Efficient biosynthesis of (2S, 3R)-4-methylsulfonylphenylserine by artificial self-assembly of enzyme complex combined with an intensified acetaldehyde elimination system

(2S, 3R)-4-methylsulfonylphenylserine [(2S, 3R)-MPS], a key chiral precursor for antibiotics florfenicol and thiamphenicol, could be asymmetrically synthesized by l-threonine transaldolase (LTTA) coupled with an acetaldehyde elimination system. The low efficiency of acetaldehyde elimination system blocked further accumulation of (2S, 3R)-MPS. To address this issue, strengthening acetaldehyde elimination system and enzyme self-assembly strategy were combined to accelerate biosynthesis of (2S, 3R)-MPS. The new multi-enzyme cascade with intensified acetaldehyde elimination system BL21 (PsLTTAD2/ScADH/BtGDH) could produce (2S, 3R)-MPS with a titer of 157.6 mM, 1.7-folds than that produced by the original system BL21 (PsLTTAD2/ApADH/CbFDH). Moreover, self-assembly of PsLTTAD2 and ScADH by respective fusion of SpyTag and SpyCatcher were carried out to develop a self-assembled multi-enzyme cascade BL21 (ST-PsLTTAD2/SC-ScADH/BtGDH). As a result, the yield of (2S, 3R)-MPS was up to 248.1 mM with 95% de. As far as we knew, that represented the highest yield of (2S, 3R)-MPS by enzymatic synthesis, and therefore was a promising and green route for industrial production of this valuable compound.