Functional Characterization of a Novel Glycosyltransferase (UGT73CD1) from Iris tectorum Maxim. for the Substrate promiscuity

Herbal textual research of Belamcanda chinensis (L.) redouté and screening of quality-markers based on 'pharmacodynamics-substance'

ETHNOPHARMACOLOGICAL RELEVANCE

Belamcanda chinensis (L.) Redouté is widely distributed in East Asia, such as China, Russia and North Korea. Belamcandae Rhizoma is the sun-dried rhizome of B. chinensis and has a long history of traditional medicinal use. It was first recorded in the Shennong's Herbal Classic, and has the effects of clearing heat and detoxifying, eliminating phlegm and benefiting the pharynx.

AIM OF THE STUDY

To systematically study the source of Belamcandae Rhizoma, summarize the evolution of its medicinal properties, efficacy and the application history of its prescriptions, summarize its biological activity, phytochemistry, synthetic metabolic pathway and toxicology, and screen the Quality-Markers of Belamcandae Rhizoma according to the screening principle of traditional Chinese medicine Quality-Markers.

MATERIALS AND METHODS

All information available on Belamcandae Rhizoma was collected using electronic search engines, such as Pubmed, Web of Science, CNKI, WFO (www.worldfloraonline.org), MPNS (https://mpsn.kew.org), Changchun University of Traditional Chinese Medicine Library collections, Chinese Medical Classics.

RESULTS

The source of Belamcandae Rhizoma is B. chinensis of Iridaceae. It has a long history of application in China. It has the effects of clearing heat and detoxifying, eliminating phlegm and promoting pharynx. Modern pharmacological studies have shown that it has anti-inflammatory, anti-oxidation, anti-tumor and other physiological activities, and is safe and non-toxic at normal application doses. At present, tectoridin, iridin, tectorigenin, irigenin and irisflorentin are identified as the Quality-Markers of Belamcandae Rhizoma.

CONCLUSIONS

As a traditional Chinese medicine, Belamcandae Rhizoma has a long history of application, and multifaceted studies have demonstrated that Belamcandae Rhizoma is a promising Chinese medicine with good application prospects. By reviewing and identifying the Quality-Markers of Belamcandae Rhizoma, this study can help to establish the evaluation procedure of it on the one hand, and identify the shortcomings research on the other hand. Currently, there are few studies on the anabolism and toxicology of it, and future studies may focus on its in vivo processes, toxicology and adverse effects.

Highly Promiscuous Flavonoid Di-O-glycosyltransferases from Carthamus tinctorius L

Safflower (Carthamus tinctorius L.) has been recognized for its medicinal value, but there have been limited studies on the glycosyltransferases involved in the biosynthesis of flavonoid glycosides from safflower. In this research, we identified two highly efficient flavonoid O-glycosyltransferases, CtOGT1 and CtOGT2, from safflower performing local BLAST alignment. By constructing a prokaryotic expression vector, we conducted in vitro enzymatic reactions and discovered that these enzymes were capable of catalyzing two-step O-glycosylation using substrates such as kaempferol, quercetin, and eriodictyol. Moreover, they exhibited efficient catalytic activity towards various compounds, including flavones (apigenin, scutellarein), dihydrochalcone (phloretin), isoflavones (genistein, daidzein), flavanones (naringenin, glycyrrhizin), and flavanonols (dihydrokaempferol), leading to the formation of O-glycosides. The broad substrate specificity of these enzymes is noteworthy. This study provides valuable insights into the biosynthetic pathways of flavonoid glycosides in safflower. The discovery of CtOGT1 and CtOGT2 enhances our understanding of the enzymatic processes involved in synthesizing flavonoid glycosides in safflower, contributing to the overall comprehension of secondary metabolite biosynthesis in this plant species.

Genome-wide analysis of UDP-glycosyltransferase gene family and identification of a flavonoid 7-O-UGT (AhUGT75A) enhancing abiotic stress in peanut (Arachis hypogaea L.)

BACKGROUND

Glycosylation, catalyzed by UDP-glycosyltransferase (UGT), was important for enhancing solubility, bioactivity, and diversity of flavonoids. Peanut (Arachis hypogaea L.) is an important oilseed and cash crop worldwide. In addition to provide high quality of edible oils and proteins, peanut seeds contain a rich source of flavonoid glycosides that benefit human health. However, information of UGT gene family was quite limited in peanut.

RESULTS

In present study, a total of 267 AhUGTs clustered into 15 phylogenetic groups were identified in peanut genome. Group I has greatly expanded to contain the largest number of AhUGT genes. Segmental duplication was the major driving force for AhUGT gene family expansion. Transcriptomic analysis of gene expression profiles in various tissues and under different abiotic stress treatments indicated AhUGTs were involved in peanut growth and abiotic stress response. AhUGT75A (UGT73CG33), located in mitochondria, was characterized as a flavonoid 7-O-UGT by in vitro enzyme assays. The transcript level of AhUGT75A was strongly induced by abiotic stress. Overexpression of AhUGT75A resulted in accumulating less amount of malondialdehyde (MDA) and superoxide, and enhancing tolerance against drought and/or salt stress in transgenic Arabidopsis. These results indicated AhUGT75A played important roles in conferring abiotic stress tolerance through reactive oxygen species scavenging.

CONCLUSIONS

Our research only not provides valuable information for functional characterization of UGTs in peanut, but also gives new insights into potential applications in breeding new cultivars with both desirable stress tolerance and health benefits.

Biochemical Characterization of Parsley Glycosyltransferases Involved in the Biosynthesis of a Flavonoid Glycoside, Apiin

The flavonoid glycoside apiin (apigenin 7-O-[β-D-apiosyl-(1→2)-β-D-glucoside]) is abundant in apiaceous and asteraceous plants, including celery and parsley. Although several enzymes involved in apiin biosynthesis have been identified in celery, many of the enzymes in parsley (Petroselinum crispum) have not been identified. In this study, we identified parsley genes encoding the glucosyltransferase, PcGlcT, and the apiosyltransferase, PcApiT, that catalyze the glycosylation steps of apiin biosynthesis. Their substrate specificities showed that they were involved in the biosynthesis of some flavonoid 7-O-apiosylglucosides, including apiin. The expression profiles of PcGlcT and PcApiT were closely correlated with the accumulation of flavonoid 7-O-apiosylglucosides in parsley organs and developmental stages. These findings support the idea that PcGlcT and PcApiT are involved in the biosynthesis of flavonoid 7-O-apiosylglucosides in parsley. The identification of these genes will elucidate the physiological significance of apiin and the development of apiin production methods.

Functional characterization and structural basis of a reversible glycosyltransferase involves in plant chemical defence

Plants experience numerous biotic stresses throughout their lifespan, such as pathogens and pests, which can substantially affect crop production. In response, plants have evolved various metabolites that help them withstand these stresses. Here, we show that two specialized metabolites in the herbaceous perennial Belamcanda chinensis, tectorigenin and its glycoside tectoridin, have diverse defensive effects against phytopathogenic microorganisms and antifeeding effects against insect pest. We further functionally characterized a 7-O-uridine diphosphate glycosyltransferase Bc7OUGT, which catalyses a novel reversible glycosylation of tectorigenin and tectoridin. To elucidate the catalytic mechanisms of Bc7OUGT, we solved its crystal structure in complex with UDP and UDP/tectorigenin respectively. Structural analysis revealed the Bc7OUGT possesses a narrow but novel substrate-binding pocket made up by plentiful aromatic residues. Further structure-guided mutagenesis of these residues increased both glycosylation and deglycosylation activities. The catalytic reversibility of Bc7OUGT was also successfully applied in an one-pot aglycon exchange reaction. Our findings demonstrated the promising biopesticide activity of tectorigenin and its glycosides, and the characterization and mechanistic study of Bc7OUGT could facilitate the design of novel reversible UGTs to produce valuable glycosides with health benefits for both plants and humans.

Identification and Characterization of CtUGT3 as the Key Player of Astragalin Biosynthesis in Carthamus tinctorius L

Safflower (Carthamus tinctorius L.) is a multipurpose economic crop that is distributed worldwide. Flavonoid glycosides are the main bioactive components in safflower, but only a few UDP-glycosyltransferases (UGT) have been identified. Three differentially expressed UGT genes related with the accumulation of 9 flavonoid O-glycosides were screened from metabolomics and transcriptome analysis. Safflower corolla protoplasts were used to confirm the glycosylation ability of UGT candidates in vivo for the first time. The astragalin content was significantly increased only when CtUGT3 was overexpressed. CtUGT3 also showed flavonoid 3-OH and 7-OH glycosylation activities in vitro. Molecular modeling and site-directed mutagenesis revealed that G15, T136, S276, and E384 were critical catalytic residues for the glycosylation ability of CtUGT3. These results demonstrate that CtUGT3 has a flavonoid 3-OH glycosylation function and is involved in the biosynthesis of astragalin in safflower. This study provides a reference for flavonoid biosynthesis genes research in nonmodel plants.

Utilization of glycosyltransferases as a seamless tool for synthesis and modification of the oligosaccharides-A review

Glycosyltransferases (GTs) catalyze the transfer of active monosaccharide donors to carbohydrates to create a wide range of oligosaccharide structures. GTs display strong regioselectivity and stereoselectivity in producing glycosidic bonds, making them extremely valuable in the in vitro synthesis of oligosaccharides. The synthesis of oligosaccharides by GTs often gives high yields; however, the enzyme activity may experience product inhibition. Additionally, the higher cost of nucleotide sugars limits the usage of GTs for oligosaccharide synthesis. In this review, we comprehensively discussed the structure and mechanism of GTs based on recent literature and the CAZY website data. To provide innovative ideas for the functional studies of GTs, we summarized several remarkable characteristics of GTs, including folding, substrate specificity, regioselectivity, donor sugar nucleotides, catalytic reversibility, and differences between GTs and GHs. In particular, we highlighted the recent advancements in multi-enzyme cascade reactions and co-immobilization of GTs, focusing on overcoming problems with product inhibition and cost issues. Finally, we presented various types of GT that have been successfully used for oligosaccharide synthesis. We concluded that there is still an opportunity for improvement in enzymatically produced oligosaccharide yield, and future research should focus on improving the yield and reducing the production cost.

Recent developments in promiscuous enzymatic reactions for carbon-nitrogen bond formation

Biocatalytic promiscuity is a new field of enzyme application in biochemistry, which has received much attention and has developed rapidly in recent years. The promiscuous biocatalysis has been promoted as a useful supplement to traditional strategy for the formation of C-heteroatom bonds. The generation of carbon-nitrogen (CN) bonds is an important issue in synthetic chemistry and is indispensable for the manufacturing of various pharmaceuticals and agrochemicals. Therefore, numerous efficient and reliable synthetic methods for the formation of CN bonds have been developed in recent years. Enzymatic CN bond forming reactions catalyzed by lipases, cytochrome P450 monooxygenases, glycosyltransferases, amine dehydrogenases, proteases, acylases, amylases and halohydrin dehalogenases are well established for synthetic purposes. This review introduces the recent progress in the construction of CN bonds using promiscuous enzymes.

Glycosyltransferases: Mining, engineering and applications in biosynthesis of glycosylated plant natural products

UDP-Glycosyltransferases (UGTs) catalyze the transfer of nucleotide-activated sugars to specific acceptors, among which the GT1 family enzymes are well-known for their function in biosynthesis of natural product glycosides. Elucidating GT function represents necessary step in metabolic engineering of aglycone glycosylation to produce drug leads, cosmetics, nutrients and sweeteners. In this review, we systematically summarize the phylogenetic distribution and catalytic diversity of plant GTs. We also discuss recent progress in the identification of novel GT candidates for synthesis of plant natural products (PNPs) using multi-omics technology and deep learning predicted models. We also highlight recent advances in rational design and directed evolution engineering strategies for new or improved GT functions. Finally, we cover recent breakthroughs in the application of GTs for microbial biosynthesis of some representative glycosylated PNPs, including flavonoid glycosides (fisetin 3-O-glycosides, astragalin, scutellarein 7-O-glucoside), terpenoid glycosides (rebaudioside A, ginsenosides) and polyketide glycosides (salidroside, polydatin).