Metabolic engineering of Escherichia coli as a heterologous host for the enhanced production of medicinal molecules derived from kynurenine pathway

Abstract

Kynurenine pathway of tryptophan metabolism is widely present, and well characterized specifically in eukaryotes where aerobic degradation of L-tryptophan takes place and ultimately NADP is produced along with production of different medicinal molecules. In a few Streptomyces species also, tryptophan metabolism proceeds through kynurenine route, and finally leading to several medically important natural products with anti-cancer properties, including actinomycins, sibiromycin, and anthramycin. This pathway of aerobic metabolism of tryptophan is generally absent in prokaryotes. Due to availability of well-established tools and strategies for metabolic engineering, the model prokaryotic organism, Escherichia coli, has emerged as a cell factory for various natural product biosynthesis. In this study, establishment of aerobic pathway of tryptophan metabolism in E. coli was explored in order to make this model organism a robust heterologous platform for production of various pharmaceutically active agents. Furthermore, competitive pathway inhibition and cofactor engineering were performed to enhance the production titers. The final engineered E. coli strains could produce 3-hydroxy-4-methylanthranilic acid (precursor to anti-tumor agents), actinocin (actinomycin D chromophore), kynurenic acid (dietary supplement) and 3-hydroxyanthranilic acid (anti-oxidant) in a minimal medium with glucose as sole carbon source. This is the first ever report of heterologous expression of kynurenine pathway in E. coli. The metabolic engineering strategies employed here could be useful for the production of other natural products in a microbial heterologous host.