Phenylalanine and tyrosine ammonia-lyases form cinnamic acid and p-coumaric acid, which are precursors of a wide range of aromatic compounds of biotechnological interest. Lack of highly active and specific tyrosine ammonia-lyases has previously been a limitation in metabolic engineering approaches. We therefore identified 22 sequences in silico using synteny information and aiming for sequence divergence. We performed a comparative in vivo study, expressing the genes intracellularly in bacteria and yeast. When produced heterologously, some enzymes resulted in significantly higher production of p-coumaric acid in several different industrially important production organisms. Three novel enzymes were found to have activity exclusively for phenylalanine, including an enzyme from the low-GC Gram-positive bacterium Brevibacillus laterosporus, a bacterial-type enzyme from the amoeba Dictyostelium discoideum, and a phenylalanine ammonia-lyase from the moss Physcomitrella patens (producing 230 M cinnamic acid per unit of optical density at 600 nm [OD 600 ]) in the medium using Escherichia coli as the heterologous host). Novel tyrosine ammonia-lyases having higher reported substrate specificity than previously characterized enzymes were also identified. Enzymes from Herpetosiphon aurantiacus and Flavobacterium johnsoniae resulted in high production of p-coumaric acid in Escherichia coli (producing 440 M p-coumaric acid OD 600 unit ؊1 in the medium) and in Lactococcus lactis. The enzymes were also efficient in Saccharomyces cerevisiae, where p-coumaric acid accumulation was improved 5-fold over that in strains expressing previously characterized tyrosine ammonia-lyases. Small organic molecules of biotechnological interest include aromatic structures that are derived from p-coumaric acid (pHCA). pHCA can be formed from phenylalanine either through deamination to cinnamic acid (CA) by phenylalanine ammonialyase (PAL; EC 4.3.1.24) and subsequent hydroxylase activity by trans-cinnamate-4-monooxygenase or through deamination of tyrosine by tyrosine ammonia-lyase (TAL; EC 4.3.1.23) (Fig. 1). Considering that the route from phenylalanine requires activity of a P450 enzyme, which has been shown to be the limiting step in previous engineering strategies (1, 2), deamination of tyrosine for production of pHCA may be preferred in microbial cell factories. Tyrosine ammonia-lyases (TAL) have been employed for the production of plant biochemicals and aromatic compounds, e.g., for pHCA itself (3-5), or in the production of stilbenes, such as resveratrol (6, 7), flavonoids, such as naringenin (8, 9), cinnamoyl anthranilates (10), or plastic precursors, such as p-hydroxystyrene (11, 12), yet the TAL reaction may be the limiting step (10, 13).Due to the significant interest in production of phenolic compounds in biotechnological processes, we aimed at increasing the range of characterized phenylalanine ammonia-lyases (PAL) and tyrosine ammonia-lyases (TAL), and in particular at identifying the optimal TAL for use in microbial cell factories...

Stilbenoids, including resveratrol and its methylated derivatives, are natural potent antioxidants, produced by some plants in trace amounts as defense compounds. Extraction of stilbenoids from natural sources is costly due to their low abundance and often limited availability of the plant. Here we engineered the yeast Saccharomyces cerevisiae for production of stilbenoids on a simple mineral medium typically used for industrial production. We applied a pull-push-block strain engineering strategy that included overexpression of the resveratrol biosynthesis pathway, optimization of the electron transfer to the cytochrome P450 monooxygenase, increase of the precursors supply, and decrease of the pathway intermediates degradation. Fed-batch fermentation of the final strain resulted in a final titer of 800 mg l−1 resveratrol, which is by far the highest titer reported to date for production of resveratrol from glucose. We further integrated heterologous methyltransferases into the resveratrol platform strain and hereby demonstrated for the first time de novo biosynthesis of pinostilbene and pterostilbene, which have better stability and uptake in the human body, from glucose.

Synthetic biology and metabolic engineering enable generation of novel cell factories that efficiently convert renewable feedstocks into biofuels, bulk, and fine chemicals, thus creating the basis for biosustainable economy independent on fossil resources. While over a hundred proof-of-concept chemicals have been made in yeast, only a very small fraction of those has reached commercial-scale production so far. The limiting factor is the high research cost associated with the development of a robust cell factory that can produce the desired chemical at high titer, rate, and yield. Synthetic biology has the potential to bring down this cost by improving our ability to predictably engineer biological systems. This review highlights synthetic biology applications for design, assembly, and optimization of non-native biochemical pathways in baker's yeast Saccharomyces cerevisiae We describe computational tools for the prediction of biochemical pathways, molecular biology methods for assembly of DNA parts into pathways, and for introducing the pathways into the host, and finally approaches for optimizing performance of the introduced pathways.