Enzymatic Production of Ascorbic Acid-2-Phosphate by Engineered Pseudomonas aeruginosa Acid Phosphatase

Rational Design of Salmonella typhi Acid Phosphatase for Efficient Production of Pyridoxal 5'-Phosphate

Pyridoxal 5'-phosphate (PLP) is highly valuable in food and medicine. However, achieving the efficient biosynthesis of PLP remains challenging. Here, a salvage pathway using acid phosphatase from Salmonella typhi (StAPase) and pyridoxine oxidase from Escherichia coli (EcPNPO) as pathway enzymes was established for the first time to synthesize PLP from pyridoxine (PN) and pyrophosphate (PPi). StAPase was identified as a rate-limiting enzyme. Two protein modification strategies were developed based on the PN phosphorylation mechanism: (1) improving the binding of PN into StAPase and (2) enhancing the hydrophobicity of StAPase's substrate binding pocket. The kcat/Km of optimal mutant M7 was 4.9 times higher than that of the wild type. The detailed mechanism of performance improvement was analyzed. Under the catalysis of M7 and EcPNPO, a PLP high-yielding strain of 14.5 ± 0.55 g/L was engineered with a productivity of 1.0 ± 0.02 g/(L h) (the highest to date). The study suggests a promising method for industrial-scale PLP production.

Mechanical properties of simulated dentin caries treated with metal cations and L-ascorbic acid 2-phosphate

This pH cycling study aimed to investigate the effects of L-Ascorbic acid 2-phosphate (AA2P) salts of Mg, Zn, Mn, Sr, and Ba on the surface microhardness, compressive strength, diametral tensile strength (DTS), and solubility of root canal dentin. 186 cylindrical dentin specimens from 93 teeth were fortified with optimal concentrations of AA2P salts of Mg (0.18 mM), Zn (5.3 µM), Mn (2.2 × 10-8 M), Sr (1.8 µM), and Ba (1.9 µM). Saline was used as the control group. These dentin specimens underwent a 3-day cycling process simulating dentin caries formation through repeated sequences of demineralization and remineralization. Surface microhardness at 100 and 500 µm depths (n = 10/subgroup), scanning electron microscopy (n = 3/group), compressive strength (n = 10/group), DTS (n = 6/group), and solubility (n = 5/group) tests were performed to analyze the dentin specimens. Data were analyzed using Kolmogorov-Smirnov, one-way ANOVA, and Post Hoc Tukey tests (p < 0.05). The control group had significantly lower microhardness at both depths (p < 0.001), reduced DTS (p = 0.001), decreased compressive strength (p < 0.001), and higher weight loss (p < 0.001) than all other groups. The Sr group had the highest compressive strength and microhardness among all the groups. The microhardness was significantly higher for the 500 µm depth than the 100 µm depth (p < 0.001), but the difference in microhardness between depths across groups was not significant (p = 0.211). All fortifying solutions provided some protection against artificial caries lesions. Therefore, these elements might have penetrated and reinforced the demineralized dentin against acid dissolution.

Producing 2-O-α-D-glucopyranosyl-L-ascorbic acid by modified cyclodextrin glucosyltransferase and isoamylase

In this study, site saturation mutagenesis was performed on the - 3 (R44, D86, S90, and D192) and - 6 subsite (Y163, G175, G176, and N189) of Bacillus stearothermophilus NO2 cyclodextrin glucosyltransferase to enhance its specificity for the donor substrate maltodextrin for 2-O-α-D-glucopyranosyl-L-ascorbic acid (AA-2G) preparation. The AA-2G yields produced by the mutants S90D, G176H, and S90D/G176H were 181, 171, and 185 g/L, respectively. Our previous study found that the mutant K228R/M230L also increased the AA-2G yield. Therefore, the mutants S90D, G176H, S90D/G176H, and K228R/M230L were further used to generate combinatorial mutants. Among these mutants, the highest AA-2G yield (217 g/L) was produced by S90D/K228R/M230L with 500 g/L maltodextrin as the glucosyl donor, which was 56 g/L higher than that produced by wild-type CGTase. In addition, AA-2G was prepared by adding isoamylase to hydrolyze α-1,6 glucosidic linkages in maltodextrin that could not be utilized by CGTase to improve the utilization rate of maltodextrin. The addition of isoamylase reduced the concentration of maltodextrin from 500 to 350 g/L, while the AA-2G yield remained high (208 g/L). The preparation of AA-2G by complexing isoamylase with mutant S90D/K228R/M230L reduced the maltodextrin concentration by 150 g/L, while the AA-2G yield increased by 47 g/L than preparation with wild-type CGTase alone, which laid a foundation for the large-scale preparation of AA-2G. KEY POINTS: • Mutants exhibited improved maltodextrin specificity. • Mutant S90D/K228R/M230L produced high yield of AA-2G with maltodextrin as substrate. • AA-2G was first synthesized by a combination of isoamylase and CGTase.

The Power of Biocatalysts for Highly Selective and Efficient Phosphorylation Reactions

Reactions involving the transfer of phosphorus-containing groups are of key importance for maintaining life, from biological cells, tissues and organs to plants, animals, humans, ecosystems and the whole planet earth. The sustainable utilization of the nonrenewable element phosphorus is of key importance for a balanced phosphorus cycle. Significant advances have been achieved in highly selective and efficient biocatalytic phosphorylation reactions, fundamental and applied aspects of phosphorylation biocatalysts, novel phosphorylation biocatalysts, discovery methodologies and tools, analytical and synthetic applications, useful phosphoryl donors and systems for their regeneration, reaction engineering, product recovery and purification. Biocatalytic phosphorylation reactions with complete conversion therefore provide an excellent reaction platform for valuable analytical and synthetic applications.

Advances in Novel Animal Vitamin C Biosynthesis Pathways and the Role of Prokaryote-Based Inferences to Understand Their Origin

Vitamin C (VC) is an essential nutrient required for the optimal function and development of many organisms. VC has been studied for many decades, and still today, the characterization of its functions is a dynamic scientific field, mainly because of its commercial and therapeutic applications. In this review, we discuss, in a comparative way, the increasing evidence for alternative VC synthesis pathways in insects and nematodes, and the potential of myo-inositol as a possible substrate for this metabolic process in metazoans. Methodological approaches that may be useful for the future characterization of the VC synthesis pathways of Caenorhabditis elegans and Drosophila melanogaster are here discussed. We also summarize the current distribution of the eukaryote aldonolactone oxidoreductases gene lineages, while highlighting the added value of studies on prokaryote species that are likely able to synthesize VC for both the characterization of novel VC synthesis pathways and inferences on the complex evolutionary history of such pathways. Such work may help improve the industrial production of VC.

Rational Design of Phospholipase D to Improve the Transphosphatidylation Activity for Phosphatidylserine Synthesis

Phosphatidylserine (PS) has been widely used in the fields of food and medicine, among others, owing to its unique chemical structure and health benefits. However, the phospholipase D (PLD)-mediated enzymatic production of PS remains a challenge due to the low transphosphatidylation activity of PLD. Therefore, in the present study, we designed a maltose-binding protein (MBP) tag and a PLD co-expression method to achieve the expression of soluble PLD in Escherichia coli. A "reconstruct substrate pocket" strategy was then proposed based on the catalytic mechanism and molecular dynamics simulation, expanding the substrate pocket and manipulating the coordination of l-Ser within the active site. The best mutant (Sr_MBPPLD^Mu6) exhibited a 2.04-fold higher transphosphatidylation/hydrolysis ratio than the wild-type Furthermore, under optimal conditions, Mu₆ produced 58.6 g/L PS with 77.2% conversion, within 12 h on a 3 L scale, which demonstrates the potential of the proposed method for industrial application.