Expanding metabolic pathway for de novo biosynthesis of the chiral pharmaceutical intermediate L-pipecolic acid in Escherichia coli.

Background: The six-carbon circular non-proteinogenic compound L-pipecolic acid is an important chiral drug intermediate with many applications in the pharmaceutical industry. In the present study, we developed a metabolically engineered strain of Escherichia coli for the overproduction of L-pipecolic acid from glucose.
Results: The metabolic pathway from L-lysine to L-pipecolic acid was constructed initially by introducing lysine cyclodeaminase (LCD). Next, L-lysine metabolic flux from glucose was amplified by the plasmid-based overexpression of dapA, lysC, and lysA under the control of the strong trc promoter to increase the biosynthetic pool of the precursor L-lysine. Additionally, since the catalytic efficiency of the key enzyme LCD is limited by the cofactor NAD ⁺ , the intracellular pyridine nucleotide concentration was rebalanced by expressing the pntAB gene encoding the transhydrogenase, which elevated the proportion of LCD with bound NAD ⁺ and enhanced L-pipecolic acid production significantly. Further, optimization of Fe ²⁺ and surfactant in the fermentation process resulted in 5.33 g/L L-pipecolic acid, with a yield of 0.13 g/g of glucose via fed-batch cultivation.
Conclusions: We expanded the metabolic pathway for the synthesis of the chiral pharmaceutical intermediate L-pipecolic acid in E. coli. Using the engineered E. coli, a fast and efficient fermentative production of L-pipecolic acid was achieved. This strategy could be applied to the biosynthesis of other commercially and industrially important chiral compounds containing piperidine rings.