Abstract
In plants, prenylation of metabolites is widely distributed to generate compounds with efficient defense potential and distinct pharmacological activities profitable to human health. Prenylated compounds are formed by members of the prenyltransferase (PT) superfamily, which catalyze the addition of prenyl moieties to a variety of acceptor molecules. Cell cultures of Hypericum calycinum respond to elicitor treatment with the accumulation of the prenylated xanthone hyperxanthone E. A cDNA encoding a membrane-bound PT (HcPT) was isolated from a subtracted cDNA library and transcript preparations of H. calycinum. An increase in the HcPT transcript level preceded hyperxanthone E accumulation in cell cultures of H. calycinum treated with elicitor. The HcPT cDNA was functionally characterized by expression in baculovirus-infected insect cells. The recombinant enzyme catalyzed biosynthesis of 1,3,6,7-tetrahydroxy-8-prenylxanthone through regiospecific C–8 prenylation of 1,3,6,7-tetrahydroxyxanthone, indicating its involvement in hyperxanthone E formation. The enzymatic product shared significant structural features with the previously reported cholinesterase inhibitor γ-mangostin. Thus, our findings may offer a chance for semisynthesis of new active agents to be involved in the treatment of Alzheimer’s disease.
Highlights
Xanthones are a class of specialized plant metabolites which serve as defense compounds against pathogenic microorganisms and herbivores
Eleven expressed sequence tags (ESTs) were identified and aligned against aromatic prenyltransferase sequences related to secondary metabolism [19,20,21,22,23]
Six of the identified ESTs shared homology with a single sequence contig. This 464-bp middle fragment encoded a peptide with a characteristic motif of aromatic prenyltransferases (Figure 2)
Summary
Xanthones are a class of specialized (secondary) plant metabolites which serve as defense compounds against pathogenic microorganisms and herbivores. While glycosylated xanthones are widely distributed in the plant family Gentianaceae, prenylated xanthones are typical of Clusiaceae and Hypericaceae [5]. The latter families contain monoprenylated compounds, and form a number of polyprenylated polycyclic metabolites possessing bridged skeletons. To gain insight into the biosynthesis of prenylated xanthones, we use elicitor-treated Hypericum calycinum cell cultures, which accumulate a monoprenylated xanthone phytoalexin, hyperxanthone E (Figure 1) [10]. BPS: benzophenone synthase, TXS: trihydroxyxanthone synthase, X6H: xanthone 6-hydroxylase, DMAPP: dimethylallyl diphosphate, HcPT: H. calycinum prenyltransferase
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