Structure-based engineering of O-succinyl-L-homoserine mercaptotransferase with improved substrate tolerance

O -Succinyl- L -homoserine mercaptotransferase (MetZ) is a key enzyme for the synthesis of L -methionine. However, the limited tolerance to high concentrations of substrate methyl mercaptan sodium restricts its industrial applications, while the “trade-off” between activity and stability has always been a challenge for protein engineering. To address this problem, a strategy of dynamic network rigidification-local flexibility regulation was applied in this study to engineer the enzyme from Chromobacterium violaceum ( Cv MetZ). Through consensus sequence analysis and structure-guided design, the hotspot amino acid residues were anchored for mutagenesis. The best mutant T59I/T119Y/A241T was obtained with synergistic enhancement of activity and stability. The half-life ( t 1/2 ) of whole cells harboring the mutant was increased from 3.3 and 1.3 h to 20.6 and 7.2 h, in the presence of 5% and 10% methyl mercaptan sodium, respectively. The engineered enzyme was successfully immobilized with ideal usability, which laid the foundation for efficient and scale-up bioproduction of L -methionine.