Aspergillus oryzae Biosynthetic Platform for de Novo Iridoid Production

Abstract

The iridoids and their derivatives monoterpene indole alkaloids (MIAs) are two broad classes of plant-derived natural products with valuable pharmaceutical properties. However, the poor source limited their application. Nepetalactol, a common iridoid scaffold of MIAs, was heterologously produced in Saccharomyces cerevisiae. Although the optimization of nepetalactol production in S. cerevisiae was achieved by metabolic engineering, the inherent metabolic constraints impose a restriction on the production. Herein, we developed a high nepetalactol-producing Aspergillus oryzae platform strain. First, the co-expression of 5 nepetalactol biosynthetic genes, in a high isopentenyl pyrophosphate (IPP)-producing strain A. oryzae AK2, succeeded in the biosynthesis of nepetalactol. Second, the improvement of the IPP supply and the suppression of the byproduct citronellol formation were simultaneously achieved. Finally, the highest titer of nepetalactol of 7.2 mg/L was obtained with the engineered strain, after the optimization of the carbon source. To the best of our knowledge, this is the highest reported titer of nepetalactol in microbial cells. The developed A. oryzae strain represents an attractive biosynthetic platform host for the de novo production of iridoids and MIAs.

Biocatalytic routes to stereo-divergent iridoids

“…Thus, identification and engineering of the biosynthesis genes that are responsible for the synthesis of these molecules presents opportunities for production of high value molecules using metabolic engineering and synthetic biology approaches. To date, 7S-cis-trans nepetalactol 3a, which is also formed spontaneously in the absence of any cyclase, albeit in greatly reduced yield, has been the main focus of microbial engineering efforts [29][30][31][32][33] . The enzymes reported in this study can be utilized in these metabolic engineering systems to expand the iridoid-derived natural product space and potentially generate natural product derivatives.…”

“…Furthermore, we expand the access to other stereoisomers via combinatorial biosynthesis, ultimately gaining access to seven of eight possible iridoid isomers and setting the stage for further derivatization into stereo-diverse iridoids. These enzymes can now be used in combination with existing microbial host systems to provide a set of divergent starting points for seco-iridoid and iridoid glucoside pathways [29][30][31][32][33] .…”

New C9‐Monoterpenoid Alkaloids Featuring a Rare Skeleton with Anti‐Inflammatory and Antiviral Activities from Forsythia suspensa

“…Thus, the biosynthetic pathway for compounds 1 and 2 was proposed as in Scheme 1. Started from the precursor geranyl pyrophosphate (GPP, i), [11] i was converted by geraniol synthase (GES) into geraniol (ii), which was oxidized by hydroxylase into 8-hydroxygeraniol (iii). Then, 8-hydroxygeraniol was oxidized to dialdehyde 8-oxogeranial (iv) by oxidase, which further underwent reductive cyclization by iridoid synthase to afford iridodial (v).…”

Reconstitution of Polyketide-Derived Meroterpenoid Biosynthetic Pathway in Aspergillus oryzae

“…These results illustrate the potential of the Aspergillus expression system to produce secondary metabolites. The recent successful syntheses of basidiomycete and plant terpenes in A. oryzae further encourage the production of secondary metabolites from other organisms besides filamentous fungi [ 38 , 39 ].…”