Rapidly directional biotransformation of tauroursodeoxycholic acid through engineered Escherichia coli

Metabolomic and lipidomic studies on the intervention of taurochenodeoxycholic acid in mice with hyperlipidemia

Bile acids are the main component of animal bile and are directly involved in the metabolic process of lipids in vivo. Taurochenodeoxycholic acid (TCDCA) is the primary biologically active substance in bile acids and has biological functions such as antioxidant, antipyretic, anti-inflammatory, and analgesic activities and improves immunity. In the present study, we assessed the impact of TCDCA on hyperlipidemia development in mouse models. Mice were fed a high-fat diet (HFD) to induce hyperlipidemia and orally administered different doses of TCDCA orally for 30 days. Then, indicators such as triglyceride (TG), total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), and high-density lipoprotein cholesterol (HDL-C) in mice were detected. Using HE and ORO staining techniques, the morphology of the mice's liver tissue was detected. Based on metabolomic and lipidomic analyses, we determined the mechanism of TCDCA in treating hyperlipidemia. The results showed that TCDCA had a significant ameliorating effect on dietary hyperlipidemia. In addition, it exerted therapeutic effects through glycerophospholipid metabolism.

Sequence and structure-guided discovery of a novel NADH-dependent 7β-hydroxysteroid dehydrogenase for efficient biosynthesis of ursodeoxycholic acid

7β-Hydroxysteroid dehydrogenases (7β-HSDHs) have attracted increasing attention due to their crucial roles in the biosynthesis of ursodeoxycholic acid (UDCA). However, most published 7β-HSDHs are strictly NADPH-dependent oxidoreductases with poor activity and low productivity. Compared with NADPH, NADH is more stable and cheaper, making it the more popular cofactor for industrial applications of dehydrogenases. Herein, by using a sequence and structure-guided genome mining approach based on the structural information of conserved cofactor-binding motifs, we uncovered a novel NADH-dependent 7β-HSDH (Cle7β-HSDH). The Cle7β-HSDH was overexpressed, purified, and characterized. It exhibited high specific activity (9.6 U/mg), good pH stability and thermostability, significant methanol tolerance, and showed excellent catalytic efficiencies (k_cat/K_m) towards 7-oxo-lithocholic acid (7-oxo-LCA) and NADH (70.8 mM^-1s^-1 and 31.8 mM^-1s^-1, respectively). Molecular docking and mutational analyses revealed that Asp42 could play a considerable role in NADH binding and recognition. Coupling with a glucose dehydrogenase for NADH regeneration, up to 20 mM 7-oxo-LCA could be completely transformed to UDCA within 90 min by Cle7β-HSDH. This study provides an efficient approach for mining promising enzymes from genomic databases for cost-effective biotechnological applications.

Biological synthesis of ursodeoxycholic acid

Ursodeoxycholic acid (UDCA) is a fundamental treatment drug for numerous hepatobiliary diseases that also has adjuvant therapeutic effects on certain cancers and neurological diseases. Chemical UDCA synthesis is environmentally unfriendly with low yields. Biological UDCA synthesis by free-enzyme catalysis or whole-cell synthesis using inexpensive and readily available chenodeoxycholic acid (CDCA), cholic acid (CA), or lithocholic acid (LCA) as substrates is being developed. The free enzyme-catalyzed one-pot, one-step/two-step method uses hydroxysteroid dehydrogenase (HSDH); whole-cell synthesis, mainly uses engineered bacteria (mainly Escherichia coli) expressing the relevant HSDHs. To further develop these methods, HSDHs with specific coenzyme dependence, high enzyme activity, good stability, and high substrate loading concentration, P450 monooxygenase with C-7 hydroxylation activity and engineered strain harboring HSDHs must be exploited.

A green strategy to produce potential substitute resource for bear bile using engineered Saccharomyces cerevisiae

BACKGROUND

Bear bile powder is a precious natural material characterized by high content of tauroursodeoxycholic acid (TUDCA) at a ratio of 1.00-1.50 to taurochenodeoxycholic acid (TCDCA).

RESULTS

In this study, we use the crude enzymes from engineered Saccharomyces cerevisiae to directionally convert TCDCA from chicken bile powder to TUDCA at the committed ratio in vitro. This S. cerevisiae strain was modified with heterologous 7α-hydroxysteroid dehydrogenase (7α-HSDH) and 7β-hydroxysteroid dehydrogenase (7β-HSDH) genes. S. cerevisiae host and HSDH gene combinatorial optimization and response surface methodology was applied to get the best engineered strain and the optimal biotransformation condition, respectively, under which 10.99 ± 0.16 g/L of powder products containing 36.73 ± 6.68% of TUDCA and 28.22 ± 6.05% of TCDCA were obtained using 12.00 g/L of chicken bile powder as substrate.

CONCLUSION

This study provides a healthy and environmentally friendly way to produce potential alternative resource for bear bile powder from cheap and readily available chicken bile powder, and also gives a reference for the green manufacturing of other rare and endangered animal-derived valuable resource.

NAD+ -Dependent Enzymatic Route for the Epimerization of Hydroxysteroids

Epimerization of cholic and chenodeoxycholic acid (CA and CDCA, respectively) is a notable conversion for the production of ursodeoxycholic acid (UDCA). Two enantiocomplementary hydroxysteroid dehydrogenases (7α- and 7β-HSDHs) can carry out this transformation fully selectively by specific oxidation of the 7α-OH group of the substrate and subsequent reduction of the keto intermediate to the final product (7β-OH). With a view to developing robust and active biocatalysts, novel NADH-active 7β-HSDH species are necessary to enable a solely NAD+ -dependent redox-neutral cascade for UDCA production. A wild-type NADH-dependent 7β-HSDH from Lactobacillus spicheri (Ls7β-HSDH) was identified, recombinantly expressed, purified, and biochemically characterized. Using this novel NAD+ -dependent 7β-HSDH enzyme in combination with 7α-HSDH from Stenotrophomonas maltophilia permitted the biotransformations of CA and CDCA in the presence of catalytic amounts of NAD+ , resulting in high yields (>90 %) of UCA and UDCA.

Large-scale production of tauroursodeoxycholic acid products through fermentation optimization of engineered Escherichia coli cell factory

Background

Bear bile powder is a valuable medicinal material characterized by high content of tauroursodeoxycholic acid (TUDCA) at a certain ratio to taurochenodeoxycholic acid (TCDCA). We had created an engineered E. coli harboring two-step bidirectional oxidative and reductive enzyme-catalyzing pathway that could rapidly convert TCDCA to TUDCA at a specific percentage in shake flasks.

Results

We reported here the large-scale production of TUDCA containing products by balancing the bidirectional reactions through optimizing fermentation process of the engineered E. coli in fermenters. The fermentation medium was firstly optimized based on M9 medium using response surface methodology, leading to a glycerol and yeast extract modified M9-GY medium benefits for both cell growth and product conversion efficiency. Then isopropylthio-β-galactoside induction and fed-stock stage was successively optimized. Finally, a special deep-tank static process was developed to promote the conversion from TCDCA to TUDCA. Applying the optimal condition, fermentation was performed by separately supplementing 30 g refined chicken bile powder and 35 g crude chicken bile powder as substrates, resulting in 29.35 ± 2.83 g and 30.78 ± 3.04 g powder products containing 35.85 ± 3.85% and 27.14 ± 4.23% of TUDCA at a ratio of 1.49 ± 0.14 and 1.55 ± 0.19 to TCDCA, respectively, after purification and evaporation of the fermentation broth. The recovery yield was 92.84 ± 4.21% and 91.83 ± 2.56%, respectively.

Conclusion

This study provided a practical and environment friendly industrialized process for producing artificial substitute of bear bile powder from cheap and readily available chicken bile powder using engineered E. coli microbial cell factory. It also put forward an interesting deep-tank static process to promote the enzyme-catalyzing reactions toward target compounds in synthetic biology-based fermentation.

Electronic supplementary material

The online version of this article (10.1186/s12934-019-1076-2) contains supplementary material, which is available to authorized users.

Enhanced activity and substrate tolerance of 7α-hydroxysteroid dehydrogenase by directed evolution for 7-ketolithocholic acid production

7-Ketolithocholic acid (7-KLCA) is an important intermediate for the synthesis of ursodeoxycholic acid (UDCA). UDCA is the main effective component of bear bile powder that is used in traditional Chinese medicine for the treatment of human cholesterol gallstones. 7α-Hydroxysteroid dehydrogenase (7α-HSDH) is the key enzyme used in the industrial production of 7-KLCA. Unfortunately, the natural 7α-HSDHs reported have difficulty meeting the requirements of industrial application, due to their poor activities and strong substrate inhibition. In this study, a directed evolution strategy combined with high-throughput screening was applied to improve the catalytic efficiency and tolerance of high substrate concentrations of NADP+-dependent 7α-HSDH from Clostridium absonum. Compared with the wild type, the best mutant (7α-3) showed 5.5-fold higher specific activity and exhibited 10-fold higher and 14-fold higher catalytic efficiency toward chenodeoxycholic acid (CDCA) and NADP+, respectively. Moreover, 7α-3 also displayed significantly enhanced tolerance in the presence of high concentrations of substrate compared to the wild type. Owing to its improved catalytic efficiency and enhanced substrate tolerance, 7α-3 could efficiently biosynthesize 7-KLCA with a substrate loading of 100 mM, resulting in 99% yield of 7-KLCA at 2 h, in contrast to only 85% yield of 7-KLCA achieved for the wild type at 16 h.