Abstract
Fenugreek (Trigonella foenum-graecum), a pharmacologically important herb, is widely known for its antidiabetic, hypolipidemic, and anticancer effects. The medicinal properties of this herb are accredited to the presence of bioactive steroidal saponins with one or more sugar moieties linked to the C-3 OH position of disogenin or its C25-epimer yamogenin. Despite intensive studies regarding pharmacology and phytochemical profiles of this plant, enzymes and/or genes involved in synthesizing the glycosidic part of fenugreek steroidal saponins are still missing so far. This study reports the molecular cloning and functional characterization of a key sterol-specific glucosyltransferase, designated as TfS3GT2 here, from fenugreek plant. The recombinant TfS3GT2 was purified via expression in Escherichia coli, and biochemical characterization of the recombinant enzyme suggested its role in transferring a glucose group onto the C-3 hydroxyl group of diosgenin or yamogenin. The functional role of TfS3GT2 in the steroidal saponin biosynthesis was also demonstrated by suppressing the gene in the transgenic fenugreek hairy roots via the RNA interference (RNAi) approach. Down-regulation of TfS3GT2 in fenugreek generally led to reduced levels of diosgenin or yamogenin-derived steroidal saponins. Thus, Tf3SGT2 was identified as a steroid-specific UDP-glucose 3-O-glucosyltransferase that appears to be involved in steroidal saponin biosynthesis in T. foenum-graecum.
Highlights
Trigonella foenum-graecum is one of the oldest traditional medicinal plant species originating from the Iran and Mediterranean regions (Mostafaie et al, 2018)
Functional Characterization of the TfS3GT Candidates To characterize the catalytic functions of the TfS3GTs in vitro, recombinant TfS3GTs were expressed in E. coli cells, and purified by GST-tag affinity chromatography (Supplementary Figure 1)
This study reports the isolation and functional characterization of a novel sterol-specific 3-O-glucosyltransferase (TfS3GT2) that is associated with the steroidal saponin biosynthesis in T. foenum-graecum
Summary
Trigonella foenum-graecum (fenugreek) is one of the oldest traditional medicinal plant species originating from the Iran and Mediterranean regions (Mostafaie et al, 2018). In traditional Chinese medicine, this plant has been prescribed for the treatment of many conditions, such as lung congestion, diabetes, epilepsy, T. foenum-graecum Sterol Glucosyltransferase and paralysis (Nagulapalli Venkata et al, 2017). Phytochemical studies of fenugreek seeds and other tissues have revealed the presence of steroidal saponins primarily based on spirostanol aglycones (e.g., diosgenin or its C25-epimer yamogenin) (Pang et al, 2012; Kang et al, 2013; Krol-Kogus et al, 2020). Dioscin is the major active ingredient of the traditional Chinese medicine product, called “Di’ao Xinxuekang capsule” (Yu et al, 2014), which is currently utilized for the prevention of cardiovascular diseases. Despite intensive studies concerning the chemical structures and medicinal activities of the saponins, the genes and enzymes involved in biosynthesis of the steroidal saponins in fenugreek remain largely unknown
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