A type III polyketide synthase from Wachendorfia thyrsiflora and its role in diarylheptanoid and phenylphenalenone biosynthesis

Abstract

Chalcone synthase (CHS) related type III plant polyketide synthases (PKSs) are likely to be involved in the biosynthesis of diarylheptanoids (e.g. curcumin and polycyclic phenylphenalenones), but no such activity has been reported. Root cultures from Wachendorfia thyrsiflora (Haemodoraceae) are a suitable source to search for such enzymes because they synthesize large amounts of phenylphenalenones, but no other products that are known to require CHSs or related enzymes (e.g. flavonoids or stilbenes). A homology-based RT-PCR strategy led to the identification of cDNAs for a type III PKS sharing only approximately 60% identity with typical CHSs. It was named WtPKS1 (W. thyrsiflora polyketide synthase 1). The purified recombinant protein accepted a large variety of aromatic and aliphatic starter CoA esters, including phenylpropionyl- and side-chain unsaturated phenylpropanoid-CoAs. The simplest model for the initial reaction in diarylheptanoid biosynthesis predicts a phenylpropanoid-CoA as starter and a single condensation reaction to a diketide. Benzalacetones, the expected release products, were observed only with unsaturated phenylpropanoid-CoAs, and the best results were obtained with 4-coumaroyl-CoA (80% of the products). With all other substrates, WtPKS1 performed two condensation reactions and released pyrones. We propose that WtPKS1 catalyses the first step in diarylheptanoid biosynthesis and that the observed pyrones are derailment products in the absence of downstream processing proteins.

In Vitro Synthesis of Curcuminoids by Type III Polyketide Synthase from Oryza sativa

“…However, we believe that the curcuminoids are biosynthesized in Zingiberaceae in a manner similar to the unique mechanism shown by CUS. Turmeric gradually accumulates curcuminoids throughout the growing season (8), probably because of low activity and low-level expression of the curcuminoid biosynthetic enzyme. These features may have prevented researchers from identifying the enzyme(s) in the past.…”

“…Although Ramirez-Ahumada et al (7) achieved curcuminoid synthesis in vitro using crude extracts of turmeric, they did not characterize the enzyme(s) responsible. WtPKS1, a type III PKS from Wachendorfia thyrsiflora known to produce curcuminoid-related compounds called phenylphenalenones, is capable of synthesizing benzalacetones from phenylpropanoid-CoAs and malonyl-CoA (8), suggesting that WtPKS1 may be involved in the synthesis of the ␤-keto acid during curcuminoid formation. However, WtPKS1 does not catalyze curcuminoid formation from a precursor of the ␤-keto acid and phenylpropanoid-CoA, which excludes the possibility that WtPKS1 alone is capable of synthesizing curcuminoids (8).…”

Biosynthesis of the Major Tetrahydroxystilbenes in Spruce, Astringin and Isorhapontin, Proceeds via Resveratrol and Is Enhanced by Fungal Infection

“…Caffeoyl-CoA and feruloyl-CoA were chemically synthesized following methods from Brand et al (2006). Identification of these compounds was confirmed by LC-MS with electrospray ionization (ESI).…”

Heterologous Production of Curcuminoids

“…Due to the immense pharmaceutical value of curcuminoids, other genes encoding type III polyketide synthase (PKS) curcumin/curcuminoid synthases are being sought. Brand et al (187) characterized a type III PKS from Wachendorfia thyrsiflora, WtPKS1 (GenBank accession number AY727928.1). W. thyrsiflora is known to synthesize phenylphenalenones which are thought to be synthesized from curcuminoids.…”