Hydrogenases are the most important enzymes in biological hydrogen production and hydrogen energy utilization. They are widely distributed, oxygen-sensitive, multiunit complexed metal enzymes. In vitro synthetic enzymatic biosystems (ivSEB) is a type of in vitro biotransformation (ivBT) technology, which is an emerging biomanufacturing powerhouse that combines microbial fermentation with enzymatic biocatalysis, allowing for novel and efficient hydrogen production, also breaking the Thauer limit and achieving a yield of hydrogen close to the theoretical value of chemistry (1 mole of glucose to produce 12 moles of hydrogen in maximum). It represents the future direction of biological hydrogen production. However, the recombinant expression of hydrogenase is the main bottleneck limiting the wide application of ivSEB for hydrogen production technology. Hydrogenases are widely distributed in all life domains, but are oxygen-sensitive and mostly consist of metalloproteins with multi-subunits, bearing [Fe] only, [NiFe] or [FeFe] dinuclear core in their catalytic center. Oxygen not only inhibits the activity of hydrogenase, but also affects the transcription of the enzyme-encoding gene and post-translational process of the enzymes. As a result, the levels of recombinant hydrogenase are usually low and the enzymatic activities are also incomparable to the native enzymes, often leading to high production costs due to the strict anaerobic purification procedures. In order to meet the requirements of industrial hydrogen production, hydrogenases must possess excellent catalytic properties, such as a high catalytic turnover number, great thermal stability, and the ability to tolerate trace amounts of oxygen. This review summarizes the studies on the structural and catalytic characterizations of hydrogenases, including their classification, oxygen resistance mechanisms, and progress in recombinant expression. Additionally, the evolution of natural electron transfer chains and the design of artificial routes, which can improve hydrogen production efficiency and reduce costs, are briefly discussed. The review also discussed the progress in the studies on the mechanisms of hydrogenases’ tolerance toward oxygen, the strategies for microbial expression of recombinant hydrogenases as well as the optimization of the artificial electron transfer chains adapted for the production of hydrogen using ivSEB, in expectations of promoting the applications of hydrogenases involved ivSEB, from renewable energy storage, anaerobic artificial respiration, to clean hydrogenation or dehydrogenation in biocatalysis.

Hydrogenases catalyze the reversible conversion of hydrogen gas into protons and electrons which is promising for industrial application. However, free hydrogenases face challenges such as oxygen sensitivity and low electron transfer rates. This review summarized the immobilization of hydrogenases by carbon materials, metals, semiconductors, polymers and metal-organic-frameworks (MOFs). Carbon materials provide the advantages of low cost and large specific surface areas, while they tend to agglomerate. Hydrogenases are immobilizated on carbon materials through adsorption, usually involving electrostatic interactions and hydrophobic interactions, and are used in bioelectrocatalysis, biofuel cells and bioreactors. Metals and semiconductors, known for high conductivity and excellent reactive activity, are expensive and less stable. Through adsorption involving electrostatic interaction and hydrophobic interaction, immobilization of hydrogenases on metals and semiconductors are normally applied in bioelectrocatalysis, biofuel cells and photoelectrocatalysis. Polymers have good biocompatibility and mechanical strength but low conductivity. Immobilization of hydrogenases on polymers can improve the stability and oxygen tolerance of hydrogenases. Immobilization on polymers is realized through adsorption and entrapment, involving hydrogen bonds, hydrophobic interactions and π-π interactions, and is often used in bioelectrocatalysis and photoelectrocatalysis. MOFs are designable and have high specific surface areas, which provide wide choices for hydrogenases immobilization. However, MOFs tend to collapse in harsh conditions. Immobilization on MOFs through adsorption and entrapment involves coordinate bonds, hydrophobic interaction, and π-π interaction. Furthermore, the prospect of immobilization of hydrogenases by novel hybrid materials was proposed which can expand the applications of immobilized hydrogenases. Immobilization of hydrogenases facilitates the stability of hydrogenases, which can be applied in efficient production and application of hydrogen, as well as biological asymmetric hydrogenation for chiral medicine preparation. Immobilization of hydrogenases provide alternative options for transforming energy structures, realizing green manufacturing and solving environmental problems.

As a class of enzymes widely distributed in nature, peroxidases are involved in important life processes such as innate immunity and epidemic prevention of organisms, anti-oxidative stress of plant microorganisms, fungal lignin degradation, plant cell wall metabolism and wound healing. With the rapid development of DNA sequencing, gene editing, recombinant protein expression and high-throughput screening technologies, more and more peroxidases have been discovered, characterized and recombinantly expressed. These peroxidases, characterized by their species diversity, abundant quantity, and excellent catalytic performance, have attracted extensive attention in many fields of application research. In recent years, remarkable progress has been made in the recombinant expression of peroxidases, further promoting their development in the field of applied research. Additionally, as we deepen our understanding of the catalytic properties of peroxidases, new opportunities have emerged for their application in the field of biosynthesis. Their high catalytic activity allows for rapid oxidation reactions under mild conditions and enables the construction of multi-enzyme cascade systems in conjunction with other enzymes, thereby facilitating the efficient synthesis of complex compounds. This paper provides a brief overview of peroxidases from the perspective of systematic evolutionary classification and function. It systematically reviews recent progress in the recombinant expression of peroxidases in Escherichia coli, yeast, and fungi, as well as their application achievements in environmental remediation and compound detection. The focus is on the latest research advances in the application of peroxidases for the biosynthesis of high-value-added compounds. The paper also discusses the current issues in this field, such as substrate and product non-specificity and the cytotoxicity of the cofactor H₂O₂. Peroxidases have enormous potential for applications in medical diagnostics, environmental protection, and biosynthesis. However, current technologies and applications still face several challenges, such as the stability and activity of peroxidases in complex environments, high production costs of enzyme preparations, and poor specificity. In the future, by integrating the latest advances in protein engineering, synthetic biology, and immobilization technology, these challenges can be effectively solved, promoting the widespread application of peroxidases across various fields.

Biomimetic compartmentalization immobilization of multi-enzyme system is a frontier for in vitro synthetic biology, focusing on the spatial and temporal separation of reactions. Compared with simple co-immobilization, biomimetic compartmentalization immobilization can form substrate channels and promote the transmission of intermediates for sequential or coupling reaction. By controlling the relative positions of the enzymes on carriers, this method improves system stability, productivity, as well as purity of product. In this review, we summarized the recent advances of carriers for biomimetic compartmentalization immobilization of multi-enzyme systems, including metal-organic frameworks (MOFs), polymer vesicles and polymer capsules. Metal-organic frameworks (MOFs) are porous coordination materials which are composed of metal ions as nodes and organic linkers. MOFs possess unique characteristics including high porosity, large specific surface area and tunable structure, which are suitable for multi-enzyme systems. The strategies involving the hierarchically porous MOFs, MOF-on-MOF and multi-MOF combinations construct compartmentalized environments for efficient catalytic reactions in vitro. Polymer vesicles are hollow nanostructures composed of amphiphilic block copolymers. The membrane structure of polymer vesicles, similar to the natural phospholipid bilayers, has good mechanical stability and biocompatibility for protecting enzyme molecules, and provides unique microenvironment for sequential reactions. Multiple small vesicles were encapsulated into the larger vesicles to form a “vesicle-in-vesicle” by mimicking the structure of cellular organelles. Polymer capsules with a core-shell spherical nanostructure are formed by the templating method, and have structural stability and excellent shape controllability. Multilayered core-shell structures created by layer-by-layer self-assembly are applied for compartmentalized immobilization of multi-enzyme. In the future, the integration of microfluidic technologies with biomimetic compartmentalization immobilization of multi-enzyme is expected to provide highly efficient and stable multi-enzyme catalytic systems for in vitro synthetic biology and green biomanufacturing.

Natural product is an important source of small-molecule drugs and probes, but its synthesis is challenging and has attracted lasting attention in the field of organic chemistry. With the continuous advancement of chromatographic techniques for separation and spectroscopic methods for structural analysis, the pace of discovering tiny bioactive natural products is accelerating, concomitantly leading to an increase in the diversity and complexity of the newly identified structures. However, to meet the demand of the quantity for the study of their structure-activity relationships, target identification, in vivo activity evaluation, etc., growing challenges in the requirement for the synthetic efficiency, economy, and scalability of natural products are emerging. Synthetic practices in a chemoenzymatic way have provided multi-dimensional visions for natural product research, which emerged as a hot research topic in recent years. On the one hand, enzymatic catalysis has provided highly efficient and selective synthetic methodologies that would complement traditional synthetic methods. On the other hand, the introduction of enzyme-catalyzed reactions would bring a new mode of strategic design for synthesis, enabling the rapid and diverse synthesis of natural products with high efficiency. In this context, how to integrate the enzyme-catalyzed reactions into the synthesis of natural products is the key to a successful chemoenzymatic synthesis. We herein summarized three roles played by the applications of enzyme-catalyzed reactions in the current practices of chemoenzymatic synthesis of natural products. ①The involvement of biocatalysis would introduce a chiral center or a key functional group into the starting material, or supply complex synthetic precursors (e.g., polysubstituted (hetero)aromatics, chiral pools, etc.) via in vitro enzyme-catalyzed reactions or fermentation, hence advancing the starting line of synthesis; ②Late-stage enzyme-catalyzed chemo-, regio-, and stereoselective modifications of substrates with heavily substituted functional groups or inert positions of complex skeletons; ③The strategic application of enzymatic catalysis as a key carbon-carbon bond-forming step in the construction of the skeleton of natural product. Finally, we have also discussed the current challenges and future trends of the chemoenzymatic synthesis of natural products in three facets, including the design of synthetic strategy, the development of synthetic methods, as well as persons involved in the research. Thus, the integration of interdisciplinary methods and technologies, including chemical synthesis and biocatalysis, would invigorate the synthesis of natural products.

Steroids exhibit a range of biological activities and are commonly described as the ‘key to life’ in nature. Steroidal-based medications have emerged as the second largest pharmaceutical category following antibiotics, owing to their remarkable bioactivities such as anti-infective, anti-inflammatory, anti-allergic, and antitumor properties. This category encompasses more than 400 drug compounds, representing approximately 17% of FDA-approved medications. The synthesis of steroidal products continues to attract significant attention due to their diverse bioactivities and physicochemical characteristics in pharmaceutical applications. With the increasing demand for steroidal drugs and the fluctuating availability of sapogenin resources, the use of Mycobacteria to convert inexpensive phytosterols to produce key intermediates for steroid drugs has been established as the most mature and sustainable industrial route. However, the complex structure of steroids, particularly their highly oxygenated skeleton, poses challenges for the well-established semi-synthesis route of complex steroid medications. Recent strides in bioinformatics and genetics have significantly advanced the studies on synthesis of steroidal compounds. This review highlights recent advancements in the synthesis of high-value steroids, including the diverse steroid drug intermediate production via external steroidal modifying enzymes expression in engineered Mycobacteria, chemo-enzymatic synthesis of complex steroids, and yeast-based de novo synthesis. It specifically highlights the significant achievements in the chemo-enzymatic synthesis, which combines the precise site- and stereoselectivity of enzymatic transformations with the efficiency of chemosynthesis, enabling the concise synthesis of complex steroidal products. Recent advancements in chemoenzymatic strategies, especially those involving P450 hydroxylase, 3-sterone-Δ¹-dehydrogenase, reductase, and enzyme cascades, have significantly contributed to the efficient and straightforward synthesis of complex steroid medications. On this basis, the future research opportunities and challenges are also discussed, aiming to provide a reference for the efficient development of more value-added steroid compounds, including the development of new generation steroid intermediates, the discovery of novel steroid biocatalysts, and the establishment of steroid synthesis pathways in mycobacteria.

Although bioactive natural products have played significant roles in pharmaceutical research, their application potential is still limited by low isolated yields and structural modification challenges. To overcome these obstacles, developing environmentally friendly and highly efficient synthetic strategies offers exceptional approaches to obtain complex bioactive natural products and their analogs. Driven by advancements in microbial genetics and enzyme engineering, chemoenzymatic strategies, which merge enzymatic and synthetic transformations, are steadily emerging as potent tools in the synthesis of bioactive natural products, pharmaceutical components and other valuable molecules. These fashionable strategies offer not only advantages of chemical synthesis, such as simplicity, flexibility and scalability, but also those of biosynthesis, including environmental friendliness, high selectivity and efficiency. This will establish a linkage into the next-generation synthesis which is expected to break the boundary between chemistry and biology. Versatile cytochrome monooxygenases, P450s, can achieve inert C—H bond selective oxidation in mild and green conditions, a classically challenging organic transformation, providing novel retrosynthetic plans for complex natural products and becoming one of the hotspots in synthetic science. This review summarizes the recent applications of chemoenzymatic synthesis of natural products using P450-catalyzed site-selective oxidations as critical steps to improve the synthetic efficiency and avoid unnecessary functional group transformations and protection/deprotection steps, categorizing the case studies by structure features, such as steroids, terpenoids, and other types of natural products. At the end of this review, the current challenges in this field, such as heavily relying on the native activities of enzymes, are also analyzed and discussed, along with emerging research directions and technologies in new enzyme mining and enzyme engineering that may provide solutions to these challenges in the future. With constantly cross fusion of biosynthesis, chemical synthesis, synthetic biology, protein engineering, machine learning and other research field, P450-catalyzed site-selective oxidations will be becoming routine tools for synthetic chemists.

Ribosomally synthesized and post-translationally modified peptides (RiPPs) are a major class of peptide natural products that often contain noncanonical amino acids and structural motifs with promising potential as drug leads. One unique structural unit found in RiPPs is the C-terminal S-[(Z)-2-aminoethenyl]-D-cysteine (AviCys) or (2S,3S)-S-[(Z)-2-aminoethenyl]-3-methyl-D-cysteine (AviMeCys). Avi(Me)Cys-containing RiPPs usually exhibit potent antimicrobial or anticancer activities, which strictly require the presence of the C-terminal AviCys motifs. Despite the potential of Avi(Me)Cys-containing RiPPs as drug leads, lack of synthetic methods and biosynthetic systems to access these type of cyclic peptides impede the application of Avi(Me)Cys-containing peptides in medicinal chemistry. In this review, we summarize the current understanding of the biosynthesis of Avi(Me)Cys-containing peptides and the progress made in the development of chemical methods to synthesize Avi(Me)Cys motifs and derivatives. This review contains two following major sections: ① The biosynthetic process of Avi(Me)Cys motifs in the different families of Avi(Me)Cys-containing RiPPs, including lanthipeptides, lipolanthines, linaridins and thioamitides, are introduced with three essential enzymatic steps: first, a cysteine decarboxylase oxidatively decarboxylated the C-terminal cysteine, generating a highly reactive enethiol; subsequently, distinct enzymes catalyze the dehydration of a serine/threonine (Ser/Thr) residue or the dethiolation of a Cys residue in the precursor peptide by incorporating a dehydroalanine (Dha) or dehydrobutyrine (Dhb) residue; finally, a putative cyclase catalyzes the Michael-type addition between the enethiol group and a Dha/Dhb residue to yield the Avi(Me)Cys motif. Detailed enzymatic investigation of these biosynthetic steps are introduced. ② The chemical synthesis of the Avi(Me)Cys building block and their analogues via diverse synthetic methodology, including the radical thiol-yne coupling, the oxidative decarboxylation/decarbonylation, and the condensation of amides with acetals. Overall, further elucidation of the complete biosynthetic pathway for Avi(Me)Cys motifs in related RiPPs, along with advancements in the chemical synthesis of Avi(Me)Cys-containing natural product peptides, will facilitate the effective utilization of these bioactive peptide natural products.

Photocatalysis has the advantages of mild reaction conditions, renewability, and strong reactivity, but the poor selectivity limits its further application in asymmetric synthesis. Enzymatic catalysis shows unique advantages of high selectivity and specificity, but it leads to some defects such as limited reaction types and relatively narrow substrate scope. Photoenzymatic catalysis combines the advantages of high reactivity of photocatalysis with high selectivity of enzymatic catalysis, providing a novel synthesis model, that is more in line with the requirements of modern green organic synthesis. The term “photoenzyme reactions” narrowly refers to the synergistic catalysis involving photoenzymes, which can be classified into the following four categories: natural photoenzymactic reactions, artificial photoenzymatic reactions, photo-biocatalysis cascade reactions, and photo-induced promiscuous enzymatic reactions. However, natural photoenzymes are rarely found in nature, the stringent substrate scope further hinders their application. Artificial photoenzymes integrate photosensitizers into the scaffold of natural enzymes, which have been well summarized in previous reviews. Photo-biocatalysis cascade reactions by combining photochemical steps and enzymatic steps can realize some complex organic synthesis processes. Since the first report on NAD(P)H-dependent KREDs-catalyzed enantioselective radical dehalogenation of lactones, photosensitive cofactor-dependent unnatural photoenzymatic catalysis demonstrated its great potential in the field of organic synthesis, and continues to thrive to date, which has addressed many problems difficult to be achieved in traditional organic synthesis. Since 2023, research into the promiscuity of photoenzyme catalysis has witnessed continuous breakthroughs, reporting diverse novel types of photoenzyme catalytic reactions and mechanisms. The precise control over stereoselectivity and even regioselectivity directly addresses the longstanding challenges in the field of organic synthesis. While there have been many publications summarizing the related research, yet rarely focused on this rapidly evolving field. In this review, we summarize the recent and representative reports of photo-induced promiscuous enzymatic reactions, and classify them according to asymmetric dehalogenation, hydrogenation, intramolecular cyclization, intermolecular C—C/C—N/C—S cross-coupling reactions through free radical pathways, etc. These reactions exhibit different mechanisms due to different enzymes and substrates. For example, in the process of redox initiation, there are two types: single-electron reduction initiation and single-electron oxidation initiation. In the radical termination process, single-electron reduction termination and single-electron oxidation termination may be used. The diversity of mechanisms also makes it possible to develop more photoenzyme-catalyzed promiscuous reactions. In the future, new photoenzymatic methods will be promoted by rapidly developing technologies such as genetic engineering, synthetic biology, enzyme engineering, flow chemistry, and artificial intelligence, and more efficient and highly selective new-to-nature reactions will emerge, significantly expanding the application range of photoenzyme catalysis in the field of green asymmetric synthesis.

Stereochemical control is an important long-standing research topic in synthetic chemistry. Enzymes, as green and highly selective natural chiral catalysts, face constrains in synthetic applications due to their evolution-defined molecular structure and catalytic mechanism. Photocatalysis represents an important strategy to initiate free radical reactions by capturing photon energy to activate the chemical bonds of substrate molecules. As an emerging synthetic tool for asymmetric synthesis, photobiocatalysis merges the advantages of photochemistry and enzyme. Unfortunately, photoenzymes are rather rare in nature. Thus far photoenzymes identified are DNA photolyases, light-dependent protochlorophyllide reductases and blue light-responsive algal photodecarboxylases. Utilization of advanced molecular biotechnologies such as protein engineering and directed evolution under the guidance of chemical mechanisms of photocatalysis enables us to explore unknown photocatalytic functions of natural coenzymes, synergize photocatalysts and enzymes, and rationally design artificial photoenzyme with defined functions. The past few years have witnessed remarkable advances in these aspects, significantly surpassing the spectrum of substrates and reactions of enzyme catalysis, compensating for the scarcity of natural photo-enzymes and expanding the chemical boundaries and synthetic space of biocatalysis. This review summarizes the latest research progress in chemically-driven photoenzymatic asymmetric reactions. Based on their merging modes, the review categorizes the integration of light and enzyme into four classes: coupling of exogenous photocatalysts and native enzymes, photobiocatalysis driven by excitation of electron donor-acceptor complex, direct photoredox catalysis by coenzymes, and energy transfer photobiocatalysis. The chemical mechanism of bond activation by photocatalysis and synergistic control of stereoselectivity by enzyme in these photobiocatalytic systems are discussed in detail. In the end of this review, we also delineate the present challenges of asymmetric photobiocatalysis including the monotonicity of native photoactive cofactors and low catalytic efficiency for abiological reactions. This review also proposes future directions from the perspectives of new natural enzyme mining, expansion of artificial photoenzymes, enzyme de novo design, and whole-cell catalysis, which are anticipated to foster green bio-manufacturing of high-value functional molecules through the fusion of chemistry and biology and push forward the sustainable development of synthetic chemistry.