Investigating the heterologous expression of plant secondary metabolic enzymes to produce curcuminoids and curcuminoid derivatives

Curcuminoids are highly bioactive polyketide chemicals produced in the rhizomes of the turmeric plant (Curcuma longa). In addition to giving turmeric powder its distinctive yellow colour and flavour, these molecules elicit a plethora of medicinal effects. This project aimed to biosynthesize curcuminoids and their derivatives using the metabolic engineering of Baker’s yeast (Saccharomyces cervisiae) and tobacco (Nicotiana benthamiana). Phenylpropanoids, sustainably derived from bio-refinery waste, were to be used as starting materials. To convert phenylpropanoids into curcuminoids three enzymatic steps were needed: this involved the cloning and expression of 4-coumarate CoA ligase 5 (4CL5) from Arabidopsis thaliana and diketide-CoA synthase (DCS) and curcuminoid synthase 1 (CURS1) from C. longa. Protein extract from yeast expressing 4CL5 was able to convert both natural and non-natural phenylpropanoids to their corresponding phenylpropanoyl-CoA esters. However, protein extracts from yeast transformed with either DCS or CURS1 did not yield the corresponding enzyme activity. Furthermore, it was concluded that tobacco was not an optimal chassis for curcuminoid production as both phenylpropanoid substrates and curcuminoid products were metabolised by endogenous enzymes in the leaf tissue.

Despite their bioactivities, curcuminoids are poorly bioavailable reducing their medicinal potential. Regiospecific glycosylation, performed by UDP-glycosyltransferases (UGTs), is a known strategy to improve a molecule’s solubility. Diglucosylated curcuminoids are 10 000 times more soluble in water than the aglycone. Using metabolomics and 14C radiolabelling assays C. longa was investigated as a source of novel curcuminoid UGTs.