₀H^-) is proximal to the acceptor (electrophilic alkene of the substrate). These findings suggest that engineered actinobacterial F₄₂₀H₂-dependent reductases are promising novel biocatalysts for the facile transformation of a wide range of α,β-unsaturated compounds.

Catalytically-active inclusion bodies-Carrier-free protein immobilizates for application in biotechnology and biomedicine

Bacterial inclusion bodies (IBs) consist of unfolded protein aggregates and represent inactive waste products often accumulating during heterologous overexpression of recombinant genes in Escherichia coli. This general misconception has been challenged in recent years by the discovery that IBs, apart from misfolded polypeptides, can also contain substantial amounts of active and thus correctly or native-like folded protein. The corresponding catalytically-active inclusion bodies (CatIBs) can be regarded as a biologically-active sub-micrometer sized biomaterial or naturally-produced carrier-free protein immobilizate. Fusion of polypeptide (protein) tags can induce CatIB formation paving the way towards the wider application of CatIBs in synthetic chemistry, biocatalysis and biomedicine. In the present review we summarize the history of CatIBs, present the molecular-biological tools that are available to induce CatIB formation, and highlight potential lines of application. In the second part findings regarding the formation, architecture, and structure of (Cat)IBs are summarized. Finally, an overview is presented about the available bioinformatic tools that potentially allow for the prediction of aggregation and thus (Cat)IB formation. This review aims at demonstrating the potential of CatIBs for biotechnology and hopefully contributes to a wider acceptance of this promising, yet not widely utilized, protein preparation.

Enantioselective Reduction of Citral Isomers in NCR Ene Reductase: Analysis of an Active-Site Mutant Library

A deeper understanding of the >99 % S-selective reduction of both isomers of citral catalyzed by NCR ene reductase was achieved by active-site mutational studies and docking simulation. Though structurally similar, the E/Z isomers of citral showed a significantly varying selectivity response to introduced mutations. Although it was possible to invert (E)-citral reduction enantioselectivity to ee 46 % (R) by introducing mutation W66A, for (Z)-citral it remained ≥88 % (S) for all single-residue variants. Residue 66 seems to act as a lever for opposite binding modes. This was underlined by a W66A-based double-mutant library that enhanced the (E)-citral derived enantioselectivity to 63 % (R) and significantly lowered the S selectivity for (Z)-citral to 44 % (S). Formation of (R)-citronellal from an (E/Z)-citral mixture is a desire in industrial (-)-menthol synthesis. Our findings pave the way for a rational enzyme engineering solution.

Kinetic resolution of (RS)-1-chloro-3-(4-(2-methoxyethyl)phenoxy)propan-2-ol: a metoprolol intermediate and its validation through homology model of Pseudomonas fluorescens lipase

Kinetic resolution of (±)-1-chloro-3-(4-(2-methoxyethyl)phenoxy)propan-2-ol: a metoprolol intermediate and its validation through homology model of Pseudomonas fluorescens lipase.

Recent Advances in Dynamic Kinetic Resolution by Chiral Bifunctional (Thio)urea- and Squaramide-Based Organocatalysts

The organocatalysis-based dynamic kinetic resolution (DKR) process has proved to be a powerful strategy for the construction of chiral compounds. In this feature review, we summarized recent progress on the DKR process, which was promoted by chiral bifunctional (thio)urea and squaramide catalysis via hydrogen-bonding interactions between substrates and catalysts. A wide range of asymmetric reactions involving DKR, such as asymmetric alcoholysis of azlactones, asymmetric Michael–Michael cascade reaction, and enantioselective selenocyclization, are reviewed and demonstrate the efficiency of this strategy. The (thio)urea and squaramide catalysts with dual activation would be efficient for more unmet challenges in dynamic kinetic resolution.

Development of in situ product removal strategies in biocatalysis applying scaled-down unit operations

An experimental platform based on scaled-down unit operations combined in a plug-and-play manner enables easy and highly flexible testing of advanced biocatalytic process options such as in situ product removal (ISPR) process strategies. In such a platform, it is possible to compartmentalize different process steps while operating it as a combined system, giving the possibility to test and characterize the performance of novel process concepts and biocatalysts with minimal influence of inhibitory products. Here the capabilities of performing process development by applying scaled-down unit operations are highlighted through a case study investigating the asymmetric synthesis of 1-methyl-3-phenylpropylamine (MPPA) using ω-transaminase, an enzyme in the sub-family of amino transferases (ATAs). An on-line HPLC system was applied to avoid manual sample handling and to semi-automatically characterize ω-transaminases in a scaled-down packed-bed reactor (PBR) module, showing MPPA as a strong inhibitor. To overcome the inhibition, a two-step liquid-liquid extraction (LLE) ISPR concept was tested using scaled-down unit operations combined in a plug-and-play manner. Through the tested ISPR concept, it was possible to continuously feed the main substrate benzylacetone (BA) and extract the main product MPPA throughout the reaction, thereby overcoming the challenges of low substrate solubility and product inhibition. The tested ISPR concept achieved a product concentration of 26.5 g_MPPA  · L^-1 , a purity up to 70% g_MPPA  · g_tot^-1 and a recovery in the range of 80% mol · mol^-1 of MPPA in 20 h, with the possibility to increase the concentration, purity, and recovery further. Biotechnol. Bioeng. 2017;114: 600-609. © 2016 Wiley Periodicals, Inc.

Accelerating Enzymatic Catalysis Using Vortex Fluidics

Enzymes catalyze chemical transformations with outstanding stereo- and regio-specificities, but many enzymes are limited by their long reaction times. A general method to accelerate enzymes using pressure waves contained within thin films is described. Each enzyme responds best to specific frequencies of pressure waves, and an acceleration landscape for each protein is reported. A vortex fluidic device introduces pressure waves that drive increased rate constants (kcat ) and enzymatic efficiency (kcat /Km ). Four enzymes displayed an average seven-fold acceleration, with deoxyribose-5-phosphate aldolase (DERA) achieving an average 15-fold enhancement using this approach. In solving a common problem in enzyme catalysis, a powerful, generalizable tool for enzyme acceleration has been uncovered. This research provides new insights into previously uncontrolled factors affecting enzyme function.