Pathway Optimization by Re-design of Untranslated Regions for L-Tyrosine Production in Escherichia coli

Abstract

L-tyrosine is a commercially important compound in the food, pharmaceutical, chemical, and cosmetic industries. Microbial production, the feasibility of which has been enhanced in recent years by greater understanding of genetic information, the existence of various engineering tools, and simple scale-up processes, is currently being spotlighted as a means to efficiently produce L-tyrosine. Although several attempts have been made to improve L-tyrosine production using rational or combinatorial approaches, translation-level expression control and carbon flux rebalancing around phosphoenolpyruvate (PEP) node, which is both a precursor of the aromatic amino acid synthetic pathway and an intermediate of the glycolysis pathway, still remain to be achieved for optimizing the pathway. Here, we demonstrate pathway optimization by altering gene expression levels for L-tyrosine production in Escherichia coli. To optimize the L-tyrosine biosynthetic pathway, a synthetic constitutive promoter and redesigned, synthetic 5′-untranslated regions (5′-UTRs) were introduced for each gene of interest to allow for control at both the transcription and translation levels. Carbon flux rebalancing was further achieved for maximum productivity by testing the effect of various expression levels of PEP synthetase gene (ppsA) on L-tyrosine yield using UTR Designer. The L-tyrosine productivity of the engineered E. coli strain was increased through pathway optimization and condition optimization and the SCK5 strain that produces recombinant Ltyrosine at 3 g/L, which is higher than that produced by the wild type strain, was generated using this approach. Thus this work demonstrates that pathway optimization by 5′-UTR redesign is an effective strategy for the development of efficient L-tyrosine-producing bacteria.