On the current role of hydratases in biocatalysis

One-pot process for the biotransformation of vegetable oils into natural deca- and dodecalactones

Deca- and dodecalactones are highly desired natural compounds that are essential for creating flavor formulations with fruity, peachy, creamy, and floral notes. Although natural ingredients are preferred by consumers, these lactones cannot be extracted from natural sources. Therefore, the biotechnological processes that produce these compounds in their natural form are crucial for the flavor industry. Here, we report a study on the biotransformation of vegetable oils into natural deca- and dodecalactones. The proposed process is performed one-pot, through the sequential use of three different biotransformation steps, namely the lipase-mediated hydrolysis of the triglycerides, the use of probiotic bacteria for the hydration of the unsaturated fatty acids and the transformation of the obtained hydroxy-fatty acids into lactones derivatives employing Yarrowia lipolytica. By using a specific vegetable oil in combination with a selected bacterial strain, it is possible to obtain a preferred lactone derivative such as γ-dodecalactone, dairy lactone, tuberose lactone, or δ-decalactone in a concentration ranging from 0.9 to 1.5 g/L. Overall, our method is suitable for the industrial production of these lactones as it is easily scalable, it can be performed in only one bioreactor and it makes use of generally recognized as safe (GRAS) microorganisms.

An unexpected hydratase synthesizes the green light-absorbing pigment fucoxanthin

The ketocarotenoid fucoxanthin and its derivatives can absorb blue-green light enriched in marine environments. Fucoxanthin is widely adopted by phytoplankton species as a main light-harvesting pigment, in contrast to land plants that primarily employ chlorophylls. Despite its supreme abundance in the oceans, the last steps of fucoxanthin biosynthesis have remained elusive. Here, we identified the carotenoid isomerase-like protein CRTISO5 as the diatom fucoxanthin synthase that is related to the carotenoid cis-trans isomerase CRTISO from land plants but harbors unexpected enzymatic activity. A crtiso5 knockout mutant in the model diatom Phaeodactylum tricornutum completely lacked fucoxanthin and accumulated the acetylenic carotenoid phaneroxanthin. Recombinant CRTISO5 converted phaneroxanthin into fucoxanthin in vitro by hydrating its carbon-carbon triple bond, instead of functioning as an isomerase. Molecular docking and mutational analyses revealed residues essential for this activity. Furthermore, a photophysiological characterization of the crtiso5 mutant revealed a major structural and functional role of fucoxanthin in photosynthetic pigment-protein complexes of diatoms. As CRTISO5 hydrates an internal alkyne physiologically, the enzyme has unique potential for biocatalytic applications. The discovery of CRTISO5 illustrates how neofunctionalization leads to major diversification events in evolution of photosynthetic mechanisms and the prominent brown coloration of most marine photosynthetic eukaryotes.

Chiral Alcohols from Alkenes and Water: Directed Evolution of a Styrene Hydratase

Enantioselective synthesis of chiral alcohols through asymmetric addition of water across an unactivated alkene is a highly sought-after transformation and a big challenge in catalysis. Herein we report the identification and directed evolution of a fatty acid hydratase from Marinitoga hydrogenitolerans for the highly enantioselective hydration of styrenes to yield chiral 1-arylethanols. While directed evolution for styrene hydration was performed in the presence of heptanoic acid to mimic fatty acid binding, the engineered enzyme displayed remarkable asymmetric styrene hydration activity in the absence of the small molecule activator. The evolved styrene hydratase provided access to chiral alcohols from simple alkenes and water with high enantioselectivity (>99 : 1 e.r.) and could be applied on a preparative scale.

Photobiocatalytic Decarboxylation for the Synthesis of Fatty Epoxides from Renewable Fatty Acids

Fatty epoxides are unique building blocks in organic transformations and materials production; however, their synthetic methodologies are currently not accessible from renewable fatty acids. Herein, a photoenzymatic decarboxylation of epoxy fatty acids into fatty epoxides was demonstrated using fatty acid photodecarboxylase (FAP) from Chlorella variabilis NC64A (CvFAP). Various fatty epoxides were synthesized in excellent selectivity by wild-type CvFAP. The decarboxylation reaction was also achieved with four new FAP homologues, potentially suggesting a broad availability of the biocatalysts for this challenging decarboxylation reaction. By combining CvFAP with lipase and peroxygenase, a multienzymatic cascade to transform oleic acid and its triglyceride into the corresponding fatty epoxides was established. The obtained fatty epoxides were further converted into rather unusual fatty compounds including diol, alcohol, ether, and chain-shortened carboxylic acids. The present photobiocatalytic synthesis of fatty epoxides from natural starting materials excels by its intrinsic selectivity, mild conditions, and independence of nicotinamide cofactors.

Selective Supercritical CO2 Extraction and Biocatalytic Valorization of Cucurbita pepo L. Industrial Residuals

The valorization of biomass residuals constitutes a key aspect of circular economy and thus a major challenge for the scientific community. Among industrial wastes, plant residuals could represent an attractive source of bioactive compounds. In this context, a residue from the industrial extraction of Cucurbita pepo L. seeds, whose oil is commercialized for the treatment of genito-urinary tract pathologies, has been selected. Supercritical CO₂ technology has been employed as a highly selective "green" methodology allowing the recovery of compounds without chemical degradation and limited operational costs. Free fatty acids have been collected in mild conditions while an enrichment in sterols has been selectively obtained from sc-CO₂ extracts by appropriate modulation of process parameters (supercritical fluid pressure and temperature), hence demonstrating the feasibility of the technique to target added-value compounds in a selective way. Obtained fatty acids were thus converted into the corresponding ethanol carboxamide derivatives by lipase-mediated biocatalyzed reactions, while the hydroxylated derivatives of unsaturated fatty acids were obtained by stereoselective hydration reaction under reductive conditions in the presence of a selected FADH₂-dependent oleate hydratase.

Towards an understanding of oleate hydratases and their application in industrial processes

Fatty acid hydratases are unique to microorganisms. Their native function is the oxidation of unsaturated C–C bonds to enable detoxification of environmental toxins. Within this enzyme family, the oleate hydratases (Ohys), which catalyze the hydroxylation of oleic acid to 10-(R)-hydroxy stearic acid (10-HSA) have recently gained particular industrial interest. 10-HSA is considered to be a replacement for 12-(R)-hydroxy stearic acid (12-HSA), which has a broad application in the chemical and pharmaceutical industry. As 12-HSA is obtained through an energy consuming synthesis process, the biotechnological route for sustainable 10-HSA production is of significant industrial interest. All Ohys identified to date have a non-redox active FAD bound in their active site. Ohys can be divided in several subfamilies, that differ in their oligomerization state and the decoration with amino acids in their active sites. The latter observation indicates a different reaction mechanism across those subfamilies. Despite intensive biotechnological, biochemical and structural investigations, surprising little is known about substrate binding and the reaction mechanism of this enzyme family. This review, summarizes our current understanding of Ohys with a focus on sustainable biotransformation.

Functional block copolymer micelles based on poly (jasmine lactone) for improving the loading efficiency of weakly basic drugs

Functionalization of polymers is an attractive approach to introduce specific molecular forces that can enhance drug–polymer interaction to achieve higher drug loading when used as drug delivery systems. The novel amphiphilic block copolymer of methoxy poly(ethylene glycol) and poly(jasmine lactone) i.e., mPEG-b-PJL, derived from renewable jasmine lactone provides free allyl groups on the backbone thus, allowing flexible and facile post-synthesis functionalization. In this study, mPEG-b-PJL and its carboxyl functionalized polymer mPEG-b-PJL-COOH were utilised to explore the effect of ionic interactions on the drug–polymer behaviour. Various drugs with different pK_a values were employed to prepare drug-loaded polymeric micelles (PMs) of mPEG-b-PJL, mPEG-b-PJL-COOH and Soluplus® (polyvinyl caprolactam–polyvinyl acetate–polyethylene glycol graft copolymer) via a nanoprecipitation method. Electrostatic interactions between the COOH pendant on mPEG-b-PJL-COOH and the basic drugs were shown to influence the entrapment efficiency. Additionally, molecular dynamics (MD) simulations were employed to understand the polymer–drug interactions at the molecular level and how polymer functionalization influenced these interactions. The release kinetics of the anti-cancer drug sunitinib from mPEG-b-PJL and mPEG-b-PJL-COOH was assessed, and it demonstrated a sustainable drug release pattern, which depended on both pH and temperature. Furthermore, the cytotoxicity of sunitinib-loaded micelles on cancer cells was evaluated. The drug-loaded micelles exhibited dose-dependent toxicity. Also, haemolysis capacity of these polymers was investigated. In summary, polymer functionalization seems a promising approach to overcome challenges that hinder the application of polymer-based drug delivery systems such as low drug loading degree.

Block copolymer micelles with a functional core have been synthesized and evaluated for their drug delivery capability. High drug loading was observed due to strong ionic interactions, while cytotoxicity of polymers was found to be low.

Semi-rational Engineering of a Promiscuous Fatty Acid Hydratase for Alteration of Regioselectivity

Fatty acid hydratases (FAHs) catalyze regio- and stereo-selective hydration of unsaturated fatty acids to produce hydroxy fatty acids. Fatty acid hydratase-1 (FA-HY1) from Lactobacillus Acidophilus is the most promiscuous and regiodiverse FAH identified so far. Here, we engineered binding site residues of FA-HY1 (S393, S395, S218 and P380) by semi-rational protein engineering to alter regioselectivity. Although it was not possible to obtain a completely new type of regioselectivity with our mutant libraries, a significant shift of regioselectivity was observed towards cis-5, cis-8, cis-11, cis-14, cis-17-eicosapentaenoic acid (EPA). We identified mutants (S393/S395 mutants) with excellent regioselectivity, generating a single hydroxy fatty acid product from EPA (15-OH product), which is advantageous from application perspective. This result is impressive given that wild-type FA-HY1 produces a mixture of 12-OH and 15-OH products at 63 : 37 ratio (12-OH : 15-OH). Moreover, our results indicate that native FA-HY1 is at its limit in terms of promiscuity and regiospecificity, thus it may not be possible to diversify its product portfolio with active site engineering. This behavior of FA-HY1 is unlike its orthologue, fatty acid hydratase-2 (FA-HY2; 58 % sequence identity to FA-HY1), which has been shown earlier to exhibit significant promiscuity and regioselectivity changes by a few active site mutations. Our reverse engineering from FA-HY1 to FA-HY2 further demonstrates this conclusion.

Fatty Acids and their Derivatives as Renewable Platform Molecules for the Chemical Industry

Oils and fats of vegetable and animal origin remain an important renewable feedstock for the chemical industry. Their industrial use has increased during the last 10 years from 31 to 51 million tonnes annually. Remarkable achievements made in the field of oleochemistry in this timeframe are summarized herein, including the reduction of fatty esters to ethers, the selective oxidation and oxidative cleavage of C-C double bonds, the synthesis of alkyl-branched fatty compounds, the isomerizing hydroformylation and alkoxycarbonylation, and olefin metathesis. The use of oleochemicals for the synthesis of a great variety of polymeric materials has increased tremendously, too. In addition to lipases and phospholipases, other enzymes have found their way into biocatalytic oleochemistry. Important achievements have also generated new oil qualities in existing crop plants or by using microorganisms optimized by metabolic engineering.

Oleate Hydratase from Lactobacillus rhamnosus ATCC 53103: A FADH2-Dependent Enzyme with Remarkable Industrial Potential

Recently, we described the preparation of the recombinant oleate hydratase from Lactobacillus rhamnosus ATCC 53103. We observed that the purified C-terminal His-tagged enzyme was completely inactive and the catalytic activity was partially restored only in presence of a large amount of flavin adenine dinucleotide (FAD). In the present work, we assess that this hydratase in the presence of the reduced form of flavin adenine dinucleotide (FADH2) is at least one hundred times as active as in the presence of the same concentration of FAD. By means of two different biochemical processes, we demonstrated unambiguously that oleate hydratase from Lactobacillus rhamnosus ATCC 53103 is a FADH2-dependent enzyme. As a first relevant application of this discovery, we devised a preparative procedure for the stereoselective synthesis of (R)-10-hydroxystearic acid. Accordingly, the hydration of oleic acid (up to 50 g/L) is performed on a multigram scale using the recombinant hydratase and FADH2 generated in situ as cofactor. The produced (R)-10-hydroxystearic acid (ee > 97%) precipitates from the reaction solvent (water/glycerol/ethanol) and is conveniently recovered by simple filtration (>90% yield).

Novel oleate hydratases and potential biotechnological applications

Abstract

Oleate hydratase catalyses the addition of water to the CC double bond of oleic acid to produce (R)-10-hydroxystearic acid. The enzyme requires an FAD cofactor that functions to optimise the active site structure. A wide range of unsaturated fatty acids can be hydrated at the C10 and in some cases the C13 position. The substrate scope can be expanded using ‘decoy’ small carboxylic acids to convert small chain alkenes to secondary alcohols, albeit at low conversion rates. Systematic protein engineering and directed evolution to widen the substrate scope and increase the conversion rate is possible, supported by new high throughput screening assays that have been developed. Multi-enzyme cascades allow the formation of a wide range of products including keto-fatty acids, secondary alcohols, secondary amines and α,ω-dicarboxylic acids.

Key points

• Phylogenetically distinct oleate hydratases may exhibit mechanistic differences.

• Protein engineering to improve productivity and substrate scope is possible.

• Multi-enzymatic cascades greatly widen the product portfolio.

Microbial Synthesis and Evaluation of Fungistatic Activity of 3-Butyl-3-hydroxyphthalide, the Mammalian Metabolite of 3-n-Butylidenephthalide

Phthalides are bioactive compounds that naturally occur in the family Apiaceae. Considering their potentially versatile applications, it is desirable to determine their physical properties, activity and metabolic pathways. This study aimed to examine the utility of whole-cell biocatalysts for obtaining 3-butyl-3-hydroxyphthalide, which is the metabolite formulated during mammalian metabolism of 3-n-butylidenephthalide. We performed transformations using 10 strains of fungi, five of which efficiently produced 3-butyl-3-hydroxyphthalide. The product yield, determined by high-performance liquid chromatography, reached 97.6% when Aspergillus candidus AM 386 was used as the biocatalyst. Increasing the scale of the process resulted in isolation yields of 29–45% after purification via reversed-phase thin layer chromatography, depending on the strain of the microorganism used. We proposed different mechanisms for product formation; however, hydration of 3-n-butylidenephthalide seems to be the most probable. Additionally, all phthalides were tested against clinical strains of Candida albicans using the microdilution method. Two phthalides showed a minimum inhibitory concentration, required to inhibit the growth of 50% of organisms, below 50 µg/mL. The 3-n-butylidenephthalide metabolite was generally inactive, and this feature in combination with its low lipophilicity suggests its involvement in the detoxification pathway. The log P value of tested compounds was in the range of 2.09–3.38.

Ionic liquids for regulating biocatalytic process: Achievements and perspectives

Biocatalysis has found enormous applications in sorts of fields as an alternative to chemical catalysis. In the pursue of green and sustainable chemistry, ionic liquids (ILs) have been considered as promising reaction media for biocatalysis, owing to their unique characteristics, such as nonvolatility, inflammability and tunable properties as regards polarity and water miscibility behavior, compared to organic solvents. In recent years, great developments have been achieved in respects to biocatalysis in ILs, especially for preparing various chemicals. This review tends to give illustrative examples with a focus on representative chemicals production by biocatalyst in ILs and elucidate the possible mechanism in such systems. It also discusses how to regulate the catalytic efficiency from several aspects and finally provides an outlook on the opportunities to broaden biocatalysis in ILs.

Biocatalysis: Enzymatic Synthesis for Industrial Applications

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.

Structure and mechanism of Staphylococcus aureus oleate hydratase (OhyA)

Flavin adenine dinucleotide (FAD)-dependent bacterial oleate hydratases (OhyAs) catalyze the addition of water to isolated fatty acid carbon-carbon double bonds. Staphylococcus aureus uses OhyA to counteract the host innate immune response by inactivating antimicrobial unsaturated fatty acids. Mechanistic information explaining how OhyAs catalyze regiospecific and stereospecific hydration is required to understand their biological functions and the potential for engineering new products. In this study, we deduced the catalytic mechanism of OhyA from multiple structures of S. aureus OhyA in binary and ternary complexes with combinations of ligands along with biochemical analyses of relevant mutants. The substrate-free state shows Arg81 is the gatekeeper that controls fatty acid entrance to the active site. FAD binding engages the catalytic loop to simultaneously rotate Glu82 into its active conformation and Arg81 out of the hydrophobic substrate tunnel, allowing the fatty acid to rotate into the active site. FAD binding also dehydrates the active site, leaving a single water molecule connected to Glu82. This active site water is a hydronium ion based on the analysis of its hydrogen bond network in the OhyA•PEG400•FAD complex. We conclude that OhyA accelerates acid-catalyzed alkene hydration by positioning the fatty acid double bond to attack the active site hydronium ion, followed by the addition of water to the transient carbocation intermediate. Structural transitions within S. aureus OhyA channel oleate to the active site, curl oleate around the substrate water, and stabilize the hydroxylated product to inactivate antimicrobial fatty acids.

Engineering of an oleate hydratase for efficient C10-Functionalization of oleic acid

Oleate hydratase catalyzes the hydration of unsaturated fatty acids, giving access to C₁₀-functionalization of oleic acid. The resultant 10-hydroxystearic acid is a key material for the synthesis of many biomass-derived value-added products. Herein, we report the engineering of an oleate hydratase from Paracoccus aminophilus (PaOH) with significantly improved catalytic efficiency (from 33 s^-1 mM^-1 to 119 s^-1 mM^-1), as well as 3.4 times increased half-life at 30 °C. The structural mechanism regarding the impact of mutations on the improved catalytic activity and thermostability was elucidated with the aid of molecular dynamics simulation. The practical feasibility of the engineered PaOH variant F233L/F122L/T15 N was demonstrated through the pilot synthesis of 10-hydroxystearic acid and 10-oxostearic acid via an optimized multi-enzymatic cascade reaction, with space-time yields of 540 g L^-1 day^-1 and 160 g L^-1 day^-1, respectively.

Polystyrene Biodegradation by Tenebrio molitor Larvae: Identification of Generated Substances Using a GC-MS Untargeted Screening Method

A GC-MS method has been applied to screen and evaluate the generation of chemical compounds during the biodegradation of polystyrene (PS) with Tenebrio molitor larvae. Several resulting compounds have been identified, including trimers 2,4,6-triphenyl-1-hexene and 1,3,5-triphenylcyclohexane, the volatiles acetophenone and cumyl alcohol, and 2,4-di-tert butylphenol, a non-intentionally added substance (NIAS) present in the plastic material. The PS monomers styrene and α-methyl styrene were also identified in the extracts. Bioactive molecules present in the biomass of the studied insects were identified, such as the free fatty acids myristic, palmitic, and oleic acid. Undecanoic acid was also found, but in lower mass fractions. Finally, biochemically formatted amides resulting from their respective fatty acids were identified, namely tetradecanamide, hexadecanamide and oleamide. The formation of all these substances seems to suggest enzymatic and biochemical activity occurring during the biodegradation of PS, and their amounts varied throughout the experience. The overall degradation rate of PS resulted in a 13% rate, which highlights the potential of biorecycling using these insects.

Photobiocatalytic synthesis of chiral secondary fatty alcohols from renewable unsaturated fatty acids

En route to a bio-based chemical industry, the conversion of fatty acids into building blocks is of particular interest. Enzymatic routes, occurring under mild conditions and excelling by intrinsic selectivity, are particularly attractive. Here we report photoenzymatic cascade reactions to transform unsaturated fatty acids into enantiomerically pure secondary fatty alcohols. In a first step the C=C-double bond is stereoselectively hydrated using oleate hydratases from Lactobacillus reuteri or Stenotrophomonas maltophilia. Also, dihydroxylation mediated by the 5,8-diol synthase from Aspergillus nidulans is demonstrated. The second step comprises decarboxylation of the intermediate hydroxy acids by the photoactivated decarboxylase from Chlorella variabilis NC64A. A broad range of (poly)unsaturated fatty acids can be transformed into enantiomerically pure fatty alcohols in a simple one-pot approach.

Natural fatty acids are important starting materials in bio-based chemical production. Here, the authors developed a two-enzyme cascade to produce enantiomerically pure secondary fatty alcohols from natural unsaturated fatty acids in one pot.

Knockout of secondary alcohol dehydrogenase in Nocardia cholesterolicum NRRL 5767 by CRISPR/Cas9 genome editing technology

Nocardia cholesterolicum NRRL 5767 is well-known for its ability to convert oleic acid to 10-hydroxystearic acid (~88%, w/w) and 10-ketostearic acid (~11%, w/w). Conversion of oleic acid to 10-hydroxystearic acid and then to 10-ketostearic acid has been proposed to be catalyzed by oleate hydratase and secondary alcohol dehydrogenase, respectively. Hydroxy fatty acids are value-added with many industrial applications. The objective of this study was to improve the Nocardia cholesterolicum NRRL5767 strain by CRISPR/Cas9 genome editing technology to knockout the secondary alcohol dehydrogenase gene, thus blocking the conversion of 10-hydroxystearic acid to 10-ketostearic acid. The improved strain would produce 10-hydroxystearic acid solely from oleic acid. Such improvement would enhance the production of 10-hydroxystearic acid by eliminating downstream separation of 10-hydroxystearic acid from 10-ketostearic acid. Here, we report: (1) Molecular cloning and characterization of two functional recombinant oleate hydratase isozymes and a functional recombinant secondary alcohol dehydrogenase from Nocardia cholesterolicum NRRL5767. Existence of two oleate hydratase isozymes may explain the high conversion yield of 10-hydroxystearic acid from oleic acid. (2) Construction of a CRISPR/Cas9/sgRNA chimeric plasmid that specifically targeted the secondary alcohol dehydrogenase gene by Golden Gate Assembly. (3) Transformation of the chimeric plasmid into Nocardia cholesterolicum NRRL 5767 by electroporation and screening of secondary alcohol dehydrogenase knockout mutants. Two mutants were validated by their lack of secondary alcohol dehydrogenase activity at the protein level and mutation at the targeted 5’ coding region and the 5’ upstream at the DNA level. The knockout mutants offer improvements by converting added oleic acid to solely 10-hydroxystearic acid, thus eliminating downstream separation of 10-hydroxystearic acid from 10-ketostearic acid. To the best of our knowledge, we report the first successful knockout of a target gene in the Nocardia species using CRISPR/Cas9/sgRNA-mediated genome editing technology.

Fatty Acid Hydratases: Versatile Catalysts to Access Hydroxy Fatty Acids in Efficient Syntheses of Industrial Interest

The utilization of hydroxy fatty acids has gained more and more attention due to its applicability in many industrial building blocks that require it, for example, polymers or fragrances. Furthermore, hydroxy fatty acids are accessible from biorenewables, thus contributing to a more sustainable raw material basis for industrial chemicals. Therefore, a range of investigations were done on fatty acid hydratases (FAHs), since these enzymes catalyze the addition of water to an unsaturated fatty acid, thus providing an elegant route towards hydroxy-substituted fatty acids. Besides the discovery and characterization of fatty acid hydratases (FAHs), the design and optimization of syntheses with these enzymes, the implementation in elaborate cascades, and the improvement of these biocatalysts, by way of mutation in terms of the substrate scope, has been investigated. This mini-review focuses on the research done on process development using fatty acid hydratases as a catalyst. It is notable that biotransformations, running at impressive substrate loadings of up to 280 g L−1, have been realized. A further topic of this mini-review is the implementation of fatty acid hydratases in cascade reactions. In such cascades, fatty acid hydratases were, in particular, combined with alcohol dehydrogenases (ADH), Baeyer-Villiger monooxygenases (BVMO), transaminases (TA) and hydrolases, thus enabling access to a broad variety of molecules that are of industrial interest.

Unexpected NADPH Hydratase Activity in the Nitrile Reductase QueF from Escherichia coli

The nitrile reductase QueF catalyzes NADPH-dependent reduction of the nitrile group of preQ₀ (7-cyano-7-deazaguanine) into the primary amine of preQ₁ (7-aminomethyl-7-deazaguanine), a biologically unique reaction important in bacterial nucleoside biosynthesis. Here we have discovered that the QueF from Escherichia coli-its D197A and E89L variants in particular (apparent k_cat ≈10^-2  min^-1 )-also catalyze the slow hydration of the C5=C6 double bond of the dihydronicotinamide moiety of NADPH. The enzymatically C6-hydrated NADPH is a 3.5:1 mixture of R and S forms and rearranges spontaneously through anomeric epimerization (β→α) and cyclization at the tetrahydronicotinamide C6 and the ribosyl O2. NADH and 1-methyl- or 1-benzyl-1,4-dihydronicotinamide are not substrates of the enzymatic hydration. Mutagenesis results support a QueF hydratase mechanism, in which Cys190-the essential catalytic nucleophile for nitrile reduction-acts as the general acid for protonation at the dihydronicotinamide C5 of NADPH. Thus, the NADPH hydration in the presence of QueF bears mechanistic resemblance to the C=C double bond hydration in natural hydratases.

Lactic acid fermentation enriches the profile of biogenic fatty acid derivatives of avocado fruit (Persea americana Mill.)

This study investigated the capability of selected autochthonous lactic acid bacteria to enrich the portfolio of bioactive compounds of avocado fruit (Persea americana Mill.), with the perspective of producing dietary supplements or pharmaceutical preparations. Fermented avocado puree resulted in high levels of total free amino acids. Fermentation also led to a marked increase of antioxidant activity, with the highest levels found in water and hexane soluble extracts. Bio-converted phenolic compounds and fatty acids derivatives resulting from bacterial metabolism were likely responsible for the increased antioxidant activity. Fermentation caused the fortification of avocado puree with some hydroxy fatty acids, which deserved marked attention due to their health-promoting activities. Oleic and linoleic acids were highly metabolized by Lactobacillus plantarum AVEF17, leading to high levels of mono, di-, and tri-hydroxy-octadecenoic acids.

The Fatty-Acid Hydratase Activity of the Most Common Probiotic Microorganisms

In this work, we studied the biotechnological potential of thirteen probiotic microorganisms currently used to improve human health. We discovered that the majority of the investigated bacteria are able to catalyze the hydration reaction of the unsaturated fatty acids (UFAs). We evaluated their biocatalytic activity toward the three most common vegetable UFAs, namely oleic, linoleic, and linolenic acids. The whole-cell biotransformation experiments were performed using a fatty acid concentration of 3 g/L in anaerobic conditions. Through these means, we assessed that the main part of the investigated strains catalyzed the hydration reaction of UFAs with very high regio- and stereoselectivity. Our biotransformation reactions afforded almost exclusively 10-hydroxy fatty acid derivatives with the single exception of Lactobacillus acidophilus ATCC SD5212, which converted linoleic acid in a mixture of 13-hydroxy and 10-hydroxy derivatives. Oleic, linoleic, and linolenic acids were transformed into (R)-10-hydroxystearic acid, (S)-(12Z)-10-hydroxy-octadecenoic, and (S)-(12Z,15Z)-10-hydroxy-octadecadienoic acids, respectively, usually with very high enantiomeric purity (ee > 95%). It is worth noting that the biocatalytic capabilities of the thirteen investigated strains may change considerably from each other, both in terms of activity, stereoselectivity, and transformation yields. Lactobacillus rhamnosus ATCC 53103 and Lactobacillus plantarum 299 V proved to be the most versatile, being able to efficiently and selectively hydrate all three investigated fatty acids.

Synthesis, and molecular modeling of bis(3-(piperazine-1-yl)propyl)tungstate (BPPT) nanoparticles, and its first catalytic application for one-pot synthesis of 4H-chromene derivatives

A novel, nano-sized, bis(3-(piperazine-1-yl)propyl)tungstate (BPPT) is introduced as an efficient and reusable organometallic catalyst which is considered as a heterogeneous Bronsted-Lowry base and applied successfully for one-pot synthesis of methyl 2-amino-4-aryl substituted-4H-chromene derivatives with good to excellent yields. BPPT has been prepared via a two-step route from natrium tungstate salt. At first, the oxygens of Na₂WO₄ react with 1-bromo-3-chloropropane via nucleophilic substitution to produce bis(3-choloro propyl)tungstate. Then nucleophilic substitution of piperazine with chlorines produced bis(3-(piperazine-1-yl)propyl) tungstate. Bis(3-(piperazine-1-yl)propyl) tungstate, which was called BPPT, characterized by fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermal gravimetric analysis (TGA), transmission electron microscopy (TEM) and scanning electron microscope (SEM). The catalyst is heterogeneous, green and recyclable. It is a thermally stable and its handling is easy. Its catalytic activity is very high and leads to the production of 4H-pyran derivatives with good to excellent yields in short reaction times. Furthermore, molecular modeling studies and ADMETox prediction revealed that not only it can inhibit acetylcholinesterase enzyme and act as an anti-Alzheimer agent but also has no variation from Lipinski's rule of five and can be a good candidate as anti-Alzheimer agents. These above-mentioned facts can be countered as advantages of the current protocol.

Engineering Escherichia coli FAB system using synthetic plant genes for the production of long chain fatty acids

Background

Sustainable production of microbial fatty acids derivatives has the potential to replace petroleum based equivalents in the chemical, cosmetic and pharmaceutical industry. Most fatty acid sources for production oleochemicals are currently plant derived. However, utilization of these crops are associated with land use change and food competition. Microbial oils could be an alternative source of fatty acids, which circumvents the issue with agricultural competition.

Results

In this study, we generated a chimeric microbial production system that features aspects of both prokaryotic and eukaryotic fatty acid biosynthetic pathways targeted towards the generation of long chain fatty acids. We redirected the type-II fatty acid biosynthetic pathway of Escherichia coli BL21 (DE3) strain by incorporating two homologues of the beta-ketoacyl-[acyl carrier protein] synthase I and II from the chloroplastic fatty acid biosynthetic pathway of Arabidopsis thaliana. The microbial clones harboring the heterologous pathway yielded 292 mg/g and 220 mg/g DCW for KAS I and KAS II harboring plasmids respectively. Surprisingly, beta-ketoacyl synthases KASI/II isolated from A. thaliana showed compatibility with the FAB pathway in E. coli.

Conclusion

The efficiency of the heterologous plant enzymes supersedes the overexpression of the native enzyme in the E. coli production system, which leads to cell death in fabF overexpression and fabB deletion mutants. The utilization of our plasmid based system would allow generation of plant like fatty acids in E. coli and their subsequent chemical or enzymatic conversion to high end oleochemical products.

Exploring Castellaniella defragrans Linalool (De)hydratase-Isomerase for Enzymatic Hydration of Alkenes

Acyclic monoterpenes constitute a large and highly abundant class of secondary plant metabolites and are, therefore, attractive low-cost raw materials for the chemical industry. To date, numerous biocatalysts for their transformation are known, giving access to highly sought-after monoterpenoids. In view of the high selectivity associated with many of these reactions, the demand for enzymes generating commercially important target molecules is unabated. Here, linalool (de)hydratase-isomerase (Ldi, EC 4.2.1.127) from Castellaniella defragrans was examined for the regio- and stereoselective hydration of the acyclic monoterpene β-myrcene to (S)-(+)-linalool. Expression of the native enzyme in Escherichia coli allowed for identification of bottlenecks limiting enzyme activity, which were investigated by mutating selected residues implied in enzyme assembly and function. Combining these analyses with the recently published 3D structures of Ldi highlighted the precisely coordinated reduction-oxidation state of two cysteine pairs in correct oligomeric assembly and the catalytic mechanism, respectively. Subcellular targeting studies upon fusion of Ldi to different signal sequences revealed the significance of periplasmic localization of the mature enzyme in the heterologous expression host. This study provides biochemical and mechanistic insight into the hydration of β-myrcene, a nonfunctionalized terpene, and emphasizes its potential for access to scarcely available but commercially interesting tertiary alcohols.

Evolving the Promiscuity of Elizabethkingia meningoseptica Oleate Hydratase for the Regio- and Stereoselective Hydration of Oleic Acid Derivatives

The addition of water to non-activated carbon-carbon double bonds catalyzed by fatty acid hydratases (FAHYs) allows for highly regio- and stereoselective oxyfunctionalization of renewable oil feedstock. So far, the applicability of FAHYs has been limited to free fatty acids, mainly owing to the requirement of a carboxylate function for substrate recognition and binding. Herein, we describe for the first time the hydration of oleic acid (OA) derivatives lacking this free carboxylate by the oleate hydratase from Elizabethkingia meningoseptica (OhyA). Molecular docking of OA to the OhyA 3D-structure and a sequence alignment uncovered conserved amino acid residues at the entrance of the substrate channel as target positions for enzyme engineering. Exchange of selected amino acids gave rise to OhyA variants which showed up to an 18-fold improved conversion of OA derivatives, while retaining the excellent regio- and stereoselectivity in the olefin hydration reaction.

Biosynthesis of Long-Chain ω-Hydroxy Fatty Acids by Engineered Saccharomyces cerevisiae

Long-chain hydroxy fatty acids (HFAs) are rare in nature but have many promising industrial applications. In this study, we developed a biosynthesis method to produce long-chain ω-hydroxy fatty acids. Through disruption of the acyl-CoA synthetases FAA1 and FAA4 and the fatty acyl-CoA oxidase POX1, a Saccharomyces cerevisiae strain was engineered to accumulate free fatty acids (FFAs). Subsequently, the cytochrome P450 monooxygenase CYP52M1 from Starmerella bombicola was introduced to convert FFAs to HFAs, leading to the production of C16 and C18 HFAs at the ω or ω-1 positions. Next, CYP52M1 was reconstituted with the homologous reductase S. bombicola CPR and the heterologous reductase Arabidopsis thaliana cytochrome P450 reductase. The results showed that the CYP52M1-AtCPR1 system significantly increased the hydroxylation in FFA. Moreover, a self-sufficient P450 enzyme system was constructed to achieve higher transformation efficiency. Finally, fed-batch fermentation yielded as much as 347 ± 9.2 mg/L ω-HFAs.

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.