Abstract
Curcuminoids found in the rhizome of turmeric, Curcuma longa, possess various biological activities. Despite much attention regarding the biosynthesis of curcuminoids because of their pharmaceutically important properties and biosynthetically intriguing structures, no enzyme systems have been elucidated. Here we propose a pathway for curcuminoid biosynthesis in the herb C. longa, which includes two novel type III polyketide synthases. One of the type III polyketide synthases, named diketide-CoA synthase (DCS), catalyzed the formation of feruloyldiketide-CoA by condensing feruloyl-CoA and malonyl-CoA. The other, named curcumin synthase (CURS), catalyzed the in vitro formation of curcuminoids from cinnamoyldiketide-N-acetylcysteamine (a mimic of the CoA ester) and feruloyl-CoA. Co-incubation of DCS and CURS in the presence of feruloyl-CoA and malonyl-CoA yielded curcumin at high efficiency, although CURS itself possessed low activity for the synthesis of curcumin from feruloyl-CoA and malonyl-CoA. These findings thus revealed the curcumin biosynthetic route in turmeric, in which DCS synthesizes feruloyldiketide-CoA, and CURS then converts the diketide-CoA esters into a curcuminoid scaffold.
Highlights
Type III polyketide synthases (PKSs),4 consisting of a homodimer of ketosynthase, play an important role in the bio
We recently discovered a type III PKS, named curcuminoid synthase (CUS), in the rice Oryza sativa, that catalyzes the formation of bisdemethoxycurcumin by condensing two p-coumaroyl-CoAs and one malonyl-CoA by the mechanism shown in Fig. 1B [17]
In vitro analysis of the two type III PKSs, diketide-CoA synthase (DCS) and curcumin synthase (CURS), isolated from the herb C. longa revealed that DCS catalyzed the formation of feruloyldiketide-CoA (3b) from feruloyl-CoA (3a) and malonyl-CoA, and CURS catalyzed the formation of curcuminoids from feruloyl-CoA (3a) and cinnamoyl-diketideNAC (4b)
Summary
Thetic activity in an extract from the leaves of turmeric. Their attempts to purify a type III PKS responsible for this reaction by anion-exchange column chromatography failed. We recently discovered a type III PKS, named curcuminoid synthase (CUS), in the rice Oryza sativa, that catalyzes the formation of bisdemethoxycurcumin by condensing two p-coumaroyl-CoAs and one malonyl-CoA by the mechanism shown in Fig. 1B [17]. The discovery of CUS supported the hypothesis proposed by Schroder [12], the type III PKS catalyzing the curcuminoid synthesis in turmeric still remained undiscovered. We describe the cloning and characterization of two type III PKSs from turmeric, which were named diketide-CoA synthase (DCS) and curcumin synthase (CURS) on the basis of their activities. DCS catalyzes the formation of a diketide intermediate via condensation of feruloyl-CoA with malonyl-CoA. CURS catalyzes the formation of curcumin from the diketide intermediate and feruloyl-CoA. We concluded that DCS and CURS participate in curcumin synthesis using the abundantly present CoA esters in turmeric
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