Abstract
Flavonoids and prenylated flavonoids are active components in medicinal plant extracts which exhibit beneficial effects on human health. Prenylated flavonoids consist of a flavonoid core with a prenyl group attached to it. This prenylation process is catalyzed by prenyltranferases (PTs). At present, only a few flavonoid-related PT genes have been identified. In this study, we aimed to investigate the roles of PT in flavonoid production. We isolated a putative PT gene (designated as BrPT2) from a medicinal ginger, Boesenbergia rotunda. The deduced protein sequence shared highest gene sequence homology (81%) with the predicted homogentisate phytyltransferase 2 chloroplastic isoform X1 from Musa acuminata subsp. Malaccensis. We then cloned the BrPT2 into pRI vector and expressed in B. rotunda cell suspension cultures via Agrobacterium-mediated transformation. The BrPT2-expressing cells were fed with substrate, pinostrobin chalcone, and their products were analyzed by liquid chromatography mass spectrometry. We found that the amount of flavonoids, namely alpinetin, pinostrobin, naringenin and pinocembrin, in BrPT2-expressing cells was higher than those obtained from the wild type cells. However, we were unable to detect any targeted prenylated flavonoids. Further in-vitro assay revealed that the reaction containing the BrPT2 protein produced the highest accumulation of pinostrobin from the substrate pinostrobin chalcone compared to the reaction without BrPT2 protein, suggesting that BrPT2 was able to accelerate the enzymatic reaction. The finding of this study implied that the isolated BrPT2 may not be involved in the prenylation of pinostrobin chalcone but resulted in high yield and production of other flavonoids, which is likely related to enzyme promiscuous activities.
Highlights
Flavonoids, including flavanones and chalcones, are major constituents in many plant species
Our results showed the content of alpinetin (463.31 ng/ml), pinostrobin (633.95 ng/ml), pinocembrin (34.04 ng/ml) and naringenin (19.74 ng/ml) in BrPT2expressing transgenic cells were significantly higher (p < 0.05) than those observed in the wild type cells (Fig. 3)
We found that the isolated BrPT2 shared the highest similarity of amino acid sequences with Musa acuminata homogentisate phytyltransferase and was placed in the same clade with phytyltransferases from other plant species
Summary
Flavonoids, including flavanones and chalcones, are major constituents in many plant species. They are synthesized through phenylpropanoid pathway, starting with aromatic amino acid phenylalanine which is derived from the shikimate pathway. Boesenbergia rotunda), exhibited considerable activity against HIV protease (Tewtrakul et al, 2003). Other compounds, such as panduratin A and 4′-hydroxypanduratin A, from this ginger exhibited inhibitory activity against dengue NS2B/3 serine protease which is mandatory for viral replication process (Tan et al, 2006). Flavanones and chalcones isolated from this ginger exhibited higher level of inhibition against the formation of methylglyoxal-derived advanced glycation end-product than the anti-glycating agent, aminoguanidine, indicating that these flavonoids could be beneficial in the prevention and treatment of diabetes (Potipiranun et al, 2018)
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