Engineering of a UDP-Glycosyltransferase for the Efficient Whole-Cell Biosynthesis of Siamenoside I in Escherichia coli

Recent advancements in mogrosides: A review on biological activities, synthetic biology, and applications in the food industry

Mogrosides are low-calorie, biologically active sweeteners that face high production costs due to strict cultivation requirements and the low yield of monk fruit. The rapid advancement in synthetic biology holds the potential to overcome this challenge. This review presents mogrosides exhibiting antioxidant, anti-inflammatory, anti-cancer, anti-diabetic, and liver protective activities, with their efficacy in diabetes treatment surpassing that of Xiaoke pills (a Chinese diabetes medication). It also discusses the latest elucidated biosynthesis pathways of mogrosides, highlighting the challenges and research gaps in this field. The critical and most challenging step in this pathway is the transformation of mogrol into a variety of mogrosides by different UDP-glucosyltransferases (UGTs), primarily hindered by the poor substrate selectivity, product specificity, and low catalytic efficiency of current UGTs. Finally, the applications of mogrosides in the current food industry and the challenges they face are discussed.

Development of New Multi-Glycosylation Routes to Facilitate the Biosynthesis of Sweetener Mogrosides from Bitter Immature Siraitia Grosvenorii Using Engineered Escherichia coli

Mogrosides, which have various pharmacological activities, are mainly extracted from Siraitia grosvenorii (Luo Han Guo) and are widely used as natural zero-calorie sweeteners. Unfortunately, the difficult cultivation and long maturation time of Luo Han Guo have contributed to a shortage of mogrosides. To overcome this obstacle, we developed a highly efficient biosynthetic method using engineered Escherichia coli to synthesize sweet mogrosides from bitter mogrosides. Three UDP-glycosyltransferase (UGT) genes with primary/branched glycosylation catalytic activity at the C3/C24 sites of mogrosides were screened and tested. Mutant M3, which could catalyze the glycosylation of nine types of mogrosides, was obtained through enhanced catalytic activity. This improvement in β-(1,6)-glycosidic bond formation was achieved through single nucleotide polymorphisms and direct evolution, guided by 3D structural analysis. A new multienzyme system combining three UGTs and UDP-glucose (UDPG) regeneration was developed to avoid the use of expensive UDPG. Finally, the content of sweet mogrosides in the immature Luo Han Guo extract increased significantly from 57% to 95%. This study not only established a new multienzyme system for the highly efficient production of sweet mogrosides from immature Luo Han Guo but also provided a guideline for the high-value utilization of rich bitter mogrosides from agricultural waste and residues.

Rationally Engineered Novel Glycosyltransferase UGT74DD1 from Siraitia grosvenorii Catalyzes the Generation of the Sweetener Mogroside III

Mogrosides are natural compounds highly valued in the food sector for their exceptional sweetness. Here, we report a novel O-glycosyltransferase (UGT74DD1) from Siraitia grosvenorii that catalyzes the conversion of mogrol to mogroside IIE. Site-directed mutagenesis yielded the UGT74DD1-W351A mutant, which exhibited the new capability to transform mogroside IIE into the valuable sweetener mogroside III, but with low catalytic activity. Subsequently, using structure-guided directed evolution with combinatorial active-site saturation testing, the superior mutant M6 (W351A/Q373 K/E49H/Q335W/S278C/D17F) were obtained, which showed a 46.1-fold increase in catalytic activity compared to UGT74DD1-W351A. Molecular dynamics simulations suggested that the enhanced activity and extended substrate profiles of M6 are due to its enlarged substrate-binding pocket and strengthened enzyme-substrate hydrogen bonding interactions. Overall, we redesigned UGT74DD1, yielding mutants that catalyze the conversion of mogrol into mogroside III. This study thus broadens the toolbox of UGTs capable of catalyzing the formation of valuable polyglycoside compounds.

Structural insights into the catalytic selectivity of glycosyltransferase SgUGT94-289-3 towards mogrosides

Mogrosides constitute a series of natural sweeteners extracted from Siraitia grosvenorii fruits. These mogrosides are glucosylated to different degrees, with mogroside V (M5) and siamenoside I (SIA) being two mogrosides with high intensities of sweetness. SgUGT94-289-3 constitutes a uridine diphosphate (UDP)-dependent glycosyltransferase (UGT) responsible for the biosynthesis of M5 and SIA, by continuously catalyzing glucosylation on mogroside IIe (M2E) and on the subsequent intermediate mogroside products. However, the mechanism of its promiscuous substrate recognition and multiple catalytic modes remains unclear. Here, we report multiple complex structures and the enzymatic characterization of the glycosyltransferase SgUGT94-289-3. We show that SgUGT94-289-3 adopts a dual-pocket organization in its active site, which allows the two structurally distinct reactive ends of mogrosides to be presented from different pockets to the active site for glucosylation reaction, thus enabling both substrate promiscuity and catalytic regioselectivity. We further identified a structural motif that is essential to catalytic activity and regioselectivity, and generated SgUGT94-289-3 mutants with greatly improved M5/SIA production from M2E in an in vitro one-pot setup.

Construction of lignan glycosides biosynthetic network in Escherichia coli using mutltienzyme modules

BACKGROUND

Due to the complexity of the metabolic pathway network of active ingredients, precise targeted synthesis of any active ingredient on a synthetic network is a huge challenge. Based on a complete analysis of the active ingredient pathway in a species, this goal can be achieved by elucidating the functional differences of each enzyme in the pathway and achieving this goal through different combinations. Lignans are a class of phytoestrogens that are present abundantly in plants and play a role in various physiological activities of plants due to their structural diversity. In addition, lignans offer various medicinal benefits to humans. Despite their value, the low concentration of lignans in plants limits their extraction and utilization. Recently, synthetic biology approaches have been explored for lignan production, but achieving the synthesis of most lignans, especially the more valuable lignan glycosides, across the entire synthetic network remains incomplete.

RESULTS

By evaluating various gene construction methods and sequences, we determined that the pCDF-Duet-Prx02-PsVAO gene construction was the most effective for the production of (+)-pinoresinol, yielding up to 698.9 mg/L after shake-flask fermentation. Based on the stable production of (+)-pinoresinol, we synthesized downstream metabolites in vivo. By comparing different fermentation methods, including "one-cell, one-pot" and "multicellular one-pot", we determined that the "multicellular one-pot" method was more effective for producing (+)-lariciresinol, (-)-secoisolariciresinol, (-)-matairesinol, and their glycoside products. The "multicellular one-pot" fermentation yielded 434.08 mg/L of (+)-lariciresinol, 96.81 mg/L of (-)-secoisolariciresinol, and 45.14 mg/L of (-)-matairesinol. Subsequently, ultilizing the strict substrate recognition pecificities of UDP-glycosyltransferase (UGT) incorporating the native uridine diphosphate glucose (UDPG) Module for in vivo synthesis of glycoside products resulted in the following yields: (+)-pinoresinol glucoside: 1.71 mg/L, (+)-lariciresinol-4-O-D-glucopyranoside: 1.3 mg/L, (+)-lariciresinol-4'-O-D-glucopyranoside: 836 µg/L, (-)-secoisolariciresinol monoglucoside: 103.77 µg/L, (-)-matairesinol-4-O-D-glucopyranoside: 86.79 µg/L, and (-)-matairesinol-4'-O-D-glucopyranoside: 74.5 µg/L.

CONCLUSIONS

By using various construction and fermentation methods, we successfully synthesized 10 products of the lignan pathway in Isatis indigotica Fort in Escherichia coli, with eugenol as substrate. Additionally, we obtained a diverse range of lignan products by combining different modules, setting a foundation for future high-yield lignan production.

Microbial synthesis of terpenoids for human nutrition - an emerging field with high business potential

Because of their complicated biosynthesis and hydrophobic nature, fermentative production of terpenoids did not play a significant role on a commercial scale until a few years ago. Driven by technological progress in metabolic engineering and process biotechnology, terpene-based food ingredients such as flavors, sweeteners, and vitamins produced by fermentation have now become viable and commercially competitive options. In recent years, several companies have developed microbial platforms for commercial terpene production. Impressive progress has been made in the fermentative production of sesquiterpenes used in flavorings. The development of sweeteners, such as steviol glycosides and mogrosides, and the production of vitamins A and E based on fermentation are also being explored. The production of monoterpenes remains challenging due to their antimicrobial effects.

Leveraging a Y. lipolytica naringenin chassis for biosynthesis of apigenin and associated glucoside

Flavonoids are a diverse set of natural products with promising bioactivities including anti-inflammatory, anti-cancer, and neuroprotective properties. Previously, the oleaginous host Yarrowia lipolytica has been engineered to produce high titers of the base flavonoid naringenin. Here, we leverage this host along with a set of E. coli bioconversion strains to produce the flavone apigenin and its glycosylated derivative isovitexin, two potential nutraceutical and pharmaceutical candidates. Through downstream strain selection, co-culture optimization, media composition, and mutant isolation, we were able to produce168 mg/L of apigenin, representing a 46% conversion rate of 2-(R/S)-naringenin to apigenin. This apigenin platform was modularly extended to produce isovitexin by addition of a second bioconversion strain. Together, these results demonstrate the promise of microbial production and modular bioconversion to access diversified flavonoids.

Plant endophytic fungi exhibit diverse biotransformation pathways of mogrosides and show great potential application in siamenoside I production

Fungal endophytes, as an untapped resource of glycoside hydrolase biocatalysts, need to be further developed. Mogroside V, the primary active compound in Siraitia grosvenorii fruit, can be converted into other various bioactive mogrosides by selective hydrolysis of glucose residues at C3 and C24 positions. In present study, 20 fungal strains were randomly selected from our endophytic fungal strain library to assess their capability for mogroside V transformation. The results revealed that relatively high rate (30%) endophytic fungal strains exhibited transformative potential. Further analysis indicated that endophytic fungi could produce abundant mogrosides, and the pathways for biotransforming mogroside V showed diverse. Among the given fungal endophytes, Aspergillus sp. S125 almost completely converted mogroside V into the end-products mogroside II A and aglycone within just 2 days of fermentation; Muyocopron sp. A5 produced rich intermediate products, including siamenoside I, and the end-product mogroside II E. Subsequently, we optimized the fermentation conditions for Aspergillus sp. S125 and Muyocopron sp. A5 to evaluate the feasibility of large-scale mogroside V conversion. After optimization, Aspergillus sp. S125 converted 10 g/L of mogroside V into 4.5 g/L of mogroside II A and 3.6 g/L of aglycone after 3 days of fermentation, whereas Muyocopron sp. A5 selectively produced 4.88 g/L of siamenoside I from 7.5 g/L of mogroside V after 36 h of fermentation. This study not only identifies highly effective biocatalytic candidates for mogrosides transformation, but also strongly suggests the potential of plant endophytic fungi as valuable resources for the biocatalysis of natural compounds.

A comprehensive review of Siraitia grosvenorii (Swingle) C. Jeffrey: chemical composition, pharmacology, toxicology, status of resources development, and applications

Siraitia grosvenorii (Swingle) C. Jeffrey (S. grosvenorii), a perennial indigenous liana from the Cucurbitaceae family, has historically played a significant role in southern China's traditional remedies for various ailments. Its dual classification by the Chinese Ministry of Health for both medicinal and food utility underscores its has the potential of versatile applications. Recent research has shed light on the chemical composition, pharmacological effects, and toxicity of S. grosvenorii. Its active ingredients include triterpenoids, flavonoids, amino acids, volatile oils, polysaccharides, minerals, vitamins, and other microconstituents. Apart from being a natural sweetener, S. grosvenorii has been found to have numerous pharmacological effects, including alleviating cough and phlegm, preventing dental caries, exerting anti-inflammatory and anti-allergic effects, anti-aging and anti-oxidative, hypoglycemic, lipid-lowering, anti-depression, anti-fatigue, anti-schizophrenic, anti-Parkinson, anti-fibrotic, and anti-tumor activities. Despite its versatile potential, there is still a lack of systematic research on S. grosvenorii to date. This paper aims to address this gap by providing an overview of the main active components, pharmacological efficacy, toxicity, current status of development and application, development dilemmas, and strategies for intensive exploitation and utilization of S. grosvenorii. This paper aims to serve as a guide for researchers and practitioners committed to exploiting the biological resources of S. grosvenorii and further exploring its interdisciplinary potential.

Siraitia grosvenorii As a Homologue of Food and Medicine: A Review of Biological Activity, Mechanisms of Action, Synthetic Biology, and Applications in Future Food

Siraitia grosvenorii (SG), also known as Luo Han Guo or Monk fruit, boasts a significant history in food and medicine. This review delves into SG's historical role and varied applications in traditional Chinese culture, examining its phytochemical composition and the health benefits of its bioactive compounds. It further explores SG's biological activities, including antioxidant, anti-inflammatory, and antidiabetic properties and elucidates the mechanisms behind these effects. The review also highlights recent synthetic biology advances in enhancing the production of SG's bioactive compounds, presenting new opportunities for broadening their availability. Ultimately, this review emphasizes SG's value in food and medicine, showcasing its historical and cultural importance, phytochemistry, biological functions, action mechanisms, and the role of synthetic biology in its sustainable use.

Design of a chimeric glycosyltransferase OleD for the site-specific O-monoglycosylation of 3-hydroxypyridine in nosiheptide

To identify the potential role of the 3-hydroxyl group of the pyridine ring in nosiheptide (NOS) for its antibacterial activity against Gram-positive pathogens, enzymatic glycosylation was utilized to regio-selectively create a monoglycosyl NOS derivative, NOS-G. For this purpose, we selected OleD, a UDP glycosyltransferase from Streptomyces antibioticus that has a low productivity for NOS-G. Activity of the enzyme was increased by swapping domains derived from OleI, both single and in combination. Activity enhancement was best in mutant OleD-10 that contained four OleI domains. This chimer was engineered by site-directed mutagenesis (single and in combination) to increase its activity further, whereby variants were screened using a newly-established colorimetric assay. OleD-10 with I117F and T118G substitutions (FG) had an increased NOS-G productivity of 56%, approximately 70 times higher than that of wild-type OleD. The reason for improved activity of FG towards NOS was structurally attributed to a closer distance (<3 Å) between NOS/sugar donor and the catalytic amino acid H25. The engineered enzyme allowed sufficient activity to demonstrate that the produced NOS-G had enhanced stability and aqueous solubility compared to NOS. Using a murine MRSA infection model, it was established that NOS-G resulted in partial protection within 20 h of administration and delayed the death of infected mice. We conclude that 3-hydroxypyridine is a promising site for structural modification of NOS, which may pave the way for producing nosiheptide derivatives as a potential antibiotic for application in clinical treatment.

Post-Ripening and Key Glycosyltransferase Catalysis to Promote Sweet Mogrosides Accumulation of Siraitia grosvenorii Fruits

Sweet mogrosides are not only the primary bioactive ingredient in Siraitia grosvenorii fruits that exhibit anti-tussive properties and expectorate phlegm, but they are also responsible for the fruit's sweetness. Increasing the content or proportion of sweet mogrosides in Siraitia grosvenorii fruits is significant for improving their quality and industrial production. Post-ripening is an essential step in the post-harvest processing of Siraitia grosvenorii fruits, but the underlying mechanism and condition of post-ripening on Siraitia grosvenorii quality improvement need to be studied systematically. Therefore, this study analyzed the mogroside metabolism in Siraitia grosvenorii fruits under different post-ripening conditions. We further examined the catalytic activity of glycosyltransferase UGT94-289-3 in vitro. The results showed that the post-ripening process of fruits could catalyze the glycosylation of bitter-tasting mogroside IIE and III to form sweet mogrosides containing four to six glucose units. After ripening at 35 °C for two weeks, the content of mogroside V changed significantly, with a maximum increase of 80%, while the increase in mogroside VI was over twice its initial amount. Furthermore, under the suitable catalytic condition, UGT94-289-3 could efficiently convert the mogrosides with less than three glucose units into structurally diverse sweet mogrosides, i.e., with mogroside III as the substrate, 95% of it can converted into sweet mogrosides. These findings suggest that controlling the temperature and related catalytic conditions may activate UGT94-289-3 and promote the accumulation of sweet mogrosides. This study provides an effective method for improving the quality of Siraitia grosvenorii fruits and the accumulation of sweet mogrosides, as well as a new economical, green, and efficient method for producing sweet mogrosides.

Efficient snailase-based production of mogrol from Luo Han Guo extract in an aqueous-organic system

To solve the insufficient availability of mogrol, an 11α-hydroxy aglycone of mogrosides in Siraitia grosvenorii, snailase was employed as the enzyme to completely deglycosylate LHG extract containing 50% mogroside V. Other commonly used glycosidases performed less efficiently. Response surface methodology was conducted to optimize the productivity of mogrol, which peaked at 74.7% in an aqueous reaction. In view of the differences in water-solubility between mogrol and LHG extract, we employed an aqueous-organic system for the snailase-catalyzed reaction. Of five tested organic solvents, toluene performed best and was relatively well tolerated by snailase. After optimization, biphasic medium containing 30% toluene (v/v) could produce a high-quality mogrol (98.1% purity) at a 0.5 L scale with a production rate of 93.2% within 20 h. This toluene-aqueous biphasic system would not only provide sufficient mogrol to construct future synthetic biology systems for the preparation of mogrosides, but also facilitate the development of mogrol-based medicines.

One-pot biosynthesis of gastrodin using UDP-glycosyltransferase itUGT2 with an in situ UDP-glucose recycling system

Gastrodin, the major effective ingredient in Tianma (Gastrodia elata), is a p-hydroxybenzoic acid derivative with various activities. Gastrodin has been widely investigated for food and medical applications. The last biosynthetic step for gastrodin is UDP-glycosyltransferase (UGT)-mediated glycosylation with UDP-glucose (UDPG) as glycosyl donor. In this study, we performed a one-pot reaction both in vitro and in vivo to synthesize gastrodin from p-hydroxybenzyl alcohol (pHBA) by coupling UDP-glucosyltransferase from Indigofera tinctoria (itUGT2) to sucrose synthase from Glycine max (GmSuSy) for regeneration of UDPG. The in vitro results showed that itUGT2 transferred a glucosyl group to pHBA to generate gastrodin. After 37 UDPG regeneration cycles with 2.5% (molar ratio) UDP, the pHBA conversion reached 93% at 8 h. Furthermore, a recombinant strain with itUGT2 and GmSuSy genes was constructed. Through optimizing the incubation conditions, a 95% pHBA conversion rate (220 mg/L gastrodin titer) was achieved in vivo without addition of UDPG, which was 2.6-fold higher than that without GmSuSy. This in situ system for gastrodin biosynthesis provides a highly efficient strategy for both in vitro gastrodin synthesis and in vivo biosynthesis of gastrodin in E. coli with UDPG regeneration.

Genome-Wide Identification and Expression Analysis of WRKY Transcription Factors in Siraitia siamensis

WRKY transcription factors, as the largest gene family in higher plants, play an important role in various biological processes including growth and development, regulation of secondary metabolites, and stress response. In this study, we performed genome-wide identification and analysis of WRKY transcription factors in S. siamensis. A total of 59 SsWRKY genes were identified that were distributed on all 14 chromosomes, and these were classified into three major groups based on phylogenetic relationships. Each of these groups had similar conserved motifs and gene structures. We compared all the S. siamensis SsWRKY genes with WRKY genes identified from three diverse plant species, and the results implied that segmental duplication and tandem duplication play an important roles in the evolution processes of the WRKY gene family. Promoter region analysis revealed that SsWRKY genes included many cis-acting elements related to plant growth and development, phytohormone response, and both abiotic and biotic stress. Expression profiles originating from the transcriptome database showed expression patterns of these SsWRKY genes in four different tissues and revealed that most genes are expressed in plant roots. Fifteen SsWRKY genes with low-temperature response motifs were surveyed for their gene expression under cold stress, showing that most genes displayed continuous up-regulation during cold treatment. Our study provides a foundation for further study on the function and regulatory mechanism of the SsWRKY gene family.

Glycosyltransferase engineering and multi-glycosylation routes development facilitating synthesis of high-intensity sweetener mogrosides

Mogrosides are widely served as natural zero-calorie sweeteners. To date, the biosynthesis of high-intensity sweetness mogrosides V from mogrol has not been achieved because of inefficient and uncontrollable multi-glycosylation process. To address this challenge, we reported three UDP-glycosyltransferases (UGTs) catalyzing the primary and branched glycosylation of mogrosides and increased the catalytic efficiency by 74-400-folds toward branched glycosylation using an activity-based sequence conservative analysis engineering strategy. The computational studies provided insights into the origin of improved catalytic activity. By virtue of UGT mutants, we provided regio- and bond-controllable multi-glycosylation routes, successfully facilitating sequential glycosylation of mogrol to three kinds of mogroside V in excellent yield of 91-99%. Meanwhile, the feasibility of the routes was confirmed in engineered yeasts. It suggested that the multi-glycosylation routes would be combined with mogrol synthetic pathway to de novo produce mogrosides from glucose by aid of metabolic engineering and synthetic biology strategies in the future.