Metabolic engineering of the E. coli L-phenylalanine pathway for the production of D-phenylglycine (D-Phg).

D-phenylglycine (D-Phg) is an important side chain building block for semi-synthetic penicillins and cephalosporins such as ampicillin and cephalexin. To produce d-Phg ultimately from glucose, metabolic engineering was applied. Starting from phenylpyruvate, which is the direct precursor of L-phenylalanine, an artificial D-Phg biosynthesis pathway was created. This three-step route is composed of the enzymes hydroxymandelate synthase (HmaS), hydroxymandelate oxidase (Hmo), and the stereoinverting hydroxyphenylglycine aminotransferase (HpgAT). Together they catalyse the conversion of phenylpyruvate via mandelate and phenylglyoxylate to D-Phg. The corresponding genes were obtained from Amycolatopsis orientalis, Streptomyces coelicolor, and Pseudomonas putida. Combined expression of these activities in E. coli strains optimized for the production of L-phenylalanine resulted in the first completely fermentative production of D-Phg.

Metabolic engineering for microbial production of shikimic acid.

Shikimic acid is a high valued compound used as a key starting material for the synthesis of the neuramidase inhibitor GS4104, which was developed under the name Tamiflu for treatment of antiviral infections. An excellent alternative to the isolation of shikimic acid from fruits of the Illicium plant is the fermentative production by metabolic engineered microorganisms. Fermentative production of shikimic acid was most successfully carried out by rational designed Escherichia coli strains by blocking the aromatic amino acid pathway after the production of shikimic acid. An alternative is to produce shikimic acid as a result of dephosphorylation of shikimate-3-phosphate. Engineering the uptake of carbon, the regulatory circuits, central metabolism and the common aromatic pathway including shikimic acid import that have all been targeted to effect higher productivities and lower by-product formation are discussed.