Indirect and direct routes to C-glycosylated flavones in Saccharomyces cerevisiae

Abstract

BackgroundC-glycosylated flavones have recently attracted increased attention due to their possible benefits in human health. These biologically active compounds are part of the human diet, and the C-linkage makes them more resistant to hydrolysis and degradation than O-glycosides. In contrast to O-glycosyltransferases, few C-glycosyltransferases (CGTs) have so far been characterized. Two different biosynthetic routes for C-glycosylated flavones have been identified in plants. Depending on the type of C-glycosyltransferase, flavones can be glycosylated either directly or indirectly via C-glycosylation of a 2-hydroxyflavanone intermediate formed by a flavanone 2-hydroxylase (F2H).ResultsIn this study, we reconstructed the pathways in the yeast Saccharomyces cerevisiae, to produce some relevant CGT substrates, either the flavanones naringenin and eriodictyol or the flavones apigenin and luteolin. We then demonstrated two-step indirect glycosylation using combinations of F2H and CGT, to convert 2-hydroxyflavanone intermediates into the 6C-glucoside flavones isovitexin and isoorientin, and the 8C-glucoside flavones vitexin and orientin. Furthermore, we established direct glycosylation of flavones using the recently identified GtUF6CGT1 from Gentiana triflora. The ratio between 6C and 8C glycosylation depended on the CGT used. The indirect route resulted in mixtures, similar to what has been reported for in vitro experiments. In this case, hydroxylation at the flavonoid 3′-position shifted the ratio towards the 8C-glucosylated orientin. The direct flavone glycosylation by GtUF6CGT1, on the other hand, resulted exclusively in 6C-glucosides.ConclusionsThe current study features yeast as a promising host for production of flavone C-glycosides, and it provides a set of tools and strains for identifying and studying CGTs and their mechanisms of C-glycosylation.Electronic supplementary materialThe online version of this article (10.1186/s12934-018-0952-5) contains supplementary material, which is available to authorized users.

Pathway-specific enzymes from bamboo and crop leaves biosynthesize anti-nociceptive C-glycosylated flavones

“…5). This phenomenon was not mentioned in the prior reports of metabolic engineering on CGF biosynthesis in yeast systems 55,56 , which indicated that E. coli probably lacked endogenous dehydratases active on 2-hydroxylated flavanone. The successful bio-production of (iso)orientin and (iso)vitexin here was achieved through synthetic approach, which involves multiple bioparts from bamboo, maize, rice, and mouse-ear cress (A. thaliana).…”

Treasure from garden: Bioactive compounds of buckwheat

“…The biosynthesis of vitexin and isovitexin begins from the intermediate compound of flavonol synthesis (Naringenin), which was hydroxylated by F2H at the 2-position of flavanone and produces 2-hydroxyflavanone. This 2-hydroxyflavanone is in equilibrium with its another open-ring form (dibenzoylmethane form), which is C -glucosylated by using C -glucosyltransferase (CGT) ( Gan et al, 2019 , Nagatomo et al, 2014 , Taguchi, 2016 , Vanegas et al, 2018 ). Two closed-circular forms of C -glucoside are 2-hydroxyflavanone 6- C -glucoside and 8- C -glucoside which are also in equilibrium with produced C -glucoside to form two flavone C -glycoside (vitexin and isovitexin) by dehydration after the sugar moiety conjugation ( Vanegas et al, 2018 ).…”

Advances on Synthesis of Flavonoid Glycosides

“…在对来自荞麦(Fagopyrum esculentum M)的碳糖基 转移酶 UGT708D1 和大豆(Glycine max)的碳糖基转移酶 UGT708C2 直接和间接进行碳糖基化研究中 [98] , 首先通 过基因工程重建酵母, 使其产生一些相关的 CGT 底物: 黄烷酮柚皮素、圣草酚、黄酮芹菜素和木犀草素, 然后 再 分 别 将 黄 烷 酮 2-羟 化 酶 UGT708C2 [95] 、 OsCYP93G2 [99] 、 SbCYP93G3 [100] 与 碳 糖 基 转 移 酶 UGT708D1 或 UGT708C2 的组合进行黄烷酮柚皮素、 圣 草酚底物间接糖基化, 分别获得了 6-C-葡糖苷黄酮异牡 荆素、8-C-葡糖苷黄酮牡荆素和 6-C-葡糖苷异荭草素、 8-C-葡糖苷荭草苷, 其中产黄烷酮柚皮素底物的酵母菌 组生成 6-C-葡萄糖苷为主, 而产圣草酚底物的酵母菌组 生成 8-C-葡萄糖苷为主. 而以来自龙胆(Gentiana triflora)的碳糖基转移酶 GtUF6CGT1 进行芹菜素、木犀草素 底物直接糖基化, 仅产生 6-C-葡糖苷, 与之前报道结果 相一致 [96] , 且 6-C-葡糖苷黄酮异牡荆素的产量超过 200 mg/L.…”