De novo artificial synthesis of hexoses from carbon dioxide

Sugar phosphatases as biocatalysts for biomanufacturing: Recent advances and applications

Phosphatases, the largest subgroup within the haloacid dehydrogenase (HAD) superfamily, catalyze the irreversible dephosphorylation of phosphate biomolecules. In in vitro synthetic enzymatic biosystems, sugar phosphatases drive the pathways of phosphorylation, transformation (isomerization, epimerization, dehydrogenation, and/or transamination), and dephosphorylation towards product formation through irreversible and exothermic reactions. This process enables enzymatic cascades based on phosphorylation-dephosphorylation to overcome the thermodynamic limitations of traditional functional sugar production methods that rely on isomerases or epimerases, potentially leading to high theoretical conversion rates. However, sugar phosphatases often exhibit broad substrate scope, which can result in dephosphorylation of intermediates within enzymatic biosystems. In this review, we begin by reviewing the classification, structural features, and catalytic mechanisms of phosphatases, followed by the molecular mechanisms underlying substrate promiscuity. The current research on the substrate specificity engineering of phosphatases is then discussed, with particular focus on the production of functional sugars using sugar phosphatase-driven in vitro synthetic enzymatic biosystems. Our goal is to provide a comprehensive overview of the current research status, challenges, and future trends related to sugar phosphatases-mediated biomanufacturing, offers valuable insights into the enzymatic modification and application of these enzymes.

The use of isomerases and epimerases for the production of the functional sugars mannose, allulose and tagatose from Fructose

Fructose, a common monosaccharide in nature extensively utilized in the food industry, poses a risk of elevated chronic disease incidence with excessive consumption. The global movement for a healthier living has sparked a quest for sugar reduction in foodstuff. The growing concern regarding the adverse impact of excessive sugar consumption on public health has led to significant interest in investigating healthier sugar alternatives. Research efforts have refocused on converting fructose into high-value, reduced-calorie functional sugars. Fructose can undergo direct conversion into three such sugars-mannose, allulose, and tagatose-via a streamlined bioconversion process. Allulose and tagatose, epimers of fructose, are derivable directly from fructose through C-3 and C-4 epimerization processes, whereas mannose, the aldose isomer of fructose, can be synthesized via isomerization pathways. This article aims to present recent advancements in the physiological functions, production methods, and applications of functional sugars derived from fructose. Particularly, it focuses on the bioproduction of mannose, allulose, and tagatose from fructose, encompassing discussions on the recent progress in the related isomerases and epimerases, such as mannose isomerase/lyxose isomerase, ketose 3-epimerase, and tagatose 4-epimerase. This review will provide a fresh perspective on the high-value biological utilization of fructose resources.

Cascade Catalytic Systems for Converting CO2 into C2+ Products

The excessive emission and continuous accumulation of CO2 have precipitated serious social and environmental issues. However, CO2 can also serve as an abundant, inexpensive, and non-toxic renewable C1 carbon source for synthetic reactions. To achieve carbon neutrality and recycling, it is crucial to convert CO2 into value-added products through chemical pathways. Multi-carbon (C2+) products, compared to C1 products, offer a broader range of applications and higher economic returns. Despite this, converting CO2 into C2+ products is difficult due to its stability and the high energy required for C-C coupling. Cascade catalytic reactions offer a solution by coordinating active components, promoting intermediate transfers, and facilitating further transformations. This method lowers energy consumption. Recent advancements in cascade catalytic systems have allowed for significant progress in synthesizing C2+ products from CO2. This review highlights the features and advantages of cascade catalysis strategies, explores the synergistic effects among active sites, and examines the mechanisms within these systems. It also outlines future prospects for CO2 cascade catalytic synthesis, offering a framework for efficient CO2 utilization and the development of next-generation catalytic systems.

Behavior, mechanisms, and applications of low-concentration CO2 in energy media

This review explores the behavior of low-concentration CO2 (LCC) in various energy media, such as solid adsorbents, liquid absorbents, and catalytic surfaces. It delves into the mechanisms of diffusion, adsorption, and catalytic reactions, while analyzing the potential applications and challenges of these properties in technologies like air separation, compressed gas energy storage, and CO2 catalytic conversion. Given the current lack of comprehensive analyses, especially those encompassing multiscale studies of LCC behavior, this review aims to provide a theoretical foundation and data support for optimizing CO2 capture, storage, and conversion technologies, as well as guidance for the development and application of new materials. By summarizing recent advancements in LCC separation techniques (e.g., cryogenic air separation and direct air carbon capture) and catalytic conversion technologies (including thermal catalysis, electrochemical catalysis, photocatalysis, plasma catalysis, and biocatalysis), this review highlights their importance in achieving carbon neutrality. It also discusses the challenges and future directions of these technologies. The findings emphasize that advancing the efficient utilization of LCC not only enhances CO2 reduction and resource utilization efficiency, promoting the development of clean energy technologies, but also provides an economically and environmentally viable solution for addressing global climate change.

Advances in the bioproduction of d-allulose: A comprehensive review of current status and future prospects

As living standards rise, the overconsumption of sugary and calorific foods has led to a rise in obesity, diabetes, and other diseases. In response to the increasing demand for healthier diets, the food industry is actively seeking sugar alternatives. Among these alternatives, d-allulose as a functional sweetener has garnered significant attention for its low-calorie content, low glycemic index, and health benefits. This review summarizes recent advancements in d-allulose research, including its physiological functions, potential applications, and bioproduction methods. This review consolidates the known physiological functions of d-allulose and assesses its potential applications in the food and medical industries. Furthermore, the review explores recent progress in biotechnological production technologies, such as enzymatic conversion and microbial fermentation, which are key to producing d-allulose. d-Allulose is a standout natural sweetener with low calories and a low glycemic index, providing health benefits like lowering blood sugar and lipids, antioxidants, preventing obesity, and regulating metabolism. In the food industry, d-allulose is suitable for use in a variety of products, including baked goods, beverages, confectionery, and yogurt. The primary methods for its production are enzymatic conversion and microbial fermentation, both of which offer scalable and sustainable approaches. Recent research has advanced the production of d-allulose using low-cost raw materials, including agricultural and forestry waste, and even CO2, highlighting a move towards more sustainable production methods. With its diverse physiological functions and broad application prospects, d-allulose holds significant potential for growth in both the food and healthcare sectors.

Redesigning glycolaldehyde synthase for the synthesis of biorefinery feedstock D-xylulose from C1 compounds

Global climate deterioration intensifies the demand for exploiting efficient CO2 utilization approaches. Converting CO2 to biorefinery feedstock affords an alternative strategy for third-generation biorefineries. However, upcycling CO2 into complex chiral carbohydrates remains a major challenge. Previous attempts at sugar synthesis from CO2 either produce mixtures with poor stereoselectivity or require ATP as a cofactor. Here, by redesigning glycolaldehyde synthase, the authors constructed a synthetic pathway for biorefinery feedstock D-xylulose from CO2 that does not require ATP as a cofactor. The artificial D-xylulose pathway only requires a three-step enzyme cascade reaction to achieve the stereoselective synthesis of D-xylulose at a concentration of 1.2 g L-1. Our research opens up an alternative route toward future production of chemicals and fuels from CO2.

Recent advances in enzymatic carbon-carbon bond formation

Enzymatic carbon-carbon (C-C) bond formation reactions have become an effective and invaluable tool for designing new biological and medicinal molecules, often with asymmetric features. This review provides a systematic overview of key C-C bond formation reactions and enzymes, with the focus of reaction mechanisms and recent advances. These reactions include the aldol reaction, Henry reaction, Knoevenagel condensation, Michael addition, Friedel-Crafts alkylation and acylation, Mannich reaction, Morita-Baylis-Hillman (MBH) reaction, Diels-Alder reaction, acyloin condensations via Thiamine Diphosphate (ThDP)-dependent enzymes, oxidative and reductive C-C bond formation, C-C bond formation through C1 resource utilization, radical enzymes for C-C bond formation, and other C-C bond formation reactions.

Scanning the active center of formolase to identify key residues for enhanced C1 to C3 bioconversion

BACKGROUND

Formolase (FLS) is a computationally designed enzyme that catalyzes the carboligation of two or three C1 formaldehyde molecules into C2 glycolaldehyde or C3 dihydroxyacetone (DHA). FLS lays the foundation for several artificial carbon fixation and valorization pathways, such as the artificial starch anabolic pathway. However, the application of FLS is limited by its low catalytic activity and product promiscuity.

FINDINGS

FLS, designed and engineered based on benzoylformate decarboxylase from Pseudomonas putida, was selected as a candidate for modification. To evaluate its catalytic activity, 25 residues located within an 8 Å distance from the active center were screened using single-point saturation mutagenesis. A screening approach based on the color reaction of the DHA product was applied to identify the desired FLS variants. After screening approximately 5,000 variants (approximately 200 transformants per site), several amino acid sites that were not identified by directed evolution were found to improve DHA formation. The serine-to-phenylalanine substitution at position 236 improved the activity towards DHA formation by 7.6-fold. Molecular dynamics simulations suggested that the mutation increased local hydrophobicity at the active site, predisposing the cofactor-C2 intermediate to nucleophilic attack by the third formaldehyde molecule for subsequent DHA generation.

CONCLUSIONS

This study provides improved FLS variants and valuable information into the influence of residues adjacent to the active center affecting catalytic efficiency, which can guide the rational engineering or directed evolution of FLS to optimize its performance in artificial carbon fixation and valorization.

One-pot sustainable synthesis of glucosylglycerate from starch and glycerol through artificial in vitro enzymatic cascade

Glucosylglycerate (R-2-O-α-D-glucopyranosyl-glycerate, GG) is a negatively charged compatible solution with versatile functions. Here, an artificial in vitro enzymatic cascade was designed to feasibly and sustainably produce GG from affordable starch and glycerol. First, Spirochaeta thermophila glucosylglycerate phosphorylase (GGP) was carefully selected because of its excellent heterologous expression, specific activity, and thermostability. The optimized two-enzyme cascade, consisting of alpha-glucan phosphorylase (αGP) and GGP, achieved a remarkable 81 % conversion rate from maltodextrin and D-glycerate. Scaling up this cascade resulted in a practical concentration of 58 g/L GG with a 62 % conversion rate based on the added D-glycerate. Additionally, the production of GG from inexpensive starch and glycerol in one-pot using artificial four-enzyme cascade was successfully implemented, which integrates alditol oxidase and catalase with αGP and GGP. Collectively, this sustainable enzymatic cascade demonstrates the feasibility of the practical synthesis of GG and has the potential to produce other glycosides using the phosphorylase-and-phosphorylase paradigm.

Mid-Long Chain Dicarboxylic Acid Production via Systems Metabolic Engineering: Progress and Prospects

Mid-to-long-chain dicarboxylic acids (DCAi, i ≥ 6) are organic compounds in which two carboxylic acid functional groups are present at the terminal position of the carbon chain. These acids find important applications as structural components and intermediates across various industrial sectors, including organic compound synthesis, food production, pharmaceutical development, and agricultural manufacturing. However, conventional petroleum-based DCA production methods cause environmental pollution, making sustainable development challenging. Hence, the demand for eco-friendly processes and renewable raw materials for DCA production is rising. Owing to advances in systems metabolic engineering, new tools from systems biology, synthetic biology, and evolutionary engineering can now be used for the sustainable production of energy-dense biofuels. Here, we explore systems metabolic engineering strategies for DCA synthesis in various chassis via the conversion of different raw materials into mid-to-long-chain DCAs. Subsequently, we discuss the future challenges in this field and propose synthetic biology approaches for the efficient production and successful commercialization of these acids.

Artificial carbon assimilation: From unnatural reactions and pathways to synthetic autotrophic systems

Synthetic biology is being increasingly used to establish novel carbon assimilation pathways and artificial autotrophic strains that can be used in low-carbon biomanufacturing. Currently, artificial pathway design has made significant progress from advocacy to practice within a relatively short span of just over ten years. However, there is still huge scope for exploration of pathway diversity, operational efficiency, and host suitability. The accelerated research process will bring greater opportunities and challenges. In this paper, we provide a comprehensive summary and interpretation of representative one-carbon assimilation pathway designs and artificial autotrophic strain construction work. In addition, we propose some feasible design solutions based on existing research results and patterns to promote the development and application of artificial autotrophy.