Pathway enzyme engineering for flavonoid production in recombinant microbes

Abstract

Metabolic engineering of microbial strains for the production of flavonoids of industrial interest has attracted great attention due to its promising advantages over traditional extraction approaches, such as independence of plantation, facile downstream separation, and ease of process and quality control. However, most of the constructed microbial production systems suffer from low production titers, low yields and low productivities, restricting their commercial applications. One important reason of the inefficient production is that the expression conditions and the detailed functions of the flavonoid pathway enzymes are not well understood. In this review, we have collected the biochemical properties, structural details, and genetic information of the enzymes in the flavonoid biosynthetic pathway as a guide for the expression and analysis of these enzymes in microbial systems. Additionally, we have summarized the engineering approaches used in improving the performances of these enzymes in recombinant microorganisms. Major challenges and future directions on the flavonoid pathway are also discussed.

Keywords: Anthocyanins; Flavones; Flavonoids; Flavonols; Isoflavonoids; Phenylpropanoic acids.

Fig. 1

The core skeleton of flavonoids. The common flavonoids contain six subgroups, including flavanone, flavone, flavonol, flavanol, flavanonol, and anthocyanin.

Fig. 2

The flavonoid biosynthesis pathway in plants. The enzymes marked in bold red are the ones described in this review. PAL, phenyl ammonia lyase; TAL, tyrosine ammonia lyase; C4H, cinnamate 4-hydroxylase; 4CL, 4-coumarate: CoA ligase; CHS, chalcone synthase; CHI, chalcone synthase; FNSI, soluble flavone synthase; FNSII, membrane-bound flavone synthase; FHT, flavanone 3b-hydroxylase; FLS, flavonol synthase; F3H, flavanone 3-hydroxylase; DFR, dihydroflavonol 4-reductase; LAR, leucocyanidin reductase; ANS, anthocyanidin synthase; HO, hydroxylase; OMT, O-methyltransferase; GT, glycotransferase; PT, prenyltransferase. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)

Fig. 3

The approaches frequently used in engineering of flavonoid pathway enzymes for improved functions in recombinant microorganisms. The strategies include codon optimization, fusion expression, enzyme scaffolding (Conrado et al., 2011; Dueber et al., 2009), and removal of signal peptides for expression of P450 pathway enzymes.