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Abstract
Erucic (22:1, cisΔ13) and gondoic acids (20:1, cisΔ11) are building blocks obtained from renewable sources for the oleochemical industry. Different biocatalytic strategies for the enrichment of these compounds with high recovery yields were developed in our group. Geotrichum candidum lipases (GCL) strongly discriminate against fatty acids longer than 18 carbon atoms. Thus, GCL‐I and ‐II were investigated using hydrolysis or ethanolysis reactions with Crambe and Camelina oils. Hydrolysis was also studied using fatty acid ethyl esters (FAEE) derived from the corresponding oil. Both isoforms were highly selective; however, interesting differences were observed. Although it has been reported that GCL‐I displays a higher preference toward 18 cisΔ9, which is present in the studied oils at high levels, GCL‐II showed higher enrichment values during hydrolysis independent of the substrate used. Hence, enrichments of 87% (Crambe oil) and 82% (Crambe FAEE) for erucic acid and 50% (Camelina oil) and 45% (Camelina FAEE) for gondoic acid, with recovery values between 89% and 99%, were achieved. On the contrary, the best enzyme for ethanolysis was GCL‐I (82% and 41% for erucic and gondoic acid, respectively). In this case, although GCL‐II also displayed good enrichment and recovery levels (77% and 28%, respectively), they were lower compared to the former reactions. In both ethanolysis reactions, the FAEE fraction contained between 92% and 97% of 18 unsaturated fatty acids.
Abstract
Methylation of free hydroxyl groups is an important modification for flavonoids. It not only greatly increases absorption and oral bioavailability of flavonoids, but also brings new biological activities. Flavonoid methylation is usually achieved by a specific group of plant O‐methyltransferases (OMTs) which typically exhibit high substrate specificity. Here we investigated the effect of several residues in the binding pocket of the Clarkia breweri isoeugenol OMT on the substrate scope and regioselectivity against flavonoids. The mutation T133M, identified as reported in our previous publication, increased the activity of the enzyme against several flavonoids, namely eriodictyol, naringenin, luteolin, quercetin and even the isoflavonoid genistein, while a reduced set of amino acids at positions 322 and 326 affected both, the activity and the regioselectivity of the methyltranferase. On the basis of this work, methylated flavonoids that are rare in nature were produced in high purity.
Abstract
Biocatalysis has found numerous applications in various fields as an alternative to chemical catalysis. The use of enzymes in organic synthesis, especially to make chiral compounds for pharmaceuticals as well for the flavors and fragrance industry, are the most prominent examples. In addition, biocatalysts are used on a large scale to make specialty and even bulk chemicals. This review intends to give illustrative examples in this field with a special focus on scalable chemical production using enzymes. It also discusses the opportunities and limitations of enzymatic syntheses using distinct examples and provides an outlook on emerging enzyme classes.
Long-chain aliphatic amines such as (S,Z)-hepta- dec-9-en-7-amine and 9-aminoheptadecane were synthesized from ricinoleic acid and oleic acid, respectively, by whole-cell cascade reactions using the combination of an alcohol dehydrogenase (ADH) from Micrococcus luteus, an engi- neered amine transaminase from Vibrio fluvialis (Vf-ATA), and a photoactivated decarboxylase from Chlorella variabilis NC64A (Cv-FAP) in a one-pot process. In addition, long chain aliphatic esters such as 10-(heptanoyloxy)dec-8-ene and octyl- nonanoate were prepared from ricinoleic acid and oleic acid, respectively, by using the combination of the ADH, a Baeyer– Villiger monooxygenase variant from Pseudomonas putida KT2440, and the Cv-FAP. The target compounds were produced at rates of up to 37 U g1 dry cells with conversions up to 90 %. Therefore, this study contributes to the preparation of industrially relevant long-chain aliphatic chiral amines and esters from renewable fatty acid resources.
Abstract
Environmentally‐friendly processes for the manufacturing of valuable industrial compounds like ω‐hydroxy fatty acids (ω‐OHFAs) are highly desirable. Herein, we present such an approach by establishing a two‐step enzymatic cascade reaction for the production of 2,15,16‐trihydroxy hexadecanoic acid (THA). Starting with the easily accessible natural compound ustilagic acid (UA) that is secreted by the corn smut fungus Ustilago maydis, the recombinantly expressed esterase BS2 from Bacillus subtilis and the commercial β‐glucosidase from almonds were applied yielding 86 % product. Both hydrolases do not require expensive cofactors, making the process economically attractive. Additionally, no harmful solvents are required, so that the product THA can be labelled natural to be used in food and cosmetic products.
Abstract
A device for the transaminase‐catalysed synthesis combined with continuous recovery of chiral amines was designed. The system enabled the separation of the reaction components in three liquid phases: a reaction phase, an organic solvent phase (where the poorly water soluble ketone substrate was supplied), and an aqueous extraction phase for continuous product recovery. The transaminase‐mediated asymmetric synthesis of (S)‐1‐methyl‐3‐phenylpropylamine was employed as model reaction. Factors influencing the performance of the system, such as reactor geometry, working volumes and operating parameters, were investigated. Specifically, reaction yield and product recovery were enhanced by i) reducing the thickness of the reaction phase, while continuously stirring and ii) reducing the volume of the extraction phase. Under the optimal condition tested, 85 % of the product formed was extracted and a product concentration value of 9 g/L was reached. However, co‐extraction of the unreacted amine donor (17 %) was observed. Advantages and drawbacks of this process compared to existing technologies, as well as possible optimization strategies are discussed.
An Ultrasensitive Fluorescence Assay for the Detection of Halides and Enzymatic Dehalogenation
(2020)
Abstract
Halide assays are important for the study of enzymatic dehalogenation, a topic of great industrial and scientific importance. Here we describe the development of a very sensitive halide assay that can detect less than a picomole of bromide ions, making it very useful for quantifying enzymatic dehalogenation products. Halides are oxidised under mild conditions using the vanadium‐dependent chloroperoxidase from Curvularia inaequalis, forming hypohalous acids that are detected using aminophenyl fluorescein. The assay is up to three orders of magnitude more sensitive than currently available alternatives, with detection limits of 20 nM for bromide and 1 μM for chloride and iodide. We demonstrate that the assay can be used to determine specific activities of dehalogenases and validate this by comparison to a well‐established GC‐MS method. This new assay will facilitate the identification and characterisation of novel dehalogenases and may also be of interest to those studying other halide‐producing enzymes.
Abstract
Certain hydrolases preferentially catalyze acyl transfer over hydrolysis in an aqueous environment. However, the molecular and structural reasons for this phenomenon are still unclear. Herein, we provide evidence that acyltransferase activity in esterases highly correlates with the hydrophobicity of the substrate‐binding pocket. A hydrophobicity scoring system developed in this work allows accurate prediction of promiscuous acyltransferase activity solely from the amino acid sequence of the cap domain. This concept was experimentally verified by systematic investigation of several homologous esterases, leading to the discovery of five novel promiscuous acyltransferases. We also developed a simple yet versatile colorimetric assay for rapid characterization of novel acyltransferases. This study demonstrates that promiscuous acyltransferase activity is not as rare as previously thought and provides access to a vast number of novel acyltransferases with diverse substrate specificity and potential applications.
Abstract
Macroalgae species are fast growing and their polysaccharides are already used as food ingredient due to their properties as hydrocolloids or they have potential high value bioactivity. The degradation of these valuable polysaccharides to access the sugar components has remained mostly unexplored so far. One reason is the high structural complexity of algal polysaccharides, but also the need for suitable enzyme cocktails to obtain oligo‐ and monosaccharides. Among them, there are several rare sugars with high value. Recently, considerable progress was made in the discovery of highly specific carbohydrate‐active enzymes able to decompose complex marine carbohydrates such as carrageenan, laminarin, agar, porphyran and ulvan. This minireview summarizes these achievements and highlights potential applications of the now accessible abundant renewable resource of marine polysaccharides.
Entdeckung und Design promiskuitiver Acyltransferase‐Aktivität in Carboxylesterasen der Familie VIII
(2021)
Abstract
Promiscuous acyltransferase activity is the ability of certain hydrolases to preferentially catalyze acyl transfer over hydrolysis, even in bulk water. However, poor enantioselectivity, low transfer efficiency, significant product hydrolysis, and limited substrate scope represent considerable drawbacks for their application. By activity‐based screening of several hydrolases, we identified the family VIII carboxylesterase, EstCE1, as an unprecedentedly efficient acyltransferase. EstCE1 catalyzes the irreversible amidation and carbamoylation of amines in water, which enabled the synthesis of the drug moclobemide from methyl 4‐chlorobenzoate and 4‐(2‐aminoethyl)morpholine (ca. 20 % conversion). We solved the crystal structure of EstCE1 and detailed structure–function analysis revealed a three‐amino acid motif important for promiscuous acyltransferase activity. Introducing this motif into an esterase without acetyltransferase activity transformed a “hydrolase” into an “acyltransferase”.
Abstract
Halide methyltransferases (HMTs) enable the enzymatic synthesis of S‐adenosyl‐l‐methionine (SAM) from S‐adenosyl‐l‐homocysteine (SAH) and methyl iodide. Characterisation of a range of naturally occurring HMTs and subsequent protein engineering led to HMT variants capable of synthesising ethyl, propyl, and allyl analogues of SAM. Notably, HMTs do not depend on chemical synthesis of methionine analogues, as required by methionine adenosyltransferases (MATs). However, at the moment MATs have a much broader substrate scope than the HMTs. Herein we provide an overview of the discovery and engineering of promiscuous HMTs and how these strategies will pave the way towards a toolbox of HMT variants for versatile chemo‐ and regioselective biocatalytic alkylations.
Fatty aldehydes (FALs) can be derived from fatty acids (FAs) and related compounds and are frequently used as flavors and fragrances. Although chemical methods have been conventionally used, their selective biotechnological production aiming at more efficient and eco-friendly synthetic routes is in demand. α-Dioxygenases (α-DOXs) are heme-dependent oxidative enzymes biologically involved in the initial step of plant FA α-oxidation during which molecular oxygen is incorporated into the Cα-position of a FA (Cn) to generate the intermediate FA hydroperoxide, which is subsequently converted into the shortened corresponding FAL (Cn-1). α-DOXs are promising biocatalysts for the flavor and fragrance industries, they do not require NAD(P)H as cofactors or redox partner proteins, and they have a broad substrate scope. Here, we highlight recent advances in the biocatalytic utilization of α-DOXs with emphasis on newly discovered cyanobacterial α-DOXs as well as analytical methods to measure α-DOX activity in vitro and in vivo.
Fast screening of enzyme variants is crucial for tailoring biocatalysts for the asymmetric synthesis of non-natural chiral chemicals, such as amines. However, most existing screening methods either are limited by the throughput or require specialized equipment. Herein, we report a simple, high-throughput, low-equipment dependent, and generally applicable growth selection system for engineering amine-forming or converting enzymes and apply it to improve biocatalysts belonging to three different enzyme classes. This results in (i) an amine transaminase variant with 110-fold increased specific activity for the asymmetric synthesis of the chiral amine intermediate of Linagliptin; (ii) a 270-fold improved monoamine oxidase to prepare the chiral amine intermediate of Cinacalcet by deracemization; and (iii) an ammonia lyase variant with a 26-fold increased activity in the asymmetric synthesis of a non-natural amino acid. Our growth selection system is adaptable to different enzyme classes, varying levels of enzyme activities, and thus a flexible tool for various stages of an engineering campaign.
p-Coumaric acid (p-CA) is a key precursor for the biosynthesis of flavonoids. Tyrosine ammonia lyases (TALs) specifically catalyze the synthesis of p-CA from l-tyrosine, which is a convenient enzymatic pathway. To explore novel and highly active TALs, a phylogenetic tree-building approach was conducted including 875 putative TALs and 46 putative phenylalanine/tyrosine ammonia lyases (PTALs). Among them, 5 TALs and 3 PTALs were successfully characterized and found to exhibit the proposed enzymatic activity. The TAL from Chryseobacterium luteum sp. nov (TALclu) has the highest affinity (Km=0.019 mm) and conversion efficiency (kcat/Km=1631 s−1 ⋅ mm−1) towards l-tyrosine. The reaction conditions for two purified enzymes and their E. coli recombinant cells were optimized and p-CA yields of 2.03 g/L after 8 hours by TALclu and 2.35 g/L after 24 h by TAL from Rivularia sp. PCC 7116 (TALrpc) in whole cells were achieved. These TALs are thus candidates for the construction of whole-cell systems to produce the flavonoid precursor p-CA.
Abstract
Enzyme activity data for biocatalytic applications are currently often not annotated with standardized conditions and terms. This makes it extremely hard to retrieve, compare, and reuse enzymatic data. With advances in the fields of artificial intelligence (AI) and machine learning (ML), the automated usability of data in the form of machine‐readable annotations will play a crucial role for their success. It is becoming increasingly easy to retrieve complex data sets and extract relevant information; however, standardized data readability is a current limitation. In this contribution, we outline an iterative approach to develop standardized terms and create semantic relations (ontologies) to achieve this highly desirable goal of improving the discoverability, accessibility, interoperability, and reuse of digital resources in the field of biocatalysis.
β-Glucosidases (Bgls) convert cellobiose and other soluble cello-oligomers into glucose and play important roles in fundamental biological processes, providing energy sources in living organisms. Bgls are essential terminal enzymes of cellulose degradation systems and attractive targets for lignocellulose-based biotechnological applications. Characterization of novel Bgls is important for broadening our knowledge of this enzyme class and can provide insights into its further applications. In this study, we report the biochemical and structural analysis of a Bgl from the hemicellulose-degrading thermophilic anaerobe Thermoanaerobacterium saccharolyticum (TsaBgl). TsaBgl exhibited its maximum hydrolase activity on p-nitrophenyl-β-d-glucopyranoside at pH 6.0 and 55 °C. The crystal structure of TsaBgl showed a single (β/α)8 TIM-barrel fold, and a β8-α14 loop, which is located around the substrate-binding pocket entrance, showing a unique conformation compared with other structurally known Bgls. A Tris molecule inhibited enzyme activity and was bound to the active site of TsaBgl coordinated by the catalytic residues Glu163 (proton donor) and Glu351 (nucleophile). Titration experiments showed that TsaBgl belongs to the glucose-tolerant Bgl family. The gatekeeper site of TsaBgl is similar to those of other glucose-tolerant Bgls, whereas Trp323 and Leu170, which are involved in glucose tolerance, show a unique configuration. Our results therefore improve our knowledge about the Tris-mediated inhibition and glucose tolerance of Bgl family members, which is essential for their industrial application.