Engineering new catalytic activities in enzymes

Directed evolution of enzymatic silicon-carbon bond cleavage in siloxanes

Volatile methylsiloxanes (VMS) are man-made, nonbiodegradable chemicals produced at a megaton-per-year scale, which leads to concern over their potential for environmental persistence, long-range transport, and bioaccumulation. We used directed evolution to engineer a variant of bacterial cytochrome P450BM3 to break silicon-carbon bonds in linear and cyclic VMS. To accomplish silicon-carbon bond cleavage, the enzyme catalyzes two tandem oxidations of a siloxane methyl group, which is followed by putative [1,2]-Brook rearrangement and hydrolysis. Discovery of this so-called siloxane oxidase opens possibilities for the eventual biodegradation of VMS.

Novel applications of photobiocatalysts in chemical transformations

Photocatalysis has proven to be an effective approach for the production of reactive intermediates under moderate reaction conditions. The possibility for the green synthesis of high-value compounds using the synergy of photocatalysis and biocatalysis, benefiting from the selectivity of enzymes and the reactivity of photocatalysts, has drawn growing interest. Mechanistic investigations, substrate analyses, and photobiocatalytic chemical transformations will all be incorporated in this review. We seek to shed light on upcoming synthetic opportunities in the field by precisely describing mechanistically unique techniques in photobiocatalytic chemistry.

Therapeutic and Diagnostic Agents based on Bioactive Endogenous and Exogenous Coordination Compounds

Metal-based coordination compounds have very special place in bioinorganic chemistry because of their different structural arrangements and significant application in medicine. Rapid progress in this field increasingly enables the targeted design and synthesis of metal-based pharmaceutical agents that fulfill valuable roles as diagnostic or therapeutic agents. Various coordination compounds have important biological functions, both those initially present in the body (endogenous) and those entering the organisms from the external environment (exogenous): vitamins, drugs, toxic substances, etc. In the therapeutic and diagnostic practice, both the essential for all living organisms and the trace metals are used in metal-containing coordination compounds. In the current review, the most important functional biologically active compounds were classified group by group according to the position of the elements in the periodic table.

How Axial Coordination Regulates the Electronic Structure and C-H Amination Reactivity of Fe-Porphyrin-Nitrene?

Detailed electronic structure and its correlation with the intramolecular C-H amination reactivity of Fe-porphyrin-nitrene intermediates bearing different "axial" coordination have been investigated using multiconfigurational complete active space self-consistent field (CASSCF), N-electron valence perturbation theory (NEVPT2), and hybrid density functional theory (DFT-B3LYP) calculations. Three types of "axial" coordination, -OMe/-O(H)Me (1-Sul/2-Sul), -SMe/-S(H)Me (3-Sul/4-Sul), and -NMeIm (MeIm = 3-methyl-imidazole) (5-Sul) mimicking serine, cysteine, and histidine, respectively, along with no axial coordination (6-Sul) have been considered to decipher how the "axial" coordination of different strengths regulates the electronic integrity of the Fe-N core and nitrene-transfer reactivity of Fe-porphyrin-nitrene intermediates. CASSCF-based natural orbitals reveal two distinct classes of electronic structures: Fe-nitrenes (1-Sul and 3-Sul) with relatively stronger axial coordination (-OMe and -SMe) display "imidyl" nature and those (2-Sul, 4-Sul, and 6-Sul) with weaker axial coordination (-O(H)Me, -S(H)Me and no axial coordination) exhibit "imido-like" character. A borderline between the two classes is also observed with NMeIm axial coordination (5-Sul). Axial coordination of different strengths not only regulates the electronic structure but also modulates the Fe-3d orbital energies, as revealed through the d-d transition energies obtained by CASSCF/NEVPT2 calculations. The relatively lower energy of Fe-3dz2 orbital allows easy access to low-lying high-spin quintet states in the cases of weaker "axial" coordination (2-Sul, 4-Sul, and 6-Sul), and the associated hydrogen atom transfer (HAT) reactivity appears to involve two-state triplet-quintet reactivity through minimum energy crossing point (3,5MECP) between the spin states. In stark contrast, Fe-nitrenes with relatively stronger "axial" coordination (1-Sul and 3-Sul) undergo triplet-only HAT reactivity. Overall, this in-depth electronic structure investigation and HAT reactivity evaluation reveal that the weaker axial coordination in Fe-porphyrin-nitrene complexes (2-Sul, 4-Sul, and 6-Sul) can promote more efficient C-H oxidation through the quintet spin state.

Engineering Enzymes for Environmental Sustainability

The development and implementation of sustainable catalytic technologies is key to delivering our net-zero targets. Here we review how engineered enzymes, with a focus on those developed using directed evolution, can be deployed to improve the sustainability of numerous processes and help to conserve our environment. Efficient and robust biocatalysts have been engineered to capture carbon dioxide (CO2) and have been embedded into new efficient metabolic CO2 fixation pathways. Enzymes have been refined for bioremediation, enhancing their ability to degrade toxic and harmful pollutants. Biocatalytic recycling is gaining momentum, with engineered cutinases and PETases developed for the depolymerization of the abundant plastic, polyethylene terephthalate (PET). Finally, biocatalytic approaches for accessing petroleum-based feedstocks and chemicals are expanding, using optimized enzymes to convert plant biomass into biofuels or other high value products. Through these examples, we hope to illustrate how enzyme engineering and biocatalysis can contribute to the development of cleaner and more efficient chemical industry.

Engineering Enzymes for Environmental Sustainability

The development and implementation of sustainable catalytic technologies is key to delivering our net-zero targets. Here we review how engineered enzymes, with a focus on those developed using directed evolution, can be deployed to improve the sustainability of numerous processes and help to conserve our environment. Efficient and robust biocatalysts have been engineered to capture carbon dioxide (CO2 ) and have been embedded into new efficient metabolic CO2 fixation pathways. Enzymes have been refined for bioremediation, enhancing their ability to degrade toxic and harmful pollutants. Biocatalytic recycling is gaining momentum, with engineered cutinases and PETases developed for the depolymerization of the abundant plastic, polyethylene terephthalate (PET). Finally, biocatalytic approaches for accessing petroleum-based feedstocks and chemicals are expanding, using optimized enzymes to convert plant biomass into biofuels or other high value products. Through these examples, we hope to illustrate how enzyme engineering and biocatalysis can contribute to the development of cleaner and more efficient chemical industry.

Non-native Intramolecular Radical Cyclization Catalyzed by a B12 -Dependent Enzyme

Despite the unique reactivity of vitamin B12 and its derivatives, B12 -dependent enzymes remain underutilized in biocatalysis. In this study, we repurposed the B12 -dependent transcription factor CarH to enable non-native radical cyclization reactions. An engineered variant of this enzyme, CarH*, catalyzes the formation γ- and δ-lactams through either redox-neutral or reductive ring closure with marked enhancement of reactivity and selectivity relative to the free B12 cofactor. CarH* also catalyzes an unusual spirocyclization by dearomatization of pendant arenes to produce bicyclic 1,3-diene products instead of 1,4-dienes provided by existing methods. These results and associated mechanistic studies highlight the importance of protein scaffolds for controlling the reactivity of B12 and expanding the synthetic utility of B12 -dependent enzymes.

Photoenzymatic Enantioselective Synthesis of Oxygen-Containing Benzo-Fused Heterocycles

New-to-nature biocatalysis in organic synthesis has recently emerged as a green and powerful strategy for the preparation of valuable chiral products, among which chiral oxygen-containing benzo-fused heterocycles are important structural motifs in pharmaceutical industry. However, the asymmetric synthesis of these compounds through radical-mediated methods is challenging. Herein, a novel asymmetric radical-mediated photoenzymatic synthesis strategy is developed to realize the efficient enantioselective synthesis of oxygen-containing benzo-fused heterocycles through structure-guided engineering of a flavin-dependent 'ene'-reductase GluER. It shows that variant GluER-W100H could efficiently produce various benzoxepinones, chromanone and indanone with different benzo-fused rings in high yields with great stereoselectivities under visible light. Moreover, these results are well supported by mechanistic experiments, revealing that this photoenzymatic process involves electron donor-acceptor complex formation, single electron transfer and hydrogen atom transfer. Therefore, we provide an alternative green approach for efficient chemoenzymatic synthesis of important chiral skeletons of bioactive pharmaceuticals.

A Co(TAML)-based artificial metalloenzyme for asymmetric radical-type oxygen atom transfer catalysis

We show that the incorporation of a biotinylated Co(TAML) cofactor within streptavidin enables asymmetric radical-type oxygen atom transfer catalysis with improved activity and enantioselectivity.

Toward three-dimensional DNA industrial nanorobots

Nanoscale industrial robots have potential as manufacturing platforms and are capable of automatically performing repetitive tasks to handle and produce nanomaterials with consistent precision and accuracy. We demonstrate a DNA industrial nanorobot that fabricates a three-dimensional (3D), optically active chiral structure from optically inactive parts. By making use of externally controlled temperature and ultraviolet (UV) light, our programmable robot, ~100 nanometers in size, grabs different parts, positions and aligns them so that they can be welded, releases the construct, and returns to its original configuration ready for its next operation. Our robot can also self-replicate its 3D structure and functions, surpassing single-step templating (restricted to two dimensions) by using folding to access the third dimension and more degrees of freedom. Our introduction of multiple-axis precise folding and positioning as a tool/technology for nanomanufacturing will open the door to more complex and useful nano- and microdevices.

Design and engineering of artificial biosynthetic pathways-where do we stand and where do we go?

The production of commodity and specialty chemicals relies heavily on fossil fuels. The negative impact of this dependency on our environment and climate has spurred a rising demand for more sustainable methods to obtain such chemicals from renewable resources. Herein, biotransformations of these renewable resources facilitated by enzymes or (micro)organisms have gained significant attention, since they can occur under mild conditions and reduce waste. These biotransformations typically leverage natural metabolic processes, which limits the scope and production capacity of such processes. In this mini-review, we provide an overview of advancements made in the past 5 years to expand the repertoire of biotransformations in engineered microorganisms. This ranges from redesign of existing pathways driven by retrobiosynthesis and computational design to directed evolution of enzymes and de novo pathway design to unlock novel routes for the synthesis of desired chemicals. We highlight notable examples of pathway designs for the production of commodity and specialty chemicals, showcasing the potential of these approaches. Lastly, we provide an outlook on future pathway design approaches.

Evidence of a Distinctive Enantioselective Binding Mode for the Photoinduced Radical Cyclization of α-Chloroamides in Ene-Reductases

We demonstrate here through molecular simulations and mutational studies the origin of the enantioselectivity in the photoinduced radical cyclization of α-chloroacetamides catalyzed by ene-reductases, in particular the Gluconobacter oxidans ene-reductase and the Old Yellow Enzyme 1, which show opposite enantioselectivity. Our results reveal that neither the π-facial selectivity model nor a protein-induced selective stabilization of the transition states is able to explain the enantioselectivity of the radical cyclization in the studied flavoenzymes. We propose a new enantioinduction scenario according to which enantioselectivity is indeed controlled by transition-state stability; however, the relative stability of the prochiral transition states is not determined by direct interaction with the protein but is rather dependent on an inherent degree of freedom within the substrate itself. This intrinsic degree of freedom, distinct from the traditional π-facial exposure mode, can be controlled by the substrate conformational selection upon binding to the enzyme.

Evolution and synthetic biology

Evolutionary observations have often served as an inspiration for biological design. Decoding of the central dogma of life at a molecular level and understanding of the cellular biochemistry have been elegantly used to engineer various synthetic biology applications, including building genetic circuits in vitro and in cells, building synthetic translational systems, and metabolic engineering in cells to biosynthesize and even bioproduce complex high-value molecules. Here, we review three broad areas of synthetic biology that are inspired by evolutionary observations: (i) combinatorial approaches toward cell-based biomolecular evolution, (ii) engineering interdependencies to establish microbial consortia, and (iii) synthetic immunology. In each of the areas, we will highlight the evolutionary premise that was central toward designing these platforms. These are only a subset of the examples where evolution and natural phenomena directly or indirectly serve as a powerful source of inspiration in shaping synthetic biology and biotechnology.

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.

Development of a magnetically stabilized fluidized bed bioreactor for enzymatic synthesis of 2-ethylhexyl oleate

This study aimed to develop and investigate the synthesis of 2-ethylhexyl oleate catalyzed by Candida antarctica lipase immobilized on magnetic poly(styrene-co-divinylbenzene) (STY-DVB-M) particles in a magnetically stabilized fluidized bed reactor (MSFBR) operated in continuous mode. The physical properties of the copolymer were characterized by Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The glass transition temperature was 85.68 °C, and the onset of thermal degradation occurred at 406.66 °C. Syntheses were performed at 50 °C using a space time of 12 h and a bed porosity of 0.892. Assays were conducted to assess the influence of magnetic field intensity (5 to 15 mT) on reaction yield, ester concentration, and productivity. The highest productivity was 0.850 ± 0.023 mmol g-1 h-1, obtained with a magnetic field intensity of 15 mT. An operational stability test was performed under these conditions, revealing a biocatalyst half-life of 2148 h (179 operation cycles) and a thermal deactivation constant of 3.23 × 10-4 h-1 (R2 = 0.9446). Computational simulations and mathematical modeling were performed using Scilab based on ping-pong bi-bi kinetics and molar balances of reaction species. The model provided consistent results of interstitial velocity and good prediction of reaction yields, with R2 = 0.926. These findings demonstrate that the studied technique can provide improvements in biocatalytic processes, representing a promising strategy for the enzymatic synthesis of 2-ethylhexyl oleate.

Modernized Machine Learning Approach to Illuminate Enzyme Immobilization for Biocatalysis

Biocatalysis is an established technology with significant application in the pharmaceutical industry. Immobilization of enzymes offers significant benefits for commercial and practical purposes to enhance the stability and recyclability of biocatalysts. Determination of the spatial and chemical distributions of immobilized enzymes on solid support materials is essential for an optimal catalytic performance. However, current analytical methodologies often fall short of rapidly identifying and characterizing immobilized enzyme systems. Herein, we present a new analytical methodology that combines non-negative matrix factorization (NMF)-an unsupervised machine learning tool-with Raman hyperspectral imaging to simultaneously resolve the spatial and spectral characteristics of all individual species involved in enzyme immobilization. Our novel approach facilitates the determination of the optimal NMF model using new data-driven, quantitative selection criteria that fully resolve all chemical species present, offering a robust methodology for analyzing immobilized enzymes. Specifically, we demonstrate the ability of NMF with Raman hyperspectral imaging to resolve the spatial and spectral profiles of an engineered pantothenate kinase immobilized on two different commercial microporous resins. Our results demonstrate that this approach can accurately identify and spatially resolve all species within this enzyme immobilization process. To the best of our knowledge, this is the first report of NMF within hyperspectral imaging for enzyme immobilization analysis, and as such, our methodology can now provide a new powerful tool to streamline biocatalytic process development within the pharmaceutical industry.

Synthesis of Metabolites and Metabolite-like Compounds Using Biocatalytic Systems

Methodologies for the synthesis and purification of metabolites, which have been developed following their discovery, analysis, and structural identification, have been involved in numerous life science milestones. The renewed focus on the small molecule domain of biological cells has also created an increasing awareness of the rising gap between the metabolites identified and the metabolites which have been prepared as pure compounds. The design and engineering of resource-efficient and straightforward synthetic methodologies for the production of the diverse and numerous metabolites and metabolite-like compounds have attracted much interest. The variety of metabolic pathways in biological cells provides a wonderful blueprint for designing simplified and resource-efficient synthetic routes to desired metabolites. Therefore, biocatalytic systems have become key enabling tools for the synthesis of an increasing number of metabolites, which can then be utilized as standards, enzyme substrates, inhibitors, or other products, or for the discovery of novel biological functions.

Molecular Engineering to Boost the Photo-Oxidase Activity of Molecular Rotors in Colorimetric Sensing of Temperatures

Some organic dyes and photosensitizers with strong visible absorption can behave as photo-responsive oxidase mimics. However, the relationship between the photo-oxidase activity and molecular structure remains unclear to date. In this work, a new type of photosensitizer with the characteristics of molecular rotors, namely DPPy, served as the molecular scaffold for further investigation. To adjust the photocatalytic oxidation ability, DAPy and CBPy were designed and synthesized based on the enhancement and diminishment of the intramolecular charge transfer (ICT) process, respectively. Kinetic studies revealed that DAPy and CBPy both exhibited highly efficient photo-activated oxidase-like activity with 3,3',5,5'-tetramethylbenzidine (TMB) as the substrate, which were in good accordance with their molecular engineering to promote either type I or type II reactive oxygen species (ROS) generation. Impressively a colorimetric method based on the visible light induced oxidase-like activity of molecular rotors was developed to determine the environmental temperature for the first time. Both DAPy and CBPy showed distinct sensitivities toward temperature as compared with several molecular rotors based on the typical fluorimetric detection. This work provides a new strategy for the application of molecular rotors to overcome the non-emissive challenge in temperature sensing.

Hydroxynitrile lyase engineering for promiscuous asymmetric Henry reaction with enhanced conversion, enantioselectivity and catalytic efficiency

Arabidopsis thaliana hydroxynitrile lyase (AtHNL) engineering has uncovered variants that showed up to 12-fold improved catalytic efficiency than the wild-type towards asymmetric Henry reaction. The AtHNL variants have displayed excellent enantioselectivity, up to >99%, and higher conversion in the synthesis of 13 different (R)-β-nitroalcohols from their corresponding aldehydes. Using cell lysates of Y14M/F179W, we demonstrated a preparative scale synthesis of (R)-1-(4-methoxyphenyl)-2-nitroethanol, a tembamide chiral intermediate, in >99% ee and 52% yield.

P450-catalyzed atom transfer radical cyclization

Cytochromes P450 have been extensively studied for both fundamental enzymology and biotechnological applications. Over the past decade, by taking inspiration from synthetic organic chemistry, new classes of P450-catalyzed reactions that were not previously encountered in the biological world have been developed to address challenging problems in organic chemistry and asymmetric catalysis. In particular, by repurposing and evolving P450 enzymes, stereoselective biocatalytic atom transfer radical cyclization (ATRC) was developed as a new means to impose stereocontrol over transient free radical intermediates. In this chapter, we describe the detailed experimental protocol for the directed evolution of P450 atom transfer radical cyclases. We also delineate protocols for analytical and preparative scale biocatalytic atom transfer radical cyclization processes. These methods will find application in the development of new P450-catalyzed radical reactions, as well as other synthetically useful processes.

Biocatalysis in Drug Design: Engineered Reductive Aminases (RedAms) Are Used to Access Chiral Building Blocks with Multiple Stereocenters

Novel building blocks are in constant demand during the search for innovative bioactive small molecule therapeutics by enabling the construction of structure-activity-property-toxicology relationships. Complex chiral molecules containing multiple stereocenters are an important component in compound library expansion but can be difficult to access by traditional organic synthesis. Herein, we report a biocatalytic process to access a specific diastereomer of a chiral amine building block used in drug discovery. A reductive aminase (RedAm) was engineered following a structure-guided mutagenesis strategy to produce the desired isomer. The engineered RedAm (IR-09 W204R) was able to generate the (S,S,S)-isomer 3 in 45% conversion and 95% ee from the racemic ketone 2. Subsequent palladium-catalyzed deallylation of 3 yielded the target primary amine 4 in a 73% yield. This engineered biocatalyst was used at preparative scale and represents a potential starting point for further engineering and process development.

Repurposing Iron- and 2-Oxoglutarate-Dependent Oxygenases to Catalyze Olefin Hydration

Mononuclear nonheme iron(II) and 2-oxoglutarate (Fe/2OG)-dependent oxygenases and halogenases are known to catalyze a diverse set of oxidative reactions, including hydroxylation, halogenation, epoxidation, and desaturation in primary metabolism and natural product maturation. However, their use in abiotic transformations has mainly been limited to C-H oxidation. Herein, we show that various enzymes of this family, when reconstituted with Fe(II) or Fe(III), can catalyze Mukaiyama hydration-a redox neutral transformation. Distinct from the native reactions of the Fe/2OG enzymes, wherein oxygen atom transfer (OAT) catalyzed by an iron-oxo species is involved, this nonnative transformation proceeds through a hydrogen atom transfer (HAT) pathway in a 2OG-independent manner. Additionally, in contrast to conventional inorganic catalysts, wherein a dinuclear iron species is responsible for HAT, the Fe/2OG enzymes exploit a mononuclear iron center to support this reaction. Collectively, our work demonstrates that Fe/2OG enzymes have utility in catalysis beyond the current scope of catalytic oxidation.

The Scent of Change: Sustainable Fragrances Through Industrial Biotechnology

Current environmental and safety considerations urge innovation to address the need for sustainable high-value chemicals that are embraced by consumers. This review discusses the concept of sustainable fragrances, as high-value, everyday and everywhere chemicals. Current and emerging technologies represent an opportunity to produce fragrances in an environmentally and socially responsible way. Biotechnology, including fermentation, biocatalysis, and genetic engineering, has the potential to reduce the environmental footprint of fragrance production while maintaining quality and consistency. Computational and in silico methods, including machine learning (ML), are also likely to augment the capabilities of sustainable fragrance production. Continued innovation and collaboration will be crucial to the future of sustainable fragrances, with a focus on developing novel sustainable ingredients, as well as ethical sourcing practices.

Fishing for Catalysis: Experimental Approaches to Narrowing Search Space in Directed Evolution of Enzymes

Directed evolution has transformed protein engineering offering a path to rapid improvement of protein properties. Yet, in practice it is limited by the hyper-astronomic protein sequence search space, and approaches to identify mutagenic hot spots, i.e., locations where mutations are most likely to have a productive impact, are needed. In this perspective, we categorize and discuss recent progress in the experimental approaches (broadly defined as structural, bioinformatic, and dynamic) to hot spot identification. Recent successes in harnessing protein dynamics and machine learning approaches provide new opportunities for the field and will undoubtedly help directed evolution reach its full potential.

Recent Synthetic Advances on the Use of Diazo Compounds Catalyzed by Metalloporphyrins

Diazo compounds are organic substances that are often used as precursors in organic synthesis like cyclization reactions, olefinations, cyclopropanations, cyclopropenations, rearrangements, and carbene or metallocarbene insertions into C-H, N-H, O-H, S-H, and Si-H bonds. Typically, reactions from diazo compounds are catalyzed by transition metals with various ligands that modulate the capacity and selectivity of the catalyst. These ligands can modify and enhance chemoselectivity in the substrate, regioselectivity and enantioselectivity by reflecting these preferences in the products. Porphyrins have been used as catalysts in several important reactions for organic synthesis and also in several medicinal applications. In the chemistry of diazo compounds, porphyrins are very efficient as catalysts when complexed with low-cost metals (e.g., Fe and Co) and, therefore, in recent years, this has been the subject of significant research. This review will summarize the advances in the studies involving the field of diazo compounds catalyzed by metalloporphyrins (M-Porph, M = Fe, Ru, Os, Co, Rh, Ir) in the last five years to provide a clear overview and possible opportunities for future applications. Also, at the end of this review, the properties of artificial metalloenzymes and hemoproteins as biocatalysts for a broad range of applications, namely those concerning carbene-transfer reactions, will be considered.

Hydrogen Sulfide Gas Amplified ROS Cascade: FeS@GOx Hybrid Nanozyme Designed for Boosting Tumor Chemodynamic Immunotherapy

Chemodynamic immunotherapy that utilizes catalysts to produce reactive oxygen species (ROS) for killing tumor cells and arousing antitumor immunity has received considerable attention. However, it is still restricted by low ROS production efficiency and insufficient immune activation, due to intricate redox homeostasis in the tumor microenvironment (TME). Herein, a metalloprotein-like hybrid nanozyme (FeS@GOx) is designed by in situ growth of nanozyme (ferrous sulfide, FeS) in a natural enzyme (glucose oxidase, GOx) to amplify ROS cascade for boosting chemodynamic immunotherapy. In FeS@GOx, GOx allows the conversion of endogenous glucose to gluconic acid and hydrogen peroxide, which provides favorable increasing hydrogen peroxide for subsequent Fenton reaction of FeS nanozymes, thus reinforcing ROS production. Notably, hydrogen sulfide (H2 S) release is activated by the gluconic acid generation-related pH decrease, which can suppress the activity of endogenous thioredoxin reductase and catalase to further inhibit ROS elimination. Thus, FeS@GOx can sustainably amplify ROS accumulation and perturb intracellular redox homeostasis to improve chemodynamic therapy and trigger robust immunogenic cell death for effective immunotherapy combined with immune checkpoint blockade. This work proposes a feasible H2 S amplified ROS cascade strategy employing a bioinspired hybrid nanozyme, providing a novel pathway to multi-enzyme-mediated TME modulation for precise and efficient chemodynamic immunotherapy.

Enantiocomplementary synthesis of β-adrenergic blocker precursors via biocatalytic nitration of phenyl glycidyl ethers

Enantiopure β-nitroalcohols, as an important class of nitro-containing compounds, are essential building blocks in pharmaceutical and organic chemistry, particularly for the synthesis of β-adrenergic blockers. In this study, we present the successful protein engineering of halohydrin dehalogenase HHDHamb for the enantioselective bio-nitration of various phenyl glycidyl ethers to the corresponding chiral β-nitroalcohols, using the inexpensive, commercially available, and safer nitrite as a nitrating agent. The chiral (R)- and (S)-1-nitro-3-phenoxypropan-2-ols were synthesized by the several enantiocomplementary HHDHamb variants through the whole-cell biotransformation, which showed good catalytic efficiency (up to 43% isolated yields) and high optical purity (up to >99% ee). In addition, we also demonstrated that the bio-nitration method was able to tolerate the substrate at a high concentration of 1000 mM (150 g/L). Furthermore, representative synthesis of two optically active enantiomers of the β-adrenergic blocker metoprolol was successfully achieved by utilizing the corresponding chiral β-nitroalcohols as precursors.

Review of covalent organic frameworks for enzyme immobilization: Strategies, applications, and prospects

Efficient enzyme immobilization systems offer a promising approach for improving enzyme stability and recyclability, reducing enzyme contamination in products, and expanding the applications of enzymes in the biomedical field. Covalent organic frameworks (COFs) possess high surface areas, ordered channels, optional building blocks, highly tunable porosity, stable mechanical properties, and abundant functional groups, making them ideal candidates for enzyme immobilization. Various COF-enzyme composites have been successfully synthesized, with performances that surpass those of free enzymes in numerous ways. This review aims to provide an overview of current enzyme immobilization strategies using COFs, highlighting the characteristics of each method and recent research applications. The future opportunities and challenges of enzyme immobilization technology using COFs are also discussed.

Reversing the Enantioselectivity of Enzymatic Carbene N-H Insertion Through Mechanism-Guided Protein Engineering

We report a computationally driven approach to access enantiodivergent enzymatic carbene N-H insertions catalyzed by P411 enzymes. Computational modeling was employed to rationally guide engineering efforts to control the accessible conformations of a key lactone-carbene (LAC) intermediate in the enzyme active site by installing a new H-bond anchoring point. This H-bonding interaction controls the relative orientation of the reactive carbene intermediate, orienting it for an enantioselective N-nucleophilic attack by the amine substrate. By combining MD simulations and site-saturation mutagenesis and screening targeted to only two key residues, we were able to reverse the stereoselectivity of previously engineered S-selective P411 enzymes. The resulting variant, L5_FL-B3, accepts a broad scope of amine substrates for N-H insertion with excellent yields (up to >99 %), high efficiency (up to 12 300 TTN), and good enantiocontrol (up to 7 : 93 er).

Charting the Evolution of Chemoenzymatic Strategies in the Syntheses of Complex Natural Products

Bolstered by recent advances in bioinformatics, genetics, and enzyme engineering, the field of chemoenzymatic synthesis has enjoyed a rapid increase in popularity and utility. This Perspective explores the integration of enzymes into multistep chemical syntheses, highlighting the unique potential of biocatalytic transformations to streamline the synthesis of complex natural products. In particular, we identify four primary conceptual approaches to chemoenzymatic synthesis and illustrate each with a number of landmark case studies. Future opportunities and challenges are also discussed.

Probiotics and biofilm interaction in aquaculture for sustainable food security: A review and bibliometric analysis

Aquaculture is one of the most significant food sources from the prehistoric period. As aquaculture intensifies globally, the prevalence and outbreaks of various pathogenic microorganisms cause fish disease and heavy mortality, leading to a drastic reduction in yield and substantial economic loss. With the modernization of the aquaculture system, a new challenge regarding biofilms or bacterial microenvironments arises worldwide, which facilitates pathogenic microorganisms to survive under unfavorable environmental conditions and withstand various treatments, especially antibiotics and other chemical disinfectants. However, we focus on the mechanistic association between those microbes which mainly form biofilm and probiotics in one of the major food production systems, aquaculture. In recent years, probiotics and their derivatives have attracted much attention in the fisheries sector to combat the survival strategy of pathogenic bacteria. Apart from this, Bibliometric analysis provides a comprehensive overview of the published literature, highlighting key research themes, emerging topics, and areas that require further investigation. This information is valuable for researchers, policymakers, and stakeholders in determining research priorities and allocating resources effectively.

Immobilization of commercial horseradish peroxidase in calcium alginate-starch hybrid support and its application in the biodegradation of phenol red dye

In this study, horseradish peroxidase (HRP) was immobilized for the first time on Ca alginate-starch hybrid beads and employed for the biodegradation of phenol red dye. The optimal protein loading was 50 mg/g of support. Immobilized HRP demonstrated improved thermal stability and maximum catalytic activity at 50 °C and pH 6.0, with an increase in half-life (t1/2) and enzymatic deactivation energy (Ed) compared to free HRP. After 30 days of storage at 4 °C, immobilized HRP retained 109% of its initial activity. Compared to free HRP, the immobilized enzyme exhibited higher potential for phenol red dye degradation, as evidenced by the removal of 55.87% of initial phenol red after 90 min, which was 11.5 times greater than free HRP. In sequential batch reactions, the immobilized HRP demonstrated good potential efficiency for the biodegradation of phenol red dye. The immobilized HRP was used for a total of 15 cycles, degrading 18.99% after 10 cycles and 11.69% after 15 cycles, with a residual enzymatic activity of 19.40% and 12.34%, respectively. Overall, the results suggest that HRP immobilized on Ca alginate-starch hybrid supports shows promise as a biocatalyst for industrial and biotechnological applications, particularly for the biodegradation of recalcitrant compounds such as phenol red dye.

Versatile Biocatalytic C(sp3 )-H Oxyfunctionalization for the Site- Selective and Stereodivergent Synthesis of α- and β-Hydroxy Acids

C(sp3 )-H oxyfunctionalization, the insertion of an O-atom into C(sp3 )-H bonds, streamlines the synthesis of complex molecules from easily accessible precursors and represents one of the most challenging tasks in organic chemistry with regard to site and stereoselectivity. Biocatalytic C(sp3 )-H oxyfunctionalization has the potential to overcome limitations inherent to small-molecule-mediated approaches by delivering catalyst-controlled selectivity. Through enzyme repurposing and activity profiling of natural variants, we have developed a subfamily of α-ketoglutarate-dependent iron dioxygenases that catalyze the site- and stereodivergent oxyfunctionalization of secondary and tertiary C(sp3 )-H bonds, providing concise synthetic routes towards four types of 92 α- and β-hydroxy acids with high efficiency and selectivity. This method provides a biocatalytic approach for the production of valuable but synthetically challenging chiral hydroxy acid building blocks.

Stereoselective amino acid synthesis by synergistic photoredox-pyridoxal radical biocatalysis

Developing synthetically useful enzymatic reactions that are not known in biochemistry and organic chemistry is an important challenge in biocatalysis. Through the synergistic merger of photoredox catalysis and pyridoxal 5'-phosphate (PLP) biocatalysis, we developed a pyridoxal radical biocatalysis approach to prepare valuable noncanonical amino acids, including those bearing a stereochemical dyad or triad, without the need for protecting groups. Using engineered PLP enzymes, either enantiomeric product could be produced in a biocatalyst-controlled fashion. Synergistic photoredox-pyridoxal radical biocatalysis represents a powerful platform with which to discover previously unknown catalytic reactions and to tame radical intermediates for asymmetric catalysis.

Enantio- and Diastereoenriched Enzymatic Synthesis of 1,2,3-Polysubstituted Cyclopropanes from (Z/E)-Trisubstituted Enol Acetates

In nature and synthetic chemistry, stereoselective [2 + 1] cyclopropanation is the most prevalent strategy for the synthesis of chiral cyclopropanes, a class of key pharmacophores in pharmaceuticals and bioactive natural products. One of the most extensively studied reactions in the organic chemist's arsenal, stereoselective [2 + 1] cyclopropanation, largely relies on the use of stereodefined olefins, which can require elaborate laboratory synthesis or tedious separation to ensure high stereoselectivity. Here, we report engineered hemoproteins derived from a bacterial cytochrome P450 that catalyze the synthesis of chiral 1,2,3-polysubstituted cyclopropanes, regardless of the stereopurity of the olefin substrates used. Cytochrome P450BM3 variant P411-INC-5185 exclusively converts (Z)-enol acetates to enantio- and diastereoenriched cyclopropanes and in the model reaction delivers a leftover (E)-enol acetate with 98% stereopurity, using whole Escherichia coli cells. P411-INC-5185 was further engineered with a single mutation to enable the biotransformation of (E)-enol acetates to α-branched ketones with high levels of enantioselectivity while simultaneously catalyzing the cyclopropanation of (Z)-enol acetates with excellent activities and selectivities. We conducted docking studies and molecular dynamics simulations to understand how active-site residues distinguish between the substrate isomers and enable the enzyme to perform these distinct transformations with such high selectivities. Computational studies suggest the observed enantio- and diastereoselectivities are achieved through a stepwise pathway. These biotransformations streamline the synthesis of chiral 1,2,3-polysubstituted cyclopropanes from readily available mixtures of (Z/E)-olefins, adding a new dimension to classical cyclopropanation methods.

Artificial Metalloenzyme-Catalyzed Enantioselective Amidation via Nitrene Insertion in Unactivated C(sp3)-H Bonds

Enantioselective C-H amidation offers attractive means to assemble C-N bonds to synthesize high-added value, nitrogen-containing molecules. In recent decades, complementary enzymatic and homogeneous-catalytic strategies for C-H amidation have been reported. Herein, we report on an artificial metalloenzyme (ArM) resulting from anchoring a biotinylated Ir-complex within streptavidin (Sav). The resulting ArM catalyzes the enantioselective amidation of unactivated C(sp³)-H bonds. Chemogenetic optimization of the Ir cofactor and Sav led to significant improvement in both the activity and enantioselectivity. Up to >700 TON and 92% ee for the amidation of unactivated C(sp³)-H bonds was achieved. The single crystal X-ray analysis of the artificial nitrene insertase (ANIase) combined with quantum mechanics-molecular mechanics (QM-MM) calculations sheds light on critical second coordination sphere contacts leading to improved catalytic performance.

Enzyme-controlled stereoselective radical cyclization to arenes enabled by metalloredox biocatalysis

The effective induction of high levels of stereocontrol for free radical-mediated transformations represents a notorious challenge in asymmetric catalysis. Herein, we describe a novel metalloredox biocatalysis strategy to repurpose natural cytochromes P450 to catalyse asymmetric radical cyclisation to arenes through an unnatural electron transfer mechanism. Empowered by directed evolution, engineered P450s allowed diverse radical cyclisation selectivities to be accomplished in a catalyst-controlled fashion: P450arc1 and P450arc2 facilitated enantioconvergent transformations of racemic substrates, giving rise to either enantiomer of the product with excellent total turnover numbers (up to 12,000). In addition to these enantioconvergent variants, another engineered radical cyclase, P450arc3, permitted efficient kinetic resolution of racemic chloride substrates (S factor = 18). Furthermore, computational studies revealed a proton-coupled electron transfer (PCET) mechanism for the radical-polar crossover step, suggesting the potential role of the haem carboxylate as a base catalyst. Collectively, the excellent tunability of this metalloenzyme family provides an exciting platform for harnessing free radical intermediates for asymmetric catalysis.

Protein-Inspired Control over Synthetic Polymer Folding for Structured Functional Nanoparticles in Water

The folding of proteins into functional nanoparticles with defined 3D structures has inspired chemists to create simple synthetic systems mimicking protein properties. The folding of polymers into nanoparticles in water proceeds via different strategies, resulting in the global compaction of the polymer chain. Herein, we review the different methods available to control the conformation of synthetic polymers and collapse/fold them into structured, functional nanoparticles, such as hydrophobic collapse, supramolecular self-assembly, and covalent cross-linking. A comparison is made between the design principles of protein folding to synthetic polymer folding and the formation of structured nanocompartments in water, highlighting similarities and differences in design and function. We also focus on the importance of structure for functional stability and diverse applications in complex media and cellular environments.

Optically Pure Double-Stranded Dinuclear Ir(III) Metallohelices Enabled Chirality-Induced Photodynamic Responses

Investigation on the interactions between enantiomers of chiral drugs and biomolecules can help precisely understand their biological behaviors in vivo and provide insights into the design of new drugs. Herein, we designed and synthesized a pair of optically pure, cationic, double-stranded dinuclear Ir(III)-metallohelices (Λ₂R₄-H and Δ₂S₄-H), and their dramatic enantiomer-dependent photodynamic therapy (PDT) responses were thoroughly studied in vitro and in vivo. Compared to the mononuclear enantiomeric or racemic [Ir(ppy)₂(dppz)][PF₆] (Λ-/Δ-Ir, rac-Ir) that with high dark toxicity and low photocytotoxicity index (PI) values, both of the optically pure metallohelices displayed negligible toxicity in the dark while exhibiting very distinctive light toxicity upon light irradiation. The PI value of Λ₂R₄-H was approximately 428, however, Δ₂S₄-H significantly reached 63,966. Interestingly, only Δ₂S₄-H was found to migrate from mitochondria to nucleus after light irradiation. Further proteomic analysis verified that Δ₂S₄-H activated the ATP-dependent migration process after light irradiation, and subsequently inhibited the activities of the nuclear proteins such as superoxide dismutase 1 (SOD1) and eukaryotic translation initiation factor 5A (EIF5A) to trigger the accumulation of superoxide anions and downregulate mRNA splicing processes. Molecular docking simulations suggested that the interactions between metallohelices and nuclear pore complex NDC1 dominated the migration process. This work presents a new kind of Ir(III) metallohelices-based agent with the highest PDT efficacy, highlights the importance of metallohelices' chirality, and provides inspirations for the future design of chiral helical metallodrugs.

Effect of Nitrogen, Air, and Oxygen on the Kinetic Stability of NAD(P)H Oxidase Exposed to a Gas-Liquid Interface

Biocatalytic oxidation is an interesting prospect for the selective synthesis of active pharmaceutical intermediates. Bubbling air or oxygen is considered as an efficient method to increase the gas-liquid interface and thereby enhance oxygen transfer. However, the enzyme is deactivated in this process and needs to be further studied and understood to accelerate the implementation of oxidative biocatalysis in larger production processes. This paper reports data on the stability of NAD(P)H oxidase (NOX) when exposed to different gas-liquid interfaces introduced by N2 (0% oxygen), air (21% oxygen), and O2 (100% oxygen) in a bubble column. A pH increase was observed during gas bubbling, with the highest increase occurring under air bubbling from 6.28 to 7.40 after 60 h at a gas flow rate of 0.15 L min-1. The kinetic stability of NOX was studied under N2, air, and O2 bubbling by measuring the residual activity, the deactivation constants (kd1) were 0.2972, 0.0244, and 0.0346 with the corresponding half-lives of 2.2, 28.6, and 20.2 h, respectively. A decrease in protein concentration of the NOX solution was also observed and was attributed to likely enzyme aggregation at the gas-liquid interface. Most aggregation occurred at the air-water interface and decreased greatly from 100 to 14.16% after 60 h of bubbling air. Furthermore, the effect of the gas-liquid interface and the dissolved gas on the NOX deactivation process was also studied by bubbling N2 and O2 alternately. It was found that the N2-water interface and O2-water interface both had minor effects on the protein concentration decrease compared with the air-water interface, whilst the dissolved N2 in water caused serious deactivation of NOX. This was attributed not only to the NOX unfolding and aggregation at the interface but also to the N2 occupying the oxygen channel of the enzyme and the resultant inaccessibility of dissolved O2 to the active site of NOX. These results shed light on the enzyme deactivation process and might further inspire bioreactor operation and enzyme engineering to improve biocatalyst performance.

Molecular Complementarity of Proteomimetic Materials for Target-Specific Recognition and Recognition-Mediated Complex Functions

As biomolecules essential for sustaining life, proteins are generated from long chains of 20 different α-amino acids that are folded into unique 3D structures. In particular, many proteins have molecular recognition functions owing to their binding pockets, which have complementary shapes, charges, and polarities for specific targets, making these biopolymers unique and highly valuable for biomedical and biocatalytic applications. Based on the understanding of protein structures and microenvironments, molecular complementarity can be exhibited by synthesizable and modifiable materials. This has prompted researchers to explore the proteomimetic potentials of a diverse range of materials, including biologically available peptides and oligonucleotides, synthetic supramolecules, inorganic molecules, and related coordination networks. To fully resemble a protein, proteomimetic materials perform the molecular recognition to mediate complex molecular functions, such as allosteric regulation, signal transduction, enzymatic reactions, and stimuli-responsive motions; this can also expand the landscape of their potential bio-applications. This review focuses on the recognitive aspects of proteomimetic designs derived for individual materials and their conformations. Recent progress provides insights to help guide the development of advanced protein mimicry with material heterogeneity, design modularity, and tailored functionality. The perspectives and challenges of current proteomimetic designs and tools are also discussed in relation to future applications.

Second-Shell Residues Contribute to Catalysis by Predominately Preorganizing the Apo State in PafA

Residues beyond the first coordination shell are often observed to make considerable cumulative contributions in enzymes. Due to typically indirect perturbations of multiple physicochemical properties of the active site, however, their individual and specific roles in enzyme catalysis and disease-causing mutations remain difficult to predict and understand at the molecular level. Here we analyze the contributions of several second-shell residues in phosphate-irrepressible alkaline phosphatase of flavobacterium (PafA), a representative system as one of the most efficient enzymes. By adopting a multifaceted approach that integrates quantum-mechanical/molecular-mechanical free energy computations, molecular-mechanical molecular dynamics simulations, and density functional theory cluster model calculations, we probe the rate-limiting phosphoryl transfer step and structural properties of all relevant enzyme states. In combination with available experimental data, our computational results show that mutations of the studied second-shell residues impact catalytic efficiency mainly by perturbation of the apo state and therefore substrate binding, while they do not affect the ground state or alter the nature of phosphoryl transfer transition state significantly. Several second-shell mutations also modulate the active site hydration level, which in turn influences the energetics of phosphoryl transfer. These mechanistic insights also help inform strategies that may improve the efficiency of enzyme design and engineering by going beyond the current focus on the first coordination shell.

Ene Reductase Enabled Intramolecular β-C-H Functionalization of Substituted Cyclohexanones for Efficient Synthesis of Bridged Bicyclic Nitrogen Scaffolds

Herein we report that ene reductases (EREDs) can facilitate an unprecedented intramolecular β-C-H functionalization reaction for the synthesis of bridged bicyclic nitrogen heterocycles containing the 6-azabicyclo[3.2.1]octane scaffold. To streamline the synthesis of these privileged motifs, we developed a gram-scale one-pot chemoenzymatic cascade by combining iridium photocatalysis with EREDs, using readily available N-phenylglycines and cyclohexenones that can be obtained from biomass. Further derivatization using enzymatic or chemical methods can convert 6-azabicyclo[3.2.1]octan-3-one into 6-azabicyclo[3.2.1]octan-3α-ols, which can be potentially utilized for the synthesis of azaprophen and its analogues for drug discovery. Mechanistic studies revealed the reaction requires oxygen, presumably to produce oxidized flavin, which can selectively dehydrogenate the 3-substituted cyclohexanone derivatives to form the α,β-unsaturated ketone, which subsequently undergoes spontaneous intramolecular aza-Michael addition under basic conditions.

Manganese-Based Antioxidase-Inspired Biocatalysts with Axial Mn-N5 Sites and 2D d-π-Conjugated Networks for Rescuing Stem Cell Fate

Constructing highly effective biocatalysts with controllable coordination geometry for eliminating reactive oxygen species (ROS) to address the current bottlenecks in stem-cell-based therapeutics remains challenging. Herein, inspired by the coordination structure of manganese-based antioxidase, we report a manganese-coordinated polyphthalocyanine-based biocatalyst (Mn-PcBC) with axial Mn-N5 sites and 2D d-π-conjugated networks that serves as an artificial antioxidase to rescue stem cell fate. Owing to the unique chemical and electronic structures, Mn-PcBC displays efficient, multifaceted, and robust ROS-scavenging activities, including elimination of H2 O2 and O2 ⋅- . Consequently, Mn-PcBC efficiently rescues the bioactivity and functionality of stem cells in high-ROS-level microenvironments by protecting the transcription of osteogenesis-related genes. This study offers essential insight into the crucial functions of axially coordinated Mn-N5 sites in ROS scavenging and suggests new strategies to create efficient artificial antioxidases for stem-cell therapies.

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.

In-depth analysis of biocatalysts by microfluidics: An emerging source of data for machine learning

Nowadays, the vastly increasing demand for novel biotechnological products is supported by the continuous development of biocatalytic applications which provide sustainable green alternatives to chemical processes. The success of a biocatalytic application is critically dependent on how quickly we can identify and characterize enzyme variants fitting the conditions of industrial processes. While miniaturization and parallelization have dramatically increased the throughput of next-generation sequencing systems, the subsequent characterization of the obtained candidates is still a limiting process in identifying the desired biocatalysts. Only a few commercial microfluidic systems for enzyme analysis are currently available, and the transformation of numerous published prototypes into commercial platforms is still to be streamlined. This review presents the state-of-the-art, recent trends, and perspectives in applying microfluidic tools in the functional and structural analysis of biocatalysts. We discuss the advantages and disadvantages of available technologies, their reproducibility and robustness, and readiness for routine laboratory use. We also highlight the unexplored potential of microfluidics to leverage the power of machine learning for biocatalyst development.

Comparative biochemical characterization of mammalian-derived CYP11A1s with cholesterol side-chain cleavage activities

Steroid drugs, the second largest class of pharmaceuticals after antibiotics, have shown significant anti-inflammatory, anti-allergic, and endocrine-regulating effects. A group of cytochrome P450 enzymes, namely, CYP11A1 isoenzymes from different organisms are capable of converting cholesterol into pregnenolone, which is a pivotal reaction in both steroid metabolism and (bio)synthetic network of steroid products. However, the low activity of CYP11A1s greatly restricts the industrial application of these cholesterol side-chain cleavage enzymes. Herein, we investigate ten CYP11A1 enzymes of different origins and in vitro characterize two CYP11A1s with a relatively higher expression level from Capra hircus and Sus scrofa, together with the CYP11A1s from Homo sapiens and Bos taurus as references. Towards five selected sterol substrates with different side chain structures, S. scrofa CYP11A1 displays relatively higher activities. Through redox partners combination screening, we reveal the optimal redox partner pair of S. scrofa adrenodoxin and C. hircus adrenodoxin reductase. Moreover, the semi-rational mutagenesis for the active sites and substrate entrance channels of human and bovine CYP11A1s is performed based on comparative analysis of their crystal structures. The mutant mBtCYP11A1-Q377A derived from mature B. taurus CYP11A1 shows a 1.46 times higher activity than the wild type enzyme. These results not only demonstrate the tunability of the highly conserved CYP11A1 isoenzymes, but also lay a foundation for the following engineering efforts on these industrially relevant P450 enzymes.

Designing artificial pathways for improving chemical production

Metabolic engineering exploits manipulation of catalytic and regulatory elements to improve a specific function of the host cell, often the synthesis of interesting chemicals. Although naturally occurring pathways are significant resources for metabolic engineering, these pathways are frequently inefficient and suffer from a series of inherent drawbacks. Designing artificial pathways in a rational manner provides a promising alternative for chemicals production. However, the entry barrier of designing artificial pathway is relatively high, which requires researchers a comprehensive and deep understanding of physical, chemical and biological principles. On the other hand, the designed artificial pathways frequently suffer from low efficiencies, which impair their further applications in host cells. Here, we illustrate the concept and basic workflow of retrobiosynthesis in designing artificial pathways, as well as the most currently used methods including the knowledge- and computer-based approaches. Then, we discuss how to obtain desired enzymes for novel biochemistries, and how to trim the initially designed artificial pathways for further improving their functionalities. Finally, we summarize the current applications of artificial pathways from feedstocks utilization to various products synthesis, as well as our future perspectives on designing artificial pathways.

Selective Oxidation of Halophenols Catalyzed by an Artificial Miniaturized Peroxidase

The development of artificial enzymes for application in sustainable technologies, such as the transformation of environmental pollutants or biomass, is one of the most challenging goals in metalloenzyme design. In this work, we describe the oxidation of mono-, di-, tri- and penta-halogenated phenols catalyzed by the artificial metalloenzyme Fe-MC6*a. It promoted the dehalogenation of 4-fluorophenol into the corresponding 1,4-benzoquinone, while under the same experimental conditions, 4-chloro, 4-bromo and 4-iodophenol were selectively converted into higher molecular weight compounds. Analysis of the 4-chlorophenol oxidation products clarified that oligomers based on C-O bonds were exclusively formed in this case. All results show that Fe-MC6*a holds intriguing enzymatic properties, as it catalyzes halophenol oxidation with substrate-dependent chemoselectivity.

Lignocellulosic biomass valorization via bio-photo/electro hybrid catalytic systems

Lignocellulosic biomass valorization is regarded as a promising approach to alleviate energy crisis and achieve carbon neutrality. Bioactive enzymes have attracted great attention and been commonly applied for biomass valorization owing to their high selectivity and catalytic efficiency under environmentally benign reaction conditions. Same as biocatalysis, photo-/electro-catalysis also happens at mild conditions (i.e., near ambient temperature and pressure). Therefore, the combination of these different catalytic approaches to benefit from their resulting synergy is appealing. In such hybrid systems, harness of renewable energy from the photo-/electro-catalytic compartment can be combined with the unique selectivity of biocatalysts, therefore providing a more sustainable and greener approach to obtain fuels and value-added chemicals from biomass. In this review, we firstly introduce the pros/cons, classifications, and the applications of photo-/electro-enzyme coupled systems. Then we focus on the fundamentals and comprehensive applications of the most representative biomass-active enzymes including lytic polysaccharide monooxygenases (LPMOs), glucose oxidase (GOD)/dehydrogenase (GDH) and lignin peroxidase (LiP), together with other biomass-active enzymes in the photo-/electro- enzyme coupled systems. Finally, we propose current deficiencies and future perspectives of biomass-active enzymes to be applied in the hybrid catalytic systems for global biomass valorization.