Multienzymatic Cascade Reactions via Enzyme Complex by Immobilization

Novel biocatalysts based on enzymes in complexes with nano- and micromaterials

In today's world, there is a wide array of materials engineered at the nano- and microscale, with numerous applications attributed to these innovations. This review aims to provide a concise overview of how nano- and micromaterials are utilized for enzyme immobilization. Enzymes act as eco-friendly biocatalysts extensively used in various industries and medicine. However, their widespread adoption faces challenges due to factors such as enzyme instability under different conditions, resulting in reduced effectiveness, high costs, and limited reusability. To address these issues, researchers have explored immobilization techniques using nano- and microscale materials as a potential solution. Such techniques offer the promise of enhancing enzyme stability against varying temperatures, solvents, pH levels, pollutants, and impurities. Consequently, enzyme immobilization remains a subject of great interest within both the scientific community and the industrial sector. As of now, the primary goal of enzyme immobilization is not solely limited to enabling reusability and stability. It has been demonstrated as a powerful tool to enhance various enzyme properties and improve biocatalyst performance and characteristics. The integration of nano- and microscale materials into biomedical devices is seamless, given the similarity in size to most biological systems. Common materials employed in developing these nanotechnology products include synthetic polymers, carbon-based nanomaterials, magnetic micro- and nanoparticles, metal and metal oxide nanoparticles, metal-organic frameworks, nano-sized mesoporous hydrogen-bonded organic frameworks, protein-based nano-delivery systems, lipid-based nano- and micromaterials, and polysaccharide-based nanoparticles.

Opportunities and Challenges of Metal-Organic Framework Micro/Nano Reactors for Cascade Reactions

Building bridges among different types of catalysts to construct cascades is a highly worthwhile pursuit, such as chemo-, bio-, and chemo-bio cascade reactions. Cascade reactions can improve the reaction efficiency and selectivity while reducing steps of separation and purification, thereby promoting the development of "green chemistry". However, compatibility issues in cascade reactions pose significant constraints on the development of this field, particularly concerning the compatibility of diverse catalyst types, reaction conditions, and reaction rates. Metal-organic framework micro/nano reactors (MOF-MNRs) are porous crystalline materials formed by the self-assembly coordination of metal sites and organic ligands, possessing a periodic network structure. Due to the uniform pore size with the capability of controlling selective transfer of substances as well as protecting active substances and the organic-inorganic parts providing reactive microenvironment, MOF-MNRs have attracted significant attention in cascade reactions in recent years. In this Perspective, we first discuss how to address compatibility issues in cascade reactions using MOF-MNRs, including structural design and synthetic strategies. Then we summarize the research progress on MOF-MNRs in various cascade reactions. Finally, we analyze the challenges facing MOF-MNRs and potential breakthrough directions and opportunities for the future.

Recent Advances on Key Enzymes of Microbial Origin in the Lycopene Biosynthesis Pathway

Lycopene is a common carotenoid found mainly in ripe red fruits and vegetables that is widely used in the food industry due to its characteristic color and health benefits. Microbial synthesis of lycopene is gradually replacing the traditional methods of plant extraction and chemical synthesis as a more economical and productive manufacturing strategy. The biosynthesis of lycopene is a typical multienzyme cascade reaction, and it is important to understand the characteristics of each key enzyme involved and how they are regulated. In this paper, the catalytic characteristics of the key enzymes involved in the lycopene biosynthesis pathway and related studies are first discussed in detail. Then, the strategies applied to the key enzymes of lycopene synthesis, including fusion proteins, enzyme screening, combinatorial engineering, CRISPR/Cas9-based gene editing, DNA assembly, and scaffolding technologies are purposefully illustrated and compared in terms of both traditional and emerging multienzyme regulatory strategies. Finally, future developments and regulatory options for multienzyme synthesis of lycopene and similar secondary metabolites are also discussed.

Orientation-Controllable Enzyme Cascade on Electrode for Bioelectrocatalytic Chain Reaction

The accomplishment of concurrent interenzyme chain reaction and direct electric communication in a multienzyme-electrode is challenging since the required condition of multienzymatic binding conformation is quite complex. In this study, an enzyme cascade-induced bioelectrocatalytic system has been constructed using solid binding peptide (SBP) as a molecular binder that coimmobilizes the invertase (INV) and flavin adenine dinucleotide (FAD)-dependent glucose dehydrogenase gamma-alpha complex (GDHγα) cascade system on a single electrode surface. The SBP-fused enzyme cascade was strategically designed to induce diverse relative orientations of coupling enzymes while enabling efficient direct electron transfer (DET) at the FAD cofactor of GDHγα and the electrode interface. The interenzyme relative orientation was found to determine the intermediate delivery route and affect overall chain reaction efficiency. Moreover, interfacial DET between the fusion GDHγα and the electrode was altered by the binding conformation of the coimmobilized enzyme and fusion INVs. Collectively, this work emphasizes the importance of interenzyme orientation when incorporating enzymatic cascade in an electrocatalytic system and demonstrates the efficacy of SBP fusion technology as a generic tool for developing cascade-induced direct bioelectrocatalytic systems. The proposed approach is applicable to enzyme cascade-based bioelectronics such as biofuel cells, biosensors, and bioeletrosynthetic systems utilizing or producing complex biomolecules.

Hierarchical covalent organic framework-foam for multi-enzyme tandem catalysis

Covalent organic frameworks (COFs) are ideal host matrices for biomolecule immobilization and biocatalysis due to their high porosity, various functionalities, and structural robustness. However, the porosity of COFs is limited to the micropore dimension, which restricts the immobilization of enzymes with large volumes and obstructs substrate flow during enzyme catalysis. A hierarchical 3D nanostructure possessing micro-, meso-, and macroporosity could be a beneficial host matrix for such enzyme catalysis. In this study, we employed an in situ CO2 gas effervescence technique to induce disordered macropores in the ordered 2D COF nanostructure, synthesizing hierarchical TpAzo COF-foam. The resulting TpAzo foam matrix facilitates the immobilization of multiple enzymes with higher immobilization efficiency (approximately 1.5 to 4-fold) than the COF. The immobilized cellulolytic enzymes, namely β-glucosidase (BGL), cellobiohydrolase (CBH), and endoglucanase (EG), remain active inside the TpAzo foam. The immobilized BGL exhibited activity in organic solvents and stability at room temperature (25 °C). The enzyme-immobilized TpAzo foam exhibited significant activity towards the hydrolysis of p-nitrophenyl-β-d-glucopyranoside (BGL@TpAzo-foam: Km and Vmax = 23.5 ± 3.5 mM and 497.7 ± 28.0 μM min-1) and carboxymethylcellulose (CBH@TpAzo-foam: Km and Vmax = 18.3 ± 4.0 mg mL-1 and 85.2 ± 9.6 μM min-1 and EG@TpAzo-foam: Km and Vmax = 13.2 ± 2.0 mg mL-1 and 102.2 ± 7.1 μM min-1). Subsequently, the multi-enzyme immobilized TpAzo foams were utilized to perform a one-pot tandem conversion from carboxymethylcellulose (CMC) to glucose with high recyclability (10 cycles). This work opens up the possibility of synthesizing enzymes immobilized in TpAzo foam for tandem catalysis.

Silver/chiral pyrrolidinopyridine relay catalytic cycloisomerization/(2 + 3) cycloadditions of enynamides to asymmetrically synthesize bispirocyclopentenes as PDE1B inhibitors

Significant progress has been made in asymmetric synthesis through the use of transition metal catalysts combined with Lewis bases. However, the use of a dual catalytic system involving 4-aminopyridine and transition metal has received little attention. Here we show a metal/Lewis base relay catalytic system featuring silver acetate and a modified chiral pyrrolidinopyridine (PPY). It was successfully applied in the cycloisomerization/(2 + 3) cycloaddition reaction of enynamides. Bispirocyclopentene pyrazolone products could be efficiently synthesized in a stereoselective and economical manner (up to >19:1 dr, 99.5:0.5 er). Transformations of the product could access stereodivergent diastereoisomers and densely functionalized polycyclic derivatives. Mechanistic studies illustrated the relay catalytic model and the origin of the uncommon chemoselectivity. In subsequent bioassays, the products containing a privileged drug-like scaffold exhibited isoform-selective phosphodiesterase 1 (PDE1) inhibitory activity in vitro. The optimal lead compound displayed a good therapeutic effect for ameliorating pulmonary fibrosis via inhibiting PDE1 in vivo.

Synthesis of Nitrogen-Containing Heterocyclic Scaffolds through Sequential Reactions of Aminoalkynes with Carbonyls

Sequential reactions of aminoalkynes represent a powerful tool to easily assembly biologically important polyfunctionalized nitrogen heterocyclic scaffolds. Metal catalysis often plays a key role in terms of selectivity, efficiency, atom economy, and green chemistry of these sequential approaches. This review examines the existing literature on the applications of reactions of aminoalkynes with carbonyls, which are emerging for their synthetic potential. Aspects concerning the features of the starting reagents, the catalytic systems, alternative reaction conditions, pathways and possible intermediates are provided.

Multiple strategies for the development of multienzyme complex for one-pot reactions

The main intention in the modern era is to make life and activities on earth more comfortable by adding necessary products through biological machinery. Millions of tons of biological raw materials and lignocellulosic biomass are wasted by burning each year without providing benefits to living organisms. Instead of being the cause of disturbing the natural environment by increasing global warming and pollutants worldwide, now, it is the need of the hour to develop an advanced strategy to utilize these biological raw materials to produce renewable energy resources to meet the energy crisis. The review presents the idea of multiple enzymes in one step to hydrolyze complex biomaterials into useful products. The paper discusses how multiple enzymes are arranged in a cascade for complete hydrolysis of raw material in one-pot to prevent multistep, time consuming, and expensive methods. Furthermore, there was the immobilization of multiple enzymes in a cascade system with in vitro and in vivo conditions for reusability of enzymes. The role of genetic engineering, metabolic engineering, and random mutation techniques is described for the development of multiple enzyme cascades. Techniques that are involved in the improvement of native strain to recombinant strain for the enhancement of hydrolytic capacity were used. The preparative steps, before enzymatic hydrolysis like acid, and base treatment methods are more effective for improving the hydrolysis of biomass by multiple enzymes in a one-pot system. Finally, the applications of one-pot multienzyme complexes in biofuel production from lignocellulosic biomass, biosensor production, medicine, food industry, and the conversion of biopolymers into useful products are described.

A two-enzyme system in an amorphous metal-organic framework for the synthesis of D-phenyllactic acid

In this study, we synthesized an amorphous metal-organic framework by adjusting the concentration of precursors, and established a two-enzyme system consisting of lactate dehydrogenase (LDH) and glucose dehydrogenase (GDH), which successfully achieved coenzyme recycling, and applied it to the synthesis of D-phenyllactic acid (D-PLA). The prepared two-enzyme-MOF hybrid material was characterized using XRD, SEM/EDS, XPS, FT-IR, TGA, CLSM, etc. In addition, reaction kinetic studies indicated that the MOF-encapsulated two-enzyme system exhibited faster initial reaction velocities than free enzymes due to its amorphous ZIF-generated mesoporous structure. Furthermore, the pH stability and temperature stability of the biocatalyst were evaluated, and the results indicated a significant improvement compared to the free enzymes. Moreover, the amorphous structure of the mesopores still maintained the shielding effect and protected the enzyme structure from damage by proteinase K and organic solvents. Finally, the remaining activity of the biocatalyst for the synthesis of D-PLA reached 77% after 6 cycles of use, and the coenzyme regeneration still maintained at 63%, while the biocatalyst also retained 70% and 68% residual activity for the synthesis of D-PLA after 12 days of storage at 4 °C and 25 °C, respectively. This study provides a reference for the design of MOF-based multi-enzyme biocatalysts.

Polymerization-Induced Proteinosome Formation Initiated by Artificial Cells

Cellular communication is essential for living cells to coordinate the individual cellular responses and make collective behaviors. In the past decade, the communications between artificial cells have aroused great interest due to the potential applications of the structures in bioscience and biotechnology. To mimic the cellular communication, artificial cell assisted synthesis of proteinosomes was studied in this research. Multienzyme proteinosomes with glucose oxidase (GOx) and horseradish peroxidase (HRP) decorated on the membranes were synthesized by the thermally triggered self-assembly approach. Free radicals produced in a cascade reaction taking place on the surfaces of the multienzyme proteinosomes initiated reversible addition-fragmentation chain transfer (RAFT) polymerization of NIPAM at a temperature above LCST of PNIPAM in the presence of bovine serum albumin (BSA) or alcohol dehydrogenase (ADH)/acetaldehyde dehydrogenase (ALDH), and daughter proteinosomes with BSA or ADH/ALDH on the surfaces were fabricated. The structures of the GOx/HRP initiator proteinosomes, and the synthesized daughter proteinosomes were characterized with transmission electron microscopy, atomic force microscopy, fluorescence microscopy, dynamic light scattering, and micro-DSC. Enzyme activity assays demonstrate the high bioactivities of the enzymes on the surfaces of the initiator and the synthesized daughter proteinosomes.

Co-Immobilization of GOD & HRP on Y-Shaped DNA Scaffold and the Regulation of Inter-Enzyme Distance

In multienzymes cascade reaction, the inter-enzyme spacing is supposed to be a factor affecting the cascade activity. Here, a simple and efficient Y-shaped DNA scaffold is assembled using two partially complementary DNA single strands on magnetic microspheres, which is used to coimmobilize glucose oxidase (GOD) and horseradish peroxidase (HRP). As a result, on poly(vinyl acetate) magnetic microspheres (PVAC), GOD/HRP-DNA@PVAC multienzyme system is obtained, which can locate GOD and HRP accurately and control the inter-enzyme distance precisely. The distance between GOD and HRP is regulated by changing the length of DNA strand. It showed that the cascade activity is significantly distance-dependent. Moreover, the inter-enzyme spacing is not the closer the better, and too short distance would generate steric hindrance between enzymes. The cascade activity reached the maximum value of 967 U mg^-1 at 13.6 nm, which is 3.5 times higher than that of free enzymes. This is ascribed to the formation of substrate channeling.

One-pot sequential cascade reaction for selective gluconic acid production from cellulose photobiorefining

We demonstrate the feasibility of cellulose photobiocatalytic conversion with >75% cellulose conversion and >75% gluconic acid selectivity from converted glucose. This process is realized via a one-pot sequential cascade reaction by cellulase enzymes and a carbon nitride photocatalyst that can realize selective glucose photoreforming into gluconic acid. Cellulase enzymes breakdown cellulose into glucose, which will subsequently be converted into gluconic acid by essential oxidative species (˙O₂^- and ˙OH) via a selective photocatalysis process with simultaneous H₂O₂ formation. This work demonstrates a good example to realize direct cellulose photobiorefining into value-added chemicals via the photo-bio hybrid system.

Mesoporous Polymeric Ionic Liquid via Confined Polymerization for Laccase Immobilization towards Efficient Degradation of Phenolic Pollutants

Laccase immobilization is a promising method that can be used for the recyclable treatment of refractory phenolic pollutants (e.g., chlorophenols) under mild conditions, but the method is still hindered by the trade-off limits of supports in terms of their high specific surface area and rich functional groups. Herein, confined polymerization was applied to create abundant amino-functionalized polymeric ionic liquids (PILs) featuring a highly specific surface area and mesoporous structure for chemically immobilizing laccase. Benefiting from this strategy, the specific surface area of the as-synthesized PILs was significantly increased by 60-fold, from 5 to 302 m2/g. Further, a maximum activity recovery of 82% towards laccase was recorded. The tolerance and circulation of the immobilized laccase under harsh operating conditions were significantly improved, and the immobilized laccase retained more than 84% of its initial activity after 15 days. After 10 cycles, the immobilized laccase was still able to maintain 80% of its activity. Compared with the free laccase, the immobilized laccase exhibited enhanced stability in the biodegradation of 2,4-dichlorophenol (2,4-DCP), recording around 80% (seven cycles) efficiency. It is proposed that the synergistic effect between PILs and laccase plays an important role in the enhancement of stability and activity in phenolic pollutant degradation. This work provides a strategy for the development of synthetic methods for PILs and the improvement of immobilized laccase stability.

Nanostructured supports for multienzyme co-immobilization for biotechnological applications: Achievements, challenges and prospects

The synergistic combination of current biotechnological and nanotechnological research has turned to multienzyme co-immobilization as a promising concept to design biocatalysis engineering. It has also intensified the development and deployment of multipurpose biocatalysts, for instance, multienzyme co-immobilized constructs, via biocatalysis/protein engineering to scale-up and fulfil the ever-increasing industrial demands. Considering the characteristic features of both the loaded multienzymes and nanostructure carriers, i.e., selectivity, specificity, stability, resistivity, induce activity, reaction efficacy, multi-usability, high catalytic turnover, optimal yield, ease in recovery, and cost-effectiveness, multienzyme-based green biocatalysts have become a powerful norm in biocatalysis/protein engineering sectors. In this context, the current state-of-the-art in enzyme engineering with a synergistic combination of nanotechnology, at large, and nanomaterials, in particular, are significantly contributing and providing robust tools to engineer and/or tailor enzymes to fulfil the growing catalytic and contemporary industrial needs. Considering the above critics and unique structural, physicochemical, and functional attributes, herein, we spotlight important aspects spanning across prospective nano-carriers for multienzyme co-immobilization. Further, this work comprehensively discuss the current advances in deploying multienzyme-based cascade reactions in numerous sectors, including environmental remediation and protection, drug delivery systems (DDS), biofuel cells development and energy production, bio-electroanalytical devices (biosensors), therapeutical, nutraceutical, cosmeceutical, and pharmaceutical oriented applications. In conclusion, the continuous developments in nano-assembling the multienzyme loaded co-immobilized nanostructure carriers would be a unique way that could act as a core of modern biotechnological research.

Metal-Catalyzed Cascade Reactions between Alkynoic Acids and Dinucleophiles: A Review

Cascade reactions provide a straightforward access to many valuable compounds and reduce considerably the number of steps of a synthetic sequence. Among the domino and multicomponent processes that involve alkynes, the cascade reaction between alkynoic acids and C-, N-, O- and S-aminonucleophiles stands out as a particularly powerful tool for the one-pot construction of libraries of nitrogen-containing heterocyclic compounds with scaffold diversity and molecular complexity. This reaction, based on an initial metal-catalyzed cycloisomerization that generates an alkylidene lactone intermediate, was originally catalyzed by gold(I) catalysts, along with silver salts or Brönsted acid additives, but other alternative metal catalysts have emerged in the last decade as well as different reaction media. This review examines the existing literature on the topic of metal-catalyzed cascade reactions of acetylenic acids and dinucleophiles and discusses aspects concerning substrate/catalyst ratio for every catalyst system, nature of the aminonucleophile involved and substrate scope. In addition, alternative solvents are also considered, and an insight into the pathway of the reaction and possible intermediates is also provided.

The enhancement of enzyme cascading via tetrahedral DNA framework modification

Enzyme clustering is widely used in many organisms to increase the catalytic efficiency of cascade reactions. Inspired by nature, organizing enzymes within a cascade reaction also draws much attention in both basic research and industrial processes. An important step for organizing enzymes precisely in vitro is enzyme modification. However, modifying enzymes without sacrificing their activity remains challenging until now. For example, labeling enzymes with DNA, one of the well-established enzyme modification methods, has been shown to significantly reduce the enzymatic activity. Herein we report an enzyme conjugation method that can rescue the reduction of enzymatic activity caused by DNA labeling. We demonstrate that immobilizing DNA-modified enzymes on the vertex of TDNs (tetrahedral DNA nanostructures) enhances the enzymatic activity compared with their unmodified counterparts. Using this strategy, we have further developed an ultra-sensitive and high-throughput electrochemical biosensor for sarcosine detection, which holds great promise for prostate cancer screening.

Recycling of Cofactors in Crude Enzyme Hydrogels as Co-immobilized Heterogeneous Biocatalysts for Continuous-Flow Asymmetric Reduction of Ketones

Flow biocatalysis involving oxidoreductase is limited by the difficulty in recycling expensive cofactors. In this study, an enzyme-rich hydrogel monolithic microreactor was developed via in situ microfluidic assembly of inexpensive crude enzymes. This porous gel biocatalyst exhibited good tethering functions to nicotinamide cofactors; thus, they were retained by the hydrogel to controllably form a novel heterogeneous biocatalyst with self-sufficient cofactors. The flow asymmetric production of a chiral alcohol in this cofactor-entrapped gel microreactor achieved >99 % enantioselectivity and a high space-time yield of 46.3 g L^-1  h^-1 at 94.8 % conversion. Moreover, the turnover number of cofactors reached as high as 4800 after continuous operation of 160 reactor volumes, realizing significantly higher utilization of the cofactors compared with many reported strategies. Furthermore, this engineered heterogeneous biocatalyst exhibited improved performance in terms of product tolerance and storage stability, paving the way for a green, cost-effective, and sustainable continuous-flow production of enantiopure alcohols.

Designing multifunctional biocatalytic cascade system by multi-enzyme co-immobilization on biopolymers and nanostructured materials

In recent decades, enzyme-based biocatalytic systems have garnered increasing interest in industrial and applied research for catalysis and organic chemistry. Many enzymatic reactions have been applied to sustainable and environmentally friendly production processes, particularly in the pharmaceutical, fine chemicals, and flavor/fragrance industries. However, only a fraction of the enzymes available has been stepped up towards industrial-scale manufacturing due to low enzyme stability and challenging separation, recovery, and reusability. In this context, immobilization and co-immobilization in robust support materials have emerged as valuable strategies to overcome these inadequacies by facilitating repeated or continuous batch operations and downstream processes. To further reduce separations, it can be advantageous to use multiple enzymes at once in one pot. Enzyme co-immobilization enables biocatalytic synergism and reusability, boosting process efficiency and cost-effectiveness. Several studies on multi-enzyme immobilization and co-localization propose kinetic advantages of the enhanced turnover number for multiple enzymes. This review spotlights recent progress in developing versatile biocatalytic cascade systems by multi-enzyme co-immobilization on environmentally friendly biopolymers and nanostructured materials and their application scope in the chemical and biotechnological industries. After a succinct overview of carrier-based and carrier-free immobilization/co-immobilizations, co-immobilization of enzymes on a range of biopolymer and nanomaterials-based supports is thoroughly compiled with contemporary and state-of-the-art examples. This study provides a new horizon in developing effective and innovative multi-enzymatic systems with new possibilities to fully harness the adventure of biocatalytic systems.

Designed Synthesis of Compartmented Bienzyme Biocatalysts Based on Core-Shell Zeolitic Imidazole Framework Nanostructures

For complex cascade biocatalysis, multienzyme compartmentalization helps to optimize substrate transport channels and promote the orderly and tunable progress of step reactions. Herein, a simple and general synthesis strategy is proposed for the construction of a multienzyme biocatalyst by compartmentalizing glucose oxidase and horseradish peroxidase (GOx and HRP) within core-shell zeolite imidazole frameworks (ZIF)-8@ZIF-8 nanostructures. Owing to the combined effects of biomimetic mineralization and the fine regulation of the ZIF-8 growth process, the uniform shell encloses the seed (core) surface by epitaxial growth, and the bienzyme system is accurately localized in a controlled manner. The versatility of this strategy is also reflected in ZIF-67. Meanwhile, with the ability to covalently bind divalent metal ions, lithocholic acid (LCA) is used as a competitive ligand to improve the pore structure of the ZIF from a single micropore to a hierarchical micro/mesopore network, which greatly increases mass transfer efficiency. Furthermore, the multienzyme cascade reaction is exemplified by the oxidation of o-phenylenediamine (OPD). The findings show that the bienzyme assembly strategy significantly affects the biocatalytic efficiency mainly by influencing the utilization efficiency of the intermediate (Hydrogen peroxide, H₂ O₂ ) between the step reactions. This study sheds new light on facile synthetic routes to constructing in vitro multienzyme biocatalysts.

MOF-Immobilized Two-in-One Engineered Enzymes Enhancing Activity of Biocatalytic Cascade for Tumor Therapy

Biocatalytic systems based on enzyme cascade reactions have attracted growing interest in the field of biocatalytic medicine. However, it is a major challenge to reasonably construct enzyme cascade reactions with high stability, selectivity, and catalytic efficiency for the in vivo biocatalytic application. Herein, two-in-one engineered glucose oxidase (GOx-Fe⁰ ) is fabricated by a biomineralization strategy, through which a nanozyme (Fe⁰ NP) is anchored within the inner cavity of GOx. Then, GOx-Fe⁰ is immobilized in a pH-sensitive metal-organic framework (MOF) zeolitic imidazolate framework-8 (ZIF-8) to establish a stable and effective MOF-immobilized two-in-one engineered enzyme, GOx-Fe⁰ @ZIF-8. In vitro studies show that GOx-Fe⁰ @ZIF-8 exhibits excellent stability and high pH/glucose selectivity, and the shorter spacing between cascade enzymes can increase the cascade throughput and effectively improve the reaction efficiency of the enzyme cascade. In vivo experiments exhibit that GOx-Fe⁰ @ZIF-8 solves the instability and systemic toxicity of free enzymes, and achieves deep tumor penetration and significant chemodynamic therapeutic efficacy through a pH/glucose-selective enzyme cascade reaction in tumor site. Taken together, such an orchestrated enzyme engineering strategy can effectively improve enzyme stability, selectivity, and enzyme cascade reaction efficiency via chemical transformations, and also provide a promising strategy for the application of biocatalytic cascade reactions in vivo.

Rhodium-Based MOF-on-MOF Difunctional Core-Shell Nanoreactor for NAD(P)H Regeneration and Enzyme Directed Immobilization

An organometallic complex-catalyzed artificial coenzyme regeneration system has attracted widespread attention. However, the combined use of organometallic complex catalysts and natural enzymes easily results in mutual inactivation. Herein, we establish a rhodium-based metal-organic framework (MOF)-on-MOF difunctional core-shell nanoreactor as an artificial enzymatic NAD(P)H regeneration system. UiO67 as the core is used to capture rhodium molecules for catalyzing NAD(P)H regeneration. UiO66 as the shell is used to specifically immobilize His-tagged lactate dehydrogenase (LDH) and serve as a protection shield for LDH and [Cp*Rh(bpy)Cl]⁺ to prevent mutual inactivation. A variety of results indicate that UiO67@Rh@UiO66 has good activity in realizing NAD(P)H regeneration. Noteworthily, UiO67@Rh@UiO66@LDH maintains a high activity level even after 10 cycles. This work reports a novel NAD(P)H regeneration platform to open up a new avenue for constructing chemoenzyme coupling systems.

Synthesis of Novel Polymer-Assisted Organic-Inorganic Hybrid Nanoflowers and Their Application in Cascade Biocatalysis

This study reports on the synthesis of novel bienzyme polymer-assisted nanoflower complexes (PANF), their morphological and structural characterization, and their effectiveness as cascade biocatalysts. First, highly porous polyamide 6 microparticles (PA6 MP) are synthesized by activated anionic polymerization in solution. Second, the PA6 MP are used as carriers for hybrid bienzyme assemblies comprising glucose oxidase (GOx) and horseradish peroxidase (HRP). Thus, four PANF complexes with different co-localization and compartmentalization of the two enzymes are prepared. In samples NF GH/PA and NF GH@PA, both enzymes are localized within the same hybrid flowerlike organic-inorganic nanostructures (NF), the difference being in the way the PA6 MP are assembled with NF. In samples NF G/PAiH and NF G@PAiH, only GOx is located in the NF, while HRP is preliminary immobilized on PA6 MP. The morphology and the structure of the four PANF complexes have been studied by microscopy, spectroscopy, and synchrotron X-ray techniques. The catalytic activity of the four PANF was assessed by a two-step cascade reaction of glucose oxidation. The PANF complexes are up to 2-3 times more active than the free GOx/HRP dyad. They also display enhanced kinetic parameters, superior thermal stability in the 40-60 °C range, optimum performance at pH 4-6, and excellent storage stability. All PANF complexes are active for up to 6 consecutive operational cycles.

Co-Immobilization of D-Amino Acid Oxidase, Catalase, and Transketolase for One-Pot, Two-Step Synthesis of L-Erythrulose

Here, we present an immobilized enzyme cascade in a basket-type reactor allowing a one-pot, two-step enzymatic synthesis of L-erythrulose from D-serine and glycolaldehyde. Three enzymes, D-amino acid oxidase from Rhodotorula gracilis (DAAORg), catalase from bovine liver (CAT), and transketolase from Geobacillus stearothermophilus (TKgst) were covalently immobilized on silica monolithic pellets, characterized by an open structure of interconnected macropores and a specific surface area of up to 300 m2/g. Three strategies were considered: (i) separate immobilization of enzymes on silica supports ([DAAO][CAT][TK]), (ii) co-immobilization of two of the three enzymes followed by the third ([DAAO+CAT][TK]), and (iii) co-immobilization of all three enzymes ([DAAO+CAT+TK]). The highest L-erythrulose concentrations were observed for the co-immobilization protocols (ii) and (iii) (30.7 mM and 29.1 mM, respectively). The reusability study showed that the best combination was [DAAO + CAT][TK], which led to the same level of L-erythrulose formation after two reuse cycles. The described process paves the way for the effective synthesis of a wide range of α-hydroxyketones from D-serine and suitable aldehydes.

Construction of Bi-Enzyme Self-Assembly Clusters Based on SpyCatcher/SpyTag for the Efficient Biosynthesis of (R)-Ethyl 2-hydroxy-4-phenylbutyrate

Cascade reactions catalyzed by multi-enzyme systems are important in science and industry and can be used to synthesize drugs and nutrients. In this study, two types of macromolecules of bi-enzyme self-assembly clusters (BESCs) consisting of carbonyl reductase (CpCR) and glucose dehydrogenase (GDH) were examined. Stereoselective CpCR and GDH were successfully fused with SpyCatcher and SpyTag, respectively, to obtain four enzyme modules, namely: SpyCatcher-CpCR, SpyCatcher-GDH, SpyTag-CpCR, and SpyTag-GDH, which were covalently coupled in vitro to form two types of hydrogel-like BESCs: CpCR-SpyCatcher-SpyTag-GDH and GDH-SpyCatcher-SpyTag-CpCR. CpCR-SpyCatcher-SpyTag-GDH showed a better activity and efficiently converted ethyl 2-oxo-4-phenylbutyrate (OPBE) to ethyl(R)2-hydroxy-4-phenylbutanoate ((R)-HPBE), while regenerating NADPH. At 30 °C and pH 7, the conversion rate of OPBE with CpCR-SpyCatcher-SpyTag-GDH as a catalyst reached 99.9%, with the ee% of (R)-HPBE reaching above 99.9%. This conversion rate was 2.4 times higher than that obtained with the free bi-enzyme. The pH tolerance and temperature stability of the BESCs were also improved compared with those of the free enzymes. In conclusion, bi-enzyme assemblies were docked using SpyCatcher/SpyTag to produce BESCs with a special structure and excellent catalytic activity, improving the catalytic efficiency of the enzyme.

Advances in 4D printing: from stimulation to simulation

The advancement of four-dimensional (4D) printing has been fueled by the rise in demand for additive manufacturing and the expansion in shape-memory materials. The printing of smart substances that respond to external stimuli is known as 4D printing. 4D printing allows highly controlled shapes to simulate the physiological milieu by adding time dimensions. The 4D printing is suitable with current progress in smart compounds, printers, and its mechanism of action. The 4D printing paradigm, a revolutionary enhancement of 3D printing, was anticipated by various engineering disciplines. Tissue engineering, medicinal, consumer items, aerospace, and organ engineering use 4D printing technology. The current review mainly focuses on the basics of 4D printing and the methods used therein. It also discusses the time-dependent behavior of stimulus-sensitive compounds, which are widely used in 4D printing. In addition, this review highlights material aspects, specifically related to shape-memory polymers, stimuli-responsive materials (classified as physical, chemical, and biological), and modified materials, the backbone of 4D printing technology. Finally, potential applications of 4D printing in the biomedical sector are also discussed with challenges and future perspectives.

Enzyme cascades for the synthesis of nucleotide sugars: Updates to recent production strategies

Nucleotide sugars play an elementary role in nature as building blocks of glycans, polysaccharides, and glycoconjugates used in the pharmaceutical, cosmetics, and food industries. As substrates of Leloir-glycosyltransferases, nucleotide sugars are essential for chemoenzymatic in vitro syntheses. However, high costs and the limited availability of nucleotide sugars prevent applications of biocatalytic cascades on a large industrial scale. Therefore, the focus is increasingly on nucleotide sugar synthesis strategies to make significant application processes feasible. The chemical synthesis of nucleotide sugars and their derivatives is well established, but the yields of these processes are usually low. Enzyme catalysis offers a suitable alternative here, and in the last 30 years, many synthesis routes for nucleotide sugars have been discovered and used for production. However, many of the published procedures shy away from assessing the practicability of their processes. With this review, we give an insight into the development of the (chemo)enzymatic nucleotide sugar synthesis pathways of the last years and present an assessment of critical process parameters such as total turnover number (TTN), space-time yield (STY), and enzyme loading.

From Protein Film Electrochemistry to Nanoconfined Enzyme Cascades and the Electrochemical Leaf

Protein film electrochemistry (PFE) has given unrivalled insight into the properties of redox proteins and many electron-transferring enzymes, allowing investigations of otherwise ill-defined or intractable topics such as unstable Fe-S centers and the catalytic bias of enzymes. Many enzymes have been established to be reversible electrocatalysts when attached to an electrode, and further investigations have revealed how unusual dependences of catalytic rates on electrode potential have stark similarities with electronics. A special case, the reversible electrochemistry of a photosynthetic enzyme, ferredoxin-NADP⁺ reductase (FNR), loaded at very high concentrations in the 3D nanopores of a conducting metal oxide layer, is leading to a new technology that brings PFE to myriad enzymes of other classes, the activities of which become controlled by the primary electron exchange. This extension is possible because FNR-based recycling of NADP(H) can be coupled to a dehydrogenase, and thence to other enzymes linked in tandem by the tight channelling of cofactors and intermediates within the nanopores of the material. The earlier interpretations of catalytic wave-shapes and various analogies with electronics are thus extended to initiate a field perhaps aptly named "cascade-tronics", in which the flow of reactions along an enzyme cascade is monitored and controlled through an electrochemical analyzer. Unlike in photosynthesis where FNR transduces electron transfer and hydride transfer through the unidirectional recycling of NADPH, the "electrochemical leaf" (e-Leaf) can be used to drive reactions in both oxidizing and reducing directions. The e-Leaf offers a natural way to study how enzymes are affected by nanoconfinement and crowding, mimicking the physical conditions under which enzyme cascades operate in living cells. The reactions of the trapped enzymes, often at very high local concentration, are thus studied electrochemically, exploiting the potential domain to control rates and direction and the current-rate analogy to derive kinetic data. Localized NADP(H) recycling is very efficient, resulting in very high cofactor turnover numbers and new opportunities for controlling and exploiting biocatalysis.

Development of a Multi-Enzymatic Biocatalytic System through Immobilization on High Quality Few-Layer bio-Graphene

In this work, we report the green production of few-layer bio-Graphene (bG) through liquid exfoliation of graphite in the presence of bovine serum albumin. Microscopic characterization evaluated the quality of the produced nanomaterial, showing the presence of 3-4-layer graphene. Moreover, spectroscopic techniques also confirmed the quality of the resulted bG, as well as the presence of bovine serum albumin on the graphene sheets. Next, for the first time, bG was used as support for the simultaneous covalent co-immobilization of three enzymes, namely β-glucosidase, glucose oxidase, and horseradish peroxidase. The three enzymes were efficiently co-immobilized on bG, demonstrating high immobilization yields and activity recoveries (up to 98.5 and 90%, respectively). Co-immobilization on bG led to an increase of apparent K_M values and a decrease of apparent V_max values, while the stability of the nanobiocatalysts prevailed compared to the free forms of the enzymes. Co-immobilized enzymes exhibited high reusability, preserving a significant part of their activity (up to 72%) after four successive catalytic cycles at 30 °C. Finally, the tri-enzymatic nanobiocatalytic system was applied in three-step cascade reactions, involving, as the first step, the hydrolysis of p-Nitrophenyl-β-D-Glucopyranoside and cellobiose.

Site-Specific and Tunable Co-immobilization of Proteins onto Magnetic Nanoparticles via Spy Chemistry

Co-immobilization of multiple proteins onto one nanosupport has large potential in mimicking natural multiprotein complexes and constructing efficient cascade biocatalytic systems. However, control of different proteins regarding their spatial arrangement and loading ratio remains a big challenge, and protein co-immobilization often requires the use of purified proteins. Herein, built upon our recently designed SpyTag-functionalized magnetic nanoparticles (MNPs), we established a modular MNP platform for site-specific, tunable, and cost-effective protein co-immobilization. SpyCatcher-fused enhanced green fluorescent protein (i.e., EGFP-SpyCatcher) and mCherry red fluorescent protein (i.e., RFP-SpyCatcher) were designed and conjugated on MNPs, and the immobilized proteins showed 3-7-fold enhancement in storage stability and greatly improved stability against the freeze-thaw process compared to free proteins. The protein-conjugated MNPs also retained desirable colloidal stability and magnetic responsiveness, enabling facile proteins' recovery. Also, one-pot co-immobilization of the two proteins could be fine-tuned with their feed ratios. In addition, MNPs could selectively and efficiently co-immobilize both SpyCatcher-fused proteins from combined cell lysates without purification, offering a convenient and cost-effective approach for multiprotein immobilization. This MNP platform provides a facile and efficient tool to construct bionano hybrid materials (i.e., protein-based MNPs) and multiprotein systems for a variety of industrial and green chemistry applications.

Co-Enzymes with Dissimilar Stabilities: A Discussion of the Likely Biocatalyst Performance Problems and Some Potential Solutions

Enzymes have several excellent catalytic features, and the last few years have seen a revolution in biocatalysis, which has grown from using one enzyme to using multiple enzymes in cascade reactions, where the product of one enzyme reaction is the substrate for the subsequent one. However, enzyme stability remains an issue despite the many benefits of using enzymes in a catalytic system. When enzymes are exposed to harsh process conditions, deactivation occurs, which changes the activity of the enzyme, leading to an increase in reaction time to achieve a given conversion. Immobilization is a well-known strategy to improve many enzyme properties, if the immobilization is properly designed and controlled. Enzyme co-immobilization is a further step in the complexity of preparing a biocatalyst, whereby two or more enzymes are immobilized on the same particle or support. One crucial problem when designing and using co-immobilized enzymes is the possibility of using enzymes with very different stabilities. This paper discusses different scenarios using two co-immobilized enzymes of the same or differing stability. The effect on operational performance is shown via simple simulations using Michaelis–Menten equations to describe kinetics integrated with a deactivation term. Finally, some strategies for overcoming some of these problems are discussed.

Hierarchically Structured CA@ZIF-8 Biohybrids for Carbon Dioxide Mineralization

Carbonic anhydrase (CA) is a powerful biocatalyst for carbon dioxide (CO₂) mineralization, of which immobilization is usually used for maintaining its catalytic activity against harsh external stimuli. However, the incorporated materials for CA immobilization would commonly increase the internal diffusion resistance during the catalytic process, thereby decreasing the catalytic efficiency. In our study, poly-L-glutamic acid (PLGA) as the structure regulator was used to induce the synthesis of CA@zeolitic imidazolate framework-8 (CA@ZIF-8) biohybrids. The introduction of PLGA that could coordinate with Zn²⁺ interfered the crystallization of ZIF-8, thereby changing the morphological structure of CA@ZIF-8 biohybrids. With the increase of PLGA amount from 0 to 60 mg, PLGA(x)-CA@ZIF-8 biohybrids were gradually transformed from a dodecahedron structure to a 3D lamellar nano-flower structure, which caused elevated exposed surface area. Accordingly, the loading ratio was increased from 34.6 to 49.8 mg g_cat^-1, while the catalytic activity was elevated from 20.6 to 23.4%. The CO₂ conversion rate was enhanced by nearly two folds compared to PLGA(0)-CA@ZIF-8 under the optimized condition. The final CaCO₃ yield could reach 5.6 mg mg_cat^-1, whereas the reaction system could remain above 80% of the initial reaction activity after 8 cycles.

A critical review on biomass-based sustainable biorefineries using nanobiocatalysts: Opportunities, challenges, and future perspectives

Biocatalysts, including live microbial cells/enzymes, have been considered a predominant and advantageous tool for effectively transforming biomass into biofuels and valued biochemicals. However, high production costs, separation, and reusability limit its practical application. Immobilization of single and multi-enzymes by employing different nano-supports have gained massive attention because of its elevated exterior domain and high enzymatic performance. Application of nanobiocatalyst can overcome the drawbacks mainly, stability and reusability, thus reflecting the importance of biomass-based biorefinery to make it profitable and sustainable. This review provides an in-depth, comprehensive analysis of nanobiocatalysts systems concerning nano supports and biocatalytic performance characteristics. Furthermore, the effects of nanobiocatalyst on waste biomass to biofuel and valued bioproducts in the biorefinery approach and their critical assessment are discussed. Lastly, this review elaborates commercialization and market outlooks of the bioconversion process using nanobiocatalyst, followed by different strategies to overcome the limitations and future research directions on nanobiocatalytic-based industrial bioprocesses.

Coimmobilized enzymes as versatile biocatalytic tools for biomass valorization and remediation of environmental contaminants - A review

Due to stringent regulatory norms, waste processing faces confrontations and challenges in adapting technology for effective management through a convenient and economical system. At the global level, attempts are underway to achieve a green and sustainable treatment for the valorization of lignocellulosic biomass as well as organic contaminants in wastewater. Enzymatic treatment in the environmental aspect thrived on being the promising rapid strategy that appeased the aforementioned predicament. On that account, coimmobilization of various enzymes on single support enhances the catalytic activity ensuing operational stability with industrial applications. This review pivoted towards the coimmobilization of enzymes on diverse supports and their applications in biomass conversion to industrial value-added products and removal of contaminants in wastewater. The limelight of this study chronicles the unique breakthroughs in biotechnology for the production of reusable biocatalysts, which inculcating various enzymes towards the scope of environment application.

Combined chemoenzymatic strategy for sustainable continuous synthesis of the natural product hordenine

To improve sustainability, safety and cost-efficiency of synthetic methodologies, biocatalysis can be a helpful ally. In this work, a novel chemoenzymatic stategy ensures the rapid synthesis of hordenine, a valuable phenolic phytochemical under mild working conditions. In a two-step cascade, the immobilized tyrosine decarboxylase from Lactobacillus brevis (LbTDC) is here coupled with the chemical reductive amination of tyramine. Starting from the abundant and cost-effective amino acid l-tyrosine, the complete conversion to hordenine is achieved in less than 5 minutes residence time in a fully-automated continuous flow system. Compared to the metal-catalyzed N,N-dimethylation of tyramine, this biocatalytic approach reduces the process environmental impact and improves its STY to 2.68 g L^-1 h^-1.

Recent advancements in enzyme-incorporated nanomaterials: Synthesis, mechanistic formation, and applications

Over the past decade, nanotechnology has been developed and employed across various entities. Among the numerous nanostructured material types, enzyme-incorporated nanomaterials have shown great potential in various fields, as an alternative to biologically derived as well as synthetically developed hybrid structures. The mechanism of incorporating enzyme onto a nanostructure depends on several factors including the method of immobilization, type of nanomaterial, as well as operational and environmental conditions. The prospects of enzyme-incorporated nanomaterials have shown promising results across various applications, such as biocatalysts, biosensors, drug therapy, and wastewater treatment. This is due to their excellent ability to exhibit chemical and physical properties such as high surface-to-volume ratio, recovery and/or reusability rates, sensitivity, response scale, and stable catalytic activity across wide operating conditions. In this review, the evolution of enzyme-incorporated nanomaterials along with their impact on our society due to its state-of-the-art properties, and its significance across different industrial applications are discussed. In addition, the weakness and future prospects of enzyme-incorporated nanomaterials were also discussed to guide scientists for futuristic research and development in this field.

A Versatile Chemoenzymatic Nanoreactor that Mimics NAD(P)H Oxidase for the In Situ Regeneration of Cofactors

Herein, we report a multifunctional chemoenzymatic nanoreactor (NanoNOx) for the glucose-controlled regeneration of natural and artificial nicotinamide cofactors. NanoNOx are built of glucose oxidase-polymer hybrids that assemble in the presence of an organometallic catalyst: hemin. The design of the hybrid is optimized to increase the effectiveness and the directional channeling at low substrate concentration. Importantly, NanoNOx can be reutilized without affecting the catalytic properties, can show high stability in the presence of organic solvents, and can effectively oxidize assorted natural and artificial enzyme cofactors. Finally, the hybrid was successfully coupled with NADH-dependent dehydrogenases in one-pot reactions, using a strategy based on the sequential injection of a fuel, namely, glucose. Hence, this study describes the first example of a hybrid chemoenzymatic nanomaterial able to efficiently mimic NOx enzymes in cooperative one-pot cascade reactions.

Co-Immobilizing Two Glycosidases Based on Cross-Linked Enzyme Aggregates to Enhance Enzymatic Properties for Achieving High Titer Icaritin Biosynthesis

Icaritin is a rare and high-value isopentane flavonoid compound with remarkable activities. Increasing yields while reducing cost has been a great challenge in icaritin production. Herein, we first reported a high titer icaritin biosynthesis strategy from epimedin C through co-immobilizing α-l-rhamnosidase (Rha1) and β-glucosidase (Glu4) using cross-linked enzyme aggregates (CLEAs). The created CLEAs exhibited excellent performances in terms of catalytic activity, thermal stability, pH stability, and reusability. Notably, Rha1-CLEAs (K_i: 1 M) and Glu4-CLEAs (K_i: 0.1 M) were more tolerant to sugars (glucose or rhamnose) than free enzymes (0.1 M for Rha1 and 0.007 M for Glu4) by immobilization, achieving the highest icaritin productivity under the highest substrate concentration ever reported. Finally, about 34.24 g/L icaritin could be obtained from 100 g/L epimedin C within 8 h, indicating the great potential for industrialization. This study also provides a promising strategy for the low-cost production of other high-value aglycone compounds by solving poor stability and sugar inhibition of glycosidase.

A Plurizyme with Transaminase and Hydrolase Activity Catalyzes Cascade Reactions

Engineering dual‐function single polypeptide catalysts with two abiotic or biotic catalytic entities (or combinations of both) supporting cascade reactions is becoming an important area of enzyme engineering and catalysis. Herein we present the development of a PluriZyme, TR₂E₂, with efficient native transaminase (k_cat: 69.49±1.77 min⁻¹) and artificial esterase (k_cat: 3908–0.41 min⁻¹) activities integrated into a single scaffold, and evaluate its utility in a cascade reaction. TR₂E₂ (pH_opt: 8.0–9.5; T_opt: 60–65 °C) efficiently converts methyl 3‐oxo‐4‐(2,4,5‐trifluorophenyl)butanoate into 3‐(R)‐amino‐4‐(2,4,5‐trifluorophenyl)butanoic acid, a crucial intermediate for the synthesis of antidiabetic drugs. The reaction proceeds through the conversion of the β‐keto ester into the β‐keto acid at the hydrolytic site and subsequently into the β‐amino acid (e.e. >99 %) at the transaminase site. The catalytic power of the TR₂E₂PluriZyme was proven with a set of β‐keto esters, demonstrating the potential of such designs to address bioinspired cascade reactions.

Rational Design of Artificial Biofilms as Sustainable Supports for Whole-Cell Catalysis Through Integrating Extra- and Intracellular Catalysis

Biofilms are promising candidates for sustainable bioprocessing applications. This work presents a rational design of biofilm catalysts by integrating extra- and intracellular catalysis systems with optimized substrate channeling to realize efficient multistep biosynthesis. An assembly of four enzymes in a "three-in-one" structure was achieved by rationally placing the enzymes on curli nanofibers, the cell surface, and inside cells. The catalytic efficiency of the biofilm catalysts was over 2.8 folds higher than that of the control whole-cell catalysis when the substrate benzaldehyde was fed at 100 mm. The highest yield of d-phenyllactic acid catalyzed by biofilm catalysts under optimized conditions was 102.19 mm, also much higher than that of the control catalysis test (52.29 mm). The results demonstrate that engineered biofilms are greatly promising in integrating extra- and intracellular catalysis, illustrating great potentials of rational design in constructing biofilm catalysts as sustainable supports for whole-cell catalysis.

Probing Crowdedness of Artificial Organelles by Clustering Polymersomes for Spatially Controlled and pH-Triggered Enzymatic Reactions

Most sophisticated biological functions and features of cells are based on self-organization, and the coordination and connection between their cell organelles determines their key functions. Therefore, spatially ordered and controllable self-assembly of polymersomes to construct clusters to simulate complex intracellular biological functions has attracted widespread attention. Here, we present a simple one-step copper-free click strategy to cross-link nanoscale pH-responsive and photo-cross-linked polymersomes (less than 100 nm) to micron-level clusters (more than 90% in 0.5-2 μm range). Various influencing factors in the clustering process and subsequent purification methods were studied to obtain optimal clustered polymeric vesicles. Even when polymeric vesicles separately loaded with different enzymes (glucose oxidase and myoglobin) are coclustered, the overall permeability of the clusters can still be regulated through tuning the pH values on demand. Compared with simple blending of those enzyme-loaded polymersomes, the rate of enzymatic cascade reaction increased significantly due to the interconnected complex microstructure established. The connection of catalytic nanocompartments into clusters confining different enzymes of a cascade reaction provides an excellent platform for the development of artificial systems mimicking natural organelles or cells.

Synergistic Improvement of 5-Aminolevulinic Acid Production with Synthetic Scaffolds and System Pathway Engineering

Engineered synthetic scaffolds to organize metabolic pathway enzymes and system pathway engineering to fine-tune metabolic fluxes play essential roles in microbial production. Here, we first obtained the most favorable combination of key enzymes for 5-aminolevulinic acid (5-ALA) synthesis through the C5 pathway by screening enzymes from different sources and optimizing their combination in different pathways. Second, we successfully constructed a multienzyme complex assembly system with PduA*, which spatially recruits the above three key enzymes for 5-ALA synthesis in a designable manner. By further optimizing the ratio of these key enzymes in synthetic scaffolds, the efficiency of 5-ALA synthesis through the C5 pathway was significantly improved. Then, the competitive metabolism pathway was fine-tuned by rationally designing different antisense RNAs, further significantly increasing 5-ALA titers. Furthermore, for efficient 5-ALA synthesis, obstacles of NADH and NADPH imbalances and feedback inhibition of the synthesis pathway were also overcome through engineering the NADPH regeneration pathway and transport pathway, respectively. Finally, combining these strategies with further fermentation optimization, we achieved a final 5-ALA titer of 11.4 g/L. These results highlight the importance of synthetic scaffolds and system pathway engineering to improve the microbial cell factory production performance.

Is enzyme immobilization a mature discipline? Some critical considerations to capitalize on the benefits of immobilization

Enzyme immobilization has been developing since the 1960s and although many industrial biocatalytic processes use the technology to improve enzyme performance, still today we are far from full exploitation of the field. One clear reason is that many evaluate immobilization based on only a few experiments that are not always well-designed. In contrast to many other reviews on the subject, here we highlight the pitfalls of using incorrectly designed immobilization protocols and explain why in many cases sub-optimal results are obtained. We also describe solutions to overcome these challenges and come to the conclusion that recent developments in material science, bioprocess engineering and protein science continue to open new opportunities for the future. In this way, enzyme immobilization, far from being a mature discipline, remains as a subject of high interest and where intense research is still necessary to take full advantage of the possibilities.

Cell-in-Catalytic-Shell Nanoarchitectonics: Catalytic Empowerment of Individual Living Cells by Single-Cell Nanoencapsulation

Cell-in-shell biohybrid structures, synthesized by encapsulating individual living cells with exogenous materials, have emerged as exciting functional entities for engineered living materials, with emergent properties outside the scope of biochemical modifications. Artificial exoskeletons have, to date, provided physicochemical shelters to the cells inside in the first stage of technological development, and further advances in the field demand catalytically empowered, cellular hybrid systems that augment the biological functions of cells and even introduce completely new functions to the cells. This work describes a facile and generalizable strategy for empowering living cells with extrinsic catalytic capability through nanoencapsulation of living cells with a supramolecular metal-organic complex of Fe³⁺ and benzene-1,3,5-tricarboxylic acid (BTC). A series of enzymes are embedded in situ, without loss of catalytic activity, in the Fe³⁺ -BTC shells, not to mention the superior characteristics of cytocompatible and rapid shell-forming processes. The nanoshell enhances the catalytic efficiency of multienzymatic cascade reactions by confining reaction intermediates to its internal voids and the nanoencapsulated cells acquire exogenous biochemical functions, including enzymatic cleavage of lethal octyl-β-d-glucopyranoside into d-glucose, with autonomous cytoprotection. The system will provide a versatile, nanoarchitectonic tool for interfacing biological cells with functional materials, especially for catalytic bioempowerment of living cells.