Cascade biocatalysis for production of enantiopure (S)-2-hydroxybutyric acid using recombinant Escherichia coli with a tunable multi-enzyme-coordinate expression system

Abstract

Racemize 2-hydroxybutyric acid is usually synthesized by organic methods and needs additional deracemization to obtain optically pure enantiomers for industrial application. Here we present a cascade biocatalysis system in Escherichia coli BL21 which employed L-threonine deaminase (TD), NAD-dependent L-lactate dehydrogenase (LDH) and alcohol dehydrogenase (ADH) for producing optically pure (S)-2-hydroxybutyric acid ((S)-2-HBA) from bulk chemical L-threonine. To solve the mismatch in the conversion rate and the consumption rate of intermediate 2-oxobutyric acid (2-OBA) formed in the multi-enzyme catalysis reaction, ribosome binding site regulation strategy was explored to control TD expression levels, achieving an eightfold alteration in the conversion rate of 2-OBA. With the optimized activity ratio of the three enzymes and using ADH for NADH regeneration, the recombinant strain ADH-r53 showed increased production of (S)-2-HBA with the highest titer of 129 g/L and molar yield of 93% within 24 h, which is approximately 1.65 times that of the highest yield reported so far. Moreover, (S)-2-HBA could easily be purified by distillation, making it have great potential for industrial application. Additionally, our results indicated that constructing a tunable multi-enzyme-coordinate expression system in single cell had great significance in biocatalysis of hydroxyl acids.

Funding

the National Key Research and Development Program of China,(2018YFA0900300)

the National Natural Science Foundation of China,(31770058)

Natural Science Foundation of Jiangsu Province,(BK20181205)

the Key Research and Development Program of Ningxia Hui Autonomous Region,(No. 2019BCH01002)

the national first-class discipline program of Light Industry Technology and Engineering,(LITE2018-06)

the 111 Project,(111-2-06)