Efficient Allitol Bioproduction from D-Fructose Catalyzed by Recombinant E. coli Whole Cells, and the Condition Optimization, Product Purification

Green biotechnological synthesis of rare sugars/alcohols: D-allulose, allitol, D-tagatose, L-xylulose, L-ribose

Rare sugars are paid more attention because of which have the characteristics of low calorie, low absorption and excellent physiological functions. Biotechnological synthesis of rare sugars has the advantages of being green, clean, simple and economic compared to chemical synthesis. Abundant enzymes for rare sugars biosynthesis are introduced and multienzyme cascade catalytic system (MECCS) used in biosynthesis of rare sugars is highlighted in this paper. Different biosynthesis pathways of five important rare sugars (D-allulose, allitol, D-tagatose, L-xylulose, l-ribose), mainly containing isomerization/epimerization reaction (existing thermodynamic equilibrium limitation), reduction-oxidation reaction (needing expensive cofactors) and phosphorylation-dephosphorylation reaction pathways (inherent constraint of thermodynamic equilibrium and requirement high-cost cofactors) etc., are reviewed. Furthermore, techniques of cofactor regeneration and enzyme/cell immobilization are provided. Finally, unique insights and expectations for future development in biosynthesis of rare sugars are given. This review provides a comprehensive analysis of the latest biotechnological advancements in the biosynthesis of rare sugars/alcohols, highlighting innovative multienzyme cascade catalytic systems and cofactor regeneration strategies.

Advances in the biosynthesis of D-allulose

D-allulose is a rare monosaccharide and a C-3 epimer of D-fructose. It has physiological functions, such as antihyperglycemic, obesity-preventing, neuroprotective, and reactive oxygen species (ROS) scavenging effects, making it an ideal sugar substitute. The synthesis methods for D-allulose include chemical synthesis and biosynthesis. Chemical synthesis requires strict reaction conditions and tends to produce byproducts. Biosynthesis is mainly an enzymatic process. Enzymatic catalysis for the conversion of starch or glycerol to D-allulose is performed mainly by enzymes such as isoamylase (IA), glucose isomerase (GI), D-allulose 3-epimerase (DPE), D-allulose-6-phosphate 3-epimerase (A6PE), D-allulose 6-phosphate phosphatase (A6PP), ribitol 2-dehydrogenase (RDH), glycerophosphate kinase (GK), glycerophosphate oxidase (GPO), and dihydroxyacetone phosphate (DHAP)-dependent aldolase. Biosynthesis is a more energy-efficient process, producing fewer harmful by-products and pollutants, and significantly reducing negative environmental impacts. Furthermore, the specific catalytic activity of enzymes facilitates the production of compounds of higher purity, thereby facilitating the isolation and purification of the products. It has thus become the main method for producing D-allulose. This article reviews the progress in research on the biosynthetic production of D-allulose, focusing on the enzymes involved and their enzymatic properties, and discusses the production prospects for D-allulose.

Light Controlled Nanobiohybrids for Modulating Chiral Alcohol Synthesis

The modulation of whole-cell activity presents a considerable challenge in biocatalysis. Conventional approaches to whole-cell catalysis, while having their strengths, often rely on complex and deliberate enzyme designs, which could result in difficulties in activity modulation and prolonged response times. Additionally, the activity of intracellular enzymes in whole-cell catalysis is influenced by temperature. To address these limitations, we introduced a relationally designed nanobiohybrid system that utilized light to modulate whole-cell catalysis for chiral alcohol production. By incorporating platinum nanoparticles onto Rhodotorula sp. cell surfaces, the nanobiohybrid capitalized on the photothermal properties of the nanoparticles to regulate the overall cell activity. When exposed to light, the Pt nanoparticles generate heat through the photothermal effect, consequently leading to an increase in the catalytic activity of the whole cells. This innovative approach facilitates control over whole-cell production and provides an efficient method for regulating biocatalytic processes. The findings of this study demonstrate the significant potential of switchable control strategies in biomanufacturing across a wide range of industries.

D-Allulose (D-Psicose) Biotransformation From Allitol by a Newly Found NAD(P)-Dependent Alcohol Dehydrogenase From Gluconobacter frateurii NBRC 3264 and the Enzyme Characterization

The NAD(P)-dependent alcohol dehydrogenase (ADH) gene was cloned from Gluconobacter frateurii NBRC 3264 and expressed in Escherichia coli BL21 star (DE3). The expressed enzyme was purified and the characteristics were investigated. The results showed that this ADH can convert allitol into D-allulose (D-psicose), which is the first reported enzyme with this catalytic ability. The optimum temperature and pH of this enzyme were 50°C and pH 7.0, respectively, and the enzyme showed a maximal activity in the presence of Co²⁺. At 1 mM Co²⁺ and allitol concentrations of 50, 150, and 250 mM, the D-allulose yields of 97, 56, and 38%, respectively, were obtained after reaction for 4 h under optimal conditions, which were much higher than that obtained by using the epimerase method of about 30%.

Reconstruction of a Cofactor Self-Sufficient Whole-Cell Biocatalyst System for Efficient Biosynthesis of Allitol from d-Glucose

The combined catalysis of glucose isomerase (GI), d-psicose 3-epimerase (DPEase), ribitol dehydrogenase (RDH), and formate dehydrogenase (FDH) provides a convenient route for the biosynthesis of allitol from d-glucose; however, the low catalytic efficiency restricts its industrial applications. Here, the supplementation of 0.32 g/L NAD⁺ significantly promoted the cell catalytic activity by 1.18-fold, suggesting that the insufficient intracellular NAD(H) content was a limiting factor in allitol production. Glucose dehydrogenase (GDH) with 18.13-fold higher activity than FDH was used for reconstructing a cofactor self-sufficient system, which was combined with the overexpression of the rate-limiting genes involved in NAD⁺ salvage metabolic flow to expand the available intracellular NAD(H) pool. Then, the multienzyme self-assembly system with SpyTag and SpyCatcher effectively channeled intermediates, leading to an 81.1% increase in allitol titer to 15.03 g/L from 25 g/L d-glucose. This study provided a facilitated strategy for large-scale and efficient biosynthesis of allitol from a low-cost substrate.