Facilitation of cascade biocatalysis by artificial multi-enzyme complexes — A review

Evidence supporting multienzyme complexes as metabolons: A review

Fungi are widespread organisms with complex multienzyme systems crucial for diverse biochemical processes. This study systematically reviewed research on multienzyme complexes, focusing on their isolation and identification, while examining their potential classification as metabolons. Using a theoretical framework based on PRISMA guidelines, the review analysed literature from 2013 to 2023 across databases such as Medline, Web of Science, and ScienceDirect, employing targeted descriptors to identify relevant studies. The articles were selected by two independent reviewers among those published in English in the last 10 years. From 2313 papers identified through bibliographic searches, 13 were selected for qualitative analysis. Purification methods for fungal multienzyme complexes vary, each offering unique advantages and requiring tailored approaches for specific enzyme systems. The isolation and characterisation of multienzyme complexes face significant challenges. Their classification as metabolons depends on three criteria: substrate channelling, functional coupling, and dynamic assembly. Although research highlights the significance of substrate channelling and the function of stabilising proteins in improving metabolic efficiency, evidence for dynamic assembly is limited. Future research should emphasise new stabilising measures, real-time monitoring of intricate dynamics, and a more profound investigation of molecular causes.

Synthetic Multienzyme Assemblies for Natural Product Biosynthesis

In nature, enzymes that catalyze sequential reactions are often assembled as clusters or complexes. The formation of multienzyme complexes, or metabolons, brings the enzyme active sites into proximity to promote intermediate transfer, decrease intermediate leakage, and streamline the metabolic flux towards the desired products. We and others have developed synthetic versions of metabolons through various strategies to enhance the catalytic rates for synthesizing valuable chemicals inside microbes. Synthetic multienzyme complexes range from static enzyme nanostructures to dynamic enzyme coacervates. Enzyme complexation optimizes the metabolic fluxes inside microbes, increases the product titer, and supplies the field with high-yield microbe strains that are amenable to large-scale fermentation. Enzyme complexes constructed inside microbial cells can be separated as independent entities and catalyze biosynthetic reactions ex vivo; such a feature gains these complexes another name, "synthetic organelles" - new subcellular entities with independent structures and functions. Still, the field is seeking new strategies to better balance dynamicity and confinement and to achieve finer control of local compartmentalization in the cells, as the natural multienzyme complexes do. Industrial applications of synthetic multienzyme complexes for the large-scale production of valuable chemicals are yet to be realized. This review focuses on synthetic multienzyme complexes that are constructed and function inside microbial cells.

Redox Biocatalysis: Quantitative Comparisons of Nicotinamide Cofactor Regeneration Methods

Enzymatic processes, particularly those capable of performing redox reactions, have recently been of growing research interest. Substrate specificity, optimal activity at mild temperatures, high selectivity, and yield are among the desirable characteristics of these oxidoreductase catalyzed reactions. Nicotinamide adenine dinucleotide (phosphate) or NAD(P)H-dependent oxidoreductases have been extensively studied for their potential applications like biosynthesis of chiral organic compounds, construction of biosensors, and pollutant degradation. One of the main challenges associated with making these processes commercially viable is the regeneration of the expensive cofactors required by the enzymes. Numerous efforts have pursued enzymatic regeneration of NAD(P)H by coupling a substrate reduction with a complementary enzyme catalyzed oxidation of a co-substrate. While offering excellent selectivity and high total turnover numbers, such processes involve complicated downstream product separation of a primary product from the coproducts and impurities. Alternative methods comprising chemical, electrochemical, and photochemical regeneration have been developed with the goal of enhanced efficiency and operational simplicity compared to enzymatic regeneration. Despite the goal, however, the literature rarely offers a meaningful comparison of the total turnover numbers for various regeneration methodologies. This comprehensive Review systematically discusses various methods of NAD(P)H cofactor regeneration and quantitatively compares performance across the numerous methods. Further, fundamental barriers to enhanced cofactor regeneration in the various methods are identified, and future opportunities are highlighted for improving the efficiency and sustainability of commercially viable oxidoreductase processes for practical implementation.

Programming an Orthogonal Self-Assembling Protein Cascade Based on Reactive Peptide-Protein Pairs for In Vitro Enzymatic Trehalose Production

Trehalose is an important rare sugar that protects biomolecules against environmental stress. We herein introduce a dual enzyme cascade strategy that regulates the proportion of cargos and scaffolds, to maximize the benefits of enzyme immobilization. Based upon the self-assembling properties of the shell protein (EutM) from the ethanolamine utilization (Eut) bacterial microcompartment, we implemented the catalytic synthesis of trehalose from soluble starch with the coimmobilization of α-amylase and trehalose synthase. This strategy improved enzymatic cascade activity and operational stability. The cascade system enabled the efficient production of trehalose with a yield of ∼3.44 g/(L U), 1.5 times that of the free system. Moreover, its activity was maintained over 12 h, while the free system was almost completely inactivated after 4 h, demonstrating significantly enhanced thermostability. In conclusion, an attractive self-assembly coimmobilization platform was developed, which provides an effective biological process for the enzymatic synthesis of trehalose in vitro.

Structural Characterization of Multienzyme Assemblies: An Overview

Multienzyme assemblies have attracted significant attention in recent years for use in industrial applications instead of single enzymes. Owing to their ability to catalyze cascade reactions, multienzyme assemblies have become inspirational tools for the in vitro construction of multienzyme molecular machines. The use of such molecular machines could offer several advantages such as fewer side reactions, a high product yield, a fast reaction speed, easy product separation, a tolerable toxic environment, and robust system operability compared to current microbial cell catalytic systems. Besides, they can provide all the benefits found in the use of enzymes, including reusability, catalytic efficiency, and specificity. Similar to single enzymes, multienzyme assemblies could offer economical and environmentally friendly alternatives to conventional catalysts and play a central role as biocatalysts in green chemistry applications. However, detailed characterization of multienzyme assemblies and a full understanding of their mechanistic details are required for their efficient use in industrial biotransformations. Since the determination of the first enzyme structure in 1965, structural information has played a pivotal role in the characterization of enzymes and elucidation of their structure-function relationship. Among the structural biology techniques, X-ray crystallography has provided key mechanistic details into multienzyme assemblies. Here, the structural characterization of multienzyme assemblies is reviewed and several examples are provided.

Glucose oxidase@zinc-doped zeolitic imidazolate framework-67 as an effective cascade catalyst for one-step chemiluminescence sensing of glucose

A chemiluminescence (CL) sensor was constructed for the one-step determination of glucose. Glucose oxidase (GOx) was successfully encapsulated into Zn-doped zeolitic imidazolate framework-67 (Zn-ZIF-67) via a simple one-pot strategy. The as-prepared GOx@Zn-ZIF-67 nanocomposite can trigger cascade reactions of glucose oxidation to generate H₂O₂ and H₂O₂-mediated luminol reaction to give an intense CL emission. The sensor responds linearly to glucose in the 20.0-400.0 μmol·L^-1 range with a limit of detection (LOD) of 4.7 μmol·L^-1. Eleven replicated measurements of 200.0 μmol·L^-1 glucose solution gives a relative standard deviation (RSD) of 1.7%. The sensor exhibits good selectivity and stability and was successfully applied to the determination of glucose in real human serum samples. Schematic representation of one-step determination of serum glucose with GOx@Zn-ZIF-67 nanocomposite triggering cascade reactions between luminol and glucose.

Multi-Enzyme Systems in Flow Chemistry

Recent years have witnessed a growing interest in the use of biocatalysts in flow reactors. This merging combines the high selectivity and mild operation conditions typical of biocatalysis with enhanced mass transfer and resource efficiency associated to flow chemistry. Additionally, it provides a sound environment to emulate Nature by mimicking metabolic pathways in living cells and to produce goods through the systematic organization of enzymes towards efficient cascade reactions. Moreover, by enabling the combination of enzymes from different hosts, this approach paves the way for novel pathways. The present review aims to present recent developments within the scope of flow chemistry involving multi-enzymatic cascade reactions. The types of reactors used are briefly addressed. Immobilization methodologies and strategies for the application of the immobilized biocatalysts are presented and discussed. Key aspects related to the use of whole cells in flow chemistry are presented. The combination of chemocatalysis and biocatalysis is also addressed and relevant aspects are highlighted. Challenges faced in the transition from microscale to industrial scale are presented and discussed.