An Aromatic Farnesyltransferase Functions in Biosynthesis of the Anti-HIV Meroterpenoid Daurichromenic Acid

Abstract

Rhododendron dauricum produces daurichromenic acid, an anti-HIV meroterpenoid, via oxidative cyclization of the farnesyl group of grifolic acid. The prenyltransferase (PT) that synthesizes grifolic acid is a farnesyltransferase in plant specialized metabolism. In this study, we demonstrated that the isoprenoid moiety of grifolic acid is derived from the 2-C-methyl-d-erythritol-4-phosphate pathway that takes place in plastids. We explored candidate sequences of plastid-localized PT homologs and identified a cDNA for this PT, RdPT1, which shares moderate sequence similarity with known aromatic PTs. RdPT1 is expressed exclusively in the glandular scales, where daurichromenic acid accumulates. In addition, the gene product was targeted to plastids in plant cells. The recombinant RdPT1 regiospecifically synthesized grifolic acid from orsellinic acid and farnesyl diphosphate, demonstrating that RdPT1 is the farnesyltransferase involved in daurichromenic acid biosynthesis. This enzyme strictly preferred orsellinic acid as a prenyl acceptor, whereas it had a relaxed specificity for prenyl donor structures, also accepting geranyl and geranylgeranyl diphosphates with modest efficiency to synthesize prenyl chain analogs of grifolic acid. Such a broad specificity is a unique catalytic feature of RdPT1 that is not shared among secondary metabolic aromatic PTs in plants. We discuss the unusual substrate preference of RdPT1 using a molecular modeling approach. The biochemical properties as well as the localization of RdPT1 suggest that this enzyme produces meroterpenoids in glandular scales cooperatively with previously identified daurichromenic acid synthase, probably for chemical defense on the surface of R. dauricum plants.

Convergent evolution of the UbiA prenyltransferase family underlies the independent acquisition of furanocoumarins in plants

“…S3a), they probably represent a natural variation. A similar substitution in this conserved sequence was observed in Rhododendron dauricum PT1 ; its native gene possesses an alanine at the same position, with replacement of this alanine by a glutamine reducing catalytic activity (Saeki et al ., ). The four proteins were therefore biochemically characterized.…”

“…). These results suggest that FcPT1a/b localize to plastids, which is consistent with the synthesis of prenyl donors for UbiA PTs, including DMAPP, via the MEP pathway (Akashi et al ., ; Saeki et al ., ).…”

Phytocannabinoids: Origins and Biosynthesis

“…Rhododendron dauricum produces the phytocannabinoid DCA. All carbon atoms in DCA are derived from acetyl-CoA and farnesyl-CoA, with orsellinic acid (OA) and grifolic acid (GA) as key intermediates [38,90,109,110]. Specialized glandular scales on the surface of predominantly young leaves are the place of DCA biosynthesis and storage [38].…”

“…Surprisingly, the farnesyl-CoA is derived from the plastidial MEP pathway, as shown by inhibitor studies. Inhibition of the MEP pathway with clomazone led to a decrease in OSA and DCA, whereas inhibition of the mevalonate-dependent pathway with mevastatin led to their increase, probably owing to compensatory upregulation of the MEP pathway [109]. RdPT1 shows moderate sequence identity to known UbiA aromatic PTs and is localized within the plastid compartment (Figure 3) [109].…”

Daurichromenic Acid from the Chinese Traditional Medicinal Plant Rhododendron dauricum Inhibits Sphingomyelin Synthase and Aβ Aggregation

“…This species of Rhododendron has been used in traditional Chinese medicine, with the medicinal herb “Manshanfong” used as an expectorant and to treat various diseases, such as acute and chronic bronchitis [ 2 ]. DCA has also been reported to have antibacterial activity against Gram-positive bacteria [ 3 ], as well as having anti-HIV [ 4 ], and anti-inflammatory [ 5 ] activity, suggesting that DCA may be a medicinal resource in the development of derivatives that can act as novel drugs to treat these conditions. Although DCA exhibits various pharmacological activities, including the induction of cell death in cultured cells [ 6 ], its molecular mechanisms of activity remain unclear.…”