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

Cavity-Based Discovery of New Fatty Acid Photodecarboxylases

Light-dependent fatty acid photodecarboxylases (FAPs) hold significant potential for biotechnology, due to their capability to produce alka(e)nes directly from the corresponding (un)saturated natural fatty acids requiring light as the only reagent. This study expands the family of FAPs through cavity-based enzyme discovery methods. Thirty enzyme candidates with potential photodecarboxylation activity were identified by matching the cavities of four related template structures against the Protein Data Bank's flavoproteins, a library of proteins identified via the Foldseek Search Server, and homology models of sequences resulting from BLAST. Subsequent docking experiments narrowed this library to ten promising enzymes, which were expressed and assessed in vitro, identifying four photodecarboxylases. Out of these enzymes, the GMC oxidoreductase from Coccomyxa sp. Obi (CoFAP) was characterized in detail, which revealed high activity in the decarboxylation reactions of palmitic acid and octanoic acid and a broad pH tolerance (pH 6.5-9.5).

Decarboxylation in Natural Products Biosynthesis

Decarboxylation reactions are frequently found in the biosynthesis of primary and secondary metabolites. Decarboxylase enzymes responsible for these transformations operate via diverse mechanisms and act on a large variety of substrates, making them appealing in terms of biotechnological applications. This Perspective focuses on the occurrence of decarboxylation reactions in natural product biosynthesis and provides a perspective on their applications in biocatalysis for fine chemicals and pharmaceuticals.

Enhanced Photobiocatalytic Cascades at Pickering Droplet Interfaces

Developing new methods to engineer photobiocatalytic reactions is of utmost significance for artificial photosynthesis, but it remains a grand challenge due to the intrinsic incompatibility of biocatalysts with photocatalysts. In this work, photocatalysts and enzymes were spatially colocalized at Pickering droplet interfaces, where the reaction microenvironment and the spatial distance between two distinct catalysts were exquisitely regulated to achieve unprecedented photobiocatalytic cascade reactions. As proof of the concept, ultrathin graphitic carbon nitride nanosheets loaded with Au nanoparticles were precisely positioned in the outer interfacial layer of Pickering oil droplets to produce H2O2 under light irradiation, while enzymes were exactly placed in the inner interfacial layer to catalyze the subsequent biocatalytic oxidation reactions using in situ formed H2O2 as an oxidant. In the alkene epoxidation and thioether oxidation, our interfacial photobiocatalytic cascades showed a 2.0-5.8-fold higher overall reaction efficiency than the photobiocatalytic cascades in the bulk water phase. It was demonstrated that spatial localization of the photocatalyst and the enzyme at Pickering oil droplet interfaces not only provided their respective preferable reaction environments and intimate proximity for rapid H2O2 transport but also protected the enzyme from oxidative inactivation caused by the photogenerated species. These remarkable interfacial effects contributed to the significantly enhanced photobiocatalytic cascading efficiency. Our work presents an innovative photobiocatalytic reaction system with manifold benefits, providing a cutting-edge platform for solar-driven chemical transformations via photobiocatalysis.

Stereodivergent Protein Engineering of Fatty Acid Photodecarboxylase for Light-Driven Kinetic Resolution of Sec-Alcohol Oxalates

Stereodivergent engineering of one enzyme to create stereocomplementary variants for synthesizing optically pure molecules with tailor-made (R) or (S) configurations on an optional basis is highly desirable and challenging. This study aimed to engineer fatty acid photodecarboxylase from Chlorella variabilis (CvFAP) using the focused rational iterative site-specific mutagenesis (FRISM) strategy to obtain two highly stereocomplementary variants with excellent selectivity (both giving products with up to 99 % e.e.). These variants were used for the CvFAP-catalyzed light-driven kinetic resolution of oxalates or oxamic acids prepared from the corresponding sec-alcohols or amines, providing a new biotransformation process for preparing chiral sec-alcohols and amines. Molecular dynamics simulation, kinetic data and transient spectra revealed the source of selectivity. This study represents the first example of the kinetic resolution of sec-alcohols or amines catalyzed by a pair of stereocomplementary CvFAPs.

Production of Biobased Ethylbenzene by Cascade Biocatalysis with an Engineered Photodecarboxylase

Production of commodity chemicals, such as benzene, toluene, ethylbenzene, and xylenes (BTEX), from renewable resources is key for a sustainable society. Biocatalysis enables one-pot multistep transformation of bioresources under mild conditions, yet it is often limited to biochemicals. Herein, we developed a non-natural three-enzyme cascade for one-pot conversion of biobased l-phenylalanine into ethylbenzene. The key rate-limiting photodecarboxylase was subjected to structure-guided semirational engineering, and a triple mutant CvFAP(Y466T/P460A/G462I) was obtained with a 6.3-fold higher productivity. With this improved photodecarboxylase, an optimized two-cell sequential process was developed to convert l-phenylalanine into ethylbenzene with 82 % conversion. The cascade reaction was integrated with fermentation to achieve the one-pot bioproduction of ethylbenzene from biobased glycerol, demonstrating the potential of cascade biocatalysis plus enzyme engineering for the production of biobased commodity chemicals.

A light-driven enzymatic enantioselective radical acylation

Enzymes are recognized as exceptional catalysts for achieving high stereoselectivities1-3, but their ability to control the reactivity and stereoinduction of free radicals lags behind that of chemical catalysts4. Thiamine diphosphate (ThDP)-dependent enzymes5 are well-characterized systems that inspired the development of N-heterocyclic carbenes (NHCs)6-8 but have not yet been proved viable in asymmetric radical transformations. There is a lack of a biocompatible and general radical-generation mechanism, as nature prefers to avoid radicals that may be harmful to biological systems9. Here we repurpose a ThDP-dependent lyase as a stereoselective radical acyl transferase (RAT) through protein engineering and combination with organophotoredox catalysis10. Enzyme-bound ThDP-derived ketyl radicals are selectively generated through single-electron oxidation by a photoexcited organic dye and then cross-coupled with prochiral alkyl radicals with high enantioselectivity. Diverse chiral ketones are prepared from aldehydes and redox-active esters (35 examples, up to 97% enantiomeric excess (e.e.)) by this method. Mechanistic studies reveal that this previously elusive dual-enzyme catalysis/photocatalysis directs radicals with the unique ThDP cofactor and evolvable active site. This work not only expands the repertoire of biocatalysis but also provides a unique strategy for controlling radicals with enzymes, complementing existing chemical tools.

Enzymatic Photodecarboxylation on Secondary and Tertiary Carboxylic Acids

Photoenzymatic decarboxylation of bulky secondary and tertiary carboxylic acids catalyzed by engineered Chlorella variabilis fatty acid photodecarboxylase (CvFAP) is reported. Rational design and directed evolution of wild-type CvFAP are used to improve the reactivity and expand potential applications. Moreover, engineered CvFAP can catalyze light-driven kinetic resolution of α-substituted carboxylic acid. Our work sheds light on the production of chiral building blocks and bioactive molecules from bulky carboxylic acids via the photoenzymatic way.

From nature to industry: Harnessing enzymes for biocatalysis

Biocatalysis harnesses enzymes to make valuable products. This green technology is used in countless applications from bench scale to industrial production and allows practitioners to access complex organic molecules, often with fewer synthetic steps and reduced waste. The last decade has seen an explosion in the development of experimental and computational tools to tailor enzymatic properties, equipping enzyme engineers with the ability to create biocatalysts that perform reactions not present in nature. By using (chemo)-enzymatic synthesis routes or orchestrating intricate enzyme cascades, scientists can synthesize elaborate targets ranging from DNA and complex pharmaceuticals to starch made in vitro from CO2-derived methanol. In addition, new chemistries have emerged through the combination of biocatalysis with transition metal catalysis, photocatalysis, and electrocatalysis. This review highlights recent key developments, identifies current limitations, and provides a future prospect for this rapidly developing technology.

Photoenzymatic Decarboxylation to Produce Hydrocarbon Fuels: A Critical Review

Photoenzymatic decarboxylation shows great promise as a pathway for the generation of hydrocarbon fuels. CvFAP, which is derived from Chlorella variabilis NC64A, is a photodecarboxylase capable of converting fatty acids into hydrocarbons. CvFAP is an example of coupling biocatalysis and photocatalysis to produce alkanes. The catalytic process is mild, and it does not yield toxic substances or excess by-products. However, the activity of CvFAP can be readily inhibited by several factors, and further enhancement is required to improve the enzyme yield and stability. In this article, we will examine the latest advancements in CvFAP research, with a particular focus on the enzyme's structural and catalytic mechanism, summarized some limitations in the application of CvFAP, and laboratory-level methods for enhancing enzyme activity and stability. This review can serve as a reference for future large-scale industrial production of hydrocarbon fuels.

Photobiocatalytic Strategies for Organic Synthesis

Biocatalysis has revolutionized chemical synthesis, providing sustainable methods for preparing various organic molecules. In enzyme-mediated organic synthesis, most reactions involve molecules operating from their ground states. Over the past 25 years, there has been an increased interest in enzymatic processes that utilize electronically excited states accessed through photoexcitation. These photobiocatalytic processes involve a diverse array of reaction mechanisms that are complementary to one another. This comprehensive review will describe the state-of-the-art strategies in photobiocatalysis for organic synthesis until December 2022. Apart from reviewing the relevant literature, a central goal of this review is to delineate the mechanistic differences between the general strategies employed in the field. We will organize this review based on the relationship between the photochemical step and the enzymatic transformations. The review will include mechanistic studies, substrate scopes, and protein optimization strategies. By clearly defining mechanistically-distinct strategies in photobiocatalytic chemistry, we hope to illuminate future synthetic opportunities in the area.

Green light enhanced the photostability and catalytic performance of fatty acid photodecarboxylase

Green light was documented to improve the photostability of fatty acid photodecarboxylase from Chlorella variabilis (CvFAP). Compared to blue light, green light increased the pentadecane yield by 27.6% and improved the residual activity of CvFAP to 5.9-fold after the preillumination. Kinetics and thermodynamics indicated that blue light facilitated a high CvFAP activity.

Autocatalytic effect boosts the production of medium-chain hydrocarbons by fatty acid photodecarboxylase

Ongoing climate change is driving the search for renewable and carbon-neutral alternatives to fossil fuels. Photocatalytic conversion of fatty acids to hydrocarbons by fatty acid photodecarboxylase (FAP) represents a promising route to green fuels. However, the alleged low activity of FAP on C2 to C12 fatty acids seemed to preclude the use for synthesis of gasoline-range hydrocarbons. Here, we reveal that Chlorella variabilis FAP (CvFAP) can convert n-octanoic acid in vitro four times faster than n-hexadecanoic acid, its best substrate reported to date. In vivo, this translates into a CvFAP-based production rate over 10-fold higher for n-heptane than for n-pentadecane. Time-resolved spectroscopy and molecular modeling demonstrate that CvFAP's high catalytic activity on n-octanoic acid is, in part, due to an autocatalytic effect of its n-heptane product, which fills the rest of the binding pocket. These results represent an important step toward a bio-based and light-driven production of gasoline-like hydrocarbons.

Ultrafast Dynamics of Fatty Acid Photodecarboxylase in Anionic Semiquinone State

Fatty acid photodecarboxylase is a newly identified blue-light driven photoenzyme that catalyzes decarboxylation of fatty acids. The catalytic reaction involves a transient anionic semiquinone of flavin cofactor (FAD^•-) as an intermediate, but photochemical properties of this anionic radical are largely unknown. Here, we have anaerobically produced the wild-type FAP in the FAD^•- state and conducted femtosecond-resolved fluorescence and absorption measurements. We have observed the multiphasic deactivation dynamics of excited states on multiple time scales from a few picoseconds even to a few nanoseconds through conical intersections between various electronic states. Interestingly, the nanosecond components can only be observed from higher electronic excited states. Our results show the complexity of the energy landscapes of various excited states and rule out the occurrence of electron or proton transfer with nearby residue(s) in the active site.

Strategies for Transferring Photobiocatalysis to Continuous Flow Exemplified by Photodecarboxylation of Fatty Acids

The challenges of light-dependent biocatalytic transformations of lipophilic substrates in aqueous media are manifold. For instance, photolability of the catalyst as well as insufficient light penetration into the reaction vessel may be further exacerbated by a heterogeneously dispersed substrate. Light penetration may be addressed by performing the reaction in continuous flow, which allows two modes of applying the catalyst: (i) heterogeneously, immobilized on a carrier, which requires light-permeable supports, or (ii) homogeneously, dissolved in the reaction mixture. Taking the light-dependent photodecarboxylation of palmitic acid catalyzed by fatty-acid photodecarboxylase from Chlorella variabilis (CvFAP) as a showcase, strategies for the transfer of a photoenzyme-catalyzed reaction into continuous flow were identified. A range of different supports were evaluated for the immobilization of CvFAP, whereby Eupergit C250 L was the carrier of choice. As the photostability of the catalyst was a limiting factor, a homogeneous system was preferred instead of employing the heterogenized enzyme. This implied that photolabile enzymes may preferably be applied in solution if repair mechanisms cannot be provided. Furthermore, when comparing different wavelengths and light intensities, extinction coefficients may be considered to ensure comparable absorption at each wavelength. Employing homogeneous conditions in the CvFAP-catalyzed photodecarboxylation of palmitic acid afforded a space-time yield unsurpassed by any reported batch process (5.7 g·L-1·h-1, 26.9 mmol·L-1·h-1) for this reaction, demonstrating the advantage of continuous flow in attaining higher productivity of photobiocatalytic processes.

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.

Valorization of Soy Lecithin by Enzyme Cascade Reactions Including a Phospholipase A2, a Fatty Acid Double-Bond Hydratase, and/or a Photoactivated Decarboxylase

A huge amount of phospholipids or lecithin is produced as a byproduct in the vegetable oil industry. However, most are just used as a feed additive. This study has focused on enzymatic valorization of lecithin. This was exploited by enzymatic transformation of soy lecithin into lysolecithin liposomes, including functional free fatty acids, hydroxy fatty acids, hydrocarbons, or secondary fatty alcohols. One of the representative examples was the preparation of lysolecithin liposomes containing secondary fatty alcohols [e.g., 9-Hydroxyheptadec-11-ene (9) and 9-heptadecanol (10)] by using a phospholipase A2 from Streptomyces violaceoruber, a fatty acid double-bond hydratase from Stenotrophomonas maltophilia, and a photoactivated decarboxylase from Chlorella variabilis NC64A. The engineered liposomes turned out to range ca. 144 nm in diameter by dynamic light scattering analysis. Thereby, this study will contribute to application of functional fatty acids and their derivatives as well as valorization of lecithin for the food and cosmetic industries.

Triplet-triplet annihilation-based photon-upconversion to broaden the wavelength spectrum for photobiocatalysis

Photobiocatalysis is a growing field of biocatalysis. Especially light-driven enzyme catalysis has contributed significantly to expanding the scope of synthetic organic chemistry. However, photoenzymes usually utilise a rather narrow wavelength range of visible (sun)light. Triplet-triplet annihilation-based upconversion (TTA-UC) of long wavelength light to shorter wavelength light may broaden the wavelength range. To demonstrate the feasibility of light upconversion we prepared TTA-UC poly(styrene) (PS) nanoparticles doped with platinum(II) octaethylporphyrin (PtOEP) photosensitizer and 9,10-diphenylanthracene (DPA) annihilator (PtOEP:DPA@PS) for application in aqueous solutions. Photoexcitation of PtOEP:DPA@PS nanoparticles with 550 nm light led to upconverted emission of DPA 418 nm. The TTA-UC emission could photoactivate flavin-dependent photodecarboxylases with a high energy transfer efficiency. This allowed the photodecarboxylase from Chlorella variabilis NC64A to catalyse the decarboxylation of fatty acids into long chain secondary alcohols under green light (λ = 550 nm).

Enzyme-photo-coupled catalytic systems

Efficient chemical transformation in a green, low-carbon way is crucial for the sustainable development of modern society. Enzyme-photo-coupled catalytic systems (EPCS) that integrate the exceptional selectivity of enzyme catalysis and the unique reactivity of photocatalysis hold great promise in solar-driven 'molecular editing'. However, the involvement of multiple components and catalytic processes challenged the design of efficient and stable EPCS. To show a clear picture of the complex catalytic system, in this review, we analyze EPCS from the perspective of system engineering. First, we disintegrate the complex system into four elementary components, and reorganize these components into biocatalytic and photocatalytic ensembles (BE and PE). By resolving current accessible systems, we identify that connectivity and compatibility between BE and PE are two crucial factors that govern the performance of EPCS. Then, we discuss the origin of undesirable connectivity and low compatibility, and deduce the possible solutions. Based on these understandings, we propose the designing principles of EPCS. Lastly, we provide a future perspective of EPCS.

Fatty Acid Photodecarboxylase Is an Interfacial Enzyme That Binds to Lipid-Water Interfaces to Access Its Insoluble Substrate

Fatty acid photodecarboxylase (FAP), one of the few natural photoenzymes characterized so far, is a promising biocatalyst for lipid-to-hydrocarbon conversion using light. However, the optimum supramolecular organization under which the fatty acid (FA) substrate should be presented to FAP has not been addressed. Using palmitic acid embedded in phospholipid liposomes, phospholipid-stabilized microemulsions, and mixed micelles, we show that FAP displays a preference for FAs present in liposomes and at the surface of microemulsions. The kinetics of adsorption onto phospholipid and galactolipid monomolecular films further suggests the ability of FAP to bind to and penetrate into membranes, with a higher affinity in the presence of FAs. The FAP structure reveals a potential interfacial recognition site with clusters of hydrophobic and basic residues surrounding the active site entrance. The resulting dipolar moment suggests the orientation of FAP at negatively charged interfaces. These findings provide important clues about the mode of action of FAP and the development of FAP-based bioconversion processes.

Recent advances in (chemo)enzymatic cascades for upgrading bio-based resources

Developing (chemo)enzymatic cascades is very attractive for green synthesis, because they streamline multistep synthetic processes. In this Feature Article, we have summarized the recent advances in in vitro or whole-cell cascade reactions with a focus on the use of renewable bio-based resources as starting materials. This includes the synthesis of rare sugars (such as ketoses, L-ribulose, D-tagatose, myo-inositol or aminosugars) from readily available carbohydrate sources (cellulose, hemi-cellulose, starch), in vitro enzyme pathways to convert glucose to various biochemicals, cascades to convert 5-hydroxymethylfurfural and furfural obtained from lignin or xylose into novel precursors for polymer synthesis, the syntheses of phenolic compounds, cascade syntheses of aliphatic and highly reduced chemicals from plant oils and fatty acids, upgrading of glycerol or ethanol as well as cascades to transform natural L-amino acids into high-value (chiral) compounds. In several examples these processes have demonstrated their efficiency with respect to high space-time yields and low E-factors enabling mature green chemistry processes. Also, the strengths and limitations are discussed and an outlook is provided for improving the existing and developing new cascades.

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.

Stabilisation of the Fatty Acid Decarboxylase from Chlorella variabilis by Caprylic Acid

The fatty acid photodecarboxylase from Chlorella variabilis NC64 A (CvFAP) catalyses the light-dependent decarboxylation of fatty acids. Photoinactivation of CvFAP still represents one of the major limitations of this interesting enzyme en route to practical application. In this study we demonstrate that the photostability of CvFAP can easily be improved by the administration of medium-chain length carboxylic acids such as caprylic acid indicating that the best way of maintaining CvFAP stability is 'to keep the enzyme busy'.

Light-Driven Enzymatic Decarboxylation of Dicarboxylic Acids

Photodecarboxylase from Chlorella variabillis (CvFAP) is one of the three known light-activated enzymes that catalyzes the decarboxylation of fatty acids into the corresponding C1-shortened alkanes. Although the substrate scope of CvFAP has been altered by protein engineering and decoy molecules, it is still limited to mono-fatty acids. Our studies demonstrate for the first time that long chain dicarboxylic acids can be converted by CvFAP. Notably, the conversion of dicarboxylic acids to alkanes still represents a chemically very challenging reaction. Herein, the light-driven enzymatic decarboxylation of dicarboxylic acids to the corresponding (C2-shortened) alkanes using CvFAP is described. A series of dicarboxylic acids is decarboxylated into alkanes in good yields by means of this approach, even for the preparative scales. Reaction pathway studies show that mono-fatty acids are formed as the intermediate products before the final release of C2-shortened alkanes. In addition, the thermostability, storage stability, and recyclability of CvFAP for decarboxylation of dicarboxylic acids are well evaluated. These results represent an advancement over the current state-of-the-art.

Light-Driven Catalytic Regulation of Enzymes at the Interface with Plasmonic Nanomaterials

Regulation of enzymes is highly relevant toward orchestrating cell-free and stepwise biotransformations, thereby maximizing their overall performance. Plasmonic nanomaterials offer a great opportunity to tune the functionality of enzymes through their remarkable optical properties. Localized surface plasmon resonances (LSPR) can be used to modify chemical transformations at the nanomaterial's surface, upon light irradiation. Incident light can promote energetic processes, which may be related to an increase of local temperature (photothermal effects) but also to effects triggered by generated hotspots or hot electrons (photoelectronic effects). As a consequence, light irradiation of the protein-nanomaterial interface affects enzyme functionality. To harness these effects to finely and remotely regulate enzyme activity, the physicochemical features of the nanomaterial, properties of the incident light, and parameters governing molecular interactions must be optimized. In this Perspective, we discuss relevant examples that illustrate the use of plasmonic nanoparticles to control enzyme function through LSPR excitation. Finally, we also highlight the importance of expanding the use of plasmonic nanomaterials to the immobilization of multienzyme systems for light-driven regulation of cell-free biosynthetic pathways. Although this concept is living its infancy, we encourage the scientific community to advance in the development of novel light-controlled biocatalytic plasmonic nanoconjugates and explore their application in biosensing, applied biocatalysis, and biomedicine.

Intensification of Photobiocatalytic Decarboxylation of Fatty Acids for the Production of Biodiesel

Light-driven biocatalytic processes are notoriously hampered by poor penetration of light into the turbid reaction media. In this study, wirelessly powered light-emitting diodes are found to represent an efficient and scalable approach for process intensification of the photobiosynthetic production of diesel alkanes from renewable fatty acids.

Production of Bio-alkanes from Biomass and CO2

Bioelectrochemical technologies such as electro-fermentation and microbial CO₂ electrosynthesis are emerging interdisciplinary technologies that can produce renewable fuels and chemicals (such as carboxylic acids). The benefits of electrically driven bioprocesses include improved production rate, selectivity, and carbon conversion efficiency. However, the accumulation of products can lead to inhibition of biocatalysts, necessitating further effort in separating products. The recent discovery of a new photoenzyme, capable of converting carboxylic acids to bio-alkanes, has offered an opportunity for system integration, providing a promising approach for simultaneous product separation and valorisation. Combining the strengths of photo/bio/electrochemical catalysis, we discuss an innovative circular cascading system that converts biomass and CO₂ to value-added bio-alkanes (C_nH_2n+2, n = 2 to 5) whilst achieving carbon circularity.

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.

The rise of continuous flow biocatalysis – fundamentals, very recent developments and future perspectives

Very recent developments in the field of biocatalysis in continuously operated systems. Special attention on the future perspectives in this key emerging technological area ranging from process analytical technologies to digitalization.