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 Fe²⁺ 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.