Heterologous production of curcuminoids

Abstract

Curcuminoids, components of the rhizome of turmeric, show several beneficial biological activities, including anticarcinogenic, antioxidant, anti-inflammatory, and antitumor activities. Despite their numerous pharmaceutically important properties, the low natural abundance of curcuminoids represents a major drawback for their use as therapeutic agents. Therefore, they represent attractive targets for heterologous production and metabolic engineering. The understanding of biosynthesis of curcuminoids in turmeric made remarkable advances in the last decade, and as a result, several efforts to produce them in heterologous organisms have been reported. The artificial biosynthetic pathway (e.g., in Escherichia coli) can start with the supplementation of the amino acid tyrosine or phenylalanine or of carboxylic acids and lead to the production of several natural curcuminoids. Unnatural carboxylic acids can also be supplemented as precursors and lead to the production of unnatural compounds with possibly novel therapeutic properties. In this paper, we review the natural conversion of curcuminoids in turmeric and their production by E. coli using an artificial biosynthetic pathway. We also explore the potential of other enzymes discovered recently or already used in other similar biosynthetic pathways, such as flavonoids and stilbenoids, to increase curcuminoid yield and activity.

FIG 1

Curcuminoid biosynthetic pathway in Curcuma longa. Cinnamic acid is synthesized from phenylalanine by phenylalanine ammonia lyase (PAL) and converted to coumaric acid by cinnamate-4-hydroxylase (C4H). Then, 4-coumarate-CoA ligase (4CL) converts coumaric acid to coumaroyl-CoA, and p-coumaroyl shikimate transferase (CST), p-coumaroyl 5-O-shikimate 3′-hydroxylase (CS3′H), and caffeoyl-CoA O-methyltransferase (CCoAOMT) convert it to feruloyl-CoA. Coumaroyl-CoA and feruloyl-CoA are then converted by diketide-CoA synthase (DCS) to diketide-CoAs by condensation with malonyl-CoA. In the end, curcumin synthases (CURSs) catalyze the formation of curcuminoids by condensing the diketide-CoAs with coumaroyl-CoA and feruloyl-CoA. Depending on the combination, different curcuminoids are produced, namely, bisdemethoxycurcumin, demethoxycurcumin, and curcumin. The route indicated by dashed arrows corresponds to a less central phenylpropanoid pathway and may not occur in vivo in C. longa.

FIG 2

Biosynthetic production pathway of some diarylheptanoids in Curcuma longa. CST, coumaroyl shikimate transferase; CS3′H, p-coumaroyl 5-O-shikimate 3′-hydroxylase; CCoAOMT, caffeoyl-CoA O-methyltransferase.

FIG 3

Biosynthesis of curcuminoids by recombinant Escherichia coli, using tyrosine and/or phenylalanine as starter substrates that are converted to carboxylic acids by PAL (phenylalanine ammonia lyase). The carboxylic acids, which can also be added directly to the medium, are converted into the corresponding CoA esters by 4CL (4-coumarate-CoA ligase) (top), which is followed by several reactions catalyzed by curcuminoids synthase (CUS) (bottom). Malonyl-CoA is overproduced by ACC (acetyl-CoA carboxylase). (Adapted from references and .)

FIG 4

Biosynthesis of aromatic amino acids in Escherichia coli. Red lines show the regulation points.

FIG 5

Pathway for biosynthesis of caffeic acid using the approaches described by Lin and Yan (140) and Huang et al. (151) (top) and Zhang and Stephanopoulos (152) (bottom). TAL, tyrosine ammonia lyase; C3H, 4-coumarate 3-hydroxylase; 4HPA3H, hydroxyphenylacetate 3-hydroxylase; 4CL, 4-coumarate-CoA ligase.

FIG 6

Metabolic pathways connecting malonyl-CoA with curcuminoid biosynthesis in Escherichia coli.