Refined Regio- and Stereoselective Hydroxylation of l‑Pipecolic Acid by Protein Engineering of l‑Proline cis-4-Hydroxylase Based on the X‑ray Crystal Structure

Enzymatic regio- and stereoselective hydroxylation are valuable for the production of hydroxylated chiral ingredients. Proline hydroxylases are representative members of the nonheme Fe2+/α-ketoglutarate-dependent dioxygenase family. These enzymes catalyze the conversion of l-proline into hydroxy-l-prolines (Hyps). l-Proline cis-4-hydroxylases (cis-P4Hs) from Sinorhizobium meliloti and Mesorhizobium loti catalyze the hydroxylation of l-proline, generating cis-4-hydroxy-l-proline, as well as the hydroxylation of l-pipecolic acid (l-Pip), generating two regioisomers, cis-5-Hypip and cis-3-Hypip. To selectively produce cis-5-Hypip without simultaneous production of two isomers, protein engineering of cis-P4Hs is required. We therefore carried out protein engineering of cis-P4H to facilitate the conversion of the majority of l-Pip into the cis-5-Hypip isomer. We first solved the X-ray crystal structure of cis-P4H in complex with each of l-Pro and l-Pip. Then, we conducted three rounds of directed evolution and successfully created a cis-P4H triple mutant, V97F/V95W/E114G, demonstrating the desired regioselectivity toward cis-5-Hypip.